Thermal cracking is the chemical process of converting larger, long straight chain alkanes found in gas oils and other crude oil fractions into shorter straight chain alkanes. These shorter alkane chains are more desired because of their use in transportation fuels like gasoline. The thermal cracking reactions are governed by free radicals. The chain reaction of free radicals starts by breaking the C-C bond in the alkanes. This forms two free radicals. This step is called the initiation reaction. The next step, the propagation reaction produces a short chain alkane and one radial, which continues the chain. The final step is the termination reaction. This process started in the 1900’s as a way to increase the yield of motor gasoline from crude oils. These high-octane fuels were used in aircraft. Catalytic cracking came into use in the 1930’s and 1940’s. Because the catalytic cracking process produced higher yields of gasoline with high octane numbers, thermal cracking is no longer a method for breaking longer chains into shorter chains for gasoline production in modern refineries. In locations where diesel fuels are in high demand thermal cracking is still used. The use of thermal cracking in modern refineries is limited to naphtha cracking of residual fractions like vacuum distillation residue.

Thermal cracking is a process that produces short straight chain paraffin from longer straight chains found in gas oils and other heavier crude oil fractions. The chemistry of thermal cracking involves free radicals that are reactive species with unpaired electrons but have a neutral electronic charge. It is the free radical chemistry that is responsible for producing gasoline with a relatively low octane number.

A Russian engineer named Vladimir Shukov introduced the first thermal cracking method in the Russian Empire in 1891. However, it was much later in 1912 that William Merriam Burton and Robert E. Humphreys designed a similar thermal cracking process which operated under temperature conditions of 700 to 750 °F and an absolute pressure of 90 psi. The advantage of the system they developed was that both the condenser and the boiler were continuously kept under pressure. A few years later in 1921, an employee at the Universal Oil Products Company, C.P. Dubbs, developed a more advanced technique which operated at higher temperatures of 750–860 °F. The design became known as the Dubbs process and was extensively used until the early 1940s.

Modern day techniques of thermal processing include visbreaking and coking. Visbreaking is a mild fom of thermal cracking whereby the viscosity of the heavy crude oil residue is lowered significantly without affecting the boiling point range. Temperatures of about 950° F are used in the distillation column. Visbreaking mostly depends on temperature and time of the reaction. Coking is a severe form of thermal cracking that is used to convert heavy residuals into lighter more useful products and distillates. The most common coking techniques include delayed coking, fluid coking and flexi coking.

Sources:

Wikipedia: http://en.wikipedia.org/wiki/Cracking_(chemistry)

Course Webpage: https://www.e-education.psu.edu/fsc432/content/chemistry-thermal-cracking

Set Laboratories: http://www.setlaboratories.com/therm/tabid/107/Default.aspx

The most notable change in the supply of petroleum fuels for the United States is the drastic growth in domestic production of both natural gas and crude oil. The development of production in tight formations, or shale formations (particularly the now well-known Marcellus Shale in the Northeastern United States) combined with the technological advances (hydraulic fracturing and directional drilling), has had far-reaching effects, including decreased both dependency on and imports from other countries. The largest change is from Africa, with imports from that region decreasing by 90% from 2010 to 2014. For comparison, 2008 tight oil production accounted for only 12% of US production, while in 2012 the number rose to 35%. By 2019, we can expect half of US oil production to be from tight oil formations. This increased domestic production has also reduced costs, allowed prices to decrease, and making natural gas a viable and inexpensive alternative to coal in the generation of electricity. While increased use of natural gas in the electricity generation sector is partially environmental policy-driven, much of this growth can be attributed to the mechanics of a price competitive market. This change is beneficial, as when comparing these two sources of energy, combustion of natural gas produces far less carbon dioxide, nitrogen oxides, and sulfur emissions than coal. Natural gas also does not contain harmful particulate matter such as mercury. Furthermore, there have also been advances in other renewable sources of energy including wind and solar power. As these sources become more competitive as costs decrease, we can expect renewable electricity generation to account for 16% of total electricity generation in the United States by 2040.

There have been many positive changes regarding the environmental concerns from combustion of petroleum fuels in internal combustion engines. Though the total miles driven and vehicles used have increased (total vehicle miles traveled increasing by 0.9% each year), it has been more than offset by the increased fuel efficiency of engines. Strict regulations and standards set in place have forced manufacturers to develop better and cleaner vehicles. The EIA website states that light-duty vehicle fuel efficiency has increased by nearly 2% each year, and can be expected to reach 37.2 miles per gallon by 2040 from 21.5 mpg in 2012. Additionally, the entire nation has been slowly and gradually moving towards diesel fuels, biofuels, hybrid, and completely electric cars (most notably Tesla, with massive growth in recent years). Overall, I believe that the United States is moving in the right direction with regards to environmental policy and sustainability. However, this is a global issue and countries such as China and India must also follow suit (though India’s new prime minister has stated that the entire country will be moving towards solar powered homes, hoping that each home is powered by the year 2019).

http://ebf301.dutton.psu.edu/2014/05/25/supply-of-petroleum-fuels-in-the-united-states-and-petroleum-fuels-in-internal-combustion-engines/

As mentioned in the lesson, the separation process of crude oil provides insufficient yields for the desired products i.e. gasoline. To satisfy the demand for more desirable products, conversion processes are used to enhance the yield. Cracking is the process of breaking down large molecules into smaller ones. Free radicals are the active intermediate species in thermal cracking (as opposed to ions in catalytic cracking). Though radicals are more stable on ternary or secondary carbons, the weakest bond in a compound is broken and the radical is typically produced on a primary carbon. Additionally, due to the fact that beta-bond scission reactions proceed faster than isomerization in a radical during the thermal cracking process, the final product is primarily composed of straight-chain parrafins and negligible amounts of branched-chain paraffins. Straight-chain parrafins have a lower octane rating – or a higher tendency to knock (self ignite) – an undesirable effect in modern gasoline engines. Therefore, presently thermal cracking is rarely used to improve gasoline yields and instead used to convert heavy gas oils into light gas oils with some byproducts of gas, gasoline, and fuel oil. However, it is still used to improve diesel yields (where knocking is desirable) in countries that primarily rely on diesel fuel.