ADSORPTION AND DESORPTION APPARATUS

Abstract

An adsorption apparatus and associated method for capturing an target gaseous adsorbate from an atmospheric air based gaseous feed stream. The adsorption apparatus comprises: a housing enclosing at least one adsorption element for adsorbing the target gaseous adsorbate, the at least one adsorption element comprising at least one substrate coated with an adsorptive composite coating that comprises at least 50 wt % metal organic framework and at least one binder, the housing having an inlet through which the gaseous feed stream can flow to the adsorption element and an outlet through which gas can flow out from the housing; and a desorption arrangement in contact with and/or surrounding the at least one adsorption element, the desorption arrangement being selectively operable between (i) a deactivated state, and (ii) an activated state in which the arrangement is configured to heat, apply a reduced pressure or a combination thereof to the adsorptive composite coating to desorb at least a portion of the adsorbed target gaseous adsorbate from the adsorptive composite coating.

Claims

1.-61. (canceled)

62. An adsorption apparatus for capturing a target gaseous adsorbate from an atmospheric air based gaseous feed stream, comprising: a housing enclosing at least one adsorption element for adsorbing the target gaseous adsorbate, the at least one adsorption element comprising at least one substrate coated with an adsorptive composite coating that comprises at least 50 wt % metal organic framework and at least one binder, the housing having an inlet through which the gaseous feed stream can flow to the adsorption element and an outlet through which gas can flow out from the housing; and a desorption arrangement in contact with and/or surrounding the at least one adsorption element, the desorption arrangement being selectively operable between (i) a deactivated state, and (ii) an activated state in which the arrangement is configured to heat, apply a reduced pressure or a combination thereof to the adsorptive composite coating to desorb at least a portion of the adsorbed target gaseous adsorbate from the adsorptive composite coating.

63. An adsorption apparatus according to claim 62, wherein the adsorptive composite coating has a thickness of at least one of: less than 200 μm, preferably no more than 100 μm; or greater than 30 μm, preferably greater than 40 μm, and more preferably about 50 μm.

64. An adsorption apparatus according to claim 62, wherein the MOF: binder ratio within the adsorptive composite coating is 7.8:1 to 200:1 based on total wt % of solids in the coating, preferably, 7.9:1.

65. An adsorption apparatus according to claim 62, wherein adsorptive composite coating comprises 80 to 97% MOF.

66. An adsorption apparatus according to claim 62, wherein the target gaseous adsorbate is selected from the group consisting of hydrogen, oxygen, argon, carbon dioxide, carbon monoxide, neon, and methane.

67. An adsorption apparatus according to claim 62, wherein the target gaseous adsorbate is carbon dioxide and the binder is hydrophobic, and the binder preferably comprises at least one siloxane compound comprising poly (hydroxymethyl) siloxane, cellulose methyl siloxane, cellulose amino methyl siloxane or a combination thereof.

68. An adsorption apparatus according to claim 67, wherein the binder comprises at least one siloxane compound and at least one additional hydrophobic binder selected from at least one cellulosic polymer selected from methyl cellulose, amino methyl cellulose, hydroxyl methyl cellulose, hydroxyethyl methylcellulose, ethylhydroxy ethylcellulose, hydroxy propyl cellulose or carboxymethylcellulose.

69. An adsorption apparatus according to claim 67, wherein the binder comprises at least one of: between 3 and 10 wt % hydroxypropylcellulose and between 0.2 and 10 wt % of a siloxane-cellulose polyester or derivative thereof; or 0.2 to 10 wt % poly (hydroxymethyl) siloxane, 3 to 10 wt % hydroxy propyl cellulose, and 0.2 to 5 wt % methyl cellulose.

70. An adsorption apparatus according to claim 62, wherein the adsorptive composite coating is hydrophobic and has a contact angle over 70 degrees.

71. An adsorption apparatus according to claim 62, wherein the target gaseous adsorbate is at least one of: oxygen and the binder is hydrophobic, preferably comprising at least one of poly (hydroxymethyl) siloxane, cellulose methyl siloxane or cellulose amino methyl siloxane, poly (ethyl vinyl acetate), methyl cellulose or hydroxypropylcellulose; or carbon monoxide, hydrogen, argon, methane, neon, and wherein the binder is selected from a hydrophobic or hydrophilic binder and the binder preferably comprises at least one of poly (hydroxymethyl) siloxane, cellulose methyl siloxane or cellulose amino methyl siloxane, poly (ethyl vinyl acetate), methyl cellulose, hydroxypropylcellulose, polyvinylpyrrolidone, polyvinyl alcohol or thermo plastic polyurethane

72. An adsorption apparatus according to claim 62, wherein the housing contains a loading of at least 30 kg/m.sup.3 of adsorptive composite coating, preferably at least 50 kg/m.sup.3 and more preferably around 60 kg/m.sup.3.

73. An adsorption apparatus according to claim 62, wherein the metal organic framework comprises a metal-organic material (MOM) of general formula [ML.sub.2TIFSIX].sub.n, n is 1 to 10.sup.18 wherein M is a divalent or trivalent metal, wherein L is a bifunctional linker molecule based upon two nitrogen donor moieties; and TIFSIX is hexafluorotitanate, hexafluorostannate or hexafluorosilicate.

74. An adsorption apparatus according to claim 62, wherein the adsorptive composite coating includes from 40 to 100 g/m.sup.2 MOF, preferably from 50 to 80 g/m.sup.2 MOF.

75. An adsorption element according to claim 62, wherein the adsorbate comprises carbon dioxide and the metal organic framework comprises at least one of SIFSIX-3-Ni or TIFSIX-3-Ni.

76. An adsorption apparatus according to claim 62, wherein the substrate is at least one of: planar, preferably a flexible sheet; comprises mesh, preferably micro wire mesh; comprised from or coated with a resistive heating material preferably comprising a non-dielectric material through which a current can flow and having a resistance sufficient to heat the adsorptive composite coating to at least 80° C., preferably between 80 and 150° C.; further comprises at least one pair of spaced apart electrodes configured to enable current to flow therebetween and through the resistive heating material; or a spiral rolled sheet, preferably a tightly spiral rolled flexible sheet, more preferably a spiral rolled cylinder.

77. An adsorption apparatus according to claim 76, comprising at least two adsorption elements having substrates comprising flexible sheets, each flexible sheet being separated by an insulating element that comprises one or more strips of insulating material extending between adjacent adsorption elements.

78. A method of capturing a target gaseous adsorbate from a gaseous feed stream comprising at least one cycle of: flowing a gaseous feed stream over at least one adsorption element enclosed within a housing, the at least one adsorption element comprising at least one substrate coated with an adsorptive composite coating that comprises at least 50 wt % metal organic framework and a binder, the binder including at least one binder, such that the adsorptive composite coating adsorbs a selected gaseous adsorbate from the gaseous feed stream; and operating at least one desorption arrangement to heat, apply a reduced pressure or a combination thereof to the adsorptive composite coating so to release at least a portion of the adsorbed gaseous adsorbate therefrom, thereby producing a gaseous product flow including the gaseous adsorbate, wherein the gaseous feed stream comprises atmospheric gas based gaseous feed stream.

79. A method according to claim 78, wherein the housing forms part of an adsorption apparatus configured according to claim 62.

80. A method according to claim 78, wherein the desorption arrangement is configured to heat the adsorptive composite coat to a temperature of between 60 to 150° C., preferably between 60 and 90° C., more preferably between 70 and 80° C. and yet more preferably about 70° C.

81. A method according to claim 78, wherein the target gaseous adsorbate is CO.sub.2 from air, said air comprising less than 500 ppm of CO.sub.2 and H.sub.2O concentrations of at least 1000 ppm and the selectivity for CO.sub.2 is greater than 50%, preferably greater than 80%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0131] The present invention will now be described with reference to the Figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[0132] FIG. 1 provides a schematic representation of the adsorption apparatus including a single adsorption chamber, blower, and vacuum pump according to one embodiment of the present invention.

[0133] FIG. 2 illustrates one embodiment of the adsorption element according to the present invention, showing (a) a sheet form of the substrate; (b) the sheet form with spaced apart electrodes attached; and (c) the sheet form with an insulative grid seated thereon prior to rolling.

