EP2652176B1 - Electrolyser having a spiral inlet tube - Google Patents

Description

The present invention can be classified in the technical field of electrolyzers.

The present invention relates to an electrolyzer as characterized in the preamble of claim 1.

Electrolysis converts electrical energy into chemical energy. This is achieved by the decomposition of a chemical compound under the action of an electric current. The solution used as electrolyte contains positively and negatively charged ions. Accordingly, the main electrolytes used are acids, bases or salts.

For example, in the production of halogen gases from aqueous alkali halide solution, the following reaction takes place on the anode side:

(1) 4 NaCl → 2 Cl ₂ + 4 Na ⁺ + 4 e ^-

The free alkali ions reach the cathode and form alkali hydroxide with the resulting hydroxide ions. In addition, hydrogen is formed:

(2) 4H ₂ O + 4e ^- → 2H ₂ + 4OH ^-

In this case, the resulting liquor is separated from the sodium chloride, which is supplied to the anode side, via a cation exchange membrane, and thereby separated from each other. Such membranes are known in the art and commercially available from a variety of suppliers.

The standard potential at the anode, which forms at the end of the above reaction, is + 1.36 V, the standard potential at the cathode at the end of the above reaction being - 0.86 V. Such a cell design is for example from WO98 / 55670 known. The difference between these two standard potentials results in an immense input of energy, which is necessary to carry out these reactions. To minimize this difference, now gas diffusion electrodes (hereinafter abbreviated as GDE) are used on the cathode side, whereby oxygen is introduced into the system and conditionally at the cathode not more reaction (2) takes place, but the following reaction:

(3) O ₂ + 2 H ₂ O + 4 e ^- → 4 OH ^-

The overall reaction underlying the NaCl GDE technology is thus defined as follows:

(4) 4 NaCl + O ₂ + 2 H ₂ O → 4 NaOH + 2 Cl ₂

Since the standard potential of reaction (3) is + 0.4V, NaCl-GDE technology provides significant energy savings compared to traditional technology.

Gas diffusion electrodes have been used for many years in batteries, electrolyzers and fuel cells. The electrochemical conversion takes place within these electrodes only at the so-called three-phase boundary. The three-phase limit is the range at which gas, electrolyte and metallic conductors meet. For the GDE to work effectively, the metallic conductor should simultaneously be a catalyst for the desired reaction. Typical catalysts in alkaline systems are silver, nickel, manganese dioxide, carbon and platinum. For the catalysts to be particularly effective, their surface area must be large. This is achieved by fine or porous powder with inner surface.

Problems in the application of such gas diffusion electrodes, as used for example in the US 4614575 revealed, result from the fact that the electrolyte, due to capillary action would penetrate into these fine-pored structures and fill them. This effect would result in the oxygen no longer being able to diffuse through the pores, thereby arresting the intended reaction.

For the reaction to be effective at the three-phase boundary, the above-mentioned problem must be avoided by appropriately selecting the pressure ratios. For example, the formation of a liquid column in a quiescent liquid, as in the electrolyte solution, requires that the hydrostatic pressure at the bottom of the column is highest, which would enhance the phenomenon described above.

This problem is solved in the form of falling-film evaporators, as can be found in the relevant literature. The liquor is allowed to pass between the membrane and the GDE through a porous medium, thus preventing the formation of a hydrostatic column. One speaks also of Percolatortechnologie.

In the WO03 / 042430 For example, the use of high density polyethylenes or perfluorinated plastic materials for this porous percolator layer is suggested.

Such a principle is for example in the DE102004018748 disclosed. Here, an electrochemical cell is described which comprises at least one anode half cell with an anode, a cathode half cell with a cathode and an ion exchange membrane arranged between anode half cell and cathode half cell, wherein the anode and / or cathode is a gas diffusion electrode, between the gas diffusion Electrode and the ion exchange membrane a gap, an electrolyte inlet above the gap and an electrolyte drain below the gap and a gas inlet and a gas outlet is arranged, wherein the electrolyte inlet is connected to an electrolyte reservoir and having an overflow.

