Methanol production method and methanol production device

Abstract

A methanol production method comprising: a step (A) for acquiring a synthesis gas comprising at least carbon dioxide and hydrogen; a step (B) for reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; a step (C) for distilling the methanol mixture to separate out each of methanol, a distillation waste liquid, and distillation wastewater; and a step (D) for subjecting the distillation waste liquid and / or the distillation wastewater to an organic matter decomposition treatment to obtain a decomposition gas and treated water.

Description

Methanol production method and methanol production apparatus

[0001] The present invention relates to a method and an apparatus for producing methanol.

[0002] In a conventional industrial methanol production process using natural gas as a feedstock, methanol is synthesized from synthesis gas obtained by steam reforming natural gas (mainly methane) with water vapor. The reaction product obtained by this synthesis is a methanol mixture containing components other than methanol (hereinafter also referred to as crude methanol). This crude methanol is then purified by a distillation process to obtain purified methanol. In the distillation process, a certain amount of distillation wastewater and distillation effluent is discharged to maintain the purity of the methanol. Therefore, reuse of these wastewater has been proposed to reduce the environmental impact. However, particularly in methanol production using carbon dioxide as a primary feedstock, it is difficult to recycle the organic matter contained in the distillation wastewater directly into the feedstock. Therefore, it is necessary to decompose the wastewater into hydrogen, carbon monoxide, or carbon dioxide for reuse.

[0003] For example, Patent Document 1 discloses a method for producing methanol by reacting carbon dioxide and hydrogen with the aim of optimizing the method for producing methanol in terms of efficiency, energy consumption, and the purity of the resulting off-gas and wastewater streams and products, wherein a predetermined methanol-containing product stream is subsequently fed to at least one distillation step, and in the at least one distillation step, at least one component, particularly water, is separated and removed from the methanol-containing product stream, and the separated and removed gas stream containing the at least one volatile component is discharged from the system in whole or in part as off-gas, and / or the separated and removed gas stream or part of the gas stream is recycled to the methanol synthesis reaction.

[0004] Special table 2019-527691 publication

[0005] However, in Patent Document 1, a part of the fraction separated from methanol etc. is recycled and used in the methanol synthesis reaction, but only the volatile components are recycled, and it is difficult to say that the distillation waste liquid etc. are sufficiently recycled.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing methanol that has an excellent carbon recovery rate from distillation waste and has a low environmental impact.

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that the present invention, which has the following features, can provide a method for producing methanol from distillery wastewater with an excellent carbon recovery rate and a low environmental impact, and have completed the present invention. That is, the present invention is as follows.

[0008] [1] A method for producing methanol, comprising: (A) a step of obtaining a synthesis gas containing at least carbon dioxide and hydrogen; (B) a step of reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; (C) a step of distilling the methanol mixture to separate methanol, stillage, and distillation wastewater; and (D) a step of subjecting the stillage and / or the distillation wastewater to organic matter decomposition treatment to obtain decomposition gas and treated water. [2] The method for producing methanol according to [1], further comprising: (E) a step of electrolyzing at least one of the distillation wastewater and the treated water to obtain electrolytic hydrogen and electrolytic oxygen. [3] The method for producing methanol according to [2], wherein the electrolytic hydrogen is used in step (A). [4] The method for producing methanol according to any of [1] to [3], further comprising: (F) a step of using the decomposition gas in step (A). [5] The method for producing methanol according to any of [1] to [4], wherein the organic matter decomposition treatment is anaerobic treatment. [6] The method for producing methanol according to any one of [1] to [5], further comprising a step (G) of combusting the decomposition gas to recover heat. [7] The method for producing methanol according to any one of [2] to [6], wherein oxygen obtained in step (E) is used for combustion in step (G). [8] The method for producing methanol according to any one of [1] to [7], wherein the organic matter decomposition treatment is aerobic treatment. [9] The method for producing methanol according to any one of [1] to [8], further comprising a step (H) of recovering carbon dioxide from the decomposition gas.

[10] A methanol production apparatus comprising a synthesis gas preparation unit, a methanol synthesis unit, a distillation unit, and an organic matter decomposition treatment unit.

[11] The methanol production apparatus according to

[10] , further comprising an electrolysis unit, wherein electrolytic hydrogen obtained by the electrolysis unit is used in the synthesis gas preparation unit.

