Studies on lignin extraction from rice husk by a soda-ethanol treatment : kinetics, separation, and characterization of products

Abstract

The delignification kinetics of lignocellulosic waste is an important tool for the study of the technical-economic viability of biorefinery processes. The aim of this work was to study the kinetic of lignin extraction by a soda-ethanol treatment of hemicelluloses-free rice husk, within the framework of a biorefinery. Additionally, the type of phenolic structures in the extracted lignin and the behavior of inorganics were evaluated. The kinetic study was carried out at 140, 150, and 160 °C, at different times between 3 and 100 min of reaction for each temperature. A first order kinetic model was adjusted to the experimental data of residual lignin in the treated solid in the fast and slow phase. The kinetic constant k0 varied from 0.021 to 0.035 min−1 for 140–160 °C. The activation energies were 38.59 kJ/mol and 33.47 kJ/mol for the fast and slow phase, respectively. The inorganics components remained in the solid and the proportion of silicon increased through all treatments. About 50% of the initial lignin with 1% of inorganics was recovered by precipitation. The percentage of total OH in lignin remained high, about 8.5%, and decreased with the temperature but not with the time of the reaction.