JP2002079035A - Method for fixing co2 - Google Patents

Abstract

(57) Abstract: performs the absorption of CO ₂ efficiently, it can immobilize the recovered CO ₂ as an industrial raw material, and further can perform absorption and immobilization with low energy CO
₍₂₎ To provide an immobilization method. The present invention provides a method for producing an aqueous solution comprising the steps of: causing an amine to act on a first aqueous phase containing salts and contacting CO ₂ in a gas phase to remove the amine as an amine salt; by forming a carbonate by reacting the CO ₂ dissolved from and cation and the gas phase cations to remain in the salt, CO ₂ fixation, characterized in that immobilizing CO ₂ as carbonate Depends on the method of conversion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
₂ ) Regarding the immobilization method.

[0002]

2. Description of the Related Art Currently used fossil fuels (oil, coal, natural gas, etc.) are mainly composed of carbon and hydrogen, and if they are burned to obtain energy, carbon dioxide (CO ₂₎ ) Is inevitable. Fossil fuel consumption is increasing year by year, and the resulting CO ₂
Increasing emissions has become one of the major energy and environmental challenges.

Conventionally, as a countermeasure to reduce CO _2, and CO ₂ recovery method of the CO ₂ efficiently recovered contained in the exhaust gas, CO ₂ fixing method for fixing the recovered CO ₂ and various studies on It has been done.

As a CO ₂ recovery method, many studies have been made on an amine absorption method in which exhaust gas is brought into contact with an amine solution to absorb CO ₂ into the amine solution. However, according to the CO ₂ recovery method, there are process problems such as high energy at the time of regenerating the amine solution and deterioration of the absorbing solution. Further, such a CO ₂ recovery method is a means for efficiently recovering CO _2, and does not disclose any means for immobilizing the CO ₂ .

On the other hand, as the CO ₂ immobilization method, a biological immobilization method, a catalytic hydrogenation method, an electrochemical immobilization method and the like have been studied.

Among them, the catalytic hydrogenation method can synthesize methanol, other alcohols, lower hydrocarbons such as methane, ethane and ethylene, carboxylic acid derivatives such as formic acid and formate, and CO. It is attracting attention as being industrially usable. However, according to this method, it is necessary to supply another reactant, hydrogen, and there is a problem in that energy production (that is, generation of CO ₂ ) is accompanied by production of hydrogen.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides
Performs absorption of ₂ efficiently, can immobilize the recovered CO ₂ as an industrial raw material, and further the object to provide a CO ₂ fixing method capable of performing the absorption and immobilization with low energy I do.

The present inventors have conducted intensive studies in view of the above problems, and as a result, have completed the following invention.

[0009]

That is, the means of the present invention comprises:
Reacting an amine with a first aqueous phase containing salts and contacting CO ₂ in a gas phase to remove the amine as an amine salt to leave cations of the salts in the first aqueous phase; by forming a carbonate by reacting the CO ₂ dissolved from cations in the gas phase, in CO ₂ fixing method characterized by immobilizing CO ₂ as carbonate.

When the salts contained in the aqueous phase are reacted with the amine and the aqueous phase is brought into contact with CO ₂ in the gas phase, and the amine is removed as an amine salt (Amine · HX). The reaction proceeds as in the following equation. _{^{Amine + X - + H 2 O}} → Amine · HX + OH - Thus, in the aqueous phase cations (M ⁺⁾ and hydroxide ion (OH ^-) remains, the aqueous phase is made basic . Thereby, the dissolution of CO ₂ which is an acidic gas is promoted, and the absorption of CO ₂ from the gas phase is performed efficiently.