[0134] FIG. 3 illustrates the sheet embodiment of the adsorption element shown in FIG. 1A rolled into a compact rolled cylinder.

[0135] FIG. 4A provides a photograph of the rolled adsorption element shown in FIG. 3 housed in the outlet of a cylindrical housing of an adsorption apparatus according to one embodiment of the present invention.

[0136] FIG. 4B provides a photograph of a sheet form of the substrate shown in FIG. 2 prior to coating with the adsorptive composite coating.

[0137] FIG. 4C provides a photograph of a support element around which a sheet adsorption element is rolled.

[0138] FIG. 4D provides a photograph of the sheet embodiment of the adsorption element shown in FIG. 2 set out with the support element prior to rolling.

[0139] FIG. 4E provides a photograph of the sheet embodiment of the adsorption element shown in FIG. 2 rolled into a compact rolled cylinder.

[0140] FIG. 4F provides a photograph of the rolled adsorption element shown in FIG. 3 housed in the inlet of a cylindrical housing of an adsorption apparatus according to one embodiment of the present invention.

[0141] FIG. 5 illustrates one embodiment an adsorption apparatus according to the present invention.

[0142] FIG. 6 provide breakthrough curves of CO.sub.2 adsorption versus time on a TIFSIX-Ni coated adsorption element operated in a canister adsorption apparatus shown in FIG. 5.

[0143] FIG. 7 illustrates the amount of CO.sub.2 produced from one canister (as illustrated in FIG. 5) with feed flow rate is 90 LPM, containing dry air (CO.sub.2˜450 ppm and H.sub.2O<300 ppm for different adsorption times of 1, 1.5, 2 (+repeat) and 3 hours.

[0144] FIG. 8 provides a comparison of CO.sub.2 delivered for ten consecutive adsorption and desorption cycles of a canister adsorption apparatus shown in FIG. 5.

[0145] FIG. 9 illustrates the adsorption and desorption profiles of a rolled adsorptive element in a canister illustrated in FIG. 5 having (a) 1.5 wt. % cellulose siloxane in the adsorptive composite coating; and (b) 5 wt. % of cellulose siloxane in the adsorptive composite coating.

[0146] FIG. 10 provides a plot of purity of CO.sub.2 in output with an adsorptive element having a MOF adsorptive composite coating loading of 200 grams in the canister (second configuration—two banks of 2 layered adsorption elements).

[0147] FIG. 11 provides a heating profile of the resistive heating function of the adsorption element showing (a) Temperature profiles under different voltages for the four planar adsorption elements per canister configuration (second configuration—two banks of 2 layered adsorption elements); and (b) Temperature profile under 120 V for the 8 planar adsorption elements per canister configuration (first configuration—two banks of 4 layered adsorption elements) with temperature controller set to 100° C.

[0148] FIG. 12 illustrates the cooling profile of the 8 planar adsorption elements configuration (first configuration—two banks of 4 layered adsorption elements) under a feed flow rate 90 LPM.

[0149] FIG. 13 illustrates (a) Preliminary breakthrough curves for a single module; and (b) Mass of CO.sub.2 and H.sub.2O produced for different adsorption times at a regeneration temperature of 80° C.

[0150] FIG. 14 illustrates the cumulative CO.sub.2 generated by the test adsorption apparatus with three CO.sub.2 adsorption modules over 500 cycles with energy consumption.

[0151] FIG. 15 illustrates CO.sub.2 breakthrough curves for different adsorption times. Feed air initially bypasses the adsorption chamber to establish a background signal before switching the feed to the chamber.

[0152] FIG. 16 illustrates the purity of CO.sub.2 produced during regeneration of the experimental CO.sub.2 adsorption module.

[0153] FIG. 17 illustrates the results of CO.sub.2 breakthrough curves for different TIFSIX—binder coating compositions.

[0154] FIG. 18 illustrates the low pressure results of CO.sub.2 breakthrough curves for different TIFSIX—binder coating compositions.

DETAILED DESCRIPTION

[0155] The present invention provides an alternate MOF based adsorption apparatus incorporating a MOF based adsorption element, and an associated adsorption method.

Adsorption Apparatus

[0156] FIG. 1 illustrates a schematic arrangement of an adsorption apparatus 50 according to one embodiment of the present invention. The adsorption apparatus 50 is designed to capture and release an atmospheric gas, such as hydrogen, oxygen, argon, carbon dioxide, carbon monoxide, neon, or methane, from an atmospheric air based gaseous feed stream using a MOF based nanocomposite adsorption element (described in more detail below). As shown in FIG. 1, a single CO.sub.2 adsorption module comprises of three major units: a blower 52, an adsorption chamber 54 including adsorption element 53, and a vacuum pump 60.

[0157] The adsorption chamber 54 comprises a housing enclosing an adsorption element 53 comprising at least one substrate coated with an adsorptive composite coating that comprises at least 50 wt % metal organic framework and at least one hydrophobic binder (described in more detail below). The adsorption chamber 54 includes an inlet 55 through which feed atmospheric gas 50 can flow to the adsorption element 53 and an outlet 56 through which gas can flow out from the housing. The outlet has is either expelled through the outlet as the adsorbate stripped gas 57 during the adsorption phase of the cycle, or the target adsorbate gas 58 during the desorption phase of the adsorption-desorption cycle (see below for more details on this cycle). The adsorption element 53 is located in the adsorption chamber 54 between the inlet and outlet of the adsorption chamber 54. As will be explained in more detail below, the configuration of the adsorption chamber 54 and the adsorption element 53 and a composite coating thereof is designed to ensure optimum mixing of the feed air with the composite coating of the adsorption element 53 thereby ensuring efficient stripping of the adsorbate from the feed air.

[0158] Whilst not specifically illustrated in FIG. 1, the adsorption chamber 54 also includes a desorption arrangement in contact with and/or surrounding the at least one adsorption element 53 used to activate the desorption phase of the adsorption-desorption cycle. In general terms, the desorption arrangement is selectively operable between (i) a deactivated state, and (ii) an activated state in which the arrangement is configured to apply heat, a reduced pressure or a combination thereof to the adsorptive composite coating to desorb at least a portion of the adsorbed gaseous adsorbate from the adsorptive composite coating.

[0159] The desorption arrangement can take any number of forms depending on whether heat and/or reduced pressure is being used to cause the adsorbed adsorbate gas to desorb from the adsorbent composite coating. In some embodiments, the apparatus is designed for pressure swing adsorption, with desorption being achieved by reducing the pressure for example using a vacuum pump to evacuate the gas from around the adsorption element. Adsorption would typically be undertaken at near atmospheric pressure. In other embodiments, temperature swing adsorption is undertaken to achieve gas adsorbate harvesting. This can be achieved using direct heating methods, or in some cases using magnetic induction swing adsorption. As will be explained in more detailed below, the exemplary form of the desorption arrangement is a resistive heating material that is in operative contact (direct or forms part of) the adsorption element 53.

[0160] The inlet 55 of adsorption chamber 54 is connected to air blower 52 which serves to blow the atmospheric air feed into the adsorption chamber 54. These blowers 52 preferably comprise low cost and energy efficient blowers to allow a high volume of air to be processed without incurring a back-pressure penalty or reduced performance. These types of blowers 52 can generate flow rates up to 50 m.sup.3h.sup.−1 with a back pressure less than 100 Pa.

[0161] The outlet 56 is connected to vacuum pump 60 which is initially used after the adsorption step to remove excess air from within the adsorption chamber 54. During the desorption phase, the vacuum pump 60 is used to creates the driving force that drains the liberated adsorbate gas from the adsorption chamber 54 after the target regeneration temperature is achieved.

Adsorption Element

[0162] FIG. 2 illustrates one embodiment of the adsorption element 100 that can be used in the adsorption chamber 54. As shown in FIG. 2, the adsorption element 100 comprises a flexible planar sheet 110 coated on both sides 102, 103 with an adsorptive composite coating 112 comprising at least 50 wt % metal organic framework (MOF) and a binder (typically at least 1 wt % binder). Whilst not illustrated, the adsorptive composite coating 112 is thin (in this case understood to be less than 200 μm).

