JP6898627B2 - Carbonated layered double hydroxide regeneration method and acidic exhaust gas treatment equipment - Google Patents

Description

The present invention relates to a method for regenerating a carbonated layered double hydroxide used for treating acidic exhaust gas generated from a combustion facility such as a thermal power plant or an incinerator, and an acidic exhaust gas treatment facility provided with the regenerating means.

Combustion exhaust gas generated in thermal power generation and waste incinerator contains harmful acidic substances such as hydrogen chloride, sulfur oxides, and nitrogen oxides. Therefore, the acidic exhaust gas containing the acidic substance is treated by various methods for removing the acidic substance.

In such a method for removing an acidic substance, the applicant has applied a carbonated Mg—Al layered double hydroxide (hereinafter referred to as a carbonated Mg—Al layered double hydroxide) as an efficient treatment technique capable of simultaneously treating and removing a plurality of types of acidic substances. , Mg-Al LDH (also referred to as Layered Double Hydroxide)) has been proposed as a treatment method and a treatment agent for acidic exhaust gas (see Patent Document 1).

The Mg-Al LDH is a treatment agent that can be regenerated and used repeatedly. Conventionally, as described in Patent Document 1, a carbonated Mg-Al LDH has been used for acid exhaust gas treatment. When converted to anionic Mg-Al LDH, this used layered double hydroxide was regenerated by mixing with an aqueous carbonic acid solution.

Japanese Unexamined Patent Publication No. 2016-190199

The means for mixing the used layered double hydroxide and the carbonated aqueous solution as described above can be carried out in a layered double hydroxide recycling facility provided outside the waste incineration facility. However, in this case, the transportation of used layered double hydroxides and regenerated layered double hydroxides between the waste incinerator and the layered double hydroxides recycling facility, and the outside separate from the waste incinerator. There was a problem that the labor and cost burden for setting up the facility was large.
In addition, when installing a used layered double hydroxide recycling facility in a waste incinerator, it is necessary to install and connect a storage tank for an aqueous carbonate solution, a mixing tank, etc., and the entire facility must be scaled up. Did not get.

The present invention has been made to solve the above technical problems, and efficiently regenerates the used anionic Mg-Al LDH in the acidic exhaust gas treatment into the carbonated Mg-Al LDH. It is an object of the present invention to provide a method for regenerating a carbonated layered double hydroxide that can be used, and an acidic exhaust gas treatment facility.

According to the present invention, the used layered double hydroxide in the acidic exhaust gas treatment is brought into contact with a gas containing water and a predetermined amount of carbon dioxide, particularly the gas after the treatment of the acidic exhaust gas, thereby efficiently carbonating. It is based on the finding that it can be regenerated into layered double hydroxides.

That is, the present invention provides the following [1] to [4].
[1] Anionic Mg-Al layered double hydroxide produced by acid exhaust gas treatment using carbonated Mg-Al layered double hydroxide contains water and carbon dioxide having a concentration of 5 vol% or more at 70 ° C. or higher. A method for regenerating a carbon dioxide-type layered double hydroxide, which regenerates a carbon dioxide-type Mg—Al-based layered double hydroxide by contacting the mixed gases of the above.
[2] The method for regenerating a carbonated layered double hydroxide according to the above [1], wherein the water content in the mixed gas is 10% or more.
[3] The acidic exhaust gas treatment is a treatment of acidic exhaust gas generated in a combustion facility, and the treated gas from which the acidic gas other than carbon dioxide after the treatment has been removed is used as the mixed gas. Alternatively, the method for regenerating a carbon dioxide-type layered double hydroxide according to [2].

[4] Carbonated Mg by the means (1) for performing acidic exhaust gas treatment using a carbonated Mg-Al layered double hydroxide and the regeneration method according to any one of the above [1] to [3]. -Acid exhaust gas treatment equipment provided with means (2) for regenerating Al-based layered double hydroxides.

According to the present invention, it is possible to regenerate the used layered double hydroxide in the acidic exhaust gas treatment into a carbonated layered double hydroxide on-site without requiring a large-scale equipment, and it is turned off. It is also more advantageous in terms of equipment, labor and cost burden than the regeneration process at the site regeneration facility.
Further, the gas after the treatment of the acidic exhaust gas treatment can be used, and the carbonated layered double hydroxide can be efficiently regenerated according to the acidic exhaust gas treatment apparatus of the present invention.

It is a schematic flow chart of the acidic exhaust gas treatment process using the acidic exhaust gas equipment of one Embodiment of this invention.

Hereinafter, the method for regenerating the carbonated layered double hydroxide of the present invention and the acidic exhaust gas treatment equipment will be partially described with reference to the drawings.

