JP7689877B2 - Zeolite manufacturing method and manufacturing device - Google Patents

Description

The present invention relates to a method for producing zeolite without using an organic structure directing agent (OSDA) and a zeolite production apparatus suitable for said method.

A method for producing zeolite without using an OSDA is known (Patent Document 1). In the method described in Patent Document 1, seed crystals are mixed into a reaction mixture consisting of a silica source, an alumina source, an alkali source, and water, and zeolite is produced under high temperature and pressure. The reaction mixture contains an aluminosilicate gel, which is a solid phase, and an aqueous alkali solution, which is a liquid phase. Patent Document 1 describes a method for producing zeolite without using an OSDA, in which the reaction mixture and seed crystals are heated and reacted in a stationary state without stirring.

International Publication No. 2011/013560

The reaction mixture containing the seed crystals is allowed to stand while being heated to a predetermined temperature and reacted for a predetermined period of time, whereby a high-quality zeolite can be obtained in high yield.
When the reaction mixture containing the seed crystals is heated, the reaction does not occur or is very slow, so it is possible to stir and mix, making it possible to heat the mixture quickly. When the reaction mixture is left to react after reaching the reaction temperature, the solid phase of the reaction mixture is deposited at the bottom of the reaction vessel and is gradually dissolved by the alkaline aqueous solution in the liquid phase at the top, and zeolite is produced while incorporating the seed crystals due to the degree of supersaturation.
However, the method of reacting the reaction mixture with the seed crystals by heating them in a stationary state has the following problems.
To control the reaction time, it is necessary to control the cooling rate of the zeolite after the reaction is complete. The cake of zeolite crystals that settles at the bottom of the reaction vessel at the end of the reaction tends to solidify in a cake-like pile. If it remains in a cake-like form, heat is transferred through a solid state from the external cooling surface, and the overall heat transfer coefficient is small, resulting in slow cooling, making it difficult to control the reaction time. Furthermore, when the reaction is scaled up, the specific surface area becomes smaller, making it even more difficult to control the cooling rate. If the reaction time cannot be accurately controlled, side reactions occur, leading to the production of zeolites other than the desired zeolite, and the introduction of impurities.
In addition, the cake of zeolite crystals, although the reason is unclear, tends to adhere to the inner wall surface of the reaction vessel, making it difficult to remove. As a result, the yield decreases, and the cost of washing the reaction vessel with an alkaline solution to dissolve and remove the adhering zeolite crystals is high. These are important problems that must be solved in industrial production, where cost and environmental issues are important. However, if the inner wall surface of the reaction vessel is treated to give it a peeling effect, the entire cake will spin freely when the stirring blades are rotated, making it even more difficult to break down the cake.

An object of the present invention is to provide a method and apparatus for producing zeolite which can eliminate the various drawbacks of the prior art described above.
That is, the present invention relates to a method and an apparatus for producing high-quality, inexpensive zeolite by crushing and fluidizing the cake of zeolite crystals deposited in the lower part of a reaction apparatus in a short period of time and enabling accurate control of the reaction time.

The present invention relates to a method for producing a zeolite-based catalyst comprising the steps of: a first step of heating a reaction mixture containing a silica source, an alumina source, an alkali source, and water, but not containing an organic structure-directing agent, and a seed crystal in a sealed reaction vessel and allowing the reaction to occur in a stationary state;
A second step of discharging the aggregated zeolite produced by the reaction from the reaction vessel,
The reaction vessel has a discharge port at a bottom for discharging the zeolite, and a bottom surface of the bottom is formed in a funnel shape having an inclined surface that is inclined downward toward the discharge port,
The reaction vessel has a stirring member,
The stirring member has a rotating shaft that is located at the center of the funnel-shaped bottom surface when the reaction vessel is viewed from above and extends in the vertical direction, a first stirring blade that is attached to the rotating shaft and has an edge portion that extends along the inclined surface of the reaction vessel, and a second stirring blade that is attached to an upper portion of the first stirring blade on the rotating shaft,
the inclined surface of the bottom of the reaction vessel and the edge of the first agitating blade are in a non-contact state;
In the second step, the rotating shaft is rotated to fluidize the zeolite with the first stirring blade and the second stirring blade, and the fluidized zeolite is discharged from the discharge outlet.

The present invention also provides an apparatus for producing a zeolite without using an organic structure-directing agent, comprising:
The apparatus includes a reaction vessel capable of heating the zeolite raw material under a sealed condition, and a stirring member that can be accommodated in the reaction vessel.
The reaction vessel has a discharge port at a bottom for discharging the fluidized zeolite, and a bottom surface of the bottom is formed in a funnel shape having an inclined surface inclined toward the discharge port,
The stirring member has a rotating shaft that is located at the center of the funnel-shaped bottom surface when viewed in a plane and extends in the vertical direction, a first stirring blade attached to the rotating shaft and having an edge portion extending along the inclined surface of the reaction vessel, and a second stirring blade attached to the upper part of the first stirring blade on the rotating shaft, and the inclined surface of the bottom of the reaction vessel and the edge portion of the first stirring blade are in a non-contact state, thereby providing a manufacturing apparatus.

According to the present invention, even when zeolite is produced by heating in a closed, stationary state without using an OSDA, the lump zeolite can be easily removed from the reaction vessel 20, and a method and method for producing zeolite that can produce high-quality zeolite while reducing production costs can be provided. The stirring member used in the present invention can be housed in an autoclave and can also be used to mix the reaction mixture and seed crystals, and has a relatively simple structure that provides excellent effects.

FIG. 1 is a partially cutaway front view showing a zeolite production apparatus according to one embodiment of the present invention. Fig. 2(a) is a perspective view showing the stirring member of the zeolite production apparatus of Fig. 1. Fig. 2(b) is an end view of the stirring member cut along line A-A in Fig. 2(a), and Fig. 2(c) is an end view of the stirring member cut along line B-B in Fig. 2(a). FIG. 3 is a graph showing the shear stress and shear rate of a zeolite slurry. FIG. 4 is a schematic diagram showing one embodiment of a zeolite production method using the zeolite production apparatus of FIG. 1, in which FIG. 4(a) shows the state of the zeolite immediately after the reaction, and FIG. 4(b) shows the process of fluidizing and discharging the zeolite. FIG. 5 is a perspective view showing an agitating member according to a different embodiment from that shown in FIG. FIG. 6 is a cross-sectional view of a reaction vessel used in a comparative example. 7(a) and (b) are perspective views of the stirring member used in the comparative example.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the zeolite production apparatus 10 used in this embodiment is an autoclave apparatus, and has a reaction vessel 20 capable of heating a zeolite raw material under a sealed condition, and a stirring member 30 that can be housed in the reaction vessel 20.

As shown in FIG. 1, the zeolite production apparatus 10 has a can body that constitutes a reaction vessel 20 for storing zeolite raw materials. That is, in the production apparatus 10, the reaction vessel 20 may be removably installed in the can body, or may be non-removably installed in the can body. This type of structure of the zeolite production apparatus 10 is preferable because the heat of the heated can body (reaction vessel 20) is directly transferred to the zeolite raw materials, making it easy to control the temperature of the zeolite raw materials and to obtain high-quality zeolite. The reaction vessel 20 is preferably made of stainless steel or the like.

The reaction vessel 20 is fitted with a lid 24 that can be opened and closed. The zeolite raw material in the reaction vessel 20 is heated by circulating a heat transfer medium or steam through a pipe (not shown) in a jacket 26 provided on the outer periphery of the reaction vessel 20.

As shown in FIG. 1, the reaction vessel 20 has an outlet 22 for discharging zeolite at the bottom 21. The bottom 21 of the reaction vessel 20 has a bottom surface 23 formed in a funnel shape. The bottom surface 23 has an inclined surface 23a that is inclined downward toward the outlet 22. The funnel shape here includes a cone shape. The inclined surface 23a is flat when the reaction vessel 20 is viewed from the side. The inclined surface 23a is continuous with the outlet 22. When the reaction vessel 20 is viewed from the side, the inclined surface 23a is preferably at an angle (angle α in FIG. 1) of 5° to 70° with respect to the horizontal plane in order to facilitate the discharge of zeolite and to increase the capacity of the reaction vessel to improve production efficiency, and more preferably at an angle of 30° to 50°. In particular, it is preferable that the angle α is greater than 42° because the fluidity is high and the discharge efficiency can be reliably improved. The horizontal plane refers to a plane perpendicular to the vertical direction in which the rotation axis 31 described later extends. Hereinafter, the up and down direction may be referred to as the "vertical direction."

The reaction vessel 20 has a bottom 21 having a bottom surface 23 formed in a funnel shape, and a straight body portion 25 continuous with the bottom 21. The straight body portion 25 is a vertical wall portion extending in the same direction as the direction of extension of the rotation shaft 31 described later. The inner surface of the straight body portion 25 is a vertical wall surface extending from the upper end of the funnel-shaped bottom surface 23 in the same direction as the direction of extension of the rotation shaft 31. The straight body portion 25 forms a bent portion 28. The bent portion 28 may be formed in a curved shape when the reaction vessel 20 is viewed from the side. A thermometer 71 (resistance temperature detector) is attached to the side of the straight body portion 25 in the reaction vessel to measure the temperature inside the zeolite solid phase synthesized inside the reaction vessel 20 and adjust it to a target temperature. The temperature inside the reaction vessel 20 is controlled using the thermometer 71 or the like.

1 and 2(a), the reaction vessel 20 has a stirring member 30 capable of stirring the internal storage. The stirring member 30 has a rotating shaft 31 that is located at the center of the funnel-shaped bottom surface 23 and extends in the vertical direction when the reaction vessel 20 is viewed in a plane, a first stirring blade 41 attached to the rotating shaft 31, and a second stirring blade 51 attached above the first stirring blade 41 on the rotating shaft 31. As shown in FIG. 1, the second stirring blade 51 is provided at a position facing the straight body portion 25 in a direction perpendicular to the rotating shaft 31. Both the first stirring blade 41 and the second stirring blade 51 have blade portions (blade portions 43, 53, 63) that extend radially outward of a circle centered on the rotating shaft 31 when the reaction vessel 20 is viewed in a plane.

In the example shown in FIG. 1 and FIG. 2(a), the second agitating blade 51 has a lower blade portion 63 located on the lower side in the direction in which the rotating shaft extends and an upper blade portion 53 located on the upper side as blade portions extending radially outward from a circle centered on the rotating shaft 31. In the example shown in FIG. 1 and FIG. 2(a), the second agitating blade 51 has an upper blade portion 53 and a lower blade portion 63. However, for example, only the upper blade portion 53 may be provided, and the lower blade portion 63 may not be provided. Each of the multiple upper blade portions 53 has a scraper (second blade portion) 47 at the tip on the radially outer side. The scraper 47 has an edge portion 42a that faces the vertically extending wall surface (hereinafter also referred to as the "vertical wall surface") of the straight body portion 25 and extends along the vertical wall surface and in the direction in which the vertical wall surface extends. In the example shown in FIG. 1 and FIG. 2(a), there are the same number of upper stage wing portions 53 and lower stage wing portions 63. When the reaction vessel 20 is viewed in plan, the directions in which each of the multiple upper stage wing portions 53 and each of the multiple lower stage wing portions 63 extend radially outward are the same. The radially outer end portion of the lower stage wing portion 63 located below is connected to the scraper 47 to which the upper stage wing portion 53 located above is connected.

As shown in FIG. 1, the rotating shaft 31 is connected to a support 32 for the rotating shaft 31 attached to the lid 24, and the support 32 has a motor (not shown) for driving the rotating shaft 31. The rotating shaft 31 is rotatable around the center of the bottom surface when the reaction vessel 20 is viewed in plan view by a motor (not shown). As the rotating shaft 31 rotates, the first stirring blade 41 and the second stirring blade 51 are driven integrally with the rotating shaft 31, making it possible to stir the contents stored inside the reaction vessel 20.

In the second step of discharging the zeolite, the first agitator 41 plays the main role of peeling off the zeolite adhering to the bottom surface 23 of the reaction vessel 20 and fluidizing it. In the second step, the second agitator 51 plays the role of peeling off the zeolite solid phase portion formed in the lower part of the straight body portion 25 of the reaction vessel 20 from the inner surface of the straight body portion 25 and fluidizing it, and at the same time, plays the role of causing a vertical flow together with the first agitator 41 by stirring the liquid phase portion above the upper surface of the solid phase portion. This vertical flow scoops up the zeolite accumulated in the lower part of the reaction vessel 20, and sends the reaction mother liquor in the upper part of the reaction vessel 20 downward, where it is incorporated into the lumpy zeolite and promotes fluidization. The agitator 30 is preferably made of stainless steel or the like.

