Acid gas treatment agent and acid gas treatment method

Abstract

Provided are an acidic gas treatment agent and an acidic gas treatment method based on an Mg-Al layered double hydroxide, said acidic gas treatment agent having a high adsorption capacity with respect to acidic substances and a long penetration time, thereby reducing the frequency of regeneration treatment of the treatment agent. The acidic gas treatment agent according to the present invention is formed from an Mg-Al layered double hydroxide having an average pore diameter of 30 nm or more as measured by a nitrogen gas adsorption method and a sulfate ion content of 1 mass% or less.

Description

Technical Field

[0001] This invention relates to acidic gas treatment agents and methods for removing acidic substances such as hydrogen chloride, sulfur oxides and nitrogen oxides from combustion exhaust gases. Background Technology

[0002] Combustion exhaust gases generated in thermal power generation, waste incineration, etc., contain hydrogen chloride and sulfur oxides (SO₄). x ) and nitrogen oxides (NO) x Harmful acidic substances such as [list of substances]. Therefore, various methods were used to remove these acidic substances from acidic gases containing them.

[0003] Regarding such treatment methods for removing acidic substances, as a highly efficient treatment technology capable of simultaneously treating multiple acidic substances, the applicant has proposed a method and treatment agent for treating acidic waste gas using Mg-Al layered double hydroxides (hereinafter, layered double hydroxides are sometimes simply referred to as LDH) (see Patent Document 1, Non-Patent Documents 1 and 2).

[0004] For example, Non-Patent Literature 1 describes a scheme in which carbonated Mg-Al LDH can effectively remove hydrogen chloride gas, and the carbonated Mg-Al LDH slurry can remove not only hydrogen chloride gas but also sulfur oxide gas. Non-Patent Literature 2 describes a scheme in which the removal rate of hydrogen chloride gas is increased by increasing the amount of carbonated Mg-Al LDH.

[0005] Furthermore, the applicant of this application has proposed a system for regenerating and repeatedly utilizing the used treatment agent of Mg-Al LDH (see Patent Documents 2 and 3).

[0006] Patent document 2 proposes an on-site regeneration method for using treated waste gas for regeneration. In addition, patent document 3 proposes a method for treating acidic waste gas using hydroxide-type Mg-Al LDH and regenerating used treatment agents.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 6954569

[0010] Patent Document 2: Japanese Patent No. 6898627

[0011] Patent Document 3: Japanese Patent No. 7130197

[0012] Non-patent literature

[0013] Non-patent literature 1: Journal of the Society of Inorganic Materials, 2014, Vol.21, pp.197-203

[0014] Non-patent literature 2: Atmospheric Pollution Research, 2020, Vol.11, Issue2, pp.290-295 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] The existing Mg-Al LDH used in the treatment of acidic waste gas may not have a high adsorption capacity for acidic substances such as nitrogen oxides and sulfur oxides, and it quickly reaches saturation, requiring high-frequency regeneration treatment. The regeneration treatment process is labor-intensive and costly.

[0017] Therefore, in order to improve the adsorption capacity of the aforementioned acidic substances in acidic waste gas and reduce the frequency of regeneration treatment, a Mg-Al based LDH with a long breakthrough time is sought.

[0018] This invention was made to solve such a problem, and its purpose is to provide an acid gas treatment agent and an acid gas treatment method based on Mg-Al LDH, wherein the acid gas treatment agent has a high adsorption capacity for acidic substances and a long penetration time, thereby reducing the frequency of regeneration treatment of the treatment agent.

[0019] Solution for solving the problem

[0020] This invention is based on the discovery that by keeping the average pore size and sulfate ion content of Mg-Al based LDH within a specified range, an acid gas treatment agent with high adsorption capacity for acidic substances and long penetration time can be obtained.

[0021] The present invention provides the following solution.

[0022] [1] An acidic gas treatment agent, which is formed from Mg-Al layered double hydroxide, wherein the average pore size of the Mg-Al layered double hydroxide, as measured by nitrogen adsorption, is greater than 30 nm and the sulfate ion content is less than 1% by mass.

[0023] [2] According to the acidic gas treatment agent of [1], wherein the aforementioned Mg-Al layered double hydroxide is of the carbonate type or hydroxide type.

[0024] [3] According to the acidic gas treatment agent of [1] or [2], wherein the molar ratio of Mg to Al in the aforementioned Mg-Al layered double hydroxide is 2 to 3.

[0025] [4] According to any one of [1] to [3], the cumulative volume 50% particle size D50 of the aforementioned Mg-Al layered double hydroxide is 13.0 to 16.0 μm, and the ratio of the cumulative volume 90% particle size D90 to the cumulative volume 10% particle size D10 (D90 / D10) is 55 to 75.

