Poly(epoxy ether) dense membranes

Abstract

The present invention relates to a method for the preparation of polyepoxyether-based dense membranes and the dense membranes produced by this method. More particularly, the method of the present invention relates to the use of a ring-opening polymerization reaction of epoxide monomers with compounds comprising a tertiary amine group to produce dense membranes. The resulting poly(epoxy)ether dense membranes consists of ether bonds and quaternary ammonium groups which can beneficially interact with components to facilitate and improve the required separation.

Description

[0001] POLY(EPOXY ETHER) DENSE MEMBRANES

[0002] Field of the invention

[0003] The present invention relates to epoxide-based dense polymeric membranes and to methods for manufacturing these membranes.

[0004] Background of the invention

[0005] Membrane separation technology has gained an important place in the water, chemical and pharmaceutical industry. In 2016, the global market size of gas separation membranes was estimated to be 1.89 bn US$, and it is expected to grow to 3.85 bn US$ in 2026. Membranes retain one (or more) component(s) of a mixture, while other components may freely permeate through the membrane under a driving force that can be a pressure, concentration or potential gradient. Membranes may be applied in the separation of a range of components of varying molecular weights in gas or liquid phases, including but not limited to desalination and gas separations. Membrane separation has several advantages to offer compared to other separation processes, such as distillation, adsorption, absorption or solvent extraction. The benefits include continuous operation, lower energy consumption, possibility of integration with other separation processes, mild operation conditions, environmentally friendly operation, easy up-scaling, feasibility of making tailor-made membranes and reduced requirement of additives during operation.

[0006] Gas separation membranes are characterized by two main parameters: permeability, i.e. how readily a gas species of interest is transported through the membrane, and selectivity, i.e. how well the membrane can separate components of a mixture. A broad range of polymeric materials can be processed into a selective membrane, including polyamides, polycarbonates, polyimides, and polysulfones. However, many of these materials suffer from an inherent permeability-selectivity trade-off, meaning that it is not possible to concurrently achieve a high selectivity and a high permeability. In addition, many polymeric materials swell or degrade under demanding conditions (presence of condensable compounds such as CO2 and hydrocarbon vapours or the presence of acid gasses such as H2S, SO2 and NOx), limiting the application of membrane technology in harsh streams.) Furthermore, the processing of promising polymers into membranes with high permeance, which retain their selectivity poses challenges, as several requirements need to be fulfilled simultaneously, such as high mechanical stability and thin-film processing (Galizia etal. (2017) Macromolecules 50, 7809-7843). There is thus an ongoing quest to achieve new membrane materials that (i) achieve high performance in terms of selectivity and permeability, (ii) are stable in challenging conditions, (iii) can be processed into thin films.

[0007] One class of materials that has been used for gas separations, especially for the selective separation of CO2 from other gases (N2, H2), is based on poly(ethylene oxide) (PEO) containing polymers. Rubbery polar membranes with ethylene oxide (EO) segments have shown excellent CO2 affinity thanks to enhanced interaction of these segments with the CO2 quadrupole moment, leading to the commercialization of the Polaris™ membrane by MTR Membrane Technology and Research, Newark, CA, USA, the current state-of-the-art ethylene oxide-based membrane (White et al. (2017) J. Membr. Sci. 542, 217-225). The ethylene oxide-segments in poly(ethylene oxide) provide one of the best combinations of CO2 permeability and CO2 / N2 and CO2 / H2 selectivity known to date (Galizia et al. cited above). The main aim of novel poly(ethylene oxide)-based materials is to break the permeability-selectivity tradeoff by increasing the membrane CO2 permeability, without compromising the CO2 / N2 selectivity, through for example, incorporating high concentrations of ethylene oxide-segments in polymers, while at the same time avoiding crystallization of the poly(ethylene oxide)-segments, as crystallization substantially decreases gas permeability.