[0009] The present invention can provide a method for producing methanol that is excellent in carbon recovery rate from distillation waste and has a low environmental impact.

[0010] FIG. 1 is a schematic diagram showing an example of a production apparatus used in the methanol production method of the present embodiment. FIG. 2 is a schematic diagram showing another example of a production apparatus used in the methanol production method of the present embodiment. FIG. 3 is a schematic diagram showing an example of a production apparatus used in a methanol production method corresponding to a comparative example. FIG. 4 is a schematic diagram showing an example of an anaerobic treatment unit of the present embodiment. FIG. 5 is a schematic diagram showing an example of a gasification preparation step of the present embodiment. FIG. 6 is a schematic diagram showing another example of the gasification preparation step of the present embodiment.

[0011] Hereinafter, a detailed description will be given of an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") with reference to the drawings as necessary, but the present invention is not limited to the present embodiment. The present invention can be modified in various ways without departing from the gist of the present invention. In the drawings, the same elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown.

[0012] [Method for producing methanol] This method for producing methanol comprises: (A) a step of obtaining a synthesis gas containing at least carbon dioxide and hydrogen; (B) a step of reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; (C) a step of distilling the methanol mixture to separate methanol, a stillage, and a distillation wastewater; and (D) a step of subjecting the stillage and / or the distillation wastewater to organic matter decomposition treatment to obtain a decomposition gas and treated water.

[0013] Hereinafter, the methanol production method of this embodiment will be described using the methanol production apparatuses shown in Figures 1 and 2. However, the methanol production method of this embodiment is not limited to the embodiment using the production apparatuses shown in Figures 1 and 2.

[0014] 1 and 2, step (A) is a step of obtaining a synthesis gas containing at least carbon dioxide and hydrogen using a synthesis gas preparation unit 200. In step (A), a carbon dioxide-containing gas 1 is supplied to the synthesis gas preparation unit 200 together with hydrogen 3 to become a synthesis gas 4. The synthesis gas 4 is a gas used in the synthesis of methanol, and is a gas containing hydrogen, carbon monoxide, and carbon dioxide as its main components.

[0015] The hydrogen is not particularly limited, but it is preferable to use hydrogen obtained using renewable energy, for example, from the viewpoint of reducing carbon dioxide emissions. More specifically, examples include blue hydrogen such as electrolytic hydrogen, by-product hydrogen from oil refineries, by-product hydrogen derived from chemical processes, by-product hydrogen obtained in combination with CCS, hydrogen whose gas composition has been adjusted by PSA or the like, and hydrogen obtained by steam reforming.

[0016] Step (A) may include a gasification preparation step in which a synthesis gas 4 is obtained by gasifying and / or combusting an organic and / or hydrocarbon-containing gas.

[0017] The organic matter is not particularly limited, but examples thereof include waste plastics, biomass, and organic waste.

[0018] The hydrocarbon-containing gas includes, but is not limited to, refined gas and fossil fuel gas. Refined gas includes, but is not limited to, methane, ethane, propane, butane, and mixtures thereof. Fossil fuel gas includes natural gas (NG), liquefied petroleum gas (LPG), and naphtha, which are mainly composed of methane.

[0019] The gasification and preparation process includes a gasification process, and may further include one or more processes selected from the group consisting of a reforming process, a gas cleaning process, a carbon dioxide separation process, a hydrogen separation process, a shift reaction process, and a shift reverse reaction process.

[0020] Here, the gasification process is not particularly limited, but a conventionally known method can be used, for example, a process using an air gasification furnace and a process using an oxygen-steam gasification furnace. These can be further classified as a fixed bed type or a fluidized bed type depending on whether the catalyst is fixed or not, and either type can be used.

[0021] The reforming process is not particularly limited, but examples thereof include steam reforming (SMR), autothermal reforming (ATR), two-stage reforming (SMR+ATR), and partial oxidation. When the hydrocarbon-containing gas is natural gas or naphtha, a pre-reformer is provided upstream of the reforming unit to reform the natural gas or naphtha at about 500°C to produce a methane-rich gas (e.g., CH ４ The reforming process may include a pre-reforming step in which the catalyst is produced at a content ratio of about 30 to 50 mol%). The reforming temperature may be a conventionally known temperature and is not particularly limited, but may be, for example, 750°C to 1000°C. A catalyst may be used in the reforming process, and a conventionally known catalyst may be used as the catalyst and is not particularly limited, but examples thereof include nickel-based catalysts.

