Iron oxyhydroxide-based hydrogen sulfide removing agent, method for producing iron oxyhydroxide-based hydrogen sulfide removing agent, and desulfurization method

Abstract

Provided is a hydrogen sulfide removing agent that can be stably used while maintaining hydrogen sulfide removing ability equivalent to that of a hydrogen sulfide removing agent comprising an amorphous iron oxyhydroxide. This iron oxyhydroxide-based hydrogen sulfide removing agent contains amorphous iron oxyhydroxide and a crystalline component. The content of the amorphous iron oxyhydroxide is not less than the content of the crystalline component.

Description

Iron oxyhydroxide-based hydrogen sulfide remover, method for producing iron oxyhydroxide-based hydrogen sulfide remover, and desulfurization method

[0001] The present invention relates to an iron oxyhydroxide-based agent for removing hydrogen sulfide and a method for producing the same, and also to a desulfurization method using the iron oxyhydroxide-based agent for removing hydrogen sulfide.

[0002] Gases generated in various facilities such as steelmaking, petrochemical, and sewage treatment facilities include hydrogen sulfide (H ２ The gas contains hydrogen sulfide, which causes foul odors and corrosion of pipes. Therefore, there is a need for technology to remove hydrogen sulfide from the gas.

[0003] Also, such gases contain a large amount of CO ２ It often contains CO ２ From the viewpoint of reducing emissions, CO in gas ２ A technology has been proposed to recycle hydrogen sulfide by converting it into methanol or other products through catalytic reactions. However, hydrogen sulfide in the gas deteriorates the catalyst, so there is a need for a technology to remove the hydrogen sulfide contained in the gas in order to prevent catalyst deterioration.

[0004] Therefore, methods have been proposed for adsorbing and removing hydrogen sulfide from gases using dry hydrogen sulfide removers made of iron oxyhydroxide (FeOOH), such as α-FeOOH (goethite) and β-FeOOH (akaganite) (see, for example, Patent Documents 1 and 2). Iron oxyhydroxide has many basic OH groups on its surface, so it can easily adsorb and remove hydrogen sulfide from acidic H ２ S is adsorbed by acid-base interaction. Therefore, iron oxyhydroxide is ２ O ３ It has superior performance as a hydrogen sulfide remover compared to other substances.

[0005] However, the hydrogen sulfide removal rate was still not sufficient, and further improvements in performance were required for use in applications such as steelmaking, petrochemicals, and sewage treatment plants.

[0006] Therefore, instead of crystalline iron oxyhydroxides such as goethite or akaganite, hydrogen sulfide removers containing amorphous iron oxyhydroxide have been proposed (Patent Document 3). According to Patent Document 3, amorphous iron oxyhydroxide is not crystallized, and therefore has a large surface area that contributes to reaction with sulfur compounds. As a result, it has a higher reaction rate with sulfur compounds than crystalline iron oxyhydroxides such as akaganite, and can completely remove low concentrations of sulfur compounds.

[0007] Japanese Patent Laid-Open No. 05-329362 Japanese Patent Laid-Open No. 2014-213281 Japanese Patent Laid-Open No. 2017-177052

[0008] As proposed in Patent Document 3, by using amorphous iron oxyhydroxide, excellent hydrogen sulfide removal performance can be obtained.

[0009] However, such hydrogen sulfide removing agents made of amorphous iron oxyhydroxide have the problem of low strength and cannot be used stably. Specifically, hydrogen sulfide removing agents made of amorphous iron oxyhydroxide are produced by reacting an aqueous iron chloride solution with an alkaline aqueous solution (neutralizing agent) and hydrogen peroxide (oxidizing agent), as described in Patent Document 3. Since crystal growth is not possible to obtain an amorphous structure, the resulting amorphous iron oxyhydroxide inevitably becomes an aggregate of extremely fine particles. A hydrogen sulfide removing agent made of such fine particles has low strength and cannot withstand its own weight when packed into a desulfurization tower, easily collapsing and pulverizing.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a hydrogen sulfide remover that can be used stably while maintaining hydrogen sulfide removal performance equivalent to that of a hydrogen sulfide remover made of amorphous iron oxyhydroxide.

[0011] The present invention aims to solve the above problems, and has the following gist and configuration.

