WO2014017203A1 - Method and device for producing trioxane - Google Patents

Abstract

The objective of the present invention is to increase the yield and selectivity of trioxane and to minimize the amount of unreacted formaldehyde when producing trioxane from an aqueous formaldehyde solution. In this production method, formaldehyde gas is generated by pyrolyzing a hemiformal concentrate obtained from an aqueous formaldehyde solution and alcohol, and using a solid acid catalyst, reaction generated gas containing trioxane is obtained from the formaldehyde gas. Then, by contacting the reaction generated gas with an organic solvent, the trioxane and the unreacted formaldehyde gas that are contained in the reaction generated gas are separated into gas and liquid, and the separated unreacted formaldehyde gas is circulated and recycled by being added to the system for obtaining the reaction generated gas.

Description

Method and apparatus for producing trioxane

The present invention relates to a method and an apparatus for producing trioxane.

Trioxane, a cyclic trimer of formaldehyde, is a raw material monomer widely used in the production of polyoxymethylene (POM) resin, and its production method has been established for a long time. For example, a non-volatile acid represented by sulfuric acid, phosphoric acid and the like is allowed to act on a high-concentration formaldehyde aqueous solution in a liquid phase to produce trioxane, and this trioxane is cooked with water containing formaldehyde, And a step of purifying the above trioxane by extraction with an organic solvent or recrystallization. However, the reaction equilibrium concentration in the liquid phase is very low. Therefore, the equilibrium concentration to trioxane is increased by vaporizing the reaction product from the reaction system, but vaporization of the reaction product containing water generally involves a great amount of energy consumption.

Therefore, a method for synthesizing trioxane directly from the formaldehyde gas in the gas phase has been studied for a long time. However, most of them focus on the gas phase trimerization reaction and the solid acid catalyst. The gas phase synthesis of trioxane from the raw material formaldehyde, the separation and recovery of the reaction products, the unreacted formaldehyde gas It is not considered as a continuous process including recycling and recycling.

For example, in Patent Documents 1 to 3, when formaldehyde gas is reacted in a gas phase, as a source of formaldehyde gas as a raw material, a method by thermal decomposition of paraformaldehyde, α-polyoxymethylene, or vaporization of an aqueous formaldehyde solution is used. Is stated. However, since water is present in the raw material at a level of several percent to several tens of percent, this is not only disadvantageous for the gas phase reaction, but the catalyst is deactivated by a large amount of water, and the formaldehyde gas that is the raw material is repolymerized. There is a problem such as easy to occur (paraformation). Furthermore, the details of the separation of the obtained reaction products are not described, and therefore, the distribution rate and recovery rate of unreacted formaldehyde gas are completely unknown, and details as a continuous production process are clear. It is not something to be done.

Further, in Patent Document 4, a reaction process is illustrated with a specific example of a catalyst to be used for trioxane gas phase synthesis from formaldehyde. According to this document, it is described that unreacted formaldehyde gas at the outlet of the reactor is separated and recovered and recycled to the reactor again. However, paraformaldehyde or formaldehyde aqueous solution is also used here as a formaldehyde gas supply source, and there is a demerit that the reaction system contains a lot of moisture. Further, details of the reaction product gas separation and recovery method are unknown, and the recovery rate is also unknown.

Patent Document 5 describes a production method for gas phase synthesis of trioxane using a solid phosphoric acid catalyst. Here, the main purpose is to use formaldehyde gas having a low water content, but it is described that the crude formaldehyde is purified or a non-oxidizing methanol dehydrogenation step is used as the method. However, regarding the purification of crude formaldehyde, the production method including the raw material is unknown, and there is also a description that a metal sodium catalyst is used for methanol dehydrogenation, which is problematic in terms of safety from an industrial point of view. In addition, the methanol dehydrogenation method cannot be said to have been sufficiently established in terms of reaction conversion rate and selectivity, and has a problem in terms of methanol usage, and is incorporated into a manufacturing process including gas phase synthesis of trioxane. There are still many difficulties.

Japanese Patent Publication No.40-12898 Japanese Patent Publication No.40-20552 Japanese Patent Publication No. 44-30735 US Pat. No. 3,496,192 JP 2001-11069 A Japanese Patent Laid-Open No. 50-62921

A number of methods for synthesizing trioxane from formaldehyde gas in the gas phase have been disclosed so far, and many solid acid catalysts relating to gas phase synthesis have been exemplified. In addition, a part of the past patent document describes a manufacturing process in which unreacted formaldehyde gas is recovered after trioxane gas phase synthesis and circulated and recycled to the reactor. However, how to separate unreacted formaldehyde gas from trioxane is hardly exemplified by specific methods.

Therefore, a comprehensive trioxane gas-phase synthesis process that includes synthesizing trioxane in the gas phase after efficiently preparing formaldehyde gas from an aqueous formaldehyde solution, and further including separation and recovery methods after synthesis and circulation recycling of unreacted formaldehyde gas It is difficult to say that the manufacturing method mentioned in the above has been shown with specific examples in the past. Including this, the establishment of a comprehensive process system for trioxane vapor phase synthesis that can greatly improve the disadvantages of conventional trioxane liquid phase synthesis has been demanded.

The present invention has been made for the purpose of solving the above problems, and discloses a continuous production process including separation and recovery and recycling steps in the gas phase synthesis of trioxane using an aqueous formaldehyde solution as a starting material. It is. Furthermore, high yield, high selectivity of trioxane by gas phase reaction, efficient separation / recovery process and recycling of unreacted formaldehyde are more efficient than conventional methods (liquid phase reaction). A process for the gas phase synthesis of trioxane is provided.

