CA2039528A1 - Electrode system for voltametric measurements - Google Patents
Electrode system for voltametric measurementsInfo
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- CA2039528A1 CA2039528A1 CA002039528A CA2039528A CA2039528A1 CA 2039528 A1 CA2039528 A1 CA 2039528A1 CA 002039528 A CA002039528 A CA 002039528A CA 2039528 A CA2039528 A CA 2039528A CA 2039528 A1 CA2039528 A1 CA 2039528A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4166—Systems measuring a particular property of an electrolyte
- G01N27/4168—Oxidation-reduction potential, e.g. for chlorination of water
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
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- Measuring Oxygen Concentration In Cells (AREA)
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Abstract
ELECTRODE SYSTEM FOR VOLTAMETRIC MEASUREMENTS
ABSTRACT OF DISCLOSURE
An electrode system for voltametric measure-ments for measuring oxidative and/or reducing compounds in electrolytes, i.e., mainly in aqueous solutions in the paper and pulp industry, said system comprising a working electrode (1), a counterelectrode (2) and a reference electrode (3) which are connected to a voltametric measuring apparatus (4), the working elec-trode (1) being made of glass-carbon.
ABSTRACT OF DISCLOSURE
An electrode system for voltametric measure-ments for measuring oxidative and/or reducing compounds in electrolytes, i.e., mainly in aqueous solutions in the paper and pulp industry, said system comprising a working electrode (1), a counterelectrode (2) and a reference electrode (3) which are connected to a voltametric measuring apparatus (4), the working elec-trode (1) being made of glass-carbon.
Description
ELECTRODE SYSTEM FOR VOLTAMETRIC MEASUREMENTS
The present invention concerns an electrode system for voltametric measurements, for measuring oxi-dative and/or reducing compounds in electrolytes, i.e.,mainly in aqueous solutions in the paper and pulp in-dustry, said system comprising a working electrode, a counterelectrode and a reference electrode. which are connected to a voltametric measuring instrument.
Normally, three electrodes are used in volta-metric measurements: a working electrode, a counter-electrode and a reference electrode. The electrodes are placed in a measuring cell or in the solution to be measured. Using the measuring apparatus and its reg-ulation component, a constant potential difference is established between the working and reference electrodes connected to the apparatus, which is usually selected to be within the so-called limit current range of the substance to be determined in the measurement, whereby the oxidation, respectively reduction of the substance to be measured has been regulated to be faster on the surface of the working electrode than the transport of said substance to this electrode. This implies that the concentration of the compound to be analyzed is O on the surface of the working electrode. The transport of the compound to be analyzed to the surface of the work-iing electrode can be arranged so that the sample flows past the working electrode, or alternatively the work-ing electrode is moved relative to the sample, e.g. by rotating.
By effect of the elec~ron transfer reaction taking place on the surface of the working electrode (i.e., oxidation or reduction of the compound to be measured), the potential difference between the working and reference electrodes tends to change. This change is observed with the aid of an electronic measuring instrument included in the measuring apparatus, and it is prevented by supplying currcnt to the working elec-trode through the reference electrode. The measured value of thls current, or the correspondlng voltage, is directly proportional to the concentration of the sub-stance to be measured, on the basis of the fact thatthe rate of diffusion to the electrode increases as the concentration o~ the substance to be analyzed increas-es In continuous analytic measurement the refer-lo ence electrode is generally the weakest point of thesystem. The working and counterelectrodes are usually metal electrodes and therefore durable and requiring little maintenance. Problems at the reference electrode may also be caused by pressure fluctuations in the sample, for instance in a process pipeline system.
Pressure changes may block or interrupt the salt bridge of the reference electrode, whereby the potential of the working electrode changes, causing a measuring error. Furthermore, installation in a pipeline of such reference electrodes as are known in the art is highly awkward, owing to large size and fragility of the ref-erence electrodes.
With a view to eliminating the drawbacks just mentioned, an electrode system has been developed in prior art in which the reference electrode is made of metal in likeness with the working and counterelec-trodes. All electrodes are appropriately mounted in one single pick-up, preferably on the end of a rod-shaped pick-up which is directly pushed into the process pipeline. With the electrode system thus achieved, an electrode system has been created which is substantial-ly superior to earlier systems in structural simplicity and durability and requires less maintenance. The elec-trode system tolerates pressure variations, mechanical loads, in addition to which the electrodes can be kept in continuous contact with the process solution, where-by they are preserved against soiling and chemical challges .
