Ferric hydroxide-based hydrogen sulfide removal agent, its manufacturing method and desulfurization method.

Abstract

This invention provides a hydrogen sulfide removal agent that maintains the same hydrogen sulfide removal performance as that of hydrogen sulfide removal agents composed of amorphous ferric hydroxide, while also being stable in use. The ferric hydroxide hydrogen sulfide removal agent of this invention contains amorphous ferric hydroxide and crystalline components; the content of the amorphous ferric hydroxide is greater than or equal to the content of the crystalline components.

Description

Technical Field

[0001] This invention relates to ferric hydroxide as a hydrogen sulfide removal agent and its manufacturing method. Furthermore, this invention relates to a desulfurization method using the aforementioned ferric hydroxide as a hydrogen sulfide removal agent. Prior Technology

[0002] Gas systems generated by various facilities such as iron ore processing, petrochemicals, and wastewater treatment contain hydrogen sulfide (H2S), which can cause foul odors and pipe corrosion. Therefore, technologies capable of removing hydrogen sulfide from gases are required.

[0003] Furthermore, these gases often contain large amounts of CO2. From the perspective of reducing CO2 emissions, a technology has been proposed to convert the CO2 in the gas into methanol and other substances through catalytic reactions for recycling. However, if the gas contains hydrogen sulfide, the catalyst will deteriorate. Therefore, in order to prevent catalyst deterioration, a technology to remove hydrogen sulfide from the gas is also required.

[0004] Therefore, methods for adsorbing and removing hydrogen sulfide from gases using dry hydrogen sulfide removal agents composed of ferric hydroxide (FeOOH) such as α-FeOOH (goethite) or β-FeOOH (tetragonal lepidocrocite) have been proposed (e.g., Patent Documents 1 and 2). Ferric hydroxide, due to the presence of numerous basic OH groups on its surface, can adsorb acidic H2S through acid / base interactions. Therefore, compared to Fe2O3, ferric hydroxide exhibits superior performance as a hydrogen sulfide removal agent.

[0005] However, the removal rate of hydrogen sulfide is still insufficient, and further performance improvements are required for its application in ironmaking, petrochemicals, wastewater treatment facilities, and other fields.

[0006] Therefore, a hydrogen sulfide removal agent containing amorphous ferric hydroxide has been proposed as a substitute for crystalline ferric hydroxide such as goethite or tetragonal lepidocrocite (Patent Document 3). According to Patent Document 3, since amorphous ferric hydroxide is not crystallized, it contributes to a large surface area for reaction with sulfur compounds. As a result, compared to crystalline materials such as tetragonal lepidocrocite, its reaction rate with sulfur compounds is greater, and low concentrations of sulfur compounds can be completely removed. [Previous Technical Documents] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 05-329362 [Patent Document 2] Japanese Patent Application Publication No. 2014-213281 [Patent Document 3] Japanese Patent Application Publication No. 2017-177052 Summary of the Invention

[0008] (The problem the invention aims to solve) As proposed in Patent Document 3, by using amorphous oxidized iron hydroxide, superior hydrogen sulfide removal performance can be obtained.

[0009] However, the hydrogen sulfide removal agent composed of this amorphous ferric hydroxide has low strength and cannot be used stably. That is, the hydrogen sulfide removal agent composed of amorphous ferric hydroxide is manufactured as described in Patent Document 3 by reacting an aqueous solution of ferric chloride with an alkaline aqueous solution (neutralizing agent) and hydrogen peroxide (oxidizing agent). In this process, because crystal growth cannot be achieved in order to create an amorphous structure, the resulting amorphous ferric hydroxide inevitably becomes an aggregate of extremely fine particles. The hydrogen sulfide removal agent composed of these fine particles has low strength and cannot withstand its own weight when filled into a desulfurization tower, easily resulting in crushing and pulverization.

[0010] In view of this situation, the present invention aims to provide a hydrogen sulfide removal agent that can maintain the same hydrogen sulfide removal performance as that of hydrogen sulfide removal agents composed of amorphous ferric hydroxide, while being stable in use. (Technical means to solve the problem)

[0011] The purpose of this invention is to solve the above-mentioned problems, and its main structure is as follows.

[0012] 1. A hydrogen sulfide removal agent based on ferric hydroxide oxide, comprising amorphous ferric hydroxide oxide and crystalline components; The content of the aforementioned amorphous iron hydroxide is greater than or equal to the content of the aforementioned crystalline components.

