Maintenance of hollow fibers and hollow fiber reactors for carbon dioxide capture

Abstract

A method (1301) of maintaining hollow fibre bundles (201, 201B, Fig. 4) of a hollow fibre reactor (901, Fig. 4), each hollow fibre bundle comprising a plurality of functionalized hollow fibres (101, F

Description

Field of the Invention The present invention relates to hollow fibers for use in carbon dioxide capture, and more particularly to the maintenance of hollow fiber bundles used within a hollow fiber reactor. Background of the Invention Carbon capture technologies have been developed to address the need to capture and store fossil and process-related carbon dioxide (CO2), whether directly at industrial installations, before release into the atmosphere, or from the general atmosphere, into which carbon dioxide maybe released from a moving source such as a vehicle. A direct air carbon capture process typically involves the stages of atmospheric air being introduced, actively or passively, to a reactor, carbon dioxide being removed from the air through binding, for example through absorption into a liquid solvent or through adsorption onto a solid sorbent, and then carbon dioxide being released from the solvent or sorbent. The captured carbon dioxide can then be utilised in some way, for example, for synthetic fuel production or carbonation of beverages, or transported to a storage facility. Solvents or sorbents used in the carbon capture process may be reused or recycled. A carbon capture process may include an adsorption phase, during which a gas mixture containing carbon dioxide contacts a carbon dioxide affine sorbent material 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. Thereafter, in a second, desorption phase, the carbon dioxide enriched sorbent material may be heated, set under vacuum, subject to an electrical current, contacted with a humid steam, and / or a separate purge gas streamed along it, to remove the carbon dioxide therefrom. It may be appreciated that various other processes may be used to release carbon dioxide from the sorbent material. This separation may result in carbon dioxide being 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. The process may be repeated to perform a cyclic adsorption and desorption of carbon dioxide. Following multiple cycles of adsorption and desorption, oxidative degradation, for example, may reduce the number of available amine sites that may react with carbon dioxide. As a result, the sorbent material may decrease its capacity to capture carbon dioxide and require replacement or regeneration. Hollow fibers (HF) are used extensively in the field of fluid separation and purification; with different applications including gas separation, water purification, desalination of seawater, and extracorporeal blood treatment. Hollow fibers may be tubular, defining a lumen extending therethrough, through which a fluid can flow, and having an intricate porous surface. The efficacy of such hollow fibers may be governed by specific BET surface area, pore size distribution, and porosity. These surface parameters can be tuned to tailor hollow fibers for different applications. For example, the pore structure distribution can be used to classify hollow fibers into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis membranes. The bulk-scale production and manufacture of hollow fibers and modules, respectively, has led to the commercialization of this technology in several fields; however, hollow fiber research for the adsorption and desorption of carbon dioxide is in the nascent stage of development. US 81 33308 B2 discloses a cylindrical cross flow contactor that comprises a plurality of hollow fiber adsorbents, each including a polymer matrix, a sorbent material, a plurality of tortuous pathways, a lumen, and a barrier layer lining the lumen to prevent fluid communication between the lumen and the sorbent material. The fibers are fixed in a parallel array and the ends of the fibers may be potted or embedded in a binding material, which may be an epoxy or a resin. Several drawbacks are associated with the parallel array structuring of hollow fibers disclosed in US 8133308 B2, including high pressure drop and substantial downtime to remove the fixed hollow fibers for maintenance. It is desirable to provide a hollow fiber module for use in carbon capture, in particular in direct air capture, that provides efficiencies with regards to performance relative to carbon dioxide capture, reactor volume, and maintenance operations, among other advantages. Summary of the Invention According to a first aspect there is provided a method of maintaining hollow fiber bundles of a hollow fiber reactor, each of the hollow fiber bundles comprising a plurality of functionalized hollow fibers that are capable of carbon dioxide sorption, the method comprising: (i) detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar; (ii) 2 removing a hollow fiber bundle from the hollow fiber reactor; and (iii) replacing the hollow fiber bundle removed from the hollow fiber reactor at (ii). In a specific example, (iii) comprises substituting the hollow fiber bundle removed from the hollow fiber reactor at (ii). Thus, a hollow fiber bundle can be removed from the hollow fiber reactor, and a different hollow fiber bundle installed in the hollow fiber reactor in place of the removed hollow fiber bundle. The substitute hollow fiber bundle may be new. The substitute hollow fiber bundle may have been used previously, in the same ora different hollow fiber reactor, and may have been reconditioned. In a specific example, the method further comprises performing at least one maintenance action on the hollow fiber bundle removed from the hollow fiber reactor at (ii). After the at least one maintenance action has been performed on the hollow fiber bundle, the hollow fiber bundle may be returned to the hollow fiber reactor. The hollow fiber bundle may be returned after being previously substituted. In an example, the at least one maintenance action comprises a cleaning process for removing foreign matter from the hollow fibers. The cleaning process may comprise the use of pressurized air. In an example, the at least one maintenance action comprises a protecting process for protecting against an accumulation of material or organisms. The protecting process may comprise the use of one or more of: a biocide, an antiscalant. In an example, the at least one maintenance action includes an amine removal process for removing amines from the hollow fibers. The amine removal process may comprise subjecting the one or more hollow fiber bundles to an elevated temperature under vacuum. In an example, the at least one maintenance action includes an amine removal process for removing amines from the hollow fibers. The amine removal process may comprise subjecting the one or more hollow fiber bundles to continuous flow or flushing with water, aqueous solvents, or amine digesting reagents. The amine digesting reagents may include but not limited to water, methanol, ethanol, isopropanol, alcohols, water-methanol, water-ethanol, water-isopropanol, water-alcohol mixtures, and combinations thereof. In another embodiment, the amine removal process may include acid digestion processes which include but not limited to acidic pH aqueous solutions, acidic pH alcoholic-aqueous solutions. In another embodiment, the amine removal process may include basic digestion processes which include but not limited to basic pH aqueous solutions, basic pH alcoholic- aqueous solutions. In an example, the at least one maintenance action includes an amine removal process for removing amines from the hollow fibers by utilizing amine digesting reagents at temperatures varying between 25 - 70 degrees Celsius. In an example, the at least one maintenance action comprises a lumen coating process, the lumen coating process involving flowing a lumen coating through a lumen of each of the plurality of hollow fibers. In an example, the at least one maintenance action comprises a regeneration process, the regeneration process involving exposing the hollow fiber bundle to an amine solution for replenishing amine sites of the hollow fibers thereof. Exposing the hollow fiber bundle to an amine solution may involve flowing the amine solution through a lumen of each of the plurality of hollow fibers. In an example, at least one maintenance action comprises a regeneration process, the regeneration process involving exposing the oxidized or degraded amines on the hollow fibers to re-activation chemical treatment to rejuvenate the amines. In an example, the at least one maintenance action may include a reactivation process of chemical reduction of the degraded, oxidized, or decomposed amines on the hollow fibers with at least one or more of: hydrogen, metal hydrides, metal catalysts, aminosilane. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: determining that a predetermined duration of operation of a hollow fiber bundle of the hollow fiber reactor has expired. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: evaluating an amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles, and comparing the evaluated amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor with a predetermined threshold amount. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: measuring a pressure difference across one or more hollow fiber bundles of the hollow fiber reactor, and comparing the measured pressure difference to a predetermined threshold pressure difference. In an example, the hollow fiber reactor comprises: (i) a lumen side inlet for introducing a flow of a liquid heat transfer medium to the lumens of the hollow fiber bundles, and a lumen side outlet for removal of the liquid heat transfer medium; and (ii) a shell side inlet for introducing a flow of a gas containing carbon dioxide to contact the hollow fiber bundles, whereby the flow of gas containing carbon dioxide gas is at a non-zero, non-straight angle with respect to the flow of a liquid heat transfer medium, and a shell side outlet for removing the carbon dioxide depleted gas. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: measuring a pressure at the lumen side inlet of the hollow fiber reactor, and comparing the measured pressure to a predetermined threshold pressure. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: evaluating a consumption level of liquid heat transfer medium by the hollow fiber reactor, and comparing the measured consumption level to a predetermined threshold consumption level. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: measuring a permeance of a fluid flow across one or more hollow fiber bundles from of the lumen to shell side of hollow fibers in the hollow fiber bundle in the hollow fiber reactor, and comparing the measured permeance to a predetermined threshold permeance difference. In an example, the hollow fiber reactor is operational to: (a) expose the plurality of hollow fiber bundles to ambient air, for adsorption of carbon dioxide from the ambient air into at least one of the plurality of hollow fibers; (b) subsequently reduce exposure of the hollow fiber bundles to the ambient air; (c) introduce a first flow of a liquid heat transfer medium, at a first temperature, to the lumen of at least one of the plurality of hollow fibers, in which the liquid heat transfer medium is prevented from flowing from the lumen through the semi-permeable layer and wherein a vapor state of the heat transfer medium is allowed to pass from the lumen through the semi-permeable layer, the first temperature sufficient to elevate the temperature of the hollow fiber for desorbing adsorbed carbon dioxide therefrom; and (d) subsequently introduce a second flow of a liquid heat transfer medium, at a second temperature that is lower than said first temperature, to the lumen of said at least one of the plurality of hollow fibers, the second temperature sufficient to cool the hollow fiber. In an example, the second temperature is sufficient to cool the hollow fiber below 40 °C. In an example, the liquid heat transfer medium is liquid water, and the vapor state of the heat transfer medium is water vapor. The flow of water vapor may lower a carbon dioxide concentration in the hollow fiber. In an example, the liquid heat transfer medium is mixed with at least one of demineralized water, water dosed with a conditioning agent, a corrosion inhibitor, an anti-frost additive, a biocide treatment, a boiling point adjuster, silicone oil, propylene glycol, ethyl glycol, polyethylene glycol, a salt, m-Xylene, ethyl benzoate, o-Xylene, decamethyltetrasiloxane (MD2M), and undecane methanol, ethanol, t-butanol, 2-propanol, I -propanol, 2-butanol, t-amyl alcohol, i-butanol, I butanol, i-amyl alcohol, 2 ethylbutanol, 2-ethylhexanol, heptane, octane, cholorobenzene, p-cymene, and tetralin. In an example, the hollow fiber bundles comprise at least two hollow fiber bundles arranged in a V-shaped configuration. Particular and preferred aspects of the present invention are set out in the dependent claims. Brief Description of the Drawings The present invention will now be more particularly described, with reference to the accompanying drawings, in which: Figure I shows an example hollow fiber; Figure 2 is an exploded view of a hollow fiber bundle according to a first example; Figure 3 illustrates a V-shaped configuration of two hollow fiber bundles, each hollow fiber bundle according to the first example of Figure 2; Figure 4 shows a plurality of hollow fiber bundles according to the first example of Figure 2, arranged in a V-shaped configuration series according to a first specific example; Figure 5 illustrates a 3-dimensional shape created by the hollow fiber bundles of the V-shaped configuration series according to the first specific example of Figure 4; Figure 6 shows a plurality of hollow fiber bundles according to a second example and arranged in a V-shaped configuration series according to a second specific example; 6 Figure 7 illustrates a 3-dimensional shape created by the hollow fiber bundles of the V-shaped configuration series according to the second specific example of Figure 6; Figure 8 shows a hollow fiber bundle according to the first example of Figure 2; Figure 9 shows a schematic of an example hollow fiber reactor provided with a hollow fiber module that comprises a plurality of hollow fiber bundles; Figure 10 illustrates an adsorption phase; Figure I I illustrates a desorption phase; and Figure I 2 illustrates a cooling phase; and Figure 13 show steps in a method of treating hollow fibers for carbon dioxide capture. Description 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. 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. 7 As used herein, a “hollow fiber bundle” refers to a plurality of hollow fibers arranged in a unitary structure. As used herein, a “hollow fiber module” refers to a plurality of hollow fiber bundles arranged in a configuration. 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. As used herein, a “filler” may refer to a non-polymeric 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., Dowex™ Marathon™ A, a resin availanic frameworks, 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-aluminophosphatable from Dow Chemical Company, etc.), zeolite, activated carbon, alumina, metal-orge, 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, ETS, CTS, metal oxide, chemisorbent, amine, organo-metallic reactant, hydrotalcite, silicalite, zeolitic imadazolate framework, covalent organic framework (COF) and metal organic framework (MOF) adsorbent compounds, and combinations thereof. As used herein, “mixed matrix hollow fibers” refer to the fibers 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. As used herein, “liquid heat transfer medium” may comprise water or any suitable liquid that takes part in heat transfer by serving as an intermediary in cooling one side of a process, transporting and storing thermal energy, and heating on another side of a process. For example, demineralized water, water dosed with a conditioning agent, which may be or comprise a corrosion inhibitor, an anti-frost 8 additive, a biocide treatment, a boiling point adjuster, for example silicone oil, propylene glycol, ethyl glycol, 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, I -propanol, 2-butanol, t-amyl alcohol, i-butanol, I butanol, i-amyl alcohol, 2 ethylbutanol, 2-ethylhexanol, other alcohol, mixtures thereof, and mixtures thereof with water. Hydrocarbons that may be suitable include but are not limited to heptane, octane, cholorobenzene, p-cymene, and tetralin. As used herein, a “coated hollow fiber” refers to a hollow fiber where an inner surface of the hollow fiber structure adjacent to the lumen has a semi-permeable layer that is impermeable to a liquid heat transfer medium but permeable to a vapor state of the heat transfer medium. 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. As used herein, an “unfunctionalized hollow fiber” refers to a hollow fiber as prepared after spinning, which does not have additional functional or reactive groups apart from those present in the polymer skeleton, on either the lumen side or the shell side of the hollow fiber. As used herein, a “functionalized hollow fiber” refers to a hollow fiber as obtained after reaction with nucleophilic groups, such as amines. As used herein, the term "ambient air" is defined herein as air at pressure, temperature, and carbon dioxide presence conditions that the hollow fiber reactor of the present disclosure is exposed to when outside. Ambient air pressure conditions typically include pressures in the range from 0.8 to I. I 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. As used herein, “rectangular” includes square. An example hollow fiber 101 is shown in Figure I. The hollow fiber 101 comprises a structure for capture of carbon dioxide sorption, indicated at 102, and a lumen, indicated at 103, extending axially 9 therethrough. A lumen side 104 and a shell side 105 of the hollow fiber 101 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. 