KR101306357B1 - Process for producing carboxylic acid - Google Patents

Abstract

Scraping means for scraping at least a portion of the carboxylic acid-containing liquid from the cooling surfaces 15 and 16 and the cooling surface before the crystallization step of crystallizing the carboxylic acid from the carboxylic acid-containing liquid in the crystallization tank 12 and 13 having the cooling surface. It supplies to the cooler 11 provided with (18, 19), and performs the preliminary process of cooling from the temperature over crystallization start temperature to below crystallization start temperature. Suitable when the carboxylic acid is especially acrylic acid and / or methacrylic acid.

Description

Production method of carboxylic acid {PROCESS FOR PRODUCING CARBOXYLIC ACID}

This invention relates to the manufacturing method of the carboxylic acid provided with the crystallization process of crystallizing carboxylic acid.

This application claims priority based on Japanese Patent Application No. 2006-026766 for which it applied to Japan Patent Office on February 3, 2006, and uses the content here.

When industrially manufacturing carboxylic acid, such as (meth) acrylic acid, the refinement | purification process which removes the impurity, a solvent, etc. which are produced | generated in a manufacturing process are essential. 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 or a high melting point, or a substance having high polymerizability, the crystallization method which can be purified from a low temperature range to high purity It is often adopted. The most common crystallization method is a method of cooling a mixture to be purified by a cooling medium via a cooling surface.

However, when (meth) acrylic acid is crystallized in this way among carboxylic acids, for example, (meth) acrylic acid tends to adhere to the cooling surface, which causes scale to gradually develop on the cooling surface, causing trouble in stable operation of the apparatus. Productivity may fall. Therefore, there is a demand for a crystallization method capable of suppressing generation of scale.

Moreover, when the crystal | crystallization of the carboxylic acid obtained is a fine particle, the deliquessing property in a post process will worsen, As a result, the purity of the carboxylic acid obtained will fall, as well as an increase in refinement load, a fall of productivity, etc. are brought about. Therefore, the crystallization method also requires a method of obtaining crystal grains having a certain particle diameter or more.

In addition, from an industrial point of view, a crystallization method suitable for mass production is required, which can be carried out with a device as inexpensive as possible.

For example, Patent Documents 1-4 and the like disclose a method of purifying crystals on a stationary surface and then purifying them by the sweating action to melt a portion thereof. In such a method, however, the cooling surface is shared by precipitation and purification of crystals. The productivity is low, and furthermore, a large amount of equipment is required, which is economically disadvantageous.

As a method using a less expensive apparatus, there is a method using a crystallization tank having a cooling surface and a scraping means for scraping off the cooling surface. By the way, in order to achieve high productivity in such a method, cooling is inevitably forced, and a firm scale difficult to peel off occurs on the cooling surface, and stable operation tends to be difficult. Thus, for example, Patent Document 5 discloses a method for reducing generation of scale on a cooling surface by adding a small amount of a solvent.

However, the method disclosed in Patent Document 5 cannot sufficiently suppress scale. In addition, in order to reduce the rigid scale, there is also a method of strengthening scraping by scraping means, but when scraping is enhanced, crystals in the bath are crushed, inhibiting crystal growth, and coarsening. One crystal grain cannot be obtained.

In addition, in the case of industrial production in large quantities using such crystallization tank, the content of crystallization tank is increased, but in the normal crystallization tank whose inner wall is the cooling surface, the area of cooling surface increases as the content increases. As it is relatively small, the defrosting load per area of the cooling surface increases, so that it cannot operate effectively, and it is difficult to operate the scraping means at a high speed in the crystallization tank having a high content, and only by increasing the content of the crystallization tank is industrial production. It is virtually difficult to respond to.

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

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

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

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

Patent Document 5: International Publication No. 99/06348 Pamphlet

DISCLOSURE OF INVENTION

Problems to be solved by the invention

This invention is made | formed in view of the said situation, and when crystallizing a carboxylic acid containing liquid in a crystallization tank, generation | occurrence | production of the firm scale to the inner wall surface which plays the role of the crystallization tank, especially the cooling surface can be suppressed, An object of the present invention is to provide a method capable of stably and economically producing industrially coarse crystal grains having excellent deliquescent property (for example, filterability and detergency) in a later step with high productivity.

