Studies On The Preparation And Gas Separation Performance Of Metal-Organic Framework Membranes

Metal-organic frameworks (MOFs) are a class of hybrid nanoporous crystalline materials, comprising of metal centers coordinated to organic linkers. MOFs have the features of low density, high specific surface area and adjustable pore size, which show potential applications in gas storage,separation, catalysis, etc. In recent years, one of MOF membrane applications, gas separation has attracted great interest of both experimental and theoretical researchers. Membrane separation technology is regarded as one of the most effective methods to capture C02 emissions from industrial sources due to its low energy consumption,simple preparation technology, no phase change. In the field of membrane separation technologies, the research and development of new membrane materials is the key point.In this work, MOF membranes and their mixed matrix membranes(MMM) have been successfully synthesized using different methods for gas separation. The synthesized membranes were characterized by scanning electron micrographs (SEM), X-ray diffraction (XRD), thermal gravity analyses (TGA), Fourier transform infrared spectroscopy (FT-IR),as well as their gas separation performance. The main contents and findings are summarized as follows:(1) ZIF-9 membranes were successfully synthesized using the conventional in-situ method. To investigate the best synthetic conditions of ZIF-9 membrane for gas separation and membrane growth, the dosage of APTES, the molar ratio of metal salt with ligand, reaction temperature and reaction time were considered in variable-controlled method. The optimum conditions are as follows: dosage of APTES in volume fraction is 2%; the molar ratio of metal salts and ligand is 1:2; the reaction temperature is 110?; and the reaction time is 72 h.(2) ZIF-9 membranes were successfully synthesized using temperature-switching synthesis method and the conventional in-situ method at a constant temperature method. These ZIF-9 membranes were characterized by SEM, XRD, and gas separation performance and so on.The results showed that both the growth and gas separation performance of the membranes synthesized using temperature-switching synthesis method were better. This method showes advantages that it separates the processes of nucleation and growth of MOF crystals. Finally, it would achieve the goal that low temperature favors for nucleation and high temperature promotes crystal growth. In this work, we chose 80? and 130 ? as the reaction temperature. Such method has not been employed in MOF-based membranes up to now to the best of our knowledge.(3) A ZIF-9 hybrid membrane covered by ionic liquids (ILs)functionalized carbon nanotubes (CNTs) was grown using heat treatment of layer-by-layer deposition method. The cracks of ZIF-9 were filled by CNT@IL. The gas separation performance of CNT@IL/ZIF-9 hybrid membrane is better than that of ZIF-9, CNT/ZIF-9 and IL/ZIF-9 membranes. In addition, to investigate the optimum operation condition,the measurement of gas permeance and selectivity were performed at different temperatures and trans-membrane pressure drops. High separation selectivity combined with good stability and reproducibility recommends the developed CNT@IL/ZIF-9 hybrid membrane as a promising choice for gas separation.(4) A mixed matrix gas separation membrane of MOF/polyether block amide (ZIF-8/PEBAX-1074) was--successfully synthesized using tape casting method. The membranes were designated according to the mass ratio percentage of ZIF-8 particles to PEBAX-1074 as 0%, 5%,10%, 15% and 20% for simplicity. The characterization and gas separation results showed that the ZIF-8/PEBAX-1074 mixed-matrix membrane had an enhanced separation performance for CO2/H2, CO2/N2,and CO2/CH4. The membrane performed the best gas separation property when the mass ratio percentage of ZIF-8 particles was 15%. PEBAX has been industrialized and commercialized, while the synthesis of ZIF-8 is low-cost and simple in MOFs. The compositing of the two materials would have broad prospects in practical application.(5) Finally, two MOFs, ZIF-9 and MIL-53(Al), had been successfully added to PEBAX-2533 to synthesize the mixed matrix membrane MIL-53(Al)/ZIF-9/PEBAX-2533. The characterization and gas separation results showed that the membrane had a better gas separation performance than those of ZIF-9/PEB AX-2533 and MIL-53(Al)/PEBAX-2533. Moreover, the effect of the amounts of the two MOF fillers on gas separation performance was studied. This work provided a new method for prapreration of membranes.