摘要:

AbstractPresent technology for production of primary zinc by the Imperial Smelting and electrolytic zinc processes followed long and expensive process development, driven by the need to improve on inefficient, small scale and labour intensive retorting processes. These newer processes are complementary, very efficient and continue to develop to meet evolving needs, with no sign of a shortage of suitable concentrates to force major change to newer technology.Several proposed intensive zinc processes to treat calcines, and an innovative direct process treating polymetallic sulphide concentrates, all need to condense bulk metallic zinc from a dust‐ or fume‐laden gas, e.g. by absorption in a lead or zinc condenser. Efficient metal recovery and process control will meet major engineering and operating difficulties. Successful commercialisation to bulk zinc, if ever achieved, will require long and expensive development, and present need does not justify the costs and effort involved.Whither zinc? Most likely down an evolutionary path from present technology, with added environmental protection whose costs must be carried by the industry, then by soci

ISSN:0268-2575    

DOI:10.1002/jctb.280510102

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractA mutant strain with high penicillin G acylase activity was derived from Escherichia coli ATCC 11105 by chemical mutagenesis, using N‐methyl‐N′‐nitro‐N‐nitrosoguanidine. Penicillin acylase was extracted from the mutant strain and highly purified by DEAE‐cellulose and hydroxyapatite column chromatography followed by preliminary precipitation steps. Vmand Kmvalues of the enzyme (specific activity: 24·81 U mg−1, protein concentration: 0.56 mg cm−3) were found to be 22.73 U cm−3mm−1and 3.18 mmold m−3penicillin G, respectively. The enzyme was shown to be uncompetitively inhibited by excess of substrate. The inhibition by phenylacetic acid was found to be competitive, and 6‐aminopenicillanic acid to be noncompetitive. Inhibition constants for excess of penicillin G, phenylacetic acid and 6‐aminopenicillanic acid were estimated as 74.20, 18.74 and 15.00 mmol dm−3respectively, at pH 8.0 and 40°C. The activation energy of the enzymatic hydrolysis reaction of penicillin G was found to be 10.78 kcal mol−1. Optimal pH and temperature values of the enzyme were determined as 8.0 and 60°C. Complete loss of the enzyme stability occurred when the enzyme was incubated at pH

ISSN:0268-2575    

DOI:10.1002/jctb.280510103

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractExamined in this study is a potential application of Vernonia galamensis lipase (acetone powder) in enzyme‐catalyzed hydrolysis of seed oils, most especially of those containing reactive functionalities which are easily affected under drastic hydrolytic and methylating/transesterification conditions during fatty acid analysis.Eight seed oils from V. galamensis, Ximenia kaffra, castor, corn, soyabean, palm kernel, sunflower and olive were hydrolyzed by lipase (acetone powder) followed by methylation using diazomethane in ethyl ether. Results obtained showed that the lipolytic hydrolysis of triglycerides by V. galamensis lipase (acetone powder) was probably nonspecific and did not result in isomerization and as such hydrolyzed the triglycerides of the seed oil in a fashion that the resulting fatty acids were unaltered during hydrolysis. The fatty acids obtained were representative of the parent seed oils. Values reported for the various seed oils were similar to those of previous studie

ISSN:0268-2575    

DOI:10.1002/jctb.280510104

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe removal of Pb(II) from aqueous solution by adsorption on china clay and wollastonite is an attractive process. The amount of Pb(II) removed by adsorption is highly dependent on the temperature of the adsorbate solution and favours low temperature. The equilibrium times were noted, i.e. 90 min for china clay and 120 min for wollastonite. The various rate parameters of the adsorption process have been determined at different temperatures. The activation energies were determined and found to be −5.345 kJ mol−1and −8.730 kJ mol−1for Pb(II)‐china clay and Pb(II)‐wollastonite systems, respectively. The adsorption isotherm was measured experimentally at various temperatures. The negative values of enthalpy change (ΔH = −77.95 kJ mol−1and −16.40 kJ mol−1for china clay and wollastonite, respectively) indicate the exothermic nature of the adsorption processes for both systems. The isosteric heats of the adsorption process have been determined at various surface coverages of the adsorbents used. The various thermodynamic parameters have been calculated to elucidate the mechanism involved in th

ISSN:0268-2575    

DOI:10.1002/jctb.280510105

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractSome quinazolinone thiosemicarbazone and 4‐thiazolidone derivatives were prepared and tested for their anticonvtdsant activity. 3‐(2‐methyl‐4‐(3H)‐quinazolinon‐3‐yl)‐4‐oxo‐thiazolin‐2‐yl‐(4‐chlorobenzaldehyde)‐hydrazone (4a) shows the maximum protecting activity against pentylenetetrazol

