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1. (WO2019025905) OLIVINE DOPED ZINC OXIDE FOR HOT AND COLD GAS CLEANING
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OLIVINE DOPED ZINC OXIDE FOR HOT AND COLD GAS CLEANING

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent

Application No. 62/539,068, filed July 31, 2017, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

[0002] The present invention generally relates to gas cleaning processes. More specifically, the present invention relates to a method for removing sulfur compounds from a gas using absorbents comprising primarily olivine doped zinc oxide.

BACKGROUND OF THE INVENTION

[0003] Sulfur, even at extremely low concentrations, is corrosive and poisonous to metal catalysts that are used in many chemical processes. For example, in catalytic methane reforming units or methanol synthesis units, trace hydrogen sulfide erodes and poisons the catalytic active sites of the noble metal catalysts (copper and/or nickel), thereby reducing the efficiency of the catalysts and increasing production costs. Therefore, it is common practice to remove sulfur impurities, such as hydrogen sulfide from natural gas or syngas before it is subjected to catalytic processes.

[0004] Amine scrubbing is one of the conventional methods used for removing hydrogen sulfide from gas. Amine in an aqueous solution effectively removes hydrogen sulfide along with carbon dioxide. However, carbon dioxide in an aqueous solution can be corrosive to carbon steel from which the amine scrubbing instrument is typically made. When carbon dioxide concentration in the gas (natural gas or syngas) is relatively high, corrosion inhibitors and high concentrations of amine have to be applied, thereby increasing production costs. Hot-gas cleanup is another process used for sulfur removal from natural gas or syngas. This method uses an absorbent to react with hydrogen sulfide at a high temperature, thereby absorbing the hydrogen sulfide. However, absorbing efficiency and/or instability of absorbents at high temperatures are still the two major factors that weigh against this method. Often, absorbent materials of high absorbing efficiency evaporate under

appropriate temperatures for sulfur removal, thereby losing the absorbent and potentially introducing impurity into the gas.

[0005] For example, zinc oxide is one of the most commonly used solid absorbents in desulfurization process for natural gas or syngas. Zinc oxide has a high surface area per volume, an ideal pore structure, and a high density, all of which make zinc oxide ideal for absorbing and removing hydrogen sulfide from a gas. However, when zinc oxide is used as the absorbent, the operating temperature has to be below 500 °C to prevent partial evaporation of zinc, which occurs at temperatures higher than 500 °C. Therefore, improvements in this field are desired.

BRIEF SUMMARY OF THE INVENTION

[0006] A method has been discovered for removing impurities, such as sulfur compounds, from a gas. By using olivine doped zinc oxide as the absorbent, the evaporation issue for zinc at a high temperature is solved while the sulfur removing performance of the absorbent remains substantially the same as pure zinc oxide (ZnO).

[0007] Embodiments of the invention include a method of removing sulfur compounds from a gas. The method may comprise contacting the gas with olivine doped zinc oxide to desulfurize the gas, and collecting desulfurized gas.

[0008] Embodiments of the invention include a method of removing sulfur compounds from a gas comprising natural gas. The method may include contacting the gas with olivine doped zinc oxide to form zinc sulfide (ZnS), iron sulfide (FeS), and purified natural gas. The method may further include collecting the product comprising the natural gas.

[0009] Embodiments of the invention include a method of removing hydrogen sulfide from a gas comprising natural gas. The method may include contacting the gas with olivine doped zinc oxide at reaction conditions sufficient to form (1) zinc sulfide (ZnS), (2) iron sulfide and (3) purified natural gas and less than 100 ppb of hydrogen sulfide. The method may further include collecting the product comprising the natural gas. Further still, the method may include regenerating the olivine doped zinc oxide from sulfidized olivine doped zinc oxide at appropriate reaction conditions.

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

[0011] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0012] The terms "wt.%", "vol.%" or "mol.%" refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol.% of component.

