JP2021010855A - Method for separating and recovering carbon dioxide - Google Patents

Abstract

To provide a method enabling high-purity carbon dioxide to be separated and recovered with low energy.SOLUTION: A method for separating and recovering carbon dioxide is provided that combines a solid absorption method and a chemical absorption method and comprises: a step (1) in which a gas including an aqueous tertiary amine solution and carbon dioxide is flowed to a solid absorbent with amine carried on a porous carrier to cause the solid absorbent to absorb carbon dioxide; a step (2) in which flow of the gas including carbon dioxide is stopped, the aqueous tertiary amine solution is supplied, and gas other than carbon dioxide is substituted with the aqueous tertiary amine solution; a step (3) in which the solid absorbent and the aqueous tertiary amine solution are heated, and carbon dioxide is desorbed; and a step (4) in which the solid absorbent and the aqueous tertiary amine solution are cooled.SELECTED DRAWING: None

Description

The present invention relates to a method for separating and recovering carbon dioxide.

In recent years, due to the problem of global warming, the separation and recovery of carbon dioxide has attracted attention, and many carbon dioxide separation and recovery methods have been developed. In particular, coal-fired power generation generates a large amount of carbon dioxide, and fuel conversion from coal to biomass and carbon dioxide recovery technology are important issues for global warming countermeasures.

Chemical absorption methods, physical absorption methods, membrane separation methods and the like have been developed as carbon dioxide separation and recovery methods.

In the chemical absorption method, an aqueous solution of amine that selectively reacts with carbon dioxide, particularly an ethanolamine-based aqueous solution, is used as an absorbent, and carbon dioxide is absorbed and desorbed by a temperature difference. That is, carbon dioxide is separated and recovered in a cycle in which carbon dioxide is absorbed by an absorbent at low temperature and carbon dioxide is released at high temperature. The chemical absorption method has been widely put into practical use because it can efficiently recover high-purity carbon dioxide, and is suitable for the treatment of combustion exhaust gas from coal-fired power generation with low carbon dioxide concentration and normal pressure. It has the disadvantage that it requires a large amount of energy to separate the reacted carbon dioxide.

The physical absorption method utilizes selective adsorption / desorption of gas by a solid adsorbent such as zeolite, and carbon dioxide is adsorbed / desorbed by a temperature difference and a pressure difference. The physical adsorption method can separate and recover carbon dioxide with lower energy than the chemical absorption method using amine, but the purity of carbon dioxide is lower than that of the chemical absorption method. In addition, the method of separating by pressure difference is not optimal for the combustion exhaust gas of thermal power generation.

The membrane separation method is a method of separating carbon dioxide using membranes having different permeation rates between carbon dioxide and other gases, such as a membrane made of a polymer having an amino group or an amine compound as a support. A supported membrane or the like is used. The membrane separation method can separate carbon dioxide with the lowest energy, but the membrane module is expensive and separates by pressure difference, so normal pressure and low concentration carbon dioxide such as combustion exhaust gas of coal-fired power generation is large. Not suitable for large-scale recovery.

As a method suitable for treating combustion exhaust gas of coal-fired power generation, a solid absorption method that combines a chemical absorption method and a physical absorption method has been proposed (see, for example, Patent Document 1). In this method, a solid absorbent material in which an amine compound is supported on a porous carrier is used, carbon dioxide is chemically (and physically) absorbed by the absorbent material, and carbon dioxide is produced by a temperature difference, a pressure difference, a release agent, or the like. Is to be desorbed. It is a method that combines the characteristics of the chemical absorption method and the physical absorption method, and is attracting attention as a method that can separate and recover high-purity carbon dioxide with low energy. The problems are that the purity of the recovered carbon dioxide is lower than that of the chemical absorption method, that it is difficult to desorb carbon dioxide only by the temperature difference, and that it is difficult to increase the size of the device. In the solid absorption method, in order to increase the purity of carbon dioxide, it is necessary to remove the raw material gas diffused in the device voids, between the grains of the solid absorbent, and in the pores by decompression, gas replacement, etc. , Invites an increase in energy, etc. Further, since the heat transfer of the porous solid absorbent material is extremely poor, the temperature of the absorbent material tends to be non-uniform, and it is not easy to enlarge the suction / desorption tower (tank). Furthermore, since the heat transfer of the solid absorbent material is poor, it is industrially difficult to control the adsorption and desorption only by the temperature difference, and carbon dioxide must be desorbed by other methods such as decompression and steam substitution.

JP 2015-9185

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for separating and recovering low-energy, high-purity carbon dioxide.

