Purification method for an electrochemical reaction

Abstract

The invention relates to a method of removal of impurities, formed by an electrochemical reaction, the electrochemical reaction being an alkaline electrolysis, from an electrolyte comprised by a first container. The first container comprises one or more catalysts. The method comprises powering the catalyst, thereby starting the electrochemical reaction forming the sulphate carbonate impurities. Additionally, a liquid connection between the first and second container is established, wherein the second container comprise a barium source. Hereby, establishing a flow of said electrolyte from the first container to the barium source. Thereby, forming a barium suspension comprising a mixture of sulphate and carbonate salts. Lastly, the barium suspension is separated from the electrolyte, forming a purified electrolyte.

Description

PURIFICATION METHOD FOR AN ELECTROCHEMICAL REACTIONField of the invention

[0001] The present invention relates to a method of purifying an electrolyte used in container for an electrochemical reaction and a system to implement such method for purification.Background of the invention

[0002] Known electrochemical reactions typically discard electrolyte used in electrochemical reactions such as electrolysis. This makes the electrolyte for the electrochemical reaction greatly expensive. Additionally, it has a negative impact on the environment.Objective of the invention

[0003] The inventors have identified the above-mentioned problems and challenges related to cost and environmental impact of electrolyte used in an electrochemical reaction and solved this by purification of an electrolyte suitable for an electrochemical reaction, and subsequently made the below-described invention which may provide a suitable purification method for an electrochemical reaction, and which may increase or provide recyclability and thus, decrease cost of hydrogen production.Summary of the invention

[0004] The invention relates to a method of removal of impurities, formed by an electrochemical reaction, the electrochemical reaction being an alkaline electrolysis, from an electrolyte comprised by a first container, wherein said first container furthermore comprises one or more catalysts, wherein said method comprises the steps of: at least partly covering said catalyst with said electrolyte in said first container, powering said catalyst, thereby starting said electrochemical reaction forming said impurities in said electrolyte, wherein said impurities comprise sulphate ions and carbonate ions, establishing a liquid connection from said first container to a second container, wherein said second container comprise a barium source, establish a flowof said electrolyte from said first container to said barium source in said second container, thereby forming a barium suspension comprising a mixture of sulphate and carbonate salts in said second container, and separating said barium suspension from said electrolyte, thereby forming a purified electrolyte, wherein said method is carried out during an activation period of said alkaline electrolysis.

[0005] Removal of impurities may be understood as part of removing unwanted particles from e.g., a solution such as removing sulphate and carbonate ions from an electrolyte. Thus, removal of impurities is advantageous in that it e.g., increase the conductivity of a given electrolyte, leading to a better outcome of an electrochemical reaction.

[0006] Further, since impurities may be soluble, they can be challenging to remove in an electrolyte such as an aqueous solution. Thus, by e.g., forming a suspension, comprising the impurities, according to the method of the present invention it is possible to remove the impurities from a electrolyte.

[0007] Further, since these impurities may damage the catalyst, it is advantageous to form such suspension in a second or different container and thereby prevent the suspension from damaging the catalyst, leading to prolonging the lifespan of a catalyst.

[0008] Accordingly, by the present invention, the removal of impurities is done in a second container different from the first container comprising the one or more catalysts. This is a very advantageous design feature in that thereby barium entering the first container is avoided and thereby precipitation of barium salts in the first container is avoided which would be very bad for the electrochemical reaction especially if the electrochemical reaction is electrolysis.

[0009] Further, having more than one catalyst, the scale of the electrochemical reaction can be increased. In this way, in case the electrochemical reaction is electrolysis, such electrolyser may have hundreds of cells connected in one stack. Further, more than one stack may be fluidly connected sharing the same electrolyte (which may be referred to as lye in case of an electrolyser) thereby the number of cells may be counted in hundreds or thousands. Hence, the first container, or the pluralityof compartments cells of the first container, may each have two catalysts, and thus together, sum up to the doublet of the number of cells.

[0010] Removal of impurities from an electrolyte may also be referred to as purifying the electrolyte. Such purification may as an example be carried out by separating solid impurities from the electrolyte e.g. by filtering. Purifying an electrolyte used for a chemical or electrochemical reaction is advantageous in that the electrolyte then could be reused for the same or other chemical reactions. Thus, decreasing the environmental impact by not discarding the contaminated electrolyte i.e. reduce chemical waste products. Further, some electrolytes such as an alkaline solution may be expensive to produce and thus by recycling such alkaline electrolyte costs (both CAPEX and OPEX) could be reduced in relation to establishing and operating an electrolyser.

[0011] A catalyst may be understood as an electrode such as an anode, a cathode (or both), or a coating, which may be used in an electrolysis process producing hydrogen and oxygen from water. Put in another way, a catalyst may be understood as an electrode which is made of or coated with a catalyst with the objective to increase the electrolysis efficiency.

[0012] A container, such as the first container, may be understood as the electrolysis cell in which the catalyst(s) is comprised. In case of larger electrolysers comprising a plurality of cells, these cells may be referred to as compartments of the first container. Hence, the first container may be the entire stack of the electrolyser comprising a plurality of compartments / cells. Alternatively, or in addition a container, such as the second container, may be understood as a vessel, different from the first container, comprising a barium source. Alternatively, or in addition a container may be understood as a vessel, different from the first and second containers, suitable for comprising an electrolyte such as lye for an electrolysis process.

[0013] In the case of an electrolyser, the stack of cells (which may be referred to as the first compartment) may be connected to a buffer tank where the electrolyte may be conditioned i.e. where the electrolyte may be cooled, pH value adjusted e.g. by addingwater, etc. Hence, such buffer tank may be used to what is sometimes referred to as balancing of plant or balancing of stack.

[0014] As used herein the term “impurity” refers to a compound that may not be of interest in a chemical reaction. Thus, an impurity could e.g., be a byproduct. As an example, ions from the electro chemical reaction could e.g., be an impurity.

[0015] As used herein the term “suspension” refers to a solid that may form a heterogeneous mixture with an electrolyte. Thus, a suspension may be formed by particles that are not dissolvable in a given mixture. Hence, a suspension could be formed in a solution by forming an insoluble salt. This could i.e., be an insoluble barium salt that could form a suspension.

[0016] As used herein the term “salt” refers to a chemical compound comprising an ionic assembly of a positively charged cation and a negatively charged anion. Thus, a salt may e.g., be organic, inorganic or a combination thereof.

[0017] As used herein the term “ions” refers to a salt in a diluted state. Thus, an ion comprises an either positively or negatively charge. Additionally, an ion may be monoatomic or polyatomic.

[0018] As used herein the term “purity” refers to a measurement of how pure a single compound or substance is. Thus, if the concentration is lower than 100 parts per million of each of the ions, the electrolyte is considered pure enough for recycling.

[0019] Electrochemical reaction may be understood as any process that involves the passage of an electric current through a solution. Thus, one example of an electrochemical reaction may be electrolysis. One example of electrolysis is the process of producing Hydrogen and Oxygen from an aqueous solution.

[0020] An electrolyte should be understood as a substance having liquid properties such as being in an electrolyte state. Additionally, an electrolyte may e.g., be used for conducting a current. The electrolyte may also sometimes be referred to as lye.

[0021] As used herein the term “solid” refers to a condition at which a compound is non-soluble. Note that non-soluble, insoluble and not dissolvable may be used interchangeably.

[0022] Barium source may be understood as a compound that comprises barium. Thus, a barium source may comprise, but are not limited to a barium salt.

[0023] A compartment may be understood as a cell and / or part of a cell of an electrolyser and the electrolyte may flow through each of the compartments and thereby each of the cells of the electrolyser.

[0024] .

[0025] Removing impurities during activation is advantageous in that it has the effect, that impurities is removed shortly after they are formed. Hence, during this part of the lifespan of e.g. an electrolyser the formation of impurities is highest. In fact, up to 90% of impurities from a catalyst contacting the liquid is formed during the activation period.

[0026] According to an advantageous embodiment of the invention said activation period last for a time period of at least 5 days, such as 1 week, such as 2 weeks, such as 1 month, such as 1.5 months, such as 2 months, such as 2.5 months, such as 3 months, such as 3.5 months, such as 4 months.

[0027] It should be mentioned that the duration of the activation period may be up to 4 months. It should further be mentioned that the time needed may be dependent on the time for oxidation of a sulphide to sulphate. Thus, the time needed may be shorter than 4 months, such as 2 months, such as 1 month, such as 2 weeks, such as 1 week, but that may require a tradeoff with an extra step of using an oxidizing agent such hydrogen peroxide.

[0028] It should be mentioned that the purity of the electrolyte may be determined by different methods. I.e., a sulphate concentration may be determined with ion chromatography and carbonate concentration may be determined with titration.

[0029] According to an advantageous embodiment of the invention said first container is divided in a plurality of compartments which are fluidly connected.

[0030] An advantage of the above embodiment is that the purification method of the present invention is independent of the scale of the electrochemical process thus, it can be used for purifying liquid of any size of electrochemical reaction. More specific the purification method can be used in an electrolysis process, no matter the number of cells of an electrolyser stack.

[0031] The fluid connection may allow for a directional flow of liquid through the compartments. Thus, a flow of liquid can be established after an electrochemical reaction has ended, or even during an electrochemical reaction. For both instances it allows a displacement of an electrolyte that comprises a mixture of impurities.

[0032] According to an advantageous embodiment of the invention said first container is a stack of an electrolyser.

[0033] According to an advantageous embodiment of the invention said first container comprise a tap via which said liquid connection to said second container is established.

[0034] This is advantageous in that the second container can be releasably mounted e.g. by one or more hoses, and thereby the purification system can be removably connected to the first container and thereby moved from one system to another system.

[0035] A tap, outlet or an inlet ensures that the established directional flow can controlled from one container to a different container. Thus, it can control an established flow e.g. via one or more valves mounted to the tap or hose.

