Composition and method for producing trioxane using same

Abstract

The present invention provides a method capable of continuously producing trioxane at a high yield. Provided is a composition containing (A) 58.5-65.5% by mass of formaldehyde, (B) 0.7-4.5% by mass of methanesulfonic acid, and (C) less than 0.007% by mass of a metal salt, the total content of (A) formaldehyde and (B) methanesulfonic acid being less than 68% by mass, and the metal salt (C) containing at least one selected from the group consisting of nitrate, nitrite, and persulfate.

Description

Technical Field

[0001] The present invention relates to a composition and a method for producing trioxane using the same. Background Art

[0002] Polyoxymethylene (POM) is widely used in electronic equipment, vehicles, etc. in the form of fibers, films, gears, bearings, etc. due to its excellent strength, elastic modulus, impact resistance, sliding properties, etc. Polyoxymethylene (POM) is inexpensive and versatile, so the demand is expanding.

[0003] The demand for trioxane (1,3,5-trioxane, TOX), which is used as a raw material for polyoxymethylene (POM), is also increasing. Therefore, a method for producing trioxane (TOX) at a high yield is required.

[0004] For example, Patent Document 1 discloses an invention related to a method for producing trioxane. The method for producing trioxane includes: 1) contacting formaldehyde with a catalyst containing at least methanesulfonic acid; 2) performing a reaction to trimerize the formaldehyde to produce trioxane; and 3) separating trioxane from a reaction medium.

[0005] Patent Document 1 describes that the trioxane production method described above can improve the trioxane yield, trioxane selectivity, and the like.

[0006] Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Publication No. 2017-523998 Summary of the invention

[0007] Technical problem to be solved by the invention Trioxane can be produced at a high yield by the method described in Patent Document 1. However, it was found that continuous production is sometimes difficult due to the use of methanesulfonic acid.

[0008] Under such circumstances, a method capable of continuously producing trioxane in high yield is required.

[0009] Technical solutions for solving technical problems The present invention includes, for example, the following aspects.

[0010] [1] A composition comprising: (A) 58.5 to 65.5% by mass of formaldehyde, (B) 0.7 to 4.5 mass % of methanesulfonic acid, and (C) less than 0.007 mass % of metal salt; The total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68% by mass (C) The metal salt includes at least one selected from the group consisting of nitrates, nitrites, and persulfates.

[0011] [2] The composition according to [1] above, wherein the content of the formaldehyde (A) is 60 to 65.5% by mass.

[0012] [3] The composition according to [1] or [2] above, wherein the content of the (B) methanesulfonic acid is 0.7 to 3.5% by mass.

[0013] [4] The composition according to any one of [1] to [3] above, wherein the content of the metal salt (C) is 0.002 to 0.004 mass %.

[0014] [5] A method for producing trioxane, comprising the step of reacting a solution containing (A) formaldehyde, (B) methanesulfonic acid, and (C) a metal salt to obtain trioxane, The reaction liquid at equilibrium in the step of obtaining trioxane is the composition described in any one of [1] to [4].

[0015] Effects of the Invention According to the present invention, a method for continuously producing trioxane in high yield can be provided. DETAILED DESCRIPTION

[0016] Hereinafter, specific embodiments of the present invention will be described in detail.

[0017] <Composition> The composition of the present invention contains (A) 58.5 to 65.5% by mass of formaldehyde, (B) 0.7 to 4.5% by mass of methanesulfonic acid, and (C) less than 0.007% by mass of a metal salt. In this case, the total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68% by mass. In addition, the (C) metal salt includes at least one selected from nitrates, nitrites, and persulfates.

[0018] By using the above composition, trioxane can be continuously produced at a high yield.

[0019] Specifically, by using (B) methanesulfonic acid as the acid catalyst, trioxane can be produced in high yield.

