KR100447847B1 - A process of preparing for the high purity trioctane - Google Patents

Abstract

The present invention relates to a method for producing high purity trioxane, wherein trioxane is discharged to the top of the distillation column when trioxane is separated by distilling an organic solvent containing trioxane and having a boiling point higher than that of trioxane in a distillation column. It is supplied into the distillation column tower (c) in which the hydrocarbon solvent having a lower boiling point and water is stored to dissolve the low boiling point impurities contained in trioxane in water, and then the water and the hydrocarbon solvent are phase separated to remove the low boiling point impurities. It is characterized by. The present invention can produce high purity trioxane with little energy, and can produce high quality polyoxymethylene using it as a raw material.

Description

Process for preparing high purity trioxane {A process of preparing for the high purity trioctane}

The present invention relates to a method for separating high purity trioxane from a trioxane-containing reaction solution when trioxane, a raw material of polyoxymethylene, is prepared from an aqueous formaldehyde solution using a catalyst. More specifically, the present invention relates to a method for separating high-purity trioxane from a trioxane-containing high-boiling organic solvent obtained by extracting a trioxane-containing reaction solution with a high-boiling organic solvent.

Polyoxymethylene is an engineering plastic with a balance of mechanical strength and impact resistance, and is widely used as a mechanical part in automobile parts and electric and electronic devices.

To date, various studies on the synthesis method of trioxane have been made. A technique frequently used in the related art is a method of obtaining formoxane by heating formaldehyde in the presence of an acid catalyst. As the acid catalyst used here, homogeneous catalysts such as sulfuric acid, phosphoric acid, boric acid, benzenesulfonic acid, solid acid catalysts such as acidic cation exchange resins and acidic zeolites, and the like are known. Among them, sulfuric acid is most commonly used because of its rapid production rate, low cost, and easy handling in homogeneous systems.

In addition, acid cationic exchange resins disclosed in JP 40-12794 and JP 64-11025 as catalysts for the production of trioxane are generally used extensively as solid acid catalysts, and because of their low price, they are useful for the adoption of industrial processes. Attention is focused.

Since the trioxane production reaction using this catalyst is an equilibrium reaction, the produced trioxane is separated from the reaction solution and the catalyst by evaporation or distillation using an azeotropy with water.

Separation of trioxane from the reaction solution and the catalyst has been widely used industrially with a simple operation. However, the concentration of trioxane in the equilibrium reaction composition is low, and there is a limitation of the gas-liquid equilibrium between trioxane, formaldehyde, and water, and according to Japanese Patent Application Laid-Open No. 7-21596, the concentration of trioxane in the gas phase does not reach 20 wt%. At least 5 tons of steam is required to obtain 1 ton of trioxane.

In other words, the conventional method of separating trioxane from the reaction solution and the catalyst by evaporation or distillation is a simple method, but has a drawback that requires a large amount of energy, and thus, a more efficient method for producing trioxane is required. In addition, as a method of separating trioxane from the reaction solution by conventional evaporation or distillation, separation of high purity trioxane is virtually difficult, and thus there is a problem in that the quality of polyoxymethylene is deteriorated.

The present invention provides a trioxane-containing organic obtained by extracting a trioxane-containing reactant heated and reacted with a high concentration of formaldehyde aqueous solution in the presence of a solid acid catalyst to solve the problems of the prior art with an organic solvent having a higher boiling point than trioxane. When the trioxane is separated from the solvent, a method of supplying and storing a hydrocarbon solvent having a lower boiling point than trioxane at the top of the distillation column is provided. In other words, the present invention provides a method for separating high purity trioxane from trioxane-containing high boiling point organic solvents using less energy.

1 is a process schematic diagram of the present invention.

※ Explanation of Codes on Major Parts of Drawings

a: distillation column b: condenser c: hydrocarbon solvent reservoir (liquid separation tank)

d: heat exchanger M: high boiling point organic solvent containing trioxane 1 ~ 8: transfer line

In order to achieve the above object, the present invention is to separate the trioxane by distilling an organic solvent containing trioxane and having a boiling point higher than the trioxane in the distillation column, the trioxane discharged to the top of the distillation column lower boiling point than trioxane It is supplied into the column tower (c) in which the hydrocarbon solvent and water are stored to dissolve the low-boiling impurities contained in trioxane in water and to remove the low-boiling impurities by phase separation of water and hydrocarbon solvent do.

Hereinafter, the present invention will be described in detail with reference to the process schematic diagram of FIG. 1.

