CONVERSION

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is related to U.S. Provisional Patent Application No. 62/716,705, filed August 9, 2018, and U.S. Provisional Patent Application No. 62/734,387, filed September 21, 2018, where the entire contents of both applications are incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to systems and methods for converting hydrogen sulfide (H2S) in a gas stream to hydrogen (H2) and sulfur. More particularly, the present disclosure relates to bimetallic alloys usable in systems and methods for generating hydrogen (H2) and sulfur streams from hydrogen sulfide (H2S) streams.

BACKGROUND

[0003] Natural gas, petroleum and coal are primarily utilized as energy sources.

However, sulfur compounds such as hydrogen sulfide (H2S) within these fuels limit their use due to the toxic and corrosive nature of such compounds. For example, exposure to H2S can be harmful for humans even at concentrations as low as lOppm. In addition, the applicability of these fuels as a feedstock for value-added chemicals is also limited due to catalyst deactivation as a result of sulfur poisoning.

[0004] Currently used processes for removing hydrogen sulfide (H2S) are intensive and demand high energy. Additionally, currently used processes cannot recover H2 along with sulfur because H2 is lost in the form of water vapor. Furthermore, the performance of solids used in hydrogen sulfide (H2S) processing can deteriorate after a single cycle. Such systems are inefficient and can require replenishing the solids after one or just a few cycles of sulfur capture and regeneration. Therefore, there is a need for an improved process to effectively convert hydrogen sulfide (H2S) into hydrogen (H2) and sulfur.

SUMMARY

[0005] Disclosed herein are systems and methods for converting hydrogen sulfide (H2S) in a gas stream to hydrogen (H2) and sulfur. In one aspect, a method utilizes metal alloy composite particles for converting hydrogen sulfide (H2S) in a gas stream to hydrogen (H2) and sulfur. The method is a two-step thermochemical decomposition of H ₂ S into H ₂ and sulfur. The first step is referred to as the sulfidation operation, wherein H ₂ S reacts with the metal alloy composite particle to form a mixture of metal sulfides and produce H2. The second step is referred to as the regeneration operation, wherein the mixture of metal sulfides is subjected to a high temperature and gas input stream to remove the captured sulfur and regenerate the metal alloy composite particle. Thereby, separate H ₂ and sulfur streams are produced from an input stream including H ₂ S. Compared to the conventionally used Claus process for sulfur recovery, which only produces sulfur and no H ₂ , the disclosed method is economically favorable. It is also beneficial to the environment as it converts a toxic, poisonous, and corrosive H ₂ S gas to valuable chemicals H ₂ and sulfur.

[0006] There is no specific requirement that a material, technique or method relating to H ₂ S conversion include all of the details characterized herein, in order to obtain some benefit according to the present disclosure. Thus, the specific examples characterized herein are meant to be exemplary applications of the techniques described, and alternatives are possible. Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 shows a schematic diagram of an exemplary system for H ₂ S conversion to H ₂ and S.

[0008] FIG. 2 shows a schematic diagram of another exemplary system for H ₂ S conversion to H ₂ and S.

[0009] FIG. 3 shows a schematic diagram of another exemplary system for H ₂ S conversion to H2 and S.

[0010] FIG. 4 shows an example method for H ₂ S conversion to H ₂ and S.

[0011] FIG. 5 shows an example method for preparing a metal alloy composite particle for use in H ₂ S conversion to H ₂ and S.

[0012] FIG. 6 shows the X-ray diffraction analysis of the iron-chromium metal alloy composite particle obtained after preparation in a fixed bed reactor.

[0013] FIG. 7 shows H ₂ S conversion for an iron-chromium alloy composite particle over five sulfidation-regeneration operations where the gas hourly space velocity for first two sulfidation operations was 5000 hr ¹ and for the last three was 2580 hr ¹ .

[0014] FIG. 8 shows X-ray diffraction analysis of solids in a fixed bed reactor after five sulfidation- regeneration operations.

[0015] FIG. 9 shows the X-ray diffraction analysis of solids after run 1 in a fixed bed reactor. [0016] FIG. 10 shows the X-ray diffraction analysis of solids after run 2 in the fixed bed reactor used to obtain data shown in FIG. 9.

[0017] FIG. 11 shows calculated thermodynamic values of FES fractional conversion as a function of iron monosulfide: chromium monosulfide molar ratio.

[0018] FIG. 12 shows calculated thermodynamic values for molar composition of iron monosulfide, chromium monosulfide and iron-chromium thiospinel as a function of iron monosulfide: chromium monosulfide molar ratio.

[0019] FIG. 13 shows the X-ray diffraction analysis of Fe-Cr alloy with M0S2 secondary material after reaction with 0.9% FES at 800 °C.

[0020] FIG. 14 shows the X-ray diffraction analysis of Fe-Cr alloy with M0S2 secondary material and S1O2 support material after reaction with 0.9% FhS at 800 °C.

[0021] FIG. 15 shows FES conversion over 12 consecutive sulfidation-regeneration cycles with Fe-Cr alloy containing 20 wt% M0S2.

[0022] FIG. 16 shows FES conversion as a function of pressure at 400°C as obtained by using FactSage 7.3 software.

DETAILED DESCRIPTION

I. Definitions

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Example methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0024] The terms“comprise(s),”“include(s),”“having,”“has, ”“can,”“contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,”“an” and“the” include plural references unless the context clearly dictates otherwise.

The present disclosure also contemplates other embodiments“comprising,”“consisting of’ and“consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.

