Preparation And Characterizations Of CO₂Perm-selective Composite Membranes

Known as a greenhouse gas, CO2also plays an important role as the carbon source insome industrial applications. The study of CO2separation and purification technology is ofgreat significance in environmental protection and carbon resource. Membrane technologyfor CO2separation has become a hot topic in the gas separation field due to its highefficiency, energy saving and environment-friendly advantages. Nowadays developing highperformance membrane for gas separation has attracted much attention. In this work, CO2perm-selective silica membranes and ZIF-8/silica composite membranes were designed andsynthesized. The membrane exhibited excellent CO2separation performance. The maincontents of this study were as follows:(1) Silica sol was synthesized by a sol-gel method choosing1,2-bis(triethoxysilyl)ethane (BTESE) as the silica precursor. During the preparation, the size of silica pore wasregulated by adjusting synthesis temperature and the amount of hydrochloric acid as catalyst.The results showed that the increase in catalyst and reaction temperature resulted in biggerpore sizes of silica. With the optimized synthesis conditions, silica precursors with two poresize distribution were prepared, and they were used in silica separation membrane.(2) Silica membrane was prepared by a two-step method on α-Al2O3porous hollowfiber support by optimizing the number and order of different silica coating. Silicamembrane with high separation performance was prepared. The best performance wasachieved when the coating order was mesoporous silica precursor-microporous silicaprecursor. The best CO2/CH4selectivity of silica membrane at room temperature and90℃was17.8and9.4, respectively.(3) ZIF-8film was obtained by secondary growth. During the synthesis, the effect of thesize and the concentration of ZIF-8seed were examined. It was confirmed that denser ZIF-8membrane was obtained when the size and concentration of ZIF-8seed was~60nm and0.5wt%.(4) On the basis of the reports of silica and ZIF-8membrane, ZIF-8/silica compositemembrane was designed and synthesized. In this paper, ZIF-8/silica composite membrane with high separation performance was successfully prepared. At room temperature, the CO2permeance of the composite membrane was2.61×10-7mol·m-2·s-1·Pa-1and the separationfactor for CO2/CH4was13.9, while the factor for H2/CH4and H2/N2were26and32.6,respectively.