JP2023045473A - Carbon dioxide treatment method - Google Patents

Abstract

To provide a novel carbon dioxide treatment method for converting carbon dioxide to a different material.SOLUTION: The carbon dioxide treatment method carrying out a carbon dioxide absorption step of bringing carbon dioxide into contact with an aqueous alkaline solution to dissolve carbon dioxide in the aqueous alkaline solution, and an electrolysis step of electrolyzing the aqueous alkaline solution in which carbon dioxide is dissolved, is characterized by applying an inter-electrode voltage in such a way that the value of electrolytic current is kept at 400 A or below when the electrolysis step is being carried out.SELECTED DRAWING: Figure 1

Description

The present invention relates to a carbon dioxide treatment method for denaturing carbon dioxide into another substance.

Global warming is a phenomenon caused by a combination of various factors, and it is believed that greenhouse gases such as carbon dioxide (CO ₂ ) emitted into the atmosphere by human industrial activities are a major factor. has become mainstream. Therefore, the reduction of carbon dioxide emissions is an international issue. In addition, research is also progressing on means for recovering the emitted carbon dioxide.

As means for recovering carbon dioxide, for example, a method (chemisorption method) has been developed in which carbon dioxide is brought into contact with an alkaline aqueous solution to dissolve carbon dioxide in the aqueous solution. In this chemisorption method, carbon dioxide is selectively recovered by heat-treating an aqueous solution in which carbon dioxide is dissolved, and the carbon dioxide is buried underground in the form of liquefied carbon dioxide.

However, the chemisorption method consumes a large amount of thermal energy when separating carbon dioxide from an aqueous solution in which carbon dioxide is dissolved, resulting in high processing costs. Regarding this point, in Patent Document 1 below, after dissolving carbon dioxide in an aqueous solution of monoethanolamine, a calcium salt such as calcium hydroxide is added to the aqueous solution to generate calcium carbonate, thereby dissolving carbon dioxide in the aqueous solution. proposed a method to fix carbon dioxide in

Further, Patent Literature 2 below proposes a means for denaturing carbon dioxide by dissolving carbon dioxide in an alkaline aqueous solution and then electrolyzing the solution.

JP 2012-131697 A Japanese Patent Application Laid-Open No. 2017-205718

The method (method for immobilizing carbon dioxide) described in Patent Document 1 is to immobilize carbon dioxide in the form of calcium carbonate in an aqueous solution. However, calcium carbonate has no substantial calorific value. Therefore, the processed material obtained by the method described in Patent Document 1 has only been found to be useful to the extent that calcium carbonate is extracted and reused as cement.

On the other hand, in the method (carbon dioxide treatment method) described in Patent Document 2, carbon dioxide is denatured into C ₁ to C ₂ organic compounds such as methane and ethane by electrolysis. Although these organic compounds can be reused as materials or fuels, they are gaseous at room temperature, so they cause a certain amount of loss during recovery and transportation.

The present invention was developed to solve the above technical problems, and it is an object of the present invention to provide a novel carbon dioxide treatment method that can convert carbon dioxide into another substance and recover it as a liquid. do.

The carbon dioxide treatment method of the present invention for solving the technical problem is a carbon dioxide treatment method for denaturing carbon dioxide, comprising a carbon dioxide absorption step of dissolving carbon dioxide in an alkaline aqueous solution, and the carbon dioxide absorption step. During or after execution, an electrolysis step of electrolyzing the alkaline aqueous solution is performed, and when the electrolysis step is performed, the voltage between the electrodes is applied so that the value of the electrolysis current is 400 A or less. (hereinafter referred to as "method of the present invention").

In the method of the present invention, it is preferable to use, as the alkaline aqueous solution, an aqueous solution containing a silicate as a solute, an aqueous solution containing an amine compound as a solute, or an aqueous solution containing an amine compound and a silicate as solutes. Become.

In the method of the present invention, it is preferable to use a copper electrode as an anode during the electrolysis step.

