heat exchanger

Abstract

The present invention provides a method for obtaining a product in a stable manner. The present invention is a heat exchanger for handling a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound. The heat exchanger is characterized by having: a scraper for scraping off substances adhering to an inner wall; a shaft connected to the scraper; and a bushing of the shaft, which bushing comes into contact with the solution or slurry when the heat exchanger is in use, and characterized that the bushing is made of a material that includes aromatic polyether ketone.

Description

[Technical Field]

[0001] The present invention relates to a heat exchanger, and more particularly to a heat exchanger, a crystallization device, a purification device, a crystallization method, a method for producing an easily polymerizable compound, and a method for purifying an easily polymerizable compound. [Background technology]

[0002] Crystallization apparatuses are widely used industrially to crystallize materials to be purified and increase their purity. In many fields of the chemical industry, there is a demand for obtaining high-quality compounds with reduced impurities, and various studies have been conducted to develop better crystallization 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] A continuous crystallization device is also desirable, and examples of continuous crystallization devices include a Votator-type heat exchanger, a scraped surface heat exchanger, and a cooling disc crystallizer.

[0005] Incidentally, in the past, in devices that handle liquids that are prone to polymerization or liquids that contain adhesive substances, specifically in pumps having a shaft, it has been described that a member (bushing) that supports the shaft portion is made of fluororesin or glass fiber reinforced fluororesin and is treated to reduce the coefficient of friction (see, for example, Patent Document 2). Such fluororesins, typified by polytetrafluoroethylene (PTFE), are known to have high chemical resistance and particularly excellent friction characteristics (low friction coefficient) among resins (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-182437 [Patent Document 2] Japanese Patent Application Publication No. 6-272688 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-175955 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the inventors have conducted extensive research into heat exchangers and crystallization devices for handling easily polymerizable compounds and have found that in continuous heat exchangers or crystallization devices having a scraper and shaft for scraping off substances or crystals adhering to the inner wall surface, even if the shaft bushing is made of a fluororesin with excellent friction properties based on conventional knowledge such as that described in Patent Document 2, a polymerization reaction occurs unexpectedly due to frictional heat, and the polymerized material gets caught in the sliding surface of the mechanical seal inside the heat exchanger or crystallization device, causing liquid leakage and preventing the heat exchanger or crystallization device from operating normally, which is a new problem. It should be noted that polymerization in the heat exchanger or crystallizer was an unexpected problem, since the liquid being introduced was at a relatively low temperature (less prone to polymerization). In this way, when the heat exchanger or crystal generation device stops functioning normally, as described in Patent Document 2, it is necessary to temporarily stop the operation of the heat exchanger or crystal generation device. Since stopping the operation has a significant impact on the entire purification system, it was desirable to quickly suppress the polymerization reaction caused by the frictional heat, etc., as described above. [Means for solving the problem]

[0008] As a result of further intensive research, the inventors have found that by forming the bushing using a material containing aromatic polyether ketone, polymerization of the easily polymerizable compound due to frictional heat can be sufficiently prevented, the above-mentioned problems can be solved, and products can be obtained stably. They have also found that even if the material of the bushing is not specified, it is sufficient to supply a solution or water containing the easily polymerizable compound from outside the device to the periphery of the mechanical seal installed on the shaft, and have arrived at the present invention.

[0009] That is, the present invention provides a heat exchanger for handling a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound, the heat exchanger comprising: a scraper for scraping off substances adhering to the inner wall surface; a shaft connected to the scraper; and a bushing for the shaft that comes into contact with the solution or the slurry when the heat exchanger is in use, the bushing being made of a material containing an aromatic polyether ketone.

[0010] The present invention also provides a crystal generation apparatus for generating crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound, the crystal generation apparatus comprising: a scraper for scraping off the crystals of the easily polymerizable compound generated on the inner wall surface; a shaft connected to the scraper; and a bushing for the shaft that comes into contact with the solution or the slurry when the apparatus is in use, the bushing being constructed using a material containing aromatic polyether ketone.

[0011] The present invention further provides a method for producing crystals, which comprises a step of producing crystals from a mother liquor of a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound using a crystal production device having a scraper for scraping off crystals produced on the inner wall surface and a shaft connected to the scraper, wherein the device further has a bushing for the shaft that comes into contact with the solution or the slurry, and the bushing is made of a material containing aromatic polyether ketone; or the method is characterized in that it comprises a step of supplying a solution or water containing an easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft.

[0012] The present invention also relates to a method for producing an easily polymerizable compound, the method comprising the step of producing crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing the crystals of the easily polymerizable compound, using a crystal production device having a scraper for scraping off crystals of the easily polymerizable compound formed on an inner wall surface and a shaft connected to the scraper, the device further comprising a bushing for the shaft that comes into contact with the solution or the slurry, the bushing being made of a material containing aromatic polyether ketone, or the method for producing an easily polymerizable compound, characterized in that it comprises the step of supplying a solution or water containing the easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft.

[0013] The present invention also relates to a method for purifying an easily polymerizable compound, comprising the step of producing crystals of the easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing the crystals of the easily polymerizable compound, using a crystal production device having a scraper for scraping off crystals of the easily polymerizable compound formed on the inner wall surface and a shaft connected to the scraper, wherein the device further has a bushing for the shaft that comes into contact with the solution or the slurry, and the bushing is made of a material containing aromatic polyether ketone; or the production method is a method for purifying an easily polymerizable compound, characterized in that it comprises the step of supplying a solution or water containing the easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft.

[0014] It is known that PTFE, a typical fluororesin, has superior friction properties (lower friction coefficient) than polyetheretherketone (hereinafter also referred to as PEEK), a typical aromatic polyetherketone (for example, JP 2009-236213 A). PTFE is also known to have superior chemical resistance (resistance to high concentrations of acid) than PEEK (for example, JP 2012-531024 A). The use of aromatic polyether ketone, which is known to have inferior friction characteristics and chemical resistance compared to PTFE, as the bushing material has the unexpected effect of suppressing polymerization caused by frictional heat, etc., even in crystallization equipment that handles high-purity, easily polymerizable compounds, thereby solving the above-mentioned problems.

