CN103233263A - Method for measuring cathodic current efficiency of ionic exchange membrane cell - Google Patents

Abstract

The invention relates to a method for measuring the cathodic current efficiency of an ionic exchange membrane cell. According to the method, the oxygen percentage in chlorine, the concentration of the alkali liquor out from the cell, the NaClO3 concentration in saline out from the cell, the Cl2 concentration in the saline out from the cell, and the NaClO3 concentration in the saline fed into the cell are measured to calculate etaNaOH, and then the cathodic current efficiency of the ionic exchange membrane cell is measured. By adopting the method provided by the invention, calculation is simplified, simultaneously, error caused by inaccurate instrument parameters is prevented, and the comparability between current efficiencies of devices of different types is achieved.

Description

A kind of measuring method of ion-exchange membrane electrolyzer cathode efficiency

Technical field

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

Background technology

In electrolytic reaction, usually with current efficiency (Current efficiency, be reduced to CE, also can represent with symbol η) represent electrolysis electricity effectively utilize degree, so 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 is the leading indicator of judging the chlor-alkali film properties and whether needing to change, but with direct current consumption, quality product and process conditions substantial connection is arranged.Because the reverse osmosis of alkali from the negative electrode to the anode and the existence of side reaction cause current efficiency to be generally less than 1, the reaction of carrying out at anode comprises:

(A) reaction of water in the chlorine of Sheng Chenging and the anolyte

Cl ₂+H ₂O→HCl+HClO

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

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

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

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

There is the current efficiency measuring method of its recommendation different chlor-alkali film suppliers and electrolyzer supply commercial city, wherein existing anodic current efficiency also has cathode efficiency, also have based on anode and add current efficiency formula (the Cheng Dianbin chief editor that the sulfate radical content in acid or the salt solution calculates, " ionic membrane legal system alkali 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 measure according to the sodium hydroxide actual output and calculate current efficiency.Cathode efficiency also has several assay methods:

(1) based on alkali determination of yield cathode efficiency

The flow of NaOH solution, the weight percent concentration of NaOH solution in elder generation's analytical unit time, the electric current that the 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 the 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 are 1.492g/ (Ah), and KOH is 2.09g/ (Ah)

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

N---unit groove number;

(2) add the acidimetric estimation cathode efficiency based on anode

In the electrolytic process, along with equaling (1-η _NaOH) migration hydroxy, the acidity of anolyte will reduce, and therefore, measure earlier fed anode liquid and will return the acidity of anolyte, according to the different current efficiency of calculating of fed anode liquid and the acidity of returning anolyte.But, this method have only the acidity of outlet anolyte enough go in and hydroxide ion the time measuring and calculating value be only accurately.

(3) based on anodic gas purity testing cathode efficiency

In the electrolytic process, along with equaling (1-η _NaOH) hydroxide radical move in the anolyte because side reaction, electrochemical oxidation etc. generate by products such as oxygen and oxymuriate, thus the current efficiency that causes loss.Also consider the variation of anolyte acidity in addition, by measuring anodic gas purity, press η _NaOH=1-(η _O2+ η _HClO+ η _ClO3)-η _HClCalculate cathode efficiency.Wherein the current efficiency of each side product species loss also respectively have 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: at first, the accuracy of measurement means has a strong impact on the accuracy of calculating, from reometer to the electric quantity integration device, from the by-pass valve control to the under meter, to liquidometer, each link all may exist the problem of either large or small accuracy from the pH meter to the densometer.In addition, to consider that also the uncertainty of accuracy, personnel operation difference, pole span and current efficiency relation of scientific rationality, analytical test of the stability of production equipment itself and fluctuation, sampling is (referring to Liang Han, a kind of method of instantaneous assessment current efficiency, light metal, 2010,2:28-33) and the ununiformity of distribution of current etc., all can the accurate mensuration of current efficiency be impacted.Simultaneously, the grooved difference of different manufacturers, film producer is different with model, and the current efficiency that has caused measuring does not have comparability.

Summary of the invention

At the deficiencies in the prior art and defective, the invention provides a kind of measuring method of ion-exchange membrane electrolyzer cathode efficiency.

