Influence of Various Factors on the Pour Point of Tomsk Oils
Abstract Generated abstract
This study examines factors affecting the pour point and solidification behavior of several Tomsk region oils and a reference mixture from the Nizhne-Vartovsk region. Using physicochemical characterization, heat treatment, cooling curves, and variation of cooling rates, the authors relate pour point behavior to the crystallization of paraffin hydrocarbons and the formation of coagulation structures. The results indicate that heat treatment can substantially lower pour points, while cooling curves show horizontal plateaus well above the pour point, attributed to staged paraffin crystallization. Within the experimental range, cooling rate did not change the crystallization temperature, but it influenced crystal size and shape, thereby affecting structural strength and rheological properties.
Full Text
INFLUENCE OF VARIOUS FACTORS ON THE POUR POINT OF TOMSK OILS
S. I. Smolyaninov, G. G. Krinitsyn, L. G. Gromova,
N. V. Yudina
(Presented by the scientific-methodological seminar of the organic departments of the Faculty of Chemical Technology)
It is known that preliminary heat treatment significantly lowers the pour point of oils, which depends mainly on the content of paraffin hydrocarbons. We investigated the influence of various factors on the pour point of Tomsk oils in order to study more deeply the processes occurring in oils during heat treatment.
The oils studied were those of the Yuzhno-Cheremshanskoye, Strezhevskoye, Krapivinskoye, and Luginetskoye fields of Tomsk Oblast, as well as a typical oil—a mixture of commercial oils from the Nizhne-Vartovsk region, whose general characteristics are given in Table 1.
The solidification of oils is caused above all by the formation of a structure from the solid paraffin hydrocarbons present in them. As a rule, solid oil paraffins consist for the most part of n-paraffins (paraffins from Far Eastern oils contain 98% n-paraffins). It is clear that the properties of solid paraffin are determined by the high content of n-paraffin hydrocarbons [1].
It is also known that naphthenic and naphtheno-aromatic hydrocarbons have comparatively high melting points and, like paraffin, separate from oils, forming crystals predominantly of the same shape [2].
When oils are cooled, paraffins separate according to definite temperature relationships (Fig. 1). Temperature plateaus on cooling curves are characterized by the serial precipitation of crystals of paraffin hydrocarbons, while the first crystals appear much earlier.
For example, in Krapivinskoye oil with a pour point of −27°C, temperature plateaus are observed at −4°C, while the first crystals appear at +2°C.
The presence of sharply pronounced horizontal plateaus indicates that the solidification of oil is caused by the formation of a coagulation structure which, encompassing the entire mass of oil, prevents its mobility. The coagulation structure in the original oils forms much earlier and more easily. This is explained by the presence in non-heat-treated oils of a certain amount of undissolved solid paraffins, which act as an additive during crystal formation.
The data obtained (Fig. 2) indicate that the cooling rate, minimal within the limits of the experiment, practically does not affect the temperature ...
Table 1
Physicochemical characteristics of oils
| Oil name | Density, g/cm³ | Molecular weight | Kinematic viscosity at 20°C | Kinematic viscosity at 50°C | Asphaltene content, % | Paraffin content, % | Resin content, %: silica-gel | Resin content, %: sulfuric-acid | Paraffin melting point, °C | Pour point, °C: without heat treatment | Pour point, °C: with heat treatment | Water content, % |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Krapivinskaya | 0,8522 | 194 | 6,67 | 3,41 | 1,79 | 1,39 | 8,14 | 20 | 52,3 | −27 | −50 | traces |
| Strezhevskaya | 0,8556 | 200 | 10,91 | 4,92 | 1,08 | 4,37 | 10,25 | 30 | 51,5 | −4 | −14 | traces |
| Luginetskaya | 0,8285 | 192 | 4,70 | 2,53 | 0,05 | 3,70 | — | 12 | 52,2 | −8 | −53 | traces |
| South Cheremshanskaya | 0,8395 | 176 | 5,06 | 2,68 | 3,59 | 2,057 | 7,15 | 40 | 50 | −26 | −32 | 0,6 |
| Tipovaya | 0,8589 | 205 | 8,66 | 4,35 | 1,47 | 3,37 | 9,61 | 31 | 55 | −14 | −43 | 1,0 |
Fig. 1. Cooling curves of Tomsk oils: — untreated; — — — heat-treated at 70°C.
1 — Yuzhno-Cheremshanskaya oil; 2 — Strezhevskaya oil; 3 — typical oil; 4 — Krapivinskaya oil.
stoppage. This situation is confirmed by theoretical considerations. With slow cooling of oil, crystal growth proceeds around the primary crystallization centers; few crystals are formed, and their size is correspondingly larger. At a high cooling rate, nu-
Fig. 2. Cooling curves of Tomsk oils at different cooling rates: — Yuzhno-Cheremshanskaya oil.
1. 3.5° per min. 2. 6.5° per min. 3. 12° per min. 4. 4° per min. (3, 4 — heat-treated)
— — — Strezhevskaya oil 5. 4.4° per min. 6. 11.2° per min.
there is a mass appearance of new crystallization centers; many small crystals are formed, but the small size is compensated for by aggregation under the action of resins [3].
Experiments have shown that the cooling rate affects the shape and size of the crystals. By changing the cooling rate, crystals of different shapes and sizes can be obtained and, consequently, a structural lattice of different strength, which affects the rheological properties of the oil.
Conclusions
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The cooling curves have sharply pronounced horizontal plateaus lying far above the pour point.
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The solidification of oils is explained by the formation of a coagulation structure from paraffins.
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The cooling rate does not affect the crystallization temperature, but it does affect the shape and size of the crystals, determining the strength of the structure and, consequently, the rheological properties of the oils.
References
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Mazes V. M. Paraffin, Its Composition and Phase Transformations of Its Main Components, Paraffinic Hydrocarbons of Normal Structure. Moscow, GOSINTI, 1960.
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Chernozhukov N. I., Vanshtein V. V., Kartinin B. G., Zezekalo V. Ya. “Chemistry and Technology of Fuels and Oils,” 1969, No. 3, pp. 15–18.
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Malin D. Zh. Crystals and Crystallization. Moscow, IL, 1966.