Depending on the composition, the physical and chemical properties of oil change in a wide range. The consistency of oil changes from light, saturated with gases, to thick, heavy, resinous. Accordingly, the color of oil changes from light to dark red and black. These properties depend on the predominance of low molecular weight light hydrocarbon compounds or heavy complex high molecular weight compounds in the oil composition.

From a chemical point of view, the composition of oil and gas is very simple. The main elements that form oil and gas are carbon - C and hydrogen - H. The carbon content in oils is 83 - 89%, the hydrogen content is 12 - 14%. In small volumes, oils contain sulfur - S, nitrogen - N and oxygen - O. Carbon and hydrogen are present in oil in the form of many compounds called hydrocarbons.

Oil is a flammable oily mobile liquid from light yellow to dark red, brown and black in color, consisting of a mixture of various hydrocarbon compounds. In nature, oil is very diverse in quality, specific gravity and consistency: from very liquid and volatile to thick resinous.

It is known that chemical elements combine with each other in certain ratios according to their valency. For example, a water molecule - H 2 O consists of two hydrogen atoms with a valence of - 1, and one divalent oxygen atom.

The simplest hydrocarbon compound in terms of chemical composition is methane - CH 4. It is a combustible gas, which is the main component of all natural combustible gases.

The next compound after methane is ethane - C 2 H 6,

Then, propane - C 3 H 8,

butane - C 4 H 10, pentane - C 5 H 12, hexane - C 6 H 14, etc.

As noted above, starting from pentane, gaseous hydrocarbons pass into liquid ones, i.e. into oil. The formula of pentane continues the same continuous series of hydrocarbon compounds belonging to the methane group.

In this group, all carbon bonds are involved, i.e. used for bonding with hydrogen atoms. Such compounds are called limiting or saturated. They are non-reactive, i.e. are unable to attach molecules of other compounds to their molecule.

Carbon in combination with hydrogen is capable of forming countless hydrocarbon compounds that differ in their chemical structure and, consequently, their properties.

There are three main groups of hydrocarbon compounds:

First group – methane(or alkanes). Their general formula is С n H 2n+2 . It is this group of compounds that was discussed above.

They are fully saturated because all valence bonds have been used. Therefore, they are chemically the most inert, not capable of chemical reactions with other compounds. The carbon skeletons of alkanes are either linear (normal alkanes) or branched chains (isoalkanes).

Second group – naphthenic(or cyclanes). Their general formula is СnH2n. Their main features are the presence of a five- or six-membered ring of carbon atoms, i.e. they form, unlike methane, a closed cyclic chain (hence the cyclanes):

These are also saturated (limit compounds). Therefore, they practically do not enter into reactions.

Third group – aromatic(or arenas). Their general formula is C n H 2n-6. They are formed by six-membered rings based on the so-called aromatic ring of benzene - C 6 H 6 . Their distinguishing feature is the presence of double bonds between atoms.

Among aromatic hydrocarbons, monocyclic, bicyclic (i.e., double rings) and polycyclic, forming multi-ring compounds of the honeycomb type, stand out.

Hydrocarbons, including oil and gas, are not substances of a definite and constant chemical composition. They represent a complex natural mixture of gaseous, liquid and solid hydrocarbon compounds of methane, naphthenic and aromatic series. But this is not a simple mixture, but a system of a complex hydrocarbon solution, where the solvent is light hydrocarbons, and the dissolved substances are other high-molecular compounds, including resins and asphaltenes, i.e. even non-hydrocarbon compounds that make up oils.

A solution differs from a simple mixture in that its constituent components are able to interact chemically and physically, while acquiring new properties that were not inherent in the original compounds.

Density

In a number of physical properties of oil, density or specific gravity is the most important. This indicator depends on the molecular weight of its constituent components, i.e. from the predominance of light or heavy hydrocarbon compounds in the composition of oil, from the presence of resinous impurities, asphaltenes and dissolved gas.

