(173b) Simulation of Simultaneous Sacharification and Fermentation of Ethanol Production from Cellulose by An Operable Model

An operable batch model of simultaneous saccharification and fermentation (SSF) for ethanol production from cellulose has been developed. The model includes four ordinary differential equations that describe the changes of cellobiose, glucose, yeast and ethanol concentration with respect to residence time. These equations were used to simulate the data for the four main components in the SSF process of ethanol production from Avicel PH101. The model parameters at 95% confidence intervals were determined by a MATLAB program based on the batch experimental data of the SSF without additional experiments. The model was used to show that the influence of the initial parametric conditions on the ethanol production as follows: initial cellulose concentration > initial enzyme concentration > initial yeast concentration. The model also showed that the conversion of cellulose to cellobiose was the rate-controlling step in a series reaction of cellulose to ethanol. The rate constants of cellobiose to glucose and glucose to ethanol were 5.3 and 5.6 times that of cellulose to cellobiose, respectively. The batch model was extended to the continuous and fed-batch operating models. For the continuous operation in the SSF, the productivities increased with increasing dilution rate, until a maximum value was attained, and rapidly decreased as the dilution rate approached the washout point. The model also predicted a relatively high ethanol mass for the fed-batch operation than the batch operation.

Keywords: Simultaneous saccharification and fermentation; Ethanol; Cellulose; Model; Operating mode