Fractionation of herbaceous biomass using a recyclable hydrotropic p–toluenesulfonic acid (p–TsOH)/choline chloride (ChCl) solvent system at low temperatures

Lignin valorization is significantly influenced by the degrees of lignin condensation measured by the amount of cleaved β O 4 ether linkages and interunit C C linkages formed during biomass fractionation. To minimize the cleavage of aryl ether and formation of C C linkages, a p–toluenesulfonic acid (p–TsOH)/choline chloride (ChCl) solvent system with hydrotropic properties was evaluated. The ChCl was chosen to control the H + concentration of the p–TsOH/ChCl solvent system. Compared with p–TsOH/H 2 O, the degradation of β O 4 was kept in a similar rate during p–TsOH/ChCl fractionation; however, the formation of C C linkage was slower. Under 75/25 p–TsOH/ChCl mass ratio at 80 °C for 20 min, 76.6 % of miscanthus lignin, with β O 4 content of 30.9 %, and 88.9 % of wheat straw lignin, with β O 4 content of 33.6 %, can be dissolved. In addition, the low polar and layered structure of hydrotropic p–TsOH/ChCl system has a strong ability to dissolve lignin, which resulted in lignin with larger particle size and lower surface charge. The results also indicated that lignin from p–TsOH/ChCl solvent system has great potential for lignin depolymerization to aromatics for valorization.