The density of oil varies over a wide range from 0.71 to 1.04 g/cm 3 . In reservoir conditions, due to the large volume of gas dissolved in oil, its density is 1.2–1.8 times less than in surface conditions after its degassing. Depending on the density, the following classes of oils are distinguished:

• Very light (up to 0.8 g / cm 3);
• Light (0.80-0.84g / cm 3)
• Medium (0.84-0.88g / cm 3)
• Heavy (0.88-0.92g / cm 3)
• Very heavy (more than 0.92 g / cm 3)

Viscosity

Oil viscosity- this is the property to resist the movement of oil particles relative to each other in the process of its movement. Viscosity determines the degree of mobility of the oil. Viscosity is measured using a device - a viscometer. In the SI system it is measured in millipascals per second (mPa s), in the CGS system - Poise, g / (cm s).

There are two types of viscosity: dynamic and kinematic. Dynamic Viscosity characterizes the force of resistance to the movement of a layer of liquid with an area of ​​​​1 cm2 per 1 cm at a speed of 1 cm / sec. Kinematic viscosity is the property of a fluid to resist the movement of one part of the fluid relative to another, taking into account the force of gravity.

Dynamic viscosity is determined by the formula:

where: A is the area of ​​moving layers of liquid (gas); F is the force required to maintain the difference in the velocities of movement between the layers by the value dv; dy is the distance between moving layers of liquid (gas); dv is the difference in velocities of moving layers of liquid (gas).

The kinematic viscosity is also used in the calculations, it is determined by the following formula:

where: μ is dynamic viscosity; ρ is the oil density at the determination temperature.

In surface conditions, oils are divided into:

1. low viscosity - up to 5 mPa s;
2. increased viscosity - from 5 to 25 mPa s;
3. high-viscosity - more than 25 MPa s.

Light oils have a lower viscosity, and heavy oils have a higher viscosity. In reservoir conditions, the viscosity of oil is ten times less than the same oil on the surface after its degassing, which is associated with its very high gas saturation in the subsoil. This property is of great importance in the formation of hydrocarbon deposits, because. determines the scope of migration.

The value of the reverse viscosity characterizes the fluidity of the liquid φ:

1. Low sulfur - up to 0.5%;
2. Sulfurous - from 0.5 to 2.0%;
3. High sulfur - more than 2%.

Paraffinity of oil

This is another important property of oil that affects the technology of its production and transportation through pipelines. Paraffinity occurs in oils due to the content of solid components in them - paraffins (from C 17 H 36 to C 35 H 72) and ceresins (from C 36 H 74 to C 55 H 112).

Their content sometimes reaches from 13 to 14%, and at the Uzen deposit in Kazakhstan - 35%. The high content of paraffin makes it extremely difficult to extract oil, because. when opening the reservoir and lifting oil through the pipes, there is a continuous decrease in pressure and temperature. At the same time, paraffin is able to crystallize and precipitate into a solid precipitate, waxing both the pores in the formation itself, and the walls of tubing, valves and all process equipment. The closer the paraffin crystallization temperature is to the formation temperature, the sooner and more intensively the waxing process begins.

1. Low paraffinic - less than 1.5%;
2. Paraffin - from 1.5 to 6.0%;
3. Highly paraffinic - more than 6.0%.

Gas content

GOR can reach 300 - 500 m 3 / t, but more often - within 30 - 100 m 3 / t. There are also less - 8 - 10 m 3 / t, for example, heavy oils of the Yaregsky field of the Ukhta region have a gas factor of 1 - 2 m 3 / t.

saturation pressure

The saturation pressure (or start of vaporization) is the pressure at which gas begins to be released from oil. Under natural conditions, the saturation pressure can be equal to or less than the formation pressure.

In the first case, all gas will be dissolved in oil, and oil will be saturated with gas. In the second case, the oil will be undersaturated with gas.

Compressibility

The compressibility of oil is due to its elasticity and is measured by the compressibility factor - β N.

where V is the initial volume of oil, m3;

∆V - change in the volume of oil, m 3;

∆р – pressure change, MPa.

