Oxygen-containing and nitrogen-containing. Certification work chemistry of the process of destructive hydrogenation

It is known that the properties of organic substances are determined by their composition and chemical structure. Therefore, it is not surprising that the classification of organic compounds is based on the theory of structure - the theory of L. M. Butlerov. Classify organic substances by the presence and order of connection of atoms in their molecules. The most durable and least changeable part of the molecule of organic matter is its skeleton - a chain of carbon atoms. Depending on the order of connection of carbon atoms in this chain, substances are divided into acyclic, which do not contain closed chains of carbon atoms in molecules, and carbocyclic, containing such chains (cycles) in molecules.
In addition to carbon and hydrogen atoms, molecules of organic substances may contain atoms of other chemical elements. Substances in the molecules of which these so-called heteroatoms are included in a closed chain are classified as heterocyclic compounds.
Heteroatoms (oxygen, nitrogen, etc.) can be part of molecules and acyclic compounds, forming functional groups in them, for example, hydroxyl - OH, carbonyl, carboxyl, amino group -NH2.
Functional group- a group of atoms that determines the most characteristic chemical properties of a substance and its belonging to a certain class of compounds.

hydrocarbons are compounds that consist only of hydrogen and carbon atoms.

Depending on the structure of the carbon chain, organic compounds are divided into compounds with an open chain - acyclic (aliphatic) and cyclic- with a closed chain of atoms.

Cycles are divided into two groups: carbocyclic compounds(cycles are formed only by carbon atoms) and heterocyclic(the cycles also include other atoms, such as oxygen, nitrogen, sulfur).

Carbocyclic compounds, in turn, include two series of compounds: alicyclic and aromatic.

Aromatic compounds in the basis of the structure of molecules have flat carbon-containing cycles with a special closed system of p-electrons that form a common π-system (a single π-electron cloud). Aromaticity is also characteristic of many heterocyclic compounds.

All other carbocyclic compounds belong to the alicyclic series.

Both acyclic (aliphatic) and cyclic hydrocarbons can contain multiple (double or triple) bonds. Such hydrocarbons are called unsaturated (unsaturated) in contrast to the limiting (saturated) containing only single bonds.

Limit aliphatic hydrocarbons called alkanes, they have the general formula C n H 2 n +2, where n is the number of carbon atoms. Their old name is often used and now - paraffins.

Containing one double bond, got the name alkenes. They have the general formula C n H 2 n .

Unsaturated aliphatic hydrocarbonswith two double bonds called alkadienes

Unsaturated aliphatic hydrocarbonswith one triple bond called alkynes. Their general formula is C n H 2 n - 2.

Limit alicyclic hydrocarbons - cycloalkanes, their general formula C n H 2 n .

A special group of hydrocarbons, aromatic, or arenes(with a closed common π-electron system), is known from the example of hydrocarbons with the general formula C n H 2 n -6.

Thus, if in their molecules one or more hydrogen atoms are replaced by other atoms or groups of atoms (halogens, hydroxyl groups, amino groups, etc.), hydrocarbon derivatives: halogen derivatives, oxygen-containing, nitrogen-containing and other organic compounds.

Halogen derivatives hydrocarbons can be considered as the products of substitution in hydrocarbons of one or more hydrogen atoms by halogen atoms. In accordance with this, there may be limiting and unsaturated mono-, di-, tri- (generally poly-) halogen derivatives.

The general formula of monohalogen derivatives of saturated hydrocarbons:

and the composition is expressed by the formula

C n H 2 n +1 Г,

where R is the remainder of the saturated hydrocarbon (alkane), hydrocarbon radical (this designation is used further when considering other classes of organic substances), Г is a halogen atom (F, Cl, Br, I).

Alcohols- derivatives of hydrocarbons in which one or more hydrogen atoms are replaced by hydroxyl groups.

Alcohols are called monatomic, if they have one hydroxyl group, and limit if they are derivatives of alkanes.

The general formula of saturated monohydric alcohols:

and their composition is expressed by the general formula:
C n H 2 n +1 OH or C n H 2 n +2 O

Examples of polyhydric alcohols are known, i.e., having several hydroxyl groups.

Phenols- derivatives of aromatic hydrocarbons (benzene series), in which one or more hydrogen atoms in the benzene ring are replaced by hydroxyl groups.

The simplest representative with the formula C 6 H 5 OH is called phenol.

