摘要:

C G Editorial The first issue of Green Chemistry follows 18 months of market research consultation and discussion with the academic industrial and public chemistry communities and detailed planning with the RSC and a very supportive editorial board. The primary decision to go ahead with a new journal was not taken lightly only after long and frank discussions over questions such as journal proliferation academic credibility and industrial relevance did chemists from a wide variety of backgrounds reach consensus on the importance and timeliness of the project. The supportive evidence for this is overwhelming and includes the number of recent relevant publications the emphasis placed on relevant research by national and transnational funding agencies an increasing awareness in industry of the importance of concepts such as waste minimisation and atom utilisation and greater involvement by governments in controlling the use of resources and the production and disposal of waste.The emergence of these and other underpinning concepts as general principles which can be used in the conception and execution of synthetic chemistry and in the usage of the chemicals produced has been critical in the evolution of Green Chemistry.1 The title Green Chemistry was itself the subject of considerable discussion and debate. We considered many alternatives but none carried the same combination of widespread use and appreciation as well as simplicity and impact. We are particularly indebted to colleagues in the United States who have been largely responsible for getting the terminology into common practice as well as for giving it credibility and value through initiatives such as the Presidential Green Chemistry Challenge Scheme.The definition of Green Chemistry given by the individual who has done most to promote it Paul Anastas and his co-author John Warner serves nicely to define the main objectives of this journal Green Chemistry is the utilisation of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design manufacture and application of chemical products.2 Green Chemistry is to be an information resource as well as a high quality international journal. It will report on research activities and interests in chemical aspects of clean technology from academic industrial and public sectors.Each issue will have two sections. The back section will contain primary research papers communications and reviews. The style and format of these articles will be very flexible to allow the widest possible range of formats. The front section of the journal will contain news and views on research industrial highlights and legislative issues grants and other promotional initiatives conferences and educational items. We seek to inform those working in relevant areas but also to promote and encourage relevant research and teaching and the application of the principles of green chemistry. Green Chemistry February 1999 G1 Green Chemistry C G The research articles in the first few issues of Green Chemistry should help to set the tone of the journal.These will cover l clean synthesis (e.g. new routes to important chemical intermediates including heterocycles) l enhanced atom utilisation (e.g. more efficient methods of bromination) l the replacement of stoichiometric reagents (e.g. catalytic oxidations using air as the only consumable source of oxygen) l new solvents and reaction media (e.g. use of supercritical fluids and reactions in ionic liquids) l water-based processes and products (e.g. organic reactions in high-temperature water) l replacements for hazardous reagents (e.g. the use of solid acids as replacements for traditional corrosive acids) l intensive processing (e.g. the use of spinning disc reactors) l novel separation technologies (e.g.the use of novel biphasic systems l alternative feedstocks (e.g. the use of plant-derived products as l new safer chemicals and materials (e.g. new natural l waste minimisation and reduction (e.g. applying the principles of such as those involving a fluorous phase) raw materials for the chemical industry) product-derived pesticides) atom utilisation and the use of selective catalysts). In the front section of Green Chemistry we will be carrying highlights from research and industry news items on recent public consultation documents and new funding initiatives networks and award schemes reports from recent conferences and a conference diary as well as letters comments and opinions on relevant issues.In addition we will have non-research articles designed to inform the reader of various important topics such as the effectiveness of environmental legislation as applied in different regions of the world the development of green chemistry teaching courses and educational packages status checks on current research programmes and introductions to specialist and emerging subjects such as new chemical reactor designs. We look forward to receiving a wide range of article types and news items with coverage reflecting the development and application of the principles of green chemistry in education industry and research. We would also like to hear your views on any educational governmental industrial public or research issue relevant to green chemistry. We intend the journal to act as a forum for the discussion of the many emergent and controversial issues surrounding green chemistry. The 20th century has been highly successful for chemistry and society has come to depend on the products of the chemical industry to maintain our current standard of living and improve our quality of life. On the eve of the 21st century however the public are more aware of the hazardous substances that many chemical processes use and generate than the benefits of the products. Chemistry and the chemical industry have tarnished images. With your help we can use this journal to convey the means and motivation for chemists to make a difference. James Clark York January 1999 1 For further background reading see J. Clark Chem. Br. 1998 34(10) 43. 2 Green Chemistry Theory and Practice P. T. Anastas and J. C. Warner Oxford University Press Oxford 1998. G2 Green Chemistry February 1999

ISSN:1463-9262    

DOI:10.1039/gc9900g1

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Soya bean glue – a new high-performance adhesive from a renewable resource The preparation of plywood involves the spraying of several sheets of wood with a glue followed by compressing the layers together to form a lamellar composite. Traditionally the glues utilised in this process have been petroleum based and thus have problems associated with control of volatile organic components as well as being derived from non-renewable resources. Glues derived from soya bean protein a cheap and renewable resource have been known for some time and can be used for a few light applications such as labelling and packaging. Unfortunately their poor performance in humid environments has precluded their use in many areas. Early attempts to rectify this problem used phenol–formaldehyde resins as modifiers to cross-link the proteins and render them more waterstable.This has not proved a viable solution since formaldehyde is slowly released leading to toxicity problems and for many years the use of soya bean protein in adhesion has not been an attractive proposition. Now this situation has changed. A research team at Kansas State University led by Xiuzhi Susan Sun has managed to dramatically improve the performance of soya bean protein as a glue without the need for treatment with cross-linkers. Their approach centres on the modification of the protein structure. Native material is globular with hydrophilic regions on the outside of the structure leading to low resistance to water and poor performance of glues in humid environments.The interior of the protein contains hydrophobic regions which should improve the water-resistance of the material. Sun's approach has been to effect structural changes to the protein converting it from a globular to a partial random coil form resulting in the exposure of the hydrophobic regions of the protein. These changes enhance the performance of the protein dramatically and make it into a very promising candidate in a variety of applications. Plywood can now be successfully fabricated from a variety of woods using the new glue. These materials can survive severe water treatment without any sign of delamination; furthermore little reduction in adhesive strength is observed.The unmodified protein by comparison shows no adhesive properties under these testing conditions. Other important benefits include the ability to spray the aqueous protein solution evenly– a consequence of good viscosity properties – allowing much better coverage and improved sticking. For further information visit http://www.oznet.ksu.edu/dp_grsi/ faculty/sun.htm New glue for plywood Biotechnology helps UK engineers win top environment award The top UK environment award in 1998 for engineers was won for work on reducing harmful emissions. The Engineering Council’s 1998 Environment Award for Engineers was won by a team from BIP Ltd. Oldbury West Midlands UK. The award which comprised a £5000 prize and the Lloyd's Register Trophy was for developing a process that brings together biotechnology and engineering.The company has developed a roofmounted bio-reactor for installation in plastics and resins plants which emit formaldehyde and methanol. The bio-reactor contains micro-organisms which feed on these compounds and hence reduce the environmental impact of the emissions. C G N E W S US MTBE controversy The US government is fighting efforts in the Californian legislature to ban methyl tert-butyl ether (MTBE) the oxygenated fuel additive which has been linked to ground water contamination in various parts of the US (Chemical Market Reporter 28 November 1998). The argument used by the National Government is that the use of MTBE as an additive improves air quality.They are concerned that if California manages to halt the use of MTBE air quality throughout the country will be adversely affected. Officials in one Californian town however claim that the problem is so bad that more than one in three drinking water wells have had to be closed down due to contamination. It has also been reported that in connection with worries about MTBE US Filter and Envirogen have agreed to develop a fluidised bed biological treatment system for the compound. (The Chemical Engineer 1998 666 8). Atom efficiency in Antwerp BASF have announced that the amount of waste produced at their Antwerp site (ChemPress 1998 32(17) 5) was 9926 tonnes in 1997 the first time that the company has achieved less than 1 kg of waste per tonne of product.Emissions to the atmosphere were up by 3% and waste to water increased by 13% on top of an increase in production of 17%. Landfill waste was down by around a third and waste to incinerators reduced by about a quarter; 76% of solid waste was recycled. New investments in the Czech Republic in refinery Ceska rafinerska (CRA) of Litvinov has announced an investment programme of CEK 10bn to the year 2002. The major thrust of this initiative is the construction of deep crude oil processing facilities. These new units will allow the company to convert heavier sulfur-rich fractions of crude oil into cleaner lighter fuels and thereby reduce the amount of polluting heavier fuel oils (Hospodarske Noviny 1998 42(189) s6).Green Chemistry February 1999 G3 N E W S Steel works are seeking to reduce mercury emissions GC Mercury under pressure The Tianjin Bohai Chemical Co (China) has announced that it is building an 85,000 tonnes per annum membrane caustic soda plant. This will replace its existing 58,000 tonnes per annum mercury process caustic soda plant which has been the cause of serious pollution problems (China Chemical Reporter 1998 9(30) 13). Three US Steel works in the Great Lakes area have signed a voluntary agreement with the Lake Michigan Forum which will lead to a reduction in New products and processes Adipic acid A new process for adipic acid that eliminates the production of nitrous oxide and gives only water as a byproduct has been announced by scientists at Nagoya University in Japan (Chemistry and Industry 1998 717).The process is based on the use of hydrogen peroxide to oxidise cyclohexene and gives a yield of about 93% adipic acid. Polymers At the University of Twente in Holland polymers that degrade to carbon dioxide water and biomass are being developed. These include poly(ester)amides and poly(ester)urethanes. Several degradable polymers are also being marketed by industry. These include an aliphatic polyester from Showa High Polymer (Japan) and random aliphatic-aromatic copolymers based on terephthalic acid adipic acid and 1,4-butanediol from both BASF (Germany) and Eastman (USA) (Chemisch Weekblad 1998 94 1).Oxidation with supercritical water Nittetsu Semiconductor (Japan) have brought into operation what is claimed to be the first supercritical water-applied oxidation system for the destruction of waste including developer stripping liquid and ammonia liquid (Japan Chemical Week 1994 39 10). Concrete removes nitrous oxide Mitsubishi Materials (Japan) has developed and tested a new type of concrete paving block which purifies the air around it by removing nitrous oxide from the atmosphere. The blocks contain titanium dioxide that can act as a photocatalyst and is activated by sunlight and rain promoting the oxidation of nitrous oxide to nitric acid which is washed away or neutralised by the alkalinity of the concrete (Chemical News 1998 69 28).mercury consumption at their steel mills. This will contribute to the implementation of the Toxics Reduction Strategy with Canada an agreement that aims to achieve a 50% reduction in the use of mercury by 2006. On a similar theme the Dutch company Begemann Milieutechniek BV has taken delivery of a cryogenic waste gas purification unit from Aga Gas BV. This will be used in Begemann's processing of mercury containing wastes (Nederlandse Chemische Industrie 1998 40(16) 9). G4 Green Chemistry February 1999 Solvent replacement in metal cleaning Avon Ames part of Avon Rubber has successfully implemented an 80% reduction in solvent use in its metal cleaning operations.This has been achieved by phasing out the use of 1,1,1-trichloroethane and replacing it with the ICI system Cleanfast DLS and the solvent Triklone LE (Rubber Trends 1998 3rd quarter 104). Trouble brewing for brominated flame retardants Following publication last autumn of research showing the presence of brominated flame retardants in fish and birds in the Baltic the Swedish environment minister has contacted the US Environmental Protection agency and Japanese Environment Agency to encourage co-operation with the European Union on tackling the problems caused by these compounds (European Chemical News 1998 69(1829) 60). In response to Sweden’s criticism of the UK over slow action on the release of these substances the UK environment minister said that any action must await the outcome of a Europe-wide assessment programme the findings of which will be made public this year (The Chemical Engineer 1998 666 11).The market – legal and illegal The US market for environmental consultancy has been worth about $7bn per annum since 1993 and remains steady. The market for remediation consultancy and remediation construction was worth a total of $8bn in 1997– an increase of 3% over 1996. It is generally considered that the environmental services market is stagnant and will decrease in the future. A thriving illegal market has developed for banned chemicals with an estimated 30,000 tonnes per annum of chemicals including CFCs and carbon tetrachloride being smuggled into industrialised countries from developing countries and the former USSR.The official consumption of CFCs in industrialised countries has decreased to less than 15,000 tonnes per annum from 1 M tonnes per annum in the mid 1980s. John Emsley the 1998-1999 John Jeyes lecturer John Jeyes lectureship The 1998-99 John Jeyes lecturer is Dr John Emsley (University of Cambridge). He was given the award for his contributions to the perception of humans and their pivotal role in the environment with good sound common sense descriptions on the beneficial aspects of modern chemistry to humankind. His lecture is entitled ‘False alarms a closer look at some environmental scares’. It is based on items of the type covered during his period writing the ‘Molecule of the Month’ column for The Independent newspaper when he responded to exaggerated scares about various chemicals that were being blamed for causing environmental pollution.He showed that while many of these Methyl bromide used as a soil fumigant in the production of many crops e.g. strawberries is being replaced because of its ozone-depleting properties alarms appeared to be based on sound scientific evidence most were eventually found to be false alarms when exposed to rigorous testing. He examines why certain chemicals find themselves in the glare of the media spotlight what effect adverse publicity has how eventually the fears are shown to be groundless and why this rarely gets reported.The ‘false alarms’ that Emsley considers include those relating to PVC phthalate plasticisers and dioxins chlorination of water supplies dichloromethane as a solvent aluminium and Alzheimer’s disease nitrate fertilisers and drinking water phosphates in detergents antimony fire-retardants food additives and E-numbers. Emsley also discusses the ways that chemists and the chemical industry might work to generate a better climate of public opinion in the coming millennium which will be needed if we want young people to study chemistry. The methyl bromide saga According to the Montreal Protocol the European Union as a developed area is not due to terminate the use of methyl bromide as a soil fumigant until 2005.However the European Commission has been seriously considering a proposal banning the use and production of the chemical by 2001 bringing Europe into line with the USA Australia and Japan. The earlier ban is not popular with producers farmers and lawmakers who have been pushing for a deferral. In the US C G N E W S Environmental Protection Agency officials have expressed a willingness to defer the ban while alternatives are developed. Some of the suggested alternatives such as methyl iodide and phosphine present their own problems. Other possible replacements include carbon dioxide and heat treatment. Companies announce improved environmental performance Schering (Germany) has committed its businesses to sustainable development and within the framework of the international responsible care programme to continuous improvement in safety environmental protection and health care conditions.In 1997 Schering invested DM 28M in environmental protection facilities mainly in improving existing plants and equipping new plant. The recycling of 13 M tonnes of solvents saved the company DM 19M of the cost of the raw material. Company targets for the year 2000 include a 12% reduction in the amount of non-recoverable waste a 15% reduction in the level of waste consumption and a 5% reduction in electric energy consumption compared to 1996 figures. They are also aiming for a reduction in their carbon dioxide emissions by the year 2005. Reckitt and Colman aims to operate an environmental policy that is globally responsible and also meets or exceeds local environmental standards. Their Hull site in the UK recycled almost half of its total waste in 1997. In their Belle Mead site in New Jersey USA a thermal oxidiser is used to destroy 98% of volatile organic waste. UPM-Kymmene (Finland) has an environmental policy based on the environment management principles laid out by the International Chamber of Commerce. Capital expenditure on environmental protection was FM 66M in 1997. Total emissions of gaseous sulfur compounds were down by 22% and by over 30% when the increase in production is taken into account. Outokumpu (Finland) have announced a fall in sulfur dioxide emissions from their Harjavalta smelter to 2700 tonnes (16 kg per tonne of metal produced) in 1997. Green Chemistry February 1999 G5