[0015] The heat exchanger of the present invention, the crystal generation apparatus of the present invention, the crystal generation method of the present invention, the method for producing an easily polymerizable compound of the present invention, and the method for purifying an easily polymerizable compound of the present invention each have the same or a corresponding special technical feature in that the shaft bushing is made of a material containing aromatic polyether ketone. At least, the heat exchanger of the present invention and the crystal generation apparatus of the present invention each have the same or a corresponding special technical feature in that the shaft bushing is made of a material containing aromatic polyether ketone. Furthermore, at least, the crystal generation method of the present invention, the method for producing an easily polymerizable compound of the present invention, and the method for purifying an easily polymerizable compound of the present invention each have the same or a corresponding special technical feature in that the shaft bushing is made of a material containing aromatic polyether ketone, or include a step of supplying a solution or water containing an easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft. [Effects of the Invention]

[0016] By using the heat exchanger of the present invention or the crystallization device of the present invention, a product can be obtained stably. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view of an example of a crystal growth apparatus of the present invention, seen from the side. [Figure 2] FIG. 2 is a cross-sectional schematic diagram of another example of the crystallization apparatus of the present invention, viewed from the side, showing how a solution or water containing an easily polymerizable compound is supplied from outside the apparatus to the periphery of a mechanical seal installed on a shaft. [Figure 3] Fig. 3(a) is a cross-sectional view of an example of a scraper, viewed from the extension direction of the shaft. Figs. 3(b) and 3(d) are cross-sectional views of other examples of scrapers, viewed from the extension direction of the shaft. Fig. 3(c) is an enlarged view of the scraper shown in Fig. 3(b). DETAILED DESCRIPTION OF THE INVENTION

[0018] 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.

[0019] In the following, the crystallization apparatus of the present invention will be first described, followed by a description of the heat exchanger of the present invention, the purification apparatus of the present invention, the method for producing an easily polymerizable compound of the present invention, the method for purifying an easily polymerizable compound of the present invention, and the method for producing crystals of the present invention. In this specification, producing crystals of an easily polymerizable compound means not only producing crystals of the easily polymerizable compound from a solution containing the easily polymerizable compound, but also producing new crystals of the easily polymerizable compound from a mother liquor of a slurry containing crystals of the easily polymerizable compound, or increasing the crystal concentration in the slurry after it is discharged from the apparatus compared to before it is supplied to the apparatus. For example, the heat exchanger or crystallization apparatus of the present invention, the crystallization method of the present invention, the method for producing an easily polymerizable compound of the present invention, and the method for purifying an easily polymerizable compound of the present invention include those in which a solution containing an easily polymerizable compound is supplied to a crystallization apparatus to obtain a slurry containing crystals of the easily polymerizable compound, as well as those in which a slurry containing crystals of the easily polymerizable compound is supplied to a crystallization apparatus to obtain a slurry with a higher crystal concentration. Note that the slurry containing crystals of the easily polymerizable compound supplied to the crystallization apparatus usually also contains the easily polymerizable compound in its mother liquid. Furthermore, when crystals are discharged from the crystallization apparatus of the present invention, they are usually discharged as a slurry containing crystals of the easily polymerizable compound.

[0020] (Crystal growth device of the present invention) The crystallization apparatus of the present invention is a crystallization apparatus for generating crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound, and the apparatus includes a scraper for scraping off the crystals of the easily polymerizable compound generated on the inner wall surface, a shaft connected to the scraper, and a bushing for the shaft that comes into contact with the solution or the slurry when the apparatus is in use, the bushing being made of a material containing aromatic polyether ketone. The bushing is for preventing vibration of the shaft.

[0021] By using a material containing aromatic polyether ketone for the bushing, polymerization of the easily polymerizable compound caused by frictional heat between the bushing and the shaft can be sufficiently prevented, and as a result, misalignment of the mechanical seal sliding surface caused by the polymer and the resulting leakage of liquid can be sufficiently prevented. This effectively prevents malfunction of the crystal generation device, allowing the crystal generation device to operate stably for long periods of time. As a result, productivity can be improved and maintenance costs can be reduced. As mentioned above, polyetheretherketone, a typical aromatic polyetherketone, has a higher friction coefficient than PTFE, so it is a surprising effect that polymerization caused by frictional heat can be suppressed by constructing a bushing using a material containing aromatic polyetherketone.

[0022] The aromatic polyether ketone is a polymer having structural units consisting of an optionally substituted divalent aromatic group (preferably a phenylene group), an ether group, and a ketone group (carbonyl group). Suitable examples of the aromatic polyether ketone include polyether ether ketone (PEEK), polyether ketone (PEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), and polyether ketone ether ketone ketone (PEKEKK). One or more of these may be used.

[0023] In the aromatic polyether ketone, the mass proportion of structural units consisting of a divalent aromatic group, an ether group, and a ketone group, which may have a substituent, in 100% by mass of the aromatic polyether ketone is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The upper limit of the mass proportion of the structural unit is not particularly limited, and may be 100 mass %, most preferably 100 mass %. Among these, the aromatic polyether ketone is preferably polyether ether ketone. In this specification, polyether ether ketone refers to a polymer having a structural unit in which functional groups are arranged in the order of an ether group, an ether group, and a ketone group, with an optionally substituted divalent aromatic group interposed therebetween. For example, it is preferable that the polyether ether ketone is a polymer having a structural unit represented by the following general formula (1):

[0024] [ka]

[0025] In the above general formula (1), R 1 ~R 12 are the same or different and represent a hydrogen atom or a hydrocarbon group. Adjacent hydrocarbon groups may be bonded to each other to form a ring structure. Suitable examples of the hydrocarbon group include an aliphatic hydrocarbon group having 1 to 12 carbon atoms and an aromatic hydrocarbon group having 6 to 12 carbon atoms. In the polyether ether ketone, the mass proportion of the structural unit represented by the general formula (1) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, still more preferably 80 mass% or more, and particularly preferably 90 mass% or more, based on 100 mass% of the polyether ether ketone. The upper limit of the mass proportion of the structure represented by the general formula (1) is not particularly limited, and it may be 100 mass %, and is most preferably 100 mass %.

[0026] Among them, R 1 ~R 12 preferably represents a hydrogen atom. That is, the polyether ether ketone is preferably a polymer having a structural unit represented by the following general formula (2).

[0027] [ka]

[0028] In the polyether ether ketone, the mass proportion of the structural unit represented by the general formula (2) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, still more preferably 80 mass% or more, and particularly preferably 90 mass% or more, based on 100 mass% of the polyether ether ketone. The upper limit of the mass proportion of the structural unit represented by the general formula (2) is not particularly limited, and it may be 100 mass %, and is most preferably 100 mass %.

[0029] The material containing the aromatic polyether ketone preferably has an aromatic polyether ketone content of 30% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the material containing the aromatic polyether ketone.

[0030] The material containing aromatic polyether ketone used to form the bushing may contain other resins such as thermoplastic resins, and additives such as pigments, but as described above, the bushing is preferably made of aromatic polyether ketone (more preferably polyether ether ketone).

