JP2011025100A - Process for recovering carbon dioxide from high-pressure gas and aqueous composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more increase the absorption quantity of carbon dioxide and actual loading quantity per a unit absorption liquid amount than before while reducing the quantity of heat necessary for the elimination of carbon dioxide in a process for removing carbon dioxide from high-pressure gas. <P>SOLUTION: This aqueous composition for recovering CO<SB>2</SB>contains 10-60 mass% of a 5-14 membered saturated heterocyclic ring which has 1-4 nitrogen atoms and may have 1-10 oxygen atoms [the nitrogen atoms possessed by the saturated heterocyclic ring are substituted with a 1-4C alkyl group which may have a hydroxy group and the saturated heterocyclic ring may be further substituted with the 1-4C alkyl group which may have a hydroxy group] (i) and a 5-14 membered unsaturated heterocyclic ring having 1-4 nitrogen atoms [the unsaturated heterocyclic ring may be substituted with a 1-4C alkyl group which may have a hydroxy group and/or an amino group which may have the alkyl group] (ii) in total. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention absorbs carbon dioxide contained in a high-pressure gas using a chemical absorption liquid to obtain a treatment gas having a low carbon dioxide component, and generates an absorption liquid loaded with carbon dioxide. Carbon dioxide is removed from high-pressure gas by releasing carbon dioxide and regenerating an absorption liquid that is poor in carbon dioxide component, and circulating and recycling the absorption liquid that is poor in carbon dioxide component to the previous carbon dioxide absorption process And an aqueous composition used in the method.

  In recent years, the rapid increase in greenhouse gas emissions such as carbon dioxide and methane associated with human social activities has been cited as one of the causes of global warming. In particular, carbon dioxide is the most important greenhouse gas, and in accordance with the Kyoto Protocol issued in 2005, measures to reduce carbon dioxide emissions are urgently needed.

  Today, CO2 contained in mixed gas is targeted for mixed gas discharged from thermal power plants, boilers in steelworks, kilns in cement plants, etc., which are fueled with coal, heavy oil, natural gas, etc., which are the sources of carbon dioxide. A series of carbon dioxide capture & storage (CCS) technologies, such as carbon capture, compression, transport, and injection, are attracting attention as bridging technologies to develop alternative energy alternatives to fossil fuels.

  In order to put this storage technology into practical use, it is necessary to reduce the cost as much as possible. In the series of processes of carbon dioxide separation and recovery, compression, transportation, and press-fitting, the cost required for the previous stage separation and recovery and compression accounts for more than 70% of the total storage cost. Technology development is important. For this reason, the development of carbon dioxide separation and recovery technology by chemical absorption method mainly composed of alkanolamine aqueous solution has been energetically promoted for atmospheric pressure exhaust gas from power plants and steelworks.

  In contrast, carbon dioxide separation and recovery technology using chemical absorption from high-pressure gas such as coal gasification product gas and mined natural gas has relatively few research examples compared to separation and recovery technology from atmospheric pressure exhaust gas. . However, since the pressure energy of the gas itself can be utilized for carbon dioxide separation recovery and compression, the cost during the carbon dioxide storage process, particularly in the separation recovery and compression process, may be significantly reduced. Therefore, the focus is on the development of chemical absorbents applicable to carbon dioxide separation from high pressure gas.

  Until now, a physical absorption method has attracted attention as a method for removing an acidic gas containing carbon dioxide from a gas having pressure. In the physical absorption method, it is known that the higher the partial pressure of the target gas component, the greater the amount of acid gas absorbed per unit absorption liquid compared to the chemical absorption method. A typical absorbent is an absorbent (SELEXOL, Union Carbide) composed of cyclotetramethylene sulfone (sulfolane) and derivatives thereof, aliphatic amide, methanol, and polyethylene glycol dialkyl ethers. However, since any of the absorption liquids requires a reduced pressure in the process of desorbing the absorbed carbon dioxide and regenerating the absorption liquid, the effect of reducing the compression cost in the subsequent compression process is extremely low.

  On the other hand, as a chemical absorption liquid that separates carbon dioxide from gas having pressure by gas-liquid contact, a tertiary amine described in Patent Document 1 is N-methyldiethanolamine (MDEA) alone or a reaction accelerator such as piperazine. An aqueous solution containing it is used.

  Further, Patent Document 2 discloses 3-dialkylamino-1,2-propanediols, which are tertiary amines that are more excellent in carbon dioxide absorption ability than MDEA aqueous solution and are advantageous in terms of energy efficiency during regeneration of the absorption liquid. The use of an aqueous solution containing as a main component is described.

  Furthermore, Patent Document 3 and Non-Patent Document 1 report that triisopropanolamine (TIPA), which is a tertiary amine, has a higher carbon dioxide solubility than MDEA under high carbon dioxide partial pressure.

  However, none of the alkanolamines used for carbon dioxide removal under high pressure conditions has sufficient carbon dioxide absorption. Furthermore, when these alkanolamines are used, a large amount of energy is required for heat regeneration in the absorption liquid regeneration step because of high carbon dioxide absorption.

  Patent Document 4 discloses the use of a mixture of a nitrogen-containing cyclic compound, alcohol, aliphatic alkanolamine, water and potassium carbonate for removing carbon dioxide up to a partial pressure of carbon dioxide of 3 MPa in the acid gas adsorption process. Is described. However, the use of nitrogen-containing unsaturated heterocyclic compounds and nitrogen-containing saturated heterocyclic compounds in which hydrogen on the nitrogen atom is substituted with an alkyl group is excluded as a carbon dioxide absorbent.

