Research On Deep Desulfurization Of Vacuum Residue By Catalytic Hydrothermal Cracking

Heavy oil can produce petroleum coke through the delayed coking process,but under the new environmental legislation,petroleum coke with a sulfur content greater than 3%can only be treated as solid waste,resulting in huge economic losses.In order to fundamentally improve the current status of petroleum coke production under high environmental pressure,desulfurization from the vacuum residue of the production raw material can avoid the problems of high temperature and high cost during the direct desulfurization of petroleum coke.The form of sulfur in petroleum coke is mainly benzothiophenes with large steric hindrance,which is difficult to be effectively removed by traditional hydrogenation process.The oxidation of thiophene sulfides to sulfones enhances the polarity and is easy to extract,so that the thiophene sulfides in heavy oil can be deeply removed.In this paper,peroxide oxidant is first used to oxidize dibenzothiophene(DBT)in model oil in the presence of MoO3 catalyst,and then the oxidized product is extracted with acetonitrile.The reaction products were analyzed using infrared spectroscopy,gas chromatography-mass spectrometry and nuclear magnetic resonance hydrogen spectroscopy to discuss the mechanism of oxidative desulfurization.Then,the catalytic oxidation-extraction process was used to desulfurize the vacuum residue,and the effects of O/S(molar ratio),reaction time,reaction temperature and other process parameters on the desulfurization performance were investigated.In view of the problems of high viscosity,complex composition and low desulfurization rate of the catalytic oxidation-extraction process,this paper innovatively proposes a new method for removing thiophene sulfur in residual oil,which use catalytic hydrothermal cracking on the basis of the principle of in-situ hydrothermal cracking and viscosity reduction of heavy oil underground.By analyzing the four components of the residue,the sulfur content distribution in the vacuum residue is obtained.On the basis of comparing the catalytic desulfurization capabilities of dispersed and oil-soluble catalysts,two representative catalysts of nano-iron and manganese naphthenate were selected,and the technological conditions of hydrothermal catalytic cracking desulfurization of residue were investigated.By means of elemental analysis,time-of-flight mass spectrometry and gas chromatography-mass spectrometry,the hydrothermal cracking products were analyzed,and the desulfurization mechanism of thiophene sulfides was discussed.Finally,simulated coking was performed on the vacuum residue after catalytic oxidation extraction and catalytic hydrothermal cracking treatment,and the extent of sulfur content reduction in petroleum coke after pretreatment by two different methods was explored.The experimental results show that:using MoO3 as a catalyst,hydroxy cumene peroxide can oxidize dibenzothiophene in the model compound to dibenzothiophene sulfone.When MoO3 is used as a catalyst and the amount is 0.25%of the residual oil mass,the reaction temperature is 120℃,the initial reaction pressure is 1.0MPa,the reaction time is 15h,and the hydroxy cumene peroxide is used as the oxidant and O/S=3(molar ratio),The desulfurization rate of vacuum residue is only 26%.Adopt vacuum residue catalytic hydrothermal cracking process,using manganese naphthenate as catalyst and the dosage is 1%of vacuum residue oil mass,reaction temperature 360℃,oil-water ratio=7:3(mass ratio)and reaction time 48h,The residual oil desulfurization rate can reach 55%;after hydrothermal cracking,the average molecular weight(Mn)of the oil sample decreases by nearly 50%,and the sulfide in the residual oil is mainly removed in the form of H2S.After hydrothermal cracking desulfurization,the sulfur content of petroleum coke after simulated coking is less than 3%,which has reached the national VI standard in 2019.