摘要:

Global carbon dioxide emission and consumption Frank Smalberg Jacob Moulijn and Herman van Bekkum from Delft University of Technology in The Netherlands provide some new estimates of global CO2 Fig. 1. Carbon cycle with flow rates in Gt(C)/annum2 (All numbers are average values over the period 1980–1989) emission and the extent of CO2 mitigation through industrial consumption Introduction Mankind has always had an immense hunger for energy the consequences of which did not seem too important for many years. It was not until the 1950s that atmospheric CO2 was suspected of being the possible cause of the temperature rise that had already been noticed between 1880 and 1940. In 1896 Svante Arrhenius wrote an article on the influence of atmospheric ‘carbonic anhydride’ on the surface temperature in the Philosophical Magazine.Unfortunately unambiguous evidence is still lacking and opinions diverge. Policymakers however have acknowledged the potential dangers of the increasing CO2 concentrations in the atmosphere which led to the well-known Kyoto Protocol in 1997. The intense discussion on CO2 emission has many participants and is based on different data and assumptions. Various plausible reactions and promising products that might help in reducing the CO2 emission have been analysed.1 But what are the CO2 streams on earth? Does it make sense to investigate chemical conversion in view of an unbalance between emission and potential use? The purpose of this article is to provide clear and objective background information helpful in the CO2 discussion.Nevertheless the figures mentioned in this article are still estimates and should be handled with care. Carbon cycle What is the effect of combustion of fossil fuels in a global perspective? To answer this question one has to look at the carbon cycle (Fig. 1) which shows that the flow rate of carbon in the earth’s ecosystem in 109 tons per annum [109 t(C) = 1 Gt(C)]. During the period 1980–1989 approximately 5.5 Gt(C)/annum corresponding to 20 Gt/a CO2 was emitted as a result of the combustion of fossil fuels. Together with changes in land use the extra—often called anthropogenic—emission rose to 7.1 Gt(C)/annum which is a relatively small increase compared to the carbon content of the atmosphere (750 Gt(C)) and to the CO2 flow caused by respiration and decay of biomass (60 Gt(C)/annum).In particular the oceans contain an enormous amount of carbon (40,000 Gt(C)). Unfortunately the earth’s ecosystem is not capable of absorbing the additional CO2 which has led to the current CO2 concentration of 370 ppm compared to the pre-industrial level of 280 ppm at the beginning of the 19th century. This increase has been calculated to represent an average accumulation of 3.3 Gt(C)/annum in the atmosphere. The remaining 3.8 Gt(C)/annum is presumably absorbed by the oceans and forests. The carbon cycle gives a good impression of the relative magnitude of human activities.The absolute figures of the cycle however have led to much discussion and should be handled with great care. Energy consumption and related emissions The anthropogenic CO2 emissions are strongly related to the consumption of energy. In 1996 the three fossil energy sources coal oil and gas were responsible for an emission of 6.2 Gt(C).3 Their supply in Mtoe (million tons oil equivalent = 41.87 3 1015 J) and the corresponding emissions are shown in Fig. 2. Note that biomass is considered to be a sustainable energy source and therefore the net production of CO2 is zero. Furthermore natural gas has the lowest CO2 production per Mtoe which makes it more CO2-friendly for use in power plants than coal. Who is producing the CO2? Several methods exist to estimate the amounts.For example the production of CO2 in the transport sector can be estimated by multiplying the fuels consumed by the corresponding emission coefficients. Methods however can be based on different definitions and categories may cover different sources. Fig. 3 shows the Green Chemistry December 2000 DOI 10.1039/b006527g F E A T U R E G97 This journal is © The Royal Society of Chemistry 2000 Fig. 2. Energy supply and related emissions in 1996.3 F E A T U R E distribution of CO2 emissions in 1996 as estimated from IEA statistics. Two methods have been used in the left diagram energy transformation in power plants is considered as a separate sector (other transformation emissions are ascribed to industry).One could argue however that the power plants are only intermediates and therefore the right diagram shows the distribution across the sectors of end-users. Not surprisingly industry is by far the largest producer of CO2 when the latter method is used [3.0 Gt(C)/annum]. 2 sources. Industry Industry is a complex sector with many different players and many CO Fig. 3. Distribution of emissions in 1996.3 Green Chemistry December 2000 G98 This journal is © The Royal Society of Chemistry 2000 Unfortunately global figures on the distribution of emissions in this sector are scarce. To give an impression Fig. 4 shows the US industry emissions in 1994. Since the US are the world’s largest CO2 producers (approx.25% of the global emissions) these figures are quite relevant. Note that here the industrial sector includes agriculture whereas this is not the case in the IEA statistics. Besides the distribution over the industrial sub-sectors it would be interesting to know which part of the industrial emission is energy-related and which part is not. The purpose of this section is to estimate the amount of non-energy-related CO2 produced by industry although not providing a 2 Fig. 4. Distribution of US industry CO emissions in 1994.4 comprehensive review of all sources. CO2 is considered non-energy-related when formed in a chemical reaction with no primary intention to fulfil a need for energy e.g. reducing carbon monoxide and carbon in steel manufacture.Obviously a specific process producing non-energy-related CO2 will also produce energy-related CO2. Table 1 shows information on the largest sources of non-energy-related CO2 dominated by the minerals metal petroleum and chemical industries. The corresponding CO2 streams are calculated by multiplying the global production by an emission coefficient obtained from the IPCC Guidelines for National Greenhouse Gas Inventories 19965 or if not available by an estimated coefficient. The production of cement is the largest CO2 source in the minerals industry followed by the production of lime. In both cases CO2 immobilised in calcium carbonate is set free. Other smaller sources are the manufacture of soda ash the production of carbides and the use of limestone e.g.in glass manufacture. In the metal industry the production of pig iron is the main source of CO2 formed during the reduction of iron oxide ore with coke and carbon monoxide. The carbon-containing iron is then used in the production of steel while scrap is added; the CO2 production in the latter step is significantly smaller. The production of aluminium forms the second largest source followed by other metals such as chromium lead nickel and zinc. Table 1 Largest producers of non-energyrelated CO2 in 1996 Industry Produc- Emission coefficient tion 2/ (Mt/a) (kgCO kg) (kgC/kg) 0.14 0.22 0.14 0.5 0.8 0.5 1488 121 30 0.44 0.49 0.44 1.6 1.8 1.6 528 21 15 0.33 1.2 125 2.26 0.18 0.26 8.3 0.67 0.96 19 12 25 Mineralsa6 Cement Lime Otherc Metalsa6 Iron Aluminum Otherd Bulk chemicalsb Ammonia7 Hydrogen (refineries and others)9 Ethylene oxide8 Ethanol10 a Emission coefficients from IPCC Guidelines5.b Estimated emission coefficients (cf. text). c Including limestone use soda ash manufacture carbides etc. d Including chromium lead nickel zinc etc. The production of synthesis gas plays an important role in the CO2 production of the chemical industry. 