JPS6411634B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing trioxane from formaldehyde, and more specifically, when an aqueous formaldehyde solution is heated and distilled using an acid catalyst, trioxane is distilled as an azeotropic mixture with a first solvent in the first column. The trioxane phase obtained by phase separation is distilled from the top of the column, and the water and formaldehyde contained in the trioxane phase are distilled from the top of the column as an azeotropic mixture with the second solvent, and the trioxane phase obtained by phase separation is distilled from the top of the column as an azeotropic mixture with the second solvent. This invention relates to a method for efficiently obtaining trioxane of high purity. Generally, trioxane is obtained by heating an aqueous formaldehyde solution in the presence of a nonvolatile acid catalyst. As an industrial method, 20-55% by weight of trioxane obtained by heating and distilling a 30-70% by weight formaldehyde aqueous solution in the presence of an acid catalyst, 10-35% by weight of formaldehyde and 20-50% by weight of water is used.
A distillate of crude trioxane consisting of % by weight is extracted by (1) cooling and excessively separating trioxane crystals, or (2) liquid extraction with a solvent that is insoluble or sparingly soluble in water, and the extract is extracted. Method of separating trioxane by rectification (Japanese Patent Publication No. 41-6344, Japanese Patent Publication No. 56-87580), or (3) method of distillation in the presence of a solvent that is insoluble or sparingly soluble in water and forms an azeotrope with water. (Tokuko Showa 49-
5351, Special Publication No. 49-28197), etc. are known. When distilling crude trioxane by heating the formaldehyde aqueous solution, a lot of reflux is required to concentrate the trioxane, and especially since the water content in the crude trioxane is relatively high,
The energy required for this is enormous and is economically disadvantageous. In this case, formaldehyde is not completely condensed in the condenser and evaporates, adhering to and depositing as paraformaldehyde on relatively cooled vessel walls, piping, etc., clogging the piping and condenser and causing long-term operation. It has drawbacks that make it difficult. Furthermore, another production method was developed in Japanese Patent Publication No. 48-26031, in which an aqueous formaldehyde solution was heated and distilled in the presence of an acid catalyst, and the generated vapor was brought into contact with a saturated hydrocarbon solvent that was azeotropic with trioxane. A method is disclosed in which a mixture is distilled out, separated into an aqueous phase and a solvent phase, and the crude trioxane contained in the solvent phase is cooled and crystallized to obtain trioxane crystals. However, this method of over-separating the crystallized product obtained by cooling the distillate is
Since trioxane crystals contain water and formaldehyde, it must be further purified by drying or extractive distillation, which has the disadvantage of complicating the process. The present inventors investigated a manufacturing method using an aqueous formaldehyde solution from the standpoint of energy saving, process simplification, and prevention of troubles such as clogging of pipes, etc. caused by formaldehyde polymers in contrast to the conventional technology described above.As a result, the following findings were made. It became clear. In other words, the composition of the azeotrope of the solvent azeotropic with trioxane, the stability of the phase separation state,
We conducted a detailed study on the distribution ratio of each component during phase separation, and found that trioxane easily remains at the top of the column in the presence of saturated aliphatic hydrocarbons or saturated alicyclic hydrocarbons with a boiling point of 60 to 110°C. When the distilled azeotrope is cooled and condensed above the crystallization temperature of trioxane, a stable two-phase solution is formed; most of the trioxane is distributed into the crude trioxane phase, and it can be easily concentrated by phase separation. , the azeotropic composition of trioxane in the overhead distillate is 15
Since it is relatively high at ~40% by weight, only a small amount of solvent is required for azeotropic trioxane distillation, and water, formaldehyde, etc. contained in the crude trioxane phase are insoluble or poorly soluble in water and are not soluble in water. It has been found that by performing azeotropic distillation in the presence of a solvent that forms an azeotrope, trioxane is discharged from the top of the column and highly purified trioxane is obtained from the bottom of the column. Based on these findings, by introducing a two-stage azeotropic distillation method, we have developed a new method for producing high-purity trioxane using less energy and which can be operated continuously without clogging pipes due to precipitation of formaldehyde polymers. We found a method and were able to arrive at the present invention. That is, the vapor generated by heating and distilling an aqueous formaldehyde solution in the presence of an acid catalyst is brought into gas-liquid contact in the first stage column in the presence of a first solvent that has a boiling point of 60 to 110°C and forms an azeotrope with trioxane. , trioxane is distilled out as an azeotropic mixture with the first solvent, the distilled vapor is cooled and condensed at a temperature higher than the crystallization temperature of trioxane, and then phase-separated into the first solvent phase and the crude trioxane phase. All or a part of the trioxane phase is supplied to the second column, and the second column supplies the trioxane phase to the second column.
