Autohydrolysis: A promising pretreatment for the improvement of acetone, butanol, and ethanol production from woody materials

Abstract

Acetone, butanol, and ethanol (ABE) were produced from softwood pine and hardwood elm using autohydrolysis pretreatment, enzymatic hydrolysis, and fermentation by Clostridium acetobutylicum. The solid residue obtained by autohydrolysis, “pretreated solids”, was hydrolyzed using a mixture of two commercially available cellulases leading to production of 162g sugar from each kg pine and 295g sugar from each kg elm in the form of “cellulosic hydrolysates”. The fermentation of cellulosic hydrolysates resulted in the production of 79.3 and 117.6g ABE from each kg of pine and elm, respectively. Through the autohydrolysis, between 187 to 195g soluble sugars and oligomers was also released from each kg of the materials into the liquid streams named “autohydrolysates”. Enzymatic hydrolysis of pretreated solid residue in the autohydrolysate liquor resulted in hydrolysates with total sugar concentration of 21–23g/l, named “overall hydrolysates”. In this process, 51% of the oligomers of pine autohydrolysate were converted to monomeric sugars and subsequently used for ABE production. Therefore, the fermentation of the overall hydrolysates resulted in the production of 104.5 and 43.4g ABE from each kg of pine and elm, respectively.