Process for preparing acetic anhydride

Claim 1

IN A PROCESS FOR PREPARING AN ALIPHATIC ACID ANHYDRIDE BY PYROLYZING A KETONE TO THE CORRESPONDING KETENE, IMMEDIATELY PASSING THE HOT GASEOUS PYROLYZED PRODUCTS INCLUDING THE KETENE, UNREACTED KETONE, AND FIXED GASES INTO AN ABSORPTION ZONE WHEREIN SAID PRODUCTS ARE CONTACTED WITH ACETIC ACID, AND REMOVING A LIQUID MIXTURE OF ACETIC ACID ANHYDRIDE AND ACETIC ACID FROM THE BOTTOM OF THE ABSORPTION ZONE, THE IMPROVEMENT WHICH COMPRISES PASSING A VAPOR STREAM OF THE UNREACTED KETONE AND FIXED GASES SUBSTANTIALLY FREE OF KETENE, FROM THE ABSORPTION ZONE TO A COOLING ZONE MAINTAINED AT A TEMPERATURE OF AT LEAST +80*F. WHEREIN ONLY A PORTION OF THE KETONE IS CONDENSED, RECYCLING SAID CONDENSED KETONE TO THE PYROLYSIS STEP, PASSING A GASEOUS STREAM CONTAINING FIXED GASES AND REMAINING UNCONDENSED KETONE VAPOR FROM THE COOLING ZONE TO A SCRUBBING ZONE MAINTAINED AT A PRESSURE OF FROM ATMOSPHERIC TO 10 PSIG. AND A TEMPERATURE OF FROM 60* TO 100*F. WHEREIN SAID GASEOUS STREAM IS CONTACTED WITH LIQUID ACETIC ACID INTRODUCED THERETO TO REMOVE THE KETONE SUBSTANTIALLY COMPLETELY, REMOVING FIXED GASES SUBSTANTIALLY FREE OF KETONE FROM SAID SCRUBBING ZONE, REMOVING A KETONE ENRICHED ACETIC ACID STREAM FROM THE BOTTOM OF THE SCRUBBING ZONE, AND PASSING SAID KETONE ENRICHED ACETIC ACID STREAM TO THE ABSORPTION ZONE.