Corrosion and material selection in epichlorohydrin (ECH) production plants

In the production process of epichlorohydrin (ECH), corrosion is a significant issue due to the use of high temperatures, strong acids, and strong bases, which places high demands on material selection. 1. High-temperature chlorination of propylene and the glycerol method: – These two methods involve high temperatures and corrosive hydrogen chloride or chlorine gas, so materials with high corrosion resistance are required. Commonly used materials include stainless steel (such as 316L), Hastelloy (such as C276), titanium, and titanium alloys. These materials can effectively resist stress corrosion cracking (SCC) and localized corrosion caused by chlorides. - For any parts that are acidic or alkaline, such as those in the post-reaction treatment stage, materials with corresponding resistance to acid and alkali corrosion should also be selected. For example, equipment coated with PTFE or FEP can provide additional protection. 2. Hydrogen peroxide method: – The hydrogen peroxide method is more environmentally friendly compared to traditional methods, but it still presents corrosion issues, mainly due to the strong oxidizing properties of hydrogen peroxide. This process may use acids or bases as catalysts or pH regulators, and it also requires the equipment to have good corrosion resistance. - Due to the strong oxidizing properties of hydrogen peroxide, austenitic stainless steels (such as 304L and 316L stainless steel), as well as non-ferrous metals like titanium or titanium alloys, are generally recommended; they exhibit good resistance to corrosion caused by low concentrations of hydrogen peroxide. - For key equipment such as heat exchangers, lining or coating technologies (such as fluoroplastic coatings) should be employed to further enhance corrosion resistance and service life. In summary, whether it is the traditional high-temperature chlorination method, the glycerol method, or the new hydrogen peroxide method, factors such as the corrosive properties of the specific chemicals and the temperature and pressure of the operating environment must be taken into account when selecting materials to ensure the long-term stable operation of the equipment. .

Thank you for your answer! 1. It is understood that, whether it is the traditional chlorohydrin method and glycerol method, or the hydrogen peroxide method that is currently being used, the corrosion problem encountered is caused by HCl produced by the decomposition of chlorinated organic compounds. 2. Fluorinated coatings are not recommended for use in reactors and heat exchangers, as damage to the coating can lead to severe localized corrosion. 3. Hastelloy C276 and C22 are indeed excellent choices for resisting hydrochloric acid, but they are relatively expensive. 4. Ti material is also an excellent choice; however, it has lower wear resistance (the HB value for titanium is 100–200, while that for stainless steel is 180–400), as well as lower thermal conductivity (the thermal conductivity of titanium is λ=15.24 W/(m·K), and that of titanium alloys is about 50% lower than that of titanium). The thermal conductivity of stainless steel ranges from 20 to 60 W/(mK), and Ti is difficult to weld, with poor plasticity and workability.

Your concerns are valid; indeed, when selecting materials, it is necessary to take into account factors such as corrosion resistance, mechanical strength, thermal conductivity, and cost. 1. **Corrosion resistance**: For corrosion caused by chlorinated compounds and HCl, Hastelloy C276 and C22 are excellent choices. Although their cost is high, they help to extend the service life of equipment over the long term, reduce the frequency of repairs and replacements, and thus may lower overall operating costs. 2. **Coating issues**: You mentioned the disadvantage of fluorinated coatings, namely that damage to the coating can lead to severe localized corrosion. This is indeed a problem; it is worth considering whether other types of coating technologies can provide better corrosion resistance and mechanical stability, or exploring the possibility of using double-layer or reinforced coatings. 3. **Disadvantages of titanium**: Regarding the issues you mentioned regarding the hardness, thermal conductivity, and welding difficulty of titanium, these are indeed limitations of this material. Titanium can be considered for use in non-critical parts where high thermal conductivity or welding is not required. At the same time, it is also possible to explore the use of titanium alloys or surface modification techniques to improve its performance. 4. **Cost-efficiency trade-offs**: The final material selection decision requires a careful balance between cost and effectiveness. Although the initial investment is high, durable materials can reduce subsequent maintenance costs and downtime. At the same time, it is possible to negotiate prices with suppliers at the time of purchase or look for alternatives. 5. **Develop new materials**: In the long run, resources can be allocated to developing new materials or technologies better suited for these corrosive environments—such as improved alloy materials and composite materials—to achieve better overall performance. Finally, it is recommended to work closely with materials science experts, mechanical engineers, and experienced chemical engineering production engineers to jointly evaluate and determine the optimal material choices and design solutions. .

The hydrochloric acid corrosion using the glycerin method is still quite severe

Yes, the graphite used in the glycerin method

For hydrochloric acid resolution, tetrafluoride and graphite materials are generally used