JP3322807B2 - Method for producing trioxane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a practical and economical method for producing trioxane, which is a raw material of polyoxymethylene, from an aqueous formaldehyde solution.

[0002]

BACKGROUND OF THE INVENTION Trioxane, a cyclic trimer of formaldehyde, is generally synthesized by heating an aqueous formaldehyde solution in the presence of an acid catalyst. At this time, it is known that the equilibrium concentration of trioxane in the liquid phase is only about 2 to 4% by weight even when the concentration of the starting formaldehyde aqueous solution is 30 to 70% by weight, and a large amount of formaldehyde remains unreacted. ing. Therefore, in order to obtain purified trioxane, it is necessary to first separate the reaction product containing trioxane from the acid catalyst, and then separate and purify trioxane from formaldehyde and water. Conventionally, as a specific method for producing such trioxane, Japanese Patent Publication No.
The publication discloses that a 30 to 70% by weight aqueous solution of formaldehyde is heated and reacted in the presence of a liquid acid catalyst such as sulfuric acid,
A method is disclosed in which a distillate containing trioxane, formaldehyde and water is separated from a liquid acid catalyst by distillation, and then trioxane is separated and purified from the distillate by a method such as solvent extraction. However, such a method using a liquid catalyst such as sulfuric acid as a catalyst for synthesizing trioxane has a problem in that a large amount of energy is required because an operation such as distillation is required to separate a component containing trioxane from the catalyst. On the other hand, as a method for facilitating the separation of the reaction product containing trioxane from the catalyst and reducing the energy required for this, various solid acids such as organic solid acids such as strongly acidic cation exchange resins and zeolites are used as catalysts. And the like, a method using an inorganic solid acid has been proposed. Further, as an economical method of purifying trioxane after separating a reaction product containing trioxane from a solid acid catalyst, a method of directly purifying trioxane by solvent extraction from the solution has been proposed (JP-A-4-49250). JP-A-6-73046). According to such a method,
There is an advantage that substantially no energy is required for separating the reaction product from the catalyst. However, as a result of additional tests by the present inventor, when the above-described method for producing trioxane using a solid acid catalyst was directly applied to an actual plant, it was practically impossible to perform stable operation for a long period of time. That is, as described above, the equilibrium concentration of trioxane when synthesizing trioxane from an aqueous formaldehyde solution in the presence of an acid catalyst is low, and a large amount of formaldehyde remains unreacted in the aqueous solution, so that a desired amount of trioxane is synthesized. Therefore, it is necessary to contact a large amount of formaldehyde aqueous solution with the solid acid catalyst, and it is necessary to collect a large amount of unreacted formaldehyde aqueous solution and reuse it as a raw formaldehyde aqueous solution for trioxane synthesis. However, the above-described method has a problem that the activity of the solid acid catalyst rapidly decreases in a short period of time, and accordingly, the amount of trioxane produced decreases, making it difficult to stably obtain a desired amount of trioxane. . In addition, in a short period of time, the pressure loss in the reactor containing the solid acid catalyst may increase or a drift may occur, which may cause a problem that it is difficult to supply the formaldehyde aqueous solution at a stable flow rate and to secure a stable trioxane generation amount.

[0003]

Means for Solving the Problems The present inventor has solved such a problem when synthesizing trioxane from an aqueous formaldehyde solution using a solid acid catalyst, and is capable of operating stably for a long period of time, and is practical and economical. As a result of intensive studies for the purpose of providing a method for producing trioxane, the present inventors have elucidated the factors causing such problems and found an effective solution thereof, and have reached the present invention. That is, the invention of claim 1 of the present invention uses, in producing trioxane from an aqueous formaldehyde solution, a production apparatus consisting of three functional steps, and mainly using a substance having an ion exchange ability in the first functional step. In the second functional step, an initial reaction of synthesizing trioxane is mainly performed from a formaldehyde aqueous solution from which the metallic impurities have been removed using a solid acid catalyst, and a solid acid catalyst is used in a third functional step. And performing a reaction for increasing the trioxane concentration to a substantially equilibrium concentration. The invention according to claim 2 is the invention according to claim 1, wherein the substance having ion exchange ability in the first functional step and the solid acid catalyst in the second and third functional steps are both strongly acidic cation exchange. This is a method for producing a resin, trioxane. A third aspect of the present invention is the method for producing trioxane according to the second aspect, wherein the functions of the apparatus in the three functional steps are continuously operated while mutually exchanging the functions. The invention according to claim 4 is the method for producing trioxane according to claim 1, wherein the apparatus in each of the three functional steps is constituted by one or more columns. A fifth aspect of the present invention is a method for producing trioxane according to the first aspect, wherein the operations in the three functional steps are all performed under an upward flow of an aqueous formaldehyde solution. The invention of claim 6 is the method for producing trioxane according to claim 1, wherein in the second functional step, the initial reaction is performed until the concentration of trioxane becomes 20 to 90% of the equilibrium concentration. In the invention of claim 7, in producing trioxane from an aqueous formaldehyde solution, three or more devices filled with a solid acid having ion exchange ability are provided, and any three of the devices are assigned different functions. A method for producing trioxane, comprising synthesizing trioxane while changing a sharing function after a predetermined time has elapsed. According to the invention of claim 8, in claim 7, the functions to be shared are a function of removing metal impurities in the aqueous formaldehyde solution, an initial reaction function of trioxane synthesis, and a reaction function of increasing the trioxane concentration to a substantially equilibrium concentration. This is a method for producing trioxane.

