Hydrogen production from hydrogen sulfide through an iodine cycle in coal conversion processes

Abstract

Hydrogen production methods combining an iodine looping cycle with a coal conversion process are described. A coal conversion process can include, but is not limited to, coal gasification, underground coal gasification, coal pyrolysis, coal liquification and coal coking.

Description

Hydrogen production from hydrogen sulfide through an iodine cycle in coal conversion processesRELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 661,286, filed on June 18, 2024. The entire teachings of the above application is incorporated herein by reference.BACKGROUND

[0002] Hydrogen iodide is a colorless vapor that readily dissolves in aqueous solutions to create a transparent solution of hydriodic acid. This acid is completely ionized in water forming iodide and hydronium ions. The mixture has an azeotrope at approximately 57 wgt% hydrogen iodide. Hydriodic acid is unstable and will spontaneously decompose into hydrogen gas and iodine. Hydriodic acid when exposed to oxygen will more quickly decompose into water and iodine.

[0003] Iodine when exposed to hydrogen sulfide will react to form hydriodic acid and sulfur, either in the form of elemental sulfur or sulfur dioxide depending on the concentration of the reactants.

[0004] The removal of hydrogen sulfide from gas streams and the production of hydrogen gas are both valuable industrial activities across a variety of industries including oil and gas, coal pulp and paper manufacturing, and waste processing.

[0005] Among coal conversion processes, coal gasification is one of the most widely employed industrial methods for hydrogen production, particularly in China, where it contributed to over 60% of the nation's total hydrogen output, reaching 33 million tons in 2021. However, there is a need for new coal gasification methods that have an improved carbon footprint of coal-to-hydrogen conversion. The versatility of the gasification process lies in its ability to utilize various feedstocks such as coal, petroleum coke, or their combinations.

[0006] In addition to coal gasification, there are other coal conversion technologies, such as underground coal gasification (UCG), coal pyrolysis, coal liquefaction, and coal coking. They also generate product gas streams containing hydrogen sulfide (ILS). Effective removal or conversion of ILS is essential in these processes to prevent corrosion, environmental harm, and catalyst poisoning. Integrating ILS conversion into hydrogen production pathwayspresents an opportunity to improve both environmental and economic performance across these coal-based systems.SUMMARY

[0007] The present disclosure describes a hydrogen production method combining an iodine looping cycle with a coal conversion process. A coal conversion process can include, but is not limited to, coal gasification, underground coal gasification, coal pyrolysis, coal liquification and coal coking.

[0008] Broadly, the coal gasification produces a hydrogen sulfide-rich syngas stream (mainly hydrogen (H2) concentration of about 25% to about 30%; carbon monoxide (CO) concentration of about 40% to about 65%) and the iodine looping cycle converts the hydrogen sulfide component to additional hydrogen gas. The syngas stream emerging from the gasifier is referred to as a hydrogen sulfide-rich syngas stream because the raw syngas has a much higher concentration of hydrogen sulfide compared to the final gas product where the hydrogen sulfide is removed / purified.

[0009] In one embodiment, methods for producing hydrogen from the hydrogen sulfide component of gasified coal with oxidized and elemental sulfur byproducts are described. The methods comprise gasifying coal to produce a syngas product stream comprising hydrogen sulfide (H2S) gas, carbonyl sulfide (COS), CO and carbon dioxide (CO2); converting the carbonyl sulfide in the syngas product stream by hydrolysis to produce hydrogen sulfide in the syngas product stream; and reacting the hydrogen sulfide in the syngas product stream with iodine and water to produce hydriodic acid and sulfur dioxide (SO2); and regenerating the iodine from the produced hydriodic acid to thereby produce hydrogen gas product.

[0010] In an embodiment, the coal is gasified by way of partial oxidation through thermal reactions under near-ambient or elevated pressures, to produce the syngas product stream. In another embodiment, the coal is gasified by way of pyrolysis through thermal reactions under near-ambient or elevated pressures, to produce the syngas product stream.

[0011] In an embodiment, the hydrogen sulfide in the syngas product stream is directly reacted with a solid iodine containing slurry. In another embodiment, the hydrogen sulfide in the syngas product stream is directly reacted with iodine solvated in an aqueous mixture. In yet another embodiment, the hydrogen sulfide component of the gasified coal is concentrated and separated before contact with an iodine solution, solid iodine or iodine solvated in an aqueous mixture.

[0012] The methods of the disclosure can further comprise removing SO2, CO2 and CO from the syngas product stream to produce a purified syngas product stream and then adding the hydrogen gas product to the purified syngas product stream.

[0013] In alternative embodiments, the hydrogen sulfide component of the gasified coal is reacted with calcium-based sorbent, like limestone (CaCOs) or dolomite (CaCOs MgCOs) to produce solid calcium sulfide (CaS). The solid calcium sulfide (CaS) can be concentrated and separated from the gasified coal. Further, the separated solid calcium sulfide (CaS) is reacted with water (H2O) or hydrochloric acid (HC1) to produce hydrogen sulfide. In this embodiment, the method can further comprise decomposing the hydriodic acid to produce hydrogen.