[0013] 2. The ferric hydroxide oxide described in 1 above is a hydrogen sulfide removal agent, wherein the content of the above-mentioned amorphous ferric hydroxide oxide is 50~80wt%.

[0014] 3. The ferric hydroxide oxide described in 1 or 2 above is a hydrogen sulfide removal agent, which contains crystalline ferric oxide as at least a part of the crystalline component.

[0015] 4. A method for manufacturing a ferric hydroxide-based hydrogen sulfide removal agent, comprising the method for manufacturing a ferric hydroxide-based hydrogen sulfide removal agent as described in any one of claims 1 to 3 above, and comprising: The neutralization step involves neutralizing an aqueous solution containing iron ions to precipitate the iron. The iron obtained from the above neutralization step is coagulated and precipitated, and the supernatant is removed to obtain a slurry containing ferric hydroxide; The solid-liquid separation step involves subjecting the above-mentioned slurry containing ferric hydroxide to solid-liquid separation to obtain a filter cake containing ferric hydroxide oxide; and The filter cake containing ferric hydroxide is dried to obtain ferric hydroxide.

[0016] 5. The method for manufacturing ferric hydroxide as a hydrogen sulfide removal agent as described in 4 above, wherein the above-mentioned aqueous solution containing iron ions is a waste liquid containing iron ions.

[0017] 6. The method for manufacturing ferric hydroxide as a hydrogen sulfide removal agent as described in 4 or 5 above, wherein a calcium compound is used as a neutralizing agent in the neutralization step described above.

[0018] 7. The method for manufacturing ferric hydroxide as a hydrogen sulfide removal agent as described in any of 4 to 6 above, wherein in the above neutralization step, the pH is set to 6 to 8.

[0019] 8. The method for manufacturing the ferric hydroxide hydrogen sulfide removal agent as described in any of 4 to 7 above, wherein an anionic polymer is used as a coagulant in the coagulation and precipitation step described above.

[0020] 9. A desulfurization method comprising using ferric hydroxide as a hydrogen sulfide removal agent as described in any one of 1 to 3 above to remove hydrogen sulfide contained in the gas. (Compared to the effectiveness of previous technologies)

[0021] The hydrogen sulfide removal agent of this invention contains an amount equal to or greater than that of amorphous ferric hydroxide, resulting in hydrogen sulfide removal performance equivalent to that of conventional hydrogen sulfide removal agents composed of amorphous ferric hydroxide. Furthermore, in addition to amorphous ferric hydroxide, the hydrogen sulfide removal agent of this invention also contains crystalline components, thus exhibiting a smaller specific surface area and larger particle size compared to conventional hydrogen sulfide removal agents composed of amorphous ferric hydroxide. Therefore, it possesses high strength and stable performance. Thus, while exhibiting superior stability, the hydrogen sulfide removal agent of this invention still possesses hydrogen sulfide removal performance equivalent to that of conventional hydrogen sulfide removal agents composed of amorphous ferric hydroxide, making it highly suitable for hydrogen sulfide removal. Simple Explanation of the Diagram

[0022] Figure 1 is a graph showing the ratio of amorphous iron hydroxide in the hydrogen sulfide remover to the amount of sulfur adsorbed per unit weight. Figure 2 is a graph showing an example of the cumulative pore capacity distribution in a hydrogen sulfide removal agent. Figure 3 is a graph showing the ratio of amorphous iron hydroxide in the hydrogen sulfide remover to the amount of sulfur adsorbed per unit surface area. Implementation

[0023] The following describes in detail the embodiments of the present invention.

[0024] Hydrogen sulfide removal agent The ferric hydroxide oxide of one embodiment of the present invention is a hydrogen sulfide removal agent, which contains amorphous ferric hydroxide oxide and crystalline components, wherein the content of the amorphous ferric hydroxide oxide is greater than or equal to the content of the crystalline components. The reasons are explained below.

[0025] As mentioned above, the hydrogen sulfide removal agent proposed in Patent Document 3 is composed of amorphous iron hydroxide and does not contain crystalline iron hydroxide. This can be explained by the fact that, as described in paragraphs

[0023] ,

[0028] and Figure 1 of Patent Document 3, only the diffraction peak of sodium chloride, which is an impurity, is observed in X-ray diffraction.

[0026] Because crystal growth cannot be achieved during the manufacturing of this amorphous ferric hydroxide, the particles constituting this amorphous ferric hydroxide inevitably become fine particles. As a result, it suffers from low strength and unstable use.

[0027] Conversely, the crystalline component is obtained through crystal growth, and therefore its particles are larger than those of amorphous ferric hydroxide. Thus, the hydrogen sulfide remover contains crystalline components in addition to amorphous ferric hydroxide, which enhances its strength and allows for stable use. Furthermore, the size variation of the particles in the hydrogen sulfide remover can be evaluated based on specific surface area, as described later.

[0028] However, in Patent Document 3, the removal performance of hydrogen sulfide is improved by utilizing the large specific surface area of ​​fine amorphous ferric hydroxide. Based on this prior art, if larger crystalline components are added, the specific surface area decreases, and it is presumed that the removal performance of hydrogen sulfide will also decrease.

[0029] However, according to the review results of the inventors in this case, it was found that even if crystalline components are mixed in the hydrogen sulfide removal agent, as long as the content of amorphous iron hydroxide is higher than that of crystalline components, the hydrogen sulfide removal performance can still be maintained almost the same as that of hydrogen sulfide removal agents composed of amorphous iron hydroxide.

[0030] For example, Figure 1 is a graph showing the proportion of amorphous iron hydroxide (FeOOH) in the hydrogen sulfide remover and its relationship with the amount of sulfur adsorbed per unit weight. Furthermore, the amount of amorphous iron hydroxide and the amount of sulfur adsorbed per unit weight were determined by the method described in the examples below. The remainder besides the amorphous iron hydroxide is essentially a crystalline component.

[0031] As can be seen from the chart, if the content of amorphous ferric hydroxide is higher than or equal to the content of the remaining crystalline component, the performance can be maintained almost identically to that when the content of amorphous ferric hydroxide is 100%. Therefore, in this invention, the content of amorphous ferric hydroxide is set to be higher than or equal to the content of the crystalline component. The content of amorphous ferric hydroxide is preferably 50 to 80 wt%. The content of amorphous ferric hydroxide can be determined by a combination of the Karl Fischer method and X-ray diffraction. That is, the content of amorphous ferric hydroxide can be obtained by subtracting the content of crystalline ferric hydroxide obtained by X-ray diffraction from the content of ferric hydroxide obtained by the Karl Fischer method. More specifically, it can be obtained by the method described in the examples.

[0032] Thus, the reason why hydrogen sulfide removal agents can still maintain superior desulfurization performance even if they contain a certain amount of crystalline components can be attributed to the following:

[0033] First, the reaction when hydrogen sulfide comes into contact with ferric hydroxide is represented by the following equation (1). 2FeOOH+3H2S → Fe2S3+4H2O…(1)

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

[0035] However, since the Fe2S3 generated by the above reaction is unstable, it is transformed into FeS and monomeric sulfur by the reaction shown in (2) below. Then, the generated FeS and monomeric sulfur gradually accumulate on the surface of the hydrogen sulfide removal agent. Fe2S3→ 2FeS + S (2)

[0036] Figure 2 is a graph showing an example of the cumulative pore volume distribution in hydrogen sulfide removal agents. The dashed line represents the hydrogen sulfide removal agent composed of amorphous ferric hydroxide (Comparative Example No. 4 in the following examples), and the solid line represents the measured value of the hydrogen sulfide removal agent containing 48 wt% crystalline components (Inventive Example No. 1 in the following examples). The specific surface area was measured by the method described in the examples.

[0037] As shown in the chart, the pores in the hydrogen sulfide remover composed of amorphous ferric hydroxide are mainly tiny pores with a diameter of less than 4.4 nm; pores with a diameter greater than 4.4 nm are almost non-existent. This can be attributed to the extremely small size of the amorphous ferric hydroxide particles themselves. Furthermore, 4.4 nm is approximately 10 times the diameter of a hydrogen sulfide molecule.

[0038] Thus, since the pores of the hydrogen sulfide removal agent composed of amorphous iron hydroxide are extremely fine, they can be considered to be blocked by the sulfur generated in the reaction of the above formula (2), and thus cannot help remove hydrogen sulfide. As a result, the amount of sulfur adsorbed per unit surface area of ​​the hydrogen sulfide removal agent composed of amorphous iron hydroxide becomes lower.

[0039] On the other hand, hydrogen sulfide removal agents containing crystalline components have a significantly increased proportion of large-diameter micropores compared to those composed of amorphous ferric hydroxide. Therefore, it can be considered that hydrogen sulfide removal agents containing crystalline components are less prone to micropore blockage caused by generated sulfur, thus maintaining higher desulfurization performance.

[0040] For example, Figure 3 is a graph showing the ratio of amorphous ferric hydroxide in the hydrogen sulfide remover to the amount of sulfur adsorbed per unit surface area under the same conditions as in Figure 1. The amount of amorphous ferric hydroxide and the amount of sulfur adsorbed per unit surface area were determined by the method described in the examples below.

[0041] As can be seen from the chart, compared to the case where the proportion of amorphous iron hydroxide is 100 wt%, the amount of sulfur adsorbed per unit surface area actually increases when there is a certain amount of crystalline component.

[0042] However, if the proportion of amorphous ferric hydroxide is less than 50 wt%, the sulfur adsorption capacity per unit surface area decreases. This is because the proportion of amorphous ferric hydroxide capable of adsorbing hydrogen sulfide on the surface of the hydrogen sulfide remover decreases. Therefore, in this respect, it is preferable to set the content of amorphous ferric hydroxide to 50 wt% or more.

[0043] (Crystal components) The aforementioned crystalline components are not particularly limited and can be any substance having a crystalline structure. Typically, the aforementioned crystalline components can be at least one selected from the group consisting of crystalline oxides, crystalline hydroxides, and crystalline metal salts.

[0044] The aforementioned crystalline oxide can be either a crystalline metal oxide or a crystalline nonmetal oxide. Examples of such crystalline oxides include oxides selected from at least one of 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] Examples of such crystalline hydroxides include hydroxides selected from at least one of the groups consisting of Fe, Al, Mg, Zn, Ni, Mn, and Cr.

[0046] Furthermore, examples of the aforementioned crystalline metal salts include metal carbonates and metal sulfates. For instance, when calcium compounds such as calcium hydroxide (Ca(OH)2) or calcium carbonate (CaCO3) are used as neutralizing agents during the manufacturing process, as described later, the resulting hydrogen sulfide remover contains crystalline calcium carbonate. Similarly, when sodium compounds such as NaOH are used as neutralizing agents, the resulting hydrogen sulfide remover contains crystalline sodium carbonate (Na2CO3). Additionally, when sulfate ions are present in the aqueous solution, it may contain crystalline sulfates such as ferric sulfate or calcium sulfate.

[0047] In this invention, the content of amorphous ferric hydroxide is sufficient to be at least equal to the content of the crystalline component. In other words, the content of the crystalline component need only be less than the content of amorphous ferric hydroxide. The preferred content of the crystalline component is 5-50 wt%. The content of the crystalline component can be determined by X-ray diffraction. More specifically, it can be determined by the method described in the examples.

[0048] (Specific surface area) As described above, the hydrogen sulfide removal agent of the present invention contains crystalline components, and therefore has a larger particle size compared to conventional hydrogen sulfide removal agents composed of amorphous ferric hydroxide. Furthermore, this difference in particle size can be evaluated based on specific surface area. That is, a smaller specific surface area generally corresponds to a larger particle size.

[0049] The specific surface area of ​​the ferric hydroxide-based hydrogen sulfide remover of the present invention is not particularly limited, but preferably is 100 m² / g or more, more preferably 110 m² / g or more, and even more preferably 120 m² / g or more. On the other hand, the upper limit of the specific surface area is not particularly limited, but typically preferably is 200 m² / g or less, more preferably 180 m² / g or less, and even more preferably 160 m² / g or less.

[0050] Furthermore, the specific surface area mentioned above refers to the BET specific surface area measured using nitrogen gas. More specifically, it can be measured using the method described in the examples.

[0051] [Manufacturing Method] Next, a method for manufacturing an ferric hydroxide-based hydrogen sulfide remover according to an embodiment of the present invention will be described. The manufacturing method of this embodiment includes the steps (1) to (4) below. Each step will be described below. (1) Neutralization steps (2) Coagulation and precipitation steps (3) Solid-liquid separation steps (4) Drying step

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

[0053] For example, when the above aqueous solution contains ferric ions, the ferric ions are precipitated as ferric hydroxide as shown in equation (3) below. Fe3++3OH-→ Fe(OH)3↓…(3)

[0054] Furthermore, the stoichiometric ratio (mole ratio) of Fe to OH in the above formula (3) is 1:3, but it is not necessarily 1:3 in actual reactions.