Means for solving the problem

As a result of earnestly examining by the present inventors, the above-mentioned subject can be solved by performing the preliminary process of cooling at least one part of a carboxylic acid containing liquid under specific conditions before the crystallization process of crystallizing a carboxylic acid from a carboxylic acid containing liquid in a crystallization tank. Found.

That is, when the preliminary step is carried out, the microcrystals produced in the preliminary step act as seed crystals in the crystallization step. In addition, since the carboxylic acid-containing liquid may not be strongly cooled in the crystallization tank, depending on the conditions, the degree of supersaturation in the liquid decreases, so that the microcrystals dissolve and reprecipitate on the surface of the larger crystal. Therefore, coarsening of a crystal | crystallization is accelerated | stimulated, and generation | occurrence | production of the scale and fine crystal grain resulting from strong cooling can be suppressed. Thus, when the preliminary process is performed, it discovered that coarse crystal grains of the carboxylic acid which are excellent in the liquid removal property in a later process can be manufactured stably with high productivity, and came to complete this invention.

The manufacturing method of the carboxylic acid of this invention supplies at least a part of carboxylic acid containing liquid to the cooler arrange | positioned at the front end of a crystallization tank which has a cooling surface and the scraping means which scrapes off the cooling surface, and crystallization start temperature of a carboxylic acid containing liquid A preliminary step of preparing the cooled carboxylic acid-containing liquid by cooling the carboxylic acid-containing liquid to a crystallization start temperature or less from a temperature exceeding the above; and crystallization of carboxylic acid from the carboxylic acid-containing liquid containing the cooled carboxylic acid-containing liquid in a crystallization tank. It is characterized by having a process.

Effects of the Invention

According to the present invention, when the carboxylic acid-containing liquid is crystallized in the crystallization tank, generation of a firm scale to the inner wall surface (hereinafter referred to as the inner wall surface) of the crystallization tank can be suppressed, and the liquid liquefaction (for example, Coarse crystal grains excellent in filterability and washability) can be industrially produced stably and economically with high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows an example of the carboxylic acid manufacturing apparatus used for the manufacturing method of the carboxylic acid of this invention,

2 is a schematic view showing a scraping means in a cooler of the apparatus of FIG. 1;

3 is a schematic block diagram showing a carboxylic acid producing apparatus used in the examples.

DESCRIPTION OF THE REFERENCE NUMERALS

10: carboxylic acid producing device 11: cooler

12: 1st crystallization tank 13: 2nd crystallization tank

30: carboxylic acid production device 31: cooler

32: Jeongseokjo

Carrying out the invention  Best form for

Hereinafter, the present invention will be described in detail.

The method for producing a carboxylic acid of the present invention is a preliminary step of cooling at least a portion of the carboxylic acid-containing liquid from a temperature above the crystallization start temperature to a crystallization start temperature or less before the crystallization step of crystallizing the carboxylic acid from the carboxylic acid-containing liquid in the crystallization tank. It is to have a process.

The carboxylic acid-containing liquid is not limited as long as it contains at least a carboxylic acid and is a liquid that precipitates crystals of the carboxylic acid as the temperature decreases. The liquid may be a liquid carboxylic acid itself, or a liquid in which the carboxylic acid is dissolved in a solvent. Specifically, the liquid which melt | dissolved the carboxylic acid to be refine | purified in a solvent, the liquid containing the carboxylic acid obtained at the manufacturing process of a carboxylic acid, the mother liquid after some crystalline crystals of a carboxylic acid, the melt liquid of a carboxylic acid crystal, etc. are mentioned, Any processing may be performed.

Although there is no restriction | limiting in particular also as a kind of carboxylic acid, According to this invention, even if it is a carboxylic acid with strong adhesiveness to an inner wall surface, since such adhesion can be suppressed, especially in the case of acrylic acid and methacrylic acid with high adhesiveness, it is effective.

FIG. 1 is a schematic configuration diagram showing an example of a carboxylic acid production apparatus 10 used in the method for producing a carboxylic acid of the present invention, in which a first crystallization tank 12 and a second crystallization tank (12) installed in series to perform a crystallization step ( 13) and the cooler 11 provided in the front end side of these crystallization tanks 12 and 13, and performing a preliminary process, and is comprised.

The cooler 11 used in this example is a double-cylindrical scraping heat exchanger, which is an inner surface 15 of a cylindrical outer cylinder and an outer surface 16 of a cylindrical inner cylinder. Each of these is a cooling surface. In addition, 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, respectively. The temperature, flow rate and the like of the cooling medium acting on the cooling surface can be adjusted individually. Specifically, such independent control can be performed on the outer cylinder side cooling surface 15 and the inner cylinder side cooling surface 16, respectively, with independent flow paths for the cooling medium or automatic or manual flow rate adjustment valves. Can be.

In the cooler 11 of this example, as the scraping means for scraping off the cooling surface, as shown in the schematic diagram of FIG. 2, the outer cylinder side scraping means 18 for scraping off the outer cylinder side cooling surface 15 and The inner cylinder side scraping means 19 for scraping off the inner cylinder side cooling surface 16 is provided.

The outer cylinder side scraping means 18 carries out the rotary scraper 20 which rotates about the axis line (center line of the longitudinal direction of an outer cylinder and an inner cylinder) of the cooler 11 along the longitudinal direction of the cooler 11, Each scraper 20 has a plate-shaped scraper (scratch member) 21 having a thickness of 10 mm made of polytetrafluoroethylene (PTFE). Therefore, by attaching each scraper part 20 in the direction shown by the arrow in the figure, the side end portion of each scraper 21 contacts the outer cylinder side cooling surface 15, while depositing the deposit on the outer cylinder side cooling surface 15. It is supposed to scrape off.

In this example, the two rows of scraping portions 20 are located symmetrically with respect to the axis of the cooler 11.

In addition, the inner cylinder side scraping means 19 is also comprised of the scraper part 22 provided with the same scraper 21 along the longitudinal direction of the cooler 11, and consists of each scraping part 22. By rotating in the direction shown by an arrow in the figure, the side end portion of each scraper 21 is scraped off the deposit on the inner cylinder side cooling surface 16 while contacting the inner cylinder side cooling surface 16. In the cooler 11 of this example, the scraper 20 and the scraper 22 are integrally rotated.

The first crystallization tank 12 and the second crystallization tank 13 are provided with a jacket for cooling or cold storage not shown in the outside, and the inner wall surfaces of the respective crystallization tanks 12 and 13 are cooling surfaces or beams. It is cold noodles. In addition, each crystallization tank 12 and 13 is provided with the rotary scraping means (a scraping vane) which abbreviate | omitted illustration for scraping off the deposit which affixed on the inner wall surface.

In addition, the supply piping 23 of the carboxylic acid containing liquid diverges in the middle, one side is connected to the cooler 11, and the other is connected to the 1st crystallization tank 12. As shown in FIG. Moreover, the supply valve 24 of an opening / closing material is provided in the middle of the supply piping 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.

Next, an example of the specific method of crystallizing carboxylic acid from a carboxylic acid containing liquid using this apparatus 10 is demonstrated.

First, the carboxylic acid-containing liquid is directly supplied from the supply pipe 23 to the first crystallization tank without closing the supply valve 24 provided in the middle of the line for supplying the carboxylic acid-containing liquid to the cooler 11 via the cooler 11. It supplies to 12 and then supplies to the 2nd crystallization tank 13 which closed the liquid repellent opening (not shown). When the carboxylic acid-containing liquid of the second crystallization tank 13 reaches a predetermined amount, the liquid repellent opening (not shown) of the first crystallization tank 12 is closed and the carboxylic acid-containing liquid of the first crystallization tank 12 is closed. When this predetermined amount is reached, the supply is stopped immediately. Subsequently, 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 temperature in the tank of the first crystallization tank 12 is increased. And each of the second crystallization tank 13 is gradually cooled so that the temperature in the tank is finally lower than or equal to the crystallization start temperature. The temperature in the bath varies depending on the kind, concentration, solvent, and the like of the carboxylic acid to be handled, but in general, it is preferable to set the slurry concentration in the crystallization bath to be 40% or less. In addition, since the temperature in a tank is usually set to be lower as much as the crystallization tank of the rear end side, also in this case, setting the temperature in the tank of the 2nd crystallization tank 13 lower than the temperature in the tank of the 1st crystallization tank 12 is performed. It is preferable.

