Hollow fibers and processes for the production of hollow fibers

Abstract

The present invention relates to hollow fibers and processes for the production of hollow fibers. The present invention also relates to carbon capture using the hollow fibers. In one aspect, we describe a HF for capturing carbon dioxide. The HF comprises a hollow fiber structure capable of carbon dioxide capture; and a semi-permeable layer coating an inside of a lumen disposed within the hollow fiber structure. We also describe a process for manufacturing a HF for capturing carbon dioxide. The process comprises extruding a dope mixture through a spinneret to form a hollow fiber structure; and coating an inside of a lumen of the hollow fiber structure with a semi-permeable layer. The semi-permeable layer comprises a material that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

Description

[0001] HOLLOW FIBERS AND PROCESSES FOR THE PRODUCTION OF HOLLOW FIBERS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to hollow fibers and processes for the production of hollow fibers. The present invention also relates to carbon capture using the hollow fibers (HF) of the present invention.

[0004] BACKGROUND

[0005] Direct air capture (DAC) is a technique to remove or capture carbon dioxide from air in order to reduce its atmospheric concentration and thus to mitigate the effects of global warming and climate change. One of the most dominating technologies of capturing carbon dioxide from the air (or other carbon dioxide-containing gas mixture) is through carbon dioxide adsorption onto a sorbent material having an affinity for binding carbon dioxide. The process comprises an adsorption phase in which the gas mixture containing carbon dioxide contacts the carbon dioxide affine sorbent material at ambient atmospheric conditions so that at least part of the carbon dioxide is bound at the surface of the sorbent material until it is sufficiently enriched or saturated. Afterwards, in a second, desorption phase, the carbon dioxide enriched sorbent material is heated, set under vacuum, subject to an electrical current, contacted with a humid stream, and / or a separate purge gas may be contacted with the sorbent material, which releases the carbon dioxide from the sorbent material. After separation from the purge gas, carbon dioxide is obtained in a concentrated form. The carbon dioxide may then be utilised in some way, for example, for synthetic fuel production, carbonation of beverages, use in a greenhouse, sequestered, or transported to a storage facility for later use. Many methods and apparatus have been proposed for executing the DAC process.

[0006] Hollow fibers are extensively used in the field of fluid separation and purification. Some of their important applications include gas separation, water purification, desalination of seawater, extracorporeal blood treatment etc. The hollow fibers have an intricate porous surface, the parameters of which (specific BET (Brunauer-Emmett-Teller) surface area, pore size distribution and porosity) govern the properties and efficacy of hollow fibers. Tunability of these surface parameters allows tailoring of hollow fibers for specific applications. Pore structure distribution can classify the hollow fibers into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membranes. Bulk-scale production and manufacture of hollow fibers and modules has led to the commercialization of this technology in several fields. Although hollow fibers have found widespread applications in gas separation membranes, hollow fiber research for selective gas adsorption cycles is at a nascent stage of development.

[0007] The inside space of a hollow fiber, referred to as a lumen, allows for a flow of a fluid that is at least partially separated from the exterior of the hollow fiber.

[0008] Hollow fiber production, commonly referred to as "spinning", can be divided into four general types:

[0009] (1) melt spinning, in which a thermoplastic polymer is melted and extruded through a spinneret into air and subsequently cooled;

[0010] (2) dry spinning, in which a polymer is dissolved in an appropriate solvent and extruded through a spinneret into air;

[0011] (3) dry-jet wet spinning, in which a polymer is dissolved in an appropriate solvent and extruded into air or any suitable gaseous chimney, such as nitrogen, and a subsequent coagulant (usually water); and

[0012] (4) wet spinning, in which a polymer is dissolved and extruded directly into a coagulant (usually water).

[0013] Common to each of these methods is the use of a spinneret, which is a device containing a hollow needle, through which solvent (referred to as ‘bore fluid’) is extruded, having an annulus through which a polymer solution (referred to as ‘dope mixture’) is co-extruded. As the polymer is extruded through the annulus of the spinneret, it retains a hollow cylindrical shape. As the polymer exits the spinneret, it coagulates into a membrane through a process known as phase inversion, for example, non-solvent induced phase inversion (NIPS). The properties of the membrane -such as average pore diameter, surface area, porosity and membrane thickness- can be finely tuned by changing the dimensions of the spinneret, the temperature and composition of the dope mixture and the bore fluid (solvent), the length of an air gap between the needle and a coagulation bath (for dry-jet wet spinning), humidity and presence of inert gas (usually nitrogen) in the air gap chimney, the temperature and composition of the coagulant, as well as the speed at which produced fiber is collected by a motorized spool. US11992811 describes a methodology for production of HFMs for gas separation, vapour separation, and liquid filtration purposes. The method includes simultaneously crosslinking polyimide-based HFs with diamines during the HF spinning through a triple orifice spinneret and then drying and annealing. US11992811 discloses “co-extruding” the amine solution with the polymer solution from the nozzle of the spinneret. The problem with co-extrusion of the amine solution is that it does not offer tunable amination conditions as the amine solution is in contact with the HF skin for a very short duration i.e. between the spinneret and the coagulation bath. This might result only in the amination of the top skin layer of the HF as the amine solution does not have sufficient time to penetrate the shell of the HF to ensure complete amination. Co-extrusion results in the formation of an outer skin layer on the HF, whereas post-spinning amination offers the synthetic advantage of attaining complete amination throughout the shell of the HF.

[0014] LIS10118136 concerns a production process for polyimide HF membranes that can be crosslinked with amines. Crosslinking is performed subsequent to a washing step. For this purpose, the hollow fiber is passed through a bath containing an amine with two or more amino groups per molecule such as, for example, a diamine, triamine, tetraamine or a polyamine. The process does not contemplate HF membrane types other than polyimides.

[0015] US 2014 / 0008292 describes a method for forming a nanofiltration hollow fiber comprising a poly(amide-imide) (PAI) hollow fiber having a polyethyleneimine cross-linked surface. The HF is described as being suitable for osmosis applications.

[0016] US8257474 describes a hollow fiber with a polymer matrix with tortuous pathways in fluid communication with a sorbent material for carbon capture from coal fired plants. The hollow fiber formation is based on a non-solvent phase inversion technique commonly referred to as “wet-spinning.” Adsorbents disclosed in US8257474 include molecular sieves, zeolites, silico-aluminophosphate (SAPO) materials, aluminosilicates, aluminophosphate (ALPO) materials, activated carbon, activated alumina, silicates, amine-grafted silica, metal-organic framework materials, covalent organic framework materials, metal organic polyhedra, zeolite-imidazolate frameworks materials, polymer-based adsorbents, and chemical functional groups. A barrier layer is coated on the lumen via either dual layer spinning or post-treatment procedures. Dual layer spinning allows the lumen layer to be directly created as the hollow fiber is forming. Post-treatment methods typically involve washing the outside of the fiber with an appropriate caulking polymer. In this design, the post-treatment would take place inside the lumen of the fiber. Polyvinylidene dichloride (PVDC) latex was chosen as the main candidate for this application. The polymer has very low water and gas permeation rates, and sufficient heat resistance for the rapid thermal cycles in this system. The latex post- treatment resulted in a very dense barrier layer that does not occupy any additional space within the bore, and requires little area within the active area of the sorbent fiber body. The latex moves through porous regions around the bore via capillary forces, allowing every pore to be filled. The latex barrier layer prevents fluid communication between the lumen and the tortuous pathways. During adsorption, water is flowed through the lumen for carbon dioxide adsorption and water, water vapor, steam, or combinations thereof is flowed through the lumen for carbon dioxide desorption. The lumen layer prevents exchange between the flue gas and the heat transfer water or steam streams.

[0017] Accordingly, there is a need for additional hollow fiber and hollow fiber membranes, particularly such media for carbon capture. The present invention seeks to address the problems of the prior art.

[0018] SUMMARY OF THE INVENTION

[0019] In its broadest sense, the present invention provides methods of preparing hollow fibers, including methods comprising hollow fiber spinning; and provides methods of coating and treatment of hollow fiber structures obtained by the methods. The present invention also provides hollow fibers including a semi-permeable layer within a lumen on the hollow fiber.

[0020] In one aspect, the present invention provides a process for manufacturing a hollow fiber for capturing carbon dioxide, the process comprising: i) extruding a dope mixture through a spinneret to form a hollow fiber structure; and ii) coating an inside of a lumen of the hollow fiber structure with a semi-permeable layer, where the semi-permeable layer comprises a material that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

[0021] In some embodiments, the dope mixture includes at least one of polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole, and chloropolyphenyleneoxide. In other embodiments, the dope mixture includes at least one filler, whereby the hollow fiber structure includes a filler.

[0022] Optionally, the at least one filler includes at least one filler selected from ion exchange resins, such as strongly basic anion exchange resins, di- and multi-amines, polyethyleneimine, desiccants, carbon molecular sieves, carbon adsorbents, graphites, activated alumina, molecular sieves, aluminophosphates, silicoaluminophosphates, zeolite adsorbents, ion exchanged zeolites, hydrophilic zeolites, hydrophobic zeolites, modified zeolites, natural zeolites, faujasites, mordenites, metal-exchanged silico-aluminophosphates, zeolites, activated carbon, alumina-based fillers, silica-based fillers, zirconium-based fillers, magnesium-based fillers, titanium-based fillers, uni-polar resins, bi-polar resins, aromatic cross-linked polystyrenic matrices, brominated aromatic matrices, methacrylic ester copolymers, graphitic adsorbents, carbon fibers, carbon nanotubes, nano-materials, metal salt adsorbents, perchlorates, oxalates, alkaline earth metal particles, metal oxides, chemisorbents, amines, organo-metallic reactants, hydrotalcites, silicalites, zeolitic imidazolate frameworks, covalent organic frameworks (COFs) and metal organic frameworks (MOFs) adsorbent compounds, and combinations thereof.

[0023] Advantageously, the filler is at least one of a metal organic framework or a zeolite or an alumina-based filler, or a silica-based filler, or a zirconium-based filler, or a magnesium- based filler, or a titanium-based filler or an ion-exchange resin.

[0024] In certain embodiments in which the dope mixture includes a filler, the dope mixture includes at least one of polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), and polytetrafluoroethylene (PTFE).

[0025] In certain embodiments, the process further comprises functionalizing the hollow fiber structure with a nucleophilic group.

[0026] In certain embodiments in which the dope mixture includes a filler, the process further comprises functionalizing the at least one filler with a nucleophilic group and adding the functionalized filler to the dope mixture to form the hollow fiber structure. In some examples, the process further comprises passing the hollow fiber structure through a coagulation bath and at least one rinse bath, where the at least one rinse bath includes a solution including a nucleophilic group; or further comprises passing the hollow fiber structure through a coagulation bath and at least one rinse bath, where the at least one rinse bath includes an amine solution including an aminosilane.

[0027] In certain examples, the amine group is an aminosilane group.

[0028] In some examples, the amine group includes a small molecule amine or a polymeric amine, or a combination thereof.

[0029] In certain embodiments, the amine group includes at least one of ethylenediamine, 1,3- propylenediamine, meta-xylylenediamine, para-xylylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and aminosilanes.

[0030] In other embodiments, the amine group includes at least one of linear polyethyleneimine, branched polyethyleneimine, and polyallylamine.

[0031] In certain embodiments, the semi-permeable layer comprises a cross-linked ethylene propylene diene monomer rubber, a polydimethylsiloxane rubber, a polychloroprene, a polystyrene, or a styrene-butadiene.

[0032] In some examples, the step of coating the inside of the lumen to form a semi-permeable layer is repeated at least once to form a semi-permeable layer comprising multiple layers, optionally wherein the multiple layers include multiple polymers.

[0033] In a second aspect, the present invention also provides a hollow fiber for capturing carbon dioxide, the fiber comprising: (a) a hollow fiber structure capable of carbon dioxide capture; and (b) a semi-permeable layer coating an inside of a lumen disposed within the hollow fiber structure, where the semi-permeable layer is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

[0034] In some embodiments, the hollow fiber structure includes at least one of polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole, and chloropolyphenyleneoxide. In certain embodiments, the hollow fiber structure includes at least one filler, whereby the hollow fiber structure includes a filler.

[0035] Optionally, the at least one filler includes at least one filler selected from ion exchange resins, di- and multi-amines, polyethyleneimine, desiccants, carbon molecular sieves, carbon adsorbents, graphites, activated alumina, molecular sieves, aluminophosphates, silicoaluminophosphates, zeolite adsorbents, ion exchanged zeolites, hydrophilic zeolites, hydrophobic zeolites, modified zeolites, natural zeolites, faujasites, mordenites, metal- exchanged silico-aluminophosphates, zeolites, activated carbon, alumina-based fillers, silica-based fillers, zirconium-based fillers, magnesium-based fillers, titanium-based fillers, uni-polar resins, bi-polar resins, aromatic cross-linked polystyrenic matrices, aromatic crosslinked polystyrenic matrix including but not limited to poly-styrene based ion-exchange resins and amine functionalized resins, brominated aromatic matrices, methacrylic ester copolymers, graphitic adsorbents, carbon fibers, carbon nanotubes, nano-materials, metal salt adsorbents, perchlorates, oxalates, alkaline earth metal particles, metal oxides, chemisorbents, amines, organo-metallic reactants, hydrotalcites, silicalites, zeolitic imidazolate frameworks, covalent organic frameworks (COFs) and metal organic frameworks (MOFs) adsorbent compounds, and combinations thereof.

[0036] In certain embodiments of hollow fiber structures including a filler, the hollow fiber structure includes an inert polymer.

[0037] In some examples, the inert polymer includes at least one of polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), and polytetrafluoroethylene (PTFE).

[0038] In some examples, the filler is functionalized with a nucleophilic group or an aminosilane.

[0039] In certain embodiments, the hollow fiber structure includes or is functionalized with a nucleophilic group or an aminosilane.

[0040] In certain embodiments, the aminosilane comprises mono-, di-, tri-, tetra- or polyamino functionalized amino- alkoxy-silanes aminosilanes. In certain examples, the nucleophilic group is an amine group.

[0041] In some examples, the amine group includes at least one of ethylenediamine, 1,3- propylenediamine, meta-xylylenediamine, para-xylylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyallylamine.

[0042] In certain embodiments, the semi-permeable layer includes at least one of polychloroprene, polystyrene, polydimethylsiloxane (PDMS), styrene butadiene rubber, crosslinked Ethylene Propylene Diene Monomer (EPDM), polypropylene, polyvinylchloride, polyimide, polyetherimide, polystyrene, polysulfone, natural rubber, amorphous fluoropolymer resins, polyethylene copolymers, polypropylene copolymers, polytetrafluoroethylene and copolymers and combinations thereof.

[0043] In some examples, the semi-permeable layer has a water vapour permeability of less than 5000 Barrer, less than 4000 Barrer, less than 3000 Barrer, less than 1000 Barrer, less than 500 Barrer, or less than 400 Barrer, optionally from 100 to 300 Barrer.

[0044] In certain examples, the semi-permeable layer is stable towards steam and water at a temperature of 70 - 110 degrees Celsius, preferably 90 - 110 degrees Celsius.

[0045] In some examples, the semi-permeable layer has a thickness between 10 - 500 micrometres.

[0046] In a further aspect, the present invention provides a process for manufacturing a hollow fiber for capturing carbon dioxide, the process comprising: i) preparing a dope mixture including a filler and an inert polymer, where the filler includes at least one of alumina-based, silica- based, zirconium-based, magnesium-based, titanium-based fillers, ion-exchange resins, or any combination thereof; ii) functionalizing the filler with at least one of an aminosilane group or a nucleophilic group or a cross-linker; and iii) extruding the dope mixture through a spinneret to form a hollow fiber structure.

[0047] In certain embodiments, the inert polymer is polyvinyldifluoride (PVDF), polysulfone (PSU) or polyethersulfone (PES), preferably polyethersulfone. In some examples, the filler is functionalized prior to preparing the dope mixture. In other examples, the filler is functionalized after the dope mixture is extruded through the spinneret.

[0048] In certain embodiments, an aminosilane group is grafted onto the filler.

[0049] In some embodiments, the nucleophilic group is bonded to the filler via impregnation or impregnation crosslinking.

[0050] In some embodiments, the process further comprises coating an inside of a lumen of the hollow fiber structure with a semi-permeable layer, wherein the semi-permeable layer comprises a material that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

[0051] In a yet further aspect, the present invention provides a hollow fiber for capturing carbon dioxide, the fiber comprising: (a) a hollow fiber structure capable of carbon dioxide capture, where the hollow fiber structure includes an inert polymer and at least one of an aluminabased, silica-based, zirconium-based, magnesium-based, and titanium-based filler functionalized with an aminosilane group, and (b) a semi-permeable layer coating an inside of a lumen disposed within the hollow fiber structure, where the semi-permeable layer is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

[0052] In these aspects, in certain embodiments, the semi-permeable layer includes composite particles.

[0053] In some examples, the composite particles include at least one of aluminosilicates, flake-like materials, polymeric particles, or nanoparticles, optionally metallic nanoparticles.

[0054] In these aspects, in certain embodiments, an inner diameter of the hollow fiber structure is within a range of 0.1 to 3.5 mm; and / or a thickness of the hollow fiber is within a range of 0.2 to 3.0 mm.

[0055] In some examples, i) the filler has a surface area above 100 m2 / g or from 10 to 1000 m2 / g, by the Brunauer-Emmett-Teller method; and / or ii) the filler has a pore size range of 1 to 200 nm’ and / or iii) 90% or more of particles of the filler have a particle size in the range of 40 nanometers to 100 micrometers; and / or iv) the filler loading in the hollow fiber is at least 30 wt.% or 30-50 wt.% or 30-70 wt.%.

[0056] In certain embodiments, the hollow fiber has pores wherein 90% or more of the pores have a pore size above 5 micrometers.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The above and other aspects of the invention will now be described in further detail, by way of example only, with reference to the following examples and the accompanying drawings, in which:

[0059] Figure 1 is a schematic perspective view of a section of an embodiment of a hollow fiber in accordance with the present invention;

[0060] Figure 2 is a schematic representation of a first embodiment of a fiber formation and treatment process in accordance with the present invention in the form of a method of hollow fiber structure spinning via NIPS followed by functionalization with a nucleophilic group or an aminosilane group, and lumen coating;

[0061] Figure 3 is a figurative representation of the development of a hollow fiber in accordance with the method of Figure 2;

[0062] Figure 4 shows scanning electron micrographs of two examples of hollow fibers obtainable by embodiments of the present invention;

[0063] Figure 5 shows a scanning electron microscope (SEM) image of the outer skin and shell side of an embodiment of a TETA-functionalized hollow fiber in accordance with the present invention;

[0064] Figure 6 is an FT-IR overlay of ungrafted and TETA-grafted hollow fibers in accordance with the present invention; Figure 7 shows carbon dioxide desorption plots comparing unfunctionalized and TETA- functionalized hollow fiber structures;

[0065] Figure 8 is a schematic representation of a second embodiment of a fiber formation and treatment process in accordance with the present invention in the form of a process of hollow fiber structure production and in-line functionalization following spinning and followed by lumen coating;

[0066] Figure 9 is a schematic representation of a third embodiment of a fiber formation and treatment process in accordance with the present invention in the form of a mixed matrix hollow fiber structure spinning with non-functionalized fillers followed by functionalization of the fillers in the hollow fiber structure and lumen coating;

[0067] Figure 10 is a schematic representation of a fourth embodiment of a fiber formation and treatment process in accordance with the present invention in the form of a process of production of mixed matrix hollow fiber structures containing fillers, and in-line functionalization of the fillers during the spinning process followed by lumen coating;

[0068] Figure 11 is a schematic representation of a fifth embodiment of a fiber formation and treatment process in accordance with the present invention in the form of a mixed matrix hollow fiber structure spinning with pre-functionalized fillers followed by lumen coating; and

[0069] Figure 12 is a scanning electron micrograph of a triamine-y-alumina-based polyethersulfone mixed matrix hollow fiber structure.

