Reactor

Abstract

To provide a technique of improving energy efficiency of reaction in a reactor.SOLUTION: A reactor that performs reductive reaction of carbon dioxide comprises: a reaction tank into which reaction substances reacting with carbon dioxide and carbon dioxide are supplied; and an infrared laser pulse irradiation part which irradiates the inside of the reaction tank with infrared laser pulse, where an infrared laser pulse generated from the infrared laser pulse irradiation part includes a wavelength corresponding to a vibration excitation wavelength of at least either one of carbon dioxide and reaction substances.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a reaction apparatus for reacting carbon dioxide.

Background Art

[0002] In recent years, various efforts have been made to reduce the emissions of carbon dioxide, which is considered to be the cause of global warming. For example, technologies for reducing the amount of carbon dioxide emitted into the atmosphere by reacting carbon dioxide with other substances are being studied.

[0003] For example, technologies for promoting the reduction reaction of carbon dioxide by vibrationally exciting carbon dioxide have been studied. Specifically, Patent Document 1 and Non-Patent Document 1 disclose technologies for vibrationally exciting carbon dioxide using plasma. Non-Patent Document 2 discloses that the bending vibration excitation of carbon dioxide drives the ER-type reaction on the copper surface.

[0004] In addition, technologies for promoting the reduction reaction of carbon dioxide by light irradiation have also been studied. Patent Document 2 discloses a technology for irradiating a photocatalyst in a reaction vessel with ultraviolet light contained in sunlight or the like, and reducing carbon dioxide with the generated photoexcited electrons. Patent Document 3 discloses a technology for heating and activating carbon dioxide and a carbon material as its reactant by irradiation with sunlight, and reducing carbon dioxide by irradiation with ultraviolet light. Patent Document 4 discloses a carbon dioxide reduction technology using a photocatalyst, in which carbon dioxide is vibrationally excited and the reduction reaction is promoted by irradiating continuous light of infrared laser light of 4.3 μm corresponding to the asymmetric stretching excitation of carbon dioxide. Non-Patent Document 3 discloses research on dissociating oxygen atoms from carbon dioxide molecules using the fundamental wave and the second harmonic wave of a titanium sapphire laser.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non - Patent Document

[0006]

Non - Patent Document 1

Non - Patent Document 2

Non - Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the technologies described in Patent Document 1 and Non - Patent Document 1, plasma is used for the vibrational excitation of carbon dioxide. To generate plasma, it is necessary to separate electrons from atoms by a high - voltage electric field, and the energy required for this is 1488 kJ / mol for hydrogen molecules and 52207 kJ / mol for carbon dioxide molecules. On the other hand, the energy required to dissociate an oxygen atom from a carbon dioxide molecule is 531.4 kJ / mol, and the energy required for plasma generation far exceeds the energy of the reaction.

[0008] Non - Patent Document 2 has been focused on elucidating the reaction mechanism and does not mention how to induce vibrational excitation.

[0009] In the technologies of Patent Document 2 and Patent Document 3, efficient and selective vibration excitation could not be caused, and there were problems with the energy efficiency in the reduction reaction of carbon dioxide. In the technology described in Patent Document 4, although excitation of molecular vibration occurred, there were almost no molecules reaching a high vibration state where the reaction occurred spontaneously, and reduction by a photocatalyst was required. In the technology described in Non-Patent Document 3, it was necessary to irradiate a high-intensity pulsed laser to cause the reduction reaction of carbon dioxide, which required a lot of energy.

[0010] The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a technique for improving the energy efficiency of a reaction in a reaction apparatus.

Means for Solving the Problems

[0011] The present disclosure has been made to solve at least a part of the above-described problems and can be realized in the following forms.

[0012] (1) According to one aspect of the present disclosure, there is provided a reaction apparatus in which a reduction reaction of carbon dioxide is carried out. This reaction apparatus includes a reactant that reacts with carbon dioxide, a reaction tank to which carbon dioxide is supplied, and an infrared laser pulse irradiation unit that irradiates an infrared laser pulse into the reaction tank. The infrared laser pulse generated from the infrared laser pulse irradiation unit includes a wavelength corresponding to the vibration excitation wavelength of at least one of carbon dioxide and the reactant.

[0013] According to this configuration, since the reaction tank is irradiated with coherent infrared light including a wavelength corresponding to the vibration excitation wavelength of at least one of carbon dioxide and the reactant, at least one of carbon dioxide and the reactant in the reaction tank can be vibrationally excited. Since molecules in a high vibration state have high reaction activity, the reduction reaction of carbon dioxide can be promoted.

[0014] In addition, since laser light is used, optical energy can be selectively injected into molecules. When a molecule is irradiated with light having a wavelength corresponding to the energy interval of the vibrational level, the molecule absorbs the optical energy and the vibrational state is excited. Since the energy of the vibrational level has a unique value for each molecular bond, by adjusting the wavelength of the laser, optical energy can be selectively injected only into specific molecular bonds involved in the reaction. When promoting the reduction reaction of carbon dioxide using heat or incoherent light, energy cannot be selectively injected as in the case of laser light. Therefore, according to the reaction apparatus of this configuration, the energy efficiency in the reduction reaction of carbon dioxide can be improved compared to the case of using heat or incoherent light.

[0015] In addition, by using laser light, at least one of carbon dioxide and the reactant can be brought into a high vibrational state that cannot be reached by the Boltzmann distribution, and high reaction activity can be imparted. Therefore, it becomes possible to cause a reduction reaction of carbon dioxide at a reaction rate exceeding the thermal limit. If the reaction activity is sufficiently high, the reaction can occur at room temperature without using a catalyst, so a high-temperature reactor is not required, and the apparatus can be miniaturized and the cost can be reduced. In addition, problems of reaction cyclicity due to catalyst deterioration such as poisoning and denaturation can be avoided.