ISSN:1463-9262    

DOI:10.1039/gc9900g3

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

F EAT U R E C G A ‘growth’ industry renewable raw materials Ian Bartle and Nigel Oliver report on an independent UK commitment towards bio-based materials and chemicals and will develop varieties of Isatis that give improved yields of indigo by a rapid programme of markerassisted plant breeding from existing lines. Also an experimental extraction process will be scaled-up to produce quantities of indigo for industrial purposes. The research will be carried out by a group from IACR-Long Ashton and University of Bristol along with Silsoe Research Institute (SRI) which will provide the appropriate engineering skills. Harvesting equipment and the extraction process will be developed by SRI in association with a seeds company and Express Separations.The end-product will be used in the manufacture of natural dyes and pigments. Semiochemicals for agency set up to promote the development of nonfood crops non-toxic biodegradable and CO2- Plants are natural clean and sustainable ‘biorefineries’– neutral– with the potential to deliver an array of raw materials for industry in place of mainly petrochemical sources. With world-wide interest in such cropderived products UK industry (British Sugar Cargill Dalgety DuPont (UK) HGCA ICI NFU PBI-Cambridge Pira International Sustainable Industries Ltd and Zeneca together with BBSRC DTI and MAFF) has been proactive in the establishment of an independent national agency ACTIN to address market opportunities supply chain issues and barriers to progress and to promote networking in this industrial i.e.non-food crops arena. Potential issues for those in industry are re-evaluation of the manufacturing process the establishment of new supply chains (where appropriate extending upstream into the research community) technical hurdles and environmental and regulatory issues. These are all major considerations towards achieving the desired end result – a novel and competitive product from a renewable feedstock. The disciplines of plant biochemistry and biotechnology; biochemical and process engineering; chemistry; materials science and processing; and life cycle analysis or processing modelling all play an important role. ACTIN (Alternative Crops Technology Interaction Network) was established in 1995 to promote cropderived oils fibres starches and speciality chemicals as renewable raw materials for industry.Dedicated ACTIN staff and the vertically-integrated group of sponsors with a diversity of viewpoints (representing the science base producers processors and end users) provide a coherent central resource supplemented by ACTIN’s extensive Database its Special Interest Group members (ACTIN2020) and links into related initiatives at the European level. There is a close association with a £4M UK Government LINK Programme (‘Competitive Industrial Materials from Non-Food Crops’) which intends to manage approximately 15 projects in this area (see below). ACTIN provides objective help to industry or the research community to facilitate and add value to particular interests in this area.A useful starting point is the Web site (http://www.actin.co.uk) or Help Desk (Tel. +44 (0)1372 802054; email info@actin.co.uk). G6 Green Chemistry February 1999 Plant-derived indigo for industrial use The earliest known source of indigo was Isatis tinctoria (woad) a biennial or perennial herb indigenous to northern Europe. Woad produces two indoxylforming substances in its leaves indican and isatan B which when exposed to the air form the blue compound indigo. ‘ACTIN promotes crop-derived renewable raw materials for industry’ Since the 17th century it has not been grown in Western Europe as a source of indigo.As a consequence there has been no recent attempt to breed woad to improve indigo precursor content or crop architecture. Changes in legislation and a growing demand from consumers and manufacturers for naturally-derived products from renewable resources have led to a revived interest in woad as a source of indigo for industry leading to the need for new systematic research on this crop. This LINK project funded by MAFF addresses the recognised need for a greater L. FUCH’S Flora 1545 There is renewed interest in woad as a source of indigo for industry aphid control Aphids are the most important group of agricultural and horticultural pests in the UK and most of Europe causing direct damage to a wide variety of crops but also transmitting virus diseases.The recent identification of the attractant pheromones produced by sexual female aphids has opened up new possibilities for the development of novel pest management strate-gies either avoiding use of broadspectrum pesticides or retaining their use for ‘fire-fighting’ when aphid problems are extreme. This project seeks to provide products for the control of pest aphid species in the field using the chemicals which occur naturally in their environment and which act by non-toxic mechanisms. It also aims to improve the method of production so as to use clean technologies rather than chemical synthesis. Aphids a serious agricultural pest could be controlled with sex pheromones Aphids are attacked by a wide range of natural enemies including parasitic wasps more correctly termed parasitoids and studies particularly at Rothamsted have demonstrated the importance of these parasitoids as natural biological control agents.However to be effective early season synchrony of parasitoids and aphids must be achieved. Recent laboratory and field studies at Rothamsted and Imperial College Silwood Park have shown that some parasitic wasps are strongly attracted to the pheromones produced by sexual female aphids to attract mates. This innate response is being used to develop a sustainable aphid control strategy based on the use of synthetic aphid sex pheromones to achieve early season synchrony between natural populations of parasitoids and aphid pests and to conserve and enhance field margin parasitoid populations in autumn.The aphid sex pheromones possess a number of chiral centres and are thus difficult synthetic targets. Two important aphid sex pheromone components are isomers of the monoterpenoids nepetalactone and nepetalactol designated as having the (4aS,7S,7aR)-configuration. A synthetic route to the (4aS,7S,7aR)- nepetalactone and the corresponding nepetalactol has been developed from commercially available starting materials which must be of a high enantiomeric purity to yield materials which exhibit biological efficacy. The high cost of the starting materials resulting in a cost exceeding £1000/g of pheromone combined with the toxic nature of some of the required reagents means that production of the pheromone from this route is not practical.The (4aS,7S,7aR)-nepetalactone is produced by the catmint Nepeta cataria and another valuable isomer (4aR,7S,7aS)-nepetalactone by Nepeta racemosa. High yields of these C G F E AT U R E from commercial production of Nepeta species is economically viable. The lactol components of the aphid sex pheromones can be derived by a simple one-step reduction of the corresponding lactone. Although this synthetic route is amenable to large scale production a cleaner approach to reduction based on the use of enzyme chemistry will be investigated for the production of high enantiomeric purity nepetalactols.The pheromone is most attractive when released into a crop area at physiological levels which involve very low concentrations. To achieve this a formulation will be developed which impregnates the pheromones into a resin. The project funded by MAFF will involve IACR-Rothamsted and three industrial partners English Hop Products which has expertise and facilities for the extraction and purification of essential oils Richard Wood Partnerships who will propagate and grow several Nepeta species cultivars to determine which give products with high enantiomeric purity and good overall yield and AgriSense-BCS which has considerable experience with pheromone formulation and currently markets several pheromone-based products.Plant fibres as ion-exchange media Ion-exchange materials based on pure cellulose have been used for the past two decades. They are characteristically available in very pure forms have high compounds of the order of 1g/kg of fresh plant material can be obtained by conventional steam distillation methods. However use of novel and more environmentally benign extraction protocols with reduced usage of organic solvents including microwave extraction are also being investigated. A high extraction efficiency combined with a yield potential of up to 10 tonne/ha of fresh plant material demonstrates that the production of aphid sex pheromones A copper adsorbent derived form sugar beet pulp produced at the BioComposites Centre Bangor UK Green Chemistry February 1999 G7 F E AT U R E GC exchange capacities and are the main alternative to synthetic (petroleum-based) ionexchange resins.Lignocellulose is also highly reactive and lends itself readily to ‘graft modification’. This principle has been investigated since the early 1970s and the range of substrates is a testament to the imagination of workers in this field. Thus to date ion-exchangers have been derived from such diverse materials as wood flour coconut coir sugar beet pulp and even empty corn cobs. The main obstacle to full exploitation has been the lack of facilities to produce these materials in quantities greater than a few kilograms. Recently through a Foresight Challenge initiative BP Chemicals has made its pilot-scale plant at Hull available to the BioComposites Centre.In the 'IONEX' project scientists at the Centre are making use of this facility to transfer their expertise in lab-scale chemical modification of plant fibres to produce low cost ion-exchangers. Hickson and Welsh in its role as end user provides guidance as to the desired properties of these materials to ensure they can be a commercially viable complement to existing ion-exchange systems. The environmental impact and fate of the new materials will be assessed by Imperial College London. The IONEX project which is funded by MAFF and EPSRC will run parallel to the wider Foresight initiative and enable the potential of chemically modified agricultural materials such as flax and hemp fibres and sugar beet pulp to be realised in true industrial applications.The project is co-ordinated by The Biocomposites Centre at Bangor who also provide the scientific input to the project. Starch for packaging materials The objective of this project is to develop technology for the conversion of starch into mouldable packaging materials. The result would be a new range of environmentally friendly materials made by clean solvent-free processing routes and which although tailored for recyclability have attractive properties for ultimate disposal by for example composting. Use of such materials would help meet future legislation and reduce the use of nonrenewable oil-based components.The Centre for Biomimetics at Reading University is currently evaluating the properties of materials produced from wheat starch compared with expanded polystyrene. Green Chemistry February 1999 G8 Sustainable surfactants The Central Science Laboratory of the UK Ministry for Agriculture Food and Fisheries (MAFF) was the venue for a one-day seminar in York last November organised by LINK in association with ACTIN (Alternative Crops Technology Interaction Network) BACS (British Association for Chemical Specialities) and the Royal Society of Chemistry (Speciality Chemicals Sector). This event entitled Sustainable Surfactants Renewable Feedstocks for the 21st Century was designed to help establish industry/education partnerships appropriate for the collaborative LINK programme on Competitive Industrial Materials from Non-Food Crops.The programme opened with an introduction by the Chairman Dr David Karsa (Akcros Chemicals and BACS) who briefly considered the goals of developing new products from non-food crops market trends and relevant chemical processes. This was followed by a presentation from Dr Guido Bognolo of ICI Surfactants on The Needs of the Natural versus man-made surfactants NATURAL/RENEWABLE Alkyl polyglucosides Biosurfactants e.g. Surfactin and Emulsan Fatty amides Fatty amines Glucamides Glycerol and polyglycerol esters Lecithins Ligoin sulfonates Phosphoric acid esters from derived fatty alcohols Protein derivtives Saponins Soaps Sorbitol and sorbitan esters Sugroglycerides Sucrose esters Sulfates from naturally derived fatty alcohols MAN-MADE Alkanolamides Alkyl and alkyl aryl ether carboxyates Alkyl aryl sulfates Alkyl aryl sulfates Alkyl aryl ether sulfates Alkyl capped ethoxylates Alkyl ether sulfates Alkyl isethionates Alkyl phenol ethoxylates Alkyl phenol/formaldehyde condenstes and their alkoxylated derivatives Alkyl sulfates from synthetic fatty alcohols Alkyl sulfonates Amino oxides Betaines and amidobetaines Ester quats Ethylene oxide/Propylene oxide copolymers Fatty acid esters ethoxylates and polysorbates Fatty acid ethoxylates Surfactants Industry.Dr Bognolo started by comparing natural and synthetic products noting that 70 – 75% of the surfactant consumption in industrialised countries is of petrochemical origin whereas natural products dominate in developing countries.In the industrialised countries there is a trend towards converting from synthetic to natural based products. This is driven by increasing demands for mildness (due to more frequent washing) for finding and using replacements for environmentally unacceptable products (such as those based on linear alkylbenzenes) and for increasing product specificity. In contrast the emergence of new manufacturing technologies in developing countries is causing a trend in the opposite direction from natural to synthetic products. It is believed that raw materials availability will not be a driving factor at the macro level but may influence the choice of specific alkyl chain lengths in the surfactant products.Dr Karl-Heinz Hill from Henkel gave a talk entitled Fats and Oils as Oleochemical Raw Materials Recent Developments and Perspectives. He began by reviewing statistics on world production and consumption of oils and fats and the basic oleochemical processes. This showed a clear trend away from the use of synthetic surfactants towards those based on natural products. For example, The strengths and weaknesses of renewable products STRENGTHS low environmental impact new opportunities new functionality WEAKNESSES/CHALLENGES natural variability cost complexity unknown technology alkyl benzenesulfonate production has recently decreased whereas the manufacture of fatty alcohol ether sulfates is increasing.A new manufacturing process based on a solid catalyst is now available for manufacturing natural product-based fatty acid ester ethoxylates. Among the new natural products alkyl polyglycerides offer many useful properties for application in personal care products and are also attracting interest for agricultural applications. ‘the potential for renewable feedstocks needs to be more widely recognised’ Dr Peter Carruthers from the University of Reading talked on LCA Environmental Benefits of Vegetable Oilbased Surfactants in which he described results from a recent research project combining life-cycle assessment (LCA) and cost-benefit analysis (CBA).Oleochemical alcohol ethoxylates use 30 – 40% fewer non-renewable raw materials than the petrochemical-based products. The environmental costs of manufacturing petroleum-based surfactants are consistently higher than those of the vegetable oil-based products with the rapeseed derived product showing the best figures. The Political Influences on the Supply Chain (Agenda 2000) was the subject of a talk given by David Clayton from MAFF. Agenda 2000 is an EU initiative paper (published in 1997) aimed at enhancing the European Community’s competitiveness opportunities for individuals and environmental performance as it grows in size.Renewable raw materials are seen as providing opportunities for agriculture and forestry and for contributing to job creation in rural areas. However the EU Commission is at an early stage of thinking on this and a report early in 1999 on any post Agenda 2000 industrial crops regime should set out its proposals. Dr Ingegard Johansson of Akzo Nobel talked on Recent Successes Industrial Applications. By using a technique known as Principal Component Analyses it is possible to screen a large number of potential new alkyl glycoside products in terms of a wide range of relevant properties. Structural variants including the chain length and the degree of branching of the hydrophobic part of the molecules have been considered and shown to be highly influential on product properties.These qualitative structure/property relationships can be used to help apply the best products to different applications such as detergency and agrochemicals. Ian Bartle outlined the collaborative programme on Competitive Industrial Materials from Non-Food Crops (See box below). Link Programme on Competitive Industrial Materials from Non-Food Crops The objectives of the programme are to overcome technical barriers to the wider use of crop-derived raw materials by industry with an emphasis on crops of medium to high value that are economically viable. The programme priorities are technologies which l improve the value of existing crops l improve the quality and reliability of crop-derived materials l address the need for changes in process strategies l produce new products from plants The Role of Renewables in Crop Protection was the title of the talk given by Dr Susan Critchley from Zeneca Agrochemicals.In a typical herbicide formulation while the active ingredient is commonly synthetic most of the other components including the F E AT U R EGC solvent and emulsifiers can be natural product-derived. There are thousands of candidates as emulsifiers. They can be ionic non-ionic or blends. Similarly there are a good variety of possible solvents. Under renewable products there are several likely emulsifiers including sucrose esters and sorbitan ester ethoxylates while alkylated vegetable oils are among the very few possible solvents.While there are many drives to encourage the increased use of renewables the reality is that the range of components currently meeting the criteria for industrial usage is relatively narrow. This provides real opportunities for the development of new natural productderived substances and for the suppliers of raw materials. In his talk on Design Criteria for Sustainable Surfactants Dr Paul Reynolds from the Bristol Colloid Centre considered the essential properties of a surfactant from first principles enabling the optimum product to be designed for individual applications. The ideal cement surfactant for example needs to be a good stabiliser have high pH tolerance and have good mobility. This could well be a polymer possessing carboxylate units which can co-ordinate surface Ca2+ ions of a cement grain. Such functionality could be provided by a synthetic-natural co-polymer. W J Mulder of ATO-DLO gave a presentation entitled Surfactants from Plant Proteins. Proteins have many useful properties including biodegradability intrinsic surface activity and a large number of functional groups suitable for chemical modification. They are readily available of reasonable cost and are from a renewable source. Protein surfactants are currently used in several food and non-food applications. Useful chemical modifications include the esterification of amino acids with long chain aliphatic alcohols. These modifications can lead to dramatic increases in emulsifying activity and future uses are likely in both food manufacture (e.g. as emulsifiers) and in non-food application (e.g. as detergents wetting agents and in cosmetics). In his concluding remarks the Chairman noted the positive attitude of this sector of the industry towards making environmental improvements in its products and processes. The area of renewable feedstocks is ripe for new research and for academic-industrial collaboration as well as commercial innovation and exploitation but it is essential that this potential is more widely recognised. G9 Green Chemistry February 1999

