Desulfurizing agent

Abstract

A desulfurizing agent according to the present disclosure removes a sulfur compound from a sulfur compound-containing raw material. The desulfurizing agent is characterized by comprising a metal-organic structure, wherein: the metal-organic structure includes copper ions, a trimesic acid, and a benzoic acid-based compound; and the benzoic acid-based compound is a compound in which a hydrogen atom at the meta- or para-position with respect to a carboxyl group of a benzoic acid is substituted with a substituent, and which has a higher electron-donating property than the benzoic acid.

Description

Technical Field

[0001] The present disclosure relates to a desulfurizing agent.

Background Art

[0002] Patent Document 1 discloses a technique for removing sulfide-based compounds (sulfur compounds) from a fuel gas (raw material gas) by bringing the fuel gas (raw material gas) containing the sulfide-based compounds (sulfur compounds) into contact with a metal-organic framework composed of copper ions and trimesic acid.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] The present disclosure provides a desulfurizing agent that can reduce the filling amount of the desulfurizing agent filled in a desulfurizer to achieve miniaturization of the desulfurizer.

Means for Solving the Problem

[0005] The desulfurizing agent according to the present disclosure is a desulfurizing agent that removes sulfur compounds from a raw material gas containing sulfur compounds, the desulfurizing agent comprises a metal-organic framework, the metal-organic framework comprises copper ions, trimesic acid and a benzoic acid-based compound, and the benzoic acid-based compound is a compound obtained by substituting a hydrogen atom at the meta position or para position relative to the carboxy group of benzoic acid with a substituent, and is characterized by having higher electron donating property than benzoic acid.

Effect of the Invention

[0006] In this disclosure, the desulfurizing agent is a benzoic acid-based compound that has higher electron-donating properties than benzoic acid. Electrons are donated to the copper ions of the metal-organic structure, increasing the affinity between the sulfur compound and the copper ions, thereby improving the adsorption capacity of the sulfur compound.

[0007] Furthermore, the metal-organic structure constituting the desulfurizing agent in this disclosure has a configuration in which a portion of the trimesic acid in a metal-organic structure composed of copper ions and trimesic acid is replaced by a benzoic acid-based compound. Therefore, compared to a metal-organic structure composed of copper ions and trimesic acid, it has a larger number of pores, which improves the adsorption capacity of sulfur compounds.

[0008] Therefore, it is possible to provide a desulfurizing agent that reduces the amount of desulfurizing agent to be filled into the desulfurizer, thereby enabling the desulfurizer to be made smaller. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic diagram showing a desulfurizer filled with desulfurizing agent in Embodiment 1 [Modes for carrying out the invention]

[0010] (Knowledge and other information that formed the basis of this disclosure) At the time the inventors conceived of this disclosure, there was a metal-organic structure composed of copper ions and trimesic acid that could be used as a desulfurizing agent to remove sulfur compounds from source gases containing sulfur compounds. This allowed for the simple and effective removal of sulfur compounds contained in the source gas.

[0011] However, the amount of adsorption of sulfur compounds was lower than the theoretical amount expected based on the copper ion content in the active site structure, making it impossible to miniaturize the desulfurizer.

[0012] Under these circumstances, the inventors conceived the idea that if a metal-organic structure composed of copper ions and trimesic acid, in which some of the trimesic acid is replaced with a benzoic acid-based compound that has higher electron-donating properties than benzoic acid, is used as a desulfurizing agent, electrons are donated to the copper ions of the metal-organic structure by the benzoic acid-based compound, increasing the affinity between sulfur compounds and copper ions, thereby improving the adsorption capacity of sulfur compounds. Furthermore, compared to a metal-organic structure composed of copper ions and trimesic acid, this structure has many pores with larger diameters, thus improving the adsorption capacity of sulfur compounds.

[0013] This disclosure provides a desulfurizing agent that can reduce the volume of desulfurizing agent to be filled into the desulfurizer, thereby enabling the desulfurizer to be miniaturized.

[0014] The embodiments will be described in detail below with reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted.

[0015] The attached drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter described in the claims.

[0016] (Embodiment 1) Embodiment 1 will be described below with reference to Figure 1.

[0017] [1-1. Structure] As shown in Figure 1, the desulfurizing agent 4 of this embodiment is filled (mounted) in a containment container 1. The containment container 1 has an inlet 2 at one end in the longitudinal direction for allowing the raw material gas before desulfurization to flow into the containment container 1, and an outlet 3 at the other end for allowing the raw material gas after desulfurization to flow out of the containment container 1.

