Preparation Of Hydrophobic TS-1 And Its Catalytic Performance For Propylene Expoxidation

The TS-1 zeolite has good catalytic oxidation activity in the preparation of propylene oxide?PO?by propylene epoxidation,which is closely related to its surface hydrophobicity.Most researchers used silane agents to modify the surface of the molecular sieve to improve its hydrophobicity,but the silyl groups on its surface are easily decomposed at high temperatures.In this paper,Adding carbon source during the synthesis of TS-1 is used to increase the hydrophobicity of TS-1.Firstly,hydrophobically modified TS-1 molecular sieves were prepared by hydrothermal synthesis and the preparation conditions were optimized.Through experiments,we chose tetrabutylorthotitanate?TBOT?as the titanium source,phenolic resin precursor as the carbon source,and tetrapropylammonium hydroxide?TPAOH?as the optimization templating agent.The hydrophobic TS-1 zeolites with different silica-to-carbon ratios?named as C-TS-1?were characterized by N₂adsorption-desorption isotherms analysis,transmission electron microscope?TEM?,scanning electron microscope?SEM?,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,contact angle measurements and so on.The characterization results showed that the synthesized C-TS-1 samples still maintained the flat microporous ordered channels and the MFI structure,while the hydrophobic property of C-TS-1 samples were significantly improved.Secondly,we studied the effect of calcination on the performance of TS-1 zeolite in N₂ and Air atmospheres during the preparation of C-TS-1 zeolite with the ratio of Si/C=5.The C-TS-1 samples calcined in different atmospheres were characterized by various characterization methods.The porous structure analysis and TEM characterization results showed that the C-TS-1 zeolites calcined in different atmospheres still maintained the microporous ordered structure with an average pore size of 0.55 nm.The results of XRD and FT-IR characterizations indicated that the C-TS-1 molecular sieves calcined in different atmospheres retained the MFI structure.The contact angle measurement showed that the hydrophobicity of the C-TS-1samples calcined under N₂ atmosphere were higher than that of the C-TS-1 calcined under the Air atmosphere.The thermogravimetric analysis?TGA?showed that the thermal stability of the C-TS-1 samples calcined in different atmospheres between0°C and 550°C were almost the same.Therefore,the catalyst was prepared by calcination in N₂ atmosphere.Finally,the effects of C-TS-1 zeolites with different silica-to-carbon ratios on the catalytic activity of propylene epoxidation were investigated.The results showed that the C-TS-1 samples with Si/C=5?N₂?had better structure properties and catalytic activities.The C-TS-1 samples with Si/C=5?N₂?as catalyst were used to investigate the effect of reaction temperature and reaction pressure on the epoxidation activity of propylene.The results showed that when the stirring speed was 840 r·min^-1,the reaction time was 1.5 h,the pressure of reaction was 0.4 MPa,and the temperature of reaction was 57°C,the catalytic activity of the C-TS-1 samples were better.The catalytic activity was higher than that of the TS-1 zeolite without carbon.The conversion of H₂O₂ reached 62.79%,the selectivity of PO was 100%,and the concentration of PO in the reaction solution reached 0.437 mol·L^-1.The research content of this topic demonstrated the feasibility of structuring high catalytic activity of hydrophobic TS-1 for catalyzing the epoxidation of propylene,which provided a theoretical basis for the industrial application of new high-efficiency hydrophobic molecular sieves.