Method for synthesizing methanol

Abstract

Provided is a method for more stably synthesizing methanol from a gas containing carbon dioxide and a sulfur compound, such as a blast furnace gas. This method comprises: a water addition step for adding water to a raw material gas G01; a hydrolysis step for hydrolyzing carbonyl sulfide contained in an obtained hydrated raw material gas into hydrogen sulfide and carbon dioxide; a water-gas shift reaction step for converting carbon monoxide and water contained in an obtained hydrolyzed gas to carbon dioxide and hydrogen; a carbon dioxide gas separation step for separating an obtained shift reaction gas into carbon dioxide gas and a gas of a component other than carbon dioxide; a desulfurization step for removing at least hydrogen sulfide among hydrogen sulfide and carbonyl sulfide contained in the carbon dioxide gas to obtain a high-concentration carbon dioxide gas; a hydrogen addition step for adding hydrogen gas to the high-concentration carbon dioxide gas; and a methanol synthesis step for reacting carbon dioxide and hydrogen contained in an obtained methanol raw material gas with each other to produce methanol.

Description

Methanol synthesis method

[0001] The present invention relates to a method for synthesizing methanol, and more particularly to a method for synthesizing methanol from a gas containing carbon dioxide and sulfur compounds such as hydrogen sulfide and carbonyl sulfide.

[0002] In recent years, carbon dioxide (CO ２ Steelworks emit large amounts of by-product gases, including blast furnace gas, which is a by-product of blast furnaces, coke oven gas, and converter gas, which is produced in converters. Blast furnace gas, which emits the most, contains a large amount of CO. ２ By-product gases such as blast furnace gas are used as an energy source within steelworks, but the CO contained in blast furnace gas ２ is emitted as is. ２ There is an urgent need to reduce emissions.

[0003] Under these circumstances, Patent Document 1 describes ２ As an effective way to utilize CO ２ and hydrogen (H ２ A method for synthesizing methanol from a raw material gas containing methyl methyl ether has been proposed.

[0004] In addition, Patent Document 2 discloses a method for producing water (H ２ O) to improve the efficiency of methanol synthesis, and ２ H by the water gas shift reaction using O ２ A method for obtaining this has been proposed.

[0005] Patent No. 7049075 Specification JP 2020-132439 A

[0006] By the way, blast furnace gas contains CO ２ , carbon monoxide (CO), H ２ In addition to these main components, hydrogen sulfide (H ) derived from the sulfur in the iron ore and coke used as raw materials ２ It also contains sulfur compounds such as carbonyl sulfide (COS) and carbonyl sulfide (COS). ２S and COS are known to deteriorate copper-based catalysts used in methanol synthesis.

[0007] In the method proposed in the above Patent Document 1, when blast furnace gas is used as the raw material gas, H ２ Since S and COS flow through the methanol synthesis catalyst, there is a problem in that the catalyst is deteriorated.

[0008] In addition, Patent Document 2 discloses a method for producing H obtained by a water gas shift reaction. ２ Although it is stated that CO is separated by pressure swing adsorption, ２ There is no mention of the use of CO ２ When separated and used for methanol synthesis, ２ S and COS are separated CO ２ However, this method also had the problem of deteriorating the methanol synthesis catalyst because it concentrates on the side of the methanol.

[0009] Furthermore, in Patent Document 2, H ２ Although the water-gas shift reaction is carried out using blast furnace gas as a sweep gas for O, the type of catalyst is not described. However, copper-based catalysts generally used in the water-gas shift reaction are ２ There is a problem that the resistance is deteriorated by S and COS.

[0010] As described above, the methods described in Patent Documents 1 and 2 make it difficult to synthesize methanol stably.

[0011] The present invention aims to solve the above problems and to provide a method for more stably synthesizing methanol from a gas containing carbon dioxide and sulfur compounds, such as blast furnace gas.

