Methods for making ammonia absorbents

Abstract

A method and system for creation of an ammonia absorbent. The method can include selecting a metal halide salt. The method can also include mixing the selected metal halide salt with a binder to form a mixture. Additionally, the method can involve adding a solvent to the mixture to solubilize the metal halide salt, thereby forming a uniform paste, where the solvent is chosen from the group consisting of water and organic solvents. The method can further include extruding the uniform paste to form long cylindrical rods. Furthermore, the method can involve drying the extruded cylindrical rods to remove moisture. Finally, the method can include cutting the dried cylindrical rods into pellets, thereby synthesizing an ammonia absorbent.

Description

METHODS FOR MAKING AMMONIA ABSORBENTSCROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims priority to U.S. Appl. Serial No. 63 / 709,145, filed October 18, 2024, entitled “Methods for Making Ammonia Absorbents” which patent application is commonly owned by the owner of the present invention. This patent application is incorporated herein in its entirety.TECHNICAL FIELD

[0001] The present disclosure is situated in the field of materials science and environmental engineering, specifically focusing on the synthesis of absorbent materials for capturing, transporting, and storing ammonia. In particular, the present disclosure leverages principles of chemical engineering, materials science, and environmental sustainability for the development of a cost-effective, energy-efficient, and environmentally friendly method for making ammonia absorbents through utilization of metal halide salts mixed with binders and solvents to create pellets with high ammonia absorption capacity.STATEMENT OF FEDERALLY FUNDED RESEARCH

[0002] None.BACKGROUND

[0003] The landscape of modem industrial processes is increasingly influenced by the demand for sustainable and environmentally friendly solutions, especially in the field of gas capture and storage. Among these, ammonia, a key chemical in various industrial applications including agriculture and refrigeration, presents significant challenges and opportunities. The conventional synthesis of ammonia, through the Haber-Bosch process, is energy-intensive and contributes substantially to global CO2 emissions. The development of efficient ammoniaabsorbents is therefore crucial for enhancing the energy efficiency and environmental sustainability of this process. The global push towards reducing greenhouse gas emissions underscores the importance of innovative materials that can efficiently capture and store ammonia.

[0004] The industry faces significant hurdles in synthesizing absorbents that are both effective and practical for large-scale use. Traditional absorbent materials often suffer from limitations such as poor mechanical integrity and complex synthesis processes that are not conducive to scalability or environmental sustainability. The incorporation of binders and the development of new synthesis techniques, such as the mechanical mixing of metal halide salts with ceramic binders, offer promising avenues for overcoming these challenges. The focus has shifted towards creating absorbents that are not only efficient in ammonia capture but also robust and easy to produce on an industrial scale.

[0005] With the increasing importance of green chemistry and the push for more sustainable industrial processes, the development of advanced materials for ammonia absorption is more critical than ever. The environmental impact of ammonia production, coupled with the need for efficient gas capture technologies, highlights the urgent need for innovation in this area. The challenges of scalability, versatility, and commercial viability of absorbent materials are significant, but they also present opportunities for groundbreaking advancements in materials science and engineering.

[0006] Graphite has long been used as a thermally conductive material for different purposes like constructing thermocouples, heater tubes, foundry tools, molds for continuous casting, etc. Flakes of graphite are often used in thermal conductivity applications. To merge porosity characteristics with conductive characteristics, expanding the graphite flakes is a popular technique. Expandable graphite is synthesized by mixing graphite flakes with intercalation compounds like sulfuric acids. These compounds are often volatile. When subjected to hightemperature like 250°C, the flakes expand or exfoliate due to pressure developed from vapor of the intercalation reagents. Volume expansion of graphite in this fashion is almost 300 times and surface area increase is ten-fold in this way.

[0007] An appropriate binder is also necessary to hold these substances together and provide the absorbent necessary mechanical strength. Binder selection is important since it should not cause too much pressure drop during absorption and provides the opportunity for the expansion of salt crystal.

[0008] Alkali metal halides (such as, for example, LiCl) , alkaline earth metal halides (such as, for example, MgCh, CaCh, MgBn, SrCh), and transition metal halides (MnCh, NiCh, ZnCh) have a greater ammonia absorption capacity compared with the capacity of adsorbents (such, for example, carbon, zeolite, alumina, silica gel). A higher surface area is important for these absorbents to have a higher capacity. Hence these materials were recently supported on porous support material to enhance the surface area and physical porosity for higher absorption quantity. The attempt to increase the surface area to increase the absorption capacity was successful to some extent but failed while being used in continuous cyclic operation as the gradual capacity loss was observed. Change in the porous area during the cyclic ammonia uptake and release led to the agglomeration of the active particles, which was identified as the reason for the reduction in capacity.

[0009] Currently, absorbents are made by impregnating a metal halide into the pores of a support such as silica. The method has been successful in increasing the surface area and absorption capacity of ammonia, but not as much in improving the cyclic uptake of ammonia over multiple cycles. Additionally, the impregnation method can become chemical-intensive and tedious.

[0010] As such, prior efforts in this field face obstacles such as optimizing the balance between absorption capacity and material stability, and achieving the desired properties at acommercially viable cost. Innovations in solvent use, binder selection, and the mechanical properties of the absorbents are under intense investigation. Yet, challenges remain in ensuring that these new materials can be produced efficiently and perform effectively under the wide range of conditions found in commercial applications.

[0011] Commercially, after ammonia is synthesized, it is separated by condensation or refrigeration requiring an array of heat exchangers to reduce the temperature to the boiling point of ammonia. This technique does not allow adaptation to renewable energy.

[0012] Accordingly, there is a need for a system and method that can efficiently synthesize ammonia absorbents using scalable, versatile, and environmentally sustainable techniques. Such advancements would not only enhance the efficiency of ammonia synthesis and capture processes but also contribute to the broader goals of reducing energy consumption and minimizing environmental impacts in industrial operations. This approach promises to address the current limitations in ammonia capture and storage technologies, offering a pathway towards more sustainable industrial practices.SUMMARY OF THE DISCLOSURE

[0013] The present disclosure is directed to the synthesis of absorbent materials that can be used as a separating medium for ammonia from the reactant effluent stream.

[0014] To address the needs disclosed above, the disclosure uses a process where the resultant absorbent can uptake ammonia in a continuous cyclic manner while retaining the structure and capacity. As such, using the method of the present disclosure, the absorbent developed by mixing binder and metal halide salts can have higher mechanical strength allowing the structure to retain shape during continuous uptake and release of ammonia.

[0015] In some embodiments, the disclosure utilizes a new technique for the synthesis of porous absorbents that will be able to retain the porous structure during the cyclic ammoniaabsorption experiments. In such embodiments, the absorbent can be made by taking the halide salt and mixing it with a binder, including but not limited to ludox, bentonite, methocel, and other ceramic binders. During mixing, a solvent, in this embodiment, either water or an organic solvent (such as, for example, methanol, ethanol, dimethylformamide) can be added to aid in solubilizing the salt so a uniform paste can be made. The choice of solvent depends on the type of salt that would be used. Further, in this embodiment, paste can be extruded into any shape, such as long cylindrical rods, dried, and cut into pellets. Accordingly, in such an embodiment, the amount of salt, binder, and solvent used to make the absorbent can vary widely to obtain the largest amount of ammonia absorbed per mole of absorbent.