[0012] 1. An iron oxyhydroxide-based hydrogen sulfide removing agent containing amorphous iron oxyhydroxide and a crystalline component, wherein the content of the amorphous iron oxyhydroxide is equal to or greater than the content of the crystalline component.

[0013] 2. The iron oxyhydroxide-based hydrogen sulfide removing agent according to item 1, wherein the content of the amorphous iron oxyhydroxide is 50 to 80 wt %.

[0014] 3. The iron oxyhydroxide-based hydrogen sulfide removing agent according to 1 or 2 above, which contains crystalline iron oxide as at least a portion of the crystalline component.

[0015] 4. A method for producing an iron oxyhydroxide-based hydrogen sulfide removing agent according to any one of items 1 to 3 above, comprising: a neutralization step of neutralizing an aqueous solution containing iron ions to precipitate iron; a coagulation and precipitation step of coagulating and precipitating the iron obtained in the neutralization step and removing the supernatant to obtain an iron hydroxide-containing slurry; a solid-liquid separation step of performing solid-liquid separation of the iron hydroxide-containing slurry to obtain an iron oxyhydroxide-containing cake; and a drying step of drying the iron oxyhydroxide-containing cake to obtain iron oxyhydroxide.

[0016] 5. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to 4 above, wherein the aqueous solution containing iron ions is a waste liquid containing iron ions.

[0017] 6. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to 4 or 5 above, wherein a calcium compound is used as the neutralizing agent in the neutralization step.

[0018] 7. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to any one of the above items 4 to 6, wherein the pH is adjusted to 6 to 8 in the neutralization step.

[0019] 8. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to any one of items 4 to 7 above, wherein an anionic polymer is used as a flocculant in the coagulation and precipitation step.

[0020] 9. A desulfurization method for removing hydrogen sulfide contained in a gas using the iron oxyhydroxide-based hydrogen sulfide remover according to any one of 1 to 3 above.

[0021] The hydrogen sulfide removing agent of the present invention contains amorphous iron oxyhydroxide in an amount equal to or greater than the amount of crystalline component, and as a result, has hydrogen sulfide removal performance equivalent to that of conventional hydrogen sulfide removing agents made of amorphous iron oxyhydroxide. Furthermore, because the hydrogen sulfide removing agent of the present invention contains a crystalline component in addition to amorphous iron oxyhydroxide, it has a smaller specific surface area, i.e., a larger particle size, than conventional hydrogen sulfide removing agents made of amorphous iron oxyhydroxide. This results in high strength and stable use. Thus, the hydrogen sulfide removing agent of the present invention has excellent stability yet possesses hydrogen sulfide removal performance equivalent to that of conventional hydrogen sulfide removing agents made of amorphous iron oxyhydroxide, making it extremely suitable for use in removing hydrogen sulfide.

[0022] 1 is a graph showing the correlation between the proportion of amorphous iron oxyhydroxide contained in the hydrogen sulfide removing agent and the sulfur adsorption amount per weight. 2 is a graph showing an example of cumulative pore volume distribution in the hydrogen sulfide removing agent. 3 is a graph showing the correlation between the proportion of amorphous iron oxyhydroxide contained in the hydrogen sulfide removing agent and the sulfur adsorption amount per surface area.

[0023] Hereinafter, embodiments of the present invention will be described in detail.

[0024] [Hydrogen sulfide removing agent] In one embodiment of the present invention, the iron oxyhydroxide-based hydrogen sulfide removing agent contains amorphous iron oxyhydroxide and a crystalline component, and the content of the amorphous iron oxyhydroxide is equal to or greater than the content of the crystalline component. The reason for this is explained below.

[0025] As described above, the hydrogen sulfide removing agent proposed in Patent Document 3 is composed of amorphous iron oxyhydroxide and does not contain crystalline iron oxyhydroxide. This is evident from the fact that, as described in paragraphs

[0023] and

[0028] and Figure 1 of Patent Document 3, only diffraction peaks of sodium chloride, an impurity, are observed in X-ray diffraction.

[0026] When producing such amorphous iron oxyhydroxide, crystal growth is not possible, and therefore the particles constituting the amorphous iron oxyhydroxide are inevitably very fine, resulting in problems such as low strength and inability to be used stably.

