Method of methanol synthesis
The method stabilizes methanol synthesis from gases containing sulfur compounds by using a series of steps and specific catalysts, addressing catalyst degradation and enhancing synthesis efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2023-11-16
- Publication Date
- 2026-07-29
AI Technical Summary
Existing methods for synthesizing methanol from blast furnace gas, which contains sulfur compounds like hydrogen sulfide and carbonyl sulfide, lead to degradation of copper-based catalysts, making stable methanol synthesis difficult.
A method involving a series of steps including water addition, hydrolysis, water-gas shift reaction, carbon dioxide separation, desulfurization, hydrogenation, and methanol synthesis, using specific catalysts and desulfurization methods to stabilize the process.
Enables stable synthesis of methanol from gases containing carbon dioxide and sulfur compounds by reducing catalyst degradation and improving synthesis efficiency.
Smart Images
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Figure 0007896599000002
Abstract
Description
Technical Field
[0001] The present invention relates to a method for synthesizing methanol, and particularly to a method for synthesizing methanol from a gas containing carbon dioxide and sulfur compounds such as hydrogen sulfide and carbonyl sulfide.
Background Art
[0002] In recent years, reduction of carbon dioxide (CO2) emissions has been demanded from the perspective of preventing global warming. In steel mills, a large amount of by-product gas is discharged, including blast furnace gas by-produced in blast furnaces, coke oven gas generated from coke ovens, and converter gas generated from converters. In particular, a large amount of CO2 is contained in blast furnace gas with a large discharge amount. Although by-product gas such as blast furnace gas is utilized as an energy source in the steel mill, the CO2 contained in the blast furnace gas is discharged as it is. Therefore, reduction of CO2 emissions is urgently required.
[0003] Under such a background, Patent Document 1 proposes a method for synthesizing methanol from a raw material gas containing CO2 and hydrogen (H2) by using a catalyst as an effective utilization method of CO2.
[0004] Further, Patent Document 2 proposes a method for improving the synthesis efficiency of methanol by separating water (H2O) using a membrane reactor having a dehydration membrane, and further obtaining H2 by an aqueous gas shift reaction using the separated H2O.
Prior Art Documents
Patent Documents
[0005]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0006] Incidentally, in addition to its main components such as CO2, carbon monoxide (CO), and H2, blast furnace gas also contains sulfur compounds such as hydrogen sulfide (H2S) and carbonyl sulfide (COS), which originate from the sulfur in the iron ore and coke used as raw materials. These H2S and COS compounds are known to degrade copper-based catalysts used in methanol synthesis.
[0007] In the method proposed in Patent Document 1 mentioned above, when blast furnace gas is used as the raw material gas, H2S and COS flow through the methanol synthesis catalyst, which has the problem of degrading the catalyst.
[0008] Furthermore, while Patent Document 2 describes separating H2 obtained by a water-gas shift reaction using a pressure swing adsorption method, it does not describe the utilization of the by-product CO2. When CO2 is separated by the pressure swing adsorption method and used in methanol synthesis, the aforementioned H2S and COS are concentrated on the separated CO2 side, which still leads to the problem of degrading the methanol synthesis catalyst.
[0009] Furthermore, Patent Document 2 describes using blast furnace gas as the sweep gas for H2O to carry out the water-gas shift reaction, but it does not specify the type of catalyst. However, copper-based catalysts generally used in water-gas shift reactions have the problem of degrading due to H2S and COS.
[0010] Thus, the methods described in Patent Documents 1 and 2 make it difficult to stably synthesize methanol.
