Tanks used in refining equipment

Abstract

The present invention provides a method for obtaining high-quality products. The present invention relates to a tank used in a refining device, characterized in that: the tank is a crystallization tank for generating a slurry that contains crystals of a compound, and / or an aging tank in which the crystals of the compound in the tank can be retained in a suspended state; the tank comprises an agitator and an obstructing plate for producing a rising flow from a swirl flow; and the tank makes it possible to form a supernatant portion comprising a supernatant and a suspension portion in which the crystals of the compound are in a suspended state.

Description

[Technical Field]

[0001] The present invention relates to a vessel used in a purification apparatus, and more particularly to a vessel used in a purification apparatus, a purification apparatus, a method for producing a compound, and a method for purifying a compound. [Background technology]

[0002] Purification apparatuses are widely used industrially to purify compounds used as raw materials for resins, etc. In many fields of the chemical industry, there is a demand for obtaining high-quality compounds with reduced impurities, and various investigations have been conducted into better purification apparatuses for this purpose.

[0003] In industry, many crude compounds before purification are purified by a continuous purification process. For example, a method for producing acrylic acid has been disclosed in which an acrylic acid-containing gas obtained by catalytic gas-phase oxidation of a raw material gas is collected and purified by crystallization, and a Michael adduct of acrylic acid contained in the remaining mother liquor is decomposed and returned to the collection step (see, for example, Patent Document 1).

[0004] In the purification step, in order to obtain a compound of higher purity in a high yield, a tank for producing a slurry containing crystals of the compound (crystallization tank) and a tank for growing crystals of the compound (aging tank) are used. Conventional purification methods using a crystallization tank or an aging tank are disclosed in Patent Documents 2 to 4. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-182437 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-28214 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-140471 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-204937 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, there is a need for a better purification device for producing compounds, and it has been desired to obtain high-quality products (compounds). The present invention has been made in view of the above-mentioned current situation, and aims to provide a method for obtaining high-quality products. [Means for solving the problem]

[0007] The present inventors have studied purification apparatuses and focused on the tanks used in the purification apparatuses. They have discovered that if a crystallization tank for producing a slurry containing compound crystals or an aging tank capable of maintaining the compound crystals in a suspended state within the tank is equipped with a stirrer and a baffle for generating an upward flow from a swirling flow, and is capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state, the compound crystals can be maintained in a sufficiently uniform suspended state within the tank for a certain period of time, and the crystals can be grown appropriately to obtain a high-quality product, thereby achieving the present invention.

[0008] That is, the present invention relates to a tank used in a purification apparatus, which is a crystallization tank for producing a slurry containing compound crystals and / or an aging tank capable of maintaining the compound crystals in a suspended state within the tank, and which is characterized by being equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state.

[0009] Although the above-mentioned Patent Documents 2 and 4 disclose baffles, the baffle described in Patent Document 2 is basically for blocking the upward flow, and is not for generating an upward flow to maintain a suspended state. Also, the stirring vessel described in Patent Document 4 is unable to mix the crystals uniformly in the suspension section, and there is a risk that coarse crystals will accumulate on the bottom and that crystals will be mixed into the supernatant. [Effects of the Invention]

[0010] By using the vessel of the present invention, a high quality product can be obtained. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an example of a tank of the present invention as seen from the side. [Figure 2] FIG. 2 is a schematic cross-sectional view of another example of the tank of the present invention as seen from the side. [Figure 3] FIG. 3 is a schematic cross-sectional view of another example of the tank of the present invention as seen from the side. [Figure 4] FIG. 4 is a cross-sectional schematic diagram of an example of a separation mechanism (reservoir) for the tank of the present invention shown in FIG. 3, seen from the side. [Figure 5] FIG. 5 is a schematic cross-sectional view of an example of a tank of the present invention as viewed from the top side (top plate side). [Figure 6] FIG. 6 is a cross-sectional schematic diagram showing another example of a separation mechanism for a tank according to the present invention, as viewed from the side. [Figure 7] FIG. 7 is a cross-sectional schematic diagram showing another example of a separation mechanism for a tank according to the present invention, as viewed from the side. [Figure 8] FIG. 8 is a cross-sectional schematic diagram showing another example of a separation mechanism for a tank according to the present invention, as viewed from the side. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. In addition, a combination of two or more of the individual preferred features of the present invention described below is also a preferred embodiment of the present invention.

[0013] In the following, first, the tank of the present invention (crystallization tank and / or aging tank used in the purification apparatus) will be explained, followed by the purification apparatus of the present invention, the method for producing the compound of the present invention, and the method for purifying the compound of the present invention.

[0014] (Tank used in refining equipment) The tank of the present invention is a crystallization tank for producing a slurry containing compound crystals and / or an aging tank capable of maintaining the compound crystals in a suspended state within the tank, and is equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and is capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state.

[0015] When the tank is in use, a portion of the tank can be kept in a suspended state by generating an appropriate upward flow from the swirling flow. In this way, the crystals can be held in a suspended state in the tank for a certain period of time, and after the crystals have grown sufficiently, they can be extracted, for example, as a slurry from near the bottom of the tank. For example, in an aging tank, by holding the crystals for a certain period of time, fine crystals melt due to Ostwald ripening, and larger crystals grow further, narrowing the crystal size distribution. This allows high-quality crystals to be obtained, and when such crystals are subjected to a purification step in a subsequent washing column, for example, the purification efficiency in the washing column can be further improved. Furthermore, even in a crystallization tank, holding the crystals for a certain period of time can be expected to achieve the same effect as in an aging tank.

[0016] The residence time of the compound in the aging tank may be adjusted appropriately depending on the type of compound to be purified, but from the viewpoint of adjusting the particle size distribution of the slurry sent to the washing column and reducing the reflux ratio in the washing column (flow rate of washing liquid / flow rate of purified compound), the residence time is preferably 0.5 to 6 hours. When the compound is (meth)acrylic acid, the residence time is more preferably 1 to 5 hours, and even more preferably 1.2 to 4.5 hours. The residence time is calculated as the volume of the suspension in the aging tank divided by the flow rate at which the slurry is supplied from the aging tank to the washing column in the next step (later stage). The size of the crystallizer is determined by taking into account the residence time and the required heat transfer area. The residence time of the compound in the crystallizer depends on the operating conditions.

[0017] The agitator is not particularly limited as long as it can generate a sufficient swirling flow in the vessel, and any known agitator can be used, including a stirrer, a mixer, a blender, a kneader, etc. The material of the agitator is not particularly limited, but metals such as stainless steel are preferred. When the above-mentioned agitator has an agitator blade, the length of the agitator blade (the distance from the agitator shaft to the tip of the agitator blade) is preferably 1 / 10 or more, more preferably 1 / 8 or more, of the inner diameter of the tank of the present invention (also referred to as the tank diameter in this specification) when viewed from above. The length of the stirring blade is usually 1 / 2 or less of the inner diameter of the vessel of the present invention. The stirring blades may be arranged in a plurality in the axial direction. In other words, the stirrer may have multi-stage blades. When the stirring blades are arranged in a plurality in the axial direction, it is preferable that the length of any one of the stirring blades is within the range of the preferred ratio to the inner diameter of the vessel described above, and it is more preferable that the lengths of all the stirring blades are within the range of the preferred ratio to the inner diameter of the vessel described above. In this specification, the inner diameter of the tank refers to the inner diameter when the tank of the present invention is viewed from above, and if the tank has a shape other than a cylindrical shape, it refers to the maximum distance (distance on a horizontal plane) between two points on the outline corresponding to the inner wall surface of the tank when the tank of the present invention is viewed from above.

