WO2017027899A1 - Method of gas separation - Google Patents

Abstract

The present invention provides a method of separating a target gas species from a mixture of non-amine gas species, the method comprising contacting the mixture of non-amine gas species with a gas separation membrane, the gas separation membrane comprising one or more solid organic ionic plastic crystal (OIPC); creating a difference in pressure across the membrane to facilitate transport of one or more gas species through the membrane so as to provide for a separated gas composition in which the concentration of the target gas species is higher compared with that in the mixture of non-amine gas species; wherein separation of the mixture of non-amine gas species is promoted by one or more of the gas species permeating through the structure of the one or more solid OIPC.

Description

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METHOD OF GAS SEMRATION

FIELD OF THE INVENTION

The invention relates in general to a method of separating a target gas species from mixture of non-amine gas species, and more specifically to a method of separating a target gas species from a mixture of non- amine gas species using a gas separation membrane. BACKGROUND OF THE INVENTIO

Separation of target gas species from mixtures of gas species is of significant importance to a large number of industries and is typically aimed at the recovery of valuable gases or to aid in pollution control. Established conventional technologies in this field include cryogenic distillation, swing adsorption techniques (e.g. pressure swin adsorption, vacuum swing adsorption, and temperature swing adsorption), and solvent absGrption (e.g. liquid extraction or stripping).

In addition to suc conventional technologies^ membrane gas separation is establishing itself as a valuable alternative technology for gas separation and is increasingly finding large scale application due to certain inherent advantages of membrane-based separation units over traditional separators. Specifically, gas separation membrane units can offer rapid mass transfer rate and high selectivity towards specific gases, are simple to operate and to install, they can operate under mild pressure d temperature conditions, and do not require use of corrosive and polluting solvents.

The efficiency of a gas separation membrane unit depends largely on the separatio performance of the membrane, which itself derives from the characteristics of the specific material from which the membrane is made. Conventional membrane-based separation technologies employ polymer-based membranes in the form of non-porous thin membranes or porous thick membranes. However, while non-porous thin membranes offer high selectivity towards the target gas species, they often suffer from poor mechanical stability at operative conditions. On the other hand, porous thick membranes offer good mechanical stability and flux rates but typically present lower gas selectivity. Accordingly, there remains an opportunity to develo a gas separation method that makes use of membranes based on non-conventional materials and offers gas separation with good selectivity while retainin mechanical integrity of the membrane during the separation process. SUMMARY OF THE INVENTION

The present invention provides a method of separating a target gas speeies from a mixture of non-amine gas species, the method comprising contacting the mixture of non-amine gas species with a gas separation membrane, the gas separation membrane comprising one or more solid organic ionic plastic crystal (OIPC); creating a difference in pressure across the membrane to facilitate transport of one or more gas species through the membrane so as to provide for a separated gas composition in which tlie concentration of the target gas species is higher compared^' with that in the ^ mixture of non-aniine gas species; wherein separation of the mixture of non-amine gas species is promoted by one or more of the gas speeies permeating through the structure of tire one or more solid OIPC.

Surprisingly, it has now been found thai gas separation membrane comprising one or more solid OIPCs is differentially permeable to gas speeies and can be used to effectively discriminate specific gas species contained in a mixture of non-amine gas species in a gas separation process. Without wishing to be limited by theory, it is believed the specific structure of solid OIPCs offers available free volume for the preferential transport of certain gas speeies relative to others.

Advantageously, the method of the invention is based on a gas separation membrane that combines good selectivity towards the target gas species while maintaining mechanical integrity during the separation. In addition, GIPCs are characterised by unique plasticity features. Specifically, they are known to undergo at least one solid-solid pfiase transition before melting. Advantageously such a solid-solid phase transition has been found to afford additional control ove the discrim ation of the targe gas species relative to traditional separation methods. It has now been found that different solid phases of the same OIPC have different permeability to the same gas species. In other words, the gas peimeahilii of a gas species through the structure of an OIPC can change as a result of a solid-solid phase transition of the OIPC; Accordingly, in one embodiment the method of the invention compri ses promoting a solid- solid phase transition in the solid OIPC to change permeability^■ of one or more of the gas species through the structure of the solid OIPC .

In another embodiment, the gas separation membrane consists essentiall of one or more solid OIPC.

In a further embodiment, the gas separation membrane further comprises a support for the one or more solid OIPC. This advantageously offers additional mechanical stability to the separation membrane. Also, by selecting a support material that itself offers gas separation capability it is possible to further enhance the efficienc of the separation membrane towards specific gas species.

In anothe embodiment, the gas separation membrane used in accordance with the invention further comprises a porous material, fo example Metal Organic Framework (MOF), Covalent Organic Framework (COF), zeolitie imidazolate frameworks (ZIFs), zeolite, activated carbon material, metal oxide, or a combination of one O more thereof. Advantageously, such porous material can act in synergy with the solid OIPC to enhance the separation performance, The presen invention is also directed to the use of one of more OIPC for separating a target gas species from a mixture of non-amine gas species, wherein separation of the mixture of non-amine gas species is promoted b one or more of the gas species permeating throug the structure of the one or more solid OIPC> hi addition to their surprising gas separation capability, OIPCs advantageously exhibit additional properties such as low to zero flamniability, negligible volatiHty and high thermal stability. Such properties are believed to be particularly advantageous in a variety of industrial activities in which it is required to isolate target gas species from niixtures of production gases* for example natural gas production, synthetic fuel production^ bulk inorganic and organic chemieals productionj and the likes,

BM!EF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be now described with reference to the following non- limiting drawings, in which:

Figure 1 shows the penneatioh rate for CO? and ¾ measured using a gas separation membrane made of methylethylpyrrolidinium tetrafiuoroborate ( C₂m }[BF₄]) in an eieetrospu polyv nylidene fluoride (PVDF) fibre support; Figure 2 shows single-gas flux rates as a function of the pressure difference across a gas separation membrane made of C¾mpy j [BF₄] in an eieetrospun PVDF fibre support;

Figure 3 shows single-gas flux rates as a function of the pressure difference across a gas separation membrame made of methyldiethylisobutyiphosphorrium hexalluorophos hate ([ i 22x4l[ P _&]) in an eieetrospun PVDF fibre support;

Figure 4 shows carbon dioxide flux versus transmembrane pressure data for a gas separation membrane made of ^m r] [BF₄] in an eieetrospun PVDF fibre support, a gas separation membrane made of Pi22i4] EP¾] n an eieetrospun PVDF fibre support, and a gas separatio merabrane made of methyipropyipyiTolidinium tetrafiuoiOborate ([C₃mpyr][BF₄]) in an eieetrospun PVDF fibre support; Figure 5 shows C0₂ and N₂ uptake ( ol %) into ([Fmi ][P¾K a»d

Figure 6 shows C0₂ uptake (ppni) into dipropylarmiioniim triflate [DP ][Tf{,

Some Figures contain colour representations or entities. Coloured versions of the Figures are available upon request.

