Titanium silicalite (TS-1) catalyst in HPPO process mechanism

In modern chemical production, propylene oxide (Propylene, PO) is an important basic chemical, widely used in plastics, resins, fibers and other fields. The traditional propylene oxide production process has the problems of high energy consumption and pollution, and the green production technology represented by HPPO(Hydrogen Peroxide to Propylene Oxide) process has gradually become a research hotspot. In this process, titanium silicalite (TS-1) catalyst has attracted much attention because of its excellent catalytic performance. In this paper, the mechanism of titanium silicate molecular sieve (TS-1) in HPPO process will be analyzed in detail.

1. Titanium silicate molecular sieve (TS-1) the basic characteristics

Titanium silicate molecular sieve (TS-1) is a kind of molecular sieve material between the micro and mesoporous, with three-dimensional ordered pore structure and specific acid sites. Its chemical composition is a solid solution of titanium and silicon oxide, which has high thermal stability and hydrothermal stability. These properties make TS-1 perform well in catalytic reactions, especially in the HPPO process, where its unique structure and acidic sites provide ideal conditions for the reaction.

2. HPPO process core reaction and its catalytic requirements

The core reaction of the HPPO process is the production of propylene oxide from hydrogen peroxide (H₂ O₂) and an olefin (such as propylene) over a catalyst. The reaction is a typical heterogeneous catalytic oxidation reaction, which requires the catalyst to have the following characteristics:

• Excellent acidic sites, able to activate hydrogen peroxide and promote the reaction;
The
• pore structure is moderate, which can accommodate reactants and provide good mass transfer performance;
• Stability is high, can be in harsh conditions of long-term use.

3. Titanium silicate molecular sieve (TS-1) of the acid site and its mechanism

The acidic site of titanium silicalite is the key to its catalytic effect in HPPO process. The acidity of the TS-1 is derived from the oxidation state of the titanium, where the titanium atoms in the framework structure can provide strong acid sites. These acidic sites can interact with the hydrogen peroxide molecule to promote its decomposition to generate reactive oxygen species, thereby attacking the double bonds in the propylene molecule and ultimately generating propylene oxide.

The microporous structure of the TS-1 can restrict the free movement of the reactants, thereby improving the activity and selectivity of the reaction. This limiting effect not only helps to stabilize the transition state, but also reduces the occurrence of side reactions and improves the yield of the target product.

4. TS-1 structural stability of HPPO process

In the HPPO process, the reaction conditions generally include higher temperatures and pressures, which place higher demands on the structural stability of the catalyst. Titanium silicalite molecular sieves have good thermal and hydrothermal stability, and can maintain their structure without being destroyed under severe conditions, thereby ensuring long-term stability of catalytic performance.

The high specific surface area and pore structure of the TS-1 make it have excellent adsorption and diffusion properties, which can quickly adsorb reactants and promote their diffusion in the pores, and further improve the reaction efficiency.

5. TS-1 in HPPO process application prospect and optimization direction

Although titanium silicalite (TS-1) has performed well in the HPPO process, there is still some room for optimization in its application. For example, by adjusting the loading of titanium, optimizing the pore structure or introducing other metal components, the catalytic activity and selectivity can be further improved. Developing more environmentally friendly synthesis methods and reducing costs are also key to industrial applications.

Conclusion

The action mechanism of titanium silicalite (TS-1) in HPPO process mainly depends on its acidic sites and ordered pore structure. Its acidic sites can activate hydrogen peroxide and promote the reaction, while its structural stability ensures the long-term use of the catalyst under severe conditions. With the in-depth study of the catalytic mechanism of TS-1 and the optimization of its structure, the application prospect of titanium silicalite in HPPO process will be more broad, providing more efficient and environmentally friendly solutions for the green production of propylene oxide.