[0055] Furthermore, when the above aqueous solution contains ferrous ions (Fe2+), it is preferable to oxidize the ferrous ions beforehand to convert them into ferric ions (Fe3+). The method of oxidizing ferrous ions is not particularly limited, but it is particularly suitable for use in the above aqueous solution for bubbling oxygen-containing gas (preferably air).

[0056] While any substance can be used as the aforementioned aqueous solution containing iron ions, from the perspective of effectively utilizing resources, it is preferable to use waste liquid containing iron ions. The type of waste liquid is not particularly limited; for example, waste liquid generated during the ironmaking process in ironworks contains a sufficient amount of iron ions, and therefore is suitable for use.

[0057] The waste liquid generated during the ironmaking process in a steel mill is not particularly limited; any waste liquid containing iron ions can be used. Examples of such waste liquid include pickling waste liquid generated during the pickling step on the surface of steel plates, and rinsing waste liquid generated during the rinsing step of washing the surface of steel plates with water after the pickling step. Furthermore, in steel mills, waste liquids generated in multiple steps are generally recycled in a mixed state and processed in batches. Therefore, in this invention, a mixed waste liquid formed by mixing waste liquids generated in multiple steps in a steel mill can also be used.

[0058] Furthermore, the waste liquid generated during the ironmaking process sometimes contains solids such as dust. As the aqueous solution containing iron ions of this invention, the waste liquid containing such solids can also be used. When the aqueous solution containing iron ions contains solids, at least a portion of these solids are mixed in as impurities in the slurry containing ferric hydroxide recovered during the coagulation and precipitation step. However, as long as the content of amorphous ferric hydroxide in the final hydrogen sulfide removal agent meets the above conditions, its function as a hydrogen sulfide removal agent is not a problem.

[0059] The pH value in the above neutralization step is not specifically limited. If the pH is too low, Fe ions will remain stable in the aqueous solution, and ferric hydroxide may not be fully precipitated. Therefore, the optimal pH is 6 or higher. On the other hand, if the pH is too high, the generated ferric hydroxide may crystallize and transform into goethite (α-FeOH), which has lower desulfurization performance. Therefore, the optimal pH is 8 or lower.

[0060] To neutralize, a neutralizing agent is simply added to the aqueous solution containing ferric ions. No particular neutralizing agent is specified, and any neutralizing agent can be used. However, when a strongly alkaline agent such as sodium hydroxide (NaOH) is used, ferric hydroxide crystallization may occur. This can be attributed to the inability to mix uniformly when NaOH is added to the aqueous solution, resulting in localized areas where the pH exceeds 8. On the other hand, if calcium compounds such as CaCO3 or Ca(OH)2 are used as neutralizing agents, the pH rises gradually. As a result, excessive localized increases in pH are prevented. Furthermore, since calcium compounds are cheaper than NaOH, the manufacturing cost of hydrogen sulfide removal agents can be reduced. For these reasons, calcium compounds are preferred as neutralizing agents, and more preferably one or both of CaCO3 and Ca(OH)2.

[0061] Among calcium compounds, Ca(OH)₂ has a superior neutralizing effect. On the other hand, although CaCO₃ has a weaker neutralizing effect, it helps to aggregate ferric hydroxide by binding the generated ferric hydroxide particles together. Therefore, it is preferable to use both Ca(OH)₂ and CaCO₃ as the aforementioned calcium compounds.

[0062] Alternatively, two or more neutralizing agents can be used for multi-stage neutralization. A preferred method is a two-stage neutralization process, initially adding CaCO3 followed by Ca(OH)2. This method reduces the amount of Ca(OH)2 used. Furthermore, by adding CaCO3 first, the CaCO3 acts as a nucleus, making precipitation more likely.

[0063] (2) Coagulation and precipitation steps Next, the iron obtained in the above neutralization step is coagulated and precipitated, and the supernatant is removed to obtain a slurry containing ferric hydroxide (coagulation and precipitation step). The method of coagulation and precipitation is not particularly limited; typically, a coagulant is simply added to the neutralized aqueous solution.

