SU1032402A1 - Mass transfer coefficient measuring method - Google Patents

Description

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9U8. 1 The invention relates to measuring the speed of mixing of liquid media, 8 in particular to the determination of the mass-transfer coefficient for estimating the intensity of mixing of a solution in apparatus with stirrers (reactors) used in the chemical and microbiological industry. A known method for determining the mass transfer coefficient lj for estimating the intensity of mixing of the solution in the reactors by the speed of the process of oxygen chemisorption with sodium sulfite solution. Let us understand the mass transfer coefficient (CCP) is determined by the rate of change in the concentration of sul phyt sodium with stirring of the solution in the presence of AI of oxygen. Taking a sample of the solution from the apparatus after a certain period of time and analyzing it for the content of sulfite, calculate the coefficient of mass transfer in the apparatus ОOv ;; r the amount of reacted sulfite; the volume of the solution in the apparatus; time between sampling; oxygen partial pressure in the apparatus. The disadvantages of the method include the complexity and duration of the analysis, the change in the rate of oxidation of sulfite in the presence of a number of ions, for example Cu (P), the error increasing at high mixing intensities. Closest to the present invention is a method for measuring the mass transfer coefficient of a solution in apparatus with agitators using electrochemical sensors. The method is carried out as follows. After preliminary extraction of oxygen from the solution (up to zero readings of the secondary device), the apparatus sets the required mixing mode, turns on the oxygen supply and removes the curve of the sensor readings over time. In the second stage of the experiment, the curve of change is shown showing the scientific research institutes of the device due to the inertia of the sensor. For this, a cap with a sodium sulfite solution is put on its membrane part (secondary device fixes no dissolved oxygen. Then a solution saturated with oxygen at a given temperature and partial pressure is poured into the apparatus. The required mixing mode is set and the cap is removed from the sensor. 5 and 8a of the sensor in this flow mode. The mass transfer coefficient is defined as the reciprocal of the surface of the figure formed by the change curve. The concentration of oxygen and the inertial curve of the sensor C ZD to determine the surface of the figure are necessary using a computer to solve a number of third and fourth order differential equations. "The known method is very complicated, time consuming, and also implies free access to the place of attachment of the sensor on the inner surface of the device and complicated by cumbersome calculations. Determining the coefficient of mass transfer in two stages reduces the accuracy of the method. The purpose of the invention is to simplify the measurement, the goal is achieved because Specifically measuring the mass transfer coefficient of a solution in apparatus with agitators using electrochemical sensors, the cathode is supplied with the potential of the limiting current of the electrochemically active substance, its limiting current is measured, and the coefficient of mass transfer is determined as proportional to the ratio of the limiting current to the concentration of this substance. Measurements are carried out using an electrolyte, the optimum composition of which is, g / l: 0.01 - 0.02, 0, 0.02 - 0.06 5-10. The decrease or increase in the concentrations of the above components affects the extent, the plateau of the limit current, reducing the measurement accuracy. In this case, an indicator electrode consisting of a cathode and an anode is used, the cathode being made of copper-plated platinum with a diameter of 5 mm and a length of 5-10 mm, and the anode in the form of a spiral. The ratio of the cathode and anode surfaces is 1:10 - 1:20, and the cathode operating potential is 1.1-1.2 V, Copper is introduced into the solution in the form of a sulfate salt. To prevent copper from being cemented on the steel parts of the apparatus into a solution of E, 3 t of complexant is sodium pyrophosphate. Simultaneously with the copper at the cathode, dissolved oxygen can be reduced to introduce an error in the measurement results. Therefore, sodium sulfite is added to the solution to restore the dissolved oxygen. Figure 1 presents the indicator electrode; Fig. 2 shows a volt-ampere curve of reduction of Cu (P) at an electrolyte stirring speed of 3500 rpm; Fig. 3 shows an electrical circuit for connecting an indicator electrode; in fig. - curves for determining mass transfer coefficients by sulfite (Q) and proposed (5 methods in installations of various types. The indicator electrode was a glass tube with a diameter of mm of arbitrary length and shape, at the end of which the cathode 2 and anode 3 were fused) plates allow each new series of experiments to compare the old sediment and precipitate a new one without changing the electrode surface.The use of electrodes of arbitrary length and shape makes it possible to introduce them to any point of the reactor for In this case, the electrode does not introduce significant distortions into the overall flow pattern in the reactor. The proposed electrochemical method for estimating mass transfer is similar to the laws describing the rate of dissolution or chemisation of oxygen and the rate of reduction of a substance at the limiting current KbO (Co – Co) where R is the rate of dissolution of oxygen 8 per unit volume of liquid; a constant equivalent to the diffusion coefficient; phase interface; (Cc, -Cd) - oxygen concentration; h is the thickness of the diffuse film at the gas – solution interface. The values of a and h cannot be determined and they are combined with K j in an expression, which is usually written as: (.) L g r 0 - o,. 3) 5 () where Q is the substance recovery rate; D is the diffusion coefficient; S is the electrode surface; C is the concentration of a substance in the electrolyte volume; GO is the concentration of a substance on the electrode surface; o is the thickness of the diffusion layer; Comparison of equations (3) and (4) shows the similarity of Ktalli and) 5 / sG The value of the current flowing in the electrochemical system is related to the speed of restoration of a substance by the relation (5; From equations (k} and (5) the expression, S5CCo-Cg) bF.,. SG follows. Since S (CQ-CQ) - nF in equation (6) is constant, the change in current depends on the ratio D / cT, the value of which is determined only by the mixing mode This makes it possible by the value of T to judge the intensity of mixing in the apparatus. To determine the mass transposition, In this way, it is necessary to set the working potential of the electrode, lIpQg-, corresponding to the site of the current limit on the polarization discharge of a substance (Fig. 2L. The speed of the electrochemical reaction and the amount of current flowing through the electrochemical system will be determined only by the speed of the substance delivery to the electrode i.e. the intensity of the mixing of the solution. To measure the intensity of the interchange, an electric

circuit (Fig. without the use of potentiostating devices.

Example. , To determine the intensity of mixing in reactors of different types. An electrolyte of composition is used, g / l: CuS04 5 HO0.01

Ma2P2.b7

0.02

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On, 0h

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The cathode of the electrode has a diameter of 0.5 mm and a length of 7 mm, the working potential of the cathode is 1.2 V. The current measurement curves (Fig.) Were obtained in a reactor with a radial-mixing stirrer in a flow-type reactor, and the curves of the mass transfer coefficient were obtained. in a known manner in the same erty reactors. Similar character

Keny curves provide experimental confirmation of the possibility of using an indicator electrode method to estimate the intensity of mixing.

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The proposed method is simple and accessible in operation, does not require lengthy analyzes or calculations, the measured values do not change with time, and also provides the ability to measure the intensity of mixing at any point of the apparatus, which can be placed indicator electrode. This makes it possible

5 to intensify the process of mass transfer due to the detection of zones with low mixing intensity. The lack of GZ proposed method of analytical definitions contributes

0 increase its accuracy.

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Claims (1)

METHOD FOR MEASURING THE MASS TRANSFER OF THE SOLUTION in devices with stirrers using electrochemical sensors, ”* 0 which is found to, in order to simplify the measurement, apply the maximum current potential of the electrochemically active substance to the cathode, measure its ultimate current and determine the mass transfer coefficient as a value proportional to the ratio limiting current to the concentration of this substance. LLC 000 FIG. 1 1 1032402