[0004]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, before solving the above-mentioned problems in the production of trioxane using a solid acid catalyst, the present inventor deeply studied the factors causing such problems,
Clarified. That is, according to the study by the present inventors,
The formaldehyde aqueous solution used in the production of trioxane in a practical plant was found to contain several ppb to several tens of ppm of metal ions. Was found to have a very significant effect on the synthesis of trioxane. More specifically, as described above, when trioxane is synthesized from an aqueous formaldehyde solution in the presence of an acid catalyst, the equilibrium concentration of trioxane is low. Yes, and
It is necessary to collect a large amount of formaldehyde aqueous solution remaining unreacted and reuse it as an aqueous formaldehyde solution for synthesizing trioxane. It is eluted from the apparatus or piping in the process or in the process of storage, transfer, concentration, etc. On the other hand, the solid acid used as a catalyst is a substance having an ion exchange ability, and adsorbs and deactivates metal ions at the acid point by ion exchange, deteriorating the function as an acid catalyst for synthesizing trioxane. It will not withstand use. As described above, it was surprising that the presence of a trace amount of metal ions in the aqueous formaldehyde solution was a fatal factor that hindered stable operation when considering a practical production process of trioxane. Also, according to further studies by the present inventors,
The higher the concentration of the raw formaldehyde aqueous solution, the easier it is to generate paraform, which is a solid formaldehyde low polymer. It has also been found that pressure loss increases, an unstable flow rate, drift occurs, and the like, which is a factor that hinders long-term stable operation. The present invention has been made as a result of earnestly examining the solution based on the elucidation of the cause and the knowledge, and as described above, in producing trioxane from an aqueous formaldehyde solution, using a production apparatus including three functional steps. In the first functional step, the metal impurities in the aqueous formaldehyde solution are mainly removed by using a substance having ion exchange ability, and in the second functional step, the metal impurities are mainly removed from the aqueous formaldehyde solution from which the metallic impurities have been removed by using a solid acid catalyst. An initial reaction of the synthesis of trioxane is performed, and a reaction for increasing the concentration of trioxane to a substantially equilibrium concentration using a solid acid catalyst in a third functional step is performed. Achieve long-term continuous stable operation by performing continuous operation while exchanging the functions of each other. A.

As the aqueous formaldehyde solution for producing trioxane, an aqueous formaldehyde solution produced according to a conventional method, a purified, concentrated or diluted formaldehyde aqueous solution, a recovered unreacted formaldehyde aqueous solution, and the like are used. These may be used in combination. The concentration of the formaldehyde aqueous solution used is not particularly limited, but is usually 30 to 80.
%, Preferably 50 to 70% by weight.

In the present invention, such an aqueous formaldehyde solution is first subjected to a first functional step, and metal impurities in the aqueous formaldehyde solution are mainly removed using a substance having an ion exchange ability. Here, the substance used for removing the metal impurities is not particularly limited as long as it has ion exchange ability. For example, many substances exemplified as solid acids in the second function step described later can be used. Among them, a cation exchange resin is preferable. The number of towers in the first functional step is not particularly limited. The residence time in the first functional step is sufficient for mainly absorbing and removing metal impurities in the raw material formaldehyde aqueous solution.
Although depending on the operating conditions and the like, for example, when a strongly acidic cation exchange resin is used, a sufficient effect is usually obtained in 1 minute to 5 minutes. If the residence time is too long, the amount of formic acid as a by-product increases, which may have an undesirable effect on the synthesis of trioxane in the subsequent second and third functional steps. In addition, the flow direction of the raw material formaldehyde aqueous solution in the first functional step may be either upward flow or downward flow. The linear velocity is preferably 5 to 50 m / h, though it depends on the substance having ion exchange capacity to be used. If the linear velocity is less than 5 m / h, the tower cross-sectional area of the apparatus becomes large compared to the throughput, there is a possibility of drift, and it may be difficult to achieve the initial purpose. If it exceeds 50 m / h, the pressure loss increases, and it may be difficult to maintain the flow velocity.