~ rhe electrode system which has been created is, however, embarrassed by a drawback which has emerg-ed in measurements carried out on aqueous solutions employed in the paper and pulp industry, such as stock suspensions in various stages of bleaching. In some instances, wide pH variations induce inaccuracy in the value of the ~neasuring voltage. On the other hand, wide pH fluctuations cause chemical reactions, whereby the chemical that is being measured may be transiently con-verted to another compound. As an example the chlorine dioxide bleaching process may be mentioned, in which with ascending pH the. chlorine dioxide reacts to become chlorite, while it reverts to chlorine dioxide in the bleaching tower. In this case the sum of chlorine diox-ide and chlorite represents the bleaching chlorine. It is only possible to measure the chlorine dioxide with the electrode system now in use.
The object of the invention is to provide a novel electrode system with which oxidation and/or re-duction potentials of electrolytes can be measured within very wide pH value limits. Moreover, the inven-tion aims to provide an electrode system for measuring oxidation and reduction potentials which is usable in particular in bleaching processes of various types.
Regarding the features characteristic of the invention, reference is made to the claims.
The invention is based on the fact, unexpect-edly observed in studies that were carried out, that a working electrode made of glass-carbon yields very good results of measurement of oxidation and/or reduction potential at various pH values, i.e., the glass-carbon electrode is exceedingly independent of the pH of the solution. Glass-carbon electrodes are therefore emi-nently usable particularly in measuring oxidationand/or reduction potentials of aqueous solutions in the paper and pulp industry within wide pH variation ranges. The glass-carbon electrode can be used ln oxl-dation and reduction potential measurements concerning chemicals used in paper and pulp bleaching, such as chlorine compounds or other compounds.
Furthermore, when a glass-carbon electrode is used, the chlorine dioxide concentration and the chlo-rite concentration ean be separately determined e.g. in connection with cellulose bleaching; the sum of these concentrations ean be used towards process control.
The glass-carbon eleetrode is comparatively durable in use. Moreover, the glass-carbon eleetrode ean be construeted so that it is easily replaeeable in case of need, for instanee after it has been worn down.
A glass-earbon eleetrode is in this eontext understood to mean eleetrode materials, known in them-selves in the art, made of glass and earbon in whieh finely divided earbon has been plaeed inside the glass, e.g. while the glass is in molten state. Carbon elec-trode materials are known, for instance, by the name of earbon paste, glassy carbon, vitreous earbon, pyrolytie graphite. Other materials made of glass and carbon and presenting substantially equivalent properties are usable in the glass-earbon eleetrode of the invention.
It has been found in experiments whieh were earried out that the glass-carbon electrode is suited for use in measuring oxidation and/or reduetion poten-tials of solutions in the paper and pulp industry at any pH between 1 and 14, for instance at pH 1.5 to 8.5, e.g. 2 to 7.
When using glass-carbon for working electrode, one may make the eountereleetrode and/or the referenee eleetrode of any eleetrode material known in itself in the art, e.g. of a metal. Advantageously an eleetrode material as stable as possible should be eontemplated, sueh as platinum, gold, silver, titanium, Hastelloy C, ete.
The eleetrodes may advantageously be mounted in one single pick-up, for instance in tllt' way describ-ed in the Finnish Patent No. 65675.
The invention i8 described in ~letail in the following with the aid of embodiment examples, refer-ring to the attached drawings, wherein:-Fig. 1 presents a schematic diagram showing the circuitof the electrode system employed in voltametric meas-urements, Fig. 2 displays the results of measurement obtained with the aid of the electrode system of the invention, at constant chlorine dioxide concentration, respective-ly constant chlorite concentration, with changing pH, Fig. 3 presents the measuring voltage plotted over C102 concentration, at constant pH values, Fig. 4 presents the measuring voltage plotted over Cl02- concentration, at constant pH values, Figs 5-6 present the correlation between chlorine diox-ide concentrations determined by the standard titrimet-ric method, respectively with the electrode system of the invention, during one day, respectively one hour, in the Dl stage of the bleaching process, Fig. 7 presents chlorine dioxide and chlorite concen-trations which were measured with the electrode system of the invention, and their sum, in the Dl stage of 2S pulp displacement bleaching, and Fig. 8 presents a measuring electrode according to the invention.
