KR102511218B1 - Regeneration method of carbonic acid layered double hydroxide and acid exhaust gas treatment facility - Google Patents

Abstract

The present invention is a method for regenerating carbonate-type layered double hydroxide, which can efficiently regenerate anionic Mg-Al-based layered double hydroxide (Mg-Al LDH), which has been used by acidic exhaust gas treatment, into carbonate-type Mg-Al LDH. and an acid exhaust gas treatment facility.
The method for regenerating carbonate-type layered double hydroxide of the present invention is anionic Mg-Al LDH produced by acidic exhaust gas treatment using carbonate-type Mg-Al LDH at 70°C containing water and carbon dioxide at a concentration of 5 vol% or more. The above mixed gas is contacted to regenerate the carbonate type Mg-Al LDH.

Description

Regeneration method of carbonic acid layered double hydroxide and acid exhaust gas treatment facility

The present invention relates to a method for regenerating carbonic acid-type layered double hydroxide used in the treatment of acidic exhaust gases generated in combustion facilities such as thermal power plants and incineration facilities, and an acid exhaust gas treatment facility equipped with a means for regenerating the same.

BACKGROUND OF THE INVENTION Combustion exhaust gas generated from thermal power generation or waste incineration contains harmful acidic substances such as hydrogen chloride, sulfur oxides, and nitrogen oxides. For this reason, the acidic exhaust gas containing the acidic substance is treated by various methods for removing the acidic substance.

In the method for removing such an acidic substance, the present applicant, as an efficient treatment technology capable of simultaneously treating and removing a plurality of acidic substances, carbonate-type Mg-Al-based layered double oxide (hereinafter referred to as Mg-Al LDH (Layered Double Hydroxide) is proposed to treat acidic exhaust gas using a treatment method and a treatment agent (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, carbonic acid type Mg-Al LDH is used for acidic exhaust gas treatment, and anionic Mg-Al LDH In the case of conversion to , this used layered double hydroxide was regenerated by mixing it with an aqueous solution of carbonic acid.

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

The means for mixing the spent layered double hydroxide and the carbonic acid aqueous solution as described above can be implemented in a layered double hydroxide recovery facility installed outside a waste incineration facility. However, in this case, the efforts and costs for transportation of used layered double oxide and regenerated layered double oxide between the waste incineration facility and the layered double oxide regeneration facility or the installation of external facilities separate from the waste incineration facility are required. I had a big problem.

In addition, when a used layered double oxide regeneration facility is installed in a waste incineration facility, it is necessary to install and connect a storage tank or a mixing tank for an aqueous solution of carbonic acid, so that the entire facility has to be scaled up.

The present invention has been made to solve the above technical problems, and carbonic acid type layered double hydroxide capable of efficiently regenerating anionic Mg—Al LDH that has been used by acid exhaust gas treatment into carbonate type Mg—Al LDH It is an object of the present invention to provide a regeneration method and an acid exhaust gas treatment facility.

The present invention effectively produces carbonic acid-type layered double hydroxide by contacting the layered double hydroxide which has been used by the acidic exhaust gas treatment with a gas containing water and a predetermined amount of carbon dioxide, in particular, the gas after the acidic exhaust gas treatment. It was made based on the discovery that it could be reproduced with

That is, the present invention provides the following [1] to [4].

[1] A mixed gas of 70° C. or higher containing water and carbon dioxide having a concentration of 5 vol% or more is added to anionic Mg—Al layered double hydroxide generated by acid exhaust gas treatment using carbonic acid Mg—Al layered double hydroxide. A method for regenerating carbonic acid-type layered double hydroxide, wherein the carbonic acid-type layered double hydroxide is regenerated by contacting the carbonic acid-type layered double hydroxide.

[2] The method for regenerating carbonic acid type layered double hydroxide according to [1] above, wherein the moisture content in the gas mixture is 10% or more.

[3] The acidic exhaust gas treatment is a treatment of acidic exhaust gas generated from a combustion facility, and the above [1] or [ 2].

[4] Means (1) for acidic exhaust gas treatment using carbonate-type Mg-Al-based layered double hydroxide, and carbonate-type Mg-Al by the regeneration method of any one of [1] to [3] above An acidic exhaust gas treatment facility comprising means (2) for regenerating layered double hydroxide.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to regenerate the layered double hydroxide which has been used by acidic exhaust gas treatment into carbonic acid type layered double hydroxide onsite without requiring large-scale facilities, and offsite It is advantageous in terms of equipment, effort, and cost compared to recycling treatment at an offsite recycling facility.

