JPS6411635B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing trioxane using formaldehyde as a starting material. [Prior Art] Generally, trioxane is obtained by heating an aqueous formaldehyde solution in the presence of a nonvolatile acid catalyst. As an industrial manufacturing method,
Utilizing the fact that trioxane-water-formaldehyde forms an azeotropic mixture, 20-55% by weight trioxane and 10-10% by weight formaldehyde are obtained by heating and distilling a 30-70% by weight formaldehyde aqueous solution in the presence of an acid catalyst. 35% by weight, and 20% water
A method has been adopted in which a distillate of crude trioxane containing up to 50% by weight is obtained and then water, formaldehyde, etc. contained in the crude trioxane are removed for purification. As a method for purifying crude trioxane, the following methods are conventionally known. (1) A method in which crude trioxane is cooled and the trioxane crystals crystallized are excessively separated. (2) Crude trioxane is extracted liquid-wise with a solvent that is insoluble or poorly soluble in water, and the extract is rectified. Method for separating trioxane (Japanese Patent Publication No. 41-6344, Japanese Patent Publication No. 46-33184, Japanese Unexamined Patent Publication No. 56-87580)
(3) A method of distilling crude trioxane in the presence of a solvent that is insoluble or sparingly soluble in water and forms an azeotrope with water (Japanese Patent Publication No. 49-5351, Japanese Patent Publication No. 49-28197) ). However, these methods have the following drawbacks. In other words, in the reaction in which trioxane is produced by heating an aqueous formaldehyde solution in the presence of an acid catalyst, the equilibrium of the reaction is largely biased toward formaldehyde, so the concentration of trioxane in the reaction solution in an equilibrium state is usually as low as several percent or less. . Therefore, heating an aqueous formaldehyde solution in the presence of an acid catalyst to generate trioxane, and concentrating the trioxane fraction using azeotropic distillation of the trioxane-water-formaldehyde system,
In order to obtain crude trioxane with a high concentration, a large amount of reflux is required, and the top distillate has a homogeneous phase, and the water content in crude trioxane is relatively high. The energy required is enormous, which is economically disadvantageous. In this case, formaldehyde is not completely condensed in the condenser and evaporates, adhering to and depositing as paraformaldehyde on relatively low-temperature vessel walls, piping, etc., clogging the piping and condenser, and causing damage to the equipment. It has drawbacks that make long-term operation difficult. Furthermore, as another manufacturing method,
As disclosed in the publication, an aqueous formaldehyde solution is heated in the presence of an acid catalyst, the generated vapor is brought into contact with a saturated hydrocarbon solvent that is azeotropic with trioxane, and trioxane is distilled out as an azeotrope with the solvent. A known method is to separate the crude trioxane into an aqueous phase and a solvent phase, cool and crystallize the crude trioxane contained in the solvent phase, and obtain crystals of trioxane by filtration. However, this method has the disadvantage that the process becomes complicated because trioxane crystals contain large amounts of water, formaldehyde, etc., and must be further purified by drying or extractive distillation. . Moreover, since the aqueous phase is not taken out of the system but is refluxed to the rectification column, it becomes difficult to maintain a constant concentration of the formaldehyde aqueous solution in the reactor. [Object of the Invention] The present invention has been made against the above background, and its purpose is to efficiently produce trioxane of high purity using a simple process with low energy consumption. It is an object of the present invention to provide a method for producing trioxane in which paraformaldehyde does not adhere to the vessel wall and deterioration of the apparatus is less likely to occur. [Structure of the invention] The above purpose is to achieve the following steps (1), (2) and steps.
