# Patent

## Title
Metal organic framework based water capture apparatus

## Abstract

An apparatus for capturing a water content from a water containing gas, the apparatus comprising: a housing having an inlet into which the water containing gas can flow; a water adsorbent located in the housing, the water adsorbent comprising at least one water adsorbent metal organic framework composite capable of adsorbing a water content from the water containing gas; and a water desorption arrangement in contact with and/or surrounding the water adsorbent, the water desorption arrangement being 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 water adsorbent to desorb a water content from the water adsorbent.

## Background
PRIORITY CROSS-REFERENCE
This application is a continuation of U.S. patent application Ser. No. 16/766,379, filed 22 May 2022, which is a National Stage Application of PCT/AU2019/050860 filed 16 Aug. 2019, which claims convention priority from Australian provisional patent application No. 2018903009 filed 16 Aug. 2018, the contents of which should be understood to be incorporated herein by this reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.


TECHNICAL FIELD
The present invention generally relates to an apparatus, a method and a system that utilises a water adsorbent metal organic framework composite to capture the water content of a water containing gas, such as atmospheric air. In one form, the invention is configured for temperature swing water harvesting. In another form, the invention can be configured for magnetic induction swing water harvesting using Magnetic Framework Composites (MFC) —a composite material formed between a metal organic framework and a magnetic material. However, it should be appreciated that the present invention could be used in other water harvesting applications that utilise a water adsorbent metal organic framework composite material.
BACKGROUND OF THE INVENTION
The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Water can be a scare resource in many parts of the world, particularly in dry or arid environments. However, water vapour and droplets in the atmosphere is a natural resource that could be captured to increase the global supply of water.
Various atmospheric water capturing systems have been previously developed which contain an adsorbent material that can capture and release water, for example by heating the adsorbent material using solar or other external means.
One type of adsorption material capable of adsorbing water vapour is Metal-Organic Frameworks (MOFs). A number of MOFs are known that are able to adsorb moisture. These known MOF adsorbents physisorb water onto the surfaces within the pores of the MOF.
Although MOFs have already been considered in numerous applications, including gas storage, separation, and dehumidification, the use of MOFs for water capturing has only recently been proposed.
One example of MOF based water capturing is taught in Yaghi et al. “Water harvesting from air with metal-organic frameworks powered by natural sunlight.” Science 356.6336 (2017): 430-434 (Yaghi 1), and in a subsequent publication (which provides further details of the system) Yaghi et al. “Adsorption-based atmospheric water harvesting device for arid climates.” Nature communications 9.1 (2018): 1191 (Yaghi 2). The system described in both papers utilised a porous metal-organic framework (microcrystalline powder MOF-801, [Zr6O4(OH)4(fumarate)6]) to capture water by vapour adsorption in ambient air with low Relative Humidity (RH) (down to RH of 20% at 35° C.). The MOF-801 powder was infiltrated into a porous copper foam brazed on a copper substrate, to create an adsorbent layer with 1.79 g of activated MOF-801 with an average packing porosity of  ̃0.85. The copper foam geometry was selected to have a high substrate area to thickness ratio to reduce parasitic heat loss. Water was released from the MOF using a non-concentrated solar flux below 1 sun (1 kW m−2), requiring no additional power input for producing water at ambient temperature outdoors. In Yaghi 1, condensation was driven using a condenser interfaced with a thermoelectric cooler (using the cooling side of the thermoelectric “peltier” device only) to maintain the isobaric conditions of  ̃1.2 kPa (20% RH at 35° C., saturation temperature of  ̃10° C.) in order to condense all of the water in the desorbed vapour. This thermoelectric cooler appears to have not been utilised in Yaghi 2. The device was reported in Yaghi 2 to capture and deliver water at 0.25 L kg/MOF/day at 20% RH and 35° C. It is noted that Yaghi 2 appears to provide corrected water production results over those published in Yaghi 1.
Despite the promising results taught in Yaghi 1 and Yaghi 2, the use of MOF infiltrated into a conductive substrate can still have a low energy conversion efficiency, particularly in the desorption phase using direct solar heating, thereby limiting the amount of possible water production using this system. For example, Yaghi 2 reports energy efficiencies reaching 60% at the gram scale. Significant thermal loss in this system is to be expected due to the energy required to heat the thermal mass of the copper foam substrate.
The limitations of Yaghi 1 and Yaghi 2 demonstrate that there are still opportunities to refine selection and further optimise the use of MOF adsorbents to capture atmospheric water. It would therefore be desirable to provide an improved or alternate water capture method and system which utilises MOFs to adsorb and thus capture water from a water containing gas such as atmospheric air.
SUMMARY OF THE INVENTION
The present invention provides an improved and/or alternate MOF based adsorption apparatus for capturing water from a water containing gas, such as air, for both commercial and domestic applications.
Water Harvesting Apparatus
A first aspect of the present invention provides an apparatus for capturing a water content from a water containing gas. The apparatus comprises:
a housing having an inlet into which the water containing gas (having a water content) can flow;
a water adsorbent enclosed within the housing (i.e. located inside the housing), the water adsorbent comprising at least one water adsorbent metal organic framework composite capable of adsorbing a water content from the water containing gas, the metal organic framework composite comprising: at least 50 wt % water adsorbent metal organic framework; and at least 0.1 wt % hydrophilic binder comprising a hydrophilic cellulose derivative; and
a water desorption arrangement in contact with and/or surrounding the water adsorbent, the water desorption arrangement being 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 water adsorbent to desorb a water content from the water adsorbent.
The present invention provides an apparatus capable of harvesting water from a water containing gas, for example ambient air, which includes a MOF based composite water adsorbent that can be used to adsorb a water content when the water desorption arrangement is in a deactivated state and then selectively operated to desorb water from the water adsorbent by activating the water desorption arrangement (operating it in the activated state). It should be understood that “selectively operable” means that a user is able to actively change the condition of the water desorption arrangement from between the deactivated state and activated state, for example switch or trigger that change of state. This active change may be through the supply of a driving force, for example electricity to power a heater, vacuum to reduce pressure or the like to the water desorption arrangement to switch/operate the device in the activated state. Removal of the driving force would change the water desorption arrangement to the deactivated state.
The apparatus is therefore configured to enable selective operation and control of the adsorbing and desorbing phases of a water harvesting cycle of the water adsorbent. This selective operation advantageously enables the optimisation of the efficiency of water desorption arrangement through the use of more efficient water desorption arrangements to desorb water from the metal organic framework based water adsorbent compared for example to utilising solar energy. In some embodiments, this selective operation can also achieve simultaneous condensation of the water content of any product gas flow which includes the desorbed water entrained or otherwise contained in that flow.
The water desorption arrangement can take any number of forms depending on whether heat and/or reduced pressure is being used to cause the adsorbed water to desorb from the water adsorbent. 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 water adsorbent. Adsorption would typically be undertaken at near atmospheric pressure. In other embodiments, temperature swing adsorption is undertaken to achieve water harvesting. This can be achieved using direct heating methods, or in some cases using magnetic induction swing adsorption.
It should be appreciated that the capture of water from a water containing gas refers to separating, stripping or otherwise removing a water content from that water containing gas. The water containing gas can comprise any gas that has a water content, for example air (particularly atmospheric air), nitrogen laden with water, oxygen laden with water or the like.
It should also be appreciated that the water containing gas can comprise any number of gases, such as nitrogen, oxygen or the like. In embodiments, the water containing gas comprises air, preferably atmospheric air, more preferably ambient air. It is to be understood that ambient air is atmospheric air located in a particular location and a given environment. It is to be understood that the term “ambient air” is intended exclude air that has been subjected to processing for example compressed air, degassed air (such as air degassed of water vapour), filtered air or the like. The apparatus can therefore be used to separate and capture water content from atmospheric air and thereby capture water.
Where atmospheric air is used, the relative humidity of the atmospheric air is preferably between 25 to 100% at 22° C., preferably between 40 to 100% at 22° C., more preferably between 40 to 80% at 22° C. In embodiments, the relative humidity of the atmospheric air is between 40 to 60% at 22° C., and preferably about 50% at 22° C.
The housing of the water apparatus can comprise any suitable container or enclosure having an inlet. The housing typically also includes an outlet through which an exit gas can flow. The exit gas typically has a lower water content than the feed water containing gas, as a water content is adsorbed by the water adsorbent.
The apparatus may also include one or more doors or other sealing arrangements which fit over or otherwise close the inlet and any outlet to enable the housing to form a closed environment (or at least a gas closed environment), and thus enhance desorption and condensation. Any number of sealing doors or sealable opening arrangements may be used. In some embodiments, the inlet and outlet include at least one fluid seal movable from an open position to allow gas to flow through the inlet and outlet, and a closed position where the inlet and outlet are substantially sealed closed to gas flow. The fluid seal can comprise at least one movable door, preferably a least one pivotable plate or flap, more preferably at least one louver.
Temperature Swing Water Harvesting
Temperature swing adsorption water harvesting is achieved in some embodiments using direct conductive heat transfer between a heat source and the water adsorbent. In these embodiments the water desorption arrangement includes at least one heat transfer arrangement in direct thermal conductive contact with the water adsorbent. The heat transfer arrangement is also preferably in thermal conductive contact with a heating device. The heat transfer arrangement typically includes one or more heat transfer elements that provide conductive heat transfer from the heating device to the water adsorbent. In some embodiments, the heat transfer arrangement includes at least one heat transfer element that extends from the heating device to the water adsorbent. That heat transfer element may comprise at least one elongate rod, pipe, rib or fin.
A number of suitable heating devices are available. In exemplary embodiments, the heating device comprises at least one peltier device. It should be appreciated that a peltier device is also known as a peltier heat pump, solid state refrigerator, thermoelectric heat pump, thermoelectric heater or thermoelectric cooler. The present specification will use the term “peltier device” to describe this element of the apparatus. However, it should be understood that each of these alternative terms could be equally used interchangeably to describe this element of the apparatus.
The peltier device is generally selected to be suitable to provide sufficient energy to desorb water from the shaped water adsorbent composite bodies. The peltier device is therefore selected to have a maximal heat flow of at least 50 W, preferably at least 75 W, more preferably at least 100 W, and yet more preferably at least 110 W. The peltier device is preferably selected to be able to heat the packed bed to at least 50° C., preferably at least 60° C., more preferably to at least 65° C., and yet more preferably to at least 70° C. In some embodiments, peltier device is selected to be able to heat the packed bed to between 50 and 90° C., preferably between 50 and 80° C., and more preferably between 60 and 80° C. In some embodiments, peltier device is selected to be able to heat the packed bed to between 65 and 85° C., preferably between 70 and 80° C., and more preferably around 75° C.
The apparatus can also further comprise at least one heat transfer arrangement in thermal communication with the peltier device in order to best utilise the heated side of the peltier device. The water adsorbent is located in contact with the heat transfer arrangement, for example being housed within or coated on at least part or the heat transfer arrangement.
The heat transfer arrangement can have any number of forms, including a variety of heat exchanger configurations. In a number of embodiments the heat transfer arrangement comprises a heat sink (i.e. a conductive heat transfer arrangement), preferably a heat sink having a plate or fin arrangement. In some embodiments, the heat sink arrangement comprises a plurality of spaced apart heat transfer elements. The heat transfer elements typically comprise a planar support element, preferably selected from at least one of plates or fins
The shaped water adsorbent composite bodies can be located around, within or in any number of other configurations in contact with the heat transfer arrangement. In preferred embodiments, the shaped water adsorbent composite bodies are located within the heat transfer arrangement. In this arrangement, the water adsorbent is housed or fitted as a packed bed between at least two heat transfer elements. The water adsorbent is packed into at least some, preferably all of the free volume of the heat transfer arrangement.
Adsorption and desorption from the shaped water adsorbent composite bodies can be enhanced by driving fluid flow through and over the water adsorbent. In some embodiments, the apparatus further includes at least one fluid displacement device to drive fluid flow through the packed bed. The fluid displacement device preferably comprises at least one fan. Flow can be driven through the packed bed at a number of flow rates. In order to optimise water adsorption and desorption, the fluid displacement device preferably creates a fluid flow of at least 3 m3/hr, preferably 3 to 300 m3/hr, and more preferably 3 m3/hr to 150 m3/hr through the packed bed. It should be appreciated that the amount of air required to flow through the packed bed depends on the moisture level in the water containing gas and the efficacy of capture.
The apparatus may also include a condenser system for cooling the product gas flow from the water adsorbent. In some embodiments, the condenser system comprises a cooling device, preferably a cooling trap. In the embodiments that include a peltier device, the peltier device can also form part of the condenser system. Here each peltier device has a hot side and a cold side, with the hot side of each peltier device being in thermal communication with at least one heat sink, and the cold side of each peltier device forming part of the condenser system.
The cold side of each peltier device can also be in thermal communication with at least one heat transfer arrangement, preferably at least one heat sink in embodiments. The heat transfer arrangement provides further surface area to contact the product gas flow to assist condensation of the water content therein.
Metal Organic Framework Composite
The metal organic framework composite can be provided in the apparatus in any suitable form. The inventors envisage that this may be in any number of formulations and forms including shaped bodies (for example pellets or extrusions), coatings, plates, sheets, strips or the like.
The water adsorbent is a metal organic framework composite comprising:
at least 50 wt % water adsorbent metal organic framework; and
at least 0.1 wt % hydrophilic binder.
That metal organic framework composite may take various forms depending on the desired application, apparatus configuration and adsorption requirements. For example, the metal organic framework composite may comprises a coating applied to the surface of the water desorption arrangement. In other embodiments, the metal organic framework composite comprises shaped water adsorbent composite body.
In one particular form, the metal organic framework composite comprises shaped water adsorbent composite body having at least one mean dimension of greater than 0.5 mm. This shaped water adsorbent composite body is formed from a mixture of a water adsorbent metal organic framework and a hydrophilic binder that is preferably optimised for use in a packed bed adsorption system. The combination of the water absorbent metal organic framework and hydrophilic binder have a surprising synergistic effect, facilitating greater water adsorption compared to the use of other types of binders, for example hydrophobic binders.
For atmospheric water harvesting/capture applications, the inventors have found that three-dimensional shaped bodies with the defined composition have excellent water adsorption properties, and suitable water adsorption kinetics, even at low H2O partial pressures. The inventive shaped water adsorbent composite body also has useful breakthrough test properties for water capture from a water containing gas (water vapour capture), and has been found to have suitable stability when consolidated, shaped and heated.
Ideally, the shaped water adsorbent composite body should have a good enough affinity for water to adsorb the water, but not have too high affinity for water that excessive energy needs to be expended to desorb water therefrom. Preferably, the heat of adsorption for water and adsorbent range from 10 to 100 kJ/mol MOF for water adsorbed in and/or on the shaped water adsorbent composite body.
Optimising the composition of a shaped water adsorbent composite body involves a number considerations, including:

    1. Water stability—the components, and in particular the MOF should be water stable.
    2. Adsorption reproducibility, the shaped water adsorbent composite body should retain adsorption capacity after multiple adsorption/desorption cycles, preferably at least 10 cycles, more preferably at least 100 cycles.
    3. Ease of production, the shaped water adsorbent composite body and components thereof should be easy to produce from readily available precursor materials.
    4. High water uptake from air even at low humidity values.
    5. A good affinity for water. The MOF component of the composite body should have a good enough affinity for water to enable the MOF to adsorb the water, but not have too high affinity for water that excessive energy needs to be expended to desorb water therefrom. Here the thermodynamics of water adsorption and desorption need consideration to ensure the MOF does not require excessive energy (kJ/mol MOF) to desorb water therefrom, and thereby adversely affect the energy efficiency of the system.


