Ammonia absorbents using salts in metal fiber matrix

Abstract

Embodiments are directed to ammonia absorbers and associated methods of producing the same, the ammonia absorbers comprising a homogeneous mixture of aluminum fibers and anhydrous powdered magnesium chloride pressed into pellets.

Description

AMMONIA ABSORBENTS USING SALTS IN METAL FIBER MATRIXCROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims the priority and benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Serial No. 63 / 606,286 filed December 5, 2023, entitled “AMMONIA ABSORBENTS USING SALTS IN METAL FIBER MATRIX.” U.S. Provisional Patent Application Serial Number 63 / 606,286 is herein incorporated by reference in its entirety.STATEMENT OF GOVERNMENT RIGHTS

[0002] This invention was made with government support under DE-EE0009802 awarded by the U.S. Department of Energy. The government has certain rights in the invention.TECHNICAL FIELD

[0003] Embodiments are generally related to the field of chemical synthesis. Embodiments are further related to energy production and storage. Embodiments are further related to sorbents. Embodiments are also related to ammonia synthesis.BACKGROUND

[0004] Ammonia is one of the world's most important chemicals. In addition to its use as a synthetic fertilizer, ammonia can also be used as an efficient means for energy storage. In 2023, an estimated 150 million tons of ammonia were produced worldwide, representing the largest source of bioavailable nitrogen, essential to modern agriculture. Ammonia production alone accounts for 2% of the world’s energy consumption and 1 .3% of total CO2 emissions.

[0005] Ammonia is typically synthesized in large-scale chemical plants through the Haber-Bosch process, where nitrogen and hydrogen are reacted at high pressure and temperature over an iron-based catalyst to form ammonia. Ammonia is separated from the resulting mixture through condensation, which requires a refrigeration system. These large, centralized facilities also necessitate infrastructure to transport the ammonia to rural farms where it is critically needed.

[0006] The low single-pass conversion to ammonia at typical reactor conditions (10-15%) allows the separation process to have an outsized influence on process economics. Alternate separation methods, particularly selective absorption using supported metal halides, enable economically feasible, small-scale, distributed ammonia plants. The higher separation temperature of these sorbents obviates refrigeration and allows the production of ammonia at lower pressures. Magnesium chloride supported on silica gel (MgCh / SiC ) has emerged as one ammonia sorbent due to its reversibility and large ammonia capacity at higher temperatures.

[0007] However, the absorption of ammonia by MgCh is highly exothermic, and the desorption is similarly endothermic. To fully regenerate MgCh, significant energy is required. This large change in enthalpy imposes significant heating requirements to regenerate the sorbent. MgC / SiC has a low thermal conductivity which both limits the speed at which the sorbent can be regenerated and imposes drastic heating and cooling requirements, requiring the use of complex and expensive absorber designs to manage the thermal load. In addition, loading MgCk into the mesoporous SiO2 gel structure requires dissolving the salt in organic solvent and precipitating it into the pores, violating green chemistry principles.

[0008] Given the increasing demand for ammonia, particularly for use in energy storage applications, and given the limitations resulting from the low thermal conductivity in ammonia sorbents, there is a need for improved systems and methods for ammonia absorbents using salts in metal fiber matrixes as disclosed herein.SUMMARY

[0009] The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0010] It is, therefore, one aspect of the disclosed embodiments to provide chemical synthesis methods.

[0011] It is another aspect of the disclosed embodiments to provide methods and systems for ammonia production.

[0012] It is another aspect of the disclosed embodiments to provide systems and apparatuses for chemical production.

[0013] It is another aspect of the disclosed embodiments to provide systems and apparatuses to facilitate energy storage.

[0014] It is another aspect of the disclosed embodiments to provide methods, systems, and apparatuses comprising ammonia absorbents using salts in a metal fiber matrix.

[0015] It is another aspect of the disclosed embodiments to provide sorption-based low- pressure green ammonia synthesis using supported metal halide salts which enable efficient interconversion between hydrogen and ammonia, allowing the high hydrogen density and well-established transportation network of ammonia to be used for green energy storage.

