Catalytic cracking and catalytic hydro cracking are two very different processes. Hydro cracking can be considered a more refined process because it is fairly new when considering refinery processes. It was first used commercially in 1958. Catalytic cracking initiates on the catalyst surface where ionic species are formed. This process produces branched chains alkanes from long straight chain alkanes. These branched chains alkanes, also called iso-alkanes, produces gasoline with very high octane #’s. This high octane gasoline is needed for modern day internal combustion engines. The high octane gasoline is produced because of the high concentrations of i- alkanes as well as the aromatics present in the catalytic cracking product. There are 3 main types of catalytic cracking Houdry, Thermafor, and Fluid catalytic cracking. Houdry catalytic cracking was the first continous commercialized catalytic cracking process. This process operates with three different reactors. This is so the process can remain continuous. This has to be done because after 10 minutes of operation there is a significant amount of coke build up in the reactor. The reactors are stripped with team and the coke burnt off before they are operational again. This process was introduced commercially in 1936. The second catalytic process is Thermafor catalytic cracking. This process was introduced in 1942. This process using one reactor and a moving bed of catalysts rather then the fixed bed in the Houdry process. This process has a much higher efficiency then the Houdry process. The Third type of catalytic cracking is Fluid catalytic cracking. This process has the highest theramal efficiency of the three and was also introduced commercially in 1942. The coke buildup is very rich in carbon which allows the production of distillates without the addition of hydrogen. All three of these processes have significant coke build up.
Catalytic hydrocracking is a much more modern process then catalytic cracking. It was first introduced commercially by chevron in 1958. The process objective of hydro cracking is similar to catalytic cracking but yet more refined. Hydrocracking aims to reduce the molecular weight and boiling point of heavy oils to produce saturated hydrocarbons. It has a wider range of feedstock then catalytic cracking. It uses highly aromatic feedstock and distillation residue, a much greater flexibility in feedstock. This process is also a hydrogen addition process unlike catalytic cracking. Catalytic cracking is a carbon rejection process. There is a advantage to hydrogen addition processes because there is no build up of low grade byproducts, such as coke. Although hydro cracking is a much more expensive process then catalytic cracking.