Methanol production method and methanol production device

Abstract

Provided is a methanol production method comprising: a step (A) for obtaining a synthesis gas that contains 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 each of methanol and distilled wastewater; a step (D) for removing, from the distilled wastewater, an acid and / or a base and salts of these; and a step (E) for using, in step (A), a gas and / or a liquid obtained in step (D).

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 raw material, methanol is synthesized from synthesis gas obtained by steam reforming natural gas (mainly methane) with the addition of steam. The reaction product obtained by this synthesis is a methanol mixture containing components other than methanol (hereinafter also referred to as crude methanol). Therefore, the crude methanol is purified by a distillation process to obtain purified methanol. In the distillation process, a certain amount of wastewater is discharged to maintain the purity of the methanol. Therefore, from the perspective of reducing the environmental impact, it has been proposed to reuse this wastewater, for example by using it for steam reforming.

[0003] For example, Patent Document 1 discloses a method for producing methanol, characterized in that, for the purpose of recovering fusel oil and converting it into methanol, the method comprises: (a) generating methanol synthesis gas by reacting a carbonaceous feedstock with a gasifying agent selected from steam, carbon dioxide, and oxygen; (b) reacting the synthesis gas over a methanol synthesis catalyst and recovering a crude methanol liquid product from the reacted gas; (c) adding an alkali metal hydroxide or carbonate to the crude methanol liquid product; (d) distilling the resulting mixture to separate from the mixture a purified methanol stream and a liquid fusel oil stream containing organic hydrocarbons having a boiling point higher than that of methanol and alkali metal compounds; and (e) recycling the fusel oil stream to a synthesis gas generation reaction to convert the organic hydrocarbons into synthesis gas.

[0004] Patent Document 2 discloses a methanol synthesis plant that, in addition to specified constituent features, includes a fusel oil stripper that strips volatile organic components from the fusel waste oil stream produced in the methanol synthesis plant, and a recycle line for supplying the stripped organic components as a hydrocarbon gas feedstock to a reforming device, with the aim of providing a method and apparatus for recovering volatile organic components from the fusel waste oil stream produced in the methanol synthesis plant to increase product yield and simultaneously reduce or eliminate waste liquid streams.

[0005] Patent Document 3 discloses a methanol production method for producing methanol from hydrocarbons, in addition to specified constituent elements, for the purpose of utilizing wastewater from a distillation step in the process, comprising the steps of: (a) reacting hydrocarbons with steam to generate a synthesis gas mainly composed of hydrogen, carbon monoxide, and carbon dioxide; (b) reacting the synthesis gas on a methanol synthesis catalyst and recovering crude methanol produced in liquid form from the reaction gas; and (c) distilling the recovered crude methanol to separate it into purified methanol and wastewater containing low-boiling organic compounds, high-boiling organic compounds, and organic acids; and wherein, in step (c), a neutralization step with an alkali metal is not performed, but the wastewater is brought into contact with gaseous hydrocarbons to humidify the hydrocarbons and then supplied to step (a).

[0006] Patent Document 4 aims to provide a method for humidifying hydrocarbons by utilizing wastewater from a distillation step to which alkali metal salts whose recovery is desired have been added, thereby reducing process steam, i.e., expensive boiler water. The method includes the steps of: (a) reacting hydrocarbons with steam to generate a synthesis gas mainly composed of hydrogen, carbon monoxide, and carbon dioxide; (b) reacting the synthesis gas on a methanol synthesis catalyst to recover crude methanol produced from the reaction gas in liquid form; and (c) distilling the recovered crude methanol to separate it into purified methanol and wastewater containing low-boiling organic compounds, high-boiling organic compounds, and organic acids. The method for producing methanol from hydrocarbons includes the steps of: bringing the hydrocarbons into contact with the wastewater that has been neutralized with an alkali metal salt or hydroxide in step (c) to humidify them; bringing the hydrocarbons into contact with condensed water separated from the synthesis gas in step (a) to humidify them; and supplying the humidified hydrocarbons to step (a).

