JPH06228126A - Synthesis of trioxane - Google Patents

Abstract

PURPOSE:To synthesize trioxane by a process capable of removing benzene and recovering active component and having low energy consumption including the energy for recovery process. CONSTITUTION:Trioxane is produced as a volatile component by the cyclization reaction of formaldehyde. The trioxane synthesis is carried out by (a) extracting benzene phase or benzene phase and water phase as a refluxing liquid from the top of a distillation column, (b) extracting a benzene phase containing dissolved trioxane from the intermediate stage of the distillation column and distilling the benzene solution containing trioxane to obtain purified trioxane and (c) separating a water phase from the column top distillate by phase- separation, bringing methylal and methyl formate dissolving in the water phase into contact with a solid acid to effect the decomposition of the solutes into methanol, formaldehyde and formic acid and extracting benzene from the top of the distillation column and an aqueous solution essentially free from benzene from the column bottom.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for synthesizing trioxane which is useful as a monomer of a polyacetal resin. More specifically, it relates to an improved process for efficiently obtaining trioxane from formalin.

[0002]

2. Description of the Related Art Several methods for obtaining trioxane from formalin have been proposed. For example, Japanese Patent Publication Sho 49-28
In 197 and Japanese Patent Publication No. 49-28518,
It is proposed that formalin is heated in the presence of an acidic catalyst and trioxane vapor obtained by distillation is brought into contact with benzene to obtain a benzene solution containing trioxane, and then trioxane is purified from the benzene solution. Further, at the top of the distillation column, a system has been proposed in which the obtained condensate is separated into two phases, and a benzene phase and an aqueous phase are separated.

Similarly, in Japanese Unexamined Patent Publication No. 57-200383, formalin is supplied to a reaction vessel containing an acidic catalyst and trioxane vapor obtained by heating and distillation is brought into contact with benzene to prepare a benzene solution containing trioxane. Then, it is proposed to separate trioxane from this benzene solution and return the benzene obtained by distillation to the distillation column for trioxane synthesis.

[0004]

The aqueous phase obtained by two-phase separation in a trioxane synthetic distillation column using these conventional methods contains effective substances such as methanol, formaldehyde, methylal and methyl formate. However, it is incinerated without being used because it also contains unnecessary traces of benzene. Further, the concentrated recovery of the formalin aqueous solution, which is subsequently performed, is also high in energy loss due to the high temperature and pressure of 140 to 150 ° C.
Further, material corrosion due to formic acid produced as a by-product at high temperature during the concentration of formalin was also a serious problem in plant operation.

[0005]

The present invention proposes a rational method for synthesizing trioxane including the entire recovery process from formalin. That is, in obtaining trioxane as a volatile component from formalin by a cyclization reaction, (a) a benzene phase or a benzene phase and an aqueous phase are used as a reflux liquid from the top of the distillation column, and (b) the middle stage of the distillation column. The benzene phase in which trioxane is dissolved is extracted, and then trioxane is purified by distillation from a benzene solution containing trioxane. (C) In the water phase obtained by separating the two phases at the top of the column, methylal dissolved in the water phase is extracted. , Methyl formate is brought into contact with a solid acid to decompose into methanol, formaldehyde and formic acid, respectively, and benzene is taken out from the top of the distillation column and an aqueous solution containing substantially no benzene is taken out from below. It is a synthetic method.

According to the present invention, at the top of the trioxane synthetic distillation column, a small amount of benzene dissolved in the aqueous phase component obtained from the lower layer of the two-phase separation tank is removed, and other effective components are recovered. Things are possible. Here, the active ingredient of the obtained aqueous phase is passed as a raw material for synthesizing methylal, and further,
The obtained methylal is used as an organic solvent,
It is oxidized and reused as formalin.

In the present invention, the formalin contained in the aqueous phase from which benzene has been removed is used for the synthesis of methylal, so that the conventional formalin concentration step is not required, the energy consumption is small, and the by-product is a by-product. Corrosion of materials due to formic acid does not occur. Hereinafter, the present invention will be described in more detail with reference to FIG. The formalin used in the present invention may be 50 to 55% formalin obtained by oxidizing methanol with a silver catalyst or an iron oxide-molybdenum oxide composite catalyst, or 70% formalin obtained by oxidizing methylal.

