Manufacture of acetic anhydkide

Claim 1

A CONTINUOUS PROCESS FOR THE PRODUCTION OF ACETIC ANHYDRIDE BY THE LIQUID PHASE OXIDATION OF ACETALDEHYDE BY MEANS OF MOLECULAR OXYGEN AT 45-55* C. WITH THE AID OF A COPPER AND COBALT CATALYST WHICH COMPRISES BRINGING MOLECULAR OXYGEN INTO INTIMATE CONTACT WITH A MIXTURE CONTAINING ACETIC ACID, ACETALDEHYDE, AT LEAST 40% OF ACETIC ANHYDRIDE AND AN AMOUNT OF WATER RESULTING FROM THE REACTION OF ACETALDEHYDE TO PRODUCE SUCH ACETIC ANHYDRIDE, IN WHICH MIXTURE IS DISSOLVED A COPPER-COBALT CATALYST IN AN AMOUNT SO THAT THE CONCENTRATION OF THE RESULTING COPPER COMPOUND, EXPRESSED IN TERMS OF METALLIC COPPER, IS BETWEEN 0.05% AND 0.5%, AND OF THE RESULTING COBALT COMPOUND, EXPRESSED IN TERMS OF METALLIC COBALT, IS BETWEEN 0.02% AND 0.2%, CONTINUOUSLY WITHDRAWING A PART OF THE REACTION MIXTURE AND REPLACING SAID PART BY FRESH ACETALDEHYDE AND CATALYST TO KEEP THE CONCENTRATION OF CATALYST IN THE REACTION MIXTURE WITHIN SAID LIMITS, ADJUSTING THE WITHDRAWAL AND THE REPLACEMENT IN SUCH A MANNER THAT THE RESIDENCE TIME OF THE REACTION MIXTURE IN THE SYSTEM IS NOT MORE THAN HALF AN HOUR, CONTINUOUSLY INTRODUCING MOLECULAR OXYGEN AT SUCH A RATE THAT THE ACETIC ANHYDRIDE CONTENT IN THE REACTION MIXTURE IS MAINTAINED AT 40% AT LEAST, AND THE CONCENTRATION OF ACETALDEHYDE THEREIN BETWEEN 2 TO 7% AND RECOVERING THE ACETIC ANHYDRIDE FROM THE PART WHICH IS WITHDRAWN.