Further, CO ₂ dissolved in water becomes carbonic acid (H ₂ CO ₃ ) or carbonate ion (HCO ₃ −), and further combines with the cation (M ⁺ ) to form HCO ₃ − + M ^+. → Reacts like M ₂ CO ₃ or MHCO ₃ to produce carbonates (M ₂ CO ₃ , MHCO _3, etc.). Therefore, CO ₂ in the gas phase can be immobilized as a carbonate. Here, the reaction steps have been described step by step, but actually, these reactions proceed almost simultaneously as in the following equation. _{Amine + MX + H 2 O +} CO 2 → Amine · HX + M
HCO ₃

[0012] Further, the means of the present invention provides a method in which a first aqueous phase containing salts and a first organic phase containing amine are allowed to act and CO ₂ in a gas phase is brought into contact with the first aqueous phase. The cation remains in the first aqueous phase by forming an amine salt, and the cation reacts with CO ₂ dissolved from the gas phase to form a carbonate, thereby converting CO ₂ into a carbonate. A method for immobilizing CO ₂ , characterized by immobilization.

According to this method, the amine can be stably present in the organic phase by interposing the first organic phase, so that separation of the amine and the aqueous phase becomes easy, The deterioration and disappearance of the amine can be reduced.

[0014] The means of the present invention comprises a step of separating the first organic phase containing the amine salt and the aqueous phase, and then regenerating the amine by a regenerating means for removing an acid from the amine salt;
In the immobilization method of CO ₂ and recovering a first organic phase containing the regenerated amine.

[0015] By removing the acid from the amine salt to regenerate the amine and recovering the first organic phase containing the regenerated amine, the amine and the first organic phase can be reused repeatedly. There is no need to newly add the amine or the organic phase, and CO ₂ can be immobilized at low cost.

Further, the means of the present invention is characterized in that the regenerating means (1) acts on the first organic phase with a second aqueous phase containing an amphipathic substance to remove the acid from the amine salt; A first extraction step of recovering the removed first organic phase containing amine and amphipathic substance and a second aqueous phase containing acid and amphipathic substance; (2) recovering from the first extraction step To extract the amphiphile from the separated first organic phase.
A second extraction step in which a third aqueous phase is allowed to act on the organic phase to recover the first organic phase from which the amphiphile is removed and containing the amine and the third aqueous phase containing the amphiphile, 3) In order to extract an amphipathic substance from the second aqueous phase recovered in the first extraction step, a second organic phase is applied to the second aqueous phase to remove the amphipathic substance and contain an acid. A third extraction step of recovering a second aqueous phase to be recovered and a second organic phase containing an amphipathic substance, and (4) extracting an amphipathic substance from the second organic phase recovered in the third extraction step. A fourth aqueous phase acting on the second organic phase to recover the second organic phase from which the amphiphile has been removed and the fourth aqueous phase containing the amphiphile And further causing the second organic phase recovered in the fourth extraction step to act in the third extraction step Used as second organic phase, and the fourth aqueous phase recovered in the third aqueous phase and the fourth extraction step was recovered in the second extraction step, the first
The method for immobilizing CO ₂ is characterized in that the CO ₂ is used as a second aqueous phase that acts in the extraction step.

According to this method, the acid constituting the amine salt is efficiently removed by the action of the amphipathic substance, and the aqueous phase containing the acid is efficiently removed by the action of the second organic phase. It becomes possible to collect. That is, this method makes it possible to simplify the processing procedure for fixing CO ₂ and reduce the energy consumption.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The amine used in the present invention is preferably insoluble in water, that is, one having low solubility in water. Further, it is preferable to use a material which easily bonds to the acid in the aqueous phase and has a certain degree of basicity so that the acid can be easily separated at the time of regeneration. Specifically, the molecular weight is 150-500.
^Primary , secondary and tertiary amines having a base dissociation constant Kb of 10 ^−7.1 to 10 ^−10.5 (when diluted with benzene) are preferred. Examples of the amine include monoalkylamine, dialkylamine, trioctylamine (TOA) and the like.

The first organic phase containing an amine includes:
It is preferable that the amine has a large dielectric constant in order to increase the basicity of the amine, and it is preferable that the amine has a low solubility in water and is easily separated from an aqueous phase, and more preferably has a large absorption coefficient of CO _2. . As the absorption coefficient of CO ₂ ,
Specifically, those having a dielectric constant of 1.5 to 2.5 Ncm ³ / cm ³ · atm are preferable, and those having a relative dielectric constant of 1 to 18 are preferable. Examples of the first organic phase include alcohols, toluene, n-hexane, benzene, and the like.