[0020] On the other hand, continuous production is sometimes difficult due to the use of (B) methanesulfonic acid. Specifically, (B) methanesulfonic acid is corrosive to metals, and therefore sometimes corrodes metal equipment (e.g., stainless steel (SUS)) used in continuous production (particularly industrial production, large-scale production) (e.g., piping). As a result, there is a possibility of causing obstacles to continuous production. In addition, methanesulfonic acid is a strong acid, so in the presence of (B) methanesulfonic acid, (A) formaldehyde sometimes polymerizes and transforms into paraformaldehyde, etc. Since paraformaldehyde, etc., adheres to and deposits on piping, etc., causing clogging, there is a possibility of causing obstacles to continuous production.

[0021] However, the composition of the present invention can continuously produce trioxane. Specifically, by using a predetermined (C) metal salt, a protective film can be formed on the surface of a metal device to prevent corrosion of the metal device. In addition, by controlling the contents of (A) formaldehyde, (B) methanesulfonic acid, and (C) metal salt in the composition within a predetermined range, the generation of paraformaldehyde and the like can be suppressed. As a result, during continuous production, corrosion of metal devices or clogging of piping and the like can be prevented, making it suitable for continuous production.

[0022] In addition, trioxane is produced by the trimerization reaction of formaldehyde, and in this case, the above reaction is an equilibrium reaction. The composition involved in the present invention refers to the reaction solution when the above reaction is in equilibrium. Since the reaction solution at equilibrium has the composition of the composition of the present invention, trioxane can be continuously produced at a high yield, and corrosion of metal equipment and clogging of pipes can be prevented during continuous production.

[0023] In this specification, "equilibrium" refers to the time point when the composition of the reaction liquid is not changed after the conditions are fixed. For example, in the case of a one-time additional addition of (A) formaldehyde in the continuous production of trioxane, the content of (A) formaldehyde in the reaction liquid increases during the addition. In this case, formaldehyde is converted into trioxane, so that the content of formaldehyde gradually decreases, and at a certain time point, the content of formaldehyde becomes a constant value. The time point at which such equilibrium is reached is the equilibrium time, and the reaction liquid at the equilibrium time is the composition of the present invention. In addition, for example, when a certain amount of the generated trioxane is continuously distilled and removed, the generated trioxane is sequentially distilled and removed, so the content of trioxane in the reaction liquid gradually decreases, and moves to a new equilibrium condition based on the continued distillation and removal of trioxane. In this case, at a certain time point, the content of formaldehyde becomes a constant value. The time point at which equilibrium is reached under such new equilibrium conditions is the equilibrium time, and the reaction liquid at the equilibrium time is the composition of the present invention. Among them, the composition of the composition (reaction liquid) can be measured according to the following method. That is, the content of (A) formaldehyde can be measured by neutralizing and titrating sodium hydroxide generated by reaction with sodium sulfite with an acid. In addition, the content of (B) methanesulfonic acid and the content of (C) metal salt can be measured by ion chromatography.

[0024] The composition of the composition of the present invention (composition of the reaction solution at equilibrium) can be adjusted by, for example, changing the reaction conditions, adding (A) formaldehyde, adding (B) methanesulfonic acid, adding (C) a metal salt, and distilling off generated trioxane.

[0025] [(A) Formaldehyde] Formaldehyde is trimerized by the action of an acid to form trioxane.

[0026] The content of formaldehyde is 58.5 to 65.5% by mass relative to the total mass of the composition, preferably 60 to 65.5% by mass, and from the viewpoint of higher trioxane production, more preferably 62 to 65.5% by mass, and further preferably 62 to 65% by mass. When the content of formaldehyde is 58.5% by mass or more, trioxane can be produced in high yield, so it is preferred. On the other hand, when the content of formaldehyde is 65.5% by mass or less, it is possible to prevent clogging of piping, etc., caused by the generation of paraformaldehyde, etc., so it is preferred.

[0027] Formaldehyde is a gas, so the raw materials used in the production of the composition include formaldehyde aqueous solution (formalin), paraformaldehyde (formaldehyde oligomer), polyoxymethylene (formaldehyde polymer), etc. In addition, as described later, the composition is preferably a solution containing water and / or an organic solvent, so in the composition, formaldehyde is dissolved in water and / or an organic solvent.