[0026] [5] A molded article comprising any one of the acidic gas treatment agents of [1] to [4].

[0027] [6] An acid gas treatment method, wherein the acid gas treatment agent of any one of [1] to [4] or the molded body of [5] is brought into contact with an acid gas containing an acidic substance, thereby removing the aforementioned acidic substance.

[0028] The effects of the invention

[0029] According to the present invention, an acid gas treatment agent formed from Mg-Al based LDH with high adsorption capacity for acidic substances and long penetration time is provided, along with an acid gas treatment method. Furthermore, according to the present invention, the frequency of regeneration treatment of the acid gas treatment agent can be reduced, and the removal efficiency of acidic substances in acidic gases can be improved. Attached Figure Description

[0030] Figure 1 This is a graph showing the breakthrough curve in the acid gas adsorption test of the embodiment. Detailed Implementation

[0031] In this specification, the numerical range indicated by "~" refers to the lower and upper limits of the values ​​before and after the "~". The preferred numerical range can be any combination of the preferred lower and upper limits.

[0032] The acidic gas treatment agent of the present invention is formed from Mg-Al LDH, wherein the average pore size of the Mg-Al LDH measured by nitrogen adsorption method is 30 nm or more, and the sulfate ion content is less than 1% by mass.

[0033] Mg-Al based LDH has a hydroxide base layer ([Mg 2+ 1-x Al 3+ x (OH)2]) and the interlayer anion (A n- The intermediate layer consisting of ) and interlayer water ([(A) n- ) x / n Nanoparticles with an alternating layered structure of ·yH2O]. The basic layer of hydroxide is an indefinite ratio of compounds with a positive charge equivalent to x and anions present in the interlayer to compensate for the negative charge.

[0034] Mg-Al LDH also exists in naturally occurring clay minerals, but it is usually synthesized by known methods.

[0035] When Mg-Al based LDH comes into contact with acidic gases, it can embed acidic substances such as hydrogen chloride, sulfur oxides, and nitrogen oxides into the interlayer while maintaining the hydroxide base layer. Interlayer anions exchange ions with anions originating from the aforementioned acidic substances, thereby exerting an adsorption capacity for these acidic substances. This adsorption capacity gradually decreases as ion exchange proceeds and the number of interlayer anions decreases, leading to the penetration of the acidic gas treatment agent formed by this Mg-Al based LDH.

[0036] The Mg-Al based LDH of the acidic gas treatment agent that has thus undergone penetration can be regenerated and reused by anion exchange to interlayer anions using known methods.

[0037] From the perspectives of good adsorption capacity for acidic substances and ease of regeneration and repeated use, Mg-Al type LDH with carbonate or hydroxide ions as interlayer anions is preferred.

[0038] Furthermore, for Mg-Al LDH, from the viewpoint of the ion exchange capacity of interlayer anions and the solid solution limit of aluminum ions as trivalent metal ions, the elemental molar ratio of Mg to Al (Mg / Al molar ratio) is preferably 2 to 3, more preferably 2 to 2.8, and even more preferably 2 to 2.5.

[0039] The acid gas treatment agent of the present invention has a high adsorption capacity for acidic substances and a long breakthrough time by setting the average pore size and sulfate ion content of Mg-Al based LDH within a specified range.

[0040] Regarding the aforementioned average pore size, specifically, the average pore size measured by nitrogen adsorption method is 30 nm or more, preferably 31 nm or more, and more preferably 32 nm or more.

[0041] Regarding the average pore size based on nitrogen adsorption, for Mg-Al LDH, 4V / A is calculated from the adsorption isotherm, the specific surface area A obtained by the BET single-point method, and the total pore volume V obtained by the single-point method. Specifically, it is determined by measurement using a specific surface area / pore distribution measuring device.

[0042] The average pore size of Mg-Al LDH is related to its adsorption capacity for acidic substances. By making the average pore size greater than 30 nm, acidic substances can more easily enter the adsorption sites between the layers of Mg-Al LDH, thereby improving the adsorption capacity for acidic substances.

[0043] From a practical point of view, the upper limit of the average aperture is preferably 50 nm or less, more preferably 48 nm or less, and even more preferably 45 nm or less.

[0044] There are no particular limitations on the method for controlling the average pore size of Mg-Al based LDH. Enlarging the average pore diameter by more than 30 nm can be achieved, for example, through mechanochemical methods. Specifically, methods such as drying after contact with water or pulverizing and mixing using mechanochemical methods can be used. By applying mechanical stress to Mg-Al based LDH, some of the fine pores deform and enlarge, thus increasing the average pore size.

[0045] Examples of pulverizing methods include using cone crushers, roller crushers, shredders, autogenous mills, pulverizers, and mortar-type grinders. When the amount of Mg-Al LDH to be pulverized is small, a household coffee grinder can also be used.