ISSN:1463-9262    

DOI:10.1039/gc9900g6

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Summary Highly active catalysts are required for the conversion of CF3CH2Cl to the CFC-alternative refrigerant, CF3CH2F, by HF vapour under heterogeneous conditions. Chromia impregnated with a very low level of zinc(ii) is a superior catalyst precursor to chromia alone. The behaviour of prefluorinated chromia and prefluorinated chromia containing zinc(ii) or nickel(ii) towards fluorine- 18 labelled HF indicates that two types of labile surface fluoride are present, only one of which is catalytically active.Proposals are made to account for the role of ZnII and NiII. Introduction The necessity to develop syntheses suitable for the large scale production of CFC-alternative refrigerants such as 1,1,1,2-tetrafluoroethane (HFC-134a) following the Montreal Protocol has led to renewed interest in the fundamental aspects of heterogeneous catalytic fluorination. The vapour phase halogen exchange reaction, CF3CH2Cl + HF ? CF3CH2F + HCl, presents a particular challenge because of its thermodynamically limited nature, hence the catalyst used must be highly active.Various metal oxides and fluorides have been evaluated, most obviously chromia, 1,2 since it was the catalyst of choice for CFC production under heterogeneous conditions.Pretreatment with HF1 or a fluorine- containing alkane2 is required, suggesting that the catalyst is a fluoride or oxofluoride phase rather than an oxide. Other active catalysts include those derived from hydrated CrF3 or CrIII hydrofluorides, in each case promoted by MgF2,3 CrF3 supported on g-AlF3,4 and CoII, MgII or CrIII supported on g-AlF3.5 Prefluorinated CoII on alumina is a catalyst for the related reaction in which CF3CHClF is converted to CF3CHF2.6 Despite this activity, in no case is definitive evidence available concerning the nature of the catalytically active sites, although for fluorinated chromia there is circumstantial evidence that catalytic activity is related to the extent to which reversible oxidation of CrIII sites in the precursors can be achieved.1b,7 In none of the previous studies has consideration been given to the nature and extent of the interactions between anhydrous HF and the surface of an, often highly fluorinated, catalyst.This important aspect of an overall mechanism is now addressed using the results of experiments in which the behaviour of HF labelled with the radioactive isotope fluorine-18 (b+ emitter, t1/2 = 110 min) towards a range of highly fluorinated catalysts of varying The hydrocarbon CF3CH2F is the current drop-in replacement for the CFC CCl2F2, which is banned under the Montreal protocol.One of the large scale preparative routes to this replacement involves the catalytic fluorination of trichloroethene with HF.The last step, the conversion of CF3CH2Cl to CF3CH2F, is limited thermodynamically. In order to carry out this process efficiently and cleanly, the catalysts used must be extremely active and very selective. This article presents results relating to such a catalyst, chromia doped with either Ni(ii) or Zn(ii). These model catalytic systems display markedly better performance compared to the undoped material.The role of the dopants is discussed. DJM Green Context Halogen exchange reactions for CFC alternatives The behaviour of fluorine-18 labelled hydrogen fluoride towards prefluorinated chromia containing nickel(II) or zinc(II) David W. Bonniface,a John R. Fryer,b Philip Landon,b John D. Scott,a William D. S. Scott,b Michael J.Watson,a Geoffrey Webb*b and John M. Winfield*b a Research and Technology Department, ICI Klea, The Heath, Runcorn, UK WA7 4QD b Department of Chemistry, University of Glasgow, UK G12 8QQ. E-mail: J.Winfield@chem.gla.ac.uk Received 15th October 1998 activities has been examined. The catalysts are derived from chromia or chromia containing nickel(ii) or zinc(ii) precursors and the behaviour of representative examples with respect to catalytic activity in the reaction CF3CH2Cl + HF, and to the individual reagents HF and CF3CH2Cl, is compared in Table 1.Results and discussion The key step in the formation of an active catalyst is an extensive prefluorination (623 K, 18 h) of the precursor by flow of anhydrous HF. Conversion of CrIII–O to CrIII–F is slow, however XPS measurements on fluorinated chromia catalysts containing NiII or ZnII provide strong evidence for the presence of NiF2 and ZnF2. In contrast, although the Cr 2p3/2 binding energies in these samples approach that of a-CrF3, there is no evidence for CrIII in a completely fluorinated environment in agreement with previous observations.1,2 Supporting evidence for the complete fluorination of NiII and ZnII is provided by TEM examination of two fluorinated catalysts containing NiII or ZnII in which lattice spacings attributable to MF2, M = Ni or Zn, were observed.Neither a-CrF3 nor a-Cr2O3 appeared to be present. The most active catalyst of those in Table 1 is derived from a precursor containing a small ZnII loading (°0.25% w/w) on chromia. This catalyst is significantly more active than the corre- Green Chemistry February 1999 9 C Gsponding undoped material.Increasing the ZnII content (for example to 4% w/w) however leads to decreased catalytic activity, even though the apparent activation energy for the reaction is lowered. The NiII study, using higher doping levels obtained by co-precipitation, shows a similar pattern, increasing NiII content resulting in decreased activity and apparent activation energy.Interactions between the fluorinated catalysts and [18F]- labelled HF under flow conditions at 573 K are substantial (Table 1). These experiments were carried out using H18F whose specific count rate (count min21 mmol21) was independently determined, enabling the interaction between HF and a fluorinated catalyst to be quantified as equivalent to mmol of HF uptake per g catalyst (Table 1).Small variations in the uptakes of [18F] are observed but no simple relationship exists between the extent of the interaction with H18F and the identity and extent of the MII dopant. However, subjecting all prefluorinated [18F]-labelled catalysts to HF flow leads to significant reductions (40–75%) in [18F] activity, Table 1.A similar situation is encountered when CF3CH2Cl is flowed over prefluorinated catalysts that have been labelled by subsequent H18F treatment but the fractions of [18F] removed (25–45%) are smaller. It appears that on these highly fluorinated surfaces, two types of labile surface fluorine are present but only that which is labile both to HF and to CF3CH2Cl treatments is catalytically active.In contrast to HF, CF3CH2Cl interacts weakly with the fluorinated catalysts. Exposure of samples of working ZnII-containing catalysts to chlorine-36 labelled CF3CH2Cl did not result in any measurable [36Cl] radioactivity being detected from the surface. However, after prolonged thermal treatment to desorb HF, the interaction of [36Cl]-CF3CH2Cl with the surface could be detected using a direct Geiger–Müller monitoring technique.8 In these experiments a substantial [36Cl] count from the surface (>1000 count min21) was obtained only when more highly ZnIIdoped catalysts were exposed to [36Cl]-CF3CH2Cl at, or above, 423 K.The [36Cl] species deposited on the surface was strongly bound, for example [36Cl] surface count rates were unaffected by removal of CF3CH2Cl vapour and by prolonged pumping at room temperature.These observations suggest that in the absence of HF, a non-catalytic halogen exchange process occurs that is similar to the Halex type and which involves ZnII–F bonds rather than Cr–F as the source of the active fluoride. The results obtained here enable several points of general relevance to the catalytic fluorination of CF3CH2Cl by HF to be made.The presence of a large quantity of labile surface fluoride as a result of the pre-fluorination of the catalyst precursors is an important factor in determining the subsequent catalytic behaviour. In this respect catalytic fluorination of CF3CH2Cl resembles catalytic fluorination of chlorofluoroethanes over fluorinated chromia.9 The presence of a large quantity of labile fluoride derived from adsorbed HF will be beneficial also in suppressing the dehydrofluorination of CF3CH2F and CF3CH2Cl, processes which in other circumstances, using unfluorinated or lightly fluorinated catalysts,2 are competitive with the conversion of CF3CH2Cl to CF3CH2F.Under the conditions used here, dehydrofluorination is not observed above trace levels.Similar considerations should apply to catalysts derived from mixed metal fluorides3–5 or fluorinated alumina.6 However, an inescapable consequence, which is illustrated by the [36Cl] study, is that the interaction of CF3CH2Cl with a catalyst surface will be inhibited and that blocking of active sites by HF will occur. Fluorinated chromia (Table 1) is likely therefore to have a relatively small number of catalytically active sites; they are possibly surface Cr atoms whose Lewis acidity has been promoted by a disordered oxygen/fluorine environment and which are highly active.Finally, an explanation for the behaviour of the MF2, M = Zn or Ni, doped fluorinated chromia catalysts (Table 1) is proposed. The presence of an MII species directly adjacent to the Cr active site will result in a perturbation of the adsorption behaviour of HF and we speculate that this is the origin of the lower apparent activation energies observed for ZnII and NiII doped catalysts (Table 1).The dopant provides an additional pathway for the transfer of catalytically active fluoride to replenish the active site and to remove surface chloride, the effect being apparent most obviously from a comparison of the first two catalysts in Table 1.At higher levels of ZnII doping and at all levels examined for NiII, it appears that the number of active Cr sites is reduced, hence the catalysts are less active. We thank EPSRC and ICI Klea for support of this work. 10 Green Chemistry February 1999 Table 1 Catalytic fluorination of CF3CH2Cl to CF3CH2F by anhydrous HF over fluorinated chromia containing zinc(ii) or nickel(ii) Catalyst precursorsa Microreactor experimentsb [18F] experiments at 573 K, flow conditionsc Precursor Conversion Apparent Uptake of [18F] remaining [18F] remaining stoichiometryd/ at 573 Ke/ activation [18F] by after after Metal(ii) mol (100 g Cr2O3)21 % m22 g energyf/kJ mol21 catalyst/mmol g21 HF flow (%) CF3CH2Cl flow (%) None — 0.18 179 0.29–0.33 31 54 Zn 0.004 0.27 113 0.32–0.33 28 60 Zn 0.067 0.11 92 0.55–0.63 60 75 Ni 0.066 0.14 152 0.61–0.96 47 66 Ni 0.658 0.055 130 0.29–0.89 25 61 a ZnII-containing precursors prepared by aqueous ZnCl2 impregnation of commercial amorphous chromia followed by calcination under N2 flow at 873 K (12 h).NiII-containing precursors prepared by coprecipitation from CrIII and NiII aqueous nitrates (mole ratios 20:1 or 2:1) followed by calcination under N2 flow (18 h) at 723 or 923 K. b Monel metal rig, HF:CF3CH2Cl = 4:1, feed rates 20 cm3 min21 (HF) and 5 cm3 min21 (CF3CH2Cl); catalysts were prefluorinated at 623 K (18 h) before use; catalytic runs were performed under temperature ramping (623–523 K) conditions.c Monel metal rig, H18F flow at 573 K (0.5 h) then cooled under N2 flow then HF or CF3CH2Cl flow at 573 K (0.5 h). d Units chosen to facilitate comparisons between ZnII and NiII catalysts. e Based on GC data and BET areas of working catalysts. CF3CH2F was the only product detected, although trace quantities (<1%) of olefinic products were observed >623 K.f Temperature range 523–573 K.References 1 (a) S. Brunet, B. Requieme, E. Colnay, J. Barrault and M. Blanchard, Appl. Catal. B, 1995, 5, 305; (b) S. Brunet, B. Requieme, E. Matouba, J. Barrault and M. Blanchard, J. Catal., 1995, 152, 70; (c) S. Brunet, B. Boussand, A. Rousset and D. Andre, Appl. Catal. A, 1998, 168, 57. 2 A. Kohne and E. Kemnitz, J. Fluorine Chem., 1995, 75, 103. 3 H. Kim, H. S. Kim, B. G. Lee, H. Lee and S. Kim, J. Chem. Soc., Chem. Commun., 1995, 2384; H. Lee, H. D. Jeong, Y. S. Chung, H. G. Lee, M. J. Chung, S. Kim and H. S. Kim, J. Catal., 1997, 167, 307 4 J. A. Lu, H. Yang, S. K. Chen, L. Shi, J. G. Pen, H. L. Li and S. Y. Peng, Catal. Lett., 1996, 41, 221. 5 H-d. Quan, Z. Li, Z-x. Zhao, H-e. Yang, J. Lu, J-g. Pen, S-k. Chen, H-f. Li and H-l. Li, Appl. Catal. B, 1996, 8, 209. 6 D. R. Coulson, J. Catal., 1993, 142, 289. 7 K. Niedersen, E. Schreier and E. Kemnitz, J. Catal., 1997, 167, 210. 8 A. S. Al-Ammar and G. Webb, J. Chem. Soc., Faraday Trans. 1, 1978, 74, 195. 9 J. Kijowski, G. Webb and J. M. Winfield, Appl. Catal., 1986, 27, 181. Paper 8/08021F Green Chemistry February 1999 11

