Strategies towards a green solvent biorefinery: Efficient delignification of lignocellulosic biomass residues by gamma-valerolactone/water catalyzed system

Abstract

Biorefineries promote the integral use of lignocellulosic biomass by separating lignin, cellulose, and hemicelluloses, so environmentally friendly solvents with good efficiency in lignin removal at mild conditions (low temperatures and pressures) are under thorough research. This study evaluates the optimization of γ-Valerolactone (GVL) systems using a solvent complying with the principles of green chemistry as an efficient delignification strategy for lignocellulosic biomass residues such as sugarcane bagasse and pine sawdust. First, depithed sugarcane bagasse was delignified by a solvent system composed of GVL/water and a low concentration of sulfuric acid (SA), considering temperature, reaction time, GVL, and SA concentration in the liquor as variables, organized following a 4-factor Draper-Lin Central Composite Design (CCD). Milder treatments compared with literature were applied, with extreme points at 130–180 °C, 40–140 min, 43–77 wt% GVL, and 0–0.01 M SA, respectively. The experimental conditions involving pine sawdust were assessed at the highest delignification point of sugarcane bagasse. Delignification from 75% to 96% was obtained for sugarcane bagasse. In the same conditions, pine sawdust delignification was slightly lower. The solid fraction characterization involved yield, ISO brightness, crystallinity index, intrinsic viscosity in cupriethylenediamine, structural carbohydrates, and lignin content, whereas sugars, byproducts, and degradation products were analyzed in the liquid fraction. The study compares different properties combined into one single combined severity factor. The evaluation also involved optical properties relevant to some uses, such as dissolving pulps or nanocellulose.