[0046] The sulfate ion content of the Mg-Al LDH in the acidic gas treatment agent of the present invention is 1% by mass or less, preferably 0.9% by mass or less, and more preferably 0.8% by mass or less.

[0047] The sulfate ion content was calculated by converting the elemental analysis value of sulfur based on fluorescence X-ray diffraction. It should be noted that sulfate ions in Mg-Al based LDH may be present, for example, as a raw material derived from Mg-Al based LDH.

[0048] The sulfate ion content of Mg-Al based LDH is correlated with its adsorption capacity for acidic substances. Sulfate ions present in the interlayer of Mg-Al based LDH hinder the adsorption of acidic substances. By reducing the sulfate ion content to below 1% by mass, anion exchange between interlayer anions and anions originating from acidic substances is facilitated, significantly improving the adsorption capacity for acidic substances and extending the breakthrough time of the acid gas treatment agent.

[0049] There is no particular limitation on the method for controlling the sulfate ion content of Mg-Al based LDH. As a method to reduce the sulfate ion content to below 1% by mass, one example is to contact an aqueous sodium carbonate solution with the Mg-Al based LDH, thereby replacing the sulfate ions in the Mg-Al based LDH with carbonate ions. Contact with the aqueous sodium carbonate solution can expand the pore size of the Mg-Al based LDH through hydration swelling and other effects, and is therefore preferred.

[0050] When contacting an aqueous sodium carbonate solution with Mg-Al based LDH, it is preferable to control the average pore size by pulverizing and mixing using mechanochemical methods after contacting and drying. Mg-Al based LDH tends to clump in a wet state; therefore, it is reasonable to control the average pore size and sulfate ion content by pulverizing only once after ensuring it is fully dried.

[0051] Furthermore, from the viewpoint of acid gas flow efficiency, the Mg-Al based LDH in the acid gas treatment agent of the present invention preferably has a cumulative volume 50% particle size D50 of 13.0 to 16.0 μm, and a cumulative volume 90% particle size D90 to cumulative volume 10% particle size D10 ratio (D90 / D10) of 55 to 75. More preferably, the Mg-Al based LDH has a D50 of 13.5 to 15.5 μm and a D90 / D10 ratio of 60 to 70.

[0052] It should be noted that D50, D10, and D90 are determined from the volumetric reference particle size distribution measured using a laser diffraction / scattering particle size analyzer. Specifically, they can be measured using the methods described in the examples.

[0053] The form of the acidic gas treatment agent of the present invention is not particularly limited as long as the average pore size and sulfate ion content of the Mg-Al based LDH are within the range specified in the present invention.

[0054] The acid gas treatment agent of the present invention can be appropriately processed from the viewpoint of its usage and ease of operation, and can also be granulated by known methods such as extrusion granulation. Alternatively, it can be used, for example, in the form of a molded body formed into granules, spherical particles, etc., using an adhesive. That is, the molded body of the present invention contains the aforementioned acid gas treatment agent.

[0055] From the viewpoint of ease of operation, the particle size of the aforementioned molded article is preferably 1 to 5 mm, more preferably 2 to 4 mm, and even more preferably 2.5 to 3.5 mm.

[0056] Here, the particle size of the so-called molded body is equivalent to its diameter if the molded body is spherical, and in the case of granular material, it refers to the length of the part where the distance between the plates becomes the largest when the granular material is held between two parallel plates (the maximum distance between the two plates). A molded body with a particle size of 1~5mm refers to granular material that passes through a sieve with a 5mm aperture but not through a sieve with a 1mm aperture.

[0057] The acid gas treatment method of the present invention involves contacting the acid gas treatment agent or molded body of the present invention with an acid gas containing acidic substances, thereby removing the aforementioned acidic substances.

[0058] The aforementioned acidic substances are not particularly limited. As mentioned above, in the case of, for example, hydrogen chloride, sulfur oxides and nitrogen oxides, these acidic substances can be suitably adsorbed onto the acidic gas treatment agent or molded body of the present invention and removed.

[0059] It should be noted that, as described above, the acid gas treatment agent of the present invention achieves its excellent effects by setting the average pore size and sulfate ion content of the Mg-Al based LDH within a specified range. For example, it can also be used in combination with LDH composed of other metal elements that have the ability to adsorb acidic substances.

[0060] Example

[0061] The present invention will now be described in detail based on embodiments. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the spirit of the invention.

[0062] [Analysis of the sample]

[0063] For the samples of the following examples and comparative examples, the average pore size and sulfate ion content were determined as follows.

[0064] (Average aperture)

[0065] The average pore size was determined by nitrogen adsorption using a specific surface area / pore size distribution measuring device (“BELSORP (registered trademark)-mini”, manufactured by MicrotracBELCorp.).

