Studies On The Productive Propylene Additives In FCC Process

As worldwide demand for propylene has been growing steadily and rapidly, it is hard for the propylene yield from traditional methods such as steam cracking to meet the market demand. So the study on productive propelene technologies has recently attracted increasing interest. It is economical to utilize FCC units as a productive propylene route in contrast to other technologies, which has a great potential in propylene production. However, nowadays the ZSM-5 zeolite used as commercial selective additives is still synthesized with the organic amine as template, which is not only contaminative but expensive. The main purpose of this paper is to synthesize the ZSM-5 zeolite by free-template route, and modify it to enhance its acidity and activity after steaming in order to improve its function of propylene production.The free-template route is adopted to investigate the factors that influence the synthesis of the ZSM-5 zeolite, such as crystallization conditions, pH value, seeding crystals amount, initial mixing Si/Al ratios, temperatures of silicon source. The results show that different crystallization time needs special optimal crystallization temperature, and the quality of the crystallization productions with the initial mixing Si/Al ratios. The optimal synthesis conditions of free-template method was obtained: crystallization time is 24 hours; crystallization temperature is 170℃; temperature of silicon source is 100℃; seeding crystals amount is 0.084, pH value is 10.5. Furthermore, the results indicate that the free-template route only adapt to synthesis of the ZSM-5 zeolite with the Si/Al ratios of about 30. On the base of last research, a novel method of forming ZSM-5 in-situ on kaolin micropheres successfully was developed.Several ZSM-5 zeolites with different Si/Al ratios is chosen for phosphorus and lanthanon modifying. The results show the introduction of P will stabilize aluminum in framework positions. In addition, but after steaming the acidity of the zeolites mainly originates the phosphorus interacting with their surfaces. There won't form strong acidity sites during the phosphorus modification, which is available to increase the Br?nsted acidity of the framework, moreover, the results indicate that the impregnant of lanthanon couldn't improve the acidity of the zeolites after steaming.The modified ZSM-5 zeolites were used as additives to obtain FCC catalysts, with the n-heptane as reactant reacting on them in the heavy oil microreactor. The reaction results indicate that when P content reach the distribution capability amounting to 3 wt% on the ZSM-5 zeolites, the pore function and acidity match with each other optimally, here the propylene yield is the highest. However, the result also indicates that there is no help for the increasing of the propylene yield, with the introduction of lanthanon.