[0027] Conversely, the crystalline component is obtained by growing crystals, and therefore has larger particles than amorphous iron oxyhydroxide. Therefore, by including a crystalline component in addition to amorphous iron oxyhydroxide in a hydrogen sulfide removal agent, the strength is improved and stable use becomes possible. Note that differences in particle size contained in hydrogen sulfide removal agents can be evaluated based on the specific surface area, as described below.

[0028] However, in Patent Document 3, the large specific surface area of ​​fine amorphous iron oxyhydroxide is utilized to improve the hydrogen sulfide removal performance. Based on the knowledge of this prior art, it is presumed that the addition of a crystalline component with large particles reduces the specific surface area, and as a result, the hydrogen sulfide removal performance also decreases.

[0029] However, as a result of investigations, the inventors have found that even if crystalline components are present in the hydrogen sulfide removal agent, as long as the content of amorphous iron oxyhydroxide is equal to or greater than the content of crystalline components, the hydrogen sulfide removal performance can be maintained at approximately the same level as that of a hydrogen sulfide removal agent made of amorphous iron oxyhydroxide.

[0030] For example, Figure 1 is a graph showing the correlation between the proportion of amorphous iron oxyhydroxide (FeOOH) contained in the hydrogen sulfide removing agent and the sulfur adsorption amount per weight. The amount of amorphous iron oxyhydroxide and the sulfur adsorption amount per weight were measured by the methods described in the Examples below. The remainder other than the amorphous iron oxyhydroxide is substantially a crystalline component.

[0031] As can be seen from this graph, as long as the content of amorphous iron oxyhydroxide is equal to or greater than the content of the remaining crystalline component, performance is maintained at approximately the same level as when the content of amorphous iron oxyhydroxide is 100%. Therefore, in the present invention, the content of amorphous iron oxyhydroxide is set to be equal to or greater than the content of the crystalline component. The content of amorphous iron oxyhydroxide is preferably 50 to 80 wt %. The content of amorphous iron oxyhydroxide can be measured by a combination of the Karl Fischer method and X-ray diffraction measurement. That is, the content of amorphous iron oxyhydroxide can be determined by subtracting the content of crystalline iron oxyhydroxide determined by X-ray diffraction measurement from the content of iron oxyhydroxide determined by the Karl Fischer method. More specifically, it can be determined by the method described in the Examples.

[0032] The reason why the hydrogen sulfide removing agent maintains excellent desulfurization performance even when it contains a certain amount of crystalline components is thought to be as follows.

[0033] First, the reaction that occurs when hydrogen sulfide is brought into contact with iron oxyhydroxide is expressed by the following formula (1): 2FeOOH + 3H ２ S → Fe ２ S ３ +4H ２ O...(1)

[0034] Since the above reaction occurs on the surface of the hydrogen sulfide removing agent, the surface area of ​​the hydrogen sulfide removing agent affects the desulfurization performance.

[0035] However, the Fe produced in the above reaction ２ S ３ Since Fe is unstable, it changes into FeS and elemental sulfur through the reaction shown in (2) below. The generated FeS and elemental sulfur accumulate on the surface of the hydrogen sulfide remover. ２ S ３ → 2FeS + S (2)

[0036] 2 is a graph showing an example of the cumulative pore volume distribution in a hydrogen sulfide removing agent, in which the dashed line represents the measured value for a hydrogen sulfide removing agent made of amorphous iron oxyhydroxide (Comparative Example No. 4 in the Examples described below), and the solid line represents the measured value for a hydrogen sulfide removing agent containing 48 wt % of a crystalline component (Invention Example No. 1 in the Examples described below). The specific surface area was measured by the method described in the Examples.

[0037] As can be seen from this graph, the pores present in the hydrogen sulfide remover made of amorphous iron oxyhydroxide are mainly fine pores with diameters of 4.4 nm or less, with almost no pores with diameters exceeding 4.4 nm. This is thought to be because the amorphous iron oxyhydroxide particles themselves are extremely fine. 4.4 nm is approximately 10 times the diameter of a hydrogen sulfide molecule.

[0038] Thus, since the pores present in the hydrogen sulfide removing agent made of amorphous iron oxyhydroxide are extremely fine, they are likely to be blocked by sulfur produced in the reaction of formula (2) above, preventing them from contributing to the removal of hydrogen sulfide. As a result, the amount of sulfur adsorbed per surface area of ​​the hydrogen sulfide removing agent made of amorphous iron oxyhydroxide is low.

