Preserving both lignin and cellulose chemical structures: flow-through acid hydrotropic fractionation at atmospheric pressure for complete wood valorization

Abstract

Poplar wood was rapidly fractionated via a flow-through reaction using aqueous solutions of an acid hydrotrope (AH), p-toluenesulfonic acid (p-TsOH), at temperatures below 98 °C. 13C−1H two-dimensional nuclear magnetic resonance (NMR) spectroscopic analyses demon-strated that the AH-solubilized lignins (AHLs) from a range of fractionation conditions with yields up to approximately 80% had a very high content of β-aryl-ether linkages compared to milled wood lignin (MWL) with a low enough condensation to facilitate subsequent reductive catalytic depolymerization resulting in a lignin monomer yield of over 30%. Gel-permeation chromatographic (GPC) and differential scanning calorimetric (DSC) analyses showed that the AHLs have high molecular weights and low glass transition temperatures T_g. These AHLs also have a pinkish color suitable for applications such as cosmetics and dye dispersants. AH fractionation (AHF) preserved the cellulose fraction as solid fibers also with a light pinkish color for the materials market and solubilized up to approximately 90% of xylan which can be converted to furfural using p-TsOH in the spent liquor without additional catalysts. The advantages herein are the use of one recyclable industrial chemical such as p-TsOH in an aqueous system below water boiling temperature to valorize all three major fractions of lignocelluloses in a short time frame, with very promising yields and well-preserved lignin and cellulose structure.

Citation

Wang, Zhaojiang; Qiu, Shi; Hirth, Kolby; Cheng, Jinlan; Wen, Jialong; Li, Ning; Fang, Yunming; Pan, Xuejun; Zhu, J.Y. 2019. Preserving both lignin and cellulose chemical structures: flow-through acid hydrotropic fractionation at atmospheric pressure for complete wood valorization. ACS Sustainable Chemistry & Engineering. 7(12): 10808-10820.