Catalytic cracking is a petroleum refining process that dates back to as early as 1915 however it came into prominence during the Second World War. There was a need for and improved process that would provide higher quality and quantity products than the brute force tactics used in thermal cracking. By applying newer, more advanced knowledge of chemistry and chemical reactions petroleum refining could produce better yields of gasoline with higher octane ratings than thermal cracking could ever hope to accomplish.

Catalytic cracking accomplishes this goal by cracking small ionic molecules, called carbocations, off of longer straight chain alkanes. These carbocations can then reattach to an alkane molecule to create an iso-alkane which has the required higher octane ratings needed in today’s society. Catalytic cracking, as noted before, runs on relatively long straight chain alkanes and therefore the feedstocks usually consist of, light cycle oils and potentially heavy gas oils or light vacuum gas oils¹. These types of oils have the size necessary to be able to be cracked while still forming the correct length range of alkane products. The primary goal of catalytic cracking is to increase the quantity of production of higher octane gasoline than could be done from straight run products or thermal cracking, however constituents such as kerosene, LPG, heating oil, and olefins are produced as well².

Catalytic hydrocracking, also known as hydrocracking, is a refinery process that was just added in the last thirty years with a main goal of enhancing catalytic cracking. The process of hydrocracking is typically completed in two main parts: first hydrotreatment must be conducted before the actual hydrocracking can take place. Catalytic hydrocracking can bring in feedstocks such as some atmospheric residue, heavy vacuum gas oil, light cycle oil, and potentially even deasphalted oil which all contain high concentrations of aromatic and heteroatom compounds³. Because these feeds contain such high concentrations, hydrogen must be added first, during hydrotreatment, in order to convert highly stable, unsaturated aromatic compounds to saturated aliphatic compounds. Once this process has taken place the newly formed cycloalkanes are cracked in the presence of more hydrogen to prevent coking. The cracking process, called hydrocracking, forms the necessary alkane molecules needed in catalytic cracking.

Catalytic hydrocracking is beneficial to catalytic cracking not only because it can produce some of its feedstock but also because it provides a way to remove heteroatoms such as nitrogen, sulfur, oxygen, and other metals before they enter the catalytic cracker. If these contaminants were to enter the catalytic cracking system they could potentially poison the catalysts which are needed to run reactions forming the iso-alkanes.

1. “Fluid catalytic cracking.” Wikipedia. Wikimedia Foundation, n.d. Web. 4 July 2014. <http://en.wikipedia.org/wiki/Fluid_catalytic_cracking#Flow_diagram_and_process_description>.
2. “Cracking.” Encyclopedia of Earth. N.p., n.d. Web. 4 July 2014. <http://www.eoearth.org/view/article/151525/>.
3. Meister, Jill , and Roger Lawrence. “Hydrocracking, Processing Heavy Feedstocks to Maximize High Quality Distillate Fuels.” UOP. N.p., n.d. Web. 4 July 2014. <http://www.uop.com/hydrocracking-processing-heavy-feedstocks-maximize-high-quality-distillate-fuels/>.