[0018] The desulfurization apparatus 10 is configured such that a raw material gas before desulfurization flows into an inlet portion 2 of a storage container 1, and the raw material gas desulfurized by a desulfurizing agent 4 filled (loaded) in the storage container 1 flows out from the inside of the storage container 1.

[0019] The inlet portion 2 is a pipe to which the raw material gas is supplied.

[0020] The raw material gas in the present embodiment is city gas containing methane as a main component, and contains tetrahydrothiophene (hereinafter referred to as THT) as a sulfur compound at a concentration of 15 ppm.

[0021] An outlet portion 3 is a pipe through which the raw material gas from which THT has been removed by the desulfurizing agent 4 is discharged.

[0022] The raw material gas discharged from the outlet portion 3 is supplied to a hydrogen generator (not shown) that produces hydrogen, converted into hydrogen by a reforming catalyst (not shown) in the hydrogen generator, and used in a hydrogen-using apparatus such as a fuel cell (not shown).

[0023] The desulfurizing agent 4 contains a metal-organic framework that adsorbs sulfur compounds. The metal-organic framework contains copper ions, trimesic acid, and a benzoic acid-based compound. The benzoic acid-based compound is a compound obtained by substituting a hydrogen atom at the meta position or para position relative to the carboxy group of benzoic acid with a substituent, and has higher electron donating property than benzoic acid.

[0024] As the desulfurizing agent 4 in the present embodiment, Cu-BTC-OH-BA-p (Example 1) containing 4-hydroxybenzoic acid having a structure in which a hydrogen atom at the para position relative to the carboxy group of benzoic acid is substituted with a hydroxy group was used as the benzoic acid-based compound.

[0025] (Method for Synthesizing Metal-Organic Framework) The metal-organic framework was synthesized by a known solvothermal method.

[0026] First, a copper ion source, trimesic acid, and a benzoic acid-based compound were added to an organic solvent to prepare the raw material solution. Next, the raw material solution was heated to grow crystals of the metal-organic structure.

[0027] The resulting metal-organic structure crystals contained unreacted copper ion sources and trimesic acid. After washing and removing these, the crystals were dried to obtain a powdered metal-organic structure.

[0028] Furthermore, the molar ratio of benzoic acid compounds contained in the metal-organic structure should preferably be between 10% and 50% relative to trimesic acid.

[0029] Normally, Cu-BTC has numerous micropores, but when the molar ratio exceeds 50%, it is thought that the number of mesopores increases due to the adjacent placement of two or more benzoic acid or isophthalic acid molecules. An increase in mesopores signifies the breakdown of the three-dimensional structure of the metal-organic structure, leading to a decrease in specific surface area, and therefore it is not suitable for use as a desulfurizing agent. In this embodiment, the molar ratio of the benzoic acid-based compound was set to 30% relative to trimesic acid.

[0030] The following describes in detail an example of a synthesis method for Cu-BTC-OH-BA-p, which is a metal-organic structure in Example 1 of Embodiment 1.

[0031] In this embodiment, we will describe Cu-BTC-OH-BA-p (Example 1), which was synthesized using 4-hydroxybenzoic acid as the benzoic acid compound.

[0032] First, anhydrous copper sulfate (3.6 mmol), trimesic acid (1.6 mmol), and 4-hydroxybenzoic acid (0.48 mmol) were mixed with ethylene glycol (40 mL) to prepare the raw material solution. In the raw material solution, the molar ratio of 4-hydroxybenzoic acid to trimesic acid was set to 30%.

[0033] The raw material solution was placed in a sealed container and heated at 120°C for 24 hours to obtain the product. The precipitate was then washed and dried at 120°C to obtain Cu-BTC-OH-BA-p (Example 1).

[0034] In Example 2, Cu-BTC-CH3-BA-p was synthesized using 4-methylbenzoic acid instead of 4-hydroxybenzoic acid in the metal-organic structure of Example 1. 4-methylbenzoic acid is a benzoic acid-based compound in which the para hydrogen atom of the carboxyl group of benzoic acid is replaced with a methyl group.

[0035] In Example 3, Cu-BTC-NH2-BA-p was synthesized using 4-aminobenzoic acid instead of 4-hydroxybenzoic acid in the metal-organic structure of Example 1. 4-aminobenzoic acid is a benzoic acid-based compound in which the para hydrogen atom of the carboxyl group of benzoic acid is replaced with an amino group.