[0016] (2) In the reaction apparatus of the above aspect, the infrared laser pulse generated from the infrared laser pulse irradiation unit may include light in a wavelength band of 500 cm -1 ~3800 cm -1 corresponding to at least one of symmetric stretching vibration excitation and asymmetric stretching vibration excitation of carbon dioxide. According to this configuration, since carbon dioxide can be excited to at least one of the symmetric stretching vibration state and the asymmetric stretching vibration state, the reduction reaction efficiency of carbon dioxide can be improved.

[0017] (3) The reaction apparatus of the above form, wherein the pulse width of the infrared laser pulse generated from the infrared laser pulse irradiation unit may be equal to or less than the mean free time at which the collision between carbon dioxide and the reactant occurs. By doing so, since one or more infrared laser pulses are included in the mean free time at which the collision between carbon dioxide and the reactant occurs, and the collision occurs in a state where at least one of carbon dioxide and the reactant is excited, the reaction efficiency of the reduction reaction of carbon dioxide can be improved.

[0018] (4) The reaction apparatus of the above form, wherein the infrared laser pulse irradiation unit is capable of generating three types of infrared laser pulses having different wavelengths from each other, and further includes a control unit that controls the infrared laser pulse irradiation unit to sequentially irradiate the three types of infrared laser pulses. The wave numbers of the three types of infrared laser pulses are respectively 1) 1600 cm corresponding to the asymmetric stretching vibration excitation of carbon dioxide -1 ~2800 cm -1 2) Carbon dioxide pair of Symmetric stretching vibration excitation and 500 cm corresponding to asymmetric stretching vibration excitation -1 ~1600 cm -1 3) Carbon dioxide pair of Symmetric stretching vibration excitation and 2800 cm corresponding to asymmetric stretching vibration excitation -1 ~3800 cm -1 It may be. By doing so, both the symmetric stretching vibration and the asymmetric stretching vibration of carbon dioxide are excited, and the reaction efficiency of the reduction reaction of carbon dioxide can be further improved.

[0019] (5) The reaction apparatus of the above form, further comprising a carbon dioxide supply unit connected to the reaction tank and supplying carbon dioxide to the reaction tank, and a reactant supply unit connected to the reaction tank and supplying the reactant to the reaction tank. The reaction apparatus having this configuration can also improve the reaction efficiency of the reduction reaction of carbon dioxide.

[0020] Note that the present disclosure can be realized in various modes, for example, in the form of a system including a reaction apparatus.

Brief Description of the Drawings

[0021]

Figure 1

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Embodiments for Carrying Out the Invention

[0022] <Embodiment> 1. Configuration of the reaction apparatus 1: Fig. 1 is a schematic diagram showing the schematic configuration of the reaction apparatus 1 of the embodiment. The reaction apparatus 1 of the present embodiment is an apparatus in which a reduction reaction of carbon dioxide (CO2) is carried out, and includes a reaction tank 10, an infrared laser pulse irradiation unit 20 that irradiates an infrared laser pulse into the reaction tank 10, a carbon dioxide supply unit 30 that supplies carbon dioxide to the reaction tank 10, and a reactant supply unit 40 that supplies a reactant to the reaction tank 10.

[0023] In the reaction tank 10, a reduction reaction of carbon dioxide is carried out inside. A carbon dioxide supply unit 30 is connected to the reaction tank 10, and carbon dioxide is supplied. At the same time, a reactant supply unit 40 is connected, and reactants are supplied. Further, a window portion 12 through which an infrared laser pulse IL can pass is formed in the reaction tank 10, and the infrared laser pulse IL is irradiated into the reaction tank 10 from the infrared laser pulse irradiation unit 20. In the present embodiment, as will be described later, since the infrared laser pulse IL having a wavelength for exciting carbon dioxide molecules is irradiated into the reaction tank 10, the carbon dioxide molecules supplied into the reaction tank 10 are excited and reduced by the reactants supplied into the reaction tank 10. It is preferable that there are no substances other than carbon dioxide and reactants in the reaction tank 10. In particular, it is preferable that there is no substance that absorbs light having a wavelength corresponding to the vibration excitation wavelength of carbon dioxide. This is because if a substance that absorbs light having a wavelength corresponding to the vibration excitation wavelength of carbon dioxide is present, the energy selectively injected into carbon dioxide will decrease. However, for example, homonuclear diatomic molecules such as nitrogen (N2) have no infrared activity and may be included. In the present embodiment, no catalyst is used either.

[0024] In the present embodiment, in the reaction tank 10, a reverse water gas shift reaction (CO2 + H2 → CO + H2O) is carried out as a reduction reaction of carbon dioxide. That is, hydrogen is used as a reactant. The product gas generated in the reaction tank 10 may be separated and stored respectively. For example, the configuration may be such that the CO gas is further reacted with hydrogen to generate a hydrocarbon gas. The configuration may also be such that H2O is reused to generate hydrogen gas by a water electrolysis device.

[0025] The infrared laser pulse irradiation unit 20 includes an optical system such as a laser light source, mirrors, lenses (not shown), and irradiates the infrared laser pulse IL into the reaction tank 10. The infrared laser pulse IL generated from the infrared laser pulse irradiation unit 20 includes wavelengths corresponding to the vibration excitation wavelengths of carbon dioxide. Here, the vibration excitation wavelength is the wavelength corresponding to the energy level difference of the vibration levels of the target molecule (carbon dioxide molecule in this embodiment). The infrared laser pulse is coherent light and is "light localized in time (photoclectric field concentrated in a short time)" in which both edges of the electric field waveform asymptotically approach zero. The signal light and idler light in difference frequency generation are also included in the laser light. The reason for using the infrared laser pulse IL is that in order to excite the molecule to a high-order vibration state where a chemical reaction occurs, it is necessary to concentrate the energy of light in an extremely short time, and it is necessary to complete the excitation before the energy dissipation due to vibration relaxation occurs.