Next, the aqueous formaldehyde solution from which metal ions have been mainly removed in the first functional step
And the initial reaction of trioxane synthesis is carried out by the solid acid catalyst. The solid acid used here may be either an organic solid acid or an inorganic solid acid. As organic solid acids, sulfonic acid groups, ion exchange resins having fluoroalkanesulfonic acid groups, etc., as inorganic solid acids, acid clay, silica, alumina, silica alumina,
Alumina boria, inorganic oxide composites such as zeolite,
Alternatively, an example in which a solid substance is impregnated with sulfuric acid, phosphoric acid, boric acid or the like is exemplified. Among them, the above-mentioned ion exchange resins which are organic solid acids are preferred, and particularly preferred are strongly acidic cation exchange resins. This is because the solid acid used in the present reaction system is used in an aqueous formaldehyde solution, and is preferably a Bronsted acid which maintains its activity as an acid in water, and preferably has no acid group outflow in water. In the present invention, the apparatus configuration of the second functional step is not particularly limited, but it is composed of one column in consideration of the balance between the synthesis efficiency of trioxane and the construction cost, and is filled with a solid acid and used. Is preferred. In the present invention, there are no particular restrictions on the operating conditions or the amount of trioxane generated in the second functional step,
In order to produce trioxane practically and economically, in the second functional step, the trioxane concentration is increased to 20 to 90% of the equilibrium concentration with respect to the supplied formaldehyde aqueous solution concentration. Preferably, an initial reaction is performed. The residence time required for this depends on the type of solid acid used, the reaction temperature, etc., but when operating at a reaction temperature of about 80 to 110 ° C. using a strongly acidic cation exchange resin, it is generally about 5 minutes. ~ 25 minutes.
The reaction to produce trioxane from an aqueous formaldehyde solution is an equilibrium reaction, and attention should be paid to the setting of the residence time, since applying a residence time longer than the equilibrium reaction arrival time will lead to an increase in the production of by-products such as formic acid. There is a need. Specifically, the preferred residence time can be easily confirmed by a simple experiment according to the type of solid acid used and the reaction conditions. The amount of the solid acid used is determined by setting the residence time. Also in the second functional step, the flow direction of the aqueous formaldehyde solution is an upward flow.
Regardless of the downward flow. The linear velocity depends on the type of solid acid used. However, in the case of an upward flow, the solid acid in the column flows to facilitate the outflow of paraform. / H is preferred.

After the initial reaction of the synthesis of trioxane is performed in the second functional step, the reaction for increasing the trioxane concentration to a substantially equilibrium concentration using a solid acid catalyst is performed in the third functional step. Although the apparatus configuration of the third functional step is not particularly limited, it is composed of one tower in consideration of the balance between the synthesis efficiency of trioxane and the construction cost, and is similar to the one exemplified in the third functional step. It is preferable to use the solid acid after filling. There are no particular restrictions on the operating conditions or the amount of trioxane produced in the third functional step, but in order to produce practically and economically trioxane, the trioxane is supplied in the second functional step. It is preferable to carry out the initial reaction under the condition that the concentration of trioxane is increased until the concentration becomes 20 to 90% of the equilibrium concentration with respect to the concentration of the aqueous formaldehyde solution. The residence time required for this depends on the type of solid acid used, the reaction temperature, etc., but when operating at a reaction temperature of about 80 to 110 ° C. using a strongly acidic cation exchange resin, it is generally about 5 minutes. ~ 25 minutes. The reaction to produce trioxane from an aqueous formaldehyde solution is an equilibrium reaction, and attention should be paid to the setting of the residence time, since applying a residence time longer than the equilibrium reaction arrival time will lead to an increase in the production of by-products such as formic acid. There is a need. Specifically, the preferred residence time can be easily confirmed by a simple experiment according to the type of solid acid used and the reaction conditions. The amount of the solid acid used is determined by setting the residence time. Also in the third functional step, the flow direction of the aqueous formaldehyde solution may be either upward flow or downward flow. In addition, the linear velocity depends on the type of solid acid used, but in the case of an upward flow, the solid acid in the column flows to facilitate the outflow of paraform,
3-15m / so that the developing tank for solid acid does not become too wide
h is preferred.

