Anionic Clusters Enhanced Catalytic Performance of Protic Acid Ionic Liquids for Isobutane Alkylation

Isobutane alkylation is a typical carbocation chain growth reaction that requires proper acidity with less acidity change for its enhanced lifetime and activity of the catalyst. In this work, a family of protic ionic liquid/triflic acid as synergistic catalysts has been developed for isobutane alkylation, with special emphasis on its reusability. The slowest acidity change was found with varied concentrations of triflic acid for the protic ionic liquids which is probably buffered by binding and releasing the solubilized acid in the formed anionic cluster [N222H]-[CF3SO3(CF3SO3H)(x)] as indicated by FT-IR and H-1 NMR spectroscopy. As a promising isobutane alkylation catalyst, the protic ionic liquids have shown a maximum selectivity toward C-8 up to 86.23%, research octane number (RON) up to 97.3, and reusability up to 36 runs, outclassing the sulfuric acid or triflic add catalysts under the same reaction conditions. Apart from the excellent catalytic performance, the new catalytic system showed better impurities compatibility and significantly less corrosion rate to carbon steel and stainless steel than sulfuric acid and pure triffic acid.