Subsurface hydrogen extraction through a sulfur dioxide / hydrogen sulfide loop

Abstract

Methods for harvesting hydrogen from a natural hydrogen production zone are described. The method comprises introducing a stream (e.g., injection stream, sequestration stream) comprising sulfur dioxide into a natural hydrogen production zone to produce a gas mixture containing hydrogen sulfide; harvesting the gas mixture containing hydrogen sulfide; and converting the hydrogen sulfide to hydrogen, thereby harvesting hydrogen from the natural hydrogen production zone. The natural hydrogen production zone can be a ground subsurface or a subsurface of the ocean floor. Introducing the stream comprising sulfur dioxide can be performed by injection, sequestration, pumping, infusion or other methods for delivering sulfur dioxide to a well (e.g., gas injection well) at the natural hydrogen production zone.

Description

6196.1005001Subsurface Hydrogen Extraction through a Sulfur Dioxide / Hydrogen Sulfide LoopRELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 717,985, filed on November 8, 2024. The entire teachings of the above application are incorporated herein by reference.BACKGROUND

[0002] Hydrogen, a colorless, low-density gas, is widely used as a chemical feedstock and energy carrier across diverse industries and regions. Key sectors such as fuel processing, fertilizer production, plastics manufacturing, and metals refining depend on hydrogen as a critical input.

[0003] Traditionally, hydrogen has been produced as a secondary energy source, primarily from fossil fuels. The most common methods include steam methane reforming (from natural gas), naphtha reforming, and coal gasification. Although alternative technologies such as water electrolysis and hydrocarbon pyrolysis have been available for decades, their commercial impact has remained limited.

[0004] Natural hydrogen extraction from deep subsurface deposits presents an emerging opportunity to access hydrogen as a primary energy source. It is theorized that groundwater reactions with iron-rich minerals, such as olivine, generate significant quantities of subsurface hydrogen. Additionally, radiation-induced chemistries may contribute to hydrogen formation in these environments.

[0005] One potential reason for hydrogen’s relative scarcity near the Earth's surface is its high reactivity during ascent. As hydrogen rises, it tends to react with surrounding materials, either escaping into the atmosphere or becoming trapped beneath impermeable rock formations. Due to hydrogen's diffusive and reactive nature, it typically transforms into other chemical species, such as methane or hydrogen sulfide, before reaching the surface. These reactions occur through both chemical and biological pathways.

[0006] There remains a need for ways of harvesting natural sources of hydrogen within the Earth.14241419. vl6196.1005001SUMMARY

[0007] Described herein are methods for harvesting hydrogen from a natural hydrogen production zone comprising: introducing a stream (e.g., injection stream, sequestration stream) comprising sulfur dioxide into a natural hydrogen production zone to produce a gas mixture containing hydrogen sulfide; harvesting the gas mixture containing hydrogen sulfide; and converting the hydrogen sulfide to hydrogen, thereby harvesting hydrogen from the natural hydrogen production zone. The natural hydrogen production zone can be a ground subsurface or a subsurface of the ocean floor. Introducing the stream comprising sulfur dioxide can be performed by injection, sequestration, pumping, infusion or other methods for delivering sulfur dioxide to a well (e.g., gas injection well) at the natural hydrogen production zone.

[0008] In one embodiment, the hydrogen sulfide in the gas mixture is further processed by reforming the hydrogen sulfide using an iodine and water looping cycle to produce sulfur dioxide and hydrogen, thereby harvesting hydrogen from the natural hydrogen production zone.

[0009] In another embodiment, the hydrogen sulfide in the gas mixture is further processed by decomposing the hydrogen sulfide in an iodine looping cycle to produce elemental sulfur and hydrogen; and then performing an oxidation reaction to convert the elemental sulfur to sulfur dioxide, thereby harvesting hydrogen from the natural hydrogen production zone. Alternative methods for decomposing hydrogen sulfide include but are not limited to thermal, plasma, catalytic (e.g., microwave catalytic, photocatalytic) or electrochemical methods, which decompose hydrogen sulfide into hydrogen gas and elemental sulfur (S°).