In the present invention, specific examples of the device type used in the first function step, the second function step, and the third function step as described above include a filling tank type, a pipe tube type, and the like.
Examples include a cage type, a fluidized tank type, and a step tower type, and are not limited thereto. Among them, a filling tank type and a fluidized tank type are preferable.

Regarding the equipment conditions and operating conditions, the properties (formaldehyde concentration, contained metal impurities, contained paraform suspension) of the raw formaldehyde aqueous solution and the treatment amount, the type of solid acid, the amount of solid acid used, and the solid acid In consideration of the metal adsorption rate and the trioxane generation rate by the solid acid catalyst, the design may be made based on the conditions described above.
In particular, the residence time in each device is determined based on the concept of dividing the column into individual columns on the basis of the metal adsorption rate and the trioxane generation rate by the solid acid catalyst, and the required solid acid amount is determined from the formaldehyde aqueous solution treatment amount. . In the present invention, it is preferable to perform a continuous operation while mutually exchanging the functions of the apparatus in the three function steps. That is, for example, in the first functional step, the performance of a substance having ion exchange ability deteriorates over time due to adsorption of metal impurities, and regeneration is required. In addition, paraform may accumulate and accumulate in the process, which may cause trouble in operation. In order to cope with such a situation and enable continuous operation, in the present invention, continuous operation is performed while exchanging the functions of the devices in the three functional steps. Specifically, the apparatus types in the first to third functional steps are the same, and usually, the first apparatus (impurity removal tower), the second apparatus (initial reaction tower), and the third apparatus (final reaction tower) And the first apparatus (impurity removal tower) is deactivated, the first apparatus is regenerated, the second apparatus is used as the impurity removal tower, and the third apparatus is used as the initial reaction tower. The synthesis is continued further by using the first apparatus after the above as the final reaction tower and circulating each other.

In each of the first to third functional steps, it is preferable to carry out the operation, that is, the synthesis of trioxane, under the upward flow of the raw formaldehyde aqueous solution. Thereby, even if paraform is brought into the apparatus or occurs in the apparatus, troubles due to the paraform can be prevented, and the paraform can be easily discharged from the tower. In the process for producing trioxane of the present invention, it is generally preferable not to add a substance known as a paraform formation inhibitor. Although the addition of such a substance prevents the generation of paraform, there is a problem in the separation of the added component from the reaction system.Furthermore, these additives accumulate in the system and not only prevent the generation of paraform, There is a problem that the production of trioxane is also inhibited.

In the present invention, the reaction product obtained by the above-mentioned method for producing trioxane is a mixture containing a large amount of formaldehyde, water and a small amount of impurities in addition to trioxane. In purifying trioxane from this reaction product, a known method can be used. Among them, a method of extracting trioxane from a reaction product with a high boiling point solvent and then separating trioxane by distillation is preferable. In addition, a large amount of unreacted formaldehyde is recovered in the form of an aqueous solution and, if necessary, subjected to a treatment such as concentration, and then is generally reused for the synthesis of trioxane.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The apparatus, raw material formaldehyde aqueous solution, operating conditions and evaluation items used in the following Examples, Comparative Examples and Reference Examples are as follows. (1) Apparatus A column with an inner diameter of 2 cm and a height of 200 cm with a heat retaining jacket A glass filter with a hole diameter of 0.05 mm at the inlet and outlet (hereinafter referred to as “tower”). The experimental apparatus system is as shown in FIG.

