Problems with methanol distillation for water extraction
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I would like to ask fellow sailors: why is an extraction water process generally not used in the distillation steps of the natural gas-based methanol production process, whereas it is employed in both the coke oven gas-based and coal-based methanol production processes? I would appreciate some guidance from an expert.
It is necessary to check the water content in crude methanol; if the water content is high, then there is no need to add extraction water
What was said on the second floor is correct; moreover, when coal or coke oven gas is used as a raw material, it contains many impurities, and adding water can change the properties of some of the azeotrope components.
Another reason is that in the production of methanol from natural gas, water from the synthesis process replaces the extraction water
Distillation of methanol from natural gas does not require extraction water because, 1) the moisture content is higher than that in methanol produced from coke oven gas, with an alcohol content of around 79%, and 2) natural gas has fewer components, resulting in fewer side reactions during synthesis and thus fewer impurities in the crude methanol； In the case of methanol production from coke oven gas, the methanol content is 81-85%, and the crude methanol contains many impurities; adding extraction water is used primarily to change the boiling point of the azeotic mixture, thereby enabling the decomposition of the azeotropes ； If the amount of water used for extraction is low, the water solubility of pure methanol will not meet the requirements.
The moisture content at the bottom of the pre-tower is 15%–20%; adding a moderate amount is sufficient. Adding more has little effect – it’s not only wasteful but can also have the opposite effect
Natural gas used in methanol production has a high water content, so no water needs to be used as an extractant.
It is necessary to check the water content of crude methanol; if the water content is high, then there is no need to add extraction water. The methanol content obtained from coal or coke oven gas can reach 95% to 97%, whereas that from natural gas is only 77% to 86%
Whether to add extraction water depends mainly on the alcohol content of the crude methanol, as well as on the quality of this crude methanol. As long as the distillation process is effective and the quality of the refined methanol is satisfactory, it is not necessary to add extraction water; this also helps save energy. The decision should be based on the actual production conditions.