[0014] Sulfur-containing components and other components of the syngas process stream can be further processed from the syngas product stream to create a purified syngas. In one embodiment, SO2 can be removed from the syngas product stream. In another embodiment, the syngas product stream produced from the gasifier can undergo a CO shift reaction with H2O to produce hydrogen and CO2, wherein the CO shift can occur before or after the H2S reaction generating H2. In yet another embodiment, the method further comprises processing the syngas product stream comprising CO2 and hydrogen to remove the CO2.

[0015] In an embodiment, the coal is gasified through underground coal gasification (UCG), a process in which coal is converted into a gaseous product stream, including syngas and other components such as ILS, within the coal seam itself, thereby eliminating the need for traditional mining. A production well delivers the resulting gas stream, comprising C1L, IL, CO, CO2, ILS, and other constituents, to a surface gas processing facility. The iodine looping cycle can be integrated into this above-ground processing system to convert the hydrogen sulfide component into hydrogen, enabling efficient hydrogen production directly from UCG-sourced gases.

[0016] In an embodiment, coal is converted into gas, liquid, and solid products through processes such as coal pyrolysis, coal liquefaction, and coal coking. Hydrogen sulfide (H2S) is primarily present in the gas product streams, along with other components such as light hydrocarbons (C1-C4), CO, CO2, and ammonia (NH3). Additional ILS can be generated by applying a hydrotreating step to the liquid and solid product streams, with the resulting ILS integrated into the gas phase. The H2S in the gas stream is then removed and converted into hydrogen and sulfur co-products via an iodine looping cycle.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments.

[0018] FIG. 1 is an example embodiment of a flowchart of a system for producing a final syngas product stream with a high H2 / CO ratio. Shown is an example system for producing hydrogen and sulfur dioxide in a gasification system that includes units for a gasifier, tar removal, CO shift, H2S reaction and CO2 removal. The H2S reaction unit generates H2 and increases the total yield of H2 and H2 / CO ratio in the final syngas product stream. Separation unit(s) may be placed in series with the unit(s) shown in FIG. 1, after H2S unit or the CO2 removal unit.

[0019] FIG. 2 is an example embodiment of a flowchart of a system for making high purity H2. Shown is an example system for producing hydrogen from hydrogen sulfide and water to increase the total H2 production in the gasification system that has hydrogen and CO as two separate product streams.

[0020] FIG. 3 is an example embodiment of a flowchart of a system for making syngas with a high H2 / CO ratio. Shown is an example system for processing the raw syngas from the gasifier with a calcium -based sorbent to form CaS. The generated CaS can be utilized to regenerate hydrogen sulfide. Hydrogen and sulfur dioxide are generated from the regenerated H2S, and the hydrogen can be combined with the final syngas in the gasification system.DETAILED DESCRIPTIONCoal Gasification

[0021] The objective of the hydrogen production from hydrogen sulfide reaction process within the coal gasification system is twofold: to enhance hydrogen yield and to eliminate hazardous hydrogen sulfide from the syngas product stream. The primary reaction involves hydrogen sulfide and water as reactants, yielding hydrogen and sulfur dioxide as products. The resulting sulfur dioxide can undergo further processing to yield sulfuric acid or elemental sulfur via the Claus process.

[0022] Gasification stands as a key industrial process that generates syngas — a blend primarily comprising CO, H2, CO2, CH4, H2O, and H2S — from carbon-based feedstocks, encompassing but not limited to coal, petroleum coke, and oil refinery bottoms. Gasificationinvolves subjecting a carbon-based feedstock to a gasifier, where it is exposed to oxygen and water steam (vaporized water at high temperature), undergoing partial oxidation through thermal reactions (temperature from about 1200 “Celsius to about 1600 “Celsius) to yield the syngas product stream under near-ambient or elevated pressures (between about 1 to about 80 bars). Pyrolysis can be performed for mild gasification of coal, and its takes place at nearambient pressure and at temperatures from about 500 “Celsius to about 800 “Celsius.Gasifiers are known in the industry and have been described at least in US4456546A, US4209304A, US9175847B2, the entire teaching of which are incorporated herein by reference.

[0023] Commercial gasifiers are categorized into several types, including fixed / moving- bed gasifiers, entrained flow gasifiers, and fluidized bed gasifiers. Notable examples of moving-bed gasifiers include the Lurgi dry ash gasifier and the British Gas / Lurgi Gasifier. Entrained flow gasifiers encompass a variety of models such as the Air Products Slurry Gasifiers (formerly GE Energy and originally Chevron Texaco), CB&I E-GAS™ Gasifiers, Shell SCGP Gasifiers, Siemens Gasifiers, Uhde - Prenflo Gasifiers, Mitsubishi Heavy Industries (MHI) Gasifiers, ECUST Opposed Multi -Burner (0MB) Gasifiers, Tsinghua OSEF Gasifier, and Huaneng Clean Energy Research Institute (HCERI) Gasifiers. Examples of fluidized bed gasifiers include the KBR Transport Gasifiers (TRIG™ Transport Integrated Gasification), GreatPoint Bluegas™ Process, High Temperature Winkler (HTW) Gasifier, and U-GAS® Gasifier.

