CN111133131A

CN111133131A - Electrolytic cell device

Info

Publication number: CN111133131A
Application number: CN201880061394.8A
Authority: CN
Inventors: M·哈恩布斯; G·施米德; K·梅尔策; D·塔罗亚塔
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2017-09-21
Filing date: 2018-09-13
Publication date: 2020-05-08
Also published as: US20200263311A1; EP3655564A1; WO2019057593A1; AU2018335098A1; DE102017216710A1

Abstract

The invention relates to an electrolytic cell arrangement with at least one electrolytic cell comprising two electrodes, namely an anode and a cathode, wherein each of the two electrodes is connected to an electrode chamber for filling with liquid electrolyte, wherein the two electrode chambers are separated from each other by a membrane, and wherein for each of the two electrodes a conveying device is provided for conveying the electrolyte through the electrode chambers in a respective circuit (cathode circuit and anode circuit) and back to the electrode chambers via at least one collecting container of each circuit. The invention is characterized in that a device for conveying an auxiliary volume flow between the cathode circuit and the anode circuit is arranged outside the electrolytic cell.

Description

Electrolytic cell device

Technical Field

The invention relates to an electrolysis cell arrangement according to claim 1 and a method for operating an electrolysis cell according to claim 12.

Background

Significant changes are currently observed in the energy market. In the context of energy transfer programs, the use of fossil energy is minimized, since fossil energy causes a large proportion of carbon dioxide emissions. At the same time, while renewable energy sources are capable of providing large amounts of power, they are not always at the desired location and at the desired time. One technical challenge is to remove carbon dioxide (CO) from carbon dioxide by using excess energy₂) Valuable products are produced, surplus energy being generated in particular when renewable energy sources are increasingly fed into the grid. One method is to produce gaseous valuable products such as carbon monoxide (CO) or ethylene (C) by electrochemical reduction of carbon dioxide₂H₄)). Such reactions are for example in the so-called CO₂Is carried out in an electrolytic cell.

CO₂A typical design of an electrolytic cell is based on an aqueous electrolyte comprising a conductive salt, i.e. a salt that dissolves in the electrolyte and is electrically conductive. Here, CO is introduced₂The electrolysis cell is discussed as an example of all electrolysis cell arrangements with liquid electrolyte. The anode and cathode compartments are kept separate from each other by a cation permeable membrane. This prevents gaseous species formed on the cathode from reaching the anode side. This also prevents the gas (typically oxygen) formed on the anode side from reaching the cathode side. Thus avoiding intermixing of the two gases. This is necessary to eliminate dangerous operating conditions, for example due to the formation of explosive gas mixtures. However, there are other reasons to avoid gas mixing. For example, there is a requirement for gas purity in the product gas, depending on the application. For example, CO for anaerobic gas fermentation allows onlyContains a trace amount of oxygen.

Although the membranes used are in fact impermeable to gases, these membranes must be permeable to ionic carriers. However, when using a conductive salt, cation transport of the conductive salt (e.g. potassium) often occurs first, i.e. potassium cations diffuse through the membrane from the anode side to the cathode side. This in turn leads to a difference in cation concentration between the electrolyte on the anode side and on the cathode side.

In summary, it can be determined that the transfer of cations (other than protons) leads to a number of disadvantages. It is therefore desirable that the composition of the anolyte (i.e. the electrolyte on the anode side) and the catholyte remain as identical as possible. Together with the already mentioned transfer of cations, water passes through the membrane, which results in dilution of the catholyte (i.e. the electrolyte on the cathode side), while the anolyte is concentrated. This effect makes it difficult to maintain the desired composition of the anolyte and catholyte the same.

It is known from the prior art that the two electrolytes can be mixed with one another in a common storage container, so that after passing through the electrolysis cell, an equilibrium concentration of ions and an equilibrium concentration of water is ensured. However, this common concentration balance also entails a certain risk, since in the respective electrolyte liquid there are always gaseous impurities which are produced by electrolysis and which are composed mainly of product gas or hydrogen and oxygen. Furthermore, the product purity which is usually required is made difficult by contamination of the product with hydrogen or oxygen.