In Fig 1 is seen the circuit diagram of the three electrodes for voltametric measurements in the conventional electrode system, and at the same time in the electrode system of the invention. The system com-prises a working electrode 1, a counterelectrode 2 and a reference electrode 3, disposed in a measuring cell 15, e.g. in a process line in which the solution to be analyzed is running. The electrodes 1, 2 and 3 are by means of leads 12, 13 and 14 connected to a measuring apparatus 4, that is to an electronic unit. The elec-tronic unit i~ arran~d to control A constant potentialdifference to ~xist hetwe~n th~ wor~ing and reference electrodes 1 and 2, which is selected to lie within the so-called limit current range of the substance to be measured. Hereby the oxidation or reduction of the sub-stance to be measured has been adjusted to be faster on the surface of the working electrode, compared with the transport of substance to this point. The concentration of the compound to be analyzed is then O on the sur-face of the working electrode~ This arrangement isfully conventional, and it has been described e.g. in the same applicant's earlier Finnish Patent FI 427666.
The measuring circult of Fig. 1 was employed in the examples following hereinafter.
In the embodiment depicted in Fig. 1, the counterelectrode 2 and reference electrode 3 are metal electrodes, for instance platinum, gold, silver. tita-nium, Hastelloy C, etc. The working electrode 1, how-ever, has been made of glass-carbon, as taught by the invention. The glass-carbon electrode is for instance made so that it is easy to replace.
The working electrode 1, counterelectrode 2 and reference electrode 3 are advantageously mounted in one single pick-up 5. The pick-up may be rod-shaped and inserted in the process pipeline through a shut-off means, e.g. a sealing tube, as has been described in the Finnish Patent No. 65675. The end of the pick-up may be planar, thereby constituting a surface which is in contact with the pulp stock to be measured, circu-lating in the pipe system. The electrodes 1, 2 and 3may have the shape of rods, rings, spatulas, or on the whole any conceivable shape, and they are advantageous-ly disposed on the end face of the pick-up, substan-tially parallelling the flow direction of the solution flowing in the pipeline.
An advantageous placement of the electrodes on the end face of a rod-shaped pick-up which is pushed into the process pipeline through a stlUt-O~ means lr, schematically shown in Fig. ~. ~lereln, t~le counterelec-~rode 2 ha6 annulAr shape and is concentric with the round pic~-up. The reference electrode 3 is placed cen-trally on the end ~ace of the pick-up, in the centre of the counterelectrode, and the working electrodes, in the embodiment here depicted four of them (their number may equally be 2 or three, or more), have been placed, in the embodiment depicted, symmetrically between the reference electrode and the counterelectrode. The work-ing electrodes and reference electrodes are pin-like.
The pick-up of Fig. 8 was used in the follow-ing examples. In the examples, the ClOz and Cl02- con-centrations were determined by titrinetry.
Example l, Voltage as a function of pH
In this study the voltage was determined as a function of pH, using for working electrode a glass-carbon electrode (GC) according to the invention. The measurements were carried out at constant chlorine di-oxide concentration (300 mg act. Cl2/l), respectively at constant chlorite concentration (300 mg act. Cl~/l).
As demonstrated by the results of measurement, presented in Fig. 2, the measuring voltage varied in the range of +200 to +150 mV, respectively -380 to -330 mV, at constant chlorine dioxide concentration and at constant chlorite concentration, respectively, when pH
varied between pH 2 and 7.
Example 2, Voltage as a function of C102 con-centration In this example the voltage of the glass-carbon electrode was measured as a function of chlorine dioxide concentration, at constant pH values. The chlo~
rine dioxide and chlorite concentrations were determin-ed by a standard titrimetric method (Wartiovaara I., The influence of pH on the Dl stage of a D/CEDl bleach-ing sequence, Paperi ja P~lu - Papper och ~'ra 6~. (1982) 9, 53~, 539-540, 5~s). ln the experiments, the c102 concentration varled in the range: lOo to ~oo mg/l act.
Cl~ and 40 to 600 mg/l act. clz. pH was 2.5 and 6.0, Fig. 3. Active chlorine is understood to be that quan-tity of elemental chlorine which in its oxidizing strength corresponds to a given quantity of any chlo-rine chemical employed in bleaching.
According to the results of measurement, the potential of the glass-carbon electrode varied in the range: 40 to 130 mV, and 40 to 115 mV.
It is noted on the basis of the measurements that the concentration dependence of the glass-carbon electrode is linear within the range studied.
