Urgent! ! ! Conditions for trichloromethane to corrode stainless steel (distillation separation of trichloromethane and DMF)
Thread Content
The company is carrying out the separation of trichloromethane and DMF, with distillation planned as the method for this separation. However, our service provider informed us that during the distillation process, the temperature at the bottom of the reactor is between 120 and 130°C. Trichloromethane decomposes to release chloride ions, which directly corrode stainless steel. He encountered a pilot-scale stainless steel tower in which the bottom of the reactor and the pipes were corroded through within just three days. We attach great importance to this issue, as our original plan was to use stainless steel distillation towers. Therefore, we have also looked up a lot of information these past few days. However, there is very little information on this topic that mentions such a situation. Consulting the solvent manual, it does not mention that trichloromethane decomposes at this temperature. Information found online includes: 1. Trichloromethane does not corrode stainless steel ； 2. Halogenated hydrocarbons cause severe corrosion of stainless steel and other metal equipment ； 3. The water content in trichloromethane has a significant impact on the corrosion of stainless steel equipment; when the water content is very low, it hardly causes any corrosion to such equipment. However, in cases with a high water content, the corrosion of stainless steel equipment is quite severe. But I really can’t tell what’s true and what’s false. I would like to ask all fellow sailors: have you ever encountered such a situation? What is the mechanism? And by what methods and means was this problem solved? Thank you!
Could corrosion-resistant materials such as enamel, graphite, or fluoropolymer-lined materials be considered? Trichloromethane certainly has a tendency to hydrolyze, especially at higher temperatures, and it is not unusual for it to corrode stainless steel.
The DMF unit in my classmate’s company was not performing well, so they hired Shanghai Kefukai Company to conduct an assessment and carry out modifications; after that, the performance improved significantly. You can contact them to ask about issues in this regard.
If it is just chloride ions, duplex steel could be considered; duplex steel exhibits good corrosion resistance to chloride ions. The specific grade to use depends on the actual chloride ion concentration. After such decomposition, water is present, which can easily lead to the formation of hydrochloric acid. Meanwhile, chloride ions cause significant intergranular corrosion in stainless steel; therefore, rapid corrosion is something that happens quite naturally. Stainless steel cannot withstand an environment consisting of both chloride ions and hydrochloric acid. It is recommended to determine the moisture content after decomposition as well as the approximate chloride ion concentration; based on this, decide whether to use duplex steel or the newer type of super duplex steel. If that doesn’t work, titanium materials may need to be considered.
System separation is easy to achieve; it’s just a matter of selecting the right material for the equipment. This material is the one after extraction; isn’t separation of the extractant from the product required?
For our chloroform distillation tower, plain carbon steel is sufficient. I’m not very knowledgeable on this topic; I’ve never heard of trichloromethane decomposing chlorine. Trichloromethane simply hydrolyzes in the presence of water to produce acids that cause corrosion. Since an azeotrope is also formed as a result, the top part of the tower is the first to be damaged. It should be fine to use it for 5 or 6 years, as long as the moisture content in the material is only 200–300 ppm
Has the issue of equipment corrosion been resolved now? Our company is also carrying out chloroform distillation recently; with a high water content, we’re not sure which material to choose.
There are still no materials that can withstand it yet; efficiency and precision are required