[0010] The sulfur dioxide can be introduced (e.g., injected, sequestrated, or others) as a solvated component of an aqueous stream. The sulfur dioxide can be introduced (e.g., injected, sequestrated, or others) as a major component (about 50 wtg% to about 99 wtg%) of the stream (e.g., an injection stream). Alternatively, the sulfur dioxide can be introduced (e.g., injected, sequestrated, or others) as a minor component (about 1.0 wtg% to about 50 wtg%) mixed with carbon dioxide as the stream (e.g., an injection stream).

[0011] A mixture of sulfur dioxide and water can be introduced into the natural hydrogen production zone to increase hydrogen production in the zone.

[0012] In some embodiments of the methods, the harvested gas mixture can contain a combination of at least hydrogen gas and hydrogen sulfide.

[0013] In some embodiments of the method, additional hydrogen sulfide is fed to the hydrogen sulfide reforming or the hydrogen sulfide decomposition reactions, to account for the24241419. vl6196.1005001 sulfur components loss due to the accumulation of these sulfur species in the natural hydrogen production zone, e.g., subsurface.

[0014] In other embodiments of the method, other processing units can be added enhance hydrogen production levels, maintain or improve the balance of sulfur compounds. Optional processing units include but are not limited to hydrogen sulfur purification unit(s), sulfur dioxide purification unit(s), sulfur oxidation unit(s).

[0015] The methods of the disclosure can be performed on a single site or distributed across associated sites from the natural hydrogen production zone.

[0016] The disclosure also pertains to systems that can be contained on a single site or distributed across associated sites from the natural hydrogen production zone. The system or systems will comprise the processing units set forth in the disclosure to carry out any of the methods disclosed herein. The system can be comprised in a chemical plant.

[0017] The methods and system of the disclosure can efficiently extract hydrogen from subsurface environments using a sulfur-based cycle. Hydrogen sulfide reforming and decomposition utilizing an iodine looping cycle offer complementary pathways for harnessing hydrogen from subsurface sources where hydrogen sulfide is prevalent.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a better understanding of the present disclosure, reference is made to the drawings below, in which like elements are referenced with like numerals, and in which:

[0019] FIG. 1 is an example diagram of a system for extracting hydrogen via the looping of sulfur gases from the subsurface, using hydrogen sulfide reforming.

[0020] FIG. 2 is an example diagram of a system for extracting hydrogen via the looping of sulfur gases in the subsurface, using hydrogen sulfide decomposition.DETAILED DESCRIPTION

[0021] The present disclosure outlines a system for efficiently extracting hydrogen from subsurface environments using a sulfur-based cycle. In this process, sulfur dioxide is injected into the subsurface where it encounters rising hydrogen. Through thermochemical and biological reactions, the injected sulfur dioxide is reduced to hydrogen sulfide. The hydrogen sulfide is then extracted to the surface, where it undergoes reforming or decomposition, producing hydrogen gas and regenerating sulfur dioxide. The harvested hydrogen can be used as a chemical feedstock or energy source. The regenerated sulfur dioxide is pressurized and reinjected into the subsurface, continuing the cycle of reduction, extraction, and reforming.34241419. vl6196.1005001

[0022] This sulfur dioxide reduction reaction is possible because hydrogen can react with sulfur dioxide, in the presence of a catalyst or at elevated temperatures and pressure. High temperature will increase the instability of sulfur dioxide and hydrogen. High pressure increases the interaction between sulfur dioxide and hydrogen. Underground the temperature and pressure are high and the earth material can act as heterogenous catalyst accelerating the reaction rateSO2+ 3H2-► H2S + 2H2O

[0023] The overall process extracts natural hydrogen from a deep subsurface zone to the surface. In the subsurface zone (6), given the high pressure and high temperature conditions, natural hydrogen can react with sulfur dioxide, reducing it to hydrogen sulfide and water. Hydrogen sulfide, being less reactive than hydrogen under the subsurface conditions, captures the hydrogen atoms, preventing rapid reactions or diffusion during ascent, thus maximizing the efficiency of hydrogen recovery.

