The functional ionic liquids (ILs) [NH2emim][OAc] and [NH2emim][BF4] were synthesized for SO2 capture. Although functional ILs have potential advantages in SO2 absorption, the high viscosity of a single IL markedly affects the SO2 absorption separation process. To improve the SO2 absorption performance, [NH2emim][OAc] and [NH2emim][BF4] were mixed with low-viscosity imidazolium-based ILs [bmim][OH]/[bmim][BF4]. When the mole ratio of [NH2emim][OAc]/[bmim][OH] is about 1:1, the binary mixture has the best SO2 absorption capacity. The SO2 absorption performance was investigated in the simulated flue gas, where SO2 partial pressure was about 0.2 kPa. Under the low SO2 partial pressure, the absorption capacity of the [NH2emim][OAc] + [bmim][OH] mixture was more than 0.7 mol of SO2/mol of IL, which was superior to that of a single IL. The regeneration test of [NH2emim][OAc] + [bmim][OH] showed that the binary mixture had high reversibility and the SO2 absorption capacity almost kept constant after 12 recycles. The viscosity and density of the IL mixture changed slightly, which only have a 2–3% increase in each cycle.

•Deuterated isobutane was used for investigating the reaction mechanism.•High solubility of C4 leads to the induction period of ionic liquid very short.•The scission of C12+ plays an import role for forming trimethylpentanes.•Dimethylhexanes are formed primary by the alkylation of sec-C4H9+ with 2-butene.•The formation of light and heavy ends should be attributed to the C12+ cations.The ionic liquid catalyzed alkylation of 2-butene with deuterated isobutane was studied in a continuous flow equipment. Product analyses with time and deuterated distribution determinations were obtained. It is found that the induction period of ionic liquid alkylation is much shorter than that of sulfuric acid. A considerable difference in isobutane solubility between ionic liquid and sulfuric acid was observed with ionic liquid having a greater tendency to dissolve isobutane at the start-up of alkylation. Deuterated product distributions indicate that trimethylpentane fractions stemmed primarily from the self-alkylation of isobutane, the direct alkylation reaction of C4 hydrocarbons, and the scission of C12+ intermediates. Most dimethylhexanes should come from the direct addition of sec-butyl carbonium ions to 2-butenes.

•Ionic liquids modified with metal compounds show superior alkylation selectivity.•The composition and acid strength of ionic liquids were studied upon NMR and FTIR.•The alkylation selectivity of the ionic liquidis mainly determined by its composition.•Increasing isobutane-to-olefin ratio of feed will increase alkylate quality.•The complexation of transition metal ions with 2-butene will improve the I/Oratio.Ionic liquid catalyzed isobutane/2-butene alkylation modified with metal compounds was studied. The effect of catalyst composition on the alkylation selectivity was investigated. 27Al NMR, ESI-MS, and FTIR spectra reveal that the catalytic selectivity of the modified ionic liquid is probably determined by the catalyst composition rather than by the acid strength. The complexation of transition metal with 2-butene can increase the internal isobutane-to-olefin ratio of feed during the alkylation reaction, which results in the better selectivity of the modified ionic liquid. The best ionic liquid catalysts were those containing CuAlCl4 complexes, giving the alkylate with 87.5 wt% trimethylpentanes and a calculated research octane number (RON) of 100.5.Ionic liquid catalyzed isobutane/2-butene alkylation modified with metal compounds was studied. The catalytic selectivity of the modified IL is determined by the catalyst composition. The complexation of CuAlCl4 with 2-butene can increase the internal isobutane-to-olefin ratio during the alkylation reaction, which results in the better selectivity of the modified IL. When ionic liquids containing transition metal complexes, high quality alkylates could be obtained.