[0028] [(B) Methanesulfonic acid] Methanesulfonic acid promotes the conversion of formaldehyde to trioxane.

[0029] The content of methanesulfonic acid is 0.7 to 4.5% by mass relative to the total mass of the composition, preferably 0.7 to 3.5% by mass from the viewpoint of higher trioxane yield, and more preferably 0.7 to 2.5% by mass from the viewpoint of preventing clogging of piping etc. caused by the generation of paraformaldehyde etc. When the content of methanesulfonic acid is 0.7% by mass or more, trioxane can be produced in high yield, so it is preferred. On the other hand, when the content of methanesulfonic acid is 4.5% by mass or less, clogging of piping etc. caused by the generation of paraformaldehyde etc. can be prevented, so it is preferred.

[0030] The total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68% by mass, preferably 50% by mass or more and less than 68% by mass, more preferably 58 to 67.5% by mass, and even more preferably 60 to 66.5% by mass, relative to the total mass of the composition. When the total content is less than 68% by mass, clogging of pipes and the like due to the generation of paraformaldehyde and the like can be prevented, which is preferred.

[0031] The mass ratio of the content of (A) formaldehyde to the total content of (A) formaldehyde and (B) methanesulfonic acid (A / (A+B)) is preferably 0.900 to 0.995, more preferably 0.930 to 0.995, further preferably 0.950 to 0.990, further preferably 0.955 to 0.990, further preferably 0.970 to 0.985. When the mass ratio is within the above range, trioxane can be produced at a high yield and clogging of piping etc. due to the generation of paraformaldehyde etc. can be prevented, which is preferred.

[0032] [Other acids] The composition according to the present invention may contain other acids. Here, "other acids" refers to acids other than (B) methanesulfonic acid.

[0033] The other acids are not particularly limited, and examples thereof include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, perchloric acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, 1,5-naphthalene disulfonic acid, etc. These other acids may be used alone or in combination of two or more.

[0034] The content of other acids is preferably 0.1 to 10 mass %, more preferably 0.1 to 3 mass %, and even more preferably 0.3 to 1 mass %, relative to the total mass of the composition. When two or more other acids are contained, the total content thereof is preferably within the above range.

[0035] [(C) Metal salt] The metal salt forms a protective film on the metal surface of the pipe, etc., to prevent the metal from being corroded by methanesulfonic acid. In this specification, "metal" refers to steel and non-ferrous metal, preferably stainless steel (SUS) and carbon steel, and more preferably stainless steel (SUS).

[0036] The metal salt includes at least one selected from the group consisting of nitrates, nitrites, and persulfates.

[0037] The nitrate is not particularly limited, and examples thereof include sodium nitrate, potassium nitrate, magnesium nitrate, cerium nitrate, cerium ammonium nitrate, iron nitrate, molybdenum nitrate, and vanadium nitrate.

[0038] The nitrite is not particularly limited, and examples thereof include sodium nitrite, potassium nitrite, magnesium nitrite, cerium nitrite, cerium ammonium nitrite, iron nitrite, molybdenum nitrite, and vanadium nitrite.

[0039] The persulfate is not particularly limited, and examples thereof include sodium persulfate, potassium persulfate, magnesium persulfate, cerium persulfate, ammonium cerium persulfate, iron persulfate, molybdenum persulfate, and vanadium persulfate.

[0040] Among these, the metal salt preferably includes at least one selected from nitrates and nitrites, more preferably includes nitrates, further preferably includes at least one selected from sodium nitrate, potassium nitrate, magnesium nitrate, cerium nitrate and cerium ammonium nitrate, and particularly preferably includes sodium nitrate and / or potassium nitrate. The above-mentioned metal salts may be used alone or in combination of two or more.

[0041] The content of the metal salt is less than 0.007% by mass, preferably 0.0001 to 0.0065% by mass, more preferably 0.001 to 0.006% by mass, relative to the total mass of the composition, and further preferably 0.002 to 0.004% by mass from the viewpoint of preventing clogging of pipes and the like due to the generation of paraformaldehyde and the like. When the content of the metal salt is less than 0.007% by mass, clogging of pipes and the like due to the generation of paraformaldehyde and the like can be prevented, and thus it is preferred.