[Regeneration method of carbonated layered double hydroxide]
In the method for regenerating a carbonated layered double hydroxide of the present invention, anionic Mg-Al LDH produced by an acidic exhaust gas treatment using carbonated Mg-Al LDH contains water and carbon dioxide having a concentration of 5 vol% or more 70. It is characterized in that carbonated Mg-Al LDH is regenerated by contacting a mixed gas having a temperature of ° C. or higher.
In this way, by performing the regeneration treatment of the anionic Mg-Al LDH after the acidic exhaust gas treatment in contact with water and a gas containing a predetermined amount of carbon dioxide, the regeneration into the carbonated Mg-Al LDH is efficient. Can be done.

<Carbonated Mg-Al LDH>
Carbonated Mg-Al LDH is composed of a hydroxide basic layer ([Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ ]) and an intermediate layer composed of interlayer carbonate ions and interlayer water ([(CO _3). ^2- ) _{x / 2} · yH ₂ O]) are nanoparticles having a structure in which they are alternately laminated. This is a non-stoichiometric compound in which the basic hydroxide layer has a positive charge equivalent to x, and carbonate ions are present in the intermediate layer as anions having a negative charge to compensate for this.
The carbonated Mg-Al LDH can take in an acid gas such as hydrogen chloride, sulfur dioxide, or nitrogen dioxide between layers while retaining the basic hydroxide layer. Therefore, it can be suitably used for acid exhaust gas treatment for removing the acid gas.

When carbonated Mg-Al LDH is used for acid exhaust gas treatment, layered double hydroxides other than carbonated Mg-Al LDH, or, for example, calcium hydroxide (slaked lime), calcium oxide, sodium bicarbonate ( Baking soda), sodium carbonate, dolomite hydroxide, light-baked dolomite, aluminum hydroxide, aluminum oxide, magnesium hydroxide, magnesium oxide and other chemicals other than layered compound hydroxide may be used in combination. However, from the viewpoint of efficiently regenerating and reusing the carbonated Mg-Al LDH, it is preferable not to mix it with other layered double hydroxides or chemicals.

Carbonated Mg-Al LDH contains naturally occurring clay minerals as hydrotalcite, but synthetic powder is usually used. The synthesis method is not particularly limited, and a known method (for example, the method described in Patent Document 1) can be used.
For example, an aqueous solution of magnesium nitrate (Mg (NO ₃ ) ₂ ) and aluminum nitrate (Al (NO ₃ ) ₃ ) mixed at Mg / Al = 2/1 (molar ratio) is kept at pH 10.5 and carbonated. Carbonated Mg-Al LDH can be obtained by dropping into an aqueous solution of sodium (Na ₂ CO _3).

In the carbonated Mg-Al LDH used for acid gas treatment, when the acidic gas was taken in between layers, the interlayer carbonate ions were exchanged with other anions derived from acidic exhaust gas such as chloride ion, sulfate ion, and nitrate ion. It becomes an anion type Mg-Al LDH. The anionic Mg-Al LDH thus produced does not have the ability to further remove acidic exhaust gas. Therefore, the anion-type Mg-Al LDH is regenerated into carbonic acid-type Mg-Al LDH by anion exchange again, and is used for reuse.

<Mixed gas>
In the method for regenerating a carbonated layered double hydroxide of the present invention, anionic Mg-Al LDH, which is a used layered double hydroxide treated with acidic exhaust gas, is mixed with water and carbon dioxide having a concentration of 5 vol% or more at 70 ° C. or higher. By exchanging anions with the mixed gas of the above, carbon dioxide type Mg-Al LDH is regenerated.
Such a regeneration method by gas contact is more efficient as a regeneration means for carbonic acid-type Mg-Al LDH than a conventional regeneration method using a liquid carbonate aqueous solution.

The mixed gas shall contain water and carbon dioxide having a concentration of 5 vol% or more.
In order to exchange the interlayer anion derived from the acidic exhaust gas in the anion type Mg-Al LDH with carbonate ion and regenerate it into the carbonate type Mg-Al LDH having the interlayer carbonate ion and the interlayer water in the intermediate layer, such Use a mixed gas containing water and carbon dioxide.
The term "water" here means gaseous water, that is, water vapor.

The content of carbon dioxide in the mixed gas is 5 vol% or more, preferably 10 to 75 vol%, and more preferably 10 to 30 vol%.
When the content is 10 vol% or more, the interlayer anion of the anion-type Mg-Al LDH can be efficiently desorbed and exchanged for the interlayer carbonate ion to regenerate the carbonate-type Mg-Al LDH.