  In the recently published Patent Document 5, 1 to 10% by mass of a cyclic compound (piperazine, imidazoles) in which two nitrogen atoms are heterocyclicly bonded as an additive to an aqueous solution (30 to 60% by mass) containing MDEA as a main component. And the use of absorbents containing 1 to 15% by weight of hindered amines. However, the main component of the absorbing solution is MDEA, and the problem that a large amount of energy is required for heat regeneration in the absorbing solution regeneration process has not been solved.

As described above, several attempts have been made to remove carbon dioxide from high-pressure gas. Absorption liquid characteristics suitable for removing carbon dioxide from high-pressure gas include large amounts of carbon dioxide absorption per unit absorption liquid and high actual loading amount (difference in carbon dioxide absorption between absorption temperature and desorption temperature) under high-pressure conditions. Is desired.
U.S. Pat.No. 4,336,233 JP 9-150029 Korean Patent No. 2004056023 Special Table 2002-519171 Chinese Patent No. 1887407 RK Chauhan, SJ Yoon, H. Lee, J.-H. Yoon, J.-G. Shim, G.-C. Song, H.-M.Eum, Fluid Phase Equilibria 208, 239-245 (2003)

  The object of the present invention is to remove carbon dioxide per unit absorption liquid amount under high-pressure conditions in comparison with alkanolamines represented by MDEA, which is a carbon dioxide absorbent conventionally used in a method for removing carbon dioxide from high-pressure gas. To increase the amount of absorption and the actual loading amount (difference in carbon dioxide absorption at the absorption temperature and desorption temperature) and to reduce the amount of heat required for carbon dioxide desorption.

As a result of intensive studies on the above problems, the present inventors have obtained the knowledge that when a specific nitrogen-containing heterocyclic compound is used, the actual loading amount under a high pressure condition is very large, and the present invention is completed. It came to. That is, the present invention provides the following items:
Item 1. An aqueous composition for recovering carbon dioxide from a high-pressure gas containing carbon dioxide,
The aqueous composition contains 10 to 60% by mass of a heterocyclic compound,
The heterocyclic compound is
(I) a 5- to 14-membered saturated heterocyclic ring having 1 to 4 nitrogen atoms and optionally having 1 to 10 oxygen atoms [on the nitrogen atom of the saturated heterocyclic ring, An alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group is substituted, and an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group may be further substituted on the saturated heterocyclic ring. . And (ii) a 5- to 14-membered unsaturated heterocycle having 1 to 4 nitrogen atoms [the unsaturated heterocycle is an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group and 1 carbon atom] Or a substituent selected from the group consisting of an amino group that may have an alkyl group of 4 to 4 (on the alkyl group of 1 to 4 carbon atoms, a hydroxyl group may be substituted) Good. ]
At least one selected from the group consisting of:
An aqueous composition used to recover carbon dioxide.

  Item 2. The heterocyclic compound is represented by the general formula [I]:

[Wherein, R ₁ represents an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group.
R ₂ , R ₃ , R ₄ and R ₅ are the same or different and represent hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group. ]
Item 2. The aqueous composition for carbon dioxide recovery according to Item 1, which is a morpholine compound represented by the formula:

  Item 3. The heterocyclic compound has the general formula [II]:

[Wherein, R ₆ , R ₇ , R ₈ and R ₉ are the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group. ]
Item 5. The aqueous composition for carbon dioxide recovery according to Item 1, which is an imidazole compound represented by the formula:

  Item 4. The heterocyclic compound is represented by the general formula [III]:

[Wherein, R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄ are the same or different and each represents hydrogen or a hydroxyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms. The amino group which may have (The hydroxyl group may be substituted on the said C1-C4 alkyl group) is shown. ]
Item 5. The aqueous composition for carbon dioxide recovery according to Item 1, which is a pyridine compound represented by the formula:

  Item 5. Item 3. The aqueous composition for carbon dioxide recovery according to Item 2, wherein the morpholine compound represented by the general formula [I] is 4-ethylmorpholine or 4- (2-hydroxyethyl) morpholine.

  Item 6. Item 4. The carbon dioxide recovery according to Item 3, wherein the imidazole compound represented by the general formula [II] is imidazole, 1-methylimidazole, 1- (2-hydroxyethyl) imidazole, 2-methylimidazole, or 4-methylimidazole. Aqueous composition.

  Item 7. Item 5. The aqueous composition for carbon dioxide recovery according to Item 4, wherein the pyridine compound represented by the general formula [III] is 2-aminopyridine.

Item 8. (1) A high pressure gas having a partial pressure of carbon dioxide of 0.5 to 5 MPa is brought into gas-liquid contact with the aqueous composition according to any one of items 1 to 7, and the carbon dioxide component in the gas is poor. Obtaining a processing gas and generating an absorption liquid loaded with carbon dioxide;
(2) heating the absorption liquid loaded with carbon dioxide to liberate carbon dioxide from the absorption liquid and regenerating an absorption liquid having a low carbon dioxide component; and (3) poor absorption of the carbon dioxide component. A method for recovering carbon dioxide from a high-pressure gas containing carbon dioxide, comprising a step of circulating a liquid and reusing it in the carbon dioxide absorption step (1).

  Item 9. Item 9. The method according to Item 8, wherein the carbon dioxide partial pressure of the high-pressure gas in the step (1) is 1 to 4 MPa (absolute pressure).

  Item 10. Item 10. The method according to Item 8 or 9, wherein in the step (2), the absorption liquid loaded with carbon dioxide is partially heated under reduced pressure.

  The present invention is described in detail below.

  Each group shown in the present invention is specifically as follows.

  Examples of the alkyl group having 1 to 4 carbon atoms include linear or branched alkyl groups having 1 to 4 carbon atoms (preferably 1 to 2), such as methyl, ethyl, propyl, isopropyl, n- Butyl, isobutyl, tert-butyl and sec-butyl groups are included.