The MOF and other component materials must also meet food for human consumption regulations in relevant countries where the shaped water adsorbent composite body is required for water production for human consumption.
The shaped water adsorbent composite body preferably has a high adsorption of water from a water containing gas such as air even at low humility levels. In embodiments, the shaped water adsorbent composite body is able to adsorb a water content from a water containing gas, preferably air, having a humidity of greater than 20% at 20° C., preferably from 20 to 100% at 20° C., preferably from 20 to 80% at 20° C., and more preferably from 25 to 60% at 22° C. In embodiments, the humidity of the water containing gas is between 25 to 100% at 22° C., preferably between 40 to 100% at 22° C., preferably between 40 to 80% at 22° C., preferably between 40 to 60% at 22° C., and more preferably about 50% at 22° C. In embodiments, the humidity of the water containing gas is between 20 to 100% at 35° C., preferably between 20 to 80% at 35° C., preferably between 20 to 60% at 35° C., and more preferably about 30% at 22° C.
The shaped water adsorbent composite body preferably has an average surface area of at least 700 m2/g, and preferably greater than 800 m2/g.
The shaped water adsorbent composite body is preferably configured with dimensions that are suitable for use in a packed bed adsorption system, in which a plurality of the shaped bodies are packed at a high packing density 0.10 to 1.0 kg/L, preferably 0.25 to 0.5 kg/L, more preferably between 0.25 and 0.35 kg/L, and yet more preferably about 0.29 kg/L between two support surfaces. The dimensions of the shaped water adsorbent composite body can be optimised to suit this application. For use in a packed bed, the shaped water adsorbent composite body has at least one mean dimension of greater than 0.5 mm. This ensures that the adsorbent composite body has sufficient size to allow gas flow around. For example, fine powder (e.g. having an average particle size of less than 10 micron) typically provides too dense a particle packing for use in a packed bed adsorption system. In some embodiments, the shaped water adsorbent composite body has at least one mean dimension of greater than 0.8 mm, preferably at least 1 mm, preferably at least 1.2 mm, and yet more preferably at least 1.5 mm. In embodiments, each of the mean width, mean depth and mean height of the shaped water adsorbent composite body are greater than 0.5 mm, and preferably greater than 1 mm.
It should be appreciated that “mean dimension” refers to the mean (average) dimension of at least one of the width, depth or height of the shaped water adsorbent composite body. Accordingly, at least one of the mean width, mean depth or mean height must be greater than the specified dimensional value.
The shaped water adsorbent composite body can have any suitable geometry. The shape of the composite bodies has an impact on the pressure drop of local fluid flow (in the vicinity of the bodies), and therefore, the performance of any packed bed adsorption system. For example, the shaped water adsorbent composite body could comprise pellets (for example, disk-shaped pellets), pills, spheres, granules, extrudates (for example rod extrudates), honeycombs, meshes or hollow bodies. In embodiments, the shaped water adsorbent composite body is formed as a three dimensional body, preferably three dimensionally shaped. In particular embodiments, the shaped water adsorbent composite body comprises an elongate body having a circular or regular polygonal cross-sectional shape. For example, the shaped water adsorbent composite body may have a square or triangular cross-sectional shape. In an exemplary form, the shaped water adsorbent composite body comprises an elongate body having a triangular cross-sectional shape, preferably equilateral triangle cross-sectional shape. In one form, the shaped water adsorbent composite body has equilateral triangle cross-section, preferably the sides of the equilateral triangle are at least 1 mm in length, preferably between 1.0 and 1.5 mm in length. The elongate shaped water adsorbent composite body is preferably from 1 to 5 mm in length (longitudinal length), more preferably 1 to 4 mm in length.
Metal-Organic Frameworks
Metal-organic frameworks (MOFs) comprise the major adsorbent constituent of the shaped water adsorbent composite body. MOFs are a crystalline nanoadsorbent with exceptional porosity. MOFs consist of metal atoms or clusters linked periodically by organic molecules to establish an array where each atom forms part of an internal surface. MOFs as a physisorbent achieve strong adsorption characteristics through the internal surfaces of the MOF porous structure. The strength of this interaction depends on the makeup of the adsorbent surface of the MOF to capture H2O molecules. Advantageously, the surface chemistry and structure of MOFs can be tuned for a specific application, where performance criteria such as adsorption/desorption rate, capacity as a function of pressure, and operating temperature may be of particular importance.
The shaped water adsorbent composite body utilises the selectivity of the MOF to adsorb water rather than other components in the air, such as oxygen and nitrogen. That is, capturing of water from a water containing gas (such as air) using a MOF adsorbent. For this functionality, the shaped water adsorbent composite body comprises at least 50 wt % water adsorbent MOF, preferably at least 70 wt % water adsorbent MOF, more preferably at least 80 wt % water adsorbent MOF, yet more preferably at least 85 wt % water adsorbent MOF and yet more preferably at least 90 wt % water adsorbent MOF.
It should be appreciated that “water adsorbent metal organic framework” means a water stable metal organic framework that has a good affinity for water, adsorbing water even at low humidity values. Preferably, the heat of adsorption for water ranges from 10 to 100 kJ/mol MOF for water adsorbed on the MOF. Ideally, a water adsorbent MOF should have a good enough affinity for water to enable the MOF to adsorb the water, but not have too high affinity for water that excessive energy needs to be expended to desorb water therefrom. Here the thermodynamics of water adsorption and desorption need consideration to ensure the MOF does not require excessive energy (kJ/mol MOF) to desorb water therefrom, and thereby adversely affect the energy efficiency of the system.
Any suitable water adsorbent metal organic framework can be used. In some embodiments, the water adsorbent metal organic framework comprises at least one of aluminium fumarate (AlFu), MOF-801, MOF-841, M2Cl2BTDD including Co2Cl2BTDD, Cr-soc-MOF-1, MIL-101(Cr), CAU-10, alkali metal (Li+, Na+) doped MIL-101(Cr), MOF-303 (Al), MOF-573, MOF-802, MOF-805, MOF-806, MOF-808, MOF-812, or mixtures thereof. In embodiments, the water adsorbent metal organic frameworks are preferably selected from aluminium fumarate, MOF-303, MOF-801, MOF-841, M2Cl2BTDD, Cr-soc-MOF-1, or MIL-101(Cr).
In particular embodiments, the water adsorbent metal organic framework includes a plurality of multidentate ligands of which at least one ligand is from selected from fumarate (fumaric acid) or 3,5-pyrazoledicarboxylic add (H3PDC) based ligands. In some embodiment, the metal ion is selected from Fe3+, Li+, Na+, Ca2+, Zn2+, Zr4+, Al3+, K+, Mg2+, Ti4+, Cu2+, Mn2+ to Mn7+, Ag+, or a combination thereof. In preferred embodiments, the metal ion is selected from Zr4, Al3+ or combinations thereof. Examples include MOF-303, [Al(OH)(C5H2O4N2)(H2O)] and MOF-573 [Al(OH)(C5H2O4N2)(H2O)] constructed by linking aluminium (III) ions and 3,5-pyrazoledicarboxylic add and AlFu.
In particular embodiments, the water adsorbent metal organic framework comprises a porous aluminium-based metal-organic framework (MOF) comprising inorganic aluminium chains linked via carboxylate groups of 1H-pyrazole-3,5-dicarboxylate (HPDC) linkers, and of formula: [Al(OH)(C5H2O4N2)(H2O)], wherein: each Al (III) ion is capped by four O atoms from four different carboxylate groups and two O atoms from two hydroxyl groups forming AlO6 octahedra, and the AlO6 octahedra form corner-sharing chains, depending on the cis- and trans-position of the two adjacent bridging hydroxyl groups, helical chains in MOF-303 (cis-) and MOF-573 (trans-) form respectively.
In embodiments, the MOF is MOF-303, wherein: the linkers further bridge two of the chains together, leading to the formation of a 3D framework delimiting square-shaped one dimensional channels with diameter of 6 Å in diameter (measured by the largest fitting sphere); the MOF-303 has a topology of xhh; and/or the MOF has permanent porosity and a Brunauer-Emmett-Teller (BET) surface area of 1380 and pore volume of 0.55 cm3 g−1.
In embodiments, the MOF is MOF-573, wherein: the linkers further bridge two of the chains together, leading to the formation of a 3D framework delimiting square-shaped one dimensional channels with diameter of 5 Å in diameter (measured by the largest fitting sphere); the MOF has a topology of upt; and/or the MOF has permanent porosity and a Brunauer-Emmett-Teller (BET) surface area of 980 m2 g−1 and pore volume of 0.56 cm3 g−1.
Water production for human consumption requires the use of materials that meet food for human consumption regulations in the relevant countries. Therefore in an exemplary embodiment, the water adsorbent MOF comprises aluminium fumarate (AlFu) MOF. Applicant notes that the advantage of using AlFu is that it is the MOF is cheap and easy to make.
The water adsorbent metal organic framework should preferably embody a number of properties to maximise the functionality of the shaped water adsorbent composite body. For example, the water adsorbent metal organic framework preferably has an average surface area of at least 700 m2/g, and preferably greater than 800 m2/g. The water adsorbent metal organic framework also preferably has a pore size of at least 2 nm, preferably greater than 5 nm. The pore size should be sufficient to at least fit a water molecule therein.
In the present invention, the water adsorbent MOF is provided as a pulverulent material preferably a powder or particulates. In embodiments, the water adsorbent metal organic framework has a particle size of less than 800 μm, preferably less than 600 μm, and more preferably less than 500 μm. In particular embodiments, the water adsorbent MOF powder has a particle size of less than 500 μm, preferably less than 300 μm, more preferably less than 212 μm, yet more preferably less than 150 μm, and in some embodiments less than 88 μm. It should be appreciated that particle size is typically measured in terms of mesh size through which the particles are sieved. Therefore in embodiments, the water adsorbent MOF powder has a particle size of less than 60 mesh (250 μm), preferably less than 100 mesh (149 μm), preferably less than 140 mesh (105 μm), and more preferably less than 170 mesh (88 μm). The water adsorbent MOF powder preferably also has a mean particle size of between 10 and 100 μm, more preferably between 20 and 80 μm. In other embodiments, the water adsorbent MOF powder has a mean particle size of between 10 and 80 μm, and preferably between 20 and 60 μm.
Hydrophilic Binder
A water adsorbent MOF powder mixture is not ideal if used in a packed bed adsorption system. Powder alone packs too densely and therefore has too great of pressure drop across the adsorption unit. Therefore powder alone cannot be used. The inventors have found that the water adsorbent MOF should be shaped prior to packing into a packed bed water adsorbent system to form a shaped water adsorbent composite body, for example a pellet, for use in a packed bed adsorption system.
The shaping process is facilitated through the use of a binder. Whilst it may be possible to form a shaped composite body without the use of a binder, shaped composite bodies that include binders in their composition tend to have greater structural strength and stability when used in a packed bed water adsorbent system. A shaped composite body such as a pellet therefore facilitates continuous operation of a packed bed adsorption system.
The inventors have surprisingly found that a hydrophilic binder must be used to impart optimal water adsorption properties to the shaped water adsorbent composite bodies. The inventors have found that non-hydrophilic binders, in particular hydrophobic binders (for example cellulose siloxane), deliriously affect the water adsorption properties of the shaped water adsorbent composite bodies. The use of a hydrophilic binder is therefore important for optimal moisture capture properties of the packed bed water adsorption system.
A variety of hydrophilic cellulose derivative binders may be used in the shaped water adsorption body. The hydrophilic binder can be organic or inorganic, and should not block the pores of the water adsorbent MOF. The hydrophilic binder comprises a hydrophilic cellulose derivative, preferably alkyl cellulose, hydroxyalkyl cellulose, or carboxyalkyl cellulose derivatives. Particularly suitable hydrophilic binders can be selected from at least one of hydroxypropyl cellulose (HPC), hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose (HPMC), ethyl hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose (CMC). However, it should be appreciated that other binders are also possible. In preferred embodiments the hydrophilic binder comprises hydroxypropyl cellulose (HPC). It should be appreciated that the additives depend on the application in which the shaped bodies are being used. Where water is being produced for human consumption the binder(s) preferably comprise an approved excipient for human consumption. Examples of approved excipients for human consumption include approved excipients for food or pharmaceuticals. Approved food grade or pharmaceutical grade binders are preferred.
The shaped water adsorbent composite body includes at least 0.1 wt % hydrophilic binder, and preferably at least 0.2 wt % hydrophilic binder. In embodiments, the shaped water adsorbent composite body includes between 0.2 and 5 wt % hydrophilic binder. In some embodiments, the shaped water adsorbent composite body can comprise between 0.5 and 3 wt % hydrophilic binder, more preferably between 0.8 and 2 wt % hydrophilic binder, and yet more preferably about 1 wt % hydrophilic binder. 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 water adsorbent MOF.
Lubricants
The shaped water adsorbent composite body preferably comprises less than 0.5 wt % lubricant, preferably less than 0.1 wt % lubricant. Suitable lubricants include surfactants and their salts. Examples of suitable lubricants include magnesium stearate, aluminium oxide, sodium oleate, glycerides, di-glycerides, tri-glycerides, fatty acids, oils including silicon oils and mineral oils and mixtures thereof. It should be appreciated that the additives depend on the application in which the shaped bodies are being used. Where water is being captured and produced for human consumption the lubricants preferably comprise an approved excipient for human consumption. Examples of approved excipients for human consumption include approved excipients for food or pharmaceuticals. Approved food grade or pharmaceutical grade lubricants are preferred. As discussed below, one or more lubricant is added to the mixture to assist with shaping and forming processes when making the shaped water adsorbent composite body.
Packed Bed Adsorption Apparatus
In some embodiments, the apparatus comprises a packed bed adsorption system that includes shaped composite MOF bodies as discussed above. In such embodiments, the water adsorbent is a metal organic framework composite comprising: at least 50 wt % water adsorbent metal organic framework; and at least 0.1 wt % hydrophilic binder and has at least one mean dimension of greater than 0.5 mm. In this aspect, the shaped bodies are collected in a packed bed that is enclosed in the housing. The housing is preferably a fluid tight housing.
The housing preferably includes two spaced apart support membranes configured to allow gas flow therethrough each membrane. The plurality of said shaped water adsorbent composite bodies form a packed bed therebetween and being compressed therebetween. In embodiments, the shaped water adsorbent composite bodies are packed at a density from 0.10 to 1.0 kg/L, preferably 0.25 to 0.5 kg/L, and more preferably between 0.25 and 0.35 kg/L. In some embodiments, the shaped water adsorbent composite bodies are packed at a density of about 0.25 kg/L. In other embodiments, the shaped water adsorbent composite bodies are packed at a density of about 0.29 kg/L. As with any packed bed, it is important that the adsorbent is packed tightly and substantially uniformly throughout the packed bed volume to avoid short circuiting of any adsorbent in that packed bed. Any flow that is able to avoid or follow a shorter/short circuit route through the packed bed will avoid having water removed from that stream. Short circuit flow would adversely affect the energy efficiency and water production rate of the system. Tight and uniform packing also ensures uniform path lengths to optimise adsorption performance.
The apparatus may use a low or reduced pressure (sometimes referred to as a vacuum environment) to direct the released water to the condenser. In embodiments, the pressure is less than 100 mbar, preferably less than 50 mbar, more preferably less than 35 mbar. In other embodiments, the pressure is less than 500 mbar. In other embodiments, the released water is entrained in a gas flow, for example a flow of the water containing gas or another gas such as an inert or other dry gas, and directed to the condenser.
The flow rate of the water containing gas can also be varied to optimise the water adsorption of the packed bed of shaped water adsorbent composite bodies. In embodiments, the water containing gas is fed through the packed bed of shaped water adsorbent composite bodies at as fast a flow rate that is possible for the apparatus whilst the water adsorbent MOF is still adsorbing water from the water containing gas. It should be appreciated that the particular flow rate is dependent on the water content of the water containing gas, as this determines the mass of water a particular volume of gas will contain. The water content of the water containing gas is dependent on the relative humidity of that containing gas as well as the temperature and pressure. Where the apparatus is fed ambient air, a higher flowrate will be required for lower humidity air as compared to higher humidity air at the same temperature to maintain a desired cycle time.
The source of humid air used can be a very low relative humidity, mimicking the humidity levels found on the driest places on Earth. In embodiments, the humidity of the air is greater than 20% at 20° C., preferably from 20 to 100% at 20° C., preferably from 20 to 80% at 20° C., and more preferably from 25 to 60% at 22° C. In embodiments, the humidity of the air is between 40 to 100% at 22° C., preferably between 40 to 100% at 22° C., preferably between 40 to 80% at 22° C., preferably between 40 to 60% at 22° C., and more preferably about 50% at 22° C. In embodiments, the humidity of the air is between 20 to 100% at 35° C., preferably between 20 to 80% at 35° C., preferably between 20 to 60% at 35° C., and more preferably about 30% at 22° C.
The packed bed adsorption system can be configured for magnetic induction swing water harvesting (adsorption-desorption cycling). Here, the water adsorbent is a Magnetic Framework Composite comprising a mixture of at least 50 wt % water adsorbent metal organic framework and from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm, and the water desorption arrangement comprises an alternating current (AC) magnetic field generator located within and/or around the water adsorbent configured to apply an AC magnetic field to the water adsorbent. The water adsorbent preferably comprises shaped water adsorbent composite bodies located in a packed bed in the housing. The shaped water adsorbent composite bodies are preferably packed at a density from 0.10 to 1.0 kg/L, preferably 0.25 to 0.5 kg/L, and more preferably between 0.25 and 0.35 kg/L.
The AC magnetic field generator preferably comprises at least one induction coil located within and/or around the packed bed of shaped water adsorbent composite bodies. The alternating current magnetic field generator is designed to irradiate the packed bed of shaped water adsorbent composite bodies with an AC magnetic field to release adsorbed water from the packed bed of shaped water adsorbent composite bodies when activated.
Magnetic Particles
Where inductive heat generation is desired to use for water desorption, the shaped water adsorbent composite body may include magnetic particles. In these embodiments the shaped water adsorbent composite body contains from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm. In some embodiments, the shaped water adsorbent composite body may comprises between 0.5 and 7 wt % magnetic particles, and in some embodiments between 1 to 5 wt % magnetic particles.
The use of this composite material combines the exceptional adsorption performance of MOFs and enables the use of high efficiency of magnetic induction heating to desorb water from the MOF. The shaped water adsorbent composite body is formed of a magnetic framework composite (MFCs), a composite material which combines magnetic particles with MOF crystals. The incorporation of magnetic particles (typically micro- or nano-sized magnetic particles) with MOFs allows the generation of heat on exposure to an alternating current (AC) magnetic field. MFCs can therefore be regenerated using an AC magnetic field, as a result of generating heat within the composite material, and which in return releases the adsorbed fluid from the pores of the MOF part of the MFC.
This process uses the heat generated as a result of static hysteresis and dynamic core losses of ferro/ferrimagnetic particles induced by an external AC magnetic field. The generation of heat via induction heating occurs remotely, and resultant heat is targeted, making the heating process isolated and thus energy efficient.
The magnetic properties of the magnetic framework composites are provided by the magnetic particles mixed within the composite. As outlined above, the magnetic particles can be utilised to generate heat on exposure to an alternating current (AC) magnetic field, and thereby can be used to conduct magnetic induction swing adsorption process for water adsorbed on the water adsorbent MOF.
The amount of magnetic particles is selected to provide a desired heat generation profile and magnitude on the application an AC magnetic field. Typically, the amount of magnetic particles in the shaped water adsorbent composite body is between 0.2 and 10 wt %. In embodiments, the shaped water adsorbent composite body may comprise between 0.5 and 7 wt % magnetic particles, and preferably between 1 to 5 wt % magnetic particles.
A wide variety of magnetic particles can be used in the inventive shaped adsorption body. In embodiments, the magnetic particles comprise ferromagnetic, paramagnetic, or superparamagnetic particles. In embodiments, the magnetic particles comprise metal chalcogenides. Suitable metal chalcogenides comprise magnetic particles comprising any combination of element or ionic form thereof of M selected from at least one of Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, TI, Si, Ge, Sn, Pb, As, Sb, Bi, or their combinations, in combination with elements or elemental form of at least one of O, S, Se, or Te. In some embodiments, the metal chalcogenide have the formula MxNyCz, where M and N are selected from at least one of Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, TI, Si, Ge, Sn, Pb, As, Sb, Bi, C is selected from at least one of O, S, Se, Te, x is any number from 0 to 10, y is any number from 0 to 10 and z is any number from 0 to 10. The metal chalcogenide particles may in some embodiments have a core-shell structure in which the core comprises at least one metal chalcogenide as previously described and the shell comprises at least one metal chalcogenide as previously described. In some forms, the core-shell structure may include multiple shells. In embodiments, the magnetic particles comprise at least one of MgFe2O4, Fe3O4, CoFe2O4, NiFe2O4, Pyridine-2,6-diamine-functionalized SiO2, Pyridine-2,6-diamine-functionalized Fe3O4, or C-coated Co.
The magnetic particles can comprise any number of shapes and configurations. In embodiments, the magnetic particles comprise particles having irregular shapes. In some embodiments, the magnetic particles comprise particles having regular three-dimensional shapes, for example spherical, platelet, rod, cylindrical, ovoidal or the like. In some embodiments, the magnetic particles comprise a plurality of magnetic nanospheres. The size of the magnetic particles is typically selected for the desired packed bed application and configuration. Generally, the magnetic particles comprise nano- or micro-particles. The magnetic particles have a mean particle diameter of less than 200 nm, preferably less than 150 nm, more preferably between 1 to 100 nm. In some embodiments the magnetic particles have a mean particle diameter of less than 50 nm. In some embodiments the magnetic particles have a mean particle diameter of between 1 and 200 nm, preferably between 5 and 100 nm, more preferably between 5 to 30 nm, and yet more preferably between 5 to 30 nm. In some embodiments, the magnetic particles have a mean particle diameter of around 20 nm. It is noted that the magnetic particles need to be large enough to not foul the pores of the water adsorbent MOF.
The combination of the magnetic particles with MOFs to form a magnetic framework composite material yields an adsorbent with exceptional adsorption behaviour as a result of the MOFs and high efficiency of induction heating as a result of the magnetic particles.
Method of Capturing Water Content from a Water Containing Gas
A second aspect of the present invention provides a method of capturing a water content from a water containing gas, comprising at least one cycle of:
feeding a water containing gas through the inlet of a housing and over a water adsorbent enclosed within the housing such that the water adsorbent adsorbs water from the water containing gas, the water adsorbent comprising at least one water adsorbent metal organic framework composite capable of adsorbing a water content from the water containing gas such that the water adsorbent adsorbs water from the water containing gas, the metal organic framework composite comprising: at least 50 wt % water adsorbent metal organic framework; and at least 0.1 wt % hydrophilic binder comprising a hydrophilic cellulose derivative,
operating at least one water desorption arrangement to change from an inactive state to an activated state to apply heat, a reduced pressure or a combination thereof to the water adsorbent so to release at least a portion of the adsorbed water therefrom into a product fluid flow, and
directing the product fluid flow to a condenser system to separate a water content from the product fluid flow,
wherein the water desorption arrangement is in contact with and/or surrounding the water adsorbent.
The second aspect of the present invention also provides a method of capturing a water content from a water containing gas using the apparatus according to the first aspect of the present invention. The method comprises at least one cycle of:
feeding a water containing gas through the inlet of the housing and over the water adsorbent such that the water adsorbent adsorbs water from the water containing gas, the water desorption arrangement being in the deactivated stated;
operating the at least one water desorption arrangement in the activated state to apply heat, a reduced pressure or a combination thereof to the water adsorbent so to release at least a portion of the adsorbed water therefrom into a product fluid flow; and
directing the product fluid flow to a condenser system to separate a water content from the product fluid flow.
In this aspect of the present invention a moisturized gas stream is fed over the water adsorbent. After the absorbent is charged with water vapour, the water desorption arrangement is activated to heat, a reduced pressure or a combination. Consequently, the water adsorbent is driven to release at least part of the adsorbed water content. The desorbed water can be condensed in a condenser system, for example in a cold trap.
It should be appreciated that the apparatus and features thereof used in the method of this second aspect of the present invention can also include the features previously taught in relation to the first aspect.
The method preferably further comprises the step of: closing the inlet and outlet of the housing prior to operating the at least one water desorption arrangement. This creates a closed gas sealed environment in the housing allowing capture of the water content therein. The relative humidity inside the housing increases to high values, and water condenses in the condenser system for collection.
It is to be understood that this method is a cyclical method, where the steps of adsorbing water in the water adsorbent, releasing that adsorbed water through operation of the water desorption arrangement and condensing that water is conducted in a repetitive cycle so to continuously produce water. The cycle time typically depends on configuration of the water adsorbent and the adsorption system, the amount of water adsorbent MOF, breakthrough point, saturation point, temperature, pressure and other process conditions. In some embodiments, one cycle of the method has a duration of less than 10 hours, preferably less than 8 hours, more preferably less than 7 hours, and more preferably 6 hours or less. In other embodiments, the cycle time of this method steps are approximately 30 minutes in duration. However, other cycle times between 10 minutes to 10 hours could be possible depending on the configuration of the apparatus.
As noted above, the apparatus of the present invention can be configured for temperature swing water harvesting (adsorption-desorption cycling). In these systems, a heat source is required to heat the packed bed of shaped water adsorbent composite bodies. In some embodiments, operating the at least one water desorption arrangement comprises operating at least one peltier device to heat water adsorbent so to release at least a portion of the adsorbed water therefrom into the product fluid flow. The at least one peltier device may also form part of the condenser system configured to cool the product fluid flow. This arrangement advantageously utilises both the heated and cooled side of the used peltier device or devices.
