CN113660996B - Acid exhaust gas treating agent, acid exhaust gas treating method, and acid exhaust gas treating apparatus - Google Patents

Abstract

Providing: when acid exhaust gas generated by combustion facilities such as thermal power plants and incineration facilities is treated with the layered double hydroxide, the acid exhaust gas treatment agent, the acid exhaust gas treatment method, and the acid exhaust gas treatment facility, which can improve the removal efficiency of nitric oxide as compared with the conventional ones, can be used. The acid waste gas treatment method of the invention comprises the following steps: a step (1) of bringing the acid off-gas into contact with the acid off-gas treating agent using an acid off-gas treating agent containing a composite of at least one of a manganese oxide and a permanganate compound, the acid off-gas treating agent containing a mg—al layered double hydroxide, and adsorbing an acidic substance in the acid off-gas; a step (2) of desorbing the acidic substance adsorbed on the acidic exhaust gas treating agent in the step (1) and regenerating the acidic exhaust gas treating agent; and (3) recovering the acidic substance desorbed from the acidic exhaust gas treating agent in the step (2).

Description

Acidic waste gas treatment agent, acidic waste gas treatment method, and acidic waste gas treatment equipment

Technical field

The present invention relates to an acidic exhaust gas treatment agent, an acidic exhaust gas treatment method, and an acidic exhaust gas treatment equipment suitable for treating acidic exhaust gas generated from combustion facilities such as thermal power plants and incineration facilities.

Background technique

Combustion exhaust gas generated from thermal power generation, waste incineration, etc. contains harmful acidic substances such as hydrogen chloride, sulfur oxides, and nitrogen oxides. Therefore, the acidic exhaust gas containing the above-mentioned acidic substances has been treated based on various methods to remove the above-mentioned acidic substances.

For the hydrogen chloride and sulfur oxides in the above-mentioned acidic substances, the following treatments have been popularized: neutralization using an alkaline agent such as slaked lime, a dry method in which the product is captured with a dust collector, and a wet method in which neutralization treatment is performed using a scrubber. processing.

In addition, for nitrogen oxides, treatments based on selective catalytic reduction (SCR) and non-catalytic reduction (SNCR) are popular. The selective catalytic reduction method is to mix reducing agents such as ammonia and urea with combustion exhaust gas and then use them. The non-catalytic reduction method is a process in which a catalyst such as vanadium or platinum supported on a carrier such as ceramics is decomposed into nitrogen and water. The non-catalytic reduction method is a process in which reducing agents such as ammonia and urea are directly sprayed into an incinerator to decompose nitrogen oxides.

However, the above-mentioned treatment based on the neutralization treatment requires a treatment step of the neutralized product and requires separate treatment of nitrogen oxides.

In addition, the treatment of nitrogen oxides by SCR and SNCR requires the use of reducing agents, catalysts, etc., and requires costs such as equipment and energy for this purpose.

In response to such a problem, the inventors of the present invention have proposed a method that can effectively treat the above-mentioned acidic exhaust gas at a lower cost using a carbonic acid-type Mg—Al-based layered double hydroxide (see Patent Document 1).

existing technical documents

patent documents

Patent Document 1: Japanese Patent Application Publication No. 2016-190199

Contents of the invention

Invent the problem to be solved

However, even if the treatment method described in the above-mentioned Patent Document 1 is used, the removal treatment of nitric oxide may not necessarily be sufficient.

Therefore, in the treatment of acidic exhaust gas using layered double hydroxide, it is required to improve the removal efficiency of nitric oxide.

The present invention was completed under such circumstances, and its object is to provide a method that can increase nitric oxide compared with conventional methods when using layered double hydroxide to treat acidic waste gas generated from combustion facilities such as thermal power plants and incineration facilities. Acidic waste gas treatment agents, acidic waste gas treatment methods, and acidic waste gas treatment equipment with high removal efficiency.

solutions to problems

The present invention is based on the discovery that a composite compound based on manganese oxide or the like of a Mg-Al based layered double hydroxide (hereinafter also referred to as Mg-Al LDH (Layered Double Hydroxide)) has excellent nitric oxide removal performance.

That is, the present invention provides the following [1] to [7].

[1] An acidic exhaust gas treatment agent containing a complex compound based on at least one of a manganese oxide and a permanganic acid compound of a Mg-Al series layered double hydroxide.

