Fermentation Kinetics and Process Economics for the Production of Ethanol.

摘要

The aim of this study was to develop and optimize fermentation technology for the production of ethanol. Using glucose as the fermentable substrate,optimal fermentation parameters of pH,temperature,oxygen tension,and sugar concentration were determined in both batch and continuous culture. The experimental results indicate that although ethanol fermentation is an anaerobic process,trace amounts of oxygen are required for maximal ethanol production. The ethanol productivity of the initial culture of Saccharomyces cerevisiae (ATCC No. 4126) was optimal at an oxygen tension of 0.7mmHg and a temperature of 35exp 0 C. However,when long term continuous culture was maintained the yeast ''adapted''after 3weeks of operation,requiring an oxygen tension of only 0.07mmHg for optimal ethanol production, 43percent higher than for unadapted yeast. A cell recycle system employing an external settler to increase the biomass concentration in continuous fermentations was examined. In addition, a novel vacuum fermentation scheme was developed whereby ethanol is boiled away from the fermentation broth as it is produced. By combining the vacuum fermentation with cell recycle,yeast cell densities of 124 g dry wt/1were achieved resulting in a 14-fold increase in ethanol productivity over simple continuous operation. From the experimental results obtained industrial size ethanol fermentation plants were designed and an economic evaluation conducted. The process design studies indicated that over a 50percent reduction in capital expenditure may be obtained by continuous rather than batch operation. Further reductions in processing costs were achieved by both cell recycle and vacuum operation. However,the cost of fermentable substrate,either molasses or enzymatic hydrolysate sugars,dominates the economics of ethanol production. (ERA citation 01:023007)