Oil is an oily and combustible liquid that is distributed in the sedimentary zone of the earth's crust. It is one of the most important minerals for humans. Oil is a very complex mixture of cyclanes, arenes and alkanes. It also contains oxygen, sulfur and nitrogen compounds. The oil contains more than a thousand specific organic substances that contain about ninety percent of carbon, fifteen percent of hydrogen, five percent of sulfur, one percent of nitrogen and three percent of oxygen. Oil also includes a small admixture of mineral compounds. The ash content of oil is very small, it does not exceed one tenth of a percent. There are three types of oil:
1. Lightweight.
2. Average.
3. Severe.
Oil burns at a heat of about 43.7-46.2 MJ / kg, which is its huge advantage among other combustible substances.
The composition of the oil may also include light fractions, which boil at two hundred degrees Celsius. They are mainly composed of methane hydrocarbons, i.e. alkanes. The content of such light fractions in petroleum products produced at different locations can vary greatly. Cycloalkanes, as well as aromatic hydrocarbons, that is, arenes, are essential in the composition of oil.
Aromatic hydrocarbons (arenas) are rightly considered the most toxic components that make up oil and oil products. They are called chronic toxicants. The most active and fastest of them are benzene, toluene and xylene, as they are low boiling substances. A large number of diverse arenas are considered dangerous mutagens and carcinogens. The most dangerous group of arenas is a group of polyaromatic hydrocarbons.
The chemical composition of oil also includes a large proportion of solid methane hydrocarbons - the so-called paraffins. Their content in it may exceed fifteen percent.
According to the content of paraffin products, oil is divided into several groups:
1. Petroleum low paraffin composition. They contain no more than one and a half percent of paraffins in the composition.
2. Oil paraffin composition. This oil contains up to six percent paraffin.
3. High paraffin oil. Here, paraffin contains more than 6 percent.
Oil contains substances such as chrysens, phenanthrenes, benzpyrenes, pyrenes, tetraphenes. It also has non-hydrocarbon components - resins and asphaltenes, which play an important role in the activity of this mineral.
From an environmental point of view, sulfur compounds are important components of oil . According to the content of these products, oil is also divided into three groups:
1. Low sulfur oil. It contains up to half a percent of sulfur.
2. Sulfur oil. Here, the sulfur content does not exceed two percent.
3. Sour oil. These are all petroleum products containing more than two percent sulfur.
The properties of oil, which are the main definition of the height of its quality, include:
1. Density. In relation to oil, most often they mean its density in relation to distilled water. The density of oil usually varies from 0.8 to 0.9 g / cm3, but there are also types of oil, the density of which can reach 0.98 g / cm3.
2. Viscosity. Conventional, kinematic and dynamic viscosity are distinguished.
3. The molecular weight. This is the most important indicator of the quality of petroleum products. The molecular weight of most of the petroleum products does not exceed 300 g / mol.
4. The refractive index. This is a very important indicator for petroleum products, which are complex mixtures of various substances.
5. Fractional composition. All substances, which even in small quantities are part of the oil, are of great importance for its quality.