49% of the hydrogen produced is used in the synthesis of ammonia 37% in the refining of petroleum (hydrocracking and hydrotreating) 8% in methanol synthesis and 6% is used for other purposes.9 The quantities of hydrogen can be estimated since the global production of ammonia is accurately known.The CO2 emission coefficients however depend on the feedstock used in the H2 process natural gas is generally used in the synthesis of ammonia heavy residues (CH1.3) are often used in refineries. The production of ethanol and ethylene oxide are other significant sources of CO2; the latter is generally produced with 75% selectivity. The above assumptions led to the coefficients listed in Table 1. Note that the CO2 related to the production of (bio)ethanol is included although the fermentation is based on renewable feedstocks. of all industrial CO2 is energy-related. Furthermore the production of mineral products and metals accounts for 84% of the remaining 570 Gt(C)/annum.The petroleum and chemical industries produce significantly less but these streams are more concentrated and pure which makes them excellent sources for commercial CO2 consumption. Consumption Table 2 shows the bulk consumers of CO2 with by far the largest in 1996 Table 2 Consumption of CO2 in 1996 As a result Fig. 5 shows that over 80% being urea production. CO2 is also used as an additive in methanol synthesis (20 Mt/annum). A CO/CO2 ratio of 3 is required to convert all hydrogen formed in steam reforming of natural gas. It is estimated that 25% of this maximum amount of CO2 is actually added. Enhanced Oil Recovery (EOR) is also a large consumer of CO2.The gas is used to flood wells in order to increase the extent of oil recovery. This method is used in the US and Turkey since large natural CO2 wells are present in these countries. EOR is often mentioned as a promising CO2 mitigation option because 50% of the CO2 remains in the well after extraction. However the maximum quantity of oil that is globally produced by EOR is less than 10%. Accordingly Carbon 2 Quantity lent (Mt/a) Process CO Equiva- Equivalent (Mt (C)/a) (Mt/a) 18 0.5 90 20 65 2 2 11 5.5 0.5 2.5 20 2 9 20 2 9 2 15 3.6 2.3 3.4 27 98 Urea11 Methanol11 Enhanced Oil Recovery12 Solid CO Liquid CO Food industry Beverage carbonation Othera Total a Including welding use in aerosols foundry firefighting medical rubber and plastics.Fig. 5. Distribution of global industrial CO2 emissions in 1996 F E A T U R E the amount of CO2 that could be sequestered in the wells is approximately 70 Mt/annum which is only a modest contribution to the mitigation (with 2.7 3 1010 barrels/annum,13 50 kg CO2/barrel14 and 50% sequestration). Solid CO2 is mainly used for refrigeration purposes while liquid CO2 has found wide applications in the food industry such as refrigeration food packaging water treatment and supercritical extraction. It is also used for beverage carbonation welding fire extinguishers etc. The amount of CO2 consumed totals 27 Mt(C)/annum which is only 0.4% of the global anthropogenic emission caused by fossil fuel combustion.Moreover it should be noted that CO2 is only sequestered permanently with EOR while the other consumers are only temporary ‘stations’ for CO2 on its way to the atmosphere. For instance urea when applied as fertiliser is bacterially converted to CO2 and ammonia. The latter compound either directly serves plant growth or does so after it has been bacterially converted to nitrate. The direct intake of urea by the plant is very small. Obviously chemical use of urea in for example organic resins leads to longer periods of immobilisation. Conclusion In 1996 energy purposes accounted for 91% of the anthropogenic CO2 emission of 6.4 Gt(C)/annum increasing to 95% when the use of cokes in the primary Green Chemistry December 2000 G99 This journal is © The Royal Society of Chemistry 2000 F E A T U R E 2 metal industry is considered energy-related.These amounts of CO2 greatly exceed consumption and even if all organic base chemicals (approx. 400 Mt(C)/annum) were made from CO emissions would only decrease by some 6–7%. CO2 could be mitigated by other technologies under debate such as disposal in oceans or by the production of methanol with solar hydrogen. Methanol is considered a future key chemical that can selectively be converted to bulk chemicals i.e. the lower olefins. However chemical use of CO2 could imply increasing emissions and is still expensive due to CO2 recovery costs and high hydrogen price.16 In conclusion it can be said that CO2 mitigation by means of industrial consumption will remain rather modest and mainly temporary and that investigations should focus on increasing efficiencies and on sustainable energy sources such as biomass wind and solar cells.Intuitively a global policy to restrict CO2 emissions is appropriate although the existence of the greenhouse effect is still under debate. Highlights Duncan Macquarrie reviews the latest research in green chemistry Chul-Ho Jun and his group at the Yonsei University in Seoul have discovered an efficient method for the ortho alkylation of aromatic imines (and thus indirectly benzaldehydes). Their work (Angew.Chem. Int. Ed. 2000 39 3440) is based on a Rh catalysis which functions by chelation and activation leading to efficient alkylation with alkenes at the position ortho to the imine. Linear alkyl groups are introduced in all cases. The chemistry can be extended to insert the alkene to the aldehydic (iminic) C–H bond (right hand example) with the aid of 2-amino-3-picoline. Green Chemistry December 2000 G100 Researchers led by Toshifumi Hirata at Hiroshima University have described an enantioselective reduction methodology based on the use of enzymes (Chem. Lett. 2000 851). The three enzymes were obtained from Nicotiana tabacum and were found to be very effective in the reduction of cyclic enones giving reduced products in good conversion and excellent ee (!95% in all but one case).Both endocyclic and exocyclic double bonds could be reduced. properties improves. Rene Roy’s group at the University of Ottawa have published details of a novel functionalisation of chitosan which renders the polymer water-soluble (Chem. Lett. 2000 862). This involves a Michael addition of acrylates to the amino groups in the structure followed by hydrolysis of the ester to acid. High degrees of functionalisation are achieved and water-soluble polymers are obtained. No indications of applications are given in the paper although biological studies are in progress. The chemical properties of such a polyacid will also be of interest. Fumio Toda and co-workers from Ehime University and the Okayama The application of biopolymers such as starch and chitosan in chemistry is growing as the ability to modify their DOI 10.1039/b008754h This journal is © The Royal Society of Chemistry 2000 Acknowledgements We would like to thank Dr John N.Armor Air Products and Chemicals Inc. Allentown (USA) for advice. Notes and references 1 X. Xiaoding and J. A. Moulijn Energy Fuels 1996 10 (2) 305-325. 