JPH04327549A - Method for utilizing carbon dioxide as resource - Google Patents

Abstract

PURPOSE:To obtain an utilizing method of carbon dioxide capable of utilizing carbon dioxide as resource in high efficiency and having variety in utilization of the resultant product, rich in safety because of reaction for utilization carried out at relatively low temperature and pressure and capable of diversifying the reaction style. CONSTITUTION:A hydrogen occluded metal, e.g. single metal such as Pd, Ti or V, magnesium based alloy such as MgCu2, rare earth based alloy such as MmNi5 (Mm is Misch metal) or rare earth based alloy such as TiFe kept in a state in which hydrogen is occluded is brought into contact with carbon dioxide to convert carbon dioxide into methanol and utilize carbon dioxide as resource. The above-mentioned method can be contributed to field for preventing earth environment and industrial field using methanol as a raw material, because carbon dioxide generated from fossil fuel, etc., accumulated in air and resulted in warming of the earth can be converted into methanol in high efficiency. The method has effects capable of carrying out plant design while coinciding with conditions and scale, because it has variety in conversion system and simplifying the process, because conversion is highly selective.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a method for recycling carbon dioxide generated from fossil fuels, etc., in which a hydrogen storage metal is used as a catalyst to react carbon dioxide with hydrogen and convert it into methanol. It is.

0002

BACKGROUND OF THE INVENTION In recent years, atmospheric carbon dioxide generated and accumulated through the use of fossil fuels and other carbon compounds as energy has become a major problem in connection with global warming. For this reason, methods of recovering carbon dioxide from exhaust gas emitted from fossil fuels and the like and further converting it into a resource are being seriously considered.

[0003] Regarding the method of turning carbon dioxide into a resource,
Until now, this has not been an active industrial issue. However, as mentioned above, this problem has begun to attract attention as a new technological issue, stemming from the recent global warming problem. The current major direction of resource recovery is a method of culturing plants, especially highly proliferative algae such as chlorella, under conditions of high carbon dioxide concentration. When using chlorella harvested in this way as a raw material, it is necessary to go through several more biochemical steps in order to use it as a raw material for the chemical industry. Resource recovery using biochemical methods is limited to low-level uses and is inappropriate for high-level uses.

Regarding methods for recycling carbon dioxide as a resource by chemical methods, reactions using several catalysts have been reported. For example, there is a process like this: 4H2+CO2→CH4+2H2O [Catalyst: Rh,
130-200℃]J. Molec. Catal. 8.
471 (1980) CO2+H2→CO+H2O [
Catalyst: Fe, 350°C] J. Catal. 67.90 (
1981) CO+3H2→CH4+H2O [Catalyst:
Ni, 177-437°C] J. Catal. 37.44
9 (1975)

These catalytic chemical methods have safety problems due to the direct involvement of relatively high-pressure hydrogen in the reaction system, and the resulting resource is gaseous methane, which poses problems in the chemical reaction process for subsequent use. There are drawbacks such as not being able to expect much diversity. In addition, there have been reports recently of cases in which CO, HCO2H (formic acid), CH4, methanol, etc. are produced by electrochemical reduction of carbon dioxide, but research is still ongoing. It is still at a stage, and the possibility of industrial use is not certain.

[0006]

[Problems to be Solved by the Invention] Therefore, the problems of this invention are to make it possible to recycle carbon dioxide as a resource with high efficiency, to have diversity in the use of the resulting recyclables, and to perform reactions during resource reclamation at low pressure and low temperature. The objective is to obtain a method for recycling carbon dioxide as a resource that is safe and allows for diversification of reaction types.

[0007]

[Means for Solving the Problems] This problem is solved by a method in which carbon dioxide is brought into contact with a hydrogen storage metal in a state in which hydrogen is stored, thereby converting it into methanol.

