EP4638567A1

EP4638567A1 - Membranes

Info

Publication number: EP4638567A1
Application number: EP23818399.0A
Authority: EP
Inventors: Jacko Hessing; Elisa Huerta Martinez
Original assignee: Fujifilm Corp; Fujifilm Manufacturing Europe BV
Current assignee: Fujifilm Corp; Fujifilm Manufacturing Europe BV
Priority date: 2022-12-22
Filing date: 2023-12-05
Publication date: 2025-10-29
Also published as: KR20250124854A; WO2024132498A1; CN119968424A; JP2025539690A

Abstract

An anion exchange membrane obtainable by curing a curable composition comprising: (a) a component (a) of Formula (I); and AR1 – (CH2)n – N+(RaRb) – (CH2)n – AR2, X- Formula (I) (b) a component (b) of Formula (II); AR3 – (CH2)n – N+(RcRd) – L – N+(ReRf)– (CH2)n – AR4, 2X- Formula (II) wherein: n, L, X-, Ra, Rb, Rc, Rd, Re and Rf are as defined in claim 1; AR1, AR2, AR3 and AR4 each independently comprise aromatic groups; and wherein the component (a) of Formula (I) and the component (b) of Formula (II) each comprises at least two curable ethylenically unsaturated groups.

Description

MEMBRANES

This invention relates to ion exchange membranes, especially anion exchange membranes (AEMs), their preparation processes and their use.

Ion exchange membranes are used in electrodialysis, electrolysis, production of acids and bases and a number of other processes. Typically the transport of ions through the membranes occurs under the influence of a driving force such as an electrical potential gradient.

Some ion exchange membranes comprise a porous support, which provides mechanical strength. Such membranes are often called “composite membranes” due to the presence of both an ionically charged polymer which discriminates between oppositely charged ions and the porous support which provides mechanical strength.

For generation of acids and bases generally BPMs are used, e.g. in a process called bipolar electrodialysis (BPED). A BPM has both a cationic layer or anion exchange layer (AEL) and an anionic layer or cation exchange layer (CEL) and thus has both a negatively charged layer and a positively charged layer.

In the BPED process acid and base are generated at the interface of a BPM by means of a water dissociation reaction (WDR). The H⁺ and OH’ ions generated travel across the corresponding ion exchange layers towards the cathode and the anode respectively. The BPED process is performed in a bipolar electrodialysis stack comprising additional to bipolar membranes monopolar anion exchange and monopolar cation exchange membranes. In the bipolar electrodialysis stack, the monopolar cation and anion exchange membranes take care of selectively separating the salt ions of the feed stream by their charge. The salt anion will then combine with the H+ formed by the WDR to form an acid and the salt cation will combine with the OH- to form a base. For example, if NaCI is used in the feed stream, the monopolar membranes will separate Na⁺ from CT whereby NaOH and HCI are formed.

For generation of acids and bases in high concentrations it is important that the monopolar membranes have a very high pH stability and high durability (high pH stability and durability increase the lifetime of the membranes). Also desired is a high efficiency of the process for generating acids and bases. This requires the membranes to have a very high permselectivity to prevent H⁺ and OH’ ions to reach the wrong channel causing recombination of H⁺ and OH’ ions forming water and hence product loss. Especially for anion exchange membranes it is difficult to obtain a high proton blocking performance at high concentrations due to the small size of protons.

It is an aim of the present invention to provide anion exchange membranes which are mechanically strong and having a high permselectivity at very low pH values which can be achieved by controlling their swelling behavior.

According to a first aspect of the present invention there is provided an anion exchange membrane obtainable by curing a curable composition comprising: (a) a component (a) of Formula (I); and

AR¹ - (CH₂)n - N⁺(R^aR^b) - (CH₂)n - AR², X Formula (I)

(b) a component (b) of Formula (II);

AR³ - (CH₂)_n - N⁺(R^cR^d) - L - N⁺(R^eR^f)- (CH₂)_n - AR⁴, 2X’ Formula (II) wherein: each n independently has a value of 1 or 2;

L is a non-aromatic linking group; each X’ independently is an anion; and

AR¹, AR², AR³ and AR⁴ each independently comprise aromatic groups;

(i) R^a, R^b, R^c, R^d, R^e and R^f are each independently an optionally substituted C-i-3-alky I group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group; or

(ii) R^a and R^b, together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring; or

(iii) one of R^a and R^b is an optionally substituted C-i-3-alkyl group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group and the other of R^a and R^b, together with the group of formula AR¹ - (CH₂)_n - N⁺, forms an optionally substituted 5- or 6-membered ring; or

(iv) R^a, together with the group of formula AR¹ - (CH₂)_n - N⁺, forms an optionally substituted 5- or 6-membered ring, and R^b, together with the group of formula N⁺- (CH₂)_n - AR², forms an optionally substituted 5- or 6-membered ring; and

(v) R^c and R^d, together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring and R^e and R^f are each independently an optionally substituted Ci-3-alkyl group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group; or

(vi) R^c and R^d, together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring and R^e and R^f, together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring; or

(vii) one of R^c and R^d is an optionally substituted Ci-3-alkyl group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH₂)_n - N⁺, forms an optionally substituted 5- or 6-membered ring, and R^e and R^f are each independently an optionally substituted Ci-3-alky I group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group; or

(viii) one of R^c and R^d is an optionally substituted Ci-3-alkyl group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH₂)_n - N⁺, forms an optionally substituted 5- or 6-membered ring, and R^e and R^f, together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring; or (ix) one of R^c and R^d and one of R^e and R^f is an optionally substituted Ci-3-alkyl group, an optionally substituted C2-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH2)n - N⁺, forms an optionally substituted 5- or 6-membered ring, and the other of R^e and R^f, together with the group of formula N⁺- (CH2)n - AR⁴, forms an optionally substituted 5- or 6-membered ring; or

(x) one of R^c and R^d is an optionally substituted Ci-3-alkyl group, an optionally substituted C2-3-alkenyl group or a vinylbenzyl group, and the other of R^c and R^d is connected to L, forming an optionally substituted ring, and R^e and R^f are each independently an optionally substituted Ci-3-alkyl group, an optionally substituted Coalkenyl group or a vinylbenzyl group; and wherein the component (a) of Formula (I) and the component (b) of Formula (II) each comprises at least two curable ethylenically unsaturated groups.

