Alkaline anion exchange blend membrane

Abstract

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

Description

[0001] Alkaline anion exchange blend membrane

[0002] Description

[0003] The present invention relates to an alkaline anion exchange membrane precursor (pAAEM) comprising a blend of at least one first polymer (P1) comprising repeating units derived from acrylonitrile and at least one second polymer (P2) comprising repeating units derived from a vinyl lactam, and an alkaline anion exchange membrane (AAEM) obtained therefrom.

[0004] The present invention, moreover, relates to a process for the preparation of the alkaline anion exchange membrane precursor (pAAEM), a process for the preparation of an alkaline anion exchange membrane (AAEM), an alkaline water electrolysis cell comprising the alkaline anion exchange membrane (AAEM), the use of the alkaline anion exchange membrane (AAEM) in an alkaline water electrolysis cell and a process for the preparation of hydrogen using the alkaline exchange membrane (AAEM).

[0005] Politics, society, and industry aim to reduce the CO2 emissions by decarbonizing industry and mobility. In this context, green hydrogen places a strategic role as it can substitute hydrocarbons for chemical and industrial processes, energy transformation and fuel cell propulsion in mobility applications.

[0006] Moreover, with the growing share from renewable sources the German energy system is changing fundamentally. According to the 2010 Energy Concept the Federal Government has set the goal to reduce greenhouse emissions in 2050 by at least 80 % compared to the year 1990. Also, in 2050 the gross final energy consumption should be supplied by 60 % on the basis of 1990 by renewable energies. For the first years the implementation of the 2010 Energy Concept requires an increasing share of renewable energies of the total energy production, but once a significant portion is supplied by renewable sources, technical solutions are required for intermediate storage of solar, wind or water energy.

[0007] Power-to-Gas (P2G) as system solution allows conversion of electricity to hydrogen or methane for usage in a variety of areas such as mobility, industrial, heat supply and electricity generation applications.

[0008] The key element for the P2G system is the water electrolyser which exists either as alkaline or proton exchange membrane electrolyser system. Today most commercial electrolysers are based on alkaline electrolysis with 30 wt% aqueous KOH electrolytes (conductivity of 1.5 S / cm at 80 °C) which can operate at current densities in the range from 1000 to 3000 A / m2. However, technically current densities <1000 A / m2are standard due to reduced efficiencies at high current densities. Porous diaphragms are used to separate evolving oxygen and hydrogen gases but also to prevent mixing of catholyte and anolyte in order to obtain high gas purities and high current efficiencies.

[0009] As diaphragm material asbestos is widely used up to temperatures of 100 °C. Also, polyantimonic acid, nickel oxide, polyphenylene sulfide (Ryton®), and polyphenylene sulfide I zirconium oxide (Zirfon®) are known as modern diaphragm materials.

[0010] The diaphragm materials described in the state of the art have thicknesses around 500 pm. They show good stability against alkaline aqueous solutions. A draw-back of the diaphragm materials used in the state of the art is that they are not gastight. By consequent, the evolving gases oxygen and hydrogen can migrate through the diaphragm material which leads to a decrease of efficiency of the electrolysis process. Moreover, the diaphragm materials are quite expensive.

[0011] Another approach recently disclosed in the state of the art is the use of alkaline anion exchange membranes in alkaline water electrolysis cells for the preparation of 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.

[0013] 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 document already show quite good properties. However, the long-term stability in view of strong alkaline aqueous solutions is not sufficient in all cases. Therefore, there is still room for improvement.

[0014] It is therefore an object of the present invention to provide in 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 in diminished 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 the use in alkaline aqueous electrolysis cells. The alkaline anion exchange membrane (AAEM), moreover, should be suitable for the preparation of hydrogen and oxygen in an alkaline aqueous electrolysis cell.

[0015] This object is achieved by an alkaline anion exchange membrane precursor (pAAEM) comprising a blend (B) of at least one first polymer (P1) comprising repeating units derived from acrylonitrile and at least one second polymer (P2) comprising repeating units derived from a vinyl lactam.

