JPH06220042A - Method for synthesizing trioxane - Google Patents

Abstract

PURPOSE:To obtain a method for efficiently producing trioxane which is a monomer of a polyacetal resin. CONSTITUTION:This method for synthesizing trioxane comprises carrying out reaction in the presence of an alkylene glycol expressed by the formula HO-R- OH (R is >=5C alkylene group) in thermally distilling an aqueous solution containing formaldehyde in the presence of an acidic catalyst and obtaining the trioxane.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently producing trioxane which is useful as a monomer of a polyacetal resin.

[0002]

It is well known to obtain a trioxane-rich component in the gas phase by heating an aqueous formaldehyde solution in the presence of an acidic catalyst and distilling it. However, the problem in this case was that the concentration of trioxane in the liquid phase was low, so the concentration of trioxane in the vapor phase was also low, and a large amount of energy was required to obtain trioxane. Further, when the formaldehyde concentration in the liquid phase is increased to increase the trioxane concentration in the liquid phase, paraformaldehyde is precipitated on the wall of the reaction tank, which makes continuous operation difficult for a long time.

On the other hand, a method for synthesizing trioxane at the same time as cyclic formal has been proposed. For example, JP-A-5
In JP-A 5-55180, a mixture of formaldehyde and diols such as ethylene glycol, 1,2-propanediol, and 1,4-butanediol is heated under an acidic catalyst to simultaneously produce trioxane and cyclic formal. Is proposed.

US Pat. No. 4,110,298 proposes that formaldehyde is heated in the presence of monobutyl ether of polypropylene glycol under an acidic catalyst to obtain trioxane.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems such as the low removal of trioxane and the precipitation of paraformaldehyde in the reactor.

[0006]

The present invention provides a general formula HO
An alkylene glycol represented by —R—OH (R is an alkylene group having 5 or more carbon atoms) is added during the synthesis of trioxane. That is, according to the present invention, an aqueous solution containing formaldehyde is heated and distilled in the presence of an acidic catalyst to obtain trioxane.
A method for synthesizing trioxane characterized in that the reaction is carried out in the presence of an alkylene glycol represented by OR-OH (where R represents an alkylene group having 5 or more carbon atoms).

In the present invention, the synthesis of trioxane is
For example, a formaldehyde aqueous solution having a concentration of 30 to 70% by weight, an acidic catalyst and an alkylene glycol were heated in the reactor, and the formaldehyde aqueous solution was continuously supplied so that the liquid level of the reactor was constant, and the formaldehyde was directly connected to the reactor. It is carried out by a method in which the evaporate is continuously extracted from the distillation column.

In the distillation step, azeotropic distillation can be carried out by bringing an organic solvent capable of azeotroping with trioxane into vapor-liquid contact. The organic solvent used is insoluble or hardly soluble in water and has a boiling point of 60 to 13 at normal pressure.
The temperature is preferably 0 ° C., preferably 60 to 110 ° C., for example, the composition ratio of trioxane in the azeotropic mixture is large.
-Hexane, iso-hexane, n-heptane, iso
-Saturated aliphatic hydrocarbons such as octane; cyclohexane,
Examples thereof include saturated alicyclic hydrocarbons such as methylcyclohexane.

Preferred alkylene glycols used in the present invention have 5 to 20 carbon atoms, and more preferred are 1,5-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol,
2-ethyl-1,3-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-
Dodecanediol, 1,14-tetradecanediol,
1,16-hexadecanediol etc. are mentioned. Particularly preferably, 1,6-hexanediol, 1,8-octanediol and 1,10-decanediol are used.

The cyclic formal derived from these alkylene glycol forms an azeotrope with water and tends to be removed from the reaction system, but the removal ratio becomes very small as the carbon number increases. Further, when an organic solvent that forms an azeotropic mixture with trioxane is used in the distillation step, volatilization is suppressed and it can be used stably for a long period of time.

In the present invention, the alkylene glycol is 1 to 100% by weight, preferably 5 to 50% by weight, more preferably 10% by weight based on the aqueous formaldehyde solution.
~ 30 wt% is used. Although a small amount of the cyclic formal is distilled out of the system, it is preferable to add the insufficient amount.

When trioxane is synthesized using these alkylene glycols, paraformaldehyde does not precipitate in the reactor and glycols are not scattered from the reaction system, so that a high concentration of formaldehyde is stable in the reaction system. It is possible to obtain a high concentration of trioxane in the vapor phase. As the catalyst used for the trioxane generation reaction, known catalysts such as sulfuric acid, phosphoric acid, benzenesulfonic acid, paratoluenesulfonic acid, and cation exchange resin are used. The amount of the catalyst used may be an amount that does not decrease the production amount of trioxane and does not increase the production of side reactions, and is 0.1% based on the total amount charged.
It is desirable to use ~ 15% by weight.

[0013]

The present invention will be described in more detail with reference to the following examples.

[0014]

Example 1 A reactor having a capacity of 1 liter was heated in an oil bath. A reactor was charged with 500 g of an aqueous solution having a formaldehyde concentration of 60% by weight and a sulfuric acid (catalyst) concentration of 5% by weight and 60 g of 1,8-octanediol. A 70% by weight formaldehyde aqueous solution (containing 2% methanol) was added at an hourly rate of 1 per hour so that the water level on the reactor surface would be constant.
The evaporate was continuously withdrawn while continuously supplying 00 g. The operation was continued for 20 hours, but no precipitation of paraformaldehyde was observed. The composition of the evaporated material after 20 hours is shown in Table 1.

