REACTOR

A reactor includes a separation membrane permeable to a product of a conversion reaction of a raw material gas containing at least hydrogen and carbon oxide to a liquid fuel, a non-permeation side flow path extending in an approximately vertical direction on a non-permeation side of the separation membrane, the raw material gas flowing through the non-permeation side flow path, and a catalyst configured to fill the non-permeation side flow path and promote the conversion reaction. The catalyst includes a first layer and a second layer disposed upward of the first layer, and a mean equivalent circle diameter of catalyst particles included in the first layer is larger than a mean equivalent circle diameter of catalyst particles included in the second layer.

TECHNICAL FIELD

The present invention relates to a reactor.

BACKGROUND ART

In recent years, reactors have been developed that can improve conversion efficiency by separating a product of a conversion reaction of a raw material gas containing hydrogen and carbon oxide to a liquid fuel such as methanol and ethanol (specifically, a fuel that is in a liquid state at normal temperature and pressure).

For example, JP 2018-8940A discloses a reactor provided with a separation membrane permeable to water vapor that is one of products of the conversion reaction, a non-permeation side flow path through which a raw material gas flows, and a catalyst filling the flow path. The catalyst promotes the conversion reaction of the raw material gas to the liquid fuel.

SUMMARY

In the reactor disclosed in JP 2018-8940A, the non-permeation side flow path extends in the vertical direction, and thus in a lower end portion of the non-permeation side flow path, the weight of the catalyst may act on the separation membrane, thereby damaging the separation membrane.

An object of the present invention is to provide a reactor capable of suppressing damage to a separation membrane.

A reactor according to the present invention includes a separation membrane permeable to a product of a conversion reaction of a raw material gas containing at least hydrogen and carbon oxide to a liquid fuel, a non-permeation side flow path extending in an approximately vertical direction on a non-permeation side of the separation membrane, the raw material gas flowing through the non-permeation side flow path, and a catalyst configured to fill the non-permeation side flow path and promote the conversion reaction. The catalyst includes a first layer and a second layer disposed upward of the first layer, and a mean equivalent circle diameter of catalyst particles included in the first layer is larger than a mean equivalent circle diameter of catalyst particles included in the second layer.

According to the present invention, a reactor capable of suppressing damage to a separation membrane can be provided.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described with reference to the drawings. However, the drawings are schematic, and ratio or the like of dimensions may differ from an actual one.

FIG.1is a cross-sectional view of a reactor1.

The reactor1is a so-called membrane reactor used to convert a raw material gas to a liquid fuel. The configuration of the reactor1can be applied to a fixed bed reactor and a monolith-type reactor.

The raw material gas contains at least hydrogen and carbon oxide. At least one of carbon monoxide and carbon dioxide can be used as the carbon oxide. The raw material gas may be a so-called synthetic gas (syngas).

The liquid fuel is a fuel that is in a liquid state at normal temperature and pressure, or a fuel that can be liquidized at normal temperature and pressurized state. Examples of the liquid fuel that is in a liquid state at normal temperature and pressure may include methanol, ethanol, liquid fuels represented by CnH2(m-2n)(m is an integer less than 90, and n is an integer less than 30), and mixtures thereof. Examples of the fuel that can be liquidized at normal temperature and pressurized state include, for example, propane, butane, and mixtures thereof.

For example, reaction formula (1) for synthesizing methanol by catalytically hydrogenating a raw material gas containing carbon dioxide and hydrogen in the presence of a catalyst is as follows.

The above reaction is an equilibrium reaction, and in order to increase both the conversion efficiency and the reaction rate, it is preferable to carry out the reactions at a high temperature and high pressure (for example, 180° C. or higher and 2 MPa or higher). The liquid fuel is in a gaseous state when it is synthesized, and is kept in a gaseous state at least until it flows out of the reactor1. The reactor1preferably has heat resistance and pressure resistance suitable for desired synthesis conditions of the liquid fuel.

As shown inFIG.1, the reactor1includes a separation membrane10, a porous support body20, a non-permeation side flow path30, a permeation side flow path40, an outer tube50, and a catalyst60.

The separation membrane10is permeable to water vapor, which is one of the products of the conversion reaction of the raw material gas to the liquid fuel. In this manner, by utilizing the equilibrium shift effect, the reaction equilibrium of the above formula (1) can be shifted to the product side. In the present embodiment, the separation membrane10is formed in a cylindrical shape.

The separation membrane10preferably has a water vapor permeability coefficient of 100 nmol/(s·Pa·m2) or more. The water vapor permeability coefficient can be determined using a known method (see Ind. Eng. Chem. Res., 40, 163-175 (2001)).

