Effect of SC-CO2 pretreatment in increasing rice straw biomass conversion

Rice straw, pretreated with supercritical carbon dioxide (SC-CO2) at 10–30 MPa and 40–110 °C for 15–45 min at a 1:1 g/g liquid: solid ratio, was analysed for glucose yield from enzymatic hydrolysis, main chemical composition, and supermolecular structure. Rice straw that was pretreated with SC-CO2 at 30 MPa and 110 °C for 30 min had a final glucose yield of 32.4 ± 0.5%, compared with 27.7 ± 0.5% for unpretreated straw, after enzymatic hydrolysis with a mixture of cellulose and β-glucosidase. Unpretreated and pretreated rice straw differed in chemical composition, with SC-CO2 pretreatment removing some non-lignocellulose material. Scanning electron microscopy showed that pretreated rice straw had extensive anomalous porosity and lamellar structures. Also, SC-CO2 pretreatment rendered fibres relatively fluffy and soft, which enhanced cellulase enzymatic hydrolysis.