Methanol production system and methanol production method

Abstract

To produce methanol without requiring carbon dioxide to be prepared in advance and without requiring high temperature and high pressure conditions.SOLUTION: The methanol production system includes a recovery unit that recovers carbon dioxide by supplying air to a recovery liquid and causing the recovery liquid to absorb the carbon dioxide, an electrolyzing unit that is connected to the recovery unit and performs electric reduction on the recovery liquid supplied from the recovery unit to produce carbon monoxide, and a production unit that is supplied with the carbon monoxide produced by the electrolyzing unit and performs electric reduction on the supplied carbon monoxide to produce methanol.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methanol production system and a methanol production method. [Background technology]

[0002] Methods for producing methanol using carbon dioxide and hydrogen are known (see, for example, Patent Documents 1 and 2). Patent Document 1 describes a method for separating methanol produced by a high-temperature catalyst using a membrane reactor having a structure in which a catalyst support and a gas separation membrane are stacked. Patent Document 2 describes a system for synthesizing methanol from carbon dioxide or carbon monoxide. Patent Document 3 describes a method for producing a gas fluid with a high carbon dioxide concentration and a gas fluid with a low carbon dioxide concentration from a gas fluid containing carbon dioxide. In this method, the produced gas fluid with a high carbon dioxide concentration is reduced to extract various carbon dioxide reduction products (e.g., formic acid, acetic acid, oxalic acid, glycolic acid, tartaric acid, malonic acid, propionic acid, glyoxylic acid, organic carboxylic acids, and methanol). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-94782 [Patent Document 2] Japanese Patent Application Publication No. 2018-150254 [Patent Document 3] Special Publication No. 2021-516290 Summary of the Invention [Problem to be solved by the invention]

[0004] In the methanol production methods described in Patent Documents 1 and 2, methanol is synthesized using a catalyst under high-temperature, high-pressure conditions. Frequent operation and shutdown of the system to set the high-temperature, high-pressure conditions may reduce the efficiency of methanol synthesis and accelerate system deterioration. The method described in Patent Document 3 can produce various carbon dioxide reduction products, but is not suitable for selectively producing a single type of carbon dioxide reduction product. Furthermore, all of the methods described in Patent Documents 1 to 3 require high-concentration carbon dioxide as a gas. To produce high-concentration carbon dioxide from dilute carbon dioxide in the atmosphere, a high-temperature, high-pressure production process is required.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and an object of the present invention is to produce methanol without the need to prepare carbon dioxide in advance and without the need for high-temperature and high-pressure conditions. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided a methanol production system comprising: a recovery unit that recovers carbon dioxide by supplying atmospheric air to a recovery liquid and causing the recovery liquid to absorb carbon dioxide, an electrolysis unit connected to the recovery unit that performs electroreduction on the recovery liquid supplied from the recovery unit to produce carbon monoxide, and a production unit that receives the carbon monoxide produced in the electrolysis unit and produces methanol by electroreduction of the supplied carbon monoxide.

[0008] According to this configuration, carbon dioxide absorbed from the atmosphere into the recovery liquid is electrolytically reduced to produce carbon monoxide. Furthermore, methanol is produced from the carbon monoxide. In this configuration, carbon dioxide is recovered from the atmosphere, eliminating the need to prepare carbon dioxide in advance for methanol production. Unlike factory exhaust gases, air is always present everywhere, meaning that the system's operating time and installation location are not limited. Because this system can operate at room temperature under atmospheric pressure, frequent system startup and shutdown can be easily performed, improving compatibility with unstable renewable energy sources. Furthermore, because this system does not require high-temperature and high-pressure conditions for methanol production, it does not require the use of materials compatible with high temperatures and pressures, reducing system costs and enabling a highly safe system configuration.

[0009] (2) The methanol production system of the above aspect may further include a gas-liquid separation unit to which the gas containing hydrogen and carbon monoxide produced in the electrolysis unit and the liquid containing the recovered liquid are supplied, the gas-liquid separation unit supplying the separated gas to the production unit and the separated liquid to the recovery unit. With this configuration, after the liquid produced in the electrolysis unit, including the recovered liquid not required for methanol production, is separated, gaseous hydrogen and carbon monoxide are supplied to the production unit. The recovered liquid is supplied again to the recovery unit and reused. Because the recovered liquid is circulated and used, the system can be operated cyclically without the need to replenish new chemicals from the outside.

[0010] (3) The methanol production system of the above aspect may further include an acquisition unit that acquires a pH of the recovered solution supplied from the recovery unit; and a control unit that, when the acquired pH is higher than a preset threshold, performs at least one of reducing the flow rate of air supplied to the recovery unit and increasing the voltage applied to the recovered solution by the electrolysis unit, and, when the acquired pH is equal to or lower than the threshold, increases the flow rate and decreases the voltage. According to this configuration, when the recovery unit recovers carbon dioxide from the atmosphere, if the carbonate ion concentration in the recovery liquid is high, i.e., if the pH of the recovery liquid is low, the recovery rate of carbon dioxide from the atmosphere decreases. On the other hand, if the pH of the recovery liquid is low, the electrolysis rate at which the electrolysis unit produces carbon monoxide increases. To improve the rate of methanol production, it is preferable that the pH of the recovery liquid is low to improve the electrolysis rate, but a low pH reduces the carbon dioxide recovery rate. In this configuration, at least one of the recovery rate and the electrolysis rate is controlled so that the pH of the recovery liquid becomes a threshold pH, thereby efficiently achieving methanol production at a desired rate.

