Process for separating hydrocarbon mixtures by rectification

Claim 1

A PROCESS OF PRODUCING PROPYLENE FROM A MIXTURE OF HYDROCARBONS HAVING THREE AND MORE CARBON ATOMS PER MOLECULE, WHICH PROCESS COMPRISES: (1) FRACTIONALLY DISTILLLING SAID MIXTURE IN A FIRST DISTILLATION COLUMN OPERATING AT A PRESSURE LOWER THAN 10 ATMOSPHERES, TO OBTAIN A C3-DISTILLATE ESSENTIALLY CONSISTING OF PROPANE AND PROPYLENE; AND (2) FRACTIONALLY DISTILLING SAID C3-DISTILLATE IN A SECOND DISTILLATION COLUMN OPERATING AT A PRESSURE BETWEEN 10 AND 25 ATMOSPHERES, TO OBTAIN A BOTTOMS OF PROPANE AND A HEAD PRODUCT OF GASEOUS PROPYLENE, AND WHEREIN: (A) SAID GASEOUS PROPYLENE HEAD PRODUCT IS PASSED THROUGH A HEAT EXCHANGER WHEREBY SAID GASEOUS PROPYLENE IS HEATED BY INDIRECT HEAT EXCHANGE CONTACT, (B) SAID HEATED GASEOUS PROPYLENE FROM (A) IS COMPRESSED TO A PRESSURE WHICH IS HIGHER THAN THE OPERATING PRESSURE OF THE SECOND DISTILLATION COLUMN, (C) SAID COMPRESSED HEATED GASEOUS PROPYLENE FROM (B) IS PASSED THROUGH THE BOTTOM OF THE SECOND DISTILLATION COLUMN, AS INDIRECT REBOILER HEATING FLUID, WHEREBY SAID PROPYLENE IS CONDENSED INTO A LIQUID, (D) A PORTION OF SAID CONDENSED LIQUID PROPYLENE FROM (C) IS PASSED THROUGH THE HEAT EXCHANGER OF STEP (A) IN INDIRECT AND COUNTER-CURRENT HEAT TRANSFER CONTACT WITH THE GASEOUS PROPYLENE OF STEP (A), WHEREBY THE LIQUID PROPYLENE IS COOLED, AND (E) SAID COOLED LIQUID PROPYLENE PORTION FROM (D) IS THEN REDUCED IN PRESSURE AND REFLUXED TO THE TOP OF SAID SECOND DISTILLATION COLUMN.