JP2863437B2 - Purification of trioxane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying trioxane. Trioxane is a polymer intermediate of polyacetal resin, but impurities such as methanol, formaldehyde, water, and formic acid in trioxane cause a decrease in molecular weight, yield, and quality of resin products. A purification method is industrially desired.

[0002]

2. Description of the Related Art Many studies have been made on a method for purifying trioxane or a method for producing high-purity trioxane. The method for producing trioxane is a method in which a formaldehyde aqueous solution is used as a raw material and the reaction is carried out in the presence of an acid catalyst. Since the synthesis reaction of trioxane is an equilibrium reaction, the trioxane-containing substance is distilled off by distillation. Here, since trioxane and water are azeotropic (azeotropic point: 91.3 ° C., azeotropic composition: trioxane: 70%, water: 30%), water is present in the dioxane-containing distillate.

[0003] In trioxane, there are formaldehyde, which is a raw material for synthesizing trioxane, and formic acid and methanol, which are by-products of the synthesis reaction (Cannizzaro reaction). A method for separating and purifying trioxane from a trioxane-containing distillate is a method in which trioxane is extracted using a solvent insoluble or hardly soluble in water, and the solvent and trioxane are separated by distillation (Japanese Patent Publication No. 49-5351). There is a method of cooling the contained distillate, crystallizing trioxane, and separating by filtration.

Further, many studies have been made on the removal of impurities remaining in trioxane purified by an extraction method, a distillation method, and a recrystallization method. For example, formaldehyde, formic acid and water can be removed by adding isocyanate before extraction or crystallization (Japanese Patent Publication No. 40-12900).

As for the removal of formic acid, there is a method of adding an alkali metal or metal hydride as a supplement (Japanese Patent Publication No. 44-17915). Furthermore, as for the removal of water from trioxane purified by an extraction method, a distillation method or a recrystallization method, there is a method using a molecular sieve (synthetic zeolite or the like) (Japanese Patent Publication No. 47-7384).

As described above, many studies have been made on the removal of formaldehyde, water and formic acid.
However, like formaldehyde, water and formic acid, it exists as an impurity in trioxane, and when trioxane is used as a raw material for polyacetal polymerization, it acts as a chain transfer agent, causing methanol to reduce the molecular weight, yield, and quality of the polymer. There are few studies on the removal of water. A method capable of reducing methanol in trioxane to several ppm has not been known.

[0007]

When trioxane is used as a raw material for polyacetal, it is necessary to reduce impurities in trioxane, prevent a decrease in molecular weight and yield of a polyacetal resin product, and further improve the quality.
As described above, the removal of water, formaldehyde and formic acid can be reduced to a considerable level. Methanol is another impurity that reduces the molecular weight, yield, and quality of the polyacetal resin, and it is necessary to reduce the amount of methanol. Conventionally, the removal of methanol in the trioxane purification method is mainly performed by distillation. However, it is very difficult to reduce the methanol in trioxane to several ppm or less by the conventional method. This is considered to be because methanol reacts with a trace amount of formaldehyde contained in trioxane to form hemiacetal as shown in the following formula.

[0008]

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Since hemiacetal is present in an equilibrium composition with methanol, it has been difficult to obtain high-purity trioxane from which methanol has been removed to several ppm or less by a simple distillation or adsorption process.

[0010]

Means for Solving the Problems In the trioxane refining system, studies have been focused on dehydration. Methanol remains stable as hemiacetal in the dehydrated system, and its removal is very difficult. The present inventors have focused on methanol removal and conducted research, and as a result, surprisingly, the new fact that methanol in purified trioxane can be reduced by adding water during the crude trioxane or trioxane purification process before purification. I found it.

[0011] That is, the invention is from trioxane solution containing 10% or less of methanol, formaldehyde, in trioxane purification process for separating methanol, formaldehyde, or to attach a water solution, or adding water to the separation step, Alternatively, the present invention relates to a method for purifying trioxane, which comprises adding water to both the solution and the separation step.

The amount of water to be added to the trioxane is preferably 100 ppm or more based on the trioxane, and more desirably, the maximum effect is obtained by adding the maximum amount of water to such an extent that water is not mixed into the purified trioxane. After the addition of water, the contact time between water and trioxane is preferably 5 minutes or more, and more preferably 10 minutes or more, the hemiacetal decomposition reaction is in an equilibrium state.

Further, regarding the temperature after the addition of water, the higher the temperature, the more the hemiacetal decomposition reaction proceeds.
It is desirable to keep it above. More desirably, if the temperature is increased to 130 ° C. or more under pressure, the reaction time can be reduced to a level of several minutes. Preferably, in order to increase the contact area between the trioxane solution and water, it is better to divide the addition nozzle into several places in the water addition method, and it is better to spray the water by dispersing the addition nozzle in a mist state. Further, there is a method of blowing water as steam.