[0011] The present invention aims to solve the aforementioned problems and provide a method for more stably synthesizing methanol from gases containing carbon dioxide and sulfur compounds, such as blast furnace gas. [Means for solving the problem]
[0012] The present invention, which solves the above problems, is as follows. [1] A methanol synthesis method comprising a raw material gas containing carbon dioxide, carbon monoxide, hydrogen sulfide, and carbonyl sulfide, and hydrogen gas, A water addition step is to add water to the raw material gas to obtain a hydrous raw material gas, The hydrolysis step involves hydrolyzing the aforementioned hydrolyzed raw material gas by converting the carbonyl sulfide contained in the hydrolyzed raw material gas into hydrogen sulfide and carbon dioxide to obtain a hydrolysis gas. The hydrolysis gas is subjected to a water-gas shift reaction step, in which the carbon monoxide and water contained in the hydrolysis gas undergo a water-gas shift reaction to form a shift reaction gas, A carbon dioxide gas separation step is performed to separate the shift reaction gas into carbon dioxide gas and gases of components other than carbon dioxide. A desulfurization step to remove hydrogen sulfide and at least hydrogen sulfide from carbonyl sulfide contained in the carbon dioxide gas to obtain high-concentration carbon dioxide gas, A hydrogenation step involves adding hydrogen gas to the aforementioned high-concentration carbon dioxide gas to obtain methanol as a raw material gas, A methanol synthesis step involves reacting carbon dioxide and hydrogen contained in the methanol raw material gas to produce methanol, A methanol synthesis method comprising the following:
[0013] [2] The methanol synthesis method according to [1], wherein the water added to the raw material gas in the water addition step is water produced as a by-product in the methanol synthesis step.
[0014] [3] The methanol synthesis method according to [2], wherein the methanol synthesis step includes a membrane separation step of separating the water produced as a by-product of the reaction between carbon dioxide and water by permeating through a membrane, and the water separated in the membrane separation step is used as the water added to the raw material gas in the water addition step.
[0015] [4] The methanol synthesis method according to [3], wherein the membrane separation step is carried out in the same container as the methanol synthesis step.
[0016] [5] The membrane separation step has a sweep step of flowing the raw material gas on one side of the membrane and sweeping the water permeated through the membrane with a sweep gas, using the raw material gas as the sweep gas, and using the raw material gas added with the water permeated through the membrane as the water-added raw material gas. The methanol synthesis method according to [3] or [4] above.
[0017] [6] The method used in the desulfurization step is a dry desulfurization method using a dry desulfurizer containing an iron compound selected from iron oxide or iron hydroxide. The methanol synthesis method according to any one of [1] to [5] above.
[0018] [7] As part or all of the iron compound, those derived from precipitates generated in the water treatment of a steel mill are used. The methanol synthesis method according to [6] above.
[0019] [8] The method used in the desulfurization step is a dry desulfurization method using a dry desulfurizer containing at least one compound selected from zinc and copper. The methanol synthesis method according to any one of [1] to [5] above.
[0020] [9] The methanol synthesis method according to any one of [1] to [8] above further has a heat exchange step of performing heat exchange between the shift reaction gas and the hydrolysis gas.
[0021]
[10] Before the sweep step, the methanol synthesis method according to any one of [5] to [9] above further has a water washing step of contacting the raw material gas with liquid-phase water for washing.
[0022]
[11] The catalyst used in the hydrolysis is a catalyst having an oxide of Al. The methanol synthesis method according to any one of [1] to
[10] above.
[0023]
[12] The catalyst used in the water gas shift reaction step is a catalyst containing a sulfide of at least one element selected from Co, Ni, and Mo. The methanol synthesis method according to any one of [1] to
[11] above.
[0024]
[13] The method for synthesizing methanol according to any one of [1] to
[12] above, wherein the catalyst used in the water gas shift reaction step is a catalyst containing an oxide of at least one element selected from Fe and Cr.
[0025]
[14] The method for synthesizing methanol according to any one of [1] to
[13] above, further comprising a hydrogen gas separation step of separating hydrogen gas from the gas of components other than the carbon dioxide separated in the carbon dioxide gas separation step.
[0026]
[15] The method for synthesizing methanol according to any one of [1] to
[14] above, wherein the raw material gas is the exhaust gas discharged from the reduction furnace.
