JP2018008940A - Method for producing methanol and methanol production device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method where, in conversion reaction from a raw material gas containing carbon dioxide and hydrogen into methanol, a conversion rate is sufficiently increased, and further, methanol is easily separated fron a reaction system.SOLUTION: There is provided a method for producing methanol, comprising: a step where a raw material gas including carbon dioxide and hydrogen is fed to the first space 11 filled with a catalyst on the non-permeation side of a separation membrane reactor 10, and the conversion reaction of the raw material gas into methanol is progressed by the action of the catalyst; a step where a sweeping gas is circulated through the second space 12 on the permeation side of the separation membrane reactor 10 to remove the heat of reaction generated with the conversion reaction, and further, water vapor as the by-products of the conversion reaction permeated through the water vapor separation membrane 13a is made to flow out from the second space 12; a step where a non-permeation fluid including the methanol generated by the conversion reaction and an unreacted gas are cooled by a heat exchanger 31, and the methanol and the unreacted gas are separated by a gas-liquid separation tank 31b; and a step where the unreacted gas is circulated through the first space 11.SELECTED DRAWING: Figure 3A

Description

  The present invention relates to a method or apparatus for producing methanol from a raw material gas containing carbon dioxide and hydrogen using a separation membrane reactor.

  In recent years, there has been an increasing need to reduce greenhouse gases, and there is an urgent need to develop a technique for fixing carbon dioxide in exhaust gas generated at power plants, steelworks, cement plants, and the like. Among them, a technology for reacting exhaust gas with hydrogen to convert it into methanol and reusing it is attracting attention. Methanol is liquid at room temperature, has excellent storage and transportability, has high utility value as a chemical raw material and clean energy, and is expected to be in great demand worldwide.

  In general, methanol is produced by catalytic hydrogenation of synthesis gas containing carbon monoxide, carbon dioxide and hydrogen in the presence of a catalyst. The reaction formula for methanol synthesis is as follows.

CO + 2H ₂ ＣＨ CH ₃ OH (1)
CO ₂ + 3H ₂ ＣＨCH ₃ OH + H ₂ O (2)
CO ₂ + H ₂ ＣＯCO + H ₂ O (3)

  The above reactions are all equilibrium reactions, and the methanol conversion rate has a thermodynamic upper limit (equilibrium conversion rate) corresponding to temperature and pressure. In order to increase the methanol conversion rate, it is desirable to proceed the reaction at a low temperature and a high pressure.

  However, since the reaction rate is remarkably reduced at a low temperature, the reaction is generally performed at a high temperature and a high pressure of 200 to 300 ° C. and 5 to 50 MPa. At that time, the single conversion rate is low, and a large amount of unreacted gas is separated from the product and recycled to the reactor again. Energy consumption accompanying the circulation of unreacted gas is large, which is a major factor in increasing the cost of methanol synthesis.

  There are roughly two types of studies for improving the single conversion rate of methanol. One is the development of high performance catalysts, and there have been many reports so far. The other is an approach that uses the equilibrium shift effect, and the reaction equilibrium (the above formulas (1) to (3)) is shifted to the product side by separating part or all of the product from the reaction system. It is a technique to make it.

  As an approach utilizing the equilibrium shift effect, a composite reactor (Patent Document 1) in which reactors and condensers are connected in multiple stages, and a reactor that condenses and separates water and methanol by a cooler arranged in the reaction tube (Patent Document 2, 3) A liquid phase synthesis method (Patent Document 4) in which methanol is synthesized in an organic solvent that reacts with water has been reported. Of particular interest is the process of separating the product from the reaction system using a separation membrane reactor (Patent Documents 5 and 6).

  In Patent Document 5, it is proposed that when producing methanol from synthesis gas, the product is removed from the reaction system by a separation membrane, and the reaction equilibrium is moved to the product side. The product is recovered from the permeate side essentially by vacuum. In a process that uses the equilibrium shift effect, the methanol synthesis reaction proceeds more efficiently than in the past, and therefore, highly efficient heat removal is required. However, in Patent Document 5, since no countermeasure is taken for removal of reaction heat, it is considered that the methanol conversion rate is seriously lowered due to a temperature rise.

  On the other hand, Patent Document 6 proposes a heat removal method using heat exchange between cooling water and a reaction gas, or self-heat exchange between a high temperature gas and an unreacted low temperature gas. The methanol-containing gas that has permeated the separation membrane is condensed and then purified by distillation to recover methanol. For this reason, the amount of energy input required for distillation purification becomes large, and the degree of completion is low and unrealistic as a process using a separation membrane reactor.

Japanese Patent Laid-Open No. 2005-13239 JP 2005-298413 A JP 2010-13422 A JP 2007-55974 A JP 9-511509 A JP 2001-9265 A

  As described above, in the process using the conventional separation membrane reactor, it is difficult to simultaneously realize the efficiency of heat removal and the simplification of the methanol separation and purification process.

  One aspect of the present invention provides a raw material gas containing carbon dioxide and hydrogen, a non-permeate side first space, a water vapor separation membrane, a permeate side second space, and a catalyst disposed in the first space. By supplying the first space of the separation membrane reactor comprising the above, allowing the conversion reaction of the raw material gas to methanol by the action of the catalyst, and circulating the sweep gas in the second space, The reaction heat generated with the conversion reaction is removed, and water vapor, which is a by-product of the conversion reaction that has permeated the water vapor separation membrane, is caused to flow out of the second space, and is generated by the conversion reaction. Cooling a non-permeate fluid containing methanol and unreacted gas, condensing methanol to separate methanol and the unreacted gas, and circulating the unreacted gas to the first space. Have It relates to a process for the production of methanol.

