Purification device

Abstract

This invention relates to a purification apparatus, characterized in that it is a purification apparatus for a compound having a crystallization device having N crystallization tanks connected in series and a washing column for forcibly transporting crystals. The washing column has a pipeline for transporting the product out and a pipeline for returning the mother liquor to the Nth crystallization tank. The crystallization device has a pipeline for supplying slurry from the Nth crystallization tank to the washing column, a pipeline for transporting slurry from the downstream crystallization tank to the upstream crystallization tank via a solid-liquid separation device, a pipeline for returning the mother liquor from which crystals have been removed by the solid-liquid separation device to the original crystallization tank, and pipelines for transporting mother liquor from the upstream crystallization tank to each of the 1st to N-1th crystallization tanks (including at least one of a pipeline for directly transporting mother liquor from the upstream crystallization tank or a pipeline for transporting mother liquor from the upstream crystallization tank via a solid-liquid separation device). The purification apparatus also has a pipeline for transporting mother liquor outside the purification apparatus. This invention can obtain high-purity compounds with high yield and low cost.

Description

Technical Field

[0001] This invention relates to a purification apparatus applicable to the purification of industrially produced compounds. Background Technology

[0002] Currently, various compounds are widely manufactured and utilized industrially. Depending on their intended use, industrially manufactured compounds require high-quality products with reduced impurities, leading to the research and development of various superior purification techniques.

[0003] As a purification technique for compounds, a purification method has been disclosed in which multiple cooling crystallizers with a clarification section 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 crystallizers are sequentially transported to the crystallizer side connected to the purification tower, allowing the crystals output from the crystallizers to settle by gravity within the purification tower. Simultaneously, a portion of the crystals, heated and melted by the heater at the bottom of the purification tower, rises as reflux liquid and contacts the settling crystals, thus cleaning the crystals (see Patent Documents 1 and 2). Another method for purifying acrylic acid has been disclosed, in which a suspension containing acrylic acid crystals generated in a crystallization tank and crude acrylic acid melt is transported to a washing column. 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 a washing liquid to clean the crystals within the washing column (see Patent Document 3). Furthermore, a purification method has been disclosed that improves the purity of acrylic acid by repeatedly suspending and crystallizing or layering crystals in an aqueous solution containing acrylic acid (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] While various purification techniques have been disclosed as described above, industrial manufacturing demands the production of high-purity compounds with high yields and low costs. The inventors' research indicates that purification apparatuses using gravity sedimentation washing columns as described in Patent Documents 1 and 2 cannot achieve sufficiently high purification efficiency and yield for industrial applications when purifying organic compounds that produce small-particle-size crystals or when purifying low-purity crude compound solutions. Furthermore, the purification apparatus described in Patent Document 3 cannot achieve high yields in the crystallization process, increasing operating costs for handling crystallization residue. To achieve high yields in the crystallization process, the purity of the crude compound solution supplied to the crystallization process needs to be increased, thus increasing purification costs before crystallization, which is disadvantageous. Additionally, while the method of repeated crystallization as described in Patent Document 4 can use crude compound solutions with low purity in the crystallization process, the process includes a temporary melting of crystals and a discharge of mother liquor, thus increasing equipment complexity, investment, and energy consumption, which is also disadvantageous. The present invention was made in view of the above-mentioned situation, and its object is to provide a compound purification apparatus that can obtain high-purity compounds in high yield and at low cost.

[0012] Solution for solving the problem

[0013] The inventors have studied purification apparatuses that can obtain high-purity compounds with high yield and low cost. They discovered that in a purification apparatus with a structure comprising N crystallization tanks or ripening tanks connected in series, including at least one crystallization tank, and the upstream crystallization tank or ripening tank connected to a washing column, the following configuration enables the purification apparatus to obtain high-purity compounds with high yield and low cost, thus completing the present invention: at least one of the pipelines that transport slurry from the crystallization tank or ripening tank to the upstream tank is configured as a pipeline for transporting slurry via a solid-liquid separation device; a pipeline for returning the mother liquor from which crystals have been removed by the solid-liquid separation device to the original tank is configured; a pipeline for returning the mother liquor from the washing column to at least the Nth tank of the crystallization apparatus is configured; further, at least one of the pipelines that directly transport the mother liquor from the upstream tank to each of the 1st to N-1th tanks of the crystallization apparatus and the pipeline that transports the mother liquor from the upstream tank via the solid-liquid separation device is configured; and a pipeline for transporting the mother liquor outside the purification apparatus is configured.

