Alkylation of isobutane/butene promoted by fluoride-containing ionic liquids

- Fluoride-containing ILs were employed as additives and their promoting performance was investigated in H2SO4 alkylation process.
- New species of HF, [PF6−x−2y(HSO4)x(SO4)y]− and [SbF6−x−2y(HSO4)x(SO4)y]− were formed through acidolysis of [Bmim][PF6] or [Bmim][SbF6] in H2SO4.
- The possible promoting mechanism of fluoride-containing ILs was proposed.

In this work, the alkylation of isobutane and butene, catalyzed by sulfuric acid in the presence of the fluoride-containing ionic liquids [Bmim][PF6] and [Bmim][SbF6], was investigated. The use of the binary mixture catalysts brought to a higher C8 selectivity and longer catalyst lifetime, compared with the results obtained when working with sulfuric acid only. This was attributed to the formation of new species when [Bmim][PF6] or [Bmim][SbF6] are added to sulfuric acid. The acidolysis of [Bmim][PF6] and [Bmim][SbF6] was accompanied by the release of hydrogen fluoride (HF) and the decomposition of anions to [PF6−x−2y(HSO4)x(SO4)y]− and [SbF6−x−2y(HSO4)x(SO4)y]−, respectively. The presence of these new species after acidolysis was measured and confirmed by ion chromatography, 1H-Nuclear Magnetic Resonance (NMR), 19F-NMR and 31P-NMR. The production of HF and the complexation of anions and carbenium ions both play an important role in stabilizing the carbenium ion and improving the catalytic performance.

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