  As the alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group, in addition to the above exemplified alkyl group having 1 to 4 carbon atoms, for example, the above exemplified 1 to 4 carbon atoms having 1 to 10 hydroxyl groups An alkyl group can be mentioned, specifically, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 1- Hydroxypropyl, 2-hydroxy-2-methylpropyl, 4-hydroxybutyl and the like are included.

  As an amino group which may have a C1-C4 alkyl group (The hydroxyl group may be substituted on the said C1-C4 alkyl group), it has a hydroxyl group of the said illustration, for example And an amino group having 1 to 2 alkyl groups having 1 to 4 carbon atoms. More specifically, amino group, methylamino group, ethylamino group, propylamino group, isopropylamino group, n-butylamino group, isobutylamino group, tert-butylamino group, sec-butylamino group, hydroxymethylamino Group, 2-hydroxyethylamino group, 3-hydroxypropylamino group, 1-hydroxypropylamino group, 2-hydroxy-2-methylpropylamino group, 4-hydroxybutylamino group and the like.

  Examples of the 5- to 14-membered saturated heterocyclic ring having 1 to 4 nitrogen atoms and optionally having 1 to 10 oxygen atoms include 1 to 4 (preferably 1) Examples of 5 to 14 (preferably 5 to 10, more preferably 5 to 6) membered saturated heterocyclic rings having a nitrogen atom and optionally having 1 to 10 (preferably 1) oxygen Specifically, oxazolidine, isoxazolidine, morpholine, piperidine, pyrazolidine, imidazolidine and the like are included.

  Examples of the 5- to 14-membered saturated heterocyclic ring having 1 to 4 nitrogen atoms and optionally having 1 to 10 oxygen atoms include 1 to 4 (preferably 1) Examples of 5 to 14 (preferably 5 to 10, more preferably 5 to 6) membered saturated heterocyclic rings having a nitrogen atom and optionally having 1 to 10 (preferably 1) oxygen Specifically, oxazolidine, isoxazolidine, morpholine, and the like are included.

  5 to 14-membered saturated heterocyclic ring having 1 to 4 nitrogen atoms and optionally having 1 to 10 oxygen atoms [having a hydroxyl group on the nitrogen atom of the saturated heterocyclic ring In some cases, an alkyl group having 1 to 4 carbon atoms may be substituted, and an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group may be substituted on the saturated heterocyclic ring. ], For example, the above-exemplified “1 to 4 nitrogen atoms” in which an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group as exemplified above is substituted on all nitrogen atoms in a saturated heterocyclic ring. And a 5- to 14-membered saturated heterocyclic ring optionally having 1 to 10 oxygen atoms.

  In the present invention, the saturated heterocyclic ring further has 1 to 3 alkyl groups having 1 to 4 carbon atoms which may have the above-mentioned hydroxyl group on atoms other than the nitrogen atom in the saturated heterocyclic ring ( Preferably 1) may be substituted.

  The 5- to 14-membered unsaturated heterocyclic ring having 1 to 4 nitrogen atoms is, for example, a 5 to 14-membered ring (preferably 5 to 5) having 1 to 4 (preferably 1) nitrogen atoms. To 6-membered ring), specifically, pyrrolyl, dihydropyrrolyl, imidazole, pyrazole, triazole, pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, quinolidine, quinazoline and the like. included.

  The unsaturated heterocyclic ring may be substituted with 1 to 3 (preferably 1) alkyl groups having 1 to 4 carbon atoms which may have the hydroxyl groups exemplified above.

Aqueous composition The present invention is an aqueous composition for recovering carbon dioxide from high-pressure gas containing carbon dioxide,
The aqueous composition contains 10 to 60% by mass of a heterocyclic compound,
The heterocyclic compound is
(I) a 5- to 14-membered saturated heterocyclic ring having 1 to 4 nitrogen atoms and optionally having 1 to 10 oxygen atoms [at least one nitrogen atom of the saturated heterocyclic ring] An alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group is substituted above, and further, an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group is substituted on the saturated heterocyclic ring. It may be. And (ii) a 5- to 14-membered unsaturated heterocycle having 1 to 4 nitrogen atoms [the unsaturated heterocycle is an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group and 1 carbon atom] -4 alkyl groups (on the alkyl group having 1 to 4 carbon atoms, a hydroxyl group may be substituted) at least one selected from the group consisting of amino groups (preferably 1 -2) may have a substituent. ]
At least one selected from the group consisting of:
An aqueous composition used to recover carbon dioxide,
I will provide a.

  Preferred heterocyclic compounds contained in the aqueous composition of the present invention include morpholine compounds, imidazole compounds and pyridine compounds.

  Examples of the morpholine compound include those represented by the general formula [I]:

[Wherein, R ₁ represents an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group.
R ₂ , R ₃ , R ₄ and R ₅ are the same or different and represent hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group. ]
And preferably include 4-alkylmorpholine, 4-hydroxyalkylmorpholine, and the like.

  Examples of 4-alkylmorpholine include morpholine having the above-exemplified alkyl group having 1 to 4 carbon atoms on the 4-position nitrogen atom, such as 4-methylmorpholine and 4-ethylmorpholine, Preferably, 4-ethylmorpholine is exemplified.

  Examples of 4-hydroxyalkylmorpholine include 4- (2-hydroxyethyl) morpholine, 4- (3-hydroxypropyl) morpholine, 1-morpholino-2-propanol, and 3-morpholino-1,2-propane. Examples thereof include morpholine having the above-exemplified alkyl group having 1 to 4 carbon atoms having 1 to 10 (preferably 1 to 3, more preferably 1) hydroxyl groups on the 4-position nitrogen atom, such as diol.

