METHODS AND MEANS OF MEASUREMENT OF HUMIDITY OF OIL

Аннотация

The article provides an overview of the methods and techniques for measuring oil moisture content. Thus, more information is given to Dina- Starka, dielectric, optical and electrical techniques. The above methods are covered in detail and there are conclusions and points about the advantages and disadvantages of the mass. Keywords: direct methods, indirect methods, Dean-Stark method, conductometric method, mass fraction of moisture. Water in oil can be in three forms: dissolved, dispersed and free. The content of dissolved water mainly depends on the chemical composition of oil, oil products and temperature. With increasing temperature, the solubility of water increases in all hydrocarbons. Methods for determining water in oil and petroleum products can be divided into two groups: qualitative and quantitative. Method for determination of water content (Dean-Stark method) The essence of the method is to distill the mixture of the test sample of oil and solvent, which is not miscible with water, and measure the volume of water condensed in a Dean-Stark trap. [1] The conductometric method is based on the dependence of the conductivity of the material on its moisture content. Pure water has a relatively low electrical conductivity (electrical resistivity at (20 ° C, 22 ∙ 106 Ohm ∙ cm). But due to the dissociation of electrolytes when they dissolve in water, the conductivity of the solution increases by several orders of magnitude. Thus, the conductivity of a wet 75 Scientific research results in pandemic conditions (COVID-19) material is determined primarily electrolytes contained in the material itself. Moisture-containing materials that, when dry, are dielectrics with electrical resistivity 10-15 ÷ 10-10 Ohm ∙ cm and more, when moistened, they become semiconductors. The electrical resistivity is reduced to 10-3 ÷ 10-2 Ohm ∙ cm. Humidity measurement is reduced to measuring the electrical resistance of the primary transducer. The nature of the dependence of the electrical resistance of the primary converter on the humidity of the solid organic material has the form shown in Fig. 3. In this regard, the conductometric method is used for measurements of low and medium humidity. The lower limit of measurement is limited by the difficulties of measuring very large resistances. For most materials, this corresponds to a moisture content of about 5 ... 8%. Fig. 1. The nature of the dependence of the electrical resistance of a solid material on moisture: W is the mass fraction of moisture; lgR - electrical resistance of the primary converter, Ohm At low and medium humidity, a sharp dependence of resistance on humidity appears, which ensures high sensitivity of the moisture meter in this humidity range. With high humidity, sensitivity decreases. Therefore, factors not related to the moisture content of the analyte (chemical composition, structure, etc.) influence the measurement result. In non-aqueous liquids, the dependence of the electrical conductivity in a narrow range can be almost linear. The electrical conductivity of wet materials, as mentioned above, is determined by the content of electrolytes in them, which, when dissolved in water, decay into ions. Electrolytes are conductors of an electric current of the second kind. The passage of electric current is determined by the movement of ions and is accompanied by chemical reactions - electrolysis. In this case, a change in the potential of the electrodes occurs - polarization. To eliminate the effect of polarization on the measurement result, in most cases, the resistance measurement is carried out on alternating current. 76 Scientific research results in pandemic conditions (COVID-19) The conductivity of materials is greatly influenced by temperature. Therefore, in the means of measuring the humidity of materials should be provided for temperature compensation or stabilization of the temperature of the analyzed materials [2]. The dielcometric (capacitive) method is based on the special electrical properties of water. Water has a number of structural features and properties that distinguish it from other substances. One of the abnormal properties of water is a very high dielectric constant. The dielectric constant of free water is ~ 80. For most solids ε <10, for liquids ε <10 ÷ 20. The dielectric constant of water depends on its state. When bonded, water loses its mobility in an electric field, and its dielectric constant decreases. For chemically bound water, ε = 4.5 ÷ 4.9. Wet material can conditionally be represented as a two-component mixture with a dielectric constant ε_cm, which is determined by the expression 𝜀 = 𝜌 𝜀 +𝜌 𝜀 см в в с с where ε_vi ε_c is the dielectric constant of water and dry material; ρ_в and ρ_с — volumetric concentration of water and dry material. The dependence of the dielectric constant of some solid materials on moisture is shown in Fig. 4. The primary transducer of the dielcometric moisture meter is a capacitor. The capacity of the ca