Synthesis method and synthesis device of hydrocarbon

Abstract

To provide a method and a device for efficiently producing hydrocarbon through a photocatalyst with respect to water in which oxygen and carbon dioxide are dissolved.SOLUTION: A synthesis method and a synthesis device of hydrocarbon HC for reducing carbon dioxide and water W into carbon monoxide and hydrogen through a photocatalyst in water in which carbon dioxide and oxygen are dissolved, and synthesizing the hydrocarbon HC by chemical reaction of the carbon monoxide and the hydrogen through the photocatalyst. The synthesis method and the synthesis device of the hydrocarbon HC achieves the problem solution by bringing an upper side interface in a layer of the hydrocarbon HC produced in an upper side region of the water W into contact with air A containing carbon dioxide of adjustable concentration.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention is directed to a method and apparatus for reducing carbon dioxide and water to carbon monoxide and hydrogen in water via a photocatalyst, and synthesizing hydrocarbons by chemical reaction of the carbon monoxide with the hydrogen via the photocatalyst. [Background technology]

[0002] The synthesis of hydrocarbons by reducing carbon dioxide in water has already been proposed in the prior art.

[0003] For example, Patent Document 1 proposes a method of producing hydrocarbons by supplying oxygen to water containing carbon dioxide in a photoelectrochemical cell and reducing the carbon dioxide (page 81, lines 4-21).

[0004] That is, the photocatalyst in Patent Document 1 is premised on a photoelectrochemical cell, and on the premise that fuel is produced from hydrocarbons or the like at the cathode (Claims 2, 77, 79).

[0005] Therefore, in Patent Document 1, reduction of carbon dioxide and water by pure photocatalysis is not realized. In fact, in Patent Document 1, activation of oxygen by irradiating water with ultraviolet light is not achieved (in this respect, it is clearly different from Patent Document 2).

[0006] As shown in Patent Document 2, the inventors of the present application have proposed a method and apparatus for producing hydrocarbons, which is premised on supplying oxygen to water containing dissolved carbon dioxide and generating oxygen nanobubbles, and reducing the carbon dioxide and water to carbon monoxide and hydrogen via a photocatalyst in the presence of active oxygen generated from the nanobubbles by irradiation with ultraviolet light.

[0007] However, in the case of Patent Document 2, the configuration is not necessarily simple in that the photocatalyst requires the generation of oxygen nanobubbles and the generation of active oxygen by irradiation with ultraviolet rays.

[0008] In Patent Documents 1 and 2, when hydrocarbons are produced via a photocatalyst, a layer of hydrocarbons is produced in an upper region above water.

[0009] In such a case, contact with the air above containing carbon dioxide is realized, and in this case, the reduction efficiency of carbon dioxide in the water depends on the concentration of carbon dioxide gas contained in the air.

[0010] However, in the conventional technologies such as those disclosed in Patent Documents 1 and 2, the basic idea of ​​efficiently producing hydrocarbons by adjusting the concentration of carbon dioxide gas in the air that comes into contact with the upper interface where the hydrocarbons are present is not proposed at all. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] WO2010 / 042196 A1 [Patent Document 2] Patent No. 6440742 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to provide a method and apparatus for efficiently producing hydrocarbons via photocatalysis of water having dissolved oxygen and carbon dioxide. [Means for solving the problem]

[0013] In order to solve the above problems, the basic configuration of the present invention is as follows: (1) A method for synthesizing hydrocarbons by reducing carbon dioxide and water to carbon monoxide and hydrogen via a photocatalyst in water containing dissolved carbon dioxide and oxygen, and then chemically reacting the carbon monoxide with the hydrogen via the photocatalyst, the method comprising contacting an upper interface of a layer of hydrocarbons produced in an area above the water with air containing carbon dioxide at an adjustable concentration; (2) A hydrocarbon synthesis apparatus which reduces carbon dioxide and water to carbon monoxide and hydrogen in water via a photocatalyst, and further synthesizes hydrocarbons by a chemical reaction between the carbon monoxide and hydrogen via the photocatalyst, the hydrocarbon synthesis apparatus comprising a reaction vessel for accommodating water in which carbon dioxide and oxygen are dissolved, a photocatalytic means in the reaction vessel, a carbon dioxide supply device above the reaction vessel, and an apparatus for adjusting the amount of carbon dioxide discharged from an outlet of the reaction vessel; It consists of: Effect of the Invention