Regarding the position of adding water, it may be added to the crude trioxane before purification, may be added to the impurity separation step in the crude trioxane, or may be added to both the crude trioxane and the impurity separation step of the trioxane before purification. The effect is great even if added to. For example, when impurities in crude trioxane are separated by distillation, a method of adding water to crude trioxane fed to a distillation column, a method of adding water to a middle stage between a raw material feed stage and a bottom of a distillation column, There is a method of adding water to both the trioxane and the raw material feed stage of the distillation column to the intermediate stage between the bottom and the bottom. The method of reducing methanol by adding water to the middle stage of the distillation column is a type of reactive distillation that preferentially extracts low-boiling methanol to the top of the column by causing a hemiacetal decomposition reaction near the water addition stage. is there.

The composition of the feed solution is a solution containing trioxane as a main component and methanol, water and formaldehyde. Further, if the process involves extracting and separating trioxane with an organic solvent in the preceding step, a process containing the organic solvent may be used. Distillation separation, adsorption separation, extraction separation,
There is a membrane separation method and the like.

In the distillation separation method, the types of distillation columns are bubble cap, sieve tray, uniflux, flexi tray, natter float, valve tray, ballast tray, cascade tray, venturi tray, kittel tray, recycling tray, chimney tray, There are jet trays, turbo grid trays, ripple trays, dual float trays, baffle trays, packed towers and the like, and the present invention can be used in all cases.

In the adsorption separation method, activated carbon, silica gel, ion exchange resin, zeolite adsorbent, etc. are used as the adsorbent, and the present invention can be used in all the adsorption separation methods. Alternatively, in the case of the extraction separation method, the organic solvent for extracting trioxane is a substance unnecessary or hardly soluble in water, for example, methylene chloride,
Chlorinated hydrocarbons such as chloroform, ethylene chloride, 1,1,1-trichloroethane, ethers such as ethyl ether, isopropyl ether, and ethyl butyl ether;
There are esters such as ethyl acetate and isopropyl acetate, ketones such as methyl ethyl ketone and diethyl ketone, and hydrocarbons such as benzene, cyclohexane, hexane and heptane, and the present invention can be used in all extraction separation methods.
In addition, the present method can be applied to further purifying a trioxane solution containing a solvent after extraction with these solvents.

According to the present invention, methanol and formaldehyde remaining as impurities in trioxane are reduced by several p
pm.

[0019]

The present invention will be described below with reference to examples.

[0020]

EXAMPLE 1 FIG. 1 shows an example of the trioxane purification process of the present invention. This trioxane purification process
Dehydration is performed by extracting trioxane with benzene in the previous step, and a mixed solution of trioxane and benzene after extraction (benzene: 49.06%, trioxane: 38.3).
5%, methanol: 2.4%, water: 2.2%) is a column (T1) for separating trioxane and benzene. Water was added below the crude trioxane feed stage. The temperature in the system at the water addition position is 110 ° C., and the contact time with water is about 4 minutes, judging from the residence time in the tower.

The amount of water added to T1 is 30, 90, 170
ppm and the methanol concentration in the bottom liquid of the T1 column .
The relationship with lioxane concentration was measured. Table 1 shows the results. With the addition of water, the methanol concentration of the T1 bottom was reduced, and the amount of water added was 170 ppm, which could be reduced to 30% of the initial concentration.

[0022]

Example 2 In a trioxane purification method by a distillation separation method, methanol (52.1 pp) was collected from the bottom of a distillation column.
m) -containing trioxane (98.5% concentration) solution was collected. While adding water to the bottom liquid, methanol was adsorbed and separated with zeolite. When the amount of water added was 188 ppm, the amount of residual methanol was reduced to 20% of the initial concentration. The results are shown in Table 2 and FIG.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

According to the present invention, the amount of methanol present in trioxane can be reduced.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of the trioxane purification method of the present invention.

FIG. 2 is a graph showing the methanol concentration versus the amount of water added in Example 2.

Claims (2)

(57) [Claims] A trioxane-containing solution obtained by reacting an aqueous formaldehyde solution in the presence of an acid catalyst is extracted with an organic solvent insoluble or hardly soluble in water, and 10% or less of methanol and formaldehyde after extraction and water are extracted. A mixed liquid of trioxane and an organic solvent is supplied to a distillation column as a raw material, an organic solvent is distilled from the top of the column, and trioxane is removed from the bottom of the column. Water in an amount of 100 ppm or more to the distillation column feed trioxane is added to the middle stage, the temperature of the water addition stage is maintained at 90 ° C. or more, and the contact residence time between trioxane and water is reduced to 4 minutes.
Min. Or more. 2. A trioxane-containing solution obtained by reacting an aqueous formaldehyde solution in the presence of an acid catalyst is extracted with an organic solvent insoluble or sparingly soluble in water, and 10% or less of methanol and formaldehyde after extraction and water are extracted. A mixed solution of trioxane and an organic solvent containing the raw material is supplied to a distillation column as a raw material, an organic solvent is distilled from the top of the column, and trioxane is obtained from a continuous distillation separation method of trioxane to remove trioxane from the bottom of the column. A method for purifying trioxane, comprising adding 100 ppm or more of water and separating by adsorption with zeolite.