[0016] It will be appreciated that the methods and systems can be achieved according to the embodiments disclosed herein. In an embodiment, an ammonia absorber comprises aluminum fibers and magnesium chloride. In an embodiment, the magnesium chloride further comprises powdered magnesium chloride. In an embodiment, the powdered magnesium chloride further comprises anhydrous magnesium chloride. In an embodiment, the aluminum fibers further comprise aluminum fibers with an exemplary width of 30-40 micrometers, anda maximum width of 150 micrometers, and a length less than 1 cm. In an embodiment, the ammonia absorber further comprises a homogeneous mix of the aluminum fibers and the magnesium chloride. In an embodiment, the homogeneous mix of the aluminum fibers and the magnesium chloride is compressed into a pellet. In an embodiment, the magnesium chloride further comprises nominally 40% of the ammonia absorber, and the aluminum fibers further comprise nominally 60% of the ammonia absorber.

[0017] In an embodiment, a method of producing an ammonia absorber comprises mixing aluminum fibers and magnesium chloride and compressing the mixed aluminum fibers and magnesium chloride into a pellet. In an embodiment, the method of producing an ammonia absorber further comprises chopping the aluminum fibers into fibers with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers, and a length less than 1 cm. In an embodiment, the magnesium chloride further comprises powdered magnesium chloride. In an embodiment, the powdered magnesium chloride further comprises anhydrous magnesium chloride. In an embodiment, of the method of producing an ammonia absorber mixing aluminum fibers and magnesium chloride further comprises homogeneously mixing the aluminum fibers and the magnesium chloride. In an embodiment, the magnesium chloride further comprises nominally 40% of the ammonia absorber, and the aluminum fibers further comprise nominally 60% of the ammonia absorber.

[0018] In an embodiment, a method of producing an ammonia absorber pellet comprises chopping aluminum into aluminum fibers, mixing the aluminum fibers with a magnesium chloride powder, and compressing the mixed aluminum fibers and magnesium chloride powder into a pellet. In an embodiment, compressing the mixed aluminum fibers and magnesium chloride powder into a pellet further comprises filling a cylinder with the mixed aluminum fibers and the magnesium chloride powder, and compressing the mixed aluminum fibers and magnesium chloride powder in the cylinder with a die. In an embodiment, compressing the mixed aluminum fibers and magnesium chloride powder into a pellet further comprises compressing the mixed aluminum fibers and magnesium chloride powder to a density of at least 0.5 g / cm3. In an embodiment, chopping aluminum into aluminum fibers further comprises chopping the aluminum fibers into fibers with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers, and a length less than 1 cm. In anembodiment, the magnesium chloride powder further comprises anhydrous magnesium chloride. In an embodiment, mixing aluminum fibers and magnesium chloride further comprises homogeneously mixing the aluminum fibers and the magnesium chloride. In an embodiment, the magnesium chloride further comprises nominally 40% of the ammonia absorber pellet, and the aluminum fibers further comprise nominally 60% of the ammonia absorber pellet.BRIEF DESCRIPTION OF THE FIGURES

[0019] The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.

[0020] FIG. 1 A depicts an ammonia absorbent pellet, in accordance with the disclosed embodiments;

[0021] FIG. 1 B depicts an image of ammonia absorbent pellets, in accordance with the disclosed embodiments;

[0022] FIG. 2A depicts steps associated with a method of producing an ammonia absorbent, in accordance with the disclosed embodiments;

[0023] FIG. 2B depicts an image of aluminum fibers used in the method for producing an ammonia absorbent, in accordance with the disclosed embodiments;

[0024] FIG. 20 depicts an image of magnesium chloride powder used in the method for producing an ammonia absorbent, in accordance with the disclosed embodiments;

[0025] FIG. 2D depicts an image of aluminum fibers and magnesium chloride powder used in a method for producing an ammonia absorbent, in accordance with the disclosed embodiments;

[0026] FIG. 2E depicts an image of a homogeneous mixture of aluminum fibers and magnesium chloride powder used in a method for producing an ammonia absorbent, in accordance with the disclosed embodiments;

[0027] FIG. 3 depicts a die for compressing an ammonia absorbent into a pellet, in accordance with the disclosed embodiments;

[0028] FIG. 4 depicts aspects of a diagram of an automated sorption apparatus, in accordance with the disclosed embodiments;

[0029] FIG. 5 depicts expansion of an ammonia absorbent pellet into a sorbent bed after the introduction of ammonia, in accordance with the disclosed embodiments;