[0031] The bushing can be obtained by molding a material containing, for example, aromatic polyether ketone, and any known molding method for molding a resin composition can be used. The bushing may be, for example, ring-shaped or cylindrical.

[0032] At least a portion of the bushing comes into contact with the solution or the slurry when the device is in (normal) use. Note that it is sufficient that the bushing comes into contact with the solution or the slurry containing crystals when the device is in use, and it is not necessary that the bushing come into contact with the solution or the slurry containing crystals when the device is not in use. In other words, the device of the present invention is not limited to an apparatus in use.

[0033] The length of the bushing (length in the longitudinal direction of the shaft) cannot be generally determined, but is usually about 10 to 200 mm.

[0034] The difference between the inner diameter of the bushing and the outer diameter of the shaft is usually 0.01 mm or more, although this cannot be generalized. This reduces the frictional heat generated between the shaft and the bushing, making it possible to more effectively prevent polymerization. The difference between the inner diameter of the bushing and the outer diameter of the shaft is preferably 1 mm or less, which makes it possible to more sufficiently prevent the shaft from wobbling.

[0035] The number of the bushings in the crystallization apparatus of the present invention is not particularly limited, and may be selected appropriately depending on the size of the apparatus. When the crystallization device of the present invention includes a plurality of the bushings, it is sufficient that at least one of the bushings comes into contact with the solution or the slurry containing the crystals when the device is in use. For example, when a plurality of bushings are arranged on the shaft, it is sufficient that any one of the bushings comes into contact with the solution or the slurry containing the crystals.

[0036] When the device of the present invention has a plurality of bushings, it is preferable that the interval between adjacent bushings is 5000 mm or less. The interval between adjacent bushings is more preferably 4500 mm or less, and even more preferably 4000 mm or less. The interval between adjacent bushings is more preferably 100 mm or more, further preferably 300 mm or more, and particularly preferably 1000 mm or more. When there are multiple spacings between adjacent bushings, it is sufficient that any one of the spacings between the adjacent bushings is within the above range, but it is preferable that all of the spacings between the adjacent bushings are within the above range.

[0037] The scraper for scraping off the crystals of the easily polymerizable compound formed on the inner wall surface of the crystal generating device (usually the inner wall surface of the crystal generating section) is not particularly limited in material, but is preferably made of a material containing a resin. In particular, in the crystal generating device of the present invention, the scraper is preferably made of a material containing aromatic polyether ketone. The scraper may be entirely made of a material containing aromatic polyether ketone, or, for example, a portion of the scraper on the inner wall surface side of the crystal generating device may be made of a material containing aromatic polyether ketone. This suppresses heat generation due to friction between the scraper and the inner wall surface of the crystal generating device, thereby preventing polymerization of the easily polymerizable compound and, moreover, is expected to result in a more stable product. The preferred type and preferred content of the aromatic polyether ketone contained in the material constituting the scraper are the same as the preferred type and preferred content of the aromatic polyether ketone described above as the material constituting the bushing. For example, the aromatic polyether ketone contained in the material constituting the scraper is preferably polyether ether ketone. That is, in the crystallization apparatus of the present invention, the bushing and / or scraper is preferably made of a material containing polyether ether ketone.

[0038] The distance from the central axis of the shaft to the part of the scraper closest to the inner wall surface can be set appropriately depending on the inner diameter of the crystal generation device of the present invention (usually the crystal generation section), but it is preferable that the scraper be in contact with the inner wall surface in order to scrape off crystals generated and attached to the inner wall surface of the crystal generation device. The shape of the scraper is not particularly limited, but is usually a thin, approximately trapezoidal plate or an approximately rectangular plate, and for example, it is preferably an approximately rectangular plate with the longer side facing the inner wall surface of the crystal growth device. The substantially rectangular plate shape is, for example, a rectangular plate shape as shown in Figure 3(a), and the inner wall surface side of the crystal growth device may be a flat side, or the inner wall surface side of the crystal growth device may be inclined like a blade to form an acute angle, as shown in Figures 3(b) and (c). The same applies to a substantially trapezoidal plate shape, and the inner wall surface side of the crystal growth device may be a flat side, or the inner wall surface side of the crystal growth device may be inclined like a blade to form an acute angle. As described above, the scraper may have an inclined tip like a blade, and the tip may be used to scrape off the crystals. The scraper and the connecting portion described later may be joined so that they are linear as shown in FIG. 3(a), or the scraper may be joined at an angle to the connecting portion as shown in FIG. 3(b). The crystal growth device of the present invention may include one scraper or a plurality of scrapers. For example, a plurality of scrapers may be arranged along the rotation direction of the shaft, or a plurality of scrapers may be arranged along the longitudinal direction of the shaft.

[0039] The crystallization device of the present invention may further include a connection part connecting the scraper and the shaft. The connecting part is not particularly limited in material, shape, etc., as long as it can connect the scraper and the shaft, and metals such as stainless steel, resins, etc. can be used. The connecting part may also be an integrated type that is integrated with the scraper. The connecting portion is preferably provided at an angle of 60° or more and 120° or less with respect to the longitudinal direction of the shaft, and more preferably at a right angle. The shape and number of the connecting portion are not particularly limited as long as the scraper and the shaft are connected via the connecting portion.

[0040] The shaft may be directly connected to the scraper or may be connected to the scraper via the connection part, but is preferably connected to the scraper via the connection part. The material of the shaft is not particularly limited, and metals such as stainless steel, resins, etc. can be used, but the shaft is preferably made of metal, and more preferably made of stainless steel (SUS). The shaft may be configured such that a plurality of shafts are connected in the longitudinal direction of the shaft to form a single shaft. The shaft is preferably one whose longitudinal direction is horizontal (horizontal type).

[0041] In the crystallization apparatus of the present invention, the easily polymerizable compound is preferably (meth)acrylic acid. That is, the crystallization apparatus of the present invention is preferably for generating (meth)acrylic acid crystals from a mother liquor of a solution containing (meth)acrylic acid or a slurry containing (meth)acrylic acid crystals. Here, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0042] The mass proportion of the easily polymerizable compound in the mother liquor of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is not particularly limited and may be low, but is preferably within the range of a preferred mass proportion described later in the method for producing an easily polymerizable compound of the present invention.

[0043] The crystal generating apparatus of the present invention has, in its crystal generating section, a supply port for a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound (hereinafter also simply referred to as a supply port for an easily polymerizable compound), and a discharge port for a slurry containing crystals of an easily polymerizable compound. The directions of the supply port and discharge port for the easily polymerizable compound are not particularly limited, and for example, the crystal generating apparatus of the present invention may have the supply port for the easily polymerizable compound below the crystal generating section and a discharge port for a slurry containing crystals of an easily polymerizable compound above it. The crystallization device of the present invention may be provided with only one supply port for the easily polymerizable compound and one discharge port for the slurry containing crystals of the easily polymerizable compound, but may also be provided with multiple ports.

