Alkaline anion exchange blend membrane

Abstract

The present invention relates to a basic anion exchange membrane precursor (pAAEM) comprising a blend of at least one first polymer (P1) comprising recurring units derived from acrylonitrile and at least one second polymer (P2) comprising recurring units derived from vinyl lactam; and to an alkaline anion exchange membrane (AAEM) obtained therefrom.

Description

[0001] Specification

[0002] The present invention relates to an alkaline anion exchange membrane precursor (pAAEM) comprising a blend of at least one first polymer (P1) and at least one second polymer (P2), wherein the first polymer (P1) comprises repeating units derived from acrylonitrile and the second polymer (P2) comprises repeating units derived from vinyl lactam; and to an alkaline anion exchange membrane (AAEM) obtained therefrom.

[0003] Furthermore, the present invention relates to a method for preparing an alkaline anion exchange membrane precursor (pAAEM), a method for preparing an alkaline anion exchange membrane (AAEM), an alkaline water electrolyzer comprising an alkaline anion exchange membrane (AAEM), the use of an alkaline anion exchange membrane (AAEM) in an alkaline water electrolyzer, and a method for producing hydrogen using an alkaline exchange membrane (AAEM).

[0004] The goals of politics, society, and industry are to reduce CO2 emissions by decarbonizing industry and transportation. In this context, green hydrogen has a strategic role, as it can replace hydrocarbons in transportation applications for chemical and industrial processes, energy conversion, and fuel cell propulsion.

[0005] Furthermore, with the growing share of renewable resources, the German energy system is undergoing a fundamental change. According to the 2010 Energy Concept, the federal government has set the goal of reducing greenhouse gas emissions by at least 80% in 2050 compared to 1990. In addition, by 2050, 60% of the total final energy consumption should be provided by renewable energy based on the level in 1990. In the initial years of implementing the 2010 Energy Concept, the share of renewable energy in the total energy production needs to be continuously increased, but once the supply of renewable energy reaches a significant proportion, technical solutions for intermediate storage for solar, wind, or hydropower are required.

[0006] As a system solution, power-to-gas (P2G) allows the conversion of electricity into hydrogen or methane for use in various fields, such as transportation, industry, heating, and power generation applications.

[0007] The key element of a P2G system is a water electrolyzer, which exists as an alkaline or proton exchange membrane electrolyzer system. Today, most commercial electrolyzers are based on alkaline electrolysis using 30 wt% aqueous KOH electrolyte (conductivity of 1.5 S / cm at 80 °C), which can be operated at current densities in the range of 1000 A / m 2 to 3000 A / m 2 However, due to the reduced efficiency at high current densities, technically a current density < 1000 A / m 2 is standard.

[0008] The porous diaphragm is used to separate the evolved oxygen and hydrogen, but also to prevent the mixing of the cathode electrolyte and the anode electrolyte in order to obtain high gas purity and high current efficiency.

[0009] As a diaphragm material, asbestos has been widely used, with a service temperature up to 100 °C. In addition, polyantimonic acid, nickel oxide, polyphenylene sulfide ( ), polyphenylene sulfide / zirconium oxide ( ) are known as modern diaphragm materials.

[0010] The diaphragm materials described in the prior art have a thickness of about 500 μm. They show good stability towards alkaline aqueous solutions. The disadvantage of the diaphragm materials used in the prior art is that they are not airtight. Therefore, the evolved oxygen and hydrogen can migrate through the diaphragm material, which results in a reduced efficiency of the electrolysis process. In addition, the diaphragm materials are quite expensive.

[0011] Another method recently disclosed in the prior art is to use an alkaline anion exchange membrane in an alkaline water electrolyzer to produce hydrogen.

[0012] "D. Aili, M. R. Kraglund, J. Tavacoli, C. Chatzichristodoulou and J. O. Jensen, Polysulfone-polyvinylpyrrolidone blend membranes as electrolytes in alkaline water electrolysis, Journal Membrane Science 2020, 598, 117674 - 117684. DOI: 10.1016 / j.memsci.2019.117674" discloses polysulfone-polyvinylpyrrolidone blend membranes as electrolytes in alkaline water electrolysis. The alkaline anion exchange membranes disclosed in this literature have shown quite good properties. However, considering strong alkaline aqueous solutions, the long-term stability is not sufficient in all cases. Therefore, there is still room for improvement.

[0013] Therefore, the object of the present invention is to provide an alkaline anion exchange membrane precursor (pAAEM) from which an anion exchange membrane (AAEM) can be obtained, which does not show the disadvantages of the prior art or only shows them in a reduced form. The preparation of the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom should be easy to carry out. The alkaline anion exchange membrane (AAEM) should be suitable for an alkaline water electrolyzer. In addition, the alkaline anion exchange membrane (AAEM) should be suitable for producing hydrogen and oxygen in an alkaline water electrolyzer.

[0014] This object is achieved by an alkaline anion exchange membrane precursor (pAAEM) comprising a blend (B) of at least one first polymer (P1) and at least one second polymer (P2), wherein the first polymer (P1) comprises repeating units derived from acrylonitrile and the second polymer (P2) comprises repeating units derived from vinyl lactam.

[0015] Furthermore, this object is achieved by an alkaline anion exchange membrane (AAEM) obtained by bringing the alkaline anion exchange membrane precursor (pAAEM) into contact with an alkaline aqueous solution.

[0016] Surprisingly, it has been found that an alkaline anion exchange membrane (AAEM) can be obtained from the alkaline anion exchange membrane precursor (pAAEM) of the present invention, which exhibits good ionic conductivity, low swelling and high stability towards strongly alkaline aqueous solutions. An alkaline anion exchange membrane (AAEM) having a lower thickness can be obtained from the alkaline anion exchange membrane precursor (pAAEM) of the present invention compared to the separator materials disclosed in the prior art.

[0017] The alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are gas-tight. Thus, by using the alkaline anion exchange membrane (AAEM) in an alkaline water electrolyzer, the migration (gas crossover) of the evolved oxygen and hydrogen can be prevented or at least reduced. This results in a higher efficiency of the electrolysis process and leads to the production of purer hydrogen and oxygen. Furthermore, the alkaline anion exchange membrane (AAEM) of the present invention shows a lower resistance compared to commercially available separator materials such as and is stable at an operating temperature of >100 °C.

[0018] The present invention will be described in more detail below.

[0019] Precursor of alkaline anion exchange membrane (pAAEM)

[0020] The blend (B) comprised in the alkaline anion exchange membrane precursor (pAAEM) comprises at least one first polymer (P1) and at least one second polymer (P2), wherein the first polymer (P1) comprises repeating units derived from acrylonitrile and the second polymer (P2) comprises repeating units derived from vinyl lactam.

[0021] First polymer (P1)

[0022] The term "at least one first polymer (P1)" in the present invention means precisely one first polymer (P1) and also a mixture of two or more different first polymers (P1). Precisely one first polymer (P1) is preferably used.

[0023] The terms "at least one first polymer (P1)" and "first polymer (P1)" in the present invention are used synonymously and are interchangeable throughout the present invention.

[0024] The first polymer (P1) comprises repeating units derived from acrylonitrile. Acrylonitrile is a monomer having the structure H2=CH-CN and having a CAS number of 107-13-1. Polyacrylonitrile is also known as prop-2-enenitrile.

[0025] The carbon-carbon double bond contained in acrylonitrile is capable of undergoing a free radical polymerization reaction. The repeating unit derived from acrylonitrile by free radical polymerization has the following formula:

[0026]

[0027] Based on the total weight of the at least one first polymer (P1) comprised in the blend (B), suitable polymers for use as the at least one first polymer (P1) in the present invention comprise preferably at least 50 wt%, more preferably at least 70 wt%, even more preferably at least 80 wt% and particularly preferably at least 90 wt% of repeating units derived from acrylonitrile.

[0028] Accordingly, another object of the present invention is an alkaline anion exchange membrane precursor (pAAEM), wherein based on the total weight of the at least one first polymer (P1) comprised in the blend (B), the at least one first polymer (P1) comprises at least 50 wt% of repeating units derived from acrylonitrile.

[0029] In a preferred embodiment, suitable first polymers (P1) for use in the present invention are acrylonitrile homopolymers and acrylonitrile copolymers.

[0030] If an acrylonitrile copolymer is used as the first polymer (P1), then based on the total weight of the at least one first polymer (P1) comprised in the blend (B), the first polymer (P1) comprises at least 50 wt%, more preferably at least 70 wt%, even more preferably at least 80 wt% and particularly preferably at least 90 wt% of repeating units derived from acrylonitrile.

[0031] If an acrylonitrile copolymer is used as the first polymer (P1), then the first polymer (P1) comprises repeating units derived from acrylonitrile and one or more, preferably precisely one, repeating unit derived from methyl acrylate, (meth)acrylate and styrene.

[0032] In a preferred embodiment, polyacrylonitrile homopolymer and / or polyacrylonitrile-co-methyl acrylate polymer is used as the first polymer (P1).

[0033] Accordingly, another object of the present invention is an alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 5, wherein the at least one first polymer (P1) is at least one polymer selected from the group consisting of polyacrylonitrile and polyacrylonitrile-co-methyl methacrylate and styrene acrylonitrile, with polyacrylonitrile and polyacrylonitrile-co-methyl methacrylate being particularly preferred.

[0034] The first polymer (P1) preferably has a weight average molecular weight (M w ) in the range of 30,000 g / mol to 1,400,000 g / mol as measured by gel permeation chromatography (GPC), which is measured according to GPC - Part 2: N,N-dimethylacetamide (DMAC) as the eluent (ISO 13885-2:2020); German version EN ISO 13885-2:2021.

[0035] Second polymer (P2)

[0036] The term "at least one second polymer (P2)" in the present invention refers to exactly one second polymer (P2), and also refers to a mixture of two or more different second polymers (P2). Exactly one second polymer (P2) is preferably used.

[0037] The terms "at least one second polymer (P2)" and "second polymer (P2)" in the present invention are used synonymously and are interchangeable throughout the present invention.

[0038] Based on the total weight of the at least one second polymer (P2) contained in the blend (B), the at least one second polymer (P2) preferably contains at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 80% by weight and particularly preferably at least 90% by weight of repeating units derived from at least one monomer of formula (I):

[0039]

[0040] wherein

[0041] n is from 3 to 12;

[0042] m is from 0 to 3;

[0043] R 1 is C1-C 10 -alkyl, C2-C 10 -alkenyl, aryl or aralkyl;

[0044] R 2 、R 3 and R 4 are each independently of one another hydrogen, C1-C10 - alkyl, C2-C 10 - alkenyl, aryl or aralkyl.

[0045] In a preferred embodiment, based on the total weight of the at least one second polymer (P2) comprised in the blend (B), the at least one second polymer (P2) comprises preferably at least 50 wt%, more preferably at least 70 wt%, even more preferably at least 80 wt% and particularly preferably at least 90 wt% of repeating units derived from exactly one monomer of formula (I).

[0046] In a preferred embodiment, the at least one second polymer (P2) comprises repeating units derived from at least one monomer of formula (I), wherein n is from 3 to 5.

[0047] In another preferred embodiment, the at least one second polymer (P2) comprises repeating units derived from at least one monomer of formula (I), wherein m is 0.

[0048] In another preferred embodiment, the at least one second polymer (P2) comprises repeating units derived from at least one monomer of formula (I), wherein R 2 、R 3 and R 4 are each hydrogen.

[0049] In a more preferred embodiment, the at least one second polymer (P2) is at least one monomer selected from the group consisting of N-vinylpyrrolidone (N-vinyl-2-pyrrolidone), N-vinylpiperidone (N-vinyl-2-piperidone) and N-vinylcaprolactam.

[0050] Accordingly, another object of the present invention is an alkaline anion exchange membrane precursor (pAAEM), wherein the at least one second polymer (P2) is at least one polymer selected from the group consisting of polyvinylpyrrolidone, polyvinylpiperidone and polyvinylcaprolactam.

[0051] The at least one second polymer (P2) preferably has a solution viscosity characterized by a K value of from 17 to 100, more preferably from 28 to 95 and particularly preferably from 85 to 92, determined by the method according to Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)).

[0052] In a preferred embodiment, the blend (B) comprised in the alkaline anion exchange membrane precursor (pAAEM) has a glass transition temperature (T of at least 100 °C, more preferably at least 110 °C, even more preferably at least 120 °C and particularly preferably at least 130 °C.g )。

[0053] In another preferred embodiment, the blend (B) comprised in the alkaline anion exchange membrane precursor (pAAEM) has a glass transition temperature (T g ) in the range of 100 °C to 180 °C, more preferably in the range of 110 °C to 170 °C, even more preferably in the range of 120 °C to 165 °C, and particularly preferably in the range of 130 °C to 155 °C.

[0054] The glass transition temperature (T g ) is preferably measured by differential scanning calorimetry (DSC) at a heating rate of 10 K / min according to ISO 11357-1 (2017) and 11357-2 (2020) during the second heating cycle.

[0055] Accordingly, another object of the present invention is an alkaline anion exchange membrane precursor (pAAEM) according to claim 1, wherein the blend (B) has a glass transition temperature of at least 100 °C as measured by differential scanning calorimetry (DSC).