[0030] FIG. 6 depicts a comparative chart of effective thermal conductivity achieved with an ammonia absorbent, in accordance with the disclosed embodiments;

[0031] FIG. 7 A depicts charts of temperature and flow rate after regeneration with a MgCh / AI sorbent, in accordance with the disclosed embodiments;

[0032] FIG. 7B depicts comparative charts of temperature and flow rate after regeneration with an MgCl2 / SiO2 sorbent;

[0033] FIG. 8 depicts comparative charts of pressure after the beginning of uptake for MgCh / AI sorbents packed with various packing methods, in accordance with the disclosed embodiments; and

[0034] FIG. 9 depicts a chart of working capacity per cycle of five different samples of MgCh / AI sorbents, in accordance with the disclosed embodiments.DETAILED DESCRIPTION

[0035] Embodiments and aspects of the disclosed technology are presented herein. The particular embodiments and configurations discussed in the following non-limiting examples can be varied, and are provided to illustrate one or more embodiments, and are not intended to limit the scope thereof.

[0036] Reference to the accompanying drawings, in which illustrative embodiments are shown are provided herein. The embodiments disclosed can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Like numbers refer to like elements throughout.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0038] Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part.

[0039] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. Itwill be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0040] It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0041] It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

[0042] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[0043] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0044] The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAG, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0045] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

[0046] The disclosed embodiments are directed to sorption-based, low-pressure, green ammonia synthesis using supported metal halide salts. The disclosed embodiments provide scalable, solventless methods for supporting MgCl2 on thermally conductive aluminum fibers (MgCh / AI). This material is a thermally conductive ammonia sorbent with a high working capacity (up to 220 mgNHs / absorbent). The high thermal conductivity of MgCh / AI allows for rapid absorption-desorption cycles, enabling easier scale-up. MgCk / AI also maintains its cyclic capacity up to 50 cycles without degradation.

[0047] FIG. 1A illustrates, a material 100, comprising a mix of aluminum fibers 102 (e.g., aluminum fibers, with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers, and being less than 1 cm in length) and powdered magnesium chloride salt 104, that is mixed together and compressed into a puck or pellet 106. This material exhibits reversible ammonia absorption without capacity degradation over a number of absorption-desorption cycles. It also has improved thermal conductivity compared tomagnesium chloride supported on silica gel.

[0048] The absorption and desorption in the synthesis of ammonia, are exothermic and endothermic, respectively. As such, heat must be transferred in and out of the material on every cycle, making thermal conductivity critically important to scaling operations. With the disclosed material, the compression also yields a high volumetric working capacity (mg NHs / mL bed material), while still stabilizing the absorbent material (as compared to using no aluminum fibers).

[0049] FIG. 1 B illustrates a photograph of an ammonia absorbent 100 in accordance with the disclosed embodiments. The ammonia absorbent material generally comprises powdered MgCh (magnesium chloride) and aluminum fibers. In other embodiments, other metal fibers can be used, although aluminum offers good thermal properties. In certain embodiments, the MgCl2 comprises nominally 40% of the material in the ammonia absorbent and the aluminum fibers comprise nominally 60% of the material in the ammonia absorbent. The aluminum fibers can be selected to be less than 1cm long although other dimensions are possible. The MgCh can comprise anhydrous MgCh powder.

[0050] The ammonia absorbent material can comprise a homogeneous mix of the MgCl2 and aluminum fiber, and is preferably mixed via slow rotation. The ammonia absorbent material is then compressed into one or more absorbent pellets 106 as shown in FIG. 1 A.

[0051] FIG. 2A illustrates a flow chart of steps associated with a method of making an ammonia absorbent material in accordance with the disclosed embodiments. The method begins at step 202.

[0052] At step 204, aluminum fibers can be collected and finely chopped. In certain embodiments, the aluminum fibers can be chopped into aluminum wool with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers. The aluminum can preferably be chopped into fibers less than 1cm in length. FIG. 2B illustrates a photograph 250 of chopped aluminum fibers 252.

[0053] Next, at step 206 the finely chopped aluminum fiber wool can be mixed withpowdered MgCk. FIG. 2C illustrates a photograph 260 of magnesium chloride powder 262. FIG. 2D illustrates a photograph 270 of the chopped aluminum fibers and powdered MgCh 272 together, but prior to mixing.

