Researches On The Direct Resource Utilization And Modified Graded Utilization Of Used Engine Oil

Engine oil or lubricating oil is widely used in various motor vehicles and mechanical equipment.However,after a long period of use,it will deteriorate due to the continuous contact with metal and air under high temperature,resulting in the formation and accumulation of some oxidation products and harmful substances,such as metal debris impurities,dust,carbon,colloid and asphaltene,which impair the oil's original functions of lubrication,antifraying,cooling,sealing,and antivibration.Then,the used engine oil?UEO?produced is difficult to meet the actual demand and needs to be replaced with fresh engine oil in time.In recent years,with the improvement of living standard of people,a large nmber of cars enter the personal family,and these cars change the engine oil at least once a year during maintenance.As of the end of June 2017,the number of motor vehicles in China has reached 304 million,according to the traffic bureau of the ministry of public security.If the oil is replaced by an average of 4 L?1.6 displacement?,the UEO produced by motor vehicles can reach 1.216×10⁹ L per year.If the UEO is discharged directly,it will have a great impact on the ecological environment and human health due to its difficulty in natural degradation.In view of the limitations of regeneration and pyrolysis process,the UEO is directly mixed with coal to prepare slurry and chemically modified to improve its added value and reduce the environmental pollution.After research,the UEO and coal can be completely made into oil–coal–water slurry fuel in the presence of additives;the SUEO dispersant obtained after chemical modification of UEO shows good dispersivity in the process of preparing coal water slurry?CWS?,and the effect of SUEO as a dispersant on the liquid-phase exfoliation of the graphite nanoplatelets into graphene was investigated.The main work includes the following 4 aspects:?1?Firstly,the coal–oil–water slurry?COWS?was successfully preparedby mixing the UEO with coal and water in the presence of additives.In the study,the slurry properties,such as slurryability,rheology,thixotropy,and stability,were studied systematically and deeply,and the dispersity and stabilization mechanism of COWS was discussed.The results showed that when increasing the amount of UEO in COWS,the apparent viscosity of COWS increased,the maximum coal content decreased,the fluidity became worse,but the stability of COWS increased evidently.At the same time,its pseudoplasticity and thixotropy behavior were also promoted as the amount of UEO was increased.When the apparent viscosity of COWS was constant,the lower heatingvalue of COWS increased with an increment in the amount of UEO.Within a certain temperature range,the apparent viscosity of COWS decreased with increasing the temperature.Therefore,increasing the temperature is beneficial to reduce the apparent viscosity and increase the fluidity of COWS in industrial applications.The COWS can not only be used for boiler combustion but also as a raw material for gasification.?2?The UEO was sulfonated by oleum,and the hydrophilic sulfonic acid groups were introduced to the certain components in UEO,so the[sulfonated used engine oil?SUEO?]with surfactant characteristics was successfully prepared.The structure and nature of SUEO dispersant was analyzed by FTIR,¹H NMR and surface tension.Then the SUEO dispersant was used to prepare coal–water slurry?CWS?,the effects of the preparation conditions of SUEO dispersant on the apparent viscosity of CWS were investigated.The performances of SUEO dispersant in CWS were analyzed through the measurement of slurryability,rheology and stability of CWS,and the dispersion mechanism of SUEO dispersant in CWS was also described.The results showed that the SUEO dispersant had the best ability of reducing viscosity than that of SDS and SL dispersant.When the dosage of SUEO dispersant was 0.3 wt.%,the CWS with 65 wt.%coal exhibited the lowest apparent viscosity?170 mPa·s?,and the maximum coal content could reach 71 wt.%.With the increase of coal content,the CWS changed from bingham fluid to yield pseudoplastic fluid.The stability of CWS prepared with SUEO dispersant was not ideal,which may be related to the relatively small molecular mass of SUEO dispersant.Since the SUEO dispersant consists of a series of sulfonates with different aromatic rings and side chains,so the amount of dispersant adsorbed on the surface of coal was large under the“filling effect”,and the hydration film was more compact,which is beneficial to improving the dispersity and stability of the CWS.?3?Since the molecular structure of tannic acid?TA?is very similar to that of coal surface and has a unique polyphenol hydroxyl structure,using TA and acrylic acid?AA?as raw materials,H₂O₂ as oxidant,KPS and NaHSO₃ as initiators,TAA dispersant with jellyfish-like 3D molecular structure,which was suitable for CWS,had been synthesized by grafting copolymerization.Employing FTIR and ¹H NMR,the molecular structure of TAA dispersant was characterizated,the pulping performance of TAA dispersant was examined,and the mechanism of the interaction between TAA dispersant and coal particles was also discussed.Then,in order to improve the pulping stability of SUEO dispersant,it was mixed with TAA dispersant for preparing CWS,investigating the effect of compound dispersant on the slurryability of CWS.The results showed that when the dosage of compound dispersant with n?SUEO?:n?TAA?=3:1 was 0.3 wt.%,the maximum coal content of CWS could reach 72 wt.%.In addition,the effect of compound dispersant on the slurryability of coal with higher degree of coalification was obvious.The SUEO and TAA dispersant were compounded and added into CWS,unde the synergistic effect they can exert each advantage,which greatly improves the coverage of dispersant on the coal surface,resulting in the significant electrostatic repulsion and steric hindrance between coal particles.The dispersant with this characteristic will be very helpful to improve the quality of CWS.?4?Base on the excellent performance of SUEO dispersant in CWS,it was employed as dispersant/stabilizer for exfoliating the graphene in an aqueous solution assisted by sonication to expand its range of application.The exfoliating and dispersing efficiency of SUEO dispersant was investigated and compared with that of traditional surfactants,such as sodium dodecyl sulfate?SDS?,sodium dodecyl benzene sulfate?SDBS?,cetyl trimethyl ammonium bromide?CTAB?,and polyvinylpyrrolidone?PVP?.The exfoliation and stabilization mechanism of SUEO dispersant was analyzed,the morphology and structure of graphene were characterized.The results showed that the SUEO dispersant had better exfoliation efficiency compared to traditional dispersants,the graphene dispersion with excellent stability had a highest concentration?0.477 mg/mL?than others at 0.5 g/L optimal SUEO dosage in 4 h sonication time.Microscopic?SEM,TEM,and AFM?and spectroscopic?XRD,XPS,and Raman?measurements revealed that the lateral dimensions of few-layer graphene sheets with smooth surface and lower levels of defects or oxidation ranged from several hundred nanometers to 2?m,and the thickness was less than 2 nm.