Preferably the water uptake of the anion exchange membrane is between 11 and 16.5%.

Preferably the ion exchange capacity of the anion exchange membrane is between 0.7 and 1.0 meq/g dry membrane.

Preferably the molar fraction of component (a) in relation to component (b) is at least 0.60 and not more than 0.96, more preferably at least 0.65 and not more than 0.95, especially at least 0.65 and not more than 0.90, more especially at least 0.70 and not more than 0.80.

In this document (including its claims), the verb “comprise” and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article “a” or “an” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article “a” or “an” thus usually mean “at least one”. A vinylbenzyl group is a CH2=CHC6H4CH2*-group wherein the asterisk denotes the point of attachment to the other part of the molecule.

Preferred curable ethylenically unsaturated groups are vinyl groups and allyl groups, most preferably vinyl groups. The vinyl groups (CH2=CH-) are non-acrylic, i.e. the vinyl groups are not attached to (C=O)O-groups or (C=O)NH-groups.

The curable ethylenically unsaturated groups are capable of reacting with other curable ethylenically unsaturated groups to form covalent bonds therewith, e.g. when heated and/or irradiated with light (e.g. ultraviolet light) or an electron beam.

Preferably L is a non-aromatic linking group comprising from 2 to 7 carbon atoms and optionally one or more atoms selected from oxygen, nitrogen and sulphur (e.g. an optionally interrupted C2-7-alkylene group or C2-7-alkelene group or an optionally substituted Cs-Ce-cycloalkylene group, wherein the optional interruptions are selected from oxygen, nitrogen and sulphur) or L forms a ring with one of the positively charged nitrogen atoms and one of R^c, R^d, R^e and R^f. Examples of L include e.g. ethylene (-CH2CH2-), propylene (-C3H6-), butylene (-C4H8-), 2,2-dimethylpropylene, methoxymethylene, diethylene ether (-CH2CH2-O-CH2CH2-), diethylenethioether (-CH2CH2-S-CH2CH2-), diallylpropylene, cyclopentylene and cyclohexylene.

Preferably both component (a) and component (b) comprise at least two curable ethylenically unsaturated groups, more preferably two and only two curable ethylenically unsaturated groups. Preferably the curable ethylenically unsaturated groups present in component (a) are present in AR¹ and/or AR², and in component (b) in AR³ and/or AR⁴. In a preferred embodiment AR¹, AR², AR³ and AR⁴ each comprise one and only one curable ethylenically unsaturated group and component (a) and component (b) each have a total of two curable ethylenically unsaturated groups. Additional curable ethylenically unsaturated groups (preferably vinyl groups) may be present in one or more of R^a, R^b, R^c, R^d, R^e and R^f.

The positively charged nitrogen atom (N⁺) shown in Formula (I) is non-aromatic, i.e. is not part of an aromatic heterocyclic ring.

Preferably the anion X’ does not react with the other components of the curable composition, i.e. X’ is inert. Preferred anions represented by X’ include hydroxide, fluoride, chloride, bromide, iodide, nitrate, thiocyanate, hexafluoroborate, methanesulfonate, trifluoromethanesulfonate, formate and acetate. Most preferably X’ is a chloride anion because this can provide a component of Formula (I) with good solubility without dramatically increasing the molecular weight of component (a) of Formula (I).

Preferably each n independently has a value of 1 . In a particularly preferred embodiment in both Formula (I) and Formula (II) both n have a value of 1 .

In one embodiment R^a, R^b, R^c, R^d, R^e and R^f are each independently selected from optionally substituted C-i-3-alkyl groups (e.g. methyl, ethyl, propyl or isopropyl), optionally substituted C2-3-alkenyl groups (e.g. -CH=CH2 or -CH2CH=CH2) and vinylbenzyl groups (CH2=CH-C6He-).

In another embodiment R^a and R^b, and/or R^c and R^d and/or R^e and R^f together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring, for example an optionally substituted pyrrolidinium, pyrrolinium, imidazolinium, piperidinium or morpholinium ring.

In another embodiment, one of R^a and R^b is an optionally substituted C-i-3-alkyl group, an optionally substituted C2-3-alkenyl group or a vinylbenzyl group and the other of R^a and R^b, together with the group of formula AR¹ - (CH2)n - N⁺ (wherein AR¹ and n are as hereinbefore defined), forms an optionally substituted 5- or 6-membered ring, for example an optionally substituted pyrrolidinium, pyrrolinium, piperidinium or morpholinium ring, in each case having an aromatic ring (e.g. a benzene ring) fused thereon (preferably with two or more, preferably one curable ethylenically unsaturated groups attached to the benzene ring).

In another embodiment R^a, together with the group of formula AR¹ - (CH2)n - N⁺ (wherein AR¹ and n are as hereinbefore defined), forms an optionally substituted 5- or 6-membered ring and R^b, together with the group of formula N⁺- (CH2)n - AR² (wherein AR² and n are as hereinbefore defined), forms an optionally substituted 5- or 6-membered ring.

In another embodiment, one of R^c and R^d and/or one or both of R^e and R^f is an optionally substituted C-i-3-alky I group, an optionally substituted C2-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH2)n - N⁺ (wherein AR³ and n are as hereinbefore defined), forms an optionally substituted 5- or 6-membered ring, for example an optionally substituted pyrrolidinium, pyrrolinium, piperidinium or morpholinium ring, in each case having an aromatic ring (e.g. a benzene ring) fused thereon (preferably with two or more preferably one curable ethylenically unsaturated groups attached to the benzene ring) and/or the other of R^e and R^f, together with the group of formula N⁺- (CH2)n - AR⁴ (wherein AR⁴ and n are as hereinbefore defined), forms an optionally substituted 5- or 6-membered ring.