The compressibility coefficient characterizes the magnitude of the change in the volume of reservoir oil with a pressure change of 0.1 MPa. This coefficient is taken into account at the early stages of development, when the elastic forces of liquids and gases are not yet wasted and therefore play a significant role in the energy of the reservoir.

where Δt 0 is the change in temperature by 1 0 С.

The coefficient of thermal expansion shows by what part of the initial volume the volume of oil changes when the temperature changes by 1 0 C. This coefficient is used in the design and application of thermal methods of influencing the reservoir.

Oil volume factor

This coefficient shows how much volume occupies in reservoir conditions 1 m 3 of degassed oil due to its saturation with gas.

where b H is the volumetric coefficient of reservoir oil, fractions of a unit;

V pl - the volume of oil in reservoir conditions, m 3;

V deg - the volume of the same oil in surface conditions after its degassing, m 0;

ρ sur – oil density in surface conditions, t/m 3 ;

ρ pl is the density of oil in reservoir conditions, t/m 3 .

The volume factor of oil is usually greater than 1, as a rule, is in the range of 1.2–1.8, but sometimes reaches 2–3 units. The volume factor is used in calculating reserves and in determining the oil recovery factor.

Shrinkage of oil and conversion factor According to the volume factor, one can determine the shrinkage of oil during its extraction to the surface - I, as well as the conversion factor - Θ.

The latter is used in the formula for calculating reserves by the volume method. The conversion factor Θ is the reciprocal of the volume factor - b H .

As you can see, this formula is an inverted formula for the volumetric coefficient. It is she who takes into account the decrease in the volume of oil (its shrinkage) during the transition from reservoir conditions to surface conditions.

Oil pour point

The pour point is the temperature at which oil cooled in a test tube does not change its level at an inclination of 45º. The pour point and melting point of oils are varied. Usually, oil lies in the reservoir in a liquid state, but some of them thicken even with a little cooling. The pour point increases simultaneously with an increase in the content of solid paraffins in it and a decrease in the content of resins. Resins have the opposite effect - with an increase in their content, the pour point decreases.

Optical properties of oil

Optical activity is expressed in the ability of oil to rotate the plane of a polarized light beam to the right (rarely to the left). Optically active substances are formed during the vital activity of organisms, and the optical activity of oil indicates its genetic connection with biological systems. The main carriers of optical activity in oil are fossil molecules of animal and plant origin - chemofossils. Oils from older deposits are less optically active than oils from younger rocks.

Oils glow when irradiated with ultraviolet rays, that is, they have the ability to luminesce. Resins luminesce in predominantly non-luminescent compounds—hydrocarbons. Luminescent substances have certain spectra of luminescence colors (brown, blue, yellow, etc.) and the intensity of the glow depends on the concentration. Light oils have blue and blue luminescence colors, heavy oils have yellow and yellow-brown.

Knowledge of the chemical composition of natural oil systems serves as a starting point for predicting their phase state and phase properties under various thermobaric conditions corresponding to the processes of production, transportation and processing of oil mixtures. The type of mixture - oil, gas condensate or gas - also depends on its chemical composition and combination of thermobaric conditions in the deposit. The chemical composition determines the possible state of the components of oil systems under given conditions - molecular or dispersed.

;Oil systems are distinguished by a variety of components that can be in a molecular or dispersed state, depending on external conditions. Among them there are the most and least prone to various kinds of intermolecular interactions (IIM), which ultimately determines the associative phenomena and the initial dispersity of oil systems under normal conditions.

The chemical composition for oil is distinguished as elemental and material.

The main elements of the composition of oil are carbon(83.5-87%) and hydrogen(11.5-14%). In addition, the oil contains:

• sulfur in an amount from 0.1 to 1-2% (sometimes its content can reach up to 5-7%, in many oils there is practically no sulfur);
• nitrogen in an amount from 0.001 to 1 (sometimes up to 1.7%);
• oxygen(found not in pure form, but in various compounds) in an amount from 0.01 to 1% or more, but does not exceed 3.6%.

