WO2007088981A1

WO2007088981A1 - Process for producing carboxylic acid

Info

Publication number: WO2007088981A1
Application number: PCT/JP2007/051827
Authority: WO
Inventors: Shigeho Tanaka; Yoshimasa Ando; Miezi Sugiyama; Haruki Sato
Original assignee: Mitsubishi Rayon Co., Ltd.
Priority date: 2006-02-03
Filing date: 2007-02-02
Publication date: 2007-08-09
Also published as: CN101410365A; CN101410365B; KR20080103981A; KR101306357B1; JP5114195B2; JPWO2007088981A1

Abstract

Before a crystallization step in which a carboxylic acid is crystallized from a carboxylic-acid-containing liquid in crystallization tanks (12) and (13) each having a cooling surface, a preliminary step is conducted in which at least part of the carboxylic-acid-containing liquid is fed to a cooling device (11) equipped with cooling surfaces (15) and (16) and scraping means (18) and (19) for scraping the cooling surfaces and is cooled from a temperature exceeding the crystallization initiation temperature to a temperature not higher than the crystallization initiation temperature. This process is preferable especially when the carboxylic acid is acrylic acid and/or methacrylic acid.

Description

Specification

Method for producing carboxylic acid

Technical field

[0001] The present invention relates to a method for producing a carboxylic acid comprising a crystallization step of crystallizing a carboxylic acid.

This application claims priority based on Japanese Patent Application No. 2006-026766 filed with the Japan Patent Office on February 3, 2006, the contents of which are incorporated herein by reference.

Background art

[0002] When industrially producing a carboxylic acid such as (meth) acrylic acid, a purification process for removing impurities and solvents generated in the production process is indispensable. As such a purification process, extraction, distillation, crystallization, etc. are common, but when the substance to be removed is a substance having a high boiling point and a high melting point, or a substance having a high polymerization property. Often, crystallization methods that can be purified to high purity at low temperatures are used. The most general crystallization method is a method in which the mixture to be purified is cooled by a cooling medium through a cooling surface.

However, among carboxylic acids, for example, when (meth) acrylic acid is crystallized by such a method,

(Meth) acrylic acid easily adheres to the cooling surface! Therefore, a scale gradually formed on the cooling surface, which hindered stable operation of the apparatus and reduced productivity. Therefore, there is a need for a crystallization method that can suppress the formation of scale.

In addition, if the resulting carboxylic acid crystals are fine particles, the liquid removal property in the post-process will be poor, and as a result, if the purity of the resulting carboxylic acid is reduced, an increase in purification load will be required. In addition, the productivity is reduced. Therefore, the crystallization method is also required to be a method capable of obtaining a crystal particle force S of a certain particle size or more.

Furthermore, from an industrial point of view, it is required to be a crystallization method that can be carried out with as low an equipment as possible and is suitable for mass production.

[0004] For example, Patent Documents 1 to 4 and the like disclose a method of purifying by a sweating action in which a crystal is deposited on a stationary surface and then partially melted. In such a method, In order to share the cooling surface for crystal precipitation and purification, low productivity and expensive equipment is required. , Economically disadvantageous.

[0005] As a method using a cheaper apparatus, there is a method using a crystallization tank provided with a cooling surface and a scraping means for scraping off the cooling surface. However, in order to achieve high productivity in such a method, cooling must be strengthened, and a strong scale that is difficult to peel off is generated on the cooling surface, and stable operation tends to be difficult. Thus, for example, Patent Document 5 discloses a method for reducing the generation of scale on the cooling surface by adding a small amount of a solvent.

However, the method disclosed in Patent Document 5 cannot sufficiently suppress the scale. In addition, in order to reduce the solid scale, there is a method of strengthening the scraping by the scraping means, but if the scraping is strengthened, the crystals in the tank are crushed, inhibiting the crystal growth, Coarse crystal grains cannot be obtained.

Furthermore, when trying to produce industrially in large quantities using such a crystallization tank, the internal volume of the crystallization tank will be increased, but the normal crystallization with the inner wall of the tank as the cooling surface will be used. In the tank, the area of the cooling surface becomes relatively smaller as the internal volume increases, so the heat removal load per area of the cooling surface increases and effective operation is not possible. However, it is difficult to respond to industrial production by simply increasing the internal volume of the crystallization tank, for example, it is difficult to operate the scraping means at high speed.