In other embodiments the apparatus of the present invention can be configured for magnetic induction swing water harvesting. Here, the step of operating the at least one water desorption arrangement comprises applying an alternating current magnetic field to a packed bed of shaped water adsorbent composite bodies, thereby generating heat within the shaped water adsorbent composite bodies, so to release at least a portion of the adsorbed water therefrom into a product fluid flow, the shaped water adsorbent composite comprises at least 50 wt % water adsorbent metal organic framework; and at least 0.1 wt % hydrophilic binder and from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm.
The shaped water adsorbent composite bodies in this method undergo magnetic induction vacuum swing adsorption to capture water from the water containing gas fed into the packed bed of shaped water adsorbent composite bodies. Application of the AC magnetic field depends on the amount of moisture adsorbed in the shaped water adsorbent composite bodies in the packed bed. This method therefore takes advantage of the high energy conversion efficiency of magnetic induction heating. In embodiments, the apparatus and method has an energy conversion efficiency of greater than 90%, preferably greater than 95% and in some embodiments up to 98% was achieved. Furthermore, the use of rapid heating through magnetic induction heating enables short cycle times to be achieved. In embodiments, the method has a cycle time of less than 2 hours, preferably less than 1 hour.
Adsorption is a transient process. The amount of material adsorbed within a bed depends both on position and time. The active adsorption region of a packed bed shifts away from the inlet and through the bed as time goes on. This mass transfer zone moves through the bed until it “breaks through”. The fluid emerging from the bed will have little or no solute remaining—at least until the bulk of the bed becomes saturated. The breakthrough point occurs when the concentration of the fluid leaving the bed spikes as unadsorbed solute begins to emerge. The bed still adsorbs water, though at a slower rate than before the breakthrough point until the bed becomes saturated, and no further water can be adsorbed, defined as the “saturation point” of the bed. Therefore, in terms of the saturation point of the packed bed, the alternating current magnetic field is preferably applied when the packed bed has adsorbed water equivalent to at least 75% of the saturation point, preferably at least 80%, more preferably at least 90% of the saturation point of the packed bed. This ensures that the adsorption capacity of the packed bed is substantially utilised, but allows the water to be released before the packed bed is fully saturated.
The AC magnetic field is applied for a length of time required to substantially release the water adsorbed on the shaped water adsorbent composite bodies in of the packed bed. That application time depends on the shape, size and configuration of the packed bed, shape, size and configuration of the AC magnetic field generator, the applied magnetic field strength and the amount of magnetic particles in the shaped water adsorbent composite bodies. In some embodiments, the AC magnetic field is applied for at least 1 second. In embodiments, the AC magnetic field is applied for between 1 and 120 seconds, preferably between 1 and 60 seconds, more preferably from 10 to 30 seconds.
The magnetic field strength applied to the packed bed of shaped water adsorbent composite bodies is typically tailored to the shape, size and configuration of that packed bed. In embodiments, the magnetic field strength is at least 10 mT, preferably at least 12 mT, preferably about 12.6 mT. However, it should be appreciated that the selected magnetic field strength depends on the particular application, and is generally selected to provide the lowest power consumption and thus lowest magnetic field strength for the maximum heat to desorb water from the water adsorbent MOF. The frequency of the AC magnetic field can be selected to provide maximum heating. In embodiments, the frequency of the AC magnetic field is between 200 and 300 kHz, preferably between 250 and 280 kHz, and more preferably from 260 to 270 kHz. Again, the frequency can be selected for a particular application and be tailored/optimised to provide the greatest heating for the lowest power consumption.
Again, it should be appreciated that the water containing gas can comprise any number of gases, such as nitrogen, oxygen or the like. In embodiments, the water containing gas comprises air, preferably atmospheric air, more preferably ambient air. The method can therefore by used to separate and capture water content from atmospheric air and thereby capture water.
The condenser system is used separate the water content of the product fluid flow (typically gas with entrained water vapour) to produce water. It is to be understood that a large variety of condenser arrangements are possible, and are selected to meet the particular requirements of a designed system. The condenser is used to convert water vapour in the product fluid flow into liquid water. In some embodiments, the condenser comprises a heat transfer/cooling device such as a cooling trap, air coils, surface condensers or another heat exchange device.
In some embodiments, the metal organic framework adsorbent can be activated before use (i.e. use for moisture adsorption) by triggering them by heating the composite bodies and passing (feeding) a dry nitrogen stream through the column. Where the water adsorbent comprises composite bodies that include magnetic particles, heating can be achieved with an alternating current magnetic field. Activation of the material was performed until the humidity of the out coming gas stream was zero.
Overall, the method and associated apparatus has a water production capacity of at least 2.8 L/kg of MOF, more preferably at least 3.5 L/kg of MOF, yet more preferably at least 4 L/kg of MOF, and in some embodiments about 4.1 L/kg of MOF at 20% RH and 35° C. The typical energy use is between 10 and 15 kWh/L, typically around 12 kWh/L water produced.
Temperature Swing Apparatus for Capturing Water from a Water Containing Gas
A third aspect of the present invention provides an apparatus for capturing a water content from a water containing gas, the apparatus comprising:
at least one heat transfer arrangement in contact with a packed bed of shaped water adsorbent composite bodies having at least one mean dimension of greater than 0.5 mm and comprising at least 50 wt % water adsorbent metal organic framework; and at least 0.1 wt % hydrophilic binder comprising a hydrophilic cellulose derivative; and
at least one peltier device in thermal communication with each heat transfer arrangement, each peltier device being configured to heat the shaped water adsorbent composite bodies to desorb water therefrom to be entrained into a product fluid flow,
wherein at least one peltier device also forms part of a condenser system for cooling the product fluid flow from the packed bed of shaped water adsorbent composite bodies.
This third aspect of the present invention provides a water capturing apparatus that includes shaped water adsorbent composite bodies that uses temperature swing induction heating to desorb water adsorbed within and on the shaped bodies. In this aspect, the shaped bodies are collected in a packed bed that is enclosed in contact with a heat sink. The apparatus also includes peltier device configured to heat the packed bed of shaped water adsorbent composite bodies to release adsorbed water from the packed bed of shaped water adsorbent composite bodies when activated. The peltier device is also configured to provide a cooling function to drive condensation of the fluid flow that is desorbed from the shaped water adsorbent composite bodies of the packed bed.
As noted above in relation to the first aspect, the peltier device is preferably selected to be suitable to provide sufficient energy to desorb water from the shaped water adsorbent composite bodies. The peltier device is therefore selected to have a maximal heat flow of at least 50 W, preferably at least 75 W, more preferably at least 100 W, and yet more preferably at least 110 W. Furthermore, the peltier device can be selected to be able to heat the packed bed to at least 50° C., preferably at least 60° C., more preferably to at least 65° C., and more preferably to at least 70° C. In some embodiments, peltier device is selected to be able to heat the packed bed to between 50 and 90° C., preferably between 50 and 80° C., more preferably between 50 and 80° C., yet more preferably between 65 and 85° C. In some embodiments, peltier device is selected to be able to heat the packed bed to between 70 and 80° C., and preferably around 75° C.
The shaped water adsorbent composite bodies can be located around, within or in any number of other configurations in contact with the heat transfer arrangement. In preferred embodiments, the shaped water adsorbent composite bodies are located within the heat transfer arrangement.
Again, the heat transfer arrangement can have any number of forms, including a variety of heat exchanger configurations. In a number of embodiments, the heat transfer arrangement comprises a heat sink (i.e. a conductive heat transfer arrangement), preferably a heat sink having a plate or fin arrangement. In some embodiments, the heat sink arrangement comprises a plurality of spaced apart heat transfer elements. In this arrangement, the shaped water adsorbent composite bodies are fitted as a packed bed between at least two heat transfer elements. The heat transfer elements typically comprise at least one of plates or fins.
Adsorption and desorption from the shaped water adsorbent composite bodies can be enhanced by driving fluid flow through and over the shaped water adsorbent composite bodies. In some embodiments, the apparatus further includes at least one fluid displacement device to drive fluid flow through the packed bed. The fluid displacement device preferably comprises at least one fan. Flow can be driven through the packed bed at a number of flow rates. In order to optimise water adsorption and desorption, the fluid displacement device preferably creates a fluid of at least 3 m3/hr, preferably 3 to 300 m3/hr, and more preferably 3 m3/hr to 150 m3/hr through the packed bed. It should be appreciated that the amount of air required to flow through the packed bed depends on the moisture level in the water containing gas and the efficacy of capture.
When operated, each peltier device develops a hot side and a cold side (as described in more detail in the detailed description). In this arrangement, the hot side of each peltier device is preferably in thermal communication with at least one heat sink, and the cold side of each peltier device forms part of the condenser system.
The condenser system may also include a heat transfer arrangement to assist in heat transfer from the surrounding gases to the cold side of the peltier device. In embodiments, the cold side of each peltier device is in thermal communication with at least one heat transfer arrangement. Similar to the hot side, the heat transfer arrangement preferably comprises a heat sink (a conductive heat transfer arrangement), and more preferably a heat sink having a plate or fin arrangement.
A fourth aspect of the present invention provides a method of capturing a water content from a water containing gas using the apparatus according to the third aspect of the present invention. The method comprises at least one cycle of:
feeding a water containing gas through the packed bed of shaped water adsorbent composite bodies of said apparatus such that the shaped water adsorbent composite bodies adsorb water from the water containing gas;
operating the at least one peltier device to heat the shaped water adsorbent composite bodies so to release at least a portion of the adsorbed water therefrom into a product fluid flow; and directing the product fluid flow to the condenser system to separate a water content from the product fluid flow.
It should be understood that operation of the at least one peltier device to heat the shaped water adsorbent composite bodies creates a heat from through the peltier device from the cold side to the hot side thereof. Operation of the at least one peltier device therefore also causes the cold side of each peltier device to operate (turn on), and thereby commencing operation of the condenser system via the cold side of the peltier devices which form part of the condenser system.
It is to be understood that this method is a cyclical method, where the steps of adsorbing water in the shaped water adsorbent composite bodies, releasing that adsorbed water through heating from the at least one peltier device and condensing that water is conducted in a repetitive cycle so to continuously produce water. The cycle time typically depends on configuration of the packed bed and the adsorption system, the amount of shaped water adsorbent composite bodies, the depth of the packed bed, breakthrough point, saturation point and characteristics of the particular pack bed, temperature, pressure, heat sink configuration, the peltier device and other process conditions. In some embodiments, the cycle time of this method steps are approximately 6 hours in duration. However, other cycle times between 1 hour to 24 hours could be possible depending on the configuration of the apparatus and packed bed and process conditions.
The condenser system is used separate the water content of the product fluid flow (typically gas with entrained water vapour) to produce water. It is to be understood that a large variety of condenser arrangements are possible, and are selected to meet the particular requirements of a designed system. The condenser is used to convert water vapour in the product fluid flow into liquid water. In some embodiments, the condenser comprises a heat transfer/cooling device such as a cooling trap, air coils, surface condensers or another heat exchange device.
Magnetic Swing Apparatus for Capturing Water from a Water Containing Gas
A fifth aspect of the present invention provides an apparatus for capturing a water content from a water containing gas, the apparatus comprising:
a housing containing therein a packed bed of shaped water adsorbent composite bodies having at least one mean dimension of greater than 0.5 mm and comprising at least 50 wt % water adsorbent metal organic framework; at least 0.1 wt % hydrophilic binder comprising a hydrophilic cellulose derivative and from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm; and
an alternating current (AC) magnetic field generator located within and/or around the packed bed of shaped water adsorbent composite bodies configured to apply an AC magnetic field to the packed bed of shaped water adsorbent composite bodies.
This fifth aspect of the present invention provides a water capturing apparatus that includes shaped bodies that uses magnetic swing induction heating to desorb water adsorbed within and on the shaped bodies. In this aspect, the shaped bodies are collected in a packed bed that is enclosed in the housing. The housing is preferably a fluid tight housing. The apparatus also includes an alternating current magnetic field generator designed to irradiate the packed bed of shaped water adsorbent composite bodies with an AC magnetic field to release adsorbed water from the packed bed of shaped water adsorbent composite bodies when activated. The apparatus is configured to enable the shaped water adsorbent composite bodies to undergo magnetic induction swing adsorption to capture water from a water containing gas fed into the packed bed of shaped water adsorbent composite bodies.
Any AC magnetic field generator can be used which is capable of applying a localised AC magnetic field to the packed bed of shaped water adsorbent composite bodies. In some embodiments, the AC magnetic field generator comprises at least one induction coil located within and/or around the packed bed of shaped water adsorbent composite bodies. Preferably, one or more induction coils are embedded within and surrounded by the shaped water adsorbent composite bodies in the packed bed so to use the whole magnetic field generated by the induction coil or coils. In some embodiments, the induction coil or coils are configured to sit within a central section of the packed bed, occupying from 50% to 90%, preferably from 70 to 80% of the axial height (depth) of the packed bed.
The housing has a fluid inlet and a fluid outlet through which a fluid, preferably the moisture containing gas and product fluid is configured to flow. The housing can have any suitable configuration. In some embodiments, the housing comprises a container or canister, for example a substantially cylindrical container or canister. The housing is preferably fluid tight, with only fluid access and egress through the inlet and outlet of that housing. In other embodiments, the housing comprises a flat, high surface area container. It should be appreciated that a variety of container and canister shapes and configurations could be used. The housing may be exchangeable or is installed fixed in the system.
The plurality of said shaped water adsorbent composite bodies is preferably arranged in the housing in a packed bed system. The housing can include two spaced apart support membranes configured to allow gas flow therethrough each membrane, the plurality of said shaped water adsorbent composite bodies forming a packed bed therebetween and preferably being compressed therebetween. The apparatus of this fifth aspect can further include a condenser system for cooling a fluid flow from the packed bed of shaped water adsorbent composite bodies. A variety of condensers can be used. In embodiments, the condenser comprises a cooling device, for example a cooling trap.
The Inventors have found that potable water can be expeditiously produced using the apparatus of this aspect of the present invention. This apparatus utilises a packed bed of the shaped water adsorbent composite bodies of the first aspect of the present invention in a magnetic induction vacuum swing adsorption system to separate and thus capture water from an water bearing gas (such as humid air) and release and harvest that captured content using a condenser.
A sixth aspect of the present invention provides a method of capturing a water content from a water containing gas using the apparatus according to the fifth aspect of the present invention, comprising at least one cycle of (the steps of):
feeding a water containing gas through the packed bed of shaped water adsorbent composite bodies of said apparatus such that the shaped water adsorbent composite bodies adsorb water from the water containing gas;
applying an alternating current magnetic field to the shaped water adsorbent composite bodies using the alternating current magnetic field generator of said apparatus, thereby generating heat within the shaped water adsorbent composite bodies, so to release at least a portion of the adsorbed water therefrom into a product fluid flow; and
directing the product fluid flow to a condenser to separate a water content from the product fluid flow.
In this sixth aspect of the present invention a moisturized gas stream is fed through a packed adsorption column. After the absorbent is charged with water vapour, an alternating current magnetic field is applied. Consequently, the pellets start heating up rapidly forcing the water to be released. The desorbed water is condensed in a condenser, for example in a cold trap. This method therefore takes advantage of the high energy conversion efficiency of magnetic induction heating. In embodiments, the apparatus and method has an energy conversion efficiency of greater than 90%, preferably greater than 95% and in some embodiments up to 98% was achieved. Furthermore, the use of rapid heating through magnetic induction heating enables short cycle times to be achieved.
It is to be understood that this method is a cyclical method, where the steps of adsorbing water in the shaped water adsorbent composite bodies, releasing that adsorbed water through application of the AC magnetic field and condensing that water is conducted in a repetitive cycle so to continuously produce water. The cycle time typically depends on the configuration of the packed bed and the adsorption system, the amount of shaped water adsorbent composite bodies, the depth of the packed bed, breakthrough point, saturation point and characteristics of the particular pack bed, temperature, pressure and other process conditions. In some embodiments, the cycle time of this method steps are approximately 30 minutes in duration. However, other cycle times between 10 minutes to 2 hours could be possible depending on the configuration of the apparatus and packed bed and process conditions.
Method of Forming Shaped Water Adsorbent Composite Body
The present invention can also provide a method of forming a shaped water adsorbent composite body for the adsorption system of the first aspect. The method comprises the steps of:
preparing a composite powder mixture comprising at least 50 wt % water adsorbent metal organic framework; at least 0.1 wt % hydrophilic binder comprising a hydrophilic cellulose derivative; and optionally 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm;
preparing a composite paste comprising a mixture of the composite powder mixture and a solvent;
forming the composite paste into a shaped body having at least one mean dimension of greater than 0.5 mm; and
heating the shaped body to substantially remove the solvent from the shaped body,
thereby producing a shaped water adsorbent composite body for use in a packed bed adsorption system.
This aspect of the present invention provides a method of forming the shaped water adsorbent composite body used in various embodiments of the present invention. In this method, the composite powder mixture (typically a pulverulent material) comprising a powder mix of metal organic framework and a hydrophilic binder, is formed into a paste using a solvent, which can then be shaped, for example by extrusion or palletising processes into the desired shaped body.
The solvent used to form the shaped body can be any suitable solvent that has good interaction with the constituents of the composite powder mixture. 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.
The hydrophilic binder and a liquid solvent are added to the composite powder mixture to assist in the formation of a suitable paste for shaping processes. It should be appreciated that the composite paste comprises a thick, soft, moist mixture. The paste preferably has sufficient viscosity to retain a form when shaped into a desired configuration in the forming/shaping step. The amount of solvent and composite powder material (a pulverulent material, preferably powder or particulates) is typically mixed to provide a suitable paste consistency for shaping processes such as extrusion or pelletising.
It is also important to appreciate that the shaped body preferably comprises the water adsorbent MOF and the hydrophilic binder. The solvent is purely used to form the paste which is evaporated or otherwise removed from the shaped composite material during the heat treatment step.
Magnetic particles can also be included in the formed shaped composite material. In these embodiments the composite powder mixture further comprises from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm.
The composite paste can be formed into the shaped body using a variety of processes. In embodiments, forming the composite paste into a shaped body comprises at least one of extruding, pelletising or moulding the composite paste into a desired three-dimensional configuration. Preferred methods include rod extrusion or tableting. Where the shaped body is formed by an extrusion or similar process such that the composite paste is extruded into an elongate body, that elongate body is preferably subsequently longitudinally divided, typically to a length suitable used in a packed bed of a packed bed adsorption system. It is preferred that after extrusion the extruded elongated body is allowed to dry, for example air dry, for a period of time prior to being longitudinally divided. That drying time can vary, but is typically at least 10 minutes. Afterwards, the extruded body is cut into 3 to 5 mm long shaped bodies, preferably pellets.
The shaping step can be performed in the presence of lubricants and/or other additional substances that stabilize the materials to be agglomerated. Suitable lubricants include surfactants and their salts. Examples of suitable lubricants include magnesium stearate, aluminium oxide, sodium oleate, glycerides, di-glycerides, tri-glycerides, fatty acids, oils including silicon oils and mineral oils and mixtures thereof. It should be appreciated that the additives depend on the application in which the shaped bodies are being used. The lubricants preferably comprise an approved excipient for human consumption where water is being produced for human consumption. Examples of approved excipients for human consumption include approved excipients for food or pharmaceuticals. Approved food grade or pharmaceutical grade lubricants are preferred. As discussed below, lubricants are added to the mixture to assist with shaping and forming processes when making the shaped body. In some embodiments, the lubricant can be mixed in the powder mixture with the binder to form part of the powder mixture. In other embodiments, the lubricant is applied to the surface of the shaping device, for example an extruder or pelletiser, to lubricate the outer surface only. The resulting shaped water adsorbent composite body preferably comprises less than 0.5 wt % lubricant, preferably less than 0.1 wt % lubricant.
The shaped body/bodies are preferably formed with dimensions that are suitable for use in a packed bed adsorption system, in which a plurality of the shaped bodies are packed at a high packing density 0.10 to 0.5 kg/L, preferably 0.25 to 0.4 kg/L between two support surfaces. The dimensions of the shaped body can be optimised to suit this application. The shaped water adsorbent composite body has at least one mean dimension of greater than 0.5 mm when used in a packed bed adsorption system. This ensures the adsorbent composite body has sufficient size to allow gas flow around. For example, fine powder (for example having an average particle size of less than 10 micron) provides too dense packing for use in a packed bed of a packed bed adsorption system. In some embodiments, the shaped body has at least one mean dimension of greater than 0.8 mm, preferably at least 1 mm, preferably at least 1.2 mm, and yet more preferably at least 1.5 mm. Preferably, each of the mean width, mean depth and mean height of the shaped body are greater than 0.5 mm, and preferably greater than 1 mm.
The shaped body can be formed to have any suitable geometry. The shape of the shaped water adsorbent composite body has an impact on the pressure drop of local fluid flow (in the vicinity of the bodies), and therefore, the performance of any packed bed adsorption system. For example, the shaped body could comprise pellets, for example, disk-shaped pellets, pills, spheres, granules, extrudates, for example rod extrudates, honeycombs, meshes or hollow bodies. In embodiments, the shaped body is three dimensional, preferably three dimensionally shaped. In particular embodiments, the shaped body comprises an elongate body having a circular or regular polygonal cross-sectional shape. In preferred embodiments, the shaped body comprises a triangular cross-sectional shape, and more preferably an equilateral triangle cross-sectional shape. For example, the shaped body may have a square or triangular cross-sectional shape. In one form, the shaped body has equilateral triangle cross-section, preferably the sides of the equilateral triangle are at least 1 mm in length, preferably between 1.0 and 1.5 mm in length. The elongate shaped body is preferably from 1 to 5 mm in length (longitudinal length), more preferably 1 to 4 mm in length. In some embodiments, the elongate shaped body is 3 to 5 mm in length.
The heating step is preferably conducted for sufficient time to remove the solvent from the shaped body. The heating step is preferably conducted at a temperature of between 80 to 150° C., preferably between 90 and 120° C. The heating step can be conducted for at least 1 hour, preferably at least 2 hours, more preferably at least 5 hours, yet more preferably at least 8 hours, and yet more preferably at least 10 hours. Similarly, the pressure is selected to assist solvent removal. In embodiments, the pressure is less than 100 mbar, preferably less than 50 mbar, more preferably less than 35 mbar. In other embodiments, the pressure is less than 500 mbar. In some embodiments, the heating step is conducted in an insert gas atmosphere, for example nitrogen or argon.
The heating step can include an additional activation step where the shaped adsorption body/bodies are dried at an elevated temperature to ensure the pores of the water adsorbent MOF are free of moisture or solvent. In some embodiments, this activation heating step comprises heating the shaped adsorption body to at least 120° C., preferably between 120 and 150° C. for at least 5 hours, preferably at least 6 hours, more preferably from 6 to 10 hours, and more preferably from 6 to 8 hours. The activation heating step is preferably conducted at a reduced pressure of less than 200 mbar, preferably less than 100 mbar, and more preferably less than 50 mbar. In some embodiments, the shaped adsorption body is heated to a temperature of 130° C. at a pressure of less than 200 mbar, preferably less than 100 mbar, more preferably less than 50 mbar to activate the MOF for 6 to 8 hours.
In other embodiments, the shaped adsorption bodies can be activated by triggering them with an alternating current magnetic field within an inert gas flow, for example dry nitrogen stream. Activation of the shaped adsorption bodies can be performed until the humidity of the out-coming gas stream is zero.
After heating, the material is preferably cooled down to at most 80° C., preferably at most 60° C. under reduced pressure of at most 500 mbar, preferably at most 100 mbar.
It should be appreciated that that water produced from the apparatus and method according to embodiments of the present invention can be used for any purpose, including but not limited to;