Subsequently, after the temperature in the tank of the 1st crystallization tank 12 and the 2nd crystallization tank 13 stabilizes to predetermined temperature, supply of the carboxylic acid containing liquid is restarted, supplying the valve 24 closed, and The liquid repellent opening of the 1st crystallization tank and the 2nd crystallization tank 13 is opened, and the carboxylic acid containing liquid containing a carboxylic acid crystal is also taken out. At this time, the supply rate of the carboxylic acid-containing liquid is less than or equal to the amount of crystallization calories to be removed in the first crystallization tank 12 and the second crystallization tank 13 and does not cause scaling, and is obtained from the second crystallization tank 13. The crystal is not particularly limited as long as it is equal to or less than the target particle diameter. Moreover, if supply temperature is temperature exceeding crystallization start temperature, it will not specifically limit, but the inside of the heat removal ability range of the 1st crystallization tank 12 and the 2nd crystallization tank 13 is preferable.

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

The flow rate through the cooler 11 of the carboxylic acid-containing liquid, the flow rate without passing through, and the total flow rate into the first crystallization tank which is a sum thereof can be adjusted according to the desired production amount. In addition, the appropriate residence time in the crystallization tank of the carboxylic acid-containing liquid is the crystal growth rate, nucleation rate, target production rate, target crystal grain diameter, and amount of heat removal in each crystallization tank from the carboxylic acid-containing liquid to be used. Since it cannot be determined uniformly, etc., it is possible to determine the appropriate stay time every 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 / min or more, respectively, and the outer cylinder side cooling surface 15 and the inner cylinder side of the cooler 11 are operated. A cooling medium is applied to the cooling surface 16 to perform a preliminary step of cooling the carboxylic acid-containing liquid. The scraping frequency is preferably 180 times / minute or more, and more preferably 200 times / minute or more. Moreover, 1000 times / minute or less are preferable and, as for the frequency of scraping off, 400 times / minute or less are more preferable.

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

In addition, a scraping frequency here is "the frequency | count of an operation in 1 minute of the scraping member which acts directly on a cooling surface." Therefore, when the scraping member consists of the rotary scraper 21 like this example, and the scraper parts 20 and 22 provided with the scraper 21 are provided in 2 rows, "the scraping out of 150 times / min or more is performed. Frequency ”can be achieved by rotating the scraping-out portions 20 and 22 at least 75 revolutions per minute. That is, when the number of columns of the scraping-out parts 20 and 22 is set to N, it can achieve by rotating more than (150 / N) rotation in 1 minute.

The preliminary step 12 and the second crystallization tank 13 are used to cool the slurry-shaped carboxylic acid-containing liquid (cooling carboxylic acid-containing liquid) that is cooled to a temperature below the crystallization start temperature by such a preliminary step to deposit some carboxylic acids. Are introduced sequentially, and a crystallization step of crystallizing is performed.

The crystal growth is promoted by this crystallization step, and from the second crystallization tank, the crystal shape is smaller than the slurry introduced into the crystallization tank 12 in the cooler 11, and the crystal nucleus per unit slurry volume contains coarse crystals. Of carboxylic acid-containing liquid is discharged.

After such a crystallization step, post-processes, such as a filtration process, a washing | cleaning process, and a drying process, are performed from a discharged carboxylic acid containing liquid as needed, and crystal grains of a carboxylic acid are collect | recovered.

Thus, at least a part of the carboxylic acid-containing liquid is cooled in the preliminary step and then supplied to the crystallization step, thereby completing the crystallization tank 12 due to the strong cooling because the carboxylic acid-containing liquid is not cooled strongly in the crystallization tanks 12 and 13. , The scale to the cooling surface of 13) and generation | occurrence | production of a fine crystal grain can be suppressed, and the coarse crystal grain of the carboxylic acid which crystallized well in the post-process is excellent and sufficient crystal growth is obtained. Further, since no scale is generated, the operation of the apparatus can be performed stably, and furthermore, since a decrease in cooling efficiency due to adhesion of the scale to the cooling surface is also suppressed, productivity can be maintained high. In addition, since it is not necessary to excessively operate the scraping blades of the crystallization tanks 12 and 13 in order to break the scale, it is possible to suppress the generation of fine particles by being broken into the scraping blades. In addition, the crystal grains precipitated in the preliminary step have a small supersaturation of the crystallization tanks 12 and 13, so that depending on the conditions, the microcrystals dissolve and reprecipitate on the surface of the larger crystal. For these reasons, in the crystallization step, crystal particles having a larger particle diameter tend to be produced.