[0039] On the other hand, the proportion of large-diameter pores in the hydrogen sulfide removal agent containing crystalline components is significantly higher than in the hydrogen sulfide removal agent made of amorphous iron oxyhydroxide. Therefore, it is thought that the hydrogen sulfide removal agent containing crystalline components is less likely to have pores clogged by generated sulfur, and as a result, it can maintain high desulfurization performance.

[0040] For example, Figure 3 is a graph showing the correlation between the proportion of amorphous iron oxyhydroxide contained in the hydrogen sulfide removing agent and the amount of sulfur adsorption per surface area under the same conditions as in Figure 1. The amount of amorphous iron oxyhydroxide and the amount of sulfur adsorption per surface area were measured by the methods described in the Examples below.

[0041] As can be seen from this graph, the amount of sulfur adsorbed per surface area is actually greater when a certain amount of crystalline components is included than when the proportion of amorphous iron oxyhydroxide is 100 wt %.

[0042] However, if the proportion of amorphous iron oxyhydroxide is less than 50 wt %, the amount of sulfur adsorbed per surface area decreases. This is because the proportion of the surface of the hydrogen sulfide remover that is occupied by amorphous iron oxyhydroxide capable of adsorbing hydrogen sulfide decreases. Therefore, from this point of view as well, it is preferable that the content of amorphous iron oxyhydroxide be 50 wt % or more.

[0043] (Crystalline Component) The crystalline component is not particularly limited and may be any substance having a crystalline structure. The crystalline component may typically be at least one selected from the group consisting of a crystalline oxide, a crystalline hydroxide, and a crystalline metal salt.

[0044] The crystalline oxide may be either a crystalline metal oxide or a crystalline non-metal oxide, and examples of the crystalline oxide include at least one oxide selected from the group consisting of Fe, Co, Ni, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Mg, Al, Zn, Ca, Mn, Cu, and Si.

[0045] The crystalline hydroxide may be, for example, at least one hydroxide selected from the group consisting of Fe, Al, Mg, Zn, Ni, Mn, and Cr.

[0046] Examples of the crystalline metal salt include metal carbonates and metal sulfates. For example, calcium hydroxide (Ca(OH) ２ ) and calcium carbonate (CaCO ３ When a calcium compound such as NaOH is used as a neutralizing agent, the final hydrogen sulfide remover contains crystalline calcium carbonate. Similarly, when a Na compound such as NaOH is used as a neutralizing agent, the final hydrogen sulfide remover contains crystalline sodium carbonate (Na ２ CO ３ In addition, when sulfate ions are present in the aqueous solution, crystalline sulfates such as iron sulfate and calcium sulfate may also be present.

[0047] In the present invention, it is sufficient that the content of amorphous iron oxyhydroxide is equal to or greater than the content of the crystalline component. In other words, it is sufficient that the content of the crystalline component is less than the content of amorphous iron oxyhydroxide. The preferred content of the crystalline component is 5 to 50 wt %. The content of the crystalline component can be measured by X-ray diffraction measurement. More specifically, it can be measured by the method described in the Examples.

[0048] (Specific Surface Area) As described above, the hydrogen sulfide removing agent of the present invention contains a crystalline component, and therefore has a larger particle size than conventional hydrogen sulfide removing agents made of amorphous iron oxyhydroxide. This difference in particle size can be evaluated based on the specific surface area. That is, the smaller the specific surface area, the larger the particle size.

[0049] The specific surface area of ​​the iron oxyhydroxide-based hydrogen sulfide remover of the present invention is not particularly limited, but is preferably 100 m ２ / g or more, and ２ / g or more is more preferable, and 120m ２ On the other hand, the upper limit of the specific surface area is not particularly limited, but is typically 200 m ２ / g or less, and ２ / g or less is more preferable, and 160m ２ It is more preferable that the SiO2 content is 1 / g or less.

[0050] The specific surface area herein refers to the BET specific surface area measured using nitrogen gas. More specifically, it can be measured by the method described in the Examples.

[0051] [Manufacturing Method] Next, a manufacturing method of an iron oxyhydroxide-based hydrogen sulfide removing agent according to one embodiment of the present invention will be described. The manufacturing method according to this embodiment includes the following steps (1) to (4). Each step will be described below. (1) Neutralization step (2) Coagulation and sedimentation step (3) Solid-liquid separation step (4) Drying step

[0052] (1) Neutralization Step First, an aqueous solution containing iron ions is neutralized to precipitate iron (neutralization step). The iron ions are not particularly limited and may be either divalent iron ions or trivalent iron ions.

