Mechanism of Lignin Dissolution and Regeneration in Ionic Liquid

Abstract

Density functional theory (DFT), atoms in molecules (AIM) theory, natural bond orbital (NBO) analysis, and Wiberg bond index (WBI) are employed to investigate the mechanism of lignin dissolution and regeneration in 1-allyl-3methylimidazolium chloride (AmimCl). Lignin is modeled with 1-(4-methoxyphenyl)-2-methoxyethanol (LigOH). From the theoretical results, it is observed that AmimCl interacts with LigOH mainly by hydrogen bonds (H bonds), and the interaction of AmimCl with LigOH is stronger than that of LigOH with LigOH; thus, it can be speculated that lignin can be dissolved in AmimCl. In addition, the H bonds between LigOH and AmimCl are weakened or even destroyed by the addition of water. The experimental results also reveal that lignin can be easily regenerated from the AmimCl−lignin solution by the addition of water. The regenerated lignin is characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry (TG), and scanning electron microscopy (SEM) compared to the original lignin.

Characterisation of lignins isolated from sugarcane bagasse pretreated with acidified ethylene glycol and ionic liquids

“…One of the possibly reasons is that our biomass pretreatment process was conducted under high acidity and with relatively high water content. In contrast, lignin dissolution dominated in pure ILs under alkali and neutral conditions with the formation of hydrogen bonds between lignin and ILs although lignin degradation also occurred [43]. Another plausible reason is that the solution pH for lignin precipitation in our process was higher than the reported IL processes (pH 3.0 vs pH 2.0), which leads to reduced lignin precipitation.…”

Synthesis and Characterization of Alkali Lignin-based Hydrogels from Ionic Liquids

“…The system was stirred at 75 °C until it became a solution. When the color of the solution turns brown, lignin is completely dissolved (Ji et al 2012). The solutions were transferred into a glass tube for hydrogel formation under a blanket of nitrogen at 75 °C for 1.5 h without stirring.…”

Modeling interactions between a β‐O‐4 type lignin model compound and 1‐allyl‐3‐methylimidazolium chloride ionic liquid

“…However, there are inconsistent results about the molecular mechanism of the dissolution of lignin in ILs. For example, the Janesko and Wang groups independently modeled interactions of the anion and cation of imidazolium chloride IL with 1‐(4‐methoxyphenyl)‐2‐methoxyethanol, a generally used the model compound of lignin, by performing density functional theory (DFT) calculations. Janesko et al found that the lignin model compound shows significant interactions with imidazolium cation via hydrogen‐bonding and π‐π stacking, proposing the importance of the cation for the dissolution of lignin in ILs.…”

“…Janesko et al found that the lignin model compound shows significant interactions with imidazolium cation via hydrogen‐bonding and π‐π stacking, proposing the importance of the cation for the dissolution of lignin in ILs. In contrast, based on the calculated results, Wang et al confirmed that lignin can be dissolved in 1‐allyl‐3‐methylimidazolium chloride ([Amim]Cl). These current results indicate that our knowledge of the dissolution mechanism of lignin in ILs is still relatively rare, and do not highlight the pivotal role of the IL anions and cations.…”