Each of the blades 43 of the first agitating blade 41 has a shape in which at least a part of the surface located on the upper side of the reaction vessel 20 is inclined with respect to the horizontal plane. For example, when viewed from a direction perpendicular to the direction in which the rotating shaft extends, the blades 43 of the first agitating blade 41 have a plate shape with its upper surface inclined with respect to the horizontal plane (hereinafter, this shape is also referred to as an "inclined plate shape"), or when viewed from the radial outside to the inside in the longitudinal direction, it is preferable that the cross section has a triangular or trapezoidal shape that narrows as it goes upward. It is preferable for the cross-sectional shape of the blades 43 of the first agitating blade 41 to be triangular or trapezoidal for the following reasons. That is, in this case, even if the rotating shaft 31 rotates in either the forward or reverse direction at the start of rotation of the rotating shaft 31, the pressure-receiving area of the shear resistance received from the zeolite solid phase can be reduced, thereby efficiently peeling off and crushing the zeolite solid phase from the bottom surface 23 of the reaction vessel 20. In particular, in the blade portion 43 of the first agitating blade 41, which tends to have a large torque load on the motor in order to agitate the solid phase of zeolite formed at the bottom, it is preferable that the cross-sectional shape is triangular or trapezoidal, and it is even more preferable that the cross-sectional shape is triangular. When the cross-sectional shape is triangular or trapezoidal, the blade portion 43 of the first agitating blade 41 is a triangular prism or trapezoidal prism. It is preferable that the trapezoidal cross-sectional shape is an isosceles trapezoid.

1 and 2(a), the blade portion 43 of the first agitating blade 41 has a cross-sectional shape formed in an isosceles triangle. This isosceles triangle has one base and two equal sides, and the apex, which is the intersection of the two equal sides, faces upward. When the cross-sectional shape is an isosceles triangle, it is preferable that the base angle is an acute angle. In this case, in either the forward or reverse rotation at the start of rotation of the rotating shaft 31, the pressure-receiving area of the shear resistance received from the zeolite solid phase can be further reduced, and the torque load of the rotating shaft 31 can be further reduced. The angle of the base angle of the isosceles triangle shape of the cross section is preferably 20° to 40°, more preferably 25° to 35°, in order to minimize the shear force when the agitating member 30 starts rotating forward or reverse after synthesis is completed, and to peel off the zeolite solid phase from the bottom surface 23 of the reaction vessel 20 and efficiently perform the subsequent crushing.

The first agitator blade 41 has an edge portion 42 that extends along the inclined surface 23a of the reaction vessel 20. In the example of FIG. 1 and FIG. 2(a), the edge portion 42 corresponds to the base or the apex of the base angle of the isosceles triangle in a cross section perpendicular to the direction in which the blade portion 43 extends. The edge portion 42 extends linearly along the inclined surface 23a. When the rotating shaft 31 rotates, the first agitator blade 41 is driven so that its edge portion 42 rotates along the funnel-shaped bottom surface 23 of the reaction vessel 20. This effectively breaks up and fluidizes the clumps of zeolite that have formed on the bottom surface of the reaction vessel 20, effectively suppressing the residue of zeolite on the bottom surface 23 of the reaction vessel 20.

In this embodiment, the inclined surface 23a of the bottom 21 of the reaction vessel 20 and the edge portion 42 of the first agitating blade 41 are in a non-contact state. The inventors believe that this configuration provides the following effects.
In the case of slurries containing nanoparticles, the viscosity of the slurry is often pseudoplastic, that is, the viscosity decreases with increasing shear rate. Furthermore, in the case of porous materials such as zeolites, the behavior of the slurry is even more susceptible to the influence of shear rate due to the large specific surface area. In other words, the viscosity of a non-fluidized zeolite slurry, or zeolite cake, is extremely high and does not easily become fluid. For example, several beta zeolites produced by adding seed crystals to a reaction mixture not containing OSDA were separated from the reaction mixture, and the relationship between shear rate and viscosity was measured using an Anton Paar MCR-501 with 25 mmφ parallel plates and a gap of 1 mm after stirring for 1 minute at a steady flow of 100/s. The plots of ▲●■ show the viscosity of a slurry with 1 volume of zeolite added to 1 volume of water, and the plots of △○□ show the viscosity of a slurry with 1 volume of the same zeolite added to 3 volumes of water. The beta zeolite used in the measurement was a slurry taken out from the reaction vessel after completion of the reaction in Comparative Example 1 described later.
As shown in Figure 3, whether the amount of zeolite in the slurry is large or small, when the shear rate of the zeolite is close to zero, the shear stress is very large and it is very difficult to give fluidity to the slurry. However, if a very small shear force can be applied, the viscosity drops rapidly and stirring and fluid transport become possible. It can also be seen that the viscosity is low when the proportion of water in the slurry is large, but the viscosity is more than 10 times higher when the proportion of zeolite is large.
Therefore, the present inventors discovered that the shear rate can be maximized by placing the edge portion 42 of the first agitating blade 41, which applies the shear rate, near the inner wall of the reaction vessel 20, and that the fluidized zeolite cake thus produced is diluted with the reaction mixture solution, thereby fluidizing the entire zeolite slurry.

The ability of the present invention to control reaction time is important in the production of zeolites.
As described above, the reaction mixture, which is a raw material for producing zeolite, contains aluminosilicate gel, which is a solid phase, and an alkaline aqueous solution, which is a liquid phase. For example, when the reaction mixture described in Patent Document 1 is heated without adding seed crystals, mordenite zeolite, which is a stable phase, precipitates, but when seed crystals of unstable phase zeolite (e.g., β zeolite) are added, β zeolite is obtained. When unstable phase zeolite is produced without using OSDA, the amount of unstable phase zeolite produced increases with reaction time, but the crystallinity increases at an accelerated rate as the reaction time increases. In addition, when the reaction time reaches the maximum crystallinity of the unstable phase zeolite, the stable phase zeolite increases little by little. If the reaction time is too short, the crystallinity of the unstable phase zeolite is low, and if the reaction time is too long, the amount of stable phase zeolite increases and at the same time the crystallinity of the unstable phase zeolite decreases, so the reaction time needs to be accurately controlled.