Patent Document 1: Japanese Patent Laid-Open No. 2001-199931

Patent Document 2: Japanese Patent Laid-Open No. 11-199524

Patent Document 3: Japanese Patent Laid-Open No. 9-227445

Patent Document 4: Japanese Patent Laid-Open No. 7-48311

Patent Document 5: International Publication No. 99Z06348 Pamphlet

Disclosure of the invention

Problems to be solved by the invention

[0007] The present invention has been made in view of the above circumstances, and when crystallization of a carboxylic acid-containing liquid in a crystallization tank, the inner wall surface of the crystallization tank, in particular, the inner wall surface serving as a cooling surface is played. Providing stable, economical industrial production of coarse crystal particles with high productivity that can suppress the formation of strong scales and have excellent liquid drainage (for example, filterability and washability) in subsequent processes Impose The title.

Means for solving the problem

As a result of intensive studies by the present inventors, at least a part of the carboxylic acid-containing liquid is removed before the crystallization step of crystallizing the carboxylic acid-containing liquid carbonate in the crystallization tank. It has been found that the above-mentioned problems can be solved by carrying out a preliminary process for cooling under specific conditions. That is, when the preliminary process is performed, the microcrystals generated in the preliminary process act as seed crystals in the crystallization process. In addition, since it is not necessary to strongly cool the carboxylic acid-containing liquid in the crystallization tank, depending on the conditions, the degree of supersaturation in the liquid decreases and the fine crystals dissolve and re-precipitate on the surface of larger crystals. Therefore, the coarsening of the crystal is promoted, and the generation of scale and fine crystal particles due to the strong cooling can be suppressed. As described above, when the preliminary process was carried out, it was found that coarse crystal particles of carboxylic acid having excellent liquid removal properties in the subsequent process could be stably produced with high productivity, and the present invention was completed.

[0009] The method for producing a carboxylic acid according to the present invention is arranged at the front stage of the crystallization tank, having at least a part of the carboxylic acid-containing liquid, a cooling surface and a scraping means for scraping off the cooling surface. A temperature force exceeding the crystallization start temperature of the carboxylic acid-containing liquid supplied to the cooler, a preliminary step of cooling the carboxylic acid-containing liquid to the crystallization start temperature or lower to produce a cooled carboxylic acid-containing liquid; And a crystallization step of crystallizing the carboxylic acid containing the cooled carboxylic acid-containing liquid in the precipitation tank.

The invention's effect

According to the present invention, when the carboxylic acid-containing liquid is crystallized in the crystallization tank, the inner wall surface of the crystallization tank

(Hereinafter referred to as the inner wall) can suppress the formation of strong scales, and the coarse crystal particles with excellent drainage (for example, filterability and washability) in the subsequent process are stable and economical with high productivity. Can be industrially produced.

Brief Description of Drawings

FIG. 1 is a schematic configuration diagram showing an example of a carboxylic acid production apparatus used in the carboxylic acid production method of the present invention.

2 is a schematic view showing a scraping means in the cooler of the apparatus of FIG.

FIG. 3 is a schematic configuration diagram showing a carboxylic acid production apparatus used in Examples. Explanation of symbols

[0012] 10 Carboxylic acid production equipment

11 Cooler

12 First crystallization tank

13 Second crystallization tank

30 Carboxylic acid production equipment

31 Cooler

32 Crystallization tank

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

The method for producing a carboxylic acid of the present invention is such that at least a part of the carboxylic acid-containing liquid exceeds the crystallization start temperature before the crystallization step of crystallizing the carboxylic acid-containing liquid force carboxylic acid in the crystallization tank. It has a preliminary process of cooling to a temperature below the crystallization start temperature.

[0014] The carboxylic acid-containing liquid may be a liquid carboxylic acid as long as it contains at least a carboxylic acid and precipitates a carboxylic acid crystal as the temperature decreases. It may be a liquid in which carboxylic acid is dissolved in a solvent. Specifically, a liquid in which a carboxylic acid to be purified is dissolved in a solvent, a liquid containing a carboxylic acid obtained in the carboxylic acid production process (mother liquor), and after a carboxylic acid crystal is partially separated. A mother liquor, a melt of carboxylic acid crystals, etc. may be mentioned, and any treatment may be performed.

The type of carboxylic acid is not particularly limited, but according to the present invention, even carboxylic acid having strong adhesion to the inner wall surface can suppress such adhesion. The case of methacrylic acid is effective.

