Influence of Various Factors on the Pour Point of Tomsk Oils
Abstract Generated abstract
This study examines factors affecting the low-temperature mobility, expressed as pour point, of oils from several Tomsk fields. Using standard pour point measurements, the authors tested the effects of heat-treatment temperature, cooling rate, holding time, water and salt content, and additions or removal of paraffins and silica-gel resins. The results indicate that cooling rate had little practical effect under the tested conditions, while heat treatment, especially near 70°C, substantially lowered the pour point of resin-rich oils but raised it in a paraffin-rich oil. Silica-gel resins acted as natural depressants, added paraffin increased pour point, and water and soluble salts adversely affected low-temperature properties.
Full Text
INFLUENCE OF VARIOUS FACTORS ON THE POUR POINT OF TOMSK OILS
S. I. Smolyaninov, L. E. Filippova, N. V. Nikolaeva
(Presented by the scientific-methodological seminar of the CTF)
The mobility of oil at low temperatures is of enormous importance in the processes of pumping and transporting it under winter conditions. It may also serve as a qualitative characteristic of the paraffin content in the oil.
The most widespread and accepted indicator of the mobility of petroleum products at low temperatures is their pour point. In particular, in petroleum-refining technology, the pour point is the principal criterion, standardized and monitored under production conditions, for the low-temperature properties of the products being produced [1].
The required low-temperature properties in a number of cases are achieved by a corresponding reduction in the pour point of the crude stock taken for processing.
In order to determine methods for lowering the pour point of petroleum products and crude oil, it is necessary to establish the presence of which components and the influence of which factors this parameter depends on. This question has not yet been studied sufficiently. It is known from the literature that the pour point depends to a significant extent on preliminary heat treatment of the oil [2, 3], and on the content of paraffin and asphalt-resin substances [4, 5, 6, 7, 8, 9], which are natural depressants.
The present work is devoted to studying the influence of various factors—heat treatment, oil composition, water and salt content, holding time, and cooling rate—on the low-temperature properties of several Tomsk oils.
Oils from the Sovetskoe, Sobolinoe, Sredne-Nyrolskoe, and Poludennoe fields were subjected to investigation.
The physicochemical characterization of the oils is given in Table 1. Determination of the pour point was carried out according to GOST 1533–42.
The influence of the cooling rate was determined as follows. Oil samples were heated in a thermostat at 50°C for 10 min, and then cooled at various temperatures of the refrigerating mixture, which was achieved by mixing liquid nitrogen and “Galosha” gasoline in different ratios.
When establishing the dependence of the pour point on the heat-treatment temperature, the oil samples under test were first held in a thermostat at various temperatures, after which the pour point was determined.
Table 1
Physicochemical characteristics of the oils
| Field | Specific gravity, \(d_4^{20}\) | Molecular weight | Kinematic viscosity, cSt, at temperature, °C: 20 | Kinematic viscosity, cSt, at temperature, °C: 50 | Asphaltene content, % | Silica-gel resins content, % | Sulfuric-acid resins content, % | Paraffin yield, % | Paraffin m.p., °C | Fraction yield, % by wt., up to 200°C | Fraction yield, % by wt., up to 300°C |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Sovetskoye | 0.8442 | 193 | 6.33 | 3.54 | 0.55 | 8.99 | 11.4 | 3.27 | 47 | 33.5 | 56.5 |
| Sobolinoye | 0.8611 | 209 | 12.72 | 4.34 | 2.21 | 6.18 | 22.0 | 3.30 | 47 | 24.1 | 43.4 |
| Poludennoye | 0.8498 | 181 | 6.89 | 3.22 | 1.10 | 3.58 | 18.0 | 4.50 | 48 | 32.8 | 56.4 |
| Sredne-Nyurolskoye | 0.8257 | 184 | 6.21 | 3.32 | 0.25 | 7.14 | 20.0 | 6.88 | 47 | 39.4 | 60.2 |
The influence of water content on the pour point of the oils was determined on samples in which the required amounts of water were added to dehydrated oil samples with vigorous shaking.
The determination of the influence of salt content on the pour point was carried out in two ways: in the first case, the necessary amount of sodium chloride was introduced into the oil samples (dehydrated), and the pour point was determined; in the second case, water was added to the oil together with the addition of salt.
The influence of silica-gel resins on the pour point of oils was studied as follows: artificial mixtures were taken as experimental samples; these were composed of de-resined oil and silica-gel resins isolated from the oil by the adsorption method (GOST 11858—66).
In determining the influence of paraffin on the pour point, commercial paraffin was added to the initial oil samples, after which the pour point was determined.
