Preparation and recovery of acetic acid

Claim 1

PROCESS FOR THE PRODUCTION OF ACETIC ACID WHICH COMPRISES OXIDIZING PROPYLENE FEEDSTOCKS WITH MOLECULAR OXYGEN IN A SOLVENT SELECTED FROM THE GROUP CONSISTING OF FULLY ESTERIFIED POLYACYL ESTERS OF POLYHYDROXYALKANES, POLYHYDROXY-CYCLOALKANES, POLYGLYCOLS AND MIXTURES THEREOF, AND THE ACYL MOIETIES IN SAID ESTERS ARE DERIVED FROM ACIDS SELECTED FROM THE GROUP CONSISTING OF ALKANOIC ACIDS HAVING FROM 1 TO 18 CARBON ATOMS, CYCLOPENTANE CARBOXYLIC ACID, CYCLOHEXANE CARBOXYLIC ACID AND BENZOIC ACID, AND THE ALKYLENE AND CYCLOALKYLENE MOIETIES IN SAID ESTERS CONTAIN FROM 2 TO 18 CARBON ATOMS, UNDER TEMPERATURES AND PRESSURES SUFFICIENT TO CAUSE THE REACTION TO PROCEED IN THE LIQUID PHASE AND RECOVERING SAID ACETIC ACID BY: (A) DIRECTING AN EFFLUENT STREAM OF THE REACTION MIXTURE FROM A REACTION ZONE THROUGH A COMBINATION ZONE COMPRISING A FLASHING ZONE FOLLOWED BY A STRIPPING ZONE, SAID FLASHING ZONE AND STRIPPING ZONE BEING MAINTAINED AT PRESSURES SUBSTANTIALLY LOWER THAN IN EACH PRECEDING ZONE AND AT TEMPERATURES NECESSARY TO SEPARATE SUBSTANTIALLY ALL OF THE ACETIC ACID AND LOWER BOILING PRODUCTS OVERHEAD AS GAS PHASE AND HIGHER BOILING COMPONENTS INCLUDING THE BULK OF THE SOLVENT AND POLYMERIC RESIDUE WHICH ARE REMOVED AS BOTTOMS FROM SAID STRIPPING ZONE, (B) PASSING SAID OVERHEAD GAS PHASE TO CONDENSING ZONES, FROM WHENCE UNCONDENSED GASES ARE DIRECTED TO AN ABSORBING ZONE INTO WHICH THE BOTTOMS STREAM FROM SAID STRIPPING ZONE IS ALSO PASSED TO ABSORB UNCONDENSED PROPYLENE, PROPANE AND MINOR AMOUNTS OF OXYGENATED COMPONENTS; REMOVING VENT GASES OVERHEAD FROM SAID ABSORBER, WHILE FEEDING THE BOTTOMS STREAM FROM SAID ABSORBING ZONE BACK TO SAID REACTION ZONE, (C) ADJUSTING REACTION CONDITIONS IN SUCH MANNER THAT AT STEADY STATE THE POLYMERIC RESIDUE CONCENTRATION IN SAID REACTION ZONE IS MAINTAINED SUBSTANTIALLY CONSTANT AT BETWEEN 25 TO 50 WEIGHT PERCENT BASED ON THE REACTION MIXTURE BY BALANCING THE AMOUNT OF POLYMERIC RESIDUE OXIDIZED AGAINST THE AMOUNT OF POLYMERIC RESIDUE FORMED, SAID POLYMERIC RESIDUE CONCENTRATION NOT EXCEEDING THE LEVEL AT WHICH ANY ADDITIONAL POLYMERIC RESIDUE IS COMPLETELY OXIDIZED, (D) FEEDING A COMBINED STREAM OF CONDENSED LIQUIDS FROM SAID CONDENSING ZONES INTO A PRIMARY PRODUCTS SPLITTING ZONE FROM WHICH AN OVERHEAD STREAM CONTAINING PROPYLENE AND PROPANE ARE REMOVED TO A SPLITTER FOR THESE COMPONENTS, THE PROPANE BEING REMOVED AS BOTTOMS WHILE PROPYLENE IS REMOVED OVERHEAD AND RECYCLED TO SAID REACTION ZONE, (E) DIRECTING A SIDESTREAM FROM SAID PRIMARY PRODUCTS SPLITTING ZONE TO