[0014] (3) Solid acid used Diaion PK216 which is a strongly acidic cation exchange resin
(Mitsubishi Chemical Corporation) (4) Operating conditions Formaldehyde aqueous solution flow rate (setting) 3000cm ³ / h Tower line speed 10m / h Temperature 100 ° C (5) Evaluation items Trioxane concentration and metal ion concentration of the solution discharged from the device Actual flow rate of formaldehyde aqueous solution Presence / absence of generation and accumulation of paraform (visual observation) Example 1 Using the experimental apparatus system shown in FIG.
The tank was charged with 200 cc and operated in an upward flow. At first, the function of the first column is the impurity removal column, the function of the second column is the first reaction column for producing trioxane (initial reaction tower), and the function of the third column is the second reaction column for producing trioxane, and the function of the fourth column is A third reaction column for producing trioxane (final reaction column) was used. 1 week (168 hours)
Thereafter, the first tower was stopped, the second tower was used as an impurity removal tower, the third tower was used as a trioxane-producing first reaction tower (initial reaction tower), the fourth tower was used as a trioxane-producing second reaction tower, and the first tower was used as a fifth tower. After a regeneration and washing treatment (2 hours) with 2% hydrochloric acid and warm water, a third reaction tower (final reaction tower) was obtained. The operation was further continued, and the functions of these towers were similarly circulated every week, and the operation was continued for 8 weeks. Paraholm was partially suspended in the tower, but did not shut down. Table 1 shows the results. Example 2 Using the experimental apparatus system shown in FIG.
It was charged with 270 cc and operated in a down flow. At first, the function of the first column is an impurity removal tower, the function of the second column is a first reaction tower for producing trioxane (initial reaction tower), and the function of the third column is a second reaction tower for producing trioxane (final reaction tower). The fourth tower was a dormant tower. After one week (168 hours), Tower 1 was shut down and
The tower is an impurity removal tower, the third tower is a first reaction tower for producing trioxane (initial reaction tower), the fourth tower is a second reaction tower for producing trioxane (final reaction tower), and the first tower is regenerated with 5% hydrochloric acid and hot water. After the washing treatment (2 hours), the tower was taken as a stop tower. The operation was further continued, and the functions of these towers were similarly circulated every week, and the operation was continued for 8 weeks. Paraholm was partially accumulated in the tower, but did not shut down. Table 2 shows the results. Comparative Example 1 Under the same experimental apparatus system and operating conditions as in Example 1, each column was continuously operated for 8 weeks without performing functional circulation. Table 3 shows the results. Comparative Example 2 Using the same experimental apparatus system as in Example 2, the fourth column was stopped, and the continuous operation from the first column to the third column was continuously performed for 8 weeks without functional circulation. Table 4 shows the results.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

In contrast to Examples 1 and 2, in Comparative Example 1, as shown in Table 3, the reaction rate gradually decreased. In Comparative Example 2, as shown in Table 4, after the third week, the first
Paraform accumulated on the resin of the column, the flow rate decreased, and as the operation continued, the reaction rate decreased.

[0020]

As described above, according to the present invention, in producing trioxane from formaldehyde aqueous solution using a solid acid catalyst, continuous and stable operation is possible, and a conventional liquid catalyst such as sulfuric acid can be used. Energy saving can be achieved as compared with the method used.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an actual continuous production apparatus for trioxane used in an embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C07D 323/06 B01J 31/10 C07B 61/00 300

Claims (8)

(57) [Claims] In producing trioxane from an aqueous formaldehyde solution, a production apparatus having three functional steps is used, and in a first functional step, metal impurities in an aqueous formaldehyde solution are mainly removed by using a substance having ion exchange capacity. In the second functional step, an initial reaction for the synthesis of trioxane is mainly performed from an aqueous formaldehyde solution from which metal impurities have been removed using a solid acid catalyst, and the equilibrium concentration is substantially increased to a substantially equilibrium concentration using a solid acid catalyst in a third functional step. A process for producing trioxane, comprising performing a reaction for increasing the concentration of trioxane. 2. The trioxane according to claim 1, wherein the substance having an ion exchange ability in the first function step and the solid acid catalyst in the second and third function steps are both strongly acidic cation exchange resins. Manufacturing method. 3. The functions of the device in three functional steps are:
The method for producing trioxane according to claim 2, wherein the continuous operation is performed while mutually exchanging functions. 4. The apparatus in each of the three functional steps has one
The method for producing trioxane according to claim 1, wherein the method comprises the above-mentioned tower. 5. The operation in each of the three functional steps is performed under an upward flow of an aqueous formaldehyde solution.
A process for producing the described trioxane. 6. The process for producing trioxane according to claim 1, wherein in the second functional step, the initial reaction is carried out until the concentration of trioxane reaches 20 to 90% of the equilibrium concentration. 7. In the production of trioxane from an aqueous formaldehyde solution, three or more devices filled with a solid acid having ion exchange ability are provided, and any three of them are assigned different functions, and a predetermined time elapses. Thereafter, a method for producing trioxane, which comprises synthesizing trioxane while changing a shared function. 8. The process for producing trioxane according to claim 7, wherein the functions to be shared are a function of removing metal impurities in the aqueous formaldehyde solution, an initial reaction function of trioxane synthesis, and a reaction function of increasing the trioxane concentration to a substantially equilibrium concentration. .