[0024] Coal emerges as the predominant feedstock for gasification, typically containing sulfur levels ranging from about 0.2% to about 5% by dry weight. During a high-temperature (e.g., from about 1200 “Celsius to about 1600 “Celsius) coal gasification process, a significant portion of the sulfur constituent is converted into H2S, accompanied by a minor quantity of COS. Prior to utilizing the syngas stream in downstream processes, it necessitates acid gas removal (AGR) targeting H2S, COS, and CO2. Current AGR solutions implemented in gasification design encompass either chemical solvent systems (e.g., amine gas treating systems employing Methyldiethanolamine (MDEA)) or physical solvent systems (e.g., RECTISOL® (Linde Engineering or Air Liquide Global E&C Solutions; acid gas removal process that uses methanol as a solvent to separate acid gases such as hydrogen sulfide and carbon dioxide at subzero temperatures) or SELEXOL™ (Dow; a mixture of dimethyl ethers of polyethylene glycols, with a high boiling point, solvent for acid gases). The objective is to eliminate 95% to >99% of the H2S and COS, which can undergo hydrolysis to produce sulfur or sulfuric acid by-products.

[0025] Diverging from conventional Acid Gas Removal (AGR) methods that solely extract or separate H2S from the syngas stream, the methods of this disclosure introduce an innovative approach to simultaneously remove H2S from the syngas stream and convert it into H2. This dual action within a single process not only mitigates the hazards associated with H2S, such as toxicity, catalyst poisoning, and corrosiveness in the syngas stream but also boosts H2 yield in the overall gasification process without consuming any hydrocarbons, consequently reducing greenhouse gas emissions (GHG) per unit of H2 produced.

[0026] In one embodiment, a method for decomposing H2S in syngas and producing H2 from H2S is disclosed. H2S within the syngas stream reacts with H2O and iodine (I2) to yield sulfur dioxide (SO2) and hydroiodic acid (HI). In certain variations, the method further decomposes hydroiodic acid to yield H2 gas. In some embodiments, SO2 is separated from the syngas stream to react with additional H2S, forming elemental sulfur. Additionally, in certain embodiments, the reaction of H2S with H2O and I2 generates a liquid stream, from which SO2 is separated, for instance, through partial flashing. Moreover, the syngas stream produced from the gasifier undergoes a CO shift reaction with H2O (CO + H2O — > H2 + CO2), which can occur before or after the H2S reaction generating H2. This CO shift reaction results in higher concentrations of H2 and CO2 and lower concentrations of CO in the syngas stream. Further, in some embodiments, CO2 separation from the syngas stream eliminates CO2 and generates a H2-rich stream with CO. The produced H2 from H2S may be combined with the H2-rich stream with CO after CO2 removal, resulting in a final product stream with a higher H2 / CO ratio. See FIG. 1. Other units shown in FIG.1 are described below.

[0027] For purposes of the disclosure, a high H2 / CO ratio is related to the increase in H2 by the process of the disclosure compared to typical coal gasification plants. For example, a typical coal gasification plant can produce a H2 / CO ratio of about 1.0 to about 3.3. H2 production yield increase according to the disclosure can be about 24%, compared to commercial coal gasification plants. As explained, H2 in commercial gasifier gas is around 25-30 vol% of total gas amount. Using the disclosure’s technology, there will be another 0.5 to 6% vol% of H2 in total gas amount produced, leading to a maximum increase from 25 vol% to (25+6)=31 vol%. This represents an about 24% H2 yield increase.

[0028] In another embodiment, a method for producing H2 by decomposing H2S in syngas and maximizing H2 purity in the coal gasification process is disclosed. This method involves separating H2 from the syngas stream after the CO shift, H2S conversion steps, and CO2 removal steps. During the H2S conversion step, H2S in the syngas stream reacts with H2O and iodine (I2) to produce sulfur dioxide (SO2) and hydroiodic acid (HI), which issubsequently decomposed into H2. The H2 separation step yields a high-purity H2 product stream suitable for applications such as fuel cells or ammonia synthesis. See FIG. 2. Other units shown in FIG.2 are described below. See also the discussion in the previous paragraph for the processing options and unit that are in common between FIG.1 and FIG. 2. Each of these processing options are applicable for this embodiment.