On the other hand, as the salts to be contained in the aqueous phase, there can be used those in which cations generated by ionization in the aqueous phase react with carbonic acid to form carbonates. Furthermore, considering that the carbonate is precipitated and separated from the aqueous phase, the solubility of the carbonate is preferably small. Therefore,
Examples of the salts include chlorides and nitrates of alkali and alkaline earth metals, and specific examples thereof include sodium chloride, potassium chloride, and calcium chloride. Among them, sodium chloride is more preferable in consideration of availability, ease of recovery of generated carbonate and acid, and industrial availability of the carbonate and acid.

Further, examples of the amphiphilic substance used in the regeneration means include acetonitrile, 1,4-dioxane, dimethylformamide, dimethylsulfoxide and the like. Among them, 1,4-dioxane is more preferably used. it can.

The second organic phase used in the regenerating means is preferably one which can easily extract the above-mentioned amphipathic substance. Specifically, a hydrocarbon compound having about 6 to 10 carbon atoms is used. Is preferred. As the amphiphilic substance, n-hexane can be exemplified.

Hereinafter, an embodiment of a process according to the CO ₂ fixing method of the present invention and an example of a process according to the process will be described with reference to FIGS.
In this embodiment and its process, a case where sodium chloride (NaCl) is used as a salt will be described.

As shown in FIG. 1, the CO ₂ immobilization method according to this embodiment includes a reaction step, a separation step, and a regeneration step.

First, in the reaction step, the first aqueous phase and the first organic phase are mixed to form a mixed phase, and the mixed phase is brought into contact with the gas phase to convert CO ₂ in the gas phase into the mixed phase. Absorb. Such a reaction step is performed in the mixing device 1 and the absorption device 2 in the process shown in FIG.

More specifically, the first organic phase containing amine and the first aqueous phase containing sodium chloride are supplied to the mixing device 1 and stirred in the mixing device 1.

Next, the mixed phase is transferred to the absorber 2,
It is supplied from the upper part of the absorber 2.

On the other hand, the gas to be treated containing CO ₂ is:
It is supplied to the lower part of the absorption tower 1. In the absorption device 2, the gas to be treated rises from the bottom to the top, and the mixed phase flows from the top to the bottom.

[0029] Thus, the amine is the following formula (underlined indicates the presence in the first organic ^{phase) Amine + Na + + Cl -} + H 2 O → Amine · HCl
⁺ Na + + OH ^- reacts as, during the first organic phase with amine hydrochloride is produced, hydrogen chloride (HCl) are removed from the first aqueous phase. On the other hand, CO ₂ in the gas phase reacts as in the following formula: CO ₂ + H ₂ O → HCO ₃ − + H ⁺ HCO ₃ − + M ⁺ → M ₂ CO ₃ or MHCO ₃ , and hydrogen carbonate ion (HCO 3 ₃ ^-) efficiently and thus it is absorbed into the first aqueous phase as.

In practice, these reactions proceed almost simultaneously, and are expressed by the following formula as a whole. _{Amine + NaCl + H 2 O +} CO 2 → Amine · HCl
+ NaHCO ₃

As a result, the CO ₂ in the gas to be treated is absorbed into the mixed phase (particularly the aqueous phase), so that the treated gas from which the CO ₂ has been removed is discharged from the upper part of the absorber 2.
From the bottom of the absorber ₂ , the mixed phase that has absorbed CO ₂ is recovered.

Subsequently, the mixed phase recovered from the reaction step is processed in a separation step as shown in FIG. The separation step is constituted by the stationary tank 3 and the solid-liquid separation device 4 in the process shown in FIG.

Specifically, the mixed phase recovered from the absorption device 2 is supplied to a stationary tank 3, where it is separated into a first organic phase and a first aqueous phase by being left, and discharged.

The first aqueous phase separated in the stationary tank 3 is
Transferred to the solid-liquid separator 4, the sodium hydrogen carbonate contained in the first aqueous phase is separated by precipitation and filtration, etc.
Collected.