Example 3, Voltage of the glass-carbon elec-trode as a function of C102- con-centration This experiment was e~uivalent in the way it was performed with that of Example 2. The ClOz- concen-trations varied in the range: 0 to 2750 mg/l and 80 to 2000 mg/l, the constant pH values were 2.5 and 6.0, Fig. 4.
Example 4, Voltage of the glass-carbon elec-trode as a function of Cl02 and Cl02- concentration, plant scale In this study, cellulose was bleached by a five-stage chlorine bleaching process (the five-stage chlorine bleaching process described in: Puumassan valmistus, Suomen Paperi-insinoorien Yhdistyksen oppi-ja kasikirja II osa 1, Virkola N.E., 2. painos 1983, Turku 1983, p.820-883). Retention time in the Dl bleach-ing tower was 4 hrs and temperature, 70~C. The stage was manually controlled. The chlorine dioxide concen-tration (in mV) was measured from the pulp ny means of the electrode system of the invention, 1 min. after chlorine. dioxide dosac~e. pH was continuously measured.
The chlorine dioxide residue and chlorite concentratlons were determlned by titrlmetric methods, lo to 20 sec-onds after sampling.
~he chlorine dioxide concentration determined with the electrode system of the invention and the cor-responding chlorine concentration determined by titri-metry (measurements made when the chlorine dioxide dosage changed) are presented in Fig. S. Correlation exists between the concentrations, coefficient of cor-relation 0.90.
In Fig. 6 is presented a similar determination as in Fig. 5, regarding chlorite concentration. Clear correlation exists between the chlorite concentrations determined with the electrode system of the invention and by titrimetry, coefficient of correlation 0.98.-No low chlorite concentrations occur in the figure owing to the circumstance that there was no chlorite at the point of measurement prior to change of dosage, and the change was made very rapidly.
Example 5, Displacement bleaching From the filtrate of the Dl stage in displace-ment bleaching separate determinations were furthermore made of the ClOz and ClOz- concentrations, 40 min.
after chlorine dioxide dosage, using the electrode sys-tem of the invention; at the same point the active chlorine was determined by titrimetric method. Dis-placement bleaching is presented in the reference, p.883-887. This is a process including a separate D2 stage.
In Fig. 7 are separately presented the chlo-rine dioxide concentration and chlorite concentration determined at the measuring point using the electrode system of the invention, and their sum. In the figure has been added the active chlorine concentration deter-mined by titrimetric method, SUM(lab). The chlorine dioxide~chlorito change of reaction equilibrium was achieved with sodium hydroxide in that pH wa~ elevated at 11.5 hrs from pH 4.5 to 5.5. In Figs 5-7 the C102, Cl02- concentrations and their sum have been calculat-ed, and stated, in units g active Cl~ per litre.
The embodiment examples are meant to illus-trate the invention without in any way confining it.
The present invention concerns an electrode system for voltametric measurements, for measuring oxi-dative and/or reducing compounds in electrolytes, i.e.,mainly in aqueous solutions in the paper and pulp in-dustry, said system comprising a working electrode, a counterelectrode and a reference electrode. which are connected to a voltametric measuring instrument.
Normally, three electrodes are used in volta-metric measurements: a working electrode, a counter-electrode and a reference electrode. The electrodes are placed in a measuring cell or in the solution to be measured. Using the measuring apparatus and its reg-ulation component, a constant potential difference is established between the working and reference electrodes connected to the apparatus, which is usually selected to be within the so-called limit current range of the substance to be determined in the measurement, whereby the oxidation, respectively reduction of the substance to be measured has been regulated to be faster on the surface of the working electrode than the transport of said substance to this electrode. This implies that the concentration of the compound to be analyzed is O on the surface of the working electrode. The transport of the compound to be analyzed to the surface of the work-iing electrode can be arranged so that the sample flows past the working electrode, or alternatively the work-ing electrode is moved relative to the sample, e.g. by rotating.
By effect of the elec~ron transfer reaction taking place on the surface of the working electrode (i.e., oxidation or reduction of the compound to be measured), the potential difference between the working and reference electrodes tends to change. This change is observed with the aid of an electronic measuring instrument included in the measuring apparatus, and it is prevented by supplying currcnt to the working elec-trode through the reference electrode. The measured value of thls current, or the correspondlng voltage, is directly proportional to the concentration of the sub-stance to be measured, on the basis of the fact thatthe rate of diffusion to the electrode increases as the concentration o~ the substance to be analyzed increas-es In continuous analytic measurement the refer-lo ence electrode is generally the weakest point of thesystem. The working and counterelectrodes are usually metal electrodes and therefore durable and requiring little maintenance. Problems at the reference electrode may also be caused by pressure fluctuations in the sample, for instance in a process pipeline system.
