Development and theoretical analyses of polymeric membranes and mixed matrix membranes for gas separation

Polymeric membranes play a vital role in many industrial separation processes.A considerable amount of work is presently in progress to improve the performance of polymeric membranes for gas separation.Many research efforts are devoted to the development of membranes that exhibit both high selectivities and permeabilities to specific gases.In this thesis, motivated by the idea that the combinations of polymer matrices and inorganic fillers could obtain the desirable properties of the individual components and probably achieve better separation performance in terms of high permeabilities and selectivities, the work focused mainly on the study of organic-inorganic mixed matrix membranes (MMMs).A comprehensive study on the effects of membrane thickness and heat treatment, the selection of inorganic fillers and the preparation methods, on the properties of the resulting membranes, is presented.Various instruments such as TGA (thermogravimetric analysis), DSC (differential scanning calorimetry), XRD (X-ray diffraction), SEM (scanning electron microscope) and TEM (transmission electron microscope) were used to characterize the membranes.The main objective of this research programme was to determine the relationship between the membrane structures and the gas separation performance.Besides the mixed matrix membranes, it was also desirable to study asymmetric membranes, researching into the effects of the preparation conditions on the separation properties of the resulting asymmetric membranes.The thesis consists of the following five parts:(1) The effects of membrane thickness and heat treatment on the gas transport Abstract III properties of P84 membranes were investigated.The results showed that the single gas permeability increased with increasing membrane thickness whilst the selectivity was independent of the membrane thickness and that the membrane annealled at low temperatures showed higher permeabilities but lower ideal selectivities.(2) Three types of inorganic fillers -fumed SiO 2 , MCM-41 and zeolite 4A, were incorporated into the P84 matrix to prepare MMMs and the effects of filler structures on the gas separation performance were comparatively studied.This work is the first systematic comparison of the effects of nonporous (SiO 2 ), microporous (zeolite 4A) and mesoporous (MCM-41) materials on the gas transport properties of P84 polymer.Results indicated that nano-SiO 2 particles proved to be the most effective inorganic filler in terms of the enhancement of the performance of gas separation.Subsequently, the effects of the modification of SiO 2 surface and the content of SiO 2 on the gas transport properties of the resulting MMMs were investigated.The permeability of the composite membranes was well matched with the predictions given by the free volume theory except that a large discrepancy was observed for the permeability of the composite membranes with higher SiO 2 loadings.(3) Polyimide-silica MMMs were also prepared using the sol-gel technique.However, with the introduction of the silica, there was no significant enhancement of the gas separation in the resulting polyimide-silica MMMs due to the strong interaction between the polymer chains and the inorganic phase.