[0014] That is, the present invention is a purification apparatus, characterized in that it is a purification apparatus for a compound having a crystallization device and a washing column. The crystallization device has a crystal formation section, the washing column forcibly transports crystals, and the crystallization device has N (N≥2) tanks connected in series with the first tank as downstream and the Nth tank as upstream. At least the first tank is a crystallization tank equipped with a cooling mechanism, and the second and subsequent tanks are crystallization tanks or ripening tanks. The crystallization device has a pipeline for supplying a purified solution containing the compound to at least one tank. The washing column has a pipeline for discharging the product and a pipeline for returning the mother liquor to the crystallization device. The pipeline returning the mother liquor to the crystallization device is connected to at least the Nth tank. The crystallization device has a pipeline for supplying the purified solution containing the compound to the washing column from the Nth tank. The purification apparatus includes a pipeline for supplying slurry, a pipeline for conveying slurry from a downstream tank to an upstream tank, and a pipeline for conveying mother liquor from an upstream tank to each of the first to N-1 tanks. At least one of the pipelines for conveying slurry from the N-1 downstream tank to the upstream tank is a pipeline for conveying slurry to the upstream tank via a solid-liquid separation device. The apparatus also includes a pipeline for returning the mother liquor, from which crystals have been removed by the solid-liquid separation device, to the original tank. The pipelines for conveying mother liquor from the upstream tank to each of the first to N-1 tanks include at least one of a pipeline for directly conveying mother liquor from the upstream tank and a pipeline for conveying mother liquor from the upstream tank via a solid-liquid separation device. The purification apparatus further includes a pipeline for conveying mother liquor outside the purification apparatus.

[0015] The first to N-1 tanks in the crystallization apparatus described above are preferably all equipped with pipelines that transport slurry to the previous tank upstream via the solid-liquid separation device and pipelines that return at least a portion of the mother liquor discharged from the solid-liquid separation device to the original tank.

[0016] Of the aforementioned 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.

[0017] At least one of the solid-liquid separation devices installed in the pipeline that transports slurry from the downstream tank to the upstream tank is preferably provided with, in addition to having a pipeline that returns the mother liquor to the original tank, one or more additional pipelines for transporting the mother liquor, which are externally connected to the tank and / or purification device that are downstream of the original tank.

[0018] At least one of the first to N-1 tanks in the crystallization apparatus described above is preferably equipped with a pipeline that directly supplies mother liquor from the upstream tank.

[0019] Preferably, it has a pipeline that transports mother liquor from the first tank contained in the crystallization device to the outside of the purification device via a solid-liquid separation device.

[0020] The cooling mechanism described above is preferably in the form of cooling the contents of the tank outside the tank.

[0021] The cleaning column may or may not have a mechanical mechanism for scraping the crystallization bed.

[0022] The above-mentioned compound is preferably (meth)acrylic acid.

[0023] In the above-mentioned crystallization device, the pipeline for conveying slurry from the downstream tank to the upstream tank is preferably a pipeline for conveying slurry from the (N-1)th tank to the Nth tank via a solid-liquid separation device. The solid-liquid separation device installed in the pipeline for conveying slurry from the (N-1)th tank to the Nth tank is a basket centrifuge or a decanter centrifuge.

[0024] The effects of the invention

[0025] The purification apparatus of the present invention can reduce the amount of crystallization residue discharged and obtain high-purity compounds in high yield, even when purifying organic compounds that produce crystals with small particle sizes or when purifying crude compound solutions with low purity. Furthermore, since the amount of washing liquid in the washing column can be reduced, the operating costs of the apparatus can be decreased. Attached Figure Description

[0026] Figure 1 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0027] Figure 2 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0028] Figure 3 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0029] Figure 4 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0030] Figure 5 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0031] Figure 6 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0032] Figure 7 This is a diagram illustrating one example of the purification apparatus of the present invention.

[0033] Figure 8 This is a diagram illustrating one example of the purification apparatus of the present invention. Detailed Implementation

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

[0035] It should be noted that combining two or more of the preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0036] The purification apparatus of the present invention comprises a crystallization device having N (N≥2) tanks connected in series and a cleaning column for forcibly transporting crystals. At least one tank in the crystallization device is a crystallization tank equipped with a cooling mechanism, the second and subsequent tanks are crystallization tanks or maturation tanks, and 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 returning at least a portion of the mother liquor discharged from the solid-liquid separation device to the original tank. Furthermore, in the purification apparatus of the present invention, all of the first to N-1 tanks in the crystallization device have 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 have a pipeline for transporting mother liquor outside the purification apparatus.

[0037] By connecting multiple crystallization tanks or maturation tanks in series, a slurry of crystals and mother liquor suspension, representing a compound, is sequentially transported to the upstream tank. Simultaneously, the mother liquor is transported from the upstream tank to the downstream tank, engaging in convective contact with the crystals. The purity of both the crystals and mother liquor increases as the material moves upstream. Furthermore, by using as many solid-liquid separation devices as possible to concentrate the slurry before transporting it to the upstream tank, the purity of both the crystals and mother liquor can be improved even more efficiently.

[0038] 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. As a result, less impurity-concentrated, low-purity mother liquor (crystallization residue) can be discharged from the downstream tank, and high-purity compounds can be obtained in high yield.

