Separation and analysis of gaseous effluent from multiple electrolysis cells operated in parallel

Abstract

Process for separating and analyzing gaseous effluent produced in multiple parallel electrolysis cells, which process comprises introducing the effluent of each of the multiple electrolysis cells separately via a dedicated vertically extending inlet into a gas-liquid separator which vertically extending inlet separates the effluent which is introduced into a gaseous effluent and liquid effluent, keeps the effluent which is introduced separate from the fluid present in the gas-liquid separator and wherein part of the gaseous effluent is withdrawn from the top of the vertically extending inlet and analyzed, and system for such process.

Description

[0001] SEPARATION AND ANALYSIS OF GASEOUS EFFLUENT FROM MULTIPLE ELECTROLYSIS CELLS OPERATED IN PARALLEL

[0002] Introduction

[0003] The present invention relates to a process for separating liquid from effluent obtained from multiple electrolysis cells operated in parallel and analyzing the gaseous phase effluent, as well as a system for separating and analyzing effluent.

[0004] Background of the invention

[0005] Hydrogen is increasingly recognized as both a promising energy carrier and a valuable base material for the chemical industry. While hydrogen can be produced from methane— typically derived from natural gas— this method yields what is known as grey hydrogen, which involves the use of fossil fuels. In contrast, there is growing interest in producing hydrogen through the electrolysis of water, a process that splits water molecules into hydrogen and oxygen using electricity. This method is gaining traction as water is abundantly available. Furthermore, electrolysis powered by renewable energy sources, such as wind or solar, enables the production of green hydrogen, which does not rely on fossil energy and significantly reduces carbon emissions. Electrolysis is carried out in specialized units known as electrolysis cells, which form the core of green hydrogen production systems.

[0006] Electrolysis cells, which convert water into hydrogen and oxygen using electrical energy, come in various types. The most promising types of electrolysis cells include Proton Exchange Membrane (PEM) cells which allow protons to pass through the membrane from the anode to the cathode during operation, Anion Exchange Membrane (AEM) cells which permit hydroxide ions to pass through the membrane during operation and Alkaline Electrolysis (AEL) systems which use a diaphragm that enables the passage of hydroxide ions during operation. Depending on the design and operating conditions, water molecules may also pass through the membrane or diaphragm. However, hydrogen and oxygen molecules are either completely blocked or pass through only in very limited quantities.

[0007] In order to get an attractive hydrogen yield from every kilowatt of energy, research is being conducted on the efficiency of these types of electrolysis cells. Such research is e.g. directed on type, material and shape of the electrodes, the membrane or diaphragm between the electrodes, operating conditions like temperature, pressure, composition of the electrolyte, electrical current and potential, and other aspects. An important feature is how effectively hydrogen and oxygen are separated during production. This separation is typically determined by the barrier such as a membrane or a diaphragm, positioned between the anode and cathode. Traditionally, researching the PEM, AEL and AEM electrolysis systems described above involve test arrangements with single cells in which elements like membranes and electrodes can be exchanged. Typical sizes for such cells for research purposes involve 10 cm2membrane / diaphragm. Such cell in a research environment will have auxiliary equipment like supply of electrolyte, regulators for the pressure and / or flow thereof, arrangements for regulating the temperature at which the cell is operated, power supply and measuring power consumption, and equipment for capturing and analyzing the gasses produced at anode and separating such from liquids such as excess electrolyte. Analysis of the gasses produced is desired to have an indication of performance of the electrolysis cell. In particular it is desired to be able to determine the composition of the gaseous effluent preferably in combination with the flow rate (amount per time unit) especially of the effluent produced at the cathode where hydrogen is produced. However, such analysis can also be desired at the anode part where oxygen is produced.

[0008] Aqueous feed is fed to the electrolysis cells. A limited amount of water from the feed tends to pass the membrane or diaphragm which separates the cathode and the anode. Hence it is required to separate liquid from the effluent before the gaseous effluent can be analyzed.

