JP5394147B2 - (Meth) acrylic acid purification method - Google Patents

Description

  The present invention relates to a method for purifying (meth) acrylic acid. In detail, it is related with the refinement | purification method of (meth) acrylic acid by cooling and crystallizing crude (meth) acrylic acid, stirring using the crystallization tank provided with the stirring apparatus.

  For the purpose of purifying (meth) acrylic acid, the crude (meth) acrylic acid is cooled in the crystallization tank of the crystallizer to crystallize (meth) acrylic acid and contain crystals of (meth) acrylic acid A (meth) acrylic acid-containing liquid is obtained (for example, Patent Document 1). A jacket provided on the outer peripheral wall side of the crystallization tank is used for cooling the crystallization tank and the inside thereof.

  However, in the method described in Patent Document 1, the (meth) acrylic acid crystal is formed on the inner wall surface because cooling is performed on the inner wall surface serving as the heat transfer surface of the crystallization tank in order to generate the (meth) acrylic acid crystal. It tends to adhere and tends to scale. Scaling reduces production efficiency as heat transfer efficiency decreases, so in order to operate stably and efficiently, it is necessary to continuously remove crystals attached to the inner wall surface to suppress scaling. Further improvement is desired.

  As a method for suppressing scaling in the crystallization tank in the crystallization method, as disclosed in Patent Document 2, a crystallization tank having a motor-driven rotating scraper unit for scraping off crystals generated in the cooling region There is a method of scraping off crystals adhering to the inner wall surface of the crystallization tank.

  As a material of the scraper, polytetrafluoroethylene (PTFE) is usually used from the viewpoint of durability (Patent Document 3).

Japanese Patent No. 3559523 Japanese Patent Laid-Open No. 06-296803 International Publication No. 2007/088981 Pamphlet

  However, when scraping off the crystals adhering to the inner wall of the crystallization tank using a conventional scraper mechanism, scratches are generated on the inner wall with long-term use, and the crystals adhering to the scratches generated on the inner wall are scraped off. If left undisturbed, the heat transfer efficiency may be reduced, and the bath life may be shortened. On the other hand, in order to suppress the occurrence of scratches, when a soft material is selected as a scraper material so that it is difficult to be scratched, or when the pressing pressure when pressing the scraper against the inner wall of the crystallization tank is reduced, Although no scratches are seen on the inner wall surface of the tank, sufficient scraping cannot be performed and the effect of suppressing scaling cannot be obtained.

  An object of the present invention is to provide a method for purifying (meth) acrylic acid capable of suppressing scaling on the inner wall surface of a crystallization tank and suppressing generation of scratches on the inner wall surface.

The method for purifying (meth) acrylic acid according to the present invention includes:
In a purification method of (meth) acrylic acid, which crystallizes (meth) acrylic acid using a crystallization apparatus comprising one or more crystallization tanks,
The crystallization tank includes a cooling mechanism having an inner wall surface of the crystallization tank as a heat transfer surface,
A stirring mechanism having a stirring blade provided with a scraper that is in contact with the inner wall surface of the crystallization tank and is stirred while scraping off the (meth) acrylic acid crystals adhering to the inner wall surface of the crystallization tank by rotation;
The scraper is made of nylon as the material of the contact portion with the inner wall surface of the crystallization tank,
(Meth) acrylic acid is crystallized by cooling the crude (meth) acrylic acid introduced into the crystallization tank with stirring by the stirring mechanism and the cooling mechanism.

  According to the method of the present invention, scaling on the inner wall surface of the crystallization tank can be suppressed, and generation of scratches on the inner wall surface can be suppressed.

It is the schematic of an example of the crystallization apparatus used for the method of this invention. It is a cross-sectional view of an example of the crystallization tanks 1 and 2 used for the method of the present invention. It is the figure which showed typically an example of the contact part of a crystallization tank inner wall surface and a scraper.

The method for purifying (meth) acrylic acid according to the present invention includes:
In a purification method of (meth) acrylic acid, which crystallizes (meth) acrylic acid using a crystallization apparatus comprising one or more crystallization tanks,
The crystallization tank includes a cooling mechanism having an inner wall surface of the crystallization tank as a heat transfer surface,
A stirring mechanism having a stirring blade provided with a scraper that is in contact with the inner wall surface of the crystallization tank and is stirred while scraping off the (meth) acrylic acid crystals adhering to the inner wall surface of the crystallization tank by rotation;
The scraper is made of nylon as the material of the contact portion with the inner wall surface of the crystallization tank,
The crude (meth) acrylic acid introduced into the crystallization tank is cooled while being stirred by the stirring mechanism and the cooling mechanism to crystallize (meth) acrylic acid.