[0054] Preferably, the metal fibers and MgCh are mixed by slow rotation (e.g., less than 10 RPM) in a container with baffles. The materials are mixed until homogeneous. In an exemplary embodiment, the mixing container can comprise an anhydrous environment, such as a container filled with IX^ gas. FIG. 2E illustrates a photograph 280 of the homogeneous mixture of chopped aluminum fibers and powdered MgCl2282.

[0055] It should be appreciated that, at first, the MgCh and aluminum fibers are separate, and the aluminum fibers clump together. As the mixture is rotated the material mixture becomes homogeneous. The salt helps prevent the aluminum fibers from clumping together.

[0056] When the mixture has been thoroughly mixed and is homogeneous, it can be inserted into a die, as illustrated at step 208. An exemplary die 300 is illustrated in FIG. 3. The die 300 is used to compress the absorbent material into pellets.

[0057] The die 300 can generally make use of a cylinder 302. The cylinder 302 can comprise a metal cylinder such as a stainless steel cylinder. The cylinder 302 can be filled with the homogeneous material mixture 282. The cylinder 302 can be fitted to a press 304.

[0058] The press 304 can comprise a hydraulic press, pneumatic press or the like. The press 304 can include a top plate 306 and support plate 308, and base plate 310. Two support dowels 312 can connect the respective plates. The support plate 308 can include an opening 314 allowing the press 304 to extend between the support plate 308 and top plate 306. The cylinder 302, filled with the homogeneous material mixture 282, can be inserted between the support plate 308 and top plate 306. The press 304 can then be used to apply pressure to the homogeneous material mixture 282 inside the cylinder 302.

[0059] The homogeneous mixture can thus be compressed, as illustrated at step 210. In certain embodiments, the die 300 can be used to compress the mixture, but in other embodiments other compression methods can be used. Although various levels ofcompression can be used, in certain embodiments, the material can be compressed up to a density of at least 0.5 g / cm3. This level of compression helps keep any MgCh from falling out of the aluminum matrix.

[0060] At step 212 the resulting pellets 106 of material 100 sorbent can be used for sorption. FIG. 4 illustrates an exemplary automated sorption apparatus 400, in accordance with the disclosed embodiments.

[0061] The automatic sorption apparatus 400 comprises fluid lines 402 connecting an ammonia source 404, nitrogen source 406, and argon source 408. An ammonia line 410 can be directly connected to the ammonia source 404. The ammonia line 410 can include a pressure regulator 412, followed by a needle valve 414, and excess flow valve 416. The nitrogen line 418, can connect directly to the nitrogen source 406, with a pressure regulator 420, and needle valve 422. Likewise, the argon line 424 can connect to the argon source 408, with a pressure regulator 426 and needle valve 428. The respective mass flow controllers regulate the flow of the respective fluids (e.g. NH3, N2, and Ar) into the fluid line 402, where they mix.

[0062] Fluid in the ammonia line can pass through a first mass flow controller 430 and check valve 432. Fluid in the nitrogen line 418 can pass through a second mass flow controller 434 and check valve 436. Fluid in the argon line 424 can pass through a third mass flow controller 438 and check valve 440.

[0063] The mixed fluid is then provided through ball valve 442 to an ammonia absorption column 444. A pressure sensor 446 can be provided between the ball valve 442 and absorption column 444. Pressure is regulated to maintain bed pressure in the ammonia absorption column 444. The ammonia absorption column 444 can comprise a metal (e.g. stainless-steel) column loaded with a bed of the sorbent material. The temperature of the bed can be maintained by a proportional-integral-derivative (PID) controller which heats the outside of the stainless-steel column using heat tape to reach the desired bed temperature.

[0064] A residual gas analyzer 458 (RGA) can be used to chemically analyze the downstream gas. The gas flows from the ammonia absorption column 444 through a particlefilter 448, back pressure regulator 450, downstream mass flow controller 452, and needle valve 454. Other gas can be vented through vent 456.

[0065] Before absorption measurements are taken, the sorbent can be pretreated to drive off any water. Then, under 50 seem of N2 flow, the bed temperature is ramped to 300°C across a period of 10 minutes, then maintained at 300°C for one additional minute, before cooling down to the uptake temperature. During ammonia uptake, a flow rate of 15 seem NH3 and 15 seem Ar can be sent through the sorbent bed. During this process the system is maintained at a temperature of 50°C and a pressure of 3 bara. The uptake phase can stop when ammonia breakthrough is detected by the RGA. The sorbent can be regenerated to its diamminated state (MgCl2*6NH3 -* MgCl2*2NH3 + 4NHs) by flowing 5 seem of N2 through the sorbent bed and heating the sorbent to a temperature of 200°C. Uptake and regeneration together constitute one cycle.