[0014] By using the method of the basic configuration (1) and the apparatus of the basic configuration (2), the concentration of carbon dioxide in the air layer in contact with the upper interface of the layer of hydrocarbons produced in the region above the water in the reaction tank can be adjusted, and an appropriate concentration can be selected, thereby enabling efficient reduction of carbon dioxide and efficient production of hydrocarbons.

[0015] Moreover, the method of basic configuration (1) and the device of basic configuration (2) are extremely simple compared to the configuration employing electrodes in Patent Document 1, and can obtain hydrocarbon fuel purely through a photocatalytic reaction without requiring the application of voltage.

[0016] Furthermore, compared to the configuration of Patent Document 2, the configuration is simpler in that it does not require a mechanism for generating oxygen nanobubbles, such as an ultrasonic vibration device.

[0017] In this way, the present invention, which is based on the method of the basic configuration (1) and the apparatus of the basic configuration (2), can realize efficient production of hydrocarbons while having a simple configuration. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram showing the method of the basic configuration (1). [Diagram 2] 1 is a schematic diagram showing the configuration of the device of basic configuration (2), in which the lower reaction tank is shown in cross section, and the upper carbon dioxide supply device and the ejection amount adjustment device are shown in side view. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Basic configuration (1), as shown in the block diagram of FIG. 1, is a method for synthesizing hydrocarbons (HC) by reducing carbon dioxide and water (W) to carbon monoxide and hydrogen via a photocatalyst in water containing dissolved carbon dioxide and oxygen, and then by a chemical reaction between the carbon monoxide and the hydrogen via the photocatalyst, characterized in that the upper interface of a layer of hydrocarbons (HC) generated in an area above the water (W) is brought into contact with air (A) containing carbon dioxide at an adjustable concentration.

[0020] The apparatus of basic configuration (2), as shown in the schematic diagram of FIG. 2, is an apparatus for synthesizing hydrocarbons HC, which reduces carbon dioxide and water W to carbon monoxide and hydrogen in water via a photocatalyst, and further synthesizes hydrocarbons HC by a chemical reaction between the carbon monoxide and hydrogen via the photocatalyst, and is characterized in that it comprises a reaction vessel 1 for storing water W in which carbon dioxide and oxygen are dissolved, a photocatalytic means in the reaction vessel 1, a carbon dioxide supplying device 2 above the reaction vessel 1, and an ejection amount adjustment device 21 at the carbon dioxide ejection port.

[0021] As in the basic configurations (1) and (2), the reduction reaction is promoted by the carbon dioxide contained in the air A that contacts the upper interface of the water W in which the hydrocarbons HC are formed, and the efficiency of the reduction reaction is determined by the content of the carbon dioxide. The following technical points can be presumed to be the basis for this.

[0022] When carbon dioxide dissolved in water is photocatalyst-treated to form radical water, that is, activated water that is prone to chemical reactions, the following reduction reactions caused by the radicalization proceed sequentially. CO2+H2O→CO+H2+O2 (1) That is, in the above formula (1), there are reduction reactions proceeding sequentially from left to right. When focusing on the individual reactions, there is also a reverse reaction in which carbon monoxide molecules are oxidized to carbon dioxide molecules, but overall, the reaction proceeds in which carbon dioxide molecules are sequentially reduced to carbon monoxide molecules.