[0012] The present invention, which solves the above-mentioned problems, is as follows: [1] A methanol synthesis method for synthesizing methanol from a feed gas containing carbon dioxide, carbon monoxide, hydrogen sulfide, and carbonyl sulfide, and hydrogen gas, comprising the following steps: a moisture addition step of adding water to the feed gas to obtain a hydrated feed gas, a hydrolysis step of hydrolyzing the carbonyl sulfide contained in the hydrated feed gas into hydrogen sulfide and carbon dioxide to obtain a hydrolyzed gas, a water-gas shift reaction step of subjecting the hydrolyzed gas to a water-gas shift reaction to convert the carbon monoxide and water contained in the hydrolyzed gas into carbon dioxide and hydrogen to obtain a shift reaction gas, a carbon dioxide gas separation step of separating the shift reaction gas into carbon dioxide gas and gases of components other than carbon dioxide, a desulfurization step of removing at least the hydrogen sulfide from the hydrogen sulfide and carbonyl sulfide contained in the carbon dioxide gas to obtain a high-concentration carbon dioxide gas, a hydrogenation step of adding hydrogen gas to the high-concentration carbon dioxide gas to obtain a methanol feed gas, and a methanol synthesis step of reacting the carbon dioxide and hydrogen contained in the methanol feed gas to produce methanol.

[0013] [2] The method for synthesizing methanol according to [1] above, 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] above, wherein the methanol synthesis step includes a membrane separation step of separating water by-produced by the reaction of the carbon dioxide and the water by passing the water through a membrane, and the water separated in the membrane separation step is used as water to be added to the raw material gas in the water addition step.

[0015] [4] The method for synthesizing methanol according to [3] above, wherein the membrane separation step is carried out in the same vessel as the methanol synthesis step.

[0016] [5] The method for methanol synthesis according to [3] or [4], wherein the membrane separation step includes a sweep step of passing the feed gas through one side of the membrane and sweeping water that has permeated the membrane with a sweep gas, the feed gas being used as the sweep gas, and the feed gas to which the water that has permeated the membrane has been added is referred to as the hydrated feed gas.

[0017] [6] The method for synthesizing methanol according to any one of [1] to [5] above, wherein the method used in the desulfurization step is a dry desulfurization method using a dry desulfurization agent containing an iron compound selected from iron oxide and iron hydroxide.

[0018] [7] The method for synthesizing methanol according to [6] above, wherein a compound derived from a precipitate generated during water treatment at a steelworks is used as part or all of the iron compound.

[0019] [8] The method for synthesizing methanol according to any one of [1] to [5] above, wherein the method used in the desulfurization step is a dry desulfurization method using a dry desulfurization agent containing at least one compound selected from zinc and copper.

[0020] [9] The method for synthesizing methanol according to any one of [1] to [8], further comprising a heat exchange step of exchanging heat between the shift reaction gas and the hydrolysis gas.

[0021]

[10] The method for synthesizing methanol according to any one of [5] to [9] above, further comprising a water washing step of bringing the raw material gas into contact with liquid water and washing it before the sweeping step.

[0022]

[11] The method for synthesizing methanol according to any one of [1] to

[10] above, wherein the catalyst used in the hydrolysis is a catalyst containing an oxide of Al.

[0023]

[12] The method for synthesizing methanol according to any one of [1] to

[11] above, 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.

[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] , further comprising a hydrogen gas separation step of separating hydrogen gas from gases of components other than 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 an exhaust gas discharged from a 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.

[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.

[0029] 1 is a flow chart of a preferred example of a method for synthesizing methanol according to the present invention; 2 is a flow chart of another preferred example of a method for synthesizing methanol according to the present invention;

[0030] The present invention provides a method for synthesizing methanol from a feed gas containing carbon dioxide, carbon monoxide, hydrogen sulfide, and carbonyl sulfide, and hydrogen gas, comprising the following steps: a water-adding step of adding water to the feed gas to produce a hydrated feed gas; a hydrolysis step of hydrolyzing the carbonyl sulfide contained in the hydrated feed gas into hydrogen sulfide and carbon dioxide to produce a hydrolysis gas; a water-gas shift reaction step of converting the carbon monoxide and water contained in the hydrolysis gas into carbon dioxide and hydrogen through a water-gas shift reaction to produce a shift reaction gas; a carbon dioxide gas separation step of separating the shift reaction gas into carbon dioxide and gases containing components other than carbon dioxide; a desulfurization step of removing at least the hydrogen sulfide from the hydrogen sulfide and carbonyl sulfide contained in the carbon dioxide gas to obtain a high-concentration carbon dioxide gas; a hydrogenation step of adding hydrogen gas to the high-concentration carbon dioxide gas to produce a methanol feed gas; and a methanol synthesis step of reacting the carbon dioxide and hydrogen contained in the methanol feed gas to produce methanol.

[0031] Fig. 1 shows 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 along the flow chart shown in Fig. 1. The methanol synthesis method according to the present invention is carried out by using CO ２ , CO, H ２ A raw material gas (G01) containing S and COS, and H ２ This is a method for synthesizing methanol from gas.