[0070] DETAILED DESCRIPTION

[0071] Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the apparatus, systems and processes described herein. It is to be understood that embodiments can be provided in many alternate forms and the invention should not be construed as limited to the specific embodiments and examples set forth herein but by the scope of the appended claims. With respect to terminology of inexactitude, the terms “about” and “approximately” may be used, interchangeably, to refer to a measurement that includes the stated measurement and that also includes any measurements that are reasonably close to the stated measurement. Measurements that are reasonably close to the stated measurement deviate from the stated measurement by a reasonably small amount as understood and readily ascertained by individuals having ordinary skill in the relevant arts. Such deviations may be attributable to measurement error, differences in measurement and / or manufacturing equipment calibration, human error in reading and / or setting measurements, minor adjustments made to optimize performance and / or structural parameters in view of differences in measurements associated with other components, particular implementation scenarios, imprecise adjustment and / or manipulation of objects by a person or machine, and / or the like, for example. In the event it is determined that individuals having ordinary skill in the relevant arts would not readily ascertain values for such reasonably small differences, the terms “about” and “approximately” can be understood to mean plus or minus 10% of the stated value.

[0072] As used herein "hollow fiber" refers to a semi-permeable tubular element with an axial lumen. The hollow fiber has a lumen side and a shell side. The hollow fiber may have a cross-sectional shape that is cylindrical, but may have an alternative cross-sectional shape, which may be symmetrical or asymmetrical, providing that it defines a lumen within.

[0073] As used herein, “hollow fiber structure” refers to the structural component of the hollow fiber structure that is capable of carbon dioxide sorption without any lumen coating. It is to be understood that the hollow fiber structure may itself be capable of carbon dioxide capture or may have sites that may be functionalized to be capable of carbon dioxide capture.

[0074] As used herein, “additives” may refer to the reagents added to a dope mixture to tune the surface morphology of the hollow fiber during the spinning process via non-solvent induced phase separation. Examples of surface morphology include without limitation pore size and surface area of the hollow fiber.

[0075] As used herein, a “filler” may refer to an organic and inorganic matrix material added, dispersed through, or otherwise incorporated into a hollow fiber structure. Non-limiting examples of fillers include, but are not limited to, an ion exchange resin, such as a strongly basic anion exchange resin (e.g., DowexTM, MarathonTM A, di- and multi-amines, polyethyleneimine, or another suitable carbon dioxide adsorbing material, such as desiccant, carbon molecular sieve, carbon adsorbent, graphite, activated alumina, molecular sieve, aluminophosphate, silicoaluminophosphate, zeolite adsorbent, ion exchanged zeolite, hydrophilic zeolite, hydrophobic zeolite, modified zeolite, natural zeolites, faujasite, mordenite, metal-exchanged silico-aluminophosphate from Dow Chemical Company, etc.), zeolite, activated carbon, alumina-based fillers, silica-based fillers, zirconium-based fillers, magnesium-based fillers, titanium-based fillers, uni-polar resin, bi-polar resin, aromatic cross-linked polystyrenic matrix, brominated aromatic matrix, methacrylic ester copolymer, graphitic adsorbent, carbon fiber, carbon nanotube, nano-materials, metal salt adsorbent, perchlorate, oxalate, alkaline earth metal particle, metal oxides (zinc oxide, titanium dioxide, zirconium dioxide, magnesium oxide, silicon dioxide, iron oxide, aluminum oxide, copper oxide, cerium oxide, yttrium oxide, hafnium dioxide, beryllium oxide, chromium oxide), chemisorbent, amine, organo-metallic reactant, hydrotalcite, silicalite, zeolitic imidazolate framework, covalent organic framework (COF) and metal organic framework (MOF) adsorbent compounds, and combinations thereof.

[0076] As used herein, references to alumina-based fillers, silica-based filler, zirconium-based fillers, magnesium-based fillers and titanium-based fillers are to be construed as encompassing alumina, silica and so on; and including fillers containing these materials, compounds of the materials and functionalized materials.

[0077] Accordingly, as used herein, the term “alumina-based fillers” refers to fillers including alumina, such as activated alumina, y-alumina, a-alumina, 0-alumina, b-alumina, aluminophosphate, silicoaluminophosphate, metal-exchanged silico-aluminophosphate, alumina, any other fillers including alumina, and combinations thereof.

[0078] As used herein, “silica-based fillers” refer to fillers including silica, such as silicoaluminophosphate (SAPO) materials, aluminosilicates, silicates, amine-grafted silica, any other fillers including silica, and combinations thereof.

[0079] As used herein, “inert polymers” refer to polymers that do not react with aminosilanes or nucleophilic groups such as amines and do not undergo chemical transformation in solutions containing aminosilanes or nucleophilic reagents. Inert polymers may be suitable for incorporation of fillers. Such polymers may be used in the preparation of mixed matrix hollow fiber structures. Inert polymers that may be suitable for structural support of fillers additives may include but not be limited to polyethersulfone (PES), polysulfone (PSU), polypropylene (PP), polyethylene (PE), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polyvinylidenedichloride (PVDC), polyphenyleneoxide (PPO), Polytetrafluoroethylene (PTFE), combinations thereof or any other suitable polymer may be used.

[0080] As used herein, “mixed matrix hollow fiber structures” refer to hollow fiber structures including filler materials. The filler materials (both functionalized and non-functionalized variants) may be dispersed throughout the hollow fiber structure during the fiber production process.

[0081] As used herein, “liquid heat flow transfer medium” may be water or comprise water, or any suitable alternative, for example demineralized water; water dosed with a conditioning agent, which may be or comprise a corrosion inhibitor, an anti-frost additive, a biocide treatment, a boiling point adjuster, for example silicone oil, propylene glycol, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, a salt, or other water miscible ingredient may be added to water or used alone. Other examples of chemical fluids that may be suitable include m- Xylene, ethyl benzoate, o-Xylene, decamethyltetrasiloxane (MD2M), and undecane. Alcohols that may be suitable include but are not limited to methanol, ethanol, t-butanol, 2- propanol, 1-propanol, 2-butanol, t-amyl alcohol, i-butanol, 1-butanol, i-amyl alcohol, 2 ethylbutanol, 2-ethylhexanol, other alcohols, mixtures thereof, and mixtures thereof with water. Hydrocarbons that may be suitable include but are not limited to heptane, octane, chlorobenzene, p-cymene, and tetralin.

[0082] As used herein, “coated hollow fiber” refers to a hollow fiber structure having an inner surface adjacent to the lumen that is coated with a semi-permeable layer that is impermeable to a liquid heat flow transfer medium but permeable to a vapor state of the heat flow transfer medium.

[0083] As used herein "nucleophile” is a chemical species that forms bonds by donating an electron pair. Examples of nucleophilic groups include amines, amide salts, alcohols, alkoxides, thiols, and metal alkyls.

[0084] As used herein, “unfunctionalized hollow fiber structure” refers to the structural component of a hollow fiber as prepared after spinning prior to incorporation of additional functional or reactive groups apart from those present in the polymer skeleton and I or the mixed matrix hollow fiber structure, on either the lumen side or the shell side of the hollow fiber structure.

[0085] As used herein, “functionalized hollow fiber structure” refers to a hollow fiber structure that may or may not contain fillers as obtained after reaction with nucleophilic molecules, such as amines or aminosilanes.

[0086] As used herein, “process heat” refers to the lower temperature heat remaining after the higher temperature heat has been used to generate electricity. Moreover, “process heat” may be provided from the use of sources of energy to produce products other than power or electrical generation. For example, primary processing such as chemical processing, production of cement, steel or aluminum, production of heat from data centers, production of energy products like coal to liquid energy products, refining, may use heat to drive the primary processing, and the unused heat remaining after the primary processing or created during the primary processing would be the process heat of such processing.

[0087] As used herein, the term "ambient air" is defined herein as air at pressure, temperature, and carbon dioxide presence conditions that the hollow fiber capture unit of the present disclosure is exposed to when outside. Ambient air pressure conditions typically include pressures in the range from 0.8 to 1.1 bar absolute. Ambient air temperature conditions typically include temperatures in the range of -40 to 60 °C, more typically -30 to 45 °C. Carbon dioxide conditions present in ambient air typically include concentrations ranging between 380 ppm and 1000 ppm.

[0088] As used herein, “impregnation” refers to a mechanism for physical loading of nucleophilic molecules into a support.

[0089] As used herein, “grafting” refers to a mechanism for covalent tethering of aminosilanes onto a support.

[0090] As used herein, “impregnation crosslinking” refers to a mechanism for chemically bonding the impregnated nucleophilic molecules in the porous support.

[0091] An example of a hollow fiber 101 is shown in Figure 1. The hollow fiber 101 comprises a structure for capture of carbon dioxide sorption, indicated at 102, and a lumen, indicated at 103, extending axially therethrough. A lumen side 104 and a shell side 105 of the hollow fiber 1010 are indicated. The lumen side 104 may be considered an “interior” side and the shell side 105 an “exterior” side. Optionally, and in this illustrated example, the hollow fiber 101 comprises a semi-permeable barrier layer 106, shown radially disposed between the structure for capture of carbon dioxide sorption 102 and the lumen 103.

[0092] In some embodiments, the structure for capture of carbon dioxide sorption may include a polymer matrix functionalized with nucleophilic groups. Examples of polymer matrices that may be suitable for functionalization by nucleophilic groups include without limitation polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole, and chloropolyphenyleneoxide.

[0093] In some embodiments, the structure for capture of carbon dioxide sorption may include an inert polymer and one or more fillers. Examples of fillers include, but are not limited to, metal-organic frameworks (MOFs), zeolites, ion-exchange resins, aromatic cross-linked polystyrenic matrices including but not limited to poly-styrene based ion-exchange resins and amine functionalized resins, activated carbon, zirconium-based fillers, magnesium- based fillers, titanium-based fillers, alumina-based fillers, silica-based fillers, alumina, silica, inorganic nanoparticles, and any other suitable filler. Such structures may rely on polymers for structural properties rather than for sites where functionalization may occur. In these cases, functionalization may occur on the filler additive instead of the polymer matrix. As such, the polymer for structures with fillers may be different from structures that include a polymer matrix functionalized with nucleophilic groups. Polymers that may be suitable for structural support of fillers additives may include inert polymers including but not be limited to polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), Polytetrafluoroethylene (PTFE), combinations thereof or any other suitable polymer may be used.

[0094] Nucleophilic groups that may be suitable for functionalization of the polymer matrix and I or the fillers additives include without limitation amines, amide salts, alcohols, alkoxides, thiols, and metal alkyls. Although not nucleophilic groups, functionalization of the polymer matrix and / or the fillers may also include functionalization with aminosilanes.

[0095] In one exemplary embodiment, the nucleophilic groups may include amine groups. Polymeric amines may benefit from more sites for chemisorption of carbon dioxide; however, such polymeric amines may be branched and I or bulky, which may impede reaction conversion to the nucleophilic group due to pore blockages and potential for crosslinking. Subsequently, the surface underneath the aminated region of polymeric amines may have reduced access to free amines to allow further functionalization. Oppositely, small molecule amines may demonstrate faster diffusion coefficients compared to the polymeric amines, leading to a more complete functionalization. As such, functionalization using a mixture of two or more amines may be beneficial. For example, the polymer matrix and I or the fillers may be functionalized with a mixture of small molecule and polymeric amines. Small molecule amine groups may include ethylenediamine (EDA), 1,3-propylenediamine (PDA), meta-xylylenediamine (meta-XyDm), para-xylylenediamine (para-XyDm), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) or pentaethylenehexamine (PEHA), Hexamethylenediamine (HMDA), Putrescine (1,4-Butanediamine), Spermidine, Spermine, Cadaverine (1 ,5-Pentanediamine), bis -hexamethylenetriamine, any other suitable small molecule amine group, or combinations thereof. Polymeric amine groups may include linear or branched polyethyleneimine, polyallylamine, polyaniline (PANI), any other suitable polymeric groups, or combinations thereof.

[0096] In another preferred embodiment, aminosilanes may be used as a functionalization group. The aminosilanes may comprise of mono-, di-, tri-, tetra- or polyamino functionalized amino- alkoxy-silanes aminosilanes.

[0097] As used herein, a “cross-linker” refers to an organic and inorganic compound that may have at least two reactive groups that are available to react with nucleophilic groups or amines. The functional electrophilic groups may be epoxides, epoxysilanes, esters, acrylamides, carbonyls, nitriles, cyano, isocyanate, or halides. Non-limiting examples of crosslinkers include, but are not limited to, bisphenyl A diglycidyl ether , N, N-diglycidyl-4- glycidyloxyanaline , 4,4’-methylenebis(N,N-diglycidylaniline), triglycidyl trimethylolpropane ether, N,N’-Methylenebis(acrylamide).

[0098] While cross-linkers may react with aminosilanes, aminosilanes may advantageously strongly bond to the filler thereby reducing dependence on cross-linkers. In a different manner, nucleophilic groups that may be rather impregnated within the filler may benefit from crosslinkers that reduces leaching thereby stabilizing the nucleophilic group. In another embodiment, “cross-linker” refers to one or more chemicals that can produce free radicals for chemical reaction with polymers via crosslinking. The “cross-linker” may comprise organic or inorganic peroxides, azobis compounds, or radical initiators.

[0099] Furthermore, in accordance with the present invention, the hollow fiber structures are provided with a semi-permeable layer, as a barrier layer, that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat transfer medium. For instance, the liquid heat transfer medium may be liquid water, and a vapor state of the heat transfer medium may be water vapor. As such, the semi-permeable layer may be formed of a material that substantially prevents the passage of the liquid heat transfer medium (e.g., liquid water, etc) but allows for the passage of a vapor state of the heat transfer medium (e.g., water vapor, etc).

[0100] The lumen coating material should present durable adhesion to the underlying hollow fiber structure. The lumen material should also be able to withstand water and steam at 70 - 110 degrees Celsius, preferably at 90 - 110 degrees Celsius.. Polymers having rubber-like characteristics are considered to be more appropriate for our requirements as they are less prone to defects and stress-induced cracking. Examples of suitable materials include nonpolar polymers, particularly non-polar polymers which are rubbery or glassy at ambient conditions. As examples, suitable materials may include ethylene propylene diene monomer (EPDM) rubber (ethylene propylene diene monomer cross-linked with dicumyl peroxide, tertbutylperoxybenzoate, lauroyl peroxide, radical initiators or combinations thereof), polychloroprene, polystyrene, polypropylene, and styrene-butadiene. Other suitable materials will be apparent to the skilled person. In certain examples, the water vapour permeability of the semi-permeable layer is selected to be less than 100 - 1000 Barrer (1 Barrer = 3.348 x 10-16 mol.m / (m2.s.Pa)).

[0101] A semi-permeable layer having a thickness of between 10 - 100 micrometers has been determined to be particularly suitable in the processes of the present invention.

[0102] As used herein, a “composite material” or “composite particle” refers to inorganic or organic materials that may be added to the lumen coating to enhance the durability and performance of the hollow fiber sorbents. These materials may also be added to reduce fouling, scaling, and degradation of the hollow fiber structure. Non-limiting types of the composite particles include, but are not limited to metallic nanoparticles of copper, silver, or other metals, inorganic nanoparticles, flake-like materials, polymeric nanoparticles.

[0103] As used herein, a “flake-like material” may refer to inorganic and organic materials that are able to order, align, and orient themselves in the lumen coating of the hollow fiber to minimize the selective permeability of a specific type of molecule, such as water. Nonlimiting types of the flake-like materials include, but are not limited to, polymeric additives such as polytetrafluoroethylene, polyvinylidene difluoride, inorganic nanoparticles, organic nanoparticles, exfoliated clay such as bentonite, sepiolite, talc, montmorillonite, or hectorite, inorganic oxide materials such as TiC>2, FeTiCh, Fe3C>4, O2O3, SiC>2, CaCCh, ZnO or mica, carbon-based materials such as carbon nanotubes, activated carbon, multi wall carbon nano tubes and graphene.

[0104] EXAMPLES

[0105] The first aspect of this invention relates to the method of preparing the hollow fiber structures, commonly known as spinning. In certain examples, hollow fiber structures have an inner diameter (ID) and an outer diameter (OD) of 1 mm and 3 mm, respectively. In other examples, hollow fiber structures have an ID of 1 mm but an OD greater than 4 mm. In each example, a wall thickness of approximately 0.5 - 2.0 mm was aimed for. Additionally in another aspect, a selective semi-permeable, dense, inner lumen coating to the hollow fiber structures was prepared having thickness of 10 - 500 pm.

[0106] Example processes

[0107] Figure 2 illustrates a first example apparatus for the formation of a first embodiment of a hollow fiber in accordance with the present invention. The hollow fiber structure synthesis may be based on non-solvent induced phase separation (NIPS), which is commonly known as “dry-wet-spinning”. This method has been extensively studied for a wide variety of polymeric materials for hollow fiber preparation.

[0108] As shown in Figure 2, a dope mixture 11 and a bore fluid 12 may be fed to a spinneret 10. The spinneret can be considered to act like an extrusion die. As is conventional, the spinneret apparatus includes containers for mixing and filtering the solutions and reservoirs for storing the solutions. These features of the apparatus will not be described in further detail. The spinneret / die 10 co-extrudes the dope mixture and bore fluid through the outer and inner orifice of the spinneret, respectively. Following the extrusion, the extrudate 13 (dope mixture) passes through a chimney (omitted for clarity) and an airgap of desired length before entering a coagulation / quench bath 14.

[0109] The chimney and airgap control the temperature and humidity around the spinneret, which allows adjustment of the surface morphology of the hollow fiber structure skin. The hollow fiber structures are formed via “phase inversion” in the coagulation bath. The non-solvent in the coagulation bath provides the driving force for solvent exchange and mass-transfer between the quench bath 14 and the solvent present in the polymeric dope mixture of the extrudate 13. The solvent exchange results in micro-phase separation and the formation of the porous hollow fiber structure. Approximately 90-95% solvent exchange happens in the coagulation bath following which the hollow fiber structure is further passed through a rinse bath to ensure complete solvent exchange. The hollow fiber structure passes through a take-up roller / wheel and is rolled multiple times on the wheel which is immersed in the first rinse bath fluid.

[0110] The excess non-solvent from the quench bath drives the composition towards a two-phase equilibrium region and liquid-liquid de-mixing occurs, forming a continuous porous polymeric network. The contents of the dope mixture, non-solvent, and coagulation bath are tuned, as described below, to obtain hollow fiber structures with desired surface morphologies - BET surface area, porosity, pore geometry, pore connectivity, and pore size distribution within the HF matrix.

[0111] The process includes rinsing baths 20, 21 as necessary to substantially rinse reactants and coagulation bath fluid from the formed hollow fiber structure 15. In some embodiments, the process includes at least two rinsing baths. The hollow fiber structure 15 may be removed from the coagulation bath 14 and passed through the rinsing baths with the aid of pulleys or wheels 22 or other suitable means. After multiple rinses, the hollow fiber structures may be vacuum dried in an oven and stored as spools or yarns in a suitable temperature and humid atmosphere.

[0112] Figures 8 to 11 illustrate example apparatus for formation of alternative embodiments of hollow fibers in accordance with the present invention. The arrangement of components of the apparatus is the same as that shown in Figure 2 and will not be described in further detail here other than to discuss differences with respect to the apparatus of Figure 2. Figures 8 to 11 are used to illustrate functionalization by amination, as discussed below. The same principles apply to other functionalizations as discussed herein. The terms ‘amination’ and ‘aminated’ in Figures 8 to 11 should be construed accordingly.

[0113] Figure 8 shows an apparatus in which the liquid in rinsing bath 21 is loaded with a functionalizing component (such as an amine group-containing component) to effect functionalization of the hollow fiber prior to lumen coating.

[0114] Figure 9 shows an arrangement in which fillers are included in the dope mixture. In this embodiment, the fillers are un-functionalized in the dope mixture. The fillers are functionalized (typically aminated functionalization) in a post-spinning step, prior to provision of the semi-permeable lumen coating.

[0115] Figure 10 illustrates a modification in which un-functionalized fillers are included in the dope mixture and rinse bath 21 includes a source of functionalization, such that hollow fibers having a mixed matrix of fiber structures and fillers are aminated during the spinning process, prior to lumen coating with the semi-permeable membrane.

