DD144118A1 - METHOD AND DEVICE FOR DETERMINING NITRITE AND NITROGEN GASES - Google Patents

Abstract

The invention relates to a method for the determination of nitrite and nitrous gases. By Influence of certain substances, such as amines, diazonium salts and / or their electrochemicals Oxidation products is caused on a anode surface complete polarization and their depolarization in the presence of nitrite and nitrous gases by measuring the Polarization voltage or a derived therefrom for the determination of nitrite and nitrous Gases applied. The measuring arrangement consists of two measuring electrodes, e.g. from gold, platinum or one another suitable material, a stabilized polarization voltage source, and an arrangement for electrolytic regeneration of the electrodes by hydrogen separation. The device can for Diazotierungskontroile or Kontroäie special dye synthesis can be used.

Description

Method and device for the determination of nitrite and nitrous gases.

Field of application of the invention

The invention relates to a method and apparatus suitable for carrying out the method for the determination of nitrite and nitrous gases _. c _e B _e both for monitoring the reaction of _{Diaaotierungen?} as well as for determination ^{1 of} the reaction end point of diazotization or "such dyestuff reactions in which diazo animal suing and coupling take place in a reaction vessel"

It is known to use "electrochemical methods for diazotization control" in which the control of the nitrite content or of the escaping nitrous gases is utilized. Thus, a potentiometrlachoo method for the diazotization control (Aiigew, CheiUe 22. (J95S) Zkh · »2kS) is given. which works with special SiC electrodes and has been described for use in continuous processes. These electrodes are said to have a reproducibility of ~ 5 ro voltage values. The electrodes have to be manufactured in a complicated way and a reproducibility of the spinaneous values is not given

Another method potentiometrisch.es sux- diazo t ie approximately j control but which in portions nitrite additives near the Reaktionsendpunlctos requires _f whereby either a change dos technological regime is necessary or flo "stimnrong jri.c.ht in Reaktionsgefä3 performed vrorden karaa, serviced itself, a special recharging electrode, Ä0-Q1 (claim * proa),

(russ _a ) A1975) 5 3Ö8-391 } " Disadvantages of these as well as of the above-mentioned electrodes is that in a relatively short operating time they pass over with a passivating adsorption layer, without whose removal further measurements become impossible."'. , .... ... , A method for utilizing Pölarisationsspanuungsmessungen for the determination of the amine by titration with Nitrite Maßlösungen was given by Büchler (Z, anal. Chem. 186 (1 962) · 15 ^ -16o) However, this method is only suitable for analytical determinations, and these measurements also show adsorption effects on the electrode surfaces which impair their effectiveness over time. <br /><br/> Different ways of cleaning electrodes by exposure to chromosulfuric acid or electrolytic deposition of hydrogen at the electrodes are known As a result of such treatment, the measured values are usually greatly shifted, and since nitrous gases escape at virtually every diazotization, sensors have been developed which measure the escaping nitrous gases (CSSR Pat 120137, Czechoslovakian Patent 120201, Federal Republic of Germany OS 2032834). The cited patents include potentiometric and biometric probes which thereby characterize are that they use a film formed and renewed by a constantly flowing absorption solution on the electrodes, which forms the electrolyte layer in which the nitrous gases are absorbed. Such sensors have a low stability in use because they are sensitive to dust and vibration. Another disadvantage is that the Nitritzugaben must be made in portions near the end point of the diazotization in order to make a statement about the end of the reaction.

Also, such as the probe according to Talanta 2J3 (1976) 811-814, which allow the separate amperometriehehe determination of nitrogen monoxide and nitrogen dioxide with Teflon specially bound and doped Au electrodes, when for the measurement of NO, a voltage of U = 1.5 V and to NO _2. "Measurement U = 0, -8 V is applied to the sensor, ⁷ should be either calibrated for diazotization or for the end point determination in diazotierutigen introduced or the nitrite additions in portions"

Aim of the Invention

Ziol the vorliegetiden invention is an electrochemical method and a suitable method for carrying out the determination of the content of nitrite or, nitrous gases, eg. B, for the control of the course and the Endpunltssanzeige of Diazotiermagen or, dye synthesis reactions with equilateral in a reaction vessel expiring diazotization and. Coupling · ('one-pot process') _} in which the addition of nitrite does not have to be done in portions _- so the original technological regime can be completely retained and the sensor has a long-term sensitivity »

Explanation of the essence of the invention

The object of the invention is a method and an associated device for determining nitrite and nitrous gases on the basis of Polarisationsspanuungsmessungen _β according to the invention is caused by the action of certain substances ₅ such as amines, diazonium salts, and / or * their electrochemical oxidation products' on an anode surface full polarization and their depolarization in the presence of nitrite and nitrous gases by measuring the polarization «spa.nnt.ing or a * derived derived size for the determination of nitrite or nitrous gases _e nitrogen used« This results in the invention, the possibility of the polarization voltage measured at complete anode polarization ( or a -derived therefrom size) j which only by that of the voltage source used specific voltage is set _s '' as a control criterion for the 3STitritfreihe t and for the freedom of extracted gases ¹ of nitrous gases from z "B ₈ Use diaotoping or dye synthesizing agents or their respective content,