This is achieved by a method for producing trioxane characterized by containing (3). Step (1) Heating an aqueous formaldehyde solution in the presence of an acid catalyst, the generated steam has a boiling point of 60 to 110℃
is brought into gas-liquid contact with a first solvent capable of azeotroping with trioxane, distilling trioxane as an azeotrope with the first solvent, and then cooling and condensing the distilled vapor to dissolve the first solvent. A step of phase separation into a phase and a crude trioxane phase. Step (2) All or part of the crude trioxane obtained in Step (1) is converted into a liquid by using a second solvent that is insoluble or poorly soluble in water, is azeotropic with water, and has a boiling point lower than that of trioxane. The process of performing extraction and extracting trioxane. Step (3) A step of separating trioxane from the extract obtained in step (2). Next, the present invention will be explained in detail with reference to FIG. FIG. 1 is an explanatory diagram schematically showing the steps of an embodiment of the present invention. In the first stage azeotropic distillation step, an aqueous formaldehyde solution fed into the reactor 2 via the conduit 1 is heated in the presence of a catalyst. The vapor generated in the reactor 2 is led to the distillation column 3 and brought into gas-liquid contact with the first solvent supplied to the top of the distillation column 3. Then, an azeotropic mixture of trioxane, water, formaldehyde and the first solvent distilled from the top of the distillation column 3 is introduced into the condenser 5 via the top conduit 4, where it is cooled and condensed. At this time, the condensation must be performed within a temperature range in which trioxane in the azeotrope does not crystallize. Due to condensation, the azeotrope is separated into two phases, a first solvent phase and a crude trioxane phase, and these are separated into their respective phases by a separator 6. Preferably the entire amount of separated first solvent phase liquid is refluxed via line 7 to the top of distillation column 3. On the other hand, the separated crude trioxane is supplied to the next extraction step. Note that, if necessary, a part of the crude trioxane can be refluxed to the top of the distillation column 3 via the conduit 8. In the second stage extraction process, the crude trioxane obtained in the first stage process is passed through the upper conduit 9 of the extraction column 10, and the second solvent is supplied from the lower conduit 11 of the extraction column 10 to each other. It is allowed to flow and is supplied into the extraction column 10. Then, the extract extracted in the extraction tower 10 is supplied to the middle part of the rectification tower 14 through the top conduit 12 of the extraction tower 10. On the other hand, a solution mainly composed of water and formaldehyde (hereinafter referred to as "raffinate") is taken out of the system through the bottom conduit 13 of the extraction column 10. Then, the distillate, which is distilled from the top of the rectification column 14 and mainly contains the second solvent and contains a small amount of water, formaldehyde, etc., is supplied to the condenser 16 via the conduit 15, where it is cooled and condensed. This condensate is further separated into a second solvent phase and an aqueous phase in a separator 17. A part of the separated second solvent phase is supplied to the extraction column 10 through the conduit 11, and the remainder is supplied to the extraction column 10 through the conduit 18.
It is then refluxed to the top of the rectification column 14. Also,
The aqueous phase is discharged out of the system via conduit 19 or is returned to the crude trioxane phase. On the other hand, high purity trioxane is taken out from the bottom of the rectification column 14 via a conduit 20. In the above apparatus, the positional relationship between the crude trioxane phase and the second solvent phase supplied to the extraction column 10, the positional relationship between the extract liquid and the raffinate liquid taken out from the extraction column 10, and the separator 16 of the rectification column 14. The vertical relationship between the second solvent phase and the aqueous phase in may be reversed depending on the type of solvent, but otherwise the relationship is the same. In addition, in the illustrated apparatus, the reactor 2 and the distillation column 3
Although these are directly connected, they may also be connected by a conduit. The first solvent used in the first azeotropic distillation step of the present invention must be capable of azeotropic distillation with trioxane, be insoluble or sparingly soluble in water, and have its boiling point is at normal pressure
There are no particular limitations as long as the temperature is 60 to 110°C. Preferably, a solvent having a boiling point of 80° C. or higher is used, which has a large composition ratio of trioxane in the azeotropic mixture, and requires a small amount of solvent circulation. Preferred examples of the first solvent include saturated aliphatic hydrocarbons such as n-hexane, iso-hexane, n-heptane, and iso-octane, and saturated aliphatic hydrocarbons such as cyclohexane and methylcyclohexane. I can do it. The second solvent used in the second extraction step of the present invention is insoluble or sparingly soluble in water,
Furthermore, it must be able to azeotrope with water and have a lower boiling point than trioxane.
Examples of the second solvent include chlorinated hydrocarbons such as ethylene chloride and trichloroethane, aromatic hydrocarbons such as benzene, and ethers such as isopropyl ether. Further, as the catalyst used in the trioxane production reaction in the first stage step, known catalysts such as sulfuric acid, phosphoric acid, benzenesulfonic acid, p-toluenesulfonic acid, or cation exchange resin are used. The amount of catalyst used may be any amount that does not reduce the amount of trioxane produced and also does not increase the production of side reactions, and it is usually desirable to use 0.1 to 15% by weight based on the total amount charged. . [Effects of the Invention] According to the present invention, as is clear from the examples described later, the first azeotropic distillation step using the first solvent and the second extraction step using the second solvent are combined. By doing so, high-purity trioxane can be efficiently produced with low energy consumption through a simple process, and there is no attachment of paraformaldehyde to the vessel wall, which prevents deterioration of the apparatus. That is, the present invention has the following effects. (b) In the first-stage azeotropic distillation step, the trioxane produced in the reactor 2 is obtained as an azeotropic mixture with the first solvent capable of azeotropic distillation with the trioxane, water, etc. Since the partitioning ratio of the solvent to the solvent is very small compared to the partitioning ratio to the water, it is possible to easily obtain the aqueous phase containing a high concentration of trioxane, that is, crude trioxane, by simply separating the first solvent phase and the aqueous phase. I can do it. (b) In the first-stage azeotropic distillation step, since the concentration of trioxane in the azeotropic mixture is relatively high, the amount of the first solvent required for azeotropically distilling trioxane may be small, which is advantageous in terms of production cost. . (c) In the first-stage azeotropic distillation process, the first solvent phase, which has a smaller latent heat of vaporization than water, is refluxed to the distillation column 3, so the energy consumption required for azeotropic distillation is small, which reduces production costs. It's advantageous. (d) In the first stage azeotropic distillation process, very little formaldehyde is contained in the vapor introduced into the condenser 5, and the introduced vapor is completely condensed within the condenser 5. Since condensation is performed at a temperature range in which trioxane in the vapor does not crystallize, paraformaldehyde does not adhere to the walls of the device. (E) In the second stage extraction process, crude trioxane containing a high concentration of trioxane is extracted with a good yield by the second solvent, and water, formaldehyde, etc. contained in small amounts in the extract are removed by using trioxane and the second solvent. During separation, it is removed together with the second solvent, yielding highly pure trioxane. [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that the trioxane production equipment has a capacity of 1
reactor, a stainless steel packed distillation column with a column diameter of 35 mm and a height of 1.8 m that is directly connected to this reactor and filled with McMahon inside, and a column diameter of 50 mm and a height of 1.2 m.
A countercurrent rotating disk extraction column with a disk spacing of 30 mm was used. Example 1 In reactor 2, 500 g of an aqueous solution with a formaldehyde concentration of 60% by weight and a sulfuric acid (catalyst) concentration of 5% by weight
When the temperature at the top of the distillation column 3 reaches approximately 76°C under atmospheric pressure, a formaldehyde aqueous solution with a concentration of 60% by weight is introduced through the conduit 1 at a flow rate of 72 g/min to maintain a constant liquid level in the reactor 2. Reactor 2 at time
On the other hand, n-heptane (first solvent) was circulated and supplied to the top of the distillation column 3 through conduit 7 at a flow rate of 207 g/hour. Next, the azeotropic mixture vapor of n-heptane, trioxane, water and formaldehyde distilled from the top of the distillation column 3 is transferred to a condenser 5.
After cooling and condensing trioxane at a temperature of 65°C so as not to crystallize it, the phase is separated in a separator 6, and the crude trioxane is continuously supplied to the next countercurrent extraction column 10 through an upper conduit 9 at a flow rate of 70 g/hour. did. On the other hand, benzene (second solvent) was continuously supplied into the countercurrent extraction column 10 from the lower conduit 11 at a flow rate of 134 g/hour.
