| The pore size (0.74nm) of FAU-type zeolite that is larger than MFI (0.55nm) and A (0.42nm), is similar to the size of many important industrial materials. Therefore, FAU-type zeolite membranes have potential applications in gases separation of large molecules and small molecules and macromolecules and macromolecules, pervaporation and catalytic membrane reactors. There is important scientific significance to develop the synthesis and application research of FAU-type zeolite membrane.Herein, the preparation of FAU-type zeolites was firstly investigated by direct crystallization without seed gel. Based on the research of conventional hydrothermal synthesis, the method of membrane synthesis was improved. The synthetic formula and excellent performance of zeolite membranes were obtained on different supports optimizing some factors of hydrothermal synthesis. Lastly, the as-prepared FAU-type zeolite membranes were applied to separation for N2/CO2 gas mixture. Moreover, a better separation performance for N2/CO2 mixture is obtained. The results achieved were as follows:(1) The hydrothermal synthesis conditions including aging time, synthesis temperature and time, water content and Na2O/SiO2 ratio in the system were investigated in detail. The results indicated that increasing aging time favored the formation of more nuclears, but too long aging time led to increase particle size of the zeolite. Prolonging crystal temperature and time would increase the crystallinity of FAU zeolite, but trans-crystalliziation phenomena was easy to occur and led to mixed-crystal; the crystallinity of product was highly affected by the ratio of Na2O/SiO2 and H2O/Al2O3, and the high crystallinity FAU zeolite were synthesized when the ratio of Na2O/SiO2 and H2O/Al2O3 was 1.0 and 160, respectively. (2) Thin and continuous faujasite membranes were prepared on the surface of a mullite tubular support using a seeding technique. Surface modified tubular were seeded with zeolite X crystals prior to film growth in a synthesis mixture. The effects of gel composition, hydrothermal treatment process and the quality of FAU membranes were investigated. The results indicated that increasing aging time accelerated the crystal growth rate, but overlong aging time could cause the generation of P-type zeolite and thicker membrane layer. Prolonging crystallization time and raising temperature would increase the rate of crystal nucleation, but readily make trans-crystallization phenomena occur. The Na/Si ratio did not play a significant role in synthesizing FAU X-type membranes in the tested range. The as-synthesized zeolite membranes with higher ratio of Si/Al accompanied with the formation of P-type crystal and the particle size on the membrane surface obviously increased. The membrane with a smoother zeolite surface and a thinner top layer was obtained with increasing H2O content. The membrane surface crystal particles were uniform, the continuity and density are better and the film thickness was about 5μm under optimal hydrothermal synthesis condition. The result for single-gases permeation indicated that the film thickness was thicker, the permeance was lower. For the N2/CO2 gas mixture N2 was prior to CO2 through FAU-type zeolite membrane and a separation factor of 7.89 was found.(3) The alumina hollow fiber membrane with asymmetrical structure which consisted of long finger-like structures near the outer and inner walls and sponge-like structures for effective separation at the center of the fiber precursor was prepared by dry-wet spinning process combined with sintering process. The N2 permeance was 4.5×10-5mol/m2•Pa•s at room temperature. Then, defect-free Al2O3-supported FAU type zeolite membranes were successfully prepared by a secondary synthesis method. The membrane surface crystal particles were uniform, the continuity and density are better and the film thickness was about 7μm. The separation factor of N2 and CO2 gas mixture was 7.00.
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