Effect of Paraffin Content, Naphthenic Acids, Mechanical Mixing, and Heat Treatment Temperature on the Pour Point of Western Siberian Oils
Abstract Generated abstract
This study examines factors affecting the pour point of Western Siberian crude oils, focusing on heat treatment, paraffin content, naphthenic acids, and mechanical stirring. Using samples from several oil fields, the authors measured pour points after controlled heating and cooling, compositional modification by paraffin addition or acid removal, and cooling under static and dynamic conditions. The results indicate that heat treatment can lower pour point for several days, added paraffin raises it, and naphthenic acids appear to act as natural depressants. Mechanical stirring temporarily reduces pour point, but the effect disappears within about an hour, suggesting a role for thixotropic structures in oil solidification.
Full Text
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The calculated regression equations adequately describe the true relationships.
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The regression equations make it possible, with accuracy sufficient for practical purposes, to predict the yield of light petroleum fractions.
References
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S. S. Nametkin. Chemistry of Petroleum. Moscow, Publishing House of the Academy of Sciences of the USSR, 1955.
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Petroleums of the Eastern Regions of the USSR. Edited by S. N. Pavlova and Z. V. Driatskaya. Moscow, Gostoptekhizdat, 1962.
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New Petroleums of the Eastern Regions of the USSR. Edited by S. N. Pavlova and Z. V. Driatskaya. Moscow, “Khimiya” Publishing House, 1967.
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Petroleums of the USSR, vol. I. Edited by S. N. Pavlova and Z. V. Driatskaya. Moscow, “Khimiya” Publishing House, 1971.
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M. A. Plokhinskii. Biometrics. Moscow State University Publishing House, 1970.
Effect of Paraffin Content, Naphthenic Acids, Mechanical Stirring, and Heat-Treatment Temperature on the Pour Point of Western Siberian Crude Oils
N. V. Nikolaeva, S. I. Smolyaninov
One of the important operational characteristics of crude oils and petroleum products, giving an indication of the mobility of these materials at low temperatures, is the pour point (GOST 1533–42), which, however, is not regarded as a physical constant [1].
Studies have established the influence of various factors on the pour point of crude oils [2–4]. Western Siberian crude oils are the least studied object in this respect.
Using a number of crude-oil samples from various fields (Table I), we studied the influence of heat-treatment temperature, paraffin content, naphthenic acids, and mechanical stirring on the pour point.
The heat-treatment process consisted in heating the crude oil to a specified temperature, followed by cooling to room temperature. The preservation of the temperature-depression effect after heat treatment was evaluated for the crude oils over several days.
Physicochemical characteristics of oils
Table 1
| Oil field | Density, g/cm³ | Molecular mass | Kinematic viscosity, cSt at 20°C | Kinematic viscosity, cSt at 50°C | Pour point of base oil, °C | Content, %: resins | Content, %: silica-gel resins | Content, %: asphaltenes | Content, %: paraffins | Melting point of paraffins, °C |
|---|---|---|---|---|---|---|---|---|---|---|
| Sovetskaya | 0,8442 | 193 | 6,33 | 3,54 | -6 | 11,4 | 8,99 | 0,55 | 3,27 | 47,6 |
| Sobolinaya | 0,8611 | 209 | 12,72 | 4,34 | -4 | 22,0 | 6,18 | 2,21 | 3,30 | 47,0 |
| Olenya | 0,8350 | 174 | — | 2,73 | -17 | — | 6,08 | 2,15 | 1,30 | 48,0 |
| Poludennaya | 0,8498 | 181 | 6,89 | 3,22 | -6 | 18,4 | 3,58 | 1,10 | 4,50 | 48,0 |
| Luginetskaya | 0,8285 | 182 | 4,70 | 2,53 | -8 | 12,0 | — | 0,05 | 3,70 | 52,5 |
| Vartovskaya | 0,8128 | 154 | — | 2,87 | 11 | — | 3,93 | 0,80 | 17,68 | 49,0 |
| Samotlorskaya | 0,8525 | 213 | — | 4,48 | -11 | — | 8,53 | 1,09 | 3,64 | 54,0 |
| Sredne-Nyurolskaya | 0,8257 | 184 | 5,64 | 2,97 | -17 | 12,2 | 5,0 | 0,82 | 6,20 | 38,0 |
The study of the effect of the chemical composition of oils on the pour point was carried out on samples prepared by the following procedure. Technical paraffin was introduced into the original oil with heating and vigorous stirring. As experimental samples for establishing the effect of naphthenic acids, the original oils and oils from which the latter had been removed were taken.
To study the effect of mechanical stirring during the cooling of oil, its pour point was determined under static and dynamic conditions.
The results obtained are given in Tables 2–4.
As follows from Table 2, heat treatment significantly lowers the pour point, which makes it possible to speak of the possibility of its practical application. However, without taking into account the time over which the temperature-depression effect persists, it is impossible to decide the question of the prospects for its use in practice.
According to the results of the study, it was established that the pour-point values acquired as a result of heat treatment are stable for several days. This, consequently, makes it possible to assume the use of the heat-treatment effect in oil transportation.
Table 3 shows the effect of the chemical composition of oil on the pour point.
As is known, the pour point of oils is determined by the complex of components included in their composition and depends to a considerable extent on the amount of paraffin in them. From the data in Table 3 it is evident that small additions of the latter substantially increase the pour point, which, in turn, can be used when it is necessary to reduce oil mobility.
Attention is drawn to the fact that a small content of naphthenic acids greatly lowers the pour point of oil. In all likelihood, naphthenic acids are natural depressants. Their action is reduced to adsorption on paraffin crystals, lowering the surface tension. In this case, evidently, the growth of paraffin crystals is inhibited to some degree.
