MgCO₃-crystal-containing mixed matrix membranes with enhanced CO₂ permselectivity

A cost-effective, facile method for simultaneously improving the CO₂ permeance and CO₂/N₂ selectivity of mixed matrix membranes (MMMs) was developed using commercially available MgCO₃ microcrystals. The MgCO₃ crystals were broken into small pieces and homogenously dispersed in polymer matrices via mechanical stirring to form MMMs. In particular, an amphiphilic comb polymer (CP) composed of poly(ethylene glycol) behenyl ether methacrylate (PEGBEM) and poly(oxyethylene methacrylate) (POEM), i.e., PEGBEM–POEM, was found to be an effective matrix due to the specific interactions between its carbonyl oxygen atoms and MgCO₃. The detailed interactions, morphologies, and structures of MgCO₃ and CP/MgCO₃ hybrids were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), N₂ adsorption-desorption isotherm measurements, wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and Fourier transform infrared (FT-IR) and Raman spectroscopies. The CP/MgCO₃ MMM with 45 wt% MgCO₃ exhibited the highest CO₂/N₂ selectivity of 93.8 and CO₂ permeance of 30.9 GPU (1 GPU = 10⁻⁶ cm³ (STP)/(s·cm²·cmHg)). This performance surpasses other MgCO₃ MMMs prepared using commercially available polymers such as PEBAX® (a polyether block amide) and poly(ethylene oxide) (PEO). The improved performance resulted from the enhanced CO₂ solubility by MgCO₃ crystals, as confirmed by the CO₂ uptake measurements.