The issue of excessive potassium permanganate value in pure methanol
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Recently, the methanol produced by our company has encountered the following issue: The synthesis capacity of methanol is maintained at 4 T/h, the inlet temperature is kept around 186 degrees, and the pressure is controlled at 50 bar. After the methanol distillation unit started operating, all other components in the analysis of pure methanol were within acceptable limits, but the permanganate value remained outside the acceptable range. We would appreciate it if experts could help analyze the cause of this problem Thank you
Should we first determine the potassium permanganate time for the pre-tower?
For the potassium permanganate test, a grade of excellence is achieved within 50 minutes, while a pass grade is obtained within 20 minutes; a failure in this test is often accompanied by a failure in terms of water solubility. In normal operations, it is necessary to raise the temperature of the pre-tower vent ； Increase the reflux flow rate of the distillation tower to control the sensitive temperature. This usually solves the problem.
It’s mainly a problem related to the distillation process. It’s necessary to properly control the temperature in the pre-distillation tower; in particular, the temperature of the second cooling stage should not drop below 40°C. Additionally, the bottom temperature of the main distillation tower should not be too high
I would like to ask: how many factors exactly can cause a failure in the potassium permanganate test? Has anyone experienced in the field studied the by-products of methanol synthesis? Which by-products have a direct impact exactly? What range of inlet temperatures in the methanol synthesis tower leads to a large number of side reactions?
Main reasons for the unsatisfactory quality of potassium permanganate: 1. Incomplete removal of light components in the pre-tower system; 2. Poor quality of the crude methanol produced; 3. Insufficient amount of extraction water used; 4. Low yield of impure alcohols; 5. Low reflux ratio, resulting in the upward movement of heavy components. Measures should be taken to address these issues
(1) The temperature control for the secondary cooling in the pre-tower is too low; it is generally maintained at (48–52), depending mainly on the quality of crude methanol. (2) Too little extraction water is used, resulting in an excess of reducing substances
The synthesis temperature depends on the active temperature of the catalyst; too high or too low a temperature can lead to side reactions. Our company uses the XNC-98 type catalyst, which is suitable for temperatures ranging from 235 to 260 degrees. If the temperature is too low, other compounds such as paraffin and Fe(CO)3 are formed. Excessively high temperatures can produce carbonyl compounds; the dehydration of ZnO yields dimethyl ether, while an excessive amount of water vapor can generate acidic substances.