(401aj) Preparation and Characterization of Zeolite-Polymer Mixed Matrix Membranes Filled with KFI and Rho Type Zeolites

Separation of CO₂ from gas mixtures is a popular subject of investigation. The tailoring of membranes for this purpose includes the development of suitable polymeric and zeolitic membranes. Fast permeability through polymeric membranes combined with high selectivity of crystalline molecular sieve zeolites may lead to improved performances in the separation of CO₂ from CH₄ as well as other applications. Up to now different types of zeolite-polymer mixed matrix membranes have been prepared by using zeolites, such as A, X/Y, silicalite/ZSM-5, SSZ-13, SAPO-34, BEA, sodalite and L. Although zeolite NaA has been determined to be very suitable for CO₂/CH₄ and CO₂/N₂ separations, the very hydrophilic nature of this zeolite results in adsorption of water which complicates the separation process.

In this study, zeolite-polymer mixed matrix membranes containing KFI and RHO type zeolites (20% by weight) were prepared. These zeolites have pore sizes comparable with that of zeolite NaA but are less hydrophilic and thus may be very useful in the separation of CO₂ from various gas mixtures. Polyvinyl acetate was selected as the polymer phase due to its compatibility with zeolites in the mixed matrix membranes. The zeolites were synthesized by using suitable conditions reported in the literature. The zeolites as well as the membranes obtained were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), adsorption and integrated gravimetric analysis (IGA) techniques.

The zeolites were identified to be crystalline without impurity phases according to the XRD analyses performed. The SEM pictures indicated a homogeneous distribution of the zeolite particles, of about 1-3 µm, in the mixed matrix membranes. Adsorption of CO₂ and N₂ in the pure zeolite and polymer as well as mixed matrix membrane samples assured the high selectivity of both KFI and RHO zeolites for CO₂. The zeolite-polymer interactions were also investigated by using adsorption data for pure and mixed phases. The results implied that the composite materials exhibited properties that could not be explained by considering the pure zeolite and polymer phases, alone. This may support the view of the existence of an interphase between the zeolite and polymer phases in the mixed matrix membranes. According to the gravimetric sorption measurements, it was determined that polymeric membranes filled with KFI and RHO type zeolites presented quite different behaviors for the sorption of CO₂ and N₂, when compared to the pure polymeric membrane, which might provide significant improvements for the separation of CO₂ from gas mixtures.

Permeability measurements should also be performed to confirm the advantages of using mixed matrix membranes filled with KFI and RHO zeolites. Different polymer types and various zeolite loadings may also be tested in order to determine the extent of the possible improvements.