Method for producing easily polymerizable compound

Abstract

The present invention provides a method for efficiently obtaining a high quality product. A method for producing an easily polymerizable compound according to the present invention is characterized by comprising: a step for mixing an easily polymerizable compound and a manganese-based polymerization inhibitor; a step for adjusting the manganese concentration in an easily polymerizable compound-containing solution obtained in the mixing step, by bringing at least a portion of the easily polymerizable compound-containing solution into contact with a cation exchange resin; and a step for crystallizing the easily polymerizable compound-containing solution that has a manganese concentration of 5 mass ppm or less and that has been obtained in the adjusting step.

Description

[Technical Field]

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

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

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

[0004] Here, it is known that, particularly in the production of easily polymerizable compounds such as acrylic acid, a polymerization inhibitor is added to prevent polymerization during the purification process (e.g., distillation step, etc.) Examples of the polymerization inhibitor include polymerization inhibitors containing transition metal components such as manganese and copper.

[0005] Patent Document 2 discloses that, in order to prevent transition metal components derived from a polymerization inhibitor contained in crude acrylic acid from deactivating an esterification reaction catalyst, water is added to the crude acrylic acid and then the crude acrylic acid is brought into contact with a cation exchange resin, thereby efficiently removing the transition metal components.

[0006] Patent Document 3 discloses that when a crystallization operation is repeated multiple times to obtain purified (meth)acrylic acid from crude (meth)acrylic acid, polymerization of (meth)acrylic acid can be easily prevented by adjusting the concentration of the polymerization inhibitor in the (meth)acrylic acid-containing solution to be subjected to the crystallization step in the first crystallization operation so that the concentration of the polymerization inhibitor in the (meth)acrylic acid-containing solution to be subjected to the crystallization step in the final crystallization operation is a predetermined concentration or more. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-182437 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-187332 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-65705 Summary of the Invention [Problem to be solved by the invention]

[0008] 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). The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide a method for efficiently obtaining a high-quality product. [Means for solving the problem]

[0009] The present inventors have investigated methods for efficiently obtaining high-quality products and focused on polymerization inhibitors. Conventionally, polymerization inhibitors, such as manganese-based polymerization inhibitors, have been added to the production of easily polymerizable compounds to prevent polymerization during the purification process. However, they have found that when a solution containing an easily polymerizable compound containing a manganese-based polymerization inhibitor is crystallized, under the crystallization conditions, particularly during suspension crystallization, manganese forms a complex with impurities in the solution containing the easily polymerizable compound, resulting in precipitation and making separation from the product difficult. For example, when the easily polymerizable compound is (meth)acrylic acid, maleic acid and manganese form a complex in the solution containing the easily polymerizable compound during the crystallization process, and the resulting manganese maleate precipitates together with the product (meth)acrylic acid crystals, making separation from the product difficult. Impurities such as maleic acid are contained in the gas containing the easily polymerizable compound when the easily polymerizable compound is obtained by a gas-phase reaction, and manganese is added as a manganese-based polymerization inhibitor, making it difficult to significantly reduce both impurities. The present inventors have found that such precipitates cause problems such as clogging of liquid removal nozzles and lines, delay or inhibition of polymerization due to the precipitates being mixed into the product, and accumulation in tanks that receive the residue.

[0010] As a result of intensive research, the present inventors have found that a method for producing an easily polymerizable compound, comprising the steps of: mixing an easily polymerizable compound with a manganese-based polymerization inhibitor; contacting at least a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution; and crystallizing the easily polymerizable compound-containing solution obtained through the adjusting step, in which the manganese concentration is 5 ppm by mass or less, can sufficiently prevent the formation of precipitates of manganese derived from the manganese-based polymerization inhibitor and impurities under crystallization conditions, thereby enabling a high-quality product to be obtained efficiently and solving the above-mentioned problems, and have thus arrived at the present invention.

[0011] That is, the present invention provides a method for producing an easily polymerizable compound, the method comprising: a step of mixing an easily polymerizable compound with a manganese-based polymerization inhibitor; a step of contacting at least a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution; and a step of crystallizing the easily polymerizable compound-containing solution obtained through the adjustment step, in which the manganese concentration is 5 ppm by mass or less. [Effects of the Invention]

[0012] By using the manufacturing method of the present invention, high-quality products can be obtained efficiently. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of the production method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] In the following, first, the method for producing an easily polymerizable compound of the present invention will be described, followed by the method for purifying an easily polymerizable compound of the present invention and the purification apparatus of the present invention.

[0016] (Method for producing the easily polymerizable compound of the present invention) The present invention provides a method for producing an easily polymerizable compound, the method comprising: a step of mixing an easily polymerizable compound with a manganese-based polymerization inhibitor; a step of contacting at least a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution; and a step of crystallizing the easily polymerizable compound-containing solution obtained through the adjustment step, in which the manganese concentration is 5 ppm by mass or less.

[0017] In the production method of the present invention, the mixing step, the adjusting step, and the crystallization step are basically performed in this order on the object to be purified. The crystallization step will be described first, followed by the mixing step, the adjusting step, and other steps. In a continuous purification process, the individual steps are usually performed simultaneously when viewed as a whole purification 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 "target compound" or "target product." In this specification, the term "impurities" refers to components other than the "easily polymerizable compound," such as raw materials, by-products, and solvents.