2 The Science of Climate Change Contribution of Working Group I to the Second Assessment of the Intergovernmental Panel on Climate Change ed. J. T. Houghton L. G. Meira Filho B. A. Callender N. Harris A. Kattenberg and K. Maskell Cambridge University Press Cambridge 1996 p. 77. 3 International Energy Agency Key World Energy Statistics 1998 http:// www.iea.org/stats/files/keystats/stats_ 98.htm 4 Emissions of Greenhouse Gases in the United States 1998 Energy Information Administration EIA/DOE-0573 USA 1999 http://www.eia.doe.gov/oiaf/ 1605/ggrpt/ 5 Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories ed.J. T. Houghton L. G. Meira Filho B. Lim K. Treanton I. Mamaty Y. Bonduki D. J. Griggs and B. A. Callender UK Meteorological Office Bracknell Chapter 2 1996. 6 Minerals Yearbook volume I Metals & Minerals U.S. Geological Survey 1997 http://minerals.usgs.gov/minerals/pubs/ commodity/myb 7 D. H. Lauriente Chemical Economics Handbook Report on ammonia SRI Consulting Menlo Park California USA 1998. 8 H. Chinn Chemical Economics Handbook Report on ethylene oxide SRI Consulting Menlo Park California USA 1997. 9 T. A. Czuppon S. A. Knez and D. S. Newsome The M.W. Kellogg Company Kirk-Othmer Encyclopedia of Chemical Technology 4th edn. New York 1996 vol. 13 p. 884. 10 F.O. Licht’s International Molasses and Alcohol Report 1999 36 (22) 408. 11 Ullmann’s Encyclopedia of Industrial Chemistry 6th edn. 1999 electronic release. 12 B. Heydorn Chemical Economics Handbook Report on carbon dioxide SRI Consulting Menlo Park California USA 1995. 13 Statistical Review of World Energy 1999 Oil Production BP Amoco 1999 http:// www.bpamoco.com/worldenergy/ download/index.htm 14 Private communication of A. de Vries Shell Exploration and Production Rijswijk The Netherlands January 2000. 15 C. Crabb Chem. Eng. 2000 July Issue p. 49–52. 16 J. N. Armor Stud. Surf. Sci. Catal. 1998 114 141-146.

ISSN:1463-9262    

DOI:10.1039/b006527g

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

F E A T U R E 2 metal industry is considered energy-related. These amounts of CO2 greatly exceed consumption and even if all organic base chemicals (approx. 400 Mt(C)/annum) were made from CO emissions would only decrease by some 6–7%. CO2 could be mitigated by other technologies under debate such as disposal in oceans or by the production of methanol with solar hydrogen. Methanol is considered a future key chemical that can selectively be converted to bulk chemicals i.e. the lower olefins. However chemical use of CO2 could imply increasing emissions and is still expensive due to CO2 recovery costs and high hydrogen price.16 In conclusion it can be said that CO2 mitigation by means of industrial consumption will remain rather modest and mainly temporary and that investigations should focus on increasing efficiencies and on sustainable energy sources such as biomass wind and solar cells.Intuitively a global policy to restrict CO2 emissions is appropriate although the existence of the greenhouse effect is still under debate. Highlights Duncan Macquarrie reviews the latest research in green chemistry Chul-Ho Jun and his group at the Yonsei University in Seoul have discovered an efficient method for the ortho alkylation of aromatic imines (and thus indirectly benzaldehydes). Their work (Angew. Chem. Int. Ed. 2000 39 3440) is based on a Rh catalysis which functions by chelation and activation leading to efficient alkylation with alkenes at the position ortho to the imine.Linear alkyl groups are introduced in all cases. The chemistry can be extended to insert the alkene to the aldehydic (iminic) C–H bond (right hand example) with the aid of 2-amino-3-picoline. Green Chemistry December 2000 G100 Researchers led by Toshifumi Hirata at Hiroshima University have described an enantioselective reduction methodology based on the use of enzymes (Chem. Lett. 2000 851). The three enzymes were obtained from Nicotiana tabacum and were found to be very effective in the reduction of cyclic enones giving reduced products in good conversion and excellent ee (!95% in all but one case). Both endocyclic and exocyclic double bonds could be reduced. properties improves. Rene Roy’s group at the University of Ottawa have published details of a novel functionalisation of chitosan which renders the polymer water-soluble (Chem.Lett. 2000 862). This involves a Michael addition of acrylates to the amino groups in the structure followed by hydrolysis of the ester to acid. High degrees of functionalisation are achieved and water-soluble polymers are obtained. No indications of applications are given in the paper although biological studies are in progress. The chemical properties of such a polyacid will also be of interest. Fumio Toda and co-workers from Ehime University and the Okayama The application of biopolymers such as starch and chitosan in chemistry is growing as the ability to modify their DOI 10.1039/b008754h This journal is © The Royal Society of Chemistry 2000 Acknowledgements We would like to thank Dr John N.Armor Air Products and Chemicals Inc. Allentown (USA) for advice. Notes and references 1 X. Xiaoding and J. A. Moulijn Energy Fuels 1996 10 (2) 305-325. 2 The Science of Climate Change Contribution of Working Group I to the Second Assessment of the Intergovernmental Panel on Climate Change ed. J. T. Houghton L. G. Meira Filho B. A. Callender N. Harris A. Kattenberg and K. Maskell Cambridge University Press Cambridge 1996 p. 77. 3 International Energy Agency Key World Energy Statistics 1998 http:// www.iea.org/stats/files/keystats/stats_ 98.htm 4 Emissions of Greenhouse Gases in the United States 1998 Energy Information Administration EIA/DOE-0573 USA 1999 http://www.eia.doe.gov/oiaf/ 1605/ggrpt/ 5 Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories ed.J. T. Houghton L. G. Meira Filho B. Lim K. Treanton I. Mamaty Y. Bonduki D. J. Griggs and B. A. Callender UK Meteorological Office Bracknell Chapter 2 1996. 6 Minerals Yearbook volume I Metals & Minerals U.S. Geological Survey 1997 http://minerals.usgs.gov/minerals/pubs/ commodity/myb 7 D. H. Lauriente Chemical Economics Handbook Report on ammonia SRI Consulting Menlo Park California USA 1998. 8 H. Chinn Chemical Economics Handbook Report on ethylene oxide SRI Consulting Menlo Park California USA 1997. 9 T. A. Czuppon S. A. Knez and D. S. Newsome The M.W.Kellogg Company Kirk-Othmer Encyclopedia of Chemical Technology 4th edn. New York 1996 vol. 13 p. 884. 10 F.O. Licht’s International Molasses and Alcohol Report 1999 36 (22) 408. 11 Ullmann’s Encyclopedia of Industrial Chemistry 6th edn. 1999 electronic release. 12 B. Heydorn Chemical Economics Handbook Report on carbon dioxide SRI Consulting Menlo Park California USA 1995. 13 Statistical Review of World Energy 1999 Oil Production BP Amoco 1999 http:// www.bpamoco.com/worldenergy/ download/index.htm 14 Private communication of A. de Vries Shell Exploration and Production Rijswijk The Netherlands January 2000. 