Study of n-Alkanes in Western Siberian Oils
Abstract Generated abstract
This study examines normal alkane hydrocarbons in oils from the Sovetskoye and Samotlor fields of Western Siberia, with attention to their distribution across light, middle, and heavy distillation fractions. Narrow fractions were analyzed using adsorption on molecular sieves, urea complex formation, freezing methods for solid hydrocarbons, and gas liquid chromatography for individual alkane identification. The two oils were found to contain nearly equal total amounts of n-paraffins up to 450°C, about 20.7% and 20.4%, with n-alkanes from C4 to C22 identified in light and middle fractions. Their distribution shows maxima mainly between C5 and C12, a decrease among higher molecular weight members, and a slight predominance of odd carbon number alkanes, supporting classification with the common low carbon maximum distribution type.
Full Text
STUDY OF n-ALKANES IN OILS FROM WESTERN SIBERIA
N. M. SMOLYANINOVA, V. A. KUZNETSOVA, O. B. ZAKARLYUK
(Presented by the Scientific-Methodological Seminar of the Organic Departments of the Faculty of Chemical Technology)
The broad use of n-paraffins in industry, and the synthesis on their basis of a variety of products that have become widespread in all branches of the national economy, have brought the question of studying the n-paraffins of oils to the forefront, since only on the basis of reliable scientific data on the hydrocarbon composition of petroleum feedstock is it possible to carry out its processing correctly, on a scientific basis.
The interpretation of such data is also of considerable scientific interest from the standpoint of petroleum genesis.
The present work is devoted to the study of n-paraffinic hydrocarbons in oils from the Sovetskoye and Samotlor fields of Western Siberia. Both oils belong to the naphthene–methane type. Predominant in their composition are paraffinic hydrocarbons, among which a significant share belongs to alkanes of normal structure.
A brief characterization of the oils is given in Table 1.
Narrow fractions obtained by atmospheric-vacuum rectification on an ARN-2 unit were subjected to investigation.
The quantitative determination of n-paraffins in gasoline distillates was carried out by adsorption on CaA molecular sieves [1]; in higher-boiling fractions, by complex formation with carbamide from the methane–naphthene portion [2], obtained by chromatographic separation on ASK silica gel.
The composition of n-alkanes in light distillates (up to 200°C) was determined by gas–liquid chromatography [5] on a “Khrom-2” chromatograph with a flame-ionization detector. For the analysis, a capillary column 100 m long and 0.5 mm in diameter was used. The temperature was 80°C. Squalane was chosen as the stationary phase. The carrier gas was nitrogen.
The individual composition of the n-alkanes of the 200–250°C, 250–300°C, and 300–350°C fractions was determined on an “LKhM-7A” chromatograph (n-paraffins were first isolated from the methane–naphthene portion of the fractions by complex formation with carbamide and subsequent decomposition of the complex with water).
For the analysis, a high-temperature phase was selected—silicone elastomer E-301, deposited on Chromosorb-1 (fraction 0.25–0.34 mm) in an amount of 10%; column length 2 m, diameter 4 mm. Chromatography was carried out in a temperature-programming regime from 170 to 300°C at a rate of 11 deg/min. The carrier gas was helium; the detector—
chromatograph. Identification of the components was carried out using reference substances.
In the fractions boiling above 350°C, quantitative determination of the content of solid hydrocarbons was carried out by the method of freezing out from a benzene–acetone–toluene solution according to GOST 11244-65, and their characteristics with respect to molecular weight and melting point were given (Table 2).
The results of the quantitative determination of \(n\)-paraffins in the indicated fractions of Sovetskoe and Samotlor oils are presented in Table 3.
It is evident from the table that the content of \(n\)-paraffins in the gasoline cuts of the oils decreases with increasing boiling limits of the fractions from 48 and 47% to 29 and 27.7%, respectively, for Sovetskoe and Samotlor oils; moreover, the gasolines of both oils practically do not differ from one another in the amount of \(n\)-alkanes.
On the whole, the content of \(n\)-paraffins in the distillates b.p.—200°C for the oils is rather high.
These data make it possible to conclude that the indicated cuts may serve as good feedstock for pyrolysis and are unsuitable for obtaining high-quality carburetor fuels for modern engines.
The middle cuts (200–350°C) are also characterized by a high content of \(n\)-paraffins—18.0 and 19.4%, respectively, for Sovetskoe and Samotlor oils.