The amount of water in the mixed gas is preferably 10% or more, more preferably 15 to 30%, still more preferably 20 to 25%.
When the water content is 10% or more, the interlayer anion of the anion-type Mg-Al LDH is efficiently desorbed to regenerate the carbonate-type Mg-Al LDH having interlayer carbonate ions and interlayer water in the intermediate layer. be able to.
The "moisture content" referred to in the present invention corresponds to the volume fraction [%] of water vapor contained in the exhaust gas in JIS Z 8808: 2013, and is based on the method using a moisture absorbing tube described in the JIS standard. It can be measured by the same method.

The mixed gas may contain a gas other than water and carbon dioxide, but preferably does not contain an acid gas other than carbon dioxide. From the viewpoint of convenience and cost in preparing a mixed gas containing a predetermined amount of water and carbon dioxide, the mixed gas is preferably prepared by mixing air.

The temperature of the mixed gas is 70 ° C. or higher, preferably 75 to 100 ° C., and more preferably 80 to 90 ° C.
When the temperature is 70 ° C. or higher, regeneration from anionic Mg-Al LDH to carbonic acid-type Mg-Al LDH can be efficiently performed.

As the mixed gas, it is preferable to use a treated gas from which acid gases other than carbon dioxide after the treatment of the acidic exhaust gas generated in the combustion facility have been removed.
By using such treated gas, the gas generated from the combustion facility can be effectively used, and on-site regeneration from anionic Mg-Al LDH to carbonated Mg-Al LDH becomes possible, and regeneration is possible. The efficiency of processing can be further improved.

[Acid exhaust gas treatment equipment]
The acidic exhaust gas treatment equipment of the present invention includes a means (1) for performing acidic exhaust gas treatment using a carbonated Mg-Al layered double hydroxide and a carbonated Mg-Al layered double hydroxide according to the above-mentioned regeneration method of the present invention. It is characterized by being provided with a means (2) for regenerating a hydroxide.
According to such an acidic exhaust gas treatment facility, it is possible to regenerate the carbonated layered double hydroxide used for the acidic exhaust gas treatment on-site while performing the acidic exhaust gas treatment.

FIG. 1 shows an acidic exhaust gas treatment process flow using the acidic exhaust gas treatment equipment according to the embodiment of the present invention. In the acidic exhaust gas treatment process flow shown in FIG. 1, first, the acidic exhaust gas a discharged from the combustion facility 10 is introduced into the layered double hydroxide storage container 20 in which the carbonated Mg-Al LDH is stored. Then, in the layered double hydroxide storage container 20, the acidic exhaust gas a is brought into contact with the carbonic acid type Mg-Al LDH to perform the acidic exhaust gas treatment, and the treated gas b is discharged into an exhaust duct by an attraction fan or the like (not shown). It is sent to 50 and released into the atmosphere.
As the acidic exhaust gas a, for example, when the combustion facility 10 is a waste incinerator, the high-temperature exhaust gas from the incinerator main body is cooled through a heat exchanger such as a boiler, and dust and the like are removed by a dust collector. The latter gas is preferably used.

When the carbonic acid type Mg-Al LDH changes to the anion type Mg-Al LDH with the passage of time of the acidic exhaust gas treatment and the acidic exhaust gas treatment capacity is lowered, the acidic exhaust gas a is separately provided in the layered double hydroxide storage container 21. The line is switched by the switching valve V1 so as to be introduced in. Further, the switching valve V2 is operated to introduce a part of the treated gas b into the layered double hydroxide storage container 20 through the bypass line 40 with an attraction fan or the like. In this way, the treated gas b, that is, the mixed gas is brought into contact with the anion-type Mg-Al LDH, and the carbonic acid-type Mg-Al LDH is regenerated.
In the regeneration treatment, the anion desorbed from the anion type Mg-Al LDH is absorbed by the condensed water (liquid) in the acidic exhaust gas a and stored in the regeneration treatment wastewater recovery container 30 as the regeneration treatment wastewater c. ..
When the regeneration process is completed, the switching valve V1 and the switching valve V2 are returned to their original positions, and the acidic exhaust gas treatment in the layered double hydroxide storage container 20 is restarted. The end of the regeneration treatment of the carbonated Mg-Al LDH can be determined based on the concentration analysis of the anion component contained in the regeneration treatment wastewater c.
If the same regeneration process is performed on the separately provided layered double hydroxide storage container 21, the layered double hydroxide storage container 20 and the layered double hydroxide storage container 21 are alternately alternated by switching the line with the switching valve V1. It is possible to continuously and efficiently treat the acidic exhaust gas without stopping the flow of the acidic exhaust gas a.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples.