[0056] In a preferred embodiment, based on the total weight of the at least one first polymer (P1) and the at least one second polymer (P2) comprised in the blend (B), preferably based on the total weight of the blend (B), the blend (B) comprised in the alkaline anion exchange membrane precursor (pAAEM) comprises 1 wt% to 50 wt% of the at least one first polymer (P1) and 50 wt% to 99 wt% of the at least one second polymer (P2).

[0057] Accordingly, another object of the present invention is an alkaline anion exchange membrane precursor (pAAEM) according to claim 1 or 2, wherein based on the total weight of the at least one first polymer (P1) and the at least one second polymer (P2) comprised in the blend (B), the blend (B) comprises 1 wt% to 50 wt% of the at least one first polymer (P1) and 50 wt% to 99 wt% of the at least one second polymer (P2).

[0058] In a more preferred embodiment, based on the total weight of the at least one first polymer (P1) and the at least one second polymer (P2) comprised in the blend (B), preferably based on the total weight of the blend (B), the blend (B) comprised in the alkaline anion exchange membrane precursor (pAAEM) comprises 10 wt% to 50 wt% of the at least one first polymer (P1) and 50 wt% to 90 wt% of the at least one second polymer (P2).

[0059] In a particularly preferred embodiment, based on the total weight of the at least one first polymer (P1) and the at least one second polymer (P2) comprised in the blend (B), preferably based on the total weight of the blend (B), the blend (B) comprised in the alkaline anion exchange membrane precursor (pAAEM) comprises 20 wt% to 30 wt% of the at least one first polymer (P1) and 70 wt% to 80 wt% of the at least one second polymer (P2).

[0060] In a preferred embodiment, the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom comprise at least one mechanical support to increase the mechanical stability of the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom.

[0061] Accordingly, another object of the present invention is the alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 7, wherein the alkaline anion exchange membrane precursor (pAAEM) comprises at least one mechanical support.

[0062] The term "at least one mechanical support" in the present invention refers to exactly one mechanical support, and also refers to a mixture of two or more different mechanical supports. Exactly one mechanical support is preferably used.

[0063] The terms "at least one mechanical support" and "mechanical support" in the present invention are used synonymously and are interchangeable throughout the present invention.

[0064] If the alkaline anion exchange membrane precursor (pAAEM) comprises a mechanical support, the mechanical support is preferably covered by the blend (B).

[0065] The mechanical support is preferably a woven fabric or a non-woven fabric.

[0066] Suitable woven fabrics are preferably selected from the group consisting of woven fabrics, woven carbon fiber mats, woven polyacrylonitrile mats, woven polyphenylene sulfide mats, and woven polyolefin fiber mats.

[0067] Preferred woven fabrics are woven polyolefin fiber mats such as woven polyethylene, woven polypropylene fiber mats, woven polyacrylonitrile mats, and / or woven polyphenylene sulfide mats.

[0068] Suitable non-woven fabrics are preferably selected from the group consisting of non-woven carbon fiber mats, non-woven polyacrylonitrile mats, non-woven polyphenylene sulfide, and non-woven polyolefin fiber mats.

[0069] Preferred non-woven fabrics are non-woven polyolefin fiber mats such as non-woven polyethylene, non-woven polypropylene fibers, non-woven polyacrylonitrile mats, and / or non-woven polyphenylene sulfide mats.

[0070] In a preferred embodiment, the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are airtight.

[0071] Thus, another object of the present invention is that the alkaline anion exchange membrane precursor (pAAEM) is airtight.

[0072] The term "airtight" means that no migration (gas crossover) of hydrogen and oxygen through the alkaline anion exchange membrane precursor (pAAEM) or the alkaline anion exchange membrane (AAEM) occurs in the alkaline water electrolyzer.

[0073] In another preferred embodiment, the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are integral.

[0074] In the context of the present invention, the term "integral" means that the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom preferably have no pores.

[0075] In another preferred embodiment, the alkaline anion exchange membrane precursor (pAAEM) has a thickness in the range of 10 μm to 250 μm, preferably in the range of 20 μm to 200 μm, more preferably in the range of 20 μm to 150 μm, and particularly preferably in the range of 20 μm to 100 μm.

[0076] Thus, another object of the present invention is the alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 9, wherein the alkaline anion exchange membrane precursor (pAAEM) has a thickness in the range of 10 μm to 250 μm.

[0077] In another preferred embodiment, the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are in the form of a flat sheet membrane.

[0078] Preparation of precursor of alkaline anion exchange membrane (pAAEM)

[0079] Another object of the present invention is a method for preparing an alkaline anion exchange membrane precursor (pAAEM), which comprises the following steps

[0080] i) Providing a solution (S), including providing a solution (S) containing the at least one first polymer (P1), the at least one second polymer (P2), and at least one polar solvent, and

[0081] ii) Separating the at least one polar solvent from the solution (S) to obtain the alkaline anion exchange membrane precursor (pAAEM).