[0008] Epoxide resins, synthesized via the reaction between an epoxide compound and an amine compound, are standard materials in many industries thanks to their high chemical, mechanical and thermal stability. These materials can be dense or porous, depending on the synthesis conditions, and can be used for a plethora of applications, including gas separations, solvent permeation, biosensors, and surface waterproofing [US8410186B2]. They are usually synthesized by combining a multifunctional epoxide compound and a primary or secondary amine, optionally letting it pre-cure, then spreading out the mixture into the desired shape and allowing it to cure until solidification occurs. When using primary or secondary amines, a step-growth polymerization reaction occurs, resulting in a poly(beta-alkanol amine) (PBA) network. This type of chemistry can also be used to synthesize porous membranes for liquid separations.Recently, epoxide curing of multifunctional epoxide compounds and tertiary amines was used to synthesize robust membranes for liquid and gas separations. The epoxide undergoes a chain growth polymerization, initiated by the tertiary amine, resulting in a so-called poly(epoxyether) (PEE) network. The formed poly(epoxyether) network is linked through ether bonds, which contribute to the membrane gas separation performance, in a similar fashion as poly(ethylene oxide). Additionally, the initiation by the tertiary amine results in the formation of quaternary ammonium (QA) groups, which are known to have exceptionally high CO2 affinities, further enhancing the membrane separation performance [Quinn & Laciak (1997) J. Membr. Sci. 131, 49-60].

[0009] Poly(epoxyether) membranes synthesized so far consisted of thin-film composite (TFC) membranes in which the selective layer is formed by interfacial initiation of polymerization of a multifunctional epoxide with a bifunctional tertiary amine for liquid and gas separations. The dense selective layer has thickness of below 200 nm and is charged as it contains QA groups.

[0010] Summary of the invention

[0011] Numbered statements of this invention are :

[0012] 1. A method of preparing an epoxide-based dense membrane comprising the steps of:

[0013] a) reacting a compound comprising a tertiary amine group, the compounds lacking primary and / or lacking secondary amine groups, with an epoxide compound, and allowing polymerization of the compounds, but not beyond the gel point, during polymerisation the solution becomes viscous and it is the viscous solution which is casted, prior to reaching the gel point when the composition becomes solid.

[0014] b) casting the polymerized material, and

[0015] c) allowing the cast polymerized material to cure until a solid film is obtained.

[0016] Herein a compound comprising a tertiary amine group are also referred to as a first compound and epoxide compound or compound comprising an epoxide group as second compound.

[0017] In the methods of the present invention typically first compounds do not comprise epoxide groups and second compounds do not comprise tertiary amine groups. Herein an epoxide compound is also referred to as a compound comprising an epoxide group.In the context of the present invention, a dense film refers to a film with the absence of pores larger than 1 nm in diameter.

[0018] 2. The method according to statement 1, wherein the epoxide compound has an epoxide equivalent weight varying between 44 and 10 000, between 44 and 1000 or between 44 and 500.

[0019] 3. The method according to statement 1 or 2, wherein the epoxide compound has between 1 and 30 000, between 1 and 10000, or between 1 and 1000 epoxide groups.

[0020] 4. The method according to any one of statements 1 to 3, wherein the epoxide compound comprises between one and twenty or between one and eight epoxide groups.

[0021] These epoxide compounds may contain a substituent selected from the group consisting of: at least 1 one aromatic ring, at least one nitrogen containing heterocycle, at least one oxygen containing heterocycle, at least one carbon-carbon double bond, at least one siloxane group, at least one (meth)acrylate group, and between 1 and 100 ether bonds which are not part of a ring structure, least one imide group, at least one sulfone group.

[0022] 5. The method according to any one of statements 1 to 3, wherein the epoxide compound has between 1 and 2 500, between 1 and 1000, or between 1 and 500 ether bonds which are not part of a ring structure.

[0023] 6. The method according to any one of statements 1 to 4, wherein the epoxide compound contains between 1 and 30 ethylene oxide repeating units.

[0024] 7. The method according to any one of statements 1 to 5, wherein the epoxide compound contains between 1 and 1 500, between 1 and 1000, or between 1 and 500 aromatic ring structures.

[0025] 8. The method according to any one of statements 1 to 6, wherein the epoxide compound contains at least one structural unit with a site of contortion.

[0026] 9. The method according to statement 8, wherein the structural group with a site of contortion is selected from the group consisting of an ethanoanthracene, a triptycene, a benzotriptycene, a spirobisindane, a spirobifluorene and a Trbger's base.

[0027] 10. The method according to any one of statements 1 to 9, wherein the epoxide compound contains at least one imide ring.11. The method according to any one of statements 1 to 9, wherein the epoxide compound consists of an epoxide functionalized nanostructure.

