GB467481A - Processes of removing water from aqueous aliphatic acids - Google Patents

Abstract

In the concentration of lower aliphatic acids (other than formic acid), an ester, ether, ketone, or alcohol-ester mixture is employed as entrainer having a boiling point between 25 DEG below and 30 DEG above the boiling point of the acid, and forming an azeotropic mixture with water boiling below 100 DEG C., the supply of entrainer and aqueous acid, and the heating of the column being so regulated that the lower part of the column is maintained free from entrainer and serves to rectify aqueous acid. The column may be in two parts, the upper one effecting the azeotropic distillation. The process may be effected in the one- or two-column apparatus shown in Specification 383,148 or more than two columns may be employed. Suitable entrainers are the alcohol-ester mixtures used in Specification 467,559, allyl, butyl, isobutyl, amyl, isoamyl, and crotonyl acetates, butyl, amyl, and isoamyl formates, propyl and butyl propionates, ethyl and butyl butyrates, dichloromethyl, ethyl isoamyl, allyl isoamyl, ethyl amyl, dibutyl, di-isobutyl, and di sec.-butyl ethers, chloroacetone, allyl acetone, mesityl oxide and ethyl <PICT:0467481/IV/1> propyl, methyl butyl, and dipropyl ketones. The process may be used for concentrating acetic, propionic and butyric acids or mixtures of them. In the apparatus shown, the azeotropic distillation is effected in a column 103 and simple distillation of the acid in a column 102. Most of the heat for the system is supplied by a " calendria " 104 connected with the column 102 by p pipes 106, 108. The liquid acid flows down by the pipe 106 and vaporized acid ascends by the pipe 108, but part is taken by a pipe 137 to a refining column 130 in which the concentrated acid is finally treated. Vaporized aqueous acid is supplied to the column 102 by a pipe 139 connected with vaporizers 146, 147. The vapour issues at the top of the column 102 by a pipe 161 leading to the column 103; from this latter column the azeotropic mixture passes to a condenser 164 and the condensate separates into two layers in a vessel 167, the entrainer returning to the column by an overflow 174, and pipe 177 while the aqueous layer is withdrawn at an overflow 176. The pipe 177 has a branch 179 connected through a sight-glass 181 and pipe 183 with the column 102. The overflow 176 carries the aqueous layer to a pipe 189 to provide a reflux in the column 103 or to a pipe 188 which may be connected with a flash column 191. When the process is effected in the apparatus shown in Fig. 2, of Specification 383,148, the column 41 contains an excess of water. Specification 356,787 also is referred to.ALSO:In the concentration of lower aliphatic acids such as acetic acid an entraining agent is used consisting of an ester, ether, ketone, or alcohol-ester mixture of a boiling point between 25 DEG C. lower and 30 DEG C. higher than the boiling-point of the acid, and forming an azeotropic mixture with water boiling below 100 DEG C., and the supply of entrainer and aqueous acid and the heating of the column are so regulated that the lower part of the column is maintained free from entraining agent and serves to rectify aqueous acid. The apparatus may have one, two or more columns. In the apparatus shown, the azeotropic distillation is effected in a column 103 and simple distillation in a column 102. Most of the heat for the system is supplied by a "calendria" 104 connected with the column 102 by pipes 106, 108. The liquid acid flows down by the pipe 106 and the vaporized acid ascends by the pipe 108, but part is taken by a pipe 137 to a refining column 130 in which the concentrated acid is finally treated. Vaporized aqueous acid is supplied to the column 102 by a pipe 139 connected with vaporizers 146, 147. The vapour issues at the top of the column 102 by a pipe 161 leading to the column 103; from this latter column the <PICT:0467481/III/1> azeotropic mixture passes to a condenser 164, and the condensate separates into two layers in a vessel 167, the entrainer returning to the column by an overflow 174 and pipe 177, while the aqueous layer is withdrawn at an overflow 176. The pipe 177 has a branch 179 connected through a sight-glass 181 and pipe 183 with the column 102. The overflow 176 carries the aqueous layer to a pipe 189 to provide a reflux in the column 103 or to a pipe 188 which may be connected to a flash column 191.