Abstract
Crude oil, also known as petroleum, is one of the most important natural resources. It is a fossil fuel that is non-renewable and has different components such as hydrocarbon compounds and other materials like oxygen, sulphur, nitrogen, salt and water. It is normally extracted from the ground, under the seas, and on land and is then transported to refineries. Most of the substances are removed in the refinery, and the oil is broken down and blended into useful products (McCants, 1989). Some of these products include medicines, plastics, fabrics, dyes, cosmetics, and transport fuels. Transportation of crude oil is done through pipelines or ships to the refineries.
The value of crude oil and natural gas is in the refined products made from them. Crude oil has different viscosities and varies in color ranging from shades of black and shades of yellow. The color largely depends on the composition of hydrocarbons in the oil. These hydrocarbons contain so much energy that the byproducts of crude oil take advantage of (McCants, 1989).
History of crude oil separation
Crude oil separation was believed to have started about 4000 years ago. The earliest known use of crude oil products is asphalt that was used in construction of the Babylon towers. The construction of these towers depended entirely on oil deposits that were found in Babylon and on the shores of river Issus. Other known oil deposits that were drilled were in China and Romania. These fields were estimated to be about 800 feet deep making them one of the deepest. Traditional drilling methods were employed in the fields whereby bamboo sticks were the common pipelines. Some early writings have also shown that ancient streets of Baghdad were carpeted with tar, indicating that crude oil was in use, in the region. Further writings contained information to show that the area had natural crude oil fields (Willsch, Clegg, Horsfield, Radke, & Wilkes, 1997).
In most of these regions where crude oil fields were discovered, separation was done to produce materials that were used for illumination and the production of weapons. The technologies that were employed in drilling and separation of crude oil were tedious, and sometimes the quantity and quality of the anticipated products was not attained. The discovery of electricity in the 19th century improved drilling and separation of crude oil. It is at this time that people began to think of large scale drilling and separation of crude oil. Due to the adoption of new technologies, engines that used crude oil were produced in large numbers thus increasing the demand for petroleum products. These engines propelled rail and steam ships and automobiles (Flynt, 2007).
In 1840s, Samuel M. Kier, the first person to refine crude oil, discovered crude oil running through his salt business. Wells normally drilled for salt water would occasionally produce stinking petroleum. Most people in the salt business thought the oil was a nuisance and would often let it pass into nearby waterways. However, Kier being an entrepreneur believed that this oil could be changed into something useful (Adeniyi, & Robert, 2013).
He first used this oil to light his salt plant at night but it produced a lot of smoke and an awful smell. Keir then sold pure crude oil as a medicine. He managed to employ a workforce to enhance sale and marketing of this medicinal product. By 1852, the medicinal fad was over and Kier needed a new way of making his oil useful. He knew that it would light up and make a good lamp oil, but the smoke made it difficult to use it as an illuminant.
In 1849, Professor James C. Booth analyzed the crude oil brought to him by Kier, and they both agreed to be that it needed refined. So in 1850, Kier began experimenting with distillation and became the first individual in the U.S. to try using liquid petroleum to generate lamp oil (Adeniyi et al., 2013).
His refining experiments did not fail and by 1851 Kier produced Carbon Oil, that burned with less smoke and odor. Kier created the first petroleum refinery in the US, Pittsburgh, Pennsylvania.
Crude oil consumption has been greatly influenced by automobile growth in the 20th and 21st century although oil products are in constant competition with other energy sources like natural gas and coal.
Components of crude oil
Crude oil is a mixture of several different hydrocarbons of different lengths and complexities. Hydrocarbons are molecules composed of hydrogen and carbon and contain a lot of energy. The amount of hydrocarbons in crude oil can vary greatly with lighter oils having about 97% and heavier oils having about 50% hydrocarbons. The major hydrocarbons in crude oil include paraffin, aromatics, naphthenes, alkenes and alkynes (Rowland, Alexander, Kagi, Jones, 1986). Paraffins comprise 15-60%, aromatics comprise 3-30%, naphthenes 30-60%, and asphaltics comprise the remaining fraction (Morrow, Gritz, & Kirton, 1975).
