Patent GB-802114-A (GB)
Title: Separation of nitriles
Inventor: MASLAN FRANK
Filed: 1956-11-26
Abstract: The separation of acrylonitrile, acetonitrile and propionitrile from aqueous solution is effected by feeding the solution into an acetonitrile extractor, into which is introduced an aqueous solution substantially saturated with acrylonitrile and propionitrile, withdrawing a fraction comprising an aqueous acetonitrile solution containing less than about 15 per cent acrylonitrile and propionitrile, passing the solution into an extractive distillation column, introducing water as solvent at the top of the column, preferably in the presence of air or oxygen and in amount to maintain the water concentration in the liquid phase above about 70 mol. per cent (more preferably at about 80 mol. per cent), withdrawing an aqueous solution of substantially pure acetonitrile from the bottom of the column, removing a mixture of acrylonitrile, propionitrile and less than about 15 per cent water, preferably less than about 10 per cent water, overhead from the column and feeding the mixture to the acetonitrile extractor as solvent; removing from the acetonitrile extractor a second fraction comprising a mixture of acrylonitrile, propionitrile and less than about 15 per cent water, preferably less than about 5 per cent water, introducing the latter mixture into an azeotropic distillation column, removing overhead from the column the water azeotropes of acrylonitrile and propionitrile, separating the latter into an aqueous phase saturated with acrylonitrile and propionitrile and an organic phase, feeding the aqueous phase to the acetonitrile extractor as solvent, returning the organic phase to the azeotropic distillation column as reflux, withdrawing a substantially anhydrous mixture of acrylonitrile and propionitrile from the bottom of the column, and fractionally distilling the mixture.  In a preferred embodiment the original solution is decanted to give an aqueous and an organic phase, the aqueous phase, comprising essentially acetonitrile and less than about 15 per cent, preferably less than about 10 per cent, acrylonitrile and propionitrile, being fed to the extractive distillation column, and the organic phase, comprising essentially acrylonitrile and propionitrile with minor amounts of acetonitrile and water, preferably less than about 5 per cent water, being fed into the acetonitrile extractor.  As solvent in the extractive distillation column there may also be used, in the presence of air or oxygen, an aqueous solution of a salt which is non-corrosive and stable to decomposition and hydrolysis at the distillation temperature, preferred salts being sodium or potassium acetate or phosphate.  Preferably the solvent is pre-heated to about 60 DEG  C. or higher.  The solvent extraction of the acetonitrile is preferably carried out at about 35 DEG  F.  The aqueous solution of substantially pure acetonitrile is preferably subjected with diethyl ether to distillation at a pressure above 100 p.s.i., more preferably with sufficient ether to azeotrope with the water present, at a pressure of 175-200 p.s.i.ALSO:The separation of acrylonitrile, acetonitrile and propionitrile from aqueous solution is effected by feeding the solution into an acetonitrile extractor, into which is introduced an aqueous solution substantially saturated with acrylonitrile and propionitrile, withdrawing a fraction comprising an aqueous acetonitrile solution containing less than about 15 per cent acrylonitrile and propionitrile, passing the solution into an extractive distillation column, introducing water as solvent at the top of the column, preferably in the presence of air or oxygen and in amount to maintain the water concentration in the liquid phase above about 70 mol. per cent (more preferably at about 80 mol. per cent), withdrawing an aqueous solution of substantially pure acetonitrile from the bottom of the column, removing a mixture of acrylonitrile, propionitrile and less than about 15 per cent water, preferably less than about 10 per cent, water, overhead from the column and feeding the mixture to the acetonitrile extractor as solvent; removing from the acetonitrile extractor a second fraction comprising a mixture of acrylonitrile, propionitrile and less than about 15 per cent water, preferably less than about 5 per cent water, introducing the latter mixture into an azeotropic distillation column, removing overhead from the column the water azeotropes of acrylonitrile and propionitrile, separating the latter into an aqueous phase saturated with acrylonitrile and propionitrile and an organic phase, feeding the aqueous phase to the acetonitrile extractor as solvent, returning the organic phase to the azeotropic distillation column as reflux, withdrawing a substantially anhydrous mixture of acrylonitrile and propionitrile from the bottom of the column, and fractionally distilling the mixture.  In a preferred embodiment the original solution is decanted to give an aqueous and an organic phase, the aqueous phase, comprising essentially acetonitrile and less than about 15 per cent, preferably less than about 10 per cent, acrylonitrile and propionitrile, being fed to the extractive distillation column, and the organic phase, comprising essentially acrylonitrile and propionitrile with minor amounts of acetonitrile and water, preferably less than about 5 per cent water, being fed into the acetonitrile extractor.  As solvent in the extractive distillation column there may also be used, in the presence of air or oxygen, an aqueous solution of a salt which is non-corrosive and stable to decomposition and hydrolysis at the distillation temperature, preferred salts being sodium or potassium acetate or phosphate.  Preferably the solvent is preheated to about 60 DEG  C. or higher.  The solvent extraction of the acetonitrile is preferably carried out at about 35 DEG  F.  The aqueous solution of substantially pure acetonitrile is preferably subjected with diethyl ether to distillation at a pressure above 100 p.s.i., more preferably with sufficient ether to azeotrope with the water present, at a pressure of 175-200 p.s.i.