[0027]
[16] The method for synthesizing methanol according to
[15] above, wherein the reduction furnace is a blast furnace in a steelworks and the raw material gas is blast furnace gas. [Effect of the Invention]
[0028] According to the present invention, methanol can be synthesized more stably from a gas containing carbon dioxide and sulfur compounds such as blast furnace gas. [Brief Description of the Drawings]
[0029] [Figure 1] It is a flow of a preferred example of the method for synthesizing methanol according to the present invention. [Figure 2] It is a flow of another preferred example of the method for synthesizing methanol according to the present invention. [Embodiments for Carrying Out the Invention]
[0030] Embodiments of the present invention will be described below with reference to the drawings. The methanol synthesis method according to the present invention is a methanol synthesis method for synthesizing methanol from a raw material gas containing carbon dioxide, carbon monoxide, hydrogen sulfide, and carbonyl sulfide, and hydrogen gas, comprising: a water addition step of adding water to the raw material gas to obtain a hydrolyzed raw material gas; a hydrolysis step of hydrolyzing the carbonyl sulfide contained in the hydrolyzed raw material gas into hydrogen sulfide and carbon dioxide to obtain a hydrolysis gas; a water gas shift reaction step of undergoing a water gas shift reaction between the carbon monoxide and water contained in the hydrolysis gas to obtain a shift reaction gas; a carbon dioxide gas separation step of separating the shift reaction gas into carbon dioxide gas and a gas of components other than carbon dioxide; a desulfurization step of removing at least hydrogen sulfide from the hydrogen sulfide and carbonyl sulfide contained in the carbon dioxide gas to obtain a high-concentration carbon dioxide gas; a hydrogen addition step of adding hydrogen gas to the high-concentration carbon dioxide gas to obtain a methanol raw material gas; and a methanol synthesis step of reacting carbon dioxide contained in the methanol raw material gas with hydrogen to produce methanol.
[0031] Figure 1 is a flow chart of a preferred example of the methanol synthesis method according to the present invention. The present invention will be described in detail below following the flow chart shown in Figure 1. The methanol synthesis method according to the present invention is a method for synthesizing methanol from a raw material gas (G01) containing CO2, CO, H2S, and COS, and H2 gas.
[0032] As the raw material gas (G01), exhaust gas discharged from a reduction furnace in a steel mill can be suitably used. Examples of such reduction furnaces include blast furnaces, coke ovens, and gasification furnaces, and blast furnace gas, coke oven gas, and gasification furnace gas can be used as the raw material gas (G01). In particular, methanol can be stably synthesized by suitably using blast furnace gas as the raw material gas (G01). In the following explanation, the case in which the raw material gas G01 contains N2, which is often found in exhaust gas discharged from a reduction furnace, will be explained as an example.
[0033] Furthermore, the raw material gas (G01) may contain H2 gas, and depending on the H2 gas content in the raw material gas (G01), additional H2 gas necessary for methanol synthesis can be prepared separately to synthesize methanol.
[0034] First, preferably, the raw material gas (G01) is supplied to a water washer (A01) and washed by bringing the raw material gas (G01) into contact with liquid phase H2O (water washing step). The water washing step adjusts the H2O contained in the raw material gas (G01) and reduces dust and other particles in the raw material gas (G01). The temperature of the H2O used in the water washing step may be set based on the ambient temperature, preferably 0°C to 100°C, more preferably 10°C to 40°C.
[0035] Next, the washed raw material gas (G01) is passed through the sweep space (A02-1) in the membrane reactor (A02), and H2O is added to the raw material gas (G01) to create a hydrous raw material gas (moisture addition step).
[0036] The membrane reactor (A02) has a sweep space (A02-1), a separation membrane (A02-2), and a methanol synthesis space (A02-3). As will be described later, methanol is synthesized in the methanol synthesis space (A02-3), and the by-product H2O permeates through the separation membrane (A02-2) and flows into the sweep space (A02-1). Therefore, it is preferable to pass the raw material gas (G01) through the sweep space (A02-1) as a sweep gas to sweep the H2O that has permeated through the separation membrane (A02-2) (sweeping step). This allows H2O to be efficiently added to the raw material gas (G01) to create a hydrolyzed raw material gas, and reduces the burden of separately adding H2O to the raw material gas (G01).
[0037] The temperature of the hydrolyzed raw material gas discharged from the sweep space (A02-1) may vary depending on the conditions of the subsequent methanol synthesis and the properties of the separation membrane (A02-2), but it is preferably set to 100°C to 250°C, more preferably 150°C to 200°C, so as to be suitable for the subsequent COS hydrolysis.
