Integrated water treatment for water electrolysis using osmotic membrane distillation and osmotic membrane distillation system

Abstract

A process for the electrolysis of water to obtain hydrogen comprises the following process steps: a) Providing an electrolyte solution (5) comprising water and at least 1 mol / l of at least one electrolyte, a feed solution comprising water, and an osmotic membrane distillation apparatus comprising at least three chambers, namely a feed chamber (21), a permeate chamber (22) and an electrolysis chamber (11), wherein the feed chamber (21) and the permeate chamber (22) are separated by a porous hydrophobic gas-permeable membrane (27) and the feed chamber (21) contains feed solution and the permeate chamber (22) contains electrolyte solution (5), b) Performing an osmotic membrane distillation, wherein water evaporates in the feed chamber (21), passes as water vapor through the membrane (27) and condenses into the electrolyte solution (5) in the permeate chamber (22), and c) Electrolysis of water of the electrolyte solution (5) in the electrolysis chamber (11), yielding hydrogen and oxygen.

Description

[0001] The present invention relates to processes for the electrolysis of water to obtain hydrogen using osmotic membrane distillation plants, as well as osmotic membrane distillation plants designed and suitable for such processes.

[0002] For the electrolysis of water to produce hydrogen, very pure water is required, otherwise its consumption will lead to an accumulation of its constituents. This can damage the electrolysis plant and disrupt hydrogen production.

[0003] In classical alkaline electrolysis, an aqueous KOH solution is electrochemically decomposed. Water is continuously consumed from the solution through its conversion to hydrogen and oxygen, as well as through the formation of water vapor. This consumption must be continuously replenished to maintain the electrolyte concentration within an optimal range. The chosen conditions—concentration and temperature—represent a compromise between, preferably, rapid kinetics and, preferably, minimal corrosion. If the water contains even traces of impurities, these will accumulate over time. The voltage losses (overvoltage) generated during electrolysis produce heat, necessitating active cooling of the electrolyte solution. Typically, the hydrogen is required at a higher pressure. To prevent subsequent compression, the electrolysis is therefore carried out under pressure.

[0004] These statements also apply in principle to other variants of electrolysis, such as polymer electrolyte membrane or alkaline electrolyte membrane electrolysis.

[0005] In classical osmosis (forward osmosis (FO)), two solutions (for example, aqueous salt solutions) of different osmolalities are brought into contact via a semipermeable, microscopically dense membrane. The resulting osmotic pressure causes water to migrate across the membrane from the side of lower osmolality to the side of higher osmolality until the osmotic pressure is equalized on both sides, without a phase change of the water. Simultaneously, the salt ions are retained. Therefore, if the aforementioned electrolyte solution (high osmolality) were brought into contact with a solution of comparatively lower osmolality, for example, seawater, via an FO membrane, the water from the seawater would migrate into the electrolyte solution.

[0006] However, the technical problem of providing water for electrolysis cannot be solved using FO membranes, as none of the membrane materials used so far – rather hydrophilic, highly cross-linked polymers, such as polyamides – can withstand the harsh conditions of electrolysis mentioned above.

[0007] In membrane distillation (MD), two solutions, particularly aqueous solutions, are brought into contact with each other via a porous, particularly hydrophobic, membrane. The membrane must be selected such that, under the given conditions, the solutions cannot wet the membrane pores, while vapor molecules can penetrate them. By controlling the temperature to create different vapor pressures on each side, molecules will migrate from the warm to the cold side of the membrane. This requires that the water molecules change from the liquid to the vapor phase. Since only volatile components are transported, salts or other non-volatile impurities, especially organic compounds, remain on the warm side, and the water can be purified by this process.

[0008] A major challenge in mechanical thermodynamics (MD) is heat transfer across the membrane, which reduces the driving force of the process and leads to significant energy losses. Therefore, MD inherently involves a trade-off between high mass transfer and low heat transfer.

[0009] There are various process engineering approaches to reduce this problem, for example by avoiding direct contact (DCMD) of the solutions with the membrane and using a gas gap as "thermal insulation" (Air Gap MD, Sweeping Gas MD, Permeate Gap MD).

[0010] However, the technical problem of providing water for electrolysis cannot be solved by means of membrane distillation, since the temperature of the electrolyte / permeate side is already high and therefore no driving force can be adjusted via the temperature.

[0011] Depending on the location and available water quality, various established water treatment methods are used to prepare water for electrolysis, such as reverse osmosis, distillation, electrodialysis, capacitive deionization or combinations of these methods, all of which have different disadvantages.

[0012] The technical problem underlying the present invention is to overcome the disadvantages of known methods for the electrolysis of water to produce hydrogen. In particular, the technical problem of the present invention is to provide a method that allows the waste heat from the electrolysis process to be used for purifying water for electrolysis and simultaneously allows the temperature to be controlled during electrolysis.

[0013] WO 2020 / 231 694 A1 discloses a system for providing water, hydrogen and oxygen from contaminated water.

[0014] US 2008 / 0173539 A1 discloses devices and methods for the processing of alkali metal salt solutions from electrolysis cells, in particular sodium chloride solutions from the electrolytic production of sodium hydroxide and chlorine.

[0015] The present invention solves the underlying technical problem in particular through the subject matter of the independent claims as well as the teachings of the dependent claims and the present description.

[0016] The invention relates to a process for the electrolysis of water to obtain hydrogen, comprising the following process steps: a) Providing an electrolyte solution comprising water and at least 1 mol / l of at least one electrolyte, a feed solution comprising water, and an osmotic membrane distillation apparatus comprising at least three chambers, namely a feed chamber, a permeate chamber and an electrolysis chamber, wherein the feed chamber and the permeate chamber are separated by a porous hydrophobic gas-permeable membrane and the feed chamber contains feed solution and the permeate chamber contains electrolyte solution, b) Performing an osmotic membrane distillation, whereby water evaporates in the feed chamber, passes through the membrane as water vapor and condenses into the electrolyte solution in the permeate chamber, and c) Electrolysis of water from the electrolyte solution in the electrolysis chamber, yielding hydrogen and oxygen.

