Patent GB-456921-A (GB)
Title: Improvements in or relating to the concentration of acetic acid
IPC: C07C51/48
Filed: 1935-07-13
Abstract: In the concentration of aqueous solutions of acetic acid by combining, in series or in parallel, treatment with a solvent in liquid phase and treatment in vapour phase employing in the evaporation of the extracting solvent the heat evolved in the condensation of the product of the vapour phase treatment, the extracting solvent used is a liquid which forms azeotropic mixtures with water from which the water can separate at least partially as a layer after condensation of the vapour.  In the series treatment, the solvent extraction follows the vapour phase operation.  Suitable extracting solvents comprise ethyl acetate, methyl propionate, isopropyl and propyl ethers.  Suitable water carriers for the vapour phase treatment comprise butyl acetate, mesityl oxide, wood oils, butyl alcohol, amyl alcohols and ethyl butyrate.  In the parallel method, part of the acetic acid solution is treated with ethyl acetate in an extraction apparatus 13 and the remainder after vaporizing in a heater 4 is distilled in the presence of butyl acetate in a column 6.  Acid, mainly water-free, from the latter is concentrated in a column 8.  The acid extract from the extractor 13 is distilled in a column 22 provided with a heater 23 supplied with the vapours of butyl acetate and steam leaving the dehydrating <PICT:0456921/IV/1> <PICT:0456921/IV/2> column 6.  Ethyl acetate vapour and steam driven off separate in a florentine 15, the ester being returned to the extracting apparatus.  The acid obtained in the column 22 mixed with ester and water is distilled in a column 29, the ester vapour and steam being returned to the column 22 through pipe line 31.  The butyl acetate and steam condensed in the heater 23 are separated in a florentine 36, the ester being returned to the dehydrating column 6.  Concentrated acid from the column 29 is mixed with that from column 8.  In the series method of working, crude pyroligneous acid from a supply vessel 41, Fig. 2, is treated in a preliminary set of apparatus 44, 45, 47, 48, 50, 54 to remove methyl alcohol, vaporized in a heater 57 and the vapours supplied to a dehydration column 6<1> supplied in counter current with wood oils of B.P. 110--120 DEG  C., and forming with water an azeotropic mixture of B.P. 92 DEG  C.  After this vapour phase treatment, the whole of the acid, still containing some water, is supplied through a pipe 59 to a container 1<1> superimposed above a liquid extraction column 13<1> of the counter-current type.  The liquid solvent, methyl propionate, is supplied to the base of this column and the solvent saturated with acid is discharged through a pipe 21<1> to a heat-exchanger 23<1> for indirect heating by the vapours of the constant boiling mixture evolved from the dehydration column 6<1>. The vapours of methyl propionate, acetic acid and water from the heat-exchanger separate in a column 22<1>, the ternary liquid mixture flowing to a column 29<1> and the vapours of solvent and water to a condenser 19<1>.  The solvent from a florentine 15<1> is re-cycled to the extraction column 13<1>.  Concentrated acid is drawn off from the column 29<1> at 32<1>.  The solvent for the vapour phase treatment is recovered as in the parallel method of working.  In a modification of the latter process, most of the plant of the series method of working is used.  Part of the original acid is supplied to the liquid extraction column 13<1> and part as vapour to the dehydration column 6<1>.  The concentrated acid from the former is obtained as before. The heavy oils saturated with acid flow from the column 6<1> to a separating column wherein the acid is removed as vapour and the solvent re-cycled to the column 6<1>.  Specifications 399,529, and 414,558, [Group II], are referred to.ALSO:In the concentration of aqueous solutions of acetic acid by combining in series or in parallel, treatment with a solvent in liquid phase and treatment in vapour phase employing in the evaporation of the extracting solvent <PICT:0456921/III/1> <PICT:0456921/III/2> the heat evolved in the condensation of the product of the vapour phase treatment, the extracting solvent used is a liquid which forms azeotropic mixtures with water from which the water can separate at least partially as a layer after condensation of the vapour.  In the series treatment, the solvent extraction follows the vapour phase operation.  Suitable extracting solvents comprise ethyl acetate, methyl propionate, isopropyl, and propyl ethers. Suitable water carriers for the vapour phase treatment comprise butyl acetate, mesityl oxide, wood oils, butyl alcohol, amyl alcohols and ethyl butyrate.  In the parallel method part of the acetic acid solution is treated with ethyl acetate in an extraction apparatus 13 and the remainder after vaporizing in a heater 4 is distilled in the presence of butyl acetate in a column 6. Acid, mainly water-free, from the latter is concentrated in a column 8.  The acid extract from the extractor 13 is distilled in a column 22 provided with a heater 23 supplied with the vapours of butyl acetate and steam leaving the dehydrating column 6.  Ethyl acetate vapour and steam driven off separate in a florentine 15, the ester being returned to the extracting apparatus.  The acid obtained in the column 22 mixed with ester and water is distilled in a column 29, the ester vapour and steam being returned to the column 22 through pipe line 31.  The butyl acetate and steam condensed in the heater 23 are separated in a florentine 36, the ester being returned to the dehydrating column 5.  Concentrated acid from the column 29 is mixed with that from column 8.  In the series method of working, crude pyroligneous acid from a supply vessel 41, Fig. 2, is treated in a preliminary set of apparatus 44, 45, 47, 48, 50, 54 to remove methyl alcohol, vaporized in a heater 57 and the vapours supplied to a dehydration column 6<1> supplied in counter current with wood oils of B.P. 110-120 DEG  C., and forming with water an azeotropic mixture of B.P. 92 DEG  C.  After this vapour phase treatment, the whole of the acid, still containing some water, is supplied through a pipe 59 to a container 1<1> superimposed above a liquid extraction column 13<1> of the countercurrent type.  The liquid solvent, methyl propionate, is supplied to the base of this column and the solvent saturated with acid is discharged through a pipe 21<1> to a heat exchanger 23<1> for indirect heating by the vapours of the constant boiling mixture evolved from the dehydration column 6<1>.  The vapours of methyl propionate, acetic acid and water from the heat-exchanger separate in a column 22<1>, the ternary liquid mixture flowing to a column 29<1> and the vapours of solvent and water to a condenser 19<1>.  The solvent from a florentine 15<1> is re-cycled to the extraction column 13<1>.  Concentrated acid is drawn off from the column 29<1> at 32<1>.  The solvent for the vapour phase treatment is recovered as in the parallel method of working.  In a modification of the latter process, most of the plant of the series method of working is used. Part of the original acid is supplied to the liquid extraction column 13<1> and part as vapour to the dehydration column 6<1>.  The concentrated acid from the former is obtained as before.  The heavy oils saturated with acid flow from the column 6<1> to a separating column wherein the acid is removed as vapour and the solvent re-cycled to the column 6<1>.  Specifications 399,529, [Group IV], and 414,558, [Group II], are referred to.