FIG. 1 is a schematic configuration diagram showing an example of a carboxylic acid production apparatus 10 used in the carboxylic acid production method of the present invention, and shows a first configuration installed in series for performing a crystallization process. The crystallization tank 12 and the second crystallization tank 13, and a cooler 11 provided on the front side of the crystallization tanks 12 and 13 for performing the preliminary process are provided. The cooler 11 used in this example is a double-cylindrical scooping-type heat exchanger ^^, where the inner surface 15 of the cylindrical outer cylinder and the outer surface 16 of the cylindrical inner cylinder are respectively It is on the cooling surface. The inner surface of the outer cylinder (hereinafter referred to as the outer cylinder side cooling surface) 15 and the outer surface of the inner cylinder (hereinafter referred to as the inner cylinder side cooling surface) 16 can be controlled independently. The temperature and flow rate of the cooling medium acting on each cooling surface can be individually adjusted. Specifically, such independent control is achieved by installing a cooling medium flow path and an automatic or manual flow control valve on the outer cylinder side cooling surface 15 and the inner cylinder side cooling surface 16, respectively. Can be possible.

[0016] In the cooler 11 of this example, as shown in the schematic diagram of FIG. 2, the outer cylinder side cooling surface 15 is scraped off as a scraping means for scraping the cooling surface. The outer cylinder side scraping means 18 and the inner cylinder side scraping means 19 for scraping the inner cylinder side cooling surface 16 are provided. The outer cylinder side scraping means 18 includes a rotary scraper 20 that rotates about the axis of the cooler 11 (the longitudinal center line of the outer cylinder and the inner cylinder) along the longitudinal direction of the cooler 11. Each scraper 20 is provided with a plate-shaped scraper (scraper) 21 made of polytetrafluoroethylene (PTFE) and having a thickness of 10 mm. Therefore, by rotating each scraping portion 20 in the direction indicated by the arrow in the figure, the side end of each scraper 21 is in contact with the outer cylinder side cooling surface 15 and the deposits on the outer cylinder side cooling surface 15 are adhered. It is supposed to scrape off.

Further, in this example, the two rows of scraping portions 20 are positioned symmetrically with respect to the axis of the cooler 11.

The inner cylinder side scraping means 19 is also configured to have two rows of scraper portions 22 having similar scrapers 21 along the longitudinal direction of the cooler 11, and each scraper By rotating the part 22 in the direction indicated by the arrow in the figure, the side end of each scraper 21 is in contact with the inner cylinder side cooling surface 16 and the deposits on the inner cylinder side cooling surface 16 are scraped off. It has become. In the cooler 11 of this example, the scraper 20 and the scraper 22 rotate together.

[0018] The first crystallization tank 12 and the second crystallization tank 13 are provided with cooling or cold insulation jackets (not shown) on the outside, and the inner wall surfaces of the crystallization tanks 12 and 13 are cooling surfaces. Or it is a cold surface. Each of the crystallization tanks 12 and 13 is provided with a rotating type scraping means (scraping blade) (not shown) for scraping off deposits adhering to the inner wall surface.

The carboxylic acid-containing liquid supply pipe 23 is branched in the middle, one connected to the cooler 11 and the other connected to the first crystallization tank 12. A supply valve 24 that can be freely opened and closed is provided in the middle of the supply pipe 23 branched to the cooler 11.

In addition, a temperature indicator 25 is provided to measure the cooler outlet temperature of the carboxylic acid-containing liquid.

[0019] Next, an example of a specific method for crystallizing carboxylic acid with carboxylic acid-containing liquid force using such an apparatus 10 will be described.

First, the supply valve 24 provided in the middle of the line for supplying the carboxylic acid-containing liquid to the cooler 11 is closed, and the first liquid containing the carboxylic acid-containing liquid is directly supplied from the supply pipe 23 without going through the cooler 11. To the second crystallization tank 13, and then to the second crystallization tank 13 whose drain port (not shown) is closed. When the carboxylic acid-containing liquid in the second crystallization tank 13 reaches a predetermined amount, the drainage port (not shown) of the first crystallization tank 12 is closed and the carboxylic acid-containing liquid in the first crystallization tank 12 is closed. When the acid-containing liquid reaches a predetermined amount, supply is stopped. Next, the scraping blades of the first crystallization tank 12 and the second crystallization tank 13 are operated, and a cooling medium is circulated through the respective cooling jackets, so that the first crystallization tank 12 The bath temperature and the second crystallization bath 13 are gradually cooled so that the bath temperature finally becomes lower than the crystallization start temperature. The temperature in the tank varies depending on the type, concentration, solvent, etc. of the carboxylic acid to be handled, but in general, it is preferable to set the crystallization tank slurry concentration at which the solubility power is calculated to be 40% or less. Also, since the temperature inside the crystallization tank is usually set lower in the latter stage crystallization tank, the temperature in the second crystallization tank 13 is also higher than the temperature in the first crystallization tank 12 in this case. It is preferable to set the internal temperature low.

