I would like to learn the key impurities in methanol. Naturally, I would think the methanol synthesis catalyst being the culprit. Pls share your thoughts and experience or expertise in this regard.
With kind regards,
Yun-feng
There are industry recognized specifications for methanol (e.g. Grade A; Grade AA; IMPCA) [For example, see http://www.methanol.org/wp-content/uploads/2016/07/IMPCA-Ref-Spec-08-December-2015.pdf ; http://kaltimmethanol.com/product.html ] These specifications have limits for chloride, sulphur, acidity, iron and non-volatile matter that should include inorganic compounds. Note that these are specifications (maximum allowed levels) and typical levels may be lower.
I have some further thoughts based on your question. After the methanol synthesis loop, the crude methanol goes to the distillation section. This mainly separates H2O from the MeOH but also removes light end by-products and heavies such as fusel oil. Therefore, any inorganic impurities passing to the final product methanol must partition into the methanol phase.
Methsyn catalyst does not tend to leach material into the gas phase product gas and any fines from catalyst degradation over time would probably be removed in filters of similar.
Although there are specifications on Cl and S, the methsyn catalyst is very good at capturing these catalyst poisons and so would not let these pass through. The methanol specification reflects what is tolerable to downstream users rather than the upstream process capability. It must also reflect possible contamination during storage and transport.
The method of methanol synthesis, and the earlier preparation of the substrates, excludes the appearance of significant amounts of impurities in the final product. Of course, there may be small amounts of by-products, e.g. higher alcohols, during the synthesis, but they are easy to remove.
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