In the method of the present invention, it is preferable to use an electrode other than a copper electrode as the anode during the decomposition step.

In the method of the present invention, it is preferable to repeatedly perform the carbon dioxide absorption step and the electrolysis step.

In the method of the present invention, it is preferable to replenish the alkaline aqueous solution before or during the second and subsequent carbon dioxide absorption steps.

According to the present invention, carbon dioxide can be denatured into another substance and recovered as a liquid.

FIG. 1(a) is a schematic diagram showing execution of the carbon dioxide absorption step in the method of the present invention, and FIG. 1(b) is a schematic diagram showing execution of the electrolysis step in the method of the present invention. Figures 2(a) and (b) are structural formulas representing compounds obtained by carrying out the method of the present invention. FIG. 3 is a chromatogram (a) and a structural formula (b) showing compounds obtained by carrying out the method of the invention. FIG. 4 is a chromatogram (a) and a structural formula (b) showing compounds obtained by practicing the method of the present invention.

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

<Method of the present invention>
In the method of the present invention, a "carbon dioxide absorption step" and an "electrolysis step" are performed.

-Carbon dioxide absorption process-
In the carbon dioxide absorption step, carbon dioxide is dissolved in the alkaline aqueous solution. Blowing a gas containing carbon dioxide into an alkaline aqueous solution to dissolve the carbon dioxide in the gas in the alkaline aqueous solution is already a known means. For example, when carbon dioxide is introduced into an alkaline aqueous solution containing an amine-based compound represented by the chemical formula of _RNH2 (R: alkyl group or alkanol group) as a solute, a bond-forming reaction between the amine-based compound and carbon dioxide ( _RNH2 + CO ₂ →RNH ₂ CO ₂ ) occurs, and carbon dioxide is dissolved in the alkaline aqueous solution by the subsequent proton elimination reaction (RNH ₂ CO ₂ +H ₂ O→RNHCO ₂ ⁻ +H ₃ O ⁺ ). With the dissolution of carbon dioxide, the pH of the alkaline aqueous solution shifts to near neutrality.

In the treatment method of the present invention, the alkaline aqueous solution is not particularly limited, but an amine compound or silicate that is safer in handling than an aqueous solution containing a strong base such as sodium hydroxide or potassium hydroxide as a solute. It is preferable to use an aqueous solution containing a weak base such as a solute. Further, it is preferable to adjust the basicity of the alkaline aqueous solution within the range of pH 10-14.

Examples of the amine compounds include alkylamines (monoalkylamines, dialkylamines, trialkylamines) in which hydrogen groups of ammonia are substituted with alkyl groups or alkanol groups, and alkanolamines (monoalkanolamines, dialkanolamines, trialkylamines). alkanolamine) can be mentioned. On the other hand, examples of the silicate include sodium silicate and potassium silicate.

It has been confirmed that the amount of dissolved carbon dioxide is improved by using an aqueous solution containing an amine compound and a silicate as solutes as the alkaline aqueous solution. In this case, the mixing ratio of the amine compound and the silicate is not particularly limited, but the silicate should be 1 to 10 parts by weight (preferably 2 to 5 parts by weight) per 100 parts by weight of the amine compound. is preferred.

-Electrolysis process-
In the electrolysis step, the alkaline aqueous solution in which carbon dioxide is dissolved is electrolyzed (two electrodes (an anode and a cathode) are brought into contact with the alkaline aqueous solution and a voltage is applied between the electrodes). The electrolysis step may be performed during execution of the carbon dioxide absorption step, or may be performed after execution of the carbon dioxide absorption step.

