Dissolution Of Cellulose In Ionic Liquids Research Articles

Mechanistic study on the cellulose dissolution in ionic liquids by density functional theory

Ionic liquids (ILs) have attracted many attentions in the dissolution of cellulose due to their unique physicochemical properties as green solvents. However, the mechanism of dissolution is still under debate. In this work, computational investigation for the mechanisms of dissolution of cellulose in [Bmim]Cl, [Emim]Cl and [Emim]OAc ILs was performed, and it was focused on the process of breakage of cellulose chain and ring opening using cellobiose as a model molecule. The detailed mechanism and reaction energy barriers were computed for various possible pathways by density functional theoretical method. The key finding was that ILs catalyze the dissolution process by synergistic effect of anion and cation, which led to the cleavage of cellulose chain and formation of derivatives of cellulose. The investigation on ring opening process of cellobiose suggested that carbene formed in ILs played an important role in the side reaction of cellulose, and it facilitated the formation of a covalent bond between cellulose and imidazolium core. These computation results may provide new perspective to understand and apply ILs for pretreatment of cellulose.

Understanding Cellulose Dissolution: Energetics of Interactions of Ionic Liquids and Cellobiose Revealed by Solution Microcalorimetry

In this report, the interactions between fifteen selected ionic liquids (ILs) and cellobiose (CB) are examined by high-precision solution microcalorimetry. The heat of mixing (Δmix H) of CB and ILs, or CB and IL/molecular solvent (MS) solutions, provides the first ever-published measure of the affinity of CB with ILs. Most importantly, we found that there is a very good correlation between the nature of the results found for Δmix H(CB) and the solubility behavior of cellulose. This correlation suggests that Δmix H(CB) offers a good estimate of the enthalpy of dissolution of cellulose even in solvents in which cellulose is insoluble. Therefore, the current findings open up new horizons for unravelling the intricacies of the thermodynamic factors accounting for the spontaneity of cellulose dissolution in ILs or IL/MS solutions.

From cellulose fibrils to single chains: understanding cellulose dissolution in ionic liquids.

Cellulose is the most abundant and renewable organic compound on Earth, it is however not soluble in common organic solvents and aqueous solutions. Cellulose dissolution is a key aspect to promote its value-added applications. Ionic liquids (ILs) have been shown to solubilize cellulose under relatively mild conditions. The easy processability of cellulose with ILs and their environmental-friendly nature prompted research in various fields such as biomass pretreatment and conversion, cellulose fiber and composite production, and chemical conversion of cellulose in ILs. Progress has been made on understanding the mechanism of cellulose dissolution in ILs, including the structural characteristics of ILs that are cellulose solvents, however many details remain unknown. In light of rapid development and importance of cellulose dissolution in the field of IL-based cellulose and biomass processing, it is necessary to provide an overview of current understanding of cellulose dissolution in ILs and outline possible future research trends. Recent literature studies suggest that synergistic effects between the anions and the cations of ILs need to be revealed, which requires refining the structure of cellulose elementary fibrils, simulation of more realistic cellulose fibrils and detailed studies on the solution structure of cellulose in ILs. After analyzing literature studies, three interacting modules are identified, which are crucial to understand the process of cellulose dissolution in ILs: (1) the structure of elementary fibrils; (2) solvation of cellulose in ILs; and (3) solution structure of cellulose solubilized in ILs. A coherent analysis of these modules will aid in better design of more efficient ILs and processes.

