WO2017065925A1

WO2017065925A1 - Liquid-phase absorption process for the recovery of ammonia from a mixed gas stream

Info

Publication number: WO2017065925A1
Application number: PCT/US2016/052160
Authority: WO
Inventors: Robert C. Schucker; Istvan Lengyel
Original assignee: Sabic Global Technologies B.V.
Priority date: 2015-10-16
Filing date: 2016-09-16
Publication date: 2017-04-20

Abstract

Methods for separating ammonia (NH₃) from a gaseous mixture that includes hydrogen (H₂), nitrogen (N₂), and NH₃ are described. A method includes contacting the gaseous mixture of H₂, N₂, and NH₃ with an organic solution of Lewis acid to produce a gaseous stream that includes the H₂ and N₂ gas and an organic liquid stream that includes the Lewis acid and a Lewis acid: NH₃ complex. The ammonia can then be separated from the complex.

Description

LIQUID-PHASE ABSORPTION PROCESS FOR THE RECOVERY OF AMMONIA

FROM A MIXED GAS STREAM

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/242,477, filed October 16, 2015, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION A. Field of the Invention

[0002] The invention generally concerns methods for separating ammonia (NH₃) from a gaseous mixture that includes ammonia and one or more additional gaseous compounds. In particular, the method includes contacting the gaseous mixture with an organic liquid composition that includes a Lewis acid to produce a liquid product stream and a gaseous product stream. The liquid product stream can include a Lewis acid-ammonia complex. The ammonia can subsequently be separated from the complex. B. Description of Related Art

[0003] Ammonia synthesis is one of the largest industrially-practiced chemical reactions due to the widespread use of ammonia. For example, ammonia is used in the production of fertilizers, explosives, fibers, plastics and pharmaceuticals, and as a refrigerant in large scale refrigeration plants and in air conditioning systems for buildings of all kinds. Ammonia is also used in the pulp and paper industry, in mining and metallurgy, and as a cleaning agent.

[0004] Commercial production of ammonia involves reacting gaseous nitrogen and gaseous hydrogen at high temperature (400-550 °C) and pressure (150-240 bar, 15 to 24 MPa) as shown in the reaction scheme (1) below:

N₂ + 3H₂ 2NH₃ ΔΗ₂₉₈ = -92.4 KJ/mol (1). From the enthalpy of reaction, it is widely recognized that this reaction requires a substantial amount of input energy to proceed. The most widely used commercial process to make ammonia is the Haber-Bosch process, which uses an iron catalyst to lower the activation energy of the reaction. However, the yield of ammonia in the Haber-Bosch process is limited by the effect of temperature on the reaction equilibrium. Specifically, decreasing the temperature of the reaction causes the equilibrium position to shift toward the formation of ammonia, resulting in a higher yield of ammonia. However, as the rate of reaction at lower temperatures is extremely slow, a higher temperature is required to obtain practical reaction rates, which reduces the amount of the yield of ammonia, i.e., typically to a level of about 10- 20%. In the industrial production of ammonia, the product gas mixture from the reactor is cooled to subzero temperature (-25 °C) to liquefy the ammonia and the remaining mixture of reactant gases is recycled back to the reactor to obtain higher overall yields. Many attempts have been made to remove ammonia gas from such cooled fluids to improve the ammonia process or other processes. By way of example, U.S. Patent No. 8,808,659 to Shiflett et al. describes a process to produce ammonia that includes solubilizing the ammonia in an ionic liquid and then removing the ammonia from the ionic liquid via distillation techniques. This method suffers in that ionic liquids are expensive and are limited by the solubility of the ammonia in the ionic liquid. SUMMARY OF THE INVENTION

[0005] A discovery has been made that solves the problems associated with the production of ammonia. The discovery is premised on the use of an energy efficient liquid phase absorption process, which operates at or near the reactor operating temperature and pressure, thereby, saving considerable energy in the overall ammonia process. Notably, the process involves selectively contacting an ammonia-containing gaseous mixture with an organic liquid composition that includes a Lewis acid to produce a gaseous product stream substantially devoid of ammonia and a liquid product stream that includes the ammonia. Without wishing to be bound by theory, it is believed that the ammonia in the gaseous mixture reacts with the Lewis acid in the liquid and forms a reversible Lewis acid:ammonia (Lewis Acid:NH₃) complex as shown in the reaction scheme (2) below.

Lewis Acid + :NH₃ — Lewis Acid:NH₃ (2).

