Preparation of aliphatic dicarboxylic acid anhydrides

Claim 1

A PROCESS FOR THE PREPARATION OF HIGH PURITY MALEIC ANHYDRIDE WHICH COMPRISES OXIDIZING ETHYLENICALLY UNSATURATED ALIPHATIC HYDROCARBONS OF FROM 4 TO 6 CARBON ATOMS IN A VAPOR STATE TO FORM A CRUDE VAPOR CONTAINING MALEIC ANHYDRIDE, DISSOLVING SAID CRUDE VAPOR IN WATER TO FORM AN AQUEOUS SOLUTION, FEEDING SAID AQUEOUS SOLUTION TO A FIRST COLUMN WHICH CONTAINS A REFLUXING STATURATED ALIPHATIC HYDROCARBON OF A BOILING POIN OF ABOUT 130*C. TO 152*C., SAID FIRST COLUMN HAVING AN INTERNAL TEMPERATURE AT THE TOP OF THE COLUMN OF NO GREATER THAN ABOUT 135*C., TAKING OFF AN AQUEOUS SOLUTION OF ACID OVERHEAD AND TAKING OFF IMPURTIES AS BOTTOMS FROM THE COLUMN, FEEDING SAID AQUEOUS SOLUTION OF MALEIC ACID TO A SECOND COLUMN WHICH CONTAINS A REFLUXING ORGANIC LIQUID WHICH FORMS AN AZEOTROPE WITH WATER, AND WHICH BOILS AT A TEMPERATURE LOWER THAN MALEIC ANHYDRIDE, WHEREBY THE MALEIC ACID IS DEHYDRATED TO MALEIC ANHYDRIDE AND THE WATER OF SOLUTION AND WATER OF HYDRATION ARE THEREBY DISTILLED OFF OVERHEAD AS AN AZEOTROPIC LMIXTURE AND THE MALEIC ANHYDRIDE IS TAKEN OFF AS BOTTOMS.