The influence of the holding time on oil samples heat-treated at 50°C was evaluated by determining the pour point after several days.
The data obtained are presented in Tables 2—5.
Table 2
Influence of holding time after heat treatment and of the oil cooling rate during heat treatment on the pour point
| Oil name | After heat treatment at 50°C | Pour point, °C, after holding for days: 1 | Pour point, °C, after holding for days: 2 | Pour point, °C, after holding for days: 5 | Pour point, °C, after holding for days: 6 | Pour point, °C, after holding for days: 7 | Pour point, °C, at cooling rate, deg/min: 1 | Pour point, °C, at cooling rate, deg/min: 3 | Pour point, °C, at cooling rate, deg/min: 5 | Pour point, °C, at cooling rate, deg/min: 7 | Pour point, °C, at cooling rate, deg/min: 9 and above |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Sovetskaya | −18 | −18 | −18 | −15 | −13 | −11 | −18 | −18 | −18 | −18 | −18 |
| Sobolinaya | −22 | −22 | −22 | −16 | −9 | −6 | −22 | −22 | −22 | −22 | −22 |
| Poludennaya | −10 | −10 | −10 | −9 | −8 | −7 | −10 | −10 | −10 | −10 | −10 |
| Sredne-Nyurolskaya | −4 | −4 | −4 | −5 | −7 | −8 | −4 | −4 | −4 | −4 | −4 |
As can be seen from Table 2, the cooling rate within the investigated range has practically no effect on the pour point of the oil, which apparently indicates the small influence of this factor under the given conditions on the mechanisms of paraffin crystallization and structure-forming processes. This circumstance has definite practical significance, since it makes it possible to simplify and accelerate the analysis for determining the pour point.
According to GOST 1533—42, the temperature of the cooling bath must be 2–4° below the pour point. This requirement makes it necessary to conduct preliminary experiments and complicates the thermostating technique, since thermostating at a variable temperature over a considerable interval is labor-intensive.
The established independence of the pour point of oils from the cooling rate makes it possible to work with a bath having a constant temperature, regardless of the pour point of the sample being tested. For these purposes it is convenient to use, as we did, a liquid-nitrogen medium.
Increasing the cooling rate by lowering the bath temperature also reduces the time required to carry out the analysis.
Table 3
Effect of heat-treatment temperature on the pour point of oils
| Heat-treatment temperature, °C | Soviet oil: pour point, °C | Sobolinaya oil: pour point, °C | Poludennaya oil: pour point, °C | Sredne-Nyurolskaya oil: pour point, °C |
|---|---|---|---|---|
| 20 | −6 | −4 | −6 | −8 |
| 30 | −9 | −8 | −8 | −6 |
| 40 | −13 | −15 | −9 | −5 |
| 50 | −18 | −22 | −10 | −4 |
| 60 | −26 | −28 | −18 | −1 |
| 70 | −36 | −37 | −35 | −1 |
| 80 | −29 | −31 | −30 | −2 |
From the data in Table 3 it may be noted that the Tomsk oils fully conform to the previously established regularities regarding the influence of heat-treatment temperature on the pour point. That is, for oils relatively rich in resins and poor in paraffins, such as Soviet, Sobolinaya, and Poludennaya, preliminary heating leads to a lowering of the pour point; conversely, in oils rich in paraffins, such as Sredne-Nyurolskaya, the pour point increases upon heat treatment.
For Tomsk oils, the well-known regularity is also observed according to which the heat-treatment temperature corresponding to the maximum lowering of the pour point lies within the range 30–70°C.
We carried out microscopic observations of paraffin crystals precipitated during cooling of Soviet oil without heat treatment and with heat treatment. It was found that the paraffin in the non-heat-treated oil has a fine-crystalline structure, whereas the heat-treated oil, upon cooling, forms larger paraffin crystals.
Thus, for the oils of the three deposits studied, a significant effect of lowering the pour point is observed upon heat treatment at 70°C. This effect is so substantial that, apparently, its possible practical significance should be discussed.
Without taking into account the influence of the holding time after heat treatment, it is impossible to resolve the question of the prospects for using the heat-treatment effect in practice. Based on the data of Table 2, it may be noted that the heat-treatment effect persists for several days; then the pour point of the heat-treated oils begins to rise, reaching the pour point of the original oils.
Thus, the heat-treatment effect persists for a sufficiently long period of time, which apparently may be used in transporting oil through pipelines.