The inventors of the present invention have made extensive studies to optimize the processes including the reaction process and separation / recovery process when synthesizing trioxane from an aqueous formaldehyde solution in the gas phase. As a result, they have not only obtained trioxane in a high yield and high selectivity, but also found a trioxane production method and apparatus having a high formaldehyde usage rate, and have completed the present invention. More specifically, the present invention provides the following.

(1) The present invention provides a first step of obtaining hemiformal from an aqueous formaldehyde solution and alcohol, a second step of generating formaldehyde gas by thermally decomposing the hemiformal, and supplying the formaldehyde gas to a trioxane generator, A third step of gas-phase synthesis of a reaction product gas containing trioxane from the formaldehyde gas using a solid acid catalyst; and contacting the reaction product gas with an organic solvent to convert trioxane contained in the reaction product gas into the organic solvent A fourth step of discharging unreacted formaldehyde gas contained in the reaction product gas to the outside in a gas phase, and the unreacted formaldehyde gas separated in the fourth step, in the third step Recycled to be recycled as formaldehyde gas Including a cycle step, the, trioxane production method.

(2) Moreover, the said alcohol of this invention is a trioxane manufacturing method as described in (1) which is 1 type, or 2 or more types of combinations selected from the monool, diol, or triol whose boiling point is 190 degreeC or more. .

(3) Further, the present invention is the trioxane production method according to (1) or (2), wherein the solid acid catalyst contains phosphoric acid supported on a siliceous inorganic support.

(4) Moreover, this invention shows ratio of the mass per unit time of the formaldehyde gas supplied to the said trioxane production | generation apparatus in the said 3rd process, and the mass of the said solid acid catalyst with which the said trioxane production | generation apparatus is filled. the value of the mass space velocity WHSV is 1 / ^{50h -1} over ^{1h -1} or less, trioxane production method according to any one of (1) (3).

(5) In the third step, the solid acid catalyst is filled in a multi-tubular fixed bed reactor in the third step, and is circulated in the formaldehyde gas obtained in the second step and the circulation recycling step. Contacting the recycled unreacted formaldehyde gas with the solid acid catalyst in a heterogeneous system, and continuously extracting trioxane from the fixed bed reactor in a gas phase state to perform gas phase synthesis of trioxane ( The method for producing trioxane according to any one of 1) to (4).

(6) Moreover, this invention is a trioxane manufacturing method in any one of (1) to (5) whose said organic solvent is 1 or more selected from benzene, toluene, xylene, ethylbenzene, and diethylbenzene.

(7) In the fourth step, the reaction product gas containing the trioxane synthesized in the third step and the unreacted formaldehyde gas unreacted in the third step is used as the boiling point of the trioxane. The trioxane production method according to any one of (1) to (6), wherein the trioxane is continuously supplied to a separation apparatus adjusted to the following temperature.

(8) Moreover, this invention is a trioxane manufacturing method as described in (7) with which the said separation apparatus is equipped with the absorption tower by any of a liquid film type, a droplet type, or a bubble type.

(9) Further, in the present invention, the absorption tower is an absorption tower of the liquid film type, and the absorption tower includes a packed tower filled with a filler, and in the fourth step, the organic solvent and the By bringing the reaction product gas into alternating current or co-current contact, trioxane contained in the reaction product gas is absorbed in the organic solvent, and the unreacted formaldehyde gas contained in the reaction product gas is kept in a gas phase and the separation device Is a trioxane production method as described in (8).

(10) Moreover, this invention is a trioxane manufacturing method in any one of (7) to (9) whose temperature inside the said separation apparatus is 60 degrees C or less.

(11) Moreover, this invention is a trioxane manufacturing method in any one of (7) to (10) whose pressure inside the said separation apparatus is 1 kgf / cm < ² > or less by a gauge pressure.

(12) In addition, the present invention uses a hemi-formal generator for obtaining hemi-formal from an aqueous formaldehyde solution and alcohol, a formaldehyde gas generator for thermally decomposing the hemi-formal to generate formaldehyde gas, and a solid acid catalyst. A trioxane generator for vapor-phase synthesis of a reaction product gas containing trioxane from the gas, and by contacting the reaction product gas with an organic solvent, the trioxane contained in the reaction product gas is absorbed in the organic solvent, A trioxane production apparatus comprising: a separation device that discharges unreacted formaldehyde gas contained in a gas phase to the outside; and a circulation device that circulates the unreacted formaldehyde gas to the trioxane generator.

According to the present invention, since formaldehyde gas is prepared from the hemi-formal method, water is sufficiently eliminated from the reaction system in advance as a process, and high yield and selectivity can be realized even in trioxane gas phase synthesis. It is. Furthermore, it is possible to effectively separate and recover unreacted formaldehyde gas by using an organic solvent with high trioxane solubility in the separation and recovery process of the reaction product gas, and to circulate and recycle this unreacted formaldehyde. As a result, the use rate of formaldehyde is increased, and it is possible to realize a process that can contribute to energy reduction during the production of trioxane.

It is the schematic which shows the trioxane manufacturing apparatus which concerns on this invention.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. can do.

<Trioxane production device 1>
FIG. 1 is a schematic view showing a trioxane production apparatus 1 according to the present invention. The trioxane production apparatus 1 uses a hemi-formal generator 2 that generates hemi-formal from an aqueous formaldehyde solution (formalin) and alcohol, a formaldehyde gas generator 3 that thermally decomposes the hemi-formal to generate formaldehyde gas, and a solid acid catalyst. A trioxane generator 4 that generates a reaction product gas containing trioxane from the formaldehyde gas, a separation device 5 that separates trioxane and unreacted formaldehyde gas from the reaction product gas, and this unreacted formaldehyde gas into the trioxane generator 4. And a circulation device 6 that circulates.

