Performance and pressure drop of CO 2 absorption into task‐specific and halide‐free ionic liquids in a microchannel

The gas–liquid two‐phase flow pattern, absorption rate and pressure drop of CO 2 absorbed into the aqueous solution of the task‐specific ionic liquids (1‐aminopropyl‐3‐methylimidazole tetrafluoroborate [Apmim][BF 4 ] and 1‐hydroxyethyl‐3‐methylimidazole tetrafluoroborate [OHemim][BF 4 ]) and halide‐free ionic liquid 1‐butyl‐3‐methylimidazolium methylsulfate [Bmim][CH 3 SO 4 ] were investigated in a microreactor. The absorption mechanism of the three ionic liquids was analyzed employing the 13 C NMR spectroscopy. The [Apmim][BF 4 ] was found to have the best ability of CO 2 capture compared with the other two ionic liquids, as chemical absorption occurred between [Apmim][BF 4 ] and CO 2 , while only physical absorption took place between [OHemim][BF 4 ]/[Bmim][CH 3 SO 4 ] and CO 2 . The sequence of CO 2 absorption rate in three ionic liquids aqueous solutions is: [Apmim][BF 4 ] > [Bmim][CH 3 SO 4 ] > [OHemim][BF 4 ]. Furthermore, the effects of gas–liquid flow rate and ionic liquids concentration on CO 2 absorption rate and pressure drop were studied, the pressure drop models based on various flow patterns were proposed.