阅读说明：本技术 改进镍电极性能的方法 (Method for improving nickel electrode performance ) 是由 V·特留 A·布兰 R·马尔肖 P·舒尔茨 M·赛赛 T·莫恩 于 2019-07-12 设计创作，主要内容包括：本发明涉及通过在电解时在低电流密度下将水溶性铂化合物添加到阴极电解液中改进经涂覆的镍电极在碱金属氯化物电解中的性能的方法。(The invention relates to a method for improving the performance of coated nickel electrodes in alkali chloride electrolysis by adding water-soluble platinum compounds to the catholyte at low current densities during electrolysis.)

1. For modifying uncoated nickel electrodes or with platinum-group-gold-based electrodesMethod for the performance of a nickel electrode coated with a metal, a platinum group metal oxide or a mixture of a platinum group metal and a platinum group metal oxide, and the nickel electrode is used in the electrolysis of sodium chloride according to the membrane method, wherein a platinum compound which is water-soluble or soluble in aqueous sodium hydroxide solution, in particular hexachloroplatinic acid or sodium platinate, particularly preferably Na, is electrolyzed₂PtCl₆And/or Na₂Pt(OH)₆Metered into catholyte, characterized in that the metered addition is in electrolytic operation, at reduced current densities of 0.2A/m to 95A/m, preferably 0.5A/m to 70A/m, particularly preferred 1A/m to 50A/m, having been dispensed, at a catholyte temperature of 40 ℃ to 95 ℃, with the platinum amounts per m electrode area of 0.3 g/m to 10 g/m, preferably 0.35 g/m to 8 g/m, particularly preferred 0.4 g/m to 5 g/m, having been dispensed, wherein the reduced current densities are retained for a total of 2 to 360 minutes, preferably 4 minutes to 300 minutes, particularly preferred 5 minutes to 200 minutes from the metered addition,

the method according to claim 1, characterized in that the reduced current density is also maintained for 2 to 300 minutes, preferably 4 to 200 minutes, particularly preferably 5 to 100 minutes,

the method according to, characterized in that the dosing is maintained at a reduced current density for a period of up to 60 minutes before the start of the dosing.

2. The process according to claim 1, characterized in that further water-soluble compounds of noble metals of transition group 8 of the periodic table of the elements, in particular compounds of the platinum group, particularly preferably compounds of palladium, iridium, rhodium, osmium or ruthenium, preferably compounds of palladium or ruthenium, are added to the platinum compound.

3. The method according to claim 2, characterized in that the further water-soluble compound of a noble metal of subgroup 8 has a noble metal content of 1 to 50 wt. -%, based on the platinum metal of the soluble platinum compound.

4. The process according to at least one of claims 1 to 4, characterized in that the temperature of the catholyte when metering in the platinum compound is 60 to 90 ℃, preferably 75 to 90 ℃.

5. The method according to at least one of claims 1 to 4, characterized in that the platinum content of the platinum compound in the catholyte after metering in is 0.01 to 310 mg/L, preferably 0.02 to 250 mg/L, particularly preferably 0.03 to 160 mg/L.

6. The method according to at least one of the claims 1 to 5, characterized in that the volume flow of the catholyte during the contact time of the electrode surface with the catholyte comprising a platinum compound is 0.1 to 10L/min, preferably 0.2 to 5L/min.

7. Method according to at least one of claims 1 to 6, characterized in that the concentration of platinum metal/platinum group metal in the catholyte exiting the electrolytic cell is monitored continuously or discontinuously.

8. The method according to at least one of claims 1 to 7, characterized in that the method is carried out at a coated nickel electrode, wherein the coating has a platinum metal/platinum metal oxide based on one or more metals of the following series: ruthenium, iridium, palladium, platinum, rhodium and osmium, preferably based on the following series: ruthenium, iridium and platinum.

9. A process for the production of chlorine, aqueous sodium hydroxide solution and hydrogen on a production scale according to the principle of electromembrane using a nickel electrode or a coated nickel electrode as cathode, having the following steps:

-feeding an aqueous solution containing sodium chloride into an anode compartment having an anode and an aqueous solution of sodium hydroxide into a cathode compartment having a cathode, wherein the anode compartment and the cathode compartment are present separated from each other by an ion exchange membrane;

-setting the production current density to at least 1 kA/m based on the electrode area meter;

-leading the solution containing sodium chloride out of the anode compartment together with the chlorine gas formed at the anode and separating the chlorine from the liquid phase;

-feeding the separated chlorine to a suitable treatment, in particular a treatment comprising at least drying, purification and optionally compression of the chlorine gas;

-feeding the solution containing sodium chloride discharged from the anode space to concentration and purification, wherein in particular at least the following steps are included: destroying chlorate by-products, dechlorinating, increasing the concentration by adding sodium chloride, purifying by removing unwanted cations by precipitant, filtration and ion exchange,

-subsequently reintroducing the solution containing sodium chloride into the anodic compartment;

-discharging the aqueous sodium hydroxide solution from the cathodic compartment together with the hydrogen formed at the cathode and separating the hydrogen from the liquid phase;

-optionally feeding the separated hydrogen to a suitable treatment and purification;

-feeding the aqueous sodium hydroxide solution discharged from the cathode space to a collection vessel and optionally to further suitable treatments and purifications;

-diluting a part amount of the aqueous sodium hydroxide solution discharged from the cathode space with water and reintroducing it into the cathode space;

characterized in that, in order to reduce the electrolysis voltage upon reaching the predetermined average highest voltage value in electrolysis operation, the current density is reduced to a value below 100A/m but at least 0.2A/m, the method according to any one of claims 1 to 8 is conducted, and subsequently the current density is again increased to the production current density and production is continued.

