GB603824A - Improvements in or relating to the manufacture of acetonitrile - Google Patents

Abstract

Aqueous acetonitrile containing acetone is purified by adding an entrainer liquid (e.g. benzene or trichlorethylene), which forms with acetonitrile and water a ternary azeotrope boiling at a lower temperature than does acetonitrile, distilling off azeotrope and acetone from the acetonitrile (which is withdrawn from the system), treating the condensed vapours (e.g. in a mixing vessel or a counter-current washer) with a volume of water equal to 1/2 to 5 times (preferably 1 1/2 to 2 1/2 times) that of the water already present so as to form aqueous and entrainer liquid layers, distilling off the acetone from the aqueous layer and leading the residual aqueous acetonitrile to the dehydrating still preferably after distilling off some water to leave an acetonitrile-water binary azeotrope. The process may be applied <PICT:0603824/III/1> to crude acetonitrile prepared by catalytic dehydration of ammonium acetate, in which case the crude acetonitrile is fed to a stripping column where free ammonia is absorbed in acid and high-boiling fractions are removed, the overheads consisting of acetone-containing water-acetonitrile binary azeotrope being fed to a distillation column and treated as above. In an embodiment of the invention, acetone-containing water-acetonitrile binary azeotrope from a stripping column (not shown) is introduced at 26 into a dehydration column 1. Acetonitrile collects in the boiler 8 and may be removed via 10 and acetone and water-acetonitrile - trichlorethylene ternary azeotrope vapours pass to the condenser 2. Part of the condensate is refluxed via 11 and part is mixed with water in 4. The mixture separates into layers in decanter 5 from which the lower, trichlorethylene, layer returns to column 1 via 14, 15 and 11, while the upper passes at 17 into the acetone still 6, where the acetone distils off and is condensed in 7 and collected via 21. Dilute aqueous acetonitrile collects in boiler 18 and is returned via 25 to the stripping column. In a modification, the condensate from 2 is treated with water after separation into layers, e.g. the whole or part of the entrainer liquid layer may be passed through a washing column in counter-current to a stream of water, in which case the washings are combined with the aqueous layer fed to the acetone still. In another modification, the aqueous extracts are collected in batches, the acetone being distilled off first, then an intermediate fraction (added to the next batch) and then the water-acetonitrile binary azeotrope (which is recycled via 26), or a mixture of acetone and azeotrope being distilled off from a residue of water and subsequently fractionated with acetone and residual azeotrope (which is recycled via 26). Specification 540,799 is referred to.