Study On Selective Hydrogenation Of Polycyclic Aromatic Hydrocarbons In Light Cycle Oil

The inferior light cycle oil has the characteristics of high density,high sulfur nitrogen content and high polycyclic aromatic hydrocarbon content.The production of clean diesel has the problems of harsh conditions,high hydrogen consumption and poor product quality.Considering the hydrothermal treatment of inferior light cycle oil and then acting as a catalytic cracking feedstock for the production of high-octane gasoline blending components.In this paper,NiMo/Al₂O₃ catalyst and Ni W/Al₂O₃-molecular sieve hydrotreating catalyst were characterized.The light cycle oil of Sinopec Qingdao Refining&Chemical Company was used as raw material to evaluate the selective hydrogenation activity of polycyclic aromatic hydrocarbons.The results showed that:under the conditions,the NiMo/Al₂O₃/Ni W/Al₂O₃-molecular sieve grading catalyst has higher conversion rate of polycyclic aromatic hydrocarbons than the NiMo/Al₂O₃ hydrotreating catalyst,and the selectivity for the formation of monocyclic aromatic hydrocarbons is low,and the cracking performance of the grading catalyst is higher than that of the hydrotreating catalyst.The catalyst carrier with different content of SSY molecular sieve was prepared by using SSY molecular sieve and macroporous aluminum hydroxide.NiMoW/SSY-Al₂O₃ catalyst was prepared by equal volume impregnation method.The carrier and catalyst were characterized.The results showed that:there are obvious B acid and L acid centers on the surface of NiMoW/SSY-Al₂O₃ catalyst;With the increase of SSY molecular sieve content,the specific surface area of the catalyst increases,the pore volume decreases,the acid center of L increases,and the total acid amount increases.The results of activity evaluation under the same conditions showed that with the increase of SSY molecular sieve content in the catalyst,the conversion of polycyclic aromatic hydrocarbons in hydrogenation products increased,the selectivity of monocyclic aromatic hydrocarbons increased slightly,the density decreased,the sulfur content decreased significantly,and the nitrogen content decreased slightly.The effects of process conditions on the selective hydrogenation performance of the best NiMoW/SSY-Al₂O₃ catalyst were investigated.The results showed that:as the reaction temperature increased,the content of bicyclic aromatic hydrocarbons in the hydrogenation products decreased,the content of monocyclic aromatic hydrocarbons increased,the content of naphthenes decreased,and the high temperature favored naphthalene compounds hydrogenation and isomerization to form tetrahydronaphthalene and indan,while inhibiting further hydrogenation.With the increase of pressure,the content of bicyclic aromatic hydrocarbons in the hydrogenation product decreased,the content of indane and tetrahydronaphthalene decreased,the content of alkylbenzene increased,the content of naphthenes increased,and the high pressure was favorable for further hydrocracking of tetrahydronaphthalene and indane.With the increase of space velocity,the content of bicyclic aromatic hydrocarbons in hydrogenation products increased,the content of indane and tetrahydronaphthalene increased first,then decreased,the content of alkylbenzene decreased,the content of naphthenes decreased,and the low space velocity facilitated the hydrogenation of naphthalene compounds and further hydrocracking of tetrahydronaphthalene and indane.The high temperature,low pressure,and suitable space velocity can satisfy the high conversion rate of polycyclic aromatic hydrocarbons and the high selectivity of monocyclic aromatic hydrocarbons.The suitable process conditions for the best NiMoW/SSY-Al₂O₃catalyst are the reaction temperature of 370°C,the space velocity of 1.25 h^-1,and the reaction pressure of 8.0 MPa.