Blog 6

Write a post reviewing the significance of thermal cracking in petroleum refining in the past and present.

After all of the various physical separations have occurred to a crude oil, such as distillation, deasphalting, and dewaxing, there is a need to now change the composition of the crude oil using chemistry, breaking and creating bonds. The yields of this product after just undergoing the physical changes does not meet the demand required so further chemical separations must be pursued. The earliest discovered method for chemical separation is known as thermal cracking where the chemical bonds are broken through changing temperature.

In the past the large demand for gasoline as a product from crude oil started with the mass produced model T automobile back in the 1920’s. Thermal cracking was the first chemical process introduced to convert heavier hydrocarbons with longer chain paraffins to lighter distillates. Thermal cracking produces shorter straight chain alkanes from longer straight chains. This was the number one method used to obtain gasoline from crude oil back in the day. It does so by using brutal heat, heating the temperatures until the compounds crack and the chemical bonds are broken. This process then delivered the gasoline, with a low octane rating, needed for automobiles at that time.

Thermal cracking proceeds through neutral reactor species called free radicals.  Another use for thermal cracking is to convert the bottom of the barrel into usable products such as fuel oils. Presently thermal cracking is not a significant process in a refinery within the United States because the gasoline that is produced from it would work properly in current automobiles. This is because the current automobiles require a fuel with a higher octane rating. This lead to the introduction of catalytic cracking.

Thermal cracking was first developed by William Merriam Burton in 1913 which operated under the temperature 700 F -750 F and pressure at 90 psi. It is probably the first commercialized cracking process. By this time, it is also the history of cracking of heavy crude oil fraction to light fraction started. However, as we learned from lesson 5, thermal cracking produces short straight chain alkanes from longer straight chains found in gas oils and the reactions were governed by the free radicals. The process actually produces gasoline that contain lower octane number than that of gasoline which produced by catalytic cracking. It is due to isomerization of free radicals is not favored. During 1920, the petroleum refining industry was facing a challenge called engine knock. In order to solve the problem, it needed more powerful and stranger engines, but that means it also require gasoline which contain higher octane number. By 1930, gasoline had achieved the octane ring around 60 and 70. The newer and more powerful engine required higher octane gasoline which up to about 100, but thermal cracking could not raise its octane number any higher. It is also the reason that thermal cracking is not common process in U.S refineries. Thermal cracking once was the primary process for distillate fuel production. Even it is not anymore, it still remain as an important process in refineries to produce diesel fuel and ethylene.