[Hemi formal generator 2]
In the hemi-formal production | generation apparatus 2, the 1st process which produces | generates a hemi-formal concentrate is performed by reacting and dehydrating formaldehyde aqueous solution and alcohol. The hemi-formal generator 2 is composed of a mixing tank 2A for mixing an aqueous formaldehyde solution and alcohol to obtain a hemi-formal aqueous solution, and a vacuum dehydration tower 2B for concentrating the aqueous hemi-formal solution by dehydration to obtain a hemi-formal concentrate having a low water content. The In the present embodiment, the hemi-formal concentrate refers to a reaction product of an aqueous formaldehyde solution and alcohol, which is obtained by mixing the aqueous formaldehyde solution and alcohol at a predetermined ratio and then dehydrating and concentrating under reduced pressure.

In the present embodiment, by adopting the hemi-formal method, it is possible to effectively remove moisture from the system in advance, so it becomes possible to prepare formaldehyde gas with a low water content in the post-process, This is advantageous in terms of reaction yield, selectivity and catalyst lifetime in trioxane gas phase synthesis. Furthermore, in the separation process of trioxane and unreacted formaldehyde gas, it is very effective to adopt the hemi-formal method because the condensation of formaldehyde in the absorption / separation tower can be reduced by reducing the water content.

[Mixing tank 2A]
In preparation of the hemi-formal aqueous solution, first, the (A) formaldehyde aqueous solution and the (B) alcohol are mixed and reacted inside the mixing tank 2A. The reaction conditions are not particularly limited, and those similar to the reaction conditions of the aqueous formaldehyde solution and alcohol in the conventionally known hemi-formalization method can be employed. For example, the reaction temperature is preferably from room temperature (about 20 ° C.) to 90 ° C. Moreover, what is necessary is just to set suitably about reaction time according to the progress of reaction, etc. Further, the mixing ratio of the two is not particularly limited, but (A) the molar ratio of the hydroxyl group in the alcohol (B) to the aqueous formaldehyde solution is preferably 0.3 or more and 5.0 or less, preferably 0.5 or more. More preferably, it is 2.0 or less. If the alcohol is too small (0.3 or less), free formaldehyde increases in the aqueous hemi-formal solution, and the loss of formaldehyde increases when the vacuum / dehydration reaction is performed in the vacuum dehydration tower 2B. Further, in the case of excessive alcohol (5.0 or more), it is necessary to supply a large amount of hemi-formal for producing a certain amount of formaldehyde gas when the hemi-formal is pyrolyzed in the formaldehyde gas generator 3, and energy required for the pyrolysis This is not preferable because it is disadvantageous.

The alcohol species used for the preparation of the hemi-formal aqueous solution is not particularly limited, but is preferably selected according to one or a combination selected from mono, di, and triol having a boiling point of 190 ° C. or higher. When the boiling point of the alcohol is lower than 190 ° C., the dehydration / concentration of the hemi-formal aqueous solution in the vacuum dehydration tower 2B is not preferable because loss due to volatilization of the alcohol itself increases and a recovery operation is required. Further, since the alcohol is volatilized when the hemi-formal is pyrolyzed by the formaldehyde gas generator 3, it is not preferable in that it is necessary to install a cooler for the purpose of recovering the alcohol.

Examples of alcohol species having a boiling point of 190 ° C. or higher include methylpentanediol, hexanetriol, pentanediol, and methylbutanediol as hydrophilic alcohols. In particular, 3-methyl-1,5-pentanediol, 1,2,6-hexanetriol, 1,5-pentanediol or 3-methyl-1,3-butanediol can be preferably used. Examples of the hydrophobic alcohol include diethylpentanediol, ethylhexanediol, octanol and the like. In particular, as diethylpentanediol, 2,4-diethyl-1,5-pentanediol, 2,3-diethyl-1,5-pentanediol, 1,4-diethyl-1,5-pentanediol, 1,5- Examples thereof include diethyl-1,5-pentanediol. Examples of ethyl hexanediol include 2-ethyl-1,3-hexanediol, 3-ethyl-1,3-hexanediol, 4-ethyl-1,3-hexanediol, and the like.

In addition to the above, alkylene glycols, polyalkylene glycols, and the like used as known techniques for preparing hemiformal can also be applied. Examples of the alkylene glycols include diethylene glycol, triethylene glycol, and tetraethylene glycol. Examples of the polyalkylene glycols include polyethylene glycol having 5 or more ethylene oxide units, and polypropylene glycol and polytetramethylene glycol. A polyalkylene glycol derivative or the like can also be used. Polyalkylene glycol derivatives include block copolymers composed of oxyethylene and oxypropylene, oxytetraethylene, and the like, and polyalkylene glycols prepared using polyhydric alcohol or the like as a chain transfer agent.

Such alcohol can be produced by a general method. Moreover, you may purchase and use a commercial item.

[Vacuum dehydration tower 2B]
In the vacuum dehydration tower 2B, the hemi-formal aqueous solution obtained in the mixing tank 2A is concentrated by dehydration to obtain a hemi-formal concentrate having a low water content. The conditions of the vacuum dehydration tower 2B are not particularly limited, but it is preferable that the temperature and pressure are appropriately adjusted for the above dehydration / concentration conditions while taking into account the amount of residual water contained in the hemi-formal concentrate. Specifically, the temperature is preferably selected from the range of 50 ° C. or higher and 80 ° C. or lower, and the pressure is preferably selected at 50 mmHg or lower.

The hemi-formal concentrate after being concentrated by the vacuum dehydration tower 2B still contains a trace amount of water, but is approximately 1.0% by mass or less depending on the operating conditions of dehydration and concentration.

