Experimental And Theoretical Studies On Solid-phase Synthesis Of β Zeolite

Zeoliteβis one of the aluminosilicate materials with three-dimensional system of interconnected 12-membered ring large-pored channels structure and high silica crystalline. Zeoliteβhad shown outstanding catalytic properties in some chemical and petrochemical processes.It is an important target to improve this zeolites synthesis technology for extensively decreasing the cost. So, the new cost-effectively synthetic method was studied, and in order to carry out the guidance and predict of the prepatation technique of new type zeolite, we have studied the synthesis mechanism of zeolite.In the present work, the thdrohermal synthesis synthetic method and DGC method are used to synthesisβzeolite firstly. By the betterment on the process of dry gel conversion of steam-assisted synthesis and introducing a cheap template TEABr, a new cost-effectively synthetic method is obtained. XRD,SEM and FT-IR indicate that the structure of zeoliteβby cost-effectively synthesis is good. Compared with steam-assisted synthesis and hydrothermal synthesis, solid-phase synthesis is promising and economical,which simplifies the synthetic process and reduce the costs. In this paper, the effect of crystallization temperature, crystallization time, alkalinity, the amount of template on the crystallinity of products is studied. The results indicate that when SiO2 is used as silicic source, NaAlO2 as aluminium source, TEABr as template, the best condition of technics is (SiO2/Al2O3=30):OH-/SiO2=0.40,TEABr/SiO2=0.15,4% crystal introduced (compared with the total mass of silicic source),130℃as crystallization temperature,4 days as crystallization time.On this condition, the structure of zeoliteβis good and the intensity of MOR is lower. Large scale repeats the result of small scale, and the crystallinity of products is higher and MOR is lower.The acidity and pore structrure of prepared samples were also characterized, respectively. The characterization results indicated that the acidity and the pore structure of the synthesized zeolite were pretty consistent with those of the standard zeoliteβ, though a trace of stray crystal of mordenite was observed.βzeolites with different Si/Al ratio were prepared and investigated in the fixed-bed microreactor. It is found that,βzeolite with Si/Al ratio of 30 exhibits higer catalytic activity for isomerization.After hydrothermal treateded at 800℃for,βzeolite maintain excellent stability and catalytic activity for n-hexene isomerization. The product of large scale as assistant catalyzer is introduced into main catalyzer for FCC reaction (especially heavy Oil, usually petroleum residue),which can obtain more propylene and improve the amount of translation of raw material and liquid. The mechanism of zeolite growth of the early stages of P and MOR zeolites are investigated by the quantum chemical calculation. The condensations of silicic acid with aluminate in alkaline environment are studied using the density-functional theory, at the 6-31+G (d, p) basis sets. The calculated results show that the activation energy of TEA+ is decreased by 9 kJ/mol.The mechanism of q2 Al species ofβand MOR zeolites are investigated. The calculated results show that theβand MOR formation of Si-O-Al linkage can proceed via a single-step process.The calculated activation energie of q2Al specie on MOR zeolite is 70 kJ/mol; and it is 67.2 kJ/mol with TEA+ in synthesis process.The calculated activation energie onβzeolite are 102.3 kJ/mol,and it is 53.1 kJ/mol with TEA+ in synthesis process.It is indicated that the synthesis ofβzeolite using TEA+ are easier.In order to understand the important information of P zeolite, Density functional theory (DFT) has been applied to study the distribution of the framework aluminum atoms at nine inequivalent T sites and the acidity of Brφnsted acid in P zeolite.The calculation was carried out at B3LYP/6-31G (d, p) level based on the 5T,8T and 22 T cluster model.According to the interaction energies between zeolite framework and TEA+, the calculated Al/Si substitution, the calculated (Al, H)/Si substitution, proton affinity, and the adsorbing energies of ammonia (NH3),it was proposed that the most favorable sites for Al substitution locate at are T5 and T6 sites,the acidity of A15-O14-Si9 is the highest in the preferable Brφnsted acid sites,and the A17-O3-Si1 site is the lowest.