[2] The acidic exhaust gas treatment agent according to the above [1], wherein the composite compound is a manganese dioxide composite Mg-Al based layered double hydroxide, and a permanganic acid type Mg-Al based layered double hydroxide. At least one of the oxides.

[3] The acidic exhaust gas treatment agent according to the above [1] or [2], which contains a carbonic acid Mg-Al based layered double hydroxide.

[4] An acid waste gas treatment method, which is a method of treating acid waste gas using the acid waste gas treatment agent according to any one of the above [1] to [3], the treatment method including the following steps: Step ( 1), bringing the aforementioned acidic exhaust gas into contact with the aforementioned acidic exhaust gas treatment agent, and adsorbing the acidic substances in the aforementioned acidic exhaust gas; step (2), desorbing the acidic substances adsorbed on the aforementioned acidic exhaust gas treatment agent in the aforementioned step (1). Attached, the above-mentioned acidic exhaust gas treatment agent is regenerated; and the step (3) is to recover the acidic substance desorbed from the above-mentioned acidic exhaust gas treatment agent in the above-mentioned step (2).

[5] The acid waste gas treatment method according to the above [4], wherein the treatment cycle including the above-mentioned steps (1) to (3) is repeated, and in at least any one of the second and subsequent treatment cycles of the above-mentioned treatment cycle In the step (1), the acidic exhaust gas treatment agent regenerated in the step (2) of at least one treatment cycle before the treatment cycle is used as at least part of the acidic exhaust gas treatment agent.

[6] Acidic exhaust gas treatment equipment, which is an equipment for treating acidic exhaust gas using the acidic exhaust gas treatment agent according to any one of the above [1] to [3]. The treatment equipment is equipped with the following device: device ( 1), the aforementioned acidic exhaust gas is brought into contact with the aforementioned acidic exhaust gas treatment agent, and the acidic substances in the aforementioned acidic exhaust gas are adsorbed; the device (2) is used to remove the acidic substances adsorbed on the aforementioned acidic exhaust gas treatment agent in the aforementioned device (1). Attached is a method for regenerating the aforementioned acidic exhaust gas treatment agent; and a device (3) for recovering the acidic substance desorbed from the aforementioned acidic exhaust gas treatment agent in the aforementioned device (2).

[7] The acidic waste gas treatment method according to the above [4], wherein the manganese dioxide composite Mg-Al based layered double hydroxide is produced by a production method that does not require a reduction step, and the manganese dioxide composite The composite Mg-Al based layered double hydroxide is produced by adding Mg-Al oxide to a potassium permanganate aqueous solution, filtering and drying the precipitate.

Effect of the invention

By using the acidic exhaust gas treatment agent of the present invention, it is possible to simultaneously remove acidic exhaust gases such as hydrogen chloride, sulfur oxides, and nitrogen oxides generated from combustion facilities such as thermal power plants and incineration facilities. In particular, it is different from the use of conventional layers. Compared with the case of double hydroxide, the removal efficiency of nitric oxide is improved.

In addition, according to the acidic exhaust gas treatment method of the present invention using the acidic exhaust gas treatment agent, acidic exhaust gas can be effectively removed with a smaller amount of treatment than in the past, and the acid exhaust gas treatment agent can be reused.

In addition, according to the acidic exhaust gas treatment device of the present invention, the above-mentioned acidic exhaust gas treatment method can be appropriately performed, and the acidic exhaust gas can be treated more effectively and at a lower cost than before.

Description of the drawings

FIG. 1 is a graph showing changes over time in the _NOx concentration of the reaction tube outlet gas in the acidic exhaust gas treatment performance evaluation test of the Example.

Figure 2 is a powder X-ray diffraction pattern of the product of Synthesis Example 1.

Figure 3 is a powder X-ray diffraction pattern of the product of Synthesis Example 2.

Figure 4 is the powder X-ray diffraction pattern of CO3 _type Mg-Al LDH.

Figure 5 is an XPS pattern of the product of Synthesis Example 1.

Figure 6 is an XPS pattern of the product of Synthesis Example 2.

Detailed ways

The acidic exhaust gas treatment agent of the present invention, the acidic exhaust gas treatment method and the acidic exhaust gas treatment equipment using the same will be described in detail below.

