RESUMO
The experiments on cellulose dissolution/regeneration have made some achievements to some extent, but the mechanism of cellulose regeneration in ionic liquids (ILs) and anti-solvent mixtures remains elusive. In this work, the cellulose regeneration mechanism in different anti-solvents, and at different temperatures and concentrations, has been studied with molecular dynamics (MD) simulations. The IL considered is 1-ethyl-3-methylimidazolium acetate (EmimOAc). In addition, to investigate the microcosmic effects of ILs and anti-solvents, EmimOAc-nH2O (n = 0-6) clusters have been optimized by Density Functional Theory (DFT) calculations. It can be found that water is beneficial to the regeneration of cellulose due to its strong polarity. The interactions between ILs and cellulose will become strong with the increase in temperature. The H-bonds of cellulose chains would increase with the rising concentrations of anti-solvents. The interaction energies between cellulose and the anions of ILs are stronger than that of cations. Furthermore, the anti-solvents possess a strong affinity for ILs, cation-anion pairs are dissociated to form H-bonds with anti-solvents, and the H-bonds between cellulose and ILs are destroyed to promote cellulose regeneration.
RESUMO
Biomass-derived γ-valerolactone (GVL) is a versatile chemical that can be used in various fields. As an efficient, cheap, and sustainable catalyst, Al(OiPr)3 has been successfully used in the conversion of methyl levulinate (ML) to GVL in the solvent isopropanol (IPA). However, the molecular mechanism of this conversion catalyzed by Al(OiPr)3 remains ambiguous. To investigate the mechanism of the conversion of ML to GVL catalyzed by Al(OiPr)3, the reaction pathways, including the transesterification, Meerwein-Ponndorf-Verley (MPV) hydrogenation, and ring-closure steps, were probed using density functional theory (DFT) calculations at the M062X-D3/def2-TZVP level. Among the elementary steps, it is found that ring-closure is the rate-determining step and that Al3+ can coordinate with the oxygen of 2-hydroxy-isopropyl levulinate (2HIPL) to catalyze the last ring-closure step. A four-centered transition state can be formed, and Al(OiPr)3 shows a strong catalytic effect in the two steps of the ester exchange reaction. The center of Al(OiPr)3 mainly coordinates with the carbonyl oxygen atom of the ester to catalyze the reaction. The present study provides some help in understanding the conversion mechanism of ML to GVL and designing more effective catalysts for use in biomass conversion chemistry.