Role of acid hydrolysis behavior on structure and depolymerization of lignin extracted from rice straw

Abstract

"Chemical reactions mostly have a dependency on catalyst concentration. Sometimes, the action of higher concentration enhances the rate very high that disrupts the product appearance and structural integrity. It is also applicable for biological material degradation. Here in this study, the degradation of rice straw biomass was executed for lignin extraction using the acid hydrolysis treatment method. This technique helps in the removal of maximum cellulosic parts like cellulose and hemicellulose by converting them into soluble sugars and remains left out lignin. It was investigated that the higher concentration of sulfuric acid as 72% v/v (80.77% w/w) caused some structural changes in chemical bonds and formed highly condensed lignin (L-72). While mild concentration of sulfuric acid 63% v/v (72.26% w/w) does not have any adverse effect on lignin structural integrity and was found as free-form lignin (L-63). The impact of condensation was observed during the depolymerization of L-72 and L63. The depolymerization efficiency of L-72 and L-63 in alkaline medium (NaOH 1.5% and Na2S 0.5%) comparatively lesser for L-72 (34%) than L-63 (98.3%) using lignin 2 g/l.FT-IR analysis also showed the presence of CO-O-CO (anhydride) and C=C (alkenes) in condensed lignin but not found in free-form lignin. This means the structural condensation decreasing the depolymerization efficiency of lignin. Hence, it is concluded that free-form, light- brown lignin should be used for depolymerization and monolignolextraction."