[0016] The object, moreover, is achieved by an alkaline anion exchange membrane (AAEM) obtained by contacting the alkaline anion exchange membrane precursor (pAAEM) with an alkaline aqueous solution.

[0017] It has surprisingly been found, that from the inventive alkaline anion exchange membrane precursor (pAAEM) an alkaline anion exchange membrane (AAEM) can be obtained, showing good ion conductivity, low swelling, and high stability against strong alkaline aqueous solutions. From the inventive alkaline anion exchange membrane precursor (pAAEM) alkaline anion exchange membranes (AAEM) can be obtained having lower thicknesses compared to the diaphragm materials disclosed in the state of the art.

[0018] The alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are gastight. Therefore, by the use of the alkaline anion exchange membrane (AAEM) in an alkaline aqueous electrolysis cell the migration (gas crossover) of the evolving gases oxygen and hydrogen is prevented or at least diminished. This leads to a higher efficiency of the electrolysis process and to the preparation of purer gases hydrogen and oxygen. The inventive alkaline anion exchange membranes (AAEM), moreover show a lower resistance compared to commercially available diaphragm materials, like Zirfon®, and is stable at operation temperatures of > 100 °C.

[0019] The present invention will be described in more detail hereinafter.

[0020] Alkaline anion exchange membrane precursor (pAAEM)

[0021] The blend (B) contained in the alkaline anion exchange membrane precursor (pAAEM) comprises at least one first polymer (P1) comprising repeating units derive from acrylonitrile and at least one second polymer (P2) comprising repeating units derive from a vinyl lactam.

[0022] First polymer (P1)

[0023] The wording “at least one first polymer (P1)” in the present invention means precisely one first polymer (P1) and also mixtures of two or more different first polymers (P1). Preferably precisely one first polymer (P1) is used. The terms “at least one first polymer (P1)” and “first polymer (P1)” in the present invention are used synonymously and are used interchangeably 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 the CAS-number 107-13-1. Polyacrylonnitrile is also called prop-2-enenitrile.

[0025] The carbon-carbon-double bond contained in the acrylonitrile is capable to react by free radical polymerization. The repeating units derived from acrylonitrile by free radical polymerization have the following formula:

[0026] Suitable polymers which can be used as the at least one first polymer (P1) in the present invention comprise preferably at least 50 % by weight, more preferably at least 70 % by weight, even more preferred at least 80 % by weight and particularly preferred at least 90 % by weight of repeating units derived from acrylonitrile, based on the total weight of the at least one first polymer (P1) comprised in the blend (B).

[0027] Another object of the present invention, therefore, is an alkaline anion exchange membrane precursor (pAAEM), wherein the at least one first polymer (P1) comprises, based on the total weight of the at least one first polymer (P1) comprised in the blend (B), at least 50 % by weight of repeating unites derived from acrylonitrile

[0028] Suitable first polymers (P1) which can be used in the present invention in a preferred embodiment are acrylonitrile-homo-polymers and acrylonitrile-co-polymers.

[0029] If an acrylonitrile-co-polymer is used as a first polymer (P1) the first polymer (P1) comprises at least 50 % by weight, more preferably at least 70 % by weight, even more preferred at least 80 % by weight and particularly preferred at least 90 % by weight of repeating units derived from acrylonitrile, based on the total weight of the at least one first polymer (P1) comprised in the blend (B).

[0030] If an acrylonitrile-co-polymer is used as a first polymer (P1) the first polymer (P1) comprises repeating units derived from acrylonitrile and one or more, preferably precisely one, repeating units derived from acrylicacidmethylester, (meth)acrylicacidmethylester and styrene. In a preferred embodiment a polyacrylonitrile-homo-polymer and / or a polyacrylonitrile-co-polyacrylicacidmethylester polymer is used as a first polymer (P1).

[0031] Another object of the present invention, therefore, is alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 5, wherein the at least on first polymer (P1) is at least one polymer selected from the group consisting of polyacrylonitrile and polyacrylonitrile-co-polyacrylicacidmethylester and polystyreneacrylonitrile, wherein polyacrylonitrile and polyacrylonitrile-co- polyacrylicacidmethylester are especially preferred.

[0032] The first polymer (P1) preferably has a weight average molecular weight (Mw) in the range of 30 000 to 1 400 000 g / mol measured by gel permeations chromatography (GPC) measured according to GPC Part 2: N,N-Dimenthylacetamide (DMAC) as eluent (ISO 13885-2:2020); German version EN ISO 13885-2:2021.

[0033] Second polymer (P2)

[0034] The wording “at least one second polymer (P2)” in the present invention means precisely one second polymer (P2) and also mixtures of two or more different second polymers (P2). Preferably precisely one second polymer (P2) is used.

[0035] The terms “at least one second polymer (P2)” and “second polymer (P2)” in the present invention are used synonymously and are used interchangeably throughout the present invention.

[0036] The at least one second polymer (P2) comprises, based on the total weight of the at least one second polymer (P2) comprised in the blend (B), preferably at least 50 % by weight, more preferably at least 70 % by weight, even more preferred at least 80 % by weight and particularly preferred at least 90 % by weight of repeating units derived from at least one monomer of the formula (I): where n is 3 to 12; m is 0 to 3;

[0037] R1is Ci- Ci o- alkyl, C2-Cio-alkenyl, aryl or aralkyl;

[0038] R2, R3and R4are each, independently of one another, hydrogen, Ci— Ci o— alkyl, C2-C -alkenyl, aryl or aralkyl.

[0039] In a preferred embodiment the at least one second polymer (P2) comprises, based on the total weight of the at least one second polymer (P2) comprised in the blend (B), preferably at least 50 % by weight, more preferably at least 70 % by weight, even more preferred at least 80 % by weight and particularly preferred at least 90 % by weight of repeating units derived from precisely one monomer of the formula (I).

[0040] In a preferred embodiment the at least one second polymer (P2) comprises repeating units derived from at least one monomer of the formula (I) where n is 3 to 5.

[0041] In another preferred embodiment the at least one second polymer (P2) comprises repeating units derived from at least one monomer of the formula (I) where m is 0.

[0042] In another preferred embodiment the at least one second polymer (P2) comprises repeating units derived from at least one monomer of the formula (I) where R2, R3and R4are each hydrogen.

[0043] 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-vinylcaprolactame.

[0044] Another object of the present invention, therefore, is an alkaline anion exchange membrane precursor (pAAEM), wherein the at least one second polymer (P2) is at least one polymer selected form the group consisting of polyvinylpyrrolidone, polyvinylpiperidone and polyvinylcaprolactame.

[0045] The at least one second polymer (P2) preferably has a a solution viscosity characterized by the K-value of 17 to 100, more preferred of 28 to 95 and especially preferred of 85 to 92 determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)).

[0046] In a preferred embodiment the blend (B), contained in the alkaline anion exchange membrane precursor (pAAEM), has a glass transition temperature (Tg) of at least 100 °C, more preferred of at least 110 °C, even more preferred of at least 120 °C and particularly preferred of at least 130 °C.

[0047] In another preferred embodiment the blend (B), contained in the alkaline anion exchange membrane precursor (pAAEM), has a glass transition temperature (Tg) in the range of at 100 °C to 180 °C, more preferred in the range of 110 to 170 °C, even more preferred in the range of 120 to 165 °C and particularly preferred in the range of 130 to 155 °C.

[0048] The glass transition temperature (Tg) preferably is measured at the second heating cycle by differential scanning calorimetry (DSC) according to ISO 11357-1 (2017) and 11357-2 (2020) at a heating rate of 10 K / min.

[0049] Another object of the present invention, therefore, is an alkaline anion exchange membrane precursor (pAAEM) according to claim 1, wherein the blend (B) has a glass transition temperature measured by differential scanning calorimetry (DSC) of at least 100 °C.