[0016] In general, in one embodiment, the disclosure features a method for synthesizing absorbent materials for separating ammonia from a reactant effluent stream. The method includes preparing expanded graphite from expandable graphite. The method includes heating the expandable graphite. The method includes further heating the expanded graphite; cooling the expanded graphite. The method includes adding the expanded graphite to a centrifuge tube along with aluminum powder, bentonite, and metal halide to form a mixture. The method includes mixing the mixture in the centrifuge tube. The method includes adding ethanol to the mixture in the centrifuge tube incrementally. The method includes mixing the mixture until a uniform paste is formed. The method includes drying the uniform paste. The method includes crushing and cutting the dried mixture into large chunks. The method includes sieving away powders from the large chunks prepared for ammonia absorption.

[0017] In general, in another embodiment, the disclosure features a method for synthesizing an ammonia absorbent. The method includes selecting a metal halide salt. The method includes mixing the selected metal halide salt with a binder to form a mixture. The method includes adding a solvent to the mixture to solubilize the metal halide salt, thereby forming a uniform paste, where the solvent is selected from the group consisting of water and organic solvents.The method includes extruding the uniform paste to form long cylindrical rods. The method includes drying the extruded cylindrical rods to remove moisture. The method includes cutting the dried cylindrical rods into pellets.

[0018] In general, in another embodiment, the disclosure features a method for producing ammonia absorbents. The method includes mixing a metal halide with a binder to create a mixture. The method includes forming the mixture into shapes. The method includes drying the shaped mixture.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other advantages of the present disclosure will be apparent from the following detailed description of the disclosure in conjunction with embodiments as illustrated in the accompanying drawings, in which:

[0020] FIG. 1A depicts a schematic of an experimental set up of the volumetric analysis, in accordance with certain embodiments of the present disclosure. FIG. IB depicts a schematic of the breakthrough setup used to evaluate the continuous working absorption capacity in accordance with certain embodiments of the present disclosure.

[0021] FIG. 2 depicts an XRD pattern of Ludox based composite absorbents all having the salt composition of 40 wt%, in accordance with certain embodiments of the present disclosure.

[0022] FIG. 3A depicts an SEM image of crystalline MgCh at a magnification of 5 micrometers, in accordance with certain embodiments of the present disclosure.

[0023] FIG. 3B depicts an SEM image of crystalline MgCh at a magnification of 2 micrometers, in accordance with certain embodiments of the present disclosure.

[0024] FIG. 3C depicts an SEM image of crystalline MgCh at a magnification of 500 nanometers, in accordance with certain embodiments of the present disclosure.

[0025] FIG. 3D depicts an SEM image of 40 wt.% MgCh_Ludox at a magnification of 10 micrometers, in accordance with certain embodiments of the present disclosure.

[0026] FIG. 3E depicts an SEM image of 40 wt.% MgC12_Ludox at a magnification of 1 micrometer, in accordance with certain embodiments of the present disclosure.

[0027] FIG. 3F depicts an SEM image of 40 wt.% MgC12_Ludox at a magnification of 500 nm, in accordance with certain embodiments of the present disclosure.

[0028] FIG. 4 depicts graphical thermogravimetric analyses of Ludox based absorbents, in accordance with certain embodiments of the present disclosure.

[0029] FIGS. 5A-5B depict the physisorption analysis results of each Ludox based absorbent with 40 wt.% of different salts, in accordance with certain embodiments of the present disclosure. FIG. 5A depicts the adsorption and desorption isotherms. FIG. 5B depicts the pore size distribution of the absorbents.

[0030] FIGS. 6A-6B depict graphical depiction of normalized pressure drop of ammonia for various Ludox based absorbents, in accordance with certain embodiments of the present disclosure.

[0031] FIG. 7 depicts a graphical depiction of the batch absorption capacity of Ludox based absorbents with different salts as a function of weight percent, in accordance with certain embodiments of the present disclosure.

[0032] FIG. 8 depicts a breakthrough analysis coordination number and working capacity of each Ludox based absorbent at 40 wt.%, in accordance with certain embodiments of the present disclosure.

[0033] FIGS. 9A-9B depict nitrogen physisorption results of expanded graphite samples, in accordance with certain embodiments of the present disclosure. FIG. 9A depicts results showing single point BET surface area versus the exposure time of expanded graphiteexfoliation. FIG. 9B depicts results showing BJH single point adsorption total pore volume versus the exposure time of expanded graphite exfoliation.

[0034] FIG. 10A depicts an SEM image of pure expanded graphite, in accordance with certain embodiments of the present disclosure.

[0035] FIG. 10B depicts the SEM image of bentonite based fresh sorbent while FIG. 10C depicts the SEM image of bentonite based spent sorbent after 45 breakthrough cycles.

[0036] FIG. 11 depicts N2 adsorption and desorption isotherms of each of fresh bentonite based absorbent (5% graphite, 5% Aluminum, 40% MgC12, 50% bentonite), the same absorbent after batch ammonia absorption experiment and the same absorbent after 45 breakthrough cycles, in accordance with certain embodiments of the present disclosure.

[0037] FIG. 12 depicts graphical thermogravimetric analyses of fresh bentonite based absorbent paste (5% graphite 5% Aluminum 40% MgC12 50% bentonite), in accordance with certain embodiments of the present disclosure.

[0038] FIG. 13 depicts XRD pattern of fresh bentonite based absorbent (5% graphite 5% Aluminum 40% MgC12 50% bentonite) and the same absorbent after 45 breakthrough cycles in accordance with certain embodiments of the present disclosure.

[0039] FIG. 14 depicts batch capacity and coordination number of bentonite based samples (MgCh wt. %-Bentonite wt. %-Graphite wt. %-Al wt. %) used in a working example analysis, in accordance with certain embodiments of the present disclosure.

[0040] FIG. 15 depicts graphs of normalized pressure drop of bentonite based samples (MgCh wt. %-Bentonite wt. %-Graphite wt. %-Al wt. %) used in this working example analysis indicating their kinetics, in accordance with certain embodiments of the present disclosure.

[0041] FIG. 16 depicts a graphical depiction of breakthrough capacity and coordination number change with cycles of 5% graphite, 5% Aluminum, 40% MgCh, and 50% bentonitesample in working example analysis, in accordance with certain embodiments of the present disclosure.NOTATION AND NOMENCLATURE

[0042] Various terms are used to refer to particular system components. Different companies may refer to a component by different names - this document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or a direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections.

[0043] The terminology used herein is for the purpose of describing particular example embodiments only, and is not intended to be limiting. Following long-standing patent law convention, the terms “a” and “an” mean “one or more” when used in this application, including the claims.

[0044] As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0045] The terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and / or sections; however, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms may be only used todistinguish one element, component, region, layer, or section from another region, layer, or section. Terms such as “first,” “second,” and other numerical terms, when used herein, do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. As used herein, the term “and / or” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and / or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D. Accordingly, as an example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. In another example, the phrase “one or more” when used with a list of items means there may be one item or any suitable number of items exceeding one.

[0046] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” “top,” “bottom,” and the like, may be used herein. These spatially relative terms can be used for ease of description to describe one element’s or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms may also be intended to encompass different orientations of the device in use, or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein interpreted accordingly.

[0047] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.DETAILED DESCRIPTION OF THE DISCLOSURE

[0048] The present disclosure is directed to methods and systems for the synthesis and application of ammonia absorbents, aiming to enhance the energy efficiency and environmental sustainability of ammonia handling processes. This involves a series of innovative steps for creating absorbents capable of efficiently capturing and storing ammonia, thereby facilitating a more environmentally friendly approach to its use in various industrial applications. The methods include mixing metal halide salts with binders, such as Ludox, bentonite, or other ceramic binders, in the presence of a solvent to form a paste. This paste is then extruded into rods, dried, and cut into pellets, which are characterized by their high ammonia absorption capacity.

