Solvent refining lubricating oils with a dual solvent system

Claim 1

A PROCESS FOR REMOVING AROMATIC, OLEFINS, WAXES AND ASPHALTENES FROM HYDROCARBON LUBRICATING OIL TO PROVIDE AN OIL OF INCREASED STABILITY AND IMPROVED VISCOSITY INDEX WHICH COMPRISES: INTRODUCING A LUBRICATING OIL CHANGE STOCK PREDOMINANTLY FORMED OF PARAFFIN HYDROCARBONS AND CONTAINING A MINOR AMOUNT OF THE UNSTABLE AND UNDESIRED HYDROCARBONS INTO AN EXTRACTION ZONE AT AN INTERMEDIATE LEVEL OF SAID ZONE, INTRODUCING CARBON DISULFIDE IN THE AMOUNT OF 1-50% BY VOLUME OF THE OIL BEING TREATED INTO THE EXTRACTION ZONE NEAR THE TOP THEREOF, INTRODUCING ACETONITRILE INTO THE EXTRACTION ZONE NEAR THE BOTTOM THEREOF, TAKING THE ACETONITRILE AND SAID UNSTABLE AND UNDESIRED HYDROCARBONS OVERHEAD FROM SAID EXTRACTION ZONE TO AN EXTRACT DISTILLATION ZONE, REMOVING SUBSTANTIALLY PURE ACETONITRILE VAPOR FROM THE TOP OF SAID EXTRACT DISTILLATION ZONE, CONDENSING SAID ACETONITRILE VAPOR AND INTRODUCING THE LIQUID ACETONITRILE INTO THE LOWER PORTION OF SAID EXTRACTION ZONE, WITHDRAWING THE UNSTABLE HYDROCARGONS FROM THE BOTTOM OF SAID EXTRACT DISTILLATION ZONE, TAKING THE CARBON DISULFIDE AND STABLE HYDROCARBON LUBRICATING OIL FROM THE BOTTOM OF SAID EXTRACTION ZONE TO A RAFFINATE DISTILLATION ZONE, REMOVING SUBSTANTIALLY PURE CARBON DISULFIDE VAPOR FROM THE TOP OF SAID RAFFINATE DISTILLATION ZONE, CONDENSING SAID CARBON DISULFIDE VAPOR AND INTRODUCING THE LIQUID CARBON DISULFIDE INTO THE UPPER PORTION OF SAID EXTRACTION ZONE, AND WITHDRAWING THE STABLE HYDROCARBON LUBRICATING OIL FROM THE BOTTOM OFSAID RAFFINATE DISTILLATION ZONE, SUBSTANTIALLY FREE OF UNDESIRABLE UNSTABLE HYDROCARBONS.