Of the other elements present in oil - iron, magnesium, aluminum, copper, tin, sodium, cobalt, chromium, germanium, vanadium, nickel, mercury, gold and others. However, their content is less than 1%.

In material terms, oil mainly consists of hydrocarbons and heteroorganic compounds.

hydrocarbons

hydrocarbons(HC) are organic compounds of carbon and hydrogen. Oil mainly contains the following classes of hydrocarbons:

Alkanes

Alkanes or paraffinic hydrocarbons are saturated (limiting) SWs with the general formula C n H 2n+2. Their content in oil is 2 - 30-70%. There are alkanes of normal structure ( n-alkanes - pentane and its homologues), isostructures ( isoalkanes - isopentane etc.) and isoprenoid structure ( isoprenes - wharf, phytane and etc.).

Oil contains gaseous alkanes from From 1 before From 4(as dissolved gas), liquid alkanes From 5 to 16, make up the bulk of the liquid fractions of oil and solid alkanes of the composition From 17 - From 53 and more, which are included in heavy oil fractions and are known as hard paraffins. Solid alkanes are present in all oils, but usually in small amounts - from tenths to 5% (wt.), in rare cases - up to 7-12% (wt.).

There are various isomers of alkanes in oil: mono-, di-, tri-, tetrasubstituted. Of these, monosubstituted ones predominate, with one branching. Methyl-substituted alkanes are arranged in descending order: 2-methyl-substituted alkanes > 3-methyl-substituted alkanes > 4-methyl-substituted alkanes.

The discovery in oils of branched alkanes of the isoprenoid type with methyl groups in positions 2, 6, 10, 14, 18, etc. dates back to the 60s. More than twenty such hydrocarbons were found in the main composition From 9 - From 20. The most common isoprenoid alkanes in any oils are phytane C 20 H 42 and jetty C 19 H 40, the content of which can reach up to 1.0 -1.5% and depends on the genesis and facial conditions of the formation of oils.

Thus, alkanes in various proportions are included in all natural mixtures and petroleum products, and their physical state in a mixture - in the form of a molecular solution or a dispersed system - is determined by the composition, individual physical properties of the components and thermobaric conditions.

Cycloalkanes

Cycloalkanes or naphthenic hydrocarbons are saturated alicyclic hydrocarbons. These include monocyclic ones with the general formula C n H 2n, bicyclic - C n H 2n-2, tricyclic - C n H 2n-4, tetracyclic - C n H 2n-6.

According to the total content of cycloalkanes in many oils prevail over other classes of hydrocarbons: their content ranges from 25 to 75% (wt.). They are present in all petroleum fractions. Usually their content increases as the fractions become heavier. The total content of naphthenic hydrocarbons in oil increases as its molecular weight increases. The only exceptions are oil fractions, in which the content of cycloalkanes decreases due to an increase in the amount of aromatic hydrocarbons.

Of the monocyclic hydrocarbons in oil, there are mainly five- and six-membered series naphthenic hydrocarbons. The distribution of monocyclic naphthenes in oil fractions, their properties are studied much more fully in comparison with polycyclic naphthenes present in medium and high-boiling fractions. The low-boiling gasoline fractions of oils contain mainly alkyl derivatives of cyclopentane and cyclohexane[from 10 to 86% (wt.)], and in high-boiling fractions - polycycloalkanes and monocycloalkanes with alkyl substituents of isoprenoid structure (the so-called hybrid hydrocarbons).

Of the polycyclic naphthenes in oils, only 25 individual bicyclic, five tricyclic, and four tetra- and pentacyclic naphthenes have been identified. If there are several naphthenic rings in a molecule, then the latter, as a rule, are condensed into a single polycyclic block.

Bicyclanes C 7 -C 9 most often present in oils of a pronounced naphthenic type, in which their content is quite high. Among these hydrocarbons found (in descending order of content): bicyclooctane (pentalan), bicyclooctane, bicyclooctane, bicyclononane (hydrindan), bicycloheptane (norbornane) and their closest homologues. From tricyclanes in oils dominate alkylperhydrophenanthrenes.

