The issue of low methanol pH levels in prognosis
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Our unit’s distillation section uses a three-tower distillation system, and the problem of methanol acid formation has been resolved. However, there is a problem: when the pH value of methanol is above 6.6, the acid level in the pressure tower is too high, while when the pH value of methanol is below 6.6, the acid level in the pressure tower remains within normal limits. If the pH value of methanol used for prognosis is kept at 6.6, the acidic methanol will corrode the equipment; could experts please discuss what the reason for this is?
The free acid content in crude methanol is on the high side; adjustments are made in the methanol synthesis workshop, and the distillation unit increases the lateral extraction from the lower column while adjusting the amount of alkali used.
It’s not just the effect of free acids; there are other factors as well. This article analyzes the reasons for excessive methanol acid value and the corresponding measures. You can take a look at http://www.chunmijishu.com/html/jiachunjishu/jiachunshengchangongyi/20090225/639.html
1. The main reason is the excessive amount of organic acids produced, which react with bases to form salts. This leads to decomposition in the subsequent towers; calculate the amount of alkali you are using – is it too much? Yet the pH remains low. 2. Consider where you add the alkali. The effects vary from place to place. 3. Adjusting the synthesis process can help reduce the formation of impurities appropriately.
I agree with what was said above; this phenomenon has also occurred in our factory. It is best to place the location for adding alkali before the crude alcohol feed pump, and the concentration of the alkaline solution should not be too high, as a higher concentration can have the opposite effect.
1. Adding alkali during feeding causes organic acids and alkalis to form salts, which do not evaporate from the top of the pre-tower at 80–90 degrees； It decomposes at temperatures of 100–120 degrees in the main tower; is it possible to adjust the location of the alkali solution inlet? 2. Adjust the synthesis pressure to minimize or reduce the formation of organic acids. 3. Reducing the amount of alkali added or stopping the alkali pump might yield better results.
It is mainly caused by an increase in synthetic side reactions
It’s possible to check the pH value of the crude alcohol; the high acidity in the pressure tower is caused by the reaction between alkalis and esters present in methanol, which results in the formation of acid.
1. It is essential to adjust the pH value of the methanol solution after treatment to between 7.5 and 8.5. Otherwise, if your pre-tower gets corroded and damaged, you will become a sinner. 2. Check the composition of the synthesized fresh gas to prevent the impact of trace components on the synthesis reaction. 3. Adjust the temperature of the synthesis reaction to reduce the occurrence of side reactions. Fix it quickly!