Process for the continuous recovery of acrylonitrile and acetonitrile by plural distillation and the addition of water

Claim 1

A PROCESS FOR THE CONTINUOUS RECOVERY OF ACRYLONITRILE AND ACETONITRILE FROM THE REACTION PRODUUCTS OF AN ACRYLONITRILE SYNTHESIS BY REACTION OF PROPYLENE WITH AMMONIA AND OXYGEN WHICH COMPRISES SUBJECTING A LIQUID MIXTURE OF WATER AND THE SAID REACTION PRODUCTS WHEREIN THE ACETONITRILE CONTENT IS 2 TO 20% BY WEIGHT BASED ON THE ACRYLONITRILE TO A THREE-STAGE FRACTIONAL DISTILLATION, THE LIQUID MIXTURE BEING INTRODUCED, IN THE FIRST STAGE, INTO THE BOTTOM PORTION OF A DISTILLATION COLUMN AT THE TOP OF WHICH IS INTRODUCED 150 TO 400 TIMES THE QUANTITY BY WEIGHT OF WATER BASED ON THE ACETONITRILE, THE TOP THREEQUARTERS OF THE COLUMN BEING MAINTAINED AT A TEMPERATURE JUST BELOW 71*C. SO THAT AN ACETONITRILE-FREE AZEOTROPE OF ACRYLONTRILE AND WATER IS OBTAINED AT THE TOP OF THE COLUMN WHILE AT THE LOWER END OF THE COLUMN THERE IS OBTAINED A MIXTURE OF ACETONITRILE, WATER AND ACRYLONITRILE, THE ACRYLONITRILE BEING IN AN AMOUNT BY WEIGHT NOT EXCEEDING THE ACETONITRILE, IN THE SECOND STAGE, SUBJECTING SAID MIXTURE OF ACETONITRILE, WATER AND ACRYLONITRILE TO AZEOTROPIC DISTILLATION IN A STRIPPER COLUMN TO DISTILL OFF THE NITRILES FROM THE MAJOR PORTION OF THE WATER CONTAINED IN SUCH MIXTURE, CONDENSING THE ACRYLONITRILE-ACETONITRILEWATER VAPORS LEAVING THE HEAD OF SUCH STRIPPER COLUMN, SEPARATING THE ORGANIC LAYER FROM THE CONDENSATION PRODUCT IN A DECANTER TO OBTAIN A LOWER WATER CONTENT ACRYLONITRILE-ACETONITRILE MIXTURE, SAID LATTER MIXTURE BEING FED IN THE THIRD STAGE TO THE TOP OF A DISTILLATION COLUMN, WHEREIN THE TOP IS MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 72*C. AND JUST BELOW 73*C. AND THE UPPER FOURFIFTHS OF THIS COLUMN PASSES THROUGH A TEMPERATURE GRADIENT FROM SUCH TEMPERATURE AT THE TOP TO 76*C., AND IN THE BOTTOM OF WHICH COLUMN SUBSTANTIALLY ANHYDROUS PURE ACETONITRILE IS OBTAINED WHILE AT THE TOP OF SAID COLUMN VAPORS CONTAINING ACRYLONITRILE AND ACETONITRILE ARE OBTAINED, CONDENSING SUCH VAPORS, SEPARATING THE ORGANIC LAYER FROM THE LATTER CONDENSATION PRODUCT IN A DECANTER AND RECYCLING THE ACRYLONITILE-ACETONITRILE-WATER CONTENT OF SUCH ORGANIC LAYER TO THE FIRST STAGE OF THE PROCESS.