The issue of adding alkali in methanol distillation
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One purpose of adding alkali during methanol distillation is to promote the decomposition of carbonyl compounds and amine compounds. I’m not quite sure why it’s necessary to cause their decomposition; couldn’t they just be removed through the vent in the pre-tower?
There are two purposes for adding alkali: 1. To neutralize the organic acids in the crude alcohol, preventing equipment corrosion and ensuring that the acidity of the pure formic acid is within acceptable levels. (Organic acids are not necessarily light components and cannot be vented.) 2. Promotes the hydrolysis of carbonyl compounds and amines. (Carbonyl compounds can form azeotropes with methanol, and neither pre-column venting nor side-stream extraction can remove them; amines are mainly primary and secondary, highly basic, and affect the alkalinity of refined methanol.) ）
Firstly, pre-tower venting only releases a portion of the light components; the main substances involved are CO2 dissolved in methanol (the majority), methanol, ether, and other compounds. The purpose of adding alkali is, first, to react with methanol to neutralize the acidic substances produced, such as formic acid, thereby preventing these acids from damaging the equipment and ensuring that the methanol quality meets the required standards in terms of acidity. Second, it helps to promote the decomposition of carbonyl compounds, mainly esters; insufficient addition of alkali will manifest itself later during the potassium permanganate testing of the purified methanol.
I’ve learned it; the reply from the second floor was perfect