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), polybenzylchloride, polybenzimidazole, and polyphenyleneoxide. In some embodiments, the structure for capture of carbon dioxide sorption may include a polymer and one or more fillers, for example, metal-organic frameworks (MOFs), zeolites, ion-exchange resins, activated carbon, 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 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 may include but not be limited to polypropylene (PP), polybenzimidazole (PBI), polyvinylenedifluoride (PVDF), polysulfone (PSU), polyethersulfone (PES), polyphenyleneoxide (PPO), or any other suitable polymer may be used. Nucleophilic groups that may be suitable for functionalization of the polymer matrix and / or the fillers include without limitation amines, amide salts, alcohols, alkoxides, thiols, and metal alkyls. 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 / 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 / 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), any other suitable small molecule amine group, or combinations thereof. Polymeric amine groups may include branched polyethyleneimine, polyallylamine, any other suitable polymeric groups, or combinations thereof. Furthermore, in some embodiments, hollow fibers may be coated, such that an inner surface adjacent to the lumen of the hollow fiber has a barrier layer. In one example, the barrier layer may be a semi-permeable 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). Suitable materials include non-polar 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, tert-butylperoxybenzoate, lauroyl peroxide, radical initiators or combinations thereof), polychloroprene, polystyrene, and styrene-butadiene. Furthermore, in some examples, the lumen coating may be a biphasic polymeric coating containing composite particles (organic, inorganic, polymeric). 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 100-3000 Barren (I Barrer = 3.348 x 10-16 mol.m / (m2.s.Pa)). A semi-permeable layer having a thickness of between 10 -500 micrometers has been determined to be particularly suitable in the processes of the present invention. An exploded view of a hollow fiber bundle 201, according to a first example, is shown in Figure 2. The hollow fiber bundle 201 includes a plurality of hollow fibers, such as hollow fibers 202, 203, 204, that are capable of carbon dioxide sorption. The hollow fibers in the bundle may be arranged into an array. According to the array shown in this Figure, the hollow fibers are arranged in a series of rows and columns that are staggered; however, it is to be appreciated that the hollow fibers may be arranged in any suitable arrangement. As shown in this Figure, the hollow fiber bundle 201 is generally rectangular in shape, having a length in a length direction L between a pair of opposed first and second sides 205, 206, a depth in a depth direction D between a pair of opposed first and second ends 207, 208 and a width in a width direction W between a pair of opposed third and fourth sides 209, 210. It is to be understood however that the hollow fiber bundle may have any suitable alternative shape and / or relative dimensions. As indicated in this Figure, the hollow fiber bundle 201 can receive a flow 211 of a first fluid, such as a liquid heat transfer medium, therethrough, flowing through the lumens of the hollow fibers, and a flow 212 of a second fluid, such as a gas containing carbon dioxide, flowing between the hollow fibers and across the flow 211 of a first fluid. For example, the flow 211 of a first fluid may be introduced to the hollow fiber bundle 201 from a lumen inlet side, indicated at 21 3, at one end 205 thereof, from which the flow 21 I is directed to first ends of the lumens of the hollow fibers, and to a lumen outlet side, indicated at 214, at the opposed end 206 thereof, to which the flow 21 I is directed from the second ends of the lumens of the hollow fibers, the first fluid flowing through the hollow fiber bundle 201, along the lumen sides of the hollow fibers, generally in the depth direction D, and the flow 212 of a second fluid may come into contact with the hollow fiber bundle 201 from one side 209 thereof, and may pass through the hollow fiber bundle 201 to the opposed side 210 thereof, the second fluid flowing through the hollow fiber bundle 201, across the shell sides of the hollow fibers, generally in the width direction W. A lumen side inlet 215 and a lumen side outlet 216 are indicated in this Figure, Any suitable number and type of fluid inlet / outlet may be used at any suitable location or locations. Any suitable type of flow guiding arrangement, for example comprising one or more manifolds, baffles and / or channels, may be used to direct, restrain and / or regulate the flow of a fluid through the hollow fiber bundle. Hollow fiber bundle 201 is shown in Figure 3 arranged with a second, like hollow fiber bundle I02B in a V-shaped configuration 300, according to a first example, in which first ends 205, 205 respectively of the two bundles 201,201 B are adjacent, with the second and the first sides 210, 209B respectively of the two bundles 201,201 B forming an internal angle 300. Thus, the second and the first sides 210, 209B respectively of the two bundles 201,201B face inwardly towards each other, with the respective first and second sides 209, 210B of the two bundles 201, 20IB facing outwardly of each other. According to the illustrated example V-shaped configuration 300, the internal angle 300 between the inwardly facing sides 210, 209B of the respective hollow fiber bundles 102, 102B is acute. A plan view of a plurality of hollow fiber bundles according to the first example of Figure I and comprising bundles arranged in a V-shaped configuration series 400, according to a first specific example, is shown in Figure 4. The V-shaped configuration series 400 comprises the V-shaped configuration 300 of the arrangement of the hollow fiber bundle 201 and the second, like hollow fiber bundle 20IB shown in Figure 3. According to this first example, a cover element 401 is arranged to extend across the adjacent ends 205, 205B of the first and second hollow fiber bundles 201,201 B of the V-shaped configuration 300. With reference to Figure 2 and the accompanying description, the cover element 401 functions to prevent the passage of a flow 212 of a second fluid, such as a gas containing carbon dioxide, between the adjacent ends 205, 205B of the first and second hollow fiber bundles 210, 201 B and to direct the second fluid to instead flow across the shell side of the hollow fibers of the hollow fiber bundles 201, 20IB, whereby carbon dioxide may be adsorbed by the hollow fibers (as described in detail below). The cover element 401 may have any suitable dimensions and may comprise any suitable material or combination of materials. For example, the cover element may comprise a plastic material and / or a metal. The V-shaped configuration series 400 further comprises third and fourth hollow fiber bundles 201C, 20 ID arranged in a second, like V-shaped configuration 300B, and fifth and sixth hollow fiber bundles 201 E, 201 F arranged in a third, like V-shaped configuration 300C. According to this first example, the magnitude of the internal angle 30 IB, 30 IC of each of the second and third V-shaped configurations 300B is substantially the same as that of the internal angle 301 of V-shaped configuration 300. In this example also, the adjacent ends 205C, 205D of the second V-shaped configuration 300B and the adjacent ends 205E, 205F of the third V-shaped configuration 300B are provided with a respective cover element 401 B, 401C like cover element 401 closing off any gap between the adjacent ends 205, 205B of the V-shaped configuration 300. As shown, the second V-shaped configuration 300B is located adjacent the V-shaped configuration 300, with the second end 206C of the third hollow fiber bundle 201C adjacent the second end 206B of the second hollow fiber bundle 201B. An internal angle 301 D between the second and third hollow fiber bundles 201 B, 201C is formed, which in this example has substantially