The closer the edge 42 of the first agitator 41 is to the inner wall of the reaction vessel 20, the greater the shear rate that can be applied. However, if it is too close, the amount of reduced viscosity slurry is reduced, and the proportion of reduced viscosity slurry required to loosen the entire zeolite cake is reduced. From the above viewpoint, the distance W (see FIG. 1) between the inclined surface 23a of the bottom 21 of the reaction vessel 20 and the edge 42 of the first agitator 41 is preferably 0.8% or more and 5.0% or less, and more preferably 1.5% or more and 3.5% or less, in terms of the ratio (W/L1) to the length L1 (see FIG. 4(b)) of the edge of the first agitator 41 when the reaction vessel 20 is viewed from the side.

In the example shown in Figures 1 and 2(a), the first mixing blade 41 has multiple blades of the same shape, preferably 1 to 6 blades, and particularly preferably 2 to 5 blades.

The second agitator blade 51 has a blade portion in which at least a part of the surface located on the upper side of the reaction vessel 20 is inclined with respect to the horizontal plane when viewed from a direction perpendicular to the extension direction of the rotation shaft. For example, when the blade portion of the second agitator blade 51 is viewed from the radial outside toward the inside in the extension direction, it is preferable that the upper surface of the blade portion of the second agitator blade 51 has a plate shape (inclined plate shape) inclined with respect to the horizontal plane, or that the cross section perpendicular to the extension direction of the blade portion has a triangular or trapezoidal shape that narrows toward the top. The cross-sectional shape of the second agitator blade 51 is preferably triangular or trapezoidal for the same reasons as those explained for the first agitator blade 41. For example, of the upper blade portion 53 and the lower blade portion 63 of the second agitator blade 51, the lower blade portion 63 may have a triangular or trapezoidal shape that narrows toward the top, and the upper blade portion 53 may have a triangular or trapezoidal shape that narrows toward the bottom.

In the example shown in Figures 1 and 2(a), the upper blade 53 and the lower blade 63 of the second agitating blade 51 are inclined plate shapes. The upper blade 53 and the lower blade 63 each have a plate shape with a substantially rectangular cross section perpendicular to the direction of extension. Therefore, the upper blade 53 and the lower blade 63 each have a shape in which at least a part of the surface located on the lower surface side of the reaction vessel 20 is inclined with respect to the horizontal plane. When the upper blade 53 and the lower blade 63 of the second agitating blade 51 are inclined plate shapes, they may be inclined in the same direction or in the opposite directions.
It is preferable to use the triangular prism-shaped first agitating blade 41 and the inclined plate-shaped second agitating blade 51, since this makes it possible to generate a vertical flow in the reaction vessel 20 without using a baffle plate. It is not preferable to install a baffle plate in the reaction vessel 20 in terms of cake adhesion and the occurrence of blind spots in cake removal.
By using a triangular prism-shaped first agitator blade 41 and an inclined plate-shaped second agitator blade 51, the phenomenon in which zeolite crystals accumulate and adhere firmly to the upper surface of the agitator blade can be prevented, and the possibility of causing the generation of impurities can be effectively reduced.

From the viewpoint of enhancing the effect of fluidizing zeolite and reducing the power required for the agitator, the inclination angle A (see FIG. 2(c)) of the blade portion 43 of the first agitating blade 41 with respect to the horizontal plane is preferably greater than 0° and greater than 60°, and more preferably greater than 5° and greater than 45°. From the viewpoint of effectively generating a vertical flow and reducing the power required for agitation, the inclination angle B (see FIG. 2(b)) of the upper blade portion 53 of the second agitating blade 51 with respect to the horizontal plane is preferably greater than 0° and greater than 60°, and more preferably greater than 5° and greater than 50°.
2B and 2C, the inclination angle A of the wing 43 with respect to the horizontal plane and the inclination angle B of the upper wing 53 with respect to the horizontal plane are, when the wing 43 or the upper wing 53 is in the form of an inclined plate, the inclination angle of the acute angle that the upper surface of the inclined plate forms with the horizontal line Lx in a cross section perpendicular to the extension direction of the wing, when the cross section perpendicular to the extension direction of the wing 43 or the upper wing 53 is triangular, the inclination angle of the maximum acute angle that any side of the triangle in the cross section forms with the horizontal line Lx, and when the cross section perpendicular to the extension direction of the wing is trapezoidal, the inclination angle of the maximum acute angle that any side of the trapezoid in the cross section forms with the horizontal line Lx (the same applies to the inclination angle C of the lower wing 63 described later).

The second agitating impeller 51 is provided with multiple blades of the same shape. The upper blade portion 53 and the lower blade portion 63 each preferably have 1 to 6 blades, and particularly preferably 2 to 5 blades. The first agitating impeller 41 and the upper blade portion 53 and/or the lower blade portion 63 of the second agitating impeller 51 may each have the same or different numbers of blades.

In this embodiment, the directions in which the first agitating blades 41, the upper blades 53, and the lower blades 63 extend from the rotation shaft 31 are consistent when the reaction vessel 20 is viewed in a plan view. In this case, there is an advantage that a large opening area can be secured when accessing the interior, such as for sample collection, from the mirror manhole (not shown) provided in the lid 24. However, the blades 43, the upper blades 53, and the lower blades 63 may extend in different directions from the rotation shaft 31 when viewed in the plan view.

As shown in the example of FIG. 2(a), the effect of fluidizing the zeolite can be further enhanced by using three stages of agitating blades, the first agitating blade 41, the upper stage blade portion 53, and the lower stage blade portion 63, to agitate the accumulated zeolite and the liquid phase above it. In particular, as shown in FIG. 4(a) described below, the first agitating blade 41 serves to peel off the zeolite 1 from the bottom of the reaction vessel 20, the lower stage blade portion 63 serves to directly loosen the zeolite 1 above the bottom of the reaction vessel, and the upper stage blade portion 53 serves to generate a vertical flow of the zeolite above the liquid phase portion 2, thereby effectively fluidizing the zeolite.

In order to improve the effect of fluidizing the zeolite and the production efficiency, the inclination angle C (see FIG. 2(b)) of the inclined surface of the lower blade portion 63 with respect to the horizontal plane is preferably greater than 0° and up to 60°, and more preferably 5° to 50°.

