Effect Of Seeds Pretreatment On The Synthesis Of Zeolite Beta

Zeolite beta is widely used as catalysts in oil refining and petrochemical because of its unique three-dimensional pore architecture composed of intersecting12-ring channels, high thermal and hydrothermal stability. However, the large quantity of organic template used in the synthesis of zeolite beta results in the high costs and limition of industrial application. In this paper, the seed-assisted method was introduced in a small amount of tetraethylammonium hydroxide template and without template systems to synthesize zeolite beta. The guiding function of the seeds and the influence of seeds pretreatment on the synthesis of zeolite beta was investigated by XRD, XRF, SEM, Raman, IR and N2physical adsorption characterization technologies. The obtained conclusions are as follows:1. The Seed-transferring in a small amount of template system was sustainable in a certain degree. The crystallization time gradually extended, SiO2/Al2O3molar ratios of the products reduced, particle sizes enlarged and the P zeolite miscellaneous crystal began to appear in the process of seed-transferring. SiO2/Al2O3molar ratios increased and relative crystallinities decreased when the seeds were pretreated by steam passivation and citric acid solution, and the pretreatment could influence the crystallization of zeolite beta.2. Seed-transferring without template is unsustainable. The transfer could only proceed with two generation, mordenite would be formed with the zeolite beta in the third generation. The particle sizes of the products gradually enlarged, SiO2/Al2O3molar ratios, specific surface and pore volume reduced when seed-transferring was going on.3. The products synthesized in the system without template were pretreated in different methods, the morphology, particle size, relative crystallinity, SiO2/Al2O2molar ratios, specific surface and pore volume of that after pretreatment was all changed more or less. The samples above were used as seeds, they had different effect on the synthesis of zeolite beta in the system without template. The citric or tartaric acid solution pretreatment had better effect, which resulted in faster crystallization speed and higher relative crystallinity of the products; when the seeds pretreated with sodium hydroxide solution the crystallization speed of the products would slow down; when the seeds pretreated with acetic acid, the relative crystallinity of the products had no changes in the first30hours during the crystallization, it almost remained the same as the initial gel; when the seeds pretreated with hydrochloric acid or oxalic acid solution, no zeolite beta could be obtained.