ISSN:0268-2575    

DOI:10.1002/jctb.280510106

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractSome new 7‐alkyl (or aryl) aminomethyl‐6‐chloroquinoline‐5,8‐quinones (II) have been obtained through the reaction of 6‐chloroquinoline‐5,8‐quinone with primary aliphatic or aromatic amines and paraformaldehyde in ethanol. On using secondary amines such as piperidine or morpholine in the above reaction, 6‐chloro‐7‐piperidino (or morpholino) methylquinoline‐5,8‐quinone (III) and (IV) respectively were obtained. The structure of the synthesised compounds was confirmed by elemental analysis and spectral data. The synthesised compounds were al

ISSN:0268-2575    

DOI:10.1002/jctb.280510107

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe superconductivity of the ceramic solid YBa2Cu3O7 − δ, prepared by heating Y2O3, BaCO3and CuO at 920°C for 22 h, was checked by the Meissner effect. Chemical analysis established the formula of the compound prepared. A thermostated aqueous suspension of the superconductor, treated with a solution of H2O2, produced oxygen, whose volume was measured at intervals in a gas burette. From the initial rates of the first‐order reaction at different temperatures, the activation enthalpy and entropy were 16 kJ mol−1and −210 J K−1mol−1respectively. The rates of gas evolution were similar to those obtained when a MnO2sample was used as a catalyst. Neither the superconductor nor its semiconductor phase photocatalysed the decomposition of KMnO4solution. Evidence of the catalysed decomposition of N2H+5by the superconductor

ISSN:0268-2575    

DOI:10.1002/jctb.280510108

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractBiotransformation ofLmalic acid intoLlactic acid was studied in a fluidised bed reactor using cells of Lactobacillus sp. 89 and Leuconostoc oenos ATCC 23278 immobilised in a calcium alginate matrix. The reactor was used in a batch or a continuous manner under a non‐oxidising atmosphere. It was shown that 3 mm diameter beads loaded with 6 and 30 mg dry matter per gram of gel were the best operating conditions for Leuconostoc and Lactobacillus respectively. The optimal working conditions were as follows: pH = 3.0–5.0, temperature = 30°C for Lactobacillus and pH = 3.0, temperature = 25°C for Leuconostoc. No inhibition due to lactic acid was observed and the internal diffusional effects were negligible. The short catalyst life that was initially observed with both strains resulted from a depletion in NAD and Mn2+, two basic cofactors for malolactic enzymes. To prevent this detrimental effect, a regeneration process for biocatalyst was pro

ISSN:0268-2575    

DOI:10.1002/jctb.280510109

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe removal of cadmium and lead ions from aqueous solutions by groundnut husks modified by reaction with EDTA (% N = 12.05) was examined by equilibrium sorption studies at 29°C. The maximum metal ion binding capacity of the EDTA‐modified husk determined from the sorption isotherm from solutions of pH 6.8 was found to be 0.36 mmol g−1and 0.19 mmol g−1for Cd(II) and Pb(II) ions, respectively. It was found that the rate of sorption was particle‐diffusion controlled, and the particle‐diffusion control rate coefficient was determined to be of the order of

ISSN:0268-2575    

DOI:10.1002/jctb.280510110

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe production of cellulases and xylanase by Clostridium celerecrescens, a new anaerobic mesophilic cellulolytic bacterium, was studied using various substrates (cellobiose, xylan and cellulose Whatman CF‐11). While both cellulase (β‐1,4‐D‐glucan glucanohydrolase) and xylanase (β‐1,4‐xylan xylanohydrolase) were produced on cellulose, only the latter was produced when xylan was used as the sole carbon source. A weak p‐nitrophenyl‐β‐D cellobiohydrolase activity was detected in the extracellular filtrates when using cellulose as a substrate. Otherwise, β‐glucosidase (p‐nitrophenyl‐β‐D‐glucopyranosidase) was always found to be associated with the bacteria and reached its maximum levels of growth on cellobiose. In all cases, enzyme production showed a cell growth associated profile. Activities of these enzymes had their optimal values within the ranges of temperature and pH reported for the corresponding enzymes from similar anaerobic mesophilic microorganisms, although a relatively high optimum temperature, 55°C, was found for xylanase. All enzymes showed a 90% reduction of half‐life time for each 8°C increment of temperature. A 50% inhibition of xylanase and β‐cellobiohydrolase activity was observed, through a competitive mechanism, by xylose (0.677 mmol dm−3) a

ISSN:0268-2575    

DOI:10.1002/jctb.280510111

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY