Absorbent for Separating and Recovering Carbon Dioxide from Gas Containing Carbon Dioxide and Method for Separating and Recovering Carbon Dioxide

Abstract

To provide an absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide, and a method for separating and recovering carbon dioxide.SOLUTION: An absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide is provided, comprising a carbon dioxide-absorbing amine compound, an alkylene urea compound and water. Based on the absorption liquid, the alkylene urea compound is 1.0-5.0 mass%. There is also provided a method for separating and recovering carbon dioxide using the absorption liquid. Preferably, the alkylene urea compound is an ethylene urea compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a carbon dioxide absorbent and a carbon dioxide separation and recovery method.

Background Art

[0002] In order to suppress global warming, attention to carbon dioxide recovery and storage technologies is increasing. As one of the carbon dioxide recovery and storage technologies, a chemical absorption method is known in which a gas containing carbon dioxide is brought into contact with an absorbent containing a compound (absorbent) that reacts with carbon dioxide to recover carbon dioxide. Carbon dioxide absorbed by the absorbent by the chemical absorption method can be recovered as high-purity carbon dioxide by releasing the carbon dioxide in the absorbent by heating or the like. Among them, as a method for separating and recovering carbon dioxide from a gas containing carbon dioxide discharged from a thermal power plant or the like, a recovery method using an absorbent containing an amine compound as an absorbent has been actively studied.

[0003] For example, in Patent Document 1, a step of bringing a gas containing carbon dioxide into contact with an aqueous solution containing 35 to 50% by mass of isopropylaminoethanol as an active ingredient to absorb carbon dioxide into the aqueous solution, and heating the aqueous solution in which carbon dioxide has been absorbed obtained in the above step at a temperature of 70 ° C. or higher to desorb and recover carbon dioxide is proposed.

[0004] Further, Patent Document 2 proposes a method for recovering carbon dioxide using an absorbent containing an amine compound as an absorbent and contained in an ionic liquid or an amide compound.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] While the absorbent described in Patent Document 1 has a high carbon dioxide absorption amount, when heating the aqueous solution in which carbon dioxide is absorbed to desorb and recover carbon dioxide, the recovery amount of carbon dioxide is not sufficient, and there is still room for improvement in terms of efficiently recovering carbon dioxide and in that the carbon dioxide absorption amount decreases when the absorbent from which carbon dioxide has been desorbed is used again as an absorbent.

[0007] Also, the method of Patent Document 2 uses an ionic liquid or an amide compound as a solvent. It is excellent in easy desorption at high temperatures, has little evaporation loss, has a low specific heat, a small heat of reaction, and an energy reduction effect can be expected for the regeneration of the carbon dioxide absorbent per amount of carbon dioxide recovered. However, the ionic liquid and amide compound used as the solvent are generally expensive, and there is still room for improvement in terms of the cost of the absorbent when treating a gas containing a large amount of carbon dioxide.

[0008] Therefore, an object of the present invention is to provide a carbon dioxide absorbent and a carbon dioxide separation and recovery method capable of industrially and efficiently separating and recovering carbon dioxide from a gas containing carbon dioxide.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that by adding a predetermined amount of an alkylene urea compound to an aqueous solution of a carbon dioxide-absorbing amine compound, the energy required for the dissipation of carbon dioxide can be reduced, and thus the present invention has been completed. That is, an absorbent according to one aspect of the present invention is an absorbent for separating and recovering carbon dioxide from a gas containing carbon dioxide, and contains a carbon dioxide-absorbing amine compound, an alkylene urea compound, and water, and contains 1.0 to 5.0% by mass of the alkylene urea compound with respect to the absorbent.

Effects of the Invention

[0010] According to the present invention, it is possible to provide an absorbent or the like that is inexpensive and requires a small amount of energy necessary for separating and recovering carbon dioxide from a gas containing carbon dioxide. Further, the absorbent of the present invention has a high carbon dioxide absorption amount and a high amount of carbon dioxide released after absorption. Therefore, it is possible to repeatedly use the absorbent after release as an absorbent for carbon dioxide, and it is possible to industrially and efficiently separate and recover carbon dioxide from a gas containing carbon dioxide.