    
    
        Water as a substrate for energy production or synthesis of chemicals or the like;
        Water for specialised use such as ultra-pure water for medical or laboratory use or the like;
        Water for use in defence or medical sectors;
        Water for industrial applications such as farming, irrigation, quenching fire or the like;
        Water for consumption such as house hold use, bottled water, food production or the like.
    
    





BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1A is a schematic of a magnetic induction swing apparatus for capturing a water content from a water containing gas according to one embodiment of the present invention.
FIG. 1B is a schematic of a magnetic induction swing apparatus for capturing a water content from a water containing gas according to another embodiment of the present invention.
FIG. 1C is a schematic of a temperature swing apparatus for capturing a water content from a water containing gas according to one embodiment of the present invention which includes a heat sink (CPU cooler) and peltier device.
FIG. 1D is a photograph of the experimental temperature swing apparatus for capturing a water content from a water containing gas according to one embodiment of the present invention which includes a heat sink (CPU cooler) and peltier device.
FIG. 1E provides schematic diagrams of operation of the thermal cycle water harvesting device shown in FIG. 1C when operated (A) during the adsorption phase; and (B) during the desorption phase.
FIG. 2A is a photograph of the experimental setup used for aluminium fumarate synthesis.
FIG. 2B is a photograph of the produced aluminium fumarate after washing procedure.
FIG. 2C provides a schematic diagram of a shaped adsorption body cording to one embodiment of the present invention utilised in the packed bed of the apparatus shown in FIGS. 1A to 1D.
FIG. 3A is photograph of the hand extruder and triangular shaped nozzle used to produce the shaped aluminium fumarate composite pellets.
FIG. 3B provides a schematic diagram of the pellet forming process.
FIG. 4 is a photograph showing the produced aluminium fumarate and aluminium fumarate composite pellets, being (A) Pristine MOF; (B) 1 wt % binder; (C) 1 wt % MNP; (D) 3 wt % MNP; and (E) 5 wt % MNP.
FIG. 5 is a schematic of the experimental setup used for induction heating experiments.
FIG. 6 is a schematic of the experimental magnetic induction swing water capturing rig.
FIG. 7 provides a PXRD pattern of aluminium fumarate, simulated aluminium fumarate and aluminium fumarate with 1 wt % binder (Batch I).
FIG. 8 provides a PXRD pattern of different aluminium fumarate magnetic composites, aluminium fumarate with 1 wt % binder (Batch I) and magnesium ferrite as reference.
FIG. 9 provides a PXRD pattern of aluminium fumarate magnetic composite, aluminium fumarate (Batch II) and magnesium ferrite as reference.
FIG. 10 provides a SEM image of aluminium fumarate metal organic framework (Batch II). Magnification: 10000 times.
FIG. 11 provides a SEM image of magnesium ferrite nanoparticles. Magnification: 10.000 times.
FIG. 12 provides a SEM image of aluminium fumarate magnetic framework composite (Batch II) at a magnification of 10000 times. The circled sections marked with A indicate the location of magnesium ferrite nanoparticles in the composite.
FIG. 13 provides an averaged BET surface area of aluminium fumarate composites as a function of magnetic nanoparticle loading.
FIG. 14 provides a plot of the pore size distribution of aluminium fumarate MOF pellets (Batch I).
FIG. 15 provides a nitrogen isotherm of aluminium fumarate pellets.
FIG. 16 provides a plot of the pore size distribution of aluminium fumarate composite pellets containing: (a) 1 wt % binder. (b) 1 wt % MNPs (c) 3 wt % MNPs (d) 5 wt % MNPs.
FIG. 17 provides water vapour adsorption isotherms for aluminium fumarate batch I and aluminium fumarate batch I composite pellets collected at room temperature.
FIG. 18 provides water vapour adsorption isotherms of aluminium fumarate batch II and aluminium fumarate batch II composite pellets collected at room temperature.
FIG. 19 provides a plot of the initial heating rate of induction heating of Aluminium Fumarate magnetic framework composites with different MNP concentrations. Field strength was 12.6 mT.
FIG. 20 provides a plot of the efficiency of induction heating of Aluminium Fumarate magnetic framework composites with different MNP loading. Field strength was 12.6 mT.
FIG. 21 provides a plot of the normalized relative humidity over time for adsorption of water vapour from a nitrogen stream.
FIG. 22 provides a plot of the temperature profile of aluminium fumarate composites during adsorption of moisture.
FIG. 23 provides a plot of the normalized relative humidity over time for the out coming stream during regeneration.
FIG. 24 provides a plot of the temperature profile of aluminium fumarate composites during regeneration of water vapour.
FIG. 25 provides a plot comparing the water vapour uptake isotherms of (A) a first batch of AlFu (Aluminium Fumarate (I)); (B) pellets comprising Aluminium Fumarate (I) and a cellulose siloxane binder; (C) a second batch of AlFu ((Aluminium Fumarate (II)); and (D) pellets comprising Aluminium Fumarate (II) and a hydroxypropyl cellulose binder.
FIG. 26 illustrates the setup of the testing rig for the temperature swing water harvesting device shown in FIGS. 1C and 1D, including with power supplies and measurement equipment.
FIG. 27 illustrates the FTIR pattern of aluminium fumarate with 1 wt % binder after the pelletisation process for each of the three batches (batch_01, batch_02 and batch_03) and t the FTIR pattern of pristine aluminium fumarate.
FIG. 28 illustrates the PXRD pattern of pristine aluminium fumarate and aluminium fumarate with 1 wt % binder of all three extrusions after the pelletisation process. Simulated pattern for comparison.
FIG. 29 illustrates water uptake isotherms at 26° C. of aluminium fumarate pellets produced in this work (Pellets_02) (squares), and literature data of aluminium fumarate from Teo et al. [28] (diamonds).
FIG. 30 illustrates mass logging of an adsorption phase with a humidity of 8:85 μm−3. This data is used to calculate theoretical adsorption times for all water harvesting cycles.
FIG. 31 illustrate the optimisation of the condensation time of the water harvesting device plotting space time yield and specific energy over different condensation times corresponding to water harvesting cycles 12, 14, 15, 16 and 17.
FIG. 32 illustrates optimisation of the desorption temperature of the water harvesting device plotting space time yield and specific energy over different desorption temperatures corresponding to water harvesting cycles 16, 18, 19 and 20.
FIG. 33 illustrates temperature and relative humidity of the adsorption of water harvesting cycle 16.
FIG. 34 illustrates the temperatures in the water harvesting device during the desorption phase of water harvesting cycle 16.
FIG. 35 illustrates the relative humidity, dew point and condenser temperature in the water harvesting device during the desorption phase of water harvesting cycle 16.
FIG. 36 illustrates the temperature and relative humidity of the adsorption of water harvesting cycle 24.
FIG. 37 illustrates the temperatures in the water harvesting device during the desorption phase of water harvesting cycle 24.
FIG. 38 illustrates the relative humidity, dew point and condenser temperature in the water harvesting device during the desorption phase of water harvesting cycle 24.
FIG. 39 illustrates the temperature and relative humidity of the adsorption of water harvesting cycle 22.
FIG. 40 provides two views of a prototype water capture apparatus using the temperature swing water harvesting embodiment showing (A) external housing; and (B) inner components, including louver system.



DETAILED DESCRIPTION
The present invention provides an apparatus that provides selective control of the adsorbing and desorbing phases of a MOF based water adsorbents water harvesting cycle. The apparatus includes a water desorption arrangement which allows the MOF based water adsorbent to adsorb water when in a deactivated state, and then apply desorption conditions to the water adsorbent to desorb water from the water adsorbent when in an activated state. This selective operation of the water desorption arrangement between the deactivated and activated states enables the efficiency of water desorption arrangement to be optimised using more efficient energy desorption arrangements to desorb water from the metal organic framework based water adsorbent compared for example to utilising solar energy, and in some embodiments that can simultaneously condense the water content of any product gas flow.
Adsorption Apparatus
The water desorption arrangement can take any number of forms depending on whether heat and/or reduced pressure is being used to cause the adsorbed water to desorb from the water adsorbent. 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 water adsorbent. Adsorption would typically be undertaken at near atmospheric pressure. In other embodiments, temperature swing adsorption is undertaken to achieve water harvesting. This can be achieved using direct heating methods, or in some cases using magnetic induction swing adsorption.
Magnetic Swing Water Adsorption Apparatus
In some cases, the apparatus can be configured as a magnetic swing water adsorption apparatus to harvest a water content from a water containing gas, such as atmospheric air. One form of this type of apparatus 200 is illustrated in FIG. 1A or 1B.
FIGS. 1A and 1B illustrate an apparatus 200 for capturing a water content from a water containing gas that uses a shaped water adsorbent composite body formulated with magnetic particles as discussed above. The apparatus 200 comprises a cylindrical housing 205 which includes inlet 208 and outlet 211. Housing 205 contains a packed bed 215 of shaped water adsorbent composite bodies 100 (see FIG. 2C), the composition of which is described in more detail below. A fluid distributor disc 210 proximate the base and lid/top of the housing 205 is used to retain the shaped adsorption material 215 between the discs 205. Each fluid distributor disc 210 comprises a metal disc with multiple holes drilled therethrough to allow fluid to flow through the packed shaped adsorption material. The shaped adsorption material forms a compressed packed bed between the discs 210, and are compressed therebetween so that the adsorbent shaped bodies 100 are tightly packed therein, thereby avoiding any flow short circuiting.
In the embodiment shown in FIG. 1A, an alternating current (AC) induction coil 250 is located within and surrounded by the packed bed 215 of shaped water adsorbent composite bodies 100 (FIG. 2C). The induction coil 250 is configured to apply an AC magnetic field to the packed bed 215 of shaped water adsorbent composite bodies. The induction coil 250 is embedded within the packed bed 215 to optimise the use of the applied magnetic field when the induction coil 250 is operated.
The housing 205 includes magnetic dampening material 255 to reduce magnetic field leakage from the container to the surroundings. This can be important in some applications where a magnetic field could deliriously affect the operation of proximate equipment, or irradiate people or objects.
In the embodiment shown in FIG. 1B, an alternating current (AC) induction coil 250 is located external of the housing 205, but in a location around the housing which extends around the packed bed 215 of shaped water adsorbent composite bodies 100. Again, the induction coil 250 is configured to apply an AC magnetic field to the packed bed 215 of shaped water adsorbent composite bodies. However, it should be appreciated that the positioning of this induction coil 250 is not as energy efficient as shown in FIG. 1A due to losses through the material of housing. Furthermore, whilst not shown in FIG. 1B, a further housing may be used to enclose the induction coil which includes magnetic dampening material 255 to reduce magnetic field leakage to the surroundings.
In use, a water containing gas is flowed through the packed bed of shaped bodies 215 such that the shaped water adsorbent composite bodies adsorb water from the water containing gas. Once the packed bed 215 reaches a desired saturation (typically 70 to 90% saturation point), the induction coil 250 is operated to apply an alternating current magnetic field thereby generating heat within the shaped water adsorbent composite bodies, so to release at least a portion of the adsorbed water therefrom into a product fluid flow. The shaped water adsorbent composite bodies therefore undergo magnetic induction vacuum swing adsorption to capture water from the water containing gas fed into the packed bed of shaped water adsorbent composite bodies 215.
Whilst not shown in FIG. 1A or 1B, a condenser can be used to subsequently separate the water content of the product fluid flow (typically gas with entrained water vapour) to produce a captured water product. A low or reduced pressure (sometimes referred to as a vacuum environment), or a positive pressure gas flow, for example a flow of the water containing gas or another gas such as an inert or other dry gas, to direct the released water to the condenser.
The above described method is cyclically applied, where the steps of adsorbing water in the shaped water adsorbent composite bodies 100, releasing that adsorbed water through application of the AC magnetic field and condensing that water is conducted in a repetitive cycle so to continuously produce water.
Temperature Swing Water Adsorption Apparatus
A temperature swing water harvesting apparatus 300 configured in according to an embodiment of the present invention is illustrated in FIGS. 1C, 1D and 1E.
The apparatus 300 shown in FIGS. 1C and 1D is configured to use the waste heat of a peltier device 310 to heat up shaped MOF composite bodies 100 (the composition of which is described in more detail below) placed in thermal contact with the hot side 312 of the peltier device 310 (via a heat sink 320, discussed below) to facilitate desorption of adsorbed water in the shapes MOF composite bodies. The cold side 314 of the peltier device 310 can be simultaneously used to condense the desorbed water vapour, and that condensed water can be collected as a liquid product below the peltier device 310.
Peltier Devices
A peltier device is a thermoelectric device with the ability to convert electrical energy into a temperature gradient, generally termed the “peltier effect”. An electrical current applied to a pair of different metal materials leads to a hot surface on the one side and a cold surface on the other side of the semiconductors and creates a heat flow through the semiconductors perpendicular to the current flow. A single pair of a p- and n-type semiconductor material coupled in series is sufficient to create a temperature gradient when a current is applied from the n-type semiconductor to the p-type semiconductor. A cold side of a peltier element is formed where the electrons flow from p- to n-type semiconductors and a hot side with the heat flow Qdis appearing on the transition from n-type to p-type semiconductors. It should be appreciated that the dissipated heat of a peltier device is higher than the electrical power due to the absorbed heat on the cold side of the peltier device.
Peltier devices are typically built of 3 up to 127 semiconductor pairs per device. The semiconductors are electrically connected in series and thermal in parallel. The heat flow in commonly available peltier devices is between 1 W to 125 W. The temperature difference between the hot and cold side of a peltier device is up to 70K for single-stage devices and up to 130K for multi-stage devices (several peltier elements connected in series).
Mechanical stress can occur in a peltier device due to the high temperature difference and thus material expansion difference between the cold and hot sides. The dimensions of peltier devices are therefore typically limited to 50 by 50 mm to keep such mechanical stress issues low. Current Peltier devices also suffer from a low efficiency of about 10% of the possible Carnot efficiency due mainly to the available properties semiconductor material used in the specific peltier device.
Temperature Swing Desorption
FIGS. 1C and 1D illustrate an embodiment of the temperature swing water harvesting apparatus 300. As shown, the device 300 comprises a sealable container 330 having a container body 332 and sealing lid 334. The container body 332 houses which a polycarbonate plate 338 positioned and spaced away from the base of the container body 332 using spacers 339 to define within the container 330 (i) an upper water adsorption-desorption chamber 340; and (ii) a lower condenser chamber 342. The container 330 is sealable using the removable sealing lid 334. Within the container body 332 sits a water harvesting device 350. The water harvesting device 350 includes the following sections:
(A). A heat sink 320 including a plurality of spaced apart fins 352. Whilst not shown in detail, the space between each of the spaced apart fins 352 is filled with shaped water adsorbent composite bodies 100 forming a packed bed 355 therein;
(B). A peltier device 310 having a hot side 312 in thermal communication with the heat sink 320 and a cool side 314 in thermal communication with the gas space of the lower condenser chamber 342. The peltier device 310 is configured to heat the shaped water adsorbent composite bodies 100 in the heat sink 320 during a desorption phase of a water harvesting cycle (see below); and

(C). A condenser system 360 located in the condenser 342, which uses the cool side 314 of the peltier device 310 to cool a fluid flow of water vapour that is produced from the packed bed 355 to condense and collect the water as a liquid product at the base of the container 330.

The apparatus 300 shown in FIGS. 10, 1D and 1E utilise both the cold side 314 and hot side 312 of the peltier device 310 during the desorption phase of a temperature swing water harvesting cycle. The dissipated heat of the hot side 312 of the peltier device 310 can be used in a temperature swing desorption cycle to heat up the shaped MOF composite bodies 100 during the desorption phase to desorb water from the shaped MOF composite bodies 100. The cold side 314 can be used to adsorb heat from the produced water vapour, and condense that water in a condenser system/chamber, to enable water to be collected as a liquid product.
For this application, it should be appreciated that the key criteria in selecting the peltier device are:

    
    
        Capability to provide sufficient heating so that at the hot side of the peltier device water is desorbed from the MOF composite.
        Capability to provide sufficient cooling for the cold side of the peltier device to be below the dew point in the condenser system for condensation to occur.
        Other factors including reliability and resistance to corrosion.

The lowest powered peltier device to be able to this will result in the highest efficiency device.

    
    


In the illustrated system (see FIG. 1D), the water harvesting device 350 is mounted within a 10 L sealable food container. The heat sink 320 comprises two NH-D15S (Rascom Computer distribution Ges.m.b.H., Wien (Austria)) CPU coolers. However, it should be appreciated that other suitable heat sink configurations could equally be used. This type of CPU cooler has a surface area of 1:0634 m2 and a free volume of 0:9967 L. This type of heat sink 320 is used as the dimensions of peltier devices are limited to sizes of around 40 mm by 40 mm due to heat stress issues (as discussed previously). The heat sink 320 ensures heat is distributed from the peltier device(s) 310 to a much larger surface, which can be used for conductive heat transfer to heat up the shaped MOF composite bodies in the packed bed 355.
The heat sink 320 has a mounting socket that fits perfectly onto a peltier device and conducts the heat with 12 heat pipes 356 to 90 metal fins 352. 45 fins 352 are stacked on top of each other with a distance of 1:92 mm. Two of these heat sink 320 stacks are assembled side by side onto the mounting socket of the heat sink 320. A 12 V fan 370 is mounted between the two heat sink 320 stacks to provide an air flow through the free volume between the fins 352 during adsorption and desorption phase. However, it should be appreciated that the fan could be included in other locations proximate to the heat sink 320 stacks. The heat sink 320 and the peltier device 310 are mounted onto the polycarbonate plate 338. The heat sink 320 is fastened onto the peltier device 310 using screws. Heat grease is applied on the connection surfaces between the peltier device 310 and the heat sink 320 to ensure sufficient heat flow through this connection. The fan 370 is selected to produce a flow rate from 3 m3/hr to 200 m3/hr. In the illustrated embodiment, the fan comprises a 12 V fan capable of flow rates up to 140 m3/hr. In most test runs it was set on a low setting generating approximately 30 m3/hr. This flow rate can be can be tuned according to the ambient humidity conditions
Whilst not illustrated, an additional small heat sink can be fixed to the cold side 314 of the peltier device 310 to increase the surface area for water condensation. It should be appreciated that the cold side 314 of the peltier device 310 with the small heat sink forms the condenser system 360 of the water harvesting device 350.
As indicated above, the free volume between the fins 352 is filled with the shaped MOF composite bodies 100. In the illustrated embodiment (FIGS. 1C to 1E), the MOF composite bodies 100 comprise aluminium fumarate triangle shaped pellets with a side length S=1:5 mm and a length L=3 mm (see FIG. 1). The heat sink 320 is sealed with a netting (not illustrated) having a small enough aperture to retain the pellets between the fins 352 of the heat sink 320. The netting comprises a commercially available fly wire having an aperture of 1 mm. 200.30 g MOF pellets are packed between the fins 352. This equals a packing density of 0:20 kg/L. Thus 198:30 g of aluminium fumarate is used as adsorbent in the water harvesting device 350.
In the illustrated test rig (see FIG. 1D and FIG. 26), six thermocouples 375 are fixed into the heat sink 320 to observe the temperature and the temperature distribution in the MOF packed bed 355 during the desorption phase. All six thermocouples are placed in one of the two sides of the heat sink 320. Three of the thermocouples are in the centre of the fins 352 in three different heights. The other three thermocouples are on the right side of the fins 352 in three different heights.
A water harvesting cycle (WHC) using this apparatus 600 can be designed with two phases:
1. An Adsorption Phase (FIG. 1E(A)) —during which the sealable container 330 is opened to the environment (i.e. lid 334 removed) and air is blown through the MOF packed bed 355 in the heat sink 320 using the fan 370. Water in the air is adsorbed by the shaped water adsorbent composite bodies 100 of the packed bed 355. During this phase, the peltier device 310 is switched off. Once the packed bed 355 reaches a desired saturation (typically 70 to 90% saturation point), the lid 334 is placed on the container body 332 to seal the container 330 and the peltier device 310 is switched on to start the desorption phase.

