The method of manufacture of gas mixtures by the dynamic method

 

(57) Abstract:

The invention relates to the study and analysis of gases, in particular to a method for preparing gas mixtures by the dynamic method used for calibration of gas analyzers. The technical result of the invention is the extension of the range of the prepared gas mixtures, in particular in the region of low concentrations of the gas being detected. The inventive method comprises the electrolysis of aqueous solutions of electric shocks, subjected to pulse width modulation to obtain a rectangular pulse with the same amplitude (power) supply, mixing highlighted in the electrolysis gas with a known volume of the diluent gas and the calculation of concentration of the selected gas according to the formula: where C is the concentration of the selected gas in the gas mixture, g/l; K-electrochemical coefficient of the selected gas, g/Ah; IA-the amplitude (power) current, A; V is the volume of the gas mixture per unit time (flow rate), l/h; - the width of the current pulses, C; T is the period of oscillation of the current, C. 1 Il.

The invention relates to the study and analysis of gases, in particular to a method for preparing gas mixtures by the dynamic method used for calibration of gas analyzers.

Known the see gas and the diluent gas. Gases pass from the cylinders under pressure, their control and regulate the use of rheometers or similar devices (Eremina, B. Gas analysis. GENTIL, L. , 1955, S. 88).

The disadvantage of this method is the need to have the cylinders with the source gases guaranteed purity and complex instrumentation.

Known analogues closest to the claimed method according to the totality of symptoms is a method for preparing gas mixtures by the dynamic method of obtaining the designated gas by electrolysis of aqueous solutions (Ariskin A. C. Dynamic installation for the preparation of hydrogen-helium gas mixtures with a trace of hydrogen. - Sat: Second Vsesojuzn. conference on analysis of inorganic gases. Abstr. 1-5 Oct. 1990 L., 1990, S. 161).

The way the prototype is the following. To obtain a defined gas-hydrogen perform electrolysis of water by direct current in a special cell; the cell continuously served the gas diluent (helium). The amount of hydrogen supplied to the gas flow, calculated according to the amount of current passing through the electrolytic cell, in accordance with Faraday's law, and the concentration of podoroskoe value DC in time, which illustrates the method of producing gas mixtures according to the prototype. The concentration selected in the electrolysis gas in the gas mixture is calculated in accordance with Faraday's law according to the formula (1)

< / BR>
where C is the concentration of the selected gas in the gas mixture, g/l;

K - electrochemical factor of the selected gas, g/Ah;

IA- the amplitude (strength) of the current, AND;

V is the volume of the gas mixture per unit time (flow rate), l/h

The prototype preparation of gas mixtures with known low concentrations of less than 110-4mol.% hydrogen by changing (reducing) the current supplied to the electrolytic cell, becomes impossible. By reducing the magnitude of the electric current below a certain value at the electrodes of the electrolyzer, the role of polarization effects, resulting in electric current is consumed not only receiving the gas to be detected, but also other competing processes, and the calculation of concentration of the selected gas in the gas mixture produced by the formula (1) using electrochemical equivalent of hydrogen becomes wrong.

The claimed invention (method of preparation of gas mixtures given concentration dynamic method) is s for the calibration of analytical instruments-analyzers.

This objective is achieved in that in the method of preparation of gas mixtures by the dynamic method, including the electrolysis of aqueous solutions of electric shock, mixing highlighted in the electrolysis gas with a known volume of the diluent gas and the concentration of the selected gas in the mixture, it is new that the electric current pre subjected to pulse width modulation, producing a current in the form of rectangular pulses with the same amplitude (power) of the current, and the concentration of the selected gas is determined by the formula (2)

< / BR>
where C is the concentration of the selected gas in the gas mixture, g/l;

K - electrochemical factor of the selected gas, g/Ah;

IA- the amplitude (strength) of the current, AND;

V is the volume of the gas mixture per unit time (flow rate), l/h;

- the width of the current pulses;

T is the period of oscillation of the current, with.

In Fig. 1(b) and 1(b) presents the dependence of the current intensity (amplitude) from the time after the preliminary power conversion using the method of pulse-width modulation, which underlies the invention. Electrical current is delivered into the cell the same pulse width (), amplitude (IAand period of oscillation (T). It is evident from Fig. 1(b) and the electrolyzer, reduced. This allows for a constant amplitude of the electric current (IA), to decrease the concentration of emitted during electrolysis gas in the gas mixture.