The liquid product stream that includes the Lewis Acid:NH₃ complex can be subjected to further conditions to separate ammonia from the complex and form a liquid composition containing the Lewis acid and the organic liquid (solvent). The produced liquid composition can be recycled to treat additional ammonia-containing gaseous mixtures. [0006] In one aspect of the invention, a method for separating ammonia from a gaseous mixture that includes ammonia and one or more additional gaseous compounds (e.g., nitrogen (N₂), hydrogen (H₂), or both) is described. The gaseous mixture can be produced from an ammonia reactor, an ammonia synthesis recycle loop, or both. The method can include (a) contacting the gaseous mixture with a liquid composition that includes a Lewis acid compound and an organic solvent to produce: (i) a liquid product stream that includes a Lewis acid-ammonia complex and the organic solvent; and (ii) a gaseous product stream that include the one or more additional gaseous compounds; and (b) separating the ammonia from the complex. Conditions for contacting can include a temperature of 50 °C or more, or 50 °C to 250 °C, preferable 125 °C to 200 °C and a pressure greater than 5 MPa, preferably 8 MPa to 25 MPa, preferably 20 MPa or at or near the pressure of the mixed gaseous feed stream. Contacting in step (a) can include flowing the gaseous feed stream in a direction counter to the direction of the flow of the liquid composition. The gaseous product stream can be substantially free of ammonia (e.g., less than 1 vol.% ammonia, more preferably less than 0.5 vol.% ammonia, and most preferably less than 0.1 vol.% ammonia). The Lewis acid can be an organoborane compound that is at least partially or substantially (e.g., a least 50%) or fully solubilized in the organic solvent. The solvent can be any solvent having an average boiling point of at least 300 °C, or 300 to 800 °C, or 300 to 500 °C. In some embodiments, the solvent is an aromatic compound or a blend of aromatic compounds. In a preferred aspect, the Lewis acid is an organoborane compound having a general structure of RiR₂R₃B, where Ri, R₂, and R₃ can be a substituted or an unsubstituted alkyl group, a substituted or an unsubstituted aromatic group, or any combination thereof. At least one of Ri, R₂, and R₃ is the substituted or an unsubstituted aromatic group having from 6 to 12 carbon atoms. In one aspect, each of Ri, R₂, and R₃ can be a substituted or unsubstituted aromatic group, preferably a substituted phenyl group. The substituted phenyl group can include from 0 to 5 or from 1 to 3 halogen atoms (e.g., fluoride, chloride, bromide, iodide, or any combination thereof. In instances, where the halogen is fluoride, Ri, R₂, and R₃ can be a para-fluorophenyl group, a 3,4-difluorophenyl group, 2,4-difluorophenyl group, a 3,4,5-trifluorophenyl group, 2,3,4,5- fluorophenyl group, a pentafluorophenyl group, and any combination thereof. The ammonia can be separated from the Lewis Acid: H₃ complex by (i) separating the liquid product stream from the gaseous product stream; and (ii) subjecting the liquid product stream to conditions suitable to produce ammonia and an additional liquid product stream that includes the Lewis acid and the organic solvent. Conditions suitable to produce ammonia from the liquid product stream include a temperature range of 150 to 350 °C and a pressure range of 0.01 MPa to 5 MPa. The additional liquid product stream can be recycled and be used in the contacting step (a). Ammonia produced from the liquid product stream can be collected and stored in a storage device.

[0007] In another aspect of the invention, a system for removing H₃ from a gaseous mixture that includes H₃ and one or more additional gases is described. The system can include a separation zone capable of separating H₃ from the gaseous mixture, where the separation zone is capable of producing (i) the gaseous product stream comprising one or more of the additional gaseous compounds and (ii) the liquid product stream comprising the Lewis acid-ammonia complex and the organic solvent; and a decomplexation zone coupled to the separation zone and configured to decomplex the Lewis acid-ammonia complex and supply the additional liquid product comprising the Lewis acid and the organic solvent to the separation zone. The separation zone can be a vertical unit. The separation zone can include a first inlet for the gaseous mixture and a first outlet for the gaseous product stream. The first inlet can be positioned at a lower elevation relative to the first outlet such that the gaseous mixture rises vertically through the liquid composition. The separation zone can also have a second inlet for the liquid composition and a second outlet for the liquid product stream. The second inlet can be positioned at a higher elevation relative to the second outlet such that the liquid composition is flowing countercurrent to the gaseous mixture. The decomplexing zone can have a third inlet for the liquid product stream, a third outlet for the produced ammonia, and a fourth outlet for the additional liquid product stream that includes the Lewis acid and the solvent. The third inlet can be in fluid communication with a storage unit configured to store the produced ammonia. The fourth outlet can be in fluid communication with the separation zone and/or the second inlet such that the additional liquid product stream comprising the Lewis acid and the solvent is recycled to the separation zone. The system can also include an ammonia reactor or an ammonia synthesis recycle loop coupled to the separation zone. The ammonia reactor can have an outlet in fluid communication with the first inlet of the separation zone such that the mixed gaseous mixture is fed to the separation zone. Such method and systems as describe separates ammonia from an ammonia product stream, and provides an overall lower energy and more efficient process than current commercial ammonia processes.

