JPH07116176B2 - Purification method of trioxane - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for producing a purified trioxane that can be used for producing polyoxymethylene.

(Prior art and problems) Trioxane is a cyclic trimer of formaldehyde,
Mainly used as a raw material for polyoxymethylene.
Sometimes trioxane can be polymerized alone,
In many cases, it is copolymerized with alkylene oxide compounds, currently formal compounds, and vinyl compounds.

In order to obtain polyoxymethylene having a sufficiently high molecular weight, it is necessary that the trioxane to be polymerized is extremely pure, that is, the concentration of so-called chain transfer agent contained in the trioxane be low.

Conventionally, as a method for purifying trioxane, a distillation method, an azeotropic distillation method and the like are well known. However, it is not always easy to obtain pure trioxane by a distillation method or the like, and a large amount of energy such as steam power is required to obtain high-purity trioxane. On the other hand
-26668 uses activated alumina,
In 4, using a molecular sieve (molecular sieve),
A method for purifying trioxane in the molten state is described. As is well known, trioxane is caused to polymerize by an acidic substance, and this tendency is remarkable especially in a molten state.
When trioxane is purified in a molten state using activated alumina and molecular sieve, partial polymerization of trioxane cannot be avoided, and the polymer is deposited on these adsorbents, so that the life of the adsorbent is significantly increased. It has the drawback of being very short.

Also, a method of removing polyoxymethylene dimethoxide by distillation has been proposed (JP-A-57-200382).

However, it is unavoidable that the reflux ratio is 20 or more and a large amount of energy is required.

(Means for Solving Problems) Therefore, as a result of detailed examination of the method for purifying trioxane, the present inventors have found a method capable of continuously and easily obtaining extremely high-purity trioxane, and completed the present invention. It came to do.

That is, the present invention uses water, formaldehyde, formic acid, methanol, methyl formate, polyoxymethylene dimethoxide (n
2, where n: oxymethylene unit number) and other trioxane-containing organic solvent containing impurities are supplied to the upper part of the distillation column 6, and the organic solvent, water, formaldehyde, methanol,
Low boiling components such as methyl formate from the top of the column, trioxane containing dioxymethylene dimethoxide and organic solvent from the middle column, and polyoxymethylene dimethoxide (n
A method of extracting high boiling components such as 3) from the bottom of the column to obtain purified trioxane from the bottom of the column is provided.

An example of the present invention will be described with reference to the drawings. A trioxane-containing organic solvent containing impurities such as water, formaldehyde, formic acid, methanol, methyl formate, and polyoxymethylene dimethoxide (n2) is supplied from the line 1 to the upper portion of the distillation column 6. To do.

From the line 2, low boiling components such as organic solvent, water, formaldehyde, methanol and methyl formate are taken out of the system. Trioxane containing dioxymethylene dimethoxide and an organic solvent are extracted from line 4, trioxane containing high-boiling components such as polyoxymethylene dimethoxide (n3) is extracted from line 5, and purified trioxane is extracted from line 3. Take it out.

Further, in order to carry out the present invention with higher efficiency and higher yield, the following systems can be carried out individually or in combination.

(I) The polyoxymethylene dimethoxide (n2) -containing trioxane extracted from lines 4 and 5 and an organic solvent are contacted with a solid acidic catalyst to decompose polyoxymethylene dimethoxide (n2), and then line 1 How to return to the distillation tower more.

(Ii) A method in which the liquids extracted from the lines 4 and 5 are combined, mixed with water, brought into contact with a solid acidic catalyst, separated into two layers, and then the organic solvent layer is returned from the line 1 to the distillation column.

(Iii) After mixing water with the organic solvent containing low boiling impurities extracted from the line 2, contact with a solid acidic catalyst,
After decomposing methyl formate, methylal, etc., after separating two layers, the organic solvent layer is recycled to the top of the column.

The organic solvent referred to in the present invention is a solvent that can be used to extract trioxane from an aqueous solution containing trioxane in the conventional trioxane synthesis technique, and is composed of water and 2
At the same time when the layers are separated, it is a solvent with a low elution amount into the aqueous layer,
In addition, it is a solvent having a lower boiling point than trioxane for substantially dissolving trioxane and distillative separation.

Examples of the solvent having such performance include methylene chloride, chloroform, carbon tetrachloride, ethyl chloride, ethylene chloride, ethylidene chloride, trichloroethylene, cyclohexane, benzene and the like.

In the present invention, polyoxymethylene dimethoxide (n
2), or as a catalyst used for decomposing methyl formate or methylal, a solid acidic catalyst is preferable, for example, an inorganic oxide complex such as acidic clay, zeolite or silica magnesia, and sulfuric acid of a metal such as nickel, iron or cadmium. Salts, inorganic solid acid catalysts such as those impregnated with silica gel, diatomaceous earth, silicon carbide, sulfonic acid groups,
Examples thereof include organic solid acid catalysts such as ion exchange resins having a fluoroalkanesulfonic acid group.

Among these, sulfonic acid type cation exchange resin and zeolite are particularly preferable.

Regarding the amount of catalyst and the decomposition temperature, it is preferable that polyoxymethylene dimethoxide (n2), methyl formate or methylal is selectively decomposed and the decomposition rate of trioxane is small, and the LHSV (Liguid Hourly Space Velocity) value is 0.
2 ~ 200Hr ^-1 , decomposition temperature range of 30 ℃ ~ 100 ℃ is preferable,
Particularly, LHSV value of 1.0 to 60 Hr ^-1 and decomposition temperature of 50 to 90 ° C are preferable.

The purified trioxane obtained by the present invention can be directly used for polymerization.

