Na+/Ca2+ aqueous ion exchange in natural clinoptilolite zeolite for polymer-zeolite composite membranes production and their CH4/CO2/N2 separation performance

In the current work, Mexican clinoptilolite was modified with CaCl2 in an aqueous solution to replace Na+ ions with Ca2+ ions to improve its gas separation performance in polymeric hybrid membranes. The modified zeolite characterized by atomic absorption spectroscopy, diffuse reflectance infrared spectroscopy, X-ray diffraction and scanning electron microscopy coupled to an energy dispersive X-ray spectrometer (EDS). Besides, porosimetry parameters, such as the specific area, volume and pore size, were determined by the standard Brunauer- Emmet-Teller and Monte-Carlo methods, respectively. Finally, the density studies were performed on all modified zeolite samples, using a helium pycnometer. The results show that ion exchange modification is obtained on the surfaces of the zeolite and in its cavities without any microstructural modification. Preliminary studies on mixed matrix membranes (MMM) based on polyether-block-amide with natural clinoptilolite enriched with Ca2+, showed improvements on their gas separation properties of ternary gas mixtures of CH4/CO2/N2. Cation-modified clinoptilolites can be potentially useful as fillers in polymeric membranes applied in mixed gases separation.