[0018] <Step of crystallizing the solution containing the easily polymerizable compound, having a manganese concentration of 5 ppm by mass or less, obtained through the adjusting step> In the crystallization step, the easily polymerizable compound-containing solution having a manganese concentration of 5 mass ppm or less, obtained through the adjustment step described below, is crystallized. By setting the manganese concentration to 5 ppm by mass or less, the concentration of the complex formed from manganese and impurities under the conditions for crystallizing the easily polymerizable compound is equal to or less than its saturated solubility, which sufficiently prevents precipitation of the complex and allows the product to be easily separated. Furthermore, since the crystallization step is usually performed at low temperatures (for example, in the case of (meth)acrylic acid, the solution or mother liquor temperature is about 0 to 12°C), there is little risk of polymerization of the easily polymerizable compound even if the manganese concentration is reduced as described above. The easily polymerizable compound-containing solution supplied to the crystallization step preferably has a manganese concentration of 5 mass ppm or less, more preferably 3 mass ppm or less, and particularly preferably 2 mass ppm or less. In the production method of the present invention, the easily polymerizable compound-containing solution supplied to the crystallization step preferably has a manganese concentration of 0.2 mass ppm or more. This further prevents polymerization of the easily polymerizable compound in the crystallization step and subsequent steps, particularly in the step of recovering the easily polymerizable compound from the mother liquor or residue separated in the crystallization step. The manganese concentration is more preferably 0.3 mass ppm or more, even more preferably 0.4 mass ppm or more, and particularly preferably 0.5 mass ppm or more. The manganese concentration is measured by the method described in the Examples. The easily polymerizable compound-containing solution supplied to the crystallization step is an easily polymerizable compound-containing solution having a manganese concentration of 5 mass ppm or less obtained through the adjusting step described above, and refers to an easily polymerizable compound-containing solution supplied to an apparatus used in the crystallization step (for example, a batch-type crystallization tank or a continuous-type apparatus consisting of a crystallization tank, an aging tank, and a washing column).

[0019] The temperature in the crystallization step may be adjusted appropriately depending on the type of easily polymerizable compound to be purified, but is generally within the range of -1 to -15°C relative to the melting point of the pure substance, 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. When the easily polymerizable compound to be purified 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 in the crystallization step is the temperature of the mother liquid or residue in the easily polymerizable compound-containing solution or the slurry containing crystals of the easily polymerizable compound that is subjected to the crystallization step. The pressure conditions in the crystallization step may be under increased pressure, normal pressure, or reduced pressure.

[0020] The crystallization step is not particularly limited as long as it produces crystals of the easily polymerizable compound, and may be continuous crystallization or batch crystallization.In addition, when the crystallization step produces a slurry containing crystals and a mother liquor as in the general continuous crystallization, the mother liquor is separated by the crystallization step, and when the crystallization step produces a melt of crystals by separating into crystals and a residue as in the batch crystallization using a falling thin film crystallizer or the like, the residue is separated by the crystallization step. In one preferred embodiment of the production method of the present invention, the crystallization step is suspension crystallization. Although precipitation of manganese maleate becomes significant in suspension crystallization, the production method of the present invention can sufficiently prevent the precipitation of manganese maleate. The crystallization step can be carried out using a crystallization tank and / or an aging tank, which will be described later. The crystallization step can be suitably carried out by supplying the easily polymerizable compound-containing solution having a manganese concentration of 5 mass ppm or less obtained through the adjustment step into the crystallization tank or aging tank.

[0021] When the crystallization step is a continuous crystallization, the residence time of the easily polymerizable compound in the crystallization tank and aging tank used in the crystallization step can be adjusted appropriately depending on the type of easily polymerizable compound to be purified. However, taking into consideration the yield of the easily polymerizable compound obtained after purification, the purification efficiency, and the capital investment cost, it is generally 0.02 to 6 hours. Furthermore, when the easily polymerizable compound to be purified is (meth)acrylic acid, the residence time is preferably 0.05 to 5 hours, and more preferably 0.1 to 4.5 hours. Furthermore, when 1st to Nth tanks are connected in series, the residence time of the Nth tank is preferably 0.5 to 6 hours in order to regulate the particle size distribution of the slurry. In the case of (meth)acrylic acid, the residence time is more preferably 1 to 5 hours, and even more preferably 1.2 to 4.5 hours. The residence time of the easily polymerizable compound in the crystallization tank referred to here means the residence time inside the tank and in the cooling mechanism outside the tank when the crystallization tank is of a type in which the contents of the tank are cooled outside the tank. The residence time of each tank is calculated as the total volume of the tank and the cooling mechanism outside the tank divided by the sum of the flow rate at which the slurry is supplied from the tank to a tank or washing column on the upstream (subsequent) side and the flow rate at which the mother liquor is sent / discharged from the tank to a tank or a purification apparatus on the downstream side.

[0022] The supply rate of the easily polymerizable compound-containing solution into the crystallization tank or aging tank is not particularly limited. In the case of an industrial-scale crystallization tank or aging tank, the supply rate is, for example, 0.2×10 3 ~4.0×10 5 kg / h.

[0023] The purification yield in the crystallization step is preferably 50 to 70%. The purification yield is the mass ratio of the product obtained in the crystallization step to the total amount of the easily polymerizable compound-containing solution supplied to the crystallization step. By undergoing the crystallization step, manganese is concentrated and contained in the mother liquor or residue depending on the purification efficiency, but according to the production method of the present invention, by previously adjusting the manganese concentration in the easily polymerizable compound-containing solution supplied to the crystallization step as described above, precipitation of the complex can be sufficiently prevented. Note that, when the purification yield is within the above preferred range, when the manganese concentration in the easily polymerizable compound-containing solution supplied to the crystallization step is 0.2 to 5 ppm by mass, the manganese concentration in the mother liquor or residue recovered in the crystallization step will be about 0.7 to 10 ppm by mass.

[0024] The easily polymerizable compound-containing solution to be supplied to the tank may be an aqueous solution of the easily polymerizable compound, etc. The easily polymerizable compound-containing solution usually contains impurities other than the easily polymerizable compound and water. In the production method of the present invention, the easily polymerizable compound-containing solution supplied to the crystallization step preferably has a purity (mass proportion) of the easily polymerizable compound of 96 mass % or less. The mass proportion of the easily polymerizable compound in the solution is preferably 60 mass % or more.

[0025] In the crystallization step, the slurry containing the crystals of the easily polymerizable compound obtained in the crystallization step may be extracted from a tank (for example, from the last tank when the purification apparatus of the present invention includes multiple tanks connected in series), and the slurry containing the crystals of the easily polymerizable compound may be supplied to a washing column.

[0026] In the crystallization step, the slurry containing the crystals of the easily polymerizable compound may be stirred in an aging tank. When the slurry containing the crystals of the easily polymerizable compound is stirred in the aging tank, the slurry containing the crystals is usually stirred using a stirrer provided in the aging tank. The rotation speed of the stirrer is preferably within the range of 5 to 500 rpm, and more preferably within the range of 10 to 300 rpm. The stirring may be intermittent, but it is preferable that the stirring is basically carried out continuously while the aging tank is in use.

