JPS6041974B2 - How to obtain particles dispersed in a medium by melt drying method - Google Patents

Description

Detailed Description of the Invention 2|4-Dinitrotoluene, p-chloronitocbenzene, etc. are produced using water as a medium, and their melting points are 70~
It is a water-insoluble compound at about 80°C.

During the production of such compounds, they are dispersed in water after the reaction. It is necessary to filter the particles of the above-mentioned compound, remove moisture contained in the particles, and dry them. However, since the above compounds have melting points that are very close to the boiling point of the medium, if the drying temperature is increased in an attempt to efficiently remove water, the particles will fuse together. The drawback is that only products with a lot of blocking can be obtained, and drying at low temperatures is unavoidable. Drying at such low temperatures requires extremely large drying equipment, which has low equipment efficiency, requires special drying methods such as vacuum drying, and requires complicated process control, making it difficult to perform on an industrial scale. There are many problems in implementation. However, in order to solve this problem and find a method for industrially advantageous obtaining of the above-mentioned compounds, the present inventors have conducted extensive research and found that a method for obtaining the above-mentioned compounds from a dispersion of particles that are substantially incompatible with the medium has been developed. When obtaining the particles, (1) heating the dispersion liquid or a wet cake of the particles filtered from the dispersion liquid at a temperature below the boiling point of the medium and above the melting point of the particles; (2) a medium layer; (3) forming two layers of fused layers of particles;
A process of cooling the system while maintaining two layers to solidify the molten layer into a lump, then separating the solid from the medium and pulverizing it into granules, or separating the molten layer and the medium layer and When combining the cooling and granulating steps, the resulting particles are substantially free of the need for removal of the medium and the drying step can be omitted, or if drying is required, it is only a light drying process. The present invention was completed based on the discovery that the desired compound particles can be obtained with great industrial advantage compared to conventional methods.

Hereinafter, each step of the present invention will be sequentially explained.

(1) A dispersion in which water-insoluble particles are dispersed or a wet cake of the particles filtered from the dispersion is heated in a temperature range below the boiling point of the medium and above the melting point of the particles. By such an operation, the particles are completely melted and present in the medium in the form of an oil. When heating a wet cake that has been separated from the dispersion liquid, it is better to use a cake that still contains as much of the medium as possible to avoid the need for extra sorting operations, as described in (2) below. This process is advantageous in that the layer separation between the medium and the melted particles is effective. If the moisture content is expressed as a specific numerical value, it is preferably 50 to 7% by weight. If there is a risk that the moisture content of the wet cake will be too low after just one p-separation operation, you can heat the dispersion as it is without performing the p-separation process, but in some cases, the wet cake that has been separated may be heated again. A method is adopted in which the material is dispersed in a small amount of medium and then heated. Heating is usually done with stirring. The feature of the present application is that instead of separating the particles from the medium and drying them, the particles are once molten and then separated from the medium. The concept of the melt-drying method was completely unknown until now.

(2) Next, two layers are formed: a medium layer and a molten layer of particles.

Such an operation can be carried out by simply stopping the stirring in step (1) and leaving the system still, allowing the system to be naturally separated into a molten layer and a medium layer. The upper and lower layers are determined depending on the difference in specific gravity, but usually the molten layer is the lower layer and the medium layer is the upper layer. During this operation, it is of course necessary to heat the system in the same manner as in operation (1). (3) Finally, one of the following two procedures is performed to obtain the desired particles.

(Part 1) A step in which the system is cooled while maintaining the two layers to solidify the molten layer into a lump, and then the solid is separated from the medium and pulverized into particles.

The cooling temperature at this time is below the melting point of the target compound. It goes without saying that you should.

After agglomeration, the medium is removed and the agglomerates are pulverized in a conventional manner to easily obtain granules. (Part 2)
The process of separating the molten layer and the medium layer, and cooling and granulating the molten layer.

Because it separates from the medium while maintaining its molten state,
With the system heated above its melting point, conventional liquid-liquid separation means are employed.

Furthermore, prior to step (3), if there are impurities present in the medium, such as acids or alkalis used in the production of the target compound, neutralization as necessary will improve the purity of the particles obtained. It is desirable to implement this method as it will result in excellent results.

In other words, it is impossible to completely neutralize the acids and alkalis contained inside the particles by normal neutralization methods, but once the particles are in a molten state, the acids and alkalis contained inside the particles can be neutralized by the medium. It is thought that a highly pure product can be obtained because such impurities are no longer incorporated into the target compound. As mentioned above, the particles obtained through steps (1), (2), and (3) contain almost no medium, so there is no need for drying, but if necessary, light drying such as air drying can be used. This is sufficient, and smooth particles can be easily obtained by such an operation.

The method of the present invention is mainly produced using an aqueous medium and is advantageously employed for water-insoluble compounds having a melting point relatively close to the boiling point of water, but is not necessarily limited to this. Any compound having a melting point below the boiling point of , and is insoluble in the medium can be widely used, and it must be said that its industrial utility value is extremely large.

Next, the method of the present invention will be explained in more detail by giving examples.

Example 1 50 y of P-nitrotoluene was added to a mixed acid consisting of 20 y of nitric acid and 200 y of concentrated sulfuric acid at a temperature of 40 to 50°C.

The temperature was gradually increased to 70°C and maintained at this temperature for 30 minutes. After cooling, 40 mL of water was added little by little to precipitate 2,4-dinitrotoluene particles. The particles were filtered to obtain a wet cake with a water content of 5% by weight. When this wet cake was dispersed in about double the amount of water and the temperature was gradually raised and maintained at about 80°C, a molten layer was formed in the lower layer and an aqueous layer was formed in the upper layer. When these two layers were allowed to cool as they were, the lower layer became lumpy. The water in the upper layer was completely removed by decantation, and the solid 2,4-dinitrotoluene was taken out and pulverized. Particles with a water content of just 1.5% by weight were obtained,
Smooth particles could be easily produced by air drying. Example 2 An experiment was conducted on P-chloronitrobenzene (melting point: 83.5°C) according to the method of Example 1, and similarly smooth particles were obtained.

Example 3 An experiment was conducted on 3,4-dinitro-0-xylene (melting point: 87C) according to the method of Example 1.

Claims (1)

[Claims] 1. When obtaining particles from a dispersion of particles that are substantially incompatible with a medium, (1) the dispersion or a wet cake of the particles filtered from the dispersion is heated below the boiling point of the medium to remove the particles. The process of heating at a temperature above the melting point, (
2) Forming two layers: a medium layer and a molten layer of particles, (
3) A step of cooling the system while maintaining the two layers to solidify the molten layer into a lump, then separating the solid from the medium and pulverizing it into particles, or separating the molten layer and the medium layer, A method for obtaining particles dispersed in a medium by a melt-drying method characterized by the combination of steps of cooling and granulating a molten layer.