[0017] The invention therefore provides a process in which hydrogen and optionally oxygen are obtained from water by means of electrolysis. For this purpose, in a first process step, a) an electrolyte solution is provided, which comprises a minimum amount of at least one electrolyte, and a feed solution, which contains at least water, wherein the feed solution may also contain one or more other substances.

[0018] Furthermore, in process step a), an osmotic membrane distillation system is provided, which has at least three chambers: at least one feed chamber, at least one permeate chamber, and at least one electrolysis chamber. The electrolysis chamber and permeate chamber contain the same solution, namely the electrolyte solution, although the conditions in the two chambers, in particular the temperature and / or pressure, may differ. The permeate chamber and feed chamber, which together form a membrane distillation unit, are separated by a porous, hydrophobic, gas-permeable membrane. This membrane ensures that the water from the feed solution can be transferred to the electrolyte solution in a purified state, since only volatile components can be transported across the membrane because the hydrophobicity of the membrane prevents the solution from wetting it.Therefore, salts or other non-volatile impurities, especially organic compounds, remain in the feed solution, which is thus concentrated. The water consumption in the electrolysis chamber is compensated for by purifying the water of the feed solution.

[0019] Additionally, heat transfer can preferably occur via the membrane from the electrolyte solution present in the permeate chamber to the feed solution present in the feed chamber. This heats the feed solution and cools the electrolyte solution, which was heated by electrolysis in the electrolysis chamber. Simultaneously, the heat transfer from the electrolyte solution to the feed solution increases the water vapor pressure above the feed solution, further promoting mass transfer across the membrane. Therefore, mass transfer is improved concurrently with the regulation of the electrolyte solution temperature.

[0020] The inventive process thus provides in process step b) that water from the feed solution evaporates and passes through the membrane in the form of vapor and subsequently condenses into the electrolyte solution in the permeate chamber.

[0021] The purified water, which is now in the permeate chamber in the electrolyte solution, is transferred to the electrolysis chamber and split there into hydrogen and oxygen by means of electrolysis.

[0022] Without being bound to theory, in a preferred embodiment of the inventive method, the waste heat from the electrolysis process is used directly for purifying the water used for electrolysis. This can preferably be done via the membrane or via a heat exchanger, or preferably both. The heat transfer via the membrane and / or the heat exchanger is used, on the one hand, to heat the feed solution and thus increase the water flow. On the other hand, the temperature of the electrolyte solution can also be controlled in this way. Preferably, apart from a small energy input for the pumps, no further energy is required for the membrane distillation itself, thus disregarding the electrolysis process.

[0023] In a preferred embodiment of the invention, the electrolyte solution provided in process step a) comprises at least 5 mol / l, in particular at least 7 mol / l, at least one, in particular one, electrolyte.

[0024] In a preferred embodiment of the invention, the at least one electrolyte of the electrolyte solution provided in process step a) is at least one base, preferably a base.

[0025] In a preferred embodiment of the invention, the at least one electrolyte of the electrolyte solution provided in process step a) is at least one readily soluble base.

[0026] In a preferred embodiment of the invention, the at least one electrolyte of the electrolyte solution provided in process step a) is at least one organic base, in particular an organic base.

[0027] In a preferred embodiment of the invention, the at least one electrolyte of the electrolyte solution provided in process step a) is selected from the group consisting of KOH, NaOH, LiOH, RbOH, CsOH and combinations thereof.

[0028] In a preferred embodiment of the invention, the at least one electrolyte of the electrolyte solution provided in process step a) is KOH.

[0029] In a preferred embodiment of the invention, the feed solution provided in process step a) is a solution selected from the group consisting of groundwater, surface water, drinking water, wastewater, brackish water, seawater and combinations thereof.

[0030] In a particularly preferred embodiment of the invention, the feed solution provided in process step a) is seawater.

[0031] In a preferred embodiment of the invention, the feed solution additionally comprises at least one additive, in particular an antiscalant.

[0032] In a particularly preferred embodiment of the invention, the feed solution additionally comprises at least one antiscalant, in particular a complexing agent, in particular ethylenediaminetetraacetate (EDTA).

[0033] In a particularly preferred embodiment, the complexing agent is selected from the group consisting of ethylenediaminetetraacetate (EDTA), diethylenetriaminepentaacetate (DTPA), nitriloacetate (NTA), bifunctional or trifunctional carboxylic acid, in particular oxalic acid, tartaric acid or citric acid, or combinations thereof, in particular ethylenediaminetetraacetate (EDTA).

[0034] The feed solution has a lower osmolality than the electrolyte solution.

[0035] In a preferred embodiment, the water vapor pressure above the feed solution in the feed chamber is higher than above the electrolyte solution in the permeate chamber.

[0036] In a preferred embodiment of the invention, the water vapor pressure prevailing above the electrolyte solution in the permeate chamber is at least 5 kPa, in particular at least 7 kPa.

[0037] In a preferred embodiment of the invention, the water vapor pressure prevailing above the feed solution in the feed chamber is at least 15 kPa, in particular at least 18 kPa.

[0038] In a preferred embodiment of the invention, the membrane distillation system provided in process step a) comprises at least one, in particular one, heat exchanger. The at least one heat exchanger can preferably transfer heat from the, in particular concentrated, electrolyte solution to the feed solution.

[0039] The at least one heat exchanger is preferably a parallel flow or counterflow heat exchanger.

[0040] In a particularly preferred embodiment, the at least one heat exchanger is located between the electrolysis chamber and the membrane distillation unit, in particular between the electrolysis chamber and the permeate chamber, and in the inlet for the feed solution into the feed chamber.

[0041] In a preferred embodiment of the invention, the membrane distillation system provided in process step a) has at least one heat exchanger, in particular between the electrolysis chamber and the permeate chamber and in the feed for the feed solution into the feed chamber and / or integrated into the feed chamber and / or integrated into the electrolysis chamber and / or integrated into the permeate chamber.