[0022] The gas washing step is not particularly limited, but a conventionally known method can be used, for example, a method using a bubble stirring tank, a spray tower, a wetted wall tower, or a packed tower.

[0023] The carbon dioxide separation step is not particularly limited, but a conventionally known method can be used, for example, a method using a carbon dioxide separation device that employs pressure swing adsorption, temperature swing adsorption, or membrane separation.

[0024] The hydrogen separation step is not particularly limited, but a conventionally known method can be used, such as a method using a hydrogen separation device that employs pressure swing adsorption, temperature swing adsorption, or membrane separation.

[0025] The shift reaction step and the reverse shift reaction step are not particularly limited, but a conventionally known method can be used. For example, the shift reaction step and the reverse shift reaction step can be performed in the presence of a catalyst. The catalyst can be a conventionally known catalyst, but is not particularly limited, for example, iron oxide (Fe ３ O ４ Examples of suitable catalysts include transition metal oxides such as platinum, platinum hydride, etc. The shift reaction process is a process for producing carbon dioxide and hydrogen from carbon monoxide and water vapor, and the reverse shift reaction is a process for producing carbon monoxide and water vapor from carbon dioxide and hydrogen in the reverse of the shift reaction.

[0026] Specific examples of the gasification preparation process are not particularly limited, but the configurations shown in Figures 5 and 6 can be used. The gasification preparation process A1 in Figure 5 is a process for obtaining synthesis gas through a gasification process A201 and a gas cleaning process A202 in that order. The gasification preparation process A2 in Figure 5 is a process for obtaining synthesis gas through a gasification process A201 and a reforming process A203 in that order. The gasification preparation process A3 in Figure 5 is a process for obtaining synthesis gas through a gasification process A201, a reforming process A203, and, if necessary, a carbon dioxide separation process A204 in that order. The gasification preparation process A4 in Figure 5 is a process for obtaining synthesis gas through a gasification process A201 and a carbon dioxide separation process A204 in that order. The gasification preparation process A5 in Figure 5 is a process for obtaining synthesis gas through a gasification process A201 and a hydrogenation process A205 in that order. The gasification preparation process A6 in Fig. 6 is a process for obtaining synthesis gas through a gasification process A201, a shift reaction process A206, and a carbon dioxide separation process A204 in that order. The gasification preparation process A7 in Fig. 6 is a process for obtaining synthesis gas through a gasification process A201, a hydrogenation process A205, and a reverse shift reaction process A207 in that order.

[0027] 1 and 2 , step (B) in the methanol production method of this embodiment is a step in which a synthesis gas 4 is supplied to a methanol synthesis unit 300 and reacted in the presence of a catalyst to obtain crude methanol 5. A part of a purge gas 12 produced as a by-product in the production of crude methanol may be supplied to the synthesis gas preparation unit 200 or a desulfurization unit that may be arranged upstream thereof.

[0028] In step (B), the reaction mixture obtained by the reaction is cooled and then subjected to gas-liquid separation, thereby obtaining crude methanol 5 as a liquid phase and purge gas 12 containing unreacted gases and the like as a gas phase. As a method for gas-liquid separation, a conventionally known method can be used, and is not particularly limited, but for example, a high-pressure separator can be used.

[0029] The purge gas is a mixed gas that may contain hydrogen, carbon monoxide, carbon dioxide, methane, nitrogen, etc., depending on the conditions of the methanol synthesis reaction. At least a portion of the purge gas is preferably supplied to the shift reaction unit and / or the boiler. This can further reduce carbon dioxide emissions.

[0030] The gas temperature at the inlet of the methanol synthesis unit 300 is set appropriately depending on the type and amount of catalyst, the shape of the reactor, the reaction pressure, etc., but is preferably 170 to 260° C., more preferably 170 to 220° C., and even more preferably 170 to 200° C. If the inlet gas temperature is 170° C. or higher, reactivity tends to improve, and if it is 260° C. or lower, equipment costs tend to be reduced.

