OA20701A

OA20701A - Methods for producing and using alkaline aqueous ferric iron solutions.

Info

Publication number: OA20701A
Application number: OA1202200160
Authority: OA
Inventors: Charles Deane Little; Yasmina Yeager
Original assignee: New Sky Energy, Llc
Priority date: 2019-10-21
Filing date: 2020-10-21
Publication date: 2022-12-30

Abstract

Methods for removing reduced sulfur compounds, such as hydrogen sulfide, from fluids employing a ferric iron salt that exhibits unusually high solubility in aqueous, alkaline solutions and has strong affinity for capture and oxidation of reduced sulfur compounds. Alkaline aqueous ferric iron salt and solutions thereof useful for removing reduced sulfur compounds from fluids and various methods of production of such salts and solutions. In addition, methods of regenerating the alkaline aqueous ferric iron salt solutions after capture of hydrogen sulfide or other reduced sulfur compounds, generally by exposure to oxygen in air. The alkali metal carbonate salt preferably comprises potassium carbonate and/or potassium bicarbonate. The alkaline aqueous ferric iron salt solutions generally comprise ferric ions, potassium ions, carbonate ions, and bicarbonate ions, optionally with one or more organic additives. In addition, aqueous-soluble, ferric iron salts and ferric iron containing solids prepared by removal of aqueous medium from solutions herein.

Description

METHODS FOR PRODUCING AND USING ALKALINE AQUEOUS FERRICIRON SOLUTIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[1] This application claims the benefit of U.S. provisional applications 62/924,166, filed October 21, 2019, 63/029,405, filed May 23, 2020, and 63/032,600, filed May 30, 2020, each of which is incorporated by reference herein in its entirety.

BACKGROUND

[2] Hydrogen sulfide (H2S) is an extremely corrosive and poisonous gas commonly présent in natural gas, oil, biogas and geothermal steams. Hydrogen sulfide removal is necessary for energy production and various industrial processes, such as the production of natural gas, oil, paper, geothermal energy and biological gas (e.g., from landfills, dairies, and wastewater treatment plants). Various technologies exist for hydrogen sulfide removal, such as Chemical scavengers (e.g., ferrie chlorîde, monoethanolamine triazine), the Amine-Claus process, liquid redox processes, and packed bed technologies (e.g., SulfaTreat® (M-l LLC, Houston Texas) and Iron Sponge technologies). Hydrogen sulfide scavengers are a very common method of hydrogen sulfide control. Hydrogen sulfide scavengers are commonly iron-based compounds that react with H2S and convert it to iron sulfide or pyrite. While effective, these single use Chemical technologies consume natural resources, produce hazardous Chemical waste, and hâve high operating costs. There remains a significant need in the art for methods and materials for hydrogen sulfide control appropriate for a variety of industrial application and which are cost-effective.

SUMMARY OF THE INVENTION

[3] The présent invention relates to methods and materials for removal of hydrogen sulfide and other reduced sulfur compounds from fluids, including gases and liquids, containing such reduced sulfur compounds. The method involves contacting the fluid with an alkaline aqueous solution containing a selected concentration of ferrie ion, Fe(III), wherein the ferrie ion is at least substantîally or completely dissolved in the aqueous medium forming a solution. Contacting results in capture and oxidation of at least a portion of the reduced sulfur compounds in the fluid, the concomitant formation of ferrons ion, Fe(II), and the formation of Fe(II) sulfide particles which are suspended in the aqueous solution and at least partial removal of reduced sulfur compounds from the fluid. After contact with the fluid, the at least partially

Page 1 of 42 reduced alkaline aqueous solution used to remove reduced sulfur and the ferrons sulfide particles suspended in it can be regenerated by treatment with oxygen in air or an alternative oxîdizing agent resulting in formation of elementai sulfur which précipitâtes from the solution and can be collected. In embodiments, capture of the reduced sulfur compound results in formation of one or more iron sulfides, such as, FeS, at least in part as a solid which can be separated from the at least partially reduced aqueous solution, if desired. Iron sulfides can be converted via oxidation to elemental sulfur and ferrie iron as îs known in the art.

[4] In general, ferrie iron salts are virtually insoluble in aqueous solutions above pH 6. In one aspect, the présent invention relates to methods for producing ferrie iron salts that are unusually soluble in aqueous solutions under alkaline conditions. In one embodiment of the invention, these salts contain anionic ferrie-bicarbonate complexes, anionic ferrie-carbonate complexes or anionic ferric-carbonate/bicarbonate complexes, optionally with hydroxyl groups, that are negatively charged and that, unlike free ferrie cations, are fully water soluble under alkaline conditions. In embodiments, water-soluble ferrie iron salts comprise carbonate, bicarbonate or a mixture thereof. In embodiments, water-soluble ferrie iron complexes comprise carbonate, bicarbonate or a mixture thereof and hydroxide. In embodiments, the counter-ion of the anionic water-soluble ferrie iron complexes is potassium. In embodiments, water-soluble ferrie iron salts may be a mixture of different salts.

[5] The présent invention also relates to aqueous-soluble, ferrie iron salts, aqueous solutions containing such salts and to solids prepared by removing water and aqueous solvent from such solutions. The invention also relates to water-soluble ferrie salts that can be purified or isolated from the alkaline aqueous ferrie iron sait solution, for example, by extraction of alkaline aqueous ferrie iron sait solutions, as described in examples herein, or précipitation by addition of one or more organic solvents to the alkaline aqueous ferrie iron sait solutions. The ferrie iron salts and ferrie iron-containing solids of this invention and aqueous solutions in which such salts and solids are dissolved are useful in various industrial processes. Water and Γ. : » aqueous solutions comprising these salts are particularly useful for removal of reduced sulfur compounds (e.g., FbS) from fluîds. Certain solutions of this invention are also useful for at least partial removal of CO2 from fluids containing CO2. Certain solutions of this invention are also useful for the removal of oxygen from fluids. Simultaneous removal of hydrogen sulfide, carbon dioxide and oxygen may be very useful in treating biogas streams, which often contain these gases.

[6] Various methods of synthesis of the water- or aqueous-soluble, ferrie iron salts are provided herein.

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⁷ Page 2 of 42

[7] Furthermore, the présent invention relates to methods for using the alkaline aqueous ferrie iron sait solutions to treat reduc ed sulfur-containing fl nids. For instance, the alkaline aqueous ferrie iron sait solutions may be used to treat lUS-contaming gases (e.g., natural gas, biogas, acid gas, geothermal vent gas or foui air from farming, industrial or wastewater operations).

[8] Ferrie iron (Fe³⁺) is soluble in acidic aqueous solutions (e.g., below pH 5). Above about pH 5, ferrie iron is typically insoluble in water and will form parti clés of one or more of the known iron oxides (e.g., ferrie oxide, ferrie oxyhydroxides). The methods of the présent invention enable the production of alkaline aqueous solutions having solubilized ferrie iron salts that are extremely effective for the treatment of reduced sulfur-containing fluids. In contrast to conventional methods of solubilizing ferrie iron at high pH, such alkaline aqueous ferrie iron sait solutions may be produced with or without organic additives as described in greater detail below.

BRIEF DESCRIPTION OF THE FIGURES

[9] FIG. 1 is an embodiment of a method for treating a reduced sulfur-containing fluid with an*alkaline aqueous ferrie iron solution.

[10] FIG. 2 is a schematic drawing of an exemplary System for treating a reduced-sulfur containing fluid with an alkaline ferrie iron sait solution of this invention and regeneratîng the alkaline ferrie iron sait solution after use.

[11] FIG. 3 is a UV-Vis spectrum of purified alkaline ferrie iron sait solution diluted in buffer as described in Example 6.

[12] FIG. 4 is a graph illustrating pH change with carbon dioxide capture and release by aqueous alkaline ferrie iron sait solutions as described in Example 8.

Page 3 of 42

DETAILED DESCRIPTION

[13] The invention relaies to methods and materials for removing reduced sulfur compounds, particularly hydrogen sulfide (HaS), from fluids containing such reduced sulfur compounds. Materials include alkaline ferrie iron sait solutions that can be used to scrub reduced sulfur compounds from the fluids. In embodiments, materials include ferrie iron sait solutions that self-assemble into complexes that are unusually soluble in alkaline solutions, and that can be efficiently used to scrub reduced sulfur compounds from the fluids. Materials also include ferrie iron-containing solid materials or salts that can be used to préparé alkaline ferrie iron solutions useful in methods herein. The invention further provides methods for making alkaline ferrie iron salts solutions herein as well as methods for making water-soluble ferrie iron salts and ferrie iron containing materials which are useful at least for préparation of alkaline ferrie iron sait solutions herein.

[14] In embodiments, the invention provides a method for removing reduced sulfur compounds from fluids. In embodiments, the fluids are gases. In embodiments, the fluids are liquids. In particular embodiments the reduced sulfur compound is hydrogen sulfide. The methods herein are particularly useful for treatment of gases, such as hydrocarbon containing gases containing hydrogen sulfide. Fluids containing hydrogen sulfide may, in embodiments, also contain one or more other reduced sulfur compound, such as mercaptans, alkyl disulfides, carbonyl sulfide or carbon disulfide. Fluids containing hydrogen sulfide and/or other reduced sulfur compounds, may, in embodiments, also contain carbon dioxide, oxygen or a combination thereof.

[15] In embodiments, the method for removing reduced sulfur compounds involves contacting an alkaline aqueous ferrie iron sait solution as described herein with a reduced sulfur-contaîning fluid, which contains at least one reduced sulfur compound. In embodiments, the alkaline aqueous ferrie iron sait solution comprises ferrie ions (Fe³⁺), potassium ions (K⁺k carbonate ions (CO3²') and bicarbonate ions (HCCU), optionally hydroxide and nitrate ions and optionally contains one or more organic additives. Contacting the ferrie iron sait solution and the reduced sulfur-containing fluid produces a reduced alkaline ferrie iron solution, and comprises oxidizing at least a portion of the at least one reduced sulfur compound in the fluid and reducîng at least a portion of the ferrie ions in the solution to ferrous ions (Fe²A- Contacting also results in formîng one or more iron sulfide compounds in the alkaline aqueous ferrie iron solution and thereby removes at least a portion of the reduced sulfur compounds from the fluid. It is believed that the direct reaction of iron with sulfide to form iron sulfide distinguishes this chemistry from other “liquid redox” processes that use organic chelating agents to solubilize

Page 4 of 42 iron. In embodiments, at least some portion of the ferrie iron remains dissolved in the alkalîne ferrie iron solution during contacting.

[16] In embodiments, the method further comprises removing iron sulfide compounds from the alkaline at least partially reduced aqueous ferrie iron solution after removal of at least a portion of the reduced sulfur compounds from the fluid. In embodiments, the method further comprises séparation of iron sulfide compounds from the alkaline at least partially reduced aqueous ferrie iron solution by précipitation, settling, centrifugation or filtration. Such séparation can be accomplished by methods that are well known in the art. In embodiments, the method further comprises oxidizing at least a portion of the ferrons iron formed in the reduced alkaline aqueous ferrie iron solution back to ferrie iron to at least in part regeneraîe the aqueous ferrie iron solution. In embodiments, the method further comprises exposing the reduced alkaline iron solution to an oxidizing agent to oxidize at least a portion of the ferrous idhs to ferrie ions, thereby producing at least a partially regenerated alkaline aqueous ferrie iron sait solution. In embodiments, the exposing step comprises producing elemental sulfur.

[17] In embodiments, prier to the contacting step, the alkaline aqueous ferrie iron sait solution comprises at least some iron-based particles, and wherein due to at least one of the contacting step (a), the producing step (b) and the exposing (oxidizing) step (c), the regenerated alkaline aqueous ferrie iron solution is free of iron-based particles.

