EP1651799A1

EP1651799A1 - Electrochemical cell

Info

Publication number: EP1651799A1
Application number: EP04740955A
Authority: EP
Inventors: Andreas Bulan; Michael Grossholz; Volker Michele; Hans-Joachim Brockhaus; Hans-Dieter Pinter; Fritz Gestermann; Rainer Weber
Original assignee: Bayer MaterialScience AG
Current assignee: Bayer Intellectual Property GmbH
Priority date: 2003-07-24
Filing date: 2004-07-13
Publication date: 2006-05-03
Anticipated expiration: 2024-07-13
Also published as: CN1829825A; CN100549239C; HK1097885A1; JP2006528730A; TW200519233A; TWI351447B; JP4680901B2; DE10333853A1; WO2005012595A1; EP1651799B1; US20050029116A1; US20110073491A1

Abstract

The invention relates to an electrochemical cell (1) at least comprising an anode half-cell (2) with an anode (21), a cathode half-cell (3) with a cathode (31), and an ion exchange membrane (4) that is disposed between the anode half-cell and the cathode half-cell. The anode and/or the cathode is/are embodied as a gas diffusion electrode. A gap (32) is located between the gas diffusion electrode and the ion exchange membrane while the half-cell encompassing a gas diffusion electrode is provided with an electrolyte inlet (33) and an electrolyte outlet as well as a gas inlet (35) and a gas outlet (36). The inventive electrochemical cell is characterized in that the electrolyte inlet is tightly connected to the gap.

Description

Electrochemical cell

The invention relates to an electrochemical cell, at least consisting of 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 cathode half cell, the anode and / or the cathode being a gas diffusion electrode. The invention further relates to a method for the electrolysis of an aqueous solution of alkali chloride.

From WO-A 01/57290 an electrolysis cell with a gas diffusion electrode is known, in which a porous layer is provided in the gap between the gas diffusion electrode and the ion exchange membrane. The electrolyte flows from top to bottom over the porous layer under the influence of gravity through the gap. The porous layer according to O-

A 01/57290 can consist of foams, wire nets or the like.

US Pat. No. 6,117,286 also describes an electrolysis cell with a gas diffusion electrode for the electrolysis of a sodium chloride solution, in which there is a layer of a hydrophilic material in the gap between the gas diffusion electrode and the ion exchange membrane. The layer of hydrophilic material preferably has a porous structure which contains a corrosion-resistant metal or resin. As a porous structure e.g. Nets, fabrics or foams can be used. Sodium hydroxide, the electrolyte, flows under the force of gravity down over the layer of hydrophilic material to the bottom of the electrolytic cell.

Furthermore, EP-A 1 033 419 discloses an electrolysis cell with a gas diffusion electrode as the cathode for the electrolysis of a sodium chloride solution. The cathode half-cell, in which the electrolyte flows downwards, separated from the gas space by a gas diffusion electrode, is a hydrophilic, porous material through which the electrolyte flows. Metals, metal oxides or organic materials come into consideration as the porous material if they are corrosion-resistant.

An ^{'disadvantage} is known from the prior art electrolysis cells having gas diffusion electrode, that the gap between the gas diffusion electrode and the ion exchange membrane due to the porous material can not be completely filled with electrolyte. This creates areas in the gap in which gas is located and accumulates. No electrical current can flow in these areas. Current flows exclusively through electrolyte-filled areas in the gap, so that locally a higher current density arises, which results in a higher electrolysis voltage. The gas collects on the ion exchange membrane, this can be damaged due to the lack of electrolyte. Porous layers also have the disadvantage that gas which has once entered the porous structure can only get out of it with difficulty. The gas can accumulate within the porous layer, which creates the disadvantages mentioned above. Under operating conditions, gas from the gas space can also pass through the gas diffusion electrode from the gas space into the gap.

The object of the present invention is therefore to provide an electrolytic cell which avoids the disadvantages of the prior art.

