RU2554663C1 - Electrochemical cell for analysing sulphur-containing gases - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: apparatus is designed for qualitative and quantitative determination of sulphur-containing gases (hydrogen sulphide and sulphur dioxide) in exhaust gases of chemical plants, thermal power plants, for analysing light- and dark-oil products and can be used to determine maximum allowable concentration of sulphur-containing gases in chemical, petrochemical, medical and food industries. An electrochemical cell for analysing sulphur-containing gases includes a pipe made of quartz glass having inside it gas inlet and outlet nozzles, graphite and nichrome current-conductors, a graphite electrode, a sulphide-conducting membrane, a comparison electrode placed in the graphite conductor and made of bismuth sulphide with an additive of bismuth metal powder, and a working electrode. According to the invention, the sulphide-conducting membrane of the electrochemical cell is a solid electrolyte (CaY₂S_4-x mol % Yb₂S₃) with the following ratio, mol %: calcium thioittrate (CaY₂S₄) - 84-100%, sesquialteral ytterbium sulphide (Yb₂S₃) - the balance.

EFFECT: reducing the lower threshold of the determined concentration of hydrogen sulphide and sulphur dioxide, high sensitivity and low operating temperature of the sensitive element.

3 dwg, 1 tbl

Description

The invention relates to devices for determining the concentrations of sulfur-containing gases in gas mixtures using solid-state gas sensors. The inventive device is intended for the qualitative and quantitative determination of sulfur-containing gases (hydrogen sulfide and sulfur dioxide) in the exhaust gases of chemical plants and thermal power plants, for the analysis of petroleum products and can be used to determine the maximum permissible concentrations (MPC) of sulfur-containing gases in the chemical, petrochemical, medical and food industries industry.

The closest in technical essence and the achieved results to this invention is an electrochemical cell for analysis of sulfur-containing media, containing a sulfide-conducting solid electrolyte, a measuring electrode and a reference electrode made of bismuth sulfide with the addition of powdered metallic bismuth [1]. As a sulfide-conducting solid electrolyte, a mixture of barium thioneodiomate (80-95 mol.%) And one-and-a-half neodymium sulfide (5-20 mol.%) Is used. Such an electrochemical cell with sufficiently high accuracy allows the analysis of sulfur-containing gases (H ₂ S and SO ₂ ). The disadvantage of this cell is the impossibility of studying the concentration of sulfur-containing gases of less than 2 vol.%, As well as the high operating temperature of the sensor (500-550 ° C).

The technical result of the invention is to expand the range of detectable concentrations of hydrogen sulfide and sulfur dioxide, increasing sensitivity and lowering the operating temperature of the device. The mentioned technical result is achieved due to the use of a solid electrolyte CaY ₂ S ₄ -Yb ₂ S ₃ as a sulfide-conducting membrane of the electrochemical cell in the following ratio of its components, mol.%:

- calcium thioittrate (CaY ₂ S ₄ ) - 84-100%;

- one and a half ytterbium sulfide (Yb ₂ S ₃ ) - the rest.

The reference electrode, by analogy with the prototype, is made of bismuth sulfide with the addition of powdered metallic bismuth.

The invention is illustrated in figure 1. The positions in the drawing indicate: 1 - a tube of quartz glass; 2 - fitting for gas supply; 3 - fitting for gas discharge; 4 - graphite electrode; 5 - graphite conductor; 6 - nichrome conductors; 7 - quartz glass; 8 - sulfide-conducting membrane; 9 - reference electrode; 10 - sealing composition; 11 - a stopper from vacuum rubber.

The cell is a quartz glass tube (1) with two fittings for supplying (2) and exhaust (3) gas. A sensor element is fixed inside the cell, pressed into a quartz glass (7). The sensitive element is a single structure consisting of elements (4), (5), (7-10). Inside the current-carrying graphite conductor (5), a recess is made in which the reference electrode (9) is placed. The free surface of the graphite conductor (5) is covered with a sealing composition (10) to prevent contact of the reference electrode (9) with the analyzed medium. The entire upper surface of the reference electrode (9) is in contact with the lower surface of the sulfide-conducting membrane (8). The upper surface of the sulfide-conducting membrane (8) is in contact with the surface of a graphite electrode perpendicular to it (4). As a second current lead, nichrome conductors are used (6).

The principle of operation of an electrochemical cell is based on measuring the emf circuit

where C | Bi, Bi ₂ S ₃ - reference electrode (9) in contact with a graphite conductor (5);

CaY ₂ S ₄ mol.% Yb ₂ S ₃ - sulfide-conducting membrane (8), which is a solid electrolyte;

H ₂ S (SO ₂ ), Ar | C - working electrode: a mixture of detectable sulfur-containing gas with argon at the graphite boundary (4) - solid electrolyte membrane (8).

The collected sensing element is dried in silica gel for 24 hours and then in a horizontal furnace for 3 hours to remove water vapor for 3 hours at a temperature of 100 ° C. Next, the element is placed in the measuring cell. The cell is evacuated ten times, washed with purified argon, followed by filling with hydrogen sulfide to saturate graphite electrodes, placed in an oven, heated to operating temperature, due to the properties of the sulfide-conducting membrane (415-515 ° C), and a sulfur-containing gas is supplied, which is a working electrode at the graphite - solid electrolyte, after which gas analysis is carried out.

