Understanding the Interactive Relationship between Aliphatic Series Deep Eutectic Solvents and Lignocellulosic Dimer Model Compounds

Abstract

Clean, efficient, and selective separation of lignin from lignocellulosic biomass is a challenging yet popular topic of study to achieve biomass conversion and high-value utilization. Unlike conventional acid, alkaline water, and most organic solvents, the main components of lignocellulosic biomass were found to selectively dissolve in certain classes of deep eutectic solvents (DESs). However, the mechanism of selective dissolution is still not well defined. In this paper, we started from the perspective of the interactive mechanism of DESs and the structural unit of lignocellulose and conducted a comprehensive analysis of the relationship between different types of DESs and complexes of DESs with four kinds of lignocellulosic dimer model compounds (interaction energy, hydrogen bond) using the molecular dynamics method. Some main findings are as follows: for the same atomic number of linear carbon chains, interaction energies of 2c-DESs or 3c-DESs are more conspicuous in the presence of an aliphatic HBD with double −COOH group compared with single −COOH, single −COOH + single OH, or double −OH; DESs with a short carbon chain HBD are more compatible with four lignocellulosic dimer model compounds (LDMCs) than DESs with a long carbon chain HBD; two-constituent DESs are more compatible with GG lignin models compared with SS when the HBD contains double −COOH or single −COOH groups. When analyzing the hydrogen bond of DESs or the complexes of DESs with lignocellulosic dimer model compounds, the coordination number of hydrogen bonds was in the order: dicarboxylic acids > hydroxy acids > diols > monocarboxylic acids in C2, C3, and C5 chain HBDs. This work intends to achieve a deeper and more comprehensive mechanism knowledge of the interaction between DESs and different components of lignocellulose and aims to help with screening the DESs for better selective conversion of components of lignocellulosic biomass, as well as opening new perspectives in the biorefinery green process.

Tailoring a suitable partner system for cholinium cation to build effective solvents for biomass deconstruction

“…22 In particular, acidic DESs such as choline chloride/lactic acid (ChCl-Lac) have strong abilities in biomass deconstruction, achieving enhanced saccharification [23][24][25][26] or high quality lignin. 27,28 Efforts have been made to elucidate the relationship between the structure and performance of DESs in biomass pretreatment. Acidity, alkyl chain length, functional groups and the molar ratio of hydrogen bond donor (HBD)/hydrogen bond acceptor (HBA) have been identified as key factors for determining the pretreatment efficacy.…”

“…40 Furthermore, the effect of the detailed structure of the HBD on the interaction between the DES and the model compounds was carefully studied by MD simulation, and the carbon chain and the number of COOH or OH in the HBD were proposed to be related to the interaction of DES and biomass. 28 However, very limited work focused on the difference in the mechanism of these two kinds of solvents (ILs and DESs) in lignocellulosic biomass fractionation. Additional in-depth studies on the effect of the partner system of cholinium cation on the solvent delignification ability at the molecular level are required.…”