[0066] In certain embodiments, the pellets as disclosed herein, are selected to be compressed into pellets because when the pellets are exposed to ammonia, the compressed pellets expand. FIG. 5 illustrates the process 500 of pellet expansion. As illustrated, pellets 106 of material 100, are provided in a tube, such as tube 302. The pellets 106 can be exposed to ammonia 502. When the pellets 106 are exposed to ammonia 502 they expand into a sorbent bed 504.

[0067] In certain embodiments, the pellets 106 can be compressed to a density between 0.5 and 1 .5 g / cm3initially, and after cycling with ammonia, the density becomes closer to 0.6 g / cm3. As the material expands, it will come into contact with adjacent pellets 106, which becomes the long sorbent bed 504 (monolith).

[0068] The absorbent material can thus comprise a 40wt% MgCl2-AI absorbent with the following exemplary material values: column capacity of roughly 220 mgNH3 / gbed; coordination number of 3.1 molNH3 / molMgci2; and expanded density of 0.60 g ed / cm3in the 6-ammonia loaded state.

[0069] FIG. 6 illustrates a chart 600 comparing effective bed thermal conductivity of mixed with aluminum fibers (28 wt%MgCl2, 42 wt% SiO2, 30 wt% Al), and plain aluminum fibers. It should be appreciated that this chart is provided for illustrative purposes.

[0070] In chart 600 the effective thermal conductivities of three materials: MgCh / SiOp sorbent, a sorbent made by mixing MgCh / SiC sorbent with aluminum fibers (MgC / SiC / AI), and pure Al fibers are illustrated. As illustrated in chart 600, there is a three-to-four times enhancement in effective thermal conductivity by incorporating only 30 wt% of aluminum fibers into the MgCh / SiC sorbent. This increase in thermal conductivity better disperses the heat generated by the exothermic absorption and reduces the time for sorbent regeneration, allowing for faster cycling in a scaled-up absorption column. This supports the uniqueness and efficacy of MgCk supported on aluminum fibers (MgCh / AI) disclosed herein. Chart 600 further suggests that directly replacing mesoporous silica gel with non-porous aluminum fibers as a support material prevents MgCh agglomeration and surface area loss, while greatly increasing the thermal conductivity of the sorbent bed.

[0071] FIG. 7A provides a chart 700 and FIG. 7B provides a chart 750. The respective charts 700 and 750 compare the thermal conductivities of the MgCh / AI and MgCh / SiOp sorbents respectively. The upper portions of the respective charts 700 and 750 display the inlet flow rates of N2 (5 seem), NH3 (0 seem), and Ar (0 seem), as well as the outlet flow rate during regeneration. The lower portions of the respective charts 700 and 750 display the temperature measured at the center of the sorbent bed, the PID setpoint temperature for the center of the sorbent bed, and the percentage power supplied by the heat tape wrapped around the outside of the column. Flow rate and temperature data from the automated sorption apparatus are also illustrated to compare their regeneration.

[0072] As illustrated in charts 700 and 750, the temperature profile flattens at approximately 150°C for both MgCl2 / AI sorbent and MgCl2 / SiO2 sorbent, respectively, which corresponds to the endothermic phase transition from hexamminated MgCl2*6NH3 to diamminated MgCl2*2NH3 at 1 bar of ammonia partial pressure.

[0073] Because the automated sorption apparatus 400 is heated using heat tape wrapped around the outside of the column, only the outer perimeter of the sorbent is initially heated during regeneration and heat propagates inward towards the center of the sorbent bed. Thetemperature of a thermally conductive sorbent is limited by the phase transition, as this occurs at the same time across the whole material. In a thermally insulating material, the sorbent bed reaches this transition temperature radially at different times, leading to a less defined plateau and a broader ammonia outlet flow peak.

[0074] As illustrated in chart 700, the MgCl2 / AI sorbent behaves as a thermally conductive sorbent - the outlet ammonia flow peak is sharp, with a well-defined temperature plateau. In contrast, the MgCh / SiC sorbent, shown in chart 750, behaves as a thermally insulating sorbent - the outlet ammonia flow peak is broad, and the temperature plateau is less defined.