In addition, gas after acid exhaust gas treatment can be used, and carbonic acid type layered double hydroxide can be efficiently regenerated according to the acid exhaust gas treatment facility of the present invention.

1 is a schematic flow chart of an acidic exhaust gas treatment process using an acid exhaust gas treatment facility in one embodiment of the present invention.

Hereinafter, a method for regenerating carbonic acid type layered double hydroxide and an acid exhaust gas treatment facility according to the present invention will be described with reference to some drawings.

[Method for regenerating carbonic acid layered double hydroxide]

The method for regenerating carbonic acid type layered double hydroxide of the present invention is anionic Mg-Al LDH generated by acidic exhaust gas treatment using carbonic acid type Mg-Al LDH at 70°C containing water and carbon dioxide at a concentration of 5 vol% or more. It is characterized in that the carbonate-type Mg-Al LDH is regenerated by contacting the above mixed gas.

In this way, by performing the regeneration treatment of the anionic Mg-Al LDH after the acidic exhaust gas treatment by contact with water and a gas containing a predetermined amount of carbon dioxide, regeneration into carbonate-type Mg-Al LDH can be efficiently performed.

<Carbonated Mg-Al LDH>

Carbonic acid type Mg-Al LDH has a hydroxide base 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]) is a nanoparticle having a structure in which layers are alternately stacked. It is an irregular compound in which the hydroxide base layer has a positive charge corresponding to x and the carbonate ion as an anion having a negative charge to compensate for this exists in the intermediate layer.

In the carbonic acid type Mg-Al LDH, an acidic gas such as hydrogen chloride, sulfur dioxide, or nitrogen dioxide can be introduced between the layers while maintaining the hydroxide base layer. For this reason, it can be used suitably for the acidic waste gas process which removes the said acidic gas.

Further, when carbonic acid type Mg-Al LDH is used for acidic exhaust gas treatment, layered double hydroxides other than carbonic acid type Mg-Al LDH, and/or, for example, calcium hydroxide (slaked lime), calcium oxide, sodium bicarbonate (sodium bicarbonate), sodium carbonate, Agents other than layered double hydroxides such as hydroxide dolomite, soft-burned dolomite, aluminum hydroxide, aluminum oxide, magnesium hydroxide, and magnesium oxide may be used in combination. However, from the viewpoint of efficiently regenerating and reusing carbonic acid type Mg-Al LDH, it is preferable not to mix it with other layered double hydroxides or chemicals.

Carbonic acid type Mg-Al LDH is a hydrotalcite, and clay minerals produced in nature also exist, 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, sodium carbonate (} Na ₂ CO ₃ ) carbonate type Mg-Al LDH can be obtained by adding it dropwise to an aqueous solution.

In the carbonic acid Mg-Al LDH used for acidic exhaust gas treatment, when the acidic gas flows in between layers, interlayer carbonate ions are exchanged for other anions derived from acidic exhaust gases such as chlorine ions, sulfate ions, and nitrate ions. It becomes a warm Mg-Al LDH. The anionic Mg-Al LDH produced in this way does not have the ability to remove acidic exhaust gas again. For this reason, the anion-type Mg-Al LDH is regenerated into carbonate-type Mg-Al LDH by anion exchange and reused.

<mixed gas>

In the method for regenerating carbonic acid type layered double hydroxide of the present invention, anionic Mg-Al LDH, which is a layered double double oxide that has been used by acidic exhaust gas treatment, is converted into a mixed gas at 70° C. or higher containing water and carbon dioxide at a concentration of 5 vol% or higher. It is regenerated into carbonate-type Mg-Al LDH by anion exchange using

This regeneration method by gas contact is more efficient as a regeneration means for carbonate-type Mg-Al LDH than the conventional regeneration method using a liquid carbonic acid aqueous solution.

The mixed gas contains water and carbon dioxide having a concentration of 5 vol% or more.

In order to exchange interlayer anions derived from acidic exhaust gas in anionic Mg-Al LDH with carbonate ions and regenerate into carbonate Mg-Al LDH having interlayer carbonate ions and interlayer water in the middle layer, such water and A mixed gas containing carbon dioxide is used.

In addition, "water" here means gaseous water, that is, water vapor.

The content of carbon dioxide in the gas mixture is 5 vol% or more, preferably 10 to 75 vol%, more preferably 10 to 30 vol%.