The optimal value of IAfor maximum gas output current, is determined experimentally, since it depends on the chemical nature of gas emitted, temperature, composition of the aqueous solution of the material of the electrodes, the structure of the cell and other factors.

The invention allows to expand the range of concentrations of gas mixtures in the region of low values of gas emitted. For this purpose, we first experimentally chosen large enough amplitude (power) of the current, which provides a maximum output current of gas emitted, and competing processes of polarization of the electrodes at a given amplitude (in some range) are negligibly small. Admission into the cell electric current is subjected to pulse width modulation, identical rectangular pulses, but with a different period of oscillation of the DC (T), allows a large interval to change the amount of electricity supplied per unit time in the cell, including very small values, not sneham gas; calculation of gas concentration in the mixture is conducted according to the formula (2).

Example. Experimental verification of the invention in comparison with the prototype was carried out during the preparation of chlorine gas mixtures with air. Allocated gas chlorine was obtained by electrolysis of 0.1-1.0 molar hydrochloric acid solution containing 30 wt.% lithium chloride.

The cell consisted of two glass vessels, separated by a diaphragm, two platinum electrodes (cathode, anode); the power of the cell was made from a stabilized DC power source. During electrolysis in the same vessel (at the cathode) was allocated hydrogen, and the other at the anode chlorine. In a vessel with chlorine continuously using a pump with the capacity of 15 l/h missed the air, as a result of the vessel was a mixture of chlorine with air. The concentration of chlorine in the gas mixture experimentally determined chemical analysis by bubbling a known volume of the gas mixture through an aqueous solution of potassium iodide (absorption of chlorine) followed by titration in solution selected iodine with standard sodium thiosulfate solution.

For the preparation of gas mixtures of chlorine with air prototype through the electrolyzer missed a continuous electrically is of the formula (3)

< / BR>
where C is the concentration of the selected gas in the gas mixture, g/l;

1.323 - electrochemical equivalent of chlorine, g/Ah;

IA- the amplitude (strength) of the current, AND;

V is the volume of the gas mixture per unit time (flow rate), l/h

(In the above conditions, the volume of the gas mixture is equal to 15 l/h, the amount of chlorine can be neglected).

The implementation of the method on the prototype for a given current amplitude provides cooking gas mixtures with concentrations of 0.0910-3to 4.410-3g/l of chlorine, in this range the current results of chemical analysis and calculated the concentration of chlorine in the mixture according to the formula (3) are the same.

But with decreasing amplitude (power) of the current below 110-3A (1 mA) observed a significant reduction of the output current of chlorine. Calculate the concentration of chlorine in the formula (3) given the value of the concentration of chlorine is much more than the results of chemical analysis. Therefore, obtaining the prototype of chlorine in the gas mixture with its guaranteed content of less 0.0910-3g/l was impossible.

With the purpose of preparation of gas mixtures according to the invention is passed through the electrolyzer DC previously, using a modulator, was subjected to the current, equal 5010-3A.

The electrical circuit of the modulator allows you to modify the ratio of the width of the current pulse () to its period of oscillation (T) in the range from 1:1 to 1:1000.

The concentration of chlorine in the gas mixture was calculated by the formula (4)

< / BR>
where C is the concentration of the selected gas in the gas mixture, g/l;

IA- the amplitude (strength) of the current, AND;

V is the volume of the gas mixture per unit time (flow rate), 15 l/h;

- the width of the current pulses;

T is the period of oscillation of the current, with.

Preparation of gas mixtures according to the invention allows to obtain mixtures with a guaranteed concentration of chlorine in the range of from 0.0000910-3to 4.410-3g/l; results of chemical analysis and calculation data of concentration according to the formula (4) are the same.

Thus, this invention allows 1000 times (0.0910-3g/l to 0.0000910-3g/l) to expand the range of concentrations of gas mixtures defined gas (chlorine), in particular, in the field of low concentrations, which greatly facilitates and simplifies the calibration of analytical instruments-analyzers.

The method of obtaining gas mixtures by the dynamic method, including the electrolysis of aqueous solutions of electric shock, mixing in the gas mixture, characterized in that the electric current is preliminarily subjected to pulse width modulation, producing a current in the form of rectangular pulses with the same amplitude, and the concentration of the selected gas is determined by the formula

< / BR>
where C is the concentration of the selected gas in the gas mixture, g/l;

K - electrochemical coefficient of the selected gas, g/Ah;

IA- the amplitude (strength) of the current, AND;

V is the volume of the gas mixture per unit time (flow rate), l/h;

- the width of the current pulses;

T - period oscillations of the current C.

 

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