As shown in Figures 1 and 2(a), in this embodiment, the second agitating blade 51 further includes a second blade portion 47 connected to the outer end of the blade portion 53, 63, and the second blade portion 47 has an edge portion 42a extending along the vertical wall surface of the straight body portion 25 and in the direction of extension of the vertical wall surface, which is preferable in terms of effectively removing zeolite attached to the straight body portion 25 of the reaction vessel 20. In the example shown in Figures 1 and 2(a), the second agitating blade 51 has an edge portion 42a as the radially outer edge portion of the second blade portion 47, which is a plate-shaped scraper arranged to extend vertically along the vertical wall surface of the straight body portion 25.

The width of the gap between the end edge portion 42a and the straight body portion 25 can be set to be the same as the width W of the gap between the end edge portion 42 and the inclined surface 23a described above.
In the reaction vessel 20, the ratio (L3/L2) of the length L3 of the part where the edge of any one of the stirring blades is close to the inner wall of the reaction vessel 20 so as to have a gap of the range given as the width W to the total length L2 in the vertical direction (see FIG. 1) is preferably 5% to 70%, more preferably 35% to 65%. In FIG. 1, L3 is the sum of L3a and L3b.

From the viewpoint of effectively fluidizing the zeolite adhering to the lower part of the straight body part 25 of the reaction vessel 20, it is preferable that the second blade part (scraper) 47 is inclined with respect to a straight line connecting the center of a circle centered on the rotation axis 31 and the second blade part 47 when the reaction vessel 20 is viewed in a plane. In this case, it is preferable that the inclination angle (acute angle) of the second blade part 47 with respect to the straight line is, for example, less than 90° and 30° or more. In the example shown in Figures 1 and 2 (a), the second blade parts 47 in the multiple second stirring blades 51 are inclined in the same direction with respect to the straight line related to the second blade part 47. In this embodiment, the second blade part 47 is a vertical plate part and is plate-shaped, and the plate surface facing the rotation axis and the plate surface opposite thereto are parallel to each other, and each plate surface is inclined with respect to the straight line at an inclination angle within the above range, but is not limited thereto.

The method for producing a zeolite according to this embodiment using the reaction vessel 20 described above will be described.
The present production method is a method for producing a zeolite, which comprises adding seed crystals to a reaction mixture containing a silica source, an alumina source, an alkali source, and water, but not containing an organic structure-directing agent, and then heating the mixture,
A first step of heating the reaction mixture and the seed crystals in a sealed reaction vessel 20 and allowing them to react in a stationary state;
A second step of discharging the aggregated zeolite produced by the reaction out of the reaction vessel 20,
In the second step, the rotating shaft 31 is rotated to fluidize the zeolite with the first stirring blade 41 and the second stirring blade 51, and the fluidized zeolite is discharged from the discharge port 22. In the second step, it is preferable to rotate the rotating shaft 31 at the same time as the start of the temperature drop to fluidize the zeolite with the first stirring blade 41 and the second stirring blade 51, since this can effectively suppress the generation of impurities while increasing the cooling efficiency for rapid cooling of the contents.

Examples of silica sources include silica itself and silicon-containing compounds capable of generating silicate ions in water. Specific examples include wet-process silica, dry-process silica, colloidal silica, sodium silicate, and aluminosilicate gel. These silica sources can be used alone or in combination of two or more.

As the alumina source, for example, a water-soluble aluminum-containing compound can be used. Specific examples include sodium aluminate, aluminum nitrate, and aluminum sulfate. Aluminum hydroxide is also a suitable alumina source. Aluminosilicate gel can also be used as an alumina source. These alumina sources can be used alone or in combination of two or more.

As the alkali source, for example, sodium hydroxide can be used. When sodium silicate is used as the silica source or sodium aluminate is used as the alumina source, sodium, which is an alkali metal component contained therein, is simultaneously regarded as NaOH and is also an alkali component. Therefore, the above Na ₂ O is calculated as the sum of all the alkali components in the reaction mixture.

In this manufacturing method, it is preferable to use the stirring member 30 not only as a fluidizing member for loosening and fluidizing the zeolite crystal cake produced, but also as a stirring member for mixing the reaction mixture and as a member for promoting heat transfer when the temperature of the contents is increased and decreased. By configuring it in this way, zeolite can be manufactured by static crystallization using a relatively simple mechanism without using an OSDA.

Prior to the reaction, the outlet 22 is closed. The reaction mixture and the seed crystals are mixed in advance or in the reaction vessel 20, and then filled into the reaction vessel 20. Although it depends on the ratio of the solid phase to the liquid phase, in many cases, if not stirred, the slurry and the seed crystals will settle and separate into a clear layer of alkaline aqueous solution at the top. For this reason, it is preferable that the reaction mixture and the seed crystals are well mixed macroscopically, and it is desirable that they are mixed more uniformly at a temperature lower than the reaction temperature after being placed in the reaction apparatus. From this point of view, it is preferable to rotate the rotating shaft 31 and stir the reaction mixture and the seed crystals with the first stirring blade 41 and the second stirring blade 51 when the reaction temperature is not reached. While continuing the stirring, steam or a heat medium is circulated through the jacket 26 installed outside the reaction vessel 20 to start raising the temperature. The reaction temperature is preferably, for example, 100 to 200°C, particularly 120 to 180°C.

Before the temperature is raised to the reaction temperature, stirring is stopped and the reaction is started in a stationary state. The solid phase consisting of the slurry and seed crystals gradually settles and collects at the bottom, and the upper part of the device becomes an alkaline aqueous solution with some aluminosilicate dissolved therein. As shown in FIG. 4(a), after the reaction, for example, the upper blade part 53 of the second stirring blade 51 located at the top (when the amount of the contents charged is small, the upper blade part 53 and the lower blade part 63) are located in the clear part 2 above the accumulation part 1 of the generated lumpy zeolite, which is preferable in terms of better exerting the effect of the second stirring blade 51 to send the reaction mother liquor at the upper part of the reaction vessel 20 downward and incorporate it into the lumpy zeolite to promote fluidization. The symbol 3 in FIG. 4(a) is the water surface.

After the reaction, the temperature inside the apparatus is lowered by stopping the steam or heat medium in the jacket 26 or by circulating a low-temperature heat medium. By stopping the steam or heat medium or circulating a low-temperature heat medium, indirect cooling of the contents of the reaction vessel 20 is started. Since rapid cooling from the reaction temperature can reduce the cause of impurity generation, it is preferable to start a motor (not shown) that rotates the rotating shaft 31 at the same time as the indirect cooling starts.
In the above-mentioned manufacturing apparatus 10, a cake layer of zeolite crystals fixed to the inner wall of the reaction vessel 20 can be effectively peeled off by applying a torque of forward and reverse rotation several times at a low speed. The rotating shaft 31 is further rotated, and the internal storage material is stirred and fluidized by the first stirring blade 41 and the second stirring blade 51 so as to generate an upward flow in the reaction vessel 20. Thereafter, the discharge port 22 at the bottom of the reaction vessel 20 is opened, and the zeolite crystals are taken out from the reaction vessel 20.