The separation membrane10preferably has a separation factor of 100 or more. The greater the separation factor is, the more permeable the separation membrane10is to water vapor, and the less permeable it is to components other than water vapor (e.g., hydrogen, carbon oxide, and liquid fuel). The separation factor can be determined using a known method (seeFIG.1of “Separation and Purification Technology 239 (2020) 116533”).

The separation membrane10is formed in a cylindrical shape. The separation membrane10is disposed inward of the cylindrical porous support body20. The separation membrane10is in contact with the inner circumferential face of the porous support body20.

An inorganic membrane can be used as the separation membrane10. The inorganic membrane is preferable because it has heat resistance, pressure resistance, and water vapor resistance. Examples of the inorganic membrane include a zeolite membrane, a silica membrane, an alumina membrane, and a composite membrane thereof. In particular, an LTA zeolite membrane having a molar ratio (Si/Al) of a silicon element (Si) and an aluminum element (Al) of 1.0 or more and 3.0 or less is suitable because of its excellent water vapor permeability. Note that the inorganic membrane has a characteristic of being easily broken by thermal shock.

The porous support body20is formed in a tubular shape. The porous support body20surrounds the separation membrane10. The porous support body20supports the separation membrane10. The porous support body20is constituted by a porous material. In the present embodiment, the porous support body20is formed in a cylindrical shape.

As the porous material, a ceramic material, a metal material, a resin material, or the like can be used, and a ceramic material is particularly preferable. As an aggregate of the ceramic material, for example, at least one of alumina (Al2O3), titania (TiO2), mullite (Al2O3—SiO2), potsherd, cordierite (Mg2Al4Si5O18), or the like can be used. As an inorganic binder for the ceramic material, for example, at least one of titania, mullite, readily sinterable alumina, silica, glass frit, a clay mineral, and readily sinterable cordierite can be used. However, the ceramic material does not need to contain an inorganic binder.

The non-permeation side flow path30is provided on a non-permeation side of the separation membrane10. In the present embodiment, the non-permeation side flow path30is a columnar space on the inner side of the separation membrane10.

The non-permeation side flow path30extends in an approximately vertical direction. The approximately vertical direction is a concept including not only a direction that matches the gravity direction, but also a direction inclined to some extent (±15°) with respect to the gravity direction.

The raw material gas is caused to flow through the non-permeation side flow path30. In the present embodiment, the raw material gas is caused to flow downward through the non-permeation side flow path30. Accordingly, the raw material gas flows in through an upper end opening30aof the non-permeation side flow path30, and the liquid fuel flows out through a lower end opening30bof the non-permeation side flow path30. Note that the raw material gas may be caused to flow upward through the non-permeation side flow path30. The liquid fuel flowing out through the lower end opening30bmay be mixed with a residual raw material gas.

The permeation side flow path40is provided on the non-permeation side of the separation membrane10. In the present embodiment, the permeation side flow path40is an annular space between the separation membrane10and the outer tube50. Water vapor that has permeated through the separation membrane10flows into the permeation side flow path40.

In the present embodiment, a sweep gas for sweeping water vapor is caused to flow through the permeation side flow path40. An inert gas (e.g., nitrogen), air, and the like can be used as the sweep gas. In the present embodiment, the sweep gas flows upward (i.e., the opposite direction to the direction in which the raw material gas flows) through the permeation side flow path40. Accordingly, the sweep gas flows in through the lower end opening40aof the permeation side flow path40, and the sweep gas that has taken in water vapor flows out through the upper end opening40bof the permeation side flow path40. Note that the sweep gas may be caused to flow downward (i.e., the same direction as the direction in which the raw material gas flows) through the permeation side flow path40.

The catalyst60fills the non-permeation side flow path30. The catalyst60advances (promotes) the conversion reaction of the raw material gas to the liquid fuel. The catalyst60is in direct contact with the separation membrane10.

The catalyst60is constituted by a plurality of catalyst particles. The catalyst particles are each constituted by a carrier and a supported catalytic component. As the carrier, for example, alumina, titania, silica, ceria, zeolite or the like can be used, but there is no limitation to this. The supported catalytic component is supported on a surface of the carrier. As the supported catalytic component, metal catalyst component (copper, palladium, and the like), oxide catalyst component (zinc oxide, amorphous zirconia, gallium oxide, and the like), and composite catalyst components thereof can be used, but there is no limitation to this.

The shape of the catalyst particles is not particularly limited, and for example, may be a spherical shape, an ellipsoidal shape, a circular columnar shape, an ellipsoidal columnar shape, a disc-like shape, a scale-like shape, a needle-like shape, a polygonal columnar shape, a sheet-like shape, or the like.

The catalyst60has a multilayer structure in which a plurality of layers are stacked in the approximately vertical direction. In the present embodiment, the catalyst60is configured as a double-layer structure having a first layer61and a second layer62.

