Solvent extraction

Claim 1

THE PROCESS OF SEPARATING A HYDROCARBON MIXTURE SELECTED FROM THE GROUP CONSISTING OF HYDROCARBON MIXTURES WITHIN THE RANGE OF 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 (S) UNDER SUFFICIENT PRESSURE TO MAINTAIN A CARBON DIOXIDE-RICH PHASE IN THE LIQUID PHASE, SAID SOLVENT(S) BEING SELECTED FROM THE GROUP CONSISTING OF FURFURAL, TRIACETIN, ETHYL MELEATE, BETA-CHLOROETHYL ACETATE, ACETONITRILE, ETHANOL, METHANOL, METHYL FORMATE, DIMETHYL FORMAMIDE, BETA-METHOXYETHANOL, CHLOROACETONE, ETHYL SULFATE, NITROETHANE AND SULFUR DIOXIDE, SAID SOLVENT (S) BEING INCAPABLE OF BEING RENDERED MISCIBLE WITH SAID HYDROCARBON MIXTURE UPON THE ADDITION THERETO OF LIQUID CO2, THE RATIO OF THE QUANTITY OF LIQUID CARBON DIOXIDE TO THE QUANTITY OF SOLVENT (S) BEING FROM ABOUT 2:1 TO ABOUT 1:2 BY WEIGHT, WHEREUPON A RAFFINATE PHASE AND AN EXTRACT PHASE ARE FORMED: EFFECTING PHASE SEPARATION OF THE RAFFINATE AND EXTRACT UNDER SAID PRESSURE; REMOVING CARBON DIOXIDE AND SOLVENT (S) FROM THE RAFFINATE PHASE, THEREBY OBTAINING A HYDROCARRBON FRACTION OF HIGHER VISCOSITY INDEX THAN THAT OF THE ORIGINAL HYDROCARBON MIXTURE.