Fractionation of c8-aromatics

Claim 1

APPARATUS FOR FRACTIONAL DISTILLATION OF C8 AROMATIC COMPONENTS HAVING LITTLE DIFFERENCE IN RELATIVE VOLATILITIES COMPRISING AT LEAST THREE SEPARATE FRACTIONATING COLUMNS CONSTITUTING RECTIFYING, "PINCH" AND STRIPPING COLUMNS FOR SAID FRACTIONAL DISTILLATION; MEANS CONNECTING SAID COLUMNS IN SERIES FOR FLOW OF VAPOR FROM THE TOP OF ONE COLUMN TO THE BOTTOM OF THE NEXT COLUMN SO THAT THE VAPOR FLOW IN EACH COLUMN IS IN AN UPWARDLY DIRECTION WITH THE RECTIFYING COLUMN CONSTITUTING THE LAST COLUMN AND THE STRIPPING COLUMN THE FIRST, MEANS FLOWING LIQUID FROM THE NOTOM OF THE RECTIFYING COLUMN TO THE TOP OF SAID "PINCH" COLUMN AND FROM THE BOTTOM OF THE "PINCH" COLUMN TO THE TOP OF THE STRIPPING COLUMN, THE LIQUID FLOW BEING IN A COUNTERCURRENT DIRECTION IN EACH COLUMN AND FROM THE LAST COLUMN TO THE FIRST; MEANS FOR REBOILING A PORTION OF THE BOTTOMS LIQUID STREAM OF SAID "PINCH" COLUMN, MEANS FOR CONDENSING A PORTION OF THE VAPOUR OVERHEAD STREAM OF SAID "PINCH" COLUMN, THE "PINCH" COLUMN AND CONDENSER MEANS THEREFOR BEING SIZED SUCH THAT THE REFLUX RATE FOR THE "PINCH" COLUMN IS NEAR THE MINIMUM REQUIRED TO ACHIEVE SEPARATION TO THE COMPONENTS, MEANS TO CONTROL THE PRESSURE OF THE "PINCH" COLUMN AT A CONSTANT VALUE; MEANS FOR CONDENSING THE VAPOR OVERHEAD PRODUCT OF THE RECTIFYING COLUMN, MEANS FOR CONTROLLING THE PRESSURE OF THE RECTIFYING COLUMN AT A CONSTANT VALUE INDEPENDENT OF THE PRESSURE IN THE "PINCH" COLUMN, SAID RECTIFYING COLUMN BEING SIZED IN DIAMETER AND PLURALITY OF TRAYS FOR OPERATION AT A LOW REFLUX RATIO AND AT A HIGH PRESSURE RELATIVE TO THE REFLUX RATIO AND PRESSURE OF SAID "PINCH" COLUMN; REBOILER MEANS FOR REBOILING A PORTION OF THE BOTTOMS STREAM OF THE STRIPPING COLUMN, MEANS FOR CONTROLLING THE PRESSURE OF THE STRIPPING COLUMN AT A CONSTANT VALUE INDEPENDENT OF THE PRESSURE IN THE "PINCH" COLUMN, AND MEANS TO CONTROL THE REFLUX FLOW TO THE STRIPPING COLUMN, SAID STRIPPING COLUMN ALSO BEING SIZED IN DIAMETER AND PLURALITY OF TRAYS FOR OPERATION AT A LOW REFLUX RATIO AND AT A HIGH PRESSURE RELATIVE TO THE REFLUX RATIO AND PRESSURE OF SAID "PINCH" COLUMN.