Gas separation membrane

Abstract

A composite membrane suitable for separating gases from a gas mixture includes a selective layer coated on a support, wherein the selective layer comprises: a) a polymer matrix comprising an amine polymer; b) a graphene oxide nanofiller; and c) a mobile carrier selected from ionic liquids or amino acid salts.

Description

Summary of the Invention

[0001] This invention relates to a composite membrane for separating gases, preferably carbon dioxide, from a gas mixture containing carbon dioxide, a method for producing the composite membrane, a method for separating gases from a gas mixture, and the use of the composite membrane for gas separation. In particular, the invention provides a composite membrane comprising a selective layer having a polymer matrix, graphene oxide nanofiller, and a mobile carrier. Background Technology

[0002] The global climate crisis following industrialization is primarily due to post-industrialization and human factors. Of all the causes, the dramatic increase in greenhouse gas emissions, most notably CO2 emissions, has been directly linked to the current global warming scenario over the past few decades. The implementation of carbon capture, utilization, and storage (CCUS) represents the most effective solution for the transition to a more sustainable energy system over the next decade. However, limitations related to the cost and technical feasibility of CO2 capture technologies (i.e., absorption, membrane separation, and adsorption) remain major challenges to be addressed in the implementation of CCUS.

[0003] Polymer gas separation membranes have been widely used in CO2 separation applications due to their low cost, high modularity, and scalability. Membrane materials with excellent permeation performance (permeability and selectivity) and good chemical and mechanical properties significantly improve the efficiency of separation processes. Conventional polymer membranes based on the solution-diffusion mechanism are affected by the inherent trade-off between permeability and selectivity, as shown by the Robeson upper limit.

[0004] One way to overcome this trade-off is to use nanofillers in the polymer-selective layer to form hybrid membranes containing nanofillers. However, research on the fabrication of hollow fiber thin composite membranes with hybrid selective layers for CO2 separation applications has been limited. Many of these solutions use thick membranes with nanofillers.

[0005] While various nanofillers exist to enhance CO2 permeation in conventional polymer membranes, 2D nanofillers such as graphene oxide (GO) for membrane fabrication have been rarely studied. When dispersed in a polymer matrix, their high surface area to volume ratio due to their 2D structure triggers changes in nanoscale properties. Even in small quantities, the effective dispersion of these flakes affects the reorientation of polymer chain stacking, leading to variations in crystallinity, free volume fraction, and CO2 solubility. Wang et al. described polyaniline-coated carbon nanotubes between graphene oxide (GO) layers in a PVAm membrane in Journal of Membrane Science 589(2019)117246.

[0006] Another approach to overcoming the permeability-selectivity “trade-off” is to use CO2-reactive carriers in polymer-selective layers. Compared to conventional polymers that follow a solution-diffusion mechanism, these enhanced transfer membranes transfer CO2 through additional reactive pathways.

[0007] Reactive carriers are typically amine groups immobilized on the polymer backbone. Recently, small CO2-loving molecules that undergo reversible reactions with CO2 have also been added to the polymer matrix as "mobile carriers" to enhance CO2 transport. These reactions require water to facilitate CO2 transmembrane transport. In J.Memb.Sci. 2019, Vol 578, 61-68, Dai et al. described the addition of amino acid salts to PVA membranes.

[0008] This invention relates to separation membranes comprising a selective layer coated on a support. In particular, the invention includes the incorporation of two-dimensional (2D) nanofillers, especially graphene oxide nanofillers, into the selective layer. Due to their large aspect ratio, 2D materials such as graphene oxide (GO) significantly influence mechanical and transport properties when added as nanofillers to composite membranes. The presence of hydroxyl groups on the GO surface also introduces hydrophilicity and increases surface interactions with CO2. Conveniently, GO nanosheets are hydrophilic when added to a transport-enhancing matrix, inducing polymer chain disruption and resulting in the distribution of water channels with increased CO2 solubility. These effects on the gas separation performance of such hybrid membranes are highly dependent on the surface chemistry of the added nanosheets and their lateral dimensions.

[0009] We have discovered that GO-based 2D nanosheets in composite membranes for CO2 separation provide a valuable class of membranes, namely hybrid enhanced transport membranes (HFTMs), which, in the form of thin film composites (TFCs), exhibit superior permeation performance even with an ultrathin selective layer. Previously, 2D nanosheets were considered to negatively impact gas separation when dispersed in polymer matrices due to their barrier properties, and fabricating TFC membranes with an ultrathin selective layer (<500 nm) composed of 2D nanosheets in enhanced transport membranes was considered challenging.

[0010] The inventors were surprised to find that using a mobile carrier, namely a low-molecular-weight CO2-loving component, further improved performance in the selective layer, and particularly facilitated CO2 / CH4 separation against carrier saturation. Specifically, the mobile carrier synergistically enhanced the modified graphene oxide-bonded amine polymer matrix to improve permeability and selectivity. The presence of the mobile carrier also reduced carrier saturation.

[0011] Size-controlled 2D graphene oxide also has a positive impact on CO2 transport, even at very low loading levels.

[0012] A surprising aspect of the invention is that, compared to the same components without a moving carrier, the composite membrane comprising a moving carrier and GO-based filler exhibits increased CO2 permeability and increased CO2 flux under industrially relevant conditions. Summary of the Invention

[0014] In one respect, the present invention provides a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a support, wherein the selective layer comprises:

[0015] a) Polymer matrix including amine polymers;

[0016] b) Graphene oxide nanofiller; and

[0017] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0018] In another aspect, the present invention relates to a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a hollow fiber support, wherein the selective layer comprises:

[0019] a) Polymer matrix including amine polymers;

[0020] b) Porous graphene oxide or PEG-modified graphene oxide nanofillers, and optionally

[0021] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0022] In another aspect, the present invention relates to a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a flat plate support, wherein the selective layer comprises:

[0023] a) Polymer matrix including amine polymers;

[0024] b) Porous graphene oxide or PEG-modified graphene oxide nanofillers, and optionally

[0025] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0026] In another aspect, the present invention relates to a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a support, such as a hollow fiber or a flat sheet support, wherein the selective layer comprises:

[0027] a) Polymer matrix including amine polymers;

[0028] b) Porous graphene oxide nanofillers or chemically modified graphene oxide nanofillers, optionally wherein the chemically modified graphene oxide nanofillers are graphene oxide grafted with organic units, preferably wherein the organic units are selected from nitrogen- and / or oxygen-containing organic units, polymers, or nitrogen- and / or oxygen-containing polymers, preferably, the chemically modified graphene oxide nanofillers are PEG-modified graphene oxide nanofillers, and optionally...

[0029] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0030] In another respect, the present invention provides a method for forming a composite membrane, comprising the following steps:

[0031] (I) Forming an aqueous solution, comprising:

[0032] a) Polymer matrix including amine polymers;

[0033] b) Graphene oxide nanofiller; and optionally

[0034] c) A mobile carrier selected from ionic liquids or amino acid salts;

[0035] (II) The aqueous solution is cast onto a support, such as a flat plate or a hollow fiber support.

[0036] Specifically, the method includes the following steps:

[0037] (I) Forming an aqueous solution, comprising:

[0038] a) Polymer matrix including amine polymers;

[0039] b) Graphene oxide nanofiller; and

[0040] c) A mobile carrier selected from ionic liquids or amino acid salts;

[0041] (II) The aqueous solution is cast onto a flat plate support using a roller to apply a selective layer.

[0042] From another perspective, the present invention provides a method for forming a composite membrane, which includes the following steps:

[0043] (I) Forming an aqueous solution, comprising:

[0044] a) Polymer matrix including amine polymers;

[0045] b) Graphene oxide nanofiller, and

[0046] c) A mobile carrier selected from ionic liquids or amino acid salts;

[0047] (II) The aqueous solution is cast onto a support using a dip-coating method to create a selective layer, preferably wherein the support is a hollow fiber support;

[0048] The present invention also provides a method for separating a gas from a gas mixture, such as a method for separating carbon dioxide from a gas mixture comprising carbon dioxide, comprising passing the gas mixture through a composite membrane as defined above. In one embodiment, the composite membrane comprises a hollow fiber support and a plurality of such composite membranes are present within the assembly.

[0049] The present invention also provides the use of composite membranes as defined above in the separation of gases from gas mixtures, such as the separation of carbon dioxide from a gas mixture comprising carbon dioxide.

[0050] Unless otherwise stated, the features of the aspects and / or embodiments pointed out herein may be used individually or in combination in all technically feasible aspects and embodiments of the invention.

[0051] definition

[0052] The following definitions apply:

[0053] The term composite membrane implies the presence of a support and a selective layer. The selective layer itself can also be called a membrane. Composite membranes facilitate gas separation, such as the separation of carbon dioxide from a gas mixture. Detailed Implementation

[0054] This invention relates to a composite membrane for gas separation. The composite membrane is suitable for separating gases from a gas mixture, and in one embodiment it includes a selective layer coated on a support, wherein the selective layer comprises:

[0055] a) Polymer matrix including amine polymers;

[0056] b) Graphene oxide nanofiller, and

[0057] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0058] support

[0059] Gas separation membranes typically come in two forms: supported or unsupported. The membrane of this invention is loaded onto a support. As described below, the support can be in the form of a flat sheet or a hollow fiber support. Both types of supports are included in this invention.

[0060] Suitable supports are known in the art, and most are permeable to the gas being transported. Therefore, supports are typically porous. Suitable supports include polyethersulfone (PES), polytetrafluoroethylene (PTFE), polypropylene, sulfonated polysulfone, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN) and related block copolymers, cellulose such as cellulose acetate (CA), polyimide, polyetherimide (PEI), aliphatic polyamide, polyetheretherketone (PEEK), polyphenylene ether (PPO), and polysulfone (PSf). Such supports are commercially available from suppliers such as Osmonics. In a preferred embodiment, the support is PVDF, particularly when the support is in sheet form. When the support is hollow fiber, PSf and, in particular, PPO are preferred, especially PPO.

[0061] Most of these supports are typically ultrafiltration supports, where the pore size in the support is on the order of 20 to 1000 angstroms, although it is more common to express the pore size in terms of molecular weight cutoff.

[0062] In some embodiments of the invention, the use of microporous support structures is also within the scope of the invention. Such supports have much larger pore sizes, for example, 0.10 to 10 μm, allowing gas to pass through very rapidly. It is not standard to express the pore size of these supports in terms of MWCO, but in this invention, microporous supports are considered to have an MWCO value greater than 100,000.

[0063] Microporous supports can be formed from any suitable material, including those mentioned above related to ultrafiltration supports and inorganic materials such as ceramics (alumina, zirconium oxide), and glass membranes such as silica. These can be prepared using sintering, sol-gel, or leaching techniques known in the art.

[0064] Traditionally, these microporous supports were considered unsuitable for use in gas separation membranes employing selective layer polymers because the pores of the support were so large that the polymer would simply collapse into the pores. This can be overcome by using high molecular weight polymers in the selective layer, which have been found to possess not only excellent permeability and selectivity but also excellent mechanical strength. Alternatively, pore fillers such as 3M can be used. TM Fluorinert TM Electro-liquid FC-72 is used to fill pores to prevent permeation of the casting solution. This is a low-viscosity, low-VOC fluorinated compound. Fluorinated hydrocarbons are preferred as pore fillers. The high Mw polymer's mechanical strength allows it to fill pores even when the pores in the support material are on the micrometer scale.