[0042] [water] The composition of the present invention preferably contains water. When the composition contains water, (A) formaldehyde can be dissolved. Thus, clogging of pipes and the like due to the generation of paraformaldehyde and the like can be prevented. In addition, when the composition contains water, trioxane and water form an azeotropic mixture (trioxane: water = 70:30 (mass ratio), azeotropic point: 91.3° C.), and trioxane can be distilled off from the reaction system. Thus, the equilibrium reaction of converting formaldehyde into trioxane can be shifted to the generation side of trioxane.

[0043] The content of water is preferably 20 to 40% by mass, more preferably 30 to 40% by mass, and further preferably 35 to 40% by mass relative to the total mass of the composition. When the content of water is 20% by mass or more, formaldehyde can be suitably dissolved, and clogging of pipes etc. caused by the generation of paraformaldehyde etc. can be prevented, and thus it is preferred. On the other hand, when the content of water is 40% by mass or less, trioxane can be produced in high yield, and thus it is preferred.

[0044] [Organic solvents] The composition of the present invention may contain an organic solvent. The organic solvent can appropriately dissolve formaldehyde and prevent the generation of paraformaldehyde and the like.

[0045] [Trioxane] The composition according to the present invention is a reaction solution at equilibrium and therefore usually contains trioxane.

[0046] The content of trioxane is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total mass of the composition.

[0047] [additive] The composition of the present invention may also contain additives. There are no particular limitations on the additives, and examples thereof include defoamers, surfactants, stabilizers, etc. These additives may be used alone or in combination of two or more.

[0048] [Combination of contents] The preferred contents of (A) formaldehyde, (B) methanesulfonic acid, and (C) metal salt contained in the composition are as described above, and they can be appropriately combined.

[0049] In one embodiment, as a preferred combination of the contents of (A) to (C) in the composition, from the viewpoint of suitably obtaining the effects of producing trioxane in high yield, preventing clogging of pipes and the like due to the generation of paraformaldehyde and the like, and preventing metal corrosion, it is preferred that (A) is 59 to 65% by mass, (B) is 0.5 to 2.5% by mass, and (C) is 0.002 to 0.004% by mass, and the total content of (A) formaldehyde and (B) methanesulfonic acid is 60 to 66% by mass. It is more preferred that (A) is 60 to 64% by mass, (B) is 1 to 2% by mass, and (C) is 0.002 to 0.004% by mass, and the total content of (A) formaldehyde and (B) methanesulfonic acid is 61 to 66% by mass. In another embodiment, as a preferred combination of the contents of (A) to (C) in the composition, from the viewpoint of suitably obtaining a high yield of trioxane, preferably, (A) is 62 to 65% by mass, (B) is 0.5 to 3.5% by mass, and (C) is 0.002 to 0.004% by mass, and the total content of (A) formaldehyde and (B) methanesulfonic acid is 64 to 67% by mass. More preferably, (A) is 63.5 to 65% by mass, (B) is 1 to 3% by mass, and (C) is 0.002 to 0.004% by mass, and the total content of (A) formaldehyde and (B) methanesulfonic acid is 65 to 67% by mass.

[0050] <Method for producing trioxane> According to one embodiment of the present invention, a method for producing trioxane can be provided. The method for producing trioxane includes a step of reacting a solution containing (A) formaldehyde, (B) methanesulfonic acid, and (C) a metal salt to obtain trioxane. In this case, the reaction solution at equilibrium in the step of obtaining trioxane is the above-mentioned composition. In addition, the method for producing trioxane may further include a trioxane purification step.

[0051] [Trioxane production process] The trioxane production step is a step of reacting a solution containing (A) formaldehyde, (B) methanesulfonic acid, and (C) a metal salt to obtain trioxane.

