The Research Of Solvent Effect On The Deep Hydrodesulfurization Of Benzothiophene

In recent years,the production of ultra-low-sulfur gasoline and diesel is the future development trend of clean fuel and ultra deep desulfurization is becoming a very important theme causing by the increasingly stringent environmental regulations.The solvent effect is inevitable in the process to produce automobile-used clean fuel by hydrodesulfurization,whether the raw material is crude oil or the by-product of coal chemical industry such as coal tar,crude benzene and heavy benzene.The removal of sulfur compounds is strongly influenced by effect of the competitive adsorption between various hydrocarbons as well as sulfur-,nitrogen-and oxygen-containing heterocycles in fuel oil and thiophenic compounds on the same catalytic sites of catalysts during the hydrotreating process.The benzothiophene HDS is intensively suppressed even by a small amount of some compounds?1.0 mol%?.Different types of hydrocarbons such as aromatics,olefins and alkanes,however,lead to a different inhibitory effect.In addition,the hydrocarbon components also has a distinct influence on the hydrodesulfurization of benzothiophene under different catalysts.Therefore,it is extremely essential to make clear the mechanism of various hydrocarbon components inhibition on HDS so as to provide theoretical basis for the actual production process including the optimization of catalyst preparation conditions,adjustment of the hydrodesulfurization technology according to different raw materials and then to achieve the purpose of ultra deep desulfurization of gasoline and diesel.The benzothiophene and cyclohexane were used as model compounds and solvent respectively.A variety of hydrocarbon components were added to compare the inhibiting effect of some benzene series such as benzene,toluene,ethylbenzene,xylene,trimethylbenzene,styrene;dicyclic hydrocarbons such as naphthalene,tetralin,decalin;alkanes such as cyclopentane,n-hexane and n-heptane;olefins such as cyclohexene,n-hexene,diisobutylene etc.during the HDS of benzothiophene on a NiMo/?-Al₂O₃ catalyst.The experiment is designed to make clear the mechanism of hydrocarbon components inhibition on HDS,analyze the nature and types of catakyst active site and speculate the competitive adsorption process between solvent components and benzothiophene on the catalyst active sites.Then,the solvent effect on the HDS over catalyst modified with P and B is investigated.Afterwords,the catalysts were characterized by N₂-BET,XRD,NH₃-TPD,H₂-TPR to research the crystal type,acid property as well as the interaction between active components and carrier of the catalyst.The main conclusions of this study are as follows:1.The removal of sulfur compounds is inhibited by effect of the competitive adsorption between various hydrocarbons and thiophenic compounds in fuel oil on the same catalytic sites of catalysts during the hydrotreating process.2.Solvent effect on HDS reactivity of benzothiophene over NiMo catalysts decreases in the order of dicyclic aromatic hydrocarbons>monocyclic aromatics>alkanes.3.The inhibition of solvent is enhanced with the increase of carbon atom and aromatic ring number of n-alkanes and aromatic hydrocarbons.The solvent effect of aromatics with the same ring number is decided by the electron density and steric effect of the molecular.4.Cyclohexene has strong inhibiting effect on benzothiophene HDS while hexene and diisobutylene is just on the contrary.The HDS of benzothiophene and olefin hydrogenation are mutual inhibited.5.The molecular adsorption-desorption on the surfaces of metal catalysts is a continuous dynamic process.The intermediates of solvent such as naphthalene,styrene and n-hexene is probably had no effects on the HDS.6.The inhibiting effect is increased with the increasing dielectric constant of the solvents.7.The effect of hydrocarbon components on the HDS of benzothiophene over NiMo/?-Al₂O₃ was stronger than that over CoMo/?-Al₂O₃,because of the different catalytic selectivity for HYD or DDS pathway of benzothiophene HDS over NiMo and CoMo/?-Al₂O₃ catalyst.