CN103233263B - A kind of measuring method of cathodic current efficiency of ionic exchange membrane cell - Google Patents

Abstract

The present invention relates to a kind of measuring method of cathodic current efficiency of ionic exchange membrane cell.The method is by measuring oxygen percentage in chlorine, going out groove concentration of lye, going out NaClO in groove salt solution ₃concentration, the Cl gone out in groove salt solution ₂concentration with enter Na in groove salt solution ₂cO ₃concentration five, calculates η _naOH, record cathodic current efficiency of ionic exchange membrane cell.Method of the present invention, while simplification calculates, avoids the inaccurate error brought of instrument parameter, the comparability of current efficiency between the device achieving different model.

Description

A kind of measuring method of cathodic current efficiency of ionic exchange membrane cell

Technical field

The present invention relates to a kind of cathodic current efficiency of ionic exchange membrane cell method for measuring, particularly a kind of measuring method of chlor-alkali perfluorinated ion-exchange membrane method electric tank cathode current efficiency, belongs to electrochemical field.

Background technology

In electrolytic reaction, usual current efficiency (Currentefficiency, be reduced to CE, also can represent with symbol η) represent the Quality degree of effective utilization of electrolysis electricity, therefore current efficiency is very important economic and technical norms of electrolytic process and the key contrast index of state of the art height.Current efficiency judges chlor-alkali film properties and the leading indicator the need of replacing, but have substantial connection with direct current consumption, quality product and process conditions.Due to the reverse osmosis of alkali from negative electrode to anode and the existence of side reaction, cause current efficiency to be generally less than 1, the reaction carried out at anode comprises:

(A) reaction of water in the chlorine generated and anolyte

Cl ₂+H ₂O→HCl+HClO

(B) reaction of the chlorine dissolved and the sodium hydroxide of coming from cathode compartment reverse osmosis

${\mathrm{Cl}}_2+2\mathrm{NaOH}\→\frac{1}{3}\mathrm{NaCl}{O}_3+\frac{5}{3}\mathrm{NaCl}+H_{2}O$

${\mathrm{Cl}}_2+2\mathrm{NaOH}\→\frac{1}{2}{O}_2+2\mathrm{NaCl}+H_{2}O$

$\mathrm{HClO}+\mathrm{NaOH}\→\frac{1}{2}{O}_2+\mathrm{NaCl}+H_{2}O$

The current efficiency measuring method that different chlor-alkali film suppliers and electrolyzer supply commercial city have it to recommend, wherein existing anodic current efficiency also has cathode efficiency, also (Cheng Dianbin edits the current efficiency formula carrying out calculating based on the sulfate radical content in anode acid adding or salt solution, " ionic membrane method alkaline production technology ", Beijing: Chemical Industry Press, 1998, p33-p37), chlor-alkali production producer acceptance level higher normally based on the cathode efficiency of caustic soda production, namely carry out measure and calculation according to sodium hydroxide actual output and obtain current efficiency.Cathode efficiency also has several assay method:

(1) based on alkali determination of yield cathode efficiency

The flow of NaOH solution, the weight percent concentration of NaOH solution in the first analytical unit time, the electric current that combining unit groove passes through and unit groove number etc., calculate cathode efficiency η NaOH by the following method:

${\mathrm{\η}}_{\mathrm{NaOH}}=\frac{Q_{\mathrm{NaOH}}\×C_{\mathrm{NaOH}}\×{\mathrm{\ρ}}_{\mathrm{NaOH}}}{{\mathrm{\ϵ}\×10}^{-3}\×I\×N}\×100\%...\left(1\right)$

In formula:

Q _naOH---the flow of NaOH solution in the unit time, m ³/ h;

C _naOH---the weight percent concentration of NaOH solution, %;

ρ _naOH---the density of NaOH solution, kg/L;

The electrochemical equivalent of ε---alkali, NaOH is 1.492g/ (Ah), KOH is 2.09g/ (Ah)

The electric current that I---unit groove passes through, kA;

N---unit groove number;

(2) acidimetric estimation cathode efficiency is added based on anode

In electrolytic process, along with equaling (1-η _naOH) migration hydroxy, the acidity of anolyte will reduce, and therefore, first measure fed anode liquid and will return the acidity of anolyte, and the difference according to fed anode liquid and the acidity that returns anolyte carrys out calculating current efficiency.But, be only accurately with measuring and calculating value when hydroxide ion during the method only has the acidity of outlet anode liquid enough to go.