[0011] (4) The methanol production system of the above aspect may further include a circulation unit that dissolves the methanol produced by the production unit in dipotassium hydrogen phosphate and circulates the dipotassium hydrogen phosphate in which methanol is dissolved to the production unit. According to this configuration, the produced methanol is dissolved in dipotassium hydrogen phosphate, and the dipotassium hydrogen phosphate is circulated through the production section. This circulation increases the concentration of methanol dissolved in dipotassium hydrogen phosphate, thereby producing highly concentrated methanol.

[0012] (5) In the methanol production system of the above aspect, the circulation unit may further include a storage unit including a heating unit that heats the storage unit storing dipotassium hydrogen phosphate in which methanol is dissolved, and a first cooling unit that cools gaseous methanol generated from the heated storage unit. According to this method, methanol dissolved in dipotassium hydrogen phosphate is evaporated by heating. The evaporated gaseous methanol is converted into a liquid by cooling. As a result, methanol with a higher concentration is obtained.

[0013] (6) The methanol production system of the above aspect may further include a second cooling unit that cools the gas generated at the anode of the production unit. With this configuration, gaseous methanol leaks from the anode side of the generation unit in addition to oxygen generated by the reaction at the anode electrode. By cooling the gas leaking from the anode side, the methanol is not released into the outside air but is recovered as liquid methanol.

[0014] The present invention can be realized in various forms, such as a methanol production apparatus, a methanol synthesis apparatus, a methanol generation apparatus, a methanol production method, a methanol synthesis method, a methanol generation method, a system including these apparatuses, a computer program for executing these apparatuses, a server apparatus for distributing this computer program, and a non-transitory storage medium storing the computer program. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic block diagram of a methanol production system according to one embodiment of the present invention. [Figure 2] 1 is a flowchart of a method for producing methanol according to the present embodiment. [Figure 3] FIG. 4 is an explanatory diagram of the amount of methanol produced by the production unit. [Figure 4] FIG. 1 is a schematic block diagram of a methanol production system according to a second embodiment. [Figure 5] FIG. 1 is an explanatory diagram showing the relationship between the pH of the recovery liquid and the recovery rate of CO2. [Figure 6] FIG. 4 is an explanatory diagram showing the relationship between the pH of the recovered liquid and the electrolysis rate of the electrolysis unit. [Figure 7] FIG. 10 is an explanatory diagram showing the relationship between the pH of the recovered liquid and the concentration of CO generated by the electrolysis unit. [Figure 8] 10 is a flowchart of CO concentration control during methanol production in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment FIG. 1 is a schematic block diagram of a methanol production system 100 according to one embodiment of the present invention. In the methanol production system 100 of this embodiment, a recovery unit 10 absorbs carbon dioxide (CO) from the atmosphere into a recovery liquid, and an electrolysis unit 20 performs electroreduction on the recovery liquid to produce hydrogen (H) and carbon monoxide (CO). A production unit 30 performs electroreduction on the produced carbon monoxide to produce methanol (CHOH). By using the methanol production system 100 of this embodiment, it is not necessary to prepare CO in advance, and methanol can be produced without high-temperature and high-pressure conditions.

[0017] As shown in FIG. 1, the methanol production system 100 of this embodiment includes a recovery unit 10 that absorbs CO2 from the atmosphere into a recovery liquid, an electrolysis unit 20 that performs electroreduction on the recovery liquid to produce H2 and CO2, a water tank 60 that stores water to be supplied to the electrolysis unit 20, a first power source BT1 that supplies power for the electroreduction to the electrolysis unit 20, a gas-liquid separator 40 that separates the CO2 and H2 generated at the cathode electrode of the electrolysis unit 20 from the recovery liquid, a production unit 30 that produces methanol by electroreduction of the separated CO2, a second power source BT2 that supplies power to the production unit 30, a storage unit 50 that stores the methanol generated at the cathode of the production unit 30, three mass flow controllers M1 to M3 that measure and control flow rates, and four pumps P1 to P4 that deliver various liquids.

[0018] The recovery unit 10 recovers CO2 by supplying atmospheric air to the recovery liquid and allowing the recovery liquid to absorb CO2 in the atmosphere. The recovery unit 10 has a cylindrical shape and is equipped therein with a bubbler (AS ONE PTFE ball filter, product number 3-2368-00), a gas-liquid contactor 11, and a spray 12. In this embodiment, the recovery liquid circulating in the recovery unit 10 is a mixture of KHCO3 and K2CO3. x CO y(0 < x < 2, 2 < y < 3) was used. Compressed air (not shown in the figure) is supplied to the recovery liquid in the recovery unit 10 by a compressor. As a result, CO2 in the atmosphere dissolves in and is absorbed by the recovery liquid. The first mass flow controller M1 controls the flow rate of the compressed air (compressed air) supplied to the recovery unit 10. A CO2 concentration meter is installed at the front of the first mass flow controller M1 and at the rear of the second mass flow controller M2, and concentration meters for CO and CO2 are installed at the rear of the third mass flow controller M3. Three analyzers (Shimadzu Portable Gas Concentration Measuring Device CGT-7100) are installed. In this embodiment, the liquid volume of the recovery liquid in the recovery unit 10 is 200 ml, and air at 9 l / min is bubbled as compressed air and held for 8 hours.