[0008] Also disclosed in the context of the present invention are embodiments 1-31. Embodiment 1 is a method for separating ammonia from a gaseous mixture comprising ammonia and one or more additional gaseous compounds, the method comprising: (a) contacting the gaseous mixture with a liquid composition comprising a Lewis acid compound and an organic solvent to produce: (i) a liquid product stream comprising a Lewis acid- ammonia complex and the organic solvent; and (ii) a gaseous product stream comprising the one or more additional gaseous compounds; and (b) separating the ammonia from the complex. Embodiment 2 is the method of embodiment 1, wherein one or more of the additional gaseous compounds are nitrogen, hydrogen, or both. Embodiment 3 is the method of any one of embodiments 1 to 2, wherein the gaseous product stream is substantially free of ammonia. Embodiment 4 is the method of any one of embodiments 1 to 3, wherein the Lewis acid is at least partially solubilized in the organic solvent. Embodiment 5 is the method of embodiment 4, wherein the Lewis acid is substantially solubilized in the organic solvent. Embodiment 6 is the method of any one of embodiments 1 to 5, wherein the Lewis acid is an organoborane compound. Embodiment 7 is the method of embodiment 6, wherein the organoborane has a general structure of R₁R₂R₃B, where Ri, R₂, and R₃ are individually selected from a substituted or an unsubstituted alkyl group, a substituted or an unsubstituted aromatic group, or any combination thereof. Embodiment 8 is the method of embodiment 7, wherein at least one of Ri, R₂, and R₃ is the substituted or an unsubstituted aromatic group having from 6 to 12 carbon atoms. Embodiment 9 is the method of embodiment 8, wherein Ri, R₂, and R₃ are each individually a substituted or unsubstituted aromatic group, preferably a substituted phenyl group. Embodiment 10 is the method of embodiment 9, wherein at least one substituted phenyl group comprises 1 to 5 halogens, preferably 1 to 3 halogens. Embodiment 11 is the method of embodiment 10, wherein the halogen is fluoride, chloride, bromide, iodide or any combination thereof. Embodiment 12 is the method of embodiment 11, wherein the halogen is fluoride, and R¹, R², and R³ individually are a para-fluorophenyl group, a 3,4-difluorophenyl group, 2,4-difluorophenyl group, a 3,4,5-trifluorophenyl group, 2, 3, 4, 5 -fluorophenyl group, a pentafluorophenyl group, and any combination thereof. Embodiment 13 is the method of any one of embodiments 1 to 12, wherein the solvent has a boiling point of at least 300 to 800 °C, preferably 300 to 500 °C. Embodiment 14 is the method of embodiment 13, wherein the solvent is an aromatic compound or a blend of aromatic compounds. Embodiment 15 is the method of any one of embodiments 1 to 14, wherein the temperature of the liquid composition is greater than 50 °C to 250 °C, preferable 125 °C to 200 °C. Embodiment 16 is the method of any one of embodiments 1 to 16, wherein separating the ammonia from the complex comprises: (i) separating the liquid product stream from the gaseous product stream; (ii) subjecting the liquid product stream to conditions suitable to produce ammonia and an additional liquid product stream comprising the Lewis acid and the organic solvent. Embodiment 17 is the method of embodiment 16, wherein subjecting the liquid product stream comprises a temperature ranging from 150 to 350 °C and a pressure ranging from 0.01 to 5 MPa. Embodiment 18 is the method of any one of embodiments 16 to 17, wherein the additional liquid stream is combined with the liquid composition in contacting step (a). Embodiment 19 is the method of any one of embodiments 1 to 18, wherein the mixed gaseous feed stream is produced from an ammonia reactor, an ammonia synthesis recycle loop, or both. Embodiment 20 is the method of any one of embodiments 1 to 19, wherein contacting is performed at a pressure greater than 5 MPa, preferably 8 MPa to 25 MPa, preferably 20 MPa, or at, or near, the pressure of the gaseous mixture. Embodiment 21 is the method of any one of embodiments 1 to 20, wherein contacting comprises: flowing the gaseous feed stream in a direction counter to the direction of the flow of the liquid composition. Embodiment 22 is the method of any one of embodiments 1 to 21, wherein the produced ammonia from the liquid product stream is stored in a storage device.