[0008] This invention will be explained in detail below. The basic structure of the present invention is to bring carbon dioxide into contact with a hydrogen storage metal that has stored hydrogen, and to convert carbon dioxide into methanol (CH3O).
H) and turn it into a resource. This conversion reaction is expressed as follows. CO2+6H→CH3OH+H2O

[0009] The hydrogen storage metal referred to in the present invention refers to a metal capable of storing hydrogen in an amount greater than the self-volume of the metal under the condition that the hydrogen pressure is 1 atm, and refers to a single metal or an alloy. As such, simple metals such as Pd (palladium) and Ti
(titanium) and V (vanadium) can be used. For alloys, Mg-Ni, Mg-Cu, Mg-Ce, Mg-La
Magnesium-based alloys such as Ca-Ni, Mitshumetal-Ca-Ni (Mishumetal is La, Ce, Pr
, a mixture of rare earth metals such as Nd), rare earth alloys such as La-Ni, misch metal-Ni, Ti-Fe, Ti-Co, Ti-Mn,
Titanium alloys such as Ti-Cr, Zr-Mn, Zr-V
Zirconium-based alloys such as V-Ti, vanadium-based alloys such as V-Ti, etc. are used. These hydrogen storage metals are 1
It can be used either as a species or as a mixture of two or more species in any proportion.

[0010] The applicability of these hydrogen storage metals to the present invention is determined by the fact that water is produced in parallel with methanol conversion, as shown in the above-mentioned carbon dioxide resource recovery chemical reaction, and the relationship between this water and metal is Determined by ease of reaction. Among the above-mentioned hydrogen storage metals, calcium-based metals tend to react with water, which limits the application of the present invention.

In the present invention, such a hydrogen storage metal is used in a state in which hydrogen is stored therein. Therefore, hydrogen must be stored in the hydrogen storage metal in advance. The manner in which the hydrogen storage metal is allowed to store hydrogen is basically arbitrary. For example, there is a method in which pressurized hydrogen is brought into contact with a hydrogen-absorbing metal to absorb it, a method in which water is electrolyzed using a hydrogen-absorbing metal as a cathode and the generated hydrogen is absorbed, or a method in which a mixed gas of hydrogen and carbon dioxide is brought into contact with each other. Any method may be selected, such as a method in which hydrogen storage and carbon dioxide methanol conversion reaction proceed in parallel. Since the reaction mechanism of the present invention is presumed to be that hydrogen stored in a hydrogen storage alloy reacts with carbon dioxide and is converted to methanol, any method or means may be used as long as this requirement is met. .

[0012] There are no particular limitations on the amount of hydrogen stored in the hydrogen storage metal. However, it has been observed that the larger the amount of absorbed hydrogen, the longer the methanol conversion reaction of carbon dioxide continues, and the larger the amount of methanol conversion per hour. Therefore, in order to obtain a desired conversion efficiency, it is effective to increase the concentration of occluded hydrogen.

[0013] The method of bringing the hydrogen-absorbing metal that has occluded hydrogen into contact with carbon dioxide is basically arbitrary. For example, any method such as contacting carbon dioxide in a gaseous state, contacting carbon dioxide dissolved in water or an organic or inorganic solvent, or contacting carbon dioxide liquefied by increasing pressure. Available. Furthermore, the pressure and temperature at which carbon dioxide and hydrogen-absorbing metal are brought into contact and converted into methanol are also arbitrary. The method of contacting at high pressure has the effect of increasing the concentration of carbon dioxide, but in order to proceed with the entire reaction in a gaseous state, conditions must be established that take into account the temperature at which the methanol produced becomes a gas. Alternatively, the reaction can be carried out at pressures and temperatures that turn carbon dioxide into a liquid. In this case, the generated methanol and unreacted carbon dioxide can be easily separated.

[0014] The reaction between occluded hydrogen and carbon dioxide is thought to proceed on the surface of the hydrogen-absorbing metal. Therefore, it is effective to increase the surface area of the hydrogen storage metal in terms of reaction efficiency. As a means for increasing the surface area, any of the following methods can be adopted: using the hydrogen storage metal as a powder, loading the hydrogen storage metal in the form of a fine powder onto a support that is normally carried out in a catalytic reaction, and using the hydrogen storage metal in the form of a thin film. Which one to adopt depends on the design of the carbon dioxide resource recovery plant. For example, a moving bed type plant can choose a powder type, while a fixed reactor type can use a thin film, with hydrogen placed on one side of a thin film of hydrogen storage metal and carbon dioxide on the other side. All you have to do is make it flow.