[0031] The gas pressure at the inlet of the methanol synthesis unit 300 is preferably 4.9 to 14.7 MPaG, more preferably 5.0 to 11.0 MPaG, and even more preferably 5.0 to 10.0 MPaG. When the inlet gas pressure is 4.9 MPaG or higher, reactivity tends to improve, and when it is 14.7 MPaG or lower, production efficiency tends to increase.

[0032] The synthesis gas 4 supplied to the methanol synthesis unit 300 has a relationship (M value) between the mole percentages of CO, carbon dioxide, and hydrogen calculated by the following formula: M value = (hydrogen mole %) / (2 × CO mole % + 3 × carbon dioxide mole %) is preferably 0.9 to 5.0, more preferably 0.9 to 3.0, even more preferably 0.9 to 2.0, and particularly preferably 1.0 to 1.5. When the M value is 1.3 or more, by-products tend to decrease, and when it is 5.0 or less, the carbon yield of methanol synthesis tends to be excellent.

[0033] Here, the carbon yield of methanol synthesis means the ratio of the molar flow rate of methanol produced in the methanol synthesis unit 300 to the total amount of the molar flow rate of carbon monoxide and the molar flow rate of carbon dioxide contained in the synthesis gas 4 supplied to the methanol synthesis unit 300.

[0034] The reaction temperature in the methanol synthesis unit 300 is preferably 200 to 300°C, more preferably 200 to 280°C, and even more preferably 200 to 270°C, from the viewpoints of maintaining reactivity, suppressing by-products, and protecting the catalyst.

[0035] The type of the methanol synthesis unit 300 is not particularly limited, but is preferably one having a mechanism for controlling the reaction temperature. Specific examples include a heat exchange reactor and a quench-type adiabatic reactor. The heat exchange reactor is not particularly limited, but examples include a multi-tubular heat exchange reactor and a radial flow reactor.

[0036] When a multi-tubular heat exchange reactor is used, the reaction temperature is controlled by indirect heat exchange with pressurized boiling water to obtain saturated vapor (steam). The boiling water circulates between a steam drum and the shell side of the reactor, and steam is recovered from the steam drum. The steam obtained in this synthesis system is preferably used as a heat source for the purification process of the methanol solution downstream of the synthesis process. The pressurized boiling water is preferably at a temperature of 220°C to 260°C.

[0037] When an adiabatic reactor is employed, it has one or more catalyst layers inside. When it has two or more layers, a part of the synthesis reactor feed gas is branched off and supplied as a quench gas as a cooling gas for the intermediate layer, thereby controlling the reaction temperature. An evaporator is provided as a heat recovery unit for the reactor outlet gas to recover steam, which can be similarly used as a heat source for the purification process of the downstream methanol solution.

[0038] The catalyst used in the synthesis is preferably a methanol synthesis catalyst containing copper and zinc atoms as essential components. Such catalysts are reduced from their oxide state by a reducing gas, such as hydrogen or carbon monoxide, or a mixture thereof, thereby activating the copper and providing catalytic activity. In addition to copper and zinc atoms, the catalyst may also contain aluminum and / or chromium atoms as a major third component. Catalysts containing copper and zinc as essential components can be prepared by known methods. Such catalysts can be prepared, for example, by the methods described in JP-B 51-44715, JP-B 2695663, JP-B 6-35401, JP-A 10-272361, and JP-A 2001-205089.

[0039] A preferred catalyst is a methanol synthesis catalyst containing copper atoms and zinc atoms in an atomic ratio (copper / zinc) of 2.0 to 3.0 and also containing aluminum atoms. Examples of such catalysts include, but are not limited to, a catalyst prepared by the method described in JP-A-8-299796 and a catalyst described in WO 2011 / 048976.

[0040] Specific examples of preferred catalysts include those used in the examples and comparative examples of WO 2011 / 048976, such as Examples 2 and 3. Furthermore, the atomic ratio of copper atoms to zinc atoms (copper / zinc) in the catalyst is more preferably in the range of 2.1 to 3.0. In addition, a methanol synthesis catalyst containing 3 to 20 mass% alumina is even more preferred. As described above, such catalysts are not particularly limited, but can be prepared, for example, by the method described in WO 2011 / 048976. More specifically, the catalyst can be prepared by a production method including the steps of: mixing an aqueous solution containing copper, an aqueous solution containing zinc, and an alkaline aqueous solution to produce a precipitate containing copper and zinc; mixing the resulting precipitate with alumina hydrate having a pseudoboehmite structure to obtain a mixture; and molding the resulting mixture to a density of 2.0 to 3.0 g / mL. Examples of molding methods include tableting, extrusion, and tumbling granulation. However, the catalyst used in this embodiment is not limited to the above catalyst and the catalyst prepared by the above preparation method, and may be another catalyst having equivalent methanol synthesis activity.