ISSN:1463-9262    

DOI:10.1039/a808021f

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

F O R UM C G Chemical synthesis in progress at the Centre for Clean Technology University of York UK The RSC Green Chemistry Network The Green Chemistry Network recently launched by the Royal Society of Chemistry will promote the practice and progress of green chemistry and publicise the benefits of sustainable development for chemists and the general public. The Green Chemistry Network will provide l educational materials for universities and schools to support the teaching of green chemistry concepts and practice l a newsletter and books on aspects of green chemistry l training courses for teachers university and industry researchers and managers l a national database on green chemistry linked to other overseas networks via the RSC web site l conferences and seminars for industry and academia l technology transfer brokerage l links to other key organisations (learned societies trade associations government departments research councils educational groups and other green chemistry networks.The hub of the Green Chemistry Network is located at the University of York within the new University Centre for Clean Technology and alongside the Science Education Group (who specialise in the development of educational material for schools and colleges) the Chemical Industry Education Centre and the award-winning Green Chemistry Research Group. The day-to-day running of the network is organised by the network manager who reports directly to the network director.The director is in turn responsible to a management board appointed by the RSC. A technical advisory board ensures representation from other key organisations and provides a valuable source of expertise for the Network. (A larger article on the Green Chemistry Network appeared recently in Chemistry in Britain October 1998 43. Interest in the GCN can be registered by email to greennet@york.ac.uk) G10 Green Chemistry February 1999 . 1998 Presidential Green Chemistry Challenge Award Winners The Presidential Green Chemistry Challenge has been running since 1995 to promote pollution prevention and industrial ecology in the chemical industry through ‘cheaper cleaner smarter chemistry’. Awards are made for three focus areas (use of alternative pathways use of alternative reaction conditions and the design of chemicals for green chemistry) and for a small business and an academic.The 1998 winners are Pyrocool Technologies Inc.– for the development and commercial introduction of an environmentally responsible fire extinguishment and cooling agent Pyrocool Technologies were rewarded for their development of a new firefighting formulation of highly biodegradable surfactants designed for use in very small quantities as a universal fire extinguishment and cooling agent. The product does not contain halon gases (ozone depleters) glycol ethers or fluorosurfactants (which can release hydrofluoric acid on use). It is a mixture of non-ionic surfactants anionic surfactants and amphoteric surfactants with a mixing ratio (with water) of only 0.4%.It has already been employed successfully against numerous fires both in America and elsewhere notably stopping a major oil tanker fire at sea in just 12.5 minutes thus saving 80% of the ship's cargo. Argonne National Laboratory –for novel membrane-based process for producing lactate esters non-toxic replacements for halogenated and toxic solvents The award-winning ANL process is based on selective membranes that permits the low-cost synthesis of high-purity ethyl lactate and other lactate esters from carbohydrate feedstocks. The process requires little energy input is highly efficient and eliminates the large volumes of salt waste produced by conventional processes.In the new process ammonium lactate is converted to the acid which is then converted to the ester. The innovation will eliminate the need for toxic substances expand the use of renewable carbohydrate feedstocks and reduce pollution and emissions. Rohm and Haas Company – for the invention and commercialisation of a new chemical family of insecticides exemplified by CONFIRM™ selective caterpillar control agent Rohm and Haas have been given their second award for a discovering a new class of chemistry the diacylhydrazines that offers farmers consumers and society a safer effective technology for insect control in turf and a variety of agronomic crops. One member of the family CONFIRM™ is a breakthrough in caterpillar control.It is chemically biologically and mechanistically novel. It does not pose any significant risk to the applicator the consumer and the ecosystem. It will replace older less effective more hazardous insecticides. Caterpillars can be controlled by diacylhydrazines – a new class of insecticides Flexsys America L.P. – for elimination of chlorine in the synthesis of 4-aminodiphenylamine a new process which utilises nucleophilic aromatic substitution for hydrogen Flexsys' award originated from their decision to explore new routes to a variety of aromatic amines which would not rely on the use of halogenated intermediates. Of particular interest was the identification of novel synthetic strategies to 4-aminodiphenylamine (4-ADPA) a key intermediate in the rubber chemicals family of antidegradants (total world market ca.150,000 tonnes per annum). The new chemistry is based on nucleophilic substitution for hydrogen (NASH). The new process for 4-ADPA generates 74% less organic waste 99% less inorganic waste and 97% less waste water. If just 30% of the world's capacity to produce 4-ADPA and related materials were converted to the new Flexsys process some 35,000 tonnes per annum less chemical waste and 0.7M tonnes per annum less waste water would be generated. (For a more thorough account of this fascinating new chemistry see the next issue of Green Chemistry) Professor Barry Trost Stanford University (academic award) – for the development of the concept of atom economy Professor Trost's award is in recognition of his enunciation of a new set of criteria by which chemical processes should be evaluated.They fall into the two categories of selectivity and atom economy. The importance of the concept of atom economy is now explicitly acknowledged throughout the chemical industry. Professor Trost has set the challenge for those involved in basic research to create new chemical processes that meet the objectives. A major application will be in the synthesis of fine chemicals and pharmaceuticals which in general are not very atom efficient. Professors Karen Draths and John Frost Michigan State University– for the use of microbes as environmentally benign synthetic catalysts The award-winning Draths-Frost syntheses of adipic acid and catechol use biocatalysis and renewable feedstocks to create alternative synthetic routes to chemicals of major industrial importance.The syntheses rely on the use of genetically manipulated microbes as synthetic catalysts. In excess of 1.9 M tonnes of adipic acid is produced annually and used in the manufacture of nylon 66. Most commercial syntheses of adipic acid use petroleum-derived benzene and involve a last step which employs nitric acid resulting in the formation of nitrous oxide by-product. This leads to some 10% of the annual increase in atmospheric nitrous oxide levels. Benzene is also the starting material for most of the catechol currently produced whereas the Draths- Frost synthesis uses a single genetically CH OH 2 OH OH O OH OH OH OH genetically engineered microbe The Draths-Frost synthesis of catechol FOR U M C G engineered microbe to catalyse the conversion of glucose to catechol.For further information on The Presidential Green Chemistry Challenge Awards Program see http://www.acs.org/govt/whatshot/ gcaward.htm and http://www.acs.org/govt/ whatshot/gcaward.htm The Green Chemistry Institute The Green Chemistry Institute (GCI) was established in 1997 by a group of people from US academia industry national laboratories and government. It is a not-for-profit organisation dedicated to environmentally benign chemical synthesis and processing research and education.The GCI organising committee comprises Sid Chao (Hughes Environmental) and Jack Solomon (Praxai) from industry Dennis Hjeresen and Bill Tumas (both Los Alamos) from the national laboratories and Joe DeSimone and Bill Glaze (both North Carolina) from academia. Joe Breen is the executive director and can be contacted by email at breenj@westat.com. A GCI Newsletter helps to keep interested parties up-to-date with information on green chemistry awards conferences and other news. Opportunities for Research Funding A number of funding bodies offer grants for research into areas related to chemical clean technology this list is by no means comprehensive but describes some of the opportunities available.United Kingdom Engineering and Physical Science Research Council The Chemical Engineering College covers the transformation of raw materials to final products by substantial physical or chemical changes of state rather than by mechanical manipulation fabrication or machining. It is also concerned with such aspects of process design as have an important impact on process technology. Key areas include waste minimisation clean processes and highly selective separations. The Synthetic and Biological Chemistry College will consider proposals in the area of clean synthesis including the development of new processes characterised by low energy consumption Green Chemistry February 1999 G11 F O R UM C G non-toxic reagents recyclable solvents clean effluent and minimum wastage.Other relevant areas include novel synthetic methodology novel reagents regioslective and stereoselective synthesis and biological chemistry. The Combustion Research Programme is aimed at enhancing the research on generic and fundamental combustion issues leading to innovation greater efficiency lower emissions greater control and enhanced safety of combustion. Calls for proposals are announced annually. The programme includes within its remit research in areas including waste incineration catalytic combustion and post-combustion clean-up. The first call for proposals for Collaborative Research involving Chemists and Chemical Engineers was announced in 1998 with a deadline for outlines last November.The scope of the call covered catalysis clean processes combustion electrochemistry and electrochemical engineering. (Web site http://www.epsrc.ac.uk) United Kingdom Biotechnology and Biological Sciences Research Council The BBSRC Engineering and Biological Systems programme includes applied biocatalysis and encourages collaboration between chemists and biologists in areas such as the control of selectivity and activity in catalysis and the integration of catalysis into synthetic processes. Under ‘environmental technology’ the two priority areas are availability of pollutants in soils to organisms and novel liquid effluent technologies. (Web site http://www.bbsrc.ac.uk) European Community Fifth Framework Programme The European Community’s Fifth Framework Programme for research technological development and demonstration activities (1998-2002) has competitive and sustainable growth as one of its thematic programmes.Within this the first key action area is innovative products processes and organisation which covers the development of new and improved methods of design advanced equipment and process technologies for production that increase the quality and reduce the costs of processes for services and products. Under ‘ecoefficient processes’ one of four subtopics the goal is to minimise ‘full lifecycle impact’ on the environment. This takes account of all essential elements of the industrial system ranging from G12 Green Chemistry February 1999 extraction through production to waste management with emphasis on resource intensive processes.The priorities are as follows l clean and eco-efficient processing technologies l research aimed at mastering basic phenomena such as synthesis catalysis separation and reaction mechanisms process modelling and simulation l impact monitoring and assessment of risks l in situ and on-line recovery of waste novel processes for treatment reuse and safe disposal of waste and for upgrading reusing or dismantling products and production systems The other sub-topics are efficient design and manufacturing (including manufacturing technologies and equipment for optimal use of resources and for product miniaturisation) intelligent production and organisation of production and work.(Web site http://cordis.lu/fifth/home.html) Green Chemistry in UK Parliament The take-home message from the 1998 RSC Parliamentary Links Day in the UK on ‘Good news from chemistry’ was clear the solutions to many environmental problems will be found through chemistry. In a series of talks to a large audience made up of members of the Houses of Commons and Lords as well as RSC members and distinguished guests it was made clear that professional chemists are cleaning up existing products and processes and in many cases replacing these with more environmentally friendly alternatives. After an introduction on Meeting the Environmental Challenge given by the then President of the RSC Professor Eddie Abel Stephen Falder of H Marcel Guest Ltd described the ingenious role of the chemists in effectively helping to preserve the tropical hardwood forests.Were it not for paints and coatings that USA Environmental Protection Agency The US Environment Protection Agency's Office of Research and Development awards research grants and fellowships to develop the sound environmental research necessary to ensure policy and regulatory decisions. (Web site http://www.epa.gov/ORD/) USA National Science Foundation The Chemical and Transport Systems Division of the National Science Foundation supports research that involves the development of fundamental engineering principles process control and optimisation strategies mathematical models and experimental techniques.Special emphasis is on environmentally benign chemical and material processing and its programmes include chemical reaction processes. The Division of Chemistry's Organic Synthesis programme includes the development of new reagents and methods for organic synthesis and new organic materials. Applications of catalysis are considered under engineering and under inorganic bioinorganic and organometallic chemistry. (Web site http://www.nsf.gov). Fuel cells are the most promising power source for the electric cars of the future permitted the use of softwoods in the industrial revolution the forests would have suffered the same fate as the medieval hardwoods of Europe.Kirsty Clode of BP Chemicals described the Cativa process for the production of acetic acid. This is based on a new catalyst and promoter system involving iridium which improves energy efficiency and reduces waste and emissions. The process took 3 years to progress from early laboratory trials to installation on a 290 kilotonne per annum plant in the USA. Fuel cells are widely considered to be the keys to the cars of the future. This was the subject of the talk given by Robert Evans of Johnson Matthey plc. While we cannot completely stop or control emissions from combustion engines electric vehicles offer zero emission with the fuel cell considered to be the most promising power source for them.The subject illustrates the importance and value of an interdisciplinary approach by bringing together the areas of environmental chemistry electrochemistry and catalysis. More and more we are looking to develop products in a sustainable way. One interesting example of this is the replacement of finite petroleum-based feedstocks by sustainable crop-based feedstocks in areas such as paints. Phil Taylor from ICI Paints described work going on in this area notably the use of the carbohydrate family and especially starch in the polymer systems used in commercial paints. Margaret Mills from Zeneca Agrochemicals gave a talk on how the agrochemicals industry is meeting the environmental challenge. This included discussion on chemical ways of reducing the amount of pesticide entering the environment through increased activity (leading to reduced dosage) and the selective use of one isomer.Finally James Clark described some clay-based and other environmentally benign catalysts that can be used as replacements for hazardous reagents and catalysts that are widely used in the manufacture of fine and speciality chemicals. He also announced the formation of the RSC Green Chemistry Network. A fuller account of the RSC 1998 Parliamentary Links Day including detailed summaries of the talks along with articles on related subjects can be found in Science in Parliament July/August 1998. Further information on the establishment of the RSC Green Chemistry Network can be found in Chemistry in Britain 1998 43.UK Government consultation paper sustainable production and use of chemicals The UK Government’s 1998 consultation paper on sustainable production and use of chemicals sought views on ways in which we might take a much more pre- C G cautionary approach to chemicals in the environment. While recognising that chemicals underpin the quality of modern life and that the chemicals industries make a significant contribution to the UK economy the paper addressed the need for the chemicals industry to respond to the challenges of sustainable development and improving eco-efficiency. It also considered the importance of policy making and regulation being more transparent.With regard to sustainable development it is recognised that important current challenges are the adoption of more eco-efficient practices in the chemical industry and encouraging innovation in resource usage. The government wants to encourage voluntary action (adopting public performance indicators environmental management systems and engaging in increased dialogue with stakeholders) but it is also considering suitable targets and indicators of progress towards better eco-efficiency. Generally the Government wants to seek ways to increase the speed of innovation reduce toxic impact and develop eco-efficient products. The consultation paper also recognises the burdens imposed by the new Chemicals Notification Scheme and the possible need for improving progress under existing legislation.It also addresses the question of possible framework legislation on chemicals at the EU or UN level. Other issues raised by the paper include options for reducing risks from chemicals such as self-assessment replacement and action against chemicals based on persistence bio-accumulation or toxicity. The paper also invited comments on proposals for facilitating informed public participation in policy making on chemicals in the environment. F O R UM Further reading Sustainable production and the use of chemicals Department of the Environment Transport and the Regions 1998. Document reference 98EP0058 Opportunities for Change Consultation Paper on a revised UK strategy for sustainable development.Department of the Environment Transport and the Regions 1998. Document reference 97EP0277. The first UK strategy on sustainable development can be found in Sustainable Development – The UK Strategy Department of the Environment CM2426 HMSO 1994 ISBN 0-10-124262-X. Green Chemistry February 1999 G13 F O R U M C G Royal Commission on Environmental Pollution In its 21st Report Setting Environmental Standards the Royal Commission on Environmental Pollution calls for a new approach to deciding environmental policies. The key feature of this new approach is that as well as drawing on rigorous and dispassionate analysis there must be greater sensitivity to people's values.The study was led by Sir John Houghton who stepped down as Chairman in the summer of 1998. The report emphasises that protecting the environment has become much more complex. Increasingly the task is to prevent damage which may be global in scale and occur some way into the future. Moreover the commitment to sustainable development means that pursuing material well-being and enhancing social equity have to be reconciled with protection of the environment. Other points covered in the report include recognising the limits of scientific assessment of environmental issues the need for independent investigation on research programmes and the care required to ensure that life cycle analysis approaches encourage rather than hinder improvements in stages of the cycle.‘the task is to prevent damage which may be global in scale and occur some way into the future’ Some of the key conclusions from the Royal Commission's 21st Report are listed below l Decisions about environmental policies must be based on the scientific evidence and an analysis of technological options but they must also take into account risks and costs. l Any body involved in setting standards should in all its pronouncements draw an explicit distinction between scientific statements and recommendations it wishes to make after considering a G14 Green Chemistry February 1999 scientific assessment in conjunction with other factors; and should identify clearly what those other factors are.l When environmental policies or standards are adopted it should always be made clear in an explicit statement whether they are designed to protect the natural environment human health or both and the degree and nature of protection they are intended to afford. l In a scientific assessment of an environmental issue there are bound to be limitations and uncertainties associated with the data at each stage. Standard setting and other decisionmaking procedures should recognise that. The requirement for sound science as the basis for environmental policy is not a requirement for absolute knowledge or certainty and should not be interpreted as such. l To prevent development of new understanding being restricted by established regulatory procedures vested interests or small closed communities of experts publicly funded programmes of environmental research should include provision for independent investigation and enquiry.l To ensure that the full range of options and repercussions are considered assessments of technological options carried out as inputs to decisions on environmental policies or standards should be on a life cycle basis. l Broadly based assessments of options on a life cycle basis must not be allowed to become an excuse for avoiding or delaying significant improvements available at particular stages in the cycle. l Environmental standards should be set for the smallest area for which it is sensible and effective to do so.l Use of a combination of direct regulation economic instruments and self-regulation is the best way to further general adoption of clean technology whilst not putting at risk compliance with numerical standards set to protect humans and the natural environment against specific hazards. (Based on a news release from the Royal Commission on Environmental Protection October 1998) The Royal Commission on Environmental Pollution (Steel House 11 Tothill Street London,UK SW1H 9RE) has a web site at http://www.rcep.org.uk Royal Society of Chemistry Millennium Conference Green chemistry and aspects of sustainability will be among the major themes for the Royal Society of Chemistry’s Annual Conference in the year 2000.The conference will be the second in a new style which is hoped will become the premier event in the RSC calendar. It will be held between 16-20 April 2000 in Manchester a key geographical centre for the UK chemical industry. There will be four half-day sessions devoted to aspects of sustainability. The first two sessions will present some of the work funded by the UK’s Engineering and Physical Sciences Research Council (EPSRC) cleaner synthesis programme. During the 1990s this programme has supported university research into a number of key areas including catalysis novel solvent systems electrochemistry and reactor design. These sessions will describe the outcome of several of these projects and include examples of industrial applications. Papers on broader aspects of green chemistry such as renewable feedstocks and substitution of cleaner products are also planned. A third session will deal with educational and promotional aspects of sustainability and will cover national and international efforts to co-ordinate relevant research and training and the development of new educational materials. Awards for innovation and best practice will be presented. The fourth will deal with general concepts of sustainability. This session should be informative provocative and sometimes controversial and will address political and socio-economic issues. A poster session is also planned and anyone interested should contact Stanley Langer at the Royal Society of Chemistry Burlington House London UK W1V 0BN (langers@rsc.org).

