Abstract: MFI nano-zeolite membranes were prepared in-situ on alumina supports by one-step constant temperature and two-step varying-temperature crystallization with urea as crystallization regulator. The structure and morphology of MFI zeolite and MFI zeolite membranes were characterized by XRD and SEM. A series of zeolite seeds with high transverse diameter ratio and longitudinal diameter ratio were obtained by adjusting the ratio of urea in the synthetic solution and the two-step in-situ hydrothermal crystallization time at variable temperature. When the amount of urea added in the synthetic solution (based on the mass ratio of urea to silicon) and the crystallization time of 120 ℃ for 6 h and then 180 ℃ for 8 h, the size of the zeolite was the smallest, and the b-axis was the shortest, only 60 nm. Under the same conditions, nano-MFI zeolite membranes with high b-axis orientation were prepared on alumina supports. Extending the crystallization time of the high temperature section to 14 h to obtain a b-axis oriented zeolite membrane with good permeability and separation ability for n-butane/i-butane liquefaction (40% of n-butane and 60% of i-butane), the osmoticflux of n-butane was 2.2×10^-7 mol/(m²·s·Pa)，and the separation factor was 23.9 under the condition of 25 ℃. The effect of 100 h continuous evaluation was not significantly decreased.

Key words: MFI nano-zeolite membrane, short b-axis, in situ directional growth, n-butane, i-butane