[0036] In Example 1, 3-methylbenzoic acid was used instead of 4-hydroxybenzoic acid in the metal-organic structure to synthesize Cu-BTC-CH3-BA-m (Example 4). 3-methylbenzoic acid is a benzoic acid-based compound in which the hydrogen atom at the meta position of the carboxyl group of benzoic acid is replaced with a methyl group.

[0037] Cu-BTC-NH2-BA-m (Example 5) was synthesized using 3-aminobenzoic acid instead of 4-hydroxybenzoic acid in the metal-organic structure of Example 1. 3-aminobenzoic acid is a benzoic acid-based compound in which the hydrogen atom at the meta position of the carboxyl group of benzoic acid is replaced with an amino group.

[0038] Cu-BTC-BA (Comparative Example 1) was synthesized using benzoic acid instead of 4-hydroxybenzoic acid in the metal-organic structure of (Example 1).

[0039] Cu-BTC-OH-BA-m (Comparative Example 2) was synthesized using 3-hydroxybenzoic acid instead of 4-hydroxybenzoic acid in the metal-organic structure of (Example 1). 3-hydroxybenzoic acid is a benzoic acid-based compound in which the hydrogen atom at the meta position of the carboxyl group of benzoic acid is replaced with a hydroxyl group.

[0040] In the metal-organic structure of Example 1, 4-nitrobenzoic acid was used instead of 4-hydroxybenzoic acid to synthesize Cu-BTC-NO2-BA-p (Comparative Example 3). 4-nitrobenzoic acid is a benzoic acid-based compound in which the para hydrogen atom of the carboxyl group of benzoic acid is replaced with a nitro group.

[0041] In the metal-organic structure of Example 1, 4-chlorobenzoic acid was used instead of 4-hydroxybenzoic acid to synthesize Cu-BTC-Cl-BA-p (Comparative Example 4). 4-chlorobenzoic acid is a benzoic acid-based compound in which the para hydrogen atom of the carboxyl group of benzoic acid is replaced with a chloro group.

[0042] [1-2. Operation] The operation and function of the desulfurizing agent 4, which is configured as described above, will be explained below.

[0043] A raw material gas containing THT at a concentration of 15 ppm is supplied to the inlet 2 of the containment container 1. The supplied raw material gas passes through the containment container 1, coming into contact with the desulfurizing agent 4 inside the container. As the desulfurizing agent 4 removes THT from the raw material gas, the raw material gas with THT reduced to 20 ppb or less is discharged from the outlet 3.

[0044] (Evaluation of sulfur adsorption performance) This section describes a method for evaluating the sulfur adsorption performance of the desulfurizing agent 4 installed in the desulfurization apparatus 10. The sulfur adsorption performance is expressed as the THT adsorption capacity (wt%), which is the ratio of the weight of sulfur atoms in adsorbed THT to the weight of the desulfurizing agent 4.

[0045] The THT adsorption capacity was evaluated by introducing the sample and THT gas into a sealed bag, leaving it at 60°C for 24 hours, and then analyzing the THT concentration in the bag to measure the THT adsorption capacity at multiple equilibrium concentrations. The adsorption isotherm was then calculated using Languir's equation, assuming that the adsorbate molecules are adsorbed in a monolayer, and the adsorption capacity at 15 ppm was determined.

[0046] Table 1 shows the THT adsorption capacity at 15 ppm for each sample in Examples 1-5 and Comparative Examples 1-5. For samples with added benzoic acid compounds, the σ value (a substituent constant determined by the type and position of substituents in Hammett's proportionality rule) indicating the electron-withdrawing properties of the benzoic acid compound is also shown. A negative σ value indicates higher electron-donating properties than benzoic acid.

[0047] [Table 1]

[0048] As shown in (Table 1), the samples from Examples 1 to 5, which had negative σ values, showed higher THT adsorption capacity than the Cu-BTC-BA of Comparative Example 1.

[0049] Furthermore, the samples in Comparative Examples 2-4, which had positive σ values, showed lower THT adsorption capacities than the Cu-BTC-BA sample in Comparative Example 1.

[0050] Furthermore, the metal-organic structure Cu-BTC, which is composed of copper ions and trimesic acid and does not contain benzoic acid compounds, had an even lower THT adsorption capacity than Comparative Example 1, as shown in Comparative Example 5.

[0051] [1-3. Effects, etc.] As described above, in this embodiment, the desulfurizing agent 4 is a desulfurizing agent that removes sulfur compounds from a raw material gas containing sulfur compounds, and the desulfurizing agent 4 includes a metal-organic structure, which includes copper ions, trimesic acid, and a benzoic acid-based compound. This benzoic acid-based compound is a compound in which a hydrogen atom at the meta or para position of the carboxyl group of benzoic acid is substituted with a substituent, and has higher electron-donating properties than benzoic acid.