The concentration of the aqueous formaldehyde solution used for preparing the hemi-formal concentrate is not particularly limited, but is preferably 1% by mass or more and 80% by mass or less as formaldehyde.

[Formaldehyde gas generator 3]
In the formaldehyde gas generator 3, a second step of generating formaldehyde gas by thermally decomposing the hemi-formal concentrate is performed. High purity formaldehyde gas is obtained by this second step, and the technique is generally known as described in Patent Document 6. The temperature condition for the thermal decomposition is performed at a high temperature (normally 140 ° C. or higher) at which the hemi-formal bond can be broken, but can be appropriately adjusted in accordance with the operation pressure in the formaldehyde gas generator 3. In general, the range of 140 to 180 ° C. is appropriate. If the temperature is too low, the decomposition rate does not increase. Conversely, if the temperature is too high, problems such as volatilization and alteration of the alcohol constituting the hemi-formal occur. It is not preferable. The formaldehyde gas generator 3 is not particularly limited, and various tank-type, tube-type and tower-type thermal decomposition apparatuses and evaporators that are implemented in batch, semi-batch, and continuous systems may be used. it can.

Formaldehyde gas generated by thermal decomposition of hemi-formal can be used as it is as a raw material for gas phase synthesis of trioxane, but in order to prevent residual moisture and reduction, and volatilized alcohol from being mixed into the trioxane generator 4. It is also possible to further purify the formaldehyde gas by attaching a cooler (condenser, not shown) to the outlet side of the formaldehyde gas generator 3 to condense residual moisture and volatile alcohol components.

[Trioxane generator 4]
In the trioxane production | generation apparatus 4, the 3rd process of carrying out the gas phase synthesis | combination of the reaction product gas containing a trioxane from a formaldehyde gas is performed using a solid acid catalyst.

In the present invention, a hemi-formal concentrate is used as a formaldehyde gas raw material, and since the amount of water in the reaction system is small, the type of the solid acid catalyst is not particularly limited, but phosphoric acid supported on a siliceous inorganic carrier. It is desirable that the solid phosphoric acid catalyst contains.

The method for preparing the solid phosphoric acid catalyst is not particularly limited, and a generally known impregnation method, a preparation method by a sol-gel reaction, or the like can be used. Further, the carrier used for phosphoric acid support / immobilization is not particularly limited, but an inorganic carrier mainly composed of siliceous materials such as porous silica gel, silica alumina, diatomaceous earth, etc. is good, and one or a mixture selected from them. Are preferably used.

An example of a method for preparing a solid phosphoric acid catalyst used in the present invention is shown below, but is not limited to this method / procedure. First, commercially available orthophosphoric acid (85%) is diluted with water in the range of 0.5 to 50% concentration to obtain a supporting liquid. A predetermined amount of porous silica gel carrier is added and immersed therein. There is no particular problem if the immersion time is usually about 1 hour or longer. Although immersion temperature is not specifically limited, it is 80 degrees C or less, Preferably it is 50 degrees C or less. At the time of immersion, the support liquid and the carrier may be sufficiently mixed by stirring. Next, the support containing the supported liquid is taken out, drained, dried, and calcined at a specific temperature after drying to prepare the catalyst.

In addition to the solid acid catalyst obtained by the above preparation method, a commercially available or commercial solid acid catalyst can be used as it is. Also, the shape of the solid acid catalyst is not particularly limited, such as powder, particles, and pellets by molding, but the trioxane generator 4 is a fixed bed reactor, and gas phase synthesis is performed in this fixed bed reactor. When performing, a molded object is used preferably. There is no particular limitation on the shape of the molded product, for example, by various methods such as extrusion, tableting, spray drying, rolling granulation, granulation in oil, etc. Furthermore, the particle size of the molded body can be used in the range of about 0.5 to 6 mm.

When performing the above gas phase synthesis, the ratio of the mass per unit time of formaldehyde gas supplied to the trioxane generator 4 to the mass of the solid acid catalyst charged in the trioxane generator 4 (this is the mass space velocity WHSV [unit; h ^-1 ]) depends on the shape of the solid acid catalyst used, the amount of the acid component supported, and the reaction conditions, and may be adjusted as appropriate according to the trioxane yield. The value of WHSV (formaldehyde gas flow rate / catalyst mass) is preferably in the range of 1/50 to 1 h ⁻¹ . When WHSV is less than 1/50 h ⁻¹ , the catalyst weight is large with respect to the supplied formaldehyde gas, and there is a possibility that the conversion rate to trioxane corresponding to the added amount of the catalyst cannot be obtained, and the cost of the catalyst is low. It can be enormous. On the other hand, when the WHSV exceeds 1h ^-1, for formaldehyde gas amount supplied to the catalyst is large, reaction conversion of not take a contact time with the catalyst sufficient trioxane may be reduced.

As other reaction conditions, in view of the fact that this reaction is an exothermic equilibrium reaction, it is generally desirable that the temperature is low, but formaldehyde gas is condensed before and after the trioxane generator 4 and inside the trioxane generator 4. It is required to set the temperature so as to avoid the polymerization (paraformaldehyde production). Specifically, the temperature inside the trioxane generator 4 is preferably 80 to 120 ° C., more preferably 90 to 110 ° C. If the reaction temperature is too low, a sufficient reaction rate cannot be obtained, and polymerization of formaldehyde proceeds to cause precipitation in the catalyst layer, which is not desirable. On the other hand, if the temperature exceeds 120 ° C., the gas phase equilibrium concentration of trioxane is greatly reduced and side reactions increase, which is not preferable. The reaction pressure is not particularly limited, but it is preferably carried out in the range of normal pressure to 5 MPa.

