At first they remove mechanical impurities and dissolved gases from oil, clear of excess salt and water in electric desalinating installations. At the same stage they also define properties of raw materials.
Then oil enters rectification columns on atmospheric distillation where it is divided into some fractions: light and heavy gasoline fraction, kerosene fraction, a diesel fraction and an atmospheric distillation residue – fuel oil. The quality of the fractions does not satisfy the requirements for commodity oil products, that's why fractions are subjected to further (secondary) processing.
The purpose of refining is production of petroleum products such as fuel (automotive, aviation, boiler) and raw material for subsequent chemical processing.
Gasoline, kerosene, diesel oils and industrial oils are subdivided into various brands depending on chemical composition. The final stage of production is obtained mixture of the received components to produce the finished product of the demanded structure. With the rapid development of the world's chemical and petrochemical industry, oil demand is increasing not only in order to increase production of fuels and oils, it is also as a source of valuable raw materials for the production of synthetic rubber and fibers, plastics, surfactants, detergents, plasticizers, additives, dyes.
Oil refining is removal of undesirable components from petroleum products, adversely affecting the operational properties of fuels and oils.
Chemical refining is made by the action of various reagents on the removable components of treated products. The easiest way of purification is made by 92-96% sulfuric acid or oleum. It is used to remove unsaturated and aromatic hydrocarbons.
Physic-chemical treatment is performed by using solvents that selectively remove unwanted components from the refining product, such as aromatic hydrocarbons, polycyclic aromatic hydrocarbons, sulfur and nitrogen compounds from oil distillates.
At the adsorption purification they remove unsaturated hydrocarbons, pitches, acids from petroleum. Adsorptive purification is carried out by contact of heated air with adsorbents or a product filtration through adsorbent grains. Catalytic purification is hydrogenation under mild conditions that used to remove sulfur and nitrogen compounds.