Distillation is carried out in the presence of a second solvent that is azeotropic with water at ℃, and water, formaldehyde, etc. distilled from the top of the column are phase-separated from the second solvent and discharged outside the system, and high-purity trioxane is produced from the bottom of the column. This is a method for producing trioxane characterized by obtaining the following. The solvents used in the present invention are as follows. In the first column, trioxane is distilled out as an azeotrope at the top of the column, and phase separation occurs above the crystallization temperature of trioxane, so the boiling point at normal pressure is 60 to 110℃.
is the first solvent azeotropic with trioxane of n-
hexane, iso-hexane, n-heptane, iso-
These are saturated aliphatic hydrocarbons such as octane, and saturated alicyclic hydrocarbons such as cyclohexane and methylcyclohexane. Particularly preferably, a solvent with a boiling point of 80° C. or higher is used, which increases the azeotropic composition of trioxane in the overhead distillate and requires less circulation of the solvent, but the solvent is not particularly limited. In the second column, the boiling point at normal pressure is 30 to 110.
A second solvent that is insoluble or sparingly soluble in water and azeotropic with water at ℃, such as chlorinated hydrocarbons such as ethylene chloride, ethylidene chloride, and chloroform, ethers such as ethyl ether, isopropyl ether, and ethyl butyl ether, methyl acetate, and acetic acid. Examples include esters such as isopropyl, ketones such as methyl ethyl ketone and diethyl ketone, and hydrocarbons such as benzene and dichlorohexane. Next, the present invention will be explained in detail with reference to the drawings. The figure shows the general steps of the invention. In the first step, an aqueous formaldehyde solution is supplied to the reaction vessel 2 through the conduit 1. Formaldehyde in the reaction vessel is 30-70% by weight, preferably
50 to 65% by weight, and catalysts include sulfuric acid, phosphoric acid,
Known methods such as benzenesulfonic acid, p-toluenesulfonic acid or cation exchange resins are used. The amount of catalyst may be any amount as long as it does not reduce the amount of trioxane produced and also does not increase the equilibrium concentration of side reaction products, but it is usually 0.1 to 15% by weight based on the total amount charged, preferably. It is desirable to use 0.5 to 10% by weight. In addition, although the reaction vessel 2 and the first distillation column 3 are directly connected in the figure, they may be connected in the form of a reactor and a distillation column through a conduit. The trioxane produced in the reactor 2 is heated and distilled, while the first solvent that is azeotropic with the trioxane is supplied to the top of the first distillation column 3 via a conduit 7 and brought into gas-liquid contact. Trioxane distilled from the top of the tower,
The azeotropic mixture of water, formaldehyde and the first solvent is cooled and condensed in a condenser 5 via a conduit 4. Here, in order to prevent crystallization of trioxane in the azeotrope, the mixture is cooled to a temperature higher than the crystallization temperature of trioxane. After phase separation into a first solvent phase and a crude trioxane phase in separator 6,
The first solvent phase is refluxed back to the top of the column via line 7. The crude trioxane phase is fed in its entirety to the second stage via conduit 9. If necessary, a portion of the crude trioxane phase is refluxed via line 8 to the first distillation column 3.
The remainder may be returned to the top of the column and supplied to the second step via conduit 9. In the second step, the crude trioxane phase is supplied from the first step to the second distillation column 11 via conduit 9, and a second solvent that is insoluble or sparingly soluble in water and is azeotropic with water is supplied to the column via conduit 15. Water, formaldehyde, etc. are supplied to the top of the column and brought into contact with the crude trioxane phase as an azeotrope mixture with a second solvent, which is then passed through pipe 1 from the top of the column.
After being cooled and condensed in a cooler 13, the water layer is separated into phases in a separator 14, and the aqueous layer is discharged to the outside of the system through a conduit 16, and the solvent phase is passed through a conduit 15 to the second distillation column 11. Returned to the top of the column as reflux. On the other hand, essentially pure trioxane is obtained from the bottom of the column via line 17. Although the figure shows the case where a solvent lighter than water is used, when a solvent heavier than water is used, the separators 6 and 14 separate the first solvent phase, the crude trioxane phase, and the second phase, respectively. Similar equipment can be used except that the solvent and aqueous phases are reversed. Examples of the present invention are shown below. Example 1 An apparatus was used in which the reaction vessel No. 1 was directly connected to a stainless steel packed column filled with McMahon and having a diameter of 35 mm and a height of 1.8 m. The experiment was conducted using sulfuric acid as a catalyst, the sulfuric acid concentration in reactor 2 was set to 5% by weight, and n-heptane was used as the first solvent. The tower top pressure is atmospheric pressure and the tower top temperature is approximately 76℃.