[0018] The baffle for generating an upward flow from a swirling flow is a baffle that can change at least a part of the horizontal flow of the swirling flow into an upward flow when the swirling flow collides with the baffle. The swirling flow is generated, for example, by stirring a slurry containing compound crystals in a tank using the above-mentioned stirrer. The vessel of the present invention is not limited in its state of use. That is, the vessel of the present invention may be any vessel that can form a supernatant portion consisting of a supernatant liquid and a suspension portion in which crystals of the compound are in a suspended state when in use. Furthermore, the baffle plate may be any vessel that can generate an upward flow from a swirling flow generated by stirring with a stirrer or the like when the vessel of the present invention is in use.

[0019] The baffle plate may be provided in the vessel so as to generate an upward flow from the swirling flow, and is preferably provided, for example, along the direction from the top plate side to the bottom side of the vessel. The baffle plate being provided along the direction from the top plate side to the bottom plate side of the tank means that the baffle plate does not have to be in contact with the top plate or the bottom plate of the tank, and it is sufficient if the inclination of the baffle plate in the longitudinal direction can be said to be in the direction from the top plate side to the bottom plate side of the tank. Among these, the baffle plate is more preferably provided so that its longitudinal direction is in the range of 0 to 30° with respect to the vertical direction, further preferably in the range of 0 to 15°, still more preferably in the range of 0 to 10°, particularly preferably in the range of 0 to 5°, and most preferably provided in the vertical direction. The longitudinal direction of the baffle plate refers to the direction of the shortest line segment connecting the highest position (top) to the lowest position (bottom) of the baffle plate.

[0020] As described above, the tank of the present invention may be any tank that, when used, can form a supernatant portion (also referred to as a clear portion in this specification) consisting of a supernatant liquid and a suspension portion in which crystals of the compound are in a suspended state. For example, by providing the baffle plate on the bottom side of the tank along the direction from the top plate side (upper surface side) of the tank to the bottom side, when the tank is in use, an upward flow can be appropriately generated from the swirling flow on the bottom side of the tank, thereby making the bottom side of the tank into a suspended state and making the upper side of the tank into a supernatant portion consisting of mother liquor (supernatant liquid). This also makes it possible to very suitably recover the mother liquor derived from the slurry from the supernatant, if necessary. In this specification, the supernatant portion is a portion where the mother liquor (supernatant) derived from the slurry is present when the tank of the present invention is used, and the suspension portion is a portion where the slurry (suspension) containing crystals of the compound is present when the tank of the present invention is used. The baffle plate is preferably provided on the bottom side of the tank. The baffle plate being provided on the bottom side of the vessel means that the height of the center of gravity of the baffle plate is located at a position that corresponds to the lower half of the vessel's internal volume.

[0021] In particular, the baffle plate is preferably one for forming a supernatant portion consisting of the supernatant liquid and a suspension portion in which the crystals of the compound are in a suspended state, with the height of the top of the baffle plate as the boundary. For example, by providing the baffle plate in a vertical direction on the bottom side of the tank, it is usually possible to form a supernatant part consisting of a supernatant liquid and a suspension part in which crystals of the compound are in a suspended state, with the height of the top of the baffle plate as the boundary.

[0022] In the vessel of the present invention, the baffle plate is preferably provided near the inner wall surface of the vessel. The baffle plate being provided near the inner wall surface of the tank means that when the tank of the present invention is viewed from above, the shortest distance between the baffle plate and the inner wall surface of the tank is 1 / 5 or less of the inner diameter of the tank of the present invention, preferably 1 / 10 or less, and more preferably 1 / 20 or less. The baffle plate may be in contact with the inner wall surface of the vessel of the present invention, but, for example, it is preferable that the shortest distance between the baffle plate and the inner wall surface of the vessel is 1 / 100 or more of the inner diameter of the vessel of the present invention. It is more preferable that the baffle plate is provided in a direction from the inner wall surface of the vessel of the present invention toward the center of the vessel.

[0023] The width of the baffle plate is, for example, preferably 1 / 30 or more of the inner diameter of the tank of the present invention, more preferably 1 / 20 or more, even more preferably 1 / 18 or more, and particularly preferably 1 / 15 or more. The width of the baffle plate is preferably 1 / 2 or less, more preferably 1 / 5 or less, and even more preferably 1 / 8 or less of the inner diameter of the vessel of the present invention. Furthermore, the height of the baffle plate is, for example, preferably 1 / 5 or more of the height of the straight body part of the tank in the tank of the present invention, more preferably 3 / 10 or more, even more preferably 2 / 5 or more, and particularly preferably 1 / 2 or more. The height of the baffle plate is preferably 9 / 10 or less, more preferably 4 / 5 or less, of the height of the straight body part of the tank. The tank barrel portion of the tank of the present invention is a columnar portion having a constant inner diameter, and is preferably the portion having the largest inner diameter. Furthermore, the tank barrel portion is preferably a cylindrical portion. The height of the baffle plate refers to the difference between the height of the top of the baffle plate and the height of the bottom of the baffle plate. In the case where the tank of the present invention has a plurality of baffles, it is sufficient and preferable that any one of the baffles satisfies the above-mentioned preferable ratio of the height of the baffle to the height of the straight body part of the tank, but it is more preferable that all of the baffles satisfy the above-mentioned preferable ratio of the height of the baffle to the height of the straight body part of the tank. When the tank of the present invention is in use, as described above, the upper side of the top of the baffle basically becomes a supernatant part, and the lower side of the top becomes a suspension part, with the height of the top of the baffle as the boundary. Therefore, by adjusting the ratio of the height of the baffle to the height of the straight body part of the tank, the volume ratio (volume proportion) of the supernatant part to the suspension part when the tank of the present invention is in use can be adjusted. Furthermore, the inner diameter of the tank of the present invention is preferably 1 / 10 or more of the height of the straight body of the tank, more preferably 1 / 8 or more, even more preferably 1 / 6 or more, and particularly preferably 1 / 4 or more. Furthermore, the inner diameter of the tank of the present invention is preferably 1 / 1 or less relative to the height of the straight body of the tank, more preferably 1 / 1.2 or less, even more preferably 1 / 1.5 or less, and particularly preferably 1 / 1.8 or less. Furthermore, the tank of the present invention is preferably configured so that the volume of the suspension portion is 1 / 5 or more of the volume of the entire contents (supernatant and suspension portion) held therein, more preferably 3 / 10 or more, even more preferably 2 / 5 or more, and particularly preferably 1 / 2 or more. The tank of the present invention is preferably configured so that the volume of the suspension portion is 9 / 10 or less of the volume of the entire contents (supernatant and suspension portion) held therein, and more preferably so that the volume is 4 / 5 or less. The thickness of the baffle plate may be any thickness that can provide sufficient strength against the collision of the swirling flow, and is preferably, for example, 1 to 100 mm. Examples of materials for the baffle plate include metals such as stainless steel, and resins. A plurality of the baffles may be provided in the tank of the present invention, and a plurality of the baffles are preferably provided. When a plurality of the baffles are provided in the tank of the present invention, the baffles are preferably arranged in positions symmetrical with respect to the center of the tank when the tank is viewed from above, for example.