[0116] Figure 11 illustrates a further process in which functionalized fillers are included in the dope mixture such that the hollow fiber structures are co-spun with functionalized fillers, prior to lumen coating with the semi-permeable membrane.

[0117] As will become apparent below, functionalization is advantageously amine-functionalization.

[0118] The skilled person will appreciate that the principles set out here and below are illustrative of aspects of the invention and that modifications are possible within the scope of the invention.

[0119] Dope (polymer) mixture

[0120] The dope mixture may include polymers suitable for functionalization by nucleophilic groups, such as amine groups, including without limitation polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole, and chloropolyphenyleneoxide. Alternately, the dope mixture may include fillers that may be suitable for functionalization by nucleophilic groups, such as metal-organic frameworks (MOFs), zeolites, ion-exchange resins, activated carbon, alumina-based fillers, zirconium- based fillers, magnesium-based fillers, titanium, titanium-based fillers, silica-based fillers, and inorganic nanoparticles, mixed with polymers that may be suitable for structural support of such fillers including inert polymers. Inert polymers include, but not be limited to, polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polytetrafluoroethylene (PTFE), polysulfone (PSU), polyethersulfone (PES), and polyphenyleneoxide (PPO).

[0121] Bore fluid

[0122] Example materials for use as the bore fluid are listed in Table 1 below.

[0123] Coagulation bath

[0124] The fluid for the coagulation bath may be any compatible fluid, including water, 2-propanol (I PA), methanol, diols and polyols, and mixtures thereof.

[0125] Additives

[0126] Conventional additives such as polyethylene glycol (PEG), lithium chloride (LiCI), lithium bromide (LiBr), lithium nitrate (LiNOa), polyvinylpyrrolidone (PVP) solvents such as N-methyl pyrrolidone (NMP), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methyl acetamide (NMAc) non-solvents such as n-hexanes, water, methanol (MeOH), 2-propanol (I PA) may be included in the compositions used in this invention.

[0127] In some embodiments, the steps of a post-amination process for producing a hollow fiber including a polymer matrix and / or a polymer-filler structure functionalized with nucleophilic groups are illustrated in Figure 3, showing formation of a hollow fiber structure (A), functionalization of the hollow fiber structure (B), and lumen coating (C) with a semi- permeable membrane. As discussed above, in some embodiments, the hollow fiber structure may include a polymer matrix functionalized with nucleophilic groups. Alternatively or in addition, the hollow fiber structure for capture of carbon dioxide sorption may include a polymer and one or more fillers.

[0128] Manufacture of Unfunctionalized Hollow Fiber Structures

[0129] A range of trials were conducted in which conditions and parameters for the hollow fiber spinning process were varied and assessed. In one embodiment of the invention, the dope mixture used for spinning the hollow fiber structure was polyetherimide (Ultern 1000TM) and NMP as the polymer and solvent, respectively. The Ultern concentration can vary between 10 - 25 wt% in NMP. In order to attain full solubility, the dope mixture was mechanically stirred at 60 - 90 °C for 12 - 48 hours. Suitable solvents may include NMP, dimethylformamide (DMF), dimethylacetamide (DMA), N-ethyl pyrrolidone (NEP), dimethyl sulfoxide (DMSO), sulfolane, tetrahydrofuran (THF) and mixtures thereof. Other solvent systems will be apparent to the skilled person.

[0130] The dope mixture was charged with pore forming additives such as polyethyleneglycol (PEG), PEG 200, PEG 400, PEG 600, PEG 800, PEG 2000, and LiNO3, polyvinylpyrrolidone (PVP) suitably at concentrations of from 1 - 22 wt%. The concentrations of such additives were optimized as per the requirement to obtain a desired porosity, surface area and pore size distribution in the varying ratios may be chosen.

[0131] In a range of trials of hollow fiber structure spinning, the bore fluid composition was varied between 0 / 100 - 60 / 40 wt% NMP / water. After complete degassing of the dope and bore fluid with N2, they were co-extruded through the double orifice spinneret. The dope flow rate and line pressure was varied between 4.5 - 10.0 mL / min and 4.6 - 12.3 bar, respectively. The dope temperature was varied between 35 - 50 °C, while the bore fluid was maintained at a constant temperature of 25 °C. The spinneret temperature was held constant at 35 °C and the connector temperature may be altered between 35 - 50 °C.

[0132] The extrudant (co-extruded dope and the bore fluid) was passed through an air gap and chimney length of 2.0 - 12.5 cm before entering the coagulation bath. The humidity, temperature, and N2 flow rate in the chimney were adjustable. Water was used as the coagulation bath liquid and the temperature of the fluid in the coagulation bath was between 35 - 50 °C.

[0133] After the coagulation bath, the hollow fiber structures were drawn to the rinse bath(s) via rollup drums / wheels. The rinse bath(s) contain water at 60 - 70 °C to ensure complete solvent exchange in the hollow fiber structures. In the final step of solvent exchange, the hollow fiber structures underwent another two rounds of solvent exchanges with I PA at 25 °C for 20 minutes each and two rounds of solvent exchanges with hexanes at 25 °C for 20 minutes each before they are dried in the vacuum oven prior to storage. The hollow fiber structures are vacuum dried at 90 - 130 °C for 12 - 48 hours and are finally stored in a moisture free environment to prevent the pore collapse.

[0134] The parameters of these trials (SP1 , SP2, SP3, SP4 and SP5) are set out in Table 1.

[0135] Table 1 : Hollow Fiber spinning conditions and parameters

[0136] The spinning process resulted in formation of unfunctionalized hollow fiber structures. A range of hollow fiber structures with different thickness were obtained in which the inner diameter (ID) and outer diameter (OD) were varied between (ID / OD) 0.89 / 1.42 to 2.00 / 2.10 mm / mm. These hollow fiber structures were further characterized to evaluate their gas permeance and surface properties and the results are set out in Table 2.

[0137] Table 2: Hollow Fiber surface and mechanical properties post-spinning

[0138] The as-spun hollow fiber structures have very high porosities varying between 69 - 76%. Ideally porosities >70% are highly desirable for gas adsorption studies.

[0139] The spinning parameters described in Table 1 offered synthetic handles for controlling the porosity, mean pore size, pore size distribution, and BET surface area of the hollow fiber structures. These can be observed by comparing the surface properties of different batches of hollow fiber structures described in Table 2 Entries 3 - 4. BET surface areas varying between 25 - 40 m2 / g could be observed. The pore size distribution of the hollow fiber structures also varied significantly. The unfunctionalized hollow fiber structures are highly robust as they demonstrated high burst pressures ranging between 20 - 33 bar and elastic modulus higher than 5200 MPa. This suggests that the hollow fiber structures have robust mechanical properties and can withstand higher strains. In one embodiment of this invention, the hollow fiber structure spools were further built into hollow fiber bundles with a desired dimension where a multitude of hollow fiber bundles are configured to form a hollow fiber module for the reactor.

[0140] The low surface area, inadequate thermal stability, and chemical properties are the main challenges faced in the development of efficient commercial hollow fibers. In addition to the above-mentioned membrane characteristics, mechanical properties such as crushing, abrasion, and attrition are also important in order to commercialize technology. Thus to meet some of these objectives and to overcome the disadvantages of individual polymeric and inorganic membranes or mixed matrix membranes are obtained by mixing the inorganic and polymeric phases, which may be linked via van der Waals forces and covalent or hydrogen bonds. Therefore, in another embodiment of the invention, mixed matrix hollow fiber structures may be prepared. To overcome the challenges in pure polymeric and inorganic membranes, mixed matrix hollow fiber structures have been proposed by dispersing organic / inorganic materials as fillers into polymeric materials as matrixes, hoping to synergistically combine the good processability of polymers and excellent gas interaction performances of fillers. Mixed matrix membranes have the advantages of enhanced mechanical and thermal stability, reduced plasticization, lower energy requirement, compacting at high pressure, enhanced performances as compared to the native polymeric membranes. A large number of organic / inorganic materials have been explored as potential fillers, including various zeolites, metal oxides, metal organic frameworks (MOFs), activated carbon, carbon molecular sieves, and mesoporous silica.

[0141] MOFs are hybrid porous materials composed of inorganic nodes connected by polytopic organic linkers via coordination bonds. Due to their high porosity, tunable pore morphologies, and rich chemical functionalities, MOFs have shown great promise for diverse applications, including gas storage and separation, thin film devices, catalysis, chemical sensing, proton conduction, and biomedical imaging. Compared to their inorganic counterparts, e.g., zeolites, MOFs are more promising fillers in mixed matrix hollow fibers. The high affinity between organic linkers in MOFs and polymer chains in the matrix largely enhances polymer-filler interactions, mitigating the formation of nonselective voids or defects at the interface. Moreover, the judicious design of MOF fillers with functional groups provide a powerful toolbox to further improve polymer-filler compatibility subsequently influencing their gas interaction properties.

[0142] Despite the significant advantages of MOFs, they are often plagued by moisture and humidity stability, exorbitant cost of production, upscaling challenges, requirement of rigorous storage facilities among others. Zeolites are well-established candidates for gas interaction applications, which possess uniform molecule-sized pores, tetrahedral, arranged by shared oxygen at the corners of aluminosilicate geometric patterns with high thermal and chemical stability. Considering the above-mentioned properties, zeolites overcome the limitations of MOFs. Zeolites also offer synthetic handles to tune their hydrophilicity by controlling the Si / AI ratio during production which plays a huge role in governing the carbon dioxide - water co-adsorption ratios. Additionally, zeolites are highly economical and are produced on an industrial scale while being essential for their commercialization. Zeolites have also been investigated as fillers in mixed matrix hollow fiber structures for gas separation applications. Zeolites may be treated with similar chemical methodologies as adopted for MOFs and are subsequently incorporated in the hollow fibers. Zeolites may be incorporated in the hollow fiber structure via the non-solvent induced phase separation (NIPS), where the fillers may be added to the polymeric dope mixture solution during the spinning process. The Zeolites may have particle sizes varying between a few hundreds of nanometer to a few millimeter while the ideal particle size is below 2 micrometer and ideally between 50 - 300 nanometers. The Zeolites may be dispersed in a solvent which dissolves the polymer or is completely miscible with the polymeric solution (such as, NMP). The Zeolites with particle sizes above 200 nm may be broken to smaller particles via mechanical ball milling process.

[0143] The Zeolites investigated in the invention may be but are not limited to molecular sieves 13X (Zeolite 13X) with a chemical composition of Na86[(AI02)86(Si02)ioe]- XH2O or molecular sieves 4 (Zeolite 4A or SYLOSIV® A4) with a chemical composition of Nai2[(AIO2)i2(SiO2)i2] .xH2O. The zeolites may be subsequently suspended in NMP with concentrations varying between 1 - 50 wt% with constant sonication and temperatures varying between 25 - 60 °C. The sonication may be carried out for 30 min to 12 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of Zeolite in solvent was obtained, the dispersion may be added to the polymer dope mixture. The polymeric dope mixture may consist of the polymer (e.g., polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polytetrafluoroethylene (PTFE), polysulfone (PSU), polyethersulfone (PES), and polyphenyleneoxide (PPO)(Ultem), solvents (NMP), additives (PEG, PVP, UNO3 water) as mentioned earlier. The Zeolite filler dispersion may be added to the polymeric dope mixture and constitute the resulting in a new dope mixture. The composition of the new dope mixture may be tuned to obtain a final zeolite loading varying between 10 - 50 wt% in the hollow fiber matrix. The new mixture may be constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope may be extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in the invention. The dope mixture after extrusion from the spinneret may pass through an air gap with controlled humidity and temperature before undergoing coagulation in the coagulation bath. The fiber containing the zeolites then may pass through one or more rinse baths before subsequent solvent exchanges with isopropanol and hexanes.

[0144] Fillers such as silica-based fillers, zirconium-based fillers, magnesium-based fillers, titanium- based fillers, and alumina-based fillers have been explored in mixed matrix hollow fiber structures for gas interaction applications. Such fillers may be decorated with polar functional groups which makes them favorable for gas interaction and also functionalizable with polar groups necessary for enhanced performance. Silica and alumina, for example, are significantly cheaper than MOFs which makes them economically more feasible for application at industrial scale. Additionally, both silica and alumina have been incorporated in mixed matrix membranes for gas separation and adsorption applications. Despite the application of these filler materials in gas separation applications they are not highly explored for selective chemisorption of carbon dioxide in direct air capture applications. Therefore, this offers an opportunity to screen the application of such filler materials in mixed matrix hollow fiber structures for direct air applications.

[0145] Hollow fiber structures were also prepared with fillers, including metal organic frameworks (MOFs), activated carbon, silica, alumina, alumina-based fillers and zeolites, allowing yet further different polymers to be used, such as polypropylene (PP), polysulfone (PSU), polyethersulfone (PES), polyvinylenedifluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene oxide (PPO), for example. The polymeric support material used in the case of the mixed matrix hollow fiber structures may be different from the polymers used due to the fundamental difference in the nature of treatment and modification of the mixed matrix hollow fiber structure. In one embodiment of the invention, the filler-based hollow fiber structures may be prepared by the following procedure. Since the mixed matrix hollow fiber structures need to be functionalized with amine functionalities to ensure selective chemisorption of carbon dioxide. Therefore, choosing a base polymeric support material inert to amines and other nucleophilic groups is central to retaining the integrity of the mixed matrix hollow fiber structures by preventing alteration of the interfacial properties of the polymers and fillers. Therefore, the mixed matrix hollow fiber structures are typically prepared from polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polytetrafluoroethylene (PTFE), polysulfone (PSU), polyethersulfone (PES), and polyphenyleneoxide (PPO).

[0146] The filler may be incorporated in the hollow fiber structure via the non-solvent induced phase separation (NIPS), where the fillers may be added to the polymeric dope mixture solution during the spinning process. The fillers may have particle sizes varying between a few hundreds of nanometer to a few millimeter while the ideal particle size is below 2 micrometer. The fillers may be dispersed in a solvent which dissolves the polymer or is completely miscible with the polymeric solution (such as, NMP). Fillers with particle sizes above 200 nm may be broken to smaller particles, for example, via a mechanical ball-milling process. The fillers are subsequently suspended in NMP with concentrations varying between 1 - 50 wt% with constant sonication and temperatures varying between 25 - 60 °C. The sonication was carried out for 30 min to 12 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation) was observed. Once a homogeneous dispersion of filler-in-solvent was obtained, the dispersion was added to the polymer dope mixture. The dope mixture may consist of the polymer, solvents , additives , for which examples are mentioned above. The filler dispersion was added to the dope mixture polymer solution and constitutes a new dope mixture. The composition of the new dope mixture is tuned in such a way to obtain a final filler loading varying between 5 - 50 wt% in the hollow fiber polymer matrix. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in the invention. The dope mixture after extrusion from the spinneret, passes through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath. The fiber containing the fillers then passes through one or more rinse baths before subsequent solvent exchanges with isopropanol and hexanes. These mixed matrix hollow fiber structures consisting of the fillers are defined as mixed matrix hollow fiber structures. After the final rounds of solvent exchanges, the fibers were dried in the vacuum oven prior to storage. The hollow fiber structures were dried in the vacuum oven at 90 - 130 °C for 12 - 48 hours and are finally stored in a moisture free environment to prevent the pore collapse.

[0147] EXAMPLE 1. Manufacture of polyetherimide polymer matrix hollow fibers

[0148] In an exemplary embodiment of this invention, polyetherimide-based hollow fiber structures were used. Commercially purchased Ultern 1000 ™ was used as the polyetherimide. The dope mixture was prepared by mixing polyetherimide, polyethyleneglycol 600, NMP, UNO3 at a ratio of 19 / 20 / 60 / 1 wt / wt% while the dope mixture was stirred at 60 °C for 12 hours. The dope was degassed with nitrogen gas prior to spinning the hollow fiber structure. After obtaining a homogeneous dope mixture, the solution was extruded through the spinneret with a bore fluid of NMP / water 82 / 18 wt / wt%. The extruded hollow fiber structure was passed through a chimney and air gap prior to undergoing phase separation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours. The hollow fiber structures prepared by this method were labelled as SP1 as shown in Table 1. The physical and surface properties of SP1 are shown in Table 2.

[0149] EXAMPLE 2. Manufacture of alternatives to polyetherimide matrix hollow fiber structures

[0150] In an exemplary embodiment of this invention, polyethersulfone-based hollow fiber structures were used. The dope mixture was prepared by mixing polyethersulfone (PES), polyethyleneglycol 600, and NMP at a ratio of 20 / 20 / 60 wt / wt% while the dope mixture was stirred at 60 °C for 12 hours. The dope was degassed with nitrogen gas prior to spinning the hollow fiber structure. After obtaining a homogeneous dope mixture, the solution was extruded through the spinneret with a bore fluid of NMP / water 88 / 12 wt / wt%. The extruded hollow fiber structure was passed through a chimney and air gap prior to undergoing phase separation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours. This resulted in the production of PES hollow fiber structures.

[0151] EXAMPLE 3. Manufacture of unfunctionalized MOF-containing mixed matrix hollow structures

[0152] In this exemplary embodiment of this invention, UiO-66 (Zr) MOF was used as a filler to prepare the mixed matrix hollow fiber structures. The UiO-66 (Zr) MOF particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of UiO-66 (Zr) in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing UiO-66 (Zr)-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of UiO-66 / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the UiO-66 (Zr) containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours. This resulted in the production of MOF-based PES hollow fiber structures.

[0153] EXAMPLE 4. Manufacture of unfunctionalized Zeolite-containing mixed matrix hollow fiber structures

[0154] In one embodiment of the invention, zeolites were incorporated in the hollow fibers to prepare zeolite-based mixed matrix hollow fiber structures. In this exemplary embodiment of this invention, Zeolite 13X with a chemical composition of Na86[(AI02)86(Si02)ioe] and average particle size of 2 microns was used as a filler material to prepare the mixed matrix hollow fiber structures. The Zeolite 13X particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of Zeolite 13X in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing Zeolite 13X-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of Zeolite 13X / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the Zeolite 13X containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 110 °C for 12 hours. This resulted in the production of Zeolite-based PES hollow fiber structures. EXAMPLE 5. Manufacture of aminosilane functionalized alumina-based fillers mixed matrix hollow fiber structures

[0155] In this exemplary embodiment of the invention, covalent bonding of the amines to y-alumina was investigated. In a 1 L round bottom flask, approx. 50 g of y-alumina was suspended in 550 mL of toluene along with 11 mL of 2-[2-(3- trimethoxysilylpropylamino)ethylamino]ethylamine (triamine) as the aminosilane. The mixture was stirred at 85 °C using a heating mantle for 24 h. The aminated y-alumina particles were collected by gravity filtration, washed two times with toluene, hexanes, and ethanol, and left to dry at 80 °C overnight, yielding the final product of aminosilane-functionalized y-alumina (also referred to below as triamine / y-alumina).

[0156] The process is not limited to triamine and may be used for aminosilanes comprising mono-, di-, tri-, tetra- or polyamino functionalized amino- alkoxy-silanes aminosilanes.

[0157] The triamine-functionalized y-alumina was used as a filler material to prepare the mixed matrix hollow fiber structures as per the procedure described in Example 3 and Example 12. Polyethersulfone was used as the polymer for preparing triamine-functionalized y-alumina- based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of triamine-y-alumina / PES / PEG / NMP. The dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C.

[0158] Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the triamine-functionalized y-alumina containing hollow fiber structures were rinsed with hexanes at 25 °C before drying in vacuum oven at 70 °C for 12 hours. These resulted in hollow fiber structures with thicker walls with ID = 1.0 mm and OD = 3.0 mm which are advantageous for enhancing packing density of hollow fibers in the DAC capture unit. Figure 12 is a scanning electron micrograph of a triamine-y-alumina-based polyethersulfone mixed matrix hollow fiber structure. Post-Functionalization of Unfunctionalized Hollow Fiber Structures

[0159] In some embodiments, post-spinning functionalization of hollow fiber structures may be used to alter surface properties of the hollow fiber structure. For example, amination of hollow fiber structures may be used to increase the carbon dioxide sorption capacity of the hollow fiber structure. Coating the shell side of the HF or chemical crosslinking of the outer surface may be used for improving the chemical resistance, mechanical strength, high selectivity, and good separation performance (permeability) of the membranes. Chemical modification via crosslinking has been studied for different types of HF membranes prepared from polyimides, poly(amide imide), polyamides.