[0082] In step i), a solution (S) is provided. The solution (S) in step i) can be provided by any method known to those skilled in the art. For example, the solution (S) can be provided in a conventional container in step i), which container may include a stirring device and preferably a temperature control device. Preferably, the solution (S) is provided by dissolving the at least one first polymer (P1) and the at least one second polymer (P2) in the at least one polar solvent.

[0083] Preferably, the at least one first polymer (P1) and the at least one second polymer (P2) are dissolved in the at least one polar solvent under stirring to provide the solution (S).

[0084] Step i) is preferably carried out at an elevated temperature, in particular a temperature in the range of 30 °C to 100 °C, more preferably in the range of 40 °C to 80 °C. Those skilled in the art will select the temperature according to the at least one polar solvent.

[0085] The solution (S) provided in step i) preferably contains the at least one first polymer (P1) and the at least one second polymer (P2) completely dissolved in the at least one polar solvent. This means that the solution (S) preferably does not contain solid particles of the at least one first polymer (P1) and the at least one second polymer (P2). Thus, the at least one first polymer (P1) and the at least one second polymer (P2) preferably cannot be separated from the solution (S) by filtration.

[0086] The solution (S) in step i) preferably contains 40 wt% to 84 wt% of the at least one polar solvent and 60 wt% to 16 wt% of the polymer (i.e., the sum of the weights of the at least one first polymer (P1) and the at least one second polymer (P2)), each based on the total weight of the solution (S).

[0087] The amounts of the at least one first polymer (P1) and the at least one second polymer (P2) in the solution (S) provided in step i) are selected such that the obtained alkaline anion exchange membrane precursor (pAAEM) in step ii) contains a blend (B) having the amounts of the at least one first polymer (P1) and at least one second polymer (P2) as described above for the blend (B).

[0088] As the at least one polar solvent, any polar solvent known to those skilled in the art for the at least one first polymer (P1) and the at least one second polymer (P2) is suitable.

[0089] In a preferred embodiment, the at least one polar solvent is at least one aprotic polar solvent.

[0090] Preferably, the at least one polar solvent is soluble in water. Thus, the at least one solvent is preferably selected from the group consisting of N-alkyl-2-pyrrolidones, preferably N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, and N-tert-butyl-2-pyrrolidone, 2-pyrrolidone, N-dimethylacetamide, dimethyl sulfoxide, dimethylformamide, N,N-dimethyl-2-hydroxypropanamide, N,N-diethyl-2-hydroxypropanamide, γ-valerolactone, dihydrolevoglucosenone, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate, and sulfolane.

[0091] Particularly preferred are N-alkyl-2-pyrrolidones, γ-valerolactone, and N-dimethylacetamide. Most preferred as the at least one polar solvent are N-methylpyrrolidone and N-dimethylacetamide.

[0092] Based on the total weight of the solution (S), the solution (S) preferably comprises the at least one solvent in the range of 40% to 84% by weight, more preferably the at least one polar solvent in the range of 50% to 70% by weight.

[0093] The duration of step i) can vary within a wide range. The duration of step i) is preferably in the range of 10 minutes to 48 hours, particularly in the range of 10 minutes to 24 hours, and more preferably in the range of 15 minutes to 12 hours. Those skilled in the art will select the duration of step i) in order to obtain a homogeneous solution of the at least one first polymer (P1) and the at least one second polymer (P2) in the at least one polar solvent.

[0094] In step ii), the at least one polar solvent (D) is separated from the solution (S) to obtain a precursor of an alkaline anion exchange membrane (pAAEM).

[0095] Before separating the at least one polar solvent from the solution (S) in step ii), the solution (S) provided in step i) can be filtered to obtain a filtered solution (fS).

[0096] The following embodiments and preferences for separating the at least one polar solvent from the solution (S) apply equally to separating the at least one polar solvent from the filtered solution (fS).

[0097] Furthermore, before separating the at least one polar solvent from the solution (S) in step i), the solution (S) provided in step i) can be degassed to obtain a degassed solution (dS). This embodiment is preferred. The following embodiments and preferences for separating the at least one polar solvent from the solution (S) are equally applicable to separating the at least one polar solvent from the degassed solution (dS).

[0098] The degassing of the solution (S) in step i) can be carried out by any method known to those skilled in the art, such as by vacuum, by sonication or by allowing the solution (S) to stand.