[0042] In a particularly preferred embodiment, the at least one heat exchanger is integrated into the membrane distillation unit, in particular its permeate chamber, its feed chamber or both.

[0043] In a particularly preferred embodiment, the at least one heat exchanger is integrated into the electrolysis chamber.

[0044] In a particularly preferred embodiment, a heat exchanger is provided between the electrolysis chamber and the membrane distillation unit, in particular between the electrolysis chamber and the permeate chamber and in the feed for the feed solution into the feed chamber, and a further heat exchanger is integrated into the permeate chamber.

[0045] In a particularly preferred embodiment, a heat exchanger is provided between the electrolysis chamber and the membrane distillation unit, in particular between the electrolysis chamber and the permeate chamber and in the feed for the feed solution into the feed chamber, and a further heat exchanger is integrated into the electrolysis chamber.

[0046] In a particularly preferred embodiment, a heat exchanger is provided between the electrolysis chamber and the membrane distillation unit, in particular between the electrolysis chamber and the permeate chamber and in the inlet for the feed solution into the feed chamber, and a further heat exchanger is integrated into the feed chamber.

[0047] In a particularly preferred embodiment, a heat exchanger is located between the electrolysis chamber and the membrane distillation unit, in particular between the electrolysis chamber and the permeate chamber and in the inlet for the feed solution into the feed chamber, a further heat exchanger is integrated into the permeate chamber and a further heat exchanger is integrated into the feed chamber.

[0048] In a particularly preferred embodiment, a heat exchanger is provided between the electrolysis chamber and the membrane distillation unit, in particular between the electrolysis chamber and the permeate chamber and in the inlet for the feed solution into the feed chamber, a further heat exchanger is integrated into the permeate chamber and a further heat exchanger is integrated into the feed chamber and a further heat exchanger is integrated into the electrolysis chamber.

[0049] In a particularly preferred embodiment, heat transfer takes place in the heat exchanger located between the electrolysis chamber and the membrane distillation unit from concentrated electrolyte solution originating from the electrolyte chamber to feed solution that is fed into the feed chamber.

[0050] In a particularly preferred embodiment, heat transfer takes place in the heat exchanger located between the electrolysis chamber and the membrane distillation unit in a direct current from concentrated electrolyte solution originating from the electrolyte chamber to feed solution that is directed into the feed chamber.

[0051] In a particularly preferred embodiment, heat transfer takes place in the heat exchanger located between the electrolysis chamber and the membrane distillation unit in a countercurrent flow from concentrated electrolyte solution originating from the electrolyte chamber to feed solution that is directed into the feed chamber.

[0052] In a particularly preferred embodiment, heat transfer takes place in the heat exchanger integrated into the feed chamber from concentrated electrolyte solution originating from the electrolyte chamber to feed solution present in the feed chamber.

[0053] In a particularly preferred embodiment, heat transfer from electrolyte solution present in the permeate chamber to fresh feed solution takes place in the heat exchanger integrated into the permeate chamber.

[0054] In a particularly preferred embodiment, heat transfer takes place in the heat exchanger integrated into the electrolysis chamber from electrolyte solution present in the electrolysis chamber, in particular concentrated electrolyte solution, to fresh feed solution.

[0055] In a particularly preferred embodiment, at least a portion of the concentrated electrolyte solution and at least a portion of the feed solution is passed through the heat exchanger located between the electrolysis chamber and the membrane distillation unit. In a particularly preferred embodiment, the entire concentrated electrolyte solution and / or the entire feed solution is passed through the heat exchanger located between the electrolysis chamber and the membrane distillation unit.

[0056] In a preferred embodiment, part of the concentrated electrolyte solution is transferred to the permeate chamber and the other part is passed through the heat exchanger located between the electrolysis chamber and the membrane distillation unit, with both parts then being transferred back to the electrolysis chamber, preferably after the two parts have been combined.

[0057] In a preferred embodiment, a portion of a concentrated electrolyte solution is transferred to the heat exchanger, preferably located between the electrolysis chamber and the membrane distillation unit, and subsequently to the permeate chamber, while the other portion is transferred to the heat exchanger, preferably integrated into the feed chamber. Both portions are then, preferably after being combined, returned to the electrolysis chamber. In a particularly preferred embodiment, at least a portion of fresh feed solution is passed directly into the feed chamber, and at least a portion of the fresh feed solution is passed through the heat exchanger located between the electrolysis chamber and the membrane distillation unit.

[0058] In a particularly preferred embodiment, the entire fresh feed solution is passed through the heat exchanger located between the electrolysis chamber and the membrane distillation unit.

[0059] In a particularly preferred embodiment, the entire concentrated electrolyte solution is passed through the heat exchanger located between the electrolysis chamber and the membrane distillation unit.

[0060] In a preferred embodiment, part of the electrolyte solution is passed directly into the permeate chamber and the other part through the heat exchanger located between the electrolysis chamber and the membrane distillation unit.

[0061] In a preferred embodiment, part of the fresh feed solution is directed into the heat exchanger located between the electrolysis chamber and the membrane distillation unit, and the other part into the heat exchanger integrated in the permeate chamber.

[0062] In a preferred embodiment, the fresh feed solution, which has been heated in a heat exchanger in an electrolysis chamber, is divided, with one part being directed into the permeate chamber and the other part being discharged from the system.

[0063] In a preferred embodiment of the invention, the membrane distillation system provided in process step a) has at least one, in particular one, throttle valve, which in particular regulates the pressure between the permeate chamber and the electrolysis chamber, preferably together with a pump.

[0064] In a preferred embodiment of the invention, the membrane distillation system provided in process step a) has at least one, in particular one, pressure exchanger, which in particular regulates the pressure between the permeate chamber and the electrolysis chamber, preferably together with a pump.

[0065] In a preferred embodiment of the invention, the porous hydrophobic gas-permeable membrane between the feed chamber and the permeate chamber is designed in the form of a flat membrane, tubular membrane or hollow fiber membrane.