15 C. Crabb Chem. Eng. 2000 July Issue p. 49–52. 16 J. N. Armor Stud. Surf. Sci. Catal. 1998 114 141-146.University of Science have published details of a solvent-free Robinson annelation reaction (Chem. Lett 2000 888). They mixed sodium methoxide a ketone and an enone together and kept the mixture at room temperature. Yields were modest but often better than the corresponding methanol-based process. The work-up involved neutralisation and extraction with ether but it is likely that a careful distillation could also eliminate the need for ether in the isolation stage. The synthesis of ethers has been studied in attempts to avoid the Williamson synthesis and the stoichiometric amounts of salts associated with it. A further contribution has come from a team led by Katsumi Kita at the Kao corporation (Chem. Lett. 2000 926).Their approach is to react an alcohol with a carbonyl compound and to reduce the This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S adduct with hydrogen and Pd/C. this approach has been used before but the new procedure requires only atmospheric pressure of hydrogen and can be run solvent-free. A flow of hydrogen through the reactor appears to remove water efficiently and drive the reaction forward. The search for clean Friedel–Crafts acylation technology continues. While aromatic ethers can be effectively acylated using zeolites and anhydrides less active substrates such as toluene continue to be a problem. A collaborative project between Avelino Corma at the University of Valencia and researchers at Rhodia have published work which goes some way towards solving this problem (J.Catal. 2000 195 161). They have concentrated on the design of a zeolite H-Beta catalyst which gets round the problems of low activity and fast deactivation to produce a catalyst capable of yields of > 50% in around an hour under reasonable conditions—a significant advance over previous work. Epoxidations continue to be of great interest. The use of an aldehyde as sacrificial oxidant has many positive aspects despite the use of an auxiliary aldehyde which is consumed during the reaction. The ability to use air as oxidant and mild non-aqueous conditions are often beneficial compared to many protocols where non-atom efficient oxidants are used or significant quantities of water are used.The Green Chemistry December 2000 so-called Mukaiyama conditions also require the use of a catalyst. Roeland Nolte of the University of Nijmegen has now published details of a nickel based catalyst where the metal is immobilised on a polybenzimidazole support (J. Chem. Soc. Perkin Trans. 1 2000 3428). This material is capable of the efficient epoxidation of a number of substrates including limonene oct-1-ene and styrene. Impressively the very labile a-pinene oxide could be prepared in 88% yield using these materials. Deactivation was apparent due to leaching of significant quantities of Ni but in a catalytically inactive form. An alternative approach to epoxidation of electron-poor alkenes is the base-catalysed reaction of hydrogen peroxide with enones (see Brunel and Macquarrie this issue).Kiyotomi Kaneda and co-workers from Osaka University have provided a method using basic hydrotalcite catalysts which works well for a range of enones (J. Org. Chem. 2000 65 6897). Their catalyst is a layered inorganic solid containing Mg and Al as well as hydroxide and carbonate units. This is capable of catalysing the conversion of a wide range of enones to the corresponding epoxides in high yields and reasonable rates using a small excess of hydrogen peroxide. A further epoxidation has been published by Matteo Guidotti’s group in Milan (Chem. Commun. 2000 1789). In this work they introduce the added twist of an acid-catalysed cyclisation followed by epoxidation of the resultant double bond.This is achieved by stirring citronellal with a mesoporous titanium silicate to effect ring closure then adding hydrogen peroxide to epoxidise the double bond in the product. This makes G101 NEWS & V I E W S use of the mild acidity of the solid surface and then the ability of the Ti centres to activate hydrogen peroxide towards epoxidation. The utility of epoxides as synthetic intermediates is largely related to their ability to undergo specific and selective ring opening. Chung Eui Song’s group from the Korea Institute of Science and Technology in Seoul have demonstrated a highly enantioselective method for ring opening of cyclic epoxides with azide using Cr-salen catalysts (Chem.Commun. 2000 1743). They use the ionic liquid bmim PF6 – as solvent and a range of cyclic epoxides. Ring opening with TMSN3 in the presence of 3 mol% catalyst gave yields of between 75 and 85% with ee’s up to 97%. The addition of amines and other nucleophiles to multiple bonds is a clean route to a range of useful compounds. A variety of transition metal salts and complexes are known to catalyse this type of reaction. Thomas Müller and colleagues from the Technische Universität in Munich have now described a heterogeneous catalyst which Green Chemistry December 2000 not only carries out the reaction but does it faster than the equivalent homogeneous system (Chem. Commun. 2000 1753).They took a zinc-exchanged BEA zeolite and used it as a catalyst in the intramolecular cyclisation of 6-amino-1-hexyne. Their Zn-BEA catalyst outperformed significantly zinc triflate and was interestingly far better than other Zn-exchanged zeolites and silicas. Monique Lasperas and co-workers from the CNRS in Montpellier (see Green Chem. 2000 G48 for a feature on this laboratory) have published findings relating to a mesoporous supported ephedrine catalyst which can be used for the enantioselective addition of diethylzinc to benzaldehyde (Chem. Commun. 2000 1773) (see scheme above). This work has led to significant improvements in the efficiency and selectivity of these materials such that they display the same enantioselectivity as the homogeneous system and can be easily recovered and reused.The improved activity comes about from a new method for loading the silica surface with a very high density of organic functions many of which are not catalytically active but which suppress the catalysis of the reaction by the silica surface which leads to non-selective reaction. Richard Broene and co-workers at the Los Alamos National Laboratory and Bowdooin College have described a simple method for the preparation of heterogeneous enantioselective hydrogenation catalysts (Chem. G102 recently published a whole-cell route to d-phenyl glycine amide a key intermediate in the synthesis of penicillin This journal is © The Royal Society of Chemistry 2000 Commun.2000 1797). They supported ionic Rh complexes onto MCM-41 and used them in the hydrogenation of enamide esters. Under their conditions complete conversions and excellent ee’s were obtained. The immobilisation works best when a H-bonding active anion is used presumably to increase interaction with the MCM surface. Reuse was possible but fouling of the catalyst with reaction products became a problem after four reuses. Roger Sheldon’s group in Delft have antiobiotics (Org. Proc. Res. Dev. 2000 4 318). This route starts from the unstable d-phenylglycine nitrile (which can undergo retro-Strecker reaction) which is hydrated by nitrile hydratase present in various strains of Rhodococcusmicroorganisms (R. rhodocrous being the most efficient).At low temperature conditions and prolonged reaction times (22 h) a yield of 95.1% could be obtained with an ee of 99.5%. Low levels of the opposite enantiomer were hydrolysed by amidase enzymes helping to achieve the very high levels of enantioselectivity achieved. b-Arylamines are an important class of compounds due to their bioactivity (e.g. dopamine) and synthetic methods to them (and the closely related and equally interesting b-exomethylene derivatives) are of great interest. The Heck reaction is one route to the latter but often insufficient regioselectivities can hamper the use of this method. A group from Uppsala University in Sweden led by Anders Hallberg has developed an extremely FOCUS ON… Professor James Clark and the York Green Chemistry Group York is justifiably regarded by many as the home of green chemistry in the UK.The Centre for Clean Technology under the directorship of Professor James Clark not only houses the Green Chemistry Research Group but is also the central hub of activity for the RSC Green Chemistry Network and is the editorial focal point for this journal. Continuing this Focus on… series Mike Lancaster looks at some of recent work of the York Green Chemistry Group. The Green Chemistry Group is one of the largest research groups within the University consisting of over 30 academics research fellows and graduate students. James Clark holds one of the ten original Royal Academy of Engineering Clean Technology Fellowships a scheme which relieves members of academic staff from most of their teaching duties allowing them to concentrate on research and public understanding activities.The latter area is of particular importance to Professor Clark and through organs such as Green Chemistry and the Green Chemistry Network he is striving to make people realise that chemistry can be done with environment awareness. He was the first to recognise that many current processes and products could be improved but wishes to get across the message that we are making good progress in this direction. Much of the group’s research is focused at solving real industrial problems by application of innovative heterogeneous catalyst technology.Waste minimisation at source is the central theme of much of Clark’s thinking1 and he is quick to point out that the principal current sources of chemical waste come from the more recent fine and speciality chemical sectors. It is in these areas where much of his work is focussed. In G103 Green Chemistry December 2000 Professor James Clark with his Green Chemistry Research Group at York This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S efficient and regioselective route to these compounds (J. Org. Chem. 2000 65 7235). They investigated the coupling of allylamines with aryl triflates with a palladium acetate / ferrocenyl-diphosphine catalyst system. They managed to achieve reasonable yields of product with excellent regioselectivites (generally > 99.5%) under thermal heating.With microwave heating reaction times were 3–5 minutes but regioselectivity was typically slightly lower but still very good. In the presence of CO amides were formed in some cases. NEWS & V I E W S contrast to the bulk chemicals area many fine & speciality chemical processes use homogeneous catalysts which are often difficult to separate from the product and reuse a considerable portion of the group’s work is aimed at heterogenising these reactions. Supported acid catalysts Friedel–Crafts chemistry ‘catalysed’ by aluminium chloride is widely used in many sectors of the chemical industry. Such catalysts are however required in at least stoichiometric amounts and lead to copious amounts of aluminous waste.Working in conjunction with Contract Chemicals Clark set out to find an environmentally acceptable solution to this problem using supported catalysts. This work resulted in the commercialisation of the Envirocat™ range of catalysts. This collaboration continued over many years and the second generation of Envirocats™ was launched in 1997. The activity and selectivity of these materials compares well with AlCl3 (Scheme 1) and they can be tailored for reactions such as alkylation acylation and sulfonylation. This kind of catalyst has important implications for the production of linear alkyl benzenes,2 precursors to the sulfonates—the world’s most widely used laundry detergent with an annual production of over 2M tpa.Although these surfactants have replaced the older branched sulfonates because of their increased biodegradability much of the current manufacturing technology is not green being based either on AlCl3- or HF-catalysed processes which produce large amounts of waste or involve hazardous reagents. Environmental pollution control through use of supported acid catalysts is one of the main research areas of Dr Karen Wilson who has recently been appointed to a lectureship after spending a number of years as postdoctoral fellow in the Clark group. Her recent work has centred on supporting the other common Lewis acid—BF Green Chemistry December 2000 G104 has shown that the resulting Bronsted acidity of the catalyst is dependant on how the catalyst is prepared.This dual acidic character has important implications in controlling selectivity for reactions such as the alkylation / etherification of phenol with olefins. Supported basic catalysts Heterogeneous acid catalysts have been the focus of much attention for about 40 years largely due to their use in the petrochemical industry. It is only more recently that heterogeneous base catalysts have found use in industrial processes such as the Sumitomo process for converting vinyl norbornene to ethylidene norbornene—a key ingredient in EPDM rubbers (Scheme 2). This process overcomes many of the ‘green’ issues associated with the previous technology—Na/K in liquid ammonia.It is in this more recent and under developed area where Dr Duncan Macquarrie a Royal Society Research Fellow (and associate editor of Green Chemistry) is concentrating a major part of his research effort. Macquarrie has found that aminopropyl functionalised silica (AMPS) is a versatile catalyst for important synthetic reactions such as the Knoevengel reaction in which the only by-product is water. Modification of AMPS by reaction with hydroxylated benzaldehydes readily gives supported phenolates,4 as shown in Scheme 3 for example. These materials are efficient and selective catalysts for a wide variety of Michael reactions the activity largely depending on the steric availability of the phenolate group.Oxidations for the production of ketones acids and epoxides often involve use of stoichiometric amounts of toxic high valent metals such as chromium and manganese. Replacement of these environmentally unfriendly and increasingly uneconomic processes by selective catalytic and Eco-efficient routes is of obvious value to the speciality and pharmaceutical industries. The Green Chemistry Group has employed its expertise