| Zeolitic imidazolate frameworks (ZIFs) are a new subgroup of metal-organic framework composed of porous crystals with extended three-dimensional structures constructed from tetrahedral metal ions as the base and bridged by imidazolate as organic links. The well defined pore sizes in conjunction with high surface areas, uniformly structured pores and channels and exceptional thermal and chemical stability make ZIFs prime candidates for molecular sieving material. So far, the preparation of MOF membrane is still in the initial stage and focus on the utilization of smooth disk as support and adding MOF nanoparticles into polymeric matirx to form mixed matrix membrane. Compared with plate support, tubular support bears many merits such as high packing density, area/volume ratio and facile package, thus making it particularly promising candidate for industrial ulitilization. In this thesis, different tubular supports were adopted to prepare dense ZIF s membranes.(1) For thin tubular support, traditional stationary preparation protocol is not applicable. ZIF-8 membranes were successfully synthesized on the inner surface of porous hollow fiber ceramic tube (HFT) and APTES-modified nonporous capillary quartz tubes in a simple flow system via in situ direct growth method. For the preparation of porous HFT supported ZIF-8 membrane, the effect of reaction temperature and flow rate in growth of the ZIF-8 membrane has been studied. Under the optimum condition, a possible growth mechnism was proposed according to the morphologies transformation along with different synthesis time. Due to the fast coodination phenomenon, the formed nuclei during the early flow stage on support surface served seed to initiate and guide the growth of a defect-free ZIF-8 membrane. The achieved ZIF-8 membrane demonstrated remarkably high H2 permeance of 1.91 ×10-6 mol·m-2·s-1·Pa-1 and H2/CO2, H2/N2, H2/CH4 ideal selectivity of 4.95,12.90 and 15.65, respectively. The free -NH2 on chemical coupling APTES reacted with Zn2+ to induce preferential nucleation and crystal growth. The thickness of ZIF-8 film layer supported on the inner surface of nonporous capillary quartz increased linearly along with prolonging synthesis time.(2) Dipcoating-rubbing method (DCRM) was developed to decorate the surface of a macroporous carbon tube with a mixture of graphite and ZIF-8 nanoparticles to prepare compact ZIF-8 membrane. The content of graphite and ZIF-8 seeds was an important factor when manipulating support surface morphology modification. ZIF-8 membranes were grown on coarse carbon tubes with in situ growth method, seeded growth method, in situ growth with graphite modification method for comparation purpose. The graphite in the composite acting as binding agent could have two functions:(a) anchoring the ZIF-8 seeds onto the carbon surface and (b) smoothing the coarse surface of the macroporous carbon tube, thus forming a high quality ZIF-8 membrane after solvothermal secodary growth. While the content of graphite and ZIF-8 seeds was 0.6 wt% and 0.5 wt%, respectively, an intermediate layer with thickness of 3 μm was formed after repeated DCRM procedure twicely. The obtained ZIF-8 membrane showed H2 permeance of 7.15×10-8 mol·m-2·s-1·Pa-1 and H2/CO2, H2/N2, H2/CH4 ideal selectivity of 5.05,7.07 and 7.80, respectively.(3) Continuous and highly stable ZIF-8 membranes were successfully synthesized on macroporous tubular α-Al2O3 supports with mean pore size of 3～4 μm which has been manual-rubbed with thin ZnO layer and dip-coated with composite of Silicalite-1 and ZnO, respectively, followed by activation and solvothermal process for ZIF-8 membrane growth. The as-prepared ZIF-8 membrane with manual-rubbing method showed H2 permeance of 4.36×10-7 mol·s-1·Pa-1 and H2/CO2, H2/N2, H2/CH4 ideal selectivity of 4.95,10.52 and 10.85, respectively. Among parallel experiments, overall 60 percent of the membranes showed approximate gas permeance performance, thus indicating abtou 60% reproducibility. The as-prepared membrane also showed superior thernal and mechanical stability. The as-prepared ZIF-8 membrane with dip-coating method showed H2 permeance of 4.16×10-7 mol·m-2·s-1·Pa-1 and H2/CO2, H2/N2, H2/CH4 ideal selectivity of 5.48,9.69 and 9.82, respectively, showing excellent molecular sieving performance.(4) PSS was applied to modify porous organic hollow fiber tube (HFT) to prepare compact ZIF-8 membrane. ZIF-8 membrane with thickness of 2.5μm were obtained after in situ solvothermal synthesis with the help of electric interaction. The effect of reaction temperature and concentration in growth of the ZIF-8 membrane has been studied. The ZIF-8 membrane exhibited high H2 permeance of 1.03×10-6 mol·m-2·s-1·Pa-1. The ideal separation factors of H2 from N2 and CH4 were 10.18 and 9.36, respectively, which showed excellent molecular sieving performance. |
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