When the content is 10 vol% or more, the carbonate Mg-Al LDH can be regenerated by efficiently desorbing the interlayer anions of the anionic Mg—Al LDH and exchanging them with interlayer carbonate ions.

The moisture content in the gas mixture is preferably 10% or more, more preferably 15 to 30%, still more preferably 20 to 25%.

When the moisture content is 10% or more, the interlayer anions of the anionic Mg—Al LDH are efficiently desorbed, and the carbonate Mg—Al LDH having interlayer carbonate ions and interlayer water in the middle layer can be regenerated.

In addition, "moisture content" as used in the present invention corresponds to the volume fraction [%] of water vapor contained in exhaust gas in JIS Z 8808:2013, and It can be measured by a method in accordance with the method described above.

The mixed gas may contain water and gas other than carbon dioxide, but preferably does not contain acidic gas other than carbon dioxide. From the viewpoint of simplicity and cost when preparing a mixed gas containing a predetermined amount of water and carbon dioxide, it is preferable to prepare the mixed gas by mixing air.

The temperature of the gas mixture is 70°C or higher, preferably 75 to 100°C, more preferably 80 to 90°C.

When the temperature is 70° C. or higher, regeneration from anionic Mg—Al LDH to carbonate Mg—Al LDH can be efficiently performed.

As the mixed gas, it is preferable to use a gas obtained after treatment of acidic exhaust gas generated from a combustion facility and from which acidic gases other than carbon dioxide have been removed.

By using the gas after such treatment, the gas generated in the combustion facility can be effectively used, and on-site regeneration from anionic Mg-Al LDH to carbonate-type Mg-Al LDH becomes possible. Further improvement in processing efficiency can be achieved.

[Acid Exhaust Gas Treatment Facility]

The acidic exhaust gas treatment facility of the present invention includes a means (1) for treating acidic exhaust gas using a carbonate-type Mg-Al-based layered double hydroxide, and a carbonate-type Mg-Al-based regeneration method according to the present invention described above. It is characterized by having a means (2) for regenerating the layered double hydroxide.

According to such an acid exhaust gas treatment facility, regeneration of carbonic acid type layered double hydroxide used for acid exhaust gas treatment can be performed on-site while acid exhaust gas treatment is performed.

1 shows the flow of an acid exhaust gas treatment process using the acid exhaust gas treatment facility of one embodiment of the present invention. In the flow of the acid exhaust gas treatment process shown in FIG. 1, first, the acid exhaust gas (a) discharged from the combustion facility 10 enters the layered double oxide storage container 20 in which the carbonic acid type Mg—Al LDH is stored. is introduced And in the layered double oxide storage container 20, the acidic exhaust gas (a) is brought into contact with carbonic acid type Mg-Al LDH to perform acidic exhaust gas treatment, and the gas (b) after the treatment is induced draft fan It is sent to the exhaust duct 50 by a lamp (not shown) and discharged 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 main body of the incinerator is cooled through a heat exchanger such as a boiler, and dust or the like is removed by a dust collector. The following gas is suitably used.

In acidic exhaust gas treatment, when carbonic acid Mg-Al LDH is changed to anionic Mg-Al LDH over time and the acidic exhaust gas treatment capacity decreases, The line is switched by the switching valve (V1) so that the acidic exhaust gas (a) is introduced. In addition, by operating the switching valve V2, a part of the post-processing gas (b) is introduced into the layered double hydroxide storage container 20 through the bypass line 40 by an induced fan or the like. In this way, the post-processing gas (b), i.e., the mixed gas is brought into contact with the anionic Mg-Al LDH to perform regeneration treatment to carbonate-type Mg-Al LDH.

In the above regeneration treatment, the anions desorbed from the anionic Mg-Al LDH are absorbed into water (liquid) in which moisture in the acidic exhaust gas (a) is condensed, and as regeneration treatment wastewater (c), a regeneration treatment wastewater recovery container ( 30) is stored.

When the regeneration process is completed, the switching valve V1 and the switching valve V2 are returned to their original states, and the acidic exhaust gas treatment in the layered double hydroxide storage container 20 is resumed. Further, the determination of the end of the regeneration treatment of carbonate-type Mg-Al LDH can be carried out based on the concentration analysis of anion components contained in the regeneration treatment wastewater (c) or the like.

If the same regeneration process is performed on the separately installed layered double hydroxide storage container 21, the layered double hydroxide storage container 20 and the layered double hydroxide storage container 21 are alternately switched by line switching by the switching valve V1. , it is possible to efficiently perform the acidic exhaust gas treatment continuously without stopping the flow of the acidic exhaust gas (a).