AN ACETALDEHYDE REMOVAL ZONE FROM WHICH ACETALDEHYDE IS REMOVED OVERHEAD AND RECYCLED TO SAID REACTION ZONE AND FROM WHICH A BOTTOMS STREAM CONTAINING METHYL ACETATE, METHYL FORMATE, ACETONE, METHANOL, PROPYLENE OXIDE AND OTHER LOW BOILERS IS REMOVED, (F) FEEDING THE BOTTOMS FROM SAID PRIMARY PRODUCTS SPLITTING ZONE TO AN ACID-SOLVENT SPLITTING ZONE WHEREIN SUBSTANTIALLY ALL OF THE SOLVENT AND HIGHER BOILING COMPONENTS ARE REMOVED AS BOTTOMS AND SUBSTANTIALLY ALL ACID VALUES, WATER AND LOW BOILERS FORMED IN SAID REACTION ZONE ARE REMOVED OVERHEAD, (G) FEEDING THE OVERHEAD FROM STEP (F) TO AN ACIDSLOW BOILERS SEPARATION ZONE WHEREIN THE LOW BOILING COMPONENTS ARE RECOVERED OVERHEAD, WHILE DIRECTING THE BOTTOMS CONTAINING SAID ACID VALUES AND WATER FROM SAID ACID-LOW BOILERS DISTILLATION ZONE TO AN AZEOTROPIC DISTILLATION COLUMN USING BENZENE AS AN AZEOTROPE-FORMER FOR WATER AND FORMIC ACID, (H) REMOVING FROM SAID AZEOTROPIC DISTILLATION ZONE AN OVERHEAD STREAM CONTAINING A MIXTURE OF BENZENEWATER AND BENZENE-FORMIC ACID ZAEOTROPES TO A CONDENSING ZONE WHEREIN BENZENE IS SEPARATED FROM WATER AND FORMIC ACID AND FEEDING THESE THREE COMPONENTS TO A COLLECTING ZONE IN WHICH BENZENE FORMS AN UPPER PHASE FROM WHICH BENZENE IS RETURNED TO SAID AZEOTROPIC DISTILLATION ZONE, WHILE WATER AND FORMIC ACID ARE REMOVED AS BOTTOMS, WHILE REMOVING FROM SAID AZEOTROPIC DISTILLATION ZONE A BOTTOMS STREAM CONTAINING ACETIC ACID TO A REFINING ZONE WHEREIN PURIFIED ACETIC ACID IS RECOVERED OVERHEAD, (I) FEEDING THE BOTTOMS FROM SAID ACID-SOLVENT SPLITTER IN STEP (F) CONTAINING MAJOR AMOUNTS OF SOLVENT FROM SAID REACTION ZONE, MINOR AMOUNTS OF PROPYLENE GLYCOL AND MONOESTERS THEREOF TO AN ESTER CONCENTRATION ZONE FROM WHICH SOME OF SAID SOLVENT SUBSTANTIALLY DEPLETED OF SAID PROPYLENE GLYCOL AND ITS MONOESTERS IS REMOVED AS BOTTOMS AND RECYCLED TO SAID REACTION ZONE, WHILE REMOVING AN OVERHEAD STREAM COMPRISED OF THE REST OF SAID SOLVENT NOW ENRICHED WITH SAID PROPYLENE GLYCOL AND ITS MONOESTERS, (J) FEEDING THE OVERHEAD FROM SAID ESTER CONCENTRATION ZONE, TOGETHER WITH MONOCARBOXYLIC ACID VALUES TO AN ESTERIFICATION ZONE WHEREIN PROPYLENE GLYCOL AND ITS MONOESTERS ARE ESTERIFLED TO PROPYLENE GLYCOL DIESTERS, (K) FEEDING AN EFFLUENT STREAM FROM SAID ESTERIFICATION ZONE COMPRISING INCREASED AMOUNTS OF SAID DIESTERS AND DECREASED AMOUNTS OF SAID ACID VALUES TO A SOLVENT STRIPPING ZONE WHEREIN SAID ACID VALUES ARE REMOVED OVERHEAD AND RECYLCED TO SAID ACIDS-LOW BOILERS SEPARATION ZONE IN STEP (G) AND SAID DIESTERS ARE REMOVED AS BOTTOMS AND RECYCLED TO SAID ESTER CONCENTRATION ZONE.