Experimental study of the effect of zeolite 4A treated with magnesium hydroxide on the characteristics and gas-permeation properties of polysulfone-based mixed-matrix membranes

Abstract

Nowadays, new methods for gas-separation processes are being quickly developed. The separation of CH4/CO2 and CH4/H2 is usually the subject of most related research studies, especially in the membrane gas-separation process, because of their important role in industry. In this study, we attempted to improve the separation properties of a polysulfone/zeolite 4A mixed-matrix membrane by modifying the zeolite particle surface. The method included a simple ion-exchange reaction of magnesium chloride with ammonium hydroxide that yielded the formation and precipitation of magnesium hydroxide whiskers on the surface of the zeolites. The whiskers could omit most of the nonselective voids by interlocking the polymer chains through them and, consequently, improve the permeability, selectivity, and elastic modulus of the membranes. X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and dynamic mechanical analysis proved all the changes recorded after the particle and membrane treatments. SEM images showed the petal-like morphology of the whiskers that formed on the surface of the particles after the reaction against the smooth surface of the untreated zeolite. At a 30 wt % loading of particles in the polymeric matrix, the selectivities for H2/CH4 and CO2/CH4 increased by 69 and 56%, respectively; in contrast, the H2 and CO2 permeabilities decreased by 2.5 and 10%, respectively. The modulus of elasticity for the treated membrane also increased by 14 and 30% compared to those of the pure and untreated membranes, respectively.