[0038] Next, the hydrolyzed raw material gas is introduced into the COS hydrolysis reactor (A03), where the COS contained in the hydrolyzed raw material gas is hydrolyzed into H2S and CO2 to produce hydrolysis gas (hydrolysis step).
[0039] In the hydrolysis process, it is preferable to use a catalyst containing an aluminum oxide. This improves the efficiency of hydrolysis, enabling efficient COS hydrolysis and increasing the desulfurization efficiency in the desulfurization process described later. It is even more preferable for the catalyst to further contain potassium in addition to the aluminum oxide.
[0040] Furthermore, the reaction temperature for hydrolysis can be determined based on the catalyst activity and chemical equilibrium, but as mentioned above, for example, it is preferably 100°C to 250°C, and more preferably 150°C to 200°C.
[0041] It is preferable to install the above-mentioned COS hydrolysis reactor (A03) upstream of the water-gas shift reactor (A04) described later, and to carry out the COS hydrolysis process before the water-gas shift reaction process described later. This is because the water-gas shift reaction is an exothermic reaction, and therefore the temperature downstream of the water-gas shift reactor (A04) rises to a temperature higher than the temperature suitable for COS hydrolysis.
[0042] Furthermore, when using a gas with a high CO concentration, such as blast furnace gas (for example, about 20% by volume), as the raw material gas (G01), H2O is consumed during the water-gas shift reaction process. This can lead to a decrease in H2O concentration downstream of the water-gas shift reactor (A04), resulting in a gas composition unsuitable for COS hydrolysis. Although COS hydrolysis is also an exothermic reaction that consumes H2O, the COS concentration in blast furnace gas (for example, 100 ppm or less) is significantly lower than the CO concentration. Therefore, the temperature and H2O concentration changes caused by the COS hydrolysis reactor (A03) are minimal, and their impact on the water-gas shift reactor (A04) is considered small.
[0043] In the hydrolysis process, some COS remains due to chemical equilibrium, but this remaining COS can be removed in the subsequent desulfurization process.
[0044] Subsequently, the hydrolysis gas is introduced into a water-gas shift reactor (A04), and the CO and H2O contained in the hydrolysis gas are subjected to a water-gas shift reaction to form CO2 and H2, thereby creating a shift reaction gas (water-gas shift reaction step).
[0045] The catalyst used in the water-gas shift reaction step can be a catalyst containing a sulfide of at least one element selected from Co, Ni, and Mo. This allows for efficient water-gas shift reaction and COS hydrolysis reaction even when sulfur compounds are present, thereby increasing desulfurization efficiency. As a result, the degradation of catalyst performance can be suppressed, and methanol can be synthesized stably.
[0046] Furthermore, the catalyst used in the water-gas shift reaction process can be a catalyst containing an oxide of at least one element selected from Fe and Cr. This allows the shift reaction to proceed efficiently even when sulfur compounds are present, and enables the shift reaction to be carried out stably.
[0047] The reaction temperature for the water-gas shift reaction can be determined based on the catalyst activity and chemical equilibrium, but as an example, the inlet gas temperature is preferably 200°C to 400°C, more preferably 200°C to 250°C.
[0048] Next, the shift reaction gas is introduced into the CO2 separation unit (A05), where it is separated into CO2 gas (separated CO2 gas (G03)) and pass-through gas (G02), which is a gas containing components other than CO2 (carbon dioxide gas separation process).
[0049] In the CO2 separation unit (A05), the CO2 gas is separated into a separated CO2 gas (G03) that mainly contains CO2 and also contains either COS or H2S, or both, and a gas containing components other than CO2 (G02), specifically a pass-through gas (G02) that mainly contains N2, CO, and H2.
[0050] Various methods can be selected for CO2 separation, including chemical absorption using amines, physical absorption using physical absorption liquids, pressure swing adsorption using adsorbents, and membrane separation using separation membranes. For example, for gases with high CO2 partial pressure, such as those found in reduction furnaces, pressure swing adsorption using zeolites as CO2 adsorbents is preferred.
