Purification methods for compounds

Abstract

The present invention relates to a purification method of a compound characterized by using a purification device having a crystallization device in which N crystallization tanks are connected in series and a washing column that forcibly carries crystals, the purification method comprising the following steps: a step of generating crystals of the compound in the crystallization device; a step of discharging at least a part of mother liquor outside the purification device; a step of separating a slurry containing the generated crystals into the mother liquor and a slurry in which the concentration of crystals is increased; a step of returning at least a part of the separated mother liquor to the original tank; a step of supplying a purified liquid containing the compound to the crystallization device to mix with the slurry in the crystallization device; a step of transporting the slurry from a downstream tank to the next upstream tank in order among the plurality of tanks included in the crystallization device; a step of supplying at least a part of the slurry from the crystallization device to the washing column, the purified liquid containing the compound being a liquid having a higher purity than the mother liquor discharged outside the purification device, the purity A1 of the mother liquor in the slurry supplied to the washing column being 80 mol% or more, and the difference A1-A2 between A1 and the purity A2 of the discharged mother liquor being 5 mol% or more.

Description

Technical Field

[0001] This invention relates to a purification method for purifying compounds suitable for industrial production. Background Technology

[0002] Today, a wide variety of compounds are manufactured and utilized industrially. Industrially manufactured compounds require high-quality products with reduced impurities, depending on their intended use, leading to the research into various superior purification techniques.

[0003] As a purification technique for compounds, a purification method is disclosed, in which multiple cooling crystallization tanks with clarification sections at the top are connected in series with a vertical purification tower having a clarification section at the top and a heater at the bottom. Crystals generated in the crystallization tanks are sequentially fed into the crystallization tank side connected to the purification tower, causing the crystals sent from the crystallization tanks to undergo gravity settling within the purification tower. Furthermore, a portion of the crystals, which have been heated and melted by the heater at the bottom of the purification tower, rises as reflux liquid and contacts the crystals undergoing gravity settling, thereby cleaning the crystals (see Patent Documents 1 and 2). Additionally, a purification method for acrylic acid is disclosed, in which a suspension containing acrylic acid crystals generated in a crystallization tank and crude acrylic acid melt is conveyed to a washing column. The crystals are forcibly transported within the washing column, and the melt obtained by melting the crystals at the bottom of the column is used as the washing liquid to clean the crystals within the washing column (see Patent Document 3). Furthermore, a purification method is disclosed that improves the purity of acrylic acid by repeatedly subjecting an aqueous solution containing acrylic acid to multiple suspension crystallizations or layered crystallizations (see Patent Document 4).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 59-66305

[0007] Patent Document 2: Japanese Patent Application Publication No. 6-91103

[0008] Patent Document 3: Japanese Patent Publication No. 2003-530376

[0009] Patent Document 4: Japanese Patent Publication No. 2010-501526 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] As described above, various purification techniques have been disclosed, but in industrial manufacturing, there is a need to produce high-purity compounds with high yields and low costs, and further improvements to purification techniques are sought. Based on the research results of the inventors, it is clear that the methods using gravity sedimentation washing columns described in Patent Documents 1 and 2, when purifying low-purity compound solutions by generating organic compounds that form fine-grained crystals, do not achieve sufficient purification effects or production volumes in industrial applications. Furthermore, in the method described in Patent Document 3, high yields are not obtained in the crystallization process, and the operating costs of the process for treating crystallization residues increase. To obtain high yields in the crystallization process, the purity of the compound solution supplied to the crystallization process needs to be increased, which increases the operating costs of the pre-crystallization processes, which is disadvantageous. Furthermore, in the method of repeated crystallization described in Patent Document 4, the purity of the compound solution supplied to the crystallization step only needs to be low. However, the crystallization process includes steps to temporarily melt the crystals and to discharge the mother liquor, which complicates the equipment and increases equipment investment and energy consumption, thus being disadvantageous. The present invention was made in view of the above-mentioned situation, and its object is to provide a purification method for obtaining high-purity compounds with high yield and low cost.

[0012] Solution for solving the problem

[0013] The inventors have researched a purification method capable of obtaining high-purity compounds in high yield and at low cost, and discovered that if purification is performed under the following conditions in the following purification method, high-purity compounds can be obtained in high yield and at low cost, thus realizing the present invention. The purification method uses a purification apparatus with a predetermined configuration having a crystallization device and a washing column. The crystallization device has N crystallization tanks or ripening tanks, including at least one crystallization tank. The purification method includes the following steps: separating a slurry containing crystals generated in the crystallization device into a mother liquor and a slurry with increased crystal concentration; and returning at least a portion of the separated mother liquor to the original tank. The process includes: a step of discharging at least a portion of the mother liquor outside the purification apparatus; a step of supplying the purified liquid containing the compound to a crystallization apparatus and mixing it with the slurry in the crystallization apparatus; a step of sequentially conveying the slurry from the downstream tank to the upstream tank among the multiple tanks included in the crystallization apparatus; and a step of supplying at least a portion of the slurry from the crystallization apparatus to a washing column, wherein the condition is that the purity of the mother liquor discharged outside the purification apparatus is lower than that of the purified liquid containing the compound supplied to the purification apparatus, and further, the purity of the mother liquor in the slurry supplied to the washing column, and the difference between the purity of the mother liquor in the slurry and the purity of the mother liquor discharged outside the purification apparatus, are within a specified range.

[0014] That is, the present invention is a method for purifying a compound, characterized in that it uses a purification apparatus having a crystallization device and a washing column. The crystallization device has a crystal formation section, and the washing column has a mechanism for forcibly transporting crystals. The crystallization device has N tanks (N≥2) connected in series with the first tank downstream and the Nth tank upstream. At least the first tank is a crystallization tank with a cooling mechanism, and the second and subsequent tanks are crystallization tanks or ripening tanks. The crystallization device has a pipeline for supplying the purified solution containing the compound to at least one tank, and the washing column has an outlet control system. The crystallization apparatus includes pipelines for supplying slurry from the Nth tank to the cleaning column, pipelines for conveying slurry from a downstream tank to the upstream tank, and pipelines for conveying mother liquor from the upstream tank to each of the 1st to N-1th tanks. At least one of the pipelines conveying slurry from the downstream tank to the upstream tank of the N-1th tank is a pipeline for conveying slurry to the upstream tank via a solid-liquid separation device. The apparatus also includes a pipeline for receiving mother liquor from which crystals have been removed using the solid-liquid separation device. The pipeline returning the mother liquor to the original tank, and the pipeline for transporting the mother liquor from the upstream tank to each of the 1st to N-1th tanks, includes at least one of a pipeline that directly transports the mother liquor from the previous upstream tank and a pipeline that transports the mother liquor from the previous upstream tank via a solid-liquid separation device. The purification method includes the following steps: a step of generating crystals of the compound in a crystallization device; a step of discharging at least a portion of the mother liquor outside the purification device; a step of separating the slurry containing the generated crystals into mother liquor and a slurry with increased crystal concentration; a step of returning at least a portion of the separated mother liquor to the original tank; and a step of... The process includes: supplying a purified liquid containing a compound to a crystallization apparatus for mixing with a slurry in the crystallization apparatus; conveying slurry sequentially from a downstream tank to the upstream tank among a plurality of tanks included in the crystallization apparatus; and supplying at least a portion of the slurry from the crystallization apparatus to a washing column, wherein the purified liquid containing the compound is a liquid with a higher purity than the mother liquor discharged from the purification apparatus, the purity A1 of the mother liquor in the slurry supplied to the washing column is 80 mol% or more, and the difference A1-A2 between A1 and the purity A2 of the discharged mother liquor is 5 mol% or more.

[0015] Preferably, the process includes: conveying the mother liquor from at least one of the second to Nth tanks included in the crystallization apparatus to a downstream tank for adjusting the liquid level in the tank.

[0016] The temperature in the crystallization tank of the crystallization apparatus described above is preferably 1 to 15°C lower than the melting point of the pure substance of the compound being purified.

[0017] The cleaning column mentioned above is preferably a hydraulic cleaning column.

[0018] The residence time in the first to N-1 cells of the crystallization apparatus described above is preferably 0.02 to 6 hours.

[0019] Preferably, it includes a step of further purifying at least a portion of the mother liquor discharged from the purification apparatus by means of distillation and / or crystallization.

[0020] The above-mentioned compound is preferably (meth)acrylic acid.

[0021] The effects of the invention

[0022] By using the purification method of the compounds of the present invention, it is possible to obtain high-purity compounds in high yield and at low cost. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0024] Figure 2 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0025] Figure 3 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0026] Figure 4 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0027] Figure 5 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0028] Figure 6 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0029] Figure 7 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0030] Figure 8 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0031] Figure 9 This is a schematic diagram of an example of a purification apparatus for carrying out the purification method of the present invention.

[0032] Figure 10 This is a schematic diagram of the purification apparatus used to purify the crude acrylic acid solution in Comparative Examples 1 and 2.

[0033] Figure 11 This is a schematic diagram of the purification apparatus used to purify the crude acrylic acid solution in Comparative Example 3. Detailed Implementation

[0034] The present invention will now be described in detail.

[0035] It should be noted that combinations of two or more of the preferred embodiments of the present invention described below are also preferred embodiments of the present invention.

[0036] The purification method of the present invention is characterized in that it is a purification method for a compound using a purification apparatus having a predetermined configuration of a crystallization device and a washing column, wherein the crystallization device has N crystallization tanks or aging tanks including at least one crystallization tank, and the washing column has a mechanism for forcibly transporting crystals. The purification method includes the following steps: a step of generating crystals of the compound in the crystallization device; a step of discharging at least a portion of the mother liquor outside the purification apparatus; a step of separating the slurry containing the generated crystals into a mother liquor and a slurry with increased crystal concentration; a step of returning at least a portion of the separated mother liquor to the original tank; and a step of purifying the compound containing the crystals... The process includes: a step of supplying the purified solution of the compound to a crystallization apparatus and mixing it with the slurry in the crystallization apparatus; a step of sequentially conveying the slurry from the downstream tank to the upstream tank among the multiple tanks included in the crystallization apparatus; and a step of supplying at least a portion of the slurry from the crystallization apparatus to a washing column, wherein the purified solution containing the compound is a liquid with a higher purity than the mother liquor discharged from the purification apparatus, and the purification is performed under the conditions that the purity A1 of the mother liquor in the slurry supplied to the washing column is 80 mol% or more, and the difference between the purity A1 of the mother liquor and the purity A2 of the mother liquor discharged from the purification apparatus is 5 mol% or more.

