Molecular Dynamics Simulation Of Cellulose Dissolution And Regeneration In Ionic Liquid

In recent years,with the rapid development of social economy and the extensive development and utilization of traditional fossil energy,resource shortage and ecological damage have become a major problem.For the sustainable development of ecological environment,renewable biomass resources have attracted extensive attention.Cellulose was one of the most abundant renewable resources.The development and utilization of cellulose was one of the important research directions in the future.However,due to its strong structural stability,it needed to be pretreated.Ionic liquids showd good application prospects in this regard.However,the dissolution of cellulose in ionic liquids,especially the regeneration mechanism,was lack of systematic explanation.In this paper,the cellulose ionic liquid system was constructed,the complete dissolution and regeneration process was obtained through molecular dynamics simulation,the dissolution process of cellulose was clarified,the influence of the types of anti-solvents on cellulose regeneration was studied,and the reason for the conformational transformation of cellulose before and after dissolution was revealed.The effects of ionic liquids on the dissolution and regeneration of cellulose were studied,and the factors affecting the conformational distribution of cellulose were explored.The main contents of the paper include:(1)Simulation study on the dissolution of cellulose in ionic liquids.The dissolution process of 7*8 cellulose bundles(7 cellulose with polymerization degree of 8)in ionic liquid N-butyl pyridinium acetate([Bpy][OAc])was explored.Through the structural change of cellulose,it was found that cellulose chains were separated from each other,indicating that[Bpy][OAc]can completely dissolve cellulose;Through hydrogen bond analysis,it was found that[OAc]~-forms a hydrogen bond with cellulose hydroxyl,which promoted the dissolution process;Through energy analysis,it was found that[Bpy]~+promoted dissolution through van der Waals interaction;In addition,the conformational transition of cellulose before and after dissolution was found:tg conformation changed to gt and gg conformation.(2)Simulation study on the regeneration of cellulose in anti-solvent.The mechanism and conformational changes of cellulose regeneration under the action of different anti solvents(water,ethanol and acetone)were studied.In order to study the regeneration mechanism,the regeneration process of dissolved cellulose system was simulated.By analyzing cellulose structure,radial distribution function(RDFs)and hydrogen bond,we found that the anti-solvent regeneration effect was ranked as follows:water>ethanol>acetone.Through the spatial distribution function,we found that the stronger the ability of anti-solvent to break the hydrogen bond between cellulose and anion,the more obvious the regeneration effect.In the process of regeneration,the conformation of cellulose also changed,gt conformation decreased and gg conformation increased.The essential reason was the energy difference of cellulose conformation.(3)Simulation study on the dissolution and regeneration of cellulose in different ionic liquids.The dissolution and regeneration of cellulose beam in three ionic liquids were simulated.The ionic liquids were N-butyl pyridinium acetate([Bpy][OAc]),N-butyl pyridinium chloride([Bpy][Cl])and 1-butyl-3-methylimidazolium acetate([Bmim][OAc]).It was found that the solubility of three ionic liquids to cellulose is ranked as:[Bpy][OAc]>[Bpy][Cl]>[Bmim][OAc].In the regeneration process,the interaction between cellulose and anions and the effects of different ionic liquids on the conformational distribution of cellulose were studied.The study found that the interaction between cellulose and[Cl]~-was the weakest in the regeneration process,so the number of hydrogen bonds between cellulose and[Cl]~-decreased the fastest,because the anti-solvent interrupted the hydrogen bond between cellulose and[Cl]~-to promote regeneration.In addition,the conformational distribution of cellulose was related to the degree of cellulose dissolution and regeneration:the better the effect of ionic liquid dissolution,the higher the degree of cellulose dissolution,the more gt conformation and the less gg conformation;The better the regeneration effect of ionic liquid and the higher the degree of cellulose regeneration,the less the gt conformation and the more the gg conformation.