Disclosure of Invention

The object of the present invention is to provide an electrolysis cell arrangement or a method for operating an electrolysis cell arrangement which is suitable for ensuring the necessary concentration balance between anolyte and catholyte in an electrolysis cell and which reduces gas pollution.

The solution to this object is an electrolysis cell with the features according to claim 1 and a method for operating an electrolysis cell with the features according to claim 12.

The electrolytic cell according to the invention, according to claim 1, comprises at least one electrolytic cell further comprising two electrodes, namely an anode and a cathode. Each of these two electrodes is connected to a so-called electrode chamber. The electrode compartment is adapted to be filled with a liquid electrolyte. The two electrode chambers are separated from each other by a membrane, wherein both electrodes comprise a delivery device for delivering the electrolyte in the respective circuits (cathode circuit and anode circuit). The invention is characterized in that a conveying device for conveying the auxiliary volume flow between the cathode circuit and the anode circuit is arranged outside the electrolytic cell.

The described invention has the advantage that cations or anions are equalized between the two circuits by the auxiliary volume flow. In addition, larger amounts of water can be equalized without transferring large amounts of product gas (such as hydrogen or oxygen) between the various circuits, thereby avoiding excessive contamination or reactive mixtures. The terms "anode circuit" and "cathode circuit" are understood to mean, respectively, a device (in particular a pipe device, in particular a pipe device with a pump device) which is suitable for circulating or circulating a corresponding electrolyte therein.

In one embodiment of the invention, a collection vessel is provided for each of the two circuits. This has process-technical advantages, since it is ensured that sufficient electrolyte is always available for both electrolysis circuits.

In one embodiment of the invention, the collecting container is divided into at least two partial containers, wherein a first partial container is connected to the cathode circuit and a second partial container is connected to the anode circuit, and the auxiliary volume flow is formed between the first partial container and the second partial container. The equalization of the electrolyte, i.e. the equalization of the anolyte and catholyte outside the electrolytic cell in two separate containers by means of a defined auxiliary volume flow (e.g. by means of a pipe with a target flow rate that can be controlled by a pump), is particularly advantageous, since the electrolyte is collected in this part of the container and the volume flow can be well regulated.

In a further advantageous embodiment of the invention, a second conveying device is provided for generating a second auxiliary volume flow between the two circuits. The second auxiliary volume flow is in the opposite direction to the first auxiliary volume flow. It can be advantageous if, for example, water and cations are conducted from the first partial volume into the second partial volume via the first auxiliary volume flow and anions can be equalized in the second auxiliary volume flow.

In one embodiment of the invention, the conveying device between the two circuits for generating the second auxiliary volume flow is embodied in the form of a membrane module.

Advantageously, the membrane module is part of both the cathode circuit and the anode circuit. As between the two electrode chambers, a membrane is arranged in the membrane module, which can serve as an exchange surface for dissolved ions. These ions are cations and anions.

The membrane between the electrode compartments is preferably a cation permeable membrane. In contrast to the porous membrane, the cation-permeable membrane is adapted to separate gases from the respective electrode compartments from each other, which gases are generated during electrolysis in the respective electrode compartments. However, this also causes cations (e.g., potassium, which is part of the conductive salt) to move through the membrane. Thereby further requiring an enhanced concentration balance between catholyte and anolyte outside the cell. When a cation permeable membrane is used, the auxiliary volume flow preferably flows from the cathode circuit to the anode circuit.

Another component of the invention is a method with the features according to claim 12, which is suitable for operating an electrolysis cell arrangement. Wherein the cell unit comprises an electrolytic cell further having two electrodes, an anode and a cathode. The electrodes each have an electrode chamber through which a liquid electrolyte is conveyed in a respective circuit (i.e. a cathode circuit and an anode circuit), the liquid electrolyte having a conductive salt dissolved therein. The electrode compartments are separated by a membrane and, therefore, the electrolyte contained in the electrode compartments is separated by a membrane. The invention is characterized in that the electrolyte is conveyed from one circuit to a second circuit in the auxiliary volume flow.