[0053] For example, when the aqueous solution contains trivalent iron ions, the iron ions are precipitated as iron hydroxide as represented by the following formula (3): ３＋ +3OH － → Fe(OH) ３ ↓ … (3)

[0054] In the above formula (3), the stoichiometric ratio (molar ratio) of Fe to OH is 1:3, but in an actual reaction, this is not necessarily 1:3.

[0055] Furthermore, when the aqueous solution contains divalent iron ions, it is preferable to oxidize the divalent iron ions to trivalent iron ions in advance. Although there are no particular limitations on the method for oxidizing the divalent iron ions, a method of bubbling an oxygen-containing gas (preferably air) into the aqueous solution is particularly preferred.

[0056] Any aqueous solution containing iron ions can be used, but from the viewpoint of effective utilization of resources, it is preferable to use a waste liquid containing iron ions. The type of the waste liquid is not particularly limited, but for example, waste liquid generated in the iron manufacturing process of a steelworks can be suitably used because it contains a sufficient amount of iron ions.

[0057] The waste liquid generated in the steelmaking process of a steelworks is not particularly limited, and any waste liquid containing iron ions can be used. Examples of the waste liquid include pickling waste liquid generated in the pickling process of the steel sheet surface and rinsing waste liquid generated in the rinsing process in which the steel sheet surface is washed with water after the pickling process. In steelworks, it is common for waste liquids generated in multiple processes to be collected in a mixed state and treated collectively. Therefore, in the present invention, a mixed waste liquid generated in multiple processes of a steelworks can be used.

[0058] Furthermore, waste liquid generated during the iron manufacturing process may contain solids such as dust. The aqueous solution containing iron ions in the present invention may also contain such solids. When the aqueous solution containing iron ions contains solids, at least a portion of the solids will be mixed as impurities into the iron hydroxide-containing slurry recovered in the coagulation and sedimentation step. However, as long as the content of amorphous iron oxyhydroxide in the finally obtained iron oxyhydroxide-based hydrogen sulfide remover satisfies the above-mentioned conditions, there will be no problem with its function as a hydrogen sulfide remover.

[0059] The pH in the neutralization step is not particularly limited, but if the pH is too low, Fe ions become stable in the aqueous solution, and iron hydroxide may not be sufficiently precipitated. Therefore, the pH is preferably 6 or higher. On the other hand, if the pH is too high, the generated iron hydroxide may crystallize and turn into goethite (α-FeOOH), which has poor desulfurization performance. Therefore, the pH is preferably 8 or lower.

[0060] To neutralize, a neutralizing agent is added to an aqueous solution containing iron ions. There are no particular limitations on the neutralizing agent, and any agent can be used. However, if a strong basic agent such as sodium hydroxide (NaOH) is used as the neutralizing agent, crystallization of iron hydroxide may occur. This is thought to be because when NaOH is added to the aqueous solution, it is not mixed uniformly, resulting in localized areas where the pH exceeds 8. On the other hand, when CaCO 2 is used as the neutralizing agent, ３ and Ca(OH) ２ The use of calcium compounds such as NaOH allows the pH to be increased gradually. As a result, it is possible to prevent the pH from becoming excessively high locally. Furthermore, calcium compounds are cheaper than NaOH, so the production cost of the hydrogen sulfide remover can be reduced. For these reasons, it is preferable to use calcium compounds as the neutralizing agent, and CaCO ３ and Ca(OH) ２ It is more preferable to use one or both of the above.

[0061] Among calcium compounds, Ca(OH) ２On the other hand, CaCO ３ Although the neutralizing effect is weak, it has the function of helping the iron hydroxide particles to be aggregated by binding them together. Therefore, as the calcium compound, Ca(OH) ２ and CaCO ３ It is more preferable to use them in combination.

[0062] Alternatively, two or more neutralizing agents may be used to carry out the neutralization in multiple stages. ３ and then Ca(OH) ２ According to this method, the neutralization is preferably carried out in two steps by adding Ca(OH) ２ In addition, the amount of CaCO ３ By adding CaCO ３ acts as a nucleus, making precipitation more likely.