[0007] Patent Document 5 discloses a method for producing biogas from organic waste, characterized by anaerobic digestion and concentration of biogas in a concentration device, with the aim of providing a method that has overall greater economic advantages compared to prior art methods for producing methanol from organic waste.

[0008] Patent Document 6 discloses a system for producing bioproducts that combines an anaerobic digester that converts biomass into a mixture of gases containing methane and carbon dioxide, a synthesis gas generator that can convert methane into a mixture of carbon monoxide and hydrogen, and a gas converter, with the aim of significantly reducing capital costs and operating costs.

[0009] Patent Document 7 discloses a biomass-utilizing methanol production apparatus that aims to inexpensively obtain hydrogen necessary for carbon dioxide fixation and use that hydrogen to convert carbon dioxide into methanol for fixation. The apparatus comprises: a methane generation section that generates methane and carbon dioxide through anaerobic fermentation of biomass; a methane decomposition section that decomposes the methane generated in the methane generation section into carbon and hydrogen using a catalyst; and a methanol production section that reacts carbon dioxide with the hydrogen generated in the methane decomposition section using a catalyst to synthesize methanol.

[0010] Japanese Patent Publication No. 03-031694 Publication No. 07-145089 Publication No. 08-002808 Patent No. 3848716 WO2018115596 Publication US10240119 Patent Publication No. 11-188262

[0011] However, in Patent Document 1, since a liquid containing an alkali metal compound is left behind, the alkali metal compound is inevitably concentrated in the water, which carries the risk of corroding equipment made of metal materials.

[0012] In Patent Document 2, the alkali content cannot be removed from the fusel oil before it is brought into contact with the unreformed gas, and although a stripper is described, there is a risk of corrosion in the stripper.

[0013] In Patent Document 3, the distillation process does not include a neutralization step using an alkali metal, and there is no need to remove alkali from the fusel oil. However, if an alkali metal is not introduced in the distillation process, impurities are likely to be insufficiently separated, which may have an adverse effect on product quality.

[0014] Patent Document 4 describes neutralization with an alkali metal in the distillation step, but does not include a step for removing the salt generated by neutralization. Therefore, although the risk of corrosion by alkali is reduced, the risk of corrosion due to concentrated salt still remains.

[0015] Patent Document 5 describes the synthesis of methanol from organic waste, but makes no mention of the distillation wastewater discharged from the distillation process, and of course makes no mention of the risk of corrosion when recycling the distillation wastewater.

[0016] Patent Document 6 describes the synthesis of methanol from biomass, but does not mention the distillation wastewater discharged from the distillation process, nor does it mention the risk of corrosion when recycling the distillation wastewater.

[0017] Patent Document 7 describes the synthesis of methanol from carbon dioxide and hydrogen using digester gas as a raw material, but makes no mention of the distillation wastewater discharged from the distillation process, and naturally makes no mention of the risk of corrosion when recycling the distillation wastewater.

[0018] As described above, the inventors' intensive studies have revealed that wastewater can be acidic due to components such as formic acid generated as a by-product of methanol, and can become alkaline when neutralized with an excessive amount of alkali, so that reusing distillation wastewater as is for steam reforming, etc., poses a risk of corroding steam reforming equipment, etc. In addition, it has been found that if alkaline distillation wastewater is reused, the carbon dioxide contained in the gas used as a raw material for methanol synthesis will react with the alkali, resulting in a deterioration in the unit consumption.

[0019] Furthermore, as a result of extensive research by the present inventors, it was found that even when wastewater is neutralized to a neutral pH, the salts generated by the neutralization still tend to corrode equipment.

[0020] 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 using natural gas or waste as a raw material, which recycles distillation wastewater while reducing corrosion of equipment caused by the distillation wastewater.

[0021] As a result of intensive research into solving the above problems, the present inventors have found that the present invention has the following features, which make it possible to recycle distillation wastewater while reducing corrosion of equipment caused by the distillation wastewater, and have thus completed the present invention.

