Regardless of the synthesis method the crude methanol produced contains impurities to a smaller or larger degree. The largest impurity is usually water which can be as much as 18 %. The first stage in a common two-step purification process is to remove the low boiling purifications, typically called “light ends”. This is done in a “topping column” where the low boiling compounds are boiled off to produce a mixture of methanol and water.
A refining column is used to separate water and methanol under heavy boiling. The refining column needs to be high as methanol and water is reluctant to separate easily. Good quality methanol eventually accumulates in the top of the column and is transferred to a storage tank. Water accumulates in the bottom and taken to a treatment facility before disposal.