[0026] In this embodiment, the infrared laser pulse IL irradiated from the infrared laser pulse irradiation unit 20 includes wavelengths corresponding to the vibration excitation wavelengths of carbon dioxide. Specifically, the infrared laser pulse IL includes light having wave numbers (reciprocals of wavelengths) corresponding to the following three types of vibration excitations. (1) 1600 cm -1 ~2800 cm -1 (2) 500 cm -1 ~1600 cm -1 (3) 2800 cm -1 ~3800 cm -1 The infrared laser pulse IL will be described in detail later.

[0027] The wavelength of the infrared laser pulse IL can be adjusted by a known method. In this embodiment, it is adjusted by difference frequency generation of two lasers.

[0028] The carbon dioxide supply unit 30 includes a carbon dioxide storage unit 32 that stores carbon dioxide, and a connection pipe 34 that connects the carbon dioxide storage unit 32 and the reaction tank 10, and supplies carbon dioxide to the reaction tank 10. The carbon dioxide supply unit 30 supplies, for example, carbon dioxide recovered from a gas containing carbon dioxide supplied from a "supply source" such as a combustion furnace or an internal combustion engine to the reaction tank 10. In the present embodiment, the carbon dioxide storage unit 32 is, for example, a high-pressure tank and stores carbon dioxide in a pressurized state. Note that the "supply source" is not limited to a combustion furnace or an internal combustion engine, and any device that generates a gas containing carbon dioxide may be used.

[0029] A carbon dioxide supply valve (not shown) is disposed in the connection pipe 34 and is electrically connected to the control unit 90. The opening degree of the carbon dioxide supply valve is controlled according to a command from the control unit 90. That is, the flow rate of carbon dioxide supplied from the carbon dioxide storage unit 32 to the reaction tank 10 is adjusted by the carbon dioxide supply valve.

[0030] The reactant supply unit 40 includes a reactant storage unit 42 that stores a reactant, and a connection pipe 44 that connects the reactant storage unit 42 and the reaction tank 10, and supplies the reactant to the reaction tank 10. In the present embodiment, as described above, the reactant is hydrogen. In the present embodiment, the reactant storage unit 42 is, for example, a high-pressure tank and stores hydrogen in a pressurized state. In other embodiments, for example, a water electrolysis device may be used instead of the reactant storage unit 42.

[0031] A hydrogen supply valve (not shown) is disposed in the connection pipe 44 and is electrically connected to the control unit 90. The opening degree of the hydrogen supply valve is controlled according to a command from the control unit 90. That is, the flow rate of hydrogen supplied from the reactant storage unit 42 to the reaction tank 10 is adjusted by the hydrogen supply valve.

[0032] The control unit 90 is a computer including a ROM, a RAM, and a CPU, and controls the entire reaction device 1. The control unit 90 controls the carbon dioxide supply unit 30 and the reactant supply unit 40 to control the supply of carbon dioxide and hydrogen by performing opening and closing control of the carbon dioxide supply valve and the hydrogen supply valve. Further, the control unit 90 controls the infrared laser pulse irradiation unit 20 to sequentially irradiate the above three types of infrared laser pulses IL. The control in the control unit 90 will be described later. The program for realizing the control performed by the control unit 90 is stored in the control unit 90 in advance. Further, the program may be provided from the program provider side via a communication network. Further, the program may be stored in a commercially available and distributed portable storage medium. In this case, this portable storage medium may be set in an external or built-in reading device, and the program may be read and executed by the control unit 90. As the portable storage medium, various types of storage media such as CD-ROM, DVD-ROM, flexible disk, optical disk, magneto-optical disk, IC card, and USB memory device can be used. The program stored in such a storage medium is read by a reading device.

[0033] 2. Infrared laser pulse IL: In the reaction device 1 of the present embodiment, the wavelength of the infrared laser pulse generated from the infrared laser pulse irradiation unit 20 is designed by the following method.

[0034] 2-1. Calculation and simulation for the carbon dioxide chemical reaction promotion method: In order to examine the influence of vibrational excitation in the reduction reaction of carbon dioxide (CO2), a simulation of the reduction process was performed by quantum dynamics calculation and first-principles molecular dynamics calculation. First, quantum dynamics calculations will be described. To perform quantum dynamics calculations, a potential energy surface (hereinafter also referred to as "PES": Potential Energy Surface) with the molecular degrees of freedom of carbon dioxide as the axis is required. Here, the PES with the two bond lengths of the C atom and the O atom as the axes was obtained by the quantum chemistry calculation program GAMESS (non-empirical molecular orbital method / density functional theory calculation program). The bending degree of freedom of CO2 was fixed at 180°, and the potential energy was calculated by changing the bond lengths of the two C=O bonds from 1.7 bohr to 3.1 bohr. Using cc-pVQZ as the basis function system, calculations were performed using a multi-reference theory with a complete active space composed of 12 molecular orbitals and 16 electrons derived from the 2s and 2p orbitals and electrons of the C atom and the O atom as a reference. For the obtained PES, the PES of the reduction reaction was simulated by adding an attractive potential (a potential that reduces the energy at the dissociation limit of the C=O bond (bond length 3.1 bohr) by 0.18 Hartree) that induces the reduction reaction to the PES. The simulation of the reduction reaction was carried out by calculating the time evolution of the quantum beam of CO2 on this PES. Using the quantum beam in the vibrationally excited state of CO2 as the initial state, the time-dependent Schrödinger equation was calculated by Suzuki-Trotter decomposition, and the dissociation probability of the O atom (the reduction probability of CO2) was obtained by calculating the probability density of the beam that reached the dissociation limit. As a result of the simulation, it was revealed that the dissociation reaction is more likely to occur in a state where the symmetric stretch is more excited. Also, when comparing states with the same quantum number of the symmetric stretch mode, it was revealed that the reaction is more likely to occur in a state where the asymmetric stretch is more excited.