[18] In embodiments, the process for removal of reduced sulfur compounds is a continuons process. In embodiments, the contacting step (a), the producing step (b), and the exposing step (cj occur concomitantly, if présent. In embodiments, the method comprises repeating steps (a)(c) at least once.

[19] In embodiments of the method, a flow of fluid is contacted with the alkaline aqueous ferrie solution for a selected contact time to remove reduced sulfur compounds from the fluid to provide a purified fluid. In embodiments, after contact with fluid, the alkaline at least partially reduced ferrie iron solution contains at least one iron sulfide and thereafter the iron sulfide is oxîdîzed to elemental sulfur and ferrie ions in the at least partially reduced alkaline aqüeous ferrie solution. In embodiments, such removal is continuons. In embodiments, the at least partially reduced alkaline aqueous ferrie solution is oxidized to at least in part regenerate the alkaline aqueous ferrie solution. Oxidation can be performed by contacting the at least in part reduced ferrie iron sait solution with oxidizing agents, such as oxygen in air or another oxygen-containing gas.

[20] In embodiments, the alkaline aqueous ferrie iron sait solution comprises ferrie ions (Fe³⁺); potassium ions (K⁺); wherein the molar ratio of the potassium ions to the ferrie ions is Page 5 of 42 at least I.û; carbonate ions (CO3²’); bicarbonate ions (HCOf); and optionally nitrate ions. In embodiments the alkaline aqueous iron sait solution comprises ferrie-carbonate complexes that are anionic in nature and exhibit unusually high solubility in alkaline solutions. In embodiments, the alkaline aqueous ferrie iron sait solution comprises nitrate ions. In embodiments, the alkaline aqueous ferrie iron sait solution comprises bicarbonate ions.

[21] In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of halîde ion of not greater than 10,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of halide ion of not greater than 1,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of halîde ion of not greater than 100 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of halîde ion of not greater than 10 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain detectible levels of halide ions. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of chloride ion of not greater than 10,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of chloride ion of not greater than 1,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of chloride ion of not greater than 100 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of chloride ion of not greater than 10 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain detectible levels of chloride ions.

[22] In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sulfate ion of not greater than 10,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sulfate ion of not greater than 1,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sulfate ion of not greater than 100 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sulfate ion of not greater than 10 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution .1 _% does not contain detectible levels of sulfate ions. In embodiments, the alkaline aqueous ferrie îron^: sait solution contains levels of sodium ion of not greater than 10,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sodium ion of not greater than 1,000 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sodium ion of not greater than 100 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution contains levels of sodium ion of not greater than 10 ppm. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain detectible levels of sodium ions. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain NaCl. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain éthanol. In

Page 6 of 42 embodiments, the alkaline aqueous ferrie iron sait solution does not contain an alcohol having 1-6 carbon atoms.

[23] In embodiments, the alkaline aqueous ferrie iron sait solution comprises one or more organic additives, other than organic solvents. In embodiments, the one or more organic additives are chelating agents. In embodiments, any organic additives, other than organic solvents, are présent in the solution at concentrations such that the molar ratio of ferrie ion in the solution to each organic additive is at least 2. In embodiments, wherein the solutions comprise one or more organic additives, ferrie ions are présent in the solution in molar excess, For instance at least 3-, at least 5-, at least 10- or at least 20- fold molar excess, over each of the organic additives. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain a chelating agent. In embodiments, the alkaline aqueous ferrie iron sait solution does not contain EDTA ions.

[24] In embodiments, the alkaline aqueous ferrie iron sait solution is made by dilution of a concentrate. In embodiments, the concentrate is diluted from 1- to up to 60-fold with an aqueous medium, and in particular embodiments, the aqueous medium used for dilution is a potassium carbonate/bicarbonate buffer. In a more spécifie embodiment, the concentrate is diluted from 10- to 30-fold with an aqueous medium, and particularly with a potassium carbonate/bicarbonate aqueous buffer. An unusual aspect of the alkaline aqueous ferrie iron sait îs that the concentrate is preferably diluted into potassium carbonate/bicarbonate buffer, rather than water. Dilution into water often results in précipitation of iron oxide particles, whereas dilution into potassium carbonate/bicarbonate buffer results in fully soluble alkaline aqueous ferrie iron sait solutions. Aqueous media used to dîlute ferrie ion sait solutions for use in methods herein can include other ionic or non-ionic components that do not deleteriously affect and may enhance solubility of the ferrie ions thereîn. --

a. Methods of Synthesis

[25] Broadly, the présent patent application also relates to methods for producing and using alkaline aqueous ferrie iron sait solutions. As described in greater detail below, the new alkaline aqueous ferrie iron sait solutions may be produced and regenerated onsite via a variety of methods at substantially lower cost and Chemical consumption than competing H2S control technologies.

i. Aqueous Synthesis Methods

[26 ]' Aqueous synthesis methods of producing the new alkaline aqueous ferrie iron sait ; ' esc solutions generally include reacting at least one ferrie iron sait reagent with at least one alkali métal carbonate sait reagent. In some embodiments, the at least one ferrie iron sait reagent

Page 7 of 42 i—, j comprises ferrie nitrate (Fe(NO₃)₃). Generally, the at least one alkali métal carbonate sait reagent comprises potassium carbonate, or potassium bicarbonate and combinations thereof. The ferrie iron sait reagent may be in any suitable form, such as dissolved in aqueous solution or as a dry or hygroscopic solid. For instance, in embodiments where at least some ferrie nitrate is used as a solid, the ferrie nitrate may be in the form of the hexahydrate sait, or the nonahydrate sait and combinations thereof. An acidic aqueous solution comprising a ferrie sait may be produced, for instance, by solubilîzing the ferrie îron from scrap métal (e.g., iron or steels) using an acidic solution (e.g., nitric acid to produce a ferrie nitrate solution).

[27] Similarly, the potassium carbonate and potassium bicarbonate may be in any suitable form. For instance, potassium carbonate may be used in the form of the anhydrous sait, or the sesquihydrate sait (K2CO₃T.5 H2O) and combinations thereof. As discussed in greater detail below, while not being bound by any theory, it is believed that at least the carbonate ions complex with and greatly enhance the solubility of the ferrie iron in the alkaline aqueous ferrie iron solutions. Furthermore, alkaline ferrie iron sait solutions comprising nitrate may be preferred since sîmilar mixtures made from different ferrie and alkali métal salts may not form alkaline aqueous ferrie iron solutions that are free of précipitâtes (e.g., particles such as ferrie iron-based particles) (see Example 1). Tn embodiments, water-soluble ferrie salts can be employed as the ferrie iron sait reagent. In spécifie embodiments, the ferrie iron sait reagent is not ferrie chloride. In spécifie embodiments, the ferrie iron sait reagent is not ferrie sulfate.

[28] As used herein, “alkali métal carbonate sait” means a carbonate sait of one or more of the alkali metals (e.g., Li, Na and K). Thus, for the purposes of this patent application, carbonate salts of the alkaline earth metals (e.g., B a, Mg, Ca, Sr) do not fall within the scope ofthê term, “alkali métal carbonate sait.”

[29] The term “alkaline aqueous solution” refers to an aqueous solution of pH greater than 7.0. Preferred alkaline aqueous solutions are those having pH greater than 8.0. Alkaline solutions include those having pH between 9-13. The terms aqueous solution and aqueous medium also include miscible mixtures of water with organic solvents, wherein water is the prédominant component (at least 50% by volume) of the aqueous medium or solution. In spécifie embodiments, one or more organic solvents which are water soluble, such as éthanol, àre present în the aqueous medium up to 20% by volume. In spécifie embodiments, one or more water-soluble organic solvents, such as éthanol are present in the aqueous medium up to 10% by volume.

[30] After the reacting step described above, the resulting alkaline aqueous ferrie iron sait solutions generally comprise ferrie ions (Fe³⁺), potassium ions (K ), carbonate ions (CO₃ ^2-) and

Page 8 of 42 bicarbonate ions (HCO3), optionally with one or more organic additives. As dîscussed in greater detail below, the molar ratio of the potassium ions to the ferrie ions is generally at least 2.0

[31 ] While not being bound by any theory, it is believed that the ability of the ferrie iron to remain highly soluble in alkaline solutions is due to the composition of the novel ferrie iron sait, specifically the formation of ferrie ion complexes with carbonate, bicarbonate and/or hydroxide or nitrate ions that are anionic in nature. It is further believed that the ability of the ferrie iron to remain highly soluble in alkaline solutions is due to the self-assembly of ferrie ions with carbonate, bicarbonate and/or hydroxide or nitrate ions to fonn complexes that are anionic in nature. As such, any suitable aqueous synthesis pathway (e.g., the spécifie reagents used or the order of combining reagents) may be chosen to produce the alkaline aqueous ferrie iron sait solutions. Some suitable methods are described below.

[32]As used herein, an “aqueous solution” includes (1) a solution where the predominating solvent (greater than 50% by volume) is water and (2) water. In the case that water is used, the water may be a purified form of water, such as deionized water or distîlled water. As noted above, aqueous medium can be a miscible mixture of water and a water-solubie organic solvent. Such aqueous media are single phase, showing no visible phase séparation. The term solution is used herein to distinguish over suspensions comprising particles and more particularly to dîstinguish solutions comprising ferrie ions complexes in aqueous medium from suspensions containing iron-based précipitâtes. For instance, suspensions of iron oxides such as ferrihydrite, hématite, akaganéite, goethite, lepidocrocite, and magnetite are distinguished from solutions comprising soluble iron ions or soluble, anionic îron-carbonate complexes. In embodiments herein, solutions, even when colored, are generally transparent on visual inspection. In embodiments herein, solutions hâve no suspended particles on visual inspection. In embodiments herein, solutions after being subjected to centrifugation do not hâve a solid pellet by visual inspection. In embodiments herein, solutions that are filtered through 0.3 micron filter paper show no visible solid particles on the filter. In embodiments herein, the solution may be a colloid solution as that term is understood in the art. In embodiments herein, ttie solution is not a colloid solution as that term is understood in the art. In embodiments herein, the solution does not exhîbit a Tyndall effect as that effect is understood in the art.

[33] The term solution is used herem as broadly as it is used in the art. In an embodiment, the term solution refers to a solution of a solid, particularly a sait, in water or an aqueous medium. Herein, a solid is soluble in water or an aqueous medium, if 1 or more grams of the solid dissolve in 100 mL of water or the aqueous medium, which may be an alkaline buffer. In

Page 9 of 42

Sôm,.

me embodiments, preferred solids and salts of this invention are very soluble in water or an aqueous medium such that 2 or more grams of the solid or sait dissolve in 100 mL of water or aqueous medium, such as alkaline buffer. Solubility is assessed at ambient room température (25 °C) and ambient pressure (1 atmosphère). It will be appreciated that solubility of a given solid in a given solvent can be affected by the presence of other solutés in the water or aqueous medium. In embodiments, certain salts and solids of this invention are soluble in water or aqueous medium such that 0.1 gram or more of sait or solid dissolves in 100 mL of the water or aqueous medium. In embodiments, certain salts and solids of this invention are soluble in water or aqueous medium such that 0.5 gram or more of sait or solid dissolves in 100 mL of the water or aqueous medium. In embodiments, certain salts and solids of this invention are Soluble in water or aqueous medium such that 1 gram or more of sait or solid dissolves in 100 mL of the water or aqueous medium. In embodiments, certain salts and solids of this invention are soluble in water or aqueous medium at a level of 5 or more grams/100 mL water or medium, fn embodiments, certain salts and solids of this invention are soluble in water or aqueous medium at a level of 50 or more grams/100 mL water or medium.