[0064] The aforementioned coagulant is not particularly limited, and any coagulant can be used, but anionic polymers are preferred. That is, the ferric hydroxide precipitated in the neutralization step exists in the form of positively charged colloidal particles, and is dispersed in the aqueous solution by the repulsive force between the positive charges. Therefore, by adding anionic polymers, and by using the negative charge of the anionic polymers to counteract the electrostatic repulsion between the colloidal particles, the particles can be effectively coagulated and precipitated.

[0065] Furthermore, when manufacturing hydrogen sulfide removal agents to industrial specifications, it is preferable to use a coagulation and precipitation device (precipitator) for gravity precipitation.

[0066] (3) Solid-liquid separation steps Next, the slurry containing ferric hydroxide obtained in the above-mentioned coagulation and precipitation step is subjected to solid-liquid separation (solid-liquid separation step). In this solid-liquid separation step, by dehydrating the slurry, the ferric hydroxide contained in the slurry gradually changes into ferric hydroxide oxide. Therefore, the solid portion obtained by solid-liquid separation (also called dehydrated filter cake) contains ferric hydroxide oxide. Therefore, in this specification, the above-mentioned solid portion is referred to as filter cake containing ferric hydroxide oxide.

[0067] The method for performing the above solid-liquid separation is not particularly limited, but when manufacturing hydrogen sulfide removal agent to industrial specifications, it is preferable to use a filter press.

[0068] (4) Drying step Subsequently, the filter cake containing ferric hydroxide is dried to obtain ferric hydroxide (drying step). As described above, at the point of neutralization, Fe exists in the aqueous solution as ferric hydroxide, but by removing water through the above solid-liquid separation step and drying step, it undergoes dehydration condensation and transforms into amorphous ferric hydroxide (FeOOH).

[0069] The composition of the final hydrogen sulfide remover varies significantly depending on the drying conditions of the aforementioned drying steps. For example, to transform ferric hydroxide into amorphous ferric hydroxide oxide, sufficient moisture must be removed. Furthermore, to ensure sufficient moisture removal, the drying temperature and drying time must be increased.

[0070] On the other hand, amorphous ferric hydroxide will crystallize if overheated. Furthermore, if overheated, it will change into crystalline iron oxide (Fe2O3) due to the reaction in equation (4) below. Therefore, in order to preserve amorphous ferric hydroxide, the drying temperature must be lowered and the drying time shortened. 2FeOOH → Fe2O3 + H2O …(4)

[0071] Therefore, to obtain the desired hydrogen sulfide removal agent, simply adjust the drying conditions. The specific drying conditions depend on production specifications, etc. For example, when drying approximately 100g of filter cake containing ferric hydroxide oxide, the following conditions are preferred.

[0072] When the drying temperature is above 100℃ and below 150℃, it is preferable to set the drying time to 3 to 10 hours. When the drying temperature is above 60℃ but below 100℃, it is preferable to set the drying time to 10~24 hours. When the drying temperature is above 30°C but below 60°C, it is preferable to set the drying time to 24-72 hours. • When no heating is performed, vacuum drying is preferred.

[0073] The above method yields an iron hydroxide-based hydrogen sulfide remover. The resulting iron hydroxide-based hydrogen sulfide remover is typically in powder form and can also be used as a hydrogen sulfide remover in this state.

[0074] Furthermore, after the aforementioned drying step, further processing such as pulverization or molding can be performed as desired. During molding, molding aids (binders) can also be added as desired. By using the molded article formed with the molding aid as a hydrogen sulfide remover, gas flow is easier compared to using it in powder form. Moreover, since the ferric hydroxide-based hydrogen sulfide remover of this invention contains crystalline components, a molded article with sufficient strength can be obtained with a relatively small amount of molding aid added. Any molding aid can be used as described above, for example, one or both of bentonite and montmorillonite. [Example]

[0075] The present invention will be described in more detail below with reference to embodiments, but the present invention is not limited to these embodiments.

[0076] (Invention Example No. 1) A hydrogen sulfide removal agent is prepared from an aqueous solution containing Fe₂O₃ and FeCl₂. Specifically, firstly, air is bubbled into the aqueous solution while CaCO₃ and Ca(OH)₂ are added for neutralization. Bubbling oxidizes the ferrous ions (Fe²⁺) in the aqueous solution to ferric ions (Fe³⁺). Next, an anionic polymeric flocculant is added to cause the precipitate to agglomerate and precipitate. After removing the supernatant, solid-liquid separation is performed by filtration. Subsequently, drying is carried out at a drying temperature of 60°C for 24 hours.