[0032] As such a raw material gas (G01), an exhaust gas discharged from a reducing furnace in a steelworks can be suitably used. Examples of the reducing furnace include a blast furnace, a coke oven, and a gasifier, and as the raw material gas (G01), a blast furnace gas, a coke oven gas, a gasifier gas, etc. can be used. Among these, blast furnace gas can be suitably used as the raw material gas (G01), which allows stable synthesis of methanol. In the following description, the raw material gas G01 is defined as N, which is often contained in the exhaust gas discharged from a reducing furnace. ２ As an example, the case where the compound contains the following as a component will be described.

[0033] The source gas (G01) is H ２ The source gas (G01) may contain H ２ Depending on the gas content, the additional H required for the synthesis of methanol ２ Methanol can be synthesized using a separate gas.

[0034] First, preferably, the raw material gas (G01) is supplied to a water washer (A01), and the raw material gas (G01) is washed with liquid H ２ The raw material gas (G01) is washed by contacting it with O (water washing step). ２ The amount of O used in the water washing step can be adjusted and the amount of dust in the raw material gas (G01) can be reduced. ２ The temperature of O may be set based on the ambient temperature, etc., and is preferably 0°C or higher and 100°C or lower, more preferably 10°C or higher and 40°C or lower.

[0035] Next, the water-washed raw material gas (G01) is passed through the sweep space (A02-1) in the membrane reactor (A02), and H is added to the raw material gas (G01). ２ O is added to obtain a hydrated raw 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 H ２ O permeates the separation membrane (A02-2) and flows into the sweep space (A02-1). Then, the raw material gas (G01) is passed through the sweep space (A02-1) as a sweep gas, and H permeates the separation membrane (A02-2). ２ It is preferable to sweep O (sweeping step). This allows the source gas (G01) to contain H ２ O can be efficiently added to the raw material gas to form a hydrated raw material gas, and H ２ The load of adding O can be reduced.

[0037] The temperature of the hydrous feed gas discharged from the sweep space (A02-1) may vary depending on the conditions for the methanol synthesis in the subsequent stage and the properties of the separation membrane (A02-2). However, the temperature is set to be an appropriate temperature for the COS hydrolysis in the subsequent stage, preferably 100°C or higher and 250°C or lower, more preferably 150°C or higher and 200°C or lower.

[0038] Next, the hydrated raw gas is introduced into a COS hydrolysis reactor (A03), and the COS contained in the hydrated raw gas is hydrolyzed by H ２ S and CO ２ The resulting mixture is then hydrolyzed to produce a hydrolyzed gas (hydrolysis step).

[0039] The catalyst used in the hydrolysis step is preferably a catalyst containing an oxide of aluminum (Al). This improves the efficiency of hydrolysis, efficiently performs COS hydrolysis, and increases the desulfurization efficiency in the desulfurization step described below. The catalyst more preferably further contains potassium (K) in addition to the oxide of Al.

[0040] The reaction temperature for hydrolysis may be set based on the activity and chemical equilibrium of the catalyst, and as described above, is preferably 100°C or higher and 250°C or lower, more preferably 150°C or higher and 200°C or lower.

[0041] It is preferable that the COS hydrolysis reactor (A03) be installed upstream of the water-gas shift reactor (A04) described below, and that the COS hydrolysis step be performed before the water-gas shift reaction step described below, because the water-gas shift reaction is an exothermic reaction, and the temperature downstream of the water-gas shift reactor (A04) rises to a temperature higher than that suitable for COS hydrolysis.

[0042] In addition, when a gas with a high CO concentration (for example, about 20% by volume) such as blast furnace gas is used as the raw material gas (G01), H ２ In order to consume O, H is generated downstream of the water gas shift reactor (A04). ２ This is because the O concentration decreases, resulting in a gas composition that is not suitable for COS hydrolysis. COS hydrolysis is also an exothermic reaction, and H ２Although this reaction consumes O, the COS concentration in the blast furnace gas (for example, 100 ppm or less) is much lower than the CO concentration. Therefore, the temperature change of the gas and the H ２ The change in O concentration is slight, and it is considered that the effect on the water gas shift reactor (A04) is also small.

[0043] In the hydrolysis step, some COS remains due to chemical equilibrium, but the remaining COS can be removed in the subsequent desulfurization step.