[0163] The thickness is selected to be less than 200 μm, preferably less than 100 μm because if the coating is too thick, the adsorbate will not have time to diffuse into the MOF and be adsorbed before it leaves the adsorption apparatus. A large content of the MOF in the coating would not be properly utilised. The coating should preferably be thicker than 30 μm, preferably thicker than 40 μm, as any thinner and the overall efficiency is not high enough as there is not enough MOF on the adsorption element.

Metal Organic Framework/Materials

[0164] The metal organic framework in the adsorptive composite coating 112 (FIG. 2) can be selected from a range of suitable MOFs as discussed above. Those MOFs are generally selected based on a number of considerations, including: [0165] 1) Stability—the MOF should be stable in the adsorption conditions and for the particular adsorbate. For example, only carbon dioxide stable MOFs should be used for carbon dioxide adsorption. [0166] 2) Adsorption reproducibility, the MOF should retain adsorption capacity after multiple adsorption/desorption cycles, preferably at least 10 cycles, more preferably at least 100 cycles. [0167] 3) Ease of production, the MOF is preferably easy to produce from readily available precursor materials. [0168] 4) High adsorbate uptake even at low concentrations. [0169] 5) A good affinity for the adsorbate. The MOF should have a good enough affinity for adsorbate to enable the MOF to adsorb the adsorbate, but not have too high affinity for the adsorbate that excessive energy needs to be expended to desorb the adsorbate therefrom. Here the thermodynamics of the adsorbate species adsorption and desorption need consideration to ensure the MOF does not require excessive energy (kJ/mol MOF) to desorb the adsorbate therefrom, and thereby adversely affect the energy efficiency of the system.

[0170] For CO.sub.2, the energy/heat required to desorb CO.sub.2 from a MOF is a measure of the binding strength between CO.sub.2 and the MOF surface. This energy can also depend on the amount of CO.sub.2 remaining in the MOF. For example, the very first CO.sub.2 molecules to adsorbed within the metal-organic framework Mg.sub.2(dobdc) generate around 42 kJ/mol of heat while the last CO.sub.2 molecules to adsorb generate around 24 kJ/mol. This is because Mg.sub.2(dobdc) comprises of open metal-sites that interact strongly with CO.sub.2. Once these metal-CO.sub.2 sites are saturated, additional adsorption occurs via CO.sub.2—CO.sub.2 interactions that are weaker, corresponding to lower heat generation. In other cases, such as for MOF-177 there is a uniform distribution of adsorption sites resulting in a uniform generation of heat during adsorption at around 14 kJ/mol. For comparison, liquid CO.sub.2 evaporates into the gaseous phase with a change of enthalpy of around 8 kJ/mol.

[0171] Where the MOF is required for production of materials for human consumption (for example water), the MOF and other materials must also meet food for human consumption regulations in relevant countries.

Binder Selection

[0172] The selection of the appropriate binder is also important to the overall properties of the adsorptive composite coating. For example, for carbon dioxide and oxygen adsorption, the inventors have found that the binder or binder mixture must include at least one hydrophobic binder to reduce/decrease the competing water adsorption properties of the adsorptive composite coating. It should be appreciated that use of a hydrophobic binder allows water adsorption to be slowed, such that where the feed gas is atmospheric air, atmospheric moisture largely blows across the adsorptive coating while the adsorbate, for example CO.sub.2, diffuses in. For other gases a hydrophobic or hydrophilic binder can be used (as previously discussed).

[0173] In the coating system of the present invention (see below) the binders thicken the slurry, keep it homogeneous, stabilise the wet coat and provide some adhesion to the substrate. On drying the binder/binder mixture provides adhesion both between the particles (within the coating—provides strength) and between the coating and the substrate (provides adhesion). It should again be appreciated that a variety of binders or mixture of binders could be used as described in detail previously.

[0174] As indicated in the following examples, one exemplary hydrophilic binder is a mixture of hydroxypropylcellulose (HPC) and a siloxane compound, typically a cellulose based siloxane compound (referred to as cellulose siloxane at some points of the specification).

[0175] HPC is used for processability and strength, and tends to provide good substrate adhesion properties. HPC is also a relatively hydrophobic example of a cellulosic binder—e.g. compared to CMC (Carboxymethylcellulose). In addition, adding cellulosic binders (starch, carboxymethyl cellulose, HPC, methylcellulose) to a slurry of small charged particles such as MOFs, clays, alumina improves the rheology of the resulting mixture such that it flows well under shear forces during coating but sets or gels into a stable film when the physical coating process ends.

[0176] The other component, a siloxane compound can be cellulose-disiloxane polyester or a cellulose-oligosiloxane polyester binder. Examples include poly (hydroxymethyl) siloxane, cellulose methyl siloxane or cellulose amino methyl siloxane. Each of these siloxane compounds have a polar-non-polar structure (as discussed above) that is thought to assist in two functions, with the polar structure (for example siloxane component) bonds/packs with the MOF in a manner that creates a 3D porous structure in the coating forming a gas permeable structure in the coating layer, and the non-polar structure provides the required hydrophobicity. In this sense, the siloxane part of this form of composite coating is thought to present a hydrophobic/CO.sub.2 permeable surface to the adsorbate air flow repelling water and preventing it from displacing CO.sub.2 in the 3D MOF structure. Moreover, the siloxane has a pronounced hydrophobicity. Nevertheless, HPC is also used in this exemplary mixture as it has good broad-spectrum properties but also its improved adhesive properties with respect to cellulose siloxane.

Binder Content

[0177] The amount of binder used in a system should also be optimised. A minimum amount of binder should be used for each particular MOF to enable the particle comprising the adsorptive composite coating to bind together when formed. However, too much binder should also be avoided as excess binder decreases the adsorption performance of the adsorptive composite coating. The lower the binder content, the lower the likelihood of pore occlusion induced by the binder.

[0178] The minimum and maximum amount of binder depends on a number of factors, including the MOF used in the adsorptive composite coating. Generally, the adsorptive composite coating preferably comprises a MOF: Binder ratio of 7.8:1 to 200:1 based on total wt % of solids in the coating, preferably, 7.9:1. The adsorptive composite coating preferably comprises 80 to 97% MOF. It should be appreciated that the amount of binder is selected based on the properties and particle size (mean size and particle distribution) of the MOF particles, the binding properties of the particular binder and the required properties of the resultant composite coating.

Solvent

[0179] The adsorptive composite coating 110 is applied to the planar sheet 110 in a coating process where a slurry is formed from a powder mixture of at least 10 wt % metal organic framework (solvent wt % basis); and at least one binder (a single binder or a mixture of different binders) in a solvent, which is then coated into the planar sheet 110 and dried using a heating technique to form the adsorptive composite coated element 100. Again, the amount of binder added depends on the amount of binder is selected based on the properties and particle size (mean size and particle distribution) of the MOF particles, the binding properties of the particular binder and the required properties of the resultant composite coating. However, the amount of binder is typically at least 0.5 wt %, and more typically from 1 to 10 wt % (solvent wt % basis). The slurry typically has a viscosity of 200 to 1000 cP.

[0180] The composite powder mixture is added to the solvent to enable the powder mixture to be formed into a slurry suitable for the coating step. Suitable solvents are preferably selected from a non-basic polar solvent and/or a non-self ionising polar solvent. The solvent preferably comprises an alcohol, such as methanol, ethanol, C2-C9 alcohols including their branched isomers, or water, more preferably deionised water. In some embodiments, the solvent comprises a mixture of a C2 to C9 alcohol and water, preferably deionised water. The solvent typically has an evaporation temperature of less than 150° C., preferably less than 120° C., more preferably less than 100° C.

[0181] The composite slurry can be coated onto the flexible sheet using a variety of processes. In embodiments, the composite slurry is coated onto the substrate by rolling, blade coating, dip coating, spray coating, slip coating, waterfall coating and vacuum dosing (precision coating). In a preferred embodiment, the planar sheet 110 is blade cast with the composite slurry in an inert atmosphere to protect the MOF from any premature degradation.