The preferred optionally substituted 5- or 6-membered rings are as hereinbefore defined (one example is a 6-azoniaspiro[5.5]undecylene ring for component (a)).

Preferred optional substituents are curable ethylenically unsaturated groups (as hereinbefore described and preferred).

Preferably AR¹, AR², AR³ and AR⁴ each independently comprise a phenyl or styrenyl group. More preferably AR¹, AR², AR³ and AR⁴ are styrenyl groups (i.e. CH2=CH-CeH4- groups).

In a preferred embodiment component (a) is of Formula (III):

Formula (III) wherein R^a, R^b and X’ are as hereinbefore defined.

Component (a) optionally comprises one or more than one component (a) of Formula (I) (more preferably Formula (III)), for example a mixture of isomers wherein curable unsaturated groups present in AR¹ and/or AR² are in different positions (e.g. ortho, meta and/or para position).

Examples of monomers which may be used as component (a) include the compounds AXL-1 to AXL-14 shown below:

In a preferred embodiment component (b) is of Formula (IV):

Formula (IV) wherein L, R^c, R^d, R^e, R^f and X’ are as hereinbefore defined.

Component (b) optionally comprises one or more than one component (b) of Formula (II) (more preferably Formula (IV)), for example a mixture of isomers wherein curable unsaturated groups present in AR³ and/or AR⁴ are in different positions (e.g. ortho, meta and/or para position). Examples of monomers which may be used as component (b) include the compounds AXL2-1 to AXL2-18 shown below:

In one embodiment the anion exchange membrane according to the first aspect of the present invention comprises at least 1 ppm of component (a), preferably at least 10 ppm, especially at least 100 ppm, and at least 1 ppm of component (b), preferably at least 10 ppm, especially at least 100 ppm (typically as a result of incomplete curing when the membrane is formed). Preferably the anion exchange membrane comprises less than 20,000 ppm of component (a), more preferably less than 10,000 ppm, and less than 20,000 ppm of component (b), more preferably less than 10,000 ppm. The amounts present in the anion exchange membrane may be determined by the method described on page 19 of WO2022162083.

The curable composition preferably comprises 35 to 70wt%, more preferably 40 to 70wt%, especially 40 to 65wt%, more especially 45 to 65wt%, most preferably 50 to 60wt% of component (a), and preferably 3 to 40wt%, more preferably 4 to 35wt%, especially 5 to 34wt%, more especially 5 to 30wt%, most preferably 15 to 30wt% of component (b).

Optionally the curable composition further comprises a monomer comprising a cationically charged group and one and only one curable ethylenically unsaturated group as component (c). Preferably the curable composition is free from component (c) or the composition comprises a small amount of component (c), e.g. the curable composition preferably comprises 0 to 10wt% of component (c), more preferably 0 to 7wt% of component (c).

In component (c) the cationically charged group is preferably a quaternary ammonium group. The one and only curable ethylenically unsaturated group present in component (c) is preferably a vinyl or allyl group, more preferably a vinyl group.

Component (c) may comprise one or more than one monomer comprising a cationically charged group and one and only one curable ethylenically unsaturated group.

In one embodiment component (c) is of Formula (SM) wherein R¹, R² and R³ each independently represents an alkyl group or an aryl group, or 2 or 3 of R¹, R² and R³ together with the positively charged nitrogen atom to which they are attached form an optionally substituted 5- or 6-membered ring; n3 represents an integer of 1 to 3; and X3⁰ represents an anion, preferably chloride, bromide, iodide or hydroxide.

Examples of component (c) of Formula (SM) include the following: compounds.

The above components may be prepared as described in, for example, US2016177006.

The curable composition optionally further comprises a radical initiator as component (d). Preferred radical initiators include thermal initiators, photoinitiators and combinations thereof. The curable composition preferably comprises 0 to 10 wt% of radical initiator, more preferably 0 to 3wt%. When the curable composition is to be cured using UV light, visible light or thermally the curable composition preferably 0.001 to 2wt%, especially 0.005 to 1 ,5wt%, of radical initiator.

Examples of suitable thermal initiators which may be used as component (d) include 2,2’-azobis(2-methylpropionitrile) (AIBN), 4,4’-azobis(4-cyanovaleric acid), 2,2’-azobis(2,4-dimethyl valeronitrile), 2,2’-azobis(2-methylbutyronitrile), 1 ,1’- azobis(cyclohexane-1 -carbonitrile), 2,2’-azobis(4-methoxy-2,4-dimethyl valeronitrile), dimethyl 2,2’-azobis(2-methylpropionate), 2,2’-azobis[N-(2-propenyl)-2- methylpropionamide, 1 -[(1 -cyano-1-methylethyl)azo]formamide, 2,2'-azobis(N-butyl-2- methylpropionamide), 2,2'-Azobis(N-cyclohexyl-2-methylpropionamide), 2,2'- Azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2- yl)propane]dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate, 2,2'- azobis{2-[1 -(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'- azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(1 -imino-1-pyrrolidino-2- ethylpropane) dihydrochloride, 2,2'-azobis{2-methyl-N-[1 , 1 -bis(hydroxymethyl)-2- hydroxyethl]propionamide} and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl) propionamide].

