Steam Explosion Pretreatment with Different Concentrations of Hydrogen Peroxide along with Citric Acid: A Former Step towards Bioethanol Production

Abstract

The present paper focuses on the utilization of the steam explosion method for efficient pretreatment of rice straw, used as a prominent substrate for bioethanol production. Native rice straw contains abundant chemical compounds in the form of cellulose, hemicellulose, and lignin 32.4%, 57%, and 12.5%, respectively. Pretreatment with different concentrations of H2O2 (0.05%, 0.1%, 0.25%, 0.5%, 0.75%, and 1%) was used as efficient impregnating agents at an optimum temperature of 121°C at 130 kPa pressure. After pretreatment, cellulosic content increases up to 54.5% while there was a reduction in the hemicellulose and lignin content up to 46.5% and 6.7%, respectively. The morphological changes were analyzed both before and after pretreatment using FTIR, TGA, and XRD. The reducing sugar estimation was carried out using DNS reagent and the absorbance was measured using a UV spectrophotometer at 540 cm-1 wavelength. Estimated results show a reducing sugar yield of 220.05 g/l from 0.05% ( $v/v$ ) H2O2 pretreated sample and 273.21 g/l from sample, pretreated with H2O2, citric acid in the ratio of 1 : 1 with the same previous concentration. The XRD data shows enhancement of cellulose accessibility upon pretreatment to 13.3% and thereafter reduction with an increase in the concentration of H2O2. While pretreatment with H2O2 combined with citric acid in 1 : 1 ratio shows enhanced accessibility of 19.6% than untreated rice straw. This work mainly focuses on the core objective of an efficient pretreatment method for sustainable bioethanol production through a novel approach to the production of fermentable sugar.