[0066] In a preferred embodiment of the invention, the electrolysis chamber is divided into two areas by a diaphragm, wherein the at least one anode and at least one cathode are located in different areas.

[0067] In a preferred embodiment, the permeate chamber and the electrolysis chamber of the membrane distillation system provided in process step a) are connected by means of a line.

[0068] In a preferred embodiment of the invention, the porous hydrophobic gas-permeable membrane between the feed chamber and the permeate chamber has a mean pore size of 0.05 to 0.9 µm, in particular 0.1 to 0.5 µm.

[0069] In a preferred embodiment of the invention, the porous hydrophobic gas-permeable membrane between the feed chamber and the permeate chamber is made of a hydrophobic polymer, in particular fluorine-containing polymers, especially polyolefins or perfluorinated polyolefins, in particular polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) or polypropylene (PP). The hydrophobic properties of the membrane are determined by the material used.

[0070] In a preferred embodiment of the invention, the porous hydrophobic gas-permeable membrane has a support. The support can mechanically stabilize the membrane.

[0071] In a particularly preferred embodiment of the invention, the support for the porous hydrophobic gas-permeable membrane is made of polysulfone, in particular polyethersulfone (PES).

[0072] In a particularly preferred embodiment of the invention, the porous hydrophobic gas-permeable membrane is made of PTFE and the support is made of polysulfone, in particular polyethersulfone (PES).

[0073] In a preferred embodiment of the invention, the membrane distillation system provided in process step a) further comprises a device for removing carbon dioxide, which removes carbon dioxide from the feed solution before it enters the feed chamber.

[0074] In a particularly preferred embodiment, the carbon dioxide in the carbon dioxide removal device is removed by heating, purging with another gas, in particular oxygen, using a membrane contactor, wherein an inert gas is present on the other side of the membrane, viewed from the side with feed solution, precipitates in the form of carbonate or combinations thereof.

[0075] In a preferred embodiment, the membrane distillation system provided in process step a) further comprises at least one filtration unit. In a particularly preferred embodiment, the at least one filtration unit is located in the feed line for the feed solution to the feed chamber.

[0076] In a preferred embodiment of the invention, the osmotic membrane distillation according to process step b) is a direct contact, air gap, vacuum or sweeping gas membrane distillation.

[0077] In a preferred embodiment of the invention, the distillation rate of water from the feed chamber via the porous hydrophobic gas-permeable membrane into the permeate chamber is at least 1 kg m³. -2 h -1 , in particular at least 2 kg m -2 h -1 , especially 2.5 kg m -2 h -1 .

[0078] In a preferred embodiment of the invention, a temperature of at least 60 °C, in particular at least 70 °C, and in particular at least 80 °C, is present during the electrolysis in process step c).

[0079] In a preferred embodiment of the invention, a temperature of 60 to 100 °C, in particular 70 to 90 °C, in particular 75 to 85 °C, in particular 80 °C, is present during the electrolysis in process step c).

[0080] In a preferred embodiment of the invention, during electrolysis in process step c) the temperature is more than 60 °C and lower than the boiling point of the electrolyte solution used.

[0081] In a preferred embodiment of the invention, during electrolysis in process step c) a pressure of 1 to 70 bar, in particular 2 to 70 bar, in particular 1 to 60 bar, in particular 1 to 5 bar, in particular 6 to 60 bar, in particular 5 bar, in particular 60 bar, is present.

[0082] In a preferred embodiment of the invention, a current density of 0.5 to 2, in particular 1 A / cm², is used in the electrolysis process step c). 2 used.

[0083] In a preferred embodiment of the invention, the electrolysis in process step c) is a polymer electrolyte membrane electrolysis, in particular a proton exchange membrane (PEM) electrolysis or anion exchange membrane (AEM) electrolysis, or alkaline electrolysis, preferably an alkaline electrolysis with a diaphragm.

[0084] In a preferred embodiment of the invention, the method additionally comprises the following process step d): supplying further feed solution to the feed chamber, wherein concentrated feed solution is withdrawn from the feed chamber.

[0085] In a particularly preferred embodiment of the invention, the concentrated feed solution taken in process step d) is used in a pressure-retarded osmosis process to generate energy.

[0086] The present invention also relates to an osmotic membrane distillation apparatus designed for a process according to the invention, wherein the apparatus has at least three chambers, namely a feed chamber, a permeate chamber and an electrolysis chamber, wherein the feed chamber and permeate chamber are separated by a porous hydrophobic gas-permeable membrane and the electrolysis chamber is connected to the permeate chamber.

[0087] The present invention also relates to an osmotic membrane distillation plant, which is characterized in particular by the features disclosed above in connection with the present method according to the invention, in particular device features, in particular heat exchangers.

[0088] In connection with the present invention, an "electrolyte solution" is understood to be a solution, preferably aqueous, comprising at least one electrolyte, in particular one, in particular two electrolytes.

[0089] In the context of the present invention, a "feed solution" is understood to be an aqueous solution comprising water. In addition to water, the solution may comprise other substances, dissolved and / or undissolved.

[0090] In connection with the present invention, a membrane distillation unit is understood to be a device comprising at least one, in particular one, feed chamber and at least one, in particular one, permeate chamber, wherein the feed chamber and the permeate chamber are separated by at least one porous hydrophobic gas-permeable membrane.

[0091] In connection with the present invention, a membrane distillation plant is understood to be a device comprising at least one membrane distillation unit and at least one electrolysis chamber, which are fluidically connected to each other via lines, and which preferably comprises at least one heat exchanger, at least one pump, a device for CO2 removal and / or valves as well as supply, connecting and / or discharge lines.

[0092] In the context of the present invention, a "feed chamber" is understood to be a region of a membrane distillation apparatus which contains feed solution and which is directly adjacent to a permeate chamber, being separated from the permeate chamber by a porous hydrophobic, gas-permeable membrane. The chamber may further comprise at least one inlet and at least one outlet, wherein fresh feed solution flows from a feed solution inlet into the feed chamber via the inlet and concentrated feed solution exits the feed chamber via the outlet. The feed chamber may also include an integrated heat exchanger.