[0077] (Invention Example No. 2) A hydrogen sulfide removal agent is prepared from an aqueous solution containing FeCl3. Specifically, firstly, Ca(OH)2 is added to the above aqueous solution for neutralization. Next, an anionic polymeric coagulant is added to cause the precipitate to coagulate and precipitate. After removing the supernatant, solid-liquid separation is performed by filtration. Subsequently, drying is carried out at a drying temperature of 60°C and a drying time of 24 hours.

[0078] (Comparative Example No. 3) For comparison, a conventional hydrogen sulfide removal agent composed of crystalline ferric hydroxide 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 removal agent composed of amorphous ferric hydroxide was used as Comparative Example No. 4. Specifically, sodium hydroxide was added dropwise to an aqueous solution of Fe(ClO4)3 for neutralization, and the precipitate was filtered. The resulting filtrate was then vacuum-dried at room temperature to obtain a hydrogen sulfide removal agent composed of amorphous ferric hydroxide.

[0080] (Comparative Example No. 5) For comparison, one of the commercially available hydrogen sulfide removers was evaluated in the same way as the other examples.

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

[0082] (Comparative Example No. 7) The waste liquid generated by the ironworks was separated into solid and liquid components by filtration. Subsequently, it was dried at a drying temperature of 60°C for 24 hours.

[0083] (Comparative Example No. 8) The waste liquid generated by the ironworks was separated into solid and liquid components by filtration. Subsequently, it was dried at a drying temperature of 60°C for 24 hours.

[0084] For each of the hydrogen sulfide removers obtained in the above manner, the content of crystalline components, the content of amorphous ferric hydroxide, and the specific surface area were determined. The results are shown in Table 1. The specific determination methods are as follows.

[0085] (Content of crystalline components) The content of crystalline components in the obtained hydrogen sulfide remover was determined by X-ray diffraction. Specifically, the content was calculated from the detection intensity of the diffraction rays. Furthermore, the individual contents of crystalline FeOOH and crystalline Fe2O3 were also determined. Table 1 shows the contents of crystalline FeOOH, crystalline Fe2O3, other crystalline components, and the total amount of crystalline components. The specific components and their contents for the aforementioned "other crystalline components" are also shown in Table 1.

[0086] (Content of amorphous iron hydroxide) The content of ferric hydroxide was determined by Karl Fischer titration according to the following procedure.

[0087] First, the bound water (CW) was quantified by Karl Fischer titration. Specifically, to remove the adsorbed water, the sample (hydrogen sulfide remover) was dried at 105°C. Subsequently, it was heated to 950°C and the amount of bound water released was determined by Karl Fischer titration. The amount of bound water thus determined was the amount of H2O released from ferric hydroxide by the reaction in equation (6) below. 2FeOOH → Fe2O3 + H2O …(6)

[0088] Based on the measured amount of bound water, the content of ferric hydroxide is calculated using the stoichiometric ratio in equation (6) above. The content of amorphous ferric hydroxide is obtained by subtracting the content of crystalline ferric hydroxide obtained by the X-ray diffraction determination from the obtained ferric hydroxide content.

[0089] (Specific surface area) The specific surface area of ​​the hydrogen sulfide remover was determined by nitrogen adsorption-desorption assay. Specifically, firstly, vacuum degassing was performed at room temperature for 12 hours before measurement. Subsequently, adsorption-desorption was performed using nitrogen to obtain adsorption isotherms. The measurement temperature was set to -196°C. Next, the surface area per unit weight (specific surface area) was calculated by Brunauer-Emmett-Teller (BET) analysis of the obtained adsorption isotherms.

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

[0091] First, the obtained hydrogen sulfide removal agent was sieved to obtain a sample with a particle size of 0.5~1.0 mm. Next, 1 cm³ of the sample was packed into a reaction tube with an inner diameter of 4 mm, and the temperature of the reaction tube was controlled at 30°C using a thermostat. 7000 ppm H₂S diluted with N₂ was passed through the inlet of the reaction tube, and the gas exiting from the outlet of the reaction tube was sampled every 15 minutes. The H₂S concentration in the gas was determined using a gas chromatography-mass spectrometry system.