[0041] [Step (C)] As shown in FIGS. 1 and 2 , the methanol production method of this embodiment includes step (C) of distilling the crude methanol 5 obtained in step (B) using a distillation unit 400 to separate methanol 13, a distillation waste liquid (side cut liquid) 6, and a distillation wastewater (bottoms) 7. In this embodiment, methanol refers to purified methanol. Here, the distillation waste liquid refers to concentrated methanol withdrawn from each stage of the distillation column, as well as concentrated liquid components containing alcohol other than methanol and water. The distillation wastewater refers to a liquid component mainly composed of water withdrawn from the bottom of the distillation column.

[0042] The step (C) can be carried out by any known method, including, but not limited to, distillation using a distillation column equipped with a reboiler and a condenser. In this case, the methanol mixture is distilled to obtain highly pure methanol from the top of the column.

[0043] In step (C), the steam recovered in step (A) may be used. For example, when distillation is performed using a distillation column, the steam can absorb or adsorb the fluid discharged from the top of the column. This can further reduce carbon dioxide emissions.

[0044] In step (C), the heat recovered in step (A) can also be used. Such heat is not particularly limited, but can be used, for example, as heat required for a reboiler when distillation is performed using a distillation column. This can further reduce carbon dioxide emissions. Alternatively, renewable energy can be supplied from an external source and used as heat.

[0045] [Step (D)] As shown in FIGS. 1 and 2 , the method for producing methanol of this embodiment includes step (D) of subjecting the stillage 6 and / or distillation wastewater 7 obtained in step (C) to organic matter decomposition treatment in an organic matter decomposition treatment unit 600 to obtain decomposed gas 9 and treated water 10.

[0046] The organic matter decomposition treatment in step (D) is not particularly limited, but examples thereof include aerobic treatment (activated sludge method), anaerobic treatment, hydrothermal gasification treatment, and combustion treatment. Depending on the type of organic matter decomposition, step (D) may include a pH adjustment step before supplying the distillery waste liquid 6 to the organic matter decomposition treatment unit 600.

[0047] Aerobic treatment is a microbial treatment carried out under conditions in which sufficient oxygen is present, and is widely practiced in water treatment plants, etc. Examples of aerobic treatment include, but are not limited to, the activated sludge method. Aerobic treatment is preferred from the viewpoint that it can be carried out relatively easily in an open system.

[0048] Anaerobic treatment is a process in which organic matter is decomposed using microorganisms in an atmosphere lacking or lacking oxygen. Anaerobic treatment is preferred because it reduces the amount of sludge produced and the gas produced is mostly composed of hydrocarbons and carbon dioxide.

[0049] Hydrothermal gasification refers to a process in which organic matter in an aqueous solution is decomposed into smaller molecules using a catalyst in a high-temperature, high-pressure liquid phase. The catalyst is not particularly limited, but conventionally known catalysts can be used, such as catalysts supporting a transition metal such as nickel. The temperature is not particularly limited, but may be set to, for example, 250 to 300°C, and the pressure is not particularly limited, but may be set to, for example, 10 to 20 MPa.

[0050] The obtained cracked gas 9 is preferably used in step (A), although there is no particular limitation thereon, and may be supplied to the synthesis gas preparation unit 200 via a combustion and heat recovery unit 800 as shown in Figures 1 and 2.