[0044] The size of the crystal growth apparatus of the present invention is not particularly limited, but for example, the inner diameter (inner diameter of the crystal growth section) is preferably 100 to 500 mm, and the horizontal length of the crystal growth section is preferably 2000 to 20000 mm.

[0045] Furthermore, the crystallization apparatus of the present invention is usually equipped with a mechanism for cooling all or part of its inner wall surface in order to generate crystals from a mother liquor of a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound. In particular, the crystal generation device of the present invention preferably includes a refrigerant supply port and a refrigerant discharge port. By using the refrigerant, the inner wall surface of the crystal generation section can be suitably cooled, and crystals can be suitably generated. The directions of the coolant supply port and discharge port are not particularly limited, and for example, the coolant supply port may be located below the crystal generation section and the coolant discharge port may be located above the crystal generation section. The crystallization device of the present invention may be provided with only one coolant supply port and one coolant discharge port, but may also be provided with a plurality of ports.

[0046] The refrigerant is not particularly limited and any liquid or gas can be used, for example, water, antifreeze, methanol water (methanol aqueous solution), gas, etc. The heat transfer medium may be appropriately selected taking into consideration the freezing point of the compound to be purified, etc.

[0047] Furthermore, the crystallization apparatus of the present invention preferably has a supply port provided around the mechanical seal installed on the shaft for supplying a solution or water containing an easily polymerizable compound from outside the apparatus. The solution containing the easily polymerizable compound is typically one whose melting point is lower than that of the mother liquid of the solution or slurry in the crystallization section. The melting point of water is typically lower than that of the mother liquid of the solution or slurry in the crystallization section. This prevents the supplied solution or water containing the easily polymerizable compound from freezing, and also sufficiently prevents the solution or slurry from the crystallization section from accumulating around the mechanical seal, further preventing misalignment of the sliding surface of the mechanical seal and liquid leakage due to polymers. In this specification, the peripheral portion of the mechanical seal refers to the gap formed between the mechanical seal and the bushing. The crystal growth apparatus of the present invention may be provided with only one supply port, but may also be provided with a plurality of supply ports.

[0048] The distance between the mechanical seal and the bushing is preferably 100 mm or less, which reduces the amount of retained fluid between the mechanical seal and the bushing. The distance between the mechanical seal and the bushing is more preferably 80 mm or less, and even more preferably 60 mm or less.

[0049] The crystal growth apparatus of the present invention may further be provided with instrumentation devices such as a thermometer, pressure gauge, level gauge (radar type, etc.), level switch (float type, etc.), and flow meter in the main body or in the vicinity thereof. Sight glasses (sight windows) may also be provided on the side plates of the crystal growth apparatus, and in this case, these can be covered with covers. Hand holes (holes for inserting hands inside during maintenance), safety valves, etc. may also be provided on the top plate, side plates, etc. of the crystal growth apparatus. There is no limit to the number of these devices that may be installed.

[0050] FIG. 1 is a cross-sectional schematic diagram of an example of a crystallization apparatus of the present invention, viewed from the side. An easily polymerizable compound, such as (meth)acrylic acid, is supplied into the crystallization section 19 of the crystallization apparatus 100 through the easily polymerizable compound supply port 9. A refrigerant flows around the crystallization section 19 through the refrigerant supply port 15 and the refrigerant outlet 17, generating crystals of the easily polymerizable compound on the cooled inner wall surface. Next, the shaft 5 is rotated using the power unit (motor) 21 of the crystallization apparatus 100, and the crystals adhering to the inner wall surface are scraped off by the scraper 3 connected to the shaft 5 via the connector 4, thereby obtaining a slurry 13 containing the crystals in the crystallization section 19. The slurry 13 containing the crystals is in contact with the bushings 1 and 1p of the shaft 5. The bushings 1 and 1p are made of a material containing aromatic polyether ketone, which effectively prevents the polymerization of the easily polymerizable compound due to frictional heat. The slurry containing the crystals of the easily polymerizable compound is discharged from the slurry containing the crystals of the easily polymerizable compound outlet 11. In the continuous purification process, the above-mentioned steps are usually carried out simultaneously when viewed as the entire crystallization apparatus. As described above, the crystallization device shown in Figure 1 can sufficiently prevent the polymerization of easily polymerizable compounds due to frictional heat, and therefore can also sufficiently prevent the sliding surface of the mechanical seal 7 from shifting and liquid leakage caused by the polymer.

[0051] Figure 2 is a cross-sectional schematic diagram of another example of the crystal generation apparatus of the present invention, viewed from the side. The crystal generation apparatus of the present invention shown in Figure 2 supplies a solution or water 23a containing an easily polymerizable compound to the periphery of a mechanical seal 7 installed on a shaft 5. The supplied solution or water 23a containing an easily polymerizable compound passes between the bushing 1 and the shaft 5 and is discharged into the crystal generation section. This sufficiently prevents the solution or slurry originating from the crystal generation section from accumulating around the periphery of the mechanical seal 7, and further prevents misalignment of the sliding surface of the mechanical seal 7 and liquid leakage caused by polymers.

[0052] (Heat exchanger of the present invention) The heat exchanger of the present invention is a heat exchanger for handling a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound. The heat exchanger includes a scraper for scraping off materials adhering to the inner wall surface, a shaft connected to the scraper, and a bushing for the shaft that comes into contact with the solution or slurry when the heat exchanger is in use. The bushing is made of a material containing aromatic polyether ketone. The scraper, shaft, and bushing in the heat exchanger of the present invention are similar to the scraper, shaft, and bushing in the crystallization apparatus of the present invention described above. The mass proportion of the easily polymerizable compound in the mother liquor of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is not particularly limited and may be low. The material adhering to the inner wall surface may be crystals of the easily polymerizable compound and / or amorphous easily polymerizable compound, or may be a component other than the easily polymerizable compound. The material adhering to the inner wall surface may be the target product or an impurity. In addition, the crystallization device of the present invention can also be said to be a type of heat exchanger, since crystals are usually generated on the inner wall surface by cooling through heat exchange with a refrigerant, and can be said to be a heat exchanger that generates crystals of an easily polymerizable compound.