This method has the advantages already discussed in connection with the electrolyzer unit. Not only is a concentration equalization of ions, anions and cations achieved by the described auxiliary volume flow, but in one circuit possibly an excess of water is returned to the other circuit without excessive mixing of the product gases, such as oxygen and hydrogen or also carbon monoxide, occurring in a common collecting vessel.

In a particular embodiment of the invention, the auxiliary volume flow is designed to have at least 0.01% and at most 10%, preferably between 0.1% and 1%, of the greater of the two main volume flows (i.e. the volume flow of the cathode circuit or the volume flow of the anode circuit). It should be noted that the term "auxiliary volume flow" in the context of the method and the electrolyzer unit is to be understood as a flow consisting of molecules and ions. The auxiliary volume flow can take place in the form of a flow of electrolyte, in particular water-based with conductive salts or corresponding ions contained therein, in a corresponding pipe, hose or trough. On the other hand, the auxiliary volume flow can also take place in the form of diffusion through the membrane. Thus, with respect to the auxiliary volume flow, the term "transport device" should be understood as any device suitable for providing the above-mentioned flow of molecules and ions. On the one hand, in particular the corresponding pump belongs to the conveying device, and also the corresponding line or groove, which generates the secondary auxiliary volume flow on the basis of a pressure difference or gravity, belongs to the conveying device. Furthermore, membranes which allow the transfer or return of ions from one circuit to another also belong to the term "transport apparatus".

It is furthermore advantageous if a gas separation vessel is provided in the cathode circuit and/or the anode circuit, and a connecting line from the at least one gas separation vessel to the educt supply device is provided. The anode gas and/or the cathode gas can thus be re-supplied to the original electrolysis process, which can again be the educt gas, depending on the process. This has a positive effect on the economics of the process.

Drawings

Other embodiments and other features of the invention are derived from the accompanying drawings. These embodiments and features do not limit the invention, as they only describe advantageous embodiments. Wherein:

figure 1 shows an electrolyzer unit with an auxiliary volume flow between the anode circuit and the cathode circuit,

figure 2 shows the cell arrangement of figure 1 with an additional separation vessel,

fig. 3 shows an electrolyzer unit with two possibilities, which is used to illustrate an apparatus for auxiliary volume flow with two collecting vessels,

fig. 4 shows an electrolyzer unit with two possibilities, which is used to illustrate the apparatus for the auxiliary volume flow,

FIG. 5 shows a schematic view of an electrolyzer unit in which two collecting vessels are located in front and

fig. 6 shows a membrane module.

Detailed Description

In fig. 1 is schematically illustrated an electrolytic cell arrangement 2 having an electrolytic cell 4, an electrolyte 5 being arranged in the electrolytic cell 4. The electrolytic cell 4 has two electrodes, a cathode 7 and an anode 6, the cathode 7 being realized in this case in the form of a gas-permeable electrode. The two electrodes, namely the anode 6 and the cathode 7, adjoin in each case one electrode chamber, wherein an electrode chamber 8 for the anode 6 and an electrode chamber 9 for the cathode 7 are distinguished. The two

electrode chambers

8, 9 are separated from each other by a membrane 10. The electrolyte 5 is located in the electrode compartment, and depending on the position of the electrolyte 5 in the electrolytic cell 4, the electrolyte 5 is referred to as anolyte 38 if the electrolyte 5 is present in the electrode compartment 8 of the anode 6, and the electrolyte 5 is referred to as catholyte 40 if the electrolyte 5 is present in the electrode compartment 9 of the cathode 7.

The electrolyte 5 (or 38 and 40) is not stationary in the

electrode chambers

8 and 9, but is located in the

loops

14, 15. For this purpose,

delivery devices

12 and 13 are provided, which supply the anode circuit 14 or the cathode circuit 15 with a corresponding volumetric flow of electrolyte 5 (or 38 and 40), respectively. Here, the electrolyte 5 moves along the respective circuits 14 (anode circuit) and 15 (cathode circuit). Considering now the cathode circuit 15 as an example, the catholyte 40 is pumped out of the electrode chamber 9 of the cathode 7 through a pipe with reference numeral 15 by means of the conveying device 13.