[0039] Furthermore, although the purity of the crystals is improved by using a portion of the liquid from the heated melting of the purified crystals as a cleaning solution in the crystallization bed through convective contact, the amount of this cleaning solution can be reduced by supplying high-purity crystals and mother liquor from the Nth tank to the cleaning column. This reduces the amount of crystals generated in the crystallization tank and decreases the operating costs of the refrigeration unit.

[0040] Thus, when multiple tanks are used to concentrate the crystals in the slurry while conveying it upstream to improve the purity of the mother liquor, in order to make the mother liquor and crystals come into convective contact and to adjust the liquid level in each tank, it is necessary to convey the mother liquor, which does not contain crystals, from the upstream side to the downstream side and from the tank inside the purification device to the outside of the purification device (preferably from the downstreammost tank to the outside of the purification device).

[0041] Regarding this, as existing technology, there is a known method that involves setting a crystal settling zone at the top of the tank, from which the crystal-free mother liquor (hereinafter sometimes referred to as clarified mother liquor) overflows from the upstream to the downstream side of the tank, and then is discharged directly from the downstreammost tank to the outside of the purification device. This method has the advantages of not requiring a transfer pump and easy adjustment of the liquid level in each tank, but the need for a crystal settling zone at the top of each tank complicates the tank structure.

[0042] Especially when purifying organic compounds that produce small crystals, or purifying low-purity compound solutions, the slow settling rate of crystals necessitates designing an excessively large settling tank to accommodate the sedimentation zone. If the crystals are too small to form a proper settling zone, problems arise such as crystals being transported downstream, leading to reduced purification efficiency of the device.

[0043] Furthermore, in the purification apparatus 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. This prevents crystals from being transported to the downstream tank, efficiently improves the purity within the upstream tank, and facilitates purification in the next step (washing column).

[0044] 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%, meaning that all N-1 pipelines transporting slurry from the downstream tank to the upstream tank are pipelines that transport slurry to the upstream tank via the solid-liquid separation device.

[0045] In addition, among the pipelines that transport slurry from the downstream tank to the upstream tank, the pipeline that transports slurry from the (N-1)th tank to the Nth tank is preferably a pipeline that transports slurry to the upstream tank via a solid-liquid separation device.

[0046] 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 to the original tank. The concentrated slurry containing crystals 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.

[0047] Furthermore, in the aforementioned crystallization apparatus, each of the first to N-1 tanks has 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 maintained at a constant level.

[0048] In the purification apparatus of the present invention, at least one of the first to N-1 tanks included in the crystallization apparatus preferably 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). The reasons for having a pipeline for directly conveying mother liquor from the Nth tank to the N-1th tank will be described later.

[0049] If the tanks in the aforementioned crystallization apparatus have a pipeline for conveying mother liquor from the upstream tank via a solid-liquid separation device, then the transport of crystals from the upstream tank to the downstream side can be efficiently suppressed through solid-liquid separation. Therefore, even when the purification apparatus is used to purify compounds with slow crystal settling rates, the purification efficiency of the purification apparatus can be maintained at a high level. Therefore, among the pipelines for conveying mother liquor from the upstream tank to each of the 1st to N-1th tanks, at least one is preferably a pipeline for conveying mother liquor from the upstream tank via a solid-liquid separation device.

[0050] In the case of a pipeline that transports mother liquor from the tank contained in the crystallization device to the next downstream tank via a solid-liquid separation device, from the viewpoint of the cost of the purification device itself and the operating cost of the device, it is preferable to install the solid-liquid separation device in the pipeline that transports slurry to the previous upstream tank. This reduces the number of solid-liquid separation devices and transfer pumps required.

[0051] In this case, the apparatus can be configured such that a solid-liquid separation device installed in the pipeline that transports the mother liquor from the upstream tank to the original tank returns it to the original tank, and one or more additional pipelines for transporting the mother liquor are further provided, which are connected to the next downstream tank relative to the original tank. Alternatively, the apparatus can be configured such that the additional pipeline further branches, connecting to the next downstream tank in addition to the tank immediately downstream of the original tank, and further connecting to the next two and subsequent downstream tanks. Furthermore, the additional pipeline can be a pipeline connected to an external purification device.

[0052] The crystallization apparatus is structured such that at least one of the solid-liquid separation devices installed in the pipeline that transports slurry from the downstream tank to the upstream tank has, in addition to a pipeline that returns the mother liquor to the original tank, one or more additional pipelines for transporting the mother liquor, which are connected to the tank and / or purification device that are downstream of the original tank. This is one of the preferred embodiments of the purification apparatus of the present invention.

[0053] In 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%.

[0054] As the aforementioned solid-liquid separation device, commonly used devices such as basket centrifuges, decanter centrifuges, hydrocyclones, and filters can be used. Examples of basket centrifuges include the Escher-Wyss pusher centrifuge from Tsukishima Machinery Co., Ltd., and examples of decanter centrifuges include the BIRD decanter centrifuge from Tsukishima Machinery Co., Ltd., and the spiral centrifuge from IHI Corporation.