Aldehydes and ketones- derivatives of hydrocarbons containing a carbonyl group of atoms (carbonyl).

In aldehyde molecules, one carbonyl bond goes to the connection with the hydrogen atom, the other - with the hydrocarbon radical.

In the case of ketones, the carbonyl group is linked to two (generally different) radicals.

The composition of limiting aldehydes and ketones is expressed by the formula C n H 2l O.

carboxylic acids- derivatives of hydrocarbons containing carboxyl groups (-COOH).

If there is one carboxyl group in the acid molecule, then the carboxylic acid is monobasic. General formula of saturated monobasic acids (R-COOH). Their composition is expressed by the formula C n H 2 n O 2 .

Ethers are organic substances containing two hydrocarbon radicals connected by an oxygen atom: R-O-R or R 1 -O-R 2 .

The radicals may be the same or different. The composition of ethers is expressed by the formula C n H 2 n +2 O

Esters- compounds formed by replacing the hydrogen atom of the carboxyl group in carboxylic acids with a hydrocarbon radical.

Nitro compounds- derivatives of hydrocarbons in which one or more hydrogen atoms are replaced by a nitro group -NO 2 .

General formula of limiting mononitro compounds:

and the composition is expressed by the general formula

C n H 2 n +1 NO 2.

Amines- compounds that are considered as derivatives of ammonia (NH 3), in which hydrogen atoms are replaced by hydrocarbon radicals.

Depending on the nature of the radical, amines can be aliphaticand aromatic.

Depending on the number of hydrogen atoms replaced by radicals, there are:

Primary amines with the general formula: R-NH 2

Secondary - with the general formula: R 1 -NH-R 2

Tertiary - with the general formula:

In a particular case, secondary as well as tertiary amines may have the same radicals.

Primary amines can also be considered as derivatives of hydrocarbons (alkanes), in which one hydrogen atom is replaced by an amino group -NH 2 . The composition of limiting primary amines is expressed by the formula C n H 2 n +3 N.

Amino acids contain two functional groups connected to a hydrocarbon radical: an amino group -NH 2 , and a carboxyl -COOH.

The composition of limiting amino acids containing one amino group and one carboxyl is expressed by the formula C n H 2 n +1 NO 2 .

Other important organic compounds are known that have several different or identical functional groups, long linear chains associated with benzene rings. In such cases, a strict definition of whether a substance belongs to a particular class is impossible. These compounds are often isolated into specific groups of substances: carbohydrates, proteins, nucleic acids, antibiotics, alkaloids, etc.

For the name of organic compounds, 2 nomenclatures are used - rational and systematic (IUPAC) and trivial names.

Compilation of names according to the IUPAC nomenclature

1) The basis of the name of the compound is the root of the word, denoting a saturated hydrocarbon with the same number of atoms as the main chain.

2) A suffix is added to the root, characterizing the degree of saturation:

An (limiting, no multiple bonds);
-en (in the presence of a double bond);
-in (in the presence of a triple bond).

If there are several multiple bonds, then the number of such bonds (-diene, -triene, etc.) is indicated in the suffix, and after the suffix, the position of the multiple bond must be indicated in numbers, for example:
CH 3 -CH 2 -CH \u003d CH 2 CH 3 -CH \u003d CH -CH 3
butene-1 butene-2

CH 2 \u003d CH - CH \u003d CH 2
butadiene-1,3

Groups such as nitro-, halogens, hydrocarbon radicals that are not included in the main chain are taken out to the prefix. They are listed in alphabetical order. The position of the substituent is indicated by a number before the prefix.

The title order is as follows:

1. Find the longest chain of C atoms.

2. Sequentially number the carbon atoms of the main chain, starting from the end closest to the branch.

3. The name of an alkane is made up of the names of side radicals, listed in alphabetical order, indicating the position in the main chain, and the name of the main chain.

Nomenclature of some organic substances (trivial and international)

Heteroorganic compounds (sulphur-, oxygen- and nitrogen-containing) of various structure and molecular weight are present in various proportions in distillate and residual oil fractions. It is especially difficult to study the nature and composition of high-molecular heteroorganic compounds, the main part of which are tar-asphalten substances. Owing to lone pairs of electrons, sulfur, oxygen, and nitrogen heteroatoms are able to act as a coordinating center in the formation of associates in oil systems.

