DE1773795C3 - Analyzer for measuring gas concentrations - Google Patents

Description

35

The invention relates to an arylation device for measuring gas concentrations with a measuring cell in the manner of a Nernst concentration core, the gas flow to be examined being guided past one of the two electrodes of the measuring cell, both of which are in contact with a solid electrolyte and have a low resistance to each other in the external circuit !are connected.

It is known to measure the concentration of one or more gas components in a gas flow by passing this gas flow past one of two electrodes, both of which are wetted by an electrolyte and separated from one another by a barrier layer (diaphragm) arranged in the electrolyte are. The gas components to be measured produce a change in the ionic concentration prevailing there at one electrode and thus a measurable electrical current in an external electrical circuit between the two electrodes in the manner of a Nernst concentration chain. Low-resistance current measurements - approximately below HQ kilo-ohms - in the outer closing circuit have the advantage over high-resistance potential measurements of a measuring current that increases linearly with the concentration of the gas components to be measured and a defined zero point.

This is important for low-resistance current measurement Nature of the between de.i Elektrodeu im Electrolyte arranged S ^ rrschicht, which an immediate circulation of the ions in the electrolyte prevented. This barrier layer must be itself as possible be low resistance and may your electrical and hers Do not change the mechanical properties in the course of the measurements.

It is known that narrow-pored, porous, with liquid Body soaked in electrolytes and completely filling the space between the electrodes Can have a barrier effect and, depending on the application, offer great advantages over thin membranes and diaphragms.

In the journal "The Review of Scientific Instruments", 32, pp. 593, 1961, an oxygen measuring cell is described in which solid calcium-stabilized zirconium oxide is used as the electrolyte. The line is used to measure oxygen partial pressures at temperatures above 500 ⁰ C and is z. B. used to monitor hot furnace exhaust gases. At temperatures well below 500 ⁰ C is the electrolyte conductivity geling.

In the case of fuel elements with aqueous electrolytes, ion exchange membranes have been used with success. In this way, a gas outlet can be avoid between the electrodes. In addition, the ion exchange membrane selectively lets only ions of a charge sign happen.

The use of ion exchangers in fuel cells is z. B. in the book by v. D ö h r e η, J Euler, The current state of fuel elements, VartaAG, Frankfurt / Main, 4th edition, 1965, on pages 51 to 53! »Wrote. Basically such membranes consist of insoluble high molecular weight organic compounds which contain groups capable of ion exchange reactions (ion exchange resins). They are not conductive in dry form. The electrical conductivity is created rather, only when the membrane is introduced into the aqueous phase. Functional ion exchangers therefore contain 20 to 70% water. For the ion exchange membranes listed on page 51 is z. B. on page 52 indicated a water content of about 45%. This is why fuel cells are with ion exchangers “rather critical with regard to 2uf Water loss. On page 56, it is expressly pointed out that the foils are very sensitive to drying out.

A disadvantage of automatic gas analyzes with such systems containing liquid electrolytes is'. the not negligible vapor pressure of the Elek'rolyte used, the z. B. in the case of aqueous electrolytes in the exchange of water vapor with the measuring gas stream, a water loss or water absorption and thus a constriction or dilution of the electrolyte or in other systems leads to a considerable loss of mass.

It has now been found that these disadvantages have been remedied and that a very simply structured measuring cell results for long-term measurements, if, according to the invention, the solid electrolyte is made up of one or more coordinated organic substances with a vapor pressure of less than 1 Torr at temperatures below 60 ⁰ C consists. According to a particular embodiment of the invention, the electrolyte has a dielectric constant of more than 20 or a dipole moment of more than 2.0 Debye and a specific resistance of less than 10 ohm · rm. An electrolyte with these properties has shown very good behavior and enables perfect measurements.

The low vapor pressure connects a noticeable

3 4

loss of mass and allows the system to be operated without .0-CHj ₈

Use disturbances also for continuous measurements. Im ₀ _ C / I

Gegensau: zu! Onsnaustauschermcmbranen has the \ _{Λ ru}

organic electrolyte of our measuring cell also with ^u ~~ ,

complete absence of water a sufficiently high 5 '

Conductivity, otherwise it is neither due to its ^c " ³
chemical composition, still according to its function

to be regarded as an ion exchanger. Its high di- Such a measuring cell as the core of an analysis constant or its large dipole moment sensor is explained using an exemplary embodiment: enable the substance to dissociate the chemical reaction from partner and thus the function of a one selected electrode material is above and electrolyte is to take over. Due to the fixed procurement, each with a central gas penetration, rapid ion exchange within the stoppers 3 and 4, which are provided with guides 5 and 6 and made of non-electrolytes, is prevented, and is closed off by the small amount of internal conductive material. The inside of the resistor, the advantageous low-resistance current 15 jacket tube 1 is made possible except for an axial, cylindrical measurement. Cavity 7, which expediently has the same diameter

An electrolyte knife has proven to be particularly suitable, such as the gas feedthroughs with which

which is filled out from a mixture of benzoic acid organic solid electrolytes 8. In the

- About 50 to 70 parts by weight - and propylene interface of the organic solid electrolyte 8 to

carbonate - about 50 to 30 parts by weight - consists. * ° Cavity 7 is the spirally wound measuring electrode 2

The great advantage of these substances is that they can be texted in at the same time through the stopper 3

Is it possible to simply use a dimensionally stable, self-electrical connection? is led. That as

load-bearing, shock and vibration-proof and lags counter-electrode serving jacket tube 1 is with the

to produce independent measuring cells and conductively connected in the maintenance connection 10,

to use free continuous operation for gas analysis. 35 The gas flow to be examined passes through the gas

For example, a measuring cell with an electrolyte duct 6 , passes through the cavity 7 and, from a mixture of 60 parts by weight of benzoin, lets the cell pass through the gas duct 5. Meth>! - l, 3-dioxolan-2-one), the 20 ° C-taste of the organic electrolyte 8 and changed and then poured into a suitable mold, 30 there the ion concentration. Allow this change »; in connection with silver as an electrode produces a measurable electrical. Current in the material is the measurement of hydrogen sulfide in a low-resistance external circuit between the gases, connections 9 and 10.

H'trzu 1 sheet of drawings

Claims (4)

! 773 claims: 1. Analyzer for measuring Gaukonzeniraiionen with a measurement similar to a Nernst concentration curve, whereby the gas flow to be investigated is passed by the two electrodes of the measuring cell, both of which are in contact with a solid electrolyte and are in the outer circuit. to resistance types are connected to one another, characterized in that the solid electrolyte (8) consists of one or several coordinated, organic substances having a vapor pressure of less than 1 Torr at temperature below 6O ⁰ C doors. 2. Analysis device according to claim 1, characterized in that the solid electrolyte (S) has a Dielectric constant greater than 20 or a dipole moment greater than 2.0 Debye and a resistivity of less than 10 ⁶ ohm cm. 3. Analysis device according to claims 1 and 2, characterized in that the solid electrolyte (8) consists of a mixture of benzoic acid and propylene ag carbonate. 4. Anaiysengerät according to claim 3, characterized in that the mixture of 50 to 70 parts by weight of benzoic acid and 50 to 30 parts by weight of propylene carbonate. 3 »