[0160] Amine functionalization of the hollow fiber structures may be carried out to maximize the carbon dioxide working capacity and adsorption / desorption (ads / des) kinetics. While the carbon dioxide working capacity may be governed by the amine grafting density, sorbent surface area, pore size distribution, amine layer thickness, and the molecular weight (MW) of amines and branching, the ads / des kinetics of the hollow fiber sorbent may be influenced by amine layer thickness, and MW of amines and branching. These performance factors may be tuned by optimizing the amination reaction conditions, such as amine concentration, temperature, solution viscosity, and type of amines. The reaction conditions controlling the performance factors are set out in Table 3.

[0161] Table 3: Tunable reaction conditions for amination

[0162] The aminations of the hollow fiber structures may be varied to improve the aforementioned parameters. Amines may range from small molecules to polymeric amines in this invention. Small molecule amines such as ethylenediamine (EDA), 1 ,3-propylenediamine (PDA), meta- xylylenediamine (meta-XyDm), para-xylylenediamine (para-XyDm), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA) may be used in this invention. Polymeric amines such as linear and branched polyethyleneimine (MW 600) and polyallylamine (MW 15000) may be used in this invention. The amine concentrations may be varied between 1 - 10 wt% while conducting the post-treatment. For most of the reactions, an amine concentration of 10 wt% may be used. Amine concentration of 5 wt% may be used in the cases where the reaction may be carried out for long durations (> 8 hours) at elevated temperatures.

[0163] The amines may be dissolved in alcoholic or aqueous-alcoholic solvents. For most of the reactions 2-propanol (I PA) may be used as the solvent, especially for small molecule amines. In certain cases, ethanol (EtOH) may be used as the reaction solvent particularly pertaining to polymeric amines.

[0164] Pure water may also be used as a solvent in some cases as all the amines are water soluble in some embodiments of this invention. The presence of aqueous amination conditions may result in high pH solutions around the HFs. Such high pH conditions may be detrimental to the HF mechanical stability as they may trigger chain hydrolysis and dissolution of the polyetherimide polymer structure in the basic solution. Since water-based solvents may result in full conversion of polyetherimide, 10 / 90 v / v% water-alcohol solutions may be investigated in one of the embodiments of this invention to enhance the amine grafting density while minimizing the HF dissolution.

[0165] Reaction temperatures may be examined between room temperature (RT) i.e. 25 °C and 90 °C. For the majority of the experiments, the reaction temperature may be selected to be about 40 °C or about 70 °C and a reaction temperature of 70 °C may be chosen for most aminations.

[0166] An optimal reaction duration is important to hollow fiber performance as it may affect both the amine grafting density and the surface morphologies and mechanical stability of the hollow fibers. The hollow fibers may be exposed to amination conditions varying between 15 minutes to 12 hours. The reaction duration may be decided as per the amine loading, reaction solvent, type of amine, and the surface properties of the unfunctionalized hollow fiber structures. When small molecule amines in water may be used, the reaction duration may be limited to 15 - 45 minutes at elevated temperatures. Using small molecule amines in aqueous and high temperature conditions may result in competing sacrificial hydrolysis which may tend to cause dissolution of HFs. Hence, in preferred embodiments, small molecule amines with IPA- or EtOH-based solvents may be used at 70 °C for 1-5 hours. A general reaction scheme of the amination reaction is shown in Scheme 1 below:

[0167] Scheme 1: Reaction mechanism of polyetherimide with small molecule amines.

[0168] Similarly, polymeric amines such as polyethyleneimine or polyallylamines may be used (Scheme 2 below) in aqueous alcoholic solvents for 3 - 5 hours. When small molecule diamines, such as EDA, PDA, may be used, the amination duration may be limited to 30 minutes as full chemical conversion was achieved during that time. In some embodiments when ethanolic solvents were used at 40 °C, the reaction duration may be extended to 18 hours. Despite the broad reaction duration window, a period of 1-5 hours may be suitable for most amination reactions.

[0169] Scheme 2: Reaction mechanism of polyetherimide with polymeric amines.

[0170] In another embodiment, amination using a mixture of two or more amines may be used to demonstrate significant improvement to the crosslinking stability and gas adsorption performance of the hollow fibers. Typically, a mixture of small molecule and polymeric amine may be chosen as the nucleophilic reaction mixture. Amination with bulky, branched or polymeric amines may result in lower reaction conversion due to pore blockages and higher chances of crosslinking. Subsequently, the surface underneath the aminated region may have a reduced number of free amines to allow further functionalization. This may be addressed by using a mixture of bulky (e.g., polymeric) and small molecule amines. Since the small molecule amines may have faster diffusion coefficients as compared to the polymeric analogues, they may improve the amination and lead to higher degrees of functionalization, while the bulky polymeric amines may provide more sites for chemisorption of carbon dioxide. In another embodiment, the hollow fiber structures may be pre-soaked in an alcoholic mixture to allow exfoliation of the polymeric chains via plasticization induced by the alcohol molecules. As a result of this pre-soaking, the amine molecules may diffuse efficiently through the polymer matrix and offer enhanced grafting density. Pre-soaking of hollow fiber structures may increase the amine loading in the sorbent material, which is advantageous for carbon dioxide adsorption. In some examples, the hollow fiber structures may be presoaked in IPA for up to 24 hours prior to exposure to the amination conditions. In some cases, the pre-soaking may be carried out by water / IPA (50 / 50 v / v%) mixture for 6 hours before immersion in the amination reaction mixture.

[0171] In another embodiment of this invention, the unfunctionalized hollow fiber structures may be cut into smaller pieces, between 1 - 5 cm, to ensure effective surface amination. Hollow fibers structures with closed outer skin layers may show improved amine loading in case of shorter hollow fiber structures. The closed skin may inhibit effective amine diffusion through the outer layer and may result in reduced degrees of amination in longer hollow fiber structures relative to the shorter hollow fiber structures. Therefore, cutting the hollow fiber structures into shorter pieces may increase the number of cross-sectional areas on the hollow fiber structure tips available for amine accessibility. In the majority of amine functionalization reactions, 1 cm hollow fiber structures may be used.

[0172] EXAMPLE 6 - Amine functionalization of hollow fiber structures with TETAr

[0173] In this exemplary embodiment, the polyetherimide hollow fiber structures were aminated with TETA is shown in Scheme 3 and discussed below.

[0174] Scheme 3: Amine functionalization of polyetherimide with triethylenetetramine (TETA).

[0175] An amination bath (150 mL) containing 10 wt% TETA in isopropanol (I PA) was prepared at room temperature. The hollow fiber structures were transferred to a 3-neck round bottom flasks (RBF) equipped with a condenser on the vertical neck and stirrer at the bottom. One of the side necks was used to pass nitrogen in the reaction vessel to establish an inert atmosphere while the other side neck was sealed with a rubber septum.

[0176] The 2.5 g hollow fiber structures were transferred to the RBF and the 150 mL of the amine solution was added with constant stirring. The RBF was then immersed in a preheated oilbath at 70 °C for 3 hours. The color of the reaction solution was monitored. After completion of the reaction, the functionalized hollow fiber structures were filtered from the amine solution and rinsed at least three times with copious amounts of water, followed by I PA and hexanes. The hollow fiber structures which presented white color before functionalization, were pale yellow in color after amination. The functionalized hollow fibers were dried in the vacuum oven at 70 °C, 50 mbar pressure for at least 8 hours. The weight of the dry aminated hollow fibers were measured to estimate the gravimetric amine loading of the HFs. SEM characterization of the hollow fibers were done as shown below. Figure 5 shows a scanning electron microscope (SEM) image of the outer skin and shell side of a TETA- functionalized hollow fiber.

[0177] Initially, Fourier Transformation Infrared (FT-IR) characterization of the hollow fibers was performed to compare the completion of the reaction (as shown below). The FT-IR spectrum is shown in Figure 6. The disappearance of the imide peaks of Ultern at 1720 cm-1(symmetric stretch) and 1780 cm-1(asymmetric stretch) and appearance of a strong resonance at 1630 cm-1corresponding to the amide peak after amination confirmed complete amination of the hollow fibers. Additionally, the TETA-functionalized hollow fiber structures demonstrated a strong resonance at 2950 cm-1which corresponds to C-H alkyl stretches from TETA’s methylene groups. Finally, the aminated hollow fiber structure showed a very strong resonance at 3600 cm-1which denotes the N-H stretching frequency and was absent in the non-aminated analog of the sample.

[0178] In one embodiment, the TETA-functionalized hollow fiber structures were exposed to carbon dioxide adsorption - desorption conditions to evaluate the carbon dioxide capacity (CO2_cap). A known amount of the aminated hollow fiber structures were transferred to an in-house developed reactor equipped with flow controllers, sensors, and heating coil. During the adsorption process ambient air or CO2 balanced with N2 was passed through the reactor containing the hollow fiber structures for 2 hours till saturation was achieved. Following the adsorption, the reactor was heated to 100 °C under vacuum (100 mbar pressure) with a constant sweep of nitrogen as the inert purge gas. The desorbed carbon dioxide was passed through a carbon dioxide sensor and a flowmeter. The total amount of carbon dioxide was calculated and compared to that of the unfunctionalized hollow fiber structures. A carbon dioxide working capacity of 0.35 mol / kg sorbent was obtained for the TETA-functionalized hollow fiber structures. The comparative carbon dioxide desorption plots of unfunctionalized and TETA-functionalized hollow fiber structures are shown below in Figure 7.

[0179] EXAMPLE 7 - Amine functionalization of hollow fiber structures with polyethyleneimine

[0180] In this exemplary embodiment, the polyetherimide hollow fiber structures were aminated with polyethyleneimine as shown in Scheme 4 and discussed below.

[0181] Scheme 4: Amine functionalization of polyetherimide with polyethyleneimine.

[0182] An amination bath (150 mL) containing 10 wt% PEI in isopropanol (I PA) was prepared at room temperature. The hollow fiber structures were transferred to a 3-neck round bottom flasks (RBF) equipped with a condenser on the vertical neck and stirrer at the bottom. One of the side necks was used to pass nitrogen in the reaction vessel to establish an inert atmosphere while the other side neck was sealed with a rubber septum.

[0183] The 2.5 g hollow fiber structures were transferred to the RBF and the 150 mL of the amine solution was added with constant stirring. The RBF was then immersed in a preheated oilbath at 70 °C for 3 hours. The color of the reaction solution was monitored. After completion of the reaction, the functionalized hollow fiber structures were filtered from the amine solution and rinsed at least three times with copious amounts of water, followed by I PA and hexanes. The hollow fiber structures which presented white color before functionalization, were pale yellow in color after amination. The functionalized hollow fibers were dried in the vacuum oven at 70 °C, 50 mbar pressure for at least 8 hours. The weight of the dry aminated hollow fibers were measured to estimate the gravimetric amine loading of the hollow fiber structures. EXAMPLE 8 - Amine functionalization of MOF-based mixed matrix hollow fiber structures with polyethyleneimine

[0184] In an exemplary embodiment of the invention, the UiO-66 based MOF mixed matrix hollow fiber structures were exposed to post-treatment conditions for amine-functionalization of the incorporated fillers, which is essential for chemisorption of carbon dioxide. This constitutes of post-treatment or post-functionalization (e.g., amination, etc.) of the filler-incorporated mixed matrix hollow fiber structures. The UiO-66-based mixed matrix hollow fiber structures were immersed in a bath containing polyethyleneimine (10 wt%) dissolved in ethanol. The reaction was carried out for a duration of 3 hours at room temperature. After the amine treatment, the aminated mixed matrix hollow fiber structures were rinsed thrice with copious amounts of water, isopropanol, and hexanes followed by vacuum drying at 100 °C for 24 hours. After vacuum drying, these aminated MOF-based mixed matrix hollow fibers were stored in a desiccator until further testing.

[0185] EXAMPLE 9 - Amine functionalization of MOF-based mixed matrix hollow fiber structures with aminosilanes

[0186] In an exemplary embodiment of the invention, covalent bonding of the amines to UiO-66 (Zr) fillers incorporated on polyethersulfone hollow fiber structures were also investigated. In a 50 mL round bottom flask, approx. 0.5 g of UiO-66 based MOF mixed matrix hollow fiber structures were suspended in 30 mL ethanol with 3 mL of (3-aminopropyl)triethoxysilane (APTES). The mixture was stirred at 80 °C in an oil bath for 24 h. After the completion of the reaction, the aminated MOF containing mixed matrix hollow fiber structures were collected from the amine bath and rinsed three times with copious amounts of water, isopropanol, and hexanes followed by vacuum drying at 100 °C for 24 hours. After vacuum drying, these aminosilane functionalized MOF-based mixed matrix hollow fibers were stored in a desiccator until further testing.

[0187] EXAMPLE 10 - Amine functionalization of Zeolite-based mixed matrix hollow fiber structures with polyethyleneimine

[0188] In an exemplary embodiment of the invention, the Zeolite 13X based MOF mixed matrix hollow fiber structures were exposed to post-treatment conditions for amine-functionalization of the incorporated fillers, which is essential for chemisorption of carbon dioxide. This constitutes post- treatment or post-functionalization (e.g., amination, etc.) of the fillerincorporated mixed matrix hollow fiber structures. The Zeolite 13X based mixed matrix hollow fiber structures were immersed in a bath containing polyethyleneimine (10 wt%) dissolved in ethanol. The reaction was carried out for a duration of 3 hours at room temperature. After the amine treatment, the aminated mixed matrix hollow fiber structures were rinsed thrice with copious amounts of water, isopropanol, and hexanes followed by vacuum drying at 100 °C for 24 hours. After vacuum drying, these aminated Zeolite-based mixed matrix hollow fibers were stored in a desiccator until further testing.

[0189] EXAMPLE 11 - Amine functionalization of Zeolite-based mixed matrix hollow fiber structures with aminosilanes

[0190] In an exemplary embodiment of the invention, covalent bonding of the amines to Zeolite 13X fillers incorporated on polyethersulfone hollow fiber structures were also investigated. In a 50 mL round bottom flask, approx. 0.5 g of Zeolite 13X based mixed matrix hollow fiber structures were suspended in 30 mL ethanol with 3 mL of (3-aminopropyl)triethoxysilane (APTES). The mixture was stirred at 80 °C in an oil bath for 24 h. After the completion of the reaction, the aminated zeolite containing mixed matrix hollow fiber structures were collected from the amine bath and rinsed three times with copious amounts of water, isopropanol, and hexanes followed by vacuum drying at 100 °C for 24 hours. After vacuum drying, these aminosilane functionalized zeolite-based mixed matrix hollow fibers were stored in a desiccator until further testing.

[0191] Pre-Functionalization of Fillers and Incorporation into Hollow Fiber Structures

[0192] Post-amination of the mixed matrix hollow fiber structures may have certain limitations, which could lead to lower stability or durability of the hollow fibers. For example, the mixed matrix hollow fiber structures may swell when exposed to polar and non-polar solvents during the amination process. Swelling of the polymer matrix might lead to loss of interfacial adhesion between the polymeric chains and the filler materials. Additionally, the amination of the fillers alters their hydrophilicity as amines are highly hydrophilic in nature. This alteration of the surface polarity of the fillers may affect the filler - polymer interactions and may pose loss of adhesion issues. Therefore, post-amination of the mixed matrix hollow fiber structures may present long-term durability challenges associated with the material. This may be avoided by conducting amination of the fillers before their incorporation in the dope solution and the hollow fiber structure.

[0193] In another embodiment of the invention, the filler materials may be exposed to amination conditions before incorporation in the hollow fiber structure to minimize challenges associated with interfacial interactions - see Figure 11 for example. This ensures that the interfacial interactions between the fillers and the polymeric chains do not change during the fiber preparation process. Polymers that may be suitable for structural support of fillers additives may include but not be limited to polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), Polytetrafluoroethylene (PTFE), combinations thereof or any other suitable polymer may be used. Additionally, this provides efficient synthetic handles to control the amination of the fillers which would be difficult to attain when the fillers are embedded in the polymer matrix. The fillers have synthetic handles to ensure immobilization and covalent grafting of amines warranted for carbon dioxide capture.

[0194] Non-limiting examples of fillers that may be functionalized may include, but are not limited to, an ion exchange resin, such as an aromatic cross-linked polystyrenic matrix including but not limited to poly-styrene based ion-exchange resins and amine functionalized resins, or a strongly basic anion exchange resin (e.g., DowexTM, MarathonTM A) or another suitable carbon dioxide adsorbing material, such as desiccant, carbon molecular sieve, carbon adsorbent, graphite, activated alumina, y-alumina, molecular sieve, aluminophosphate, silicoaluminophosphate, zeolite adsorbent, ion exchanged zeolite, hydrophilic zeolite, hydrophobic zeolite, modified zeolite, natural zeolites, faujasite, mordenite, metal-exchanged silico-aluminophosphate from Dow Chemical Company, etc.), zeolite, activated carbon, alumina, uni-polar resin, bi-polar resin, aromatic cross-linked polystyrenic matrix, brominated aromatic matrix, methacrylic ester copolymer, graphitic adsorbent, carbon fiber, carbon nanotube, nano-materials, metal salt adsorbent, perchlorate, oxalate, alkaline earth metal particle, metal oxides (zinc oxide, titanium dioxide, zirconium dioxide, magnesium oxide, silicon dioxide, iron oxide, aluminium oxide, copper oxide, cerium oxide, yttrium oxide, hafnium dioxide, beryllium oxide, chromium oxide), chemisorbent, amine, organo-metallic reactant, hydrotalcite, silicalite, zeolitic imidazolate framework, covalent organic framework (COF) and metal organic framework (MOF) adsorbent compounds, and combinations thereof. Amination strategies of both impregnation and covalent bonding of amines may be used.

[0195] Non-limiting examples of amines that may be used for amine functionalization include small molecule amines such as ethylenediamine (EDA), 1,3-propylenediamine (PDA), meta- xylylenediamine (meta-XyDm), para-xylylenediamine (para-XyDm), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) or pentaethylenehexamine (PEHA), hexamethylenediamine (HMDA), Putrescine (1 ,4-butanediamine), Spermidine, Spermine, Cadaverine (1,5-pentanediamine), b / s-hexamethylenetriamine, (3- aminopropyl)triethoxysilane (APTES), 2-[2-(3- trimethoxysilylpropylamino)ethylamino]ethylamine (triamine), [3-(2- aAminoethylamino)propyl]trimethoxysilane, any other suitable small molecule amine group, or combinations thereof. Polymeric amines may include linear or branched polyethyleneimine, polyallylamine, polyaniline (PANI), any other suitable polymeric groups, or combinations thereof

[0196] After amine functionalizations, the filler particles may be incorporated into the hollow fibers. The amine-functionalized fillers may be suspended in NMP with concentrations varying between 1 - 70 wt% with constant sonication and temperatures varying between 25 - 60 °C. The sonication may be carried out for 30 min to 12 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of the amine-functionalized fillers in solvent was obtained, the dispersion may be added to the polymer dope mixture. The polymeric dope mixture may consist of the polymer (polysulfone, polyethersulfone, polypropylene, polyvinylidenedifluoride), solvents (NMP, DMF, Dimethylacetamide), additives (PEG, PVP, water, UNO3) as mentioned earlier. The amine-functionalized fillers dispersion may be added to the polymer solution and may constitute the resulting new dope mixture. The composition of the dope mixture may be tuned to obtain a final filler loading varying between 5 - 70 wt% in the hollow fiber matrix. The mixture may be constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope may be extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in the invention. The dope mixture after extrusion from the spinneret, may pass through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath.