[34] In one embodiment, reacting the reagents comprises combining a first aqueous solution and a second aqueous solution. In one embodiment, the first aqueous solution comprises the at least one ferrie iron sait reagent and the second aqueous solution comprises the at least one alkali métal carbonate sait reagent. The first aqueous solution and/or the second aqueous solution may comprise at least one of the one or more organic addîtives. Furthermore, at least one of the one or more organic additives may be added to the produced alkaline aqueous ferrie iron solution.

[35] As noted above, the required reagents are at least one ferrie iron sait and at least one alkali métal carbonate sait. Due in part to the acidic nature of the at least one ferrie sait and the basic nature of the alkali métal carbonate sait, the contacting step results in a vigorous, somewhat exothermic reaction that generates carbon dioxide gas. At least some of the ..p: .1.· .

generated carbon dioxide is released from the reaction mixture as a gas. In an embodiment, 10% or more of the total CO2 in carbonate is released. In embodiments, up to 20% of the total carbonate in CO2 is released.

[36] As used herein, “organic additives” means any molécule having at least one carbon atom and at least one hydrogen atom. Organic additives include among others include one or more chelating agent. Organic addîtive reagents may be included in any suitable form. For

'.or .

Page 10 of 42 instance, ethylenediaminetetraacetic acid (“EDTA”) may be included in its acidic foim (EDTA) or any of its sait forms (e.g., NajEDTA, Na4EDTA, K2EDTA and K4EDTA).

[37] In some embodiments, the reacting comprises fully combining the at least one ferrie iron sait reagent with the alkali métal carbonate sait reagent to produce the alkaline aqueous ferrie iron solution. In an embodiment, ferrie iron reagent is converted on reaction to a watersoluble alkaline ferrie iron sait. The resulting alkaline aqueous ferrie iron sait solutions are preferably free of particles, such as iron-based particles. In embodiments, a step of filterîng, settling, or centrifugation can be employed to remove precipitate formed on reaction, so long as the filtered or centrifuged solution is stable to further précipitation of solid or sait from the solution. In embodiments, no step of filterîng, settling, or centrifugation is required because a fully soluble solution is formed.

[38] The presence of particles, particularly iron-oxide- or oxyhydroxide-based particles, in the alkaline aqueous ferrie iron solution is not preferred for several reasons. For instance, contacting the alkaline aqueous ferrie iron solutions with a reduced sulfur-containing fluid and exposing the resulting solution to an oxidizing agent produces elemental sulfur. Elemental sulfur is insoluble in water and in the alkaline aqueous ferrie iron solutions of the présent invention. Accordingly, the elemental sulfur is generally removed by a simple liquîd-solid séparation process that results in high recovery of the alkaline aqueous ferrie iron solution, thus minimizing ioss of the active ferrie iron. Conversely, iron-based particles tend to embed themselves in elemental sulfur, thereby resulting in the loss of ferrie iron in such liquid-solid séparation processes. Thus, the presence of iron-based particles in alkaline aqueous ferrie iron solutions is not preferred. Furthermore, while not being bound by any theory, it is believed that the presence of particles (e.g., iron-based particles) may promote (e.g., catalyze) the formation of other, chemically unreactive or less reactive iron-based particles from the alkaline aqueous ferrie iron solutions, resulting in the loss of active iron as a reduced sulfur capture agent.

[39] As noted above, the alkaline aqueous ferrie iron sait solutions are preferably free of particles (e.g., free of iron-based particles). However, the inventors of the présent invention hâve found that particles may sometimes form after production of more highly concentrated alkaline aqueous iron solutions. For instance, an alkaline aqueous ferrie iron solution that is supersaturated with ferrie iron may be thermodynamically unstable and precipitate iron-based particles. In some instances, these alkaline aqueous iron solutions are free of any organic additives. However, such iron-based particles may be dissolved into solution with the addition of organic additives at low concentrations (e.g., sub-stoîchiometric) as described herein.

Page 11 of 42 addîÈT''

Altematively, such particles may be fïltered from the solution. Unexpectedly, the inventors of the présent invention hâve found that an alkaline aqueous ferrie iron solution comprising at least some particles (e.g., iron-based particles) may be contacted with a reduced sulfurcontaining fluid and subsequently exposed to an oxidizing agent, e.g., air or oxygen, thereby producing an alkaline aqueous ferrie iron solution that is free of particles.

[40] As used herein, “free of particles” means that an alkaline aqueous ferrie iron solution is visually free of any particles. In one embodiment, an alkaline aqueous ferrie iron solution is free'ôf iron-based particles. As used herein, “iron-based particles” means any particles (e.g., précipitâtes) comprising iron that may form during or after production of alkaline aqueous ferrie iron sait solutions. For instance, iron-based particles may be iron oxides, iron oxyhydroxides, mixed métal oxides and any combinations thereof. In one embodiment, an alkaline aqueous ferrie iron solution is free of iron oxide particles (e.g., ferrihydrite, hématite, akaganéite, goethite, lepidocrocite, and magnetite).

[41] Iron-based particles can be detected in general by any analytical method known in the ait - ^JFor example, iron-based particles can be detected by filtration of any precipitate from liquid medium followed by analyzing the precipitate using inductively coupled plasma (TCP).

ii. Additional Methods

[42] As noted above, alkaline aqueous ferrie iron sait solutions may be produced and subsequently empioyed for the treatment of fluids comprising reduced sulfur compounds (e.g., H2S). In addition to such synthèses, alkaline ferrie iron sait solutions can be produced from intermediate forms, includîng at least partially reacted solid mixtures and at least partially reacted wet solid mixtures. For instance, such at least partially reacted mixtures may be produced by combining solids of a ferrie iron sait reagent and an alkaline carbonate sait reagent, optionally with one or more first organic addîtives, followed by forceful mixing (e.g., bail milling) to react at least some of the reagents. The term ferrie iron sait reagent is used to designate the ferrie iron sait that is used to préparé the solutions of the invention and to distinguish that sait reagent from the soluble ferrie iron sait that is formed during préparation. This mixing may be done in the absence of added water (note that water can be présent in salts and solids, such as is présent in the ferrie nitrate hexahydrate sait and/or ferrie nitrate nonohydrate sait) or with an amount of water or aqueous medium that is insufficîent to fully SOlubiîize and react the ferrie iron sait and/or alkali métal carbonate reagents. The solution is then prepared by adding water or aqueous medium to fully solubilize the ferrie iron sait formed on reaction.

Page 12 of 42 iit Drying and Rehydration

[43] After their production, the alkaline aqueous ferrie iron sait solutions, those thaï are concentrated, may be diluted for use in treating reduced sulfur-containing fluids. It has been found that diluting alkaline aqueous ferrie iron sait can be done by adding a concentrated alkaline aqueous ferrie iron solution to an aqueous alkali métal carbonate solution or an aqueous alkali métal carbonate-bicarbonate buffer. In an embodiment, for example, the concentrated alkaline aqueous ferrie iron solution is added to an aqueous alkali métal carbonate-bicarbonate buffer (e.g., an aqueous potassium carbonate-bicarbonate buffer) of pH range 8.5-11. Diluting alkaline aqueous ferrie iron sait solutions in an aqueous métal carbonate or aqueous métal carbonate-bicarbonate buffer may be preferred as it has been found that substantially diluting alkaline aqueous ferrie iron solutions with aqueous solutions at circumneutral pH (e.g., distilled water, deionized water) may lead to the formation of iron-based particles.

[44]'³ After their production, alkaline aqueous ferrie iron sait solutions may be dried to form a solid ferrie iron-containing sait mixture that may be rehydrated to form alkaline aqueous ferrie iron sait solutions. For instance, the drying may be performed by évaporation or spray drying and combinations thereof, among other methods. After drying, the solid materials may be rehydrated, for instance, using an aqueous solution (e.g., water), an aqueous alkali métal carbonate solution and/or an aqueous alkali métal carbonate-bicarbonate buffer solution (e.g., an aqueous potassium carbonate-bicarbonate buffer solution). The rehydration solution may be added to the solid material or vice-versa. Such solid ferrie iron-containing mixtures may advantageously be produced at a centralized processing facility, then subsequently diluted at a location doser to the point of usage.

b. Products and Composition i, Alkaline Aqueous Ferrie Iron Solutions

[45] Generally, the resulting alkaline aqueous ferrie iron sait solutions of the présent invention comprise ferrie ions (Fe³), potassium ions (K*), carbonate ions (CCh^2-) and bicarbonate ions (HCO3·). In some embodiments, an alkaline aqueous ferrie iron sait solution further comprises at least some hydroxide ion (OH) or nitrate ion (NOf). In some embodiments, an alkaline aqueous ferrie iron solution comprises one or more organic additives. In some preferred embodiments, an alkaline aqueous ferrie iron sait solution is free of particles. In some embodiments, an alkaline aqueous ferrie iron solution is free of ferrie iron-based particles.

Page 13 of 42

[46] In embodiments, the alkaline aqueous ferrie iron sait solutions hâve a concentration of ferrie iron from 0.005 to 5.0 mols/L. Higher concentration alkaline aqueous ferrie iron sait solutions may be produced with precipîtated solids (e.g., water-soluble iron-based solids) therein that may dissolve upon the addition of an aqueous solution (e.g., water or an alkaline aqueous buffered solution). The pH ofthe alkaline aqueous ferrie iron solutions may generally be from S.O to 13.0. In one embodiment, thepH of an alkaline aqueous ferrie iron sait solution is at least 8.0. In another embodiment, the pH of an alkaline aqueous ferrie iron sait solution îs at least 8.5. In yet another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is at least 9.0. In another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is at least 9.5. In another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is at least 10.0. In yet another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is at least 10.5. In another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is at least 11.0. In yet another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is at least 11.5. In one embodiment, the pH of an alkaline aqueous ferrie iron sait solution is not greater than 13.0. In another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is not greater than 12.5. In yet another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is not greater than 12.0. In another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is not greater than 11.5. In yet another embodiment, the pH of an alkaline aqueous ferrie iron sait solution is not greater than 11.0.

[47]^T In embodiments, the alkaline aqueous ferrie iron sait solution has a pH of at least 8, or at least 8.5, or at least 9, or at least 9.5, or at least 10, or at least 10.5, or at least 11.0; or between 8 and 13.5; or between 8.5 and 13.5; or between 9 and 13.5 or between 10 and 13.5; or between 10.5 and 13.5; or between 11 and 13.5 or between 9 and 12.5; or between 9 .5 and 12; or between 9 and 11; or between 9 and 10; or between 11 and 13.5; or between 11 and 13; or between 11 and 12; or between 12 and 13.5; or between 12 and 13; or 9, or 10 or II or 12 or 13.

kit Solid Products

[48] As noted above, the alkaline aqueous ferrie iron solutions may be produced from an intermediate solid material and/or the solid material produced by drying an alkaline aqueous ferrie iron sait solution (i.e., a “solid ferrie iron-containing material”). Such solid products may hâve the advantage of decreased storage space and lower shippîng costs to the point of use, among others. While not being bound by any theory, it is believed that the ferrie iron sait in these materials may be présent as a complex ferrie métal sait, where the mixed métal sait comprises the ferrie iron ions and one or more of potassium ions, carbonate ions, bicarbonate _; Page 14 of 42 ions, nitrate ions (when présent), hydroxîde ions, and water. In embodiments, the mixed métal potassium/ferric sait formed on reacting as described herein is soluble in water or aqueous medium. In spécifie embodiments, the molar ratio of potassium ions to ferrie ions in the sait is 3 or more. In embodiments, the sait can be a mixture of one or more of such mixed métal salts. In an embodiment, the sait comprises K6[Fe2(OH)2(CO3)s]. In spécifie embodiments, the molar ratio of potassium ions to ferrie ions in the alkaline aqueous sait solution is 6 or more, or 6.6 or more, or 7 or more, or 8 or more, or 9 or more, or 10 or more, or 11 or more, or 12 or more.