  Another aspect of the present invention is arranged in the first space on the non-permeate side into which the source gas containing carbon dioxide and hydrogen is introduced, the water vapor separation membrane, the second space on the permeate side, and the first space. A separation membrane reactor that advances a conversion reaction of the raw material gas into methanol by the action of the catalyst, a raw material gas supply unit that supplies the raw material gas to the first space, and the first A sweep gas supply unit that supplies a sweep gas to two spaces; a first recovery unit that recovers a non-permeating fluid containing methanol and unreacted gas generated by the conversion reaction from the first space and condenses the methanol; A second recovery unit for causing water vapor, which is a byproduct of the conversion reaction permeated through the water vapor separation membrane, to flow out from the second space together with the sweep gas, and an unreacted gas separated from the non-permeated fluid. Circulate in the first space It includes a circulation unit that, the relates to methanol production apparatus.

  According to the present invention, in the conversion reaction of raw material gas containing carbon dioxide and hydrogen to methanol, an equilibrium shift effect is obtained, and the reaction heat is efficiently removed, so that the methanol conversion rate is sufficiently high. Can be increased. Further, since methanol can be easily separated from the reaction system, the separation and purification process can be simplified.

It is a graph which shows the equilibrium conversion rate in the synthesis | combination of methanol (MeOH) from carbon monoxide. It is a graph which shows the equilibrium conversion rate in the methanol synthesis | combination from a carbon dioxide. It is a schematic block diagram which shows an example of the methanol manufacturing apparatus which concerns on embodiment of this invention in a cross section. It is a conceptual diagram which shows an example of the cross-sectional structure of 1st space, a membrane complex, and 2nd space. Is a diagram illustrating the relationship between methanol conversion and temperature in the methanol conversion reaction of the material gas _{(H 2 / CO x = 3} ). It is a diagram showing the relationship between the methanol recovery and temperature from the non-permeate side of the methanol conversion reaction (first space) of the raw material gas _{(H 2 / CO x = 3} ).

  The methanol production method according to the present invention includes a step of using a separation membrane reactor to advance a conversion reaction of a raw material gas containing carbon dioxide and hydrogen into methanol. Here, the separation membrane reactor comprises a first space on the non-permeate side to which the raw material gas is supplied, a water vapor separation membrane, and a second space on the permeate side.

  In the first space, a catalyst for proceeding the conversion reaction of the raw material gas to methanol is disposed. A method of arranging the catalyst in the first space is not particularly limited. For example, the catalyst may be filled in the first space, or the catalyst may be supported on the first space side of the water vapor separation membrane.

  In the first space, methanol is generated by the action of the catalyst, and water vapor is also generated as a by-product as shown in the above formulas (2) to (3). The water vapor selectively permeates the water vapor separation membrane and moves from the first space to the second space. On the other hand, methanol and unreacted gas are recovered from the first space as a non-permeating fluid.

  In addition, the above manufacturing method removes reaction heat generated by the conversion reaction by circulating a sweep gas through the second space, and collects water vapor as a by-product from the second space, or externally. A step of causing the liquid to flow out. The reaction heat generated along with the conversion reaction moves to the sweep gas flowing through the second space and is removed from the second space together with the sweep gas. At this time, water vapor that has moved to the second space is also removed from the second space together with the sweep gas. Thereby, the reaction equilibrium of said Formula (2)-(3) shifts to the product side, and a methanol conversion rate improves.

  Moreover, the said manufacturing method comprises the process of cooling the non-permeated fluid containing methanol and unreacted gas collect | recovered from 1st space, and condensing methanol. As a result, condensable methanol and non-condensable unreacted gas are separated, and high-purity methanol is recovered. That is, steps necessary for separation and purification of methanol such as distillation can be omitted or shortened.

  Next, the manufacturing method includes a step of circulating unreacted gas to the first space. Thereby, unreacted gas is reused, but the amount of unreacted gas to be circulated is reduced by improving the methanol conversion rate. Therefore, energy consumption accompanying the circulation of unreacted gas is suppressed. A part of the unreacted gas to be circulated may be purged to adjust the composition of the raw material gas introduced into the first space.

  As described above, according to the method for producing methanol according to the present invention, the reaction for generating methanol from the raw material gas and the separation and purification of methanol can be performed in parallel, and steps such as distillation can be omitted or shortened. Is possible. Further, by allowing the sweep gas to flow through the second space, reaction heat generated by the catalytic reaction is efficiently removed, and further, water vapor as a by-product is removed from the second space by the sweep gas. A shift effect is obtained, and the methanol conversion is improved.

  In the methanol production according to the present invention, the reaction equilibrium of the above formulas (2) to (3) shifts to the product side, so that conventional methanol production conditions (200 ° C. to 300 ° C., 5 MPa to 50 MPa) are maintained. In comparison, it is possible to obtain high reaction efficiency at moderate temperatures or pressures. For example, even when the temperature of the raw material gas in the separation membrane reactor is less than 200 ° C. (for example, 150 ° C. to 180 ° C.) and the pressure of the raw material gas in the separation membrane reactor is less than 5 MPa (for example, 0.9 MPa to 2 MPa), The conversion reaction proceeds efficiently. That is, in the conversion reaction of the raw material gas to methanol, the methanol conversion rate can be increased beyond the equilibrium conversion rate under a predetermined temperature and pressure.

  As the sweep gas, nitrogen and / or air are preferable because they can be procured at low cost, and air is particularly preferable. The pressure of the sweep gas may be, for example, in the range of 10 kPa to 500 kPa, and may be atmospheric pressure. From the viewpoint of obtaining a sufficient effect of removing reaction heat, the flow rate of the sweep gas flowing through the second space is preferably equal to or more than the flow rate of the raw material gas supplied to the separation membrane reactor, and more preferably 2 to 10 times.

As the raw material gas, a by-product gas of an ironworks to which hydrogen is added can be used. As a by-product gas of the steelworks, blast furnace gas or converter gas can be mentioned. Among them, a large amount of Blast Furnace Gas (BFG) is discharged in the process of reducing iron ore and producing pig iron. BFG _{typically, H 2: 4vol%, N} 2: 52vol%, CO: 22vol%, CO 2: having the composition of 22 vol%, contains a large amount of carbon monoxide and carbon dioxide. Therefore, it is desired to use BFG effectively.