[0019] The alkaline recovery liquid and the CO2 contained in the compressed air react as shown in the following reaction formulas (1) and (2). Therefore, the higher the amount of air recovered, the higher the concentration of hydrogen carbonate ions (HCO3 - (hereinafter also referred to as "bicarbonate ions")) increases.

Equation

[0020] A portion of the recovered liquid in the collection section 10 is sent by the first pump P1 to the spray 12, which is located vertically above the collection section 10. The spray 12 sprays the sent recovered liquid toward the gas-liquid contactor 11, which is located vertically below the spray 12 within the collection section 10. The recovered liquid adhering to the gas-liquid contactor 11 moves vertically downward within the collection section 10. Meanwhile, at least a portion of the gas is released from the collection section 10 to the atmosphere. In this embodiment, the first pump P1 sends the recovered liquid at a flow rate of 40 to 50 ml / min to the spray 12. A standard filled cone nozzle (Ikeuchi, product number 1 / 8MJJXP010S303) made of SUS303 was used as the spray 12. A precision micro-liquid delivery pump (Takumina QT-100-VE-PS) was used as the first pump P1 and pumps P2 to P4, which will be described later. The gas-liquid contactor 11 used was a PVC punched plate (AS ONE K-5840L3) with a Bell Eater EB (Aion) stapled to it. The surface area of ​​the gas-liquid contact surface, which was stacked in a direction perpendicular to the vertical direction, was approximately 250 cm. 2 is.

[0021] The recovered liquid in the recovery unit 10 was sent by the second pump P2 to the electrolysis unit 20 connected to the recovery unit 10. In this embodiment, the recovered liquid was sent to the electrolysis unit 20 at a flow rate of 10 ml / min.

[0022] The electrolysis unit 20 performs electroreduction on the recovered solution supplied from the recovery unit 10 and the water supplied from the water tank 60, using power supplied from the first power source BT1. Due to the electroreduction, reactions represented by the following reaction formulas (3) to (6) occur at the cathode electrode of the electrolysis unit 20.

[0023]

number

[0024] As shown in reaction equation (3), carbonate ions (CO3 2-) is converted to bicarbonate ions. The bicarbonate ions are converted to CO2 as shown in formula (4). CO2 is reduced to CO as shown in reaction formula (5). At the cathode electrode, H2 is generated as a side reaction by the reaction shown in reaction formula (6). At the anode electrode of the electrolysis unit 20, O2 is generated by the reaction shown in reaction formula (7).

[0025] The H2O stored in the water tank 60 is sent to the electrolysis unit 20 by the fourth pump P4. The O2 generated on the anode side as shown in reaction formula (7) is sent to the water tank 60 and discharged from the water tank 60 to the atmosphere. The H2O sent to the water tank 60 is circulated between the electrolysis unit 20 and the water tank 60 by the fourth pump P4. The CO and H2 generated at the cathode electrode of the electrolysis unit 20 are supplied to the gas-liquid separator 40.

[0026] In this embodiment, a carbon paper (Toray Paper TGP-H-060) coated with nanoporous gold (np-Au) was used as the cathode electrode for CO synthesis. A 200 nm-thick alloy film of gold and silver in a weight ratio of 50:50 was used as the np-Au, which was dealloyed with 70 wt% nitric acid. Platinum 100 mesh (Kurea) was used as the anode electrode for O2 generation. The electrode area of ​​each of the cathode and anode electrodes was 16 cm. 2 The dimensions were 4 cm x 4 cm. A Nafion (registered trademark) 117 membrane (DuPon) was used as the electrolyte membrane to form an MEA (Membrane Electrode Assembly). The MEA was sandwiched between parallel liquid flow paths with 0.5 mm-wide grooves, and a voltage was applied from a first power supply BT1. A gold 100 mesh (Kurea) was installed as a current collector on the cathode side. A 2450 Sourcemeter (Keithley) was used as the first power supply BT1. In this embodiment, a current of 0.3 A was applied to the recovered liquid sent from the recovery unit 10 to the electrolysis unit 20 at a flow rate of 10 ml / min. The applied voltage in this case was 3.7 V to 3.8 V.

[0027] The gas-liquid separator 40 is supplied with a gas containing H and CO generated at the cathode electrode of the electrolysis unit 20 and a liquid containing the recovery liquid. The gas-liquid separator 40 supplies the separated gas to the generation unit 30. The gas-liquid separator 40 supplies the separated recovery liquid to the recovery unit 10. The separated recovery liquid is returned into the recovery unit 10 from vertically above the recovery unit 10, as shown in FIG. 1.

[0028] The generator 30 receives the H2 and CO produced in the electrolysis unit 20 via the gas-liquid separator 40 and produces methanol by electroreduction of the CO. The H2 and CO are supplied to the cathode side of the generator 30, where methanol is synthesized. A 0.25 mol / L solution of dipotassium hydrogen phosphate (K2HPO4) is supplied to the anode side of the generator 30. When power is supplied to the generator from the second power supply BT2 in this state, the following reaction formulas (8) and (9) occur at the cathode electrode of the generator 30. The following reaction formula (10) occurs at the anode electrode.