Furthermore, in the cell arrangement there is a educt supply line 42 and a product discharge line 44, through which educt supply line 42 educt (for example carbon dioxide) is introduced into the electrolytic cell 4. During electrolysis when an electric current is applied to the cathode 7 and the anode 6, the carbon dioxide is reduced to carbon monoxide in this example, which in turn exits the electrolytic cell 4 through the product discharge conduit 44. During this electrolysis, both protons and cations of a conductive salt (e.g., potassium) dissolved in the electrolyte 5 move through the membrane 10, which membrane 10 is in this embodiment in the form of a cation permeable membrane. This results in the anolyte 38 and catholyte 40 having different concentrations of cations (particularly cations of the conductive salt) as the electrolytic activity increases. This can be tolerated up to a certain degree (about 2%) of difference, from which the economics and profitability of the electrolysis process cannot be ensured. It is therefore advantageous to have a continuous exchange between the anolyte 38 and the catholyte 40. According to the prior art, in the simplest form a single collecting container is used, which is part of both the anode circuit 14 and the cathode circuit 15. In a common collecting container (not shown here), concentration equalization and complete mixing of the electrolyte 5 accumulated or consumed in the electrolytic cell takes place. However, the product gases, in particular hydrogen in the cathode circuit 15 and oxygen from the anode circuit 14, are also conveyed into the common collecting vessel (not shown here). This may lead to explosive mixtures, and in addition product gases, such as carbon monoxide, which are present in the common collecting vessel in the same small amounts, may be contaminated with oxygen and hydrogen.

In order to solve this problem, provision is made for an auxiliary volume flow 20 to be provided, which auxiliary volume flow 20 is provided by means of the auxiliary volume flow device 18. The concentration is exchanged between the anode circuit and the cathode circuit and vice versa by means of the auxiliary volume flow. The flow direction of the secondary volume flow depends on the respective process control. Preferably, the auxiliary volume flow is at most 10% of the volume flow of the electrolyte in the cathode circuit 15 or the anode circuit 14. The auxiliary volume flow is at least 0.01% of the electrolyte volume flow, in particular the interval in which the auxiliary volume flow 20 varies is between 0.1% and 1% of the electrolyte volume flow. If the two electrolyte volume flows are not the same size, the larger of the two electrolyte volume flows is used as a reference value for the auxiliary volume flow.

Advantageously, in steady state operation, the pH of the anolyte is between 4 and 5 and the pH of the catholyte is between 7 and 9.

Fig. 2 shows a similar embodiment of the device according to fig. 1, wherein

separation vessels

53, 55 are provided in the cathode circuit 15 and the anode circuit 14, respectively, in which

separation vessels

53, 55 the gaseous components of the electrolyte can be separated, respectively. In the case of the separation vessel 53, the separated carbon dioxide can be fed back to the educt feed apparatus 42, for example.

In fig. 3, it is provided that the cathode circuit 15 has a collecting container 23, into which collecting container 23 the catholyte 40 is fed, and that the anode circuit 14 has a collecting container 22, into which collecting container 22 the anolyte 38 is fed. The two collecting

vessels

23 and 22 are in principle separated from one another, but in another embodiment the two collecting vessels also have a device 18 for generating the auxiliary volume flow 20. This device 18 is very schematically shown in fig. 3, the device 18 being realized for example in the form of an overflow trough, wherein a small part amount can pass from one container to the other by a defined inclination or a defined gradient. The auxiliary volume flow 20 between the container 22 and the container 23 can also be caused by a corresponding pipe (not shown here) or a corresponding hose, which auxiliary volume flow 20 is caused, for example, by gravity or a pressure difference.

In fig. 5, a device 18 for generating the auxiliary volume flow 20 is illustrated, which device 18 is in the form of a pipe in which a pump 30 is integrated. It can also be advantageous according to fig. 5 if, in order to ensure a concentration equilibrium between the anolyte 38 and the catholyte 40 with respect to anions, a second auxiliary volume flow 26 is provided, which second auxiliary volume flow 26 is produced by the second delivery device 24 (for example in the pump device 30 according to fig. 5). It is also advantageous that the two

partial containers

22, 23 contain a stirring device 27, which stirring device 27 ensures a homogeneous mixing of the

electrolytes

38, 40 in the

respective containers

22 and 23. Of course, good mixing can also be achieved in some of the vessels without active stirring devices, for example by means of suitable flow deflectors.

