Purification of maleic anhydride by flash vaporization and two stage fractional distillation

Claim 1

THE PROCESS OF PURIFYING DRY CRUDE MALEIC ANHYDRIDE CONTAINING IMPURITIES WHICH INCLUDE HYDROCARBON COMPOUNDS HAVING A BOILING POINT BELOW THAT OF MALEIC ANHYDRIDE, BEING THEREBY MORE VOLATLE THAN THE MALEIC ANHYDRIDE, AND FURTHER CONTAINING TARRY IMPURITIES HAVING A BOILING POINT HIGHER THAN THAT OF MALEIC ANHYDRIDE AND BEING THEREBY LESS VOLATILE, BOTH TYPES OF IMPURITIES ASSOCIATED WITH THE MALEIC ANHYDRIDE RESULTING FROM OXIDATION OF HYDROCARBON IN THE FORMATION OF THE MALEIC ANHYDRIDE, COMPRISING HEATING SAID CRUDE MALEIC ANHYDRIDE ABOVE ITS BOILING POINT SUFFICIENT NOT ONLY TO VAPORIZE THE SAID MORE VOLATILE IMPURITY COMPONENTS, TOGETHER WITH ALL OF THE MALEIC ANHYDRIDE, BUT ALSO TO VAPORIZE SOME OF THE LESS VOLATILE COMPONENTS CONTAINED IN THE TARRY IMPURITIES, THEREAFTER FLASHING THE SAID HEATED CRUDE MALEIC ANHYDRIDE MIXTURE IN A FLASH DRUM TO IMMEDIATELY VAPORIZE ALL OF SAID VAPORIZABLE COMPONENTS, PASSING SAID VAPORS TO A DISTILLATION COLUMN CONTROLLED TO A TEMPERATURE AND PRESSURE TO REMOVE AS VAPORIZED OVERHEAD ALL OF THE SAID MORE VOLATILE COMPONENTS IN SAID COLUMN AND LEAVING AS LIQUID RESIDUE BOTH MALEIC ANHYDRIDE AND SAID LESS VOLATILE COMPONENTS THAT WERE FIRST VAPORIZED THEREWITH, AND PASSING THE SAID LIQUID RESIDUE TO A SECOND DISTILLATION COLUMN CONTROLLED IN TEMPERATURE AND PRESSURE TO SEPARATE AS OVERHEAD VAPORS PURE MALEIC ANHYDRIDE AND LEAVE IN SAID COLUMN THE SAID LESS VOLATILE IMPURITIES AS LIQUID BOTTOMS.