It is interesting to note the effect of mechanical stirring of the oil on the pour point. As a result of cooling the oil under dynamic conditions (Table 4), the pour point is [[unclear: text continues on next page]].
Table 2
Effect of holding time on the pour point of thermally treated oils
| Oil | Pour point of the original oil, °C | Pour point, °C: holding time in the hot state after heat treatment at 50°C, h — 0 | Pour point, °C: holding time in the hot state after heat treatment at 50°C, h — 1 | Pour point, °C: holding time in the hot state after heat treatment at 50°C, h — 2 | Pour point, °C: holding time in the hot state after heat treatment at 50°C, h — 3 | Pour point, °C: holding time in the hot state after heat treatment at 50°C, h — 4 | Pour point, °C: holding time in the hot state after heat treatment at 50°C, h — 5 | Pour point, °C: holding time in the cold state after heat treatment, h — 1 | Pour point, °C: holding time in the cold state after heat treatment, h — 2 | Pour point, °C: holding time in the cold state after heat treatment, h — 3 | Pour point, °C: holding time in the cold state after heat treatment, h — 4 | Pour point, °C: holding time in the cold state after heat treatment, h — 5 | Pour point, °C: after 50°C, days — 6 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| [[unclear: …nartovskaya]] | 11 | 9 | 9 | 9 | 9 | 10 | 11 | 9 | 9 | 9 | 10 | 12 | 12 |
| Sredne-Provskaya | -17 | -29 | -29 | -29 | -28 | -28 | -27 | -29 | -29 | -28 | -24 | -20 | -18 |
| Sovetskaya | -6 | -15 | -15 | -15 | -15 | -14 | -14 | -15 | -15 | -15 | -12 | -8 | -4 |
| [[unclear: oil name ending in “-oleya”]] | -17 | -30 | -30 | -30 | -30 | -28 | -28 | -30 | -30 | -30 | -30 | -28 | -23 |
| Samotlorskaya | -11 | -4 | -4 | -4 | -4 | -3 | -1 | -4 | -4 | -4 | -3 | 1 | 2 |
| Mutinskaya | -8 | -14 | -14 | -14 | -14 | -12 | -11 | -14 | -14 | -14 | -14 | -13 | -10 |
Table 3
Effect of paraffin and naphthenic-acid content on the pour point
| Oil | Paraffin content in oil, % | Naphthenic-acid content in oil, % | Pour point, °C: paraffin content, % of oil — 1 | Pour point, °C: paraffin content, % of oil — 2 | Pour point, °C: paraffin content, % of oil — 3 | Pour point, °C: in the presence of naphthenic acids | Pour point, °C: in the absence of naphthenic acids |
|---|---|---|---|---|---|---|---|
| Sovetskaya | 3,24 | 0,027 | 3 | 7 | 13 | −6 | 8 |
| Sobolinaya | 3,30 | 0,003 | 2 | 9 | 16 | −4 | 10 |
| Poludennaya | 2,10 | 0,056 | 4 | 6 | 9 | −6 | 7 |
| Sredne-Nirolskaya | 6,88 | – | −1 | 8 | 10 | −8 | −3 |
Table 4
Effect of mechanical action on the pour point
| Oil | Pour point, °C: without stirring | Pour point, °C: with stirring | Pour point, °C: holding time after stirring, h — 0,5 | Pour point, °C: holding time after stirring, h — 1 |
|---|---|---|---|---|
| Samotlorskaya | −11 | −17 | −17 | −11 |
| Vartovskaya | 11 | 7 | 6 | 11 |
| Sovetskaya | −7 | −8 | −8 | −7 |
| Olenya | −17 | −22 | −21 | −17 |
| Sredne-Nirolskaya | −1 | −5 | −4 | −1 |
| Putinetskaya | −22 | −24 | −24 | −22 |
decreased by several degrees. However, the pour point returned to its initial value one hour after mechanical stirring, which quite definitely indicates the role of thixotropic structures in the loss of mobility by oil.
Conclusions
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It has been shown that the pour point of Western Siberian oils decreases in the presence of naphthenic acids, increases with increasing paraffin content, and returns to its initial value some time after mechanical stirring, which indicates the role of thixotropy in the solidification of oil.
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It has been established that, for the oils studied, the duration of preservation of the temperature depression lasts several days.
Literature
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S. S. Nametkin. Chemistry of Oil. Moscow, Publishing House of the Academy of Sciences of the USSR, 1955, p. 46.
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T. P. Zhuze. “Colloid Journal,” 1950, 12, no. 4, 265–274.
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O. M. Al’chikov, V. P. Konovalov. Proceedings of the Institute of Petroleum Chemistry and Natural Salts, Academy of Sciences of the Kazakh SSR, 1971, 3, pp. 96–99.
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Kh. A. Akhmedzhanov, B. U. Urazgaliev, O. M. Al’chikov. Proceedings of the Institute of Petroleum Chemistry and Natural Salts, Academy of Sciences of the Kazakh SSR, 1970, 1, 46–49.
On the Analysis of the Temperature Dependence of Anodic Peaks in the PSA Method
S. N. Karbainova
Earlier /1–5/ we studied the temperature dependence of the height ($i$) and coefficient of the anodic peak ($K_a$), the half-peak width ($\delta_{1/2}$), and the peak potential ($\psi_n$) over a wide range of changes in the rate of potential variation ($w$) and electrode dimensions, both for a mercury film electrode ($\ell$ — thickness of the mercury film) and for a stationary mercury drop electrode ($r$ — drop radius). The results of these studies made it possible to reveal the complex nature of the temperature dependence of the above-mentioned