An important feature is the selectivity of the solvent, the ability to extract unwanted components of the feed. Necessary selectivity of the process is usually provided by varying the temperature and pressure of the system, which is controlled by the process of supercritical extraction [2] -[4] .

Now the using of carbon dioxide (CO₂) is in the focus because of its relatively low critical parameters (T_cr- 37˚C), light reconditioning, high volatility, non-incendive, cheapness and availability. It should be noticed that the main directions of the use of supercritical solvent in the process of refining and petrochemical industries were determined since the beginning of 2000. This process is used for deasphalting of heavy residues, because it makes possible the appreciable reduction of the ratio of solvent to remove of the raw materials and their components selectively, thereby improving the efficiency of the processes.

Azerbaijan supercritical technologies were first used in the process of extracting oil from oil-bearing rocks and soils, under the leadership of A. H. Mirzajanzadeh and his colleagues [5] -[10] .

More research in this direction started in the 90s of the last century in the Kazan University [3] [11] , and continue to this day [12] .

The monograph provides the properties of supercritical fluids, new ways of defining asphaltenes in oil and heavy residues deasphalting developed under the guidance and with the participation of the author of the monograph and demetallization of heavy oil residues, dehydration and desalting using SC CO₂, increasing the solvent power of supercritical fluid by adding of cosolvents-cleaning oil fraction, deasphalting of residual oil fraction (tar), the allocation of oil from the tar sands of Azerbaijan.

The main disadvantages of the most common and well-known methods of determining asphaltene (method of Golde and standard methods) are the use of large amounts of solvent (40 fold) to coagulate asphaltenes dilution of the test sample (5 - 10 g) of mineral oil, a suitable solvent, the duration of analysis and blurred separation.

The energy needs of the process under supercritical CO₂ are significantly less than that in conventional processes using a hydrocarbon extraction solvent.

The preparative method for the determination of asphaltenes in crude oil and heavy oil residues using the unique properties of supercritical CO₂ is created and patented in IPCP of ANAS [13] .

New developed method allows the product to increase from 5 - 10 to 100 g; the amount of the solvent reduces its dilution from 40 to 1 - 2 fold to improve clarity of asphaltene precipitation, and to reduce the duration of the analysis in comparison with the known number of sample test [14] .

The proposed method can be used to improve existing standards-ГОСТ 1185-85 and its application is used for the quantitative determination of asphaltenes in petroleum and petroleum products, and also to highlight sufficient quantity to study their composition and properties.

In the IPCP of ANAS developed supercritical extraction of heavy oil residues using SC CO₂ [13] [15] and compared with the Doben process, which is widely used for the preparation of heavy oil residues for further pro- cessing.

The comparative data from the known and the proposed method are given in Table 1 [15] .

Figure 1 is a scheme of the laboratory setup for deasphalting of oil and heavy residues with CO₂ in its super-

^*)In both cases we use the same hydrocarbon solvent.

critical conditions. The characteristics of heavy oil residues before and after deasphalting using CO₂ in its supercritical and microelement composition are shown in Table 2 and Table 3.

The studies of microelement composition of the residue of deasphalted oil (tar) showed that they significantly (up to 30% - 50% wt.) enriched with metals, i.e. raw material is cleaned of metals and asphaltenes which are not detected in the feed (Table 4) [13] -[16] .

To optimize the parameters of the process the effect of dilution of raw material with hydrocarbon solvent, pressure and temperature on the results of cleaning of the mixture of low paraffinic oils and its heavy residue are studied [16] -[18] .

The preparation of oil for processing is an important step in the refining technologies. Therefore, not only cleaning of oil from the asphaltenes and metals, as well as water, salts, solids is important.

The water content of the oil transported through pipelines, is up to 1%, and in arriving at the refineries it should be no more than 0.5% [19] .

For the study the mixtures of Neft Dashlary, Shirvan and Surakhany oils, processed at the refinery named after Heydar Aliyev were used. The data of content of oils in mixtures I, II, III are shown in Table 4.

In Figure 2 the scheme of an oil extraction of undesired components with SC CO₂ is shown.

The results of the comparison of existing and proposed (SC-CO₂) methods of dehydration and desalting are shown in Table 5.

^*)The yields of oil and tar, respectively, 60.2% and 30.4% for oil. ^**)At 100˚C.

Supercritical fluid extraction process is carried out in the presence of CO₂ and a co-solvent-acetone, n-heptane, toluene or mixtures of toluene and n-heptane with acetone and ethyl alcohol. The extraction process is conducted in the presence of SC CO₂ content n-heptane or acetone in an amount of 5%, 10%, 15% and 25%. With increasing the concentration of acetone from 5% to 25%, the viscosity of oil at 20˚C rises from 17.33 to 21.28 mm²/s, its pour point changes from minus 41˚C to minus 31˚C, coking increases from 1.74% to 2.33%.

