In methanol synthesis, the pH of crude methanol is greater than 7, and the alkalinity of purified methanol exceeds the specified limits. What are the reasons for this, and how can it be resolved?
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I would like to ask the experts here: Our company has just completed maintenance work, and after the methanol synthesis system was put back into operation, the pH level of the crude methanol was found to be greater than 7; previously it was always below 7. As a result, the alkalinity level of the purified methanol in the distillation products exceeded the acceptable limits. May I ask: why is the pH of the crude methanol higher than 7? Is there any solution?
The information provided by the poster is a bit limited; I can only share my views. 1. Before maintenance, the synthesis system needs to be purged with nitrogen. Nitrogen should be used to maintain pressure, and blind flanges should be installed on the synthesis tower at the areas being maintained to prevent air from entering. 2. If it is the synthesis tower that is under maintenance, the synthesis catalyst must first be completely deactivated, and then fully reduced after the maintenance is completed. 3. After maintenance, the equipment and pipelines involved should be purged with nitrogen to ensure they are clean before being reconnected to the system. 4. Before connecting to the gas supply, circulation should be carried out while maintaining pressure with nitrogen
Remedial measures: 1. Analyze the crude methanol to determine if there are any changes in its composition, and to check whether any substances have leaked into it. 2. Adjustment is made through distillation and the addition of alkali, with the target pH maintained at around 7.5.
Could you elaborate on the changes that occurred before and after the maintenance?
I read a book today that said ammonia, when it leaks into a system, becomes alkaline.
If ammonia leaks into the system, it’s no longer just a matter of the pH level of the crude methanol.
Ammonia leaking into the system also produces methylamine, giving methanol a fishy odor