ISSN:1463-9262    

DOI:10.1039/gc990g10

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Summary In this study, a combination of three chemicals (cashew nut shell liquid, sulfited wattle tannin and copper(ii) chloride) has been used to develop an environmentally friendly termite preservative. Cashew nut shell liquid (CNSL) is a by-product of cashew nut kernel processing factories and its use in the preservative formulations minimises the wastes from the factory as well as the amount of conventional hazardous preservatives from entering the environment. The formulated preservatives were tested for their ability to preserve wood blocks from a soft wood, ponderosa pine (Pinus ponderosa) and a hard wood, trembling aspen (Populus tremuloide).Sulfonated wattle tannins alone or combined with copper chloride at different concentrations, and cashew nut shell liquid (CNSL) without or with copper chloride were used in treating the 14 3 14 3 14 mm wooden blocks from the two wood species.The samples were exposed to termite attack in the surveyed fields in Arusha and Moshi, Tanzania. After 108 days exposure, evaluation of termite attack by measuring the weight losses and damage showed that the test wood treated with the combinations 40% CNSL + 1% CuCl2 and 40% CNSL + 2% CuCl2 were among the least damaged.Introduction Termites are destructive insects which attack both field and harvested produce. Wood products are also subject to termite and other bio-hazard attack if preventative measures are not taken. These bio-hazard attacks reduce the service life of wood products. In Tanzania for instance, the average service life of a nondurable wood species is about three years although it can be extended by the use of wood preservatives.1 The extended durability period depends on, among other things, the species of wood, the type of preservative used and the place at which the wood is stored or used.In Tanzania, a survey reports1 that wood preservation is carried out using creosote (60%), pentachlorophenol (20%), and copper chromium arsenate (20%).The common wood preservatives documented elsewhere to be effective against termites include chlorinated products, boric acid and arsenic compounds.2–5 Apart from creosote, which is moderately toxic when heated to decomposition, pentachlorophenol, arsenic and chromium compounds are rated as highly toxic industrial materials.6,7 Chromate salts are associated with cancer of the lungs while arsenic compounds can cause a variety of skin abnormalities including itching, pigmentation and even cancerous changes.6 Work on preventing termite attack by adding insecti- Preventing termite attack Environmentally friendly chemical combinations of cashew nut shell liquid, sulfited wattle tannin and copper(II) chloride Gerold C.J. Mwalongo,*a Lupituko L. Mkayula,a B. Dawson-Andoh,b Egid B. Mubofu,a J. Shieldsb and Bonaventura A. Mwingirac a Chemistry Department,University of Dar es Salaam, P.O. Box 35061, Dar es Salaam, Tanzania b Forintek Canada Corp., Ottawa, Canada c Tanzania Industrial Research and Development Organisation, Dar es Salaam, Tanzania Received 20th October 1998 cides to wood adhesives used on fabricated building materials has been done and showed good anti-termite properties.4 The resistance of wood treated with copper(ii) compounds derived from tri- and di-alkylamine–boric acid complexes to termite attack is also found to be good, and is environmentally more acceptable than the use of conventional wood preservatives.8 Copper complexed with condensed tannin is observed to be an efficacious wood preservative although the combination of the sulfited bark extract (tannin) and copper chloride is reported to be a more effective wood preservative.9 A notable advantage of using a combination of copper compounds instead of conventional wood preservatives is that termites readily acquire toxic doses by consuming small amounts of the treated wood and thus the nearby untreated wood is protected from termite attack.Moreover, copper compounds are active against fungal attack and hence can also protect the wood in this way. Despite their environmental acceptability over conventional wood preservatives, large doses of copper complexes are environmentally less friendly than chemicals mainly derived from natural sources.The wood preservatives commonly used in Tanzania exert a negative environmental impact as their effluent streams contain particularly persistent toxic compounds such as pentachlorophenol, arsenic and chromium compounds, this calls for the development of alternative wood preservatives from local natural materials. The latter entails finding more environmentally acceptable substances from natural sources like wattle tannins and cashew nut shell liquid (CNSL) that are less toxic than the Green Chemistry February 1999 13 The discovery and application of environmentally benign new products and product mixtures which can effectively replace hazardous chemicals are important areas of green chemistry.Traditional wood preservatives used in developing countries are often based on a potent mixture of toxic species such as chlorinated phenols, arsenic and chromium compounds.Copper-based preservatives are promising alternatives but can involve unacceptably large quantities of combinations of compounds. In this article the novel combination of cashew nut shell liquid, sulfited wattle tanin and small amounts of copper are shown to be effective mixtures for the prevention of termite attack.DJM Green Context C Gconventional wood preservatives used in Tanzania.6 The possible effluents from either pilot or full scale processes using this new technology will comprise the less toxic cashew nut shell liquid, tannin and small concentrations of copper chloride. As might be expected from its biological origin, wattle bark extract contains, as well as tannins, a number of chemically distinct constituents.The common hydrolysis product of tannin is gallic acid shown in structure I. In the tree bark, tannin is said to be involved in the protection of the tree from insect and fungal attack.10 The wattle tannin based adhesive from Tanzania has been extensively characterised and was useful in the formulation of anti-termite compounds.11 On the other hand, CNSL is an extensively studied,12–14 naturally occurring phenol obtained as a by-product during the processing of cashew kernels, and contains several phenolic compounds.A major monophenol component of the technical CNSL distillate is cardanol which has a C15 side chain in the meta position, as shown in structure II. The other two chief constituents of the CNSL are anarcadic acid and cardol, shown in structures III and IV respectively. Minor components include 2-methylcardol (V) and a small percentage of polymeric materials.The degree of saturation of the C15 alkyl side chain varies from complete saturation to partial unsaturation as shown in structure VI. The phenolic character and the unsaturation in the alkyl side chain make CNSL constituents important reactive materials in the preparation of binders for coatings and anti-corrosive paints and resins.13 Cashew nut shell liquid is also reported to be used in protecting wood against termites and is especially used in making insecticidal formulations.15 Since some of these plant natural products have good insecticidal activity and low toxicity to humans, interest in using them as wood preservatives is inevitable.OH HO HO COOH OH C15H31- n OH C15H31- n COOH I II III OH C15H31- n OH C15H31- n H3C HO HO IV V n = 0 n = 2 n = 4 n = 6 ( Z )-pentadec-8-enyl (8 Z,11 Z )-pentadeca-8,11-dienyl (8 Z,11 Z )-pentadeca-8,11,14-trienyl VI (structures of C15 chains in II–V) Ar Ar Ar Ar The above reported use of these natural products against termites has stimulated our interest in developing an anti-termite wood preservative from combinations of cashew nut shell liquid (CNSL), copper(ii) chloride, and sulfited wattle tannins. The study objective was to develop a wood preservative using Tanzanian natural products with insecticidal and biocidal activities.Screening of the ability of CNSL and sulfited wattle tannins from Tanzania in combination with commercial wood preservatives to protect against termite attack was done.The wood preservative formulations included the combination of CNSL and CuCl2 at different concentrations, wattle tannins and copper chloride, CNSL alone, wattle tannin alone, copper chloride alone and the control was copper chromium arsenate (CCA). The uptake and commercialisation of this technology on a large scale is technically feasible by on site recycling of these byproducts.This can be achieved by proper engineering design and innovation so as to incorporate the technology into the existing processing factories. On a pilot scale however, off-site recycling is a necessity in order to establish technical and economic viability towards large scale technology.Success in the recycling of cashew nut shell liquid and wattle tannins will be a step towards a cleaner technology which is about minimising the environmental impact of the by-products from the processes. The cost of designing and re-designing the process seems to be one of the probable barriers against commercialisation of the technology. Other likely barriers are the standard of the end-use material and the availability of markets for these preservatives and their products.This paper reports and discusses the termite preservatives formulated from various combinations of compounds. The amount of CNSL in the combinations was large as cashew nut shell liquid is a by-product of the process and its use in preservative formulations will reduce process releases to the environment.The call for the latter aims at replacing the conventional environmentally hazardous compounds. The results of field tests against termite attack of wood blocks on the formulated preservatives are also reported and discussed. Materials and methods Test wood sample preparation and treatment The test wood blocks were prepared from sapwood of two species; a soft wood ponderosa pine (Pinus ponderosa) and a hard wood, trembling aspen (Populus tremuloide).Seven hundred and seventy sapwood blocks, each of 14 3 14 3 14 mm size, were cut from air-dried sapwood of the two wood species. The test wood blocks were labelled and conditioned to 50% relative humidity and constant temperature (70 °F) to a constant weight.The blocks were randomly assigned to various treatments as per American Wood Preserver Association (AWPA) standard E10-91.16 The weight of each block was recorded after treatment with the formulated preservative compounds. Formulation of preservatives and wooden block treatment The preservatives were formulated from sulfited wattle tannins, CNSL and copper salts in different concentrations.The control treatments included CCA, copper chloride, dimethyl sulfoxide (DMSO) and distilled water. The treatments were recorded in two categories coded as AS and PP for trembling aspen and ponderosa pine wood species respectively. The original weights of the treated test wood blocks were recorded and thereafter screened against harvesting termites of Kalotermes spp.for 108 days field exposure in Arusha and Moshi, Northern Tanzania. The test cubes were spread on top of the pre-cleaned experimental grounds before covering them with the dry plant materials. 14 Green Chemistry February 1999Water at an amount of 1000 cm3 m22 was sprinkled on the plant materials to provide an appropriate environment for termite activity underneath. Damage assessment of wood blocks Damage and weight loss were recorded at an interval of two weeks, with a few exceptions.Damage on the block surfaces was observed visually whereas the block weight losses were determined by collecting the samples from the field and exposing to the laboratory atmosphere for moisture stabilisation before weighing them using a Sartorios analytical balance.Results and discussion Field surveys The fields for exposure of the test wood blocks were surveyed and a large number of termite mounds, measuring up to three metres, on the open plains of Babati, West Kilimanjaro, Sanya plains and along the wheat growing belt of Mbulu Tanzania, were recorded. Damage on big trees, fallen timber, and in seedbeds was also recorded in West Kilimanjaro, Karatu and in Sanya plains.The damage incidence in field crops including beans, maize and wheat was at a peak during the harvesting period (July/August–October) in this part of Northern Tanzania. Considerable damage was also recorded on storage structures in some homesteads visited. Termite screening responses The results of different termite screening responses on the remaining percentage weight of the wood blocks after 108 days of field exposure are shown in Fig. 1 and 2. Some of these damage responses showed better results than the commercially used CCA. From the results in the figures, three distinct groups of treatment responses have been identified although they were not all consistent. The first group is that of the least damaged treated test wood with their mean percentage weight losses after 108 days of field exposure: 3% CCA (2.2%), 1.5% CCA (3.3%), 0.5% CCA (4.8%), 2% CuCl2 (5.5%), 40% CNSL + 2% CuCl2 (10.0%), 2.5% CuCl2 (10.5%), 40% CNSL + 1% CuCl2 (10.8%).The fact that there were no dead termites recorded on the test ground surfaces suggests that the observations can be explained by the possibility that the blocks were not, or only slightly, damaged because either the impregnated chemicals acted as termite repellants or the chemicals made the blocks unpalatable to termites.The repellency effect by some of the plant materials to some insects, including aphid species, is well reported elsewhere.17 The second group consists of susceptible impregnated wood blocks. This group includes the following treatments with their percentage loss at 108 days of exposure: water (49.2%), DMSO (30.7), 5% tannin (20.5) and 2% tannin (15.6).These observations may be explained as being due to the effect of the impregnated chemicals in that either the test blocks were still palatable to termites or the chemicals acted as termite attractants. The latter possibility is supported by the well documented literature in that the choice of plant materials for consumption by insects is influenced by a complicated processes involving physical and/ or chemical responses.18 The third group was evaluated as that of moderate damage.It should be noted however, that there was no consistency in weight losses in all the identified groups. This may have been due to uptake of either moisture or soil particles from the test grounds and a study is underway to identify the cause of this inconsistency.Fig. 1 Remaining percentage weight of wooden blocks after 108 days of field exposure of sample (AS). Fig. 2 Remaining percentage weight of wooden blocks after 108 days of field exposure of sample (PP). Conclusion Sharp differences between preservative effectiveness on test wood damage have been noticed in terms of the test wood damage response and weight loss. The survival of the termites in the test wood blocks shows that the formulated preservative does not act by killing the termites but is rather linked to the possibility that the compounds made the wood blocks unpalatable to termites or were termite repellents.The least damaged blocks are suggested for a screen against other termite species so as to establish the suitability as anti-termite compounds.If the formulated preservatives are active against other termite species, there is a necessity to try the preservative on a large scale, for it may turn out to replace the environmentally unfriendly wood preservatives currently used in the country. Cleaner technology is about minimising the adverse environmental impact of releases from industrial processes, and the success in recycling cashew nut shell liquid and wattle tannin will reduce wastes from these processing factories.Acknowledgements Special thanks are directed to the International Development Research Centre (IDRC) for their financial support and to Dr. B. Uronu, of Tanzania Pesticide Research Institute (TPRI) for his technical assistance on termite screening and to the staff of Forintek Canada Corp.for their valuable co-operation and assistance in the course of doing the research. Green Chemistry February 1999 15References 1 K. K. Murira and G. S. Klem, Deterioration of creosote treated eucalypt transmission poles in Tanzania, M.Sc. Thesis, Faculty of Forestry, Sokoine University of Agriculture, Morogoro, Tanzania, Record No. 41, 1989. 2 P. C. Pantua, A study of termite resistance of foreign chipboard treated with boric acid and other compounds, University of the Philippines, Laguna, Philippines, 1985, vol. XVI (2 & 3), p. 51. 3 G. E. Brown and H. M. Alden, For. Prod. J., 1960, 10, 434. 4 R. H. Beal, For. Prod. J., 1979, 29, 29. 5 I. Stolley, Some methods for treating particle boards to increase their resistance to fungi and termites, Proc. Int. Consultation on Insulating Boards, Hard boards, and Particle boards, FAO/ECE/Board cons/pap.5.38, 1958, vol. 4, p. 66. 6 Dangerous properties of Industrial Materials, ed. N. Irving Sax, Reinhold Publishing Corporation, 1963. 7 P. M. Try and G. J. Price, in Issues in Environmental Science and Technology, ed.R. E. Hester and R. M. Harrisson, RSC, Cambridge, 1995, vol. 3, p. 17. 8 G. C. Chen, G. R. Esenther and R. M. Rowell, For. Prod. J., 1986, 36, 18. 9 P. E. Laks, Holzforschung, 1988, 42, 299. 10 Kirk-Othmer Encyclopaedia of Chemical Technology, ed. H. F. Mark, J. J. McKetta, jr., D. F. Othmer and A. Standen, John Wiley and Sons, New York, 1968, vol. 16, p. 690. 11 L. Calve’, G. C. J. Mwalongo, B. A. Mwingira, B. Riedl and J. A. Shields, Holzforschung, 1995, 49, 259. 12 J. H. P. Tyman, V. Tychopolous and P. Chan, J. Chromatogr., 1984, 303, 137. 13 J. H. P. Tyman, J. Chromatogr., 1975, 111, 277. 14 V. Madhusudhan, M. A. Sivasamban, R. Vaidyeswaran and M. Bhagawantha Rao, Ind. Eng. Chem. Process. Res. Dev., 1981, 20, 625. 15 E. S. Lepage, and A. T de Lelis, For. Prod. J., 1980, 30, 35. 16 American Wood Preserver Association, AWPA standard method of testing wood preservatives by Laboratory soilblock etiltures, E10-91: 1992, pp. 243–253. 17 T. H. Hsiao and G. Fraenkel, in The role of secondary plant substances in the food specificity of the Colorado beetle, Ann. Entomol. Soc. Am., 1968, 61, 485. 18 M. Kogan, Ecological theory and integrated pest management practice, Wiley, New York, 1986. Paper 8/08022D 16 Green Chemistry February 1999