[0035] Next, first-principles molecular dynamics calculations will be described. The reverse water-gas shift reaction (CO2 + H2 → CO + H2O) was targeted as the CO2 reduction reaction, and the reaction was simulated using the first-principles molecular dynamics calculation program TeraChem. Langevin dynamics at 1500 K and 2000 K was performed using the 6-31G basis function system and the B3LYP exchange-correlation functional, and the number of molecules reduced from CO2 to CO was counted. To investigate the effect of the vibrational excitation of CO2 on the ease of occurrence of the reduction reaction, simulations were performed starting from two initial states, the symmetric stretching excited state and the asymmetric stretching excited state, with a vibrational energy of 0.19 Hartree. As a result of the simulations, it was revealed that a higher CO conversion rate is obtained when the symmetric stretching is excited. From the above results, it became clear that symmetric stretching excitation is more important than asymmetric stretching excitation for promoting the CO2 reduction reaction.

[0036] 2-2. Design of infrared laser pulses: As described above, from the results of quantum dynamics calculations and first-principles molecular dynamics calculations, it became clear that symmetric stretching excitation is more important than asymmetric stretching excitation for promoting the CO2 reduction reaction. An infrared laser pulse for designing such a vibrational excited state was designed using quantum optimal control theory. As the physical quantity for the optimal control, the linear sum 0.8·NSS + 0.2·NAS (NSS: quantum number of symmetric stretching vibration, NAS: quantum number of asymmetric stretching vibration) of the quantum numbers of each vibrational mode included in the quantum beam of CO2 after infrared laser pulse irradiation was adopted. By weighting so that the coefficient of the quantum number of symmetric stretching becomes larger, symmetric stretching excitation was emphasized more.

[0037] FIG. 2 is a diagram showing the waveform of the infrared laser pulse obtained by the above-described quantum optimal control theory. FIG. 3 is a diagram showing the time-dependent spectrum of the infrared laser pulse shown in FIG. 2. As shown by the color bar representing the relationship between the shading and the electric field strength in FIG. 3, the whiter the area, the stronger the intensity of the light of that wave number (amplitude of the optical electric field). FIG. 4 is a diagram showing the amplitude spectrum intensity (electric field spectrum) of the infrared laser pulse shown in FIG. 2. From the electric field spectrum shown in FIG. 4, it can be seen that the infrared laser pulse contains light of three wave numbers (reciprocals of wavelengths) corresponding to three types of vibrational excitations. Also, from the time-dependent spectrum shown in FIG. 3, after initially exciting the asymmetric vibration with the light of (2) above (wave number: 500 cm -1 ~1600 cm -1 ), simultaneous irradiation with the light of (1) (wave number: 1600 cm -1 ~2800 cm -1 ), the light of (2) (wave number: 500 cm -1 ~1600 cm -1 ), and the light of (3) (wave number: 2800 cm -1 ~3800 cm -1 ) causes symmetric vibration excitation and asymmetric vibration excitation. In the reaction apparatus 1 of the present embodiment, by controlling the infrared laser pulse irradiation unit 20 by the control unit 90, three types of infrared laser pulses are generated in order as shown in FIG. 3, and the infrared laser pulse shown in FIG. 2 is irradiated into the reaction tank 10. By irradiating this infrared laser pulse onto CO2, the vibrational excitation state of CO2 is realized, and the reduction reaction is promoted.

[0038] In FIG. 4, the three types of light contained in the infrared laser pulse are the light of (1) (wave number: 1600 cm -1 ~2800 cm -1 ), the light of (2) (wave number: 500 cm -1 ~1600 cm -1 ), and the light of (3) (wave number: 2800 cm -1 ~3800 cm -1) are indicated by numbers in parentheses. By irradiating the light of (1), the vibration state of the CO2 molecule is excited to a state where the asymmetric vibration quantum number NAS increases by 1. By irradiating the light of (2), the vibration state of the CO2 molecule is excited to a state where the symmetric vibration quantum number NSS increases by 1 and the asymmetric vibration quantum number NAS decreases by 1 (de-excitation for the asymmetric stretching motion). By irradiating the light of (3), the vibration state of the CO2 molecule can be excited to a state where the symmetric vibration quantum number NSS is 1 and the asymmetric vibration quantum number NAS increases by 1. Here, the symmetric vibration quantum number NSS and the asymmetric vibration quantum number NAS are numbers representing the intensity of the symmetric stretching motion and the asymmetric stretching motion, respectively (the larger the number, the more intense the motion).

[0039] The pulse width of the infrared laser pulse shown in FIG. 2 is 2.00 [ps], which is less than the mean free time (tens to hundreds of [ps] at 1 atm and 300 K (room temperature)) at which collisions between carbon dioxide and the reactant (hydrogen) occur. Therefore, since the mean free time at which collisions between carbon dioxide and the reactant occur contains one or more infrared laser pulses and collisions between carbon dioxide and hydrogen occur in the excited state of carbon dioxide, the reaction efficiency of the reduction reaction of carbon dioxide can be improved. Note that since the mean free time of hydrogen gas at 1 atm and 300 K (room temperature) is 69 ps, the mean free time of carbon dioxide gas is 118 ps, and the single gas systems of other molecules are also on the order of tens to hundreds of ps, the mean free time of the mixed gas system of carbon dioxide and hydrogen was estimated to be about tens to hundreds of ps. A pulse width of 2 ps is considered to be sufficiently shorter than the time scale at which such molecules collide with each other.