As shown in the above formulas (1) to (3), in the reaction between H ₂ and CO _x (x = 1 or 2), the methanol conversion reaction proceeds approximately at a molar ratio of H ₂ : CO _x = 3: 1. To do. That is, if hydrogen is added to BFG so as to satisfy H ₂ : CO _x = 3: 1, a raw material gas composition suitable for the methanol conversion reaction can be obtained. However, the molar ratio between H ₂ and CO _x is not particularly limited, and may be appropriately adjusted so that the H ₂ / CO _x ratio is in the range of 1 to 4.

Although a large amount of nitrogen is contained in BFG, if the molar fraction of nitrogen is sufficiently reduced to, for example, 25% or less by adding hydrogen, the methanol conversion reaction is not greatly inhibited by nitrogen. When hydrogen is added to BFG so as to satisfy H ₂ : CO _x = 3: 1, the composition (vol%) of the source gas (BFG + H ₂ ) is typically as shown in Table 1.

As the source gas, an off-gas generated when purifying hydrogen by a pressure fluctuation adsorption method (PSA method) may be used. For example, the off-gas after separating hydrogen contained in the synthesis gas contains carbon monoxide and carbon dioxide. If hydrogen is added to the off gas and the H ₂ / CO _x ratio is appropriately adjusted within the range of 1 to 4, it can be used as a raw material gas for methanol synthesis.

As the raw material gas, exhaust gas generated after utilization of woody biomass may be used. Woody biomass generates gas containing carbon dioxide by being directly combusted or reformed into a gas component in a gasification furnace and then subjected to combustion. Further, a gas containing carbon dioxide is also generated by steam reforming the gas component and performing a water gas shift reaction. If hydrogen is added to these gases and the H ₂ / CO _x ratio is appropriately adjusted within a range of 1 to 4, it can be used as a raw material gas for methanol synthesis. In addition, the thermal energy produced | generated by combustion of woody biomass is used by a power generation facility etc.

As described above, the technical significance of using a gas containing a large amount of carbon dioxide as a raw material is great. The reaction heat (ΔH ⁰ ₂₉₈ ) in the above formula (1) (CO + 2H ₂ ＣＨCH ₃ OH) is −90.97 kJ / mol, and the above formula (2) (CO ₂ + 3H ₂ ＨCH ₃ OH + H ₂ O). The heat of reaction (ΔH ⁰ ₂₉₈ ) at −49.81 kJ / mol. That is, as the concentration of carbon dioxide contained in the source gas is higher, the heat of reaction is reduced, so that temperature control becomes easier. Furthermore, if the by-product gas of the steel works can be used as it is as raw material gas, methanol synthesis, such as a process for removing carbon dioxide, a reforming process by water gas shift reaction, etc., as in the case of using synthetic gas as a raw material. Can eliminate expensive processes in

From the above, the methanol production method according to the present invention is particularly effective when a by-product gas or off-gas having a carbon dioxide concentration of 20 vol% or more is used as at least part of the raw material gas. In this case, the composition of the raw material gas supplied to the separation membrane reactor, appropriately adjusted by hydrogenation such that the molar ratio of H ₂ and CO _x (H ₂ / CO _x ratio) is within the range of 1-4 Is done. When the source gas contains carbon monoxide together with carbon dioxide, the molar ratio of carbon monoxide to carbon dioxide (CO / CO ₂ ratio) is preferably in the range of 0 to 1, and in the range of 0.125 to 1 Is more desirable.

  Next, a specific problem that becomes apparent when methanol is synthesized from carbon dioxide will be described. FIG. 1 shows the equilibrium conversion in methanol synthesis from carbon monoxide, and FIG. 2 shows the equilibrium conversion in methanol synthesis from carbon dioxide. Here, the region where water and / or methanol exist as gas is shown by a solid line, and the region where condensation and liquefaction are shown by a dotted line. As apparent from FIGS. 1 and 2, under the same conditions of temperature and pressure, the equilibrium conversion rate in the synthesis of methanol from carbon dioxide is significantly reduced. For example, the equilibrium conversion rate in methanol synthesis from carbon dioxide at 200 ° C. at 5 MPa is about 33%, which is comparable to the equilibrium conversion rate (about 92%) in methanol synthesis from carbon monoxide under the same conditions. It becomes low. In addition, in the synthesis of methanol from carbon dioxide, water vapor that is equimolar with carbon dioxide is generated. On the other hand, the methanol production method according to the present invention achieves both the improvement of the conversion rate due to heat removal and the equilibrium shift effect and the separation and purification of methanol. .

Next, the methanol production apparatus according to the present invention will be described.
The methanol production apparatus includes a separation membrane reactor that advances a methanol conversion reaction of a raw material gas containing carbon dioxide and hydrogen. The separation membrane reactor includes a first space for introducing a raw material gas, a water vapor separation membrane, a second space for a permeable side, and a first space for proceeding a conversion reaction of the raw material gas to methanol. And a catalyst disposed on the surface. The water vapor separation membrane is disposed so as to isolate the first space and the second space.

The water vapor separation membrane preferably has a water vapor transmission rate of 1 × 10 ⁻⁷ mol / (s · Pa · m ² ) or higher, and preferably has a water vapor transmission rate of 1 × 10 ⁻⁶ mol / (s · Pa · m ² ) or higher. More preferably, it has a speed. As the water vapor transmission rate increases, the water vapor generated in the first space easily moves to the second space, and the reaction equilibrium of the above formulas (2) to (3) shifts to the product side. It is possible to obtain high reaction efficiency with pressure. On the other hand, in the case of less than 1 × 10 ⁻⁷ mol / (s · Pa · m ² ), the efficiency of methanol production can be reduced by the amount by which the movement of water vapor is delayed. However, if the water vapor separation rate is too high, defects may occur in the water vapor separation membrane. Therefore, the water vapor transmission rate of the water vapor separation membrane is preferably 1 × 10 ⁻⁵ mol / (s · Pa · m ² ) or less.