[0182] Following the coating process, the composite coating is heated at a temperature of between 60 to 150° C., preferably between 60 and 90° C. for sufficient time to remove the solvent from the composite coating. The heating step can also be conducted in an insert gas atmosphere, for example nitrogen, helium or argon.

[0183] Following coating, the adsorptive composite coated planar sheet is then coiled up and the electrical connections made (as detailed below). This is typically done very quickly to minimise air exposure. The rolled adsorption element 110A is then inserted and sealed in an adsorption apparatus 200 (described in more detail below).

[0184] An activation step is then undertaken after application of the composite coating 112 to the planar sheet 110. Activation is the removal of solvents of synthesis to leave the exposed pores within the MOFs for the direct air capture. In some embodiments, this is achieved by applying heat and vacuum. In other embodiments, particularly MOF having extremely small pores, activation can be achieved using a method of flowing the adsorptive composite coated substrate through helium gas to expunge the solvents and activate the MOF. For TIFSIX MOF based adsorptive composite coatings, the activation step preferably comprises locating the adsorptive coated substrate in a helium, gas flow at a temperature of at least 800° C., preferably around 100° C. for at least 1 hour, preferably at least 5 hours, more preferably around 24 hours.

Resistive Heating Mesh

[0185] A major factor that contributes to the cost of direct air capture is the amount of energy required to liberate the captured adsorbate, for example CO.sub.2. To overcome this challenge, the adsorption element includes a resistive heating material for the regeneration phase of the adsorption-desorption cycle. Experiments (see Example 3) revealed an optimum desorption temperature of 80° C. The heating rate is controlled by the voltage range between 20-120 V. As shown in FIG. 11(a), the target regeneration temperature of 80° C. can be achieved within 5 minutes.

[0186] Whilst not illustrated in detail in the Figures, the planar sheet 110 comprises mesh, and in this case micro wire mesh. In the illustrated Figures, this comprises a fibreglass mesh sheet. The use of a mesh provides a multitude of apertures, preferably micro size apertures, thereby providing a high surface area on which the adsorptive composite coating can be applied, whilst also providing a suitable flow path having a reasonably low pressure drop across the substrate (of course relative to the size and configuration of the mesh) compared to other adsorber configurations for example packed beds. The mesh comprises a woven wire screens, or pressed metal wire screens with 100 to 1000 or more flow channels per square centimeter.

[0187] The planar sheet 110 is coated with a resistive heating material. However, it should be appreciated that in other embodiments, the planar sheet 110 may be formed from a resistive heating material. As discussed previously, the use of resistive heating material advantageously provides a means of local heat generation in the substrate on the application of a current flow through the resistive heating material. Suitable resistive heating material that the mesh can be formed from include (but are not limited to) at least one of nichrome, tungsten, Kanthal/Fecralloy, Cupronickel, carbon fibre, graphite, fibreglass coated with graphitic materials, molybdenum disilicide, PTC ceramic materials, PTC polymer materials or platinum. Suitable resistive heating coating material includes (but is not limited to) graphite or graphitic materials such as a carbon and graphite composite mixture, typically a mixture of graphite and carbon bound together with a binder, typically a polymer binder such as PTFE.

[0188] The planar sheet 110 illustrated in FIGS. 4A to 4F comprises a graphitic material coated fibreglass mesh. As shown in FIG. 4B, the planar sheet comprises a fibre glass mesh comprises a woven fibreglass cloth as the substrate. A woven fibre glass cloth has a resistive heating coating 101 comprising a mixture of carbon and graphite (in proportion according to the electrical properties desired) with PTFE as a binder sintered thereon under high temperature and pressure. The base cloth having predictable unit square resistance is then cut to width according to physical requirement. The cut cloth then has electrodes 120 fitted down each side comprising tinned-copper strips for electrical connection making it a finished ‘element’ with specific resistance and watt-density. An adsorptive composite coating 112 is then applied over that resistive heating coating 101 as explained below. The combination of a resistive heating layer with a MOF containing composite coating 112 allows the generation of heat on application of a current through the resistive heating layer. The MOF in the composite coating 112 can therefore be regenerated using direct and controlled heating, and which in return releases the adsorbed fluid from the pores of the MOF part of the composite coating 112.

[0189] As shown in FIG. 2(B), FIG. 4B and FIG. 4D, the planar sheet 110 includes a pair of spaced apart electrodes 120 for applying current flow through the substrate. The electrodes 120 comprise conductive strips positioned along the longitudinal edge of each planar sheet 110. The resistive heating material extends between each electrode 120. As noted above, these comprise tin covered copper strips (copper coated with solder, which it should be appreciated to be an alloy containing tin by itself or in combination with copper, silver, bismuth, indium, zinc, antimony, lead and traces of other metals) in the illustrated embodiment. However, any suitable conducting material could be used. Conductive connection wire 122 extends from each electrode 120 for connection to a suitable power source (not illustrated).

[0190] As shown in FIG. 3 and FIG. 4E, the adsorption element 100 is configured as a spiral rolled sheet, formed into a spiral rolled cylinder 100A. In embodiments, that rolled configuration can be formed by rolling the planar sheet 110 over a hollow support element 145 (best illustrated in FIGS. 4C, 4D and 4E). That spiral rolled sheet 110A is housed in cylindrical housing 200 as shown in FIGS. 4A and 4F (described in more detail below). The adjacent sections of the planar sheet 110 need to be electrically isolated from adjacent sections of the planar sheet in the spiral roll configuration. The planar sheet 110 therefore includes a Teflon insulating lattice 130 (FIG. 3(C)) which extends over and is seated on the upper surface 102 of the planar sheet 110. The Teflon insulating lattice 130 is configured to extending between adjacent sections of the planar sheet 110 when rolled up. It should be appreciated that the insulating lattice 130 could be formed from any suitable flexible insulating material, for example another polymer or plastic. The electrodes 120 equally should be electrically isolated in the rolled up configuration. Whilst not illustrated, it should be appreciated that the electrodes 120 are therefore preferably covered using an insulating tape, for example a Kevlar tape.

[0191] As shown in FIGS. 4C to 4F, the planar sheet 110 and Teflon insulating lattice 130 are typically rolled around a cylindrical support element 145, a bar which enables the sheet 110 to be rolled into a tight roll (spiral rolled cylinder 100A) to maximise the amount of sheet area that can be inserted into the housing/canister 210 of adsorption apparatus 200. The support element 145 includes a conical/cone shaped head 146 shaped to distribute the inlet gas flow away from the support element 145 to and through the spiral rolled cylinder 100A (adsorption element 100). As shown in FIG. 4F the cone shaped head 146 is position in the inlet 114A of the adsorption apparatus 200. The support element 145 also includes longitudinal slot 147 into which one end of the planar sheet 110 is inserted, with electrical connections and wires 122, which then runs through the center of the hollow support element 145, for example as shown in FIG. 4E.

[0192] As best shown in FIG. 4D, four 2 m planar sheets 100 are attached to the cylindrical support element 145, through slot 147 and overlaid to form a four-layer sandwich, separated by a Teflon insulating lattice 130. These four layers of planar sheet 110 are rolled together to form the spiral rolled cylinder 100A shown in FIG. 4E. This forms one of two banks of roller adsorption elements 100A that is inserted into cavity 211 of the adsorption apparatus/canister 200.

[0193] Whilst not wishing to limit the invention, it should be appreciated that the Inventors considered a number of adsorption element configurations when designing the adsorption apparatus 200 and adsorption system 300 shown in FIGS. 4A, 4F and 5. Firstly, a ceramic monolith coated with the composite coating was investigated. However, ceramic monoliths were found to be too thermally insulating and required too much energy to achieve the required liberation of the captured CO.sub.2. Conductive mesh arrangements were also investigated. However, it was found that a flexible resistive heating mesh spiral rolled into a coil to tightly pack within the adsorption canister provides a low enough thermal mass that it can be rapidly heated and cooled to shorten the requisite cycle time as much as possible and provided the necessary low pressure drop for a high volumetric feed gas flow rate.

