High productivity processes are critical for commercial production of cellulosic ethanol. One high productivity process-continuous hydrolysis and fermentation-has been applied in corn ethanol industry. However, little research related to this process has been conducted on cellulosic ethanol production. Here, we report and compare the kinetics of both batch SHF (separate hydrolysis and co-fermentation) and SSCF (simultaneous saccharification and co-fermentation) of AFEX™ (Ammonia Fiber Expansion) pretreated corn stover (AFEX™-CS). Subsequently, we designed a SSCF process to evaluate continuous hydrolysis and fermentation performance on AFEX™-CS in a series of continuous stirred tank reactors (CSTRs). Based on similar sugar to ethanol conversions (around 80% glucose-to-ethanol conversion and 47% xylose-to-ethanol conversion), the overall process ethanol productivity for continuous SSCF was 2.3- and 1.8-fold higher than batch SHF and SSCF, respectively. Slow xylose fermentation and high concentrations of xylose oligomers were the major factors limiting further enhancement of productivity.
Biofuels Bioreactors