Modification Of USY Zeolite And Study On Catalytic Cracking Of Polycyclic Aromatic Hydrocarbons

With the crude oil all over the world becoming heavier and inferior,the challenges of catalytic cracking processes that play an important role in petroleum refining are increasing.Increasingly stringent environmental regulations and the demand for clean oils are driving improvements in the catalytic cracking process.The high concentration of aromatic hydrocarbons in heavy oil,especially polycyclic aromatic hydrocarbons(PAHs),which are very harmful to the environment due to their volatility and biological toxicity.However,the chemical properties of PAHs are very stable due to the ?-bond.The consumption of PAHs by catalytic cracking can not only reduce pollution,but also produce certain aromatic resources by-products and increase the efficiency of refineries.As the core active component in catalytic cracking,the catalytic performance of Y-zeolites will be directly related to the final performance of catalytic cracking of PAHs,thus modifying the commercial USY to enhance its ability to crack PAHs in the heavy oil is very important for the comprehensive utilization of heavy oil.This study used commercial USY-zeolite as parent zeolite,and modified the zeolite by EDTA-2Na,oxalic acid,citric acid,tartaric acid and high temperature hydrothermal aging treatment.The research firstly investigated the modification effect of different organic acid treatments with gradient concentration and different hydrothermal temperatures,including the modification of the crystallinity,pore structure and acid properties of USY.The best treatment concentration or hydrothermal temperature to represent the modification effect was selected.The composite modification of different organic acid treatment after high-temperature hydrothermal was investigated.Different organic acid treatments can effectively improve the specific surface area,crystallinity and acid properties of USY.The hydrothermal aging treatment expanded the micropores,decreased the acid site density and improved the strong acidity due to the dealuminization and silicon supplementation effect.However,the hydrothermal treatment would produce many non-framework species blocking pores and acid sites.Combined with acid treatment,the pore structure and acid properties of the molecular sieve would be further improved.Naphthalene,the most simple polycyclic aromatic hydrocarbon,was used as a model compound to evaluate the catalytic cracking of PAHs on the catalytic cracking microreactor.It was found that the catalysts after hydrothermal treatment at 600 °C achieved better results in the catalytic cracking of model reaction due to better acidity distribution,rich mesoporous distribution and fewer micropores.And the coke yield is relatively lower than the commercial USY and acid-treated USY.The requirements for the pore structure and acid properties of USY for catalytic cracking of naphthalene were investigated.Combined with products analysis and characterization of the catalysts,the catalytic cracking process of naphthalene was reasonably speculated and the obtained experience was helpful for the development and improvement of catalytic cracking of PAHs.