As the trioxane synthesis catalyst, an inorganic acid such as sulfuric acid, a heteropoly acid, an ion exchange resin having a sulfonic acid group, a solid acid such as a zeolite catalyst can be used.
The trioxane-containing vapor 3 discharged from the trioxane synthesis tank 1 is supplied to the trioxane synthesis distillation column 4. Formalin is supplied to the distillation column 4 through the conduit 2. The trioxane vapor obtained at the bottom of the trioxane synthetic distillation column rises from the lower part of the distillation column to the upper part thereof, contacts benzene 8 supplied in the middle stage of the distillation column, and trioxane is extracted with benzene. The benzene solution containing trioxane passes through a conduit 6 and is separated into an aqueous phase and a benzene phase containing trioxane in a two-phase separation tank 7, and the aqueous phase is returned to the synthetic distillation column 4 again through the conduit 5. At the top of the synthesis tower, the generated vapor is liquefied by a condenser 10 through a conduit 9 and separated into a benzene phase and an aqueous phase in a two-phase separation tank 11. The benzene phase or a part of the benzene phase and the aqueous phase is fed to the distillation column 4 through a conduit 12
Returned through. On the other hand, the aqueous phase is supplied to the benzene separation distillation column 20 through the conduit 13. This aqueous phase contains a trace amount of benzene, formaldehyde, methanol, methylal, methyl formate, trioxane and the like. From the top of the benzene separation distillation column 20, through the conduit 14,
The liquid condensed in the condenser 15 is separated into a benzene phase 17 and an aqueous phase in the two-phase separation tank 16. The aqueous phase is then led to a fixed bed 18 containing the solid acid, methyl formate being hydrolyzed to methanol and formic acid and methylal hydrolyzed to methanol and formaldehyde. Also, when trioxane is present, it is also decomposed to formaldehyde.
As the solid acid, an ion exchange resin containing a sulfonic acid group,
Acidic zeolite etc. are mentioned. The aqueous phase containing the hydrolyzed components is refluxed through conduit 19. From the bottom of the column, an aqueous solution containing substantially no benzene but containing formaldehyde, methanol and formic acid is recovered through the conduit 21.

These aqueous solutions can be reused as raw materials for synthesizing methylal. The benzene solution containing trioxane is introduced into the benzene-trioxane separation distillation column 23 via the conduit 22. Benzene is separated from the top of the column, and purified trioxane is extracted from the bottom of the column.

[0010]

The present invention will be described in more detail with reference to the following examples, which, however, do not limit the scope of the present invention.

[0011]

Example 1 55% obtained by oxidizing methanol
1 kg of formalin (containing 1% methanol) per hour,
It was supplied to a trioxane synthesis distillation column 4 at a column height of 3 m, a column diameter of 50 mmφ, a column bottom temperature of 104 ° C., and atmospheric pressure. In the trioxane synthesis tank 1, heating was performed at 103 ° C. with 2% sulfuric acid as a catalyst, and vapor containing trioxane was supplied to the trioxane synthesis distillation column 4.

600 g of benzene / hour in the middle stage of the distillation column 4.
The benzene solution containing trioxane was supplied and 1 kg per hour was extracted from the upper part of the two-phase separation tank. At the top of the synthetic distillation column 4, the benzene phase of the two-phase separation tank was refluxed to the synthetic distillation column, and 600 g of an aqueous solution containing 0.2% benzene was extracted from the conduit 13 per hour. The composition of the water phase is 20% formaldehyde, 0.8% methanol, 1.5 methylal.
%, Methyl formate 2.5%, and trioxane 1.8%.

The concentration of trioxane in the benzene solution containing trioxane was 40%, followed by a tower height of 3 m,
Purification of trioxane is carried out in a trioxane-benzene separation distillation column 23 at atmospheric pressure, a column bottom temperature of 120 ° C., and a column top temperature of 80 ° C.
0 g, and 598 g of benzene was extracted from the top of the column every hour.