The type and reaction type of the reactor used as the trioxane generator 4 are not limited, and flow-type reactions such as a batch type, semi-batch type, continuous flow type, fixed bed, fluidized bed, moving bed, etc. using a tank type reactor. However, since this reaction is an exothermic equilibrium reaction, it is desirable to efficiently remove heat from the catalyst layer using a fixed bed flow reactor. The fixed bed reactor is a multitubular tube reactor, and a heat medium circulates outside. It is important that the inner diameter per tube is not too large in order to enhance the temperature control and heat removal effect by the heat medium, and is preferably 50 mmφ or less. In a reactor exceeding 50 mmφ, a temperature gradient is likely to occur in the radial direction of the packed catalyst, and heat is easily stored inside the packing, which is disadvantageous for the reaction and is not preferable. Further, even if the inner diameter of the reactor tube is too small, inconvenience arises in filling the catalyst compact, so that the inner diameter is preferably at least 10 mmφ.

As for the flow method of formaldehyde gas to the trioxane generator 4, when the trioxane generator 4 is a fluidized bed type reactor, either an upward flow or a downward flow may be used. Be careful because there is a risk of blowing up the catalyst when the superficial velocity increases.

Further, in this embodiment, the type of gas used for the upward flow or the downward flow is not particularly limited, and can be performed under an inert gas stream such as nitrogen or argon.

[Separator 5]
In the separation device 5, a fourth step of separating trioxane and unreacted formaldehyde gas from the reaction product gas produced by the trioxane production device 4 is performed. As shown in FIG. 1, in this embodiment, trioxane contained in the reaction product gas is absorbed in an organic solvent using an absorption tower or the like to obtain a trioxane solution, while unreacted formaldehyde gas contained in the reaction product gas is removed. The phase is discharged to the outside of the separation device 5. The type of the absorption tower is not particularly limited, and may be any of a liquid film type, a droplet type or a bubble type.

Examples of liquid film types include packed towers, wet wall towers, liquid column towers, continuous ball towers, disk towers, etc., and as droplet types, spray towers (spray type absorption devices), various scrubbers, There are centrifugal absorption devices, fluidized bed packed absorption towers and the like. Furthermore, examples of the bubble type include a bubble tower, a stirring tower, a plate tower, and the like. Among these, a packed tower is preferably used in order to increase the contact area of gas and liquid and to realize efficient distribution of trioxane to the liquid phase side.

Also, in the case of a packed tower, various kinds of packings represented by Raschig rings can be filled inside. The material and shape of the filler are not particularly limited, and any material made of magnetic material, carbon, or steel, or a ring shape, saddle shape, or other various shapes can be used. Further, the size of the packing can be appropriately determined according to the column diameter of the packed column.

On the other hand, it is conceivable to separate the trioxane component from the unreacted formaldehyde gas by condensing the trioxane component using a condenser or the like. However, if the temperature inside the condenser is low, the trioxane component is condensed inside the condenser. This is not preferable because it easily solidifies, and the unreacted formaldehyde component is also easily solidified, and the separation of formaldehyde gas into the gas phase is greatly reduced. Further, even if the temperature in the condenser is increased, trioxane tends to escape to the overhead side of the condenser in the vapor phase, and the separation and recovery properties are lowered, which is not preferable. In addition, it is conceivable to separate trioxane and unreacted formaldehyde gas by solidifying and crystallizing trioxane using a cooling tower or the like, but the temperature in the cooling tower is too low as in the case of using a condenser or the like. The trioxane component is easily solidified inside the cooling tower, and the unreacted formaldehyde component is also easily solidified, and the separation of the formaldehyde gas into the gas phase is greatly reduced.

Hereinafter, as shown in FIG. 1, a case where a trioxane solution is obtained by absorbing trioxane contained in a reaction product gas into an organic solvent using an absorption tower or the like will be described. First, a reaction product gas containing trioxane and unreacted formaldehyde gas is continuously supplied to the separation device 5.

The inside of the separation device 5 is adjusted to the boiling point (114.5 ° C.) or lower of trioxane. Exceeding the boiling point of trioxane is not preferable because trioxane cannot be properly absorbed by an organic solvent. In order to increase the absorption efficiency into the organic solvent, the inside of the separation device 5 is more preferably adjusted to 60 ° C. or less.

The internal pressure of the separating device 5 is not particularly limited, it is preferable in terms of ensuring the separation of the gas phase of unreacted formaldehyde gas is 1 kgf / cm ² or less in gauge pressure . If the pressure exceeds 1 kgf / cm ² , the interaction between the formaldehyde gases in the separation device is increased, and problems such as polymerization and easy precipitation as a paraform in the solvent phase occur.

Subsequently, the trioxane contained in the reaction product gas is absorbed by the organic solvent by bringing the reaction product gas supplied to the separation device 5 into contact with the organic solvent. Then, unreacted formaldehyde gas contained in the reaction product gas is discharged to the outside of the separation device 5 in a gas phase.

The organic solvent may be any organic solvent that has high solubility in trioxane and low solubility in formaldehyde. For example, as an example of an aromatic compound, benzene, toluene, xylene, ethylbenzene, Examples include diethylbenzene, cumene, methoxybenzene, ethoxybenzene, chlorobenzene, and naphthalene. Examples of the alicyclic compound include cyclohexane, cyclohexanone, methylcyclohexanone, decahydronaltalene, and the like. Of these, benzene, toluene, xylene, ethylbenzene, diethylbenzene and the like can be mentioned in consideration of the distribution of trioxane to the solvent, and benzene is particularly preferable in consideration of separation / purification operations such as distillation in the final purification step. . An inorganic solvent is not preferable because it has low solubility in trioxane and a sufficient distribution ratio of trioxane to the solvent cannot be obtained.