[Acid exhaust gas treatment agent]

The acidic exhaust gas treatment agent of the present invention contains a complex compound of Mg-Al LDH based on at least one of manganese oxide and permanganic acid compound (hereinafter also referred to as Mn-O compound.).

In this way, by using Mg-Al LDH as a complex compound based on manganese and oxygen compounds (Mn-O compounds) as an acidic exhaust gas treatment agent, it is different from the conventional Mg-Al LDH that is a layered double hydroxide. Compared with the situation, the removal efficiency of nitric oxide can be improved.

It can be speculated that this is because although Mg-Al LDH itself is not easy to adsorb nitric oxide, under the catalytic action of the complexed Mn-O compound, nitric oxide is oxidized to nitrogen dioxide, and then becomes easily oxidized to nitric acid. The radical ions become easily adsorbed on the Mg-Al LDH complex.

Manganese may have an oxidation number of +2 to +7, but from the viewpoint of its function as an oxidation catalyst, it is preferably one with a larger oxidation number. From the viewpoint of ease of synthesis, for example, a manganese dioxide composite Mg-Al layered double hydroxide based on manganese with an oxidation number of +4 (hereinafter also referred to as MnO ₂ composite Mg-Al LDH) is preferable. .), or permanganate-type Mg-Al based layered double hydroxide based on manganese with an oxidation number of +7 (hereinafter also referred to as MnO ₄ -type Mg-Al LDH.), etc. The above-mentioned composite compound may contain one type alone, or may contain two or more types.

The structural formula of the MnO ₂ composite Mg-Al LDH is represented by the following formula (1), and the structural formula of the MnO _4- type Mg-Al LDH is represented by the following formula (2).

Mg _1-x Al _x (OH) ₂ (MnO ₂ ) _2.5x (Cl) _x ·mH ₂ O (1)

Mg _1-x Al _x (OH) ₂ (MnO ₄ ) _x ·mH ₂ O (2)

In the aforementioned formulas (1) and (2), x=0.20 to 0.40 and m=1 to 12 are usually used.

The acidic exhaust gas treatment agent preferably contains carbonic acid type Mg-Al based layered double hydroxide (hereinafter also referred to as CO ₃ type Mg-Al LDH.).

As described in the above-mentioned Patent Document 1, CO ₃ type Mg-Al LDH is a compound that can be suitably used for the treatment of acidic exhaust gas, and can effectively remove, for example, hydrogen chloride, sulfur dioxide, nitrogen dioxide, etc. in addition to nitrogen monoxide contained in the acidic exhaust gas. of acidic compounds. Therefore, it is preferably used in combination with the aforementioned composite compound.

In this case, the content ratio of the aforementioned composite compound and CO ₃ type Mg-Al LDH in the aforementioned acidic exhaust gas treatment agent is not particularly limited, and may depend on the amount of nitric oxide contained in the acidic exhaust gas to be treated and other components of the acidic exhaust gas. Set the composition appropriately.

CO ₃ type Mg-Al LDH also exists as hydrotalcite in naturally occurring clay minerals, but when synthesized, the synthesis method is not particularly limited, and a known method can be used (for example, the method described in the above-mentioned Patent Document 1).

For example, an aqueous solution of magnesium nitrate (Mg(NO ₃ ) ₂ ) and aluminum nitrate (Al(NO ₃ ) ₃ ) mixed with Mg/Al = 2/1 (molar ratio) is maintained at pH 10.5 while dripping It can be obtained by adding it to sodium carbonate (Na ₂ CO ₃ ) aqueous solution. Specifically, it can be synthesized by the method shown in the following Examples.

In addition, the synthesis method of MnO ₂ composite Mg-Al LDH and MnO ₄ type Mg-Al LDH is not particularly limited. It can be synthesized by using CO ₃ type Mg-Al LDH as a raw material compound and utilizing the anion exchange function based on its insertion. .

For example, CO ₃ type Mg-Al LDH is pre-calcinated at 500°C to obtain Mg-Al oxide, and then added to an aqueous solution of potassium permanganate (KMnO ₄ ) and mixed, thereby synthesizing a captured permanganate ion ( MnO ₄ ^- ) MnO ₄ type Mg-AlLDH.

Furthermore, MnO ₄ type Mg-Al LDH becomes MnO ₂ composite Mg-Al LDH in potassium permanganate (KMnO ₄ ) aqueous solution.