[0037] If a crystallization device is used to separate the mother liquor from a slurry containing compound crystals, and the slurry with a crystal concentration increased until the purity A1 of the mother liquor reaches 80 mol% or more is fed to a cleaning column, the slurry fed to the cleaning column contains less impurities. This reduces the amount of cleaning solution used in the cleaning column, thereby increasing the yield of crystals recovered from the purification device and reducing variable costs.

[0038] Furthermore, if the difference between the purity A1 of the mother liquor in the slurry supplied to the washing column and the purity A2 of the mother liquor discharged to the purification device is 5 mol% or more, it can be said that the purified liquid sufficiently generates crystals of the compound in the crystallization device, and the impurities are concentrated in the mother liquor and discharged to the purification device. Thus, more compounds can be obtained in the form of a product and in a high yield from the purified liquid containing the compound supplied to the purification device.

[0039] The purity A1 of the mother liquor in the slurry supplied to the above-mentioned cleaning column is only required to be 80 mol% or more, preferably 82 mol% or more. More preferably 83 mol% or more, and even more preferably 84 mol% or more.

[0040] Furthermore, the difference between the purity A1 of the mother liquor in the slurry supplied to the cleaning column and the purity A2 of the mother liquor discharged from the purification device is only 5 mol% or more, preferably 6.5 mol% or more. More preferably, it is 8 mol% or more, and even more preferably 10 mol% or more.

[0041] It should be noted that the purity of the mother liquor in this invention refers to the ratio of the number of moles of the compound to be purified in the mother liquor to the total number of moles of the compound to be purified and other impurities (byproducts, solvents, polymerization inhibitors, etc.).

[0042] The purification apparatus used in the purification method of the present invention comprises a crystallization device with N tanks (N≥2) connected in series and a cleaning column for forced crystal transport. The crystallization device includes at least a first tank equipped with a cooling mechanism, and the second and subsequent tanks are either crystallization tanks or maturation tanks. The Nth tank is connected to the cleaning column. Slurry is sequentially transported from the downstream tank to the upstream tank and from the Nth tank to the cleaning column. Furthermore, at least one of the pipelines transporting slurry sequentially from the downstream tank to the upstream tank is a pipeline transporting slurry to the upstream tank via a solid-liquid separation device, and has a pipeline for returning at least a portion of the mother liquor discharged from the solid-liquid separation device back to the original tank. Furthermore, in the purification apparatus of the present invention, each of the first to N-1 tanks in the crystallization device has at least one of a pipeline directly transporting mother liquor from the upstream tank and a pipeline transporting mother liquor from the upstream tank via a solid-liquid separation device, and also has a pipeline for transporting mother liquor outside the purification apparatus.

[0043] By connecting multiple crystallization tanks or ripening tanks in series, the suspension of compound crystals and mother liquor (i.e., slurry) is sequentially transported to the upstream tank. Simultaneously, the mother liquor is transported from the upstream tank to the downstream tank, allowing for convective contact with the crystals. This process increases the purity of both the crystals and the mother liquor as it moves upstream. Furthermore, by using as many solid-liquid separation devices as possible, the slurry is concentrated and transported to the upstream tank, thereby more effectively improving the purity of both the crystals and the mother liquor.

[0044] Therefore, in the purification apparatus of the present invention, the pipeline for conveying the mother liquor to the outside of the purification apparatus is preferably a pipeline for conveying the mother liquor to the outside of the purification apparatus from the downstream tank, thereby enabling less discharge of low-purity mother liquor (crystallization residue) concentrated with impurities from the downstream tank, and enabling the high-purity compound to be obtained in high yield.

[0045] In addition, in the cleaning column, a portion of the liquid obtained by heating and melting the purified crystals is used as the cleaning solution (reflux liquid) and convectively contacts the crystallization bed to improve the purity of the crystals. By supplying high-purity crystals and mother liquor from the Nth tank to the cleaning column, the amount of the cleaning solution can be reduced.

[0046] That is, the step of generating compound crystals in the crystallization apparatus of the purification method of the present invention is the step of generating compound crystals in the crystallization tank of the crystallization apparatus, and the step of separating the slurry containing crystals into mother liquor and slurry with increased crystal concentration is the step of separating the slurry containing crystals into mother liquor and slurry with increased crystal concentration using a solid-liquid separation device.

[0047] Furthermore, the purification method of the present invention includes: using a crystallization apparatus having multiple crystallization tanks or ripening tanks connected in series, each including at least one crystallization tank, a step of conveying slurry taken from a downstream tank to an upstream tank, wherein at least one of this step involves conveying the slurry taken from the tank to the upstream tank via a solid-liquid separation device. Additionally, the step of supplying at least a portion of the slurry from the crystallization apparatus to a washing column is a step of supplying at least a portion of the slurry from the most upstream tank included in the crystallization apparatus to the washing column.

[0048] Furthermore, in the purification apparatus used in the purification method of the present invention, at least one of the pipelines that sequentially transport slurry from the downstream tank to the upstream tank has a pipeline that transports slurry to the upstream tank via a solid-liquid separation device. By operating in this way, crystals can be prevented from being transported to the downstream tank, effectively improving the purity within the upstream tank and facilitating purification in subsequent processes (washing columns).

[0049] Of the N-1 pipelines that transport slurry from the downstream tank to the upstream tank, the proportion of pipelines that transport slurry to the upstream tank via the solid-liquid separation device is preferably 60% or more. Most preferably, it is 100%, that is, all N-1 pipelines that transport slurry from the downstream tank to the upstream tank are pipelines that transport slurry to the upstream tank via the solid-liquid separation device.

[0050] The tanks included in the crystallization apparatus described above have a pipeline for conveying slurry to the upstream tank via a solid-liquid separation device, and a pipeline for returning at least a portion of the mother liquor discharged from the solid-liquid separation device back to the original tank. The slurry containing concentrated crystals that has been separated by the solid-liquid separation device is conveyed to the upstream tank, and at least a portion of the remaining mother liquor is returned to the original tank.

[0051] Furthermore, in the aforementioned crystallization apparatus, each of the first to N-1 tanks is provided with at least one of the following: a pipeline for directly supplying mother liquor from the upstream tank and a pipeline for supplying mother liquor from the upstream tank via a solid-liquid separation device. By having these pipelines, the liquid level in the tank can be kept constant.

[0052] Thus, the purification method of the compound of the present invention includes a step of adjusting the liquid level of the tank by transferring the mother liquor to the next downstream tank for all of the 2nd to Nth tanks included in the crystallization apparatus.

[0053] In the purification apparatus of the present invention, preferably, at least one of the first to N-1 tanks included in the crystallization apparatus has a pipeline for directly conveying mother liquor from the upstream preceding tank. More preferably, the N-1 tank has a pipeline for directly conveying mother liquor from the upstream preceding tank (the Nth tank).

[0054] That is, a suitable embodiment of the purification method of the compound of the present invention includes a step of directly conveying the mother liquor from at least one of the 2nd to Nth tanks included in the crystallization apparatus to the next downstream tank, and more preferably includes a step of directly conveying the mother liquor from the Nth tank to the next downstream tank.

[0055] The reasons for preferring a pipeline that directly supplies mother liquor from the Nth tank to the (N-1)th tank are explained below.

[0056] One known method for directly conveying mother liquor from the tank is to establish a crystal settling zone at the top of the tank and then convey crystal-free mother liquor (hereinafter sometimes referred to as clarified mother liquor) from this zone via overflow. This method has the advantages of not requiring a delivery pump and facilitating easy adjustment of the liquid level in each tank.

[0057] However, in this method, the tank structure becomes complex because a crystal settling zone is needed at the top. Furthermore, in cases of purifying compounds that produce fine crystals or purifying low-purity compound solutions, the slow crystal settling rate necessitates excessively large tank sizes to accommodate the settling zone design. Additionally, if the crystals are too fine, they may be transported downstream if a settling zone cannot be formed effectively, sometimes reducing the purification efficiency of the device.

[0058] If the crystallization apparatus described above includes a tank with a pipeline for conveying mother liquor from the upstream tank via a solid-liquid separation device, then solid-liquid separation can effectively suppress the flow of crystals from the upstream tank to the downstream side and maintain a constant liquid level in the tank. Therefore, even when the purification apparatus is used to purify compounds that generate fine crystals with slow crystal settling rates, the purification efficiency of the apparatus can be maintained at a high level. Furthermore, the tank itself does not need to have a crystal settling area for obtaining the mother liquor, thus reducing the size of the tank itself.

[0059] Therefore, among the pipelines that transport mother liquor from the upstream tank to each of the 1st to N-1th tanks, at least one is preferably a pipeline that transports mother liquor from the previous upstream tank via a solid-liquid separation device.

[0060] That is, a suitable embodiment of the compound purification method of the present invention includes the step of conveying mother liquor from at least one of the 2nd to Nth tanks included in the crystallization apparatus to the next downstream tank via a solid-liquid separation device.

[0061] In the case of a pipeline that transports mother liquor from the tank included in the crystallization unit to the next downstream tank via a solid-liquid separation unit, from the viewpoint of the cost of the purification unit itself and the operating cost of the unit, it is preferable to share the solid-liquid separation unit installed in the pipeline that transports slurry to the previous upstream tank. By doing so, the number of solid-liquid separation units and liquid delivery pumps can be reduced.

[0062] In this case, the device can be configured as follows: a solid-liquid separation device installed in the pipeline that transports slurry from the upstream tank returns the mother liquor to the original tank, and one or more additional pipelines for transporting the mother liquor are further provided, connected to the next tank downstream of the original tank. Alternatively, the device can be configured such that the additional pipeline further branches, connecting to two or more tanks downstream of the next tank downstream of the original tank. Furthermore, the additional pipeline can be connected outside the purification device.

[0063] One suitable embodiment of the purification apparatus for carrying out the purification method of the present invention is that the crystallization apparatus is configured such that at least one of the solid-liquid separation devices provided in the pipeline for conveying slurry from the downstream tank to the upstream tank has, in addition to having a pipeline for returning the mother liquor to the original tank, one or more additional pipelines for conveying the mother liquor, which are connected to the tank and / or purification apparatus that are downstream of the original tank.