  These morpholine compounds can be appropriately selected according to conditions such as equipment used, carbon dioxide recovery temperature, and the like.

  For example, the boiling point of 4-methylmorpholine is about 116 ° C at normal pressure and lower than about 139 ° C of 4-ethylmorpholine, and scattering to the atmosphere during operation becomes a problem, but its molecular weight is low and its solubility in water is low. Is easy to handle.

  In addition, 4- (2-hydroxyethyl) morpholine, 4- (3-hydroxypropyl) morpholine, 1-morpholino-2-propanol and 3-morpholino-1,2-propanediol are compared to 4-ethylmorpholine. Thus, the solubility of carbon dioxide is slightly inferior, but the solubility in water is high.

  Further, by substituting 4-alkylmorpholine with one or more hydroxyl groups, hydroxymethyl groups and / or hydroxyethyl groups, the boiling point can be increased and the solubility in water can be improved.

  As an imidazole compound, for example, the general formula [II]:

[Wherein, R ₆ , R ₇ , R ₈ and R ₉ are the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group. ]
The imidazole compound shown by these can be mentioned, Preferably, an imidazole, alkyl imidazole, etc. are mentioned.

  Examples of the alkyl imidazole include 2-methylimidazole, 4-methylimidazole, 1-methylimidazole, 2-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole. 1,5-dimethylimidazole, 2,4-dimethylimidazole, 4,5-dimethylimidazole, 1,2,4-trimethylimidazole, 1,4,5-trimethylimidazole, 2,4,5-trimethylimidazole, etc. Examples thereof include imidazoles substituted with 1 to 3 (preferably 1) alkyl groups having 1 to 4 (preferably 1) carbon atoms.

  In the present invention, among these imidazole compounds, imidazole, 1-methylimidazole, 1- (2-hydroxyethyl) imidazole, 2-methylimidazole, and 4-methylimidazole are preferably used.

  Examples of the pyridine compound include a general formula [III]:

[Wherein, R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄ are the same or different and each represents hydrogen or a hydroxyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms. The amino group which may have (The hydroxyl group may be substituted on the said C1-C4 alkyl group) is shown. ]
The pyridine compound shown by these can be mentioned, Preferably, a pyridine, a substituted or unsubstituted aminopyridine, etc. are mentioned.

  Examples of the substituted or unsubstituted aminopyridine include 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,3-diaminopyridine, 2,4-diaminopyridine, 2,5-diaminopyridine, 2, 6-diaminopyridine, 3,4-diaminopyridine, 3,5-diaminopyridine, 3,6-diaminopyridine, 2- (methylamino) pyridine, 3- (methylamino) pyridine, 4- (methylamino) pyridine, 2- (methylamino) pyridine, 3- (dimethylamino) pyridine, 4- (dimethylamino) pyridine, 2,3-bis (methylamino) pyridine, 2,4-bis (methylamino) pyridine, 2,5- Bis (methylamino) pyridine, 2,6-bis (methylamino) pyridine, 3,4-bis (methylamino) pyridine, 3,5-bis (methylamino) pyridine, 3,6-bis (methylamino) pyridine 2-amino-3- (methylamino) pyridine, 2-amino-4- (methylamino) pi Gin, 2-amino-5- (methylamino) pyridine, 2-amino-6- (methylamino) pyridine, 3-amino-4- (methylamino) pyridine, 3-amino-5- (methylamino) pyridine, 3-amino-6- (methylamino) pyridine, 3-amino-2- (methylamino) pyridine, 3-amino-4- (methylamino) pyridine, 3-amino-5- (methylamino) pyridine, 3- Amino-6- (methylamino) pyridine, 4-amino-2- (methylamino) pyridine, 4-amino-3- (methylamino) pyridine, 2- (2-ethylamino) pyridine, 3- (2-ethyl Examples thereof include pyridine substituted with 1 to 3 (preferably 1) amino groups which may have an alkyl group having 1 to 4 carbon atoms such as amino) pyridine and 4- (2-ethylamino) pyridine.

  In the present invention, among these pyridine compounds, 2-aminopyridine is preferably used.

  The concentration of the heterocyclic compound in the aqueous composition of the present invention is usually 10 to 60% by mass, preferably 20 to 50% by mass, and more preferably 30 to 50% by mass.

  Aqueous compositions containing heterocyclic compounds in the above concentration range have significantly higher carbon dioxide absorption and actual loading required for absorption / desorption cycles, and nitrogen-containing compound components are mixed uniformly with water. It is preferable in that it is difficult to cause problems such as foaming and emulsification when the pH of the liquid is lowered by absorbing carbon dioxide and increasing the viscosity.

  In addition, the aqueous composition of the present invention includes an organic solvent that assists in dissolving the nitrogen-containing compound in water, an anticorrosive agent for preventing corrosion of the equipment, an antifoaming agent for preventing foaming, and an anti-deteriorating agent for the absorbent. Antioxidants, inorganic bases that promote absorption, and the like may be added.

The method for recovering carbon dioxide from a high-pressure gas The present invention also includes (1) bringing a high-pressure gas having a partial pressure of carbon dioxide of 0.5 to 5 MPa into gas-liquid contact with the aforementioned aqueous composition, and A process for obtaining a treatment gas having a low carbon component and generating an absorption liquid loaded with carbon dioxide;
(2) heating the absorption liquid loaded with carbon dioxide to liberate carbon dioxide from the absorption liquid and regenerating an absorption liquid having a low carbon dioxide component; and (3) poor absorption of the carbon dioxide component. A method for recovering carbon dioxide from a high-pressure gas containing carbon dioxide, including a step of circulating a liquid and reusing it in the carbon dioxide absorption step (1) is provided.