[0024] The tank of the present invention preferably includes, above the top of the baffle, a supply port for supplying a slurry containing compound crystals to the tank, a withdrawal port for withdrawing the mother liquor from the tank, and a partition plate provided between the supply port and the withdrawal port along the direction from the top plate side to the bottom plate side of the tank. The partition plate being provided between the supply port and the discharge port means that the partition plate is provided so as to separate the supply port and the discharge port when the tank of the present invention is viewed from the top and / or side.

[0025] The partition plate is preferably provided at a position closer to the supply port than to the withdrawal port when the tank of the present invention is viewed from above. Furthermore, when the tank of the present invention is viewed from above, the partition plate, together with the inner wall surface of the tank, preferably separates an area where the supply port is located from an area where the withdrawal port is located, and is preferably arranged so that the ratio of the area where the supply port is located to the area where the withdrawal port is located is 1 or more, more preferably 2 or more, even more preferably 3 or more, and particularly preferably 3.5 or more. Moreover, from the viewpoint of enabling the supply ports to be suitably arranged, the area ratio is preferably set to, for example, 20 or less. In addition, if the partition plate is inclined and the area ratio varies depending on the height, it is sufficient that the area ratio is within the preferred range at any height, but it is preferable that the area ratio is within the preferred range at any height.

[0026] When the tank of the present invention is viewed from above, the partition plate, together with the inner wall surface of the tank, preferably separates an area where the supply port is located from an area where the discharge port is located, and is perpendicular to one of the inner diameters of the tank of the present invention. In this case, the ratio of the length of the inner diameter portion in the area where the supply port is located to the length of the inner diameter portion in the area where the discharge port is located is preferably 1 or more, more preferably 2 or more, and even more preferably 2.5 or more. The upper limit of the length ratio is not particularly limited, but can be set to, for example, 10 or less. In addition, if the partition plate is inclined and the length ratio varies depending on the height, it is sufficient that the length ratio is within the preferred range at any height, but it is preferable that the length ratio is within the preferred range at any height.

[0027] When the tank of the present invention is viewed from the top, the distance between the withdrawal port and the supply port is preferably at least 2 / 5 of the inner diameter of the tank of the present invention, more preferably at least 1 / 2, and even more preferably at least 3 / 5. The upper limit of the distance is not particularly limited, but is usually equal to or less than the inner diameter of the tank of the present invention. When there are a plurality of outlets and / or supply ports, it is preferable that any one of the distances between the outlets and the supply ports falls within the above ratio range, but it is more preferable that all of the distances between the outlets and the supply ports fall within the above ratio range.

[0028] The partition plate being arranged along the direction from the top plate side to the bottom plate side of the tank means that the partition plate does not have to be in contact with the top plate or bottom plate of the tank, as long as its longitudinal inclination can be said to be in the direction from the top plate side to the bottom plate side of the tank. In particular, it is more preferable that the partition plate is arranged so that its longitudinal direction is in the range of 0 to 30° relative to the vertical direction, even more preferably in the range of 0 to 15°, still more preferably in the range of 0 to 10°, particularly preferably in the range of 0 to 5°, and most preferably in the vertical direction. The longitudinal direction of the partition plate refers to the direction of the shortest line segment connecting the highest position (top) to the lowest position (bottom) of the partition plate.

[0029] For example, the width of the partition plate is preferably 1 / 5 or more of the inner diameter of the tank of the present invention, more preferably 2 / 5 or more, even more preferably 3 / 5 or more, and particularly preferably 4 / 5 or more. The width of the partition plate is usually equal to or smaller than the inner diameter of the vessel of the present invention, and is preferably equal to or smaller than 19 / 20, for example. The height of the partition plate is preferably 1 / 20 or more, more preferably 1 / 10 or more, and even more preferably 1 / 8 or more of the height of the tank body portion. The height of the partition plate is preferably 3 / 5 or less, more preferably 2 / 5 or less, of the height of the straight body portion of the tank. The width and height of the partition plate can be appropriately set according to the size of the tank, as described above. The thickness of the partition plate may be any thickness that provides sufficient strength, and is preferably, for example, 1 to 100 mm. Examples of materials for the partition plate include metals such as stainless steel, and resins. A plurality of the partition plates may be provided in the tank, but it is preferable that only one partition plate is provided in the tank.

[0030] The partition plate is preferably provided so as to be angled within a range of 0 to 30°, more preferably within a range of 0 to 15°, further preferably within a range of 0 to 10°, and particularly preferably within a range of 0 to 5°, relative to the baffle plate as viewed from above. In particular, in the tank of the present invention, it is most preferable that the partition plate is provided parallel to the baffle plate. This prevents the partition plate from acting as a baffle (causing an upward flow from the swirling flow) when the tank is in use, and more effectively prevents crystals from being mixed into the supernatant.

[0031] The supply port, the withdrawal port, and the partition plate are provided above the top of the baffle plate, in other words, the supply port, the withdrawal port, and the partition plate are provided in the supernatant portion. From the viewpoint of further preventing the incorporation of crystals into the mother liquor extracted from the supernatant, the vertical distance between the partition plate and the baffle plate is preferably 1 / 20 or more, more preferably 1 / 18 or more, even more preferably 1 / 15 or more, and particularly preferably 1 / 10 or more of the height of the straight body part of the tank. This also prevents the partition plate from acting as a baffle plate, and the effect of preventing the incorporation of crystals into the supernatant part is remarkable. The upper limit of the vertical distance between the partition plate and the baffle plate relative to the height of the tank body is not particularly limited, but is usually 4 / 5 or less. The vertical distance between the partition plate and the baffle plate is the vertical distance between a position where the partition plate exists and a position where the baffle plate exists, and is the minimum distance, and is usually the difference between the height of the bottom of the partition plate and the height of the top of the baffle plate (for example, the vertical distance d shown in FIG. 2). When a plurality of the partition plates and / or the baffles are provided in the tank, it is preferable that any one of the vertical distances between the partition plates and the baffles falls within the range of the above ratio, but it is more preferable that all of the vertical distances between the partition plates and the baffles fall within the range of the above ratio.

[0032] It is preferable that the supply port and the baffle plate are spaced as far apart as possible in the horizontal direction, and the distance between the supply port and the baffle plate, when the tank of the present invention is viewed from above, is preferably 1 / 20 or more of the diameter of the tank, more preferably 1 / 10 or more, even more preferably 1 / 8 or more, still more preferably 1 / 5 or more, and particularly preferably 2 / 5 or more. The upper limit of the distance between the supply port and the baffle plate relative to the diameter of the tank is not particularly limited, but is usually 9 / 10 or less. As described above, the distance between the supply port and the baffle plate is the shortest horizontal distance between the supply port and the baffle plate when the tank of the present invention is viewed from above. When a plurality of the supply ports and / or the baffles are provided in the tank, it is preferable that any one of the distances between the supply ports and the baffles falls within the range of the above ratio, but it is more preferable that all of the distances between the supply ports and the baffles fall within the range of the above ratio.

