KR20140003233A - Preparing method of formic acid by electrochemical reduction of carbon dioxide and apparatus therefor - Google Patents

Abstract

The present invention relates to a method for preparing formic acid by the electrochemical reduction of carbon dioxide and a device therefor. The method for preparing formic acid according to the present invention electrochemically reduces carbon dioxide using a metal-mercury amalgam electrode material. [Reference numerals] (AA) Formic acid; (BB) Formic acid

Description

Process for producing formic acid by electrochemical reduction of carbon dioxide and reduction apparatus therefor {PREPARING METHOD OF FORMIC ACID BY ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE AND APPARATUS THEREFOR}

The present application relates to a method for producing formic acid by electrochemical reduction of carbon dioxide and an electrochemical reduction apparatus for the carbon dioxide.

Response to climate change due to the acceleration of global warming has become the most important issue in the current international society. Carbon dioxide, which is considered the main cause of global warming, is mostly emitted by the use of fossil fuels such as coal and petroleum. Since carbon dioxide is the carbon compound having the lowest energy, the input of energy is essential for the conversion technology that uses it as a useful resource.

There are two main ways to use carbon dioxide: non-conversion method that uses carbon dioxide usefully in itself, and conversion method that converts carbon dioxide to useful compounds and reuses them. . The conversion technology of carbon dioxide using the conversion method is a technology that converts the most stable carbon dioxide of carbon compounds to other useful compounds, it is necessary to develop a catalyst that minimizes the use of energy and improves the selectivity of the reaction. There is a need for the development of electrode materials that are selective for reduction. In order to convert carbon dioxide into a useful compound, various forms of energy sources can be utilized, and utilization of hydrogen energy, solar energy, and electric energy has been actively studied.

Among them, the method of converting carbon dioxide through electric energy, in particular, electrochemical method, has been reported to have many advantages over the conversion method using hydrogen energy or solar energy. The electrochemical conversion of carbon dioxide is possible with high efficiency in the conversion of various organic materials such as carbon monoxide, formic acid, oxalic acid, methanol, ethanol, acetaldehyde, etc. under normal temperature and atmospheric pressure conditions, and the selectivity according to which catalyst is used is relatively good. . In addition, it is possible to use electricity produced from solar, wind, hydro, geothermal, etc., and it is possible to implement in a small area because it is inexpensive and miniaturized in constructing an electrochemical system. Scale-up is relatively simple. In addition, the conversion of carbon dioxide using electric energy is a very useful technology when applied on-site by utilizing the idle power of a power plant. It is evaluated. Therefore, for the efficient production of useful products, it is essential to construct an effective system capable of obtaining high yield value-added products with low electrical energy through the development of electrode materials and the development of selective and efficient catalysts. In this regard, international publication WO 2007/041872 describes a technique for converting carbon dioxide based on Sn electrodes.

The present inventors have completed the present application by discovering that carbon-metal can be electrochemically reduced with high efficiency using a metal-mercury amalgam electrode material.

Accordingly, the present application is to provide a method for producing formic acid, including the electrochemical reduction of carbon dioxide using a metal-mercury amalgam electrode material and an electrochemical reduction device of carbon dioxide.

However, the problems to be solved by the present invention are not limited to the problems described above, and other problems not described can be clearly understood by those skilled in the art from the following description.

A first aspect of the present application provides a method of preparing formic acid, which includes electrochemically reducing carbon dioxide using a metal-mercury amalgam electrode material.

A second aspect of the present application, the anode chamber including the anode and the anolyte; A cathode chamber comprising a cathode and a catholyte; And a separation membrane formed between the anode and the cathode, wherein the cathode provides an electrochemical reduction apparatus of carbon dioxide including a metal-mercury amalgam electrode material.

Formic acid production method according to the present invention, by using a metal-mercury amalgam electrode material, can be converted into formic acid by electrochemically reducing the carbon dioxide with high efficiency and high stability, re-conversion to a useful material at a low cost simultaneously with the treatment of carbon dioxide It can produce high added value.