[0049] In certain embodiments, the absorbents, developed through this novel synthesis process, are designed for use in a wide range of sectors, potentially revolutionizing industries such as agriculture, refrigeration, and energy storage. The absorbents can be particularly beneficial in improving the Haber-Bosch process for synthesizing ammonia, making it less energy-intensive and reducing its carbon footprint. With the increasing demand for sustainable industrial processes, these absorbents provide a critical solution to the challenges of energy consumption and environmental degradation associated with conventional ammonia production and handling methods.

[0050] The present disclosure provides detailed methods and systems for the scalable production of these absorbents. For instance, the choice of metal halide salts, binders, and solvents can be varied to optimize the absorbents for specific applications, including but not limited to ammonia capture and storage. The versatility of the synthesis process allows for customization based on the desired application, ensuring that the absorbents meet the necessary performance criteria for effective use in commercial settings.

[0051] In certain embodiments, the synthesis process can be adapted to include additional steps for enhancing the mechanical integrity and ammonia absorption efficiency of the pellets. These steps might involve the optimization of drying and curing conditions, as well as the application of surface treatments to improve the pellets' physical and chemical properties. The adaptability of the synthesis process ensures that the absorbents can be tailored to meet the requirements of a broad range of applications, further increasing their commercial viability.

[0052] In some embodiments of the present disclosure, the effectiveness of the ammonia absorbents in capturing and releasing ammonia can be quantified through various analytical techniques. These techniques may include breakthrough analysis and volumetric analysis to evaluate the absorption capacity and efficiency under different conditions. The absorbents' performance can be further characterized through physical and chemical analyses, such as BET surface area measurements, powder X-ray diffraction (PXRD) for phase identification, and scanning electron microscopy (SEM) for morphological examination.

[0053] The potential for recycling and reusing these ammonia absorbents in a closed-loop system is also explored, highlighting the environmental benefits of this approach. In certain embodiments, used absorbents can be regenerated through a series of steps designed to restore their original absorption capacity, thereby extending their lifecycle and reducing waste. This aspect of the disclosure emphasizes the sustainability and economic advantages of the novelammonia absorbents, aligning with the global push towards greener and more efficient industrial processes.

[0054] In some embodiments, the synthesis method begins with calculating the amount of Ludox needed to reach the desired salt weight percent. In such an embodiment, the weight percentage is based off the amount of salt and the amount of silica in the Ludox, not the overall Ludox volume. Ludox is a 40% suspension of SiCh in water and it has a density of 1.295 g / mL. Accordingly, in such an embodiment, to make each absorbent, the weight percentage can be calculated using the following equation: salt (a) wt% salt = — — 773 — i — — T salting ) + 0.4 * Ludox(g)

[0055] Where the total gram of silica is 0.4 * Ludox^g). Specifying the desired weight percent and grams of salt gives the grams of Ludox needed and dividing by the density gives the total milliliters.

[0056] In some embodiments, the selected salt can be weighed out and put in a 50mL centrifuge tube. The Ludox can then be added slowly to the tube while being continuously mixed on the vortex mixer, to create a uniform paste. From this, in such an embodiment, the paste can then be extruded. In some embodiments, the extrusion can be performed using a meat grinder. The paste can be extruded into small cylindrical rods, where it will then be dried in a tube furnace to remove all of the water. The extruded paste can be loaded into a glass tube to be heated under vacuum and the flow of nitrogen. In some embodiments, the tube can be heated in the furnace to 300°C at a rate of 5°C / min. After being left to cool, in such an embodiment, the cylindrical rods can be cut into small pellets where the absorption capacity can now be tested.

[0057] Working examples testing the absorption capacity as described herein. The absorption capacity has been tested in two different ways, with a breakthrough system and with a volumetric analyzer. Both tests evaluate the capacity the absorbent has for absorbing ammonia.Volumetric analysis involves loading the absorbent into a vessel, pressurizing it with ammonia and determining the uptake over a period of time. A breakthrough system measures the absorption capacity at varying temperatures and pressures as ammonia flows through a bed packed with the absorbent. This allows for observing how the absorption capacity changes as well as evaluating the cyclic ability of the absorbent as it can be absorbed and desorbed multiple times.

[0058] FIG. 1A depicts a schematic of an experimental set up of the volumetric analysis, in accordance with certain embodiments of the present disclosure. FIG. IB depicts a schematic of the breakthrough setup used to evaluate the continuous working absorption capacity in accordance with certain embodiments of the present disclosure.

[0059] In the depicted procedure, a predetermined quantity of the absorbent, ranging between 0.5 and 1 gram, is subjected to pressurization with both nitrogen and ammonia gases to measure the differential pressure over a specified timeframe. Initially, the system is pressurized with nitrogen gas to a pressure of 60 psi, rapidly actuating the nitrogen valve alongside the analyzer's valves to achieve the desired pressure. This initial phase, lasting approximately two hours, aims to identify any potential leaks or valve-related pressure changes, given that the absorbent material does not absorb nitrogen. Typically, a minimal pressure difference of about 5 psi is observed, indicating negligible leakage and primarily reflecting the mechanical effects of valve operation.

[0060] Following this nitrogen-based leakage assessment, the volumetric analyzer is systematically depressurized before repeating the pressurization process, this time utilizing ammonia gas. The subsequent phase involves recording the maximum and minimum pressures achieved with both nitrogen and ammonia, allowing for the calculation of absorbed ammonia quantities.

[0061] This analytical method facilitates the precise determination of the number of moles of ammonia absorbed by the absorbent, taking into account any minor losses attributable to operational factors such as valve manipulation or incidental leaks during the testing duration.

[0062] To find the absorption capacity, first the maximum and minimum nitrogen and ammonia pressures are found. The difference in these two pressures will give the moles of nitrogen lost and the moles of ammonia absorbed following the equation:

[0063] Using the ideal gas law, the first term is the difference in pressure converted to atmospheres. The second term is the volume of the volumetric analyzer which is 300 cubic centimeters converted to liters. Then dividing by the gas constant and the temperature (room temperature) the number of moles is calculated. The moles of nitrogen lost is subtracted from the moles of ammonia to account for pressure lost due to closing the valves and any slight leakage during the 2-hour test.

[0064] The moles of salt loaded are now calculated to get the absorption capacity and coordination number.„ .. , Moles(NH3)Coordination Number = - Moles { - —salt -)

[0065] Where MWNHgis the molecular weight of ammonia.

[0066] As shown, the absorption capacity is derived through the application of the ideal gas law, incorporating the noted pressure variances (converted to atmospheres) and the controlledvolume of the analyzer (approximately 300 cubic centimeters, converted to liters), adjusted for room temperature using the gas constant.

[0067] Furthermore, as shown, the procedure enables the calculation of the absorbent's coordination number, which represents the ratio of absorbed ammonia moles to the initial moles of salt present in the absorbent. The resulting data, expressed as milligrams of absorbed ammonia per gram of absorbent, underscore the efficiency and potential of the synthesized materials for practical applications in ammonia capture and storage.

[0068] The absorption capacity, in some embodiments, can also be tested through a breakthrough test to further assess the absorbent's capacity under dynamic conditions, simulating a packed bed scenario where ammonia gas is continuously passed through the absorbent material. The critical metric in this test, the breakthrough time, is determined by monitoring the thermal conductivity detector (TCD) signal as ammonia permeates the absorbent bed. This temporal marker, defined as the point at which 5% of the TCD’s saturation signal is reached, serves as a basis for calculating the absorbent's capacity using a predefined equation that incorporates the flow rate of ammonia, the molecular weight of ammonia, and the quantity of absorbent utilized.

[0069] To obtain the surface area and pore volume of pure salts and as-synthesized absorbents, nitrogen physisorption test can be performed. In the working examples, such test was performed with the Micromeritics 3Flex Adsorption analyzer instrument (GA, USA).