[0023] Following the reaction formula (1) above, in the radical water, the following reaction formula for producing hydrocarbons HC proceeds due to the radicalization: (2n+1)H2+nCO→C n H 2n+2 +nH2O (2) Therefore, C generated in the upper region of the water W n H 2n+2 The layer of hydrocarbons HC is derived from the above reaction formula (2).

[0024] In such a case, the carbon dioxide contained in the air A above the layer of hydrocarbons HC has an affinity for the hydrocarbons HC, so it permeates the layer of hydrocarbons HC and migrates to the water W in the lower region and dissolves.

[0025] As a result of the dissolution, the reduction reaction of the formula (1) is promoted by the supply of carbon dioxide, and thus the reaction of the formula (2) is also promoted. However, since the degree of dissolution of carbon dioxide in the aqueous solution in which the reactions of the above formulas (1) and (2) take place is uncertain, the appropriate concentration of carbon dioxide to be in contact with the upper interface of the hydrocarbon HC layer is not yet determined.

[0026] Reflecting the above situation, in the basic configurations (1) and (2), the concentration of hydrocarbons HC contained in the air A at the upper interface is made freely adjustable.

[0027] As far as the reaction formulas (1) and (2) are concerned, the higher the concentration of the adjustable hydrocarbons HC above the interface, the more the reactions of the formulas (1) and (2) are promoted.

[0028] However, according to the experience of the inventors, it has been found that the higher the concentration of carbon dioxide, the more the reactions of the above formulas (1) and (2) are not promoted, and when the concentration of carbon dioxide above the interface exceeds a certain level, the production of hydrocarbons (HC) may actually decrease.

[0029] Specifically, when the concentration of carbon dioxide exceeds 9000 ppm, the efficiency of generating hydrocarbons (HC) often decreases.

[0030] The exact reason why the efficiency of hydrocarbon HC production decreases when the carbon dioxide concentration exceeds a certain value is not clear at present. However, it can be estimated that the function of the photocatalyst in the reaction formulas (1) and (2) above will decrease if the carbon dioxide concentration exceeds a certain level.

[0031] The appropriate concentration of carbon dioxide at the upper interface depends on the amount of carbon dioxide contained in the water, but in most cases, the appropriate carbon dioxide concentration can be set within the range of 450 ppm to 5000 ppm.

[0032] The basic configurations (1) and (2) cover the cases where the water temperature is natural, cooled, or heated. However, the water temperature does not have a significant effect on the efficiency of generating hydrocarbons (HC).

[0033] The basis for this is believed to be that the photocatalyst, which acts through the reduction reaction of formula (1) and the synthesis reaction of hydrocarbons HC of formula (2), locally generates molecular vibrations in the water with frequencies orders of magnitude higher than thermal vibrations, and that the thermal vibrations that affect the water temperature have almost no effect on the molecular motion.

[0034] As already explained, in the prior invention of Patent Document 2, oxygen nanobubbles are generated and active oxygen is generated by irradiation with ultraviolet rays.

[0035] However, when nanobubbles are generated by ultrasonic waves, vibrations are inevitably applied to the water W involved in the reaction formula (1) above, which inevitably causes an impediment to the progress of the reduction reaction due to the equilibrium of the reaction formula (1) under calm conditions. However, the fact remains that active oxygen is effective in the reduction reaction of the above formula (1).

[0036] Taking into consideration the effectiveness of such active oxygen, in the basic configuration (1), an embodiment can be adopted in which at least a portion of the dissolved oxygen is activated only by irradiating it with ultraviolet light, and in the basic configuration (2), an embodiment can be adopted in which an ultraviolet irradiation device is provided for activating at least a portion of the oxygen dissolved in the reaction tank 1. Incidentally, when a part of the dissolved oxygen is activated by irradiation with ultraviolet rays, the efficiency of carbon dioxide reduction can be significantly improved compared to when the oxygen is not activated.