[0022] [1] A method for producing methanol, comprising: (A) obtaining a synthesis gas containing at least carbon dioxide and hydrogen; (B) reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; (C) distilling the methanol mixture to separate methanol and distillation wastewater; (D) removing an acid and / or a base and their salts from the distillation wastewater; and (E) using the gas and / or liquid obtained in step (D) in step (A). [2] The method for producing methanol according to [1], wherein the molar flow rate of carbon atoms contained in the gas and / or liquid obtained in step (D) is 70 mol % or more relative to the molar flow rate of carbon atoms contained in the distillation wastewater. [3] The method for producing methanol according to [1] or [2], wherein step (A) comprises step (F) of reforming hydrocarbons contained in the gas and / or liquid obtained in step (D) to obtain a reformed gas. [4] The method for producing methanol according to any of [1] to [3], further comprising a desulfurization step (G). [5] The method for producing methanol according to any one of [1] to [4], wherein step (D) comprises removing an acid and / or a base and salts thereof using an ion exchanger. [6] The method for producing methanol according to any one of [1] to [5], wherein step (D) comprises removing an acid and / or a base and salts thereof by anaerobic treatment. [7] The method for producing methanol according to any one of [1] to [6], further comprising step (H) of combusting the gas obtained by the anaerobic treatment to recover heat. [8] A methanol production apparatus comprising: a synthesis gas preparation unit; a methanol synthesis unit; a distillation unit; and a deionization unit or an anaerobic treatment unit, wherein the gas and / or liquid obtained by the deionization unit or the anaerobic treatment unit is used in the synthesis gas preparation unit. [9] The methanol production apparatus according to [8], wherein the synthesis gas preparation unit comprises a reformer.

[10] The methanol production apparatus according to [8] or [9], further comprising a desulfurization unit.

[0023] According to the present invention, it is possible to provide a method for producing methanol that recycles distillation wastewater while reducing corrosion of equipment caused by the distillation wastewater.

[0024] 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 another example of a production apparatus used in a methanol production method corresponding to a comparative example. FIG. 5 is a schematic diagram showing another example of a production apparatus used in a methanol production method corresponding to a comparative example. FIG. 6 is a schematic diagram showing an example of an anaerobic treatment unit of the present embodiment. FIG. 7 is a schematic diagram showing an example of a gasification preparation step of the present embodiment. FIG. 8 is a schematic diagram showing another example of the gasification preparation step of the present embodiment.

[0025] 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.

[0026] [Method for Producing Methanol] The method for producing methanol of this embodiment includes: a step (A) of obtaining a synthesis gas containing at least carbon dioxide and hydrogen; a step (B) of reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; a step (C) of distilling the methanol mixture to separate methanol and distillation wastewater; a step (D) of removing an acid and / or a base, and salts thereof, from the distillation wastewater; and a step (E) of using the gas and / or liquid obtained in step (D) in step (A).

[0027] 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.

[0028] 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. When the methanol production method of this embodiment includes a desulfurization step (G) using a desulfurization unit 100, the hydrocarbon-containing gas 1, together with a recycle gas 2, if any, passes through the desulfurization unit 100 to become a desulfurized gas 3, which is then supplied to the synthesis gas preparation unit 200 together with the deionized distillation wastewater 7 or the digester gas 8, where it is prepared into a synthesis gas 4. The synthesis gas 4 is a gas used in the synthesis of methanol and is a gas composed mainly of hydrogen, carbon monoxide, and carbon dioxide.

[0029] [Step (F)] From the viewpoint of improving the methanol yield, etc., step (A) preferably includes a reforming step in which the hydrocarbon-containing gas 1 is reformed in a reforming device to obtain a reformed gas, and in particular, it is more preferable that step (A) includes step (F) in which the hydrocarbon-containing gas 1 contained in the gas and / or liquid obtained in step (D) described below is reformed to obtain a reformed gas.

