Immobilization Of Chiral Salen Catalysts Onto Membranes And Catalytic Performances Of The Heterogeneous Catalysts

Chiral salen catalysts are of demonstrated activities and selectivities in the asymmetric catalytic reaction, which can supply important building blocks for synthesizing a variety of valuable chiral compounds such as pharmaceuticals and agrochemicals. Since it is difficult to separate the catalysts from the homogeneous reaction system, many works focused on the immobilization of the salen catalysts. But the reported immobilization methods still exit the following problems:(1) the immobilized catalysts still need to be separated for recycling, however, the separation of the catalysts in suspension is also a challenge in industry field applications, especially for ultrafine particles.(2) the supported catalysts cannot be distributed homogeneously in the reaction system, which has an adverse influence on mass transfer.(3) powder catalysts were produced due to the collision of the heterogeneous catalysts, and it is difficult to recover the broken catalysts, which leads to the leaching of salen catalysts. Immobilizing catalyst onto porous membranes and constructing catalytic membrane reactor have been proposed in this thesis in order to resolve the above problems. This method can realize reusing the catalyst without separation operation, and enforcing the mass transfer of the reaction system by reducing mass transfer resistance in the confined space in mesoporous and microprous supports through recycling the reaction mixture.First, mono-chlorolymethyl-salen-Mn( â…¢), tetra-tert-butyl-salen-Mn( â…¢) and di-chlorolymethyl-salen-Co(â…¢) catalysts were synthesis from the raw metarials such as 2-tert-butylphenol, 2,4-di-tert-butylphenol, and(1R,2R)-(-)- cyclohexanediamine. The structures of the three catalysts were tested by FI-IR spectroscopy analysis. The influences of reaction time, mol ratio of catalyst, dose of 3-chloroperbenzoic acid(m-CPBA) and solvent on catalytic performances were discussed when using mono-chlorolymethyl-salen-Mn(â…¢) to catalyzing the asymmetric epoxidation of styrene and indene. The mol ratio of catalyst, dose of water and reaction temperature were discussed when using di-chlorolymethyl-salen-Co(â…¢) to catalyze the hydrolytic kinetic resolution(HKR) of racemic epichlorohydrin.Amino groups were induced onto ceramic membranes, and mono-chlorolymethyl-salen-Mn(â…¢) catalyst was immobilized onto membranes through chemical bonding of the amion groups and chlorolymethyl groups of the salen catalyst. Then the catalytic membrane reactor was constructed. FT-IR spectroscopy and X-ray photoelectron spectroscopy(XPS) were used to characterize the ceramic membrane. The results suggested that amino groups and salen catalyst were introduced onto ceramic membranes. In compared with homogeneous catalyst, mono-chlorolymethyl-salen-Mn(â…¢) membrane reactor can improve the catalytic efficiency of the catalyst in catalyzing the epoxidation of styrene. For the membrane reactor, the conversion rate of styrene was 31.7% and the enantioselectivity was 39.9% for 9 hours epoxidation reaction, while the dose of styrene was 4 mmol and the mol ratio of catalyst was 0.129% compared with styrene. In contrast to membrane catalyst in segments, membrane reactor can improve the catalytic properties of the catalysts, and can reuse the catalyst without separation. Tetra-tert-butyl-salen-Mn(â…¢) catalyst was immobilized onto ceramic membranes though coordinate bond of amino group and metal center. The comparison of the results of asymmetric epoxidation of styrene catalyzed by the tetra-tert-butyl-salen-Mn( â…¢) membrane reactor and mono-chlorolymethyl-salen-Mn(â…¢) membrane reactor suggested that, the way of immobilizing catalyst through the groups of catalyst ligand on to membrane is better than through coordinate bond of amino group and metal center.Based on the analysis above, di-chlorolymethyl-salen-Co( â…¢) catalyst was immobilized onto ceramic membrane under the proper reaction conditions. Salen-Co(â…¢) membrane reactor was constructed and used in catalyzing the HKR of racemic epichlorohydrin for testing the catalytic performances. Similar catalytic properities with the conresponding homogeneous catalyst were obtained for the membrane catalyst in reactor under the same reaction conditions. The membrane was stable and can be reused more than three times. It was proved that immobilizing catalyst onto ceramic membrane and constructing membrane reactor are also possible for salen-Co(â…¢) catalyst.Based on the studying of ceramic membrane reactor, in order to increase the immobilization degree through increasing the membrane surface area, symmetrical microporous carbon membranes were chosen for immobilizing mono-chlorolymethyl-salen-Mn(â…¢) catalyst. Amion groups were induced onto carbon membrane through oxidation, chlorixation, and amination reactions. Then mono-chlorolymethyl-salen-Mn(â…¢) catalyst were immobilized on to the membranes through chemical bonding of amino and chlorlmethyl groups. Flat sheet membrane reactor and tublar membrane reactor were constructed. Scanning electron microscope(SEM) and XPS analysis were used to characterize the changes of the membrane after grafting and immobilizing reactions. When the thickness of the flat sheet membrane was 4 mm, the conversion rate and ee value for catalyzing epoxidation of styrene were 58.7% and 35.6%, respectively. For the tublar membrane reactor packing with seven membrane tubes, the conversion rate and ee value for catalyzing epoxidation of styrene reached up to 58.7% and 35.6%, respectively. In compared with ceramic membrane reactor, carbon membrane can obtain higher conversion rate due to the higher immobilization degree, but ratively low ee value which can be ascribed to that the pore size of carbon membrane was larger and the structure of carbon membrane was nonuniform. But the chemical bonding of salen-Mn(â…¢) catalyst onto the carbon membranes is more stable than that onto the ceramic membrane, which was proved by the results of ICP-AES.