[0051] The organic matter decomposition treatment is not particularly limited, and conventionally known methods can be used. For example, when the organic matter decomposition treatment is anaerobic treatment, methods using an acid-producing reaction tank with acid-producing bacteria or a methane-producing reaction tank with methanogens can be used. Figure 4 shows a method using a methane-producing reaction tank with methanogens. The stillage 6 introduced into the system is first introduced into a methane-producing reaction tank 610 containing microorganisms. There, the organic matter is decomposed by the microorganisms 601, generating digester gas as decomposition gas 9. Since the digester gas contains methane, carbon dioxide, etc., it can be supplied to a combustion / heat recovery unit or a synthesis gas preparation unit 200 for use. A portion of the solvent in the methane-producing reaction tank is sent to a settling tank 611 and then extracted as treated water 10. In addition, returned sludge 603, which is part of the sludge 602 accumulated in the methane generation reaction tank 610 and the sedimentation tank 611, is supplied again to the methane generation reaction tank 610 as organic matter, and the remainder is sent to the sludge concentration tank 612 for concentration treatment, and then dehydrated in the sludge dewatering unit 604 before being recovered as dehydrated sludge 605.

[0052] [Step (G)] The methanol production method of this embodiment preferably further includes step (G) of combusting the decomposition gas 9 obtained by the organic matter decomposition treatment to recover heat. The heat recovered in the combustion / heat recovery unit 800 can be recycled as a heat source for the synthesis gas preparation unit 200, etc., and carbon dioxide produced by the combustion can be supplied to the synthesis gas preparation unit 200 as recycled gas 11. The oxygen used for combustion can be electrolytic oxygen obtained in step (E), which will be described later.

[0053] In the method for producing methanol of this embodiment, from the viewpoint of the carbon recovery rate from the stillage and / or distillation wastewater, the molar flow rate of carbon atoms contained in the cracked gas 9 is preferably 70 mol % or more, more preferably 80 mol % or more, even more preferably 90 mol % or more, and particularly preferably 95 mol % or more, relative to the molar flow rate of carbon atoms contained in the stillage 6 and the distillation wastewater 7.

[0054] [Step (H)] The methanol production method of this embodiment preferably further includes a step (H) of recovering carbon dioxide from the cracked gas. The carbon dioxide separation method may be a conventionally known method, and is not particularly limited. Examples of the method include physical absorption, physical adsorption, chemical absorption, chemical adsorption, membrane separation, cryogenic separation, and electroadsorption.

[0055] [Step (E)] As shown in FIG. 2 , the methanol production method of this embodiment preferably further includes step (E) of electrolyzing at least one of the distillation wastewater 7 and the treated water 10 in an electrolysis unit 100 to obtain electrolytic hydrogen 14 and electrolytic oxygen 15.

[0056] The electrolytic hydrogen 14 is preferably combined with hydrogen 3 and supplied to the synthesis gas preparation unit for use in step (A), and the electrolytic oxygen 15 is preferably supplied to the combustion and heat recovery unit 800 for use in heat recovery.

[0057] The electrolysis can be performed by any conventionally known method, and is not particularly limited. For example, the electrolysis can be performed by supplying power from a power source to an electrolytic cell composed of two electrodes (anode and cathode) separated by an ion exchange membrane.

[0058] [Desulfurization process]

[0059] The methanol production method of this embodiment may include a desulfurization step using a desulfurization unit. The desulfurization step is a step in which the carbon dioxide-containing gas 1 and the recycle gas 11 are supplied to the desulfurization unit to obtain a desulfurized gas from which sulfur has been removed. The desulfurized gas is supplied to the synthesis gas preparation unit 200. Because sulfur compounds are catalytic poisons for the catalysts used in steps (A) and (B), if the carbon dioxide-containing gas 1 contains sulfur, it is preferable to remove the sulfur compounds in advance in the desulfurization step. As a desulfurization method, a conventionally known method can be used, and is not particularly limited. Examples include a dry method using an adsorbent or catalyst, and a wet method using an amine-based absorption liquid. When a dry method is used, the operating temperature can be set to 0 to 400°C, although this depends on the type of sulfur compounds to be removed and the type of catalyst used.

[0060] [Other Steps] The method for producing methanol according to the present embodiment may include other steps, if necessary, in addition to the steps described above.

[0061] [Methanol Production Apparatus] The methanol production apparatus of this embodiment is an apparatus for carrying out the above-described methanol production method, and examples thereof include the apparatuses shown in FIGS.

[0062] The methanol production system of this embodiment includes a synthesis gas preparation unit 200, a methanol synthesis unit 300, a distillation unit 400, and an organic matter decomposition treatment unit 600. The methanol production system of this embodiment preferably further includes an electrolysis unit 100, and electrolytic hydrogen 14 obtained by the electrolysis unit 100 is preferably used in the synthesis gas preparation unit 200. The methanol production system of this embodiment may also include other units as necessary.