The invention relates to an electrochemical cell, at least consisting of an anode half cell with an anode, a ^" cathode half cell with a cathode and ion exchange membrane arranged between the anode half cell and cathode half cell, the anode and / or the cathode being a gas diffusion electrode and between the gas diffusion electrode and the Ion exchange membrane is arranged a gap and the half cell with gas diffusion electrode has an electrolyte inlet and an electrolyte outlet and a gas inlet and a gas outlet, characterized in that the

Electrolyte inlet is tightly connected to the gap.

When the electrochemical cell according to the invention is in operation, the electrolyte flows through the half cell from top to bottom in the gap between the gas diffusion electrode and the ion exchange membrane. The gap is completely filled with electrolyte. The remaining space of the half cell, the gas space, is filled with gas which is fed in through the gas inlet and discharged through the gas outlet. According to the invention, the electrolyte feed is tightly connected to the gap. This prevents gas from the gas space from entering the gap via the electrolyte inlet. Due to the tight connection between the electrolyte inlet and the gap, the electrolyte can be conveyed through the gap with the aid of a pump, so that the electrolyte stream does not flow freely in the gap along the gas diffusion electrode. With the help of the pump, the volume flow of the electrolyte flowing through the gap can be adjusted. The volume flow is preferably set so that the flow rate of the electrolyte is lower than in free fall.

In a preferred embodiment, flow guiding structures are provided in the gap. The flow guide structures also prevent a free fall of the electrolyte in the gap, so that the flow speed is reduced compared to the free fall. At the same time, however, the electrolyte must not build up in the gap due to the flow guide structures. The flow guide structures are chosen so that the pressure loss the hydrostatic liquid column in the gap is compensated. If flow guiding structures are provided, they can completely take over the function of the pump, namely the reduction of the flow speed in the gap, so that no pump is necessary. However, a pump can also be used in combination with flow guide structures.

The flow guide structures consist of thin plates, foils or the like, which have openings for the electrolyte to flow through. They are across, i.e. arranged perpendicular or obliquely to the flow direction of the electrolyte in the gap. The plate-shaped flow guide structures are preferably inclined with respect to the horizontal, wherein they are inclined either only in one axis or in both axes. If the flow guide structures are arranged obliquely to the direction of flow, they can be inclined both in the direction of the ion exchange membrane and in the direction of the gas diffusion electrode. The inclination in the direction of the gas diffusion electrode or the ion exchange membrane corresponds to an inclination about an axis which runs parallel to the gas diffusion electrode or ion exchange membrane and horizontally. In addition, the flow guide structures can be inclined across the width of the electrochemical cell. This corresponds to an inclination about an axis that runs perpendicular to the gas diffusion electrode or ion exchange membrane. This inclination can be 0 to 45 °, preferably 3 to 15 °.

Since small amounts of gas from the space behind the gas diffusion electrode, i.e. that facing away from the ion exchange membrane

Space of the half cell through which the gas diffusion electrode enters the gap through which electrolyte flows must ensure that the gas is removed from the gap. If the content of gas in the electrolyte increases, the resistance of the electrolyte increases. If flow guiding structures are present in the gap, the gas can either escape upward through openings in the flow guiding structures or it is carried downward by the electrolyte flow. The inclination of the flow guide structures in particular promotes the removal of the gas bubbles upwards.

The flow guide structures are also arranged such that they contact the gas diffusion electrode on the one hand and the ion exchange membrane on the other. The electrolyte therefore only passes through the openings of the conductive structures. The flow control structures can be fixed or detachably connected to the gas diffusion electrode and the ion exchange membrane. The flow guide structures are preferably clamped between the gas diffusion electrode and the ion exchange membrane. In a particularly preferred In one embodiment, the flow guide structures are fastened to a holding structure which is arranged essentially vertically in the gap, ie essentially parallel to the gas diffusion electrode and the ion exchange membrane. The holding structure runs, for example, in the middle of the gap, so that the flow guide structures project on the one hand in the direction of the ion exchange membrane and on the other hand in the direction of the gas diffusion electrode. The holding structure consists, for example, of a thin plastic rod, the diameter of which is smaller than the gap width between the gas diffusion electrode and the ion exchange membrane. The number of holding structures, for example in the form of plastic rods, over the length of the gas diffusion electrode, and thus of the flow guide structures, depends on the material thickness of the flow guide structures, since the plastic rods

Stability, e.g. when assembling the electrolyzer.

