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

The first thermal cracking processes were developed in 1913 with the purpose of heating atmospheric tower residues and heavy gas oils until the molecules cracked and broke apart.¹ The reason for conducting this process was to break up the less desirable petroleum products and form them into highly valuable light middle distillates such as naphtha, gasoline, and diesel fuel among others². Thermal cracking became incredibly important with the invention of the automobile which uses an internal combustion engine fired by diesel or gasoline. With more people driving, the demand for fuel skyrocketed and the cracking process made it possible to produce more gasoline and diesel than was produced from crude oil as a straight run product³. For twenty to thirty years it was the pinnacle of petroleum refining processes, however by the start of World War II thermal cracking could no longer generate the quantity or quality that was demanded. At this time automobiles and planes required higher octane fuels that simply are not capable of being produced from the simple brute force cracking process¹. Instead, a new process called catalytic cracking was introduced which was capable of yielding larger amounts of higher quality fuel. While limited in use, thermal cracking is still used today with its primary roles being the production of diesel fuel and ethylene².

1. “Petroleum Refining Process.” Petroleum Refining Process. N.p., n.d. Web. 26 June 2014. <http://www.ilo.org/oshenc/part-xii/oil-and-natural-gas/item/384-petroleum-refining-process>.
2. Semih, Eser. “Lesson 6: Thermal Conversion Processes.” FSC 432: Petroleum Processing. N.p., n.d. Web. 28 June 2014. <https://www.e-education.psu.edu/fsc432/content/lesson-6-thermal-conversion-processes>.
3. Solomon, Lee. “Visbreaking, thermal cracking, and coking.” Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 28 June 2014. <http://www.britannica.com/EBchecked/topic/454440/petroleum-refining/81801/Visbreaking-thermal-cracking-and-coking>.

Thermal cracking was the first commercially used conversion process to process crude oils. It was initially implemented to produce more gasoline as well as higher octane gasoline. The higher octane gasoline was mainly used for fuels for aircrafts. The main reason thermal cracking came along was to produce light to middle distillates from heavier fractions of the crude oil. Thermal cracking became obsolete for gasoline production in modern refineries when catalytic cracking was initiated. Catalytic cracking came around in the 1930’s and could produce more gasoline at a higher octane number, then thermal cracking. Thermal cracking is still used in some modern refineries with visbreaking and coking. Visbreaking is a thermal cracking process that uses VDR as a feedstock to produce fuel oil and light products to increase distillation output of a refinery. The main goal of visbreaking is to reduce viscosity in a feedstock, but could also be used to produce lighter distillates from fuel oil. The second thermal cracking process that is used in refineries is called coking. Coking is the most severe thermal cracking process used in a refinery. It cracks the heaviest of the crude oil fractions, such as vacuum residue. Three coking processes are used to maximize the yield of distillation products. Thermal cracking is no longer the main process of a refinery but it is still plays a small role in increasing the yields of distillates.