Study On Fuel Oil Desulfurization Based On Organic-inorganic Polyoxometalate Catalysts

Fuel oil is an important energy source in human production and life,which is widely used in the fields of transportation,electric power and building materials.The existence of sulfur compounds in fuel oil has brought serious harm to natural environment,human health and industrial production.Faced with the hazards caused by sulfur compounds in fuel oil,various countries and regions have introduced increasingly stringent fuel sulfur standards,and 10 ppm is already the highest sulfur content limit in fuel oil.It is imperative to implement efficient and practical fuel desulfurization technology because of pollution and environmental protection regulations.At present,the most commonly fuel desulfurization technology in the industry is hydrodesulfurization(HDS),but HDS needs to consume expensive hydrogen and needs to be carried out under high temperature and pressure conditions,which greatly increases economic cost.For this reason,various non-hydrodesulfurization technologies have been developed,such as extractive desulfurization(EDS),adsorption desulfurization(ADS),biological desulfurization(BDS)and oxidative desulfurization(ODS).Among the non-hydrodesulfurization technologies,ODS is considered to the most promising alternative to HDS in industry due to mild operation conditions and good removal effect on thiophene sulfides.The development and application of catalyst is one of the cores of ODS technology.Polyoxometalates(POMs)are highly efficient and multifunctional catalytic materials processing various structures and excellent properties.When POMs is used as catalyst for ODS,the interphase mass transfer problem makes it impossible for reactants to fully contact each other,which seriously hinders the improvement of ODS efficiency.Therefore,organic-inorganic hybrid materials based on POMs have developed rapidly in ODS field.This kind of material can make use of the lipophilicity of organic cations to promote the sulfide in the oil to approach the oxidation active center,reduce the mass transfer resistance,and make the reactants fully contact,thereby improving the desulfurization efficiency.Based on this,this paper takes POMs as the basic unit to chemically link with organic cations to construct new organic-inorganic hybrid materials.The properties of hybrid materials are often better than those of the two materials themselves.Through the ODS experiment and characterization analysis,the activity,structure and morphology of the catalyst were studied in detail,and the influence of different reaction conditions on the ODS efficiency was investigated,and the recovery effect and industrial value of the catalyst were evaluated.This article provides a basis for the design of various organic-inorganic polyoxometalate catalysts.The detailed work is as follows:(1)H3PWxMo12-XO40(x=1,3,6)and H4SiWxMo12-xO40(x=0,1,3,6,12)heteropolyacids with Keggin structure were prepared.The catalytic desulfurization performance of the prepared materials was compared in the simulated oil-extraction two-phase ODS system.Selecting the best catalytic activity[PW6Mo6O40]3-as the basic unit,through the substitution reaction with different quaternary ammonium cations for organic linkage,constructed three organic-inorganic hybrid catalysts.The structure and properties of prepared catalysts were analyzed by FT-IR,XRD and TGA,and the catalytic performance of organic-inorganic catalysts in the ODS system was compared.The result shows that ODAPW6Mo6 catalyst has the best catalytic desulfurization performance.Taking ODAPW6Mo6 as catalyst,various facters including catalyst dosage,oxygen-sulfur ratio,temperature and extractant were investigated.The DBT conversion rate reached 98.1%within 180 min using ODAPW6Mo6 catalyst.The experimental result of ODAPW6Mo6 catalyst for different sulfides shows that the order of sulfides reaction activity is:DBT>4,6-DMDBT>BT.The catalyst recovery experiment proved that the ODAPW6Mo6 catalyst can still maintain a high desulfurization rate after three ODS cycles.The catalyst also showed good catalytic activity in real diesel.(2)Three organic-inorganic hybrid catalysts based[SMo12O40]2-were prepared.Through FT-IR,XRD,SEM,TGA,XPS and other characterization methods,the catalyst structure,morphology,thermal stability and valence were analyzed in detail.The catalytic performance of each catalyst was evaluated using H2O2 as the oxidant and acetonitrile as the extractant.The experimental result shows that[TBA]2SMo12O40 catalyst has the best catalytic desulfurization performance.Using[TBA]2SMo12O40 as a catalyst,the impact of different reaction conditions on ODS efficiency were investigated.Under the best operation conditions,the DBT conversion rate reached 99.89%within 10 minutes.The catalyst has a good removal effect on different sulfides.The[TBA]2SMo12O40 and[Bmim]2SMo12O40 catalyst has good reuse performance.In addition,the catalyst can still maintain good catalytic activity in real diesel.In this system,the catalyst activity is high,the desulfurization time is short,and the optimal reaction temperature is room temperature,which highly decreases the economic input and has a good industrial application value.(3)The hot spot material carbon quantum dots(C-dots)was introduced,and three supported organic-inorganic catalysts with different supports were prepared.Through FT-IR,SEM,BET,EPR and other research techinques,the catalyst structure,morphology,specific surface area and mechanism of action have been investigated.The catalytic desulfurization performance of each catalyst was compared in the ODS system using H2O2 as the oxidant and acetonitrile as the extractant.The experimental result shows that[TBA]2SMo12O40/C-dots@MIL-101(Cr)catalyst has the best desulfurization effect.Using[TBA]2SMo12O40/C-dots@MIL-101(Cr)as the catalyst,the effect of the active component[TBA]2SMo12O40 loading,C-dots loading and oxygen-sulfur molar ratio on the desulfurization efficiency at room temperature were investigated.The optimal reaction conditions are as follows:[TBA]2SMo12O40 loading is 80%,C-dots loading is 1%,and oxygen-sulfur molar ratio is 6.Under the above reaction conditions,the DBT conversion rate reached 99.9%after 180 minutes of reaction.In addition,[TBA]2SMo12O40/C-dots@MIL-101(Cr)catalyst can remove 98%of sulfides in real diesel,and the reaction activity is not affected by complex oil components.The catalyst in this system is easy to recover,the amount of H2O2 is reduced,the desulfurization efficiency in real diesel is high,therefore it has great application potential in the actual desulfurization process.(4)Four organic-inorganic hybrid catalysts based on vacant silicotungstic acid were synthesized.The catalyst structure was determined by FT-IR and XRD,and the catalytic performance of each catalyst was investigated in ODS system.The catalyst activity investigation result shows that the[ODA]10SiW9O34 catalyst has the strongest catalytic activity.Under the optimal experimental conditions,the DBT conversion rate reached 97.92%after 120 min using[ODA]10SiW9O34 as the catalyst.By investigating the catalytic performance of[ODA]10SiW9O34 catalyst for different sulfides,it is concluded that the order of sulfide reaction activity follows:DBT>4,6-DMDBT>BT.