in modifying silica to synthesis a number of supported metal Scheme 3 Example of Michael reaction using supported phenolate catalyst Scheme 2 Sumitomo isomerisation process using Na / NaOH on gamma alumina Scheme 1 Alkylation of benzene Clean oxidations Fluoroaromatics are important in the pharmaceutical fine chemical and advanced materials industries; traditional 3—on silica.3 This work This journal is © The Royal Society of Chemistry 2000 oxidation catalysts.A convenient route to these catalysts involves reaction of a cyanoalkylsilane with mesoporous silica gel followed by hydrolysis of the nitrile to leave a chemisorbed carboxylic acid. This acid has the capability of strongly binding divalent transition metal ions including Co(ii). The metal species are tightly bound and are not removed by common organic solvents. These materials are capable of catalysing the air oxidation of alkyl aromatics (e.g. diphenylmethane to benzophenone) and of olefins to epoxides (in the presence of sacrificial aldehydes which act as oxygen transfer agents).Baeyer–Villiger oxidation of ketones to esters and cyclic ketones to lactones (e.g. conversion of cyclohexanone to caprolactone) is also important industrially. This type of reaction centres on the use of peracetic acid or other potentially hazardous peroxides as oxidant. A Ni-based catalyst has been prepared similar to the above but based on modified AMPS.5 This catalyst used in conjunction with benzaldehyde as sacrificial agent and oxygen has proved capable of carrying out the cyclohexanone–caprolactone transformation in yields of over 90% at ambient temperature. Clean routes to organofluorine compounds routes involving halogen exchange for example often give rise to harmful waste products. In recent years Clark has become interested in fluorodenitration as a more selective and more environmentally friendly technique for introducing fluorine groups.Nucleophilic sources of fluoride such as tetramethylammonium bifluoride which is particularly thermally stable have proved highly effective in replacing aromatic nitro groups with fluorine. This reagent does not in general lead to formation of phenols and ethers which are significant by-products with other ‘onium’ fluorides. One particularly interesting example which once again highlights the group’s attention to finding solutions to real industrial issues is in the formation of 4,4A-difluorobenzophenone (BDF) from 4,4A-dinitrophenylmethane. The synthesis of BDF used in the manufacture of PEEK thermoplastics for the aerospace and other industries involves hazardous reagents and generation of toxic by-products.This work,6 which utilises both the basic and nucleophilic properties of the fluoride ion has shown that combined fluorodenitration and oxidation can be achieved using Estonia in a small country in Northern Europe with an area of 45,215 sq km and a population of about 1.5 million. Its educational centres are in the capital Tallinn in the north and in Tartu in the south. The Tallinn Technical University is the main source of engineering education including chemical engineering. The Estonian alma mater is in Tartu – the University of Tartu was established by the Swedes in 1632 and has been a very important academic centre through different periods of Estonian history.Most of the industry in Estonia is located in the north of the country consisting of power plants oil-shale mining and chemistry and textile factories as well as construction materials and metal processing plants. Environmental protection has a relatively long history in Estonia going References 1 Chemistry of Waste Minimisation ed. J. 3 Synthesis of a novel supported solid acid BF3 catalyst K. Wilson and J. H. Clark Chem. Commun. 1998 2135. 4 Supported phenolates as efficient catalysts of the Michael reaction D. J. Macquarrie Tetrahedron Lett. 1998 39 4125. Green chemistry in Estonia Sirli Sipp and Mihkel Koel of the Institute of Chemistry at Tallinn Technical University in Estonia describe their country’s progress in the spreading the ‘gospel’ of green chemistry This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S tetramethylammonium fluoride (TNAF) in an oxygen atmosphere.The reaction is highly solvent-dependant with dimethyl acetamide affording the highest yields. The York Green Chemistry Group has grown considerably in recent years largely through direct industrial sponsorship and until recently initiatives such as the Clean Technology Programme. Whilst there is almost universal acceptance that clean technology and green chemistry are worthy causes Clark believes there is a current lack of funding opportunities and that there should be a more consistent and longer-term mechanism to maintain and encourage new green chemistry research.Manufacturing molecules is one new future initiative that may prove beneficial. Although Clarke’s group has made much progress in cleaning up Friedel–Crafts reactions he would like to solve the difficult but highly relevant problem of carrying out acylations on unactivated substrates with genuine catalysts under moderate conditions; green chemistry solutions to this problem are currently limited to activated substrates. The scope and activity of the Green Chemistry Group continues to expand and now attracts a number of back to the last century. In 1853 the Estonian Naturalists’ Society was established. Classical ideas of wildlife conservation influenced by the pioneering work done in Germany spread to Estonia leading to the foundation of the first Nature Reserve area for sea-birds in 1910.Although the first Nature Protection Law of the Republic was passed in 1935 the Soviet occupation truncated any development in the field until 1957 when the first legislation on nature protection after the beginning of the Soviet occupation was embodied in law once again. Fifty years of development under conditions of unbalanced economic relations in the closed society of the former Soviet Union resulted in the irrational use of natural resources in Estonia. The nature preservation system Green Chemistry December 2000 students and postdoctoral workers from all over the world—proof if any were needed that green chemistry solutions to industrial problems are of truly global interest and importance.H. Clark Chapman & Hall London 1996. 2 Enhanced selectivity in the preparation of linear alkyl benzenes using hexagonal mesoporous silica supported aluminium chloride P. M. Price J. H. Clark K. Martin D. J. Macquarrie and T. W. Bastock Org. Proc. Res. & Dev. 1998 2 221. 5 Environmentally friendly liquid phase oxidation enhanced selectivity in the aerial oxidation of alkyl aromatics epoxidations and the Baeyer–Villiger oxidation using novel silica supported transition metal ions J. H. Clark et al. J. Chem. Technol. Biotechnol. 1999 74 923. 