[0093] In the context of the present invention, a "feed solution inlet to the feed chamber" is understood to be a piping system capable of supplying fresh feed solution, in particular from a feed solution source, for example a tank or a body of water, to the feed chamber. A filtration unit can be integrated into the "feed solution inlet to the feed chamber" to separate undissolved components.

[0094] In connection with the present invention, a "permeate chamber" is understood to be a section of a membrane distillation apparatus containing an electrolyte solution and directly adjacent to a feed chamber, from which it is separated by a porous, hydrophobic, gas-permeable membrane. The permeate chamber is further connected to the electrolysis chamber, in particular via a line, and electrolyte solution, enriched with purified water from the feed solution, can flow from the permeate chamber into the electrolyte chamber and, in a concentrated form, can flow back from the electrolyte chamber to the permeate chamber, preferably via a line. Different conditions, in particular different temperatures and / or pressures, can prevail in the permeate chamber compared to the electrolysis chamber. The permeate chamber can also include an integrated heat exchanger.

[0095] In the context of the present invention, an "electrolysis chamber" is understood to be a section of a membrane distillation system used for the electrolysis of water from an electrolyte solution. It has at least one anode and at least one cathode, the electrodes optionally being separated by a membrane / diaphragm. According to the invention, the electrolysis chamber is connected to the permeate chamber of the membrane distillation unit, in particular via a conduit, wherein electrolyte solution, enriched with purified water from the feed solution, flows from the permeate chamber into the electrolysis chamber, and concentrated electrolyte solution flows from the electrolysis chamber into the permeate chamber. Different conditions, in particular different temperatures and / or pressures, can prevail in the electrolysis chamber compared to the permeate chamber. In the electrolysis chamber, the electrolysis of water into hydrogen and oxygen is carried out.The electrolysis chamber may also have an integrated heat exchanger.

[0096] In connection with the present invention, an “antiscalant” is understood to be an additive which reduces and / or prevents the precipitation of, in particular sparingly soluble, salts and thus the deposition of particles on a membrane surface.

[0097] In connection with the present invention, a “concentrated feed solution” is understood to be a feed solution in which, as a result of osmotic membrane distillation, in particular vapor pressure membrane distillation, the amount of water in the solution has decreased and the concentration of dissolved and / or undissolved substances in it has been increased.

[0098] In connection with the present invention, a “concentrated electrolyte solution” is understood to be an electrolyte solution in which, as a result of electrolysis, the amount of water has decreased and the concentration of dissolved, at least one, electrolyte has increased due to the gases and / or water vapor produced by electrolysis.

[0099] In connection with the present invention, a "fresh feed solution" is understood to be a feed solution that has not yet been subjected to any process step b) according to the invention and / or a heat exchanger step, in particular neither concentrated nor heated.

[0100] In the context of the present invention, the term "at least one" is understood to mean a quantity that expresses a number of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and so on. In a particularly preferred embodiment, the term "at least one" can represent exactly the number 1. In another preferred embodiment, the term "at least one" can also mean 2, 3, 4, 5, 6, or 7.

[0101] Where quantitative information, in particular percentages, of components of a product or composition is given in connection with the present invention, these, unless explicitly stated otherwise or it is evident to a person skilled in the art, add up together with the other explicitly stated or evident further components of the composition or product to 100% of the composition and / or the product.

[0102] Insofar as the “presence”, “containing”, “exhibiting” or “content” of a component is expressly mentioned or implied in connection with the present invention, this means that the respective component is present, in particular in a measurable quantity.

[0103] Where the presence, containment or presence of a component in an amount of 0 [unit], in particular mg / kg, µg / kg or wt.%, is expressly mentioned or implied in connection with the present invention, this means that the respective components are not present in a measurable amount, in particular are not present.

[0104] The number of decimal places given corresponds to the precision of the measurement method used.

[0105] In the context of the present invention, the term "and / or" means that all members of a group connected by the term "and / or" are disclosed both alternatively to one another and cumulatively to one another in any combination. For the expression "A, B and / or C", this means that the following disclosure content is to be understood: a) A or B or C, or b) (A and B), or c) (A and C), or d) (B and C), or e) (A and B and C).

[0106] In the context of the present invention, the terms "comprising" and "comprising" are understood to mean that, in addition to the elements explicitly covered by these terms, further, unmentioned elements may be present. In the context of the present invention, these terms are also understood to mean that only the explicitly mentioned elements are covered and no further elements are present. In this particular embodiment, the meaning of the terms "comprising" and "comprising" is synonymous with the term "consisting of." Furthermore, the terms "comprising" and "comprising" also encompass compositions that, in addition to the explicitly mentioned elements, contain further unmentioned elements that are, however, of a functionally and qualitatively subordinate nature. In this embodiment, the terms "comprising" and "comprising" are synonymous with the term "essentially consisting of."The term "consisting of" means that only the explicitly mentioned elements are present and the presence of further elements is excluded.

[0107] Further embodiments of the present invention are the subject matter of the dependent claims and further independent claims.

[0108] The invention is explained in more detail with reference to the following examples and the accompanying figures.