[0075] The higher thermal conductivity of MgCh / AI allows the salt to overcome the endotherm of the phase transition more quickly. This means a faster absorber cycling is achievable with the more thermally conductive MgCh / AI sorbent disclosed herein.

[0076] Upon ammination at the uptake temperature, in this example (50°C), MgC forms MgCl2*6NH3 and expands in volume to accommodate ammonia within its crystal structure. In MgCb / AI, the expansion of individual MgCh particles within the aluminum fiber matrix uniformly drives the aluminum fiber matrix outwards in the direction of least resistance. This uniform expansion causes the sorbent to retain its integrity after cycling.

[0077] Experimentally, a sample of the MgCh / AI sorbent exhibits homogeneous expansion of three-to-four times the original compressed volume of the sorbent. When the sorbent is given sufficient room to expand, the pressure drop increases with each cycle until sometime between the second and fifth cycle, at which point the pressure drop peaks (< 12 psi). Following this, the pressure drop decreases with each subsequent cycle until the sorbent reaches a cyclic steady state at its lowest pressure drop (1 psi) after 15 cycles. Experimental support for this behavior is illustrated in chart 800, chart 825, chart 850, and chart 875 in FIG. 8.

[0078] Chart 800 illustrates the experimental pressure drop curve for a restricted 40 wt% MgCb / AI sample. The sample was not given adequate room to expand within the column, causing the pressure upstream of the sample to rise during cycle 3 to the point where gas was no longer able to flow through the sample and the test was stopped. Chart 825, chart850, and chart 875 show experimental pressure drop curves during uptake for three unrestricted 40 wt% MgCh / AI samples. In chart 825 the results show a sample hydraulically compressed to 100 MPa. In chart 850 the results show a sample hydraulically compressed to 100 MPa. In chart 875, the results are provided for a sample that was hand compressed (5-8 MPa). These samples were all given enough room to expand within the column.

[0079] The experimental pressure drop behavior of unrestricted MgC AI shown in chart 825, chart 850, and chart 875, are the result of limiting diffusion of solid ammonia through the bulk of the crystal. Ammonia is absorbed at the solid-gas interface, leading to only the surface of the salt crystal initially converting to a hexamminated state during uptake. As the sorbent is thermally cycled, ammonia diffuses deeper into the core of the salt crystals, causing a slight volume expansion after each cycle. In effect, a net positive amount of ammonia is absorbed and then is released as the material is cycled, increasing the salt core size. This fills the void space within the aluminum matrix of the MgCh / AI sorbent, resulting in a higher pressure drop in earlier cycles due to the expanded salt impeding gas flow. With further cycling, however, the MgCl2 rearranges itself, both by adhering onto the aluminum fibers, and by expanding the aluminum fiber matrix. This causes the pressure drop to decrease as gas flow becomes less impeded after every cycle. After extensive cycling, ammonia has fully saturated the core of all the salt crystals, leading to a more consistent expansion during uptake and contraction during regeneration. Resultingly, a consistent cyclic steady state pressure drop curve is observed after roughly 15 cycles.

[0080] The unrestricted sorbent also has a large variance in early-cycle pressure drop behavior with a large difference between peak pressure drops and the exact cycle in which this peak pressure drop occurs. However, the sorbent will reach a consistent steady state pressure drop after several cycles. Similar behavior with high initial variance leading to consistency after several cycles was observed experimentally in the working capacity of MgCl2 / AI sorbents precompressed at different pressures.

[0081] FIG. 9 provides a chart 900 comparing the experimentally identified working capacity of NH3 uptake per cycle between MgCh / AI samples that are hydraulically compressed (at either 50 MPa or 100 MPa) or hand compressed. As illustrated in chart 900,samples hydraulically compressed at 100 MPa exhibit sample-to-sample variability when compressed at 100 MPa. In certain embodiments, the MgCh / AI can be compressed with a die at a pressure of up to 100 MPa.

[0082] Chart 900 further shows experimentally identified working capacities for various compressed samples, regardless of compression technique. It should be noted that they all reach the same steady state working capacity after an initial conditioning period. In certain embodiments, the steady state working capacity can be at 220 ± 4 mgNH3 / gbed using a 95 % confidence interval. Thus, embodiments disclosed herein can be compressed with various techniques and that, regardless of the compression technique, the overall steady state performance of MgCh / AI reaches a predictable level, which allows for flexibility in the choice of compaction equipment used to create samples.