[49] In embodiments, salts and solids of the invention do not contain nitrate ions at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or ai levels greater than 10 ppm or at detectible levels. In embodiments, salts and solid of the invention do not contain chloride ions (Cl') at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or at levels greater than 10 ppm or at detectible levels. In embodiments, salts and solid of the invention do not contain halide ions (e.g., Cl', Fl, Bf) at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or at levels greater than 10 ppm or at detectible levels. In embodiments, salts and solid of the invention do not contain sodium chloride (NaCl) at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or at levels greater than 10 ppm or at detectible levels. In embodiments, salts and solid of the invention do not contain sodium halide at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or at levels greater than 10 ppm or at detectible levels. In embodiments, salts and solid of the invention do not contain sulfate ions at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or at levels greater than 10 ppm or at detectible levels. In embodiments, salts and Solids of the invention do not contain sodium ions greater than the amount that is added with ftié one or more organic additive that may be présent, such as Na2EDTA. In embodiments, salts and solids of the invention do not contain sodium ions at levels greater than 10,000 ppm, or at levels greater than 1,000 ppm, or at levels greater than 100 ppm or at levels greater than 10 ppm or at detectible levels.

[50] In addition to using solid ferrie iron-containing materials to produce alkaline aqueous ferrie iron sait solutions, the solid ferrie iron-containing materials themselves may be useful in their solid form to treat reduced sulfur containing fluids. For instance, a solid ferrie ironôontaining material may be processed into particles (e.g., impregnated into an inert substrate) that may be used as packing in a column for treating reduced sulfiir-containing fluids.

Page 15 of 42 ^u ' iii. Composition

[51] As noted above, the products resulting from the synthesis methods of sections a.i and a.ii generaliy comprise (and in some instances, consist of, or consist essentially of) ferrie iron, potassium, carbonate, bicarbonate, hydroxîde, and optionally nitrate, optionally with one or more organic additives. The compositions of such products are described in greater detail below. For the purposes of this section, the term, “products” includes alkaline aqueous ferrie iron sait solutions and solid ferrie iron-containing materials.

[52]^;,J In one embodiment, a product comprises ferrie iron (e.g., ferrie ions) and one or more organic additives, where a molar ratio of the ferrie iron to each of the organic additives is greater than 2.0. In this regard, the molar ratio of the one or more organic additives to the ferrie iron may be sub-stoichiometric, meaning that the product comprises more moles of iron than the organic additive. The use of sub-stoichiometric amounts of organic additives relative to iron offers significant cost savings and other benefits. The method herein provides significant cost improvements over existing technologies (e.g., LoCat, Streamline, Eco-Tec) that require utilizing organic additives, such as chelating agents that are présent in stoichiometric équivalent amounts, or more frequently in a stoichiometric excess of the ferrie iron. In yet another embodiment, the molar ratio is at least 2.0. In another embodiment, the molar ratio is at least 3.0. In yet another embodiment, the molar ratio is at least 4.0. In another embodiment, the molar ratio is at least 5.0. In yet another embodiment, the molar ratio is at least 7.5. In another embodiment, the molar ratio is at least 10. In yet another embodiment, the molar ratio is at least 15. In another embodiment, the molar ratio is at least 50. In one embodiment, the molar ratio is not greater than 1000. In another embodiment, the molar ratio is not greater than 100. Such above-descrîbed molar ratios apply individually to any first organic additives, second ôrgâhic additives, and so on and so forth that are présent in the product.

[53] The production of water soluble alkaline ferrie iron solutions at pH above 8.0 containing no or sub-stoichiometric ratios of organic additives to ferrie iron distinguishes the technology described herein and offers significant cost savings and other advantages relative to competing H? S control chemistries that use high ratios of organic additives, such as chelating agents, to solubîlize iron. Specifically, the alkaline ferrie salts produced by these methods are believed to be inherently soluble in water or aqueous medium, and do not require high ratios of expensive chelating agent to solubilize the iron at high pH. In embodiments, alkaline ferrie sàlts produced by these methods are believed to self-assembled into ferrie-carbonate complexes that are anionic in nature and that are inherently soluble in water or aqueous medium, and do not require high ratios of expensive chelating agent to solubilize the iron at high pH. It is Page 16 of 42 fi-' ' believed that the majority of ferrie ions in the alkaline solutions described herein are not chelated by organic chelating agents, and they are able to freely contact and react with reduced sulfur compounds in a reduced sulfur-contaming fluid. The ability to react directly with hydrogen sulfïde and form ferrous sulfide provides what is believed to be a novel and much more efficient reaction pathway for capture and oxîdation of hydrogen sulfide. This reaction pathway is understood to capture the sulfur atoms from 1.5 hydrogen sulfide molécules for every iron atom. In contrast, competîng H2S control technologies that utilize 1:1 or hîgher ratios of organic addîtives to iron ions must rely on indirect électron transfer across the organic chelating agents embedding the iron ions, which is kinetically slower and requires two iron ions to oxîdize one H2S molécule. It is currently believed that the rôle of the low levels of organic additives used in the technology described herein is to scavenge relatively low levels of free (i.e., non-complexed) ferrie ions to prevent them from combining to form iron oxide particles. Because most of the iron ions are at any moment are either complexed with sulfide (as iron sulfide, after H2S capture) or complexed with carbonate, bicarbonate and potassium as a water-soluble ferrie sait (before hydrogen sulfide capture and after oxidative régénération) there are believed to be few free ferrie ions in solution, and hence little chance to form ferrie oxide particles. It is believed that trace or low-level amounts of organic additives, as described herein, help scavenge low levels of free ferrie ions, further reducing the possibility of iron particle formation.

[54] In one embodiment, a product comprises ferrie iron (e.g. ferrie ions) and one or more organic additives, where a molar ratio of the ferrie iron to the organic additives, in total, is greater than 2.0. In y et another embodiment, the molar ratio is at least 2.5. In another embodiment, the molar ratio is at least 3.0. In yet another embodiment, the molar ratio is at least 4.0. In another embodiment, the molar ratio is at least 5.0. In yet another embodiment, the molar ratio is at least 7.5. In another embodiment, the molar ratio is at least 10. In yet another embodiment, the molar ratio is at least 15. In another embodiment, the molar ratio is at least 50. In one embodiment, the molar ratio is not greater than 1000. In another embodiment, the molar ratio is not greater than 100. Such above-described molar ratios also apply to the sum of ail organic additives present in the product.

In embodiments, of products herein, including solutions and solids, the molar ratio of the ferrie iron to each of the one or more organic additives is greater than 1, or at least 1.5, or at least 2, or at least 2.5, or at least 3, or at least 4, or at least 5, or at least 7.5, or at least 10, or at least 15, or at least 50; or between 1.1 and 50; or between 1.5 and 50; or between 2 and 50;

Page 17 of 42 or between 3 and 50; or between 4 and 50; or between 5 and 50; or between 7.5 and 50; or between 10 and 50; or between 15 and 50; or between 10 and 100; or between 50 and 100.

[56] Suîtable organic additives may comprise one or more functionai groups, such as one or more hydroxyl groups, one or more carboxylic acid groups and one or amino groups, among ’others. In one embodiment, an organic additive is a polyol (i.e., an organic additive having at least two hydroxyl groups). In one embodiment, an organic additive is a sugar alcohol (i.e,, having a Chemical formula CnHm+zOn). In one embodiment, an organic additive is a linear sugar alcohol, such as any of the C3-C24 linear sugar alcohols. In one embodiment, an organic additive is a sugar alcohol, where the sugar alcohol is sorbitol (e.g., D-sorbitol, or L-sorbitol and combinations thereof). Other sugar alcohols that may be used include one or more of glycerol, erythritol, threitol, mannitol, galactitol, iditol, arabitol, ribitol, xylitol, volemitol, lactïtol, maltotriitol, maltotetraitol, and polyglycîtol. Any of the D- or L- isomers of these compounds may be used, as well as mixtures thereof (e.g., racemic mixtures).

[57] Other polyol organic additives that may be suitable include monosaccharides, disaccharides, oligosaccharides and polysaccharides. In one embodiment, an organic additive is a polysaccharide, where the polysaccharide is pectin. Furthermore, extracts of plants, partîcularly extracts of fruits, leaves or stems of fruits may be used as an organic additive. For instance, an extract of fruit of the genus Prunus, or the leaves of the genus Prunus, or the stems of the genus Prunus and combinations thereof may be used. The extracts of fruits, leaves ànd/or stems of other plants may similarly be used.

[58] In one embodiment, an organic additive comprises at least one carboxylic acid group. In one embodiment, an organic additive comprises at least one amino group. In one embodiment, an organic additive is an aminopoly carboxylic acid (i.e., having at least one amino group and at least two carboxylic acid groups). In one embodiment, an aminopolycarboxylic acid is ethylenediaminetetraacetic acid (“EDTA”), While not being bound by any theory, it is believed that aminopolycarboxylic acids such as EDTA improve the rate of oxidation of reduced alkaline iron sait solutions.

[59] ' As noted above, the new alkaline aqueous ferrie iron sait solutions may comprise at least some nitrate ions (NOE). While not being bound by any theory, it is believed that nitrate anions may increase the solubility of the ferrie iron relative to the counter-ions of other commercially available ferrie salts (e.g., ferrie chloride, ferrie sulfate). Furthermore, nitrate ions may hâve additional benefits, such as being less corrosive than other ions (e.g., halides) to Steel, aluminum and other materials that may be exposed to the alkaline aqueous ferrie iron sait solutions during commercial operation. In one embodiment, a product comprises a molar ratio . Page 18 of 42 of nitrate to ferrie iron of at least 1.0. In another embodiment, a product comprises a molar ratio of nitrate to ferrie iron of at least 1.2. In yet another embodiment, a product comprises a molar ratio of nitrate to ferrie iron of at least 1.5. In another embodiment, a product comprises a molar ratio of nitrate to ferrie iron of at least 2.0. In yet another embodiment, a product comprises a molar ratio of nitrate to ferrie iron of at least 2.5. In another embodiment, a product comprises a molar ratio of nitrate to ferrie iron of at least 3.0.

[60] The alkaline aqueous ferrie iron sait solution as a concentrate or in diluted form does not corrode iron or carbon Steel.

[61] As noted above, the new alkaline aqueous ferrie iron sait solutions generally comprise at least some potassium (K⁺). While not being bound by any theory, it îs believed that potassium cations increase the solubility of the ferrie iron-carbonate complex, and may act as counter-ions to the negatively charged ferrie iron-carbonate complexes. In one embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 1.0. In another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 2.0. In yet another embodiment, a molar ratio of potassium to ferrie iron of at least 3.0. In another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 4.0. In yet another embodiment, a molar ratio of potassium to ferrie iron of at least 5.0. In another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 6.0. In yet another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 7.0. In yet another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 9.0. In yet another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 10. In yet another embodiment, a product comprises a molar ratio of potassium to ferrie iron of at least 12.

[62] In concentrâtes of the alkaline ferrie iron sait solutions herein the ratio of potassium ion to ferrie ion ranges from 6 to 11 and more preferably 6.6 to 12. In a spécifie embodiment, the ratio of potassium ion to ferrie ion in the solution concentrâtes ranges from 8.5 to 9.5 or from 8.9 to 9.1. In an embodiment, the ratio of potassium ion to ferrie ion in the solution concentrâtes is 9.

[63] In solutions prepared by dilution of solution concentrâtes, which are working solutions used to scrub reduced sulfur compounds from fluids, in embodiments, the ratio of potassium ion to ferrie ion is generally very high largely because concentrâtes are typically diluted using potassium carbonate/bicarbonate buffers. For example, in diluted working solutions, the ratio of potassium ion to ferrie ion can be greater than 20, or greater than 50 or greater than 75, or

Page 19 of 42 fit greater than 1Q0. In spécifie diluted working solutions, the ratio of potassium ion to ferrie ion is 65 or 95.