[0109] The figures show: Fig. Figure 1 shows a schematic drawing of a membrane distillation system according to the invention, comprising a feed chamber, a permeate chamber (both of which, together with the porous, hydrophobic membrane arranged between the two chambers, form a membrane distillation unit), and an electrolysis chamber. A direct current heat exchanger, arranged between the electrolysis chamber and the permeate chamber and in the feed solution inlet to the feed chamber, transfers heat from the concentrated electrolyte solution to the feed solution. The system also includes a device for removing CO2 and water pumps for transporting the feed solution and electrolyte solution. The anode and cathode are separated by a diaphragm in the electrolysis chamber. Fig. Figure 2 shows a schematic drawing of a membrane distillation system according to the invention, comprising a feed chamber, a permeate chamber, and an electrolysis chamber. A countercurrent heat exchanger transfers heat from the concentrated electrolyte solution to the feed solution. According to the present embodiment, the flow of the concentrated electrolyte solution after the electrolysis chamber is divided, with the first portion of the electrolyte solution being used to heat the feed solution before it is fed into the MD unit, and the second portion flowing into the permeate chamber. Furthermore, the system includes a device for removing CO2 and water pumps for transporting the feed solution and electrolyte solution. The anode and cathode are separated by a diaphragm in the electrolysis chamber. Fig. Figure 3 shows a schematic drawing of a membrane distillation apparatus according to the invention, comprising a feed chamber, a permeate chamber, and an electrolysis chamber. A direct current heat exchanger and the membrane between the feed chamber and the permeate chamber transfer heat from the concentrated electrolyte solution to the feed solution. The apparatus also includes throttle valves and water pumps to create a vacuum in the feed and permeate chambers, thereby increasing the distillation rate. Furthermore, the apparatus includes a device for CO2 removal. The anode and cathode are separated by a diaphragm in the electrolysis chamber. Fig. Figure 3a shows a schematic drawing of a membrane distillation system according to the invention, comprising a feed chamber, a permeate chamber, and an electrolysis chamber. A direct current heat exchanger and the membrane between the feed chamber and the permeate chamber transfer heat from the concentrated electrolyte solution to the feed solution. The system also includes a throttle valve in the line from the electrolysis chamber to the heat exchanger and water pumps to generate overpressure in the electrolysis chamber. Furthermore, the system includes a device for removing CO2. The anode and cathode are separated by a diaphragm in the electrolysis chamber. Fig. Figure 4 shows a schematic drawing of a membrane distillation system according to the invention, comprising a feed chamber, a permeate chamber, and an electrolysis chamber. A counterflow heat exchanger, arranged between the electrolysis chamber and the permeate chamber, as well as in the feed solution inlet to the feed chamber, transfers heat from the concentrated electrolyte solution to the feed solution. The concentrated electrolyte solution from the electrolysis chamber is split into two lines: one flows through the heat exchanger into the permeate chamber, and the other into a heat exchanger integrated into the feed chamber. The two flows then combine and, after being enriched with water from the feed chamber, return to the electrolysis chamber. In addition to the heat transfer in the heat exchanger between the electrolysis chamber and the membrane distillation system, heat is also transferred by separately adding concentrated electrolyte solution to the heat exchanger in the feed chamber.By separately supplying fresh feed solution in a separate inlet (i.e., a separate line) to a further heat exchanger in the permeate chamber, heat from the permeate chamber is transferred to and removed from this fresh feed solution. The system also includes a CO2 removal device and water pumps for transporting the feed solution and electrolyte solution. The anode and cathode are separated by a diaphragm in the electrolysis chamber. Fig. Figure 5 shows a schematic drawing of a membrane distillation system according to the invention, comprising a feed chamber, a permeate chamber, and an electrolysis chamber. A heat exchanger integrated into the electrolysis chamber transfers heat from the electrolyte solution to fresh feed solution. The feed solution flow is split after the heat exchanger, with the first portion being discharged via an outlet and the second portion flowing into the feed chamber. The system also includes a CO2 removal device and water pumps for transporting the feed solution and electrolyte solution. The anode and cathode are separated by a diaphragm in the electrolysis chamber. Fig. 6 A schematic drawing of an experimental setup for determining the distillation rate across a membrane in a membrane distillation unit with feed chamber, permeate chamber and hydrophobic, porous membrane. REFERENCE MARK LIST 1 anode 2 Cathode 3 Gas extraction Oxygen 4. Gas extraction: Hydrogen 5 Electrolyte 6 Diaphragm 7 Flow of the electrolyte solution 7a Flow of electrolyte solution, branched off to the membrane distillation unit 7b Flow of electrolyte solution, branched off to the heat exchanger 7c Flow of electrolyte solution, diverted to heat the membrane distillation unit 7d Flow of the electrolyte solution, diverted via heat exchanger to the membrane distillation unit 8 Electrolyte solution pump 8a Electrolyte solution pump in suction mode 9 Water pump 9a Water pump in suction mode 10 heat exchangers in direct current operation 10a Heat exchanger in counterflow operation 10b Heat exchanger, integrated into the electrolysis chamber 11 Electrolyte chamber 12 Device for CO2 removal 13 Water Inlet 14 River of Water 14a Flow of water, branched off after the integrated heat exchanger to the water outlet 15a 14b Flow of water, diverted after the integrated heat exchanger and fed to the MD unit 14c Flow of water, diverted for cooling the membrane distillation unit 14d Flow of water, diverted via heat exchanger to the membrane distillation unit 15.15a Water outlet 16 Throttle valve for electrolyte solution 17 Throttle valve for water 18,19 pressure sensors 20 Membrane distillation unit (MD unit) 20a Air Gap MD Unit 21 Feed chamber 22 Permeate chamber 23, 24 Built-in heat exchangers of the membrane distillation unit 25 Inlet Electrolysis Chamber 26 Outlet Electrolysis Chamber 27 porous hydrophobic gas-permeable membrane between permeate chamber and feed chamber EXAMPLES Example 1

[0110] A schematic drawing of the membrane distillation plant according to embodiment 1 can be found in Fig. 1.

[0111] The fresh feed solution, in this case seawater, from inlet 13 is pumped by pump 9. The solution passes through the CO2 removal device 12, then through the direct-flow heat exchanger 10, through the membrane distillation unit 20, in particular through the feed chamber 21, and is discharged from outlet 15 (see flow 14 in [reference]). Fig. 1).

[0112] The electrolyte solution 5, in this example a concentrated alkali, namely 40 wt% KOH solution (7 M) in water, is extracted from the electrolysis chamber 11 by means of pump 8. The solution passes through the heat exchanger 10, through the membrane distillation unit 20, in particular through the permeate chamber 22, and is then fed back into the electrolysis chamber 11 (see flow 7 in Figure 1). Fig. 1).