[0027] When the residue from the crystallization step is received in a tank, the retention of the manganese-containing easily polymerizable compound solution may cause manganese maleate to precipitate in the tank, leading to deposition in the tank and blockage of the line, etc. Therefore, the manganese concentration may be reduced by passing the residue through an ion exchange resin. The method for passing the residue through the ion exchange resin is not particularly limited, and for example, the ion exchange resin may be installed between the crystallization step and the tank that received the residue, or the ion exchange resin may be installed in the circulation line of the tank.

[0028] <Step of Mixing Easily Polymerizable Compound and Manganese-Based Polymerization Inhibitor> In the mixing step, the easily polymerizable compound and the manganese-based polymerization inhibitor are mixed together. The mixing of an easily polymerizable compound and a manganese-based polymerization inhibitor is not particularly limited as long as the easily polymerizable compound and the manganese-based polymerization inhibitor are mixed together, and for example, the manganese-based polymerization inhibitor may be added to the easily polymerizable compound, the easily polymerizable compound may be added to the manganese-based polymerization inhibitor, or the easily polymerizable compound and the manganese-based polymerization inhibitor may be added to the same container and mixed together. Furthermore, the easily polymerizable compound and the manganese-based polymerization inhibitor used for mixing may each be in a gaseous state, a solution state, or a solid state. The mixing step may involve mixing the easily polymerizable compound and the manganese-based polymerization inhibitor in an absorption tower, for example, by directly introducing the manganese-based polymerization inhibitor into the middle of the absorption tower or by absorbing the easily polymerizable compound-containing gas into a liquid (e.g., water) containing the manganese-based polymerization inhibitor. Furthermore, for example, after obtaining an easily polymerizable compound-containing solution in the absorption tower, when the easily polymerizable compound-containing solution is purified in a light boiling point separation tower, the manganese-based polymerization inhibitor may be added to the easily polymerizable compound-containing solution in advance, or the manganese-based polymerization inhibitor may be directly introduced into the middle of the tower. Alternatively, the easily polymerizable compound and the manganese-based polymerization inhibitor may be mixed in the absorption tower, and then the manganese-based polymerization inhibitor may be further added in the light boiling point separation tower. In particular, it is preferable to mix the easily polymerizable compound with a manganese-based polymerization inhibitor in the absorption tower. The manganese-based polymerization inhibitor is not particularly limited as long as it contains manganese, and examples thereof include manganese dialkyldithiocarbamate, manganese diphenyldithiocarbamate, manganese formate, manganese acetate, manganese octanoate, and manganese naphthenate.

[0029] In the mixing step, the mass ratio of the manganese-based polymerization inhibitor to be mixed with the easily polymerizable compound is preferably 0.1 to 100 mass ppm, more preferably 0.5 to 90 mass ppm, and even more preferably 1 to 80 mass ppm, in terms of manganese concentration relative to the easily polymerizable compound.

[0030] 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. The solution containing the easily polymerizable compound is not limited to one obtained by self-synthesis, but may be one procured from another source.

[0031] <Step of contacting at least a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution> In the adjusting step, at least a portion of the easily polymerizable compound-containing solution obtained through the mixing step is brought into contact with a cation exchange resin to reduce the manganese concentration in the easily polymerizable compound-containing solution. By using a cation exchange resin, the manganese concentration in the easily polymerizable compound-containing solution can be adjusted more energy-efficiently than by distillation or the like. Examples of methods for contacting at least a portion of the easily polymerizable compound-containing solution with a cation exchange resin include a continuous method and a batch method. Preferably, the easily polymerizable compound-containing solution is passed through the cation exchange resin by a continuous method or the like. The resin tank is not particularly limited, and examples thereof include a fixed bed and a fluidized bed. The used cation exchange resin can also be reused by treating it with a strong acid solution such as sulfuric acid, nitric acid, or hydrochloric acid. The flow rate of the solution containing the easily polymerizable compound can be appropriately selected, but the space velocity (SV) is set to 0.01 h -1 More than 0.05h is preferable. -1 More than 0.1h is preferable. -1 More preferably, the liquid passing rate is 10 h -1 Less than 5 hours is preferable -1 Less than 1h is preferable. -1 The following is even more preferred:

[0032] The temperature at which at least a portion of the easily polymerizable compound-containing solution is brought into contact with the cation exchange resin is not particularly limited, but can be within the range from the melting point to the boiling point of the easily polymerizable compound, and when the easily polymerizable compound is (meth)acrylic acid, can be within the range of, for example, 15 to 50°C. The pressure conditions when at least a part of the easily polymerizable compound-containing solution is brought into contact with the cation exchange resin may be under increased pressure, normal pressure, or reduced pressure.

[0033] The water concentration of the easily polymerizable compound-containing solution brought into contact with the cation exchange resin in the adjusting step is preferably 0.3 to 4 mass%. In other words, in the production method of the present invention, the easily polymerizable compound-containing solution supplied to the adjusting step preferably has a water concentration of 0.3 to 4 mass%. When the water concentration is 0.3 mass% or more, manganese removal by the cation exchange resin becomes more efficient. Furthermore, when the water concentration is 4 mass% or less, purification before crystallization is unnecessary or purification during crystallization is easy.

[0034] In the adjusting step, a part of the easily polymerizable compound-containing solution may be contacted with the cation exchange resin, or the whole of the easily polymerizable compound-containing solution may be contacted with the cation exchange resin, but it is preferable to contact a part of the easily polymerizable compound-containing solution with the cation exchange resin. This makes it possible to easily adjust the manganese concentration in the easily polymerizable compound-containing solution supplied to the crystallization step, and is advantageous in terms of extending the life of the cation exchange resin and miniaturizing the apparatus, since the whole of the easily polymerizable compound-containing solution is not contacted with the cation exchange resin. For example, in the production method of the present invention, the adjusting step preferably includes a step of contacting a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin, and a step of mixing a part of the easily polymerizable compound-containing solution with the easily polymerizable compound-containing solution that has been contacted with a cation exchange resin, without contacting the part of the easily polymerizable compound-containing solution with the cation exchange resin.