[0013] The term "substantially" and its variations are defined to include ranges within

10%, within 5%, within 1%, or within 0.5%.

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

[0015] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0016] The use of the words "a" or "an" when used in conjunction with the term

"comprising," "including," "containing," or "having" in the claims or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0017] The words "comprising" (and any form of comprising, such as "comprise" and

"comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0018] The term "collect," as that term is used in the specification and/or claims, means collecting in storage means, and/or transferring or feeding to subsequent equipment or production unit for further processes.

[0019] The term "doped" and/or "doping" when used in the specification and/or claims, refers to the process of intentionally introducing impurities into a structure for the purpose of modulating the properties of such structure.

[0020] The process of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc., disclosed throughout the specification.

[0021] In the context of the present invention at least twenty embodiments are now described. Embodiment 1 is a method of removing sulfur compounds from a gas. The method includes the steps of contacting the gas with olivine doped zinc oxide; and collecting desulfurized gas. Embodiment 2 is the method of embodiment 1, wherein the sulfur compounds comprise hydrogen sulfide. Embodiment 3 is the method of any of embodiments 1 and 2, wherein the gas contains natural gas and/or syngas. Embodiment 4 is the method of any of embodiments 1 to 3, wherein olivine in the olivine doped zinc oxide contains 7 to 10 wt.% of iron oxides. Embodiment 5 is the method of any of embodiments 1 to 4, wherein the olivine doped zinc oxide contains 10 to 20 wt. % ZnO, and 80 to 90 wt.% olivine. Embodiment 6 is the method of any of embodiments 1 to 5, wherein the contacting the gas with olivine doped zinc oxide is performed at reaction conditions sufficient to form zinc sulfide (ZnS) and a product containing desulfurized gas. Embodiment 7 is the method of embodiment 6, wherein the reaction conditions sufficient to form zinc sulfide and a gas product include a temperature in a range of 400 °C to 800 °C. Embodiment 8 is the method of any of embodiments 1 to 7, wherein the gas before the contacting contains 10 to 100 ppm of hydrogen sulfide. Embodiment 9 the method of any of embodiments 1 to 8, wherein the desulfurized gas contains less than 100 ppb of hydrogen sulfide. Embodiment 10 is the method of any of embodiments 1 to 9, wherein the desulfurized gas is used to produce methanol. Embodiment 11 is the method of any of embodiments 1 to 10, wherein the gas is natural gas and the desulfurized gas contains primarily methane. Embodiment 12 is the method of any of embodiments 1 to 11, wherein the gas is syngas and the desulfurized gas comprises primarily carbon monoxide and hydrogen. Embodiment 13 is the method of any of embodiments 1 to 12, wherein the olivine doped zinc oxide is prepared by steps including wet-impregnating zinc nitrate with olivine to form an impregnated material; and calcining the impregnated material to form olivine doped zinc oxide. Embodiment 14 is the method of embodiment 13, wherein the impregnated material is calcined at a temperature of 500 °C to 800 °C. Embodiment 15 is the method of any of embodiments 1 to 14, wherein the olivine doped zinc oxide has a molar ratio of zinc to iron in a range of 1 to 1.7. Embodiment 16 is the method of any of embodiments 1 to 15, wherein the olivine doped zinc oxide has a surface area of less than 1 m2/g and a density of 3.2 to 3.4 g/cm3. Embodiment 17 is the method of any of embodiments 1 to 16, wherein the olivine doped zinc oxide is disposed in a fixed bed reactor. Embodiment 18 is the method of any of embodiments 1 to 17, further including the step of regenerating the olivine doped zinc oxide. Embodiment 19 is the method of embodiment 18, wherein the olivine doped zinc oxide is regenerated at a reaction temperature of 500 to 800 °C. Embodiment 20 is the method of any of embodiments 18 and 19, wherein the olivine doped zinc oxide is regenerated at an oxygen concentration of 10 to 20 vol. %.