[0092] During the initial short period after the start of the experiment, no hydrogen sulfide was detected in the outlet gas because all hydrogen sulfide in the reaction tube was adsorbed. However, after a certain period of time, the concentration of hydrogen sulfide in the outlet gas increased sharply. This was because the hydrogen sulfide removal agent in the reaction tube could no longer completely adsorb hydrogen sulfide. Therefore, the amount of sulfur adsorbed per unit weight (adsorption capacity) was calculated from the amount of gas flowing through the outlet gas during the period from the sharp increase in the hydrogen sulfide concentration to the point where it increased sharply.

[0093] Furthermore, the amount of sulfur adsorbed per unit weight is calculated by dividing the amount of sulfur adsorbed per unit weight by the specific surface area of ​​the hydrogen sulfide remover.

[0094] As shown in Table 1, the hydrogen sulfide removal agent meeting the conditions of this invention contains crystalline components, resulting in a smaller specific surface area compared to the hydrogen sulfide removal agent composed of amorphous ferric hydroxide (Comparative Example No. 4). Therefore, the hydrogen sulfide removal agent of this invention can be used stably due to its larger particle size and higher strength. Moreover, although the hydrogen sulfide removal agent meeting the conditions of this invention has a smaller specific surface area, its sulfur adsorption capacity per unit weight is approximately 10 wt%, still exhibiting the same superior hydrogen sulfide removal performance as the hydrogen sulfide removal agent composed of amorphous ferric hydroxide (Comparative Example No. 4).

[0095] [Table 1] No. Content (wt%) characteristic Remark Amorphous FeOOH Crystalline components Specific surface area (m2 / g) Sulfur adsorption capacity (a) Crystalline FeOOH (b) Crystalline Fe2O3 (c) Other Total amount (=a+b+c) per unit weight (wt%) per unit surface area (μmol / m2) 1 52 0 11 37 CaCO3 6% 48 131 10.1 twenty four Invention Examples 2 77 0 0 twenty three Al2O3 5% twenty three 144 9.9 21.4 Invention Examples 3 [0] 100 0 0 - 100 16.7 0.3 5.73 [Comparative Example] 4 100 0 0 0 - [0] 316 10.9 10.8 [Comparative Example] 5

[42] 0 0 58 CaSO4 63% 58 86.1 4.9 18 [Comparative Example] 6

[35] 2 0 63 Fe3O4 25% SiO2 2% CaSO4 12% 65 50.8 2.67 16.4 [Comparative Example] 7 [twenty one] 3 7 69 SiO2 1% CaCO3 3% 79 41.3 1.04 7.83 [Comparative Example] 8

[20] 0 0 80 Fe3O4 25% FeO 25% Fe 10% SiO2 2% CaCO3 5% 80 17 0.72 13.2 [Comparative Example]

Claims

1. A ferric hydroxide-based hydrogen sulfide removal agent, comprising amorphous ferric hydroxide and crystalline components; wherein the content of the amorphous ferric hydroxide is greater than or equal to the content of the crystalline components; and wherein crystalline ferric oxide is present as at least a portion of the crystalline components.

2. If the ferric hydroxide oxide in request item 1 is a hydrogen sulfide removal agent, then... The content of the above-mentioned amorphous iron hydroxide is 50~80wt%.

3. A method for manufacturing a ferric hydroxide-based hydrogen sulfide removal agent, which is the method for manufacturing the ferric hydroxide-based hydrogen sulfide removal agent according to claim 1 or 2, 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 above neutralization step to remove the supernatant and obtain a slurry containing ferric hydroxide; a solid-liquid separation step of performing solid-liquid separation on the above ferric hydroxide-containing slurry to obtain a filter cake containing ferric hydroxide; and a drying step of drying the above filter cake containing ferric hydroxide to obtain ferric hydroxide; wherein in the above neutralization step, the pH is set to 6-8.

4. A method for manufacturing ferric hydroxide as a hydrogen sulfide removal agent as described in claim 3, wherein, The above-mentioned aqueous solution containing iron ions is a waste liquid containing iron ions.

5. A method for manufacturing ferric hydroxide as a hydrogen sulfide removal agent as claimed in claim 3 or 4, wherein, In the above neutralization step, a calcium compound is used as a neutralizing agent.

6. A method for manufacturing the ferric hydroxide-based hydrogen sulfide removal agent as described in claim 3 or 4, wherein, In the above-mentioned coagulation and precipitation steps, anionic polymers are used as coagulants.

7. A desulfurization method comprising removing hydrogen sulfide from a gas by using the ferric hydroxide-based hydrogen sulfide removal agent of claim 1 or 2.

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