[Regeneration test of carbonated layered double hydroxide]
According to Preparation Example 1 below, chlorine-type Mg-Al LDH (anion-type Mg) in which the carbonate-type Mg-Al LDH is brought into contact with hydrogen chloride gas as a test acidic exhaust gas and the interlayer carbonate ions are replaced with the interlayer chloride ions. -Al LDH sample) was prepared. 20 g of this chlorine-type Mg-Al LDH was filled in a column made of acrylic resin having an inner diameter of 40 mm, and a regeneration treatment test was conducted under each condition of the following Examples and Comparative Examples.
The chlorine content in Mg-Al LDH before and after the regeneration treatment test was measured by an ion chromatograph method, and the desorption rate of chloride ions was determined to evaluate the regeneration efficiency of the carbonated layered double hydroxide. .. It can be said that the higher the desorption rate of chloride ions, the higher the regeneration efficiency from chlorine-type Mg-Al LDH to carbonic acid-type Mg-Al LDH.

(Preparation Example 1)
A column made of acrylic resin with an inner diameter of 40 mm is filled with carbonated Mg-Al LDH (“Kyoward (registered trademark) 500 PL”, manufactured by Kyowa Chemical Industry Co., Ltd., synthetic hydrotalcite), and hydrogen chloride gas is added to the air. A hydrogen chloride-containing gas having been introduced and adjusted to a hydrogen chloride concentration of about 1000 ppm and 100 ° C. was circulated until hydrogen chloride was detected at the column outlet to obtain a chlorine-type Mg-Al LDH.
The formation of chlorine-type Mg-Al LDH was confirmed by a powder X-ray diffraction measurement method and an ion chromatograph method.

(Example 1)
A mixed gas prepared by introducing water and carbon dioxide into the air to have a water content of 20%, a carbon dioxide concentration of 30 vol%, and 80 ° C. was circulated in the column filled with chlorine-type Mg-Al LDH for 8 hours. A regeneration process test was conducted.
The desorption rate of chloride ions in the regeneration treatment test was 96%.

(Comparative Example 1)
A mixed gas at room temperature (25 ° C.) adjusted to a carbon dioxide concentration of 30 vol% by introducing carbon dioxide into the air was circulated in the column filled with chlorine-type Mg-Al LDH for 24 hours to carry out a regeneration treatment test. went.
The desorption rate of chloride ions in the regeneration treatment test was 6%.

(Comparative Example 2)
Water was introduced into the air, and a mixed gas adjusted to have a water content of 20% and 80 ° C. was circulated in the column filled with chlorine-type Mg-Al LDH for 8 hours to carry out a regeneration treatment test.
The desorption rate of chloride ions in the regeneration treatment test was 37%.

(Comparative Example 3)
A regenerative treatment test was conducted by introducing carbon dioxide into the air and passing a mixed gas at 80 ° C. adjusted to a carbon dioxide concentration of 30 vol% through the column filled with chlorine-type Mg-Al LDH for 8 hours.
The desorption rate of chloride ions in the regeneration treatment test was 30%.

From the test results of the above Examples and Comparative Examples, the anionic Mg-Al LDH can be efficiently regenerated into the carbonated Mg-Al LDH by contacting the anionic Mg-Al LDH with a gas containing water and a predetermined amount of carbon dioxide. It was recognized that

10 Combustion facility 20, 21 Layered double hydroxide storage container 30 Recycled wastewater recovery container 40 Bypass line 50 Exhaust duct V1, V2 Switching valve a Acid exhaust gas b Treated gas c Recycled wastewater

Claims (3)

Anionic Mg-Al layered double hydroxide converted from the carbonated Mg-Al layered double hydroxide by acid exhaust gas treatment using carbonated Mg-Al layered double hydroxide, water and concentration 5 vol% Carbonate-type Mg-Al-based layered double hydroxide that exchanges the interlayer anion of the anion-type Mg-Al-based layered double hydroxide with interlayer carbonate ions by contacting the mixed gas containing the above carbon dioxide at 70 ° C. or higher. It ’s a way to regenerate things,
The acidic exhaust gas treatment is a treatment of acidic exhaust gas generated in a combustion facility.
The treated gas from which the acid gas other than carbon dioxide after the treatment has been removed is used as the mixed gas.
A method for regenerating a carbonated layered double hydroxide. The method for regenerating a carbonated layered double hydroxide according to claim 1, wherein the water content in the mixed gas is 10% or more. Regeneration of carbonated Mg-Al layered double hydroxide by means (1) for performing acidic exhaust gas treatment using carbonated Mg-Al layered double hydroxide and the regeneration method according to claim 1 or 2. An acidic exhaust gas treatment facility equipped with a device for performing the means (2).

Images