[0030] The reforming method 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 1 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 content ratio may be about 30 to 50 mol %. A pre-modification step may be included to produce the polyolefin.

[0031] The reforming temperature can be any conventionally known temperature, and is not particularly limited, but can be, for example, 750° C. to 1000° C. Furthermore, a catalyst may be used in the reforming, and such a catalyst can be any conventionally known catalyst, and is not particularly limited, but examples thereof include nickel-based catalysts.

[0032] The hydrocarbon-containing gas 1 is not particularly limited, but examples thereof include refined gas and fossil fuel gas. The refined gas is not particularly limited, but examples thereof include methane, ethane, propane, butane, and mixtures thereof. The fossil fuel gas includes natural gas (NG), liquefied petroleum gas (LPG), and naphtha, which are mainly composed of methane. When the hydrocarbon-containing gas is a fossil fuel gas, sulfur is contained in the gas components, so it is preferable to use a desulfurized gas 3 that has been subjected to a desulfurization step (G) described below in step (A).

[0033] Step (A) may include a gasification and preparation step in which an organic material is gasified and / or combusted to obtain a synthesis gas 4. Examples of the organic material include, but are not limited to, waste plastics, biomass, and organic waste. The gasification and preparation step includes a gasification step and may further include one or more steps selected from the group consisting of a reforming step, a gas cleaning step, a carbon dioxide separation step, a hydrogenation step, a hydrogen separation step, a shift reaction step, and a shift reverse reaction step.

[0034] Here, the gasification preparation step is not particularly limited, but a conventionally known method can be used, for example, a process using an air gasifier and a process using an oxygen-steam gasifier. Furthermore, these can be further classified as a fixed bed type or a fluidized bed type depending on whether or not the catalyst is fixed, but either can be used. The reforming step can be the same process as described above. The gas scrubbing 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. 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 using pressure swing adsorption, temperature swing adsorption, or membrane separation. The hydrogen separation step is not particularly limited, but a conventionally known method can be used, for example, a method using a hydrogen separation device using pressure swing adsorption, temperature swing adsorption, or membrane separation. 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.

[0035] In the hydrogenation step, hydrogen produced outside the system may be used, and in this case, although there are no particular limitations, it is preferable to use hydrogen obtained using renewable energy, for example, from the viewpoint of reducing carbon dioxide emissions. More specifically, examples of hydrogen that can be used include blue hydrogen such as 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, hydrogen obtained by water electrolysis or saline electrolysis, hydrogen obtained by other electrolysis techniques, and hydrogen obtained by steam reforming.

[0036] Specific examples of the gasification preparation process are not particularly limited, but the configurations shown in Figures 7 and 8 can be used. The gasification preparation process A1 in Figure 7 is a process of obtaining synthesis gas through a gasification process A201 and a gas cleaning process A202 in that order. The gasification preparation process A2 in Figure 7 is a process of obtaining synthesis gas through a gasification process A201 and a reforming process A203 in that order. The gasification preparation process A3 in Figure 7 is a process of 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 7 is a process of 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 7 is a process of obtaining synthesis gas through a gasification process A201 and a hydrogenation process A205 in that order. The gasification preparation process A6 in Fig. 8 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. 8 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.

[0037] 1 and 2 , in step (B) of the methanol production method of this embodiment, 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. In addition, a portion of a purge gas 9 produced as a by-product in the production of crude methanol may be supplied as a recycle gas 2 to the synthesis gas preparation unit 200 or a desulfurization unit 100 located upstream thereof.

[0038] 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 a purge gas 9 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.

[0039] The purge gas refers to the gas separated from the crude methanol after the methanol synthesis reaction. The purge gas mainly includes gases not used in the reaction. The purge gas is a mixed gas that may contain hydrogen, carbon monoxide, carbon dioxide, methane, nitrogen, and the like, 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 allows for further reduction in carbon dioxide emissions.

[0040] 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.

[0041] 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.