Pressure changes may block or interrupt the salt bridge of the reference electrode, whereby the potential of the working electrode changes, causing a measuring error. Furthermore, installation in a pipeline of such reference electrodes as are known in the art is highly awkward, owing to large size and fragility of the ref-erence electrodes.
With a view to eliminating the drawbacks just mentioned, an electrode system has been developed in prior art in which the reference electrode is made of metal in likeness with the working and counterelec-trodes. All electrodes are appropriately mounted in one single pick-up, preferably on the end of a rod-shaped pick-up which is directly pushed into the process pipeline. With the electrode system thus achieved, an electrode system has been created which is substantial-ly superior to earlier systems in structural simplicity and durability and requires less maintenance. The elec-trode system tolerates pressure variations, mechanical loads, in addition to which the electrodes can be kept in continuous contact with the process solution, where-by they are preserved against soiling and chemical challges .
~ rhe electrode system which has been created is, however, embarrassed by a drawback which has emerg-ed in measurements carried out on aqueous solutions employed in the paper and pulp industry, such as stock suspensions in various stages of bleaching. In some instances, wide pH variations induce inaccuracy in the value of the ~neasuring voltage. On the other hand, wide pH fluctuations cause chemical reactions, whereby the chemical that is being measured may be transiently con-verted to another compound. As an example the chlorine dioxide bleaching process may be mentioned, in which with ascending pH the. chlorine dioxide reacts to become chlorite, while it reverts to chlorine dioxide in the bleaching tower. In this case the sum of chlorine diox-ide and chlorite represents the bleaching chlorine. It is only possible to measure the chlorine dioxide with the electrode system now in use.
The object of the invention is to provide a novel electrode system with which oxidation and/or re-duction potentials of electrolytes can be measured within very wide pH value limits. Moreover, the inven-tion aims to provide an electrode system for measuring oxidation and reduction potentials which is usable in particular in bleaching processes of various types.
Regarding the features characteristic of the invention, reference is made to the claims.
The invention is based on the fact, unexpect-edly observed in studies that were carried out, that a working electrode made of glass-carbon yields very good results of measurement of oxidation and/or reduction potential at various pH values, i.e., the glass-carbon electrode is exceedingly independent of the pH of the solution. Glass-carbon electrodes are therefore emi-nently usable particularly in measuring oxidationand/or reduction potentials of aqueous solutions in the paper and pulp industry within wide pH variation ranges. The glass-carbon electrode can be used ln oxl-dation and reduction potential measurements concerning chemicals used in paper and pulp bleaching, such as chlorine compounds or other compounds.
Furthermore, when a glass-carbon electrode is used, the chlorine dioxide concentration and the chlo-rite concentration ean be separately determined e.g. in connection with cellulose bleaching; the sum of these concentrations ean be used towards process control.
The glass-carbon eleetrode is comparatively durable in use. Moreover, the glass-carbon eleetrode ean be construeted so that it is easily replaeeable in case of need, for instanee after it has been worn down.
A glass-earbon eleetrode is in this eontext understood to mean eleetrode materials, known in them-selves in the art, made of glass and earbon in whieh finely divided earbon has been plaeed inside the glass, e.g. while the glass is in molten state. Carbon elec-trode materials are known, for instance, by the name of earbon paste, glassy carbon, vitreous earbon, pyrolytie graphite. Other materials made of glass and carbon and presenting substantially equivalent properties are usable in the glass-earbon eleetrode of the invention.
It has been found in experiments whieh were earried out that the glass-carbon electrode is suited for use in measuring oxidation and/or reduetion poten-tials of solutions in the paper and pulp industry at any pH between 1 and 14, for instance at pH 1.5 to 8.5, e.g. 2 to 7.
When using glass-carbon for working electrode, one may make the eountereleetrode and/or the referenee eleetrode of any eleetrode material known in itself in the art, e.g. of a metal. Advantageously an eleetrode material as stable as possible should be eontemplated, sueh as platinum, gold, silver, titanium, Hastelloy C, ete.
The eleetrodes may advantageously be mounted in one single pick-up, for instance in tllt' way describ-ed in the Finnish Patent No. 65675.