[0020] Next, after the internal temperatures of the first crystallization tank 12 and the second crystallization tank 13 stabilize at a predetermined temperature, the supply valve 24 remains closed and the supply of the carboxylic acid-containing liquid is resumed. At the same time, the discharge ports of the first crystallization tank and the second crystallization tank 13 are opened, and the extraction of the carboxylic acid-containing liquid containing carboxylic acid crystals is started. At this time, the supply rate of the carboxylic acid-containing liquid is the crystallization calorimetric force scaling to be removed in the first crystallization tank 12 and the second crystallization tank 13. The amount is not particularly limited as long as the amount of the crystal obtained from the second crystallization tank 13 is not more than the target particle size. The supply temperature is not particularly limited as long as it exceeds the crystallization start temperature, but is preferably within the heat removal capability range of the first crystallization tank 12 and the second crystallization tank 13.

Thus, the supply valve 24 is opened, and a part of the carboxylic acid-containing liquid is branched and introduced into the cooler 11.

The flow rate of the carboxylic acid-containing liquid that passes through the cooler 11, the flow rate that does not pass through the cooler 11, and the total flow rate to the first crystallization tank can be adjusted according to the target production amount. In addition, the appropriate residence time of the carboxylic acid-containing liquid in the crystallization tank is the crystal growth rate, nucleation rate, target production rate, target crystal grain size, crystallization tank of the carboxylic acid-containing liquid force used. It depends on the amount of heat removed in the room, so it cannot be determined in general, but the appropriate staying time can be determined each time by chemical engineering techniques. Then, the outer cylinder side scraping means 18 and the inner cylinder side scraping means 19 are operated at a scraping frequency of 150 times Z or more respectively, and the outer cylinder side cooling surface 15 and the inner cylinder of the cooler 11 are operated. A cooling medium is allowed to act on the side cooling surface 16 to perform a preliminary process for cooling the carboxylic acid-containing liquid. The scraping frequency is preferably 180 times Z minutes or more, more preferably 200 times Z minutes or more. The scraping frequency is preferably 1000 times Z minutes or less, more preferably 400 times Z minutes or less.

By such a preliminary process, the carboxylic acid-containing liquid is cooled so that the cooler outlet temperature is equal to or lower than the crystallization start temperature of the carboxylic acid-containing liquid (hereinafter simply referred to as the crystallization start temperature). Part of the carboxylic acid contained in the precipitates as fine crystal particles. The crystallization start temperature is a temperature at which carboxylic acid crystals begin to precipitate when the carboxylic acid-containing liquid is cooled.

[0022] Here, the scraping frequency is "the number of operations per minute of the scraping member that acts directly on the cooling surface". Therefore, when the scraping member is composed of a rotary scraper 21 as shown in this example and two rows of scraping portions 20 and 22 equipped with the scraper 21 are provided, “150 times or more of Z min. The “frequency of scraping” can be achieved by rotating the scrapers 20, 22 at least 75 revolutions per minute. That is, when the number of rows of the scraping portions 20 and 22 is N, this can be achieved by rotating more than (150ZN) rotations per minute. [0023] The slurry-like carboxylic acid-containing liquid (cooled carboxylic acid-containing liquid) that has been cooled to a temperature lower than or equal to the crystallization start temperature by such a preliminary process and in which a part of the carboxylic acid has precipitated is converted into the first crystal. A crystallization process is performed in which the crystals are sequentially introduced into the crystallization tank 12 and the second crystallization tank 13 for crystallization.

Crystal growth is promoted by such a crystallization process. From the second crystallization tank, the number of crystal nuclei per unit slurry volume is smaller than that of the slurry introduced from the cooler 11 to the crystallization tank 12. A slurry-like carboxylic acid-containing liquid containing crystals is discharged.

After such a crystallization process, post-processes such as a filtration process, a washing process, and a drying process are performed as necessary from the discharged carboxylic acid-containing liquid, and carboxylic acid crystal particles are recovered.

[0024] By cooling at least a part of the carboxylic acid-containing liquid in the preliminary step and then supplying it to the crystallization step, the carboxylic acid-containing liquid need not be strongly cooled in the crystallization tanks 12 and 13. Therefore, it is possible to suppress the scale on the cooling surface of the crystallization tanks 12 and 13 and the generation of fine crystal particles due to the strong cooling, and excellent crystal drainage in the subsequent process and sufficient crystal growth. Coarse crystal particles of carboxylic acid can be obtained. In addition, since no scale is generated, the operation of the apparatus can be performed stably, and a reduction in cooling efficiency due to adhesion of the scale to the cooling surface is suppressed, so that productivity can be maintained high. Further, since it is not necessary to excessively operate the scraping blades of the crystallization tanks 12 and 13 in order to crush the scale, it is possible to suppress the generation of fine particles due to the shattering blades. In addition, since the crystal grains precipitated in the preliminary process have a low degree of supersaturation in the crystallization tanks 12 and 13, depending on the conditions, the microcrystals dissolve and re-precipitate on the surface of larger crystals. For these reasons, crystal grains having a larger particle size are more likely to be generated in the crystallization process.