[0009] Research tends to be conducted using single electrolysis cells. While such single-cell experiments provide valuable insights, scaling up research output requires high-throughput screening of materials and conditions. This involves operating multiple electrolysis cells in parallel, typically in configurations of four, eight, or more cells, running at least partially simultaneously. However, without additional design improvements, a setup with, for example, four cells would necessitate fourfold duplication of all auxiliary systems, including electrolyte supply, off-gas treatment, and analytical equipment. This significantly increases the complexity, spatial footprint, and cost of the research infrastructure.

[0010] There is a clear need for a process and system that enable the parallel operation of multiple electrolysis cells especially for hydrogen production from an aqueous feed. Such process and system could support simultaneous research on several cells, thereby increasing experimental throughput. Importantly, despite incorporating multiple cells, the system should avoid excessive complexity or cost in auxiliary equipment. It should still allow for individual cell performance assessment— for example, by measuring the gas composition and preferably also the flow rate, particularly of the hydrogen-producing side of each cell.

[0011] Summary of the invention

[0012] It has now been found that the above objective(s) may be achieved, at least in part, by a process for separating and analyzing gaseous effluent produced in multiple parallel electrolysis cells, which process comprises: (1) supplying aqueous feed to the multiple parallel electrolysis cells and applying an electric potential thereby converting at least part of the feed into effluent comprising an aqueous liquid phase and a gaseous phase, (2) introducing the effluent of each of the multiple electrolysis cells separately via a dedicated vertically extending inlet into a gas-liquid separator which vertically extending inlet is closed at the top and open at the bottom and is located in the upper part of the gas-liquid separator and which vertically extending inlet separates the effluent which is introduced into a gaseous effluent and liquid effluent, and (3) combining at least part of the gaseous effluents obtained from the vertically extending inlets and combining at least part of the liquid effluents obtained from the vertically extending inlets and removing the combined gaseous effluents and the combined liquid effluents separately from the gas-liquid separator, wherein each vertically extending inlet keeps the effluent which is introduced separate from the fluid present in the gas-liquid separator and wherein part of the gaseous effluent is withdrawn from the top of the vertically extending inlet and analyzed.

[0013] Furthermore, the above objective(s) may be achieved, at least in part, by a system for separating effluent obtained from multiple parallel electrolysis cells into a liquid and a gaseous phase and analyzing the gaseous phase effluent, which system comprises (a) multiple electrolysis cells which are each separately in fluid communication with a gas-liquid separator (13) via a line (1), (b) vertically extending inlets (6) located at an upper part of the gas-liquid separator (13) which vertically extending inlets are in fluid communication with line (1) and with the gas-liquid separator (13) which vertically extending inlets (6) are closed at the top and open at the bottom and which vertically extending inlets (6) are suitable for (i) separating fluid which is introduced from fluid present in the gas-liquid separator, and (ii) separating liquid effluent from gaseous effluent, and (c) an opening at the bottom part of the gas-liquid separator for removing liquid phase effluent and an opening at the top part of the gas-liquid separator for removing gaseous phase effluent, wherein the upper part of one or more vertically extending inlets (6) are in fluid communication with an analytical device (14).

[0014] Brief description of the drawing

[0015] Fig. 1 displays a schematic overview of a system according to the present invention.

[0016] Detailed description of the invention

[0017] Herein, the expressions "top" and "upper" have the common meaning which is that it is positioned higher than and above other parts during normal operation of the system and process. The expression "bottom" also has its common meaning which is being positioned lower than other parts during normal operation of the system and process. The expression "introduced downwardly" has the common meaning which is that the opening of the inlet is directed downwards which makes that the fluid also flows downward. The expression "vertical" means that it is substantially perpendicular to the horizon.

[0018] A "tubular inlet" is an inlet which has the form of or consists of a tube which means that the inlet is substantially longer than it is wide, substantially round and is hollow. While the vertically extending inlet is closed at the top, it contains openings at the top to allow entry of the lines which introduce the effluent into the gas-liquid separator and for a line through which gas can flow to an analytical device.

