Development of Zeolite

 


Back to the old days, the primary technique used to produce gasoline before the implementation of catalytic cracking in the refining industry was by significantly heating the crude oil in excess of 750 Fahrenheit in a still under pressure of around 90psig.

Until there came a chemist from Gulf Refining Company in 1915 named Almer M. McAfee, who first established the application of anhydrous aluminium chloride to catalytically crack the heavy petroleum oil. Unfortunately, it was not widely accepted as it faced challenges where the cost of the catalyst was pricey and the process produced a corrosion waste as a by-product.

This makes the discovery of Fuller’s earth which was a naturally occurring aluminosilicate clay by Eugene J. Houdry later in 1920s as a highly capable active acid catalyst for catalytic cracking. The Fuller’s earth (in the clay form) was treated with an acid in particular to get rid of the impurities and unwanted compounds such as iron, mainly to isolate and produce a residual structure compromising only silica and alumina. Besides, this approach by Houdry acted as a key economical step where it can regenerate the catalyst by burning off the accumulated carbon, where this seemed as a challenge to McAfee before. This acid-activated catalyst by Houdry also set a good remark for the future of the catalyst development as it notably grew the cracking activity.

Behind time, in 1942, a synthetic fluid cracking catalyst was created in order to support the ‘powdered catalyst’ operation in PCLA No. 1. During this time, the catalyst material which contained 13% alumina was grinded finely to allow the fluidization of the catalyst. Thus, this evolved the expansion of fluid catalytic cracking technology and caused rise to more than 430 FCC units worldwide.

In 1950s, Zeolite Type X was manufactured, which accommodates a faujasite framework (FAU) with a three-dimensional aluminosilicate skeleton portraying a larger pore opening. This Type X Zeolite with 1.2 of Si-to-Al ratio was synthesized in Na form and need first to be ion exchanged in order to undergo acid catalytic activity.

This improved fluid catalytic cracking catalyst continued to appear useful for the industry until there came an outbreak in 1960s about the establishment of synthetic aluminosilicate zeolite which aimed to enhance the activity and selectivity of catalyst for more outstanding cracking properties. This alternative was not wasted as it resulted in a strong Bronsted acid site as well as easily accessible Lewis acid sites, making the hydrogen transfer reaction more efficient.

Later on, in 1962, a new catalyst incorporated of Zeolite Y was taken in by Mobil Oil. A small amount of zeolite was added into the matrix of silica-alumina catalyst during the production. Zeolite Type Y was established also with FAU but consisting a Si-to-Al ratio of 2.5-3 as it was studied that a higher ratio found to be more stable in favour of acid treatment and ruthless hydrothermal condition. Hence, this new catalyst formulation overshadowed the existing catalysts and marked the first commercial zeolite-based FCC catalysts in revolutionizing the industry.

 To an extent, an advancement was made where the Zeolite Y was treated with chemical calcination to undergo dealumination in a controlled order, then later on healing it with silicon in manner to create a secondary mesoporous structure within the catalyst. Not just that, this progress also resulted to a higher Si-to-Al ratio with a reduced unit cell size in producing an ultra-stable zeolite known as Zeolite USY. This basis of uttermost high cracking activity of FCC catalyst was implemented until today.

However, living in a modern era, a recent research made found that there was a complication for the heavy oil (molecular diameter ranged from 1.2-1.5nm) to pass through the micropores of FAU-Type Y-Zeolite with inlet diameter of 0.74nm. This came to a deduction that the desired FCC catalyst need to undergo an enhancement regarding its diffusion abilities along with its acid sites accessibilities, named developing hierarchical zeolitic materials.




        As referred to the above figure, core shell zeolite composites recruited a hardly dissolved material commercial Y-Zeolite as the core and poly-crystalline nano ZSM5 accumulated meso- and macroporous as the outer was accomplished for the first time. This high crystallinity invented portrayed not just good thermal and hydrothermal stability, but also endowed an intensified ability to catalytically crack the bulky molecules of heavy oils. Besides, it also employed an adjustable chemical composition that shown more controlled acidic properties which was an important role in performing the process for the fluid catalytic cracking.

Thus, this synthesisation of special structured material of FCC catalyst has created an excellent improvised technology for the refinery of the heavy oil.

 





References

Komvokis, V., Xin, L., Tan, L., Clough, M., Pan, S. S., & Yilmaz, B. (n.d.). Zeolites in Fluid Catalytic Cracking ( FCC ). 271–297.

Pan, M., Zheng, J., Liu, Y., Ning, W., Tian, H., & Li, R. (2019). Construction And Practical Application Of A Novel Zeolite Catalyst For Hierarchically Cracking Of Heavy Oil. Journal of Catalysis, 369, 72–85.


    

0 comments