solvent extraction - refining process used to separate reactive components (unsaturated hydrocarbons) from lube distillates in order to improve the oil’s oxidation stability, viscosity index (V.I.), and response to additives. Commonly used extraction media (solvents) are: phenol, N methyl pyrrolidone (NMP), furfural, liquid sulfur dioxide, and nitrobenzene. The oil and solvent are mixed in an extraction tower, resulting in the formation of two liquid phases: a heavy phase consisting of the undesirable unsaturates (see hydrocarbon unsaturates) dissolved in the solvent, and a light phase consisting of high quality oil with some solvent dissolved in it. The phases are separated and the solvent recovered from each by distillation. The unsaturates portion, or extract, while undesirable in lubricating oils, is useful in other applications, such as rubber extender oils (see rubber oil) and plasticizer oils.