Gas-phase Propylene Epoxidation Over Ag/TS-1 Prepared In Microemulsion

Propylene oxide (PO) is a kind of very important chemical feedstock in organic chemical engineering. It is widely used for the producing of polyurethane, surfactant and resins. Today, propylene oxide is mainly manufactured via chlorohydrin process or Halcon process. However, the pollutions to the environments in the former process and high investments & lots of byproducts in the latter are the main drawbacks of the two industrial processes. Gas phase propylene epoxidation for the production of PO attracts much interest for its friendly to the environments and mild operation conditions.In this article, gas-phase propylene epoxidation with hydrogen and air feedstock catalyzed by Ag/TS-1 prepared by microemulsion method is investigated. Firstly, the Ag/TS-1 is synthesized in a AOT/n-heptane/K.2CO3 (aq) /AgNO3 (aq) double microemulsion system. The effects of surfactant to water molar ratio on Ag particle size, size distribution and catalytic performance is discussed. Also, we prepared Ag/TS-1 by hydrazine reduction to single microemulsion stystem consists of AOT/n-hepatane/AgNO3 (aq). Parameters in the preparation process like the stirring speed, Ag loading, CO2 producing and calcinations temperature have much effects on propylene conversion and PO selectivity. A brief postulation of the effects of the physical loading situation of Ag particles may have on propylene epoxidation is discussed. We come to the following conclusion:1. Ag/TS-1 prepared by microemulsion method exhibits good performance to gas-phase propylene epoxidation at relative low reaction temperature of 100℃. The Ag/TS-1 prepared by microemusion has a narrow particle size distribution and the optimal reaction temperature can decreased 50℃ compared with that prepared by deposition-precipitation method.2. Ag/TS-1 of different Ag particles can be acquired through the adjustment of water to surfactant ratio. These catalysts exhibited different performance to propylene epoxidation. The Ag particle size has much effect on propylene epoxidation. Small Ag particles may decrease the reaction temperature, but does not greatly affect the conversion of propylene. Large Ag particles exhibit equivalent catalytic activity at relative high reaction temperature.3. The catalytic performance of Ag/TS-1 prepared by microemulsion method is sensitive to the temperature change from 110 to 130℃. At temperature lower than 110℃, PO is acquired with high selectivity, while at temperature higher than 130℃, CO2 is high selectively acquired.4. Stirring speed greatly affects the Ag particle size when Ag/TS-1 is prepared by single microemulsion method. High stirring speed leads to large Ag particles and low stirring speed leads to small Ag particles.5. 0.5 wt%Ag/TS-1 and 1.0 wt%Ag/TS-1 calcined at 540 ℃ exhibit good catalytic performance to propylene epoxidation, while on the catalyst of 2.0 wt%Ag/TS-1 and 3.0 wt%Ag/TS-1, propylene mainly converted to CO2.6. Lots of CO2 producing leads to lots of heat, and the catalyst bed temperature rise accordingly. The temperature increase in turn promotes the produce of more CO2.7. Ag particles is embedded in TS-1 with different depth, and the depth may affect the catalytic activity of Ag/TS-1. The calcinations temperature may affect the depth of embedding.