The first layer61is located at the lowermost layer of the catalyst60. The first layer61is disposed in the lower end portion of the non-permeation side flow path30. The lower end portion of the non-permeation side flow path30is a region that is lower than the center of the non-permeation side flow path30in the approximately vertical direction.

The second layer62is disposed upward of the first layer61. Since the catalyst60has the double layer structure in the present embodiment, the second layer62is disposed on the first layer61. The second layer62is disposed in a region, of the non-permeation side flow path30, where the first layer61is not disposed.

Here, the mean equivalent circle diameter of the catalyst particles included in the first layer61is larger than the mean equivalent circle diameter of the catalyst particles included in the second layer62. In this manner, damage to the separation membrane10due to the weight of the catalyst60acting on the separation membrane10can be suppressed. The mechanism that can suppress damage to the separation membrane10is as follows.

First,FIGS.2and3schematically show a comparative example in which the mean equivalent circle diameter of the catalyst particles included in the first layer61is equal to the mean equivalent circle diameter of the catalyst particles included in the second layer62.FIG.2shows a case where the catalyst particles have a spherical shape, andFIG.3shows a case where the catalyst particles have a circular columnar shape. In the modes inFIGS.2and3, since positions of the catalyst particles contained in the first layer61and the catalyst particles contained in the second layer62are likely to horizontally shift, when a force F1acting on the catalyst particles included in the first layer61is divided into a horizontal component F2and a vertical component F3, the horizontal component F2is large. As a result, a large force acts on the separation membrane10by the catalyst particles included in the first layer61, and the separation membrane10is likely to be damaged.

On the other hand,FIGS.4and5schematically show examples in which the mean equivalent circle diameter of the catalyst particles included in the first layer61is larger than the mean equivalent circle diameter of the catalyst particles included in the second layer62.FIG.4shows a case where the catalyst particles have a spherical shape, andFIG.5shows a case where the catalyst particles have a circular columnar shape. In the modes inFIGS.4and5, since horizontal shifting of the positions of the catalyst particles included in the first layer61and the catalyst particles included in the second layer62can be suppressed, when a force F10acting on the catalyst particles included in the first layer61is divided into a horizontal component F20and a vertical component F30, the horizontal component F20can be made smaller than the horizontal component F2shown inFIGS.2and3. As a result, a force acting on the separation membrane10by the catalyst particles included in the first layer61can be reduced, and damage to the separation membrane10can be suppressed.

Also, since the mean equivalent circle diameter of the catalyst particles included in the second layer62is relatively small, the total surface area can be increased by improving the filling rate of the catalyst particles, and thus a number of supported catalytic components can be supported. As a result, the overall catalytic performance of the catalyst60can be ensured.

The mean equivalent circle diameter can be obtained as follows.

First, a resin (e.g., epoxy) is cast in the non-permeation side flow path30to be cured, and then the catalyst60is cut along the approximately vertical direction.

Next, cross-sectional images of the first layer61and the second layer62are respectively obtained using a SEM (Scanning Electron Microscope). The magnifying power of the SEM is selected from a range of 1-fold or more and 100-fold or less such that 10 or more (preferably 100 or more) catalyst particles can be observed in one observation field. In this case, when both cross sections of the separation membrane (cross sections on both sides in the horizontal direction of the non-permeation side flow path30) are not seen in one observation field, the observation field can be divided into two observation fields for observing the cross sections of the separation membrane and one or more observation fields between the two observation fields.

Next, using SEM-EDS (energy dispersive X-ray analysis), elements of the substance exposed on the respective cross sections of the first layer61and the second layer62are specified, and thereby the catalyst particles are specified on the respective cross-sectional images of the first layer61and the second layer62. Note that the method for specifying the catalyst particles is not limited to the method using the SEM-EDS, and a method using WDS (wavelength dispersive X-ray analysis) may also be adopted, for example.

Next, the arithmetic mean value of the equivalent circle diameters of 30 or more catalyst particles randomly selected from the cross-sectional image of the first layer61is obtained, and the arithmetic mean value of the equivalent circle diameters of 30 or more catalyst particles randomly selected from the cross-sectional image of the second layer62is obtained. The arithmetic mean value of the first layer61obtained as above is the mean equivalent circle diameter of the catalyst particles included in the first layer61, and the arithmetic mean value of the second layer62is the mean equivalent circle diameter of the catalyst particles included in the second layer62. Note that the equivalent circle diameter of the catalyst particle means the diameter of a circle having the same area as a catalyst particle.