The water vapor transmission rate Q may be obtained by a known method. For example, a permeation cell as described in Non-Patent Document 1 (Ind. Eng. Chem. Res., 40, 163-175 (2001)) is used. Can be measured. When a mixed gas of methanol and water vapor having an arbitrary composition is supplied to the water vapor separation membrane at an arbitrary temperature and the permeation side is depressurized by a vacuum pump, a part of the mixed gas permeates the separation membrane. Subsequently, the permeated gas is collected by a cold trap, and the mass and molar composition of the condensate may be measured. The water vapor transmission rate Q is calculated from the following formula: Q = A / {(P1-P2) · S · t}. Here, A is the permeation amount of water vapor (mol), P1 is the water vapor partial pressure (Pa) on the supply side, P2 is the water vapor partial pressure (Pa) on the permeation side, and S is the apparent area (m ² ) of the water vapor separation membrane. , T represents the measurement time (seconds) when the transmission amount is A. The molar composition of the collected condensate can be easily measured by using a gas chromatograph or a Karl Fischer moisture meter.

  The water vapor separation membrane is preferably an inorganic membrane. The inorganic film is stable even at temperatures exceeding 100 ° C., and it is easy to enhance pressure resistance and water vapor resistance. Examples of the inorganic film include a zeolite film, a silica film, an alumina film, and a composite film thereof. Among them, a zeolite film having a molar ratio of silicon element (Si) to aluminum element (Al) on the surface: Si / Al of 50 or less (preferably 10 or less, more preferably 2 or less) in view of excellent water vapor permeability. Is preferred.

Here, the water vapor separation membrane is preferably an inorganic membrane having a water vapor / methanol separation factor of 230 or more. The water vapor / methanol separation factor (hereinafter referred to as αW / M) is determined by the following formula (4) according to the composition of water and methanol (xW, xM) on the non-permeate side and the composition of water and methanol (yW, yM) on the permeate side. ).
αW / M = (yW / yM) / (xW / xM) (4)

A separation membrane having a larger αW / M has the property of being more permeable to water vapor and less permeable to methanol. For example, when a raw material gas having CO: CO ₂ = 1: 8 and CO _x : H ₂ = 1: 3 is passed through a separation membrane reactor under a pressure of 1 MPa, αW / M = about 230 or more. 99% of the produced methanol can be recovered from the first space on the non-permeate side. αW / M is preferably as large as possible, more preferably 450 or more (corresponding to a methanol recovery rate of 99.5%), more preferably 2200 or more (corresponding to a methanol recovery rate of 99.9%).

  The above numerical values are values in the equilibrium state of the reaction and the equilibrium state of water vapor permeation, and are calculated by the following assumptions and calculation procedure.

(Assumption 1)
In the first space on the non-permeating side of the separation membrane reactor, the CO _x methanolization reaction and the water gas shift reaction have reached an equilibrium state.

(Assumption 2)
The permeation of water vapor to the water vapor separation membrane has reached equilibrium, and the water vapor partial pressure in the first space on the non-permeation side is equal to the water vapor partial pressure in the second space on the permeation side.

(Assumption 3)
The amount of methanol that permeates the membrane along with the water vapor is determined according to the separation factor. That is, the composition (yM) of methanol on the permeate side follows the above formula (4),
yM = (1 / αW / M) × yW / (xW / xM) (5)
It is requested from. Components other than water and methanol do not permeate the water vapor separation membrane.

(Procedure 1)
According to a known method, the composition of each substance in the reaction equilibrium state when there is no membrane permeation is determined.

(Procedure 2)
The reaction progress degrees ξ ₂ and ξ ₃ and the water vapor transmission amount ξ ₄ of the above formulas (2) and (3) are defined, and the methanol permeation amount is expressed using ξ ₂ to ξ ₄ based on the above formula (4). In addition, the composition of all components on the non-permeation side in the equilibrium state between the reaction and the membrane permeation based on the above assumption is expressed using the initial composition and ξ ₂ to ξ ₄ .

(Procedure 3)
Assuming that the gas in the system is an ideal gas, 3 indicates that the composition determined in Procedure 1 satisfies the pressure equilibrium constants of the above formulas (2) and (3), and that the partial pressure difference of water vapor is zero. Establish a simultaneous system.

(Procedure 4)
If ξ ₄ is eliminated from the simultaneous equations obtained in procedure 3, quartic and quadratic equations are obtained for ξ ₂ and ξ ₃ respectively, so that a solution is obtained by convergence calculation such as Newton-Raphson method. In addition, physical constants required for calculation, such as standard free energy and enthalpy of formation, such as methanol, carbon monoxide, carbon dioxide, hydrogen, and specific heat coefficient, can be obtained from, for example, the sixth edition of the Chemical Engineering Handbook. .

  The thickness of the water vapor separation membrane is preferably 0.5 μm to 10 μm, for example. Thereby, the permeation | transmission speed | velocity | rate of water vapor | steam becomes high enough, and it becomes easy to move water vapor | steam from 1st space to 2nd space efficiently. Since the water vapor separation membrane alone has low strength, it is desirable to carry it on the surface of the porous substrate.

  The material of the porous substrate is not particularly limited, but can be selected from silica, alumina, zirconia, cordierite, titania, silicon nitride, silicon carbide, stainless steel, copper, aluminum, titanium and the like.

  For example, a zeolite membrane is prepared by applying a zeolite seed crystal on the surface of a porous substrate and then hydrothermally synthesizing it in an aqueous suspension containing water, silica material, alumina material, organic structure-directing agent and the like. The

  When forming a water vapor separation membrane having αW / M of 230 or more, in order to form a dense membrane, it is necessary to apply a seed crystal in the vicinity of the surface of the porous substrate in advance and form the membrane by a secondary growth method. desirable.

