Mechanism of Deep Eutectic Solvent Delignification: Insights from Molecular Dynamics Simulations

Abstract

Based on the field of ReaxFF, the pretreatment of a lignin−carbohydrate complex model in a choline chloride-based deep eutectic solvent was proposed. The results showed that the β-O-4 ether and glycosidic bonds in the model were broken at an optimal temperature of 373 K. The best pretreatment solvent was choline chloride/lactic acid (1:2), and 40% of the model compounds were decomposed. Free protons in deep eutectic solvents were one of the critical factors in the process of biomass delignification, and thus acidic hydrogen binding donors generally had a high lignin removal rate, but there was no significant correlation with the acidity of the hydrogen bonding donors. In the deep eutectic solvents of choline chloride/lactic acid, the delignification effect tended to decrease with the increase of lactic acid content. The delignification effect of monocarboxylic acid hydrogen bond donors decreased with the increasing molecular chain length, while the opposite effect of delignification was observed for dicarboxylic acids. The molecular dynamics simulations showed that choline chloride/glycerol (1:2) with a slightly weaker hydrogen bonding network could bind better and solubilize the product molecules, with interaction energies of −170.89 and −61.99 kJ/mol with carbohydrates and phenolic compounds, respectively.

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

“…The total interaction energy (Δ E t ) is a measurement of the theoretical stability of the complex. Generally, a bigger magnitude of Δ E t (negative value) between the molecules indicates that the complex is stable in theory and the dissolution effect is satisfactory. ,, …”

“…Generally, a bigger magnitude of ΔE t (negative value) between the molecules indicates that the complex is stable in theory and the dissolution effect is satisfactory. 16,24,27 To gain an insight into the energy properties of DESs themselves, the ΔE t of different combinations of 16 2c-DES complexes (each composed of 10 ChCls and 20 HBDs) was investigated first, calculated using formula 2, as shown in Figure 3a. The ΔE t of the 16 2c-DESs (labeled as No.1−16) was a negative value, which indicated these 2c-DES complexes were stable in theory and their dissolution effect was satisfactory in theory.…”

“…Diols with longer carbon chain lengths showed increased solubility of lignin, while diols with shorter carbon chain lengths showed increased insolubility for carbohydrates. Xu et al reported the delignification effect of monocarboxylic acid HBD decreased with the increasing molecular chain length, while the opposite effect of delignification was observed for dicarboxylic acids. The molecular dynamics simulations showed that ChCl/glycerol with a slightly weaker hydrogen bonding network could bind better and solubilize the product molecules, with interaction energies of about −170 and −60 kJ/mol with carbohydrates and phenolic compounds, respectively.…”

Separation of Lactic Acid Based on Amide-Based Hydrophobic Deep Eutectic Solvents: Insights from Experiments and Molecular Dynamics Simulations

“…The simulation was performed with the GROMACS 2020.3 , software, and the MD package using parameters contained its GROMOS54A7 force field. , The simulated density of DBB (0.886 g/cm 3 ) at 298.15 K and 1 atm was compared with the experimental density (0.889 g/cm 3 ) at the same temperature–pressure conditions to verify the validity of the force field parameters. The SPC/E model was employed to describe the water interactions.…”

Lewis acidic deep eutectic solvents as catalysts for rosin polymerization

“…17 Notably, DESs are superior to ILs due to their unique properties such as low cost, easy preparation techniques, non-toxicity, and biodegradability. [18][19][20] Therefore, DESs have been found to be applicable in the extraction of metal processing, removal of sulfur compounds from fuel oil, absorption of acidic and alkaline gases, pretreatment of solvents, extraction of biomass, and so on. [21][22][23][24][25] DESs used as acidic catalysts have several advantages such as similar or higher catalytic activity than the acid itself alone, high stability, economy, good recyclability and reusability without the need for further purification, and so on.…”