The overflow of the electrolyte should ensure a uniform feeding over the full width of the cell. The amount of electrolyte flowing from the receiver tank into the electrolyte feed depends on the height difference between the liquid level of the electrolyte in the feed tank and the liquid level in the electrolyte feed. The liquid level in the electrolyte feed, in turn, depends on the height of the overflow, which determines how much the electrolyte in the electrolyte feed is dammed up.

If more electrolyte is added than can flow through the overflow channel and the gap, the pressure of the electrolyte in the channel-shaped electrolyte inlet increases above the gap. By selecting the height of the overflow channel, the pressure in the electrolyte inlet can be adjusted. As the pressure increases, more electrolyte can therefore be passed through the gap and the flow velocity in the gap can be selectively varied. By varying the ratio of the described height differences to one another, the pressure in the electrolyte inlet can be adjusted in a targeted manner.

Out US4417970A For example, a distribution structure for the electrolyte is known, which is equipped with spiral tubes for each half-cell.

Under an electrolyzer is now understood an apparatus consisting of several juxtaposed in a stack and in electrical contact standing plate-shaped electrolytic cells is constructed, which has inlets and outlets for all the necessary and resulting liquids and gases. It is therefore a series connection of several individual elements, each having electrodes which are separated by a suitable membrane and which are fitted into a housing for receiving these individual elements. Such electrolyzers are for example in the DE 196 41 125 A1 and in the DE 102 49 508 A1 disclosed.

To protect the metallic components such as nickel, copper, silver and gold, which consists of an electrolytic cell with gas diffusion electrode, a polarization can be carried out at standstill, such as during startup, shutdown, interruptions or malfunctions. This is the case, inter alia, when an electrolysis cell is filled and heated to be put into operation. Even if the cell is taken out of the electrolysis operation, the polarization is to be maintained until the chlorine-free state of the anodic liquid and cooling has taken place.

The polarization current ensures that the metallic components of the electrolysis cell are in a potential range in which no corrosion reactions take place, which lead to the dissolution of the metals that make up individual components of the cell cathode. The polarization current must be selected so high that after loss by stray currents through the Elektrolytzu- and processes in the Elektrolyseurmitte still sufficient positive current is present to ensure a defined potential range in which no critical corrosion reactions occur.

The following is an electrochemical cell for the conventional hydrogen-forming chlor-alkali electrolysis considered according to the state of the art according to DE 196 41 125 A1 and DE 102 49 508 A1 is constructed. In order to ensure proper operation of such electrolysis cells, a minimum polarization current must be maintained after the main electrolysis current has been switched off in order to protect the electrodes against corrosion reactions of the coating. Achieving adequate corrosion protection via the lowest possible polarization currents with the help of a drainage channel in conjunction with a drain pipe made of PTFE is in DE 102 49 508 A1 described. In this case, the part of the polarization current thus fed in, which is discharged via the supply and discharge lines of the cell via the electrolytes, is minimized by the constructive measures mentioned. The inflow of the brine and brine takes place via a conventional inlet distributor.

To quantify these currents, an electrolyzer 1 is considered below as an example, as in FIG Fig. 1 A , which consists of 160 individual electrolysis elements, which are arranged in two electrolyzer stacks 2 and 3. In the case of this electrolyzer, a polarization current of 27 A is fed on the anode side, so that a total voltage of theoretically about 250 V is obtained without stray current losses. An electrical model, which takes into account the different ohmic resistances of the elemental components and the electrolytes as well as the corresponding electrochemical equations, can be used to calculate the current intensity per element. The results are in Fig. 1 B reproduced, which maps the current in the element relative to the element number, ie the position in the electrolyzer.

