| Nowadays considerable attention has been paid to atmospheric environmental problems.Various countries in the world have issued strict standards for the motor vehicle fuel oils which is the main source of the atmospheric pollutions.As one of the main pollutants in fuel oil,the removal of the sulfur-containning compounds has become a hot topic for both industry and academia.Sulfur compounds will be converted to SOx after combustion,which is the main cause of acid rain formation,and also can promote the aggrevation of haze.Besides,soulfur compounds can posion the three-way catalyst in vehicle pipelines,thereby indirectly increasing the emission of hydrocarbon and CO,aggrevating the air pollution.In refining industry,the widely used desulfurization technology is hydrodesulfurization?HDS?.But the reaction condation of HDS is very harsh which need high temperature,high pressure and sufficient hydrogen.In addition,because for the steric-hinerance effect,HDS has difficulties removing the thiophene derivatives which occupy a high content in fuel oil.So,higher cost is needed to accomplish the ultra deep desulfurization to meet the latest standard of China for clean fuel.Various of alternative non-hydrodesulfurization methods have been developed such as extraction desulfurization?EDS?,biological desulfurization?BDS?,adsorption desulfurization?ADS?and oxidative desulfurization?ODS?.Among new methods,ODS is considered as the most potential alternative technology to HDS because of its mild reaction conditions,high desulfurization ability of thiophene sulfides and low cost.However,in order to realize the industrial application of oxidative desulfurization process,there are still many problems to be solved urgently.For example,the activity of Keggin-type heteropoly acid is not high enough and a large amount of oxidant H2O2 is consumed.In other oxidative desulfurization systems using H2O2 as oxidant,the utilization rate of H2O2 is too low.And a large amount of H2O2 is decomposed into oxygen and water rather than participating in the oxidation desulfurization reaction,resulting in waste of resources.In the process of oxidative desulfurization,acetonitrile and other extractive solvents are needed to separate oxidized sulfur compounds from oils.The use of such organic solvents not only increases the cost of investment,but also has certain environmental toxicity,and the use of nitrogen-containing extractants may cause secondary pollution of oils.In order to solve the above problems,several new catalytic systems and catalysts have been explored in this paper.On the basis of the original research,the classical Keggin type polyacid catalyst has been heat-treated to enhance its activity greatly.The morphology,activity and reaction mechanism of the catalyst were analyzed in detail through simulated oxidation desulfurization experiments and different characterization analysis.The effects of different reaction conditions on sulfide removal efficiency in different reaction systems were investigated.?)Graphene oxide?GO?and nitric acid modified carbon black?mCB?were prepared as adsorbents.The oxidative-adsorptive desulfurization experiments of simulated oil containing 250 ppm DBT were carried out in octanal-air oxidation system without any catalyst and extractant.XRD,SEM,TEM and FT-IR were used to characterize the structure,morphology and surface functional groups of the prepared carbon materials.It was found that monolayer GO was successfully prepared,and both GO and modified mCB had abundant oxygen functional groups.By investigating the effects of reaction temperature,octanaldehyde dosage and adsorbent dosage on the oxidative desulfurization efficiency,it was found that the removal efficiency of DBT by mCB and GO could reach 90%after 5 hours of reaction at the reaction condition of 60 ?,n?DBT?:n?octanaldehyde?= 1:24,m?simulated oil?:m?adsorbent?