[0194] FIGS. 4A, 4F and 5 illustrate an adsorption apparatus 200 according to one embodiment of the present invention. The adsorption apparatus 200 comprises a canister which includes a cylindrical housing 210 which encloses a cavity 211 into which the previously described adsorption element 100 is inserted in a tightly spiral rolled configuration as shown in FIG. 3. The cylindrical housing 210 is made fluid tight using end plates 213A and 213B which are bolted on and seal over the ends of cylindrical housing 210. End plate 213A includes inlet 214A configured to allow a gaseous feed stream to flow into cavity 211 and flow across the adsorption element 100 through to outlet 214B included in end plate 213B. Outlet 214B is fluidly linked to fan 220 which operates to draw the gaseous feed stream from the inlet 214A to the outlet 214B of the adsorption apparatus 200. Flow through inlet 214A and outlet 214B are controlled by ball valves 215A and 215B respectively. In the illustrated embodiments, the volume ratio of empty volume: adsorbent element within the housing 210 is around 1.3:1. The rolled adsorptive element 110A therefore occupies about 42% of the volume of the housing 210.

[0195] Whilst not illustrated, it should be understood that the adsorption system of the present invention can be constructed to include multiple adsorption apparatus 200 (canisters) each including housings 210 enclosing adsorption elements, for example a 3×3 array of individual adsorption apparatus 200. Each adsorption apparatus 200 in the adsorption system is connected in parallel to the gaseous feed stream. In this way, the adsorption capacity of the adsorption system is scalable. It should be appreciated that each adsorption apparatus 200 can be operated independently, in a different part of the adsorption and desorption (release) cycle described below. In this way a continuous adsorbate product can be generated from the adsorption system. The inventors have found that at least three parallel adsorption apparatus 200 need to be operated across spaced apart and different points the adsorption and regeneration cycles to provide continuous production of a particular gas.

[0196] Whilst not illustrated, it should be appreciated that the product flow gas from the outlet 214B can flow to a variety of secondary processes. For example, for carbon dioxide capture, the adsorption apparatus 200 can be integrated with a liquefier and/or dry ice pelletiser to provide dry ice on-demand.

Adsorption Apparatus Operation

[0197] The adsorption apparatus 200 is operated to capture a gaseous adsorbate, for example carbon dioxide, from a gaseous feed stream, for example atmospheric gas. For example, where the feed gas is atmospheric air, the adsorbate can be at least one of hydrogen, oxygen, argon, carbon dioxide, neon, helium or methane. In exemplary embodiments, the adsorption apparatus 200 is operated to capture carbon dioxide. However, a number of other adsorbates can be harvested (captured and released) as previously discussed.

[0198] The adsorption apparatus 200 is operated on a repetitive adsorption and desorption cycle, running through multiple cycles of:

(A) flowing a gaseous feed stream through the inlet 214A and across the adsorption element 100 of the apparatus 200 such that the adsorptive composite coating adsorbs a selected gaseous adsorbate from the gaseous feed stream; followed by
(B) heating the adsorptive composite coating by applying a current through the spaced apart electrodes 120, thereby generating heat within resistive heating material of the planar sheet 110 so as to release at least a portion of the gaseous adsorbate therefrom into a product fluid flow.

[0199] The steps of adsorbing the adsorbate in the adsorptive composite coating of the adsorption element and releasing that adsorbate through application of heat in a repetitive cycle so to produce the adsorbate. The cycle time can vary depending on factors as discussed above. However, it is expected that the cycle time would be between 10 minutes to 2 hours, more typically 10 to 30 minutes. As noted above, where multiple parallel connected adsorption apparatus 200 are used, the adsorption apparatus 200 can be operated simultaneously through different parts of this cycle, and therefore continuously produce the adsorbate in a product flow.

[0200] The heating step is preferably conducted at a temperature of between 60 to 150° C., preferably between 60 and 90° C., more preferably about 70° C.

[0201] In general, the adsorption apparatus 200 is designed to run at a high gaseous feed stream flow rate. The higher the flow, the more adsorbate passes over the adsorptive element 100, the higher the amount of adsorbate adsorbed. Accordingly, the gaseous feed stream preferably flows through the at least one adsorption element at a flow rate of at least 20 m.sup.3/hour, preferably at least 50 m.sup.3/hour, more preferably at least 60 m.sup.3/hour.

[0202] Where moisture is an issue (again for example atmospheric air), adsorption can be run in non-equilibrium conditions, and preferably well away from equilibrium conditions (as detailed above).

EXAMPLES

Example 1—Method of Coating an Adsorptive Composite Coating on a Flexible Substrate

1.1. General Adsorptive Composite Coating Preparation—(13 wt % TiFSiX, 1 wt % HPC, 1.5 wt % Cellulose Siloxane)

[0203] A slurry comprising 13 wt % TIFSIX-3-Ni (referred to hereinafter as TiFSiX), 1 wt % hydroxypropylcellulose (HPC) (binder 1), 1.5 wt % cellulose siloxane (binder 2) in an ethanol solvent was formed for coating a flexible substrate using the following steps: [0204] 1. To prepare HPC (MW 1000 kDa) solution, 5 g of HPC is slowly added (bit by bit to avoid clumps) into a stirring 500 mL ethanol. [5 g HPC/500 g ethanol=1 wt %] [0205] 2. The solution is put on a stirrer for at least 24 hr on high stirring rate (>600 rpm). [0206] 3. After the HPC solution is homogenously mixed, 65 g of TiFSiX is added to it to achieve 13 wt % MOF in the slurry, the slurry is stirred for at least 2 days with occasional manual shaking to help breaking up clumps. [65 g TiFSiX/500 g ethanol=13 wt %] [0207] 4. 40 g of binder (see below for steps of making this) can be added along with TiFSiX in step 3) or can be added a few hours after TiFSiX has been added. [40 g×0.025 g/g/65 g TiFSiX=1.5 wt % binder to TiFSiX] [0208] 5. The resulting slurry is ready for coating.

1.2. Binder (Cellulose Siloxane Mixture) Preparation

[0209] A cellulose siloxane mixture binder solution (0.025 g binder/g solution) was prepared using the following steps: [0210] 1. 6 g polymethylhydroxysiloxane (PMHS) is added into a mixture of 240 g ethanol and 240 g deionised water. [0211] 2. 6 g methyl cellulose (MC) (MW 86 kDa) is then added to (1) very slowly, making sure that the cellulose is fully dissolved each time before the next addition. The mixture is put on a roller, or stirrer on high speed. [(6 g+6 g) binder/480 g ethanol water=0.025 g/g] [0212] 3. After the binder has achieved homogenous consistency, it is then put on a roller to ensure good dispersion over time.

1.3. Other MOF Compositions Used for Coating at Various Binder Additions

[0213] Table 1 provides the composition of three alternate adsorptive composite coating compositions formed in ethanol and deionised water solvent.

TABLE-US-00001 TABLE 1 Alternative adsorptive composite coating compositions Coating slurry various binder TiFSiX mass HPC mass PMHS mass MC mass concentrations added (g) added (g) added (g) added (g) MOF @ 1 65 5 0.33 0.33 wt % binder MOF @ 1.5 65 5 0.50 0.50 wt % binder MOF @ 5 65 5 1.65 1.65 wt % binder

1.4. Coating Process

[0214] Each of the coatings were blade cast/coated onto the flexible planar sheet 110 shown in FIG. 4B in an inert atmosphere to protect the MOF from any premature degradation. As described above, that sheet comprises a woven fibre glass cloth having a resistive heating coating 101 comprising a mixture of carbon and graphite (in proportion according to the electrical properties desired) with PTFE as a binder sintered thereon under high temperature and pressure. The sheet 110 has electrodes 120 fitted down each side comprising tinned-copper strips for electrical connection making it a finished ‘element’ with specific resistance and watt-density.

[0215] After blade casting, the coating is dried by heating the wet coated substrate to between 60 to 100° C. to substantially remove the solvent from the coating. The coated substrate is then coiled up and the electrical connections made (as shown in FIGS. 4D and 4E and described in more detail above). This is typically done very quickly to minimise air exposure.