[0040] 3. Comparison with thermal excitation and incoherent optical excitation: The infrared laser pulse used in the reactor 1 of the present embodiment was compared with the vibrational excitation of CO2 molecules by heat and incoherent light in order to confirm the superiority of the infrared laser pulse (coherent light) designed by the above-described quantum optimal control. The vibrational excitation by coherent light was obtained by performing a quantum dynamics simulation of CO2 under infrared laser pulse irradiation. Regarding thermal excitation, it was obtained by determining the occupancy of each vibrational level from 300 K (room temperature) to 2000 K based on the Boltzmann distribution. Regarding incoherent light excitation, pseudo-incoherent light was generated by randomizing the phase of each frequency component of the coherent light, and the average of the quantum dynamics simulation results by a plurality of pseudo-incoherent lights was taken.

[0041] FIG. 5 is a diagram showing the occupancy of the vibrational levels of CO2 molecules after excitation by an infrared laser pulse (coherent light), FIG. 6 is a diagram showing the occupancy of the vibrational levels of CO2 molecules after thermal excitation (2000 K), and FIG. 7 shows the occupancy of the vibrational levels of CO2 molecules after incoherent light excitation. In FIGS. 5 to 7, the darker the color of the level, the higher the occupancy (excited to that state). Also, in FIGS. 5 to 7, it is shown that the vibration of the symmetric vibration increases as it goes to the right of the drawing, and the vibration of the asymmetric stretch increases as it goes up on the drawing.

[0042] As shown in FIG. 5, looking at the occupancy after irradiation with coherent light (the infrared laser pulse of the present embodiment), it can be seen that both the symmetric stretch and the asymmetric stretch are excited to higher vibrational states. When a reactant approaches such a CO2 molecule that is vibrating violently in symmetric / asymmetric stretching and an attractive potential acts, it is expected that the dissociation of oxygen atoms (reduction reaction) will occur quickly.

[0043] On the one hand, looking at the results of thermal excitation at 2000K shown in Fig. 6, it can be seen that although there is slight vibrational excitation, most of the molecules remain in the ground state. In the conventional reaction control method of promoting chemical reactions by raising the temperature of the system, there is a thermal equilibrium limit determined by the Boltzmann distribution. By irradiating with infrared laser pulses as in this embodiment to put the molecules out of the thermal equilibrium state, that is, into a non-equilibrium state, it is expected that a reaction rate exceeding the thermal equilibrium limit can be realized (Fig. 5).

[0044] Also, looking at the results of incoherent light excitation shown in Fig. 7, although the number is smaller compared to the case of coherent light (Fig. 5), the molecules are excited to higher vibrational levels than in the case of thermal excitation (Fig. 6). However, in incoherent light excitation, even when excited to vibrational levels, most are in the asymmetric stretching excitation state, and symmetric stretching excitation hardly occurs. When a reactant approaches such vibrationally excited CO2 molecules, it takes time for the dissociation of oxygen atoms (reduction reaction). Since the approach (collision) of the reactant occurs on a fast time scale, the fact that it takes time for dissociation means that the reduction reaction is difficult to occur.

[0045] As described above, the generated incoherent light has the same spectral intensity as the coherent light (the infrared laser pulse of this embodiment), so it contains light of the wavelength required for vibrational excitation. However, due to the randomization of the phase of the light, it cannot efficiently excite to higher vibrational levels like coherent light. Also, incoherent light is a collection of light with random phases, and since the aspects of vibrational excitation by each random-phase light are not equal, selective excitation to the target vibrational state cannot be realized. That is, although the light from a high-temperature heat source or an incandescent lamp also contains infrared light of the wavelength corresponding to the vibrational excitation of CO2 molecules, since these lights are incoherent light with non-uniform phases, selective vibrational excitation as in the case of using coherent light cannot be realized.

[0046] Also, here, as pseudo-incoherent light, light in which only the phase is randomized while the spectral intensity of the coherent light is left unchanged was used. However, originally, incoherent light does not have a narrow-linewidth spectrum like coherent light, but has a broad spectrum with a wide wavelength distribution. Even if the wavelength band of the incoherent light can be controlled to some extent by temperature control of the heat source or the like, since the wavelength band cannot be concentrated on the vibration excitation wavelength of the molecule, there are components of light that are not absorbed by the molecule. Therefore, incoherent light excitation is inferior in energy efficiency compared to coherent light excitation such as that of a laser. By using coherent light generated by an infrared laser as infrared light, it becomes possible to efficiently and selectively excite to a high vibrational state.

[0047] Typical CO2 reduction reactions such as the reverse water-gas shift reaction and the Sabatier reaction have conventionally been carried out using a catalyst in a high-temperature environment of several hundred degrees Celsius. Heat and the catalyst play a role in increasing the Boltzmann factor that determines the reaction rate in the thermal equilibrium process. In order to achieve a reaction rate and energy efficiency that surpass such conventional thermochemical reaction methods, it is necessary to deviate from the thermal equilibrium process. That is, by bringing the reactants into a non-equilibrium state that deviates from the thermal equilibrium state, there is a possibility of realizing a reaction rate that exceeds the thermal equilibrium limit. In this embodiment, the reduction reaction of CO2 is promoted by irradiating an infrared laser pulse onto CO2 and the reactant. The advantage of using laser light is that efficient and selective energy injection into molecules is possible. When a molecule is irradiated with light (infrared light) having a wavelength corresponding to the energy interval between vibrational levels, the molecule absorbs the light energy and the vibrational state is excited. Since the energy of the vibrational levels has unique values for each molecular bond, by adjusting the wavelength of the laser, it is possible to selectively inject light energy only into specific molecular bonds involved in the reaction. In the case of heat, due to the equipartition law of energy, thermal energy is evenly distributed among all degrees of freedom of molecular motion, so selective energy injection like laser light is impossible and the energy efficiency is inferior. Also, even in a non-equilibrium process using light, when incoherent light is used, since the wavelengths and phases of the light are not aligned, selective energy input like laser light cannot be realized. Molecules that reach a high vibrational state that cannot be reached in the Boltzmann distribution by laser light have high reaction activity and can cause a CO2 reaction at a reaction rate that exceeds the thermal limit. If the reaction activity is sufficiently high, the reaction can occur at room temperature without using a catalyst, eliminating the need for a high-temperature reactor and avoiding problems with the cyclicity of the reaction caused by catalyst deterioration such as poisoning and denaturation.