[0197] The mixed matrix hollow fiber structure containing the amine-functionalized fillers may then pass through one or more rinse baths before subsequent solvent exchanges with isopropanol and hexanes. After vacuum drying, the amine-functionalized mixed matrix hollow fibers structures composed of aminated fillers may be prepared for carbon dioxide capture applications. EXAMPLE 12 - Amine functionalization of UiO-66 (Zr) MOF with polyethyleneimine followed by incorporation in PES hollow fiber structures

[0198] In this exemplary embodiment of the invention, UiO-66 (Zr) MOF was used as a filler. First UiO-66 (Zr) was dried in a vacuum oven at 100 °C (50 mbar) prior to the amination to remove any adsorbed impurities on the surface of the material. Approximately 0.7 g of UiO- 66 (Zr) was weighed into a 20 mL scintillation vial equipped with a mechanical stirrer. In another vial an amine solution was prepared. In one embodiment, polyethyleneimine was used as the aminating agent. 10 wt% polyethyleneimine solution was prepared in ethanol with constant stirring to ensure a homogeneous amine solution. The polyethyleneimine solution was transferred to the glass vial containing UiO-66 (Zr). The reaction mixture was stirred at room temperature for 12 hours. Finally, the volatile solvent ethanol solvent was removed from the reaction mixture. The solids were dried in a vacuum oven at 80 °C for 8 hours to yield polyethyleneimine incorporated-UiO-66 ready for further incorporation in the hollow fiber dope mixture prior to spinning.

[0199] The polyethyleneimine functionalized UiO-66 (Zr) MOF was used as a filler material to prepare the mixed matrix hollow fiber structures as per the procedure described in Example 3. The amine functionalized MOF particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of polyethyleneimine-functionalized UiO-66 (Zr) in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing polyethyleneimine-functionalized UiO-66 (Zr)-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of aminated MOF / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the polyethyleneimine-functionalized UiO-66 (Zr) containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours. Apart from the above exemplary condition, other types of MOFs that may be used are as follows: HKUST-1, ZIF-8, MIL-53, MOF-545, MOF-74, MIL-101 etc.

[0200] EXAMPLE 13 - Amine functionalization of UiO-66 (Zr) MOF with aminosilane followed by incorporation in PES hollow fiber structures

[0201] In this exemplary embodiment of the invention, covalent bonding of the amines to UiO-66 (Zr) were also disclosed. In a 50 mL round bottom flask, approx. 0.5 g of UiO-66 (Zr) was suspended in 30 mL ethanol with 3 mL of (3-aminopropyl)triethoxysilane (APTES). The mixture may be stirred at 80 °C in an oil bath for 24 h. The aminated MOF particles were collected by centrifugation, washed two times with ethanol, and left to dry at 80 °C overnight, thus, yielding the final product of aminosilane-functionalized UiO-66 (Zr), referred to as APTES / UiO-66. The amination strategy is not limited to APTES and may be used for aminosilanes.

[0202] The APTES-functionalized UiO-66 (Zr) MOF was used as a filler material to prepare the mixed matrix hollow fiber structures as per the procedure described in Example 3 and Example 12. Polyethersulfone was used as the polymer for preparing APTES-functionalized UiO-66 (Zr)-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of APTES-MOF / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the APTES-functionalized UiO-66 (Zr) containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours.

[0203] EXAMPLE 14 - Amine functionalization of Zeolite 13X with polyethyleneimine followed by incorporation in PES hollow fiber structures

[0204] In this exemplary embodiment, the Zeolites were investigated in the invention. Commercially purchased molecular sieves 13X (Zeolite 13X) with a chemical composition of Na86[(AIO2)86(SiO2)i06].xH2O was used as the filler material for preparing zeolite-based mixed matrix hollow fiber structures. The synthesis of polyethyleneimine-immobilized Zeolite 13X was achieved by anchoring polyethyleneimine on zeolite 13X through a physical impregnation method. The immobilization of amine i.e. polyethyleneimine on zeolite was carried out using an alcoholic solution of amine. An amine solution of 10 wt% polyethyleneimine in methanol was prepared at room temperature with constant stirring. The polyethyleneimine solution was transferred to the glass vial containing 1 g Zeolite 13X. The reaction mixture was stirred at room temperature for 12 hours. Finally, the amine solvent was filtered or decanted off and the modified zeolite slurry may be dried in an oven at 100 °C for 12 hours to produce polyethyleneimine-functionalized zeolite 13X sample.

[0205] The polyethyleneimine-functionalized zeolite 13X was used as a filler material to prepare the mixed matrix hollow fiber structures as per the procedure described in Example 3 and Example 12. Polyethersulfone was used as the polymer for preparing polyethyleneimine- functionalized zeolite 13X-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of aminated zeolite 13X / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the polyethyleneimine-functionalized zeolite 13X containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours.

[0206] EXAMPLE 15 - Amine functionalization of Zeolite 13X with aminosilane followed by incorporation in PES hollow fiber structures

[0207] In this exemplary embodiment of the invention, covalent bonding of the amines to Zeolite 13X were also disclosed. In a 50 mL round bottom flask, approx. 1 g of Zeolite 13X was suspended in 30 mL ethanol with 3 mL of (3-aminopropyl)triethoxysilane (APTES). The mixture may be stirred at 80 °C in an oil bath for 24 h. The aminated Zeolite 13X particles were collected by centrifugation, washed two times with ethanol, and left to dry at 80 °C overnight, thus, yielding the final product of aminosilane-functionalized Zeolite 13X, referred to as APTES / Zeolite 13X. The amination strategy is not limited to APTES and may be used for aminosilanes.

[0208] The APTES-functionalized Zeolite 13X was used as a filler material to prepare the mixed matrix hollow fiber structures as per the procedure described in Example 3 and Example 12. Polyethersulfone was used as the polymer for preparing APTES-functionalized Zeolite 13X- based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of APTES- 13X / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the APTES-functionalized Zeolite 13X containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours.

[0209] EXAMPLE 16 - Amine functionalization of y-alumina with aminosilane followed by incorporation in PES hollow fiber structures

[0210] In this exemplary embodiment of the invention, covalent bonding of the amines to y-alumina was investigated. In a 1 L round bottom flask, approx. 50 g of y-alumina was suspended in 550 mL of toluene along with 11 mL of 2-[2-(3- trimethoxysilylpropylamino)ethylamino]ethylamine (triamine) as the aminosilane. The mixture was stirred at 85 °C using a heating mantle for 24 h. The aminated y-alumina particles were collected by gravity filtration, washed two times with toluene, hexanes, and ethanol, and left to dry at 80 °C overnight, yielding the final product of aminosilane-functionalized y-alumina (also referred to below as triamine / y-alumina).

[0211] The triamine-functionalized y-alumina was used as a filler material to prepare the mixed matrix hollow fiber structures. Polyethersulfone was used as the polymer for preparing triamine-functionalized y-alumina-based mixed matrix hollow fiber structures. The final dope has a concentration of 12 / 26 / 5.8 / 14.7 / 41.5 wt% of PES / PVP / H2O / triamine-y-alumina / NMP. The dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C.

[0212] Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the triamine-functionalized y-alumina containing hollow fiber structures were rinsed with hexanes at 25 °C before drying in a vacuum oven at 70 °C for 12 hours. These resulted in hollow fiber structures with thicker walls with ID = 1.0 mm and OD = 3.0 mm.

[0213] In some embodiments, it may be desirable to produce a multi-layer hollow fiber, such as a two-layer hollow fiber. For example, a triple-orifice spinneret configuration enables the simultaneous co-extrusion of two distinct polymer streams. The outer annular channel is fed with a polymer dope mixture containing alumina or other fillers, while the inner annular channel delivers a neat base polymer dope devoid of additives. This innovative approach results in hollow fibers with a functionalized outer shell and a clean, dense inner lumen layer, free from defects and pinholes, all formed in a single step. Unlike conventional single-dope filler-loaded fibers, which often suffer from particle detachment on the bore surface during handling or subsequent lumen-coating processes, the triple-orifice design eliminates such issues by ensuring the inner layer remains particle-free. This defect-free bore surface facilitates the application of uniform lumen coatings, reduces water-vapor permeability, and enhances the overall transport properties and long-term stability of the hollow fibers, making them highly suitable for advanced applications such as carbon capture and selective gas separation.

[0214] The method includes extruding a dope mixture containing alumina or other fillers through the outer annular channel, then extruding a second dope mixture through the inner annular that is a neat base polymer dope devoid of additives. For example, the first dope mixture may have a higher amount of fillers than the second dope mixture. Further, the second dope mixture may be devoid of fillers. The dope mixtures may be co-extruded while a bore fluid is injected. During the hollow fiber formation process, the first dope forms an external filler-containing shell, and the second dope simultaneously forms an internal lumen layer that acts as an integral coating. This configuration prevents filler particles from being exposed at the bore surface, thereby avoiding particle detachment and associated defect formation that hinder subsequent lumen-coating steps and lead to uncontrolled water-vapour permeability. The process results in hollow fibers with a defect-free inner surface, improved interfacial adhesion, and simplified manufacturing by eliminating separate post-processing coating operations.

[0215] Amine impregnation and crosslinking in v-alumina

[0216] Amine-functionalization of the alumina sorbent may also be done via nucleophilic amines impregnation and crosslinking. Impregnation of the amines may result in amine leaching and loss of CO2 capacity over multiple sorption cycles due to the small molecular size of the amines. In order to prevent amine leaching, the impregnated amine molecules may be crosslinked with multi-functional crosslinkers to increase their molecular size. The amine crosslinking provides an affordable strategy for alumina-based sorbent production. The synthetic procedure of impregnation and impregnation - crosslinking may be easier to carry out as compared to the covalently bonding pathways. This synthetic strategy may also present an easier methodology for optimization of amine loading and pore structure may also be advantageous during the HF spinning process when the filler-incorporated HFs pass through the rinse baths during the HF spinning process. Amine impregnation and crosslinking may also present a more economical and offer better control over the structure morphology.

[0217] An embodiment of the present invention may include fillers impregnated with nucleophilic multi- and poly- amines crosslinked with at least one of the polyepoxides, epoxy silanes, aminosilanes, acrylamide-based crosslinkers.

[0218] EXAMPLE 17 - Amine impregnation and crosslinking of amines and polyepoxides in y- alumina followed by incorporation in PES hollow fiber structures

[0219] In this exemplary embodiment, y-alumina was investigated. Commercially purchased y- alumina was used as the filler material for preparing y-alumina-based mixed matrix hollow fiber structures. The synthesis of polyethyleneimine-crosslinked y-alumina was achieved by anchoring polyethyleneimine on y-alumina through a physical impregnation method followed by crosslinking with triepoxide such as N, N-diglycidyl-4-glycidyloxyaniline. The impregnation- crosslinking of amine i.e. polyethyleneimine on y-alumina, was carried out using an ethanolic solution of amine. An amine solution of 5 wt% polyethyleneimine and N,N-diglycidyl-4- glycidyloxyaniline in methanol was prepared at room temperature with constant stirring. The polyethyleneimine and crosslinker solution was transferred to the glass vial containing 1 g y- alumina. The reaction mixture was stirred at 40 °C for 4 hours. Finally, ethanol was removed under vacuum with constant stirring of the reaction mixture. The modified y-alumina was dried in an oven at 70 °C for 12 hours to produce a polyethyleneimine-crosslinked y-alumina sample.

[0220] The polyethyleneimine-crosslinked y-alumina was used as a filler material to prepare the mixed matrix hollow fiber structures as per the procedure described in Example 3 and Example 12. Polyethersulfone was used as the polymer for preparing polyethyleneimine- crosslinked y-alumina based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of amine-crosslinked y-alumina / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation.

[0221] Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described in Example 2. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing water at 60 °C. Following the rinse baths, the hollow fiber structures were rinsed twice with isopropanol at 25 °C. Finally, the polyethyleneimine-crosslinked y-alumina containing hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours.

[0222] In-Line Functionalization Of Hollow Fiber Structures

[0223] Post-treatment of hollow fiber structures is commonly done to install additional properties which may be absent in the unfunctionalized hollow fiber structures. The conventional methods involves spinning of the hollow fiber structures followed by vacuum drying and storage then finally exposing them to the treatment conditions. Such strategies are almost always adopted for gas-separation membranes. The post-treatment of the hollow fiber structures offer an additional step for functionalization and may incur requirement of efficient storage units, additional reaction vessels or reactors, and subsequent washing, rinsing, and vacuum drying. During this post treatment process the fibers are exposed to at least 2 rinse conditions (one during spinning, and second after post treatment) as well as 2 vacuum drying conditions. This warrants wetting the fibers twice during the process followed by two vacuum drying steps. Multiple wetting and drying steps of the hollow fiber structures may impose additional stress to the mechanical integrity of the material. These mechanical stress are induced due to swelling (or exfoliation) of the hollow fiber structures during wetting which results in increasing the length and outer diameters of the hollow fiber structures. Posttreatment when the hollow fiber structures are exposed to vacuum drying conditions, the hollow fiber structures shrink and at times also may get twisted. Since hollow fiber structures are designed for long-term applications, these additional stresses might reduce the durability of the fibers.

[0224] The efficiency of the post-treatment strategies are highly dependent on the wetting of the hollow fiber structures. Improper wetting of the hollow fiber structures might lead to poor post treatment and introduction of defects in the material. Additionally, two step post-treatment strategies may be expensive when attempted on a larger scale due to the requirement of additional solvents, reaction vessels, and energy demand for drying and storage. Therefore, to not only omit time-consuming post treatment steps and the associated challenges, single- step hollow fiber spinning and treatment is beneficial as described in Figure 8 and Figure 10. The hollow fiber spinning process offers handles for treatment of the hollow fiber structures during the spinning process. Amine-functionalization is the most essential treatment method used for the hollow fiber structure productions in this invention. The baths (coagulation and / or rinse) used in the hollow fiber spinning process may be charged with the amines to ensure amine-functionalization of the hollow fiber structures. The amine-functionalization of the hollow fiber structures during the spinning process is defined as “in-line” functionalization of the hollow fiber structures.

[0225] In one embodiment of the invention, the hollow fiber structures may be aminated in the inline functionalization process (Figure 8). In one embodiment, the dope mixture may include polymers suitable for functionalization by nucleophilic groups, such as amine groups, including without limitation polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole. In one embodiment of the invention, the dope mixture used for spinning the hollow fiber structure may include polyetherimide (Ultern 1000TM) and NMP as the polymer and solvent, respectively. The Ultern concentration may vary between 10 - 25 wt% in NMP. In order to attain full solubility, the dope mixture may be mechanically stirred at 60 - 90 °C for 12 - 48 hours. Suitable solvents may include NMP, dimethylformamide (DMF), dimethylacetamide (DMA), N-ethyl pyrrolidone (NEP), dimethyl sulfoxide (DMSO), sulfolane, tetrahydrofuran (THF) and mixtures thereof. Other solvent systems will be apparent to the skilled person.

[0226] The dope mixture may be charged with pore forming additives such as polyethyleneglycol (PEG), PEG 200, PEG 400, PEG 600, PEG 800, PEG 2000, and LiNO3, polyvinylpyrrolidone (PVP), PVP K12, PVK K17 suitably at concentrations of from 1 - 22 wt%. The concentrations of such additives may be optimized as per the requirement to obtain a desired porosity, surface area and pore size distribution in the varying ratios may be chosen.

[0227] In a range of trials of hollow fiber structure spinning, the bore fluid composition may be varied between 0 / 100 - 60 / 40 wt% NMP / water. After complete degassing of the dope and bore fluid with N2, they may be co-extruded through the double orifice spinneret. The dope flow rate and line pressure may be varied between 4.5 - 10.0 mL / min and 4.6 - 12.3 bar, respectively. The dope temperature may have varied between 35 - 50 °C, while the bore fluid may be maintained at a constant temperature of 25 °C. The spinneret temperature may be held constant at 35 °C and the connector temperature may be altered between 35 - 50 °C.

[0228] The extrudant (co-extruded dope and the bore fluid) may be passed through an air gap and chimney length of 2.0 - 12.5 cm before entering the coagulation bath. The humidity, temperature, and N2 flow rate in the chimney may be adjustable. Water may be used as the coagulation bath liquid and the temperature of the fluid in the coagulation bath was between 35 - 50 °C. After the coagulation bath, the hollow fiber structures may be drawn to the rinse bath(s) via roll-up drums / wheels. The rinse baths may contain solvents charged with amines with concentrations varying between 1 - 50 wt% at 60 - 70 °C to ensure in-line amine functionalization of the hollow fiber structures. The coagulation bath may also be charged with amine solutions but ideally rinse baths may be more suitable for amine functionalization as the temperature of the rinse baths can be increased up to 70 °C and the hollow fiber structures may spend longer time in the rinse baths as per the required reaction conditions of the functionalization as shown in Figure 8. Finally, after the amine-functionalization in-line, the hollow fiber structures may undergo several rounds of solvent exchange with water, isopropanol, and hexanes. The hollow fiber structures may be vacuum dried at 90 - 130 °C for 12 - 48 hours and are finally stored in a moisture free environment to prevent the pore collapse. This process defines single-step spinning and amine-functionalization of hollow fiber structures. Small molecule multi-amines and polymeric multi-amines may be used during the amination in combination with alcoholic and aqueous alcoholic solvents in varying concentrations and ratios, as described above.

[0229] In another embodiment of the invention, single-step mixed matrix hollow fiber structure spinning and in-line amine-functionalization may be investigated as shown in Figure 10. In this embodiment, filler materials may include metal organic frameworks (MOFs), aluminosilicates, zeolites, silica, alumina, activated carbon, or combinations thereof. The fillers may be added to the polymeric dope mixture solution during the spinning process. The fillers may be dispersed in a solvent which dissolves the polymer or is completely miscible with the polymeric solution (eg. NMP). The fillers with particle sizes above 200 nm may be broken to smaller particles via mechanical ball milling process. The fillers may be subsequently suspended in NMP with concentrations varying between 1 - 50 wt% with constant sonication and temperatures varying between 25 - 60 °C. Sonication may be carried out for 30 min to 12 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation) may be obtained. Upon obtaining a homogeneous dispersion, the dispersion may be added to the polymer dope mixture. The polymeric dope mixture may consist of the polymer, (e.g., polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polytetrafluoroethylene (PTFE), polysulfone (PSU), polyethersulfone (PES), and polyphenyleneoxide (PPO), solvents (NMP), additives (PEG, PVP, Li NO3, water) as mentioned earlier. The filler dispersion may be added to the dope mixture polymer solution and constitutes a new dope mixture. The composition of the new dope mixture may be tuned to obtain a final filler loading varying between 5 - 50 wt% in the hollow fiber polymer matrix. The dope may be extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS as described previously. The dope mixture after extrusion from the spinneret, may pass through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath. After the coagulation bath, the hollow fiber structures may be drawn to the rinse bath(s) via roll-up drums / wheels. The rinse baths may contain solvents charged with amines with concentrations varying between 1 - 50 wt% at 60 - 70 °C to ensure in-line amine functionalization of the hollow fiber structures. The coagulation bath may also be charged with amine solutions but ideally rinse baths may be more suitable for amine functionalization as the temperature of the rinse baths can be increased up to 70 °C and the hollow fiber structures may spend longer time in the rinse baths as per the required reaction conditions of the functionalization as shown in Figure 10. Finally, after the amine-functionalization inline, the hollow fiber structures may undergo several rounds of solvent exchange with water, isopropanol, and hexanes. The hollow fiber structures may be vacuum dried at 90 - 130 °C for 12 - 48 hours and are finally stored in a moisture free environment to prevent the pore collapse. This process defines single-step spinning and amine-functionalization of mixed matrix hollow fiber structures. Small molecule multi-amines and polymeric multi-amines may be used during the amination in combination with alcoholic and aqueous alcoholic solvents in varying concentrations and ratios.