The carbon dioxide resource recovery method of the present invention is also characterized by high selectivity in methanol conversion. In the electrochemical reduction method currently under research, it is produced as a multicomponent mixture, as described above. Compared to these,
The composition after the reaction of the present invention is methanol and water, which are the main components of the reaction, as well as unreacted carbon dioxide and a small amount of hydrogen that cannot participate in the reaction and is released from the hydrogen storage metal. Therefore, it is easy to separate and recover recycled methanol, which has the advantage of requiring a simple separation system.

Examples of the present invention will be described below. (Example 1) As hydrogen storage metals, single metals of Pd, Ti, and V; as alloys, Mg2Cu, MmNi
5 (Mm is misch metal), LaNi5 and TiFe
A thin section (10 x 10 x 1 mm) was prepared. Similar flakes of Cu, Fe, and Ni were prepared for comparison. Each thin piece was heated for 100 minutes in a hydrogen atmosphere at a pressure of 10 kg/cm2.
Cycle treatment of 1 hour at °C and 1 hour at room temperature was repeated three times.
Pretreatment and hydrogen storage treatment were performed. Each metal flake with hydrogen storage treatment and P without hydrogen storage treatment
The thin slices of d and d were separately immersed in water in which carbon dioxide was saturated and dissolved in a glass container, and held at room temperature for 2 hours while flowing carbon dioxide into the upper space.

Each of the waters was analyzed by gas chromatography to confirm methanol and other components. Gas chromatography analyzes hydrogen, CO (carbon monoxide), and CH4 (methane) using an activated carbon column for component separation and a thermally conductive TCD as a detector.
and methanol, CH4, and other organic compounds were detected using a Porapak-Q column and an FID as a detector, respectively. The results were as shown in Table 1.

[0018]

[Table 1]

Gas chromatography analysis results for hydrogen storage metals subjected to hydrogen storage treatment are as follows: activated carbon column/TCD
Air components such as hydrogen, N2, O2, and CO2 were detected, but CO, CH4, etc. were not detected. Also, Por
Apak-Q/FID detected methanol, but
No organic compounds other than methanol were detected. Pd without hydrogen storage treatment and Cu with hydrogen storage treatment,
For Fe and Ni, methanol was not detected, and hydrogen was also not detected. In this way, in the present invention, carbon dioxide is converted into methanol and recycled.

(Example 2) Pd was used as the cathode, Pt was used as the anode, and 0.1M of KHCO was used as the electrolyte.
Electrochemical reduction of carbon dioxide was performed using an aqueous solution of 3 under conditions of -1.5V vs SCE. For analysis of electrochemical reaction products, gas chromatography was performed for those in gaseous form (gaseous organic compounds, CO and hydrogen) and those dissolved in the liquid. Analysis was performed every 2 hours after the start of electrolysis, and after 8 hours, the current was cut off and analysis was performed 2 hours later. What corresponds to the present invention is what happens after the current is cut off. The analysis results were as shown in Table 2.

[0021]

[Table 2]

As seen in the table above, -1.5V vs S
In the electrolysis of CE, methanol was not produced, but in addition to hydrogen, CO, HCO2H, and CH4 were produced. On the other hand, Pd, which has absorbed hydrogen after 8 hours of energization, produces methanol when the current is cut off.
CO, CH4, etc. are not generated. As can be seen from this example, the electrolysis in this example can be considered to be a process for causing Pd, which is a hydrogen storage metal, to store hydrogen.

