Modification of polyetherimide membranes with ZIFs fillers for CO2 separation

Abstract

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 () of 39.6 and 27.5, respectively, higher than the of the reference membrane PEI, while the membrane with filler of ZIF-Mix (PZ-Zn/Co) showed the lowest

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.