[0025] The modifier“about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). The modifier“about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression“from about 2 to about 4” also discloses the range “from 2 to 4.” The term“about” may refer to plus or minus 10% of the indicated number. For example,“about 10%” may indicate a range of 9% to 11%, and“about 1” may mean from 0.9-1.1. Other meanings of“about” may be apparent from the context, such as rounding off, so, for example“about 1” may also mean from 0.5 to 1.4.

[0026] Definitions of specific functional groups and chemical terms are described in more detail below. For purposes of this disclosure, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75 ^th Ed., inside cover, and specific functional groups are generally defined as described therein.

[0027] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated. For example, when a pressure range is described as being between ambient pressure and another pressure, a pressure that is ambient pressure is expressly contemplated.

II. Metal Alloy Composite Particles

[0028] Disclosed herein are metal alloy composite particles for use in systems and methods for converting H2S into hydrogen (H2) and sulfur (S). Typical metal alloy composite particles disclosed and contemplated herein include metal alloy material, secondary material, and support material. Without being bound by a particular theory, it is believed that each component plays a role in H2S processing. For instance, the metal alloy material captures sulfur generated from dissociation of H2S. Additionally, efficient capture of sulfur appears to be linked to the formation of spinel phase, which thermodynamically favors near, or complete, sulfur capture. The secondary material forms active centers on the surface of the metal alloy composite particle where it catalytically dissociates H2S to H2 and sulfur. The metal alloy material is dispersed in the support material to prevent sintering and

agglomeration of the metal alloy composite particle, which could reduce the regenerability of the particle.

A. Metal Alloy Material

[0029] Metal alloy material comprises a first metal component and a second metal component. The first metal component comprises a first metal, a first metal sulfide comprising the first metal, a first metal oxide comprising the first metal, or combinations thereof. The second metal component comprises a second metal, a second metal sulfide comprising the second metal, a second metal oxide comprising the second metal, or combinations thereof.

[0030] Usually, each of the first metal and second metal is selected from: iron (Fe), chromium (Cr), nickel (Ni), Zinc (Zn), cobalt (Co), manganese (Mn) and copper (Cu). For example, the first metal component may comprise iron and the second metal component may comprise chromium. In some embodiments, the first metal component comprises iron sulfide and the second metal component comprises chromium sulfide.

[0031] The metals of the metal alloy material may be dispersed uniformly as this results in high conversion of FES to Fh and also improves the regenerability of the metal alloy composite particle. Non-uniform dispersion and/or a layered structure may result in diffusion limitations of FES in the metal alloy composite particle product layer and lower the reaction kinetics.

B. Secondary material

[0032] The metal alloy composite particle may further comprise one or more secondary material components. In some instances, secondary material is a dopant, as that term is typically understood in the art. In some instances, secondary material has similar properties to a dopant and/or imparts similar characteristics as a dopant, but exists as a different phase. In various implementations, the secondary material is dispersed uniformly along the surface of the particle and is surrounded by the alloy material.

[0033] Typically, secondary material is in the form of MS _* , where M is a metal, S is sulfur, and x is in the range of values between 0 and 2. For example, x maybe 0, 1, or 2. X may also be a non-integer value. For example, x may be 0.5 or 1.5. Example metals M include, but are not limited to, molybdenum, nickel, cobalt, manganese, tungsten, vanadium and combinations thereof.

[0034] The secondary material may be a sulfide. For example, the secondary material may be a molybdenum disulfide, a nickel sulfide, a cobalt sulfide, a manganese sulfide, a tungsten sulfide, vanadium sulfide or combinations thereof.

[0035] In some instances, secondary material is a metal oxide. For example, the secondary material may be a molybdenum oxide, a nickel oxide, a cobalt oxide, a manganese oxide, a tungsten oxide, a vanadium oxide or combinations thereof.

C. Support Material [0036] The metal alloy composite particle may further comprise one or more support materials. The support material can be any inert material. The one or more support materials can be metals, metal oxides, non-metal oxides, zeolites or metal organic frameworks.

Suitable support materials include, but are not limited to, alumina, bauxite, titania, silicon, zirconium, and alumina silicate. For example, the support material may be an aluminum oxide, a silicon oxide, a titanium oxide, a zirconium oxide, and the like.

D. Example Amounts and Sizes

[0037] The metal alloy composite particle may comprise any suitable ratio of components to produce the desired effect. For example, the metal alloy composite particle may comprise 10-95% by weight of the first metal component, 5-80% by weight of the second metal component, and 0-50% by weight of the secondary material. For example, the metal alloy composite particle may comprise 10-95% by weight iron, 5-80% by weight chromium, and 0- 50% by weight of the secondary material.

[0038] For example, the metal alloy composite particle may comprise about 10%, about 15%, about 20%, about 25%, about 30%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, or about 95% by weight of the first metal component. In various implementations, the metal alloy composite particle comprises 10 wt% to 50 wt%; 40 wt% to 95 wt%; 20 wt% to 75 wt%; 30 wt% to 50 wt%; 35 wt% to 65 wt%; 50 wt% to 80 wt%; or 40 wt% to 70 wt% of the first metal component.

[0039] The metal alloy composite particle may comprise about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, or about 80% by weight of the second metal component. In various implementations, the metal alloy composite particle comprises 5 wt% to 50 wt%; 45 wt% to 80 wt%; 15 wt% to 65 wt%; 10 wt% to 35 wt%; 35 wt% to 60 wt%; 60 wt% to 80 wt%; or 20 wt% to 45 wt% of the second metal component.