[0009] Embodiment 23 is a system for separating ammonia from a mixed gaseous mixture comprising ammonia and one or more additional gaseous compounds using the methods of embodiments 1 to 22, the system comprising: a) a separation zone capable of separating the ammonia from the mixed gaseous mixture, wherein the separation zone is capable of producing (i) the gaseous product stream comprising one or more of the additional gaseous compounds and (ii) the liquid product stream comprising the Lewis acid-ammonia complex and the organic solvent; and b) a decomplexation zone coupled to the separation zone and configured to decomplex the Lewis acid-ammonia complex and supply the additional liquid product comprising the Lewis acid and the organic solvent to the separation zone. Embodiment 24 is the system of embodiment 23, wherein the separation zone is a vertical unit. Embodiment 25 is the system of any one of embodiments 23 to 24, wherein the separation zone comprises a first inlet for the gaseous mixture and a first outlet for the gaseous product stream, wherein the first inlet is positioned at a lower elevation relative to the first outlet such that the gaseous mixture rises vertically through the liquid composition. Embodiment 26 is the system of embodiment 25, further comprising a second inlet for the liquid composition and a second outlet for the liquid product stream. Embodiment 27 is the system of embodiment 26, wherein the second inlet is positioned at a higher elevation relative to the second outlet such that the liquid composition is capable of flowing countercurrent to the gaseous mixture. Embodiment 28 is the system of any one of embodiments 23 to 27, wherein the decomplexation zone comprises a third inlet for the liquid product stream, a third outlet for the produced ammonia, and a fourth outlet for the additional liquid product stream comprising the Lewis acid and the solvent. Embodiment 29 is the system of embodiment 28, wherein the fourth outlet is in fluid communication with the separation zone and/or the second inlet such that the additional liquid product stream comprising the Lewis acid and the solvent is recycled to the separation zone. Embodiment 30 is the system of any one of embodiments 23 to 29, further comprising an ammonia reactor or an ammonia synthesis recycle loop coupled to the separation zone, wherein the ammonia reactor has an outlet in fluid communication with the first inlet of the separation zone such that the mixed gaseous mixture is fed to the separation zone. Embodiment 31 is the system of any one of embodiments 23 to 30, further comprising a storage unit coupled to the decomplexation zone and configured to store the produced ammonia.

[0010] The following includes definitions of various terms and phrases used throughout this specification.

[0011] The term a "complexing" refers to forming coordinate bonds (e.g., dipolar bonds) between a Lewis acid and ammonia.

[0012] The term "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0013] The term "substantially" and its variations are defined as including ranges within 10%, within 5%, within 1%, or within 0.5%.

[0014] The terms "inhibiting" or "reducing" or "preventing" or "avoiding" or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.

[0015] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result. [0016] The use of the words "a" or "an" when used in conjunction with any of the terms "comprising," "including," "containing," or "having," in the claims 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." [0017] The terms "wt.%", "vol.%", or "mol.%" refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0018] 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.

[0019] The methods and systems of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase "consisting essentially of," in one non-limiting aspect, a basic and novel characteristic of the methods and systems of the present invention is the ability to separate ammonia from a gaseous mixture that includes one or more additional gases. [0020] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings. [0022] FIG. 1 is a schematic of system of an embodiment for separating ammonia and from a gaseous mixture.

[0023] FIG. 2 is a schematic of an embodiment of a system for separating ammonia from a gaseous mixture in combination with a decomplexing unit.

[0024] FIG. 3 is a schematic of an embodiment for separating ammonia that includes the system of the present invention in combination with an ammonia generation unit.

[0025] FIG. 4 are graphs of equilibrium constants versus temperature for Lewis acid: H₃ complexes structures (II) through (VIII) of the present invention.

[0026] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0027] A discovery has been made that address the low yields and energy requirements in current commercial ammonia production processes. The discovery is premised on the ability to separate ammonia from a gaseous mixture at elevated temperature and reactor pressure thereby, saving considerable energy and increasing the overall yield by shifting the equilibrium constant towards the production of ammonia. This can be done by complexing the ammonia with a liquid composition comprising a Lewis acid compound and an organic solvent. The ammonia can then be released from the Lewis acid under mild conditions.

A. Process to Separate Ammonia from a Gaseous Mixture [0028] Systems and methods to separate ammonia from a gaseous mixture are described. The gaseous mixture can be contacted with a Lewis Acid at elevated temperature and reactor pressure such that all or, substantially all, of the ammonia is removed from the gaseous mixture to produce a gaseous product stream essentially devoid of ammonia. The resulting gaseous product stream can include hydrogen, nitrogen, or both. The gaseous product stream can be collected stored, transported, recycled to the ammonia process, or further processed using the methods described throughout the specification. The resulting liquid product stream can be further processed to release the ammonia from the Lewis acid: H₃ complex. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the figures.