[0055] When using a basket 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. When using a decanter centrifuge, the concentrated crystal concentration is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more.

[0056] When using a 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 too high, the fluidity decreases and the risk of piping 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.

[0057] While basket centrifuges and decanter centrifuges increase initial investment and operating costs when used as solid-liquid separation devices, they offer the advantage of improved compound purification efficiency due to the high concentration efficiency of the slurry (crystals). Conversely, while hydrocyclones have lower slurry (crystal) concentration efficiency and require multiple tanks within the crystallization unit to achieve sufficient purification, they offer advantages such as lower initial investment and operating costs, and the avoidance of malfunctions caused by rotary separators.

[0058] As described above, in the crystallization apparatus, the pipeline for conveying slurry from the downstream tank to the upstream tank is preferably a pipeline for conveying slurry from the (N-1)th tank to the Nth tank via a solid-liquid separation device. In this case, the solid-liquid separation device provided in the pipeline for conveying slurry from the (N-1)th tank to the Nth tank is preferably a basket centrifuge or a decanter centrifuge.

[0059] 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, but from the viewpoint of maximizing the purity of the crystals and mother liquor, it is preferable to have two or more when using a basket centrifuge or a decanter centrifuge as the solid-liquid separation device; otherwise, three or more are preferred. Furthermore, the more tanks there are, the better 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 is disadvantageous. Therefore, the total number of crystallization tanks and maturation tanks is independent of the type of solid-liquid separation device, and is preferably six or less, more preferably five or less.

[0060] 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. The number of ripening tanks included in the crystallization apparatus is preferably 0 to 2. More preferably, it is 0 to 1.

[0061] The tanks included in the above-described crystallization apparatus are preferably structured to form a clear mother liquor layer 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 clear mother liquor layer at the top of the upstream tank via overflow. Furthermore, one preferred embodiment of the purification apparatus of the present invention is a pipeline that conveys mother liquor to the outside of the purification apparatus via overflow.

[0062] As described above, the purification apparatus of the present invention preferably has a pipeline for conveying mother liquor from the first downstream tank contained in the crystallization device to the outside of the purification apparatus. However, one preferred embodiment of the purification apparatus of the present invention is a pipeline that conveys the clarified mother liquor layer at the top of the first tank contained in the crystallization device to the outside of the purification apparatus by overflow.

[0063] In cases where a clear mother liquor layer does not form at the top of the tank in the aforementioned crystallization apparatus, 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 the next and subsequent tanks downstream. Alternatively, the mother liquor separated by the solid-liquid separation device can be discharged outside the purification apparatus. One preferred embodiment of the purification apparatus of the present invention is a pipeline that transports the mother liquor from the first tank in the crystallization apparatus to the outside of the purification apparatus via the solid-liquid separation device.

[0064] In the crystallization apparatus described above, the first to N-1 tanks preferably contain 30% or more, more preferably 60% or more, and most preferably all tanks up to the N-1th tank. The structure is such that the mother liquor is conveyed via a solid-liquid separation device to the next downstream tank (or the two downstream tanks and beyond) and / or discharged outside the crystallization apparatus. This arrangement reduces the size of the tanks and decreases investment and construction area. Furthermore, as mentioned above, from a cost perspective, the solid-liquid separation device is preferably shared with a solid-liquid separation device installed in the pipeline that conveys the slurry to the upstream tank.

[0065] However, since the Nth tank is preferably larger in capacity than the downstream tank in order to maintain / mature the slurry supplied to the cleaning column, and the purity of the slurry is improved, the crystal diameter is more likely to grow larger than that of the downstream tank, thus the design of the crystal settling region at the top of the tank, i.e., the clarified mother liquor layer, is relatively easy. Therefore, the Nth tank is preferably structured to directly supply the mother liquor to the downstream tank via overflow.

[0066] The crystallization apparatus of the present invention includes a crystallization tank equipped with a cooling mechanism. The crystallization tank is not particularly limited, as long as it can cool the solution of the compound to precipitate crystals and generate a slurry containing crystals and mother liquor. Generally, there are two types: one where the tank itself has a cooling jacket that directly cools the tank to generate crystals; and another where the cooling mechanism is separate from the tank but connected via piping, allowing for simultaneous cooling / crystal generation through circulation.

[0067] While the method of using a cooling jacket attached to the tank itself has the advantage of requiring fewer pieces of equipment, it necessitates increasing the size of the tank itself to increase the heat transfer area. In situations requiring high production capacity, an excessively large tank presents disadvantages in terms of initial investment and floor space.

[0068] 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, 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 crystallization tank can be easily scaled up.

[0069] In this case, there is no particular limitation on the cooling mechanism, as long as it is a mechanism that can cool the solution of the compound and cause crystals to precipitate. However, it is preferable to use a shell-and-tube heat exchanger, a spiral heat exchanger, or a cooling disc crystallizer or a scraping cooling crystallizer that can ensure a large heat transfer area.