[0113] In the present embodiment, the electrolysis chamber 11 is divided into two sections by means of a diaphragm 6: one section with an anode 1, a gas extraction port for oxygen 3, an inlet 25 for electrolyte solution, and an outlet 26 for concentrated electrolyte solution; and the other section with a cathode 2 and a gas extraction port for hydrogen 4. It is also possible for the cathode 2 and the gas extraction port for hydrogen 4 to be located on the side with the inlet 25 and outlet 26, and the anode 1 and the gas extraction port for oxygen 3 to be located on the other side of the diaphragm. In the direct-flow heat exchanger 10, the two fluid flows, i.e., seawater and electrolyte solution, are brought to an approximately equal temperature, which lies between the operating temperature in the electrolysis chamber (around 80 °C in the present embodiment) and the ambient temperature.The temperature at the outlet of heat exchanger 10 can be controlled by the ratio between the two mass flows. This temperature is optimized to strike a balance between the distillation rate, which increases with rising temperature, and the stability of the membrane 27 in the chemically aggressive alkali, which must be considered at higher temperatures.

[0114] In the membrane distillation unit 20, water is transferred as vapor from the feed chamber 21 to the electrolyte solution 5 in the permeate chamber 22. Since distillation in this configuration takes place under nearly isothermal conditions, the driving force is predominantly osmotic: the activity of water, or its vapor pressure, is significantly lower in the electrolyte solution 5 than in the feed solution. For example, at 60 °C, the saturated vapor pressure of water is approximately 145 Torr (approximately 19 kPa), while for 40 wt% KOH solution, this value is only approximately 55 Torr (approximately 7 kPa).

[0115] The water transferred to the electrolyte solution 5 compensates for the water consumption caused both by the conversion of water into hydrogen and oxygen and by losses due to evaporation in the electrolysis chamber 11. The distillation process guarantees the high purity of the introduced water, which is very important for the continuous operation of the electrolysis chamber.

[0116] At the same time, waste heat from the process is removed from the electrolysis chamber because the electrolyte solution being fed back in has a lower temperature. Example 2

[0117] A schematic drawing of the membrane distillation plant according to embodiment 2 can be found in Fig. 2.

[0118] The main difference compared to embodiment 1 is that the temperature of the distillation process and thus the process rate can be optimized by means of a counterflow heat exchanger 10a.

[0119] The concentrated electrolyte solution 5, extracted from electrolysis chamber 11, is divided into two partial flows 7a and 7b. Partial flow 7b is fed into the countercurrent heat exchanger 10a, where it raises the water temperature of the fresh feed solution to almost the original temperature of the electrolyte solution 5 in electrolysis chamber 11, which is approximately 80 °C. This ensures that feed chamber 21 is supplied with hot feed solution via feed stream 14. This hot water is then fed into the MD unit 20, specifically feed chamber 21, as the feed solution. The diverted partial flow 7a of the electrolyte solution 5 is introduced into the permeate chamber 22 of the membrane distillation unit 20 and enriched with water transferred via the vapor phase from feed chamber 21.In this embodiment, the distillation process takes place, as in embodiment 1, i.e., under approximately isothermal conditions, but at a significantly higher temperature and accordingly has a higher process rate.

[0120] Subsequently, the partial flows of electrolyte 7a and 7b, after being combined, are fed back into the electrolysis chamber 11. As in embodiment 1, the water is thus introduced into the electrolysis chamber 11 and the waste heat is discharged. Example 3

[0121] A schematic drawing of the membrane distillation plant according to embodiment 3 can be found in Fig. 3. This system essentially corresponds to that of the Fig. 1 (Exemplary 1), the description of which is referenced.

[0122] In this embodiment, however, distillation is carried out under a lower pressure than vacuum membrane distillation. For this purpose, pumps 8a and 9a are operated in suction mode, and the flow of the electrolyte solution 5 is limited by the throttle valves 16 and 17, thereby creating a vacuum. The vacuum is detected by sensors 18 and 19. Pressure control can be achieved in a feedback loop by adjusting the pump output as well as by controlling the throttle valves.

[0123] Instead of generating a vacuum using throttle valves, a pressure exchanger can optionally be used. Example 3a

[0124] In a further embodiment as a variation of embodiment 3 (see Fig. 3a) Electrolysis is carried out under increased pressure, for example as medium-pressure electrolysis at 5 bar or as high-pressure electrolysis at 60 bar. The throttle valve 16 and the pump 8a are used to reduce the pressure of the electrolyte solution in the membrane distillation unit to approximately atmospheric pressure. A pressure exchanger can optionally be used instead of the throttle valve for pressure reduction. In this case, the creation of a vacuum in the feed circuit, and thus the throttle valve 17, can be omitted. Example 4

[0125] A schematic drawing of the membrane distillation plant according to embodiment 4 can be found in Fig. 4.

[0126] In this version, the distillation is carried out under non-isothermal conditions. This is analogous to Example 2 and... Fig. 2. A counterflow heat exchanger 10a is used to lower the temperature of the electrolyte solution 5 and raise the temperature of the feed solution. Subsequently, the two flows 7d and 14d are fed into the membrane distillation unit 20a. The temperature difference maximizes the process rate; the process represents a combination of conventional and osmotic membrane distillation. Significant heat transfer from the feed to the permeate side occurs due to the latent heat of vaporization and condensation, which would quickly equalize the temperature difference. To prevent this, the respective chambers of the distillation unit 20a are additionally cooled and heated, respectively, using the integrated heat exchangers 23 and 24.The cooling medium can be diverted fresh, i.e. cold, feed solution 14c (heat exchanger 23 integrated in permeate chamber 22), and the heating medium can be diverted hot electrolyte solution 7c (heat exchanger 24 integrated in feed chamber 21).