Carbon dioxide absorption process High-pressure gas generation source containing carbon dioxide is produced by gasification by hydrogen production process for ammonia synthesis that produces ammonia from hydrogen and nitrogen obtained by gasifying fossil fuel or partial oxidation process of coal Coal gasification combined power generation (IGCC) process, which is a high-efficiency power production system that uses a gas turbine and a steam turbine, which are mainly composed of carbon monoxide and synthesis gas as raw materials, is included. The partial pressure of carbon dioxide is usually about 0.5 to 5 MPa, preferably about 1 to 4 MPa (absolute pressure). Note that the high-pressure gas containing carbon dioxide may contain gas such as water vapor and carbon monoxide in addition to carbon dioxide.

  There is no particular limitation on the method for bringing the high-pressure gas containing carbon dioxide into contact with the aqueous solution containing the aforementioned heterocyclic compound. For example, a method of bubbling and absorbing a high-pressure gas containing carbon dioxide in the aqueous solution, a method of dropping the aqueous solution into a high-pressure gas stream containing carbon dioxide, or containing a magnetic or metal mesh filler It is carried out by a method in which a high pressure gas containing carbon dioxide and the aqueous solution are brought into countercurrent contact in an absorption tower.

  The temperature at which the high-pressure gas containing carbon dioxide is absorbed in the aqueous solution containing the nitrogen-containing compound is usually from room temperature to 60 ° C. or less, preferably 50 ° C. or less, more preferably about 20 to 45 ° C. The lower the temperature, the greater the carbon dioxide absorption, but the extent to which the temperature is lowered is determined by the gas temperature in the process, the heat recovery target, and the like. The pressure during carbon dioxide absorption is usually 0.5 to 5 MPa, preferably 1 to 4 MPa (absolute pressure).

Carbon dioxide desorption step Carbon dioxide is desorbed from a heterocyclic-containing aqueous composition that has absorbed carbon dioxide (sometimes referred to as an absorbent loaded with carbon dioxide in this specification), and high pressure and high concentration carbon dioxide. As a method of recovering, the aqueous solution is heated and bubbled and desorbed, and the liquid interface is expanded and heated in a plate tower, spray tower, desorption tower containing a magnetic or metal mesh filler. And the like. As a result, carbon dioxide is liberated and released.

  The liquid temperature at the time of desorption of carbon dioxide is usually 70 ° C. or higher, preferably 80 ° C. or higher, more preferably about 90 to 120 ° C. The higher the temperature, the greater the amount of desorption, but the higher the temperature, the greater the energy required to heat the absorbent, so the temperature is determined by the process gas temperature, heat recovery target, etc.

  The pressure during carbon dioxide desorption is usually 0.5 to 5 MPa, preferably 1 to 4 MPa (absolute pressure).

  The desorption of carbon dioxide can be reduced to a lower pressure in order to improve the desorption performance, but in order to suppress the compression cost in the subsequent compression step, it can be performed by heating or a combination of heating and partial pressure reduction. preferable.

  The pressure for partial pressure reduction is usually 0.05 to 1 MPa, preferably 0.1 to 0.5 MPa.

Step of Reusing Carbon Dioxide Absorbing Solution The heterocyclic compound-containing aqueous composition after desorbing carbon dioxide is sent again to the carbon dioxide absorbing step and reused. In addition, the heat generated during carbon dioxide absorption is generally cooled by heat exchange in a heat exchanger in order to preheat the aqueous solution injected into the desorption tower in the aqueous solution recycling process.

  The purity of the high-pressure carbon dioxide recovered in this way is as extremely high as about 95% by volume. This high-pressure and pure carbon dioxide is used as a chemical product, a raw material for synthesizing a high-molecular substance, a cooling agent for freezing food, and the like. In particular, it is possible to significantly reduce the carbon dioxide separation and recovery costs including the compression process by isolating and storing the recovered high-pressure carbon dioxide in the underground or the like where technological development is currently underway.

  Normally, the amount of carbon dioxide absorption is measured by collecting an absorption liquid sample from a reaction vessel and performing atmospheric pressure gas chromatography or titration. In the case of a high pressure absorption liquid, the absorption liquid under atmospheric pressure is used. It is difficult to directly measure the amount of carbon dioxide absorbed in the absorbent under high pressure because of its high carbon dioxide emission. Therefore, in the present invention, after the absorption liquid is saturated with high-pressure carbon dioxide, the supply of carbon dioxide is stopped, and the amount of carbon dioxide released from the absorption liquid when the pressure in the reaction vessel is reduced to atmospheric pressure is measured with a dry gas meter. The measured value and the amount of carbon dioxide absorbed in the absorbing solution after completion of carbon dioxide release under atmospheric pressure were evaluated by the sum of the amount of inorganic carbon measured with a gas chromatographic total organic carbon meter.

  As a result of measuring the carbon dioxide absorption amount of the aqueous solution containing 30% by mass of the nitrogen-containing compound of the present invention in the above manner, the actual carbon dioxide loading amount between 40 ° C. and 70 ° C. near the partial pressure of carbon dioxide of 0.1 MPa is It is about 0.10 to 0.29 mol / mol-nitrogen-containing compound per mole of nitrogen-containing compound, and about 20-48 g / L-absorbing liquid per unit absorption liquid amount. However, the actual carbon dioxide loading between 40 ° C and 70 ° C near the partial pressure of carbon dioxide is about 0.25 to 0.36 mol / mol-nitrogen-containing compound per mole of nitrogen-containing compound, and 41 per unit absorbed liquid amount. About 51 g / L-absorbent. Further, the actual loading amount of carbon dioxide between 40 ° C. and 70 ° C. near the partial pressure of carbon dioxide of 4 MPa is about 0.11 to 0.25 mol / mol-nitrogen-containing compound per mol of nitrogen-containing compound, and 12 per unit absorbed liquid amount. About 50 g / L-absorbent.