6 The formation of 4,4A-difluorobenzophenone from 4,4A-dinitrophenyl methane D.J. Adams J. H. Clark and H. McFarland J. Fluorine Chem. 1998 92 1998 127. has gradually improved since then. In 1990 the Law on Nature Protection of Estonia was passed and in 1997 the National Environmental Strategy for Estonia was approved by Parliament. This strategy covers all aspects of life in society and its principles can be formulated in the Priority goals of the National Environmental Strategy for the next ten years • Stimulation of environmental awareness and environmentally friendly consumption patterns • Promotion of clean technologies • Reduction of environmental impacts of the energy sector • Improvement of air quality including reduction of transport emissions • Improvement of waste management reduction of waste generation G105 NEWS & V I E W S resources • Surface water protection and rational use of water bodies • Preservation of landscape and biodiversity • Modification of built environment in line with human needs and environmental health requirements According to Article 53 of the Constitution of the Republic of Estonia every person is obliged to preserve the natural environment and to compensate for the damage they cause to the environment.Universal education on this matter is one of the important goals on the transition to sustainability as a long-term strategic issue for society. Unfortunately the emphasis put on education in sustainable development and green chemistry in the academic sector has so far been insufficient.The promotion of research activities in chemical aspects of clean technology has not reached the expected level even in those universities that have departments directly working on environmental chemistry Tallinn Technical University (www.ttu.ee) Tartu University (www.ut.ee) and the Estonian Agricultural University (www.eau.ee). The amount of technical knowledge that is needed to support sustainable development in new alternative solvents and in syntheses that are less polluting requires rapid improvement. The growing popularity amongst students of graduate courses on new materials and dense fluids chemistry can definitely be considered as the first success in green chemistry activities in Estonia.The bigger step towards a “greener” teaching system has been made by establishing the Green Chemistry Institute of Estonia in Tallinn Technical University in December 1999. The web page describing the principles of and news in “green chemistry” to the students researchers and public in Estonia will open at the end of October. Professor Mihkel Koel from the Chemistry Institute at Tallinn Technical University has skilfully performed an assignment in supervising and encouraging several students in actively Green Chemistry December 2000 taking part in sustainable chemistry advancement worldwide. For example Ms. Maia Sokolova and Ms. Sirli Sipp are the first young chemists from Estonia who have attended the Summer School in Green Chemistry which has been held in Venice Italy annually since 1998.The success of the young scientists is remarkable Ms. Sokolova’s poster won second place in Venice and Ms. Sipp was named as the Joseph Breen Memorial Fellow for 2000 and was sponsored by American Chemical Society‘s International Endowment Fund for participation in the Green Chemistry and Engineering Conference in Washington DC USA. Both Maia and Sirli are helping Professor Koel to raise the awareness of Estonian students in the field of new technologies and solvents in environmental chemistry. Use of supercritical CO2 Supercritical extraction (SFE) is a very suitable method for geochemical studies of fossil fuels though less applicable for large scale processing at the moment.1 From studies in the laboratory of Professor Koel it was estimated that the yields of the Soxhlet and SFE carbon dioxide extracts from the Estonian oil shale Kukersite are very similar.Carbon dioxide modified with methanol extracts compounds that conventionally are extracted from Kukersite with chloroform after treatment with hydrochloric acid and benzene/methanol mixture. Moderate increases in the temperature of the SFE leads to increases in the extract yield. However by 200 °C partial heterolytic cracking of the kerogen of Kukersite occurs. Geochemical parameters G106 stimulation of recycling • Clean-up of past pollution • Sustainable use of groundwater These priority goals form a good philosophical basis for green chemistry activities.Education on sustainable development Some recent results Professor Mihkel Koel and colleagues at the Chemistry Institute at Tallinn Technical University This journal is © The Royal Society of Chemistry 2000 calculated on the basis of chemical composition are similar in both SFE and Soxhlet extracts of Kukersite. There is a strong predominance in the relative distribution of n-alkanes n-alkanones n-alkylbenzenes and n-alkylcyclohexanes indicating the immaturity of overburden material (OM) of Kukersite is characteristic of both SFE and Soxhlet extracts. Another promising application of supercritical CO2 studied in this laboratory is extraction of local medicinal herbs.Collaboration with the Department of Pharmacy of Tartu University has two aims characterization of plants and the search for practical applications of extracts. Use of ionic liquids Room temperature liquid salts or ionic liquids are materials with environmentally friendly properties. There is now an intensive search for better applications for these materials including work in Professor Koel’s laboratory. In one project gas chromatography and capillary electrophoresis are used to describe the physical and chemical properties of alkylimidazolium ionic liquids. Another project involves the study of possible applications of ionic liquids in oil shale chemistry.2 The conversion of oil shale into value-added products is a challenging goal of chemistry and chemical engineering.There is an urgent need for the development of efficient processes that are capable of providing useful products such as alternative synthetic fuels or high-quality chemical feed stocks. The first step is the development of efficient means to characterise the various components of the shales. Two different types of ionic liquids have been examined for their ability to extract organic compounds particularly oxygenated compounds from the Estonian oil shale named kerogen in the Tallinn Technical University. 1-Butyl-3-methylimidazolium hexafluorophosphate and chloroaluminate were synthesised and applied to kerogen extraction at various temperatures.In addition the effect of the Lewis acidity of the chloroaluminate salt was examined. At room temperature there was no evidence of extraction from the kerogen using either ionic liquid. However these extractions are favoured at elevated temperatures up to the thermal degradation temperature of kerogen (above 400 ºC). At 175 °C the extraction yield of soluble products was increased Winners of the first UK Green Chemistry Awards were announced in September. The Green Chemistry Network on behalf of the sponsors (the Salters’ Company the Jerwood Charitable Foundation and the Royal Society of Chemistry) administer these awards with financial support from the Department of Trade and Industry. The awards are designed to recognise outstanding achievements in the development of green chemical technology and to encourage more R&D in the area from both the academic and industrial communities.The winner of the The Jerwood Salters’ Environment Award in this category went to Dr Chris Braddock of Imperial College London for his work on “Novel Recyclable Catalysts For Atom Economic