Further, in the preliminary step, it is preferable to operate each scraping means 18 and 19 of the cooler 11 so that the scraping frequency is 150 times / minute or more, and the scale of the scales to the cooling surfaces 15 and 16 is preferable. Since the cooling efficiency of the cooler 11 is improved by suppressing accumulation, etc., the carboxylic acid-containing liquid can be cooled from the temperature exceeding the crystallization start temperature to below the crystallization start temperature easily and stably. Further, the lower the scraping frequency, the lower the amount of heat generated by friction between the scraper and the cooling surface provided in the scraping means, so that the cooling efficiency of the cooler 11 is improved.

In addition, in the preliminary step, the carboxylic acid-containing liquid may be cooled to a temperature below the crystallization start temperature, but it is preferable to set it to a temperature range where the slurry concentration at the outlet of the cooler 11 is below a concentration which does not cause a problem in subsequent transfer. 40 volume% or less is preferable and, as for the slurry concentration, 20 volume% or less is more preferable.

Further, in the preliminary step, the heat removal loads of the first crystallization tank 12 and the second crystallization tank 13 in the crystallization step are each less than the heat removal load causing scaling, more specifically, 8.4 MJ / hr / m 2 or less, Moreover, it is preferable to cool so that it may become 7.5 MJ / hr / m <2> or less. By preliminary cooling to such a degree in the preliminary step, it is not necessary to strongly cool the carboxylic acid-containing liquid in the crystallization step, and scale generation on the cooling surfaces of the crystallization tanks 12 and 13 due to the strong cooling in the crystallization tank In addition to reducing the formation of fine particles in the crystallization tank, the microcrystals produced in the preliminary step dissolve and the crystallization component is precipitated on the surface of the coarse crystals, resulting in coarse crystals excellent in de-liquidation and detergency. It is easy to get.

Moreover, the heat removal load of the crystallization tanks 12 and 13 is "the amount of heat transfer per 1m <2> of cooling surfaces of a crystallization tank", and the crystallization tanks 12 and 13 cool a cooling surface by a cooling jacket like this example. In the case of, it may be calculated from the difference between the calories of the cooling medium flowing into the cooling jacket and the cooling medium flowing out of the cooling jacket, or may be calculated from the calorie change of the carboxylic acid-containing liquid in the crystallization tanks 12 and 13. have. Here, it is defined by the following formula.

Heat removal load

only,

(Enthalpy) = (supernatant flow rate) × (liquid specific heat) × (temperature) + (crystal flow rate) × (crystal specific heat) × (temperature)-(crystal flow rate) × (heat of crystallization (absolute value))

In the preliminary step, the carboxylic acid-containing liquid is cooled to the temperature below the crystallization start temperature by the cooler 11, but preferably, the preliminary step is preferably started up stepwise as follows.

First, the temperature of the carboxylic acid-containing liquid discharged from the cooler 11 is equal to or lower than the crystallization start temperature, such that the cooling medium is applied to only one of the cooling surfaces of the outer cylinder side cooling surface 15 or the inner cylinder side cooling surface 16. In other words, it is cooled to a certain temperature t above the crystallization start temperature (first step). Then, after the temperature of the carboxylic acid-containing liquid discharged from the cooler 11 is stabilized at this temperature (t) exceeding the crystallization start temperature, the cooling medium is also acted on the other cooling surface. It cools to the temperature below the crystallization start temperature (2nd step).

Although temperature t is temperature beyond the crystallization start temperature here, it is suitable that it is temperature lower than the supply temperature of a carboxylic acid containing liquid, and is 2 degrees C or less higher than the crystallization start temperature.

By starting up the preliminary step in this manner, the carboxylic acid-containing liquid can be easily and stably cooled to the crystallization start temperature or lower in the preliminary step. Here, "the temperature is stable" means that the difference between the minimum temperature and the maximum temperature for at least 5 minutes is within 1 ° C.

In this manner, the first stage is operated so that the temperature of the carboxylic acid-containing liquid does not become below the crystallization start temperature. However, in order to achieve such temperature conditions, the outer cylinder side cooling surface 15 or the inner cylinder side cooling surface 16 is described above. The method of applying the cooling medium only to the cooling surface on either side of the c) is an easy and effective method. In addition, a method may be employed in which the carboxylic acid-containing liquid does not come into contact with the other cooling surface, or a method of adjusting the temperature or flow rate of the flowing cooling medium. In some cases, the cooling surface may be heated by heating means prepared separately. May be combined.