In addition, by adding the aforementioned MnO ₄ type Mg-Al LDH to a manganese chloride (MnCl ₂ ) aqueous solution and mixing, MnO ₂ composite Mg-Al LDH can be synthesized.

The aforementioned acidic exhaust gas treatment agent may include, for example, calcium hydroxide (slaked lime), calcium oxide, sodium bicarbonate (sodium bicarbonate), sodium carbonate, dolomite hydroxide, and lightly burned dolomite within the scope that does not impair the effect of the present invention. , aluminum hydroxide, aluminum oxide, magnesium hydroxide, magnesium oxide and other agents other than layered double hydroxides. However, in the acidic exhaust gas treatment method described below, when the acidic exhaust gas treatment agent is regenerated and reused, it is preferable not to include these chemicals from the viewpoint of the purity of the regenerated product, recovery operation, etc.

[Acid waste gas treatment method]

The method of treating acidic exhaust gas using the aforementioned acidic exhaust gas treatment agent is not particularly limited. The aforementioned acidic exhaust gas treatment agent (hereinafter also referred to as treatment agent for short) is preferably suitable for the acidic exhaust gas treatment method of the present invention.

The acidic waste gas treatment method of the present invention includes the following steps: step (1), bringing the acidic waste gas into contact with the aforementioned treatment agent, and adsorbing the acidic substances in the aforementioned acidic waste gas; step (2), making the acidic waste gas adsorbed in the aforementioned step (1) The acidic substance desorbed from the treatment agent is desorbed and the treatment agent is regenerated; and the step (3) is to recover the acidic substance desorbed from the treatment agent in the step (2).

According to the above-described treatment method, the regenerated treatment agent can be reused. In addition, the acidic substance may be dissolved in water and recovered as an acid (aqueous solution), and the acid may be used for industrial purposes or the like.

In the aforementioned step (1), nitric oxide is oxidized by the aforementioned composite compound in the aforementioned treatment agent. In addition, the aforementioned compound is oxidized by anion exchange in which acidic substances in the acidic exhaust gas are incorporated between the layers of the layered double hydroxide. Acidic substances are adsorbed on the aforementioned treatment agent.

Next, in the aforementioned step (2), the acidic substance adsorbed on the treatment agent is desorbed from the treatment agent through reversible anion exchange or the like. The anion exchange at this time can be performed by mixing and stirring various aqueous solutions in the same manner as the synthesis methods of CO ₃ type Mg-Al LDH, MnO ₂ composite Mg-Al LDH and MnO ₄ type Mg-Al LDH. , the treatment agent can be easily regenerated.

The treatment agent regenerated in this way can be reused, thus reducing the cost of acidic waste gas treatment.

In the aforementioned step (3), the acidic substance desorbed from the aforementioned treatment agent in the aforementioned step (2) is recovered. For example, it can be dissolved in water and recovered as an acid (aqueous solution). The acid can also be utilized for industrial purposes and the like.

As described above, the treatment method of the present invention is a method that has excellent recyclability not only of the aforementioned treatment agent but also of the acidic exhaust gas to be treated.

In the above-mentioned treatment method, it is preferable that the treatment cycle including the above-mentioned steps (1) to (3) is repeated, and in the step (1) of at least any one of the second and subsequent treatment cycles, the treatment agent is At least part of the treatment cycle uses the treatment agent regenerated in step (2) of at least one treatment cycle before this treatment cycle.

In this way, when the above treatment method is repeated, by reusing the treatment agent regenerated in the previous step, the total amount of treatment agent required for the treatment of acidic exhaust gas can be reduced, thereby reducing the treatment cost of acidic exhaust gas.

The acid waste gas treatment method of the present invention as described above can simultaneously remove various acidic substances in the acid waste gas using a single treatment agent, and therefore has excellent work efficiency. In particular, by using the above-mentioned composite compound as a treatment agent, the removal efficiency of nitric oxide can be improved compared to conventional methods.

In addition, neutralization products are not generated during treatment, and the processing load of waste generated during treatment can be reduced.

[Acid waste gas treatment equipment]

The equipment for treating acidic exhaust gas using the aforementioned acidic exhaust gas treatment agent is not particularly limited, and the aforementioned treatment agent is preferably applied to the acidic exhaust gas treatment equipment of the present invention.

