JPS5930701B2 - Method for crystallizing m-xylene sulfonic acid crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously discovering m-xylene sulfonic acid from a reaction product liquid obtained by reacting xylene and sulfuric acid.

Conventionally, concentrated sulfuric acid has often been used as a sulfonating agent for xylenes.

However, in order to carry out the sulfonation reaction using sulfuric acid, there is a limit value of the sulfuric acid concentration, and below this limit concentration, the reaction hardly progresses. In the sulfonation reaction of m-xylene, the sulfuric acid concentration is 68% by weight (the rest is water, the same applies below).
There are limit values before and after.

However, in the sulfonation reaction of m-xylene with sulfuric acid, equimolar amounts of water are produced as the reaction progresses, and the sulfuric acid concentration decreases. Therefore, in order to keep the reaction rate of m-xylene high, it is necessary to add a large excess of sulfuric acid to m-xylene, and industrially, the molar ratio of sulfuric acid/m-xylene =
1.5 to 2 have been adopted. Therefore, the reaction product liquid contains a large amount of unreacted sulfuric acid. On the other hand, the solubility of m-xylene sulfonic acid in an aqueous sulfuric acid solution varies markedly depending on the sulfuric acid concentration, and the solubility is low at a sulfuric acid concentration of 50 to 70% by weight, which is the early release temperature for industrial use.
Below 0°C, solubility is substantially very low.

Therefore, m-xylene sulfonic acid can be continuously separated from the reaction product solution under such conditions, but
When crystallization separation is performed in a stirred continuous finding tank, the slurry, which was transparent during batch operation, becomes cloudy during continuous operation, and this is due to the generation of a large number of extremely fine crystals. There was found. For example, in the batch method, the average grain size of the crystals is 1 to 1.2 mm, but when the grain size is continuously found, it is 0.3 mm.
The particle size was as small as ~0.5 mm, and many fine particles of 0.2 mm or less were also observed. Furthermore, after continuous operation for a long time, crystals adhering to the vessel wall became more noticeable.

In this continuous crystallization operation, the crystal grain size is small, so it is difficult to shake off the liquid, and the crystals contain a large amount of sulfuric acid, so in order to ensure quality, the sulfuric acid content must be kept below a certain level. requires a large amount of rinsing, and therefore the yield of m-xylene sulfonic acid is poor and is very uneconomical.
In order to overcome the above drawbacks, a detector with a classifier is usually used for continuous recording, or a multi-stage detector is used in the case of a stirred tank type to reduce the temperature drop per stage, approaching the batch operation method. Measures such as these will be taken.

However, all of these methods involve an increase in construction costs. As a result of intensive research into a method for increasing and making the crystal grain size uniform in a stirred tank type single-stage crystallizer having a simple structure such as that used in the continuous crystallization experiment, the present inventor found that When performing continuous crystallization at a temperature of As a result, it was discovered that the grain size of the crystals increased abnormally after the temperature was raised, and the present invention was achieved.

That is, in the present invention, m-xylene and sulfuric acid are reacted to produce m-xylene sulfonic acid, and the reaction product liquid is cooled to produce m-xylene sulfonic acid.
In the method of continuously crystallizing and separating xylene sulfonic acid crystals, the mother liquor temperature at the time of crystallization is 30 to 40°C,
In this method, fine crystals in the mother liquor are dissolved and disappeared by intermittently raising the temperature of the mother liquor to 45 to 50°C, and then the mother liquor is cooled again to 30 to 40 °C to continue the crystallization operation.

The crystallization conditions in the present invention are sulfuric acid concentration of 50 to 70% by weight (
The remainder is water), and the temperature is preferably 30 to 40°C.

Here, the sulfuric acid concentration refers to the sum of sulfuric acid and water in the reaction solution as 100
This is the sulfuric acid content expressed as % by weight. The solubility of m-xylene sulfonic acid in an aqueous sulfuric acid solution has a minimum value around a sulfuric acid concentration of 60% by weight (the remainder being water), and a minimum value of 50 to 70% by weight exists.
The difference in solubility is small within the range of weight %, which is suitable for crystallization operations. It is preferable to keep the crystallization temperature as low as possible because it can prevent dissolution loss of m-xylene sulfonic acid, but in the present invention, since the temperature raising and lowering operations are repeated intermittently, energy loss during that time is taken into account. Therefore, it is desirable to crystallize at a relatively high temperature, and from the viewpoint of operability and economy, the temperature is preferably 30 to 40°C. Furthermore, in relation to the crystallization temperature, the temperature at which fine crystals are dissolved and disappeared is preferably 45 to 50°C. This temperature corresponds to the saturation temperature at which % to % of the total crystals can be dissolved. The slurry concentration is usually 30 to 50% by weight,
In particular, 35 to 45% by weight gives good results. The frequency at which microcrystals are dissolved and disappeared cannot be generally specified due to differences in sulfuric acid concentration, slurry concentration, stirring speed, impurity concentration, maximum temperature and time required for dissolution and disappearance, etc., but in general If continuous crystallization is carried out 2 to 4 times per average residence time, crystals with an efficient particle size can be obtained.