[0033] In this specification, "above the top of the baffle" means a position higher than the height of the top of the baffle, and is not limited to directly above the baffle. Although Fig. 1, which will be described later, shows a case in which only one supply port and one withdrawal port are provided in the tank, a plurality of each may be provided in the tank. For example, 3 to 12 supply ports may be provided in the tank. Furthermore, the nozzle constituting the supply port may have a bent tip so that the slurry is supplied along the inner wall surface of the tank, or the tip may be placed in the liquid so that the slurry is supplied into the liquid.

[0034] The tank of the present invention preferably comprises, above the top of the baffle, a separation mechanism including an outlet for withdrawing the mother liquor from the tank and a weir for causing the supernatant liquid to overflow and flow into the outlet so as to prevent crystals of the compound from being mixed into the mother liquor. By providing the tank of the present invention with the separation mechanism, it is possible to sufficiently prevent crystals from being mixed into the withdrawal port, and the mother liquor can be suitably withdrawn.

[0035] The separation mechanism is usually composed of a bottom portion and a weir portion (side portion) so as to cover the withdrawal port from the bottom and side of the tank of the present invention, but part of the weir portion can be replaced by the inner wall surface of the tank. A notch may also be provided at the top of the weir portion (side portion). The shape of the notch is not particularly limited, but examples of suitable shapes include a triangular (inverted triangular) or rectangular weir portion when viewed from the side. The upper surface of the separation mechanism is partially or entirely uncovered, and the mother liquor that has overflowed the weir section can be introduced into the separation mechanism via this upper surface. The bottom surface may be horizontal, but is preferably inclined at an angle of, for example, 0.5 to 30° relative to the horizontal so that the height decreases toward the outlet, which allows the mother liquor in the separation mechanism to flow more efficiently into the outlet. The size and material of the bottom portion and weir portion can be designed and selected as appropriate.

[0036] As mentioned above, the vessel of the present invention preferably includes a withdrawal port for withdrawing the mother liquor from the vessel. The tank of the present invention further includes a spare outlet for withdrawing the mother liquor from the tank, located above the outlet for withdrawing the mother liquor from the tank, and the spare outlet is preferably provided so that the height of the lower end of its opening is equal to or lower than the height of the top of the weir portion included in the separation mechanism. The spare outlet is intended to be used in place of the outlet for extracting the mother liquor from the tank when the outlet becomes unusable due to blockage or the like, and is capable of extracting the mother liquor that can be stored in the separation mechanism. As described above, the auxiliary withdrawal port may be located above the withdrawal port for withdrawing the mother liquor from the tank, and the height of the opening of the auxiliary withdrawal port may be adjusted appropriately within this range. Examples of the height (position) of the auxiliary withdrawal port include those shown in Figures 6 to 8. In Figures 6 to 8, the height of the top of the weir included in the separation mechanism is indicated by a dashed line. The nozzle 114a constituting the auxiliary withdrawal port shown in Figure 6 has a lower opening height that coincides with the top of the weir included in the separation mechanism. The nozzle 114a constituting the auxiliary withdrawal port shown in Figures 7 and 8 has a lower opening height that is lower than the top of the weir included in the separation mechanism.

[0037] It is preferable that the separation mechanism and the baffle plate are spaced as far apart as possible in the horizontal direction, and the distance between the separation mechanism and the baffle plate, when the tank of the present invention is viewed from above, is preferably 1 / 50 or more of the diameter of the tank, more preferably 1 / 40 or more, even more preferably 1 / 30 or more, still more preferably 1 / 20 or more, and particularly preferably 1 / 15 or more. The upper limit of the distance between the separation mechanism and the baffle plate relative to the diameter of the tank is not particularly limited, but is usually 9 / 10 or less. The distance between the separation mechanism and the baffle plate is the shortest horizontal distance between the separation mechanism and the baffle plate when the tank of the present invention is viewed from above. When a plurality of the separation mechanisms and / or the baffles are provided in the tank, it is preferable that any one of the distances between the separation mechanisms and the baffles falls within the range of the above ratio, but it is more preferable that all of the distances between the separation mechanisms and the baffles fall within the range of the above ratio.

[0038] The tank of the present invention is preferably provided with an outlet below the top of the baffle plate for withdrawing the slurry containing the compound crystals from the tank, and the outlet is preferably arranged so that the slurry containing the compound crystals is withdrawn along the tangent direction of the outline corresponding to the inner wall surface of the tank when the tank is viewed from above. The term "below the top of the baffle" is not limited to being directly below the baffle as long as it is lower than the height of the top of the baffle. The outlet is preferably provided at a position lower than the center of gravity of the baffle, and more preferably at a position equal to or lower than the height of the bottom of the baffle.

[0039] The phrase "the outlet for withdrawing the slurry is arranged so that, when the vessel is viewed from above, the slurry containing compound crystals is withdrawn along the tangent direction of the outline of the vessel's inner wall surface" means that the nozzle or line constituting the outlet is arranged within an angle of 15° or less with respect to the tangent direction of the outline of the vessel's inner wall surface, more preferably within an angle of 10° or less with respect to the tangent direction, even more preferably within an angle of 5° or less, and particularly preferably parallel to the tangent direction. By providing the withdrawal port in this manner, the slurry containing the compound crystals can be efficiently withdrawn by utilizing the swirling flow, and the deposition of the crystals on the bottom of the tank can be sufficiently prevented. It is preferable that the outlet for withdrawing the slurry and the baffle are separated horizontally as far as possible, and the distance between the outlet and the baffle is preferably 1 / 30 or more, and more preferably 1 / 20 or more, of the diameter of the tank when the tank of the present invention is viewed from above. The upper limit of the distance between the outlet and the baffle plate relative to the diameter of the tank is not particularly limited, but is usually 9 / 10 or less. The distance between the outlet and the baffle plate is the shortest horizontal distance between the outlet and the baffle plate when the vessel of the present invention is viewed from above. The slurry can be extracted using, for example, a pump, and preferred pumps include a centrifugal pump, a diaphragm pump, and a rotary pump. Furthermore, if the tank bottom is flat, crystals may become trapped in the corners depending on the stirring conditions, so the corners may be chamfered or rounded.

[0040] The size of the tank of the present invention is not particularly limited, but for example, it is preferable that the inner diameter is 100 to 50,000 mm, and the height is 200 to 100,000 mm.

[0041] Instrumentation devices such as thermometers, pressure gauges, level gauges (radar type, etc.), and level switches (float type, etc.) may be provided in the main body or periphery of the crystallization tank or aging tank of the present invention. Sight glasses (sight windows) may be provided on the side plates, etc. of the aging tank, and in this case, these may be covered with covers. Manholes, handholes (holes for reaching inside during maintenance), etc. may be provided on the top plate, side plate, etc. of the aging tank, and ruptures, etc. may be provided on the top plate, etc. of the aging tank. There is no limit to the number of these devices that may be provided.

[0042] FIG. 1 is a schematic cross-sectional view of an example of a vessel of the present invention, viewed from the side. Crystal-containing slurry 11a is supplied into vessel 1 via nozzle 4. Next, the agitator shaft of vessel 1 is rotated in agitation direction 9a, and the crystal-containing slurry is agitated by impeller 3, generating a horizontal swirling flow. This causes the crystal-containing slurry flow 9b to collide with baffles 2a and 2b, forming an upward flow. By creating an upward flow in crystal-containing slurry flow 9b, suspension section 8 is favorably suspended. The crystal-containing slurry can be maintained in suspension section 8 for a certain period of time, allowing the crystals in the slurry to grow. Crystal-containing slurry 21 can then be withdrawn, for example, from near the bottom of the vessel via outlet 20. Furthermore, mother liquor 13 can be withdrawn from supernatant section 7 via mother liquor outlet 12 and reused. In FIG. 1, the boundary between the supernatant portion 7 and the suspension portion 8 is indicated by a broken line.