1 shows an H-type cell according to a comparative example of the present application.
Figure 2 is a cyclic voltammogram (a), -1.5 V vs. when using a tin electrode material according to a comparative example of the present application. It is a graph showing charge accumulation (b) and formic acid current efficiency (c) during electrolysis at the Ag / AgCl potential.
Figure 3 is a cyclic voltage current diagram when using the lead electrode material according to a comparative example of the present application and a graph showing the voltage of the cathode when electrolysis at a constant current of 5 mA / cm2.
Figure 4 is a cyclic voltammogram when using a tin-mercury amalgam electrode material according to an embodiment of the present application (a), the voltage (b) and formic acid production current efficiency of the electrode when electrolysis at a constant current of 5 mA / cm ² It is a graph which shows (c).
FIG. 5 is a graph showing the voltage of the cathode when electrolyzed at 5 mA / cm ² daily current for 22 hours when the tin-mercury amalgam electrode material is used according to an embodiment of the present disclosure.
Figure 6 shows the internal structure of the flow cell according to an embodiment of the present application.
7 shows a lab scale flow cell system according to one embodiment of the present application.
Figure 8 is a graph showing the total cell voltage during constant current electrolysis at 5 mA / cm ² using a metal-mercury amalgam electrode material according to an embodiment of the present application.
Figure 9 schematically shows an electrochemical reduction apparatus of carbon dioxide according to an embodiment of the present application.

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout this specification, when a member is located "on" another member, this includes not only when one member is in contact with another member but also when another member exists between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

Throughout this specification, the term "combination of these" included in the expression of the makushi form means one or more mixtures or combinations selected from the group consisting of constituents described in the expression of the makushi form, wherein the constituents It means to include one or more selected from the group consisting of.

A first aspect of the present application provides a method of preparing formic acid, which includes electrochemically reducing carbon dioxide using a metal-mercury amalgam electrode material.

According to one embodiment of the present application, the method of preparing formic acid of the present invention comprises supplying a catholyte including carbon dioxide to a cathode chamber of an electrochemical reactor and a cathode including the metal-mercury amalgam electrode material, and a current to the anode. It may include a step of reducing the carbon dioxide by applying, but is not limited thereto.

According to the exemplary embodiment of the present application, the metal-mercury amalgam may be converted to formic acid by reducing carbon dioxide by the electrode material, but is not limited thereto.

According to an embodiment of the present disclosure, the metal may include, but is not limited to, a metal selected from the group consisting of tin, lead, and combinations thereof. The mercury may be usefully used as a reducing electrode material of carbon dioxide because the energy barrier to hydrogen generation has the greatest characteristic and thus inhibits hydrogen generation upon reduction of carbon dioxide, but is not limited thereto. For example, by using the amalgam of tin and mercury as electrode material, the efficiency is increased by about 2 times or more than when using only tin as electrode material, and the stability of the electrode is also increased by about 3 to 5 times, resulting in high efficiency. Carbon dioxide can be converted to formic acid.

According to one embodiment of the present application, the metal-mercury amalgam electrode material may be prepared by impregnating a metal electrode in a mercury solution, but is not limited thereto.

According to one embodiment of the present application, the catholyte and the anolyte may include a KHCO ₃ solution, for example, the catholyte may include a KHCO ₃ solution saturated with carbon dioxide, but is not limited thereto. . The catholyte may further include KCl to prevent elution of mercury ions from the metal-mercury amalgam electrode material to the catholyte, but is not limited thereto. When mercury ions are eluted from the metal-mercury amalgam electrode material, they react with KCl and precipitate as Hg ₂ Cl ₂ solids directly on the electrode surface.

According to one embodiment of the present application, the carbon dioxide may be converted to formic acid with a current efficiency of about 50% or more, for example, about 60% or more, about 70% or more, about 80% or more and about 90% or more, It is not limited to this.

According to an embodiment of the present disclosure, the current is about 2 mA / cm ² to about 15 mA / cm ² , for example about 5 mA / cm ² to about 15 mA / cm ² , about 10 mA / cm ² to About 15 mA / cm ² , about 2 mA / cm ² to about 10 mA / cm ² , or about 2 mA / cm ² to about 5 mA / cm ² , but is not limited thereto.

A second aspect of the present application, the anode chamber including the anode and the anolyte; A cathode chamber comprising a cathode and a catholyte; And a separation membrane formed between the anode and the cathode, wherein the cathode comprises a metal-mercury amalgam electrode material.

According to one embodiment of the present application, the metal may include a metal selected from the group consisting of tin, lead, and combinations thereof, for example, tin may be used, but is not limited thereto. The mercury may be usefully used as a reducing electrode material of carbon dioxide because the energy barrier to hydrogen generation has the greatest characteristic and thus inhibits hydrogen generation upon reduction of carbon dioxide, but is not limited thereto. For example, by using the amalgam of tin and mercury as electrode material, the efficiency was increased by about 2 times or more than when only metal was used as the electrode material, and the stability of the electrode was also increased by about 3 to 5 times. Carbon dioxide can be converted to formic acid.

