Catalytic Cracking Of FCC Gasoline To Propylene Over ZSM-5 Zeolite

The catalytic cracking of heavy oil to propylene is a hot technology in the FCC field at present. Adding ZSM-5 additive to FCC main catalyst is one of the most effective and the simplest method to increase the propylene yield. In this paper, the effect of hydrothermal treatment, Phosphorus and Lanthanated modification on the pore structure, the distribution of acidity and catalytic cracking performance of nano-ZSM-5 zeolites was studied in a fixed bed microreactor, the catalysts were characterized by X-ray diffraction (XRD), NH3 temperature programmed desorption (NH3-TPD) and N2 physical adsorption technologies.We also discussed the effect of the operating conditions on the catalytic performance, such as the reaction temperature, residence time and the ratio of catalyst to oil.The following results have been obtained:(1) Appropriate hydrothermal treatment can increase the selectivity and yield of propylene, but the too high hydrothermal temperature or too long hydrothermal time to increase the propylene selectivity, the catalytic activity drops obviously.(2) Increasing reaction temperature was conducive to propylene production. However, the raletive high temperature resulted in the increase of dry gas and coke production. Longer residence time and Increasing ratio of catalyst to oil could enhance the reaction depth, but the hydrogen transfer reaction increased led to the decrease of propylene selectivity.(3) The addition of phosphorus improved the hydrothermal stability, increased the amount of acid catalyst and catalytic activity enhanced. With the increase of phosphorus loading, FCC gasoline conversion, the yield of propylene and aromatics increased. The excessive phosphorus loadingresulted in the blocking of zeolite pore by the formation of P2O5, and the decrease of catalytic activity.(4) La modification also could improve the hydrothermal stability of the ZSM-5. Compared with the unmodified ZSM-5, the yield of propylene and aromatics over La/ZSM-5 increased. However, the acid centers, strong B acid sites were held by excessive La ions particularly, which resulted in a decrease of catalytic activity.