When the temperature was near, a 60% by weight aqueous formaldehyde solution was continuously supplied from conduit 1 so that the liquid level in reaction vessel 2 remained constant, while the solvent was circulated through conduit 7 at a rate of 207 g/hour. The azeotropic mixture vapor of n-heptane, trioxane, formaldehyde, and water distilled from the top of the first stage azeotropic distillation column 3 is cooled and condensed at 65±5°C in a condenser 5 to prevent trioxane from crystallizing. The phases were separated in a separator 6, and the trioxane phase was fed through a conduit 9 to a second azeotropic distillation column 11 at a rate of 70 g/hour. The composition of the main liquid in the conduit related to distillation column 3 is shown in Table 1.
It is shown in This shows that the concentration of trioxane in the crude trioxane phase exceeds 50% by weight, and that no formaldehyde polymers were found in the condenser, piping, etc. even after operation for more than a month, indicating that continuous operation is possible. Ivy. Next, in the second stage azeotropic distillation step, using ethylene chloride as the second solvent, the crude trioxane phase is supplied to the middle part of the distillation column 11, and the temperature of the reboiler 10 is adjusted.
The temperature was maintained at 115-117°C and the tower top temperature was operated at around 72°C. The azeotropic mixture vapor distilled from the top of the column is cooled and condensed in a condenser 13, then phase-separated in a separator 14, and the solvent phase is passed through a conduit 15 to the distillation column 11 at a rate of 336 g/hour.
The aqueous phase was discharged from the system through conduit 16 at a rate of 32 g/hour. Trioxane was obtained from the bottom of the column via conduit 17 and had high purity as shown in Table 1. Similar to the first stage process, no formaldehyde polymers were found in the condenser, piping, etc., and it became clear that long-term operation was possible. Example 2 Trioxane was synthesized and purified from an aqueous formaldehyde solution in the same manner as in Example 1, except that methylcyclohexane was used as the first solvent in the first azeotropic distillation step and benzene was used as the second solvent in the second azeotropic distillation step. The results are shown in Table 1. Comparative Example Using the same equipment as in Example 1, instead of the first-stage azeotropic distillation method, a method was used in which the vapor distilled from the reactive distillation column was condensed without using a solvent. A reactor was charged with 500 g of an aqueous solution of 60% formaldehyde and 5% sulfuric acid, and 60% by weight of formaldehyde was continuously fed so that the liquid level in the reactor remained constant. When the trioxane concentration was set to 54% by weight, a reflux ratio of 6 or more was required. After 12 hours of operation, an open inspection revealed paraformaldehyde adhesion to the condenser wall. A comparison of the energy consumed by cooling water, etc. from the tower top condenser when the concentration and outflow amount of trioxane in the tower overhead distillate are constant, shows that the method of the present invention is approximately 70% more energy consumed than the conventional technology. It turns out that it saves money. 【table】

[Brief explanation of drawings]

The figure is a process diagram of one embodiment of the present invention. 2... Reaction vessel, 3... First distillation column, 5, 13...
... Condenser, 6, 14 ... Separator, 10 ... Reboiler, 11 ... Second distillation column, 1, 4, 7, 8, 9,
12, 15, 16, 17... Conduit.

Claims (1)

[Claims] 1. A formaldehyde aqueous solution is heated and distilled in the presence of an acid catalyst, and the generated vapor is brought into gas-liquid contact in the presence of a first solvent with a boiling point of 60 to 110°C and forming an azeotrope with trioxane in the first stage column. Trioxane is distilled out as an azeotropic mixture with the first solvent, and the distilled vapor is cooled and condensed at a temperature higher than the crystallization temperature of trioxane, and then phase-separated into the first solvent phase and the crude trioxane phase. All or part of the trioxane phase is supplied to the second column, where it is treated in the presence of a second solvent that is insoluble or sparingly soluble in water and has a boiling point of 30 to 110°C and is azeotropic with water. A method for producing trioxane, which comprises performing distillation, discharging water, formaldehyde, etc. distilled from the top of the column after phase separation from the second solvent, and obtaining highly pure trioxane from the bottom of the column.