[0043] Fig. 2 is a cross-sectional schematic diagram of another example of the tank of the present invention, viewed from the side. In Fig. 2, by providing a partition plate 5 in the supernatant portion 7, it is possible to separate the nozzle 4, which is the slurry supply port, from the mother liquor outlet 12, and to prevent crystals from being mixed into the mother liquor outlet 12.

[0044] Fig. 3 is a cross-sectional schematic diagram of another example of the tank of the present invention, viewed from the side. In Fig. 3, mother liquor outlet 12 is covered with separation mechanism 6, which prevents crystals from entering mother liquor outlet 12. In addition, mother liquor 13 can be suitably withdrawn from mother liquor outlet 12.

[0045] Figure 4 is a cross-sectional schematic diagram of an example of a separation mechanism (reservoir) for the tank of the present invention shown in Figure 3, viewed from the side. Nozzle 112a, which constitutes the mother liquor outlet provided in the supernatant portion of the tank, is covered by separation mechanism 6, which consists of a weir portion and a bottom portion, thereby sufficiently preventing crystals from entering nozzle 112a. The bottom portion of separation mechanism 6 may be inclined so that its height decreases toward nozzle 112a. This allows mother liquor in separation mechanism 6 to flow very efficiently into nozzle 112a.

[0046] FIG. 5 is a cross-sectional schematic diagram of an example of a tank according to the present invention, viewed from the top (top plate side). As shown in FIG. 5, nozzle 120b constituting the withdrawal port is arranged so that, when tank 1 is viewed from the top, slurry 21 containing crystals is withdrawn parallel to the tangent direction of the outline corresponding to the inner wall surface of the tank. This allows the slurry containing compound crystals to be efficiently withdrawn by utilizing a swirling flow. Furthermore, deposition of crystals on the bottom surface of the tank can be sufficiently prevented.

[0047] 6 to 8 are schematic cross-sectional side views of another example of a separation mechanism for a tank according to the present invention. In FIGS. 6 to 8, the tank further includes a nozzle 114a, which serves as a backup outlet for withdrawing mother liquor from the tank, located above nozzle 112a, which serves as an outlet for withdrawing mother liquor from the tank. Nozzle 114a is located above nozzle 112a, and the height of its opening must be equal to or lower than the height of the top of the weir included in the separation mechanism. The height of the nozzle 114a can be adjusted appropriately within this range. For example, as described above, the nozzle 114a serving as a backup outlet shown in FIG. 6 has a bottom opening that is the same as the top of the weir included in the separation mechanism. Furthermore, the nozzle 114a serving as a backup outlet shown in FIGS. 7 and 8 has a bottom opening that is lower than the height of the top of the weir included in the separation mechanism. This allows mother liquor 15 to be suitably extracted through nozzle 114a when nozzle 112a is clogged or the like and mother liquor 13 cannot be extracted through nozzle 112a.

[0048] (Purification device of the present invention) The present invention is also a purification apparatus comprising a vessel of the present invention. The purification apparatus of the present invention is preferably capable of carrying out a continuous purification step, and may further include, for example, an aging tank which is the tank of the present invention, a crystallization tank as a stage preceding the aging tank, and a washing column (preferably a washing column for forcibly transporting crystals) as a stage subsequent to the aging tank of the present invention.

[0049] When the purification apparatus of the present invention includes the crystallization tank, it can have one or more crystallization tanks. When the purification apparatus of the present invention has multiple crystallization tanks (1st to Nth crystallization tanks), it is preferable that these multiple crystallization tanks are connected in series. In this case, the purification apparatus of the present invention usually has a line for sending a slurry containing compound crystals from one crystallization tank to another crystallization tank, optionally via a solid-liquid separation device. In addition, in this case, the purification apparatus of the present invention has a line for supplying a solution containing the compound to be purified to at least one crystallization tank. Furthermore, it is preferable that the purification apparatus of the present invention has a line for supplying a slurry containing compound crystals to an aging tank to at least the Nth crystallization tank. When the purification apparatus of the present invention includes a crystallization tank and an aging tank, at least one of the crystallization tank and the aging tank may be the tank of the present invention.

[0050] When the purification apparatus of the present invention further includes the washing column, it is preferable that the purification apparatus of the present invention has a line for supplying a slurry containing crystals of the compound from the tank of the present invention to the washing column. The purification apparatus of the present invention preferably further comprises a line for discharging the product from the washing column. The purification apparatus of the present invention may further include a line for returning the mother liquor from a downstream tank or apparatus to a upstream tank or apparatus. The purification apparatus of the present invention may further include a mechanism for controlling the amount of the slurry sent and the amount of the mother liquor returned. Examples of such a control mechanism include valves attached to various lines. The refining apparatus of the present invention may also include other devices that are generally used in refining apparatuses.

[0051] (Method for producing the compound of the present invention) The present invention is a method for producing a compound, comprising the steps of: supplying a slurry containing compound crystals to a tank; stirring the slurry containing the compound crystals in the tank; and withdrawing the slurry containing the compound crystals stirred in the stirring step from the tank; the tank is a crystallization tank that produces a slurry containing compound crystals and / or an aging tank that can maintain the compound crystals in a suspended state within the tank, and is characterized in that the tank is equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and is capable of forming a supernatant part consisting of a supernatant liquid and a suspension part in which the compound crystals are in a suspended state. In the method for producing a compound of the present invention, the compound is preferably (meth)acrylic acid.

[0052] In the method for producing a compound of the present invention, the supplying step, the stirring step, and the withdrawing step are basically performed in this order for the target to be purified. (For example, as shown in FIG. 1, a crystal-containing slurry 11a is supplied into a vessel 1 via a nozzle 4. Next, the stirring shaft of the agitator in the vessel 1 is rotated in the stirring direction 9a, and the crystal-containing slurry is stirred by the stirring blades 3, generating a horizontal swirling flow that collides with the baffles 2a and 2b, forming an upward flow. By generating an upward flow in the crystal-containing slurry flow 9b in this way, the suspension section 8 is suitably suspended, and the crystal-containing slurry can be maintained in the suspension section 8 for a certain period of time, allowing the crystals in the slurry to grow. Thereafter, the crystal-containing slurry 21 is withdrawn, for example, from near the bottom of the vessel via an outlet 20.) Below, the supplying step, stirring step, and withdrawing step will be described in order, followed by the mother liquor withdrawing step and other steps. Note that in a continuous purification process, each step is usually performed simultaneously when viewed as the vessel as a whole. In this specification, "compound" refers to a compound obtained by the production method of the present invention, and does not refer to raw materials, by-products, or solvents in the production method of the present invention. "Compound" can be rephrased as "target compound" or "target product." In this specification, "impurities" refer to components other than "compound," such as raw materials, by-products, and solvents.