[0063] The synthesis gas preparation unit 200 may include one or more of a reformer, a gasifier, a gas scrubber, a carbon dioxide separator, a hydrogen separator, a shift reactor, a reverse shift reactor, and a reforming reactor. Among these, from the viewpoint of improving the carbon yield of methanol synthesis, it is preferable that the synthesis gas preparation unit 200 include a reformer.

[0064] The methanol synthesis unit 300 includes a methanol synthesis reactor that reacts the synthesis gas 4 obtained by the synthesis gas preparation unit 200 in the presence of a catalyst to produce crude methanol 5 and purge gas 12, and may also include other devices as necessary.

[0065] The distillation unit 400 may be a conventionally known one, and is not particularly limited, but may be, for example, a distillation column equipped with a reboiler and a condenser.

[0066] The organic matter decomposition treatment unit 600 is not particularly limited, and examples thereof include an anaerobic treatment unit, an aerobic treatment unit, a hydrothermal gasification treatment unit, and a combustion treatment unit. The aerobic treatment unit is not particularly limited as long as it is an apparatus having a decomposition tank using aerobic microorganisms. The anaerobic treatment unit is not particularly limited as long as it is an apparatus having a decomposition tank using anaerobic microorganisms. The hydrothermal gasification treatment unit is not particularly limited as long as it has a reactor that breaks down organic matter in an aqueous solution into smaller molecules using a catalyst in a high-temperature, high-pressure liquid phase. The combustion treatment unit is not particularly limited as long as it has a combustion device.

[0067] The electrolysis unit 100 may be a conventionally known one and is not particularly limited. For example, an electrolytic cell connected to a power source and composed of two electrodes (anode and cathode) separated by an ion exchange membrane may be used.

[0068] Although not shown, the methanol production system of this embodiment preferably further includes a desulfurization unit as needed. The desulfurization unit includes a desulfurizer that removes sulfur from carbon dioxide gas, and may also include other devices as needed.

[0069] EXAMPLES The method and apparatus for producing methanol according to the present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples at all.

[0070] The catalyst used for methanol synthesis was one of the following: a catalyst prepared by the method described in Example 1 of JP-B-51-44715 (methanol synthesis catalyst A), a catalyst prepared by the method described in Example 1 of JP-A-8-299796 (methanol synthesis catalyst B), a catalyst prepared by the method described in Example 3 of WO 2011 / 048976 (methanol synthesis catalyst C), or a catalyst prepared by the method described in Comparative Example 4 of JP-A-8-299796 (methanol synthesis catalyst D). The amounts of catalyst used in each of the following Examples and Comparative Examples were all the same.

[0071] Example 1 In Example 1, the production apparatus shown in FIG. 1 was used. The conditions were as shown in Table 1. Specifically, 81.2 kmol / h of carbon dioxide 1 was mixed with hydrogen 3 so that the ratio of the molar flow rate of hydrogen to the molar flow rate of carbon dioxide (hydrogen / carbon dioxide) was 3.05 to obtain synthesis gas 4, and then methanol was synthesized using synthesis gas 4. Methanol synthesis catalyst C was used as the catalyst in the methanol synthesis reactor in the methanol synthesis unit 300. A multi-tubular heat exchange reactor was used as the methanol synthesis reactor. The set conditions were: pressure of the fluid in contact with the catalyst in the reactor: 10.0 MPaG, shell pressure: 4.0 MPaG, circulation ratio: 4.0, and temperature: 200 to 234°C. Distillation was performed under conditions of a methanol distillation efficiency of 99% and an ethanol overhead composition of 5 ppm. Table 1 shows the results of Example 1, including the methanol production amount (tons / D).

[0072] In Example 2, as shown in Figure 2, an electrolysis unit 100 was added, and treated water 10 obtained from the organic matter decomposition treatment unit 600 and distillation wastewater 7 obtained from the distillation unit 400 were supplied to the electrolysis unit 100. Electrolytic hydrogen 14 obtained in the electrolysis unit 100 was combined with hydrogen 3 and supplied to the synthesis gas preparation unit 200, and electrolytic oxygen 15 was supplied to the combustion and heat recovery unit 800. The remaining operations were the same as those in Figure 1. The results of Example 2, such as the methanol production amount (ton / D), are shown in Table 1.

