(694f) Sulfuric Acid-Catalyzed Isobutane Alkylation with C4 Olefin Promoted By Sulfonic-Acid-Functionalized Ionic Liquids

Weizhen Sun, Piao Cao, and Ling Zhao

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

The alkylate produced by the C4 alkylation reaction with a high-octane number, no content of aromatics and sulfur and clean burning, is an ideal blending component for gas upgrading. The current worldwide alkylation mainly relies on the concentrated H₂SO₄ as the main commercial catalyst, which has high catalytic activity and selectivity while suffers from equipment corrosion, and environmental pollution. To overcome these problems in the H₂SO₄-catalyzed alkylation, the green and alternative catalysts or co-catalysts need to be developed for the C4 alkylation process.

As a dual solvent-catalyst, sulfonic-acid-functionalized ionic liquids (SFILs) are promising catalysts for the C4 alkylation because of their considerable advantages, including the high-catalytic activity and stability, easy separation from the product, strong Brønsted acidity, negligible-vapor pressure and designable structures. However, few work related to the effect of the SFILs on the interfacial behaviors of the H₂SO₄-catalyzed alkylation has been focused on. In addition, for the SFIL/H₂SO₄-catalyzed alkylation, the addition ratio of the SFIL to H₂SO₄ is the first important factor that needs to be studied, because the addition amount of the SFIL determines the interfacial properties as well as the acidity of the C4 alkylation process, and further determines the quality of alkylate. In this work, we focus on the effect of the 1-octyl-3-sulfopropyl-imidazolium hydrogen sulfate ([OPSim][HSO₄]) with different ratios to the H₂SO₄ on the catalytic performance and interfacial properties for the H₂SO₄-catalyzed alkylation by the combination of experiments and MD simulation.

Experimental results indicated that compared to pure H₂SO₄, the introduction of the SFILs can contribute to a higher selectivity of C8-alkylates as well as Research Octane Number (RON), suggesting a higher quality of alkylate. Moreover, the catalytic performance of the SFIL/H₂SO₄ catalyst is improved with the increased addition ratio of the SFIL into the H₂SO₄ within the range of 10 wt%. MD simulation results reveal that the obvious density enrichment of the cations of the SFILs at the interface results in a larger interface width, and higher interface number and better dispersion of C4 hydrocarbons at the interface, which can be ascribed to the location of the alkyl chains close to the C4 hydrocarbon phase with the extended and perpendicular behaviors. The improvement of interfacial properties due to the addition of the SFILs is favorable to the enhancement of the quality of alkylate, which is in excellent agreement with experimental results. Hopefully, the useful information in this work can provide a reference to the design of the SFILs and the optimization of the C4 alkylation process.