In the present invention, unreacted sulfuric acid contained in the mother liquor after crystallization and separation of m-xylene sulfonic acid in the reaction product solution is waste
It is discarded as a liquid after being neutralized with alkali.

According to the present invention, it is not only possible to obtain m-xylene sulfonic acid crystals with a large particle size and a low sulfuric acid content while using a crystallizer with an extremely simple structure, but also with a shorter residence time compared to conventional methods. Since it can be made shorter, the construction cost of the crystallization device can be significantly reduced.

Example 1 A reaction product liquid consisting of 68% by weight of m-xylene-4-sulfonic acid, 23% by weight of unreacted sulfuric acid, 8% by weight of water, and 1% by weight of other substances and 48.8% by weight of dilute sulfuric acid were each added per unit time. A ratio of 190 parts by weight and 221 parts by weight was supplied to a glass crystallizer equipped with a stirrer and a full jacket, and continuous crystallization was carried out at 40° C. under atmospheric pressure.

The average residence time at this time was about 3 hours. Furthermore, the sulfuric acid concentration of the mother liquor at this time was 60% by weight (the rest was water), m-
The solubility of xylene-4-sulfonic acid was 2% by weight, and the slurry concentration was 40% by weight. By raising and lowering the temperature of the cooling water flowing through the jacket every hour, the crystallization temperature was raised from 40°C to 48°C in 3 minutes, maintained at the same temperature for 5 minutes, and then started the cooling operation. Transfer to 40℃ in about 7 minutes
The temperature was lowered to

By repeating this operation, the fine crystals in the slurry in the crystallizer disappeared, and it was possible to maintain the same transparency as in the batch operation. By centrifuging 411 parts by weight of the slurry extracted from the overflow, crude crystals and f liquid,
156 parts by weight and 255 parts by weight were obtained, respectively. Next, when rinsing with 15.6 parts by weight of water corresponding to 10% of the crude crystals, the fine crystals and the rinsing liquid were each 110 parts by weight and 61 parts by weight.
．． 6 parts by weight were obtained. The sulfuric acid content in the crude crystals and fine crystals was 3.3 and 0.6% by weight, respectively. The average grain size of the crystals is approximately 1m! It was hot. Example 2 Crystallization and separation were carried out under the same conditions as in Example 1, and only the dissolution and disappearance operation was performed in the following manner.

That is, the crystallization temperature was raised from 40°C to 50°C in 4 minutes,
The operation of maintaining the same temperature for 4 minutes and then lowering the temperature to 40° C. over 8 minutes was repeated every 2 hours. The sulfuric acid content contained in the obtained crude crystals and fine crystals was 3.7% by weight and 0.0% by weight, respectively.
It was 9% by weight.

The average grain size of the crystals was about 1 mm, which is the same as in Example 1. Comparative Example 1 A continuous crystallization/separation experiment was conducted using the conventional method under the same conditions as in Example 1.

When continuous crystallization was continued for a long time, the crystals became fine and the slurry became cloudy.

The sulfuric acid content in the obtained crude crystals and fine crystals was 5.
．． They were 4% by weight and 2.1% by weight.

Claims (1)

[Claims] 1 In a method in which m-xylene and sulfuric acid are reacted to produce m-xylene sulfonic acid, and the reaction product liquid is cooled to continuously crystallize and separate crystals of m-xylene sulfonic acid, the mother liquor at the time of crystallization is By setting the temperature to 30 to 40°C and intermittently raising the mother liquor temperature to 45 to 50°C, the fine crystals in the mother liquor are dissolved and disappeared, and then the mother liquor is heated again to 30 °C.
A method for crystallizing m-xylene sulfonic acid crystals, which comprises cooling to ~40°C and continuing the crystallization operation.