Rectification of liquid mixtures boiling at low temperatures

Claim 1

PROCESS FOR THE RECTIFICATION INTO TWO FRACTIONS OF A LOW BOILING LIQUID, NORMALLY GASEOUS, MIXTURE IN AT LEAST THREE SEPARATE COLUMNS IN SERIES, THE COMPONENTS OF THE MIXTURE HAVING BOILING POINTS VERY CLOSE TO EACH OTHER, WHICH COMPRISES: SUPPLYING THE MIXTURE TO A FIRST COLUMN IN WHICH THE HIGHEST PRESSURE IS MAINTAINED, AT A POINT IN WHICH THE HIGHEST PRESSURE IS MAINTAINED, AT A POINT BETWEEN THE HEAD AND THE BOTTOM THEREOF DEPENDING ON THE COMPOSITION OF SAID MIXTURE; SEPARATING THE MIXTURE THEREIN INTO A FIRST SUBSTANTIALLY PURE OVERHEAD PRODUCT AND AN IMPURE BOTTOMS PRODUCT; DELIVERING THE IMPURE BOTTOMS PRODUCTS IN THE VAPORIZED STATE TO THE SERIALLY SECOND COLUMN, WHICH IS UNDER A LOWER PRESSURE THAT SAID FIRST COLUMN, AT A POINT BETWEEN THE HEAD AND THE BOTTOM THEREOF; SEPARATING SAID IMPURE BOTTOMS PRODUCT THEREIN INTO SAID FIRST SUBSTANTIALLY PURE OVERHEAD PRODUCT SUBSTANTIALLY IDENTICAL WITH THE OVERHEAD PRODUCT OF THE FIRST COLUMN AND A FURTHER IMPURE BOTTOMS PRODUCT; DELIVERING SAID FURTHER IMPURE BOTTOMS PRODUCTS IN THE VAPORIZED STATE TO THE SERIALLY NEXT COLUMN, UNDER STILL LOWER PRESSURE, AT A POINT BETWEEN THE HEAD AND THE BOTTOM THEREOF AND SEPARATING IT THEREIN; WITHDRAWING A FRACTION OF THE SAID FIRST SUBSTANTIALLY PURE OVERHEAD PRODUCT FROM THE TOP OF EACH COLUMN; BRINGING PART OF EACH OF