[0025] Further, in the preliminary process, it is preferable to operate the scraping means 18 and 19 of the cooler 11 so that the scraping frequency is 150 times Z or more, respectively. Since the cooling efficiency of the cooler 11 is improved by suppressing the accumulation of scale on the chiller, the temperature force that exceeds the crystallization start temperature of the carboxylic acid-containing liquid can be easily and stably reduced to the crystallization start temperature or lower. Can be cooled. Further, as the scraping frequency is lower, the amount of heat generated by the friction between the scraper provided in the scraping means and the cooling surface is reduced, so that the cooling efficiency of the cooler 11 is improved. [0026] Further, in the preliminary process, the carboxylic acid-containing liquid may be cooled to a temperature not higher than the crystallization start temperature, but the slurry concentration at the outlet of the cooler 11 is not higher than a concentration that does not cause a problem in the subsequent transfer. Preferably in the temperature range. The slurry concentration is preferably 40% by volume or less, and more preferably 20% by volume or less.

Furthermore, in the preliminary process, the heat removal load of the first crystallization tank 12 and the second crystallization tank 13 in the crystallization process is less than or equal to the heat removal load that causes scaling, more specifically, 8.4 MjZhrZm. ² or less, and it is more preferable to cool such that 7. 5MjZhrZm ² below. By vigorously cooling to such a degree in the preliminary process, there is no need to strongly cool the carboxylic acid-containing liquid in the crystallization process, and the crystallization tank resulting from the strong cooling in the crystallization tank. In addition to reducing the generation of scales on the cooling surfaces of 12 and 13 and the generation of fine particles in the crystallization tank, the crystals produced in the preliminary process dissolve and the crystallized components are coarser. It is easy to obtain coarse crystals that deposit on the surface of the material and have excellent dewatering and cleaning properties.

[0027] The heat removal load of the crystallization tanks 12 and 13 is the "heat transfer amount per lm ² of the cooling surface of the crystallization tank", and the crystallization tanks 12 and 13 are in this example. In the case where the cooling surface is cooled by the cooling jacket, it is possible to calculate the differential force between the amount of heat between the cooling medium flowing into the cooling jacket and the cooling medium flowing out from the cooling jacket. It is also possible to calculate the calorimetric change force of the carboxylic acid-containing liquid in the crystallization tanks 12 and 13. Here, it is defined by the following formula.

(Heat removal load) = {(crystallization tank inflow enthalpy)-(crystallization tank outflow enthalpy)} /

(Cooling surface area)

However,

(Enthalpy) = (supernatant flow) X (liquid specific heat) X (temperature) + (crystal flow) X (crystal specific heat) X (temperature) (crystal flow) X (crystallization heat (absolute value))

[0028] Further, in the preliminary process, the power for cooling the carboxylic acid-containing liquid to a temperature not higher than the crystallization start temperature by the cooler 11, preferably, the preliminary process is preferably started up stepwise as follows.

First, apply to only one of the cooling surfaces of the outer cylinder side cooling surface 15 or the inner cylinder side cooling surface 16. Cooling is performed so that the temperature of the carboxylic acid-containing liquid discharged from the cooler 11 does not become lower than the crystallization start temperature, that is, to a certain temperature (t) that exceeds the crystallization start temperature, for example, by applying a cooling medium. To do. (First step). Then, after the temperature of the carboxylic acid-containing liquid discharged from the cooler 11 is stabilized at this temperature (t) that exceeds the crystallization start temperature, a cooling medium is allowed to act on the other cooling surface, etc. The carboxylic acid-containing liquid is cooled to a temperature not higher than the crystallization start temperature (second step).

Here, the temperature (t) is a temperature that exceeds the crystallization start temperature, but is lower than the supply temperature of the carboxylic acid-containing liquid and not more than 2 ° C higher than the crystallization start temperature. Is preferable.

It is preferable to start up the preliminary process stepwise in this manner, because the carboxylic acid-containing liquid can be easily and stably cooled to the crystallization start temperature or lower in the preliminary process. “Temperature stable” here means that the difference between the minimum and maximum temperature for at least 5 minutes is within 1 ° C! Uh.