[0036] As mentioned, the electrochemical reaction is preferably an electrolysis but the invention may also be applied to a redox reaction.

[0037] In case the electrochemical reaction is an electrolysis such as an alkaline electrolysis, the invention is advantageous in that it is possible to remove sulphatesand carbonates from such strong alkaline conditions while at the same time, regenerate consumed hydroxide. Thus, maintaining the alkaline environment.

[0038] According to an advantageous embodiment of the invention said electrolyte comprise a volume of at least 0.1 cubic meter such as 1 cubic to 100 cubic meters such as 25 to 75 cubic meters, such as 35 to 65 cubic meters.

[0039] This is advantageous in that it allows industrial scale production. Thus, it allows purification of a more efficient production such as hydrogen production. Further, this is advantageous in that all liquid in an electrolyser can be purified.

[0040] According to an advantageous embodiment of the invention a temperature of said electrolyte is altered in said second container.

[0041] This is advantageous in that it allows to alter the solubility of the suspension. Thus, by i.e., decreasing the temperature, the solubility may be reduced, leading to a larger formation of suspension and thereby, increase removal of impurities.

[0042] In some instances, the solubility of a salt can be temperature dependent. Thus, altering the temperature may enhance the formation of a suspension, and increase purity.

[0043] As the electrochemical reaction preferably is an alkaline electrolysis, the electrolyte from which the impurities are removed, preferably is an alkaline solution.

[0044] In some instances, a specific type of electrochemical reaction can depend on the environment. Thus, an electrochemical reaction may i.e., depend on an alkaline environment an example of such electrochemical reaction may be electrolysis.

[0045] According to an advantageous embodiment of the invention said electrolyte is a lye solution comprising sodium hydroxide, potassium hydroxide or a combination thereof.

[0046] A reference to an electrolyte is a refence to a liquid for use in a electrochemical reaction and a reference to a lye or lye solution is a reference to an alkalic liquid such as a liquid comprising potassium hydroxide or sodium hydroxide.

[0047] According to an advantageous embodiment of the invention pH of said electrolyte is adjusted by altering a lye concentration from a 10%-20% solution to a 20%-30% solution such as from a 12%- 17% solution to a 22%-27% solutions such as from a 15% solution to a 25% solution.

[0048] Advantageous in that it allows to alter the solubility of the suspension. Thus, by i.e., increasing pH, the solubility may be reduced, leading to a larger formation of suspension and thereby, increase removal of impurities.

[0049] According to an advantageous embodiment of the invention pH of said electrolyte is adjusted in said second container.

[0050] In some instances, the solubility of a salt can be pH dependent. Thus, altering the pH in the second container where the purification process occur may enhance the formation of a suspension, and increase purity of the liquid. The pH may be adjusted by adding demineralized water or, in case the electrolyte is an alkaline electrolyte, by adding potassium hydroxide.

[0051] According to an advantageous embodiment of the invention a temperature of said second container is altered.

[0052] This is advantageous in that it allows to alter the solubility of the suspension in a different container than the one that can be used for an electrochemical reaction. Formation of suspension may interfere with the electrochemical reaction, thus formation of suspension in a second or different container can be used to avoid damage on i.e., a catalyst. The temperature may be altered by circulating the electrolyte in a heat exchanger of a cooling system.

[0053] According to an advantageous embodiment of the invention at least one catalyst is active or inactive.

[0054] According to an advantageous embodiment of the invention said catalysts comprise a metal and nonmetal.

[0055] This is advantageous in that nonprecious metals catalysts usually comprises a mixture of elements such as nickel and sulphur. Further, the leaching of the non- metallic element may be detrimental to the electrolysis process. As an example, a purification method may allow removal of sulphur as potassium sulphate and therefore allows for the usage of nonprecious metal catalysts.

[0056] According to an advantageous embodiment of the invention said catalyst comprises a metal sulphide.

[0057] This is advantageous in that any metal, that can form sulphides and / or sulphates can be utilized in the catalyst for the invention. Note that the catalyst may also comprise selenates (SeO4).

[0058] According to an advantageous embodiment of the invention said metal in said metal sulphide is selected from the list comprising iron, copper, nickel, cobalt, silver, zinc or any combinations thereof.

[0059] This is advantageous in that alkaline electrolysis may have carbonate content in the alkaline solution or lye. The carbonate content may arise from contents in the air surrounding the container. Thus, the carbonate content is independent of the catalyst. Further, the carbonate content may increase over time and the method of the present invention can also be used for removal of carbonates by using a barium source.

[0060] According to an advantageous embodiment of the invention said electrochemical reaction is powered by a power supply comprising an AC / DC or DC / DC converter.

[0061] Power supply such as a power converter may connect a power source such as a utility grid, wind turbine, photovoltaic unit, etc. to the catalysts and thereby powering the electrochemical reaction. Accordingly, both AC and DC power sources may supply the electrochemical reaction.

[0062] A DCDC or ACDC converter is advantageous in that a suitable DC voltage can be provided on the second side of the converter (DC / electrolyser side) independent on the voltage of the first side (power supply side). A suitable DC voltage should be understood as the DC voltage that is required for the electrochemical reaction to start, stop and ensure stable production of e.g. hydrogen in case the electrochemical reaction is electrolysis.

[0063] As a non-limiting example, a suitable DC voltage is in the range of 500- 1500V such as 1000V. With this said the required voltage may be determined on the number cells in a stack and thus if more than one stacks are connected e.g. in series

[0064] According to an advantageous embodiment of the invention said power supply is able to deliver a current of at least 40kAto said one or more catalysts.

[0065] This is advantageous in that an electrolyser supplied with power from such power supply, can operate at varying current levels and thereby varying operation modes. As an example an electrolyser may be operated at a current between IkA and 5kA, but as mentioned, the current consumption may be up to 40ka or even higher.

[0066] According to an advantageous embodiment of the invention said flow in said first liquid connection of said electrolyte is established by a pump or gravity.

[0067] The flow from first to second container may be provided by a first pump. A second pump may facilitate flow through the first container such as through the compartments of the first container such as through the stack of an electrolyser. A pump is advantageous in that flow speed can be regulated. Such regulation of flow speed may be made by a controller based on information of e.g. temperature and pH of the liquid in the second container and thereby ensure the liquid is sufficient time in the second container to establish the barium suspension.

[0068] If e.g. an electrolyser design allows, then gravity is advantageous to use instead of a pump, however using gravity to establish flow puts constrains to footprint and design of such electrolyser.

[0069] According to an advantageous embodiment of the invention said method comprise adding said barium source to said second container prior to establishing said first liquid connection.

[0070] This is advantageous in that the barium source is positioned in the second container when there is not electrolyte therein. Accordingly, there is no need to establish a later access to the second container and the electrolyte thereof which reduces the risk of hazardous situations occurring.

[0071] The barium source may alternatively be added to said second container after establishing said flow in said first liquid connection.

[0072] This is advantageous in that additional barium can be added if needed during the purification process. It is possible to add additional barium to the second container in case all of the barium of the original barium source is consumed.

[0073] According to an advantageous embodiment of the invention said barium source is a barium salt.

[0074] According to an advantageous embodiment of the invention said barium source is barium hydroxide.

[0075] Utilizing a salt or by putting salt in a solution comprising ions, may result in an ion exchange. Thus, a different salt may arise as a result of the ion exchange.

[0076] An advantage of the above embodiment is that the barium source further provides hydroxide ions. Thus, the barium source comprising hydroxide can be used to replenish hydroxide ions consumed in an electrochemical reaction.

[0077] Further, the addition of hydroxide ions alters the pH of a solution or electrolyte in the second container. This could further be an advantage since pH may alter the solubility of salt. Thus, by adding a hydroxide source (alone or together with a barium salt) in the second container, could lead to an increase of suspension formation and increase the purity of an electrolyte comprising salts, which solubility is affected by pH.

[0078] According to an advantageous embodiment of the invention said purified electrolyte is circulated from said second container back to said first container.

[0079] An advantage of the above embodiment may be that no new electrolyte is needed (beside what was used to produce gas such as hydrogen and oxygen), and thus no electrolyte waste is created. It should be noted that circulation could i.e., be via a separation unit.

[0080] According to an advantageous embodiment of the invention said second container comprise a tap for connecting said first liquid connection to said second container.

[0081] This is advantageous in that the second container can be releasably mounted to the liquid connection, and thereby the purification system can be removably connected to the first container and thereby the liquid can move from one container / system to another container / system.

[0082] It should be noted that a tap may also be referred to as an outlet and / or inlet to a container such as the first or second container and the flow of electrolyte and / or gas through the tap may be controlled by a valve.

[0083] According to an advantageous embodiment of the invention separation of a solid and electrolyte comprise conducting said electrolyte through a centrifuge or a filter.

[0084] Different separation methods may be applicable alone or in combination to an electrochemical reaction. Such separation methods could be, but are not limited to a centrifuge, or a filter. Such separation methods could be used to retain solid particles, such as salts, and prevent solid particles to be carried by an electrolyte from the second container / separation unit and to the first container. Thus, separation is advantageous in that it enables a separation of solid (such as the barium suspension) from electrolyte (such as the electrolyte of the first container) either in the container comprising the barium source or in a separate container.

[0085] According to an advantageous embodiment of the invention said separation is established in a separation unit.

[0086] The separation unit may be portable. A portable separation unit is advantageous in that it can be used to purify electrolyte of different systems i.e., moved from one system to another such as from one electrolyser to another electrolyser. Thereby, increasing utilization of the separation unit. Portable should here be understood as being possible to lift by a forklift onto a vehicle such as a truck trailer and move it on the truck trailer from the location of one electrolysis to the location of another. Thus, a portable separation using may simply be located on the ground while in use without any fixation to the ground. Alternatively, the separation unit may stay located on the truck trailer while in use.

