Study On Coking In Residue Thermal Reaction And Regeneration Of Waste Catalyst

Coking induced by thermal and coking on catalysts accompany the whole petroleum processing process.Coking induced by thermal not only wastes petroleum resources,but also produces residues of heating kettle classified as HW11 hazardous waste.Coking on catalysts is one of the main causes of catalyst deactivation.China produces hundreds of thousands of tons of spent catalysts in petrochemical industry every year.Heavy metals in these spent catalysts are very harmful to the environment,so they are classified as HW50 hazardous waste.If they can be regenerated efficiently and cheaply,not only their harm to the environment will be greatly reduced,but also the economic benefits of enterprises can be improved.In addition,the exhaust gas from coke removal in fluid catalytic cracking(FCC)process also cause environmental hazards.Of course,coking is not always a bad thing,delayed coking is the process of partial lightening of heavy oil by coking quite right.Therefore,recognizing and controlling coking induced by thermal and developing efficient and cheap on-line regeneration technology of coke on spent catalyst are the main directions of environmental friendly petroleum processing.Coking induced by thermal,coking on catalysts and coke removal on spent catalysts,discussed above,can be attributed to the thermal reaction mechanism of complex hydrocarbons,which is essentially a radical reaction process initiated by thermal.Based on the new understanding of the coking reactions,the stable radicals,active radicals and the reactions induced by active radicals in the thermal reaction process of coal,coal tar,oil shale,biomass and heavy oil by the author's research group,this paper deepens it to the petroleum processing,reveals the inherent law of coking and removing coke on catalyst process in a view point of radical reaction,which is the nature of thermal reaction,and makes efforts to develop new technologies to reduce the harm of spent catalyst,waste gas and waste residue caused by coking to the environment with friendly environment,high efficiency and low cost.In this paper,the coking and radical formation rule in residue thermal reaction,the influence of hydrotreating on coking and radical formation behavior of residue,the influence of residue components on the formation rule of stable radicals and active radicals in residue thermal reaction,and the coke removal process on spent catalyst were studied.The main conclusions are as follows:(1)During residue thermal reaction at 400-500? and within 60 min,the coking law can be fitted by a general kinetic equation including the coking of residue cracking and the coking of coke autocatalysis,the kinetic order of the coking law can be determined by the parameters in the general analytical kinetic equation,the formation law of stable radicals can be fitted by a combination of the two first-order kinetics including residue cracking and coke cracking.The proposal of radical formation by coke cracking provides a way to regulate the evolution of coke structure in a view point of radical reaction,and provides a theoretical basis for regulating the generation of coke in the heating furnace classified as HW11 hazardous waste.(2)During residue thermal reaction,more than 90%of the stable radicals produced by residue cracking exist in coke when the coking rate is higher than 8%.The spectral width of stable radicals in residue can be used to characterize the growth of aromatic nuclei in coke qualitatively.The change of g value in residue reflects the migration of heteroatoms.(3)Hydrotreating weakens the effect of temperature on residue cracking coking reaction,but increases the effect of temperature on coke catalytic coking reaction by increasing the temperature-dependent rate of active radicals formation from residue and coke cracking.(4)During residue thermal reaction,the resin content of residue is positively correlated with the production of stable radicals,the resin promotes the production of stable radicals more than asphaltene,the aromatics can inhibit the production of stable radicals at higher reaction temperature,the saturation can promote the production of stable radicals.(5)During residue thermal reaction,monocyclic aromatic hydrocarbons with branched chains can inhibit the generation of stable radicals through hydrogen transfer,and nitrogen compounds have more obvious inhibitory effect on the generation of stable radicals than sulfur compounds.(6)When the content of dihydrophenanthrene(DHP)is sufficient(>5 wt%),DHP can effectively capture the active radicals,as hydrogen donor,produced by cracking of residue,hence effectively inhibit coking by changing the active radical reaction path of residue.(7)The coke deposited on the Mo sulfide sites of spent diesel hydrogenation Mo-Co-Ni/W-A1 catalyst can be removed and the activity of the spent hydrogenation catalyst can be restored by a tetrahydronaphthalene(THN)treatment at 300-400? in 3 min.Based on this,an on-line regeneration technology for spent hydrogenation catalysts has been developed,and a patent has been applied for.A coke removal mechanism is proposed,which includes activation(or subtraction)of H in THN,hydrogenation of coke by Mo sulfide and dissolution of the hydrogenation products,which provides a theoretical basis for on-line regeneration of spent catalysts classified as HW50 hazardous waste.(8)The coke on the Mo sulfide sites is pitch-like and reactive with a stable radical concentration around 42.6 ?mol/g.The coke on the catalyst support is more condensed in structure than that on the Mo sulfide sites,more stable in the THN treatment,and has a stable radical concentration of around 4.4 ?mol/g.