1. Separation of Ammonia From Ammonia-Containing Gaseous Mixture

[0029] Systems and methods to separate ammonia from a gaseous mixture are described herein. FIG. 1 is a schematic of a system 100 used to carry out the method of separating ammonia from a gaseous mixture that includes ammonia and other gases. System 100 can include a separation unit 102. The separation unit 102 can be a gas-liquid contacting apparatus (e.g., a bubble column contactor). The materials of construction, size and shape of separation unit 102 can be determined using standard engineering practice and modeling programs to achieve the maximum flow rates and contact time. The separation unit 102 includes a gaseous mixture inlet 104 (first inlet), a gaseous product stream outlet 106 (first outlet), a liquid composition inlet 108 (second inlet), and a liquid product stream outlet 1 10 (second outlet). In this configuration, the gaseous mixture inlet 104 is preferably at a lower elevation than the gaseous product stream outlet 106 to allow the gaseous mixture 1 12 to flow in an upwardly direction through the organic liquid composition 1 14 to maximize contact time between the gaseous mixture 1 12 and the organic liquid composition 1 14. The organic liquid composition 1 14 includes the free Lewis acid that is at least partially or fully dissolved in the organic solvent. In preferred aspects, the Lewis acid present in the organic solvent in an amount up to its solubility limit in the organic solvent. In a preferred aspect, the liquid composition inlet 108 is at a higher elevation than the liquid product stream outlet 1 10. During separation, the liquid composition 1 14 is charged via the second inlet 108 and the liquid product stream 1 16 is removed via the second outlet 1 10 at a rate sufficient to replenish the concentration of Lewis acid and remove the Lewis acid: H₃ complex from the separation unit 102. Movement of the liquid composition 1 14 and the liquid product stream 1 16 can be accomplished using known mechanical apparatus (e.g., pumps, valves, or the like that are not shown). The liquid composition 1 14, which is described throughout the specification, can be charged to, or circulated through, the separation unit 102 prior to introduction of gaseous mixture 1 12. The gaseous mixture 1 12 can be introduced at the bottom of the separation unit 102 through the gaseous inlet 104. Although, the process is described such that the gaseous mixture is introduced into the liquid composition, it should be understood that the liquid composition can be introduced into the gaseous mixture or both mixtures can be introduced into the separation unit at the same time. The gaseous mixture can be slightly below or near the pressure of a mixed gaseous stream as it exits from an ammonia producing unit (e.g., gaseous mixture inlet 104 is in fluid communication with a gas outlet of the ammonia producing unit, See, for example FIG. 3). In some embodiments, the gaseous mixture is received directly from other ammonia producing processes. The gaseous mixture inlet 104 or the separation unit 102 can include a diffuser, sparger, a drilled pipe, or other equipment capable of introducing the gaseous mixture into the liquid composition as small bubbles. By way of example, bubble size can vary depending on the pore size of the sparger plate. In some aspects, the bubble size can range from 1 to 10 nm. Introduction of the gaseous mixture 112 into liquid composition 114 can be at a rate sufficient to mix the gaseous mixture with the liquid composition with high agitation (e.g. turbulently). As the gaseous mixture flows upwardly in the separation unit, it contacts the solubilized or partially solubilized Lewis acid in the liquid composition, which is flowing in a countercurrent direction (e.g. downwardly). Contact of the Lewis acid and the diffused gaseous mixture can allow the ammonia molecules to be complexed or adsorbed by the Lewis acid, which results in the gaseous product stream 118 and the liquid product stream 116. The gaseous product stream 120, which can have less ammonia when compared with the gaseous mixture entering the inlet 104, can exit the top of the separation unit 102 via the gaseous product outlet 106 and be recycled back to an ammonia processing unit (See, for example, FIG. 3), collected (e.g., cooled), stored in a storage unit, used to produce energy, be used as a feedstock, or recycled back through the gaseous mixture inlet 104 to remove any remaining ammonia present in the gaseous mixture. The liquid product stream 116 can be transported to a storage unit, a decomplexation unit or both. The liquid product stream 116 can include the Lewis acidi FL complex, free Lewis acid, and/or an organic solvent. If the liquid product stream has sufficient Lewis acid it can be recycled back to the separation unit 102 without treatment to remove the ammonia from the complex. By way of example, during start-up of the separation unit 102 or during the initial contact of the gaseous mixture with the liquid composition, the liquid product stream can have minimal to no Lewis acidi FL complex, and, thus be circulated on a continuous basis through the separation unit 102. [0030] The processing conditions in the separation unit (reaction chamber) 102 can be varied to achieve a desired result (e.g., removal of substantially all of the ammonia from the gaseous stream). The processing conditions include temperature, pressure, gaseous mixture flow, liquid composition flow and/or charge, gaseous product flow, liquid product flow, or any combination thereof. Processing conditions are controlled, in some instances, to produce streams with specific properties. The separation unit 102 can be operated at temperatures and pressures near or slightly below the temperature of a gaseous feed stream (e.g., temperature and pressure of a product stream from an ammonia processing unit). The separation unit 102 also includes valves, thermocouples, controllers (automated or manual controllers), computers or any other equipment deemed necessary to control or operate the separation unit. A temperature of the separation unit can be 505 °C or more to 250 °C, preferable 125 °C to 200 °C, or 50 °C, 75 °C, 100 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C, 250 °C, or any value or range there between. A pressure of the separation can be greater than 5 MPa, or 8 MPa to 25 MPa, or 20 MPa, or 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 1 1 MPa, 12 MPA, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa, 25 MPa or any value there between. The flow of the gaseous mixture and the liquid composition into the separation chamber can be adjusted and controlled to maintain optimum contact of the gaseous mixture with the liquid composition. In some embodiments, computer simulations can be used to determine flow rates for vessels of various dimensions.