DETAILED DESCRIPTION OF THE INVENTION

The method of the invention separates a target gas species from a mixture of non-amine gas species.

By the expression 'mixture of non-amine gas species' is rrieartt a combination of two or more gas species in which no gas specie has the chemical stracture NR₃, where each R group is independently hydrogen or an organic grou (e.g. alfcyi). An example of a NR₃ gas species is ammonia (N¾).

Apart from being a non-amine, there is no other limitation on the type of gas species sed in the method of the i vention. For example, the method of the invention may be used in the separation of .N₂ o Q₂ from air, separation of H₂ from N₂/¾ .and€¾ ¾ mixtures, recovery of CO or .¾ from hydrocarbon gases (e.g. in oil refinery processes), separation of C.H4 from the other components of biogas, enrichment of air ^'with O2 for medical or metallurgical purposes, enrichment of ullage with ]% in meeting systems designed to prevent fuel tank explosions, removal of water vapour from natural gas and other gases, removal of SO?, CQ₂ a d/or ¾S from natural gas, removal of volatile organic compounds (VOCs) from exhaust streams, or separation of CO and/or C0₂ from combustion gases.

In one embodiment, the method involves separating C0₂ from a mixture of gas species comprising CQ₂ and one o more of N₂, B_¾ CFI4, Q₂, ¾ , H S, SO_x, and NG_X. In another embodiment, the method of the invention involves separating CO₂ from a mixture of CG₂ and N₂, and/or separating C0₂ from a mixture of CQ₂ and C¾.

The method of the invention provides for a separated gas compositio in which the concentration of the target gas species is higher compared with that in the mixture of ironamine gas species. As the efficiency of the gas separation membrane increases so too will the concentration of the target gas species in the separated gas composition.

For avoidance of doubt, any reference herein to 'target gas species' is to be intended as a reference to the one Or more gas species that is/are of interest to separate/isolate from the non- amine gas mixture in which they are originally present. In this context, any reference herein to 'gas species' is to be intended as reference to any ne (or more than one) gas species present i the non-amme gas mixture, i.e. irrespective of whether it is a (or they are) 'target' gas species. There is no particular limitation on the concentration of the target gas species in the separated gas composition, provided it is higher compared With that of the target gas species in the mixture of non-amine gas species that was subjected to separation. In some embodiments, the concentration of the target gas species in the separated gas composition is at least 1.5, 2, 2.5, 3, 3.5. 4, 4.5, 5, 10, 20 or 50 times higher compared with that of the target gas species in the mixtyre of non-amihe gas species that was subjected to separation.

The method of the invention is performed using a gas separation membrane which comprises one or more solid organic ionic plastic crystal (OIPC). The expression 'organic ionic plastic crystal' (QIPC) used herein is intended to mean a salt that (i) contains a organic ion, (if) is a plastic crystal and (in) has ionic conductivity of at least 10^"s S cm when in its sub-melting phase.

In relation to (i) above, by the salt containing an 'organic ion' is meant a salt having a cation arid an anion wherein at least one of the cation and the anion is organic. In this context, by the ion being 'organic^* is meant that the ion contains a least one carbon atom. In one embodiment, both the cation and anion are organic.

In relation to (ii) above, as used herein the expressio 'plastic crystal' is meant to indicate that the salt displays at least one temperature-driven solid-solid phase transition before melting. In some cases this phase transition is difficult to observe or the lower temperature phase is difficult to form. In these cases the plastic crystal properties ca be indicated by the ionic conductivity of the material in its sub-melting phase.

By the expression 'solid-solid phase transition' is mean a temperature promoted rearrangement of the atomic structure, or parts of the atomie structure, of the GIPC. In the art, different solid phases of an OIPC are also referred to as 'rotator phases', and the solid- solid phase transition of an OIPC is accordingly referred to as 'rotator phase transition'. Those transitions are associated with temperature promoted onset of rotational or translational motions of the ions (or parts of the ions) resulting i a progressive transformation of the salt stractufe from^' a first lattice aiTangement to a second arrangement. The second arrangement is characterised by increased disorder., for example rotational disorder whereby all or part of the ion is in rotational motion. When in a plastic phase, the OIPC is more mechanically plastic. A person skilled in the art would be aware pi technique that can be adopted to measure and characterise a solid-solid phase transition of an OIPG. For th purpose of this application the technique of choice is Differential Scanning C orimetry (DSC). As it. would he known to the skilled person, DSC characterisation is performed at increasing temperatures and allows to obtain a plot of the heat flow into the OIPC versus a reference sample. From this, the heat capacity of the OIPC as a function of the test temperature can also be detenmined.

In general, a DSC plot allows visualising phase transitions of a material i the form of a discontinuity of the heat flow, versus a reference, at specific temperatures, for example in the form of a spike in the hea flow signal. Accordingly, for the purpose of this application solid-solid phase transition of an OIPC is characterised by a. DSC plot in which a discontinuity (e.g. a spike) of the heat flow in th sub-melting temperature range is Observed. For avoidaiiee of doubt, such discontinuity will be in addition to, and distinct from, the discontinuity arising from the solid-liquid traiisition of the OIPC (i.e. melting). In relation to (ai) above, the expression 'ionic conductivity of at least IG^"8 S/eni when in sub-melting phase' refers to the value of ionic conductivity that is deteniiined by Electrochemical Impedance Spectroscopy (IIS) according to the following procedure. The OIPC is first shaped into a pellet (1 mm thick and 13 mm in diameter under dry conditions, then sandwiched between two stainless steel blocking electrodes that are looked together, ^'The ionic conductivit is measured b EIS using a frequency response analyzer driven by an impedance measurement software (which ould be available t skilled person.) , Data is collected over a 10 MHz to 0.1 Hz frequency range and at a temperature at which the OIPC is solid and i the sub-melting phase. The temperature of the cell is controlled using a -high accuracy temperature cont iler (with accuracy better than ± 1°C), with the te erature measured using a thermocouple attached to one of the blocking electrodes, The sample is heated (typically at < 0,5^oC/niin) and thei^*mally equilibrated (typically for at least 5 minutes) prior to impedance measurement at each temperature point. The chemical nature of the anion and cation that constitute the salt for use in the invention is not particularly limited;, provided their combination results ifi an OIPC that satisfies (i)- (iii) above.

Examples of anions suitable to form the salt used in the invention include BF4^*, PE , N.(C )₂ (CF₃S0₂)₂N^~, (FSO^aN^", OCN^', SCN^~, dicyanomethanide, carbamoyl cyano(nitroso)methanide, (C₂F₃S0₂)₂N\ (CF₃SG_2:):₃C^", B(CN)₄ ^",

alkyl-SOsi perfluoroalkyl-S0₃ ^", aryl-SOs^", ^'Γ, H₂P0₄", HPO4^2", sulfate, sulphite, nitrate, triiluoiOmethanesulfonate, p-toluenesulfonate, bis(oxalate)borate_s acetate, formate, gall-ate,, glycolate, BF₃(CN)^", BF₂(CN)₂ ^", BF(CN)₃ BF₃(K|^", BP₂(R)₂ ^", BF(R)₃ ^" where R is an alkyl group such as Methyl, Ethyl, Propyl etc. and anions made from transition metal complexes, e.g. [Tb(hexafluoroaeetyiaeetonate)4].

As used herein, the term 'alkyl', used either alone or in compound words^ describes a group composed of at least one Carbon and Hydrogen atom, and denotes straight chain, branched or cyclic alkyl, for example Ci-ao alkyl, e.g. C.J-.IO or <¾. Examples of straight chain and branched alkyl include methyl ethyl, w-propyi, isopropyl, Λ-butyL see-butyl, ΐ- butyl, R-pentyl. 1,2-diniethylpropyl, 1,1-dimethyl-propyl, hexyl, 4-meth:>¾pentyl, 1- niethylpentyl, 2-met ylpentyl, 3-methylpentyl, l,i-dimethylbutyi, 2,2-dimethylbutyl, 3.,3- dimethylbutyl, 1,2-dimethylhutyl, 1,3-dimethylbntyl, l^^-trimethylpropyl, 1,1,2- trimethylpropyl, heptyl, 5~methylhexyl, 1 -methylhexyl, 2^2-dimethylpentyi, 3,3- dimethylpentyk 4,4-dimethylpentyl, tj2÷di ethylpemtyl, 1,3-dimethylpentyl, 1,4- dimethyl-pentyl, 1,2,3-trimethylbutyl, 1,1,2-triniethylbuty!, l,l_:,3-trimethylbutyl, Octyl, 6- methylheptyl, i-methylheptyl, l,l,3 -teteamethylbutyl, nonyt 1-, 2-, 3-, 4-, 5-, 6- or 7- methyloctyl, 1-, 2-, 3-, 4- or 5 -ethyl heptyl, 1-, 2- or 3-propylhexyI, decyl, 1-, 2-, 3-, 4-, 5-, 6-, 7- and 8-methylnonyl, 1-, 2-, 3~, 4-, 5- or 6~eth loctyL 1-, 2-, 3- or 4-propyiheptyl undecyl, .1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-methyldecyi, 1-, 2-, 3-, 4-, 5-, 6- or 7-ethyliionyL 1-, 2-, 3-, 4- or 5-propyloctyl, 1-, 2- or 3-butylheptyl i-pentylhexyl, dodeeyl 1-, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9- or 10-methyiundecyi, 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-ethyldecy 1, 1-, 2-, 3-, 4-, 5- or 6-propylnonyl, 1-, 2-, 3- or 4-butyloctyl, ! -2-pentylheptyl and the like. Examples of cyclic alkyl include mono- or polycyelie alkyl groups such as cyciopropyi, cyelobutyl, cyclopentyl, eyclohexyl, cyeloheptyl, eycloaetyl, eyelononyl, cyclodecyl and the like, Where an alkyl group is teieired to generally as 'propyl', ^'butyl* etc, it will be understood that this can refer to any of straight, branched and cyclic isomers where appropriate. An a kyl group may be optionally substituted by one or more optionaksubstituents as herein defined.

The term 'aryi' (or^■ carboaryl') denotes any of single, polynueiear, conjugated and fused residues of aromatic hydrocarbon ring systems (e.g. o C₆,ig), Examples of aryl include- phenyl, biphenyi, terphenyl, quatei heiiyl, ttaphthyl. tetrahydronaphthyl, anthracenyi, dihydroanthracenyl. benzanthracenyl, dibenzanthraeeiiyl, phenanthrenyl, fi orenyl, pyrenyl, idenyl, azulenyl, clirysenyl. Preferred aryl include phenyl and naphthyi. An aryl grou may of may not be optionally substituted by one or more optional substituents as herein defined. The term ' ary!ene^:' is intended to denote the divalent form of aryl

Examples of cations suitable to form the salt used in the inventio include dialkylpyi Olidmium, pyrrolidmium, monoalkylpyr Olidinium, dialkylimidazoliuiri, monoalkyiammottium, imidazoliiim, tetraalkyiammonium, quaternar ammonium, trialkylammomum, diaiky!ammcmium, dialkanolalkylammonim , alkanoidialkyl ammonium, bis(a&yii idazolium)₅ bis(dialkyl)amnioni im, bis(irialkyl)ammomi¾n, diallylammonium, dialkanGlammonium, aikylalkanolammoriium, alkylaliylam omum, guanidinium, diazabicyclooctane, tetraalkyl phosphoniums, trialkyiphosphoniums, triaikylsuif niums, tertiarysulfelimum¾ imidazoHnium, cholinium, fbrmamidinium, fbrmadinium, bicyelic (spiro) atnmoniurri, pyrazOli^:mti, . 6j¾idraidaz6iiura, dibenzylammomum, caffiileium, piperazimum, dialkyi amino)arnmomum, alk ^diatmi^ammon m, triaminoammonium; aminopynOlidium, and amraoimidazoliiam

in the method of the inventio the OIPC is solid. By the OIPC being 'solid' is meant that the OIPC is in, and maintains, a solid state under the gas separation conditions of temperature, pressure and eliemical nature of the gas species being separated, and exhibits a non-zero value of shear modulus at low applied stress. The solid may exhibit plastic flow at values of applied stress above its yield stress. Accordingly, the expression 'solid state^* used herein, will be understood as being in contrast with 'molten state' or 'solution state' (i.e dissociated by solvation).

In the method of the invention gas separation is achieved b promoting transport of gas species through a gas separation membrane comprising a solid OIPC. Specifically, gas separation of a mixture of non-amine gas species occurs as a result of one or more gas species permeating tlirough the structure of the solid OIPC,

By the one or more gas species pefmeating 'through the stmeture of the solid OIPC it is meant that (a) th gas species are transported tlnOiig the gas separation membrane by passin through, the atomic stmcture of the QWC, and that in doing so (h) the OIPG maintains its solid state. Accordingly, the structure of the OIPC remains in a solid state during the method of the invention,

In relation to (a) above, without wishing to be limited by theory it is believed permeation of gas species through an OIPC is associated with, and made possible by. presence of defects in the OIPC atomic shucture. For example, it is postulated that the permeation occurs through either vacancies in the lattice or throug extended defects such as dislocations or grain boundaries within the structure of the solid OIPC .

The presence of defects may also be associated with increased rotational and translational disorder of the ions. The onset of additional disorder when an OIPC undergoes a solid- solid phase transition can also result in a significant increase in the OIPC free volume.

Collectively, it is postulated that all lattice defects within an OIPC makes for a significant amount of excess free volume in addition to the free volume that inherently exists in the OIPC when In its fully packed crystalline form, In relation to (b) above, the definition is intended t exclud a situation where a gas species, when in contact with the gas separation membrane, dissolves the OIPC. For example, the situation where a solid OIPG liquefies when In contact wit an arnine-gas such as amanoma_^ in contrast, according to the method of the present invention gas separation occurs by one or more of the gas species permeating through the structure of the solid OIPC, with the solid state of the OIPC being maintained throughout the gas separation process.

As use herein, the term 'peraieating' and analogous forms such as 'permeateis)^* or 'permeation', is intended to mean transport of the gas species throug the atomic structure of the solid OIPC, Such transport can be faeiiitated when a pressure difference exists aexoss the separation rnembrane.

As a skilled person would ^'know_., permeation of gas speeies through membrane materials is facilitated by the affinity between the gas speeies and the composition of the membrane, Without wishing to be limited by theory, peHneatiOn of gas speeies through the solid OIPC structure is believed to be facilitated in a similar manner.

During the separation process according to the present invention gas speeies are believed to be absorbed into the stmeture of the solid OIPC, diffuse throug the OIPC driven by the concentratio gradient within the OIPC, and desorb at the lower pressure side.

According to commonly accepted gas separatio theories, gas separation, is typically quantified using terms such as ^'permeability' (P), 'diillisiyity .(D) .and ^'^so^T iiiiy (S).

The permeability P of the gas species is correlated to the diffusivity D and the solubility S by the relation:

P - D x S,

where D is a kinetic parameter and S a thennodynamie parameter. According to the present invention, without wishing to be limited by theory it is believed gas separation occurs as a result of different solubilities in the OIPC of the target gas compared to other gas species in the gas mixture. The diffusivity of the target gas may also be different than that of gas species in the gas mixture. The pemiselsetivity, ¾ is the ratio of pei-meability P of two gases A and B being separated. Thus, this can be determined by measurement of the permeability of the -two gases individually then .calculated using;

For high -selectivity, this good diffusivity needs to be combined with high, soluhihty- selectivity for the target gas over- another gas, e>g, CO* versus ¾¾. In one embodiment, the one or more gas species peimeaflng through the structure of the solid OIPC coixespond to the target gas species. In such an embodiment, the separated gas composition is collected from a permeate side of the gas separation membrane.

In anothe embodiment, the one or more gas species permeating through the structure of the solid OIPC do not correspond to the target gas species. In that case, the separated gas composition is collected from a reteniate side of the gas separation membrane, in other words, the target gas species is separated as a result of the other gas species in the gas mixture penxieatin through the solid OIPC.

In one embodiment, the method of the invention further comprises promoting a solid-solid phase transition in the one or more solid organic ionic plastic crysta to thereby change permeability of one or more of the gas species through the structure of the one or more solid organic ionic plastic crystal.

A skilled person would know how to promote a solid-solid phase transition in an OIPC. in one embodiment, the OIPC solid-solid phase transition is promoted by changin the temperature at which the gas separation is effected from a temperature Tj to a temperature T₂. There is no limitation as to what are the values of Ti and T_¾ provided that when selected from a DSC plot of the coiTesponding OIPC, ¾. and T₂ .are. selected from temperature ranges characterising two different solid phases of the OIPC, as identified in the DSC plot In some embodiments, the absolute difference between T_x and T? is 15()°C, 100°C, 75°C, 50°C, 25°C, 1.0:°C, or 5°C.

In some embodiments i is a temperature between about D and about 30°C, arid Ti is a temperature between about 60 and ^'9G°^'C.

Practical procedures and devices to effect such a temperatiire change would be known t

ilie skilled person. These may include, for example, providing means to modify the temperature of the mixture of lion- amine gases contacting the gas sejparatio membrane (e.g. by ay of a heat exchanger that uses heat from another process stream), or providin the gas separation membrane itself with heating means (e.g. an embedded resistance coil heater).

As used herein, the expression 'gas separation membrane' refers to a material through which at least two gas species can permeate at different rates. I this context, there is no limitation to the composition, form, or shape of the 'gas separation membrane', provided it comprises one or more solid OIPC.

In one embodiment, the gas separation membrane consists essentially of one or more solid OIPC. Membranes according to mat embodiment may be of any shape or form, provided they maintain mechanical stability during gas separation. i¾r example, these membranes ma be formed by pressing the OIPC into sheet or pellet form of varying thicknesses, wliieh may be in the range of 0.001 to i mm.

In another embodiment, the gas separation membrane further comprises a support for the solid OIPC_* There is no particular limitation on the nature or configuration of the support, as long as it assists with providing mechanical integrity of the gas separation membrane during the gas separation. The support should also not adversely affect the gas separation.

In one embodiment, the suppor is in the form, of a porous substrate having a first and second surface region between wliieh the gas species can flow. In such an embodiment the OIPC is located on at least one of the first and second surface regions to interject the direction of flow of the gas species.

The porous substrate contains pores that enable gas to flow through the substrate between the first and second surface regions. By the substrate being 'porous' or the substrate containing 'pores' is meant that the substrate contains voids or holes that arc suitably arranged to provide passageways within the substrate that enable the transport of gas between the first and second surface regions.

The porous substrate may not provide an form of selectivit function of a mixture of gases that passes through' it, In other words, the pores within the substrate may be large enough for the mixture of gas species to pass through without undergoin any significant degree of separation. In that case, the porous substrate should provide little if no resistance to gas flow.

Provided the porous substrate can be fabricated into the gas separation membrane in accordance with the invention there is no particular limitaiioh on the shape or dimensions which it may take.

In one embodiment, the porous substrate is in the form o a sheet material or a hollow fibre. Where the porous substrate is in the form of a hollow fibre, for avoidance of an doubt it will be appreciated that tire wall structure of the hollow fibre presents as the porous substrate per se. hi that case, the inner wall surface of the hollow fibre may be considered to be the first surface region of the porous substrate and the outer wall surface of the fibre may be considered to be the second surface region of the porous substrate, or vice Versa.

There is no limitation as to the thickness of the porous substrate. The 'thickness' of the substrate is intended to be the distance betwee the first and second surface region between which the gas species ill flow. Generally, the porous substrate will have a thickness ranging from about 0.001 to 1 mm.

In one embodiment, the support is in the form of a matrix within which the one or more solid OIPC is contained.

As used herein, the term 'matrix' is intended to mean a secondary solid component of the separation membrane. There is no iimitation regarding the nature of the matrix provided the solid OIPC cam be distributed, throughout the matrix, and that the matrix does not adversely affect the gas separation. The matrix may provide mechanical integrity to the separation membrane, or facilitate the solubility of gas species in the membrane, thereby aiding the gas separation. In one embodiment, the matrix is homogeneous polymer. For example, the gas separation membrane may be prepared b dispersing the ©IPC within monomer which is subsequently polymefised and/of cross-linked to form a polymer matrix with n which the OIPC is distributed. Alternatively, the matrix may be i the form of fibres, for example^■polymer fibres. In that case, the gas separation membrane may be provided from a combination of the solid OIPC and fibres. Such a, membrane may be provided by (i) casting a solution of OIPC dissolved in a solvent onto a bundle of fibres, (ii) removing the solvent to form solid 03PG throughout the fibre bundle, and (iii) forming the gas separation membranie by shaping the fibre bundle and solid OIPC into a desired shape. In this context, shaping may be achieved by any means known to the skilled person, for example by compression o kneading. Examples of shapes into which the gas separation membrane ma be formed include pellets, discs, and flat sheets, In one embodiment, the fibres are eleetrospim polymer fibres. Tec ologies and methodologies for producing eleetrospun polymer fibres are known to those skilled in the art.

In one embodiment the support is made of an inorganic material, for example a ceramic material, for example a metal oxide such as alumin or silica.

In another embodiment the support is made of an organic material, for example polymer.

Examples of polymers suitable for making a support according to the present inventio include sulfonic acid polymers such as poly(2-acxyIamido-2-m©^

acid) (PAMP), polyvinylidene fluoride (also known as poiyvinylidene difmoiide) (PVDF). sulfonated poly(ether ether ketone) (SPEEKL). in one embodiment, polymers suitable for making a support according to the present invention also assist in the separation of the gas species. Such polymers are know to have porosity characteristics that make them selectively permeable to certain gas species relative to others. When combined with the OIPC to form a gas separation membrane according to the invention these polymers act synergisticall with the OIPC in the separation of the target gas species by increasing the solubility or diffusivity of ceitain gas species in the separation membrane. Depending on the nature of the target gas species, a person skilled i the art would be capable of devising an suitable combination between one or more polymers of this kind and the appropriate OIPC in order to achieve such synergy .

Examples of polymers known to have porosity characteristics that make them selectivel permeable to certain gas species include substituted polyaeetylenes (e.g> poly (1- (trimethylsilyl)-l-piOpyne) (PTMSPs), poly (l-idimethyl-f^propylsilyl)-i-propyne), poly ( 1 -(dimethyl-n-butylsily 1 )-l -propyne), poly ( i -pheny 1-1 ÷propyne)poly

(dipheilyiaeetylene), poly (i-butylaCetylene), poly {i-phenyl-2-j!7-trimethylsilylphenyl- acetylene), pol (1 -phenyl -2-^?~hydroxypheny]-acetylene), co-polymers thereof, or any mixtures thereof), poiy(ethylene .oxides)* polyamides, polyimides, polysulfoiies, polycarbonates,, polyarylates, poly(phenyleneoxide)s, polyanilines, thermally rearranged polymers, and polymers of intrinsic microporosity (PlMs) (e.g. polyphtalocyanines, polyspirobismdanes, polybenzidioxanes, or any combination thereof), and any combinations thereof. When the gas separation membrane comprises a support, the OIPC will typically constitute at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the membrane total weight. In one embodiment, the OIPC constitutes between 5% to 95%, 1 % to 95%. 20% to 95%, 30 to 95%, 40 to 95%, 50% to 95%, 60% to 95%, 70% to 95%, 80% t 95%, or 90% to 95% of the membrane total weight, hi another embodiment, the OIPC constitutes between 5% to 75%, 10% to 75%, 20% to 75%, 30% to 75%, 40 to 75%, 50% to 75%, 60% to 75%, or 70% to 75% of the membrane total weight. In another embodiment, the OIPC constitutes between 5% to 50%, 10% to 50%, 20% to 50%, 30 to 50%, or 40: to: 50% of the membrane total weight.

In one embodiment, the gas separation membrane further comprises a porous material, for example a nanopofous material

As used herein, the expression 'porous material' means a material containing voids, and specifically voids that allow passage of gas species through the material. As used herein, the expression 'nanoporous' material refers to a material that in its native state has a porosity deriving from voids or cavities whic smallest dimension is not larger than 100 nm.

The porous material may act syiiergistically with the OIPC in the separation of the target gas Species by increasing the solubility of diffusivity of certain gas species in the separation membrane relative to the separation membrane absent the porous material.

Examples of suitable porous material include Metal Organic Framework (MOF), a C¾vaSent Organic Framework (COF), a zeolite, an activated carbon material, a metal oxide, or any combination thereof.

Examples of MOFs suitable for use in the present invention meiude cai¾oxylate-based MOFs, heterocyclic azolate-based MOFs, metal-cyanide MOFs, and an combination thereof. Specific examples of MOFs that are suitable for use in the present m etition include those commonly known in the art as CD-MOP- 1, CD-MOF-2, CD-MQF~3, CPM- 13, FJ!-F FMOF-i, HKUST-1, IRMOF- , MMOF-2, IRMOF-3, IRMQF-6, iRM F-8, 1RMOF-9, I M F-13, IRMOF-20, JUC-4S,. JUC-62, MIL 01, Mll-IDO, M L-125, ^'MIL- 53, MiL-88 (including MIL-88A, MIL-88S, MIL~88C, MIL-8SD series), MOF-5, MOF- 74, MQF-177, MOF-210, MQF-200, MOF-205, MOF-505, MOR F-2, MOROF-1, OTT-100, NOTT-101 , NQTT-1Q2, NOTT-1:03, ΝΌΤΤ-105, NOTT- 06, NOTT-107, NGTT-1Q9, NGTT-l lQ, NOTT-l l l, KOTT-112, MOTT-113, NGTT-114., NQTT-140, NU-100, rho-ZMOF, PCN-6, ΡΟΝ-ό', PCN9, PCN10, PCN12, PCN12', PCN14, PCN16, PCN-17, PCN-21 , PCN46, PCN 6, PCN68, PMQF-2(Cu), PMOF^, S U-5, SNU-15', SNU-21 S,. SNU-21H, SNU-50, SNU-77H, TJiO-66, UiO-67, soc-MOF, sod-Z OF, TUBMOF-i, TJMCM-2, UMCM-150, IJTSA-20, ZIF¾ ZIF^3, ZIF-4, ZIF-8, ΖΪΡ-9, ZIF- 10, ZIF-11 ZIF-12, ZIF-14, ZIF-2G, ZIF~2f, ZlF-23, ZIF~60, ZIF-61, ZIF-62, ZIF-64, ZIF-65, ZIF-67, ZIF-68, ΖΓΡ-09, ZiF-70, ZIF-71 , ZIF-72, ZIF-73, ZIF-74, ZiF-75, ZIF-76, ZIF~77, ZIF-90, and any combinations thereof.

Further examples of MOFs suitable for use in the present inventio are disclosed in WO 2010/075610, the content of which is included herein as reference in its entirety.

Examples of COFs suitable for use in the present invention include those conunonly known in the art as COF-1 , COF-5, COF-6, CGF-8, COF-10, COF-42, C F-66, COF-43, COF 02, COF-103, COF-105, COF-108, COF-202, COF^QO, CQF-366, triazme-based COFs (e.g. CTF-l, CTF-2), TP-COF, NiPoCOF, NiPc-BDTA-COF, ZnP-CQF, CuP-CQF, H₂P-COF, HHTP-DPB-CGF, ZnPc-PPE-COF, PPy-CGF, D-A GOF, CTC-COB, and any combinations thereof.

Further examples of COFs suitable for use in the presen invention and details on their synthesis are disclosed in. X. Feng et al, Chemical Society Reviews 2012,_: Vol. 41, Pages 6010-6022 , the content of which is included herein as reference in its entirety .

Examples of zeolites suitable for use in the present invention include zeolite A (e.g, Na, , Ag, Mg, Ca forms), zeolite X (e.g. Na, Li, Ca, Ba form)., mordenite (e.g. Na, H, Ca form), chabazite (e.g. Na, Ca form), elinoptilolite (e.g. K, C form), silicalite, and any combination thereof.

Examples of activated carbon suitable for use in the present invention include powdered activated carbon (R 1, PAG), granular activated carbon (GAG), extruded activated carbon (EAC), bead activated .carbon. (BAG), impregnated carbon (e.g, iodine, silver, and cations such as Al, Mn, Zn. Pe, Li, Ca impregnated carbon), and any combination thereof. Examples of metal oxides suitable for use in th invention include aluminium oxide, chromium(ii) oxide, chromium(iii) oxide, diiOiiiium(iv) oxide, elTi niiurn(vi) oxide, e balt(ii) oxide, cobalt(ii, iii) oxide, cobalt(iii) oxide, eopper(i) oxide, eopper(ii) oxide, iron(ii) oxide, ironiii, iii) oxide, iron(iii) oxide, litliium oxide, magnesium oxide, manganese(ii) oxide, manganese(iii) oxide, manganese(iv) oxide, manganese(vii) oxide, nickei(ii) oxide, nickel(iii) oxide, silicon dioxide, lin(ii) oxide, iirsiiv) oxide, titanium diox de, zinc oxide, and any combination thereof.

If used, the porous material may constitute at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the total weight of the membrane, or between 0.5% to 50%, 1% to 30%, 1 % to 20%, 1% to 10%, or 1% to 5% of me total weight of the membrane.

The method of the invention comprises creating a -difference, in pressure across the membrane to facilitate transport of one or mo e gas species through the membrane.

^'Techniques for creating such a differential pressure across a gas separation membrane are well knoWn to those skilled in the art., and are not particularly limited to an specific technique provided it results in a differential pressure acros the membrane, For example, opposing sides of a membrane may be isolated from each other (in terms of ga flow) and the mixture of gas species to be separated applied under pressure to one side of the membrane. In practice this may achieved in separation modules of the kind known in the art, examples of which include flat sheet modules (e.g. plate-and-frarne and spirally- wound modules) and tubular modules (e.g. fine capillaries or tubes housed like a shell and tube heat exchanger) .

As a person skilled in the art would know, pressure conditions suitable m the invention may be expressed in terms of pressure ratio R:

P_r

R

Where P_r and P_p are, respectively, the absolute pressure at the retentate and -permeate side of the gas separation membrane, measured at the corresponding surface of the separation membrane.

There is no particular limitation to the values of pressure ratio suitable for use in the invention, provided ^'there is a difference in pressure acros the membrane to facilitate transport of one or more gas species through- the membrane. m one embodiment, the pressure ratio R is in the range < R ! 0,000, 1 < R 5^000, 1 R <1,000, 1 < R 750, 1 < R <500, 1 < R <250, 1 < R 100, t < <50, 1 < <25. 1 < R≤i 0j, 1 < R≤5, 1 < R <2. In some embodimeMs, the pressure ratio R is in the range 2 < R <IO,OO0, 2 < 1,0Q0, 2 <R <75G, 2 < 500, 2 < <250, 2 <R≤100, 2≤R <5⁽). 2 <R≤25, 2≤R≤10^ or 2≤R≤5. some embodiments, the pressure ratio R is in the range 5 < R≤1O,OO0, 5 <1,000, 5 <R <?50. 5 < ≤50¾ 5 <R 5 <R _≤100, 5

<R <50, 5 <R <25, or 5 R < ! 0, In some embodiments- the pressure ratio R is in the range 10 < R≤10,000, 10 <R≤1,000, 10≤R≤J50, 10≤R≤5QQ, 10 <R <250, 10≤R <100, 10 <R <50, 10≤R <25, In some embodiments, the pressure ratio is in the range 25 < R≤10,000, 25 <R 1,000, 25 <R <750, 25≤K 50Q, 25 <R 250, _: 25 R <100 or 25 <R <50. There is no particular limitation as to the operative temperature at which gas separation is effected, provided the GiPC is solid at that temperature. In one embodiment, the temperature is between about 20°C and 120°C.

The present invention also provides for the use of one or more GIPC for separating a target gas species from a mixture of non- amine gas species, wherein sepai¾tion of the mixture of iion-amine gas species is promoted by one or more of the gas species permeating through the struciure of the one or more solid OIPC.

Specific embodiments of the invention will now be described with reference to the following non-liniiting examples, EXAMPLES

The- e amples described herein include gas permeation measurements performed on single gas species, which are indicative of the relative penneabilit of the same gases when separated from a mixture 'Containing those gas species. This approach is supported by the reports of J. B. AlexopouioS et al. Polymer 10 (1969) 265-269, and is eonimonl used i the field (see for example Hassan et al. Journal of Membrane Science 104 (1995) 27-42, Tome et al. Journal of Membrane Science 428 (2013) 260-266}. EXAMPLE 1

Synthesis of OIPCs

Synthesis of methyldiethylisobutylphosphGnium hexafluorophosphate ([Pi22_¾][P¾]) ^was performed according to the procedure described i detail in Journal of Materials Chemistry (2011) 21, 7640-7650, the content of which is incorporated herein in it entirety.

Synthesis of dipropylaminOniuna inflate ([DPAJfTfj), which is a protic OIPC, was perfoimed by adding slowly one mole of aqueous solution of triflic acid to one mole of dipropylamine cooled in an ice bath. After the addition, the contents were stirred for another 30 minutes and then the mixture dried on a rotary evaporator at 70°C The solid product was further dried at room temperature by storage in a vacuum desi ccator. EXAMPLE 2

Synthesis of OlPC/p&lymer fibre gas separation membranes Poiyvinylidene fluoride (PVDF) mats were made using ©leetrospun PVDF fibres as described in Journal of Materiais Chemistry A 3 (2015) 6038-6052^, the content of which is incorporated herein hi its entirety. Pellets of 12.5mm diameter were punched frotn the resulting mats, for use in the membrane. [C mpyT][BF₄]/PVDF membranes were made by preparing solution of 1 :5 w/w OIPC in methanol and easting the solution onto the PVDF mats obtained as described above. The mass of the PVDF fibres was 4mg and the mass of OIPC used was l ¾hg, giving a total dry mass of 23mg after removal of th methanol. The membranes were dried in a vacuum oven overnight at 55°C before pressing. The thickness of the membrane was 150_, m, prepared by pressing the pellet on a 1 ton press for 1/2 an hou at 70°C.

[Gjm i] [BF^/PVDF membranes were made by preparing a solution of 1 :5 w/w OIPC in ethanol and easting the solution onto the PVDF mats described above, The mass of the PVDF fibre was 2mg and the mass of OIPC used was 9mg, giving a total dry mass of l lmg after removal of the ethanol. The membranes were dried in a vacuum oven overnight at 55°C before pressing. The thickness of the membrane was 7ίμΐα, prepare by pressing the pellet on a 1 ton press for 1/2 an hour at room temperature,

[Pi i ][PFg P DF membranes were made by preparing a solution of 1 :5 w/ OIPC in ethanol and castin the solution onto the PVDF mats described above. The mass of the PVDF fibre was 4mg and the mass of OIPC used was 20mg, giving a total dry mass of 24mg after removal of the etlianol. The membranes were dried in a vacuum oven overnight at 55°C before pressing. The thickness of the membrane was 143 , prepared by pressing the pellet on 1 ton press for 1/2 an hour at room temperature, EXAMPLE 3

Set up ofgas pe ieahiiity measurements using OlPC/paiymer fibre membranes Penxicatioii measurernents were performed usin a permeation apparatus based, i construction and valve placement, On tie one described in detail in Journal qf Membrane Science 428 (2013) 260-266, the content of which is incorporated herein in its- entirety.

The gas contacting surfaces were all stainless steel witli Swageloi fittings and Viton o- rings. The feed- and pe meate-side pressure transducers were both Keller Series 35X HT absolute-range transducers witli a 4-20 mA output and a compensated temperature range of 20-120^cC, The feed tank was 2200 ml/ with a 0-10 Bar(abs) transducer and the permeate tank was 35niL with a 0-iBar(abs) transducer. A type-k therinocouple was used to measure the temperature, and the vacuum used was 4x10^"" iuBar, This apparatus was housed in a Binder BF 115 Model incubator with temperature control from 5°C above room temperatur to i00°C, with 0,2°C accuracy. Transducer and thermocouple outputs were recorded using an MCC USB-2404-UI model data acquisition unit with 24-bit resolution. In a typical experiment;, the sample was mounted in the sample holde which was positioned between the feed and permeate tanks and which was constructed in such a way as to prevent circumvention of the mounted membrane by the gas. in other words, if a gas moves From the feed tank to the permeate tank, it must necessarily have flawed through the mounted membrane. After mounting, vacuum was drawn on both sides of the membrane in preparation: for the first permeation experirneni. The apparatus was then allowed to equilibrate at the desired experimental temperature and left under vacuum overnight before introducing the penetrant gas and beginning the experimeni.

A single gas was tested at a time. Between experiments using the same gas, a time greater than or equal to ten times the 'time-lag' was allowed to elapse, during which time a vacuum was maintained on both sides of the membrane. The 'time-lag' approach is consistent with that reported by El. L. Frisch Journal of Physical Chemistry 61(1) (1957) 93—95, and J. B, Alexopoulos et al. Polymer IQ (1969) 265-25 and Toirie et aL Journal of Membrane Science 428 (2013) 260-266, the content of which is incorporated herein in its entirety.

For example, if the 'time-lag' was ten minutes, meaning it took ten minutes to reach a Steady State of flux across the membrane, then the membrane was kept unde vacuum for one hundred minutes between the conclusion of one permeation experiment and the commencement of the next peraieation experiment provided the gas type had not been changed.

In the case that gas type was changed between permeation experiments, the membrane was kept under vacuum overnight before the next permeation experiment was started. EXAMPLE 4

Gas permeability measurements using OlPC/palymer fibre membranes

Data shown in Figure 1 were obtained using [C^rm J[BF₄} ^D polymer fibre gas separation membrane obtained according to the procedure described in Example 2 (90° C), on an instrument consisting of a large feed tank; and a small permeate tank separated by the gas separation membrane. A transmembrane pressure gradient is: established by pressurising the feed tank with a single gas species at a time and pulling a vac um on the pemieate tank. Gas flux through the membrane is measured by monitoring the increase in pressure in the permeate tank.

Figure 1 is a graph plotting the change in permeate tank pressure over time. A gas species will tend to follow the pressure gradient from the feed tank, across the membrane, and into the permeate tank. As this occurs, the permeate tank pressure increases. The graph shows that€G₂ permeates through the [C₂mpyr] [BF₄]/P¥DF polymer fibre membrane a a higher rate than nitrogen. Data shown in Figure 2 were^■obtained us¾g a [C2m rJ BF ]/PVDF polymer^' fibre gas separation membrane obtained according to the procedure described in Example 2, at 35' C over a pressure range of 1 to 2 Bar and using the same setup use to obtain the data shown in Figure 1. The graph in Figure 2 plots single-gas flux rates as a function of tlie pressure difference acros the membrane. One curve from Figure 1 becomes a single point on this graph. The representation of infonnalion in Figure 2 allows more precise calculation of flux rates because the can be normalized against changes in transmembraiie pressure. This representation is useful when flux rates for a particular gas are very low. The membrane in use is the same as was used to produce the data in Figure 1 and when these data are fitted (blue line), they sho w that the flux of nitrogen causes an increase of approximately 6 rtBar per second pe Bar of transmembrane pressure.

Data shown in Figure 3 were obtained using a [Pj2 i4]£PFgJ PVB polymer fibre gas separation membrane obtained according to the procedure described in Example 2, at 35°C and at a pressure range of 1 to 5 Bar. The graph depicted in Figure 3 shows the same representation of data as Figure 2. The data show consistent increase in flux as the transmembrane pressure is increased to 5 B;ai_¾ which was the highest pressure tested. From the ratio of the fitted slopes of the individual gas species, a selectivity of 23 is calculated .

-M -

EXAMPLE 5

Gas Absorption tests using OIPCs A smaller experimental setup consisting of a small main volume and an isolated sample chamber was constructed using similar components used for the permeability apparatus described in Example 3, The main volume and the sample chamber were isolated by a valve. The sample was held under vacuum at the desired temperature overnight and the main volume was pressurized. The experiment was started by opening the alve which separated the main volume and the sample chamber, thereby introducing the gas to the sample. This is initially recorded by the msta entation as a shar dro in head pressure as the gas from the main volume fills the volume f the sample chamber, followed by the curve corresponding to iptake of the gas by the sample. This drop hi head pressure was measured over time as the sample absorbed the gas.

Figure 5 shows gas uptake data measured using £PI22H}[P¾]. The GTPC was placed in a. small chamber and exposed to vacuum overnight between experiments. A single-gas (either ^'C0₂ ^'or 1%) was then introduced and the change i head pressure was recorded fo several hours. This was performed at both 35 and S°C The plot of Figure 5 shows a larger reduction in head pressure under a carbon dioxide atmosphere tha under a nitrogen atmosphere, which is consistent with selective absorption of C0₂ over N₂,

Figure 6 shows gas uptake data measured usin Dipropylammonium triflate ([DPA][TfJ), using the same procedure adopted to obtain the data shown in Figure 5. In the chemical structure of [DP A] [Tf] the cation has mobile proton. This is in contrast to the OIPCs used in the tests described in relation to Figures 1 -5, which do not have mobile protons on the cation. The data in Figure 6 shows the ability of dipropylarmnonium triflate to absorb 00?· Every formulation- or combination of components described o exemplified herein can be used to practice the invention, unless otherwise stated. Specific names of compounds are intended to be exernplaiy, as it is known that one of ordinary skill in the art can name the same compounds differently.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word 'comprise', and variations such as 'comprises' and 'comprising', will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step of group of integers or steps.

The reference in this specification to any prior publication (or inclination derived from it), or to aity matter which is known, is not, and should not be taken as an acknowledgment or admission or any form, of suggestion that that prior publication (or information derived fi m it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE I VENTIDH ARE AS FOLLOWS

1. A method of separating a target gas species torn a mixture of -noil- amine gas species, the method comprising:

■contacting' the mixture of non-amine gas species with gas separation membrane, the gas separation membrane comprising one or more solid organic ionic plastic crystal (©IPC);

creating a difference in. pressure across the membrane ·*ø facilitate transport of one or more gas species through, the membrane s as to provide for a separated gas composition in which the concentration of the target gas species is higher compared with that in the mixture of non-aniine gas species;

wherein separatio of the mixture of non-amine gas species is promoted by one or more of the gas species permeating: through, the structure of the one or more solid ©IPC. 2. The method of claim 1, further comprising promoting a solid-solid phase transition in the solid OIPC to change permeability of one or more of the gas species through the stmcture of the solid OIPC .

4. The method of any one of claims 1 to 3, wherein the one or more solid OIPC comprises a cation selected from diaikylpyrt'olidiiiiiiin, pynOiidinium, monoaikylpyrrQiidifflum, diaikjiimidazolium, monoalkylammonram, imidazoli urn, ietraalkylammonium, quaternary ammonium, trialkylammonium, diaikylaiurnomum, dialkanolaikjdammonium, aikanoldialkylammomuni, bis:(alkylimiclazolium), -3:1 -

6. The method of any one of claims 1 to .. wherein the separation membrane comprises a support for the one or more solid OIPC.

7. The method of claim 6, wherein the support is a porous substrate,

8. The method of claim 6, wherein the support is i the form of fibres.

9. The method of claim 8, wherein the fibres are polymer fibres. 10. The method of claim 9, wherein the polymer is selected from poly(2-acrylamido-2- methyl-l-propanesulfonie acid) (PA P), Polyvinylidene fluoride (PVDF), sulfonated poly(ethe ether ketone) (SPEEK a substituted polyacetylerie, a polyethylene oxide), a polyamide, a polyimide, a polysulfone, a polycarbonate, a polyarylate, a poly(phenyleneoxide), a polyaniline, a thermall rearranged polymer, a polymer of intrinsie microporasity (PIM), and any combinations thereof.

11. The method of any one of claims 8 to 10, wherein the fibres are electrospun polyme fibres. 12. The method of any one of claims 6 to 11, wherein the solid OIPC constitutes between 5% to 95% of the total weight of the gas separation membrane.

13. The method of any one of claims 1 to 12, wherein the: separation membrane further comprises a nanoporous material.

14. The method of claim 13, wherein the nanoporous material is selected from a Metal Organic Framework (MOF), a Covalent. Organic Framework (COF), a Zeofitie Imidazolate Framework (ZIFs), a zeolite, a activated carbon material, a metal oxide, and any combination thereof.

15. The method of claim 33 or 14, wherein the nanoporous material constitutes between 0.5% to 50% of the total weight of the membrane.

16. The method of any one of claims 1 to 15, wherein the difference in pressure across the membrane provides for a pressure ratio R in the range 1 < R≤ilG,0G0<

17. The method of any one of claims 1 to 16, wherein the mixture of non-amine gas species comprises CO2.

18. The method of any one of claims 1 to 17,. wherein CO2 is separated from a mixture of gas species comprising C0₂ and one or more of ¾ H_¾, CH4, <¾, ¾S, ^'SO*,, and

NO_x„

19. The method of claim 18, wherein G0₂ is separated from a mixture of CO2 and N₂ or C(¾ and CH₄.

20. U se of one or more solid organic ionic plastic crystal (OIPC) for separating a target gas species from a mixture of non- amine gas species, wherein sepai-ation of the mixture of non-amine gas species is promoted by one or more of the gas species permeating through the structure of the one or more solid OIPC,