[0064] Therefore, a suitable embodiment of the purification method for the compound of the present invention includes the following steps: conveying mother liquor from at least one of the 2nd to Nth tanks included in the crystallization apparatus to the original tank and the next downstream tank, or to the next downstream tank and further to the next two or more downstream tanks or outside the purification apparatus via a solid-liquid separation device.

[0065] Among the solid-liquid separation devices installed in pipelines that transport slurry from downstream tanks to upstream tanks, the proportion of solid-liquid separation devices having such additional pipelines is preferably 30% or more, more preferably 60% or more, and even more preferably 100%.

[0066] As the aforementioned solid-liquid separation device, common methods such as basket-type centrifuges, decanting centrifuges, liquid hydrocyclones, filters, and centrifuges can be used. Examples of basket-type centrifuges include the Escher-Weiss extrusion centrifuge from Tsukishima Machinery Co., Ltd., and examples of decanting centrifuges include the Bird-decanting centrifuge from Tsukishima Machinery Co., Ltd., and the screw decanting centrifuge from IHI Corporation.

[0067] When using a basket-type centrifuge, the crystal concentration in the filter cake after solid-liquid separation is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0068] When using a decanting centrifuge, the concentration of the concentrated crystals is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more.

[0069] When using a liquid hydrocyclone separator, the crystal concentration in the concentrated slurry is preferably 25% or more, more preferably 30% or more, and even more preferably 35% or more. If the slurry concentration is excessively increased, the fluidity decreases and the risk of pipe blockage increases. Therefore, the concentration of the concentrated slurry is preferably 55% or less, more preferably 50% or less, and even more preferably 45% or less.

[0070] While using basket-type centrifuges and decanting centrifuges as solid-liquid separation devices increases initial investment and operating costs, they also offer high slurry (crystal) concentration efficiency, thus improving compound purification efficiency. Conversely, using liquid hydrocyclones results in lower slurry (crystal) concentration efficiency, requiring multiple tanks within the crystallization unit to achieve sufficient purification. However, this approach offers advantages such as lower initial investment and operating costs, and the elimination of malfunctions originating from the hydrocyclone.

[0071] The aforementioned crystallization apparatus includes multiple crystallization tanks or maturation tanks, with at least one crystallization tank. The total number of crystallization tanks and maturation tanks is not particularly limited. From the viewpoint of maximizing the purity of the crystals and mother liquor, when using a basket-type centrifuge or a decanting-type centrifuge as the solid-liquid separation device, two or more are preferred; otherwise, three or more are preferred. Furthermore, the more tanks there are, the greater the effect on improving the purity of the crystals and mother liquor. However, too many tanks increase equipment investment and the power consumption of pumps, agitators, etc., attached to the tanks, which becomes disadvantageous. Therefore, the total number of crystallization tanks and maturation tanks does not depend on the type of solid-liquid separation device and is preferably six or less. More preferably, five or less.

[0072] The crystallization apparatus described above only needs to include at least one crystallization tank. The other tanks can be either crystallization tanks or ripening tanks. Preferably, the crystallization apparatus includes 0 to 2 ripening tanks. More preferably, it includes 0 to 1.

[0073] The crystallization apparatus described above preferably includes a tank structure capable of forming a layer of clear mother liquor at the top. If any of the 1st to N-1th tanks in the crystallization apparatus has a pipeline for directly conveying mother liquor from the upstream tank, this pipeline is preferably a pipeline that directly conveys the layer of clear mother liquor at the top of the upstream tank via overflow. Furthermore, one suitable embodiment of the purification apparatus for carrying out the purification method of the present invention is a pipeline that discharges mother liquor to the outside of the purification apparatus via overflow.

[0074] The purification apparatus of the present invention preferably has a pipeline for conveying the mother liquor from the first downstream tank included in the crystallization device to the outside of the purification apparatus. This pipeline is one of the suitable embodiments of the purification apparatus of the present invention, which is a pipeline for conveying the layer of clarified mother liquor in the upper part of the first tank included in the crystallization device to the outside of the purification apparatus by overflow.

[0075] Therefore, a suitable embodiment of the purification method of the compound of the present invention includes a step of directly conveying the layer of clarified mother liquor at the top of at least one of the second to Nth tanks included in the crystallization apparatus to the downstream tank by overflow. A suitable embodiment of the purification method of the compound of the present invention also includes a step of directly discharging the layer of clarified mother liquor at the top of the tank to the outside of the purification apparatus by overflow from the first tank at the downstream end.

[0076] If the tank included in the aforementioned crystallization apparatus does not form a layer of clear mother liquor at the top, a solid-liquid separation device can be provided. This device separates the mother liquor and crystals from the slurry taken from the tank and transports the mother liquor to one or more downstream tanks. Alternatively, the mother liquor separated by the solid-liquid separation device can be discharged outside the purification apparatus. One suitable embodiment of the purification apparatus for carrying out the purification method of the present invention is a pipeline that discharges the mother liquor from the first tank included in the crystallization apparatus to the purification apparatus via the solid-liquid separation device.

[0077] Furthermore, the purification method for the compounds of the present invention preferably includes a step of repurifying at least a portion of the mother liquor discharged from the purification apparatus by distillation and / or crystallization. By repurifying at least a portion of the mother liquor discharged from the purification apparatus and recovering the compounds contained in the discharged mother liquor, the amount of compounds contained in the residue discharged from the purification apparatus can be reduced. The recovered compounds can be reintroduced into the purification apparatus along with the purified liquid supplied to the purification apparatus, or they can be returned to the preceding step for obtaining the purified liquid. Therefore, a suitable embodiment of the purification method of the present invention includes a step of reintroducing the compounds recovered through the above-described repurification step into the purification apparatus, or returning the recovered compounds to the preceding step for obtaining the purified liquid.

[0078] Preferably, in the crystallization apparatus described above, of the 1st to N-1th tanks, at least 30%, more preferably at least 60%, and most preferably all tanks up to the N-1th tank, the mother liquor is conveyed via a solid-liquid separation device to the next downstream tank (or two or more downstream tanks further downstream) and / or discharged outside the crystallization apparatus. This reduces the size of the tanks, thereby reducing investment and construction area. Furthermore, as mentioned above, from a cost perspective, it is preferable that the solid-liquid separation device in this case shares a common solid-liquid separation device within the pipeline that conveys the slurry to the previous upstream tank.

[0079] In order to maintain and mature the slurry supplied to the cleaning column, the capacity of the Nth tank is preferably larger than that of the downstream tank. This increases the purity of the slurry, and the crystal diameter is more likely to grow significantly compared to the downstream tank. Therefore, it is easier to design the crystal settling zone at the top of the tank, in other words, the layer of clarified mother liquor. Therefore, it is preferable that the Nth tank is designed to directly supply mother liquor to the downstream tank via overflow.

[0080] Therefore, a suitable embodiment of the compound purification method of the present invention includes a step of directly conveying the layer of clarified mother liquor at the top of the Nth tank of the crystallization apparatus to the downstream tank via overflow.

[0081] The crystallization apparatus described above includes a crystallization tank equipped with a cooling mechanism. There are no particular limitations as long as the solution of the compound is cooled to precipitate crystals and generate a slurry containing crystals and mother liquor. Broadly speaking, it can be categorized as follows: the tank itself has a cooling jacket, directly cooling the tank to generate crystals; or the cooling mechanism is separate from the tank, connected via piping, and circulates while simultaneously cooling / generating crystals.

[0082] While the method of attaching a cooling jacket to the tank itself has the advantage of requiring fewer pieces of equipment, it requires increasing the size of the tank itself to increase the heat transfer area. When high production capacity is required, the tank size is too large, which has disadvantages in terms of initial investment and floor space.

[0083] Therefore, in cases where the size of the tank itself is limited or in the purification of compounds requiring high production capacity, a tank in the form of one where the contents of the tank are cooled outside the tank is preferred. In this way, if the tank and the cooling mechanism are connected by piping, and a portion of the compound solution (or slurry containing crystals) in the tank is supplied to the cooling mechanism, crystals are generated within the cooling mechanism, and the slurry containing the generated crystals is returned to the tank, then by adding a cooling mechanism, the heat transfer area can be easily increased, and the batch production of crystallization tanks can be easily scaled up.

[0084] In this case, there is no particular limitation on the cooling mechanism, as long as it can cool the compound solution and cause crystals to precipitate. However, it is preferable to use shell and tube heat exchangers, spiral heat exchangers, etc., which can ensure a large heat transfer area, or cooling disc crystallizers, scraping cooling crystallizers, etc., which perform crystallization while scraping the cooling surface.

[0085] A cooling disc crystallizer simply cools the solution of the compound to cause crystals to precipitate, and then scrapes off the precipitated crystals. A crystallizer with the following structure can be used: it consists of a tube and multiple cooling plates that are separated from each other. Crystals are generated on the walls of the cooling plates, and stirring blades with scrapers rotate inside the tube to scrape off the crystals.

[0086] A scraping-type cooling crystallizer simply cools the compound solution to cause crystals to precipitate, and then scrapes off the precipitated crystals. A crystallizer with the following structure can be used: it consists of a double-layered tube, in which refrigerant flows through the outer tube and a compound solution (or a slurry containing crystals) flows through the inner tube. Crystals are formed on the wall of the inner tube, and a shaft with scraping blades rotates inside the inner tube to scrape off the crystals.

[0087] Therefore, a suitable embodiment of the purification method for the compound of the present invention is that the step of generating compound crystals in the crystallization apparatus of the purification method for the compound of the present invention is to transport a portion of the compound solution (or slurry containing crystals) in the tank to a cooling mechanism and generate crystals in the cooling mechanism, and then return the slurry containing the generated crystals to the tank.

[0088] The crystallization apparatus described above may or may not have a aging tank, but it is preferred to have one. In this invention, the aging tank does not have a cooling mechanism for crystal precipitation; instead, it is a tank that allows the compound crystals to grow by holding them in place for a certain period of time. By growing the crystals, making them as uniform as possible, and then conveying them to the cleaning column, impurities can be removed efficiently in the cleaning column, and a higher purity compound can be obtained with a high yield. Therefore, it is preferable that the tank conveyed to the cleaning column, i.e., the Nth tank, is a aging tank.

