Production and recovery of propylene oxide by plural distillation

Claim 1

PROCESS FOR THE CONTINUOUS PRODUCTION AND RECOVERY OF PROPYLENE OXIDE WHICH COMPRISES THE DIRECT OXIDATION OF PROPYLENE FEEDSTOCKS WITH MOLECULAR OXYGEN IN A SOLVENT SELECTED FROM THE GROUP CONSISTING OF FULLY ESTERIFIED POLYACYL ESTERS OF POLYHYDROXYALKANES, POLYHYDROXYCYCLOALKANES, POLYGLYCOLS AND MIXTURES THEROF, WHEREIN SAID ESTERS CONTAIN FROM 1 TO 18 CARBON ATOMS IN EACH ACYL MOIETY AND FROM 2 TO 18 CARBON ATOMS IN EACH ALKYLENE AND CYCLOALKYLENE MOIETY, AND RECOVERING FORMED PROPYLENE OXIDE BY: (A) DIRECTING AN EFFUENT STREAM OF THE REACTION MIXTURE FROM A REACTION ZONE THROUGH A PLURALITY OF SUCCESSIVE FLASHING DISTILLATION ZONES MAINTAINED AT ESSENTIALLY THE SAME TEMPERATURE AS THE OXIDATION REACTION, BUT EACH SUCCESSIVE FLASHING ZONE BEING MAINTAINED AT PRESSURES SUBSTANTIALLY LOWER THAN IN PRECEDING ONES AND IN SAID REACTION ZONE IN ORDER TO SEPARATE MOST OF THE LOW AND INTERMEDIATE BOILING PRODUCTS AS GAS PHASE FROM THE BULK OF THE SOLVENT WHICH IS REMOVED AS BOTTOMS FROM EACH FLASHING ZONE AND DIRECTED TO THE SUCCEEDING ONE, (B) PASSING SAID GAS PHASE TO CONDINSING ZONES, FROM WHENCE UNCONDENSED GASES ARE DIRECTED TO AN ABSORBING ZONE INTO WHICH EFFUENT SOLVENT FROM SAID FLASHING ZONES IS ALSO PASSED TO ABSORB UNCONDENSED PROPYLENE AND PROPYLENE OXIDE, (C) DIRECTING A SIDE-STREAM OF SAID EFFLUENT SOLVENT IN (B) THROUGH A POLYMERIC RESIDUE HAVING A BOILING POINT ABOVE THAT OF SAID SOLVENT REMOVAL DISTILLATION ZONE WHERE RESIDUE IS REMOVED AS BOTTOMS AND SOLVENT IS DISTILLED OVERHEAD AND COMBINED WITH THE SOLVENT BOTTOMS FROM SAID ABSORBING ZONE AND RECYCLED TO SAID REACTION ZONE, (D) PASSING A COMBINED STREM OF CONDENSED LIQUIDS FROM SAID CONDENSING ZONES INTO AN ACIDS-SEPARATION DISTILLATION ZONE WHERE ORGANIC ACIDS ARE REMOVED AS BOTTOMS AND PROPYLENE OXIDE, PROPYLENE, PROPANE, ACETALDEHYDE AND METHYL FORMATE ARE DISTILLED OVERHEAD, (E) DIRECTING THE OVERHEAD DROM (D) TO A C3 REMOVAL DISTILLATION ZONE WHERE PROPYLENE AND PROPANE ARE DISTILLED OVERHEAD AND PROPYLENE OXIDE, ACETALDEHYDE AND METHYL FORMATE ARE REMOVED AS BOTTOMS, (F) PASSING SAID BOTTOMS FROM SAID C3 REMOVAL ZONE TO A DISTILLATION ZONE WHERE ACETALDEHYDE IS DISTILLED OVERHEAD AND PROPYLENE OXIDE AND METHYL FORMATE ARE REMOVED AT BOTTOMS, (G) PASSING THE BOTTOMS FROM (F) TO AN ATMOSPHERIC EXTRACTIVE DISTILLATAION ZONE USING AS EXTRACTIVE SOLVENT A HYDROCARBON SOLVENT BOILING ABOVE 67*C. AND WHEREIN METHYL FORMATE IS REMOVED OVERHEAD AND SAID EXTRACTIVE SOLVENT CONTAINING PROPYLENE OXIDE IS REMOVED AS BOTTOMS, AND (H) FEEDING THE BOTTOMS FROM (G) TO A PROPYLENE OXIDE DISTILLATION REFINING ZONE FROM WHICH PURIFIED PROPYLENE OXIDE IS DISTILED OVERHEAD AND RECOVERED.