JPH0411241B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystallization method using seed crystals and an apparatus used therein.

When a solution containing a substance to be crystallized is subjected to operations such as cooling or vacuum concentration to generate crystals, if a supersaturation phenomenon occurs, crystals will suddenly come out at a certain point, so there will be many fine crystals. Another drawback is that the crystal sizes are irregular. In order to prevent this, a method is known in which seed crystals are added to a supersaturated solution to perform crystallization. This method is not only used on a laboratory scale, but when carried out on an industrial scale, various troubles often occur. For example, the method of directly supplying seed crystals to a solution in a crystallization tank with a concentration close to the saturated state uses fine powder as the seed crystals, which has poor fluidity and is easily clogged in the supply pipe, making it difficult to maintain smooth flow. Moreover, it is difficult to quickly supply the crystallizer to the crystallization tank. Furthermore, since solids are handled, foreign matter is likely to get mixed in during the work, which can have a serious impact on product quality. In addition, when adopting a method in which the seed crystals are suspended in the same solvent as that of the solution to be treated and the suspension is supplied to the crystallization tank,
When seed crystals are supplied to the suspension preparation tank, troubles similar to those described above occur. Furthermore, no matter which of the above methods is employed, it is difficult to supply the seed crystals in a closed system and completely automatically.

The object of the present invention is to provide a method which does not have the disadvantages of the above-mentioned methods and therefore allows the preparation and supply of seed crystals to be carried out automatically in a closed system. Another object of the present invention is to provide a method in which the particle size distribution of seed crystals is narrow and the particle size can be freely adjusted. In connection with the above object, the present invention also aims at achieving a smooth crystallization operation and homogenizing the target crystal grain size, grain size distribution, grain shape, etc.

That is, according to the present invention, in a crystallization method in which crystals are generated from a solution using a seed crystal, inert gas is blown into a small amount of solution in which (A) a substance to be crystallized is dissolved in a seed crystal generation tank. , a method by evaporation of the solvent and accompanying cooling; (B) supercooling the small amount of solution;
A suspension of seed crystals is obtained by adding a poor solvent; or (C) supercooling the small amount of solution and stirring it at high speed, and then transferring it to a crystallization tank. A method of crystallization is provided, characterized in that crystals are formed by adding the suspension to a treatment solution maintained at an appropriate temperature therein. In order to smoothly carry out the above method, the present invention provides a crystallizer comprising a seed crystal generation tank and a crystallization tank connected thereto, the seed crystal generation tank being provided with a liquid spraying section. be done.

In the present invention, first, a suspension of seed crystals is generated from a small amount of solution in which a substance to be crystallized is dissolved in a seed crystal generation tank. The solvent of this solution does not need to be the same as the solvent used in the crystallizer. The most preferred method for producing the suspension is method (A) in which an inert gas is blown into the small amount of the solution to evaporate the solvent and cool the solution accordingly. Inert gas is a solvent,
A substance that does not chemically change the solute in a substantial sense, such as nitrogen gas or nitrogen gas containing a small amount of oxygen, is preferably used. In method (A), the grain size of the seed crystal can be adjusted with good accuracy by adjusting the flow rate of the inert gas, so it is said that it is easy to obtain uniform grain size and grain size distribution of the crystals obtained in the crystallization tank. There are advantages.

In addition, in this method, in order to avoid extreme supersaturation and precipitate seed crystals with good particle size distribution with good reproducibility, the inert gas blowing speed is preferably 0.5 m/min or more superficially, particularly preferably 0.5 m/min or more.
It is desirable to set the speed to 1.0m/min or more. However, if the small amount of solution is foamable, it is not preferable to increase the superficial velocity too much, so it is preferably kept within a range of 5.0 m/min or less, particularly preferably 3.0 m/min or less.
Since the amount of seed crystals produced can be calculated, for example, by detecting the temperature of the suspension, the supply of inert gas may be stopped when desired.

As another method for producing a suspension of seed crystals, method (B) of supercooling a small amount of a solution containing a substance to be crystallized and adding a poor solvent can also be adopted. This method requires the use of a poor solvent, which places a slight burden on the accuracy of solvent recovery afterwards, and the adjustment of particle size is not necessarily easier than in method (A), but it is still industrially viable. This method is useful in that it provides seed crystals with acceptable particle size and can be operated automatically in a closed system. The poor solvent may have a stronger affinity with the solvent than the substance to be crystallized, and the solubility of the crystallized substance is considerably lower than that of the solvent. The reason why the solution is kept in a supercooled state in this method is to instantly precipitate crystals by adding a poor solvent. Since it is not preferable to use too much of the poor solvent, it is preferably used in an amount of 0.01 to 0.1 part by volume, particularly preferably 0.01 to 0.05 part by volume, per 1 part by volume of the small amount of solution.

Another method for producing a suspension of seed crystals is a method (method C) in which the small amount of the solution is supercooled and a stirrer is rotated at high speed. Although methods A and B are preferably carried out with stirring, low-speed stirring is sufficient in this case. In this C method, for example, the supercooled state is achieved by rotating at a low speed until the supercooled state is reached, and then rotating at a high speed, for example, at a circumferential speed of 0.5 to 10 m/sec, preferably 1 to 5 m/sec. Crystals can be precipitated from solution.
This method makes it easy to adjust the crystal grain size by adjusting the cooling temperature and rotation speed, but requires equipment for high-speed rotation.