[0042] 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, carbon yield tends to be excellent.

[0043] Here, the carbon yield 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 reformed gas supplied to the methanol synthesis unit 300.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] [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 10 and distillation wastewater 6. In this embodiment, methanol refers to purified methanol. Here, distillation wastewater refers to a liquid component containing distillation waste (side cut liquid) and may further contain distillation wastewater (bottoms). Distillation wastewater refers to concentrated methanol withdrawn from each stage of the distillation column and a liquid component containing concentrated alcohol other than methanol and water. Distillation wastewater refers to a liquid component mainly composed of water withdrawn from the bottom of the distillation column.

[0052] As the distillation unit 400, a conventionally known method can be used, and there is no particular limitation, but for example, a distillation column equipped with a reboiler and a condenser can be used. In this case, by distilling the methanol mixture, high-purity methanol can be obtained from the bottom or middle of the column.

[0053] 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.

[0054] 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.

[0055] [Step (D)] The method for producing methanol according to the present embodiment includes step (D) of removing an acid and / or a base and salts thereof from the distillation wastewater 6 obtained in step (C), as shown in Figures 1 and 2. Step (D) is not particularly limited, and examples thereof include the following first and second aspects.

[0056] 1, the first embodiment of step (D) includes a step of removing acids and / or bases and their salts from stillage 6 using a deionization unit 500 (hereinafter also referred to as the deionization step). The stillage 6 is deionized by the deionization unit 500 to become stillage 7.

[0057] The deionization unit 500 is not particularly limited, but conventionally known devices can be used, such as an ion exchanger or an electrodeionization device. Among these, an ion exchanger is preferred from the viewpoints of the accuracy of deionization and the recovery efficiency of the carbon source in the distillation wastewater. The ion exchanger is not particularly limited, but examples thereof include an ion exchange resin and an ion exchange membrane.

[0058] As shown in Figure 2, the second embodiment of step (D) includes a step of removing acids and / or bases and their salts from the distillery wastewater 6 using an anaerobic treatment unit 600. The anaerobic treatment unit 600 does not directly deionize the distillery wastewater 6, but it can selectively extract carbon sources and the like from the distillery wastewater 6, thereby enabling indirect deionization. Here, anaerobic treatment refers to a process in which organic matter is decomposed using microorganisms in an atmosphere in which oxygen is absent or insufficient. The specific configuration of the anaerobic treatment unit is not particularly limited, but can be represented, for example, as shown in Figure 6.

[0059] Specifically, in anaerobic treatment, microorganisms decompose organic matter to produce digestion gas 8 and treated water 11, and the digestion gas 8 can be supplied to the synthesis gas preparation unit 200 in FIG.

[0060] The anaerobic treatment method is not particularly limited, and conventional methods can be used, such as a method using an acid-producing reaction tank with acid-producing bacteria or a method using a methane-producing reaction tank with methanogens. For example, FIG. 6 shows a method using a methanogen-producing reaction tank. The distillery wastewater 6 is first introduced into a methane-producing reaction tank 610 containing microorganisms. The microorganisms 601 decompose the organic matter, generating digester gas 8. Since the digester gas 8 contains methane and carbon dioxide, it can be recovered and used in the synthesis gas preparation unit 200 as a gas unaffected by the acids and / or bases and their salts contained in the distillery wastewater 6. A portion of the solvent in the methane-producing reaction tank is sent to a settling tank 611 and then extracted as treated water 11. 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.

[0061] [Step (H)] When step (D) is anaerobic treatment, the methanol production method of this embodiment preferably further includes step (H) of combusting the gas obtained by the anaerobic treatment to recover heat. Among these, step (H) more preferably includes a step of supplying the gas as fuel for step (A).

[0062] In the methanol production method of this embodiment, the molar flow rate of carbon atoms contained in the gas and / or liquid obtained in step (D) 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 distillery wastewater. This numerical range is not particularly limited, and can be adjusted, for example, by changing the type of ion exchanger in step (D).