[0099] The separation of the at least one polar solvent from the solution (S) can be carried out by any method known to those skilled in the art suitable for separating solvents from polymers.

[0100] Preferably, the at least one polar solvent is separated from the solution (S) via a phase inversion method.

[0101] Therefore, another object of the present invention is also a method for preparing a precursor of an alkaline anion exchange membrane (pAAEM), wherein the separation of the at least one polar solvent in step ii) is carried out via a phase inversion method.

[0102] The phase inversion method in the context of the present invention refers to a method in which at least one dissolved first polymer (P1) and at least one dissolved second polymer (P2) are converted into a solid phase, wherein the solid phase comprises a blend (B).

[0103] Therefore, the phase inversion process can also be represented as a precipitation process. According to step ii), this conversion is carried out by separating the at least one polar solvent from the at least one first polymer (P1) and the at least one second polymer (P2). Those skilled in the art know suitable phase inversion methods.

[0104] The phase inversion process can be carried out, for example, by cooling the solution (S). During this cooling, the at least one first polymer (P1) and the at least one second polymer (P2) contained in the solution (S) precipitate and form a blend (B).

[0105] In a preferred embodiment, step ii) comprises the following steps:

[0106] ii-1) Casting the solution (S) provided in step i) to obtain a membrane of the solution (S),

[0107] ii-2) Separating the at least one polar solvent from the membrane of the solution (S) obtained in step ii-1).

[0108] To obtain a precursor of an alkaline anion exchange membrane (pAAEM) in the form of a film.

[0109] The separation in step ii-2) is preferably carried out by evaporating said at least one polar solvent from the film of the solution (S).

[0110] The evaporation of said at least one solvent is preferably carried out at an elevated temperature in the range of 30 °C to 100 °C under reduced pressure.

[0111] Thus, in a particularly preferred embodiment, step ii) comprises the following steps:

[0112] ii-1) Casting the solution (S) provided in step i) to obtain a film of the solution (S),

[0113] ii-2) Evaporating said at least one polar solvent from the film of the solution (S) obtained in step ii-1),

[0114] To obtain a precursor of an alkaline anion exchange membrane (pAAEM) in the form of a film.

[0115] This means that the precursor of the alkaline anion exchange membrane (pAAEM) is formed by evaporating said at least one polar solvent from the film of the solution (S).

[0116] In step ii-1), the solution (S) can preferably be cast by any method known to those skilled in the art. Generally, the solution (S) is cast using a casting knife, a comma bar, a Meyer rod, a slot die or a reverse roll, which is preferably heated to a temperature in the range of 20 °C to 150 °C, preferably in the range of 40 °C to 100 °C, more preferably in the range of 60 °C to 85 °C.

[0117] In step ii-1), the solution (S) is preferably cast onto a substrate (carrier material) that does not react with said at least one first polymer (P1) and said at least one second polymer (P2) and / or said at least one polar solvent comprised in the solution (S).

[0118] For example, suitable substrates (carrier materials) are steel belts, drying cylinders or polymer films. The substrate (carrier material) is generally not part of the final precursor of the alkaline anion exchange membrane (pAAEM), but is only used for processing purposes.

[0119] The solution (S) can also be cast onto a porous support layer, which becomes part of the precursor of the alkaline anion exchange membrane (pAAEM).

[0120] After step ii), the precursor of the alkaline anion exchange membrane (pAAEM) can be further processed. For example, the precursor of the alkaline anion exchange membrane (pAAEM) can be washed with water.

[0121] Alkaline anion exchange membrane (AAEM)

[0122] Another object of the present invention is an alkaline anion exchange membrane (AAEM) obtained from a precursor of an alkaline anion exchange membrane (pAAEM). For the alkaline anion exchange membrane (AAEM), the explanations and preferred requirements regarding the precursor of the alkaline anion exchange membrane (pAAEM) apply accordingly.

[0123] In a preferred embodiment, the alkaline anion exchange membrane (AAEM) is obtained by contacting the precursor of the alkaline anion exchange membrane (pAAEM) with an alkaline aqueous solution.

[0124] Accordingly, another object of the present invention is an alkaline anion exchange membrane (AAEM) obtained by contacting the precursor of the alkaline anion exchange membrane (pAAEM) with an alkaline aqueous solution.

[0125] In a preferred embodiment, the alkaline anion exchange membrane (AAEM) is obtained by immersing the precursor of the alkaline anion exchange membrane (pAAEM) in an alkaline aqueous solution having a temperature in the range of 20°C to 99°C, more preferably in the range of 50°C to 95°C, for a duration in the range of 1 minute to 10 hours, preferably in the range of 10 minutes to 4 hours.