Embodiment for Carrying Out the Invention

[0011] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope shown in the claims. That is, embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention. Further, all of the patent documents described in this specification are incorporated herein by reference. Further, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)".

[0012] (Absorbent) The carbon dioxide absorbent of the present invention contains a carbon dioxide-absorbing amine compound, an alkylene urea compound, and water, and is characterized by containing 1.0 to 5.0% by mass of the alkylene urea compound.

[0013] (Carbon dioxide-absorbing amine compound) The amine compound with carbon dioxide absorption property according to the present invention contains at least one amine selected from the group consisting of primary amines, secondary amines, and tertiary amines. The amine contained in the amine compound with carbon dioxide absorption property is not particularly limited, and may be used alone or in combination of two or more. Hereinafter, in this specification, "polyamine" refers to an amine having a plurality of nitrogen atoms in one molecule. When there are a plurality of nitrogen atoms in one molecule and these nitrogen atoms are of different grades, the grade of the amine is the lower grade. For example, when a primary nitrogen atom and a secondary nitrogen atom are present in one molecule, the amine is a primary amine.

[0014] Examples of primary amines include primary alkanolamines such as monomethanolamine, monoethanolamine, monopropanolamine, monobutanolamine, 1-amino-2-propanol, and 2-amino-2-methyl-1-propanol; at least one compound selected from primary polyamines such as N-methyl-1,3-diaminopropane, N,N-dimethyl-1,3-diaminopropane, N,N-diethyl-1,3-diaminopropane, and tetraethylenepentamine can be mentioned.

[0015] Examples of secondary amines include secondary alkanolamines such as 2-methylaminoethanol, 2-ethylaminoethanol, 2-n-propylaminoethanol, 2-isopropylaminoethanol, and 2-n-butylaminoethanol; linear secondary polyamines such as N,N'-dimethylethylenediamine and N,N'-diethylethylenediamine; at least one compound selected from secondary amines having a heterocyclic ring such as piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, and homopiperazine can be mentioned.

[0016] Examples of tertiary amines include at least one compound selected from tertiary alkanolamines such as methyldiethanolamine, diethylaminopropanol, diethylaminoethanol, dimethylaminoethanol, dimethylaminomethylpropanol, N-ethyl-N-methylethanolamine, 3-(dimethylamino)propanol, 4-(dimethylamino)butanol; and tertiary amines having a heterocyclic ring such as 1-methyl-2-piperidinemethanol, 1-ethyl-3-piperidinemethanol, 1-(2-hydroxyethyl)piperidine.

[0017] As the above amine compound, primary amines and secondary amines are preferable in terms of their fast carbon dioxide absorption rate, and a mixture of a primary amine and a secondary amine is more preferable.

[0018] The above primary amine is preferably a primary polyamine, and more preferably at least one selected from the group consisting of N-methyl-1,3-diaminopropane, N,N-dimethyl-1,3-diaminopropane, and N,N-diethyl-1,3-diaminopropane.

[0019] The above secondary amine is preferably a secondary alkanolamine, and more preferably 2-isopropylaminoethanol.

[0020] The above mixture of a primary amine and a secondary amine is preferably a mixture of a primary polyamine and a secondary alkanolamine, and more preferably a mixture of N-methyl-1,3-diaminopropane and 2-isopropylaminoethanol.

[0021] Regarding the mixing ratio of amines when using a mixture of the above primary amine and secondary amine, there is no particular limitation, and it may be appropriately determined in consideration of the carbon dioxide absorption rate and desorption efficiency of the amine species to be combined. Generally, the higher the concentration of the primary amine with a faster carbon dioxide absorption rate, the greater the amount of carbon dioxide absorbed near room temperature. However, if the concentration of the primary amine is too high, the carbon dioxide dissipation at high temperatures decreases, and the energy required for the dissipation of the absorbed carbon dioxide increases. Therefore, the concentration of the primary amine is preferably 1.0 to 5.0% by mass, more preferably 1.2 to 3.5% by mass, based on the absorption liquid.