ISSN:1463-9262    

DOI:10.1039/a808022d

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

The obtrusive towers of today’s chemical complexes should be replaced with more compact and inconspicuous equipment Process Intensification and Green Chemistry Colin Ramshaw from the Centre for Process Intensification and Innovation at the University of Newcastle upon Tyne in the UK advocates a step change in the of the process system. In addition the process intensification philosophy should be applied across the whole spectrum of unit operations used in the plant. Bearing in mind the dramatic size reduction which is sought process intensification will probably involve novel and unusual approaches to equipment design. It is not a strategy for the faint-hearted. Herein lies one of its main disadvantages namely the lack of new design codes to engender confidence in those who specify new equipment.Radical and unconventional approaches will be the order of the day. Many searching questions will be posed such as the need for turbulent flow in pipes the use of batch rather than continuous operation and the application of merely terrestrial acceleration to multi-phase systems to name but a few. It is a sobering thought that if chemical engineers were given a free hand to philosophy of plant and process design When the concept of process intensification was developed within ICI in the late 1970s the main intention was to make big reductions in the cost of processing systems without impairing their production rate. The term ‘Process Intensification’ describes the strategy of making dramatic (100-1000 fold) reductions in plant volume in order to meet a given production objective.It is well known that the cost of the main plant items (e.g. reactor separators etc.) only represents around 20% of the cost of a production system with the remainder being incurred by pipework structural support installation and so on. A major reduction in equipment size with hopefully a high degree of telescoping of plant function could lead to large cost savings by eliminating support structure column foundations and long pipe runs. Advantages The degree of miniaturisation involved is that needed to generate the cash savings required. Thus volume reductions of the order of 100 times must be our target ‘major reductions in equipment size could lead to large cost savings’ in order to secure the desired impact on costs.While an individual intensified unit may cost a little more than the conventional equivalent (although hopefully it will not) it must generate substantial overall savings in the cost F EAT U R E C G Green Chemistry February 1999 G15 F E AT U R E GC design the human digestive and metabolic system our bodies would be much larger and require many kilowatts to operate them. On the other hand nature operates unobtrusively with laminar flow in high density matrices (kidneys and lungs) on a semi-continuous basis and copes with fouling problems by coughing. As scientists and engineers we should not be too arrogant to learn a few lessons from the natural world.While cost reduction was the original target for process intensification it quickly became apparent that there were other important benefits particularly in respect of improved intrinsic safety reduced environmental impact and energy consumption. Given the anticipated plant volume reductions the toxic and flammable inventories of intensified plant are correspondingly reduced thereby making a major contribution to intrinsic safety. This point has been well made by Trevor Kletz who has commented that ‘what you don't have cannot leak’.1 With regard to the environment the intensified plant of the future will be much less obtrusive with the distillation and absorption towers of our present chemical complexes being replaced by more compact and inconspicuous equipment which may be hidden by the boundary tree line.In addition the cost of effluent treatment systems will be less allowing tighter emission standards to be reached economically. However the most telling environmental influence of process intensification could well be in the development of new reactor design for truly clean technology. Rather than accept mere ‘end of pipe’ solution we must create fluid dynamic environments which allow the intrinsic chemical kinetics free rein. We then have a far better prospect of designing reactors which operate intensively and which give high selectivity. This would facilitate the delivery of a high quality product without an expensive downstream purification sequence.The high heat and mass transfer coefficients which can be generated in intensified equipment can be exploited to reduce the concentration/temperature driving forces needed to operate energy transformers such as heat pumps furnaces electrochemical cells etc. This enhances the equipment's thermodynamic reversibility and hence its energy efficiency. For example we have shown at Newcastle that the application of elevated acceleration fields to a simple chlorine cell can reduce its voltage by over 0.4 V.2 Similarly the Rotex absorption air conditioner3 which will soon be entering G16 Green Chemistry February 1999 Spinning disc reactor technology field trials demonstrates a very high performance while avoiding the arcton/chlorofluorocarbon working fluids used in vapour compression air conditioners.Instead a water solution of mixed alkali metal hydroxides is employed. Therefore innovative applications of process intensification thinking can improve our capacity to meet the energy and global warming targets which were recently agreed at Kyoto. The nuclear reprocessing industry is likely to be a major beneficiary of process intensification on several counts. Much of the life cycle cost associated with any nuclear operation is involved in the final decommissioning of the equipment. Intensified plant with its dramatically reduced size and shielding requirement allows the overall life costs to be significantly reduced.In addition reprocessing operations must take into account the permitted inventories in each of the process units in view of criticality considerations. This can result in operation at lower concentrations than those preferred from an economic point of view. Intensified reprocessing avoids this limitation and facilitates the use of higher more economic concentrations. The envisaged size reductions inevitably mean that process residence times will be much less than those we are currently used to and our control philosophy must be amended accordingly. Indeed we must ask whether we need control at all in the conventional sense of requiring ultra-rapid feedback from novel fast-response process sensors. The parallel between the slow-response Aga cooker and a fast-response gas flame is relevant here and it is common knowledge that food can be effectively prepared using either! Fast-response reactors open up the possibility of switching to more severe process conditions that would be prohibited in conventional units in view of the tendency to degrade the product.It may be possible to exploit a virtuous circle:- short residence time – higher temperature –faster kinetics –smaller reactor – shorter residence time. In a more general business sense there will be an improved ability to change the process output in response to market demand. Therefore rather than transport hazardous chemicals on the railways and public highways it may be feasible to operate a distributed production strategy with economic manufacture on a customer’s site as is currently done for oxygen and nitrogen.This has obvious environmental and safety advantages. However the R & D community must generate appropriate cost-effective process engineering equipment and most importantly this must be marketed effectively so that it is widely used. Example The manufacture of fine chemicals is conventionally performed in stirred vessels operated batchwise to produce typically 50-5000 tonnes per annum. The drug industry operates on a similar basis but with a lower output (5-100 tonnes per annum) having a very high value. In both cases there is a very strong incentive to improve intrinsic safety by minimising process inventories and avoid reaction ‘run-away’.As far as the drug industry is concerned there is also strong pressure to reduce the time needed to bring new molecules to market in order to maximise the profitable manufacturing period available within the 20-year life of the patent. Therefore regulatory authority approval for a new process will be achieved much more quickly when continuous production at the laboratory scale can be achieved for the desired rates using proven equipment because the need for approval at larger scale has been eliminated i.e. the laboratory scale is the full scale. Finally in the context of reducing process labour costs there is a strong business interest in eliminating interbatch cleaning by operating the process continuously (on a ‘desktop’) while being controlled by its dedicated computer.Recent research at Newcastle University4 has shown that spinning disc reactors (SDRs) are eminently suitable for helping to meet these business objectives for several important processes. Their key characteristic is an ability to stimulate intense heat/mass transfer between a highly sheared liquid film and the rotating disc over which it moves or the adjacent gas phase. This allows rapid reactions which involve viscous liquids or large exotherms to be precisely controlled. Following extensive discussions with potential industrial partners in the pharmaceuticals/fine chemicals area it has become evident that there is considerable interest in the opportunities presented by spinning disc reactor technology.The target reactions are those which are intrinsically fast and exothermic but which are currently limited by poor heat and mass transfer when performed in conventional stirred vessels. This can result in large inventories of hazardous material possible reactor run-away and poor quality product. A reactor design based on spinning discs provides an excellent heat and mass transfer environment for the reacting liquid and promises to overcome these disadvantages. SDR technology offers the possibility of a step change in manufacturing operations particularly with respect to the following attributes l Ability to cope with very fast exothermic reactions (corresponding to heat fluxes of up to 100 kW/m2 .l Low inventory/intrinsic safety (liquid film thickness are 50-200 (mm). l Rapid response (liquid residence times are 1– 5 seconds). l Easy cleaning. l Close control (due to short residence times). However in general it is perceived that the biggest obstacle to the adoption of SDR technology will be business process issues rather than technology. In particular chemists involved in process development have both a lack of awareness of SDRs and a fear of ‘mechanical’ innovations. At Newcastle we are tackling this problem by manufacturing prototype SDRs in our workshops and then arranging to have them operated in the laboratories of our industrial collaborators.Initial results are very promising and it is anticipated that several joint projects will emerge in order to perfect the technology for each client's application. Ultimately it is the intention to have simple proven versions of SDRs available when the process route is being developed by the chemist. Hopefully this will encourage the adoption of a continuous processing strategy from the GC outset because once beakers or flasks are used in the initial process development it is very difficult thereafter to gain support for a continuous option. It is recognised that a typical fine chemical/drug process involves many operations in addition to the reaction stage. These may be extraction precipitation solids removal drying distillation etc.In order to bring the desk top plant to reality intensified versions of the relevant conventional equipment must be made readily available to the process research chemist otherwise we will end up with the same old pots and pans as before. Although this is a challenging target the business benefits justify its enthusiastic acceptance. F E AT U R E Conclusions l A strategy of process intensification requires a step change in the philosophy of plant and process design. l If effectively implemented it will lead to major improvements in environmental acceptability energy efficiency intrinsic safety and capital cost. l A major cultural change is required on behalf of chemists engineers and managers and it is this rather than technical difficulty which represents the main obstacle to progress. References 1 ‘What you don’t have can’t leak,’ T. Kletz Chem. Ind. May 6 1978. 2 ‘Electrochemistry in a centrifugal field,’ H. Cheng K. Scott and C. Ramshaw Proc. Conf. on Process Innovation and Intensification October 21-22 1998 Manchester UK (Inst. Chem. Eng.). 3 ‘An intensified absorption heat pump,’ C. Ramshaw and T. L. Winnington Proc Int. Refrigeration 1998 vol. 85 p. 26. 4 ‘The spinning disc reactor for styrene polymerisation,’ K. V. K Boodhoo R. J. J. Jachuck and C. Ramshaw Proc. Conf. on Process Innovation and Intensification October 21-22 1998 Manchester UK (Inst. Chem. Eng.). Green Chemistry February 1999 G17

