Optimizing Liquid Hot Water pretreatment conditions to enhance sugar recovery from wheat straw for fuel-ethanol production

Abstract

Wheat straw is nowadays being considered a potential lignocellulose raw material for fuel-ethanol production as an alternative to starch- or sugar-containing feedstock. In this work, the optimization of process variables (temperature and residence time) in Liquid Hot Water (LHW) pretreatment of wheat straw for ethanol production was addressed by means of design of experiments. The recovery of hemicellulose-derived sugars (HDS) in the liquid fraction and the enzymatic susceptibility of the solid residue obtained after filtration of pretreated material were considered as response variables to different processes conditions. Results show that when optimization was performed considering response variables jointly, optimal conditions were 188 °C and 40 min, leading to HDS recovery yield of 43.6% of HDS content in raw material and enzymatic hydrolysis (EH) yield of 79.8% of theoretical. Nonetheless, when response variables were analyzed separately, 71.2% of HDS recovery was obtained at 184 °C and 24 min, whereas, conditions of 214 °C and 2.7 min led to a maximum EH yield of 90.6% of theoretical. So, a two-step pretreatment would be the most adequate process configuration to get a maximum recovery of fermentable sugars although economic and energetic aspects of such approach should be considered.