[0029]

number

[0030] Methanol produced by reaction (8) is dissolved in a K2HPO4 solution and sent to storage unit 50. O2 produced by reaction (10) is sent to storage unit 50 together with the K2HPO4 solution in which methanol is dissolved. H2 produced at the cathode electrode by reaction (9) and unreacted CO from the CO supplied from gas-liquid separator 40 are discharged into the atmosphere. The CO and CO2 concentrations in the gas discharged into the atmosphere are measured by an analyzer.

[0031] In this embodiment, the cathode electrode of the production unit 30 where methanol is synthesized was prepared by spraying a CoPc / CNT catalyst ink, in which cobalt phthalocyanine (CoPc) is supported on carbon nanotubes (CNT), onto carbon paper (Sigracet 39BB, SGL Carbon). CoPc / CNT was prepared by adding a CNT dispersion to a CoPc dispersion and drying. Specifically, the cathode electrode was prepared by the following procedure. The CoPc dispersion was prepared by adding 3.0 mg of CoPc (product code C3252, Tokyo Chemical Industry Co., Ltd.) to 250 ml of a dimethyl sulfoxide (DMSO) dispersion solvent, ultrasonically dispersing the mixture for 1 hour, and then stirring overnight with a stirrer. The CNT dispersion was prepared by adding 20 mg of CNT to 200 ml of a DMSO dispersion solvent, ultrasonically dispersing the mixture for 1 hour. The CNT dispersion was added to the CoPc dispersion, and the mixture was stirred overnight with a stirrer. This mixture was filtered under suction and washed with the dispersion solvent and ethanol. The resulting solid was then vacuum dried at 60°C to remove the dispersion solvent and obtain CoPc / CNT. The catalyst ink was prepared by mixing CoPc / CNT and Nafion (registered trademark, Fujifilm Wako Pure Chemical Industries, Ltd.) in an ethanol solvent at a weight ratio of 10:1, followed by ultrasonic dispersion for 30 minutes. The coating amount of the catalyst ink was 1 mg / cm2 in terms of catalyst weight. 2 The cathode electrode is 1 cm 2 Cut it into pieces (1cm x 1cm) and use 1cm of CO2Anode (Dioxide Materials) as the anode electrode. 2An MEA was formed using a 1 cm x 1 cm diameter tube and Sustainion® X37-50 Grade RT Membrane as the electrolyte membrane. This MEA was sandwiched between 100 gold mesh (clear) and placed in a PEEK cell with parallel liquid flow paths with 0.5 mm wide grooves. A CO2-containing gas was supplied to the cathode side from the electrolysis unit 20. A 10 ml portion of a 0.25 mol K2HPO4 solution was circulated to the anode side at a flow rate of 10 ml / min by a third pump P3. The K2HPO4 solution was prepared using Fujifilm K2HPO4 and ion-exchanged water. A VersaSTAT4 (Princeton Applied Research) was used as the second power supply BT2, and a voltage of 2.5 V was applied to the generator 30. The current flowing through the MEA in the generator 30 gradually increased from approximately 18 mA to 25 mA.

[0032] The storage unit 50 shown in Fig. 1 stores a K2HPO4 solution in which methanol is dissolved. Of the K2HPO4 solution and O2 supplied to the storage unit 50, O2 is discharged to the atmosphere. The third pump P3 circulates the K2HPO4 solution between the storage unit 50 and the production unit 30. The storage unit 50 and the third pump P3 correspond to a circulation unit.

[0033] Fig. 2 is a flowchart of the methanol production method of this embodiment. In the methanol production flow shown in Fig. 2, first, a recovery step is performed in which the recovery unit 10 supplies air to a recovery liquid and causes the recovery liquid to absorb the carbon dioxide, thereby recovering carbon dioxide (step S1). Compressed air, which is air compressed, is bubbled through the recovery liquid in the recovery unit 10, so that CO2 in the air is dissolved in and absorbed by the recovery liquid.

[0034] The electrolysis unit 20 performs electrolytic reduction on the recovered solution after the recovery step to produce H2 and CO2 (step S2). The electrolysis unit 20 performs electrolytic reduction on a mixture of the recovered solution supplied from the recovery unit 10 and water supplied from the water tank. As a result, CO2 is produced from the cathode electrode of the electrolysis unit 20 according to the above reaction formula (5) and H2 is produced according to the reaction formula (6).

[0035] The gas-liquid separator 40 separates the gas containing H2 and CO generated by the electrolysis unit 20 from the liquid containing the recovered liquid (step S3). The H2 and CO separated by the gas-liquid separator 40 are supplied to the production unit 30. The production unit 30 performs a production step in which the CO supplied via the gas-liquid separator 40 is subjected to electroreduction to produce methanol (step S4). The produced methanol is dissolved in K2HPO4 circulating between the storage unit 50 and the production unit 30 and collected.

[0036] FIG. 3 is an explanatory diagram of the amount of methanol produced by the production unit 30. In FIG. 3, the time course of the cumulative amount of methanol produced (mol) is shown by line L1, and the time course of the concentration (%) of CO produced by the electrolysis unit 20 is shown by line L2. As shown by line L1 in FIG. 3, methanol is gradually produced over time. As shown by line L2 in FIG. 3, the concentration of CO produced increases and decreases within a predetermined concentration range. Because methanol is produced using CO, the fact that the concentration of CO produced within a predetermined range indicates that CO is being produced over time. The amount of methanol produced can be evaluated from the amount of methanol contained in the gas on the cathode side of the production unit 30 and the amount of methanol dissolved in the KHPO solution on the anode side. In this embodiment, quantitative analysis of methanol dissolved in KHPO on the anode side was performed using a gas chromatograph (7890A-7697A, Agilent Technologies) equipped with a headspace sampler. The concentrations of CO produced and CO2 produced were measured using an analytical device (CGT7100, Shimadzu Corporation) and calculated.