Tetracyclanes oils are represented mainly by derivatives cyclopentano-perhydrophenanthrene - steranes.

To pentacyclanes oils include hydrocarbons of the series hopana, lupana, fridelana.

Reliable identification information polycycloalkanes with a large number of cycles is absent, although based on the structural group and mass spectral analysis, it can be assumed that naphthenes with a number of cycles greater than five are present. According to some data, high-boiling naphthenes contain up to 7-8 cycles in molecules.

Differences in the chemical behavior of cycloalkanes are often due to the presence of excess stress energy. Depending on the size of the ring, cycloalkanes are subdivided into small C 3 , C 4- although cyclopropane and cyclobutane not found in oils), normal ( C 5 -C 7), average ( C 8 -C 11) and macrocycles (from C 12 and more). This classification is based on the relationship between the size of the cycle and the stresses that arise in it, affecting the stability. For cycloalkanes and, above all, their various derivatives are characterized by rearrangements with a change in the size of the ring. So, when cycloheptane is heated with aluminum chloride, methylcyclohexane is formed, and cyclohexane at 30-80 ° C turns into methylcyclopentane. Five- and six-membered carbon rings form much more easily than smaller and larger rings. Therefore, much more derivatives of cyclohexane and cyclopentane are found in oils than derivatives of other cycloalkanes.

Based on the study of the viscosity-temperature properties of alkyl-substituted monocyclohexanes in a wide temperature range, it was found that the substituent, as it elongates, reduces the average degree of association of molecules. Cycloalkanes, Unlike n-alkanes with the same number of carbon atoms are in an associated state at a higher temperature.

Arenas

Arenas or aromatic hydrocarbons- compounds in the molecules of which there are cyclic hydrocarbons with π-conjugated systems. Their content in oil varies from 10-15 to 50% (wt.). These include representatives of monocyclic: benzene and its homologues ( toluene, o-, m-, p-xylene etc.), bicyclic: naphthalene and its homologues, tricyclic: phenanthrene, anthracene and their homologues, tetracyclic: pyrene and its homologues and others.

Based on the generalization of data on 400 oils, it was shown that the highest concentrations of arenes (37%) are typical for oils of a naphthenic base (type), and the lowest (20%) for oils of a paraffin type. Among petroleum arenes, compounds containing no more than three benzene rings per molecule predominate. Arene concentrations in distillates boiling up to 500°C, as a rule, decrease by one or two orders of magnitude in the following series of compounds: benzenes >> naphthalenes >> phenanthrenes >> chryzenes >> pyrenes >> anthracenes.

The general pattern is an increase in the content of arenes with an increase in the boiling point. At the same time, arenas of higher oil fractions are characterized not by a large number of aromatic rings, but by the presence of alkyl chains and saturated cycles in molecules. All theoretically possible arene homologues were found in gasoline fractions C6-C9. Hydrocarbons with a small number of benzene rings dominate among arenes even in the heaviest oil fractions. So, according to experimental data, mono-, bi-, tri-, tetra- and pentaarenes are respectively 45-58, 24-29, 15-31, 1.5 and up to 0.1% of the mass of aromatic hydrocarbons in distillates 370-535 °C of various oils.

Oil monoarenes are represented by alkylbenzenes. The most important representatives of high-boiling petroleum alkylbenzenes are hydrocarbons containing up to three methyl substituents and one long substituent of a linear, α-methylalkyl or isoprenoid structure in the benzene ring. Large alkyl substituents in alkylbenzene molecules can contain more than 30 carbon atoms.

The main place among the bicyclic petroleum arenes (diarenes) belongs to naphthalene derivatives, which can account for up to 95% of the total diarenes and contain up to 8 saturated rings per molecule, and the secondary place belongs to derivatives of diphenyl and diphenylalkanes. All individual alkylnaphthalenes have been identified in oils S 11 , S 12 and many isomers C 13 -C 15. The content of diphenyls in oils is an order of magnitude lower than the content of naphthalenes.