The aqueous solution extracted by the two-phase separation from the top of the trioxane synthetic distillation column was then 2 m in height.
It was passed to the benzene separation column 20 at atmospheric pressure and a column bottom temperature of 102 ° C. The top condensate of the benzene separation column was separated into two phases, and a small amount of benzene was recovered from the upper layer. The lower aqueous phase then passes through a fixed bed 18 filled with a granular ion exchange resin having a sulfonic acid group, and the top components such as methyl formate, methylal, and trioxane are decomposed into methanol, formic acid, and formaldehyde, respectively, and transferred to the distillation column 20. It was returned. From the bottom of the column, 599 g of an aqueous solution in which benzene was not detected was obtained every hour. The composition was formaldehyde 22.3%, methanol 4.1%, and formic acid 1.9%.

[0015]

Example 2 70% obtained by oxidizing methylal
1k / h of formalin (containing 1.5% methanol)
g to the same trioxane synthesis distillation column 4 as in Example 1. In the trioxane synthesis tank, heating was performed at 103 ° C. with 2% sulfuric acid as a catalyst, and vapor containing trioxane was supplied to the trioxane synthesis distillation column 4.

In the middle stage of the distillation column 4, 870 g of benzene per hour
Then, 1.45 g of the benzene solution containing trioxane was extracted from the upper part of the two-phase separation tank per hour. At the top of the synthetic distillation column, the benzene phase of the two-phase separation tank was refluxed to the synthetic distillation column, and 420 g of an aqueous solution containing 0.2% benzene was extracted from the conduit 13 per hour. The composition of the water phase is 20% formaldehyde, 1.1% methanol, 3.5 methylal.
%, Methyl formate 3.6%, and trioxane 2.4%.

The concentration of trioxane in the benzene solution containing trioxane was 40%, and then trioxane was purified in the same trioxane-benzene separation distillation column 23 as in Example 1, and the purified trioxane was purified from the bottom of the distillation column. 580 g / h, benzene from the top of the tower is 869 g / h
It was pulled out. The aqueous solution extracted by the two-phase separation from the top of the trioxane synthetic distillation column was then treated in Example 1
It was sent to a benzene separation column 20 similar to. The top condensate of the benzene separation column was separated into two phases, and a small amount of benzene was recovered from the upper layer.

The lower aqueous phase then passes through a fixed bed 18 filled with a granular ion exchange resin having sulfonic acid groups, and the top components such as methyl formate, methylal and trioxane are decomposed into methanol, formic acid and formaldehyde, respectively.
It was returned to the distillation column 20. From the bottom of the column, 420 g of an aqueous solution in which benzene was not detected was obtained per hour. The composition is 24% formaldehyde, 6.6% methanol, 3.6 formic acid.
%Met.

[0019]

INDUSTRIAL APPLICABILITY By using the present invention, it is possible to remove benzene and recover an active ingredient in the synthesis of trioxane, and thus it is possible to construct a process with low energy consumption including recovery. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

[Explanation of symbols]

 1 Trioxane synthesis tank 2, 3 conduit 4 Trioxane synthesis distillation tower 5, 6 conduit 7 Two-phase separation tank 8 Benzene 9 conduit 10 Condenser 11 Two-phase separation tank 12, 13, 14 Conduit 15 Condenser 16 Two-phase separation tank 17 Benzene Phase 18 Solid acid fixed bed 19 Conduit 20 Benzene separation distillation column 21, 22 Conduit 23 Benzene-trioxane separation distillation column 24, 25 Conduit 26 Heater

Claims (1)

[Claims] 1. When (1) obtaining trioxane as a volatile component from formalin by a cyclization reaction, (a) a benzene phase or a benzene phase and an aqueous phase are used as a reflux liquid from the top of a distillation column, and (b) ) A benzene phase in which trioxane is dissolved is extracted from the middle stage of the distillation column, and then trioxane is purified by distillation from a benzene solution containing trioxane, and (c) in an aqueous phase obtained by separating the two phases at the top of the column,
Methylal and methyl formate dissolved in the aqueous phase are contacted with a solid acid to decompose into methanol, formaldehyde and formic acid, respectively, and benzene is added from the top of the distillation column and an aqueous solution containing substantially no benzene is added from below. A method for synthesizing trioxane, which is characterized in that it is taken out.