[0029] As described above, in the first step, the carboxylic acid-containing liquid is operated so that the temperature thereof does not become the crystallization start temperature or lower. A method of allowing a cooling medium to act on only one of the side cooling surface 15 and the inner cylinder side cooling surface 16 is an easy and effective method. In addition to this, a method for preventing the carboxylic acid-containing liquid from coming into contact with one cooling surface, a method for adjusting the temperature and flow rate of the cooling medium to be passed may be employed, and depending on circumstances. For example, combine the heating method with a separate heating means.

[0030] As described above, according to the method having the preliminary process and the crystallization process described above, the crystallization tanks 12, 13 can be obtained only by using an apparatus having a simple configuration without using an expensive apparatus. It is possible to suppress the formation of strong scale on the cooling surface, excellent liquid drainage in the subsequent process (for example, filterability and washability), and stable and high-quality coarse carboxylic acid crystal particles with sufficient crystal growth. Can be manufactured economically. In addition, since the heat removal load in the crystallization process can be reduced, even if the internal volume of the crystallization tank is increased and the area of the cooling surface is relatively reduced during industrial mass production, problems are unlikely to occur.

[0031] In the above description, as the cooler used in the preliminary process, a plurality of independently controllable devices are used. Although a double-cylindrical scraped heat exchanger having a cooling surface is illustrated, there is no particular limitation on the form of the cooler. However, since it is preferable to start up the preliminary process step by step as described above, it is provided with a cooler capable of such start-up, that is, with a plurality of independently controllable cooling surfaces. I prefer a cooler that can activate the rest after actuating some first.

[0032] Also, the form of the scraping means provided in the cooler and the scraping method should be capable of scraping the cooling surface and ensuring a scraping frequency of 150 times Z or more. For example, it is not limited to a rotary type, and may be a belt type, a screw type, a cooling surface rotary type, or the like. Also, as shown in the example, there are one or more rows of rotary scrapers 20, 22 that rotate about the axis of the cooler 11 in the longitudinal direction of the cooler. In the case where the scraper 21 is mounted, the thickness of each scraper 21 is preferably 10 mm or less, more preferably 5 mm or less. In addition, in the case of a cooler having a plurality of cooling surfaces, each has a scraping means, and each must operate at a scraping frequency of 150 times Z or more. The form of the heat sink may be different or the same for each cooling surface.

[0033] A plurality of crystallization tanks may be provided in series as shown in the drawing, or a plurality of crystallization tanks may be provided in parallel. Each crystallization tank can be a general stirring tank, tank, or the like, which is not limited in volume and form, as long as the residence time sufficient for the carboxylic acid to grow sufficiently can be secured. The crystallization tank is preferably provided with a scraping means, but is not necessarily provided. The residence time of the carboxylic acid-containing liquid in the cooler is preferably 1% or less, which is preferably 10% or less of the residence time of the carboxylic acid-containing liquid in the crystallization tank because fine crystals can be obtained. . There is no particular restriction on the ratio between the volume of the crystallization tank and the volume of the cooler, but in order to configure the equipment in a space-saving and low-cost manner, it has sufficient cooling capacity to remove the excessive amount of heat during the crystallization process This can be achieved by selecting a vessel.

In the illustrated example, only a part of the carboxylic acid-containing liquid is subjected to the preliminary process and the rest is directly subjected to the crystallization process. However, the entire amount of the carboxylic acid-containing liquid may be subjected to the preliminary process. ! ヽ. In order to efficiently generate fine crystals in the cooler, cool the carboxylic acid-containing liquid. It is preferable to supply the container with a single pass.

Example

Hereinafter, the method of the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Example 1]

Using the apparatus shown in Fig. 1, the preliminary process and the crystallization process were performed.

As the cooler 11, “Tarmouth Therm (trade name, manufactured by N • V. Machinefabriek Terlet)” was used as a double-cylindrical type heat exchanger. This heat exchange ^^ consists of two rows of scrapers 20, 22 with scrapers (thickness 10mm, made of PTFE) 21 as outer cylinder side scraping means 18 and inner cylinder side scraping means 19. It is what you have.

On the rear stage side of the cooler 11, a first crystallization tank 12 and a second crystallization tank 13 each having a scraping blade were installed in series. The volume of the cooler 11 was 0.16% of the total volume of the first crystallization tank 12 and the second crystallization tank 13.