[0050] In a preferred embodiment the blend (B), contained in the alkaline anion exchange membrane precursor (pAAEM), comprises from 1 to 50 % by weight of the at least one first polymer (P1) and from 50 to 99 % by weight of the at least on second polymer (P2) 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).

[0051] Another object of the present invention, therefore, is an alkaline anion exchange membrane precursor (pAAEM) according to claim 1 or 2, wherein the blend (B) comprises from 1 to 50 % by weight of the at least one first polymer (P1) and from 50 to 99 % by weight of the at least on second polymer (P2) 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)

[0052] In a more preferred embodiment the blend (B), contained in the alkaline anion exchange membrane precursor (pAAEM), comprises from 10 to 50 % by weight of the at least one first polymer (P1) and from 50 to 90 % by weight of the at least on second polymer (P2) 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).

[0053] In a particularly preferred embodiment the blend (B), contained in the alkaline anion exchange membrane precursor (pAAEM), comprises from 20 to 30 % by weight of the at least one first polymer (P1 ) and from 70 to 80 % by weight of the at least on second polymer (P2) 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). 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.

[0054] Another object of the present invention, therefore, is alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 7, wherein the alkaline anion exchange membrane precursor (pAAEM) comprises at least one mechanical support.

[0055] The wording “at least one mechanical support” in the present invention means precisely one mechanical support and also mixtures of two or more different mechanical supports. Preferably precisely one mechanical support is used.

[0056] The terms “at least one mechanical support” and “mechanical support” in the present invention are used synonymously and are used interchangeably throughout the present invention.

[0057] If the alkaline anion exchange membrane precursor (pAAEM) comprises a mechanical support, the mechanical support is preferably covered with the blend (B).

[0058] The mechanical support is preferably a woven or a non-woven.

[0059] Suitable woven are preferably selected from the group consisting of woven, woven carbon fibre mats, woven polyacrylonitrile mats, woven polyphenylenesulfide mats and woven polyolefin fibre mats.

[0060] Preferred woven are woven polyolefin fibre mats like woven polyethylene, woven polypropylene fibre mats woven polyacrylonitrile mats and / or woven polyphenylenesulfide mats.

[0061] Suitable non-woven are preferably selected from the group consisting of non-woven carbon fibre mats, non-woven polyacrylonitrile mats, non-woven polyphenylenesulfide and non-woven polyolefin fibre mats.

[0062] Preferred non-woven are non-woven polyolefin fibre mats like non-woven polyethylene, non-woven polypropylene fibre non-woven polyacrylonitrile mats and / or non-woven polyphenylenesulfide mats.

[0063] In a preferred embodiment the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are gastight. Another object of the present invention, therefore, is the alkaline anion exchange membrane precursor (pAAEM) is gastight.

[0064] The term “gastight” means that no migration (gas crossover) of the gases hydrogen and oxygen through the alkaline anion exchange membrane precursor (pAAEM) or the alkaline anion exchange membrane (AAEM) in an alkaline aqueous electrolysis cell occurs.

[0065] In another preferred embodiment the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom are monolithic.

[0066] In the context of the present invention, the term “monolithic” means that the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane (AAEM) obtained therefrom preferably have no pores.

[0067] In another preferred embodiment the alkaline anion exchange membrane precursor (pAAEM) has a thickness in the range of 10 to 250 pm, preferably in the range of 20 to 200 pm, more preferred in the range of 20 to 150 pm, and particularly preferred in the range of 20 to 100 pm.

[0068] Another object of the present invention, therefore, is alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 9, wherein the alkaline anion exchange membrane precursor (pAAEM) has a thickness in the range of 10 to 250 pm.

[0069] In another preferred embodiment the alkaline anion exchange membrane precursor (pAAEM) and the alkaline anion exchange membrane precursor (AAEM) obtained therefrom have the form of a flat sheet membrane.