Thus, only about 40% of the electricity in the elements arrive, the remaining 60% are lost through stray currents. Fig. 1 C and Fig. 1 D show in detail the stray currents that are passed through the electrolyte inlets and outlets for each element. In Fig. 1 C are stray currents on the element number, ie the element position in the electrolyzer, shown, which are discharged through the brine supply lines (represented by open triangles) and the Laugezuleitungen (represented by filled triangles). Fig. 1 For comparison, D shows in detail the currents lost through the caustic discharge line (represented by filled triangles) and the anolyte discharge line (represented by open triangles). Disadvantage of this technology is thus that very high stray currents arise, which in turn make high polarization currents necessary.

The use of the above-described technologies in such an electrolyzer is therefore problematic insofar as the uniform feeding with electrolyte not only a single element, but all the individual elements connected in series is necessary to ensure effective operation. Often, despite the intended overflow of the individual elements, uneven liquor distribution in the electrolysis plant due to uneven pressures, which also contributes to the above-described problem of stray current formation, which in turn leads to corrosion and a reduction in current efficiency.

It is therefore an object of the present invention to provide a construction which ensures a uniform distribution of the electrolyte in the electrolysis operation comprising a plurality of individual electrolysis elements, by providing a constant pressure in the electrolyte supply structure as well as sufficient amounts of electrolyte. In addition, it should increased electrical stray currents caused, inter alia, by an uneven electrolyte distribution can be avoided in order to keep necessary polarization currents as low as possible.

The object is achieved by the use of an electrolyzer comprising at least one individual electrolysis element which in each case comprises an anode half cell with an anode, a cathode half cell with a cathode and an ion exchange membrane arranged between anode half cell and cathode half cell, wherein the anode and / or the cathode comprises a gas diffusion Electrode is provided between the gas diffusion electrode and the ion exchange membrane, a gap, wherein above the gap an electrolyte inlet and below the gap an electrolyte effluent and a gas inlet and a gas outlet are arranged, the electrolyte effluent discharges into a drain collection channel, and wherein Electrolyte inlet is connected to an electrolyte reservoir and has an overflow, and the overflow is connected to the drain collection channel, wherein for connecting the electrolyte reservoir and the electrolyte inlet, a spiral-shaped hose is provided and wherein the V Connection of the overflow with the drain collection channel a spiral-shaped hose is provided.

In a further embodiment of the invention, spiral-shaped tubes of a length of 1.5 m to 3.5 m, preferably from 1.75 m to 3 m, and particularly preferably from 2.25 to 2.75 m are provided. Especially advantageous are hoses with a length of 2.5 m.

Advantageously, spiral-shaped tubes are provided which have an inner diameter of 5 mm to 15 mm, preferably an inner diameter of 7.5 to 12.5 mm, and particularly preferably 9 mm to 11 mm. Especially advantageous are hoses which have an inner diameter of 10 mm.

Preferably, the overflow is provided with a through opening having a diameter of 2 mm to 4 mm, and preferably from 2.5 to 3.5 mm.

In a preferred embodiment, 50 to 200 individual electrolysis elements, preferably 70 to 180 individual electrolysis elements, and particularly preferably 100 to 160 individual electrolysis elements are provided in the electrolyzer.

Furthermore, the present invention comprises the electrolysis of an aqueous alkali halide solution. In operation, the pressure drop at the overflow provided with the spiral-shaped hose is up to 200 mbar, preferably 100 to 200 mbar.

Furthermore, in a preferred embodiment, the pressure drop at the electrolyte inlet provided with the spiral-shaped hose is 30 mbar to 200 mbar, preferably 80 to 170 mbar, and particularly preferably 100 mbar to 150 mbar.

Advantageously, the hoses used are made of PTFE.

Fig. 1:

Elektrolyseur aus dem Stand der Technik. Fig. 1A zeigt einen schematischen Aufbau eines derartigen Elektrolyseurs. Fig. 1B zeigt den Verlauf der Stromstärke über die Einzelelemente, aus denen sich der Elektrolyseur zusammensetzt. Fig. 1C zeigt die Streuströme, die bei jedem Element über Sole- und Laugezulauf geleitet werden, Fig. 1D die Streuströme, die über Katholytablauf (Laugeablauf) sowie Anolytablauf geleitet werden.