Examples of suitable photoinitiators which may be included in the curable composition as component (d) include aromatic ketones, acylphosphine compounds, aromatic onium salt compounds, organic peroxides, thio compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkyl amine compounds. Preferred examples of the aromatic ketones, the acylphosphine oxide compound, and the thio-compound include compounds having a benzophenone skeleton or a thioxanthone skeleton described in "RADIATION CURING IN POLYMER SCIENCE AND TECHNOLOGY", pp.77-117 (1993). More preferred examples thereof include an alpha-thiobenzophenone compound described in JP1972-6416B (JP-S47-6416B), a benzoin ether compound described in JP1972-3981 B (JP-S47-3981 B), an alpha-substituted benzoin compound described in JP1972-22326B (JP-S47-22326B), a benzoin derivative described in JP1972-23664B (JP-S47-23664B), an aroylphosphonic acid ester described in JP1982-30704A (JP-S57-30704A), dialkoxybenzophenone described in JP1985- 26483B (JP-S60-26483B), benzoin ethers described in JP1985-26403B (JP-S60- 26403B) and JP1987-81345A (JPS62-81345A), alpha-amino benzophenones described in JP1989-34242B (JP H01 -34242B), U.S. Pat. No. 4,318, 791 A, and EP0284561A1 , p-di(dimethylaminobenzoyl) benzene described in JP1990-211452A (JP-H02- 211452A), a thio substituted aromatic ketone described in JP1986-194062A (JPS61 -194062A), an acylphosphine sulfide described in JP1990-9597B (JP-H02- 9597B), an acylphosphine described in JP1990-9596B (JP-H02-9596B), thioxanthones described in JP1988-61950B (JP-S63-61950B), and coumarins described in JP1984-42864B (JP-S59-42864B). In addition, the photoinitiators described in JP2008-105379A and JP2009-114290A are also preferable. In addition, photoinitiators described in pp. 65 to 148 of "Ultraviolet Curing System" written by Kato Kiyomi (published by Research Center Co., Ltd., 1989) may be used.

Especially preferred photoinitiators include Norrish Type II photoinitiators having an absorption maximum at a wavelength longer than 380nm, when measured in one or more of the following solvents at a temperature of 23°C: water, ethanol and toluene. Examples include a xanthene, flavin, curcumin, porphyrin, anthraquinone, phenoxazine, camphorquinone, phenazine, acridine, phenothiazine, xanthone, thioxanthone, thioxanthene, acridone, flavone, coumarin, fluorenone, quinoline, quinolone, naphtaquinone, quinolinone, arylmethane, azo, benzophenone, carotenoid, cyanine, phtalocyanine, dipyrrin, squarine, stilbene, styryl, triazine or anthocyanin- derived photoinitiator. Optionally the curable composition further comprises a monomer free from cationically charged groups, preferably comprising at least two curable ethylenically unsaturated groups, as component (e).

Preferably the curable composition comprises 0 to 5wt% of component (e). More preferably the curable composition is free from component (e).

The curable composition preferably further comprises solvent as component (f). The solvent is preferably an inert solvent. Inert solvents do not react with any of the other components of the curable composition. In a preferred embodiment component (f) comprises water and optionally an organic solvent, especially where some or all of the organic solvent is water miscible. The water is useful for dissolving components (a) and (b) and possibly also component (c) and the organic solvent is useful for dissolving any organic components present in the curable composition.

Component (f) is useful for reducing the viscosity and/or surface tension of the curable composition. In a preferred embodiment, the curable composition comprises 10 to 40wt%, especially 20 to 30 wt%, of component (f).

Examples of inert solvents which may be used as or in component (f) include water, alcohol-based solvents, ether-based solvents, amide-based solvents, ketone- based solvents, sulphoxide-based solvents, sulphone-based solvents, nitrile-based solvents and organic phosphorus-based solvents. Examples of alcohol-based solvents which may be used as or in component (f) (especially in combination with water) include methanol, ethanol, isopropanol, n-propanol, n-butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and mixtures comprising two or more thereof. In addition, preferred inert, organic solvents which may be used in component (f) include dimethyl sulphoxide, dimethyl imidazolidinone, sulpholane, N- methylpyrrolidone, dimethyl formamide, acetonitrile, acetone, 1 ,4-dioxane, 1 ,3- dioxolane, tetramethyl urea, hexamethyl phosphoramide, hexamethyl phosphorotriamide, pyridine, propionitrile, butanone, cyclohexanone, tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, ethylene glycol diacetate, cyclopentylmethylether, methylethylketone, ethyl acetate, y-butyrolactone and mixtures comprising two or more thereof.

The curable composition may further comprise other components such as inhibitors, wetting agents for improving coating properties, biocides, stabilizers, preferably in low amounts such as between 0 and 3wt%.

The AEMs preferably have a low water permeance so that (hydrated) ions may pass through the membrane and (free) water molecules do not easily pass through the membrane. Preferably the water permeance of the AEMs is lower than 1.10’¹¹ m³/m².s.kPa, more preferably lower than 5.1 O’¹² m³/m².s.kPa, especially lower than 4.10’¹² m³/m².s.kPa.

The distance between the two cationically charged nitrogen atoms in component (b) is preferably at least 0.35 nm as this enhances pH stability of the resultant membrane. Preferably the distance between the two cationically charged nitrogen atoms in component (b) is less than 1.5 nm since a short distance enhances crosslinking density of the resultant membrane.

Preferably component (a) and component (b) each have a molecular weight of less than 600 Dalton, more preferably less than 550 Dalton. A higher molecular weight would lead to a membrane having a high electrical resistance.

The molar fraction of the sum of component (a) and component (b) in relation to all curable compounds present in the curable composition is preferably at least 0.95. A high ratio of components (a) and (b) in relation to all curable compounds present in the curable composition is preferred to obtain a membrane having a high crosslink density and hence a high permselectivity. The molar fraction of components (a) and (b) in relation to all curable compounds present in the curable composition is preferably up to 1.0. The molar fraction of the sum of components (a) and (b) in relation to all curable compounds present in the curable composition may be calculated by dividing the sum of the molar amount of components (a) and (b) by the sum of the molar amounts of all curable compounds present in the curable composition. Alternatively, the molar fraction may be determined by measuring the extractables from the anion exchange membrane, e.g. as described on page 19 of WO2022162083.