A suspension of seed crystals produced by any of methods (A), (B), and (C) is added to a solution to be treated maintained at an appropriate temperature in a crystallization tank, for example, in a saturated state or above. It is added to a solution to be treated that is maintained at a temperature that is slightly supersaturated to cause crystallization. Once crystals are precipitated, the amount of crystals precipitated can be increased by further reducing the pressure or cooling.

In the seed crystal generation tank, crystals tend to adhere to the walls and stirring rods near the liquid level, and may remain even after the seed crystal suspension is transferred from the seed crystal generation tank to the crystallization tank, and may be repeatedly These lumps may get mixed in during operation and cause trouble. Therefore, the solution supply port for seed crystal generation should be sprayed near the liquid surface of the wall surface or stirring rod to prevent adhering crystals. The structure should be such that it can be washed off.

FIG. 1 shows an example of a crystallizer used in the present invention.

A predetermined amount of a solution containing a substance to be crystallized, preferably a solution having a concentration close to saturation, is charged into the seed crystal generation tank 2 through a filter 1 through a liquid dispersion pipe 4. It is preferable that the liquid dispersion pipe 4 has a structure in which the charged liquid washes away crystals that have adhered to the stirring rod (shaft) and around the inner wall of the tank during the previous use. It has the effect of cleaning and redissolving the crystals. For this reason, for example, the liquid dispersion pipe should be an annular porous pipe, and should be installed as concentrically as possible in the upper part of the seed crystal generation tank, with the hole oriented so that the charged liquid directly hits the stirring rod (shaft) and the crystal adhesion area on the wall surface. preferable. An inert gas is blown into the solution charged in the seed crystal generation tank 2 through the inert gas introduction part 5, and a part of the solvent is entrained in the gas, evaporated, and cooled. It is preferable to stir the inside of the system using a stirrer 3. The flow rate of the inert gas may be adjusted by detecting, for example, the temperature inside the tank, and its supply is stopped when the tank has cooled to a predetermined temperature. By adjusting the gas flow rate, the particle size of the seed crystal can be adjusted. Note that the inert gas accompanied by the solvent is cooled in the condenser 6, and the solvent is condensed and recovered separately, while the inert gas is discharged out of the system. In contrast to such seed crystal generation methods, methods such as simply removing the solvent by reducing pressure or using only external cooling,
This is not preferred because it is difficult to control the timing at which the seed crystals start forming, and it is difficult to obtain homogeneous seed crystals.

On the other hand, the crystallization tank 8 is charged with the solution to be treated, and after bringing it to a nearly saturated state or a slightly supersaturated state by reducing pressure or external cooling while operating the stirrer 9, the valve 7 is opened to seed crystals. When the suspension in the production tank is transferred, crystals begin to be produced, so that the desired amount of crystals can be produced by further increasing the degree of vacuum or intensifying the cooling. All of the above operations can be performed in a closed system and can be automated. This method is particularly suitable for use in cases where supersaturation tends to occur and the solvent is easily volatile. As an example of this application, a case will be described in which dicumyl peroxide is crystallized from a reaction mixture of cumene hydroperoxide obtained by oxidation of cumene and α-cumyl alcohol. The crude dicumyl peroxide obtained by the above condensation reaction includes cumene,
Contains impurities such as α-cumyl alcohol and acetophenone. Even if this crude dicumyl peroxide is cooled and crystallized as it is, the amount of dicumyl peroxide crystals recovered is small. Dicumyl peroxide crystals can be recovered in good yield by directly cooling to precipitate a portion of dicumyl peroxide and adding lower alcohol or water-containing lower alcohol to the remaining mother liquor for crystallization. When dicumyl peroxide is precipitated from such a lower alcohol solution, a supersaturation phenomenon tends to occur, so it is effective to apply the method of the present invention.

Next, examples will be shown.

Example 1 For 100 parts by weight of crude dicumyl peroxide (dicumyl peroxide content 80%) obtained by the reaction of cumene hydroperoxide and α-cumyl alcohol,
A solution containing 55 to 65 parts by weight of methanol is charged into a crystallization tank, the pressure is gradually reduced while stirring, and the solution is cooled until saturated.

On the other hand, a portion of the crystallization raw material is charged into a seed crystal generation tank using a liquid dispersion pipe in an amount of 1.5 to 2.0 parts by weight based on 100 parts by weight of the raw material to be charged in the crystallization tank. At this time, after the previous use, the crystals adhering to the inner wall of the tank and the stirring shaft are washed and redissolved. When the preparation is completed, nitrogen is blown into the tank through the annular porous pipe at the bottom of the tank to cool it and precipitate seed crystals. The nitrogen blowing speed at this time is set at a superficial speed of 2.5 to 3 m/min in consideration of the following points.

(1) The internal liquid has foaming properties.

