Deep eutectic solvents from hemicellulose-derived acids for the cellulosic ethanol refining of Akebia' herbal residues

- Herb residues has the potential to be a feedstock for ethanol production.
- ChCl-Fa has a high selectivity of lignin removal and glucan remaining.
- ChCl loading could enhance the selectivity of lignin dissolution significantly.
- DES has a good biocompatibility with high enzymatic digestibility and ethanol yield.

Here, the potential use of herbal residues of Akebia as feedstock for ethanol production is evaluated. Additionally, five deep eutectic solvents from hemicellulose-derived acids were prepared to overcome biomass recalcitrance. Reaction temperatures had more significant influences on solid loss and chemical composition than the molar ratios of choline chloride (ChCl) to derived acids. Glycolic acid resulted in the maximum levels of lignin, xylan and glucan removal, which were 60.0%, 100% and 71.5%, respectively, at 120 °C with a 1:6 M ratio of ChCl-glycolic acid. In contrast, ChCl-formic acid resulted in the greatest level of glucan retention, at 97.8%, with a lignin removal rate of 40.7% under the same pretreatment conditions. Moreover, ChCl loading could significantly enhance the selectivity of carboxylic acid for lignin dissolution. A 98.0% level of subsequent enzymatic saccharification and a 100% ethanol yield were achieved after ChCl-formic acid pretreatments of Akebia' herbal residues.