As described above, in the separation step, the first organic phase is recovered by removing the first aqueous phase from the mixed phase, and the amine in the first organic phase is amine hydrochloride, It cannot be reused as it is.

Therefore, as shown in FIG. 1, the first organic phase is further subjected to a regeneration treatment to remove hydrochloric acid from amine hydrochloric acid in a regeneration step, whereby the first organic phase containing amine is recovered. Is done.

This is specifically shown in the process shown in FIG. 2. The regeneration step comprises mixing tanks 5 to 8 and stationary separation tanks 9 to 12.

That is, the first organic phase separated in the stationary separation tank 3 is mixed with the second aqueous phase containing the amphiphilic substance in the mixing tank 5 and then transferred to the stationary separation tank 9. Is done. By this operation, hydrochloric acid is removed from the amine hydrochloric acid, and the first organic phase containing the regenerated amine and the second aqueous phase containing hydrochloric acid and the amphiphilic substance are separated from the stationary separation tank 9. , Will be collected.

However, the first organic phase recovered from the stationary separation tank 9 contains not only the regenerated amine but also the amphipathic substance. Then, the first organic phase is transferred to the mixing tank 6 and mixed with the third aqueous phase, and then transferred to the stationary separation tank 10. As a result, the amphiphilic substance in the first organic phase is recovered in the third aqueous phase, and the first organic phase contains only the amine, and is recycled to the reaction step again and can be reused. It becomes something.

On the other hand, hydrochloric acid recovered from the stationary separation tank 9,
The second aqueous phase containing the amphiphilic substance is mixed with the second organic phase in the mixing tank 7 and then transferred to the stationary separation tank 11. By this operation, the amphipathic substance contained in the second aqueous phase is extracted into the second organic phase, and the second amphiphilic substance containing the amphipathic substance is extracted from the stationary separation tank 11.
The organic phase is recovered and from the other a second containing only hydrochloric acid
The aqueous phase is recovered.

Further, the second containing the amphiphilic substance
The organic phase is further mixed with the fourth aqueous phase in the mixing tank 8 and then transferred to the stationary separation tank 12. As a result of this treatment, the amphiphilic substance contained in the second organic phase is extracted into the fourth aqueous phase, and the second organic phase regenerated from the stationary separation tank 12 is mixed with the amphiphilic substance. A fourth aqueous phase containing the substance is recovered.

The second organic phase recovered from the stationary separation tank 12 is transferred to the mixing tank 7 and reused. on the other hand,
The fourth aqueous phase containing the amphiphilic substance recovered from the stationary separation tank 12 is transferred to the mixing tank 5 together with the third aqueous phase containing the amphiphilic substance recovered from the stationary separation tank 10. Is reused as the second aqueous phase.

As described above, the amine hydrochloride in the first organic phase is regenerated as an amine. Further, the amphiphilic substance and the second organic phase used in the regeneration step are also reused to circulate in the system, so that they are not discharged out of the system. That is, by utilizing these substances in the system and circulating them,
Overall equation becomes a to react as _{NaCl + H 2 O + CO 2} → NaHCO 3 + HCl, can be immobilized as sodium bicarbonate (NaHCO ₃₎ is a CO ₂ useful industrial materials.

In the above process, the step of regenerating amine from amine hydrochloride is performed only by the above-mentioned extraction operation, so that all of these steps can be performed at normal temperature and normal pressure. It is possible to regenerate amines with low energy.

In the above process, the amine was mixed with the first aqueous phase while being contained in the first organic phase, but the present invention is not limited to this process. That is, it is also possible to extract the amine hydrochloride into the first organic phase by adding only the amine to the first aqueous phase and reacting after adding the first organic phase. However, it is preferable to use the amine regenerated from amine hydrochloride, and in view of this point, it is more efficient to use the amine together with the first organic phase as shown in the above process.

In the extraction operation in the above-mentioned process, the extraction can be carried out in an optimal condition of the temperature condition or by another separation means such as a distillation operation. In the case of installation in a chemical factory, a power plant, or the like, these operations can be performed at lower cost by using exhaust heat released from the facility.