[0022] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0024] FIG. 1 shows a schematic diagram of a system used for removing hydrogen sulfide from a gas, according to embodiments of the invention;

[0025] FIG. 2 shows a schematic flowchart of a method of removing hydrogen sulfide from a gas, according to embodiments of the invention; and

[0026] FIG. 3 shows breakthrough curves for a first absorbent comprising olivine doped zinc and a second absorbent comprising pure ZnO, respectively, in a desulfurization process, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] A method has been discovered for removing sulfur impurities, for example hydrogen sulfide, from a gas. By using olivine doped zinc oxide as an absorbent in both hot and cold gas cleaning processes, the zinc evaporation that occurs when using pure zinc oxide as an absorbent is minimized with sulfur removal rate comparable to pure zinc oxide. Further, the olivine doped zinc oxide may be regenerated, thereby reducing production costs.

[0028] With reference to FIG. 1, a process schematic diagram is shown as sulfur removal system 100 for removing hydrogen sulfide from a gas, according to embodiments of the invention. As shown in FIG. 1, sulfur removal system 100 may include reactor 101 with olivine doped zinc oxide disposed therein. In embodiments of the invention, reactor 101 may be a fixed bed reactor. The fixed bed may include an absorbent comprising primarily olivine doped zinc oxide. Heat exchanger 102 may be in fluid communication with an inlet of reactor 101. In embodiments of the invention, heat exchanger 102 may be configured to heat the gas to a reaction temperature sufficient for removing hydrogen sulfide therefrom.

[0029] Heat exchanger 103 may be in fluid communication with an inlet of reactor 101. In embodiments of the invention, heat exchanger 103 may be configured to heat oxygen enriched air. The heated oxygen enriched air may be used to regenerate the olivine doped zinc oxide from sulfidized olivine doped zinc oxide, after the hydrogen sulfide removing process. Steam reforming unit 104 may be in fluid communication with an outlet of reactor 101, configured to generate syngas from desulfurized natural gas in the effluent of reactor 101. In embodiments of the invention, the formed syngas then flows to methanol production unit 105. The syngas may comprise primarily carbon monoxide, hydrogen and carbon dioxide. The syngas may be used to generate methanol over noble metal catalysts comprising copper and/or nickel. Because the reaction temperature for methanol production from syngas may be 200 °C to 260 °C, in embodiments of the invention, the hydrogen sulfide is substantially eliminated by reactor 101 to prevent it from poisoning and eroding the copper and/or nickel catalysts. Sulfur dioxide treatment unit 106 may be in fluid communication with an outlet of reactor 101. In embodiments of the invention, sulfur dioxide treatment unit 106 may be configured to convert sulfur dioxide generated from regeneration of the olivine doped zinc oxide to elemental sulfur and/or sulfuric acid.

[0030] As described above, zinc oxide is a solid absorbent commonly used in desulfurization process for natural gas or syngas. However, the desulfurization temperature when zinc dioxide is used as the absorbent has to be under 500 °C due to partial evaporation of zinc at temperatures higher than 500 °C. The low reaction temperature may reduce the reaction rate of zinc oxide sulfidation and decrease a breakthrough time of the absorbent, which can lead to hydrogen sulfide slippage. Olivine is a silicate of magnesium and iron. Foreign ions such as Ni2+, Fe2+ and Zn2+ may be introduced into the olivine structure. In embodiments of the invention, Zn-Fe oxides may be generated in the olivine structure at a high calcination temperature to increase the stability of zinc at a high reaction temperature. Using such stable material (Zn-olivine) at high temperature improves hydrogen sulfide removal.

