Preparation Of ZIF-8 Membrane For Gas Separation And Its Permeability

The ZIF-8 of the zeolite imidazole framework materials (ZIFs) has potential separability for C02 and low-carbon organic gases due to its channel structure controllability. Because the binding capacity between the membrane and the surface of the inorganic material is poor, there are some defects for commonly used ZIFs membrane preparation methods such as in situ synthesis,seeded growth method in the membrane preparation process. In order to improve the film forming effect of ZIF-8 membrane on the outer surface of alumina ceramic tube, in this paper, an improved seeded growth which coupling agent to seed crystal solution is proposed. Then we take gas permeability test for H2, CO2 and other common gas.In view of the literature of the ZIF-8 crystal preparation methods have their own advantages and disadvantages, so in this paper we firstly explore suitable method for the preparation of ZIF-8 crystal. We find that the purity, crystal morphology and particle size (100 nm) of the ZIF-8 crystals is prepared with methanol as solvent, what's more, this way was the most simple.There are two conditions that could make effect for preparation of ZIF-8 membrane, and they are seed crystal concentration and reaction crystallization time.And the optimum conditions for them were 1 w% and 5 h. In order to solve the problem of the weak binding force between the film and the supporter, this paper explores the effect of PEI and APTES as coupling agents and their dosage on the film forming effect, and the gas permeation evaluation. The results showed that the effect of coupling agent on the film formation was APTES>PEI> without coupling agent. When the addition amount of PEI is 1w%, the ZIF-8 membrane is the best, and its surface is relatively flat, but it is still defective. The crystal growth condition is well, most of them are the form of six-membered ring cell, and the film thickness at 10-15 ?m. There are relatively large permeation fluxes for H2 and C02,which are 43.5×10-8 and 11.2×10-8 mol·s-1·Pa-1·m-2.For H2/N2,H2/CH4 separation factor of 12.39,19.08.When the addition amount of APTES is 2w%, the membrane formation effect is the best,the film surface is smooth and compact, and the surface crystal growth pattern is the form of six-membered ring unit cell, the agglomeration phenomenon is rare,the film is uniform and the thickness is about 20 ?m. the permeation flux for H2 is 27.2×10-8 mol·s-1·Pa-1·m-2.The ideal separation factor for H2/N2, H2/CH4 is 12.39, 19.08, and for CO2/CH4, the separation factor is 6.13.