[0051] When using the pressure swing adsorption method, it is preferable to reduce the H2O concentration in the shift reaction gas beforehand. Methods for reducing the H2O concentration include, for example, cooling condensation using a condenser, and a desiccant method using zeolite, alumina, silica, etc., as H2O adsorbents. The appropriate dew point of the shift reaction gas after dehumidification varies depending on the CO2 adsorbent, but for example, when using zeolite as a CO2 adsorbent, it is preferably 0°C or lower, and more preferably -20°C or lower.
[0052] Next, the separated CO2 gas (G03) is introduced into the desulfurization equipment (A06) to remove at least the H2S from the H2S and COS contained in the separated CO2 gas (G03) and obtain high-concentration CO2 gas (desulfurization process).
[0053] Examples of desulfurization equipment (A06) include equipment based on scrubbers using chemical solutions, chemical absorption methods using amines, physical absorption methods using physical absorption liquids, and dry desulfurization methods using desulfurizing agents. When reducing the sulfur concentration of separated CO2 gas (G03) to 0.1 ppm or less, dry desulfurization is preferable. Examples of dry desulfurization methods include a multi-stage desulfurization method in which a reactor filled with a dry desulfurizing agent containing an iron compound selected from iron oxide or iron hydroxide is placed in the first stage, and a reactor filled with a dry desulfurizing agent containing at least one compound selected from zinc and copper, such as copper oxide, is placed in the second stage. In this case, H2S is removed in the first stage reactor, and COS is removed in the second stage reactor. The temperature in these desulfurization facilities (A06) is preferably 10°C to 50°C in reactors filled with iron-containing desulfurizing agents, and 10°C to 400°C in reactors filled with dry desulfurizing agents containing at least one compound selected from zinc and copper, such as copper oxide.
[0054] Subsequently, H2 gas (G04) is added to the high-concentration CO2 to produce methanol raw material gas (G05) (hydrogenation step).
[0055] Methods for obtaining the above-mentioned raw material H2 gas (G04) include vaporization of liquefied hydrogen, electrolysis of H2O, and separation from H2-containing gases.
[0056] Next, the methanol raw material gas (G05) is compressed in the compressor (A07), and then passed through the methanol synthesis space (A02-3) inside the membrane reactor (A02) which is filled with a methanol synthesis catalyst. There, the CO2 and H2 contained in the methanol raw material gas (G05) are reacted according to the following reaction equation (1) to synthesize methanol. CO2 + 3H2 → CH3OH + H2O (1)
[0057] The pressurization in the compressor (A07) is preferably 1.0 MPa or higher, more preferably 3.0 MPa or higher. To prevent heating during compression and a decrease in compression efficiency, it is preferable to compress the raw material gas (G05) using multiple stage compressors (A07).
[0058] A portion of the H2O produced in the methanol synthesis space (A02-3) permeates through the separation membrane (A02-2) and flows into the sweep space (A02-1), where it is swept by the raw material gas (G01) as described above.
[0059] In the membrane reactor (A02), the sweep space (A02-1), separation membrane (A02-2), and methanol synthesis space (A02-3) are all located within the same vessel. This allows for the separation of H2O by membrane separation, thereby shifting the chemical equilibrium of methanol synthesis in a manner favorable to methanol production and improving methanol synthesis efficiency.
[0060] Examples of catalysts to be packed into the methanol synthesis space (A02-3) include catalysts containing Cu and Zn. The methanol synthesis reaction temperature can be set based on catalyst activity, gas pressure, chemical equilibrium, etc., but as an example, it is preferably 200°C to 250°C, and more preferably 200°C to 230°C.
[0061] Meanwhile, methanol-containing gas (G06) discharged from the methanol synthesis space (A02-3) is introduced into a condenser / gas-liquid separator (A08) for cooling and separation into methanol-containing liquid (L01) and recycled gas (G07). The separated recycled gas (G07) is introduced into a compressor (A09) for pressurization and then circulated back through the methanol synthesis space (A02-3).