  On the other hand, the actual carbon dioxide loading between 40 ° C and 70 ° C for an aqueous solution containing 30% by mass of alkanolamine type MDEA used in the current technology is 0.03 mol / mol- The use of a carbon dioxide absorbing solution that is not more than MDEA and contains the nitrogen-containing compound of the present invention as a main component is more efficient than the MDEA 30% by mass aqueous solution and can reduce the amount of heat required for carbon dioxide desorption.

  In addition, the carbon dioxide absorption per unit absorbent volume with respect to a 30% by weight aqueous solution of MDEA at a carbon dioxide partial pressure of about 4 MPa is 96 g / L-absorbent, but the nitrogen-containing composition of the present invention has a lower molecular weight than alkanolamines. The use of compounds, particularly imidazoles, can improve carbon dioxide absorption up to about 135 g / L-absorbing solution.

  Thus, even when the temperature at the time of carbon dioxide desorption is relatively low at 70 ° C., a good carbon dioxide desorption amount can be achieved from the absorbing solution at a carbon dioxide partial pressure of 1 and / or 4 MPa. Of course, when the temperature at the time of carbon dioxide desorption exceeds 70 ° C., for example, the amount of carbon dioxide desorption further increases as it rises to 80 ° C., 90 ° C., 100 ° C., 110 ° C., and 120 ° C.

  On the other hand, hindered alkanolamines represented by triethanolamine (TEA) have an improved carbon dioxide actual loading amount under high carbon dioxide partial pressure compared to MDEA. Since CO2 has a lower molecular weight than TEA, it absorbs more carbon dioxide per unit absorbent volume. This is advantageous compared with the current alkanolamines in downsizing or increasing the throughput of a high-pressure gas processing apparatus containing an acidic gas.

  The method for separating and recovering carbon dioxide from high-pressure gas by the high-pressure chemical absorbent of the present invention is high even when the temperature at the time of desorption of carbon dioxide is relatively low at 70 ° C. as compared with known high-pressure carbon dioxide absorbent. Not only the carbon dioxide actual loading amount under the carbon dioxide partial pressure condition is large, but also the carbon dioxide absorption amount per unit absorbent volume is large. As a result, the carbon dioxide absorption tower, the carbon dioxide desorption tower, and the devices associated therewith can be miniaturized, the amount of liquid circulation can be reduced, energy loss can be reduced, and construction costs can be reduced.

  Hereinafter, the present invention will be described in detail with reference to an example in which the high-pressure carbon dioxide absorption performance of a nitrogen-containing compound used as an absorbent in the present invention was examined with a small-scale absorption test apparatus, but the present invention is limited to this example. Is not to be done.

Example 1
Carbon dioxide gas cylinder, carbon dioxide supercritical system (intelligent supercritical carbon dioxide pump (SCF-Get type, manufactured by JASCO)), and operating pressure programmable back pressure regulator (SCF-Bpg type) , Manufactured by JASCO Corporation)), a water vapor trap, and a dry gas meter (DC-1C, manufactured by Shinagawa Co., Ltd.) were sequentially used.

  Set the pressure (1-4 MPa) and pressure reduction rate (0.5 MPa / min) of the SCF-Bpg back pressure valve, and a pressure-resistant reaction vessel containing 30% by mass of 4-ethylmorpholine (EMO) in water (30 mL) and stirring The pressure-resistant reaction vessel is connected between the intelligent supercritical carbon dioxide pump and the operating pressure programmable back pressure regulator, on the magnetic stirrer (RCX-1000, manufactured by Tokyo Rika Kikai Co., Ltd.). installed. In all experiments, the stirring speed was fixed on a constant scale. Piping from SCF-Get pump, piping to SCF-Bpg back pressure valve, digital pressure gauge (DLS-5028, manufactured by Toyo Sokki Co., Ltd.) and digital thermometer (TI-2068-01, Japan) Spectroscopic Co., Ltd.) was connected, and heating (40 or 70 ° C.) and stirring to a set temperature with a desktop low temperature water bath (CH-201 type, manufactured by Synics) were started.

The trap was ice-cooled, carbon dioxide gas cylinder regulator main stopper and SCF-Get pump valve were opened, and carbon dioxide gas was vented to the pressure vessel. After supplying about 100 L of carbon dioxide gas over 2 hours, the valve of the SCF-Get pump and then the main stopper of the carbon dioxide cylinder were closed. The scale of the gas meter, gas outlet temperature, atmospheric pressure and pressure inside the reaction vessel were recorded, and the SCF-Bpg back pressure valve was opened to atmospheric pressure. The gas meter scale 2 hours after the start of atmospheric pressure release was recorded. Remove the pipe to the SCF-Bpg back pressure valve, sample 6 mL of the test solution from the reaction vessel using a syringe, cool with ice, and measure the amount of carbon dioxide in the test solution using a gas chromatographic total organic carbon meter (TOC-V _CSH Shimadzu Corporation). The value obtained here was the carbon dioxide absorption at 0.1 MPa.

  The high-pressure carbon dioxide absorption at the set temperature and set pressure is calculated by adding the carbon dioxide emission from the test solution calculated from the change in the gas meter scale before and after the back pressure valve is opened to atmospheric pressure and the residual carbon dioxide content in the test solution. Was obtained by data processing using as an ideal gas, and the high-pressure carbon dioxide absorption characteristics were evaluated.