The invention i8 described in ~letail in the following with the aid of embodiment examples, refer-ring to the attached drawings, wherein:-Fig. 1 presents a schematic diagram showing the circuitof the electrode system employed in voltametric meas-urements, Fig. 2 displays the results of measurement obtained with the aid of the electrode system of the invention, at constant chlorine dioxide concentration, respective-ly constant chlorite concentration, with changing pH, Fig. 3 presents the measuring voltage plotted over C102 concentration, at constant pH values, Fig. 4 presents the measuring voltage plotted over Cl02- concentration, at constant pH values, Figs 5-6 present the correlation between chlorine diox-ide concentrations determined by the standard titrimet-ric method, respectively with the electrode system of the invention, during one day, respectively one hour, in the Dl stage of the bleaching process, Fig. 7 presents chlorine dioxide and chlorite concen-trations which were measured with the electrode system of the invention, and their sum, in the Dl stage of 2S pulp displacement bleaching, and Fig. 8 presents a measuring electrode according to the invention.
In Fig 1 is seen the circuit diagram of the three electrodes for voltametric measurements in the conventional electrode system, and at the same time in the electrode system of the invention. The system com-prises a working electrode 1, a counterelectrode 2 and a reference electrode 3, disposed in a measuring cell 15, e.g. in a process line in which the solution to be analyzed is running. The electrodes 1, 2 and 3 are by means of leads 12, 13 and 14 connected to a measuring apparatus 4, that is to an electronic unit. The elec-tronic unit i~ arran~d to control A constant potentialdifference to ~xist hetwe~n th~ wor~ing and reference electrodes 1 and 2, which is selected to lie within the so-called limit current range of the substance to be measured. Hereby the oxidation or reduction of the sub-stance to be measured has been adjusted to be faster on the surface of the working electrode, compared with the transport of substance to this point. The concentration of the compound to be analyzed is then O on the sur-face of the working electrode~ This arrangement isfully conventional, and it has been described e.g. in the same applicant's earlier Finnish Patent FI 427666.
The measuring circult of Fig. 1 was employed in the examples following hereinafter.
In the embodiment depicted in Fig. 1, the counterelectrode 2 and reference electrode 3 are metal electrodes, for instance platinum, gold, silver. tita-nium, Hastelloy C, etc. The working electrode 1, how-ever, has been made of glass-carbon, as taught by the invention. The glass-carbon electrode is for instance made so that it is easy to replace.
The working electrode 1, counterelectrode 2 and reference electrode 3 are advantageously mounted in one single pick-up 5. The pick-up may be rod-shaped and inserted in the process pipeline through a shut-off means, e.g. a sealing tube, as has been described in the Finnish Patent No. 65675. The end of the pick-up may be planar, thereby constituting a surface which is in contact with the pulp stock to be measured, circu-lating in the pipe system. The electrodes 1, 2 and 3may have the shape of rods, rings, spatulas, or on the whole any conceivable shape, and they are advantageous-ly disposed on the end face of the pick-up, substan-tially parallelling the flow direction of the solution flowing in the pipeline.
An advantageous placement of the electrodes on the end face of a rod-shaped pick-up which is pushed into the process pipeline through a stlUt-O~ means lr, schematically shown in Fig. ~. ~lereln, t~le counterelec-~rode 2 ha6 annulAr shape and is concentric with the round pic~-up. The reference electrode 3 is placed cen-trally on the end ~ace of the pick-up, in the centre of the counterelectrode, and the working electrodes, in the embodiment here depicted four of them (their number may equally be 2 or three, or more), have been placed, in the embodiment depicted, symmetrically between the reference electrode and the counterelectrode. The work-ing electrodes and reference electrodes are pin-like.
The pick-up of Fig. 8 was used in the follow-ing examples. In the examples, the ClOz and Cl02- con-centrations were determined by titrinetry.
Example l, Voltage as a function of pH
In this study the voltage was determined as a function of pH, using for working electrode a glass-carbon electrode (GC) according to the invention. The measurements were carried out at constant chlorine di-oxide concentration (300 mg act. Cl2/l), respectively at constant chlorite concentration (300 mg act. Cl~/l).
As demonstrated by the results of measurement, presented in Fig. 2, the measuring voltage varied in the range of +200 to +150 mV, respectively -380 to -330 mV, at constant chlorine dioxide concentration and at constant chlorite concentration, respectively, when pH
varied between pH 2 and 7.