[0230] EXAMPLE 18 - In-line polyetherimide hollow fiber structure spinning and TETA functionalization

[0231] In an exemplary embodiment of this invention, polyetherimide-based hollow fiber structures were used. Commercially purchased Ultern 1000 ™ was used as the polyetherimide. The dope mixture was prepared by mixing polyetherimide, polyethyleneglycol 600, NMP, UNO3 at a ratio of 19 / 20 / 60 / 1 wt / wt% while the dope mixture was stirred at 60 °C for 12 hours. The dope was degassed with nitrogen gas prior to spinning the hollow fiber structure. After obtaining a homogeneous dope mixture, the solution was extruded through the spinneret with a bore fluid of NMP / water 82 / 18 wt / wt%. The extruded hollow fiber structure was passed through a chimney and air gap prior to undergoing phase separation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% triethylenetetramine (TETA) in isopropanol at 70 °C. The fibers had a residual time of 1 hour in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours.

[0232] EXAMPLE 19 - In-line polyetherimide hollow fiber structure spinning and polyethyleneimine functionalization

[0233] In an exemplary embodiment of this invention, polyetherimide-based hollow fiber structures were used. Commercially purchased Ultern 1000™ was used as the polyetherimide. The dope mixture was prepared by mixing polyetherimide, polyethyleneglycol 600, NMP, UNO3 at a ratio of 19 / 20 / 60 / 1 wt / wt% while the dope mixture was stirred at 60 °C for 12 hours. The dope was degassed with nitrogen gas prior to spinning the hollow fiber structure. After obtaining a homogeneous dope mixture, the solution was extruded through the spinneret with a bore fluid of NMP / water 82 / 18 wt / wt%. The extruded hollow fiber structure was passed through a chimney and air gap prior to undergoing phase separation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% polyethyleneimine in isopropanol at 70 °C. The fibers had a residual time of 1 hour in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours.

[0234] EXAMPLE 20 - In-line MOF-based mixed matrix hollow fiber structure spinning and TETA functionalization

[0235] In this exemplary embodiment of this invention, UiO-66 (Zr) MOF was used as a filler material to prepare the mixed matrix hollow fiber structures. The UiO-66 (Zr) MOF particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of UiO-66 (Zr) in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing UiO-66 (Zr)-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of UiO-66 / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% triethylenetetramine (TETA) in isopropanol at 70 °C. The mixed matrix hollow fiber structures had a residual time of 1 hour in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 100 °C for 12 hours.

[0236] EXAMPLE 21 - In-line MOF-based mixed matrix hollow fiber structure spinning and polyethyleneimine functionalization

[0237] In this exemplary embodiment of this invention, UiO-66 (Zr) MOF was used as a filler material to prepare the mixed matrix hollow fiber structures. The UiO-66 (Zr) MOF particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of UiO-66 (Zr) in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing UiO-66 (Zr)-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of UiO-66 / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% polyethyleneimine in isopropanol at 70 °C. The mixed matrix hollow fiber structures had a residual time of 1 hour in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 100 °C for 12 hours.

[0238] EXAMPLE 22 - In-line MOF-based mixed matrix hollow fiber structure spinning and aminosilane functionalization

[0239] In this exemplary embodiment of this invention, UiO-66 (Zr) MOF was used as a filler material to prepare the mixed matrix hollow fiber structures. The UiO-66 (Zr) MOF particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of UiO-66 (Zr) in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing UiO-66 (Zr)-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of UiO-66 / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% (3- aminopropyl)triethoxysilane (APTES) in ethanol at 70 °C. The mixed matrix hollow fiber structures had a residual time of 3 hours in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 100 °C for 12 hours followed by storing them in a desiccator.

[0240] EXAMPLE 23 - In-line Zeolite-based mixed matrix hollow fiber structure spinning and TETA functionalization

[0241] In this exemplary embodiment of this invention, Zeolite 13X was used as a filler material to prepare the mixed matrix hollow fiber structures. The Zeolite 13X particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of Zeolite 13X in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing Zeolite 13X-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of Zeolite 13X / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% triethylenetetramine (TETA) in isopropanol at 70 °C. The mixed matrix hollow fiber structures had a residual time of 1 hour in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 100 °C for 12 hours.

[0242] EXAMPLE 24 - In-line Zeolite-based mixed matrix hollow fiber structure spinning and polyethyleneimine functionalization

[0243] In this exemplary embodiment of this invention, Zeolite 13X was used as a filler material to prepare the mixed matrix hollow fiber structures. The Zeolite 13X particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of Zeolite 13X in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing Zeolite 13X-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of Zeolite 13X / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% polyethyleneimine in isopropanol at 70 °C. The mixed matrix hollow fiber structures had a residual time of 1 hour in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 100 °C for 12 hours.

[0244] EXAMPLE 25 - In-line Zeolite-based mixed matrix hollow fiber structure spinning and aminosilane functionalization

[0245] In this exemplary embodiment of this invention, Zeolite 13X was used as a filler material to prepare the mixed matrix hollow fiber structures. The Zeolite 13X particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of Zeolite 13X in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing Zeolite 13X-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of Zeolite 13X / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation. Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 10 wt% (3-Aminopropyl)triethoxysilane (APTES) in ethanol at 70 °C. The mixed matrix hollow fiber structures had a residual time of 3 hours in the rinse baths. Following the rinse baths, the hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the hollow fiber structures were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 100 °C for 12 hours followed by storing them in a desiccator.

[0246] EXAMPLE 26 - In-line ysilumina-based mixed matrix hollow fiber structure spinning and amine impregnation-crosslinking

[0247] In this exemplary embodiment of this invention, y-alumina was used as a filler material to prepare the mixed matrix hollow fiber structures. The y-alumina particles were suspended in NMP at a concentration of 10 wt% with constant sonication and stirring. The sonication was carried out for 3 hours until a homogeneous dispersion (i.e. no particle agglomeration, aggregation, and / or precipitation was observed). Once a homogeneous dispersion of y- alumina in solvent was obtained, the dispersion was added to the polymer dope mixture. Polyethersulfone was used as the polymer for preparing y-alumina-based mixed matrix hollow fiber structures. The final dope has a concentration of 5 / 25 / 6 / 66 wt% of y- alumina / PES / PEG / NMP. The new dope mixture was constantly stirred to obtain a homogeneous dope mixture without polymer and / or filler aggregation or precipitation.

[0248] Finally, the dope was extruded through the double annular spinneret similar to the generic hollow fiber spinning process via NIPS. The dope mixture after extrusion from the spinneret was passed through an air gap with controlled humidity, and temperature before undergoing coagulation in the coagulation bath containing water at 35 °C. The coagulated hollow fiber structures were then pulled through two rinse baths containing 5 wt% polyethyleneimine and N,N-diglycidyl-4-glycidyloxyaniline in ethanol at 40 °C. The mixed matrix hollow fiber structures had a residual time of 3 hours in the rinse baths. Following the rinse baths, the mixed matrix hollow fiber structures were rinsed twice each with water and isopropanol at 25 °C. Finally, the mixed matrix hollow fiber structures containing impregnated - crosslinked polyethyleneimine were rinsed with hexanes at 25 °C before drying them in the vacuum oven at 70 °C for 12 hours followed by storing them in a desiccator.

[0249] In accordance with aspects of the present invention, the nonsolvent of the coagulation bath 14 includes a source of amine groups to effect amination of the polymer matrix of the hollow fiber.

[0250] In a conventional procedure, passage of the hollow fiber through the coagulation bath is followed by at least one rinsing bath 20, 21 to rinse reactants and coagulation bath fluid from the formed hollow fiber 15. In accordance with aspects of the present invention, the rinsing fluid of rinsing bath 20, or of at least one of a plurality of rinsing baths 20,21 includes a source of amine groups to effect amination of the polymer matrix of the hollow fiber.

[0251] The hollow fiber 15 travels through the coagulation bath 14 and the rinsing baths with the aid of pulleys or wheels 22 or other suitable means. After rinsing, the hollow fibers are vacuum dried in an oven and stored as spools or yarns in a suitable temperature and humid atmosphere.

[0252] Accordingly, it can be considered that the sequence of steps of the processes of the present invention follows a conventional sequence and the components of the process apparatus also follow a conventional arrangement. However, in accordance with the present invention, at least one of the fluids of the coagulation / quench bath and / or the fluid of at least one of the rinsing baths includes a source of amine groups for the polymer matrix of the hollow fiber.

[0253] The steps of the process are also illustrated in Figure 2, figuratively showing the result of formation of extrudate 13 from the spinneret (A), functionalization by the amine-containing coagulation bath to form an amine-functionalized hollow fiber (B) and lumen coating (C) with a semi-permeable membrane, as will be described in further detail below.

[0254] After the coagulation bath, the hollow fibers were drawn to the rinse bath(s) via roll-up drums / wheels. The rinse bath(s) contain water at 60 - 70 °C to ensure complete solvent exchange in the hollow fiber membranes. In the preferred examples, the rinse baths both contain one or more amine sources, as described above. Both rinse baths may contain the same amines or mixtures of amines, which may be the same or different from an amine or amines provided in the coagulation bath.

[0255] Once treated, the hollow fibers were dried in a vacuum oven prior to storage. The hollow fibers are vacuum dried at 90 - 130 °C for 12 - 48 hours and are finally stored in a moisture free environment to prevent the pore collapse

[0256] Steam Permeable Lumen Coating of Hollow Fiber Structures

[0257] Hollow fiber structures offer facilities to apply a coating inside the lumen of the hollow fiber structure. These types of “lumen” coatings are typically used to cover any skin defects on the inner side of the fiber which might have formed during the spinning process. Since hollow fibers are extensively used in gas separation mixtures, ascertaining a defect free inner layer is essential to their performance. Typically, coating solutions containing solvents, which do not affect the fiber integrity, are used and are circulated a couple of times through the lumen of the fiber to form multilayer coatings.

[0258] We have determined that applying a dense, semi-permeable lumen coating is advantageous for carbon dioxide adsorption / desorption performance. The lumen material chosen allows selective transmission of water vapour through the hollow fiber structure while blocking liquid water.

[0259] The exact function of the lumen layer is described below. During the desorption stage, hot liquid water may be passed through the lumen of the hollow fiber while the hollow fiber bundle is under vacuum conditions. The lumen acts as a semi permeable membrane between the water molecules on the bore and shell side of the hollow fiber with significantly lower concentrations on the shell side. This creates the driving force for the diffusion and permeation of the water molecules through the lumen coating due to the concentration gradient. As the lumen selectively allows only water vapours to pass through but not liquid water, the water molecules pass through as steam from the bore to the shell side of the HF. While the water vapours pass through the shell they come in contact with the tortuous microstructure of the HFs. During this process, the carbon dioxide molecules which have desorbed in the pores of the HF are diluted by the water vapour while the entire system is under reduced pressure. This causes localized steam in the pores and reduces the carbon dioxide partial pressure in the pores. Thus, this enhances the driving force for the carbon dioxide desorption and also increases the carbon dioxide working capacity of the HF sorbent.

[0260] The lumen coating material was chosen based on certain criteria. First, the solvent used for the coating should not chemically and physically modify the hollow fiber structures’ microstructure, which would result in loss of chemical integrity and alteration of the surface morphology of the hollow fiber structure, respectively. The lumen coating should have a water vapour permeability below 3000 Barrer (1 Barrer = 3.348 x 10-16 mol.m / (m2.s.Pa)). Coatings with water vapour permeability between 1000 - 3000 Barrer could also be used while thicker lumen coating would be required to inject the same amount of steam. Ideally polymeric coatings with water vapour permeability < 1000 Barrer, preferably below 500 Barrer, particularly in the range of about 200 Barrer to 300 Barrer, would be the most suitable for the desired steam injection as they would not warrant thicker lumen coating which would increase the thermal weight of the corresponding hollow fiber structure. The lumen coating material should present durable adhesion to the underlying polyetherimide support. The lumen material should also be able to withstand water and steam at 70 - 100 °C, preferably at 90 - 100 °C.. Polymers having rubber-like characteristics are considered to be more appropriate for our requirements as they are less prone to defects and stress- induced cracking.

[0261] In some examples, the step of coating the inside of the lumen to form a semi-permeable layer is repeated at least once to form a semi-permeable layer comprising multiple layers. Each layer of the multiple layers may comprise a different polymers, allowing adjustment of the properties of the semi-permeable layer.

[0262] Composite lumen coating materials

[0263] In another embodiment of the invention, polymer composite lumen coatings may be used to coat the inner lumen side of the hollow fiber structures. Polymer composites are multi-phase systems consisting of particles dispersed in a polymer matrix. If the dispersed particle has a dimension in the nano scale, then this system may be referred to as a polymer nanocomposite. Typically, addition of these composites in the polymer matrix may alter the effective diffusion pathway of the molecule as the addition of such particles to the polymer matrix or coating may lead to change in the tortuosity within the polymer matrix. These alternations to the material tortuosity may influence the diffusion path length, porosity, mechanical properties, pore structure and volume. Changes to the tortuosity may also exert control on the permeability characteristics of the polymer coating. The permeating molecule (eg. water in this invention) may encounter the composite materials embedded in the polymer matrix. These interactions with the composite materials may present additional resistance or hindrance to the pathway of the water molecule. Therefore the diffusion pathlength of the permeating water molecule may be significantly increased and thus may affect the permeability of the coating material. Since selective water vapour permeation is central to the controlled steam injection and generation aspect of our injection, addition of composites to the lumen coating may provide another tunable handle to tune the amount of steam generated during the desorption process. The diffusion of the water vapour molecule may be governed by the composite loading in the lumen coating as well as the lumen polymer and the thickness of the lumen coating. The composite lumen coating may be advantageous in creating a very thin lumen coating on the inner wall of the hollow fiber structure.

[0264] The permeability of films and coatings may be reduced by using a new polymer, by adding impermeable and aligned flakes, or by incorporating reactive functional materials. Flakes may reduce both the steady permeability and may increase the lag before the permeation. Such types of flake materials are a specific type of composite particles. These composite materials may increase the effective path length for diffusion of molecules due to increased tortuosity introduced by such materials. These composite materials may align themselves as ribbons or ordered plates and hinder three-dimensional diffusion, as a result may inhibit the molecular diffusion through the films or coatings.

[0265] Incorporation of composite particles inside the lumen coating could serve multiple purposes, such as, foul resistant additive and / or reduction of the water vapour permeability. The foul resistance can be enhanced by incorporation of anti-fouling nanoparticles of copper, silver, or other metallic or inorganic compounds. Incorporation of particles in the lumen may have a pronounced impact on the water vapour permeability and the steam generation during the HF operation process. Controlling the water vapour permeability may result in optimizing the amount of steam generated during the desorption process and in turn, may result in a more cost effective process. The steam generation may be controlled by the choice of the lumen polymer or the thickness of the lumen coating. The presence of composite materials may also offer another handle to tune the amount of steam generation. The dense composite particles may hinder the diffusion path length of the water vapour molecules when traversing through the shell of the HF.

[0266] A very small composite incorporation (<5% by weight) may be sufficient to bring about reinforcement behavior. This may be also accompanied by significant changes in the mechanical and permeability properties of the polymeric composite. Typically, for achieving control on the permeability and the mechanical properties, nano fillers such as layered silicates (clays such as bentonite, montmorillonite and sapiolite, talc, hectorite etc.), aluminosilicates, exfoliated clays, natural fibers (sisal, agave, cellulose, banana, etc.), particulates like TiC>2, FeTiCh, Fe3C>4, O2O3, SiC>2, CaCCh, ZnO, montmorillonites, bentonite, Laponite, oxide coated mica substrates (Sn, Sb, Fe, Ti oxides) etc., speciality materials like carbon nanotubes (CNT; or multi wall nano tubes- MWNT), graphene, fullerenes, etc. may be used. Dispersion of non-soluble polymeric microparticles in a given polymer matrix may also be used to prepare polymeric-composite coating materials. The composite particles may be loaded in the lumen coating solution with a concentration varying between 1 - 20 wt%.

[0267] Additionally, incorporation of inorganic composite particles such as silver-, copper-, zinc- based additives may result in a polymeric coatings with anti-microbial properties. Typically, silver-based additives are used as anti-bacterial and anti-fungal agents. Copper-based composites are often exploited due to their anti-microbial properties, while zinc-based composite particles are highly effective against fungi and are used in coatings and rubber products. Therefore, addition of such inorganic composite particles in the lumen coating might be useful to prevent microbial growth and scaling on the lumen side of the hollow fiber structures which may increase the durability and the longevity of the hollow fiber structures and may also warrant lower maintenance of the sorbent material.

[0268] The composite particles that may be used in this embodiment are not limited to nano fillers such as layered silicates (clays such as bentonite, montmorillonite and sapiolite, talc, etc.), natural fibers (sisal, agave, cellulose, banana, etc.), particulates like TiC>2, FeTiCh, Fe3C>4, Cr2C>3, SiC>2, CaCCh, ZnO, montmorillonites, bentonite, laponite, oxide coated mica substrates (Sn, Sb, Fe, Ti oxides) etc., speciality materials like carbon nanotubes (CNT; or multi wall nano tubes- MWNT), graphene, fullerenes, and inorganic composites of copper, silver, or zinc.

[0269] EXAMPLE 27. Ethylene Propylene Diene Monomer (EPDM) Lumen Coating

[0270] In one embodiment, lumen coating experiments were initiated with ethylene propylene diene monomer (EPDM) rubber. While EPDM is elastic in nature, it is stable in petroleum ether and does not impact the underlying hollow fiber structure. It is stable towards steam and water at elevated temperatures. EPDM solutions commercially available as Trilene® 65 were used in the presence of various thermally initiated crosslinkers. The unfunctionalized hollow fiber structures were placed in a stainless steel module and were coated in situ with the coating solution. The module with 30 cm length, 0.012 m2inner surface area and 1 inch connections was equipped with 5 - 12 hollow fiber structures. The hollow fiber structures were epoxyed at the top and bottom to ensure that they are not mobile during the treatment. In our case, up to 5 cm from the top and bottom of the hollow fiber structures were epoxyed in the module. The effective length of the hollow fiber structure in the module varied between 20 - 23 cm. The coating solution (Trilene® 65 and crosslinkers) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess EPDM solution. Finally, the module was cured in the vacuum oven at temperatures varying between 90 - 160 °C. Two - three coating attempts were applied to ensure a lumen coating of homogeneous thickness. In the demonstrated embodiment, a coating solution of Trilene® 65 and dicumyl peroxide (DCP crosslinker) was used, to provide EPDM crosslinking to obtain a durable lumen layer.

[0271] The viscosity of the lumen coating solution was optimized to prevent the pressure drop during the coating process, restrict asymmetric pore penetration, and obtain a homogeneous coating. Preliminary lumen coating experiments were carried out by varying the EPDM and crosslinker concentration in petroleum ether as set out in Table 4 below. Since the crosslinkers initiated thermal crosslinking of EPDM, curing conditioning at 160 °C for 5 - 18 hours was required.

[0272] Preliminary results obtained by using dicumyl peroxide and tert-butylperoxybenzoate (Luperlox® P (Lup P)) as crosslinkers resulted in complete pore penetration and the solution leached out to the outer side of the hollow fiber. A high curing temperature significantly decreased the viscosity of the lumen coating solution and resulted in full pore penetration.

[0273] Table 4: Lumen coating composition for hollow fiber coating

[0274] Lauroyl peroxide (Lau) was chosen for crosslinking for further trials as the thermal treatment required milder conditions than the previously used analogues. The Lau-crosslinked coating also showed a better coating, without solution leaching or pore penetration. A CO2 / N2 selectivity of 5.6 was obtained.

[0275] Scanning electron microscope (SEM) images of the EPDM coated hollow fiber structures are shown in Figure 4 and demonstrate the proof-of-concept of in-module lumen coating of the hollow fiber structure bundle. Lumen coating of varying thicknesses were obtained. In certain examples, the lumen coating had thickness varying between 10 - 500 pm. The hollow fiber structure lumen was coated multiple times to increase the lumen thickness.

[0276] In another embodiment, polymeric coatings comprising single systems i.e. devoid of crosslinker were also evaluated. Polymers with low water vapour permeability (< 1000 Barrer) and soluble in n-hexanes, toluene, xylenes, or petroleum ether were coated in a module. Lumen coatings of polychloroprene, polystyrene, styrene butadiene rubber, and polydimethylsiloxane (PDMS) were applied in the hollow fiber module consisting of 1 - 2 unfunctionalized HFs. Multiple lumen layer coatings were applied as per the requirements to increase the thickness of the lumen layer.

