EP2652176A1 - Electrolyser having a spiral inlet tube - Google Patents

Abstract

Electrolyser comprising at least one single electrolysis element which in each case comprises an anode half cell having an anode, a cathode half cell having a cathode and an ion-exchange membrane arranged between anode half cell and cathode half cell, where the anode and/or the cathode is a gas diffusion electrode and a gap is provided between the gas diffusion electrode and the ion-exchange membrane, where an electrolyte inlet is arranged above the gap and an electrolyte outlet and also a gas inlet and a gas outlet are arranged below the gap, where the electrolyte outlet opens into an outflow collection channel and where the electrolyte inlet is connected to an electrolyte stock vessel and has an overflow and the overflow is connected to the outflow collection channel, where a spiral tube is provided for connecting the electrolyte stock vessel and the electrolyte inlet and a spiral tube is provided for connecting the overflow to the outflow collection channel.

Description

 Electrolyzer with spiral inlet hose

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.

In electrolysis, electrical energy is converted 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 + Na ⁺ + 4 e The alkali ions reach the cathode and form alkali hydroxide with the hydroxide ions formed there. In addition, hydrogen is formed:

(2) 4 H ₂ 0 + 4 e ^" -> 2 H ₂ + 4 0H-

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 - 0.86 V. Such a thing

Cell design is known, for example, from WO98 / 55670. 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) on the

Used 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) 0 ₂ + 2 H ₂ 0 + 4 e ^" 4 0H-

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

(4) 4 NaCl + 0 ₂ + 2 H ₂ 0 4 NaOH + 2 Cl ₂

Since the standard potential of reaction (3) is +0.4 V, the NaCl GDE technology results in significant energy savings compared to conventional technology. Gas diffusion electrodes have been used in batteries for many years,

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

In order for the reaction to be effective at the three-phase boundary, the above-mentioned problem must be avoided by appropriately selecting the pressure ratios. The formation of a liquid column in a quiescent liquid, as is the case in the electrolyte solution, conditioned

For example, the hydrostatic pressure at the bottom of the column is highest, which would enhance the phenomenon described above. This problem is, as can be found in the relevant literature, solved in the form of falling film evaporators. 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. WO03 / 042430 discloses the use of high density polyethylenes or perfluorinated plastics for these porous ones

Percolator layer proposed.

Such a principle is disclosed for example in DE102204018748. Here, an electrochemical cell is described which consists of at least one

Anode half cell with an anode, a cathode half cell with a cathode and arranged between the anode half cell and cathode half cell

ion exchange membrane, 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 has an overflow.

The overflow of the electrolyte is intended to ensure a uniform feeding over the full width of the cell. The amount of electrolyte flowing into the electrolyte feed from the receiver tank is dependent on the difference in height between the liquid level of the electrolyte in the receiver tank and the electrolyte

Liquid level in the electrolyte feed dependent. 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 drain over the overflow channel and the gap, the pressure of the electrolyte increases in the channel-shaped

Electrolyte feed 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.

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 from each other via a suitable membrane and which are fitted into a housing for receiving these individual elements. Such electrolyzers are disclosed, for example, in DE 196 41 125 A1 and in DE 102 49 508 A1.

To protect the metallic components such as nickel, copper, silver and gold, which consists of an electrolytic cell with gas diffusion electrode, at standstill, such as commissioning, decommissioning,

 Interruptions or malfunctions, a polarization can be performed. 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 electrolytic 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.

In the following, consider an electrochemical cell for the conventional hydrogen-forming chlor-alkali electrolysis, which was constructed according to the prior art according to DE 196 41 125 A1 and DE 102 49 508 A1. To ensure proper operation of such electrolysis cells, after switching off the main electrolysis current, a minimum polarization current

be maintained to the electrodes against corrosion reactions of the

Protect coating. Achieving adequate corrosion protection via the lowest possible polarization currents by means of a drainage channel in conjunction with a drainage pipe made of PTFE is described in DE 102 49 508 A1. In this case, the part of the polarization current thus fed in, via the supply and

Drain lines of the cell is discharged through the electrolytes, minimized by said constructive measures. The inflow of the brine and brine takes place via a conventional inlet distributor. To quantify these currents is an example below

Considered electrolyzer 1, as shown in Fig. 1A, which from 160

Consists of 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. About an electrical model that the different

Ohmic resistances of the elemental components and of the electrolytes as well as the corresponding electrochemical equations are taken into account, the course of the current intensity per element can be calculated. The results are shown in FIG. 1B

reproduced, which maps the current in the element relative to the number of elements, ie the position in the electrolyzer.