2. A Desorption Phase (FIG. 1E(B)) —where the peltier device 310 is switched on and the packed bed 355 in the heat sink 320 is heated up to elevated temperatures so to release at least a portion of the adsorbed water from the shaped water adsorbent composite bodies 100 in the packed bed 355 into a product fluid flow while the container 330 is sealed closed. The relative humidity in the container 330 increases to high values and water condenses on the cold side 314 of the peltier device 310. Liquid water is collected under the cold side 314 of the peltier device 310 after each water harvesting cycle.

The above described water harvesting cycle is cyclically applied, where the steps of adsorbing water in the shaped water adsorbent composite bodies 100, releasing that adsorbed water through operation of the peltier device and condensing that water is conducted in a repetitive cycle so to continuously produce water.
Adsorption Medium
The apparatus illustrated in FIGS. 1A to 1E each use a shaped water adsorbent composite body 100 (FIG. 2C) in a packed bed as the water adsorbent. However, it should be appreciated that the metal organic framework composite can be provided in an apparatus of the present invention in any form suitable to the particular apparatus configuration. The inventors envisage that this may be in any number of composite forms including (but not limited to) shaped bodies (for example pellets or extrusions), coatings, plates, sheets, strips or the like.
Shaped Metal Organic Framework Composite Body
The shaped water adsorbent composite body 100 (FIG. 2C) used in the apparatus discussed in relation to the apparatus shown in FIGS. 1A to 1E comprises a mixture of water adsorbent metal organic framework (MOF), and a hydrophilic binder which is optimised for use in a packed bed adsorption system. That mixture is composed of at least 50 wt % water adsorbent metal organic framework and at least 0.1 wt % hydrophilic binder.
In the embodiments shown in FIGS. 1A and 1B, the shaped water adsorbent composite body 100 is configured to harvest water using a magnetic induction swing adsorption system. In these embodiments, the shaped water adsorbent composite body additionally contains from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm. The use of magnetic particles in the composition forms enables inductive heat generation to be used for water desorption. This type of composite, known as a magnetic framework composite, combines the exceptional adsorption performance of MOFs and the high efficiency of magnetic induction heating.
The metal organic framework composite material can be shaped into any suitable configuration for use in a packed adsorption system. In the present invention, the metal organic framework composite material is exemplified as a elongate shaped water adsorbent composite body 100 having a triangular cross-section, for example as shown in FIG. 2C. However, it should be appreciated that other shapes for example spherical, cylindrical, cubic, ovoid or the like could equally be used.
Referring to FIG. 2C, the shaped water adsorbent composite body 100 comprises an elongate body having an equilateral triangle cross-sectional shape. The sides S of the equilateral triangle are at least 1 mm in length, preferably between 1.0 and 1.5 mm in length. The shaped water adsorbent composite body is preferably from 1 to 5 mm in length (longitudinal length, L), more preferably 1 to 4 mm in length. The elongated triangular shape is selected to increase packing density of the shaped water adsorbent composite bodies 100 within a packed bed (for example packed bed 215 shown in FIGS. 1A and 1B). Previous studies have shown that this shape has one of the highest packing densities in packed bed configurations. A high packing density is preferred for optimum utilisation and heat generation from an applied heat source. For example, a cylindrical pellet shape has a packing density of around 0.19 kg/L. An elongated equilateral triangular shaped pellet has a packing density of around 0.29 kg/L.
Water Adsorbent Metal Organic Framework
The water adsorbent metal organic framework used in the shaped water adsorbent composite body 100 can be selected from a range of suitable water adsorbent MOFs. A wide variety of water adsorbent MOFs are known, for example as discussed in Furukawa et al “Water Adsorption in Porous Metal-Organic Frameworks and Related Materials” Journal of the American Chemical Society 136(11), March 2014 and H W B Teo and A Chakraborty 2017 IOP Conf. Ser.: Mater. Sci. Eng. 272 012019 the contents of which should be understood to be incorporated into this specification by these references. In selected embodiments, the water adsorbent metal organic framework comprises at least one of aluminium fumarate, MOF-303 (Al), MOF-573 (Al), MOF-801 (Zr6O4(OH)4(fumarate)6), MOF-841 (Zr6O4(OH)4(MTB)2(HCOO)4(H2O)4), M2Cl2BTDD (including Co2Cl2BTDD), Cr-soc-MOF-1, MIL-101(Cr), CAU-10, alkali metal (Li+, Na+) doped MIL-101(Cr), MOF-802 (Zr6O4(OH)4(PZDC)5(HCOO)2(H2O)2), MOF-805 (Zr6O4(OH)4[NDC—(OH)2]6), MOF-806 (Zr6O4(OH)4[NDC—(OH)2]6), MOF-808 (Zr6O4(OH)4(BTC)2(HCOO)6), MOF-812 (Zr6O4(OH)4(MTB)3(H2O)4) or a mixture thereof. Preferred water adsorbent metal organic frameworks are aluminium fumarate, MOF-303 (Al), MOF-801, MOF-841, M2Cl2BTDD, Cr-soc-MOF-1, and MIL-101(Cr).
Optimising the selection of a water adsorbing MOF involves a number considerations, including:

    1. Water stability—the MOF should be water stable.
    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.
    3. Ease of production, the MOF should be easy to produce from readily available precursor materials.
    4. High water uptake from air even at low humidity values.
    5. A good affinity for water. The MOF should have a good enough affinity for water to enable the MOF to adsorb the water, but not have too high affinity for water that excessive energy needs to be expended to desorb water therefrom. Here the thermodynamics of water adsorption and desorption need consideration to ensure the MOF does not require excessive energy (kJ/mol MOF) to desorb water therefrom, and thereby adversely affect the energy efficiency of the system. Typical heats of adsorption for water for the MOF range from 10 to 100 kJ/mol MOF for water adsorbed on the MOF (550 to 5500 kJ/kg). Careful MOF selection is important to the operation of the device as the cost of the water will be directly linked to the energy required to desorb the water from the MOF.


Where the MOF is required for water production for human consumption, the MOF and other materials must also meet food for human consumption regulations in relevant countries. The Applicant has found that the water adsorbent MOF preferably comprises aluminium fumarate (AlFu) MOF in these embodiments. The water adsorption properties of AlFu are published in a number of research studies available in the published literature.
Aluminium Fumarate
Aluminium fumarate (AlFu) is used as a preferred MOF in the shaped water adsorbent composite body 100. The structure and water adsorption properties of AlFu are well known, for example as detailed in Teo et al. (2017). Experimental study of isotherms and kinetics for adsorption of water on Aluminium Fumarate. International Journal of Heat and Mass Transfer Volume 114, November 2017, Pages 621-627, the contents of which are to be understood to be incorporated into this specification by this reference. As outlined in Teo, the crystal structure of AlFu resembles MIL-53 as it also consists of infinite Al OH Al chains connected by fumarate linkers. AlFu has a permanently porous 3D structure of formula [Al(OH)(O2C—CH═CH—CO2)] with square channels.
Overall, aluminium fumarate was selected as a preferred choice of MOF for the inventive water capturing apparatus and system due to:

    1. Ease of manufacture—this MOF can be synthesised in water. Following synthesis, processing the MOF is simple as outlined in the Examples.
    2. Good thermal stability and is highly water stable (unlike many other MOFs);
    3. It is robust to handling in ambient conditions and can withstand multiple temperature cycles without degradation.
    4. It has a well-studied water adsorption behaviour;
    5. High water uptake from air even at low humidity values; Aluminium fumarate has a water capacity between 0.09 to 0.5 grams of water per gram of MOF depending on the relative humidity. The typical heat of adsorption of Aluminium fumarate for water is well known and ranges between 60 and 30 kJ/mol depending on the ambient humidity
    6. It can be cheaply and easily produced using non-toxic constituents/precursor material—i.e. environmentally friendly synthesis and is easy to handle and process; and
    7. Low cost of its constituents.


Nevertheless, it should be appreciated that the MOF component of the present invention is not restricted to Aluminium fumarate, and that other water adsorbent MOFs can also be used in the composition of the water adsorbent composite body.
Hydrophilic Binder
The selection of the appropriate binder is also important to the overall properties of the shaped adsorption body. The inventors have surprisingly found that a hydrophilic binder must be used to impart optimal water adsorption properties to the shaped water adsorbent composite bodies. The inventors have also found that non-hydrophilic binders and in particular hydrophobic binders (for example cellulose siloxane) reduce/decrease the water adsorption properties of the shaped water adsorbent composite bodies. The use of a hydrophilic binder is therefore important for optimal moisture capture properties of the packed bed water adsorption system. However whilst other binders are also possible, it is again noted that particularly suitable hydrophilic binders can be selected from at least one of hydrophilic cellulose derivatives such as hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose (HPMC), ethyl hydroxyethyl cellulose, methyl cellulose, or carboxymethyl cellulose (CMC) as previously set out in this specification. As indicated in the following examples, one exemplary hydrophilic binder is hydroxypropyl cellulose (HPC).
Lubricant
The shaped water adsorbent composite body can further comprise a lubricant content, preferably less than 0.5 wt % lubricant, and more preferably less than 0.1 wt % lubricant. Suitable lubricants include surfactants and their salts. Examples of suitable lubricants include magnesium stearate, aluminium oxide, sodium oleate, glycerides, di-glycerides, tri-glycerides, fatty acids, oils including silicon oils and mineral oils and mixtures thereof. As mentioned previously, the lubricant content can assist with the shaping and forming processes of the shaped water adsorbent composite body.
Magnetic Particles
The shaped water adsorbent composite bodies can be configured to harvest water using a magnetic induction swing adsorption system. In these embodiments, the shaped water adsorbent composite body 100 (FIG. 1) comprises a mixture composed of at least 50 wt % water adsorbent metal organic framework, at least 0.1 wt % hydrophilic binder and from 0.2 to 10 wt % magnetic particles having a mean particle diameter of less than 200 nm. The mixture is optimised for use in a packed bed adsorption system.
As discussed previously, a wide variety of magnetic particles can be used in the inventive shaped adsorption body. In embodiments, the magnetic particles comprise a ferromagnetic, paramagnetic, or superparamagnetic particles (typically micro or nano-particle). In embodiments, the magnetic particles comprise metal chalcogenides. Suitable metal chalcogenides comprise magnetic particles comprising any combination of element or ionic form thereof M selected from at least one of Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, TI, Si, Ge, Sn, Pb, As, Sb, Bi, or their combinations, in combination with elements or elemental form of at least one of O, S, Se, or Te. In some embodiments, the crystallisation facilitators comprise metal chalcogenide having the formula MxNyCz, where M,N are selected from at least one of Li, Na, K, Rb, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, B, Al, Ga, In, TI, Si, Ge, Sn, Pb, As, Sb, Bi, C is selected from at least one of O, S, Se, Te, x is any number from 0 to 10, y is any number from 0 to 10 and z is any number from 0 to 10. The metal chalcogenide particles may in some embodiments have a core-shell structure in which the core comprises at least one metal chalcogenide as previously described and the shell comprises at least one metal chalcogenide as previously described. In some forms, the core-shell structure may include multiple shells. In embodiments, the magnetic particles comprise at least one of MgFe2O4, Fe3O4, C-coated Co, CoFe2O4, NiFe2O4, Pyridine-2,6-diamine-functionalized SiO2, or Pyridine-2,6-diamine-functionalized Fe3O4.
The advantages of these magnetic materials are:

    
    
        Local heat generation—i.e. heat can be generated insitu the material by applying an AC magnetic field (as discussed previously) as opposed to using an external heating source;
        Fast heating of material, due to local heat generation avoiding thermal and energy loss through thermal heating of surrounding materials; and
        High energy conversion efficiency
    
    


The combination of the magnetic particles with MOFs to form a magnetic framework composite material yields an adsorbent with exceptional adsorption behaviour as a result of the MOFs and high efficiency of induction heating as a result of the magnetic particles.
EXAMPLES
The following examples use AlFu as the water adsorbent MOF in the magnetic framework composite material. It should be appreciated that the magnetic framework composite material could use any number of other water adsorbent MOFs through direct substitution of that MOF within the magnetic framework composite material pellets.
Example 1—Magnetic Induction Swing Water Harvesting
1. Magnetic Framework Composite Material
The synthesis of AlFu and the preparation of shaped water adsorbent composite bodies comprising AlFu magnetic framework composite material (MFC), hereafter referred to as MFC pellets, are described. The examples demonstrate that the experimental system can produce water repeatedly, with 1.2 grams of water having been produced from roughly 3 cycles of the described method and system. Cycle times were approximately 30 minutes in duration. In the examples outlined below, 0.4 g of water was captured using 5 g of the inventive shaped composite material within 28 minutes. This provides the following production and energy use:

    
    
        Anticipated water production capacity: 4.3 L/kg of MOF a day with a cycle time of 28 mins; and
        Anticipated energy use: 12 kWh/L.
    
    


As a comparison, the system described in Yaghi 1 and Yaghi 2 (referred to in the Background of the Invention section) uses sunlight as energy source for regeneration of the MOF. This device was reported as being capable of capturing 2.8 litres of water per kilogram of MOF daily at relative humidity levels as low as 20% at 35° C. in Yaghi 1. Yaghi 2 indicates that about 0.75 g of water was produced from 3 g of MOF within 16.5 hours in the same conditions. This equates to an anticipated water production capacity of 0.25 L/kg of MOF daily. The process of the present invention therefore has a significantly higher water production rate than the system taught in Yaghi.
The inventors note that Yaghi 1 originally claimed that their device was capable of capturing 2.8 litres of water per kilogram of MOF daily at relative humidity levels as low as 20% at 35° C. However, this higher production rate appears to have been greatly overestimated in that paper, as further experimental work published in Yaghi 2 using the same set up reports a production rate being an order of magnitude lower at 0.25 litres of water per kilogram of MOF daily at 20% RH and 35° C. Inventors consider that the production rate published in Yaghi 2 reflects the actual production rate of this MOF-801 based system.
1.1 Preparation of Magnetic Framework Composites
The synthesis of aluminium fumarate MOF and the preparation of aluminium fumarate MFC pellets are described.
1.1.1 Aluminium Fumarate Synthesis
Within this work, two different scaled batches of aluminium fumarate were synthesized. For the evaluation of different contents of magnetic nanoparticles on moisture adsorption and induction heating performance of the composite material a smaller batch, designated Batch I, was prepared. While for experiments with the water capture rig 600 (see FIG. 6), a larger batch, designated Batch II, was synthesized.
The experimental setup 400 of the aluminium fumarate synthesis reaction is presented in FIG. 2A.
The two precursor solutions named A and B were synthesized as follows:
For solution A, aluminium sulfate octadecahydrate was dissolved in deionized water using a magnetic stirrer 406. Precursor solution B was prepared by dissolving sodium hydroxide pellets and fumaric acid with a purity of 99% in deionized water under stirring with a magnetic stirrer (not shown). The composition of both solutions can be taken from Table 1.







TABLE 1







Composition of precursor solutions for aluminium fumarate


synthesis








Precursor Solution A
Precursor Solution B













Aluminium
Deionized
Sodium
Fumaric
Deionized



Sulfate
Water
Hydroxide
Acid
Water





Batch I
35 g
  150 ml
13.35 g
 12.9 g
  191 ml


Batch II
90 g
385.7 ml
34.33 g
33.17 g
491.1 ml









Solution B was then filled into a round bottom flask 410 and heated up to 60° C. using a heating mantel 408. A mechanical stirrer 402 was used to stir the liquid. When 60° C. were reached, precursor solution A was added. The mixture was then stirred for 20 minutes at 60° C. measured using temperature transducer 404.
Afterwards, the suspension was filled into centrifuge tubes (not shown) and centrifuged for 8 to 10 minutes at 6000 rpm for Batch I and 4500 rpm for Batch II, respectively. The liquid was then removed from the sedimented MOF crystals. After that aluminium fumarate was washed using the following procedure. At first, deionized water was added to the MOF crystals. The suspension was then shaken by hand until the sediments were homogenously mixed up. Furthermore, the suspension was mixed for 15 minutes onto a roller mixer for Batch I and an orbital shaker for Batch II, respectively. Afterwards, the suspension was centrifuged using the same settings as mentioned before. After removing the liquid, the washing procedure with deionized water was repeated for another three times.
Subsequently, aluminium fumarate was washed with methanol for one time following the same procedure as described before. Aluminium fumarate after the washing procedure is shown in FIG. 2B.
After the washing steps, the MOF crystals were pre-dried overnight in a glove bag under nitrogen atmosphere. Afterwards, the MOF was dried overnight in an oven at 100° C. under nitrogen atmosphere. Subsequently, the temperature was increased to 130° C. and the oven was evacuated to activate the MOF for 6 to 8 hours.
1.1.2 Aluminium Fumarate Composite-Pellet Preparation
A smooth paste needs to be prepared for the extrusion of MOF pellets. Therefore, the MOF was ground using a mortar and a pastel (not illustrated) for the smaller Batch I and a coffee grinder (not illustrated) for the larger Batch II, respectively. After grinding, the MOF was sieved through a 212 μm sieve. In case of Batch II, the aluminium fumarate powder was sieved through a 150 μm sieve. The MOF powder was then weighed into a jar. Afterwards, magnetic nanoparticles (MNPs) were added. In this work, magnesium ferrite was chosen as magnetic nanoparticles. However, it should be appreciated that other magnetic nanoparticles could equally be used. The powder mixture was then shook by hand for about 10 minutes until the colour of the powder was homogenously brownish. Afterwards, the powder was filled into a bowl and a hydrophilic binder (hydroxypropyl cellulose (HPC)) was added. To investigate the effect of the amount of magnetic nanoparticles on water uptake and magnetic induction heating, different composites were prepared. The composition of the prepared samples is provided in Table 2.







