Pathways of Crude Oil Refining

Fossil fuels derived from the petroleum reservoirs are refined in order to suit the various application purposes, from car fuels to airplane fuels and space fuels. Fossils fuels are a complex mixture of hydrocarbons varying in composition depending on source and origin. Depending on the number of carbon atoms the molecules contain and their arrangement, the hydrocarbons in the crude oil have different boiling points. In order to take advantage of the difference in boiling points of different components in the mixture, fractional distillation is used to separate the hydrocarbons from the crude oil. Figure 12.3 shows the fractional distillation column in which the temperature is lower at the top and increases as it goes down the column.

Figure 12.3 gives a general schematic of the activities from the storage of crude oil to the complete refining process. The stored



Aircraft fuel

Ca la lytic crackina


Solvent extraction

Crystal I cation

^ "Asphalt" Bitumen



Crude oi

Petrochemical industries Aromatic recovery

Diesel. Kerosene ndustna l'Jc-iS



Figure 12.3 Fractional distillation unit for hydrocarbon refining (Chhetri and Islam, 2009).

crude oil is transported into the place where either vacuum distillation or atmospheric distillation is used for hydrocarbon separation. Chemical impurities of crude oil, such as sulfur or wax, are separated.

Crude oil is refined through distillation, or fractionation, in order to form several different hydrocarbon groups, such as gasoline, diesel, aircraft fuel, kerosene, asphalt, and waxes. The fractions emerging from crude oil distillation are divided out based on their increasing molecular weight and boiling temperature in the distillation column. The distillation process continues until all the fractions are separated.

Fractional distillation is the process of separating crude oil in atmospheric and vacuum distillation towers into groups of hydrocarbon compounds of different boiling points. The hydrocarbon conversion process consists of alkylation, thermal and catalytic cracking for decomposition, and polymerization for combining the hydrocarbon molecules and rearranging with catalytic reforming. To remove or separate the naphthenes, aromatics, and other undesirable compounds, various treatment processes, such as dissolving, adsorption, and precipitation, are carried out. In addition to this, desalting, drying, hydrodesulfurizing, solvent refining, sweetening, solvent extraction, and solvent dewaxing are also done to remove impurities from the fractions. Other activities, such as formulating and blending, are carried out to produce finished products with desired properties. Refining operations also include the treatment of wastewaters contaminated due to petroleum operations, solid waste management, process water treatment, and cooling and sulfur recovery. Other auxiliary operations include power generation and management for process operations, the flare system, the supply of air, nitrogen, steam, and other necessary system inputs, along with the administrative management of the whole refining systems.

Even though distillation results in separate hydrocarbons, the resulting products of petroleum are directly related to the properties of the processed crude oil. These distillation products are further processed into more conventionally usable products by using cracking, reforming, and other conversion processes.

The pathways of oil refining illustrate that the oil refining process utilizes toxic catalysts and chemicals, and the emission from oil burning also becomes extremely toxic. Figure 12.4 shows the pathway of oil refining. During the cracking of the hydrocarbon molecules, different types of acid catalysts are used along with high heat and

Figure 12.4 Pathway of oil refining process.

pressure. The process of breaking the hydrocarbon molecules is the thermal cracking. During alkylation, sulfuric acids, hydrogen fluorides, aluminum chlorides, and platinum are used as catalysts. Platinum, nickel, tungsten, palladium, and other catalysts are used during hydro processing. In distillation, high heat and pressure are used as catalysts.

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