GB623991A - Improvements in or relating to a process for the dehydration of acetic acid and other lower fatty acids - Google Patents

Abstract

An aqueous solution of an aliphatic acid having not more than three carbon atoms in the molecule is extracted with a water-immiscible organic solvent, which has a boiling point above that of the acid but below 150 DEG C., using an <PICT:0623991/III/1> amount in excess of that required to remove, azeotropically, the water contained in the solvent extract; the extract is distilled to remove this water, and finally the dehydrated acid is distilled from the residual solvent, the latter being returned to the extraction stage. In an example, an aqueous solution containing 28 per cent of acetic acid was fed from tank 11 into extractor 10 where it was extracted countercurrently with n-amyl acetate, the ratio of solvent to aqueous acid being 4 to 1. The extract passing from the top of the extractor through line 14, was distilled in column 30. The vapours were condensed in condenser 32 and the condensate separated into an aqueous layer and a solvent layer in decanter 33. The former contained some acetic acid and was returned to the extractor through line 15. The mixture of amyl acetate and acetic acid passing from the base of column 30 was distilled in column 40 from which anhydrous acetic acid was obtained as head product. The amyl acetate, stripped of acid, was returned to extractor 10 by way of line 44 and tank 12. The amyl acetate in the water passing out of the base of the extractor was recovered using stripping column 20, condenser 22 and decanter 23. Other examples describe the use of methyl amyl ketone, and of a mixture of amyl acetate and amyl alcohol, as solvents. Butyl acetate may also be used, but in this case the acetic acid is removed from the anhydrous extract by azeotropic distillation using as entrainer toluene, heptane, octane or a narrow petroleum cut. The acetic acid is separated from the hydrocarbon in the homogeneous condensate by adding a small amount of water; it is then passed to another column for final dehydration. Formic, propionic and acrylic acids may be treated by the process; and it may also be used for the recovery of acids from cellulosic and other liquids containing non-volatile impurities. In the latter case, a multiple effect pre-evaporator may be used to separate the solids. The vapours of the dilute acids may be extracted instead of the liquid. Specification 312,046, [Class 32], is referred to.ALSO:An aqueous solution of an aliphatic acid having not more than three carbon atoms in the molecule is extracted with a water-immiscible organic solvent, which has a boiling point above that of the acid but below 150 DEG C., using an <PICT:0623991/IV (b)/1> amount in excess of that required to remove, azeotropically, the water contained in the solvent extract; the extract is distilled to remove this water, and finally, the dehydrated acid is distilled from the residual solvent, the latter being returned to the extraction stage. In an example, an aqueous solution containing 28 per cent of acetic acid was fed from tank 11 into extractor 10 where it was extracted counter-currently with n-amyl acetate, the ratio of solvent to aqueous acid being 4 to 1. The extract passing from the top of the extractor through line 14, was distilled in column 30. The vapours were condensed in condenser 32 and the condensate separated into an aqueous layer and a solvent layer in decanter 33. The former contained some acetic acid and was returned to the extractor through line 15. The mixture of amyl acetate and acetic acid passing from the base of column 30 was distilled in column 40 from which anhydrous acetic acid was obtained as head product. The amyl acetate, stripped of acid, was returned to extractor 10 by way of line 44 and tank 12. The amyl acetate in the water passing out of the base of the extractor was recovered using stripping column 20, condenser 22 and decanter 23. Other examples describe the use of methyl amyl ketone, and of a mixture of amyl acetate and amyl alcohol, as solvents. Butyl acetate may also be used, but in this case the acetic acid is removed from the anhydrous extract by azeotropic distillation using as entrainer toluene, heptane, octane, or a narrow petroleum cut. The acetic acid is separated from the hydrocarbon in the homogeneous condensate by adding a small amount of water; it is then passed to another column for final dehydration. Formic, propionic and acrylic acids may be treated by the process; and it may also be used for the recovery of acids from cellulosic and other liquids containing non-volatile impurities. The vapours of the dilute acids may be extracted instead of the liquid. Specification 312,046, [Class 2 (iii)], is referred to.