Immediately after the discharge port 22 is opened, the sludge-like zeolite that has been crushed by the first agitator blade 41 and the second agitator blade 51 accumulates near the discharge port 20 because its specific gravity is greater than the specific gravity of the liquid phase inside the reaction vessel 20, causing bridging and blocking the discharge port 22, which may prevent the internal slurry from being discharged smoothly.
In this case, in order to smoothly discharge the internal slurry, it is preferable to install a small-diameter inlet pipe 94 for introducing pressurized dry air between a first discharge valve 90 attached immediately adjacent to the discharge port 22, an elbow pipe 92 attached to the atmosphere side flange 91 of the first discharge valve 90, and a second discharge valve 93 attached to the other end, as shown in Figures 1 and 4.

According to the above mechanism, the first discharge valve 90 is closed, the second discharge valve 93 is closed, pressurized dry air is introduced from the introduction pipe 94, and the dry air is introduced and stored between the first discharge valve 90 and the second discharge valve 93. Next, the introduction of dry air into the elbow pipe 92 is stopped once, the first discharge valve is suddenly opened, and the dry air stored in the elbow pipe 92 is blown into the inside of the reaction vessel 20. By performing this operation several times, the zeolite solidified at the bottom of the reaction vessel can be dispersed, the bridging caused by the sludge-like zeolite blocking the vicinity of the discharge port 22 is eliminated, and the slurry inside the reaction vessel 20 can be discharged smoothly and forcefully. This operation drastically shortens the time it takes to discharge the slurry to the outside. The elbow pipe 90 and the introduction pipe 94 correspond to the air pipe in a preferred embodiment of the present invention.

The state of the contents after synthesis in the reaction vessel 20 is roughly divided into a zeolite solid phase and a liquid phase above it. When synthesis is performed according to the procedure of (2) synthesis of OSDA free beta zeolite in Comparative Example 1 described below, the ratio of the volume (Vs) of the zeolite solid phase in the reaction vessel to the volume (VT) of the contents after synthesis is preferably 20% to 60%, more preferably 30% to 40%. By setting it in this range, it is possible to prevent the torque for rotating the stirring member 30 from increasing due to hardness caused by too much solid phase, while improving production efficiency. The composition of the reaction mixture can be adjusted to achieve the above volume ratio.

Considering the proportion of the zeolite solid phase in the entire contents, the first agitator 41 has the role of peeling the zeolite solid phase from the bottom of the reaction vessel 20, so it is preferable that the height position at which it is installed on the funnel-shaped bottom 21 of the reaction vessel 20 is as follows. Specifically, the height position of the first agitator 41 is preferably set at a position where the volume of the reaction vessel below that height is 5% to 115% of the total volume of the zeolite solid phase after the reaction, and more preferably set within a range of 20% to 50%. The height position of the first agitator 41 refers to the upper end of the height position where the blade portion 43 is attached to the rotating shaft.

The lower blade section 63 of the agitator 51 is installed on the straight body section 25 of the reaction vessel 20 in order to peel off the zeolite solid phase from the straight body surface of the reaction vessel 20, and its height position is preferably set within a range in which the volume of the reaction vessel below that position is 38% to 100% of the total volume of the zeolite solid phase after the reaction, and more preferably set within a range in which it is 70% to 95%. The height position of the lower blade section 63 refers to the height position at which the lower blade section 63 is attached to the rotating shaft.

The upper blade section 53 of the second agitator is installed in the straight body of the reaction vessel 20, and is preferably installed at a height position where the volume of the reaction vessel below that position is 55% to 155% of the total volume (VL) of the solution phase of the mother liquor formed directly above the zeolite solid phase in the reaction vessel, and more preferably 100% to 120%. The height position of the upper blade section 53 refers to the height position where the upper blade section 53 is attached to the rotating shaft.

In this embodiment, it is preferable to measure the temperature by disposing a thermometer 71 at a height where the volume from the bottom of the reaction mixture storage portion of the reaction vessel is 20% to 30% of the total volume, and to control the zeolite synthesis temperature using the measured temperature. This is because zeolite production involves heat absorption and heat generation due to dissolution and crystallization, and it is believed that the reaction temperature can be controlled more accurately by having a thermometer at a position where the temperature of the solid phase during the static reaction can be measured. Also, if the thermometer is positioned too low, it will interfere with the stirring at the bottom. From this perspective, in this embodiment, the first stirring blade 41 and the second stirring blade 51 are configured so that they are not connected at any part other than the rotating shaft, and are disposed at a height position between the first stirring blade 41 and the second stirring blade 51.

As described above, the method for producing zeolite without using OSDA is limited in that the reaction mixture is a slurry-like solid, the product immediately after the reaction is lumpy, and the zeolite raw material cannot be mixed during the reaction. However, this production method improves the zeolite yield with a simple mechanism and greatly improves the zeolite removal process in the equipment.

The zeolite may be any zeolite obtained by a method for producing zeolite in which seed crystals are added to a reaction mixture not containing an organic structure directing agent and then heated. Examples of the crystal type include beta type, chabazite type, MWW type, MSE type, MTW type, MEL type, and PAU type, and beta type is preferable. The reason why beta type is preferable is as follows. As described above, when a reaction mixture containing an aluminosilicate gel (solid phase) and an alkaline aqueous solution (liquid phase) is heated without adding seed crystals, mordenite type zeolite is precipitated. However, beta type zeolite can be obtained by adding beta type zeolite seed crystals to this reaction mixture and heating it in a stationary state. On the other hand, when beta type zeolite seed crystals are added to the reaction mixture and reacted at the reaction temperature, mordenite type zeolite is often produced by applying a certain amount of stirring. The reason for this physical phenomenon has not been elucidated, but it is speculated that even if beta zeolite precipitates, it will rearrange to the thermodynamically more stable mordenite zeolite when physical energy such as stirring is applied. As such, beta zeolite is prone to producing impurities due to stirring during the reaction, particularly when it is produced by mixing seed crystals with a reaction mixture to which no OSDA has been added and heating it, and therefore requires production by static crystallization. It is preferable to apply the present invention to such beta zeolite, as it has great industrial significance.