Fig. 2:

Erfindungsgemäßer Elektrolyseur. Fig. 2A zeigt einen schematischen Aufbau eines erfindungsgemäßen Elektrolyseurs. Fig. 2B zeigt den Verlauf der Elementspannung unter Polarisation über die Einzelelemente, aus denen sich der Elektrolyseur zusammensetzt. Fig. 2C zeigt den Verlauf der Stromstärke unter Polarisation über die Einzelelemente, aus denen sich der Elektrolyseur zusammensetzt. Fig. 2D zeigt die Streuströme, die bei jedem Element über Sole- und Laugezulauf abgeleitet werden. Dabei sind die Streuströme über die Solezuläufe über gefüllte Kreise dargestellt, die Streuströme über die Laugezuläufe über offene Kreise. Fig. 2E zeigt die Streuströme, die über Anolytablauf, Katholytablauf und Katholytüberlauf verloren werden. Die Streuströme über die Anolytablaufleitungen sind durch gefüllte Dreiecke dargestellt, die Streuströme über die Katholytablaufleitungen durch offene Quadrate, die Streuströme über die Katholytüberlaufleitungen durch offene Rauten.

Fig. 3:

Seitenansicht eines erfindungsgemäßen Einzelelektrolyseelements mit Anordnung der spiral-förmigen Schläuche.

The present invention will be explained in more detail with reference to figures:

Fig. 1:

Electrolyzer from the prior art. Fig. 1A shows a schematic structure of such an electrolyzer. Fig. 1B shows the course of the current through the individual elements that make up the electrolyzer. Fig. 1C shows the stray currents that are conducted via brine and liquor feed for each element, Fig. 1D the stray currents, which are conducted via Katholytablauf (Laugeablauf) and anolyte effluent.

Fig. 2:

Electrolyzer according to the invention. Fig. 2A shows a schematic structure of an electrolyzer according to the invention. Fig. 2B shows the course of the element voltage under polarization over the individual elements that make up the electrolyzer. Fig. 2C shows the course of the current under polarization over the individual elements that make up the electrolyzer. Fig. 2D shows the stray currents, which are derived for each element via brine and lye feed. The stray currents via the brine inlets are shown by filled circles, the stray currents via the liquor inlets via open circles. Fig. 2E shows the stray currents that are lost through Anolyteablauf, Katholytablauf and Katholytüberlauf. The stray currents through the Anolytablaufleitungen are represented by filled triangles, the stray currents through the Katholytablaufleitungen by open squares, the stray currents through the Katholytüberlaufleitungen by open diamonds.

3:

Side view of a single electrolysis element according to the invention with arrangement of the spiral-shaped hoses.

As a comparative experiment with the prior art is an electrolyzer according to the invention, with the described in claim 1 spiral-shaped tubes equipped has been used. It was considered an electrolyzer, which worked from four electrolyzer stacks, each equipped with 60 Einzelelektrolyseelementen. The initial theoretical resulting total voltage under polarization without stray current losses is here also at a maximum of 250V, ie, the pure ohmic resistance of the electrolyzer under polarization is in the range of electrolyzer according to the prior art, the results in Fig. 1 be described so that those with those in Fig. 2 shown results can be compared directly.

In Fig. 2 A is the current flow through the electrolyzer 4 according to the invention. The electrolyzer stacks are provided with the reference numerals 5, 6, 7, 8. Again, the electrolyzer is fed from the anodic end with a polarization current, which goes from the polarization rectifier 9.