As a result of diligent studies on the method for separating and recovering carbon dioxide, the present inventor has found a novel fact that high-purity carbon dioxide can be easily separated and recovered by a novel method combining a solid absorption method and a chemical absorption method. The invention has been completed.

That is, the present invention is a method for separating and recovering carbon dioxide as shown below.

[1] (1) A step of flowing a tertiary amine aqueous solution and a gas containing carbon dioxide through a solid absorbent material on which amine is supported on a porous carrier to absorb carbon dioxide.
(2) A step of stopping the flow of a gas containing carbon dioxide, supplying a tertiary amine aqueous solution, and replacing a gas other than carbon dioxide with a tertiary amine aqueous solution.
(3) A step of heating a solid absorbent and a tertiary amine aqueous solution to desorb carbon dioxide.
(4) Step of cooling the solid absorbent and the tertiary amine aqueous solution,
A method for separating and recovering carbon dioxide consisting of.

[2] Amines are ethanolamines such as monoethanolamine, diethanolamine, and triethanolamine, alkylated products thereof, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, piperazin, aminoethylpiperazin, and the like. The method for separating and recovering carbon dioxide according to the above [1], which is at least one selected from ethylene amines, alkylated products thereof, ethylene oxide adducts and propylene oxide adducts.

[3] The method for separating and recovering carbon dioxide according to the above [1] or [2], wherein the porous carrier is at least one selected from silica, alumina, activated carbon, and a polymer.

[4] Methylation of tertiary amines such as ethanolamines such as triethanolamine, N, N-dimethylethanolamine and N-methyldiethanolamine, tetrakis (hydroxyethyl) ethylenediamine, tetrakis (hydroxypropyl) ethylenediamine and hydroxyethylethylenediamine. Any of the above [1] to [3], which is at least one selected from the body, an ethyleneamine derivative such as a methylated form of hydroxyethylpiperazine, a morpholin derivative such as methylmorpholin and hydroxyethylmorpholin, and an imidazole derivative such as dimethylimidazole. The method for separating and recovering carbon dioxide described in Crab.

Hereinafter, the present invention will be described in detail.

The method for separating and recovering carbon dioxide of the present invention uses a solid absorbent and a chemical absorbent (tertiary amine aqueous solution).

In the method of the present invention, previously proposed amines can be used as the solid absorbent, but those having a stronger interaction with the carrier than the tertiary amine used in the chemical absorbent are preferable.

In general, primary amines and secondary amines have a stronger interaction with carriers than tertiary amines, and amines with a higher boiling point have stronger interactions with carriers. Examples of amines used in the method of the present invention are alkylation of ethanolamines such as monoethanolamine, diethanolamine and triethanolamine, and ethanolamines such as N-methylethanolamine, N-ethylethanolamine and aminomethylpropanol. Body, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, piperazine, ethyleneamines such as aminoethylpiperazine, alkylated compounds of ethyleneamines such as methylethylenediamine and methyldiethylenetriamine, hydroxyethylethylenediamine, hydroxy Examples thereof include ethylene oxide adducts and propylene oxide adducts of ethylene amines such as propylethylenediamine, but amines other than these may be used at all.

In the method of the present invention, a carrier is used as the solid absorbent. As the carrier, generally known ones can be used, but those having a large surface area and resistance to amines are preferable. Examples of the carriers used in the method of the present invention include inorganic oxide carriers such as silica, alumina, titania, zirconia, silica alumina, and zeolite, activated carbon, and porous polymers, but other carriers are used. There is no problem at all. Of the inorganic oxides, silica is the most widely used and industrially preferred. Silica has crystalline and non-crystalline (amorphous), and various types such as zeolite-like silica having pores and mesoporous silica are known. In the method of the present invention, the silica used is not particularly limited, and industrially distributed silica can be used, but silica having a large surface area is preferable. The larger the surface area, the more efficiently the amine acts. Generally, the larger the surface area, the smaller the pore diameter tends to be, so it is difficult to support high molecular weight and high viscosity amines. However, depending on whether silica is crystalline or non-crystalline and its structure, the pore diameter It is difficult to limit the optimum surface area of silica in the method of the present invention because the relationship between surface area and surface area changes.

In the method of the present invention, the particle size of the solid absorbent is not particularly limited, but if it is too small, pressure is required for the flow of the liquid and the gas, and if it is too large, the dispersion and contact of the liquid and the solid are lowered. Above, 2 cm or less is preferable.