As a method for synthesizing OSDA free beta zeolite, for example, the method described in International Publication No. 2011/013560 can be used. In addition, the method described in Chinese Patent Application Publication No. 101249968 can also be used. Furthermore, the method described in Chemistry of Materials, Vol. 20, No. 14, p. 4533-4535 (2008) can also be used.

An example of a method for synthesizing OSDA free beta zeolite is as follows.
(i) mixing a silica source, an alumina source, an alkali source, and water to obtain a reaction mixture having a composition represented by the molar ratios shown below;
a Si/Al molar ratio of 4 or more and 100 or less, particularly 5 or more and 100 or less, an _OH /Si molar ratio of 0.35 or more and 0.8 or less, particularly 0.37 or more and 0.7 or less, and an H 2 O/Si molar ratio of 10 or more and 50 or less, particularly 12 or more and 25 or less; (ii) a beta zeolite having a SiO ₂ /Al ₂ O ₃ molar ratio of 8 to 30 and an average particle size of 150 nm or more, particularly 150 to 1000 nm, and containing no organic compounds, is used as seed crystals, which are added to the reaction mixture in a ratio of 0.1 to 20 mass% based on the silica component in the reaction mixture,
(iii) The reaction mixture to which the seed crystals have been added is sealed and heated at 100 to 200° C., particularly 120 to 180° C. The average particle size refers to the particle diameter of the most frequent crystals when observed with a scanning electron microscope.

One method for obtaining a reaction mixture in the above range is to use an aluminosilicate gel as the reaction mixture. The aluminosilicate gel can be used as a silica source and an alumina source. When an aluminosilicate gel is used as the reaction mixture, it has the advantage that it is easier to maintain the composition of the reaction mixture uniformly than a mixture of silica powder and sodium aluminate, even if the reaction mixture is held in a large reaction apparatus without stirring. A specific method is, for example, a method of mixing an aluminosilicate gel with sodium hydroxide and water to obtain a reaction mixture. In this case, the mixing ratio may be as long as it satisfies the preferred molar ratio of (i) above. The aluminosilicate gel preferably accounts for 70% by mass or more of the silica source and 70% by mass or more of the alumina source constituting the reaction mixture, more preferably 80% by mass or more of the silica source and 80% by mass or more of the alumina source, and all of the silica source and alumina source may be aluminosilicate gel.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the manufacturing apparatus 10 of the present invention may use the stirring member 30' shown in FIG. 5 instead of the stirring member 30 shown in FIG. 2(a).

In the stirring member 30', the first stirring blade 41 is in the form of an inclined plate. In addition, only the lower blade portion 63 in the second stirring blade 51 has a scraper 67 having an edge portion that extends along the wall surface of the straight body portion, and the upper blade portion 53 and the lower blade portion 63 are not connected. In other respects, the stirring member 30' is similar to the stirring member 30.

Example 1
(1) Synthesis of seed crystals Using tetraethylammonium hydroxide as an organic SDA, sodium aluminate as an alumina source, and fine powder silica (Mizukasil P707) as a silica source, a beta zeolite having a _SiO2 / _{Al2O3 molar} ratio of 24.0 was synthesized by stirring and heating at 165°C for 96 hours by a conventionally known method. This was fired in an electric furnace at 550°C for 10 hours while circulating air, to produce crystals that do not contain organic matter. The crystals were observed with a scanning electron microscope, and the average particle size was 280 nm. This beta zeolite crystal that does not contain organic matter was used as a seed crystal.
(2) Production of reaction mixture 20 kg of the seed crystals were added to 820 kg of industrial water and stirred while mixing. 1920 kg of aluminosilicate gel (= "powdered product precursor", water content 70.1 mass%, Si/Al molar ratio = 8.0) was added to the mixed solution and stirred while mixing. Furthermore, 320 kg of 30 mass% sodium hydroxide was added and stirred and mixed to obtain a reaction mixture (OH/Si molar ratio: 0.5, _H2O /Si molar ratio: 16.5).
(3) Synthesis of OSDA free beta zeolite The production apparatus 10 shown in FIG. 1 (tilt angle A and tilt angle C were 30°, tilt angle B was 45°, α was more than 42° and not more than 50°, W/L1 was 2.5%, L3/L2 was 53.9%, and the internal space volume of the reaction vessel 20 was 3.5 ^m3 ) was used.
The reaction mixture obtained above was placed in a stainless steel reaction vessel 20 and was statically heated at 150° C. for 47 hours under autogenous pressure without aging.
The height position of the thermometer and the height positions of the blades 43, 53, 63 were such that the volume of the reaction vessel below the height was within the most preferable range among the above-mentioned ranges.
After the reaction time had elapsed, the reaction vessel 20 was switched from heating to cooling, and then torque was applied to rotate forward and backward several times at a low speed as necessary. Then, the rotating shaft 31 was rotated clockwise in a plan view, and the internal storage was stirred by the first stirring blade 41, the upper stage blade portion 53 of the second stirring blade 51, and the lower stage blade portion 63 of the second stirring blade 51 so as to generate an upward flow in the reaction vessel 20, and the zeolite was fluidized. The rest of the experiment was the same as in Comparative Example 1. After the zeolite was discharged, almost no adhesion of zeolite was observed on the inner wall surface of the reaction vessel 20.
Similar results were obtained when the amounts of each component were reduced to one-fourth and a similar production apparatus with a capacity of 500 liters was used.

(Comparative Example 1)
Instead of the reaction apparatus of Fig. 1, a stainless steel reaction vessel 120 having an elliptical bottom as shown in Fig. 6 was used. The amount of each component was reduced to one-fourth, and the capacity of the reaction vessel 120 was set to 500 liters. Other than that, the reaction was carried out in the same manner as in Example 1. The stirring member shown in Fig. 7(a) was used for stirring before the reaction, but stirring after the reaction was not performed.
After the reaction was completed, the valve 121 that had been blocking the outlet 122 at the bottom of the reaction vessel 120 was opened, but the zeolite that had been produced was not discharged. After cooling, the lid 123 was opened, and the zeolite in the reaction vessel 120 was stirred with a stirring rod to fluidize it, and discharged from the outlet 122. When the inside of the reaction vessel 120 was then observed, it was confirmed that the zeolite had accumulated at the bottom and was fixed to the inner wall of the reaction vessel 120. An attempt was made to peel off the zeolite that had been fixed to the inner wall of the reaction vessel 120 with a high-pressure cleaning device, but almost none of it could be removed. Finally, the vessel was cleaned by adding a 1 to 10 mass % caustic soda solution and stirring at 80°C for 12 hours.

