Synthesis Of Intracrystal Mesopores Silicalite-1in The Presence Of Silane

Silicalite-1is a pure silica zeolite with MFI type. Ascribed to the large specific surface areas, good hydrothermal stability, high resistance to acid and alkali, and shape-selective microporous channel, silicalite-1is usally used as adsorbent and catalyst support in the fields of adsorption and separation and catalysis. Notably, the diffusion of guest molecules in the microporous channels of silicalite-1is the type of configurational diffusion. The shape-selectivity also brings fourth a strong diffusion limitation, resulting in the reduction of utilization effectiveness and the ease of deactivation.Synthesis of hierarchical zeolites is an efficient way to improve the diffusivity of silicalite-1. The accessability of guest molecules to the adsorption sites can be enhanced by shorten the characteristic diffusion distance in micropores. In the thesis, hierarchical silicalite-1with intracrystal mesopores was hydrothermally synthesized in the presence of3-Glycidoxypropyl-trimethoxysilane (GPTMS) using inexpensive water glass as the silica source and tetrapropylammonium bromide (TPABr) as the template. The thesis mainly consists of three parts as follows:1) Silicalite-1zeolites with intracrystal mesopores were hydrothermally synthesized by a two-step crystallization method. The effects of various factors including type of silane coupling agent, dosage of silane coupling agent, crystallization time, alkalinity etc., on the crystallization behaviors, crystal shape and properties of the synthesized silicalite-1were investigated. The results indicated that prismatic shaped silicalite-1with intracrystal mesopores were successful synthesized in the presence of GPTMS. The alkalinity of the synthesis system seriously affected the size and uniformity of the silicalite-1crystals. In addition, the crystallization time at different crystallization temperature has great influence on the crystallinity. If only crystallized at180℃for1d without a precrystallization at110℃, the obtained product exibited a low crystallinity. On the other hand, too long crystallization time at110℃would hamper the formation of silicalite-1through destruction of nucleary process. Under the optimal crystallization conditions, i.e.110℃for2d and110℃for4d, samples with high crystallinity and large specific surface areas were obtained.2) The liquid phase adsorption of xylene and cresol isotherms on the syntheized silicalite-1was studied. The investigations on the equilibrium adsorption of single component xylene revealed that the synthesized silicalite-1with intracrystalline mesopores exhibited large equilibrium adsorption amount which is187and73mg/g for p-xylene and o-xylene, respectively. The dynamic absorption curves p-xylene indicated the silicalite-1zeolites synthesized in the presence of GPTMS showed an improved p-xylene uptake rate. The good mass transfer properties of the hierarchical silicalite-1with intracrystalline pores were also confirmed by the n-butane adsorption uptake experiments. The competitive adsorptions of binary component showed that the improvement of mass transfer properties did not sacrifice of selectivity for p-xylene.The adsorption behaviors of p-cresol and m-cresol on the synthesized silicalite-1zeolites were also investigated. The competitive adsorptions of cresol mixtures indicated that the adsorption of m-cresol had superiority at low mass fractions, while the adsorption of p-cresol became dominance when the mass fraction excessed0.1. The synthesized silicalite-1zeolites with intracrystalline mesopores exhibited a good cresol adsorption performance in terms of both uptake rate and capacity.3) Shape-controlable silicalite-1zeolites with uniform size were synthesized by adjusting the recipt of the starting materials from the synthesis system with TEOS as the silica source and TPAOH as the template. Preparation of silicalite-1membranes were explored from the above synthesis system.