Environmentally friendly acetic acid/steam explosion/supercritical carbon dioxide system for the pre-treatment of wheat straw.

It is well established that pretreatment of lignocellulosic biomass is required to achieve an effective enzymatic saccharification process. At the present time, most of the touted pre-treatment technologies would cause environmental pollution and unsustainable water use for the pretreated material prior to enzymatic saccharification. To address these shortcomings, the pretreatment technology which combines the supercritical CO, SC-CO (a green solvent), acetic acid, and steam explosion was used to assess the pretreatment of wheat straw for enzymatic saccharification. The effects of solvent concentration, impregnation temperature and time, pre-treatment time, and temperature, as well as SC-CO pressure, contact time, and temperature, were evaluated. The results identified that at the optimum SC-CO pressure of 18 MPa, the highest amount of reducing sugars (RS) was produced from the cellulosic pulp using Acetic acid/Steam/SC-CO at 200 °C for 30 min, a value 20% more than the pulp produced with the Water/Steam/SC-CO. The effectiveness of the pretreatment process was attributed not only to delignification and defibrillation but also to the exposure of the cellulose structure evidenced from the proportion of the β-glycosidic linkages as shown by FTIR. Passing SC-CO after the pretreatment reduces the amounts of fermentation inhibitors and eliminates the use of wash water.