The tertiary amine used in the method of the present invention is not particularly limited, but one in which the bicarbonate or carbonate formed by reacting with carbon dioxide becomes insoluble in water is not preferable. An aqueous solution of a tertiary amine containing imidazoles and a hydroxyl group is less likely to precipitate bicarbonate and can be suitably used for the method of the present invention. Examples of tertiary amines that can be used in the method of the present invention include ethanolamines such as triethanolamine, N, N-dimethylethanolamine and N-methyldiethanolamine, tetrakis (hydroxyethyl) ethylenediamine, tetrakis (hydroxypropyl) ethylenediamine, Examples thereof include ethyleneamine derivatives such as methylated products of hydroxyethylethylenediamine and methylated products of hydroxyethylpiperazine, morpholin derivatives such as methylmorpholin and hydroxyethylmorpholin, and imidazole derivatives such as dimethylimidazole. There is no problem at all.

In the method of the present invention, the tertiary amine is used as an aqueous solution. Although it can be carried out using a solvent other than water, it is industrially costly and flammable, so care must be taken in handling. Further, since water has a high specific heat, there is an advantage that the temperature change is small when a heated tertiary amine aqueous solution is supplied to the solid absorbent. Furthermore, carbon dioxide and its reaction products have high solubility, and carbon dioxide can be efficiently separated and recovered. It is difficult to limit the concentration of the tertiary amine aqueous solution because it varies greatly depending on the type of amine, but for example, it is 0.1% by weight to 50% by weight, preferably 1% by weight to 30% by weight. If the concentration is less than 0.1% by weight, the effect of the tertiary amine is so small that it is not industrial, and if the concentration exceeds 50% by weight, the effect of the tertiary amine does not increase significantly.

In the method of the present invention, the device for separating and recovering carbon dioxide is not particularly limited, but a generally widely used fixed floor gas suction / desorption device can be used. A solid absorbent is filled in a column (or tank) that can be heated and cooled so that a gas to be treated containing carbon dioxide and a tertiary amine aqueous solution can flow. If there are a plurality of towers (or tanks) filled with a solid absorbent, carbon dioxide can be continuously separated and recovered.

In the method of the present invention, the step of separating and recovering carbon dioxide from the gas to be treated comprises the following steps.
(1) A step of circulating a tertiary amine aqueous solution and a gas to be treated through a solid absorbent material to absorb carbon dioxide.
(2) A step of stopping the flow of the gas to be treated, supplying a tertiary amine aqueous solution, and replacing a gas other than carbon dioxide with a tertiary amine aqueous solution.
(3) A step of heating a solid absorbent and a tertiary amine aqueous solution to desorb carbon dioxide.
(4) Step of cooling the solid absorbent and the tertiary amine aqueous solution,
In the step (1), by supplying a chemical absorbent (tertiary amine aqueous solution) in addition to the solid absorbent, the temperature of the solid absorbent can be controlled, the carbon dioxide absorption efficiency is enhanced, and the solid The life of the absorbent material can also be extended.

By substituting an unnecessary gas other than carbon dioxide with a chemical absorption liquid (tertiary amine aqueous solution) in the step (2), the purity of the recovered carbon dioxide can be increased. In this case, if the inside of the pores of the solid absorbent material is also replaced with a chemical absorbent (tertiary amine aqueous solution), the purity of carbon dioxide is further increased.

In the step (3), by heating the chemical absorbent (tertiary amine aqueous solution) in addition to the solid absorbent, the temperature of the solid absorbent can be controlled, the emission efficiency of carbon dioxide is improved, and the solid The life of the absorbent material can also be extended. At this time, the distribution of the tertiary amine aqueous solution may be stopped or distributed, but the distribution efficiency of carbon dioxide is improved.

In the step (4), the solid absorbent and the chemical absorbent (tertiary amine aqueous solution) can absorb carbon dioxide again.

With the above four steps, the problems of the solid absorption method, the carbon dioxide purity, and the heat transfer that have been conventionally proposed can be solved.

In the method of the present invention, various additives can be mixed with the tertiary amine aqueous solution and supplied to the solid absorbent. The use of amines used in solid absorbents as additives can extend the life of solid absorbents. In addition, the addition of a catalyst can improve the absorption and emission performance of carbon dioxide.

The method for separating and recovering carbon dioxide of the present invention can separate and recover high-purity carbon dioxide with low energy, and is extremely useful industrially.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. The following abbreviations are used for the sake of brevity.

Silica: Amorphous silica (manufactured by Fuji Silysia Chemical Ltd., spherical, 2 mm diameter)
DETA: Diethylenetriamine (manufactured by Tosoh Corporation)
MDEA: N-Methyldiethanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Examples 1-4
20 g of a 10 wt% aqueous solution of DETA was added to 20 g of silica, and the mixture was allowed to stand for 2 hours. Water was removed with an evaporator to prepare a solid absorbent. This was filled in a glass absorption tube having an internal volume of 60 mL and kept at 40 ° C. To this, a mixed gas of 46.5 g of a 30 wt% aqueous solution of MDEA, 100 mL / min of nitrogen, and 50 mL / min of carbon dioxide was circulated until carbon dioxide was no longer absorbed.