[0062] The temperature at which methanol is condensed from the synthesized methanol-containing gas (G06) in the condenser / gas-liquid separator (A08) is preferably a low temperature above the freezing point of methanol, preferably 50°C or lower, and more preferably 30°C or lower. The condensed methanol-containing liquid (L01) and the recycled gas (G07) are separated by gas-liquid separation.
[0063] Thus, as shown in the flow chart in Figure 1, by synthesizing methanol while removing H2O using a membrane reactor (A02), equilibrium constraints can be relaxed and the methanol synthesis efficiency can be increased. Furthermore, the H2O separated by the separation membrane (A02-2) can be used to carry out COS hydrolysis and the aqueous gas shift reaction sufficiently. In addition, in the sweep step, the heat generated in the methanol synthesis step heats the hydrolyzed feedstock gas to a temperature suitable for COS hydrolysis, thus reducing the energy consumption required to heat the hydrolyzed feedstock gas.
[0064] Figure 2 shows a flow chart of another preferred example of the methanol synthesis method according to the present invention. The flow shown in Figure 2 differs from the flow shown in Figure 1 in that, in addition to the above, it includes: (A) the use of blast furnace gas discharged from the blast furnace (A10) of the steelworks as the raw material gas (G01); (B) a further heat exchange step (first heat exchange step) in which heat is exchanged between the raw material gas (G01) after the washing process in the washing machine (A01) and methanol-containing gas (G06) discharged from the methanol synthesis space (A02-3) using a heat exchanger HX1; (C) a further heat exchange step (second heat exchange step) in which heat is exchanged between the hydrolysis gas discharged from the COS hydrolysis reactor (A03) and the shift reaction gas discharged from the water gas shift reactor (A04) using a heat exchanger HX2; and (D) a further hydrogen gas separation step in which H2 gas is separated from the pass-through gas (G02) discharged from the CO2 separation unit (A05) by an H2 separation unit (A11), and this is used as part of the raw material H2 gas (G04).
[0065] Regarding the above difference (B), heat exchange between the raw material gas (G01) after the washing process in the washer (A01) and the methanol-containing gas (G06) discharged from the methanol synthesis space (A02-3) increases the temperature of the raw material gas (G01) circulating in the sweep space (A02-1), thereby suppressing a decrease in the activity of the methanol synthesis catalyst. The temperature of the raw material gas (G01) is preferably 100°C or higher, and more preferably 150°C or higher.
[0066] Regarding the above difference (C), the heat exchange between the hydrolysis gas discharged from the COS hydrolysis reactor (A03) and the shift reaction gas discharged from the water gas shift reactor (A04) allows the heat generated in the water gas shift reaction to be used to set the temperature of the hydrolysis gas to a temperature suitable for the hydrolysis reaction. The temperature of the hydrolysis gas discharged from the COS hydrolysis reactor (A03) after heat exchange can be set based on the catalyst activity and chemical equilibrium, but as an example, it is preferably 200°C to 300°C, and more preferably 220°C to 260°C.
[0067] Regarding the above difference (D), the H2 separation device (A11) separates the H2 gas into H2 gas mainly containing H2 and separation gas (G08) mainly containing N2 and CO. Various methods can be selected for H2 separation, such as pressure swing adsorption using an adsorbent or membrane separation using a separation membrane. By using the H2 gas separated in this device as raw material H2 gas (G04), the cost of raw material H2 gas can be reduced. [Industrial applicability]
[0068] According to the present invention, valuable substances such as methanol can be synthesized more stably from gases containing carbon dioxide and sulfur compounds, such as blast furnace gas, making it useful in the steel industry. [Explanation of Symbols]
[0069] A01 Water washer A02 Membrane reactor A02-1 Sweep Space A02-2 Separation membrane A02-3 Methanol Synthesis Space A03 COS Hydrolysis Reactor A04 Water-gas shift reactor A05 CO2 separation equipment A06 Desulfurization equipment A07, A09 Compressors A08 Condenser / Gas-Liquid Separator A10 blast furnace A11 H2 separation equipment G01 Raw material gas G02 Through Gas G03 Separated CO2 gas G04 Raw material H2 gas G05 Methanol feedstock gas G06 Methanol-containing gas G07 Recycled Gas G08 Separation gas HX1,HX2 heat exchanger L01 Methanol-containing liquid
Claims