[0216] A further activation step is undertaken after application of the composite coating 112 to the planar sheet 110 to remove the solvents of synthesis to leave the exposed pores within the MOFs. This is achieved by heating the composite coating 112 in a 1500 SCCM flow of helium gas at 100° C. for 24 hours.

[0217] The resulting planar adsorption element 100 has the dimensions of 2 m length×0.32 m width and a loading of approximately 30 to 80 g/m.sup.2 MOF (in some embodiments around 37 glm.sup.2), where the where the surface area m.sup.2 is including both coated sides of the adsorption element 100.

Example 2—Method of Coating an Adsorptive Composite Coating on a Flexible Substrate (Higher Cellulose Siloxane Binder Content)

2.1. General Adsorptive Composite Coating Preparation—(13 wt % TiFSiX, 1 wt % HPC, 5 wt % Cellulose Siloxane)

[0218] A slurry comprising 13 wt % TIFSIX-3-Ni (referred to generally hereinafter as TiFSiX), 1 wt % hydroxypropylcellulose (HPC) (binder 1), 5 wt % cellulose siloxane (binder 2) in an ethanol solvent was formed for coating a flexible substrate using the following steps: [0219] 1. To prepare HPC (MW 1000 kDa) solution, 5 g of HPC is slowly added (bit by bit to avoid clumps) into a stirring 500 mL ethanol. [5 g HPC/500 g ethanol=1 wt %] [0220] 2. The solution is put on a stirrer for at least 24 hr on high stirring rate (>600 rpm). [0221] 3. After the HPC solution is homogenously mixed, 65 g of TiFSiX is added to it to achieve 13 wt % MOF in the slurry, the slurry is stirred for at least 2 days with occasional manual shaking to help breaking up clumps. [65 g TiFSiX/500 g ethanol=13 wt %] [0222] 4. 80 g of binder (see below for steps of making this) can be added along with TiFSiX in step 3) or can be added a few hours after TiFSiX has been added. [80 g×0.041 g/g/65 g TiFSiX=5 wt % binder to TiFSiX] [0223] 5. The resulting slurry is ready for coating.

2.2. Binder (Cellulose Siloxane Mixture) Preparation

[0224] A cellulose siloxane mixture binder solution (0.025 g binder/g solution) was prepared using the following steps: [0225] 1. 9.72 g polymethylhydroxysiloxane (PMHS) is added into a mixture of 240 g ethanol and 240 g deionised water. [0226] 2. 9.72 g methyl cellulose (MC) (MW 86 kDa) is then added to (1) very slowly, making sure that the cellulose is fully dissolved each time before the next addition. The mixture is put on a roller, or stirrer on high speed. [(9.72 g+9.72 g) binder/480 g ethanol water=0.041 g/g] [0227] 3. After the binder has achieved homogenous consistency, it is then put on a roller to ensure good dispersion over time.

[0228] The coating process follows the steps taught in Example 1, section 1.4.

Example 3—Adsorption Cycles Using Single Canister Adsorption Device

3.1 Adsorption

[0229] The CO.sub.2 uptake capacity of the planar adsorption element 100 formed in Example 1 was studied using a single adsorption canister set up. The planar adsorption element 100 was formed with a loading of approximately 400 g of MOF. An example of a single adsorption apparatus/canister 200 is shown in FIG. 5. The illustrated adsorption canister 200 is 650 mm in length and has an internal diameter of 123.8 mm. Four adsorption elements 100 were loaded in the canister 200 in a scroll/rolled up orientation as detailed above allowing free flow of the feed gas through the canister 200.

[0230] In a first configuration, the canister 200 has 2 banks with four 2 m adsorption elements 100 (meshes) scrolled together to make a bank. Each bank comprises four 2 m meshes attached to the cylindrical support element 145 and overlaid together. These four layers of meshes are rolled together to form the rolled adsorption element 100A shown in FIG. 4E. The overall canister provides a MOF loading of 400 g, with a substrate surface area of 1234 m.sup.2/m.sup.3 with a MOF packing density of about 6% volume of MOF over the total volume of canister.

[0231] In a second configuration, each bank comprises two 2 m meshes attached to the cylindrical support element 145 and overlaid together. These two layers of meshes are rolled together to form the rolled adsorption element. The overall canister provides a MOF loading of 200 g, with a substrate surface area of 1234 m.sup.2/m.sup.3 with a MOF packing density of about 3% volume of MOF over the total volume of canister.

[0232] Dry (containing 200 ppm H.sub.2O and 450-500 ppm CO.sub.2) and wet (containing 1.5-1.8% H.sub.2O and 450-500 ppm CO.sub.2) feed was used to evaluate the performance of our MOF for direct air capture. Prior to the first adsorption run, freshly coated mesh was activated by heating the MOF under 1500 SCCM of He at 100° C. for 24 hours. Post activation, air (wet or dry) is flowed through the mesh at flowrates 20-1000 L/m for 1-3 hours. The target flowrate was 1000 L/m (60 m.sup.3/hr). The pressure in the canister is monitored using pressure transducers and depending on the feed flowrate, a backpressure of 1.3-1.7 bar is generated in the canister.

[0233] Breakthrough curves for CO.sub.2 and H.sub.2O are collected analysing the gas exiting the canister with the aid of a mass spectrometer. FIG. 6 provides examples of CO.sub.2 breakthrough curves for the adsorptive element formed according to Example 1 (13 wt % TiFSiX, 1 wt % HPC, 5 wt % cellulose siloxane) for dry air flow conditions (as above) at 20, 40 and 50 L/min gas flow and wet air flow conditions (as above) at 20, 40 and 50 L/min gas flow.

3.2 Regeneration

[0234] At the end of the adsorption process, a pre-purge tank is used to evacuate the canister to 0.08 bar within 20 seconds. The adsorption elements 100 are then heated up by supplying voltage (60-120 V) a variable power supply. The rate of heating depends on the voltage supplied, the higher the voltage the faster the heating rate. The temperature in the canister 200 is monitored through two thermocouples (not illustrated) inserted in each adsorption element 100 in the canister 200. One of the thermocouples is connected through a PID controller and the power supply to control the maximum temperature in the canister which is set to 80° C.

[0235] Due to pressure limitations on the mass spectrometer used, regeneration is carried out under a gentle He flow (500 SCCM). The characteristics of the He carrier gas is analysed real time with the mass spectrometer. He is then subtracted from the CO.sub.2 and H.sub.2O peaks to evaluate the volume/mass generated. At the end of the regeneration, the adsorption process is repeated and the cyclability of the MOF is evaluated.

[0236] FIG. 7 illustrates the amount of CO.sub.2 produced from one canister as described above having an MOF adsorptive composite coating loading of 400 grams. Feed flow rate is 90 LPM, containing dry air (CO.sub.2 ˜450 ppm and H.sub.2O<300 ppm). The feed flow was fed through the canister for different adsorption times of 1, 1.5, 2 (+repeat) and 3 hours. A vacuum purge was conducted after adsorption to 100 mbar then back-filled with helium to 1 bar. Desorption achieved at 80-100° C. using 120 V and slow flow of helium (900 sccm). Appreciable amounts of CO.sub.2 (˜5 g) are shown to be produced in less than 75 mins.

[0237] FIG. 8 provides an indication of the amount of CO.sub.2 delivered over 10 cycles, for dry air adsorption at 40 L/min for 1 hour, and desorption for 1 hour. The results illustrate that the canister provides a reasonably repeatable CO.sub.2 delivery over multiple adsorption and desorption cycles.

[0238] The hydrophobicity of the adsorptive composite coating was investigated by varying the cellulose siloxane content from 1.5% to 5% as indicated by the different composite coating compositions detailed in Example 1 and Example 2. The CO.sub.2 uptake for each of adsorptive composite coatings were measured, with the results shown in FIG. 9.

