Process for purifying acrylonitrile

Claim 1

AN IMPROVED PROCESS FOR PURIFYING ACRYLONITRILE WHICH COMPRISES CONTINUOUSLY FEEDING SEMIREFINED ACRYLONITRILE CONTAINING HYDROGEN CYANIDE INTO A FIRST ZONE WITHIN A FRACTIONATING COLUMN, WATER IN THE UPPER PART OF SAID FIRST ZONE BEING MAINTAINED AT A HIGHER CONCENTRATION THAN THAT IN THE FEED; CONTINUOUSLY ADDING WATER TO SAID FIRST ZONE; CONTINUOUSLY REMOVING FROM AN UPPER ZONE WITHIN SAID COLUMN AND ABOVE SAID FIRST ZONE, HYDROGEN CYANIDE, ACRYLONITRILE-WATER AZEOTROPE, AND OTHER COMPONENTS BOILING AT A TEMPERATURE LOWER THAN SAID ACRYLONITRILEWATER AZEOTOPE; CONTINUOUSLY REFLUXING WATER AND ACRYLONITRILE, THE TOTAL WATER FED TO SAID COLUMN INCLUDING SAID REFLUXED WATER BEING EQUAL TO THAT WITHDRAWN FROM SAID UPPER ZONE; CONTINUOUSLY REMOVING SUBSTANTIALLY ANHYDROUS PURIFIED ACRYLONITRILE IN VAPOR FORM FROM A LOWER ZONE WITHIN SAID COLUMN AND BELOW SAID FIRST ZONE; CONTINUOUSLY HEATING A LIQUID COLUMN BOTTOM CONTAINING ACRYLONITRILE AND COMPONENTS HAVING A BOILING TEMPERATURE HIGHER THAN ACRYLONITRILE IN A BOTTOM ZONE BELOW SAID LOWER ZONE TO PROVIDE ACRYLONITRILE VAPORS, SAID VAPORS PASSING UPWARD THROUGH THE RESPECTIVE ZONES IN SAID COLUMN IN HEAT-EXCHANGE RELATIONSHIP WITH DOWNCOMING LIQUIDS; AND REMOVING FROM SAID BOTTOM ZONE SAID COMPONENTS BOILING HIGHER THAN ACRYLONITRILE WHICH ACCUMULATE THEREIN.