As described above in detail, it is possible to continuously obtain high-purity trioxane by the method of the present invention, and the energy consumption of steam, electric power, etc. is greatly reduced as compared with the conventional method. At the same time, the equipment can be greatly simplified.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

Example 1 65.7 wt% benzene, 30 wt% trioxane, 1.5 wt% formaldehyde, 0.4 wt% water, 1.5 wt% methanol, 0.3 wt% methyl formate, 0.1 wt% formic acid, 0.2 wt% methylal, 0.2 wt% dioxymethylene dimethoxide. %, Trioxymethylene dimethoxide 0.1 wt% solution is fed at 300 g / Hr to the 5th stage from the top of the 50th stage Older's Day distillation apparatus (line 1).

The 20th plate from the top of the tower was controlled at 95 ° C, and distilled at RR = 2.5. The solution was extracted from the 15th stage at 25 g / H (line 4).

Trioxane was extracted at 66 g / Hr from the 45th plate from the top of the column (line 3).

The bottom of the column controlled the liquid depth and the increased amount was extracted (line 5).

As a result, a solution containing 74 wt% of trioxane, 24 wt% of benzene and 2.4 wt% of dioxymethylene dimethoxide was obtained from the line 4, and most of dioxymethylene dimethoxide was removed from the line 4.

The composition of the purified trioxane obtained from line 3 is shown in Table-1.
Shown in.

Example 2 The raw material liquid used in Example 1 was fed in the same manner as in Example 1 at 300 g / Hr in the fifth stage from the top of the Older's Dough distillation apparatus,
Distilled at RR = 2.5.

Control the 25th stage from the top of the tower to 100 ° C,
The solution was extracted with 5 g / Hr and ferriolite zeolite 15 m
The amount of catalyst was controlled to 75 ° C by filling l (inner diameter 12 mm
φ) Supplied on top. The liquid flowing out from the lower part of the catalyst layer was guided to the raw material liquid supply line and returned to the distillation column together with the raw material liquid.

Trioxane was withdrawn from the bottom of the column at 5 g / Hr, and combined with the liquid extracted from the 25th stage, and led to the catalyst layer.

Purified trioxane was extracted from the 45th stage from the top of the column while controlling the liquid depth at the bottom of the column. At this time, the extraction amount is
It was 88 g / Hr. The composition of purified trioxane is shown in Table 1.

Example 3 Trioxane 38.5 wt%, formaldehyde 1.2 wt%, water
0.6wt%, methanol 1.5wt%, methyl formate 0.5wt%, formic acid 0.2wt%, methylal 0.2wt%, dioxymethylene dimethoxide 0.3wt%, trioxymethylene dimethoxide 0.2
A benzene solution containing wt% was added in the same manner as in Example 1 at 300 g / Hr at the 5th stage from the top of the 50th stage Older'syou distillation apparatus.
And then distilled.

The distillate from the top of the column was mixed with 15 g / Hr of water and then at 70 ° C.
40 ml of cation-exchange resin (Levatit SP 112 Mitsui Toatsu Huaine (KK) layer was temperature-controlled). The liquid leaving the cation-exchange resin layer was separated into two layers, and the benzene layer and RR became 2. I returned to the top of the tower.

Control the 25th stage from the top of the tower to 100 ° C, and start from the 25th stage to 3
The solution was drawn out at 0 g / Hr.

Trioxane was extracted from the bottom of the column at 5 g / Hr. The liquids extracted from the 25th plate and the bottom of the column were combined, then mixed with 5 g / Hr of water and introduced into 2 ml of a cation exchange resin layer (Levatit SP 112) whose temperature was controlled at 80 ° C.

The liquid discharged from the cation exchange resin layer was led to a raw material feed line, and after separating it into two layers, the benzene layer was fed to the fifth stage of the distillation column.

Purified trioxane was extracted from the top of the tower from the 45th plate while controlling the liquid depth at the bottom of the tower.

The amount of purified trioxane withdrawn at this time was 113 g / Hr. The composition of the purified trioxane is shown in Table 1.

[Brief description of drawings]

FIG. 1 shows a schematic view of a distillation apparatus used in the present invention, a supply line 1, and a withdrawal line 2, 3, 4, 5.

Claims (2)

[Claims] 1. Water, formaldehyde, formic acid, methanol, methyl formate, polyoxymethylene dimethoxide (n
≥2, where n: the number of oxymethylene units) and other trioxane-containing organic solvent containing impurities are supplied to the upper part of the distillation column, and low boiling components such as organic solvent, water, formaldehyde, methanol and methyl formate are supplied from the top of the column. , Trioxane containing dioxymethylene dimethoxide, an organic solvent and the like from the middle stage of the tower, and polyoxymethylene dimethoxide (n ≧
A method for purifying trioxane, which comprises extracting high boiling components such as 3) from the bottom of the column and obtaining purified trioxane from the bottom of the column. 2. Water, formaldehyde, formic acid, methanol, methyl formate, polyoxymethylene dimethoxide (n
≧ 2, where n: the number of oxymethylene units) and other trioxane-containing organic solvent containing impurities are supplied to the upper part of the distillation column, and low boiling components such as organic solvent, water, formaldehyde, methanol and methyl formate are supplied from the top of the column. , Trioxane containing dioxymethylene dimethoxide, an organic solvent and the like from the middle stage of the column, and polyoxymethylene dimethoxide (n ≧
3) and other high boiling components are extracted from the bottom of the column, the liquid extracted from the middle and bottom of the column is contacted with the solid acidic catalyst, and then supplied to the upper part of the column to obtain purified trioxane from the lower part of the column. A characteristic method for purifying trioxane.