The acidic waste gas treatment equipment of the present invention is equipped with the following devices: device (1), which makes the acidic waste gas contact the aforementioned treatment agent and adsorb the acidic substances in the aforementioned acidic waste gas; device (2), which causes the acidic waste gas to be adsorbed in the aforementioned device (1). The acidic substance of the aforementioned treatment agent is desorbed and the aforementioned treatment agent is regenerated; and a device (3) is used to recover the acidic substance desorbed from the aforementioned treatment agent in the aforementioned device (2).

The device (1) may be configured, for example, by providing a flow path for acidic exhaust gas in a container containing the treatment agent.

The device (2) may be configured, for example, as an immersion tank that can utilize the treatment agent taken out from the container through which the acidic exhaust gas has circulated, combined with the above-mentioned CO ₃ type Mg-Al LDH and MnO ₂ The synthesis method of Mg-Al LDH and MnO _4- type Mg-Al LDH is the same. According to the chemical type to be complexed with Mg-Al LDH, it is immersed in various aqueous solutions and mixed.

The device (3) may be configured as an aqueous solution storage tank that is dissolved in water and recovered as acid (aqueous solution), for example.

The aforementioned acidic waste gas treatment equipment can be attached to combustion equipment in thermal power generation, waste incineration, etc. For example, when treating acidic waste gas generated by a waste incinerator, the structure can be as follows: following the boiler, waste gas cooling device, and dust collector that are sequentially installed in the combustion waste gas system of the incinerator body, the above-mentioned acid waste gas treatment is provided Equipment that introduces the treated exhaust gas from the acidic exhaust gas treatment equipment into the chimney through a suction ventilator, etc., and releases it from the chimney into the atmosphere.

Example

The present invention will be described in more detail below, but the present invention is not limited to the following examples.

[Synthesis Example 1] Synthesis of MnO ₂ composite Mg-Al LDH

Magnesium nitrate hexahydrate and aluminum nitrate nonahydrate were used to prepare a mixed aqueous solution with a magnesium concentration of 0.33 mol/L and an aluminum concentration of 0.17 mol/L (magnesium/aluminum = 2/1 (molar ratio)).

This mixed solution was added dropwise to an aqueous sodium carbonate solution with a concentration of 0.1 mol/L at 30° C. while stirring. At this time, a sodium hydroxide aqueous solution with a concentration of 1.25 mol/L was added dropwise to maintain the pH at 10.5.

After completion of the dropwise addition, the mixture was stirred at 30° C. for 1 hour. Then, the precipitate was filtered and washed repeatedly, and then dried under reduced pressure at 40°C for 40 hours to obtain _CO3 type Mg-Al LDH.

The obtained CO ₃ type Mg-Al LDH was pre-calcinated at 500°C for 2 hours, then put into a potassium permanganate aqueous solution with a concentration of 0.2 mol/L under a nitrogen gas flow, and stirred at 30°C for 6 hours. Then, the precipitate was filtered and washed repeatedly, and the product dried under reduced pressure at 40° C. for 40 hours was put into a manganese chloride aqueous solution with a concentration of 0.1 mol/L under a nitrogen gas flow, and stirred at 30° C. for 3 hours. . Then, the precipitate was filtered and washed repeatedly, and then dried under reduced pressure at 40°C to obtain MnO ₂ composite Mg-Al LDH (Mg _0.62 Al _0.38 (OH) ₂ (MnO ₂ ) _0.95 (Cl) _0.38 ·1.13H ₂ O).

[Synthesis Example 2] Synthesis of MnO ₂ composite Mg-Al LDH

Magnesium nitrate hexahydrate and aluminum nitrate nonahydrate were used to prepare a mixed aqueous solution with a magnesium concentration of 0.33 mol/L and an aluminum concentration of 0.17 mol/L (magnesium/aluminum = 2/1 (molar ratio)).

This mixed solution was added dropwise to an aqueous sodium carbonate solution with a concentration of 0.1 mol/L at 30° C. while stirring. At this time, a sodium hydroxide aqueous solution with a concentration of 1.25 mol/L was added dropwise to maintain the pH at 10.5.