[0277] EXAMPLE 28. Polydimethylsiloxane (PDMS) Lumen Coating

[0278] In another embodiment, PDMS was used as a lumen coating for the hollow fiber structures. PDMS is widely used to heal the surface defects on the lumen side of the hollow fiber structures. Commercially available Sylgard® 184 (referred to as Sylgard) from Dow Chemicals was used as the PDMS elastomeric material for the coating applications. The solubility of PDMS in n-hexanes makes it feasible to be used as a coating material as hexanes would not affect the chemical and mechanical integrity of the hollow fiber structure. Sylgard solutions of concentrations varying between 5 - 60 wt% loading in hexanes were obtained with constant stirring at room temperature for 30 mins - 24 hours. Homogeneous solutions were obtained in all cases. The viscosities of the PDMS / hexanes solutions varied between 4 - 30 mPa.s. The PDMS solutions were prepared by mixing the Sylgard PDMS along with the hydrosilane crosslinker present in the Sylgard® 184 elastomeric kit. The ratio of PDMS and the crosslinker was maintained at 10:1 wt / wt% in all the PDMS / hexanes solutions.

[0279] PDMS solutions with 50 - 60 wt% PDMS content in hexanes were deemed to be highly suitable for coating the hollow fiber structures because of their suitable viscosities with acceptable pressure drop. The unfunctionalized hollow fiber structures were placed in a stainless steel or clear plastic tube module and were coated in situ with the coating solution. The module with 30 cm length, 0.012 m2inner surface area and 1 inch connections was equipped with 1 - 14 hollow fiber structures. The hollow fiber structures were epoxyed at the top and bottom to ensure that they are not mobile during the treatment. In our case, up to 5 cm from the top and bottom of the hollow fiber structures were epoxyed in the module. The effective length of the hollow fiber structure in the module varied between 20 - 23 cm. The coating solution (Sylgard® 184 and crosslinkers in hexanes) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess PDMS solution. Finally, the module was cured in the vacuum oven at temperatures varying between 40 - 90 °C with a constant N2 sweep gas flow. Two - three coating attempts were applied to ensure a lumen coating of homogeneous thickness.

[0280] In another embodiment, amine-functionalized hollow fiber structures were also coated with PDMS solution. The TETA- and polyethyleneimine-functionalized hollow fiber structures were constructed into the hollow fiber module containing 1 - 14 hollow fiber structures. A similar hollow fiber module creation process was used as described above. Then the coating solution (Sylgard® 184 and crosslinkers in hexanes) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess PDMS solution. Finally, the module was cured in the vacuum oven at temperatures varying between 40 - 90 °C with a constant N2 sweep gas flow. Two - three coating attempts were applied to ensure a lumen coating of homogeneous thickness.

[0281] The integrity of the PDMS coatings were qualitatively investigated through gas permeation tests. The PDMS coated hollow fiber structures in the clear plastic modules were injected with water on the shell side by using a syringe. The shell was completely filled with water and taped to prevent flow of water through the pin hole created by the syringe. Nitrogen gas was passed through the lumen side of the hollow fiber with a pressure varying between 1 - 5 bar. The number of bubbles created on the shell surface of the fibers were visually investigated for qualitative screening of the PDMS coating. The PDMS coated hollow fibers resulted in significantly less bubbles as compared to the uncoated hollow fibers. This could be attributed to the presence of the PDMS lumen layer which significantly impedes the permeation of the nitrogen gas through the layer.

[0282] EXAMPLE 29. Ethylene Propylene Diene Monomer (EPDM) Lumen Coating with Silver Nanoparticles

[0283] In another one embodiment, EPDM was used as a lumen coating for the hollow fiber structures. EPDM solutions commercially available as Trilene® 65 were used in one embodiment of the invention in the presence of Lauryl peroxide (Lau) as the thermally initiated crosslinker. EPDM with the crosslinker was charged with silver (Ag) nanoparticles with a composition of 20 / 3 / 1 wt / wt% EPDM / Lau / Ag nanoparticles balanced with petroleum ether used as a solvent. This solution mixture was used as the composite lumen coating solution.

[0284] The TETA-functionalized polyetherimide hollow fiber structures were placed in a stainless steel module and were coated in situ with the composite coating solution containing Ag nanoparticles. The module with 30 cm length, 0.012 m2inner surface area and 1 inch connections was equipped with 5 hollow fiber structures. The hollow fiber structures were epoxyed at the top and bottom to ensure that they are not mobile during the treatment. In our case, up to 5 cm from the top and bottom of the hollow fiber structures were epoxyed in the module. The effective length of the hollow fiber structure in the module varied between 20 cm. The coating solution (Trilene® 65, Lau, Ag nanoparticles dispersed in petroleum ether) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess composite coating solution. Finally, the module was cured in the vacuum oven at temperatures varying between 100 °C. Two coating attempts were applied to ensure a lumen coating of homogeneous thickness. This demonstrated the preparation of hollow fiber structures with the composite lumen coating solutions.

[0285] EXAMPLE 30. Ethylene Propylene Diene Monomer (EPDM) Lumen Coating with Exfoliated Clay Particles

[0286] In another embodiment, EPDM was used as a lumen coating for the hollow fiber structures. EPDM solutions commercially available as Trilene® 65 were used in one embodiment of the invention in the presence of Lauryl peroxide (Lau) as the thermally initiated crosslinker. EPDM with the crossliner was charged with exfoliated hectorite (a type of smectite clay) with a composition of 20 / 3 / 1 wt / wt% EPDM / Lau / hectorite clay particles balanced with petroleum ether used as a solvent. This solution mixture was used as the composite lumen coating solution.

[0287] The aminosilane-functionalized y-alumina-containing polyethersulfone (PES) hollow fiber structures were placed in a stainless steel module and were coated in situ with the composite coating solution containing hectorite. The module with 30 cm length, 0.012 m2inner surface area and 1 inch connections was equipped with 5 hollow fiber structures. The hollow fiber structures were epoxyed at the top and bottom to ensure that they are not mobile during the treatment. In our case, up to 5 cm from the top and bottom of the hollow fiber structures were epoxyed in the module. The effective length of the hollow fiber structure in the module varied between 20 cm. The coating solution (Trilene® 65, Lau, hectorite clay dispersed in petroleum ether) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess composite coating solution. Finally, the module was cured in the vacuum oven at temperatures varying between room temperature - 100 °C. Two coating passes were applied to ensure a lumen coating of homogeneous thickness. This demonstrated the preparation of hollow fiber structures with the composite lumen coating solutions.

[0288] Carbon dioxide adsorption / desorption studies

[0289] The amine-functionalized hollow fibers were further utilized as sorbent materials for carbon dioxide capture from the ambient air. The amine-functionalized hollow fibers are suitable for selective capture or removal of carbon dioxide from a gas stream. Since these hollow fibers have high gravimetric surface area and pore sizes in the range of 5 - 100 nm (in certain examples, in the range of 5 to 25 nm), they are suitable for selective chemisorption of carbon dioxide molecules. The carbon dioxide capture performances of the hollow fibers were studied in a tubular reactor built in-house. The reactor (0.5 x 0.035 x 11.8 in x in x in) was designed to hold a maximum of 20 hollow fiber structures for the adsorption and desorption studies. The hollow fibers were of a length of 30 cm and were potted with thermally cured epoxy prior to placement in the reactor. The resulting hollow fibers were pre-dried in the vacuum oven at 70 °C overnight to remove any pre-adsorbed carbon dioxide and moisture.

[0290] During adsorption, the feed stream is passed through the reactor column at a rate of 1 L / min and pressure 1 bar. The feed stream is either a mixture of CO2 / N2 gases (with concentration ranging from 0 - 100% CO2 in N2, usually 400 ppm) or an air stream generated by an air compressor. The humidity of the gas stream is controlled by passing the feed stream through a water humidifier while the humidities varied between 0 - 90% RH. After a certain duration the hollow fiber reactor bed got saturated i.e. breakthrough of the gas stream and that denoted the completion of the adsorption cycle. The adsorption cycle was between 0.5 - 3.0 hours while the typical adsorption duration was approximately around 2.5 hours.

[0291] The captured carbon dioxide molecules in the hollow fibers were released during the desorption step where thermal energy was provided to facilitate desorption. Since exposure of the amine-functionalized sorbent to air at elevated temperatures may be detrimental to the amines, the reactor was placed under vacuum swing conditions before heating the reactor. While the vacuum pressure inside the reactor varied between 20 - 200 mbar, typically 50 - 100 mbar vacuum pressure was used. In one embodiment of this invention, temperature vacuum swing assisted desorption was used to undertake desorption. Here, the hollow fiber reactor was heated using a heating and cooling jacket. The desorption temperature was chosen between 50 - 110 °C with an optimum temperature around 95 °C. A flush gas of N2 stream was used to enhance the desorption kinetics. The N2 flow rate of 0.1 - 1.0 may be used, while 0.1 - 0.2 L / min was ideally used. The desorption was carried out for 1 - 12 hours but ideally for 2 hours. EXAMPLE 31. Temperature vacuum swing assisted CO2 desorption of hollow fiber structures

[0292] In this exemplary embodiment the aminated and coated hollow fiber structures were constructed in a reactor module followed by CO2 adsorption and temperature vacuum swing assisted desorption. In this example, fifteen 30 cm long polyetherimide (Ultern) hollow fibers were exposed to amination conditions. The hollow fibers were aminated with triethylenetetramine (TETA). The 30 cm hollow fibers were placed in a stainless steel cylindrical reactor which had 2 outlets for the fluids to flow. An amination bath (150 mL) containing 10 wt% TETA in isopropanol (I PA) was prepared at room temperature with constant stirring. The amine solution was circulated through the stainless steel reactor containing the 30 cm long fibers. The reactor was placed in a heating jacket at 70 °C and the amine solution in the round bottom flask was placed in a pre-heated oil bath at 70 °C. Since the amination was performed at 70 °C, it was essential to minimize the heat loss. The amine solution from the round bottom flask was circulated through the cylindrical reaction by using a peristaltic pump. The recirculation was carried out for 1 hour at 70 °C. After 1 hour, the circulation of the amine solution was stopped and the hollow fibers were removed from the stainless steel reactor and washed 3 times each with water, isopropanol, and hexanes. Following the rinsing step, the fibers were air dried with a stream of nitrogen flowing at a rate of 0.2 LPM for 3 hours. Finally, the fifteen hollow fibers were dried in the vacuum oven at 70 °C for 12 hours.

[0293] The TETA-functionalized hollow fiber structures were placed in a clear plastic tube module and were coated in situ with the PDMS. The module with 30 cm length, 0.012 m2inner surface area and 1 inch connections was equipped with ten 30 cm hollow fibers. The hollow fiber structures were epoxyed at the top and bottom to ensure that they are not mobile during the treatment. In our case, up to 5 cm from the top and bottom of the hollow fiber structures were epoxyed in the module. The effective length of the hollow fiber structure in the module varied between 20 - 23 cm. The coating solution (Sylgard® 184 and crosslinkers in hexanes) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess PDMS solution. Finally, the module was cured in the vacuum oven at temperatures varying between 40 - 90 °C with a constant N2 sweep gas flow. Two coating attempts were applied to ensure a lumen coating of homogeneous thickness. The hollow fiber module containing TETA-functionalized fibers with PDMS lumen coating was next exposed to CO2 adsorption - desorption conditions.

[0294] The resulting hollow fibers module was pre-dried in the vacuum oven at 70 °C overnight to remove any pre-adsorbed carbon dioxide and moisture.

[0295] During adsorption, the feed stream of air was passed through the reactor column at a rate of 1 L / min and pressure 1 bar. The feed stream of ambient air typically had a CO2 concentration of 400 ppm was flushed through the shell side of the hollow fiber in the reactor by using an air compressor. The humidity of the air stream varied between 30 - 50% RH during the course of adsorption at room temperature conditions. Adsorption was stopped after 2 hours of saturation.

[0296] The captured carbon dioxide molecules in the hollow fibers were released during the desorption step where thermal energy was provided to facilitate desorption. The hollow fiber module was exposed to vacuum conditions to remove air before heating the fibers to minimize oxidative degradation of the aminated hollow fibers. A vacuum pressure of 50 mbar was used. After the vacuum conditions, the hollow fiber module was heated using a heating coil at 95 °C with a sweep of inert N2 purge gas flowing at a rate of 0.2 LPM. The desorbed CO2 was passed through the CO2 sensor and a flow meter. The desorption was carried for 2 hours and the total amount of collected CO2 was calculated. The difference between the adsorbed CO2 and desorbed CO2 provided the CO2 working capacity (CO2_cap). A CO2_cap of 0.12 mol / kg was observed.

[0297] In another embodiment of this invention, the hollow fiber reactor was connected to distinct air and water flow channels and steam-assisted desorption was carried out. Adsorption was achieved via the crossflow of the carbon dioxide stream on the outer shell side at temperatures varying between 20 - 50 °C, but ideally around 20 - 40 °C, and ideally at room temperature. The desorption was carried out by passing hot water through the lumens of the hollow fibers. After the completion of adsorption, hot water (T = 80 - 100 °C) was passed through the connectors attached to the inner lumen side of the hollow fiber while the reactor was placed under vacuum. As the hot water passed through the lumen of the hollow fibers, CO2 desorption was initiated. The steam permeable lumen coating allowed selective permeation of the steam generated from the hot water stream to pass through the porous tortuous shell matrix of the hollow fiber and escape out due to the driving force created by the low pressure on the shell side of the fiber. During this process, the steam resulted in localized decrease of the carbon dioxide partial pressure in the porous network which enhanced the desorption kinetics. To further enhance the driving force for CO2 desorption, an inert sweep gas may be passed through the shell side of the hollow fiber structure along with the applied vacuum. The temperature of the thermal fluid, composition of the thermal fluid i.e. water, PEG / water etc, thickness of the lumen layer, polymeric material used in the lumen coating were optimized to achieve the steam flow rate of up to 0.1 - 0.2 kg steam / kg sorbent. Following the desorption, the hollow fibers were cooled by passing cold water through the lumen of the hollow fibers. The hollow fibers module was cooled down to 25 - 35 °C before exposing them to iterative CO2 adsorption - desorption cycles.

[0298] EXAMPLE 32. Steam assisted CO2 desorption of hollow fiber structures

[0299] The TETA-functionalized hollow fiber structures were placed in a clear plastic tube module and were coated in situ with the EPDM. The module with 30 cm length, 0.012 m2 inner surface area and 1 inch connections was equipped with ten 30 cm hollow fibers. The hollow fiber structures were epoxyed at the top and bottom to ensure that they are not mobile during the treatment. In our case, up to 5 cm from the top and bottom of the hollow fiber structures were epoxyed in the module. The effective length of the hollow fiber structure in the module varied between 20 - 23 cm. The coating solution (EPDM and peroxide crosslinkers in hexanes) was passed against gravity through the hollow fiber structures module. Subsequently, the module was flipped upside down and the coating solution was passed from the other end of the module (again against gravity). Following this nitrogen gas was passed through the module to remove any excess EPDMsolution. Finally, the module was cured in the vacuum oven at temperatures varying between 40 - 90 °C with a constant N2 sweep gas flow. Two coating attempts were applied to ensure a lumen coating of homogeneous thickness, while the next coating was applied from the opposite end of the module. The hollow fiber module containing TETA-functionalized fibers with EPDMIumen coating was next exposed to CO2 adsorption - desorption conditions.

[0300] The resulting hollow fibers module was pre-dried in the vacuum oven at 70 °C overnight to remove any pre-adsorbed carbon dioxide and moisture.

[0301] During adsorption, the feed stream of air was passed through the reactor column at a rate of 1 L / min and pressure 1 bar. The feed stream of ambient air typically had a CO2 concentration of 400 ppm was flushed through the shell side of the hollow fiber in the reactor by using an air compressor. The humidity of the air stream varied between 30 - 50% RH during the course of adsorption at room temperature conditions. Adsorption was stopped after 2 hours of saturation.

[0302] The captured carbon dioxide molecules in the hollow fibers were released during the desorption step where thermal energy was provided to facilitate desorption. The hollow fiber module was exposed to steam-assisted vacuum conditions to enhance the CO2 desorption kinetics. At first the hollow fiber module was exposed to vacuum conditions followed by passing hot water at 90 °C through the lumen of the hollow fiber. A vacuum pressure of 50 mbar was applied while the water inside the lumen was at 90 °C. A localized steam was generated at a rate of 0.1 kg steam / kg hollow fiber. A sweep of inert N2 purge gas was flowed at a rate of 0.2 LPM on the shell side of the hollow fiber. The desorbed CO2 was passed through the CO2 sensor and a flow meter. The desorption was carried for 2 hours and the total amount of collected CO2 was calculated. The difference between the adsorbed CO2 and desorbed CO2 provided the CO2 working capacity (CO2_cap). A CO2_cap of 0.12 mol / kg was observed.

[0303] In another embodiment of the invention, the heat demand for the desorption step may be accounted for by integrating waste heat (e.g., cooling tower return streams, etc). Low grade heat sources may be integrated into the process to assist desorption. Heat sources at temperatures above 120 °C may be leveraged via a heat exchanger to obtain temperatures required for desorption, i.e. 80 - 110 °C. Process heat from industrial processes may act as a source of low grade heat. Process heat may be provided by other types of energy sources, such as, for example, fossil fuel, geothermal, nuclear, biomass, and other renewable energy sources. The term “process heat” as used herein refers to the lower temperature heat remaining after the higher temperature heat has been used to generate electricity. Moreover, “process heat” may be provided from the use of sources of energy to produce products other than power or electrical generation. For example, primary processing such as chemical processing, production of cement, steel or aluminum, production of energy products like coal to liquid energy products, refining, may use heat to drive the primary processing, and the unused heat remaining after the primary processing or created during the primary processing would be the process heat of such processing.

[0304] When low grade heat is available at lower temperatures (typically below 90 °C), then a heat pump may be utilized to attain the desorption temperature conditions. Such type of heat may be obtained from cooling towers at industrial processes. Low grade heat offered by dairy industries and breweries may be typically within the temperature range of 65 - 85 °C and may also be integrated into the process. Solar-heating for Industrial Processes (SHIP) offer heat sources ranging between 60 - 100 °C and may potentially offer a valuable solution to power carbon dioxide desorption in DAC processes. While SHIP integration might be intermittent as it depends on the weather patterns, it may be used to reduce the Operating Expenditure (OPEX) of the DAC process.

[0305] In another embodiment of the invention, a two-step desorption profile may be adopted. A thermal heating ramp of two isothermal steps may be chosen to selectively desorb water in the first step and carbon dioxide in the second step. A two-step desorption process may result in obtaining a higher purity of the carbon dioxide gas stream as compared to the single-step desorption process. Typically, the carbon dioxide output stream may be contaminated with water vapour during the desorption step in a single-step desorption process, which may necessitate separation in a gas-liquid separation vessel. Therefore, a two-step desorption process might eliminate or minimize the carbon dioxide contamination with water as well as bypass the separation vessel.

[0306] The carbon dioxide working capacity (CO2_cap) i.e. the difference between the amount of adsorbed carbon dioxide (CO2_ads) and the amount of desorbed carbon dioxide (CO2_des) was calculated for the different variants of the aminated hollow fiber structures. The CO2_cap varied between 0.05 - 0.35 mol / kg. The unfunctionalized HFs devoid of any amine functionalities demonstrated a CO2_cap ~ 0.005 mol / kg. Diligent amine functionalization by different types of amines, amine concentration, and reaction conditions resulted in drastically higher CO2_cap. An interdependence of the amine concentration, reaction temperature, type of amines, and reaction temperature on the CO2_cap was observed. The best optimized HF sorbent with highest CO2_cap of 0.35 mol / kg was obtained through the aminations. This demonstrates the successful synthesis of carbon dioxide capture active sorbents from the carrier material as compared to the untreated or unfunctionalized counterparts.