Of the naphthenodiarens, acenaphthene, fluorene and a number of its homologues containing methyl substituents in positions 1-4 were found in oils.

Triarenes are represented in oils by derivatives of phenanthrene and anthracene (with a sharp predominance of the former), which can contain up to 4-5 saturated cycles in molecules.

Petroleum tetraarenes include hydrocarbons of the chrysene, pyrene, 2,3- and 3,4-benzophenanthrene and triphenylene series.

The increased tendency of arenes, especially polycyclic ones, to molecular interactions is due to the low excitation energy in the process of homolytic dissociation. Compounds such as anthracene, pyrene, chrysene, etc. are characterized by a low degree of exchange correlation of π-orbitals and an increased potential energy of the MMW due to the occurrence of an exchange correlation of electrons between molecules. Arenes form rather stable molecular complexes with some polar compounds.

The interaction of π-electrons in the benzene nucleus leads to the conjugation of carbon-carbon bonds. The conjugation effect results in the following properties of arenes:

• planar structure of the cycle with a C-C bond length (0.139 nm), which is intermediate between a single and a double C-C bond;
• equivalence of all C-C bonds in unsubstituted benzenes;
• propensity to reactions of electrophilic substitution of a proton for various groups in comparison with participation in reactions of addition on multiple bonds.

Ceresins

Hybrid hydrocarbons (ceresins)- hydrocarbons of a mixed structure: paraffin-naphthenic, paraffin-aromatic, naphtheno-aromatic. Basically, these are solid alkanes with an admixture of long-chain hydrocarbons containing a cyclane or aromatic nucleus. They are the main component of paraffin deposits in the processes of extraction and preparation of oils.

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Oil is a resource that underlies modern energy. Many countries are making a lot of efforts to find a new type of fuel, however, today and in the near future, it is oil products that occupy this niche. Despite the fact that not a single news release is complete without mentioning the current price of oil or other things related to it, a lot of people do not know what oil really is. In this material, we will talk about the chemical formula of oil, and what elements it consists of.

Story

It is worth noting that people got acquainted with oil back in the days of Babylon. Then this resource was used in construction because of its astringent qualities. In Russia, on the Ukhta River, people collected oil from the surface and used it as an ointment. Only centuries later, when serious studies were carried out, did mankind learn the chemical composition of oil and its true purpose. However, even today the question of what oil consists of cannot be answered in one word.

Chemical formula of oil

Oil Formula

Oil is a complex colloidal chemical system consisting of many components. The liquid phase of oil is liquid hydrocarbons (about five hundred different substances). Also, "black gold" contains semi-solid elements - "heavy" hydrocarbons (for example, resins), which are suspended in a liquid.

In addition to the hydrocarbon mixture, oil includes sulfur, nitrogen, mineral salts, water, solutions of hydrocarbon gases.

It is worth noting that raw materials extracted from different sources differ in chemical composition. Each oil is a unique system, therefore the classification of oil is accepted, depending on the composition. The higher the content of light hydrocarbons and the lower the content of mechanical impurities, sulfur and other by-products, the higher the value of a particular type of "black gold".

Chemically, oil is a complex mixture of hydrocarbons and carbon compounds, it consists of the following main elements: carbon (84-87%), hydrogen (12-14%), oxygen, nitrogen and sulfur (1-2%), the sulfur content increases sometimes up to 3-5%.

In oil, a hydrocarbon, asphalt-resinous part, porphyrins, sulfur and an ash part are isolated.

The main part of the oil is made up of three groups of hydrocarbons: methane, naphthenic and aromatic.

Asphalt-resinous part of oil is a dark-colored substance. It is partially soluble in gasoline. The dissolved part is called asphaltene, the undissolved part is called resin. The composition of the resins contains oxygen up to 93% of its total amount in oil.

Porphyrins are special nitrogenous compounds of organic origin. It is believed that they are formed from plant chlorophyll and animal hemoglobin. At temperature, porphyrins are destroyed.

