Engineering Zeolite Composite Catalysts for Enhanced n-Heptane Cracking to Light Olefins

Abstract

Global demand for light olefins (ethylene (C2=), propylene (C3=), and butylene (C4=)) hasincreased due to the rapid growth of the global economy and population. Currently, steam cracking is one of the main processes used petroleum refining industry to convert naphthato light olefins. Alternative technologies are necessary to meet the growing demand. Fluid catalytic cracking (FCC) offers a potential alternative. FCC catalyst composition is improved by tuning the formulation and adding various components such as additives and zeolites. Zeolite Y, a major ingredient in this formulation, has unique physicochemical properties,such as strong acidity, shape-selectivity, and thermal stability ideal for catalytic cracking. Nonetheless, its microporous structure restricts access to some molecules, necessitatingfurther optimization. This PhD research focusses on the development of a new zeolite composition based on FCC catalysts. The formation of micro/mesoporous systems within the catalyst aims to enhancethe mass transfer of heavy hydrocarbons, increasing activity, and achieving better deactivation resistance. Firstly, the research presents a systematic investigation into the interactions between zeolites (of ZY and ZSM-5) and binders (of Kaolin and Bentonite) in the forms of extrudate and pellet. For example, using a kaolin binder as extrudates (ZY/ZSM-5/K composite (20:20:60 wt.%)) to develop micro/mesoporous structures. The catalytic cracking of n-heptane was used as the model reaction, and the results showed an improved conversion of ~90% and a light olefin yield increase of ~33% compared with a commercial FCC catalyst. Secondly, to address binders' limitations, a formulation method was developed for prepare the zeolite-mesoporous silica composite (KIT-6, SBA-15, and MCM-41) by replacing the binder was replaced by mesoporous silica. The produced composite catalysts showed the enhanced characteristics, such as a large surface area with external surface areas in the range of 301-564 m2 g -1 . Based on results in n-heptane (n-C7) cracking, the zeolite composition achieved a higher catalytic performance with a conversion of 95% and an ethylene/propylene selectivity ratio of 8%. Based on the success of the zeolite-mesoporous silica composite, the third research investigated the potential to improve performance further by incorporating metal additives. In the composites containing Ce and Zn showed the highest conversion (96%) with light olefin yields improved by 25% and 21%, respectively, compared to the pristine composites. Finally, an innovative approach to preparing zeolite composites using a synthesis-gel (SG) method was explored. The results showed that the SG method achieved the highest light olefin selectivity of 34% compared to physical mixing and ball milling methods, which deserved to be explored further.