[0089] Therefore, the purification method of the compound of the present invention preferably includes a step of aging the slurry containing the compound crystals in an aging tank. When using the crystallization apparatus having N tanks, it is preferable to include a step of aging the slurry containing the compound crystals in the Nth tank at the uppermost end of the crystallization apparatus, i.e., the aging tank.

[0090] The aforementioned aging tank is not particularly limited as long as it can keep the compound crystals in a suspended state within the tank. By holding the crystals for a certain period of time, the fine crystals are melted through Ostwald aging, further growing into larger crystals with a narrower crystal diameter distribution, which can further improve the purification efficiency in the washing column. Furthermore, even with a crystallization tank, by holding the crystals for a certain period of time, the same effect as the aging tank can be expected.

[0091] A slurry containing compound crystals is fed from the crystallization apparatus into a cleaning column of the purification apparatus used in the purification method of the present invention, where the crystals are cleaned to obtain high-purity compound crystals in the form of a product. In the preferred embodiment of the cleaning column of the present invention, when the specific gravity of the crystals is greater than that of the mother liquor, the crystals move downward within the column to form a crystallization bed. Furthermore, the crystallization bed is shaving off at the bottom of the column, heated and melted, and a portion of the resulting molten liquid is removed in the form of a product. The remaining molten liquid, in the form of a cleaning liquid, comes into convective contact with the crystallization bed, which can be used to improve crystal purity. Additionally, the mother liquor and cleaning liquid in the cleaning column are returned to the crystallization apparatus via a line that returns the liquid to the crystallization apparatus. When the specific gravity of the crystals is less than that of the mother liquor, in the opposite manner, the crystals move upward within the column, and the crystallization bed is suspended, melted, and the product is removed at the top of the column.

[0092] In the purification apparatus of the particularly preferred embodiment of the present invention described above, the line for returning the mother liquor to the crystallization apparatus is connected to at least the Nth tank, and may be further connected to a downstream tank. Additionally, a line may be included to return a portion of the mother liquor back to the washing column.

[0093] Therefore, in the purification method of the compound of the present invention, when using the crystallization apparatus having N tanks as described above, it is preferable to include a step of conveying a slurry containing compound crystals from the Nth tank of the crystallization apparatus to a cleaning column. Additionally, it is preferable to include the following steps: removing a portion of the crystals from the bottom of the cleaning column and heating and melting them; removing a portion of the resulting melt as a product; returning the remaining melt to the cleaning column and subjecting it to convective contact with the crystallization bed within the column to clean the crystals.

[0094] Furthermore, the purification method for the compound of the present invention preferably includes a step of returning the mother liquor from the washing column to the crystallization apparatus. When using the crystallization apparatus having N tanks described above, it is preferable to include a step of returning the mother liquor from the washing column to the Nth tank of the crystallization apparatus, and then returning it to a downstream tank. Furthermore, it may include a step of returning a portion of the mother liquor taken from the washing column back to the washing column.

[0095] The cleaning column in this invention is a cleaning column that forcibly transports the crystallization bed. Specifically, examples include mechanical cleaning columns that use pistons to compact crystals to form / transport the crystallization bed; and hydraulic cleaning columns (water pressure cleaning columns) that use pumps to deliver slurry to the column and extract mother liquor from a filter located within the column to form / transport the bed. The working principles of these cleaning columns are described in the book *Melt Crystallization* (Edited by Joachim Ulrich, Heike Glade, Shaker Verlag, Aachen 2003).

[0096] There are no particular limitations on the type of cleaning column, as long as it can clean crystals; it can be either a mechanical or hydraulic cleaning column. Mechanical cleaning columns are characterized by high operational stability and high compound purification efficiency. On the other hand, hydraulic cleaning columns are characterized by high production capacity per unit column cross-sectional area, fewer driving components within the cleaning column, and fewer malfunctions caused by the device. When purifying easily polymerizable substances, using a hydraulic cleaning column with fewer driving components can sometimes suppress polymer formation within the cleaning column.

[0097] As a preferred type of cleaning column, a cleaning column having a mechanical structure for cutting the crystallization bed can be cited (see US Patent 3872009A). In a cleaning column having a forced conveying mechanism for the crystallization bed, a method is used to cut the purified crystallization bed with a scraper or the like, so that it is resuspended and then melted.

[0098] Another preferred form of cleaning column is a cleaning column that does not have a mechanical structure for cutting the crystallization bed (see US Patent 7425273B2). In this method, the crystallization bed is cut by the dynamic pressure of the circulating fluid; since there are no sliding surfaces such as shaft seals, the generation of polymers caused by liquid retention, sliding heat, etc., can sometimes be suppressed when purifying easily polymerizable substances.

[0099] The compound solution, which is the liquid to be purified, can be supplied to any tank included in the crystallization apparatus in the purification apparatus for the purification method of the present invention. From the viewpoint of purification efficiency, it is preferable to supply the second and subsequent tanks.

[0100] Therefore, in the purification method of the compound of the present invention, when using a crystallization apparatus having multiple tanks, it is preferable to include a step of supplying a solution containing the compound as a purification solution to the second and subsequent tanks.

[0101] The optimal location varies depending on the composition of the feed liquid, the crystallization yield, and the crystal concentration efficiency in the solid-liquid separation device, and can therefore be selected appropriately.

[0102] The crystallization temperature in the crystallization tank of the purification method of the present invention can be adjusted appropriately according to the type of compound being purified. It is generally within the range of -1 to -15°C, preferably -1.5 to -13.5°C, more preferably -3.5 to -12.5°C, and even more preferably -5 to -11.5°C, relative to the melting point of the pure substance. When the 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. Therefore, the step of generating compound crystals in the crystallization apparatus of the purification method of the present invention is preferably carried out at these temperatures.

[0103] If the temperature of the crystallizer is high, high-purity crystals will be formed. However, if a scraper-type cooling crystallizer is used in the crystallizer, as described later, it may result in problems such as requiring more power to scrape the crystals from the crystallizer. In addition, if the temperature difference between the refrigerant and the crystallizer is too high, for example, if a scraper-type cooling crystallizer is used in the crystallizer, it may result in problems such as blockage of the scraper, which may make it difficult to continue operation.

[0104] Therefore, under high crystallization tank temperatures, it is necessary to reduce the temperature difference between the refrigerant and the crystallization tank to decrease the amount of crystals formed per unit heat transfer area. If the crystallization tank temperature is low, the purity of the formed crystals decreases. However, when a scraping-type cooling crystallizer is used in the crystallization tank, the power required to scrape the crystals in the tank is small, and even if the temperature difference between the refrigerant and the crystallization tank is increased, it is difficult to cause blockage of the scraper. As a result, the temperature difference between the refrigerant and the crystallization tank can be increased, increasing the amount of crystals formed per unit heat transfer area. However, if the crystallization temperature is too low, there is a tendency for the formed crystals to have smaller particle sizes and for the crystals to be difficult to settle.

[0105] The residence time of compounds in the crystallization tank and the ripening tank can be adjusted appropriately according to the type of compound to be purified. However, considering the yield of the purified compound, the purification efficiency, and the equipment investment cost, the residence time in the first to N-1 tanks of the crystallization device is approximately 0.02 to 6 hours.

[0106] Regarding the Nth tank, in order to adjust the particle size distribution of the slurry delivered to the cleaning column and reduce the reflux ratio (cleaning liquid flow rate / purified acrylic acid flow rate) in the cleaning column, the residence time is preferably longer than a certain level, preferably 0.5 to 6 hours, more preferably 1 to 5 hours, and even more preferably 1.2 to 4.5 hours.

[0107] Furthermore, for the first to N-1 tanks, since they are not connected to the cleaning column, a longer residence time is not necessarily required. Shortening the residence time allows for a reduction in the size of the tank itself, which is advantageous in terms of equipment investment costs. Therefore, for the first to N-1 tanks, the residence time is preferably 0.03 to 4 hours, more preferably 0.04 to 3 hours, further preferably 0.05 to 2 hours, and most preferably 0.1 to 1.5 hours.

[0108] It should be noted that the residence time of the compound in the crystallization tank mentioned here refers to the residence time within the cooling mechanisms inside and outside the tank, in the case where the crystallization tank is of the type described later where the contents of the tank are cooled outside the tank. It should also be noted that the residence time of each tank is calculated as follows: the total capacity of the tank and the external cooling mechanism divided by the sum of the flow rate of the slurry supplied from that tank to the upstream tank or cleaning column and the flow rate of the liquid transported / discharged from each tank to the downstream tank or purification unit.

[0109] The purification method of the present invention can be used for the purification of any compound, but as mentioned above, it is also suitable for the purification of crystals with poor sedimentation properties, and therefore suitable for the purification of (meth)acrylic acid. Therefore, purifying (meth)acrylic acid using the purification method of the present invention is one of the preferred embodiments of the present invention.

[0110] In this case, the compound solution supplied to the purification method of the present invention is an aqueous solution of (meth)acrylic acid or a crude (meth)acrylic acid solution. An aqueous solution of (meth)acrylic acid refers to a solution in which (meth)acrylic acid is dissolved in water. A crude (meth)acrylic acid solution refers to a solution containing (meth)acrylic acid, which contains impurities such as byproducts from the manufacture of (meth)acrylic acid. These solutions can be obtained, for example, by capturing the gaseous product of the compound obtained through the gas-phase oxidation reaction of propylene and isobutylene in an absorption tower and distilling it as needed, but are not limited to solutions synthesized in-house; solutions purchased from elsewhere can also be used. Cooling the aqueous or crude (meth)acrylic acid solution, for example, can yield a slurry containing (meth)acrylic acid crystals.

[0111] It should be noted that the aforementioned byproducts may 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 and orthoamino acids. In addition, solvents such as toluene and methyl butyl ketone may sometimes be included.

[0112] In this specification, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0113] An example of the purification apparatus used in the purification method of the present invention is shown below. Figures 1-9 .

[0114] Figure 1 In this device, which is a crystallization apparatus, there is a crystallization tank and a maturation tank. It is equipped with a pipeline that directly supplies mother liquor from the maturation tank, which is the upstream tank, to the crystallization tank, and a pipeline that directly discharges residue (mother liquor) from the crystallization tank, which is the downstream tank.

