Fractional distillation system with fluid product discharge control

Claim 1

A PROCESS FOR THE RECOVERY OF PENTANE FROM A MIXTURE CONTAINING N-PENTANE, BUTENES, LIGHTER BOILING HYDROCARBONS AIR AND CARBON DIOXIDE COMPRISING INTRODUCING SAID MIXTURE INTO A FRACTIONATION ZONE, HEATING SAID FRACTION ZONE WITH HEAT EXCHANGE FLUID BY INDIRECT HEAT EXCHANGE, REMOVING THE BUTENES, LIGHTER BOILING HYDROCARBONS AIR AND CARBON DIOXIDE OVERHEAD FROM SAID ZONE ALONG WITH A MINOR AMOUNT OF N-PENTANE, PASSING SAID OVERHEAD THROUGH A COOLING ZONE TO CONDENSE SAID NPENTANE WITHOUT CONDENSING THE BUTENES, PASSING THE RESULTANT CONDENSATE AND REMAINING VAPORS TO A STORAGE ZONE, REMOVING VAPORS THEREFROM, REFLUXING SAID CONDENSED N-PENTANE TO SAID FRACTIONATION ZONE, WITHDRAWING A SUBSTANTIALLY PURE-N-PENTANE FRACTION FROM A LOWER PORTION OF SAID ZONE, PASSING SAID N-PENTANE FRACTION TO A PRODUCT RECOVERY ZONE, MEASURING THE AMOUNT OF BUTENE IN SAID N-PENTANE FRACTION AND WHEN THE AMOUNT OF BUTENE EXCEEDS 5 WEIGHT PARTS PER MILLION INCREASING THE AMOUNT OF HEAT APPLIED TO SAID FRACTIONATION ZONE BY SAID HEAT EXCHANGE FLUID AND DIVERTING SAID N-PENTANE FRACTION FROM SAID PRODUCT RECOVERY ZONE, SAID INCREASE OF HEAT AND DIVERSION CONTINUING UNTIL THE BUTENE CONTENT IS LOWERED TO SAID VALUE, AND RECYCLING SAID DIVERTED N-PENTANE FRACTION TO SAID STORAGE ZONE.