[0083] It should be appreciated that the compaction stress level does influence the amount of conditioning required to reach a steady state working capacity. Any level of compaction helps remove large-scale macroscopic void space and creates structurally sound starting material. Assuming that the MgCk> starting powder has a granular microstructure, small porous structures between the MgCh grains and / or between the MgCh grains and the Al fiber network must still exist to allow NH3 to flow through the sample during cycling. As such, the higher compaction stresses reached using hydraulic-assisted compression results in MgCh / AI microstructures being more conducive to quicker conversion of MgCh to MgCI2*2NH3.

[0084] According to the disclosed embodiments, hydraulically pressed samples may have preammination microstructures that are somewhat consistent with one another as these samples reach steady state working capacity after -30 cycles.

[0085] According to embodiments disclosed herein, a sorbent material is disclosed with a large working capacity of MgCl2 / AI (220 ± 4 mgNH3 / gbed) and, in particular, has a larger thermal conductivity as compared to MgC / SiC sorbent. This difference in thermal conductivity halves the time required for regeneration, enabling faster cycling. The disclosed material also quickly approaches a cyclic steady state in both pressure drop and working capacity after several cycles. MgCh / AI also maintains its cyclic steady state working capacity up to at least50 cycles without degradation.

[0086] The green, facile synthesis of MgCh / AI only requires mixing and compacting aluminum fibers and anhydrous MgCh powder, which obviates solvents and enhances scalability. As such embodiments are directed to MgCh / AI as an ammonia sorbent for scaling up low-pressure ammonia synthesis to enable ammonia-based green energy storage. The disclosed ammonia absorbent material can be used in ammonia production, especially small- scale, and solid-state ammonia storage, especially thermochemical solar energy, as this requires a flow-through bed.

[0087] Based on the foregoing, it can be appreciated that a number of embodiments, preferred and alternative, are disclosed herein. In an embodiment, an ammonia absorber comprises aluminum fibers and magnesium chloride. In an embodiment, the magnesium chloride further comprises powdered magnesium chloride. In an embodiment, the powdered magnesium chloride further comprises anhydrous magnesium chloride. In an embodiment, the aluminum fibers further comprise aluminum fibers with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers, and a length less than 1 cm. In an embodiment, the ammonia absorber further comprises a homogeneous mix of the aluminum fibers and the magnesium chloride. In an embodiment, the homogeneous mix of the aluminum fibers and the magnesium chloride is compressed into a pellet. In an embodiment, the magnesium chloride further comprises nominally 40% of the ammonia absorber, and the aluminum fibers further comprise nominally 60% of the ammonia absorber.

[0088] In an embodiment, a method of producing an ammonia absorber comprises mixing aluminum fibers and magnesium chloride and compressing the mixed aluminum fibers and magnesium chloride into a pellet. In an embodiment, the method of producing an ammonia absorber further comprises chopping the aluminum fibers into fibers with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers, and a length less than 1 cm. In an embodiment, the magnesium chloride further comprises powdered magnesium chloride. In an embodiment, the powdered magnesium chloride further comprises anhydrous magnesium chloride. In an embodiment, of the method of producing an ammonia absorber mixing aluminum fibers and magnesium chloride further comprises homogeneously mixingthe aluminum fibers and the magnesium chloride. In an embodiment, the magnesium chloride further comprises nominally 40% of the ammonia absorber, and the aluminum fibers further comprise nominally 60% of the ammonia absorber.