[0019] An "analytical device" is to be understood as a device for analyzing the composition and / or flow of a gaseous phase.

[0020] The present invention applies to multiple parallel electrolysis cells. "Parallel" herein means that multiple cells are operated, at least partially at the same time, wherein all cells obtain a fresh aqueous feed of electrolyte and produce effluent containing a gaseous phase which is diverted from the cells to storage means, vent or analytical means. This is opposed to serial electrolysis, often referred to as a stack of cells. The present invention allows multiple cells, which may be different cells, to be operated at the same time. The effluent of at least one of the electrode sides of each electrolysis cell is sent separately to a gas-liquid separator. The present invention allows to analyze the composition of the gaseous phase of effluent produced by an electrolysis cell by keeping the effluent of each electrolysis cell separate and introducing it into the gas-liquid separator via a dedicated and specific vertically extending inlet. It is attractive to have a common gas-liquid separator for the multiple electrolysis cells in which liquid is removed from the effluents of multiple electrolysis cells and the pressure is reduced.

[0021] The invention works for any number of parallel cells from two onwards, but is in particular beneficial when having more than two parallel cells. Hence, in the present invention it is preferred that the system comprises at least four and more preferably at least eight parallel electrolysis cells.

[0022] The gas-liquid separators have parts which are dedicated to a specific electrolysis cell such as the vertically extending inlets and parts which are shared or common for all electrolysis cells. The shared part conveniently is the collection of the liquid, and the way in which the gas-liquid separator is maintained under pressure in a pressurized vessel. The pressure at which the pressurized vessel operates is determined by the pressure at which the electrolysis cells are operated.

[0023] Preferably, the system according to the invention contains a pressurized vessel comprising (i) a bottom section (4) suitable for holding liquid and an upper section (5) suitable for holding gas which upper section (5) and bottom section (4) are in fluid communication, (ii) a level controller (3) connected to a bottom valve (7) for maintaining a pre-selected level of the liquid in the bottom section (4) which bottom valve (7) is connected to a drain, and (iii) a pressure controller (8) connected to a top valve (9) in the upper part of the gas-liquid separator which top valve (9) is connected to a vent (10).

[0024] The aqueous feed can be de-ionized water or di-ionized water with a specific salt dissolved therein, such as metal hydroxides such as potassium hydroxide. A limited amount of water optionally together with electrolyte tends to be lost by diffusion through the membrane or diaphragm which separates the cathode and the anode in the electrolysis cell. Hence the need in the present invention to separate the gaseous phase and the liquid phase of the effluent. As electrolytes are valuable, it is preferred that any electrolyte entrained in the effluent is captured, regenerated where needed, and reused. Hence, in the present invention, it may be preferred to remove the liquid phase from the gas-liquid separator and regenerate it for re-use as electrolyte feed source.

[0025] The actual gas-liquid separation can be achieved by conventional means, suitably by so-called gravity gas-liquid separation in which effluent enters a space in which gravity ensures that the liquid falls down contrary to the gaseous phase which forms a headspace above the liquid phase. The gaseous phase can subsequently be removed via an opening which preferably is connected to an outlet line including a valve such as a shut-off valve, a selector valve, a vent or an analytical device. Therefore, it is preferred that the gas-liquid separator is a gravity gas-liquid separator.

[0026] In the present invention, the vertically extending inlets can be separation plates which are appropriately positioned to achieve the desired effect or tubular inlets. The vertically extending inlets preferably are tubular inlets. The vertically extending inlets separate effluent from an individual electrolysis cell by gravity into a gaseous phase and a liquid phase. The separated liquid is collected in the common or shared part of the gas-liquid separator. The separated gaseous phase initially is kept separate to allow analysis of the composition of the effluent of the cathode and / or anode per electrolysis cell. There is less need to analyze the liquid part of the effluent.

[0027] From the above it is clear that the present invention allows to keep the gaseous effluents from the multiple electrolysis cells initially separate in a single pressurized vessel while the liquid effluent from the multiple electrolysis cells is allowed to become mixed upon entering the gas liquid separator and can be removed together.