[64] Unlike other liquid redox technologies used to scrub reduced sulfur compounds from fluîds the aqueous alkaline ferrie iron sait solutions described herein do not produce any détectable sulfate when oxidized, and do not lose alkalinity during multiple H2S captureregeneration cycles. In laboratory tests, samples of the aqueous alkaline ferrie iron sait solutions that had undergone repeated H2S capture/regeneration cycles were neutralized to pH 7 and tested with Quantofix sulfate test strips (Machery-Nagel, Duren, Germany). No evidence of sulfate was observed (<200 mg/L). In addition, repeated H2S capture régénération cycles, even in the presence of 40% CO2 gas streams, did not resuit in graduai loss of alkalinity, as would be expected if sulfate or thiosulfate was produced during sulfide oxidation. During a Ίmonth pilot project utilizing the saine 70 liter batch of the aqueous alkaline ferrie iron solution observed pH’s never dropped below 8.5. It appears that virtually ail captured sulfide is in the aqueous alkaline ferrie iron solutions described herein is converted to elemental sulfur, not sulfate or thiosulfate.

[65] “ The absence of sulfate l thiosulfate production and rétention of alkalinity by the aqueous alkaline ferrie iron complex described herein are major advantages over competing liquid redox processes for H2S removal. While not bound by any theory it is believed that the direct reaction of reduced sulfur compounds with the ferrie iron-carbonate complex to form iron sulfide immediateiy removes virtually ail captured sulfide ions from the solution, which in turn prevents the formation of sulfate and loss of alkalinity during oxidative régénération. In LoCat and similar liquid redox technologies sulfide is initially captured by an alkaline buffer, with no direct conversion to iron sulfide. The captured sulfide ions are partially oxidized to sulfate and thiosulfate during régénération. As a resuit, the solution gradually loses alkalinity and requires a regular purge stream to remove the accumulated sulfate, as well as regular addition of sodium hydroxi de or other bases to retain alkalinity. In embodiments, the aqueous alkaline ferrie iron sait solutions described herein, when used to scrub fluids containing reduced sulfur compounds (particularly H2S), do not produce any détectable sulfate when oxidized, and do not lose alkalinity during multiple H2S capture-regeneration cycles. In embodiments, the level of sulfate produced in the aqueous alkaline ferrie iron sait solutions when used in such scrubbing applications is less than 500 mg/L. In embodiments, the level of sulfate produced in the aqueous alkaline ferrie iron sait solutions when used in such scrubbing applications is less than 400 mg/L. In embodiments, the level of sulfate produced in the aqueous alkaline ferrie iron sait solutions when used in such scrubbing applications is less than 300 mg/L. In embodiments,

Page 20 of 42 eSafe the level of sulfate produced in the aqueous alkaline ferrie iron sait solutions when used in such scrubbing applications is less than 200 mg/L.

c. Methods of Using Alkaline Aqueous Ferrie Iron Solutions

[66] As noted above, the alkaline aqueous ferrie iron sait solutions of the présent invention may be used to treat reduced sulfur-containing fluids. For instance, the new alkaline aqueous ferrie iron sait solutions may be used to treat natural gas streams, biogas streams (e.g., from wastewater, landfilis, among others), oil, geothermal vent gas and effluents from paper mills, among others. Furthermore, the new alkaline aqueous ferrie iron sait solutions may be used to treat the effluent from an amine process where the effluent is predominately comprised of acid gases (CO? and H? S). The solid ferrie iron-containing materials described herein may also be useful for treating these types of reduced sulfur-containing fluids.

[67] With reference now to FIG. 1, an embodiment of a method (100) for treating a reduced sulfur-containing fluid is shown. As shown, the method (100) generally comprises first Contacting an alkaline aqueous ferrie iron solution with a reduced sulfur-containing fluid (110). The alkaline aqueous ferrie iron solution comprises ferrie ions (Fe³⁺), potassium ions (K⁺), carbonate ions (COj^2-) and bicarbonate ions (HCCb'), optionally with one or more organic additives. The reduced sulfur-containing fluid generally comprises at least some of at least one reduced sulfur compound, such as H2S.

[68] As used herein, “reduced sulfur compound” means any sulfur compound having an oxidation state of -2. For instance, hydrogen sulfide (H?S) is a compound where the oxidation State of the sulfur is -2. Other reduced sulfur compounds include carbonyl sulfide (COS), carbon disulfide (CS?) and mercaptans. Oxidized forms of sulfur that may be produced using tlie alkaline aqueous ferrie iron solutions of the présent invention include elemental sulfur, which has an oxidation State of 0.

[69] Concomitantly with the contacting (110), the method generally comprises producing a reduced alkaline iron solution or suspension of reduced iron particles, e.g., ferrons sulfide (FeS) or related iron sulfides (120). The producing step (120) generally comprises oxidizing at least some of the at least one reduced sulfur compounds via the alkaline aqueous ferrie iron solution, thereby reducing at least some of the ferrie ions to ferrons ions. The oxidation-reduction reaction generally couverts reduced sulfur compounds such as H? S to ferrons sulfide or elemental sulfur, for instance. Furthermore, the producing step (120) generally comprises producing at least some iron sulfide compounds. While not being bound by any theory, the resulting ferrons ions (Fe²⁺) are understood to ultimately react with the reduced sulfur compounds to form ferrons sulfide (e.g., FeS), which is a black precipitate.

Page 2Ï of 42

[70] Generally, concomitantly to the contacting step (a, 110) and producing step (b, 120), the method (100) comprises discharging a purified fluid containing little or no reduced sulfur compounds. In other words, the purified fluid (outlet fluid) has a substantîally lower concentration of reduced sulfur compounds than the reduced sulfur-containing fluid (inlet fluid)/ For instance, an inlet natural gas stream or inlet biogas gas stream containing H2S may be discharged as a purified gas stream having a substantîally reduced H2S concentration. In this regard, it has been found in laboratory and pilot tests that the alkaline aqueous ferrie iron sait solutions of the présent invention can reduce high concentrations of H2S (e.g., as high as 100,000 ppm) to non-detectable levels. Other “liquid redox” H2S control technologies that use 1:1 or hîgher ratios of chelating agents to ferrie iron hâve trouble reducing H2S to less than 10 ppm in part because the électron transfer process between iron and sulfide is believed to be indirect, through the organic chelating agent. In contrast the current invention is believed to ailôw immédiate and direct reaction between ferrie iron and hydrogen sulfide, forming ferrous sulfide.

[71 ] After or concomitantly with the contacting (110) and producing ( 120) steps, the method generally comprises exposing the reduced alkaline iron solution or suspension of ferrous sulfide particles to an oxidizing agent (130). Suitable oxidizing agents may include oxygen (e.g., in air) and hydrogen peroxîde, among others. The exposing step (130) thereby produces a regenerated alkaline aqueous ferrie iron sait solution. Furthermore, this step generally comprises producing at least some elemental sulfur (e.g., from the ferrous sulfide formed in the producing step (120)). Thus, the regenerated alkaline aqueous ferrie iron solution is generally a mixture of solid elemental sulfur and the alkaline aqueous ferrie iron solution. The contacting (110), producing (120) and exposing (130) steps may be repeated at least one time. Due to the reduced alkaline aqueous ferrie iron solution’s ability to be regenerated back into an alkaline aqueous ferrie iron sait solution, it has been found that these steps may be repeated indefmitely. [72] In addition, elemental sulfur can periodically or continuously be separated (140) from the regenerated alkaline iron solution.

[73] Unexpectedly, the inventors hâve found that performing the contacting (110), producing (120) and exposing steps (130) on an alkaline aqueous ferrie iron solution that comprises at least some iron oxide-based particles may be bénéficiai for reducing the concentration of such iron-based particles. For instance, it has been found that the iron-based particles may be reduced or eliminated completely via these steps (110, 120 and 130). Thus, in one embodiment, prior to the contacting step (110), an alkaline aqueous ferrie iron solution comprises at least some iron-based particles, and due to the contacting step (110), producing

Page 22 of 42 rr.¹ step (120) and the exposing step (130), the regenerated alkaline aqueous ferrie iron solution has a reduced concentration of iron-based particles (e.g., free of iron-based particles). It is believed that hydrogen sulfide may attack the iron oxide particles and upon oxidation they revert to the soluble aqueous alkaline ferrie iron sait.

[74] In some embodiments, the contacting step (110), producing step (120) and exposing step (130) occur concomîtantly. For instance, a scrubbing column utilizing an alkaline aqueous ferrie iron sait solution may be contacted with a reduced sulfur-containing fluid and exposed to an oxidizing agent concomîtantly. An example of where this might be useful is for odor control (e.g., in the production of paper or municipal wastewater treatment). Odiferous fluids containing reduced sulfur compounds such as FFS that are not présent in a concentration sufficient to be a combustion hazard may be combined with an oxidizing fluid such as air. The resulting gas mixture may be passed through a scrubbing column. A similar process may be used in the treatment of an acid gas effluent from an amine process, which may be low in combustible hydrocarbons. These examples differ from natural gas stream or biogas stream where there is a safety concem of adding an oxidant (e.g., O2) to a combustible fluid (e.g., methane).

[75] As noted above, elemental sulfur is produced via the method (100). Thus, the method (100) generally produces a solid-Hquid mixture, where the liquid component is an alkaline aqueous ferrie iron sait solution, and the solid component comprises (or consists essentially of) elemental sulfur. Thus, the solid elemental sulfur may be separated from the alkaline aqueous ferrie iron solutions via any suitable solid-liquid séparation technique. For instance, the solid elemental sulfur may be readily separated from the regenerated alkaline aqueous ferrie iron solution by passing the solid-liquid mixture through a barrier that is at least partially impénétrable by the elemental sulfur, such as a sieve and/or filter. Additional séparations may be employed to further purify the elemental sulfur and/or recover the alkaline aqueous ferrie iron solution. For instance, the sulfur-rich solid-liquid mixture may be heated under pressure to form elemental sulfur, which readily séparâtes from the alkaline aqueous ferrie iron sait solution. Furthermore, the sulfur-rich solid-liquid mixture may be separated via froth flotation. [76] With reference to FIG. 2, an exemplary System (200) of the invention for removing a reduced sulfur compound, such as H2S, from a reduced sulfur compound-containing fluid is schematically illustrated. A réservoir also termed a primary accumulator (205) is provided for holding the alkaline aqueous ferrie iron solution (scrubber solution). It is also to this primary accumulator (205) that regenerated scrubber solution is retumed after régénération.