[0066] (Sulfate ion content)

[0067] Elemental analysis was performed using a fluorescence X-ray analysis device, and the sulfur content was converted into sulfate ion content to obtain the result.

[0068] (50% of the cumulative volume of particle size D50, 90% of the cumulative volume of particle size D90, and 10% of the cumulative volume of particle size D10)

[0069] Using a laser diffraction / scattering particle size analyzer ("MT-3300 EXII", manufactured by MicrotracBEL Corp.), sample powder (transmittance 80~95%) was added to a sample circulator containing a 0.025% by mass sodium hexametaphosphate aqueous solution. The particle size distribution of the volume standard was measured, and D50 and D90 / D10 were determined.

[0070] [Sample Preparation]

[0071] (Example 1)

[0072] Dissolve 8.6 g of sodium carbonate in 1 L of deionized water and heat to 70 °C to prepare an aqueous sodium carbonate solution. Add 100 g of Mg-Al LDH (1) (manufactured by Sakai Chemical Industry Co., Ltd.; Mg / Al molar ratio of 2) to the aqueous sodium carbonate solution and stir at 70 °C for 1 hour to mix. Filter the resulting mixture and wash the solid components on the filter paper with deionized water until the conductivity of the washing solution is below 100 μS / cm. Dry the washed solid components at 105 °C and grind them with a household coffee grinder for 30 seconds to obtain Mg-Al LDH (2) as a sample (average pore size: 32.0 nm, sulfate ion content: 0.55% by mass, D50: 14.5 μm, D90 / D10: 65.8).

[0073] (Comparative Example 1)

[0074] The Mg-Al LDH (1) used in Example 1 was used as a sample in its untreated state (average pore size: 28.5 nm, sulfate ion content: 2.76% by mass, D50: 30.2 μm, D90 / D10: 81.0).

[0075] (Comparative Example 2)

[0076] The Mg-Al LDH (1) used in Example 1 was pulverized for 30 seconds using a household coffee grinder to obtain Mg-Al LDH (3) as a sample (average pore size: 29.5 nm, sulfate ion content: 2.75% by mass, D50: 12.0 μm, D90 / D10: 48.7).

[0077] [Acidic Gas Adsorption Test]

[0078] 0.15 g of sample was placed into a reaction tube (17 mm inner diameter) filled with glass wool, and the tube was covered with glass wool to ensure ventilation. The reaction tube was then heated in a tubular electric furnace at a set temperature of 150 °C. Hydrogen chloride gas was allowed to flow downwards (linear velocity 1.0 m / min) through the reaction tube while the supply was controlled by a mass flow controller at a concentration of 300 ppm (equilibrium gas: nitrogen).

[0079] The concentration of hydrogen chloride gas at the outlet of the reaction tube was determined using a gas analysis infrared spectroscopy device.

[0080] Figure 1 The figure shows the flow time of hydrogen chloride gas on the horizontal axis and the concentration ratio of hydrogen chloride gas at the inlet and outlet of the reaction tube on the vertical axis (outlet concentration C). out / Inlet concentration C in The penetration curve of the sample at time ).

[0081] Depend on Figure 1 It can be seen that the breakthrough time of the samples in Comparative Examples 1 and 2 is less than 60 minutes, while the breakthrough time of the sample in Example 1 is more than 110 minutes. In addition, the concentration of hydrogen chloride gas at the outlet of the reaction tube of the sample in Example 1 is lower than that of the samples in Comparative Examples 1 and 2, thus confirming that the adsorption capacity of hydrogen chloride gas is high.

Claims

1. An acidic gas treatment agent, which is formed from a Mg-Al layered double hydroxide, wherein the average pore size of the Mg-Al layered double hydroxide, as measured by nitrogen adsorption, is greater than 30 nm and the sulfate ion content is less than 1% by mass.

2. The acidic gas treatment agent according to claim 1, wherein, The Mg-Al layered double hydroxide is of the carbonate type or hydroxide type.

3. The acidic gas treatment agent according to claim 1, wherein, The molar ratio of Mg to Al in the Mg-Al layered double hydroxide is 2 to 3.

4. The acidic gas treatment agent according to claim 1, wherein, The cumulative volume 50% particle size D50 of the Mg-Al layered double hydroxide is 13.0~16.0 μm, and the ratio of the cumulative volume 90% particle size D90 to the cumulative volume 10% particle size D10, i.e., D90 / D10, is 55~75.

5. A molded article comprising the acidic gas treatment agent of claim 1.

6. A method for treating acidic gases, wherein, The acidic gas treatment agent of claim 1 or the molded body of claim 5 is brought into contact with an acidic gas containing acidic substances, thereby removing the acidic substances.

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