  The size, shape, and the like of the water vapor separation membrane are appropriately designed according to the configuration and method of the separation membrane reactor. For example, the shape may be a cylindrical shape, a flat plate shape, a honeycomb shape, or the like.

  As the catalyst for proceeding the conversion reaction of the raw material gas to methanol, copper, palladium and the like are known as the metal catalyst, and zinc oxide, zirconia, gallium oxide and the like are known as the oxide catalyst. Examples of the catalyst in which these are combined include copper-zinc oxide, copper-zinc oxide-alumina, copper-zinc oxide-chromium oxide-alumina, or a catalyst in which palladium is modified. These may be carried on at least the non-permeation side (that is, the first space side) of the water vapor separation membrane.

  The methanol production apparatus further includes a source gas supply unit that supplies a source gas to the first space, a sweep gas supply unit that supplies a sweep gas to the second space, and methanol generated by a conversion reaction from the first space; A first recovery part for recovering a non-permeating fluid containing unreacted gas; a second recovery part for recovering water vapor that has permeated through the water vapor separation membrane from the second space together with the sweep gas; A circulation unit for circulating the unreacted gas separated from the permeating fluid to the first space.

  The source gas supply unit may be any means that can supply the source gas to the first space while controlling the flow rate of the source gas, and may include a compressor, a pump, or the like that can pressurize the first space to atmospheric pressure or higher. desirable. The source gas supply unit may include a pipeline for transferring BFG generated in a blast furnace at a steel plant to the first space.

  The sweep gas supply unit may be any means that can supply the sweep gas to the second space while controlling the flow rate of the sweep gas. The sweep gas supply unit desirably includes, for example, a compressor, a pump, a fan, and the like that send air in the atmosphere to the second space.

  The first recovery unit has a space that can at least temporarily store a non-permeated fluid containing methanol and unreacted gas generated by the conversion reaction. In the first recovery unit, the non-permeating fluid is cooled, the methanol is condensed, and the non-condensable unreacted gas and methanol are separated.

  The second recovery unit may have a space that can at least temporarily store the sweep gas accompanied by water vapor, and may have a function of opening the water vapor and the sweep gas to the atmosphere as they are or purifying them. . Moreover, it may have a function of cooling the sweep gas accompanied by water vapor, condensing the water vapor, and separating the condensed water and the sweep gas. When purifying the sweep gas before being released into the atmosphere, the sweep gas may be passed through a filter containing an adsorbent such as activated carbon.

  The circulation unit that circulates the unreacted gas to the first space may have a function of transferring the unreacted gas to the first space directly or indirectly after purging a part of the unreacted gas. The circulation unit includes, for example, a pipeline, a compressor, and a pump that connect the first recovery unit and the first space. The unreacted gas may be merged with the source gas supplied to the first space from the source gas supply unit, or may be supplied directly to the first space.

  The methanol manufacturing apparatus may further include a cooling medium flow path adjacent to the first space and a cooling medium supply unit that supplies the cooling medium flow path to the cooling medium flow path. Thereby, it becomes possible to control the temperature of the separation membrane reactor more easily. The cooling medium flow path is desirably formed of a corrosion-resistant metal such as stainless steel. Boiler water can be used as the cooling medium. The boiler water circulates through the cooling medium flow path while being vaporized by absorbing the reaction heat of the methanol conversion reaction.

Hereinafter, an example of the methanol production apparatus according to the embodiment of the present invention will be specifically described with reference to FIGS. 3A and 3B.
The methanol production apparatus 1 shown in FIG. 3A includes a separation membrane reactor 10, a raw material gas supply unit 21 that introduces a raw material gas (FG) into a raw material gas inlet that communicates with the first space 11 in the separation membrane reactor 10, A sweep gas supply unit 22 that introduces a sweep gas (SG) into a sweep gas inlet that leads to the second space 12 in the membrane reactor 10, and a first recovery unit 31 that recovers a non-permeated fluid (RG) from the first space 11. And the second recovery part 32 that recovers the sweep gas (SG) together with the water vapor (PG) from the second space 12 and the unreacted gas (UG) recovered by the first recovery part 31 is transferred to the first space 11. And a circulation unit 40.

  The separation membrane reactor 10 includes a first space 11 on the non-permeation side, a water vapor separation membrane 13a, and a second space 12 on the permeation side. The water vapor separation membrane 13 a is disposed so as to separate the first space 11 and the second space 12. As shown in FIG. 3B, the water vapor separation membrane 13a has, for example, a cylinder having a first surface that is an outer peripheral surface and a second surface that is an inner peripheral surface, and pores that allow the first surface and the second surface to communicate with each other. The cylindrical membrane composite 13 is formed on the first surface of the porous substrate 13b and the porous substrate 13b. The first space 11 is filled with a catalyst 15 that causes a methanol conversion reaction to proceed, and the methanol conversion reaction of the raw material gas proceeds in the first space 11.

  The amount of catalyst is appropriately designed according to the shape of the separation membrane and the performance of the separation membrane, but the apparent volume Va of the catalyst 15 arranged in the first space 11 so as not to be excessively limited in terms of catalyst reaction or membrane permeation. The ratio Va / Vb of the total apparent volume Vb of the water vapor separation membrane 13a and the porous substrate 13b is preferably 0.43 to 25.0. Thereby, methanol can be manufactured efficiently. The apparent volume Va of the catalyst means a space volume filled with the catalyst. When the catalyst is fully filled in the first space, the apparent volume Va of the catalyst is synonymous with the volume of the first space. Vb is an apparent volume that does not consider voids in the water vapor separation membrane and the porous substrate.

