Thermal cracking is a process by which heavy residues under severe thermal conditions are cracks.¹ This process allows for the formation of heavy fractions such as coke, once properly treated and finished.¹ The first refinery opened in 1861, however the first thermal cracking process was not developed until years later in 1913.² The first thermal cracker took heavy fuels and subjected them to both pressure and high heat, physically breaking the molecules into smaller ones, producing additional gasoline and distillate products.² With this additional process added, the yield of products per gallon of gasoline was increased, making petroleum refining more profitable. In the 1930s this process was even further improved to produce more desirable, valuable products.² Until the 1936 thermal cracking remained the method of choice.³ As technology developed, thermal cracking started to phase out because Catalytic cracking became more popular, as the costs for the process were being reduced. Catalytic cracking utilizes carbocation chemistry, utilizing a carbonium ion intermediate.³ Thermal cracking which was advance at its time, then became less utilized since the process produced random cuts in the hydrocarbon chains, yielding random length carbon chains.³ Catalytic cracking was the solution for this problem, whose produced in an organized manner, cutting chains near the middle.³ Thermal cracking remains an important process in petroleum refining today, however improved combined processes of thermal cracking have been developed for various purposes to improve yield and quality of products.³

1. Mohamed A. Fahim, Taher A. Alsahhaf and Amal Elkilani, Fundamentals of Petroleum Refining
2. http://www.ilo.org/oshenc/part-xii/oil-and-natural-gas/item/384-petroleum-refining-process
3. Jennifer Clemons , Brian Senger, Nicholas Filippelli, Fluidized Catalytic Cracking