Solvent extraction with liquid carbon dioxide

Claim 1

THE PROCESS OF SEPARATING A HYDROCARBON MIXTURE SELECTED FROM GROUP CONSISTING OF HYDROCARBON MIXTURES RANGING FROM GAS OILS TO LUBRICATING OIL STOCKS, INTO FRACTIONS AT LEAST ONE OF WHICH HAS A HIGHER VISCOSITY INDEX THAN THAT OF THE ORIGINAL MIXTURE, WHICH COMPRISES: CONTACTING THE MIXTURE WITH LIQUID CARBON DIOXIDE AND A SOLVENT UNDER SUFFICIENT PRESSURE TO MAINTAIN A CARBON DIOXIDE-RICH PHASE AND AN EXSTATE, WHEREUPON A RAFFINATE PHASE AND AN EXTRACT PHASE ARE FORMED, SAID SOLVENT BEING AT LEAST PARTIALLY MISCIBLE WITH LIQUID CARBON DIOXIDE AND WITH THE ORIGINAL MIXTURE, AND DOES NOT FORM THREE PHASES WITH THE MIXTURE AND LIQUID CARBON DIOXIDE EFFECTING PHASE SEPARATING OF THE ROFFINATE AND EXTRACT UNDER SAID PRESSURE; REMOVING CARBON DIOXIDE FROM THE EXTRACT PHASE; SETTLING THE EXTRACT PHASE SUBSTANTIALLY FREE OF CARBON DIOXIDE, WHEREUPON AN EXTRACT-RAFFINATE AND AN EXTRACT-EXTRACT ARE FORMED; EFFECTING PHASE SEPARATION OF THE EXTRACT-RAFFINAATE AND THE EXTRACTEXTRACT; REMOVING SOLVENT FROM THE EXTRACT-RAFFINATE, THEREBY OBTAINING A HYDROCARBON FRACTION OF HIGHER VISCOSITY INDEX THAN THAT OF THE ORIGINAL HYDROCARBON MIXTURE.