[0070] Preparation of the alkaline anion exchange membrane precursor (pAAEM)

[0071] Another object of the present invention is a process for the preparation of the alkaline anion exchange membrane precursor (pAAEM) comprising the steps i) providing a solution (S) comprising providing a solution (S) comprising the at least one first polymer (P1 ), the at least one second polymer (P2), and at least on polar solvent, and ii) separating the at least one polar solvent from the solution (S) to obtain the alkaline anion exchange membrane precursor (pAAEM). In step i) a solution (S) is provided. The solution (S) in step i) can be provided by any method known to the skilled person. For example, the solution (S) can be provided in step i) in customary vessels that may comprise 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.

[0072] The dissolution of the at least one first polymer (P1) and the at least one second polymer (P2) in the at least one polar solvent to provide the solution (S) is preferably effected under agitation.

[0073] Step i) is preferably carried out at elevated temperatures, especially in the range from 30 to 100 °C, more preferably in the range from 40 to 80 °C. A person skilled in the art will choose the temperature in accordance with the at least one polar solvent.

[0074] The solution (S) provided in step i) preferably comprises 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 comprises no solid particles of the at least one first polymer (P1) and the at least one second polymer (P2). Therefore, 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.

[0075] The solution (S) in step i) preferably comprises from 40 to 84 % by weight of the at least one polar solvent, and from 60 to 16 % by weight of polymers (i.e. the sum of weight 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).

[0076] 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 chosen in such a way that the the alkaline anion exchange membrane precursor (pAAEM) obtained in step ii) comprises a blend (B) having the above-described amounts of the at least one first polymer (P1) and the at least one second polymer (P2) in view of the blend (B).

[0077] As the at least one polar solvent, any polar solvent known to the skilled person for the at least one first polymer (P1) and the at least one second polymer (P2) is suitable.

[0078] In a preferred embodiment the at least on polar solvent is at least one aprotic polar solvent.

[0079] Preferably, the at least one polar solvent is soluble in water. Therefore, the at least one solvent is preferably selected from the group consisting of N-alkyl-2-pyrrolidone, preferably N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone and N- tert.-butyl-2-pyrrolidone, 2-pyrrolidone, N-dimethylacetamide, dimethylsulfoxide, dimethylformamide, N,N-dimethyl-2-hydroxypropan amide, N,N-diethyl-2- hydroxypropan amide, y-valerolactone, dihydrolevoglucosenone, methyl 5- (dimethylamino)-2-methyl-5-oxopentanoate and sulfolane.

[0080] N-alkyl-2-pyrrolidone, y-valerolactone and N-dimethylacetamide are particularly preferred. N-methylpyrrolidone and N-dimethylacetamide are most preferred as the at least one polar solvent.

[0081] The solution (S) preferably comprises in the range from 40 to 84% by weight of the at least one solvent, more preferred in the range from 50 to 70% by weight of the at least one polar solvent, based on the total weight of the solution (S).

[0082] The duration of step i) may vary between wide limits. The duration of step i) is preferably in the range from 10 min to 48 h (hours), especially in the range from 10 min to 24 h, and more preferably in the range from 15 min to 12 h. A person skilled in the art will choose the duration of step i) so as 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.

[0083] In step ii), the at least one polar solvent (D) is separated from the solution (S) to obtain the alkaline anion exchange membrane precursor (pAAEM).

[0084] It is possible to filter the solution (S) provided in step i) before the at least one polar solvent is separated from the solution (S) in step ii) to obtain a filtered solution (fS).

[0085] The following embodiments and preferences for separating the at least one polar solvent from the solution (S) apply equally for separating the at least one polar solvent from the filtered solution (fS).

[0086] Moreover, it is possible to degas the solution (S) provided in step i) before the at least one polar solvent is separated from the solution (S) in step i) 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) apply equally for separating the at least one polar solvent from the degassed solution (dS).

