Study On Separation Of Used Lubricants By Supercritical Fluid Extraction And Its Molecular Composition Regulation

Lubricants are essential petrochemical products,which can effectively reduce friction damage between machinery and prolong its service life.As a consumable,the reserves of used lubricants increase year by year.The non-ideal components of used lubricants are relatively minor,their recycling can effectively alleviate the problems of resource shortage and environmental pollution.Because of the high economic value,it is possible to recycle the ideal components.As the mainstream regeneration process presently,there are some problems in distillation and hydrogenation,such as coking of heavy components by thermal reaction,resulting in equipment damage.Molecular distillation and membrane separation are challenging to industrialize due to the high cost and slight separation amount.Supercritical fluid extraction technology utilizes the characters of solvents with extremely high solubility under low temperature and high pressure,which can effectively separate the non-ideal components of used lubricants,reduce the coke production of extractions,and facilitate the subsequent thermal processing and refining process.At the same time,with the introduction of“petroleomics”,the cognition of petroleum products has risen to the molecular level.Mass spectrometry and other means can help us understand the extraction and separation process from the molecular level and provide adequate theoretical support for subsequent optimization.In this thesis,firstly,the extraction effects of different solvents are compared with the help of the supercritical fluid extraction separation device.Propane and CO₂are carried to the supercritical extraction experiments respectively.The properties of the fractions and residues are analyzed.The results show that compared with supercritical propane,supercritical CO₂can separate used lubricants by narrow fractions according to different boiling point distributions.The removal rates of oxides,metal impurities and heavy components are higher,and the industrial application value is higher.After that,the molecular composition of extractions and residues under different supercritical CO₂extraction conditions are characterized and analyzed.Orbitrap Fusion combined with varying ionization sources is used to analyze the composition changes of main hydrocarbons and oxides of used lubricants during extraction.The results show that increasing pressure and decreasing temperature can increase the distributions of carbon number and the double bond equivalence（DBE）,and the influence of pressure on composition is more significant than temperature.As CO₂is a non-polar solvent,it has low solubility to polar compounds.At the same time,with the increase of complexity of compounds,the solubility of CO₂gradually decreases,so the polar non-ideal components in used lubricants can be effectively removed.Finally,the coke components of used lubricants are studied.The coking process is simulated by the thermogravimetric experiment,and the coke production of the extraction fractions and the residues in supercritical CO₂separation of used lubricants is compared.The results show that compared with feedstocks,the coke production of extraction fractions decreases obviously,and the coke production of residues increases significantly.According to the mass spectrometry results,small molecule compounds in used lubricants do not participate in the coking process.Compounds with high carbon numbers and high condensation degree have a higher contribution to the coking process.