[0048] As described above, according to the reaction apparatus 1 of the present embodiment, since the infrared laser pulse irradiation unit 20 that irradiates the infrared laser pulse IL including the wavelength corresponding to the vibration excitation wavelength of the carbon dioxide molecule is provided in the reaction tank 10 to which carbon dioxide and hydrogen as a reactant are supplied, the carbon dioxide molecule can be brought into a high vibration state, and the reduction reaction of carbon dioxide can be promoted.

[0049] That is, in the reaction apparatus 1, infrared laser light is used for vibration excitation of carbon dioxide molecules, and in this process, since it does not involve electron excitation that requires a large amount of energy such as plasma generation, compared with the case of using plasma for vibration excitation of carbon dioxide molecules (for example, the techniques described in Patent Document 1 and Non-Patent Document 1), it is possible to promote the reaction with energy saving.

[0050] The reaction apparatus 1 uses a technique of causing a chemical reaction by exciting molecular vibration by irradiating infrared laser light, and since it does not require a photocatalyst that serves as a supply source of electrons necessary for reduction as in Patent Document 2, it is possible to avoid the problem of catalyst deterioration.

[0051] Further, for example, in the technique described in Patent Document 3, carbon dioxide is heated and activated using incoherent light with wavelengths and phases that are not aligned, such as sunlight, and it is not possible to cause efficient and selective vibration excitation of carbon dioxide molecules, so reduction by ultraviolet light is required in the subsequent stage. On the other hand, in the reaction apparatus 1, since laser light, which is coherent light as infrared light, is used, light energy can be injected efficiently and selectively, and it can be excited to a high vibration state where the reaction occurs spontaneously. Therefore, since the subsequent reduction step by ultraviolet light in the technique of Patent Document 3 is not required, the energy efficiency of the reaction can be improved.

[0052] In addition, in the reaction apparatus 1, since laser light, which is coherent light as infrared light, is used, energy can be selectively injected as compared with the case of promoting the reduction reaction of carbon dioxide using heat or incoherent light, and the energy efficiency in the reduction reaction of carbon dioxide can be improved as compared with the case of using heat or incoherent light.

[0053] Also, for example, in the technique described in Patent Document 4, carbon dioxide molecules are vibrationally excited using continuous light of infrared laser light. Although the excitation of molecular vibration occurs, there are almost no molecules that reach a high vibration state where the reaction occurs spontaneously. Therefore, reduction by a photocatalyst is required in the technique of Patent Document 4. On the other hand, since the reaction apparatus 1 uses a pulsed laser, the energy of light can be concentrated in a short time, and a high vibration state of carbon dioxide molecules can be achieved. As a result, reduction by a photocatalyst can be made unnecessary.

[0054] Also, for example, the technique of Non-Patent Document 3 is a study on dissociating oxygen atoms from carbon dioxide molecules by irradiation with a pulsed laser, and the fundamental wave and the second harmonic of a titanium sapphire laser are used as the pulsed laser. Since this wavelength does not correspond to the vibration excitation wavelength of carbon dioxide molecules, the absorbance for the molecules is not large. Therefore, it is necessary to irradiate with a high-intensity pulsed laser to cause a reaction, which requires a large amount of energy, so there is a problem with energy efficiency. On the other hand, since the reaction apparatus 1 of the present embodiment uses infrared laser light corresponding to the vibration excitation of carbon dioxide molecules, it is possible to efficiently inject energy into the molecules, so it is possible to cause a reduction reaction with a relatively low-intensity laser, and the energy efficiency can be improved.

[0055] That is, according to the reaction apparatus 1 of the present embodiment, by irradiating infrared pulsed laser light having a wavelength corresponding to vibration excitation, it is possible to excite carbon dioxide molecules to a high vibration state so that a reaction occurs spontaneously, and a photocatalyst or ultraviolet light irradiation is not required to cause the reaction. As a result, it is possible to provide a reaction apparatus excellent in the energy efficiency of the reaction, cost savings, and space savings of the apparatus. In addition, by avoiding the problem of catalyst deterioration, it is possible to improve the cycle performance of the reaction.

[0056] In the reaction apparatus 1 of the present embodiment, the infrared laser pulse irradiation unit 20 can generate three types of infrared laser pulses having different wavelengths, and the wave numbers of the three types of infrared laser pulses are, respectively, 1) 1600 cm corresponding to the asymmetric stretching vibration excitation of carbon dioxide -1 ~2800 cm -1 , 2) carbon dioxide pair of corresponding to symmetric stretching vibration excitation and asymmetric stretching vibration excitation 500 cm -1 ~1600 cm -1 , 3) carbon dioxide pair of corresponding to symmetric stretching vibration excitation and asymmetric stretching vibration excitation 2800 cm -1 ~3800 cm -1 . As described above, by irradiating these three types of infrared laser pulses into the reaction tank 10 by the control unit 90, it is possible to efficiently generate a state in which the symmetric / asymmetric stretching motion that most promotes the reduction reaction is simultaneously excited. As a result, the reaction efficiency of the reduction reaction of carbon dioxide can be improved.