[0052] As a result, electrons are donated to the copper ions of the metal-organic structure by benzoic acid-based compounds, which have higher electron-donating properties than benzoic acid itself. This increases the affinity between the sulfur compound and the copper ions, thereby improving the adsorption capacity of the sulfur compound.

[0053] Furthermore, the metal-organic structure constituting the desulfurizing agent in this disclosure has a configuration in which a portion of the trimesic acid in a metal-organic structure composed of copper ions and trimesic acid is replaced by a benzoic acid-based compound. Therefore, compared to a metal-organic structure composed of copper ions and trimesic acid, it has a larger number of pores, which improves the adsorption capacity of sulfur compounds.

[0054] Therefore, it is possible to provide a desulfurizing agent that can reduce the amount of desulfurizing agent 4 to be filled into the desulfurizer (container container 1), thereby enabling the desulfurizer (container container 1) to be made smaller.

[0055] Furthermore, the benzoic acid compound may also be 4-hydroxybenzoic acid.

[0056] As a result, 4-hydroxybenzoic acid, which has a higher electron-donating capacity than benzoic acid, donates electrons to the copper ions in the metal-organic structure, increasing the affinity between the sulfur compound and the copper ions. Furthermore, because the functional group (substituent) is small in size, it does not clog the pores of the metal-organic structure, thus further improving the sulfur adsorption capacity.

[0057] Furthermore, the benzoic acid compound may also be 4-methylbenzoic acid.

[0058] As a result, 4-methylbenzoic acid, which has higher electron-donating properties than benzoic acid, donates electrons to copper ions in the metal-organic structure, increasing the affinity between sulfur compounds and copper ions, further improving sulfur adsorption capacity, and enabling cost reduction of desulfurizing agents due to the low cost of 4-methylbenzoic acid.

[0059] Therefore, the amount of desulfurizing agent 4 to be filled into the desulfurizer (container container 1) can be reduced, making the desulfurizer (container container 1) smaller, and providing an inexpensive desulfurizing agent.

[0060] Furthermore, the benzoic acid compound may also be 4-aminobenzoic acid.

[0061] As a result, 4-aminobenzoic acid, which has a higher electron-donating capacity than benzoic acid, donates electrons to the copper ions of the metal-organic structure, increasing the affinity between the sulfur compound and the copper ions. Furthermore, the basic functional group further increases the affinity with the sulfur compound, thus improving the sulfur adsorption capacity.

[0062] Therefore, it is possible to provide a desulfurizing agent that can reduce the amount of desulfurizing agent 4 to be filled into the desulfurizer (container container 1), thereby enabling the desulfurizer (container container 1) to be made smaller.

[0063] (Other embodiments) As described above, Embodiment 1 has been presented as an example of the technology disclosed in this application. However, the technology in this disclosure is not limited to this and can be applied to embodiments that have been modified, replaced, added, or omitted. Furthermore, it is possible to create new embodiments by combining the components described in Embodiment 1.

[0064] Therefore, other embodiments are illustrated below.

[0065] In Embodiment 1, city gas mainly composed of methane was used as an example of the raw material gas, but LPG, natural gas, or hydrogen may also be used.

[0066] Since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the scope of the claims or their equivalents. [Industrial applicability]

[0067] This disclosure is applicable to desulfurization methods for removing sulfur compounds contained in raw material gases. Specifically, this disclosure is applicable to fuel cell systems and hydrogen production equipment equipped with hydrogen generators that produce hydrogen from city gas or LPG, and fuel cell systems that generate electricity using hydrogen containing sulfur compounds.

Claims

1. A desulfurizing agent for removing sulfur compounds from a raw material gas containing sulfur compounds, The desulfurizing agent comprises a metal-organic structure. The aforementioned metal-organic structure contains copper ions, trimesic acid, and a benzoic acid-based compound. The benzoic acid-based compound is a desulfurizing agent characterized by being a compound in which a hydrogen atom at the meta or para position of the carboxyl group of benzoic acid is replaced with a methyl group.

2. The desulfurizing agent according to claim 1, wherein the benzoic acid compound is 3-methylbenzoic acid.

3. The desulfurizing agent according to claim 1, wherein the benzoic acid compound is 4-methylbenzoic acid.

4. The desulfurizing agent according to any one of claims 1 to 3, wherein the molar ratio of the benzoic acid compound is 10% or more and 50% or less with respect to the trimesic acid.

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