Example 2, Voltage as a function of C102 con-centration In this example the voltage of the glass-carbon electrode was measured as a function of chlorine dioxide concentration, at constant pH values. The chlo~
rine dioxide and chlorite concentrations were determin-ed by a standard titrimetric method (Wartiovaara I., The influence of pH on the Dl stage of a D/CEDl bleach-ing sequence, Paperi ja P~lu - Papper och ~'ra 6~. (1982) 9, 53~, 539-540, 5~s). ln the experiments, the c102 concentration varled in the range: lOo to ~oo mg/l act.
Cl~ and 40 to 600 mg/l act. clz. pH was 2.5 and 6.0, Fig. 3. Active chlorine is understood to be that quan-tity of elemental chlorine which in its oxidizing strength corresponds to a given quantity of any chlo-rine chemical employed in bleaching.
According to the results of measurement, the potential of the glass-carbon electrode varied in the range: 40 to 130 mV, and 40 to 115 mV.
It is noted on the basis of the measurements that the concentration dependence of the glass-carbon electrode is linear within the range studied.
Example 3, Voltage of the glass-carbon elec-trode as a function of C102- con-centration This experiment was e~uivalent in the way it was performed with that of Example 2. The ClOz- concen-trations varied in the range: 0 to 2750 mg/l and 80 to 2000 mg/l, the constant pH values were 2.5 and 6.0, Fig. 4.
Example 4, Voltage of the glass-carbon elec-trode as a function of Cl02 and Cl02- concentration, plant scale In this study, cellulose was bleached by a five-stage chlorine bleaching process (the five-stage chlorine bleaching process described in: Puumassan valmistus, Suomen Paperi-insinoorien Yhdistyksen oppi-ja kasikirja II osa 1, Virkola N.E., 2. painos 1983, Turku 1983, p.820-883). Retention time in the Dl bleach-ing tower was 4 hrs and temperature, 70~C. The stage was manually controlled. The chlorine dioxide concen-tration (in mV) was measured from the pulp ny means of the electrode system of the invention, 1 min. after chlorine. dioxide dosac~e. pH was continuously measured.
The chlorine dioxide residue and chlorite concentratlons were determlned by titrlmetric methods, lo to 20 sec-onds after sampling.
~he chlorine dioxide concentration determined with the electrode system of the invention and the cor-responding chlorine concentration determined by titri-metry (measurements made when the chlorine dioxide dosage changed) are presented in Fig. S. Correlation exists between the concentrations, coefficient of cor-relation 0.90.
In Fig. 6 is presented a similar determination as in Fig. 5, regarding chlorite concentration. Clear correlation exists between the chlorite concentrations determined with the electrode system of the invention and by titrimetry, coefficient of correlation 0.98.-No low chlorite concentrations occur in the figure owing to the circumstance that there was no chlorite at the point of measurement prior to change of dosage, and the change was made very rapidly.
Example 5, Displacement bleaching From the filtrate of the Dl stage in displace-ment bleaching separate determinations were furthermore made of the ClOz and ClOz- concentrations, 40 min.
after chlorine dioxide dosage, using the electrode sys-tem of the invention; at the same point the active chlorine was determined by titrimetric method. Dis-placement bleaching is presented in the reference, p.883-887. This is a process including a separate D2 stage.
In Fig. 7 are separately presented the chlo-rine dioxide concentration and chlorite concentration determined at the measuring point using the electrode system of the invention, and their sum. In the figure has been added the active chlorine concentration deter-mined by titrimetric method, SUM(lab). The chlorine dioxide~chlorito change of reaction equilibrium was achieved with sodium hydroxide in that pH wa~ elevated at 11.5 hrs from pH 4.5 to 5.5. In Figs 5-7 the C102, Cl02- concentrations and their sum have been calculat-ed, and stated, in units g active Cl~ per litre.
The embodiment examples are meant to illus-trate the invention without in any way confining it.
Claims (4)
1. An electrode system for voltametric meas-urements for measuring oxidative and/or reducing com-pounds in electrolytes, i.e., mainly in aqueous solu-tions in the paper and pulp industry, said system com-prising a working electrode (1), a counterelectrode (2) and a reference electrode (3) which are connected to a voltametric measuring apparatus (4), characterized in that the working electrode (1) is made of glass-carbon.