[0053] (Purification device of the present invention) The present invention also relates to a purification device comprising the heat exchanger or crystallization device of the present invention. The purification apparatus of the present invention is preferably capable of carrying out a continuous purification process. The purification apparatus of the present invention purifies the crystals produced in the heat exchanger or crystallization apparatus of the present invention by solid-liquid separation to obtain purified crystals. A preferred solid-liquid separation apparatus is, for example, a wash column. If necessary, the heat exchanger or crystallization apparatus of the present invention may have tanks, pumps, etc., upstream and / or downstream thereof.

[0054] 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.

[0055] (Method for producing the easily polymerizable compound of the present invention) The present invention is a method for producing an easily polymerizable compound, the method comprising the step of producing crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing the crystals of the easily polymerizable compound, using a crystal production device having a scraper for scraping off crystals of the easily polymerizable compound formed on an inner wall surface and a shaft connected to the scraper, the device further having a bushing for the shaft that comes into contact with the solution or the slurry, the bushing being made of a material containing aromatic polyether ketone, or the method is also a method for producing an easily polymerizable compound, characterized in that it comprises the step of supplying a solution or water containing the easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft.

[0056] Regarding the method for producing an easily polymerizable compound of the present invention, the step of producing crystals of the easily polymerizable compound will be described below, followed by the other steps. In a continuous purification step, each step is usually carried out simultaneously when viewed as the entire crystal production apparatus. In this specification, the term "easily polymerizable compound" refers to an easily polymerizable compound obtained by the production method of the present invention, and does not refer to the raw materials, by-products, or solvents used in the production method of the present invention. The term "easily polymerizable compound" can be rephrased as "polymerizable compound," "target compound," or "target product." In this specification, the term "impurities" refers to components other than the "easily polymerizable compound" obtained by the production method of the present invention, such as raw materials, by-products, and solvents. However, the crystallization apparatus of the present invention is also effective when the raw materials, by-products, or solvents are polymerizable.

[0057] <Step of generating crystals of easily polymerizable compound> The production method of the present invention includes a step of generating crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound using the crystal generation apparatus of the present invention. In the apparatus of the present invention, the temperature of the crystallization section for generating crystals of an easily polymerizable compound from a mother liquid of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound may be adjusted appropriately depending on the type of easily polymerizable compound, but is generally in the range of preferably -1 to -15°C, more preferably -1.5 to -13.5°C, even more preferably -3.5 to -12.5°C, and particularly preferably -5 to -11.5°C relative to the melting point of the pure substance. This allows the above crystals to be generated favorably. When the easily polymerizable compound is (meth)acrylic acid, the temperature is preferably 0 to 12°C, more preferably 1 to 10°C, and even more preferably 2 to 8.5°C. The temperature of the crystallization section can be obtained by measuring the temperature of the slurry inside the apparatus or in the outlet (piping) with a thermometer.

[0058] The supply temperature of the coolant supplied to the crystallization apparatus of the present invention may be appropriately selected taking into consideration the freezing point of the compound to be purified, and is not particularly limited, but is preferably 3 to 30°C lower than the temperature of the crystallization section. That is, the supply temperature of the coolant is preferably 3°C or more lower than the temperature of the crystallization section, and more preferably 5°C or more lower. Furthermore, the supply temperature is preferably within 30°C, more preferably within 25°C, and even more preferably within 20°C of the temperature of the crystallization section.

[0059] The amount of the coolant supplied to the crystallization device of the present invention may be appropriately selected depending on the amount of crystals to be generated and the pressure loss from the coolant supply port to the outlet port, and is not particularly limited.

[0060] In the step of generating the crystals, it is preferable to rotate the shaft and rotate a scraper connected to the shaft within the crystal generation section to scrape off the crystals adhering to the inner wall of the crystal generation section. A motor or the like can usually be used to rotate the shaft. In the step of generating the crystals, the shaft is preferably rotated at a rotation speed of 1 to 80 rpm. The rotation speed of the shaft is more preferably 10 rpm or more, and even more preferably 20 rpm or more, and more preferably 60 rpm or less, and even more preferably 50 rpm or less. In the crystal-forming step, the shaft is preferably rotated at a peripheral speed of 0.02 to 1.2 m / s. The peripheral speed of the shaft is more preferably 0.15 m / s or higher, and even more preferably 0.3 m / s or higher. The peripheral speed is more preferably 0.9 m / s or lower, and even more preferably 0.8 m / s or lower. The rotation of the shaft may be intermittent or may be essentially continuous during use of the crystallization apparatus of the present invention. Regardless of whether the rotation of the shaft is intermittent or continuous, it is preferable that the rotational speed be within the above-mentioned preferred range.

[0061] In the production method of the present invention, the easily polymerizable compound is preferably an easily polymerizable compound having a reactive double bond. In particular, in the production method of the present invention, the easily polymerizable 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.

[0062] <Step of Supplying a Solution Containing an Easily Polymerizable Compound or a Slurry Containing Crystals of an Easily Polymerizable Compound to a Crystallization Apparatus> The production method of the present invention preferably includes a step of supplying a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound to a crystallization device. In the above-mentioned supplying step, a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound is usually supplied from outside the crystal generation apparatus to the crystal generation section of the crystal generation apparatus, but the solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound may be, for example, one obtained in an apparatus upstream of the crystal generation apparatus.

[0063] In the above-mentioned supplying step, the supply rate of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is not particularly limited, but in an industrial-scale crystallization apparatus, it is, for example, 10 to 1000 t / h.

[0064] In the above-mentioned supplying step, the supply temperature of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound can be appropriately adjusted within the range of, for example, 0 to 25°C. For example, when the easily polymerizable compound is (meth)acrylic acid, the supply temperature of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is preferably 1 to 10°C, and more preferably 2 to 8.5°C.

[0065] Examples of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound include those consisting of the easily polymerizable compound, an aqueous solution of the easily polymerizable compound, or an aqueous slurry containing crystals of the easily polymerizable compound. Note that the mother liquor of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound usually contains impurities other than the easily polymerizable compound, and the aqueous solution of the easily polymerizable compound or the aqueous slurry containing crystals of the easily polymerizable compound usually contains impurities other than the easily polymerizable compound and water. In the method for producing an easily polymerizable compound of the present invention, the solution containing the easily polymerizable compound or the mother liquid of the slurry containing crystals of the easily polymerizable compound preferably has a purity (mass proportion) of the easily polymerizable compound of 99 mass % or less, and preferably has a purity equal to or higher than the eutectic point with impurities. When the easily polymerizable compound is (meth)acrylic acid, its purity (mass proportion) is preferably 99% by mass or less, more preferably 98.5% by mass or less, and even more preferably 95% by mass or less, and is preferably 80% by mass or more, and more preferably 85% by mass or more. The mass proportion of the easily polymerizable compound in the solution containing the easily polymerizable compound or in the mother liquid of the slurry containing crystals of the easily polymerizable compound is preferably 75 mass % or more. In the slurry containing crystals of the easily polymerizable compound, the mass proportion of the easily polymerizable compound refers to the mass proportion of the easily polymerizable compound in the mother liquid.