the same magnitude as the internal angle 301 of V-shaped configuration 300. In addition, in this example, a cover element 401 D is provided to block off any gap between the adjacent ends 206B, 206C of the second and third hollow fiber bundles 201B, 201C to fluid flow. As also shown, the third V-shaped configuration 300C is located adjacent to the second V-shaped configuration 300B, with the second end 206E of the fifth hollow fiber bundle 201 E adjacent the second 13 end 206D of the fourth hollow fiber bundle 20ID. An internal angle 30IE is formed between the fourth and fifth hollow fiber bundles 20ID, 20IE. In this example, the internal angle 40IE has substantially the same magnitude as that of the internal angle 301 of V-shaped configuration 300. Further, according to this example, a cover element 401 E is provided across the adjacent ends 206D, 206E of the second and third hollow fiber bundles 20IB, 20IC to prevent the passage of a fluid therebetween. It is important to understand that the hollow fiber bundles are independent components. Thus, each hollow fiber bundle may be provided with its own individual fluid inflow / outflow arrangement. In addition, each hollow fiber bundle may be removable from a hollow fiber module separately from each other hollow fiber bundle. Hence, hollow fiber bundles may be arranged in a series according to any suitable configuration, whether or not involving any V-shaped configuration, and be independently removable from that series. As illustrated, hollow fiber bundles 201 and 20IB of V-shaped configuration 300, and hollow fiber bundles 20IC and 20ID of the second V-shaped configuration 300B together form a W-shaped configuration (or M-shaped configuration, depending on the direction of viewing). Within the V-shaped configuration series 400, N-shaped configurations of hollow fiber bundles can be identified, such as is formed by hollow fiber bundles 201 B, 201C and 201 D and by hollow fiber bundles 201 D, 20 IE and 20 IF. The V-shaped configuration series 400 extends, in the manner of forming knife (or accordion) pleats, in a generally linear direction as indicated by arrow 402. Although the first example of a V-shaped configuration series 400 is illustrated to contain 6 hollow fiber bundles, it is to be appreciated that other examples may contain any plural even or odd number of hollow fiber bundles. Further, although the first example of a V-shaped configuration series 400 is illustrated to contain hollow fiber bundles arranged such that substantially similar internal angles are formed between each pair of adjacent hollow fiber bundles, it is to be appreciated that other examples may contain hollow fiber bundles arranged differently so that at least two different internal angles are formed between different pairs of adjacent hollow fiber bundles. The hollow fiber bundles of the V-shaped configuration series 400 create a 3-dimensional shape that is generally rectangular cuboid, such as the generally rectangular cuboid shape indicated by outline 501 in Figure 5. In this Figure, arrow 21 I indicates a lumen side direction of flow of a first fluid to the lumens of the hollow fiber bundles, and arrow 212 indicates a shell side direction of flow to the hollow fiber bundles. The shown shell side direction of flow crosses the lumen side direction of flow substantially perpendicularly but may extend relative to the lumen side direction at any suitable alternative angle (non-zero, non-straight, in other words between 0 and 180 degrees). A plan view of a plurality of hollow fiber bundles according to a second example and comprising bundles arranged in a V-shaped configuration series 600 according to a second specific example is shown in Figure 6. The V-shaped configuration series 600 comprises a plurality of like, hollow fiber bundles, including bundles 601, 601B, 601C and 601D, which are similar to, but dimensioned differently from, the hollow fiber bundles 201,201B, 210C and 201 shown in Figure 4, and which are also arranged to form a W-shaped configuration (or M-shaped configuration); however, as shown, the W-shaped configuration (or M-shaped configuration) is curved around a central axis 602. The hollow fiber bundles of the V-shaped configuration series 600 create a 3-dimensional shape that is generally tubular, such as the generally tubular shape indicated by outline 701 in Figure 7. As can be seen, the cross-sectional shape in a plane through which the central axis 402 extends perpendicularly is generally star-polygonal. Although the first example of a V-shaped configuration series 600 is illustrated to contain 16 hollow fiber bundles, it is to be appreciated that other examples may contain any other suitable plural number of hollow fiber bundles, with any suitable internal angle formed between adjacent pairs of hollow fiber bundles. In Figure 7, arrow 21 I indicates a lumen side direction of flow of a first fluid to the lumens of the hollow fiber bundles, and arrow 212 indicates a shell side direction of flow to the hollow fiber bundles. The shown shell side direction of flow crosses the lumen side direction of flow substantially perpendicularly but may extend relative to the lumen side direction at any suitable alternative angle (non-zero, non-straight, in other words between 0 and 180 degrees). Advantageously, arranging the bundles in a V-shaped configuration makes effective use of the volume available in which to locate a hollow fiber module. Beneficially, each bundle of the V-shaped configuration series is removable independently from the hollow fiber module for replacement, which reduces the total reactor downtime. A hollow fiber bundle 201’ is shown in Figure 8, which is like the hollow fiber bundle 201 of Figure 2 but in which the lumen side inflow and outflow openings 215’, 216’ are in different positions. A hollow fiber reactor 901 according to a first example is illustrated in Figure 9. The hollow fiber reactor 901 comprises a casing, indicated at 902 that defines an interior chamber 903 for housing a hollow fiber module 904 that comprises a plurality of hollow fiber bundles. In this specific example, the hollow fiber module 904 illustrated within the interior chamber 903 comprises hollow fiber bundles 201, 20IB, 20IC, which are shown to be arranged in a V-shaped configuration, as discussed above. It is to be appreciated that the hollow fiber module 904 may comprise any suitable type, number and alternative arrangement of hollow fiber bundles to that shown, and therefore that the use of a V-shaped configuration as disclosed herein is optional. The hollow fiber reactor 901 comprises at least one lumen side inlet 905 for selectively introducing a flow 211 of a liquid heat transfer medium to the lumens of the hollow fiber bundles, and at least one a shell side inlet 906 for selectively introducing a flow of a gas containing carbon dioxide to contact the hollow fiber bundles, whereby the flow 212 of a gas containing carbon dioxide is at a non-zero, non-straight angle with respect to the flow 211 of a liquid heat transfer medium. The hollow fiber reactor 901 further comprises at least one lumen side outlet 907, and at least one shell side outlet 908. It is to be understood that the flow 212 of a gas containing carbon dioxide between the hollow fibers of each hollow fiber bundle 201,201 B may be controlled by one or more flow control arrangements. The flow 212 of a gas containing carbon dioxide to the hollow fiber bundles 201, 20IB within the hollow fiber reactor 901 may be active, with movement of the gas containing carbon dioxide into contact with the hollow fibers being facilitated by use of a flow drive arrangement (not shown), for example comprising one or more fans, so that travel of the gas containing carbon dioxide through each hollow fiber bundle is assisted, or may be passive, with gas containing carbon dioxide being allowed to move freely into contact with the hollow fibers, open sides of the hollow fiber bundles 201, 20IB being exposed to ambient gas containing carbon dioxide, so that travel of the gas containing carbon dioxide through each hollow fiber bundle 201,201 B is in the manner of natural ventilation. In an example, the hollow fiber reactor 901 is provided with a flow drive arrangement comprising one or more fans (not shown) for encouraging the flow of gas containing carbon dioxide through the shell side inlet 906 into contact with the hollow fiber bundles 201, 20IB and / or is provided with a flow regulator arrangement, for example comprising a movable closure element such as a door or shutter (not shown), for controlling an extent of flow of gas containing carbon dioxide through the shell side inlet 906 into contact with the hollow fiber bundles 201,201 B. In a specific example, the