[0087] After operating the electrochemical reaction such as an electrolysis, a period of time such as i.e. 2-4 years such as 3 years, the system required to perform the purification method (i.e. the second container and separation unit (if the latter is needed)) can be connected to e.g. the electrolyser again and thereby purify the electrolyte hereof for any impurities that has been generated over time.

[0088] The system or separation unit may be stationary, which is advantageous in that, when needed, the purification system or method of the present invention can be used or started.

[0089] According to an advantageous embodiment of the invention said separation is continuous during said time period.

[0090] In some instances, the impurities of the electrochemical reaction may be removed continuously. As an example, it could be used to avoid a decrease of conductivity and avoid a build-up of impurities in the container for an electrochemical reaction i.e. in the first container.

[0091] This is advantageous in that the separation occur as long as the purification method is happening. Thus, the impurities of the electrochemical reaction may beremoved continuously as they are or shortly after they are formed thereby decreasing the amount of impurities in the first container.

[0092] According to an advantageous embodiment of the invention an oxidizing agent such as hydrogen peroxide is used in said second container.

[0093] Chemical compounds can be used to speed up certain reactions. As an example, hydrogen peroxide can be used to speed up oxidization. As a further example, sulphide species may be oxidized to sulphates. Thus, by transferring one chemical specie to a different species, it may be possible to alter different properties such as solubility.

[0094] In an aspect, the invention relates to a purification system configured to remove impurities from an electrolyte used in an electrochemical reaction, the electrochemical reaction being an alkaline electrolysis, wherein said system comprise: a power supply, a first container configured to comprise said electrolyte and one or more catalysts, a liquid connection from said first container to a second container, a second container comprising a barium source wherein said barium source, and said impurities of said electrolyte, is forming a barium suspension in said electrolyte when comprised by said second container, and a separation unit configured to remove said barium suspension from said electrolyte, wherein said method is carried out during an activation period of said alkaline electrolysis.

[0095] According to an advantageous embodiment of the invention said system is configured to: supply electric power to said one or more catalysts, establish a flow of said electrolyte in said first container passing through said one or more catalysts thereby contaminating said electrolyte with at least sulphate ions and carbonate ions, establish a flow of said contaminated electrolyte from said first container to said second container via said liquid connection, wherein said contaminated electrolyte is passing by said barium source comprised by said second container, thereby forming said barium suspensions in said second container, establish a flow of said electrolyte comprising said barium suspensions through said separation unit, thereby separatingsaid barium suspension from said electrolyte, and thereby forming a purified electrolyte.

[0096] Such system comprising a separation unit is advantageous in that insoluble barium salts are not added back into the electrolyser. Hence, external from the first container, the purification comprises precipitation and subsequent solid-liquid separation.

[0097] Such purification system is advantageous in that it has the effect, that the electrolyte, also sometimes referred to as lye, used during activation, which may be part of a commissioning procedure, can be recycled. By recycling a massive cost reduction is obtained as well as environmental benefits are obtained, in that the volume of contaminated electrolyte that need to be disposed, is significantly reduced, if not eliminated. It should also be noted that though the lye circulates in a closed loop, air may cause carbonate formation. However, it has turned out, that the carbonate may be removed by the disclosed purification system and method. Put in another way, it has been found that a secondary effect of the present invention is decarbonisation of the lye. This is one argument, for a continuous purification of the lye according to the present invention or at least to repeat the purification in intervals. Such intervals may be between 1 and 4 years.

[0098] Commissioning should be understood as the time during which the manufacture of the electrolyser still owns the electrolysis system even though it is installed on site i.e. prior to final test / acceptance of the costumer. The activation period, the duration of which may as an example be 2 months of running / testing the electrolyser is often considered as part of the commissioning process. Accordingly, the purification of the electrolyte would typically be referred to as being part of the commissioning process. The activation may take place externally to the electrolysis system in a container different from the electrolysis stack.

[0099] A separation unit may be understood as a unit that facilitate separation of particles having a different physical state. Thus, a separation unit according to thepresent invention may be used for separation an electrolyte from a solid or from a suspension such as the barium suspension.

[0100] According to an advantageous embodiment of the invention said system has a second liquid connection from second container or a separation unit back to first container.

[0101] An advantage of the above embodiment may be that recirculation is possible.

[0102] According to an advantageous embodiment of the invention said system comprise a pump to establish said flow of electrolyte.

[0103] An advantage of the above embodiment may be that the flow to and from the first container is directionally controlled. Further, speed of flow may be controlled be such pump.

[0104] According to an advantageous embodiment of the invention said first and second liquid connections, second container, pump and / or separation unit are portable.

[0105] A portably purification system is advantageous in that it has the effect, the after the activation period of a first electrolyser, the system can be moved and used at a second electrolyser.

[0106] According to an advantageous embodiment of the invention said first and second liquid connections, second container, pump and / or separation unit are located on a vehicle.

[0107] This is advantageous in that it thereby is easy to move the system from one site to a different site. A vehicle may be a truck, trailer or truck trailer sufficiently small to move into a room where the first container is located. Alternatively, the vehicle is transporting the individual parts which then is moved from the trailer to the electrolyser where it is mounted / connected.

[0108] Alternatively, the first and second liquid connections are implemented as hoses, which are sufficiently long to connect the first container to a second containerlocated on a vehicle outside the room of the first container. Similarly, the second liquid connection is sufficiently long to connect a second container or separation unit (if needed), located on a truck outside the room of the first container, to the first container. Obviously, one or more pumps may be needed to facilitate the circulation of liquid through the long liquid hoses / connections. Connections which in this case may be more than 10 meters e.g. up to 50 meters

[0109] Preferably the power supply is located on site i.e., stationary with a permanent installation to the catalysts.

[0110] According to an advantageous embodiment of the invention a portion of said electrolyte is configured to bypass said purification system.

[0111] According to an advantageous embodiment of the invention said portion of said electrolyte is mixed with said purified electrolyte in the liquid connection between said second container and said first container.

[0112] In some instances, it might be necessary to establish a bypass liquid connection, that can direct electrolyte to a different container than the purification system. This could i.e., be that in a continuous setup, at which a portion of the electrolyte is transported to a second container, while a different portion of the electrolyte is bypassing the second container. Thus, some impurities may be initially removed by separation unit such as a filter.

[0113] Advantageous in that some insoluble salts may be formed and cause precipitation prior to purification system. Thus, using i.e., a filter for retention can capture of any insoluble precipitates or salts, before the electrolyte is transported to a container different from first container. An example, if there is barium dissolved in the electrolyte it would precipitate as sulphate upon entering back into the electrolyser. By pre-mixing the treated with untreated electrolyte, any further precipitate can be removed before the return of the electrolyte to the electrolyser.

[0114] According to an advantageous embodiment of the invention said purified electrolyte is substantially free from impurities.

[0115] An electrolyte is considered purified when the suspension is substantially removed. Thus, the electrolyte is considered purified when it can be reused or recirculated. One definition of pure electrolyte may be when the electrolyte is free of particles but also free of soluble sulphates and / or carbonates.

[0116] According to an advantageous embodiment of the invention said purified electrolyte comprises a sulphate and / or carbonate concentration of less than 100 parts per million preferably less than 50 parts per million, most preferably less than 10 parts per million.

[0117] According to an advantageous embodiment of the invention said concentration is measured with ion chromatography and / or titration.

[0118] According to an advantageous embodiment of the invention said purified electrolyte is collected and transported.

[0119] An advantage of the above embodiment may be that the electrolyte can be reused on a different site or in a different container, without substantially compromising the purity. Accordingly, if the purified electrolyte is not to be recirculated to the first container it may be conducted to an additional container which may be located on a truck or pallet. In this way the purified electrolyte can be transported to a different site and used. It may be so that such batch of purified electrolyte may be used in several electrolysers during activation. After activation, the operator of the electrolyser would like or require new electrolyte, hence the purified electrolyte can then be reused in another site instead of ending as waste.

[0120] According to an advantageous embodiment of the invention said purified electrolyte is recycled to one or more additional containers.

[0121] This is advantageous in that the purification system can be adjusted in size. Thus, e.g., a production of hydrogen can be tailored to produce a certain amount of hydrogen from an electrochemical reaction. For example, an additional container can act as reservoir or buffer tank if the production needs to be downscaled, if theelectrolyte level in the first container needs to be adjusted if the catalyst needs to be changed, etc.

[0122] It should be mentioned that the purified electrolyte may be recycled to a different or additional container or multiple different or additional containers before said purified electrolyte is recycled back to said first container.

[0123] According to an advantageous embodiment of the invention said second container comprise said separation unit.

[0124] This is advantageous in that it may ease the access for removing a suspension. Thus, an operator may have improved access to a formed suspension or a filter which comprises the suspension.

[0125] According to an advantageous embodiment of the invention said barium suspension is collected by said separation unit and discarded from said separation unit.

[0126] This is advantageous in that a suspension is not carried back to the first container where it may damage the catalyst. Thus, removing the suspension from the electrolyte may prevent damaging the catalyst and prolonging the lifespan of a catalyst.

[0127] According to an advantageous embodiment of the invention said separation unit comprise a centrifuge, or a filter.

