Fractions and chemical composition of petroleum

Petroleum is a complex mixture of various organic compounds. It consists of different hydrocarbons and heteroatomic compounds. It is technically impossibly to separate petroleum into individual compounds. In any case, it is unnecessary to separate the petroleum to the component level in order to obtain a technological or industrial classification. 

In the industrial method, fractionation is achieved by the method of rectification. Using this method, the fractions with boiling point up to 350°C are separated at atmospheric pressure. These are called the light fractions. Usually, during atmospheric rectification, the following individual fractions are obtained  

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The residue after atmospheric distillation is called atmospheric residue . This fraction, with a boiling point over 350°C, is usually distillated further at a low pressure or in a vacuum. This residue can be classified in two different ways depending on the intended application  

All the fractions obtained from atmospheric residue are called heavy fractions . On the other hand, the products obtained after secondary processing of the heavy fractions are considered to be light fractions if boiling of the fraction ends at 350°C, and to be heavy fractions if boiling begins at 350°C. 

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It is necessary to make a chemical classification of petroleum since chemical properties are very crucial in selecting the right method for processing the oil. There are many classifications with regard to fractions and chemical compositions of petroleum. In this chapter we will present the basis for these classification methods. 

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