[0063] [Step (E)] The method for producing methanol of this embodiment includes step (E) of using the gas and / or liquid obtained in step (D) in step (A). Specifically, when step (D) is a deionization step, step (E) uses deionized distillation wastewater 7 obtained in the deionization step in step (A). When step (D) is anaerobic treatment, step (E) uses digestion gas 8 obtained thereby in step (A).

[0064] [Step (G)] The methanol production method of this embodiment preferably further includes a desulfurization step (G). As shown in FIGS. 1 and 2, step (G) is a step in which a hydrocarbon-containing gas 1 is supplied to a desulfurization unit 100 to obtain a desulfurized gas 3 from which sulfur has been removed. When the hydrocarbon-containing gas is a fossil fuel gas, the desulfurization step (G) is particularly required because it contains sulfur. That is, sulfur compounds act as catalyst poisons for the catalysts used in steps (A) and (B). Therefore, when the hydrocarbon-containing gas 1 contains sulfur, it is preferable to remove the sulfur compounds in advance in step (G). 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.

[0065] [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.

[0066] [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 the schematic diagrams of FIGS.

[0067] 1 and 2 , the methanol production apparatus of this embodiment includes a synthesis gas preparation unit 200, a methanol synthesis unit 300, a distillation unit 400, and a deionization unit 500 or an anaerobic treatment unit 600, and gas and / or liquid obtained by the deionization unit 500 or the anaerobic treatment unit 600 is used in the synthesis gas preparation unit 200. The methanol production apparatus of this embodiment may also include other units as necessary.

[0068] 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, it is preferable that the synthesis gas preparation unit 200 includes a reformer.

[0069] 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 methanol and unreacted gas, and may also include other equipment as necessary.

[0070] 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.

[0071] The deionization unit 500 is a device that can directly remove ions contained in wastewater, and is not particularly limited, and examples thereof include a device using an ion exchanger and an electrodeionization device. The anaerobic treatment unit 600 is not particularly limited as long as it is a device that has a decomposition tank using anaerobic microorganisms.

[0072] Preferably, the methanol production system of this embodiment further includes a desulfurization unit 100 as shown in FIGS.

[0073] The desulfurization unit 100 includes a desulfurizer that removes sulfur from a hydrocarbon-containing gas, and may include other devices as needed.

[0074] 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.

[0075] 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.

[0076] [Example 1] In Example 1, the production apparatus shown in Figure 1 was used. The conditions were as shown in Table 1. That is, shale gas (CH ４ : 94.3 mol%, C ２ H ６ : 2.7 mol%, C ３ H ８ : 0.6 mol%, C ４ H １０ : 0.2 mol%, C ５ H １２ : 0.2 mol%, carbon dioxide: 0.5 mol%, N ２ A steam reforming reaction was carried out using 1.5 mol% methanol, followed by the synthesis of methanol using the resulting synthesis gas. Methanol synthesis catalyst C was used as the catalyst in the methanol synthesis reactor in the methanol synthesis unit. A multi-tube heat exchange reactor was used as the methanol synthesis reactor. The set conditions were a pressure of 10.0 MPaG for the fluid in contact with the catalyst in the reactor, a shell pressure of 4.0 MPaG, and a temperature between 200 and 234°C. The reaction pressure in the reformer was 1.9 MPaG and a temperature of 860°C. Distillation was carried out under conditions of a methanol distillation efficiency of 99% and an ethanol overhead composition of 5 ppm. The deionization unit 500 used an ion exchanger and device similar to those described in Japanese Patent No. 3,468,259.

[0077] In Example 2, as shown in Figure 2, the same operation as in Figure 1 was carried out, except that the deionization unit 500 was replaced with an anaerobic treatment unit 600, and the digester gas obtained from the anaerobic treatment unit 600 was supplied to the synthesis gas preparation unit 200. The results of Example 2, such as the methanol production amount (ton / D), are shown in Table 1. The anaerobic treatment unit 600 used was the same device as in Japanese Patent Publication No. 58-33040.