[0070] A cooling disc crystallizer is any crystallizer that cools a solution of a compound to precipitate crystals and then scrapes off the precipitated crystals. However, a crystallizer can be constructed by multiple cooling plates consisting of tubes and sections divided between the tubes, where crystals are generated on the walls of the cooling plates, and a stirring blade with a scraper rotates inside the tube to scrape off the crystals.

[0071] A scraping-type cooling crystallizer is any crystallizer that cools a solution of a compound to precipitate crystals and then scrapes off the precipitated crystals. However, crystallizers with a double-structure tube can be used, in which refrigerant flows in the outer tube and a solution of the compound (or a slurry containing crystals) flows in the inner tube. Crystals are formed on the wall of the inner tube, and a structure in which the shaft of a scraping blade rotates inside the inner tube to scrape off the crystals.

[0072] The crystallization apparatus of the present invention may or may not have a ripening tank, but it is preferred to have one. In this invention, the ripening 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 into as uniform a crystal as possible and conveying them to the cleaning column, impurities can be efficiently removed 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 ripening tank.

[0073] The ripening tank described above is not particularly limited, as long as it can maintain the compound crystals in a suspended state within the tank. By holding the crystals for a certain period of time, through Ostwald ripening, small crystals melt and further grow into larger crystals, narrowing the crystal diameter distribution, thereby further improving the purification efficiency in the washing column. Furthermore, even a crystallization tank, by holding the crystals for a certain period, can be expected to achieve the same effect as a ripening tank.

[0074] In the purification apparatus of the present invention, a slurry containing crystals of the compound is conveyed from the Nth tank of the crystallization apparatus to clean the crystals, thereby obtaining high-purity compound crystals as 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, at the lower part of the column, a portion of the crystals from the crystallization bed is extracted and heated to melt while suspended in a circulating liquid (cleaning liquid circulating within the cleaning column), and a portion of the circulating liquid containing the resulting melt is extracted as a product. A portion of the remaining circulating liquid (cleaning liquid) is brought into convective contact with the crystallization bed to clean the crystals. Additionally, the mother liquor in the cleaning column is returned to the crystallization apparatus via a pipeline that returns the mother liquor to the crystallization apparatus.

[0075] The pipeline that returns the mother liquor to the crystallization apparatus is connected to at least the Nth tank, but may also be connected to a tank further downstream. Alternatively, a pipeline may be included to return a portion of the mother liquor back to the cleaning column.

[0076] When the specific gravity of the crystals is less than that of the mother liquor, the crystals move upwards within the column, and the crystallization bed is suspended, melted, and the product is extracted at the top of the column, contrary to the above.

[0077] The purification apparatus of the present invention includes a cleaning column that forcibly transports the crystallization bed. Specifically, examples include mechanical cleaning columns that use a piston to compact crystals to form / transport the crystallization bed, and hydraulic cleaning columns (water pressure cleaning columns) that use a pump to deliver slurry to the column and extract mother liquor from a filter disposed 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).

[0078] There are no particular limitations on the cleaning column; it only needs to be able to clean crystals and can be either a mechanical or hydraulic cleaning column. Mechanical cleaning columns are characterized by high operational stability and high compound purification efficiency. Hydraulic cleaning columns, on the other hand, are characterized by high production capacity per unit column cross-sectional area, fewer driving components, and fewer malfunctions caused by the device. When purifying easily polymerizable substances, the use of hydraulic cleaning columns with fewer driving components can sometimes suppress polymer formation within the cleaning column.

[0079] As a preferred form of cleaning column, a cleaning column having a mechanical structure for scraping the crystallization bed can be cited (see U.S. Patent No. 3,872,009A). In cleaning columns with a forced transport mechanism for the crystallization bed, a method is used to scrape the purified crystallization bed with a scraper or the like, causing it to resuspend and then melt it.

[0080] Another preferred form of cleaning column is a cleaning column that does not have a mechanical structure for scraping the crystallization bed (see U.S. Patent No. 7,425,273B2). In this method, the crystallization bed is scraped by the dynamic pressure of the circulating liquid. The absence of sliding surfaces such as shaft seals can sometimes suppress the formation of polymers caused by liquid stagnation, sliding heat, etc., when purifying easily polymerizable substances.

[0081] The supply of the solution of the compound to be purified into the purification apparatus of the present invention can be carried out in any tank contained in the crystallization apparatus, but from the viewpoint of purification efficiency, it is preferable to carry it out in the second and subsequent tanks. Since the optimal location varies depending on the composition of the supply solution, the crystallization yield, and the concentration efficiency of the crystals in the solid-liquid separation apparatus, it can be appropriately selected.

[0082] The crystallization temperature in the crystallization tank of the purification apparatus of the present invention can be appropriately adjusted according to the type of compound to be purified, but it is generally -1 to -15°C relative to the melting point of the pure substance, preferably -1.5 to -13.5°C, more preferably -3.5°C to -12.5°C, and even more preferably in the range of -5 to -11.5°C. Furthermore, 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.