Sulfur compounds belong to the most representative group of heteroatomic components of gas condensate and oil systems. The total sulfur content in oil and gas systems varies widely: from hundredths of a percent to 6-8% (wt.) and more. A high content of total sulfur is characteristic of gas condensates from the Astrakhan, Karachaganak (0.9%) and other fields. The content of sulfur-containing compounds in some oils reaches 40% (wt.) and above, in some cases, the oil consists almost entirely of them. Unlike other heteroatoms, which are predominantly concentrated in CAB, a significant proportion of sulfur is contained in distillate fractions. As a rule, the sulfur content in straight-run fractions increases as their boiling point and total sulfur content of the original oil increase.

Minor amounts of inorganic sulfur-containing compounds (elemental sulfur and hydrogen sulfide) are present in oil and gas systems, they can also be formed as secondary decomposition products of other sulfur-containing compounds at high temperatures in the processes of distillation, destructive processing. Among the sulfur-containing compounds found in oil, the following have been identified (according to the Institute of Petroleum Chemistry, TF SB RAS).

1. Aliphatic, alicyclic and aromatic thiols (mercaptans) R-SH:

C 6 H 5 C n H 2 n +1 SH C n H 2 n +1 C 6 H 5 SH C 10 H 7 SH

arenoalkanothiols thionaphthols

2. Thioethers (sulfides) of the following main types:

R-S-R" C 6 H 5 -S-C 6 H 5

thiaalkanes, thiaalkenes, thiaalkyne diarylsulfides

thiacycloalkanes alkylarylsulfides arylthiaalkanes

(R, R" - saturated and unsaturated aliphatic hydrocarbon substituents).

3. Dialkyd disulfides R-S-S-R", where R, R" are alkyl, cycloalkyl or aryl substituents.

4. Thiophenes and their derivatives, the most important of which are the following arenothiophenes:

alkylbenzothiophenes alkylbenzothiophenes alkyldibenzothiophenes

The distribution of various groups of sulfur-containing compounds in oils and in oil fractions is subject to the following regularities.

Thiols are contained in almost all crude oils, usually in small concentrations and make up 2-10% (wt.) Of the total content of sulfur-containing compounds. In gas condensates, there are mainly aliphatic mercaptans C 1 -C z. Some oils and gas condensates and their fractions are natural concentrates of mercaptans, examples of which are gasoline fractions of the super-giant Caspian field; fraction 40-200°C of gas condensate of the Orenburg field, containing 1.24% (wt.) of total sulfur, including 0.97% mercaptan; light kerosene fraction 120-280°C of oil from the Tengiz field, containing 45-70% mercaptan sulfur of the total content of sulfur-containing compounds. At the same time, the reserves of natural thiols in the hydrocarbon raw materials of the Caspian region correspond to the level of their global synthetic production. Natural thiols are promising raw materials for the synthesis of pesticides (based on symmetrical triazines) and odorization of liquefied gases. Russia's prospective demand for thiols for odorization is currently 6,000 tons/year.

Thioethers account for up to 27% of the total sulfur-containing compounds in crude oils and up to 50% in medium fractions; in heavy vacuum gas oils, the content of sulfides is lower. Methods for separating petroleum sulfides are based on their ability to form complex compounds of the donor-acceptor type by transferring a lone pair of electrons from a sulfur atom to a free acceptor orbital. Metal halides, haloalkyls, and halogens can act as electron acceptors. Complexation reactions with petroleum sulfides, unfortunately, are not selective; other heteroatomic components of oil can also take part in the formation of complexes.

Dialkyl disulfides are not found in crude oils, they are usually formed during the oxidation of mercaptans under mild conditions and therefore are present in gasolines (up to 15%). The main share of sulfur-containing compounds in oils falls on the so-called "residual" sulfur, which is not determined by standard methods. Thiophenes and their derivatives predominate in its composition, therefore, earlier, "residual" sulfur was called "thiophene", however, using negative ion mass spectrometry, previously undetectable sulfoxides, sulfones, and disulfane were found in it. In gasoline fractions, the content of thiophene derivatives is low; in medium and especially high-boiling fractions, it reaches 50-80% of the total sulfur-containing compounds. The relative content of thiophene derivatives, as a rule, coincides with the degree of aromaticity of the oil system. Difficulties arising in the isolation of sulfur-containing compounds (especially from high-boiling fractions) are caused by the closeness of the chemical properties of arenes and thiophenes. The similarity of their chemical behavior is due to the aromaticity of thiophenes, which arises as a result of the incorporation of a sulfur heteroatom into the π-electron system up to an aromatic sextet. The consequence of this is an increased tendency of petroleum thiophenes to intense intermolecular interactions.

