Patent GB-1112397-A (GB)
Title: Processing mixtures containing acetic acid
Inventor: HOHENSCHUTZ HEINZ
Filed: 1965-09-10
Abstract: Aqueous acetic acid containing up to 3% by weight of formic acid, e.g. aqueous acetic acid obtained by reacting methanol with carbon monoxide under pressure in the presence of cobalt iodide as catalyst, is purified by introducing the aqueous acetic acid into the upper section of a fractionating column wherein it is fractionated in the presence of an entrainer (ester, aldehyde or ketone) which distils over with the water and formic acid, while maintaining the lower section of the column at a temperature within 5 DEG  C. of the boiling point of acetic acid.  The following entrainers are specified: butyl formate, propyl acetate, butyl acetate, 2-ethylbutyl acetate, n-butyraldehyde, 2-ethylbutanol, 2-ethylhexanol, cyclohexylaldehyde, methyl propyl ketone, methyl ethyl ketone, diethyl ketone, and cyclopentanone.  In the case of acetic acid obtained from methanol and carbon monoxide, neutral substances formed in the course of the synthesis may be used as entrainers.  In an example, the reaction product is freed from low-boiling components and catalyst, and is then introduced in the vapour state above the 44th plate (from the base) of a 50-plate column.  The temperature gradient from the base of the column to the 25th plate is 123 DEG  to 116 DEG  C.  The vapour mixture, withdrawn from the top of the column is condensed; and the condensate separates into two layers. The upper layer is refluxed to the column; and the lower layer is mixed with the feedstock for the synthesis.  Anhydrous acetic acid, containing less than 0.02% of formic acid is withdrawn from the base of the column.ALSO:Aqueous acetic acid containing up to about 3% by weight of formic acid, e.g. aqueous acetic acid obtained by reacting methanol with carbon monoxide under pressure in the presence of cobalt iodide as catalyst, is purified by introducing the aqueous acetic acid into the upper section of a fractionating column wherein it is fractionated in the presence of an entrainer (ester aldehyde or ketone) which distils over with the water and formic acid, while maintaining the lower section of the column at a temperature within 5 DEG C. of the boiling point of acetic acid.  The following entrainers are specified:- butyl formate, propyl acetate, butyl acetate, 2-ethylbutyl acetate, n-butyraldehyde, 2-ethylbutanal, 2-ethylhexanal, cyclohexylaldehyde, methyl propyl ketone, methyl ethyl ketone, diethyl ketone, and cyclopentanone. In the case of acetic acid obtained from methanol and carbon monoxide, neutral substances formed in the course of the synthesis may be used as entrainers.  In an example, the reaction product is freed from low-boiling components and catalyst, and is then introduced in the vapour state above the 44th plate (from the base) of a 50-plate column.  The temperature gradient from the base of the column to the 25th plate is 123 DEG  to 116 DEG C.  The vapour mixture, withdrawn from the top of the column is condensed; and the condensate separates into two layers.  The upper layer is refluxed to the column; and the lower layer is mixed with the feedstock for the synthesis.  Anhydrous acetic acid, containing less than 0.02% of formic acid is withdrawn from the base of the column.