[0063] (2) Coagulation and Sedimentation Step Next, the iron obtained in the neutralization step is coagulated and precipitated, and the supernatant is removed to obtain an iron hydroxide-containing slurry (coagulation and sedimentation step). The method for coagulation and precipitation is not particularly limited, but typically, a coagulant is added to the aqueous solution after neutralization.

[0064] The flocculant is not particularly limited and any suitable one can be used, but it is preferable to use an anionic polymer. The iron hydroxide precipitated in the neutralization step exists as positively charged colloidal particles, which are dispersed in the aqueous solution due to the repulsive forces between the positive charges. Therefore, by adding an anionic polymer, the negative charge of the anionic polymer offsets the electrostatic repulsive forces acting between the colloidal particles, allowing for effective flocculation and precipitation.

[0065] When the hydrogen sulfide removing agent is produced on an industrial scale, it is preferable to carry out gravity sedimentation using a coagulation sedimentation device (thickener).

[0066] (3) Solid-Liquid Separation Step Next, the iron hydroxide-containing slurry obtained in the coagulation and sedimentation step is subjected to solid-liquid separation (solid-liquid separation step). In this solid-liquid separation step, the slurry is dehydrated, and the iron hydroxide contained in the slurry gradually begins to convert to iron oxyhydroxide. Therefore, the solid content obtained by solid-liquid separation (also referred to as dehydrated cake) contains iron oxyhydroxide. Therefore, in this specification, the solid content is referred to as an iron oxyhydroxide-containing cake.

[0067] The method for carrying out the solid-liquid separation is not particularly limited, but when the hydrogen sulfide removing agent is produced on an industrial scale, it is preferable to use a filter press.

[0068] (4) Drying Step: The iron oxyhydroxide-containing cake is then dried to obtain iron oxyhydroxide (drying step). As described above, Fe exists in the aqueous solution as iron hydroxide at the time of neutralization, but as water is removed through the solid-liquid separation step and drying step, Fe is dehydrated and condensed to form amorphous iron oxyhydroxide (FeOOH).

[0069] The composition of the final hydrogen sulfide remover varies greatly depending on the drying conditions in the drying step. For example, sufficient moisture must be removed to convert iron hydroxide into amorphous iron oxyhydroxide. To achieve sufficient moisture removal, the drying temperature must be increased and the drying time must be prolonged.

[0070] On the other hand, amorphous iron oxyhydroxide crystallizes when heated too much. Furthermore, excessive heating causes the crystalline component iron oxide (Fe) to be converted into the crystalline component by the reaction of the following formula (4): ２ O ３ Therefore, in order to leave amorphous iron oxyhydroxide, it is necessary to lower the drying temperature and shorten the drying time. 2FeOOH → Fe ２ O ３ + H ２ O...(4)

[0071] Therefore, the drying conditions may be adjusted so as to obtain a hydrogen sulfide removing agent having a desired composition. Specific drying conditions vary depending on factors such as the production scale. For example, when drying approximately 100 g of an iron oxyhydroxide-containing cake, the following conditions are preferred.

[0072] When the drying temperature is 100°C or higher and 150°C or lower, the drying time is preferably 3 to 10 hours. When the drying temperature is 60°C or higher and lower than 100°C, the drying time is preferably 10 to 24 hours. When the drying temperature is 30°C or higher and lower than 60°C, the drying time is preferably 24 to 72 hours. When no heating is performed, vacuum drying is preferred.

[0073] The iron oxyhydroxide-based hydrogen sulfide removing agent can be obtained by the above method. The obtained iron oxyhydroxide-based hydrogen sulfide removing agent is usually in powder form and can be used as a hydrogen sulfide removing agent as it is.

[0074] After the drying step, optional processing such as pulverization or molding can be performed. A molding aid (binder) can also be added during molding. Using a molded product molded using a molding aid as a hydrogen sulfide removal agent can improve gas flow compared to using the agent in powder form. Furthermore, because the iron oxyhydroxide-based hydrogen sulfide removal agent of the present invention contains crystalline components, a molded product with sufficient strength can be obtained with a relatively small amount of molding aid added. Any molding aid can be used, but for example, one or both of bentonite and montmorillonite may be used.