[0015]

Example 2 The same operation as in Example 1 was carried out except that 1,10-decanediol was used instead of 1,8-octanediol in Example 1. Again, no precipitation of paraformaldehyde was observed. The composition of the evaporated material after 20 hours is shown in Table 1.

[0016]

Example 3 The same operation as in Example 1 was carried out except that 1,12-dodecanediol was used in place of 1,8-octanediol in Example 1. No precipitation of paraformaldehyde on the walls of the reactor was observed. The composition of the evaporated material after 20 hours is shown in Table 1.

[0017]

Comparative Example 1 The same operation as in Example 1 was carried out except that 1,8-octanediol was not added. The reaction tank was clouded 5 hours after the start of the operation, and paraformaldehyde was deposited, which made continuous operation difficult. The composition of the evaporate after 5 hours is shown in Table 1.

[0018]

Comparative Example 2 The same operation as in Example 1 was performed except that ethylene glycol was used in place of 1,8-octanediol in Example 1. In order to maintain a constant water level on the liquid surface of the reactor, 100 g of 70% formalin /
The temperature of the oil bath was adjusted while supplying the oil. After 5 hours, the reactor became cloudy and precipitation of paraformaldehyde was observed, making continuous operation difficult.

[0019]

Example 4 Trioxane was synthesized using the apparatus shown in FIG. The manufacturing equipment for trioxane has a capacity of 1
A liter reactor was used, which was directly connected to the reactor and was filled with McMahon and had a diameter of 35 mm and a height of 2.2 m.

In the reactor 2, the formaldehyde concentration is 6
Aqueous solution 500 with 0 wt% and sulfuric acid (catalyst) concentration of 5 wt%
g and 120 g of hexanediol were charged and the reactor was heated. The top temperature of the distillation column 3 is about 76 at atmospheric pressure.
When the temperature reached ℃, formaldehyde aqueous solution (2%
Of methanol) was continuously fed to the reactor 2 through the conduit 1 at a flow rate of 100 g / hour, while n-heptane was circulated through the conduit 7 to the top of the distillation column 3. Then, the distillation tower 3
N-heptane, trioxane, water distilled from the top of
A mixture vapor containing methanol, methyl formate, methylal, formaldehyde and a small amount of benzene was cooled and condensed in the condenser 5, and then refluxed to the distillation column. The liquid was extracted from above the distillation column 3 and separated into phases by a separator 6, and crude trioxane was continuously supplied to a mixer 10 through an upper conduit 9. On the other hand, the flow rate of benzene from the conduit 12 to the mixer 10 is 1
It was continuously fed at 90 g / hour for extraction. Mixer 10
The temperature was maintained at 60 ° C. Benzene containing trioxane was continuously withdrawn from the conduit 13 of the separator 11 and supplied to the middle portion of the rectification column 14. The rectification column 14 is operated under atmospheric pressure, the overhead distillate is cooled and condensed in the condenser 16 at a temperature of 60 ° C., and then phase-separated in the separator 17, and the aqueous phase is separated from the system through the conduit 19. Discharged to. On the other hand, a part of the benzene phase was supplied to the mixer 10 through the conduit 12 at a flow rate of 190 g / hour, and the rest was refluxed to the top of the rectification column 14 through the conduit 18. From the bottom of the rectification tower 14, the conduit 2
The purified trioxane was taken out through 0.

The aqueous phase of the separator 11 was refluxed to the distillation column 3 through the conduit 21. In the distillation column 3, the conduit 22 is introduced from the middle stage.
The liquid was extracted by using the above, and a part of the aqueous phase was extracted from the conduit 24 in the two-phase separation tank 23 by 34 g per hour. The remaining liquid phase was returned to the distillation column again. Furthermore, at the top of the distillation column, a mixture containing light boiling components such as methanol, methylal, methyl formate and benzene and substances such as water, trioxane, formaldehyde, and heptane, which have passed through the condenser 5, is supplied from the conduit 25 at a rate of 5 hours per hour.
g out of the system.

The heptane and benzene which had been reduced by the extraction from the system were replenished from the outside as needed. The obtained results are shown in Table 2.

[0023]

Example 5 The same operation as in Example 4 was carried out except that 1,8-octanediol was used instead of hexanediol in Example 4. The obtained results are also shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

【The invention's effect】

(A) Glycols are less scattered from the reaction system, and formaldehyde in the reaction system is stably maintained at a high concentration. (B) As a result, the trioxane in the vapor composition is kept at a high concentration. (C) Trioxane contains almost no other cyclic formals, and high-purity trioxane can be taken out.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention.

[Explanation of symbols]

 2 ... Reactor 3 ... Distillation tower 5 ... Condenser 6, 11 ... Separator 10 ... Mixer 14 ... Fractionation tower

Claims (1)

[Claims] 1. An aqueous solution containing formaldehyde is heated and distilled in the presence of an acidic catalyst to obtain trioxane, which is represented by the general formula HO—R—OH (wherein R represents an alkylene group having 5 or more carbon atoms). A method for synthesizing trioxane, which comprises reacting in the presence of alkylene glycol.