Study On The Mechanism Over Solid Titanium Catalyst For Oxidative Desulfurization With Acid Catalysis

Sulfur compounds which are existed in crude oil,are known for causing the most air pollution.Particularly,they could directly lead to corrosion,deactivating some refining catalysts and causing acid rains.The hydrodesulfurization process performs in high temperature and pressure conditions(300-400℃ and 30-130 atm)and also using hydrogen will cost additional expenses as well,while oxidative desulfurization has attracted extensive attention for its mild operating conditions and high desulfurization efficiency.Titanium-containing material was considered to be one of the most efficient catalysts for oxidative desulfurization.In this paper,large size irregular nanoparticles were prepared by sol-gel method with isopropyl titanate as raw material.The optimal experimental conditions over titanium dioxide(TiO2-TBOT)which prepared from tetrabutyl titanate were investigated of 60℃,reaction time of 60 min,the catalyst dosage of 0.100 g,n(H2O2)/n(DBT)=4.The content of DBT in the model oil at different reaction time was determined by GC-MS,which proved that DBT was completely oxidized to DBTO2 in the catalytic oxidation process.In addition,the mechanism was studied by Raman,FT-IR,NH3-TPD and molecular simulation.Firstly,the active Ti-peroxo species((?))were formed via reacting between TiO2+and H2O2 simultaneously.Then,Ti-peroxo species((?))passed*[O]to the oxidation of DBT,and the preliminary production DBTO was further oxidized to DBTO2.Finally,the higher polar DBTO2 was retained in the extractant phase,which resulting in a continuous reduction in DBT concentration in the oil.It was note worthy that the active Ti-peroxo species((?))returned back to TiO2+continuously,which was forced to stop until H2O2 exhausted fully.In order to solve the problem of poor selectivity over titanium dioxide,titanium nanotubes were prepared by hydrothermal method with TiO2-TBOT,commercial TiO2 and P25 as precursors.They were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),N2 adsorption-desorption(BET)and infrared(FT-IR).The catalytic oxidation desulfurization performance of the catalyst NT-TBOT for DBT almost was 100%of 70℃.,reaction time of 30 min,the catalyst dosage of 0.100 g,n(H2O2)/n(DBT)=4.When different mass fractions of cyclohexane,1-octene and xylene were added into DBT simulated oil respectively to simulate the hydrocarbon compounds in real oil and carry out oxidation desulfurization experiment,the removal rate of DBT did not decrease obviously,which showed better selective oxidation.Moreover,the NT-TBOT catalyst could be recycled at least six times for deep desulfurization.Finally,Raman,NH3-TPD and A AS were used to study the possible mechanism.H from the precursor TiO2-TBOT to form TiOH species on the NT-TBOT,and then TiOOH active species were formed during the reaction with hydrogen peroxide.The TiOOH active species provided*[O]to oxidize DBT,initially producing DBTO and further was oxidized to DBTO2.Finally,DBTO2 with higher polarity was retained in the extractive phase,which resulted in a continuous reduction in DBT concentration.The TiOOH active species then returned to the TiOH species,forming a catalytic cycle until the hydrogen peroxide was completely exhausted.