[0083] High temperatures in the crystallization tank produce high-purity crystals. However, when using a scraper-type cooling crystallizer (described later) in the crystallization tank, problems such as requiring excessive power to scrape the crystals from the tank may occur. Furthermore, if the temperature difference between the refrigerant and the crystallization tank is too high, problems such as blockage of the scraper used for scraping may occur, potentially hindering continued operation, especially when using a scraper-type cooling crystallizer in the crystallization tank.

[0084] 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. Low crystallization tank temperatures result in lower crystal purity. However, when a scraping-type cooling crystallizer is used in the crystallization tank, the power required to scrape the crystals is small, and even increasing the temperature difference between the refrigerant and the crystallization tank is unlikely 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, when the crystallization temperature is too low, the formed crystal grain size tends to be smaller, and the crystals are difficult to settle.

[0085] The residence time of compounds in crystallization tanks and aging tanks can be adjusted appropriately according to the type of compound to be purified, but considering the yield of the purified compound, the purification efficiency, and the equipment investment cost, it is approximately 0.02 to 6 hours.

[0086] 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 a certain time or more. Preferably, it is 0.5 to 6 hours, more preferably 1 to 5 hours, and even more preferably 1.2 to 4.5 hours.

[0087] 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 can reduce 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.

[0088] 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 in the form of a tank with external cooling, as described later. Furthermore, the residence time of each tank is calculated by dividing the total capacity of the tank and the external cooling mechanism 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 liquid transported / discharged from each tank to the lower-level tank or purification unit.

[0089] The purification apparatus of the present invention can be used for the purification of any compound, but as mentioned above, since it is also applicable to the purification of crystals with poor sedimentation properties, it can be used for the purification of (meth)acrylic acid. Therefore, purifying (meth)acrylic acid using the purification apparatus of the present invention is one of the preferred embodiments of the present invention.

[0090] In this case, the solution of the compound supplied to the purification apparatus 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 is a solution composed of (meth)acrylic acid, referring to a solution containing 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 solution or crude (meth)acrylic acid solution, for example, can yield a slurry containing (meth)acrylic acid crystals.

[0091] It should be noted that the aforementioned byproducts may include, for example, 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 protoanemonin. In addition, solvents such as toluene and methyl butyl ketone may sometimes be present.

[0092] In this specification, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0093] Figures 1-8 An example of the purification apparatus of the present invention is shown.

[0094] Figure 1 It is a crystallization device having one crystallization tank and one maturation tank, and is equipped with a pipeline for directly conveying mother liquor from the maturation tank (the upstream tank) to the crystallization tank, and a pipeline for directly discharging residue (mother liquor) from the crystallization tank (the downstream tank).

[0095] Solution 1 of the compound supplied to the purification unit is introduced into maturation tank 21. The slurry, cooled in crystallization tank 11 equipped with a cooling mechanism and containing precipitated crystals, is conveyed to solid-liquid separation unit 31 via pipeline 51. In 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 maturation tank 21 via pipeline 52, while the mother liquor is returned to crystallization tank 11 via pipeline 61. Additionally, residue 2 is discharged from crystallization tank 11 to the outside of the purification unit via pipeline 71, thereby adjusting the liquid level in crystallization tank 11. After crystal growth in maturation tank 21, the crystal slurry is conveyed to mechanical cleaning column 41 via pipeline 53. Furthermore, to adjust the liquid level in maturation tank 21, mother liquor is directly conveyed from maturation tank 21 to crystallization tank 11 via pipeline 72.

[0096] Within the mechanical cleaning column 41, crystals are compacted by a piston to form a crystallization bed. Then, the crystallization bed is scraped, suspended in a circulating liquid, and heated to melt at the bottom of the column. A portion of the circulating liquid, containing the resulting melt, is transported out as high-purity compound 3. The remaining portion of the circulating liquid (cleaning liquid) is returned to the mechanical cleaning column 41, where it comes into convective contact with the crystallization bed to clean the crystals. Furthermore, the mother liquor within 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.

[0097] Figure 2 This is a crystallization apparatus comprising one crystallization tank and one maturation tank. It is equipped with a pipeline for directly supplying mother liquor from the maturation tank (the upstream tank) to the crystallization tank, and a pipeline for directly discharging residue (mother liquor) from the crystallization tank (the downstream tank). Furthermore, the crystallization tank is a type of tank that cools the contents of the tank outside the main tank. The following discussion focuses only on... Figure 1 The different parts of the purification device will be explained.

[0098] The crystallization tank 11 consists of a tank 11A and an external cooling mechanism 11B, connected by pipelines 111 and 121. A solution of the compound (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 slurry is transported to solid-liquid separation device 31 via pipeline 51.