Table 1
Physicochemical characteristics of the oils of the Sovetskoe and Samotlor fields [3, 4]
| Indicator | Value for Sovetskoe oil | Value for Samotlor oil |
|---|---|---|
| Density, \(\rho_4^{20}\) | 0.8362 | 0.8525 |
| Molecular weight | 193 | 213 |
| Kinematic viscosity at 50°C, cSt | 3.54 | 4.48 |
| Pour point with thermal treatment, °C | −18 | −7 (50°C) |
| Saturated vapor pressure at 38°C, mm Hg | 162 | 145 |
| Paraffin content, % | 3.27 | 3.64 |
| Silica-gel resin content, % | 8.99 | 8.53 |
| Asphaltene content, % | 0.55 | 0.71 |
| Coking value, % | 1.72 | 3.15 |
| Sulfur content, % | 0.69 | 0.95 |
| Distillation, wt. % (according to ITK), up to 200°C.... | 30.8 | 28.8 |
| Distillation, wt. % (according to ITK), up to 300°C.... | 53.0 | 49.0 |
From the standpoint of evaluating the middle fractions as diesel fuels, the significant content of \(n\)-alkanes in them, on the one hand, is favorable, since it should increase the cetane numbers; but, on the other hand, the presence of \(n\)-alkanes raises the pour point of diesel fuels, which limits their use in winter (causing the need for partial dewaxing; moreover, the \(n\)-paraffins separated in this process are a good feedstock for the synthesis of SFA, SFS, and protein–vitamin concentrate).
In the fractions boiling above 350°C of both oils, the content of \(n\)-paraffins decreases (for fr. 350–450°C, the amount of \(n\)-paraffins is 11.3 and 11.0%, respectively, for Sovetskoe and Samotlor oils) in comparison with the middle cuts.
Table 2
Characteristics of solid paraffins from heavy oil fractions
| Boiling limits, °C | Yield on oil, % | Content of solid paraffins in fraction, % | Content of n-paraffins in solid hydrocarbons, % | Molecular mass of n-paraffins | Melting temperature of n-paraffins, °C |
|---|---|---|---|---|---|
| Sovetskaya oil | |||||
| 300—350 | 8,8 | 4,5 | 92,5 | 295 | 41,3 |
| 350—400 | 9,1 | 9,45 | 79,8 | 332 | 46,0 |
| 400—450 | 9,4 | 7,15 | 59,9 | 390 | 50,2 |
| Residue | 21,8 | 5,9 | — | — | 52,0 |
| Samotlorskaya oil | |||||
| 300—350 | 10,0 | 6,8 | 85,5 | 291 | 44,0 |
| 350—400 | 9,7 | 9,3 | 78,0 | 350 | 47,0 |
| 400—450 | 7,0 | 8,1 | 59,6 | 381 | 51,0 |
| Residue | 28,7 | 5,5 | — | — | 53,0 |
Table 3
Content of n-paraffinic hydrocarbons in oils of the Sovetskoye and Samotlorskoye fields
| Boiling limits of fractions, °C | Sovetskaya oil: fraction yield on oil, % | Sovetskaya oil: n-paraffin content, % | Samotlorskaya oil: fraction yield on oil, % | Samotlorskaya oil: n-paraffin content, % |
|---|---|---|---|---|
| i.b.p.—60 | 3,6 | 48,0 | 3,0 | 47,0 |
| 60—95 | 5,6 | 31,0 | 5,5 | 30,0 |
| 95—122 | 4,9 | 24,0 | 3,6 | 23,0 |
| 122—150 | 6,0 | 22,0 | 5,6 | 21,0 |
| 150—200 | 10,4 | 29,0 | 8,6 | 24,9 |
| 200—250 | 9,8 | 16,3 | 9,2 | 26,0 |
| 250—300 | 10,6 | 18,3 | 9,2 | 11,0 |
| 300—350 | 8,8 | 21,0 | 10,0 | 21,0 |
| 350—400 | 9,1 | 14,3 | 9,6 | 13,0 |
| 400—450 | 9,4 | 8,4 | 7,0 | 8,2 |
| i.b.p.—200 | 30,5 | 29,0 | 26,3 | 27,7 |
| 200—350 | 29,2 | 18,0 | 28,4 | 19,4 |
| i.b.p.—350 | 59,7 | 23,6 | 54,7 | 23,3 |
| 350—450 | 18,5 | 11,3 | 16,6 | 11,0 |
| i.b.p.—450 | 78,2 | 20,7 | 71,6 | 20,4 |
These fractions can be used as feedstock for catalytic cracking in order to obtain motor gasoline rich in aromatics and isoparaffins.
The results of determining the individual composition of \(n\)-paraffins in the light and middle fractions of the oils are presented in Table 4. It can be seen from the table that, in the distillate portion (end boiling point—350°C), \(n\)-paraffins with a number of carbon atoms from \(C_4\) to \(C_{22}\) were identified.
For both oils it is characteristic that the maximum content of \(n\)-paraffins lies between \(C_5\) and \(C_{12}\). The maximum amount of \(n\)-paraffins for the Sovetskaya oil falls at \(C_5\) (1.48%) and \(C_{10}\) (1.45%); for the Samotlor oil, at \(C_8\) (1.15) and \(C_{10}\) (1.29%).