[0037] As described above, as shown in FIG. 1, the methanol production system 100 of this embodiment includes a capture unit 10 that absorbs CO2 from the atmosphere into a recovery liquid, an electrolysis unit 20 that electroreduces the recovery liquid to produce H2 and CO, and a production unit 30 that electroreduces CO2 and H2 supplied from the electrolysis unit 20 to produce methanol. In this embodiment, CO2 absorbed from the atmosphere into the recovery liquid is electroreduction-produced to produce H2 and CO2. Methanol is then produced from the CO2 produced. In this embodiment, CO2 is captured from the atmosphere, eliminating the need for pre-prepared CO2 for methanol production. Unlike factory exhaust gases, air is always present, which has the advantage of allowing the system to be installed anywhere. The methanol production system 100 of this embodiment can be operated at room temperature under normal pressure, facilitating frequent system startup and shutdown, improving compatibility with unstable renewable energy sources. Furthermore, the methanol production system 100 of this embodiment does not require high-temperature and high-pressure conditions for methanol production, eliminating the need for materials compatible with high temperatures and pressures, thereby reducing system costs.

[0038] In addition, the gas containing H2 and CO produced at the cathode of the electrolysis unit 20 and a liquid containing the recovered liquid are supplied to the gas-liquid separator 40 of this embodiment. The gas-liquid separator 40 supplies the separated gas to the production unit 30. The gas-liquid separator 40 supplies the separated recovered liquid to the recovery unit 10. In this embodiment, after the liquid produced in the electrolysis unit 20 and containing the recovered liquid that is not necessary for methanol production is separated, the gaseous H2 and CO2 are supplied to the production unit 30. The recovered liquid is supplied again to the recovery unit 10 and is reused. Because the recovered liquid is circulated and used, the methanol production system 100 can be operated cyclically without the need to replenish new chemicals from the outside.

[0039] In this embodiment, the storage unit 50 stores a KHPO solution in which methanol is dissolved. The third pump P3 circulates the KHPO solution between the storage unit 50 and the production unit 30. In this embodiment, the produced methanol is dissolved in KHPO, and the KHPO circulates through the production unit 30. This circulation increases the concentration of methanol dissolved in KHPO, thereby producing highly concentrated methanol.

[0040] Second Embodiment 4 is a schematic block diagram of a methanol production system 100a according to the second embodiment. The second embodiment differs significantly from the first embodiment in that the recovery rate of CO2 from the atmosphere and the electrolysis rate in the electrolysis unit 20 are increased or decreased depending on the pH of the recovered liquid, the storage unit 50 is heated to distill and concentrate methanol, and methanol contained in the gas discharged from the anode side of the production unit 30 is recovered. Therefore, in the second embodiment, a description of the same configuration as in the first embodiment will be omitted, and only the differences will be described.

[0041] The methanol production system 100a of the second embodiment further includes, in addition to the components of the methanol production system 100 of the first embodiment, a heating unit 51 that heats the storage unit 50, a first tank TK1 to which gas generated from the storage unit 50 is supplied, a first cooling unit 70 that cools the first tank TK1, a second tank TK2 to which gas discharged from the anode side of the production unit 30 is supplied, a second cooling unit 80 that cools the second tank TK2, a pH sensor (acquisition unit) SS that acquires the pH of the recovered liquid that is supplied from the recovery unit 10 to the electrolysis unit 20, and a control unit 90 that controls the power supplied by the first power source BT1 and the first mass flow controller M1.

[0042] The heating unit 51 is a heater that heats the storage unit 50 from the outside to 60 to 70 degrees Celsius (°C). When the K2HPO4 in the storage unit 50 is heated to this temperature, the methanol dissolved in the K2HPO4 evaporates. As shown in FIG. 4, the first tank TK1 is supplied with gas discharged from the storage unit 50. The first cooling unit 70 cools the gas generated in the first tank TK1, so that the gaseous methanol supplied from the storage unit 50 changes into liquid and is stored in the first tank TK1.

[0043] In addition to CO and H2, the anode side of the production unit 30 contains gaseous methanol that did not dissolve in K2HPO4. In the second tank TK2, the gaseous methanol discharged from the anode side of the production unit 30 is cooled by the second cooling unit 80, and is converted into a liquid and stored in the second tank TK2.

[0044] The control unit 90 controls at least one of the recovery rate of CO2 recovered from the atmosphere by the recovery unit 10 and the electrolysis rate at which CO2 is produced by the electrolysis unit 20, depending on the pH of the recovery solution acquired by the pH sensor SS. In this embodiment, the control unit 90 at least one of decreases the recovery rate and increases the electrolysis rate when the acquired pH is higher than a threshold value, and at least one of increases the recovery rate and decreases the electrolysis rate when the acquired pH is equal to or lower than the threshold value. In this embodiment, the control unit 90 increases or decreases the recovery rate by controlling the flow rate of air supplied to the recovery solution in the recovery unit 10 by the first mass flow controller M1. The control unit 90 also increases or decreases the electrolysis rate by controlling the voltage applied to the electrolysis unit 20 by the first power supply BT1.