Technical scheme of the present invention is as follows:

A kind of measuring method of ion-exchange membrane electrolyzer cathode efficiency, step is as follows:

(1) adopts oxygen volumn concentration in the gas chromatography determination anode export house steward gas, be designated as O ₂% namely contains oxygen per-cent in the chlorine;

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

(3) adopt the spectrophotometry anode to go out NaClO in the groove salt solution ₃Concentration, the g/L of unit is designated as

(a);

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

(5) adopt the determination of acid-basetitration anode to advance Na in the groove salt solution ₂CO ₃Concentration, the g/L of unit is designated as (f);

(6) press following formula (I) and calculate η _NaOH, record the ion-exchange membrane electrolyzer cathode efficiency:

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

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

Preferably, step (1) adopts oxygen volumn concentration in the gas chromatography determination anode export house steward gas, has easy, quick, characteristic of accurate.The vapor-phase chromatography that provides referring to Cheng Dianbin " ionic membrane legal system alkali production technology " (Chemical Industry Press, September 1 2008 date of publication, 308-309 page or leaf).

Preferably, step (4) employing iodometric determination anode goes out the free Cl in the groove salt solution ₂Concentration

(a), adopt classical iodimetry,iodometry, have easy, quick, characteristic of accurate.The iodimetric analysis method that provides referring to Cheng Dianbin " ionic membrane legal system alkali production technology " (Chemical Industry Press, September 1 2008 date of publication, the 280th page).

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

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

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

2, compare based on alkali determination of yield cathode efficiency and add the prior art of acidimetric estimation cathode efficiency based on anode, cathode efficiency measuring method of the present invention, avoid measuring parameters such as importing and exporting flow, acidity, reduced the inaccurate problem of current efficiency because instrumented datas such as under meter and acidometer fluctuate and error causes.

3, compare based on anodic gas purity testing cathode efficiency, the measuring method of cathode efficiency of the present invention needing to be avoided location parameter too much and is depended critically upon the problem of data analysis, simple and directly understands easy handling;

4, adopt the measuring method of ion-exchange membrane electrolyzer cathode efficiency of the present invention, the comparability of the current efficiency between the electrolyzer of different process is increased greatly.

Embodiment

By the following examples the present invention is further specified, 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 Instr Ltd.).Adopt vapor-phase chromatography referring to Cheng Dianbin " ionic membrane legal system alkali production technology " (Chemical Industry Press, September 1 2008 date of publication, 308-309 page or leaf; Iodimetry,iodometry is referring to Cheng Dianbin " ionic membrane legal system alkali production technology ", Chemical Industry Press, the 280th page.

Embodiment 1: a kind of measuring method of ion-exchange membrane electrolyzer cathode efficiency, and step is as follows:

At a multipole type natural circulation electrolyzer, useful area 2.7m ², running current density 4.5kA/m ²Oxygen volumn concentration in the gas chromatography determination anode export house steward gas records and contains oxygen 0.6%(O in the chlorine ₂%); Acid base titration records negative electrode and goes out alkali concn 420g/L(c in the groove alkali lye _NaOH), acid base titration records anode and advances Na in the groove salt solution ₂CO ₃Concentration 0.4g/L(

(f)); Spectrophotometry records anode and goes out NaClO in the groove salt solution ₃Concentration 8g/L(

(a)); Adopt iodimetry,iodometry to record anode and go out Cl in the groove salt solution ₂Concentration 3g/L( (a)); After formula (I) calculating, record ion-exchange membrane electrolyzer cathode efficiency 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 the same grooved and condition, calculate according to the actual product alkali number of accurate measurement, according to existing (1) kind measuring method in the background technology, calculate through formula (1), record η _NaOH=94.12%.

Embodiment 2～embodiment 12: the measuring method of the ion-exchange membrane electrolyzer cathode efficiency of different grooveds, operation steps is identical with embodiment 1, result data list in the 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 very approaching according to formula (1) result calculated based on alkali determination of yield cathode efficiency, can well react the current efficiency under the practical situation.

Detect 5 parameters and the ion-exchange membrane electrolyzer cathode efficiency obtain when the different grooveds of table 1 and processing condition

Claims (1)

1. the measuring method of an ion-exchange membrane electrolyzer cathode efficiency, step is as follows:

(1) adopts oxygen volumn concentration in the gas chromatography determination anode export house steward gas, be designated as O ₂% namely contains oxygen per-cent in the chlorine;

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

(3) adopt the spectrophotometry anode to go out NaClO in the groove salt solution ₃Concentration, the g/L of unit is designated as

(a);

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

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

(6) press following formula (I) and calculate η _NaOH, record the ion-exchange membrane electrolyzer cathode efficiency:

。