[0028] The vertically extending inlets can thus be tube-like members extending downwards in the pressurized vessel, open at the bottom, and having an entry point for the effluent to be separated halfway or near the top of such tube-like member. The effluent can be obtained by conversion of feed at the anode or at the cathode, preferably at the cathode. The vertically extending inlets are in fluid communication with an analytical device via an outlet near the top of the tube-like member.

[0029] The opening of the vertically extending inlet can be at any desired point in the gas-liquid separator. It may be chosen such it is lower than the level of the liquid phase present in the gas-liquid separator. This will make that the surplus of gas will bubble through the liquid phase.

[0030] A convenient way to minimize mixing of gas of one gas-liquid separator with the gas of another gas-liquid separator is to ensure the flow of the gas that is actually analyzed is only a fraction of the gas that is produced by the electrolysis cells. By doing so, the chance is reduced that gas from one vertically extending inlet flows to the vertically extending inlet of another vertically extending inlet. Hence, it is preferred that the flow rate of the gaseous effluent withdrawn from the top of the vertically extending inlet to be analyzed is at least less than 50%, preferably less than 20%, more preferably less than 10%, of the flow rate of the effluent entering the vertically extending inlet.

[0031] As the effluent from the different electrolysis cells are introduced in a single vessel, it is preferred that all electrolysis cells are operated under the same operating pressure.

[0032] The gaseous effluent is analyzed for its composition and preferably also for its flow rate. Hence, in the present invention, the analytical device preferably comprises a gas chromatograph, mass spectrometer or online gas sensor and / or a device for measuring flow rate. Feeding gaseous effluent directly to such analytical device would require each electrolysis cell to have its own analytical device. This leads to complexity and increased expenses. Therefore, the present system and process are especially attractive with four or more, more specifically eight or more electrolysis cells operated in parallel.

[0033] It is preferred that there is a single analytical device for analyzing the gaseous effluent of multiple, preferably all, parallel electrolysis cells in the system. To enable such, the various lines through which gaseous effluent is withdrawn from the vertically extending inlets are connected with a means to select gaseous effluent of an electrolysis cell to be analyzed. The various lines are can be in fluid communication with a multiport selector valve. In such embodiment, multiple vertically extending inlets (6) are in fluid communication with a multiport selector valve which allows to supply gas from selected vertically extending inlets (6) to the analytical device (14) via line (11). Alternatively, each line which samples gaseous effluent from a vertically extending inlet can be connected with an analyzer via a shut-off valve. Both embodiments enable gaseous effluent of a specific electrolysis cell to be analyzed whilst the effluent of other cells can remain in the gas-liquid separator by closing the line. Preferably, gaseous effluent which is not analyzed is removed via a gas valve and fed to a vent. Generally, most gaseous effluent will be removed and fed to the vent as it is not needed to continuously analyze the gaseous effluent during the electrolysis.

[0034] It may also be preferred to dilute the effluent with an inert gas, preferably nitrogen, before introduction into the gas-liquid separator. A reason for such dilution is that it can be used as internal standard to calculate gas flow rate. When a known amount of dilution gas such as nitrogen or argon is added, it will be possible to determine the molar flow rate of oxygen and hydrogen. This can be calculated by measuring the concentration of inert gas and hydrogen and oxygen which is removed from the gas liquid separator and multiply this ratio by the molar gas flow rate of the added inert gas. In this way, the flow rate and thereby the total amount of hydrogen and oxygen produced can be determined without separating the complete gas stream. And an additional advantage of such dilution gas is to reduce any safety risk by diluting the oxygen and hydrogen. Additionally, it can help in avoiding any back mixing in the vertically extending inlet as the addition of inert gas will increase the gas velocity so any back mixing due to diffusion will be less likely to happen.