[0053] <Supply process> In the supplying step, a slurry containing crystals of a compound is supplied to the tank. The slurry containing the crystals is a suspension of compound crystals and a mother liquor. In other words, the liquid portion of the slurry containing compound crystals supplied to the tank is the mother liquor. As will be described later, the slurry containing the crystals can be obtained by generating crystals in a compound-containing solution (e.g., a crude (meth)acrylic acid aqueous solution or a crude (meth)acrylic acid solution). The compound-containing solution may be prepared by the manufacturer or may be procured from another source. When the tank is an aging tank, the compound-containing solution and the mother liquor returned from the next step (such as a washing column) may be supplied to the tank (e.g., an aging tank). The compound-containing solution referred to here also includes a crude compound.

[0054] From the viewpoint of obtaining a product more stably, the mass proportion of the crystals in the slurry containing the crystals supplied to the tank is preferably 25 mass% or more, more preferably 30 mass% or more, and even more preferably 35 mass% or more. From the viewpoint of improving the fluidity of the slurry and further reducing the risk of pipe clogging, the mass proportion of the crystals is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. The crystal-containing slurry to be supplied to the tank may be concentrated using a solid-liquid separator, for example. In this specification, when simply referring to "slurry containing crystals to be supplied to a tank," the slurry containing crystals to be supplied to the tank refers to a slurry containing crystals immediately before being supplied to the tank, for example, a slurry containing crystals in a pipe or nozzle for supplying the slurry containing crystals to the tank.

[0055] The crystal-containing slurry supplied to the tank preferably contains the compound in its mother liquor. Examples of the mother liquor include the compound and an aqueous solution of the compound. The mother liquor usually contains impurities other than the compound and water. In the method for producing a compound of the present invention, the purity (mass proportion) of the compound in the mother liquor of the crystal-containing slurry supplied to the tank is preferably 99 mass % or less. The mass proportion of the compound in the mother liquor is preferably 80 mass % or more.

[0056] In the production method of the present invention, the compound is preferably an easily polymerizable compound having a reactive double bond. In particular, in the production method of the present invention, the compound is more preferably an unsaturated carboxylic acid, further preferably (meth)acrylic acid, and particularly preferably acrylic acid. In this specification, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0057] In the above-mentioned supplying step, the supply rate of the crystal-containing slurry is not particularly limited, but in an industrial-scale tank, it is, for example, 0.2 × 10 3 ~4.0×10 5 kg / h.

[0058] In the supplying step, the supply temperature of the crystal-containing slurry can be appropriately set depending on the melting point of the compound, and can be adjusted appropriately within the range of 0 to 80°C, for example. For example, when the compound is (meth)acrylic acid, the supply temperature of the slurry containing the crystals is preferably 5 to 13°C, and more preferably 6 to 12°C. The supply temperature of the crystal-containing slurry is the temperature of the mother liquor in the crystal-containing slurry immediately before it is supplied to the tank (e.g., the crystal-containing slurry in the pipe or nozzle that supplies the crystal-containing slurry to the tank).

[0059] <Mixing process> In the stirring step, the slurry containing the compound crystals is stirred in the tank. In the stirring step, the crystal-containing slurry is usually stirred using a stirrer provided in the tank. Specific examples of the stirrer are as described above. In the stirring step, the rotation speed of the stirrer is preferably within the range of 5 to 500 rpm, and more preferably within the range of 10 to 300 rpm. Stirring may be intermittent, but is preferably essentially continuous during use of the vessel of the present invention.

[0060] <Extraction process> In the extracting step, the slurry containing the crystals of the compound stirred in the stirring step is extracted from the tank.

[0061] For example, in the slurry containing the crystals extracted from the tank, the mass proportion of the crystals is preferably 1 mass% or more, more preferably 3 mass% or more, even more preferably 5 mass% or more, and particularly preferably 10 mass% or more. The mass proportion of the crystals is preferably 50 mass % or less, more preferably 40 mass % or less, and even more preferably 30 mass % or less. In this specification, the term "slurry containing crystals or crystals extracted from the tank" refers to a slurry containing crystals immediately after being extracted from the tank, for example, a slurry containing crystals or crystals in a nozzle constituting a slurry extraction port or in an extraction line (pipe) for extracting the slurry.

[0062] The withdrawal rate of the crystal-containing slurry from the vessel is not particularly limited, but in an industrial-scale vessel, it is, for example, 0.2 × 10 3 ~4.0×10 5 kg / h. As described above, the extraction step can be suitably carried out using a pump such as a centrifugal pump, a diaphragm pump, or a rotary pump.

[0063] The inside of the tank may be operated under increased pressure, normal pressure, or reduced pressure.

[0064] <Step of removing the mother liquor> The production method of the present invention includes a step of removing the supernatant mother liquor from the vessel. The extracted mother liquor can be recycled and reused. For example, by supplying the extracted mother liquor to a preceding apparatus (for example, a crystallization tank for an aging tank) and reusing it, the quality of the compound can be further improved.

[0065] The mother liquor extracted in the step of extracting the mother liquor usually contains the compound. Examples of the mother liquor include a liquid in which the compound is dissolved and an aqueous solution of the compound. The mother liquor usually contains impurities other than the compound and water. The step of extracting the mother liquor may be carried out using a pump or the like.

[0066] <Step of obtaining a slurry containing crystals> The production method of the present invention preferably further comprises the step of obtaining a slurry containing crystals of the compound from the compound-containing solution. The compound-containing solution is preferably a crude (meth)acrylic acid aqueous solution or a crude (meth)acrylic acid solution. The crude (meth)acrylic acid aqueous solution refers to a solution in which (meth)acrylic acid is dissolved in water and contains impurities such as by-products produced during the production of (meth)acrylic acid. The crude (meth)acrylic acid solution refers to a solution consisting of (meth)acrylic acid and containing impurities such as by-products produced during the production of (meth)acrylic acid. These can be obtained, for example, by collecting in an absorption tower and optionally distilling the gas of a compound that is a reaction product obtained by the gas-phase oxidation reaction of propylene and isobutylene. However, they are not limited to those synthesized by themselves and may be procured from other sources. For example, the crude (meth)acrylic acid aqueous solution or crude (meth)acrylic acid solution can be cooled to obtain a slurry containing (meth)acrylic acid crystals.

[0067] Examples of the impurities include acids such as propionic acid, acetic acid, maleic acid, benzoic acid, and acrylic acid dimer, aldehydes such as acrolein, furfural, formaldehyde, and glyoxal, acetone, and protoanemonin. In addition, solvents such as toluene and methyl isobutyl ketone may be contained. The production method of the present invention makes it possible to sufficiently remove impurities contained in the compound-containing solution.

[0068] <Step of Obtaining a Compound-Containing Solution> In the production method of the present invention, it is preferable that the production method further comprises a step of obtaining a compound-containing solution from a raw material.

[0069] The step of obtaining the compound-containing solution is not particularly limited as long as a compound-containing solution can be obtained. When the compound is (meth)acrylic acid, the step can be suitably carried out, for example, by a synthesis step of acrylic acid or a collection step of acrylic acid described in JP-A-2007-182437 (Patent Document 1). In the method for producing the compound of the present invention, the (meth)acrylic acid is preferably prepared from at least one raw material selected from the group consisting of propane, propylene, acrolein, isobutene, methacrolein, acetic acid, lactic acid, isopropanol, 1,3-propanediol, glycerol, and 3-hydroxypropionic acid. The (meth)acrylic acid and / or the raw material may be derived from a renewable raw material, thereby producing a bio-based (meth)acrylic acid.