  Details of the method embodiments according to the present invention will be described below, but the present invention is not limited thereto.

(Rough (meth) acrylic acid)
In the present invention, crude (meth) acrylic acid is used as a raw material to be purified.

  Here, crude (meth) acrylic acid refers to crude methacrylic acid or crude acrylic acid. Crude methacrylic acid can be produced by various methods such as a direct oxidation method and an ACH method. As a method for producing such crude methacrylic acid, for example, any one compound selected from the group consisting of isobutylene, tertiary butyl alcohol, methacrolein, and isobutyraldehyde is reacted in one or two steps with molecular oxygen. A methacrylic acid aqueous solution obtained by adding water to a condensed liquid obtained by condensing a reactive gas obtained by a direct oxidation method subjected to catalytic gas phase oxidation, or by condensing a reactive gas into water. Extraction of methacrylic acid using an organic solvent and removal of the organic solvent and non-volatile components by distillation to obtain crude methacrylic acid, separation of methacrylic acid by-produced by the ACH method by extraction or distillation to obtain crude methacrylic acid The method of obtaining etc. are mentioned.

  Crude acrylic acid can be obtained in the same manner as in the case of crude methacrylic acid, for example, by subjecting propylene and / or acrolein to catalytic gas phase oxidation with molecular oxygen in a one-stage or two-stage reaction.

  Moreover, you may add the component for adjusting a crystal precipitation temperature to crude (meth) acrylic acid as needed. For example, the crystal precipitation temperature can be lowered by adding a polar organic substance that does not form a solid solution with (meth) acrylic acid. Specific examples of polar organic substances include methanol, ethanol, propanol, butanol and the like. Among these, methanol is preferable. The addition amount of the polar organic material is preferably in the range of 1 to 35% by mass.

(Precooling of crude (meth) acrylic acid)
FIG. 1 is a diagram showing a schematic diagram of an example of a crystallization apparatus used in the method according to the present invention. In FIG. 1, crude (meth) acrylic acid is cooled to the vicinity of the crystallization temperature by a cooler 3 in advance. Since the melting point of acrylic acid is about 12 ° C. and the melting point of methacrylic acid is about 16 ° C., it is preferable to cool at a temperature at which no crystals are formed in order to avoid the generation of scales and blockages associated with the generation of crystals. Specifically, when a solvent is added to methacrylic acid, the cooling temperature is 10 to 15 ° C., and when a solvent is added to acrylic acid, the cooling temperature is 6 to 11 ° C. It is preferable in that it does not occur and is easy to operate.

(Crystallization of (meth) acrylic acid in the first crystallization tank)
Next, the cooled crude (meth) acrylic acid is introduced into the first crystallization tank 1 and cooled to a predetermined temperature while stirring to crystallize (meth) acrylic acid.

  The first crystallization tank 1 used in the method according to the present invention includes a jacket 5 as a cooling mechanism for cooling the slurry in the first crystallization tank 1. The jacket 5 is disposed so as to cover the first crystallization tank 1 and exists in the first crystallization tank 1 through the heat transfer surface with the inner wall surface of the first crystallization tank 1 as a heat transfer surface. Heat exchange with the slurry can be performed and the slurry can be cooled to the desired temperature. Specifically, for example, a crystallization tank described in “Chemical Engineering Handbook Revised Sixth Edition” published by Maruzen Co., Ltd., 1999, pages 505 to 520 can be used.

  Further, the first crystallization tank 1 used in the method according to the present invention is in contact with the inner wall surface of the first crystallization tank 1 and (meth) acrylic acid adhered to the inner wall surface of the first crystallization tank 1 by rotation. An agitation mechanism having an agitation blade 6 provided with a scraper 11 for agitation while scraping crystals, a support 7 for supporting the agitation blade 6, and an agitation power M for rotating a rotating shaft connected to the support 7 is provided.

  In FIG. 2, the cross-sectional view of the 1st crystallization tank 1 is shown. The stirring mechanism of FIGS. 1 and 2 has two rows of stirring blades 6 including scrapers 11 that rotate about the central axis of the first crystallization tank 1 along the inner wall surface of the first crystallization tank 1. By rotating the support 7 that supports the stirring blade 6, not only the slurry in the first crystallization tank 1 is stirred, but also the inner wall surface by the rotation of the scraper 11 in contact with the inner wall surface of the first crystallization tank 1. (Meth) acrylic acid crystals adhering to can be scraped off. Thereby, the adhesion of crystals to the inner wall surface, so-called scaling can be suppressed. In FIG. 1, the scrapers 11 are alternately arranged so that the entire inner wall surface can be scraped off by the rotation of the scraper 11. However, this invention is not limited to this, What is necessary is just the arrangement | positioning which can scrape off the whole inner wall surface.