[0040] The metal alloy composite particle may comprise about 0%, about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 40%, about 45%, or about 50% by weight of the secondary material. In various implementations, the metal alloy composite particle comprises 5 wt% to 45 wt%; 10 wt% to 50 wt%; 20 wt% to 40 wt%; 30 wt% to 50 wt%; 10 wt% to 20 wt%; 15 wt% to 35 wt%; or 20 wt% to 30 wt% of the secondary material.

[0041] The metal alloy composite particle has a diameter of between about lOOpm and about lOmm. For example, the metal alloy composite particle may have a diameter of about IOOmih to about lOmm, about lmm to about 9mm, about 2mm to about 8mm, about 3mm to about 7mm, or about 4mm to about 6mm.

[0042] The grain size of the first metal component, the second metal component, and the secondary material can vary depending on the type of material used and the temperature at which the metal alloy composite particle is sintered. A smaller grain size is preferred as it results in faster reaction kinetics due to elimination of diffusion limitations in the metal alloy composite particle.

[0043] The range of grain size for the first metal component, the second metal component, and the secondary material can be between 10 ³ pm to 50 pm. For example, the grain size can be about 10 ³ pm, about 10 ² pm, about lpm, about 5pm, about lOpm, about l5pm, about 20pm, about 25pm, about 30pm, about 35pm, about 40pm, about 45pm, or about 50pm.

[0044] Another parameter that affects the reaction kinetics is the porosity of the metal alloy composite particle which determines the gas diffusion within the metal alloy composite particle. Porosity of the metal alloy composite particle is proportional to the concentration of support material and it can be in the range of 10 ³ to 5 cm ³ /g. The surface area of the metal alloy composite particle is dependent on the grain size as well as the porosity and is in the range of 0.1 to 100 m ² /g.

III. Systems and Methods for Converting ¾S into Hydrogen (¾) and Sulfur

[0045] Disclosed herein are systems and methods for converting H2S into hydrogen (H2) and sulfur. The system for converting H2S into hydrogen (H2) and sulfur may comprise multiple reactors. For example, the system may comprise a sulfidation reactor and a regeneration reactor. The conditions in each of the sulfidation reactor and the regeneration reactor are modified as described below to ensure that the appropriate sulfidation and regeneration reactions occur in each reactor. In other embodiments, the system may comprise one reactor. The conditions in the single reactor may be modified such that the sulfidation and regeneration operations can occur in the single reactor.

[0046] Broadly speaking, the disclosed systems and methods reduce the amount of H2S in the input gas stream. For example, the disclosed method can be used to reduce the amount of H2S in the gas stream to below lOOppm. For example, the disclosed method can be used to reduce the amount of H2S in the gas stream to less than about 100 ppm, less than about 90 ppm, less than about 80ppm, less than about 70ppm, less than about 50ppm, less than about 40ppm, less than about 30ppm, less than about 20ppm, less than about lOppm, less than about 5ppm, less than about lppm, less than about lppm, or less than about O.lppm. For example, the disclosed method can be used to reduce the amount of FES in the gas stream to less than O. lppm.

A. Sulfidation Operation

[0047] The disclosed method comprises a sulfidation operation. The sulfidation operation can be performed in a sulfidation reactor. The sulfidation reactor can be a fixed bed reactor, a fluidized bed reactor, a co-current moving bed reactor, or a counter-current moving bed reactor. A moving bed reactor configuration also includes a packed moving bed, staged fluidized bed, a downer and/or a rotary kiln.

[0048] The sulfidation operation comprises contacting a first gaseous stream comprising FES with a metal alloy composite particle. The first gaseous stream may further comprise additional gases. For example, the FES-containing gas stream can also include CO, FE. and/or hydrocarbons. Example hydrocarbons include but are not limited to methane, ethane, propane, butane and higher alkanes. The first gaseous stream may contain FES and additional gases in other proportions or quantities. Usually, the first gaseous stream includes trace amounts or no oxygen (O2).

[0049] The sulfidation operation may be performed at any suitable temperature to facilitate sulfidation of the metal alloy composite particle. For example, the sulfidation operation may be performed at about l00°C to about 950°C. For example, the sulfidation operation may be performed at about l00°C, about l50°C, about 200°C, about 250°C, about 300°C, about 350°C, about 400°C, about 450°C, about 500°C, about 550°C, about 600°C, about 650°C, about 700°C, about 750°C, about 800°C, about 850°C, about 900°C, or about 950°C. In some instances, the sulfidation operation is performed at about 300 °C to about 450 °C. As another example, the sulfidation operation is performed at about 350 °C to about 400 °C.

[0050] The equilibrium of sulfidation reaction favors operating at lower temperatures, but the reaction kinetics is faster at higher temperatures. As such, some embodiments perform the sulfidation operation at a temperature of 300 °C to 450 °C. Performing sulfidation at 300 °C to 450 °C can eliminate the need for cooling and reheating the FES containing gas stream as is done for conventional FES removal processes such as Selexol, Rectisol, or amine based processes.

