Modeling the Lignin Degradation Kinetics in an Ethanol/Formic Acid Solvolysis Approach. Part 1. Kinetic Model Development

Abstract

A formal kinetic model describing the main reaction pathways yielding demethoxylated monomeric phenols from wheat straw lignin in a hydrogen-enriched solvolysis reaction system using ethanol as cosolvent has been developed. The simplified lump model combines both a detailed focus on the deoxygenation reactions at molecular level as well as the reactions of global bulk lumps. The results show that depolymerization of lignin structures is quickly achieved and that deoxygenation reactions largely follow a main route pathway via intermediate methoxyphenols and catechols to give stable phenols in the liquid phase. Observed ethyl group substituents of phenolics are seen to originate from either alkylation reactions of the intermediates, or directly from the depolymerizing structures. A high correlation between primary 4-ethylphenol products and para-coumaryl units in the examined lignin suggests that main reaction pathways are strongly dependent on the type of plant lignin used.

Catalytic depolymerization of alkali lignin in subcritical water: influence of formic acid and Pd/C catalyst on the yields of liquid monomeric aromatic products

“…This indicated the ability of formic acid to act as a capping agent to prevent or delay re-polymerization of products. Hence, nearly 98 wt% conversion of the original lignin mainly into liquid and gas products, was obtained in these tests, which agreed with some reported results in literature [24].…”

Recent Development in Chemical Depolymerization of Lignin: A Review

“…A relatively low temperature range of 78 to 200 ∘ C used in this research was not high enough to break the complex lignin structure into monomeric compounds for further usage. Recently, acid-catalyzed method was investigated at a higher temperature range in order to depolymerize lignin [20,21]. 10 wt.% of formic acid associated with 77 wt.% of ethanol was employed in the reaction with wheat straw lignin by Gasson et al [20].…”

Low-Power Microwave Radiation-assisted Depolymerization of Ethanol Organosolv Lignin in Ethanol/Formic Acid Mixtures

“…Liquefaction is a good method to degrade lignin, and solvent selection is crucial to improve the economics of the process (Xiao et al 2011;Xie et al 2015). Ethanol as a swelling agent and formic acid as a hydrogen donor solvent have been used to establish a mild and environmentally friendly system to convert lignin to small molecular products (Pandey and Kim 2011;Gasson et al 2012). Ethanol is attractive for lignin degradation because of its high solvency for biomass and low critical temperature (Gasson et al 2012).…”

“…Ethanol as a swelling agent and formic acid as a hydrogen donor solvent have been used to establish a mild and environmentally friendly system to convert lignin to small molecular products (Pandey and Kim 2011;Gasson et al 2012). Ethanol is attractive for lignin degradation because of its high solvency for biomass and low critical temperature (Gasson et al 2012). In addition, using ethanol as a solvent results in a less oxygenated oil fraction and virtually no solid residue (Gellerstedt et al 2008;Gasson et al 2012).…”

“…Ethanol is attractive for lignin degradation because of its high solvency for biomass and low critical temperature (Gasson et al 2012). In addition, using ethanol as a solvent results in a less oxygenated oil fraction and virtually no solid residue (Gellerstedt et al 2008;Gasson et al 2012). Formic acid decomposes into CO2 and active hydrogen under heating conditions, which results in lignin hydrogenation (Pandey and Kim 2011).…”