(3) based on anodic gas purity testing cathode efficiency

In electrolytic process, along with equaling (1-η _naOH) hydroxide radical move in anolyte, because side reaction, electrochemical oxidation etc. generate the by product such as oxygen and oxymuriate, thus the current efficiency caused loss.Also the change of anolyte acidity is considered in addition, by measuring anodic gas purity, by η _naOH=1-(η _o2+ η _hClO+ η _clO3)-η _hClcalculate cathode efficiency.Wherein the current efficiency loss of each side product species also respectively has complicated calculation formula (Ren Jianfen, the discussion of ionic membrane current efficiency calculating formula, Chinese chlor-alkali, 2003,7:15-17), and quite high to the accuracy requirement of analytical data.

The measuring method of existing cathode efficiency has the following disadvantages in actual applications: first, the accuracy of measurement means has a strong impact on the accuracy of calculating, from reometer to electric quantity integration device, from by-pass valve control under meter, to liquidometer from pH meter to densometer, links all may also exist the problem of either large or small accuracy.In addition, also to consider the stability of production equipment itself and fluctuation, the scientific rationality of sampling, the accuracy of analytical test, human users's difference, pole span and current efficiency relation uncertainty (see Liang Han, a kind of method of instantaneous assessment current efficiency, light metal, 2010,2:28-33) and the ununiformity etc. of distribution of current, all can impact the Accurate Determining of current efficiency.Meanwhile, the grooved of different manufacturers is different, and film producer is different with model, and the current efficiency that result in mensuration does not have comparability.

Summary of the invention

For shortcomings and deficiencies of the prior art, the invention provides a kind of measuring method of cathodic current efficiency of ionic exchange membrane cell.

Technical scheme of the present invention is as follows:

A measuring method for cathodic current efficiency of ionic exchange membrane cell, step is as follows:

(1) adopt oxygen volumn concentration in gas chromatography determination anode export house steward gas, be designated as O ₂%, i.e. oxygen percentage in chlorine;

(2) employing determination of acid-basetitration negative electrode goes out the alkali concn in groove alkali lye, and unit g/L, is designated as c _naOH;

(3) spectrophotometry anode is adopted to go out NaClO in groove salt solution ₃concentration, unit g/L, is designated as (a);

(4) employing iodometric determination anode goes out the free Cl in groove salt solution ₂concentration, unit g/L, is designated as cCl ₂(a);

(5) determination of acid-basetitration anode is adopted to enter Na in groove salt solution ₂cO ₃concentration, unit g/L, is designated as (f);

(6) η is calculated by following formula (I) _naOH, record cathodic current efficiency of ionic exchange membrane cell:

${\mathrm{\η}}_{\mathrm{NaOH}}=\frac{1}{1+2\×\frac{O_2\%}{100}+\frac{80}{c_{\mathrm{NaOH}}}\×(\frac{3\×c_{\mathrm{NaCl}{O}_3}\left(a\right)}{106}+\frac{c_{{\mathrm{Cl}}_2{\mathrm{CO}}_3}\left(f\right)}{71})}\×\%...\left(I\right)$

The present invention is particularly suitable for the mensuration of chlor-alkali perfluorinated ion-exchange membrane method electric tank cathode current efficiency.

Preferably, step (1) adopts oxygen volumn concentration in gas chromatography determination anode export house steward gas, have easy, fast, feature accurately.See the vapor-phase chromatography that Cheng Dianbin " ionic membrane method alkaline production technology " (Chemical Industry Press, September 1 2008 date of publication, 308-309 page) provides.

Preferably, step (4) employing iodometric determination anode goes out the free Cl in groove salt solution ₂concentration a (), adopts classical iodimetry,iodometry, have easy, fast, feature accurately.See the iodimetric analysis method that Cheng Dianbin " ionic membrane method alkaline production technology " (Chemical Industry Press, September 1 2008 date of publication, the 280th page) provides.

Preferred according to the present invention, acid base titration is by GB GB/T4348.1; Spectrophotometry presses GBT11200.1-1989.

Compared with prior art, excellent results of the present invention is as follows:

1, the measuring method of cathodic current efficiency of ionic exchange membrane cell of the present invention, the parameter adopted mainly anodic gas oxygen level, the alkali lye degree of depth, enter groove salt solution concentration of sodium carbonate, turnover groove salt solution sodium chlorate and to go out in groove salt solution five parameters such as chlorine gas concentration, can analyze convenient, fast, exactly and obtain corresponding data.The analysis of anode chlorine purity adopts the analytical procedure of gas-chromatography, and accuracy and precision all reach quite high degree.