[0070] In the process of obtaining the compound-containing solution, impurities such as by-products are generally produced. For example, when the compound is (meth)acrylic acid, impurities that are produced include water, acids such as propionic acid, acetic acid, maleic acid, benzoic acid, and acrylic acid dimer, aldehydes such as acrolein, furfural, formaldehyde, and glyoxal, acetone, methyl isobutyl ketone, toluene, and protoanemonin. However, by using a tank according to the production method of the present invention, the impurities can be separated with excellent efficiency, and the product can be obtained efficiently.

[0071] (Method for purifying compounds) The present invention also relates to a method for purifying a compound, comprising the steps of: supplying a slurry containing compound crystals to a tank; stirring the slurry containing the compound crystals in the tank; and withdrawing the slurry containing the compound crystals stirred in the stirring step from the tank, wherein the tank is a crystallization tank that produces a slurry containing compound crystals and / or an aging tank that can maintain the compound crystals in a suspended state within the tank, and is equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and is capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state.

[0072] According to the purification method of the present invention, a slurry containing crystals can be purified efficiently. A preferred embodiment of the purification method of the present invention is the same as the preferred embodiment of the production method of the present invention described above. [Example]

[0073] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the above and below-described aims, and all such modifications are included in the technical scope of the present invention. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass".

[0074] (How to obtain acrylic acid aqueous solution) According to the method described in WO 2010 / 032665, propylene was subjected to catalytic gas phase oxidation to obtain an acrylic acid-containing gas, and the obtained acrylic acid-containing gas was treated in an absorption tower to obtain an aqueous acrylic acid solution.

[0075] (How to obtain the supply slurry) An aqueous solution of acrylic acid was supplied to a crystallization tank. A refrigerant was supplied to a jacket attached to the peripheral wall of the crystallization tank to indirectly cool the crystals. Crystals adhering to the inner surface of the crystallization tank were scraped off with a scraper attached inside the crystallization tank, thereby preparing a slurry containing crystals (supply slurry).

[0076] (Purification equipment / purification conditions) The purification apparatus used included the crystallization tank as the upstream stage and an aging tank. The aging tank used was the same as the aging tank shown in Figure 3, except that the baffles 2a and 2b were spaced apart from the inner wall surface of the aging tank, and a spare outlet was provided above the mother liquor outlet 12, and a partition plate was provided between the supply port 4 for supplying the crystal-containing slurry to the aging tank and the outlet 12 for withdrawing the mother liquor from the aging tank. Although not shown, the compound-containing solution and the mother liquor returned from the next process (such as a washing column) were supplied to the aging tank. The purification apparatus was composed of the following equipment. Aging tank 1: Inner diameter (tank diameter) 240 mm, internal height (height of tank body) 480 mm Residence time: 2 hours Slurry supplied to aging tank 1: concentration (mass ratio of crystals in the slurry) 40%, temperature 10°C, compound purity in the mother liquor 96% Concentration of the slurry extracted from the aging tank 1 (mass ratio of crystals in the slurry): 25% Agitator: rotation speed 131 rpm, agitator shaft diameter 8 mm, shaft length 550 mm, agitator blade 3 blade diameter (Distance from the stirring shaft to the tip of the stirring blade) 72 mm, number of blade stages: 2 Baffle plates 2a and 2b: Height 320 mm, width 18 mm, thickness 2 mm, material: stainless steel, number: 2, installation direction: vertical, horizontal distance from the inner wall of the tank to the baffle plates: 6 mm Partition plate 5: Height 96 mm, width 209 mm, thickness 2 mm, material: stainless steel, number: 1, installation direction: vertical, parallel to the baffle plate Separation mechanism 6: With weir, with a notch at the top of the weir (a notch shaped like an inverted triangle when viewed from the side), and a bottom inclination of 1° Slurry withdrawal port 20: A nozzle constituting the slurry withdrawal port is provided parallel to the tangent direction of the outline corresponding to the inner wall surface of the maturation tank when the maturation tank is viewed from above. Slurry extraction method: When the maturation tank is viewed from above, the slurry is extracted in the tangent direction of the outline corresponding to the inner wall surface of the maturation tank. Reserve extraction port: Yes (as shown in Figure 7, the height of the top of the nozzle opening is the same as the height of the top of the weir part included in the separation mechanism)

[0077] When the maturation tank 1 is viewed from above, the area ratio of the area where the supply port 4 for supplying the crystal-containing slurry to the maturation tank is located to the area where the withdrawal port 12 for withdrawing the mother liquor from the maturation tank is located is 4. When the aging tank is viewed from above, the ratio of the length of the inner diameter portion of the region having the supply port 4 for supplying the crystal-containing slurry to the aging tank, to the length of the inner diameter portion of the region having the discharge port 12 for discharging the mother liquor from the aging tank, in the inner diameter perpendicular to the partition plate, is 2.9. Distance from partition plate 5 to baffle plates 2a and 2b: 72 mm Horizontal distance from supply port 4 to baffle plate 2b: 170 mm Horizontal distance from separation mechanism 6 to baffle plate 2a: 24 mm Horizontal distance from the slurry outlet 20 to the baffle plate 2a: 14 mm Horizontal distance from the supply port 4 for supplying the crystal-containing slurry to the aging tank to the withdrawal port 12 for withdrawing the mother liquor from the aging tank: 208 mm

[0078] Example 1 When the aging tank of Example 1 was operated, a swirling flow was generated by the agitator stirring the slurry containing acrylic acid crystals in the aging tank, and an upward flow was generated by the collision of the swirling flow with the baffle plate. As a result, a supernatant part consisting of a supernatant liquid and a suspension part in which acrylic acid crystals were in a suspended state were formed. If the total volume inside the aging tank was taken as 1, the volume ratio of the suspension was 2 / 3 and the volume ratio of the supernatant was 1 / 3. The suspension state of the suspension was uniform, and no accumulation of crystals or the like was found at the bottom of the aging tank. Furthermore, the mother liquor could be extracted and recovered from the supernatant without being contaminated with the crystals in the supplied slurry, and normal operation could be continued. This allowed the crystals to grow favorably in the aging tank.

[0079] (Comparative Example 1) The aging tank was operated in the same manner as in Example 1, except that no baffle was provided in the aging tank. The agitator stirred the slurry containing acrylic acid crystals in the aging tank, generating a swirling flow. However, the liquid rotated in a co-rotating manner without vertical flow, generating a rotating vortex around the agitator shaft, resulting in uneven stirring. As a result, no supernatant was formed, and crystals accumulated at the bottom of the aging tank. Furthermore, when the mother liquor was withdrawn, the crystals in the supplied slurry were mixed into the mother liquor, making normal operation difficult.

[0080] Example 2 The aging tank was operated in the same manner as in Example 1, except that no partition plate was provided in the aging tank. The agitator stirred the slurry containing acrylic acid crystals in the aging tank, generating a swirling flow, and the swirling flow collided with the baffle plate, generating an upward flow. As a result, a supernatant portion consisting of a supernatant liquid and a suspension portion in which acrylic acid crystals were in a suspended state were formed. The suspension state of the suspension was uniform, and no crystals or other deposits were found at the bottom of the aging tank. The supernatant / suspension interface was slightly disturbed, and a small amount of crystals from the supplied slurry were mixed into the mother liquor when the mother liquor was withdrawn, but normal operation continued. This allowed for favorable crystal growth in the aging tank.

