Modification of polyetherimide membranes with ZIFs fillers for CO₂ separation

Flat hybrid membranes composed of polyetherimide (PEI) as matrix and zeolitic imidazolate frameworks (ZIFs) as fillers at concentrations of 10 and 20 wt% were prepared. Apparent permeability coefficient and apparent diffusivity coefficient of gases (CO₂ and N₂) for these hybrid membranes (PZIFs) were determined by the “time-lag” method. The experimental conditions used were from 25 °C to 55 °C with pressures of 2, 3 and 5 bar. The PZIFs with fillers of ZIF-8 (PZ-Zn) and ZIF-67 (PZ-Co) showed apparent selectivities (α_{Pa(CO2)/Pa(N2)}) of 39.6 and 27.5, respectively, higher than the α_{Pa(CO2)/Pa(N2)} of the reference membrane PEI, while the membrane with filler of ZIF-Mix (PZ-Zn/Co) showed the lowest α_{Pa(CO2)/Pa(N2)} selectivity of 10.3 in the membrane series (under conditions of 25 °C and 2 bar). It is proposed that the selectivity of the membrane series can be attributed to two critical factors: the particle size/distribution ratio in the polymer base and sorption of CO₂ at local sites of the bimetallic mixture. On the other hand, gas permeation studies (O₂, CO₂ and CH₄, and CO₂/CH₄ and CO₂/C₂H₄ mixtures), were carried out in the series of PZIFs membranes. Permeability data were obtained by an isostatic method based on a permeation cell connected in series to a gas chromatograph where the rate of permeated gases was analyzed until a stationary state was reached. The complementary characterization techniques were: scanning electron microscopy, thermogravimetric analysis, and powder X-ray diffraction, which support the existence of the amorphous/crystalline phases of the PZIFs.