Hydrogenation Reaction Kinetics And Hindered Diffusion Of Heavy Oil Model Sulfides

With the emphasis on minimization of sulfur content in gasoline and diesel around the world,catalytic hydrodesulfurization is becoming more crucial to oil refining industry.However,the understanding of hydrogenation reaction kinetics of petroleum sulfides is limited.Light sulfur compounds,such as benzothiophene,dibenzothiophene,and alkyl-substituted dibenzothiophenes,have been studied extensively.But the reaction kinetics about heavy sulfur-containing components of petroleum are rarely reported.It is well known that heavy components face big resistance to diffuse in the catalyst pore,which leads to a reduction of catalyst efficiency.Although the increase in pore size can effectively improve the accessibility of the catalyst active sites,but will reduce the specific surface area of the catalyst.Therefore,it is of theoretical and practical significance to investigate the diffusion performance and catalytic conversion of heavy oil molecules in the catalyst channels.In this paper,2,8-bis?4-pentylphenyl?dibenzothiophene was synthesized as a representative model compound,another three model sulfides were selected for hydrogenation and membrane diffusion experiments including dibenzothiophene,2,8-dimethyldibenzothiophene and diacenaphtho[1,2-b:1',2'-d]thiophene.Moreover,the hydrogenation products were characterized by GC-MS,UHPLC,and FT-ICR MS.The results showed that dibenzothiophene reacted in two pathways include hydrogenolysis and hydrogenation,the removal of sulfur almost contributed by hydrogenolysis due to the competitive adsorption of tetrahydronaphthalene on the catalyst active sites.And 2,8-dimethyldibenzothiophene also mainly reacted in hydrogenolysis pathway,but some isomerization reactions occurred to it.For 2,8-bis?4-pentylphenyl?dibenzothiophene,it had similar reaction pathways as dibenzothiophene,the relative ratio of hydrogenolysis to hydrogenation was 13.28 in condition of 350?,6 MPa and 10 h^-1.In addition,comparative experiments showed high temperature favored hydrogenolysis,low liquid hourly space velocity favored hydrogenation,intra-particle diffusion had no effect on the selectivity of hydrogenolysis and hydrogenation.However,diacenaphtho[1,2-b:1',2'-d]thiophene reacted fast in the reactor even without catalyst,so it was not considered in subsequent hindered diffusion studies.Takenoaccountofdiacenaphtho[1,2-b:1',2'-d]thiophene,2,8-bis?4-pentylphenyl?dibenzothiophene had the fastest reaction rate constant in the experiment condition,thus the effect of intra-particle diffusion to reaction was the most severe in three sulfides.The effectiveness factor of 2,8-bis?4-pentylphenyl?dibenzothiophene decreased from 0.424 to 0.375 as the temperature increased from 270? to 350?,and the effectiveness factor of dibenzothiophene decreased from 0.782 to 0.467.It should be noted that 2,8-dimethyldibenzothiophene had a higher reaction rate and a lower effectiveness factor than dibenzothiophene in 270?,but a lower reaction rate and a higher effectiveness factor in 310 or 350?.From the perspective of reaction pathway,it may resulted from some molecular isomerizations of 2,8-dimethyldibenzothiophene in the reactor.The kinetic molecular size of different sulfides were measured by membrane diffusion experiment,ranging from 0.34 to 0.79 nm.Thus,a mathematical model of hindered diffusion was obtained in condition of 270? and 6 MPa.The correlation equation of hindered diffusion factor could be described as F???=?1-??^6.45,which indicated that the model sulfides faced a severe diffusion resistance in the catalyst channel.