[0031] FIG. 2 shows method 200 for removing sulfur compounds from a gas, according to embodiments of the invention. Method 200 may be implemented by sulfur removal system 100 as shown in FIG. 1. As shown in block 201, zinc nitrate, which may be used as a precursor salt for the wet-impregnation, is dissolved in deionized water to form a homogeneous solution. The solution can be applied to the olivine material. In embodiments of the invention, the zinc nitrate solution may have a zinc concentration in a range of 10 to 20 wt.% and all ranges and values there between, including 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, and 19 wt.%. Block 202 shows that the impregnated material may be calcined to form an absorbent comprising primarily olivine doped zinc oxide. In embodiments of the invention, the impregnated material may be calcined at a temperature of 500 °C to 800 °C and all ranges and values there between, including 500 °C to 515 °C, 515 °C to 530 °C, 530 °C to 545 °C, 545 °C to 560 °C, 560 °C to 575 °C, 575 °C to 590 °C, 590 °C to 605 °C, 605 °C to 620 °C, 620 °C to 635 °C, 635 °C to 650 °C, 650 °C to 665 °C, 665 °C to 680 °C, 680 °C to 695 °C, 695 °C to 710 °C, 710 °C to 725 °C, 725 °C to 740 °C, 740 °C to 755 °C, 755 °C to 770 °C, 770 °C to 785 °C, or 785 °C to 800 °C.

[0032] In embodiments of the invention, the absorbent may have a molar ratio of zinc to iron in a range of 1 to 1.7 and all ranges and values there between, including 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7. The olivine doped zinc oxide may comprise 10 to 20 wt.% zinc oxide (ZnO) and 80 to 90 wt.% olivine.

[0033] Further, the olivine doped zinc oxide may include iron oxide (Fe2Cb). The weight percentage of the iron oxide in the olivine doped zinc oxide may be 7 to 10 wt.% and all ranges and values there between, including 7 to 7.2 wt.%, 7.2 to 7.4 wt.%, 7.4 to 7.6 wt.%, 7.6 to 7.8 wt.%, 7.8 to 8.0 wt.%, 8.0 to 8.2 wt.%, 8.2 to 8.4 wt.%, 8.4 to 8.6 wt.%, 8.6 to 8.8 wt.%, 8.8 to 9.0 wt.%, 9.0 to 9.2 wt.%, 9.2 to 9.4 wt.%, 9.4 to 9.6 wt.%, 9.6 to 9.8 wt.%, or 9.8 to 10 wt.%). In embodiments of the invention, the olivine doped zinc oxide has a surface area of less than 1 m2/g and a density of 3.2 to 3.4 g/cm3 and all ranges and values there between.

[0034] As shown in block 203, method 200 may include contacting the gas with olivine doped zinc oxide. Method 200 may be performed using reactor 101 that includes an absorbent comprising primarily olivine doped zinc oxide. As described above, reactor 101 may be a fixed bed reactor. In embodiments of the invention, the sulfur compounds may comprise hydrogen sulfide. The gas may be natural gas and/or syngas.

[0035] In embodiments of the invention, the contacting in block 203 may include contacting the gas with olivine doped zinc oxide at reaction conditions sufficient to form zinc sulfide and a product comprising desulfurized gas. Main reactions in block 203 may include:


Fe203 + 4H2S > 2FeS2 +3H20 + H2 (ii)

Fe203 + 2H2S +H2 >2FeS + 3H20 (iii)

The reaction conditions sufficient to form zinc sulfide, iron sulfide, and a product comprising desulfurized gas may include a reaction temperature in a range of 400 °C to 850 °C and all ranges and values there between, including 400 °C to 415 °C, 415 °C to 430 °C, 430 °C to 445 °C, 445 °C to 460 °C, 460 °C to 475 °C, 475 °C to 490 °C, 490 °C to 505 °C, 505 °C to 520 °C, 520 °C to 535 °C, 535 °C to 550 °C, 550 °C to 565 °C, 565 °C to 580 °C, 580 °C to 595 °C, 595 °C to 610 °C, 610 °C to 625 °C, 625 °C to 640 °C, 640 °C to 655 °C, 655 °C to 670 °C, 670 °C to 685 °C, 685 °C to 700 °C, 700 °C to 715 °C, 715 °C to 730 °C, 730 °C to 745 °C, 745 °C to 760 °C, 760 °C to 775 °C, 775 °C to 790 °C, 790 °C to 805 °C, 805 °C to 820 °C, 820 °C to 835 °C, or 835 °C to 850 °C.