[0066] The solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound immediately before being supplied to the crystal generation device (for example, a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound in a pipe or nozzle that supplies the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound to the crystal generation device).

[0067] During the above-mentioned supplying step, a slurry containing crystals of the easily polymerizable compound is usually discharged from the crystallization device.

[0068] The slurry containing crystals discharged from the crystallization apparatus is a suspension of easily polymerizable compound crystals and mother liquor; in other words, the liquid portion of the slurry containing easily polymerizable compound crystals is the mother liquor. The solution containing the easily polymerizable compound or the slurry containing easily polymerizable compound crystals supplied to the crystallization apparatus may be prepared by the manufacturer or procured from another source. The solution containing the easily polymerizable compound or the slurry containing easily polymerizable compound crystals referred to here also includes crude compounds.

[0069] In the slurry containing crystals discharged from the crystal generation apparatus, the mass proportion of the crystals is preferably 1 mass% or more, more preferably 5 mass% or more, even more preferably 10 mass% or more, and particularly preferably 15 mass% or more. The mass proportion of the crystals is preferably 40 mass % or less, more preferably 38 mass % or less, and even more preferably 35 mass % or less.

[0070] The slurry containing the crystals discharged from the crystallization apparatus preferably contains the easily polymerizable compound in its mother liquid. Examples of the mother liquid include the easily polymerizable compound and an aqueous solution of the easily polymerizable compound. The mother liquid usually contains impurities other than the easily polymerizable compound, and the aqueous solution of the easily polymerizable compound or the aqueous slurry containing the crystals of the easily polymerizable compound usually contains impurities other than the easily polymerizable compound and water. In the method for producing an easily polymerizable compound of the present invention, the purity (mass proportion) of the easily polymerizable compound in the mother liquid of the slurry containing crystals discharged from the crystallization apparatus is preferably 99% by mass or less. Furthermore, the purity is preferably equal to or higher than the eutectic point with impurities. When the easily polymerizable compound is (meth)acrylic acid, its purity (mass proportion) is preferably 99% by mass or less, more preferably 98.5% by mass or less, and even more preferably 95% by mass or less. Furthermore, it is preferably 80% by mass or more, and more preferably 85% by mass or more. The mass proportion of the easily polymerizable compound in the mother liquor is preferably 70 mass % or more. In the mother liquor, the mass proportion of water is preferably 1% by mass or more, and more preferably 10% by mass or less.

[0071] The discharge rate of the crystal-containing slurry discharged from the crystallization apparatus is not particularly limited, but in an industrial-scale crystallization apparatus, it is, for example, 10 to 1000 t / h.

[0072] <Step of supplying a solution or water containing an easily polymerizable compound from the outside of the crystallization apparatus to the peripheral portion of the mechanical seal installed on the shaft> The manufacturing method of the present invention preferably further comprises the step of supplying a solution or water containing an easily polymerizable compound from outside the device to the periphery of the mechanical seal installed on the shaft. In the method for producing an easily polymerizable compound of the present invention, from the viewpoint of preventing freezing of the solution containing the easily polymerizable compound or the water used in the supplying step, it is preferable that the melting point of the solution containing the easily polymerizable compound or the mother liquid of the slurry in the crystal production section for producing crystals of the easily polymerizable compound from the solution containing the easily polymerizable compound or the mother liquid of the slurry containing crystals of the easily polymerizable compound in the apparatus is higher than the melting point of the solution containing the easily polymerizable compound or the water used in the supplying step. For example, the melting point of the solution or the mother liquid of the slurry in the crystallization section is more preferably 1°C or more higher, even more preferably 2°C or more higher, and particularly preferably 3°C or more higher than the melting point of the solution containing the easily polymerizable compound or water used in the supplying step. The upper limit of the difference between the melting point of the solution or the mother liquid of the slurry in the crystallization section and the melting point of the solution containing the easily polymerizable compound or water used in the supplying step is not particularly limited, but is usually 10°C or less. In the supplying step, the solution or water containing the easily polymerizable compound is usually supplied from outside the apparatus.

[0073] In the above-mentioned supplying step, the supply rate of the solution or water containing the easily polymerizable compound may be set appropriately as long as it is sufficient to prevent the solution or slurry originating from the crystal generation section from stagnating around the mechanical seal. The supply may be intermittent or may be continuous during use of the crystallization apparatus of the present invention.

[0074] In the supplying step, the supply temperature of the solution containing the easily polymerizable compound or water can be appropriately adjusted within the range of, for example, more than 0°C and 40°C or less. For example, when the easily polymerizable compound is (meth)acrylic acid, the temperature at which the solution or water containing the easily polymerizable compound is supplied is preferably 3 to 12°C, and more preferably 4 to 10°C. The supply temperature of the solution or water containing the easily polymerizable compound is the temperature of the solution or water containing the easily polymerizable compound immediately before being supplied to the crystal generation apparatus (for example, the temperature of the solution or water containing the easily polymerizable compound in a pipe or nozzle that supplies the solution or water containing the easily polymerizable compound to the crystal generation apparatus).

[0075] The crystallization apparatus may be operated under increased pressure, normal pressure, or reduced pressure. In the supplying step, the supply rate of the solution or water containing the easily polymerizable compound is not particularly limited, but it is preferable that the pressure around the mechanical seal 7 is higher than the pressure inside the crystallization apparatus, and more preferably that the pressure is always maintained higher than the pressure inside the crystallization apparatus. For example, a supply rate of 0.01 to 5.0 L / h is preferable, and 0.1 to 3.0 L / h is more preferable.

[0076] <Step of obtaining a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound from raw materials> In the production method of the present invention, the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is not limited to one obtained by self-synthesis as described above, and may be one procured from another source. However, it is preferable that the production method of the present invention further includes a step of obtaining the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound from raw materials.

[0077] The process for obtaining the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound is not particularly limited as long as it can obtain a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound. For example, the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound can be obtained by collecting the gas of the easily polymerizable compound, which is the reaction product obtained in the reactor, in an absorption tower. Furthermore, the crude compound obtained by roughly purifying the collected compound is also included in the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound. Furthermore, the mother liquor of the collected compound or the slurry containing the crystals discharged from the collected compound, which is fed to the crystallization apparatus of the present invention, is also included in the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound. When the easily polymerizable compound is (meth)acrylic acid, the process for obtaining the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound can be suitably performed, for example, by the acrylic acid synthesis process, acrylic acid collection process, and optional additional crystallization process described in JP 2007-182437 A (Patent Document 1). In the method for producing an easily polymerizable compound of the present invention, the (meth)acrylic acid is preferably prepared 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.