[0075] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0076] (Invention Example No. 1) Fe ２ O ３ and FeCl ２ A hydrogen sulfide removing agent was produced from an aqueous solution containing CaCO 3 . Specifically, first, while bubbling air into the aqueous solution, ３ and Ca(OH) ２The solution was neutralized by adding ammonium hydroxide. Bubbling allowed the divalent iron ions present in the aqueous solution to be oxidized to trivalent iron ions by air. Next, an anionic polymer flocculant was added to flocculate and precipitate the precipitate. After removing the supernatant, the solution was subjected to solid-liquid separation by filtration. The solution was then dried at a drying temperature of 60°C for 24 hours.

[0077] (Invention Example No. 2) FeCl ３ A hydrogen sulfide remover was produced from an aqueous solution containing Ca(OH) ２ The solution was neutralized by adding an anionic polymer flocculant. Then, an anionic polymer flocculant was added to flocculate and precipitate the precipitate. After removing the supernatant, the solid-liquid separation was performed by filtration. Thereafter, the solution was dried at a drying temperature of 60°C for 24 hours.

[0078] (Comparative Example No. 3) For comparison, a conventional hydrogen sulfide removing agent made of crystalline iron oxyhydroxide was used as Comparative Example No. 3. Specifically, a commercially available crystalline α-FeOOH (goethite) reagent was used.

[0079] (Comparative Example No. 4) For comparison, a conventional hydrogen sulfide removing agent made of amorphous iron oxyhydroxide was used as Comparative Example No. 4. Specifically, Fe(ClO ４ ) ３ Sodium hydroxide was added dropwise to the aqueous solution to neutralize it, and the precipitate was filtered. The filtered cake was then vacuum dried at room temperature to obtain a hydrogen sulfide remover made of amorphous iron oxyhydroxide.

[0080] Comparative Example No. 5 For comparison, one of the commercially available hydrogen sulfide removing agents was evaluated in the same manner as in the other examples.

[0081] Comparative Example No. 6 For comparison, one commercially available hydrogen sulfide remover (a product different from the hydrogen sulfide remover used in No. 5) was evaluated in the same manner as in the other examples.

[0082] Comparative Example No. 7 Wastewater discharged from an ironworks was subjected to solid-liquid separation by filtration, followed by drying at a drying temperature of 60° C. for 24 hours.

[0083] Comparative Example No. 8 Wastewater discharged from a steelworks was subjected to solid-liquid separation by filtration, followed by drying at a drying temperature of 60° C. for 24 hours.

[0084] The hydrogen sulfide removing agents obtained as described above were each measured for the content of crystalline components, the content of amorphous iron oxyhydroxide, and the specific surface area. The measurement results are shown in Table 1. The specific measurement methods were as follows.

[0085] (Content of crystalline component) The content of the crystalline component contained in the obtained hydrogen sulfide removing agent was measured by X-ray diffraction measurement. Specifically, the content was calculated from the detected intensity of the diffraction line. ２ O ３ The individual contents of crystalline FeOOH and crystalline Fe were also determined. ２ O ３ The contents of the other crystalline components and the total amount of the crystalline components are shown in Table 1. Note that for some of the "other crystalline components," specific components and their contents are also shown in Table 1.

[0086] (Amorphous Iron Oxyhydroxide Content) The iron oxyhydroxide content was determined by the Karl Fischer titration method according to the following procedure.

[0087] First, the amount of combined water (CW) was quantified by Karl Fischer titration. Specifically, the sample (hydrogen sulfide removal agent) was dried at 105°C to remove adsorbed water. Then, the sample was heated at 950°C and the amount of combined water released was measured by Karl Fischer titration. The amount of combined water measured in this way was determined by the amount of H released from iron oxyhydroxide according to the reaction of the following formula (6): ２ The amount of O is 2FeOOH → Fe ２ O ３ + H ２ O...(6)

[0088] The content of iron oxyhydroxide was calculated from the measured amount of combined water and the stoichiometric ratio in formula (6). The content of amorphous iron oxyhydroxide was determined by subtracting the content of crystalline iron oxyhydroxide determined by the X-ray diffraction measurement described above from the content of iron oxyhydroxide thus obtained.

[0089] (Specific Surface Area) The specific surface area of ​​the hydrogen sulfide removing agent was measured by nitrogen adsorption / desorption measurement. Specifically, first, the sample was vacuum degassed at room temperature for 12 hours before measurement. Then, adsorption / desorption measurement was performed using nitrogen gas to obtain an adsorption isotherm. The temperature during measurement was set to -196°C. Next, the surface area per weight (specific surface area) was calculated by Brunauer-Emmett-Teller (BET) analysis of the obtained adsorption isotherm.