[0028] 12. The method of statement 11, wherein the epoxide-functionalized nanostructure is selected from the group consisting of a polyhedral oligomeric silsesquioxane (POSS), a metal organic framework (MOF), a zeolite, a silica, a carbon nanotube, a carbon nanosheet, a graphene oxide, and a covalent organic frameworks (COF).

[0029] 13. The method according to any one of statements 1 to 12, wherein the epoxide compound is glycidyl POSS (G-POSS) or poly(ethylene glycol) glycidyl POSS (EO-G-POSS).

[0030] 14. The method according to any one of statements 1 to 13, wherein the compound comprising a tertiary amine group does not contain hydroxyl groups. 15. The method according to any one of statements 1 to 14, wherein the compound comprising a tertiary amine group contains between 1 and 30000 tertiary amine groups.

[0031] 16. The method according to any one of statements 1 to 15, wherein the compound comprising a tertiary amine group is part of a multi-cyclic compound. 17. The method according to statement 16, wherein the compound comprising a tertiary amine group is l,4-diazabicyclo[2.2.2]octane or 1,3,5,7-Tetraazotricyclo [3.3.1.13, 7]decane.

[0032] 18. The method according to any one of statements 1 to 17, wherein the compound comprising a tertiary amine group contains at least one structural unit with a site of contortion.

[0033] 19. The method according to any one of statements 1 to 18, wherein the structural unit with a site of contortion is selected from the group consisting of an ethanoanthracene, a triptycene, a benzotriptycene, a spirobisindane, a spirobifluorene, and a Trdger's base.

[0034] 20. The method according to any one of statements 1 to 19, wherein the compound comprising a tertiary amine group is an imidazole, such as 1-Methylimidazole.

[0035] 21. The method according to any one of statements 1 to 20, wherein the compound comprising a tertiary amine group comprises a functionalized nanostructure.

[0036] 22. The method of statement 21, wherein the functionalized nanostructure is selected from the group consisting of a polyhedral oligomeric silsesquioxane (POSS),a metal organic framework (MOF), a zeolite, a silica, a carbon nanotube, a carbon nanosheet, a graphene oxide, and a covalent organic framework (COF).

[0037] 23. The method according to statement 21 or 22 to wherein the compound comprising a tertiary amine group has between one and four functionalities selected from the group consisting of N,N-dimethylhexamine, N,N-Dimethylcyclohexylamine, N,N,N',N '-Tetra methylethylenediamine, N,N,N',N '-Tetra methyl- 1,3-propanediamine, N,N,N',N '-Tetra methyl- 1,4-butanedia mine, N, N, N ', N '-Tetra methyl-1,6-hexanediamine, N,N',N",N "-Penta methyldiethylenetriamine, 1,1,4,7,10,10-Hexa methyltriethylenetetra mine, Tris[2-(dimethyl-amino)ethyl]amine, Bis[2-(N,N-dimethylamino)ethyl] ether, N,N,N',N'-Tetraethylethylenediamine, 4,4'-(Oxydi-2,l-ethanediyl)bismorpholine and 4-(Dimethylamino)pyridine.

[0038] 24. The method according to any one of statements 1 to 23, wherein in step b) the epoxide compound and the compound comprising a tertiary amine group is heated or cooled during polymerization.

[0039] 25. The method according to any one of statements 1 to 24, wherein the polymerized material is heated or cooled during casting.

[0040] 26. The method according to any one of statements 1 to 25, wherein an aprotic solvent is added to the epoxide compound and the compound comprising a tertiary amine of step a).

[0041] 27. The method according to any one of statements 1 to, wherein the polymer formed in step a) is dissolved in an aprotic solvent prior to the casting of step b). 28. The method according to any one of statements 1 to 27, wherein an additive, such as a ring opening polymerization catalyst and a reactive compound, is added to the epoxide compound and the compound comprising a tertiary amine group of step a).

[0042] 29. The method according to any one of statements 1 to 26, wherein a ring opening polymerization catalyst is added to the epoxide compound and the compound comprising a tertiary amine group of step a).

[0043] 30. The method according to any one of statements 1 to 29, wherein the polymerized material is cast in step b) on a supporting structure.

[0044] 31. The method according to any one of statements 1 to 30, comprising the step post-curing the solid film at an elevated temperature up to maximum 400 °C.

[0045] 32. The method according to any one of statements 1 to 31, wherein the cast polymerized solution of step b) is sprayed with a compound reacting with functional groups remaining in the cast polymerized solution.33. The method according, to any one of statement 1 to 32, wherein the epoxide compound is Ethylene Oxide Glycidyl Polyhedral Oligomeric Silsesquioxane (EO-G-POSS) and wherein the compound comprising a tertiary amine groups is N,N,N',N'-tetramethyl hexanediamine (TMHD), which are mixed in a stoichiometric epoxide:amine ratio ranging from 1:1-10:1, and wherein the polymerisation is performed for between 1 h to 24h at between 35°C and 55 °C, preferably at 45°C, and the cast polymerised material is cured at between 35°C and 55 °C, preferably at 45°C.

[0046] 34. An epoxide-based dense semi-permeable membrane comprising up to 15 atomic % quaternary ammonium groups covalently-bound to carbon and lacking 0-alkanol amines.

[0047] 35. The membrane according to statement 34, comprising 0.01 - 0.1 atomic % covalently-bound quaternary ammonium groups, or comprising 0.1 - 5 atomic % covalently-bound quaternary ammonium groups..

[0048] 36. The membrane according to statement 34 or 35, comprising aromatic groups, nanostructures, or spirocenters.

[0049] 37. The use of a membrane according to any one of statements 34 to 36, or obtained by the method of any one of statements 1 to 33, in gas separations.

[0050] 38. The use according to statement 37, in separating carbon dioxide from gas mixtures comprising carbon dioxide and nitrogen.

[0051] 39. The use according to statement 37, in separating carbon dioxide from gas mixtures comprising carbon dioxide and nitrogen at temperatures varying between 0 and 150°C and at relative humidities varying from 0-100%.

[0052] 40. The use according to statement 37, in separating carbon dioxide from hydrogen.

[0053] 41. The use according to statement 37, in separating water vapor from air or from nitrogen.

[0054] 42. The use according to statement 37, in separating carbon dioxide from gas mixtures comprising carbon dioxide and methane.

[0055] 43. The use of a membrane according to any one of statements 34 to 37, or obtained by the method according to any one of statements 1 to 33, in in electrodriven membrane processes.This invention was made with government support under Grant no. DE-SC0023343 awarded by the Department of Energy. The government has certain rights in the invention.

[0056] Brief description of drawings

[0057] Figure 1: Chemical structures of exemplary epoxides and amines used for poly(epoxyether) synthesis.

[0058] Figure 2: Scanning electron microscopy images of dense membranes

[0059] Description

[0060] The present invention relates to a facile method for preparation of poly(epoxyether)-based dense membranes and the dense membranes produced by this method. More particularly, the present invention provides an easy method comprising an initiator-induced ring-opening polymerization reaction of epoxide monomers for making a poly(epoxyether) polymer with a dense structure (that is, without permanent porosity) containing positively charged QA groups, that can be used as such, or deposited onto a porous support.

[0061] The scope of the applicability of the present invention will become apparent from the detailed description and drawings provided below. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications are also within the spirit and scope of the invention as apparent from this detailed description. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0062] One aspect of the present invention provides poly(epoxyether)-based dense membranes that do not contain beta-alkanol amine bonds and that comprise quaternary ammonium groups covalently bound to carbon (C-NRs+). XPS can be used to detect these positively charged QA groups, but their content can fall below the detection limit of this analytic technique. The structure is dense and thus does not contain any porosity (below 10%), as is apparent from SEM images [figure 2]. The membranes can comprise of aliphatic groups, aromatic groups, nanostructures, i.e. structures that range between 1 nm (molecular scale) and 1000 nm in at least onedimension, and compounds containing a site of contortion, e.g., compounds that have at least two molecular rings sharing one common atom.

[0063] One aspect of the present invention provides a method for preparation of poly(epoxyether)-based dense membranes, involving a ring-opening polymerization reaction of epoxide monomers with an initiator. First, an epoxide compound is allowed to polymerize with a compound comprising a tertiary amine, the tertiary amine lacking primary and / or lacking secondary amines. Before the gel point, i.e. the point at which the solution undergoes gelation as reflected in a steep increase in viscosity or loss in fluidity, is reached the polymerized material is cast ((i.e. uniformly smeared with a casting knife of a specific height, or poured into a mold of a desired shape and height) or coated (i.e. uniformly deposited as a layer on a substrate by dipping the substrate in the solution or by depositing the solution onto the substrate). Then, the cast or coated polymerized material is allowed to further cure until a solid film is obtained.

[0064] The dense membrane can be further tuned during or after synthesis by modifying the synthesis parameters. During synthesis, the blend of the epoxide compound and the amine compound can be heated or cooled during polymerization or during casting / coating. Aprotic solvents can be added to the epoxide-amine blend, or can be used as the solvent for the formed polymer prior to casting / coating. Additives can be added to the epoxide-amine blend to speed up the reaction rate or modify the polymer structure. In particular, a ring-opening polymerization catalyst, such as aluminium-based catalysts, Vandenberg catalyst and more general group 13 and transition- metal-containing initiators and catalysts, can be added. The epoxide-amine blend can also be cast / coated onto a supporting structure, which is porous and can consist of several layers, including a highly porous substructure and a highly permeable gutter layer. More specifically, the support structure can be a supporting membrane, a supporting ultrafiltration membrane, or a supporting UF membrane with a gutter layer. The cast polymerized solution, either on a supporting structure or as such, can also be sprayed with a compound that reactions with the functional groups remaining in the cast polymer solution. After synthesis, the cast polymerized material can be post-cured to allow further reaction between unreacted groups and further densification of the network at an elevated temperature up to maximum 400 °C.The term "epoxide compound" refers to compounds having at least one and up to 30 000 oxirane rings, highly reactive due to their high ring strain (20 kcal / mol). More specifically, they should have an epoxide equivalent weight, that is the number of grams of epoxy resin required to provide 1 mole of epoxy groups, varying between 44 and 1000. To improve the affinity between CO2 and the polymer network and the mechanical properties, the epoxide compound preferably contains specific functionalities, such as: at least one ether bond which is not part of a ring structure, between 1-30 ethylene oxide repeating units, an imide ring and between one and eight epoxide groups. In other embodiments of the present invention, the epoxide monomer contains at least one aromatic ring structure, or at least one structural unit with a site of contortion, or with functional groups selected from ethanoanthracene, a triptycene, a benzotriptycene, a spirobisindane, a spirobifluorene and a Trbger's base. The use of epoxide compounds consisting of epoxide functionalized nanostructures is also envisioned, for example from the group consisting of polyhedral oligomeric silsesquioxanes (POSS), metal organic frameworks (MOF), zeolites, silica, carbon nanotubes, carbon nanosheets, graphene oxides, and covalent organic frameworks (COF). Functionalized POSS cages such as glycidyl POSS (G-POSS) or poly(ethylene glycol) glycidyl POSS (EO-G-POSS) are envisioned.

[0065] The term 'tertiary amine' refers to compounds comprising at least a tertiary amine functional group. In preferred embodiments, the tertiary amine does not contain hydroxyl groups, contains between 1 and 30000 tertiary amine groups and epoxu amine is part of a multi-cyclic compound. More specifically, the tertiary amine can be l,4-diazabicyclo[2.2.2]octane or 1,3,5,7-Tetraazotricyclo[3.3.1.13,7]decane. For specific applications, inducing additional free-volume in the membranes might be beneficial, which can be achieved by using a tertiary amine that contains at least one structural unit with a site of contortion, present in spiro-compounds, including but not limited to ethanoanthracene, a triptycene, a benzotriptycene, a spirobisindane, a spirobifluorene, and a Trbger's base. The tertiary amine compounds can be chosen from N,N-dimethylhexamine, N,N-Dimethylcyclohexylamine, N,N,N',N'-Tetra methylethylenediamine, N,N,N',N '-Tetra methy I- 1,3-propanedia mine, N, N, N ', N '-Tetra methy I- 1,4-butanedia mine, N,N,N',N '-Tetra methyl- 1,6-hexanediamine, N,N',N",N "-Penta methyldiethylenetriamine, 1,1,4,7,10,10- Hexa methyltriethylenetetra mine, Tris[2-(dimethylamino)ethyl]amine, Bis[2-(N,N-dimethylamino)ethyl] ether, N,N,N',N'-Tetraethylethylenediamine, 4,4'-(Oxydi-2,l-ethanediyl)bismorpholine and 4-(Dimethylamino)pyridine.Another aspect of the present invention relates to the use of the dense membranes of the present invention, for the separation of gases, including the separation of carbon dioxide from nitrogen, at elevated temperatures and at different relative humidities, as is relevant for, for example, post-combustion carbon capture. The membranes can be also be used for the separation of carbon dioxide from hydrogen, as is relevant for syngas purification or for the separation of carbon dioxide from methane, as is relevant for natural gas purification. The membranes can also be used for dehumidification processes, including the separation of water vapor from air, especially from nitrogen,. The membranes can also be used for electro-driven membranes processes, including in batteries and in alkaline water electrolysis.

[0066] Examples

[0067] Example 1: preparation of dense poly(epoxyether) membranes

[0068] Dense poly(epoxyether) (PEE) membranes were prepared using the monomer ethylene oxide glycidyl polyhedral oligomeric silsesquioxane (EO-G-POSS) combined with several tertiary amine initiators (figure 1). A fixed amount of EO-G-POSS was mixed with varying amounts of amine and in some cases solvent to obtain the casting solution (Table 1). These casting solutions were first pre-cured for several hours at 45°C to obtain a castable viscosity (Table 1). As soon as this castable viscosity was reached, films were prepared through doctor blade casting, using a Teflon substrate, and subsequently cured overnight at 45°C to allow the reaction to proceed till completion.

[0069] Example 2: preparation of dense membranes with varying amine:epoxide ratio

[0070] Dense poly(epoxyether) (PEE) membranes were prepared using the monomer ethylene oxide glycidyl polyhedral oligomeric silsesquioxane (EO-G-POSS) and / V^ / V' / V'-tetramethyl hexanediamine (TMHD) in varying ratios. Varying the epoxide / amine ratio in the sample is expected to control the relative extent of quaternary ammonium (QA) and poly(ether) chain growth polymerization, with high amine concentration resulting in more QA formation and low amine concentrations in more poly(ether) chain growth polymerization, as indicated by X-ray photoelectron spectroscopy measurement (Table 2). These casting solutions were first pre-cured for several hours at 45°C to obtain a castable viscosity (Table 1). As soon as this castable viscosity was reached, films were prepared through doctor blade casting,using a Teflon substrate, and subsequently cured overnight at 45°C to allow the reaction to proceed till completion.

[0071] Example 3: gas separation performance of dense poly(epoxyether) membranes

[0072] The gas separation characterization of the membranes described in example 1 and 2 show thatboth with varying amine concentration as well as with varying amine chemical structures, selective membranes with high CO2 / N2 selectivity and CO2 permeability could be obtained (Table 1). Gas separation testing was caried out by exposing the membranes to pure feed gasses at a transmembrane pressure of 2 bar and at an operational temperature of 35°C. Permeability was obtained using the constant volume varying pressure method. CO2 / N2 selectivity was calculated by taking the ratio of the pure gas permeability of CO2 and N2.Table 1: Synthesis conditions and gas separation performance of poly(epoxyether) membranes prepared using epoxides and amines from Figure 1. For DMHA 0.716g acetone was added to the mixture.

[0073]

[0074] Table 2: QA content of poly(epoxyether) membranes prepared using EO-G-POSS and TMHD and varying epoxide-amine ratios.

[0075]

Claims

Claims1. A method of preparing an epoxide-based dense membrane, the method comprising the steps of:a) reacting a first compound comprising a tertiary amine group, said compound lacking primary and / or lacking secondary amine groups, and said compound lacking an epoxide group with a second compound comprising an epoxide group and lacking an amine group, and allowing polymerization of the compounds obtaining an increase in viscosity, but not beyond the gel point,b) casting the viscous polymerized material, andc) allowing the cast polymerized material to cure until a solid film is obtained.

2. The method according to claim 1, wherein the compound comprising an epoxide group comprises between one and twenty epoxide groups.

3. The method according to claim 1 or 2, wherein the compound comprising an epoxide group comprises between one and eight epoxide groups.

4. The method according to any one of claim 1 to 3 , wherein the compound comprising an epoxide group has between 1 and 100 ether bonds which are not part of a ring structure.

5. The method according to any one of claims 1 to 4, wherein compound comprising epoxide groups has terminal epoxide groups.

6. The method according to any one of claims 1 to 5, wherein the compound comprising an epoxide group consists of an epoxide functionalized nanostructure.

7. The method according to claim 6, wherein the nanostructure is selected from the group consisting of a polyhedral oligomeric silsesquioxane (POSS), a metal organic framework (MOF), a zeolite, a silica, a carbon nanotube, a carbon nanosheet, a graphene oxide, and a covalent organic framework (COF).

8. The method according to any one of claims 1 to 7, wherein the compound comprising an epoxide group consists of an epoxide functionalized nanostructure, and comprises between one and twenty epoxide groups.

9. The method according to any one of claims 1 to 7, wherein the compound comprising an epoxide group consists of an epoxide functionalized nanostructure, and comprises between one and eight epoxide groups.

10. The method according to any one of claims 6 to 9, wherein the nanostructure is a polyhedral oligomeric silsesquioxane (POSS),11. The method according to any one of claims 1 to 10, wherein the compound comprising an epoxide group is glycidyl POSS (G-POSS) or poly(ethylene glycol) glycidyl POSS (EO-G-POSS).

12. The method according to any one of claims 1 to 11, wherein the compound comprising a tertiary amine group contains between 1 and 10 tertiary amine groups.

13. The method according to any one of claims 1 to 12, wherein the compound comprising a tertiary amine group is an imidazole, such as 1-Methylimidazole (1-MIM).

14. The method according to any one of claims 1 to 13, wherein the compound comprising a tertiary amine group is selected from the group consisting of N,N-di methyl hexa mine, N,N-Dimethylcyclohexylamine, N,N,N',N'-Tetra- methylethylenediamine, N, N, N ', N '-Tetra methyl- 1,3-propanedia mine, N, N, N ', N '-Tetra methy I- 1,4-butanedia mine, N,N,N',N '-Tetra methyl- 1,6- hexanediamine, N,N',N",N "-Penta methyldiethylenetriamine, 1,1,4,7,10,10- Hexa methyltriethylenetetra mine, Tris[2-(dimethylamino)ethyl]amine, Bis [2- (N,N-dimethylamino)ethyl] ether, N,N,N',N'-Tetraethylethylenediamine, 4,4'- (Oxydi-2,l-ethanediyl)bismorpholine and 4-(Di methylamino) pyridine.

15. The method according to any one of claims 1 to 14, wherein the compound comprising an epoxide group is Ethylene Oxide Glycidyl Polyhedral Oligomeric Silsesquioxane (EO-G-POSS) and wherein the compound comprising a tertiary amine is selected from the group consisting of N,N-dimethylhexamine (DMHA), N,N-Dimethylcyclohexylamine, N,N,N',N'- Tetramethylethylenediamine (TMHD), Tris[2-(dimethylamino) ethyl]amine (Me6TREN), and 1-Methylimidazole (1-MIM).

16. The method according to any one of claim 1 to 15, wherein the compound comprising an epoxide group is Ethylene Oxide Glycidyl Polyhedral Oligomeric Silsesquioxane (EO-G-POSS) and wherein the compound comprising a tertiary amine group is Tris[2-(dimethyl-amino)ethyl]amine which are mixed in a stoichiometric epoxide:amine ratio ranging from 1:1-10:1, and wherein the polymerisation is performed for between 1 h to 24 h at between 35°C and 55 °C, preferably at 45°C, and the cast polymerised material is cured at between 35°C and 55 °C, preferably at 45°C.

17. An epoxide-based dense semi-permeable membrane, made by casting a mixture monomers on a support, the membrane comprising up to 15 atomic % quaternary ammonium groups covalently-bound to carbon, as determined by X-ray photoelectron spectroscopy measurement, and lacking -alkanol amines.

18. The membrane according to claim 17, comprising 0.01 - 0.1 atomic % covalently-bound quaternary ammonium groups, or comprising 0.1 - 5 atomic % covalently-bound quaternary ammonium groups.

19. The membrane according to claim 17 or 18, which lacks sulfonic acid groups.

20. The use of a membrane according to any one of claims 17 to 19, in separating carbon dioxide from gas mixtures comprising carbon dioxide and nitrogen.

21. The use of a membrane obtained by the method according to any one of claims 1 to 16, in separating carbon dioxide from gas mixtures comprising carbon dioxide and nitrogen.

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