[0035] In the step of mixing the easily polymerizable compound-containing solution that has been brought into contact with the cation exchange resin with the easily polymerizable compound-containing solution, the mixing ratio of the easily polymerizable compound-containing solution that has been brought into contact with the cation exchange resin to the easily polymerizable compound-containing solution that has not been brought into contact with the cation exchange resin may be appropriately adjusted so that the manganese concentration in the easily polymerizable compound-containing solution to be subjected to the crystallization step becomes the predetermined concentration described above. In the step of mixing the easily polymerizable compound-containing solution that has been brought into contact with the cation exchange resin, for example, a purification apparatus having a bypass line, which will be described later, can be suitably used. Note that, in order to adjust the mass ratio of the easily polymerizable compound-containing solution that is brought into contact with the cation exchange resin, a distribution mechanism such as a valve or a flow meter (a valve attached to a line for sending the easily polymerizable compound-containing solution to a column or the like packed with a cation exchange resin and / or a bypass line) can be used as appropriate.

[0036] Examples of the cation exchange resin include strongly acidic cation exchange resins having sulfonic acid (salt) groups, etc., and weakly acidic cation exchange resins having carboxylic acid (salt) groups, etc., and one or more of these can be used, but for example, strongly acidic cation exchange resins are preferred. As the cation exchange resin, a gel type or porous type cation exchange resin can be used, the latter being more preferred.

[0037] <Step of recovering the easily polymerizable compound from the mother liquor or residue separated by the crystallization step> The production method of the present invention preferably further comprises a step of recovering the easily polymerizable compound from the mother liquor or residue separated in the crystallization step. The mother liquor or residue containing concentrated impurities used in the recovery step usually contains an easily polymerizable compound (easily polymerizable compound-containing solution). The easily polymerizable compound recovered in the recovery step can be reused. The recovered easily polymerizable compound can be used in another process, but loss of the easily polymerizable compound can be reduced by, for example, supplying it to an apparatus in the previous stage and reusing it.

[0038] The recovery step is not particularly limited, but is preferably, for example, a distillation step. The distillation step may be for removing low-boiling components, or for removing high-boiling components such as dimers of easily polymerizable compounds, or may be for both purposes. In the distillation step, the separated mother liquor or residue is usually heated. However, in the production method of the present invention, by adjusting the amount of manganese removed in the adjusting step, a trace amount of manganese-based polymerization inhibitor remains in the separated mother liquor or residue, thereby sufficiently preventing polymerization and making further addition of a polymerization inhibitor in the recovery step unnecessary or reducing the amount. In the distillation step, the temperature and time for heating the separated mother liquor or residue can be appropriately set depending on the purpose of the distillation, the boiling points of the easily polymerizable compound and impurities contained therein, and the like. The distillation step may be carried out under increased pressure, normal pressure, or reduced pressure.

[0039] In the production method of the present invention, the solution containing the easily polymerizable compound is preferably an aqueous (meth)acrylic acid solution or a crude (meth)acrylic acid solution. The aqueous (meth)acrylic acid solution refers to a solution in which (meth)acrylic acid is dissolved in water. The crude (meth)acrylic acid solution refers to a solution consisting of (meth)acrylic acid and containing impurities such as by-products produced during the production of (meth)acrylic acid. Examples of the impurities include acids such as propionic acid, acetic acid, maleic acid, benzoic acid, and acrylic acid dimer; aldehydes such as acrolein, furfural, formaldehyde, and glyoxal; acetone, methyl isobutyl ketone, toluene, and protoanemonin. The production method of the present invention makes it possible to sufficiently remove impurities contained in the solution containing the easily polymerizable compound.

[0040] <Step of obtaining a solution containing an easily polymerizable compound from raw materials> In the production method of the present invention, the production method preferably includes a step of obtaining a solution containing an easily polymerizable compound from a raw material. The step of obtaining an easily polymerizable compound-containing solution from a raw material preferably includes a step of obtaining an easily polymerizable compound-containing gas from the raw material, and a step of obtaining an easily polymerizable compound-containing solution from the easily polymerizable compound-containing gas.

[0041] The process for obtaining an easily polymerizable compound-containing gas from the above raw materials is not particularly limited as long as an easily polymerizable compound-containing gas can be obtained. When the easily polymerizable compound is (meth)acrylic acid, for example, the process can be suitably carried out by the synthesis process of acrylic acid (catalytic gas-phase oxidation reaction) described in JP 2007-182437 A (Patent Document 1). The step of obtaining an easily polymerizable compound-containing solution from the easily polymerizable compound-containing gas is not particularly limited as long as an easily polymerizable compound-containing solution can be obtained, but when the easily polymerizable compound is (meth)acrylic acid, it can be suitably carried out, for example, by the acrylic acid collection step described in Patent Document 1. The step of obtaining an easily polymerizable compound-containing solution from the easily polymerizable compound-containing gas may be carried out simultaneously with the step of mixing the easily polymerizable compound with the manganese-based polymerization inhibitor described above. In the production method of the present invention, the (meth)acrylic acid is preferably prepared from at least one raw material selected from the group consisting of propane, propylene, acrolein, isobutene, methacrolein, acetic acid, lactic acid, isopropanol, 1,3-propanediol, glycerol, and 3-hydroxypropionic acid. The (meth)acrylic acid and / or the raw material may be derived from a renewable raw material, thereby producing bio-based (meth)acrylic acid.

[0042] In the process of obtaining the easily polymerizable compound-containing gas, impurities such as by-products are basically generated. 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 using a purification process such as a crystallization process according to the production method of the present invention, the impurities can be separated with excellent efficiency, and the product can be obtained efficiently.

