CO2 Capture with Capsules of Ionic Liquid/Amines

Carbon capture remains an urgent issue that has gained a great deal of attention over the past few decades. Aqueous amines have excellent selectivity, but present corrosion and volatility issues, whereas ionic liquids (ILs) have negligible volatility and tunable physical properties, but high viscosities. One approach to improve the practical performance of these liquids is encapsulating them in a CO2 permeable polymer shell to enhance the accessibility of the liquid and the CO2 absorption rate. In this work, we report the encapsulation of a mixture of amine and IL (i.e., monoethanolamine (MEA) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]­[BF4])) and demonstrate enhanced carbon capture performance. A soft-template approach and interfacial polymerization are used to give capsules with liquid core (64 wt %) and polyurea shell. Compared to the bulk liquid, the encapsulated liquid shows improved thermal stability over cycles of absorption at 25 °C, and desorption at 75 °C. The capsules with core of [BMIM]­[BF4]-MEA show 0.2 mol CO2/kg of capsules at 1 bar CO2, compared to the bulk liquid, which has 0.05 mol CO2/kg of sorbent. This is attributed to the limited evaporation of the amines. Alternatively, the same capsules but with 5 wt % of piperazine (Pz) in the core have doubled gravimetric CO2 capacity of the capsules (0.4 mol CO2/kg of capsules); performance is evaluated over 10 capture–release cycles showing minimal mass loss. Characterization of the CO2 uptake of the polymer shell itself reveals that the shell contributes only ∼10% of the observed capacity, likely attributed to amine functionalities of the polymer. This facile approach to encapsulating such “active” liquids can be applied to other CO2 selective solvents that are volatile, viscous, and corrosive.