After completion of the dropwise addition, the mixture was stirred at 30° C. for 1 hour. Then, the precipitate was filtered and washed repeatedly, and then dried under reduced pressure at 40°C for 40 hours to obtain _CO3 type Mg-Al LDH.

The obtained CO ₃ type Mg-Al LDH was pre-calcinated at 500°C for 2 hours, then put into a potassium permanganate aqueous solution with a concentration of 0.2 mol/L under a nitrogen gas flow, and stirred at 30°C for 6 hours. Then, the precipitate was filtered and washed repeatedly, and then dried under reduced pressure at 40° C. for 40 hours.

In addition, CO ₃ type Mg-Al LDH, MnO ₄ type Mg-Al LDH, and MnO ₂ composite Mg-Al in Synthesis Example 1 and Synthesis Example 2 were identified by powder X-ray diffraction measurement (powder XRD) LDH. For CO3 _type Mg-Al LDH, Figure 4 shows the powder X-ray diffraction pattern. In addition, the X-ray diffraction measuring device used was "RINT-2200VHF" manufactured by Rigaku Corporation, and CuKα rays (1.5418A) were used for measurement as characteristic X-rays. In addition, elemental analysis values based on inductively coupled plasma luminescence spectroscopy (ICP-AES) are also shown for the complex compound based on the Mn—O compound. In addition, the MnO ₄ type Mg-Al LDH and MnO ₂ composite Mg-Al LDH in Synthesis Example 1 and Synthesis Example 2 were identified by determining the oxidation number of Mn using X-ray photoelectron spectroscopy (XPS).

[Acid exhaust gas treatment performance evaluation test]

(Example 1)

1.0 g of the MnO ₂ composite Mg-Al LDH obtained in Synthesis Example 1 was filled on the glass wool in the reaction tube (inner diameter 16 mm) of the tubular electric furnace. Set the set temperature of the tubular electric furnace to 170°C, adjust the flow rate of the test gas (carrier gas: nitrogen, nitric oxide gas concentration 150 volppm, oxygen concentration 10 vol%) through a mass flow controller, and flow in at a linear speed of 1.0 m/min. in the reaction tube. The temporal change (90 minutes) in the _NOx concentration of the outlet gas of the reaction tube was measured using a combustion exhaust gas analyzer (manufactured by Testo SE & Co. KGaA) based on the potentiostatic electrolysis method.

(Comparative example 1)

In Example 1, the evaluation test was performed in the same manner as in Example 1, except that the MnO ₂ composite Mg-Al LDH was changed to the CO ₃ type Mg-Al LDH obtained during the synthesis process of Synthesis Example 1.

The graph in FIG. 1 shows the temporal change in the _NOx concentration of the outlet gas of the reaction tube in Example 1 and Comparative Example 1.

In addition, the reaction rate of nitric oxide gas in the test gas was calculated from the cumulative concentration of _NOx concentration. The results showed that Example 1 was 91.5 vol% and Comparative Example 1 was 2.2 vol%.

From these results, it is clear that the composite compound of manganese dioxide and Mg-Al series layered double hydroxide has superior nitric oxide removal performance than the CO ₃ type Mg-Al LDH.

[Analysis based on the presence ratio of MnO ₂ composite Mg-Al LDH based on Synthesis Example 1 and Synthesis Example 2]

The powder X-ray diffraction patterns of the products based on Synthesis Example 1 and Synthesis Example 2 are shown in FIGS. 2 and 3 . In addition, XPS patterns of the products based on Synthesis Example 1 and Synthesis Example 2 are shown in FIGS. 5 and 6 .

Judging from the elemental analysis values, the Mg/Al molar ratios of the products of Synthesis Example 1 and Synthesis Example 2 are 1.9 and 1.6 respectively, which are basically consistent with the initial Mg/Al molar ratio of 2.0.

According to the powder X-ray diffraction patterns in Figures 2 and 3, X-ray peaks attributed to LDH are shown, and it is confirmed that the interplanar spacing (d 003) is Any product has an LDH structure.

According to the XPS patterns of Figures 5 and 6, the peak of Mn(IV) derived from _MnO2 was confirmed, and the presence of Mn(IV) in an amount of 95% or more relative to the total amount of Mn was confirmed from the peak area.

Based on these results, it was confirmed that MnO ₂ composite Mg-Al LDH can be synthesized even without the reduction step of introducing the manganese chloride aqueous solution shown in Synthesis Example 1 as in Synthesis Example 2.