As described above, according to the method having the preliminary step and the crystallization step described above, it is possible to secure the cooling surfaces of the crystallization tanks 12 and 13 only by using a device having a simple configuration without using an expensive device. Formation of one scale can be suppressed, and the coarse carboxylic acid crystal grains which are excellent in the liquid releasing property (for example, filterability, washing | cleaning property) in a post process, and sufficient crystal growth can be manufactured stably and economically with high productivity. Moreover, since the heat removal load in a crystallization process can be reduced, even if the area of a crystallization tank is made large and the cooling surface area becomes comparatively small in industrial mass production, a problem does not arise.

In the above description, as the cooler used in the preliminary step, a double cylindrical scraping-type heat exchanger having a plurality of independent controllable cooling surfaces is exemplified, but the shape of the cooler is not particularly limited. However, it is preferable to start up the preliminary process step by step as described above, so that this start-up type of cooler is provided, that is, with a plurality of independent controllable cooling surfaces, the part of which is operated first, and then the rest is operated. A cooler that can

Moreover, as a form of the scraping means with which a cooler is equipped, and a scraping method, it is not limited to rotation as long as it can scrape a cooling surface, and it can ensure 150 or more times of scraping-offs, and it is a belt type and a screw type Or cooling surface rotary may be used. In addition, as shown in the example, the scraper 21 has at least one row in the longitudinal direction of the cooler which rotates around the axis of the cooler 11 in the longitudinal direction of the cooler. In the case of being attached, it is preferable that each scraper 21 is 10 mm or less in thickness, More preferably, it is 5 mm or less. Moreover, in the case of the cooler provided with two or more cooling surfaces, each scraping means is provided and it is necessary to operate each of the scraping frequency 150 times / min or more, but the form of the scraping means etc. is for every cooling surface It may be different or the same.

As shown in the example, the crystallization tank may be provided in plural in series, plural in parallel, or only one. In addition, as long as the crystallization tank can ensure the residence time enough for carboxylic acid to sufficiently crystallize, there is no restriction in the volume and form, and a general stirring tank, a tank or the like can be used. Moreover, although it is preferable that a scraping means is provided in a crystallization tank, it is not necessarily provided. The stay time of the carboxylic acid-containing liquid in the cooler is preferably 10% or less of the stay time of the carboxylic acid-containing liquid in the crystallization tank, so that fine crystals can be obtained, and more preferably 1% or less.

Although there is no restriction | limiting in particular in the ratio of the volume of a crystallization tank and the volume of a cooler, In order to comprise a space-saving and low cost, it can achieve by selecting the cooler of the ability which can remove the excess heat amount in a crystallization process sufficiently necessary. have.

In addition, although only a part of carboxylic acid containing liquid is used for a preliminary process, and the remainder is used directly for a crystallization process in the example of illustration, you may make the whole quantity of a carboxylic acid containing liquid be used for a preliminary process. In addition, in order to efficiently generate fine crystals in the cooler, it is preferable to supply the carboxylic acid-containing liquid to the cooler in one pass.

Hereinafter, although the method of this invention is demonstrated concretely by an Example, this invention is not limited by these Examples.

Example 1

The preliminary process and the crystallization process were performed using the apparatus shown in FIG.

In the cooler 11, "Tarosum (brand name, the product made by N.V. Machinefabriek Terlet)" was used as a double cylindrical scraping-type heat exchanger. This heat exchanger is an outer cylinder side scraping means 18 and an inner cylinder side scraping means 19, and each of the scrapers 20 and 22 with a scraper (thickness 10 mm, made of PTFE) 21 is attached. Having heat.

On the rear end side of the cooler 11, the 1st crystallization tank 12 and the 2nd crystallization tank 13 which respectively have a scraping blade | wing were provided 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, 4 mass% of carboxylic acid-containing liquid (methacrylic acid is mixed with methanol in the crystallization tanks 12 and 13), adjusted to a solidification point (crystallization start temperature) of 8.5 ° C, and cooled to 12 ° C. The liquid (A) was thrown in, and the scraping blades of the respective crystallization tanks 12 and 13 were rotated so that the scraping frequency of the cooling surface became 40 times / minute. Finally, the cooling medium flow rate of the cooling jacket of each crystallization tank 12 and 13 so that the tank internal temperature of the 1st crystallization tank 12 may be 6.3 degreeC, and the tank temperature of the 2nd crystallization tank 13 is 5.4 degreeC. Was adjusted to cool.