[0029] In another embodiment, a calcium-based sorbent, such as limestone or dolomite, is introduced into certain gasifiers like fluidized bed reactors. The calcium-based sorbent reacts with H2S in raw syngas to form calcium sulfide (CaS), thereby removing sulfur compounds from the syngas. CaS exits the gasification system as solid particles. In some variations, EES gas is regenerated by reacting CaS with water or acid. The regenerated EES reacts with FEO and iodine (E) to generate sulfur dioxide (SO2) and hydroiodic acid (HI), which is then decomposed into H2. This method enables H2 production from H2S in syngas without impacting the H2 concentration in the final syngas stream. See FIG. 3. Other units shown in FIG. 3 are described below. The processing options and unit that are in common with FIG. 1 or FIG. 2 have been described above and such options are applicable for this embodiment.

[0030] Based on the processes illustrated in FIGs. 1-3, the resultant gasifier gas stream typically consists of 25-30 vol% hydrogen (H2), 40-65 vol% carbon monoxide (CO), 1-15 vol% carbon dioxide (CO2), 0-8 vol% methane (CH4), 3-20 vol% water (H2O), 1-4 vol% nitrogen (N2), as well as 1000-15000 ppmv hydrogen sulfide (H2S) and carbonyl sulfide (COS), 1500-5000 ppmv ammonia (NH3) and hydrogen cyanide (HCN), 40-700 ppmv hydrogen chloride (HC1).

[0031] Within the coal gasification system, a significant portion of the sulfur present in coal converts to hydrogen sulfide (H2S), with a smaller fraction — about 3% to about 10% of the sulfur — forming carbonyl sulfide (COS) depending on gasification conditions. COS hydrolysis is an essential step in sulfur removal, often carried out prior to H2S conversion. The reaction,COS + H2O H2S + CO2 facilitated by passing syngas through a catalytic hydrolysis reactor within a water scrubber, yields H2S and CO2, with over 99% of COS converted to H2S. This process boosts the availability of H2S for hydrogen production, thus increasing the overall hydrogen yield.

[0032] The composition of raw syngas from the coal gasifier typically ranges from about 0.1% to about 1.5% hydrogen sulfide. In the hydrogen production from hydrogen sulfide reaction process, three molecules of hydrogen gas are generated per molecule of hydrogen sulfide consumed. Consequently, this process can elevate the hydrogen yield in the coalgasification system from about 25-30% to about 30-35%, representing an about 20% increase in hydrogen production from the same amount of coal reacted.

[0033] In China, over 60% of the nation's total hydrogen output is derived from coal, amounting to 33 million tons annually. However, the carbon footprint of coal-to-hydrogen conversion, even with CO2 capture and storage, remains considerably high. Conversely, the reaction of this disclosure for producing hydrogen from hydrogen sulfide involves carbon- free molecules as reactants — hydrogen sulfide and water — resulting in no CO2 emissions. Thus, the net carbon footprint of the H2S conversion process of the disclosure ranges between 0.05-1.4 CCheq / kg H2, factoring in all energy inputs and consumption.

[0034] The estimated cost of hydrogen production from the hydrogen sulfide reaction ranges from $1.0 to $1.8 USD. This cost is significantly lower than that of hydrogen produced via water splitting, offering a substantial economic advantage. Moreover, compared to conventional methods like steam methane reforming or coal gasification, the hydrogen sulfide technology demonstrates cost competitiveness while boasting a significantly lower carbon footprint per unit of hydrogen produced.

[0035] Overall, the technology for producing hydrogen from hydrogen sulfide brings substantial economic benefits to the coal industry by enhancing hydrogen production and reducing environmental impact. It achieves this by eliminating toxic chemicals and integrating a low-002 emissions process into a traditionally high-CO2 emissions system, namely coal gasification.

[0036] The following reaction series creates hydrogen and sulfur dioxide from hydrogen sulfide and water, using iodine. Iodine participates in both the first and second reaction steps, but no net consumption or production in the net overall reaction.

[0037] The first step reaction involves hydrogen sulfide, water, and iodine as reactants, and forms hydroiodic acid and sulfur dioxide: H2S + 3 I2 + 2 H2O — > 6 HI + SO2

[0038] The second step reaction decomposes hydroiodic acid into hydrogen and iodine, so I2 is recycled after hydrogen formation: 6 HI — > 3 H2 + 3 I2

[0039] The net overall reaction is H2S + 2 H2O — > 3 H2 + SO2

[0040] Iodine looping cycles have been described in W02019140068A1, and US PatentNo. : 11, 104,574B2, the teachings of which are incorporated in their entirety herein. In an embodiment, the hydrogen sulfide in the syngas product stream is directly reacted with a solid iodine containing slurry. In another embodiment, the hydrogen sulfide in the syngas product stream is directly reacted with iodine solvated in an aqueous mixture (water, hydrogen iodide and iodine). In yet another embodiment, the hydrogen sulfide component ofthe gasified coal is concentrated and separated before contact with an iodine solution, solid iodine or iodine solvated in an aqueous mixture.

