Insights into the Lignin Dissolution Mechanism of Water Content Tailored-choline Chloride (ChCl) Based Green Solvents for Biomass Pretreatment

This work studies the ternary deep eutectic solvents (DESs) as green solvents to enhance the performance of biomass dissolution and tunability of DESs for varying applications. For this purpose, water is extremely suitable, as it is both a hydrogen bond acceptor and a hydrogen bond donor. There are limited studies on modulating the properties of DES. ChCl/Malic acid 1:1 (CCMA) and ChCl/Lactic acid 1:18 (CCLA) DESs with varying water content were synthesized and characterized. Fourier transform infrared spectroscopy (FTIR) demonstrated the formation of hydrogen bonds. The latter was concluded from broadened OH stretching, diminished choline chloride characteristic peak associated with its OH group, and bathochromic shift of the C=O stretching associated with carboxylic acids. The addition of water also caused 2.8 and 3.6 reduction in the density of CCMA and CCLA, respectively, due to the lowered free volume of DESs with 50 wt of water content. CCLA showed the highest lignin solubility at 6.32 wt, and further addition of water resulted in weakened structure that negatively affected the dissolution performance. Both CCMA and CCLA with water content are green solvents that hindered self-degradation by esterification reaction, showing great potential for use in biomass pretreatment. © 2022,Physical Chemistry Research. All Rights Reserved.