The Selective Separation Of Sulfur Compounds In Heavy Fraction Oils And Kinetics Of Hydrodesulfurization

Due to the increasing trend of heavy and inferior petroleum and more stringent environmental regulations for vehicle fuels,highly efficient conversion of heavy oils and production of clean fuels have become one of the key issues in the refining industry.Hydrotreatment of heavy oils has become a key technology for efficient and clean conversion of heavy oil resources because of its high yield and good quality of products.Effective removal of sulfur compounds is the main purpose of hydrogenation.Differences of molecular size and composition structure lead to great differences in the diffusion and reaction behavior of sulfur compounds in catalyst channels,which limits the further understanding of the molecular hydrogenation kinetics of sulfur compounds in heavy oils.Hence,thiophenic fractions,sulfidic fractions and polar sulfur fractions in Venezuelan vacuum gas oil,light vacuum residue deasphalted oil and heavy deasphalted oil are selectively separated and enriched by methylation/demethylation method,and used to conduct kinetics researches of hydrodesulfurization reactions by fixed bed reactor.The results show that the hydrodesulfurization of all the fractions followed two order law.And the reaction rate constants of sulfidic fractions and thiophenic fractions are much larger than that of polar sulfur fractions.The rate constants of fraction oils fall among the values of their enriched fracions.The internal diffusion effective factors of sulfidic fractions are much larger than that of thiophenic fractions.Furthermore,the heavier fraction oils are,the smaller internal diffusion effective factors are,the greater effects of diffusion on the reaction are.With the increase of temperature,the internal diffusion effective factors of all fraction oils and their enriched fractions decrease,indicating that effects of diffusion on the reaction increase at higher temperature,which results in the lower utilization efficiency of the catalyst.Thereafter,three kinds of fraction oils and their enriched fractions together with hydrotreating products are analyzed by positive ion ESI FT-ICR MS,and their molecular transformation rules are obtained: as for thiophenic fractions and sulfidic fractions,sulfur compounds with two sulfur atoms(S2 class),naphthenic sulfides(DBE < 5 S1 class)and polycyclic thiophenes(DBE>12 S1 class)with less substituents are easily desulfurized,while sterically hindered hexahydrodibenzothiophenes,dibenzothiophenes,phenanthrenothiophenes and benzonaphthothiophenes with more substituents are difficultly desulfurized.With respect to polar sulfur fractions,polyheteroatomic sulfur compounds such as N1S2,O1S1 and O2S1 class are easily converted to corresponding compounds by hydrodesulfurization.Nevertheless,owing to the enrichment of some heteroatomic compounds with unknown structure,hydrogenation conversion rules of different fraction oils and their polar sulfur fractions are incomplete agreement.