In the distillation column (a) of the present invention, a condenser (b), a tank (c), and a heat exchanger (d) are respectively provided. The condenser (b) serves to condense the trioxane-containing vapor discharged to the top of the distillation column into a liquid phase. The tank (c) is stored with a hydrocarbon solvent having a lower boiling point than trioxane and serves as a liquid liquid separation tank.

First, in the present invention, the organic solvent (M) containing trioxane and having a higher boiling point than trioxane through the transfer line (1) is supplied to the distillation column (a) for distillation.

The trioxane-containing high-boiling organic solvent (M) is then extracted with an organic solvent having a higher boiling point than trioxane in an extractor by continuing the trioxane-containing reactant prepared by heating a high concentration of formaldehyde aqueous solution in a reactor under a solid acid catalyst. Obtained by treatment.

The reason why the organic solvent is used as the extractant is that the distribution ratio of trioxane to the aqueous formaldehyde solution is easy, as described in Special Publication No. 42-12671. Dichlorobenzene, xylene, diethylbenzene, etc. are used as an organic solvent with a higher boiling point than trioxane.

When the distillation process is performed in the distillation column (a), the vapor of the trioxane and the low boiling point component is discharged to the upper portion of the distillation tower (top), and the organic solvent has a higher boiling point than the trioxane. Exit Trioxane is also recovered via the transfer line 3. Low-boiling components mixed with the vapor discharged to the column top include methanol, formic acid, methyl formate, methylal, formaldehyde, water and the like.

The steam exiting the top of the distillation column is processed in the condenser (b) to turn into a liquid phase. The temperature of the liquid coming out of the condenser (b) needs to be maintained at 63 ° C or higher, which is the melting point of trioxane, but the condenser discharge temperature should not be higher than 114.5 ° C, which is the boiling point of trioxane.

Therefore, it is preferable to set the conditions to condense all vapor components, in which case the low boiling point components partially condense to become impurities of trioxane. Methanol, formic acid, etc., which are low boiling point components in the vapor component, promote the chain transfer during polymerization and increase the unstable end groups of the polymer, thereby degrading the quality of the obtained resin.

Water is dissolved in the trioxane-containing organic solvent supplied to the distillation tower (a), and these are included in the vapor discharged to the top of the distillation tower (a) during the distillation process, condensed in the condenser and then transferred to the tank (c).

As a method for removing the low boiling point component in the steam component, it is conceivable to change the condensation temperature by operating the distillation column by vacuum or pressurization, but the trioxane loss is reduced because the trioxane is not condensed in the condenser under vacuum. It becomes large, and under pressure, the column top temperature rises, and there exists a possibility of the quality deterioration of an organic solvent.

As a countermeasure to avoid mixing the low boiling point component with trioxane, the inventors take trioxane out of the system through the transfer line 3 at the top of the distillation column and together with the distillation column top, that is, in the tank c, The present inventors have found a method for producing trioxane with high quality by removing impurities by condensing the vapor of the column with a low boiling hydrocarbon solvent.

A hydrocarbon solvent having a lower boiling point than trioxane in the tank c may be supplied through a transfer line 6 to separate and remove water and low boiling components introduced into the tank.

Specifically, the water and the hydrocarbon solvent in the tank is phase separated by the difference in specific gravity, and the phase separated water is taken out of the tank through the transfer line (5). At this time, the low boiling point component dissolved in water is also taken out. The supply and storage of a hydrocarbon solvent having a lower boiling point than trioxane in the tank (c) is because polyoxymethylene polymerization is not affected even when a small amount of the solvent is mixed in trioxane.

Paraffin, cycloparaffin, aromatic compounds, etc. can be used as a hydrocarbon solvent lower boiling point than trioxane. Specifically, benzene, cyclohexane, normal heptane and the like, more preferably benzene can be used.

Depending on the impurity composition of the organic solvent supplied to the distillation column (a), the water contained in the steam discharged to the upper part of the distillation column (a) in the distillation process is solidified in the condenser (b) to interfere with the continuous operation of the distillation column (a). Since there is a possibility, it is preferable to continuously supply water through the transfer lines 7 and 8.

By continuously supplying water in this way, the solidification trouble can be solved and the removal of low boiling point components (impurities) can be promoted to improve the purity of trioxane.

However, if the amount of water supplied is increased too much, the loss of trioxane dissolved in water and discharged out of the system increases, and the energy requirement of the distillation column (a) increases (when supplied to the transfer line 7). Therefore, the amount of water supplied is preferably adjusted to 50% or less of the amount of trioxane.

