Ionic Liquid Membranes Supported by Hydrophobic and Hydrophilic Metal–Organic Frameworks for CO2 Capture

CATEGORY: CARBON CAPTURE
J. Phys. Chem. C, 2013, 117 (11), pp 5792–5799, DOI: 10.1021/jp312404k
Ionic Liquid Membranes Supported by Hydrophobic and Hydrophilic Metal–Organic Frameworks for CO2 Capture
Krishna M. Gupta , Yifei Chen , and Jianwen Jiang *
chejj@nus.edu.sg
Department of Chemical and Biomolecular Engineering, National University of Singapore, 117576 Singapore
Abstract
Researchers conducted atomistic simulation to study CO₂ capture in ionic liquid (IL) membranes supported on metal–organic frameworks (MOFs). The IL under study is 1-n-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], while hydrophobic ZIF-71 and hydrophilic Na-rho-ZMOF with the same topology and similar pore size are used as supports.
The [SCN]⁻ anion prefers to locate near the metal cluster of ZIF-71 and the Na⁺ ion of Na-rho-ZMOF. In contrast, the bulky and chainlike [BMIM]⁺ cation resides in the open cage. In both membranes, the [SCN]⁻ interacts more strongly than the [BMIM]⁺ with the MOF supports. With regard to CO₂ capture from CO₂/N₂ mixture, CO₂ adsorption is greater than N₂, while CO₂ diffusion is slower in both membranes, particularly in [BMIM][SCN]/ZMOF. This is due to the fact that the Na⁺ ions in Na-rho-ZMOF act as strong binding sites for CO₂. The permselectivity of CO₂ over N₂ is governed by adsorption selectivity, since diffusion selectivity remains a constant over the pressure range examined. Compared to many polymer membranes and polymer-supported ILs, [BMIM][SCN]/ZMOF shows higher permeability and permselectivity. It also surpasses the Robeson’s upper bound. Results of the simulation study indicate that hydrophilic support is superior to the hydrophobic counterpart.
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