(82f) Depolymerization of Lignin During Solvent Liquefaction

Lignin, one of the main components of lignocellulosic biomass, is a complex polymer made up of monolignol monomers that are methoxylated to various degrees. . Lignin has potential as feedstock for biobased chemicals and fuels if it can be effectively depolymerized and/or deoxygenated. Solvent liquefaction is able to depolymerize lignin under relatively mild conditions and solvent combinations. However, depolymerization of lignin is usually accompanied by repolymerization of depolymerization products.  We are investigating whether polymerization can be reduced or prevented under carefully controlled solvent liquefaction conditions.  The effect of different solvents and solvent combinations on thermal depolymerization of lignin was investigated in micro- and gram-scale bath reactors. Organosolv lignin extracted from corn stover was reacted with various solvents in the micro reactor at temperatures from 300 to 400 °C and reaction times from 5 to 20 min. At the end of reaction volatiles released from the reactor were directly analyzed by online GC/MS. Lignin and selected solvents were also reacted in a gram-batch reactor to recover bio-oil. The molecular weight distribution of bio-oil was analyzed using GPC and bio-oil was subjected to aging tests to evaluate stability of bio-oil produced. The tested solvents were tetralin, formic acid, isopropanol, 1, 4-dioxane and water.

The preliminary results showed that hydrogen donor solvents mainly increased the yields of alkylphenolic monomers by saturating C=C bonds in the phenolic side chains and the selectivity of alkylphenols increased with increasing reaction temperature. The yield of alkylphenols first increased then decreased with longer reaction times. Secondary reactions between decomposition products were also investigated.