  The generated methanol stays in the first space 11 and is recovered as a non-permeated fluid (RG) in the first recovery part 31 together with the unreacted gas. The first recovery unit 31 includes a heat exchanger 31a that cools the non-permeating fluid (RG) and condenses methanol, and a gas-liquid separation tank 31b, and liquid methanol is taken out from the gas-liquid separation tank 31b. Since the unreacted gas (UG) contains almost no water and the raw material gas is non-condensable, only methanol is easily recovered from the non-permeated fluid (RG). Therefore, high-purity methanol can be obtained without requiring a process with a large energy load such as distillation.

  On the other hand, the unreacted gas (UG) remaining after the methanol is removed includes carbon dioxide, hydrogen, and the like. After a part of the unreacted gas (UG) is purged as necessary, the pressure is increased by the compressor 40a included in the circulation unit 40, and the unreacted gas (UG) is circulated to the first space 11 through the pipeline 40L.

  Water vapor (PG) as a by-product passes through the membrane complex 13 and moves to the hollow second space 12 surrounded by the membrane complex 13. The water vapor (PG) that has moved to the second space 12 is recovered by the second recovery part 32 from the permeate side outlet together with the sweep gas (SG). The sweep gas (SG) accompanied by water vapor (PG) is released into the atmosphere after passing through a filter for collecting a small amount of impurities in the second collection unit 32, for example.

  The first space 11 on the non-transmission side is surrounded by a cooling wall 14 made of stainless steel, and the cooling wall 14 forms a cooling medium flow path 14 g adjacent to the first space 11. In other words, the space regulated by the cooling wall 14 and the water vapor separation membrane 13a is the first space 11, and the first space 11 is heat from the cooling medium (for example, boiler water) flowing through the cooling medium flow path 14g. The reaction is cooled and the heat of reaction is removed. The cooling medium is supplied from a cooling medium supply unit 50 including a pump 50a that controls the flow rate, a pipeline 50L that serves as a flow path for the cooling medium, and the like.

  The source gas supply unit 21 includes a compressor 21a that boosts the source gas (FG), and a pipeline 21L that serves as a distribution path for the source gas (FG). The source gas supply unit 21 may include a controller that controls the flow rate or flow rate of the source gas (FG).

  The sweep gas supply unit 22 includes a pump 22a that controls the flow rate of the sweep gas (SG) and a pipeline 22L that serves as a flow path for the sweep gas (SG). The sweep gas supply unit 22 may have a controller that controls the flow rate or flow rate of the sweep gas (FG). The partial pressure of water vapor in the second space 12 can be controlled by the flow rate of the sweep gas (SG).

  Generally, when the methanol conversion rate increases, the reaction heat increases, but the first space 11 in which the reaction heat is easily accumulated is cooled by a heat exchanger constructed by the cooling medium flow path 14g and the cooling medium, and at the same time, It is also cooled by the sweep gas (SG) through the water vapor separation membrane 13a. The water vapor (PG) once condenses inside the water vapor separation membrane 13a, but when it moves to the second space 12, it is accompanied by the sweep gas (SG) and is discharged out of the reaction system. Since the sweep gas (SG) transports the heat of vaporization at that time, the cooling by the sweep gas (SG) is more efficient than the simple heat exchange between the gas and sufficient cooling is possible. Further, since the partial pressure of water vapor (PG) decreases on the non-permeation side (first space 11) of the water vapor separation membrane 13a on which the catalyst 15 is supported or filled, the sintering of the metal component contained in the catalyst 15 due to water vapor. Rings are avoided and the effect of preventing the activity of the catalyst 15 from being lowered is also obtained.

FIG. 4 is a diagram showing the relationship between the methanol conversion rate and the temperature in the methanol conversion reaction of the raw material gas in which CO: CO ₂ = 1: 8 and CO _x : H ₂ = 1: 3, and the above assumptions 1 to 3 are used. And procedures 1 to 3. FIG. 4 also shows the equilibrium conversion rate (thermodynamic equilibrium) when a separation membrane reactor is not used as a comparison object. Here, in the case of using a methanol production apparatus as shown in FIG. 3A, the pressure on the first space side is set to 5 MPa, the total pressure in the second space is 0.1 MPa, and the partial pressure of the permeated gas is 0.01 MPa. The result when set to. Compared with the case of the membrane (αW / M = 10) that permeates both water and methanol assumed in Patent Documents 5 and 6, the membrane that selectively permeates water vapor (αW / M = 230) has a slight conversion rate. Although reduced, a high conversion is obtained compared to the equilibrium conversion in a conventional process that does not use a membrane.

FIG. 5 shows the relationship between the methanol recovery rate from the non-permeate side (first space) and the temperature in the methanol conversion reaction of the raw material gas with CO: CO ₂ = 1: 8 and CO _x : H ₂ = 1: 3. It is a figure shown and is calculated | required by the said assumptions 1-3 and the procedures 1-4. Again, in the case of using a methanol production apparatus as shown in FIG. 3, the pressure on the first space side is set to 5 MPa, the total pressure in the second space is 0.1 MPa, and the partial pressure of the permeated gas is 0.01 MPa. The result when set to. In the case of αW / M = 10, the methanol recovery rate is as low as 88% or less, and it is necessary to recover methanol together with water from the permeate side and purify it by distillation. On the other hand, in the case of αW / M = 230, 99% or more of methanol can be recovered, and distillation purification is unnecessary, so that the profitability as a process is excellent.

  Hereinafter, the result by the chemical engineering simulation of methanol production by the methanol production apparatus according to the embodiment of the present invention will be described. A separation membrane reactor that realizes two kinds of unit operations of membrane permeation and reaction in a single device is not packaged as a device in a commercially available process simulator, so the user needs to newly describe a routine. The inventors independently created a routine using the VBA code.