[0070] The samples can be degassed under a vacuum at 300 °C for 3 hours before the measurements to remove moisture and other impurities. The surface area was obtained using Brunauer-Emmett-Teller (BET) method and the single-point desorption pore volumes reported here were all at 0.89 P / Po. The result is added in Table 1. As seen from the Table, irrespective of the type of binder used with any type of salt, obtained surface area increased by more than a factor of 15 in comparison with the unsupported salt. Binders (for example, but not limitedto, Ludox, Bentonite) are successful of creating bonds with the halide salt of alkali, alkaline earth metal and transition metals as seen from Table 1 as well as from other characterizations described below.

[0071] Table 1. BET surface area, total pore volume and pore size for pure salts and as- synthesized Ludox based absorbents.

[0072] FIG. 2 depicts XRD pattern of composite absorbents all having the salt composition of 40 wt.%, in accordance with certain embodiments of the present disclosure.

[0073] In these embodiments, the X-ray diffraction patterns were collected using a Rigaku Miniflex II, which was set to operate with CuKa radiation (1=0.154 nm) and a scan speed of 5° per minute, covering a scanning range between 10° to 90°.

[0074] In the working example embodied in FIG. 2, two distinguishable features common across all the XRD patterns of the absorbents are shown. As shown in FIG. 2, the samples are hydrated to some extent, yet retain the structural integrity of the actual salt.

[0075] In certain working examples, SEM was performed by field emission-SEM Hitachi S- 4700 (Japan) at 2.0 kV acceleration voltage to obtain the surface morphology.

[0076] FIG. 3A depicts an SEM image of crystalline MgCh at a magnification of 5 micrometers, in accordance with certain embodiments of the present disclosure.

[0077] FIG. 3B depicts an SEM image of crystalline Mg Ch at a magnification of 2 micrometers, in accordance with certain embodiments of the present disclosure.

[0078] FIG. 3C depicts an SEM image of crystalline Mg Ch at a magnification of 500 nanometers, in accordance with certain embodiments of the present disclosure.

[0079] FIG. 3D depicts an SEM image of 40 wt.% MgCh Ludox at a magnification of 10 micrometers, in accordance with certain embodiments of the present disclosure.

[0080] FIG. 3E depicts an SEM image of 40 wt.% MgCh Ludox at a magnification of 1 micrometer, in accordance with certain embodiments of the present disclosure.

[0081] FIG. 3F depicts an SEM image of 40 wt.% MgCh Ludox at a magnification of 500 nm , in accordance with certain embodiments of the present disclosure.

[0082] As shown in FIGS. 3 A, 3B, and 3C, the crystalline MgCh has kinks and steps that are visible in the SEM. Alternatively, the binder-based absorbents shown in FIGS. 3D-3F display a porous distribution on the surfaces. Accordingly, the FIGS. 3A-3F conform with the surface area noted in Table 1, above, due to the binder-based absorbents having high surface area and increased pore volume. While the working example depicted in FIGS. 3A-3F represents only MgCh based absorbents developed by Ludox, alternative salts could be utilized in other embodiments of the present disclosure and would likewise show similar results.

[0083] The working examples further involved analysis using thermogravimetric analysis. In some embodiments of the working examples, the thermogravimetric analysis was performed with Netzsch STA 409 PC at a heating rate of 5 °C / min from 20 °C to 600 °C for the samples with different salt types.

[0084] For working examples using MgCh-based samples, the temperature range was 20-600 °C but the heating ramp was maintained the same.

[0085] In each working example, approximately 20 mg of homogeneous paste was taken in the sample holder which was calibrated before any test. In such an embodiment, all the tests were continued at a 50 mL / min gas flow rate (Argon). The thermogravimetric analysis was then, in this working example, performed to understand the stability of the developed absorbents.

[0086] FIG. 4 depicts graphical thermogravimetric analyses, in accordance with certain embodiments of the present disclosure.

[0087] For all working example using the salts depicted in FIG. 4, the weight loss was caused by the dehydration of colloidal Ludox. In such an embodiment, the presence of residual moisture is also evident from the thermogravimetric analysis profile as none of them crossed the line for the weight loss of Ludox itself.

[0088] Further, in the working example, the XRD profile confirms the presence of hydrated salts, as then confirmed by the thermogravimetric analysis.

[0089] Additionally, as shown by FIG. 4, both diluted and undiluted samples experienced substantial weight loss. In some embodiments, the weight loss can be caused by the highly soluble nature of MgCh.

[0090] FIGS. 5A-5B depict the physisorption analysis results of each absorbent with 40 wt.% of different salts. FIG. 5A depicts the adsorption and desorption isotherms and FIG. 5B depicts the pore size distribution of the absorbents. This type of hysteresis is conducive to pores made from particles tightly wedged together with openings on both sides. This makes sense as both the salts and Ludox are not microporous, but mesoporous and mixed.

[0091] FIGS. 6A-6B depict graphical depictions of normalized pressure drop of ammonia for various absorbents in batch experiment, in accordance with certain embodiments of the present disclosure.

[0092] The batch absorption capacity of different Ludox based absorbents are shown in Table 2, below.

[0093] Table 2. The coordination number and absorption capacity for pure salts and as- synthesized absorbents.

[0094] As noted in respect to the data displayed in Table 2, each metal halide salt has a salt weight percent of 40% with no additional dilution. The normalized pressure drop shown in FIGS. 6A-6B highlights each absorbent’s uptake of ammonia over a period of 100 minutes. Further, as shown by FIGS. 6A-6B, magnesium chloride, nickel chloride, and manganese chloride all absorbed a similar amount of ammonia at a similar rate, only absorbing for the first 20 minutes before remaining at a steady pressure, whereas calcium chloride and lithium chloride absorbed at a slower rate and have a larger difference in pressure leading to a greater absorption capacity.

[0095] The working examples also involved evaluation using the volumetric analyzer, which provides an evaluation of salt weight percent on the absorption capacity.

[0096] FIG. 7 depicts a graphical depiction of the absorption capacity of different salts as a function of weight percent, in accordance with certain embodiments of the present disclosure. In the working example, MgCh, CaCh. MnCh, NiCh and LiCl were used to synthesize four different absorbents at weight percents of 40, 50, 70 and 100 percent with no additional dilution.

[0097] Additionally, in the working example, a breakthrough test was performed on a sample containing 40 weight percent of different salts. In this embodiment, the absorbent was synthesized with 5g of each salt, and the necessary amount of Ludox and dilution water was added which varied with the solubility of salt in water.

[0098] FIG. 8 depicts a breakthrough analysis coordination number and working capacity of each absorbent at 40 wt.%. The capacity of the absorbents seen in volumetric analysis are much higher than those seen in breakthrough analysis. NiCh was found to have the highest working absorption capacity followed by MnCh, MgCh, CaCh, and LiCl.

[0099] As confirmed by the working examples herein, the method of the present disclosure can be used to optimize the synthesis of absorbent materials that can be used as a separating medium for ammonia from the reactant effluent stream.

[0100] In some embodiments, the method for the synthesis of absorbent materials begins with the preparation of expanded graphite from expandable graphite. For example, the method can utilize commercially available expandable graphite. In some embodiments, the expandable graphite is at first heated at 60°C in an air circulation oven for 24hr in order to remove moisture and other volatile compounds from the surface. Next, in some embodiments, the method continues with heating the graphite in a tube furnace to 650°C at 20°C / min ramp and kept at that temperature for 5 minutes. After cooling, in such an embodiment, certain mass of expandedgraphite is taken in a 50 mL centrifuge tube and subsequently, other substances are added starting with aluminum powder, bentonite and then magnesium chloride.