[0024] Referring to FIGs. 1 and 2, a gas extraction well (1) extracts a gas mixture primarily composed of hydrogen sulfide to the surface. This may be followed by an optional FbS purification unit (2) to concentrate the hydrogen sulfide stream before entering an H?S reformer (3) or an FbS decomposition unit (7). In the H2S reformer (3), hydrogen sulfide reacts with water to produce hydrogen and sulfur dioxide. In the H2S decomposition unit (7), hydrogen sulfide decomposes into hydrogen and elemental sulfur, which is subsequently oxidized to sulfur dioxide (8). Both processes yield hydrogen gas, with the H2S reformer (3) producing additional hydrogen from water. The sulfur dioxide produced remains in the loop for reinjection into the subsurface.

[0025] A sulfur dioxide purification unit may be installed between sulfur dioxide production (3) or (8) and the gas injection well (5). The gas injection well (5) injects either sulfur dioxide alone or co-injects sulfur dioxide with carbon dioxide. The injected sulfur dioxide reacts with natural hydrogen in the subsurface, completing the cycle.

[0026] The system does not achieve 100% efficiency in sulfur conversion reactions, particularly in subsurface sulfur dioxide reduction. Some sulfur dioxide may reduce to elemental sulfur or other compounds, which cannot be extracted to the surface, instead of hydrogen sulfide. To maintain sulfur balance, two optional streams may be added: an additional hydrogen sulfide stream to the H2S reformer (3) or H2S decomposition unit (7), and an additional sulfur dioxide stream to the gas injection well (5).44241419. vl6196.1005001

[0027] The present disclosure provides methods for recovering natural hydrogen from deep subsurface environments, utilizing two primary systems: (1) a hydrogen sulfide (H2S) reforming or decomposition system for converting hydrogen sulfide into sulfur dioxide (SO2) and hydrogen gas (H2), and (2) an acid gas injection system capable of injecting sulfur dioxide into subsurface hydrogen-rich zones and harvesting the resulting gas mixtures. These components work in tandem to establish a closed-loop cycle that maximizes hydrogen extraction from naturally occurring sources deep within the Earth’s crust.

[0028] The first system, the EES reforming or decomposition system, is designed to process the extracted hydrogen sulfide. Hydrogen sulfide reforming is a known technology in which hydrogen sulfide reacts with water, producing hydrogen gas and sulfur dioxide through a catalytic or thermochemical process. This reforming method has been disclosed in prior patents, including US20200369518, and has been demonstrated as an efficient route for hydrogen recovery. In contrast, the hydrogen sulfide decomposition system breaks hydrogen sulfide into its elemental components — hydrogen gas and elemental sulfur — without the need for water. Elemental sulfur is subsequently oxidized back to sulfur dioxide, which is reintegrated into the cycle. This decomposition technology has been documented in various patents, such as US2979384A, US20090263312A1, US11413574B2, and US8562928B2. Both processes, whether reforming or decomposition, generate hydrogen gas as the primary product, while regenerating sulfur dioxide for further use.