Accordingly, only about 40% of the electricity in the elements, the remaining 60% are lost through stray currents. FIG. 1C and FIG. 1D show, in detail, the stray currents that are conducted through the electrolyte inlets and outflows for each element. In Fig. 1C, stray currents are above the element number, i. the element position in the electrolyser, shown by the brine supply lines

(represented by open triangles) and the Laugezuleitungen (represented by filled triangles) are dissipated. Fig. 1 D shows for comparison in detail the currents flowing through the Laugeablaufleitung (represented by filled triangles) and the

Anolyte drain line (represented by open triangles) are lost. 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 so problematic in that the uniform

Feeding with electrolyte not only a single element, but all the individual elements connected in series is necessary to an effective operation

guarantee. Often it comes despite the intended overflow to the

Individual elements to an uneven lye distribution in Elektrolyseurbetrieb by uneven pressures, which also contributes to the above-mentioned problem of stray current formation, which in turn leads to corrosion and a reduction in current efficiency.

The object of the present invention is therefore to provide a construction which ensures a uniform distribution of the electrolyte in the

Electrolysis operation comprising a plurality of individual electrolysis elements to ensure by a constant pressure in the electrolyte supply structure and sufficient amounts of electrolyte are provided. 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 Einzelelektrolyseelement, each comprising an anode half-cell with an anode, a cathode half-cell with a cathode and a arranged between the anode half-cell and cathode half-cell ion exchange membrane, wherein the anode and / or the cathode is 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 a

 Electrolyte drain and a gas inlet and a gas outlet are arranged, the electrolyte effluent discharges into a drain collection channel, and wherein the electrolyte inlet is connected to an electrolyte reservoir and having an overflow, and the overflow is connected to the drain collection channel, wherein for connection of the electrolyte reservoir and the electrolyte inlet is provided spiral-shaped hose and wherein a spiral-shaped hose is provided for connecting the overflow to the drain collection channel.

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 more preferably provided from 2.25 to 2.75 m. Especially advantageous are hoses with a length of 2.5 m.

Advantageously, spiral-shaped tubes are provided, the one

Inner diameter of 5 mm to 15 mm, preferably an inner diameter of 7.5 to 12.5 mm, and more preferably from 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 are 50 to 200 in the electrolyzer

Single electrolysis, preferably 70 to 180 Einzelelektrolyseelemente, and more preferably provided 100 to 160 Einzelelektrolyseelemente.

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, the pressure drop is in a preferred embodiment at the provided with the spirai-shaped hose electrolyte inlet 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.

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. 1 B shows the course of the current across the individual elements of which the electrolyzer is composed. Fig. 1 C shows the stray currents, which are conducted at each element via brine and Laugezulauf, Fig. 1 D, the stray currents, which are passed through Katholytablauf (Laugeablauf) and anolyte effluent.

Fig. 2: Inventive electrolyzer. Fig. 2 A shows a

 schematic structure of an electrolyzer according to the invention. Fig. 2 B shows the course of the element voltage below

 Polarization over the individual elements that make up the electrolyzer. Fig. 2 C shows the course of the current under polarization over the individual elements of which the electrolyzer is composed. Fig. 2 D shows the stray currents that are derived for each element via brine and Laugezulauf. The stray currents over the

 Solezuläufe over filled circles represented, the stray currents over the Laugezuläufe over open circles. Fig. 2 E shows the

 Stray currents, the Anolyteablauf, Katholytablauf and

 Catholyte overflow will be lost. 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.

Fig. 3: side view of an inventive

 Single electrolysis element with arrangement of spirai-shaped hoses.

As a comparative experiment with the prior art is an inventive electrolyzer, with the spirai-shaped tubes described in claim 1 equipped has been used. It was considered an electrolyzer, which worked from four electrolyzer stacks, each equipped with 60 Einzelelektrolyseelementen. The initially theoretical resulting total stress below

Polarization without stray current losses is here also at a maximum of 250V, i. the pure ohmic resistance of the electrolyzer under polarization is in the range of the electrolyzer of the prior art, the results of which are described in Fig. 1, so that they can be directly compared with those shown in Fig. 2 results.

In Fig. 2 A, the current flow through the electrolyzer 4 according to the invention is shown. 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 a minimum flow in the electrolysis center to

guarantee. The calculations have shown that through the supply and

Drain pipes via the electrolyte ^ as much current is discharged that in the middle elements of the electrolyzer no sufficient positive current is available. Therefore, the injected polarization current was increased to 50 A and the

Cell voltage (Fig. 2 B) or the current (Fig. 2 C) in each element using the same calculation method which was also based on Fig. 1, 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 of FIG. 1, the power drops significantly and is lowest in the middle elements of the electrolyzer. If the course of the stray currents via the inlets and outlets of each individual cell element is considered, the image shown in FIG. 2C and FIG. 2D results.

While the stray currents in the brine inlet and anolyte effluent are low and do not differ qualitatively from the quantities known from the calculation of the conventional electrolyzer shown in FIG. 1, the calculations on the cathode side show a different picture.

Considering the calculation results for the electrolyte feed shown in Fig. 2 C, 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 the electrolyte feed with a Electrolyte storage tank connects, so that is Although the amount of lost stray currents is greater than that lost through the brine feed. Overall, however, the lost stray current is smaller by a factor of 2 compared to the conventional technology shown in FIG. 1. The reduced stray current is thus due to the use of the spiral-shaped hose.