[0045] FIG. 5 is an explanatory diagram illustrating the relationship between the pH of the recovery liquid and the CO2 recovery rate (mol / s). FIG. 6 is an explanatory diagram illustrating the relationship between the pH of the recovery liquid and the electrolysis rate (mol / s) of the electrolysis unit 20. The pH of the recovery liquid sent from the recovery unit 10 to the electrolysis unit 20 shown in FIGS. 5 and 6 varies depending on the carbonate ion concentration (Equation (2)) contained in the recovery liquid. Therefore, a low pH of the recovery liquid indicates a high carbonate ion concentration contained in the recovery liquid. Therefore, according to the relationship shown in FIG. 5, the higher the carbonate ion concentration contained in the recovery liquid, the slower the CO2 recovery rate by the recovery unit 10. On the other hand, according to the relationship shown in FIG. 6, the higher the carbonate ion concentration contained in the recovery liquid, the faster the electrolysis rate at which CO2 is generated by the electrolysis unit 20. As a result, when the pH of the recovery liquid is low, a high concentration of CO2 gas is generated by the electrolysis unit 20, which increases the methanol production rate but decreases the CO2 recovery rate from the atmosphere. Therefore, it is preferable to control the pH of the recovery liquid based on a threshold value, such as the desired CO2 concentration, to be generated in the electrolysis unit 20.

[0046] Fig. 7 is an explanatory diagram of the relationship between the pH of the recovered liquid and the concentration of CO generated by the electrolysis unit 20. Fig. 7 shows the relationship between the pH of the recovered liquid sent from the recovery unit 10 to the electrolysis unit 20 and the CO concentration (%) of the gas sent from the cathode side of the electrolysis unit 20 to the gas-liquid separator 40. The CO concentration shown in Fig. 7 is calculated based on the current of 40 mA / cm for the MEA of the electrolysis unit 20. 2 This is the numerical value when a current density of 100 kJ / s is applied. In this embodiment, the control unit 90 uses a preset CO concentration as a threshold (e.g., 10%) and controls the CO recovery rate and the electrolysis rate of the electrolysis unit 20 based on the threshold. The CO recovery rate and the CO concentration generated by the electrolysis unit 20 are calculated from the CO concentration and CO concentration measured by an installed analyzer.

[0047] Fig. 8 is a flowchart of CO2 concentration control during methanol production in the second embodiment. In the CO2 concentration control flow shown in Fig. 8, first, the control unit 90 sets initial values ​​for the CO2 recovery rate and the electrolysis rate of the electrolysis unit 20, and a set pH as a threshold value (step S11). The initial values ​​for the recovery rate and the electrolysis rate and the set pH may be, for example, preset values ​​or may be input each time.

[0048] The control unit 90 acquires the pH of the recovery liquid sent from the recovery unit 10 to the electrolysis unit 20, detected by the pH sensor SS (step S12). The control unit 90 determines whether the acquired pH of the recovery liquid is higher than a set pH, which is a threshold value (step S13). If it is determined that the acquired pH of the recovery liquid is higher than the set pH (step S13: YES), the control unit 90 at least increases the recovery rate of CO2 by the recovery unit 10 or decreases the electrolysis rate of the electrolysis unit 20 (step S14).

[0049] If it is determined in the process of step S13 that the pH of the obtained recovered liquid is equal to or lower than the set pH (step S13: NO), the control unit 90 at least one of decreases the recovery rate of CO2 by the recovery unit 10 and increases the electrolysis rate of the electrolysis unit 20 (step S15). After the process of step S14 or step S15 is performed, the control unit 90 determines whether or not to terminate methanol production (step S16). The termination of methanol production is determined by the elapse of a preset production time, receipt of a termination input by a user, or the like. If it is determined not to terminate methanol production (step S16: NO), the control unit 90 continues the process from step S11 onwards. If it is determined to terminate methanol production (step S16: YES), the control unit 90 terminates the CO concentration control flow.

[0050] As described above, in the methanol production system 100a of the second embodiment, the control unit 90 controls at least one of the recovery rate of CO2 recovered from the atmosphere by the recovery unit 10 and the electrolysis rate at which CO2 is produced by the electrolysis unit 20, depending on the pH of the recovered solution acquired by the pH sensor SS. In this embodiment, the control unit 90 at least one of decreases the recovery rate and increases the electrolysis rate when the acquired pH is higher than a threshold value, and at least one of increases the recovery rate and decreases the electrolysis rate when the acquired pH is equal to or lower than the threshold value. In the second embodiment, when the recovery unit 10 recovers CO2 from the atmosphere, if the carbonate ion concentration in the recovered solution is high, i.e., if the pH of the recovered solution is low, the recovery rate of CO2 from the atmosphere decreases. On the other hand, if the pH of the recovered solution is low, the electrolysis rate at which CO2 is produced by the electrolysis unit 20 increases. To improve the rate of methanol production, it is preferable to have a low pH of the recovered solution to improve the electrolysis rate, but a low pH reduces the CO2 recovery rate. In the second embodiment, at least one of the recovery rate and the electrolysis rate is controlled so that the pH of the recovered solution becomes equal to the threshold value, thereby efficiently achieving methanol production at a desired rate.

