Method for producing easily polymerizable compound

Abstract

The present invention provides a method for efficiently obtaining a high-quality product. The present invention is a method for producing an easily polymerizable compound using a refining device having a crystallization tank for generating crystals of an easily polymerizable compound from a mother liquor of a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound and / or a ripening tank for growing crystals of an easily polymerizable compound, and also having a washing column, the method for producing an easily polymerizable compound being characterized in that: the refining device furthermore has a line having ten or fewer bends, the ratio R / D of the curvature radius R and the line inside diameter D of the line exceeding 4, and the line being connected to at least one selected from the group consisting of the crystallization tank, the ripening tank, and the washing column; and the production method includes a step for sending a slurry containing crystals of the easily polymerizable compound through the line.

Description

Technical Field

[0001] The present invention relates to a method for producing an easily polymerizable compound. More specifically, the present invention relates to a method for producing an easily polymerizable compound, a method for purifying an easily polymerizable compound, and a purification apparatus for an easily polymerizable compound.

Background Art

[0002] Purification apparatuses are widely used industrially for purifying compounds used, for example, as raw materials for resins. In many fields of the chemical industry, high-quality compounds with reduced impurities are required, and various improved purification apparatuses have been studied.

[0003] Industrially, many crude compounds before purification of compounds are purified through a continuous purification process. In a continuous purification process, lines (hereinafter, a "line" means a connected state of piping or a state connected by piping) are configured to enable transportation between apparatuses by connecting the apparatuses with piping, and the liquid to be purified is transported through the lines. For example, as a method for producing acrylic acid, which is an easily polymerizable compound, a raw material gas is subjected to a catalytic gas-phase oxidation reaction, and the obtained acrylic acid solution collected is supplied to a crystallization apparatus through a line for purification, and the residual mother liquor is supplied to a reactive distillation apparatus through a line, and after decomposing the Michael adduct of acrylic acid, it is returned to a collection step through a line (see, for example, Patent Document 1).

[0004] Regarding the transportation of a slurry containing solids, when recycling a catalyst such as an ion-exchange resin used in the production of an unsaturated carboxylic acid ester, by specifying the shape of the piping for transporting the slurry containing the resin (catalyst) as a solid, the resin concentration of the slurry, and the flow rate, it is disclosed that retention of the slurry in the piping and crushing of the resin can be prevented (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] As described above, there has been a demand for a better method for producing an easily polymerizable compound, and a method for efficiently obtaining a high-quality product (easily polymerizable compound) has been desired. The present invention has been made in view of the above situation, and an object thereof is to provide a method for efficiently obtaining a high-quality product. [Means for Solving the Problems]

[0007] The present inventors have studied a method for efficiently obtaining a high-quality product, focused on a continuous purification apparatus capable of efficient purification, and generated crystals of an easily polymerizable compound from a solution containing the easily polymerizable compound or the mother liquor of a slurry containing crystals of the easily polymerizable compound. Various studies were conducted on a purification apparatus having a crystallization tank and / or an aging tank for growing crystals of the easily polymerizable compound and a washing column. And, when producing an easily polymerizable compound in such a purification apparatus, it was found that there is a problem that the impurity concentration in the product increases depending on the conditions of the line when feeding a slurry containing crystals through the line. Here, as a result of intensive studies, the present inventors have found that in the method for producing an easily polymerizable compound using the above purification apparatus, the purification apparatus further has a line having a curved portion connected to at least one selected from the group consisting of a crystallization tank, an aging tank, and a washing column, and the ratio R / D of the radius of curvature R to the inner diameter D of the line exceeds 4 and is 10 or less. By making the production method include a step of feeding a slurry containing crystals of the easily polymerizable compound through the line, a high-quality product can be obtained, and it is also possible to sufficiently prevent the line from being blocked by crystals, and the above problems can be solved, and the present invention has been achieved. Note that high-quality products can be obtained by the above manufacturing method because the curvature of the curved part of the line becomes gentle, which can sufficiently prevent uneven crystal growth or crystal crushing in the line and the broadening of the crystal particle size distribution, and a crystal bed with a substantially uniform crystal shape can be formed in the washing column, improving its washability.

[0008] That is, the present invention is a method for producing an easily polymerizable compound using a purification apparatus having a crystallization tank for generating crystals of the easily polymerizable compound from a solution containing the easily polymerizable compound or the mother liquor of a slurry containing crystals of the easily polymerizable compound and / or an aging tank for growing crystals of the easily polymerizable compound, and a washing column, wherein the purification apparatus further has a line having a curved part with a ratio R / D of the radius of curvature R to the inner diameter D of the line exceeding 4 and being 10 or less, which is connected to at least one selected from the group consisting of the crystallization tank, the aging tank, and the washing column, and the manufacturing method includes a step of feeding a slurry containing crystals of the easily polymerizable compound through the line.

[0009] Note that Patent Document 2 discloses the transportation of a slurry, but it is only related to the transportation of a slurry in which the solid matter is a resin (catalyst), and does not disclose anything about the transportation of a slurry containing crystals of an easily polymerizable compound, nor does it disclose anything about obtaining a high-quality target product.

Effects of the Invention

[0010] By using the manufacturing method of the present invention, high-quality products can be obtained efficiently.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

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

[0013] Hereinafter, first, the method for producing the easily polymerizable compound of the present invention will be described. Next, the purification method of the easily polymerizable compound of the present invention and the purification apparatus of the present invention will be described in order.

[0014] (Method for Producing the Easily Polymerizable Compound of the Present Invention) The production method of the present invention is a production method of an easily polymerizable compound using a purification apparatus having a crystallization tank for generating crystals of the easily polymerizable compound from a solution containing the easily polymerizable compound or the mother liquor of a slurry containing crystals of the easily polymerizable compound and / or an aging tank for growing the crystals of the easily polymerizable compound, and a washing column, wherein the purification apparatus further has a line having a bent portion with a ratio R / D of the radius of curvature R to the inner diameter D of the line exceeding 4 and being 10 or less, which is connected to at least one selected from the group consisting of the crystallization tank, the aging tank, and the washing column, and the production method includes a step of feeding a slurry containing crystals of the easily polymerizable compound through the line.

[0015] Hereinafter, first, the step of feeding the liquid will be described, and then the other steps will be described in order. In a continuous purification process, usually, each step is performed simultaneously when viewed as the entire purification apparatus. In the present specification, the "easily polymerizable compound" refers to the easily polymerizable compound obtained by the production method of the present invention, and does not refer to raw materials, by-products, and solvents in the production method of the present invention. The "easily polymerizable compound" can be paraphrased as the "target compound" or the "target product". In the present specification, the "impurities" refer to components other than the "easily polymerizable compound", for example, raw materials, by-products, and solvents.

[0016] Note that in the present specification, generating crystals of the easily polymerizable compound from a solution containing the easily polymerizable compound or the mother liquor of a slurry containing crystals of the easily polymerizable compound means not only generating crystals of the easily polymerizable compound from a solution containing the easily polymerizable compound, but also newly generating crystals of the easily polymerizable compound from the mother liquor of a slurry containing crystals of the easily polymerizable compound, and the crystal concentration in the slurry increases after being taken out from the crystallization tank compared to before being supplied to the crystallization tank. For example, in the method for producing an easily polymerizable compound of the present invention, the method for purifying the easily polymerizable compound of the present invention, and the purification apparatus of the present invention, in addition to supplying a solution containing the easily polymerizable compound to a crystallization tank to obtain a slurry containing crystals of the easily polymerizable compound, there is also included a process of supplying a slurry containing crystals of the easily polymerizable compound to the crystallization tank to obtain a slurry with a higher crystal concentration. Note that the slurry containing crystals of the easily polymerizable compound supplied to the crystallization tank usually also contains the easily polymerizable compound in its mother liquor. When taking out crystals from the crystallization tank of the present invention, usually, they are taken out as a slurry containing crystals of the easily polymerizable compound.

[0017] <Step of feeding a slurry containing crystals of an easily polymerizable compound> In the step of feeding in the production method of the present invention, a slurry containing crystals of the easily polymerizable compound is fed by a line having a curved portion where the ratio R / D of the radius of curvature R to the inner diameter D of the line is more than 4 and 10 or less, and which is connected to at least one selected from the group consisting of a crystallization tank, an aging tank, and a washing column, which the purification apparatus has. The radius of curvature R is the reciprocal of the curvature at the curved portion of the line, and as shown in FIG. 1, it corresponds to the radius of the circle corresponding to the arc when the center line at the curved portion of the line is regarded as an arc. The larger the radius of curvature R, the gentler the curvature of the curved portion.

[0018] By setting the ratio R / D of the radius of curvature R to the inner diameter D of the line to be more than 4, it becomes possible to obtain a high-quality easily polymerizable compound. This is presumably because the curvature of the curved portion becomes gentle, sufficiently preventing the crystal growth from being biased or the crystals from being crushed in the line, and thus the particle size distribution of the crystals from spreading, and because it is possible to form a crystal bed with a substantially uniform crystal shape in the washing column. Also, it is possible to sufficiently prevent the line from being blocked by the crystals. The ratio R / D of the radius of curvature R to the inner diameter D of the line is preferably 4.5 or more, and more preferably 5 or more. In the production method of the present invention, the ratio R / D of the above-mentioned radius of curvature R to the inner diameter D of the line is 10 or less. Thereby, the scale of the purification apparatus does not become too large, and the line can be suitably installed. From the viewpoint of the scale of the purification apparatus, the ratio R / D of the radius of curvature R to the inner diameter D of the line is preferably 9 or less, and more preferably 8 or less. The radius of curvature R is not particularly limited, but in a purification apparatus on an industrial scale, it is preferably, for example, 50 to 5000 mm, and more preferably 100 to 2500 mm. The inner diameter D of the line is preferably, for example, 10 to 500 mm, and more preferably 20 to 250 mm in a purification apparatus on an industrial scale. The curved portion is not particularly limited, but the angle formed by the curved portion (the angle formed by the lines extending before and after the curved portion) is preferably 75 to 165°, and more preferably 90 to 150°.

[0019] The above-mentioned line is connected to at least one selected from the group consisting of a crystallization tank, an aging tank, and a washing column. Examples of the above-mentioned line include a line connecting a crystallization tank to a crystallization tank, a line connecting a crystallization tank to an aging tank, a line connecting a crystallization tank or an aging tank to a washing column, a line connecting a washing column to a facility for melting the melt loop described later, etc. It may be one of these, or two or more. The line connecting a crystallization tank to a crystallization tank may be a line connecting the slurry extraction port and the slurry supply port in a certain crystallization tank, or when using a plurality of tanks (crystallization tanks) connected in series, it may be a line connecting the downstream tank and the upstream tank. In addition, other devices may be installed in the middle of these lines. For example, an external cooling mechanism for crystallization or a solid-liquid separation device may be installed in the middle of the line connecting the slurry extraction port and the slurry supply port. The above-mentioned line is preferably a line connecting a crystallization tank to a crystallization tank, a line connecting a crystallization tank to an aging tank, or a line connecting a crystallization tank or an aging tank to a washing column.

[0020] Among them, in the production method of the present invention, the above-mentioned line is a line connecting a crystallization tank or an aging tank and a washing column, and in the step of feeding the liquid, it is more preferable to feed a slurry containing crystals of an easily polymerizable compound from the crystallization tank or the aging tank to the washing column through the above-mentioned line. By making the ratio R / D at the bent portion of the above-mentioned line within the range of R / D according to the present invention, a crystal bed with a more uniform crystal shape can be formed in the washing column, and a product of higher quality can be obtained. As the crystallization tank or the aging tank connected to the line, for example, when the purification device of the present invention includes a plurality of tanks connected in series, the last tank (crystallization tank or aging tank) can be used. The above-mentioned line is not particularly limited in terms of its material, but it is preferably composed of a metal or an alloy such as stainless steel.

[0021] In the production method of the present invention, in the step of feeding the liquid, it is preferable that the linear velocity of the slurry is 1.5 m / s or more and 4.0 m / s or less. When the linear velocity of the above-mentioned slurry is 1.5 m / s or more, when feeding the slurry through the line having a bent portion according to the present invention, uneven crystal growth can be further prevented. In addition, blockage of the line by crystals can be further prevented. The linear velocity of the slurry is more preferably 1.8 m / s or more, and even more preferably 2.0 m / s or more. When the linear velocity of the above-mentioned slurry is 4.0 m / s or less, when feeding the slurry through the line having a bent portion according to the present invention, crushing of the crystals contained in the slurry can be further prevented. The linear velocity of the slurry is more preferably 3.5 m / s or less, and even more preferably 3.0 m / s or less. That is, when the linear velocity of the slurry is 1.5 m / s or more and 4.0 m / s or less, uneven crystal growth in the line, blockage in the line, and crushing of crystals can be further prevented, and these remarkable effects can be obtained simultaneously. The linear velocity of the slurry can be calculated by directly measuring the volume flow rate in the straight pipe section with a flow meter, or by measuring the mass flow rate in the straight pipe section with a flow meter, calculating the volume flow rate by dividing the measured value by the slurry density, and then dividing the volume flow rate by the cross-sectional area through which the slurry flows in the curved section.

[0022] In the production method of the present invention, in the step of feeding the liquid, it is preferable that the crystal concentration of the slurry is 1% by mass or more and 40% by mass or less. When the crystal concentration of the slurry is 1% by mass or more, the flow rate of the slurry becomes appropriate, and products can be obtained efficiently without increasing the size of equipment such as pumps. More preferably, the crystal concentration of the slurry is 5% by mass or more, and still more preferably 10% by mass or more. When the crystal concentration of the slurry is 40% by mass or less, when the slurry is fed through the line having a curved portion according to the present invention, the fluidity of the slurry is made sufficient and blockage of the line can be sufficiently prevented. More preferably, the crystal concentration of the slurry is 38% by mass or less, and still more preferably 35% by mass or less.

[0023] In the production method of the present invention, it is preferable that the line is provided with a heating mechanism. Examples of the heating mechanism include a heat preservation mechanism, a jacket using a heat medium such as warm water, cooling water (CW), brine, a steam trace, an electric heater, etc., and one or more of these can be used. The heating temperature by the heating mechanism may be appropriately set in consideration of the melting point of the easily polymerizable compound, etc. For example, in the production method of the present invention, the line is provided with a heating mechanism, and in the step of feeding the liquid, it is preferable that the temperature of the slurry is 1°C or more and 50°C or less. Also, it is preferable that the temperature difference between the heating temperature by the heating mechanism and the slurry temperature is 1 to 40°C. When the temperature difference is 1 °C or more, when feeding the slurry through the line having the bent portion according to the present invention, uneven crystal growth in the line and blockage of the line due to freezing can be further prevented. The temperature difference is more preferably 2 °C or more, and even more preferably 3 °C or more. When the temperature difference is 40 °C or less, when feeding the slurry through the line having the bent portion according to the present invention, it is possible to further prevent the crystals in the slurry from partially melting and the particle size distribution from broadening. The temperature difference is more preferably 30 °C or less, even more preferably 20 °C or less, and particularly preferably 10 °C or less.

[0024] The pressure condition in the line in the step of feeding the liquid may be under pressure, under normal pressure, or under reduced pressure. The step of feeding the liquid may be intermittent, but in the production method of the present invention, it is preferably basically continuously performed.

[0025] The washing column included in the purification apparatus of the present invention is not particularly limited as long as it can wash the crystals, but it is preferably one that forcibly conveys the crystal bed. Specific examples of the washing column that forcibly conveys the crystal bed include a mechanical washing column that forms / conveys the crystal bed by pressing the crystals with a piston, and a hydraulic washing column (hydraulic pressure washing column) that forms / conveys the bed by feeding the slurry to the column with a pump and extracting the mother liquor from a filter disposed in the column. The washing column is more preferably a hydraulic washing column in terms of high production capacity and few driving parts in the washing column, resulting in few troubles caused by the apparatus. The washing column may have, for example, a mechanical mechanism for scraping off the crystal bed.

[0026] In the production method of the present invention, the easily polymerizable compound is preferably an easily polymerizable compound having a reactive double bond. Among them, in the production method of the present invention, it is more preferable that the easily polymerizable compound is an unsaturated carboxylic acid, still more preferably (meth)acrylic acid, and particularly preferably acrylic acid. In the present specification, (meth)acrylic acid means acrylic acid and / or methacrylic acid. Note that the solution containing the easily polymerizable compound is not limited to those obtained by self-synthesis, and may be those procured from other sources.

[0027] <Crystallization step> The production method of the present invention may include a step of crystallizing a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound. By this crystallization step, crystals of the easily polymerizable compound can be generated from the mother liquor of the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound.

[0028] The temperature in the above crystallization step may be appropriately adjusted according to the type of the easily polymerizable compound to be purified, but is generally in the range of -2 to -15°C with respect to the melting point of the pure substance. Further, when the easily polymerizable compound to be purified is (meth)acrylic acid, it is preferably 0 to 12°C. More preferably, it is 1 to 11°C, and still more preferably 2 to 10°C. The temperature in the above crystallization step is the temperature of the mother liquor in the solution containing the easily polymerizable compound or the slurry containing crystals of the easily polymerizable compound to be subjected to the crystallization step. The pressure conditions in the above crystallization step may be under pressure, under normal pressure, or under reduced pressure.

[0029] The above crystallization step is not particularly limited as long as it produces crystals of the easily polymerizable compound, and may be a continuous crystallization or a batch crystallization, but continuous crystallization is preferred. The above crystallization step can be carried out using a crystallization tank and / or an aging tank described later.

[0030] Note that when extracting the slurry containing crystals of the easily polymerizable compound, it is preferably extracted from near the bottom of the tank.

[0031] In the production method of the present invention, the solution containing the easily polymerizable compound is preferably a crude (meth)acrylic acid aqueous solution or a crude (meth)acrylic acid solution. The crude (meth)acrylic acid aqueous solution is a solution in which (meth)acrylic acid is dissolved in water and contains impurities such as by-products during the production of (meth)acrylic acid. The crude (meth)acrylic acid solution is a solution composed of (meth)acrylic acid and contains impurities such as by-products during the production of (meth)acrylic acid. Examples of the above 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; and acetone, methyl isobutyl ketone, toluene, protoanemonin, and the like. By the production method of the present invention, impurities (particularly, furfural, etc.) contained in the solution containing the easily polymerizable compound or the slurry containing the crystal of the easily polymerizable compound can be sufficiently removed, and a high-quality product can be obtained. In the present specification, a high-quality product means a product in which at least one kind of the above-mentioned impurities (for example, furfural) is sufficiently reduced. For example, the amount of furfural contained in the product of the easily polymerizable compound obtained by the present production method is preferably 10 ppm or less, more preferably 5 ppm or less, and particularly preferably 0.2 ppm or less.

[0032] <Step of feeding a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound to a crystallization tank or an aging tank> The production method of the present invention may include a step of feeding a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound to a crystallization tank or an aging tank. Examples of the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound to be supplied into the above-mentioned tank include those composed of the above-mentioned easily polymerizable compound, an aqueous solution of the above-mentioned easily polymerizable compound, an aqueous slurry containing the crystals of the easily polymerizable compound, and the like. Note that the mother liquor of the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound usually contains impurities other than the easily polymerizable compound and water. In the production method of the present invention, it is preferable that the purity (mass ratio) of the easily polymerizable compound in the mother liquor of the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound is 99% by mass or less. The mass ratio of the easily polymerizable compound in the mother liquor of the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound is preferably 60% by mass or more. When the solution containing the easily polymerizable compound or the slurry containing the crystals of the easily polymerizable compound is supplied to the crystallization tank or the aging tank, the supply rate is not particularly limited. However, in an industrial-scale crystallization tank or aging tank, for example, 0.2×10 3 ~4.0×10 5 kg / h.

[0033] <Step of recovering the easily polymerizable compound from the mother liquor separated by the crystallization step> The production method of the present invention may further include a step of recovering the easily polymerizable compound from the mother liquor separated by the above-mentioned crystallization step. The mother liquor used in the above-mentioned recovery step can be obtained, for example, by extracting and separating it from the supernatant of the slurry containing the crystals of the easily polymerizable compound in the crystallization tank or the aging tank. The mother liquor usually contains the easily polymerizable compound (solution containing the easily polymerizable compound). The extracted mother liquor can be recovered and reused in the recovery step. By supplying the recovered easily polymerizable compound, for example, to a tank or apparatus on the downstream (preceding stage) side and reusing it, the easily polymerizable compound contained in the mother liquor separated by the above-mentioned crystallization step can be reduced. The above-mentioned recovery step is not particularly limited, and examples thereof include a distillation step. The extraction of the mother liquor may be performed using a pump or the like.

[0034] <Step of stirring in the aging tank> The production method of the present invention may include a step of stirring a slurry containing crystals of an easily polymerizable compound in an aging tank. In the above stirring step, usually, a slurry containing crystals is stirred using a stirrer provided in the aging tank.

[0035] <Step of supplying to the washing column> The production method of the present invention may include a step of extracting a slurry containing crystals of an easily polymerizable compound from a crystallization tank or an aging tank and supplying it to a washing column. Note that the step of supplying to the above washing column corresponds to the case where, in the step of feeding the slurry containing crystals of the easily polymerizable compound described above, the line for feeding the slurry is a line connecting the crystallization tank or the aging tank and the washing column. In the step of supplying to the above washing column, the feeding temperature of the slurry containing crystals can be appropriately set according to the melting point of the easily polymerizable compound, etc., and can be appropriately adjusted, for example, within the range of 1 to 50 °C. For example, when the easily polymerizable compound is (meth)acrylic acid, the feeding temperature of the slurry containing crystals is preferably 5 to 13 °C, and more preferably 7 to 11.5 °C. The feeding temperature of the slurry containing crystals is the temperature of the mother liquor in the slurry containing crystals immediately before it is fed to the above washing column (for example, the slurry containing crystals in the pipe or nozzle for feeding the slurry containing crystals to the washing column).

[0036] <Step of obtaining a solution containing an easily polymerizable compound from a raw material> In the production method of the present invention, it is preferable that the above production method includes a step of obtaining a solution containing an easily polymerizable compound from a raw material. The step of obtaining a solution containing an easily polymerizable compound from a raw material preferably includes a step of obtaining a gas containing an easily polymerizable compound from a raw material and a step of obtaining a solution containing an easily polymerizable compound from the gas containing an easily polymerizable compound.

[0037] Regarding the step of obtaining a gas containing an easily polymerizable compound from the above raw materials, it is not particularly limited as long as a gas containing an easily polymerizable compound can be obtained. When the easily polymerizable compound is (meth)acrylic acid, for example, it can be preferably carried out by the synthesis step (catalytic gas-phase oxidation reaction) of acrylic acid described in JP-A-2007-182437 (Patent Document 1). Regarding the step of obtaining a solution containing an easily polymerizable compound from the gas containing an easily polymerizable compound, it is not particularly limited as long as a solution containing an easily polymerizable compound can be obtained. When the easily polymerizable compound is (meth)acrylic acid, for example, it can be preferably carried out by the collection step of acrylic acid or the like described in Patent Document 1. In the production method of the present invention, the above (meth)acrylic acid is preferably made from at least one selected from the group consisting of propane, propylene, acrolein, isobutene, methacrolein, acetic acid, lactic acid, isopropanol, 1,3-propanediol, glycerol, and 3-hydroxypropionic acid as a raw material. Further, the above (meth)acrylic acid and / or the raw material may be derived from renewable raw materials to produce bio-based (meth)acrylic acid.

[0038] In the step of obtaining the gas containing an easily polymerizable compound, basically, impurities such as by-products are generated. For example, when the easily polymerizable compound is (meth)acrylic acid, acids such as water, propionic acid, acetic acid, maleic acid, benzoic acid, and acrylic acid dimer, aldehydes such as acrolein, furfural, formaldehyde, and glyoxal, and acetone, methyl isobutyl ketone, toluene, protoanemonin, etc. are generated as impurities. However, by the production method of the present invention, the product can be efficiently obtained with excellent separation efficiency of impurities (especially furfural, etc.).

[0039] FIG. 1 is a schematic diagram showing an example of a bent portion of a line used in the production method of the present invention. As shown in FIG. 1, the above-described radius of curvature R corresponds to the radius of a circle corresponding to the arc when the center line (a line passing through the center of the inner diameter D of the line) of the bent portion of the line is taken as an arc. The above-mentioned line inner diameter D is the inner diameter at the curved portion of the line. In the curved portion of the line used in the production method of the present invention, by setting the ratio R / D of the above-mentioned curvature radius R to the line inner diameter D to exceed 4, the curvature of the curved portion becomes gentle, and the effect of the present invention that can efficiently produce high-quality products can be exhibited. Further, by setting the ratio R / D to 10 or less, the scale of the purification device does not become too large, and the line can be suitably installed.

[0040] Figures 2 to 8 are schematic diagrams showing examples of lines to which the present invention is applicable in the purification device of the present invention. In Figures 2 to 8, a line connected to at least one selected from the group consisting of a crystallization tank, an aging tank, and a washing column, into which a slurry containing crystals of an easily polymerizable compound is fed, is a line to which the present invention is applicable. In Figures 2 to 8, the lines with underlined numbers are the corresponding lines. In the present invention, any of the curved portions of the line connected to at least one selected from the group consisting of a crystallization tank, an aging tank, and a washing column, into which a slurry containing crystals of an easily polymerizable compound is fed, only needs to satisfy the ratio R / D of the above-mentioned curvature radius R to the line inner diameter D. However, it is more preferable that all of the curved portions of the above-mentioned line satisfy the ratio R / D. Hereinafter, the usage mode of the purification device of the present invention shown in Figures 2 to 8 will be described in detail.

[0041] Figure 2 is a device having one crystallization tank and one aging tank as a crystallization device. A line for directly feeding mother liquor from the aging tank, which is one upstream tank, to the crystallization tank is installed, and a line for directly discharging residue (mother liquor) from the crystallization tank, which is the most downstream tank, is installed. The solution 1 of the compound to be fed into the purification device is introduced into the aging tank 21. It is cooled in the crystallization tank 11 equipped with a cooling mechanism, and the slurry containing the precipitated crystals is sent to the solid-liquid separation device 31 through line 51. In the solid-liquid separation device 31, the slurry is separated into the mother liquor and the concentrated crystal slurry. The concentrated crystal slurry is sent to the adjacent aging tank 21 through line 52, and the mother liquor is returned to the crystallization tank 11 through line 61. Also, the residue 2 is discharged outside the purification device from the crystallization tank 11 through line 71, and the liquid level of the crystallization tank 11 is adjusted. After the crystals are grown in the aging tank 21, the crystal slurry is fed to the mechanical washing column 41 through line 53. Also, for adjusting the liquid level of the aging tank 21, the mother liquor is directly sent from the aging tank 21 to the crystallization tank 11 through line 72. In the mechanical washing column 41, the crystals are compacted by the piston to form a crystal bed. And at the lower part of the column, shaving of the crystal bed, suspension in the circulating liquid, and heat melting are performed. A part of the circulating liquid containing the obtained melted liquid is carried out as the high-purity compound 3. A part of the remaining circulating liquid (washing liquid) is returned to the mechanical washing column 41 and brought into countercurrent contact with the crystal bed to wash the crystals. Also, the mother liquor in the washing column is returned to the aging tank 21 through line 75 for returning the mother liquor to the crystallization device. In this way, the purification of the compound is carried out and a high-purity compound is obtained.

[0042] Figure 3 shows an apparatus having one crystallization tank and one aging tank as the crystallization device. A line for directly feeding the mother liquor from the aging tank, which is one upstream tank, to the crystallization tank is installed, and a line for directly discharging the residue (mother liquor) from the crystallization tank, which is the most downstream tank, is installed. Also, as the crystallization tank, a type in which the content of the tank is cooled outside the tank is used. Only the parts different from the purification device in Figure 2 will be described below. The crystallization tank 11 is composed of the tank 11A and the cooling mechanism 11B outside the tank, and is connected by lines 111 and 121. The solution of the compound (or the slurry containing the crystals of the compound) sent from the tank 11A to the cooling mechanism 11B through line 111 is cooled in the cooling mechanism 11B, and the slurry containing the precipitated crystals is sent to the tank 11A through line 121. A part of the slurry containing the crystals of the compound from the tank 11A is sent to the cooling mechanism 11B through line 111, and the rest is fed to the solid-liquid separation device 31 through line 51.

[0043] Figure 4 shows an apparatus having two crystallization tanks as a crystallization device. A line for directly feeding mother liquor from crystallization tank 12, which is one upstream tank, to crystallization tank 11 is installed, and a line for directly discharging residue (mother liquor) from crystallization tank 11, which is the most downstream tank, is installed. Further, the washing column is a hydraulic type and has a mechanical mechanism for scraping the crystal bed. Only the parts different from the purification device in Fig. 2 will be described below. The solution 1 of the compound to be subjected to the purification device is introduced into crystallization tank 12. Crystallization tank 11 is composed of tank 11A and an external cooling mechanism 11B, and is connected by lines 111 and 121. The solution of the compound (or slurry containing crystals of the compound) sent from tank 11A to the cooling mechanism 11B through line 111 is cooled by the cooling mechanism 11B, and the slurry containing the precipitated crystals is sent to tank 11A through line 121. A part of the slurry containing the crystals of the compound from tank 11A is sent to the cooling mechanism 11B through line 111, and the rest is sent to the solid-liquid separation device 31 through line 51. Similarly, crystallization tank 12 is composed of tank 12A and an external cooling mechanism 12B, and is connected by lines 112 and 122. A part of the slurry containing the crystals of the compound from tank 12A is sent to the cooling mechanism 12B through line 112 and returned to tank 12A through line 122. The crystal slurry is sent from crystallization tank 12 to the hydraulic washing column 42 through line 53. At the lower part of the hydraulic washing column 42, the crystal bed is scraped off by a mechanical mechanism (scraper), extracted while suspended in the circulating liquid, heated and melted, and a part of the circulating liquid containing the obtained melted liquid is carried out as the high-purity compound 3. A part of the remaining circulating liquid (washing liquid) is returned to the hydraulic washing column 42 and brought into countercurrent contact with the crystal bed to wash the crystals.

[0044] Figure 5 shows an apparatus having two crystallization tanks and one aging tank as a crystallization device. A line for directly feeding mother liquor from one upstream tank is installed between the three tanks, and a line for directly discharging residue (mother liquor) from the most downstream tank is installed. Only the parts different from the purification device in Fig. 2 will be described below. It is cooled in the crystallization tank 11 equipped with a cooling mechanism, and the slurry containing the precipitated crystals is sent to the solid-liquid separator 31 through line 51. In the solid-liquid separator 31, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is sent to the adjacent crystallization tank 12 through line 52, and the mother liquor is returned to the crystallization tank 11 through line 61. Also, the residue 2 is discharged from the crystallization tank 11 to the outside of the purification device through line 71, and the liquid level of the crystallization tank 11 is adjusted. In the crystallization tank 12, the same operation as that of the crystallization tank 11 is performed, and the slurry containing crystals is sent from the crystallization tank 12 to the solid-liquid separator 32 through line 53. In the solid-liquid separator 32, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is sent to the adjacent aging tank 21 through line 54, and the mother liquor is returned to the crystallization tank 12 through line 62. Also, for adjusting the liquid level of the crystallization tank 12, the mother liquor is directly sent from the crystallization tank 12 to the crystallization tank 11 through line 72. After growing the crystals in the aging tank 21, the crystal slurry is sent to the mechanical washing column 41 through line 55. Also, for adjusting the liquid level of the aging tank 21, the mother liquor is directly sent from the aging tank 21 to the crystallization tank 12 through line 73 connecting the aging tank 21 and the crystallization tank 12.

[0045] Fig. 6 shows an apparatus having three crystallization tanks and one aging tank as a crystallization apparatus. A line for directly sending mother liquor from one upstream tank is installed between the four tanks, and a line for directly discharging residue (mother liquor) from the most downstream tank is installed. Also, the washing column is a hydraulic type and has a mechanical mechanism for scraping the crystal bed. Only the parts different from the purification device in Fig. 5 will be described below. The solution 1 of the compound to be fed into the purification device is introduced into the crystallization tank 13. A slurry containing crystals is fed from the crystallization tank 12, which is the second tank from the most downstream, to the solid-liquid separation device 32 through line 53. In the solid-liquid separation device 32, the slurry is separated into mother liquor and a concentrated crystal slurry. The concentrated crystal slurry is sent to the adjacent crystallization tank 13 through line 54, and the mother liquor is returned to the crystallization tank 12 through line 62. Also, for the purpose of adjusting the liquid level of the crystallization tank 12, the mother liquor is directly sent from the crystallization tank 12 to the crystallization tank 11 through line 72. In the crystallization tank 13, the same operation as that in the crystallization tank 12 is performed. A slurry containing crystals is fed from the crystallization tank 13 to the solid-liquid separation device 33 through line 55. In the solid-liquid separation device 33, the slurry is separated into mother liquor and a concentrated crystal slurry. The concentrated crystal slurry is sent to the adjacent aging tank 21 through line 56, and the mother liquor is returned to the crystallization tank 13 through line 63. Also, for the purpose of adjusting the liquid level of the crystallization tank 13, the mother liquor is directly sent from the crystallization tank 13 to the crystallization tank 12 through line 73. After growing the crystals in the aging tank 21, the crystal slurry is fed to the hydraulic washing column 42 through line 57. Also, for the purpose of adjusting the liquid level of the aging tank 21, the mother liquor is directly sent from the aging tank 21 to the crystallization tank 13 through line 74 connecting the aging tank 21 and the crystallization tank 13. At the lower part of the hydraulic washing column 42, the crystal bed is scraped off by a mechanical mechanism (scraper), withdrawn while suspended in the circulating liquid, heated and melted, and a part of the circulating liquid containing the obtained melted liquid is carried out as high-purity compound 3. A part of the remaining circulating liquid (washing liquid) is returned to the hydraulic washing column 42 and brought into countercurrent contact with the crystal bed to wash the crystals.

[0046] Figure 7 shows a device having two crystallization tanks and one aging tank as a crystallization device. A line for feeding mother liquor from one upstream tank to the solid-liquid separation device is installed between the three tanks, and a line for discharging residues from the most downstream tank through the solid-liquid separation device is installed. Only the parts different from the purification device in Figure 5 will be described below. In the crystallization tank 11 of Fig. 7, instead of a line for directly discharging residues, a solid-liquid separation device 33 for separating residues from the slurry in the crystallization tank and a line for discharging residues through the solid-liquid separation device 33 are installed. The slurry taken out from the crystallization tank 11 is sent to the solid-liquid separation device 33 through line 81. The residues 2 separated by the solid-liquid separation device 33 are discharged outside the purification device through line 91. The remaining concentrated crystal slurry is returned to the crystallization tank 11 through line 82, and the liquid level of the crystallization tank 11 is adjusted. In the crystallization tank 12, instead of a line for directly feeding the mother liquor to the crystallization tank 11, a solid-liquid separation device 34 and a line for feeding the mother liquor to the crystallization tank 11 through the solid-liquid separation device 34 are installed. The slurry taken out from the crystallization tank 12 is sent to the solid-liquid separation device 34 through line 83. The mother liquor separated by the solid-liquid separation device 34 is sent to the crystallization tank 11 through line 92 for liquid level adjustment. The remaining concentrated crystal slurry is returned to the crystallization tank 12 through line 84. In the aging tank 21, instead of a line for directly feeding the mother liquor to the crystallization tank 12, a solid-liquid separation device 35 and a line for feeding the mother liquor to the crystallization tank 12 through the solid-liquid separation device 35 are installed. The slurry taken out from the aging tank 21 is sent to the solid-liquid separation device 35 through line 85. The mother liquor separated by the solid-liquid separation device 35 is sent to the crystallization tank 12 through line 93 for liquid level adjustment. The remaining concentrated crystal slurry is returned to the aging tank 21 through line 86. The washing column 43 is of a hydraulic type and does not have a mechanical mechanism for scraping off the crystal bed.

[0047] FIG. 8 shows an apparatus having two crystallization tanks and one aging tank as a crystallization apparatus. A line for feeding mother liquor from the second crystallization tank to the most downstream (first) crystallization tank via a solid-liquid separation device and a line for discharging residue from the most downstream tank via a solid-liquid separation device are installed. A line for directly feeding mother liquor from the aging tank to the second crystallization tank is installed. The solid-liquid separation device for separating mother liquor from the slurry taken out from the second crystallization tank and sending it to the most downstream crystallization tank and the solid-liquid separation device for separating the residue discharged outside the purification device from the most downstream crystallization tank are shared (used in common) with the solid-liquid separation devices provided in the lines for feeding slurry to the tank one upstream respectively. Further, as the crystallization tank, a type in which the content of the tank is cooled outside the tank is used. Only the parts different from the purification device of FIG. 7 will be described below. In the apparatus of FIG. 8, the crystallization tank 11 is composed of a tank 11A and a cooling mechanism 11B outside the tank, and is connected by lines 111 and 121. The solution of the compound (or the slurry containing the crystals of the compound) sent from the tank 11A to the cooling mechanism 11B through the line 111 is cooled by the cooling mechanism 11B, and the slurry containing the precipitated crystals is sent back to the tank 11A through the line 121. A part of the slurry containing the crystals of the compound from the tank 11A is sent to the cooling mechanism 11B through the line 111, and the rest is sent to the solid-liquid separation device 31 through the line 51. Similarly, the crystallization tank 12 is composed of a tank 12A and a cooling mechanism 12B outside the tank, and is connected by lines 112 and 122. A part of the slurry containing the crystals of the compound from the tank 12A is sent to the cooling mechanism 12B through the line 112, and the rest is sent to the solid-liquid separation device 32 through the line 53. Also, in the apparatus of FIG. 8, a part of the slurry containing the crystals of the compound from tank 11A is sent to the solid-liquid separator 31 through line 51. In the solid-liquid separator 31, the slurry is separated into a mother liquor and a concentrated crystal slurry, and the concentrated crystal slurry is sent to the adjacent tank 12A through line 52. A part of the mother liquor separated by the solid-liquid separator 31 is returned to tank 11A through line 61, and the remainder is discharged outside the purification apparatus through the additional line 101 connected to line 61. Similarly, in tank 12A, a part of the slurry containing the crystals of the compound is sent to the solid-liquid separator 32 through line 53. In the solid-liquid separator 32, the slurry is separated into a mother liquor and a concentrated crystal slurry, and the concentrated crystal slurry is sent to the adjacent aging tank 21 through line 54. A part of the mother liquor separated by the solid-liquid separator 32 is returned to the crystallization tank 12 through line 62, and the remainder is sent to tank 11A through the additional line 102 connected to line 62. In the purification apparatus of FIG. 8, line 51 → solid-liquid separator 31 → lines 61, 101 corresponds to line 81 → solid-liquid separator 33 → lines 82, 91 in the apparatus of FIG. 7. Instead of installing the solid-liquid separator 33, the solid-liquid separator 31 provided in the line for feeding the slurry to the upstream tank is shared (used in common). Similarly, line 53 → solid-liquid separator 32 → lines 62, 102 corresponds to line 83 → solid-liquid separator 34 → lines 84, 92 in the apparatus of FIG. 7. Instead of installing the solid-liquid separator 34, the solid-liquid separator 32 provided in the line for feeding the slurry to the upstream tank is shared (used in common). The apparatus of FIG. 8 has a line 73 for directly sending the mother liquor from the aging tank 21 to tank 12A instead of the line in the apparatus of FIG. 7 for sending the mother liquor from the aging tank 21 to the crystallization tank 12 through the solid-liquid separator 35.

[0048] (Method for purifying an easily polymerizable compound) The present invention also relates to a method for purifying a polymerizable compound using a purification apparatus having a crystallization tank for generating crystals of the polymerizable compound from a solution containing the polymerizable compound or a mother liquor of a slurry containing crystals of the polymerizable compound and / or an aging tank for growing crystals of the polymerizable compound, and a washing column, wherein the purification apparatus further has a line having a curved portion with a ratio R / D of the radius of curvature R to the inner diameter D of the line exceeding 4 and being 10 or less, which is connected to at least one selected from the group consisting of the crystallization tank, the aging tank, and the washing column, and the purification method includes a step of feeding a slurry containing crystals of the polymerizable compound through the line.

[0049] By the purification method of the present invention, the polymerizable compound can be purified efficiently and with high quality. A preferred form in the purification method of the present invention is the same as the preferred form in the production method of the present invention described above.

[0050] (Purification apparatus of the present invention) The present invention relates to a purification apparatus for a polymerizable compound, which has a crystallization tank for generating crystals of the polymerizable compound from a solution containing the polymerizable compound or a mother liquor of a slurry containing crystals of the polymerizable compound and / or an aging tank for growing crystals of the polymerizable compound, and a washing column, wherein the purification apparatus further has a line having a curved portion with a ratio R / D of the radius of curvature R to the inner diameter D of the line exceeding 4 and being 10 or less, which is connected to at least one selected from the group consisting of the crystallization tank, the aging tank, and the washing column, and the line is for feeding a slurry containing crystals of the polymerizable compound.

[0051] The above line is not particularly limited as long as it has a curved portion with a ratio R / D of the radius of curvature R to the inner diameter D exceeding 4 and being 10 or less, but is preferably a line connecting the crystallization tank or the aging tank and the washing column. That is, in the purification apparatus of the present invention, the above-mentioned line is a line connecting the crystallization tank or the aging tank and the washing column, and it is preferable that the line is for feeding a slurry containing crystals of the easily polymerizable compound from the crystallization tank or the aging tank to the washing column. As the above-mentioned line and other apparatuses included in the purification apparatus of the present invention, those described above can be preferably used.

[0052] The above-mentioned crystallization tank can be provided with a cooling mechanism, and as long as it can cool a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound to precipitate crystals and generate crystals, it is not particularly limited. Note that a cooling jacket is attached to the tank itself, and it can be roughly classified into a method of directly cooling the inside of the tank to generate crystals (see Figures 2, 5, 6, 7) and a method in which the cooling mechanism is separated from the tank and is connected by piping and cooled while circulating to generate crystals (see Figures 3, 4, 8).

[0053] The cooling mechanism in the form where the cooling mechanism is separated from the tank is not particularly limited as long as it can cool a solution containing an easily polymerizable compound or a slurry containing crystals of an easily polymerizable compound to precipitate crystals, but it is preferable to use a cooling disc crystallizer, a scraped surface heat exchanger, a Votator type heat exchanger, etc. that can ensure a large heat transfer area.

[0054] The crystallization temperature in the above-mentioned crystallization tank can be the temperature in the crystallization step described above.

[0055] The purification apparatus of the present invention has the above-mentioned crystallization tank and / or aging tank, and can have one or more tanks. When the purification apparatus of the present invention has a plurality of tanks (tanks numbered from 1 to N with the first tank being downstream and the Nth tank being upstream), these plurality of tanks are preferably connected in series. In this case, the purification apparatus of the present invention usually has a line for feeding a slurry containing crystals of the easily polymerizable compound from tank to tank, optionally via a solid-liquid separation device. Also, in this case, the purification apparatus of the present invention has a line for supplying a solution containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound to at least one tank. Also, the purification apparatus of the present invention only needs to have a crystallization tank and / or an aging tank as described above, and may or may not have an aging tank, but it is preferable to have an aging tank. In the present invention, the aging tank is a tank for growing crystals of a compound. By growing the crystals into crystals with a substantially uniform crystal shape as much as possible and then feeding them to a washing column, impurities can be efficiently removed in the washing column, and a higher purity compound can be obtained in a high yield. Therefore, it is preferable that the tank for feeding the washing column, that is, the Nth tank, is an aging tank. Most preferably, the purification apparatus of the present invention has a line for feeding a slurry containing crystals of a compound from the aging tank to a washing column.

[0056] The above-mentioned aging tank is not particularly limited as long as it can hold the crystals of the easily polymerizable compound in a suspended state in the tank. By holding the crystals for a certain period of time, small crystals melt by Ostwald ripening, large crystals further grow, and the crystal size distribution becomes narrow. Thereby, high-quality crystals can be obtained, and by using such crystals in a purification process in a hydraulic washing column or the like in the next step, the purification efficiency in the hydraulic washing column can be further improved. The temperature in the above-mentioned aging tank can be the same as the temperature in the above-mentioned crystallization step.

[0057] The above-mentioned aging tank usually has a discharge port near the bottom for discharging a slurry containing crystals of the easily polymerizable compound from the aging tank.

[0058] The size of the above crystallization tank or aging tank is not particularly limited. For example, it is preferably such that the inner diameter thereof is 100 to 50,000 mm, and the height thereof is preferably 1,000 to 100,000 mm.

[0059] The purification apparatus of the present invention may further have an absorption tower for collecting a gas containing an easily polymerizable compound to obtain a solution containing the easily polymerizable compound, and a line for feeding the solution containing the easily polymerizable compound from the absorption tower to the above crystallization tank or the above aging tank. The above absorption tower can obtain a solution containing an easily polymerizable compound by absorbing the gas containing the easily polymerizable compound, which is a reaction product obtained by a reactor, into water in which a polymerization inhibitor is dissolved. The line for feeding the solution containing the easily polymerizable compound from the above absorption tower to the above crystallization tank or aging tank may be provided with an intermediate tank, a resin tank filled with an ion exchange resin, a distillation apparatus for light-boiling distillation, etc. in the middle thereof. As described above, when the easily polymerizable compound is (meth)acrylic acid, examples of the light-boiling components removed by light-boiling distillation include acrolein, acetic acid, water, etc.

[0060] The purification apparatus of the present invention preferably can perform a continuous purification process. For example, it further includes a washing column (preferably a washing column for forcibly transporting crystals) as the subsequent stage of the tank according to the present invention. The purification apparatus of the present invention may also include a line for extracting a circulating slurry containing crystals from the washing column, and a facility for melting the crystals contained in the extracted circulating slurry. The crystals are derived from a crystal bed formed at the lower part of the washing column. The extraction of the crystals can be performed, for example, using a mechanism for extracting crystals from the crystal bed in the washing column. In the extraction of the crystals, usually, the circulating liquid is also extracted together, and it is extracted as a circulating slurry containing crystals and supplied to the melting step.

[0061] The purification apparatus of the present invention may include a line (extraction line) connecting the crystal extraction port in the washing column and the facility for melting, and a return line connecting the facility for melting and the return port of the circulating liquid containing the melt of the extracted crystal provided in the washing column. In these lines and at the location connecting the return port and the crystal extraction port in the washing column, the circulating liquid is circulating. This circulation path is also referred to as a melt loop.

[0062] As the facility for melting, a heater can be used. Examples of the heater include structures that efficiently transfer heat to the slurry containing crystals, such as vertical multi-tube heat exchangers, horizontal multi-tube heat exchangers, double-tube heat exchangers, spiral heat exchangers, plate heat exchangers, electric heaters, etc. The heater is preferably provided in the melt loop, and the circulating slurry (after melting, it is the circulating liquid) is of a forced circulation type that circulates by a pump provided in the melt loop. The purification apparatus of the present invention may further have a line for carrying out the product from the washing column, which is connected to the return line.

[0063] The purification apparatus of the present invention may further have a line for returning the mother liquor from the upstream (rear-stage) tank or apparatus to the downstream (front-stage) tank or apparatus, as described above. Also, the purification apparatus of the present invention may further include a mechanism for controlling the feeding amount of the slurry and the return amount of the mother liquor. Examples of the control mechanism include valves attached to various lines. The purification apparatus of the present invention may appropriately include apparatuses generally used in other purification apparatuses.

Examples

[0064] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and it is also possible to appropriately modify and implement it within the range that conforms to the gist of the foregoing and following descriptions, and all of them are included in the technical scope of the present invention. Unless otherwise specified, "% " means "mass %" and "part(s)" means "parts by mass".

[0065] (Measuring equipment for gas chromatography and liquid chromatography) Gas chromatography: GC-2014 manufactured by Shimadzu Corporation High performance liquid chromatography: LC-20AD HPLC unit manufactured by Shimadzu Corporation Using these, the measurement of furfural was carried out.

[0066] (Method for obtaining an aqueous acrylic acid solution) According to the method described in International Publication No. 2010 / 032665, propylene was catalytically gas-phase oxidized 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.

[0067] (Method for obtaining a feed slurry) An aqueous acrylic acid solution was supplied to a crystallization tank having an inner diameter of 650 mm. By supplying a refrigerant to a jacket provided on the peripheral wall of the crystallization tank and indirectly cooling it, the crystals adhering to the inner surface of the crystallization tank were scraped off with a scraper provided inside the crystallization tank to prepare a slurry containing crystals (feed slurry).

[0068] (Method for purifying the slurry) As a washing column for purifying the above feed slurry, a hydraulic washing column was used. The above feed slurry was fed through the following feed line and supplied to the washing column. While extracting the mother liquor of the feed slurry from a filter provided in the washing column, the crystal bed formed in the column was moved to the lower part of the column by hydraulic pressure, and the crystals were melted in a melt loop to obtain a product.

[0069] <Purification apparatus and implementation conditions> The prepared crystallization tank and the washing column were connected by a supply line with an inner diameter of 25 mm. The supply line had three bends, and the angles formed by the bends were all 90°. The supply slurry prepared in the crystallization tank was fed through the supply line under the conditions of a crystal concentration of 11.0% by mass of the slurry and a liquid feeding temperature of 10.5 °C of the slurry to be supplied to the washing column, and a product was obtained from the supply slurry. Further, the supply line was equipped with a jacket as a heating mechanism, and a heat medium set at 15 °C was introduced into the jacket.

[0070] <Example 1> The ratio R / D of the radius of curvature R to the inner diameter D of all the bends in the supply line was set to 5, the linear velocity of the supply slurry was set to 1.5 m / s, and acrylic acid was obtained as the product. The concentration of furfural in the product, the furfural ratio, and the blockage status of the piping are shown in Table 1.

[0071] <Examples 2 and 3> Acrylic acid was obtained as the product in the same manner as in Example 1 except that the linear velocity of the supply slurry was changed as described in Table 1. The concentration of furfural in the product, the furfural ratio, and the blockage status of the piping are shown in Table 1.

[0072] <Example 4> Acrylic acid was obtained as the product in the same manner as in Example 1 except that the ratio R / D of the radius of curvature R to the inner diameter D of all the bends in the supply line was changed to 10 and the linear velocity of the supply slurry was changed to 1.8 m / s. The concentration of furfural in the product, the furfural ratio, and the blockage status of the piping are shown in Table 1.

[0073] <Example 5> Acrylic acid was obtained as the product in the same manner as in Example 1 except that the linear velocity of the supply slurry was changed as described in Table 1. The concentration of furfural in the product, the furfural ratio, and the blockage status of the piping are shown in Table 1.

[0074] <Example 6> Acrylic acid was obtained as the product in the same manner as in Example 1 except that the crystal concentration of the supply slurry was changed as described in Table 1. The blockage status of the piping is shown in Table 1.