Table 4
Effect of salt and water content on the pour point of oils
| Oil name | Salt content in dehydrated oil, %, 0.10 | Salt content in dehydrated oil, %, 0.25 | Salt content in dehydrated oil, %, 0.50 | Salt content in dehydrated oil, %, 1.00 | Salt content in non-dehydrated oil*, %, 0.01 | Salt content in non-dehydrated oil*, %, 0.1 | Salt content in non-dehydrated oil*, %, 1.0 | Water content, % relative to dehydrated oil, 0.00 | Water content, % relative to dehydrated oil, 0.25 | Water content, % relative to dehydrated oil, 0.50 | Water content, % relative to dehydrated oil, 1.0 | Water content, % relative to dehydrated oil, 2.0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sovetskaya | −6 | −2 | −1 | 4 | −1 | 2 | 5 | −6 | −2 | 0 | 1 | 3 |
| Sobolinaya | −4 | −3 | −2 | 1 | −3 | 0 | 3 | −4 | −2 | −1 | 0 | 2 |
| Poludennaya | −5 | −3 | 0 | 6 | −4 | 2 | 4 | −6 | −4 | −2 | −1 | 1 |
| Sredne-Nyurolskaya | −7 | −5 | 0 | 4 | −2 | 0 | 3 | −8 | −5 | −3 | −1 | 2 |
* In non-dehydrated oil the water content is 1.0%.
The influence of water and salt content is shown in Table 4. With an increase in the water and salt content within the investigated limits, the pour point rises. Unfortunately, the question of the influence of water and salts on the pour point has not been studied, but it may be assumed that water and salts also affect the mechanism of paraffin crystallization.
Table 5
Effect of additions of silica-gel resins and paraffin on the pour point of oils
| Oil name | Resin-free oil | Oil with resin addition in amounts relative to the original, wt. %, 25 | Oil with resin addition in amounts relative to the original, wt. %, 50 | Oil with resin addition in amounts relative to the original, wt. %, 75 | Oil with resin addition in amounts relative to the original, wt. %, 100 | Original oil, heat-treated | Oil with paraffin addition, wt. % of oil, 1 | Oil with paraffin addition, wt. % of oil, 2 | Oil with paraffin addition, wt. % of oil, 3 |
|---|---|---|---|---|---|---|---|---|---|
| Sovetskaya | 9 | 5 | 2 | −2 | −5 | −18 | 3 | 7 | 13 |
| Sobolinaya | 0 | −1 | −1 | −2 | −3 | −22 | 2 | 9 | 16 |
| Poludennaya | 2 | 0 | −2 | −3 | −4 | −10 | 4 | 6 | 9 |
| Sredne-Nyurolskaya | 1 | 0 | −1 | −2 | −3 | −4 | −1 | 8 | 10 |
Table 5 shows the influence of the content of resins and paraffin, from which it is evident that the addition of silica-gel resins to oil leads to a lowering of the pour point, since the content of natural depressants increases, while an increase in the paraffin content leads to a rise in the pour point.
Conclusions
-
The pour point of oils does not depend on the cooling rate, which makes it possible to use substances with lower temperatures as cooling baths and to carry out the analysis in a shorter time.
-
For oils relatively rich in resins, heat treatment leads to a lowering of the pour point; that is, the use of heat treatment is highly advisable when transporting and pumping oils at low temperatures.
-
The minimum pour point is achieved by heat treatment at 70°C.
-
Silica-gel resins may be regarded as natural depressants in oils; their removal leads to an increase in the pour point.
-
The presence of water and water-soluble salts has an unfavorable effect on the pour point.
References
-
S. S. Nametkin. Chemistry of Petroleum. Moscow, Publishing House of the Academy of Sciences of the USSR, 1955.
-
L. G. Gurvich. Scientific Principles of Petroleum Refining. ONTI, 1925.
-
V. N. Degtyarev. Proceedings of the GiproVostokneft Institute, issue 10, 35–37, 1967.
-
V. I. Chernikin. Pumping of Viscous and Congealing Oils. Moscow, Gostoptekhizdat, 1958.
-
V. M. Fokeev. Scientific and Technical Collection on Oil Production. Issue 2, 27–31, 1959.
-
B. T. Kotin and L. N. Stoyanovskaya. Proceedings of the Turkmen Branch of VNII NP, issue 5, 8–12, 1962.
-
V. V. Usachev. Urea Dewaxing. Moscow, “Khimiya,” 1967.
-
L. G. Gurvich. Scientific Principles of Petroleum Refining. Moscow, Gostoptekhizdat, 1940.
-
K. S. Ramaya. Viscosity of Liquids and Polymers. Vol. 2, ONTI, 1944.