The permselectivity (PS) of the membranes of the present invention for protons is preferably at least 50%, more preferably at least 60%, when determined as described below (in a 0.05M - 4M HCI system).

The electrical resistance of the membranes of the present invention is preferably less than 15 ohm/cm², more preferably less than 12 ohm/cm², especially less than 10 ohm/m², when determined as described below (in 2M NaCI).

Preferably the ion exchange capacity (IEC) of the anion exchange membrane according to the present invention is at least 0.7 meq/g dry membrane, more preferably at least 0.8 meq/g dry membrane when measured by the method described below. Such lECs can provide anion exchange membranes having low electrical resistance.

Preferably the IEC of the anion exchange membrane according to the present invention is below 1.00 meq/ g dry membrane, more preferably below 0.95 meq/g dry membrane when measured by the method described below. Such lECs can provide anion exchange membranes which do not swell too much and therefore retain good permselectivity in use.

Thus preferably the IEC of the anion exchange membrane according to the present invention is between 0.7 and 1 .0 meq/g dry membrane when measured by the method described below.

Generally, it is preferred that the PS is as high as possible, and the ER is low as possible. The skilled person knows that there is generally a trade-off between PS and ER: a very high PS can be achieved at the cost of a higher ER and when a low ER is desired one has to sacrifice permselectivity. The membranes of the present invention exhibit a very high PS and an acceptable ER. A suitable parameter to select good membranes in a simple way is to measure the water uptake (Wil) of the membrane. The water uptake is preferably between 11 and 16%, more preferably between 12 and 16%.

However, the ion exchange capacity (IEC) has a large influence on the swelling properties and thus on the permselectivity as well as on the electrical resistance of the membrane. A more precise method to select a good membrane is therefore based on both the water uptake and the ion exchange capacity, e.g. the product of the water uptake value and the ion exchange capacity value. Preferably Wil * IEC is between 8.5 and 15.5, more preferably between 9.0 and 15.0, especially between 9.2 and 14.7, wherein the water uptake is expressed in percentage (%) and the ion exchange capacity in meq/g dry membrane. The water uptake and ion exchange capacity may be determined as described below in the experimental section.

The anion exchange membrane of the present invention preferably further comprises a porous support.

As examples of porous supports which may be used there may be mentioned woven and non-woven synthetic fabrics and extruded films. Examples include wetlaid and drylaid non-woven material, spunbond and meltblown fabrics and nanofiber webs made from, e.g. polyethylene, polypropylene, polyacrylonitrile, polyvinyl chloride, polyphenylenesulfide, polyester, polyamide, polyaryletherketones such as polyether ether ketone and copolymers thereof. Porous supports may also be porous membranes, e.g. polysulphone, polyethersulphone, polyphenylenesulphone, polyphenylenesulfide, polyimide, polyethermide, polyamide, polyamideimide, polyacrylonitrile, polycarbonate, polyacrylate, cellulose acetate, polypropylene, poly(4- methyl 1 -pentene), polyinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene and polychlorotrifluoroethylene membranes and derivatives thereof.

The porous support preferably has an average thickness of between 10 and 800pm, more preferably between 15 and 300pm, especially between 20 and 150pm, more especially between 30 and 130pm, e.g. around 60pm or around 100pm.

Preferably the porous support has a porosity of between 30 and 95%, more preferably of 55 to 75%, wherein (in the final membrane) the pores are filled with an anion exchange polymer derived from curing the composition, i.e. the membrane preferably comprises 25 to 45vol% of porous (non-charged) support material and 75 to 55vol% of anion exchange polymer material (i.e. cured composition according to a first aspect of the present invention). The free volume of the porous support may be calculated from thickness (m) and weight (g/m²) and fiber density (g/m³) data.

The porosity of the support, prior to making the membrane, may be determined by a porometer, e.g. a Porolux™ 1000 from IB-FT GmbH, Germany.

The porous support, when present, may be treated to modify its surface energy, e.g. to values above 45 mN/m, preferably above 55mN/m. Suitable treatments include corona discharge treatment, plasma glow discharge treatment, flame treatment, ultraviolet light irradiation treatment, chemical treatment or the like, e.g. for the purpose of improving the wettability of and the adhesiveness to the porous support to the anion exchange membrane.

Commercially available porous supports are available from a number of sources, e.g. from Freudenberg Filtration Technologies (Novatexx materials), Lydall Performance Materials, Celgard LLC, APorous Inc., SWM (Conwed Plastics, DelStar Technologies), Teijin, Hirose, Mitsubishi Paper Mills Ltd and Sefar AG.

Preferably the porous support is a porous polymeric support. Preferably the porous support is a woven or non-woven synthetic fabric or an extruded film without covalently bound ionic groups.

Preferably the anion exchange membrane of the present invention has an average thickness of between 15pm and 600pm, more preferably of between 15 and 300 pm, especially of between 20pm and 200pm and more especially between 50 and 140pm.

According to a second aspect of the present invention there is provided a process for preparing an anion exchange membrane comprising curing a curable composition as defined (and preferred) in relation to the first aspect of the present invention.

The process according to the second aspect of the present invention preferably comprises the steps of: i. providing a porous support; ii. impregnating the porous support with the curable composition; and iii. curing the curable composition; wherein the curable composition is as defined above.

The curable composition may be cured by any suitable process, including thermal curing, photocuring, electron beam (EB) irradiation, gamma irradiation, and combinations of the foregoing.

Preferably the process according to the second aspect of the present invention comprises a first curing step and a second curing step (dual curing). Dual curing is preferred since it increases the crosslink density of the resultant anion exchange membrane which in turn improves permselectivity.