[0044] Thereafter, the hydrolysis gas is introduced into a water gas shift reactor (A04), and the hydrolysis gas is separated into CO and H contained in the hydrolysis gas. ２ O and CO ２ and H ２ The water-gas shift reaction is carried out with the sulphur dioxide and the sulphur dioxide to produce 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 cobalt (Co), nickel (Ni), and molybdenum (Mo). This allows the water-gas shift reaction and COS hydrolysis reaction to proceed efficiently, even when sulfur compounds are present in the stream, thereby increasing desulfurization efficiency. As a result, deterioration of catalytic performance can be suppressed, and methanol can be synthesized stably.

[0046] The catalyst used in the water-gas shift reaction step may contain an oxide of at least one element selected from iron (Fe) and chromium (Cr), which allows the shift reaction to proceed efficiently and stably even when sulfur compounds are present.

[0047] The reaction temperature of the water gas shift reaction may be set based on the activity and chemical equilibrium of the catalyst, and is preferably 200°C or higher and 400°C or lower, more preferably 200°C or higher and 250°C or lower, in terms of the inlet gas temperature.

[0048] Next, the shift reaction gas is ２ The shift reaction gas is introduced into a separation device (A05) and CO２ Gas (separated CO ２ gas (G03)) and CO ２ The carbon dioxide gas is separated into a passing gas (G02) which is a gas containing components other than the carbon dioxide gas (carbon dioxide gas separation step).

[0049] CO ２ In the separation unit (A05), mainly CO ２ and further containing COS or H ２ Separated CO containing one or both of S ２ Gas (G03) and CO ２ Gas (G02) containing components other than N ２ , CO, H ２ and a passing gas (G02) containing

[0050] CO ２ The separation method may be selected from various methods such as chemical absorption using amines, physical absorption using a physical absorption solution, pressure swing adsorption using an adsorbent, and membrane separation using a separation membrane. ２ For gases with high partial pressure, zeolite is used to ２ Pressure swing adsorption is preferred as the adsorbent.

[0051] When the pressure swing adsorption method is used, H contained in the shift reaction gas ２ It is preferable to reduce the O concentration in advance. ２ As a method for reducing the O concentration, for example, cooling and condensation using a condenser, or immersing zeolite, alumina, silica, etc. in H ２ The dew point of the shift reaction gas after dehumidification is ２ The optimum range varies depending on the adsorbent. For example, zeolite is used for CO ２ When used as an adsorbent, the temperature is preferably 0°C or lower, more preferably -20°C or lower.

[0052] Next, separated CO ２ The gas (G03) is introduced into the desulfurization equipment (A06) and separated CO ２ H contained in gas (G03) ２ At least H of S and COS ２ Removes S and high-concentration CO２ Gas is obtained (desulfurization process).

[0053] Examples of the desulfurization equipment (A06) include equipment based on a scrubber using a chemical solution, a chemical absorption method using an amine, a physical absorption method using a physical absorption solution, and a dry desulfurization method using a desulfurization agent. ２ When the sulfur concentration of the gas (G03) is reduced to 0.1 ppm or less, it is preferable to use dry desulfurization. Examples of the dry desulfurization method include a multi-stage desulfurization method in which a reactor filled with a dry desulfurization agent containing an iron compound selected from iron oxide or iron hydroxide is installed in the first stage, and a reactor filled with a dry desulfurization agent containing at least one compound selected from zinc (Zn) and copper (Cu), for example, copper oxide, is installed in the second stage. In this case, H ２ S is removed in the first-stage reactor, and COS is removed in the second-stage reactor. The temperature in these desulfurization facilities (A06) is, for example, preferably 10°C or higher and 50°C or lower in the case of a reactor filled with a desulfurization agent containing Fe, and 10°C or higher and 400°C or lower in the case of a reactor filled with a dry desulfurization agent containing at least one compound selected from Zn and Cu, for example, copper oxide.

[0054] Then, high-concentration CO ２ Raw material H ２ A gas (G04) is added to produce a methanol raw material gas (G05) (hydrogenation step).

[0055] The above raw material H ２ Methods for obtaining gas (G04) include vaporization of liquefied hydrogen, H ２ Electrolysis of O, H ２ and separation from the gases contained therein.

[0056] Next, the methanol raw material gas (G05) is compressed by a compressor (A07), and then passed through a methanol synthesis space (A02-3) filled with a methanol synthesis catalyst inside the membrane reactor (A02). CO contained in the methanol raw material gas (G05) is converted into CO according to the following reaction formula (1): ２ and H ２ Methanol is synthesized by reacting with CO ２ +3H ２ →CH ３ OH+H２ O (1)

[0057] The pressure in the compressor (A07) is preferably 1.0 MPa or more, more preferably 3.0 MPa or more. In order to prevent heating during compression and a decrease in compression efficiency, it is preferable to compress the raw material gas (G05) using a multi-stage compressor (A07).