[0115] The compound solution 1 supplied to the purification unit is introduced into the maturation tank 21. The slurry, cooled in the crystallization tank 11 equipped with a cooling mechanism and containing precipitated crystals, is transported to the solid-liquid separation unit 31 via pipeline 51. In the solid-liquid separation unit 31, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is transported to the adjacent maturation tank 21 via pipeline 52, while the mother liquor is returned to the crystallization tank 11 via pipeline 61. Additionally, residue 2 is discharged from the crystallization tank 11 to the outside of the purification unit via pipeline 71, adjusting the liquid level in the crystallization tank 11. After crystal growth in the maturation tank 21, the crystal slurry is transported to the mechanical cleaning column 41 via pipeline 53. Furthermore, to adjust the liquid level in the maturation tank 21, mother liquor is directly supplied from the maturation tank 21 to the crystallization tank 11 via pipeline 72.

[0116] Within the mechanical cleaning column 41, crystals are compacted by a piston to form a crystallization bed. Then, the crystallization bed is cut, the circulating liquid is suspended, and the crystals are heated and melted at the bottom of the column. A portion of the circulating liquid, containing the resulting melt, is removed as high-purity compound 3. The remaining portion of the circulating liquid (cleaning liquid) is returned to the mechanical cleaning column 41, where it convects with the crystallization bed to clean the crystals. Furthermore, the mother liquor in the cleaning column is returned to the ripening tank 21 via the line 75 that returns the mother liquor to the crystallization apparatus. This purification process yields a high-purity compound.

[0117] Figure 2 In this system, the crystallization apparatus comprises one crystallization tank and one ripening tank. The crystallization tank is equipped with a pipeline that directly supplies mother liquor from the upstream ripening tank, and a pipeline that discharges residue (mother liquor) from the downstream crystallization tank via a solid-liquid separation device. Furthermore, a hydraulic cleaning column is used as the cleaning column. The following only describes the... Figure 1Different parts of the purification device.

[0118] The slurry containing precipitated crystals, cooled in the crystallization tank 11 equipped with a cooling mechanism, is transported by pipeline 51 to the solid-liquid separation device 31. In the solid-liquid separation device 31, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is transported by pipeline 52 to the adjacent ripening tank 21. A portion of the mother liquor is returned to the crystallization tank 11 via pipeline 61, and the remainder is discharged outside the purification device as residue 2 via pipeline 101, adjusting the liquid level in the crystallization tank 11.

[0119] Furthermore, in the hydraulic cleaning column 43, crystals move downwards to form a crystallization bed. The crystallization bed is then shaved, suspended in the circulating fluid, and heated to melt at the bottom of the column. This hydraulic cleaning column 43 does not have a mechanical mechanism for shaving the crystallization bed; instead, the shaving is performed by the dynamic pressure of the circulating fluid.

[0120] Figure 3 In this crystallization apparatus, there is one crystallization tank and one ripening tank. A pipeline is installed to directly supply mother liquor from the upstream ripening tank to the crystallization tank, and a pipeline is installed to directly discharge residue (mother liquor) from the downstream crystallization tank. Furthermore, the crystallization tank is used in the form of an external cooling tank for the contents of the crystallization tank. The following discussion focuses only on... Figure 1 The different parts of the purification device will be explained.

[0121] The crystallization tank 11 consists of a tank 11A and an external cooling mechanism 11B, connected by pipelines 111 and 121. The compound solution (or a slurry containing crystals of the compound) transported from tank 11A to the cooling mechanism 11B via pipeline 111 is cooled in the cooling mechanism 11B. The slurry containing the precipitated crystals is transported back to tank 11A via pipeline 121. A portion of the slurry containing the compound crystals is transported from tank 11A to the cooling mechanism 11B via pipeline 111, and the remaining slurry is transported to the solid-liquid separation device 31 via pipeline 51.

[0122] Figure 4 In this crystallization apparatus, there are two crystallization tanks. A pipeline is provided to directly supply mother liquor from the upstream crystallization tank 12 to the crystallization tank 11, and a pipeline is provided to directly discharge residue (mother liquor) from the downstream crystallization apparatus 11. Furthermore, a hydraulic cleaning column is used as the cleaning column. The following only addresses... Figure 1 The different parts of the purification device will be explained.

[0123] The compound solution 1 supplied to the purification device is introduced into the crystallization tank 12.

[0124] The crystallization tank 11 consists of a tank 11A and an external cooling mechanism 11B, connected by pipelines 111 and 121. The compound solution (or crystal slurry containing the compound) transported from tank 11A to cooling mechanism 11B via pipeline 111 is cooled in cooling mechanism 11B, while the slurry containing precipitated crystals is transported back to tank 11A via pipeline 121. A portion of the slurry containing the compound crystals is transported from tank 11A to cooling mechanism 11B via pipeline 111, and the remaining slurry is transported to solid-liquid separation device 31 via pipeline 51.

[0125] The crystallization tank 12 is also composed of a tank 12A and an external cooling mechanism 12B, which are connected by pipelines 112 and 122. A portion of the slurry containing the crystals of the compound is transported from the tank 12A to the cooling mechanism 12B through pipeline 112, and then returned to the tank 12A through pipeline 122.

[0126] Crystal slurry is transported from the crystallization tank 12 to the hydraulic cleaning column 42 via pipeline 53. At the bottom of the hydraulic cleaning column 42, a mechanical mechanism (scraper) scrapes the crystallization bed, suspending it in the circulating liquid while heating and melting it. A portion of the circulating liquid containing the resulting melt is removed in the form of high-purity compound 3. A portion of the remaining circulating liquid (cleaning liquid) is returned to the hydraulic cleaning column 42 to clean the crystals through convective contact with the crystallization bed. Additionally, the mother liquor in the cleaning column is returned to the crystallization tank 12 via pipeline 75, which returns the mother liquor to the crystallization apparatus.

[0127] Figure 5 In this system, the crystallization apparatus comprises two crystallization tanks and one ripening tank. A pipeline connects the three tanks, directly supplying mother liquor from the upstream tank and discharging residue (mother liquor) directly from the downstream tank. Furthermore, the cleaning column is hydraulic and includes a mechanical mechanism for abrading the crystallization bed. The following discussion focuses only on... Figure 1 The different parts of the purification device will be explained.

[0128] The slurry containing precipitated crystals, cooled in the crystallization tank 11 equipped with a cooling mechanism, is conveyed to the solid-liquid separation unit 31 via pipeline 51. In the solid-liquid separation unit 31, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is conveyed to the adjacent crystallization tank 12 via pipeline 52, while the mother liquor is returned to the crystallization tank 11 via pipeline 61. Additionally, residue 2 is discharged from the crystallization tank 11 to the outside of the purification unit via pipeline 71, and the liquid level in the crystallization tank 11 is adjusted. The same operation is performed in the crystallization tank 12 as in the crystallization tank 11, where the slurry containing crystals is conveyed from the crystallization tank 12 to the solid-liquid separation unit 32 via pipeline 53. In the solid-liquid separation unit 32, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is conveyed to the adjacent ripening tank 21 via pipeline 54, while the mother liquor is returned to the crystallization tank 12 via pipeline 62. In addition, to adjust the liquid level in the crystallization tank 12, mother liquor is directly supplied from the crystallization tank 12 to the crystallization tank 11 via pipeline 72. After crystal growth in the maturation tank 21, the crystal slurry is transported to the hydraulic cleaning column 42 via pipeline 55. Furthermore, to adjust the liquid level in the maturation tank 21, mother liquor is directly supplied from the maturation tank 21 to the crystallization tank 12 via pipeline 73 connecting the maturation tank 21 and the crystallization tank 12.

[0129] At the lower part of the hydraulic cleaning column 42, a mechanical mechanism (scraper) is used to scrape the crystallization bed, suspending it in the circulating liquid while removing it, and then heating and melting it. A portion of the circulating liquid containing the resulting melt is removed in the form of high-purity compound 3. A portion of the remaining circulating liquid (cleaning liquid) is returned to the hydraulic cleaning column 42 to clean the crystals through convective contact with the crystallization bed.

[0130] Figure 6 In this system, the crystallization apparatus comprises three crystallization tanks and one ripening tank. Pipelines are installed between the four tanks to directly supply mother liquor from the upstream tank, and a pipeline is also installed to directly discharge residue (mother liquor) from the downstream tank. Furthermore, the cleaning column is hydraulic and has a mechanical mechanism for abrading the crystallization bed. The following discussion focuses only on... Figure 5 The different parts of the purification device will be explained.

[0131] The compound solution 1 supplied to the purification unit is introduced into the crystallization tank 13. The slurry containing crystals is transported from the crystallization tank 12 (the second tank from the downstream end) to the solid-liquid separation unit 32 via pipeline 53. In the solid-liquid separation unit 32, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is transported to the adjacent crystallization tank 13 via pipeline 54, while the mother liquor is returned to the crystallization tank 12 via pipeline 62. Additionally, to adjust the liquid level in the crystallization tank 12, mother liquor is directly supplied from the crystallization tank 12 to the crystallization tank 11 via pipeline 72. The same operation as in the crystallization tank 12 is performed in the crystallization tank 13, where the slurry containing crystals is transported from the crystallization tank 13 to the solid-liquid separation unit 33 via pipeline 55. In the solid-liquid separation device 33, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is transported to the adjacent maturation tank 21 via pipeline 56, while the mother liquor is returned to the crystallization tank 13 via pipeline 63. Additionally, to adjust the liquid level in the crystallization tank 13, mother liquor is directly transported from the crystallization tank 13 to the crystallization tank 12 via pipeline 73. After crystal growth in the maturation tank 21, the crystal slurry is transported to the hydraulic cleaning column 42 via pipeline 57. Furthermore, to adjust the liquid level in the maturation tank 21, mother liquor is directly transported from the maturation tank 21 to the crystallization tank 13 via pipeline 74 connecting the maturation tank 21 and the crystallization tank 13.

[0132] Figure 7 In this system, the crystallization apparatus comprises two crystallization tanks and one ripening tank. A pipeline connects the three tanks, supplying mother liquor from the upstream tank via a solid-liquid separation device, and a pipeline discharges residue from the downstream tank via the same device. The following discussion focuses only on... Figure 5 The different parts of the purification device will be explained.