In the electrolyzer according to the invention, a fed-in current of 27 A is not sufficient to ensure a minimum current in the electrolysis center. The calculations have shown that so much current is drained through the inlet and outlet pipes via the electrolytes that there is no longer sufficient positive current in the middle elements of the electrolyzer. Therefore, the injected polarization current was increased to 50 A and the cell voltage ( Fig. 2 B) or the current ( Fig. 2C) in each element using the same calculation method which includes the Fig. 1 was calculated. Fig. 2 B and 2 C show the calculation result in the form of the course over the elements of the electrolyzer.

As in the example of a conventional electrolyzer Fig. 1 the current drops significantly and is lowest in the middle elements of the electrolyzer. If the course of the stray currents on the inlets and outlets of each individual cell element is considered, then this results in Fig. 2 C and Fig. 2 D picture shown.

While the stray currents in the brine inlet and Anolytablauf are low and qualitatively not very different from the amounts resulting from the calculation of conventional and in Fig. 1 The electrolysis calculations show a different picture.

Looking at the in Fig. 2 C shown calculation results for the electrolyte feed, which was provided in the experiment with a spiral-shaped inlet hose made of PTFE a length of 2.5 m and an inner diameter of 10 mm, and connects the electrolyte inlet with an electrolyte reservoir, this is Although the amount of lost stray currents is greater than that lost through the brine inflow. Overall, however, the lost stray current by a factor of 2, compared to the in Fig. 1 illustrated conventional technology, smaller. The reduced stray current is thus due to the use of the spiral-shaped hose.

Like the inlet, the catholyte overflow is ensured by a spiral inlet hose made of PTFE with a length of 2.5 m and an inside diameter of 10 mm, which connects the intended overflow to the drainage collection channel. As in Fig. 2 D , results in a low stray current for the overflow, which hardly differs from the stray current lost by the brine feed (s. Fig. 2C) , Despite the required higher polarization current of 50 A, this stray current has a similar order of magnitude as the stray current which is lost at 27 A in the conventional electrolysis cell due to the influx of catholyte (see FIG. Fig. 1C) ,

The arrangement of electrolyte inlet and overflow hoses in a spiral-shaped design therefore results in that stray currents are kept as low as possible during operation of an electrochemical cell, although compared to the conventional chlor-alkali electrolysis, a slightly higher polarization current must be fed to effectively prevent corrosion processes ,

In Fig. 3 a single electrolysis element 10 according to the invention is shown. In this case, the internal structure of the electrolytic cell is not shown. By juxtaposing a plurality of individual electrolysis elements 10 in so-called cell stacks in the corresponding devices provided for this purpose, the claimed electrolysers are created. In this case, the individual electrolysis elements are electrically conductively connected to one another via contact strips provided on the outer wall 11, the current flowing through the electrolyzer in operation from the anodic end.

The filling of the electrolyte takes place via a spiral-shaped hose 13. As a result, the electrolyte flows uniformly over the entire width of the Einzelelektrolyseelements 10. The electrolyte feed takes place from top to bottom via a falling film (not shown).

The overflow of the electrolyte is also provided with a spiral-shaped hose 14. In the installed state, this overflow is connected by way of example to the oxygen drainage channel, from which excess electrolyte can be removed into the drainage collection channel of the electrolyzer (not shown).

By the simultaneous throttling action of the spiral hoses 13 and 14, a uniform distribution of the electrolyte during the Elektrolyseurbetriebs is ensured by a constant pressure in the electrolyte supply structure, and sufficient amounts of electrolyte are provided.

The throttling effect of the spiral tube 13 furthermore prevents a considerable part of the electrolyte entering via the spiral tube 14 from leaving the individual electrolysis element via a siphoning effect, instead of flowing through the single electrolysis element as a falling film as intended. Thus, 13 can be prevented by the design of the spiral tube 13 depletion of electrolyte in areas of the single electrolysis cell, which would affect the electrolytic operation of the single electrolysis cell.