Further, as for the absorption tower, the mixing tank and the like in the above-mentioned process, the most suitable apparatus can be used according to the physical properties of the substance to be used, the scale of the facility, and the like.

[0048]

As described above, according to the method for immobilizing CO ₂ according to the present invention, it is possible to efficiently absorb CO ₂ in the gas phase into the aqueous phase by utilizing the action of the amine. become together, that supplies salts and water are useful carbonates and acids can be recovered, it is possible to provide a method of immobilizing breakthrough CO _2.

Further, by using the amine contained in the organic phase, the amine can be stably present in the organic phase and the amine can be easily separated from the aqueous phase.
It is possible to reduce the deterioration and disappearance of the amine.

Further, by regenerating the amine using the amphiphilic substance and the second organic phase, the amine can be regenerated with lower energy, and therefore, the energy for fixing CO ₂ can be reduced. It becomes possible.

When sodium chloride is used as the salt, inexhaustible seawater or the like is used to fix CO ₂ at lower cost and produce industrially useful sodium hydrogen carbonate and hydrochloric acid. Can be recovered.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a processing step in a CO ₂ fixing method according to the present invention.

FIG. 2 is a diagram showing an example of a process for the CO ₂ fixing method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mixing tank, 2 ... Absorption tower, 3, 9, 10, 11, 12 ...
Stationary separation tank, 4 ... solid-liquid separator, 5, 6, 7, 8 ... mixing tank

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D002 AA09 BA02 BA20 CA02 DA31 DA35 DA70 EA02 EA13 EA14 4D020 AA03 BA16 BB03 BC06 BC10 CB18 CC02 CC30 4G046 JA04 JB06 JC06 4G075 AA04 AA62 BB03 BD13 BD15 CA51 CA57

Claims (4)

[Claims] An amine acts on a first aqueous phase containing salts.
And CO in the gas phase _TwoAnd contact the amine with an amine.
Cations of the salts in the first aqueous phase
And the cations and dissolved CO from the gas phase
_TwoTo form a carbonate, whereby CO 2_TwoTo
CO characterized by being immobilized as carbonate_TwoImmobilization
Method. 2. A salt is contacted with the first organic phase and the CO ₂ in and in the gas phase by the action of containing a first aqueous phase and amine containing, thereby generating the amine salt in the first organic phase and CO ₂ dissolved from and cation and the gas phase leaving a cation in the first aqueous phase is reacted by forming a carbonate by, characterized in that immobilizing CO ₂ as carbonate CO ₂ immobilization method. 3. A first organic phase containing the amine salt,
After separating from the first aqueous phase, the acid is removed from the amine salt.
Regenerating amine by regenerating means
Recovering a first organic phase containing
Item 2 CO _TwoImmobilization method. 4. The regenerating means (1) reacts a second aqueous phase containing an amphipathic substance with a first organic phase to remove an acid from an amine salt, and removes the acid and the amine from the acid salt. A first extraction step of recovering a first organic phase containing the amphiphile and a second aqueous phase containing the acid and the amphiphile, (2)
In order to extract the amphipathic substance from the first organic phase recovered from the first extraction step, a third aqueous phase is applied to the first organic phase to remove the amphipathic substance and to remove the amphipathic substance containing amine. 1
A second extraction step of recovering an organic phase and a third aqueous phase containing an amphipathic substance; (3) extracting an amphipathic substance from the second aqueous phase recovered in the first extraction step; The second
A third extraction step of allowing the second organic phase to act on the aqueous phase, removing the amphipathic substance and recovering the second aqueous phase containing the acid and the second organic phase containing the amphipathic substance, 4) The third
Causing a fourth aqueous phase to act on the second organic phase to extract the amphiphile from the second organic phase recovered by the extraction step;
A fourth extraction step of recovering a second organic phase from which the amphipathic substance has been removed and a fourth aqueous phase containing the amphipathic substance;
The organic phase is used as a second organic phase to act in the third extraction step, and the third aqueous phase recovered in the second extraction step and the fourth aqueous phase recovered in the fourth extraction step are used. , claim 3 CO ₂ fixing method, wherein the use as a second aqueous phase to act in the first extraction step.