[0133] exist Figure 7 In the crystallization tank 11, instead of the pipeline that directly discharges the residue, a solid-liquid separation device 33 is provided for separating the residue from the slurry in the crystallization tank. The slurry taken out from the crystallization tank 11 is transported to the solid-liquid separation device 33 through the pipeline 81. The residue 2 separated by the solid-liquid separation device 33 is discharged out of the purification device, and the remaining crystals are returned to the crystallization tank 11 to adjust the liquid level in the crystallization tank 11.

[0134] In the crystallization tank 12, instead of the pipeline that directly supplies the mother liquor to the crystallization tank 11, a solid-liquid separation device 34 is provided. The slurry taken out from the crystallization tank 12 is transported to the solid-liquid separation device 34 through the pipeline 83. The mother liquor separated by the solid-liquid separation device 34 is transported to the crystallization tank 11 for liquid level adjustment, and the remaining crystals are returned to the crystallization tank 12.

[0135] In the maturation tank 21, instead of the pipeline that directly supplies the mother liquor to the crystallization tank 12, a solid-liquid separation device 35 is installed. The slurry taken out from the maturation tank 21 is transported to the solid-liquid separation device 35 through the pipeline 85. The mother liquor separated by the solid-liquid separation device 35 is transported to the crystallization tank 12 for liquid level adjustment, and the remaining crystals are returned to the maturation tank 21.

[0136] The cleaning column 43 is hydraulic and does not have a mechanical structure for cutting the crystallization bed.

[0137] Figure 8 In this device, the crystallization apparatus comprises two crystallization tanks and one maturation tank. A pipeline is provided between the three tanks to transport mother liquor from the upstream tank via a solid-liquid separation device, and a pipeline is provided to discharge residue from the downstream tank via a solid-liquid separation device. The solid-liquid separation device used to separate mother liquor from the slurry taken from the second crystallization tank and transport it to the downstream (first) crystallization tank, and the solid-liquid separation device used to separate the residue discharged from the downstream (first) crystallization tank to the outside of the purification apparatus, are shared with the solid-liquid separation device installed in the pipeline transporting slurry to the upstream tank. The following discussion focuses only on the solid-liquid separation device used in the first crystallization tank. Figure 7 The different parts of the purification device will be explained.

[0138] exist Figure 8 In the apparatus, the slurry, cooled in the crystallization tank 11 and containing precipitated crystals, is conveyed to the solid-liquid separation unit 31 via pipeline 51. In the solid-liquid separation unit 31, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is conveyed to the adjacent crystallization tank 12 via pipeline 52. A portion of the mother liquor separated by the solid-liquid separation unit 31 is returned to the crystallization tank 11 via pipeline 61, and the remaining mother liquor is discharged outside the purification unit via an additional pipeline 101 connected to pipeline 61.

[0139] Additionally, the slurry cooled in the crystallization tank 12 and containing precipitated crystals is conveyed to the solid-liquid separation unit 32 via pipeline 53. In the solid-liquid separation unit 32, the slurry is separated into mother liquor and concentrated crystal slurry. The concentrated crystal slurry is conveyed to the adjacent ripening tank 21 via pipeline 54. A portion of the mother liquor separated by the solid-liquid separation unit 31 is returned to the crystallization tank 12 via pipeline 62, and the remaining mother liquor is conveyed to the crystallization tank 11 via an additional pipeline 102 connected to pipeline 62.

[0140] exist Figure 8 In the purification device, pipeline 51 → solid-liquid separation device 31 → pipelines 61, 101 and Figure 7The pipelines 81 → solid-liquid separation device 33 → pipelines 82 and 91 in the device correspond to each other, replacing the solid-liquid separation device 33. This reduces the number of devices by sharing the solid-liquid separation device 31 in the pipeline that transports the slurry to the upstream tank. Similarly, pipelines 53 → solid-liquid separation device 32 → pipelines 62 and 102 are... Figure 7 The pipelines 83 → solid-liquid separation device 34 → pipelines 84 and 92 in the device correspond to each other, and the solid-liquid separation device 34 is installed instead of the solid-liquid separation device 34. The number of devices is reduced by sharing the solid-liquid separation device 32 installed in the pipeline that transports slurry to the upstream tank.

[0141] Figure 9 In this crystallization apparatus, there are two crystallization tanks and one maturation tank. The apparatus includes pipelines for conveying mother liquor from the second crystallization tank to the downstream (first) crystallization tank via a solid-liquid separation device, and pipelines for discharging residue from the downstream tank via the solid-liquid separation device. A pipeline is also provided for directly conveying mother liquor from the maturation tank to the second crystallization tank. The solid-liquid separation devices used to separate mother liquor from the slurry taken from the second crystallization tank and convey it to the downstream crystallization tank, as well as the solid-liquid separation device for separating the residue discharged from the downstream crystallization tank to the outside of the purification apparatus, are shared with the solid-liquid separation device installed in the pipeline conveying slurry from the upstream tank. Furthermore, the crystallization tank is a type of tank where the contents are cooled outside the tank. The following discussion focuses only on... Figure 8 The different parts of the purification device will be explained.

[0142] exist Figure 9 In the apparatus, the crystallization tank 11 consists of a tank 11A and an external cooling mechanism 11B, connected by pipelines 111 and 121. A compound solution (or a slurry containing crystals of the compound) is transported from tank 11A to cooling mechanism 11B via pipeline 111 and cooled in cooling mechanism 11B. The slurry containing the precipitated crystals is transported back to tank 11A via pipeline 121. A portion of the slurry containing the compound crystals is transported from tank 11A to cooling mechanism 11B via pipeline 111, and the remaining portion is transported to solid-liquid separation device 31 via pipeline 51.

[0143] The crystallization tank 12 is also composed of a tank 12A and an external cooling mechanism 12B, which are connected by pipelines 112 and 122. A portion of the crystal containing the compound is transported from the tank 12A to the cooling mechanism 12B through pipeline 112, and the remaining slurry is transported to the solid-liquid separation device 32 through pipeline 53.

[0144] exist Figure 9 In the device, replacing Figure 8 The apparatus has a pipeline for conveying mother liquor from the maturation tank 21 to the crystallization tank 12 via the solid-liquid separation device 35, and a pipeline 73 for conveying mother liquor directly from the maturation tank 21 to the tank 12A.

[0145] Example

[0146] The present invention is described in more detail below with examples, but the present invention is not limited to these examples. It should be noted that, unless otherwise specified, "parts" refers to "parts by weight" and "%" refers to "% by mass".

[0147] Manufacturing Example 1

[0148] The gas containing acrylic acid, obtained by contact gas-phase oxidation of propylene, is fed into a collection tower and collected with water containing a polymerization inhibitor to produce a crude acrylic acid solution with the following composition.

[0149] Composition of crude acrylic acid solution

[0150] Acrylic acid 94.1%

[0151] Acetic acid 2.0%

[0152] furfural 800ppm

[0153] Maleic acid 5000ppm

[0154] Benzaldehyde 350ppm

[0155] Water 2.2%

[0156] Hydroquinone 500ppm

[0157] Other 1.0%

[0158] Example 1

[0159] The crude acrylic acid solution obtained in Manufacturing Example 1 is supplied to a device having... Figure 2In a purification apparatus of the same structure, acrylic acid purification is performed continuously. A crude acrylic acid solution is continuously supplied to the second tank 21 at a rate of 10 kg / h. Acrylic acid crystals are generated using a cooling mechanism (heat exchanger) installed in the first crystallization tank. The slurry containing crystals and mother liquor is then transported upstream to the tank 21, where crystals are concentrated using a solid-liquid separation device 31 while being transported via pipeline 52. Additionally, crystal-free mother liquor is directly overflowed (72) from the second tank 21 to the first tank 11, and discharged (101) from the first tank 11 outside the crystallization apparatus via the solid-liquid separation device 31, thereby maintaining a constant liquid level in each tank. The solid-liquid separation device 31 uses a basket-type centrifuge, resulting in a crystal concentration of 90% in the concentrated slurry and 25% in the slurry held in the second tank 21. Slurry is continuously fed from the second tank 21 into the hydraulic cleaning column 43 to purify and melt the crystals. A portion of the melt is used as cleaning fluid for cleaning the crystallization bed in the cleaning column, and the remainder is obtained at a rate of 6 kg / h to purify acrylic acid. The amount of cleaning fluid is adjusted so that the furfural concentration in the product is less than 1 ppm. In addition, the mother liquor is taken out from the top of the cleaning column and returned (75) to the second tank 21. The flow rate of the mother liquor (crystallization residue) discharged from the first tank 11 to the outside of the purification device via the solid-liquid separation device 31 is 4.0 kg / h.

[0160] The yield (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) of the crystallization apparatus under normal operation is 60%, and the reflux ratio (washing solution flow rate / purified acrylic acid flow rate) in the washing column is 0.43. Furthermore, the composition of the purified acrylic acid is shown below.

[0161] The concentration of acrylic acid (purity of the mother liquor) in the mother liquor was 73.4 mol% in tank 11 and 90.2 mol% in tank 21. The temperature of each tank was 3.3℃ in tank 11 and 9.8℃ in tank 21. The residence time in each tank was 1.5 hours in tank 11A and 3.1 hours in tank 21.

[0162] Through a series of purification operations, high-purity purified acrylic acid can be obtained in high yield and with energy saving (low reflux ratio).

[0163] Composition of purified acrylic acid

[0164] 99.8% acrylic acid

[0165] Acetic acid 1500ppm

[0166] furfural 0.8 ppm

[0167] Maleic acid 4.5 ppm

[0168] Benzaldehyde 0.3 ppm

[0169] 25ppm water

[0170] Hydroquinone 0.4 ppm

[0171] Other 900ppm

[0172] Example 2

[0173] The crude acrylic acid solution obtained in Manufacturing Example 1 is supplied to a device having... Figure 9 In a purification apparatus of the same structure, acrylic acid is continuously purified. A crude acrylic acid solution is continuously supplied to the third tank 21 at a rate of 10 kg / h. Acrylic acid crystals are generated using cooling devices (heat exchangers) 11B and 12B installed outside the first and second tanks. The slurry containing crystals and mother liquor is transported to an upstream tank while the crystals are concentrated using liquid hydrocyclones 31 and 32 (52, 54). In addition, mother liquor without crystals is directly transported (73) from the third tank 21 to the second tank 12A via overflow. Mother liquor is transported (102) from the second tank 12A to the first tank 11A via solid-liquid separation device 32. Mother liquor is discharged (101) from the tank 11A to the outside of the crystallization device via solid-liquid separation device 31, thereby adjusting the liquid level of each tank to a constant level. The crystal concentration in the slurry concentrated by each liquid hydrocyclone was 40%, and the crystal concentration in the slurry held in the third tank 21 was 25%. The slurry was continuously fed from the third tank 21 into the hydraulic cleaning column 43 to purify and melt the crystals. A portion of the melt was used as a cleaning solution for cleaning the crystallization bed in the cleaning column, and the remainder was obtained at a rate of 6 kg / h in the form of purified acrylic acid. The amount of cleaning solution was adjusted so that the furfural concentration in the product was less than 1 ppm. In addition, the mother liquor was taken out from the top of the cleaning column and returned (75) to the third tank 21. The flow rate of the mother liquor (crystallization residue) discharged from the first tank 11A was 4.0 kg / h.

