Thermodynamic And Transport Properties Of1-ethyl-3-methylimidazolium Acetate And Its Mixtures With Cellobiose And Water

As one of sustainable resources which exist in nature widely,lignocellulose has attracted increasing attention. Owing to therecalcitration of the plant cell walls, the costly pretreatment process isalways the biggest stumbing block which from the extensive applicationof the lignocellulose. Ionic liquids are another new solvent which arecomposed of different cations and anions, and become a hot topic as theirlower vapour pressure and better diversified designability. Now someliteratures has been reported that several ionic liquids could dissolvelignocellulose under milder conditions, alought the mechanism of it is notclear. We performed many molecular dynamics simulations using ionicliquids ([emim][Ac]) and cellobiose (the smallest repeating unit ofcellulose) as materials in this article.At present, the force fields using in ILs-cellulose MD simulations are lackof a direct comparison and validation with the experimental data, so wesimulated the density, isobaric thermal expansion coefficient, self-diffusivity, shear viscosity and rotational correlational time of bothpure [emim][Ac] systems in the temperature range from303.15K to393.15K and [emim][Ac]-cellobiose systems in the temperature rangefrom303.15K to353.15K in this work, and our MD results are goodagreement with the experimental data. On the basis of them, we foundthat it can form a stronger hydrogen-bond between anion and thehydroxyl groups of cellobiose by analyzing the radial distributionfunctions (RDFs). Even though the hydrogen-bond can also be formedbetween the active hydrogen atoms of the imidazolium ring of the cationsand the hydroxyl groups of the cellobiose, its much weaker than thebefore ones. In [emim][Ac]-cellobiose mixed systems, the order of therelative strength of the hydrogen-bond is like this: anion-cellobiose>cation-anion> cation-cellobiose, and this is sonsistent with the protonchemicalo shift results analyzed by NMR method.Because water is inevitable in the practical application of ionicliquids and also can be used to the regeneration process of the amorphouscellulose in the pretreatment process of the cellulose, we also simulatedthe [emim][Ac]-cellobiose-water mixed systems in this work. Keepingthe numbers of [emim][Ac] and cellobiose molecules as constant, westudied the factors that affected the cellobiose dissolved in ionic liquidsand focused upon the analysis of the hydrogen-bond network. Our resultsalso show that when we add water molecules to the [emim][Ac]-cellobiose mixed systems, the interaction between cationsand anions are significantly weakened, and these added water moleculescan also form strong hydrogen-bond with the cellobiose molecules.