Oxygen compounds contained in oil systems from 0.1-1.0 to 3.6% (wt.). With an increase in the boiling point of distillate fractions, their content increases, and the main part of oxygen is concentrated in tar-asphalten substances. The composition of oils and distillates contains up to 20% or more oxygen-containing compounds.

Among them, substances of an acidic and neutral nature are traditionally distinguished. The acid components include carboxylic acids and phenols. Neutral oxygen-containing compounds are represented by ketones, anhydrides and acid amides, esters, furan derivatives, alcohols and lactones.

The presence of acids in oils was discovered a very long time ago due to the high chemical activity compared to hydrocarbons. The history of their discovery in oil is as follows. When obtaining high-quality kerosene for lighting purposes, it was treated with alkali (acid-base purification) and, at the same time, the formation of substances with high emulsifying ability was observed. Subsequently, it turned out that the emulsifiers are sodium salts of acids contained in distillate fractions. Extraction with aqueous and alcoholic solutions of alkalis is still a classic method for extracting acidic components from oils. Currently, methods for isolating acids and phenols are also based on the interaction of their functional groups (carboxylic and hydroxyl) with any reagent.

Carboxylic acids are the most studied class of oxygen-containing oil compounds. The content of petroleum acids by fractions varies according to an extreme dependence, the maximum of which, as a rule, falls on light and medium oil fractions. Various types of petroleum acids have been identified by chromato-mass spectrometry. Most of them are monobasic (RCOOH), where almost any fragment of hydrocarbon and heteroorganic compounds of oil can be used as R. It has long been noted that the group compositions of acids and oils correspond to each other: aliphatic acids predominate in methane oils, naphthenic and naphthenoaromatic acids predominate in naphthenic oils. Aliphatic acids from C 1 to C 25 with a linear structure and some with a branched structure have been found. At the same time, the ratio of n-alkanoic and branched acids in petroleum acids coincides with the ratio of the corresponding hydrocarbons in oils.

Aliphatic acids are represented primarily by n-alkanoic acids. Of the branched acids, those containing a methyl substituent in the main chain are more common. All the lower isomers of this type are found in oils, down to C 7 . Another important group of aliphatic acids is isoprenoid acids, among which prestanic (C 19) and phytanic (C 20) acids dominate.

Alicyclic (naphthenic) acids of oil are monocyclocarboxylic acids - derivatives of cyclopentane and cyclohexane; polycyclic can contain up to 5 rings (data for California oil). The COOH groups in the molecules of monocyclic acids are directly connected to the cycle or are located at the end of aliphatic substituents. There can be up to three (most often methyl) substituents in the cycle, the most common positions of which are 1, 2; thirteen; 1, 2, 4; 1, 1, 3 and 1, 1, 2, 3.

Molecules of tri-, tetra- and pentacyclic acids isolated from oils are built mainly from condensed cyclohexane rings.

The presence of hexacyclic naphthenic acids with cyclohexane rings in oils has been established. Aromatic acids in oils are represented by benzoic acid and its derivatives. Many homologous series of polycyclic naphthenoaromatic acids were also found in oils, and monoaromatic steroid acids were identified in Samotlor oil.

From oxygen-containing compounds, petroleum acids are characterized by the highest surface activity. It has been established that the surface activity of both low-resin and high-resin oils significantly decreases after the removal of acidic components (acids and phenols) from them. Strong acids take part in the formation of associates of oils, which is shown in the study of their rheological properties.

Phenols have been studied much worse than acids. Their content in oils from West Siberian fields ranges from 40 to 900 mg/l. In West Siberian oils, the concentrations of phenols increase in the order C 6<С 7 << С 8 <С 9 . В нефтях обнаружены фенол, все крезолы, ксиленолы и отдельные изомеры С 9 . Установлено, что соотношение между фенолами и алкилфенолами колеблется в пределах от 1: (0,3-0,4) до 1: (350-560) и зависит от глубины залегания и возраста нефти. В некоторых нефтях идентифицирован β-нафтол. Высказано предположение о наличии соединений типа о-фенилфенолов, находящихся в нефтях в связанном состоянии из-за склонности к образованию внутримолекулярных водородных связей. При исследовании антиокислительной способности компонентов гетероор-ганических соединений нефти установлено, что концентраты фенольных соединений являются наиболее активными природными ингибиторами.

