Optimization of Lignin Extraction from Pine Wood for Fast Pyrolysis by Using γ-valerolactone-Based Binary Solvent System

Fast pyrolysis of lignin is a promising method to produce aromatic chemicals and fuels. Lignin structure and pyrolysis conditions determine the liquid yield and product selectivity. Extraction of pine wood using γ-valerolactone (GVL) mixed with water in the presence of diluted sulfuric acid obtains lignin (GVL-lignin) which shows different product yield and selectivity. The composition of the extraction medium influences the yield of GVL-lignin and affects its native structure. The GVL-to-water ratio affects the lignin yield without significantly modifying the structure of the extracted lignin, whereas the sulfuric acid concentration affects both the extraction yield and the extracted lignin structure. These structural changes influence the products distribution after fast pyrolysis, which generates phenols and alkoxy phenols as the main products in the liquid fraction. Lignin extracted with a mixture of 4/1 of GVL/H2O (w/w) with 0.075 M sulfuric acid solution produces the highest pyrolysis liquid yield. Pyrolysis of GVL-lignin at 750 °C generates the maximum liquid yield. The amount of phenols in fast pyrolysis products increases with increasing temperature and sulfuric acid concentration used in the GVL-lignin extraction. This indicates that the extraction conditions of GVL-lignin may be optimized to increase the selectivity in fast pyrolysis.