[0035] It is important to send to the gas-liquid separator either the effluent produced at the cathode side containing hydrogen of the multiple parallel electrolysis cells or of the anode side containing oxygen. If both effluents would be sent to a single vessel, hydrogen and oxygen would be mixed as the gaseous effluent which is not analyzed will collect in the upper part of the gas-liquid separator. This is undesired from a safety point of view as it would increase the risk of explosion. Therefore, it is strongly preferred to introduce into the gas-liquid separator either the effluent produced at the cathode of the multiple parallel electrolysis cells or the effluent to the anode. Typically, research of electrolysis of an aqueous feed to produce hydrogen is focused on the yield of hydrogen. Hydrogen is formed at the cathode side for the most common electrolysis cells PEM, AEL and AEM. Therefore, it is preferred to separate and analyze the gaseous effluent produced by conversion at the cathode of the electrolysis cells. Alternatively, the gaseous effluent produced at the anode of the multiple parallel electrolysis cells can be analyzed.

[0036] It can be desired to analyze the effluent of both the anode and cathode of the electrolysis cells. In such case, it is preferred to use a second gas-liquid separator. In this set-up, the two gas-liquid separators will be similar but will differ in that the one receives effluent only from the anode side of the multiple parallel electrolysis cells while the other receives effluent only from the cathode side of the multiple parallel electrolysis cells.

[0037] The present invention can be used with a various types of electrolysis cells. Most suitable are cells of the type PEM, AEM, AEL. Hence, it may be preferred that in the present invention, electrolysis cells are selected from the group consisting of: a proton exchange membrane cell (PEM), an anion exchange membrane cell (AEM), and an alkaline electrolysis cell (AEL).

[0038] The present invention further relates to a process for electrolyzing an aqueous feed to produce hydrogen and oxygen using a system according to the present invention, and as set out above. If the cells are for conducting research, the electrolyte flow rates per cell preferably are between 10 and 500 ml / minute. Hence, it is preferred that in such process the electrolyte flow rate per cell is between 10 and 500 ml / min, preferably between 50 and 300 ml / min. Cells typically have sizes such that the membrane or diaphragm have a surface area of between 1 and 25 cm2, more preferably between 1 and 12 cm2. Hence, it is preferred that in the present invention the electrolysis cells have a membrane or diaphragm having a surface area of between 1 and 25 cm2, preferably between 1 and 12 cm2. Preferably, in the present process the electrolysis cells are operated at a pressure of between 6 x

[0039] 105Pa and 101 x 105Pa, preferably between 11 x 105Pa and 51 x 105Pa. The electrolysis cells are preferably operated at a temperature of between 20 and 200°C, preferably between 50 and 150°C, more preferably between 50 and 90°C. Fig. 1 shows a schematic concept of a system according to the present invention.

[0040] In a system according to Fig. 1, effluent comprising gas and liquid is passed via lines (1) from individual electrolysis cells to vertically extending inlets (6), optionally admixed with an controlled and known amount of inert gas supplied via lines (2). The vertically extending inlets (6) are located at an upper part of the gas-liquid separator (13) and connected with lines (1) . The gas-liquid separator (13) is in this case a pressure vessel. Liquid will flow down the vertically extending inlets (6) to the bottom of the gasliquid separator (13) and become part of the liquid in the bottom section (4). The upper section (5) contains gas. The level of liquid in the pressurized vessel can be controlled by a measuring device or level controller (3), which controls or operates a drain valve (7), so as to maintain a constant liquid level even if more liquid enters. Similarly, the pressure of the gaseous phase in the headspace can be controlled by pressure controller (8) which operates or controls a valve (9) which allows to vent gas via line (10).

[0041] A fraction of the gas separated by the vertically extending inlet will be removed via valves (12), which can send a specified amount to vent (11) and which also may be connected permanently or temporarily to analytical device (14).

