Pretreatment of agricultural residues by supercritical CO2 at 50–80 °C to enhance enzymatic hydrolysis

Abstract

Abstract Various agricultural crop residues including corn stover, corn cob, and sorghum stalk with a moisture content of 75 wt% were subjected to a long pretreatment (12–60 h) with supercritical CO2 (scCO2), at low temperature (50–80 °C) and a pressure of 17.5–25.0 MPa. The sugar yields from the enzymatic hydrolysis (EH) of the pretreated samples were as much as three- to fourfold greater than those afforded by the raw materials. However, when pretreatment was conducted within a short time (e.g. 0.5 h), as previously reported in the literature, only a slight increase in the EH sugar yields was observed. The proposed scCO2 pretreatment mechanism demonstrated the role of moisture in the system. Wetting, softening, and swelling were observed to mainly affect the lignocellulose when a suitable amount of water was added. Finally, the samples were analysed by X-ray diffraction and scanning electron microscopy, before and after pretreatment, to investigate the changes in the microscopic structure of the biomass.