Since the adjustment of the complete anode polarization is due to adsorption processes on the anodic surface, the measurement sensitivity decreases with increasing use time, which is why regeneration of these surfaces is necessary in order to obtain reproducible statements on the content of nitrite and nitrous gas This is done by hydrogen separation in such a way that

an approximately constant .Elelctrodenempf are mutually coordinated according to the invention to be applied regeneration voltage Regenerateonsdauerj time to reestablish the anode polarization and measurement time of the electrodes and set j which indiich- * ness is secured, wherein the regeneration duration needs to be short in relation to Meßdäuor very ¹ " to carry out the measurement is a erfindungsgemäßen'Verfahrens arrangement of Figure 1 suitable _e, which consists of two Meße.lektroden k Yio B "j Au, Pt or other suitable material, a stable ized Polarisationsspamiungsquelle 1, a limiting resistor 7 s of a voltmeter in Position 5 or 6, a voltage source 2 for the regeneration of the electrodes, an auxiliary electrode 8 and a switch 3 for switching the regeneration circuit is built on the measuring circuit.

Embodiment 1 j

Control of the hydrochloric acid diazotization of o = »chloro-p« isritraniline via the course of nitrite conversion

* o

In a technical reaction vessel, which is cooled to approximately 0 C _? 100 kg o-chloro-p-KTitranilin in 2800 1 water with stirring, registered. The Anschlätnmung is stirred for at least 1 hour, then 58O 1 hydrochloric acid (20 Be) are added and stirred for a further hour, driving the Anschlämmzeit is cooled to 0 C.

The measuring device used consists of two platinum electrodes, which have been provided with a hydrophobicizing silicone film for the purpose of passivation protection, and are immersed in the batch to be investigated. The electrodes have a diameter of 1 mm and 10 mm in length and are framed in glass. Via the stabilized polarization voltage source 1, a voltage of UIc = 0.300 V is applied to the measuring electrodes. Over the limiting resistor 7 of R = 100 K becomes a limitation of the maximum Current on i = 3 / u. A reaches «

With the help of voltmeter 5, the polarization voltage is determined in the measuring cell. The complete polarization of the anode builds up after about 1 h

(Intestine is measured at voltmeter 5, the applied .Polarisationsspaierung of UIc = Oj. 300 V) '

Analogous results are obtained, one measures the. Voltage drop across the resistor 7 »This is at full anode polarization U = 0 _e 000 V, since no current flows (6). The diazotization is by. Addition of 77 kg of sodium nitrite (solid 98 / oig) initiated, "The anode is depolarized by the nitrite, the voltage 5 drops to close ¥ OV off" Due to the current flowing at-resistor 7, a voltage drop 6 ₀ by the diazotization reaction If nitrite is broken down, after approx. 80 min. last nitrite traces are destroyed with sulfamic acid. The anode of the probe is fully polarized again and Uk '= 0 _e 300 V reached, whereby Nitrite freedom is detected. The voltage drop 6 measured at the resistor 7 is 0 _c 000 V ₈ If it is still to be tested for complete amine conversion, z * B ₆ 1 fo the total amount of nitrite nachgesetzte rises which in turn apostate polarization voltage on the voltmeter 5 no longer is the complete conversion of reactive amine he "follows" Remaining nitrite residues can vxiö destroyed Amidosulf ons äure '. this be controlled with the measuring device ,,

Exemplary embodiment 2 % regeneration of the electrodes

Regeneration. If the measuring electrodes h are switched cathodically against an auxiliary electrode 8 (U = 1? 5 V) and the time of the hydrogen separation in a 2 M hydrochloric acid is limited to 30 s, then one hour of stirring time in the diazo tierungssatz suffices to restore the complete anode polarization. ' The regeneration process is triggered by actuating the switch 3 i "Figo & 1 and also terminated ₀ After surveying a full Diazotierungsrealction starts is cycle from the front,

Example of use 3 %

Control of the Synthesis of the Colorant Fantagen Orange 2 PJb /

The su-use device is diegleiche as in the execution bsispiol 1 (see FIG _e "ΐ) _β is controlled to the nitrite conversion at d ° he common diazo tie tion and coupling von'p ~ nitroaniline and

