Study On The Preparation And Performanceof Novel Catalytic Materials Based On Deep Oxidativedesulfurization Of Fuel Oil

The combustion of sulfur compounds in fuel oil will produce sulfur oxides(SOx).As one of the major atmospheric pollutants,the excessive SOx emissions not only result in acid rain,but also lead to haze weather,thus inducing human respiratory disease,angiocardiopathy and even cancers.Besides,the sulfur compounds in fuel oil will poison the catalysts of exhaust treatment in automobile,thus greatly increasing the emissions of nitrogen oxides(NOx),carbon monoxide(CO)and hydrocarbons(CH),to further pollute the atmospheric environment.Facing these hazards caused by sulfur compounds in fuel oil,governments have promulgated increasingly stringent sulfur emission standards,and the efficient and practical fuel desulfurization technology has become the effective way to solve suchpollution problems and meet the requirements of environmental regulations.Among many fuel oil desulfurization methods,the oxidative desulfurization(ODS)is considered as a technology with great application potentials,due to its mild reaction condition,low energy consumption,high desulfurization efficiency,and satisfactory removal efficiency for the aromatic heterocyclic sulfur compounds including thiophene(TH),benzothiophene(BT),dibenzothiophene(DBT),4,6-dimethyldibenzothiophene(4,6-DMDBT)and so on.The development and application of novel catalytic materials is the core driving force for the progress of this technology.Based on this,a series of novel materials including Dawson-type polyoxometalates,polyoxometalates-graphene oxide(GO)composites,amphipathic C-Si particles supported with phosphotungstic acid,and sulfonated carbon materials were prepared successively in this article,and used as the catalysts in different ODS sytems.Through the adjustment of the structure-activity relationship,the ODS reactions in traditional air/octanal system,emulsion system and ozone system were improved.The detailed work is as follows:(1)In the traditional air/octanal system,the excessive amount of aldehyde additives leads to the increase of raw material cost.Also,the produced carboxylic acid after reaction will affect the oil quality.To overcome these shortcomings,a series of Dawson-type polyoxometalates were prepared and characterized by Fourier transform infrared spectroscopy(FT-1R),inductively coupled plasma emission spectroscopy(ICP-OES)and nuclear magnetic resonance phosphorus spectroscopy(3'P NMR).Then,the prepared materials were used as catalysts for ODS reaction in air/octanal system.The results showed that K6[?-P2W18O62]·14H2O exhibited the best catalytic performance among the prepared polyoxometalates.Using it as the catalyst,the effects of temperature,initial sulfur content and different sulfur compounds on the reaction were discussed in detail to determine the optimum reaction conditions.The kinetic study showed that the reaction conformed to the first order kinetic equation.Then,its catalytic performance was compared with K3PW12O40 IOH2O and aldehyde assistant.The result showed that its catalytic performance was superior to K3PW-2O40 10H2O.Compared with only using aldehyde assistant as catalyst,the desulfurization ratio was increased from 85.43%to 99.63%,the reaction time was decreased from 4 h to 2 h,and the molar ratio of octanal to sulfur atom was decreased from 24:1 to 4:1.The decrease of aldehyde additives not only reduces raw material cost,but also depresses the produced carboxylic acid after reaction to improve the oil quality.Finally,the reaction products were identified as sulfone and octanoic acid by gas chromatography-mass spectrometry(GC-MS).The reaction mechanism was studied in detail by gas chromatography analysis and comparative experiments,and the active species in the reaction were identified as peroxo polyoxometalate and peroxo acid.(2)To solve the problems caused by the oxidation products removal process in the traditional systems,such as the high equipment investment and complex technological process.K6[a-P2W18O62]·14H2O with the best catalytic performance was supported on graphene oxide(GO)by hydrothermal method to prepare K6P2W18O62/GO multifunctional composites,and characterized by FT-IR,ICP-OES.X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),transmission electron microscopy(TEM).X-ray photoelectron spectroscopy(XPS)and nitrogen adsorption-desorption.Then,the prepared material was used as the catalyst-sorbent for ODS reaction in air/octanal system,and the effects of temperature,initial sulfur content and different sulfur compounds on the reaction were discussed in detail to determine the optimum reaction conditions.Due to the excellent adsorption performacne of GO for the oxidation product sulfone,in-situ removal of sulfur compounds from fuel oil could be achieved without post-treatment for the oxidation products,and the catalyst still exhibited good catalytic activity after at least 5 resues.Compared with the ODS reaction using GO as adsorbent,the desulfurization ratio was increased from 89.21%to 96.10%,and the molar ratio of octanal to sulfur atom was decreased from 24:1 to 4:1,when the laoding amount of potassium phosphotungstate in K6P2W18O62/GO was 17.5%.To overcome the mass loss of K6P2W18O62/GO in the recycle processes,K6P2W18O62/mGO was prepared by using magnetic graphene oxide(mGO)insteadof GO as carrier.The result showed that K6P2W18O62/mGO exhibited the same