In the method of the present invention, the voltage between the electrodes is applied so that the value of the electrolysis current is 400 A or less (preferably 150 to 300 A) during the electrolysis step. It has been confirmed that if the electrolysis step is performed so that the value of the electrolysis current is 400 A or less, the carbon dioxide dissolved in the alkaline aqueous solution is denatured into a substance that can remain in the alkaline aqueous solution. On the other hand, it has been confirmed that when the value of the electrolysis current exceeds 400 mA during the electrolysis step, the carbon dioxide dissolved in the alkaline aqueous solution is denatured into C ₁ to C ₂ organic compounds such as methane and ethane. ing. However, at the present stage, the details of the mechanism of this carbon dioxide denaturation have not been clarified.

When performing the electrolysis step, even if the voltage between the electrodes is the same, the value of the electrolysis current varies depending on the formulation of the alkaline aqueous solution, the distance between the electrodes, the size of the electrolytic cell, and the like. In other words, the value of the electrolysis current can be controlled to 400 A or less by increasing or decreasing the voltage between the electrodes. Therefore, in the method of the present invention, the inter-electrode voltage during the electrolysis step is not particularly limited. Also, the inter-electrode voltage may be increased or decreased during execution of the method of the present invention. However, if the voltage between the electrodes is increased, the amount of electrical energy consumed for carrying out the method of the present invention increases. preferably.

<Example>
-Alkaline aqueous solution-
Table 1 below shows the formulations of the alkaline aqueous solutions (temperature conditions of 25° C.) according to Examples 1 to 3. In the table, "MEA" means monoethanolamine, "DEA" means diethanolamine, "TEA" means triethanolamine, and "CG" means silicate aqueous solution (sodium silicate 1.0%, plant interface 0.5% active agent, 98.5% water).

-Carbon dioxide absorption process-
A high-concentration carbon dioxide gas (99.9%) was enclosed in an aluminum bag B and introduced (bubbling) into the alkaline aqueous solution 1 according to each example using a tubing pump P as shown in FIG. 1(a). The carbon dioxide gas was introduced at an introduction rate of 13.0 ml/min for 90 minutes.

-Electrolysis process-
Table 2 below shows the conditions under which the electrolysis step was carried out. As shown in FIG. 1(b), the electrolysis step includes immersing each end of the two electrodes (anode (PP) and cathode (NP)) in an alkaline aqueous solution so that the electrolysis current does not exceed 400A. was performed by applying a voltage between the electrodes. Further, as a comparative example, a case where the voltage between the electrodes was applied so that the electrolysis current was 500A was also carried out. Further, in Examples 4 and 5, an electrolysis process was also performed in which the cathode (NP) was a stainless steel electrode and the anode (PP) was a copper electrode.

As a result, it was confirmed that gas was generated during the electrolysis in all of the comparative examples (comparative examples 1 and 2) in which the electrolysis was performed under the condition that the value of the electrolysis current exceeded 400 A. As a result of collecting this gas and performing component analysis by gas chromatography (GC-TCD), methane (CH ₄ ), carbon monoxide (CO), ethylene oxide (C ₂ H ₄ O), ethylene (C ₂ H ₂ ), and the presence of ethane _{( C2H5} ).

On the other hand, in each of the examples in which the electrolysis step was performed under the condition that the value of the electrolysis current was 400 A or less, the alkaline aqueous solution darkened with the passage of time. It was confirmed that it was generated and dissolved in the alkaline aqueous solution. After the electrolysis step was carried out until the water concentration of the alkaline aqueous solution reached 20±5%, when a fire was brought close to it, it ignited and combustion continued. was confirmed.

Therefore, when the method of the present invention was performed under the conditions of Examples 1 to 3, component analysis was performed by TIC (total ion current) chromatogram, and the compound (2-morpholinoethanol) having the structure shown in FIG. , and the presence of relatively low-molecular-weight compounds such as the compound (oxazolidin-2-one) shown in FIG. 1(b).

In addition, when a copper electrode is used as the anode (PP) (Examples 4-2 and 5-2), the compound (2-morpholinoethanol) having the structure shown in FIG. The presence of relatively low molecular weight compounds such as the compound (oxazolidin-2-one) shown in 1(b) was confirmed.

