Fermentable Sugars Production from Acid-Catalysed Steam Exploded Barley Straw

Barley straw is being considered a potential lignocellulosic raw material for fuel-ethanol production. Ethanol production from lignocellulosic biomass consists in three main steps: pretreatment, enzymatic hydrolysis and fermentation. In order to improve the accessibility of the enzymes during enzymatic hydrolysis, a dilute phosphoric acid steam explosion pretreatment was applied. A three factor experimental design with temperature (160-200 ºC), residence time (10 – 30 min) and phosphoric acid concentration (1 – 3 % w/v) as relevant factors was performed after a previous stage of overnight soaking. Once the pretreatment was done, both liquid and pretreated solids were separated by filtration and analysed. The pretreated solids were further subjected to enzymatic hydrolysis (S/L= 5 %, 50 ºC, 150 rpm, 15 FPU / g substrate, pH = 4.8) and the released glucose was determined. Optimal pretreatment conditions were determined based on highest recovery of hemicellulosic sugars and minimum inhibitors in the liquid fraction, and highest concentration of glucose after enzymatic hydrolysis of the solid residue. The best operational conditions were found to be 160 ºC pretreatment temperature, 30 min residence time and 2.88 % phosphoric acid concentration, which resulted in the recovery of 44.0 % of xylose in the liquid fraction together with 7.5 % of the initial glucose. The enzymatic hydrolysis of the pretreated solid in these conditions resulted in the release of 61.0 % of the glucose contained in the raw material.