[0101] In some embodiments, 7-15 micron aluminum powder can be used. In certain embodiments, the aluminum powder can be kept inside argon atmosphere of a glove box with very low concentration oxygen for 24h before mixing it with other material. In such an embodiment, these steps allow aluminum oxide layer to be formed over the aluminum powder and makes it safe to use for sample preparation.

[0102] In some embodiments, bentonite can be utilized as amorphous powder. In some embodiments, magnesium chloride in crystalline form. In some embodiments, 10g of sorbent can be made in the centrifuge tube and the mass composition which showed maximum capacity was graphite 5%, aluminum 5%, magnesium chloride 40% and bentonite 50%. The mixture, in such an embodiment, then can be shaken in a vortex mixer at maximum speed for 2 minutes.

[0103] Following, in an exemplary embodiment of the present disclosure, multiple mL of ethanol should be added as solvent to form a paste. In some embodiments, ethanol can be added by 1 mL with subsequent shaking in vortex mixer until a uniform paste is formed. After that, the method may continue, in certain embodiments with drying in a tube furnace to 350°C at 5°C / min ramp and keeping the dried mixture at that temperature for 1 hour. After cooling, the method in some embodiments continues with crushing the dried mixture carefully by mortar and pestle along with cutting by knife to produce large chunks roughly with a dimension of 0.25 inches. The powders and small chunks should be sieved away. At this point, the sample is ready for ammonia absorption.

[0104] Physisorption analysis was performed to determine changes in surface area, pore volume, and characteristics of the expandable graphite. In the working example analysis, a Micromeritics 3Flex Adsorption analyzer instrument was used to conduct the nitrogen physisorption test. The main parameters of significance were single point BET surface area at0.30 P / PO, micropore area, micropore volume, single point adsorption total pore volume of pores less than 102.653 A radius at 0.90 P / PO and adsorption average pore diameter (4V / A by BET). The samples were degassed in vacuum for 2 h at 200°C. Approximately 0.2 g of sample was taken for assessment.

[0105] FIGS. 9A-9B depict nitrogen physisorption results of expanded graphite samples, in accordance with certain embodiments of the present disclosure. FIG. 9A depicts results showing single point BET surface area versus the exposure time of expanded graphite exfoliation. FIG. 9B depicts results showing single point adsorption total pore volume versus the exposure time of expanded graphite exfoliation.

[0106] As shown in FIGS. 9A-9B, at about 650°C expansion temperature and 5 minutes exfoliation time showed the maximum pore volume as well as surface area. These physisorption analyses identified a 650°C temperature and 5 min exposure time to be appropriate for expansion of graphite since maximum surface area and pore volume are needed for attaining a porous structure.

[0107] SEM analysis was conducted to show how salt crystals distribute over expanded graphite and interaction between bentonite and expanded graphite.

[0108] FIG. 10A depicts an SEM image of pure expanded graphite, in accordance with certain embodiments of the present disclosure. FIG. 10B depicts the SEM image of bentonite based fresh sorbent while FIG. 10C depicts the SEM image of spent sorbent after 45 breakthrough cycles.

[0109] The dotted circles in FIGS. 10A-10B represent the salt particles in the absorbent chunk. The salt particles and graphite can be seen binded by the bentonite binder and expansion of lumps can be observed after multiple breakthrough cycles.

[0110] FIG. 11 depicts N2 adsorption and desorption isotherms of each of fresh bentonite based absorbent (5% graphite, 5% Aluminum, 40% MgC12, 50% bentonite), the same absorbent afterbatch ammonia absorption experiment and the same absorbent after 45 breakthrough cycles, in accordance with certain embodiments of the present disclosure. FIG. 11 indicates presence of mesopores. As shown in FIG. 11, the pore volume also increases with the batch ammonia uptake, but breakthrough cycles take it to the initial fresh structure with comparatively less pore volume.

[0111] Thermogravimetric analysis was performed in NETZSCH STA 409 PC TGA analyzer at a heating rate of 2.5°C / min from 20°C to 600°C under argon flow of 40 seem. TGA analyses were performed to determine thermal changes occurring during ammonia desorption, effect of drying for paste sample and stability of absorbent in contact with moisture and after breakthrough cycles. XRD tests were performance to determine crystallographic properties using a Rigaku Miniflex 6G with monochromatic Cu Ka radiation (30 kV, 15 mA) from 10° to 90° at 2.5° / min.

[0112] FIG. 12 depicts graphical thermogravimetric analyses of fresh bentonite based absorbent paste (5% graphite 5% Aluminum 40% MgC12 50% bentonite), in accordance with certain embodiments of the present disclosure. Complete ethanol removal is achieved in this process which is evident from TGA analysis where 30% of total paste mass was ethanol. Within 200°C, all ethanol is dried out. It is also observed in FIG. 12 that, within 400-500°C, ~ 15% more mass is decreased in paste sample. This is attributed to decomposition of hydrated magnesium chloride resulting from exposure of the sample in air even for about a few minutes.

[0113] FIG. 13 depicts XRD pattern of fresh bentonite based absorbent (5% graphite 5% Aluminum 40% MgC12 50% bentonite) and the same absorbent after 45 breakthrough cycles in accordance with certain embodiments of the present disclosure. Presence of magnesium chloride crystals can be confirmed from XRD results for both fresh and spent samples along with magnesium chloride hydrated crystals. The XRD data also confirms presence of all significant components namely, graphite, Al and bentonite being present in both fresh and spentsamples. This implies that sufficient absorption sites exist within the material for absorption but is limited by diffusion kinetics during the absorption breakthrough experiment.

[0114] Working examples were tested to confirm absorption capacity. From a breakthrough test, a half-inch column was used for breakthrough experiment. Before performing the breakthrough analysis, the column was self-packed by ammonia gas in order to avoid pressure drop. In this process, a temporary storage vessel is first filled with ammonia and the connection between temporary storage and source gas cylinder is closed.

[0115] Now, in the working example, the pressure in temporary vessel is recorded and maintained at almost 60 psi. Next, in such an embodiment, the needle valve downstream of temporary vessel is slowly opened, such that ammonia comes out and enters the breakthrough column which is closed at the downstream.

[0116] In the working example, change in pressure in breakthrough column is observed as a volumetric analysis. Following, the column was desorbed of ammonia completely before starting the breakthrough experiments. During self packing, a 3 inch empty space was kept at top of column to allow expansion of the bed.

[0117] In order to assess the full potential of ammonia absorption capacity and to shortlist the right material, volumetric analysis was performed for a working example on the samples at 25° C in a 320 mL stainless steel vessel. In this working example, the initial absorption pressure was around 65 psi.

[0118] FIG. 14 depicts capacity and coordination number of samples used in a working example analysis, in accordance with certain embodiments of the present disclosure. In the working example, with results shown in FIG. 14, the experiments were started with only bentonite which had some potential of absorbing ammonia. Gradually, bentonite composition was increased and a nice linear trend was observed in the capacity of ammonia absorption. 40% magnesium chloride was taken as the optimum amount due to the issue of comparatively lowerpressure drop during dynamic breakthrough experiment. Keeping this salt composition constant, graphite was gradually added from 5% to 20% and independently aluminum powder was added following the same range of composition. At last, both were added together and both absorption and coordination number were determined.

[0119] As shown in FIG. 14, for both independent addition of graphite and aluminum or addition of both, as before, it was observed that the absorption capacity followed the 40% salt content (marked by red rectangle) and there was not much affected by the addition of conductive additive.

[0120] Further working examples assessed the kinetics of absorption through batch volumetric experimentation, as shown in FIG. 15.