According to embodiments of the invention, the reaction conditions sufficient to form zinc sulfide, iron sulfide and a product comprising desulfurized gas may further include an operating pressure of 0.1 to 1 MPa and all ranges and values there between including 0.1 MPa to 0.2 MPa, 0.2 MPa to 0.3 MPa, 0.3 MPa to 0.4 MPa, 0.4 MPa to 0.5 MPa, 0.5 MPa to 0.6 MPa, 0.6 MPa to 0.7 MPa, 0.7 MPa to 0.8 MPa, 0.8 MPa to 0.9 MPa, and 0.9 MPa to 1.0 MPa. In embodiments of the invention, the reaction conditions sufficient to form zinc sulfide, iron sulfide and a product comprising desulfurized gas may further still include a gas hourly space velocity of 1000 to 5000 hr"1, and all ranges and values there between including 1000 hr"1 to 2000 hr"1, 2000 hr^ to 3000 hr 1, 3000 hr^ to 4000 hr"1, and 4000 hr^ to 5000 hr"1.

[0036] In embodiments of the invention, the gas may comprise 10 to 100 ppm of hydrogen sulfide before the contacting in block 203. In embodiments of the invention, the desulfurized gas, which may include desulfurized natural gas and/or desulfurized syngas, may have a hydrogen sulfide concentration of less than 100 ppb. In embodiments of the invention, when the gas is primarily natural gas, the desulfurized gas may comprise primarily methane. Additionally or alternatively, when the gas is primarily syngas, the desulfurized gas may comprise primarily carbon monoxide and hydrogen. Block 204 shows that the desulfurized gas may be collected. In the collecting desulfurized gas, it may be flowed to a separate unit such as a methanol production unit. In embodiments of the invention, the methanol may be produced by reacting the desulfurized gas over a copper and/or nickel catalyst. If the gas is natural gas, the desulfurized natural gas may be flowed to the steam reforming unit to form syngas. The formed syngas may further flow to the methanol production unit to produce methanol.

[0037] In embodiments of the invention, as the absorbent comprising primarily olivine doped zinc oxide removes hydrogen sulfide, the zinc oxide and iron oxide is consumed via sulfidation. As shown in block 205, the olivine doped zinc oxide in the absorbent may be regenerated from sulfidized olivine doped zinc oxide under appropriate reaction conditions. The main reactions in the regenerating may include:

2ZnS + 302 ^ 2ZnO + 2SC-2 (iv)

4FeS + 702 2Fe203 + 4S02 (v)

[0038] The regenerated absorbent comprising primarily olivine doped zinc oxide may be placed back for desulfurization of gas containing sulfur compounds. The formed sulfur dioxide may be treated further to form elemental sulfur via the CLAUS process. Alternative to or in addition to forming elemental sulfur, the formed sulfur dioxide may be treated to form sulfuric acid. In embodiments of the invention, the reaction conditions for regenerating olivine doped zinc oxide may include a temperature of 500 to 800 °C and all ranges and values there between including ranges of 500 °C to 520 °C, 520 °C to 540 °C, 540 °C to 560 °C, 560 °C to 580 °C, 580 °C to 600 °C, 600 °C to 620 °C, 620 °C to 640 °C, 640 °C to 660 °C, 660 °C to 680 °C, 680 °C to 700 °C, 700 °C to 720 °C, 720 °C to 740 °C, 740 °C to 760 °C, 760 °C to 780 °C, and 780 °C to 800 °C. The reaction conditions for regenerating olivine doped zinc oxide may further include reaction pressure of 0.1 to 1 MPa and all ranges and values there between including 0.1 MPa to 0.2 MPa, 0.2 MPa to 0.3 MPa, 0.3 MPa to 0.4 MPa, 0.4 MPa to 0.5 MPa, 0.5 MPa to 0.6 MPa, 0.6 MPa to 0.7 MPa, 0.7 MPa to 0.8 MPa, 0.8 MPa to 0.9 MPa, and 0.9 MPa to 1.0 MPa. The reaction conditions for regenerating olivine doped zinc oxide may further still include an oxygen concentration of 10 to 20 vol.% and all ranges and values there between, including 11 vol.%, 12 vol.%, 13 vol.%, 14 vol.%, 15 vol.%), 16 vol.%), 17 vol.%, 18 vol.%, and 19 vol.%. According to embodiments of the invention, the gas hourly space velocity for regenerating olivine doped zinc oxide may be in a range of 1000 to 5000 per hour and all ranges and values there between including 1000 hr"1 to 2000 hr-1, 2000 hr-1 to 3000 hr-1, 3000 hr-1 to 4000 hr-1, and 4000 hr 1 to 5000 hr 1. The olivine doped zinc oxide may be regenerated for at least 10 cycles.

