Oil distillation, primary and secondary oil refining

Oil is divided into fractions to produce oil products in two stages, that is, the distillation of oil passes through primary and secondary processing.

Primary Refining Process

At this stage of distillation, preliminary dehydration and desalting of crude oil is carried out on special equipment to isolate salts and other impurities that can cause corrosion of equipment and reduce the quality of refined products. After that, oil contains only 3-4 mg of salt per liter and not more than 0.1% of water. The prepared product is ready for distillation.

Due to the fact that liquid hydrocarbons boil at different temperatures, this property is used in the distillation of petroleum to separate individual fractions from it at different boiling phases. Oil distillation at the first refineries allowed the following fractions to be distinguished depending on the temperature: gasoline (boiled at 180 ° C and below), jet fuel (boiled at 180-240 ° C) and diesel fuel (boiled at 240-350 ° C). From residual oil remains fuel oil.

In the process of distillation, the oil is divided by the boiling point into fractions (constituent parts). As a result, commodity petroleum products or their components are obtained. Distillation of oil is the initial stage of its processing at specialized plants.

When heated, a vapor phase is formed, the composition of which is different from the liquid. The fractions obtained by distillation of oil are usually not a pure product, but a mixture of hydrocarbons. Individual hydrocarbons can be identified only through the multiple distillation of petroleum fractions.

Direct distillation of oil is carried out

- by single evaporation (so-called, equilibrium distillation) or simple distillation (fractional distillation);

- using rectification and without it;

- with the aid of an evaporating agent;

- under vacuum and at atmospheric pressure.

Equilibrium distillation less clearly separates oil into fractions than simple distillation. At the same time, in the first case, more oil passes into the vapor state at the same temperature than in the second.

Fractional distillation of oil makes it possible to obtain various fuels (gasoline, fuel for diesel and jet engines), as well as raw materials (benzene, xylenes, ethylbenzene, ethylene, butadiene, propylene), solvents and other products.

Further, the secondary distillation of oil is already carried out from the products obtained, the so-called cracking.

Process of secondary oil refining

Secondary distillation of petroleum is carried out by a method of chemical or thermal catalytic cleavage of those products that are separated from it as a result of primary oil refining. This produces a greater number of gasoline fractions, as well as raw materials for the production of aromatic hydrocarbons (toluene, benzene and others). The most common technology of secondary oil refining is cracking.

Cracking refers to the process of high-temperature processing of petroleum and isolated fractions to produce (mainly) products that have a lower molecular weight. These include motor fuel, lubricants, etc., raw materials for the petrochemical and chemical industries. The cracking proceeds with the breakage of the C-C bonds and the formation of carbanions or free radicals. The breakdown of the C-C bonds is carried out simultaneously with the dehydrogenation, isomerization, polymerization and condensation of the intermediates and the starting materials. The last two processes form a cracking residue, i.e. Fraction with a boiling point above 350 ° C and coke.

The distillation of oil by the cracking method was patented in 1891 by VG Shukhov and S. Gavrilov, then these engineering solutions were repeated by U. Barton in the construction of the first industrial plant in the USA.

Cracking is carried out by heating the raw materials or by exposing the catalysts and high temperature.

Cracking allows you to extract more useful components from fuel oil.