[0121] FIG. 15 depicts graphs of normalized pressure drop of samples used in this working example analysis indicating their kinetics, in accordance with certain embodiments of the present disclosure.

[0122] FIG. 15 shows that, with addition of conductive additive, kinetic performance increases compared to sample with no conductive material. Compared to aluminum, graphite addition contributes to kinetic performance more. Graphite containing substances, blue and purple curves, surpass bentonite kinetics and reach the normalized unit value faster but other samples follow the bentonite kinetic curve mostly in the latter part. FIG. 15 indicates a greater superiority of graphite overcoming the slow mass transfer posed by bentonite. Aluminum, despite having a greater thermal conductivity value, could not surpass the bentonite kinetic resistance.

[0123] In the working examples, breakthrough tests were also performed starting with 2.5% of both the additives and increasing them simultaneously to 7.5%.

[0124] In the working example on the breakthrough test, three parameters namely absorption capacity, coordination number and pressure drop were scrutinized during each experiment andsuccessful experiments in terms of pressure drop, as discussed in more detail below in respect to Table 3.

[0125] Table 3. Breakthrough capacity, coordination number and maximum pressure drop at different compositions of conductive additive and bentonite in (MgCh wt. %-Bentonite wt. %- Graphite wt. %-Al wt. %).

[0126] In the working example, there was also a synergy observed between breakthrough capacity and pressure drop. Too much conductive additive decreased the absorption performance as well as when the total content was 20%, making the experiment difficult due to very high pressure drop. With this in mind, the sample with 5% graphite and 5% Aluminum was considered the most optimized composition for reasonable breakthrough capacity and pressure drop. The highest capacity achieved was around 350 mg ammonia / g sorbent and associated coordination number was 5 mol ammonia / mol salt. The capacity and coordinationnumber from the present disclosure is higher than reported ammonia absorption values using traditional absorbents.

[0127] FIG. 16 depicts a graphical depiction of breakthrough capacity and coordination number change with cycles of 5% graphite, 5% Aluminum, 40% MgCh, and 50% bentonite sample in working example analysis, in accordance with certain embodiments of the present disclosure.

[0128] In the working example of FIG. 16, for all three cases, coordination number was close to 5 mol ammonia / mol salt. For all the experiments, absorption temperature was 25°C, desorption temperature was 400°C and pressure was 40 psi. For the experiment with highest capacity, pressure drop was reasonable and close to 15 psi. Pressure drop decreased with increasing number of cycles as with time, the bed became stabilized. The material showed nearly the same capacities in all the cycles. The standard deviation for breakthrough capacity was 5.57 and that of breakthrough coordination number was 0.08. These low standard deviation values are indicative of excellent stability of the absorbents.

[0129] Graphite and aluminum make the sample porous and brittle. In some of the embodiments, channeling was observed if there was too much of a gap between chunks or if the chunk size was too small. Thus, both sample preparation and packing of the material inside the breakthrough column is equally important as using the correct composition. It is also to be noted that self-packing improves bed structure and gives reasonable capacity with reasonable pressure drop.

[0130] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it should be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustiveor to limit the described embodiments to the precise forms disclosed. It should be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

[0131] While embodiments of the disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the disclosure disclosed herein are possible and are within the scope of the disclosure. The scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.

[0132] Embodiments can include a system, a method, and / or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.

[0133] Those skilled in the art will appreciate that the steps described herein may be carried out in a variety of ways and that no particular ordering is required. It will be further understood from the foregoing description that modifications and changes may be made in various embodiments of the present disclosure without departing from its true spirit. The descriptions in this specification are for purposes of illustration only and are not to be construed in a limiting sense.

[0134] Consistent with the above disclosure, the examples of systems and methods enumerated in the following clauses are specifically contemplated and are intended as a non-limiting set of examples.

[0135] Clause 1. A method for synthesizing absorbent materials for separating ammonia from a reactant effluent stream, including preparing expanded graphite from expandable graphite;heating the expandable graphite; further heating the expanded graphite; cooling the expanded graphite; adding the expanded graphite to a centrifuge tube along with aluminum powder, bentonite, and magnesium chloride to form a mixture; mixing the mixture in the centrifuge tube; adding ethanol to the mixture in the centrifuge tube incrementally; mixing the mixture until a uniform paste is formed; drying the uniform paste; crushing and cutting the dried mixture into large chunks; and sieving away powders from the large chunks prepared for ammonia absorption.

[0136] Clause 2. The method of any foregoing clause, where the heating of the expandable graphite is performed in an air circulation oven.

[0137] Clause 3. The method of any foregoing clause, where the air circulation oven is at a temperature of 60°C.

[0138] Clause 4. The method of any foregoing clause, where the heating of the expandable graphite is performed for 24 hours.

[0139] Clause 5. The method of any foregoing clause, where the heating of the expanded graphite is performed in a tube furnace.

[0140] Clause 6. The method of any foregoing clause, where the tube furnace is at a temperature of 650°C.

[0141] Clause 7. The method of any foregoing clause, where the heating of the expanded graphite is performed at a rate of 20°C / min.

[0142] Clause 8. The method of any foregoing clause, where the expanded graphite is maintained at a temperature of 650°C for a period of 5 minutes.

[0143] Clause 9. The method of any foregoing clause, where the mixing of the mixture in the centrifuge tube is performed using a vortex mixer.

[0144] Clause 10. The method of any foregoing clause, where the vortex mixer is at maximum speed.

[0145] Clause 11. The method of any foregoing clause, where the mixing of the mixture occurs for 2 minutes.

[0146] Clause 12. The method of any foregoing clause, where the drying of the uniform paste is performed in a tube furnace.

[0147] Clause 13. The method of any foregoing clause, where the tube furnace is at a temperature of 350°C.

[0148] Clause 14. The method of any foregoing clause, where the drying of the uniform paste is performed at a rate of 5°C / min.

[0149] Clause 15. The method of any foregoing clause, where the uniform paste is maintained at a temperature of 350°C for a period of 1 hour.

[0150] Clause 16. The method of any foregoing clause, where the large chunks have a dimension of approximately 0.25 inches.

[0151] Clause 17. The method of any foregoing clause, where the expandable graphite is commercially available.

[0152] Clause 18. The method of any foregoing clause, where the aluminum powder used has a particle size of 7-15 microns.

[0153] Clause 19. The method of any foregoing clause, where the aluminum powder is exposed to an argon atmosphere with very low oxygen concentration for 24 hours before mixing.

[0154] Clause 20. The method of any foregoing clause, where exposing the aluminum powder under these conditions allows for the formation of an aluminum oxide layer over the powder.

[0155] Clause 21. The method of any foregoing clause, where the bentonite is utilized in its amorphous powder form.

[0156] Clause 22. The method of any foregoing clause, where magnesium chloride is used in its crystalline form.

[0157] Clause 23. The method of any foregoing clause, where the mass composition of the mixture in the centrifuge tube is graphite 5%, aluminum 5%, magnesium chloride 40%, and bentonite 50%.

[0158] Clause 24. The method of any foregoing clause, further including a step of preparing the sample for ammonia absorption testing following the sieving step.

[0159] Clause 25. A method for synthesizing an ammonia absorbent, including: selecting a metal halide salt; mixing the selected metal halide salt with a binder to form a mixture; adding a solvent to the mixture to solubilize the metal halide salt, thereby forming a uniform paste, where the solvent is selected from the group consisting of water and organic solvents; extruding the uniform paste to form long cylindrical rods; drying the extruded cylindrical rods to remove moisture; and cutting the dried cylindrical rods into pellets.

[0160] Clause 26. The method of any foregoing clause, where the metal halide salt includes any metal ionically bonded to any halogen.