[0126] The alkaline aqueous solution may contain an alkali metal hydroxide and / or an alkaline earth metal hydroxide. Preferably, the alkaline aqueous solution contains an alkali metal hydroxide. For alkali metal hydroxides, sodium hydroxide (NaOH) and potassium hydroxide (KOH) are particularly preferred. Most preferably, it is potassium hydroxide (KOH).

[0127] The concentration of the alkali metal hydroxide aqueous solution is preferably in the range of 1 mol / l to 10 mol / l, preferably in the range of 4 mol / l to 8 mol / l.

[0128] If an alkaline aqueous solution containing potassium hydroxide (KOH) is used, the concentration of the solution is preferably in the range of 15 wt% to 40 wt%, more preferably in the range of 15 wt% to 35 wt%.

[0129] Accordingly, another object of the present invention is a method for preparing an alkaline anion exchange membrane (AAEM), which includes the step of contacting a precursor of the anion exchange membrane (pAAEM) with an alkaline aqueous solution.

[0130] In a preferred embodiment, the alkaline anion exchange membrane (AAEM) has a specific resistance of less than 0.2 Ω·cm in a 6 M potassium hydroxide solution at a temperature of 20°C. The membrane is sandwiched between two areas of 0.25 cm 2 and 2Between the gold electrodes. The cell was sealed with a torque of 4 Nm, and the conductivity was extracted from the impedance spectrum at a phase angle of 0 degrees. The membrane was measured after being immersed in an aqueous KOH solution of 20 wt% or 30 wt% overnight at room temperature. The membrane could be directly taken out of the KOH solution for measurement, or measured after post-treatment by immersing or dipping the membrane in DI water. The conductivity was determined from the area specific resistance measured by this method and the thickness measured with a micrometer.

[0131] Another object of the present invention is the use of an alkaline anion exchange membrane (AAEM) in an alkaline water electrolyzer.

[0132] Another object of the present invention is a method for producing hydrogen using an alkaline anion exchange membrane (AAEM).

[0133] The present invention is illustrated more specifically by the following examples, but is not limited thereto. Examples

[0134] Components used :

[0135] First polymer (P1) :

[0136] P1a: Polyacrylonitrile homopolymer with a weight average molecular weight (Mw) of 200,000 g / mol ( H-PAN; from Dolan GmbH)

[0137] P1b: Polyacrylonitrile-co-methyl acrylate polymer with a weight average molecular weight (Mw) of 80,000 g / mol ( N-PAN; from Dolan GmbH)

[0138] Second polymer (P2) :

[0139] P2a: Polyvinylpyrrolidone, with a molecular weight M w ranging from 1,000,000 g / mol to 1,500,000 g / mol, and the solution viscosity characterized by a K value of 90 determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) (abbreviated as "K90" (from BASF SE K90)

[0140] Comparative diaphragms and comparative membrane materials :

[0141] A diaphragm comprising polyphenylene sulfide coated with zirconia (from Agfa Gevert NV, Mortel, Belgium UTP500 diaphragm)

[0142] P1v: Polyethersulfone with a glass transition temperature (DSC, 10 °C / min; according to ISO 11357-1 / -2) of 225 °C and a weight average molecular weight (Mw) of 75,000 g / mol (E 6020P from BASF SE)

[0143] Preparation of alkaline anion exchange membrane (AAEM) :

[0144] General procedure

[0145] Prepare a polymer solution for membrane preparation, which contains 5 wt% of a first polymer (P1a, P1b or P1v) and 15 wt% of a second polymer (P2a) dissolved in 80 wt% of N-methyl-2-pyrrolidone (NMP). In a SpeedMixer TM DAC 600.1Vac-P (Hauschild & Co. KG, Hamm, Germany), homogenize the polymer solution at speeds of 200 rpm, 800 rpm and 1200 rpm for a mixing time of 30 minutes. Before membrane casting, characterize the polymer solution by dynamic viscosity measurement results (Brookfield DI-prime, RV6 spindle, 20 rpm, 60 °C).

[0146] To prepare a flat-sheet alkaline anion exchange membrane precursor (pAAEM), spread the polymer solution at 5 mm / s (0.3 m / min) on a glass support to a thickness of 300 μm with a casting knife (Coatmaster510, Erichsen GmbH & Co. KG, Hemer, Germany) at 60 °C, and then dry it under vacuum at 50 °C. Then, transfer the membrane to a water bath and store it in water after detaching the membrane from the glass plate.