Page 23 of42

[77] Scrubber solution is pumped, e.g., via centrifugal or displacement pump (206), to scrubber column (210, also termed a contacter) through fill conduit (207). Scrubber solution îs întroduced to the scrubber column (210), for example, through a plurality of sprayers (208). The scrubber column (210) is optionally provided with fdler (211), preferably a high-surface area filler, (e.g., column packing, such as random column packing) to enhance contact between the fluid to be scrubbed and the scrubber solution. In an embodiment, scrubber solution cscades downward, via gravity, through the filler (211). The fluid to be scrubbed, illustrated as a gas containing reduced sulfur compound, such as biogas, is întroduced into the scrubber column via inlet conduit (221) though a gas înlet (220) which facilitâtes dispersai of the reduced sulfurcontaining gas into the scrubber column in contact with scrubber solution. Scrubbed gas from which reduced sulfur compound(s) hâve been removed exits the scrubber column (210) via gas outlet conduit (222). The flow rate of reduced sulfur-containing gas and scrubber solution into the scrubber column is adjusted to decrease the reduced sulfur compound level(s) in the gas to a desired level. In an embodiment, at least 98% (v/v) of the reduced sulfur compound can be removed from the reduced sulfur-containing fluid. In an embodiment, at least 98% (v/v) of H2S présent can be removed from the reduced sulfur-containing fluid. In an embodiment, at least 99% (v/v) of H2S présent can be removed from the reduced sulfur-containing fluid. In multiple laboratory and pilot tests H2S removal was greater than 99.9%

[78] Ferrie iron in the scrubber solution is at least partially reduced to ferrous iron on contact with the reduced sulfur-containing fluid. In addition, after contact with the reduced sulfurcontaining fluid, the at least partially reduced scrubber solution contains sulfur, particularly in the form of iron sulfide and more particularly as FeS. The at least partially reduced scrubber solution may also contain precipitated elemental sulfur. At least partially reduced scrubber solution includîng iron sulfide and any precipitated elemental sulfur is pumped from the sump tegiori (213) of the scrubber column (210) through sump conduit (214) to régénération tank (230) via sump pump (216, e.g., a centrifugal pump). Ferrous iron is oxidîzed to ferrie iron and elemental sulfur is formed in the régénération tank (230). The régénération tank is provided with an air inlet (231) to provide oxygen for régénération of the at least partially reduced scrubber solution to form elemental sulfur. Air is optionally dispersed into the at least partially reduced scrubber solution via one or more dispersers (232, e.g., gas spargers).

[79] Elemental sulfur formed on régénération (i.e., via the oxidation by air) floats to the top àf the liquid in the régénération tank (230) and spills into weir (234) provided for collection of elemental sulfur and a portion of the regenerated scrubber solution (elemental sulfur-rich regenerated scrubber solution). Regenerated scrubber solution without elemental sulfur is

Page 24 of 42 collected from the régénération tank via collection conduit (239), for example by gravity flow, and retumed to the primary accumulator (205). Sulfur-rich regenerated scrubber solution may be passed through a bubble trap (235) to remove entrained gas and is collected in the sulfurrich accumulator (240). Collected sulfur-rich regenerated scrubber solution is passed to sulfur filter (242) where elemental sulfur is separated from regenerated scrubber solution and is washed via wash water feed (243). The separated regenerated scrubber solution is collected in accumulator (244) and pumped through return conduit (247) via return pump (246) to primary accumulator (205). Separated sulfur that has been substantially dried is passed to the dry sulfur accumulator (250).

[80] The system as illustrated is typically operated continuously with a selected flow of scrubber solution and reduced sulfiir-containmg fluid into the scrubber column (210) to achieve the desired level of reduced sulfur removal. At least partially reduced scrubber solution is continuously conveyed to the regenerator tank and regenerated scrubber solution is retumed to the primary accumulation tank. In the illustrated system, sulfur filtration is performed pefiodically in a batch-wise mode when a preselected amount of elemental sulfur has accumulated. The illustrated scrubber column (210) is one example of a number of known means for contacting a scrubber solution with a fluid. For instance, other means for contacting a scrubber solution with a reduced sulfur-containing fluid include fluid filled contactors (i.e., absent filier (211)), static mixers and Venturi Systems. One of ordinary skill in the art can readily choose an appropriate known contactor configuration for a given application for removal of reduced sulfur from a given fluid.

d. Misceilaneous

[81] As noted above, the alkaline aqueous ferrie iron sait solutions of the présent invention exhibit important advantages over the prier art. For instance, the alkaline aqueous ferrie iron sait solutions may be produced via various methods that reduce costs, and alkaline aqueous ferrie iron solutions may be used in an H2S capture-oxidative régénération cycle to treat reduced sulfiir-containing fluids. An additional advantage is that the alkaline aqueous ferrie iron solutions may be at least partially frozen and then thawed without negatively impacting the ability of the solution to treat reduced sulfur-containing fluids. Although crystallization of the solution may occur at low températures (e.g., 1-5°C), upon heating to room température the crystals dissolve, reconstituting the active alkaline aqueous ferrie iron sait solutions. Thus, alkaline aqueous ferrie iron sait solutions may be stored from minus 20°C to 55°C without the need for température régulation. This differs from technologies thatutilize particles suspended

Page 25 of 42 in a solution (e.g., iron oxide slurries) that may not recover their ability to treat reduced sulfurcontaining fluids after heating or a single freeze-thaw cycle.

[82] When a Markush group or other grouping is used herein, ail individual members of the group and ail combinations and sub-combinations possible of the group are intended to be îndividually included in the disclosure. Every formulation or combination of components described or exemplified can be used to practice the invention, unless otherwîse stated. Spécifie names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently.

[83] One of ordinary skill in the art will appreciate that methods, including préparation methods and analytical methods, materials and device and System éléments other than those specifically exemplified can be employed in the practice of the invention without resort to undue expérimentation. Ail art-known functional équivalents of any such methods or materials are intended to be included in this invention.

[84] Whenever a range is given in the spécification, for example, a composition range, a range of process conditions, a range of pressures or températures or the like, ail intermediate ranges and sub-ranges, as well as ail individual values included in the ranges given are intended to be included in the disclosure. Ail ranges listed in the disclosure are inclusive of the range endpoints listed.

[85] The invention illustratively described herein suitably may be practiced in the absence of any element or éléments, limitation or limitations that is not specifically dîsclosed herein.

[86]¹¹ Without wishing to be bound by any particular theory, there can be discussion herein of beliefs or understandings of underlying pnnciples or mechanisms of action relating to the invention. It is recognized that regardless of the ultimate correetness of any mechanistic explanation or hypothesis, an embodiment of the invention can nonetheless be operative and useful.

[87] AH references throughout this application, for example patent documents including issued or granted patents or équivalents; patent application publications; and non-patent lîterature documents or other source material; are hereby incorporated by reference herein in tiièir entireties, as though îndividually incorporated by reference.

[88] Sengupta AK and Nandi AK (1974) “Complex Carbonates of Iron (III) Z, anorg. Allg. Chem., 403, 327-336 and references cited therein are each incorporated by reference herein in its entirety for description of complex carbonate salts of Fe(III) and certain water-soluble salts of Fe(III). The reference also includes descriptions of the synthesis of the sait Ké[Fe2(OH)2(CO3)5]· H?O and methods of identifying and characterizing such salts, by Page 26 of 42

U.V./visîble spectroscopy and Infrared spectroscopy, among others. The reference includes visible spectra (Figure. 1, therein) of 1.198 mg Fe³⁺ in KHCO3 solution (35%) which exhibits a maximum absorbance at 460 nm. The description of such methods and the characterization of salts is incorporated by reference herein.

[89] All patents and publications mentioned in the spécification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the State of the art, in some cases as of their filing date, and it is intended that this information can be employed herein, if needed, to exclude (for example, to disclaim) spécifie embodiments that are in the prior art. The ternis and expressions which hâve been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any équivalents of the features shown and described or portions thereof, but it is recognized that varions modifications are possible within the scope of the invention claimed. Thus, it shouid be understood that although the présent invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

îlP'ÎTi’

Page 27 of42

THE EXAMPLES EXAMPLE 1

[90] A panel of experiments was performed using a variety of ferrie salts and alkali métal bases. Pairwise combinations of (1) dry powders of the ferrie salts (FeCh, FeafSO^S’X^O and Fe(NO3)y9H2O) and (2) the alkali métal bases (NaOH, KOH, Na2CÛ3, K2CO3, NaHCÛ3, and KHCO3) were placed in test tubes. The alkali métal bases were added in a ratio of 6.8 to 1 with respect to the moles of alkali métal to the moles of iron. Approximately 5 mL of water was added to each test tube and each test tube was shaken to completely mix the water with the ferrie sait and alkali métal base. In the case of alkali métal carbonates, a vigorous reaction with CO2 production occurred. The resulting mixture for each experiment was then visually observed for presence of particies (e.g., iron oxide particles). The results of the panel of experiments are summarized in Table 1, below. A désignation of “PPT” indicates that précipitâtes were observed în the resulting mixture.

TABLE 1

Chemicals used and the level of ~ their purity.	Base
NaOH	KOH	NajCOs	K2CO3	NaHCO₃	KHCO3	K2CO3+ KHCO3*
FeCh (anhydrous)	PPT	PPT	PPT	PPT	PPT	PPT	PPT
Fe₂(SO₄)3-9H2O	PPT	PPT	PPT	PPT	PPT	PPT	PPT
Fe(NO3)3-9H₂O	PPT	PPT	PPT	Soluble	PPT	PPT	PPT

*Approximately 2 moles of bicarbonate salts were used for each mole of carbonate salts, to maiiitain comparable alkali métal concentrations.

[91] As shown above in Table 1, the only combination that resulted in a fully soluble mixture upon initial mixing was the Fe(NO3)3'9H2O and K2CO3 pair.

EXAMPLE 2

[92] An alkaline aqueous ferrie iron sait solution was manufactured by first preparing a solid mixture having 213.7g of ferrie nitrate nonahydrate (Fe(NÛ3)3‘9H2O), 250g of anhydrous potassium carbonate (K2CO3) and 9.62g of D-sorbitol. The solid mixture was placed in a behÉêt with a magnetic stir bar on a magnetic stir plate. While stirring, 793 mL of an aqueous

Page 28 of 42 solution having 19.7g of the disodium sait of EDTA was added to the beaker. The addition of the water resulted in a vigorous reaction that released C0₂ gas. The alkaline aqueous ferrie iron sait solution was diluted using an aqueous potassium carbonate-bicarbonate buffer at a ratio of 1:25 alkaline aqueous ferrie iron sait solution to aqueous potassium carbonatebicarbonate buffer by adding the alkaline aqueous ferrie iron solution into the aqueous potassium carbonate/bi carbonate buffers. The exemplary buffer solution used to dilute the concentrated ferrie iron solutions was a 50:50 (vokvol) mixture of 0.9 M aqueous K2CO3 and 1.8 M KHCO3 at pH 10.1. Useful ferrie iron solutions can be prepared by dilution of the concentrated solution with potassium carbonate-bicarbonate buffer. Useful ferrie iron solutions can be prepared by dilution of the concentrated solution with potassium carbonatebicarbonate buffer where the dilution is 1:1 (vol/vol) up to 1:60 (vokvol) concentrate: buffer. [93] Concentrate of the alkaline aqueous ferrie iron solutions is stable for at least one year for use in préparation of working solutions by appropriate dilution (e.g., a 1:20 dillution with buffer)

[94] Afterwards, the diluted alkaline aqueous ferrie iron solution was used to scrub hydrogen sulfide from a hydrogen sulfide containing gas. After capturing the hydrogen sulfide gas, the alkaline aqueous ferrie iron solution was regenerated by sparging room température air through the solution, thereby producing solid sulfur and regeneratîng the ferrie iron sait solution. Solid sulfur was removed from the mixture by passing the sulfur-alkaline aqueous ferrie iron solution over a 25-micrometer screen. The capture-regeneration cycle was repeated numerous rimes, resulting in an average of over 100 hydrogen sulfide molécules being captured and oxîdized for every iron atom in the original mixture with no apparent loss of EUS capture or régénération activity over the course of the experiment.

EXAMPLE 3

[95] Preferred mole ratios of potassium and ferrie iron and organic additives in concentrated and dilute working solutions

[96] Various mole ratios of potassium, sorbitol, EDTA and ferrie iron were tested to détermine short and long term solubility of concentrated aqueous alkaline iron solutions, with the goal of determining preferred mole ratios that maintain high solubility. In these experiments dry solids of ail Chemicals were mixed and deionized water (10 mL) was added to the mixed solids. Ail test samples contained 1.3465g of Fe(NOï)3.9H2O, which resulted in a final molarity of 0.278 M FefNChh. Potassium carbonate, D-sorbitol and Na2-EDTA were added as needed to achieve the mole ratios listed in the Table 2. Upon addition of water to the

Page 29 of 42 dry solids a vigorous reaction occurred and either a clear, dark, fully soluble solution or a solution with precipitate of iron oxide particles resulted.