[0039] In summary, embodiments of the invention involve methods of removing sulfur compounds from a gas. Olivine doped zinc oxide is used as an absorbent to remove the sulfur compounds. By forming Zn-Fe oxides in the olivine doped zinc oxide, the evaporation of zinc at the temperature above 500 °C can be minimized while the sulfur removal ability of the olivine doped zinc oxide may be substantially the same as pure zinc oxide (ZnO). Further, the olivine doped zinc oxide may be regenerated and recycled in the sulfur removing process.

[0040] Although embodiments of the present invention have been described with reference to blocks of FIG. 2, it should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIG. 2. Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 2.

[0041] As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLES

Example 1

(Comparison of Desulfurization Performances between ZnO and Olivine Doped ZnO)

[0042] To evaluate and benchmark desulfurization performance of olivine doped zinc oxide over commercial ZnO, 2 g of each was used for desulfurizing a FhS-helium stream that comprises 1 vol.% FhS. The reaction conditions included a reaction temperature of 600 °C and a reaction pressure of 1 bar for olivine doped zinc oxide and a reaction temperature of 400 °C and a reaction pressure of 1 bar for ZnO (commercial, 99 wt.%). The total sulfur removal capacity of olivine doped zinc oxide and zinc oxide (ZnO) were determined.

[0043] The results show that the performance of Zn-olivine, which is a less expensive material, is comparable to the pure ZnO in the desulphurization process. Furthermore, Zn-olivine absorbent can be regenerated and reused for at least 5 to 10 cycles for the desulfurization process. FIG. 3 shows comparisons of the breakthrough curves of sulfidation for a Zn-olivine absorbent comprising 20 wt.% Zn/20 wt.% Fe/olivine and a ZnO absorbent comprising pure ZnO (commercial grade). The two absorbents have shown comparable performances with similar breakthrough time and full sulfur removal capacity, which was determined by integration of the area over the breakthrough curves and was found to be respectively 24 wt.% for the Zn-olivine absorbent and 39 wt.% for the ZnO absorbent.

[0044] The low sulfur removal capacity of Zn-olivine absorbent compared to the ZnO absorbent is due to the low Zn weight percentage (20 wt.%) in the Zn-olivine absorbent and the presence of iron in the structure of olivine. In addition, the major advantage of the Zn-olivine absorbent resides in the stability of the absorbent performances at high and low temperature. The Zn-olivine absorbent could be used as a guard for sulfur between desulfurizer reactors and steam methane reformer reactor. The gas stream that requires

desulfurization typically contains less than 100 ppb H2S or at most 100 ppm H2S in the gas stream coming from desulfurizer reactors.

[0045] In conclusion, impregnation/insertion of Zn and/or iron in the olivine structure which was calcined at 800 °C leads to activation of H2S and stabilization of Zn-olivine structure at low and high temperature. This Zn-olivine structure can be used as a guard after desulfurizer reactors for temperature range of 400 °C to 800 °C.

[0046] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.