Fractionation and characterization of lignin from sugarcane bagasse using a sulfuric acid catalyzed solvothermal process

Abstract

Background: Conversion of lignocellulosic residue to bioenergy and biofuel is a promising platform for global sustainability. Fractionation is an initial step for isolating lignocellulosic components for subsequent valorization. The aim of this research is to develop the solvothermal fractionation of sugarcane bagasse to produce high purity lignin. Physio-chemical structure of isolated lignin from this process was determined.Results: In this study, a central composite design-based response surface methodology (RSM) was used to optimize an acid promoter for isolating lignin from sugarcane bagasse using a solvothermal fractionation process. The reaction was carried out with sulfuric acid, in the concentration of 0.01-0.02 M and a reaction temperature of 180-200°C for 30-90 min. The optimal conditions for the experiment were obtained at the acid concentration of 0.02 M with a temperature of 180ºC for 90 min in methyl isobutyl ketone (MIBK)/methanol/water (35%:25%:40% v/v%). The results showed that 87.1% of lignin recovery was conducted in the organic phase, while 88.0% of lignin removal was done in the solid phase. Furthermore, the change in the physico-chemical characteristics of solid residue and lignin recovery was recorded using various techniques. A GPC analysis of recovered lignin from the organic fraction showed a low average Mw/Mn (1374/785 g/mol) and lower polydispersity index (1.75) compared to commercial organosolv lignin. The maximum lignin degradation temperatures of recovered lignin and commercial organosolv lignin were estimated to be 310°C and 334°C, which can point to potential relationships with the degradation of β-O-4 cross-links. The results indicated that recovered lignin is mostly cross-linked by the β-O-4 cross-links.Conclusions: The development of sulfuric acid catalyzed solvothermal process in this study provides the efficient extraction of high-value organosolv lignin from sugarcane bagasse and the production of recovered lignin in organic phase with low contamination from other contents. The lignin characteristic data can contribute to the development of lignin valorization in value-added applications.