[0078] In addition, in the process of obtaining the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound, impurities such as by-products are basically generated, and the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound contains impurities other than the easily polymerizable compound, and the aqueous solution of the easily polymerizable compound or the aqueous slurry containing the crystals of the easily polymerizable compound usually contains impurities other than the easily polymerizable compound and water. For example, when the easily polymerizable compound is (meth)acrylic acid, impurities that are generated 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 purifying these impurities using the crystallization apparatus according to the production method of the present invention, a high-quality product can be efficiently obtained.

[0079] In the production method of the present invention, the solution containing the easily polymerizable compound is preferably an aqueous solution of crude (meth)acrylic acid 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 contains impurities such as by-products produced during the production of (meth)acrylic acid. According to the production method of the present invention, impurities contained in a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound can be sufficiently removed.

[0080] (Method for purifying easily polymerizable compound) The present invention also relates to a method for purifying an easily polymerizable compound, comprising the step of producing crystals of the easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing the crystals of the easily polymerizable compound, using a crystal production device having a scraper for scraping off crystals of the easily polymerizable compound formed on the inner wall surface and a shaft connected to the scraper, wherein the device further has a bushing for the shaft that comes into contact with the solution or the slurry, and the bushing is made of a material containing aromatic polyether ketone; or the production method is also a method for purifying an easily polymerizable compound, characterized in that it comprises the step of supplying a solution or water containing the easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft.

[0081] According to the purification method of the present invention, an easily polymerizable compound 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.

[0082] (Crystal generation method) The present invention also relates to a method for producing crystals, which comprises a step of producing crystals from a mother liquor of a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound using a crystal production device having a scraper for scraping off crystals produced on the inner wall surface and a shaft connected to the scraper, wherein the device further has a bushing for the shaft that comes into contact with the solution or the slurry, and the bushing is made of a material containing aromatic polyether ketone; or the production method is also a method for producing crystals, which comprises a step of supplying a solution or water containing an easily polymerizable compound from outside the device to the peripheral area of ​​a mechanical seal installed on the shaft.

[0083] The crystals obtained by the crystal production method of the present invention may be crystals of an easily polymerizable compound, or may be a component other than the easily polymerizable compound. That is, the easily polymerizable compound in the crystal production method of the present invention does not have to be a product, but may be a raw material, by-product, solvent, etc. in a solution or slurry. Other preferred embodiments of the crystal production process are as described above. Furthermore, preferred embodiments of the shaft bushing are also as described above. Crystals can also be efficiently purified by the production method of the present invention. [Example]

[0084] 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".

[0085] (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.

[0086] (Crystal generator) As a crystallization apparatus, a purification apparatus similar to the purification apparatus (or a part thereof) shown in FIG. 1 was used, except that an intermediate bushing was also provided in addition to bushings 1 and 1p, and the purification apparatus was configured including the following equipment. Crystallization device 100: Inner diameter 150 mm, heat transfer area 1.4 m 2 Bushings (3 pieces: located at the power side, middle, and end of the crystallization device. Length of the bushing on the power side and the bushing at the end: 80 mm, length of the bushing at the middle: 50 mm, distance between the bushing at the power side and the middle: 400 mm, distance between the bushing at the middle and the bushing at the end: 3000 mm. When the crystallization device is operating, all three bushings at the power side, middle, and end come into contact with a solution containing acrylic acid or a slurry containing acrylic acid crystals.) Scraper 3 (material: PEEK, as shown in Figure 3(b)) for scraping off acrylic acid crystals formed on the inner wall surface Connection part 4 (material: stainless steel. Connection part 4 is provided perpendicular to the longitudinal direction of the shaft.) A shaft 5 (material: stainless steel) connected to the scraper 3 via a connection part 4 Mechanical seal 7 (shortest distance to bushing: 60 mm) The crystallizer was operated under the following conditions:

[0087] (How to obtain the supply slurry) An aqueous solution of acrylic acid was supplied to the crystallization section 19 of the crystallization apparatus 100 from the supply port 9 for the easily polymerizable compound (acrylic acid). A refrigerant was supplied to a jacket provided on the peripheral wall of the crystallization apparatus to indirectly cool the aqueous solution of acrylic acid, and the crystals that had formed and adhered to the inner wall surface of the crystallization apparatus 100 were scraped off with a scraper 3 provided inside the crystallization apparatus, thereby producing a slurry containing crystals of acrylic acid.

[0088] Example 1 (Operating conditions) Shaft rotation speed: 25 rpm Amount of the slurry supplied to the crystallization apparatus: 3,000 kg / h, supply temperature of the slurry: 8.0°C, crystal concentration of the slurry: 10.0% by mass Refrigerant flow rate: 11m 3 / h, refrigerant supply temperature: -6.1°C, mother liquor composition of the above slurry: acrylic acid 92.7% by mass, acetic acid 2.5% by mass, water 3.1% by mass

[0089] A slurry containing acrylic acid crystals was supplied from the supply port 9 for an easily polymerizable compound (acrylic acid) to the crystal generation section 19 of the crystal generation apparatus 100. A refrigerant was supplied to a jacket provided on the peripheral wall of the crystal generation apparatus to indirectly cool the mother liquid of the slurry containing acrylic acid crystals, and the crystals that had formed and adhered to the inner wall surface of the crystal generation apparatus 100 were scraped off with a scraper 3 provided inside the crystal generation apparatus, thereby generating a slurry containing acrylic acid crystals. The crystallization device used PEEK bushings, and operated stably for 50 hours without polymerization due to frictional heat in the bushings. The crystallization rate was 40 kg / h, the crystal concentration at the outlet was 11.5% by mass, the temperature of the crystallization section (discharge temperature) was 7.9°C, and the mother liquor composition of the slurry discharged from the crystallization section was 92.6% by mass of acrylic acid, 2.6% by mass of acetic acid, and 3.1% by mass of water.

[0090] Example 2 The crystallization apparatus was operated in the same manner as in Example 1 except that the bushing material was PTFE and water was supplied to the periphery of the mechanical seal 7 at 0.5 L / h, and the apparatus operated stably for 50 hours.