[0043] FIG. 1 is a schematic diagram showing an example of the production method of the present invention. An easily polymerizable compound-containing gas 11a is supplied into the absorption tower 1. Absorption water 13a containing a manganese-based polymerization inhibitor is introduced into the absorption tower 1 to absorb the easily polymerizable compound-containing gas 11a. The absorption water 13a absorbs the easily polymerizable compound-containing gas 11a and becomes an easily polymerizable compound-containing solution (aqueous solution). The easily polymerizable compound-containing solution is sent from the absorption tower to the resin tank through a line 15 for sending the easily polymerizable compound-containing solution. Note that an intermediate tank, a distillation apparatus (e.g., a light boiling point separation tower), a filtration apparatus, etc. may be further installed along the line 15. The easily polymerizable compound-containing solution sent from the absorption tower to the resin tank corresponds to the easily polymerizable compound-containing solution obtained through the mixing step according to the present invention. The easily polymerizable compound-containing solution obtained through the mixing step may be the easily polymerizable compound-containing solution obtained through the mixing step, or may be an easily polymerizable compound-containing solution obtained by further purifying the mixture obtained through the mixing step through a distillation step such as light boiling point distillation, a filtration step, etc. As described above, a step of previously mixing the manganese-based polymerization inhibitor may be carried out during the distillation step such as light boiling distillation. When the easily polymerizable compound is (meth)acrylic acid, examples of low-boiling components removed by light boiling distillation include acrolein, acetic acid, and water. A portion of the easily polymerizable compound-containing solution obtained through the mixing step is sent to resin tank 3 through a line for sending the easily polymerizable compound-containing solution to the resin tank. The remainder of the easily polymerizable compound-containing solution is mixed with the easily polymerizable compound that has passed through resin tank 3 through bypass line 17. The mixed easily polymerizable compound-containing solution has a manganese concentration adjusted to 5 ppm by mass or less, and corresponds to the easily polymerizable compound-containing solution obtained through the adjusting step according to the present invention, having a manganese concentration of 5 ppm by mass or less. The easily polymerizable compound-containing solution with an adjusted manganese concentration that is supplied to the crystallization step may be the easily polymerizable compound-containing solution obtained through the adjusting step, or it may be an easily polymerizable compound-containing solution obtained by further purifying the easily polymerizable compound-containing solution obtained through the adjusting step by a distillation step, a filtration step, or the like. The easily polymerizable compound-containing solution having a manganese concentration of 5 ppm by mass or less is supplied to a crystallization step 5 (e.g., a batch-type crystallization step or a continuous crystallization step using a crystallization tank, a aging tank, and a washing column) through a line 19 for transferring the easily polymerizable compound-containing solution from a resin tank to a crystallization tank or an aging tank, and the crystallization step is carried out. An intermediate tank, a distillation apparatus (e.g., a low-boiling separation column), a filtration apparatus, etc. may be further installed along the line 19. In the crystallization step, the precipitation of precipitates derived from the manganese-based polymerization inhibitor is sufficiently prevented. As a result, a high-quality easily polymerizable compound (product) 21a can be efficiently obtained from the crystallization step 5, and the mother liquor or residue 23a can be suitably recovered and recycled.

[0044] (Method for purifying easily polymerizable compound) The present invention also relates to a method for purifying an easily polymerizable compound, the method comprising: a step of mixing an easily polymerizable compound with a manganese-based polymerization inhibitor; a step of contacting at least a portion of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution; and a step of crystallizing the easily polymerizable compound-containing solution obtained through the adjustment step, in which the manganese concentration is 5 ppm by mass or less.

[0045] The purification method of the present invention makes it possible to efficiently purify a high-quality easily polymerizable compound. Preferred embodiments of the purification method of the present invention are the same as the preferred embodiments of the production method of the present invention described above.

[0046] (Purification device of the present invention) The present invention also relates to an apparatus for purifying an easily polymerizable compound, which comprises: a resin tank for bringing a solution containing an easily polymerizable compound into contact with a cation exchange resin; a crystallization tank capable of producing crystals of the easily polymerizable compound and / or an aging tank for growing crystals of the easily polymerizable compound; and a line for transporting the solution containing the easily polymerizable compound from the resin tank to the crystallization tank and / or the aging tank.

[0047] The resin tank is not particularly limited as long as it is used to bring the easily polymerizable compound-containing solution into contact with a cation exchange resin. However, it is preferable that the easily polymerizable compound-containing solution is passed through a cation exchange resin, and an example of such a resin tank is a resin tank filled with a cation exchange resin. As the cation exchange resin, those mentioned above can be suitably used. The size of the resin tank is not particularly limited, but it is preferable that the inner diameter is 100 to 5000 mm, and the height is 200 to 10000 mm, for example. The resin tank preferably has a cation exchange resin filling capacity of 10 to 100,000 L.

[0048] The crystallization tank can be equipped with a cooling mechanism and is not particularly limited as long as it can cool the solution containing the easily polymerizable compound to precipitate crystals, thereby producing a slurry containing the crystals and mother liquor, or separate the crystals from the residue to produce a melt of the crystals. Examples of the crystallization tank include continuous crystallization tanks such as a cooled disk crystallizer (CDC), a scraped surface cooling heat exchanger, a double propeller (DP) crystallizer, a Kureha continuous crystallization purification unit (KCP), and a melt crystallization purification facility equipped with a scraped surface crystallizer and a purification tower, as well as batch crystallization tanks such as a falling film crystallizer and a static crystallizer.

[0049] For the purification of easily polymerizable compounds such as (meth)acrylic acid, which require high productivity, a system in which the contents of the tank are cooled outside the tank is preferred. In this way, if the tank and a cooling mechanism are connected by piping, and a portion of the easily polymerizable compound-containing solution (or slurry containing crystals) in the tank is sent to the cooling mechanism to produce crystals in the cooling mechanism, and the slurry containing the produced crystals is returned to the tank, the heat transfer area can be easily increased by adding more cooling mechanisms, and the crystallization tank can be easily scaled up.

[0050] In this case, the cooling mechanism is not particularly limited as long as it can cool the solution of the easily polymerizable compound to precipitate crystals, but it is preferable to use a cooled disk crystallizer (CDC), a scraped surface cooling heat exchanger, or the like, which can ensure a large heat transfer area. The cooling disk crystallizer may be any device that cools a solution of an easily polymerizable compound to precipitate crystals and scrapes off the precipitated crystals. For example, a device that is composed of a tube and a plurality of cooling plates that separate the tube, in which crystals are formed on the wall surfaces of the cooling plates, and in which stirring blades with wipers are rotated inside the tube to scrape off the crystals, can be used.