  Specifically, first, the raw material gas is supplied to the first space of the separation membrane reactor to produce methanol and by-product water. At this time, since water vapor mainly passes through the water vapor separation membrane, the amount of product on the first space side filled with the catalyst is reduced, and an equilibrium shift effect is exhibited. The non-permeating fluid containing methanol and unreacted gas remaining in the first space is recovered in a condenser (first recovery unit) assuming vapor-liquid equilibrium at 40 ° C., and methanol and a trace amount of condensable components are collected. Moisture is recovered as a liquid. The unreacted gas separated from the non-permeating fluid without being condensed is merged with the raw material gas and sent to the first space again. However, when the unreacted gas is circulated, a gas (such as nitrogen) that does not participate in the reaction circulates and is concentrated as the unreacted gas is integrated, and the reaction efficiency decreases. Therefore, a part of the unreacted gas is removed at a predetermined purge rate, and then merged with the raw material gas.

Purge of the unreacted gas, from the viewpoint of effective use of CO ₂ as a raw material, it is preferable to set 0.1 to 10%, and more preferably set to 1-6%. The purge rate is the volume ratio of the gas to be removed with respect to the entire unreacted gas.

  The recycle ratio represented by (flow rate of unreacted gas circulated to the membrane reactor) / (flow rate of raw material newly supplied to the membrane reactor) is preferably 10 or less, preferably 5 or less. More preferably.

  Usually, in the simulation of the methanol conversion reaction of the raw material gas, a tubular reactor assuming an extruding flow is assumed, and the assumed reactor is divided into a plurality of micro cells along the gas flow direction. Gas inflow and outflow, gas composition change resulting from the reaction, and temperature change are calculated. By integrating the change in the minute cell along the gas flow direction, the amount of methanol produced in the entire reactor, the purity of methanol produced, and the like can be obtained.

  In the separation membrane reactor, in addition to the methanol conversion reaction, it is necessary to consider gas permeation through the water vapor separation membrane and heat transport derived therefrom. Therefore, each of the first space on the non-permeate side and the second space on the permeate side filled with the catalyst was divided into minute cells, and the mass balance and heat balance were calculated in consideration of both reaction and membrane permeation.

As a model for the CO _x methanol conversion reaction, Graaf et al. Chemical Engineering Science Vol. 43, pp. The reaction rate equation described in 3185-3195 (1988) was used. The gas state was expressed using the Soave-Redrich-Kwon equation of state. Assuming that the gas that permeates the water vapor separation membrane is Joule-Thomson expansion, the differential pressure ΔP [Pa] of each gas obtained from the mass balance and the gas permeation rate Q [mol / (s · Pa · m ² ) given in advance. ], The permeation flux F [mol / (s · m ² )] was determined as F = QΔP.

  Regarding heat transport, the effect of heat removal by the cooling medium from the outer wall of the first space filled with the catalyst, heat conduction through the water vapor separation membrane and the porous substrate itself, and heat transport of the permeating gas itself were taken into consideration. . The cooling medium was subjected to heat removal by boiling heat transfer, and the necessary heat transport coefficient was obtained using a known estimation formula (described in Chemical Engineering Handbook 6th Edition (edited by the Chemical Engineering Society)).

  In the simulation, the amount of methanol produced, etc. is solved for a membrane reactor equipped with a single tubular reactor, but the amount of methanol produced when the separation membrane reactor comprises a number of tubes is the same as the solution obtained. It can be obtained by simply multiplying the number of tubes.

In the separation membrane reactor, the length of the tubular reactor was fixed at 78 cm, the inner diameter of the outer wall defining the first space was 22 mm, and the outer diameter of the water vapor separation membrane was variable. However, each thickness was 2 mm. The source gas was a stoichiometric ratio of CO ₂ and H ₂ (CO ₂ : H ₂ = 1: 3 (molar ratio)). The reaction temperature was optimized with an accuracy of 5 ° C. so that the single conversion rate would be a maximum value.

The purge rate of the unreacted gas was adjusted so that the overall yield of the process on a carbon atom basis was 95.00% (± 0.3%) in order to effectively use CO ₂ as a raw material. The calculation convergence condition was a material balance error of 0.01% or less. Recycle ratio: (flow rate of unreacted gas circulated to the membrane reactor) / (flow rate of raw material newly supplied to the membrane reactor) was controlled as shown in Table 3.

  Of the generated methanol, the amount recovered from the first space on the non-permeate side without flowing out to the permeate side or purge side is defined as the methanol (MeOH) recovery rate, and the condenser (first recovery) from the non-permeate side Part) was defined as methanol concentration / (methanol amount + water content) as methanol concentration (molar concentration), and these were calculated. Further, the ratio of the apparent volume of the catalyst filled in the first space and the volume of the separation layer (corresponding to the membrane composite 13 including the porous substrate and the water vapor separation membrane) is defined as the catalyst / membrane occupation volume ratio. Defined and calculated.

  Six cases of simulation were performed. The calculation conditions for each case are shown in Table 2, and the results are shown in Table 3. At an extremely low pressure of 4.5 MPa or less, the methanol recovery rate reached 99% or more, and the methanol concentration at this time was 98% or more. The water content is comparable to that of fuel alcohol, and is a concentration that can be sold without purification such as distillation.

As a comparative example, Table 4 shows simulation results (cases 7 to 9) when the pressure is 2.5 to 4.5 MPa and the makeup SV is 400 hr ⁻¹ in a tubular reactor not using a water vapor separation membrane. Makeup SV means a physical quantity obtained by converting the amount of raw material supplied into space velocity (hr ⁻¹ ). Compared with cases 1 to 6 of the example, since the equilibrium shift effect cannot be obtained, the single conversion rate is greatly reduced and the recycle ratio is increased. The obtained condensate is an aqueous solution in which water and methanol are approximately equimolar, and a purification step such as distillation is essential.

In order to verify the calculation accuracy and consistency of the built simulator, the measured conversion rate was compared with the simulation conversion rate. In the following examination, a fixed bed type methanol synthesis reactor was prepared, and a methanol synthesis reaction experiment using CO ₂ and H ₂ as raw materials was performed.