hollow fiber reactor 901 is provided with a flow regulator arrangement (not shown) that allows at least the shell side inlet 906 of the shell side inlet 906 and the shell side outlet 907 to be selectively fully shut, to prevent a flow 212 of gas containing carbon dioxide into / through the interior chamber 903. This allows, for example, the interior chamber 103 to be opened to an inflow of air (or other gas containing carbon dioxide) through the shell side inlet 906 of the hollow fiber reactor 901, for adsorption, and then to be sealed, for desorption. The or each lumen side inlet, the or each lumen side outlet, the or each shell side inlet and the or each shell side outlet may, individually, have any suitable form and be provided by any suitable arrangement. For example, one or more of at least one lumen side inlet, at least one lumen side outlet, at least one shell side inlet and at least one shell side outlet may comprise an aperture defined in a surface of the hollow fiber reactor or may be provided by an opening or a space, the extent of which can be adjusted, to decrease / increase the area through fluid can flow, by a flow control arrangement, of any suitable type, for example comprising a door or a shutter. One or more of at least one lumen side inlet, at least one lumen side outlet, at least one shell side inlet and at least one shell side outlet may be in communication with at least one conduit, of any suitable type, and may be associated with one or more valves, of any suitable type. The interior chamber 903 of the hollow fiber reactor 901 may provide a vacuum chamber in which the hollow fiber module 904 is hermetically sealable, during a desorption phase. Figures 10, II and 12 illustrate an adsorption phase, a desorption phase and a cooling phase respectively of an example carbon capture process. 17 In Figure 10, the shell side 105 of hollow fiber 101 is shown exposed to a flow 1001 of a gas comprising carbon dioxide, in this specific example, air. The air comprising carbon dioxide contacts the hollow fiber 102, thus adsorbing the carbon dioxide to the hollow fiber and depleting the air surrounding the hollow fiber 101 of carbon dioxide. Thus, the hollow fiber 102 acts as a solid sorbent for capturing carbon dioxide from the gas. In this Figure, the gas comprising carbon dioxide is shown flowing, on the shell side 104 of the hollow fiber 101, in the direction indicated by arrow 1002, towards a first side 1003 of the hollow fiber 101 (as carbon dioxide laden gas) and flowing from a second, opposite side 1004 of the hollow fiber 101 (as carbon dioxide depleted gas); however, it is to be appreciated that the gas comprising carbon dioxide may flow across, along or around the shell side 104 of the hollow fiber 101 in any direction or directions. Optionally, a liquid heat transfer medium (not shown) may be passed through the lumen to adjust the temperature of the hollow fiber as appropriate during the adsorption phase. Typically, adsorption occurs under ambient conditions. However, as exposure of the hollow fiber to elevated temperatures may be detrimental to the performance of the hollow fiber, the temperature of the hollow fiber may be reduced from ambient conditions during adsorption using a cold or cool water as the liquid heat flow transfer medium, such as water. For example, for particularly hot ambient conditions (e.g., temperatures above 40 degrees Celsius, etc.), it may be beneficial to reduce the temperature of the hollow fiber during adsorption so as to reduce oxidative degradation of the hollow fiber due to exposure to oxygen in the air at elevated temperatures. In Figure I I, a flow 1101 of a liquid heat transfer medium, in this example comprising water, at a first, hot temperature is shown being fed into the lumen 103 of the hollow fiber 101. In some instances, the liquid heat transfer medium, such as water, may be fed into the lumen in absence of a vapor form of the heat transfer medium (i.e. water vapor). The thermal energy of the liquid heat transfer medium results in a temperature increase of the hollow fiber 101 and desorption of carbon dioxide and water from the hollow fiber 101. Single water molecules diffuse through the semi-permeable layer, leaving it as steam thereby reducing the concentration of carbon dioxide within the polymer matrix and allowing for improved desorption kinetics. This form of steam formation is called pervaporation. The desorption phase is typically carried out under vacuum. Beneficially, mixing water with water miscible liquids with liquid heat transfer mediums having high boiling points, such as polyethylene glycol, may reduce the water permeation tendency. In this Figure, the liquid heat transfer medium is shown flowing, in the direction indicated by arrow I 102, along the lumen side 104 of the hollow fiber 101. In Figure 12, a flow I 102 of a liquid heat transfer medium, in this example comprising water, at a second, cooler temperature is shown being fed into the lumen 103 of the hollow fiber 101, so as to cool the hollow fiber 101 in preparation for another adsorption phase. In this Figure, the liquid heat transfer medium is shown flowing, in the direction indicated by arrow 1202, along the lumen side 104 of the hollow fiber 101. A method of operating the hollow fiber reactor 901, comprises the steps of: exposing the hollow fiber module 904 to ambient air for adsorption of carbon dioxide from the ambient air into a least one of the plurality of hollow fibers, subsequently reducing exposure of the hollow fiber module 904 to the ambient air; introducing a first flow of a liquid heat transfer medium, at a first temperature, to the lumen of at least one of the plurality of hollow fibers, in which the liquid heat transfer medium is prevented from flowing from the lumen through the semi-permeable layer and wherein the vapor state of the heat transfer medium is allowed to pass from the lumen through the semi-permeable layer, the first temperature sufficient to elevate the temperature of the hollow fiber for desorbing adsorbed carbon dioxide therefrom; and subsequently introducing a second flow of a liquid heat transfer medium, at a second temperature that is lower than said first temperature, to the lumen of said at least one of the plurality of hollow fibers, the second temperature sufficient to cool the hollow fiber. In an example, the liquid heat transfer medium is water and a vapor state of the heat transfer medium is water vapor. In an example, the flow of water vapor lowers a carbon dioxide concentration in the hollow fiber. In an example, the step of reducing exposure of the hollow fiber module 904 to the ambient air comprises closing the shell side inlet 906 of the hollow fiber reactor 901. In an example, the method comprises hermetically sealing the hollow fiber reactor 901 and reducing a pressure within the hollow fiber reactor 901 prior to introducing the first flow of a liquid heat transfer medium, at the first temperature, to the lumen of the least one of the plurality of hollow fibers. As mentioned above, following multiple cycles of adsorption and desorption, oxidative degradation, for example, may reduce the number of available amine sites that may react with carbon dioxide. As a result, the sorbent material may decrease its capacity to capture carbon dioxide and require replacement or regeneration. A method of treating hollow fibers for carbon dioxide capture will now be described. The method comprises identifying a hollow fiber module of a hollow fiber reactor, the hollow fiber module including a plurality of hollow fiber bundles, each hollow fiber bundle including a plurality of functionalized hollow fibers that are capable of carbon dioxide sorption, (ii) determining the presence of an indicator that a condition is met for one or more of the hollow fiber bundles to be subjected to one or more treatments; and (iii) subjecting the one or more of the hollow fiber bundles to at least one treatment, the at least one treatment including a regeneration treatment, the regeneration treatment comprising exposing the one or more of hollow fiber bundles to an amine solution for replenishing amine sites of the hollow fibers thereof. Figure 13 shows steps in an example method 1301 of maintaining hollow fiber bundles of a hollow fiber reactor. Each of the hollow fiber bundles comprises a plurality of functionalized hollow fibers that are capable of carbon dioxide sorption. At step I 302, an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar is detected. A hollow fiber bundle is removed from the hollow fiber reactor at step I 303. At step I 304 the hollow fiber bundle removed from the hollow fiber reactor at I 302 is replaced. An indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar may be an indicator that a particular one or more of hollow fiber bundles is underperforming or an indicator that operation of a hollow fiber module is not meeting an expected standard. The performance of a hollow fiber bundle may be impaired for a variety of reasons, for example, but not limited to, an initial defect in, or damage to, that hollow fiber bundle, typical deterioration through use, a problem relating to one or more other hollow fiber bundles or the structure of the hollow fiber reactor, or due to an issue with fluid flow or temperature control during operation of the hollow fiber reactor. In an example, a hollow fiber bundle is removed at step I 302 and at step 1303 a different hollow fiber bundle is installed in the hollow fiber reactor to replace the removed hollow fiber bundle. The substitute hollow fiber bundle may be new. The substitute hollow fiber bundle may have been used previously, in the same or a different hollow fiber reactor, and may have been reconditioned. In an example, a hollow fiber bundle is removed at step I 302 and then at least one maintenance action is performed on that hollow fiber bundle. After the least one maintenance action has been performed on the hollow fiber bundle, it may be returned to the hollow fiber reactor. The hollow fiber bundle 20 may be returned after being previously substituted. Thus, a hollow fiber bundle may be removed and replaced by another hollow fiber bundle, which may subsequently be removed and replaced by the previous hollow fiber bundle (or, alternatively, a different previous hollow fiber bundle). The at least one maintenance action may comprise a cleaning process for removing foreign matter from the hollow fibers, such as solid particles or contaminants that may impair performance. In an example, the cleaning process comprises the use of pressurized air. The at least one maintenance action may comprise a protecting process for protecting against an accumulation of material or organisms. In an example, the protecting process involves the use of one or more chemicals. In an example, a product may be applied to the hollow fiber bundle, or the hollow fiber bundle may be exposed to a product, to protect against one or more of: biofouling, mineral scaling. A biocide may be used to remove and / or inhibit microbial growth, preferably on both or the inner and outer surface of the hollow fibers. An antiscalant may be applied to the inner surfaces of the hollow fibers. The at least one maintenance action may comprise an amine removal process for removing amines from the hollow fibers. In an example, the amine removal process comprises subjecting the one or more hollow fiber bundles to an elevated temperature under vacuum. R.e-amination may be performed after amine de-grafting. The at least one maintenance action may comprise a regeneration process, which may involve exposing the hollow fiber bundle to an amine solution for replenishing amine sites of the hollow fibers thereof. The regeneration of the carbon capture capacity of amino based sorbents may use a metal hydride of a metal catalyst and hydrogen. In an example, the oxidized amines may be revived through chemical treatment with alkyl silanes compounds through hydrosilation reaction in presence of transition-metal catalytic complexes of Ti, Mo, R.u, Os, Fe. In an example, the degraded amines may be revived through chemical reduction via catalytic hydrogenation in presence of bimetallic catalytic complexes while using hydrogen as the reducing agent. In an example, the degraded amines may be revived through chemical reduction by metal hydride complexes such as lithium aluminium hydride, sodium borohydride, di-isobutylaluminum hydride, sodium triacetoxyborohydride. The at least one maintenance action may comprise a lumen coating process, which may involve flowing a lumen coating through a lumen of each of the plurality of hollow fibers. Other different maintenance actions, which may be the purpose of treating and / or reconditioning, may be performed on a hollow fiber bundle after removal from a hollow fiber reactor. It is understood that one or more actions may be performed on a hollow fiber bundle while installed within a hollow fiber reactor. An indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar may be based on a single ground or condition, or a combination of grounds, conditions or grounds and conditions, for example, but in no way limited to, one or more of: a number of adsorption / desorption cycles, a period of use, a deviation from an anticipated level of performance, which may be determined by reference to an absolute or a relative value, a fixed or percentage value of difference from a predetermined value or range of values. An indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar may be detected during a monitoring routine. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises determining that a predetermined duration of operation of a hollow fiber bundle of the hollow fiber reactor has expired. It may be expected that the performance of a hollow fiber bundle will diminish over a period of use; therefore, the hollow fiber bundle may be inspected, tested and / or subjected to one or more maintenance actions after expiry of a period in service. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises evaluating an amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor, and comparing the evaluated amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor with a predetermined threshold amount. It can be expected that the carbon capture performance of a hollow fiber bundle will decrease through use, from which an inverse relationship between the amount of carbon dioxide already adsorbed to the plurality of hollow 22 fibers and the potential amount of carbon dioxide that could be adsorbed to the plurality of hollow fibers is based. Hence, if the outcome of the comparison is that the evaluated amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor is above a predetermined threshold then this indicates that the carbon capture performance has fallen to a sufficient extent that maintenance is justifed. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises measuring a pressure difference across one or more hollow fiber bundles of the hollow fiber reactor, and comparing the measured pressure difference to a predetermined threshold pressure difference. A change in pressure across a hollow fiber bundle, or group of hollow fiber bundles, can indicate, for example, but not limited, to, a mechanical failure, accumulation of foreign matter, a blockage. As mentioned above, a hollow fiber reactor can comprise a lumen side inlet for introducing a flow of a liquid heat transfer medium to the lumens of the hollow fiber bundles, and a lumen side outlet for removal of the liquid heat transfer medium; and a shell side inlet for introducing a flow of a gas containing carbon dioxide to contact the hollow fiber bundles, whereby the flow of gas containing carbon dioxide gas is at a non-zero, non-straight angle with respect to the flow of a liquid heat transfer medium, and a shell side outlet for removing the carbon dioxide depleted gas. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises measuring a pressure at the lumen side inlet of the hollow fiber reactor, and comparing the measured pressure to a predetermined threshold pressure. A change in pressure at the lumen inlet side can indicate, for example, but not limited, to, a blockage, scale build-up, damage. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: evaluating a consumption level of liquid heat transfer medium by the hollow fiber bundles, and comparing the measured consumption level to a predetermined threshold consumption level. A change in the level of consumed liquid heat transfer medium can indicate, for example, but not limited, to, a change in permeation of vapour through the hollow fibers or a leakage of liquid heat transfer medium due to a damaged hollow fiber. In an example, detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises: measuring a permeance of a fluid flow across one or 23 more hollow fiber bundles from of the lumen to shell side of hollow fibers in the hollow fiber bundle in the hollow fiber reactor, and comparing the measured permeance to a predetermined threshold permeance difference. 5 As mentioned above, the ability to independently remove and replace hollow fiber bundles of the hollow fiber reactor advantageously provides a modular approach that offers a robust strategy for attending to maintenance of the hollow fiber bundles. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference 10 to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments and examples shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims. 15

