In this work, we have conducted first principle study on the conversion of furan into methyl levulinate using local base method within the DFT framework in order to classify the solvation characteristic of methylal.
To this end, first-principles density functional calculations were applied to elucidate the molecular structure of the intermediates in the conversion of furan to levulinic acid esters in a methylal solvent, to evaluate the reaction energy and activation energy, and to elucidate the mechanism.
For modeling and simulation, we adopted two different ways of PAO-DZP basis sets for super cell modeling and 6-311+G* basis sets for cluster modeling. The methanol solvent effect was considered explicitly by including 25 and 40 methanol molecules in the super cells with lattice constants of 1.2nm and 1.4nm for the super cell modeling and implicitly by using the COSMO approach for the cluster modeling. The geometrical features of individual molecules of methylal, furan, MMF and MLA were analyzed with comparison between those by different methods and models.
Through the analysis of the Fukui functions, we identify the reactive sites in the individual molecules. With the calculated DFT total energies, corrected by the zero-point and thermal energies for the cases of cluster modeling calculations, we determined the reaction energies for the reactions of "methylal + furan" to "MMF + methanol" and "MMF + water" to MLA.
It was revealed that the first reaction was endothermic in vacuum but became exothermic in methanol solvent, while the second reaction was exothermic in both vacuum and solvent environments. Using the predicted reaction pathways, we carried out the NEB simulations to clarify the real reaction pathways and determine the activation energies for these two reactions without and with a protonated methanol molecule.
Our calculations provide the detailed mechanism of conversion of biomass-derived furan to MLA used as fuel additive with the detailed geometries and frequencies of the intermediates.
The results have been published in "Materials Advances" under the title of "Ab initio insight into furan conversion to levulinate ester in reaction with methylal and methanol."(https://doi.org/10.1039/d4ma00446a).