2. Electrode system according to claim 1, characterized in that the counterelectrode (2) is made of a metal selected from the group: platinum, gold, silver, titanium, and Hastelloy C.
3. Electrode system according to claim 1 or 2, characterized in that the reference electrode (3) is made of a metal selected from the group: platinum, gold, silver, titanium, and Hastelloy C.
4. Electrode system according to any one of claims 1-3, characterized in that the pH of the elec-trolyte is 1 to 14, suitably 2 to 7.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI901636A FI86671C (en) | 1990-03-30 | 1990-03-30 | ELECTRICAL SYSTEM VOLTAMETRISKA MAETNINGAR. |
| FI901636 | 1990-03-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2039528A1 true CA2039528A1 (en) | 1991-10-01 |
Family
ID=8530185
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002039528A Abandoned CA2039528A1 (en) | 1990-03-30 | 1991-04-02 | Electrode system for voltametric measurements |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH06341971A (en) |
| CA (1) | CA2039528A1 (en) |
| DE (1) | DE4109909A1 (en) |
| FI (1) | FI86671C (en) |
| SE (1) | SE9100906L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU201055U1 (en) * | 2020-08-06 | 2020-11-25 | Федеральное государственное бюджетное учреждение науки Институт проблем химической физики Российской Академии наук (ФГБУН ИПХФ РАН) | CELL FOR MEASURING CONDUCTIVITY AND WINDOWS OF ELECTROCHEMICAL STABILITY OF LIQUID ELECTROLYTE |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH08508575A (en) * | 1994-01-25 | 1996-09-10 | ケメロヴスキ・ゴスダルストヴェニ・ユニヴィルシテット | Electrode system and device for testing substances by coulometric analysis using the system |
| DE19748124C1 (en) * | 1997-10-31 | 1999-03-18 | Fraunhofer Ges Forschung | Low volatility substance detection by an electrochemical sensor |
| FR2798996A1 (en) * | 1999-09-23 | 2001-03-30 | Suisse Electronique Microtech | SELF-DIAGNOSTIC ELECTROCHEMICAL SENSOR |
| DE10240043A1 (en) * | 2002-08-27 | 2004-03-04 | Prominent Dosiertechnik Gmbh | Sensor for volumetric measurement of chlorite concentration in aqueous solution, e.g. drinking water, comprises working electrode made from glass-carbon |
| DE102007016174A1 (en) | 2007-04-02 | 2008-10-09 | Reiss, Gerhard, Dr. | Multi-electrode measuring cell, has shaft with outer thread and embedded electrodes, whose free ends lie free on front side of shaft and cover with inner thread |
| DE102007016173A1 (en) | 2007-04-02 | 2008-10-09 | Reiss, Gerhard, Dr. | Single-rod measuring cell for determining e.g. chlorine, in drinking water, has operating electrode and reference electrode forming electrically independent measuring systems, where system are commonly connected at electrode |
| DE102020118202A1 (en) | 2020-07-09 | 2022-01-13 | Endress+Hauser Conducta Gmbh+Co. Kg | Sensor module, probe body and probe for measuring at least one measured variable of a measuring liquid |
-
1990
- 1990-03-30 FI FI901636A patent/FI86671C/en not_active IP Right Cessation
-
1991
- 1991-03-26 DE DE4109909A patent/DE4109909A1/en not_active Withdrawn
- 1991-03-26 SE SE9100906A patent/SE9100906L/en not_active Application Discontinuation
- 1991-03-30 JP JP3235330A patent/JPH06341971A/en active Pending
- 1991-04-02 CA CA002039528A patent/CA2039528A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| RU201055U1 (en) * | 2020-08-06 | 2020-11-25 | Федеральное государственное бюджетное учреждение науки Институт проблем химической физики Российской Академии наук (ФГБУН ИПХФ РАН) | CELL FOR MEASURING CONDUCTIVITY AND WINDOWS OF ELECTROCHEMICAL STABILITY OF LIQUID ELECTROLYTE |
Also Published As
| Publication number | Publication date |
|---|---|
| DE4109909A1 (en) | 1991-10-02 |
| FI86671C (en) | 1992-09-25 |
| FI901636A (en) | 1991-10-01 |
| FI86671B (en) | 1992-06-15 |
| SE9100906D0 (en) | 1991-03-26 |
| FI901636A0 (en) | 1990-03-30 |
| SE9100906L (en) | 1991-10-01 |
| JPH06341971A (en) | 1994-12-13 |
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