As a reference, when electrolysis was performed when carbon dioxide was not dissolved in the alkaline aqueous solution (when carbon dioxide was not present in the reaction system), the formation of the above-mentioned compound was not confirmed.

On the other hand, in the reaction systems (Examples 4-1 and 5-1) using a stainless steel electrode as the anode (PP), substances exhibiting the mass chromatograms shown in FIGS. 2(a) and 3(a) were obtained. was taken. When the chemical structure was analyzed from each mass chromatogram, the compound (1-methoxy-2,8,9-trioxa-5-aza-1-sylabicyclo[3,3,3]) having the structure shown in FIG. undecane) and the compound (1-isobutylsulfanimethyl-2,8,9-trioxa-5-aza-1-sylabicyclo[3,3,3]undecane) having the structure shown in FIG. confirmed.

That is, it was confirmed that when a silicate was present in the reaction system and an electrode other than a copper electrode was used as the anode (PP), a compound having a silabicycloundecane as a basic skeleton was produced. This result was the same even when an electrode (carbon electrode, etc.) other than a copper electrode was used for the anode (PP).

On the other hand, it was confirmed that when a copper electrode is used as the anode (PP), a relatively low-molecular-weight compound containing no silica in its structural framework is produced. This result was the same even when silicate was present in the reaction system.

Thus, it has been observed that carbon dioxide can be transformed into another substance and recovered as a liquid as a result of the practice of the method of the present invention.

By the way, in each of the above examples, an aqueous solution containing a weak base as a solute was used as the alkaline aqueous solution, but it was confirmed that similar results were obtained even when a strong base such as sodium hydroxide was used. ing.

Further, in each of the above examples, a stainless steel electrode was used as the cathode (NP). ing.

Furthermore, in the present embodiment, the electrolysis step is performed after the carbon dioxide absorption step is performed, but the electrolysis step may be performed during the carbon dioxide absorption step. Further, the carbon dioxide absorption step and the electrolysis step may be repeated.

In this case, it has been confirmed that carbon dioxide can be treated more efficiently by replenishing the alkaline aqueous solution before or during the second and subsequent carbon dioxide absorption steps.

In addition, the present invention can be embodied in various other forms without departing from its spirit or essential characteristics. Therefore, the above-described embodiments are merely illustrative in all respects and should not be construed in a restrictive manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Furthermore, all modifications and changes within the equivalent range of claims are within the scope of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be suitably used as means for modifying carbon dioxide.

1 alkaline aqueous solution

Claims (6)

A carbon dioxide treatment method for denaturing carbon dioxide,
A carbon dioxide absorption step of dissolving carbon dioxide in an alkaline aqueous solution;
an electrolysis step of electrolyzing the alkaline aqueous solution during or after the carbon dioxide absorption step;
and run
A carbon dioxide treatment method, wherein an inter-electrode voltage is applied such that an electrolysis current value is 400 A or less during execution of the electrolysis step. In the carbon dioxide treatment method according to claim 1,
As the alkaline aqueous solution,
A carbon dioxide treatment method using an aqueous solution containing a silicate as a solute, an aqueous solution containing an amine compound as a solute, or an aqueous solution containing an amine compound and a silicate as solutes. In the carbon dioxide treatment method according to claim 1 or 2,
A carbon dioxide treatment method using a copper electrode as an anode during the electrolysis step. In the carbon dioxide treatment method according to any one of claims 1 to 3,
A carbon dioxide treatment method using an electrode other than a copper electrode as an anode during the decomposition step. In the carbon dioxide treatment method according to any one of claims 1 to 4,
A carbon dioxide treatment method in which the carbon dioxide absorption step and the electrolysis step are repeatedly performed. In the carbon dioxide treatment method according to claim 5,
A carbon dioxide treatment method in which the alkaline aqueous solution is replenished before or during the second and subsequent carbon dioxide absorption steps.

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