(2) If the nitrogen supply rate is slow, the liquid will become supersaturated. In view of the phenomenon (1), the hole diameter of the annular porous pipe is preferably 3 mm or more.

The amount of seed crystals can be arbitrarily changed within a certain range by changing the set value of the cooling end temperature. When the temperature of this system reaches the set value, e.g. 20°C to 15°C, the target amount of seed crystals (e.g. 0.27 to 0.36 parts by weight)
After the precipitation of the seed crystals is completed, the suspension containing the seed crystals is transferred to a crystallization tank containing a saturated solution. The temperature inside the crystallizer is set at a set value (e.g.,
Cool to 18°C to 13°C and continue crystallization. Thus, when the crystallization operation is completed, the suspension
From 100 parts by weight, 25 to 30 parts by weight of crystals can be obtained. These crystals have a uniform particle shape, and the particle size distribution is 90 to 100 parts by weight per 100 parts by weight of the crystals obtained.
95 parts by weight is within the target range (e.g.
500μ to 1000μ) and narrow distribution width (e.g. 800μ
(normal distribution with 70%) can yield crystals.

Example 2 A methanol solution of crude dicumyl peroxide (dicumyl peroxide concentration 48.4wt) was prepared in the same manner as in Example 1.
%). 2 parts by weight of the solution was charged into a seed crystal generation tank, and 0.04 parts by weight of water cooled to 15°C was added to obtain a 35% by weight seed crystal slurry. On the other hand, 100 parts by weight of the above solution was charged into a crystallization tank, cooled to 23.5°C, and then the above seed crystal slurry was added. The degree of vacuum in the crystallization tank was increased and the mixture was cooled to 13°C to obtain 30 parts by weight of crystals. The average grain size of the crystals was 850μ, with more than 90% falling within the range of 500μ to 1000μ.

Example 3 A seed crystal generation tank was charged with 2 parts by weight of the methanol solution of the crude dicumyl peroxide of Example 2, and cooled to 17° C. under low speed rotation (300 rpm). Next, the rotational speed of the stirrer was set to 300 rpm (peripheral speed 2.8 m/sec) to obtain a 32% by weight seed crystal slurry.

The slurry was crystallized in a crystallization tank in the same manner as in Example 2 to obtain 28 parts by weight of dicumyl peroxide crystals. The average grain size of the crystals was 671μ, with more than 83% falling within the range of 500μ to 1000μ.

[Brief explanation of drawings]

FIG. 1 is a drawing showing a crystallizer. 2...Seed crystal generation tank, 4...Liquid dispersion pipe, 5...
Gas introduction pipe, 8...crystallization tank.

Claims (1)

[Claims] 1. A lower alcohol is added to a reaction mixture of cumene hydroperoxide obtained by oxidation of cumene and α-cumyl alcohol, and dicumyl peroxide is crystallized from this lower alcohol solution using seed crystals. In this method, the lower alcohol solution is charged into a crystallization tank, and at the same time, a part of the lower alcohol solution is charged into a seed crystal generation tank, and in the seed crystal generation tank, (A) an inert substance is added to the lower alcohol solution; Method by blowing gas, evaporation of solvent and accompanying cooling; (B)
The seed crystals can be suspended by employing either of the following methods: (C) supercooling the lower alcohol solution and adding a poor solvent; or (C) supercooling the lower alcohol solution and stirring at high speed. The method is characterized in that a suspension of cumene hydroperoxide is obtained, and then this suspension is added to a lower alcohol solution of cumene hydroperoxide maintained at an appropriate temperature in the crystallization tank to generate crystals of cumene hydroperoxide. Crystallization method. 2. The crystallization method according to claim 1, wherein the lower alcohol solution of cumene hydroperoxide is a saturated solution. 3. An apparatus for adding a lower alcohol to a reaction mixture of cumene hydroperoxide obtained by oxidation of cumene and α-cumyl alcohol, and crystallizing dicumyl peroxide from this lower alcohol solution using seed crystals, , while charging the lower alcohol solution to a crystallization tank, a part of the lower alcohol solution is also charged to a seed crystal generation tank, and in this seed crystal generation tank, (A) blowing an inert gas into the lower alcohol solution; , method by evaporation of solvent and associated cooling; (B)
The seed crystals can be suspended by employing either of the following methods: (C) supercooling the lower alcohol solution and adding a poor solvent; or (C) supercooling the lower alcohol solution and stirring at high speed. In an apparatus for producing crystals of cumene hydroperoxide by obtaining a suspension and then adding this suspension to a lower alcohol solution of cumene hydroperoxide maintained at an appropriate temperature in the crystallizer, A seed crystal generation tank for obtaining a crystal suspension, a crystallization tank for charging a liquid to be treated, and a pipe for transferring the suspension from the seed crystal generation tank to the crystallization tank. In the crystallizer, the seed crystal generation tank has a stirrer with a stirring shaft, and when charging the solution in which the substance to be crystallized is dissolved into the seed crystal generation tank, the solution is mixed with the stirring shaft and/or the seed crystal. A crystallizer characterized in that it is equipped with a spray pipe for spraying toward the wall of a generation tank.