[0057] <Modification Example of the Present Embodiment> The present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

[0058] ·In the above embodiment, the reverse water gas shift reaction (CO2 + H2 → CO + H2O) was exemplified as the reduction reaction of carbon dioxide. However, the reduction reaction of carbon dioxide in the reaction tank is not limited to the above embodiment, and various carbon dioxide reduction reactions can be carried out. For example, the following carbon dioxide reduction reactions may be carried out. (Example 1) Reaction with hydrogen (Sabatier reaction): CO2 + 4H2 → CH4 + 2H2O (Example 2) Reaction with methane: CO2 + CH4 → 2CO + 2H2 (Example 3) Reaction with water (water splitting + CO2 reduction): CO2 + H2O → CO + H2 + O2 (Example 4) Direct alcohol synthesis from CO2 (methanol: CO2 + 3H2 → CH3OH + H2O, ethanol: 2CO2 + 6H2 → C2H5OH + 3H2O) (Example 5) Fischer-Tropsch reaction via the reverse water gas shift reaction (CO2 + H2 → CO + H2O) (nCO + 2nH2 → (CH2) n + nH2O) According to each reduction reaction, the internal pressure of the reaction tank may be increased or a catalyst may be used.

[0059] ·In the above embodiment, an example of vibrationally exciting CO2 by infrared laser pulse irradiation was shown. However, a substance (reactant) that reacts with CO2 may be vibrationally excited by infrared laser pulse irradiation, or both CO2 and the reactant may be vibrationally excited. By vibrationally exciting both CO2 and the reactant, the reactivity can be further improved. Among the reactants of the above CO2 reduction reaction, hydrogen is a homonuclear diatomic molecule and thus has no infrared light absorption, while methane and water molecules have infrared absorption.

[0060] FIG. 8 is a diagram showing the infrared absorption spectra of carbon dioxide and reactants. FIG. 8(A) shows the infrared absorption spectrum of carbon dioxide (gas), FIG. 8(B) shows the infrared absorption spectrum of methane (gas), and FIG. 8(C) shows the infrared absorption spectrum of water (gas). In addition to the vibration excitation wavelength of CO2, by irradiating infrared laser light having the infrared absorption wavelength of the reactant, both CO2 and the reactant can be vibrationally excited, and the reaction may be promoted more than when only one of them is vibrationally excited. Note that even for homonuclear diatomic molecules such as hydrogen, vibrational excitation can be caused by using the induced Raman process by irradiating laser light of two kinds of wavelengths.

[0061] That is, the wavelength of the infrared laser pulse is not limited to the above-described embodiment, and may include a wavelength corresponding to the vibration excitation wavelength of the target molecule to be vibrationally excited. For example, when the reduction reaction of the above (Example 2) is performed in the reaction tank 10 and methane is vibrationally excited, the infrared laser pulse has a wavenumber of 1200 cm -1 ~1400 cm -1 of light and a wavenumber of 2800 cm -1 ~3200 cm -1 of light. Further, for example, when the reduction reaction of the above (Example 3) is performed in the reaction tank 10 and water is vibrationally excited, the infrared laser pulse has a wavenumber of 1300 cm -1 ~2000 cm -1 of light and a wavenumber of 3400 cm -1 ~4000 cm -1 of light.

[0062] ·In the above embodiment, an example in which the pulse width of the infrared laser pulse is equal to or less than the mean free time at which the collision between carbon dioxide and the reactant (hydrogen) occurs is shown. However, the pulse width of the infrared laser pulse may be larger than the mean free time at which the collision between carbon dioxide and the reactant occurs. Even in this case, the promoting effect of the reduction reaction can be obtained by the vibrational excitation of the carbon dioxide molecule. However, it is preferable that the pulse width of the infrared laser pulse is equal to or less than the mean free time at which the collision between carbon dioxide and the reactant occurs because the reduction reaction is further promoted.

[0063] ·In the above embodiment, the infrared laser pulse irradiation unit 20 can generate three types of infrared laser pulses having different wavelengths, and the wave numbers of the three types of infrared laser pulses are respectively 1) 1600 cm corresponding to the asymmetric stretching vibration excitation of carbon dioxide -1 ~2800 cm -1 , 2) carbon dioxide pair of symmetric stretching vibration excitation and asymmetric stretching vibration excitation corresponding to 500 cm -1 ~1600 cm -1 , 3) carbon dioxide pair of symmetric stretching vibration excitation and asymmetric stretching vibration excitation corresponding to 2800 cm -1 ~3800 cm -1 are shown as examples. However, the infrared laser pulses irradiated from the infrared laser pulse irradiation unit 20 are not limited to three types, and may be one type, two types, or four or more types. For example, the wave number of the infrared laser pulse may be only 1600 cm -1 ~2800 cm -1 corresponding to the asymmetric stretching excitation of carbon dioxide molecules, or may be only 2800 cm -1 ~3800 cm -1 corresponding to symmetric and asymmetric stretching excitations. Also, for example, it may be two types including both of them.

[0064] ·In the above embodiment, the reaction apparatus 1 is exemplified as having a configuration including a control unit 90 that controls the infrared laser pulse irradiation unit 20 to sequentially irradiate three types of infrared laser pulses. However, the reaction apparatus may be configured without the control unit 90. For example, as described above, in the case of a configuration that irradiates one type of infrared laser pulse, it may be configured such that the infrared laser pulse is irradiated by turning on a switch. Also, when irradiating two or more types of infrared laser pulses, it may be configured to irradiate them simultaneously. Further, the control unit may be configured to sequentially irradiate two types or four or more types of infrared laser pulses.

[0065] ·In the above-described embodiment, the reaction apparatus 1 is exemplified as having a carbon dioxide supply unit 30 and a reactant supply unit 40. However, the reaction apparatus may not include the carbon dioxide supply unit 30 and the reactant supply unit 40. For example, an external carbon dioxide supply apparatus and a reactant supply apparatus may be connected to the reaction apparatus.