Then, unreacted formaldehyde gas contained in the reaction product gas is discharged to the outside of the separation device 5 in a gas phase.

The separation device 5 includes a packed tower packed with Raschig rings, and in this packed tower, the organic solvent and the reaction product gas are contacted with each other by alternating current or cocurrent flow, thereby absorbing trioxane contained in the reaction product gas into the organic solvent, More preferably, the unreacted formaldehyde gas contained in the reaction product gas is discharged to the outside of the packed tower in a gas phase.

[Circulating device 6]
In the circulation device 6, a circulation recycling process is performed in which the unreacted formaldehyde gas separated by the separation device 5 is recycled as formaldehyde gas used in the trioxane generation device 4. In this gas circulation, a general gas circulation device (fan, Nash pump, etc.) can be used. In order to circulate the gas to the gas-phase trimerization reactor, it is necessary to compress the gas by the amount corresponding to the differential pressure. Therefore, a fan pump having this function can be used.

Hereinafter, although an Example and a comparative example are shown and demonstrated concretely, this invention is not limited to these Examples.

<Preparation of hemi-formal concentrate>

(Numerical values indicate the ratio of the number of moles of hydroxyl group contained in alcohol to 1 mole of formaldehyde)

[Preparation Example A]
A formaldehyde aqueous solution containing 50% by mass of formaldehyde and 2,4-dimethyl-1,5-pentanediol (trade name: PD-9, manufactured by Kyowa Hakko Chemical Co., Ltd.), a hydroxyl group contained in alcohol relative to formaldehyde contained in the formaldehyde aqueous solution Was mixed so that the molar ratio (number of moles of hydroxyl group contained in alcohol / number of moles of formaldehyde contained in formaldehyde aqueous solution) was 1.3 and reacted at room temperature for 12 hours to perform hemi-formalization. The aqueous hemi-formal solution produced by this reaction is continuously supplied to a vacuum dehydration tower at a rate of 1000 g / hr, dehydrated under conditions of 75 ° C. and 35 mmHg, and the hemi-formal concentrate according to Preparation Example A (hereinafter referred to as “hemi-formal concentrate”). A ”).

[Preparation Example B]
Preparation Example B was prepared in the same manner as Preparation Example A, except that 3-methyl-1,5-pentanediol (manufactured by Kuraray Co., Ltd.) was used instead of 2,4-dimethyl-1,5-pentanediol. Such a hemi-formal concentrate (hereinafter referred to as “hemi-formal concentrate B”) was obtained.

<Preparation of solid acid catalyst>

(In addition, commercially available alumina was used as catalyst B.)

[Preparation Example A1]
Distilled water was added to an orthophosphoric acid reagent (manufactured by Wako Pure Chemical Industries, Ltd.) having a concentration of about 85% to dilute the phosphoric acid concentration to 25%. Then, 50 g of silica gel (trade name: CARiACT Q-50, manufactured by Fuji Silysia Chemical Co., Ltd.) is added to 100 ml of the diluted phosphoric acid aqueous solution, and the impregnation operation is performed for 1 hour or more, followed by filtration to remove an unnecessary aqueous solution that is not impregnated. Excluded. The phosphoric acid carrier thus obtained was calcined in an oven at 150 ° C. for 2 hours to obtain a solid acid catalyst according to Preparation Example A1 (hereinafter referred to as “solid acid catalyst A1”).

[Preparation Example A2]
According to Preparation Example A2, the same method as Preparation Example A1, except that distilled water was added to the orthophosphoric acid reagent and diluted so that the phosphoric acid concentration was 5% and the baking temperature was 300 ° C. A solid acid catalyst (hereinafter referred to as “solid acid catalyst A2”) was obtained.

[Others]
In addition, alumina Sphere (α-type) “SAS-10” (trade name: obtained from BASF Japan) was used as it was. Hereinafter, this alumina is referred to as “catalyst B”.

<Examples and Comparative Examples>

In Tables 3 and 4, catalysts A1 and A2 are solid phosphoric acid catalysts, and catalyst B is alumina.

[Example 1]
[Preparation of hemi-formal concentrate A]
First, the said hemi-formal concentrate A was obtained in the hemi-formal production | generation apparatus.

[Preparation of formaldehyde gas]
Next, in the thermal decomposition of hemi-formal concentrate A, first, 600 ml of hemi-formal concentrate A is charged into an autoclave equipped with a 1 L pressure vessel, and hemi-formal can be continuously supplied and discharged from the outside of the flask at a constant rate of 300 ml / h. A roller pump was installed. Further, nitrogen was supplied as a carrier gas into the autoclave container at a constant flow rate (50 to 100 ml / min). A hemi-formal pyrolysis reaction was performed at a liquid temperature of the autoclave between 160 and 170 ° C. to prepare a mixed gas of formaldehyde gas and nitrogen. Here, the nitrogen flow rate and the decomposition temperature were adjusted as appropriate so that the composition ratio of formaldehyde gas and nitrogen was higher than the molar ratio of 70:30.

[Gas phase synthesis from formaldehyde gas to reaction product gas containing trioxane]
The gas phase trimerization reaction to trioxane was performed by contacting formaldehyde gas obtained by thermal decomposition of the hemi-formal concentrate A with the solid acid catalyst A1. The trioxane generator is a fixed bed reactor (made by Okura Riken) having an inner diameter of 30 mmφ, filled with 135 g of the solid acid catalyst A1 prepared in advance, and heated to 100 ° C. by a jacket flow (oil) outside the reaction tube. Warmed up. Formaldehyde gas was continuously fed by downward flow into the fixed bed reactor filled with the solid acid catalyst A1. The reaction product gas was continuously discharged to the outside of the trioxane production device through a pipe made of SUS316 kept at about 125 ° C., and further guided to the separation device.