[0174] The yield (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) of the crystallization apparatus under stable operation was 60%, and the reflux ratio (washing solution flow rate / purified acrylic acid flow rate) in the washing column was 0.67. Furthermore, the composition of the purified acrylic acid is shown below.

[0175] The concentration of acrylic acid (purity of the mother liquor) in the mother liquor was 73.4 mol% in tank 11A, 81.0 mol% in tank 12A, and 86.4 mol% in tank 21. The temperature in each tank was 3.3℃ in tank 11A, 6.3℃ in tank 12A, and 8.3℃ in tank 21. The residence time in each tank was 1.0 hour in tank 11A, 0.4 hours in tank 12A, and 1.8 hours in tank 21.

[0176] Through a series of purification operations, high-purity purified acrylic acid can be obtained in high yield and with energy saving (low reflux ratio).

[0177] Composition of purified acrylic acid

[0178] 99.7% acrylic acid

[0179] Acetic acid 1800ppm

[0180] furfural 0.9 ppm

[0181] Maleic acid 6.0 ppm

[0182] Benzaldehyde 0.4 ppm

[0183] 30ppm water

[0184] Hydroquinone 0.6 ppm

[0185] Other 1100ppm

[0186] Example 3

[0187] The crude acrylic acid solution obtained by the same method as in Manufacturing Example 1 is supplied to a vessel having the same characteristics as... Figure 5 A purification device with the same structure is used to continuously purify acrylic acid.

[0188] Crude acrylic acid solution was continuously supplied to the third tank 21 at a rate of 10 kg / h. Instead of transferring the mother liquor from the second tank 12 to the first tank 11 via a solid-liquid separation device, the mother liquor without crystals was directly supplied via overflow (72). Instead of discharging the mother liquor from the first tank 11 to the crystallization device via a solid-liquid separation device, the mother liquor without crystals was directly discharged via overflow (71). Otherwise, purification was performed using the same method as in Example 2, and purified acrylic acid was obtained at a rate of 6 kg / h. The yield of the crystallization device during stable operation (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) was 60%, and the reflux ratio in the washing column (washing liquid flow rate / purified acrylic acid flow rate) was 0.69. The composition of the purified acrylic acid is as follows.

[0189] The concentration of acrylic acid (purity of the mother liquor) in the tanks was 72.8 mol% in tank 11, 80.7 mol% in tank 12, and 86.1 mol% in tank 21. The temperatures in each tank were 3.1°C in tank 11, 6.1°C in tank 12, and 8.2°C in tank 21. The residence time in each tank was 1.0 hour in tank 11, 0.4 hours in tank 12, and 1.8 hours in tank 21. During operation, although trace amounts of mother liquor were discharged and transported from tanks 11 and 12 via overflow, it still contained crystals. Through a series of purification operations, high-purity purified acrylic acid can be obtained with high yield and energy saving (low reflux ratio).

[0190] Composition of purified acrylic acid

[0191] 99.7% acrylic acid

[0192] Acetic acid 1800ppm

[0193] furfural 0.9 ppm

[0194] Maleic acid 6.2 ppm

[0195] Benzaldehyde 0.5 ppm

[0196] 30ppm water

[0197] Hydroquinone 0.7 ppm

[0198] Other 1100ppm

[0199] Comparative Example 1

[0200] The crude acrylic acid solution obtained by the same method as in Manufacturing Example 1 is supplied to a vessel having the same characteristics as... Figure 10 A purification device with the same structure continuously purifies acrylic acid. A crude acrylic acid solution is continuously supplied to tank 11 at a rate of 10 kg / h. Acrylic acid crystals are generated using a heat exchanger installed in tank 11. The refrigerant temperature is adjusted so that the crystal concentration in the slurry in the tank is 25%. Slurry is continuously fed from tank 11 to a hydraulic cleaning column 43 to purify and melt the crystals. A portion of the melt is used as a cleaning liquid for cleaning the crystallization bed in the cleaning column to obtain (3) the remaining portion in the form of purified acrylic acid. The amount of cleaning liquid is adjusted so that the furfural concentration in the product is less than 1 ppm. In addition, mother liquor is taken from the top of the cleaning column and returned (75) to tank 11. The mother liquor without crystals is discharged from the tank by overflow (71) in a way that keeps the liquid level constant as crystallization residue. The purified acrylic acid flow rate / the slurry flow rate fed to the cleaning column is adjusted so that the acrylic acid concentration in the mother liquor in tank 11 is 86 mol%. The yield (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) of the crystallization apparatus under stable operation was 16%, and the reflux ratio in the washing column (washing solution flow rate / purified acrylic acid flow rate) was 0.67. Furthermore, the flow rate of purified acrylic acid was 1.6 kg / h, and the composition is shown below.

[0201] The flow rate of the crystallization residue is 8.4 kg / h.

[0202] The concentration of acrylic acid (purity of mother liquor) in the mother liquor in tank 11 is 86.4 mol%, the temperature in tank 11 is 8.3℃, and the residence time in tank 11 is 2.0 hours.

[0203] Although a series of purification operations can yield high-purity purified acrylic acid, the crystallization yield is very low, and it is impossible to obtain a sufficient amount of purified acrylic acid.

[0204] Composition of purified acrylic acid

[0205] 99.7% acrylic acid

[0206] Acetic acid 1800ppm

[0207] furfural 0.9 ppm

[0208] Maleic acid 6.1 ppm

[0209] Benzaldehyde 0.4 ppm

[0210] 30ppm water

[0211] Hydroquinone 0.7 ppm

[0212] Other 1100ppm

[0213] Comparative Example 2

[0214] The crude acrylic acid solution obtained by the same method as in Manufacturing Example 1 is supplied to a vessel having the same characteristics as... Figure 10 A purification device with the same structure is used to continuously purify acrylic acid. A crude acrylic acid solution is continuously supplied to tank 11 at a rate of 10 kg / h. Acrylic acid crystals are generated using a heat exchanger installed in tank 11. The temperature of the refrigerant is adjusted so that the crystal concentration in the slurry in the tank is 25%. The slurry is continuously fed from tank 11 to a hydraulic cleaning column 43 to purify and melt the crystals. A portion of the melt is used as a cleaning liquid for cleaning the crystallization bed in the cleaning column. The remaining portion is obtained at a rate of 6 kg / h in the form of purified acrylic acid. The amount of cleaning liquid is adjusted so that the furfural concentration in the product is less than 1 ppm. In addition, the mother liquor is taken out from the top of the cleaning column and returned (75) to tank 11. The mother liquor without crystals is discharged from the tank by overflow (71) in a way that keeps the liquid level constant as crystallization residue.

[0215] The yield of the crystallization apparatus (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) was 60%, and the reflux ratio in the washing column 41 (washing solution flow rate / purified acrylic acid flow rate) was 4.0. Furthermore, the composition of the purified acrylic acid is shown below.

[0216] The flow rate of the crystallization residue is 4 kg / h.

[0217] The concentration of acrylic acid (purity of mother liquor) in the mother liquor in tank 11 is 73.4 mol%, the temperature in tank 11 is 3.3℃, ​​and the residence time in tank 11 is 1.5 hours.

[0218] Although high-purity purified acrylic acid can be obtained through a series of purification operations, the reflux ratio in the washing column is high, and more energy is required to obtain the product.

[0219] Composition of purified acrylic acid

[0220] 99.6% acrylic acid

[0221] Acetic acid 2500ppm

[0222] furfural 0.9 ppm

[0223] Maleic acid 6.2 ppm

[0224] Benzaldehyde 0.5 ppm

[0225] 30ppm water

[0226] Hydroquinone 0.7 ppm

[0227] Other 1100ppm

[0228] Comparative Example 3

[0229] The crude acrylic acid solution obtained by the same method as in Manufacturing Example 1 is supplied to a vessel having the same characteristics as... Figure 11 A purification device with the same structure using a gravity settling column is used to continuously purify acrylic acid. A crude acrylic acid solution is continuously supplied to the third tank 21 at a rate of 10 kg / h. Acrylic acid crystals are generated using cooling devices 11B and 12B installed outside the first and second tanks. The slurry containing crystals and mother liquor is transported to the upstream tank while the crystals are concentrated using liquid hydrocyclones 31 and 32 (52, 54). In addition, mother liquor without crystals is directly transported (73) from the third tank 21 to the second tank 12A via overflow. Mother liquor (102) is transported from the second tank 12A to the first tank 11A via solid-liquid separation device 32. Mother liquor (101) is discharged from the first tank 11A to the outside of the crystallization device via solid-liquid separation device 31, thereby adjusting the liquid level of each tank to a constant level.

[0230] The crystal concentration in the slurry concentrated using a liquid hydrocyclone separator was 40%, and the crystal concentration in the slurry held in the third tank 21 was 25%. The slurry was continuously fed from the third tank 21 to a gravity settling washing column 44 for crystal purification and melting. A portion of the melt was used as a washing liquid for washing the crystallization bed in the washing column, and the remaining portion was obtained at a rate of 6 kg / h in the form of purified acrylic acid. In addition, the mother liquor was taken from the top of the washing column and returned (75) to the third tank 21. The mother liquor (crystallization residue) discharged from the first tank 11A by overflow was 4.0 kg / h.