[0051] The scraping-type cooling heat exchanger may be any type that cools a solution of an easily polymerizable compound to precipitate crystals and scrapes off the precipitated crystals, but it may also be configured to have a double-structured tube in which a refrigerant flows through the outer tube and a solution of the easily polymerizable compound (or a slurry containing the crystals) in a tank flows through the inner tube to form crystals on the wall of the inner tube, and a shaft with a scraping blade rotates inside the inner tube to scrape off the crystals.

[0052] The crystallization temperature in the crystallization tank can be the temperature in the crystallization step described above. High-purity crystals are produced when the crystallization tank temperature is high. However, for example, when the crystallization tank uses a scraped-surface cooling heat exchanger, problems such as the need for a lot of power to scrape the crystals in the crystallization tank may occur. Furthermore, if the temperature difference between the refrigerant and the crystallization tank is too high, problems such as blocking of the scraping scraper may occur when the crystallization tank uses a scraped-surface cooling heat exchanger, making it difficult to continue operation. Therefore, under conditions where the temperature of the crystallization tank is high, it is necessary to reduce the temperature difference between the refrigerant and the crystallization tank and reduce the amount of crystals produced per heat transfer area. Although the purity of the crystals produced decreases when the crystallization tank temperature is low, when the crystallization tank uses a scraped-surface cooling heat exchanger, less power is required to scrape the crystals in the crystallization tank, and scraper blocking is less likely to occur even if the temperature difference between the refrigerant and the crystallization tank is increased. As a result, the temperature difference between the refrigerant and the crystallization tank can be increased, increasing the amount of crystals produced per heat transfer area. However, if the crystallization temperature is too low, the particle size of the generated crystals tends to be small and the crystals tend not to settle easily.

[0053] The purification apparatus of the present invention has the crystallization tank and / or aging tank, and can have one or more tanks. When the purification apparatus of the present invention has multiple tanks (tanks 1 to N, with the first tank downstream and the Nth tank upstream), it is preferable that these multiple tanks are connected in series. In this case, the purification apparatus of the present invention usually has a line for sending a slurry containing crystals of the easily polymerizable compound from tank to tank, optionally via a solid-liquid separation device. In addition, in this case, the purification apparatus of the present invention usually has a line for supplying a liquid to be purified containing the easily polymerizable compound or a slurry containing crystals of the easily polymerizable compound to at least one tank. Furthermore, when the purification apparatus of the present invention further includes an aging tank, it is preferable that the tank that sends a liquid to the washing column, i.e., the Nth tank, is the aging tank.

[0054] The aging tank is not particularly limited as long as it can maintain the crystals of the easily polymerizable compound in a suspended state within the tank. By maintaining the crystals for a certain period of time, fine crystals melt due to Ostwald ripening, and larger crystals grow further, narrowing the crystal size distribution. This allows high-quality crystals to be obtained, and by subjecting such crystals to the subsequent purification step in a washing column or the like, the purification efficiency in the washing column can be further improved. The temperature in the aging tank can be the temperature in the crystallization step described above.

[0055] The aging tank is usually provided with a withdrawal port near the bottom for withdrawing the slurry containing the easily polymerizable compound crystals from the aging tank. The aging tank may be provided with a baffle therein. Examples of materials for the baffle plate include metals such as stainless steel, and resins. A plurality of the baffles may be provided in the aging tank.

[0056] The aging tank may further include a drain port near the top plate for draining the supernatant mother liquor from the aging tank. The drained mother liquor can be recycled, thereby improving the yield of the easily polymerizable compound. For example, the drained mother liquor can be returned to the tank related to the previous step (previous stage). The nozzle or pipe constituting the drain port is not particularly limited in terms of material, and can be made of, for example, a metal such as stainless steel or an alloy. The maturation tank may be provided with only one or more outlets for withdrawing the mother liquor.

[0057] The aging tank may be provided with a mechanism (such as a partition plate or a weir) for preventing crystals of the easily polymerizable compound from entering the mother liquor outlet, thereby further preventing the mother liquor outlet from being contaminated with crystals.

[0058] The size of the crystallization tank or aging tank is not particularly limited, but it is preferable that the inner diameter is 100 to 50,000 mm, and the height is 1,000 to 100,000 mm, for example.

[0059] Instrumentation devices such as thermometers, pressure gauges, level gauges (radar type, etc.), and level switches (float type, etc.) may be provided in or around the crystallization tank or aging tank. Sight glasses (sight windows) may be provided on the side plates, etc. of the aging tank, and in this case, these may be covered with covers. Manholes, handholes (holes for reaching inside during maintenance), etc. may be provided on the top plate, side plate, etc. of the aging tank, and ruptures, etc. may be provided on the top plate, etc. of the aging tank. There is no limit to the number of these devices that may be provided.

[0060] It is preferable that the purification apparatus of the present invention further includes a bypass line for circulating at least a portion of the easily polymerizable compound-containing solution without contacting it with a cation exchange resin, and a mixing section for mixing the easily polymerizable compound-containing solution that has circulated through the bypass line with the easily polymerizable compound-containing solution that has been in contact with the cation exchange resin. The mixing section is not particularly limited as long as it is used to mix the easily polymerizable compound-containing solution that has flowed through the bypass line with the easily polymerizable compound-containing solution that has been brought into contact with the cation exchange resin, and may be, for example, a simple T-shaped line or a mixing tank. The bypass line is usually branched off from a line for transferring the easily polymerizable compound-containing solution to the resin tank, and is connected to a line for transferring the easily polymerizable compound-containing solution from the resin tank to the crystallization tank and / or aging tank.

[0061] In the purification apparatus of the present invention, the line for sending the easily polymerizable compound-containing solution to the resin tank and / or the bypass line preferably includes a distribution mechanism for controlling the flow rate. Examples of the distribution mechanism include a valve, a flow meter, and the like attached to the line for delivering the easily polymerizable compound-containing solution to the resin tank and / or the bypass line. A valve (such as a three-way valve) for switching flow paths may be installed at a T-junction between the line for delivering the easily polymerizable compound-containing solution to the resin tank and the bypass line. When a valve for switching flow paths is installed at the T-junction, a valve or the like may or may not be installed in the line for delivering the easily polymerizable compound-containing solution to the resin tank and / or the bypass line.