(Example 3) Ti was used as the cathode, Pt was used as the anode, and 0.2 Mol. NaCl
1 at a current density of 1 mA/cm2 in O4 aqueous solution (PH3)
Hydrogen storage treatment was performed for 0 hours. After that, 0.1Mol
．． NaClO4 and 0.1Mol. For a solution (PH6) in which carbon dioxide is saturated in a phosphate buffer solution, the electrolysis voltage is set to -0.6V vs. Ag/AgCl.
Electrolysis was performed as follows. The generated components are methanol and hydrogen; expressed in terms of current efficiency, methanol is 59% and hydrogen is 41%.
Met. When a Ti electrode without hydrogen storage treatment was used as the cathode under the same electrolysis conditions, not only no methanol was generated, but also the current efficiency of hydrogen generation was about 60%. Electrolysis was further continued, and analysis was performed 10 hours later, and it was confirmed that methanol was produced. The former method, in which hydrogen storage treatment is performed in advance, is an example of a method in which carbon dioxide is converted to methanol while hydrogen is stored by electrolysis. The latter is a case where hydrogen storage treatment is not performed in advance, and is an example showing that the initial stage of electrolysis is a process corresponding to hydrogen storage treatment, and when a certain amount of hydrogen storage is reached, methanol is generated.

(Example 4) T with a specific surface area of 50 cm2/g
0.1Mol of i-sponge. After washing with an aqueous H2SO4 solution, the sample was brought into contact with hydrogen at a pressure of 20 kg/cm2 at room temperature for 10 hours to absorb hydrogen. This hydrogen-absorbing Ti sponge was brought into contact with carbon dioxide in various states, and the presence or absence of methanol production was analyzed by gas chromatography. The contact conditions were room temperature and 5 hours. The conditions for the contacting carbon dioxide were 2 kg of carbon dioxide saturated in pyridine.
Three types of carbon dioxide were tried: carbon dioxide gas at a pressure of /cm2 and carbon dioxide liquefied by pressurizing at 70 kg/cm2. In the case of a pyridine carbon dioxide solution, the solution was directly analyzed by gas chromatography. For those in contact with gaseous carbon dioxide, a small amount of benzene was added to dissolve methanol in benzene, and this was analyzed. In the case of liquefied carbon dioxide, the pressure was rapidly lowered and the residual liquid of solidified carbon dioxide produced by vaporization of carbon dioxide was analyzed. As a result of analysis, methanol was detected in all of them.

(Example 5) A polycarbonate/dimethylformamide solution was applied to an unglazed porous ceramic tube, and the tube was immersed in cold water to form a Loeb membrane having a maximum pore diameter of 1 mm or less. Approximately 0% LaNi5 was deposited on this film by sputtering.
．． It was coated to a thickness of 3 μm. The tube processed in this way corresponds to a model of a fixed reactor, and by placing pressurized hydrogen inside the tube and carbon dioxide outside the tube, continuous methanol conversion of carbon dioxide can be achieved. The hydrogen pressure inside the tube was 20 kg/cm2, and the tube was brought into contact with 1 atm of carbon dioxide at a temperature of 50° C., and the methanol concentration was checked at regular intervals. The concentration of methanol after 5 hours is 0.5
It was 8%. Although the increase in concentration over time showed a tendency to gradually decrease, the methanol concentration continued to increase even after 240 hours. When the hydrogen gas pressure inside the tube is lowered to 15 kg/cm2, the amount of methanol produced in the initial 5 hours is 0.
．． It was 40%. It is presumed that the decrease in hydrogen pressure inside the pipe reduced the stored hydrogen concentration.

[0026]

[Effects of the Invention] As explained above, according to the method of recycling carbon dioxide of the present invention, (1) carbon dioxide can be converted into methanol with high efficiency, so it can be used in the field of global environmental conservation and methanol is used as a raw material. Can contribute to the industrial field. (2) Since the carbon dioxide resource conversion product is methanol, which can be used in a variety of ways, it can contribute to industry as a new chemical raw material. (3) Since there is a variety of methods for converting carbon dioxide to methanol, plants can be designed to suit conditions and scale. (4) Basically, high temperature and high pressure are not required, and depending on the process design, hydrogen can be isolated, contributing to process safety. (5) Since carbon dioxide can be converted to methanol with high selectivity, the process can be simplified. Effects such as this can be obtained.

Claims (1)

[Claims] 1. A method for recycling carbon dioxide as a resource, which comprises bringing carbon dioxide into contact with a hydrogen storage metal in a state in which hydrogen is stored, thereby converting carbon dioxide into methanol.