Purification of olefinically unsaturated nitriles

Claim 1

THE PROCESS FOR PURIFICATION OF AN OLEFINICALLY UNSATURATED NITRILE SELECTED FROM THE GROUP CONSISTING OF ACRYLONITRILE AND METHACRYLONITRILE WHICH CONTAINS SMALL AMOUNTS OF WATER AND A SATURATED CARBONYL COMPOUND COMPRISING: (A) CONTINUOUSLY FEEDING THE IMPURE NITRILE INTO A FRACTIONAL DISTILLATION COLUMN HAVING AT LEST ABOUT 45 PLATES AT AN INTERMEDIATE POINT BETWEEN THE TOP AND BOTTOM OF THE COLUMN; (B) CONDENSING THE OVERHEAD AND MAINTAINING POT AND COLUMN TEMPERATURES SUCH THAT THE MOLE RATIO OF THE LIQUID DOWNFLOW TO THE VAPOR UPFLOW IN THE COLUMN IS AT LEAST 1; (C) MAINTAINING AT THE TOP OF THE FRACTIONATION COLUMN AN OVERHEAD REFLUX RATIO OF FROM ABOUT 300:1 TO 1000:1; (D) CONTINUOUSLY WITHDRAWING A PORTION OF THE DOWNFLOWING LIQUID AT A POINT IN THE COLUMN WHICH IS SLIGHTLY ABOVE THE POINT WHERE THE FEED IS INTRODUCED IN A AND THEN (1) COOLING THE WITHDRAWN PORTION UNTIL IT SEPARATES INTO TWO LIQUID PHASES, (2) SEPARATING THE WATER PHASE FROM THE ORGANIC PHASE, AND DISCADING THE WATER PHASE, AND (3) REHEATING THE ORGANIC PHASE AND INTRODUCING IT BACK INTO THE COLUMN AT A POINT SLIGHTLY ABOVE THE POINT AT WHICH THE FEED IS INTRODUCED, (E) RECOVERING ACRYLONITRILE FROM THE BOTTOM STREAM.