Claims

I. A method of maintaining hollow fiber bundles of a hollow fiber reactor, each of the hollow fiber bundles comprising a plurality of functionalized hollow fibers that are capable of carbon dioxide sorption, the method comprising:(i) detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar;(ii) removing a hollow fiber bundle from the hollow fiber reactor; and(iii) replacing the hollow fiber bundle removed from the hollow fiber reactor at (ii).

2. The method of claim I, wherein (iii) comprises substituting the hollow fiber bundle removed from the hollow fiber reactor at (ii).

3. The method of claim I, further comprising performing at least one maintenance action on the hollow fiber bundle removed from the hollow fiber reactor at (ii).

4. The method of claim 3, further comprising, after said at least one maintenance action has been performed on the hollow fiber bundle removed from the hollow fiber reactor at (ii), returning the hollow fiber bundle removed from the hollow fiber reactor at (ii) to the hollow fiber reactor.

5. The method of claim 3 or 4, wherein said at least one maintenance action comprises a cleaning process for removing foreign matter from the hollow fibers.

6. The method of claim 5, wherein said cleaning process comprises the use of pressurized air.

7. The method of claim 3 or 4, wherein said at least one maintenance action comprises aprotecting process for protecting against an accumulation of material or organisms.

8. The method of claim 7, wherein said protecting process comprises the use of one or more of: a biocide, an antiscalant.

9. The method of claim 3 or 4, wherein said at least one maintenance action includes an amine removal process for removing amines from the hollow fibers.

10. The method of claim 9, wherein said amine removal process comprises subjecting the one or more hollow fiber bundles to an elevated temperature under vacuum.I I. The method of claim 9, wherein said amine removal process comprises subjecting the one or more hollow fiber bundles to a continuous flow of amine digesting liquid or agent.

12. The method of claim I I, wherein said amine digesting liquid may consist of aqueous, alcoholic, acidic, basic solution or combinations thereof at temperatures varying between 25 - 70 degrees Celsius.

13. The method of claim 3 or 4, wherein said at least one maintenance action includes a reactivation process of degraded, oxidized, or decomposed amines on the hollow fibers.

14. The method of claim 13, wherein said at least one maintenance action includes a reactivation process of chemical reduction of the degraded, oxidized, or decomposed amines on the hollow fibers with at least one or more of: hydrogen, metal hydrides, metal catalysts, aminosilane.

15. The method of claim 3 or 4, wherein said at least one maintenance action comprises a regeneration process, the regeneration process involving exposing the hollow fiber bundle to an amine solution for replenishing amine sites of the hollow fibers thereof.

16. The method of claim 15, wherein the exposing the hollow fiber bundle to an amine solution involves flowing the amine solution through a lumen of each of the plurality of hollow fibers.

17. The method of claim 3 or 4, wherein said at least one maintenance action comprises a lumen coating process, the lumen coating process involving flowing a lumen coating through a lumen of each of the plurality of hollow fibers.

18. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:determining that a predetermined duration of operation of a hollow fiber bundle of the hollow fiber reactor has expired.

19. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:26evaluating an amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor, andcomparing the evaluated amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor with a predetermined threshold amount.

520. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:measuring a pressure difference across one or more hollow fiber bundles of the hollow fiber reactor, and10 comparing the measured pressure difference to a predetermined threshold pressuredifference.

21. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:15 measuring a permeance of a fluid flow across one or more hollow fiber bundles from of thelumen to shell side of hollow fibers in the hollow fiber bundle in the hollow fiber reactor, andcomparing the measured permeance to a predetermined threshold permeance difference.

22. A method as claimed in any one of claims I to 17, wherein said hollow fiber reactor comprises:20 (i) a lumen side inlet for introducing a flow of a liquid heat transfer medium to the lumens ofthe hollow fiber bundles, and a lumen side outlet for removal of the liquid heat transfer medium; and(ii) a shell side inlet for introducing a flow of a gas containing carbon dioxide to contact the hollow fiber bundles, whereby the flow of gas containing carbon dioxide gas is at a non-zero, nonstraight angle with respect to the flow of a liquid heat transfer medium, and a shell side outlet for25 removing the carbon dioxide depleted gas.

23. The method of claim 22, when dependent upon any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:30 measuring a pressure at the lumen side inlet of the hollow fiber reactor, andcomparing the measured pressure to a predetermined threshold pressure.

24. The method of claim 22, when dependent upon any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:evaluating a consumption level of liquid heat transfer medium by the hollow fiber bundles, and comparing the measured consumption level to a predetermined threshold consumption level.

25. A method as claimed in any one of claims I to 24, wherein said hollow fiber reactor is operational to:(a) expose the plurality of hollow fiber bundles to ambient air, for adsorption of carbon dioxide from the ambient air into at least one of the plurality of hollow fibers;(b) subsequently reduce exposure of the hollow fiber bundles to the ambient air;(c) introduce a first flow of a liquid heat transfer medium, at a first temperature, to the lumen of at least one of the plurality of hollow fibers, in which the liquid heat transfer medium is prevented from flowing from the lumen through the semi-permeable layer and wherein a vapor state of the heat transfer medium is allowed to pass from the lumen through the semi-permeable layer, the first temperature sufficient to elevate the temperature of the hollow fiber for desorbing adsorbed carbon dioxide therefrom; and(d) subsequently introduce a second flow of a liquid heat transfer medium, at a second temperature that is lower than said first temperature, to the lumen of said at least one of the plurality of hollow fibers, the second temperature sufficient to cool the hollow fiber.

26. The method of claim 25, wherein said second temperature is sufficient to cool the hollow fiber below 40 °C.

27. The method of claim 24 or claim 25, wherein the liquid heat transfer medium is liquid water, and the vapor state of the heat transfer medium is water vapor.

28. The method of claim 27, in which the flow of water vapor lowers a carbon dioxide concentration in the hollow fibers.

29. The method of claim 24 or claim 25, wherein the liquid heat transfer medium is mixed with at least one of demineralized water, water dosed with a conditioning agent, a corrosion inhibitor, an antifrost additive, a biocide treatment, a boiling point adjuster, silicone oil, propylene glycol, ethyl glycol, polyethylene glycol, a salt, m-Xylene, ethyl benzoate, o-Xylene, decamethyltetrasiloxane (MD2M), and undecane methanol, ethanol, t-butanol, 2-propanol, I -propanol, 2-butanol, t-amyl alcohol, i-butanol, I28butanol, i-amyl alcohol, 2 ethylbutanol, 2-ethylhexanol, heptane, octane, cholorobenzene, p-cymene, and tetralin.