TABLE 2







Composition of different aluminium fumarate composite samples










Concentration of




Magnesium Ferrite
Concentration of


Batch
[wt %]
Binder [wt %]





Batch I
0
0



0
1



1
1



3
1



5
1


Batch II
3
1









Furthermore, a solvent, in this case deionised water was added to make the mixture pastier. In case of Batch I, also small amounts of ethanol were added. The components were then well mixed until an ice cream like paste has formed.
For the extrusion of composites made from Batch I, a syringe with a round nozzle was used (not illustrated). In case of Batch II, a hand extruder 500 with a triangular shaped nozzle 505 was chosen. The extruder is illustrated in FIG. 3A. The triangular shaped extrusion attachment 505 was chosen in order to increase the packing density of the produced pellets as explained previously. Furthermore, magnesium stearate was used as lubricant for preparation of pellets from Batch II. The magnesium stearate powder was greased onto the inner walls of the hand extruder 500. The paste was extruded onto filter paper and dried for at least 10 minutes. Afterwards, the extruded MOF was cut into 3 to 5 mm long pellets using a razor blade.
The pellets were then dried in an oven at 100° C. under vacuum (reduced pressure of less than 100 mbar) for 24 hours. The different MOF composite pellets (Aluminium fumarate and aluminium fumarate composite pellets) are presented in FIG. 4 which show (A) Pristine MOF; (B) 1 wt % binder; (C) 1 wt % MNP; (D) 3 wt % MNP; and (E) 5 wt % MNP. A schematic of this overall process is shown in FIG. 3B.
1.2 Analysis of Aluminium Fumarate Composites
The first part of this section deals with different analysis methods that have been used to characterize the structure of aluminium fumarate composites. Furthermore, methods that evaluate the performance of the composites regarding water uptake and magnetic induction heating are described.
1.2.1 X-Ray Diffraction
All samples have been characterized using powder X-ray diffraction (PXRD) as well as small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). For X-ray diffraction analysis, the pellets were ground first to fill them into the sample holder.
Powder X-ray diffraction was performed employing a Bruker D8 Advance X-ray Diffractometer operating under CuKα radiation. The diffractometer was equipped with a Lynx Eye detector. All samples were scanned over the 28 range 5° to 105° with a step size of 0.02° and a count time of 1.6 seconds per step. To give an equivalent time of 284.8 seconds per step, 178/192 of the sensor strips on the Lynx Eye were used. The Bruker XRD search match program EVATM4.2 was used to perform analyses on the collected PXRD data.
Aluminium Fumarate is not present in the JCPDS database. Therefore, for reference a simulation of the structure of aluminium fumarate was generated in TOPAS using a simplified model for the geometry of the mentioned diffractometer.
Small- and wide-angle X-ray scattering was performed at the Australian Synchrotron. The samples were mounted onto sample holder plates. All samples despite of magnesium ferrite control samples were analysed with 1% Flux and an exposure time of 1 sec. Magnesium ferrite samples were analysed at 100% Flux.
1.2.2 Infrared Spectroscopy
Infrared spectra analysis was performed using a Thermo Scientific Nicolet 6700 FT-IR spectrometer. The samples were analysed in the wavenumber range from 500 to 4000 cm−1.
1.2.3 Scanning Electron Microscope Imaging
Specimens for scanning electron microscope (SEM) imaging were prepared by diluting the samples in water and then trickling the suspension onto a silicon waver. The silicon waver was then stuck onto a SEM specimen stub using carbon tape. Before scanning, the samples were coated with iridium to increase the signal to noise ration during microscopy. The SEM images were taken using a Carl Zeiss Gemini SEM 450 instrument at 10000 times magnification.
1.2.4 Surface Area and Porosity Measurements
Surface area and porosity measurements of aluminium fumarate composites were analysed using a Micrometrics ASAP 2420 high throughput analysis system.
At first, composite pellets were filled into pre-weighed analysis tubes and capped with Transeal caps. The samples were then degassed for 24 hours at 140° C. under vacuum. Afterwards, the tubes with the containing degassed samples were weighed to determine the mass of the dried pellets. The tubes were then transferred to the analysis ports of the instrument. Langmuir and Brunauer-Emmett-Teller (BET) surface areas as well as pore size distribution of all samples were determined by collecting nitrogen isotherms at 77K in a liquid nitrogen bath. Pore size distribution was determined using density functional theory (DFT).
The BET surface area of samples made from batch I was measured three times in order to determine the variation within the analysis. The averaged surface area x was calculated using Equation 1.1:



 
  
   
    
     
      x
      _
     
     =
     
      
       1
       n
      
      ⁢
      
       
        ∑
        i
        n
       
       
        x
        i
       
      
     
    
   
   
    
     (
     1.1
     )
    
   
  
 



Where n is the total number of experiments and xi is the surface area of the experiment i.
Furthermore, the standard deviation sn was calculated. This was done by using Equation 1.2.



 
  
   
    
     
      s
      n
     
     =
     
      
       
        1
        n
       
       ⁢
       
        
         ∑
         i
         n
        
        
         
          (
          
           
            x
            _
           
           -
           
            x
            i
           
          
          )
         
         2
        
       
      
     
    
   
   
    
     (
     1.2
     )
    
   
  
 



1.2.5 Water Uptake Capacity Determination

Water Uptake capacity was measured using a Quantachrome Instruments Autosorb-1 analyser.
The samples were filled into pre-weighed analysis tubes. After that, the material was degassed for 16 hours at 140° C. under vacuum. Afterwards, the weight of the dried pellets was determined. The tubes were then connected to the analysis port for water vapour adsorption measurement. In order to ensure a constant temperature during the analysis, the sample tubes were put into a water bath at room temperature. Water vapour uptake was measured using pure water vapour at relative pressures p/p0 from 0.1 to 0.5 with a step size of 0.1. The water vapour adsorption experiments have only been performed once because it takes almost one week to run a single isotherm.
1.2.6 Investigation of Magnetic Induction Heating
To evaluate magnetic induction heating of magnetic framework composites, heating rate and efficiency of induction heating have been investigated.
For the induction heating experiments an Ambrell Easy Heat 1.2 kW induction unit was used. The induction coil 560 that was attached to the work head is made from copper. It had three turns, an inner diameter of 4 cm and a length of 2.5 cm. A water chiller 562 was used to cool down the coil 560 during the experiment.
The setup 550 for the induction heating and efficiency experiments is shown in FIG. 5. A certain amount of the sample was filled into a glass vial 565. To monitor the temperature increase of the sample over time during induction heating a fibre optic cable sensor 566 was introduced into the centre of the bed 567. The sensor 566 was connected to an OpSens FOTS100 temperature data logger 570. The glass vial 565 was put into the centre of the coil 560 so that the middle of the bed's height was in line with the middle of the coil's height.
To monitor the energy that is consumed by the induction heating unit during the experiment a Cabac Power-MateTM power meter 575 was used. The power that is needed to heat up the sample was calculated as following.
At first, the coil was operated without any sample in the magnetic field to get a baseline. Therefore, the energy was measured for 5 minutes. The power was then calculated using Equation 1.3.



 
  
   
    
     
      Power
      ⁢
         
      consumed
     
     =
     
      
       Energy
       ⁢
          
       consumed
       ⁢
          
       over
       ⁢
          
       5
       ⁢
          
       
        minutes
           
        [
        kWh
        ]
       
      
      
       Time
       ⁢
          
       
        
         (
         
          5
          ⁢
             
          minutes
         
         )
        
        [
        h
        ]
       
      
     
    
   
   
    
     (
     1.3
     )
    
   
  
 



During heating of the sample, energy was also measured for the first 5 minutes of induction heating. The power was then calculated the same way as mentioned before.
For investigating the heating effect of magnetic framework composites exposed to an external magnetic field, temperature of the sample was measured over time for different composites and for different amounts of the composite pellets. All experiments were performed for more than 20 minutes. After this time the heating curve for induction heating was constant for all samples.
The initial heating rate was used to quantify the induction heating effect. This rate was determined by calculating the linear slope of the temperature profile (dT/dt)t=0 at the beginning of the experiment. The heating curve is therefore approximated by Equation 1.4:



 
  
   
    
     
      T
      ⁡
      (
      t
      )
     
     =
     
      
       T
       0
      
      +
      
       Δ
       ⁢
       
        
         T
         max
        
        [
        
         1
         -
         
          e
          
           t
           T
          
         
        
        ]
       
      
     
    
   
   
    
     (
     1.4
     )
    
   
  
 



Where T0 is the initial temperature of the pellets, ΔTmax is the saturation temperature increase (Tmax−T0) and T is the time constant of heating which corresponds to the time when the temperature reaches approximately 63% of ΔTmax.
Efficiency of induction heating of magnetic framework composites was quantified using Equation 1.5.



 
  
   
    
     
      Efficiency
      ⁢
         
      %
     
     =
     
      
       
        P
        Coil
       
       
        P
        SAR
       
      
      ×
      100
      ⁢
      %
     
    
   
   
    
     (
     1.5
     )
    
   
  
 



In this equation, PCoil is the power that is consumed by the coil during induction heating and it is calculated by using Equation 1.6.

PCoil=Pconsumed,heating MFC−Pconsumed, without MFC in field  (1.6)

The specific adsorption rate (SAR) is usually used to estimate the heating effect of magnetic nanoparticles exposed to an external magnetic field. The SAR was determined by dispersing 10 mg of magnetic nanoparticles in 100 ml of deionized water. The suspension was then put into the centre of the induction coil and triggered with a magnetic field. The temperature increase of the suspension was measured using an optic fibre cable and a temperature data logger. The specific adsorption rate can then be calculated using Equation 1.7.



 
  
   
    
     SAR
     =
     
      
       C
       water
      
      ×
      
       
        m
        water
       
       
        m
        nanoparticles
       
      
      ×
      
       
        (
        
         dT
         dt
        
        )
       
       
        t
        =
        0
       
      
     
    
   
   
    
     (
     1.7
     )
    
   
  
 



In this equation, Cwater is the specific heat capacity of water, mwater is the mass of water, mnanoparticles is the mass of magnetic nanoparticles in the suspension and (dT/dt)t=0 is the initial heating rate. The initial gradient of the heating curve was calculated as mentioned before.
Finally, the power that is generated by the magnetic nanoparticles in the composite PSAR can then be calculated using Equation 1.8.

PSAR=SAR×Magnetic nanoparticle content of MFC pellet (g)  (1.8)

All experiments for determination of the initial heating rate and efficiency of induction heating were carried out for three times to determine a standard variation.
1.3 Proof of Concept Experiments for Magnetic Induction Vacuum Swing Adsorption
This subsection deals with different methods that have been used to evaluate the performance of a magnetic induction vacuum swing adsorption process for water capture from ambient air. These experiments were carried out with a self-constructed water capturing rig on bench scale. The schematic process flow diagram of the Water capturing rig 700 is provided in FIG. 6.
Moisturized nitrogen was used as test gas for water capture and breakthrough experiments. A nitrogen stream from gas supply 702 at 1 bar was split up into a dry gas stream 704 and a wet gas stream 706 that was moisturized by bubbling it through deionized water in bubbler 708. Flow of each stream were measured using flowmeters 710 and 711. The desired humidity of the feed stream for the adsorption column was reached by setting the ratio of the dry gas stream 704 and the wet gas stream 706.
A vertically orientated adsorption column 720 was used comprising a 1 inch polyether ether ketone tube. A perforated Teflon spacer was glued in the bottom part of the tube to hold the adsorption bed thereon within the tube (not illustrated but enclosed within adsorption column 720). Furthermore, glass wool was used to prevent pellets from falling through the holes of the spacer. The tube was connected to the feed and outlet pipes using stainless steel ultra-Torr vacuum fittings purchased from Swagelok.
In these experiments an Ambrell EasyHeat 3542 LI induction coil 725 with a system power of 4.2 kW was used. A copper coil with 5 turns, an inner diameter of 4 cm and a length of 5 cm was connected to the work head of the induction coil 725. The feed and outlet pressure were monitored using manometers 730. To measure the temperature in the adsorption bed, a fibre optic cable 732 was introduced into the middle of the packed bed and connected to a temperature data logger. A RS 1365 Data logging Humidity-Temperature Meter 735 was used to monitor the humidity of the outlet stream 745 of the adsorption column 720.
For water capture, the out-coming stream 645 was lead through a cold trap 740 containing dry ice to condensate the moisture to produce water 755. A vacuum pump 750 was used to generate the driving force for the desorbed gas stream 745.
1.3.1 Water Collection Experiments
For water collection experiments, aluminium fumarate magnetic framework composite pellets made from batch I containing 3 wt % magnetic nanoparticles were filled into the adsorption column. In order to increase the packing density, the pipe was tapped onto the bench for a few times.
A dry nitrogen stream with different volume flow rates was flown through the packed adsorption column in order to determine the back pressure as a function of the flow rate.
The determined back pressure was then used to calculate the desired relative humidity of the feed stream. For the desired humidity, desert like conditions were chosen. The relative humidity in these areas is about 35% at 35° C. and atmospheric pressure. To simplify the experimental set up, the water uptake experiments in this work were carried out at room temperature. This simplification is justified because the temperature dependence of water vapour uptake on aluminium fumarate in this temperature region is negligible. However, in order to get comparable results, calculations of humidity were based on water content in the desert like air. The dessert like conditions correspond to a water content of 11273 ppmV in a pure nitrogen atmosphere (calculated with Michel Instruments Humidity Calculator—http://www.michell.com/us/calculator/).
Based on this water content, the ratio of the dry and the moisturized gas stream can then be calculated.
For water capturing experiments, MFC pellets were activated by triggering them with an alternating current magnetic field and directing a flow of dry nitrogen stream through the column. Activation of the material was performed until the humidity of the out coming gas stream was zero. It is noted that this activation step was used for experimental date collection purposes only in order to obtain a dry MOF for measurement accuracy. A commercial system would not generally require this activation/drying step to be performed as any preadsorbed moisture in the MOF material in the system would simply be desorbed in the first cycle of operation of the system.
Before charging the MFC pellets with water vapour, volume flow rates of the dry and the moisturized streams were set. The resulting feed stream was first vented to allow the humidification of the gas stream to stabilize. After three minutes, the valve in front of the adsorption column was switched to enable the feed to flow through the column.
During moisture adsorption, the humidity of the outlet stream of the column was measured and noted down every 30 seconds in order to determine breakthrough curves. After the humidity of the vented stream had stabilized, the feed stream was turned off and the valve was closed towards the column.
For regeneration, in a first experiment only humidity was measured during desorption in order to determine the duration of the regeneration step. Therefore, during induction heating, a dry nitrogen stream was lead through the adsorption bed to flush the column.
In order to determine breakthrough curves, the relative humidity that was measured in the outlet stream of the column has been normalized. Therefore, the measured humidity was divided by the humidity of the out coming stream that is reached when the adsorption bed is saturated.
2. Results and Discussion
In this section, results of characterisation and performance analysis of aluminium fumarate composites and its ability for capturing water from ambient air using a magnetic induction vacuum swing adsorption process are presented and discussed.
2.1. Structural Characterisation of Composite Material
The PXRD pattern of aluminium fumarate and aluminium fumarate with 1 wt % of binder is presented in FIG. 7. Furthermore, a simulated pattern of aluminium fumarate is plotted. It can be seen that most of the peaks in the trace of the pristine MOF and the MOF with 1 wt % binder are a reasonable match to the simulated phase.
The PXRD pattern of different aluminium fumarate magnetic framework composites made from Batch I can be taken from FIG. 8. Furthermore, the trace of magnesium ferrite is plotted as reference.
The traces of all composites match the PXRD pattern of aluminium fumarate containing only the binder.
For the composite containing 1 wt % of magnetic nanoparticles, the PXRD pattern does not reveal a significant evidence of magnesium ferrite in the sample. Presumably, any magnetic nanoparticles present in this sample are below the detection limit.
The PXRD pattern of composites with 3 wt % and 5 wt % of magnesium ferrite look fairly similar with a trace of magnetic nanoparticles being visible at the 2θ angle 35°.
The PXRD trace of the magnetic framework composite made from Batch II are presented in FIG. 9. The pattern matches the trace of the pristine MOF of this batch. Similar to the composites made from Batch I, there is a trace of magnesium ferrite visible at the 2θ angle 35°.
The surface morphology of aluminium fumarate has been studied using scanning electron microscopy and is presented in FIG. 10. It can be observed from this Figure that this MOF has a quite rough surface and a poorly crystalline structure.
The narrow particle size distribution of magnesium ferrite nanoparticles are presented in FIG. 11. The average particle size of this sample is about 150 nm.
The incorporation of aluminium fumarate and magnesium ferrite nanoparticles can be observed from FIG. 12. The circled sections marked with A indicate examples of the location of magnesium ferrite nanoparticles in the composite. It can be seen, that the nanoparticles are fairly equally distributed within the MOF structure.
The average BET surface area of aluminium fumarate magnetic framework composites as a function of magnetic nanoparticle loading is shown in FIG. 13. The sample containing no magnesium ferrite refers to composite pellets that were made only from the MOF and binder. The average surface area of pristine aluminium fumarate pellets is 976 m2/g. The standard deviation of the measurements for this sample is 33 m2/g.
From the plot and the surface area of the pristine MOF it can be taken, that there is not a significant change in the BET surface area for adding the binder and for an increasing magnetic nanoparticle concentration. Even though there is a slight decrease in surface area visible for higher nanoparticle loadings, the average surface area is still in the same order of magnitude. Furthermore, the standard deviation for the different experiments does not substantiate the decreasing trend.
The BET surface area of the second batch and composite pellets prepared from this batch is shown in Table 3. It can be seen that there is also not a significant difference in the surface area between the pristine MOF and its composite. However, the surface area of MOF pellets from batch II is lower that on pellets prepared from the first batch.







TABLE 3







BET surface area of aluminium fumarate batch II and aluminium


fumarate batch II composite












Concentration MNPs
BET Surface Area



Sample
[wt %]
[m2/g]







Pristine MOF
0
876



Composite
3
849










The pore size distribution of aluminium fumarate pellets are presented in FIG. 14. The main pores size distribution is in the microporous area which is below 2 nm. The microporosity of this sample can also be confirmed with the nitrogen adsorption-desorption isotherm which is shown in FIG. 15. According to IUPAC classification of adsorption isotherms, the shape of this isotherm corresponds to a physisorption isotherm type H4. This shape is typical for microporous materials where the high uptake at low relative pressures is associated with the filling of micropores.
FIG. 16 illustrates that most of the pores of aluminium fumarate composite pellets are also present in the microporous are below 2 nm. Only for the sample containing 3 wt % of magnesium ferrite nanoparticles, there are pores in the mesoporous area between 2 nm and 50 nm.
2.2 Performance Analysis of Aluminium Fumarate Composites
In this subsection, water uptake results and magnetic induction heating performance of the prepared material are presented and discussed. Furthermore, the results of induction heating experiments are compared to a conventional heating method.
2.2.1 Water Uptake Performance
The water vapour adsorption isotherms of samples prepared for pre studies on the effect of an increasing amount of nanoparticles in the MOF can be taken from FIG. 17. All isotherms were collected at room temperature. The plots show that there is not a significant difference between the moisture uptake capacities for the different composites. This was already shown with nitrogen isotherms in section 2.1. In order to check the accuracy of the measurements, the isotherm of the composite containing 5 wt % magnesium ferrite was collected two times. The Figure shows that the values of the second measurement vary by approx. 70% from the first measurement. Regarding this accuracy, it can be confirmed that moisture uptake of the composite pellets does not differ strongly from vapour uptake from pristine aluminium fumarate pellets.
The water vapour isotherms of aluminium fumarate and aluminium fumarate composite pellets prepared from the larger batch are presented in FIG. 18. Regarding the experimental variance of moisture adsorption experiments, it can be indicated that the water vapour uptake of the composite does not significantly differ to the one of the pristine MOF.
2.2.2 Induction Heating Performance and Comparison to a Conventional Heating Method
The induction heating performance was evaluated, using the initial heating rate. The initial heating rate was determined as described in Section 1.2.6. Results of these experiments are shown in FIG. 19. The field strength in these experiments was 12.6 mT. It can be seen, that the initial heating rate increases with the concentration of magnetic nanoparticles incorporated into the metal organic framework. Furthermore, the heating rate increases fairly linear with the amount of sample that is triggered by the alternating current magnetic field.
In addition to the initial heating rate, the energy conversion efficiency of induction heating of the prepared composites is shown in FIG. 20. The field strength was 12.6 mT. Similar to the initial heating rate, the efficiency also increases with an increase in magnetic nanoparticle loading and an increase in sample weight. The increase in efficiency with an increasing sample mass is counterintuitive as one would know from conventional heating methods. However, with an increasing amount of magnetic framework composite pellets, the amount of magnetic nanoparticles triggered by the magnetic field also increases. Therefore, the coupling between the nanoparticles is improved.
For applications on industrial scale, where much larger amounts of MFC pellets are used, the energy conversion efficiency is expected to be even higher than shown in this experiment. That is because of a loss of heat that is caused by non-existent insulation of the heated sample. The loss is not considered in the calculation of the SAR value. To minimize this heat loss, an adiabatic experimental set up needs to be used. However, the non-adiabatic system delivers quick and reliable SAR values without the need for extensive, time-consuming and expensive adiabatic measurements.
In addition to that, the efficiency could be further improved by utilizing induction heating systems that are not water cooled. Water cooled systems require separate support systems with pumps and connections that increase complexity and costs of the system. Induction heating systems that do not need direct cooling have been reported to achieve up to 90% energy efficiency.
2.3 Proof of Concept: Magnetic Induction Vacuum Swing Adsorption
The normalized humidity in the outlet stream of the column during adsorption of moisture is presented in FIG. 21. For this experiment, the relative humidity in the feed stream was set to 50% at a surrounding temperature of 22° C. This corresponds to the same moisture concentration that is present in the driest areas of the world. The volume flow rate for the moisturized and the dry nitrogen stream were both set to 4 SLPM. With these settings, the adsorption bed is fully saturated after approximately one hour. After about 17 minutes the humidity of the out coming stream stabilizes for approx. 8 minutes. This might be due to a sectional higher packing density along the column length which is caused by the inhomogeneity of the pellet length.
In order to reduce the cycle time, for further experiments the breakthrough point where adsorption is stopped was set to the time when 90% of the maximum outlet humidity is reached. This is after approx. 27 minutes.
The temperature that was measured during adsorption of water vapour is shown in FIG. 22. The temperature increases in the beginning due to the released heat of adsorption.
The normalized humidity during regeneration is shown in FIG. 23. Due to the height of the adsorption bed, the induction coil needed to be placed at two different positions in order to heat up the whole material. First, the coil was placed at the upper part of the column. After approx. 2 minutes, the humidity increases drastically due to the rapid heating rate of magnetic induced heating. Almost 20 minutes later, the humidity of the out coming stream decreases as the water amount captured in the MOF also decreases. Right before the humidity in the outlet stream settles, the coil was moved to the lower part. The water that is still adsorbed on the material in the lower part of the column is therefore released. The power of the induction coil was shut off when the humidity reached zero.
The temperature over time during regeneration of water vapour can be taken from FIG. 24. It can be seen from that Figure and the plot of the normalized humidity during regeneration that as soon as the temperature reaches about 50° C., water release starts. The temperature decreases as the coil was moved to the lower part of the column. That is because the temperature sensor sits above the middle of the adsorption bed.
Based on the adsorption isotherms for moisture and the pre studies on the behaviour of the column regarding water adsorption and regeneration, a theoretical yield for the rig can be calculated.
In order to evaluate the energy consumption and efficiency of a magnetic induction vacuum swing adsorption process, energy was measured during regeneration of the MOF composite. For these measurements the 1.2 kW induction heating system was chosen. The parameters for energy efficiency experiments can be taken from Table 4. The energy consumption was monitored using an energy data logger.