[0051] In the second embodiment, the storage unit 50 is heated by the heating unit 51, and the first tank TK1, to which the gas generated from the storage unit 50 is supplied, is cooled by the first cooling unit 70. In the second embodiment, methanol dissolved in KHPO is evaporated by heating. The evaporated gaseous methanol is then converted into a liquid by cooling. As a result, highly concentrated methanol is obtained.

[0052] In the second embodiment, the second tank TK2, to which the gas discharged from the anode side of the generator 30 is supplied, is cooled by the second cooling unit 80. In the second embodiment, gaseous methanol leaks from the anode side of the generator 30 in addition to O2 generated by a reaction at the anode electrode. By cooling the gas leaking from the anode side, the methanol is not released into the outside air but is recovered as liquid methanol.

[0053] <Modifications of the embodiment> The present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the gist thereof. For example, the following modifications are possible. Also, in the above-described embodiments, a part of the configuration that was assumed to be realized by hardware may be replaced with software, or conversely, a part of the configuration that was assumed to be realized by software may be replaced with hardware.

[0054] <Modification Example 1> In the above-described First Embodiment and Second Embodiment, an example of the methanol production systems 100 and 100a was described. However, the methanol production systems 100 and 100a can be modified within the range where the recovery unit 10 recovers CO2 from the atmosphere with a recovery liquid, the electrolysis unit 20 generates CO by electrochemically reducing the recovery liquid, and the production unit 30 generates methanol by electrochemically reducing CO.

[0055] The recovery liquid used in the recovery unit 10 was a mixed solution of KHCO3 and K2CO3 with KH x CO y (0 < x < 2, 2 < y < 3), but well-known solutions may be used as long as they can absorb and recover CO2 contained in the atmosphere. An alkaline solution may be used as the recovery liquid. For example, calcium carbonate, sodium carbonate, barium carbonate, magnesium carbonate, and lithium carbonate may be used. As the recovery liquid, it is preferable to use KH x CO y and sodium carbonate. The spray 12 and the gas-liquid contactor 11 provided in the recovery unit 10 may also be modified as long as the recovery liquid can recover CO2. For example, the spray 12 and the gas-liquid contactor 11 may not be provided. In the above-described First Embodiment, an example was given of the specific devices, sample sizes, etc. used as the recovery unit 10, the electrolysis unit 20, and the production unit 30, but the devices, samples, etc. can be modified within the well-known range. The flow rate of KH x CO y sent from the recovery unit 10 to the electrolysis unit 20, and the flow rate of KH x CO yThe flow rate may be an amount and rate different from those in the first embodiment.

[0056] In the generation unit 30, methanol is stored in a state of being dissolved in K2HPO4, but gaseous methanol may be cooled and recovered. Also, a known solution other than K2HPO4 may be used as the solution for dissolving methanol, such as K2SO4, KHCO3, Na2HPO4, RB2HPO4, or Cs2HPO4. While K2HPO4 is circulated between the generation unit 30 and the storage unit 50, it does not have to be circulated.

[0057] 2, gas-liquid separation (step S3) is performed by the gas-liquid separator 40. However, the methanol production system 100 may not include the gas-liquid separator 40, and gas-liquid separation may not be performed. In this case, for example, the gas and liquid containing CO and H produced in the electrolysis unit 20 may be supplied directly to the production unit 30. The methanol production system 100 may include the recovery unit 10, the electrolysis unit 20, and the production unit 30, and may not include other components (for example, the gas-liquid separator 40, the water tank 60, etc.).

[0058] <Variation 2> In the second embodiment, the increase or decrease in the CO2 recovery rate by the recovery unit 10 is controlled by increasing or decreasing the flow rate of air supplied by the first mass flow controller M1 to the recovery liquid in the recovery unit 10, but it may be controlled by other methods. For example, the increase or decrease in the CO2 recovery rate may be controlled by increasing or decreasing the supply rate of the recovery liquid supplied to the sprayer 12. Furthermore, the increase or decrease in the electrolysis rate at which CO2 is produced by the electrolysis unit 20 is controlled by increasing or decreasing the voltage applied to the electrolysis unit 20 by the first power supply BT1, but it may be controlled by other methods. For example, the increase or decrease in the electrolysis rate by the electrolysis unit 20 may be controlled by increasing or decreasing the supply rate of recovery water supplied to the electrolysis unit 20.

[0059] In the second embodiment, the control unit 90 controlled the CO2 recovery rate by the recovery unit 10 and the electrolysis rate by the electrolysis unit 20 based on the pH of the recovery liquid sent from the recovery unit 10 to the electrolysis unit 20, but various controls may also be performed based on the pH of the recovery liquid flowing through different locations. For example, the control unit 90 may control using the pH of the recovery liquid supplied from the generation unit 30 to the recovery unit 10, or may control using the pH of the recovery liquid at multiple locations.

[0060] The locations and numbers of the three mass flow controllers M1 to M3 and the four pumps P1 to P4 can be modified. For example, the mass flow controllers may be arranged as separate devices, with the CO / CO2 concentration ratio detector and the mass flow controller being separate devices, and some of the three mass flow controllers M1 to M3 may not detect the CO / CO2 concentration ratio.