First, liquid containing carboxylic acid in crystallization tanks 12 and 13 (mixed with 4% by weight of methanol in methacrylic acid, adjusted to a freezing point (crystallization start temperature) of 8.5 ° C, and cooled to 12 ° C. (Hereinafter referred to as the raw material liquid (A)), and the scraping blades of the crystallization tanks 12 and 13 were rotated so that the cooling surface scraping frequency was 40 times Z minutes. . Each crystallization tank 12 and the final crystallization tank 12 so that the temperature in the first crystallization tank 12 is 6.3 ° C and the temperature in the second crystallization tank 13 is 5.4 ° C. Cooling was performed by adjusting the cooling medium flow rate of 13 cooling jackets.

Next, the raw material liquid (A) was continuously supplied to the supply pipe 23 at a supply rate (flow rate) at which the total residence time in the crystallization tanks 12 and 13 was 6 hours. At this time, each of the crystallization tanks 12, 13 is adjusted so that the temperature in the first crystallization tank 12 is 6.3 ° C. and the temperature in the second crystallization tank 13 is 5.4 ° C. The cooling medium flow rate of the cooling jacket was adjusted. In addition, the scraping blades of the crystallization tanks 12 and 13 were rotated so that the cooling surface scraping frequency was 40 times Z.

[0036] Next, the supply valve 24 is opened, and the raw material liquid (A) of 27% of the total flow rate is branched and introduced into the cooler 11, and the inner cylinder side scraping means 19 and the outer cylinder side of the cooler 11 are introduced. Both the scraping means 18 and the scraping frequency are rotated 90 rpm each so that the scraping frequency is 180 times Z, and the outer cylinder side cooling surface 15 is only 10 ° C. The cooling medium is continuously passed through The carboxylic acid-containing liquid discharged from the cooler 11 was cooled until the cooler outlet temperature reached 9.5 ° C. (= t) over 1.3 hours.

After confirming that the temperature of the carboxylic acid-containing liquid discharged from the cooler 11 was stable at 9.5 ° C, continuously apply a cooling medium of -10 ° C to the inner cylinder side cooling surface 16 of the cooler 11. The liquid started to pass through.

As a result, from the cooler 11, a slurry-like carboxylic acid-containing liquid containing 3.3% by mass of methacrylic acid crystal particles having a cooler outlet temperature of 8.3 ° C and a particle size of approximately 80 m was continuously produced. Were exhausted. When such operation was continued, the operation status was stable even after 100 hours had passed, and the outlet of the second crystallization tank 13 contained 37% by mass of methacrylic acid crystal particles having a particle size of approximately 225 m. A slurry-like carboxylic acid-containing liquid was obtained. The residence time of the carboxylic acid-containing liquid in the cooler was 1.8 minutes.

At this time, the heat removal load of the first crystallization tank 12 was 6.2 Mj / hr / m ² , and the heat removal load of the second crystallization tank 13 was 7.4 MjZhrZm ² .

[0037] [Example 2]

The apparatus was operated in the same manner as in Example 1 except that the scraper 21 included in the inner cylinder side scraping means 19 and the outer cylinder side scraping means 18 was replaced with a 3.5 mm thick bakelite scraper.

As a result, from the cooler 11, a slurry-like carboxylic acid-containing liquid having a cooler outlet temperature of 8.0 ° C and containing 8.9% by mass of crystal particles of methacrylic acid having a particle size of approximately 80 m was continuously produced. Were exhausted. When such operation was continued, the operation status was stable even after 100 hours had passed, and the outlet of the second crystallization tank 13 contained 37% by mass of methacrylic acid crystal particles having a particle size of approximately 225 m. A slurry-like carboxylic acid-containing liquid was obtained.

At this time, the heat removal load of the first crystallization tank 12 was 6. OMj / hr / m ² , and the heat removal load of the second crystallization tank 13 was 7.2 MjZhrZm ² .

[0038] [Comparative Example 1]

The apparatus was operated in the same manner as in Example 1 using an apparatus having the same configuration as in FIG. 1 except that the cooler 11 was not installed.

As a result, the torque of the scraping blade of the first crystallization tank 12 is significantly increased by scaling. After 100 hours, it increased by 5%, and after about 2000 hours the torque reached the upper limit and had to stop driving.

At this time, the heat removal load of the first crystalliser 12 was 10. OMjZhrZm ^2.

[0039] [Example 3]

Use carboxylic acid production apparatus 30 shown in FIG. ^3, it was carried out a preliminary step and crystallization step. The apparatus 30 in FIG. 3 includes a crystallization tank 32 for performing a crystallization process, and a cooler 31 provided on the front side of the crystallization tank 32 for performing a preliminary process! /

As the cooler 31, “ONRATOR (trade name, manufactured by Sakai Seisakusho Co., Ltd.)” was used as a cylindrical scooping-type heat exchanger. In this heat exchanger, the inner surface 33 of the cylinder is a cooling surface, and as a scraping means 34 for scraping off the cooling surface, the rotary outer surface of the cooler 11 used in Example 1 is used. The cylinder side scraping means 18 is the same. A cooling jacket (not shown) is installed outside the crystallization tank 32, and the inner surface of the crystallization tank 32 is a cooling surface. Further, the crystallization tank 32 is provided with a rotary scraping means (scraping blade) (not shown) for scraping off deposits adhering to the cooling surface.