Extracted. The temperature of the countercurrent extraction column 10 was maintained at 65°C. Benzene containing trioxane is continuously extracted from the top conduit 12 of the countercurrent extraction column 10,
It was supplied to the middle part of the rectification column 14. The rectification column 14 is operated under atmospheric pressure, and the top distillate is cooled and condensed in a condenser 16 at a temperature of 65°C, then phase-separated in a separator 17, and the aqueous phase is sent out of the system through a conduit 19. was discharged to. On the other hand, the benzene phase has a part flow rate
134 g/h to the extraction column 10 via conduit 11;
The remainder is sent to rectification column 14 via conduit 18 at a flow rate of 27 g/hour.
The mixture was refluxed to the top of the column. Purified trioxane was taken out from the bottom of the rectification column 14 via a conduit 20. Example 2 n-heptane (first solvent) in Example 1
Trioxane was synthesized and purified in the same manner as in Example 1, except that the flow rate was 51 g/hour instead of the circulating supply amount of 207 g/hour. Example 3 In Example 1, methylcyclohexane was used instead of n-heptane (first solvent), ethylene chloride was used instead of benzene (second solvent), and the crude trioxane supplied to the extraction column 10 and the second Positional relationship with the solvent, positional relationship between the extract and raffinate taken out from the extraction column 10, and the separator 1 of the rectification column 14
Trioxane was synthesized and purified in the same manner as in Example 1, except that the vertical relationship between the second solvent phase and the aqueous phase in Example 6 was reversed. In the above Examples 1 to 3, the compositions of the main conduit liquids related to the distillation column 3, extraction column 10, and rectification column 14 are shown in Table 1. In addition, Table 1 also lists the presence or absence of paraformaldehyde adhesion to the condenser and the amount of steam required to obtain 1 ton of purified trioxane.

[Table] Comparative Example 1 Trioxane was produced and purified in the same manner as in Example 1, except that the vapor distilled from the distillation column 3 was directly condensed without using the first solvent.
At this time, when the flow rate of the reflux material continuously supplied to the top of the distillation column 3 was adjusted to make the trioxane concentration of the distillate 54% by weight, the reflux ratio was required to be 6 or more. After operating the apparatus continuously for 12 hours, the apparatus was opened and inspected, and paraformaldehyde was found to be attached to the wall of the condenser 5.
Further, the amount of steam required to obtain 1 ton of purified trioxane with a composition ratio of 99.9% by weight or more was 8.9 t. From the above results, according to the manufacturing method of the present invention,
It was confirmed that highly pure trioxane could be obtained efficiently and that the apparatus was not contaminated by paraformaldehyde. Furthermore, when the concentration and outflow amount of trioxane distilled from the top of the distillation column 3 were fixed, the energy consumption in the condenser 5 was calculated and investigated from cooling water, etc., and it was found that the production method of the present invention It was found that the manufacturing method of Comparative Example 1 resulted in a savings of about 75%.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing the steps of an embodiment of the present invention. 2... Reactor, 3... Distillation column, 5, 16... Condenser, 6, 17... Separator, 10... Extraction column, 1
4... Rectification column, 1, 4, 7, 8, 9, 11, 1
2, 13, 15, 19, 20... Conduit.

Claims (1)

[Claims] 1. A method for producing trioxane, which comprises the following steps (1), (2), and (3). Step (1) Heating an aqueous solution of formaldehyde in the presence of an acid catalyst, the generated steam has a boiling point of 60 to 110
℃ and is in gas-liquid contact with a first solvent capable of azeotroping with trioxane, trioxane is distilled out as an azeotropic mixture with the first solvent, and the distilled vapor is then cooled and condensed to form a first solvent. A step of phase separation into a solvent phase and a crude trioxane phase. Step (2) All or part of the crude trioxane obtained in Step (1) is converted into a liquid by using a second solvent that is insoluble or poorly soluble in water, is azeotropic with water, and has a boiling point lower than that of trioxane. The process of performing extraction and extracting trioxane. Step (3) A step of separating trioxane from the extract obtained in step (2).