All the simplest alkyl ketones C3-C6, acetophenone and its naphtheno- and areno-derivatives, fluorenone and its closest homologues were found in neutral oxygen-containing compounds of Californian oils. The yield of ketone concentrate from Samotlor oil, consisting mainly of dialkyl ketones, is 0.36%, while the degree of extraction of ketones is only 20%, which indicates the presence of ketones of large molecular weights that cannot be recovered by this method. In the study of ketones in the oils of Western Siberia, it was found that they contain C 19 -C3 2 ketones, and aliphatic ketones predominate in methane oils, and cyclane and aromatic substituents predominate in naphthenic oils.

It can be assumed that oils contain alcohols in the free state; in the bound state, they are part of esters. Of the heteroorganic compounds of oil, the propensity of oxygen-containing compounds to intense intermolecular interactions has been most studied.

The study of nitrogen-containing compounds is possible in two ways - directly in crude oil and after their isolation and separation. The first way makes it possible to study nitrogen-containing compounds in a state close to natural, however, the occurrence of noticeable errors due to the low concentration of these compounds is not ruled out. The second way allows such errors to be reduced, but in the process of chemical action on oil during separation and isolation, a change in their structure is possible. It has been established that nitrogen-containing compounds in oil are represented mainly by cyclic compounds. Aliphatic nitrogen-containing compounds are found only in products of destructive oil refining, in which they are formed as a result of the destruction of nitrogenous heterocycles.

All nitrogen-containing oil compounds are, as a rule, functional derivatives of arenes, and therefore have a molecular weight distribution similar to them. However, unlike arenes, nitrogen-containing compounds are concentrated in high-boiling oil fractions and are a component of CAB. Up to 95% of the nitrogen atoms present in oil are concentrated in resins and asphaltenes. It has been suggested that during the isolation of resins and asphaltenes, even relatively low molecular weight nitrogen-containing compounds are co-precipitated with them in the form of donor-acceptor complexes.

In accordance with the generally accepted classification according to the acid-base characteristic nitrogen-containing compounds are dividedinto nitrogenous bases and neutral compounds.

Nitrogen-containing bases are, apparently, the only carriers of the main properties among the components of oil systems. The proportion of nitrogen-containing bases in oil titrated with perchloric acid in an acetic acid medium ranges from 10 to 50%. Currently, more than 100 alkyl- and areno-condensed analogues of pyridine, quinoline, and other bases have been identified in oils and oil products.

Strongly basic nitrogen-containing compounds are represented by pyridines and their derivatives:

Weakly basic nitrogen-containing compounds include anilines, amides, imides and N-cycloalkyl derivatives having alkyl, cycloalkyl and phenyl groups as a substituent in the pyrrole ring:

In the composition of crude oils and straight-run distillates, pyridine derivatives are most often found. With an increase in the boiling point of fractions, the content of nitrogen-containing compounds usually increases, while their structure changes: if pyridines predominate in light and medium fractions, then their polyaromatic derivatives predominate in heavier fractions, and anilines are present to a greater extent in the products of thermal processing at elevated temperatures. Nitrogenous bases predominate in light fractions, and neutral nitrogen-containing compounds, as a rule, dominate in heavy fractions.

Neutral nitrogen-containing compounds that do not contain other heteroatoms in their molecules, except for the nitrogen atom, and isolated from oil, include indoles, carbazoles and their naphthenic and sulfur-containing derivatives:

When isolated, neutral nitrogen-containing compounds form associates with oxygen-containing compounds and are extracted along with nitrogen-containing bases.

Along with the named monofunctional compounds, the following nitrogen-containing compounds have been identified in oils:

1. Polyaromatic with two nitrogen atoms in the molecule:

2. Compounds with two heteroatoms (nitrogen and sulfur) in one cycle - thiazoles and benzthiazoles and their alkyl and naphthenic homologues:

3. Compounds with two nitrogen and sulfur heteroatoms in different cycles: thiophene-containing alkyl-, cycloalkylindoles and carbazoles.

4. Compounds with a carbonyl group in a nitrogen-containing heterocycle, such as piperidones and quinolones:

5. Porphyrins. The structure of porphyrins, which are complex compounds with vanadyl VO, nickel, and iron, will be discussed below.