[0041] One embodiment of the process comprises the processing steps as shown in FIG 1. Coal gasification is a partial oxidation process wherein either air or pure oxygen, sourced from an air separation unit, serves as the oxidant for coal oxidation. Typically, the oxidant comprises 25%-40% of the theoretical requirement to generate adequate heat for gasifying the remaining unoxidized fuel, thereby yielding raw syngas and solid particulates such as ash. The solid particulates exit the gasifier through the bottom outlet. The raw syngas primarily comprises hydrogen and carbon monoxide, alongside varying amounts of carbon dioxide, methane, water, and nitrogen. Additionally, the raw syngas contains a viscous liquid byproduct, coal tar, and acidic gases including hydrogen sulfide (H2S), carbonyl sulfide (COS), and carbon dioxide (CO2), necessitating removal within the gasification system. A tar removal unit can be integrated after the gasifier, preceding the CO-shift reactor. The final product is the purified syngas gas, which can be used for the applications of gas combined cycle power generation, methanation for synthetic natural gas, methanol synthesis, and Fischer-Tropsch process for liquid hydrocarbons or sustainable aviation fuel synthesis.

[0042] The CO-shift reaction, often referred to as water-gas shift, is an important component of the gasification system aimed at adjusting or augmenting the hydrogen / carbon monoxide (H2 / CO) ratio to meet downstream process specifications. Following tar removal, the syngas undergoes catalytic conversion in a reactor, where CO and water transform into additional H2 and CO2.

[0043] The H2S reaction step may involve COS hydrolysis and generating H2 from H2S and water, according to this disclosure. While the majority of sulfur in the gasifier's syngas exists as H2S, approximately 3%-10% is present as COS. Through COS hydrolysis, over 99% of COS is converted into H2S, consequently elevating H2S concentrations in the syngas stream.

[0044] The syngas stream, boasting an augmented concentration of H2S and minimal COS, is directed into a first reactor of the present disclosure for H2 generation from H2S and water (also referred to as the H2S reactor; H2S + 3 I2 + 2 H2O — > 6 HI + SO2. H2S reacts with iodine and water to form hydrogen iodide and sulfur dioxide). This reactor, which may adopt various configurations such as a bubble column, spray tower, or agitated tank reactor, operates optimally within a temperature range of about 20 “Celsius to about 150 “Celsius and a pressure range of about 1 bar to about 45 bars. Within this reactor, H2S in the syngas stream reacts with iodine and water, yielding a mixture of hydroiodic acid (HI) and sulfur dioxide(SO2). In embodiments, the preferred concentration of HI in the resultant liquid product mixture falls between about 20 weight percent and about 56 weight percent. A portion of the SO2 dissolves in the water / HI mixture, and the dissolved SO2 can subsequently be extracted and isolated from the mixture by subjecting between about 0.1 percent and about 30 percent of the liquid stream to vapor flashing at temperatures ranging from about 80 “Celsius to about 250 “Celsius and pressures from about 1 bar to about 50 bars. In some embodiments, the SO2 can undergo further purification via an adsorption unit utilizing water or another polar solvent for enhanced separation.

[0045] The liquid HI stream undergoes vaporization subsequent to the SO2 separation phase, transforming into a gas-phase hydrogen iodide. This vaporization process can be achieved through various means such as combustion furnaces, waste heat from other processes, solar thermal energy, integrated streams, or alternative heat sources. The heated gaseous hydrogen iodide is subjected to decomposition into hydrogen and iodine, a process that can be catalyzed or un-catalyzed, typically occurring within a reactor operating at temperatures ranging from about 200 “Celsius to about 700 “Celsius and pressures between about 1 bar and about 50 bars. The reactor effluent stream may pass through a heat exchanger to yield a cooled reactor effluent stream.

[0046] The hydrogen produced is subsequently separated from the cooled reactor effluent stream, a task achieved through various methodologies including condensers with vaporliquid separators and pressure swing adsorption units. Following hydrogen separation, the resulting liquid mixture, comprised of water, hydrogen iodide, and iodine, is recycled back to the first reactor. Alternatively, in certain embodiments, the liquid mixture undergoes separation into a waste stream containing impurities, which exits the process, and a recycled stream returned to the first reactor.

[0047] A CO2 removal step follows the H2S reaction to obtain a purified syngas stream devoid of CO2. The separated CO2 can undergo sequestration to prevent CO2 emissions during the coal gasification process. The final purified syngas stream may be combined with the hydrogen produced in the H2S reaction step, thereby increasing both the hydrogen yield and the H2 / CO ratio.

[0048] Another embodiment of the process comprises the processing step as shown in FIG 2.

[0049] An additional H2 separation step is incorporated into the coal gasification system following syngas purification. This step aims to extract H2 from CO and other gases presentin the syngas stream to obtain high-purity hydrogen. Hydrogen separation can be achieved through membrane separation processes, pressure swing adsorption, or cryogenic distillation.

[0050] The separated H2 can then be combined with the hydrogen from the H2S reaction step utilizing the methods disclosed herein. The resulting high-purity hydrogen product finds applications in ammonia synthesis, fuel cells for electricity generation, and power generation through co-firing with natural gas or coal.

[0051] Another embodiment of the process comprises the processing steps as shown inFIG 3.