[0052] (Solution) The solution contains (A) formaldehyde, (B) methanesulfonic acid and (C) a metal salt, and may also contain other acids, water, an organic solvent, additives and the like.

[0053] As (A) formaldehyde, (B) methanesulfonic acid, (C) metal salt, other acid, water, organic solvent, additives and the like, the above-mentioned compounds can be used.

[0054] The contents of (A) formaldehyde, (B) methanesulfonic acid and (C) metal salt in the solution are preferably such that the reaction solution at equilibrium becomes the above-mentioned composition after taking into account the production conditions set in the trioxane production step. The amounts of other acids, water, organic solvents, additives, etc. added may also be appropriately set.

[0055] (reaction) Trioxane is produced by trimerizing (A) formaldehyde in the presence of (B) methanesulfonic acid. In this case, the trimerization is an equilibrium reaction.

[0056] In addition, due to side reactions, formic acid and glycolic acid (CH 2 In addition, these by-products react to form further by-products. However, when the reaction solution at equilibrium is adjusted to the composition of the present invention, trimerization of formaldehyde can further occur selectively, so trioxane can be produced in high yield.

[0057] The reaction method is not particularly limited, and a known method can be applied. As an example of the reaction method, a method of heating a solution can be mentioned.

[0058] The reaction temperature is not particularly limited, but is preferably 70 to 150° C., more preferably 80 to 120° C., and particularly preferably 90 to 120° C. By adjusting the reaction temperature, generated trioxane can be distilled off from the reaction system, and trioxane can be obtained at a higher yield.

[0059] The reaction pressure is not particularly limited, but is preferably 0.1×10 5 ~10×10 5 Pa, more preferably 1×10 5 ~5×10 5 Pa, more preferably 1×10 5 ~2×10 5 By adjusting the reaction pressure, the generated trioxane can be distilled off to the outside of the reaction system, and trioxane can be obtained in a high yield.

[0060] The reaction time is not particularly limited, but is preferably 0.1 to 10 hours, more preferably 0.3 to 5 hours, and even more preferably 0.5 to 4 hours. By adjusting the reaction time, trioxane can be produced efficiently.

[0061] Since trimerization of formaldehyde is an equilibrium reaction, it is preferred to distill off trioxane as a product from the reaction system during the reaction. For example, when the composition contains water, trioxane and water form an azeotropic mixture and are distilled off to the outside of the reaction system under predetermined reaction conditions.

[0062] The trioxane removed by distillation (for example, an azeotropic mixture of trioxane and water) is preferably purified directly in the trioxane purification step described later.

[0063] In the case of continuous production of trioxane, it can be carried out by sequentially adding a formaldehyde aqueous solution to a reaction system in which methanesulfonic acid and a metal salt are present, and sequentially distilling off the obtained trioxane to the outside of the reaction system. In this case, the formaldehyde aqueous solution added is preferably added in an amount such that the reaction solution at equilibrium has the composition of the composition involved in the present invention, taking into account the reaction conditions, the amount of trioxane distilled off to the outside of the reaction system, and the like.

[0064] [Trioxane purification process] The trioxane purification step is a step of purifying the trioxane obtained in the trioxane production step. In this case, the “obtained trioxane” may include the trioxane (preferably an azeotropic mixture of trioxane and water) distilled out of the reaction system during the reaction, and the reaction solution after the reaction. In this case, the “obtained trioxane” may contain formaldehyde, water, an organic solvent, additives, by-products (formic acid, glycolic acid (CH 2 OHCOOH), methanol, carbon dioxide), components from droplets generated in the reaction system, components from piping, etc.

[0065] The purification method is not particularly limited, and examples thereof include distillation, crystallization, filtration, extraction, etc. Among these, the purification method preferably includes distillation and / or extraction, and more preferably includes distillation. In addition, the above-mentioned purification method can appropriately adopt a known method.

[0066] It is preferred that at least one of the impurities other than trioxane separated in the purification step, such as formaldehyde, water, and an organic solvent, be reused in the trioxane production step.

[0067] Example Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.