[0128] This is advantageous in that such suspension unit may aid in collecting a suspension and prevent the suspension from being carried back to the first container. Further, such suspension unit may prevent damaging the catalyst, prolonging the lifespan of a catalyst in that it is ensured that a very reduced amount of suspension preferably no suspension are returned to the first container. Additionally, the filtered electrolyte is considered purified electrolyte and may enhance the conductivity of electrolyte in the first container, leading to a more efficient process such as an electrolysis process.THE DRAWINGS

[0129] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. The drawings illustrate embodiment of the invention and elements of different drawings can be combined within the scope of the invention: fig. 1 illustrates an electrolyser, fig. 2 illustrates an electrolysis cell, fig. 3 illustrates a purification system and illustrates the movement of electrolyte for purification from a first container to a second container, fig. 4 illustrates a schematic presentation of electrolyte movement, wherein the electrolyte moves through a separation unit, fig. 5 illustrates a schematic presentation of electrolyte movement, wherein the electrolyte movement is generated by a pump, fig. 6 illustrates a schematic presentation of a bypass system wherein a part of the electrolyte is not transported to the second container, fig. 7 illustrates a schematic presentation of a bypass system wherein a part of the electrolyte is transported from the second container to the first container, fig. 8 illustrates a schematic presentation of electrolyte movement, wherein the electrolyte is transported by a vehicle, fig. 9 illustrates a schematic presentation of electrolyte movement from multiple first containers, wherein the electrolyte movement is generated by a pump and transported between containers by a vehicle, and fig. 10 which illustrates the movement of electrolyte from one site to another site, facilitated by a vehicle.DETAILED DESCRIPTION

[0130] The present invention is described in view of exemplary embodiments only intended to illustrate the principles and implementation of the present invention. The skilled person will be able to provide several embodiments within the scope of the claims.

[0131] Fig. 1 illustrates an apparatus in the form of an electrolyser ELY suitable for carrying out an electrochemical reaction according to the present invention. The electrolyser ELY shown in fig. 1 may be a part of a facility or a production plant for the production of hydrogen.

[0132] The electrolyser ELY of fig. 1, in which an electrochemical reaction according to the present invention may take place, may be built from a plurality of electrolyser cells ELYC together referred to as a stack STA. Thus, the first container ICON illustrated in fig. 1 comprises one stack STA i.e. multiple cells ELYC. It should be noted, that the ICON may also include parts of not disclosed manifold systems. Also illustrated in fig. 1 is two vessels VE used for storing the gas products formed during electrolysis process. In fig. 1 a first fluid outlets FO1 is shown, for transporting the produced hydrogen to the vessel VEHY and a second fluid outlet FO2 is shown for transporting the produced oxygen to the vessel VEOX. Further a fluid outlet FO is illustrated as an outlet for the electrolyte. Fluid inlets FI are illustrated as inlets for electrolyte to the anode and cathode compartments. The fluid inlet FI and fluid outlet FO may be connected to external vessels, heat exchangers, etc. e.g. for controlling of pH and temperature of the electrolyte.

[0133] A plurality of electrolytical cells may as mentioned form a stack STA i.e. anode, cell frame with bipolar plate, cathode, diaphragm, anode, cell frame with bipolar plate, cathode diaphragm, and so on. Hence, an opening in the frame CF may in an embodiment comprise a bipolar plate BP. The bipolar plate BP may be a metal or plastic plate with electrically conductive elements that is forming a gas and liquid tight barrier separating flow of gas and electrolyte on the two sides of the cell frame / bipolar plate. Therefore, one side of the bipolar plate BP could be said to form one end wall of one compartment. The other end wall of such compartment would then be the diaphragm DIA. As mentioned, the electrolytical cell will comprise two such compartments referred to as anode compartment and cathode compartment respectively, referring to the location of an anode and a cathode located in these compartments. Hence, the electrolytical cell comprises two cell frames 1CF, 2CF each with a bipolar plate.

[0134] As mentioned, the diaphragm DIA is porous, more specific it is porous to ions and water. Hence, the diaphragm DIA ensures that no hydrogen or oxygen can pass through. Accordingly, the diaphragm DIA is impermeable to gases but must be selectively permeable to ions and water.

[0135] It should be mentioned that diaphragm is porous due to the material of which it is made, the material is designed to be resistant to a specific environment such as an alkaline environment. Hence, a porous diaphragm can be made, e.g., of a fabric material resistant to a specific environment such an alkaline environment. Another type of diaphragm are composite materials consisting of a polymer mesh impregnated with inorganic fillers (i.e. zirconium oxide). Accordingly, various types of porous diaphragms may be used in the present invention.

[0136] The anodes and cathodes from the plurality of electrolyser cells ELYC are powered from a power source (not illustrated). This power source may ultimately be a wind turbine, solar system or other power plants which is electrically connected to the anodes and cathodes directly or via the utility grid. Once the anodes and cathodes are powered with a certain DC voltage, the electrochemical reaction happens in the compartments of the first container. The connection of power to the stack STA may be established by non-illustrated electric terminals at the end plates. Hence a negative pole of a DC supply may be connected to the illustrated endplate and a positive pole of the DC supply may be connected to terminals of the opposite endplate.

[0137] Fig. 2 illustrates the principles of an electrolytic cell ELYC. Such cell comprising two electrodes such as an anode ANO and a cathode CAT. As mentioned,the two electrodes are separated by a diaphragm DIA, which is inserted to delimit both a cathodic compartment, containing the cathode, and an anodic compartment containing the anode. The diaphragm DIA may be held in place between the two cell frames 1CF, 2CF which may be rubber coated metal frames RF. Additionally, the diaphragm DIA separates the anode compartment ANOC from the cathode compartment CATC. One way of securing the diaphragm is to place it in or on the structural part of one cell frame which may subsequently be rubber coated. Hence, during the fabrication of the cell frame, the diaphragm is positioned on the structural part which is subsequently rubber coated by injection of the rubber, which is thereby formed around the diaphragm, securing it in place.

[0138] The rubber coating is used to electrically insulate the outside of the cell frame from the inside of the cell frame and to insulate neighboring bipolar plates so there is not direct electric contact between two cell frames. The rubber coated cell frames and further comprises two fluid inlets FI supplying the anode and cathode compartments with respectively with electrolyte. Each of the anode and cathode compartments comprises two fluid outlets FO1, FO2. The two outlets allow the produced gas together with electrolyte to be extracted from each compartment, where the gas is collected in a vessel VE and the electrolyte may be circulated e.g. via external units for analysis, pH adjustment, temperature adjustment, etc. The anode ANO and cathode CAT are electrically connected by an adjacent bipolar plate BP. The bipolar plate may also act as structural reinforcement of the electrodes. The assembly further comprise a catalyst CLY. In the shown electrolytic cell, the catalyst CLY is applied as a surface coating on the electrodes indicated by the thicker line denoted CLY. The catalyst CLY may cover all or part of the electrodes.

[0139] Accordingly, the electrochemical reaction performed at the catalyst CLY, can in an embodiment of the invention produce hydrogen from the electrolysis of water.

[0140] It should be noted that the frames do not solely comprise rubber, but that the frames comprise a rubber coating.

[0141] It should be mentioned that the cathode CAT and anode ANO, are either made of or coated with catalysts CLY. Thus, the cathode CAT and anode ANO may comprise or consist of a catalyst CLY. It should further be mentioned that a catalyst CLY may comprise a metal such as nickel. Further, it should be mentioned that the catalyst layer may differ for cathodes and anodes. The catalyst layer may be the same material or two different materials, one for the cathode and one for the anode.

[0142] The inventive purification method described in this document has turned out to be advantageous when electrodes of an electrolysis system comprise a nickel containing an activation layer. Thus, it is by this invention possible / advantageous to use the present purification method on electrolysis system comprising nickel-sulfide containing activation layers on electrodes. Accordingly, the lifetime of surface treated electrodes is prolonged if the present purification method is applied.

[0143] It should be mentioned that non-preci ous metals catalysts CLY are typically used and are usually comprised of a mixture of elements, i.e., nickel and sulphur. The leaching of the non-metallic element may be detrimental to the electrolysis process.

[0144] The electrodes, such as an anode and cathode, may comprise a metal such as nickel and non-metal such as sulphur. In such an embodiment, the catalyst reaction under activation / commissioning of the electrolyser ELY would be as in eq. (1)Eq (1) NiS + 2e ^ Ni + S2’

[0145] Typically, the electrolytic cell ELYC is obtained by the combination of two electrode compartments separated by a porous diaphragm / membrane as described above. The diaphragm is inserted between the compartments to delimit both a cathodic compartment, containing the cathode, and an anodic compartment containing the anode towards each other. The other side of the compartments are defined by bipolar plates comprised by a cell frame. This design is illustrated in fig. 2.

[0146] In an alternative design, it is the diaphragm that is integrated in the cell frame as described above and the bipolar plate that is squeezed between the cell frames. Hence, at least two designs are available when designing bipolar electrolysers, in thefirst design the bipolar plate is enclosed in a cell frame and the diaphragm is squeezed the two cell frames. The second design is to enclosing the diaphragm in a cell frame and squeeze the bipolar plate between the two cell frames.

[0147] The cell frames CF1, CF2 are preferably electrically insulated from the bipolar plates e.g. by a rubber coating. The cell frames include two inlets and two outlets to allow electrolyte to be fed individually to the cathodic and anodic compartments as well as to allow the produced gas and electrolyte to be extracted from each compartment. One inlet and one outlet are in the design of fig. 2 on both sides of the bipolar plated. If the diaphragm was embedded in the frame part, one inlet and one outlet would be on each side of the embedded diaphragm. Thus, an electrolytic cell ELYC comprises two cell frames. Hence, the electrolyte is introduced into each of the compartments of the electrolyser cells ELYC / cell frames from the electrolyte inlet which is fluidly joint between cells throughout the stack forming what may be referred to as an inlet manifold (one for each of the anode and cathode compartments). In the same way, the produced hydrogen and oxygen escapes from the compartments via the fluid outlet which is also fluidly joint between cells through the stack forming what may be referred to as an outlet manifold (one for each of the anode and cathode compartments). The output manifold from cathode compartment transports hydrogen gas and electrolyte. The electrolyte and hydrogen gas are separated outside the stack and the hydrogen is stored in one of the vessels VE. The same applies to the outlet manifold from the anode compartment where oxygen is produced. As this is the general principle of an electrolyser according to the present invention and thereby known by a person skilled in the art, this is not illustrated nor described in further details.