[0029] The second system, the acid gas injection system, facilitates the reinjection of sulfur dioxide into the subsurface, specifically targeting natural hydrogen generation zones within the Earth's crust. Acid gas injection is a well-established technology in the energy sector, especially in regions such as the southwestern United States and central Canada, where it has been used for enhanced oil recovery (EOR) and other subsurface processes. The injection of SO2 into subsurface zones has been studied, with particular interest in its behavior when co-injected with carbon dioxide (CO2). Research studies, such as (Diana H. Bacon et al., Energy Procedia, Vol 1, 3283-3290, 2009), (Lauren E. Crandell et al., Environmental Science & Technology, Vol 44, 349-355, 2010), and (Morteza Akbarabadi and Mohammad Piri, Advances in Water Resources, Vol 77, 44-56, 2015), have demonstrated the feasibility and chemical dynamics of SO2-CO2 co-inj ection. Bacon et al. modeled the co-inj ection of CO2 and SO2 into deep saline formation and found the addition of SO2 to the injection results in the precipitation of anhydrite near the injection well. Crandell et al. explored the potential of geologic sequestration of CO2 and SO2 together by co-inj ection. They found that small amounts of SO2 (1-5%) are predicted to have a negligible effect on the critical point of CO2 but will increase phase density by as54241419. vl6196.1005001 much as 12% for mixtures containing 5% SO2. Akbarabadi and Piri experimentally showed that 62.7% to 76.8% of the initial supercritical CO2+SO2 volume was trapped through capillary trapping, indicating that a significant portion of the CO2 in-placed at the end of the drainage process will be trapped permanently due to chase brine injection with the lowest risk of leakage.

[0030] In addition to acid gas injection, this system shares similarities with geothermal energy technologies, which also involve injecting fluids into deep subsurface zones and harvesting them after interacting with geothermal reservoirs. Geothermal systems for injecting and harvesting water from beneath the Earth’s surface have seen widespread application, particularly in regions with active geothermal energy development, such as the United States, Iceland, and parts of Southeast Asia. Similar principles are applied in the present method, with the key difference being the use of sulfur dioxide instead of water or other geothermal fluids. These geothermal systems, such as those disclosed in US8826638B1, US11168673B2, US11161694B2 have demonstrated the technical viability of deep subsurface fluid injection and retrieval, and their success serves as a foundation for the methods disclosed herein.

[0031] The integration of these two primary systems — H2S reforming or decomposition, and acid gas injection — creates a robust, continuous cycle for harvesting natural hydrogen from deep within the Earth’s crust. By leveraging the reactivity of sulfur dioxide with naturally occurring subsurface hydrogen, and utilizing proven methods for gas injection and retrieval, this disclosure offers an efficient and scalable approach to hydrogen production, addressing key challenges such as hydrogen diffusion and reactivity that have historically limited subsurface hydrogen recovery efforts.

[0032] This disclosure represents a unique combination of these processes / technologies. In short it first creates hydrogen from harvested hydrogen sulfide, and sulfur dioxide is the coproduct. Second, a gas stream of sulfur dioxide and other components or a liquid stream of sulfur dioxide-rich water is injected into a natural hydrogen generation subsurface zone. Third, within this hydrogen generation zone, sulfur dioxide is reduced to hydrogen sulfide by natural hydrogen, and the hydrogen sulfide is harvested from the subsurface before reaching the surface. Finally, the harvested hydrogen sulfide is reformed at the surface to produce hydrogen and sulfur dioxide.

[0033] The systems of this disclosure are comprised of the following elements: 1) A conversion unit(s) that processes hydrogen sulfide (EES) into hydrogen gas (EE) and sulfur dioxide (SO2); 2) An acid gas injection well equipped with compressors, capable of injecting a gas stream, primarily composed of sulfur dioxide, into the subsurface zone from the surface;64241419. vl6196.1005001 and 3) A gas extraction well with associated equipment to extract gas mixtures from subsurface hydrogen generation zones for further processing at the surface.

[0034] In one embodiment, hydrogen sulfide conversion is achieved through hydrogen sulfide reforming, a two-step process that uses iodine and water. This approach enables the production of both hydrogen and sulfur dioxide from hydrogen sulfide. The chemical reactions involved in this process are outlined below:

[0035] In the first step, hydrogen sulfide reacts with iodine (L) and water (H2O) to produce hydrogen iodide (HI) and sulfur dioxide (SO2):H2S + 3I2+ 2H2O -► 6HI + SO2

[0036] In the second step, the hydrogen iodide (HI) produced in the first reaction is decomposed into hydrogen gas (H2) and iodine (L):6HI -► 3I2+ 3H2

