On the Interrelationships of Certain Physicochemical Characteristics of Oils
Abstract Generated abstract
This paper examines relationships among physicochemical properties of crude oils in order to reduce the number of laborious measurements needed for practical assessment of oils as fuel and petrochemical feedstocks. Using standardized data for 350 oil samples from fields across the Soviet Union, the authors apply correlation analysis by computer to ten principal characteristics, including density, viscosity, sulfur content, pour point, carbon residue, paraffin content, molecular weight, light fraction yields, and resin-asphaltene or aromatic-naphthenic content. The analysis identifies strong correlations, especially involving density, viscosity, molecular weight, carbon residue, and resin-asphaltene content, while sulfur, paraffin, pour point, and light fraction yields show weaker or more selective associations. The results suggest that correlation analysis can guide the choice of variables for regression equations to estimate difficult or less accurately determined oil characteristics such as paraffin content, resin-asphaltene substances, and molecular weight.
Full Text
ON THE INTERRELATIONSHIPS OF CERTAIN PHYSICOCHEMICAL CHARACTERISTICS OF OILS
G. G. Blagopoluchnaya, N. M. Smolyaninova
(Presented by the scientific-methodological seminar of the organic departments of the KhTF, TPI)
The expansion of the fields of application of oil as a raw material for petrochemistry and for the production of a broad assortment of fuels and oils leads to an increase in the number of indicators used in assessing the quality of oils and serving as a basis for designing technological processes, which is associated with the need to carry out lengthy, labor-intensive, and costly studies. In this connection, the task of revealing the interrelationships among certain properties of oils and their fractions, and of selecting a comparatively small set of indicators by means of which, with accuracy sufficient for practical purposes, oil can be characterized as a raw material for various directions of its utilization, is of interest.
In the present work, the first results of investigations in this direction are presented, obtained by the method of correlation analysis with the use of an electronic computer. To process the experimental data, characteristics of 350 oil samples from various fields of the Soviet Union were used [1, 2]. In selecting indicators characterizing the properties of oils, we proceeded from the two principal directions of their refining: fuel and petrochemical. Such mutually correlated indicators may include the content of total sulfur, pour point, viscosity, density, flash point, ash content, coke-forming tendency, molecular weight, yield of fractions boiling up to 200°C and up to 300°C, paraffin content, and content of resinous-asphaltene substances in the oil. All the indicated characteristics are comparable and reliable, since they were obtained by standardized methods (GOSTs).
The statistical processing of the indices of oil properties consisted in calculating mean values, standard deviations, and identifying the maximum and minimum measurement results. The presence of a relationship between oil characteristics, as well as the closeness and direction of that relationship, was established from the magnitude and sign of the pair correlation coefficients \[3, 4, 5\]. Table I presents the results of statistical processing of indices of certain oil properties.