TABLE 4







Parameter energy consumption measurements











Parameter
Value
Unit















Mass MFC pellet
5
g



Flow rate dry N2 stream
4
SLPM



Flow rate wet N2 stream
4
SLPM



Surrounding temperature
22
°C.



Current induction heating system
225.6
A



Frequency induction heating system
268
kHz










Before the actual experiment a breakthrough curve for the set up described in Table 4 was determined. Therefore, the activated MOF composite pellets were charged with water vapour for twenty minutes. After this time the adsorption bed was fully loaded with moisture. The breakthrough curve is presented in FIG. 21.
However, in order to increase the overall efficiency of the process, the breakthrough point where adsorption is stopped for the experiments was chosen to be when 90% of the maximum outlet humidity was reached.
After adsorption of water vapour, the regeneration was started and energy consumption of the induction heating system was monitored. Regeneration of the adsorption bed was performed for twenty minutes. This experiment was repeated three times. The results can be taken from Table 5. In this table, the cycle time is the total time for adsorption and regeneration. The capture efficiency is calculated as the ratio between the amount of moisture that is fed into the column and the amount of water that is captured by the absorbance. The calculated price per litre shows there are reasonable prices for water captured from air using this methodology.







TABLE 5







Results water capture experiments















Yield

Energy
Energy
Price 



Cycle
[L
Capture
Con-
Conversion
per


Cycle 
Time
kg−1
Efficiency
sumption 
Efficiency 
Litre* 


No
[min]
day−1]
[%]
[kWh/L]
[%]
[$/L]
















1
28
4.1
57.3
12.8
98.3
3.5


2
28
4.6
64.4
10.4
106.7
2.9


3
28
4.1
57.3
13.0
96.4
3.6





*Excluding capital costs






3. Water Analysis
An IPC analysis was conducted on a comparative Milli-Q water sample and a Milli-Q water sample mixed with water captured using the inventive method from cycle 1 (Table 5) in with a dilution ratio of 1:15 of inventive water to Milli-Q. Water collected from cycle 1 was analysed to test the water for its suitability as potable water. The sample was diluted with ultrapure water with a dilution rate of 1:15. The water sample was analysed for cations (Ca+, K+, Mg+, Na+, S+) and metals (Al, As, B, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, P, Pb, Sb, Se, Si, Sr, Zn) using inductively coupled plasma mass spectrometry. Additionally, ion chromatography was performed to analyse the water for anions (F−, Cl−, Br−, NO3−, SO4−).
IPC analysis of both samples followed testing standards as follows:

    
    
        Fluoride, bromide, sulfate [APHA method 4110]. These common anions are determined by ion chromatography using a Dionex ICS-2500 system with 2 mm AS19 anion separation column and potassium hydroxide eluent generated on line, followed by conductivity detection after chemical suppression. With a flow rate of 0.25 mL per minute the anions F−, Cl−, Br−, NO3− and SO42− are eluted between 3.5 and 25 minutes. Each ion concentration is calculated from peak areas using a 25 μL injection and compared to calibration graphs generated from a set of mixed standards with a range of concentrations.
        Cations and metals [APHA method 3120]. A range of elements are determined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICPOES). The sample is nebulised into the plasma of an Agilent 5100 ICPOES. The emission spectra of the elements of interest are measured simultaneously. This determines the major cations (Ca, K, Mg and Na) along with trace elements (Al, B, Cu, Fe, Mn, Sr and Zn) and the non-metallic elements P, S and Si.
    
    


The results of the IPC analysis are provided in Tables 6A and 6B.







TABLE 6A







Results of IPC Analysis of water samples part 1












|----Ion Chromatography---|
ICP Majors




















F—
Cl—
Br—
NO3—
SO4═
Ca
K
Mg
Na
S

















Sample #
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L





















1
MIlli-Q 
<0.05
<0.05
<0.05
1.6
<0.05
<0.1
<0.2
<0.1
<0.2
<0.2



Water












2
Sample +
<0.05
<0.05
<0.05
4.1
<0.05
<0.1
<0.2
<0.1
<0.2
<0.2



MIlli-Q 













Water
















TABLE 6B







Results of IPC Analysis of water samples—part 2


ICP Minors


























Al
As
B
Cd
Co
Cr
Cu
Fe
Mn
Mo
Ni
P
Pb
Sb
Se
Si
Sr
Zn


#
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L





1
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.1
<0.05
<0.05
<0.05
<0.2
<0.05
<0.1
<0.05
<0.2
<0.05
<0.05


2
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.1
<0.05
<0.05
<0.05
<0.2
<0.05
<0.1
<0.05
<0.2
<0.05
<0.05









The results indicate that sample water produced using the method and apparatus of the present invention have a similar content to Milli-Q water, i.e. ultrapure water as defined by a number of authorities such as ISO 3696. Thus, apart from nitrate concentrations (NO3−), the concentration of all compounds in each sample (reference and inventive cycle 1) is below the detection limit.
The only significant difference is the nitrate concentrations (NO3−), concentrations. The concentration of nitrate in the water sample collected from cycle 1 is about 60.8 mg/L. In the “Guidelines for drinking-water quality” the World Health Organisation (WHO) has restricted nitrate concentration in potable water to 50 mg/L. The concentration of nitrate in the control/reference ultrapure water sample is also elevated being 1.6 mg/L. The concentration of NO3− in ultrapure water type I however should be lower than 0.2 mg/L according to ISO 3696. It is thought that the abnormal nitrate concentrations of both water samples may be the result of contamination either during sample preparation or during sample analysis.
Example 2—Binders
4. Comparative Example—Binders
The following provides a comparative example of the water adsorption properties of a water adsorption body/pellet formed using a hydrophobic binder. The inventors have surprisingly found that a hydrophilic binder must be used to impart optimal water adsorption properties to the shaped water adsorbent composite bodies. Non-hydrophilic binders such as hydrophobic binders deliriously affect the water adsorption properties of the shaped water adsorbent composite bodies compared to pellets formed using hydrophobic binders.
A study was conducted on the effect on adsorption properties of Aluminium Fumarate pellets using different binders in aluminium fumarate pellet preparation.
Pellets were prepared following the methodology set out in section 1.1.2. However, the binder composition was varied between two batches of pellets. A first batch of pellets was made using the first batch (batch I discussed above) of AlFu (designated Aluminium Fumarate (I)) and a cellulose siloxane binder, which is a hydrophobic binder. A second batch of pellets was made using the second batch (batch II discussed above) of AlFu (designated Aluminium Fumarate (II)) and a hydroxypropyl cellulose binder, which is a hydrophilic binder. The water uptake capacity of each batch of pellets was determined following the methodology herein outlined.
The results of the water uptake capacity determination are provided in FIG. 25. A comparison of each batch to the Water Uptake Capacity isotherm for the comprising Aluminium Fumarate batch—i.e. Aluminium Fumarate (I) and Aluminium Fumarate (II) is also shown. It is noted that the adsorption isotherms between these batched differed due to differences in the properties of the formed Aluminium Fumarate MOF.
It is also noted from FIG. 25 that aluminium fumarate has a water capacity between 0.09 to 0.5 g of water per gram of MOF depending on the relative humidity. The typical heat of adsorption of aluminium fumarate for water is well known and ranges between 60 and 30 kJ/mol depending on the ambient humidity
The water vapour uptake isotherms shown in FIG. 25 clearly indicate that using cellulose siloxane decreases the performance of the MOF. However, when using hydroxypropyl cellulose as a binder, there is no decrease win moisture uptake visible.
Example 3—Temperature Swing Water Harvesting
5. Experimental
5.1 Testing Rig
FIG. 26 shows the testing rig 600 for the temperature swing water harvesting device 350 (as illustrated in FIGS. 1C to 1E), with the water harvesting device 350, power supplies and measurement equipment. The illustrated testing rig 600 comprises the previously described apparatus 300 (FIGS. 1C and 1D) equipped with the following measurement devices:

    
    
        Relative humidity data logger 682 “EL-USB-2-LCD+” (Lascar Electronics Ltd., Wiltshire (United Kingdom)) to measure relative humidity and air temperature within the container 630 during adsorption and desorption phase of each water harvesting cycle (WHC).
        Power meter 683 “Digital DC Watt Meter” (KickAss®, Australia) to measure the energy consumption of the peltier device 610 during each desorption phase.
        Temperature data logger 684 “TC-08” (Pico Technology Ltd., Cambridgeshire (United Kingdom)) to log the temperature data of all thermocouples 375 during each desorption phase.
    
    


A regulated DC power supply 685 (0-16 V, 0-10 A) was used to power the peltier device 610, and a digital-control power supply (0-30 V, 0-3 A) 686 was used to power the fan 670. Furthermore, a laptop 687 was used to collect the data from the relative humidity data logger 682 and the temperature data logger 684. A precision bench scale 689 “EK-15KL” (A&D Co. Ltd., Tokyo (Japan)) was also used to weigh the water harvesting device 350 before and after each adsorption or desorption cycle. The difference was calculated to determine the amount of water adsorbed during the adsorption phase or desorbed during the desorption phase.
5.2 Water Harvesting Experiments
Each water harvesting cycle was run with the same setup and using the following protocol:
The adsorption phase of the ith water harvesting cycle commences using an assembled water harvesting device 350 and a desorbed MOF packed bed 355. All thermocouples 375 were disconnected from the data logger 684 and the power supplies 685, 686 were disconnected from the peltier device 310 and the fan 370. The lid 334 of the container 330 was removed and the relative humidity data logger 682 was removed from the container 330. The whole water harvesting device 350 was put on a scale 689 to determine the weight mdes,i-1 with the desorbed MOF packed bed 355. After the RH data logger 682 was set up (sampling rate: 5 min) and started on the laptop 687, the fan 370 was connected to its power supply 686 and switched on to start the air flow through the heat sinks 320 and packed bed 355 and thus commencing the adsorption phase. The fan 370 was switched off and disconnected from its power supply 686 after a set adsorption time. The water harvesting device 350 was put on the scale 689 again to determine the weight mads,i with a water adsorbed MOF packed bed 355. The adsorbed amount of water mwater,ads can be calculated using:

mwater,ads=mdes,i-1−mads,i  (4.1)

where i is the number of the present water harvesting cycle and i−1 is the number of the previous water harvesting cycle. Furthermore, the RH data logger 682 was synchronised with the laptop 687 and the data collected during adsorption was saved. The RH data logger 687 was prepared (sampling rate: 15 s) for the desorption phase.

The thermocouples 375 were connected to their data logger 684, and the peltier device 310 and the fan 370 were connected to the power supplies 685, 686 to start the desorption phase. The RH data logger 682 was started and placed in the container 330. The lid 334 of the container 330 was placed over the container body 332 and was sealed in place with electrical tape. The power supply 685 of the peltier element 310 was switched on after starting the temperature data logger 684 on the laptop 687. The fan 370 was started either together with the peltier element 310 or after the MOF packed bed 355 was heated up to a set temperature, depending on the experiment.
The peltier device 310 and fan 370 were switched off after a set desorption time. The lid 334 of the container 330 was removed from the container body 332 and the data from both data loggers 682, 684 was saved on the laptop 687. The energy consumption of the peltier device 310 was read off the power meter 683. The energy consumption of the fan WFan was calculated using:

WFan=IFan×UFan×trun  (4.2)

where IFan the operating current of the fan, UFan is the operating voltage is of the fan 370, and trun is the runtime of the fan 370. Condensed water was collected with a syringe (not illustrated) from the base of the container 330. The water volume was measured and the water harvesting device 350 was put on the scale 689 after removing the power supplies 685, 686 and the thermocouples 375 were disconnected. The weight of the water harvesting device 350 after desorption mdes,i was used to calculate the amount of desorbed water mwater,des with:

mwater,des=mads,i−mdes,i  (4.3)

The water harvesting cycle was now completed and the water harvesting device 350 was ready to start the next adsorption phase.
5.3 Performance of Peltier-Heated Water Harvesting Device
The aluminium fumarate pellets were characterised to evaluate the performance of the water harvesting device. The pellets were characterised again after the water harvesting cycles to show the usability of aluminium fumarate pellets for water harvesting purposes. Subsequently, 24 water harvesting cycles were run with the device to determine optimised operation conditions.
5.3.1 Characterisation of MOF Pellets
The MOF pellets, containing 99 wt % aluminium fumarate and 1 wt % binder, was characterised using FTIR, PXRD, nitrogen sorption isotherms, water sorption isotherms, and calculated BET surface area.
Infrared spectroscopy was used to investigate changes in the aluminium fumarate due to mixing with binder and solvent during the pelletisation process. FIG. 27 shows the FTIR patterns of aluminium fumarate with 1 wt % hydroxypropyl cellulose (HPC) binder. Three extrusion batches were made to produce 200 g of pellets. Aluminium fumarate for all three batches was prepared as discussed in Example section 1.1.1. The pellets were prepared following a similar procedure outlined in Example section 1.1.2, though in this case the composition of the pellets was formulated using aluminium fumarate with 1 wt % hydroxypropyl cellulose (HPC) binder with no magnetic nanoparticle content.
The first batch of pellets, designated “Pellets_01” were mixed with water and ethanol as solvents to get the required consistency of the paste for extrusion. However, this solvent formulation leads to a paste strand that dried too slowly for desired cutting behaviour in the pelletisation process (as described in section 1.1.2). The subsequent pellet batches, Pellets_02 and Pellets_03, were made with pure ethanol as solvent. This results in a quicker drying of the paste during the pelletisation. Furthermore, as FIG. 27 shows, the use of the different solvents results in different FTIR patterns. The pellets made with water and ethanol showed a stronger peak at wave numbers 3400 cm−1 and 1150 cm−1 and a weaker peak at 980 cm−1 compared to the other batches made with pure ethanol as solvent.
FIG. 27 also compares the FTIR pattern of Pellets_01, Pellets_02 and Pellets_03 to pristine aluminium fumarate. The pattern of Pellets_01 was in good accordance with the pattern of pristine aluminium fumarate with both showing a strong and wide peak around a wave number of 3400 cm−1. The pristine MOF was not activated prior to the infrared spectroscopy. The pellets made with just ethanol as solvent show a slightly different FTIR pattern compared to the pristine MOF. The pellets were dried over night at 100° C. The pristine MOF and the pellets with water and ethanol as solvent exhibit strong peaks at 3400 cm−1 and 1150 cm−1 as well as a weaker peak around 980 cm−1. This difference may be attributable to water adsorbed to the MOF.
A powder X-ray diffraction analysis was run on the samples, to evaluate the crystallinity of the produced aluminium fumarate pellets. The pattern was compared to the pristine aluminium fumarate as well as a simulated PXRD pattern. FIG. 28 shows the PXRD patterns. The strong peaks in the patterns of all three pellet batches indicate the crystallinity of the material. The three PXRD patterns were very similar, confirming that the difference in the FTIR pattern was due to the adsorbed water in one of the pellet batches. The PXRD pattern of the pellets also matches the pristine MOF well. Similarly, the simulated pattern matches the other patterns satisfactorily.
Samples from all extrusion batches were analysed with a nitrogen uptake measurement, to characterise the aluminium fumarate pellets in regard to their adsorption characteristics. The BET surface area was determined as a quantitative value to compare the adsorption capability. Table 5.4 shows the BET and Langmuir surface areas of all three pellet extrusion batches and the surface areas of the pristine aluminium fumarate.







TABLE 5.4







BET and Langmuir surface areas calculated from nitrogen


sorption isotherms of pristine aluminium fumarate and


aluminium fumarate pellets.










BET surface area
Langmuir surface area


Sample
(m2 g−1)
(m2 g−1)





Pristine aluminium fumarate
884
1064


Pellets_01
805
1042


Pellets_02
817
1061


Pellets_03
824
1071









The surface areas of the pellets were 9%, 8% and 7% lower for Pellets_01, Pellets_02 and Pellets_03, respectively. This is likely a result of the added binder and the processing with solvents during the pelletisation process. Furthermore, the MOF was packed in a rigid shape and not in a powder like the pristine aluminium fumarate. The pellets extruded with a mixture of ethanol and water show a slightly lower surface area. It was decided that pellet extrusion should use pure ethanol as solvent for enhanced pellet quality.
Water isotherms were measured for the batch Pellets_02, to determine the water uptake capacity of this batch. FIG. 29 shows the water uptake isotherm of the aluminium fumarate pellets compared to a water uptake isotherm for pristine aluminium fumarate were reported in the literature by Teo et al. (2017). Experimental study of isotherms and kinetics for adsorption of water on Aluminium Fumarate. International Journal of Heat and Mass Transfer Volume 114, November 2017, Pages 621-627.
Firstly looking at the experimental isotherm (noting that this isotherm only shows the adsorption phase as desorption was not measured due to the very long equilibrate phases during the isothermal desorption): Aluminium fumarate pellets follow a type-IV isotherm. A first increase of water uptake is shown in the relative pressure range of 0:01 to 0:03, followed by a plateau with a lower slope. A second steep increase was observed at relative pressures between 0:2 and 0:4, again followed by a plateau region. The water uptake at a relative pressure of 0:4 was around 0:3 gwater=gMOF and a maximal water uptake of 0:34 gwater=gMOF was observed at a relative pressure of 0:6.
Now looking at the comparison to the Teo isotherm in FIG. 29, it can be seen that Teo's reported water uptake isotherms of aluminium fumarate were of type-IV as well and have the steep increases of water uptake in the same relative pressure range. The water uptake in low relative pressure ranges was lower in the data of Teo, compared to the pellets of this work. In high relative pressure ranges the water uptake reported by Teo was higher compared to the pellets of this work. This might be due to the rigid pellet form as well as the 1 wt % binder in the aluminium fumarate pellets. Thus, the isotherm of the pellets show water uptake in g per g of MOF pellets, containing 99 wt % aluminium fumarate.
In conclusion, the produced aluminium fumarate pellets were of high crystallinity and structure comparable to simulated data of X-ray diffraction analysis. The use of ethanol as solvent during the pelletisation process provided the best surface area results. Furthermore, the produced pellets were of still a good quality in regards to water uptake behaviour with a maximum water uptake of 0:34 g/g.
5.3.2 Water Harvesting Experiments
Water harvesting cycles with the water harvesting device were run in the testing rig. For each cycle, containing an adsorption and a desorption phase the following date was recorded:

    
    
        the relative humidity during adsorption and desorption;
        the temperature in the MOF bed during desorption;
        the energy consumption of the peltier device and the fan; and
        the desorbed amount of water.
    
    


Twenty four water harvesting cycles were run with the device. The goal of the experiments was to select a suitable peltier device and determine an optimal temperature range for desorption of the MOF bed. Once the best peltier device was determined the operating parameters were optimised with respect to energy consumption and water yield per day. All experiments were run with ambient air in March 2019 in Melbourne (Clayton), Australia. Table 5.1 shows all water harvesting cycles.







TABLE 5.1







List of all water harvesting cycles with operating parameters


(Fan parameter: HF - high flow rate [I = 0:09 A],


LF - low flow rate [I = 0:02 A],


‘*’ fan switched on during heating and condensation, in all


other experiments the fan was just switched on during


condensation).