The Katholytüberlauf is like the feed via a spiral

Supply hose made of PTFE with a length of 2.5 m and an inner diameter of 10 mm, which connects the intended overflow with the drainage collecting duct. As shown in Fig. 2D, there is little leakage current for the overflow, which hardly differs from the stray current lost by the brine feed (see 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 occurs at 27A in the

conventional electrolytic cell is lost by the Katholytzulauf (see Fig. 1 C).

The arrangement of electrolyte inlet and overflow tubes 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 corrosion processes effectively prevent.

FIG. 3 shows a single electrolysis element 10 according to the invention. In this case, the internal structure of the electrolytic cell is not shown. By

Stringing together 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 12 provided on the outer wall 11, with the electrolyzer being flowed through by current during operation from the anodic end.

The filling of the electrolyte is done via a spiral-shaped

As a result, the electrolyte flows uniformly over the entire width of the individual electrolysis element 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). Due to the simultaneous throttling action of the spiral tubes 13 and 14, a uniform distribution of the electrolyte during the

Elektrolyseurbetriebs ensured by a constant pressure in the

Electrolyte supply design, as well as sufficient amounts of electrolyte are provided.

Due to the throttling action of the spiral tube 13 is in

Furthermore, a significant part of the electrolyte entering via the spiral-shaped hose 14 is prevented from leaving the individual electrolysis element via a siphon effect, instead of flowing through the single electrolysis element as a falling film as intended. Thus, by the design of the spiral tube 3 depletion of electrolyte in areas of the single electrolysis cell can be prevented, which would affect the electrolytic operation of the single electrolysis cell.

Optionally, the amount of electrolyte via a valve and a

Adjust the flowmeter in the electrolyte inlet before entering the spiral-shaped hose 14, if the counter-elements arranged in the electrolyzer stack show very different backpressures. 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 scored

Streustromminimierung and the uniform electrolyte distribution is the

 Interplay of both attached to the electrolyte element elements spiral-shaped tubes required.

Advantages of the present invention: uniform distribution of the electrolyte in the electrolyzer

Ensuring sufficient quantities of electrolyte in the falling film

 Prevention of electrolyte losses due to a siphon effect in the

 Electrolyte overflow of each Einzelelektrolyselements

Minimization of stray currents, whereby necessary polarization currents can be kept low can be easily integrated into existing electrolyzers measure ugszeichenliste

 electrolyzer

 Elektrolyseurstapel

Elektrolyseurstapel

electrolyzer

 Elektrolyseurstapel

Elektrolyseurstapel

Elektrolyseurstapel

Elektrolyseurstapel

Polarization rectifier

Single electrolysis element

outer wall

 Contact strip spiral-shaped hose spiral-shaped hose

Claims

claims 1 electrolyzer comprising at least one Einzelelektrolyseelement, each having an anode half-cell with an anode, a cathode half-cell with a cathode and arranged between the anode half-cell and cathode half-cell  Ion exchange membrane comprises, wherein the anode and / or the cathode is a gas diffusion electrode, a gap is provided between the gas diffusion electrode and the ion exchange membrane, wherein above the gap an electrolyte inlet and below the gap an electrolyte effluent and a  Gas inlet and a gas outlet are arranged, wherein the electrolyte effluent flows into a Ablaufsammeikanal, and wherein the electrolyte feed with a  Electrolyte reservoir is connected and has an overflow, and the overflow is connected to the drain collection channel,  characterized in that  a spiral-shaped hose is provided for connecting the electrolyte reservoir tank and the electrolyte inlet, and that a spiral-shaped hose is provided for connecting the overflow to the drainage collector duct. 2 electrolyzer according to claim 1, characterized in that provided 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. 3 electrolyzer according to one of claims 1 or 2, characterized in that spiral-shaped hoses having an inner diameter of 5 mm to 15 mm, preferably an inner diameter of 7.5 to 12.5 mm, and particularly preferably from 9 mm to 11 mm, are provided. 4 electrolyzer according to one of claims 1 to 3, characterized in that the overflow is provided with a through opening, the one  Diameter of 2 mm to 4 mm, and preferably from 2.5 to 3.5 mm. 5 electrolyzer according to one of claims 1 to 4, characterized in that  50 to 200 individual electrolysis elements, preferably 70 to 180  Single electrolysis elements, and more preferably 100 to 160 Single electrolysis elements are provided. Electrolysis of an aqueous alkali halide solution using an electrolyzer according to claim 1, characterized in that the pressure drop at the provided with the spiral-shaped tube overflow up to 200 mbar, preferably 100 to 200 mbar. Electrolysis of an aqueous alkali halide solution according to claim 6, characterized in that the pressure drop at the provided with the spiral-shaped hose electrolyte inlet 30 mbar to 200 mbar, preferably 80 to 170 mbar, and particularly preferably 100 mbar to 150 mbar.