[0147] To prepare an alkaline anion exchange membrane (AAEM), immerse the alkaline anion exchange membrane precursor (pAAEM) in a 30 wt% aqueous potassium hydroxide solution.

[0148] Measure the membrane thicknesses of the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) using a Mitutoyo ID-C112XB (Mitutoyo Corporation, Kawasaki, Japan).

[0149] After storing in a 30 wt% aqueous potassium hydroxide solution at 80 °C for 14 days, measure the resistance (EIS: [Ω]), conductivity (C: [mS / cm]) and specific resistance (R: [Ω cm 2 )). The results are shown in Table 2.​

[0150] Table 1 shows the viscosity of the polymer solution before casting, the membrane thickness of the alkaline anion exchange membrane precursor (pAAEM), and the alkaline stability.

[0151] Table 1 :

[0152]

[0153] Table 2 :

[0154]

[0155] Compared with commercially available separator materials such as UTP500, the alkaline anion exchange membrane (AAEM) according to the present invention shows significantly lower resistance.

[0156] The scanning electron microscope SEM cross-section (5000x magnification) of the pAAEM membrane from Example 1 is shown in Figure 1 in.

Claims

1. An alkaline anion exchange membrane precursor (pAAEM) comprising a blend (B) of at least one first polymer (P1) and at least one second polymer (P2), wherein the first polymer (P1) comprises repeating units derived from acrylonitrile and the second polymer (P2) comprises repeating units derived from vinyl lactam.

2. The alkaline anion exchange membrane precursor (pAAEM) according to claim 1, wherein the blend (B) has a glass transition temperature of at least 100 °C measured by differential scanning calorimetry (DSC) at a heating rate of 10 K / min in a second heating cycle according to ISO 11357-1 (2017) and 11357-2 (2020).

3. The alkaline anion exchange membrane precursor (pAAEM) according to claim 1 or 2, wherein based on the total weight of the at least one first polymer (P1) and the at least one second polymer (P2) comprised in the blend (B), the blend (B) comprises 1 wt% to 50 wt% of the at least one first polymer (P1) and 50 wt% to 99 wt% of the at least one second polymer (P2).

4. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 3, wherein based on the total weight of the at least one first polymer (P1) comprised in the blend (B), the at least one first polymer (P1) comprises at least 50 wt% of repeating units derived from acrylonitrile.

5. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 4, wherein based on the total weight of the at least one second polymer (P2) comprised in the blend (B), the at least one second polymer (P2) comprises at least 50 wt% of repeating units derived from at least one monomer of formula (I): wherein n is from 3 to 12; m is from 0 to 3; R 1 is C1-C 10 -alkyl, C2-C 10 -alkenyl, aryl or aralkyl; R 2 、 R 3 and R 4 are each independently hydrogen, C1-C 10 -alkyl, C2-C 10 -alkenyl, aryl or aralkyl.

6. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 5, wherein the at least one first polymer (P1) is at least one polymer selected from the group consisting of polyacrylonitrile and polyacrylonitrile-co-methyl acrylate.

7. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 6, wherein the at least one second polymer (P2) is at least one polymer selected from the group consisting of polyvinylpyrrolidone, polyvinylpiperidone, and polyvinylcaprolactam.

8. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 7, wherein the alkaline anion exchange membrane precursor (pAAEM) comprises at least one mechanical support.

9. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 8, wherein the alkaline anion exchange membrane precursor (pAAEM) is airtight.

10. The alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 9, wherein the alkaline anion exchange membrane precursor (pAAEM) has a thickness in the range of 10 μm to 250 μm.

11. A method for preparing the alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 10, comprising the following steps i) providing a solution (S) comprising the at least one first polymer (P1), the at least one second polymer (P2) and at least one polar solvent, and ii) separating the at least one polar solvent from the solution (S) to obtain the alkaline anion exchange membrane precursor (pAAEM).

12. An alkaline anion exchange membrane (AAEM) obtained by contacting the alkaline anion exchange membrane precursor (pAAEM) according to any one of claims 1 to 10 with an alkaline aqueous solution.

13. The alkaline anion exchange membrane (AAEM) according to claim 12, wherein the alkaline anion exchange membrane (AAEM) has a specific resistance of less than 0.2 Ωcm in a 6 M potassium hydroxide solution at a temperature of 20 °C 2 .

14. An alkaline water electrolyzer comprising the alkaline anion exchange membrane (AAEM) according to claim 12 or 13.

15. A method for producing hydrogen using the alkaline anion exchange membrane (AAEM) according to claim 12 or 13.

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