No abstract

The all-atom force field for concentrated sulfuric acid (98.30 wt %) was developed in this work based on ab initio calculations. The structural and dynamical properties of sulfuric acid and the mixing behaviors of sulfuric acid with ionic liquids (ILs), i.e., SFIL (1-methyl-3-(propyl-3-sulfonate) imidazolium bisulfate ([PSMim][HSO])) and non-SFIL (1-methyl-3-propyl imidazolium bisulfate ([PMim][HSO])), were investigated using a molecular dynamics simulation. For sulfuric acid, most HO ions were found beside HSO ions, forming a contact ion pair with the HSO ions, and three-dimensional hydrogen-bonding networks existed in the sulfuric acid. Analyses indicate that both ILs could be miscible with sulfuric acid with a strong exothermic character. The new strong interaction site between the sulfonic acid group of SFIL and an HSO molecule through a strong hydrogen-bonding interaction was observed, which was beneficial to the catalytic activity and stability of the sulfuric acid. This observation is in good agreement with the experimental results that indicate SFILs could enhance the reusability of sulfuric acid for the isobutane alkylation about 4-fold compared to that of non-SFILs. Hopefully this work will provide insights into the screening and designing of new isobutane alkylation catalysts based on sulfuric acid and SFILs.

Seven typical quaternary ammonium ionic liquids, amino acid ionic liquids, and imidazolium ionic liquids were synthesized, characterized, and investigated as co‐catalyst for the sulfuric acid catalyzed isobutane alkylation. The results show that the introduction of [OPSIm][HSO4] or [Pr3NPS][HSO4] both leads to a better catalytic performance and higher quality of alkylate products. The molecular dynamic simulation indicates that the [OPSIm][HSO4] can promote the dissolution of isobutane molecules at interface, further improving the ratio of isobutane to olefin from 1.02 to 1.18. Differently, the [Pr3NPS][HSO4] can significantly increase the interface width from 0.66 to 0.97 nm and reduce the interface tension from 28.49 to 14.62 mN/m, thereby enhancing the reaction area and improving the ion transfer. The [Pro][HSO4] and [Gly][HSO4] result in a worse quality of alkylate products due to no positive effect on the interfacial properties such as interfacial solubility of isobutane.