Single stage refining of high-viscosity lubricating oil using N-methyl-2-pyrrolidone (NMP) was carried out. The suitable operating conditions of the NMP refining were determined by orthogonal test and mathematical ways. On this basis, a simulate-three-stage extraction and dewaxing tests of NMP were done. The results show that the operation conditions of NMP anhydrous extraction are [KG*4]as follows: extracting [KG*4]temperature 87 ℃, the [KG*4]volume [KG*4]ratio [KG*4]of [KG*4]solvent to oil is 0.75. Under same conditions, NMP anhydrous single-stage extraction are as follows: the yield of refined oil is 90.1%, the refractive index is 1.464 5 at 60 ℃. NMP anhydrous simulate-three-stage extraction are as follows: the yield of refined oil is 90%, the refractive index is 1.462 2 at 60 ℃. Volume fraction of water 1.5% of extraction suitable operating conditions are as follows: extracting temperature 88.5 ℃, the volume ratio of solvent to oil is 1.38.Under same conditions, NMP single-stage extraction are as follows: the yield of refined oil is 87.7%, the refractive index is 1.463 1;NMP simulate-three-stage extraction are as follows: the yield of refined oil is 87%, the refractive index is 1.461 0 at 60 ℃. From refractive index changes to know that the effect of simulate-three-stage test is better than single-stage extraction test.  

High-viscosity lubricating oil,    ,  NMP (N-methyl pyrrolidone),    , Viscosity index,    ,  Single-stage extraction,    ,  Simulate-three-stage extraction