[0075] <Comparative Example 1> Acrylic acid was obtained as a product in the same manner as in Example 1, except that the ratio R / D of the radius of curvature R to the inner diameter D of all the curved portions in the supply line was changed to 3 and the linear velocity of the supplied slurry was changed to 1.8 m / s. The concentration of furfural, the furfural ratio, and the blockage status of the piping in the product are shown in Table 1.

[0076] <Example 7> Acrylic acid was obtained as a product in the same manner as in Example 1, except that the linear velocity of the supplied slurry was changed as described in Table 1. The concentration of furfural, the furfural ratio, and the blockage status of the piping in the product are shown in Table 1.

[0077]

Table 1

[0078] As shown in Table 1 (Examples 2, 4, Comparative Example 1), it can be seen that when R / D is small (4 or less), the furfural concentration in the product increases and the purity of the product decreases. Also, it can be seen that even if R / D is increased, as long as it is 5 or more, the furfural concentration in the product becomes almost constant. Therefore, as described above, it is preferable that the ratio R / D of the radius of curvature R to the inner diameter D is 10 or less. It can be seen that even if R / D is 10 or more, while the scale of the purification apparatus increases, the production of higher-quality acrylic acid cannot be expected.

[0079] In addition, from the results of Table 1 (Examples 1, 3, 5, 7), it can be seen that at least when the linear velocity of the supplied slurry is within a specific range (1.5 m / s or more and 4.0 m / s or less), a high-quality product with a low furfural concentration can be efficiently obtained.

[0080] Also, from the results in Table 1 (Examples 1 and 6), it can be seen that at least the crystal concentration of the feed slurry is within a specific range (1% by mass or more and 40% by mass or less), and clogging in the bent portions of the pipes of the purification apparatus can be sufficiently prevented. In general, as the crystal concentration of the slurry decreases, it becomes less likely to clog. Thus, it can be seen that there is no problem with pipe clogging when the crystal concentration of the feed slurry shown in Example 1 is 11.0% by mass or less.

[0081] From the above results, in the method for producing an easily polymerizable compound, when using a purification apparatus having a tank such as a crystallization tank and a washing column, and feeding a slurry containing crystals of the easily polymerizable compound through a line having a bent portion where the ratio R / D of the radius of curvature R to the inner diameter D of the line is more than 4 and 10 or less, which is connected to the tank and / or the washing column, it was found that high-quality products can be obtained, and also clogging of the line by crystals can be sufficiently prevented, and high-quality products can be obtained efficiently. The reason that high-quality products can be obtained by the above production method is considered to be that in the above line, uneven crystal growth and crystal crushing can be sufficiently prevented, and the crystal size distribution can be prevented from broadening, and a crystal bed with a substantially uniform crystal shape can be formed in the washing column, thereby improving its washability.

Explanation of Reference Signs

[0082] 1: Solution containing easily polymerizable compound 2: Residue 3: High-purity easily polymerizable compound 11, 12: Crystallization tank having a cooling mechanism 11A: Tank (constituting the most downstream crystallization tank [the first crystallization tank]) 11B, 12B: Cooling mechanism (outside the tank) 12A: Tank (constituting the second crystallization tank) 21: Aging tank 31 - 35: Solid-liquid separation device 41: Mechanical washing column 42: Hydraulic washing column (having a mechanical mechanism for scraping off the crystal bed) 43: Hydraulic washing column (not having a mechanical mechanism for scraping off the crystal bed) 51 - 57: Lines for feeding slurry from the downstream tank to the upstream tank or the washing column 61 - 63: Lines for returning the mother liquor separated by the solid - liquid separator from the slurry to the original tank 71: Line for discharging residue (mother liquor) directly out of the purification device from the most downstream tank 72 - 74: Lines for directly feeding mother liquor from the upstream tank to the one - downstream tank 75: Line for returning mother liquor from the washing column to the aging tank 81 - 86: Lines for separating the slurry taken out from the tank into a slurry containing crystals concentrated by the solid - liquid separator and returning it to the original tank 91: Line for discharging the residue (mother liquor) separated by the solid - liquid separator from the slurry taken out from the tank out of the purification device 92, 93: Lines for feeding the mother liquor separated by the solid - liquid separator from the slurry taken out from the tank to the one - downstream tank 101: Additional line for discharging a part of the mother liquor separated by the solid - liquid separator from the slurry taken out from the most downstream tank out of the purification device 102: Additional line for feeding a part of the mother liquor separated by the solid - liquid separator from the slurry taken out from the second tank to the most downstream tank 111, 112, 121, 122: Lines connecting the tank of the crystallization tank in the form of cooling the content of the tank outside the tank and the cooling mechanism D: Inner diameter of the line R: Radius of curvature

Claims

1. A method for producing a polymerizable compound using a purification apparatus having a crystallization tank for producing crystals of the polymerizable compound from a solution containing the polymerizable compound or a mother liquor of a slurry containing crystals of the polymerizable compound and / or an aging tank for growing crystals of the polymerizable compound, and a washing column, wherein the purification apparatus further has a line having a bent portion with a ratio R / D of the radius of curvature R to the inner diameter D of the line exceeding 4 and being 10 or less, at least one end of the line is connected to the crystallization tank, the aging tank, or the washing column, the production method includes a step of feeding a slurry containing crystals of the polymerizable compound through the line, the feeding step is characterized in that the linear velocity of the slurry is 1.5 m / s or more and 4.0 m / s or less. A method for producing a polymerizable compound.

2. The line is a line connecting the crystallization tank or the aging tank and the washing column, the feeding step is characterized in that a slurry containing crystals of the polymerizable compound is fed from the crystallization tank or the aging tank to the washing column through the line. The method for producing a polymerizable compound according to claim 1.

3. The feeding step is characterized in that the crystal concentration of the slurry is 1% by mass or more and 40% by mass or less. The method for producing a polymerizable compound according to claim 1 or 2.

4. The washing column is a hydraulic washing column. The method for producing a polymerizable compound according to claim 1 or 2.

5. The line is provided with a heating mechanism, the feeding step is characterized in that the temperature of the slurry is 1°C or more and 50°C or less. The method for producing a polymerizable compound according to claim 1 or 2.

6. The production method includes a step of obtaining a polymerizable compound-containing gas from a raw material, and a step of obtaining a solution containing the polymerizable compound from the polymerizable compound-containing gas. The method for producing a polymerizable compound according to claim 1 or 2.

7. The polymerizable compound is (meth)acrylic acid. The method for producing a polymerizable compound according to claim 1 or 2.

8. The (meth)acrylic acid is characterized in that it is made from at least one selected from the group consisting of propane, propylene, acrolein, isobutene, methacrolein, acetic acid, lactic acid, isopropanol, 1,3-propanediol, glycerol, and 3-hydroxypropionic acid as a raw material. The method for producing a polymerizable compound according to claim 7.

9. A method for purifying a polymerizable compound using a purification apparatus having a crystallization tank for forming crystals of the polymerizable compound from a solution containing the polymerizable compound or a mother liquor of a slurry containing crystals of the polymerizable compound and / or an aging tank for growing crystals of the polymerizable compound, and a washing column, wherein the purification apparatus further has a line having a curved portion with a ratio R / D of the radius of curvature R to the inner diameter D of the line exceeding 4 and being 10 or less, at least one end of the line is connected to the crystallization tank, the aging tank, or the washing column, the purification method includes a step of feeding a slurry containing crystals of the polymerizable compound through the line, and the feeding step is characterized in that the linear velocity of the slurry is 1.5 m / s or more and 4.0 m / s or less.

Images