[0148] Once built / assembled on site, before commercial hydrogen production, the electrolyser has to be commissioned or activated. Activation may be understood as the period of time where the electrolyser manufacture is still in charge of the electrolyser, but the electrolyser is located on the costumer site. During the activation period (which may also be referred to as commissioning), the electrolyser is adjusted for optimalproduction, and it is during this “start-up period” the electrolyte is especially exposed to being polluted.

[0149] It is advantageous to implement the present invention during the activation period, especially when the electrodes comprise Sulphur / are coated with an activation layer comprising Sulphur. This is because during this activation period, the release of Sulphur is highest and if the concentration of Sulphur in the lye is too high, the quality of the lye will be reduced and ultimately not usable. Further, Sulphur may oxidise which may lead to damages and / or clocking in / of the electrolysis system. Thus, it is important that the purification process, is happening outside the electrolysis stack to avoid the impurities / particles are damaging the electrolysis process and system.

[0150] It should be noted that the whole period of assembly, activation and tests may be referred to as commissioning. Upon final site acceptance test, terminating the commissioning, the electrolyser is ready to operate on a given site.

[0151] As mentioned, the electrolyser cell ELYC comprises inlet manifold, inlet duct (between manifold and compartment), compartment, outlet manifold and outlet duct (between manifold and compartment) which together forms what is referred to as a first container ICON of one electrolyser cell ELYC. When a plurality of cells is sandwiched together forming a stack, the volume of this first container is increased. Thus, the first compartment may include what can be referred to as the flow path of the electrolyte ELE through all the cells i.e. through the stack and sometimes also including the vessels VE. It should be mentioned that typically, the electrolyte for purification is drained from the vessels VE. Note that an electrolyser ELY may comprise more than one stack. In this situation the first container may comprise more than one stack. Alternatively, electrolyte of each individual stack may be purified separately according to the method of the present invention.

[0152] Accordingly, in this first container an electrically conductive liquid referred to as an electrolyte ELE is provided. The electrolyte ELE is the medium that provides the ion transport between the cathode and anode through the diaphragm (alsosometimes referred to as a membrane) in the cell and thereby creating the resulting hydrogen and oxygen of the electrolysis process.

[0153] As the catalyst CLY would form nickel metal and sulphide ions especially when powered during activation, the sulphide ions (S2‘) would in an embodiment of the invention form sulphate (SO42) from a redox reaction. As shown in eq. (2), S2' is oxidized to SCU2' by consumption of hydroxide ions. Thus, the oxidation of sulphide to sulphate is a byproduct of the hydrogen and oxygen production.

[0154] During activation the electrochemical reaction shown in eq. (1), generates more S2' than during normal operation (after activation). Via oxidation, this S2' turns into sulphates which is polluting the electrolyte and thus referred to as an impurity. Thus, especially during but also after activation it is advantageous to perform a purification of the electrolyte according to the present invention. Hence, in this specific example the electrolyte consists of potassium hydroxide and demineralized water. When the electrolyte interacts with the catalyst of the electrodes the electrolyte reacts resulting in sulphide impurities.

[0155] Purification for removal of the impurity ions such as carbonate and sulphate may be of interest, when the concentration of carbonate and / or sulphate is more than 800 parts per million. However, the electrolyser ELY may be damaged from the impurities, when reaching a concentration of more than 100 parts per million such as 800 parts per million.

[0156] Purification may be measured with ion chromatography to get a concentration of an ion of interest, Thus, the specific concentration of the impurity ions such as sulphate and carbonate in an electrolyte ELE may be determined through this method. Additionally, titration may also be used for measurement for the concentration of carbonate ions.

[0157] According to the invention, the electrolyte may be considered clean and ready for recycling if the impurities are in a concentration of less than 50 parts per million.

[0158] Further, after activation, during normal operation of the electrolyser ELY, it is possible to measure the contents of impurities such as e.g. sulphates in the electrolyte and determine if purification of the electrolyte is needed. Besides, if purification is not needed at the given time, it may be possible to predict when purification is needed from impurity measurements in the electrolyte.

[0159] During activation the formation of S2' is faster than the oxidation and conversion to the precipitable SCU2' shown in eq. (2). Thus, for speeding up the oxidation during activation, and speeding up the formation of precipitable sulphates, an oxidizing agent such as hydrogen peroxide may be used. Additionally, the conversion of S2' to SCU2' consumes hydroxide (OH"). Thus, during activation and the subsequent operation, the alkaline concentration of the electrolyte may decrease.

[0160] It should be mentioned that it may not be all the S2' which is removed in the oxidated SC 'form, during activation. This is due to more S2' being released during the years ahead. Therefore, purification of the electrolyte may be relevant also after activation.

[0161] In an embodiment of the invention, as the catalyst CLY is activated during commissioning, the electrolyte may absorb carbon dioxide from the atmosphere and cause accumulation of carbonate (CO32) in an alkaline electrolyte. Thus, accumulation of both sulphate and carbonate impurities in the electrolyte is a result of the electrochemical reaction in the initial phase i.e., at least during activation.

[0162] In electrochemistry, particularly in the context of hydrogen production through water electrolysis, a stack STA refers to an assembly of multiple electrochemical cells typically connected in series as illustrated in fig. 1. Alternatively, stacks can be connected in parallel to enhance the efficiency and overall performance of the hydrogen production process. Each electrochemical cell within the stack is configured to receive an electrolyte, typically an aqueous solution of an alkaline or acidic compound in compartments comprising an anode and a cathode respectively.

[0163] A stack STA allows for the efficient and continuous production of high-purity hydrogen gas, which can be used for a wide range of applications, including fuel cells,industrial processes, and energy storage. The design and engineering of the stack play a critical role in determining the efficiency and cost-effectiveness of hydrogen production.

[0164] The stack STA may comprise one or more catalyst CLY or electrochemical cells. The number of cells or catalysts CLY in the stack can vary depending on the desired hydrogen production capacity and efficiency.

[0165] Through the compartments and manifolds of the stack the electrolyte ELE flows. The electrolyte is usually an aqueous solution of either an alkaline compound (e.g., potassium hydroxide, KOH) or an acidic compound (e.g., sulphuric acid, H2SO4). The choice of electrolyte depends on the desired type of electrochemical reaction.

[0166] The stack may comprise a gas distribution system for gases produced at the cathode and anode, respectively, this gas need to be efficiently collected and removed. The gas distribution system is employed to transport the gases out of the stack for further processing or storage e.g. in the vessels VE or in truck tanks. This gas distribution system includes the above-mentioned outlet duct and fluid outlet.

[0167] The stack may comprise cooling and thermal management. Effective cooling is essential to maintain stable operating temperatures within the stack. Excessive heat can degrade the performance and lifespan of the electrochemical cells or catalysts. Thus, heat exchangers or cooling systems may be integrated into the stack for this purpose. In an embodiment the operation temperature may be in the range of 50°C - 100°C such as around 80°C. An example is using the electrolyte as temperature regulating media inside the stack i.e. the electrolyte is cooled before entering the inlet manifolds.

[0168] The stack may comprise a monitoring and control system, which is used to optimize the operation of the gas production, maintain constant voltage, or current, monitor leakage and thereby ensure safety and optimal operation. These systems help regulate the flow rates of reactants, control temperature, and provide real-time data on stack performance.

[0169] Fig. 3 illustrates an electrolysis system according to an embodiment of the invention. The illustrated electrolysis system provides a process that uses electricity to break down an aqueous solution into its constituent elements. This is done as described in this document by passing an electric current through the aqueous solution. Thereby, positive ions are attracted to the negative electrode (cathode), while negative ions are attracted to the positive electrode (anode). When the ions reach the electrodes, they gain or lose electrons, forming new substances. Hence, in case the aqueous solution is water, the water molecules split into hydrogen and oxygen. Hydrogen ions (H+) are attracted to the cathode and form hydrogen gas (H2), while hydroxide ions (OH-) are attracted to the anode and form oxygen gas (O2).

[0170] The electrolysis system is illustrated by only one electrolyser cell ELYC which, as the cell illustrated in fig. 2 comprises two cell frames CF1, CF2 each comprising a bipolar plate BP electrically connecting an anode and a cathode. It should be noted that only one side of the bipolar plate and only one part of the cell frames CF1, CF2 are illustrated. Hence, fig. 3 illustrates only the part of a cell of fig. 2 that are needed to explain the circulation of electrolyte ELE from the first to the second container i.e. the anode and cathode compartments.

[0171] It should be noted that a cell frame plus the bipolar plate and / or the associated catalyst may be referred to as an electrode assembly. Anode and cathodes of adjacent cells are illustrated with stipulated lines, adjacent to the electrolytic cell ELYC. These are electrically connected to the bipolar plates of the cell frames. The anode and cathode are separated by the diaphragm DIA forming the anode and cathode compartments. Via the two cell frames CF each compartment is supplied with electrolyte from fluid inlet FI and produced gas escapes via the fluid outlets FO. The inlets and outlets may as described be part of an inlet and an outlet manifold respectively. These manifolds and the compartments may together be referred to as a first container ICON.

[0172] Fig. 3 illustrates such a first container ICON. Besides, the first container ICON, the system comprises a power source PS powering the electrochemicalreaction. The positive potential of the power supply is connected to the anode and the negative potential is connected to the cathode.

[0173] Moreover, fig. 3 illustrates a first liquid connection 1LC between the first container ICON and a closed second container 2CON. In the first liquid connection 1LC, the electrolyte ELE is separated from the gas. The gas is guided to the storage vessels VE while the electrolyte is guided to the second container. Note that the electrolyte ELE is illustrated by the arrows in the compartments and liquid connections.

[0174] The second container 2CON is where the actual purification takes place by a chemical reaction between the electrolyte and a purification medium such as a barium source BAS. As illustrated, electrolyte is forced through the barium source BAS thereby forming the barium suspension SUS. As such, the first liquid connection 1LC may provide a way to transport the electrolyte ELE between the first container where it may be polluted and second container where it may be purified. Additionally, a second liquid connection 2LC may provide a route of transport for the purified electrolyte ELE back to the first container ICON from the second container 2CON.