[0087] The degassing of the solution (S) in step i) can be carried out by any method known to the skilled person, for example, via vacuum, via ultrasonic treatment, or by allowing the solution (S) to rest. The separation of the at least one polar solvent from the solution (S) can be performed by any method known to the skilled person which is suitable to separate solvents from polymers.

[0088] Preferably, the separation of the at least one polar solvent from the solution (S) is carried out via a phase inversion process.

[0089] Another object of the present invention is therefore also a process for the preparation of an alkaline anion exchange membrane precursor (pAAEM), wherein the separation of the at least one polar solvent in step ii) is carried out via a phase inversion process.

[0090] A phase inversion process within the context of the present invention means a process wherein the dissolved at least one first polymer (P1) and the dissolved at least one second polymer (P2) are transformed into a solid phase, wherein the soldi phase comprises the blend (B).

[0091] Therefore, a phase inversion process can also be denoted as precipitation process. According to step ii), the transformation is performed by separation of the at least one polar solvent from the at least one first polymer (P1) and the at least one second polymer (P2). The person skilled in the art knows suitable phase inversion processes.

[0092] The phase inversion process can, for example, be performed by cooling down the solution (S). During this cooling down, the at least one first polymer (P1) and the at least one second polymer (P2) comprised in the solution (S) precipitate and the blend (B) is formed.

[0093] In a preferred embodiment step ii) comprise the following steps: ii-1) casting the solution (S) provided in step i) to obtain a film of the solution (S), ii-2) separating the at least one polar solvent from the film of the solution (S) obtained in step ii-1) to obtain the alkaline anion exchange membrane precursor (pAAEM) which is in the form of a film.

[0094] The separating in step ii-2) is preferably carried out by evaporating the at least one polar solvent from a film of the solution (S).

[0095] The evaporating of the at least one solvent is preferably carried out under reduced pressure under elevated temperatures in the range of 30 to 100 °C.

[0096] Therefore, in a particularly preferred embodiment, step ii) comprise the following steps: ii-1) casting the solution (S) provided in step i) to obtain a film of the solution (S), ii-2) evaporating the at least one polar solvent from the film of the solution (S) obtained in step ii-1) to obtain the alkaline anion exchange membrane precursor (pAAEM) which is in the form of a film.

[0097] This means that the alkaline anion exchange membrane precursor (pAAEM) is formed by evaporating the at least one polar solvent from a film of the solution (S).

[0098] In step ii-1), the solution (S) can be preferably cast by any method known to the skilled person. Usually, the solution (S) is cast with a casting knife, a coma bar, a meyer bar, a slot die or a reverse roll which are preferably heated to a temperature in the range from 20 to 150 °C, preferably in the range from 40 to 100°C, more preferably between 60 and 85°C.

[0099] In step ii-1) the solution (S) is preferably cast on a substrate (carrier material) that does not react with at least one first polymer (P1) and the at least one second polymer (P2) and / or the at least one polar solvent comprised in the solution (S).

[0100] Suitable substrates (carrier materials) are for example steel belts, drying cylinders or polymer films. The substrates (carrier materials) are generally not part of the finished alkaline anion exchange membrane precursor (pAAEM) but are only used for processing purpose.

[0101] It is also possible to cast the solution (S) on a porous support layer which becomes part of the alkaline anion exchange membrane precursor (pAAEM).

[0102] After step ii) the alkaline anion exchange membrane precursor (pAAEM) can be further processed. The alkaline anion exchange membrane precursor (pAAEM) can for example be washed with water.

[0103] Alkaline anion exchange membrane (AAEM)

[0104] Another object of the present invention is an alkaline anion exchange membrane (AAEM) obtained from the alkaline anion exchange membrane precursor (pAAEM). For the alkaline anion exchange membrane (AAEM) the explanations and preferences in view of the alkaline anion exchange membrane precursor (pAAEM) apply accordingly. In a preferred embodiment the alkaline anion exchange membrane (AAEM) is obtained by contacting the alkaline anion exchange membrane precursor (pAAEM) with an alkaline aqueous solution.