The importance of nitrogen-containing compounds of oil as natural surfactants is very high; they, along with CAB, largely determine the surface activity at liquid phase boundaries and the wetting ability of oil at rock-oil, metal-oil interfaces. Nitrogen-containing compounds and their derivatives - pyridines, hydroxypyridines, quinolines, hydroxyquinolines, imidazolines, oxazolines, etc. - are natural oil-soluble surfactants that have inhibitory properties in the corrosion of metals during the production, transportation and refining of oil. Weaker surface-active properties are characteristic of such nitrogen-containing oil compounds as homologues of pyrrole, indole, carbazole, thiazoles and amides.

Resin-asphalten substances (CAB). One of the most representative groups of heteroorganic macromolecular oil compounds are CAB. The characteristic features of CAB - significant molecular weights, the presence of various heteroelements in their composition, polarity, paramagnetism, a high tendency to MMW and association, polydispersity and the manifestation of pronounced colloidal disperse properties - contributed to the fact that the methods usually used in the analysis turned out to be unsuitable for their study. low boiling components. Given the specifics of the object under study, Sergienko S.R. more than 30 years ago, he singled out the chemistry of macromolecular oil compounds as an independent branch of petroleum chemistry and made a major contribution to its formation with his fundamental works.

Until the 1960s and 1970s, researchers determined the physicochemical characteristics of CAB (some of them are given in Table 2.4) and tried to represent the structural formula of the average molecule of asphaltenes and resins based on instrumental structural analysis data.

Similar attempts are being made at the present time. The values of the elemental composition, average molecular weights, density, solubility, etc. varying within a significant range for CAB samples of various domestic and foreign oils reflect the diversity of natural oils. Most of the heteroelements present in oil and almost all metals are concentrated in resins and asphaltenes.

Nitrogen in CAB mainly enters into heteroaromatic fragments of pyridine (basic), pyrrole (neutral), and porphyrin (metal complex) types. Sulfur is part of heterocycles (thiophene, thiacyclane, thiazole), thiol groups, and sulfide bridges that cross-link molecules. Oxygen in resins and asphaltenes is presented in the form of hydroxyl (phenolic, alcohol), carboxyl, ether (simple, complex lactone), carbonyl (ketone, quinone) groups and furan cycles. There is a certain correspondence between the molecular weight of asphaltenes and the content of heteroelements (Fig. 2.2).

Let us characterize the modern level of ideas about CAB. Yen notes the universal nature of asphaltenes as a constituent of natural carbon sources, not only caustobioliths (oils and solid fuels), but also sedimentary rocks and meteorites.

According to the classification of hydrocarbon-based natural resources proposed by Abraham, oils include those that contain up to 35-40% (mass.) CAB, and natural asphalts and bitumens contain up to 60-75% (mass.) CAB, according to other sources - up to 42-81%. In contrast to the lighter components of oil, which were attributed to their groups by the similarity of their chemical structure, the criterion for combining compounds into a class called CAB is their proximity in solubility in a particular solvent. When oil and oil residues are exposed to large amounts of petroleum ether, low-boiling alkanes, precipitation of substances called asphaltenes, which are soluble in lower arenas, and the solvation of other components - maltenes, consisting of a hydrocarbon part and resins.

Rice. 2.2. Dependence of the molecular mass of asphaltenes (М) on the average total content of heteroelements (O+N+S) in oil from the Safagna (1), Cerro Negro (2), Boscan (4), Batiraman (5) and light Arabic oil fields ( 3)

Modern schemes for separating the heavy part of oil are based on the classical methods first proposed by Markusson. Substances insoluble in carbon disulfide and other solvents are classified as carboids. Substances that are soluble only in carbon disulfide and precipitated by carbon tetrachloride are called carbenes. Carboids and carbenes, as a rule, are found in the composition of heavy products of destructive oil refining in an amount of several percent and will be considered separately below. They are practically absent in the composition of crude oils and in the residues of primary oil refining.

The properties of isolated asphaltenes also depend on the solvent. The consequence of differences in the nature and properties of solvents is that the molecular weight of asphaltenes from Arab oils when dissolved in benzene is on average 2 times higher than in tetrahydrofuran. (Table 2. 5).