Although there is no limitation on the value of the mean equivalent circle diameter of the catalyst particles included in the first layer61, the value can be 1000 μm or more and 10000 μm or less, for example. Note that if the mean equivalent circle diameter of the catalyst particles in the first layer61is set small, variation in the pressure loss increases, which incurs uneven flow of the gas. As such, the mean equivalent circle diameter of the catalyst particles in the first layer61is preferably 500 μm or more. Also, tension stress is likely to act on the separation membrane10provided on the inner side of the porous support body20. As such, by setting the mean equivalent circle diameter of the catalyst particles in the first layer61to 500 μm or more, the stress acting on the separation membrane10can be suppressed.

Although there is no limitation on the value of the mean equivalent circle diameter of the catalyst particles included in the second layer62, the value can be 6000 μm or less, for example. Note that if the mean equivalent circle diameter of the catalyst particles in the second layer62is set small, variation in the pressure loss increases, which incurs uneven flow of the gas. As such, the mean equivalent circle diameter of the catalyst particles in the second layer62is preferably 500 μm or more. Also, tension stress is likely to act on the separation membrane10provided on the inner side of the porous support body20. As such, by setting the mean equivalent circle diameter of the catalyst particles in the second layer62to 500 μm or more, the stress acting on the separation membrane10can be suppressed.

The catalyst60can be formed by putting the catalyst particles for the first layer61into the non-permeation side flow path30from above, and then putting the catalyst particles for the second layer62into the non-permeation side flow path30from above.

Modification of Embodiment

Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention.

Although the inner side of the separation membrane10is the non-permeation side flow path30and the outer side of the separation membrane10is the permeation side flow path40in the above embodiment, a configuration is also possible in which the outer side of the separation membrane10is the non-permeation side flow path30and the inner side of the separation membrane10is the permeation side flow path40. In this case, it is preferable that the separation membrane10is formed surrounding the outer side of the porous support body20.

Although the catalyst60has a double-layer structure having the first layer61and the second layer62in the above embodiment, the catalyst60may have a structure that includes three or more layers. For example, as shown inFIGS.6and7, the catalyst60may have a triple layer structure that includes a third layer63in addition to the first layer61and the second layer62.

InFIG.6, the third layer63is disposed between the first layer61and the second layer62in the approximately vertical direction. It is preferable that the mean equivalent circle diameter of the catalyst particles included in the third layer63is smaller than the mean equivalent circle diameter of those included in the first layer61and larger than the mean equivalent circle diameter of the catalyst particles included in the second layer62. In this manner, since a force acting on the separation membrane10by the catalyst particles included in the first layer61can be further reduced, damage to the separation membrane10can be further suppressed. Also, since a force acting on the separation membrane10by the catalyst particles included in the third layer63can also be further reduced, the range in which damage to the separation membrane10can be suppressed can be made wider.

Note that other layers may be disposed between the first layer61and the third layer63, and between the second layer62and the third layer63. It is preferable that the mean equivalent circle diameter of the catalyst particles included in such layers are larger in the lower layer and smaller in the upper layer.

InFIG.7, the third layer63is disposed below the first layer61in the approximately vertical direction. The third layer63includes at least one of the catalyst particles and the filler particles. The filler particles need not include catalytic function. The filler particles can be constituted by, for example, ceramic material (alumina, titania, silica, ceria, zeolite, or the like). In the case where the third layer63includes the catalyst particles, the mean equivalent circle diameter of the catalyst particles included in the third layer63may be larger than, smaller than, or the same as the mean equivalent circle diameter of the catalyst particles included in the first layer. Also, in the case where the third layer63includes the filler particles, the mean equivalent circle diameter of the filler particles included in the third layer63may be larger than, smaller than, or the same as the mean equivalent circle diameter of the catalyst particles included in the first layer.

In this manner, even in the case where the first layer61is not disposed at the lowermost layer, damage to a portion of the separation membrane10that is in contact with the first layer61can be suppressed. Note that in a case where the mean equivalent circle diameter of the catalyst particles or the filler particles included in the third layer63is small, a portion of the separation membrane10that is in contact with the third layer63may be damaged, and thus it is preferable that the first layer61is disposed as the lowermost layer.

Although the separation membrane10is permeable to water vapor that is a product of the conversion reaction of the raw material gas to the liquid fuel in the above embodiment, the present invention is not limited thereto. The separation membrane10may be permeable to the liquid fuel itself, which is a product of the conversion reaction of the raw material gas to the liquid fuel. In this case as well, the reaction equilibrium of the above formula (1) can be shifted to the product side.

Also, when the separation membrane10is permeable to the liquid fuel, even when generating the liquid fuel through a reaction in which no water vapor is generated (e.g., 2H2+CO↔CH3OH), the reaction equilibrium can be shifted to the product side.

REFERENCE SIGNS LIST