Comparison of two acid hydrotropes for sustainable fractionation of birch wood

Abstract

This study reports on acomparative study of acid hydrotropic fractionation (AHF) of birch wood using maleic acid (MA) and p-toluenesulfonicacid (p-TsOH). Under the same level of delignification, lignin dissolved by MA is much less condensed with ahigher content of ether aryl b-O-4 linkages. Lignin depolymerization dominated in MA hydrotropic fractionation (MAHF) and resulted in asinglelower molecular weightpeak, in contrast to the competitive depolymerizationand repolymerization in p-TsOH AHF with abimodal distribution. The less condensed MA-dissolved lignin facilitated catalytic conversion to monophenols. Carboxylationofresidual lignin in fractionated cellulosic water-insoluble solids (WISs) enhanced enzymatic saccharification by decreasing nonproductive cellulase binding to lignin. At alow cellulase loading of 10 FPUg@1 glucan, sac- charification of WIS-M_T120 from MAHF at 120°C was 95% compared with 48% for WIS-P_T85 from p-TsOH AHF at 85°C under the same level of delignification of 63%. Residual lignin carboxylation also facilitated nanofibrillation of WIS for producing lignin-containing cellulose nanofibrils (LCNFs) through an enhanced lignin lubrication effect, which substantially decreases fibrillation energy.LCNFs from only one pass of microfluidization of WIS-MT120 have the same morphologyasthose from WIS-P_T85 after three passes. MA also has a lower solubility and higherminimal hydrotropic concentration,which facilitated acid recovery. MAisU.S. Food and Drug Administration (FDA)approved as an indirect food additive, affording significant advantages compared with p-TsOH for biorefinery applications.

Citation

Cai, Cheng; Li, Jian; Hirth, Kolby; Huber, George W.; Lou, Hongming; Zhu, J. Y. 2020. Comparison of two acid hydrotropes for sustainable fractionation of birch wood. ChemSusChem. 13(17): 4649-4659.