Synthesis, Characterization And Catalytic Properties In Propylene Epoxidation Of Titanium Silicalites

With the new century coming, people pay more attention to the environment and ask the chemical industry to reduce the pollution as possible as it could Zeolite can take the important role in developing the clearer chemical technology. Taramasso et al. firstly reported the synthesis of titanium silicalite TS-1 in 1983 and it was found that TS-1 exhibited the unique catalytic performance in oxidation reaction involving H202 as the oxidant. Many reactions using TS- I as the catalyst such as the hydroxylation of phenol and the epoxidation of propylene have been investigated recently. But the application of IS-i in the industry was hindered seriously by many defects of the classical synthesis such as the high cost of the raw material and the severe preparation condition. Many problems in the synthetic procedures and the catalytic scheme were still unclear, which made the titanium silicalite was mainly synthesized according experiencesIn the classical synthesis of TS-1 alkali free TPAOH is used as the template and TS-l is produced at the severe condition and high cost, which makes the synthesis difficult to be industrialized. In this paper many techniques such as solidstate NMR, XRD, IR, UV-Vis, SEM and ESR were used to study the template effect, crystallization mechanism, crystallization kinetics and titanium species existing in titanium silicalite and the synthesis using TPABr as the template was selected according the above workTS-1 was synthesized using TPABr as the template and ammonia, nButylaniine, TEAOH etc were used to adjust the p!-1 value of the gel Effect of the synthesis parameters such as the crystallization time, TPABr I Si02, Si02 I T102, base amount etc. were systematically discussed. A better synthesis was selected and was enlarged in a IOOL autoclave As-obtained TS-l was used to catalyzepropylene into prcpylene oxide (P0). Effect of the teaction parameters, the solvents and the pH value of the medium on the epoxidation result was investigated. At last, a catalytic scheme of propylene epoxidation was given. All the above work has afforded valuable information to industrialize the synthesis of propylene oxide (P0) from propylene and hydrogen peroxide using IS-I as the catalystFrom the systematical studies in this paper, the following results have been obtained.1.Template effect was investigated systematically using 慔棐? C CP / MAS NMR It has been shown that both TPABr and TBAOH serve as ternplating agent in TPABr ?TBAOH system. But in other systems, when there is enough TPABr, other organic amines or ammoniums only work as the bases TEAOH or nbutylamine can take the role of template when less TPABr is added It indicates that the ability of organic amines or ammoniums to direct the pentasil structure decreases as following: TPA? 18K > TEK > n-butylamine etc Some TEA? TPA4 in the channel may decompose It is important for the formation of the channels of zeolite that the sum of lengths of two neighboring alkyl chains matches with the distance of two consecutive cages in the channel2Titanium species existing in titanium silicalite were investigated using chemical analysis, XRD, 20Si MAS NMR, UV-Vis, ESR, UV-Raman. It has been observed that several kinds of titanium species may exist in titanium silicalite There are different kinds and different amount of titanium species in IS-I samples synthesized using different methods. The form that titanium atoms incorporate into the framework of titanium silicalite synthesized using TPABr as template differs from that using the classical method and the unit cell volume does not significantly expand But the symmetry changes from monoclinic to orthorhombic with the increase of titanium content in both methods The Ti-02~ originated from framework titanium and H202 has the moderate stability and may be active site in oxidation reaction. IS-i synthesized using TPABr astemplate does not contain anatase, but contains a kind of partly condensed titanium species with six-fold coordination. The titanium species may co...