[0307] DISCUSSION

[0308] Solid-supported aminated materials, such as silica-supported amines, alumina-supported amines, activated carbon-supported amines, zeolite-supported amines can act as low temperature chemisorbants, with strong affinity towards CC>2-surface interactions. While the polymeric amine-based sorbents offer higher amine loading density and might yield higher CO2 capacities, they suffer from slow CO2 diffusion kinetics and extended cycle times. Small molecule amines offer better CO2 diffusion and reaction kinetics which improve the cycle duration. Inorganic porous support sorbents, acting as “fillers”, have the surface functionalities to covalently graft such small molecule amines onto their surface. The covalent bonding (or grafting) of small molecule amines to highly porous inorganic fillers offers high surface area filler materials with enhanced mass transfer kinetics within the tortuous pathways of the filler materials.

[0309] Inorganic fillers, such as activated carbon, silica, zeolites, alumina, and MOFs, were screened and were compared on the basis of ease of amination, hydrothermal stability under steam at 100 °C conditions, tunable surface properties, and a secure supply chain network. Difficulty in tuning the amine loading, high water co-adsorption ability, and unreliable supply chain aspects of activated carbon, zeolites, and MOFs, respectively, present a challenge to use them as sorbents for bulk-scale applications. Hence, we have determined that silica and alumina are more feasible to be used as sorbents.

[0310] The surface chemistry of alumina can be harnessed to not only undertake amine impregnation, but also offer functionalities for covalent bonding of the amine-containing molecules (eg. aminosilanes). Additionally the manufacturing process of alumina can result in different types of alumina with tunable surface morphologies (such as the pore sizes, microscopic surface area, and porosity), particle size and geometry. The chemical treatment methods used for the synthesis of alumina results in tunable pore structures which is highly advantageous for sorption applications. Additionally, the high volumetric density of alumina as compared to polymeric sorbents results in higher sorption gravimetric capacities. The steam stability of alumina at elevated temperature makes it a robust support material for sorption and catalysis applications. The high commercial affordability of alumina makes it a suitable sorbent material for scaled up applications and hence, is highly desirable for our technology.

[0311] Advantageously, alumina also provides synthetic handles to alter the surface properties such as hydrophobicity and basicity via doping with metals and non-metals. Silicon doping on y- alumina may increase the surface hydrophobicity and hydrothermal stability of the corresponding y-alumina. Zirconium or titanium doping of y-alumina may enhance the thermal stability and water resistance at elevated temperatures. Y“alum'nadoping with magnesium, lanthanum may reduce the phase transformation from y- to a- phase which would otherwise impact the sorption and catalytic activity of y-alumina.

[0312] Accordingly, in certain embodiments of the present invention y-alumina may be used as the porous inorganic support material for functionalization with nucleophilic amines and aminosilanes.

[0313] In certain embodiments of the present invention, y-alumina may be doped with metals or non-metals such as silicon, zinc, magnesium, titanium, zirconium, or lanthanum, to provide for a more robust and durable y-alumina support for amine functionalization.

[0314] Particle size

[0315] The particle size control of alumina is controlled and tuned during the synthesis step. Different synthetic methodologies such as, calcination, sol-gel method, and precipitation method with varying the concentration of the templating agents affect the particle size as well as the surface and pore morphology of the alumina sample. The particle size may introduce mass transfer restriction on the CO2 interaction with the inorganic porous alumina material. Therefore, larger particle sizes may be detrimental to the diffusion and reaction kinetics of the incoming CO2 molecule. Additionally, larger particles may be detrimental to the HF dope composition as they may be plagued by sedimentation and result in an inhomogeneous dope mixture for the HF spinning. Larger particles in the HF matrix may also result in flaking or delamination during the operational phase of the HF. Larger particles may stick out of the shell of the HF and their delamination may create large voids or defects on the body of the HF which will affect the operational stability of the HF. Therefore, judicious choice of the particle sizes can be advantageous to the operation and performance of the HF sorbents.

[0316] Extremely small particles, although offering uniform dispersion feasibility within the HF matrix, are difficult to wet and, hence, require a large volume of solvents to obtain a stable suspension or dope mixture for HF spinning. Higher solvent loading in the dope mixture results in lower filler / alumina loading in the dope mixture and consequently the HF. Lower alumina loading reduces the active sorbent in the HF and hence, reduces CO2 capacity. Smaller filler particles may tend to form agglomerates and induce bulk particle sedimentation in the dope mixture which may consequently lead to inhomogeneous alumina particle distribution on the HF matrix. The agglomerated particles may impose significant mass transfer limitations as the effective particle diameter increases upon agglomeration. Hence, extremely small particles may preferably be avoided in the HF spinning process. This suggests that there may be an optimal particle size distribution to enhance the performance of the filler material through enhancing the mass transfer and diffusion kinetics as well as the filler loading in the HF.

[0317] Accordingly, in certain embodiments of the present invention, the filler particle size distribution is selected to be between 1 nanometers and 100 micrometers, or specifically between 10 nanometers to 100 micrometers, or more than 90% of the particles have particle size ranging between 40 nanometers to 100 micrometers.

[0318] Filler and hollow fiber pore size

[0319] The mass transfer inside the pores of the fillers also plays a key role in governing the CO2 diffusion within the pores, which influences the amine sites accessibility of the CO2 molecules. Extremely small pores of the filler material may inhibit diffusion of CO2 molecules and reduce the probabilities of CO2 interaction with the amines located inside the pores of the filler. Smaller pores could also get clogged during the amine functionalization of the porous filler material and pore blockage minimizes the active surface area accessible to CO2. On the contrary, extremely large pores may deliver unwanted voids on the filler material as larger pores reduce the surface area of the material. Large pores may reduce the effective surface area available for CO2 capture and hence, result in decrease of the CO2 capacity of the sorbent.

[0320] Accordingly, in certain embodiments of the present invention, the pore size range of the fillers may vary between 1 - 250 nm, or specifically between 1 - 200 nm, or below 150 nm.

[0321] In certain embodiments of the present invention, the microscopic BET surface area (Brunauer-Emmett-Teller method) of the filler sorbent may range between 10 - 1000 m2 / g, or specifically between 10 - 250 m2 / g, or below 200 m2 / g.

[0322] The pore size of the HFs may also affect the CO2 diffusion through the HF matrix as well as the fillers. In order to minimize the CO2 mass transfer limitation, the fillers may be readily accessible to the CO2 molecules i.e. minimal mass transfer resistance if offered by the HF matrix. Hence extremely small pores in the HF matrix may result in Knudsen diffusion of CO2 molecules and large pores may cause loss in active surface area for the high sorbent capacity.

[0323] Accordingly, in certain embodiments of the present invention, the pore size distribution of the HF ranges between 2 - 5000 nm, or specifically between 10 - 2000 nm or specifically 90% of the pores may vary between 50 - 5000 nm or above 5 micrometers.

[0324] HF wall thickness

[0325] The hollow fiber wall thickness may govern the volumetric capacity of the sorbent. Thicker HF walls may result in incorporation of larger quantities of active sorbents in a given volume. Typically, HFs with thinner walls are used for industrial applications to enhance the surface area-to-volume ratio. Whereas, in this present invention, the microscopic surface area of the fillers may contribute significantly to the surface area of the mixed matrix hollow fiber structures. The HFs may have larger pores with well defined porosity while the filler particles have ideal pore sizes that have pronounced effect on the surface area and the volumetric surface area of the sorbent material. Hence, thicker HFs may have higher filler loading with interconnected pore structure and may result in significantly higher volumetric CO2 capacity.

[0326] Addition of the inorganic porous fillers to the polymeric dope mixture may result in higher viscosity of the dope mixture which inherently may result in thicker HFs during the HF spinneret. Spinning mixed matrix hollow fiber structures with the same polymer content in the dope mixture may result in HFs with thicker walls as compared to their non-filler based analogs.

[0327] Accordingly, in certain embodiments of the present invention, inorganic filler materials such as, alumina, silica, MOFs may be used to spin thicker polyethersulfone mixed matrix hollow fiber structures suitable for CO2 capture applications.

Claims

1. CLAIMS1. A process for manufacturing a hollow fiber for capturing carbon dioxide, the process comprising: i) extruding a dope mixture through a spinneret to form a hollow fiber structure; and ii) coating an inside of a lumen of the hollow fiber structure with a semi-permeable layer, where the semi-permeable layer comprises a material that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

2. The process of claim 1 wherein the dope mixture includes at least one of polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole, and chloropolyphenyleneoxide.

3. The process of claim 1 wherein the dope mixture includes at least one filler, whereby the hollow fiber structure includes a filler.

4. The process of claim 3 wherein the at least one filler includes at least one filler selected from ion exchange resins, such as strongly basic anion exchange resins, aromatic cross-linked polystyrenic matrices including but not limited to polystyrene based ionexchange resins and amine functionalized resins, di- and multi-amines, polyethyleneimine, desiccants, carbon molecular sieves, carbon adsorbents, graphites, alumina-based fillers, silica-based fillers, zirconium-based fillers, magnesium-based fillers, titanium-based fillers activated alumina, molecular sieves, aluminophosphates, silicoaluminophosphates, zeolite adsorbents, ion exchanged zeolites, hydrophilic zeolites, hydrophobic zeolites, modified zeolites, natural zeolites, faujasites, mordenites, metal-exchanged silico-aluminophosphates, zeolites, activated carbon, alumina, uni-polar resins, bi-polar resins, aromatic cross-linked polystyrenic matrices, brominated aromatic matrices, methacrylic ester copolymers, graphitic adsorbents, carbon fibers, carbon nanotubes, nano-materials, metal salt adsorbents, perchlorates, oxalates, alkaline earth metal particles, metal oxides, chemisorbents, amines, organo-metallic reactants, hydrotalcites, silicalites, zeolitic imidazolate frameworks, covalent organic frameworks (COFs) and metal organic frameworks (MOFs) adsorbent compounds, and combinations thereof.

5. The process of claim 4 wherein the filler is at least one of a metal organic framework, a zeolite, an ion-exchange resin, alumina, silica, an alumina-based filler or silica-based filler.

6. The process of any one of claims 3 to 5 wherein the dope mixture includes at least one of polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), and polytetrafluoroethylene (PTFE).

7. The process of any preceding claim further comprising functionalizing the hollow fiber structure with a nucleophilic group or an aminosilane.

8. The process of any one of claims 3 to 7 further comprising functionalizing the at least one filler with a nucleophilic group or crosslinker or an aminosilane group and adding the functionalized filler to the dope mixture to form the hollow fiber structure.

9. The process of any preceding claim further comprising passing the hollow fiber structure through a coagulation bath and at least one rinse bath, where the at least one rinse bath includes a solution including a nucleophilic group, optionally an amine group.

10. The process of any one of claims 1 to 8 further comprising passing the hollow fiber structure through a coagulation bath and at least one rinse bath, where the at least one rinse bath includes an amine solution including an aminosilane.

11. The process of any one of claims 7 to 9 where the nucleophilic group is an amine group.

12. A process as claimed in claim 11 wherein the amine group or the amine solution includes a small molecule amine or a polymeric amine, or a combination thereof.

13. A process as claimed in claim 12 wherein the amine group or amine solution includes at least one of ethylenediamine, 1,3-propylenediamine, meta-xylylenediamine, para- xylylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, aminosilanes, and mono-, di-, tri-, tetra- and poly- amino functionalized amino- alkoxysilanes aminosilanes.

14. A process as claimed in claim 12 wherein the amine group includes at least one of linear polyethyleneimine, branched polyethyleneimine, and polyallylamine.

15. A process as claimed in any preceding claim wherein the semi-permeable layer comprises a cross-linked ethylene propylene diene monomer rubber, a polychloroprene, a polystyrene, or a styrene-butadiene, a polypropylene, a polyvinylchloride, a polyimide, a polyetherimide, a polystyrene, a polysulfone, a natural rubber, an amorphous fluoropolymer resin, polyethylene, polypropylene, polytetrafluoroethylene, or copolymers, mixtures and combinations thereof, or a polydimethylsiloxane and combination thereof.

16. A process as claimed in any preceding claim wherein the step of coating the inside of the lumen to form a semi-permeable layer is repeated at least once to form a semi- permeable layer comprising multiple layers.

17. A process as claimed in claim 16 wherein the semi-permeable layer includes composite particles.

18. A process as claimed in claim 17 wherein the composite particles include at least one of aluminosilicates, flake-like materials, polymeric particles, or nanoparticles, optionally metallic nanoparticles.

19. A process as claimed in any one of claims 16 to 18, where the multiple layers include single or multiple polymer coating formulations.

20. A process as claimed in claim 1 where the dope mixture is a first dope mixture is extruded through an outer annular channel of a triple orifice spinneret and further comprising extruding a second dope mixture through an inner annular channel of the triple orifice spinneret; optionally wherein the second dope mixture does not contain any filler.

21. A hollow fiber for capturing carbon dioxide, the fiber comprising:(a) a hollow fiber structure capable of carbon dioxide capture; and(b) a semi-permeable layer coating an inside of a lumen disposed within the hollow fiber structure, where the semi-permeable layer is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

22. The hollow fiber of claim 21 wherein the hollow fiber structure includes at least one of polyetherimide, polyvinylchloride (PVC), polyimides (Pls), poly(vinylbenzyl chloride), polybenzimidazole, and chloropolyphenyleneoxide.

23. The hollow fiber of claim 21 or claim 22 wherein the hollow fiber structure includes at least one filler, whereby the hollow fiber structure includes a filler.

24. The hollow fiber of claim 23 wherein the at least one filler includes at least one filler selected from ion exchange resins, di- and multi-amines, polyethyleneimine, desiccants, carbon molecular sieves, carbon adsorbents, graphites, activated alumina, molecular sieves, aluminophosphates, silicoaluminophosphates, zeolite adsorbents, ion exchanged zeolites, hydrophilic zeolites, hydrophobic zeolites, modified zeolites, natural zeolites, faujasites, mordenites, metal-exchanged silico-aluminophosphates, zeolites, activated carbon, alumina, y-alumina, uni-polar resins, bi-polar resins, aromatic cross-linked polystyrenic matrices, aromatic cross-linked polystyrenic matrices including but not limited to polystyrene based ion-exchange resins and amine functionalized resins, ion exchange resins, cation exchange resins, anion exchange resins, Lewatit, Purolite, brominated aromatic matrices, methacrylic ester copolymers, graphitic adsorbents, carbon fibers, carbon nanotubes, nano-materials, metal salt adsorbents, perchlorates, oxalates, alkaline earth metal particles, metal oxides, chemisorbents, amines, organo-metallic reactants, hydrotalcites, silicalites, zeolitic imidazolate frameworks, covalent organic frameworks (COFs) and metal organic frameworks (MOFs) adsorbent compounds, and combinations thereof.

25. The hollow fiber of claim 23 or claim 24 wherein the hollow fiber structure includes at least one of polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), and Polytetrafluoroethylene (PTFE).

26. The hollow fiber of any one of claims 23 to 25 wherein the filler is functionalized with a nucleophilic group.

27. The hollow fiber of any one of claims 21 to 26 wherein the hollow fiber structure includes a nucleophilic group, optionally an amine group or a group comprising cross-linked amines.

28. The hollow fiber of claim 26 or 27 wherein the nucleophilic group is an amine group, optionally wherein the hollow fiber structure includes an aminosilane group.

29. A fiber as claimed in claim 28 wherein the amine group includes at least one of ethylenediamine, 1,3-propylenediamine, meta-xylylenediamine, para-xylylenediamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, and polyallylamine.

30. The hollow fiber as claimed in any one of claims 21 to 29 wherein the semi- permeable layer includes at least one of polychloroprene, polystyrene, polydimethylsiloxane (PDMS), styrene butadiene rubber, crosslinked Ethylene Propylene Diene Monomer (EPDM), polypropylene, polyvinylchloride, polyimide, polyetherimide, polystyrene, polysulfone, natural rubber, amorphous fluoropolymer resins, polyethylene copolymers, polypropylene copolymers, polytetrafluoroethylene and copolymers, mixtures and combinations thereof.

31. A hollow fiber as claimed in any one of claims 21 to 30 wherein the semi-permeable layer has a water vapor permeability of less than 5000 Barrer, less than 4000 Barrer, less than 3000 Barrer, less than 1000 Barrer, less than 500 Barrer, or less than 400 Barrer, optionally from 100 to 300 Barrer.

32. A hollow fiber as claimed in any one of claims 20 to 30 wherein the semi-permeable layer is stable towards steam and water at a temperature of 45 - 110 °C or 70 - 110 °C or 90 -110 °C.

33. A hollow fiber as claimed in any one of claims 20 to 32 wherein the semi-permeable layer has a thickness between 5 - 500 micrometres.

34. A hollow fiber as claimed in any one of claims 20 to 33 wherein the semi-permeable layer contains solid composite particles or nanoparticles; optionally polymeric-composite particles or nanoparticles; further optionally having a concentration of 1 - 20 wt%.

35. A hollow fiber as claimed in claim 34 wherein the composite particles include at least one of aluminosilicates, flake-like materials, polymeric particles, or nanoparticles, optionally metallic nanoparticles.

36. A process for manufacturing a hollow fiber for capturing carbon dioxide, the process comprising: i) preparing a dope mixture including a filler and an inert polymer, where the filler includes at least one of alumina-based, silica-based, zirconium-based, magnesium- based, titanium-based or ion-exchange resin fillers, or any combination thereof; ii) functionalizing the filler with at least one of an aminosilane group or a nucleophilic group or a cross-linker; and iii) extruding the dope mixture through a spinneret to form a hollow fiber structure.

37. A process as claimed in claim 36 wherein the inert polymer is polyvinylidene difluoride (PVDF), polysulfone (PSU) or polyethersulfone (PES), preferably polyethersulfone.

38. A process as claimed in claim 36 or claim 36 wherein the filler is functionalized prior to preparing the dope mixture.

39. A process as claimed in claim 36 or claim 36 wherein the filler is functionalized after the dope mixture is extruded through the spinneret.

40. A process as claimed in any one of claims 36 to 39 wherein an aminosilane group is grafted onto the filler.

41. A process as claimed in any one of claims 36 to 40 wherein the nucleophilic group is bonded to the filler via covalent bonds, impregnation or impregnation crosslinking.

42. A process as claimed in any one of claims 36 to 41 , further comprising coating an inside of a lumen of the hollow fiber structure with a semi-permeable layer, where the semi- permeable layer comprises a material that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

43. A hollow fiber for capturing carbon dioxide, the fiber comprising:(a) a hollow fiber structure capable of carbon dioxide capture, where the hollow fiber structure includes an inert polymer and at least one of an ion-exchange resin, an alumina-based filler, silica-based filler, zirconium-based filler, magnesium-based filler and titanium-based filler functionalized with an aminosilane group, and(b) a semi-permeable layer coating an inside of a lumen disposed within the hollow fiber structure, where the semi-permeable layer is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat flow transfer medium.

44. A process as claimed in claim 41 or a hollow fiber as claimed in claim 42 wherein the semi-permeable layer includes composite particles.

45. A process or hollow fiber as claimed in claim 44 wherein the composite particles include at least one of aluminosilicates, flake-like materials, polymeric particles, or nanoparticles, optionally metallic nanoparticles.

46. A hollow fiber as claimed in any one of claims 43 to 45 wherein an inner diameter of the hollow fiber structure is within a range of 0.1 to 3.5 mm.

47. A hollow fiber as claimed in any one of claims 43 to 46 wherein a thickness of the hollow fiber is within a range of 0.2 to 3.0 mm.

47. A process as claimed in any one of claims 36 to 42 or claim 44, or a hollow fiber as claimed in any one of claims 43 to 47 wherein: i) the filler has a surface area of from 10 to 1000 m2 / g, by the Brunauer-Emmett-Teller method; and / or ii) the filler has a pore size range of 1 to 200 nm and / or iii) 90% or more of particles of the filler have a particle size in the range of 40 nm to 100 micrometer; and / or iv) the filler loading in the hollow fiber is at least 30 wt.% or 30-50 wt.% or 30-70 wt.%.

48. A process as claimed in in any one of claims 36 to 42, 44 or 48, or a hollow fiber as claimed in any one of claims 43 to 48 wherein the hollow fiber has pores wherein 90% or more of the pores have a pore size in the range of 50 to 2000 nm or above 5000 nm.

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