[0061] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0062] The present invention can also be realized in the following forms. [Application example 1] 1. A methanol production system comprising: a recovery unit that recovers carbon dioxide by supplying air to a recovery liquid and causing the recovery liquid to absorb carbon dioxide; an electrolysis unit connected to the recovery unit, which performs electrical reduction on the recovery solution supplied from the recovery unit to generate carbon monoxide; a generation unit to which carbon monoxide generated in the electrolysis unit is supplied and which generates methanol by performing electrical reduction on the supplied carbon monoxide; A methanol production system comprising: [Application example 2] The methanol production system according to Application Example 1, further comprising: a gas-liquid separation unit to which a gas containing hydrogen and carbon monoxide produced in the electrolysis unit and a liquid containing the recovered liquid are supplied, the gas-liquid separation unit supplying the separated gas to the production unit and the separated liquid to the recovery unit. [Application example 3] The methanol production system according to Application Example 1 or Application Example 2, further comprising: an acquisition unit that acquires the pH of the recovery liquid supplied from the recovery unit; a control unit that, when the acquired pH is higher than a preset threshold, performs at least one of reducing the flow rate of the air supplied to the recovery unit and increasing the voltage applied by the electrolysis unit to the recovered solution, and, when the acquired pH is equal to or lower than the threshold, performs at least one of increasing the flow rate and decreasing the voltage; A methanol production system comprising: [Application example 4] The methanol production system according to any one of Application Examples 1 to 3, further comprising: a circulation unit that dissolves the methanol produced in the production unit in dipotassium hydrogen phosphate and circulates the dipotassium hydrogen phosphate in which methanol is dissolved to the production unit. [Application example 5] The methanol production system according to any one of Application Examples 1 to 4, further comprising: a heating unit that heats a storage unit that is included in the circulation unit and stores dipotassium hydrogen phosphate in which methanol is dissolved; a first cooling unit that cools the gaseous methanol generated from the heated storage unit; A methanol production system comprising: [Application Example 6] The methanol production system according to any one of Application Examples 1 to 5, further comprising: A methanol production system comprising a second cooling unit that cools the gas generated at the anode of the production unit. [Application Example 6] 1. A method for producing methanol, comprising: a recovery step of recovering carbon dioxide by supplying air to a recovery liquid and allowing the recovery liquid to absorb carbon dioxide; an electrolysis step of performing electroreduction on the recovered solution after the recovery step to generate carbon monoxide; a generation step in which carbon monoxide generated in the electrolysis step is supplied and the supplied carbon monoxide is subjected to electroreduction to generate methanol; A method for producing methanol, comprising: [Explanation of symbols]

[0063] 10...Collection section 11...Gas-liquid contactor 12...Spray 20...Electrolysis section 30...Generation section 40…Gas-liquid separator 50...Storage section (circulation section) 51...Heating part 60...Water tank 70...1st cooling section 80…Second cooling section 90...Control unit 100,100a...Methanol production system BT1…1st power supply BT2…Second power supply M1: Mass flow controller No. 1 M2: Second mass flow controller M3: Third mass flow controller P1: First pump P2: Second pump P3: Third pump (circulation section) P4: 4th pump SS...pH sensor (acquisition part) TK1...1st tank TK2...Second tank

Claims

1. 1. A methanol production system comprising: a recovery unit that recovers carbon dioxide by supplying air to a recovery liquid and causing the recovery liquid to absorb carbon dioxide; an electrolysis unit connected to the recovery unit, which performs electrical reduction on the recovery solution supplied from the recovery unit to generate carbon monoxide; a generation unit to which carbon monoxide generated in the electrolysis unit is supplied and which generates methanol by performing electrical reduction on the supplied carbon monoxide; A methanol production system comprising:

2. The methanol production system according to claim 1, further comprising: a gas-liquid separation unit to which a gas containing hydrogen and carbon monoxide produced in the electrolysis unit and a liquid containing the recovered liquid are supplied, the gas-liquid separation unit supplying the separated gas to the production unit and the separated liquid to the recovery unit.

3. The methanol production system according to claim 1, further comprising: an acquisition unit that acquires the pH of the recovered liquid supplied from the recovery unit; a control unit that, when the acquired pH is higher than a preset threshold, performs at least one of reducing the flow rate of the air supplied to the recovery unit and increasing the voltage applied to the recovery solution by the electrolysis unit, and, when the acquired pH is equal to or lower than the threshold, performs at least one of increasing the flow rate and decreasing the voltage; A methanol production system comprising:

4. The methanol production system according to claim 1, further comprising: a circulation unit that dissolves the methanol produced in the production unit in dipotassium hydrogen phosphate and circulates the dipotassium hydrogen phosphate in which methanol is dissolved to the production unit.

5. The methanol production system according to claim 4, further comprising: a heating unit that heats a storage unit that is included in the circulation unit and stores dipotassium hydrogen phosphate in which methanol is dissolved; a first cooling unit that cools the gaseous methanol generated from the heated storage unit; A methanol production system comprising:

6. The methanol production system according to any one of claims 1 to 5, further comprising: a second cooling unit configured to cool the gas generated at the anode of the production unit;

7. 1. A method for producing methanol, comprising: a recovery step of recovering carbon dioxide by supplying air to a recovery liquid and allowing the recovery liquid to absorb carbon dioxide; an electrolysis step of performing electroreduction on the recovered solution after the recovery step to generate carbon monoxide; a generation step in which carbon monoxide generated in the electrolysis step is supplied and the supplied carbon monoxide is subjected to electroreduction to generate methanol; A method for producing methanol, comprising:

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