The flow guide structures can be flat. In order to facilitate the clamping of the flow guide structures between the gas diffusion electrode and the ion exchange membrane, the flow guide structures can have, for example, a Z, L, T, double T or trapezoidal profile. The flow guide structures can also be angled or curved as desired. They preferably consist of an elastic plate which is wider than the width of the gap. When pinching between the gas diffusion electrode and the ion exchange membrane and under the action of the electrolyte current in the gap, the elastic plates bend downward. The flow guide structures are then curved downwards. However, it is also possible to use flow guide structures that are curved upward. Curved flow guide structures are advantageous because they compensate for the manufacturing tolerances of the electrochemical cell, which are expressed, for example, in the width of the gap.

The opening in the flow guide structures can have any shape, e.g. round or angular. The openings in flow guidance structures arranged one above the other or one below the other can either lie one above the other or one below the other, i.e. the openings coincide. The electrolyte flow runs essentially vertically through the gap. However, they can also be offset from one another so that the electrolyte flow does not flow through the gap in a straight line, but rather, for example, in a zigzag or meandering manner. This reduces the formation of dead zones.

The flow guiding structures can be made of an alkali-resistant material, in particular an alkali-resistant metal or plastic. For example, nickel or PTFE can be used as the material. The number of flow guide structures and the number and cross-sectional area of the openings are chosen so that the flow rate of the electrolyte is lower than in free fall. With an overall height of the electrolyzer of, for example, 1.3 m and an amount of electrolyte of, for example, 180 1 / h, for example 26 flow guide structures with 64 openings can be used. The openings have a diameter of 1 mm, for example. As an alternative, 6 flow guide structures with 127 openings with a diameter of 0.5 mm could also be used. Depending on the flow, appropriate pressure compensation can be achieved via the dragon knife and the number of openings and the number of flow guide structures. The electrolyte flowing down in the gap must not build up on the flow guide structures. It must therefore be ensured that the sum of the cross-sectional areas of all openings of a flow guide structure is the same for all flow guide structures. This can be done by varying the number of openings or the cross-sectional area. Regardless of whether the electrolyte flows through the gap with the aid of a pump or whether flow guidance structures are provided or both, the preferred volume flow of the electrolyte in the gap (with a width of the gap of, for example, 3 mm) is 100 to 300 1 / h. The volume flow is preferably a maximum of 500 1 / h. The flow rate is preferably a maximum of 1 cm / s. The advantage of flow guide structures over the porous layers known from the prior art lies in the improved removal of gas bubbles which enter the gap through the gas diffusion electrode. Furthermore, the electrolyte is pumped through the gap between the gas diffusion electrode and the ion exchange membrane, whereby this gap is completely filled with electrolyte. Porous structures which the electrolyte passes through in free fall according to the prior art are usually not completely filled with electrolyte, which is noticeable by a higher electrolysis voltage.

The electrochemical cell according to the invention can be used for different electrolysis processes in which at least one electrode is a gas diffusion electrode. The gas diffusion electrode preferably functions as a cathode, particularly preferably as an oxygen consumable cathode, the gas supplied to the electrochemical cell being an oxygen-containing gas, for example air, oxygen-enriched air or oxygen itself. The cell of the invention for the electrolysis of an aqueous solution of an alkali halide ^•, in particular of sodium chloride is preferably used.