A cylindrical double tube reactor made of stainless steel capable of storing a glass tube having a diameter of 12 mm and a length of 150 mm as an inner tube was prepared. The inner diameter of the reactor corresponding to the inner diameter of the outer wall defining the first space was 41.2 mm, and the outer diameter φ was 48.6 mm. Both ends of the glass tube of the inner tube are fixed and sealed using graphite packing, and a Zn—Cu catalyst (JGC) is formed outside the central portion 50 mm (gap between the double tubes) of the glass tube as shown in FIG. 3B. (Made by Catalytic Chemical Co., Ltd.). The Zn—Cu catalyst was classified to a particle diameter of 1 to 2 mm with a sieve, and the packing density of the Zn—Cu catalyst after classification was 1300 kg / m ³ .

The reactor temperature was set to 180 ° C., and a mixed gas of CO ₂ : H ₂ = 25: 75 (mol / mol) was supplied to the catalyst packed bed in the reactor. The supplied gas flow rate was adjusted so that SV (space velocity) = 40, 80, 240 hr ^−1, and the conversion rate under any conditions was calculated. The gas flow rate at the inlet and outlet of the reactor was measured with a soap film flow meter, the gas composition was measured with a gas chromatograph, and the actual conversion was calculated from the change in the CO ₂ molar flow rate at the inlet and outlet. On the other hand, predetermined experimental conditions were input to the constructed simulator, and the conversion rate of the simulation was calculated. Table 5 shows the results of the three cases.

Under the experimental conditions of a supply pressure of 0.9 MPa, a reaction temperature of 180 ° C., and SV = 40 hr ⁻¹ , the actual conversion is 11.8%, the simulation conversion is 10.5%, and the simulation conversion is The result was very close to the conversion rate. The actual conversion rate when the supply flow rate of the mixed gas was increased to SV = 80 hr ⁻¹ was 10.5%, and the simulation conversion rate was 9.1%. The actual conversion rate when SV = 240 hr ⁻¹ was set was 6.5%, and the simulation conversion rate was 5.7%. Since good agreement was shown even under different SV conditions, it was found that the actual measurement result could be sufficiently predicted using the built simulator.

  The methanol production method and the methanol production apparatus according to the present invention are particularly suitable when effectively using a by-product gas of an ironworks containing a large amount of carbon dioxide as a raw material gas or an off-gas of hydrogen PSA.

1: methanol production apparatus, 10: separation membrane reactor, 11: first space, 12: second space, 13: membrane complex, 13a: water vapor separation membrane, 13b: porous substrate, 15: catalyst, 14: Cooling wall, 14g: cooling medium flow path, 21: raw material gas supply unit, 21a: compressor, 21L: pipeline, 22: sweep gas supply unit, 22a: pump, 22L: pipeline, 31: first recovery unit, 31a : Heat exchanger, 31b: gas-liquid separation tank, 32: second recovery unit, 40: circulation unit, 40a: compressor, 40L: pipeline, 50: cooling medium supply unit, 50a: pump, 50L: pipeline

Claims (10)

A separation membrane reaction comprising a raw material gas containing carbon dioxide and hydrogen, a non-permeate side first space, a water vapor separation membrane, a permeate side second space, and a catalyst arranged in the first space. Supplying to the first space of the vessel, and causing the conversion reaction of the raw material gas to methanol by the action of the catalyst;
By allowing sweep gas to flow through the second space, reaction heat generated by the conversion reaction is removed, and water vapor that is a byproduct of the conversion reaction that has permeated the water vapor separation membrane is added to the second space. A process of flowing out of the space;
Cooling a non-permeate fluid containing methanol and unreacted gas generated by the conversion reaction, condensing methanol, and separating methanol and the unreacted gas;
Circulating the unreacted gas to the first space.   The method for producing methanol according to claim 1, wherein the sweep gas is nitrogen and / or air.   The methanol production method according to claim 1 or 2, wherein the water vapor separation membrane is an inorganic membrane having a water vapor / methanol separation factor of 230 or more. 4. The method for producing methanol according to claim 1, wherein the water vapor separation membrane is an inorganic membrane having a water vapor transmission rate of 1 × 10 ⁻⁷ mol / (s · Pa · m ² ) or more.   The methanol production method according to any one of claims 1 to 4, wherein the raw material gas contains a by-product gas of an ironworks to which hydrogen is added.   The methanol production method according to claim 5, wherein the by-product gas of the ironworks is a blast furnace gas or a converter gas.   The method for producing methanol according to any one of claims 1 to 6, wherein the source gas contains an off-gas generated when purifying hydrogen by a pressure fluctuation adsorption method (PSA method). A non-permeate-side first space into which a raw material gas containing carbon dioxide and hydrogen is introduced, a water vapor separation membrane, a permeate-side second space, and a catalyst disposed in the first space, A separation membrane reactor that proceeds the conversion reaction of the raw material gas into methanol by the action of the catalyst;
A source gas supply unit for supplying the source gas to the first space;
A sweep gas supply unit for supplying a sweep gas to the second space;
A first recovery unit for recovering a non-permeating fluid containing methanol and unreacted gas generated by the conversion reaction from the first space, and condensing the methanol;
A second recovery unit for causing water vapor, which is a by-product of the conversion reaction permeated through the water vapor separation membrane, to flow out from the second space together with the sweep gas;
And a circulation unit that circulates the unreacted gas separated from the non-permeating fluid to the first space.   The methanol production apparatus according to claim 8, further comprising: a cooling medium flow path adjacent to the first space; and a cooling medium supply unit that supplies the cooling medium flow path to the cooling medium flow path. The water vapor separation membrane is supported on the surface of a porous substrate;
The ratio of the apparent volume Va of the catalyst to the total apparent volume Vb of the water vapor separation membrane and the porous substrate: Va / Vb is 0.43 to 25.0, or The methanol production apparatus according to 9.