2, compare based on alkali determination of yield cathode efficiency and the prior art adding acidimetric estimation cathode efficiency based on anode, cathode efficiency measuring method of the present invention, avoid measuring and import and export the parameter such as flow, acidity, decrease the inaccurate problem of current efficiency because the fluctuation of the instrumented data such as under meter and acidometer and error cause.

3, compare based on anodic gas purity testing cathode efficiency, the measuring method of cathode efficiency of the present invention, avoid needing location parameter too much and the problem depending critically upon data analysis, simple and direct clear, easy handling;

4, adopt the measuring method of cathodic current efficiency of ionic exchange membrane cell of the present invention, the comparability of the current efficiency between the electrolyzer of different process can be made greatly to increase.

Embodiment

By the following examples the present invention is further described, but the present invention is not limited only to following examples.Acid base titration GB/T4348.1, spectrophotometry GBT11200.1-1989, gas chromatograph GC9890A type (Shanghai Ling Hua Instrument Ltd.).Adopt vapor-phase chromatography see Cheng Dianbin " ionic membrane method alkaline production technology " (Chemical Industry Press, September 1 2008 date of publication, 308-309 page; Iodimetry,iodometry, see Cheng Dianbin " ionic membrane method alkaline production technology ", Chemical Industry Press, the 280th page.

Embodiment 1: a kind of measuring method of cathodic current efficiency of ionic exchange membrane cell, step is as follows:

At a multipole type electrolyzer with natural circulation, useful area 2.7m ², running current density 4.5kA/m ²; Oxygen volumn concentration in gas chromatography determination anode export house steward gas, records in chlorine containing oxygen 0.6%(O ₂%); Acid base titration records negative electrode and goes out alkali concn 420g/L(c in groove alkali lye _naOH), acid base titration records anode and enters Na in groove salt solution ₂cO ₃concentration 0.4g/L( (f)); Spectrophotometry records anode and goes out NaClO in groove salt solution ₃concentration 8g/L( (a)); Adopt iodimetry,iodometry to record anode and go out Cl in groove salt solution ₂concentration 3g/L( (a)); After being calculated by formula (I), record cathodic current efficiency of ionic exchange membrane cell η NaOH=94.25%.

${\mathrm{\η}}_{\mathrm{NaOH}}=\frac{1}{1+2\×\frac{O_2\%}{100}+\frac{80}{c_{\mathrm{NaOH}}}\×(\frac{3\×c_{\mathrm{NaCl}{O}_3}\left(a\right)}{106}+\frac{c_{{\mathrm{Cl}}_2{\mathrm{CO}}_3}\left(f\right)}{71})}\×\%...\left(I\right)$

Under same grooved and condition, the actual product alkali number according to accurate measurement is calculated, and according to existing (1) planting measuring method in background technology, calculating, record η through formula (1) _naOH=94.12%.

Embodiment 2 ~ embodiment 12: the measuring method of the cathodic current efficiency of ionic exchange membrane cell of different grooved, operation steps is identical with embodiment 1, result data list in table 1.As can be seen from Table 1, according to the cathode efficiency that method of the present invention and formula (I) obtain, with the result calculated according to formula (1) based on alkali determination of yield cathode efficiency closely, well can react the current efficiency under practical situation.

5 parameters obtained and cathodic current efficiency of ionic exchange membrane cell is detected when the different grooved of table 1 and processing condition

Claims (1)

1. a measuring method for cathodic current efficiency of ionic exchange membrane cell, step is as follows:

(1) adopt oxygen volumn concentration in gas chromatography determination anode export house steward gas, be designated as O ₂%, i.e. oxygen percentage in chlorine;

(2) employing determination of acid-basetitration negative electrode goes out the alkali concn in groove alkali lye, and unit g/L, is designated as c _naOH;

(3) spectrophotometry anode is adopted to go out NaClO in groove salt solution ₃concentration, unit g/L, is designated as (a);

(4) employing iodometric determination anode goes out the free Cl in groove salt solution ₂concentration, unit g/L, is designated as (a);

(5) adopt acid base titration GB/T4348.1 to measure anode and enter Na in groove salt solution ₂cO ₃concentration, unit g/L, is designated as (f);

(6) η is calculated by following formula (I) _naOH, record cathodic current efficiency of ionic exchange membrane cell:

${\mathrm{\η}}_{NaOH}=\frac{1}{1+2\×\frac{O_2\%}{100}+\frac{80}{c_{NaOH}}\×(\frac{3\×c_{{\mathrm{NaClO}}_3}\left(a\right)}{106}+\frac{c_{{\mathrm{Cl}}_2}\left(a\right)-2c_{{\mathrm{Na}}_2{\mathrm{CO}}_3}\left(f\right)}{71})}\×100\%...\left(I\right).$