[0022] (Concentration of carbon dioxide-absorbing amine compound in the absorption liquid) The concentration of the carbon dioxide-absorbing amine compound in the carbon dioxide absorption liquid of the present invention is not particularly limited. Generally, the higher the concentration of the carbon dioxide-absorbing amine compound, the greater the amount of carbon dioxide recovered per unit amount of the absorption liquid. Therefore, from the viewpoints of reducing energy consumption, downsizing of plant facilities, and carbon dioxide treatment efficiency, etc., the concentration of the carbon dioxide-absorbing amine compound is preferably 35% by mass or more, more preferably 40% by mass or more. On the other hand, if the concentration of the carbon dioxide-absorbing amine compound is too high, problems such as a decrease in the amount of carbon dioxide absorbed near room temperature, a decrease in the miscibility of the amine components, and an increase in viscosity may occur. Therefore, the concentration of the carbon dioxide-absorbing amine compound is preferably 60% by mass or less, more preferably 55% by mass or less.

[0023] Regarding the concentration of the primary amine when the above carbon dioxide-absorbing amine compound is a mixture of a primary amine and a secondary amine, there is no particular limitation, and it may be appropriately determined in consideration of the carbon dioxide absorption rate and desorption efficiency of the amine species to be combined. Generally, the higher the concentration of the primary amine with a faster carbon dioxide absorption rate, the greater the amount of carbon dioxide absorbed near room temperature tends to be. On the other hand, if the concentration of the primary amine is too high, the carbon dioxide dissipation at high temperatures decreases, and the energy required for the dissipation of the absorbed carbon dioxide increases. Therefore, the concentration of the primary amine is preferably 1.0 to 5.0% by mass, more preferably 1.2 to 3.5% by mass, based on the absorption liquid.

[0024] (Alkylene urea compound) The type of the alkylene urea compound according to the present invention is not particularly limited, and it may be used alone or in combination of two or more kinds.

[0025] Examples of the alkylene urea compound include ethylene urea compounds such as 2-imidazolidinone, 1,3-dimethyl-2-imidazolidinone, 1-(2-hydroxyethyl)-2-imidazolidinone; and at least one compound selected from propylene urea compounds such as tetrahydro-2-pyrimidinone and N,N'-dimethylpropyleneurea.

[0026] The alkylene urea compound is preferably an ethylene urea compound, and more preferably at least one selected from the group consisting of 2-imidazolidinone and 1,3-dimethyl-2-imidazolidinone.

[0027] By adding the alkylene urea compound to the carbon dioxide absorption liquid, the carbon dioxide emission at high temperature is promoted. The higher the concentration of the alkylene urea compound in the carbon dioxide absorption liquid, the more the diffusivity tends to improve, but when it exceeds a certain concentration, the diffusivity does not change. On the other hand, if the concentration of the alkylene urea compound is too high, the amount of carbon dioxide absorbed near room temperature decreases. Therefore, the concentration of the alkylene urea compound is preferably 1.0 to 5.0% by mass, and more preferably 1.2 to 3.5% by mass. When the concentration of the alkylene urea compound is in this range, the decrease in the amount of carbon dioxide absorbed near room temperature is exceeded by the increase in the amount of carbon dioxide emitted at high temperature, and the carbon dioxide recovery amount per unit absorption liquid amount is improved.

[0028] (Water) The type of water according to the present invention is not particularly limited, and distilled water, ion-exchanged water, tap water, industrial water, groundwater, etc. may be used.