[0068] [Example 1] (Manufacturing of trioxane) A solution containing (A) formaldehyde, (B) methanesulfonic acid, (C) sodium nitrate and water is placed in a reactor (having a structure of reactor - pipe (distillation removal pipe) - Allihn cooler - distillate storage flask - pipe (reflux pipe) - reactor) connected by two pipes (distillation removal pipe and reflux pipe), and heated at a heat medium temperature of 130° C. for 3 hours to produce trioxane. The content of (A) formaldehyde in the reaction solution (composition) at equilibrium after 3 hours is determined by neutralizing methanesulfonic acid and by-product acid components (formic acid, etc.) in the composition with dilute hydrochloric acid in advance, and then titrating the sodium hydroxide generated by the reaction with sodium sulfite with acid neutralization. In addition, the content of (B) methanesulfonic acid and the content of (C) metal salt in the reaction solution (composition) at equilibrium were measured by ion chromatography (apparatus name: Dionex ICS-2100, chromatographic columns: Dionex IonPac AS11-HC and Dionex IonPac AG11-HC). As a result, the content of (A) was 60% by mass, the content of (B) was 1% by mass, and the content of (C) was 0.003% by mass relative to the total mass of the composition.

[0069] At this time, in the above reaction, the trioxane produced forms an azeotropic mixture with water and is distilled off from the reaction system. As a result, the equilibrium reaction of generating trioxane from formaldehyde is shifted to the trioxane generating side. The azeotropic mixture of trioxane and water is cooled and liquefied by the Aline cooler through the pipe (distillation removal pipe) connected to the reactor, and is stored as a trioxane distillate in the distillate storage flask connected to the Aline cooler. When the storage capacity of the distillate storage flask is exceeded, the trioxane distillate in the distillate storage flask is returned to the reactor through the pipe (reflux pipe).

[0070] [Example 2] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64% by mass.

[0071] [Example 3] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass % and the content of (B) was adjusted to 2 mass %.

[0072] [Example 4] A composition was produced in the same manner as in Example 1 except that the content of (B) in the reaction solution (composition) at equilibrium was adjusted to 3% by mass.

[0073] [Example 5] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64% by mass and the content of (B) was adjusted to 3% by mass.

[0074] [Example 6] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 63% by mass and the content of (B) was adjusted to 4% by mass.

[0075] [Example 7] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass %, the content of (B) was adjusted to 2 mass %, and the content of (C) was adjusted to 0.005 mass %.

[0076] [Example 8] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 63 mass %, the content of (B) was adjusted to 4 mass %, and the content of (C) was adjusted to 0.005 mass %.

[0077] [Example 9] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass %, the content of (B) was adjusted to 2 mass %, and the content of (C) was adjusted to 0.001 mass %.

[0078] [Comparative Example 1] A composition was produced in the same manner as in Example 1 except that the content of (B) in the reaction solution (composition) at equilibrium was adjusted to 0.5% by mass.

[0079] [Comparative Example 2] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass % and the content of (B) was adjusted to 0.5 mass %.

[0080] [Comparative Example 3] A composition was produced in the same manner as in Example 1 except that the content of (B) in the reaction solution (composition) at equilibrium was adjusted to 5% by mass.

[0081] [Comparative Example 4] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 66% by mass.

[0082] [Comparative Example 5] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass % and the content of (B) was adjusted to 4 mass %.

[0083] [Comparative Example 6] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 58% by mass and the content of (B) was adjusted to 2% by mass.

[0084] [Comparative Example 7] A composition was produced in the same manner as in Example 1 except that the content of (B) in the reaction solution (composition) at equilibrium was adjusted to 2 mass % and the content of (C) was adjusted to 0.01 mass %.

[0085] [Comparative Example 8] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass %, the content of (B) was adjusted to 2 mass %, and the content of (C) was adjusted to 0.01 mass %.

[0086] [Comparative Example 9] A composition was produced in the same manner as in Example 1 except that the content of (B) in the reaction solution (composition) at equilibrium was adjusted to 4 mass % and the content of (C) was adjusted to 0.01 mass %.