[0231] The yield of the crystallization apparatus under stable operation (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) was 60%. Furthermore, we wanted to adjust the reflux ratio (washing liquid flow rate / purified acrylic acid flow rate) in the washing column to achieve a furfural concentration of less than 1.0 ppm in the purified acrylic acid. However, even when the reflux ratio was increased to 9.0, the composition of the purified acrylic acid remained as shown below, and we could not obtain the product of the desired quality.

[0232] At this point, the acrylic acid concentration (purity of the mother liquor) in the tank was 73.4 mol% in tank 11A, 82.6 mol% in tank 12A, and 88.7 mol% in tank 21. The temperature in the tanks was 3.3°C in tank 11A, 6.8°C in tank 12A, and 9.2°C in tank 21. Furthermore, the residence time in each tank was 1.2 hours in tank 11A, 0.4 hours in tank 12A, and 1.9 hours in tank 21.

[0233] The purified acrylic acid obtained contains a large amount of furfural, which acts as a polymerization delay agent, and hydroquinone, which acts as a polymerization inhibitor, making it unsuitable for use as a raw material for superabsorbent resins and the like.

[0234] Composition of purified acrylic acid

[0235] 99.7% acrylic acid

[0236] Acetic acid 1500ppm

[0237] furfural 19ppm

[0238] Maleic acid 120ppm

[0239] Benzaldehyde 8ppm

[0240] 500ppm water

[0241] Hydroquinone 12ppm

[0242] Other 1100ppm

[0243] Comparative Example 4

[0244] The crude acrylic acid solution obtained by the same method as in Manufacturing Example 1 is supplied to a vessel having the same characteristics as... Figure 9A purification apparatus of identical structure is used to continuously purify acrylic acid. A crude acrylic acid solution is continuously supplied to the third tank 21 at a rate of 10 kg / h. Acrylic acid crystals are generated using cooling mechanisms 11B and 12B located outside the first and second tanks. The slurry containing crystals and mother liquor is then transported upstream to a tank, where the crystals are concentrated using liquid hydrocyclones 31 and 32 (52, 54). Additionally, crystal-free mother liquor is directly overflowed from the third tank 21 to the second tank 12A (73), and mother liquor is transported from the second tank 12A to the first tank 11A via a solid-liquid separation device 32 (102). Mother liquor is transported from the first tank 11A to the outside of the crystallization device via a solid-liquid separation device 31 (101), thereby maintaining a constant liquid level in each tank. The crystal concentration in the slurry concentrated using the liquid hydrocyclones is 14%, and the crystal concentration in the slurry held in the third tank 21 is 10%. The slurry is continuously fed from the third tank 21 to the hydraulic cleaning column 43 to purify and melt the crystals. A portion of the melt is used as cleaning fluid for cleaning the crystallization bed in the cleaning column, and the remaining portion is obtained at a rate of 6 kg / h in the form of purified acrylic acid. The amount of cleaning fluid is adjusted so that the furfural concentration in the product is less than 1 ppm. In addition, the mother liquor and cleaning fluid are taken out from the top of the cleaning column and returned to the third tank. The flow rate of the mother liquor (crystallization residue) discharged from the first tank 11A is 4.0 kg / h.

[0245] The yield (purified acrylic acid flow rate / crude acrylic acid flow rate × 100) of the crystallization apparatus under stable operation was 60%, and the reflux ratio (washing solution flow rate / purified acrylic acid flow rate) in the washing column was 3.0. Furthermore, the composition of the purified acrylic acid is shown below.

[0246] The concentration of acrylic acid (purity of the mother liquor) in the mother liquor was 73.4 mol% in tank 11A, 76.5 mol% in tank 12A, and 79.3 mol% in tank 21. The temperature in each tank was 3.3℃ in tank 11A, 5.3℃ in tank 12A, and 6.8℃ in tank 21. The residence time in each tank was 0.5 hours in tank 11A, 0.2 hours in tank 12A, and 1.8 hours in tank 21.

[0247] Although high-purity purified acrylic acid can be obtained through a series of purification operations, the reflux ratio in the washing column is high, and more energy is required to obtain the product.

[0248] Composition of purified acrylic acid

[0249] 99.7% acrylic acid

[0250] Acetic acid 1600ppm

[0251] furfural 0.9 ppm

[0252] Maleic acid 5.9 ppm

[0253] Benzaldehyde 0.4 ppm

[0254] 30ppm water

[0255] Hydroquinone 0.6 ppm

[0256] Other 1100ppm

[0257] Explanation of reference numerals in the attached figures

[0258] 1: Solution of the compound

[0259] 2: Residue

[0260] 3: High-purity compounds

[0261] 11-13: Crystallization tank with cooling mechanism

[0262] 11A, 12A: Tank

[0263] 11B, 12B: Cooling mechanism

[0264] 21: Curing tank

[0265] 31-35: Solid-liquid separation device

[0266] 41: Mechanical cleaning column

[0267] 42: Hydraulic cleaning column (with a mechanical mechanism for removing crystallization beds)

[0268] 43: Hydraulic cleaning column (without a mechanical mechanism for removing the crystallization bed)

[0269] 44: Gravity settling cleaning column

[0270] 51–57: Pipelines that transport slurry (or crystals) from downstream tanks to upstream tanks or cleaning columns.

[0271] 61-63: Pipelines that return the mother liquor separated from the slurry by the solid-liquid separation device to the original tank.

[0272] 71: The pipeline that discharges the residue (mother liquor) directly from the downstream tank to the outside of the purification unit.

[0273] 72-74: Pipelines that directly transport mother liquor from the upstream tank to the next downstream tank.

[0274] 75: The pipeline that returns the mother liquor from the washing column to the crystallization unit.

[0275] 81-86: Pipelines for separating crystals from the slurry taken from the tank using a solid-liquid separation device and returning it to the original tank.

[0276] 91: The pipeline that discharges the residue (mother liquor) separated from the slurry taken from the tank by the solid-liquid separation device to the outside of the purification device.

[0277] 92, 93: Pipelines for conveying the mother liquor separated from the slurry taken from the tank by a solid-liquid separation device to the next downstream tank.

[0278] 101: An additional pipeline used to discharge a portion of the mother liquor separated from the slurry taken from the downstream tank by the solid-liquid separation unit to the outside of the purification unit.

[0279] 102: An additional pipeline for conveying a portion of the mother liquor separated from the slurry taken from the second tank by a solid-liquid separation device to the downstream tank.

[0280] 111, 121, 112, 122: Pipelines connecting the crystallization tank and the cooling mechanism to the tank in the form of cooling the contents of the external cooling tank.

Claims

1. A method for purifying a compound, characterized in that, It uses a purification apparatus with a crystallization device and a washing column. The crystallization device has a crystal formation section, and the washing column has a mechanism for forcibly transporting the crystals. The crystallization apparatus has N cells, where N ≥ 2, connected in series with the first cell as downstream and the Nth cell as upstream. At least the first cell is a crystallization cell equipped with a cooling mechanism, and the second and subsequent cells are either crystallization cells or ripening cells. The crystallization apparatus has a pipeline for supplying a purified solution containing the compound to at least one tank. The cleaning column has a pipeline for discharging the product and a pipeline for returning the mother liquor to the crystallization apparatus. The pipeline returning the mother liquor to the crystallization apparatus is connected to at least the Nth tank. The crystallization apparatus has a pipeline for supplying slurry from the Nth tank to the cleaning column, a pipeline for conveying slurry from the downstream tank to the previous upstream tank, and a pipeline for conveying mother liquor from the upstream tank to each of the 1st to N-1th tanks. At least one of the pipelines that transport slurry from the downstream tank to the upstream tank of N-1 is a pipeline that transports slurry to the upstream tank via a solid-liquid separation device, and has a pipeline that returns the mother liquor, from which crystals have been removed by the solid-liquid separation device, back to the original tank. The pipelines for supplying mother liquor from the upstream tank to each of the 1st to N-1th tanks include at least one of the following: a pipeline that directly supplies mother liquor from the previous upstream tank and a pipeline that supplies mother liquor from the previous upstream tank via a solid-liquid separation device. The purification method includes the following steps: The process of generating crystals of a compound in a crystallization apparatus; The process of discharging at least a portion of the mother liquor outside the purification unit; The process of separating the slurry containing the generated crystals into mother liquor and slurry with increased crystal concentration; The process of returning at least a portion of the separated mother liquor to the original tank; The process of supplying the purified solution containing the compound to a crystallization apparatus and mixing it with the slurry in the crystallization apparatus; The process of conveying slurry from the downstream tank to the upstream tank in sequence among the multiple tanks contained in the crystallization device; The process of supplying at least a portion of the slurry from the crystallization unit to the cleaning column. The purified liquid containing the compound is a liquid with a higher purity than the mother liquor discharged from the purification device. The purity A1 of the mother liquor in the slurry supplied to the washing column is 80 mol% or more, and the difference A1-A2 between A1 and the purity A2 of the discharged mother liquor is 5 mol% or more. The Nth tank in the crystallization device has a larger capacity than the downstream tank, and the Nth tank is designed to directly supply mother liquor to the downstream tank via overflow.

2. The purification method for the compound according to claim 1, characterized in that, include: The process of transferring the mother liquor from at least one of the 2nd to Nth tanks included in the crystallization apparatus to a downstream tank for adjusting the liquid level in the tank.

3. The purification method for the compound according to claim 1 or 2, characterized in that, The crystallization apparatus contains a crystallization tank at a temperature 1-15°C lower than the melting point of the pure substance of the purified compound.

4. The purification method for the compound according to claim 1 or 2, characterized in that, The cleaning column is a hydraulic cleaning column.

5. The purification method for the compound according to claim 1 or 2, characterized in that, The residence time in the first to N-1 cells of the crystallization apparatus is 0.02 to 6 hours.

6. The method for purifying the compound according to claim 1 or 2, characterized in that, include: The process of further purifying at least a portion of the mother liquor discharged from the purification device through distillation and / or crystallization operations.

7. The method for purifying the compound according to claim 1 or 2, characterized in that, The compound is (meth)acrylic acid.

8. The method for purifying the compound according to claim 1 or 2, characterized in that, The residence time in the Nth cell of the crystallization apparatus is 0.5 to 6 hours.

9. The method for purifying the compound according to claim 1 or 2, characterized in that, The cleaning column does not have a mechanical structure for cutting the crystallization bed.

10. The method for purifying the compound according to claim 1 or 2, characterized in that, The solid-liquid separation device is a liquid cyclone separator.

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