[0029] The concentration of water in the carbon dioxide absorbent is not particularly limited. However, generally, a lower water concentration and a higher concentration of the carbon dioxide-absorbing amine compound tend to result in a larger amount of carbon dioxide recovered per unit volume of the absorbent. Therefore, from the perspectives of reducing energy consumption, downsizing plant facilities, and carbon dioxide treatment efficiency, etc., the water concentration is preferably 65% by mass or less, more preferably 60% by mass or less. On the other hand, if the water concentration is too low, problems such as a decrease in the amount of carbon dioxide absorbed near room temperature, a decrease in the miscibility of the amine component, and an increase in viscosity may occur. Therefore, the water concentration is preferably 40% by mass or more, more preferably 45% by mass or more.

[0030] (Carbon Dioxide Separation and Recovery Method) The carbon dioxide absorbent of the present invention can separate and recover carbon dioxide from a gas containing carbon dioxide. Examples of the gas containing carbon dioxide include combustion exhaust gas generated in a boiler of a thermal power plant using fossil fuels such as heavy oil, natural gas, and coal as fuel, exhaust gas generated from a kiln in a cement factory, exhaust gas generated from a blast furnace in a steelworks, reformed gas such as natural gas, etc. The gas containing carbon dioxide can contain other components. Examples of other components include water vapor, carbon monoxide, hydrogen sulfide, sulfur monoxide, sulfur dioxide, nitrogen monoxide, nitrogen dioxide, nitrogen, oxygen, hydrogen, dust, etc.

[0031] A method for separating and recovering carbon dioxide using the carbon dioxide absorbent of the present invention will be described. The carbon dioxide separation and recovery method of the present invention includes a separation step of bringing the carbon dioxide absorbent into contact with the gas containing carbon dioxide to separate carbon dioxide from the gas, and a recovery step of recovering carbon dioxide from the absorbent that has absorbed carbon dioxide obtained in the separation step. The absorbent contains a carbon dioxide-absorbing amine compound, an alkyleneurea compound, and water, and is an absorbent containing 1.0 to 5.0% by mass of the alkyleneurea compound with respect to the absorbent.

[0032] (Separation Step) In the separation step, the carbon dioxide-containing gas is brought into contact with the carbon dioxide absorption liquid to absorb carbon dioxide into the absorption liquid, thereby separating carbon dioxide from the gas.

[0033] The method of bringing the carbon dioxide absorption liquid into contact with the carbon dioxide-containing gas is not particularly limited, and examples include bubbling the carbon dioxide-containing gas in the absorption liquid, spraying or spraying the absorption liquid into the air flow of the carbon dioxide-containing gas, and countercurrent gas-liquid contact between the absorption liquid and the carbon dioxide-containing gas in an absorption tower filled with a packing material.

[0034] The temperature of the absorption liquid when bringing the carbon dioxide absorption liquid into contact with the carbon dioxide-containing gas is not particularly limited, but is preferably 50°C or lower, more preferably 20 to 45°C. The contact between the absorption liquid and the carbon dioxide-containing gas may be carried out under atmospheric pressure or under pressure.

[0035] (Recovery step) In the recovery step, the absorption liquid that has absorbed carbon dioxide obtained in the separation step is heated to dissipate and recover carbon dioxide from the absorption liquid. By using a carbon dioxide absorption liquid containing an alkylene urea compound in the separation and recovery method of the present invention, the dissipation energy in the recovery step can be reduced.

[0036] The method of dissipating carbon dioxide from the absorption liquid that has absorbed carbon dioxide is not particularly limited, and examples include a method of heating the absorption liquid that has absorbed carbon dioxide in a reactor to dissipate carbon dioxide, a tray tower, a spray tower, and a method of increasing the surface area of the absorption liquid that has absorbed carbon dioxide in a dissipation tower filled with a packing material and heating it.

[0037] The temperature of the absorption liquid when recovering carbon dioxide in the recovery step is not particularly limited as long as it is higher than the temperature in the separation step, but is preferably 70°C or higher, more preferably 80 to 110°C. Conventional carbon dioxide absorption liquids dissipate at a high temperature of 120°C or higher, but the carbon dioxide absorption liquid of the present invention can obtain a sufficient recovery amount even at a lower temperature than in the past.