Table 2.5

Solvent Solution parameter Dielectric Dipole moment, Dpermeability permeability

Tetrahydrofuran 9.1 7.58 1,75 Benzene 9.2 2.27 0

In the process of developing ideas about the structure and nature of petroleum CABs, two main stages can be distinguished, related by the general idea of a colloidal-dispersed structure, but differing in the methodological approach to assessing the structure of a single element of a colloidal structure. At the first stage - the stage of chemical ideas about the structure of CAB molecules - a standard chemical approach was used to identify the structure of an unknown compound. After establishing the molecular weight, elemental composition and molecular formulas of resins and asphaltenes C n H 2 n - z N p S g O r . Then the z value was calculated. For resins, it was 40-50, for asphaltenes - 130-140. A typical example of the results of such studies for CAB samples of various domestic and foreign oils is presented in Table. 2.4. (see Table 1.4). As can be seen, asphaltenes differ from resins from the same source in higher carbon and metal content and lower hydrogen content, larger polyaromatic cores, shorter average length of large aliphatic substituents, and fewer acyclic fragments directly fused with aromatic nuclei.

The second stage can be characterized as the stage of development of physical ideas about the structure of asphaltenes and analysis of the reasons for the tendency of asphaltenes to associate. Indeed, the explanation of the dependence of the molecular weight on the conditions of determination (see Table 2.5), as well as its linear dependence on the size of asphaltene particles (Fig. 1.5) became possible within the framework of qualitatively new ideas about the structure of asphaltenes.

In 1961 T. Yen proposed the so-called "plate to plate" stack model of the structure of asphaltenes. The model was based not on the necessity of its compliance with the calculated structural parameters of the composition of asphaltenes, but on the fundamental possibility of a plane parallel orientation of polyaromatic fragments of different molecules. Their association as a result of intermolecular (π - π, donor-acceptor, etc.) interactions occurs with the formation of layered stacking structures (the term "stacking" is used in molecular biology to denote a stack-like arrangement of molecules one above the other).

Rice. 2.5. Correlation between the particle size of asphaltenes (D) and their molecular weight (M)

In accordance with the Yen model based on X-ray diffraction data, asphaltenes have a crystalline structure and are stacking structures with a diameter of 0.9-1.7 nm from 4-5 layers spaced 0.36 nm apart. The size of stacking structures along the normal to the plane of aromatic plates is 1.6–2.0 nm (Fig. 2.6). Rectilinear segments show flat polyaromatic fragments, and broken segments show saturated fragments of molecules. Polyaromatic fragments are represented by relatively small, most often no more than tetracyclic, nuclei. Of the aliphatic fragments, the most common are short alkyl groups C 1 -C 5, primarily methyl, but there are also linear branched alkanes containing 10 carbon atoms or more. There are also polycyclic saturated structures in CAB molecules with 1-5 condensed rings, mainly bicyclanes.

Within the framework of the Jena model, the dependence of the molecular weight of asphaltenes on the conditions of isolation and the nature of the solvent noted above can be easily explained by an association that suggests several levels of structural organization of asphaltenes: a molecularly dispersed state (I), in which asphaltenes are in the form of separate layers; colloidal state (II), which is the result of the formation of stacking structures with characteristic dimensions; a dispersed kinetically stable state (III) arising from the aggregation of stacking structures; and a dispersed kinetically unstable state (IV) accompanied by precipitation.

Rice. 2.6. Asphaltene structure model according to Jen

Models of the pack structure of the structure of asphaltenes are followed by many modern researchers. Unger F.G. expressed an original point of view on the process of occurrence and existence of CAB in oil. Oils and oil systems containing CAB, in his opinion, are thermodynamically labile paramagnetic associated solutions. The cores of associates of such solutions are formed by asphaltenes, in which stable free radicals are localized, and the solvate layers surrounding the cores consist of diamagnetic resin molecules. Some of the diamagnetic resin molecules are capable of transitioning to an excited triplet state and undergoing hemolysis. Therefore, resins are a potential source of asphaltenes, which explains L.G. the ease of converting resins to asphaltenes.

Thus, the novelty of the presented ideas is connected with the assertion of the special role of exchange interactions for explaining the nature of CAB. In contrast to the pack model, the idea of a centrally symmetric structure of the CAB particle is being developed. It was first postulated by D. Pfeiffer and R. Saal, who proposed a static model of the structure of the structural unit of asphaltenes. According to it, the core of the structural unit is formed by high molecular weight polycyclic hydrocarbons and is surrounded by components with a gradually decreasing degree of aromaticity. Neumann G. emphasized that it is energetically beneficial to turn polar groups inside the structural unit, and hydrocarbon radicals - outward, which is in agreement with the polarity equalization rule according to Rehbinder.