If a cation-permeable membrane is applied as membrane 10, many cations from the conductive salt move from the anode side (i.e. from the anolyte 38 present in the electrode compartment 8 of the anode 6) through the membrane 10 into the electrode compartment 9 of the cathode 7. Water (so-called Drag-Wasser) moves through the membrane with the cations, so that equalization (in particular from the cathode circuit 15 into the anode circuit 14) is necessary. Thus, in this case, when a cation-permeable membrane is used, the first auxiliary volume flow passes from the cation circuit 15 into the anode circuit 14. The first auxiliary volume flow is preferably formed between the collecting reservoir 23 of the cathode circuit 15 and the collecting reservoir 22 of the anode circuit 14, to be precise in the described direction. The second auxiliary volume flow is then used to equalize the anions which are provided between the container 22 and the container 23 by the second auxiliary volume flow 26.

Another possible way of generating the auxiliary volume flow is in the form of a membrane module 28, in which membrane module 28 a membrane 29 is arranged (see fig. 3 and 4). According to fig. 3, both the cathode circuit 15 and the anode circuit 14 flow through the membrane module 28. In addition to the membrane 29, the membrane module 28 has two module chambers, a first module chamber 46 through which the anode circuit 14 passes and a second module chamber 47 through which the cathode circuit 15 passes. Thus, catholyte 40 is located in module chamber 47, and anolyte 38 is located in module chamber 46. The membrane 29 provides an exchange surface for ions (more specifically cations and anions) dissolved in the

electrolytes

38 and 40. A porous membrane which is as thin as possible is particularly suitable for this task. The porous membrane has a relatively low transport resistance, so that a relatively small membrane surface is sufficient. Transport (osmosis) in porous membranes is caused by two different mechanisms, one being forced transport outside through the pores (i.e. pure convection transport) and the other being transport based on diffusion of dissolved components. The transport mechanism of ions through the porous membrane corresponds to diffusion, which proceeds without energy consumption. By applying a small pressure difference, it is also possible to force so-called drag water through the membrane by convection.

The desired size of the porous membrane 29 may be determined by the maximum expected mass flow of cations within the cell in such a way as to simultaneously determine the maximum allowable concentration difference (e.g., 0.2mol/L) between the anolyte 38 and the catholyte 40. With the aid of the known permeability coefficients, it can be estimated that, when using thin porous membranes 29, the membrane modules 28 can be constructed to be significantly smaller than the area provided for this in the electrolytic cell 4 or the expanded membranes 10. The total membrane surface of membrane 29 is less than the total cell surface of membrane 10, but the total membrane surface of membrane 29 is at least one percent of the membrane surface of membrane 10. Particularly advantageously, the ratio between the membrane 29 and the membrane 10 is between 1:20 and 1: 5.

In principle, water can also be transported through the porous membrane 29 by the presence of a small pressure difference within the membrane module 28. The pressure difference is preferably less than 100 mbar.

By means of the described overall arrangement, cross-mixing of the gases generated during the carbon dioxide electrolysis of the electrolysis cell 4 can be avoided, thereby eliminating complex handling of the electrolyte 5 or the generated gases. For example, catholyte 40 therefore does not contain oxygen that contaminates the catholyte product gas. In addition, virtually neither product gases (e.g., carbon monoxide, methane, or hydrogen) nor educt gases (such as carbon dioxide) are lost through the anolyte 38.

A certain degree of deviation of the compositions of anolyte 38 and catholyte 40 from each other, and thus of the pH values of anolyte 38 and catholyte 40, cannot be avoided by using two separate electrolytic circuits, namely anode circuit 14 and cathode circuit 15. In addition, drag water from the anolyte 38 enters the catholyte 40. Conventional processing can result in high energy consumption, for example, by thermal or vacuum degassing. Alternatively, additives may be added to the process that chemically bind the undesired gases. However, the use of additives is expensive. Furthermore, it is unpredictable to what extent possible additives affect the electrochemical process. The catalytic removal of the undesired gases likewise leads to high energy consumption. The described device therefore represents a simple solution to ensure a corresponding equalization of ions and water between the anode circuit 14 and the cathode circuit 15.

