The pH value issue at the bottom of the distillation pre-column
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In our company’s distillation system, the pH at the bottom of the pre-column is always maintained between 11 and 12; if it is too low, the quality of the product suffers. I’ve been to several methanol plants where the level is kept between 7 and 9; could it be that there are too many reducing substances in the crude methanol? Are there any other reasons? Fellow colleagues, please share your opinions
The purpose is to prevent corrosion of the equipment in the methanol liquid caused by an excessive amount of acidic substances such as formic acid.
Could you tell me what’s wrong with the product – is it the acid value, oxidation time, or something else?
It’s unlikely to be rich in amine compounds or alkaline substances; our normal pH is around 9
A low pH value results in insufficient water solubility of potassium manganate, which affects the experiments
It is generally kept between 7 and 9; it isn’t controlled at such a high level. Controlling the pH value is mainly to prevent corrosion of the equipment, with it usually maintained around 7-9, so the acid value remains low~~
Reply to 1# YKQB: I suggest that you stop adding alkali for now, and observe the situation including the pH value and the quality of the product. Then gradually add alkali again, making sure to monitor the pH value at all times; it’s sufficient for it to be slightly alkaline – a higher pH level leads to waste of alkali.
Reply 1# YKQB: Do you produce gas from coal? Still. . .
The pH value at the bottom of the tower has no relation to product quality; the addition of alkali is intended to prevent trace acidic substances in crude methanol from corroding the internal components of the tower and to facilitate the decomposition of amines and carbonyl compounds. It could be due to operational disturbances in the atmospheric tower and the pressurized tower, which may result in substandard product output from the pressurized tower.
We produce gas from coal; currently the pH value is 11–12. The results of other tests such as those involving potassium permanganate, water solubility, acidity, and carbonyl compounds are all within the acceptable range for high-quality products