[0066] ·In each of the above embodiments, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced with hardware. Further, when a part or all of the functions of the present disclosure are realized by software, the software (computer program) can be provided in a form stored in a computer-readable recording medium. The "computer-readable recording medium" includes not only portable recording media such as flexible disks and CD-ROMs, but also various internal storage devices in a computer such as various RAMs and ROMs, and external storage devices fixed to a computer such as hard disks. That is, the "computer-readable recording medium" has a broad meaning including any recording medium capable of fixedly storing data packets, not temporarily.

[0067] As described above, the present aspect has been described based on the embodiments and modified examples. However, the embodiments of the above-described aspects are for facilitating the understanding of the present aspect and do not limit the present aspect. The present aspect can be changed and improved without departing from its gist and the scope of the claims, and equivalents thereof are included in the present aspect. Further, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

[0068] The present disclosure can also be realized as the following application examples. [Application Example 1] A reaction apparatus in which a reduction reaction of carbon dioxide is carried out, a reactant that reacts with carbon dioxide, and a reaction tank to which carbon dioxide is supplied, an infrared laser pulse irradiation unit that irradiates an infrared laser pulse into the reaction tank, comprising The infrared laser pulse generated from the infrared laser pulse irradiation unit includes a wavelength corresponding to at least one of the vibration excitation wavelengths of carbon dioxide and the reactant. Reaction apparatus. [Application Example 2] The reaction apparatus according to Application Example 1, The infrared laser pulse generated from the infrared laser pulse irradiation unit is Light in the wavelength band of 500 cm -1 ~3800 cm -1 corresponding to at least one of the symmetric stretching vibration excitation and the asymmetric stretching vibration excitation of carbon dioxide. Reaction apparatus. [Application Example 3] The reaction apparatus according to Application Example 1 or Application Example 2, The pulse width of the infrared laser pulse generated from the infrared laser pulse irradiation unit is equal to or less than the mean free time at which the collision between carbon dioxide and the reactant occurs. Reaction apparatus. [Application Example 4] The reaction apparatus according to any one of Application Examples 1 to 3, The infrared laser pulse irradiation unit is capable of generating three kinds of infrared laser pulses having different wavelengths from each other. Furthermore, The apparatus includes a control unit that controls the infrared laser pulse irradiation unit to sequentially irradiate the three kinds of infrared laser pulses. The wave numbers of the three kinds of infrared laser pulses are respectively 1) 1600 cm corresponding to the asymmetric stretching vibration excitation of carbon dioxide -1 ~2800 cm -1 2) 500 cm corresponding to the asymmetric stretching vibration excitation and the asymmetric stretching vibration excitation of carbon dioxide -1 ~1600 cm -1 3) 2800 cm corresponding to the asymmetric stretching vibration excitation and the asymmetric stretching vibration excitation of carbon dioxide -1 ~3800 cm -1 as follows. Reactor [Application Example 5] The reactor according to any one of Application Examples 1 to 4, furthermore, a carbon dioxide supply unit connected to the reaction tank and supplying carbon dioxide to the reaction tank, a reactant supply unit connected to the reaction tank and supplying the reactant to the reaction tank, comprising Reactor

Explanation of Reference Numerals

[0069] 1... Reactor 10... Reaction tank 12... Window portion 20... Infrared laser pulse irradiation unit 30... Carbon dioxide supply unit 32... Carbon dioxide storage unit 34... Connecting pipe 40... Reactant supply unit 42... Reactant storage unit 44... Connecting pipe 90... Control unit

Claims

1. A reaction apparatus in which a reduction reaction of carbon dioxide is carried out, a reaction vessel to which a reactant that reacts with carbon dioxide and carbon dioxide are supplied, an infrared laser pulse irradiation unit that irradiates an infrared laser pulse into the reaction vessel, comprising: the infrared laser pulse generated from the infrared laser pulse irradiation unit includes a wavelength corresponding to at least one of the vibration excitation wavelengths of carbon dioxide and the reactant, the pulse width of the infrared laser pulse generated from the infrared laser pulse irradiation unit is equal to or less than the mean free time at which a collision between carbon dioxide and the reactant occurs, a reaction apparatus.

2. The reaction apparatus according to claim 1, wherein the infrared laser pulse generated from the infrared laser pulse irradiation unit is Light in the wavelength band of 500 cm -1 to 3800 cm -1 including light corresponding to at least one of symmetric stretching vibration excitation and asymmetric stretching vibration excitation of carbon dioxide a reaction apparatus.

3. The reaction apparatus according to claim 1, wherein the infrared laser pulse irradiation unit is capable of generating three types of infrared laser pulses having different wavelengths from each other, furthermore, it comprises a control unit that controls the infrared laser pulse irradiation unit to sequentially irradiate the three types of infrared laser pulses, the wave numbers of the three types of infrared laser pulses are respectively 1) 1600 cm corresponding to the asymmetric stretching vibration excitation of carbon dioxide -1 ~2800 cm -1 2) 500 cm corresponding to symmetric stretching vibration excitation and asymmetric stretching vibration excitation of carbon dioxide -1 ~1600 cm -1 3) 2800 cm corresponding to symmetric stretching vibration excitation and asymmetric stretching vibration excitation of carbon dioxide -1 ~3800 cm -1 as follows, a reaction apparatus.

4. The reaction apparatus according to any one of claims 1 to 3, furthermore, a carbon dioxide supply unit connected to the reaction vessel and supplying carbon dioxide to the reaction vessel, a reactant supply unit connected to the reaction vessel and supplying the reactant to the reaction vessel, comprising: a reaction apparatus.

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