Claims

CLAIMS1. Process for separating and analyzing gaseous effluent produced in multiple parallel electrolysis cells, which process comprises:(1) supplying aqueous feed to the multiple parallel electrolysis cells and applying an electric potential thereby converting at least part of the feed into effluent comprising an aqueous liquid phase and a gaseous phase,(2) introducing the effluent of each of the multiple electrolysis cells separately via a dedicated vertically extending inlet into a gas-liquid separator which inlet is located in the upper part of the gas-liquid separator and separates the effluent which is introduced into a gaseous effluent and liquid effluent, and(3) combining at least part of the gaseous effluents obtained from the vertically extending inlets and combining at least part of the liquid effluents obtained from the vertically extending inlets and removing the combined gaseous effluents and the combined liquid effluents separately from the gas-liquid separator, wherein each vertically extending inlet keeps the effluent which is introduced separate from the fluid present in the gas-liquid separator and wherein part of the gaseous effluent is withdrawn from the top of the vertically extending inlet and analyzed.

2. Process according to claim 1, wherein the vertically extending inlet is a tubular inlet which is closed at the top and open at the bottom.

3. Process according to claim 1, wherein the effluent is produced by conversion of the feed at the cathode of the electrolysis cells.

4. Process according to any of claims 1 to 3, wherein the flow rate of gaseous effluent withdrawn from the top of the vertically extending inlet to be analyzed is less than 50%, preferably less than 20%, more preferably less than 10%, of the flow rate of the effluent entering the vertically extending inlet.

5. Process according to any of claims 1 to 4, wherein the effluent is diluted with inert gas, preferably nitrogen, before being introduced into the gas-liquid separator (13).

6. Process according to any one of claims 1 to 5, wherein the electrolyte flow rate per electrolysis cell is between 10 and 500 ml / min, preferably between 50 and 300 ml / min,7. Process according to any one of claims 1 to 6, wherein the membrane or diaphragm of each of the electrolysis cells has a surface area of between 1 and 25 cm2, preferably between 1 and 12 cm2.

98. System for separating effluent obtained from multiple parallel electrolysis cells into a liquid and a gaseous phase and analyzing the gaseous phase effluent, which system comprises a. multiple electrolysis cells which are each separately in fluid communication with a gasliquid separator (13) via a line (1), b. vertically extending inlets (6) located at an upper part of the gas-liquid separator (13) which vertically extending inlets are in fluid communication with line (1) and with the gas-liquid separator (13) which vertically extending inlets (6) are closed at the top and open at the bottom and which vertically extending inlets (6) are suitable for (i) separating fluid which is introduced from fluid present in the gas-liquid separator, and (ii) separating liquid effluent from gaseous effluent, and c. an opening at the bottom part of the gas-liquid separator for removing liquid phase effluent and an opening at the top part of the gas-liquid separator for removing gaseous phase effluent, wherein the upper part of one or more vertically extending inlets (6) are in fluid communication with an analytical device (14).

9. The system according to claim 8, wherein the gas-liquid separator (13) comprises:(i) a bottom section (4) suitable for holding liquid and an upper section (5) suitable for holding gas which upper section (5) and bottom section (4) are in fluid communication,(ii) a level controller (3) connected to a bottom valve (7) for maintaining a pre-selected level of the liquid in the bottom section (4) which bottom valve (7) is connected to a drain, and(iii) a pressure controller (8) connected to a top valve (9) in the upper part of the gas-liquid separator which top valve (9) is connected to a vent (10).

10. The system according claim 8 or 9, wherein the vertically extending inlet is a tubular inlet which is closed at the top and open at the bottom.

11. The system according to any of claims 8 to 10, wherein multiple vertically extending inlets (6) are in fluid communication with a multiport selector valve which allows to supply gas from selected vertically extending inlets (6) to the analytical device (14) via line (11).

12. The system according to any one of claims 8 to 11, wherein the gas-liquid separator is a gravity gas-liquid separator.

13. The system according to any of claims 8 to 12, wherein the electrolysis cells are selected from the group consisting of proton exchange membrane cells, anion exchange membrane cells and alkaline electrolysis cells.

14. The system according to any of claims 8 to 13, wherein the system comprises multiple parallel electrolysis cells, preferably at least four, more preferably at least eight electrolysis cells.

15. Process according to any of claims 1 to 7 using a system according to any one of claims 8 to 14.11

Images