2. Separation of Ammonia From A Lewis Acid:NH₃ Complex

[0031] Referring to FIG. 2, system 200 includes the separation unit 102 in combination with a decomplexing unit 202. The decomplexation unit 202 can be used to decomplex (e.g., release) the ammonia from the Lewis acid. The liquid product stream 1 16 can exit the separation unit and can enter the decomplexation unit 202 via a decomplexation unit inlet 204, while the liquid composition stream 1 14 containing the Lewis acid is being introduced into the separation unit 102 via a liquid composition inlet 108. In the decomplexation unit 202, the ammonia is released and free Lewis Acid is produced. The pressure of the decomplexation unit 202 is maintained at a lower pressure and temperature than the separation unit 102, to allow l¾ to be released from the Lewis acid: l¾ complex. A temperature of the decomplexing unit 202 can be 150 °C to 350 °C, or 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C, 250 °C, 255 °C, 260 °C, 265 °C, 270 °C, 275 °C, 280 °C, 295 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C or any value or range there between at. A pressure of the decomplexing unit 202 can be 0.01 MPa to 5 MPa, or 0.1 MPa to 3 MPa, or 2 MPa, or 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPA, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa or any value there between. The free ammonia exits the decomplexation vessel 202 via an ammonia outlet 206 and can be sent to other units for condensation and recovery. As shown, the decomplexation unit 202 is vessel that includes a sprayer 208. The liquid product stream can injected (e.g., sprayed) into the decomplexation vessel 202 to promote separation of the ammonia from the Lewis acid: H₃ complex. The liquid Lewis acid composition (additional product stream) 1 14' or a portion thereof can be exit the decomplexation unit 202 via a decomplexation outlet 210 and be supplied to the separation unit 102 via the inlet 108 to continue the process and/or a storage unit reservoir (not shown). In a storage reservoir, the liquid Lewis Acid composition 1 14' can be stored or mixed with liquid composition 1 14 and then supplied to the separation unit 102 via the second inlet 108.

3. Process to Ammonia Generation in Combination with Ammonia Separation

[0032] Referring to FIG. 3, the separation systems described in FIGS. 1 and 2 can be combined with an ammonia processing unit. Such a combination can produce ammonia at higher yields and uses less energy than conventional ammonia producing processes. Referring to FIG. 3, the system 300 includes an ammonia unit 302, the separation unit 102 and the decomplexing unit 202. In FIG. 3, a feed stream 304 containing a mixture of nitrogen and hydrogen gases can enter the ammonia unit 302 via an ammonia unit inlet 306. The ammonia unit 302 can contain a suitable catalyst for ammonia product (e.g., an iron catalyst). A mole ratio of the hydrogen gas and nitrogen gas in the feed stream can be about 3 : 1. The ammonia unit 302 can be operated at a temperature and pressure sufficient to produce ammonia (for example, a temperature of about 300 °C to about 550 °C, and at a pressure of about 8 MPa to about 40 MPa). The ammonia unit 302 may be any suitable gas reactor known in the art that is able to withstand the temperature and pressure ranges used in the reaction. The equilibrium conversion to ammonia in the ammonia can be in the range of about 10-20%, and the mixed gaseous stream can exit the ammonia unit 302 via an ammonia outlet 308. The produced gaseous mixture 1 12 can include large amounts of unreacted hydrogen and nitrogen along with the ammonia. The gaseous mixture can enter the separation zone 102 via the inlet 104 and be processed as previously described in FIGS. 1 and 2. The gaseous product stream 1 18 can exit the separation unit 102 and be recycled to the ammonia unit 302 and/or be combined with feed stream 304. While the units in FIGS. 1-3 are shown as standalone units, it should be understood that the units can be portions or zones in a chemical unit, be housed in the same unit and/or structure.

[0033] The ammonia produced may be used in the production of fertilizers, explosives, fibers, plastics and pharmaceuticals, and as a refrigerant in large scale refrigeration plants and in air conditioning systems for buildings of all kinds. The ammonia may also be used in the pulp and paper industry, in mining and metallurgy, and as a cleaning agent.

