The Selectivity And Transformation Of Coke On FCC Catalysts

Due to the depletion of oil resources, most of fluid catalytic cracking (FCC) units in the world have to process heavy oil and residue oil. It increases the coke yield of the FCC catalysts, and thus the deactivated FCC catalysts will release more heat during the regeneration process, which increases the heat load of the regenerator and even makes the FCC unit work incorrectly. Meanwhile, due to more and more demands on diesel because of its high thermal efficiency the oil refining industry needs to adjust the production distribution of different petrochemical products correctly.The first part of our work focused on the FCC additives, where a small proportion of catalyst additives were added into the FCC catalysts in order to reduce the yield of coke and increase the yield of diesel. Firstly, we used kaolin microsphere modified by basic oxide species as the additives, where the kaolin microspheres were firstly calcined at the temperature of<1000℃, and then the microspheres were treated with alkaline solution before the impregnation with alkali metal. According to the change of spherical morphology of FCC additives after the modification and their FCC activity, we found that the sample using the TMAOH as the alkaline source with a TMA+/Si02molar ratio of0.15had the best effect. Furthermore, kaolin microspheres calcined at950℃and then impregnated with25wt.%Mg or Ca species had a positive impact on the catalytic performance as the additives, which could reduce the yield of coke and increase the diesel production. Secondly, we prepared the FCC additives using ionic liquid-modified halloysite as the matrix. It was found that the ionic liquid strongly interacted with the surface hydroxyl of halloysite during the preparation of FCC catalyst additives, where the strong interaction between ionic liquid and halloysite effectively prevented the binder and the debris of USY zeolite entering the inner pores of halloysite. As a result, the macropores in FCC additives were produced after the additives were calcined and the ionic liquid was removed at high temperature. The additives exhibited good catalytic cracking activity and could reduce the yield of coke. At last, the FCC additives (LCS) containing both MgO and halloysite were prepared. Then we studied the catalytic performance of the FCC additives by changing the reaction parameters like CTO ratio (catalyst to oil ratio) and reaction temperature, the LCS could reduce the yield of coke and increase the yield of LCO in a wide range of reaction temperature.In the second part, we paid our attention to the coke steam reforming reaction. We can use this reaction to remove the coke from the spent FCC catalyst surface, and reduce the heat load of the regenerator, what’s more, the high value hydrogen can be produced in the reaction. Firstly, we built the fixed bed reactor derived from a MAT unit for the coke steam reforming reaction. Then the hydrotalcite and the introduction of different metals were studied to understand whether they could improve the activity of steam reforming. The hydrotalcite and the metals had little influence on the coke steam reforming reaction, but they could improve the water gas shift reaction. What’s more, the FCC additives were prepared with hydrotalcite as the matrix, the additives showed a good cracking activity and good coke selectivity (low coke yield).