Catalyst Optimization Of Two-Stage Riser Catalytic Pyrolysis For Maximizing Propylene Yield

The Two-Stage Riser Catalytic Pyrolysis for Maximizing Propylene Yield (TMP) is a new developed technology based on TSRFCC which features maximizing propylene yield and considering both of yield and quality of light oil simultaneously. The active component of the special catalyst for TMP technology is ZSM-5 zeolite, however, few studies have been made on the deactivation process of ZSM-5 catalyst up to now. The TMP industrialize experiment unit has been built in Daqing Petrochemical Refinery and the treatment capacity reached 120 kt/a. Preliminary data indicated that the content of ZSM-5 in catalyst was low and the propylene yield could not reach designed value i.e. 20%. Therefore, investigating the deactivation process of ZSM-5 catalyst and optimizing the special catalyst for TMP are urgent work.In this paper, LTB-2 catalyst deactivation phenomenon was studied in riser pilot unit, which could accomplish continuous cracking reaction and catalyst regeneration. The experiment data indicated that the yield of dry gas and coke decreased during continuous operation of 100h when the reaction temperature and regeneration temperature are 510oC and 700~710oC, respectively, while the yield of gasoline and diesel maintained nearly constant value. The yield of the LPG increased by 4.33%, the yield of propylene increased from 9.68% to 16%. The olefin contents in dry gas, LPG and gasoline all increased, the conversion of heavy oil maintained at 84%. XRD and FT-IR characterization data indicated that after reaction the framework of zeolite was not damaged obviously. Most of Bronsted acid sites on catalyst were strong sites, while both weak and strong sites existed in quantity for Lewis acid sites, and the content of moderate Lewis acid sites were low. Both of the content of Bronsted acid and Lewis acid reduced after reaction, moreover, the reduction of Bronsted acid was larger than Lewis acid. The reduction of the acid content resulted in suppress of hydrogen transfer, therefore the yield of olefin increased.In view of the insufficiency in conversion of recycled lighter gasoline and the low olefins selectivity during the industrialize experiment, catalyst optimization experiments using the micro-reactor and the riser pilot unit were carried out. The MMC-2/LTB-2 ratio and LCC-2/LTB-2 ratio were investigated. When using Fushun AR as feed stock, and the LTB-2 and LCC-2 was mixed with equal proportion, the yield of propylene, gasoline, diesel and liquid could reach 20.45%, 18.98%, 18.87% and 80.90%, respectively. The yield of propylene could reach 16.14% even when the naphthenic base VGO was used as feedstock. The industrialize calibration experiment data indicated that when using the above catalyst scheme, the yield of propylene was 21.29%, the total yield of dry gas and coke was only 14.05%, and the gasoline obtained was high octane number blending component with low olefin content and high aromatic content, the cetane number of the diesel was about 30, attaining the designed goal which indicated that both the TMP technology and catalyst can full display their advantages when the above catalyst scheme was adopted.