[0091] (Comparative Example 1) The crystallization apparatus was operated in the same manner as in Example 1, except that the bushing material was changed to PTFE. After about 5 hours, polymerization occurred due to frictional heat in the bushing, and the polymer became trapped in the mechanical seal inside the apparatus, causing a liquid leak from the mechanical seal and causing the apparatus to stop. [Explanation of symbols]

[0092] 1, 1p: Bushing 3: Scraper 4: Connection part 5: Shaft 7: Mechanical seal 9: Supply port for a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound 11: Outlet for slurry containing easily polymerizable compound crystals 13: Slurry containing crystals 15: Refrigerant supply port 17: Refrigerant outlet 19:Crystal generation part 21: Power unit (motor) 23a: Solution or water containing an easily polymerizable compound 100: Crystal generator

Claims

1. A heat exchanger for handling a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound, The heat exchanger has a scraper for scraping off substances adhering to an inner wall surface, a shaft connected to the scraper, and a bushing of the shaft that comes into contact with the solution or the slurry when the heat exchanger is in use; the bushing is constructed using a material including aromatic polyether ketone; The heat exchanger is characterized in that the easily polymerizable compound is acrylic acid.

2. 2. The heat exchanger according to claim 1, wherein the heat exchanger is a crystallization device for generating crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound.

3. 3. The heat exchanger according to claim 1, wherein the scraper is made of a material containing aromatic polyether ketone.

4. 3. The heat exchanger according to claim 1, wherein the bushing and / or the scraper are made of a material containing polyetheretherketone.

5. 3. The heat exchanger according to claim 1, wherein the heat exchanger has a plurality of bushings, and the interval between adjacent bushings is 5000 mm or less.

6. A crystallization apparatus for generating crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound, comprising: the apparatus comprises a scraper for scraping off crystals of the easily polymerizable compound formed on an inner wall surface, a shaft connected to the scraper, and a bushing for the shaft that comes into contact with the solution or the slurry when the apparatus is in use; the bushing is constructed using a material including aromatic polyether ketone; The crystallization apparatus is characterized in that the easily polymerizable compound is acrylic acid.

7. 7. The crystallization apparatus according to claim 6, wherein the scraper is made of a material containing aromatic polyether ketone.

8. 8. The crystallization apparatus according to claim 6 or 7, wherein the bushing and / or scraper is made of a material containing polyetheretherketone.

9. 8. The crystallization apparatus according to claim 6, wherein the apparatus has a plurality of bushings, and the interval between adjacent bushings is 5000 mm or less.

10. A purification device comprising the heat exchanger according to claim 1 or 2, or the crystallization device according to claim 6 or 7.

11. A method for producing crystals, comprising: The production method includes a step of producing crystals from a mother liquor of a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound using a crystal production device having a scraper for scraping off crystals produced on an inner wall surface and a shaft connected to the scraper, the apparatus further comprising a bushing on the shaft in contact with the solution or the slurry; the bushing is made of a material containing aromatic polyether ketone, or the method for producing the bushing includes a step of supplying a solution or water containing an easily polymerizable compound from the outside of the device to a peripheral portion of a mechanical seal installed on the shaft, The method for producing crystals, wherein the easily polymerizable compound is acrylic acid.

12. 12. The method for producing crystals according to claim 11, wherein the aromatic polyether ketone is polyether ether ketone.

13. A method for producing crystals as described in claim 11 or 12, characterized in that the melting point of the solution containing the easily polymerizable compound or the mother liquor of the slurry containing the crystals of the easily polymerizable compound in the crystal production section of the device for producing crystals of the easily polymerizable compound from the solution containing the easily polymerizable compound or the mother liquor of the slurry containing the crystals of the easily polymerizable compound is higher than the melting point of the solution containing the easily polymerizable compound or water used in the supplying process.

14. The method for producing crystals according to claim 11 or 12, characterized in that the temperature of the crystal production section in the device for producing crystals of the easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound is in the range of −1 to −15° C. relative to the melting point of a pure substance of the easily polymerizable compound.

15. 13. The method for producing a crystal according to claim 11, wherein in the step of producing the crystal, the shaft is rotated at a rotation speed of 1 to 80 rpm.

16. A method for producing an easily polymerizable compound, comprising: The production method includes a step of generating crystals of an easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound using a crystal generating device having a scraper for scraping off crystals of the easily polymerizable compound generated on the inner wall surface and a shaft connected to the scraper, the apparatus further comprising a bushing on the shaft in contact with the solution or the slurry; the bushing is made of a material containing aromatic polyether ketone, or the manufacturing method includes a step of supplying a solution or water containing an easily polymerizable compound from the outside of the device to a peripheral portion of the mechanical seal installed on the shaft, The method for producing an easily polymerizable compound, wherein the easily polymerizable compound is acrylic acid.

17. 17. The method for producing an easily polymerizable compound according to claim 16, wherein the aromatic polyether ketone is polyether ether ketone.

18. 18. The method for producing an easily polymerizable compound according to claim 16 or 17, wherein the melting point of the solution containing the easily polymerizable compound or the mother liquid of the slurry containing crystals of the easily polymerizable compound in a crystal production section of the device for producing crystals of the easily polymerizable compound from the solution containing the easily polymerizable compound or the mother liquid of the slurry containing crystals of the easily polymerizable compound is higher than the melting point of the solution containing the easily polymerizable compound or water used in the supplying step.

19. 18. The method for producing an easily polymerizable compound according to claim 16 or 17, wherein a temperature of a crystallization section in the device for producing crystals of the easily polymerizable compound from a mother liquid of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound is in the range of −1 to −15° C. relative to the melting point of a pure substance of the easily polymerizable compound.

20. 18. The method for producing an easily polymerizable compound according to claim 16, wherein in the step of generating the crystals, the shaft is rotated at a rotation speed of 1 to 80 rpm.

21. 18. The method for producing an easily polymerizable compound according to claim 16 or 17, wherein the acrylic acid is produced using at least one raw material selected from the group consisting of propane, propylene, acrolein, acetic acid, lactic acid, isopropanol, 1,3-propanediol, glycerol, and 3-hydroxypropionic acid.

22. A method for purifying an easily polymerizable compound, comprising: The purification method includes a step of generating crystals of the easily polymerizable compound from a mother liquor of a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound using a crystal generating device having a scraper for scraping off crystals of the easily polymerizable compound generated on an inner wall surface and a shaft connected to the scraper, the apparatus further comprising a bushing on the shaft in contact with the solution or the slurry; the bushing is made of a material containing aromatic polyether ketone, or the purification method includes a step of supplying a solution or water containing an easily polymerizable compound from the outside of the device to a peripheral portion of a mechanical seal installed on the shaft, The method for purifying an easily polymerizable compound, wherein the easily polymerizable compound is acrylic acid.

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