Enhanced production of cellulosic butanol by simultaneous co-saccharification and fermentation of water-soluble cellulose oligomers obtained by chemical hydrolysis

Abstract

Butanol attracted interests as a drop-in biofuel obtainable from cellulosic wastes. However, the process typically used for cellulose bioconversion, i.e., separate hydrolysis and fermentation (SHF) of pretreated cellulose (Process I), is insufficient for energy-efficient production of fuel grade butanol due to the limited obtainable butanol titer. Recently, post-hydrolysis of chemically formed water-soluble cellulose oligomers was suggested for acetone-butanol-ethanol (ABE) production in SHF mode of operation (Process II). In this study, it was found that simultaneous saccharification and fermentation of the soluble oligomers (oligomeric-SSF) (Process III) and simultaneous co-saccharification and fermentation (SCSF) of soluble oligomers along with regenerated cellulose (Process IV) are promising alternatives for upgrading the titer and yield of cellulosic butanol production by Clostridium acetobutylicum. In Process III, utilizing the oligomeric hydrolysate obtained through dilute acid hydrolysis at 120 °C for 60 min using 1% acid through oligomeric-SSF led to 14.2 g/L ABE production, i.e., 65% higher than Process I. In addition, using the oligomeric hydrolysate in SCSF resulted in 24 g/L ABE (16 g/L butanol) production with an overall yield of 182 g ABE/kg cellulose. Process IV showed 191% higher titer and 14% higher yield of ABE production, compared with Process I.