[0058] H produced in the methanol synthesis space (A02-3) ２ A part of O permeates the separation membrane (A02-2) and flows into the sweep space (A02-1), and is swept by the source gas (G01) as described above.

[0059] The sweep space (A02-1), separation membrane (A02-2) and methanol synthesis space (A02-3) in the membrane reactor (A02) are configured in the same vessel. ２ By separating O, the chemical equilibrium of methanol synthesis can be changed to favor the production of methanol, thereby improving the efficiency of methanol synthesis.

[0060] The catalyst to be filled in the methanol synthesis space (A02-3) may be a catalyst containing Cu or Zn. The methanol synthesis reaction temperature may be set based on the catalyst activity, gas pressure, chemical equilibrium, etc., and is preferably 200°C or higher and 250°C or lower, more preferably 200°C or higher and 230°C or lower.

[0061] Meanwhile, the methanol-containing gas (G06) discharged from the methanol synthesis space (A02-3) is introduced into a condenser / gas-liquid separator (A08) where it is cooled and separated into a methanol-containing liquid (L01) and a recycled gas (G07). The separated recycled gas (G07) ​​is introduced into a compressor (A09) where it is pressurized, and then circulates again through the methanol synthesis space (A02-3).

[0062] The temperature at which methanol is condensed from the methanol-containing gas (G06) after synthesis in the condenser / gas-liquid separator (A08) is preferably a low temperature equal to or higher than the freezing point of methanol, preferably 50° C. or lower, 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, according to the flow shown in FIG. 1, H ２ By synthesizing methanol while removing O, the equilibrium constraint can be alleviated and the efficiency of methanol synthesis can be increased. ２ The presence of O allows the COS hydrolysis and the water-gas shift reaction to proceed satisfactorily. Furthermore, in the sweep step, the hydrated feed gas is heated by the heat generated in the methanol synthesis step to a temperature appropriate for COS hydrolysis, thereby reducing the energy consumption required to heat the hydrated feed gas.

[0064] Fig. 2 shows a flow chart of another preferred example of the methanol synthesis method according to the present invention. In addition to the flow chart shown in Fig. 1, the flow chart shown in Fig. 2 has the following features: (A) blast furnace gas discharged from a blast furnace (A10) of a steelworks is used as the raw material gas (G01); (B) a heat exchange step (first heat exchange step) is performed by a heat exchanger HX1 between the raw material gas (G01) after the water-washing step in the water washer (A01) and a methanol-containing gas (G06) discharged from the methanol synthesis space (A02-3); (C) a heat exchange step (second heat exchange step) is performed by a heat exchanger HX2 between the hydrolysis gas discharged from the COS hydrolysis reactor (A03) and the shift reaction gas discharged from the water-gas shift reactor (A04); and (D) a CO ２ H from the passing gas (G02) discharged from the separation device (A05) ２ H by a separation device (A11) ２ The method further comprises a hydrogen gas separation step of separating the raw material H ２ The difference is that it is used as part of the gas (G04).

[0065] Regarding the difference (B), heat exchange between the raw material gas (G01) after the water washing step in the water 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) flowing through the sweep space (A02-1), thereby preventing a decrease in the activity of the methanol synthesis catalyst. The temperature of the raw material gas (G01) is, for example, preferably 100°C or higher, more preferably 150°C or higher.

[0066] Regarding the above difference (C), the temperature of the hydrolysis gas can be set to a temperature appropriate for the hydrolysis reaction by utilizing the heat generated in the water-gas shift reaction through 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). The temperature of the hydrolysis gas discharged from the COS hydrolysis reactor (A03) after heat exchange can be set based on the activity and chemical equilibrium of the catalyst, and is, for example, preferably 200°C or higher and 300°C or lower, and more preferably 220°C or higher and 260°C or lower.

[0067] Regarding the above difference (D), H ２ In the separation device (A11), mainly H ２ containing H ２ gas, and mainly N ２ and a separated gas (G08) containing CO. ２ The separation method can be selected from various methods such as pressure swing adsorption using an adsorbent or membrane separation using a separation membrane. ２ Gas is raw material H ２ By using it as gas (G04), the raw material H ２ Gas costs can be reduced.

