Encapsulated ionic liquids for CO2 capture

Abstract

Aiming to improve the gas diffusion in ionic liquid (IL) and give full play to the selectivity of IL for CO2 sorption, dispersed 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), tri-n-butyl propyl phosphonium succinimide ([P4443][SUC]) and tri-n-butyl propyl phosphonium iminodiacetic acid ([P4443]2[IDA]) droplets as core materials were encapsulated in silica gel, polysulfone and polystyrene by sol-gel method, solvent evaporation and suspension polymerization method to form the novel microcapsules containing ionic liquid. The microcapsules were evaluated by infrared analysis, thermogravimetry, morphology and CO2/N2 sorption. It is concluded that the preparation method and IL type have a great influence on loading amount and morphology, which further affect CO2 sorption. The IL-based microcapsules display irregular or spherical particles and contain relatively high amounts of ionic liquid (~60–70 wt%) by sol-gel method and suspension polymerization. Encapsulated ionic liquid materials have the better CO2 sorption capacity and CO2/N2 selectivity than the supporters, especially phosphonium ionic liquid ([P4443][SUC]) microcapsules prepared by sol-gel method. The loss of CO2 sorption capacity is only about 0.104 wt% after being recycled for 8 times. Additionally, CO2 sorption kinetics of the ionic liquid microcapsules follow pseudo-second-order model and microcapsules have a drastic increase in mass transfer rate.