  The actual loading of carbon dioxide between 40 ° C and 70 ° C for the EMO test solution is 0.28, 0.36, and 0.11 mol / mol-EMO per mole of EMO at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. And 31, 41, and 12 g / L-EMO test solution per unit EMO test solution amount, respectively. The carbon dioxide absorption at 40 ° C at a partial pressure of carbon dioxide of 4 MPa was 99 g / L-EMO test solution.

Example 2
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated using an aqueous solution (30 mL) containing 30% by mass of imidazole (Im) under the same conditions as a test solution. The actual loading of carbon dioxide between 40 ° C and 70 ° C of Im test solution is 0.1, 0.25, and 0.25 mol / mol-Im per mole of Im at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. And 20, 51 and 50 g / L-Im test solution per unit Im test solution amount, respectively. Further, the carbon dioxide absorption at a partial pressure of carbon dioxide of 4 MPa and 40 ° C. was 129 g / L-Im test solution.

Example 3
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated using an aqueous solution (30 mL) containing 30% by mass of 2-methylimidazole (2MeIm) under the same conditions as a test solution. The actual loading of carbon dioxide between 40 ° C and 70 ° C for the 2MeIm test solution is 0.29, 0.27, and 0.14 mol / mol-2MeIm per mole of 2MeIm at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. 48, 44, and 23 g / L-2 MeIm test solution per unit of 2 MeIm test solution amount, respectively. The carbon dioxide absorption at a partial pressure of carbon dioxide of 4 MPa and 40 ° C. was 135 g / L-2MeIm test solution.

Example 4
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated under the same conditions using an aqueous solution (30 mL) containing 4-methylimidazole (4MeIm) at 30% by mass as a test solution. The actual loading of carbon dioxide between 40 ° C and 70 ° C for the 4MeIm test solution is 0.22, 0.31, and 0.21 mol / mol-4MeIm per mole of 4MeIm at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. And 36 g, 50 g, and 34 g / L-4 MeIm test solution per 4 MeIm test solution amount, respectively. Further, the carbon dioxide absorption at a partial pressure of carbon dioxide of 4 MPa and 40 ° C. was 127 g / L-4MeIm test solution.

  Table 1 shows the actual loading amount of carbon dioxide between 40 ° C. and 70 ° C. (absorption difference) at a partial pressure of carbon dioxide of 0.1, 1, and 4 MPa using an aqueous solution containing 30% by mass of the nitrogen-containing compound of the present invention as a test solution ), And carbon dioxide absorption at 4 MPa and 40 ° C. Abbreviations in the table are EMO = 4-ethylmorpholine, Im = imidazole, 2MeIm = 2-methylimidazole, 4MeIm = 4-methylimidazole.

Comparative Example 1
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated using an aqueous solution (30 mL) containing 30% by mass of N-methyldiethanolamine (MDEA) under the same conditions as a test solution. The actual CO2 loading between 40 ° C and 70 ° C for the MDEA test solution is 0.37, 0.03, and ~ 0 mol / mol-MDEA per mole of MDEA at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. , 41, 3, and ˜0 g / L-MDEA test solution per unit MDEA test solution amount, respectively. In addition, the carbon dioxide absorption at 40 ° C at a carbon dioxide partial pressure of 4 MPa was 96 g / L-MDEA test solution. It can be seen that the actual loading amount of carbon dioxide between 40 ° C and 70 ° C under high pressure conditions (around 1 to 4 MPa) and the carbon dioxide absorption amount at a partial pressure of carbon dioxide of 4 MPa and 40 ° C are small compared to all examples. It was. These results indicate that the absorption liquid containing the nitrogen-containing compound of the present invention can separate and recover carbon dioxide efficiently and with low energy under high pressure conditions as compared with known absorption liquids.

Comparative Example 2
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated using an aqueous solution (30 mL) containing 30% by mass of triethanolamine (TEA) under the same conditions as a test solution. The actual carbon dioxide loading between 40 ° C and 70 ° C of the TEA test solution is 0.32, 0.20, and 0.02 mol / mol-TEA per mole of TEA at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. The amounts were 30, 19, and 1 g / L-TEA test solution per unit TEA test solution amount, respectively. Further, the carbon dioxide absorption at 40 ° C. under a partial pressure of carbon dioxide of 4 MPa was 76 g / L-TEA test solution. Aqueous carbon dioxide loading at 40 ° C and 70 ° C under high pressure conditions (around 1 to 4 MPa) and carbon dioxide absorption at 4 ° C and 40 ° C are both aqueous solutions of Examples 1-4. It was found to be smaller than

  Table 2 shows an actual carbon dioxide loading (absorption) between 40 ° C. and 70 ° C. in the vicinity of carbon dioxide partial pressures of 0.1, 1 and 4 MPa using an aqueous solution containing 30% by mass of alkanolamine known as a comparative example as a test solution. (Quantity difference), and carbon dioxide absorption at 4 MPa and 40 ° C. Abbreviations in the table are MDEA = N-methyldiethanolamine, TEA = triethanolamine.

Example 5
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated using an aqueous solution (30 mL) containing 30% by mass of 4- (2-hydroxyethyl) morpholine (HEMO) under the same conditions as a test solution. The actual loading of carbon dioxide between 40 ° C and 70 ° C of the 4MeIm test solution is 0.11, 0.34, and 0.22 mol / mol-HEMO per mole of HEMO at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. The amounts were 11, 35, and 23 g / L-HEMO test solution per unit HEMO test solution amount, respectively.

Example 6
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated under the same conditions using an aqueous solution (30 mL) containing 30% by mass of 1-methylimidazole (1MeIm) as a test solution. The actual loading of carbon dioxide between 40 ° C and 70 ° C of the 1MeIm test solution is 0.07, 0.27, and 0.19 mol / mol-1MeIm per mole of 1MeIm at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. The amounts were 11, 44, and 31 g / L-1 MeIm test solution per unit of 1 MeIm test solution, respectively.