[0078] In Comparative Example 1, as shown in Fig. 3, the same operations as in Example 1 were carried out, except that the deionization unit 500 was not provided and the distillation wastewater was not supplied to the synthesis gas preparation unit 200. The results of Comparative Example 1, such as the methanol production amount (ton / D), are shown in Table 1.

[0079] In Comparative Example 2, as shown in Fig. 4, the same operation as in Example 1 was carried out, except that the deionization unit 500 was not provided. The results of Comparative Example 2, such as the methanol production amount (ton / D), are shown in Table 1.

[0080] In Comparative Example 3, as shown in Fig. 5, the same operation as in Example 1 was carried out, except that a neutralization unit 700 was used instead of the deionization unit 500. The results of Comparative Example 3, such as the methanol production amount (ton / D), are shown in Table 1.

[0081]

[0082] From the above, it was shown that in Examples 1 and 2, the distillery wastewater can achieve a pH and salt concentration that does not damage equipment, while the components in the distillery wastewater can be recycled.

[0083] The present invention has industrial applicability in a method and apparatus for producing methanol.

[0084] This application is based on a Japanese patent application (Patent Application No. 2023-218417) filed on December 25, 2023, the contents of which are incorporated herein by reference.

[0085] 1...hydrocarbon-containing gas, 2...recycle gas, 3...desulfurized gas, 4...synthesis gas, 5...crude methanol, 6...distillation wastewater, 7...deionized distillation wastewater, 8...digestion gas, 9...purge gas, 10...methanol, 11...treated water, 12...neutralized distillation wastewater, 200...synthesis gas preparation unit, 300...methanol synthesis unit, 400...distillation unit, 500...deionization unit, 600...anaerobic treatment unit, 601...microorganisms, 602... Sludge, 603...returned sludge, 604...sludge dehydration unit, 605...dehydrated sludge, 610...methane production reaction tank, 611...sedimentation 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...hydrogen addition process, A206...shift reaction process, A207...reverse shift reaction process, A208...hydrogen separation process.

Claims

1. A process (A) of obtaining synthesis gas containing at least carbon dioxide and hydrogen; a process (B) of reacting the synthesis gas in the presence of a catalyst to obtain a methanol mixture; a process (C) of distilling the methanol mixture to separate methanol and distilled wastewater respectively; a process (D) of removing acids and / or bases and their salts from the distilled wastewater; and a process (E) of using the gas and / or liquid obtained in the process (D) in the process (A). A method for producing methanol.

2. The molar flow rate of carbon atoms contained in the gas and / or liquid obtained in the process (D) is 70 mol% or more with respect to the molar flow rate of carbon atoms contained in the distilled wastewater. The method for producing methanol according to claim 1.

3. The process (A) includes a process (F) of reforming hydrocarbons contained in the gas and / or liquid obtained in the process (D) to obtain reformed gas. The method for producing methanol according to claim 1 or 2.

4. Further includes a desulfurization process (G). The method for producing methanol according to claim 1 or 2.

5. The process (D) includes a process of removing acids and / or bases and their salts by an ion exchanger. The method for producing methanol according to claim 1 or 2.

6. The process (D) includes a process of removing acids and / or bases and their salts by anaerobic treatment. The method for producing methanol according to claim 1 or 2.

7. Further includes a process (H) of burning the gas obtained by the anaerobic treatment to recover heat. The method for producing methanol according to claim 6.

8. A methanol production apparatus comprising a synthesis gas preparation unit, a methanol synthesis unit, a distillation unit, and a deionization unit or an anaerobic treatment unit, and using the gas and / or liquid obtained by the deionization unit or the anaerobic treatment unit in the synthesis gas preparation unit.

9. The synthesis gas preparation unit includes a reformer. The methanol production apparatus according to claim 8.

10. Further includes a desulfurization unit. The methanol production apparatus according to claim 8 or 9.

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