In a preferred embodiment of the process according to the second aspect of the present invention the curable composition is cured first by photocuring, e.g. by irradiating the curable composition with ultraviolet (UV) or visible light, or by gamma or electron beam radiation, and thereby causing curable components present in the curable composition to polymerise, and then applying a second curing step. The second curing step preferably comprises thermal curing, gamma irradiation or EB irradiation of the product of the first curing step whereby the second curing step preferably applies a different curing technique to the first curing step. When gamma or electron beam irradiation is used in the first curing step preferably a dose of 60 to 200 kGy, more preferably a dose of 80 to 150 kGy is applied to the curable composition. In one embodiment the process according to the second aspect of the present invention comprises curing the curable composition in a first curing step to form the anion exchange membrane, winding the anion exchange membrane onto a core (optionally together with an inert polymer foil) and then performing the second curing step on the wound product of the first curing step.

In a preferred embodiment the first and second curing steps are respectively selected from (i) UV curing (first curing step) then thermal curing (second curing step); (ii) UV curing then electron beam curing; and (iii) electron beam curing then thermal curing.

Component (d) may comprise just one radical initiator or more than one radical initiator, e.g. a mixture of several photoinitiators (e.g. for single curing) or a mixture of photoinitiators and thermal initiators (e.g. for dual curing).

In one embodiment the second curing step is performed using gamma or electron beam (EB) irradiation. For the second curing step by gamma or EB irradiation preferably a dose of 60 to 200 kGy is applied to the product of the first curing step, more preferably a dose of 80 to 150 kGy is applied.

For the optional second curing step, thermal curing is preferred. The thermal curing is preferably performed at a temperature between 50 and 100°C, more preferably between 60 and 90°C. The thermal curing is preferably performed for a period between 2 and 72 hours, e.g. around 3 hours for a sheet, between 8 and 16 hours, e.g. about 10 hours for a small roll and between 24 and 72 hours for a large roll. Optionally after the first curing step a polymer foil is applied to the product of the first curing step before winding it onto a spool (this reduces oxygen inhibition, drying out and/or sticking of the product of the first curing step to itself).

In a preferred process according to the second aspect of the present invention, the curable composition is applied continuously to a moving (preferably porous) support, preferably by means of a manufacturing unit comprising a curable composition application station, one or more irradiation source(s) for curing the curable composition, a membrane collecting station and a means for moving the support from the curable composition application station to the irradiation source(s) and to the membrane collecting station.

The curable composition application station may be located at an upstream position relative to the irradiation source(s) and the irradiation source(s) is/are located at an upstream position relative to the membrane collecting station.

Examples of suitable coating techniques for applying the curable composition to a support include slot die coating, slide coating, air knife coating, roller coating, screen-printing, and dipping. Depending on the used technique and the desired end specifications, it might be desirable to remove excess coating from the substrate by, for example, roll-to-roll squeeze, roll-to-blade or blade-to-roll squeeze, blade-to-blade squeeze or removal using coating bars. Curing by light is preferably done for the first curing step, preferably at a wavelength between 300 nm and 800 nm using a dose between 40 and 20000 mJ/cm². In some cases additional drying might be needed for which temperatures between 40°C and 200°C could be employed. When gamma or EB curing is used irradiation may take place under low oxygen conditions, e.g. below 200 ppm oxygen.

According to a third aspect of the present invention there is provided use of (a method of using) the anion exchange membrane according to the first aspect of the present invention for use in electromembrane processes, for example for the treatment of polar liquids (e.g. desalination), for the production the acids and bases or for the generation or storage of electricity.

According to a fourth aspect of the present invention there is provided an electrodialysis or reverse electrodialysis device, a bipolar electrodialysis device, an electrodeionization module, a flow through capacitor, a diffusion dialysis apparatus, a membrane distillation module, an electrolyser, a redox flow battery, an acid-base flow battery or a fuel cell, comprising one or more anion exchange membranes according to the first aspect of the present invention.

The invention will now be illustrated by the following, non-limiting examples in which all parts and percentages are by weight unless specified otherwise.

Water uptake (Wil)

The water uptake (Wil) was determined as follows:

Membrane samples (having a size of at least 44cm²) were equilibrated in deionized water for 24 hours at room temperature and gently dried with a tissue to remove hanging water droplets. Each sample was placed in a dry open container, and the container with sample was dried for 24 hours at 80°C. After 24 hours the container was closed with a lid and the container was allowed to cool to room temperature. The container with sample was weighed again and the water uptake was calculated by Formula (A) wherein the weight of the membrane was determined by subtracting the weight of the empty container from the weight of the container containing the membrane sample.

Water uptake (%) = (weight wet membrane/weight dry membrane * 100) - 100 Formula (A)

Permselectivity (PS)

The permselectivity (PS) (%) (i.e. the selectivity of the anion exchange membranes to the passage of ions of opposite charge) was measured as follows:

The anion exchange membrane to be tested was placed in a two-compartment system. One compartment was filled with a 0.05M solution of HCI and the other with a 4M solution of HCI with the membrane under test separating the two compartments. Settings: • the capillaries as well as the Ag/AgCI reference electrodes (Metrohm type 6.0750.100) contained 3M KCI;

• the effective membrane area was 9.62 cm²;

• the distance between the capillaries was ca 15 mm;

• the measuring temperature was 21 .0 ±0.2 °C;

• a Cole Parmer Masterflex console drive (77521 -47) with easy load II model 77200-62 gear pumps was used for the two compartments;

• Porter Instrument flowmeters (type 150AV-B250-4RVS) and Cole Parmer flowmeters (type G-30217-90) were used to control the flow constant at 500 ml/min;

• The anion exchange membrane samples were equilibrated for at least 1 hr in a 0.25M HCI solution prior to measurement. The voltage was read from a regular VOM (multitester) after 20 minutes.

The PS was calculated from the voltage reading using the Nernst equation. Preferably the PS for HCI was at least 50%, more preferably at least 60%.