[0175] It should be mentioned that the first and second liquid connections may be releasably connected to the first and second compartments. Thus, the fluid outlet and fluid inlet of the first compartment may be equipped with a tap the flow through which is controllable by a valve. In the same way the second container may comprise a tap and valve. In this way, the second container is releasably connected to the first container via hoses or pipes.

[0176] Further, it should be mentioned, that even tough referred to as a liquid connection it may in fact be a fluid connection in that it may also transport gas or liquid and gas simultaneously.

[0177] Further, it should be mentioned, that demineralized water may be added to the first or second containers or to the liquid connections therebetween.

[0178] Finally, a separation unit SEP is shown. The separation unit may e.g., be a filter, that can withhold solid barium particles also referred to as barium suspension BAS in the second container 2CON, while the electrolyte ELE is flowing back to the first container ICON.

[0179] In an embodiment of the invention, one liquid connection may be enough for transport the electrolyte ELE between containers. This is true at least if the electrolyte is not going to be reused in the first container of origin but may be transported to an alternative location, another electrolyser, etc.

[0180] It should be mentioned that a separation unit may be located in the first liquid connection. Such separation unit may be relevant if impurities is formed in the first container ICON.

[0181] In fig. 3 the first liquid connection 1LC and second liquid connection 2LC may be used to displace the electrolyte ELE from one container to another container. For displacement, the first liquid connection 1LC or second liquid connection 2LC can establish a flow from one container to another. Such flow may be generated by e.g. gravity or by a pump PUM (see fig. 5). In the visualized figure 3 the first container ICON comprises an electrolyser cell ELYC. Furthermore, the first liquid connection may comprise two different fluid outlets FO1, FO2 leading the flow of electrolyte ELE out of the electrolyser cells ELYC. During the electrochemical reaction, gasses such as hydrogen and oxygen are formed. These are illustrated as gas bubbles GB. Each of the fluid outlets are connected to a vessel VE for collecting the produced gas during the electrochemical reaction. Hence, the gas bubbles may accumulate in a vessel VE. Afterwards, the electrolyte ELE is guided to a barium source BAS in the second container 2CON. After reaching the barium source, barium suspension SUS my be formed by impurities that were previously dissolved in the electrolyte ELE. Next, the electrolyte is guided through a separation unit. Finally, the electrolyte ELE is guided back to the first container ICON by the two fluid inlets FI.

[0182] A power source PS is placed externally from the first container ICON comprising electrolyser cells ELYC which facilitate the electrochemical reaction withing the electrolyser cells ELYC.

[0183] After collecting the produced gasses in vessels VE the electrolyte ELE may substantially be free from gasses and / or gas bubbles GB. Obviously, may the first container ICON comprise multiple electrolyser cells ELYC.

[0184] Additionally, the flow speed may be regulated e.g. by controlling orifice of a regulation valve or speed of the pump. Such regulation of flow speed may be made by a controller (not illustrated) based on information of e.g., temperature, pEI of the liquid in the second container, amount of impurities, etc. and thereby ensure the liquid is sufficient time in the second container to be purified i.e. to establish a barium suspension BAS.

[0185] A controller such as an industrial PLC (PLC; Programmable Logic Controller) may control status of valves located in the flow path between the first and second containers. Thereby, the controller may control a flow of liquid in the first liquid connection 1LC and / or second liquid connection 2LC. The controller may receive feedback from one or more sensors, thereby, regulating the flow of liquid in the first liquid connection 1LC or second liquid connection 2LC. Such regulation may also change the gas / electrolyte fraction in the compartments, the temperature of the cell (as the electrolyte is used as temperature regulating medium), etc. The sensor may be one or more of a flow speed sensor, pEI sensor, pressure sensor, temperature sensor, etc. Accordingly, an entire process system is required to control the electrolysis process.

[0186] The controller may regulate the speed between a certain minimum and maximum flow speed. Thus, the flow speed in either the first liquid connection 1LC or second liquid connection 2LC can have a certain minimum or maximum flow which may depend on the residence time, for forming barium suspension BAS. Such flow control may be utilized when e.g., providing flow of the electrolyte through a purification column packed with barium hydroxide (also referred to as barium source).The flow control becomes important to give enough time for the purification reaction described below to complete. The time the electrolyte is in the second container may thus, be dependent on the design of the purification column. Note that such column through which the electrolyte is conducted is one way to provide the barium source in the second container.

[0187] Such purification column may be separating the second container forcing the electrolyte to pass through or it may be positioned so that to enter the second container the electrolyte has to pass through the column just to mention a few implementations. After the electrolyte has been guided through such purification column it is considered purified and thus it may be recycled back to the first container ICON.

[0188] In an embodiment, the second container may comprise both the purification column and a separation unit SEP separating the electrolyte ELE from impurities after the electrolyte ELE has passed through the purification column. In such embodiment, the electrolyte ELE may enter the second container at one end or side, pass through the purification column before it can leave the second container e.g. return to the first container.

[0189] It should be mentioned, that in the above, a reference to a purification column is used. This, however, should not be limiting to the present invention. The purification of the electrolyte may also be facilitated by adding a purification agent to the second container which is not in the form of a column such as the barium source BAS illustrated in the bottom of the second container 2CON in fig. 3.

[0190] In an embodiment, the barium suspension may be removed by a fixed bed adsorption column. In a fix bed column, the electrolyte is led through a column that comprise an adsorbent, which would withhold the solid particles making up the barium suspension.

[0191] In an embodiment, the barium suspension is removed by a fluidized bed process. In a fluidized bed process, a gas inlet is utilized for moving solid particles to the surface in a liquid. Different methods may be used for moving solid to the particlesto the surface, such as an agitator or a propeller. Thus, the fluidized bed process may be used for purification or ease the purification.

[0192] Alternatively, one of the first and second liquid connections may be implemented as a hose, which are sufficiently long to connect the first container to a second container located outside the room of the first container e.g. on a vehicle VEH. Similarly, the second liquid connection may be sufficiently long to connect a second container 2CON or separation unit SEP, if needed, located on a vehicle such as a truck trailer outside the room of the first container, to the first container. This may be applicable in a batch reaction, where the electrochemical reaction is halted in the first container ICON.Then the electrolyte is drained from the first container ICON guide to the second container where it is purified and later returned to the in the first container ICON.

[0193] Obviously, one or more pumps may be needed to facilitate the circulation of liquid through the long liquid hoses / connections. Connections which in this case may be more than 10 meters e.g. up to 50 meters or more.

[0194] As mentioned, the electrolyte ELE may comprise impurities such as sulphates formed by oxidation of sulphide from the electrochemical reaction, or carbonates formed by reaction with CO2 from air. Thus, providing the electrolyte in contact with a barium source BAS would, in the specifically illustrated embodiment, result in the following reaction of eq. (3) and eq. (4):Eq. (3) Ba(OH)2(S) + SC>42'(aq) BaSO4(s) + 2OH'(aq)Eq. (4) Ba(OH)2(S) + CC>32'(aq) BaCC>3(s) + 2OH'(aq)

[0195] Barium sulphate (BaSO4(s)) and barium carbonate (BaCO3(S)) are low solubility salts. Thus, a barium suspension SUS will be formed in the second container with electrolyte ELE and the barium source BAS. The barium suspension SUS will appear as solid particles in the electrolyte in the second container. It is mandatory that the barium suspension SUS does not get into the cells of the first container and therefore some kind of filter arrangement need to be provided at the outlet of thesecond container. Upon purification, the electrolyte ELE can both be displaced directly back to the first container ICON by the established first or second liquid connection that may comprise a separation unit. Preferably the electrolyte would pass through the separation unit SEP (see fig. 4), since a separation unit SEP may ensure, that solid particles are withheld in the separation unit and / or in the second container while providing transportation of liquid to the first container.

[0196] After the purification, the concentration of carbonate may be lower than the concentration of sulphate, since the formation of barium carbonate in eq. (3) is more favorable than the formation of barium sulphate in eq. (4).

[0197] In an embodiment of the invention the temperature may be altered throughout the system comprising the two containers to optimize solubility of impurities such as carbonates and sulphates. Hence, with a high temperature a high solubility is obtained and vice versa. Thus, with respect to the purification process, it may be advantageous to raise the temperature in the first container, to increase solubility of the impurities including sulphates and carbonates, avoiding precipitation in the first container ICON. Further, it may be advantageous to reduce the temperature in the second container 2CON, where the purification process happens, to increase the precipitation. This is due to the solubility of some salts, such as carbonates and sulphates, which can be altered by altering the temperature. Thus, by maintaining a temperature, based on the content of the purification medium, it is ensured to optimize the condition for / increase the formation of barium suspension SUS. In case the purification medium is a barium source, the preferred temperature range of the electrolyte in the second container is from 20 to 50 C.

[0198] The temperature may be decreased by different methods such as refrigeration with cool air, cooling coils or heat exchangers or liquid cooling. Such cooling / heating systems may be controlled by the same controller as the controller controlling the electrolysis. Alternatively, the purification system may be a stand-alone system including its own controller (such as an industrial PLC).

[0199] In an embodiment of the invention the pH of the electrolyte may be altered throughout the system. Such change of pH is advantageous especially in the second container / purification container. This is due to the solubility of some salts, such as carbonates and sulphates, can be reduced if the pH is increased e.g., by altering the concentration of hydroxide ions in the electrolyte ELE. Therefore, increasing the pH / hydroxide concentration in the second container may increase the generation of barium suspension.

[0200] The pH regulation of the electrolyte ELE may be carried out by e.g., altering the hydroxide concentration of the electrolyte. As an example, the alteration could be a change in hydroxide concentration of an electrolyte from 10% to 30% i.e. leading to an increase of the pH.