[0161] Clause 27. The method of any foregoing clause, where the binder is selected from the group consisting of Ludox, bentonite, and ceramic binders.

[0162] Clause 28. The method of any foregoing clause, where the step of drying the extruded cylindrical rods is performed in a tube furnace at temperatures ranging from 100°C to 500°C.

[0163] Clause 29. The method of any foregoing clause, where the drying temperature is specifically set to 300°C to optimize the moisture removal process.

[0164] Clause 30. The method of any foregoing clause, further including the step of testing the ammonia absorption capacity of the pellets using a volumetric analyzer.

[0165] Clause 31. The method of any foregoing clause, where the testing step includes pressurizing the pellets with ammonia gas to measure the absorption capacity.

[0166] Clause 32. The method of any foregoing clause, where the metal halide salt is selected from the group consisting of magnesium chloride, calcium chloride, manganese chloride, nickel chloride, and lithium chloride.

[0167] Clause 33. The method of any foregoing clause, where the metal halide salt is magnesium chloride.

[0168] Clause 34. The method of any foregoing clause, where the Ludox binder is utilized at a concentration of 40% suspension of SiCh in water.

[0169] Clause 35. The method of any foregoing clause, where the solvent includes an organic solvent selected from the group consisting of ethanol, methanol, and acetone.

[0170] Clause 36. The method of any foregoing clause, further including the step of adding a plasticizer to the mixture before the extrusion step to enhance the flexibility of the cylindrical rods.

[0171] Clause 37. The method of any foregoing clause, where the plasticizer is polyethylene glycol.

[0172] Clause 38. The method of any foregoing clause, where the cutting step includes sizing the pellets to have a uniform diameter ranging from 1 mm to 5 mm.

[0173] Clause 39. The method of any foregoing clause, further including the step of activating the surface of the pellets after cutting to increase the surface area available for ammonia absorption.

[0174] Clause 40. The method of any foregoing clause, where the activation step involves treating the pellets with a gas phase reactant under elevated temperatures.

[0175] Clause 41. The method of any foregoing clause, where the gas phase reactant is selected from the group consisting of ammonia, nitrogen, and steam.

[0176] Clause 42. The method of any foregoing clause, further including the step of packaging the pellets in a moisture-barrier container to preserve their absorption capacity until use.

[0177] Clause 43. A method for producing ammonia absorbents, including mixing a metal halide with a binder to create a mixture; forming the mixture into shapes; and drying the shaped mixture.

[0178] Clause 44. The method of any foregoing clause, where the metal halide includes a halogen selected from the group consisting of chlorine, bromine, iodine, and fluorine.

[0179] Clause 45. The method of any foregoing clause, where the binder is an inorganic material.

[0180] Clause 46. The method of any foregoing clause, where the forming step involves extrusion.

[0181] Clause 47. The method of any foregoing clause, where the drying step is performed at a temperature between 100°C and 300°C.

[0182] Clause 48. The method of any foregoing clause, further including a step of activating the dried shaped mixture to increase ammonia absorption capacity.

[0183] Clause 49. The method of any foregoing clause, where activating the dried shaped mixture involves a chemical treatment.

[0184] Clause 50. The method of any foregoing clause, where the chemical treatment includes exposure to steam.

[0185] Clause 51. The method of any foregoing clause, where the shapes formed are selected from the group consisting of pellets, beads, and rods.

[0186] Clause 52. The method of any foregoing clause, where the mixture further comprises a solvent to aid in mixing the metal halide with the binder.

[0187] Clause 53. The method of any foregoing clause, where the solvent is water.

[0188] Clause 54. The method of any foregoing clause, further including the step of cutting the extruded mixture into predetermined lengths before the drying step.

[0189] Clause 55. The method of any foregoing clause, further including the step of coating the dried shapes with a protective layer to prevent moisture absorption.

[0190] Clause 56. The method of any foregoing clause, where the protective layer is a polymer.

[0191] Clause 57. The method of any foregoing clause, where the metal halide and binder are mixed in a weight ratio ranging from 1 : 1 to 5 : 1.

[0192] Clause 58. The method of any foregoing clause, further including testing the ammonia absorption capacity of the dried shapes using a volumetric analysis method.

[0193] Clause 59. An ammonia-absorbent composition including a metal halide salt phase dispersed within a continuous inorganic binder phase to form a porous composite to form a composite, where the composite is configured to reversibly absorb ammonia with a coordination number between 3 and 8 mol NHs per mol of the metal halide at 25 °C and an initial pressure between 40 and 65 psi, and shaped as pellets, beads, rods, or combinations thereof.

[0194] Clause 60. The ammonia-absorbent composition of any foregoing clause, where the metal halide salt is selected from the group consisting of magnesium chloride, calcium chloride, manganese chloride, nickel chloride, and lithium chloride.

[0195] Clause 61. The ammonia-absorbent composition of any foregoing clause, where the inorganic binder comprises colloidal silica, bentonite, a ceramic binder, or any combination thereof.

[0196] Clause 62. The ammonia-absorbent composition of any foregoing clause, where the composite comprises from 30 wt.% to 70 wt.% of the metal halide salt and from 30 wt.% to 70 wt.% of the inorganic binder.

[0197] Clause 63. The ammonia-absorbent composition of any foregoing clause, where the composite once has a diameter between 1 mm and 5 mm and a length between 1 mm and 10 mm.

[0198] Clause 64. The ammonia-absorbent composition of any foregoing clause, where the composite further includes from 2 wt.% to 10 wt.% expanded graphite and from 2 wt.% to 10 wt.% aluminum powder.

[0199] Clause 65. The ammonia-absorbent composition of any foregoing clause, where the ammonia absorption capacity is at least 250 mg NHs per gram of the composite.

[0200] Clause 66. The ammonia-absorbent composition of any foregoing clause, where an average pore diameter is between 10 nm and 30 nm.

[0201] Clause 67. The ammonia-absorbent composition of any foregoing clause, where the composite has a BET surface area that is at least 10 times greater than the BET surface area of the corresponding neat metal halide salt.

[0202] Clause 68. The ammonia-absorbent composition of any foregoing clause, further including a moisture-barrier coating on the pellets, beads, rods or combinations thereof, the moisture-barrier coating including a polymeric layer configured to reduce adventitious water uptake.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A method for synthesizing absorbent materials for separating ammonia from a reactor effluent stream, comprising:(a) preparing expanded graphite from expandable graphite;(b) heating the expandable graphite;(c) further heating the expanded graphite;(d) cooling the expanded graphite;(e) adding the expanded graphite to a centrifuge tube along with aluminum powder, bentonite, and magnesium chloride to form a mixture;(f) mixing the mixture in the centrifuge tube;(g) adding ethanol to the mixture in the centrifuge tube incrementally;(h) mixing the mixture until a uniform paste is formed;(i) drying the uniform paste;(j) crushing and cutting the dried mixture into large chunks; and(k) sieving away powders from the large chunks prepared for ammonia absorption.

2. The method of Claim 1, wherein the heating of the expandable graphite is performed in an air circulation oven.

3. The method of Claim 2, wherein the air circulation oven is at a temperature of 60°C.

4. The method of Claim 1, wherein the heating of the expandable graphite is performed for 24 hours.

5. The method of Claim 1, wherein the heating of the expanded graphite is performed in a tube furnace.

6. The method of Claim 5, wherein the tube furnace is at a temperature of 650°C.

7. The method of Claim 1, wherein the heating of the expanded graphite is performed at a rate of 20°C / min.

8. The method of Claim 7, wherein the expanded graphite is maintained at a temperature of 650°C for a period of 5 minutes.