[0090] Next, the sulfur adsorption amount per weight and the sulfur adsorption amount per surface area of ​​the obtained hydrogen sulfide removing agent were evaluated by the following methods. The measurement results are shown in Table 1.

[0091] First, the obtained hydrogen sulfide removing agent was sieved to obtain a sample with a particle size of 0.5 to 1.0 mm. Next, the sample was placed in a reaction tube with an inner diameter of 4 mm, and 1 cm ３ The temperature of the reaction tube was controlled at 30° C. using a thermostatic bath. ２ 7000 ppm H diluted with ２ S was flowed, and the gas coming out from the outlet side of the reaction tube was sampled every 15 minutes, and the H in the gas was analyzed using a gas chromatograph. ２ The S concentration was measured.

[0092] For a while after the start of the test, all hydrogen sulfide was adsorbed inside the reaction tube, so no hydrogen sulfide was detected in the outlet gas. However, after a certain amount of time had passed, the hydrogen sulfide concentration in the outlet gas increased rapidly. This was because the hydrogen sulfide removal agent in the reaction tube was no longer able to adsorb all of the hydrogen sulfide. Therefore, the amount of sulfur adsorption (adsorption capacity) per weight was calculated from the amount of gas flowing until the hydrogen sulfide concentration in the outlet gas increased rapidly.

[0093] Furthermore, the sulfur adsorption amount per surface area was calculated by dividing the obtained sulfur adsorption amount per weight by the specific surface area of ​​the hydrogen sulfide removing agent.

[0094] As can be seen from the results shown in Table 1, the hydrogen sulfide removing agent satisfying the conditions of the present invention contained crystalline components, and therefore had a smaller specific surface area than the hydrogen sulfide removing agent made of amorphous iron oxyhydroxide (Comparative Example No. 4). Therefore, the hydrogen sulfide removing agent of the present invention has large particles and high strength, making it stable for use. Furthermore, despite its small specific surface area, the hydrogen sulfide removing agent satisfying the conditions of the present invention had a sulfur adsorption capacity per weight of approximately 10 wt %, providing excellent hydrogen sulfide removal performance similar to that of the hydrogen sulfide removing agent made of amorphous iron oxyhydroxide (Comparative Example No. 4).

[0095]

Claims

1. Contains amorphous iron oxyhydroxide and crystalline components, An iron oxyhydroxide-based hydrogen sulfide removing agent, wherein the content of the amorphous iron oxyhydroxide is equal to or greater than the content of the crystalline component.

2. 2. The iron oxyhydroxide-based hydrogen sulfide removing agent according to claim 1, wherein the content of the amorphous iron oxyhydroxide is 50 to 80 wt %.

3. 3. The iron oxyhydroxide-based hydrogen sulfide removing agent according to claim 1, which contains crystalline iron oxide as at least a portion of the crystalline component.

4. A method for producing the iron oxyhydroxide-based hydrogen sulfide removing agent according to claim 1, comprising the steps of: a neutralization step of neutralizing an aqueous solution containing iron ions to precipitate iron; a coagulation and precipitation step in which the iron obtained in the neutralization step is coagulated and precipitated, and the supernatant liquid is removed to obtain an iron hydroxide-containing slurry; a solid-liquid separation step of subjecting the iron hydroxide-containing slurry to solid-liquid separation to obtain an iron oxyhydroxide-containing cake; and a drying step of drying the iron oxyhydroxide-containing cake to obtain iron oxyhydroxide.

5. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to claim 4, wherein the aqueous solution containing iron ions is a waste liquid containing iron ions.

6. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to claim 4 or 5, wherein a calcium compound is used as the neutralizing agent in the neutralization step.

7. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to claim 4 or 5, wherein the pH is adjusted to 6 to 8 in the neutralization step.

8. The method for producing an iron oxyhydroxide-based agent for removing hydrogen sulfide according to claim 4 or 5, wherein an anionic polymer is used as a flocculant in the coagulation and precipitation step.

9. A desulfurization method, comprising removing hydrogen sulfide contained in a gas using the iron oxyhydroxide-based hydrogen sulfide remover according to claim 1.