A comparison of the solvent liquefaction of lignin in ethanol and 1,4-butanediol

Authors: Mullen, Charles; Strahan, Gary; Elkasabi, Yaseen

Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2022
Publication Date: 4/8/2022
Citation: Mullen, C.A., Strahan, G.D., Elkasabi, Y.M. 2022. A comparison of the solvent liquefaction of lignin in ethanol and 1,4-butanediol. Journal of Analytical & Applied Pyrolysis. 164:105522. https://doi.org/10.1016/j.jaap.2022.105522.
DOI: https://doi.org/10.1016/j.jaap.2022.105522

Interpretive Summary: Conversion of lignocellulosic biomass in facilities called biorefineries is critical to large scale development of bio-renewable carbonbased materials including biofuels, chemicals and materials. Crop residues, purpose grown energy crops such as grasses, and wood waste are all sources of biomass and comprise cellulose, hemicellulose and lignin. Both the pulp and paper industry and biorefineries that produce fuel ethanol from cellulose produce an underutilized lignin byproduct that has been difficult to convert to higher value products. However, because lignin can account for 15-30% of the available renewable carbon, its efficient conversion is important to the economic viability of biorefineries. In this paper we considered a process called solvent liquefaction to produce biooil from lignin. Solvent liquefaction uses heat and pressure to induce chemical reactions that break lignin into smaller molecules. If the pressure requirement could be reduced the cost of the process will be reduced. We tested a high boiling renewable solvent, 1,4-butanediol (BD) and compared its use with a conventional liquefaction solvent, ethanol. Use of BD did reduce the pressure requirement and broke down the lignin at a similar rate to ethanol, but the chemical makeup of the bio-oil was different. When using BD fewer of the smallest most valuable compounds, phenolic monomers, were produced. However, the bio-oil produced in BD showed more promise as a feedstock to produce a renewable industrial carbon product called bio-pitch. This work showed that the properties of the bio-oil produced could be tailored to end uses by change of the reaction conditions, particularly the choice of solvent. The results of this work will allow for the further development of lignin conversion methodologies and will be of interest to those looking to utilize residual lignin to produce renewable industrial chemical feedstocks.

Technical Abstract: This study compares the depolymerization of soda lignin via solvent liquefaction in ethanol and 1,4-butanediol (BD). The commercial soda lignin was fractionated based on solubility in ethyl acetate and methanol providing three fractions (F1 – soluble in ethyl acetate and methanol, F2 - insoluble in ethyl acetate and soluble methanol, F3 – insoluble in either) which varied mostly based on their molecular weight ranges with the average molecular weight following the order F1