Ion exchange capacity (IEC)

Prior to measurement, the membranes are brought in the chloride form by immersing the samples in 2 M NaCI solution for 1 hour. The 2 M NaCI solution was refreshed once, and the samples were equilibrated for another 24 hours. Subsequently, the membrane samples were rinsed with Milli-Q® water, immersed for 1 hour in fresh Milli-Q® water and rinsed once more with Milli-Q® water.

From the membrane samples with chloride as counter ion 2.0 cm diameter samples were punched out (12.57 cm²), dried for 24 hours at 40°C and weighed. Then the samples were placed in 75 ml of milli-Q® water for 24 hours, to remove all none- counter ions, followed by rinsing with Milli-Q® water, soaking each sample in 10.00 ml of a 0.1 M AgNOs solution, and shaking the solutions with the samples for 24 hours. During the shaking CT-ions were fully exchanged by NOs' ions as the Ag⁺-ions removed the CT-ions by precipitation of AgCI salt. Subsequently, the samples were taken out of the AgNOs solutions and rinsed with small portions of Milli-Q® water. The rinsing water of each sample and the corresponding AgNOs solution remaining after shaking the membrane sample were combined and titrated with a calibrated 0.1 M KBr solution, and the results were compared with the titration of a blank solution of 10.00 ml of 0.1 M AgNOs which had not contained a membrane sample. The difference between titration results of the blank solution and the test solution of each sample was correlated to the ion exchange capacity of the corresponding membranes using Equation (I):

IEC (meq/g dry membrane) = (Y-X)*0.1/W Equation (I) wherein

Y is the amount of 0.1 M KBr (in ml) used in the titration of the blank AgNOs solution; X is the amount of 0.1 M KBr (in ml) used in the titration of the AgNOs solution in which the membrane sample had been soaked combined with the Milli-Q® water used for rinsing the membrane sample after soaking in the AgNOs solution; and

W is the dry weight of the membrane (in gram).

Porosity of the porous support

The porosity of the porous support was calculated from thickness (m) and weight (g/m²) and fiber density (g/m³) data as provided by the supplier.

Electrical resistance (ER)

ER (ohm. cm²) of the anion exchange membranes prepared in the Examples was measured by the method described by Dlugolecki et al., J. of Membrane Science, 319 (2008) on page 217-218 with the following modifications:

• the auxiliary membranes were CMX and AMX from Astom, Japan;

• the capillaries as well as the Ag/AgCI references electrodes (Metrohm type 6.0750.100) contained 3M KCI;

• the calibration liquid and the liquid in compartment 2, 3, 4 and 5 was 2.0 M NaCI solution at 25°C;

• the effective membrane area was 9.62 cm²;

• the distance between the capillaries was 5.0 mm;

• the measuring temperature was 25°C;

• a Cole Parmer Masterflex console drive (77521 -47) with easy load II model 77200-62 gear pumps was used for all compartments;

• the flowrate of each stream was 475 ml/min controlled by Porter Instrument flowmeters (type 150AV-B250-4RVS) and Cole Parmer flowmeters (type G- 30217-90); and

• the samples of anion exchange membrane were equilibrated for at least 1 hour at room temperature in a 0.5 M solution of NaCI prior to measurement.

The ER is preferably low, e.g. below 15 ohm. cm², more preferably below 10 ohm. cm².

Determination of the distance between the cationically charged nitrogen atoms within the component (b)

The distance between cationically charged nitrogen atoms in each component (b) was determined by simulation using the open-source Avogadro software version 1.2.0 (see Marcus D Hanwell, Donald E Curtis, David C Lonie, Tim Vandermeersch, Eva Zurek and Geoffrey R Hutchison; “Avogadro: An advanced semantic chemical editor, visualization, and analysis platform” Journal of Cheminformatics 2012, 4:17). The structure of each component (b) was drawn in the software and by using the autooptimization tool the optimal chemical structure was determined. The auto-optimization tool was run with the following settings: Force field: UFF

Steps per update: 4

Algorithm: Molecular Dynamics (300K) No atoms were fixed or ignored When the auto-optimization tool was finished (dE=0), the distance between the cationically charged nitrogen atoms was determined using the ‘click to measure’ tool.

Table 1 : Ingredients General procedure for the preparation of AXL-1 , 3, 4 To a 40% solution in PW of the corresponding amine (1 mmol) containing 4-OH- TEMPO (0.1 g), CMS-14 (2.02 mmol) was added dropwise for a 1 -hour period. After that the mixture was stirred vigorously for 2 hours. Diethyl ether was added, and the aqueous phase was extracted three times (3 x 200 mL). The product was isolated from the water as a pale-yellow solid by spray drying.

Table 2: Structural elements of the AXL’s and the corresponding amines

General procedure for the preparation of AXL-9

5-Ethenyl-2,3-dihydro-1 H-isoindole (1 mmol) with 4-OH-TEMPO (0.01 mmol) was dissolved in chloroform (140 ml, 10 wt%). Potassium carbonate (2 mmol) was suspended in the mixture and iodomethane (1.05 mmol) was added dropwise. The mixture was stirred at room temperature for 1 hour. Water was added to the reaction and the organic layer was separated and subsequently washed with saturated ammonium chloride (2x150 ml). The organic layer was placed in a flask provided with a reflux, 1 mmol of CMS-14 was added dropwise. The mixture was gently warmed up to 40°C and stirred overnight. After completion, the product was filtered off and washed three times with diethyl ether. AXL-9 was obtained as a pale-yellow solid in a 65% yield.

General procedure for the preparation AXL2-1 to 2-4

To a 50% solution in ethyl acetate of the corresponding diamine (1 mmol) containing 4-OH-TEMPO (0.1 g), CMS-14 (2.02 mmol) was added dropwise for a 1 - hour period. After that the mixture was stirred vigorously for 2 hours. The obtained precipitate was filtered, rinsed with additional ethyl acetate and dried. The diammonium salts were isolated as a white solid. Table 3 below shows the structures of the crosslinking agents so prepared and their yield.