[0037] The basis for this is that hydrogen peroxide (H2O2) is formed by the activation of dissolved oxygen, which results in the efficient reduction of carbon dioxide, as shown in the following chemical formula: CO2+H2O2→CO+H2+3O2 / 2 ···(3) The following will explain the present invention based on examples. EXAMPLES

[0038] The first embodiment is characterized in that in the basic configuration (1), the humidity at the interface and in the vicinity above it is set to 50% or less.

[0039] If the humidity at the upper interface is high, the carbon dioxide contained in the air A near the interface will merge with water droplets forming water vapor in the air and drift away, thereby exacerbating the problem of not falling to the interface.

[0040] Considering such adverse effects, in the first embodiment, the humidity at the interface is set to 50% or less.

[0041] By setting an upper humidity limit of 50% or less, the drift of carbon dioxide can be reduced. In order to adjust the humidity in this manner, it is advisable to employ either heat drying above the interface or wind drying, which generates horizontal wind force to suppress an increase in humidity due to water vapor from the water W below the interface. EXAMPLES

[0042] Example 2 is characterized in that in the basic configuration (2), the horizontal area of ​​the interface in the reaction vessel 1 is at least twice as large as the cross-sectional area in the up-down direction perpendicular to the horizontal direction.

[0043] Due to these characteristics, in the device of the basic configuration (2), the area of ​​the interface where the hydrocarbons HC are generated can be set relatively wide, and thus the reduction of the above formula (1) and the hydrocarbon reaction of the formula (2) can be efficiently promoted. [Industrial Applicability]

[0044] The present invention, which is based on the method of the basic configuration (1) and the apparatus of the basic configuration (2), has a great advantage in that it can efficiently produce hydrocarbons by a simple configuration in which the interface at which hydrocarbons are produced is brought into contact with air containing carbon dioxide, the concentration of which can be adjusted, and has enormous industrial applicability. [Explanation of symbols]

[0045] W water A. Air HC Hydrocarbon 1 Reactor 2 Carbon dioxide supply device 21 Spout amount adjustment device

Claims

1. A method for synthesizing hydrocarbons by reducing carbon dioxide and water to carbon monoxide and hydrogen via a photocatalyst in water containing dissolved carbon dioxide and oxygen, and then chemically reacting the carbon monoxide with the hydrogen via the photocatalyst, characterized in that the method for synthesizing hydrocarbons comprises contacting an upper interface of a layer of hydrocarbons produced in an area above the water with air containing carbon dioxide at an adjustable concentration.

2. 2. The process for synthesizing hydrocarbons according to claim 1, wherein the concentration of carbon dioxide is 9,000 ppm or less.

3. 3. The method for synthesizing hydrocarbons according to claim 2, wherein the concentration of carbon dioxide is 450 ppm to 5000 ppm.

4. 2. The method for synthesizing hydrocarbons according to claim 1, wherein the dissolved oxygen is at least partially activated only by irradiation with ultraviolet light.

5. 2. The method for synthesizing hydrocarbons according to claim 1, wherein the humidity at the upper interface is set to 50% or less.

6. A hydrocarbon synthesis apparatus which reduces carbon dioxide and water to carbon monoxide and hydrogen in water via a photocatalyst, and further synthesizes hydrocarbons through a chemical reaction between the carbon monoxide and hydrogen via the photocatalyst, comprising a reaction vessel for storing water in which carbon dioxide and oxygen are dissolved, a photocatalytic means within the reaction vessel, a carbon dioxide supply device above the reaction vessel, and an apparatus for adjusting the amount of carbon dioxide ejected from an outlet of the reaction vessel.

7. 7. The apparatus for synthesizing hydrocarbons according to claim 6, further comprising an ultraviolet ray irradiation device for activating at least a part of the oxygen dissolved in the reaction vessel.

8. 7. The apparatus for synthesizing hydrocarbons according to claim 6, wherein the horizontal area of ​​the interface in the reaction vessel is at least twice as large as the cross-sectional area in the vertical direction perpendicular to the horizontal direction.

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