ISSN:1463-9262    

DOI:10.1039/gc990g15

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Summary Sulfated metal oxides are a useful group of strong acid catalysts. The nature of their acidity, the identities of the active sites and their use in hydrocarbon transformation reactions are discussed. Introduction Acid catalysis is of fundamental industrial importance. It plays a vital role in the petroleum industry where acid catalysts are employed in the various isomerisation, cracking and alkylation reactions used to upgrade oil.Acids are also employed as catalysts for large scale polymerisation processes and display activity for hydration/dehydration reactions such as the interconversion of ethanol and ethylene. In the following, we briefly describe the interest which one particular class of solid catalyst has attracted because of its extremely high efficacy for some such reactions.Supported metal oxides and their preparation Some metal oxides, when sulfated, develop the ability to catalyse reactions characteristic of very strong acid catalysts at low temperatures, although with limited lifetimes. This not only presents the opportunity of saving energy but also generates a thermodynamic advantage. Isomerisation of straight chain alkanes to more highly branched isomers, which not only have higher octane numbers but are more useful as intermediates for further synthesis, is more favourable at lower temperature.Arata has identified a range of active sulfated oxides including those based on SO4 22/ZrO2, SO4 22/Fe2O3, SO4 22/SnO2, SO4 22/TiO2, SO4 22/SiO2, SO4 22/Al2O3 and SO4 22/HfO2.1,2 With the exception of Al2O3, sulfation must be performed on the amorphous precursors of the oxides such as hydroxides or oxyhydroxides in order to result in high activity.Although a variety of sulfation reagents can be used, most researchers have employed either dilute sulfuric acid (usually 0.5 mol dm23) or an aqueous solution of ammonium sulfate. The oxide precursor is generally immersed in the sulfating solution, left for a period of time, filtered, dried and calcined (heated in air or oxygen). Variation of any of these parameters can markedly affect the resultant catalytic activity.The temperature of calcination required to generate maximum performance depends upon both the oxide and the sulfation reagent. For example, in the case of sulfated iron oxide, maximum activity for n-butane isomerisation develops after calcination at 500–550 °C and for sulfated zirconia after 600–650 °C.Only a small uptake of sulfate is required, with optimum sulfur content being in the region of 1–2 wt%. As well as promoting a variety of acid catalysed reactions, sulfation is also observed to affect physical properties, for example, it lowers crystallinity and increases surface area.The latter effect is always an important consideration in heterogeneously catalysed processes where reactions occur on surfaces. In the oxides where polymorphism (i.e. two or more crystal forms of the same Sulfated metal oxide catalysts Superactivity through superacidity? Adrian S. C. Brown and Justin S. J. Hargreaves Catalysis Research Laboratory, Department of Chemistry and Physics, Nottingham Trent University, Clifton Lane, Nottingham, UK NG11 8NS Received 5th October 1998 chemical composition) occurs, sulfation has been observed to preferentially stabilise one form.Zirconia is an example of such a material. It can exist in the monoclinic, tetragonal, cubic and orthorhombic crystal forms depending upon the method of preparation and conditions.Sulfate is one of a range of dopants observed to favour the formation of the tetragonal phase over the more commonly encountered monoclinic form.3 The nature of their activity It is always of interest to understand the mechanism of operation of a catalyst, since in some cases this can allow one to improve existing catalysts or develop new ones. n-Butane isomerisation to produce isobutane is probably the most well studied reaction catalysed by sulfated metal oxides.One mechanism of this reaction involves the generation of an intermediate substituted protonated cyclopropane cation (i) and primary carbenium ion (ii) which undergoes C–C and C–H bond fission and rearrangement (the unimolecular or intramolecular route—adapted from ref. 4); see Scheme 1.This process is characteristic of strong acid catalysis—the intermediate carbenium ion can be produced by either a Lowry–Brønsted acid route (1) or a Lewis acid route (2) (Scheme 2). The observation that sulfated systems exhibit greater activity than concentrated sulfuric acid indicates that the oxides do not simply function as supports for H2SO4, although this is a point of debate.5 Many researchers have therefore concluded that these systems are ‘superacidic’.Following Gillespie, a superacid is defined as a Green Chemistry February 1999 17 Of all the classes of industrial transformations, the conversion of hydrocarbon feedstocks into useful functional building blocks is arguably the most fundamental, since it provides all other processes with their raw materials.These reactions are typically catalysed by strong acids. It is therefore no surprise that there has been a great deal of work on solid acids, although the exact nature of their mode of action is not always clear. One particularly good example of this is given by the sulfated metal oxides. This review, intended for the non-specialist, provides an accessible description of the nature of these materials.While their activity is greater than that of sulfuric acid, their acidity is less clearly defined, with opinion moving away from the original position that these materials were superacids. This is based on the accumulation of reaction evidence as well as refinements in the physical techniques used to characterise the materials. DJM Green Context C GScheme 1 Intramolecular butane isomerisation mechanism.Scheme 2 Acidic activation routes of butane. material which exhibits an acid strength greater than 100% H2SO4 (i.e. has a Hammett acidity function @ 212).6 This is, of course, a Lowry–Brønsted based definition. A definition of superacidity exists for Lewis acidity in that any material exhibiting an acid strength greater than anhydrous AlCl3 is termed superacidic.6 Initially attempts to measure the acid strengths of sulfated oxides centred around the use of Hammett acidity indicators.In this method, the acid strength of the material is determined by its ability to change an organic base adsorbed onto the solid into its conjugate acid form which is associated with a colour change. Therefore, if an indicator changes colour it is indicative that the material possesses a Hammett acidity value equal to or lower than its pKa.A wide range of such indicators are available with different pKa values. Samples of the material are suspended in an inert solvent (e.g. sulfuryl chloride) and tested with indicators of varying strength. Although application of this method indicates that the materials are strong acids, it is not without limitations: (i) equilibrium between the base and solid sample must be established which can take very long times; (ii) interaction with the solvent molecules or the adsorbate can generate misleading results, for example it has been reported that red shifts can occur which generate erroneous conclusions;7 (iii) a colour change must be observed which can be difficult when the sample is coloured, e.g.SO4 22/Fe2O3; (iv) with most indicators it is not possible to distinguish between Lowry–Brønsted and Lewis acidity. More favoured approaches to determining the acid site strengths and densities of solids involve studies of the adsorption of base probe molecules such as ammonia and pyridine, and also the use of test reactions such as the dehydration of isopropanol to produce propylene.8 Microcalorimetry in conjunction with uptake measurements allows one to determine the heat of adsorption of a probe molecule which can be related to site strength and density.An example of the application of this method is provided in a study of sulfated zirconia by Dumesic and co-workers9 who have studied the heat of adsorption of ammonia at 150 °C as a function of uptake—in this way, they determined a differential heat of adsorption which relates to the population of sites of various acid strength.By selective poisoning of the sets of these sites, it may be possible to determine the strength of sites responsible for a particular catalytic reaction. Thermal desorption meth- H H (2) (1) (A = Lewis acid) + AH– + A + H2 + H+ + + + H CH2 H (ii) (i) + + + + ods determine site strength and density by measuring the loss of adsorbed probe molecules as a function of sample temperature.However, these approaches have been limited in their application due to adsorbate decomposition (e.g. ref. 10) which means that the true interaction of the probe molecule with the acid site is not being examined.Consequently, thermal desorption studies of adsorbed substituted benzenes (which are weaker bases than those generally used) was suggested as suitable. Subsequently, in some systems this method itself was shown to suffer the limitation of oxidation of benzene and even the evolution of SO2 during heating.11 So, in summary, many of the adsorption/desorption measurements have been limited by the intrinsic high reactivity of these materials.Therefore, spectroscopic studies of adsorbed molecules, which can also provide valuable information on acidic properties of solids, have been quite widely adopted in this field. Following work by Parry in the 1960s, infra-red spectroscopic studies of the adsorption of pyridine have become routine for the discrimination of Lowry–Brønsted and Lewis acid sites on heterogeneous catalysts.12 Pyridine interacts with the two types of site respectively in the manner shown in Scheme 3.Scheme 3 Interaction of pyridine with Lowry–Brønsted (H+) and Lewis acid (A) sites. Infra-red bands unique to each form can be distinguished in the 1400 to 1700 cm21 region of the spectrum.Furthermore, a knowledge of the absorption coefficient for each species makes quantification possible and acid site strength can be determined from the loss of band intensity as a function of temperature. However, it has been shown that application of some these methods to determine the acidic properties to sulfated metal oxides is severely limited due to oxidation and/or decomposition reactions which occur between adsorbent and adsorbate, e.g.ref. 13. Consequently, techniques such as FTIR studies of carbon monoxide adsorption have been applied. When CO interacts with Lewis acidic sites, the CNO stretching frequency increases via sbond donation. The shift in frequency can be directly related to Lewis acid strength.14 Low temperature studies of the influence of CO adsorption on the OH groups of the oxides can be used to determine Lowry–Brønsted strength.As mentioned below, many of the studies currently published employing these techniques indicate that although sulfated metal oxides may be strong acids, they are not superacidic. Here we have only briefly touched on some of the measurements of acid site strength which have been reported, however, a more detailed description of various methods of acid site strength determination on solids along with their associated limitations is available elsewhere.15 The nature of the active site Many different proposals describing the nature of the active catalytic site have been made.Generally, these have been based around the symmetry of the co-ordinated sulfate ion.In principle a number of symmetries for SO4 22 are possible (Scheme 4). It is possible to distinguish these forms by examination of the sample infra-red spectra in the 1200 to 900 cm21 SNO stretching region.16 As a consequence of the gross selection rule that a change in dipole moment must occur for a transition to be infrared active, the different forms of sulfate give different numbers of bands.The Td form of SO4 22 (i.e. tetrahedral symmetry like the N N A •• + H 18 Green Chemistry February 1999CH4 molecule) gives two infra-red active transitions in this region, the C3v form (i.e. pyramidal symmetry like the NH3 molecule) three and the C2v form (i.e. symmetry like the H2O molecule) four. An additional consideration is that the C2v form of sulfate can occur in bridging or chelating configuration.Both C2v and C3v forms have been commonly reported by different researchers in the literature and therefore different models of the active site have been made.17 Scheme 4 Different SO4 22 symmetries. One such proposal from Arata for SO4 22/ZrO2 is shown in Scheme 5, in which sulfate adopts a bridging C2v symmetry. It is argued that the sulfate group enhances the Lewis acidity of the Zr cations by an inductive effect (Lowry–Brønsted acidity can be generated from this form as described below).Scheme 5 Proposed active site in SO4 22/ZrO2. Alternative proposals for catalytic activity Increasingly, based on spectroscopic and calorimetric studies, the consensus is emerging that sulfated metal oxides do not possess the superacidity originally postulated.A number of recent studies have demonstrated that the acid strength is similar to that encountered for transitional aluminas or protonic zeolites. An example of this is provided in a study by Drago and Kob18 in which they have applied the ‘cal-ad’ method to the determination of acidity of sulfated zirconia and related systems. In this method a calorimetric titration of a basic probe is carried out in a hydrocarbon solvent of similar molecular mass.It is claimed that this technique allows the determination of the number, equilibrium constant and site strengths of different acid sites on solids. The results for the highest enthalpies of pyridine adsorption in cyclohexane for various SO4 22/ZrO2 samples along with silica and the zeolites HZSM-5 and HY are given in Table 1.Table 1 Results of ‘cal-ad’ measurements of pyridine adsorption on various solids—adapted from ref. 18 2DHads(pyridine)/ Material kJ mol21 SiO2 50 ± 4 H-ZSM-5 171 ± 4 HY 142 ± 4 SO4 22/ZrO2 calcined at 600 °C 130 ± 8 SO4 22/ZrO2 calcined at 300 °C 63 ± 4 Pt/SO4 22/ZrO2 125 ± 4 Fe/Mn/SO4 22/ZrO2 109 ± 4 S O O O O Zr O Zr+ + S O O O O S O O O O S O O O O S O O O O C3v Td C2v C2v Along with many other studies, the data in Table 1 certainly suggest that SO4 22/ZrO2 based systems are not superacidic. However, this view is still contentious.Amongst those who believe that superacidic sites are present, there continues to be disagreement as to whether these are Lowry–Brønsted or Lewis in nature. A possible explanation for the division of opinion on all these matters relates to the observation that the catalytic activity of these materials is strongly dependent upon storage/pre-treatment conditions.Inter-conversion of Lewis and Lowry–Brønsted sites can occur by hydration/dehydration processes— Scheme 6 Proposed interconversion of Lewis and Lowry–Brønsted acidic sites in SO4 22/ZrO2.see Scheme 6. An important question, therefore, is if not superacidity, what is the origin of the exceptional behaviour of these catalysts? Sachtler and coworkers have performed experiments which aim to address this problem.19 They noted that although Fe/Mn/SO4 22/ZrO2 (reputedly the strongest ‘superacidic’ sulfated metal oxide known to date) had acid sites of similar strength to SO4 22/ZrO2 in their measurements, its butane isomerisation activity was much greater.Furthermore, they pointed out that the occurrence of the unimolecular isomerisation mechanism described above is not expected at the low temperatures of activity for these catalysts because of the primary carbenium ion intermediate. By analysing the product distributions in reactions using doubly isotopically labelled butane, 13CH3CH2CH2 13CH3, they have shown that the reaction occurs by formation of a bimolecular (intermolecular) intermediate which isomerises to give the 2,4,4-trimethylpentyl carbenium ion, followed by b-fission to yield an isobutene molecule and the isobutyl carbenium ion (Scheme 7).The catalytic cycle then progresses by the loss of a hydride species from the n-butane reactant to the isobutyl carbenium ion to generate the isobutane product and the C8 intermediate via reaction with the isobutene.Unlike the intramolecular process, this pathway does not involve the intermediacy of the unfavourable primary carbenium ion. Scheme 7 Decomposition route of C8 intermediate. They proposed that the activity of sulfated metal oxides arises from their ability to stabilise reaction intermediates possibly by the formation of C–O–S bonds such as sulfate esters.Farcasiu and colleagues have made a comprehensive study of the pathways involved in the reaction of adamantane over SO4 22/ZrO2.20 They have proposed that rather than behaving as a superacid, this system operates via a one electron oxidation mechanism in which an electron is transferred between the substrate and the sulfate group.A sulfite ester is proposed to be an intermediate in the reaction, as shown in Scheme 8. Scheme 8 Adamantyl sulfite ester. Ad = adamantyl radical. Zr O S OAd O + + + S O O O O Zr O Zr+ S O O O O Zr O Zr+ O H H + H2O –H2O + Green Chemistry February 1999 19Limitations to application Despite the current controversy over the mechanism of operation of sulfated metal oxides, it is obvious that they possess extraordinary catalytic behaviour.However, to our knowledge, they have not yet found commercial application. They deactivate quickly on use due to poisoning of active sites by the deposition of coke (carbonaceous residues). This can be overcome to some extent by including hydrogen in the feed, which hydrogenates the coke as it is formed, or by the inclusion of additional catalyst components, e.g.Pt, which retard coke deposition. Such deactivation is not necessarily a limitation to industrial application. Fluidised catalytic cracking is a large scale catalytic process in which zeolites are used to convert long chain hydrocarbons into more useful shorter chain forms.In operation the catalyst becomes rapidly deactivated by coking, its lifetime is usually about 3 seconds! However, the process has been engineered such that regeneration, which involves the exothermic combustion of coke by air, supplies the heat necessary to conduct the reaction. A major limitation for the application of sulfated metal oxides relates to preparation. It is difficult to prepare separate batches of catalyst which exhibit reproducible catalytic performance.This problem, which may relate to inhomogeneous sulfation, needs to be addressed and has already been the subject of some research attention.21 Summary In this short article, we have attempted to briefly describe some of the current interest in sulfated metal oxide catalysts. Due to limitations of space, we have not been able to fully describe some of the emerging areas of interest.We have only briefly mentioned the inclusion of additional metallic components. In some cases these may have proved beneficial by suppressing deactivation (e.g. Pt/SO4 22/ZrO2) whereas in others they enhance the intrinsic catalytic activity (e.g. Fe/Mn/SO4 22/ZrO2).22 The range of reactions to which these materials are being applied is also broadening.In our own work, we are investigating the effect of combining the unique activity of sulfated systems with the underlying catalytic activity of the base oxides for methane oxidation (see for example refs. 23, 24). In experiments performed at elevated pressure using iron oxide based catalysts, we have observed that the sulfation procedure suppresses the low temperature (i.e.<400 °C) total oxidation activity of these materials, (presumably by a site blocking mechanism) whilst enhancing activity at higher temperature (i.e. >500 °C) leading to some production of selective oxidation products (methanol and higher hydrocarbons) probably as a consequence of the stabilisation of higher surface areas and the formation of new types of active site.In the case of iron oxide systems prepared from goethite, the sulfation procedure also generates interesting structural effects which are currently the subject of further study. Although much remains to be explained about sulfated metal oxides in general, their remarkable catalytic activity is clear. References 1 K.Arata, Adv. Catal., 1990, 37, 165. 2 K. Arata, Appl. Catal. A: Gen., 1996, 46, 3. 3 C. J. Norman, P. A. Golding and P. J. Moles, Stud. Surf. Sci. Catal., 1994, 90, 269. 4 D. M. Brouwer and H. Hogeveen, Prog. Phys. Org. Chem., 1972, 9, 179. 5 F. Babou, B. Bigot, G. Coudrier, P. Sautet and J. C. Vedrine, Stud. Surf. Sci. Catal., 1994, 90, 519. 6 G. Olah, G. K. S. Prakash and J. Sommer, Superacids, John Wiley and Sons, New York, 1985. 7 B.S. Umansky and W. K. Hall, J. Catal., 1990, 124, 97. 8 R. Franklin, P. Golding, J. Haviland, R. W. Joyner, I. McAlpine, P. Moles, C. Norman and T. Nowell, Catal. Today, 1991, 10, 405. 9 G. Yaluris, R. B. Larson, J. M. Kobe, M. R. Gonzalez, K. B. Fogash and J. A. Dumesic, J. Catal., 1996, 158, 336. 10 C-H. Lin and C-Y. Hsu, J. Chem. Soc., Chem. Commun., 1992, 1479. 11 A. Jatia, C. Chang, J. D. MacLeod, T. Okubo and M. E. Davis, Catal. Lett., 1994, 25, 21. 12 E. P. Parry, J. Catal., 1963, 2, 371. 13 J. S. Lee and D. S. Park, J. Catal., 1989, 120, 46. 14 M. Zaki and H. Knozinger, Spectrochim. Acta, Part A, 1987, 43, 1455. 15 A. Corma, Chem. Rev., 1995, 95, 559. 16 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Co-ordination Compounds, Wiley, New York, 1986. 17 X. M. Song and A. Sayari, Catal. Rev. Sci. Eng., 1996, 38, 329. 18 R. S. Drago and N. Kob, J. Phys. Chem. B, 1997, 101, 3360. 19 V. Adeeva, G. D. Lei and W. H. M. Sachtler, Appl. Catal. A: Gen., 1994, L11. 20 D. Farcasiu, A. Ghenciu and J. Q. Li, J. Catal., 1996, 158, 116. 21 D. Farcasiu, J. Q. Li and S. Cameron, Appl. Catal. A: Gen., 1997, 154, 173. 22 C. R. Vera, J. C. Yori and J. M. Parera, Appl. Catal. A: Gen., 1998, 167, 75. 23 A. S. C. Brown, J. S. J. Hargreaves and B. Rijniersce, Catal. Lett., 1998, 53, 7. 24 A. S. C. Brown, J. S. J. Hargreaves and B. Rijniersce, Catal. Today, 1998, 45, 47. Paper 8/07963C 20 Green Chemistry February 1999

