Formic acid corrosion
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Formaldehyde is distilled at 150°C and 0.5 MPa. Since it contains trace amounts of formic acid, which causes severe corrosion at temperatures above 100°C, 316L material is used for the pipes; leaks resulting from sand holes occur after the pipes are welded for a while, and these leaks must be repaired by welding. The condenser’s tube bundles thin out after 2 years of use, and frequent shutdowns due to pipe blockages force the replacement of the condenser. I’m not sure what alternative materials could be used in such operating conditions; I would appreciate it if those with experience in this area could share their insights. Thank you in advance.
Raise the material grade； The process strives to reduce the formic acid content
317L titanium or zinc can be used; it’s just that the price is a bit higher
Only pipes made of special materials can solve this issue, but this involves technical confidentiality and restrictions
Now, equipment is made from composite materials; for example, the all-titanium material mentioned earlier is expensive, but stainless steel substrates can be used along with spray-coated or explosion-composite titanium alloys. Can the owner’s problem be solved using equipment for spraying tetrafluoroethylene?
Composite plastic pipes can be considered for the pipelines; graphite-based condensers should be preferred wherever possible. I’ve also suffered a lot because of this! Hehe... just consider it as tuition! ! !
Can a certain amount of alkaline solution be added before formaldehyde distillation to neutralize formic acid?
We are also in the formic acid manufacturing industry; currently we use glass tubes for the condensation of formic acid, but we could consider using titanium coiled tubes instead.
1. Titanium alloy is the best choice, but it requires a significant investment. 2. Using PTFE-lined pipes is a good choice.
It is recommended to use pure titanium or titanium-molybdenum-nickel alloys; although the initial investment is somewhat high, it helps to reduce downtime for maintenance and thus improves production efficiency. Additionally, the price of titanium materials is currently relatively low as well. The density of titanium is 4.51, while the density of stainless steel is above 7.9. Moreover, due to the need to account for corrosion, stainless steel is used in thicker layers. For a condenser with the same heat exchange area, the total cost of using titanium is roughly equivalent to that of using stainless steel. On average, titanium is still the more cost-effective option.