Study On Coking Of Model Compounds Of Diesel During Catalytic Reaction

In the process of diesel quality upgrade,coking has a significant impact on catalyst deactivation,equipment fouling,and pipe blockage.Therefore,the understanding of the formation mechanism of coke and the study of the properties of coke are having guiding significance on the upgrading of hydrogenation catalysts and the optimization of the process to reduce the formation of coke.In this paper,naphthalene(NAP),phenanthrene(PHE),pyrene(PYR),1-methylnaphthalene(1-MNA),4,6-dimethyldibenzothiophene(4,6-DMDBT),1-methylisoquinoline(1-MIQ)were used as model compounds.Changes of coke and free radicals in different systems were investigated at 380?.13C NMR,SEM-EDS mapping,ESR and other technologies were used to characterize the coke on the catalyst,and the evolution of the coke on the catalyst with the reaction conditions was analyzed.The main conclusions are as follows:1.Under the catalyst conditions,the amount of coke and the concentration of stable radicals both showed a rapid increase in the early stage and a slow increase in the later stage;aromatic hydrocarbon model materials containing S and N heteroatoms are more likely to form coke than polycyclic aromatic hydrocarbon model materials;the more condensed rings of cyclic aromatic hydrocarbons,the more coke and stable radicals;the methyl functional groups significantly promote the formation of coke on the catalyst.2.After the two models are mixed,there is an induction and synergistic effect during the reaction to promote the formation of coke;(sulfur-containing components+polycyclic aromatic hydrocarbons)are more likely to form coke than(nitrogen-containing components+polycyclic aromatic hydrocarbons),and free in the coke The more the base,the more the number of condensed aromatic rings,the longer the phase of the rapid increase of carbon deposition,the more the coke.3.As the reaction time increases,the concentration of active radicals gradually increases(the nitrogen-containing model has special characteristics);there is a competitive relationship between the coupling reaction of active radicals and the neutralization reaction of active radicals by hydrogen-donating solvents,and the coupling rate is slightly about the neutralization rate.4.In the catalytic reaction of polycyclic aromatic hydrocarbons and 4,6-DMDBT,coke are first formed on the catalyst carrier,and 1-MIQ coke are first formed in the W active center;the induction of free radicals promotes the production of coke and the conversion process of polycyclic aromatic hydrocarbons The formation of medium coke is a uniform rate process,and the formation of heterocyclic aromatic coke is an accelerated process.5.The structure of the coke changes with the increase of coke.The coupling probability of stable radicals of the two models is larger than that of the reaction of the two models alone.