Why Refining Methanol

As described ab%ady in Sect. 3.3.1 above, raw methanol contains not only water stemming essentially from the reaction of CO2 with H2 and, to a lesser extent, from the formation of dimethyl ether and higher alcohols according to the reactions 

The raw methanol may also contain substances which were not formed in the synthesis reactions but come from the synthesis gas or from the equipment (such as iron). 

Unlike the raw methanol produced at high pressures over a zinc-oxide/chro-mium-oxide catalyst in the past, the reaction of copper catalysts produces hardly any aldehydes or ketones. Although the fact that methyl formiate or methyl acetate can be detected, suggests that minor quantities of formic acid and acetic acid are formed as well, corrosion by formic acid in the raw methanol condensation section, which had been so much dreaded in the high-pressure synthesis processes, has not been described for low-pressure syntheses. 

The objective of methanol purification is to remove these impurities until a marketable product is obtained. Raw methanol produced over copper catalysts is today purified exclusively by way of distillation, except for a few cases in which traces of impurities (such as amines) have to be eliminated by ion exchange. 

Color Not darker than color standard No. 5 of ASTM Platinum Cobalt Scale same 

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