[0037] The overall net reaction reforms hydrogen sulfide by reacting it with water, producing three molecules of hydrogen gas and one molecule of sulfur dioxide for every molecule of hydrogen sulfide processed. This reforming method maximizes hydrogen production, offering a high hydrogen yield per molecule of hydrogen sulfide.H2S + 2H2O - 3H2+ SO2

[0038] In another embodiment, hydrogen sulfide is converted using hydrogen sulfide decomposition. This process can be carried out through thermal, plasma, microwave catalytic, photocatalytic or electrochemical methods, which decompose hydrogen sulfide into hydrogen gas and elemental sulfur (S°):H2S ^ H2+ S°

[0039] Research on hydrogen sulfide decomposition has demonstrated various methods for converting H2S into hydrogen and sulfur. Faraji et al. (Farhad Faraji et aL, International Journal of Hydrogen Energy, Vol 23, 451-456, 1998) reported a noncatalytic thermal process achieving a 65.8% conversion at 1200 °C and 0.050 atm. In contrast, Reddy et al. (E. Linga Reddy et al., Applied Energy, Vol 95, 87-92, 2012) showed that nonthermal plasma requires less energy than steam methane reforming, offering an efficient alternative. Xu et al. (Wentao Xu et al., Energy Conversion and Management, Vol 149, 219-227, 2017) applied a microwave catalytic process to overcome thermal limitations, enhancing conversion efficiency. Other approaches include photocatalytic decomposition with light, as explored by Prakash et al. (Arvind Prakash et al., Solar Energy Materials and Solar Cells, Vol 180, 205-212, 2018), and electrochemical methods, verified by Garg et al. (Kalpana Garg et al., ACS Applied Materials74241419. vl6196.1005001& Interfaces, Vol 15, 27845-27852, 2023), further expanding the methods available for efficient hydrogen production from H2S.

[0040] In some implementations, hydrogen sulfide decomposition can occur in two steps through an iodine looping cycle, involving iodine as a reactant. In the first step, hydrogen sulfide reacts with iodine (L) to form elemental sulfur (S°) and hydrogen iodide (HI):H2S + I2- S° + 2HI

[0041] In the second step, hydrogen iodide (HI) is decomposed into hydrogen gas (H2) and iodine (L), which can then be recycled.2HI - I2+ H2

[0042] The overall reaction is equivalent to the single-step hydrogen sulfide decomposition: H2S ^ H2+ S°

[0043] The elemental sulfur (S°) produced during hydrogen sulfide decomposition is in solid form at surface conditions, given its melting point of 112.8°C. Due to its insolubility in water and solid-state nature, elemental sulfur cannot be easily injected into the subsurface zone. Therefore, a necessary oxidation step is included to convert the solid sulfur into gasphase sulfur dioxide (SO2) for reinjection. This is achieved through a combustion reaction in which sulfur burns in the presence of oxygen (O2) to form sulfur dioxide (SO2):S° + O2- SO2

[0044] This oxidation step ensures that the sulfur is converted into a form that is both gaseous and suitable for re-injection into the subsurface environment, maintaining the continuous loop of hydrogen extraction and sulfur cycling.

[0045] In one embodiment, a gas stream rich in sulfur dioxide (SO2) is produced from the H2S reformer (3) in FIG. 1 or from the sulfur oxidation unit (8) in FIG. 2. This gas stream contains a high concentration of sulfur dioxide, typically comprising about 50 weight percent (wt%) or higher, such as about 75 wt% to about 99 wt%. Other components of the stream may include trace amounts of hydrogen sulfide (H2S), nitrogen (N2), carbon dioxide (CO2), and other minor constituents. The concentration of sulfur dioxide can be further increased up to 99.9% purity by utilizing an optional SO2 purification unit (4), which is positioned upstream of the gas injection well (5). Once purified, this high-purity sulfur dioxide stream is injected from the surface into the designated subsurface zone for interaction with natural hydrogen or other subsurface materials.