  As the test solution, an aqueous solution containing 30% by mass of 1- (2-hydroxyethyl) imidazole (1HEIm) was used instead of the aqueous solution containing 30% by mass of 1MeIm, and the high-pressure carbon dioxide absorption characteristics were evaluated in the same manner as described above. . As a result, for the 1HEIm aqueous solution, the actual carbon dioxide loading between 40 ° C and 70 ° C was 0.22 mol / mol-1HEIm per mole of 1HEIm and 27 g per unit of 1HEIm test liquid at a partial pressure of carbon dioxide of 1 MPa. / L-1HEIm test solution showed high value.

Example 7
Using the same apparatus as in Example 1, high-pressure carbon dioxide absorption characteristics were evaluated using an aqueous solution (30 mL) containing 30% by mass of 2-aminopyridine (2APy) under the same conditions as a test solution. The actual loading of carbon dioxide between 40 ° C and 70 ° C of the 2APy test solution is 0.09, 0.25, and 0.26 mol / mol-2APy per 2APy moles at carbon dioxide partial pressures of 0.1, 1, and 4 MPa, respectively. The amount was 14, 36, and 38 g / L-2APy test solution per unit 2 APy test solution amount, respectively.

  Table 3 shows the actual loading amount of carbon dioxide (absorption amount) between 40 ° C. and 70 ° C. in the vicinity of carbon dioxide partial pressures of 0.1, 1, and 4 MPa using an aqueous solution containing 30% by mass of the nitrogen-containing compound of the present invention as a test solution. Difference). The abbreviations in the table are HEMO = 4- (2-hydroxyethyl) morpholine, 1MeIm = 1-methylimidazole, 2APy = 2-aminopyridine.

  As is clear from Examples 5 to 7, HEMO, 1MeIm, 1HEIm, and 2APy were also subjected to a high partial pressure of carbon dioxide in the same manner as the aqueous solutions containing EMO, Im, 2MeIm, and 4MeIm used in Examples 1-4. And showed a high actual carbon dioxide loading.

  Tables 1, 2 and 3 show that the aqueous composition of the present invention can separate and recover carbon dioxide efficiently and at low energy under high pressure conditions as compared with known absorbents.

Claims (10)

An aqueous composition for recovering carbon dioxide from a high-pressure gas containing carbon dioxide,
The aqueous composition contains 10 to 60% by mass of a heterocyclic compound,
The heterocyclic compound is
(I) a 5- to 14-membered saturated heterocyclic ring having 1 to 4 nitrogen atoms and optionally having 1 to 10 oxygen atoms [on the nitrogen atom of the saturated heterocyclic ring, An alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group is substituted, and an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group may be further substituted on the saturated heterocyclic ring. . And (ii) a 5- to 14-membered unsaturated heterocycle having 1 to 4 nitrogen atoms [the unsaturated heterocycle is an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group and 1 carbon atom] Or a substituent selected from the group consisting of an amino group that may have an alkyl group of 4 to 4 (on the alkyl group of 1 to 4 carbon atoms, a hydroxyl group may be substituted) Good. ]
At least one selected from the group consisting of:
An aqueous composition used to recover carbon dioxide. The heterocyclic compound is represented by the general formula [I]:

[Wherein, R ₁ represents an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group.
R ₂ , R ₃ , R ₄ and R ₅ are the same or different and represent hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group. ]
The aqueous composition for carbon dioxide recovery according to claim 1, which is a morpholine compound represented by the formula: The heterocyclic compound has the general formula [II]:

[Wherein, R ₆ , R ₇ , R ₈ and R ₉ are the same or different and each represents hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a hydroxyl group. ]
The aqueous composition for carbon dioxide recovery according to claim 1, which is an imidazole compound represented by the formula: The heterocyclic compound is represented by the general formula [III]:

[Wherein, R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄ are the same or different and each represents hydrogen or a hydroxyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms. The amino group which may have (The hydroxyl group may be substituted on the said C1-C4 alkyl group) is shown. ]
The aqueous composition for carbon dioxide recovery according to claim 1, which is a pyridine compound represented by the formula: The aqueous composition for carbon dioxide recovery according to claim 2, wherein the morpholine compound represented by the general formula [I] is 4-ethylmorpholine or 4- (2-hydroxyethyl) morpholine. The carbon dioxide recovery of Claim 3 whose imidazole compound shown by the said general formula [II] is imidazole, 1-methylimidazole, 1- (2-hydroxyethyl) imidazole, 2-methylimidazole, or 4-methylimidazole. Aqueous composition. The aqueous composition for carbon dioxide recovery according to claim 4, wherein the pyridine compound represented by the general formula [III] is 2-aminopyridine. (1) A high-pressure gas having a carbon dioxide partial pressure of 0.5 to 5 MPa is brought into gas-liquid contact with the aqueous composition according to any one of claims 1 to 7, and the carbon dioxide component in the gas Obtaining a poor process gas and generating an absorption liquid loaded with carbon dioxide;
(2) heating the absorption liquid loaded with carbon dioxide to liberate carbon dioxide from the absorption liquid and regenerating an absorption liquid having a low carbon dioxide component; and (3) poor absorption of the carbon dioxide component. A method for recovering carbon dioxide from a high-pressure gas containing carbon dioxide, comprising a step of circulating a liquid and reusing it in the carbon dioxide absorption step (1). The method according to claim 8, wherein the carbon dioxide partial pressure of the high-pressure gas in the step (1) is 1 to 4 MPa (absolute pressure). The method according to claim 8 or 9, wherein, in the step (2), the absorption liquid loaded with carbon dioxide is partially heated under reduced pressure.