After stopping the flow of the mixed gas and filling the absorption tube with the MDEA aqueous solution, the glass absorption tube was kept warm at 80 ° C. The amount of carbon dioxide released was measured with a flow meter until no carbon dioxide was released. Excess MDEA was removed from the absorption tube and the absorption tube was cooled to 40 ° C.

The results of repeating this suction / detachment operation are shown in Table 1. The CO ₂ absorption amount and the desorption amount were represented by the CO ₂ amount (L) per 1 L of the solid absorbent material.

Comparative Examples 1 to 4
The same solid absorbent material used in Examples 1 to 4 was filled in a glass absorbent tube and kept at 40 ° C. A mixed gas of 100 mL / min of nitrogen and 50 mL / min of carbon dioxide was circulated through the mixture until carbon dioxide was no longer absorbed.

The flow of the mixed gas was stopped, and the glass absorption tube was kept warm at 80 ° C. The amount of carbon dioxide released was measured with a flow meter until no carbon dioxide was released.

The results of repeating this suction / detachment operation are shown in Table 2. The CO ₂ absorption amount and the desorption amount were represented by the CO ₂ amount (L) per 1 L of the solid absorbent material.

Comparative Example 5
A mixture of 100 mL / min of nitrogen and 50 mL / min of carbon dioxide was circulated in 46.5 g of a 30 wt% aqueous solution of MDEA at 40 ° C. until carbon dioxide was no longer absorbed. The amount of carbon dioxide absorbed per 1 kg (1 L) of a 30 wt% aqueous solution of MDEA was 0.33 L. This was set to 80 ° C., and the amount of carbon dioxide desorbed was measured. The amount of carbon dioxide desorbed per 1 kg (1 L) of a 30 wt% aqueous solution of MDEA was 0.14 L.

Reference example 1
The space of the solid absorbent material was replaced with an aqueous solution of MDEA, and the amount of impurity gas present in the solid absorbent material and the absorption tube was measured.

The solid absorbent used in Comparative Examples 1 to 4 was filled in a glass absorbent tube, and the absorbent tube was completely filled with a 30 wt% aqueous solution of MDEA. The amount of impurity gas released was 0.64 L per 1 L of solid absorbent.

In the case of Comparative Examples 1 to 4 in which the MDEA aqueous solution was not used, it was found that this impurity gas reduced the purity of the released CO ₂ . Further, in the cases of Examples 1 to 4 in which the MDEA aqueous solution was used and the impurity gas was replaced, it was found that the impurity gas did not remain in the solid absorbent or the absorption tube.

Claims (4)

(1) A step of flowing a tertiary amine aqueous solution and a gas containing carbon dioxide through a solid absorbent material on which amine is supported on a porous carrier to absorb carbon dioxide.
(2) A step of stopping the flow of a gas containing carbon dioxide, supplying a tertiary amine aqueous solution, and replacing a gas other than carbon dioxide with a tertiary amine aqueous solution.
(3) A step of heating a solid absorbent and a tertiary amine aqueous solution to desorb carbon dioxide.
(4) Step of cooling the solid absorbent and the tertiary amine aqueous solution,
A method for separating and recovering carbon dioxide consisting of. Amines are ethanolamines such as monoethanolamine, diethanolamine and triethanolamine, alkylated forms of these, ethyleneamine such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, piperazine and aminoethylpiperazine. The method for separating and recovering carbon dioxide according to claim 1, which is at least one selected from the class, alkylated products thereof, ethylene oxide adducts and propylene oxide adducts. The method for separating and recovering carbon dioxide according to claim 1 or 2, wherein the porous carrier is at least one selected from silica, alumina, activated carbon, and a polymer. Tertiary amines are ethanolamines such as triethanolamine, N, N-dimethylethanolamine, N-methyldiethanolamine, tetrakis (hydroxyethyl) ethylenediamine, tetrakis (hydroxypropyl) ethylenediamine, methylated form of hydroxyethylethylenediamine, hydroxy. The carbon dioxide according to any one of claims 1 to 3, which is at least one selected from an ethyleneamine derivative such as a methylated form of ethylpiperazine, a morpholin derivative such as methylmorpholin and hydroxyethylmorpholin, and an imidazole derivative such as dimethylimidazole. Separation and recovery method.