9. The method of Claim 1, wherein the mixing of the mixture in the centrifuge tube is performed using a vortex mixer.

10. The method of Claim 9, wherein the vortex mixer is at maximum speed.

11. The method of Claim 9, wherein the mixing of the mixture occurs for 2 minutes.

12. The method of Claim 1, wherein the drying of the uniform paste is performed in a tube furnace.

13. The method of Claim 12, wherein the tube furnace is at a temperature of 350°C.

14. The method of Claim 1, wherein the drying of the uniform paste is performed at a rate of 5°C / min.

15. The method of Claim 14, wherein the uniform paste is maintained at a temperature of 350°C for a period of 1 hour.

16. The method of Claim 1, wherein the large chunks have a dimension of approximately 0.25 inches.

17. The method of Claim 1, wherein the expandable graphite is commercially available.

18. The method of Claim 1, wherein the aluminum powder used has a particle size of 7-15 microns.

19. The method of Claim 18, wherein the aluminum powder is exposed to an argon atmosphere with very low oxygen concentration for 24 hours before mixing.

20. The method of Claim 19, wherein exposing the aluminum powder under these conditions allows for the formation of an aluminum oxide layer over the powder.

21. The method of Claim 1, wherein the bentonite is utilized in its amorphous powder form.

22. The method of Claim 1, wherein magnesium chloride is used in its crystalline form.

23. The method of Claim 1, wherein the mass composition of the mixture in the centrifuge tube is graphite 5%, aluminum 5%, magnesium chloride 40%, and bentonite 50%.

24. The method of Claim 1, further comprising a step of preparing the sample for ammonia absorption testing following the sieving step.

25. A method for synthesizing an ammonia absorbent, comprising the steps of:(a) selecting a metal halide salt;(b) mixing the metal halide salt with a binder to form a mixture;(c) adding a solvent to the mixture to solubilize the metal halide salt, thereby forming a uniform paste, wherein the solvent is selected from the group consisting of water and organic solvents;(d) extruding the uniform paste to form cylindrical rods;(e) drying the cylindrical rods to remove moisture; and(f) cutting the cylindrical rods into pellets.

26. The method of Claim 25, wherein the metal halide salt comprises any metal ionically bonded to any halogen.

27. The method of Claim 25, wherein the binder is selected from the group consisting of Ludox, bentonite, and ceramic binders.

28. The method of Claim 25, wherein the step of drying the cylindrical rods is performed in a tube furnace at one or more drying temperature ranging from 100°C to 500°C.

29. The method of Claim 28, wherein the drying temperature is specifically set to 300°C.

30. The method of Claim 25, further comprising the step of testing the ammonia absorption capacity of the pellets using a volumetric analyzer.

31. The method of Claim 30, wherein the testing step includes pressurizing the pellets with ammonia gas to measure the absorption capacity.

32. The method of Claim 26, wherein the metal halide salt is selected from the group consisting of magnesium chloride, calcium chloride, manganese chloride, nickel chloride, and lithium chloride.

33. The method of Claim 32, wherein the metal halide salt is magnesium chloride.

34. The method of Claim 25, wherein the Ludox binder is utilized at a concentration of 40% suspension of SiCh in water.

35. The method of Claim 25, wherein the solvent includes an organic solvent selected from the group consisting of ethanol, methanol, and acetone.

36. The method of Claim 25, further comprising the step of adding a plasticizer to the mixture before the extrusion step to enhance the flexibility of the cylindrical rods.

37. The method of Claim 36, wherein the plasticizer is polyethylene glycol.

38. The method of Claim 25, wherein the cutting step includes sizing the pellets to have a uniform diameter ranging from 1 mm to 5 mm.

39. The method of Claim 25, further comprising the step of activating the surface of the pellets after cutting to increase the surface area available for ammonia absorption.

40. The method of Claim 39, wherein the activation step involves treating the pellets with a gas phase reactant under elevated temperatures.

41. The method of Claim 40, wherein the gas phase reactant is selected from the group consisting of ammonia, nitrogen, and steam.

42. The method of Claim 25, further comprising the step of packaging the pellets in a moisture-barrier container to preserve their absorption capacity until use.

43. A method for producing ammonia absorbents, comprising:(a) mixing a metal halide with a binder to create a mixture;(b) forming the mixture into a shape, wherein the forming results in a shaped mixture; and(c) drying the shaped mixture.

44. The method of Claim 43, wherein the metal halide includes a halogen selected from the group consisting of chlorine, bromine, iodine, and fluorine.

45. The method of Claim 43, wherein the binder is an inorganic material.

46. The method of Claim 43, wherein the forming step (b) involves extrusion.

47. The method of Claim 43, wherein the drying step (c) is performed at a temperature between 100°C and 300°C.

48. The method of Claim 43, further comprising a step of activating the dried shaped mixture to increase ammonia absorption capacity.

49. The method of Claim 48, wherein activating the dried shaped mixture involves a chemical treatment.

50. The method of Claim 49, wherein the chemical treatment includes exposure to steam.

51. The method of Claim 43, wherein the shapes formed in step (b) are selected from the group consisting of pellets, beads, and rods.

52. The method of Claim 43, wherein the mixture further comprises a solvent to aid in mixing the metal halide with the binder.

53. The method of Claim 52, wherein the solvent is water.

54. The method of Claim 43, further comprising the step of cutting the extruded mixture into predetermined lengths before the drying step.

55. The method of Claim 43, further comprising the step of coating the dried shapes with a protective layer to prevent moisture absorption.

56. The method of Claim 55, wherein the protective layer is a polymer.

57. The method of Claim 43, wherein the metal halide and binder are mixed in a weight ratio ranging from 1 : 1 to 5 : 1.

58. The method of Claim 43, further comprising testing the ammonia absorption capacity of the dried shapes using a volumetric analysis method.

59. An ammonia-absorbent composition comprising:(a) a metal halide salt phase dispersed within a continuous inorganic binder phase to form a porous composite to form a composite, wherein the composite is:(i) configured to reversibly absorb ammonia with a coordination number between 3 and 8 mol NBC per mol of the metal halide at 25 °C and an initial pressure between 40 and 65 psi, and(ii) shaped as pellets, beads, rods, or combinations thereof.

60. The ammonia-absorbent composition of Claim 59, wherein the metal halide salt is selected from the group consisting of magnesium chloride, calcium chloride, manganese chloride, nickel chloride, and lithium chloride.

61. The ammonia-absorbent composition of Claim 59, wherein the inorganic binder comprises colloidal silica, bentonite, a ceramic binder, or any combination thereof.

62. The ammonia-absorbent composition of Claim 59, wherein the composite comprises from 30 wt.% to 70 wt.% of the metal halide salt and from 30 wt.% to 70 wt.% of the inorganic binder.

63. The ammonia-absorbent composition of Claim 59, wherein the composite once has a diameter between 1 mm and 5 mm and a length between 1 mm and 10 mm.

64. The ammonia-absorbent composition of Claim 59, wherein the composite further comprises from 2 wt.% to 10 wt.% expanded graphite and from 2 wt.% to 10 wt.% aluminum powder.

65. The ammonia-absorbent composition of Claim 59, wherein the ammonia absorption capacity is at least 250 mg NBC per gram of the composite.

66. The ammonia-absorbent composition of Claim 59, wherein an average pore diameter is between 10 nm and 30 nm.

67. The ammonia-absorbent composition of Claim 59, wherein the composite has a BET surface area that is at least 10 times greater than the BET surface area of the corresponding neat metal halide salt.

68. The ammonia-absorbent composition of Claim 59, further comprising a moisturebarrier coating on the pellets, beads, rods or combinations thereof, the moisture-barrier coating comprising a polymeric layer configured to reduce adventitious water uptake.

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