Monday, April 30, 2007

Ethanol and succinic acid production from AFEX-treated sugar cane biomass

Farzaneh Teymouri, Michael Guettler, Susanne Kleff, and Chris Saffron. MBI International, 3900 Collins Road, Lansing, MI 48910

Ammonia fiber expansion (AFEX) was used as a pretreatment method to increase enzyme digestibility of sugar cane bagasse and cane leaf matter (CLM).  The AFEX process parameters, i.e. reaction time, reaction temperature, ammonia loading, and moisture content, were varied to improve the glucose and xylose yields. The efficiency of the AFEX process was evaluated via enzyme hydrolysis and the most effective process parameters were established. 

The fermentability of AFEX-treated bagasse and CLM was assessed via a separate hydrolysis and fermentation (SHF) process for ethanol and succinic acid production.  Zymomonas mobilis 37821 (pZB5) was used for ethanol and Actinobacillus succinogenes (FZ45) for succinic acid production.  Both organisms are able to metabolize glucose and xylose. Product inhibition during enzyme hydrolysis results in low product concentrations and leads to unfavorable economics.  Therefore, the fermentability of AFEX-treated bagasse to ethanol was evaluated using simultaneous saccharification fermentation (SSF) process with Saccharomyces cerevisiae D5A.  At the end of the fermentation, the solids were removed and the ethanol was distilled from the liquid stream.  The remaining liquid was concentrated and a xylose rich liquid was generated.  This stream provided the sole carbon source in a second fermentation for the production of succinic acid using A. succinogenes.  The organism is capable of  utilizing a second ethanol waste-product, CO2, which is incorporated into the succinic acid product.

The experimental details, maximum glucose and xylose yields obtained from AFEX-treated bagasse and CLM, and fermentations yields for ethanol and succinic acid will be presented.  Economics of the processes will be discussed.