[0127] The membrane distillation unit 20a can advantageously be designed as a so-called air-gap membrane distillation unit. The air gap minimizes the additional heat transfer between the feed and permeate sides caused by the thermal conductivity of the membrane 27, which is undesirable in this context. By constructing the air-gap MD unit such that the air gap is located between the membrane 27 and the electrolyte solution 5, direct contact between the membrane 27 and the lye, and the associated membrane stability problems, are avoided. Example 5

[0128] A schematic drawing of the membrane distillation plant according to embodiment 5 can be found in Fig. 5.

[0129] The key difference compared to embodiment 1 is that the temperature of the feed solution is brought to almost the same temperature as the electrolyte solution 5 in the electrolysis chamber 11 by means of a heat exchanger 10b integrated into the electrolysis chamber. The integrated heat exchanger 10b cools the electrolyte solution directly within the electrolyte chamber. After the heat exchanger, the feed flow is split into two partial flows 14a and 14b. The partial flow 14a of the feed solution, which is not required for membrane distillation due to its quantity, is removed from the membrane distillation system and thus from the process via outlet 15a.

[0130] In partial flow 14b, the CO2 removal device 12 is positioned upstream of the feed chamber 21. The increased temperature of the feed solution allows for optimized carbon dioxide removal.

[0131] Membrane distillation takes place under near-isothermal conditions at almost the original temperature of the electrolyte solution 5. Example 6

[0132] In Fig. Figure 6 shows a membrane distillation unit 20. In this embodiment, the distillation rate of water from a feed solution (B) to an electrolyte solution (C) within a membrane distillation unit (A) with a feed chamber and permeate chamber (not shown) was determined. The unit utilizes a porous, hydrophobic, gas-permeable membrane with a mean pore size of 100 nm, the membrane being made of PTFE and having a polysulfone, in particular polyethersulfone (PES), support. For this purpose, feed solution and electrolyte solution were supplied to a membrane distillation unit from feed containers using peristaltic pumps, and the mass increase in the electrolyte solution was determined after 3 hours. Conditions • .. Feed (feed solution): ultrapure water (0.8 mS cm -1 ) • Draw (electrolysis solution): 4 M KCl (equivalent to 4 M KOH, since the ionic strength is the same) • Gravimetric determination of the mass increase in electrolyte solution / draw solution (before and after measurement) • .. Circulation via peristaltic pumps (30 rpm) • .. Measurement duration 3h Result: • .. Water flow across the membrane: 2.6 kg / m² 2 h

[0133] As a result, a distillation rate across the membrane of 2.6 kg / m² was obtained. 2 measured in h.

Claims

A process for the electrolysis of water to obtain hydrogen, comprising the following process steps: a) providing an electrolyte solution (5) comprising water and at least 1 mol / l of at least one electrolyte, a feed solution comprising water, and an osmotic membrane distillation apparatus comprising at least three chambers, namely a feed chamber (21), a permeate chamber (22), and an electrolysis chamber (11), wherein the feed chamber (21) and the permeate chamber (22) are separated by a porous hydrophobic gas-permeable membrane (27), and the feed chamber (21) contains feed solution and the permeate chamber (22) contains electrolyte solution (5); b) carrying out osmotic membrane distillation, wherein water in the feed chamber (21) evaporates, passes as water vapor through the membrane (27), and condenses into the electrolyte solution (5) in the permeate chamber (22); and c) electrolyzing water from the electrolyte solution (5). in the electrolysis chamber (11),whereby hydrogen and oxygen are obtained. Method according to claim 1, wherein the membrane distillation apparatus provided in process step a) has at least one heat exchanger (10, 10a), in particular between electrolysis chamber (11) and permeate chamber (22) and / or integrated into the feed chamber (21) and / or integrated into the electrolysis chamber (11) and / or integrated into the permeate chamber (22). Method according to one of claims 1 or 2, wherein the membrane distillation apparatus provided in process step a) comprises at least one pressure exchanger. Method according to one of the preceding claims, wherein the porous hydrophobic gas-permeable membrane (27) is designed in the form of a flat membrane, tubular membrane or hollow fiber membrane. Method according to one of the preceding claims, wherein the membrane distillation apparatus provided in process step a) further comprises a device for removing carbon dioxide (12) which removes carbon dioxide from the feed solution before it enters the feed chamber (21). A method according to any of the preceding claims, wherein the feed solution provided in process step a) is a solution selected from the group consisting of groundwater, surface water, drinking water, wastewater, brackish water, seawater and combinations thereof. A method according to any of the preceding claims, wherein the feed solution provided in process step a) additionally comprises at least one antiscalant. Method according to any of the preceding claims, wherein the osmotic membrane distillation according to process step b) is a direct contact, air gap, vacuum or sweeping gas membrane distillation. Method according to one of the preceding claims, wherein the distillation rate of the water from the feed chamber (21) via the porous hydrophobic membrane (27) into the permeate chamber (22) is at least 1 kg m-2h-1. Method according to one of the preceding claims, wherein a temperature of at least 60 °C is present during the electrolysis in process step c). Method according to one of the preceding claims, wherein the electrolysis in process step c) is a polymer electrolyte membrane electrolysis, in particular a proton exchange membrane electrolysis or anion exchange membrane electrolysis, or alkaline electrolysis, preferably an alkaline electrolysis with diaphragm. Method according to one of the preceding claims, wherein the method additionally comprises the following process step: d) supplying further feed solution to the feed chamber (21), wherein concentrated feed solution is withdrawn from the feed chamber (21). Method according to claim 12, wherein the concentrated feed solution taken in process step d) is used in a pressure-retarded osmosis process to generate energy. Osmotic membrane distillation apparatus designed for a process according to one of claims 1 to 13, wherein the apparatus has at least three chambers, namely a feed chamber (21), a permeate chamber (22) and an electrolysis chamber (11), wherein the feed chamber (21) and permeate chamber (22) are separated by a porous hydrophobic gas-permeable membrane (27) and the electrolysis chamber (11) is connected to the permeate chamber (22).

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