Optionally, the amount of electrolyte can be adjusted via a valve and a flow meter in the electrolyte inlet before entering the spiral-shaped hose 14, when the elements arranged in the electrolyzer stack strongly different back pressures occur. Valves and flowmeters are used to adjust the flow rate to maintain a minimum flow of electrolyte in the spiral tube 14 to provide the necessary inlet pressure through the resulting hydrostatic column. For the achieved Streirkomminimierung and the uniform electrolyte distribution, the interaction of both attached to the electrolyte single elements spiral-shaped hoses is required.

• gleichmäßige Verteilung des Elektrolyten im Elektrolyseur
• Sicherstellung ausreichender Mengen an Elektrolyt im Fallfilm durch Verhinderung von Elektrolytverlusten infolge eines Siphoneffektes im Elektrolytüberlauf eines jeden Einzelelektrolyselements
• Minimierung von Streuströmen, wodurch notwendige Polarisationsströme gering gehalten werden können
• einfach in bestehende Elektrolyseure zu integrierende Maßnahme

Advantages of the present invention:

• uniform distribution of the electrolyte in the electrolyzer
• Ensuring sufficient amounts of electrolyte in the falling film by preventing electrolyte leakage due to a siphon effect in the electrolyte overflow of each individual electrolytic element
• Minimization of stray currents, whereby necessary polarization currents can be kept low
• easy to integrate into existing electrolyzers measure

LIST OF REFERENCE NUMBERS

1

electrolyzer

2

Elektrolyseurstapel

3

Elektrolyseurstapel

4

electrolyzer

5

Elektrolyseurstapel

6

Elektrolyseurstapel

7

Elektrolyseurstapel

8th

Elektrolyseurstapel

9

Polarization rectifier

10

Single electrolysis element

11

outer wall

13

spiral-shaped hose

14

spiral-shaped hose

Claims (7)

1. Electrolyzer comprising at least one single electrolysis element, comprising an anode half-cell with an anode, a cathode half-cell with a cathode, and an ion exchange membrane arranged between the anode half-cell and the cathode half-cell, said anode and/or said cathode being a gas diffusion electrode, with a gap being provided between the gas diffusion electrode and the ion exchange membrane, wherein an electrolyte inlet is arranged above the gap and an electrolyte outlet, a gas inlet and a gas outlet are arranged below the gap, wherein the electrolyte outlet ends in an outlet collection channel, and wherein the electrolyte inlet is connected to an electrolyte storage tank and has an overflow, and the overflow is connected to the outlet collection channel,
   characterized in that
   a spiral-shaped tube is provided for connecting the electrolyte storage tank and the electrolyte inlet, and that a spiral-shaped tube is provided for connecting the overflow and the outlet collection channel.
2. Electrolyzer according to claim 1, characterized in that spiral-shaped tubes are provided having a length of 1.5 m to 3.5 m, preferably from 1.75 m to 3 m, and particularly preferably 2.25 m to 2.75 m.
3. Electrolyser according to one of claims 1 or 2, characterized in that spiral-shaped tubes are provided having an inner diameter of 5 mm to 15 mm, preferably an inner diameter of 7.5 mm to 12.5 mm, and particularly preferably from 9 mm to 11 mm.
4. Electrolyser according to one of claims 1 to 3, characterized in that the overflow is provided with a through opening, which has a diameter of 2 mm to 4 mm, and preferably 2.5 mm to 3.5 mm.
5. Electrolyser according to one of claims 1 to 4, characterized in that 50 to 200 individual elements, preferably 70 to 180 single electrolysis elements, and particularly preferably 100 to 160 individual electrolysis elements are provided.
6. Electrolysis of an aqueous alkali halide solution using an electrolyser according to claim 1, characterized in that the pressure drop at the overflow, which is provided with the spiral-shaped tube, is up to 200 mbar, preferably 100 mbar to 200 mbar.
7. Electrolysis of an aqueous alkali halide solution according to claim 6, characterized in that the pressure drop at the electrolytic inlet, which is provided with the spiral-shaped tube, is 30 mbar to 200 mbar, preferably 80 mbar to 170 mbar, and particularly preferably from 100 mbar to 150 mbar.

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