[97] The results of these tests are listed in Table 2. In the absence of sorbitol and EDTA (samples 1-4 in Table 2 below) fully soluble aqueous alkaline ferrie iron solutions occurred at K:Fe mole ratios of 9:1 and 12:1, but substantial précipitation of iron oxide particles occurred at lower K:Fe mole ratios (4:1 and 6.6:1). The 9:1 and 12:1 K:Fe solutions remained clear and soluble for 4-5 days but then precipitated after one week. However 1:20 dilutions of the 9:1 and 12:1 K:Fe concentrâtes with a potassium carbonate-bicarbonate buffer (0.9M KHCO3:0.45M K2CO3) remained fully soluble. The K:Fe mole ratios of these dilute solutions are much higher, 138:1 and 141:1 forthe diluted 9:1 and 12:1 concentrâtes, respectively. These results demonstrate that at K:Fe mole ratios >8 the aqueous alkaline ferrie iron solutions described herein are inherently highly soluble even in the absence of organic additives. This is a highly unusual resuit for ferrie iron compounds, which are normally Virtually insoluble at pH’s above 5-6.

[98] In the presence of D-sorbitol and EDTA at 1:10 mole ratios relative to ferrie iron (samples 5-8) somewhat different results occurred. The 6.6:1, 9:1 and 12:1 K:Fe concentrated solutions were fully water soluble and remained so for at least 7 days, while the 4:1 K:Fe test precipitated immediately. 1:20 dilutions of these soluble concentrâtes into the same potassium carbonate-bicarbonate buffer described above remained fully soluble as well. It should be noted that the dilute solutions with high K:Fe ratios described herein are the “working solutions” of aqueous, alkaline ferrie salts that are used to scrub hydrogen sulfide and other reduced sulfur compounds from gas streams. Exemplary working solutions are made by diluting concentrâtes such as those listed in Table 2 with potassium carbonate-bicarbonate buffer (0.9M KHCO₃:0.45M K2CO3) at 1:10, 1:20 or 1:30 dilution ratios.

Page 30 of 42

TABLE 2

Sample	K:Fe Mole ratio	SorbitokFe Mole ratio	EDTA:Fe Mole ratio	Solution after mixing	Solution after 1 day	Solution after 1 week
1	4:1	0	0	PPT	PPT	PPT_______
2	6.6:1	0	0	PPT	PPT	PPT
3	9:1	0	0	Fully soluble, dark brown	Fully soluble, dark brown	PPT
4	12:1	0	0	Fully soluble, dark brown	Fully soluble, dark brown	PPT
5	4:1	1:10	1:10	PPT	PPT	PPT__
6	6.6:1	1:10	1:10	Fully soluble, dark brown	Fully soluble, dark brown	Fully soluble, dark brown
7	9:1	1:10	1:10	Fully soluble, dark brown	Fully soluble, dark brown	Fully soluble, dark brown______
8	12:1	1:10	1:10	Fully soluble, dark brown______	Fully soluble, dark brown	Fully soluble, dark brown

EXAMPLE 4

[99] Purification of mixed métal salts from aqueous alkaline ferrie sait solutions.

[100] Using an 80:20 acetone-water mixture as an extractant, we concentrated and purified various mixed métal salts from concentrated aqueous alkaline ferrie sait solutions. In general, a given volume of concentrated aqueous alkaline ferrie sait solution was sequentially extracted with a 1 Ox volume of 80:20 acetone-water. With each extraction, a reduced volume of viscous, darkly colored, fully water-soluble ferrie iron solution was formed below the acetone-water layer. The acetone-water layer was then removed, the separated layer of ferrie iron solution was made up to its original volume by addition of deionized water, and then the acetone-water extraction was repeated. The final volume of purified aqueous alkaline ferrie iron sait solution was made up to its original volume by addition of deionized water and the purified ferrie iron sait sample and the acetone-water extractions were analyzed for total iron, potassium, sodium, nitrate, and carbonate/bicarbonate. A sample of a concentrate of the aqueous alkaline ferrie sait solution was also analyzed.

[101] The concentrate of the alkaline ferrie iron solution which was purified had the following composition:

Page 31 of 42

Iron: 32,600 mg/L / 0.58 Μ

Potassium: 133,000 mg/L /3.41 M

Sodium: 4,050 mg/L / 0.176 M

Nitrate: 14,700 mg/L / 0.245 M

Carbonate: 7.4 mg/L

Bicarbonate: 104,000 mg/L

[102] After one lOx acetone-water extraction of the concentrate solution above, the slightly purified ferrie iron solution contained:

Iron: 28,400 mg/L / 0.507 M

Potassium: 55,300 mg/L / 1.42 M

Sodium: 2,720 mg/L / 0.118 M

Nitrate: 2,520 mg/L / 0.042 M

Carbonate: 4.4 mg/L

Bicarbonate: 67,200 mg/L

[103] The potassium to ferrie iron mole ratio in the once-purified ferrie complex is 2.8 to 1, suggesting a K₃Fe-carbonate complex, or a KéFez-carbonate complex. The bicarbonate to ferrie iron mole ratio is 2.17, although this value is likely low due to limitations of the bicarbonate analysis.

[104] After three sequential lOx acetone-water extractions the purified ferrie iron solution contained:

Iron: 23,200 mg/L / 0.414 M

Potassium: 38,700 mg/L / 0.992 M

Nitrate: Not detected

[105] The potassium to ferrie iron mole ratio is 2.4 to 1. This is still suggestive of KjFe or KâFe2 mixed métal carbonate complexes, but less so than the prevîous resuit. It is possible that the complexes are KsFe or KaFcî or KsFea mixed métal carbonate complexes.

Thé'disappearance of nitrate after three sequential extractions suggests that nitrate is not part of the mixed métal ferrie iron complex(es). The nitrate has apparently been removed in the extractions. Carbonate and bicarbonate were not tested in this analysis but are clearly shown to be présent by reaction of the purified solution with 8M hydrochloric acid which results in significant bubbling, indicating release of CO2.

[ 106] These results indîcate that potassium, ferrie iron and bicarbonate are part of the purified compound. There is approximately three times as much potassium as ferrie iron in the purified complex. There is at least twice as much bicarbonate as ferrie iron in the complex. Nitrate Page 32 of 42 does not appear to be présent. A small amount ofsodium is présent, but it cannot be determined if sodium is présent in the complex. We note that there may be more than one complex in the purified material.

EXAMPLE 5

[107] An alkaline aqueous ferrie iron sait solution was prepared using 1.3465g of ferrie nitrate nonahydrate, 1.5755g of potassium carbonate, 0.0605g of D-sorbitol, and 0.124g of Na?EDTA. The molar ratios of the organic additives (D-sorbitol and NasEDTA) were each 1:10 • l.’CS relative to ferrie iron. After the production of the alkaline aqueous femc iron sait solution, a purified ferrie iron sait solution was obtained in a manner consistent to Example 4 using an acetone-water mixture (80-20 (v/v) solution). Two serial extraction steps were performed on the alkaline aqueous ferrie iron sait solution. Purities and sources of the materials used in this procedure are provided in Table 3.

TABLE 3

Material	Source	Purîty
Ferrie nitrate nonahydrate	Carolina Biological	High purity reagent grade
Potassium carbonate	Carolina Biological	Reagent grade ___
D-Sorbitol	Sigma-Aldrich	>=98 wt. %
Disodium sait, EDTA	Carolina Biological	Reagent grade
Potassium bicarbonate	Carolina Biological	Reagent grade
Dowex 21K chloride anion exchange resin	Sigma-Aldrich	N/A
Amberlite IR 120 sodium cation exchange resin	Sigma-Aldrich	N/A
Acetone	Carolina Biological	99.5 wt. %____ _

[108] Four glass sample vials (two experimental vials and two control vials) were packed with 1/4-inch beds of ion exchange resin. Two of the vials were packed with Dowex 21K (Cl ) anion exchange resin and the other two vials were packed with Amberlite IR120 (Na ) cation exchange resin.

[109] After packing the vials with the ion exchange resins, the experimental vials were prepared as follows. One vial of cation exchange resin and one vial of anion exchange resin were charged with 3 mL of 1.8 M potassium bicarbonate buffer solution. After approximately 5 minutes, the excess fluid was decanted from the ion exchange resin beads. The ion exchange resin beads were then rinsed with distîlled water to remove excess buffer solution and suspended in 0.45M potassium bicarbonate buffer. After suspending in buffer, the excess

Page 33 of 42 buffer was decanted off and 200 microiiters of the purified ferrie iron sait solution was added to each of the experimental vials. The experimental vials were then decanted approximately 2 minutes later to remove the excess liquid from the vials. After decanting, a 0.45 M potassium bicarbonate buffer solution was added to the experimental vials to thoroughly rînse the ion exchange resins to remove any unbound ferrie iron sait.

[110] After packing the vials with the ion exchange resins, the control vials were prepared as follows. One of each cation exchange resin and anion exchange resin was suspended in distilled water. The control vials were then decanted approximately 2 minutes later to remove the excess liquid from the vials. After decanting, a 0.45 M potassium bicarbonate buffer solution was added to the control vials to thoroughly rinse the ion exchange resins.

[111] After washing both the experimental vials and control vials with the 0.45 M buffer solution, the experimental cation exchange resin was identical in color (bronze) to the control sample of the cation exchange resin. Conversely, the anion exchange resin treated with the purified mixed métal ferrie sait was a deep amber color, similar in color to the purified alkaline ferrie'iron sait solution. Furthermore, the control anion exchange resin sample had a light brown color. The significantly darker color of the anion exchange resin compared to control anion exchange resin indicates binding of negatively charged (anionic) ferrie species from the isolaîed ferrie iron sait solution. In contrast, the lack of a significant différence in color between treated and control cation exchange resin, respectively, indicates no sîgnificant binding of cationîc ferrie species.

[112] It is assumed with high confidence that the ferrie iron complex, whether anionic or cationic in nature, is responsable for the dark amber color found in solutions described herein. Thus, since no color change was observed with the experimental cation exchange resin relative to the control, it is believed that the ferrie iron complex of the solutions described herein is not cationic in nature. In contrast, the color change of the anion exchange resin to a dark amber color demonstrates that the ferrie ion complex of the solutions described herein is negatively charged, i.e., the ferrie complex is an anion. This anionic ferrie iron complex is believed to be critical to the unusual solubility of the ferrie iron at high pH (>8) and its direct reactivity with reduced sulfur compounds (e.g., H2S) in reduced sulfur-containing fluids. Conversely, positively charged ferrie ions are virtually insoluble at pH greater than 6.

[113] In sum. the ability to create and use thermodynamically stable, fully aqueous soluble, negatively charged ferrie iron complexes may create a wide range of potential industrial applications in addition to this patent application’s focus on the treatment of reduced sulfurcontaining fluids.