These data show that the closest relationships exist between oil density and viscosity, density and coking capacity, density and the yield of fractions up to \(200^\circ\mathrm{C}\), up to \(300^\circ\mathrm{C}\), density and molecular weight, density and the content of resin–asphaltene substances in the oil, between viscosity and molecular weight; the pour point of the oil and its paraffin content, coking capacity and the content of resin–asphaltene substances in the oil, molecular weight and the yield of fractions up to \(200^\circ\mathrm{C}\), up to \(300^\circ\mathrm{C}\). The least connected are the density and viscosity of the oil with the content of total sulfur, paraffin, and the pour point of the oil; the total sulfur content in the oil with the pour point, coking capacity of the oil, molecular weight, and paraffin content; coking capacity with paraffin content and the yield of light fractions; and the yield of light fractions with the content of resin–asphaltene substances. The pour point of the oil is determined mainly by its content of solid paraffin. The viscosity, density, and molecular weight of oil depend on its chemical composition. The larger value of the correlation coefficient between molecular weight and viscosity, compared with the correlation coefficient between density and viscosity, is apparently a consequence of the predominance, in the composition of petroleum hydrocarbons, of representatives of cyclanes and iso-alkanes, since the difference in the chemical nature of hydrocarbons affects viscosity somewhat more strongly than density at identical or similar molecular weights. The correlation coefficients between the content of total sulfur in the oil and the yield of fractions up to \(200^\circ\mathrm{C}\) and \(300^\circ\mathrm{C}\) are respectively \(-0.4\) and \(-0.2\). The distribution of sulfur among different distillate cuts of the same oil depends on the nature of the sulfur compounds. In addition, if the oil is distilled without decomposition, the sulfur content, as a general rule, increases from the lower cuts to the higher ones: the least of it is contained in gasoline, more in kerosene, and still more (usually more than 50% of all the sulfur) in fuel oil. In those cases where distillation of the oil proceeds with decomposition, the indicated
Table 1
Matrix of correlation coefficients
| Parameter | \(d_4^{20}\) | \(V_{20}\) | \(S_{\text{total}}\) | \(T_{\text{pour}}\) | \(K\) | \(P\) | \(M\) | \(b_{200}\) | \(b_{300}\) | \(CA\) |
|---|---|---|---|---|---|---|---|---|---|---|
| Density, \(d_4^{20}\) | 1 | 0,6 | 0,26 | 0,07 | 0,82 | −0,22 | 0,86 | −0,45 | −0,5 | 0,82 |
| Kinematic viscosity, cSt, \(V_{20}\) | 0,6 | 1 | 0,15 | 0,11 | 0,3 | −0,14 | 0,83 | −0,29 | −0,31 | 0,35 |
| Sulfur content, \(S_{\text{total}}\) | 0,26 | 0,15 | 0 | −0,13 | 0,08 | 0,17 | 0,27 | −0,4 | −0,2 | 0,82 |
| Pour point, °C, \(T_{\text{pour}}\) | 0,07 | 0,11 | −0,13 | 1 | 0,3 | 0,6 | 0,13 | −0,02 | −0,04 | −0,1 |
| Carbon residue, %, \(K\) | 0,82 | 0,3 | +0,84 | 0,3 | 1 | 0,2 | 0,59 | 0,25 | −0,15 | 0,91 |
| Paraffin content, %, \(P\) | −0,22 | −0,14 | 0,17 | 0,6 | 0,2 | 1 | 0,14 | 0,07 | −0,11 | 0,04 |
| Molecular weight, \(M\) | 0,86 | 0,83 | 0,27 | 0,13 | 0,59 | 0,14 | 1 | −0,55 | −0,45 | 0,26 |
| Distilled off up to 200°C, \(b_{200}\) | −0,45 | −0,29 | −0,4 | −0,02 | 0,25 | 0,07 | −0,55 | 1 | 0,37 | 0,076 |
| Distilled off up to 300°C, \(b_{300}\) | −0,5 | −0,31 | −0,2 | −0,04 | −0,15 | −0,11 | −0,45 | 0,37 | 1 | 0,142 |
| Content of aromatic–naphthenic hydrocarbons, % \(CA\) | 0,82 | 0,35 | 0,82 | −0,1 | 0,91 | 0,04 | 0,26 | 0,076 | 0,142 | 1 |
regularity may be violated.
Conclusions
-
The correlation dependences between ten principal parameters of the physicochemical characterization of oil have been investigated.
-
On the basis of correlation analysis, it is possible to select the arguments of regression equations for calculating the oil characteristics that are the most difficult, time-consuming, and inaccurately determined: the content of paraffin, resin-asphaltene substances, and molecular weight.
References
-
Oils of New Regions of the USSR. Reference book edited by S. I. Pavlova and Z. V. Dryatskaya. Moscow, “Khimiya,” 1967.
-
Oils of the Eastern Regions of the USSR. Reference book edited by S. I. Pavlova and Z. V. Dryatskaya. Moscow, “Khimiya,” 1962.
-
S. A. Aivazyan. Statistical Studies of Dependences. Moscow, “Metallurgiya,” 1968.
-
N. A. Plokhinskii. Biometrics. Moscow State University Press, 1970.
-
V. A. Silich, M. M. Shepelina. In: Cybernetics and Higher Education, issue 4, Tomsk Polytechnic Institute Press, 1970.