JPS6159762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystallization method for obtaining crystals with a large shape, and more specifically, a liquid containing a target component to be crystallized (hereinafter referred to as "undiluted solution") is cooled and solidified, and the solidified product is broken. The present invention relates to a crystallization method in which, after crushing, the solidified product is poured into a stock solution maintained at a temperature at which the component to be crystallized can be handled as a slurry, allowed to remain for a predetermined period of time to grow crystals, and then taken out.

Conventionally, it has been widely practiced to separate a target substance as crystals by crystallizing it from a liquid containing a component to be crystallized. Normally, industrially, crystallization is performed by cooling under stirring using heat transfer or the latent heat of vaporization of components with low boiling points, but in this case, the faster the cooling rate, the smaller the crystals formed. . Furthermore, in the case of cooling crystallization using heat transfer, it is inevitable that crystals will deposit and adhere to the cooling wall surface, resulting in a decrease in cooling efficiency.

It is extremely preferable that the crystals obtained by crystallization have a large shape when used for subsequent excessive separation or purification. Of course, large crystals can be obtained by crystallizing at a slow cooling rate while standing still, but this is not industrially practical.

As a result of research on a crystallization method for obtaining crystals with a large shape that are easy to overseparate industrially, the present inventor solidified a liquid containing the target component to be crystallized, crushed it, and When the crushed and solidified material is put into a growth tank containing an undiluted solution maintained at a temperature at which the crystals are replaced as a slurry, and taken out after residence for a predetermined period of time, it contains almost no fine crystals and large-shaped crystals. It was discovered that the present invention can be obtained.

The present invention involves fixing a liquid containing a component to be crystallized on the surface of a cooled rotating drum, exfoliating and crushing the adhered material, and then producing fine crystals containing an undiluted solution that maintains the component to be crystallized at a temperature that allows it to be handled as a slurry. This is a method in which the crushed and fixed material is placed in a growth tank with an upward flow for floating, allowed to stay there for a predetermined period of time to grow crystals, and then taken out. That is, the stock solution is once solidified, and the latent heat of fusion of impurities and fine crystals is used to grow the crystals.

In carrying out the present invention, for example, an apparatus as shown in the accompanying drawings is used. In the drawing, reference numeral 1 denotes a fixed liquid tank, and a stock solution containing the target component to be crystallized is supplied to this liquid tank 1 through a supply pipe 2. Solidification of the stock solution is done in liquid tank 1.
A cooled rotating door installed partially immersed in
This is done on the surface of the ram 3. A refrigerant is passed through the rotating drum 3 for cooling, or a liquid with a low boiling point, such as Freon (trade name), methane, etc.
is supplied and the latent heat of vaporization is used for cooling. Cooling is carried out to such an extent that the entire solution that comes into contact with it solidifies. When this rotary drum 3 is rotated slowly while partially immersed in the stock solution, the stock solution will stick to its surface. This stuck material is continuously scraped off with a scraping blade 4, and further crushed with a crusher 5.
supply to. The inside of the growth tank 6 is filled with the same stock solution as that supplied to the fixed liquid tank 1, and is kept cool at a temperature at which the supplied crystals can be handled as a slurry. In order to keep this temperature constant, a portion of the stock solution is also supplied to the growth tank 6 from the supply pipe 7. Further, a stirrer 8 is provided in the growth tank 6, and stirring is performed to generate an upward flow to the extent that fine crystals float to the top. That is, the agitation is such that many grown crystals are present in the lower part of the tank, and relatively many fine crystals are present in the upper part. The solidified raw solution that adheres to the drum surface and is exfoliated and crushed will be melted in such a growth tank by melting the low melting point crystals containing fine crystals and impurities. As the slurry liquid is cooled, crystals with a higher melting point and higher purity begin to precipitate and gradually grow. In addition, some of the suspended fine crystals are melted by the sensible heat of the high-temperature stock solution supplied from the supply pipe 7, increasing the degree of supersaturation of the solution in the tank, thereby promoting crystal growth.

The slurry concentration in the growth tank is preferably 25 to 50% on average, preferably 30 to 40% for ease of handling. The residence time here is determined depending on the type of crystal component and the desired size of the crystals, but in most cases it is 4 to 20 hours. The crystals that have remained in the growth tank at a predetermined temperature for a certain period of time are sequentially taken out as a slurry through an extraction pipe 9. According to the method of the present invention, in which the liquid to be crystallized is continuously solidified in this way, and then the target crystal is grown and taken out, a crystal with a large crystal shape and a high concentration can be obtained.

In addition, since both the rotation of the rotary drum type cooling crystallizer and the rotation of the agitator in the growth tank used in carrying out the present invention only require gentle rotation, it consumes less energy than other crystallizers and is inexpensive to manufacture. This has the advantage that failures are unlikely to occur.

The present invention will be explained below with reference to Examples.

Example: A fixed liquid tank in which a part of a rotating drum cooler with a diameter of 500 mm and a length of 300 mm is immersed, and a diameter of 600 mm and a height of 500 mm.
Using a device as shown in the attached drawing, which consists of a growth tank with an internal capacity of about 140 mm and a stirring blade inside,
Paradichlorobenzene was crystallized by supplying a solution containing 42% at 60° C. to the fixing liquid tank at 16 kg/Hr and to the growth tank at 1.5 Kg/Hr.

At this time, the surface of the rotating drum was cooled to −25° C. using methanol brine and rotated at 0.13 rpm. After the crystals deposited on the surface of the rotating drum were successively scraped and crushed, they were continuously fed into a growth tank kept cool at 5°C. A stirring blade is used in the growth tank.
After staying for an average of 8 hours while rotating at 15 rpm, a slurry containing approximately 40% crystals was obtained from the bottom of the tank.
Kg/Hr was taken out continuously. The paradichlorobenzene crystals thus obtained were apparently columnar crystals with a major axis of about 2000 to 4000 μm and a short axis of about 500 to 1000 μm.

[Brief explanation of the drawing]

The accompanying drawings are cross-sectional views of the apparatus used in the present invention. In the drawing, 1 is a fixed liquid tank, 2 is a supply pipe, 3 is a rotating drum,
4 is a scraping blade, 5 is a crusher, 6 is a growth tank, 7 is a supply pipe, 8 is a stirrer, and 9 is an extraction pipe. 〓〓〓

Claims (1)

[Scope of Claims] 1. Solidify a stock solution containing a component to be crystallized, crush the solidified stock solution, put the crushed solidified product into a growth tank containing a slurry stock solution of the component to be crystallized, and A crystallization method characterized by growing crystals of the component to be crystallized in a growth tank. 2. The crystallization method according to claim 1, characterized in that an upward flow that floats fine crystals is generated in the growth tank, and the stock solution is supplied to the upper part of the growth tank. 3. Claim 1, characterized in that the stock solution is solidified and crushed by fixing the stock solution containing the component to be crystallized on the surface of a cooled rotating drum, and peeling off and crushing the stuck material. Or the crystallization method described in Section 2.