[0065] The molecular weight cutoff (MWCO) of the support is preferably kept as high as possible. MWCO is essentially a measure of the pore size in the support, with a larger MWCO value representing a larger pore size. In this invention, the MWCO is preferably greater than 20,000, for example at least 35,000, more preferably greater than 50,000, more preferably at least 60,000, and particularly at least 75,000. In a highly preferred embodiment, the MWCO is at least 100,000. In fact, the present invention can use supports with MWCOs as high as 300,000, for example, from 30,000 to 300,000. In one embodiment, the MWCO may be less than the molecular weight Mw of the polymer from the selective layer cast on top.

[0066] It has been found that when the composite membrane of the present invention is prepared using a high molecular weight selective layer, the "filling" problem is minimized even when a high molecular weight support is used. This then allows the use of a high MWCO support, thus leading to improvements in permeability and selectivity.

[0067] Unwilling to be limited by theory, when using porous supports with larger pore sizes, whether for ultrafiltration or microfiltration, the increased pore size not only reduces the mass transfer resistance to the gases to be separated but also alters the separation mechanism of the support itself. Ultrafiltration supports with low pore size (low MWCO) can, for example, be selective for nitrogen but not for carbon dioxide via Knudsen diffusion.

[0068] As will be explained in more detail below, the use of polymers with high Mw selectivity layers allows for the use of porous supports with larger pores, resulting in low mass transfer resistance to gas molecules separated by the selective layer without affecting mechanical stability.

[0069] In a preferred embodiment, the support may have a porous lower layer and a thin, dense upper layer. Dense means that the dense upper layer has no pores.

[0070] The thickness of the dense top layer is preferably no more than 60 nm, for example, about 40 nm or less. However, within the scope of this invention, the dense layer may have a greater thickness, such as 100 to 1000 nm, like 200 to 700 nm, for example 600 nm.

[0071] The support with a dense top layer is preferably a hollow fiber support and ideally can be formed from PPO. The dense top layer is formed during the spinning process. In this case, pore fillers are not required.

[0072] polymer matrix

[0073] The selective layer comprises an amine polymer. The polymer matrix may comprise one or more polymers. "Polymer matrix" refers to the polymer component a) in the selective layer of the composite membrane. The polymer matrix comprises an amine polymer, such as a polymer having a hydrocarbon backbone with side amine groups or a polyamine (i.e., having amine groups in the backbone). Preferably, the polymer matrix comprises a polymer having a hydrocarbon backbone with side amine groups. More preferably, this is a polyallylamine or polyethyleneamine polymer. The polyallylamine or polyethyleneamine polymer comprises modified polyallylamine ('PAA') or polyethyleneamine ('PVAm'), for example, structural modification at the amino groups. Polyallylamine polymers are particularly preferred.

[0074] In a particular embodiment, the polymer matrix comprises a sterically hindered polymer of formula (I):

[0075]

[0076] R1 and R2 are independently selected from hydrogen or C1-C. 10 The hydrocarbon group, preferably a C1-C6 hydrocarbon group, is preferably a C1-C6 alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl, more preferably isopropyl or sec-butyl. Preferably, one of R1 and R2 is hydrogen, and the other is C1-C6. 10 Hydrocarbon group, preferably C1-C6 hydrocarbon group, preferably C1-C6 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl, more preferably isopropyl or sec-butyl.

[0077] The integer m is usually 0-6, preferably 0-2, more preferably 0-1, and most preferably 1.

[0078] The integer n is used to represent the polymeric properties of the structure, and the value of n typically causes the polymer matrix to have Mw as defined below or in the claims. This definition of n is valid for the definition of the structure below.

[0079] It has been demonstrated that the steric hindrance of solid-phase amine polymers enhances the gas permeation performance of transfer membranes.

[0080] In a particular embodiment, the polymer matrix comprises a sterically hindered polyallylamine ('SHPAA') of formula (II):

[0081]

[0082] Where R is C1-C 10The hydrocarbon group, preferably a C1-C6 hydrocarbon group, is preferably a C1-C6 alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl, more preferably R is isopropyl or sec-butyl. Therefore, in a particular embodiment, SHPAA is selected from:

[0083]

[0084] Typically, SHPAA(A) is used with a flat support, and SHPAA(B) is used with a hollow fiber support. In certain embodiments, SHPAA(B) is preferred.

[0085] Similarly, the selective layer polymer can be a sterically hindered polyethyleneimine polymer (SHPVAm) of formula (III):

[0086]

[0087] R is defined above as sterically hindered polyallylamine (SHPAA).

[0088] The polymer matrix may comprise a single polymer or a combination of two or more polymers. In certain embodiments, the polymer matrix consists of at least one polymer. Typically, the polymer matrix comprises at least 60 wt%, preferably at least 70 wt%, more preferably at least 80 wt%, and even more preferably at least 85 wt%, of an amine polymer as defined herein or in the claims. Typically, the polymer matrix comprises 60-99 wt%, preferably 70-98 wt%, and 80-95 wt%, of an amine polymer. In some embodiments, the amine polymer is the only polymer in the polymer matrix.

[0089] Typically, the polymer matrix constitutes at least 50 wt% of the selective layer, for example, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, or at least 95 wt% of the selective layer. Typically, the polymer matrix constitutes 50-99 wt% of the selective layer, preferably 60-95 wt%, more preferably 70-95 wt%.

[0090] In certain embodiments, the amine polymer (e.g., SHPAA) can be combined with another polymer, particularly an oxygen-containing polymer such as polyvinyl alcohol (PVA). The oxygen-containing polymer may include an oxygen-based functional group in the polymer backbone or as a side-group functional group. The oxygen-based group is preferably hydroxyl. The oxygen-based group is preferably a side-group. The use of PVA is preferred.

[0091] The combination of amine polymers with a second polymer, particularly PVA, results in reduced brittleness of the selective layer and excellent transport properties due to the water-swelling properties of PVA.

[0092] In another aspect, the present invention provides a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a support, wherein the selective layer comprises:

[0093] a) A polymer matrix including amine polymers and PVA;

[0094] b) Graphene oxide nanofiller; and

[0095] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0096] This advantage is most pronounced when the second polymer, such as PVA, is present in an amount of 2-20 wt%, preferably 5-15 wt%, based on the total weight of the amine polymer and the second polymer. This ensures low brittleness without compromising the separation properties of the selective layer.

[0097] The weight-average molecular weight (Mw) of the polymer matrix used in this invention ranges from 10,000 to 3,000,000, preferably 20,000 to 750,000, more preferably 30,000 to 500,000, and even more preferably 80,000 to 300,000 (unless otherwise stated, molecular weight is given herein in g / mol).

[0098] The weight-average molecular weight (Mw) of the selective layer polymer is typically at least 50,000. Preferably, the Mw of the selective layer polymer is at least 100,000.

[0099] The weight-average molecular weight (Mw) of the amine polymer is typically at least 50,000. Preferably, the Mw of the selective layer polymer is at least 100,000, such as 80,000 to 300,000.

[0100] The weight-average molecular weight (Mw) of oxygen polymers such as PVA is typically at least 50,000. Preferably, the Mw of selective layer polymers is at least 100,000, such as 80,000 to 300,000.

[0101] It has been found that using higher Mw produces selective layer strength. This allows for the use of supports with higher MWCO. In a particular embodiment, the present invention therefore provides a selective layer polymer with a support having at least 100,000 Mw and a support having at least 60,000 MWCO.

[0102] It was also observed that even when using higher molecular weight polymers, this did not lead to a decrease in permeability or selectivity. Using higher Mw polymers means that the selective layer actually used will tend to be denser than that formed with lower Mw polymers. Surprisingly, the inventors found that even at higher densities, the composite membrane still exhibited very high permeability and good gas selectivity.

[0103] Another benefit of using a higher Mw polymer matrix involves water absorption. Higher Mw polymers have more densely packed molecular chains, which means more densely packed amino groups. This results in a greater water absorption rate compared to lower Mw polymers, which promote the reactivity of amino groups with carbon dioxide, in particular.

[0104] Technicians could also expect the increased water absorption to cause swelling of the selective layer and thus result in lower permeability values, since a thicker selective layer would obviously make it more difficult for gas to pass through. However, any swelling that did occur was limited and offset by increased carbon dioxide transfer, which was facilitated by higher water absorption.

[0105] Therefore, the combination of higher molecular weight polymer matrix and high MWCO support provides composite membranes with excellent performance.

[0106] Another advantage of using a higher Mw polymer matrix is ​​their ability to withstand greater pressures. Existing membranes are typically used at low pressures. However, flue gas from industrial plants can be at relatively high pressures, such as up to 15 bar, and ideally, any composite membrane should be able to separate gases at such high pressures. In particular, it is preferred that the permeability and selectivity obtained at higher pressures are not reduced (or not significantly reduced) compared to operation at lower pressures. Another feature of the invention is that the claimed composite membrane is capable of handling gases at pressures, for example, up to 20 bar, such as up to 15 bar, or even pressures such as 2 to 15 bar or 2 to 10 bar.

[0107] Crosslinking high-molecular-weight polymers actually leads to a decrease in permeability and selectivity because it causes the selective layer to densify, making it more difficult for carbon dioxide to contact the amine groups in the polymer. However, for lower molecular weight polymers, crosslinking is often essential to provide a selective layer with sufficient strength so that it does not “fill” the pores in the support.

[0108] When using a higher Mw polymer matrix, crosslinking with a crosslinking agent is no longer necessary because the higher Mw provides sufficient strength to overcome the filling problem in the selective layer. Furthermore, although using a higher Mw polymer matrix results in overall densification of the selective layer compared to a lower Mw polymer matrix, no reduction in permeability or selectivity was observed due to the use of the higher Mw polymer matrix. In fact, the opposite was observed, and the membrane actually performed better than its crosslinked counterpart. Therefore, this is particularly preferred if the selective layer is not crosslinked using an external crosslinking agent.

[0109] Heat treatment of composite membranes can provide advantageous properties, especially when the composite membrane will be operated at elevated pressures, such as above 10 bar.

[0110] Heat treatment refers to exposing the composite membrane (i.e., the membrane on the support) to heat to induce strength therein. Suitable heat treatment conditions include heating to 50 to 150°C, for example 80 to 120°C, especially 90 to 110°C. This heat treatment step is not considered a crosslinking step because no external crosslinking agent is used, but it does impart additional strength to the composite membrane, likely by promoting intermolecular interactions between polymer chains and between the polymer matrix and the porous support.

[0111] Clearly, when this is supported, heat treatment of the selective layer occurs. Not wanting to be limited by theory, it is believed that the heat treatment step also alters the support, thus allowing for improved permeability values. This is likely due to an improved interaction between the support and the amine polymer dense layer.

[0112] Graphene oxide nanofillers

[0113] The selective layer of the composite film of the present invention further includes graphene oxide nanofillers, particularly 2D graphene oxide nanofillers. The term 2D means that one of the dimensions of the filler is very small, for example, 10 nm or less. Therefore, the graphene oxide filler is in the form of a sheet, or can be considered as a plane having width and height but very low thickness. Thus, graphene oxide (GO) is a two-dimensional material, and therefore the terms nanofiller, nanosheet, or nanopanel are used interchangeably herein. The term graphene oxide also encompasses graphene oxide that has been physically or chemically modified.

[0114] The membranes of this invention are typically "hybrid" membranes. Therefore, the graphene oxide nanofillers are typically dispersed in a polymer matrix comprising amine polymers.

[0115] The terms "nanofiller," "nanoflake," or "nanofashelf" refer to graphene oxide with an average size of 1000 nm or less, for example, in the range of 10-1000 nm, preferably 100-1000 nm, more preferably 300-900 nm, and even more preferably 400-800 nm. These dimensions refer to the average lateral dimension, i.e., in the 2D plane of the nanosheet. These dimensions can be measured using atomic force microscopy (AFM).

[0116] Surprisingly, the size of the GO flakes was found to affect gas permeation performance, with optimal results observed in an average size range of 400–800 nm. Average particle sizes exceeding 1000 nm (i.e., “micro” fillers) led to performance degradation. The average thickness of graphene oxide nanosheets is typically 10 nm or less, such as 2.0 nm or less, particularly 1.0 nm or less. In certain embodiments, the nanosheets are at least one layer thick of graphene oxide, for example, at least two layers thick. In certain embodiments, the graphene oxide nanofiller is in the form of a single layer of graphene oxide.

[0117] In certain embodiments, the nanofillers are size-controlled, meaning the particles are uniform or substantially uniform in their size distribution. The size distribution curve is typically unimodal. Generally, at least 75%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 99% of the nanofiller particles are within ±50%, preferably ±25%, and even more preferably ±10% of the average size. Alternatively, at least 75%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 99% of the nanofiller particles may have an (average) lateral dimension of less than 1000 nm. Alternatively, at least 75%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 99% of the nanofiller particles may have an (average) lateral dimension in the range of 10-1000 nm. Alternatively, at least 75%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 99% of the nanofiller particles may have an (average) lateral dimension in the range of 100-1000 nm. Alternatively, at least 75%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 99% of the nanofiller particles may have an (average) lateral dimension in the range of 300-900 nm. Alternatively, at least 75%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 99% of the nanofiller particles may have an (average) lateral dimension in the range of 400-800 nm.

[0118] Different suppliers of GO offer dispersions with varying flake sizes. Flake size is typically optimized for best performance. The inventors used GO from the commercial supplier Graphene-XT in certain hollow fiber composite membranes and prepared their own nanofillers for flat-sheet composite membranes. Nanofillers from either source can be exfoliated by ultrasonic treatment to obtain monolayer GO. Different ultrasonic treatment times can be used to control flake size and influence gas permeation performance. Using ultrasonic treatment to control flake size can be valuable. Longer ultrasonic treatments result in smaller flakes. Ultrasonic treatment durations of 4 to 8 hours appear to yield the desired GO flake size.

[0119] Furthermore, graphene oxide can be further engineered to improve gas permeation in composite membranes. Physically and chemically modified GO nanosheets with a range of properties can be synthesized and successfully dispersed in a polymer matrix. These physically and chemically modified GO nanosheets can also be subjected to ultrasonic treatment to a priori control over sheet size.

[0120] In certain embodiments, the graphene oxide nanofiller has been physically modified, for example, using hydrogen peroxide, to make it porous. Such modification can occur at high temperatures, such as 100 to 250°C. Therefore, in certain embodiments, the graphene oxide is porous. Typically, the average pore size is 1-200 nm, such as 2-20 nm.

[0121] The physical modification of GO to create porosity is expected to generate defects in a plane perpendicular to the gas transport direction while preserving the 2D morphology of the initial flakes. More generally, the increased porosity and defects across thickness generated during the processing induce nanoscale changes in polymer stacking, resulting in enhanced permeability.

[0122] The GO nanofiller of the present invention can be subjected to ultrasonic treatment to control particle size and physical modification to impart porosity in the nanofiller.

[0123] In another embodiment, graphene oxide is chemically modified to have organic units (preferably oxygen- and / or nitrogen-containing organic units) grafted thereon, preferably polymers, preferably nitrogen- and / or oxygen-containing organic polymers, more preferably oxygen-containing organic polymers, such as polyethers, such as polyalkylene polyols grafted thereon, such as polyethylene glycol (PEG). Thus, in a particular embodiment, graphene oxide is modified with polyalkylene glycol groups such as PPG (polypropylene glycol) and / or PEG (polyethylene glycol) groups. The nitrogen-containing polymer can be, for example, a polyamine polymer, such as polyethyleneimine (PEI). The polyether can include, for example, a polyether backbone (e.g., based on polyglycerol, such as hexaglycerol) having side PEG groups. When using the term polyalkylene polyol, a mixture of polyalkylene polyols (e.g., PPG and PEG) can be used. An example of oxygen- and nitrogen-containing polymers is a PEG / PEI hybrid.

[0124] Oxygen and / or nitrogen introduce polarity into the grafted polymer, which can be beneficial to membrane performance. In certain embodiments, oxygen is typically present in repeating units (e.g., ethers) and / or at the ends (e.g., -OH). In certain embodiments, nitrogen is typically present in repeating units (e.g., amines) and / or at the ends (e.g., terminal amine groups, such as -NH2).

[0125] In a particular embodiment, the graphene oxide nanofiller is a polymer-modified graphene oxide nanofiller. Preferably, the polymer grafted onto the graphene oxide nanofiller is a polymer selected from or including polyamines and / or polyethers, more preferably a polymer selected from or including polyethyleneimine and / or polyalkylene glycols, more preferably a polymer selected from or including PEI, PPG and / or PEG, more preferably a polymer selected from or including PPG and / or PEG, and more preferably a polymer including PEG.

[0126] The organic units or polymers grafted onto the graphene oxide nanofiller can be branched or linear. In the case of branched nitrogen-containing polymers, such as branched polyethyleneimine, the polymer can have primary, secondary, or tertiary amine groups, as is well known in the art.

[0127] Other groups (such as terminal groups like terminal -NH2 groups) can be present in the polymer units grafted onto graphene oxide nanofillers. For example, if a PEG-containing polymer is grafted onto graphene oxide, the PEG unit contains other groups, such as terminal -NH2 groups or hexaglycerol cores, as in the following 8-arm PEG:

[0128]

[0129] (n makes Mn defined within the following range), which is also within the scope of this invention.

[0130] Organic groups (e.g., PEG) can be grafted onto graphene oxide via any typical coupling reaction, such as EDC coupling. Therefore, a linking group can be present between the graphene oxide and the organic moiety. Typically, the molecular weight of the grafted group (e.g., nitrogen- and / or oxygen-containing polymers) is in the range of 1,000-500,000, preferably 1,000-100,000, preferably 2,000 to 50,000, preferably 5,000 to 20,000 g / mol. The molecular weight of the grafted group is typically expressed as a number average molecular weight M. n Given. A suitable example is a commercially available 8-arm PEG with M... n It is 10,000.

[0131] The GO nanofiller of the present invention can be subjected to ultrasonic treatment to control particle size and chemical modification.

[0132] In certain embodiments, the graphene oxide nanofiller is porous (i.e. physically modified) or has PEG groups grafted thereon (i.e. chemically modified).

[0133] The amount of graphene oxide nanofiller in the selective layer is typically less than 5 wt%, preferably less than 1 wt%, more preferably less than 0.5 wt%. Suitable ranges include 0.05 wt% to 5.0 wt%, preferably 0.1 to 1.0 wt%, preferably 0.1 to 0.5 wt%, or preferably 0.1 to 0.3 wt%. These wt% values ​​are determined on a dry weight basis.

[0134] The inventors were surprised to discover that, at very low loading levels (e.g., as low as 0.2 wt% nanofiller), graphene oxide could effectively increase CO2 permeability by approximately 200% compared to unmodified selective layers, without a significant change in selectivity. At low loading levels, graphene oxide (whether it be graphene oxide, porous graphene oxide, or chemically modified graphene oxide) effectively disrupts polymer chain stacking while simultaneously increasing CO2 adsorption and reorienting water distribution within the matrix.

[0135] In certain embodiments, the nanofillers are aligned or substantially aligned within the selective layer, meaning the plane formed by the 2D shape of the nanofiller particles is parallel or substantially parallel to, preferably parallel or substantially parallel to, the plane formed by the selective layer. In other words, the nanofiller particles are generally aligned or parallel along their larger two-dimensional plane. Alternatively, the nanofillers may be coplanar or substantially coplanar, for example, coplanar or substantially coplanar with the plane formed by the selective layer. “Substantially” aligned, parallel, or coplanar generally means 75% or more, preferably 90% or more, for example, 95% or more of the nanofiller particles are offset from the plane formed by the selective layer by ±45° or less, preferably ±25° or less, more preferably ±10° or less. The in-plane alignment of GO is attributed to the reduced surface free energy of the GO-based filler, resulting in enhanced gas permeation. Furthermore, for selective layers in the hundreds of nanometers range, nanofiller alignment is generally necessary because otherwise the lateral dimensions may exceed the thickness of the selective layer.

[0136] In the case of porous graphene oxide, the nanofiller particles typically have uniformly distributed pores. Generally, the pores in each nanofiller particle are uniformly distributed throughout each layer of graphene oxide. Therefore, in a particular embodiment, each layer of graphene oxide in the nanofiller particles is porous, preferably each layer of graphene oxide has a similar number of pores (e.g., within ±50%, for example within ±25%, or within ±10% of the average number of pores per layer of particles). In a particular embodiment, per 100 nm 2The porosity deviates by at most ±50%, for example, at most ±25%, or at most ±10%. Uniform pore distribution can be achieved by generating porous nanoparticles in a dispersed state (e.g., by hydroxide treatment of already cleaved monolayers in a GO dispersion). The generation of dispersed pores ensures the creation of pores in all monolayer graphene oxide nanofillers. If porous graphene oxide is generated in a solid state (e.g., thermal annealing of aggregated GO powder), the porosity is typically non-uniform. Therefore, porosity in graphene oxide is typically generated in a dispersion. In certain embodiments, the pores in the graphene oxide are not prepared by solid-state treatment of graphene oxide (e.g., thermal annealing of solid GO).

[0137] mobile carrier

[0138] To increase the number of CO2-reactive sites for interaction within the selective layer, low molecular weight CO2-loving components can be added. These are referred to herein as mobile supports because they diffuse through the polymer matrix and enhance permeation. The use of mobile supports in the selective layer improves performance and is particularly helpful for CO2 / CH4 separation against support saturation. Mobile supports are typically dispersed in a polymer matrix comprising amine polymers.

[0139] A surprising aspect of the invention is that, under industrial-related conditions, the composite membrane including the moving carrier exhibits increased CO2 permeability and increased CO2 flux compared to the same components without the moving carrier.

[0140] In use, in the presence of water, the amine groups of the polymer matrix reversibly react with CO2 to transport CO2 across the composite membrane. Although polymers such as polyethyleneamine and polyallylamine contain a high density of amine groups relative to the hydrocarbon content in the polymer repeating units, their role in promoting CO2 transport depends on the contact between CO2 and the amine groups and proximity to form continuous channels for CO2 reaction and transfer. However, the amine groups in the polymer matrix are locked within the polymer, limiting their mobility.

[0141] To increase diffusivity, mobile carriers, which are also CO2-loving, are added to the matrix. The addition of these mobile carriers not only enhances the density of the CO2-loving portion in the polymer matrix but also increases the mobility of the CO2-reactant, thereby increasing the diffusivity of CO2 in the host matrix. Key characteristics of such mobile carriers include (1) low molecular weight (higher mobility), (2) high CO2 uptake capacity, and (3) the ability to form weak bonds with CO2, which enhances CO2 transport (reversible CO2 association / dissociation) and promotes its release on the permeate side through the water-swellable composite membrane matrix.

[0142] The mobile carrier is an ionic liquid or an amino acid salt.

[0143] Ionic liquids are salts that are liquid at 25°C and atmospheric pressure. Room temperature ionic liquids include bulky and asymmetric organic cations, typically based on heterocycles, such as 1-alkyl-3-methylimidazolium, 1-alkylpyridinium, fluorosulfonyl-trifluoromethanesulfonylimide (FTFSI), N-methyl-N-alkylpyrrolidineium, and ammonium ions. Phosphorus cations are also possible. A wider range of anions are used, ranging from simple halides to inorganic anions such as tetrafluoroborate and hexafluorophosphate, to small or large organic anions such as bis(trifluoromethanesulfonyl)imide, acetate, cyanamide, trifluoromethanesulfonate, or toluenesulfonate.

[0144] Suitable ionic liquids include [Emin][OAc], [Emim][Cl], [Emim][dicyandiamide], and 1-butyl-3,5-dimethylpyridinium bromide. In certain embodiments, the ionic liquid comprises cationic 1-ethyl-3-methylimidazolium ([Emim]) or 1-butyl-3-methylimidazolium. 1-Ethyl-3-methylimidazolium acetate ([Emim][OAc]) is particularly preferred. Typically, ionic liquids have melting points in the range of 25 to 100°C.

[0145] Amino acid salts are salts of compounds that include a COOH group and a primary, secondary, or tertiary amino group. The salt preferably forms with an acid moiety, i.e., the salt is a cation and the amino acid forms an anion.

[0146] Suitable amino acid salts are salts of any naturally occurring amino acid, such as any essential amino acid, preferably Gly, Arg, Cys, or Pro. Preferred amino acid salts are proline salts (e.g., ι-proline), such as potassium salts of proline (i.e., 'ProK'). The cation in the salt is ideally an alkali metal.

[0147] [Emim][OAc] is a room-temperature ionic liquid that reacts with CO2 via a carbene pathway to form a carbene-CO2 adduct. One of the main advantages of using [Emim][OAc] as a mobile carrier is that its interaction with CO2 via the carbene pathway does not affect the viscosity of the solution, which may help reduce the mass transfer resistance during CO2 adsorption in selective layers.

[0148] Carbene-CO2 adducts (as shown in Scheme A below) have reportedly exhibited faster diffusion.

[0149]

[0150] ProK (L-proline potassium), a secondary amino acid, reacts with CO2 to form the carbamate and bicarbonate / carbonate substances shown in Scheme B above.

[0151] PZEA-Sarc is an amino acid salt containing one primary amine, two secondary amines (one from sarcosine), and one tertiary amine. CO2 interacts with this mobile carrier to form primary and secondary monocarbamates (Scheme C above).

[0152] The mobile carrier is typically present in the selective layer in an amount of 1.0-40 wt%, preferably 2.0-30 wt%, more preferably 5.0-25 wt% (dry weight). Particularly suitable ranges for ionic liquids include 2.0-40 wt%, preferably 5.0-15 wt%, and particularly suitable ranges for amino acid salts include 5.0-40 wt%, preferably 15-25 wt%.

[0153] In another aspect, the present invention provides a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a support, wherein the selective layer comprises:

[0154] a) A polymer matrix comprising at least 50 wt% of an amine polymer;

[0155] b) 0.05 to 5.0 wt% of graphene oxide nanofiller; and

[0156] c) 1.0 to 40 wt% of a mobile carrier selected from ionic liquids or amino acid salts.

[0157] In one embodiment, the present invention relates to a composite membrane suitable for separating gases from a gas mixture, the composite membrane comprising a selective layer coated on a hollow fiber or flat sheet support, wherein the selective layer comprises:

[0158] a) A polymer matrix comprising amine polymers and preferably PVA;

[0159] b) Porous graphene oxide or PEG-modified nanofillers, and optionally

[0160] c) A mobile carrier selected from ionic liquids or amino acid salts.

[0161] All preferred embodiments discussed above also apply to this embodiment.

[0162] Other selective layer components

[0163] It is preferred that the selective layer of the present invention is substantially composed of a polymer matrix, graphene oxide nanofiller, and a mobile carrier. Therefore, aside from small amounts of any necessary additives, such as stabilizers, antioxidants, or residual solvents, these materials are typically the only materials used in the selective layer. The combination of the polymer matrix, graphene oxide nanofiller, and mobile carrier preferably forms at least 95 wt% of the selective layer, such as at least 98 wt%, and especially at least 99 wt%. Preferably, the selective layer of the present invention consists of a polymer matrix, graphene oxide nanofiller, and a mobile carrier.

[0164] Support formation

[0165] The support can be in the form of a flat plate or hollow fiber. The techniques for manufacturing these supports are known in the art.

[0166] Hollow fiber spinning typically involves dissolving a support material in a suitable solvent to form a solution, and then spinning the solution to form hollow fibers. During spinning, the support solution is pumped into a spinneret and subsequently extruded. The core liquid passes through the center of the spinneret to ensure the formed fiber is hollow. The fiber flows out from the bottom of the spinneret and eventually enters a coagulation bath. However, an air gap exists between the bottom of the spinneret and the coagulation bath. The presence of this air gap allows solvent evaporation and simultaneously allows the fibers to elongate and straighten under their own weight. This hollow fiber spinning technique is well-known to those skilled in the art.

[0167] It is understood that, in the presence of hollow fibers, the selective layer can be formed on the outside or inside of the fibers (although it is not preferred that both are formed simultaneously). External coating can be simply performed by spraying or dipping in a solution containing the element for the selective layer. Internal coating of hollow fibers involves circulating the solution within the hollow fiber cavity and then drying it as with external dipping. This process is repeated until a thin, defect-free layer of the selective layer polymer is formed. Internal coating is preferred.

[0168] In a preferred embodiment, the support may have a porous lower layer and a thin, dense upper layer. The support with the dense upper layer is preferably a hollow fiber support, and ideally can be formed from PPO or PSf. The dense upper layer is formed during the spinning process.

[0169] Composite membrane formation

[0170] The first stage in the formation of the composite film of the present invention involves casting a solution comprising a polymer matrix, graphene oxide nanofiller, and a mobile carrier onto a support. The support can typically be in the form of a flat sheet or a bundle of hollow fibers. The casting of the solution is performed using known techniques. Various options exist for coating the support with the film, including dip coating, vapor deposition, spin coating, and spray coating. According to the present invention, these techniques are considered "casting".

[0171] When the support is hollow fiber, the term casting typically refers to the impregnation or spraying of the hollow fiber support. When the selective layer is located within the hollow fiber, the term casting encompasses the aforementioned process.

[0172] The casting solution is usually water-based, but other solvents can also be used.

[0173] The casting solution preferably has a solid content of 0.01 to 20 wt%, more preferably 0.05 to 10 wt%, more preferably 0.05 to 5.0 wt%, and even more preferably 0.1 to 3.0 wt% ('solid' herein refers to the content of the polymer matrix, and the graphene oxide nanofiller is only in the casting solution). The mobile carrier is likely to dissolve in the casting solution.

[0174] For casting onto a flat plate support, the casting solution preferably has a solids content of 0.1-10 wt%, more preferably 0.5-5.0 wt%. For casting onto a hollow fiber support, the casting solution preferably has a solids content of 0.01-1.0 wt%, for example 0.05-0.5 wt%. Clearly, the relative amounts of the polymer matrix, graphene oxide nanofiller, and mobile carrier in the casting solution depend on the desired concentrations in one or more selective layer polymers.

[0175] Once the solution is cast onto a planar support, a selective layer can be prepared using rod coating. Rod coating flattens the selective layer, aligns the nanofillers, and allows for reduction of the selective layer thickness as needed. Meyer rods are typically used, such as… Figure 3 As shown in the image.

[0176] Composite membrane

[0177] The thickness of the selective layer will vary depending on the concentration of the solute in the casting solution; higher concentration solutions will produce thicker films. However, the thickness can also be adjusted using a casting tool or reduced using a bar coating method. Therefore, in a typical embodiment, the film is prepared by casting. In particular, the polymer matrix component is typically dissolved in the casting solution before evaporation. For example, polymer matrices comprising amine polymers are typically not formed by interfacial polymerization.

[0178] Clearly, polymer matrices, including amine polymers, graphene oxide nanofillers, and mobile carriers, typically form monolayers.

[0179] The thickness of the selective layer of the present invention can be less than 100 μm, preferably less than 10 μm, more preferably less than 1 μm, and even more preferably less than 500 nm. Typically, the thickness of the selective layer is in the range of 20 nm to 100 μm, preferably 50 nm to 10 μm, more preferably 100 nm to 5 μm, more preferably 100 nm to 1 μm, and even more preferably 100 nm to 500 nm. Thin selective layers tend to have higher permeability values, but also lower strength. Selective layers with a thickness of less than 200 nm are particularly preferred.

[0180] It will also be understood that any selective layer is ideally defect-free.

[0181] The thickness of the support on which the selective layer can be carried can vary, although it can be on the order of 50 to 500 μm, for example, about 100 μm. However, it should be understood that the invention includes both planar supports and hollow fiber supports. When the support is a hollow fiber support, the thickness of the support is considered to be the wall thickness of the hollow fiber. The support should be porous.

[0182] After a selective layer is formed on the support, the solvent is removed, for example, by evaporation. If necessary, this can be achieved using gentle heat, such as approximately 60°C.

[0183] To avoid any potential loss of selective layer forming material during its integration into the support, it is normal for there to be a reasonable difference between the average molecular weight of one or more selective layer polymers and the molecular weight cutoff of the support structure. This difference can be greater than about 10,000, such as greater than about 15,000, for example greater than about 20,000, and especially greater than 50,000. Alternatively, a pore-filling material can be used prior to casting with a casting solution containing the selective layer component.

[0184] If desired, the formed selective layer can then be cross-linked. Chemical cross-linking can be performed using cross-linking agents such as glutaraldehyde or ammonium fluoride. However, as mentioned above, it is preferable if the selective layer is not cross-linked.

[0185] It is precisely at this stage of the manufacturing process that the composite membrane can undergo heat treatment.

[0186] Due to the high concentration of amino groups, the resulting membrane acts as a stationary carrier (FSC) for the transport of gases such as carbon dioxide.

[0187] The composite membrane of the present invention can be made into a component for use in a gas separation system.

[0188] application

[0189] Tests show that the composite membrane of the present invention can be used for at least 800 hours without any significant loss of activity, which forms another aspect of the present invention.

[0190] The composite membranes of the present invention work most effectively in humid conditions. Therefore, they can swell in the presence of water, for example, in the form of vapor, before use. Ideally, the composite membranes of the present invention should operate in a humid environment, such as at least 75% relative humidity, like 75 to 100% humidity.

[0191] Therefore, the method for preparing the composite membrane of the present invention preferably further includes the steps of contacting the composite membrane with water, for example with water vapor, and / or operating the membrane in a humid environment.

[0192] It can be assumed that the presence of water vapor in the composite membrane facilitates the transfer of carbon dioxide across the composite membrane.

[0193] The gases that can be separated from gas mixtures using the composite membrane of the present invention include carbon dioxide containing various components such as nitrogen, methane, carbon monoxide, oxygen, volatile organic compounds, or hydrogen. Separation of mixtures including hydrogen is also envisioned. These gases can be present in any environment, such as in industrial and domestic gas streams.

[0194] In use, the gas mixture to be separated is typically flowed through the composite membrane under pressure. The temperature used can vary, but is generally in the range of 10 to 90°C, preferably 20 to 65°C. Temperatures above 40°C, 50°C, or 55°C are preferred. However, operation can be performed at even higher temperatures, and separation at temperatures above 100°C may provide better results.

[0195] Preferably, the composite membrane is used to separate carbon dioxide from nitrogen or methane. In this latter aspect, the composite membrane of the present invention can therefore be applied to fields where these gases are present in mixtures, such as flue gas, biogas (e.g., biogas upgrading), natural gas (e.g., natural gas upgrading), syngas, or possibly natural gas desulfurization.

[0196] The pressure applied to the composite membrane by the gas mixture is important because it affects the flow rate through the membrane and can influence its selectivity. Therefore, the feed pressure can range from 0.5 to 100 bar, for example, 1.0 to 20 bar, especially 1.5 to 15 bar. The feed pressure can range from 1 bar (typical flue gas) to 80 bar (typical natural gas). The composite membrane of this invention is best suited for applications at pressures below 10 bar.

[0197] Operating the composite membrane under vacuum on the permeate side can be advantageous, especially when the feed gas is at a low pressure, such as 1.0 to 5 bar. This can enhance the performance of the composite membrane.

[0198] The composite membrane of the present invention preferably exhibits a selectivity of at least 20, more preferably at least 50, especially at least 100, and most especially at least 150. Selectivity is measured as described in the examples.

[0199] Penetration rate in GPUs (where 1 GPU = 10) -6 cm 3 (STP)cm -2 s -1 cmHg -1 =3.35 x 10 - 10 mol m -2 s -1 Pa -1 Preferably at least 700, preferably at least 800, preferably at least 1000, preferably at least 1050. The preferred range includes 1050-6000, preferably 1080-4000.

[0200] The composite membrane of the present invention has been found to have increased flux compared to membranes without nanofillers and without mobile carriers. In a particular embodiment, the membrane of the present invention has a flux greater than 300 NL m. -2 h -1 Preferably greater than 350NLm -2 h -1 More preferably greater than 370NL m -2 h -1 The CO2 flux is [value missing]. Preferably, the membrane of the present invention has a CO2 flux of 370-1000 NLm. -2 h -1 CO2 flux within the range.

[0201] The invention will now be further described with reference to the following non-limiting embodiments and accompanying drawings. Attached image description:

[0202] Figure 1 This is a flowchart of the gas permeation test method. Flue gas from the cement kiln is used as the feed gas in the permeation test. A membrane pump (KNF model N036-ST-11-E) is used to draw the flue gas from the chimney. Basic operating conditions are: feed flow rate 10 L / min; feed pressure 1.7 bar; temperature 60°C; no purge gas. Synthesis flue gas (CO2 / O2 / N2 mixture, 12.6 / 14 / 73, 4 vol%) is used as the tail gas to adjust the moisture content in the feed gas using a water evaporator (IAS model HOVACAL).

[0203] Figure 2 This is a cross-sectional SEM image of (A) a porous PVDF support and (B) a composite membrane containing SHPAA / PVA with 0.2 wt% pGO.

[0204] Figure 3 This is a schematic diagram of the alignment of GO-based fillers in a composite membrane manufactured using rod coating technology.

[0205] Figure 4 This is a SEM image of the frozen fractured hollow fiber (A) and cross-section (B) of the net SHPAA / PVA composite membrane.

[0206] Figure 5 Mixed gas permeation properties of various SHPAA / PVA-based selective layers, measured at 35 °C, are shown for use in planar composite membranes.

[0207] Figure 6 The mixed gas permeation performance of the hollow fiber composite membrane with GO-based filler, measured at 35°C, is shown as a function of filler loading.

[0208] Figure 7 The CO2 / N2 mixed gas permeation performance of hollow fiber composite membranes with various (A) 0.2 wt% (B) 0.5 wt% loadings of GO-based membranes is shown at 35 °C.

[0209] Figure 8 The CO2 / N2 mixed gas permeation performance of hollow fiber composite membranes with various (A) 0.2 wt% (B) 0.5 wt% loadings of pGO-based membranes is shown at 35 °C.

[0210] Figure 9 The mixed gas permeation performance of various hollow fiber composite membranes (A) CO2 / N2 gas pair at 1.7 bar and (B) CO2 / CH4 gas pair at 35 °C is shown.

[0211] Figure 10 The CO2 / CH4 mixed gas permeation performance of various 0.2wt% hollow fiber composite membranes was shown, measured at 35°C.

[0212] Figure 11 The permeation performance of the module with SHBPAA / PVA + 0.2wt% pGO membrane was shown (tested at 60°C; permeation side: 0.3 mbar vacuum; feed: flue gas @ 10 L / min). -1 ).

[0213] Figure 12 The permeation performance of modules with and without a moving carrier, SHBPAA / PVA + 0.2wt% pGO membranes, is shown (tested at 60°C; permeation side: 0.3 mbar vacuum; feed: flue gas @ 10 L / min). -1 ).

[0214] Figure 13 SO was displayedx and NO x Effects on composite membranes with mobile carriers – (A) Effects of NO and (B) SO2 on CO2 purity of component 2; (C) Effects of NO and (D) SO2 on CO2 purity of component 3.

[0215] Material

[0216] Poly(allylamine hydrochloride) (Mw = 120,000-200,000) was purchased from Thermo Fisher Scientific, Sweden, and purified and modified to sterically hindered polyallylamine.

[0217] For hollow fiber research, graphene oxide powder (2.5 wt% in water) was supplied by Graphene-XT of Italy and used as a dilution dispersion.

[0218] Polyvinyl alcohol (Mw = 89,000-98,000, 89% hydrolyzed), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, N-hydroxythiosuccinimide, and 8-arm-polyethylene glycol-NH2 (hexaglycerol core, Mn = 10,000) were used. A polyvinylidene fluoride (PVDF) ultrafiltration membrane (50 kMW) with a polypropylene (PP) substrate was obtained from Synder Filtration, USA.

[0219] Using 3M received from Kemi-Intressen, Sweden TM Fluorinert TM Electronic liquid FC-72.

[0220] L-proline ≥99wt%), 1-(2-aminoethyl)piperazine (99wt%), 1-ethyl-3-methylimidazolium acetate (97wt%), and sarcosine (N-methylglycine) (98wt%) were purchased from Sigma-Aldrich.

[0221] The poly(p-phenylene oxide) (PPO) hollow fibers used for hollow fiber supports with an inner diameter of 350 μm and an outer diameter of 540 μm were obtained from Parker A / S in Norway.

[0222] The CO2 / N2 mixture (10 vol% CO2 in N2), CO2 / CH4 mixture (40 vol% CO2 in CH4), and N2 and CH4 (99.95%) used for permeation testing were supplied by AGA, Norway. Hydrogen peroxide (H2O2, 30% in water) used for GO modification was supplied by SigmaAldrich, Norway.

[0223] Characterization methods

[0224] Chemical changes in the nanofiller were monitored using Fourier transform infrared (FTIR) spectroscopy with a ThermoNicoletNexus spectrometer equipped with a smart durable reflection cell in diamond crystal attenuated total internal reflection mode. The reaction was carried out at 4000 cm⁻¹. -1 and 800cm -1 Use within the range with a resolution of 4cm -1 An average of 16 scans were used to construct the spectrum.

[0225] The surface chemical composition of the synthesized GO was analyzed using X-ray photoelectron spectroscopy (XPS, XPS-θ probe, Thermo Fisher Scientific Co., USA), which was equipped with a monochromatic Al Kα source with C-correction of 284.5 eV.

[0226] The film morphology was analyzed using field emission SEM APREO (FEI, Thermo Fisher Scientific, USA) in immersion mode with an in-lens detector. Prior to analysis, the sample was coated with an 8 nm Pd / Pt alloy by sputtering.

[0227] polymer

[0228] Polymer Example 1 - Synthesis of Steric Hindered Polyallylamine (SHPAA) - for Sheet Films

[0229] Steric hindered polyallylamine was obtained by modifying purified polyallylamine with 2-bromopropane. Polyallylamine and 2-bromopropane reacted with 2-bromopropane in the presence of stoichiometric amounts of KOH under reflux of methanol at 50°C to generate poly-N-isopropylallylamine, as shown in reaction scheme 1.

[0230]

[0231] Option 1. Spatial hindrance of polyallylamine

[0232] The poly-N-isopropylallylamine prepared in this paper has an estimated Mw of 120 to 250 K.

[0233] Polymer Example 2 - Synthesis of Steric Hindered Polyallylamine (SHPAA) - for Hollow Fibers

[0234] Polyallylamine hydrochloride was purified by precipitating KCl through reaction with an equal amount of KOH in MeOH. Subsequently, the purified PAA was modified into poly-N-isobutylallylamine (Scheme 2) by reaction with an equal amount of 2-bromobutane and KOH in MeOH at 50 °C. The resulting polymer was purified by separating the precipitated KCl crystals and then drying them in a N2 atmosphere at 60 °C.

[0235]

[0236] Option 2. Spatial hindrance of polyallylamine

[0237] The prepared polymer has an estimated Mw of 120 to 250 K.

[0238] mobile carrier

[0239] Synthesis of mobile carriers

[0240] Equal amounts of 1-proline and KOH were dissolved in DI water to form a solution with a total solids content of 10 wt%. The solution was then stirred at high speed overnight at room temperature to form potassium L-proline (ProK).

[0241] Similarly, equal amounts of 1-(2-aminoethyl)piperazine and sarcosine were stirred in calculated amounts of DI water at room temperature to obtain 37.7 wt% of 2-(1-piperazinyl)ethylamine sarcosine salt (PZEA-SARC).

[0242] 1-Ethyl-3-methylimidazolium acetate ([Emim][OAc]) was dissolved in DI water to form a 10 wt% solution and stirred overnight at room temperature.

[0243] Nanofillers

[0244] The preparation of nanofillers for flat sheet membranes is as follows:

[0245] Example 1: Synthesis of Graphene Oxide

[0246] Graphene oxide for sheet membranes was synthesized using a modified Hummer method. 10 g of graphite powder was mixed with 450 ml of sulfuric acid and stirred at 5 °C for 1 h. Then, 30 g of potassium permanganate was added and stirred for 30 min, resulting in a color change from black to dark green. The solution was further heated to 40 °C and maintained for 1 h. 450 ml of deionized water was carefully added dropwise to avoid a rapid temperature rise. The solution was characterized by a dark brown color at this point. The temperature was then maintained at 95 °C for 30 min, followed by the addition of 300 ml of a 10% hydrogen peroxide solution and stirring for 15 min. A light brown color indicated successful synthesis of graphene oxide. GO was then purified multiple times using approximately 5 L of 10% hydrochloric acid through a Whatman glass microfiber filter, followed by washing in 3 L of acetone. The filtered GO cake was then dried under vacuum at 40 °C for two days to obtain graphene oxide sheets, referred to herein as GO.

[0247] A 2mg ml -1The solution was subjected to GO solution and treated with a tip sonication for 3 hours, followed by bath sonication for 30 minutes. AFM analysis showed the presence of flakes with a lateral dimension of 1 μm or larger in the solution.

[0248] Example 2 - Physical Modification of Graphene Oxide

[0249] To physically modify the GO flakes for better diffusion of the permeating agent, random pores were introduced by hydrothermal treatment of GO (Example 1) with hydrogen peroxide. 75 ml of 1 mg / ml solution was adjusted with 1M NaOH. -1 GO solution (from previously prepared 2 mg / ml) -1 To adjust the pH of the solution (after dilution), take 75 ml of 1 mg / ml solution. -1 GO solution (from previously prepared 2 mg / ml) -1 The solution was diluted, and the pH was adjusted to 10 with 1M NaOH solution. The mixture was stirred at high speed for 5 min, and then sonicated in a bath for 10 min. Then 10 ml of 3% diluted hydrogen peroxide solution was added to the mixture, and the solution was stirred at high speed for 10 min, and then sonicated in a bath for 10 min. The resulting mixture was then treated in a Teflon autoclave at 180 °C for 6 h, and then cooled to room temperature.

[0250] The obtained pGO (porous graphene oxide) dispersion has a concentration of approximately 1 mg / ml in water. -1 The concentration of (pGO) is expected to be [not specified]. The flakes are expected to inherit the same lateral dimensions as the GO from Example 1.

[0251] Example 3 - Chemical Modification of Graphene Oxide

[0252] PEG groups were grafted onto the GO surface using an EDC coupling reaction. The synthesized GO dispersion was acidic in water. However, to activate multiple sites for PEG grafting to form amide bonds, 4 mg of GO from 20 ml of sample from Example 1 was treated with an equal volume of 3M NaOH. -1 GO dispersion was then sonicated in a bath at 25°C for 1 h to further introduce carboxylic acid groups onto the GO surface. This reaction converts the esters in GO to carboxylic acid groups through hydrolysis. Diluted HCl was then added to neutralize the solution, followed by dilution to 1 mg / mL. -1 A dispersion of carboxylated GO in water was obtained. Then, 100 mg of NHS and 150 mg of EDC were added to the GO-COOH dispersion, followed by sonication in an ice bath for 30 min to activate the catalyst. Next, 200 mg of 8-arm PEG was added to the mixture, and the solution was stirred at room temperature for 24 h. The solution was then centrifuged at 7000 rpm to remove aggregates, and then dialyzed using a Spectra / dialysis membrane. 3. Dialyze the dispersion in water to remove catalyst, salts, and other unreacted components. The residual dispersion contains approximately 1 mg / ml. -1 GO-PEG concentration.

[0253] It is expected that the sheet will inherit the same lateral dimensions as the GO from Example 1.

[0254] The preparation of nanofillers for hollow fiber composite membranes is as follows:

[0255] Example 4 - GO / pGO nanosheets - for hollow fiber composite membranes

[0256] One important parameter affecting the gas permeation performance of GO flakes is the flake size (lateral dimension). Different GO suppliers offer dispersions with different flake sizes. For hollow fiber composite membrane experiments, we used GO from the commercial supplier Graphene-XT.

[0257] First, dilute the received GO dispersion to 1 mg / g. -1 The solution was prepared, and the pH was adjusted to 10 using 1M NaOH. The diluted solution was then sonicated in a sonic bath at 25°C for 30 minutes. The dispersion was then placed in an ultrasonic grinder (Vibra-Cell). TM An ultrasonic liquid processor pulses at 60% amplitude in an ice bath for 3 seconds, then pauses for 2 seconds. This procedure is performed to simultaneously peel and control the size of the GO sheet by varying the operation time.

[0258] The ultrasonic treatment lasted for 3, 6, or 9 hours, and the resulting GO slices were designated as GO3, GO6, and GO9, respectively.

[0259] An ultrasonic-assisted exfoliation procedure was used to obtain a monolayer of GO in an aqueous dispersion. To ensure the reproducibility of this method, the concentration of the GO dispersion was maintained at 2 mg / mL. -1 Furthermore, the sample volume for all procedures was maintained at 300 mL. The ultrasonic treatment process imparts the protein from the defective sp... 3 The mechanical damage in the region caused random fragmentation of the 2D nanosheets. These random tears were followed by crack propagation, leading to a reduction in sheet size.

[0260] AFM analysis revealed large flakes in GO3 with lateral dimensions exceeding 1 μm. Subsequent sonication resulted in smaller flakes in GO6 and GO9, respectively, within the 400–800 nm and below 500 nm ranges. All samples were then subjected to hydrothermal treatment to introduce random porosity.

[0261] Size-controlled GO dispersions were also subjected to hydrothermal treatment to introduce random, non-selective pores. The GO dispersions were mixed with a 3 wt% H₂O₂ solution and the mixture was vigorously stirred for 10 min, followed by ultrasonic treatment in a bath for 10 min. Subsequently, the mixture was treated in a Teflon autoclave at 180 °C for 6 h. The pGO dispersions obtained from GO₃, GO₆, and GO₹ samples were named pGO₃, pGO₆, and pGO₹, respectively.

[0262] Representative S(T)EM images of GO3 and pGO3 confirmed the successful introduction of non-selective pores into GO nanosheets via hydrothermal treatment.

[0263] Representative imaging of pGO slices shows a further reduction in slice size after hydrothermal treatment. This size reduction is confirmed by the relative increase in the presence of carbonyl groups exposed along the edges of pGO (observed by FTIR) compared to GO.

[0264] The chemical changes in GO nanosheets during the hydrothermal treatment process were investigated using FTIR spectroscopy. The ultrasonic treatment procedure had almost no effect on the chemical structure of GO and pGO nanosheets.

[0265] However, a significant peak variation was observed between GO and pGO.

[0266] support

[0267] flat

[0268] The plate support is made of PVDF as a plate. It has an MWCO of 50,000. The PVDF support is first washed in tap water at 45°C for 1 hour, then washed with DI water for 30 minutes to remove the pore protectant. The support is dried overnight at room temperature, and then coated with casting solution using a bar coater (see...). Figure 3 FC-72 pore filler is used to fill pores to prevent the casting solution from seeping into them.

[0269] Hollow fiber support

[0270] PPO is used as a hollow fiber support. It has a MWCO of 30,000 to 50,000. To manufacture the hollow fiber support, the PPO support, prepared by conventional hollow fiber spinning technology, is suspended vertically and sealed at the end with a paperclip, which also generates tension and prevents the fiber from loosening. The fiber is washed twice with DI water to remove dust particles that may adhere to the surface, and then dried at room temperature.

[0271] Composite membrane formation

[0272] flat sheet membrane

[0273] A 4 wt% PVA aqueous solution was prepared by dissolving PVA particles in deionized water under reflux at 80°C for 4 h. The SHPAA-modified solution (polymer example 1) in methanol was vacuum dried overnight at 60°C to remove residual solvent. The resulting pristine polymer was then dissolved in water at room temperature for 24 h to obtain a 6 wt% solution.

[0274] In the case of a flat support, a casting solution concentration of approximately 1 wt% "solids" is used. Based on the total polymer "solids" present in the solution, the SHPAA / PVA blend polymer solution consists of 90 wt% SHPAA and 10 wt% PVA. The percentage amount of nanofiller (from Ex GO1 to GO3) is measured relative to the total amount of polymer and nanofiller present in the casting solution. For example, 0.5 wt% GO in the SHPAA / PVA blend indicates that the amount of GO is 0.5% of the total "solids" content, i.e., the polymer and nanofiller in the solution.

[0275] The casting solution, comprising 1 wt% of nanofillers and blends of SHPAA [0.5 wt% and 99.5 wt%], and a PVA polymer blend, is applied to a PVDF support to prepare a selective layer with a thickness of less than 200 nm.

[0276] In this embodiment, the selective layer is applied by a bar coating method, such as... Figure 3 As shown in the image.

[0277] Hollow fiber composite membrane

[0278] The purified and dried post-modified SHPAA (polymer Example 2) was dissolved in DI water to obtain a 6 wt% solution, and the polymer solution was stirred at room temperature for at least 2 days to obtain a clear polymer solution. In the case of PVA, a 4 wt% solution was prepared by dissolving PVA particles in DI water at 80°C for 4 hours under reflux conditions.

[0279] To prepare the casting solution, a calculated amount of polymer solution was added to DI water and diluted to a casting solution concentration of 0.15 wt% of total "solids". The amount of mobile carrier was measured as the ratio of the polymer phase, while the amount of nanofiller (Ex GO4) was measured as the total solids content, as described in Equations 1 and 2, respectively.

[0280]

[0281] w nf =w pol ×(c nf / 100) (2)

[0282] Where w mc It is the weight (g) of the mobile carrier, wpol It is the total weight (g) of the dry polymer, w nf It is the weight (g) of the nanofiller, c mc It is the concentration of the mobile carrier (wt%), and c nf It represents the concentration (wt%) of the nanofiller.

[0283] By using the casting solution at a constant low speed (6-8 cm / s) -1 A thin selective layer was achieved by dip-coating fibers in two directions (within the specified range), with a 30-minute time interval between consecutive coating processes. Coating in opposite directions ensured a defect-free selective layer. Furthermore, due to the low solids content and the low viscosity of the casting solution, the uniformity of the selective layer thickness was independent of the coating speed and filler load. The hollow fibers were then dried at room temperature and subsequently dried under vacuum at 60°C for 2 hours to remove residual solvent components. The resulting hollow fibers exhibited an excellent shiny appearance due to the presence of the ultrathin selective layer coating. The thickness of the selective layer was approximately 200 nm.

[0284] To assemble the coated hollow fiber composite membrane into components, a small number of fibers (ranging from 2 to 5) are carefully inserted using 1 / 4-inch or 3 / 8-inch Swagelok fiber optic cables. TM The components are pre-assembled into stainless steel hollow fiber assemblies. The ends are then sealed with epoxy resin adhesive. The core side of the fiber is opened by tapping the cured adhesive onto the extension assembly.

[0285] Composite membrane morphology

[0286] Flat composite film

[0287] Stable dispersions of GO-based fillers with PVA and SHPAA / PVA blend matrices were obtained across a GO filler loading range of 0.2 wt% to 1 wt%. The SHPAA / PVA blend polymer solution consisted of 90 wt% SHPAA and 10 wt% PVA, based on the total polymer "solids" present in the solution.

[0288] The concentration of the casting solution was maintained at 1 wt% solids. Representative cross-sectional SEM imaging of the selective layer loaded with 0.2 wt% pGO revealed an ultrathin selective layer with a thickness of less than 200 nm on the PVDF porous support. Surface images of the selective layer showed a clear difference between the net polymer and the polymer loaded with nanofillers.

[0289] Although the net polymer layer exhibits a relatively smooth surface, dark spots were observed in the composite film samples, which may be related to the aligned GO-based filler flakes. No obvious protrusions or aggregations of the nanofillers were observed from the smooth surface, which confirms that the GO nanosheets are aligned along their larger two-dimensional parallel to the coating surface. The in-plane alignment of GO is attributed to the reduced surface free energy of the GO-based filler and the mechanically forced alignment of the thin 2D flakes to the tangent of the cylindrical surface of the rod at the contact points. Figure 2 The image shows a cross-sectional SEM image of (A) a porous PVDF support and (B) a composite membrane containing SHPAA / PVA with 0.2 wt% pGO.

[0290] Laboratory-scale gas permeation performance

[0291] Sheet film with SHPAA polymer matrix for promoting delivery

[0292] Besides the dissolution-diffusion mechanism, CO2 transport through the transport membrane is also facilitated by a reaction pathway. The transport-enhancing effect is caused by amine groups attached to the backbone of the SHPAA polymer matrix, which undergo a reversible reaction with CO2 in the presence of water.

[0293] Gas permeability

[0294] The gas permeation performance of the composite membrane was evaluated using a wet mixed gas permeation test bench. The feed consisted of a 90 / 10 v / v CO2 / N2 mixture or a 40 / 60 v / v CO2 / CH4 mixture. The feed flow rate was 300 ml / min for the CO2 / N2 test. -1 And for CO2 / CH4 testing, the minimum concentration is 400-600 ml / min. -1 The difference in feed flow rate is primarily to compensate for differences in membrane area and to target extremely low stage cuts (below 0.5%). The purge gas for CO2 / N2 testing is CH4, and for CO2 / CH4 testing, N2 is used. In both cases, the feed and purge gas flows are humidified in a bubble chamber before the membrane module. The shell side of the membrane is used for the feed gas, and the core side of the fibers is used for the permeate / purge side. For CO2 / N2 testing, the pressure on the feed side is kept constant at 1.7 bar, and varies between 2 and 20 bar for CO2 / CH4 testing. The purge side pressure is maintained at 1.02 bar. The operating temperature is maintained at 35°C for all tests. The composition of the outlet gas on both the feed and purge sides is continuously monitored using pre-calibrated gas chromatographs (490 MicroGC, Agilent, for CO2 / N2 testing, and MG5, SRI Instruments Inc., for CO2 / CH4 testing). The permeability of component 'i' is obtained using the following formula.

[0295]

[0296] Where the total permeation flow V p With ml s -1 The measurement unit is a bubble flow meter used at the outlet under steady-state conditions. and y i represents the mole fraction of water and permeate in the permeate flow, respectively. p represents the partial pressure p of substance 'i' in the feed, residual material, and permeate. i,f p i,r and p i,p respectively in cm Hg -1 Units are specified. Component permeability is expressed in GPUs, where 1 GPU = 102 -6 cm 3 (STP)cm -2 s -1 cmHg -1 =3.35x10 -10 mol m -2 s -1 Pa -1 The separation factor is calculated using the permeability of each component according to the following formula.

[0297]

[0298] The separation performance of the net SHPAA / PVA blend membrane is a CO2 permeability of 383 GPU and a CO2 / N2 separation factor of 55, as shown below. Figure 5 As shown.

[0299] Figure 5 The separation performance of SHPAA / PVA flat-sheet composite membranes with GO filler was summarized. At a low loading of 0.2 wt%, both GO and pGO effectively disrupted polymer chain stacking while simultaneously increasing CO2 adsorption and reorienting water distribution within the matrix. Consequently, CO2 permeability increased sharply to ~455 GPU with 0.2 wt% GO and to 610 GPU with 0.2 wt% pGO. The selectivity of the membranes containing 0.2 wt% GO and pGO loadings decreased rapidly to ~34.

[0300] In membranes with low GO-PEG loadings, CO2 permeability decreased to ~250 GPU, and the CO2 / N2 separation factor was ~37. This performance degradation can be explained by the effect of filler loading. Membranes with GO-PEG characteristics are classic examples of rigid interfaces between nanofillers and polymer matrices. Due to the strong interaction between the -OH groups and the amine-containing transport-promoting matrix, a close-packed polymer interface exists between the GO surface and the adjacent polymer matrix. The close-packed chains, combined with the barrier properties of GO, form a rigid interfacial volume, leading to reduced CO2 permeability while significantly increasing CO2 / N2 selectivity at higher loadings. Therefore, at a high loading of 1 wt% filler, the CO2 / N2 separation factor increases sharply to ~90, while CO2 permeability decreases to 205 GPU.

[0301] Similar effects were observed at higher loadings of GO nanosheets, where the tortuous path of N2 permeation due to the multilayer alignment of GO resulted in an increase of approximately 65 in the CO2 / N2 separation factor at a 1 wt% loading. Therefore, an optimal loading of GO-based filler for enhanced permeation was observed to be 0.2 wt%, above which both the barrier properties of GO and the effect of its tortuosity on gas permeation became apparent. At this loading, the enhanced CO2 permeation, due to polymer chain breakage and increased adsorption caused by the high aspect ratio nanosheets, offset the resistance caused by the additional tortuosity of the impermeable sheets.

[0302] In the case of pGO, the presence of non-selective pores reduces tortuosity, but the overall distribution of small-sized impermeable sheets remains important. Therefore, CO2 permeability decreases with increasing filler loading, although not as drastically as in GO or GO-PEG.

[0303] Figure 6 The effect of nanofiller loading on permeability and selectivity is shown.

[0304] Therefore, technicians can adjust membrane properties to improve permeability or selectivity by changing the content of nanofillers.

[0305] Laboratory-scale gas permeation performance

[0306] Hollow fiber membrane

[0307] Both GO and pGO nanofillers (GO Example 4) were dispersed in a SHPAA / PVA solution, with loadings of 0.2 wt% and 0.5 wt% respectively in the selective layer. The total solids content (i.e., total polymer + GO) in the casting solution was maintained at a low level of 0.15 wt% (based on polymer), resulting in an ultrathin selective layer thickness of approximately ~200 nm on the PPO hollow fibers. The amount of mobile carrier added is also shown below. Figure 4The composite film of the present invention is shown, having a net polymer in the selective layer. The simplified dip-coating process also ensures in-plane alignment of the GO due to shear alignment.

[0308] Hollow fiber membranes based on GO and pGO were developed, where the size of GO varied with ultrasonic treatment time, resulting in GO3 / 6 / 9 and the corresponding pGO3 / 6 / 9. Testing followed the same protocol explained above for flat sheet membranes. The net polymer membrane with SHBPAA / PVA exhibited a CO2 permeability of 407 GPU and a CO2 / N2 separation factor of 32.2.

[0309] Add a small amount of 0.2 wt% pGO6 (from Figure 7 and 8 (Optimization) doubled the penetration rate to 790 GPUs, while maintaining selectivity at 31. Figure 7 and 8 The optimal loading and size of the nanofiller were demonstrated.

[0310] Addition of mobile carrier

[0311] Hollow fiber membrane with mobile carrier

[0312] To increase the amount of CO2-responsive sites for interaction within the selective layer, low molecular weight CO2-loving components are added. These are called mobile carriers because they diffuse across the membrane matrix and enhance permeation.

[0313] 0.2 wt% pGO was dispersed in a polymer matrix containing 10 wt% [Emim][OAc] or 20 wt% ProK. The composition was selected based on experimental results and the optimal composition reported in the preceding sections. These resulting composite membranes with mobile carriers exhibited increased CO2 / N2 separation performance, with CO2 permeability increasing to 810 GPU for membranes containing ProK. Figure 9 As shown in A. (As indicated by...) Figure 9As shown in B, even better CO2 / CH4 separation performance was observed. For these tests, a feed gas consisting of a 40 / 60 v / v CO2 / CH4 mixture was used to simulate typical biogas composition. Both membranes containing mobile carriers were characterized by a significantly increased CO2 permeability while maintaining a constant CO2 / CH4 separation factor of around 20. At a feed pressure of 2 bar, the composite membrane containing 0.2 wt% pGO6 and 20% ProK exhibited the highest CO2 permeability of 825 GPU and a CO2 / CH4 separation factor of 20, while the net polymer membrane had a CO2 permeability of 497 GPU and a CO2 / CH4 separation factor of 21. The corresponding composite membrane containing 0.2 wt% pGO6 and no mobile carrier was limited to 727 GPU under CO2 / CH4 feed gas mixture conditions. A similar increase in CO2 permeability was observed in the membrane containing 10% [Emim][OAc], reaching as high as 782 GPU. Under CO2 / CH4 feed mixture conditions and a total upstream pressure of 2 bar, membranes containing mobile carriers exhibit increased CO2 permeability due to increased CO2 partial pressure and lower rejection rate (higher feed flow rate).

[0314] The effect of pressure on the composite membrane performance was also investigated. Upstream pressure was increased from 2 bar to a maximum of 20 bar. Increasing the feed pressure resulted in further distinguishable separation performance. The composite membrane of this invention is characterized by carrier saturation under high CO2 partial pressures in the feed. Since the availability of CO2 immobilization carriers (amine groups) in the polymer matrix is ​​limited, increasing the CO2 partial pressure in the feed gas leads to carrier saturation, thereby reducing CO2 permeability. Therefore, in all systems discussed in this work, an increase in feed-side pressure reflects a decrease in CO2 permeability, such as... Figure 10 As shown.

[0315] Interestingly, the composite membrane loaded with 2D fillers GO6 and pGO6 exhibited increased resistance to carrier saturation, especially at pressures of 5 bar and 10 bar. Therefore, at the typical operating pressure of 5 bar for biogas upgrading, the corresponding CO2 permeability remained at 340 GPU and 450 GPU, compared to 300 GPU for the net polymer.

[0316] As expected, the composite membranes containing mobile carriers further demonstrated resistance to carrier saturation, even due to the increased availability of effective CO2 carriers. This effect remained evident across the entire test pressure range for membranes loaded with 10 wt% [Emim][OAc] and 20 wt% Pro-K. At a feed pressure of 5 bar, these membranes exhibited CO2 permeabilities of 463 GPU and 468 GPU, respectively, and CO2 / CH4 separation factors of 24 and 25.

[0317] The selected membrane was scaled up proportionally and tested on-site.

[0318] Industrial testing of composite membranes with mobile carriers

[0319] Hollow fiber composite membranes were prepared using the same PPO support as described above. A selective layer was applied by dip coating. The coating solution concentration was approximately 0.15 wt% total solids, and the amount of pGO was consistently maintained at an optimized concentration of 0.2 wt% relative to the polymer content in the solution. The amount of mobile carrier was 10 wt% for [Emim][OAc] and 20 wt% for ProK.

[0320] Three scaled-up components, with membrane areas ranging from 130 cm² 2 Up to 200cm 2 Each component underwent assembly and testing. The material configuration and mechanical aspects of the components are summarized in Table 1.

[0321] Table 1. Summary of the second prototype component with third-generation materials

[0322]

[0323] Gas testing was conducted using flue gas from an exhaust chimney (height: 105m) located near the 5th stage cyclone preheater of the clinker production line at the Colacem cement plant in Gubbio, Italy (PG).

[0324] The sampling point was located 30 meters below the top of the chimney. A hole was made in the side wall of the chimney, and a vacuum pump was used to draw the flue gas from the chimney into the membrane module. A 2μm ceramic filter, part of the gas sampling probe (M&C Model SP180H), was used to remove suspended particulate matter from the flue gas. During factory testing, the flue gas temperature from the chimney was approximately 115°C. The composition of the dried flue gas during factory testing is summarized in Table 2.

[0325] Table 2. Composition of flue gas from ash clinker production line

[0326]

[0327]

[0328] The flowchart of the on-site membrane permeation test is as follows: Figure 1As shown. No further pretreatment of the feed gas was performed except for the removal of suspended particulate matter from the flue gas via a filter. All gas transfer lines were covered by electrically heated tube bundles to control the required testing temperature, primarily to prevent moisture condensation. A needle valve was placed on the retentate side to control the feed pressure. The gas composition of the feed gas was measured using an ABB SpA multi-component analysis system ACF-NT, while the gas composition of the permeate and diffuser flows was measured using HORIBAPG 350SRM and TESTO Model 350XL-350S gas analyzers. The flow rates of all three flows were measured using a TSI Model 4143 and confirmed by several floating element flow meters selected according to the flow rate to be measured. Unless otherwise specified, all tests were conducted without a vacuum or purge gas. When using purge gas, the composition of the IP-grade gas was: 20.93% oxygen and 79.07% nitrogen.

[0329] Component 1: Effects of Vacuum and Stability Testing

[0330] Component 1 demonstrated a significant increase in CO2 flux when a vacuum was applied to the permeate side of the membrane. The recorded flux was twice that when a purge was applied. The testing period was also extended by two weeks to simultaneously assess the membrane's stability at maximum performance. Figure 11 Given that trace amounts of SO were still present... x and NO x Pretreatment of the flue gas yields long-term performance improvements that translate into significant material stability. Furthermore, the decrease in flux can be attributed to water condensation in the pores and real-time fluctuations in feed moisture content.

[0331] Components 2 and 3: Effect of Moisture Content

[0332] Water plays a crucial role in promoting the transfer membrane. Because the three components 1, 2, and 3 have three different chemical configurations in terms of amine chemistry, these components are susceptible to variations in the water content of the feed. An external evaporator system (HOVACAL) is used to force additional water into the feed stream. Permeation performance results are as follows... Figure 12 As shown.

[0333] Generally, all modules exhibited increased CO2 flux and purity with increasing total water content in the feed gas. This demonstrates that water, as a carrier, plays a major role in promoting the activation of amine groups present in the polymer backbone. Furthermore, the high flux in modules containing ProK and [Emim][OAc] was evident due to the increased total amount of CO2-reactive groups present in the selective layer. [Emim][OAc] also acts as a physical solvent for CO2, and therefore the purity of modules containing [Emim][OAc] was lower than the other two modules due to the physical adsorption of CO2 and N2 in the mobile phase.

[0334] Components 2 and 3 were also tested on SO x and NO x Stability in the presence of SO₂. A composite membrane containing mobile carriers (ProK and [Emim][OAc]) was exposed to simulated flue gas containing SO₂. x and NO x Furthermore, almost no change in CO2 purity was observed in the permeate. The results are as follows... Figure 13 As shown.

[0335] Comparison with existing membranes in pilot-scale testing

[0336] Compared to laboratory-scale testing, the performance of larger-scale membrane modules has been quantified in the literature in terms of CO2 flux and selectivity / purity in the permeate. However, estimating flux using GPUs presents challenges (1 GPU = 10^ ... -6 cm 3 (STP)cm -2 s -1 cmHg -1 =3.35x10 -10 mol m -2 s -1 Pa -1 The permeability (flux) in the GPU can only be calculated under the assumption of steady-state driving forces across the membrane. Under these assumptions, the fabricated membranes have the following permeabilities (GPUs), as shown in Table 3.

[0337] These estimates are based on the following assumptions -

[0338] Due to the small component size and the use of continuous vacuum, the CO2 partial pressure on the permeation side is negligible.

[0339] • A flat CO2 concentration distribution on the feed side, which can be demonstrated by a low rejection rate (<5%) and a short component length.

[0340] Table 3: Estimation of CO2 permeability (varying with water content) in the pre-test components

[0341]

[0342]

[0343] Therefore, a surprising aspect of the present invention is that, under industrial-related conditions, membranes including a moving carrier have increased CO2 permeability and increased CO2 flux compared to the same components without a moving carrier.

[0344] The benchmark performance of the manufactured membrane and other membranes tested in industrial trials can be completed using Table 5, obtained from Int. J. Greenhouse Gas Control, 86 (2019), pp. 191-200, as shown below. (References for each membrane can be found in the article).

[0345] Table 4: Summary of CO2 capture tests at the pilot-scale membrane scale.

[0346]

[0347] (HF = hollow fiber).

[0348] in conclusion

[0349] Composite membranes containing GO-based fillers in ultrathin selective layers were fabricated and tested. GO-based fillers were found to enhance the CO2 separation properties of the composite membranes, depending on their lateral dimensions and loading. pGO fillers derived from size-optimized GO nanosheets formed continuous CO2 permeation pathways along the CO2-loving pGO surface at a loading of 0.2 wt%, exhibiting reoriented water channels around a 2D structure within the matrix. These composite membranes are characterized by a high CO2 permeability of 780 GPU and a corresponding CO2 / N2 separation factor of 30. Composite membranes with mobile carriers that reversibly react with CO2 were also developed as hollow fibers.

[0350] The mobile carriers ProK and [Emim][OAc] were discovered to particularly enhance the separation performance of stationary SHPAA / PVA membranes due to their high mobility and reversible interactions with CO2 to form bicarbonate / carbonate substances and carbene-CO2 adducts, respectively. As a novel concept, composite membranes were combined with mobile carriers to produce membranes with a CO2 permeability of 825 GPU. These membranes were evaluated for CO2 / N2 and CO2 / CH4 gas pairs, resulting in a CO2 / N2 separation factor of 31 and a CO2 / CH4 separation factor of 20. The composite membranes with mobile carriers were stable at feed pressures up to 20 bar and exhibited increased resistance to carrier saturation due to the relatively increased content of CO2-loving substances and the enhancement from the addition of pGO. This high stability and gas separation performance, combined with easily scalable hollow fiber configurations, establishes the commercial viability of the fabricated membranes for CO2 separation applications.

[0351] In particular, a surprising aspect of the invention is that, under industrial-related conditions, membranes including a moving carrier exhibit increased CO2 permeability and increased CO2 flux compared to the same components without a moving carrier.

Claims

1. A composite membrane suitable for separating a gas from a gas mixture, comprising a selective layer coated on a support, wherein the selective layer comprises: a) a polymeric matrix comprising an amine polymer; b) an oxidized graphene nanofiller having an average lateral dimension of 1000 nm or less; and, c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the oxidized graphene nanofiller is present in the selective layer in an amount of 1 wt% or less.

2. The composite film of claim 1, wherein, the polymeric matrix comprises a polymer comprising repeat units of formula (I): (I)， wherein R1and R2are independently selected from hydrogen or C1-C 10 hydrocarbyl groups, and the integer m is 0-6.

3. The composite film of claim 2, wherein, the polymeric matrix comprises a polyallylamine having repeat units of formula (II): (I), (II), wherein R is a C1-C 10 hydrocarbyl groups.

4. The composite film according to any one of claims 1-3, wherein, the oxidized graphene is physically or chemically modified.

5. The composite film according to any one of claims 1-3, wherein, the oxidized graphene is porous and / or comprises a polymer grafted thereto.

6. The composite film of any one of claims 1-3, wherein, the oxidized graphene nanofiller has an average lateral dimension in the range 10-1000 nm.

7. The composite film of any one of claims 1-3, wherein, the support is a flat sheet or is in the form of one or more hollow fibres.

8. The composite film of any one of claims 1-3, wherein, the nanofiller is present in the selective layer in an amount of less than 1 wt%.

9. The composite film of any one of claims 1-3, wherein, the amount of mobile carrier in the membrane is in the range 1.0-40 wt%.

10. The composite film of any one of claims 1-3, wherein, the mobile carrier comprises an ionic liquid in which the cation is selected from 1-alkyl-3-methylimidazolium, 1-alkylpyridinium, fluorosulfonyl-trifluoromethanesulfonimide (FTFSI), N-methyl-N-alkylpyrrolidinium, or a salt comprising a naturally occurring amino acid.

11. The composite film of any one of claims 1-3, wherein, the selective layer has a thickness in the range 20 nm to 100 pm.

12. The composite film of any one of claims 1-3, wherein, the support is made from polyether sulfone (PES), polytetrafluoroethylene (PTFE), polypropylene, sulfonated polysulfone, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN) and related block copolymers, cellulose, polyimide, polyetherimide (PEI), aliphatic polyamide, polyether ether ketone (PEEK), polyphenylene oxide (PPO) and polysulfone (PSf).

13. The composite film of any one of claims 1-3, wherein, the support is porous.

14. A method for forming a composite membrane according to any one of claims 1 to 13, comprising the steps of: (I) forming an aqueous solution comprising: a) a polymeric matrix comprising an amine polymer; b) an oxidized graphene nanofiller, and, c) a mobile carrier selected from an ionic liquid or an amino acid salt; (II) casting the aqueous solution onto a support.

15. The method of claim 14, wherein, the support is a flat sheet support and the casting process uses a rod roll to apply the selective layer; or wherein the support is a hollow fibre and the casting process comprises dip coating.

16. The method of any one of claims 14-15, wherein, the support is treated with a pore filler prior to casting the aqueous solution in step (II).

17. A method of separating a gas from a gas mixture, comprising the step of contacting the gas mixture with a membrane according to any one of claims 1 to 13.

18. Use of a membrane according to any one of claims 1 to 13 in separating a gas from a gas mixture.

19. Use of a membrane according to any one of claims 1 to 13 in separating carbon dioxide from a mixture containing carbon dioxide.

20. A composite membrane suitable for separating a gas from a gas mixture comprising a selective layer coated on a hollow fiber or flat sheet support, wherein, the selective layer comprises: a) a polymeric matrix comprising an amine polymer; b) the porous graphene oxide nanofillers or PEG-modified graphene oxide nanofillers have an average lateral dimension of 1000 nm or less, and c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the graphene oxide nanofillers are present in the selective layer in an amount of 1 wt% or less.

21. The composite membrane of claim 20, comprising a selective layer coated on a hollow fiber support, wherein the selective layer comprises: a) a polymer matrix comprising an amine polymer and a polyvinyl alcohol; b) the porous graphene oxide nanofillers have an average lateral dimension of 1000 nm or less, and c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the graphene oxide nanofillers are present in the selective layer in an amount of 1 wt% or less.

22. A composite membrane suitable for use in separating a gas from a gas mixture, comprising a selective layer coated on a support, wherein the selective layer comprises: a) a polymer matrix comprising an amine polymer; b) the porous graphene oxide nanofillers or chemically-modified graphene oxide nanofillers have an average lateral dimension of 1000 nm or less, optionally wherein the chemically-modified graphene oxide nanofillers are graphene oxides on which organic units are grafted, and c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the graphene oxide nanofillers are present in the selective layer in an amount of 1 wt% or less.

23. The composite film of any one of claims 20-22, wherein, The composite membrane, support, selective layer, polymer matrix, graphene oxide nanofillers, and / or mobile carrier are as defined in the composite membrane of any one of claims 2 to 13. b) the porous graphene oxide nanofillers or PEG-modified graphene oxide nanofillers have an average lateral dimension of 1000 nm or less, and c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the graphene oxide nanofillers are present in the selective layer in an amount of 1 wt% or less.

21. The composite membrane of claim 20, comprising a selective layer coated on a hollow fiber support, wherein the selective layer comprises: a) a polymer matrix comprising an amine polymer and a polyvinyl alcohol; b) the porous graphene oxide nanofillers have an average lateral dimension of 1000 nm or less, and c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the graphene oxide nanofillers are present in the selective layer in an amount of 1 wt% or less.

22. A composite membrane suitable for use in separating a gas from a gas mixture, comprising a selective layer coated on a support, wherein the selective layer comprises: a) a polymer matrix comprising an amine polymer; b) the porous graphene oxide nanofillers or chemically-modified graphene oxide nanofillers have an average lateral dimension of 1000 nm or less, optionally wherein the chemically-modified graphene oxide nanofillers are graphene oxides on which organic units are grafted, and c) a mobile carrier selected from an ionic liquid or an amino acid salt; wherein the graphene oxide nanofillers are present in the selective layer in an amount of 1 wt% or less. The composite membrane, support, selective layer, polymer matrix, graphene oxide nanofillers, and / or mobile carrier are as defined in the composite membrane of any one of claims 2 to 13.

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