The liquid trioxane-containing organic solvent in which the low boiling point component and water are separated and removed in the tank (c) is circulated back to the distillation column (a) and distilled. The organic solvent is discharged through the transfer line 4 to the lower end of the tank (c).

The trioxane separated from the distillation column is extracted out of the system through the transfer line (3). At this time, as disclosed in Japanese Patent Application Laid-Open No. 7-116176, trioxane containing dioxymethylene dimethyl ether (oxymethylene unit number 2) is taken out to the top of the distillation column (a), and dioxymethylene dimethyl ether (oxymethylene unit 3 The trioxane containing the high boiling point such as above can be further improved in quality by removing the trioxane at the bottom of the distillation column (a).

Trioxane, which is extracted out of the system, is usually of high purity, but in order to further increase the purity, it may be eluted with a little hydrocarbon solvent and then distilled again. When the hydrocarbon solvent contained in the trioxane to be out of the system increases, the energy requirement in the distillation column (a) is increased, so it is preferable to adjust these amounts to 50% by weight or less relative to the trioxane weight.

As such, the hydrocarbon solvent in the system may be insufficient as the hydrocarbon solvent leaves the system such as trioxane. The present invention thus supplies hydrocarbon solvents in situ via transfer lines 7 and 8.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited only to the following examples.

Example 1

Trioxane was prepared using a distillation column a (multistage column: top diameter: 50 mm, 50 stages, sheave tray) arranged in the same process flow as in FIG. 1. 170g per hour was supplied to a reactor [formula styrene strong acid cation exchange resin (Diion or IB) 300M ³ filled with Mitsubishi Chemical Co., Ltd.] maintained at 95 ° C. in which formalin (55% formaldehyde concentration) was sufficiently brought into contact with the same amount of diethylbenzene at room temperature. did. The liquid composition after reaction was 56.9 weight% of formaldehyde and 3.2 weight% of trioxane. Trioxane of this reaction solution was extracted with diethylbenzene to prepare diethylbenzene containing 4.0% by weight of trioxane. Diethylbenzene was fed through line 1 to the distillation column a at a feed rate of 3000 g / hour and benzene through a line 7 at a feed rate of 10 g / hour. Trioxane was withdrawn from line 3 and diethylbenzene was withdrawn from line 2. Water was withdrawn from tank (c) through line 5 at 6 g / hr. Benzene was withdrawn from line 4 to keep the liquid level of benzene on tank (c) constant. The impurity analysis value of the obtained trioxane was high quality of 40 weight ppm of formaldehyde, 3 weight ppm of methanol, 11 weight ppm of water, 5 weight ppm of formic acid, and 10 weight ppm of benzene.

Example 2

The distillation column at 3000 g / h for diethylbenzene containing 4.0% by weight of trioxane via line 1 of the apparatus of Example 1 at 10 g / h for cyclohexane via line 7 and 5 g / h of water through line 8 via line 8 supplied in (a). Trioxane was extracted from line 3 and diethylbenzene was extracted from line 2. Water was withdrawn via line 5 to maintain a constant two phase interface of cyclohexane and water in tank (c). The impurity value of the obtained trioxane was high quality of 20 weight ppm of formaldehyde, 2 weight ppm of methanol, 7 weight ppm of water, 3 weight ppm of formic acid, and 7 weight ppm of cyclohexane.

Comparative Example 1

In the apparatus of Example 1, diethylbenzene containing 4.0% by weight of trioxane was fed to distillation tower (a) at a rate of 3000 g per hour via line 1. Trioxane is extracted from line 3 and diethylbenzene is extracted from line 2. The tank (c) was subjected to phase separation. The impurity value of trioxane obtained from line 3 was 100 ppm by weight of formaldehyde, 20 ppm by weight of methanol, 40 ppm by weight of water, and 11 ppm by weight of formic acid, and the impurity content was higher than that of Examples 1 and 2.

The present invention can produce high purity trioxane with little energy use. The trioxane produced in the present invention has high purity and when used as a raw material, the quality of the final product polyoxymethylene is improved.

Claims (3)

In separating trioxane by distilling an organic solvent containing trioxane and having a boiling point higher than that of trioxane in a distillation column, the hydrocarbon solvent and water having a lower boiling point than trioxane are stored in the trioxane discharged to the top of the distillation column. A method for producing high purity trioxane, characterized in that the low boiling point impurities contained in trioxane are dissolved in water after being fed into the column top of the distillation column to remove water and the hydrocarbon solvent by phase separation. delete The process for producing high purity trioxane according to claim 1, wherein the hydrocarbon solvent is benzene.