[0099] Figure 3 This is a crystallization apparatus with two crystallization tanks. It is equipped with a pipeline for directly supplying mother liquor from the upstream crystallization tank 12 to the downstream crystallization tank 11, and a pipeline for directly discharging residue (mother liquor) from the downstream crystallization tank 11. Furthermore, the cleaning column is hydraulic and has a mechanical structure for scraping the crystallization bed. The following only pertains to... Figure 1 The different parts of the purification device will be explained.

[0100] The solution 1 of the compound supplied to the purification device is introduced into the crystallization tank 12.

[0101] The crystallization tank 11 consists of a tank 11A and an external cooling mechanism 11B, connected by pipelines 111 and 121. A solution of the compound (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 slurry is transported to solid-liquid separation device 31 via pipeline 51.

[0102] 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.

[0103] Crystal slurry is transported from crystallization tank 12 to hydraulic cleaning column 42 via pipeline 53. At the bottom of hydraulic cleaning column 42, a mechanical mechanism (scraper) scrapes the crystallization bed, suspending it in circulating liquid while simultaneously removing it and heating it to melt. A portion of the circulating liquid containing the resulting melt is transported out as high-purity compound 3. The remaining portion of the circulating liquid (cleaning liquid) is returned to hydraulic cleaning column 42, where it convects with the crystallization bed to clean the crystals.

[0104] Figure 4 This is a crystallization apparatus with two crystallization tanks and one ripening tank. A pipeline connects the three tanks, directly supplying mother liquor from the upstream tank, and a pipeline directly discharging residue (mother liquor) from the downstream tank. The following only applies to... Figure 1 The different parts of the purification device will be explained.

[0105] 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, thereby adjusting the liquid level in the crystallization tank 11. The same operation is performed in the crystallization tank 12, where the slurry containing 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, 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 mechanical cleaning column 41 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.

[0106] Figure 5 This is a crystallization apparatus with three crystallization tanks and one ripening tank. Pipelines are installed between the four tanks to directly supply mother liquor from the upstream tank, and pipelines are also installed to directly discharge residue (mother liquor) from the downstream tank. Furthermore, the cleaning column is hydraulic and has a mechanical structure for scraping the crystallization bed. The following only pertains to... Figure 4 The different parts of the purification device will be explained.

[0107] The compound solution 1 supplied to the purification unit is introduced into the crystallization tank 13. The slurry containing crystals is transported from the second downstream 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 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 transported 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. 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.

[0108] At the lower part of the hydraulic cleaning column 42, the crystallization bed is scraped by a mechanical mechanism (scraper), and while it is suspended in the circulating liquid, it is taken out and heated to melt. A portion of the circulating liquid containing the resulting melt is transported out as high-purity compound 3. The remaining portion of the circulating liquid (cleaning liquid) is returned to the hydraulic cleaning column 42, where it comes into convective contact with the crystallization bed to clean the crystals.

[0109] Figure 6 This is a crystallization apparatus with two crystallization tanks and one ripening tank. A pipeline is installed between the three tanks to transport mother liquor from the upstream tank via a solid-liquid separation device, and a pipeline is also installed to discharge residue from the downstream tank via the solid-liquid separation device. The following only applies to... Figure 4 The different parts of the purification device will be explained.

[0110] exist Figure 6 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 sent back to the crystallization tank 11, thereby adjusting the liquid level in the crystallization tank 11.

[0111] 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 sent back to the crystallization tank 12.

[0112] 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 sent back to the maturation tank 21.

[0113] The cleaning column 43 is hydraulic and does not have a mechanical structure for scraping the crystallization bed.

[0114] Figure 7 This is a crystallization apparatus comprising two crystallization tanks and one maturation tank. It has a pipeline connecting the three tanks, through which mother liquor is transported from the upstream tank via a solid-liquid separation device, and a pipeline connecting the downstream tank via a solid-liquid separation device to discharge residue. 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, as well as the solid-liquid separation device used to separate the residue discharged from the downstream (first) crystallization tank to the purification apparatus, are shared with the solid-liquid separation device installed in the pipeline transporting slurry to the upstream tank. The following only applies to... Figure 6 The different parts of the purification device will be explained.

[0115] exist Figure 7 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 apparatus via an additional pipeline 101 connected to pipeline 61.

[0116] 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 being 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 returned to the crystallization tank 11 via an additional pipeline 102 connected to pipeline 62.

[0117] exist Figure 7 In the purification device, pipeline 51 → solid-liquid separation device 31 → pipelines 61, 101 and Figure 6 The 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 6 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.

[0118] Figure 8 This is a crystallization apparatus comprising two crystallization tanks and one maturation tank. It 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 a solid-liquid separation device. It also includes a pipeline for directly conveying mother liquor from the maturation tank to the second crystallization tank. The solid-liquid separation device 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 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 externally. The following only applies to... Figure 7 The different parts of the purification device will be explained.

[0119] exist Figure 8 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 solution of the compound (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 crystals of the compound 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.

[0120] 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 the remaining slurry is transported to the solid-liquid separation device 32 through pipeline 53.

