CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application No 63/139,211 filed January 19, 2021, which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates generally to water harvesting, and more specifically to systems and methods for harvesting water from surrounding air in changing atmospheric conditions.

BACKGROUND

[0003] Drinking water is scarce, especially in desert areas of North Africa and the Middle East. However, it is plentiful in the atmosphere, even in dry regions. In the last few years, atmospheric water harvesting using porous materials have been devised. See Atmospheric Water Harvesting: A Review of Material and Structural Designs, X. Zhou, H. Lu, F. Zhao, and G. Yu, ACS Materials Lett. 2020, 2, 7, 671-684. In particular, a class of metal organic frameworks (MOFs) with high water affinity has been developed that exhibits superior atmospheric water production. See H. Furukawa, F. Gandara, Y. B. Zhang, J. Jiang, W. L. Queen, M. R. Hudson, and O. M. Yaghi, Water Adsorption in Porous Metal-Organic Frameworks and Related Materials, J. Am. Chem. Soc. 2014, 136, 11, 4369-4381; M. J. Kalmutzki C. S. Diercks, and O. M. Yaghi, Metal-Organic Frameworks for Water Harvesting from Air, Advanced Materials Volume 30, Issue 37, 2018, 1704304; and N. Hanikel et al., Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester; ACS Cent. Sci. 2019, 5, 10, 1699-1706, August 27, 2019. This discovery has spurred the development of devices that could be deployed in the home, or in desert areas where no drinking water is available. See WO 2020/154427.

[0004] Depicted in FIG. 1 is a schematic of the water adsorption properties of various porous materials. The amount of water adsorbed (in mass %) is typically represented as a function of the relative humidity (in %) of the surrounding air in what is referred to as an adsorption isotherm. To first order and for all practical purposes, these curves are independent of temperature. MOF

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SUBSTITUTE SHEET RULE 26 materials exhibit a step-like characteristic, which lets them capture and release water in a very narrow range of humidity (FIG. 2). This is in contrast with more conventional materials such as silica gel that exhibit a much more gradual isotherm, or zeolites that only desorb water at extremely low humidity levels (FIG. 1). Another advantage of MOF material is that the relative humidity RHo where adsorption occurs (adsorption threshold) can be adjusted by changing the molecular characteristics of the material itself. In fact, a continuous range of RHo can be obtained by mixing various organic or inorganic constituents into multivariational MOFs of different water affinity. See W02020112899; Janiak, C. et al. Solid-Solution Mixed-Linker Synthesis of Isoreticular Al-Based MOFs for an Easy Hydrophilicity Tuning in Water- Sorption Heat Transformations Chem. Mater. 2019, 31, 11, 4051-4062; and Fang, Y. et al. One-Pot Synthesis of Two-Linker Mixed Al-Based Metal-Organic Frameworks for Modulated Water Vapor Adsorption Cryst. Growth Des. 2020, 20, 10, 6565-6572. Finally, a large adsorption capacity in mass % is also a requirement for a practical water harvester.

[0005] What is needed in the art are atmospheric water harvesters designed for optimal harvesting conditions in changing atmospheric conditions.

BRIEF SUMMARY

[0006] In some aspects, an atmospheric water harvesting system includes: a plurality of modules arranged into at least one adsorption stack; a desorption chamber, configured to receive a module saturated or nearly saturated with water from an adsorption stack, and cause desorption of water from the module positioned therein in the form of water vapor; a condensation chamber, positioned adjacent to or near the desorption chamber, and configured to condense at least a portion of the water vapor from the desorption chamber into liquid water; and a robotic arm, configured to (i) select and grasp a module in an adsorption stack that is saturated or nearly saturated with water, and (ii) transfer the module into the desorption chamber. In some embodiments, each module independently includes at least one metal organic framework positioned on or incorporated into a support. In some variations, at least one metal organic framework adsorbs water from surrounding air when the module is positioned within an adsorption stack.

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SUBSTITUTE SHEET (RULE 26) [0007] In certain aspects, provided is also a method of harvesting water from the atmosphere using any of the atmospheric water harvesting systems described herein.

DESCRIPTION OF THE FIGURES

[0008] The present application can be best understood by reference to the following description taken in conjunction with the accompanying figures included in the specification.

[0009] FIG. 1 depicts a graph comparing adsorption isotherms of MOF with conventional adsorbents such as silica gel and zeolite.

[0010] FIG. 2 depicts a graph showing adsorption and desorption in the context of atmospheric water harvesting using MOFs.

[0011] FIG. 3 depicts a graph showing optimization of water harvesting, in terms of productivity as compared to energy cost.

[0012] FIG. 4 depicts a decision tree for selecting the optimal type of MOF module to be moved to the desorption or condensation chambers

[0013] FIG. 5A depicts an exemplary atmospheric water harvesting system with changeable MOF modules in a circular configuration.