[0038] After the absorbent has released carbon dioxide, it is sent back to the separation step and recycled. During this recycling process, the heat added in the recovery step can be effectively utilized to increase the temperature of the liquid heading towards the recovery step through heat exchange with the liquid, thereby reducing the overall energy consumption of the recovery process.

[0039] When releasing carbon dioxide from the absorbent that has absorbed carbon dioxide, releasing all of the carbon dioxide held by the absorbent is not carried out from the perspective of energy consumption. Generally, it is recycled to the separation step while retaining a part of the absorbed carbon dioxide. The separation and recovery method of the present invention can reduce the amount of carbon dioxide retained after release and increase the amount of carbon dioxide recovered by using a carbon dioxide absorbent containing an alkylene urea compound. Therefore, the amount of absorbent per unit amount of carbon dioxide recovered is reduced, and a reduction in the energy required for heating and downsizing of the plant facilities are expected.

[0040] The highly pure carbon dioxide recovered as described above can be used not only for underground storage and the like to reduce the amount of carbon dioxide discharged into the atmosphere, but also as a raw material for chemicals or synthetic raw materials for polymer substances, food, beverages, refrigerants for refrigeration, and the like.

[0041] (Summary) An absorbent according to one aspect of the present invention is an absorbent for separating and recovering carbon dioxide from a gas containing carbon dioxide, and contains a carbon dioxide-absorbing amine compound, an alkylene urea compound, and water, and contains 1.0 to 5.0% by mass of the alkylene urea compound with respect to the absorbent.

[0042] In the above absorbent, the alkylene urea compound may be an ethylene urea compound.

[0043] The above ethylene urea compound may be at least one selected from the group consisting of 2-imidazolidinone and 1,3-dimethyl-2-imidazolidinone.

[0044] The absorbent may contain 35 to 60% by mass of the carbon dioxide-absorbing amine compound with respect to the absorbent.

[0045] The carbon dioxide-absorbing amine compound includes a primary amine and a secondary amine, and the absorbent may contain 1.0 to 5.0% by mass of the primary amine with respect to the absorbent.

[0046] The absorbent may contain 40 to 65% by mass of water with respect to the absorbent.

[0047] A method for separating and recovering carbon dioxide according to one embodiment of the present invention is a method for separating and recovering carbon dioxide from a gas containing carbon dioxide, including a separation step of bringing an absorbent into contact with a gas containing carbon dioxide to separate carbon dioxide from the gas, and a recovery step of recovering carbon dioxide from the absorbent that has absorbed carbon dioxide obtained in the separation step, wherein the absorbent includes a carbon dioxide-absorbing amine compound, an alkylene urea compound, and water, and the absorbent contains 1.0 to 5.0% by mass of the alkylene urea compound with respect to the absorbent.

Examples

[0048] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples. The carbon dioxide-absorbing amine compounds and alkylene urea compounds used in the following examples and comparative examples are as follows, and general purity products of Tokyo Chemical Industry Co., Ltd. were used in all cases.

[0049] · Carbon dioxide-absorbing amine compound 2-Isopropylaminoethanol (IPAE) N-Methyl-1,3-diaminopropane (MDAP) · Alkylene urea compound 2-Imidazolidinone (IML) 1,3-Dimethyl-2-imidazolidinone (DMI)

[0050] (Example 1) A glass reaction vessel was filled with 150 g of an aqueous solution containing 47.0% by mass of 2-isopropylaminoethanol (IPAE), 1.0% by mass of 2-imidazolidinone (IML), and 52.0% by mass of water as a carbon dioxide absorbent. The glass reaction vessel was immersed in a water bath and heated with a magnetic stirrer while stirring so that the temperature of the aqueous solution reached 40 °C. A mixed gas containing 12% by volume of carbon dioxide and 88% by volume of nitrogen at atmospheric pressure was blown into the aqueous solution at a rate of 3.5 liters per minute and absorbed for 60 minutes.