[0105] Another object of the present invention, therefore, is an alkaline anion exchange membrane (AAEM) obtained by contacting the alkaline anion exchange membrane precursor (pAAEM) with an alkaline aqueous solution.

[0106] In a preferred embodiment the alkaline anion exchange membrane (AAEM) is obtained from the alkaline anion exchange membrane precursor (pAAEM) by immersing in an aqueous alkaline solution having a temperature in the range of 20 to 99 °C, more preferred in the range of 50 to 95 °C for duration of 1 minute to 10 hours, preferably in the range of 10 minutes to 4 hours.

[0107] The alkaline aqueous solution can comprise alkali metal hydroxides and / or earth alkali hydroxides. Preferably, the alkaline aqueous solution comprises alkali hydroxides. Under the alkali hydroxides sodium hydroxide (NaOH) and potassium hydroxide (KOH) are especially preferred. Most preferred is potassium hydroxide (KOH).

[0108] The concentration of the alkali hydroxide aqueous solution is preferably in the range of 1 to 10 mol / l, preferably in the range of 4 to 8 mol / l.

[0109] If in alkaline aqueous solution comprising potassium hydroxide (KOH) is used the concentration of this solution is preferably in the range of 15 to 40 % by weight, more preferably in the range of 15 to 35 % by weight.

[0110] Another object of the present invention is therefore a process for the preparation of an alkaline anion exchange membrane (AAEM) comprising the steps of contacting the anion exchange membrane precursor (pAAEM) with an alkaline aqueous solution.

[0111] In a preferred embodiment the alkaline anion exchange membrane (AAEM) has a specific resistance of less than 0.2 ohm cm2at a temperature of 20 °C in a 6 M potassium hydroxide solution. The membranes were sandwiched between two gold electrodes of 0.25 cm2area. The cell was closed with a torque of 4 Nm and the conductivity was extracted from the impedance spectrum at 0-degree phase angle. Membranes were measured after impregnation of the film either in 20 or 30 wt% aqueous KOH solution over night at room temperature either directly out of the KOH solution or post treated by dipping or immersion in DI water. Conductivity was determined from the area specific resistance as determined by this method and the thickness as measured with a micrometer. Another object of the present invention is the use of the alkaline anion exchange membrane (AAEM) in an alkaline water electrolysis cell.

[0112] Another object of the present invention is a process for the preparation of hydrogen using the alkaline anion exchange membrane (AAEM).

[0113] The present invention is more particularly elucidated by the following examples without being restricted thereto.

[0114] Examples:

[0115] Components used:

[0116] First polymer (P1 ):

[0117] P1a: polyacrylonitrile-homo-polymer with a weight average molecular weight (Mw) of 200 000 g / mol (Dolanit®H-PAN; from Dolan GmbH)

[0118] P1b: polyacrylonitrile-co-polyacrylicacidmethylester polymer with a weight average molecular weight (Mw) of 80 000 g / mol (Dolanit®N-PAN; from Dolan GmbH)

[0119] Second polymer (P2):

[0120] P2a: Polyvinylpyrrolidone with a molecular weight Mwof 1000000 to 1500000 g / mol and a solution viscosity characterized by the K-value of 90, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)), which is abbreviated as “K90” (Luvitec®K90 from BASF SE)

[0121] Comparative Diaphragm and comparative membrane materials:

[0122] Diaphragm comprising poylpenylene sulfide coated with zirconium dioxide (Zirfon® LITP500 diaphragma from Agfa Gevert NV, Mortsel, Belgium

[0123] P1v: polyethersulfone with a glass transition temperature (DSC, 10°C / min; according to ISO 11357-1 / -2) of 225 °Cand a weight average molecular weight (Mw) of 75 000 g / mol (Ultrason®E 6020 P from BASF SE)

[0124] Preparation of the alkaline anion exchange membrane (AAEM):

[0125] General procedure

[0126] Polymer solutions for the membrane preparation where prepared comprising 5 % by weight of the first polymer (P1a, P1b or P1v), and 15 % by weight of the second polymer (P2a) dissolved in 80 % by weight of N-methyl-2-pyrrolidone (NMP). The polymer solutions were homogenized is a Speed Mixer™ DAC 600.1 Vac-P (Hauschild & Co. KG, Hamm, Germany) at speeds of 200, 800 and 1200 rpm within 30 min of mixing time. Prior to membrane casting the polymer solutions were characterized by dynamic viscosity measurements (Brookfield Dl-prime, RV6 spindle, 20 rpm, 60°C).