[0121] exist Figure 8 In the device, replacing Figure 7The 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.

[0122] Explanation of reference numerals in the attached figures

[0123] 1: Solution of the compound

[0124] 2: Residue

[0125] 3: High-purity compounds

[0126] 11-13: Crystallization tank with cooling mechanism

[0127] 11A, 12A: Tank

[0128] 11B, 12B: Cooling mechanism

[0129] 21: Curing tank

[0130] 31-35: Solid-liquid separation device

[0131] 41: Mechanical cleaning column

[0132] 42: Hydraulic cleaning column (with mechanical structure for scraping the crystallization bed)

[0133] 43: Hydraulic cleaning column (without mechanical structure for scraping the crystallization bed)

[0134] 51–57: Pipelines that transport slurry (or crystals) from downstream tanks to upstream tanks or cleaning columns.

[0135] 61-63: Pipelines that return the mother liquor separated from the slurry by the solid-liquid separation device to the original tank.

[0136] 71: A pipeline that discharges the residue (mother liquor) directly from the downstream tank to the outside of the purification unit.

[0137] 72-74: Pipelines that directly transport mother liquor from the upstream tank to the next downstream tank.

[0138] 75: The pipeline that returns the mother liquor from the cleaning column to the crystallization unit.

[0139] 81-86: Pipelines for separating crystals from slurry taken from the tank and returning it to the original tank using a solid-liquid separation device.

[0140] 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.

[0141] 92, 93: Pipelines for conveying the mother liquor separated from the slurry taken from the tank using a solid-liquid separation device to the next downstream tank.

[0142] 101: An additional pipeline used to discharge a portion of the mother liquor separated from the slurry taken from the downstream tank of the solid-liquid separation unit to the outside of the purification unit.

[0143] 102: An additional pipeline for conveying a portion of the mother liquor separated from the slurry taken from the second tank by the solid-liquid separation unit to the downstream tank.

[0144] 111, 121, 112, 122: Pipelines connecting the crystallization tank to the cooling mechanism in the form of cooling tank contents outside the tank.

Claims

1. A purification device, characterized in that, It is a purification device for compounds, comprising a crystallization apparatus and a washing column. The crystallization apparatus has a crystal formation section, and the washing column forcibly transports the crystals. The cleaning column is either a mechanical cleaning column that uses a piston to compact the crystals to form / transport a crystallization bed, or a hydraulic cleaning column that uses a pump to deliver slurry to the column and extracts mother liquor from a filter located inside the column to form / transport a bed. 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 transporting the product out and a pipeline for returning the mother liquor to the crystallization apparatus, the pipeline returning to the crystallization apparatus being 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 N-1 downstream tanks to the upstream tank 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, to the original tank. At least one of the solid-liquid separation devices installed in the pipeline that transports slurry from a downstream tank to an upstream tank has, in addition to a pipeline that returns the mother liquor to the original tank, one or more additional pipelines for transporting the mother liquor, which are connected to a tank and / or purification device downstream of the original tank. The pipelines that transport 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 transports mother liquor from the upstream tank above it, and a pipeline that transports mother liquor from the upstream tank above it via a solid-liquid separation device. The purification device also has a pipeline for conveying the mother liquor outside the purification device.

2. The purification device of claim 1, wherein, The crystallization apparatus contains tanks 1 to N-1, each having 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 to the original tank.

3. Purification device according to claim 1 or 2, characterized in that Of the pipelines that transport mother liquor from the upstream tank to each of the 1st to N-1th tanks, at least one is a pipeline that transports mother liquor from the previous upstream tank via a solid-liquid separation device.

4. The purification device of claim 1 or 2, wherein, At least one of the 1 to N-1 tanks in the crystallization apparatus has a pipeline that directly supplies mother liquor from the upstream tank above.

5. The purification device of claim 1 or 2, wherein, It has a pipeline for conveying mother liquor from the first tank contained in the crystallization device to the outside of the purification device via a solid-liquid separation device.

6. The purification device of claim 1 or 2, wherein, The cooling mechanism is in the form of cooling the contents of the tank from outside the tank.

7. The purification device of claim 1 or 2, wherein, The cleaning column has a mechanical mechanism for scraping the crystallization bed.

8. The purification device of claim 1 or 2, wherein, The cleaning column does not have a mechanical mechanism for scraping the crystallization bed.

9. The purification device of claim 1 or 2, wherein, The compound is (meth)acrylic acid.

10. The purification device of claim 1 or 2, wherein, Of the slurry-carrying pipelines of the crystallization device that transport slurry from the downstream tank to the upstream tank, at least the pipeline transporting slurry from the (N-1)th tank to the Nth tank is a pipeline that transports slurry from the upstream tank via the solid-liquid separation device. The solid-liquid separation device installed in the pipeline that transports slurry from the (N-1)th tank to the Nth tank is a basket centrifuge or a decanter centrifuge.

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