Catalytic action of hydronium-ion in rice straw pretreatment and enhancement of enzymatic hydrolysis and ethanol production

Abstract

The present investigation will focus on the catalytic effect of hydronium ion during liquid-water/ dilute sulfuric acid/ferric chloride pretreatment (LWP/ SAP/ FCP) on the hydrolysate and pretreated rice straw. The overall pretreatment process has been represented as a sequential catalytic reactions. The temperature range of pretreatment is varied in the range of 140–180 °C and the concentration of dilute sulfuric acid and ferric chloride is 0.1 M. The first order rate constants of xylan and glucan degradation have been determined for LWP/ SAP/ FCP. The maximum xylan and glucan conversion of 96.8% w/wand 31.4%w/w respectively are achieved for FCP at 180 °C. Xylose, glucose, furfural, 5-hydroxymethyl furfural, acetic acid and formic acid appear as the main products for all pretreatments. Only in case of FCP levulinic acid also appears as a hydrolysis product. The thermal characteristics, functional groups, crystallinity, surface morphology of untreated and pretreated rice straw have been evaluated. Among all pretreatment processes under study, the highest values of glucose yield of 78.96% (w/w) using enzymatic hydrolysis and 83.79% of theoretical yield of ethanol using Saccharomyces cerevisiae have been achieved for ferric chloride pretreatment.