[0052] In some coal gasification systems, syngas production and H2S removal occur within a single reactor gasifier, such as a fluidized bed reactor. Calcium-based sorbents like limestone (CaCCh) and dolomite (CaCCh MgCCh) are employed in such gasifiers for in-bed removal of H2S.

[0053] In some embodiments utilizing limestone, a calcination reaction may occur depending on the partial pressure of carbon dioxide. This reaction converts CaCCh into calcium oxide (CaO) and carbon dioxide. The produced CaO then reacts with the H2S released from coal to form calcium sulfide (CaS) and water.CaCO3(s) CaO (s) + CO2CaO(s) + H2S CaS(s) + H2OFor the uncalcined limestone, a reaction between CaCO3and H2S can take place to form CaS, carbon dioxide, and water.CaCO3(s) + H2S CaS(s) + CO2 + H2O

[0054] In some embodiments employing dolomite, direct reaction with H2S does not occur. Instead, dolomite decomposes into CaO or CaCO3, and the resultant CaO or CaCO3reacts with H2S to produce CaS. The chemical reactions involved are as follows:CaCO3MgCO3(S) CaO(s) + MgO(s) + 2CO2CaO(s) + H2S CaS(s) + H2O orCaCO3MgCO3(S) CaCO3(s) + MgO(s) + CO2 CaCO3(s) + H2S CaS(s) + CO2 + H2O

[0055] The only solid product resulting from the reaction between calcium-based sorbents and H2S is CaS. Alongside other solid by-products or impurities, CaS exits the gasifier as part of a solid mixture. In some embodiments, separation of CaS from other solid components may be necessary.

[0056] A subsequent reaction step involving CaS generates a gas stream with a high concentration of H2S. In certain embodiments, CaS decomposes upon contact with water, yielding Ca(SH)(OH). This intermediate product can further react with water to form Ca(OH)2and H2S.CaS + H2O Ca(SH)(OH) Ca(SH)(OH) + H2O Ca(OH)2+ H2SIn some embodiments, CaS reacts with an acid such as hydrochloric acid (HC1) to produce its corresponding calcium salt along with H2S.CaS + 2 HC1 CaCh + H2S

[0057] The resulting H2S from the CaS reaction step exhibits an increased concentration compared to H2S concentration in raw syngas, ranging from about 10% to about 95%. The methods of the disclosure for hydrogen production from hydrogen sulfide and water can efficiently process high concentration H2S. The resulting products include hydrogen and sulfur dioxide, with the hydrogen being combined with either the purified syngas or the high- purity hydrogen separated from the purified syngas.

[0058] In some embodiments, H2S is not entirely removed by calcium-based sorbents in the gasifier, resulting in a portion of H2S remaining in the raw syngas exiting the gasifier. After the tar removal step and the CO shift reaction, the processed syngas stream can be merged with the H2S from the CaS reaction step. The combined syngas stream then undergoes the H2S reaction to convert COS into H2S, thereafter utilizing the H2S reaction n described herein to produce hydrogen and sulfur dioxide from H2S and water.

[0059] Referring to the figures, several possible variations will be described below.

[0060] In one variation, a raw syngas gas produced from the gasifier can comprise the following components:

[0061] Between about 500 ppm and about 2 vol% hydrogen sulfide, for example about 2 vol%;

[0062] Between about 50 ppm and about 0.5 vol% carbonyl sulfide, for example about 0.1 vol%;

[0063] Between about 10% and about 35 vol% hydrogen, for example about 25 vol%;

[0064] Between about 20% and about 70 vol% carbon monoxide, for example about 45 vol%;

[0065] Between about 1% and about 15 vol% carbon dioxide, for example about 6 vol%;

[0066] Between about 0% and about 20 vol% water, for example about 5 vol%;

[0067] Between about 1% and about 45 vol% nitrogen, for example about 5 vol%;

[0068] Referring to FIG 1, one variation will be described below.

[0069] If the gasification system is not targeting high H2 / CO ratio, the CO shift reaction step can be removed. The syngas stream after tar removal can directly be processed by the H2S reaction step. Without the CO shift reaction step, there will be less CO2 in the CO2 removal step.

[0070] Referring to FIG 1, another variation will be described below.

[0071] The hydrogen produced from the H2S reaction step can be an independent product stream of the coal gasification system.

[0072] Referring to FIG 2, one variation will be described below.

[0073] If the gasification system is not targeting high H2 / CO ratio, the CO shift reaction step can be removed. The syngas stream after tar removal can directly be processed by the H2S reaction step. Without the CO shift reaction step, there will be less CO2 in the CO2 removal step.

[0074] Referring to FIG 2, another variation will be described below.

[0075] The hydrogen produced from the H2S reaction step can be an independent product stream of the coal gasification system.

[0076] Referring to FIG 3, one variation will be described below.

[0077] The high concentration H2S stream from the CaS reaction step can be combined with the syngas stream after the tar removal step. The H2S reaction step will process the combined stream to remove H2S and produce hydrogen.

