Liquor re-use strategy in lignocellulosic biomass fractionation with ethanol-water mixtures

Liquor recycle in lignocellulosic biomass fractionation with ethanol-water has been studied. Runs have been carried out in a 6 L tank reactor with liquor recirculation. The liquors obtained in six successive fractioning operations have been analyzed together with the solid phase remnant. Experimental results revealed that the number of re-uses reduces solids recovery (from 52.2 to 42.6%) and cellulose recovery (from 28.1 to 23.3%) with minor or no effect on the hemicelluloses and lignin removal. The more remarkable effect is an increase of the glucose yield (from 76.7 to 95.3% after enzymatic hydrolysis during 72 h). The accumulation of acetic acid in the spent liquors (until 1.3 g/L) seems to be responsible of the higher enzymatic hydrolysis yield, from 76.3 (first use) to 87.7% (fifth re-use). Liquor re-use is effective to improve the sustainability of the pre-treatment obtaining a cellulose-rich solid easy to hydrolysate to sugars reducing energy consumption.