Detoxification of biomass hydrolysates by reactive membrane extraction

Abstract

Economical conversion of lignocellulosic biomass into biofuels is essential to reduce the world's dependence on fossil fuels. The typical biochemical process for biomass conversion includes a thermochemical pretreatment step to improve enzymatic cellulose hydrolysis and to release hemicellulosic sugars from the polymer matrix. However compounds that are toxic to microorganisms in subsequent fermentation steps may also be released. This work investigates the use of membrane extraction to detoxify or remove these toxic compounds from corn stover hydrolysates pretreated using dilute sulphuric acid. Extraction of sulphuric, acetic, formic and levulinic acid as well as 5-hydroxymethylfurfural and furfural has been investigated. Octanol and oelyl alcohol were used as organic phase solvents. Alamine 336 was used as the aliphatic amine extractant. Reactive extraction of sulphuric, acetic, formic and levulinc acid was observed while 5-hydroxymethylfurfural and furfural were extracted due to their distribution in the organic solvent. Significant removal of all toxic compounds investigated was obtained as well an increase in pH from 1.0 to 5.0. As small quantities of the organic phase transferred into the hydrolysate during extraction, the toxicity of the organic phase must be considered. As it is likely that detoxification will require the use of another unit operation in combination with membrane extraction, the economical viability of the combined process must be considered.