[0051] The sulfidation operation may be performed at any suitable pressure. For example, the pressure at which sulfidation operation occurs can be about 1 atm to about 150 atm. For example, the pressure can be about latm, about 2 atm, about 3 atm, about 4 atm, about 5 atm, about 6 atm, about 7 atm, about 8 atm, about 9 atm, about 10 atm, about 15 atm, about 20 atm, about 25 atm, about 30 atm, about 35 atm, about 40 atm, about 45 atm, about 50 atm, about 55 atm, about 60 atm, about 65 atm, about 70 atm, about 75 atm, about 80 atm, about 85 atm, about 90 atm, about 95 atm, about 100 atm, about 105 atm, about 110 atm, about 115 atm, about 120 atm, about 125 atm, about 130 atm, about 135 atm, about 140 atm, about 145 atm, or about 150 atm. In various instances, the pressure at which the sulfidation operation occurs is from 1 atm to 30 atm; 1 atm to 5 atm; 1 atm to 60 atm; 5 atm to 20 atm; 2 atm to 10 atm; or 1 atm to 15 atm. Generally, the kinetics of the sulfidation reaction appear to be faster at higher pressures and there is not an effect of pressure on the equilibrium of sulfidation reaction.

[0052] The kinetic rate of sulfidation reaction determines the gas residence time in the sulfidation reactor for maximum conversion of FkS. The gas residence time can vary from 0.2 seconds to 45 minutes. It is preferred to have the gas residence time between 0.5 s to 15 min. For example, the gas residence time can be around 0.5 seconds, about 1 second, about 30 seconds, about 1 minute, about 2.5 minutes, about 5 minutes, about 7.5 minutes, about 10 minutes, about 12.5 minutes, or about 15 minutes.

[0053] The amount of FkS gas that can be treated by the disclosed process is dependent on the composition of the metal alloy composite particle. The ratio of gas to metal alloy composite particle that can be used in the disclosed systems and methods can be about 1 :5 to about 10: 1. Preferably, the ratio of gas to metal alloy composite particle ranges from about 1:2 to about 5: 1. For example, the ratio of gas to metal alloy composite particle can be about 1:2, about 1 : 1, about 2: 1, about 3: 1, about 4: 1, or about 5: 1.

[0054] In the sulfidation operation, the hydrogen sulfide (FkS) in the first gaseous input stream reacts in a sulfidation reaction with the metal alloy composite particle to generate hydrogen gas (Fk) and one or more sulfide minerals. The hydrogen gas (Fk) may be collected and stored for future use in other processes. The sulfide mineral is selected from the group consisting of a metal sulfide, a thiospinel and combinations thereof. Without being bound by a particular theory, it appears that the presence of thiospinel is responsible for favorable equilibrium towards FkS decomposition and is non- reactive towards other gases that may be present in the FkS containing gas stream. For example, the sulfide mineral may be an iron sulfide, a chromium sulfide, or combinations thereof. In some embodiments, sulfide mineral comprises FeCr2S4.

B. Regeneration operation [0055] The disclosed method further comprises a regeneration operation. Typically, the regeneration operation occurs at higher temperatures than those used during the sulfidation operation. The regeneration operation can be performed in a regeneration reactor. The regeneration reactor can be a fixed bed reactor, a fluidized bed reactor, a co-current moving bed reactor, or a counter-current moving bed reactor. A moving bed reactor configuration also includes a packed moving bed, staged fluidized bed, a downer and/or a rotary kiln.

[0056] The regeneration operation comprises contacting a second gaseous input stream comprising at least one inert gas with the one or more sulfide minerals generated during the sulfidation operation. The regeneration operation thereby generates sulfur gas and regenerates the metal alloy composite particle for subsequent use. The sulfur gas obtained from the regeneration operation can be collected for future use in downstream applications. For example, the sulfur gas can be condensed and removed as solid or liquid sulfur based on its downstream application.

[0057] The at least one inert gas can include nitrogen, carbon dioxide and combinations thereof. For example, the at least one inert gas can be nitrogen. For example, regeneration operation can comprise contacting FeCnSi produced during the sulfidation operation with nitrogen gas, thereby regenerating iron sulfide and chromium sulfide and producing sulfur gas.

[0058] The regeneration operation may be performed at any suitable regeneration temperature to facilitate regeneration of the metal alloy composite particle. The regeneration temperature is dependent on the sulfur pressure in the regeneration reactor. A lower sulfur pressure in the regeneration reactor favors the equilibrium towards removal of sulfur and hence lower regeneration temperatures can be used. The regeneration temperatures can vary from 500°C to 1 l00°C. For example, the regeneration operation may be performed at about 750°C, about 800°C, about 850°C, about 900°C, about 950°C, about l000°C, about l050°C, or about H00°C. In various implementations, the regeneration temperature may be from 600°C to l000°C; from 700°C to 1 l00°C; from 800°C to l000°C; or from 700°C to 900°C.

[0059] The regeneration operation may be performed under vacuum. Alternatively, the regeneration operation may be performed under pressure conditions. The pressure conditions in the regeneration reactor can range from 1 atm to 150 atm. For example, the pressure can be about latm, about 2 atm, about 3 atm, about 4 atm, about 5 atm, about 6 atm, about 7 atm, about 8 atm, about 9 atm, about 10 atm, about 15 atm, about 20 atm, about 25 atm, about 30 atm, about 35 atm, about 40 atm, about 45 atm, about 50 atm, about 55 atm, about 60 atm, about 65 atm, about 70 atm, about 75 atm, about 80 atm, about 85 atm, about 90 atm, about 95 atm, about 100 atm, about 105 atm, about 110 atm, about 115 atm, about 120 atm, about 125 atm, about 130 atm, about 135 atm, about 140 atm, about 145 atm, or about 150 atm.

[0060] In some instances, a high gas: solids ratio is employed for the regeneration operation as it keeps the sulfur pressure low in the regeneration reactor, thus enabling a relatively lower regeneration temperature. For example, the gas: solids molar ratio can range from 0.2 to 10, preferably, from 0.5 to 5. For example, gas:solids molar ratio can be about 1:2, about 1 : 1, about 2: 1, about 3: 1, about 4: 1, or about 5: 1.

