Pretreatment of wheat straw by supercritical CO2 and its enzymatic hydrolysis for sugar production

Because of its high content of cellulose, wheat straw is a good raw material for ethanol production. For the bioconversion of lignocellulosic materials to ethanol, pretreatment of the material prior to enzymatic hydrolysis is essential to obtain high overall yields of sugar and ethanol. Here, an experimental apparatus has been designed to investigate the effect of pretreatment of dry and wet wheat straw using supercritical carbon dioxide alone and the combination of supercritical CO2 + steam by varying the temperature (160–200 °C) and the residence time (10, 30, 60 or 70 min). Supercritical CO2 was used as a powerful solvent for separation of cellulose from the other contents of wheat straw. The pretreatment of dry wheat straw by supercritical CO2 alone at 190 °C and 30 min resulted in the best overall yield for sugar (1 kg wheat straw yielded 149.1 g sugar). The pretreatment of wheat straw that impregnated with water by supercritical CO2 at 185 °C and 30 min resulted in the best overall yield for sugar (208.4 g kg−1). The pretreatment of dry wheat straw by steam explosion and supercritical CO2 at steam temperature and retention time of 200 °C and 15 min and supercritical CO2 conditions of 12 MPa, 190 °C and 60 min, resulted in the best overall yield for sugar (234.6 g kg−1).