Trace solvent recovery in selective solvent extraction

Claim 1

In a process for solvent refining a petroleum based lubricating oil stock containing aromatic and non-aromatic components wherein said lubricating oil stock is contacted with substantially water-free N-methyl-2-pyrrolidone as solvent effecting separation of said lubricating oil stock into an aromatics-rich extract fraction comprising a major portion of said solvent and an aromatics-poor raffinate fraction comprising a minor portion of said solvent, and solvent is recovered from each of said fractions by distillation and steam stripping, the improvement which comprises steam stripping said raffinate to a residual solvent content in the range of 0.1 to 1.0 weight percent, and contacting the resulting stripped raffinate fraction with water in a water extraction step in an amount equivalent to 4 to 10 parts water by weight per part solvent contained in said stripped raffinate thereby extracting substantially all remaining solvent from said raffinate and producing a solvent-free raffinate product and wash water comprising solvent recovered from said product, separating water from said wash water by distillation and thereby recovering water-free solvent from said wash water, and returning said water-free solvent to said lubricating oil stock contacting step as a portion of the solvent therefor.