30. The method of any one of claims I to 29, the hollow fiber bundles comprising at least two 5 hollow fiber bundles arranged in a V-shaped configuration."Amendments to the claims have been filed as follows."26 06 25ClaimsI. A method of maintaining hollow fiber bundles of a hollow fiber reactor, each of the hollow fiber bundles comprising a plurality of functionalized hollow fibers that are capable of carbon dioxide 5 sorption, the method comprising:(i) detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar;(ii) removing a hollow fiber bundle from the hollow fiber reactor; and(iii) replacing the hollow fiber bundle removed from the hollow fiber reactor at (ii);10 wherein (i) comprises evaluating an amount of carbon dioxide adsorbed to the plurality ofhollow fibers of the hollow fiber bundles of the hollow fiber reactor and comparing the evaluated amount of carbon dioxide adsorbed to the plurality of hollow fibers of the hollow fiber bundles of the hollow fiber reactor with a predetermined threshold amount.15 2. The method of claim I, wherein (iii) comprises substituting the hollow fiber bundle removedfrom the hollow fiber reactor at (ii).

3. The method of claim I, further comprising performing at least one maintenance action on the hollow fiber bundle removed from the hollow fiber reactor at (ii).

204. The method of claim 3, further comprising, after said at least one maintenance action has been performed on the hollow fiber bundle removed from the hollow fiber reactor at (ii), returning the hollow fiber bundle removed from the hollow fiber reactor at (ii) to the hollow fiber reactor.25 5. The method of claim 3 or 4, wherein said at least one maintenance action comprises a cleaningprocess for removing foreign matter from the hollow fibers.

6. The method of claim 5, wherein said cleaning process comprises the use of pressurized air.30 7. The method of claim 3 or 4, wherein said at least one maintenance action comprises aprotecting process for protecting against an accumulation of material or organisms.

8. The method of claim 7, wherein said protecting process comprises the use of one or more of: a biocide, an antiscalant.26 06 259. The method of claim 3 or 4, wherein said at least one maintenance action includes an amine removal process for removing amines from the hollow fibers.

10. The method of claim 9, wherein said amine removal process comprises subjecting the one or 5 more hollow fiber bundles to an elevated temperature under vacuum.I I. The method of claim 9, wherein said amine removal process comprises subjecting the one or more hollow fiber bundles to a continuous flow of amine digesting liquid or agent.10 12. The method of claim I I, wherein said amine digesting liquid may consist of aqueous, alcoholic,acidic, basic solution or combinations thereof at temperatures varying between 25 - 70 degrees Celsius.

13. The method of claim 3 or 4, wherein said at least one maintenance action includes a 15 reactivation process of degraded, oxidized, or decomposed amines on the hollow fibers.

14. The method of claim 13, wherein said at least one maintenance action includes a reactivation process of chemical reduction of the degraded, oxidized, or decomposed amines on the hollow fibers with at least one or more of: hydrogen, metal hydrides, metal catalysts, aminosilane.2015. The method of claim 3 or 4, wherein said at least one maintenance action comprises a regeneration process, the regeneration process involving exposing the hollow fiber bundle to an amine solution for replenishing amine sites of the hollow fibers thereof.25 16. The method of claim 15, wherein the exposing the hollow fiber bundle to an amine solutioninvolves flowing the amine solution through a lumen of each of the plurality of hollow fibers.

17. The method of claim 3 or 4, wherein said at least one maintenance action comprises a lumen coating process, the lumen coating process involving flowing a lumen coating through a lumen of each 30 of the plurality of hollow fibers.

18. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:determining that a predetermined duration of operation of a hollow fiber bundle of the hollow 35 fiber reactor has expired.26 06 2519. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:measuring a pressure difference across one or more hollow fiber bundles of the hollow fiber 5 reactor, andcomparing the measured pressure difference to a predetermined threshold pressure difference.

20. The method of any one of claims I to 17, wherein detecting an indicator that indicates that at 10 least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:measuring a permeance of a fluid flow across one or more hollow fiber bundles from of the lumen to shell side of hollow fibers in the hollow fiber bundle in the hollow fiber reactor, and comparing the measured permeance to a predetermined threshold permeance difference.15 21. A method as claimed in any one of claims I to 17, wherein said hollow fiber reactor comprises:(i) a lumen side inlet for introducing a flow of a liquid heat transfer medium to the lumens of the hollow fiber bundles, and a lumen side outlet for removal of the liquid heat transfer medium; and (ii) a shell side inlet for introducing a flow of a gas containing carbon dioxide to contact the hollow fiber bundles, whereby the flow of gas containing carbon dioxide gas is at a non-zero, non-20 straight angle with respect to the flow of a liquid heat transfer medium, and a shell side outlet for removing the carbon dioxide depleted gas.

22. The method of claim 21, when dependent upon any one of claims I to 17, wherein detecting an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is25 operationally subpar comprises:measuring a pressure at the lumen side inlet of the hollow fiber reactor, and comparing the measured pressure to a predetermined threshold pressure.

23. The method of claim 21, when dependent upon any one of claims I to 17, wherein detecting 30 an indicator that indicates that at least one hollow fiber bundle of the hollow fiber reactor is operationally subpar comprises:evaluating a consumption level of liquid heat transfer medium by the hollow fiber bundles, and comparing the measured consumption level to a predetermined threshold consumption level.26 06 2524. A method as claimed in any one of claims I to 23, wherein said hollow fiber reactor is operational to:(a) expose the plurality of hollow fiber bundles to ambient air, for adsorption of carbon dioxide from the ambient air into at least one of the plurality of hollow fibers;5 (b) subsequently reduce exposure of the hollow fiber bundles to the ambient air;(c) introduce a first flow of a liquid heat transfer medium, at a first temperature, to the lumen of at least one of the plurality of hollow fibers, in which the liquid heat transfer medium is prevented from flowing from the lumen through the semi-permeable layer and wherein a vapor state of the heat transfer medium is allowed to pass from the lumen through the semi-permeable layer, the 10 first temperature sufficient to elevate the temperature of the hollow fiber for desorbing adsorbed carbon dioxide therefrom; and(d) subsequently introduce a second flow of a liquid heat transfer medium, at a second temperature that is lower than said first temperature, to the lumen of said at least one of the plurality of hollow fibers, the second temperature sufficient to cool the hollow fiber.1525. The method of claim 24, wherein said second temperature is sufficient to cool the hollow fiber below 40 °C.

26. The method of claim 23 or claim 24, wherein the liquid heat transfer medium is liquid water, 20 and the vapor state of the heat transfer medium is water vapor.

27. The method of claim 26, in which the flow of water vapor lowers a carbon dioxideconcentration in the hollow fibers.25 28. The method of claim 23 or claim 24, wherein the liquid heat transfer medium is mixed with atleast one of demineralized water, water dosed with a conditioning agent, a corrosion inhibitor, an antifrost additive, a biocide treatment, a boiling point adjuster, silicone oil, propylene glycol, ethyl glycol, polyethylene glycol, a salt, m-Xylene, ethyl benzoate, o-Xylene, decamethyltetrasiloxane (MD2M), and undecane methanol, ethanol, t-butanol, 2-propanol, I -propanol, 2-butanol, t-amyl alcohol, i-butanol, I30 butanol, i-amyl alcohol, 2 ethylbutanol, 2-ethylhexanol, heptane, octane, cholorobenzene, p-cymene, and tetralin.

29. The method of any one of claims I to 28, the hollow fiber bundles comprising at least two hollow fiber bundles arranged in a V-shaped configuration.35s

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