Claims

1. An electrolytic cell arrangement (2) with at least one electrolytic cell (4), which electrolytic cell (4) comprises two electrodes (6, 7), which are an anode (6) and a cathode (7), wherein each of the two electrodes (6, 7) is connected to an electrode chamber (8, 9), which electrode chambers (8, 9) are intended for liquid-filled electrolyte (5), wherein the two electrode chambers (8, 9) are separated from each other by a membrane (10), and wherein conveying means (12, 13) are provided for both electrodes (6, 7) for conveying the electrolyte (5) through the electrode chambers (8, 9) in respective circuits (14, 15) comprising a cathode circuit (15) and an anode circuit (14), characterized in that outside the electrolytic cell (4) there is provided a circuit for conveying the cathode circuit (15) and the anode circuit (14) And a device (18) for conveying an auxiliary volume flow (20) therebetween.

2. An electrolysis cell arrangement according to claim 1, wherein the cathode circuit and the anode circuit each have one collecting vessel (22, 23).

3. An electrolyser unit as claimed in claim 2, characterized in that the first auxiliary volume flow is formed between the first collection reservoir (22, 23) and the second collection reservoir (22, 23).

4. An electrolysis cell arrangement according to claim 1, characterised in that a second conveying device (24) is provided for generating a second auxiliary volume flow (26) between the two circuits (14, 15), the second auxiliary volume flow (26) being in the opposite direction to the first auxiliary volume flow (20).

5. Electrolysis cell arrangement according to claim 4, characterized in that said second conveying means (24) for generating said second auxiliary volume flow (26) is embodied in the form of a membrane module (28).

6. An electrolyser plant according to claim 5, characterized in that said membrane modules (28) pass through both said cathodic circuit (15) and said anodic circuit (14).

7. An electrolyser plant according to claim 4, characterized in that a pump device (30) is provided between said collection containers (22, 23) for generating said second auxiliary volume flow (26).

8. Electrolysis cell arrangement according to any one of claims 2 to 5, wherein an overflow (32) or a pump device (34) is provided between the two collection vessels (22, 23) to generate the first partial volume flow (20).

9. A cell arrangement according to any one of the preceding claims, characterized in that said membrane (10) between said electrode compartments (8, 9) is a cation permeable membrane.

10. An electrolysis cell arrangement according to claim 8, wherein the auxiliary volume flow (20) is from the cathode circuit (15) to the anode circuit (14).

11. An electrolysis cell arrangement according to any preceding claim, wherein a gas separation vessel (53, 55) is provided in the cathode circuit (15) and/or the anode circuit (14), and a connection conduit (54) is provided from one of the gas separation vessels (53, 55) to an educt supply device (42).

12. A method for operating an electrolytic cell having at least one electrolytic cell (4), the electrolytic cell (4) further comprising two electrodes (6, 7) which are an anode (6) and a cathode (7), wherein each electrode (6, 7) has an electrode chamber (8, 9), through which liquid electrolyte (5) is conveyed in a main volume flow in a respective conveying circuit (14, 15) respectively, the electrolyte (5) having a conductive salt dissolved therein, the conveying circuit comprising a cathode circuit (15) and an anode circuit (14), and wherein the two electrode chambers (8, 9) are separated by a membrane (10) and thus the electrolyte (5) contained in the two electrode chambers (8, 9) is separated by the membrane (10), characterized in that the electrolyte (5) is conveyed in the auxiliary volume flow (20) from one circuit (14, 15) into the second circuit (14, 15).

13. A method according to claim 12, wherein the auxiliary flow is at least 0.01% and at most 10% of the larger of the two main volumetric flows.

14. The method according to claim 13, wherein the auxiliary flow is at least 0.1% and at most 1% of the larger of the two main volumetric flows.

15. Method according to any one of claims 12 to 14, characterized in that one collecting container (22, 23) is provided in each of the two circuits (14, 15), and that the electrolyte is transported in the auxiliary volume flow (20) from a first collecting container (22, 23) to a second collecting container (22, 23).