[0046] In another embodiment, the sulfur dioxide stream is mixed with carbon dioxide before injection. The gas injection well (5) facilitates the co-inj ection of this SO2 and CO284241419. vl6196.1005001 mixture into the subsurface zone. This method leverages existing commercial acid gas injection infrastructure that is increasingly being utilized in carbon capture, utilization, and storage (CCUS) projects. While these facilities are primarily designed for carbon dioxide injection, research has demonstrated the feasibility of blending about 1% to about 5% sulfur dioxide into carbon dioxide streams for co-inj ection, validating its technical and operational compatibility. Studies in this field have shown that the co-inj ection of sulfur dioxide can enhance the overall injection process, providing an additional pathway for sulfur management in subsurface zones. The co-inj ection conditions can be optimized to secure carbon sequestration in the subsurface and facilitate the reaction between SO2 and the subsurface hydrogen.

[0047] In one embodiment, natural hydrogen is produced in the subsurface zone through the process of radiolysis of water. In this process, trace radioactive elements naturally present in rocks, such as uranium, thorium, and potassium-bearing minerals, emit radiation that splits water molecules (H2O), releasing hydrogen (H2) and oxygen (O2). This is a slow process, making ancient rock formations the most likely candidates for generating substantial amounts of hydrogen over geological time scales. Such formations may serve as significant reservoirs of hydrogen for extraction using the disclosed methods.

[0048] In another embodiment, a primary source of natural hydrogen production is serpentinization, a fast, renewable geochemical reaction that occurs when water interacts with iron-rich rocks, such as olivine, under subsurface conditions. This process typically occurs at temperatures of about 200°C to about 400°C, where water reacts with minerals like those found in ophiolites, generating hydrogen. Serpentinization is recognized as one of the dominant natural hydrogen production processes and occurs in regions rich in ultramafic rocks, particularly at tectonic plate boundaries and mid-ocean ridges.

[0049] In another embodiment, natural hydrogen originates from Earth's core and mantle. Hydrogen streams generated in the mantle may migrate upward along tectonic plate boundaries and faults, reaching subsurface zones accessible by extraction wells. These upward flows of hydrogen are hypothesized to contribute to subsurface hydrogen reservoirs, providing a potentially renewable source of natural hydrogen over geological timescales.

[0050] Within the subsurface zone, sulfur dioxide is expected to primarily react with hydrogen to form hydrogen sulfide (EES) and water (H2O). However, side reactions may occur, producing other sulfur compounds, such as elemental sulfur (S°). These reactions reduce the efficiency of the hydrogen extraction loop, as some sulfur compounds may not be recoverable through the gas extraction well (1) depicted in FIG. 1 and FIG. 2. The accumulation of these sulfur species in the subsurface can result in an imbalance between the sulfur compounds94241419. vl6196.1005001 injected into and extracted from the subsurface, which must be managed to maintain the stability and efficiency of the entire hydrogen extraction process loop.

[0051] To address this imbalance, in one embodiment, an additional H2S feedstock may be introduced into the system. This feedstock is injected into either the H2S reformer (3) in FIG.1 or the H2S decomposition unit (7) in FIG. 2 to provide additional sulfur materials and maintain sulfur material balance within the loop. The hydrogen sulfide feedstock may be sourced from natural gas processing plants, refineries, or coal gasification plants, all of which produce hydrogen sulfide as a byproduct.

[0052] In another embodiment, an additional SO2 feedstock may be introduced into the system, either at the gas injection well (5) in FIG. 1 and FIG. 2, to ensure sulfur material balance. This feedstock can be obtained from industrial processes where sulfur combustion occurs, such as in chemical plants, refineries, and power plants. By introducing additional sulfur dioxide into the loop, the system can maintain stable sulfur cycling and ensure that sulfur recovery processes at the surface remain efficient.

