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Application of Zeolite as Catalyst in The Cracking Process for Petroleum Industry

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In petroleum chemistry, cracking is known as the process of breaking down heavy or complex organic hydrocarbon molecules into lighter, much simpler and more functional molecules with the presence of heat and usually pressure. Cracking, also referred to as pyrolysis, is the secondary step in oil refining process. Sometimes, the participation of catalyst is also required throughout the cracking process. The presence of catalyst and the amount of heat supplied (temperature) will determine the rate of cracking process as well as the type of products formed by the end of the process.

In 1913, the first thermal cracking process was developed by William Merriam Burton, which was adapted from the Shukhov Cracking Process found by Vladimir Shukhow in 1891. The process was then diversely enhanced in the year 1920s, in which Eugene Houdry, a French chemist introduced the addition of catalysts which leads to higher-octane products obtained. Catalytic cracking was then further improved in the 1940s by incorporating the use of moving or fluidized beds of powdered catalyst. In the 1950s, there were high demands for jet and automobile fuels therefore, hydrocracking was developed.

Cracking process is one of the most crucial part in the commercial production of gasoline and diesel fuel as it helps in keeping the balance between availability of the various fractions and the demands for those fractions. Some of the most significant products of distillation of crude oil include petrol, naphta, kerosene, liquefied petroleum gas and gas oil.  Since during cracking, bigger hydrocarbons is transformed into various kinds of smaller molecules which plays important roles in various applications, the supply of fuel is increased. At the same time, the demands and supply of the fuel can be balanced. For instance, among the types of oil produced by cracking of petroleum are light oils which refers to gasoline, middle-range oils which are widely used as diesel fuel, residual heavy oils, solid carbonaceous products termed as coke, and gases like methane, ethane, propane and so on.

As of now, there are four main types of cracking methodologies known as Fluid Catalytic Cracking (FCC), Hydrocracking, Steam Cracking, Thermal Cracking and Catalytic Cracking.

1.  Fluid Catalytic Cracking (FCC): FCC is primarily used in petroleum refiners. Initially, it involves the use of low activity alumina catalyst and a reactor where the catalyst particles will be suspended in a rising flow of feed hydrocarbons in a fluidized bed. Later on, the reactions process is improvised in which it utilizes very active zeolite-based catalyst to vaporize the feed and catalyze the cracking reactions.

2. Hydrocracking: One of the catalytic cracking process which requires the presence of hydrogen gas at elevated partial pressure. Normally, this process is aided by bi-functional catalyst that can not only rearrange and break the hydrocarbon chains, but also add the hydrogen to aromatics and olefins.

3. Steam Cracking: This is a petrochemical process that converts saturated hydrocarbons into lighter alkenes and olefins such as ethane and propene. Steam is used to dilute gaseous or liquid hydrocarbon feed before they are briefly heated in a furnace at around 850 ºC. The composition of the feed, the hydrocarbon to steam ratio, the cracking temperature and furnace residence time will determine the products formed.

4. Thermal Cracking: This type of cracking involves implementation of high temperatures and pressures of about 800ºC and 700kPa respectively. A variety of free radicals-based chemical reactions take place during this process including initiation reaction, hydrogen abstraction, radical decomposition, radical addition and termination reactions.

5. Catalytic Cracking: Zeolite catalyst and moderately high temperature of 400-500ºC are used in this process. During this process, carbonaceous products deposits known as coke are produced due to the accumulation of intermediate cations on the catalysts’ active sites. Typically, burning process is employed to remove the deposits and restore catalysts activity.





References:

Britannica, T. E. (2020, June 02). Cracking. Retrieved January 04, 2021, from Encyclopaedia Britannica: https://www.britannica.com/technology/cracking-chemical-process

Cracking and Related Refinery Processes. (2014, September 7). Retrieved from The Essential Chemical Industry - online: https://www.essentialchemicalindustry.org/processes/cracking-isomerisation-and-reforming.html

 

 


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.


    

 




    Zeolites are very stable solids that withstand many other materials in the kinds of environmental environments that threaten them. Since they have relatively high melting points (over 1000 ° C), extreme temperatures will not affect them, and they don't burn. They also withstand high temperatures, do not dissolve in the water, and do not oxidize in water or other inorganic solvents. As zeolites a very stable substance, they do not cause health problems to humans, whether through skin contact or inhalation. However, in fibrous form, they may have carcinogenic effects. Besides, zeolites are synthesized based on naturally occurring minerals; thus, they also don't have any harmful environmental impacts. In the petrochemical industry, zeolites are very common as catalysts. They are used in catalytic crackers to split massive hydrocarbon molecules into oil, diesel, kerosene, and waxes, and all sorts of other petroleum by-products.

Numerous pores in the open structure of a zeolite are like thousands of tiny test tubes in which atoms and molecules become trapped and chemical reactions readily occur. Zeolite catalysts may operate selectively on particular molecules since the pores in a specific zeolite are of a defined size and form, hence why they were also known as shape-selective catalysts (they can select the molecules they work on in other ways beside shape and size). Zeolites can be used repeatedly, as most of the other catalysts. Zeolites have become more relevant over the years. Industrial catalysis without zeolites is hard to imagine due to their outstanding properties that can be simplified as below:

  • High surface area
  • Pore sizes in the molecular range;
  •  High adsorption capacity
  •  Have controllable adsorption properties
  •  Have inherent active sites
  •   Shape selectivity
  •    Very stable/ unreactive

Catalytic cracking is one of the industrial catalysis processes that used zeolites as the catalyst. It's a method in the essential oil industry where petroleum vapor moves through catalysts (zeolites) low-density bed, allowing the heavier fractions to 'crack,' creating smaller, more desirable goods. They are used in the petrochemical industry on an unprecedented scale to manufacture polyolefins. There are many benefits and drawbacks of the use of the catalyst in the cracking process.

Advantages of catalytic cracking process:

  • Catalytic cracking takes place at lower temperature and pressure (3000C -4000C and 1-5kg/cm2)
  • Catalytic cracking yields a high quantity of branched-chain, unsaturated, aromatic hydrocarbons
  • Catalytic cracking is a better-controlled process
  • Petrol obtained by catalytic cracking has lesser sulfur content.
  • It increased the lower heating value of the fuel.
  • Better burning due to usage of gaseous hydrocarbons.
  • The use of catalyst in the cracking process is cheaper than other cracking methods  because it saves energy as lower temperatures and pressures are used

Disadvantages of catalytic cracking processes:

  • Incomplete conversion of the fuel

  • Loss of activity in the catalyst due to the deposition of undesirable carbonaceous products, metallic compounds, and asphaltenes on the catalyst surface (coking).
  • The structural changes including thermally or attrition of catalyst lead to the catalyst deactivation








REFERENCES

(Bhaskar, Rao., Modern Petroleum Refinery Processes (5th ed.). Oxford & IBH Publishing Co. Pvt Ltd., New Delhi.

https://chemrevise.files.wordpress.com/2015/09/6-2-alkanes

https://prezi.com/yxalvrg9603h/catalytic-cracking

https://www.explainthatstuff.com/zeolites.html#catalysts

https://www.intechopen.com/books/processing-of-heavy-crude-oils-challenges-and-opportunities/catalysts-for-hydroprocessing-of-heavy-oils-and-petroleum-residues

https://www.polytechnichub.com/advantages-catalytic-cracking-thermal-cracking/




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