Next, the raw material liquid A was continuously supplied to the supply piping 23 at the feed rate (flow rate) which becomes 6 hours of the total stay time in the crystallization tank 12,13. At this time, the cooling medium flow rate of the cooling jacket of each crystallization tank 12 and 13 so that the tank internal temperature of the 1st crystallization tank 12 may be 6.3 degreeC, and the tank internal temperature of the 2nd crystallization tank 13 is 5.4 degreeC. Adjusted. Moreover, the scraping blades of each crystallization tank 12 and 13 were rotated so that the scraping frequency of a cooling surface might be 40 times / min.

Next, the supply valve 24 is opened to branch-introduce 27% of the raw material liquid A of the total flow rate into the cooler 11, and the inner cylinder side scraping means 19 and the outer cylinder side scraping of the cooler 11 are carried out. The betting means 18 is rotated at a rotation speed of 90 revolutions / minute, respectively, so that the scraping frequency is 180 times / minute, and the cooling medium of -10 ° C is continuously passed through only the outer cylinder side cooling surface 15 to act. The carboxylic acid-containing liquid discharged from the cooler 11 was cooled until the cooler outlet temperature became 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, the liquid medium of -10 ° C was continuously passed through to the inner cylinder-side cooling surface 16 of the cooler 11.

As a result, from the cooler 11, the cooler exit temperature was 8.3 degreeC, and the slurry carboxylic acid containing liquid containing 3.3 mass% of crystal grains of methacrylic acid of about 80 micrometers of particle diameters was discharged continuously. When such operation was continued, the operation condition was stabilized even after 100 hours had elapsed, and from the outlet of the second crystallization tank 13, a slurry shape containing 37% by mass of crystal particles of methacrylic acid having a particle diameter of about 225 µm was obtained. A carboxylic acid containing liquid of was obtained. The residence time of the carboxylic acid-containing liquid in the cooler was 1.8 minutes.

In addition, the heat removal load of the 1st crystallization tank 12 was 6.2MJ / hr / m <2>, and the heat removal load of the 2nd crystallization tank 13 was 7.4MJ / hr / m <2>.

[Example 2]

The apparatus was operated like Example 1 except having changed the scraper 21 with which the inner cylinder side scraping means 19 and the outer cylinder side scraping means 18 was changed to the bakelite scraper of thickness 3.5mm.

As a result, from the cooler 11, the coolant outlet temperature was 8.0 degreeC, and the slurry carboxylic acid containing liquid containing 8.9 mass% of crystal grains of methacrylic acid of about 80 micrometers of particle diameters was discharged continuously. When such operation was continued, the operation condition was stabilized even after 100 hours had elapsed, and from the outlet of the second crystallization tank 13, a slurry shape containing 37% by mass of crystal particles of methacrylic acid having a particle diameter of about 225 µm was obtained. A carboxylic acid containing liquid of was obtained.

In addition, the heat removal load of the 1st crystallization tank 12 was 6.0 MJ / hr / m <2>, and the heat removal load of the 2nd crystallization tank 13 was 7.2MJ / hr / m <2>.

Comparative Example 1

The apparatus was operated like Example 1 using the apparatus of the structure similar to FIG. 1 except that the cooler 11 was not provided.

As a result, the torque of the scraping blade of the 1st crystallization tank 12 rose significantly by scaling, and it rose 5% after 100 hours, and the torque value reached the upper limit after about 2000 hours, and it was forced to stop operation. .

At this time, the heat removal load of the 1st crystallization tank 12 was 10.0 MJ / hr / m <2>.

[Example 3]

The preliminary process and the crystallization process were performed using the carboxylic acid manufacturing apparatus 30 shown in FIG.

The apparatus 30 of FIG. 3 is provided with the crystallization tank 32 for performing a crystallization process, and the cooler 31 provided in the front end side of this crystallization tank 32, and performs a preliminary process.

