Synthesis of ZSM-5, silicalite, and X zeolite films under elevated gravity and their characterization

Continuous and non-composite ZSM-5, silicalite and X zeolite films are produced under elevated gravity. The synthesis mechanisms of the films are studied by visual observation method. The silicalite films are also fabricated into membranes. The pure component and mixture permeation of the membranes are then investigated by using light alkanes.; The ZSM-5 zeolite films, with a thickness from 100 μm to 1000 μm, are synthesized in the silica-TPABr gel system at 170°C and under 16 G. The synthesis mechanism of the ZSM-5 zeolite films is postulated to be liquid ion transportation mechanism; The nucleation and crystal growth primarily occur in the interface of the solid gel and the liquid. This explains why the high gravity is beneficial to form a compact film. The high gravity helps the segregation of the densified gel and liquid. The high gravity also brings the crystals closer promoting intergrowth, and thus improves the quality of the film as compared to the film produced under normal gravity. In addition, there exists an optimum value of water content (25.5) in the formation of a thin ZSM-5 zeolite film. The thickness of the film can be changed by the alkalinity of the gel because the alkalinity modifies the morphology of the zeolite crystals. High alkalinity leads to rounded crystals with poor crystal intergrowth. Considerable crystal intergrowth can be obtained by secondary nucleation on the surface of a seeding film, the resulting film is a compact and uniform film.; The silicalite films, with a thickness from 100 μm, to 4000 μm, are also produced in the silica-TPABr gel system at 170°C under 16 G and 67 G. The synthesis mechanism of the silicalite films appears to be the same as that of ZSM-5 zeolite films. The crystal size in the film decreases with the increasing gravity; The thick silicalite films are composed of uniform zeolite crystals.; The zeolite X films, with a thickness of approximately 300 μm, are synthesized in the silica-NaAlO₂ gel system at 70°C under 16 G. The synthesis mechanism of the zeolite X films is believed to be liquid ion transportation mechanism at the early stage of the crystallization. During the later stages of the crystallization, the solid-solid transformation mechanism may act. On the other hand, at high crystallization temperature (100°C), the zeolite X film transfers to P zeolite film.; The permeation results reveal that the silicalite membrane has a measured separation factor of 1.92 toward methane at pressure of 18.0 torr from a mixture of methane and butane. For the mixture of butane and isobutane, the membrane has a measured separation factor of 1.6 toward isobutane at a pressure of 10 torr. These results conflict with the prediction based on pure component permeation experiments. Also, the adsorption isotherms of pure components can not explain the mixture permeation performance. The membrane selectivity depends on both adsorption and diffusion of molecules. Low separation factors may result from small molecule size difference and compensating effects of adsorption and diffusion of molecules at ambient temperature.