'N-ethyl' »N- 'cyanäthyla.nilin for the preparation of the dye Fan» tagenoraage 2 RL in a Realctloiasgofäß. To carry out the synthesis in 20 ml of water under 'Stirring 1 _? 38 g of p-Nitrani .1An, added 6 ml of hydrochloric acid (20 Be) and 1 _s 85 ml of N-ethyl-N-cyanäthylanilin ($ 96), and stirred at 15-20 C for 1.5 × »2 a c two gold electrodes are {1.5 mm By "· knife j 5 now length) ;, the (in epoxy EpiloK ERQi9 _f Haex ter8 ^s) bordered sindj used for the measurement. By adding 2 _S 5 M sodium nitrite solution in defined portions (see _"see Table 1), the Färb ™ product synthesis realized since the nitrite is partly gasified, is to fully implement over ''. Stöchiometrisclie the amount necessary ·

Table 1 below shows the course of the control of the dye synthesis reaction of Fantagenoraugo 2 RL by eolibration voltage measurement,

Tab. 1

Control DER dye synthesis of Fantagenoraiage 2 RL by Polarisationsspaiinung'smessung

vfml] -UTaIrI ₁ v] TIk (V]

0.5 0.249 0 _} . 300 1.0 0,200 0,300 ''? Oj ₁ 292 0,300 2, Ό .0,297 Oj 300 2.5 0 _} . 297 0 _? 300 3.0 0 _f 270 .0,300 3.5 OJ 243 0 _? 300 4 * 0 OJ 241 0j300 4.1 Oj285 0,300 4 _? 2 0 ^ 88 Oj 300 * · "3 0 * 285 Oj 300 4.4  0.286 Oj3OÖ Oj286 .0,300 4 * 6 0.287 Oj, 300 4.7 Ό, 287 o _f 300 4.8 Oj288 O _f 296

V - Völtiraen to 2.5 M NaNO "-Lösmag Umin" added to the batch - voltage at the moment after addition of the nitrite aliquot OTc .'-. Kon tr oll spun clothes _f geinessen after no change in voltage · rnGhr be determined

After the control value of Uk '=: 0 _? 300 V is not reached, the dye synthesis is finished. In order to ensure a constant measuring sensitivity, the regeneration of the electrodes is carried out periodically as in Example 2.

-.8th

Embodiment h

Control of nitrosyl sulfuric acid diazotization of 2-aminobenzthiazole using the escaping nitrous gases

In 7j8 g 2-Arainobenzthiazol be after addition of. 50 g of ice are added dropwise in 30 min. 37 ml of H ₂ SO ₄ (96 parts). Cool to 0 C within 10 min. Cool cooled nitrosylglycidic acid (20 ml HgSO 4 - 96 $ and 3.5 g NaNO ₂ ) is given as a template and stirred _e -

A sensor according to FIG. 2 is already put into operation ", it consists of a glass body _f which has an inlet nozzle 10 and an inlet nozzle for the gas to be analyzed _. a supply line for the absorption solution 11 with a nozzle-shaped · trained end 13 ^ an outlet opening 9 for the Absorptionslösungs gas mixturej a cavity 12 for mixing gas and liquid and for receiving the electrodes 8 _? which are provided with wire leads I5 which connect to the measuring circuit according to FIG. 1, as well as a storage vessel 16 for the absorption solution and a device 17 for regulating the rate of absorption of the absorption solution. The electrodes used are an anode and a silver cathode * The measuring circle in Fig. 1 * 1. is analogous to FIG. 1 and dimensioned as in Example 1. The absorption solution used is 2 M HCl, with an addition of 0 _f 02 g / L ^ Ciilor-pn-nitraniline. When the sensor described above is used, a control voltage Ulc = 0 _y 300 V is measured. The diazotization is the same Measure escaping nitrous gases, resulting in a reaction course according to Fig * 3 β Is dia reaction has almost come to a standstill (Fig "3 point" A), by Amidosulfonsäurezusatz excess Nitrosylschwe ™. Feisäure zex ^ be disturbed «

The sensor shows the nitrite freedom of the attachment by the appearance of the control voltage. UIc = 0.300 V (Fig. 3 Fct. B). Thus, the course and reaction end of a nitrosylsulfuric diazotization can be controlled via the escaping nitrous gasesc

Claims (1)

Erf induagsansprucli "Method for Determining Nitrite and Nitrous Gases, ζ" B, for Monitoring the Reaction Course of Diazo ™. tions, characterized in that the by. Action of certain substances such as amines _? Diazonium salts and / or their electrochemical oxidation products, on. complete polarization caused by an anode surface and its depolarization. in the presence of nitrite and nitrous gases, by measuring the polarization voltage or a quantity derived therefrom for the determination of nitrite and nitrous gases _s 2 _e device zyr Implementation of the method for the determination of nitrite and nitrous "gases, z" B "for tracking the reaction course of diazotizations according to item 1, characterized by a measuring arrangement consisting of two measuring electrodes h of z, B, gold, platinum or another suitable substance _{) of} a stabilized polarization voltage source 1 _ί a limiting resistor J _t a voltmeter in the position 5 or 6 _{S of} a voltage source 2 for regeneration of the electrodes, an auxiliary electrode 8 and a changeover switch 3 for switching the regeneration circuit to the dexi measuring circuit is. '^ V t J