[0081] Example 3 The aging tank was operated in the same manner as in Example 1, except that no separation mechanism was provided in the aging tank. The agitator stirred the slurry containing acrylic acid crystals in the aging tank, generating a swirling flow, and the swirling flow collided with the baffle plate, generating an upward flow. As a result, a supernatant portion consisting of a supernatant liquid and a suspension portion in which acrylic acid crystals were in a suspended state were formed. The suspension state in the suspension part was uniform, and no crystals or other deposits were found at the bottom of the aging tank. Furthermore, when the mother liquor was withdrawn, a small amount of crystals from the supplied slurry was mixed into the mother liquor, but normal operation continued. This enabled the crystals to grow favorably in the aging tank.

[0082] Example 4 The aging tank was operated in the same manner as in Example 1, except that the nozzle constituting the slurry withdrawal port was arranged parallel to the normal direction of the outline corresponding to the inner wall surface of the aging tank when viewed from above, and the slurry was withdrawn in the normal direction by side plate withdrawal rather than tangential withdrawal. The agitator stirred the slurry containing acrylic acid crystals in the aging tank, generating a swirling flow, and the swirling flow collided with the baffle plate, generating an upward flow. As a result, a supernatant portion consisting of a supernatant liquid and a suspension portion in which acrylic acid crystals were suspended were formed. The suspension state of the suspension was almost uniform, but a small amount of crystals was deposited at the bottom of the aging tank. Furthermore, the mother liquor could be extracted and recovered from the supernatant without being contaminated with the crystals in the supplied slurry, and normal operation could be continued. This allowed the crystals to grow favorably in the aging tank. In addition, tangential drawing in Examples 1 to 3 is a method of drawing the slurry using a nozzle along the tangential direction of the outline corresponding to the inner wall surface of the aging tank when viewed from the top side, and side plate drawing in Example 4 is a method of drawing the slurry using a nozzle along the normal direction of the outline corresponding to the inner wall surface of the aging tank when viewed from the top side.

[0083] From the results of Examples 1 to 4, it was found that if the aging tank capable of maintaining the compound crystals in a suspended state in the tank is equipped with a stirrer and a baffle for generating an upward flow from the swirling flow, and is capable of forming a supernatant portion consisting of the supernatant liquid and a suspension portion in which the compound crystals are in a suspended state, the suspension state of the suspension portion can be made sufficiently uniform, and the deposition of coarse crystals at the bottom of the aging tank can be sufficiently prevented. It was also found that the mixing of crystals into the supernatant portion can be sufficiently prevented, and normal operation can be continued. It is believed that this allows the crystals to grow favorably in the aging tank and obtain a high-quality product. [Explanation of symbols]

[0084] 1: (Aging) tank 2a, 2b: Baffle board 3: Mixing blade 4: Nozzle (feed port) (for feeding the crystal-containing slurry into the aging tank) 5: Partition board 6: Separation mechanism 7: Supernatant 8: Suspension section 9a: Stirring direction 9b: Flow of slurry containing crystals 11a: (Provided) Slurry containing crystals of the compound 12: (Mother liquor) extraction port 13, 15: Mother liquor 20: Drain port (for withdrawing the slurry containing the crystals from the aging tank) 21: (Extracted) Slurry containing crystals 112a: Nozzle (forming the mother liquor outlet) 114a: Nozzle (constituting a spare outlet for withdrawing the mother liquor from the maturation tank) 120b: Nozzle (forming an outlet for the crystal-containing slurry) d: Vertical distance

Claims

1. A vessel for use in a purification apparatus for purifying a compound, comprising: The tank is a crystallization tank for producing a slurry containing compound crystals and / or an aging tank capable of holding the compound crystals in a suspended state within the tank, and is equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and is capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state, the vessel is provided with an outlet port below the top of the baffle plate for withdrawing a slurry containing crystals of the compound from the vessel; the withdrawal port is provided so that, when the tank is viewed from above, the slurry containing the compound crystals is withdrawn along a tangential direction of a contour line corresponding to an inner wall surface of the tank; The compound is an easily polymerizable compound having a reactive double bond.

2. 2. The tank according to claim 1, further comprising: a supply port for supplying a slurry containing compound crystals to the tank, a withdrawal port for withdrawing a mother liquor from the tank, and a partition plate provided between the supply port and the withdrawal port and extending in a direction from the top plate side to the bottom plate side of the tank, all located above a top of the baffle plate.

3. 2. The tank according to claim 1, further comprising: a separation mechanism, above a top of the baffle, including an outlet for withdrawing the mother liquor from the tank; and a weir for causing the supernatant liquid to overflow and flow into the outlet so as to prevent crystals of the compound from being mixed into the mother liquor.

4. the tank further includes a spare withdrawal port for withdrawing the mother liquor from the tank, the spare withdrawal port being located above the withdrawal port for withdrawing the mother liquor from the tank; 4. The tank according to claim 3, wherein the auxiliary extraction port is provided so that the height of the bottom end of the opening is equal to or lower than the height of the top of the weir portion included in the separation mechanism.

5. 4. The tank according to claim 1, wherein the baffle plate is provided near an inner wall surface of the tank.

6. A purification device comprising the tank according to any one of claims 1 to 3.

7. A method for producing a compound, comprising: The method includes the steps of supplying a slurry containing crystals of a compound to a tank; agitating a slurry containing crystals of the compound in the tank; and and a step of withdrawing the slurry containing the compound crystals stirred in the stirring step from the tank; The tank is a crystallization tank for producing a slurry containing compound crystals and / or an aging tank capable of holding the compound crystals in a suspended state within the tank, and is equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and is capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state, the vessel is provided with an outlet port below the top of the baffle plate for withdrawing a slurry containing crystals of the compound from the vessel; the withdrawal port is provided so that, when the tank is viewed from above, the slurry containing the compound crystals is withdrawn along a tangential direction of a contour line corresponding to an inner wall surface of the tank; The compound is an easily polymerizable compound having a reactive double bond.

8. The method for producing a compound according to claim 7, wherein the compound is (meth)acrylic acid.

9. 9. The method for producing a compound according to claim 8, wherein the (meth)acrylic acid is produced using at least one raw material selected from the group consisting of propane, propylene, acrolein, isobutene, methacrolein, acetic acid, lactic acid, isopropanol, 1,3-propanediol, glycerol, and 3-hydroxypropionic acid.

10. 1. A method for purifying a compound, comprising: The purification method includes the steps of: supplying a slurry containing crystals of the compound to a vessel; agitating a slurry containing crystals of the compound in the tank; and and a step of withdrawing the slurry containing the compound crystals stirred in the stirring step from the tank; The tank is a crystallization tank for producing a slurry containing compound crystals and / or an aging tank capable of holding the compound crystals in a suspended state within the tank, and is equipped with a stirrer and a baffle plate for generating an upward flow from a swirling flow, and is capable of forming a supernatant portion consisting of a supernatant liquid and a suspension portion in which the compound crystals are in a suspended state, the vessel is provided with an outlet port below the top of the baffle plate for withdrawing a slurry containing crystals of the compound from the vessel; the withdrawal port is provided so that, when the tank is viewed from above, the slurry containing the compound crystals is withdrawn along a tangential direction of a contour line corresponding to an inner wall surface of the tank; The method for purifying a compound, wherein the compound is an easily polymerizable compound having a reactive double bond.