[0051] The carbon dioxide concentration in the gas at the outlet of the glass reaction vessel was continuously measured with an infrared carbon dioxide concentration meter, and the carbon dioxide absorption amount was calculated from the difference in the carbon dioxide flow rates at the inlet and outlet. If necessary, the amount of carbon dioxide held in the aqueous solution was measured with an all-in-one analyzer and compared with the amount held calculated from the infrared carbon dioxide concentration meter.

[0052] Next, the flow rate of the mixed gas was changed to 1.75 liters per minute, the glass reaction vessel was immersed in an oil bath, the temperature of the aqueous solution was raised to 80 °C in a few minutes, and carbon dioxide was released for 45 minutes.

[0053] The carbon dioxide concentration in the gas at the outlet of the glass reaction vessel was continuously measured with an infrared carbon dioxide concentration meter, and the carbon dioxide recovery amount was calculated from the difference in the carbon dioxide flow rates at the inlet and outlet. Also, from the carbon dioxide absorption amount and the carbon dioxide recovery amount, the amount of carbon dioxide held in the aqueous solution after release was calculated. The results are shown in Table 1. In Table 1, "absorption amount" is the amount of carbon dioxide (mL) absorbed per gram of the absorbent during carbon dioxide absorption at 40 °C, "recovery amount" is the amount of carbon dioxide (mL) recovered per gram of the absorbent during carbon dioxide release at 80 °C, and "amount held after release" is the amount of carbon dioxide (mL) held per gram of the absorbent after carbon dioxide release at 80 °C.

[0054] (Examples 2 to 7, Comparative Examples 1 to 4) Carbon dioxide absorption and release were carried out in the same manner as in Example 1 except that the carbon dioxide absorbent shown in Table 1 was used, and the absorption amount and the recovery amount were calculated. The results are shown in Table 1.

[0055]

Table 1

[0056] From the results of Examples 1 to 5 and Comparative Examples 1 and 2, and Examples 6 and 7 and Comparative Examples 3 and 4, it was confirmed that the absorbent containing the alkylene urea compound had an increased carbon dioxide recovery amount and a reduced retention amount after dissipation, and had excellent dissipation performance.

Claims

1. An absorbent for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising: a carbon dioxide-absorbing amine compound, an alkylene urea compound, and water, wherein the absorbent contains 1.0 to 5.0% by mass of the alkylene urea compound with respect to the absorbent, Absorbent.

2. The absorbent according to claim 1, wherein the alkylene urea compound is an ethylene urea compound.

3. The absorbent according to claim 2, wherein the ethylene urea compound is at least one selected from the group consisting of 2-imidazolidinone and 1,3-dimethyl-2-imidazolidinone.

4. The absorbent according to any one of claims 1 to 3, wherein the absorbent contains 35 to 60% by mass of the carbon dioxide-absorbing amine compound with respect to the absorbent.

5. The absorbent according to any one of claims 1 to 4, wherein the carbon dioxide-absorbing amine compound contains a primary amine and a secondary amine, and the absorbent contains 1.0 to 5.0% by mass of the primary amine with respect to the absorbent.

6. The absorbent according to any one of claims 1 to 3, wherein the absorbent contains 40 to 65% by mass of water with respect to the absorbent.

7. A method for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising: a separation step of bringing an absorbent into contact with a gas containing carbon dioxide to separate carbon dioxide from the gas; and a recovery step of recovering carbon dioxide from the absorbent that has absorbed carbon dioxide obtained in the separation step, wherein the absorbent contains a carbon dioxide-absorbing amine compound, an alkylene urea compound, and water, and the absorbent contains 1.0 to 5.0% by mass of the alkylene urea compound with respect to the absorbent. Separation and recovery method.

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