[0062] It is preferable that the purification apparatus of the present invention further includes an absorption tower for collecting the easily polymerizable compound-containing gas to obtain an easily polymerizable compound-containing solution, and a line for sending the easily polymerizable compound-containing solution from the absorption tower to the resin tank. The absorption tower is capable of absorbing the easily polymerizable compound-containing gas, which is the reaction product obtained in the reactor, into water in which a polymerization inhibitor is dissolved, thereby obtaining an easily polymerizable compound-containing solution. The line for transferring the easily polymerizable compound-containing solution from the absorption tower to the resin tank may be provided with an intermediate tank, a distillation apparatus for light boiling distillation, a filtration apparatus, etc. 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, and water.

[0063] The purification apparatus of the present invention is preferably capable of carrying out a continuous purification process, and may further include, for example, a washing column (preferably a washing column for forcibly transporting crystals) downstream of the tank of the present invention. When the purification apparatus of the present invention further includes the washing column, the purification apparatus of the present invention may have a line for supplying the slurry containing the crystals of the easily polymerizable compound from a tank included in the purification apparatus of the present invention (for example, the last tank when the purification apparatus of the present invention includes multiple tanks connected in series) to the washing column, instead of a line for unloading the slurry as a product from the tank. The purification apparatus of the present invention may further include a line for discharging the product from the wash column. The purification apparatus of the present invention may further include a line for returning the mother liquor from a downstream tank or apparatus to a upstream tank or apparatus. The purification apparatus of the present invention may further include a mechanism for controlling the amount of the slurry sent and the amount of the mother liquor returned. Examples of such a control mechanism include valves attached to various lines. The refining apparatus of the present invention may also include other devices that are generally used in refining apparatuses. [Example]

[0064] 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".

[0065] (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 brought into contact with water containing manganese acetate added as a polymerization inhibitor in an absorption tower to obtain an aqueous acrylic acid solution.

[0066] The manganese concentration in the aqueous acrylic acid solution obtained in the absorption tower was 10 ppm by mass, and the water concentration was 4% by mass.

[0067] (resin tank) The resin tank used was an apparatus having the following shape. Inner diameter: 400mm Height: 800mm Cation exchange resin packing capacity: 50L The cation exchange resin used in the resin tank was DIAION PK208 manufactured by Mitsubishi Chemical Corporation.

[0068] (Crystallization process) An aqueous solution of acrylic acid was fed at 20 kg / h to a scraping crystallizer with a refrigerant fed to the jacket, and the crystal concentration was adjusted to 15%, to obtain an acrylic acid slurry. The slurry was fed to a hydraulic washing column at 110 kg / h, and the crystals were melted in a heat exchanger, and the column was operated so that the purification yield was 50%.

[0069] (Recovery process) A portion of the mother liquor extracted from the washing column in the crystallization step was fed to the distillation column at a rate of 10 kg / h. The distillation column was operated at an operating pressure of 100 hPa and an operating temperature of 100°C.

[0070] (Manganese concentration analysis) The aqueous acrylic acid solution obtained in the absorption tower, the aqueous acrylic acid solution immediately before being supplied to the crystallization step, and the product (acrylic acid) were each sampled and diluted 10 times with a 0.1 wt % aqueous nitric acid solution, and then the manganese concentration was measured using an ICP atomic emission spectrometer (iCAP6000SERIES, manufactured by Thermo Scientific).

[0071] Example 1 The aqueous acrylic acid solution obtained in the absorption tower was supplied to a resin tank (25°C) filled with the cation exchange resin. At this time, a bypass line that did not flow through the resin tank was provided so that the manganese concentration in the aqueous acrylic acid solution to be supplied to the crystallization step could be adjusted, and the flow rate was adjusted to 10 kg / h on the resin tank side and 10 kg / h on the bypass line side. Thereafter, the aqueous acrylic acid solutions that had flowed through both lines were mixed and supplied to the crystallization step. At this time, the manganese concentration in the aqueous acrylic acid solution immediately before being supplied to the crystallization step was 5 ppm by mass. As a result, no manganese maleate was precipitated during the crystallization process, and no manganese was detected in the resulting product (acrylic acid). There was no line blockage due to manganese maleate precipitation, and the mother liquor recovery process was able to operate stably without the addition of any additional polymerization inhibitor. The results are shown in Table 1.

[0072] <Example 2> The same procedure as in Example 1 was carried out, except that the aqueous acrylic acid solution was circulated at a rate of 19.6 kg / h through the resin tank side and 0.4 kg / h through the bypass line side. In this case, the manganese concentration in the aqueous acrylic acid solution immediately before being supplied to the crystallization step was 0.2 ppm by mass. As a result, no manganese maleate was precipitated during the crystallization process, and no manganese was detected in the resulting product (acrylic acid). There was no line blockage due to manganese maleate precipitation, and the mother liquor recovery process was able to operate stably without the addition of any additional polymerization inhibitor. The results are shown in Table 1.

[0073] <Comparative Example 1> The same procedures as in Example 1 were carried out, except that the aqueous acrylic acid solution was supplied only to the bypass line without being supplied to the resin tank side in Example 1. In this case, the aqueous acrylic acid solution immediately before being supplied to the crystallization step did not flow through the resin tank, and therefore was the same as the aqueous acrylic acid solution obtained in the absorption tower, and the manganese concentration therein was 10 ppm by mass. As a result, manganese maleate precipitated during the crystallization process, contaminating the resulting product (acrylic acid) with manganese, resulting in a decline in product quality. Operation continued, but line blockages due to manganese maleate occurred, forcing the plant to be shut down. The results are shown in Table 1.

[0074] <Comparative Example 2> The same procedure as in Example 1 was carried out, except that the aqueous acrylic acid solution was circulated at a rate of 8 kg / h through the resin tank side and 12 kg / h through the bypass line side. In this case, the manganese concentration in the aqueous acrylic acid solution immediately before being supplied to the crystallization step was 6 ppm by mass. As a result, manganese maleate precipitated during the crystallization process, and manganese was mixed into the resulting product (acrylic acid), resulting in a decrease in product quality. Operation continued thereafter, and unlike Comparative Example 1, no blockage occurred. However, adhesion of manganese maleate to the line was observed, and operation was somehow possible by performing operations such as increasing the pressure. The results are shown in Table 1.

