Preparation And Gas Separation Performance Of Carbon/Zeolite Hybrid Membranes

Gas separation membranes have been developed fast due to their high separation efficiency, low energy consumption and simple operation. The application of polymeric membranes is widely limited in gas separation because they can't exceed the Robesen upper bound and can't endure high temperature and corrosive environments. Carbon membrane is a novel inorganic membrane material which shows enormous potential in gas separation because of its super microporous, good thermal and chemical resistance. But the low gas permeability of carbon membrane limited its industry application. In order to settle this problem, we incorporate zeolite of uniform micro porous into carbon membrane precursors. The Zeolite/Carbon hybrid membranes exhibit higher gas permeability and without losing the O₂/N₂ selectivity compared with the traditional pure carbon membranes.Zeolite /Carbon hybrid carbon membranes were fabricated by carbonizing the polyimide precursors hybridized by zeolites such as ZSM-5, 6, and Y. The gas permeation performance of the hybrid carbon membranes were tested by using pure single gases including H₂, CO₂, O₂ and N₂, and the microstructure of the hybrid carbon membranes were characterized by XRD and TEM. The effects of zeolite loading, particle size, channel structure, cationic form and thermal stability on the permeability and microstructure of the hybrid carbon membranes were also investigated.The results show that the Zeolite /Carbon hybrid membranes exhibit higher O₂ gas permeability without losing the O₂/N₂ selectivity compared to the traditional pure carbon membranes. As zeolite loading increase , the gas permeability of Zeolite /Carbon hybrid membranes increases and the gas selectivity decrease. The O₂ permeability of the Zeolite Y /Carbon hybrid membranes prepared at 700℃with the zeolite loading of 15% is 501bareer with a O₂/N₂ selectivity of 15.6. The increase of particle size which caused by zeolite agglomeration has little effect on gas permeability of the hybrid membrane, but decreases the gas selectivity. As the zeolite particle size increase which caused by the increase of zeolite single crystal diameter, the gas permeability of Zeolite /Carbon hybrid membranes increases, but the gas selectivity decrease. It is believed that the gas diffusion resistance in zeolite /carbon hybrid membranes decreases with the increase of zeolite pore size. Thus, the Zeoliteβ/carbon membrane shows higher gas permeability than that of ZSM-5/carbon membrane because the pore of zeolite 8 is larger than that of zeolite ZSM-5. The change of cations will affect the adsorption capacity of zeolite; Zeolite NaY's adsorption of CO₂ is stronger than that of HY. The CO₂ permeability of the Zeolite NaY /Carbon hybrid membranes is lower than that of Zeolite HY because of the stronger adsorption of CO₂ in NaY zeolite. Carbonization temperature has an important influence on gas separation of zeolite/carbon hybrid membranes. As the carbonization temperature increase the gas permeability of Zeolite /Carbon hybrid membranes decrease, the selectivity increase. Increase the carbonization temperature from 700℃to 800℃, the gas permeability of both Zeolite I3/Carbon hybrid membranes and Zeolite Y/Carbon hybrid membranes decrease significantly. The crystal structure of Zeolite Y is destroyed due to its thermal unstability which lead to the gas permeability of Zeolite Y /Carbon hybrid membranes is close to that of traditional pure carbon membrane.