Patent GB-596217-A (GB)
Title: Improvements in or relating to the dehydration of acetic acid
IPC: C07C51/46
Filed: 1941-01-10
Abstract: <PICT:0596217/III/1> The process of dehydrating aqueous acetic acid or mixtures of acetic acid and acetic anhydride according to the parent Specification, in which the solutions are dehydrated by distillation in presence of a mixed entrainer comprising acetic ester as principal constituent and a supplementary entrainer insoluble in water and capable of forming an azeotropic mixture with water and the ester entrainer, e.g., aliphatic or aromatic hydrocarbons, is applied to solutions rich in acetic ester, the same ester being used as the principal entrainer and an amount thereof equivalent to that introduced in the initial solution being continuously withdrawn from the distillation column, preferably from a baffle plate in the column constituting a reserve of liquid.  This baffle plate may be constructed as described in French Specification 832,892.  The distillation is carried out in a column A provided with condenser B and separator C and charged as in the parent Specification with ethyl acetate and a volatile oil of boiling point 84-85 DEG C.  A mixture comprising 82 per cent. ethyl acetate, 10 per cent. acetic acid and 8 per cent. water is fed in through line 1.  A quantity of liquid regulated by valve 61 to correspond with the amount of ethyl acetate introduced into the column is withdrawn through line 6 and cooler H and decanted in separator D, the layers formed being distilled in columns E, F to recover overhead binary mixtures of ethyl ecetate and water, which are returned to decanter D, and at the bottom of the columns water and ethyl acetate respectively.  Anhydrous acetic acid is recovered at the bottom of the main column through pipe 5.  When a compound, e.g., cyclohexane which forms a ternary azeotrope with the water and ester is used, the overhead is returned to the condenser B by the main column.  Specification 290,992, [Class 2 (iii)], is referred to.ALSO:The process for dehydrating acetic acid solutions, which may contain anhydride, using a mixture of entrainers which is placed initially in the column and containing an acetic ester and a supplementary entrainer, insoluble in water and capable of forming with water or with water and the ester entrainer, a heteroazeotrope of lower boiling point than the ester-water azeotrope, is applied to solutions rich in acetic ester, the same ester being used as a constituent of the mixed entrainer, and an amount of said ester equivalent to that introduced in the initial solution being continuously withdrawn from the column in a zone containing the ester only.  This withdrawal may be effected on a baffle plate of increased capacity constituting a reserve of liquid.  This hydrated ester may be used directly for extracting acetic acid from solutions, or dehydrated.  A special baffle plate as described in French Specification 832,892 may be provided to permit decanting of the liquid within the column itself to give a product very rich in ester. In examples: (1) the column is charged with ethyl acetate and an oil of boiling point 84-85 DEG  C., and a mixture resulting from the extraction of dilute acetic acid with ethyl acetate is introduced mid-way, above which point two zones, the lower ethyl acetate and the upper the oil, form.  Water coming overhead is separated by decantation and eliminated. Liquid equal to the ethyl acetate in the feed mixture is withdrawn from the ethyl acetate zone, cooled and decanted, and returned to the extraction.  Anhydrous acetic acid is collected at the base of the column; (2) a mixture of ethyl acetate, acetic acid and anhydride, and water is introduced into the column, and liquid withdrawn from the ester zone as in (1), cooled and decanted to separate an ester and an aqueous layer which are treated separately in two columns yielding ester and water respectively as bottoms, and an ester-water azeotrope as overhead which is returned to the decanter or, when a compound forming a ternary azeotrope with water and ester is used such as cyclohexane, to the condenser of the main column.  Specification 290,992, [Class 2 (iii)], also is referred to.