[0014] FIG. 5B depicts an exemplary atmospheric water harvesting system with changeable MOF modules in a stacked configuration.

DETAILED DESCRIPTION

[0015] The following description sets forth exemplary systems, methods, parameters and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments.

[0016] In some aspects, provided are atmospheric water harvesters that include a MOF adsorbent system with an optimal adsorption threshold, based on energy cost and water availability considerations. Provided are also methods of harvesting water from surrounding air

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SUBSTITUTE SHEET (RULE 26) using the atmospheric water harvesters described herein. In some embodiments, the design of the atmospheric water harvesters include several adsorbent assemblies, each made with MOF of various adsorption thresholds. Such harvesters allow for a real time adjustment of the MOF material for optimal harvesting conditions in changing atmospheric conditions, whether for daily or seasonal humidity variations. In some embodiments, the atmospheric water harvester is configured such that the adsorption process is fully separated from the desorption and condensation processes. This allows for multiple design configurations.

[0017] In one aspect, provided is an atmospheric water harvesting system comprising a plurality of MOF modules; a desorption chamber, a condensation chamber, and a robotic arm. Each MOF module contains at least one MOF. In some embodiments, the MOF modules are arranged into an adsorption stack. The adsorption stack can contain either MOF modules of the same MOF material (MOF “A”) or MOF modules with the MOF material of different adsorption threshold RHo (MOF “A”, “B”, “C” etc.).

[0018] In some variations, the MOF comprises organic ligands having acid and/or amine functional group(s). In certain variations, the organic ligands have carboxylic acid groups. In other variations, the organic ligands have acid and/or amine functional group(s). In certain variations, the organic ligands have carboxylic acid groups. Any suitable MOFs capable of adsorbing and desorbing water may be employed in the systems provided herein. Suitable MOFs may include those described in, for example, Kalmutzki et al., Adv. Mat., 30(37), 1704304 (2018); Furukawa et al., J. Am. Chem. Soc. 2014, 136, 4369-4381; Y.Tuet al, Joule, Vol 2, Issue 8(15), 1452-1475 (2018). In some variations, the MOF is: MOF-303: A1(OH)(HPDC), where HPDC is lH-pyrazole-3,5-dicarboxylate; CAU-10: A1(OH)(IPA), where IPA is isophthalate; MOF-801: Zr ₆ O4(OH)4(fumarate)6; MOF-841: Zr6O4(OH)4(MTB)6(HCOO)4(H ₂ O) ₂ ; Aluminum Fumarate: Al(OH)(fumarate); MIL- 160: A1(OH)(FDA), where FDA is 2,5-furandicarboxylate; MIL-53: A1(OH)(TPA), where TPA is terephthalate; or Aluminum Phosphate: A1PO4-LTA. In some variations, the MOFs have pore sizes between about 0.5 nm about 1 nm, or between about 0.7 nm to about 0.9 nm. In certain variations, the MOFs have a hydrophilic pore structure. In certain variations, the MOFs have a hydrophilic pore structure comprising acid and/or amine functional groups. In certain variations, the MOFs have ID channels that allow for reversible water adsorption. Any combinations of the MOFs described herein may also be used. In some

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SUBSTITUTE SHEET (RULE 26) embodiments, the MOF is mixed with a binder to improve its properties for adhesion to a substrate or support.

[0019] Air is blown across the MOF modules, which are configured in such a way as to maximize its surface to volume ratio for rapid humidity exchange with the air. For example, in some variations, the MOF modules contain uniform layers of MOF coated on parallel plates. Water is adsorbed when the ambient relative humidity RHamb is larger than the adsorption threshold RHo (see FIG. 2), and adsorption rate Rads can be expressed as:

Rads ~ S(Tamb) ^x (RHamb — RHo) Eq(l) where S(T) is the water saturation vapor pressure at temperature T, and Tan* is the temperature of the ambient air. Adsorption rate directly affects water productivity (e.g. in liter per day, see FIG. 3).

[0020] The robotic arm (automation system) is configured to select and pick up the optimal MOF module based on the weather conditions. The robotic arm selects and grasps a MOF module from the adsorption stack after saturation (or near saturation) with water, and transfers such MOF module to the desorption chamber. The robotic arm replaces the MOF module after it is desorbed, grasping the desorbed MOF module from the desorption chamber and placing it back into the adsorption stack to reach saturation.

[0021] In some variations, the robotic arm includes robotic effectors, vacuum effectors, mechanical effectors, or electromechanical effectors. In certain variations, robotic end effectors may include flexible structures that may be manipulated between various orientations. For example, in one variation, the structures may include silicon bodies or other flexible material. In certain variations, vacuum end effectors may grasp items using suction. In other variations, mechanical or electromechanical end effectors may include pinchers, claws, grippers, or other rigid components that may be actuated relative to one another for grasping an item.

