Performance of mild acetone organosolv fractionation on lignocellulosic feedstocks from new cropping systems for production of advanced bioethanol

Various lignocellulose feedstocks were sourced through an innovative double crop rotation system for production of advanced bioethanol. Dedicated biomass crops that grow with high yields with low cost and greenhouse gas emissions (hemp, biomass sorghum, and sunn hemp) were integrated with the cultivation of conventional food crops to recover agricultural residues (wheat straw, corn stover). These feedstocks with low indirect land use change risk were subjected to a biorefinery approach for the production of advanced ethanol from cellulosic and hemicellulosic sugars and co-production of lignin. The processing steps included tandem pre-extraction and acetone organosolv fractionation, followed by enzymatic hydrolysis of the obtained cellulose-enriched pulp (producing mainly C6 sugars), detoxification of hemicellulose hydrolysate (mainly C5 sugars) and fermentation of C5 and C6 sugars to ethanol. High recovery of cellulose in the pulp (87–100 %), C5 oligomeric and monomeric sugars in the hydrolysate (80–90 %) and isolated lignin (72–84 %) showed that process efficiency can be maintained across the various types of feedstocks. The ethanol production titres and productivity obtained by fermentation by Saccharomyces cerevisiae yeast on the C6 sugar enzymatic hydrolysates were robust and similar to those values obtained on model glucose substrate. C5 sugar hydrolysates after detoxification and evaporation were readily converted to ethanol with Spathaspora passalidarum CBS 10155. Sunn hemp and hemp feedstocks showed both less optimal enzymatic digestibility of cellulosic pulps and lower ethanol production rates from their hemicellulose hydrolysates. The present work shows the applicability of the aforementioned biorefinery approach for the production of advanced ethanol with a diverse set of lignocellulosic feedstocks obtained from an integrated food and bioenergy production system based on rotating crops. It also highlights that the most critical processing steps for process monitoring and optimisation are the pulp enzymatic hydrolysis of pulps and the detoxification of the C5 sugar hydrolysates.