Process of purifying dimethyl terephthalate and other compounds which sublime

Claim 1

A CONTINOUS PROCESS OF PURIFYING A COMPOUND MELTING ABOVE 20*C. AND CAPABLE OF SUBLIMING, CONTAMINATED WITH SUBSTANCES LOWER BOILING AND HIGHER BOILING THAN ITSELF, BY DISTILLATION AT REDUCED PRESSURE, WHICH COMPRISING DISTILLING IN A FIRST DISTILLING COLUMN, A SOLUTION OF THE CRUDE SUBLIMABLE COMPOUND IN A SOLVENT BOILING BETWEEN 125*C. AND THE BOILING POINT OF THE SUBLIMABLE COMPOUND, DISTILLING OFF SOLVENT AT THE HEAD OF THE FIRST DISTILLING COLUMN AND RETURNING A PORTION OF THE SOLVENT TO THE FIRST DISTILLING COLUMN AS A REFLUX, REMOVING IMPURITIES LOWER BOILING THAN THE SUBLIMABLE COMPOUND AS A SIDE STREAM FROM THE FIRST DISTILLING COLUMN, OVERFLOWING THE SUBLIMABLE COMPOUND AND HIGHER BOILING IMPURITIES FROM THE BASE OF THE FIRST DISTILLING COLUMN INTO A BASE HEATER WHICH IS CONNECTED TO THE FIRST DISTILLING COLUMN AND IS ALSO CONNECTED TO A SECOND DISTILLING COLUMN WHICH HAS A DEPHLEGMATOR AT ITS HEAD, VAPORIZING THE SUBLIMABLE COMPOUND FROM THE BASE HEATER INTO THE SECOND DISTILLING COLUMN, RECTIFYING IT IN THE SECOND DISTILLING COLUMN, REFLUXING A PORTION OF THE SUBLIMABLE COMPOUND FROM THE BASE OF THE SECOND COLUMN TO THE BASE HEATER, SLUDGING THE HIGH BOILING IMPURITIES TOGETHER WITH SOME OF THE SUBLIMABLE COMPOUND FROM THE BASE HEATER, TAKING OFF PURIFIED SUBLIMABLE COMPOUND AS A LIQUID SIDE STREAM FROM THE SECOND DISTILLING COLUMN, AND ALLOWING A SMALL AMOUNT OF THE SUBLIMABLE COMPOUND VAPOR TO PASS THE THE CONDENSING SURFACE OF THE DEPHLEGMATOR AND RE-ENTER THE FIRST DISTILLING COLUMN AT A POINT WHERE THE TEMPERATURE IS ABOVE THE MELTING POINT OF THE SUBLIMABLE COMPOUND, AND WHERE THE PRESSURE DROP FROM THE BASE HEATER THE RE-ENTRY POINT IN THE FIRST DISTILLING COLUMN IS GREATER THAN THE PRESSURE DROP ACROSS THE SECOND DISTILLING COLUMN WHEREBY SUBLIMATION OF THE SUBLIMABLE COMPOUND IS PREVENTED.