According to one embodiment of the present application, the metal-mercury amalgam electrode material may be prepared by impregnating an electrode containing the metal in a mercury solution, but is not limited thereto.

According to one embodiment of the present application, the catholyte and the anolyte may include a KHCO ₃ solution, for example, the catholyte may include a KHCO ₃ solution saturated with carbon dioxide, but is not limited thereto. . The catholyte may further include KCl to prevent elution of mercury ions from the metal-mercury amalgam electrode material to the catholyte, but is not limited thereto. When mercury ions are eluted from the metal-mercury amalgam electrode material, they react with KCl and precipitate as Hg ₂ Cl ₂ solids directly on the electrode surface.

According to one embodiment of the present application, the carbon dioxide may be converted to formic acid with a current efficiency of about 50% or more, for example, about 60% or more, about 70% or more, about 80% or more and about 90% or more, It is not limited to this.

According to an embodiment of the present disclosure, the current is about 2 mA / cm ² to about 15 mA / cm ² , for example about 5 mA / cm ² to about 15 mA / cm ² , about 10 mA / cm ² to About 15 mA / cm ² , about 2 mA / cm ² to about 10 mA / cm ² , or about 2 mA / cm ² to about 5 mA / cm ² , but is not limited thereto.

According to one embodiment of the present application, the separation membrane may include a cation exchange membrane such as Nafion membrane, CMI-7000, but is not limited thereto.

According to an embodiment of the present disclosure, Ar gas may be blown into the anode chamber to minimize the effect of oxygen generated from water by oxidation, and carbon dioxide may be injected into the cathode chamber to saturate the cathode chamber with carbon dioxide. Can be blown continuously, but is not limited thereto.

According to an embodiment of the present disclosure, the anode includes one selected from the group consisting of Pt, Au, Pd, Ir, Ag, Rh, Ru, Ni, Al, Mo, Cr, Cu, Ti, W, and combinations thereof. It may be, but is not limited thereto.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited thereto.

[ Example ]

Comparative Example  One

The production of formic acid by electrochemical reduction of carbon dioxide was evaluated using tin and lead as electrode materials, respectively.

First, a batch H-type cell was configured as shown in FIG. 1 (FIG. 1), and an anode compartment and a cathode compartment were divided using a Nafion membrane. Carbon dioxide was reduced at a cross-sectional area of 2 cm ² using a rectangular electrode of 0.5 cm in width and 2 cm in length as the working electrode. At room temperature and atmospheric pressure, 0.5 M KHCO ₃ was used as an electrolyte. The anode part was blown with Ar gas to eliminate the influence of oxygen generated by the oxidation reaction of water, and the cathode part was continuously blown with carbon dioxide to saturate.

As can be seen in Figure 2, when tin (Sn) is used as the electrode material, -1.5 V vs. When a potential of Ag / AgCl was applied, a reduction current of about 5 mA / cm ² flowed and a constant charge amount was accumulated (FIG. 2B). As a result of confirming the product produced over time, since the initial 30 minutes, it shows a stable current efficiency of 30% to 40%, carbon dioxide was converted to formic acid.

As shown in FIG. 3, when lead (Pb) was used as the electrode material, a constant current of 5 mA / cm ² was applied, and the voltage of the cathode was -1.6 V to -1.7 V vs. It was maintained at Ag / AgCl. The first 10 minutes showed a current efficiency of 30% to 40%, but after one hour it was observed that the efficiency sharply drops to less than 10%. In addition, the lead surface was easily oxidized in aqueous solution, and no matter how clean the surface immediately before the experiment, it was confirmed that the efficiency was not good at 10% or less after 1 hour.

Example  One

The mercury / tin amalgam electrode material was prepared by immersing a tin electrode in a mercury solution and confirming its characteristics in the same H-type cell as the cell of FIG. 1. In order to prevent the generation of mercury ions that may come out of the aqueous solution, KHCO ₃ KCl was added to the solution to precipitate Hg ₂ Cl ₂ solids directly on the electrode surface when mercury was leaked. After completion of the experiment to confirm the effect, the solution was taken and the metal element analysis (ICP-Mass) was performed. It was confirmed in the solution phase that the presence of mercury was not measured. In the case of using the mercury / tin amalgam electrode, the voltage of 0.4 ~ 0.5 V should be applied more than the tin electrode under the same conditions. It was confirmed through four experiments to maintain a constant up to time and efficiently convert carbon dioxide to formic acid (FIG. 4). In addition, the concentration of formic acid was also produced up to 0.4 M to 0.5 M for 12 to 18 hours (Table 1). When tin / mercury amalgam was used as the electrode than when only tin was used (Comparative Example 1), it was confirmed that the efficiency was increased by 2 times or more, and the stability of the electrode was increased by 3 to 5 times or more. It could be confirmed that it can be generated.

