Research On The Classification Regeneration Method And Tribological Performance Of Recovered Lubricating Oils

The shortage of petroleum resource has become an indisputable fact. The demand andconsumption of the lubricating oil increase sharply year by year in China. It is animportant practical significance to recycle used lubricating oils whether from theresource conservation or environmental protection. China has larger accumulationamount and the relatively backward recycling technology of used lubricating oilscomparing with developed countries. The improper disposal of used oils will result inwaste of resources and bring great pressure to the environment. According to thecharacteristics of used oils in China and the mature experience of used oils recycling inthe developed country, it is an important and practical problem to analyze the failurenature of used lubricating oils, explore the new regeneration method and develop thepractical recycling technology.In this dissertation, based on the failure analysis of20kinds of waste lubricating oils,the―classification regeneration additive‖method was put forward. Different usedlubricating oils, including industrial lubricants, gasoline engine oils and marine systemoils were recycled. The relevant recycling method and key technology were studied, andtheir recycling effect was evaluated by measuring physical and chemical properties andtribological performances. The oxidation process and mechanism of lubricating oils wereanalyzed and discussed by means of instrumental analysis and molecular dynamicssimulation method. The abrasive grain and friction surface were examined to analyzemechanismas of used lubricating oils lost losing efficacy and why recycled oils canrecover their lubrication performances. The main research contents and conclusions aredisplayed as follows.(1) According to the examination results about the conventional physical and chemicalproperties, infrared spectroscopic analysis, elemental analysis, particulate contaminationtesting and tribological performance analysis, the failure characteristics and regenerativepossibility of used hydraulic and engine oils were concluded.Additives in the lubricating oils depleted, the base oil oxidized partially, and a certaindegree of external and internal pollutants occurred whether for hydraulic oils or engineoils in the use process.Additive function declines in the changed chemical environment where the total acidnumber increases because of the oxidation of the lubricating oil. The tribological andchemical reaction film cannot be formed to lead the extreme pressure, anti-wear andantifriction performances to decline in the constant decrease of additives due to the oxidation reaction with metals on the friction surface and oxygen in the environment.The increasing of metal grindings results in three body abrasive wear, and it also plays acatalytic role of the lubricating oil oxidation. External liquid and solid pollutantsaccelerate the oxidation of lubricating oil and the additive failure. The interaction ofthese four led to the lubricating oil failure.The degrees of oxidation, additive depletion and pollution are different because of thedifferent use conditions of different types or same types and different grades oflubricating oils. Their failure will result some physical and chemical properties in aserious recession beyond the standard, and the tribological performance of used oilsdecline in part compared with that of fresh oils.But used lubricants still had a certain lubrication performance and potentialapplication.(2) Based on the failure analysis of used oils,10kinds of used industrial oils,including hydraulic oils, film bearing oils, steam turbine oils and gear oils were recycledto solve their invalidation problem and improve their tribological performances by theclassification regeneration additive method.The microanalysis of the wear scar surface by SEM (Scanning Electron Microscope),EDS (Energy Dispersive Spectrometer) and Raman spectrum showed that additivesdecomposed at a certain temperature in recycled o ils by reclamation and replenishingadditives. And the friction chemical reaction happened on the friction surface because ofthe active elements in molecules to produce the protective film containing FeS,orthophosphate and amorphous carbon so that they can provide excellent tribologicalperformances.Prepared regeneration additives provided excellent refortification function and hadpreferable adaptation. Different kinds of lubricating oils with similar problems can berecovered functionally and recycled by the given regeneration additives.(3) The tribological performances of recycled oils were studied at different loads (low,medium and high) and different sliding speeds (low, medium and high), with differentfriction pairs (steel/steel and brass/steel) for the diversity and complexity of the useconditions of industrial lubricating oils,Whether at the low or high load and sliding speed, whether friction pairs weresteel/steel or brass/steel, the recycled industrial lubricating oils all provided favorablelubrication performances.There is not common and immutable effect law of tribological systematic parameters(friction pairs, loads, sliding, etc.) on the tribological performances. (4) According to the failure characteristics of gasoline engine oils, suitablere-processed treatment process was brought up and regeneration additives were prepared.Used engine oils were recycled by the classification regeneration additive method. Theexperimental results confirmed that the typical physical and chemical performances,oxidation resistance and tribological performances of used engine oils were improvedremarkably, close to or exceeded that of fresh oils. The engine oils for the normalreplacement can be recycled effectively and its service life can be lengthened by theclassification regeneration additive method.(5) The used marine system oils were tried to recycle and upgrade to cylinder oils.Based on the systematic comparisons between differences of the marine diesel engine oiland the cylinder oil, the primary additives to improve total base number, kinematicviscosity, dispersion of clean and lubrication performance were prepared to recycle andupgrade the used system oils. The physical and chemical properties, total base numbers,tribological performances of marine oils recycle were close to those of fresh cylinderoils sold whose viscosity grade and total base number are SAE (Society of AutomotiveEngineers)50and70mgKOH/g, respectively.(6) The thermal oxidation law of lubricating oils with straight-chain andbranched-chain paraffin, cycloparaffin and aromatic base oils were investigated by themolecular dynamics simulation.It can be found that dehydration, oxidation, decomposition and cracking reactionsoccurred to generate unsaturated composites, the ring, alcohol, aldehyde, ketone,carboxylic acid and volatile organic compounds with small molecular weight in theoxidation process of mineral base oils with different structures. The oxidationmechanism and rule of mineral base oils by the molecular dynamics simulation confirmthe classic free radical chain reaction mechanism of lubricating oils.