Examples

The following experimental examples were carried out on an industrial electrolyser with 144 elements each (electrolyser), the nickel cathode of which has a coating based on a ruthenium/ruthenium oxide mixture from Denora.

The average voltage of each electrolyzer was calculated from the average of 144 elements. To compare the voltage or voltage change of electrolysis, the voltage value at the current density in the electrolysis operation of 4.5 kA/m was used.

In case a voltage value cannot be obtained at the current density due to the electrolytic device not being operated at the respective read point in time at the current density, the measured voltage is converted into a voltage corresponding to the current density of 4.5 kA/m. The scaling is performed by means of a linear regression of the current-voltage data in the range of 3 to 5 kA/m. Within this current range, the current-voltage characteristics of the electrolyzer are linear.

Example 1

The industrial electrolysis device was operated at an average voltage of 3.27V and a current density of 4.5 kA/m.

The following process is carried out:

within 30 minutes, the current density was dropped from 4.5 kA/m to the current density of 11.8A/m, and was held constant at this value. After 10 minutes, 8L of hexachloroplatinate solution (25 g Pt/L) were metered into the aqueous sodium hydroxide solution (32%) at 0.8L/min over 10 minutes. Here, the platinum content of the platinum compound in the aqueous sodium hydroxide solution was increased to at most 16 mg/L. The current density is here kept at a constant value of 11.8A/m, at which value it is kept for another 30 minutes after successful addition. From the start of the addition, the time during which the current density was held at 11.8A/m amounted to 40 minutes. The current density is then raised again to 4.5 kA/m in 45 minutes.

The temperature of the aqueous sodium hydroxide solution was varied in the range of 76 to 90 ℃ throughout the process.

During the metering time, the volume flow of the aqueous sodium hydroxide solution was 3.6L/min per element.

Thus, 200g of platinum reached on the surfaces of 144 cathodes (surface area of cathode: 2.7 m). This is equivalent to the amount of platinum of 0.51 g/m.

After addition, the average voltage at 4.5 kA/m had dropped from the starting value of 3.27V to 3.10V. This corresponds to a voltage drop of 170 mV.

After another 126 days of operation, the average voltage at 4.1 kA/m was 3.07V. The current density scaled to 4.5 kA/m, which corresponds to an average voltage of 3.13V, has been restored. The voltage drop was still 140 mV.

After discontinuation and a total of 129 days of operation after metering in, the average voltage at 4.5 kA/m had been 3.16V. The voltage drop was still 110 mV.

After another pause and a total of 133 days of operation after metering in, the average voltage at 4.5 kA/m had been 3.17V. The voltage drop was still 100 mV.

Example 2

Comparative example:

the industrial electrolysis device was operated at an average voltage of 3.15V and a current density of 4.2 kA/m. The current density converted into 4.5 kA/m has the voltage of 3.19V.

The following process is carried out:

while running, 6L of hexachloroplatinate solution (7.1 g Pt/L) were metered into aqueous sodium hydroxide solution (32%, 90 ℃) at 1L/h over 6 hours. The current density is in the range from 4.3 to 4.7 kA/m²May be varied within the range of (1).

Therefore, 43 g of platinum reached on the surfaces of 144 cathodes (surface area of cathode: 2.7 m). This is equivalent to the amount of platinum of 0.11 g/m.

After complete addition of the hexachloroplatinate solution, an average voltage of 3.17V was obtained at a current density of 4.7 kA/m. The current density converted into 4.5 kA/m has the result that the average voltage of 3.14V is obtained. This corresponds to a voltage drop of 50 mV.

After 5 days of operation, the average voltage measured at 4.5 kA/m was 3.16V. The voltage drop is therefore only still 20 mV.

After a total of 8 days of operation after metering in, the electrolysis apparatus was switched off. After shutdown, the average voltage measured at 4.4 kA/m was 3.17V. Conversion to 4.5 kA/m gave an average voltage of 3.18V. The initially realized voltage reduction is thereby almost completely counteracted.

Example 3

Another comparative example

The industrial electrolysis device was operated at an average voltage of 3.17V and a current density of 4.3 kA/m. The current density converted into 4.5 kA/m has been converted into a voltage of 3.2V.

The following process is carried out:

within 30 minutes, the current density was dropped from 4.3kA/m to the current density of 11.8A/m, and was held constant at this value. After 10 minutes, 8L of hexachloroplatinate solution (6.25 g Pt/L) were metered into the aqueous sodium hydroxide solution at 0.8L/h over a period of 10 minutes. The current density is here kept at a constant value of 11.8A/m, at which value it is kept for another 30 minutes after successful addition. From the start of the addition, the time during which the current density was held at 11.8A/m amounted to 40 minutes. The current density is then raised to 3.8 kA/m in 45 minutes.

The temperature of the aqueous sodium hydroxide solution was varied in the range of 76 to 90 ℃ throughout the process.

Therefore, 50 g of platinum reached on the surfaces of 144 cathodes (surface area of cathode: 2.7 m). This is equivalent to the amount of platinum of 0.13 g/m.

After addition, an average voltage of 3.0V was determined at a current density of 3.8 kA/m. The current density scaled to 4.5 kA/m, which results in an average voltage of 3.1V, has been used. Thus, the voltage drops to 100 mV.

After a total of 8 days of operation after metering-in and switching-off, the average voltage measured at a current density of 4.5 kA/m had been 3.19V. The voltage drop is therefore only still 10 mV and is therefore almost completely cancelled out.