Peltier
Heating
Condensation
Condensation



No.
device
current (A)
current (A)
time (h)
Fan





 1
 29 W
3.0
3.0
3.0 (incl. heating)
—


 2
 29 W
3.5
3.5
3.0 (incl. heating)
—


 3
 29 W
4.0
4.0
3.0 (incl. heating)
—


 4
 29 W
4.0
4.0
3.0 (incl. heating)
 HF*


 5
 29 W
4.0
4.0
2.0 (incl. heating)
—


 6
 29 W
4,0
4.0
1.5 (incl. heating)
—


 7
 29 W
4.0
4.0
1.0 (incl. heating)
—


 8
110 W
5.0
4.5
2.0
—


 9
110 W
5.5
4.5
2.0
—


10
110 W
6.0
4.5
2.0
—


11
110 W
6.5
4.5
2.0
—


12
110 W
6.5
6.0
2.0
 LF*


13
110 W
6.5
6.5
2.0
HF


14
110 W
6.5
6.5 . . . 5.5
1.5
LF


15
110 W
6.5
6.5 . . . 6.0
1.0
LF


16
110 W
6.5
6.5 . . . 6.0
0.5
LF


17
110 W
6.5
6.5
0.083
LF


18
110 W
6.5
6.5 . . . 5.5
0.5
LF


19
110 W
6.5
6.5 . . . 5.5
0.5
LF


20
110 W
6.5
6.5 . . . 4.0
0.5
LF


21
110 W
6.5
6.5 . . . 5.5
0.5
LF


22
110 W
6.5
6.5 . . . 5.5
0.5
LF


23
110 W
6.5
6.0
0.5
LF


24
110 W
6.5
6.5
0.5
LF









The first tested peltier device (Adaptive [53] AP2-162-1420-1118 Max Current 7:8 A) had a maximal temperature difference of 95° C. and a maximal heat flow of 29.3 W. The second tested peltier device (Multicomp [54] MCTE1-12712L-S Max Current of 12:0 A) had a maximal temperature difference of 68° C. and a maximal heat flow of 110 W. The tested electrical currents for the peltier device in water harvesting cycle 1 to 3 and 8 to 11 were selected by heating experiments, run prior to the water harvesting cycles.
The heating experiments were run with the peltier device and an unloaded heat sink to determine the maximal temperatures in the heat sink in the current range of the peltier devices. Based on this data the initially tested currents with the loaded heat sink were elected. Further experiments were run with currents based on the previous water harvesting cycles. All experiments were evaluated with respect to the space time yield (STY) of the present operating parameters and the energy consumption of the device per kg of harvested water. Table 5.2 shows the results of the experiments.







TABLE 5.2







Evaluation of all water harvesting cycles.


Cycle times marked with ‘*’ were calculated with a theoretical


adsorption time, calculated from Adsorption_14.













Water
Water
Cycle

Specific



desorbed
collected
time
STY
energy


No.
(g)
(mL)
(hh:mm)
(L kg−1 d−1)
(kW h kg−1)















 1
9.3
4.1
20:05
0.025
21.95


 2
32.4
17.5
20:20
0.106
7.43


 3
44.8
28.1
25:30
0.170
5.34


 4
11.5
7.9
*5:00
0.192
18.34


 5
34.9
21.9
*4:00
0.664
4.67


 6
22.5
12.3
 3:30
0.426
5.87


 7
13.1
4.9
*3:00
0.198
8.60


 8
35.2
29.1
*5:00
0.705
4.20


 9
33.4
27.6
 4:42
0.712
4.43


10
32.0
24.5
*4:30
0.660
4.58


11
26.9
23.1
 4:21
0.664
4.42


12
57.9
51.7
*7:31
0.833
3.06


13
49.2
36.7
*5:24
0.824
5.61


14
52.7
42.8
*5:32
0.938
3.37


15
44.8
37.2
*4:31
0.998
3.05


16
32.3
26.3
*3:08
1.018
2.75


17
19.1
11.2
*1:37
0.838
3.67


18
17.9
10.7
*1:51
0.701
3.85


19
8.8
2.9
*1.21
0.260
7.12


20
3.0
0.6
*1:21
0.054
17.77


21
10.2
2.8
 2:50
0.120
18.67


22
11.3
6.6
 2:55
0.274
7.92


23
27.4
21.6
*3:09
0.833
3.35


24
30.7
25.2
 3:04
0.998
3.27









As the reported, desorption temperature of aluminium fumarate was 110° C., the peltier device with the greatest temperature difference was tested in the first place. The device was tested with three different currents in WHC 1 to 3. The temperature in the MOF bed during desorption was up to 65° C., 70° C. and 80° C. in WHC 1, 2 and 3, respectively.
With increasing temperature in the MOF bed, the amount of desorbed water increases as well. The space time yield in the first three cycles was calculated with the actual adsorption time prior to the desorption phase. The adsorption was carried out overnight. Thus, the cycle times were around 24 h. The peltier device was switched on for three hours for the desorption phase in these experiments after the adsorption was completed. The water was collected afterwards. The highest STY of 0:170 L kg−1 d−1 and lowest specific energy consumption of 5:34 kW h kg−1 were measured in WHC 3.
WHC 4 was run with the same current as WHC 3. The influence of the fan during the desorption phase was tested in this cycle. The fan was switched on simultaneously with the peltier device. A high air convection was created in the container 630. Hence, the MOF bed heats up more slowly during the desorption phase compared to the third cycle. As a result the highest temperature in the MOF bed after three hours was just 50° C. and the resulting amount of harvested water was 7:9 mL, significantly lower than the 28:1 mL in WHC 3. The maximal dissipated heat of the 29.3 W peltier device was not sufficient to heat up the MOF bed with a high convection. The subsequent experiments with this device were therefore carried out without a fan in the container 630 during desorption.
Beginning with WHC 4, the space time yield was calculated with a theoretical adsorption time. To calculate a comparable cycle time for all experiments, the adsorption behaviour was logged for one adsorption phase. The weight of the device was logged during the adsorption of WHC 14. The adsorption starts with a MOF bed temperature of 60° C. to take the cooling from the previous WHC into account. Thus, a water adsorption curve over time was created as shown in FIG. 30. The adsorption time could then be calculated from the desorbed amount of water.
In WHC 5 to 7 the runtime of the desorption phase was shortened. Consequently, less water needed to be adsorbed allowing more cycles to be run per day, increasing the STY. However, the results reveal a decline in the STY with shorter desorption phases. This might be a result of the fact that a majority of the time was used to heat up the MOF bed to elevated temperatures and that with shorter desorption phases the maximal reachable temperature decreases. For example, the maximal temperature in WHC 7 with just 1 h desorption time was 65° C. The highest space time yield of 0:664 L kg−1 d−1 was thus reached with a desorption time of 2 h and a corresponding adsorption time of 2 h. Furthermore, the specific energy consumption per harvested litre of water was greater even though the runtime of the peltier device was shorter as the amount of harvested water was significantly lower.
The peltier device was resultantly changed to the 110 W peltier device for the subsequent experiments, which was found to be sufficient to heat the MOF bed to a temperature a temperature of around 70° C. At 70° C. in WHC 3, 82% of the adsorbed water is desorbed after 3 h. Again the first experiments were run with different currents of the peltier device between 5:0 A and 6:5 A. The MOF bed was heated up with this current. As soon as the MOF bed reached a temperature of 68° C. the current was lowered to maintain the temperature. A new time parameter designated ‘condensation time’ was used which correlated to the time after which the MOF bed had reached the temperature of 68° C. The current to maintain the temperature during the condensation time was set to 4:5 A in WHC 8 to 11, based on the data from the heating experiments.
As expected, the highest current of 6:5 A lead to the shortest heating time for the MOF and thus to the highest space time yield of harvested water. At the same time the specific energy consumption was lowest at this current. The subsequent experiments were carried out with a heating current of 6:5 A.
In the subsequent two experiments the influence of the fan, mounted between the fins of the heat sink, was investigated with the 110 W peltier device. As the change in the temperature in the MOF bed was very high in the first experiment with the fan (WHC 4), two different flow rates of the fan were tested: A high flow rate with a fan current of 0:09 A and a low flow rate with a fan current of 0:02 A. Besides, the temperature to change to condensing current was set to 75° C. to enhance the amount of desorbed water. The amount of harvested water in WHC 12 with the low flow rate was 51:7 mL, the highest amount so far. As a result, this experiment has the highest space time yield and lowest energy consumption thus far with 0:833 L kg−1 d−1 and 3:06 kW h kg−1, respectively. The amount of harvested water in WHC 13 with the high flow rate was just 36:7 mL, even though the fan was switched on after the MOF bed was heated up. In the previous experiment the fan was running the whole time, including during the heating phase. Resultantly, the subsequent experiments were carried out using the fan with a low flow rate. Furthermore, the fan was switched on when the MOF bed reaches the final desorption temperature, as the initial heating rate was 2:73° C. min−1 compared to 2:13° C. min−1 when the fan was switched on during the heating phase. The higher initial heating rate leads to shorter desorption times and thus to shorter cycle times.
Based on these thirteen experiments, the 110 W peltier device was used for the further optimisation of the water harvesting device using the following parameters for water harvesting cycle 14 to 24:

    
    
        Peltier device MCTE1-12712L-2, 110 W.
        Heating current 6:5 A.
        Fan flow rate Low (I=0:02 A).
        Fan run time Start after MOF bed heated up.

5.3.3 Optimisation of Operating Parameters

    
    


In the next experiments the condensation time; and desorption temperature were optimised. For this the condensation time was varied between 2 h and 5 min with a desorption temperature of 75° C. in WHC 14 to 17, respectively. Subsequently the desorption temperature was varied between 75° C. and 45° C. with the best desorption time, determined in the previous experiments, in WHC 18 to 20, respectively.







TABLE 5.3







Optimisation of the condensation time of the water harvesting


device. Collected water over different condensation times.












Condensation time
Water collected



WHC
(min)
(mL)







12
120
51.7



14
 90
42.8



15
 60
37.2



16
 30
26.3



17
 5
11.2










Table 5.3 and FIG. 31 show the collected water, space time yield and specific energy consumption of the device over different condensation times. As expected, the amount of water collected was greater for higher condensation times. However, the space time yield was better in a range of low condensation times with a maximum at 30 min. This was due to the significantly lower adsorption time that was necessary to adsorb the amount of water which was desorbed during the desorption phase. Only for very short desorption times of 5 min, the space time yield was lower as the time was not long enough to desorb a significant amount of water from the MOF bed. The specific energy consumption also had a local minimum at a condensation time of 30 min. Thus the optimal condensation time for the water harvesting device was determined to be 30 min. Based on this condensation time the optimal desorption temperature was determined in the subsequent experiments.







TABLE 5.4







Optimisation of the desorption temperature of the water


harvesting device. Collected water over different desorption


temperatures.









WHC
Desorption Temp (° C.)
Water collected (mL)












16
75
26.3


18
65
10.7


19
55
2.9


20
45
0.6









Table 5.4 and FIG. 32 show the collected water, space time yield and specific energy consumption of the device over different desorption temperatures. All three parameters were greater with higher desorption temperatures. The most important factor was the specific energy consumption as depicted in FIG. 32. The energy consumption was greater for lower desorption temperatures as the energy was used to heat up the MOF and the heat sink but not for the desorption of water. In conclusion, the best solution in terms of energy efficiency and space time yield was to heat the device to 75° C. before switching on the fan and condense for 30 min.
Water harvesting cycle 16 was the experiment with the highest space time yield and the lowest specific energy consumption. The logged data of this cycle during adsorption and desorption is shown in FIGS. 33, 34 and 35.
The adsorption phase, shown in FIG. 33, was under isothermal conditions with a varying relative humidity between 50% and 70%. The average loading of water in the air was 11:11 gm−3. The changes in relative humidity were caused by the air conditioning system in the lab and the weather outside. The high temperature in the beginning was caused by the hot MOF bed and heat sink from the previous water harvesting cycle. The data logger was placed next to the heat sink, thus the air in the beginning was hotter than the ambient air.
FIG. 34 shows the temperatures in the water harvesting device during the desorption phase. The MOF bed was heated up to 75° C. before the fan was switched on after 33 min. The temperature in the MOF bed decreases after the fan was switched on, due to the higher convection in the container. After the first decrease, the temperature increases slowly and the current of the peltier device was changed to 6:0 A after 53 min to maintain a temperature of slightly above 70° C. The change in the current was shown by the bend in the temperature curve of the MOF bed and the ΔT. The ΔT plot shows the temperature difference between the MOF bed and the condenser. This difference changes due to the higher convection when the fan was switched on and due to the current change after 53 min. The air temperature in the container increased at nearly a constant rate until the fan was switched on. The higher convection also results in a higher air temperature as the heat was transported from the MOF bed into the air in the container.
FIG. 35 shows the temperature of the condenser as well as the relative humidity and dew point in the container. The increase of relative humidity was caused by desorption of water from the MOF bed. The relative humidity decreases afterwards as liquid water condenses, and the amount of new desorbing water decreases as well. The peak in the relative humidity graph might be a result of a droplet on the humidity meter probe and was thus ignored in the discussion. This graph shows that the condenser temperature was always lower than the dew point in the system. Hence water vapour will condense on the condenser and can be collected afterwards. It was also observed that the walls of the device act as a second condenser, as a lot of droplets were forming on the walls during the experiments.
With only the adsorption changed, the experiment was repeated under the same conditions in WHC 24 to show the reproducibility of the results of WHC 16. The adsorption phase was started with a desorbed and hot MOF bed from the previous experiment. The duration of the adsorption phase was set to the length of the theoretical adsorption time used to calculate the space time yield of WHC 16. Hence the adsorption time in WHC 24 was 2:0 h and the desorption time was 1:06 h, resulting in a real cycle time of 3:06 h.
FIG. 36 shows the adsorption phase of WHC 24. Compared to WHC 16 the water loading in the air was lower with just 9:27 gm−3. 25:2 mL of water was collected after the desorption phase. This resulted in a space time yield of 0:998 L kg−1 d−1. Compared to WHC 16 the space time yield deviates by 2%. This demonstrates the reproducibility of the experiments with high space time yields and confirms the calculation of the theoretical adsorption time, used to calculate the space time yield in most of the experiments.
As shown in FIGS. 37 and 38 the temperature graph of the MOF bed has a good match with the graph of WHC 16. The temperature after the fan was switched on was increasingly slower compared to WHC 16. Due to this the current was not lowered in WHC 24 to maintain temperatures slightly above 70° C. Additionally, ΔT was higher in WHC 24 than in WHC 16. This was due to the replacement of the heat grease between the heat sink and the peltier device after WHC 20 affecting the thermal conductivity between the peltier device and the heat sink.
Furthermore, two water harvesting cycles, WHC 21 and 22, were run on the same dry day (Aug. 3, 2019, Melbourne (AUS)) under very dry conditions during the adsorption phase. The relative humidity was between 25% and 30% with a temperature of slightly about 20° C. The average water loading in the air was 5:50 gm−3. FIG. 39 shows the adsorption phase of WHC 22. The experiments of WHC 21 and WHC 22 showed that the low relative humidity leads to much longer adsorption times to adsorb the same amount of water. As the adsorption time was constant, the amount of water adsorbed was lower compared to a higher relative humidity. As a consequence the amount of harvested water in WHC 21 and 22 was lower than in the previous cycles, with a space time yield of 0:120 L kg−1 d−1 and 0:274 L kg−1 d−1 for WHC 21 and 22, respectively. This was a deviation of 88% and 73%, respectively. Nevertheless, these results demonstrate that the water harvesting device stills works in very dry and desert-like conditions.
Finally, FIG. 40 provides two views of a prototype water capture apparatus 800 that uses the temperature swing water harvesting apparatus 300 shown in FIGS. 1C to 1E. FIG. 40(A) illustrates the external housing 802 including the water dispensing outlet 805 activated by control panel 808; and FIG. 40(B) illustrates the inner components, which essentially show the fan 810 and louver system 820 for creating a flow of atmospheric air into and over the water adsorbent, i.e. fan is operated, and pivots open the louvers of the louver system 820 allowing air to flow over and through the packed bed of MOF adsorbent (not shown in FIG. 40) inside the apparatus packed into the heat sink (not shown in FIG. 40), and when the fan is inactive, the louvers of the louver system 820 pivot closed to create a closed environment, allowing the desorption phase and condensation processes of the water harvesting cycle to take place in a closed/sealed environment.
Comparison Between Devices
Table 5.8 below provides a comparison between the water harvesting device as developed in this work in accordance with embodiments of the present invention and to Yaghi's MOF based water harvesting devices as described in the background of the invention section. STYdevice is the space time yield with regard to the device's volume. Xmin provides a measure of the environmental conditions, i.e. the humidity (minimum water content) of the air fed over the MOF adsorbent.







TABLE 5.8







Comparison between the water harvesting devices developed


in this work to other MOF based water harvesting devices.














Energy

STY
mass 



Output
consumption
Xmin
device
of


Device
(L/day)
(kWh/L)
(g m−3)
(L/m3/d)
MOF















Yaghi Prototype*
0.078
sunlight
4.6
1.77
825


Inventive Induction 
0.23
10.4
9.7
~0.05
28


device (Example 1)







Inventive Peltier device
0.202
2.75
9.3
4.59
~200


(high RH) (Example 3)







Inventive Peltier device
0.054
7.92
5.5
1.23
~200


(low RH) (Example 3)










*F. Fathieh, M. J. Kalmutzki, E. A. Kapustin, P. J. Waller, J. Yang, and O. M. Yaghi. “Practical water production from desert air”. In: Science Advances 4.6 (2018).






The comparison indicate that both the tested embodiments of induction and Peltier device water capture apparatus of the present invention have a better water output compared to the Yaghi devices.
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.
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.

## Claims

1. A water adsorbent configured to capture a water content from air, the water adsorbent comprising:
at least one water adsorbent metal organic framework composite capable of adsorbing a water content from the air, wherein the at least one water adsorbent metal organic framework composite comprises at least 70 wt % water adsorbent metal organic framework and,
wherein the water adsorbent metal organic framework comprises:
a metal ion selected from the group consisting of Fe3+, Li+, Na+, Ca2+, Zn2+, Zr4+, Al3+, K+, Mg2+, Ti4+, Cu2+, Mn2+ to Mn7+, Ag+, or combinations thereof; and
at least 0.1 wt % of a hydrophilic binder selected from the group consisting of an alkyl cellulose, a hydroxyalkyl cellulose, a carboxyalkyl cellulose derivative, or combinations thereof, and

wherein the at least one water adsorbent metal organic framework composite has an average surface area of at least 700 m2/g and is configured to adsorb a water content from the air.

2. The water adsorbent according to claim 1, wherein the at least one metal organic framework composite comprises at least one of pellets, pills, spheres, granules, extrudates, honeycombs, meshes, hollow bodies, or combinations thereof.

3. The water adsorbent according to claim 1, wherein the hydrophilic binder is selected from at least one of hydroxypropyl cellulose (HPC), hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose (HPMC), ethyl hydroxyethyl cellulose, methyl cellulose, or carboxymethyl cellulose (CMC).

4. The water adsorbent according to claim 1, comprising between 0.5 wt % and 3 wt % of the hydrophilic binder.

5. The water adsorbent according to claim 1, comprising between 0.8 wt % and 2 wt % of the hydrophilic binder.

6. The water adsorbent according to claim 1, wherein the at least one water adsorbent metal organic framework composite comprises at least one of a pellet, a coating, a plate, a sheet, or a strip.

7. The water adsorbent of according to claim 1, wherein the at least one water adsorbent metal organic framework composite comprises a shaped water adsorbent composite body comprising an elongate body having a circular or regular polygonal cross-sectional shape.

8. The water adsorbent according to claim 1, wherein the at least one water adsorbent metal organic framework comprises at least one of aluminium fumarate, MOF-801, MOF-841, CAU-10, MOF-303, MOF-573, MOF-802, MOF-805, MOF-806, MOF-808, MOF-812, or mixtures thereof.

9. The water adsorbent according to claim 1, wherein the at least one water adsorbent metal organic framework composite has a particle size of less than 800 μm.

10. An apparatus for capturing a water content from air, the apparatus comprising:
a water adsorbent according to claim 1; and
a water desorption arrangement in contact with and/or surrounding the water adsorbent, the water desorption arrangement being 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 water adsorbent to desorb a water content from the water adsorbent.

11. The apparatus of claim 10, wherein the at least one water adsorbent metal organic framework composite comprises a coating applied to the surface of the water desorption arrangement or is in thermal conductive contact with the water desorption arrangement.

12. The apparatus according to claim 10, wherein the water desorption arrangement includes at least one heat transfer arrangement in direct thermal conductive contact with the water adsorbent and the heat transfer arrangement is in thermal conductive contact with a heating device.

13. The apparatus according to claim 12, wherein the heat transfer arrangement includes at least one heat transfer element that extends from the heating device to the water adsorbent.

14. The apparatus according to claim 12, further including a condenser system for cooling the product gas flow from the water adsorbent, wherein the heating device comprises at least one peltier device, and each peltier device has a hot side and a cold side, with the hot side of each peltier device being in thermal communication with the at least one heat transfer arrangement, and the cold side of each peltier device forming part of the condenser system.

15. The apparatus of claim 14, wherein the cold side of each peltier device is in thermal communication with at least one heat transfer arrangement.

16. The apparatus according to claim 14, wherein the peltier device is capable of heating the packed bed to at least 50° C.

17. The apparatus according to claim 12, wherein the water adsorbent is housed within or coated on at least part of the heat transfer arrangement.

18. A method of capturing a water content from air, comprising at least one cycle of:
feeding air over a water adsorbent according to claim 1 such that the water adsorbent adsorbs water from the air; and
applying heat, a reduced pressure or a combination thereof to the water adsorbent so to release at least a portion of the adsorbed water therefrom.

19. The method according to claim 18, wherein the water adsorbent is a shaped water adsorbent metal organic framework having an average surface area of at least 700 m2/g.