[0089] In an embodiment, a method of producing an ammonia absorber pellet comprises chopping aluminum into aluminum fibers, mixing the aluminum fibers with a magnesium chloride powder, and compressing the mixed aluminum fibers and magnesium chloride powder into a pellet. In an embodiment, compressing the mixed aluminum fibers and magnesium chloride powder into a pellet further comprises filling a cylinder with the mixed aluminum fibers and the magnesium chloride powder, and compressing the mixed aluminum fibers and magnesium chloride powder in the cylinder with a die. In an embodiment, compressing the mixed aluminum fibers and magnesium chloride powder into a pellet further comprises compressing the mixed aluminum fibers and magnesium chloride powder to a density of at least 0.5 g / cm3. In an embodiment, chopping aluminum into aluminum fibers further comprises chopping the aluminum fibers into fibers with an exemplary width of 30-40 micrometers, and a maximum width of 150 micrometers, and a length less than 1 cm. In an embodiment, the magnesium chloride powder further comprises anhydrous magnesium chloride. In an embodiment, mixing aluminum fibers and magnesium chloride further comprises homogeneously mixing the aluminum fibers and the magnesium chloride. In an embodiment, the magnesium chloride further comprises nominally 40% of the ammonia absorber pellet, and the aluminum fibers further comprise nominally 60% of the ammonia absorber pellet.

[0090] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, it should be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

CLAIMSWhat is claimed is:1 . An ammonia absorber comprising: aluminum fibers; and magnesium chloride.

2. The ammonia absorber of claim 1 wherein the magnesium chloride further comprises: powdered magnesium chloride.

3. the ammonia absorber of claim 2 wherein the powdered magnesium chloride further comprises: anhydrous magnesium chloride.

4. The ammonia absorber of claim 1 wherein the aluminum fibers further comprise: aluminum fibers with a maximum width of 150 micrometers, and a length less than 1 cm.

5. The ammonia absorber of claim 1 further comprising: a homogeneous mix of the aluminum fibers and the magnesium chloride.

6. The ammonia absorber of claim 5 wherein the homogeneous mix of the aluminum fibers and the magnesium chloride is compressed into a pellet.

7. The ammonia absorber of claim 1 wherein the magnesium chloride further comprises: nominally 40% of the ammonia absorber; and the aluminum fibers further comprise: nominally 60% of the ammonia absorber.

8. A method of producing an ammonia absorber comprising: mixing aluminum fibers and magnesium chloride; andcompressing the mixed aluminum fibers and magnesium chloride into a pellet.

9. The method of producing an ammonia absorber of claim 8 further comprising: chopping the aluminum fibers into fibers with a maximum width of 150 micrometers, and a length less than 1 cm.

10. The method of producing an ammonia absorber of claim 8 wherein the magnesium chloride further comprises: powdered magnesium chloride.1 1. The method of producing an ammonia absorber of claim 10 wherein the powdered magnesium chloride further comprises: anhydrous magnesium chloride.

12. The method of producing an ammonia absorber of claim 8 wherein mixing aluminum fibers and magnesium chloride further comprises: homogeneously mixing the aluminum fibers and the magnesium chloride.

13. The method of producing an ammonia absorber of claim 8 wherein the magnesium chloride further comprises: nominally 40% of the ammonia absorber; and the aluminum fibers further comprise: nominally 60% of the ammonia absorber.

14. A method of producing an ammonia absorber pellet comprising: chopping aluminum into aluminum fibers; mixing the aluminum fibers with a magnesium chloride powder; and compressing the mixed aluminum fibers and magnesium chloride powder into a pellet.

15. The method of producing an ammonia absorber pellet of claim 14, wherein compressing the mixed aluminum fibers and magnesium chloride powder into a pellet further comprises:filling a cylinder with the mixed aluminum fibers and the magnesium chloride powder; and compressing the mixed aluminum fibers and magnesium chloride powder in the cylinder with a die.

16. The method of producing an ammonia absorber pellet of claim 14, wherein compressing the mixed aluminum fibers and magnesium chloride powder into a pellet further comprises: compressing the mixed aluminum fibers and magnesium chloride powder to a density of at least 0.5 g / cm3.

17. The method of producing an ammonia absorber pellet of claim 14, wherein chopping aluminum into aluminum fibers further comprises: chopping the aluminum fibers into fibers with a maximum width of 150 micrometers, and a length less than 1 cm.

18. The method of producing an ammonia absorber pellet of claim 14, wherein the magnesium chloride powder further comprises: anhydrous magnesium chloride.

19. The method of producing an ammonia absorber pellet of claim 14, wherein mixing aluminum fibers and magnesium chloride further comprises: homogeneously mixing the aluminum fibers and the magnesium chloride.

20. The method of producing an ammonia absorber pellet of claim 14, wherein the magnesium chloride further comprises: nominally 40% of the ammonia absorber pellet; and the aluminum fibers further comprise: nominally 60% of the ammonia absorber pellet.

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