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6ТЕХНИЧЕСКИЕ НАУКИ (TECHNICAL SCIENCE)
УДК 54.084
Gallamova A.E.
Master student of the Department of analytical, colloid chemistry and chemistry of rare elements Al-Farabi Kazakh national University (Kazakhstan, Almaty)
Kumargaliyeva S.SH.
Candidate of chemical Sciences, associate Professor of the Department of analytical, colloid chemistry and chemistry of rare elements Al-Farabi Kazakh national University (Kazakhstan, Almaty)
DEPENDENCE OF THE SURFACE TENSION ON THE TEMPERATURE AT DIFFERENT INTERFACES
Abstract: Surface tension is one of the main characteristics. The appearance of surface stress can be explained by the fact that the molecules of a substance (gas-liquid, liquid-solid) at the interface have more energy than the molecules in the volume of the phase. Surface tension is used to explain capillaries (the rise of a liquid into a capillary), moisture retention (whether the liquid is spreading over the surface or in the form of droplets), and many other areas. Surface tension plays an important role in the process of distillation (formation of bubbles during boiling) and purification of natural gas from hydrogen sulfide. The presence of hydrocarbons and the amount of surface stress determine the foaming of the processing agent, its degree of penetration and "overflow " of the treatment tower.
Keywords: surface tension, surfactant, interface.
Surface tension plays a particularly important role in the oil production process. Some substances used in these processes can reduce the surface tension of the liquid. This substance is called a surfactant.
Water-related carboxylic acids, alcohols, aldehydes, amines, proteins, and other organic compounds are surfactants. The structure of the surfactant molecule is as follows:
The circle denotes the polar group, and the tail denotes the non-polar hydrocarbon part.
This structure of the surfactant molecule is called amphiphilic, that is, the molecule is close to two phases (the parents ' sensations) with different polarities. Such molecules can be oriented (adsorbed) to the interphase boundaries and balance the polarity of these phases, thereby reducing the surface tension between them.
The importance of surfactants used in the oil and gas industry is due to the need to increase oil recovery (ER) of the reservoir. Under favorable physical and geological conditions, the recovery rate usually does not exceed 40%.
There are many ways to extract oil and increase the degree of recovery, among which the method of physical and chemical filling of water with surfactants has become popular. These processes are accompanied by complex physical and chemical micro-processes, and understanding and accounting for these processes depends on the development of the well and additional processing methods and the degree of recovery of hydrocarbons from the reservoir.
Surface tension refers to the thermodynamic properties of the interface, which is defined as the work of a reversible isothermal structure of cells that are flat on the surface. For liquids, it is assumed that the surface tension affects the unit length of the surface profile and tries to minimize the surface force at a given phase volume.
The oil is a dispersed oil system consisting of a dispersed phase and a dispersing medium.
On the surface of particles of the dispersed phase (for example, in the Association of asphaltenes, water spheres, etc.), there Is a certain excess surface energy Fs, which is proportional to the surface layer of the interface S:
The value D can be considered not only as a specific surface energy, but also as a force applied to the surface in a direction perpendicular to the contour and to the length of the contour that is trying to tighten or reduce the surface. This force is called surface tension.
Схема поверхностного натяжения
The effect of surface tension can be graphically represented as a set of forces that attract the edge of the surface to the center.
The length of each vector arrow represents the amount of surface tension, and the distance between them corresponds to an acceptable unit of face contour length. D is used as the size [j / m2] = 103 [erg / cm2], [N / m] = 103 [DIN / cm].
Due to the influence of surface tension, the liquid tends to lower its surface, and if the gravity is small, the liquid has a spherical shape, and the surface area per unit volume is minimal.
The surface tension of different hydrocarbon groups is different - the maximum value of aromatic compounds and the minimum value of paraffin. As the molecular weight of the hydrocarbon increases, it increases.
Many heteroatomic compounds are polar and have a lower surface tension than hydrocarbons. This is very important because their presence plays an important role in the formation of water-oil and gas-oil emulsions and the subsequent decomposition of these emulsions.
Parameters affecting surface tension
The surface tension depends significantly on the temperature and pressure, as well as on the chemical composition of the liquid and the phase in contact with it (gas or water).
As the temperature increases, the surface tension decreases and at the critical temperature is zero. As the pressure increases, the surface tension in the gas - liquid system also decreases.
The surface tension of petroleum products can be calculated using the equation:
or
The conversion of a from one temperature T0 to another T can be performed by the ratio:
Surface tension values for some substances.
Substances whose addition to a liquid reduces its surface tension are called surfactants (surfactants).
The surface tension of oils and petroleum products depends on the amount of surfactant contained in them (resin, naphthenic acid, other organic acids, etc.).
Petroleum products with a low content of active ingredients have the highest surface tension value at the water interface and the lowest content with the highest content.
Refined petroleum products have a high voltage when interacting with water.
The decrease in surface tension can be explained by the adsorption of surfactants at the interface. As the concentration of the added surfactant increases, the surface tension of the liquid first decreases rapidly and then stabilizes, indicating that the surface layer is completely saturated with molecules. Natural surfactants that can radically change the surface tension of oils and petroleum products are alcohols, phenols, resins and various organic acids.
Humidification and capillary phenomena are related to surface forces in the interaction of the solid and liquid phases, including oil migration in the reservoir, the rise of kerosene and oil along the oil outlet from the lamp and oil lamp.
Experimental determination of surface tension
In practice, different methods are used to determine the surface tension of oil and petroleum products.
p^oi
а б в г
Методы определения поверхностного натяжения:
о —отрыв кольца; б— капиллярный; в — падение капли; г — наибольшее давление пузырька
The first method (a) is based on measuring the force required to obtain a ring from a two-phase interface. This force is proportional to the double circumference of the ring. The capillary method (b) measures the height of the liquid in the capillary. The disadvantage is that the height of the liquid rise depends not only on the surface tension, but also on the wetting properties of the capillary wall of the studied liquid. The most accurate version of the capillary method is the suspension method (C), which is based on measuring the mass of a drop of liquid exiting the capillary. The measurement result depends on the density of the liquid and the size of the drops, but not on the wetting angle of the liquid on a solid surface. Using this method, you can determine the surface tension in the pressure vessel.
The most common and convenient method for measuring surface stress is the maximum pressure (g) method of bubbles or drops. The interpretation of this method is simple construction, high accuracy and lack of moisture.
This method is based on the fact that when a bubble or drop of a drop is released from a narrow capillary into another liquid, the stress of the drop contacting the flowing liquid is proportional to the maximum pressure required to create the drop.
The surface tension o is included in the expression for the so-called parahor P-the value that binds the molecular mass M of hydrocarbons and their density in the liquid phase of the RJ and in the vapors of the RP:
The parachor of hydrocarbons depends on the structure of their molecules: with an increase in the number of side chains, double bonds, aromatic and naphthenic cycles, the parachor value decreases. At the same boiling point of hydrocarbons, the parachor decreases in the following order: paraffins-olefins - naphthenes - aromatic hydrocarbons.
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