Insight into the Cosolvent Effect of Cellulose Dissolution in Imidazolium-Based Ionic Liquid Systems

Recently, it has been reported that addition of a cosolvent significantly influences solubility of cellulose in ionic liquids (ILs), but little is known about the influence mechanism of the cosolvent on the molecular level. In this work, four kinds of typical molecular solvents (dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), CH₃OH, and H₂O) were used to investigate the effect of cosolvents on cellulose dissolution in [C₄mim][CH₃COO] by molecular dynamics simulations and quantum chemistry calculations. It was found that dissolution of cellulose in IL/cosolvent systems is mainly determined by the hydrogen bond interactions between [CH₃COO](-) anions and the hydroxyl protons of cellulose. The effect of cosolvents on the solubility of cellulose is indirectly achieved by influencing such hydrogen bond interactions. The strong preferential solvation of [CH₃COO](-) by the protic solvents (CH₃OH and H₂O) can compete with the cellulose-[CH₃COO](-) interaction in the dissolution process, resulting in decreased cellulose solubility. On the other hand, the aprotic solvents (DMSO and DMF) can partially break down the ionic association of [C₄mim][CH₃COO] by solvation of the cation and anion, but no preferential solvation was observed. The dissociated [CH₃COO](-) would readily interact with cellulose to improve the dissolution of cellulose. Furthermore, the effect of the aprotic solvent-to-IL molar ratio on the dissolution of cellulose in [C₄mim][CH₃COO]/DMSO systems was investigated, and a possible mechanism is proposed. These simulation results provide insight into how a cosolvent affects the dissolution of cellulose in ILs and may motivate further experimental studies in related fields.

An Orthogonal Experiment of Bagasse Cellulose Dissolution in Ionic Liquid by Microwave Heating

In this paper, bagasse cellulose was dissolved in ionic liquid (1-butyl-3-methylimidazolium chloride) by microwave heating. The orthogonal test and variance analysis were applied to obtain the optimum dissolution condition of bagasse in ionic liquid. The effects of microwave power, temperature and the mass fraction of cellulose were examined by an orthogonal experiment designed through the different dissolution time and the yield of regeneration bagasse. Results showed that the optimal dissolution condition for faster dissolution time was 1% of bagasse cellulose in ionic liquid at 140°C, 500W; while, to get the most yield of cellulose, the condition was 2% of bagasse cellulose at 130°C, 500W.

Effects of Cationic Structure on Cellulose Dissolution in Ionic Liquids: A Molecular Dynamics Study

In recent years, great progress has been made in the dissolution of cellulose with ionic liquids (ILs). However, the mechanism of cellulose dissolution, especially the role the IL cation played in the dissolution process, has not been clearly understood. Herein, the mixtures of cellulose with a series of imidazolium-based chloride ionic liquids and 1-butyl-3-methyl pyridinium chloride ([C(4)mpy]Cl) were simulated to study the effect that varying the heterocyclic structure and alkyl chain length of the IL cation has on the dissolution of cellulose. It was shown that the dissolution of cellulose in [C(4)mpy]Cl is better than that in [C(4)mim]Cl. For imidazolium-based ILs, the shorter the alkyl chain is, the higher the solubility will be. In addition, an all-atom force field for 1-allyl-3-methyl imidazolium cation ([Amim](+)) was developed, for the first time, to investigate the effect the electron-withdrawing group within the alkyl chain of the IL cation has on the dissolution of cellulose. It was found that the interaction energy between [Amim](+) and cellulose was greater than that between [C(3)mim](+) and cellulose, indicating that the presence of electron-withdrawing group in alkyl chain of the cation enhanced the interaction between the cation and cellulose due to the increase of electronegativity of the cations. These findings are used to assess the cationic effect on the dissolution of cellulose in ILs. They are also expected to be important for rational design of novel ILs for efficient dissolution of cellulose.

Dissolution of Cellulose in Ionic Liquids Assisted with Ethanol Pretreatment

One of the major current challenges to the chemical industry is the efficient use of renewable lignocellulosic biomass for the production of performance materials, platform chemicals, and biofuels. Dissolution of natural polymers including cellulose in ionic liquids has attracted much more attention around all over the world. However, the time for complete dissolution of cellulose in ionic liquids was too long for processing and derivatization to produce industrial materials. Herein, ethanol pretreatment was introduced to improve cellulose dissolution in ionic liquids. The pretreated cellulose was easily wetted and penetrated for dissolution in ionic liquids, which efficiently avoided the formation of the agglomerates of cellulose mixed with air wrapped with viscous ionic liquids. The dissolution time of pretreated cellulose could decrease to 75 min under the given conditions. FT-IR and CP/MAS 13C-NMR analyses indicated that ethanol pretreatment and dissolution in ionic liquid did not lead to any functionalization of cellulose. It was also found that the crystalline structure of native cellulose was destroyed and the regenerated cellulose was mainly composed of amorphous structure. The thermal stability of cellulose decreased and the pyrolysis residues increased after dissolution and regeneration.