In the case of the electrolysis of an aqueous sodium chloride solution, the gas diffusion electrode is constructed, for example, as follows: the gas diffusion electrode consists at least of an electrically conductive carrier and an electrochemically active coating. The electrically conductive carrier is preferably a mesh, woven fabric, braid, knitted fabric, fleece or foam made of metal, in particular made of nickel, silver or silver-plated nickel. The electrochemically active coating preferably consists of at least one catalyst, e.g. Silver (I) oxide, and a binder, e.g. Polytetrafluoroethylene (PTFE). The electrochemically active coating can be constructed from one or more layers. In addition, a gas diffusion layer, for example made of a mixture of carbon and polytetrafluoroethylene, can be provided, which is applied to the carrier.

Electrodes made of titanium, for example, can be used as anode, e.g. are coated with ruthenium-iridium oxides or ruthenium oxide.

A commercially available membrane, e.g. from DuPont,

Nafion X2010.

The electrolysis cell according to the invention, which is suitable for the electrolysis of an aqueous sodium chloride solution, has a gap between the gas diffusion electrode and the ion exchange membrane with a width of the order of 3 mm. The flow guide structures are preferably made of thin plates made of PTFE or PVDF and have a thickness of 0.1 to 0.5 mm

The electrolyte inlet is a channel, for example a tube, which extends over the entire length of the gas diffusion electrode. In this case, the electrolyte feed can be used to feed the electrolyte evenly over the entire length from above into the gap between the gas diffusion electrode and the ion exchange membrane. Instead of an electrolyte feed, which extends over the entire length of the gas diffusion electrode, the feed can also take place only in one area, for example in the upper area of one of the two ends of the gas diffusion electrode. In this case, the flow guide structures, which are inclined in an axis perpendicular to the gas diffusion electrode or to the ion exchange membrane, can be used to achieve a uniform distribution of the electrolyte over the entire length of the gap. Another object of the invention is a method for the electrolysis of an aqueous alkali halide solution in an electrochemical cell, at least consisting of 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, the anode and / or the cathode is a gas diffusion electrode and between the

Gas diffusion electrode and the ion exchange membrane a gap is arranged and the half cell with a gas diffusion electrode has an electrolyte inlet and an electrolyte outlet and a gas inlet and a gas outlet, characterized in that the electrolyte flows by means of a pump in the gap from top to bottom, the gap being completely with Electrolyte is filled.

The invention is explained in more detail below with reference to the accompanying drawings. Show it:

1 shows a schematic cross section of a first embodiment of the electrochemical cell according to the invention without flow guide structures in the gap between the gas diffusion electrode and the ion exchange membrane

FIG. 2 shows a schematic cross section of a second embodiment of the electrochemical cell according to the invention with flow guide structures in the gap between the gas diffusion electrode and the ion exchange membrane

FIG. 1 shows an electrochemical cell 1 according to the invention, which is constructed from an anode half cell 2 with an anode 21 and a cathode half cell 3 with a gas diffusion electrode 31 as the cathode. The two half cells 2, 3 are separated from one another by an ion exchange membrane 4. The gas diffusion electrode 31 is separated from the ion exchange membrane 4 by a gap 32. Seals 39 seal the half cell 3 from the outside. The cathode half-cell 3 has an electrolyte inlet 33 and an electrolyte outlet 34 as well as a gas inlet 35 and a gas outlet 36. The electrolyte inlet 33 is tightly connected to the gap 32. The electrolyte is supplied to the half cell 3 via the electrolyte inlet 33 and flows downward in the gap 32 before it is removed from the half cell 3 via the electrolyte outlet 34. The gap 32 is completely filled with electrolyte during operation of the electrolysis cell 1. Gas is supplied to the gas space 37 of the half cell 3 via the gas inlet 35, flows upward in the gas space 37 and is discharged from the half cell 3 via the gas outlet 36. The tight connection of the electrolyte inlet 33 with the gap 32 allows the electrolyte to be conveyed through the gap 32 with the aid of a pump and thus a desired volume flow or a desired flow adjust the speed of the electrolyte in the gap 32. The tight connection must prevent gas from flowing out of the gas space 37 into the gap 32. For this purpose, the electrolyte inlet 33 is completely filled. The equalizing opening 38 is to be dimensioned such that a very low volume flow of the electrolyte flows out into the gas space 37 via the opening 38. The volume flow through the opening 38 into the rear space is preferably less than 5% of the total volume flow. At the same time, the compensating opening 38 allows gas to escape, which is released in small quantities during operation of the electrolytic cell 1