1. A methanol synthesis method comprising synthesizing methanol from a source gas containing carbon dioxide, carbon monoxide, hydrogen sulfide, and carbonyl sulfide, and hydrogen gas, A water addition step is to add water to the raw material gas to obtain a hydrous raw material gas, The hydrolysis step involves hydrolyzing the aforementioned hydrolyzed raw material gas by converting the carbonyl sulfide contained in the hydrolyzed raw material gas into hydrogen sulfide and carbon dioxide to obtain a hydrolysis gas. The hydrolysis gas is subjected to a water-gas shift reaction step, in which the carbon monoxide and water contained in the hydrolysis gas undergo a water-gas shift reaction to form a shift reaction gas, A carbon dioxide gas separation step is performed to separate the shift reaction gas into carbon dioxide gas and gases of components other than carbon dioxide. A desulfurization step to remove hydrogen sulfide and at least hydrogen sulfide from carbonyl sulfide contained in the carbon dioxide gas to obtain high-concentration carbon dioxide gas, A hydrogenation step involves adding hydrogen gas to the aforementioned high-concentration carbon dioxide gas to obtain methanol as a raw material gas, A methanol synthesis step involves reacting carbon dioxide and hydrogen contained in the methanol raw material gas to produce methanol, A methanol synthesis method comprising the following:
2. The methanol synthesis method according to claim 1, wherein the water added to the raw material gas in the water addition step is water produced as a by-product in the methanol synthesis step.
3. The methanol synthesis method according to claim 2, wherein the methanol synthesis step includes a membrane separation step of separating the water produced as a by-product of the reaction between carbon dioxide and water by permeating through a membrane, and the water separated in the membrane separation step is used as the water added to the raw material gas in the water addition step.
4. The methanol synthesis method according to claim 3, wherein the membrane separation step is performed in the same container as the methanol synthesis step.
5. The methanol synthesis method according to claim 3 or 4, wherein the membrane separation step includes a sweep step in which the raw material gas is passed through one side of the membrane and the water that has permeated through the membrane is swept by a sweep gas, the raw material gas is used as the sweep gas, and the raw material gas to which the water that has permeated through the membrane has been added is used as the hydrolyzed raw material gas.
6. The methanol synthesis method according to any one of claims 1 to 4, wherein the method used in the desulfurization step is a dry desulfurization method using a dry desulfurizing agent containing an iron compound selected from iron oxide or iron hydroxide.
7. The methanol synthesis method according to claim 6, wherein some or all of the iron compound is derived from precipitate generated during water treatment at a steel mill.
8. The methanol synthesis method according to any one of claims 1 to 4, wherein the method used in the desulfurization step is a dry desulfurization method using a dry desulfurizing agent containing at least one compound selected from zinc and copper.
9. A methanol synthesis method according to any one of claims 1 to 4, further comprising a heat exchange step of performing heat exchange between the shift reaction gas and the hydrolysis gas.
10. The methanol synthesis method according to claim 5, further comprising a water washing step in which the raw material gas is brought into contact with liquid water to wash it, prior to the sweep step.
11. The methanol synthesis method according to any one of claims 1 to 4, wherein the catalyst used for the hydrolysis is a catalyst having an Al oxide.
12. The methanol synthesis method according to any one of claims 1 to 4, wherein the catalyst used in the water-gas shift reaction step is a catalyst containing a sulfide of at least one element selected from Co, Ni, and Mo.
13. The methanol synthesis method according to any one of claims 1 to 4, wherein the catalyst used in the water-gas shift reaction step is a catalyst containing an oxide of at least one element selected from Fe and Cr.
14. A methanol synthesis method according to any one of claims 1 to 4, further comprising a hydrogen gas separation step for separating hydrogen gas from the gas of components other than carbon dioxide separated in the carbon dioxide gas separation step.
15. The methanol synthesis method according to any one of claims 1 to 4, wherein the raw material gas is exhaust gas discharged from a reduction furnace.
16. The methanol synthesis method according to claim 15, wherein the reduction furnace is a blast furnace in a steel mill, and the raw material gas is blast furnace gas.