Porphyrins are typical examples of native petroleum complex compounds. Porphyrins with vanadium as the focal point (in the form of vanadyl) or nickel (see 11). Oil vanadylporphyrins are mainly homologues of two series: alkyl-substituted porphyrins with different total number of carbon atoms in the side substituents of the porphine ring and porphyrins with an additional cyclopentene ring. Metal porphyrin complexes are present in natural bitumen up to 1 mg/100 g, and in high-viscosity oils - up to 20 mg/100 g of oil. In the study of the nature of the distribution of metal porphyrin complexes between the constituent parts of the SDS in the work by extraction and gel chromatography, it was found that 40% of vanadylporphyrins are concentrated in dispersed particles (approximately equally in the composition of the core and solvate layer), and the rest of them and nickel porphyrins are contained in the dispersion environment.

Vanadylporphyrins in the composition of asphaltenes make a significant contribution to the surface activity of oils, while the intrinsic surface activity of asphaltenes is low. Thus, a study of oils from Bashkiria showed that the surface tension of oils at the boundary with water strongly correlates with the content of vanadylporphyrins in them, while the correlation coefficient with the content of asphaltenes in them is relatively low (Fig. 2.7).

To a lesser extent, the effect of metal porphyrins on the disperse structure of oil and the conditions for the occurrence of phase transitions in oil systems has been studied. There is evidence of their negative effect, along with other heteroatomic components, on the catalytic processes of oil refining. In addition, they should strongly influence the kinetics and mechanism of phase transitions in SSS.

Rice. 2.7. Isotherms of interfacial tension a at the boundary with water:

a - benzene solutions of asphaltenes: 1 - asphaltenes with porphyrins; 2-5 - asphaltenes as porphyrins are removed after one, five, seven, thirteen extractions, respectively; b - oil of Bashkiria

Organic substances are a class of compounds containing carbon (with the exception of carbides, carbonates, carbon oxides and cyanides). The name "organic compounds" appeared at an early stage in the development of chemistry and scientists speak for themselves ... Wikipedia

One of the most important types of organic compounds. They contain nitrogen. They contain carbon-hydrogen and nitrogen-carbon bonds in the molecule. Oil contains nitrogen-containing pyridine heterocycle. Nitrogen is part of proteins, nucleic acids and ... ... Wikipedia

Organogermanium compounds are organometallic compounds containing a germanium carbon bond. Sometimes they are called any organic compounds containing germanium. The first organogerman compound tetraethylgermane was ... ... Wikipedia

Organosilicon compounds are compounds in the molecules of which there is a direct silicon-carbon bond. Silicone compounds are sometimes called silicones, from the Latin name for silicon, silicium. Silicone compounds ... ... Wikipedia

Organic compounds, organic substances are a class of chemical compounds containing carbon (excluding carbides, carbonic acid, carbonates, carbon oxides and cyanides). Contents 1 History 2 Class ... Wikipedia

Organometallic Compounds (MOCs) Organic compounds in whose molecules there is a bond between a metal atom and a carbon atom/atoms. Contents 1 Types of organometallic compounds 2 ... Wikipedia

Organohalogen compounds are organic compounds containing at least one bond C Hal carbon halogen. Organohalogen compounds, depending on the nature of the halogen, are divided into: Organofluorine compounds; ... ... Wikipedia

Organometallic Compounds (MOCs) are organic compounds in whose molecules there is a bond between a metal atom and a carbon atom/atoms. Contents 1 Types of organometallic compounds 2 Methods for obtaining ... Wikipedia

Organic compounds in which a tin-carbon bond is present may contain both divalent and tetravalent tin. Contents 1 Synthesis methods 2 Types 3 ... Wikipedia

- (heterocycles) organic compounds containing cycles, which, along with carbon, also include atoms of other elements. They can be considered as carbocyclic compounds with heterosubstituents (heteroatoms) in the ring. Most ... ... Wikipedia

By clicking on the "Download archive" button, you will download the file you need for free.
Before downloading this file, remember those good essays, control, term papers, theses, articles and other documents that are unclaimed on your computer. This is your work, it should participate in the development of society and benefit people. Find these works and send them to the knowledge base.
We and all students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

To download an archive with a document, enter a five-digit number in the field below and click the "Download archive" button

Oxygen-containing and nitrogen-containing. Certification work chemistry of the process of destructive hydrogenation

Nomenclature of some organic substances (trivial and international)

Similar Documents