Conditioning of pretreated birch by liquid–liquid organic extractions to improve yeast fermentability and enzymatic digestibility

Abstract

By-products from hydrothermal pretreatment of lignocellulosic biomass inhibit enzymatic saccharification and microbial fermentation. Three long-chain organic extractants (Alamine 336, Aliquat 336 and Cyanex 921) were compared to two conventional organic solvents (ethyl acetate and xylene) with regard to conditioning of birch wood pretreatment liquid (BWPL) for improved fermentation and saccharification. In the fermentation experiments, extraction with Cyanex 921 resulted in the best ethanol yield, 0.34 ± 0.02 g g⁻¹ on initial fermentable sugars. Extraction with xylene also resulted in a relatively high yield, 0.29 ± 0.02 g g⁻¹, while cultures consisting of untreated BWPL and BWPL treated with the other extractants exhibited no ethanol formation. Aliquat 336 was most efficient with regard to removing by-products, but the residual Aliquat after the extraction was toxic to yeast cells. Enzymatic digestibility increased by 19–33% after extraction with the long-chain organic extractants. The investigation demonstrates that conditioning with long-chain organic extractants has the potential to relieve inhibition of both enzymes and microbes.