[0053] In another embodiment, an additional elemental sulfur feedstock may be introduced along with a sulfur oxidation unit to supply supplemental sulfur dioxide (SO2) at the gas injection well (5) shown in FIG. 1, ensuring that the sulfur material balance is maintained throughout the process. The elemental sulfur feedstock is typically in solid form, making it easy to transport, store, and handle. This feature offers practical advantages, especially in regions where natural hydrogen is present but there is a scarcity of hydrogen sulfide (H2S) or sulfur dioxide supplies. By using elemental sulfur as a starting material, the system can generate sulfur dioxide through an oxidation process, ensuring the continuous operation of the natural hydrogen extraction cycle without relying on external hydrogen sulfide or sulfur dioxide sources. This approach is particularly valuable for large-scale projects that aim to harness natural hydrogen resources in geographically isolated regions where existing supplies of sulfur compounds are limited or absent.

[0054] In another embodiment, an additional elemental sulfur feedstock may be introduced at the sulfur oxidation unit (8) depicted in FIG. 2 to supply sulfur dioxide and maintain sulfur material balance in the hydrogen extraction process. As with the previous embodiment, the use of solid elemental sulfur simplifies transportation and storage logistics, enabling the hydrogen extraction system to be deployed in remote or resource-constrained regions where natural hydrogen is abundant, but local supplies of hydrogen sulfide or sulfur dioxide are insufficient. The elemental sulfur is oxidized at the surface to produce sulfur dioxide, which is subsequently injected into the subsurface via the gas injection well. This method ensures that the extraction104241419. vl6196.1005001 loop continues efficiently, providing a steady supply of sulfur dioxide for the subsurface reactions with natural hydrogen. The solid-state form of elemental sulfur makes it an economically and logistically favorable option for maintaining a sustainable supply of sulfur dioxide across a range of geographic and operational conditions, ensuring the long-term feasibility of hydrogen production in regions that lack direct access to other sulfur compounds.

[0055] In another embodiment, an additional stream of water may be introduced at the gas injection well (5) in FIG. 1 and FIG. 2, where it is co-injected with the sulfur dioxide (SO2) stream into the subsurface. The co-inj ection of water with SO2 serves a dual purpose: dissolving SO2 into water to inj ect a liquid stream, facilitating the generation of hydrogen in the subsurface to enhance the efficiency of the overall hydrogen extraction process. Water plays a crucial role in key subsurface processes that produce hydrogen, such as the radiolysis of water and serpentinization.

[0056] Radiolysis, driven by the natural radioactivity of subsurface minerals (e.g., uranium, thorium, and potassium-bearing minerals), splits water molecules into hydrogen and oxygen. Although this process is slow, it represents a significant source of hydrogen over geological timescales. By injecting additional water into the subsurface, the radiolysis process can be augmented, potentially boosting the rate of hydrogen generation. Similarly, the process of serpentinization — which involves water reacting with iron-rich minerals like olivine in the presence of heat (typically from about 200°C to about 400°C) — is another important pathway for subsurface hydrogen production. The reaction between water and these minerals generates hydrogen, as well as hydroxide ions, contributing to the overall hydrogen yield from the subsurface environment. The injected water acts as a reactant in serpentinization, further driving these reactions, particularly in geologic formations that are rich in iron-bearing minerals.

[0057] The co-inj ection of water and SO2 allows for increased hydrogen production in these subsurface zones. The natural hydrogen generated from radiolysis or serpentinization reacts with the injected SO2, producing hydrogen sulfide (H2S) and water. This reaction not only helps to efficiently extract hydrogen atoms but also maintains the continuous cycling of sulfur compounds, thereby ensuring that the hydrogen extraction process operates at a high level of efficiency. The additional water serves as a replenishable reactant that sustains these hydrogen-producing processes, particularly in areas where natural subsurface water supplies may be insufficient to support large-scale hydrogen generation.

[0058] In certain configurations of the system, additional purification processes may be required to separate hydrogen sulfide from other gases produced during extraction. These114241419. vl6196.1005001 purification methods may include amine systems, membrane-based purification, or pressure swing adsorption (PSA) systems, which are capable of selectively separating hydrogen sulfide from nitrogen, carbon dioxide, and other inert gases, ensuring that a high-purity hydrogen sulfide stream is available for conversion.

