Method of rerefining waste oil by distillation and extraction

A process for recovering base oil of lubricating viscosity from used oil, said process comprising the steps of:

• distilling said used oil in a distillation apparatus comprising a packed column;
• withdrawing at least a portion of at least two distillate fractions from said distillation apparatus for further treatment;
• extracting impurities from at least one of said withdrawn distillate fractions with a liquid extractant;
• removing at least a major portion of said extractant, and impurities dissolved therein, from said at least one of said withdrawn distillate fractions;
• wherein said distillation apparatus has more than one theoretical plate interposed between any two immediately adjacent distillate fractions withdrawn from said distillation apparatus.

A process for recovering base oil of lubricating viscosity from used oil, said process comprising the steps of:

• distilling said used oil in a distillation apparatus comprising a packed column;
• withdrawing at least one distillate fraction and a bottoms fraction from said distillation apparatus;
• extracting impurities from at least one said distillate fraction with a liquid extractant;
• removing at least a major portion of said extractant, and impurities dissolved therein, from at least one of said withdrawn distillate fractions;
• wherein said distillation apparatus has more than one theoretical plate for separating the bottoms fraction from the heaviest distillate fraction from which impurities are extracted using said liquid extractant.

A process for recovering base oil of lubricating viscosity from used oil, said process comprising the steps of:

• distilling said used oil in a distillation apparatus comprising a packed column;
• withdrawing at least two distillate fractions from said distillation apparatus;
• extracting impurities from at least one said withdrawn distillate fractions with a liquid extractant;
• removing at least a major portion of said extractant, and impurities dissolved therein, from at least one said withdrawn distillate fractions;
• wherein said distillation apparatus has more than one theoretical plate for separating the lightest withdrawn distillate fraction from the immediately adjacent heavier distillate fraction from which impurities are extracted using said liquid extractant.

A process for recovering base oil of lubricating viscosity from used oil, said process comprising the steps of:

• distilling said used oil in a distillation apparatus comprising a packed column;
• withdrawing at least one distillate fraction and light by-product from said distillation apparatus;
• extracting impurities from at least one said withdrawn distillate fractions with a liquid extractant;
• removing at least a major portion of said extractant, and impurities dissolved therein, from at least one of said withdrawn distillate fractions;
• wherein said distillation apparatus has more than one theoretical plate for separating said light by-product from the immediately adjacent heavier distillate fraction from which impurities are extracted using said liquid extractant.