[0075] Example 3 The same procedures as in Example 1 were carried out except that the aqueous acrylic acid solution was supplied only to the resin tank side and not to the bypass line. In this case, the manganese concentration in the aqueous acrylic acid solution immediately before being supplied to the crystallization step was 0 ppm by mass. As a result, no manganese maleate was precipitated during the crystallization process, and no manganese was detected in the resulting product (acrylic acid). Although no line blockages due to manganese maleate precipitation occurred, polymerization occurred during the mother liquor recovery process, so operation was temporarily halted and restarted after adding new polymerization inhibitor. The results are shown in Table 1.

[0076] [Table 1]

[0077] From the above-mentioned Examples and Comparative Examples, it has been found that the critical significance of the numerical ranges of the present invention can be stated as follows: That is, it has been found that by crystallizing an easily polymerizable compound-containing solution having a manganese concentration of 5 mass ppm or less, a significant advantageous effect of efficiently obtaining a high-quality product is exerted.

[0078] In the above-described examples and comparative examples, an aqueous acrylic acid solution is used as the easily polymerizable compound-containing solution. However, when a manganese-based polymerization inhibitor is added to the easily polymerizable compound during the purification process for its production to prevent polymerization, and when an easily polymerizable compound-containing solution, particularly an aqueous (meth)acrylic acid solution or a crude (meth)acrylic acid solution, containing the manganese-based polymerization inhibitor is crystallized, the impurities in the easily polymerizable compound-containing solution form a complex with manganese under the crystallization conditions, resulting in the precipitation of the complex, making separation from the product difficult. Therefore, it can be said that the advantageous effects of the present invention are reliably realized by crystallizing an easily polymerizable compound-containing solution having a manganese concentration of 5 ppm by mass or less. At least, when an aqueous (meth)acrylic acid solution or a crude (meth)acrylic acid solution having a manganese concentration of 5 ppm by mass or less is crystallized, the advantageous effects of the present invention are fully demonstrated in the above-described examples and comparative examples, supporting the technical significance of the present invention. [Explanation of symbols]

[0079] 1: Absorption tower 3:Resin tank 5: Crystallization process 11a: Gas containing easily polymerizable compound 13a: Absorbed water 15: Line (for sending the solution containing the easily polymerizable compound from the absorption tower to the resin tank) 17: Bypass line 19: Line (for sending a solution containing an easily polymerizable compound from a resin tank to a crystallization tank or aging tank) 21a: Easily polymerizable compounds (products) 23a: Mother liquor or residue

Claims

1. A method for producing an easily polymerizable compound, comprising: The production method includes a step of mixing an easily polymerizable compound and a manganese-based polymerization inhibitor; a step of contacting at least a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution; and a step of crystallizing the easily polymerizable compound-containing solution having a manganese concentration of 0.2 ppm by mass or more and 5 ppm by mass or less obtained through the adjusting step, The easily polymerizable compound is an unsaturated carboxylic acid. A method for producing an easily polymerizable compound, comprising:

2. 2. The method for producing an easily polymerizable compound according to claim 1, wherein the easily polymerizable compound-containing solution supplied to the adjusting step has a water concentration of 0.3 to 4% by mass.

3. The adjusting step includes a step of contacting a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin, and a step of mixing a part of the easily polymerizable compound-containing solution with the easily polymerizable compound-containing solution that has been contacted with a cation exchange resin, without contacting the part of the easily polymerizable compound-containing solution with the cation exchange resin. The method for producing an easily polymerizable compound according to claim 1 or 2.

4. The production method further includes a step of recovering the easily polymerizable compound from the mother liquor or residue separated by the crystallization step. The method for producing an easily polymerizable compound according to claim 1 or 2.

5. The solution containing the easily polymerizable compound is an aqueous (meth)acrylic acid solution or a crude (meth)acrylic acid solution. The method for producing an easily polymerizable compound according to claim 1 or 2.

6. The production method includes a step of obtaining an easily polymerizable compound-containing gas from a raw material; A step of obtaining a solution containing an easily polymerizable compound from a gas containing an easily polymerizable compound is included. The method for producing an easily polymerizable compound according to claim 1 or 2.

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

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

9. A method for purifying an easily polymerizable compound, comprising: The purification method includes a step of mixing an easily polymerizable compound with a manganese-based polymerization inhibitor; a step of contacting at least a part of the easily polymerizable compound-containing solution obtained through the mixing step with a cation exchange resin to adjust the manganese concentration in the easily polymerizable compound-containing solution; and a step of crystallizing the easily polymerizable compound-containing solution having a manganese concentration of 0.2 ppm by mass or more and 5 ppm by mass or less obtained through the adjusting step, The easily polymerizable compound is an unsaturated carboxylic acid. A method for purifying an easily polymerizable compound, comprising:

10. An apparatus for purifying an easily polymerizable compound, comprising: The purification apparatus includes a resin tank for bringing the easily polymerizable compound-containing solution into contact with a cation exchange resin, a crystallization tank capable of producing crystals of the easily polymerizable compound and / or an aging tank for growing crystals of the easily polymerizable compound, and a line for transferring the easily polymerizable compound-containing solution from the resin tank to the crystallization tank and / or the aging tank, the easily polymerizable compound is an unsaturated carboxylic acid, The purification device includes a bypass line for allowing at least a portion of the easily polymerizable compound-containing solution to flow without contacting the solution with a cation exchange resin; The system further includes a mixing section for mixing the easily polymerizable compound-containing solution that has flowed through the bypass line with the easily polymerizable compound-containing solution that has been brought into contact with a cation exchange resin. An apparatus for purifying an easily polymerizable compound, comprising:

11. The purification device further includes an absorption tower for collecting the easily polymerizable compound-containing gas to obtain an easily polymerizable compound-containing solution, and a line for sending the easily polymerizable compound-containing solution from the absorption tower to the resin tank. The apparatus for purifying an easily polymerizable compound according to claim 10.

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