As the cooler 31, "on-aerator (brand name, product of Sakura Corporation)" was used as a cylindrical scraping-type heat exchanger. The heat exchanger is a rotary outer cylinder in the cooler 11 used in Example 1 as the scraping means 34 for scraping off the cooling surface while the inner surface 33 of the cylinder is a cooling surface. It has the same thing as the side scraping means 18. As shown in FIG.

A cooling jacket (not shown) is provided outside the crystallization tank 32, and the inner surface of the crystallization tank 32 is a cooling surface. Moreover, the crystallization tank 32 is provided with the rotary scraping means (scraping blade) which abbreviate | omits illustration for scraping off the deposit which affixed on the cooling surface.

In addition, the volume of the cooler 31 was 0.5% of the volume of the crystallization tank 32.

Carboxylic acid-containing liquid (2.6 mass% of methanol was mixed in methacrylic acid, adjusted to a solidification point (crystallization start temperature) to 10.0 ° C, and cooled to 20.4 ° C) in the supply pipe 35 of the apparatus 30. Was continuously supplied at a feed rate (flow rate) at which the stay time in the crystallization tank 32 was 5.7 hours. The residence time of the carboxylic acid-containing liquid in the cooler was 1.7. The scraping blade of the crystallization tank 32 was rotated so that the scraping frequency of the cooling surface might be 40 times / min.

Next, the scraping means 34 of the cooler 31 is rotated at a rotation speed of 100 revolutions / minute so that the scraping frequency is 200 times / minute, and a cooling medium of -7 ° C is continuously connected to the cooler 31. Passed through. In the meantime, the cooling medium was not supplied to the jacket of the crystallization tank 32, and it was made into the heat insulation thermal insulation state (that is, the heat removal load of the crystallization tank 32 is 0 MJ / hr / m <2>).

As a result, from the cooler 31, the coolant outlet temperature represented by the temperature indicator 36 is 8.8 degreeC, and the slurry type carboxylic acid containing liquid containing 40 mass% of crystal grains of methacrylic acid of about 50 micrometers of particle diameters. Was discharged continuously. After the operation was continued, the operation condition was stabilized even after 6 hours, and from the outlet of the crystallization tank 32, a slurry-like composition containing 40% by mass of crystal particles of methacrylic acid having a particle diameter of about 200 μm was obtained. A carboxylic acid containing liquid was obtained.

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 rotations / minute so that the scraping frequency was 140 times / minute.

As a result, the cooler outlet temperature became 10.2 degreeC, and crystal | crystallization of methacrylic acid was not seen in the carboxylic acid containing liquid discharged | emitted from the cooler 31. FIG. Therefore, in this example, crystals of methacrylic acid could not be obtained.

According to the present invention, when the carboxylic acid-containing liquid is crystallized in the crystallization tank, formation of a firm scale on the inner wall surface of the crystallization tank can be suppressed, and the bath having excellent deliquescent property (for example, filterability and detergency) in the post-process. The crystal grains can be industrially produced stably and economically with high productivity.

Claims (6)

At least a portion of the carboxylic acid-containing liquid is supplied to a cooler disposed at the front end of the crystallization tank having a cooling surface and a scraping means for scraping off the cooling surface, the crystallization starting temperature from a temperature exceeding the crystallization starting temperature of the carboxylic acid-containing liquid. A preliminary step of cooling the carboxylic acid-containing liquid to produce a cooled carboxylic acid-containing liquid such that the heat removal load of the crystallization tank in the crystallization step is equal to or lower than the heat removal load causing scaling up to the following; And Crystallization process of crystallizing carboxylic acid from the carboxylic acid containing liquid containing the said cooling carboxylic acid containing liquid in a crystallization tank. Method for producing a carboxylic acid having a. The method of claim 1, And said scraping means of said cooler operates at a scraping frequency of at least 150 times / min. delete The method of claim 1, In the said preliminary process, the stay time of the carboxylic acid containing liquid of the said cooler is 1% or less of the stay time of the carboxylic acid containing liquid in the crystallization tank in the said crystallization process. The method of claim 1, At the start of operation of the preliminary step, A first step of cooling to a temperature at which the temperature of the carboxylic acid-containing liquid discharged from the cooler exceeds the crystallization start temperature, and A second step of cooling the carboxylic acid-containing liquid to a temperature below the crystallization start temperature Method for producing a carboxylic acid having a. The method of claim 1, And said cooler is a double cylindrical scraping-type heat exchanger having a plurality of cooling surfaces.

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