It should be noted that the MnO ₂ composite Mg-Al LDH in Synthesis Example 2 is considered to be produced as follows.

First, CO ₃ type Mg-Al LDH is pre-baked at 500°C for 2 hours, and the generated Mg-Al oxide (Mg _{1- x} Al _x O _1+x/2 ) is added to a concentration of 0.2 mol under a nitrogen gas flow. /L potassium permanganate aqueous solution, when stirred at 30°C for 6 hours, MnO ₄ type Mg-Al LDH (Mg _1-x Al _x (OH) ₂ (MnO ₄ ) is generated as shown in formula (3) _x ).

Mg _1-x Al _x O _1+x/2 +xMnO ₄ ^- +(1+x/2)H ₂ O

→Mg _1-x Al _x (OH) ₂ (MnO ₄ ) _x +xOH- (3)

Furthermore, in the potassium permanganate aqueous solution, the reaction shown in formula (4) occurs, and MnO ₂ type Mg-Al LDH (Mg _{1- x} Al _x (OH) ₂ (MnO ₂ ) _x ) is produced.

Mg _1-x Al _x (OH) ₂ (MnO ₄ ) _x +x/2H ₂ O

→Mg _1-x Al _x (OH) ₂ (MnO ₂ ) _x +3/4xO ₂ +xOH- (4)

Claims (6)

1. An acid exhaust gas treatment method for treating an acid exhaust gas with an acid exhaust gas treatment agent, comprising the steps of:

a step (1) of bringing the acid off-gas into contact with the acid off-gas treating agent and adsorbing an acidic substance in the acid off-gas;

a step (2) of desorbing the acidic substance adsorbed on the acidic exhaust gas treating agent in the step (1) and regenerating the acidic exhaust gas treating agent; and

A step (3) of recovering the acidic substance desorbed from the acidic exhaust gas treatment agent in the step (2),

the acidic exhaust gas treatment agent contains a compound represented by the following formula (1),

Mg _1-x Al _x （OH） ₂ （MnO ₂ ） _2.5x （Cl） _x ·mH ₂ O （1）

in the formula (1), x=0.20 to 0.40 and m=1 to 12,

the acid waste gas contains nitric oxide.

2. The acid exhaust gas treatment method according to claim 1, wherein the acid exhaust gas treatment agent comprises a carbonic acid type Mg-Al-based layered double hydroxide.

3. The method for treating an acidic exhaust gas according to claim 1, wherein the treatment cycles including the steps (1) to (3) are repeated, and the acidic exhaust gas treating agent regenerated in the step (2) of at least any one of the treatment cycles before and after the treatment cycle is used as at least a part of the acidic exhaust gas treating agent in the step (1) of at least any one of the treatment cycles 2 and after the treatment cycle.

4. The method for treating acidic exhaust gas according to claim 1, wherein the compound represented by the formula (1) is produced by a method that does not require a reduction step, wherein the compound represented by the formula (1) is produced by adding Mg-Al oxide obtained by pre-calcining a carbonic acid type Mg-Al layered double hydroxide at 500 ℃ to an aqueous potassium permanganate solution, filtering and drying the precipitate.

5. An acid exhaust gas treatment apparatus for treating an acid exhaust gas with an acid exhaust gas treatment agent, the treatment apparatus comprising means for performing the steps of:

means (1) for bringing the acid off-gas into contact with the acid off-gas treatment agent and adsorbing an acid substance in the acid off-gas;

means (2) for desorbing the acidic substance adsorbed on the acidic exhaust gas treatment agent in the means (1) to regenerate the acidic exhaust gas treatment agent; and

Means (3) for recovering the acidic material desorbed from the acidic exhaust gas treatment agent in said means (2),

the acidic exhaust gas treatment agent contains a compound represented by the following formula (1),

Mg _1-x Al _x （OH） ₂ （MnO ₂ ） _2.5x （Cl） _x ·mH ₂ O （1）

in the formula (1), x=0.20 to 0.40 and m=1 to 12,

the acid waste gas contains nitric oxide.

6. The acid exhaust gas treatment apparatus according to claim 5, wherein the acid exhaust gas treatment agent comprises a carbonic acid type Mg-Al-based layered double hydroxide.