[0061] A low gas residence time is preferred to aid in maintaining low sulfur pressures in the regeneration reactor. The gas residence time can vary from 0.05 seconds to about 5 minutes, preferably from about 0.1 s to about 2 minutes. For example, the gas residence time can be about 0.05 seconds, about 0.1 seconds, about 1 second, about 5 seconds, about 10 seconds, about 30 seconds, about 60 seconds, about 90 seconds, about 2 minutes, about 3 minutes, about 4 minutes, or about 5 minutes.

[0062] The disclosed method can be operated in batch operational mode, a semi-batch operational mode, or continuous operation mode. The method can further comprise contacting the metal alloy composite particle produced following the regeneration operation, (i.e. the regenerated metal alloy composite particle) with a subsequent first gaseous input stream, thus repeating the process of isolating hydrogen gas (Fk) and sulfur from an FkS containing feed stream. The hydrogen gas (Fk) production performance of the regenerated metal alloy composite particle can be similar to the performance of the original metal alloy composite particle.

C. Example Configurations of Systems and Method for H ₂ S conversion

[0063] FIG. 1, FIG. 2, and FIG. 3 are schematic diagrams of exemplary systems for conversion of FkS. Various aspects regarding possible operating conditions for the exemplary systems, such as temperature, pressure, residence time, etc., as well as exemplary metal alloy composite particles usable in the exemplary systems ,are described in greater detail above, apply to the following discussion, and are not repeated below for the purpose of conciseness.

[0064] FIG. 1 shows a schematic diagram of exemplary system 100 for FkS conversion to Fk and S. As shown in FIG. 1, system 100 comprises sulfidation reactor 102 and regeneration reactor 104. The sulfidation reactor 102 includes a metal alloy composite particle as disclosed herein. An FkS containing gas stream is provided into the sulfidation reactor 102, resulting in the formation of hydrogen gas (Fk) and one or more sulfide minerals. The hydrogen gas (Fk) is collected, and the one or more sulfide minerals are provided to the regeneration reactor 104. An inert gas stream is provided into the regeneration reactor 104, resulting in the formation of sulfur gas and regeneration of the metal alloy composite particle. The metal alloy composite particle is provided back to the sulfidation reactor 102 and the sulfur gas is collected.

[0065] FIG. 2 shows a schematic diagram of exemplary system 200 for FkS conversion to Fk and S. In system 200, alloy material reacts with FkS or FhS containing gas (stream number 251) in reactor 202. The alloy material with the captured sulfur is then transferred to reactor 204, where the alloy material is regenerated by an inert gas such as N ₂ . The N ₂ sent to reactor 204 (stream number 252) is preheated with the gas outlet from reactor 204 and additional heating may be provided by burning fuel gas. The sulfur is removed in reactor 204, and the sulfur is then condensed by cooling with water and finally separated from N ₂ in a gas- liquid separator 206. The regenerated solids are sent to reactor 208, where they are fluidized with heated N ₂ (stream number 253) and then transported back to reactor 202. N ₂ and solids separation occurs in the cyclone separator 210. The separated N ₂ is recycled back to reactor 204 (stream number 255). The separated N ₂ can also be sent to the reactor 208 for fluidization (stream number 256) or to an outlet of reactor 204 (stream number 257) for pushing the solids into reactor 208. H ₂ is injected as a zone seal gas to prevent gas mixing between reactor 202, reactor 204 and cyclone separator 210. This is important to reduce downstream H ₂ product gas purification.

[0066] Reactors 202 and 204 are operated as countercurrent moving bed reactors. The residence time of gas and solids in reactors 202 and 204 may be controlled such that there is complete H ₂ S conversion in reactor 202 and complete regeneration in reactor 204. Reactor 208 is a fluidized bed reactor and its main purpose is for transporting solids via a riser back to reactor 202.

[0067] FIG. 3 shows a schematic diagram of exemplary system 300 for FhS conversion to Fk and S. System 300 includes three fixed bed reactors. At a given time, sulfidation occurs in reactor 302, regeneration in reactor 304 and reactor 306 is on standby. FhS or FhS containing gas (stream number 351) is sent to reactor 302 and the outlet gas is sent to a pressure swing adsorption (PSA) unit 308 to produce high purity Fk. N ₂ (stream number 352) is heated in two stages by preheater and then by fuel gas, before being sent to reactor 304 for removing sulfur from the solids. The sulfur removed is then condensed out in a sulfur condenser and the cooled down N ₂ is recycled (stream number 353) back to the preheater. Once reactor 302 is saturated with sulfur, it is switched to regeneration with the use of remote operated valves. Reactor 306 is switched to sulfidation as it contains regenerated solids and reactor 304 is switched to standby. The number of reactors and switching time is contingent on the gas flow rates and amount of solids used in each of the reactors.

[0068] FIG. 4 shows an example method 400 for FkS conversion to Fk and S. Method 400 begins by contacting the metal alloy composite particle (such as a metal alloy composite particle prepared by example method 500) with an FkS containing gas stream in a sulfidation reactor (operation 402). Operation 402 results in the formation of hydrogen gas (Fk) and one or more metal sulfides. Next, the hydrogen gas (Fk) is collected (operation 404). The remaining sulfide minerals are provided to the regeneration reactor (operation 406). The sulfide minerals are contacted with an inert gas in the regeneration reactor (operation 408). Operation 408 results in the formation of sulfur gas and regeneration of the metal alloy composite particle. The sulfur gas is collected (operation 410). The regenerated metal alloy composite particle is provided back to the sulfidation reactor (operation 412). The process then begins again by contacting the regenerated metal alloy composite particle with an FkS containing gas stream in the sulfidation reactor (operation 414). The process may be repeated for any desired number of cycles.