Page 34 of 42

EXAMPLE 6

[114] A Thermo Scientific UV-VIS spectrophotometer was used to obtain a UV-Vis spectrum of a sample of purified aqueous alkaline ferrie iron sait solution. The sample used in the analysis was prepared by first producing a concentrated aqueous alkaline ferrie iron sait solution from 1.3465g of ferrie nitrate nonahydrate, 1.5755g of potassium carbonate, 0.0605g of D-Sorbitol, and 0.124g of Naz-EDTA. The mole ratios of D-sorbitol and EDTA relative to ferrie iron are each 1:10. From this concentrate, the purified ferrie iron sait solution was purified by extraction in a manner consistent with Example 4. Two serial extractions were performed using a 1:10 ratio of concentrated aqueous alkaline ferrie iron sait solution to an 80:20 (v/v) acetone-water mixture. The purified ferrie iron sait solution was then diluted in a ratio bf 1:200 (v/v) purified ferrie iron solution to buffer solution. The buffet used for this dilution was prepared using equal volumes of 1.8 M potassium bicarbonate and 0.9 M potassium carbonate. After dilution, 3.5mL of the diluted ferrie iron sait solution was placed in a clean cuvette, then analyzed in the spectrophotometer. The spectrum of the diluted ferrie iron sait solution was taken from 190 nm to 1100 nm. The spectrum of the diluted ferrie iron sait solution can be seen in FIG. 3. As shown in the figure, there is a strong peak having a λ maximum of about 298 nm, centered at approximately 325 nm, extending from approximately 250 nm to 500 nm. The strong peak decreases in absorbance from the peak at 298 nanometers, taillftg off into the visible part of the spectrum, eventually reaching approximately 0 absorbance at about 550 nm. This blue-violet absorbance in the near UV range explains the intense amber color of the suspected compound(s) in the purified aqueous alkaline ferrie iron sait solution.

EXAMPLE 7

[115] Pilot test of aqueous alkaline ferrie iron solutions on bîogas containing high hydrogen sulfide levels.

fi 16] A 70 liter volume of the alkaline aqueous ferrie iron solution was used to treat biogas containing -16,000 ppm hydrogen sulfide at a pulp and paper mill. The same 70 liter solution had previously been used 4-5 days per week for 7 months at a wastewater plant to scrub biogas containing 150-450 ppm H₂S and had been regenerated repeatedly by oxidation with air. The pilot System was arranged as depicted in Figure 2, with the exception that the sulfur filtration System was not included in this pilot.

Page 35 of 42

[Π7] Six scfm of warm, humid bîogas entered the base of the scrubber column via a 2 inch PVC pipe and rose through a layer of plastic (polypropylene) packing, exiting the column via a 2 inch PVC pipe. Regenerated solution was pumped by an S liter per minute positive dîsplacement pump to the top of the scrubber column, where a shower head type sprayer distributed the alkaline ferrie iron solution evenly on the top of the packing. The solution trickled down through the packing, in close contact with the rising stream of biogas. Hydrogen sulfide in the biogas was absorbed into the solution and is believed to be quickly converted to ferrons sulfide (FeS) or ferrie sulfide (Fe₂Sj). At the bottom of the column, the partially reduced solution accumulated into a shallow sump, where it was continuously pumped by an identical 8 liter-per-minute positive displacement pump to the base of a 1 ft diameter x 30^mch tall régénération column. Approximately 3 scfm of air was pumped through a sparger into the régénération column, regenerating the reduced alkaline iron solution to its active ferrie form and simultaneously oxidizing the captured sulfide to elemental sulfur. The regenerated solution was then pumped to a primary accumulator and then to the top of the scrubber column, completing the H₂S capture-regeneration cycle.

[118] Due to the high H₂S levels present, colorimétrie Draeger tubes were used to measure H₂S in untreated gas. High range Draeger Glass Detector tubes (Model #CH28101) detect H₂S in the range 0.2 to 7% Vol. Measuring Range Mfr. The level measured in untreated biogas using the high range Draeger tubes was -16-18,000 ppm H₂S in multiple samples. Hydrogen sulfide levels in treated biogas were measured using an AMI digital H₂S monitor and also with low range Draeger tubes. Low range Draeger Glass Detector tubes (Model#810146) detect H₂S in the range 0.2 to 5 ppm. At 6 scfm gas flow, the AMI monitor consistently reported H₂S levels in treated biogas of-4 ppm and low range Draeger tubes recorded H₂S levels in treated biogas of 0-3 ppm in multiple samples.

EXAMPLE 8

[119] Carbon dioxide capture and release by aqueous alkaline ferrie iron sait solutions.

[120] In both laboratory and field pilot studies, the aqueous alkaline ferrie iron sait solutions used for H₂S scrubbing also capture carbon dioxide during biogas gas H₂S-scrubbing cycles and release it during air régénération cycles. CO₂ capture and release by the aqueous alkaline ferrie iron sait solution has been confirmed by pH studies in batch samples in the laboratory, as well as by pH measurements and gas analyses of régénération air streams sampied dunng pilot studies. A rapid 0.75-1-unit pH drop occurs when aqueous alkaline ferrie iron solutions arè exposed to biogas streams containing 20% or higher amounts of CO₂ during H₂S scrubbing

Page 36 of 42 experiments. It is believed that the pH drop in the scrubber solution occurs because COz, an acid gas, is captured from the biogas, reacts with potassium carbonate to form potassium bicarbonate in the scrubber solution, and thus decreases the pH of the solution. During régénération cycles, pH values of the scrubbing solution rise by 0.75-1 pH units to stable levels as CO2 is released to the air. The graph provided in FIG. 4 shows regular pH swings over four H₂S capture/air régénération cycles in a batch-wise gas scrubbing experiment conducted in our laboratory. Initial pH measurements presented in this figure were later determined to be high by 1.5 pH units. Corrected pH units are provided in FIG. 4.

[121]¹ CO₂ capture/release was confirmed by similar changes in pH levels during scrubbing and régénération cycles in pilot studîes and by gas chromatographie (GC) analysis of gas samples from the air régénération stream. The régénération air sircam was shown by GC to contain over 4% carbon dioxide, which had been removed from the biogas stream and released to the air during régénération. Likewise, a 0.5 pH unit drop was observed in the scrubber solution during the brief biogas scrubbing cycle, followed by a similar rise during air régénération of the used scrubber solution.

h;

no 1 y

EXAMPLE 9

[122] Samples of the alkaline aqueous ferrie iron sait concentrate were diluted 1:10 and 1:20 in buffer solutions containing various ratios of 0.9M potassium carbonate and 1 .SM potassium bicarbonate in distilled water. The buffer ratios used were 100% (0.9M) carbonate, 100% (1.8M) bicarbonate and 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:4 vokvol carbonate:bicarbonate.

[123] Ail 1:20 concentrate:buffer solutions were initially fully soluble but after 14 days iron oxide précipitâtes were observed in the 100% (1.8M) bicarbonate buffer, the 100% (0.9M) carbonate buffer and the 4:1 vokvol bicarbonate-carbonate buffer. After 34 days, iron précipitâtes were also observed in the 3:1 vokvol bicarbonate-carbonate buffer.

[124] Ail 1:10 concentrate:buffer solutions remained soluble in ail buffer mixtures with the exception ofthe 1:10 dilution into 100% (0.9M) carbonate buffer, which remained soluble for 56 days, but then precipitated by day 70. From these results it appears that both the 1:10 and 1:20 dilutions of iron sait concentrate into potassium carbonate-bicarbonate buffers are broadly and stably soluble across a wide range of carbonate bicarbonate ratios, but that the 1:20 concentratebuffer dilutions are less stable at very high and low-very low ratios of carbonatebicarbonate buffer.

Page 37 of 42

Table 4: Results of Dilution of Concentrate with Potassium Carbonate:Bicarbonate

Buffer

Iron sait concentrate diluted 1:10 into potassium carbonate: bicarbonate buffer ___
100% (1.8M) Bicarbonate	1 to 4 (v:v)	1 to 3	1 to2	1 to 1	2 to 1	3 to 1	4 to 1	100% (0.9M) Carbonate
S (soluble)	S	S	S	S	S	S	S	PPT
pH 9.23	pH 9.46	pH 9.57	pH 9.74	pH 10.03	pH 10.34	pH 10.50	pH 10.67	pH 11.82
Iron sait concentrate c	iluted 1:20 into potassium carbonate:bicarbonate bu	fer______
100% (1.8M) Bicarbonate	1 to 4 v:v	1 to 3	1 to2	1 to 1	2 to 1	3 to 1	4 to 1	100% (0.9M) Carbonate
PPT (precipitate)	PPT	PPT	S	S	S	S	S	PPT
pH 9.27	pH 9.48	pH 9.59	pH 9.78	pH 10.06	pH 10.35	pH 10.53	pH 10.68	pH 11.86

-a [-125] While various embodiments of the invention described herein hâve been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the presently disclosed invention.

Claims

Claims

Claim 1 : A method for removal of reduced sulfur compounds from a fluid containing reduced sulfur compounds comprising:

(a) contacting an alkaline aqueous ferrie iron sait solution that contains anionic ferrie iron-carbonate complexes with a reduced sulfur-containing fluid;

(i) wherein the alkaline aqueous ferrie iron sait solution comprises ferrie ions (Fe3+), potassium ions (K+), carbonate ions (C03 2-) and bicarbonate ions (HC03-) and one or more organic additives;

(ii) wherein a molar ratio ofthe potassium ions to the ferrie ions is at least 1.0; [126] (iii) wherein a molar ratio of ferrie ions to a sum total of the one or more organic additives is greater than 1 ;

(iv) wherein the alkaline aqueous ferrie iron sait solution is a fully soluble aqueous alkaline ferrie iron sait solution;

[127] (v) wherein the alkaline aqueous ferrie iron sait solution has a pH of at least 8:

(b) producing, due to the contacting, a reduced alkaline iron solution, wherein the producing comprises:

(i) forming one or more iron sulfide compounds in the alkaline aqueous ferrie iron sait solution to thereby remove at least a portion of the reduced sulfur compounds from the reduced sulfur-containing fluid; and (ii) oxidizing at least a portion of the at least one reduced sulfur compound and reducing at least a portion ofthe ferrie ions to ferrous ions (Fe2+).

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[128]
Claim 2: The method of claim 1, further comprising, after removal of at least a portion of the reduced sulfur compounds from the fluid, (c) oxidizing at least a portion of ferrous iron formed in the at least partially reduced alkaline aqueous ferrie iron solution to at least in part regenerate the alkaline aqueous ferrie iron sait solution with concomitant oxidation of at least a portion of the sulfide of iron sulfide in the at least partially reduced alkaline aqueous ferrie iron solution to elemental sulfur.
Claim 3: The method of claim 2, wherein the regenerated alkaline aqueous ferrie iron sait solution is free of iron oxide-based or iron oxyhydroxide-based particles.
Claim 4: The method of claim 2, wherein oxidizing at least a portion of the ferrous ions comprises exposing the at least partially reduced alkaline aqueous ferrie iron solution to an oxidizing agent to oxidize at least a portion of the ferrous ions therein to ferrie ions, thereby producing a regenerated alkaline aqueous ferrie iron sait solution, wherein the exposing comprises producing the elemental sulfur.
Claim 5: The method of claim 1, wherein the one or more organic additives are selected from the groups consisting of a polyol, an extract of a fruit, leaves or roots of a fruit, and any combination thereof, a pectin from any source, and an aminopolycarboxylic acid.
Claim 6: The method of claim 1, wherein the alkaline aqueous ferrie iron sait solution has a pH of at least 9.
Claim 7: The method of claim 1, wherein a flow of reduced sulfur-containing fluid is contacted with the alkaline aqueous ferrie iron sait solution for a selected contact time to remove the at least one reduced sulfur compound from the reduced sulfurcontaining fluid to provide a purified fluid and thereafter iron sulfide(s) is oxîdized in the at least partially reduced alkaline aqueous ferrie iron solution to at least in part regenerate the alkaline aqueous ferrie iron sait solution.

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Claim 8: The method of claim 1, wherein the alkaline aqueous ferrie iron sait solution further comprises nitrate ions (N03-).
Claim 9: The method of claim 1, wherein a molarity of ferrie ions in the alkaline aqueous ferrie iron sait solution is from 0.005 to 3.0 moîs/L.
Claim 10: The method of claim 1, wherein the alkaline aqueous ferrie iron sait solution comprises the one or more organic additives, wherein a molar ratio of ferrie ions to each organic additive is 2 or more.