[0073] In Comparative Example 1, as shown in Fig. 3, the same operation as in Example 1 was carried out, except that the organic matter decomposition treatment unit 600, the combustion and heat recovery unit 800, and the electrolysis unit 100 were not provided. The results of Comparative Example 1, such as the methanol production amount (ton / D), are shown in Table 1.

[0074] Regarding (*1) in the table above, the amount of carbon dioxide released into the atmosphere refers to the amount of change due to a change in the general methanol synthesis process, and is not the amount of carbon dioxide released into the atmosphere from the entire process. Regarding (*2) in the table above, the total amount of stillage and distillation wastewater that is not recycled refers to the amount of change due to a change in the general methanol synthesis process, and is not the amount of carbon released from the entire process. In Examples 1 and 2, the carbon recovery rate from stillage by anaerobic treatment was 70%.

[0075] From the above, it was shown that Examples 1 and 2 are methanol production methods with a lower environmental load because they have a higher recycling efficiency of distillation wastewater and emit less carbon dioxide into the atmosphere than Comparative Example 1.

[0076] INDUSTRIAL APPLICABILITY The present invention has industrial applicability as a methanol production method and a methanol production apparatus.

[0077] This application is based on a Japanese patent application (Patent Application No. 2023-218416) filed on December 25, 2023, the contents of which are incorporated herein by reference.

[0078] 1...carbon dioxide-containing gas, 3...hydrogen, 4...synthesis gas, 5...crude methanol, 6...distillation waste liquid, 7...distillation wastewater, 9...cracked gas, 10...treated water, 12...purge gas, 13...methanol, 14...electrolytic hydrogen, 15...electrolytic oxygen, 100...electrolysis unit, 200...synthesis gas preparation unit, 300...methanol synthesis unit, 400...distillation unit, 600...organic matter decomposition treatment unit, 800...combustion / heat recovery unit, 601 ...Microorganisms, 602...Sludge, 603...Returned sludge, 604...Sludge dewatering unit, 605...Dewatered sludge, 610...Methane production reaction tank, 611...Settling tank, 612...Sludge concentration tank, 700...Neutralization unit, A1 to A8...Gasification preparation process, A201...Gasification process, A202...Gas cleaning process, A203...Reforming process, A204...Carbon dioxide separation process, A205...Hydrogenation process, A206...Shift reaction process, A207...Reverse shift reaction process.

Claims

1. Step (A) of obtaining a synthesis gas containing at least carbon dioxide and hydrogen; step (B) of reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; step (C) of distilling the methanol mixture to separate methanol, distillation waste liquid, and distillation wastewater, respectively; and step (D) of subjecting the distillation waste liquid and / or the distillation wastewater to organic matter decomposition treatment to obtain decomposed gas and treated water. A method for producing methanol, comprising these steps.

2. The method for producing methanol according to claim 1, further comprising step (E) of electrolyzing at least one of the distillation wastewater and the treated water to obtain electrolytic hydrogen and electrolytic oxygen.

3. The method for producing methanol according to claim 2, wherein the electrolytic hydrogen is used in step (A).

4. The method for producing methanol according to any one of claims 1 to 3, further comprising step (F) of using the decomposed gas in step (A).

5. The method for producing methanol according to claim 4, wherein the organic matter decomposition treatment is an anaerobic treatment.

6. The method for producing methanol according to claim 4 or 5, further comprising step (G) of burning the decomposed gas for heat recovery.

7. The method for producing methanol according to claim 6, wherein in step (G), the oxygen obtained in step (E) is used for combustion.

8. The method for producing methanol according to claim 1, wherein the organic matter decomposition treatment is an aerobic treatment.

9. The method for producing methanol according to claim 1, further comprising step (H) of recovering carbon dioxide from the decomposed gas.

10. A methanol production apparatus comprising a synthesis gas preparation unit, a methanol synthesis unit, a distillation unit, and an organic matter decomposition treatment unit.

11. The methanol production apparatus according to claim 10, further comprising an electrolysis unit, and the electrolytic hydrogen obtained by the electrolysis unit is used in the synthesis gas preparation unit.

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