The volume of the cooler 31 was 0.5% of the volume of the crystallization tank 32.

[0040] A carboxylic acid-containing liquid (methacrylic acid and methanol 2.

6% by mass, adjusted so that the freezing point (crystallization start temperature) becomes 10.0 ° C and cooled to 20.4 ° C), the residence time in the crystallization tank 32 is 5.7. It was continuously supplied at a supply rate (flow rate) that is equivalent to time. The residence time of the carboxylic acid-containing liquid in the cooler was 1.7 minutes. The scraping blade of the crystallization tank 32 was rotated so that the cooling surface scraping frequency was 40 times Z.

[0041] Next, the scraping means 34 of the cooler 31 is rotated at a rotation speed of 100 rotations Z so that the scraping frequency is 200 rotations Z minutes, and a 7 ° C cooling medium is The liquid was continuously passed through the cooler 31. During this time, the cooling medium was not supplied to the jacket of the crystallization tank 32 and the heat insulation was maintained (that is, the heat removal load of the crystallization tank 32 was 0 Mj / hr / m ² ).

As a result, from the cooler 31, the cooler outlet temperature indicated by the temperature indicator 36 is 8.8 ° C., and the slurry-like carboxylic acid containing 40% by mass of crystal particles of methacrylic acid having a particle size of approximately 50 m is obtained. The acid-containing liquid was continuously discharged. When this kind of operation was continued, The operating condition was stable even after the passage of time, and a slurry-like carboxylic acid-containing liquid containing 40% by mass of crystal particles of methacrylic acid having a particle size of approximately 200 m was obtained from the outlet of the crystallization tank 32.

[0042] [Comparative Example 2]

The apparatus was operated in the same manner as in Example 3 except that the scraping means 34 was rotated at 70 revolutions Z minutes so that the scraping frequency was 140 times Z minutes.

As a result, the cooler outlet temperature was 10.2 ° C, and methacrylic acid crystals were observed in the carboxylic acid-containing liquid discharged from the cooler 31. Therefore, in this example, methacrylic acid crystals could not be obtained.

Industrial applicability

[0043] According to the present invention, when the carboxylic acid-containing liquid is crystallized in the crystallization tank, it is possible to suppress the formation of a strong scale on the inner wall surface of the crystallization tank, and the liquid removal property in the subsequent process (for example, Coarse crystal particles excellent in filterability and cleanability) can be industrially produced stably and economically with high productivity.

Claims

The scope of the claims

[1] At least a part of the carboxylic acid-containing liquid is supplied to a cooler disposed in the front stage of the crystallization tank, which has a cooling surface and a scooping means for scraping off the cooling surface. A preliminary step of producing a cooled carboxylic acid-containing liquid by cooling the carboxylic acid-containing liquid from a temperature exceeding the crystallization start temperature of the liquid to not more than the crystallization start temperature;

A crystallization step of crystallizing carboxylic acid from a carboxylic acid-containing liquid including the cooled carboxylic acid-containing liquid in a crystallization tank;

The manufacturing method of carboxylic acid which has this.

[2] The scraper of the cooler operates at a scraping frequency of 150 times Z or more.

The method for producing a carboxylic acid according to 1.

[3] In the preliminary step, the carboxylic acid-containing liquid is further cooled by the cooler so as to be equal to or less than a heat removal load causing the heat removal load of the crystallization tank in the crystallization step. The method for producing a carboxylic acid according to claim 1.

[4] The residence time of the carboxylic acid-containing liquid in the cooler during the preliminary step is 1% or less of the residence time of the carboxylic acid-containing liquid in the crystallization tank in the crystallization step. The manufacturing method of carboxylic acid of this.

[5] At the start of operation of the preliminary process,

A first step of cooling to a temperature at which the temperature of the carboxylic acid-containing liquid discharged exceeds the crystallization start temperature;

A second step of cooling the carboxylic acid-containing liquid to a temperature not higher than the crystallization start temperature;

The method for producing a carboxylic acid according to claim 1, comprising:

6. The method for producing carboxylic acid according to claim 1, wherein the cooler is a double cylindrical scraped heat exchanger having a plurality of cooling surfaces.