By proceeding SC CO₂ extraction with heptane positive results in reducing the pour point of the oil up to minus 60 - minus 62˚C compared to minus 52˚C at the feed oil. Coking ability is also reduced from 1.69% to 1.46% at 25% of n-heptane mixture with SC CO₂.

There are ways to increase the effectiveness of solvents for cleaning oil fractions using paired solvents.

The influence of the pair of solvents on the selective treatment processes, deasphalting; influence of components of the solvent pair-one of the solvents should dissolve the contaminants, other cleansing oil, shows the effect of polar and nonpolar nature of the components in the mixture of solvents when using paired solvents, and changing the solvent and selective solvent capacity with temperature change [20] -[23] . For each system, the selection of the optimal temperature and the ratio of its components are conducted.

The book also contains the results of studies of selective purification of oil fractions with medium and high viscosity with viscosity of 7 - 8 mm²/s at 100˚C based on the two-phase solvent N-methylpyrrolidone and furfurol with carbon dioxide in supercritical conditions.

For selective treatment of feedstock we used medium viscosity oil fraction from a mixture low-paraffinic Azerbaijani oil, processed at “Azerneftyag” refinery. It is found that the oil fraction has a low viscosity index (63.3), dark color, high acid number −0.32 mg KOH/g.

The cleaning in the two-phase system (pair solvent) was carried out on the pilot installation of supercritical extraction of the Institute.

The possibility of achieving a high degree of purification with a lower ratio of oil using two-phase solvent fraction SC CO₂ + co-solvent at a lower temperature and less is shown.

With the continuous depletion of conventional oil, the content of so-called bituminous sands becomes very important.

Deposits of oil in bituminous rocks exist in Girmaky rocks in Azerbaijan.

Earlier IPCP conducted the pilot projects to obtain oil from the Girmaky sands by thermal extraction in high- performance machines [24] .

The alternative to a large number of hydrocarbons (methane, propane, etc., and mixtures thereof), introduced for the extraction of carbon dioxide may serve as the supercritical state.

The use of supercritical extraction processes in oil production and refining in order to increase oil recovery is one of the most pressing problems; its solution allows you to create high-waste technologies to maximize oil recovery.

With increasing pressure and temperature of CO₂ into the liquid phase, and then at a pressure higher than 7.3 MPa is converted into a supercritical (SC) fluid, where its properties are shown as both gas and liquid.

The fluid has a high penetrating ability and solubility, which is higher than that of traditional solvents [25] .

SC CO₂, pumped into the formation, dissolves in the oil by its own expansion and liquefaction oil extracts.

In IPCP of ANAS and AzNIPI the investigations of separation of oil from bituminous minerals, study of its properties and further processing of the selected oil were carried out [26] -[28] . Oil extracted from the oil-satu- rated sand with the relaxation method had a density at 20˚C of 1143.9 kg/m³, viscosity at 100˚C of 9.5 mm²/s. The composition and properties of the oil, the possibility of obtaining oils and fuels are given in [26] . The methods of refining of oil from oil-saturated sand through its catalytic treatment with α-olefins and hydrotreating oil-saturated sands without prior isolation of the organic part (oil), occur simultaneously with upgrading and separation of oil from the sand [27] .

Along with the studies, which are described above, the separation of oil and bitumen from the oil-saturated ground with the mixture of carbon dioxide and supercritical solvents (heptane and the mixture of alcohol and benzene) is conducted. The proposed method ensures the effective allocation of oil with less solvent consumption. The advantages of this method are its low cost, high safety, easy separation of carbon dioxide from the crude oil. Experiments were conducted in a pilot plant of the Institute for supercritical extraction.

The oil from the oil-saturated ground of Mashtaga deposits is separated with SC CO₂ and heptanes (1:1); they were fed to the reactor at a temperature of 40˚C, the pressure of 8 MPa and carbon dioxide was supplied for 2 hours. After the experiment was complete and the obtained sludge was separated from the ground and oil heptane solution, the reactor was charged with the ground and mixture of alcohol and benzene (1:4) at a ratio of 100 ml newly supplied carbon dioxide (1:1) (T-40˚C, P-8 MPa) for 2 hours, extracted resinous-asphaltene substances (RAS). Yields after SC-extraction from bituminous sands are shown in Table 6. The data in Table 6 shows that oil can be isolated from bituminous ground in an amount of 99% of capacity, including oil and RAS 66.7% - 33.2% by weight using a solvent + SC CO₂. The process of isolation oil using only SC CO₂ without solvent hardly occurs.

After distillation with heptane and alcohol-benzene, the output of oil and resin-asphaltene substances (RAS) is determined.

The application of SC CO₂ during the extraction of oil from bituminous sands allows reducing the amount of solvents more than two times, as well as fully extraction of RAS containing saturated hydrocarbons with a high

^*)After an additional sediment yield of RAS is reduced to ~10%.

degree of branching, type of fused aromatic compounds. This can be explained by the fact that the SC CO₂ re- duces oil viscosity and improves the solubility of carbon dioxide, which contributes to the deposition of the asphalt-resinous substances.