Zeolite-filled PMMA composite membranes: influence of coupling agent addition on gas separation properties

The adhesion between the polymer phase and the external surface of the particle appeared to be a major problem in the preparation of zeolite-filled polymeric membranes when the polymer is in the glassy state at room temperature. Interfacial void-free PMMA membranes filled with zeolite 4A were prepared by introducing 3-(trimethoxysilyl) propylmethacrylate (TMOPMA) as a way to improve the gas separation properties of the polymeric membranes. It was found that the oxygen permeability of zeolite-filled PMMA membranes was lower than pure PMMA membranes. In addition, the oxygen permeability of zeolite-filled PMMA membranes decreased with increasing zeolite 4A loading up to 33.3 wt%. At the same zeolite composition, zeolite surface modification with TMOPMA significantly improved the solubility and diffusivity coefficients of the zeolite-filled PMMA membranes. The sorption behaviors of PMMA/zeolite 4A and PMMA/zeolite 4A/TMOPMA membranes can be well described by the dual-mode sorption model. Surface modification of the zeolite particles increases the gas sorption in the Henry sites but decreases the gas sorption in the Langmuir sites. The solubility of the zeolite-filled PMMA membrane is predicted by the rule of mixtures at a zeolite loading less than 20 wt%.