Sulfur is widely distributed in oil and hydrocarbon gas and is contained either in the free state or in the form of compounds (hydrogen sulfide, mercaptans). Its amount ranges from 0.1% to 5%.

The ash part is the residue resulting from the combustion of oil. These are various mineral compounds, most often iron, nickel, vanadium, sometimes sodium salts.

Oil varies greatly in color (from light brown, almost colorless, to dark brown, almost black) and in density (from light 0.65-0.70 to heavy 0.98-1.05).

The onset of oil boiling is usually above 280C. the pour point ranges from +300 to -600C and depends mainly on the content of paraffin (the more it is, the higher the pour point). Viscosity varies over a wide range and depends on the chemical and fractional composition of oil and tar content (the content of asphalt-resinous substances in it). Oil is soluble in organic solvents, practically insoluble in water under normal conditions, but can form stable emulsions with it.

Oil can be classified according to different criteria.

2. According to the potential content of fractions boiling up to 3500C

3. By potential oil content

4. By the quality of oils

The combination of designations of the class, type, group, subgroup and type makes up the code for the technological classification of oil.

Depending on the field, oil has a different qualitative and quantitative composition. For example, Baku oil is rich in cycloparaffins and relatively poor in saturated hydrocarbons. There are significantly more saturated hydrocarbons in Grozny and Ferghana oil. Permian oil contains aromatic hydrocarbons.

As every schoolchild knows, without oil and oil products, the normal development of our civilization would be absolutely impossible, because cars and planes fly on various types of fuel obtained from oil. A huge number of different vehicles and all kinds of equipment (for example, mobile power plants) today work on petroleum products. However, not everyone knows the chemical composition of oil and some of its physical properties. And to fill this gap, we have prepared this article for you. Let's start with general information about oil.

general information

Oil is a flammable oily liquid produced in nature, which consists of a rather complex mixture of various organic compounds, in particular hydrocarbons. Depending on the place of extraction, the chemical composition of oil may change, which entails a change in the color of this combustible liquid. Oil can be almost black, and red-brown, and greenish-yellow, and even completely colorless. Also, oil has a specific smell. In nature, oil occurs at depths ranging from several tens of meters to several kilometers. So, in some wells, oil is pumped out from a depth of up to 2-3 km. The vast majority of oil deposits in the earth are located at a depth of 1 to 3 km. Also, oil can occur at shallow depths and even naturally come to the surface. True, in these cases, under the influence of atmospheric air, oil turns into bitumen and bituminous sands, as well as into semi-solid asphalt and rather thick malta. Further, we will talk mainly about the chemical and physical composition and properties of oil. We only note that oil has a similar chemical structure with asphalt and natural combustible gases: all these substances are called petrolites in chemistry. Petrolites are combustible substances of biological origin, which include, among other things, many types of not only liquid, but also solid fuels.

The chemical composition of oil

How many simpler substances do you think oil is made of? Out of ten? Out of a hundred? In fact, oil is a mixture of about a thousand (!) Various substances, of which approximately 80% are liquid hydrocarbons (more than five hundred substances). The share of sulphurous substances in oil (and there are about two hundred and fifty of them) accounts for approximately 3%. Somewhat less oxygen (80-85) and nitrogenous (30) substances. Oil can also contain up to 10% water and up to 4% dissolved hydrocarbon gases. The composition of oil also includes a certain amount of metal-containing substances containing nickel and vanadium. Well, among other things, oil in various proportions can contain mineral salts, and solutions of salts of various organic acids, and, of course, all kinds of mechanical impurities.