[0078] Referring to FIG 3, another variation will be described below.

[0079] If the gasification system is not targeting high H2 / CO ratio, the CO shift reaction step can be removed. The syngas stream after tar removal can directly be processed by the H2S reaction step. Without the CO shift reaction step, there will be less CO2 in the CO2 removal step.

[0080] Referring to FIG 3, yet another variation will be described below.

[0081] The hydrogen produced from the H2S reaction step can be an independent product stream of the coal gasification system.Other Coal Conversion Processes

[0082] The disclosure further pertains to methods for producing hydrogen from the hydrogen sulfide component of a coal conversion process, such as underground coal gasification (UCG), coal pyrolysis, coal liquification and coal coking. According to themethods, a coal conversion process is performed to produce a gas product stream comprising hydrogen sulfide (H2S) gas; reacting the hydrogen sulfide in the gas product stream with iodine and water to produce hydriodic acid and SO2; and regenerating the iodine from the produced hydriodic acid to thereby produce hydrogen. A discussion of the iodine looping cycle from above is applicable to this section. In addition to producing hydrogen sulfide, the conversion process produces hydrogen from hydrogen sulfide. Additionally, hydrogen sulfide is also producing elemental sulfur or oxidized sulfur (like SO2) products as the coproducts with hydrogen.

[0083] The processes of the previous section and their discussion apply to this section as well and their details are incorporated by reference. For example, underground coal gasification (UCG) is very similar to coal gasification. Therefore, steps like COS conversion by hydrolysis to produce hydrogen sulfide, tar removal, CO shift, CO2 removal, as previously discussed, are all applicable to underground coal gasification. For coal pyrolysis, coal liquification and coal coking, since the coal is heated in the absence of oxygen, the amount of COS, CO and CO2 in the process streams is limited. Therefore, in coal pyrolysis, coal liquification and coal coking, tar removal and CO2 removal are applicable, as discussed above for coal gasification.

[0084] In one embodiment, coal is gasified through underground coal gasification by injecting oxygen and water into a coal seam via an injection well. Gasification reactions occur in situ within the coal seam, generating a product gas stream containing H2, CH4, CO, CO2, H2S, and other minor components. A production well is constructed to transport the gas stream to the surface, where it undergoes gas cleaning and separation for downstream applications such as electricity generation. Hydrogen sulfide must be removed from the product gas stream during these processing steps. The separated ILS can be used as feedstock for the iodine-looping cycle, reacting with iodine and water to produce hydrogen and sulfur dioxide (SO2). While the composition of the ILS stream in UCG may differ from that produced in above-ground gasification processes, the objective remains the same: effective ILS removal and conversion to enhance hydrogen yield from the same quantity of coal.

[0085] In another embodiment, processes such as coal pyrolysis, coal liquefaction, and coal coking convert coal into gas, liquid, and solid products. These processes are thermally driven and involve the release of volatile gas components from coal, among which ILS is a common constituent. In coal pyrolysis, coal is heated in the absence of oxygen, leading to thermal decomposition typically at temperatures about 400 °C to about 700 °C. The resulting gas product stream comprises C , IL, CO, CO2, ILS, and other gaseous species.

[0086] In coal liquefaction, coal is contacted with hydrogen in the presence of a catalyst and solvent at elevated temperatures (about 400 °C to about 450 °C) and pressures (about 150 bar to about 300 bar), producing a raw liquid product that is subsequently refined into liquid fuels. The unreacted hydrogen is recycled via a gas recovery treatment unit, where it is separated from light hydrocarbons (C1-C4), ILS, CO, CO2, and ammonia (NH3). The iodine- looping cycle can be applied to the separated H2S to produce additional hydrogen, which can be reintegrated into the recycled hydrogen stream to support continued liquefaction reactions.

[0087] Coal coking is a process similar to pyrolysis, in which coal undergoes thermal decomposition in the absence of oxygen. However, coal coking typically occurs at higher temperatures, generally above 600 °C, and often between 1000 °C and 1100 °C. The primary product of coal coking is a solid residue known as metallurgical coke or petroleum coke. A secondary gas product stream is also generated, containing ILS and other components. The ILS in this gas stream can be converted into hydrogen via the iodine-looping cycle.Definitions

[0088] It is to be understood that the terminology used herein is for describing particular embodiments only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains.

[0089] Although any methods and materials similar or equivalent to those described herein may be used in the practice for testing of the present disclosure, exemplary materials and methods are described herein.

[0090] When a list is presented, unless stated otherwise, it is to be understood that each individual element of that list, and every combination of that list, is a separate embodiment. For example, a list of embodiments presented as “A, B, or C” is to be interpreted as including the embodiments, “A,” “B,” “C,” “A or B,” “A or C,” “B or C,” or “A, B, or C ”

[0091] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. The conjunctive term “and / or” between multiple recited elements is understood as encompassing both individual and combined options. For instance, where two elements are conjoined by “and / or,” a first option refers to the applicability of the first element without the second. A second option refers to the applicability of the second element without the first. A third option refers to the applicability of the first and second elements together. Any one of theseoptions is understood to fall within the meaning, and therefore satisfy the requirement of the term “and / or” as used herein. Concurrent applicability of more than one of the options is also understood to fall within the meaning, and therefore satisfy the requirement of the term “and / or.”