[0201] The displacement or transport of electrolyte described in relation to fig. 3a and 3b may be facilitated by the previously mentioned liquid connections that may be driven by i.e., pumps or gravity.

[0202] The displacement / purification of electrolyte ELE may be referred to as a batch process, where the electrochemical reaction is stopped in the first container, and all the electrolyte ELE is moved to the second container for purification. After purification the purified electrolyte ELE may be introduced back to the first container ICON.

[0203] Alternatively, the purified electrolyte ELE may be transported elsewhere by e.g., a vehicle VEH (shown in fig. 10)

[0204] Alternatively, the displacement of electrolyte may be referred to as a continuous process, where a part of the electrolyte ELE, is continuously transported from the first container ICON to the second container 2CON where it is purified. Thus, in a continuous setup, the electrochemical reaction is not necessarily needed to be halted i.e., hydrogen can be produced simultaneously with the purification process.

[0205] The second container 2CON may in the illustrated system in fig. 3a and 3b act as purification unit, that can comprise a separation unit SEP. The second container 2CON may additionally, comprise a barium source BAS.

[0206] It should be noted that the purification agent e.g. from a barium source may be dispensed automatically from a purification agent dispenser (not illustrated). Hence a controller CTRL may receive input from one or more impurity measuring device IMD. Based on such input, the controller may determine if an additional amount of purification agent such as barium should be added to the second container.

[0207] The controller may control one or more relevant valves, pumps, etc. based on input form one or more relevant sensors and measuring devices to facilitate the purification according to the present invention.

[0208] The following part of the description relating to fig. 4-10 describes and illustrates various alternatives to the implementation of the present invention.

[0209] Fig. 4 illustrates a system according to an embodiment of the invention. In the illustrated embodiment the electrolyte ELE is displaced or transported from the first container ICON to the second container 2CON by a liquid connection, that may either be first liquid connection 1LC as shown or second liquid connection 2LC or both (not shown). Further, the electrolyte passes through a separation unit SEP back to the first container ICON via the first liquid connection 1LC or second liquid connection 2LC or both. The purpose of the separation unit SEP is the separate the impurities, such as the barium suspension SUS, captured from the electrolyte before it enters the first container again. The separation unit may be implemented e.g., a centrifuge or a filter.

[0210] The separation unit SEP is in fig. 4 not shown as an integrated part of the second container 2CON but may as mentioned be an integrated part of the second container 2CON.

[0211] Fig. 5 illustrates a system according to an embodiment of the invention. In the illustrated embodiment the electrolyte ELE is transported from the first containerICON, to the second container 2CON, via a pump located in the first liquid connection 1LC as shown or second liquid connection 2LC or both (not shown). Alternative to using a pump, the electrolyte ELE may be transported between the containers by use of gravity.

[0212] Fig. 6 illustrates a system according to an embodiment of the invention. In the illustrated embodiment, a portion of the electrolyte ELE is transported from the first container ICON to the second container 2CON via a first liquid connection 1LC, and further, to a separation unit implemented as a filter FIL. After the electrolyte has passed through the filter, it may be transported back to the first container ICON via a second liquid connection 2LC. Additionally, a different portion of the electrolyte ELE, may bypass the second container and directly go through a filter FIL.

[0213] The bypass system may be used in e.g., a continuous flow setup. In a continuous system, the electrolyser is still operated. Thus, a continuous purification of the electrolyte ELE would be carried out in such system since the electrolyser may not operate without electrolyte ELE. Thus, a fraction of the impure electrolyte would constantly pass through a purification container.

[0214] As a result, since a fraction is constantly purified, it would take longer for the electrolyte to reach an upper threshold level of impurities. The upper threshold of a given impurity ion, such as carbonate and / or sulphate may be considered 800 parts per million, determined by ion chromatography or titration. Advantageously, the continuous setup, may not reach such upper threshold level of 800 parts per million of a given ion, and thus operation stop due to polluted electrolyte is avoided.

[0215] Additionally, the continuous setup can be used for prolonging the need for a batch treatment, by keeping the amount of impurities below a threshold. After some time however, it can be decided to halt the production. In such case, the electrolyser ELY is turned off, and the entire batch would be purified in a second container 2CON.

[0216] Additionally, a portion of the electrolyte ELE can go through purification in the second container 2CON simultaneously with a portion of the electrolyte ELE bypassing the second container 2CON.

[0217] Fig. 7 illustrates a system according to an embodiment of the invention. In the illustrated embodiment, a portion of the electrolyte ELE is transported from the first container ICON to the second container 2CON via a first liquid connection 1LC, and further, directly back to the first container ICON via a second liquid connection 2LC. This is possible without barium suspension is transported to the first container if the barium suspension have had the time to settle in the second container and the second liquid connection is above the settled barium suspension.

[0218] The system according to fig. 7. is a bypass system, that may be necessary in a system comprising a column as a separation unit. The system may be used since some dissolved barium source can trigger precipitation in the first container ICON. This can be avoided by premixing treated and untreated electrolyte before the filtration step and thus, the amount of barium source in the electrolyte is reduced. Additionally, a different portion of the electrolyte ELE, may bypass the second container and directly go through a filter FIL as a separation unit SEP. This is to ensure any impurities that can be filtered from the electrolyte is removed. As described previously, this may be advantageous in a continuous setup, that can prolong the operating time for an electrolyser ELY. The operating time is prolonged since the impurities are removed from the electrolyte ELE in parallel with the impurities formed in the electrochemical reaction to produce hydrogen and oxygen. Thus, it may take longer for the electrolyte ELE to reach a certain threshold, that require stopping the electrochemical reaction.

[0219] As mentioned, in some embodiments, the separation unit SEP, may be integrated into the second container 2CON. In such embodiments, the electrolyte ELE may be transported directly from the second container 2CON back to the first container ICON after purification in the second container 2CON.

[0220] Multiple separation units may be integrated into the system according to any embodiment. This may for example be a combination of a centrifuge and a filter. Besides, multiple methods for separating liquid from solids, may be combined in a single separation unit SEP.

[0221] The amount of electrolyte ELE that bypass may vary between systems depending on the impurity of electrolyte ELE. For example, if the concentration of either carbonate or sulphate ions reaches more than 100 parts per million, the electrolyte may bypass.

[0222] Fig. 8 illustrates a system according to an embodiment of the invention. In the illustrated embodiment, the movement of electrolyte ELE from the first container ICON to the second container 2CON, is facilitated by a first liquid connection 1LC to a vehicle VEH such as a truck trailer. Alternative, pipes may be used to move electrolyte from the first container to a second container. Thus, the purification may take place on a different site than the site where the first container ICON is located. After purification the electrolyte may be transported back to the first container ICON via a second liquid connection 2LC.

[0223] The vehicle VEH may also be used for transporting electrolyte ELE after the purification in the second container 2CON. Thus, the first container ICON and the second container 2CON may be located on the same site, but after the purification, the electrolyte ELE may be transported to a container on a different site.

[0224] Fig. 9 illustrates a system according to an embodiment of the invention. In the illustrated embodiment, multiple first containers are located on the same production site and may be electrically connected in series or in parallel to match an output from a power supply. The electrolyte ELE from the electrochemical reaction of such plurality of stacks may be transported to a second container 2CON via one or more pumps PUM in a first liquid connection 1LC. After transportation to and purification in the second container, the electrolyte ELE is transported back to multiple first containers via a second liquid connection 2LC.

[0225] Obviously, it should be mentioned, that the multiple first containers may be containers from different sites. Thus, the second container may act as a facility for purification for electrolyser systems located at different sites. In such situation, the electrolyte may be transported by a truck-trailer between the first and second containers.

[0226] Fig. 10 illustrates a system according to an embodiment of the invention. In the illustrated embodiment, the electrolyte ELE is moved from a first container ICON that is located on Site 1 to a vehicle VEH via a first liquid connection 1LC and transported to a Site 2. At site 2, the electrolyte ELE is moved from the vehicle VEH to a second container 2CON via a first liquid connection.

[0227] The movement of electrolyte ELE from a first container ICON to e.g., a vehicle VEH, may be via a liquid connection as previously described, or e.g., a system of hoses / pipes and pumps. Obviously, the same methods for movements apply for movement of the electrolyte ELE from the vehicle VEH to the second container 2CON.

[0228] The transport or movement of electrolyte ELE may be facilitated e.g. by a pump.

[0229] The vehicle may e.g., be a truck, rail tank cars or shipping tankers as an alternative to pipes and hoses.

[0230] Obviously, the purification container may be large enough to hold a capacity of multiple facilities or site 1. Thus, the second container 2CON, may i.e., be a purification facility handling electrolyte from several electrolyser sites. Even though not illustrated, purification at a site different than the site of the pollution may also require a “clean” storage vessel. Hence, after being purified in the second container, the electrolyte may be moved to the clean intermediate vessel before moved back to a first container.

[0231] In the following various features of a system according to the present invention is described. These features include that: the electrolyte is an electric conductive liquid, that the electrolyte is an aqueous solution and that the catalyst is an anode or a cathode or a coating on the electrodes

[0232] In an embodiment of the invention the power source is connected to the electrolyser ELY before said liquid connection is established between the first and second containers and / or the power source is connected to the electrolyser after adding a barium source to the second container.

[0233] Further, in an embodiment of the invention the first and / or second container is free of halides and the electrochemical reaction is free of cadmium.

[0234] Finally, it should be mentioned that in an embodiment of the invention the system comprise more than one purification containers i.e. more than one second containers.