B. Gaseous Mixture and Gaseous Product Stream

1. Gaseous Mixture

[0034] The gaseous mixture can include a mixture of hydrogen, nitrogen and ammonia. In some instances, one or more inert gases (e.g., helium or argon) may be included in the gaseous stream. The gaseous mixture can be obtained from any application that produces ammonia, for example, the reaction product stream of ammonia reaction or from any waste stream containing ammonia. The amount of ammonia in the stream can be about 1 vol.% to 20 vol.%. Continuous removal of smaller amounts of ammonia may allow the ammonia reactor to operate at a substantially lower temperature.

2. Gaseous Product Stream

[0035] The gaseous product stream can include hydrogen and nitrogen. The gaseous product stream can include substantially no ammonia or 0.1 vol.% or less, 0.015 vol.% or less, or 0.01 vol.% or less. In some embodiments, the gaseous mixture is essentially pure hydrogen and nitrogen.

C. Liquid Composition

1. Solvent [0036] The liquid composition can include a Lewis acid and an organic solvent. The solvent can be any solvent that has an average boiling point of at least 300 °C, preferably at least 300 °C, or more preferably 300 °C to 800 °C, 325 °C to 600 °C, 350 °C to 500 °C or 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, 510 °C or more, or any range or value there between and be of sufficient polarity to solubilize the Lewis acid. In some embodiments, the solvent is an aromatic solvent or a blend of aromatic compounds. A non-limiting example of suitable solvents are light catalytic cracking cycle oil (LCO or LCCO) or heavy catalytic cracking cycle oil (HCO or HCCO) both of which boil above 350 °C.

2. Lewis Acid

[0037] The Lewis acid can be any Lewis acid that is capable of undergoing a reversible reaction with ammonia and is soluble or partially soluble in an organic solvent. Non-limiting examples of such Lewis acids include organoborane compounds. The organoborane compound can have a general structure of:

R 1

(I) where Ri, R₂, and R₃ can be a substituted or an unsubstituted alkyl group, a substituted or an unsubstituted aromatic group, or any combination thereof.

[0038] In some embodiments, Ri, R₂, and R₃ is a substituted or an unsubstituted aromatic group having from 6 to 12 carbon atoms. In one aspect, each of Ri, R₂, and R₃ can be a substituted or unsubstituted aromatic group, preferably a substituted phenyl group. The substituted phenyl group can include one or more alkyl, aromatic, or aliphatic groups, substituted alkyl aromatic, or aliphatic groups, halogens or the like. The melting points and boiling points of these Lewis acid compounds can be increased by changing the nature of the aromatic components (i.e., from phenyl groups to biphenyl, triphenyl or other higher molecular weight aromatic species). The substituted phenyl group can include from 0 to 5 or from 1 to 3 halogen atoms (e.g., fluoride, chloride, bromide, iodide, or any combination thereof). In instances, where the halogen is fluoride, R¹, R², and R³ can be a para- fluorophenyl group, a 3,4-difluorophenyl group, 2,4-difluorophenyl group, a 3,4,5-fluorophenyl group, 2, 3, 4, 5 -fluorophenyl group, a pentafluorophenyl group or any combination thereof. Representative structures of trisphenylborane and substituted trisphenyl borane compounds are shown below. Fluorophenyl borane compounds are available for commercial vendors such as Sigma-Aldrich®, USA.

where X in structures (II) through (VII) is a fluoride, chloride, bromide, iodide atom, or combinations thereof. In a particular instance, X is fluoride and the halogenated compounds are:

(II) (III) (IV) (V) , or any combination thereof.

[0039] While not wishing to be bound by theory, it is believed that Lewis acids (electron acceptors) can react with Lewis bases (electron donors) to form complexes. A non-limiting example of this reaction is the reaction between boron trifluoride and a generic amine as shown in reaction equation (3):

F₃B + : R₃ ¾ I· ;B:\ R ; (3).

The ammonia lone pair of electrons is donated to the Lewis acid to form a reversible complex rather than an irreversible covalent compound (as with Bransted acids and bases). Bransted acids (proton donors) react with Bransted bases (proton acceptors) to form salts in what is known as neutralization. This process is irreversible and an example of this reaction is shown in reaction equation (4).

HC1 + NaOH→ NaCl + H₂0 (4).

This Lewis acid mechanism can be used to selectively recover ammonia from mixed gas streams using a boron-based Lewis acid as shown in reaction equation (5) using triphenylborane as an exemplary Lewis acid.

Ph₃B + : H₃ → Ph₃B : H₃ (5).