D. Example Improvements and Industrial Applications

[0069] The systems and methods disclosed herein result in conversion of a poisonous, toxic and corrosive gas like FkS to highly valuable chemicals like hydrogen (Fk) and sulfur (S2). The methods can use a two-reactor system with few heat exchangers, or a one reactor system, to produce Fk and sulfur from FkS. Therefore, there are capital cost benefits in using fewer processing units compared to typically used methods. Moreover, the methods described herein are robust towards other gases, like carbon monoxide, hydrogen and hydrocarbons, commonly found in industrial process streams that contain FkS. Therefore, the instant systems and methods typically do not require separating these gases before treating H2S, which allows for savings in energy and capital costs that are usually involved with separating these gases.

[0070] The methods described herein allow FkS to be treated at very high temperatures. Treating at high temperatures reduces or eliminates the need for cooling and reheating the FkS containing gas stream as is typically done for conventional FkS removal processes such as Selexol, Rectisol, or amine based processes. Moreover, the disclosed methods and process utilize solids with high recyclability, resulting in the capacity for long term use and minimal replacement and waste management costs.

[0071] The methods described herein can be used in multiple industrial applications. For example, the methods described herein can be used for coal gasification to produce synthesis gas (syngas). The major components of synthesis gas are carbon monoxide (CO) and Fk and this gas stream is at >500 °C. This gas can be directly sent to the process disclosed herein without the need for cooling the gas stream or removing CO or Fk.

[0072] The methods described herein can be used in natural gas processing methods. TkS is typically removed from natural gas before it is sent to catalytic processes, such as steam methane reforming, to produce syngas and Tk. Steam methane reforming occurs in temperature range of 700-1000 °C and requires very low concentrations of TkS in the gas stream. The methods described herein can be used to reduce TkS concentrations in a gas stream to the desired values before use of the gas stream in catalytic processes such as steam methane reforming.

[0073] The methods described herein can be used in crude oil processing. Sulfur from crude oil is typically removed in a hydrodesulfurization unit by treating it with Tk in a temperature range from 300-400 °C. The gas from this unit is a mixture of TkS and Tk. The gas from such a hydrodesulfurization unit can be directly treated by a method described herein to produce Tk and sulfur.

IV. Systems and Methods for Producing Metal Alloy Composite Particles

[0074] Further disclosed herein are systems and methods for producing metal alloy composite particles. The metal alloy composite particle may be produced by mixing the first metal component and the second metal component in their respective desired amounts. The mixture of the first metal component and the second metal component is reacted with TkS at a temperature of about 300°C to about 900°C. For example, the mixture of the first metal component and the second metal component can be reacted with FkS at a temperature of about 300°C, about 350°C, about 400°C, about 450°C, about 500°C, about 550°C, about 600°C, about 650°C, about 700°C, about 750°C, about 800°C, about 850°C, or about 900°C. The time of the reaction is dependent on the amount of first metal component and the second metal component used. A mixture of thiospinel and higher metal sulfides is formed at the end of the reaction.

[0075] Nitrogen is then passed over the reacted mixture in a temperature range of about 600°C to about l200°C. For example, nitrogen may be passed over the reacted mixture at a temperature of about 600°C, about 650°C, about 700°C, about 750°C, about 800°C, about 850°C, about 900°C, about 950°C, about l000°C, about l050°C, about H00°C, about H50°C, or about l200°C.

[0076] Subsequently, a secondary material can be mixed together with the alloy material. Additionally, a support material can be mixed together with the alloy material. The mixture is then sintered at a temperature of about 700°C to about l400°C. For example, the mixture may be sintered at a temperature of about 700°C, about 750°C, about 800°C, about 850°C, about 900°C, about 950°C, about l000°C, about l050°C, about H00°C, about H50°C, about l200°C, about l250°C, about l300°C, about l350°C, or about l400°C.

[0077] FIG. 5 shows an example method 500 for preparing a metal alloy composite particle for use in the disclosed method of FhS conversion to Fk and S. Method 500 begins by mixing the first metal component and the second metal component (operation 502). The mixture of the first metal component and the second metal component is reacted with a gas containing FkS (operation 504). Next, nitrogen is passed over the mixture (operation 506). Next, a secondary material (operation 508) and a support material (510) are added to the mixture. Lastly, the mixture is sintered (operation 512).

V. Experimental Examples

Example 1

Iron-Chromium (Fe-Cr) Metal alloy Preparation

[0078] Iron sulfide (FeSx, 0<x<2) and chromium sulfide (CrSy, 0<y<l.5) were mixed in a molar ratio of 1:2. Iron oxide, chromium oxide, iron metal, chromium metal or a mixture of these compounds can also be taken as the starting material. The said mixture was reacted with gas containing FkS at a concentration of 0.9% in a fixed bed reactor kept in a horizontal tube furnace. The said gas containing FhS was reacted at a temperature of 800 °C. After reaction with FhS, the gas was switched to N2 and the temperature was increased to 950 °C. FIG. 6 shows the X-ray diffraction (XRD) analysis of the solid sample obtained after cooling down to room temperature under the N2. The presence of an Fe-Cr alloy is clearly visible from the XRD spectra.