[0239] FIG. 9 shows the adsorption and desorption profiles with 1.5 wt. % (A) and 5 wt. % (B) of cellulose siloxane in the MOF composite. In these runs the feed gas flow rate is 40 LPM, containing air (CO.sub.2 ˜450 ppm and H.sub.2O 1500 ppm) and was run for 3 hours. Desorption was conducted using vacuum purge after adsorption to 100 mbar then back-filled with helium to 1 bar. Desorption achieved at 80 to 100° C. using 60 V (left) and 80 V (right) and slow flow of helium 500 sccm (left) and 900 sccm (right). Importantly, increasing the cellulose siloxane content (hydrophobic binder) increases the hydrophobicity, significantly reducing the H.sub.2O update, without a loss in CO.sub.2 uptake.

[0240] The purity of the CO.sub.2 produced was also measured. FIG. 10 illustrates the purity of CO.sub.2 in output. MOF composite loading of 200 grams. Feed flow rate was 20 LPM, containing air (CO.sub.2 ˜500 ppm and H.sub.2O ˜350 ppm) and adsorption was undertaken for 3 hours. Desorption was achieved using vacuum purge after adsorption to 100 mbar then back-filled with helium to 1 bar. Desorption achieved at 80-100° C. using 48 V and slow flow of helium (500 sccm). Back filling with helium or another inert gas is important to prevent mixing of CO.sub.2 into air. Purity of the CO.sub.2 produced peaks at around 90 mins.

[0241] The heating profile of the resistive heating element system of the adsorption element 100 shown in FIGS. 3A to 3F was investigated to determine the optimum voltage required to heat the substrate to 80° C. in 300 s or less. FIG. 11 illustrates the heating profile of the substrate. (A) Temperature profiles under different voltages for the 4 planar adsorption elements per canister configuration (second configuration—two banks of 2 layered adsorption elements). (B) Temperature profile under 120 V for the 8 planar adsorption elements per canister configuration (first configuration—two banks of 4 layered adsorption elements) with temperature controller set to 100° C. The results indicate that at least 45V was required to meet the time target using the first canister configuration.

[0242] The cooling profile of the 8 planar adsorption elements configuration (first configuration—two banks of 4 layered adsorption elements) under a feed flow rate 90 LPM was also measured. These results are shown in FIG. 12.

Example 4

4.1 Adsorption-Desorption Cycle of Single Adsorption Modules

[0243] The suitability of the adsorption element 54 for adsorbing CO.sub.2 was determined using breakthrough experiments performed on a single adorption module (as shown in FIG. 1) under the conditions listed in Table 2. The adsorption chamber 54 of this single adsorption module contained a loading of 60 kg/m.sup.3 for the MOF-polymer nanocomposite (as provided on the adsorption element 53 described above) and of the same composition as detailed in the preceding examples, in particular Example 3 (13 wt % TiFSiX (relative to solvent mass), 1 wt % hydroxy propyl cellulose (HPC) (relative to solvent mass), 1.5 wt % cellulose siloxane (CS) (relative to TiFSiX mass). The adsorption chamber 54 was fitted with pressure transducers and thermocouples on the inlet side and outlet side. The concentration of each component including CO.sub.2, H.sub.2O, O.sub.2 and N.sub.2 was monitored using a Pfeifer Omnistar GSD 320 O series mass spectrometer.

[0244] FIG. 13(a) shows a typical breakthrough curve during the adsorption phase for the major components of the feed air at a flow rate of 5.4 m.sup.3h.sup.−1. The slow flow rate was chosen to carefully measure capacity and kinetics of the adsorption phase. According to the resulting output stream there was no obvious uptake of either N.sub.2 or O.sub.2 by the nanocomposite. Due to the design and configuration of the adsorption module, the CO.sub.2 breakthrough time is almost instantaneous while the equilibration or saturation time is between 60-90 minutes. FIG. 15 provides the results for multiple experiments with varying adsorption times.

[0245] The desorption phase was tested at 80° C. using a helium carrier gas at a flow rate of 500 cm.sup.3 min.sup.−1, see FIG. 13(b). The use of a carrier gas during desorption allowed the output to be measured more accurately than with a vacuum-driven desorption. The results reveal a slight difference in the amount of CO.sub.2 produced from the module after different adsorption times. The 3 hour adsorption time recorded the highest yield of 6.34 g of CO.sub.2, with the 2 hour and 1 hour adsorption time recording a yield of 5.88 and 5.48 g respectively. The configuration and composition of the module ensured minimal water uptake. The mass of H.sub.2O produced after 120 minutes of regeneration for 3, 2 and 1 hour(s) of adsorption was 0.29, 0.16 and 0.16 g respectively. Prolonging the adsorption time by 1 extra hour resulted in almost double the H.sub.2O uptake (180%) compared with a minor increase in CO.sub.2 uptake (108%). Therefore, the kinetics of the system may be exploited by shortening the adsorption time.

[0246] The purity of the CO.sub.2 released as a function of regeneration time was also monitored, as indicated in FIG. 16. More than 70% purity was achieved after 1 hour of regeneration. Note that the purity is calculated by subtracting the amount of helium in the feed, i.e. the balance contains N.sub.2, O.sub.2 and H.sub.2O.

[0247] From these results on a single module, the design of a continuous adsorption-regeneration system utilizing multiple modules was implemented and discussed in the next section.

TABLE-US-00002 TABLE 2 Process parameters for each module in the adsorber demonstrator Preliminary Pilot-Scale Testing Demonstration Parameter (units) (single module) (per module) Feed flow rate (m.sup.3h.sup.−1) 5.4 50 Adsorption time (min) 180 60 Regeneration time (min) 120 30 Feed H.sub.2O (ppm) 180 1000 Feed CO.sub.2 (ppm) 450 400 Regeneration 80 80 Temperature (° C.) Regeneration Helium Vacuum Carrier or Method CO.sub.2 Output (g) 6 2 Energy Consumption (Wh) Heating — 1.6 Fans 0.6 Vacuum 0.1
4.2 Continuous Production using Multiple Modules

[0248] Results obtained from the single adsorption module were used as a basis to build an experimental adsorber demonstrator with three modules capable of continuous capture and production. The demonstrator was automated to combine the product of the three modules. Each module included an adsorption chamber 54 having the same configuration as the adsorption chamber 54 of the single module shown in FIG. 1.

[0249] A cascading process of adsorption-regeneration steps was automated according to Table 3. The automation involved a 1 hour adsorption/cooling time and 30 minutes regeneration time designed to be alternated from one module to the other. Process parameters are listed in Table 2. In all scenarios, the modules were equipped with CO.sub.2 sensors to monitor the purity of CO.sub.2 generated during the regeneration process. Temperature, pressure and power consumed by the process were parameters also monitored during the operation. For the adsorption run, air with CO.sub.2 concentrations of 400-500 ppm and H.sub.2O concentration of 1000 ppm at 25° C. was fed into each adsorption chamber at a flow rate of 50 m.sup.3h.sup.−1. Regeneration via resistive heating of the adsorption element (as detailed above) was carried out at 80° C. under a voltage of 120 V.

[0250] FIG. 14 presents the CO.sub.2 output from the three module demonstrator consisting of 3 modules over 11 days of operation and 500 cycles. The demonstrator produced more than 350 g of CO.sub.2 at an average energy consumption of 2.3 Wh/g-CO.sub.2. The energy consumption per cycle for the module included the power consumption of the fans, the vacuum pump and the resistive heating. Power usage was uniform across all cycles as the operation times were identical for each module and is not affected by CO.sub.2 output.

[0251] Analysis of the resistive heating process revealed that the energy required to achieve desorption of the CO.sub.2 from the nanocomposite adsorbent in the module to be 1.6 kWh/kg-CO.sub.2. In comparison to 5.25 GJ of gas and 366 kWh of electricity required per ton of CO.sub.2 captured in an aqueous sorbent system. The performance of the nanocomposite adsorbent the inventive module also revealed a very good level of stability of the system with no evidence of capacity loss over the 500.

[0252] It should be appreciated that resistive heating can be powered with renewable energy sources like solar, hydrothermal or wind. Assuming that the cost of renewable energy is $0.05 USD/kWh, the demonstrator could produce CO.sub.2 at an operational cost of $115 USD/ton-CO.sub.2. Alternatively, the heating method could be replaced with free waste heat from industrial processes that would bring the cost down further to $35 USD/ton-CO.sub.2. In the short term, energy prices of around $0.15 USD/kWh are readily available and lead to an operational cost of $345 USD/ton-CO.sub.2.