Dialkylimidazolium Ionic Liquids Hydrolyze Cellulose Under Mild Conditions

The average molecular weight of cellulose derived from filter paper, poplar, and Avicel decreases by up to two orders of magnitude during typical mild dissolution protocols using ionic liquids (ILs). About an order of magnitude greater cellulose depolymerization rate during ionic liquid dissolution occurs in 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-ethyl-3-methylimidazolium chloride (EmimCl) compared to 1-ethyl-3-methylimidazolium acetate (EmimOAc), and, unintuitively, greater IL purity results in greater cellulose depolymerization. The following data support the mechanism of cellulose hydrolysis to be acid-catalyzed: (i) increase in number of reducing ends following cellulose dissolution in IL; (ii) addition of N-methylimidazolium base suppresses cellulose depolymerization during dissolution in IL; (iii) small amounts of glucose and traces of hydroxymethyl furfural are present following cellulose dissolution in IL. The acid is presumably synthesized via IL decomposition to generate a carbene and proton, consistent with hypothesis derived from molecular modeling. Titration experiments conducted here measure the amount of acid synthesized to be in the 4000 ppm range for high-purity BmimCl IL during mild processing conditions for cellulose dissolution. This data is relevant for understanding the extent of IL decomposition during biomass dissolution.

Determining relative rates of cellulose dissolution in ionic liquids through in situ viscosity measurement

Using in situ viscosity measurement, the rate of cellulose dissolution in a number of ionic liquids has been determined allowing their performance as solvents to be quantitatively assessed. 1-Butyl-3-methylimidazolium ethanoate was shown to dissolve cellulose faster than analogous ionic liquids with chloride or dimethylphosphate anions. Analysis of the data highlights the influence of both anion basicity and relative concentration on the rate of dissolution.

Microwave‐assisted derivatization of cellulose in an ionic liquid: An efficient, expedient synthesis of simple and mixed carboxylic esters

AbstractMicrowave (MW)‐assisted cellulose dissolution in ionic liquids (ILs) has routinely led either to incomplete biopolymer solubilization, or its degradation. We show that these problems can be avoided by use of low‐energy MW heating, coupled with efficient stirring. Dissolution of microcrystalline cellulose in the IL 1‐allyl‐3‐methylimidazolium chloride has been achieved without changing its degree of polymerization; regenerated cellulose showed pronounced changes in its index of crystallinity, surface area, and morphology. MW‐assisted functionalization of MCC by ethanoic, propanoic, butanoic, pentanoic, and hexanoic anhydrides has been studied. Compared with conventional heating, MW irradiation has resulted in considerable decrease in dissolution and reaction times. The value of the degree of substitution (DS) was found to be DSethanoate > DSpropanoate > DSbutanoate. The values of DSpentanoate and DShexanoate were found to be slightly higher than DSethanoate. This surprising dependence on the chain length of the acylating agent has been reported before, but not rationalized. On the basis of the rate constants and activation parameters of the hydrolysis of ethanoic, butanoic, and hexanoic anhydrides in aqueous acetonitrile (a model acyl transfer reaction), we suggest that this result may be attributed to the balance between two opposing effects, namely, steric crowding and (cooperative) hydrophobic interactions between the anhydride and the cellulosic surface, whose lipophilicity has increased, due to its partial acylation. Four ethanoate‐based mixed esters were synthesized by the reaction with a mixture of the two anhydrides; the ethanoate moiety predominated in all products. The DS is reproducible and the IL is easily recycled. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 48: 134–143, 2010