JPS62247802A - Crystallization method - Google Patents

Abstract

PURPOSE:To obtain the titled convenient and highly universal crystallization method by crystallizing a part of a solute on cooling than heating the soln., and recooling the soln. before the crystal is completely dissolved. CONSTITUTION:A solute is firstly dissolved, the cooling is started, cooling is stopped after a crystal is deposited, and the soln. is heated. The heating at a temp. lower than the temp. at which the crystal is completely dissolved is stopped, recording is started, the soln. is cooled to a desired temp., and the crystallization is finished. Consequently, a roughly large-sized crystal can be conveniently obtained, hence a crystal of low liq. content can be obtained in good yield by solid-liq. separation, and the succeeding drying stage can be economically carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a batch cooling crystallization method, and particularly to a method for obtaining coarser crystals.

<Prior Art and Problems> In the chemical industry and the like, when the final product is a powder, a method of purifying it by crystallization is often adopted.

Particularly in multi-purpose plants that aim to produce small quantities and a large number of items, batch cooling crystallization is used because the equipment is sparse, it is easy to switch to different types of products, and the operation is simple. It is often preferable to use

The purpose of the crystallization operation is to separate the target solute from a liquid mixture as crystals. When the obtained crystals are used as products, not only the purity but also the crystal shape and particle size are often considered issues.

However, one of the problems that often arises in crystallization operations is that crystal growth does not proceed, resulting in fine crystals.

Usually, the crystallization step is followed by a solid-liquid separation step and a drying step to produce a powder product, but in the case of fine crystal slurry, this "post-process" causes serious problems.

For example, in solid-liquid separation, ■ Separation time takes a long time;
Problems include (2) leakage of crystals into the e-liquid, and (2) high liquid content in the separated wet powder. Also, if there is a drying process, when drying wet powder with a high liquid content, ■ Drying time may take a long time.
■Problems such as rolling may occur during drying. In addition to these problems that reduce productivity,
This may lead to quality problems such as insufficient purity.

On the other hand, in batch cooling crystallization, conventional methods used to thicken the crystals include adjusting the cooling rate,
Adjustment of solute concentration, adjustment of solvent composition, etc. are taken, and furthermore, crystal modifiers may also be considered. However, even if these methods are considered, if no improvement is achieved, or if changing the composition or concentration is difficult in the process and there is no room for consideration, there is a risk that production may become impossible.

The object of the present invention is to provide a simple and highly versatile crystallization method that solves the above-mentioned problems.

<Means to solve the problem> As a result of intensive studies regarding the coarsening of crystals in batch cooling crystallization operations, taking into account the shortcomings of conventional methods, the inventors have devised an operation that can be easily carried out. We discovered a method and led to the present invention. That is, in the batch cooling crystallization of the present invention, cooling is started, and after a part of the solute has precipitated into crystals, cooling is stopped and the heating is heated to J4 temperature, and heating is stopped before the precipitated crystals are completely dissolved. This is a crystallization method characterized by cooling again.

In carrying out the present invention, cooling is started after the solute is dissolved in a solvent without stirring, and cooling is stopped after crystals are precipitated.
Heat and raise the temperature (re-heat). Then, the temperature increase at a temperature lower than the complete solution temperature is stopped, and the cooling operation is switched again, and the crystallization is completed by cooling to the target temperature 1. Optimum conditions for the timing of switching from cooling to temperature raising, the timing of switching from temperature raising to cooling again, etc. differ depending on the system being handled, but these are determined as appropriate through experiments.

Basically, the temperature of the slurry obtained by the first cooling is raised again, but at this time, the fine crystals are dissolved, and the coarse crystals are not dissolved and remain as they are. When cooling is started again before complete dissolution, the crystal nuclei are present from the beginning because they are cooled in the presence of coarse crystals, just as seed crystals have been added. Since the crystals grow using these seed crystals, it is thought that it is possible to obtain crystals with a larger particle size and better separability than the slurry obtained by the first cooling.

(Effects of the Invention) By the method of the present invention, it is possible to easily obtain crystals with coarser grain size. Therefore, crystals with a low liquid content can be obtained in good yield by solid-liquid separation. Also, as a result, the subsequent drying step can be carried out economically.

<Example> Hereinafter, the method of the present invention will be specifically explained with reference to Examples.

Example 1 A crystallization operation of pyromellitic acid (l, 2,4,5 benzenetetracarboxylic acid) was performed under the following conditions.

0 liquid composition Pyromellitic acid 17.5wt% Nitric acid 1
6.1 u Water 66.4 ttO crystallization operation■ Raise the temperature at loo'C'j to dissolve completely.

■ Cool from 100℃ to 40℃ at approximately 15℃/HR.

Precipitation of crystals was observed at about 60°C.

■ When the temperature reaches 40℃, stop cooling and raise the temperature to 80℃ again.
The temperature rose in a matter of seconds. Even at 80°C, complete dissolution was not achieved and the presence of crystals was observed.

(2) After stirring at 80°C for about 30 minutes, a cooling operation was started. The cooling rate was adjusted to an average of 10°C/HR, and the temperature was reduced to 20°C.

0? Using 5CP paper, suction the obtained slurry with a vacuum cleaner.
It's too late.

Filtration conditions Slurry amount: 500 g Vacuum in the suction bottle -200 Hg Deliquing time: 15 molecules The liquid content of the wet cake filtered was 5.5 wt%.

Comparative Example-1 The same liquid as in Example-■ was heated to 95°C to completely dissolve it, and then cooled to 20°C at an average cooling rate of 10°C/HR.

The obtained slurry was filtered under the same conditions as in Example 1.

The liquid content of the obtained wet cake was 29.5 wt%.

Claims (1)

[Claims] In batch cooling crystallization, cooling is started, and after a portion of the solute has precipitated into crystals, cooling is stopped and the temperature is raised, and heating is stopped before the precipitated crystals are completely dissolved and cooled again. A crystallization method characterized by: