Separation of fluid mixtures

Claim 1

APPARATUS FOR SEPARATING A FLUID MIXTURE CONTAINING METHANE AND OTHER COMPONENTS OF HIGHER BOILING POINTS INTO A FIRST STREAM SUBSTANTIALLY FREE OF METHANE AND A SECOND STEAM CONTAINING METHANE AND ANY COMPONENTS PRESENT IN THE FLUID MIXTURE WHICH HAVE BOILING POINTS LOWER THAN THE BOILING POINT OF METHANE WHICH COMPRISES A FRACTIONATION COLUMN, MEANS TO INTRODUCE THE FLUID MIXTURE TO BE SEPARATED INTO SAID COLUMN, MEAND TO WITHDRAW A FIRST STREAM FROM THE LOER REGION OF SAID COLUMN, AN ACCUMULATOR, A CONDENSER, MEANS TO PASS VAPORS FROM THE UPPER REGION OF SAID COLUMN THROUGH SAID CONDENSER TO SAID ACCUMULATOR, MEANS TO RETURN LIQUID FROM SAID ACCUMULATOR TO SAID COUMN AS REFLUX, MEANS TO WITHDRAW A SAMPLE STREAM FROM THE LOWER REGION OF SAID COLUMN, MEANS TO MEASZURE TH EREFRACTIVE INDEX OF SAID SAMPLE STREAM, MEANS TO WITHDRAW VAPOR FRM SAID ACCUMULATOR AS A SECOND STREAM, AND MEANS RESPONSIVE TO SAID MEANS TO MEASURE TO REGULATE THE REAT OF WITHDRAWAL OF SAID SECOND STREAM SO THAT THE RATE OFG WITHDRAWAL IS INCREASED AS THE MEASURED REFRACTIVE INDEX DECREASES AND IS DECREASED IF THE MEASURED REFRACTIVE INDEX INCREASES.