desulfurization performance as K6P2W18O62/GO,and K6P2W18O62/mGO could be easily recovered after reation with the introduction of an external magnetic field.According to the recovery experiment,it could be seen that K62W18O62/mGO was also a stable catalyst-sorbent,exhibiting good catalytic activity after at least 5 resues.Besides,the catalyst could be magnetically separated even after being reused 5 times.Through the magnetic separation to recover the catalyst,the recovery ratio of catalyst was greatly improved,thus avoiding the mass loss caused by the conventional filtration operation.Besides,combined with acetonitrile extraction,the desulfurization process could be completed in a very short time,under the multiple effects of oxidation,adsorption and extraction.GC-MS analysis showed that most of the oxidation products sulfone and octanoic acid could be removed by adsorption.Combined with extraction,all the products could be removed to obtain the ultra-clean model oil.(3)To overcome the mass transfer resistance between interfaces in traditional bi-phase system and the difficulty of recovery for traditional amphiphilic catalysts,the high active Keggin-type phosphotungstic acid component was supported on Janus C-Si nanoparticles by one-step synthesis method,and the obtained amphiphilic catalytic material was characterized by FT-IR.XPS,SEM,EDS,TEM and nitrogen adsorption-desorption.Using H202 as oxidant,its catalytic performance in different systems including octane/aceton itri le,octane/methanol,octane/BimPF6,octane/BimBF4 and octane/water were studied.According to the experiment,the uniform and stable Pickering emulsions were formed in octane/acetonitrile and octane/methanol systems,while the catalytic materials were dispersed uniformly in the hydrophilic phase of other systems.According to the analysis,this phenomenon was caused by the difference of two phases' polarities.For the formed emulsion systems,the octane/acetonitrile system showed better desulfurization performance than octane/methanol system.From the observation by an electron microscope.smaller micron droplets of acetonitrile were formed to enlarge the contact area between oil phase and water phase,thus overcoming the mass transfer resistance between interfaces and improving the desulfurization efficiency.Then,the effects of catalyst dosage,temperature,initial sulfur content,molar ratio of H2O2 to sulfur atom,pre-contact time of catalyst in H2O2 and different sulfur compounds on the reaction were discussed in detail to determine the optimum reaction conditions.After reaction,the catalyst could be easily recovered by centrifugal operation,and it still maintained a good catalytic performance after 5 recyles.Also,the system was applicable for real oil,and its desulfurization performance was better than the traditional bi-phase system and emulsion system,even the reaction was carried out without stirring.According to the study on reaction mechanism,the desulfurization capacity of prepared material was attributed to its Janus feature and the catalytic activity of phosphotungstic acid.(4)To activate the oxygen at room temperature and overcome the shortcomings using ozone as oxidatant,such as the hazards to atmospheric environment and adverse effect on oil quality,a series of sulfonated graphene materials were prepared using GO as raw material by reduction-sulfonation method.hydrothermal method,or direct sulfonation process by concentrated sulfuric acid,named as r-SGO,th-SGO and dir-SGO,respectively.Sulfonated starch carbon materials were prepared from starch carbon through the hydrothermal method or direct sulfonation process by concentrated sulfuric acid,named as th-SC and dir-SC.The prepared materials were characterized by XRD,Raman spectroscopy,FT-IR,XPS,SEM,EDS,TEM and nitrogen adsorption-desorption.Then,using ozone and oxygen mixture as oxidant and acetonitrile as extractant,photocatalysis-ozonation desulfurization system was studied at a very low concentration of oxidant.The results showed that r-SGO exhibited the best performance,due to its high C-OH content,substantial defect sites,high surface area and excellent dispersity,the sulfur compounds could be compleltely removed in the model oil.Based on this system,the reduction of ozone supply and the application of the self-made experimental device have overcome the environmental problems and the degradation of oil quality caused by excessive ozone emission and its direct contact with model oil.In addition,the prepared sulfonated carbon materials were dispersed in acetonitrile solution byultrasound,and pretreated by gas oxidant under UV irradiation for a period of time to obtain the dispersion containing peroxy-sulfonated carbon materials.Without adding any oxidant,the obtained dispersion was directly mixed with the model oil to achieve deep desulfurization at a given temperature.The result showed that th-SC with the most number of sulfonic groups exhibited the best catalytic performance.On one hand,this experimental design solved the environmental problems caused by excessive ozone emission and avoided the degradation of oil quality resulted from its direct contact with model oil.On the other hand,this system showed much cleaner GC-MS spectra than the photocatalytic system and single ozonation system after reaction,which indicated that an excellent selectivity was exhibited in the reaction to obtain the sole sulfone product,due to the mild reactivity of peroxo-sulfonic group.