For the middle fractions of the oils, two maxima in the content of \(n\)-paraffins are also characteristic: for the Sovetskaya oil—\(C_{15}\) (0.99%) and \(C_{19}\) (0.46%); for the Samotlor oil—\(C_{14}\) (0.62%) and \(C_{17}\) (0.80%).
The minima in the content of \(n\)-paraffins for the Sovetskaya oil fall at \(C_9\) (0.95%), \(C_{12}\) (0.39%), and \(C_{17}\) (0.29%); for the Samotlor oil—at \(C_8\) (0.75%), \(C_{11}\) (0.097%), and \(C_{17}\) (0.80%).
For both oils a sharp decrease in the amount of \(n\)-paraffins in the region \(C_{11}\)—\(C_{12}\), and then a slight increase, is characteristic.
On the basis of these data, curves of the distribution of \(n\)-alkanes in the oils according to the number of carbon atoms in the molecule were constructed (Fig. 1).
Table 4
Distribution of \(n\)-paraffins by the number of carbon atoms in the molecules for fractions with end boiling point—350°C of oils from the Sovetskoye and Samotlor fields
| \(n\)-paraffins | Yield on oil, % | Yield on oil, % |
|---|---|---|
| \(n\)-paraffins | Sovetskaya | Samotlor |
| \(C_4H_{10}\) | 0.06 | 0.10 |
| \(C_5H_{12}\) | 0.89 | 1.48 |
| \(C_6H_{14}\) | 1.03 | 1.37 |
| \(C_7H_{16}\) | 1.15 | 1.03 |
| \(C_8H_{18}\) | 1.17 | 0.75 |
| \(C_9H_{20}\) | 0.95 | 1.39 |
| \(C_{10}H_{22}\) | 1.28 | 1.46 |
| \(C_{11}H_{24}\) | 0.89 | 0.09 |
| \(C_{12}H_{26}\) | 0.39 | 0.33 |
| \(C_{13}H_{28}\) | 0.57 | 0.55 |
| \(C_{14}H_{30}\) | 0.53 | 0.62 |
| \(C_{15}H_{32}\) | 0.99 | 0.61 |
| \(C_{16}H_{34}\) | 0.86 | 0.57 |
| \(C_{17}H_{36}\) | 0.29 | 0.80 |
| \(C_{18}H_{38}\) | 0.35 | 0.69 |
| \(C_{19}H_{40}\) | 0.46 | 0.49 |
| \(C_{20}H_{42}\) | 0.39 | 0.39 |
| \(C_{21}H_{44}\) | 0.27 | 0.28 |
| \(C_{22}H_{46}\) | 0.20 | 0.09 |
| Total | 12.79 | 12.62 |
The maximum content of \(n\)-paraffins between \(C_5\) and \(C_{12}\) agrees with the data of Martin, Winters, and Williams [6], who indicate two principal types of distribution of \(n\)-alkanes in American oils. The same types of distribution have been found in oils from other parts of the world.
According to the first type, the distribution curve has a maximum located between \(C_5\) and \(C_{12}\). Quite often this maximum corresponds to \(C_6\) or \(C_7\).
The second type of distribution is encountered less often. It was found for \(n\)-alkanes contained in oils only from Cenozoic deposits. In this case the maximum of the distribution curve shifts to the higher members of the \(n\)-alkane series, between \(C_{19}\) and \(C_{25}\).
On the basis of these two types of distribution of \(n\)-paraffins, it is probably possible to assign the oils of the Sovetskoye and Samotlor fields
to the first type, since from the graph in Fig. 1 it is evident that the content of high-molecular-weight solid n-paraffins for both oils decreases as the number of carbon atoms in the molecules increases.
The ratio \(C_{\text{odd}}/C_{\text{even}}\) for Sovetskoye and Samotlor oils is, respectively, 1.04 and 1.06; that is, n-paraffins with an odd number of carbon atoms slightly predominate over n-paraffins with an even number of carbon atoms.
Fig. 1. Distribution of n-paraffins by the number of carbon atoms in the molecules for the fractions b.p.—350° C of oils from the Sovetskoye and Samotlor fields.
1 — Sovetskoye oil; 2 — Samotlor oil
Conclusions
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The content of n-paraffins in the oils of the Sovetskoye and Samotlor fields has been determined, and it has been established that both oils contain nearly the same amount of them (20.7% and 20.4%, respectively).
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By the GLC method, the presence of n-alkanes from \(C_4\) to \(C_{22}\) in the light and middle fractions of the oils was established.
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The results of studying the individual composition of the n-paraffins made it possible to establish the nature of their distribution as a function of the number of carbon atoms.
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