Example 2

H ₂ S Conversion by Exemplary Metal Alloy Composite Particles

[0079] FIG. 7 shows the performance of an Fe-Cr alloy in a fixed bed reactor for FhS conversion to Fk and S over multiple sulfidation and regeneration operations. The temperatures of sulfidation and regeneration operations were 800 °C and 950 °C, respectively. A 0.9%H2S/N2 gas was injected into the fixed bed reactor during sulfidation operation and N2 was injected during the regeneration operation. The gas hourly space velocity (GHSV) for sulfidation operation for the first and second cycle was 5000 hr-l, whereas, GHSV for third, fourth and fifth sulfidation operation was 2580 hr-l. The concentration of gas leaving the fixed bed reactor was measured using a Siemens

CALOMAT 6E ¾ analyzer. The gas was also intermittently sampled by InterScan’s Model RMl7-500m Toxic gas monitor to measure H2S concentration in the reactor outlet. H2S conversion was calculated based on the H2 concentration detected by the H2 analyzer. A high H2S conversion over multiple GHSVs repeated over several sulfidation-regeneration operations demonstrates excellent performance and recyclability of the Fe-Cr alloy. FIG. 8 shows the presence of iron-chromium thiospinel (FeCnS^ via XRD analysis of the solids after the fifth sulfidation operation.

[0080] Table 1 shows the inlet and outlet composition of gas sent during sulfidation operation for two different runs at 800 °C in a fixed bed reactor containing Fe-Cr alloy. In run 1, 50 ml/min of 0.9%H2S/N2 and 46.95 ml/min 9.6% methane (CH4)/l9%CO/8l.4%N2 was co- injected into the fixed bed reactor for 30min. The reactor outlet gas concentration was measured using a Siemens Ultramat 23 gas analyzer to measure CO, CO2 and C¾ concentrations and Siemens Calomat 6E gas analyzer to measure H2 concentration. In run 2, 100 ml/min of 0.9% H2S/N2 and 100 ml/min of 100% H2 was co-injected into the fixed reactor for 30min. The reactor outlet gas concentration was measured using a Siemens CALOMAT 6E H2 analyzer. The fact that the inlet and outlet gas compositions are the same indicates that CH4, CO and H2 do not react with the Fe-Cr alloy.

Table 1. Inlet and outlet gas composition for two experiments in a fixed bed reactor at 800 °C, (*based on XRD analysis results and mass balance).

[0081] XRD analysis of the sample at the end of the Run 1 and Run 2 shown in FIG. 9 and FIG. 10, respectively, proved that sulfur in H2S was captured by the Fe-Cr alloy and FeCr2S4 was formed.

[0082] FIG. 11 and FIG. 12 illustrate the favorable effect that FeCnS4 formation has on the thermodynamic equilibrium conversion of H2S to H2. Equilib module in FactSage 7.1 software was used to perform the thermodynamic calculations. A basis of 1 mol of iron monosulfide (FeS) and 1 mol of H2S was selected whereas the moles of chromium

monosulfide (CrS) were varied. In FIG. 12, FeCnSr is observed to form at FeS:CrS molar ratio of 2 and from that value of ratio onwards the corresponding H2S fractional conversion to H2 is 1 as seen in FIG. 11.

Example 3

Fe-Cr bimetallic alloy comparison with Fe-Cr bimetallic alloy and M0S2 secondary material

[0083] Table 2 shows the comparison of H2S conversion by Fe-Cr alloy material (sample 1) against that of Fe-Cr alloy material added with M0S2 secondary material (sample 2). The primary phases present in the Fe-Cr alloy based on XRD analysis are FeCrcSr (31.3 wt%), FeCr or 410 L stainless steel (63.4 wt%) and CnCb (5.2 wt%). The composition of sample 2 is 50 wt% of the Fe-Cr alloy (sample 1) and 50 wt% M0S2. For both samples, powder of size less than 125 microns was placed in between quartz wool and supported in the heated region of a 0.5 inch inner diameter ceramic reactor. The samples were heated to a temperature of 800°C under nitrogen followed by reaction with 0.9% FhS in the sulfidation step, where the gas flow rate was varied to test different gas hourly space velocities (GHSVs). The sulfidation step was followed by a regeneration step under nitrogen flow at 950 °C. Multiple sulfidation and regeneration steps were conducted for both the samples where different GHSVs were tested during the sulfidation step. The reactor outlet gas composition was measured using a Siemens CALOMAT 6E ¾ analyzer for H2 concentration and

intermittently using InterScan’s Model RMl7-500m Toxic gas monitor for H2S concentration. A high H2S conversion for sample 2 indicates faster reaction kinetics of the solid sample with H2S, which may be a result of addition of M0S2 as the secondary material. The XRD analysis of Sample 2 after reaction is shown in FIG. 13, where FeCrcSr and M0S2 phases have been marked.

[0084] Table 2. H2S conversion comparison between sample 1 and sample 2 at 800 °C with 0.9% H2S

Example 4

Fe-Cr bimetallic alloy comparison with Fe-Cr bimetallic alloy with M0S2 secondary material and S1O2 support material

[0085] Table 3 compares the H2S conversion of Fe-Cr alloy (sample 3) with that of Fe-Cr alloy with added M0S2 secondary material and S1O2 as the support material (sample 4).

