Amino acid ionic liquids (AAILs) are potential green substitutes of aqueous amine solutions for carbon dioxide (CO2) capture. However, the viscous nature of AAILs greatly hinders their further development in CO2 capture applications. In this contribution, 1-ethyl-3-methylimidazolium lysine ([EMIM][Lys]) was synthesized and immobilized into a porous poly(methyl methacrylate) (PMMA) microsphere support for post-combustion CO2 capture. The [EMIM][Lys] exhibited good thermal stability and could be facilely immobilized into porous microspheres. Significantly, the [EMIM][Lys]-PMMA sorbents retained their porous structure after [EMIM][Lys] loading and exhibited fast kinetics. When exposed to CO2 at 40 °C, [EMIM][Lys]-PMMA sorbent exhibited the highest CO2 capacity compared to other counterparts studied and achieved a capacity of 0.87 mol/(mol AAIL) or 1.67 mmol/(g sorbent). The capture process may be characterized by two stages: CO2 adsorption on the surface of sorbent and CO2 diffusion into sorbent for further adsorption. The calculated activation energies of the two-stage CO2 sorption were 4.1 and 4.3 kJ/mol, respectively, indicating that, overall, the CO2 can easily adsorb onto this sorbent. Furthermore, multiple cycle tests indicated that the developed sorbents had good long-term stability. The developed sorbent may be a promising candidate for post-combustion CO2 capture.

Mixed-matrix membranes (MMMs) were formed by incorporating M 2 (dobdc) (M = Mg, Ni; dobdc 4− = 2,5-dioxido-1,4-benzenedicarboxylate) metal−organic framework (MOF) nanoparticles in a series of poly(ether-imide) copolymers. Addition of the MOF nanoparticles improved the permeability of H 2 , N 2 , CH 4 , and CO 2 relative to the pure copolymer by increasing gas solubility and, in most cases, diffusivity. More limited improvements in diffusivity were observed for the more strongly adsorbing gases. Because of such transport considerations, improvements in permeability and selectivity were most pronounced for H 2 /CH 4 and H 2 /N 2 separations. Incorporation of a greater ether content within the copolymers led to the formation of defect-free MMMs by physically sealing polymer−MOF interfacial defects, allowing higher MOF loadings to be achieved. For Mg 2 (dobdc), selective, defect-free films could be formed with loadings of up to 51 wt %. However, at these high loadings, films became weak and brittle. The mechanical properties of the composite materials were therefore quantified by tensile tests and compared to those of the neat polymers used commercially for membrane film formation. High contents of flexible ether units and small MOF nanoparticle sizes were found to be necessary to form strong and ductile MMMs, although clear trade-offs exist between transport performance, MOF loading, and mechanical properties. These trade-offs are critically examined to evaluate the current limitations and potential benefits to forming M 2 (dobdc) MMMs using this rubber toughening approach.

The proton-coupled electron transfer (PCET) reaction of a quinone has been used to create a pH gradient capable of the active pumping of CO2 through a liquid membrane. The quinone redox couples, hydroquinone/benzoquinone and 2,6-dimethylbenzoquinone/2,6-dimethylhydroquinone, have been investigated in the proton transfer mechanisms associated with electron transfer in sodium bicarbonate solutions. These same conditions have then been applied to an active liquid membrane for proton pumping across a membrane electrode assembly under potential bias, acting as an active membrane for CO2 separation. Qualitative results are reported toward the development of an active redox membrane for CO2 separation from flue gas.

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