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Preparation Of TS-1 Composites And Their Catalytic Properties In Epoxidation Of Allyl Chloride

Posted on:2011-02-19Degree:MasterType:Thesis
Country:ChinaCandidate:H S XiaFull Text:PDF
GTID:2121330338477704Subject:Industrial Catalysis
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Epichlorohydrin (ECH) is an important intermediate in medicine and chemical industry fields. Traditional industrial methods have some defects such as serious environmental pollution, high energy consumption or price fluctuations of raw materials. Direct epoxidation of allyl chloride with hydrogen peroxide as oxidant, heterogeneous catalysts is an environmental-friendly process. Among various catalysts, microporous zeolitic titanium silicalite (TS-1) is the most promising. However, the commercial value of TS-1 catalyst is still under question because of its difficult separation and recovery in pilot-scaled practice. To solve this problem head-on, we developed two types of recycable TS-1 composites by1) immobilization of TS-1 on clay support and 2) introduction magnetic properties into TS-1 crystallites.The structure and properties of synthetic composites were characterized by using modern physical and chemical techniques, such as X-ray diffraction (XRD), Fourier transformation infra-red spectra (FT-IR), ultraviolet-visible spectra (UV-Vis), nitrogen adsorption-desorption isotherms, scanning electron micrograph (SEM). Their catalytic properties in the epoxidation of allyl chloride with H2O2 were investigated.A magnetic core/ TS-1 zeolite shell structure (MFeCTS) was successfully synthesized by using TS-1 precursor, silica-coated hematite and (NH4)2CO3. The presence of silica-coated hematite in synthesis gel of MFeCTS didn't influence the formation of TS-1 crystals as well as the degree and state of Ti incorporation. The addition of (NH4)2CO3 to the synthesis gel resulted in the formation of larger crystals with a"brick-like"morphology of size ca. 400 nm×200 nm×200 nm, thus making the size of TS-1 zeolites and silica-coated hematite match well. Moreover, the presence of (NH4)2CO3 in the synthesis system prompted the incorporation of Ti into the framework of TS-1 zeolite shell in the MFeCTS, leading to a drastic improvement in activity. Consequently, MFeCTS composite achieved 68.9% conversion of allyl chloride with very high epichlorohydrin selectivity (91.9%) and showed high catalytic activity while the maganetic properties were added to such catalysts. It has showed an excellent magnetic separation and reusability.The clay-based TS-1 catalytic composite was synthesized using hydrothermal treatment to crystallize TS-1 on clay support. Bentonite, hectorite and flurohectorite were used as the support in this process and their corresponding composites were synthesized. However, the presence of these clay minerals, particular flurohectorite, deteriorates their composites'catalytic property compared with TS-1 synthesized without additive. The reasonable interpretation for this phenomenon is the existence of basic-metal impurities such as Na+ and Li+ in the used clay. Focusing on the investigation of flurohectorite and its corresponding composite, we found the synthesized TS-1 composite using purified flurohectorite as support show excellent catalytic property. The conversion of allyl chloride was 68.4%, selectivity of epichlorohydrin was 97.3%, and the utilization efficiency of H2O2 was 95.2%. In addition to the high catalytic activity, the excellent settling efficiency of this clay-based TS-1 composite allowed it to become a reusable catalyst.
Keywords/Search Tags:TS-1, magnetic separation, clay, catalytic epoxidation, composite
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