Table 3: Structural elements of the AXL’s and the corresponding amines

Preparation of Examples Ex1 to Ex11 and Comparative Examples CEx1 to CEx4

The compositions shown in Table 4 below were prepared by mixing sequentially the stated amounts of solids (in wt%) in a mixture of water and n-propanol at a temperature of 40°C. Anion exchange membranes according to the first aspect of the present invention and Comparative Examples were prepared by applying at room temperature (21 °C) each of the compositions described in Table 4 onto porous support PS1 (26 g/m² PP/PE porous support of 80 pm thickness, porosity 67.5 %) using a 100pm Mayer bar, removing the excess using a 4pm Mayer bar and then curing the composition. UV curing was performed by placing the samples of the supports comprising the compositions on a conveyor at 5 m/min equipped with a D bulb in a Light Hammer® 10 of Fusion UV Systems Inc. and exposing the samples to the UV light emitted from the D bulb at 50% power.

The UV cured samples were covered by a 60pm polyethylene terephthalate (PET) foil (from Toray) without any surface treatment and were placed into a metallized bag. The bag was vacuumized and sealed. The bag containing the membrane was placed in a regular oven and the membrane was thermally cured for 3 hours at 90°C.

Table 4: Curable Compositions and results

Table 4: Curable Compositions and results (continued)

Claims

1. An anion exchange membrane obtainable by curing a curable composition comprising:

(a) a component (a) of Formula (I); and

AR¹ - (CH₂)n - N⁺(R^aR^b) - (CH₂)n - AR², X Formula (I)

(b) a component (b) of Formula (II);

L is a non-aromatic linking group; each X’ independently is an anion;

AR¹, AR², AR³ and AR⁴ each independently comprise aromatic groups;

(vii) one of R^c and R^d is an optionally substituted Ci-3-alkyl group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH₂)_n - N⁺, forms an optionally substituted 5- or 6-membered ring, and R^e and R^f are each independently an optionally substituted Ci-3-alky I group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group; or (viii) one of R^c and R^d is an optionally substituted Ci-3-alkyl group, an optionally substituted C₂-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH₂)_n - N⁺, forms an optionally substituted 5- or 6-membered ring, and R^e and R^f, together with the positively charged nitrogen atom to which they are attached, form an optionally substituted 5- or 6-membered ring; or

(ix) one of R^c and R^d and one of R^e and R^f is an optionally substituted Ci-3-alkyl group, an optionally substituted C2-3-alkenyl group or a vinylbenzyl group and the other of R^c and R^d, together with the group of formula AR³ - (CH2)n - N⁺, forms an optionally substituted 5- or 6-membered ring, and the other of R^e and R^f, together with the group of formula N⁺- (CH2)n - AR⁴, forms an optionally substituted 5- or 6-membered ring; or

2. The anion exchange membrane according to claim 1 having a water uptake of between 11 and 16.5%.

3. The anion exchange membrane according to any one of the preceding claims wherein the ion exchange capacity of the ion exchange membrane is between 0.7 and 1 .0 meq/g dry membrane.

4. The anion exchange membrane according to any one of the preceding claims wherein the product of the water uptake value and the ion exchange capacity value is between 8.5 and 15.5, wherein the water uptake is expressed in percentage (%) and the ion exchange capacity in meq/g dry membrane.

5. The anion exchange membrane according to any one of the preceding claims which further comprises a porous support.

6. The anion exchange membrane according to any one of the preceding claims wherein in Formula (I) and in Formula (II) n has a value of 1 .

7. The anion exchange membrane according to any one of the preceding claims wherein AR¹, AR², AR³ and AR⁴ each comprise a curable ethylenically unsaturated group.

8. The anion exchange membrane according to any one of the preceding claims wherein the curable ethylenically unsaturated groups are vinyl groups.

9. The anion exchange membrane according to any one of the preceding claims wherein the molar fraction of component (a) in relation to component (b) in the curable composition is at least 0.60 and not more than 0.96.

10. The anion exchange membrane according to any one of the preceding claims wherein the curable composition comprises 35 to 70wt% of component (a) and 3 to 40wt% of component (b).

11 . The anion exchange membrane according to any one of the preceding claims wherein the components (a) and (b) each have a molecular weight of less than 600 Dalton.

12. The anion exchange membrane according to any one of the preceding claims wherein L is a non-aromatic linking group comprising from 2 to 7 carbon atoms and optionally one or more atoms selected from oxygen, nitrogen and sulphur.

13. The anion exchange membrane according to any one of the preceding claims wherein in Formula (I) AR¹ and AR², and in Formula (II) AR³ and AR⁴ each independently comprise a phenyl or a styrenyl group.

14. The anion exchange membrane according to any one of the preceding claims wherein the curable composition further comprises a radical initiator.

15. The anion exchange membrane according to any one of the preceding claims wherein the curable composition further comprises a monomer free from cationically charged groups.

16. The anion exchange membrane according to any one of the preceding claims wherein the curable composition further comprises solvent.

17. The anion exchange membrane according to any one of the preceding claims comprising at least 1 ppm of component (a) and at least 1 ppm of component (b).

18. A process for preparing an anion exchange membrane which comprises curing a curable composition as defined in any one of the preceding claims.

19. The process according to claim 18 which comprises the steps of:

(i) providing a curable composition as defined in any one of the claims 1 to 17;

(ii) applying the curable composition onto a porous support whereby at least a part of the curable composition impregnates the porous support; and

(iii) curing the curable composition.

20. An electrodialysis device, a bipolar electrodialysis device, an electrolyser, a redox flow battery, an acid-base flow battery or a fuel cell comprising one or more anion exchange membranes according to any one of claims 1 to 17.

21. Use of the anion exchange membrane according to any one of claims 1 to 17 for the treatment of polar liquids, for the production the acids and bases or for the generation or storage of electricity.