What is the Difference Between Catalytic Cracking and Hydrocracking

The key difference between catalytic cracking and hydrocracking is that catalytic cracking involves carbon rejection, whereas hydrocracking involves a hydrogen addition process.

Cracking processes are very important in petroleum refineries and help in converting large molecules to small compounds, which in turn increase the octane rating of gasoline. Catalytic cracking, or more precisely fluid catalytic cracking, is the conversion of hydrocarbons with high boiling points and high molecular weights into gasoline, olefinic gases, and other petroleum products. Hydrocracking is the process of converting high boiling constituents into low boiling constituents.

CONTENTS

1. Overview and Key Difference
2. What is Catalytic Cracking  
3. What is Hydrocracking
4. Catalytic Cracking vs Hydrocracking in Tabular Form
5. Summary – Catalytic Cracking vs Hydrocracking

What is Catalytic Cracking?

Catalytic cracking, or more precisely fluid catalytic cracking, is the conversion of high boiling point, high molecular weight hydrocarbons into gasoline, olefinic gases, and other petroleum products. This is a conversion process useful in petroleum refineries. There is a high boiling point, high molecular weight fraction of crude oil (petroleum) that undergoes catalytic cracking.

Originally, the cracking process of petroleum was done using thermal techniques. However, now it is replaced largely by catalytic cracking. This is because the latter yields a greater volume of high octane rating gasoline. Moreover, it produces byproduct gases having more carbon=carbon double bonds, such as olefins. Therefore, catalytic cracking is more economically valuable than the thermal cracking process.

For the fluid catalytic cracking process, the feedstock is heavy gas oil. It is the portion of petroleum having an initial boiling temperature of 340 Celsius degrees or above. Moreover, the molecular weight ranges from 200 to 600 or higher in these fractions.

What is Hydrocracking?

Hydrocracking is the process of converting high boiling constituents into low boiling constituents. That means the reactants of hydrocracking reaction are constituents of petroleum oil having high boiling points, and the products are compounds having low boiling points. Furthermore, this process is important because low boiling products are more valuable hydrocarbons, which include gasoline, kerosene, jet fuel, diesel, etc.

The process of hydrocracking is named as such because the breakdown of large molecules occurs in the presence of hydrogen gas. Generally, hydrocracking is done under severe conditions. It is because the reactants of hydrocracking feedstock are exposed to the reactor temperature for a long time.

We can define this process as a type of catalytic cracking because it also uses a catalyst to speed up the process; a metal catalyst. Typically, this process gives saturated hydrocarbons. However, the type of hydrocarbon given is dependent on the reaction conditions, which include the temperature of the reaction mixture, pressure, and catalytic activity. The products may include ethane, LPG, and isoparaffins.

What is the Difference Between Catalytic Cracking and Hydrocracking?

Cracking processes are very important in petroleum refineries and help in converting large molecules into small compounds, which in turn increase the octane rating of gasoline. The key difference between catalytic cracking and hydrocracking is that catalytic cracking involves carbon rejection, whereas hydrocracking involves a hydrogen addition process. Moreover, catalytic cracking is an endothermic process while hydrocracking is an exothermic process.

The below infographic presents the differences between catalytic cracking and hydrocracking in tabular form for side by side comparison.

Summary – Catalytic Cracking vs Hydrocracking

Catalytic cracking, or more precisely, fluid catalytic cracking, is the conversion of high boiling point, high molecular weight hydrocarbons into gasoline, olefinic gases, and other petroleum products. Hydrocracking is the process of converting high boiling constituents into low boiling constituents. The key difference between catalytic cracking and hydrocracking is that catalytic cracking involves carbon rejection, whereas hydrocracking involves a hydrogen addition process.

Reference:

1. “Catalytic Cracking.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Fluid Catalytic Cracker” By Valero Energy Corporation/TX – (Public Domain) via Commons Wikimedia
2. “Slovnaft – residual hydrocracking (RHC)” By Mikulova – Own work (CC BY-SA 3.0) via Commons Wikimedia