What are the types of catalytic cracking

There are different types of catalytic cracking and they are named based on the type of feedstock used. Catalytic cracking is the process in which petroleum is converted into gasoline and other liquid fuels while the gaseous hydrocarbons produced are burned without intermediate processing. Catalytic cracking is a very important step in a fuel production process.

Types of catalytic cracking

1.Fluid catalytic cracking (FCC)

This type of catalytic cracking was discovered by Eugene Houdry in the year 1931. It is a type of thermal cracking process and it is done in the liquid phase. In this process, a catalyst is used to break down a large hydrocarbon molecule into smaller molecules. The benefits of fluid catalytic cracking are as follows:

-Refining gasoline to motor car standards.

-Burning of undesirable hydrocarbon fractions without intermediate processing.

-Producing low boiling point gases like butane and propane which are used in a variety of industries.

This refining process is done in many different types of equipment named fluid catalytic cracker and they include fixed bed, slurry phase and moving bed systems. Fluid catalytic cracking has one main advantage over other refining processes; it produces high quality gasoline from the very complex petroleum feedstocks. It also has some disadvantages; it creates a lot of coke or solid carbon on the catalyst and when this coke builds up to a certain level, the process becomes inefficient and can even shut down the plant.

2.Moving-bed catalytic cracking

This process was discovered by Gail and Richard Sherrell in 1976. It is also known as liquid solvent cracking. This process is done in the liquid phase and it uses a rotating fixed-bed catalytic reactor called a moving-bed reactor (MBR). The main difference between the chemical reactions of FCC cracking and MBR is that there are three chemical reactions occurring at the same time in this process:

1: Hydrocarbon to lighter hydrocarbon products.

2: Formation of desirable gasoline fractions such as aromatics, olefins, and ethers.

3: Formation of undesirable higher boiling point products such as paraffins (synethic aromatics), sulphur compounds, heavier hydrocarbons, etc. This creates a variety of gasoline fractions depending on the feedstock.

Fluid catalytic cracking and MBR have some disadvantages as well; they both produce a lot of coke while they are operating. In order to keep the catalyst clean, it is necessary to use acid gases such as sulfuric acid or hydrogen sulphide or other compounds that can dissolve and remove the solid carbon build-up. Also, both processes produce hydrocarbon gases when they are operating. These gases have high carbon monoxide content and can affect vehicles if not handled properly. This is why in MBR plants only low-sulphur fuels such as diesel fuel are used because diesel fuel does not contain high quantities of hydrocarbons like gasoline does.

3.Thermofor catalytic cracking (TCC)

This catalytic cracking process was discovered in the year 1969 by Robert Bussard. The main difference between TCC process and other types of catalytic cracking is that in this process, a chemical reaction takes place mainly in one phase while the other type of catalytic cracking converts a hydrocarbon feedstock into hydrocarbons and gases at the same time.

The reason why this type of cracking is named Thermofor is because the conditions needed to operate TCC are very close to those required for thermo-catalysts or like a heat activated catalyst system (HAZMAT). Thermofoors are used for transportation, power generation and other industries where oxygen is present but it has more advantages than disadvantages as compared to FCC units. The advantages of TCC over FCC process are as follows;

-It produces high quality gasoline from many different types of hydrocarbon feedstocks. The required amount of sulfur and nitrogen in the feed is high and this advantage can be used for converting heavy fuel oil into diesel fuel.

-It uses less coke than the FCC units. This is a very important advantage because coke has been shown to be a carcinogen. In some countries, coke plants are banned because of this reason but there are still many coke plants operating around the world.

-Thermofoors do not create hydrocarbon gases while they are operating.

In conclusion, types of catalytic cracking can be divided into 3 categories based on the type of hydrocarbon feedstock used. Each category of catalytic cracking is a useful step in the fuel production process and they also create a variety of gasoline or diesel fuels depending on the feedstock.