[0059] In one embodiment, sulfur dioxide is injected into the subsurface as a compressed gas. This allows for efficient storage, handling, and injection of sulfur dioxide under pressure, enabling precise control of the injection process and optimizing the interaction between sulfur dioxide and natural hydrogen in the subsurface.

[0060] In another embodiment, sulfur dioxide is injected into the subsurface as a solvated aqueous mixture. This approach may offer advantages in certain geological conditions, where the solvation of sulfur dioxide in water or other solvents can enhance its reactivity with subsurface materials, facilitating its conversion into hydrogen sulfide and improving the overall efficiency of the hydrogen extraction process.Definitions

[0061] 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.

[0062] 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.

[0063] 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 ”

[0064] 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 these options is understood to fall within the meaning, and therefore satisfy the requirement of the term “and / or” as used124241419. vl6196.1005001 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.”

[0065] 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.”

[0066] “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.

[0067] 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 particular implementation 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.134241419. vl

Claims

6196.1005001CLAIMSWhat is claimed is:

1. A method for harvesting hydrogen from a natural hydrogen production zone comprising: introducing a stream comprising sulfur dioxide into a natural hydrogen production zone to produce a gas mixture containing hydrogen sulfide; harvesting the gas mixture containing hydrogen sulfide; and converting the hydrogen sulfide to hydrogen, thereby harvesting hydrogen from the natural hydrogen production zone.

2. A method for harvesting hydrogen from a natural hydrogen production zone comprising: introducing a stream comprising sulfur dioxide into a natural hydrogen production zone to produce a gas mixture containing hydrogen sulfide; harvesting the gas mixture containing hydrogen sulfide; and converting the hydrogen sulfide to hydrogen using an iodine looping cycle for a) decomposing the hydrogen sulfide to produce elemental sulfur and hydrogen; and performing an oxidation reaction to convert the elemental sulfur to sulfur dioxide, or b) reforming the hydrogen sulfide to produce sulfur dioxide and hydrogen, thereby harvesting hydrogen from the natural hydrogen production zone.

3. The method of claim 1, wherein the converting the hydrogen sulfide to hydrogen is performed by a decomposition process selected from a thermal process, a plasma process, a catalytic process, or an electrochemical process, to thereby decompose hydrogen sulfide into hydrogen gas and elemental sulfur (S°).

4. The method of any one of claims 1-3, wherein sulfur dioxide is introduced as a solvated component of an aqueous stream.

5. The method of any one of claims 1-3, wherein sulfur dioxide is introduced as a major (about 50 wtg% to about 99 wtg%) component of the stream.144241419. vl6196.10050016. The method of any one of claims 1-3, wherein sulfur dioxide is injected as a minor (about 1.0 wtg% to about 50 wtg%) component mixed with carbon dioxide as the stream.

7. The method of any one of claims 1-3, wherein a mixture of sulfur dioxide and water is introduced to increase subsurface hydrogen production.

8. The method of claim 1 or 2, wherein the converting is performed by hydrogen sulfide reforming.

9. The method of claim 1 or 2, wherein the converting is performed by hydrogen sulfide decomposition.

10. The method of any one of claims 1-3, wherein the harvested gas mixture contains a combination of at least hydrogen gas and hydrogen sulfide.

11. The method of any one of claims 1-3, wherein additional hydrogen sulfide is fed to the hydrogen sulfide reforming or the hydrogen sulfide decomposition reactions, to account for the sulfur components loss due to the accumulation of these sulfur species in the subsurface.

12. The method of any one of claims 1-3, wherein additional sulfur dioxide is introduced to account for the sulfur components loss due to the accumulation of these sulfur species in the subsurface.

13. The method of any one of claims 1 to 12, wherein the stream is introduced into the natural hydrogen production zone through a well or an injection well.

14. The method of any one of claims 1-3, wherein elemental sulfur is added using a sulfur oxidation unit to feed additional sulfur dioxide to the natural hydrogen production zone.

15. The method of any one of claims 1-14, wherein the method is performed on a single site or distributed across associated sites from the natural hydrogen production zone.154241419. vl

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