Aromatic Nitration” (see Green Chemistry 1999 1(4) G97-98). Aromatic nitration is practised across the chemical industry and is a key reaction for products such as dyes pharmaceuticals plastics and fine chemicals. However the conventional reaction employing excess amounts of concentrated nitric and sulfuric acids produces large amounts of ‘spent acid’ waste which requires treatment and disposal.Lewis acids are known to References The environmental policy of the 2 M. Koel W. K. Hollis T. J. Lombardo B. F. Smith J. B. Rubin Ionic Liquids for oil shale extraction Proceedings of NATO ARW Crete 2000. Republic of Estonia has contributed to the development of green chemistry. It is implemented through executive action UK Green Chemistry Awards The Young Academic Category The Industrial Category This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S 10 times over that obtained using conventional organic solvents such as hexane and ethylene chloride. Significant differences were observed in the extraction behaviours between different types of Estonian oil shale because of the unique chemical composition and structure of their organic components.These are only a few examples of studies related to green chemistry. The search for new materials and the development of new processes cannot ignore their environmental impact. Despite the limited resources of this small country the ideas of sustainable development are spreading and the principles of green chemistry are increasingly being introduced into the chemistry curriculum in Estonian Universities. catalyse the reaction overcoming the need for sulfuric acid but because of their water sensitivity they are also required in stoichiometric amounts. Braddock’s novel approach to solving this problem involved the use of lanthanide catalysts (e.g. ytterbium triflate) and molar amounts of nitric acid.These lanthanide catalysts are unusual in that they are strong Lewis acids but are very stable in the presence of water and are therefore only required in true catalytic amounts (down to 1 mole %). Braddock has also demonstrated that that the catalysts can be recovered and recycled opening the way for a waste free nitration process. The mechanism of the reaction has been extensively probed and a strong correlation between charge to size ratio of the lanthanide centre and catalytic activity has been found. Extrapolation of these results led to the prediction that Green Chemistry December 2000 programs following the elaboration of environmental strategy trends. The application of resource and pollution changes has provided a solid basis for integrating the principles of environmental protection into economic activities.Investments financed from the national budget by different enterprises local municipalities and various funds have been made to help address environmental problems; foreign assistance has also been significant. 1 M. Koel E. Bondar Application of supercritical fluid extraction to organic geochemical studies Fuel 77 1998 3 211–213. E. Bondar M. Koel M. Liiv A comparative study of the composition of biomarkers in SFE and solvent extracts of oil shales Fuel 77 1998 3 215–219. Group IV metal triflates of hafnium and zirconium would be excellent nitration catalysts. This prediction was correct and these catalysts proved to be very active for industrially important nitration of electron deficient aromatics such as o-nitrotoluene.Further studies showed that for optimum catalytic activity the counter ion should be the conjugate base of a very strong acid this acting as a phase-transfer catalyst for the nitronium ion. Accordingly synthetic routes to ytterbium and scandium tris(trifluoromethanesulfonyl)methides were developed; these catalysts enabled the quantitative conversion of o-nitrotoluene into dinitrotoluene to be achieved. The winner in this category was BASF plc. Cheadle Hulme Cheshire for their work on “Super-Efficient Dyes for the Coloration of Cotton; the Procion XL+ Range. Globally around 80,000 tpa of reactive dyes are used to colour cotton by exhaust technology.This dyeing process uses 4 3 108 tpa of fresh water which is ultimately discarded in a contaminated state. This contamination includes 24,000 tpa dye and 2.8 3 106 tpa of salt. Most aqueous effluent is discarded via local G107 NEWS & V I E W S watercourses. Whilst the dyehouses remove some colour a significant amount of colour together with salt and other additives find their way to the treatment works and often further. The environmental impact of the dye industry is therefore appreciable and has a wide impact. BASF designed the Procion XL+ high strength dyes to utilise their carbon frameworks more efficiently to deliver colour. These dyes are based on monochlorotriazine reactive groups attached to carefully designed chromophores.• Reduction in energy use by 50% • Reduction in water consumption of 40% • Reduction in salt use by up to 33% • Higher dye fixation resulting reduced Green Chemistry December 2000 The winners were Industrial Copolymers Limited of Preston for their nomination entitled “Oxazolidine Diluents Reacting for the Environment”. The automotive paint market is one of the major contributors to solvent emissions to atmosphere. The EU introduced legislation in 1999 to restrict emissions to 70% of 1990 levels which will affect 400,000 firms and impact on 10 million jobs. In the main automotive finishes consist of 2-component solvent-based polyurethane coatings. In order to comply with legislation there are possible routes to reduce solvents replacing them with water-based alternatives and employing high-solids coatings. Both of these approaches have some technical disadvantages the former requiring investment in new equipment and at the same time generating contaminated aqueous waste whilst the latter has limitations in spray applications imposed by the higher viscosity. Industrial Copolymers have developed G108 • Doubles productivity by reducing dye-processing time The Small & Medium Enterprise Category The key benefits of these new dyes include; effluent BOD COD and TDS a reactive diluent Incozol LV based on bisoxazolidine to overcome all these problems. This journal is © The Royal Society of Chemistry 2000 Incozol LV can be used to replace organic solvent in the polyol component of the finish at levels of up to 30% which leads to a significant reduction in VOC enabling the finisher to exceed legislative requirements. The bisoxazolidine is reacted into the polyurethane coating via a mechanism that initially involves hydrolysis by trace amounts of water in the finish or in the atmosphere The amino alcohol generated then reacts with the isocyanate to form urea couplings incorporating the Incozol LV into the backbone. Extensive testing has shown that the cure and coating properties of the finish are not adversely altered by the presence of the reactive diluent. More detailed papers from all the award winners will appear in the next issue of Green Chemistry. Papers describing the technology behind these awards will also be presented at the Green Chemistry Sustainable Products & Processes Conference to be held in Swansea (3–6 April 2001).

ISSN:1463-9262    

DOI:10.1039/b008754h

出版商:RSC    

年代:2000

数据来源: RSC