[0068] INDUSTRIAL APPLICABILITY The present invention is useful in the steel industry because it enables valuable materials such as methanol to be synthesized more stably from gases containing carbon dioxide and sulfur compounds, such as blast furnace gas.

[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 CO ２ Separation equipment A06 Desulfurization equipment A07, A09 Compressor A08 Condenser / gas-liquid separator A10 Blast furnace A11 H ２ Separation device G01 Raw gas G02 Passing gas G03 Separation CO ２ Gas G04 Raw Material H ２ Gas G05 Methanol raw material gas G06 Methanol-containing gas G07 Recycle gas G08 Separation gas HX1, HX2 Heat exchanger L01 Methanol-containing liquid

Claims

1. A method for synthesizing methanol from a feed gas containing carbon dioxide, carbon monoxide, hydrogen sulfide, and carbonyl sulfide, and hydrogen gas, comprising the steps of: a moisture addition step of adding water to the feed gas to obtain a hydrated feed gas; a hydrolysis step of hydrolyzing the carbonyl sulfide contained in the hydrated feed gas into hydrogen sulfide and carbon dioxide to obtain a hydrolysis gas; a water-gas shift reaction step of subjecting the hydrolysis gas to a water-gas shift reaction of the carbon monoxide and the water contained in the hydrolysis gas into carbon dioxide and hydrogen 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 the 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 feed gas; and a methanol synthesis step of reacting the carbon dioxide contained in the methanol feed gas with hydrogen to produce methanol.

2. The method for synthesizing methanol according to claim 1, wherein the water added to the raw material gas in the moisture addition step is water produced as a by-product in the methanol synthesis step.

3. The method for synthesizing methanol according to claim 2, wherein the methanol synthesis step includes a membrane separation step of separating water produced as a by-product of the reaction between the carbon dioxide and the water by passing it through a membrane, and the water separated in the membrane separation step is used as the water to be added to the raw material gas in the water addition step.

4. The method for synthesizing methanol according to claim 3, wherein the membrane separation step is carried out in the same vessel as the methanol synthesis step.

5. A method for synthesizing methanol according to claim 3 or 4, wherein the membrane separation step includes a sweep step of passing the feed gas through one side of the membrane and sweeping water that has permeated the membrane with a sweep gas, the feed gas being used as the sweep gas, and the feed gas to which the water that has permeated the membrane has been added is referred to as the hydrated feed gas.

6. The method for synthesizing methanol according to any one of claims 1 to 5, wherein the method used in the desulfurization step is a dry desulfurization method using a dry desulfurization agent containing an iron compound selected from iron oxide and iron hydroxide.

7. The method for synthesizing methanol according to claim 6, wherein a part or all of the iron compound is derived from a precipitate generated during water treatment in a steelworks.

8. The method for synthesizing methanol according to any one of claims 1 to 5, wherein the method used in the desulfurization step is a dry desulfurization method using a dry desulfurization agent containing at least one compound selected from the group consisting of zinc and copper.

9. The method for synthesizing methanol according to any one of claims 1 to 8, further comprising a heat exchange step of exchanging heat between the shift reaction gas and the hydrolysis gas.

10. The method for synthesizing methanol according to any one of claims 5 to 9, further comprising a water washing step of bringing the raw material gas into contact with liquid water and washing it prior to the sweeping step.

11. The method for synthesizing methanol according to any one of claims 1 to 10, wherein the catalyst used in the hydrolysis is a catalyst having an oxide of Al.

12. The method for synthesizing methanol according to any one of claims 1 to 11, wherein the catalyst used in the water-gas shift reaction step is a catalyst containing a sulfide of at least one element selected from the group consisting of Co, Ni and Mo.

13. The method for synthesizing methanol according to any one of claims 1 to 12, wherein the catalyst used in the water-gas shift reaction step is a catalyst containing an oxide of at least one element selected from the group consisting of Fe and Cr.

14. The method for synthesizing methanol according to any one of claims 1 to 13, further comprising a hydrogen gas separation step of separating hydrogen gas from gases of components other than carbon dioxide separated in the carbon dioxide gas separation step.

15. The method for synthesizing methanol according to any one of claims 1 to 14, wherein the raw material gas is an exhaust gas discharged from a reduction furnace.

16. The method for synthesizing methanol according to claim 15, wherein the reduction furnace is a blast furnace in a steelworks, and the raw material gas is blast furnace gas.

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