[0022] To get the water out of a MOF module that is saturated or nearly saturated with water, the robotic arm transfers the selected MOF module to the desorption chamber. In the desorption chamber, the humidity in the MOF module needs to be brought below RHo (FIG. 2). In some variations, this may be accomplished by elevating the air temperature, which raises the water

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SUBSTITUTE SHEET (RULE 26) saturation vapor pressure S(T), hence decreasing the relative humidity. The temperature Tdes at which water starts to desorb can be calculated using the following equation:

Sides') x RHo = S(T _amb ) x RHamb Eq(2)

[0023] Equation (2) states that the absolute humidity (or water vapor concentration) is conserved during heating from Tamb to Tdes. In addition to the adsorption energy Eads required to desorb the water from the MOF, there is an energy cost s also associated with raising the temperature (sensible energy). E _s directly scales with desorption temperature, and an example of the variation of Es vs RHo is shown schematically in FIG. 3.

[0024] As temperature is raised, a small flow of air allows the desorbing moisture to get transferred to a condensation chamber housing at least one condenser. Once moist air arrives to the condenser, the liquid water condenses and is collected. In some variations, the moist air encounters a series of cold plates, arranged to maximize surface area, allowing the liquid water to condense.

[0025] FIG. 4 illustrates the process by which a control system will select the optimal MOF module for the robotic arm to pick up. The system keeps track of the adsorption process to ensure that the modules have reached sufficient adsorption state before being selected for the desorption or condensation process. Based on the weather condition, the system will further pick the optimal type of MOF module to be moved to the desorption or condensation chambers, according to the decision tree shown in FIG. 4 (the algorithm that defines (RHo) ideal, and the value of x% are user defined). For example, in a high relative humidity environment and when the water demand is not too severe, a MOF with high RHo can be selected to save on energy cost. Conversely, a low AHoMOF module can be selected when the environment relative humidity is low.

[0026] With reference to FIGS. 5A & 5B, exemplary atmospheric water harvesting systems are depicted. These figures show systems where the adsorption process is fully separated from the desorption and condensation processes. FIG. 5A depicts a circular configuration with stacks of MOF modules 1020, arranged radially with desorption chamber 2020, condensation chamber 2030 and water collection tank 2040 and central automated material handler 3020 (a robotic arm

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SUBSTITUTE SHEET (RULE 26) in this example). As depicted in this exemplary embodiment of the system, adsorption stack 1020 includes MOF modules containing MOF material of different adsorption thresholds RHo. As depicted in the figure, MOF module 1022 is an adsorbing module, and modules 1024 and 1026 are depicted in idle mode. The MOF modules sit in pre-arranged adsorption stack 1020 with air flow 4020 controlled by airflow management system 4022 (adsorption fans in this example) to optimize the adsorption process. Once desorbing MOF module 1022b is selected by the system, robotic arm 3020 will pick it up and place it in desorption chamber 2020 where water is desorbed using heat. Desorption chamber 2020 includes gate 2022 that opens in order to receive desorbing MOF module 1022b transferred by the robotic arm 3020 from an adsorption stack and close after the MOF module undergoes desorption. The resulting steam is then guided to the condensation chamber 2030 where liquid water is produced and collected into the water tank 2040. Once desorption is complete, the robotic arm will transfer this MOF module from the desorption chamber back to its original position in the adsorption stack. The next MOF module will then be picked up by the robotic arm and placed into desorption chamber 2020 for desorption, and the process continues. FIG 5A shows a circular configuration, but multiple geometries can be used according to space and footprint conditions. FIG. 5B for instance shows a similar concept, but in a stacked configuration.

[0027] With reference again to FIG. 3, the value of RHo has a direct effect on both adsorption and desorption efficiencies. During adsorption, the rate of water capture scales with (RHamb- RHo), as shown on Equation (1) above. Hence, for a given location/climate, a lower adsorption threshold enhances adsorption kinetics and water productivity. During desorption, however, the MOF modules (which may include, for example, MOF material and support) needs to be heated up in order to bring the relative humidity back below RHo (FIG. 2), and here a low adsorption threshold will require more thermal energy.

[0028] FIG. 3 graphically illustrates the choice to make when designing a MOF-based water harvester. In dry climates, where relative humidity RHamb of the ambient air is low, then the MOF material needs to have a low adsorption threshold RHo in order to capture water. However, when relative humidity is high, then the user has a choice between a lower energetic cost at the expense of water productivity (high RHo), or a high water productivity at the expense of energetic cost (low RHo). For instance, when water reserves are plentiful, the choice of a lower

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SUBSTITUTE SHEET (RULE 26) energy cost would be made, but when water is in high demand, a MOF with lower RHo will be preferred. Examples of this type of situation could be the daily variation of humidity in dry areas where lower temperatures during the night result in higher relative humidity. Also, annual humidity variation between seasons in a given area might also benefit from an adjustment of the MOF adsorption threshold.

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SUBSTITUTE SHEET (RULE 26)