Crude oil is usually composed of light distillates, medium distillates and residue. The light distillates include naphtha and kerosene. Naphtha is a flammable liquid and is made into gasoline and petrochemicals. Kerosene is commonly used as a heating fuel and in fire toys. Middle distillates are light gas oils, which are made into jet fuels, and heavy gas oils, which are made into naphtha and other products. Residue is the heaviest component of crude oil and is further processed into heavy fuel oil, waxes, asphalts, greases, and refinery fuels (Rowland et al., 1986).
On average, crude oils are made of these compounds: carbons (84%), sulfur (1-3%), nitrogen (<1%), oxygen (<1%), metals (<1%), and salts (<1%). Iron, vanadium, nickel and copper are the basic metal components found in crude oil. (Rowland et al., 1986).
The phases of separation
Crude oil extraction can be done in two major ways: upstream and downstream. In the upstream method, wells are drilled, and unprocessed oils are recovered to the surface. Downstream involves refining of the oil and selling of the final products.
After extraction, crude oil separation is done through fractional distillation. This separates the different components of crude oil on the basis of their boiling points, so that they can be refined further. Desalting is a step that must be done first to prevent corrosion in the rest of the process downstream and of the equipment. If salt has not been removed it can cause faulting of the pipes, furnaces and equipment. Desalting involves washing crude oil in caustic and water where salts get diluted. In the process of fractional distillation, fractions found at the top of the fractionating column have lower boiling points than those at the bottom. There are several basic steps involved in the refining process: distillation, cracking, treating and reforming. Distillation involves pumping oil into and through pipes in hot furnaces. This separates light hydrocarbons from heavy ones in downstream distillation towers. Atmospheric and vacuum distillation methods are used in this process. Fractions of crude oil that have higher boiling points usually have higher molecular weights; they are more branched, have darker colors and are usually difficult to burn and more viscous (Dark, 1982).
Cracking is done to convert middle distillate, residue and gas oil into gasoline, diesel and jet fuels. It is done using processing plants that "crack" large molecules into smaller, lighter ones. Heat and catalysts convert these heavier oils to lighter end products using three different "cracking" methods: fluid catalytic cracking (FCC), thermal cracking (coking), and hydrocracking (Isomax). In FCC, the catalyst is a hot fluid of 10000 degrees Fahrenheit that cracks the heavy gas oils to produce gasoline and diesel oils. Hydrocracking is almost similar to FC but utilizes a different catalyst, higher pressure, lower temperatures, and hydrogen gas. It cracks heavy oils to kerosene and gasoline. In thermal cracking, very high temperatures are used to break apart hydrocarbons. Steam can also be used to break naphtha, ethane and butane into benzene and ethylene, which are then used to manufacture other chemicals (Tutunjian, & Vinegar, 1994).
Treating involves removing impurities. A process called hydrotreating is used to reduce air pollution when these fuels are used. The fractions are passed through a sulphuric acid column, an absorption column that has drying agents for water removal, and sulfur treatment to remove any sulfur compounds remaining. In the last process of reforming, the hydrocarbon molecules are reformed into high octane gasoline components referred to as reformates. The reformates contain hydrocarbons with complex structures and molecular shapes. This is done through a process called catalytic reforming. A catalyst is used to pool low weight naphtha to form aromatics, which are then used in blending gasoline and to make chemicals. Hydrogen gas is produced in significant amounts as a byproduct and is then used for hydrocracking or is sold (Tutunjian et al., 1994).
Types of crude oil separation
Crude oil can be separated using two types of processes: break down of large and heavy hydrocarbon molecules, and rebuilding the hydrocarbon molecules. Since crude oil is composed of a mixture of hydrocarbons with dissimilar boiling temperatures, it can be separated by distillation. There are two types of distillation: atmospheric and vacuum. In atmospheric distillation, a certain order is usually followed during the distillation process where some products precede the others during the process. Naptha is the first product to be produced followed by gasoline, kerosene and light gas oil. Heavy gas oil and reduced bottom are the last products produced (Mohammed, Bailey, Luckham, & Taylor, 1994).
In vacuum distillation, residue generated as a result of atmospheric distillation is sent to a vacuum distillation chamber. In this chamber, additional liquid is recovered at 4.8 to 10.3 kPa. More than 90% of the refining industries in northern America especially the United States of America possess vacuum distillation units. Heavier oils from the atmospheric distillation are subjected to vacuum distillation and a high temperature of 750o F is employed to produce lighter petroleum products. Boiling point is used to separate these products which as the name implies, is usually carried out under vacuum (Mohammed et al., 1994).
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