Gas space 37 enters the gap 32 through the gas diffusion electrode 31 and in the form of

Gas bubbles rise upwards. In this way, the gas can reach the gas space 37 from the gap 32 via the equalization opening 38 in the electrolyte inlet 33.

In comparison to the embodiment shown in FIG. 1, the electrolytic cell 1 in FIG. 2 has flow-guiding structures 51, 52, 53, 54 in the gap 32 in addition to the tight connection of the electrolyte inlet 33 to the gap 32. The flow guide structures 51, 52, 53, 54 reduce the flow rate of the electrolyte in the gap 32 compared to the flow rate that the electrolyte would assume in free fall. The flow guide structures 5b 52, 53, 54 consist of thin plates with openings 56 which allow the electrolyte to pass through. In the illustrated embodiments, they are clamped between the ion exchange membrane 4 and the gas diffusion electrode 31. The flow guide structures 51 are substantially horizontal in the gap 32, i.e. arranged transversely to the flow direction of the electrolyte. Likewise, the flow guide structures 53 can be inclined, i.e. at an angle to the direction of flow, e.g. in the direction of the ion exchange membrane 4. In a further embodiment, the flow guide structures 53 are V-shaped. The flow guide structures 54 are curved downward.

Claims

claims:

1. . An electrochemical cell (1), at least consisting exchange membrane from an anode half-cell (2) having an anode (21), a cathode half-cell (3) having a cathode (31) and arranged between the anode half-cell (2) and cathode half-cell (3) ^ion-'( 4), the anode (21) and / or the cathode (31) being a gas diffusion electrode and a gap (32) being arranged between the gas diffusion electrode (31) and the ion exchange membrane (4) and the half cell (2, 3) having a gas diffusion electrode (31) has an electrolyte inlet (33) and an electrolyte outlet (34) as well as a gas inlet (35) and a gas outlet (36), characterized in that the electrolyte inlet (33) is tightly connected to the gap (32). is. ,

2. Electrochemical cell according spoke 1, characterized in that flow guide structures (51; 52; 53; 54) are arranged in the gap (32).

3. Electrochemical cell according to one of claims 1 or 2, characterized in that the flow guide structures (51; 52; 53; 54) are clamped between the gas diffusion electrode (31) and the ion exchange membrane (4).

4. Electrochemical cell according to one of claims 1-3, characterized in that the flow guide structures (51; 52; 53; 54) are inclined with respect to the horizontal.

5. A method for the electrolysis of an aqueous alkali halide solution in an electrochemical cell (1), at least consisting of an anode half-cell (2) with an anode (21), a cathode half-cell (3) with a cathode (31) and an anode half-cell (2 ) and cathode half cell (3) arranged ion exchange membrane (4), the anode (21) and / or the cathode (31) being a gas diffusion electrode and a gap (32) arranged between the gas diffusion electrode (31) and the ion exchange membrane (4) and the half-cell (2, 3) with a gas diffusion electrode (31) having an electrolyte inlet (33) and an electrolyte outlet (34) and a ^• gas inlet (35) and a gas outlet (36), characterized in that the electrolyte by a pump flows in the gap (32) from top to bottom, the gap (32) being completely filled with electrolyte. Method according spoke 5, characterized in that in the gap

Flow guide structures (51; 52; 53; 54) are arranged.