(Comparative Example 2)
After the reaction was completed, the zeolite was cooled and then stirred with the stirring member shown in Fig. 7(a) without opening the valve 121. The rest of the procedure was the same as in Comparative Example 1. However, when the stirring member shown in Fig. 7(a) was used, the zeolite could not be fluidized.

(Comparative Example 3)
The stirring member was changed from that shown in Fig. 7(a) to that shown in Fig. 7(b). Other than that, the comparative example was the same as in Comparative Example 2. As a result, the same results as in Comparative Example 2 were obtained.

10 Zeolite manufacturing equipment
20 Reaction vessel
21 Bottom
23 Bottom
23a Slope
30 Stirring member
31 Rotation axis
32 Support
41 First stirring blade
42 Edge
51 Second stirring blade

Claims (15)

A first step of heating a reaction mixture containing a silica source, an alumina source, an alkali source, and water, but not containing an organic structure-directing agent, and a zeolite raw material containing seed crystals in a sealed reaction vessel and allowing the reaction to occur in a stationary state;
A second step of discharging the aggregated zeolite produced by the reaction from the reaction vessel,
The reaction vessel has a discharge port at a bottom for discharging the zeolite, and the bottom is formed in a funnel shape having an inclined surface that is inclined downward toward the discharge port,
The reaction vessel has a stirring member,
The stirring member has a rotating shaft that is located at the center of the funnel-shaped bottom surface when the reaction vessel is viewed from above and extends in the vertical direction, a first stirring blade that is attached to the rotating shaft and has an edge portion that extends along the inclined surface of the reaction vessel, and a second stirring blade that is attached to an upper portion of the first stirring blade on the rotating shaft,
the inclined surface of the bottom of the reaction vessel and the edge of the first agitating blade are in a non-contact state;
In the second step, the rotating shaft is rotated to fluidize the zeolite with the first stirring blade and the second stirring blade, and the fluidized zeolite is discharged from the discharge port. In a plan view of the reaction vessel, the first agitating blade and the second agitating blade each have a blade portion extending radially outwardly of a circle centered on the rotation shaft,
The method for producing zeolite as described in claim 1, wherein when viewed from a direction perpendicular to the direction in which the rotation shaft extends, the blade portions of the first agitating blade and the second agitating blade each have a shape having an upper surface that is inclined with respect to a horizontal plane. The method for producing zeolite according to claim 2, wherein the blade portion of the first agitating blade has a cross section perpendicular to the direction in which it extends that is triangular and tapered upward. The reaction vessel has a vertical wall surface extending in the same direction as the rotation shaft from an upper end of a funnel-shaped bottom surface,
The method for producing zeolite described in claim 2 or 3, wherein the second agitating blade further comprises a second blade portion connected to the outer end of the blade portion, and the second blade portion has an edge portion extending along the vertical wall surface and along the direction in which the vertical wall surface extends. The method for producing zeolite according to any one of claims 2 to 4, wherein the blade portion of the second agitating blade has a lower blade portion located on the lower side in the direction in which the rotating shaft extends and an upper blade portion located on the upper side. The method for producing zeolite according to any one of claims 1 to 5, wherein the stirring member has a structure in which the first stirring blade and the second stirring blade are not connected except to the rotating shaft. The method for producing zeolite according to any one of claims 1 to 6, wherein the inclined surface of the bottom has an angle of greater than 42° with the horizontal plane when the reaction vessel is viewed from the side. The method for producing zeolite according to any one of claims 1 to 7, wherein in the first step, the reaction mixture and the seed crystals are heated while being stirred by the first stirring blade and the second stirring blade, the stirring is stopped, and then the reaction mixture and the seed crystals are reacted in a stationary state under heating, and after the reaction, the zeolite is fluidized by the first stirring blade and the second stirring blade in the second step at the same time as the temperature starts to decrease. The method for producing zeolite according to any one of claims 1 to 8, which has an air pipe for introducing air into the discharge port, and disperses the zeolite solidified at the bottom of the reaction vessel by introducing air from the air pipe when discharging the zeolite. The method for producing zeolite according to any one of claims 1 to 9, wherein a temperature measuring resistor is disposed at a height position where the volume from the bottom of the reaction mixture storage portion of the reaction vessel is 20% to 30% of the total volume of the reaction mixture storage portion, the temperature is measured, and the measured temperature is used to control the zeolite synthesis temperature. The method for producing zeolite according to any one of claims 1 to 10, in which zeolite is produced so that the solid phase accumulates up to a height position where the volume from the bottom of the reaction mixture storage portion of the reaction vessel is 30% to 40% of the total volume of the reaction mixture storage portion. The method for producing a zeolite according to any one of claims 1 to 11, wherein the zeolite is a beta zeolite. The composition of the reaction mixture is
Si/Al molar ratio is 4 or more and 100 or less,
OH/Si molar ratio is 0.35 or more and 0.8 or less,
The method for producing a zeolite according to claim 12, wherein the H ₂ O/Si molar ratio is 10 or more and 50 or less. The method for producing a zeolite according to any one of claims 1 to 13, wherein an aluminosilicate gel is used as the reaction mixture. A manufacturing apparatus for manufacturing a zeolite without using an organic structure directing agent, comprising:
The apparatus includes a reaction vessel capable of heating the zeolite raw material under a sealed condition, and a stirring member that can be accommodated in the reaction vessel.
The reaction vessel has a discharge port at a bottom for discharging the fluidized zeolite, and a bottom surface of the bottom is formed in a funnel shape having an inclined surface inclined toward the discharge port,
The stirring member has a rotating shaft that is located at the center of the funnel-shaped bottom surface and extends in the vertical direction when viewed in a plane, a first stirring blade attached to the rotating shaft and having an edge portion extending along the inclined surface of the reaction vessel, and a second stirring blade attached to the upper part of the first stirring blade on the rotating shaft, and the inclined surface of the bottom of the reaction vessel and the edge portion of the first stirring blade are not in contact with each other.

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