Example  2

The effect was observed similarly to Example 1 using the lead-mercury amalgam electrode. As in tin, the current efficiency is 55% to 75%, which is about 2 times higher than that of lead electrodes, and in the case of lead electrodes, the efficiency drops to less than 10% after 1 hour. After 24 hours of use, over 60% of current efficiency was maintained, producing about 0.5 M of formic acid.

Experimental Example  One

As can be seen in Example 1, it was confirmed that formic acid of about 0.4 M to 0.5 M accumulates when electrolysis is performed for 12 hours to 20 hours with a tin electrode formed of mercury and amalgam. Further experiments were carried out in H type cells using tin / mercury amalgam electrodes to determine the maximum formic acid accumulation concentration under current conditions. Initially, the mercury / tin amalgam electrode was added to a solution containing 0.45 M formic acid, and electrolysis was further performed for 10 hours. Formic acid was continuously generated and accumulated up to 0.9 M.

Example  3

A system for implementing a flow cell by scaling up the electrode area by 5 times based on the basic experimental results of finding a high efficiency electrode in a batch-type cell using a 2 cm ² electrode in Example 1 It was configured. Each part of the flow cell was fabricated as shown in FIG. 6. A tin / mercury electrode having a good performance as a carbon dioxide reduction electrode was 1 cm × 10 cm in size, and a platinum plate having the same size was used as the anode. The two electrodes were separated by a Nafion membrane and both sides were fixed with O-rings to separate the positive and negative electrodes. In addition, a tubing made of PVC material was connected to the cathode and the anode to connect the pump.

Experimental Example  2

After constructing the flow cell as in Example 3, using a peristaltic pump (peristaltic pump) to circulate each 20 mL of the solution at the rate of 40 mL / min to confirm the formation of formic acid by electrolysis of carbon dioxide It was. The overall system was configured as shown in FIG. In this case, 2 M KCl was added to 0.5 M KHCO ₃ to minimize the dissolution of mercury biomass. When the current density was set at 5 mA / cm ² , the voltage between the positive electrode and the negative electrode was applied at about 3.5 V to 4.0 V (FIG. 8). When electrolysis was performed for about 1 hour, 40 mM formic acid was generated and the current efficiency was 84%. It was.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (14)

A method for producing formic acid, comprising electrochemically reducing carbon dioxide using a metal-mercury amalgam electrode material.
The method of claim 1,
Supplying a catholyte comprising carbon dioxide to a cathode chamber of an electrochemical reactor; And
And a cathode including the metal-mercury amalgam electrode material, and reducing carbon dioxide by applying a current to the anode.
The method of claim 1,
Carbon dioxide is reduced by the metal-mercury amalgam electrode material, method of producing formic acid.
The method of claim 1,
Wherein the metal comprises a metal selected from the group consisting of tin, lead and combinations thereof.
The method of claim 1,
The mercury is to suppress the generation of hydrogen when the reduction of carbon dioxide, a method of producing formic acid.
The method of claim 1,
The metal-mercury amalgam electrode material is prepared by impregnating an electrode containing the metal into a mercury solution.
3. The method of claim 2,
The catholyte comprises a KHCO ₃ solution, method of producing formic acid.
The method of claim 7, wherein
The KHCO ₃ solution further comprises KCl, method of producing formic acid.
The method of claim 1,
A process for producing formic acid, which shows a current efficiency of at least 50%.
3. The method of claim 2,
The current is 2 mA / cm ² to 15 mA / cm ² , the method of producing formic acid.
An anode chamber comprising an anode and an anolyte solution;
A cathode chamber comprising a cathode and a catholyte; And
A separation membrane formed between the anode and the cathode
/ RTI >
Wherein the cathode comprises a metal-mercury amalgam electrode material,
Electrochemical reduction apparatus of carbon dioxide.
The method of claim 11,
The catholyte and the anolyte will comprise a KHCO ₃ solution, electrochemical reduction apparatus of carbon dioxide.
13. The method of claim 12,
The KHCO ₃ solution further comprises KCl, electrochemical reduction apparatus of carbon dioxide.
The method of claim 11,
Wherein said metal comprises a metal selected from the group consisting of tin, lead and combinations thereof.

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