[0127] For preparing flat sheet alkaline anion exchange membrane precursors (pAAEM) the polymer solutions was spread with 300 pm with 5 mm / s (0.3 m / min) at 60 °C on a glass support by the means of a casting knife (Coatmaster 510, Erichsen GmbH & Co. KG, Hemer, Germany) and subsequently dried under vacuum at 50 °C. Then, the film was transferred to a water bath and after the film had detached from the glass plate stored in water.

[0128] For the preparation of the alkaline anion exchange membranes (AAEM) the alkaline anion exchange membrane precursors (pAAEM) were immersed in a 30 % by weight aqueous potassium hydroxide solution.

[0129] Film thicknesses of the alkaline anion exchange membrane precursors (pAAEM) and the alkaline anion exchange membranes (AAEM) were measured with a Mitutoyo ID- CI 12XB (Mitutoyo Corporation, Kawasaki, Japan).

[0130] The electrical resistance (EIS: [ohm]), the conductivity (C: [mS / cm]) and the specific resistance (R: [ohm cm2]) were measured after storing in a 30 % by weight aqueous potassium hydroxide solution at 80 °C for 14 days. The results are shown in table 2.

[0131] Table 1 shows the viscosity of the polymer solutions before casting, the Film thicknesses of the alkaline anion exchange membrane precursors (pAAEM) the alkaline stability.

[0132] Table 1 :

[0133] Table 2: Alkaline anion exchange membranes (AAEM) according to the invention are showing a significant lower resistance compared to commercially available diaphragm materials like Zirfon® UTP500.

[0134] A scanning electron micrograph SEM cross-section (5000 x magnification) of pAAEM membrane from example 1 is shown in figure 1.

Claims

Claims1. Alkaline anion exchange membrane precursor (pAAEM) comprising a blend (B) of at least one first polymer (P1) comprising repeating units derived from acrylonitrile and at least one second polymer (P2) comprising repeating units derived from a vinyl lactam.

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

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

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

5. The alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 4, wherein the at least one second polymer (P2) comprises, based on the total weight of the at least one second polymer (P2) comprised in the blend (B), at least 50 % by weight of repeating unites derived from at least one monomer of the formula (I):where n is 3 to 12; m is 0 to 3;R1is Ci- Ci o- alkyl, C2-C -alkenyl, aryl or aralkyl;R2, R3and R4are each, independently of one another, hydrogen, Ci— Ci o— alkyl, C2-C -alkenyl, aryl or aralkyl.

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

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

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

10. The alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 9, wherein the alkaline anion exchange membrane precursor (pAAEM) has a thickness in the range of 10 to 250 pm.A process for the preparation of the alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 10 comprising the steps i) providing a solution (S) comprising the at least one first polymer (P1), the at least one second polymer (P2), and at least on polar solvent, and ii) separating the at least one polar solvent from the solution (S) to obtain the alkaline anion exchange membrane precursor (pAAEM). Alkaline anion exchange membrane (AAEM) obtained by contacting the alkaline anion exchange membrane precursor (pAAEM) according to any of claims 1 to 10 with an alkaline aqueous solution. 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 ohm cm2at a temperature of 20°C in a 6 M potassium hydroxide solution. Alkaline water electrolysis cell comprising the alkaline anion exchange membrane (AAEM) according to claim 12 or 13. Process for the preparation of hydrogen using the alkaline anion exchange membrane (AAEM) according to claim 12 or 13.

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