TABLE-US-00003 TABLE 3 Continuous production process using a cascade adsorption- regeneration steps through the three modules. X indicates adsorption/cooling time and Y indicates regeneration time. CYCLE 1 CYCLE 2 . . . CYCLE N Time (mins) 30 60 90 180 . . . N × 90 Module 1 X X Y REPEAT . . . REPEAT Module 2 X Y X Module 3 Y X X

Example 5

[0253] A number of different MOF composite coatings was tested to determine the best coating composition for maximising carbon dioxide adsorption whilst minimising water adsorption. The coating compositions with binder contents are listed in Table 5 comprising mixtures of MOFs SiFSiX and TiFSiX with cellulose siloxane, polyvinyl fluoride (PVDF), poly(hexafluoropropylene) (PHFP) or a copolymer of 1,3-Bis(4-aminophenoxy) benzene (TPE-R) Bisphenol A diphthalic anhydride (BPADA) and Polydimethylsiloxane (PDMS), (TPE-R-BPADA-PDMS). The coatings were formulated following the methods outlined in Examples 1 and 2.

[0254] The adsorption capacity of these coatings was measured as follows: The water vapour uptake was measured by using Quantachrome Autosorb-1-C unit which employed Vapor Sorption Option. The vapor generator was housed within the unit manifold chamber, where it was heated to 50° C. and thermostatically controlled. A solenoid valve opened the pump ballast for all-important venting of condensable vapours. Water vapor adsorption was conducted from P/P0=10.sup.−3 to 0.5 with distilled water as the vapor source. The bath temperature was held below room temperature with a minimum of 5° C. difference. Equilibration bandwidth was set at 0.02 or 98%. Water uptake was measured at 50% relative humidity. Carbon dioxide uptake was measured at 0.4 mbar and 298 K by a volumetric method using a Micromeritics 3Flex instrument. Samples were activated at 150° C. under dynamic vacuum at 10.sup.−6 Torr for 24 h prior to measurements. The results of these comparative experiments are set out in Table 4.

TABLE-US-00004 TABLE 4 Water adsorption and Carbon Dioxide adsorption in composite coatings of different compositions. Water vapour uptake (@ 50% CO.sub.2 uptake RH, 17° C.) (@ 400 ppm) MOF composite composition mL (STP) mL (STP) Pristine SiFSiX 329 6 add 2.5 wt % Cellulose Siloxane 144 4.53 add 5.0 wt % Cellulose Siloxane 218 1.29 add 5.0 wt % PVDF-PHFP 233 4.44 add 5.0 wt % TPE-R-BPADA-PDMS 230 2.99 Pristine TiFSiX 131 6.72 TiFSiX + 5 wt % PVDF 63.8 2.24 TiFSiX + 5 wt % PVDF + 1 wt % HPC 69.2 3.316 TiFSiX + 1 wt % Cellulose Siloxane R 81 9.86 TiFSiX + 1 wt % Cellulose Siloxane 63.6 9.63 TiFSiX + 2 wt % Cellulose Siloxane 7.84 TiFSiX + 3 wt % Cellulose Siloxane 56.3 7.17

[0255] The results indicate that the addition of Cellulose Siloxane provides good hydrophobicity properties. Moreover, use of Cellulose Siloxane in the binder with TiFSiX provides the unexpected result of providing increased CO.sub.2 uptake while decreasing water uptake.

Example 6

[0256] A number of different MOF composite coatings was tested to determine the different TiFSiX coating compositions for carbon dioxide adsorption whilst minimising water adsorption. The coating compositions comprised TiFSiX mixed with different binder contents, and were mixtures of MOF TiFSiX with (wt % solid basis): [0257] 5 wt % cellulose siloxane (CS); [0258] 5 wt % CS and 1 wt % hydroxy propyl cellulose (HPC); [0259] 2.5 wt % and 1 wt % HPC; [0260] 5% polydimethylsiloxane (PDMS); and [0261] 2.5 wt % CS.

[0262] The coatings were formulated following the methods outlined in Examples 1 and 2. The adsorption capacity of these coatings was measured following the methodology set out in Example 5. Carbon dioxide uptake was estimated from breakthrough experiments with CO.sub.2 having a partial pressure of 0.4 mbar and feed temperature of 298 K.

[0263] The results of these comparative experiments are set out in FIGS. 17 and 18 which illustrate the CO.sub.2 breakthrough curves for the different TIFSIX—binder coating compositions. The CS based coatings show good adsorption results. However, the 5 wt % PMHS coating surprisingly shows much greater adsorption characteristics, providing the best initial (FIG. 18) and overall (FIG. 17) CO.sub.2 adsorption.

Example 7—Preparation of Tifsix-3-Ni MOF {[Ni(Pyrazine).SUB.2.(Tif6)]n}

[0264] The following example provides the typical procedure for producing fluoride free TIFSIX-3-Ni for use in the adsorptive composite coating demonstrated in the preceding examples. The procedure is as follows:

[0265] Nickel nitrate hexahydrate (174.5 g, 0.6 mol) and ammonium hexafluorotitanate (118.8 g, 0.6 mol) were dissolved in 150 mL and 450 mL of deionised water, respectively. The two solutions were then mixed together and pyrazine (712.3 g, 8.9 mol) dissolved in 300 mL of deionised water added slowly, at a flow rate between 10-20 mL/min, to the resultant mixture. The combined solutions were put on the roller or shaker at 100 rpm for 3 days at room temperature to yield a precipitate of TIFSIX-3-Ni. The precipitate was washed with distilled water 5 times, followed by methanol 3 times and air dried in fume hood at room temperature for 3-5 days until fully dried. The dried solid was heated at 160° C. under vacuumed condition of 2 mbar for 48 h to obtain the desired TIFSIX-3-Ni MOF.

[0266] It should be appreciated that this method can be readily adapted to other M-XF6 MOF materials (M-Ni, Cu, Zn; X═Ti, Si) with minor modifications.

Example 8

[0267] Whilst the preceding examples all relate to adsorption of CO.sub.2 on a TiFSiX based composite coating, it should be appreciated that the adsorptive composite coating could include other MOFs suitable for adsorbing different atmospheric gases. Table 5 provides examples of other MOFs and binders that could be used for alternate target gas adsorbates:

TABLE-US-00005 TABLE 5 Examples of suitable MOFs for adsorbing different target atmospheric gases. Binder Gas MOF hydrophobicity Binder Oxygen CuBTC/Mg or Hydrophobic Hydrophobic = Cellulose Mn-MOF74 methyl siloxane, cellulose tridecanoate siloxane carbon CuBTC, PCN-250, Hydrophobic Hydrophobic = EVA, monoxide MIL-100, FeBTC or Hydrophilic Cellulose methyl siloxane Hydrophilic = PVP, PVA, TPU Hydrogen NOTT400, Mg or Hydrophobic Hydrophobic = Cellulose Mn-MOF74 or Hydrophilic methyl siloxane Hydrophilic = TPU Nitrogen M-MOF-74 series, Hydrophobic Hydrophobic = EVA, FeBTC, UIO66 and or Hydrophilic Cellulose methyl siloxane UIO66-NH2, Hydrophilic = PVP, MOF808, PVA, TPU Argon M-MOF-74 series Hydrophobic Hydrophobic = EVA, or Hydrophilic Cellulose methyl siloxane Hydrophilic = PVP, PVA, TPU Methane CuBTC, MOFs with Hydrophobic Hydrophobic = EVA, high content aromatic or Hydrophilic Cellulose methyl siloxane rings (Cu2(ADIP), Hydrophilic = PVP, PVA M-MOF-74 series, PCN-250 Neon Mg-MOF-74, SIFSIX, Hydrophobic Hydrophobic = EVA, CuBTC or Hydrophilic Cellulose methyl siloxane Hydrophilic = PVP, PVA

[0268] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0269] Where the terms “comprise”, “comprises”, “comprised” or “comprising” are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.