  In the present invention, nylon is used as the material of the contact portion of the scraper 11 with the first crystallization tank 1. By using nylon, the (meth) acrylic acid crystals adhering to the inner wall surface can be efficiently scraped without damaging the inner wall surface of the first crystallization tank 1. The nylon is preferably a monomer casting nylon obtained by polymerizing and molding a main raw material nylon monomer under atmospheric pressure, and “MC nylon” (trade name, manufactured by Nippon Polypenco Co., Ltd.) can be used as a commercial product. However, the present invention is not limited to this. Further, the entire scraper 11 may be made of nylon, or only a part of the scraper 11 in contact with the inner wall surface of the first crystallization tank 1 may be made of nylon. In addition, as a material of the inner wall surface of the 1st crystallization tank 1, SUS304, SUS316, etc. can be used, However, It is not limited to these, What is necessary is just a material which has hardness higher than the nylon to be used. .

  FIG. 3 shows a schematic diagram of an example of a contact state between the scraper 11 and the inner wall surface of the first crystallization tank 1. The tip of the scraper 11 has an acute angle shape, and the tip is in contact with the inner wall surface of the first crystallization tank 1. The scraper 11 is pressed against the inner wall surface of the first crystallization tank 1 by spring pressure. When the angle α of the tip of the scraper 11 is 20 to 60 degrees, the inner wall surface of the first crystallization tank 1 is not damaged, and the (meth) acrylic acid crystals adhering to the inner wall surface can be efficiently scraped off. From the viewpoint of being able to. For the same reason, the contact angle β of the scraper 11 with the inner wall surface of the first crystallization tank 1 is preferably 20 to 70 degrees. As is clear from FIG. 3, it is necessary to satisfy the relationship of α <β.

  The pressing pressure of the scraper 11 when pressing the scraper 11 against the inner wall surface of the first crystallization tank 1 by the spring pressure is also an important factor. Note that the pressing pressure (kg / m) of the scraper 11 is determined by measuring the scale (kg) when the scraper is pulled up and lifted away from the heat transfer surface by a spring-type balance, and the scraper 11 scraping length (m ), The pressing pressure per unit scraping length can be measured. The pressing pressure is preferably 5 to 25 kg / m from the viewpoint of scraping efficiency and the life of the stirring blade 6. If the pressing pressure is lower than 5 kg / m, the (meth) acrylic acid crystals adhering to the inner wall surface of the first crystallization tank 1 cannot be sufficiently scraped off, so that the effect of suppressing scaling cannot be sufficiently obtained. There is a case. Moreover, when the pressing pressure is higher than 25 kg / m, the inner wall surface of the first crystallization tank 1 may be damaged. In addition, since a large load is applied to the stirring blade 6, the life of the scraper 11 may be shortened. More preferably, the pressing pressure of the scraper 11 is 10 to 20 kg / m.

  In FIGS. 1 and 2, the stirring mechanism having two rows of stirring blades 6 provided with the scraper 11 along the inner wall surface of the first crystallization tank 1 is shown. However, two or more stirring blades 6 are provided. You may have. The number of supports 7 that support the stirring blade 6 is not limited. Moreover, as shown in FIG. 1 and FIG. 2, the stirring blades 6 may be installed over the entire longitudinal direction of the inner wall surface of the first crystallization tank 1, or a plurality of stirring blades 6 are installed alternately, and a scraper is rotated by rotation. 11, the entire inner wall surface of the first crystallization tank 1 may be scraped off.

  The introduction of the crude (meth) acrylic acid is performed from the introduction port 4 provided in the upper part of the first crystallization tank 1.

  The temperature of the slurry of the (meth) acrylic acid crystals (hereinafter referred to as slurry) in the first crystallization tank 1 is 0 to 10 ° C. in the case of methacrylic acid, and −4 to 6 ° C. in the case of acrylic acid. It is preferable from the viewpoint of easy crystallization operation. More preferably, it is 3 to 9 ° C. in the case of methacrylic acid, and −1 to 5 ° C. in the case of acrylic acid.

