Why is the acidity level in the pure methanol storage tank too high?
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The purified methanol produced on a regular basis is sent to the storage tank for purified methanol after passing the quality tests. However, each time distillation is stopped for a period of time, the acidity level of the purified methanol in that storage tank increases and can even exceed the allowable limits. Why is this?
Has any of the seniors encountered a similar situation?
If the quality of the distilled product is satisfactory, the possible reasons for this situation are as follows: 1. Anti-corrosion treatment was applied to the tank; prolonged exposure to methanol caused the anti-corrosion layer to peel off and break down, resulting in an elevated acid value. 2. Impurities have entered or were not thoroughly cleaned before the tank was put into use. 3. Analyze the problem
It is not clear whether the exhaust from the crude methanol tank and the pure methanol tank is connected to the atmosphere or to an vent line. If it is connected to a vent line, then during normal start-up and shutdown operations, acidic gases such as carbon dioxide present in that vent line may flow into the pure methanol tank due to the high pressure there. Also, if the exhaust gases from the crude methanol tank and the refined methanol tank are combined, the acidic gases in the crude methanol tank may also enter the refined methanol tank. The best approach is to ensure that the methanol in the intermediate tank area meets the required standards at the start of the parking for maintenance, after which it can be sent to the finished product tank area; meanwhile, the liquid level in the pure methanol tank should be reduced to the lowest possible level to prevent air from contaminating the pure methanol.
Your question is quite typical: the crude methanol storage tank and the purified methanol storage tank usually share the same nitrogen sealing pipeline. When the plant is shut down for an extended period, the nitrogen sealing system stops supplying nitrogen, and the volatile light components as well as acidic gases present in the crude methanol can enter the purified methanol storage tank through this nitrogen pipeline, resulting in an increase in acidity levels in the previously qualified purified methanol. Restoring the nitrogen sealing function resolves this issue; this phenomenon has occurred in many factories. To resolve this completely, I believe it would be best to install a check valve on the nitrogen seal line at the top of the precision tank to prevent other gases from entering.
I support the views on floors 4 and 6; our factory has also encountered this phenomenon
The reason has been found: it’s due to insufficient nitrogen sealing, which allowed air to enter the tank and contaminate the product. Thank you to everyone who contributed their insights