Because this is a reversible reaction, recovery of the ammonia can be performed when the equilibrium constant is around 1.0, where the equilibrium constant (K_e) is defined in equation (6) as:

K_e = [Ph₃B: H₃]/[Ph₃B][ H₃] (6). In some embodiments, the equilibrium constant can be tailored to a given temperature by the addition of electron withdrawing groups (e.g., halogen) to the phenyl rings as shown in structures (II) through (VII).

EXAMPLES

[0040] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

(Computational Modeling)

[0041] Equilibrium constants of fluoride substituted trisphenylboranes were determined using computational program Gaussian-09, method G3MP3B3 level (Gaussian, Inc. USA). FIG. 4 shows graphs of equilibrium constant versus temperature for fluorinated-Ph₃B: H₃, and Ph₃B: H₃ complexes of structures (II) through (VIII). From the calculations, it was determined that Lewis acid complexes of fluorinated compounds (II), (III), (V), and Ph₃B: H₃ (VIII) had equilibrium constants of 1 between the temperatures of 150 to 300 °C, and, thus it is believed that these compounds would absorb and release ammonia at these temperatures.

Claims

1. A method for separating ammonia from a gaseous mixture comprising ammonia and one or more additional gaseous compounds, the method comprising:

(a) contacting the gaseous mixture with a liquid composition comprising a Lewis acid compound and an organic solvent to produce:

(i) a liquid product stream comprising a Lewis acid-ammonia complex and the organic solvent; and

(ii) a gaseous product stream comprising the one or more additional gaseous compounds; and

(b) separating the ammonia from the complex.

2. The method of claim 1, wherein one or more of the additional gaseous compounds are nitrogen, hydrogen, or both.

3. The method of claim 1, wherein the gaseous product stream is substantially free of ammonia.

4. The method of claim 1, wherein the Lewis acid is at least partially solubilized in the organic solvent.

5. The method of claim 4, wherein the Lewis acid is substantially solubilized in the organic solvent.

6. The method of claim 1, wherein the Lewis acid is an organoborane compound.

7. The method of claim 6, wherein the organoborane has a general structure of R₁R₂R₃B, where Ri, R₂, and R₃ are individually selected from a substituted or an unsubstituted alkyl group, a substituted or an unsubstituted aromatic group, or any combination thereof.

8. The method of claim 7, wherein at least one of Ri, R₂, and R₃ is the substituted or an unsubstituted aromatic group having from 6 to 12 carbon atoms.

9. The method of claim 8, wherein Ri, R₂, and R₃ are each individually a substituted or unsubstituted aromatic group, preferably a substituted phenyl group.

10. The method of claim 9, wherein at least one substituted phenyl group comprises 1 to 5 halogens, preferably 1 to 3 halogens.

11. The method of claim 10, wherein the halogen is fluoride, chloride, bromide, iodide or any combination thereof.

12. The method of claim 11, wherein the halogen is fluoride, and R¹, R², and R³ individually are a para-fluorophenyl group, a 3,4-difluorophenyl group, 2,4- difluorophenyl group, a 3,4,5-trifluorophenyl group, 2, 3, 4, 5 -fluorophenyl group, a pentafluorophenyl group, and any combination thereof.

13. The method of claim 1, wherein the solvent has a boiling point of at least 350 °C, preferably at least 400 °C.

14. The method of claim 1, wherein the temperature of the liquid composition is greater than 125 °C to 250 °C, preferable 125 °C to 200 °C.

15. The method of claim 1, wherein separating the ammonia from the complex comprises:

(i) separating the liquid product stream from the gaseous product stream;

(ii) subjecting the liquid product stream to conditions suitable to produce ammonia and an additional liquid product stream comprising the Lewis acid and the organic solvent.

16. The method of claim 15, wherein subjecting the liquid product stream comprises a temperature ranging from 150 to 350 °C and a pressure ranging from 0.01 to 5 MPa.

17. The method of claim 15, wherein the additional liquid stream is combined with the liquid composition in contacting step (a).

18. The method of claim 1, wherein the mixed gaseous feed stream is produced from an ammonia reactor, an ammonia synthesis recycle loop, or both.

19. The method of claim 1, wherein contacting is performed at a pressure greater than 5 MPa, preferably 8 MPa to 25 MPa, preferably 20 MPa, or at, or near, the pressure of the gaseous mixture. A system for separating ammonia from a mixed gaseous mixture comprising ammonia and one or more additional gaseous compounds using the method of claim 1, the system comprising: a) a separation zone capable of separating the ammonia from the mixed gaseous mixture, wherein the separation zone is capable of producing (i) the gaseous product stream comprising one or more of the additional gaseous compounds and (ii) the liquid product stream comprising the Lewis acid-ammonia complex and the organic solvent; and b) a decomplexation zone coupled to the separation zone and configured to decomplex the Lewis acid-ammonia complex and supply the additional liquid product comprising the Lewis acid and the organic solvent to the separation zone.