  In the present invention, the stirring speed of the slurry by the stirring blade 6 is preferably 18 to 36 rpm from the viewpoint of the stability of the liquid level in the tank and the scraping efficiency. When the stirring speed is slower than 18 rpm, the scraping frequency of the inner wall surface of the first crystallization tank 1 is lowered and scaling is likely to occur. Moreover, there is a possibility that a large film heat transfer coefficient in the first crystallization tank 1 cannot be obtained due to the occurrence of scaling. On the other hand, when the speed is higher than 36 rpm, vortices are generated in the first crystallization tank 1 and troubles may occur in operation. More preferably, it is 22 to 32 rpm.

  A part of the slurry in the first crystallization tank 1 is extracted from a discharge port 8 provided in the lower part of the first crystallization tank 1 and introduced into the second crystallization tank 2.

(Crystallization of (meth) acrylic acid in the second crystallization tank)
Next, the slurry extracted from the first crystallization tank 1 is introduced into the second crystallization tank 2 from the introduction port 9, and the slurry is further cooled. Thereby, the crystal of (meth) acrylic acid produced | generated in the 1st crystallization tank 1 can be further grown as a seed crystal, and crystallization can be accelerated | stimulated.

  As the second crystallization tank 2, a crystallization tank having the same configuration as the first crystallization tank 1 can be used. Further, like the crystallization in the first crystallization tank 1, it is preferable to cool the slurry while stirring at a predetermined stirring speed.

  The temperature of the slurry in the second crystallization tank 2 is lower than the slurry temperature in the first crystallization tank 1, and is −2 to 8 ° C. for methacrylic acid and −6 to 4 ° C. for acrylic acid. It is preferable from the viewpoint of easy crystallization operation and crystallization promotion. More preferably, it is 1 to 7 ° C in the case of methacrylic acid, and -3 to 3 ° C in the case of acrylic acid.

  A part of the slurry in the second crystallization tank 2 is extracted from the discharge port 10 provided in the lower part of the second crystallization tank 2.

  In this embodiment, an example is shown in which crystallization is performed using two crystallization tanks, a first crystallization tank 1 and a second crystallization tank 2, but only one tank or three or more tanks are crystallized. You may crystallize (meth) acrylic acid using the crystallizer which connected the tank in series. When three or more crystallization tanks are used, the slurry temperature in each crystallization tank is set to be lower in the order of connection.

(Separation of (meth) acrylic acid crystals and mother liquor)
A part of the slurry in the second crystallization tank 2 in which the (meth) acrylic acid crystals have grown is extracted from the discharge port 10, and the (meth) acrylic acid crystals and the mother liquor are separated and transferred to a purification tower. The method for separating the (meth) acrylic acid crystal from the mother liquor is not particularly limited as long as it is a method capable of separating a solid and a liquid. For example, a known solid-liquid separation method such as a filtration method or a centrifugation method may also be used. Can be used.

(Purification in the purification tower)
The (meth) acrylic acid crystals supplied to the purification tower are purified in the purification tower. Specific examples of the purification tower are described in, for example, “Purification of organic compounds by Kureha continuous crystal purification apparatus”, published by Tadazo Shimizu, published by Chemical Engineering, Vol. 27, No. 3 (1982), page 49. A KCP apparatus etc. are mentioned. The type of separation operation may be either batch or continuous.

[Example 1]
Crude methacrylic acid was purified using a crystallization tank having the same structure as in FIGS. However, only one stage of the crystallization tank in FIG. 1 was used. The crystallization tank is provided with a cooling jacket using a 40% by mass ethylene glycol aqueous solution as a heat medium. Moreover, the stirring mechanism which has the stirring blade which equipped the scraper in the contact part with the inner wall face of this crystallization tank is provided. As a material of the scraper, “MC nylon” (trade name, manufactured by Nippon Polypenco Co., Ltd.) was used. Further, SUS304 was used as a material for the inner wall surface of the crystallization tank.

  Crude methacrylic acid is an organic solvent derived from an aqueous methacrylic acid solution obtained by absorbing in water a reaction gas obtained by a direct oxidation method in which tertiary butyl alcohol is subjected to catalytic gas phase oxidation with molecular oxygen in a two-stage reaction. The methacrylic acid was extracted using, and the one obtained by removing the organic solvent and nonvolatile components by distillation was used. Methanol was added to the crude methacrylic acid to prepare a crude methacrylic acid mixed solution having a methanol concentration of 5% by mass. The crude methacrylic acid mixed solution was precooled to 11 to 13 ° C., then continuously supplied to the crystallization tank at 1900 kg / hour, and cooled to crystallize methacrylic acid.