ISSN:1463-9262    

DOI:10.1039/a807963c

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

C G P E R S P E C T I V E S in a much higher proportion (compared to the BrCCl3 adduct) under sonolysis than photolysis indicating a preference for Br formation under the former conditions. The authors concluded that under sonolysis the radicals are formed in high concentrations in heterogeneous localised ‘hotspots’ making them prone to dimerisation. In contrast photolysis forms radicals in a dispersed state and will either recombine or take part in chain reactions. OH Pinacol coupling Researchers at Tulane University in New Orleans have recently described a simple and clean method for performing pinacol coupling reactions (W.-C. Zhang and C.-J. Li J. Chem Soc. Perkin Trans 1 1998 3131). Previously reported methods for this important organic reaction which leads to the formation of a carbon-carbon bond have included the use of strong reducing agents such as sodium metal HO O Mg H 2O R H R R 41-90% yield chromium vanadium or TiCl3 under anhydrous conditions in organic solvents.The new method simply involves reacting the aldehyde or ketone with magnesium metal in water. The reaction rate and yield are enhanced by addition of a catalytic quantity of ammonium chloride giving isolated yields of 41 to 90% for a large range of substrates. The reaction is most efficient for aromatic aldehydes and can be performed successfully on alkyl alkoxy and halo-substituted benzaldehydes. Ultrasonic activation The activation of reactions using nonconventional heating methods such as microwaves or ultrasound is currently the subject of considerable research effort (see Raj Varma’s review article in this issue).Takahide Kimura and co-workers at the Shiga University of Medical Science Japan have recently demonstrated the existence of an intrinsic difference in reactivity between radicals formed by photolysis and those formed on treatment with ultrasound (J. Org. Chem. 1998 63 6719). Both forms of irradiation caused fragmentation of bromotrichloromethane (BrCCl3) into bromine and trichloromethyl radicals but only the ultrasonic method produced the dimeric product Cl3CCCl3. Also when irradiating mixtures of oct-1-ene and BrCCl3 they found that 1,2-dibromooctane was formed G18 Green Chemistry February 1999 2 Sol-gel encapsulated biological material– efficient stable catalysts For several years researchers have tried with some success to immobilise biological catalysts (e.g.enzymes catalytic antibodies whole cells) on or in robust matrices in order to enhance their lifetimes. Similar approaches have also been investigated for other applications such as biosensors. One commonly utilised approach is the encapsulation of the catalytic species inside a silica sol-gel polymer. Such polymers are robust and should be good host materials for the biocatalysts being stable and allowing the preparation of a variety of final forms such as films powders and fibres. Further fine-tuning is also possible through the use of organically modified silanes leading to a silica with enhanced organophilicity.Such materials are particularly good hosts for lipases which are much more active in more hydrophobic silica hosts (Reetz et al. Angew. Chem. Int. Ed. Engl. 1995 34 301). Other notable successes include trypsin immobilised in silica which remains active long after solution phase trypsin has autodigested (Shtelzer et al. Biotech Appl. Biochem. 1992 15 227). Acid phosphatase has also been reported to have a half-life of 720 seconds in silica at 70 oC and pH = 5.6 but only 6 seconds in solution under the same conditions. (Braun et al. in Biotechnology Bridging Research and Application ed. D Kamely et al. Kluwer Boston 1991). Difficulties in this approach are many – the formation of a sol-gel polymer involves the hydrolysis of SiOR groups generating alcohols which often irreversibly damage the catalyst.Similarly the silica precursors can react with the catalyst directly rendering it inactive. Other difficulties include shrinkage of the gel upon drying leading to localised pressure and a reduction in enzyme activity and poor diffusion characteristics causing slow reaction. Recent research published by Gill and Ballesteros (J. Am. Chem. Soc. 1998 120 8587) and carried out in Madrid and the UK has highlighted a general approach to the problem which has been shown to give excellent results in a variety of areas. The key to their approach was to move away from the standard silica precursors such as (MeO)4Si and (EtO)4Si both of which liberate damaging low molecular weight alcohols replacing them with glycerol silicates.The glycerol liberated during the preparation of the materials is biocompatible and helps the gel to dry in a controlled fashion leading to stable matrices for the enzyme. The activity of the encapsulated materials is high between 83 and 98% of the native material for a range of enzymes and whole cells (yeast R. miehei and P. oleovorans were all successfully J6 encapsulated). The amounts of biomaterial encapsulated can also be much higher than with traditional methods with 20-30 wt% biomaterial being achieved in many cases. A striking example of the importance of the glycerol-based route over the traditional route is given by the hydrolysis of the nerve agent diethyl 4-nitrophenyl phosphate by a phosphatase enzyme.>95% hydrolysis was achieved under continuous conditions over a period of 700 hours compared with a steady 35-40% hydrolysis with conventional material. Under the same conditions polyurethane encapsulated material initially very active had lost ca. 30% of its original activity. A series of synthetically useful transformations are also possible including the synthesis of a pentapeptide N-Cbz-L-[Leu5]-YGGFLNH2 resolution of (R,S)-ibuprofen methyl ester to (S)-ibuprofen selective hydrocyanation of hexadienal and reduction of a ketoester. In all cases initial activity was higher (2-50%) than that of the nonimmobilised material and loss in activity after prolonged use was much less. The authors suggest that the excellent results obtained in a wide range of reactions are an interplay of the lower toxicity of the synthesis procedure the better mixing of the host and the biomaterial and the excellent porosity characteristics of the host.

ISSN:1463-9262    

DOI:10.1039/gc990g18

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Teaching green chemistry After a career as a synthetic chemist and polymer chemist in industry Albert Matlack from the University of Delaware in the USA has developed a course in green chemistry. He had been inspired by reading a report in Chemical and Engineering News (April 4 1994 p34) on a symposium on Environmental Chemistry Education which put forward the idea of teaching green chemistry. Choosing the material for the course involved making a list of every environmental problem that I could think of that involved chemistry. The next step was to attend the symposium on Green Chemistry at the Washington meeting of the American Chemical Society in August 1994. Putting these two together along with a lot of journal reading resulted in the following course1 outline 1 The need for Green Chemistry 2 Doing without toxic chemicals (illustrated by phosgene) 3 The chlorine controversy 4 Toxic heavy metal ions 5 Solid catalysts and reagents for ease of work-up 6 Solid acids and bases 7 Separations 8 Working without organic solvents 9 Biocatalysis and biodiversity 10 Stereochemistry 11 Agrochemicals 12 Materials for a sustainable economy 13 Chemistry of longer wear 14 Chemistry of recycling 15 Energy and the environment 16 Population and the environment 17 Environmental economics 18 Greening Some of the impetus for 16 and 17 came from attending meetings of the Ecological Society of America and the American Association for the Advancement of Science.Green chemistry is the chemistry of a sustainable future.A sustainable future is one that allows future generations as many options as we have today. The industrial ecology being studied by engineers and green chemistry are both parts of one approach to a sustainable future. On the other hand environmental chemistry as taught today is largely the study of what man has put into the environment and its effect as well as how to remediate contaminated sites. Green chemistry is interdisciplinary. When I lecture on waste minimisation ion exchange resins and zeolites I sound like a chemical engineer. When I talk about population and the environment I sound like a physician When I go into renewable energy I act like a physicist.The social impact of scientific discoveries is included two common criticisms of scientists are that their training is too narrow and that they do not consider the social impact of their work. I now read at ‘green chemistry is the chemistry of a sustainable future’ a lot of journals that I barely looked at before such as Progress in Organic Coatings Waste Age’s Recycling Times Rubber World TAPPI Journal etc. and I look at the catalysis and chemical engineering journals more carefully that I used to. Review articles in the Encyclopaedia of Chemical Technology and Ullmann’s Encyclopaedia of Industrial Chemistry have also been very useful. Gordon Research Conferences on biocatalysis membranes and zeoloites have also helped.The course was first given in the spring of 1995 and was taught for the fourth time in the fall of 1998. Since C G there was no text I have written one with about 3000 references. There are several messages which I would like students to take home from the course F EAT U R E l If you don’t use a chemical you don’t have to buy it and you can’t lose it. l Green chemistry need not be expensive. If the whole chemical process is rethought and modified the result may be cheaper. l It may be not be possible to green every step of the process at once. For example a recent synthesis of ibuprofen reduces the number of steps from six to three but still caries out an acylation step with acetic acid and hydrogen fluoride.It may be possible to substitute a solid acid such as a zeolite for the hydrogen fluoride. l Each of us is part of the problem in that we buy cars painted with solvents have a bathroom in the house use electricity use single-use disposable items etc. l The problems are social and political as well as technological and are not just economic. l There is often a hierarchy of approaches to a problem. To illustrate trichloroethene is often used to clean metal parts and has become a common contaminant of groundwater and the atmosphere. Putting a lid on the degreasing tank will reduce losses to the air. If the tank is sealed whilst in use the solvent drained and then vacuumed out and the vacuum released before opening very little trichloroethene is lost.If the cleaning is done with an aqueous Green Chemistry February 1999 G19 F E AT U R E GC detergent then there is no chlorinated solvent to lose. The biggest change comes from altering the manufacturing process for the metal part so that there is no grease to be removed. The course is taught for three hours one evening a week to seniors graduate students and to people working outside the university who want to keep up with developments. Some of the most interested students are those from industry who can relate to the subject matter better. One chemical engineer from DuPont would bring in photocopies of papers that he felt would be useful for the rest of the class. Each section has required outside reading and student exercises which are designed to be more than just plugging numbers into a formula.Students may be asked to give an opinion on a question such as Is nuclear energy the solution to global warming or does it have too many problems? I have them go to the local farm and garden supply store to see what is being sold to put on lawns and crops. Then they look up the toxicities of the chemicals and decide what might happen if these substances washed off into the nearest stream. The next step is to consider friendlier alternatives. The course is designed to take them to the frontiers of research in green chemistry and they are expected to apply what they learn not just memorise a list for a quiz. A frequent exam question involves a procedure from organic syntheses that uses a lot of different solvents and toxic chemicals.They are asked what might be done to make it greener. The challenge of a three-hour class is to use enough interactive class exercises to keep the students awake and alert. If done properly these can help the students learn to speak in public and to lead group discussions. One exercise involves the selection of two discussion leaders by lot to lead a discussion of a paper assigned for outside reading. I have had the class help me list the toxic heavy metal ions on the blackboard then completed the list as needed. Then each student gets to pick one to report on at the next class. Every student is required to know the material on all the metal ions for future exams.If reports are longer and cover an applications area then a dry run may be required. About half an hour before the end of the class I often divide the students into groups to work on a real life problem. After about fifteen minutes or whenever they seem to have stopped working constructively we put their suggestions on the board rotating among the group G20 Green Chemistry February 1999 spokespersons. I then add or delete from their list as needed. A modification of this approach seems to be a good way to revise for exams. They are split into two groups and each student in group 1 gets to ask one question of group 2. I keep score on the board but if the same person answers two questions in a row I only award half a point.When group 1 finishes the questioning and answering is reversed. After alternating a few times we decide which team has won. Field trips are possible. These might include visits to a solar house a farm using sustainable agriculture a tannery a plant manufacturing solar cells etc. Term papers are also possible. These might take the form of investigative reporting where the students check companies to see how green their processes are. For both field trips and term papers the reports should identify what chemicals are being used ‘the biggest challenge of green chemistry is to get people to adopt it’ and make proposals for reducing the use of energy and toxic chemicals etc. The present course does not have a laboratory but students could profit by having one that introduces them to techniques that they might not encounter in their regular courses.Experiments might include l The synthesis characterisation and evaluation of a zeolite. l Running a reaction in an extruder l Using a catalytic membrane reactor l Adding ultrasound or microwaves to a reaction l Making a chemical by plant cell culture l Performing biocatalysis l Making a compound by organic electrosynthesis l Running a reaction in supercritical carbon dioxide l Using a heterogeneous catalyst Ideally the students would use a known reaction first then do one which hasn’t been done before. This may help them to write research proposals.Some of the other faculty are very sympathetic to the course in green chemistry. Others however would prefer that their students take ‘core’ courses such as advanced organic chemistry and organometallic chemistry. My goal is to stop teaching green chemistry as a separate course and instead insert portions of it into all the other chemistry and chemical engineering courses. However the chance of getting these faculties to take my course so that they can do this is virtually nil. Some faculty members are happy with what they are doing now and couldn’t care less about how things are done in industry. Some schools don’t even teach polymer chemistry! There is still the perception that the chemistry of industrial processes and of applications is simpler and less elegant than that done in schools. The artificial delineation of disciplines works against interdisciplinary research although this is where much new knowledge is found. With chemistry biology and chemical engineering departments in separate buildings it is not too surprising that cross fertilisation is low. The biggest challenge of green chemistry is to get people to adopt it. We would like to see it incorporated into every course from high school onwards. We would like to see all of industry embrace it. The reasons that business has been slow to adopt it are not just economic (see for example J. Johnson Chemical and Engineering News August 17 1998 p. 34). They may involve a perception of risk in unfamiliar methods or a corporate culture that does not reward risk taking or a change so large that the company is reluctant to start. While my course attracts a few students from industry I need a lot more. 1 For an alternative description of a course in Green Chemistry see Terrence Collins Journal of Chemical Education 1995 72 965.

ISSN:1463-9262    

DOI:10.1039/gc990g19

出版商:RSC    

年代:1999

数据来源: RSC