Difference Between Catalytic Cracking and Catalytic Reforming

Main Difference – Catalytic Cracking vs Catalytic Reforming

Catalytic cracking and catalytic reforming are two processes used in the conversion of crude oil into useful products. Catalytic cracking is the breakdown of large hydrocarbon compounds into small hydrocarbon molecules with the use of moderate temperatures and pressures in the presence of catalysts. Catalytic reforming is the conversion of low octane naphtha into high-octane reformate products. Both these processes use a catalyst for the progression of the reaction. Therefore, both these reactions are very useful in increasing the octane number of the fuel that is obtained from the refinery. The main difference between catalytic cracking and catalytic reforming is that catalytic cracking gives cracked products whereas catalytic reforming gives reformate products.

Key Areas Covered

1. What is Catalytic Cracking
      – Definition, Technique, and Applications
2. What is Catalytic Reforming
      – Definition, Technique, and Applications
3. What is the Difference Between Catalytic Cracking and Catalytic Reforming
      – Comparison of Key Differences

Key Terms: Catalyst, Catalytic Cracking, Catalytic Reforming, Fluid Catalytic Cracking, Hydrocracking, Isoparaffins, Naphtha, Octane Number, Paraffin, Reformate Products

What is Catalytic Cracking

Catalytic cracking is the breakdown of large compounds into small hydrocarbons in the presence of a catalyst. Here, moderate temperatures and pressures are provided for the cracking process. The temperatures used for this process ranges between 475-530^oC. The pressure used for this process is around 20 atm.

Unlike thermal cracking, the catalytic cracking process is much easier to maintain since moderate temperatures are required. Modern refineries use zeolite as the catalyst. It can help in breaking down carbon-carbon bonds in hydrocarbon molecules.

Types

Catalytic cracking can be found in two types as:

1. Fluid catalytic cracking
2. Hydrocracking/vapor phase catalytic cracking

Fluid catalytic cracking is useful in converting high molecular weight hydrocarbons into useful gasoline like products. Here, the catalyst used for the reaction should be pre-heated and powdered. The powdered catalyst works better than granular or other heavy solid forms due to increased surface area.

Figure 1: A hydrocracking unit of a refinery in the USA

In hydrocracking, the breakdown of large hydrocarbons is done in the presence of hydrogen gas. It is a two-stage process. It includes cracking followed by hydrogenation.

What is Catalytic Reforming

Catalytic reforming is the process of converting low octane naphtha into high-octane reformate products. This process includes the rearrangement of hydrocarbon molecules in the naphtha feedstock. The produced high-octane reformate products are later used for gasoline blending and aromatic production. In other words, the catalytic reforming process converts paraffin into branched structures (isoparaffins) and cyclic forms. This also includes the breakdown of larger compounds into smaller compounds. The naphtha feedstock is composed of heavy paraffin compounds.

Process

The steps of the catalytic reforming include the following.

1. Feed preparation – Here the naphtha undergoes hydro-treatment. This step eliminates catalyst poisons from the naphtha feed. It causes the long life of the catalyst.
2. Preheating – The temperature is the most important operating parameter.
3. Catalytic reforming – The reforming process is carried on. The catalyst also should be recovered and circulated.
4. Product separation – Removal of undesirable byproducts and recovery of the desirable products. Aromatic compounds are also recovered for other uses.

Figure 2: The process of catalytic reforming and the extraction of the reformate products

The chemical reactions that occur in the process of catalytic reforming include dehydrogenation, isomerization, aromatization, and hydrocracking. The most common catalysts used in catalytic reforming are Platinum or Rhenium on a silica base.

Difference Between Catalytic Cracking and Catalytic Reforming

Definition

Catalytic Cracking: Catalytic cracking is the breakdown of large compounds into small hydrocarbons in the presence of a catalyst.

Catalytic Reforming: Catalytic reforming is the process of converting low octane naphtha into high-octane reformate products.

Catalyst

Catalytic Cracking: The most commonly used catalyst for catalytic cracking is Zeolite.

Catalytic Reforming: The most commonly used catalysts for catalytic reforming are Platinum or Rhenium on a silica base.

Mechanism

Catalytic Cracking: The catalytic cracking includes the breakdown of larger hydrocarbons into smaller hydrocarbons.

Catalytic Reforming: The catalytic reforming includes the rearrangement of hydrocarbons in order to form different products.

Feed

Catalytic Cracking: The feed for the catalytic cracking is distillates obtained from crude oil distillation.

Catalytic Reforming: The feed for the catalytic reforming is naphtha feedstock.

Products

Catalytic Cracking: Catalytic cracking mainly gives small alkanes and alkenes.

Catalytic Reforming: Catalytic reforming mainly gives isomerized products and aromatic products.

Conclusion

Catalytic cracking and catalytic reforming processes are very important reactions used in the processing of crude oil. There are separate sections or units to conduct these processes in a refinery. Although both these processes give different products in the presence of a catalyst, there are considerable differences between the two processes. The main difference between catalytic cracking and catalytic reforming is that catalytic cracking gives cracked products whereas catalytic reforming gives reformate products.

References:

1. “Catalytic reforming.” Wikipedia, Wikimedia Foundation, 31 Aug. 2017, Available here. Accessed 18 Sept. 2017.
2. “Fluid catalytic cracking.” Wikipedia, Wikimedia Foundation, 31 Aug. 2017, Available here. Accessed 18 Sept. 2017.
3. “Catalytic cracking.” Encyclopædia Britannica, Encyclopædia Britannica, inc., Available here. Accessed 18 Sept. 2017.

Image Courtesy:

1. “Slovnaft – residual hydrocracking (RHC)” By Mikulova – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “BTX-ReformateExtraction” By Mbeychok – Own work (CC BY-SA 3.0) via Commons Wikimedia