Method for pre-hydrotreating and purifying waste lubricating oil

A method for pre-hydrotreating and purifying waste lubricating oil, comprising the steps of:

• S100) removing small-particle mechanical impurities from waste lubricating oil with a filter;
• and separating free water and a portion of light hydrocarbons from the waste lubricating oil having been filtered in a flash distillation column to obtain a bottom product;
• S200) mixing the bottom product with hydrogen gas and a self-sulfurizing oil-soluble transition metal catalyst to obtain a mixture;
• and pre-hydrotreating the mixture in a slurry bed hydrogenation reactor to obtain a first output;
• S300) separating the first output to obtain a hydrogen-rich gas and a second output;
• removing hydrogen sulfide and hydrogen chloride from the hydrogen-rich gas in an adsorption tower;
• and recycling with a circulating hydrogen compressor the hydrogen-rich gas from which hydrogen sulfide and hydrogen chloride have been removed;
• S400) separating the second output with a first-stage hydrocyclone separator and a second-stage hydrocyclone separator to obtain a liquid product;
• causing a tailing residue obtained from the first-stage hydrocyclone separator to mix with a solvent and then enter the second-stage hydrocyclone separator;
• and causing a tailing residue obtained from the second-stage of hydrocyclone separator to enter a solvent recovery tower from which a solid residue is discharged;
• and
• S500) mixing the liquid product from the first-stage hydrocyclone separator and from the second-stage hydrocyclone separator with an output from a top of the solvent recovery tower to obtain a purified lubricating oil product, wherein:
• in S200, the mixture enters the slurry bed hydrogenation reactor through a bottom of the slurry bed hydrogenation reactor and then flows upwards
• the self-sulfurizing oil-soluble transition metal catalyst includes one of molybdenum, nickel, iron and cobalt;
• and
• S400 further includes setting the first-stage hydrocyclone separator and the second-stage hydrocyclone separator to operate at a temperature of 50-180° C.