Synthesis of lignin-based biosurfactant derived from kraft black liquor and its effect on enzymatic hydrolysis of pretreated biomass

Abstract

Lignin, the main constituent in black liquor of up to 40%, can be converted into a value-added commodity such as a biosurfactant. In this study, lignin was extracted from the Acacia mangium black liquor kraft by acid precipitation (L1S) and ethanol fractionation (L2S). Subsequently, dried lignin was characterized physically and chemically. Biosurfactant was obtained by reacting lignin with polyvinyl alcohol (PVA). To evaluate the fruitfulness of biosurfactants on enzymatic hydrolysis, some optimizations have been conducted: volume ratio PVA: lignin, concentration PVA: lignin, different lignin source, substrate variation, and the effect of an initiator (potassium peroxodisulfate). Lignin by ethanol fractionation resulted in higher lignin content, methoxyl, molecular weight, and syringil but lower particle size and ash content. However, the thermal stability of these two lignins is similar. The ratio of PVA: lignin gave a positive effect on boosting reducing sugar yield (RSY) while the high concentration of PVA: lignin had the opposite effect. The best volume of PVA: lignin was 250 μL with a concentration of biosurfactant 0.4% to get the highest RSY per biomass about 80%. Meanwhile, biosurfactant-based L2S released more RSY than L1S and lignin sigma Aldrich. Kraft process of sweet sorghum bagasse (SSB) obtained more sugar than other substrates such as an alkaline autoclave SSB, jabon soda pulp, and microwave-assisted sulfuric acid pretreated of oil palm empty fruit bunch (EFB). The initiator addition during synthesizing of biosurfactant was predicted to contribute to achieving higher RSY compared to that of that non-initiator addition. This study demonstrates the ability of lignin-based biosurfactants to improve enzymatic hydrolysis yet the best condition was depending on the ratio, concentration, and volume of PVA: lignin, lignin types, substrates, and initiator.