What causes the high acidity in the pre-tower?
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For some time, the acidity level in our unit’s pre-treatment tower was consistently too high. At first, we thought it was because too little alkali was being added, so we increased the amount of alkali used; yet the acidity level continued to rise. Eventually, we reduced the amount of alkali, and the acidity level became within acceptable limits. What could be the reason for this?
I’ve never heard of something like this; could it be that the poster has made a mistake?
Crude methanol inevitably contains some esters; adding alkali to the reactor to adjust the pH value promotes the hydrolysis of these esters, resulting in the formation of certain low-boiling-point organic acids. These acids escape along with the product in the distillation tower, causing the acid value of the product to exceed the specified limits. Reduce the pressure in the tower to below 50 kPa, maintain a high level of venting and appropriate temperature, do not add too much alkali – keep the pH between 7 and 9. Also, what is the alcohol content of your crude methanol? Desalinated water can be obtained in the recirculation tank, with the alcohol content maintained at 75%–80%, and the recirculation temperature raised above 50 degrees. This issue has been discussed many times on forums; you can search for it there