[0235] From the above it is now clear that the invention relates to a method and a system that allow purification of electrolyte which is polluted in an electrochemical process such as an electrolysis process for producing hydrogen. Slow oxidation of sulphides to sulphates and absorption of CO2 from the air cause accumulation of sulphate and carbonate impurities in the electrolyte used e.g. in alkaline electrolysis with nickel sulphide catalysts. The in-situ activation of electrodes using e.g. a 15% KOH releases sulphide ions that slowly oxidize to sulphate. At least in large installations, during commissioning with a 15% KOH electrolyte the installation may only be partial loaded due to the lower conductivity of 15% electrolyte. After the activation, an upgrade of the electrolyte concentration to 25% is needed which causes precipitation of potassium sulphate in an external lye tank. A total replacement of the 15% electrolyte is costly since it comprises not only the cost of new electrolyte but also the transport and destruction of the used 15% electrolyte.

[0236] Thus, the present invention suggest that oxidation of sulphides and intermediate oxo-anions of sulfur (e.g. S2O32-) to sulphate (SO42-) can be accomplished in alkaline conditions using e.g. hydrogen peroxide. Sulphates and carbonates can then be removed e.g. by precipitation with barium ions. Addition of Barium hydroxide after the oxidation of sulphides leads to the formation of a suspension, that may initially consist of sparingly soluble Ba(OH)2. The barium reagent may then convert to BaSO4 and BaCO3 with the soluble sulphates and carbonates impurities being replaced by hydroxide ions. Filtration or centrifugation can be used to remove any unreacted reagent as well as precipitated impurities. This allow the purified electrolyte to either be re-used for further activation cycles of other electrolyzers as well as be upgraded to 25% for permanent usage.

[0237] Hence, in addition to removal of Sulphate, carbonate may also removed according to the present invention. The latter is especially relevant with using nickel sulfur containing electrodes. The removal of carbonates-based impurities (decarbonization) obtained by the present invention may be more relevant during the continuous operation of the electrolysis than during the activation period. Whereas the removal of sulfur-based impurities may be more relevant during the activation period than during the continuous operation.

[0238] Accordingly, the present invention provides an automated purification method where a controller is controlling flow of electrolyte / lye e.g. by controlling valves, pumps, etc. Further, the controller is communicating with an impurity measuring device for determining the purity of the lye. In addition input from such impurity measuring devices may be used be the controller to control automatic dispensing of the purification agent such as barium hydroxide. Hence, the barium source i.e. the purification agent may be dispensed from a dispenser via control of a valve or similar thereby providing the purification agent to the interior of the second container.

[0239] Accordingly, a system purified according to the present invention may comprise an active / operational / main part which may be an electrolysis stack. Further, such system may comprise a purification part, a separate container, in which the actual purification is taking place. Active control of flow of lye from the main part to the purification part is automated by the controller controlling necessary parts to allow such flow.LIST OF REFERENCE SIG S:ICON first container2CON second container1LC first liquid connection2LC second liquid connectionANO anodeANOC anode compartmentBAS barium sourceBP bipolar plateCAT cathodeCATC cathode compartmentCLY catalystCTRL controllerDIA diaphragmELY electrolyserELYC electrolyser cellsELE electrolyteFI fluid inletFO fluid outletFO1 fluid outlet 1FO2 fluid outlet 2FIL filterGB gas bubbleIMD impurity measuring deviceMEM membranePS power sourcePUM pumpRF rubber frameST A stackSUS barium suspensionSEP separation unitVE vesselVEH vehicleVEHY vessel for hydrogenVEOX vessel for oxygen

Claims

CLAIMS1. A method of removal of impurities, formed by an electrochemical reaction, the electrochemical reaction being an alkaline electrolysis, from an electrolyte comprised by a first container, wherein said first container furthermore comprises one or more catalysts, wherein said method comprises the steps of: at least partly covering said catalyst with said electrolyte in said first container, powering said catalyst, thereby starting said electrochemical reaction forming said impurities in said electrolyte, wherein said impurities comprise sulphate ions and carbonate ions, establishing a liquid connection from said first container to a second container, wherein said second container comprise a barium source, establish a flow of said electrolyte from said first container to said barium source in said second container, thereby forming a barium suspension comprising a mixture of sulphate and carbonate salts in said second container, and separating said barium suspension from said electrolyte, thereby forming a purified electrolyte, wherein said method is carried out during an activation period of said alkaline electrolysis.

2. A method according to claim 1, wherein said activation period last for a time period of at least 5 days, such as 1 week, such as 2 weeks, such as 1 month, such as 1.5 months, such as 2 months, such as 2.5 months, such as 3 months, such as 3.5 months, such as 4 months.

3. A method according to claim 1 or 2, wherein said first container is divided in a plurality of compartments which are fluidly connected.

4. A method according to any of the preceding claims, wherein said first container is a stack of an electrolyser.

5. A method according to any of the preceding claims, wherein said first container comprise a tap via which said liquid connection to said second container is established.

6. A method according to any of the preceding claims, wherein said electrolyte comprise a volume of at least 0.1 cubic meter such as 1 cubic to 100 cubic meters such as 25 to 75 cubic meters, such as 35 to 65 cubic meters.

7. A method according to any of the preceding claims, wherein a temperature of said electrolyte is altered in said second container.

8. A method according to any of the preceding claims, wherein said electrolyte is a lye solution comprising sodium hydroxide, potassium hydroxide or a combination thereof.

9. A method according to any of the preceding claims, wherein pH of said electrolyte is adjusted by altering a lye concentration from a 10%-20% solution to a 20%-30% solution such as from a 12%- 17% solution to a 22%-27% solutions such as from a 15% solution to a 25% solution.

10. A method according to any of the preceding claims, wherein pH of said electrolyte is adjusted in said second container.

11. A method according to any of the preceding claims, wherein a temperature of said second container is altered.

12. A method according to any of the preceding claims, wherein at least one catalyst is active or inactive.

13. A method according to any of the preceding claims, wherein said catalysts comprise a metal and nonmetal.

14. A method according to any of the preceding claims, wherein said catalyst comprises a metal sulphide15. A method according to claim 14, wherein said metal in said metal sulphide is selected from the list comprising iron, copper, nickel, cobalt, silver, zinc or any combinations thereof.

16. A method according to any of the preceding claims, wherein said electrochemical reaction is powered by a power supply comprising an AC / DC or DC / DC converter.

17. A method according to claim 16, wherein said power supply is able to deliver a current of at least 40kA to said one or more catalysts.

18. A method according to any of the preceding claims, wherein said flow in said first liquid connection of said electrolyte is established by a pump or gravity.

19. A method according to any of the preceding claims, wherein said method comprise adding said barium source to said second container prior to establishing said first liquid connection.

20. A method according to any of the preceding claims, wherein said barium source is a barium salt.

21. A method according to any of the preceding claims, wherein said barium source is barium hydroxide.

22. A method according to any of the preceding claims, wherein said purified electrolyte is circulated from said second container back to said first container.

23. A method according to any of the preceding claims, wherein said second container comprise a tap for connecting said first liquid connection to said second container.

24. A method according to any of the preceding claims, wherein separation of a solid and electrolyte comprise conducting said electrolyte through a centrifuge or a filter.

25. A method according to any of the preceding claims, wherein said separation is established in a separation unit.

26. A method according to any of the preceding claims, wherein said separation is continuous during said time period.

27. A method according to any of the preceding claims, wherein an oxidizing agent such as hydrogen peroxide is used in said second container.

28. A purification system configured to remove impurities from an electrolyte used in an electrochemical reaction, the electrochemical reaction being an alkaline electrolysis, wherein said system comprise: a power supply, a first container configured to comprise said electrolyte and one or more catalysts, a liquid connection from said first container to a second container, a second container comprising a barium source wherein said barium source, and said impurities of said electrolyte, is forming a barium suspension in said electrolyte when comprised by said second container, and a separation unit configured to remove said barium suspension from said electrolyte wherein said method is carried out during an activation period of said alkaline electrolysis.

29. A purification system according to claim 28, wherein said system is configured to: supply electric power to said one or more catalysts, establish a flow of said electrolyte in said first container passing through said one or more catalysts thereby contaminating said electrolyte with at least sulphate ions and carbonate ions, establish a flow of said contaminated electrolyte from said first container to said second container via said liquid connection, wherein said contaminatedelectrolyte is passing by said barium source comprised by said second container, thereby forming said barium suspensions in said second container, establish a flow of said electrolyte comprising said barium suspensions through said separation unit, thereby separating said barium suspension from said electrolyte, and thereby forming a purified electrolyte.

30. A purification system according to claim 28 or 29, wherein said system has a second liquid connection from second container or a separation unit back to first container.

31. A purification system according to any of the claims 28-30, wherein said system comprise a pump to establish said flow of electrolyte.

32. A purification system according to any of the claims 28-31, wherein said first and second liquid connections, second container, pump and / or separation unit are portable.

33. A purification system according to any of the claims 28-32, wherein said first and second liquid connections, second container, pump and / or separation unit are located on a vehicle.

34. A purification system according to any of the claims 28-33, wherein a portion of said electrolyte is configured to bypass said purification system.

35. A purification system according to any of the claims 28-34, wherein said portion of said electrolyte is mixed with said purified electrolyte in the liquid connection between said second container and said first container.

36. A purification system according to any of the claims 28-35, wherein said purified electrolyte is substantially free from impurities.

37. A purification system according to any of the claims 28-36, wherein said purified electrolyte comprises a sulphate and / or carbonate concentration of less than 100 parts per million preferably less than 50 parts per million, most preferably less than 10 parts per million.

38. A purification system according to claim 37, wherein said concentration is measured with ion chromatography and / or titration.

39. A purification system according to any of the claims 28-38, wherein said purified electrolyte is collected and transported.

40. A purification system according to any of the claims 28-39, wherein said purified electrolyte is recycled to one or more additional containers.

41. A purification system according to any of the claims 28-40, wherein said second container comprise said separation unit.

42. A purification system according to any of the claims 28-41 wherein said barium suspension is collected by said separation unit and discarded from said separation unit.

43. A purification system according to any of the claims 28-42 wherein said separation unit comprise a centrifuge, or a filter.

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