The measurements are carried out in a dynamic unsteady mode with a pulsed introduction of sulfur-containing gas into the laminar flow of argon passed through the measuring cell.

The electrochemical cell operates in potentiometric mode. The signal of the electrochemical cell (ΔE) is obtained in the form of the difference between the extreme and the initial value of the EMF circuit (I). An analytical signal of the dependence of the EMF on the concentration of sulfur-containing gas was used to construct the corresponding calibration curves for the analysis of H ₂ S and SO ₃ (figure 2, 3). The range of measured concentrations is: 0.1-10 vol.% H ₂ S and 0.01-10 vol.% SO ₂ .

Example 1. When performing the analysis of a gas mixture containing H ₂ S of unknown concentration, the measured value of the EMF was 133.6 mV. Using the calibration dependence for H ₂ S (figure 2), we determine that the value of A E = 133.6 mV corresponds to IgC (H ₂ S) = 0.115. The concentration of hydrogen sulfide in the gas mixture is 1.30 vol.%.

Example 2. Similarly, the concentration of SO ₂ corresponding to the sensor signal (ΔE) = 30.8 mV is determined. According to the calibration dependence (figure 3) for this response, the value of IgC (SO ₂ ) = - 0.056. The concentration of sulfur dioxide in the gas mixture is 0.88 vol.%.

Data on signal values, sensitivity of the claimed electrochemical cell, which includes CaY ₂ S ₄ -Yb ₂ S ₃ , and prototype cells (sulfide-conducting membrane - BaNd ₂ S ₄ -Nd ₂ S ₃ ) from the content of the analyzed gas are given in the table.

The sensitivity (S _S ) depends on the slope of the lines in the coordinates ΔЕ = f (logC, vol.%) And is defined as

where pC of _{sulfur-containing gas} = -lgC of sulfur-containing gas is 254 mV / pCH ₂ S and 54.4 mV / pC _SO2 .

The advantages of the claimed electrochemical cell are the use of calcium thioitrate doped with ytterbium sulfide (CaY ₂ S ₄ -mole.% Yb ₂ S ₃ ), which allows:

- reduce the lower threshold of the determined concentrations to values lower than the MPC of the working area: 0.1 vol.% for the determination of hydrogen sulfide and 0.02 vol.% for sulfur dioxide (for the prototype: 1.8 vol.% for both gases);

- lower the operating temperature of the sensor to 415 ° C;

- increase the sensitivity to 254 mV / pC (H ₂ S) (for the prototype: 80 mV / pC (H ₂ S)).

Information sources

1 Patent RU No. 2089894 C1, IPC G01N 27/46. Application No. 94037123/25; priority: 09/28/1994; published: 09/10/1997. Electrochemical cell for analysis of sulfur-containing media. Authors of the invention: L.A. Kalinina, G.I. Shirokova, I.V. Murin, M.Yu. Lyalina.

The dependence of the signal values, the sensitivity of the claimed electrochemical cell, which includes CaY ₂ S ₄ -Yb ₂ S ₃ , and the prototype cell (sulfide-conducting membrane - BaNd ₂ S ₄ -Nd ₂ S ₃ ) on the content of the analyzed gas No. p / p The composition of the sulfide-conducting membrane Working temperature ° C The content of H ₂ S, vol.% E, mV Sensitivity,
mV / pC _H2S The content of SO ₂ , vol.% E, mV Sensitivity, MB / pC _SO2 one BaNd ₂ S ₄ -Nd ₂ S ₃ 500-550 8.77 593 80 8.77 305 78 2 7.14 586 7.14 290 3 5.45 576 5.45 293 four 3.77 563 3.77 280 5 1.89 540 1.89 257 6 0.96 - 0.96 - 7 8 0.38 - 0.38 - 0.1 - 0.1 - 9 CaY ₂ S ₄ -Yb ₂ S ₃ (claimed) 415-475 8.77 338 254 8.77 83 54 10 7.14 317 7.14 79 12 5.45 288 5.45 73 13 3.77 243 3.77 65 fourteen 1.89 173 1.89 46 fifteen 1.44 143 1.44 42 16 0.96 96 0.96 33 17 0.57 41 0.57 22 eighteen 0.38 27 0.38 eleven 19 0.19 21 0.19 8.6 twenty 0.1 13 0.1 8.25 21 - - 0.01 7

Claims (1)

An electrochemical cell for analysis of sulfur-containing gases, including a quartz glass tube with gas supply and exhaust fittings located inside it, current-carrying graphite and nichrome conductors, a graphite electrode, a sulfide-conducting membrane, a reference electrode located in a graphite conductor and made of bismuth sulfide with a powder additive metallic bismuth, and the working electrode, which is the analyzed medium at the boundary "graphite - sulfide-conducting membrane", distinguishes schayasya that sulfidprovodyaschey membrane as a solid electrolyte is used with unipolar ion conductivity sulfur CaY ₄ -Yb ₂ S ₂ S ₃ in the following ratio of its components, mol.%:
- calcium thioittrate (CaY ₂ S ₄ ) - 84-100%;
- one and a half ytterbium sulfide (Yb ₂ S ₃ ) - the rest.

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