Improvements in and relating to the concentration of aqueous acetic acid solutions by distillation

摘要

PICT:0699358/III/1 Aqueous solutions of acetic acid are concentrated by distilling them in the presence of one of the following solvents: - methoxy triglycol acetate, diglycol diacetate, methoxy diglycol acetate, ethoxy triglycol acetate, dimethoxy triglycol, dimethoxy diglycol. Water is obtained as distillate leaving a mixture of solvent and concentrated acid, which is then separated by fractional distillation, preferably under reduced pressure. The molecular ratio of solvent to the water present in the solution is preferably within the range from 1:1 to 5:1. The process is particularly applicable to the concentration of aqueous solutions containing up to 15 per cent of acetic acid where the usual azeotropic distillation processes are uneconomical. A 10 per cent aqueous acetic acid solution was passed continuously through pipe 3 into distillation column 1 heated by boiler 2 and diglycol diacetate (1 part by weight per part of aqueous acid) was introduced into the upper part of the column through pipe 4. The boiler 2 was maintained at a temperature of 120 DEG C, and the top of the column at 100 DEG C. The vapours from the head of the column were p passed to condenser 6, and water containing only 0.2 per cent of acetic acid was obtained as condensate. A mixture containing 9.2 per cent acetic acid, 89.4 per cent diglycol diacetate and 1.4 per cent water collected in boiler 2, and was passed through pipe 8 into column 9. The boiler 10 of column 9 was maintained at 160 DEG C, and the pressure within the column was maintained at 25 mm. Hg. by vacuum pump 14. A mixture containing 87 per cent of acetic acid and 13 per cent water was condensed in condenser 12, and collected in receiver 15. A mixture of 99.5 per cent of diglycol acetate and 0.5 per cent of acetic acid collected in boiler 10, and was returned to column 1 via pipe 4. The second Provisional Specification also refers to the use of diethoxy triglycol as solvent. Specifications 652,844, [Group IV(a)], and 670,751 are referred to.