Based on XRD analysis, sample 3 has FeCnSr (37.3 wt%), FeCr or 410 L stainless steel (25 wt%) and Feo.879S (37 wt%) as the major phases. The composition of sample 4 is 37.5 wt% Fe-Cr alloy (sample 3), 25 wt% M0S2 and 37.5 wt% SiC . Multiple sulfidation-regeneration steps were conducted on both the samples in a 0.5 inch inner diameter ceramic reactor. The sulfidation temperature was 800 °C and regeneration temperature was 950 °C. FhS conversion was measured during one of the sulfidation steps at the same H2S flow rate per unit active material weight for both the samples. The active material consists of both the Fe- Cr alloy as well as the secondary material- M0S2. The reactor outlet gas composition was measured using a Siemens CALOMAT 6E H2 analyzer for Fh concentration and

intermittently using InterScan’s Model RMl7-500m Toxic gas monitor for FhS concentration. The FhS conversion of sample 4 is slightly higher than sample 3 which may be a result of faster reaction kinetics with FhS. The H2S conversion for sample 4 may be further enhanced by varying its alloy, secondary material and/or support material composition. FIG. 14 shows the FeCnS4 and M0S2 phases present in sample 4 based on XRD analysis.

[0086] Table 3. FhS conversion comparison between sample 3 and sample 4 at 800 °C with 0.9% FhS

Example 5

Fe-Cr bimetallic alloy with M0S2 secondary material with different gas mixtures

[0087] Fe-Cr alloy with 20 wt% M0S2 was tested with four different gas mixtures, shown in Table 4 below, and at a pressure of 1.8 bar. Table 4. Reaction performance of Fe-Cr alloy with 20 wt% M0S2 with different gas mixtures [*HCs= (1.04 vol%) 1,3 -butadiene, (2.02 vol%) 2-butene, (6.04 vol%) hydrogen, (7.25 vol%) methane, (2.07 vol%) n-pentane, (2 vol%) propylene, (79.58 vol%) ethylene].

[0088] The Fe-Cr alloy was used in powder form with particle size <125 microns in a ceramic fixed bed reactor of 0.5 inch inner diameter. The reactor was heated using an electrical heater to a temperature of 400°C under the flow of N ₂ . Once the reactor temperature reached 400°C, mixing of the various gas compositions mentioned in Table 4 was started.

[0089] Gas hourly space velocity (GHSV) shown in the second to last column in Table 4 was calculated based on the gas flow rate and metal alloy composite bed volume. FhS conversion was measured based on measuring sulfur content in the alloy before and after the reaction. Sulfur content was measured using a Thermo Fisher Scientific TS 3000 total sulfur analyzer (Waltham, Massachusetts). The FhS conversion for the different gas mixtures is shown in the last column of Table 4.

[0090] For gas mixtures 1 and 3, no oxides were observed in the solids from XRD analysis. Moreover, no carbon deposition was observed for gas mixture 4 based on XRD analysis of the reacted sample. Therefore, the alloy appears to be resistant to oxidation with CO2 and CO along with being resistant to carbon deposition in presence of hydrocarbons at 400°C. This resistance allows for application of the alloy for FES capture from a variety of process streams that can contain any of the contaminants mentioned in Table 4.

Example 6

Recyclability of Fe-Cr alloy sample

[0091] Recyclability of exemplary Fe-Cr alloy particles was tested by performing twelve consecutive sulfidation-regeneration cycles over Fe-Cr alloy with 20 wt% M0S2 in a fixed bed reactor. The fixed bed reactor was made of ceramic material and had an inner diameter of 0.5 inch. The sulfidation temperature was 400°C and the regeneration temperature was 950°C. The gas feed during sulfidation step was 0.9% FES balanced with N2 at a GHSV of 1490 hr ¹ . The reactor pressure was 1 bar for all the sulfidation steps except for the 8 ^th step where the reactor pressure was increased to 1.8 bar. H2S conversion was calculated based on the H2 concentration measured using a Siemens CALOMAT 6E H2 analyzer. Nearly 100% conversion (FIG. 15) was observed over the 12 cycles, which indicated excellent recyclability of the Fe-Cr alloy.

Example 7

Effect of pressure on H ₂ S conversion with Fe-Cr alloy

[0092] Effects of pressure on EhS conversion with a Fe-Cr alloy were tested.

Thermodynamic calculations conducted in FactSage 7.3 software demonstrate no effect of pressure on the conversion of FES. The FES input was 1 mole, whereas, FeS and CrS input was 1 mole and 2 moles, respectively. FIG. 16 shows that at 400°C, FES conversion is nearly 100% for all the pressures between 1 to 60 atm.

[0093] Experimentally, pressure was observed to improve the kinetics of FES conversion. Fe-Cr alloy powder of particle size < 125 microns was reacted with 0.9% FES in a 0.5 inch inner diameter ceramic reactor. FES conversion was calculated based on the EE concentration measured using a Siemens CALOMAT 6E EE analyzer and intermittently with InterScan’s Model RMl7-500m Toxic gas monitor for FES concentration. At 400°C reactor temperature, the FES conversion was 32% higher at 1.8 atm compared to 1 atm for a GHSV of 4500 hr ¹ .

Example 8

Performance of Fe-Cr alloy material with Ni

[0094] Fe-Cr alloy material with Ni was tested in a fixed bed reactor for FES conversion. The sample consisted of 45 wt% Fe-Cr alloy, 10 wt% N13S2 and 45 wt% SiCh. The Fe-Cr alloy material was used in a powder form in a 0.5 inch inner diameter ceramic reactor, which was heated by an electrical heater to a temperature of 800°C. H2S conversion was calculated by measuring the H2S concentration in the reactor outlet using InterScan’s Model RM17- 500m Toxic gas monitor. 0.9% H2S balanced with N2 was reacted with Sample 1 at a GHSV of 3800 hr ¹ . The maximum H2S conversion was >90%.