  During the crystallization of methacrylic acid, the stirring blade equipped with the “MC nylon” scraper of α = 30 ° in FIG. 3 was rotated at a rotational speed of 26 rpm in the crystallization tank, and the stirring blade was rotated at β = 33 °. Crystallization was carried out while scraping the crystals by pressing the scraper. The pressing pressure of the scraper at this time was adjusted to be 10 to 20 kg / m for all the scrapers. Moreover, the cooling temperature of the circulating heat medium was adjusted to −1 to 3 ° C., and the slurry temperature inside the crystallization tank was set to 4 to 7 ° C. As a result, a methacrylic acid-containing liquid containing methacrylic acid crystals was obtained.

  While separating the methacrylic acid-containing liquid containing the methacrylic acid crystal into a methacrylic acid crystal and a filtrate in a solid-liquid separator, the methacrylic acid crystal was transferred to a purification tower and purified.

  When the crude methacrylic acid mixture was purified for 1000 hours continuously, a large amount of methacrylic acid crystals adhered to the crystallization tank heat transfer surface, resulting in a decrease in the overall heat transfer coefficient, and the scale adhering to the heat transfer surface. The work of melting was necessary. However, after refining the crude methacrylic acid mixture and melting the scale and operating for one year, the period until the overall heat transfer coefficient decreases and the operation becomes impossible is stably 1000 hours. A methacrylic acid-containing liquid containing methacrylic acid crystals could be obtained. One year later, an open inspection was carried out, and when the inner wall surface of the crystallization tank was visually confirmed, no scratches due to the scraper were observed.

[Comparative Example 1]
The crude methacrylic acid mixed solution was purified in the same manner as in Example 1 except that a scraper having the same shape made of PTFE was used instead of the scraper made of “MC nylon”.

  The period until the overall heat transfer coefficient decreased was about 1000 hours at the beginning, which was the same as the case of using the “MC nylon” scraper in Example 1. However, when the crude methacrylic acid mixture was purified and the scale was melted repeatedly, the period until the overall heat transfer coefficient decreased gradually decreased, and after 1 year, the overall heat transfer coefficient decreased. The period was 700 hours. As a result, the operation was stopped and the frequency of scale melting increased, so that the productivity of the methacrylic acid solution containing the crystallized methacrylic acid was lowered. One year later, an open inspection was conducted and the inner wall surface of the crystallization tank was visually confirmed. Scratches due to PTFE scrapers were observed, and it was estimated that the overall heat transfer coefficient was reduced due to the scales adhering to the scratches. did.

1 First crystallization tank 2 Second crystallization tank 3 Cooler 4 Inlet (first crystallization tank)
5 Jacket 6 Stirring blade 7 Support 8 Discharge port (first crystallization tank)
9 Inlet (second crystallization tank)
10 Discharge port (second crystallization tank)
11 Scraper α Angle of tip of scraper β Contact angle of scraper with inner wall of first crystallization tank M Stirring power

Claims (6)

In the purification method of (meth) acrylic acid, which crystallizes (meth) acrylic acid using a crystallization apparatus including one or more crystallization tanks,
The crystallization tank includes a cooling mechanism having an inner wall surface of the crystallization tank as a heat transfer surface,
A stirring mechanism having a stirring blade provided with a scraper that is in contact with the inner wall surface of the crystallization tank and is stirred while scraping off the (meth) acrylic acid crystals adhering to the inner wall surface of the crystallization tank by rotation;
The scraper is made of nylon as the material of the contact portion with the inner wall surface of the crystallization tank,
A method for purifying (meth) acrylic acid that crystallizes (meth) acrylic acid by cooling the crude (meth) acrylic acid introduced into the crystallization tank while stirring with the stirring mechanism and the cooling mechanism.   The method for purifying (meth) acrylic acid according to claim 1, wherein a tip portion of the scraper has an acute-angle shape, and the tip portion is in contact with an inner wall surface of the crystallization tank.   The method for purifying (meth) acrylic acid according to claim 1 or 2, wherein the scraper is pressed against an inner wall surface of the crystallization tank by a spring attached to the stirring blade.   The method for purifying (meth) acrylic acid according to claim 3, wherein the pressing pressure when pressing the scraper against the inner wall surface of the crystallization tank is 5 to 25 kg / m.   The method for purifying (meth) acrylic acid according to any one of claims 1 to 4, wherein the stirring speed of the crude (meth) acrylic acid by the stirring mechanism is 18 to 36 rpm.   The method for purifying (meth) acrylic acid according to any one of claims 1 to 5, wherein a material of an inner wall surface of the crystallization tank is SUS304 or SUS316.

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