ISSN:0006-3592    

DOI:10.1002/bit.260250102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractA mathematical model was developed for a percolation reactor in connection with consecutive first‐order reactions. The model was designed to simulated acid‐catalyzed cellulose or hemicellulose hydrolysis. The modeling process resulted in an analytically derived reactor equation, including mass‐transfer effects, which was found to be useful in process desing and reactor optimization. The modedl was verified by experimental data obtained from hemicellulose hydro

ISSN:0006-3592    

DOI:10.1002/bit.260250103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractPentosan hydrolysis at low aqueous liquid‐to‐biomass ratios (2.5–15 mL/g) with sulfuric acid as the catalyst is studied in the temperature range of 125–155°C. To facilitate heat transfer and mixing a second insoluble oil is added to the reaction mixture. It is found that even at high slurry concentrations, the reaction is the rate‐controlling step. In addition, such systems give higher pentosan yields compared with dilute slurry systems. This is explained using the concept of acid loading which is defined as the acid present per unit mass

ISSN:0006-3592    

DOI:10.1002/bit.260250104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractThe effects of structural properties and their changes during cellulose hydrolysis on the enzymatic hydrolysis rate have been studied from the reaction mechanism point of view. Important findings are the following: (1) The crystallinity index (CrI) of partially crystalline cellulose increases as the hydrolysis reaction proceeds, and a significant slowing down of the reaction rate during the enzymatic hydrolysis is, in large part, attributable to this structural change of cellulose substrate. (2) The crystallinity of completely disordered cellulose, like phosphoric‐acid‐treated cellulose, does not change significantly, and a relatively high hydrolysis rate is maintained during hydrolysis. (3) The specific surface area (SSA) of partially crystalline cellulose decreases significantly during enzymatic hydrolysis while the change in SSA of regenerated cellulose is found to be negligible. (4) The value of degree of polymerization (DP) of highly ordered crystalline cellulose remains practically constant whereas the change in DP of disordered regenerated cellulose is found to be very significant. (5) Combination of these structural effects as well as cellulase adsorption, product inhibition, and cellulase deactivation all have important influence on the rate of cellulase reaction during cellulose hydrolysis. More experimental evidence for a two‐phase model, which is based on degradation of cellulose by simultaneous actions of cellulase complex on the crystalline and amorphous phases, has been obtained. Based on experimental results from this study and other results accumulated, the mode of cellulase action and a possible reaction mechanism are pro

ISSN:0006-3592    

DOI:10.1002/bit.260250105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractA new type of reactor, an attrition bioreactor, was tested to achieve a higher rate and extent of enzymatic saccharification of cellulose than is possible with conventional methods. The reactor consisted of a jacketted stainless‐steel vessel with shaft, stirrer, and milling media, which combined the effect of the mechanical action of wet milling with cellulose hydrolysis. The substrates tested were newsprint and white‐pine heartwood. The performance of the reactor was excellent. The extent and rate of enzymatic hydrolysis could be markedly improved over other methods. The power consumption of the attrition bioreactor was also measured. The cellulase enzyme deactivation during attrition milling was not signific

ISSN:0006-3592    

DOI:10.1002/bit.260250106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractCellulose and hemicellulose in renewable biomass resources such as cornstover and wheat straw have been examined as substrates for the production of ethanol. A mixed culture of selected strains ofClostridium thermocellumandClostridium thermosaccharolyticumare used to accomplish both the hydrolysis and fermentation of these carbohydrates in a single step. However, lignin and related phenolic materials are shown to diminish the rate, extent, and yield at which these carbohydrates can be utilized for ethanol production. In order to overcome this problem, a selective solvent pretreatment with alkaline–ethanol–water mixtures was examined for the delignification of cellulosic biomass under conditions where very little loss of fermentable carbohyrates results. Under optimal conditions, up to 67% of the initial lignin in cornstover can be extracted while 95% of the α‐cellulose and pentosan carbohydrates remain insoluble. Subsequent mixed culture fermentation of the treated material has shown a 400% increase in the rate of degradation and greater than 85% utilization of the substrate. The effects of various extraction parameters on delignification kinetics and subsequent fermentation performance are dis

