Employing bottoms of a second fractionator as a refrigerant medium for first fractionator overhead

Claim 1

IN A METHOD FOR OPERATING A FRACTIONATION SYSTEM WHICH COMPRISES CHARGING TO A FRACTIONATION ZONE A FEED TO BE FRACTIONATED THEREIN, FRACTIONATING SAID FEED TO PRODUCE A BOTTOMS PRODUCT WHICH IS WITHDRAWN THEREFROM AND AN OVERHEAD CONTAINING GAS OR VAPOR, PASSING SAID OVERHEAD TO A COOLING ZONE, THEREIN COOLING SAID OVERHEAD, PASSING THE THUS COOLED OVERHEAD TO AN ACCUMULATION ZONE, IN SAID ACCUMULATION ZONE SEPARATING A LIQUID PHASE AND A GAS OR VAPOR PHASE CONTAINING SAID DESIRED GAS OR VAPOR, REMOVING THE LIQUID PHASE FROM SAID ACCUMULATION ZONE, PASSING AT LEAST A PORTION OF THE REMOVED LIQUID PHASE TO SAID FRACTIONATION ZONE AS REFLUX THEREFOR AND PASSING THE REMAINDER THEREOF TO A SECOND FRACTIONATION ZONE WHEREIN A BOTTOMS PRODUCT AND AN OVERHEAD PRODUCT ARE OBTAINED, PASSING GAS OR VAPOR PHASE IN SAID ACCUMULATION ZONE TO A CONDENSING ZONE WHEREIN DESIRED GAS OR VAPOR IS CONDENSED AND RECOVERED AND THE REMAINING GAS OR VAPOR REMOVED OVERHEAD FROM SAID CONDENSING ZONE, THE IMPROVEMENT WHICH COMPRISES UTILIZING AT LEAST A PORTION OF THE BOTTOMS PRODUCT FROM SAID SECOND FRACTIONATION ZONE AS A PRIMARY COOLANT IN SAID CONDENSING ZONE.