Hydrocarbon composition of oil

As you just learned, the largest percentage of any oil is hydrocarbon compounds. Depending on the deposit, their share can be more than 80% - up to 90%. What are these connections? First of all, the so-called naphthenic and paraffinic. Naphthenic to the volume of the total hydrocarbon is from 25 to 70%, and paraffin can contain from 30 to 50%. Also in the composition of the oil are aromatic hydrocarbon compounds, and hybrid: naphtheno-aromatic, paraffin-naphthenic and others. By the way, the listed names of the compounds also serve as names for various types of oil. There are paraffinic, naphthenic, methane, aromatic oils (among oilmen, the word “oil” can be pluralized in the meaning of “types of oil”). Oil is given a name according to the class of hydrocarbons, of which more than 50% is present in it. If two classes dominate (for example, 30% paraffinic and naphthenic hydrocarbons each), this type of oil receives a double name for both classes. In our example, this is the paraffin-naphthenic type. The first in the name is the class of hydrocarbons, which is represented in one or another type of oil in a slightly larger amount. Therefore, there are, for example, methane-aromatic and aromatic-methane types, naphtheno-aromatic and aromatic-naphthenic, naphtheno-methane and methane-naphthenic, etc.

Composition of oil by elements

Since oil, depending on its origin, can have a rather heterogeneous composition, the percentage ratio of certain chemical elements in it can be very conditional. Nevertheless, we note that in various types of oil, the main constituent elements are carbon, hydrogen and sulfur, less often oxygen and nitrogen. In total, up to 80 different chemical elements can be present in a single type of oil. Some of them are present in such microscopic quantities that their percentage is measured using negative powers. So, for example, the nickel content in certain types of oil ranges from 10?4 to 10?3% or, if expressed using a decimal fraction: from 0.0001 to 0.001%. That is, a kilogram of an oil product may contain a thousandth or a hundredth of a gram of nickel. As for the percentage of carbon, it can range from 82 to 87%. Hydrogen is contained in oil in amounts from 11 to 14%, and sulfur - from 0.01 to 8%. Also, oil can contain up to 1.8% nitrogen and up to 0.35% oxygen. Of the sulfur-containing substances, we note the presence of thiophanes, thiophenes, mercaptans, and mono- and disulfides. Nitrogen-containing substances are represented by pyrroles, carbazoles, indoles, quinolines, porphyrins and pyridines, and oxygen-containing substances are represented by phenols, naphthenic acids and resinous-asphaltene substances.

The physical composition of oil

More precisely, we will focus here on its physical properties. Depending on the chemical composition, oil has a large number of shades of color. As a rule, the color of oil ranges from dark brown, almost black, to light brown, almost transparent. However, there are types of oil even emerald hue, as well as red-brown. The molecular weight of oil can range from 200 to 450 g/mol of the substance. The density of oil usually ranges from 0.7 to 1 g per cubic cm. By density, oil is divided into light (0.83 and below), medium (0.83-0.86) and heavy (from 0.86). It should also be noted that the density of oil depends primarily on the pressure and temperature of the substance. The boiling point can also vary. Light oil can boil even at 30 degrees Celsius, and heavy oil - from 100 and above. The crystallization temperature of oil depends entirely on the content of paraffin in it. Oil with a low paraffin content crystallizes only at very low temperatures (up to -60 degrees Celsius), and oil with a high paraffin content sometimes requires +30 degrees. It is also impossible not to say that oil is a substance, as a rule, highly flammable, but, depending on the type, it can flare up at negative temperatures from -30 -35 degrees and at very high temperatures - from +120 degrees. Oil does not dissolve in water, but forms stable emulsions with it. As for the dehydration of oil, which is required by various industries, today there are several effective methods for separating oil and water.

Fractional composition of oil

This is one of the most important indicators of oil quality. During the distillation of oil, various components are separated from it by a gradual increase in temperature - the so-called fractions. So, the petroleum fraction boils away at temperatures up to 100 degrees Celsius, gasoline - up to 180, naphtha - at temperatures from 140 to 180 degrees, kerosene - from 140 to 220 and, finally, at temperatures from 180 to 350 degrees, the diesel fraction also boils away. . Gasoline fractions are called light because they boil away before anyone else, kerosene - medium, and diesel - heavy. The residue that does not boil away even at a temperature of 350 degrees is called fuel oil. Fuel oil dispersed under vacuum to a temperature of over 500 degrees is called tar. Fuel oil is the main component for the production of various oils.