ISSN:0006-3592    

DOI:10.1002/bit.260250107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractThe utilization and conversion ofD‐xylose,D‐xylulose,L‐arabinose, and xylitol by yeast strains have been investigated with the following results: (1) The majority of yeasts tested utilizeD‐xylose and produce polyols, ethanol, and organic acids. The type and amount of products formed varies with the yeast strains used. The most commonly detected product is xylitol. (2)The majority of yeasts tested utilizeD‐xylulose aerobically and fermentatively to produce ethanol, xylitol,D‐arabitol, and organic acids. The type and amount of products varies depending upon the yeast strains used. (3) Xylitol is a poor carbon and energy source for most yeasts tested. Some yeast strains produce small amounts of ethanol from xylitol. (4) Most yeast strains utilizeL‐arabinose, andL‐arabitol is the common product. Small amounts of ethanol are also produced by some yeast strains. (5) Of the four substrates examined,D‐xylulose was the perferred substrate, followed byD‐xylose,L‐arabinose, and xylitol. (6) Mutant yeast strains that exhibit different metabolic product patterns can be induced and isolated fromCandidasp.Saccharomyces cerevisiae, and other yeasts. These mutant strains can be used for ethanol production fromD‐xylose as well as for the study of metabolic regulation of pentos

ISSN:0006-3592    

DOI:10.1002/bit.260250108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractInhibition by secondary fermentation products may limit the ultimate productivity of new glucose to ethanol fermentation processes. New processes are under development whereby ethanol is selectively removed from the fermenting broth to eliminate ethanol inhibition effects. These processes can concentrate minor secondary products to the point where they become toxic to the yeast. Vacuum fermentation selectively concentrates nonvolatile products in the fermentation broth. Membrane fermentation systems may concentrate large molecules which are sterically blocked from membrane transport. Extractive fermentation systems, employing nonpolar solvents, may concentrate small organic acids. By‐product production rates and inhibition levels in continuous fermentation withSaccharomyces cerevisiaehave been determined for acetaldehyde, glycerol, formic, lactic, and acetic acids, 1‐propanol, 2‐methyl‐1‐butanol, and 2,3‐butanediol to assess the potential effects of these by‐products on new fermentation processes. Mechanisms are proposed for the various inhibition eff

ISSN:0006-3592    

DOI:10.1002/bit.260250109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractIndustrialized nations face a critical problem in replacing the sources of liquid fuels that traditionally have been supplied by petroleum. One solution that has gained increasing support in this country is the use of ethanol produced by fermentation of renewable biomass as an extender in, or supplement to, gasoline for transportation fuel. Distillation, the present method of separating ethanol from the fermentation broth, is an energy‐intensive one and frequently uses more energy than is available from the ethanol recovered. There are many investigations under way to find alternative, less energy‐intensive techniques for the ethanol–water separation. The separations method described in this article involves the use of solid materials to preferentially remove ethanol from fermentation broths. Subsequent stripping of the ethanol from the sorbent with a dry gas reduces dramatically the energy required for the separation. Three solid sorbents have been investigated experimentally. Their sorption/desorption characteristics are described, and their incorporation in an ethanol recovery process is evaluated. Three sorbents were investigated: two commercially available divinylbenzene crosslinked polystyrene resins in bead form (one with a nominal surface area of 300 m2/g, the other with 750 m2/g) and an experimental proprietary molecular sieve with hydrophobic properties. Equilibrium adsorption isotherms for two of the sorbents were obtained at ambient temperature (21°C) for ethanol–water solutions containing up to 12 wt. % ethanol. In addition, 40°C isotherms were obtained for the polystyrene sorbents. Although different, the equilibrium isotherms for the sorbents indicated that ethanol could be preferentially sorbed from a dilute solution. Column breakthrough curves indicated very favorable kinetics. Desorption of the ethanol was readily effected with warm (60–80°C),

ISSN:0006-3592    

DOI:10.1002/bit.260250110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY

摘要:

AbstractThe macromolecular compounds excreted during growth by yeasts as exocellular fractions were studied and found to contain a high proportion of carbohydrates. On the basis of the specificity of these fractions, an attempt was made to distinguish between nine strains of a single species of yeast—Saccharomyces cerevisiae.Each strain came from a different source. The electrophoretic patterns of the exocellular fractions tested made it possible to distinguish between the nine strains, on the basis of Lodder's criteria for the morphological and physiological identification of yeasts. We considered that strains giving exocellular fractions distinguishable by electrophoresis belonged to distinct clones. Consequently, this technique enables us to go further than diagnosis of the specie

ISSN:0006-3592    

DOI:10.1002/bit.260250111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1983

数据来源: WILEY