(Separation of reaction product gas)
A packed tower having a jacket type double tube (about 25 mmφ) was used as a separation device. The packed tower was filled with 6 mmφ porcelain Raschig rings. Then, while continuously supplying the reaction product gas from the lower part of the double tube and supplying benzene from the upper part at a flow rate of 200 ml / h, the reaction product gas and benzene were brought into AC contact. Gaseous trioxane was absorbed by benzene and discharged from the bottom of the packed tower as a liquid phase. On the other hand, unreacted formaldehyde gas was discharged from the upper part of the packed tower in a gaseous state without being absorbed by benzene. The temperature in the packed tower was adjusted to 30 ° C. with cooling water flowing through the jacket.

[Recycling unreacted formaldehyde gas]

Subsequently, unreacted formaldehyde gas discharged from the upper part of the packed tower was circulated and supplied to the trioxane generator.

[Example 2]
The separation apparatus was a bubble column instead of a packed column, and trioxane was removed by the same method as in Example 1 except that the reaction product gas was separated into the bubble column by blowing the reaction product gas directly into the benzene solution. Manufactured.

[Example 3]
Trioxane was produced by the same method as in Example 1 except that the hemi-formal concentrate obtained in the hemi-formal generator was not the hemi-formal concentrate A but the hemi-formal concentrate B.

[Example 4]
Trioxane was produced by the same method as in Example 1 except that the solid acid catalyst A2 was used instead of the solid acid catalyst A1 and the amount of organic solvent (benzene) supplied to the packed tower was 400 g / h. .

[Comparative Example 1]
Trioxane was produced by the same method as in Example 1 except that the raw material supplied to the formaldehyde gas generator was not a hemi-formal concentrate but a 50% aqueous formaldehyde solution was used as it was.

[Comparative Example 2]
Trioxane was produced by the same method as in Example 1 except that alumina (catalyst B1) was used instead of the solid phosphoric acid catalyst.

[Comparative Example 3]
Trioxane was produced by the same method as in Example 1, except that the solid acid catalyst A2 was used instead of the solid acid catalyst A1, and distilled water was used instead of benzene as the solvent used in the separator.

[Comparative Examples 4 to 5]
The solid acid catalyst A2 is used instead of the solid acid catalyst A1, a jacket type condenser (with an inner diameter of about 25 mmφ) is used instead of the packed tower as a separation device, and the gas-liquid of the reaction product gas is directly used without a solvent in the condenser. Attempted separation. In Comparative Example 4, the internal temperature by the jacket was 30 ° C., and in Comparative Example 5, it was 50 ° C.

<Evaluation>
About each of the Example and the comparative example, the driving | operation of the trioxane manufacturing apparatus was performed continuously for 6 hours or more. Then, (1) in the trioxane generator, the yield of trioxane and reaction selectivity were evaluated, and (2) in the separator, the distribution ratio of trioxane to the solvent and the distribution ratio of formaldehyde to the gas phase were evaluated.

The yield of trioxane and the distribution ratio to the solvent were calculated by calculating the trioxane concentration in the solvent by gas chromatography (device name: GC-2014, manufactured by Shimadzu Corporation, column: TSG-1 (15%) 4 m length). The amount of the trioxane component that escaped to the gas phase side was once collected with water, and this aqueous solution was measured by gas chromatography on another column (device name: GC-9A, manufactured by Shimadzu Corporation, column: Chromsorb 101, 5 m long). Calculated by

The reaction selectivity of trioxane was measured by gas chromatography (equipment name: GC-9A, manufactured by Shimadzu Corporation, column: Chromsorb 101, 5 m length) by measuring the concentrations of methanol, methyl formate and methylal as reaction byproducts. After calculating the concentration of formic acid by titration, the trioxane selectivity was calculated from these results.

The distribution ratio of formaldehyde to the gas phase is that once the gas is extracted from the overhead of the absorption tower and absorbed with water, the concentration of this aqueous formaldehyde solution is calculated by titration by the sodium sulfite method and distributed to the absorption liquid side. The formaldehyde component was similarly calculated by titration, and the ratio between the two was calculated. The results are shown in Tables 5 and 6.

<Result>

 

A first step of obtaining hemiformal from an aqueous formaldehyde solution and alcohol, a second step of generating formaldehyde gas by thermally decomposing the hemiformal, supplying the formaldehyde gas to a trioxane generator, using a solid acid catalyst, A third step of gas-phase synthesis of a reaction product gas containing trioxane from formaldehyde gas, and by contacting the reaction product gas with an organic solvent, the trioxane contained in the reaction product gas is absorbed in the organic solvent, and the reaction product is produced. A fourth step of discharging unreacted formaldehyde gas contained in the gas to the outside in a gas phase, and a circulation for recycling the unreacted formaldehyde gas separated in the fourth step as the formaldehyde gas in the third step Recycling process When producing trioxane Te, along with a higher significant yield and selectivity of the reaction of trioxane in trioxane generator, it was confirmed the distribution rate in the separation device is also significantly better (Examples 1-4).

On the other hand, in the formaldehyde gas generator, when the formaldehyde aqueous solution was supplied as a raw material instead of the hemi-formal concentrate, the yield of trioxane was remarkably low, and it was confirmed that trioxane could not be produced as efficiently as the examples (Comparative Example 1). . This is not only disadvantageous for the gas phase reaction because of the high concentration of water in the raw material, but also the deactivation of the solid acid catalyst by a large amount of water and the repolymerization of formaldehyde gas (paraformation). It is considered that this is likely to occur. In addition, since the yield of trioxane is remarkably low, the evaluation of the separation apparatus is not performed.