= 200:1.And the desulfurization ability of GO was remained after three times recycles.The results of desulfurization experiments on simulated oil containing different thiophene sulfides by oxidation adsorption desulfurization system show that the removal efficiency of 4,6-DMDBT and TH is the best when mCB is used as adsorbent,reaching 96.1%and 95.2%respectively.The order of reactivity of four kinds of sulfides when mCB is used as adsorbent is:4,6-DMDBT>TH>DBT>BT;when GO is used as adsorbent,the removal efficiency of TH reched the best of 98.4%.The order of reactivity of four sulfides on GO adsorbent is TH>DBT>4,6-DMDBT>BT.Through the comparative experiments,it was also found that the adsorption capacity of the two adsorbents for oxidized sulfides?45.4 mg-S/g-sorb?was far greater than that for unoxidized DBT?8.1 mg-S/g-sorb?,which also provided theoretical support for the combination of oxidized desulfurization and adsorption desulfurization in the industrial application.?)Several oxide and carbide catalysts containing transition metal W and Mo were prepared.The removal efficiency of DBT from simulated oil was investigated with hydrogen peroxide as oxidant,and PWOx prepared by phosphotungstic acid calcination possessing the best desulfurization activity was screened out.The effects of reaction temperature,oil concentration,hydrogen peroxide dosage and catalyst dosage on oxidative desulfurization were investigated.It was found that the desulfurization effect of PWOx could reach 100%after 4 hours when the reaction temperature was 40 ?,the initial sulfur content of simulated oil was 50 ppm,the dosage of hydrogen peroxide was O/S=10,and the dosage of catalyst was m?PWOx?:m?oil?=0.5%.FT-IR characterization showed that PWOx retained the structure of Keggin-type heteropoly acid,which may be the main reason for its strong catalytic activity.PWOx was loaded on g-C3N4 prepared from urea to synthesized the composite catalyst PWOx/g-C3N4.The effects of loading methods of PWOx on the desulfurization activity of PWOx/g-C3N4 composites were investigated.It was found that the catalytic activity of supported catalysts decreased significantly compared with that of unsupported PWOx,regardless of the loading methods.Through FT-IR characterization analysis,it can be seen that only the characteristic peak of g-C3N4 was found in the spectrum of PWOx/g-C3N4 composite,but there was no characteristic component of polyacid structure in PWOx catalyst.Therefore,it was concluded that the reason for the decrease of catalyst activity after loading was that the structure of PWOx changed during the loading process or the active site of PWOx was covered by g-C3N4,which will both resulted in the decrease of composite activity.The reaction conditions of oxidative desulfurization of PWOx/g-C3N4 composites were optimized.It was found that the maximum desulfurization efficiency of the composites was 79.55%when the reaction temperature was 40 ?,the PWOx loading was 33%,the initial sulfur content of simulated oil was 200 ppm,and the O/S ratio was 1:16.The reaction mechanism was preliminarily explored by adding ·OH trapping agent dimethyl sulfoxide.It was found that the desulfurization efficiency of PWOx decreased from 100%to 30%after adding OH trapping agent,which indicated ·OH was the main active species in the system.?)Three classical Keggin-type heteropoly acids HPW,HSiW and HPMo were heat-treated by calcination.The oxidative desulfurization effect of the samples obtained at different calcination temperatures was investigated.The optimum calcination temperature for each heteropoly acid was determined.The experimental results showed that the activity of HSiW and HPMo reached the maximum at 250 ? for 1 h,and the maximum desulfurization rates were 68.3%and 95.5%,respectively.The activity of HPW reaches the maximum after calcining at 550 ? for 1 h,and the desulfurization rate can reach 100%.After the best desulfurization effect is achieved,the desulfurization activity of calcined samples decreases with the further increase of temperature.The effect of calcination time on desulfurization efficiency of HPW was investigated.It was found that the desulfurization activity of HPW decreased with the increase of calcination time after calcination for 1 hour at 550 °C.XRD,FT-IR and TGA were used to characterize the structure and catalytic activity of HPW in different calcination conditions.Heat treatment of HPW at 250-350 ? will lose the adsorbed water on the surface and the crystalline water inside the crystal structure.This process is conducive to the full exposure of the active sites inside HPW and can promote the its catalytic oxidation activity.When the temperature reaches 450-550 ?,the Keggin structure in HPW crystals will be defective,resulting in "denuded" polyacid anion(PW12O38)3-,which has strong catalytic activity,and the desulfurization performance of the heat treated PW samples will be significantly enhanced.Although there are obvious O vacancies in the crystals under this condition,the Keggin structure of polyacids can remain intact.(PW12O38)3-has a certain thermal stability,but when the heat treatment time exceeds 3 hours at 550 ? or the calcination temperature further increases to 650?,the Keggin-structured(PW12O38)3-will be decomposed into small particles of WO3,which gradually deprives the catalyst of oxidative desulfurization activity.The reason for the enhanced activity of HPW after calcination was analyzed by NMR characterization.It was found that the sample PW5501 abtained by calcination at 550? for 1h contained a large number of defective states?PW,2O38?3-.Compared with the HPW with intact Keggin structure,the defective states(PW12O38)3-was easier to be attacked by hydrogen peroxide at the same concentration of hydrogen peroxide to produce peroxy polyacid(PO4[WO?O2?2]4}3-),so it has strong desulfurization ability in oxidative desulfurization system using hydrogen peroxide as oxidant.The desulfurization activity of STAPW5501 amphiphilic catalyst synthesized by PW5501 and surfactant STAB was further enhanced.Under the conditions of reaction temperature 50 ?,catalyst dosage 0.05 g and hydrogen peroxide dosage O/S=2:1,98.8%desulfurization rate could be achieved in 60 minutes.The catalyst has strong desulfurization activity,high utilization rate of oxidant H2O2,reduced the cost of oxidant input,and has a good prospect of industrial application.?)Using QPW synthesized from PW5501 and STAB as active component,a three component core-shell composite SiO2@C-dots/QPW was successfully prepared by sol-gel method using C-dots prepared as an assistant catalyst and SiO2 as carrier?The synthesized composite material was used as both catalyst and adsorbent in the oxidative desulfurization of simulated oil products.The specific surface area,pore structure,morphology and element composition distribution of the composites were characterized by N2 adsorption and desorption,SEM-EDX and TEM.It is found that the composite material is a mesoporous spherical material with a diameter of about 200 nm-1 ?m.SiO2 is act as a spherical core,C-dots and QPW cover the surface of SiO2 to form a shell with a thickness of 20-50 im.The effect of the loading of QPW and C-dots on the desulfurization activity of the catalyst was investigated through the experiment of oxidation adsorption desulfurization,and the amount of hydrogen peroxide in the process of oxidation adsorption desulfurization was optimized.The experimental results show that when the load of QPW is 25%and the load of C-dots is 0.45%,SiO2@C-dots/QPW can achieve 98.08%desulfurization rate under the condition of O/S=1.75 of the amount of hydrogen peroxide.The TOF and pseudo-first-order kinetics equation fitting of the oxidation-adsorption desulfurization reaction show that C-dots play an important role in the catalytic process of SiO2@C-dots/QPW.After loading 0.45%C-dots,the desulfurization rate of the catalyst in OADS can be increased by nearly 20 times.EPR characterization tests show that C-dots in composites can react with H2O2 to produce OH with strong oxidation ability in the process of OADS using H2O2 as oxidant.The OH generated can directly participate in oxidation reaction by oxidizing DBT,on the other hand,it can indirectly participate in oxidative desulfurization by oxidizing the highly active polyacid type active component(PW12O38)3-in QPW to peroxide polyacid {PO4[WO?O2?2]4}3-.Therefore,C-dots as a co-catalyst can not only improve the efficient utilization of hydrogen peroxide,but also promote the catalytic efficiency of QPW.By characterizing the reaction products by GC-MS and HPLC-MS,the oxidation products DBTO,which need one oxygen,and DBT02,which need two oxygen,are both formed in the reaction process and adsorbed on the catalyst materials efficiently.In conclusion,the synergistic effect of high activity[PW12O38]3-,core-shell microsphere structure and co-catalyst C-dots ensures that the prepared SiO2@C-dots/QPW still has very high desulfurization performance at low oxidant dosage.In this system,the catalyst activity is significantly enhanced,the utilization efficiency of hydrogen peroxide is greatly improved,the amount of hydrogen peroxide is obviously reduced,and no extractant is needed.It has important reference significance for the practical application of oxidative desulfurization process. |
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