(Example)

Below, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

[Regeneration treatment test of carbonic acid layered double hydroxide]

According to Preparation Example 1 below, chlorine-type Mg-Al LDH in which interlayer carbonate ions are replaced with interlayer chloride ions (anionic Mg-Al LDH sample ) was prepared. 20 g of this chlorine-type Mg-Al LDH was packed in an acrylic resin column having an inner diameter of 40 mm, and regeneration treatment tests were conducted under the conditions of each of the following Examples and Comparative Examples.

The chlorine content in the 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 carbonic acid type 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 carbonate-type Mg-Al LDH.

(Preparation Example 1)

In an acrylic resin column having an inner diameter of 40 mm, carbonate type Mg-Al LDH ("KYOWAAD (registered trademark) 500 PL", manufactured by Kyowa Chemical Industry Co., Ltd.) , synthetic hydrotalcite) was charged, hydrogen chloride gas was introduced into the air, and the hydrogen chloride-containing gas adjusted to a hydrogen chloride concentration of about 1000 ppm and 100° C. was flowed through the column outlet until hydrogen chloride was detected. Mg-Al LDH was obtained.

In addition, the production of chlorine-type Mg-Al LDH was confirmed by powder X-ray diffraction measurement and ion chromatography.

(Example 1)

A mixed gas adjusted to 80° C. with a water content of 20% and a carbon dioxide concentration of 30 vol% by introducing water and carbon dioxide into the air was passed through the column filled with chlorine-type Mg—Al LDH for 8 hours to conduct a regeneration treatment test.

The desorption rate of chloride ions in the regeneration treatment test was 96%.

(Comparative Example 1)

A mixed gas at room temperature (25° C.), which was adjusted to a carbon dioxide concentration of 30 vol% by introducing carbon dioxide into the air, was passed through the column filled with chlorine-type Mg—Al LDH for 24 hours, and a regeneration treatment test was conducted.

The desorption rate of chloride ions in the regeneration treatment test was 6%.

(Comparative Example 2)

A mixed gas adjusted to 20% moisture content and 80°C by introducing water into the air was passed through the column filled with chlorine-type Mg-Al LDH for 8 hours, and a regeneration treatment test was conducted.

The desorption rate of chloride ions in the regeneration treatment test was 37%.

(Comparative Example 3)

A gas mixture at 80° C., which was adjusted to a carbon dioxide concentration of 30 vol% by introducing carbon dioxide into the air, was passed through the column filled with chlorine-type Mg—Al LDH for 8 hours, and a regeneration treatment test was conducted.

The desorption rate of chloride ions in the regeneration treatment test was 30%.

From the test results of the above Examples and Comparative Examples, it was confirmed that the anionic Mg-Al LDH can be efficiently regenerated into carbonate-type Mg-Al LDH by bringing water and a gas containing a predetermined amount of carbon dioxide into contact with it.

10: Combustion facility
20, 21: layered double oxide container
30: recovery wastewater recovery container
40: bypass line
50: exhaust duct
V1, V2: switching valve
a: acid exhaust gas
b: gas after treatment
c: recycling treatment multiple

Claims (4)

Water and carbon dioxide having a concentration of 5 vol% or more are added to the anionic Mg-Al layered double hydroxide converted from the carbonic acid Mg-Al layered double hydroxide by acidic exhaust gas treatment using the carbonic acid Mg-Al layered double hydroxide. A method for regenerating a carbonate-type Mg-Al-based layered double hydroxide in which an interlayer anion of the anionic Mg-Al-based layered double hydroxide is exchanged with an interlayer carbonate ion by contacting a mixed gas having a temperature of 70° C. or higher containing
The acid exhaust gas treatment is a treatment of acid exhaust gas generated from a combustion facility,
Using the gas after the treatment in which acid gases other than carbon dioxide after the treatment are removed for the mixed gas
A method for regenerating carbonic acid type layered double hydroxide.
According to claim 1,
A method for regenerating carbonic acid-type layered double hydroxide having a moisture content of 10% or more in the gas mixture.
means (1) for performing acidic exhaust gas treatment using a carbonate-type Mg-Al-based layered double hydroxide;
An acidic exhaust gas treatment facility comprising a device for implementing the means (2) for regenerating the carbonate-type Mg-Al-based layered double hydroxide by the regeneration method according to claim 1 or 2.
delete

Images