Further, when trioxane was obtained from formaldehyde gas using a catalyst, it was confirmed that when alumina was used instead of a solid acid catalyst, the yield of trioxane was remarkably low, and trioxane could not be produced as efficiently as the examples ( Comparative Example 2). This is considered to reduce the action of the acid catalyst as a protonic acid that is originally effective for the production of trioxane due to the influence of the base point on the catalyst surface of alumina. In addition, since the yield of trioxane is remarkably low, the evaluation of the separation apparatus is not performed.

Further, it was confirmed that when the solvent used in the separation apparatus is an inorganic solvent (distilled water), it is difficult to perform gas phase separation of unreacted formaldehyde gas (Comparative Example 3).

In addition, when a jacket-type condenser is used as a separation device and an attempt is made to perform gas-liquid separation of the reaction product gas directly without using a solvent in the condenser, if the temperature in the condenser is low, trioxane is contained inside the condenser. It was confirmed that the components are easily condensed and solidified, and the unreacted formaldehyde component is easily solidified, and the separation of the formaldehyde gas into the gas phase is greatly reduced, which is not preferable (Comparative Example 4). Moreover, when the temperature in the condenser was high, it was confirmed that trioxane was not preferable because it was easy to escape to the overhead side of the condensed gas in the gas phase, and the separation and recovery were reduced (Comparative Example 5).

DESCRIPTION OF SYMBOLS 1 Trioxane production apparatus 2 Hemi formal production apparatus 3 Formaldehyde gas generation apparatus 4 Trioxane production apparatus 5 Separation apparatus 6 Circulation apparatus

Claims (12)

1. A first step of obtaining hemiformal from an aqueous formaldehyde solution and alcohol;
   A second step of generating formaldehyde gas by pyrolyzing the hemiformal;
   A third step in which the formaldehyde gas is supplied to a trioxane generator, a solid acid catalyst is used, and a reaction product gas containing trioxane is vapor-phase synthesized from the formaldehyde gas;
   By bringing the reaction product gas into contact with an organic solvent, trioxane contained in the reaction product gas is absorbed into the organic solvent, and unreacted formaldehyde gas contained in the reaction product gas is discharged outside in a gas phase. Process,
   A circulation recycling step of circulating and recycling the unreacted formaldehyde gas separated in the fourth step as the formaldehyde gas in the third step;
   A method for producing trioxane, comprising:
2. The method for producing trioxane according to claim 1, wherein the alcohol is one or a combination of two or more selected from monool, diol or triol having a boiling point of 190 ° C or higher.
3. The method for producing trioxane according to claim 1 or 2, wherein the solid acid catalyst contains phosphoric acid supported on a siliceous inorganic carrier.
4. In the third step, the mass space velocity WHSV indicating the ratio of the mass per unit time of formaldehyde gas supplied to the trioxane generator and the mass of the solid acid catalyst charged in the trioxane generator is 1 / 50h is ^-1 or more ^{1h -1} or less, trioxane production method according to any one of claims 1 to 3.
5. In the third step,
   Packing the solid acid catalyst into a multitubular fixed bed reactor,
   Contacting the solid acid catalyst in a heterogeneous system with the formaldehyde gas obtained in the second step and the unreacted formaldehyde gas circulated and recycled in the circulation and recycling step;
   Trioxane is vapor-phase synthesized by continuously withdrawing trioxane from the fixed bed reactor in the gas-phase state.
   The trioxane manufacturing method in any one of Claim 1 to 4.
6. The method for producing trioxane according to any one of claims 1 to 5, wherein the organic solvent is one or more selected from benzene, toluene, xylene, ethylbenzene, and diethylbenzene.
7. In the fourth step, a separation apparatus in which the reaction product gas containing trioxane synthesized in the third step and unreacted formaldehyde gas unreacted in the third step is adjusted to a temperature not higher than the boiling point of the trioxane. The method for producing trioxane according to any one of claims 1 to 6, wherein the trioxane is continuously supplied to the reactor.
8. The method for producing trioxane according to claim 7, wherein the separation device includes an absorption tower of any one of a liquid film type, a droplet type and a bubble type.
9. The absorption tower is an absorption tower by the liquid film type,
   The absorption tower includes a packed tower that is filled with a filler,
   In the fourth step, trioxane contained in the reaction product gas is absorbed into the organic solvent by bringing the organic solvent and the reaction product gas into alternating current or cocurrent contact with each other, and the unsolved product contained in the reaction product gas is absorbed. The method for producing trioxane according to claim 8, wherein the reaction formaldehyde gas is separated outside the separation device in a gas phase.
10. The method for producing trioxane according to any one of claims 7 to 9, wherein the temperature inside the separator is 60 ° C or lower.
11. The trioxane production method according to any one of claims 7 to 10, wherein the pressure inside the separation device is 1 kgf / cm ² or less in terms of gauge pressure.
12. A hemi-formal generator for obtaining hemi-formal from an aqueous formaldehyde solution and alcohol;
    A formaldehyde gas generator that thermally decomposes the hemiformal to generate formaldehyde gas;
    Using a solid acid catalyst, a trioxane generator for vapor-phase synthesis of a reaction product gas containing trioxane from the formaldehyde gas, and
    A separation device that absorbs trioxane contained in the reaction product gas into the organic solvent by bringing the reaction product gas into contact with an organic solvent, and discharges the unreacted formaldehyde gas contained in the reaction product gas to the outside in a gas phase. When,
    A circulation device for circulating the unreacted formaldehyde gas to the trioxane generator;
    An apparatus for producing trioxane.

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