[0092] Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and synonyms and variants thereof such as “have” and “include”, as well as variations thereof, such as “comprises” and “comprising”, are to be construed in an open, inclusive sense, e.g., “including, but not limited to.” The transitional terms “comprising,” “consisting essentially of,” and “consisting of’ are intended to connote their generally accepted meanings in the patent vernacular; that is, (i) “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open- ended and does not exclude additional, unrecited elements or method steps; (ii) “consisting of’ excludes any element or step not specified in the claim; and (iii) “consisting essentially of’ limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.Embodiments described in terms of the phrase “comprising” (or its equivalents) also provide as embodiments those independently described in terms of “consisting of’ and “consisting essentially of.”

[0093] “About” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, z.e., the limitations of the measurement system. Unless explicitly stated otherwise within the disclosure, claims, result or embodiment, “about” means within one standard deviation per the practice in the art, or can mean a range of ± 20%, ± 10%, ± 5%, ±4, ±3, ±2 or ± 1% of a given value. It is to be understood that the term “about” can precede any particular value specified herein, except for particular values used in the Examples. For example, an “about” azeotropic mixture of hydriodic acid and water will include 57% by weight (±10 %).

[0094] All percents are intended to be weight percent unless otherwise specified. The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particularimplementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims

What is claimed is:

1. A method for producing hydrogen from the hydrogen sulfide component of gasified coal with oxidized and elemental sulfur byproducts, comprising: gasifying coal to produce a syngas product stream comprising hydrogen sulfide (H2S) gas, carbonyl sulfide (COS), CO and CO2; converting the carbonyl sulfide in the syngas product stream by hydrolysis to produce hydrogen sulfide in the syngas product stream; and reacting the hydrogen sulfide in the syngas product stream with iodine and water to produce hydriodic acid and SO2; and regenerating the iodine from the produced hydriodic acid to thereby produce hydrogen.

2. The method of claim 1, wherein the coal is gasified by way of partial oxidation through thermal reactions under near-ambient or elevated pressures, to produce the syngas product stream.

3. The method of claim 1, wherein the coal is gasified by way of pyrolysis through thermal reactions under near-ambient or elevated pressures, to produce the syngas product stream.

4. The method of claim 1, wherein the syngas product stream is directly reacted with a solid iodine containing slurry.

5. The method of claim 1, wherein the syngas product stream is directly reacted with iodine solvated in an aqueous mixture.

6. The method of claim 1, wherein the hydrogen sulfide component of the gasified coal is concentrated and separated before contact with an iodine solution.

7. The method of claim 1, further comprising removing SO2, CO2 and CO from the syngas product stream to produce a purified syngas product stream and then adding the hydrogen gas product to the purified syngas product stream.

8. The method of claim 1, wherein the hydrogen gas is merged with hydrogen separated from a purified syngas stream.

9. The method of claim 1, wherein the hydrogen sulfide component of the gasified coal is reacted with calcium-based sorbent, like limestone (CaCCh) or dolomite (CaCCh MgCCh) to produce solid calcium sulfide (CaS).

10. The method of claim 9, wherein the solid calcium sulfide (CaS) is concentrated and separated from the gasified coal.

11. The method of claim 10, wherein the separated solid calcium sulfide (CaS) is reacted with water (H2O) or hydrochloric acid (HC1) to produce hydrogen sulfide.

12. The method of claim 11, further comprising decomposing hydriodic acid to produce hydrogen.

13. The method of claim 1, further processing the syngas product stream to remove SO2.

14. The method of claim 1, further processing the syngas product stream produced from the gasifier to undergo a CO shift reaction with H2O to produce hydrogen and CO2, wherein the CO shift can occur before or after the H2S reaction generating H2.

15. The method of claim 14, further comprising processing the syngas product stream comprising CO2 and hydrogen to remove the CO2.

16. The method of claim 15, further comprising separating hydrogen from the syngas product stream to produce purified hydrogen.

17. A method for producing hydrogen from hydrogen sulfide component of a coal conversion process, with oxidized and elemental sulfur byproducts, comprising: performing a coal conversion process to produce a gas product stream comprising hydrogen sulfide (H2S) gas; reacting the hydrogen sulfide in the gas product stream with iodine and water to produce hydriodic acid and SO2; and regenerating the iodine from the produced hydriodic acid to thereby produce hydrogen.

18. The method of claim 17, wherein the coal conversion process is underground coal gasification (UCG), coal pyrolysis, coal liquefaction, or coal coking.

19. The method of claim 17, further comprising decomposing hydriodic acid to produce hydrogen.

Images