[0087] [Comparative Example 10] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 64 mass %, the content of (B) was adjusted to 2 mass %, and (C) was not added.

[0088] [Comparative Example 11] A composition was produced in the same manner as in Example 1 except that the content of (A) in the reaction solution (composition) at equilibrium was adjusted to 63 mass %, the content of (B) was adjusted to 4 mass %, and (C) was not added.

[0089] The compositions of Examples 1 to 9 and Comparative Examples 1 to 11 are shown in Table 1 below.

[0090] [Table 1] [evaluate] Various evaluations were performed on the compositions of Examples 1 to 9 and Comparative Examples 1 to 11 or the trioxane distillates in the distillate storage flasks.

[0091] (Trioxane content) The trioxane distillate was recovered from the distillate storage flask after reaching the reaction equilibrium (after 3 hours), and the trioxane content contained in the trioxane distillate was measured by gas chromatography, and the trioxane content (TOX content) relative to the total mass of the trioxane distillate was calculated. At this time, in the gas chromatography measurement, Nexis GC-2030 (manufactured by Shimadzu Corporation) was used as an apparatus, and DB-WAX (manufactured by Agilent Technology) was used as a chromatographic column. When the TOX content is high, it means that trioxane can be produced in high yield. The obtained results are shown in the following Table 2.

[0092] (Appearance of reaction solution) The reaction solution (composition) in the reactor after reaching reaction equilibrium (after 3 hours) was visually observed, and the appearance of the reaction solution was evaluated according to the following criteria. When the evaluation result of the reaction solution appearance is good, it means that no paraformaldehyde or the like is generated from formaldehyde during the production process of trioxane. Therefore, when the composition is used to produce trioxane, it is not easy to cause clogging of the piping, etc., so it can be said that it is suitable for continuous production. The obtained results are shown in the following Table 2.

[0093] ○: colorless and transparent; △: slightly white and turbid; ×: Significant white turbidity.

[0094] (Stainless steel (SUS) corrosion) After reaching reaction equilibrium (3 hours later), a SUS316L test piece (60 mm in length, 20 mm in width, 2 mm in thickness, with welding wires of the same material on both sides and φ4 mm drill through holes) was immersed in 100 g of the reaction solution (composition) in the reactor and allowed to stand at 90°C for 1 day. The mass reduction rate (mass) of the test piece after immersion was calculated using the following formula.

[0095] The SUS corrosion resistance was evaluated according to the following criteria. A good result of the SUS corrosion resistance indicates that the composition is unlikely to corrode SUS equipment. The obtained results are shown in Table 2 below.

[0096] ○: Mass reduction rate is less than 0.2 mass %.

[0097] ×: The mass reduction rate is 0.2 mass% or more.

[0098] [Table 2] The results in Table 2 show that the compositions of Examples 1 to 9 can produce trioxane at high yield, prevent the generation of byproducts such as paraformaldehyde, and prevent corrosion of SUS. Therefore, the compositions of Examples 1 to 9 can produce trioxane at high yield and can be said to be suitable for continuous production.

Claims

1. A composition, characterized in that contain: (A) 58.5 to 65.5% by mass of formaldehyde, (B) 0.7 to 4.5 mass % of methanesulfonic acid, and (C) less than 0.007 mass % of metal salt; The total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68% by mass (C) The metal salt includes at least one selected from the group consisting of nitrates, nitrites, and persulfates.

2. The composition according to claim 1, characterized in that: The content of the formaldehyde (A) is 60 to 65.5% by mass.

3. The composition according to claim 1 or 2, characterized in that: The content of the (B) methanesulfonic acid is 0.7 to 3.5% by mass.

4. The composition according to any one of claims 1 to 3, characterized in that: The content of the (C) metal salt is 0.002 to 0.004 mass %.

5. A method for producing trioxane, characterized in that: The method comprises the steps of reacting a solution containing (A) formaldehyde, (B) methanesulfonic acid and (C) a metal salt to obtain trioxane, The reaction liquid at equilibrium in the step of obtaining trioxane is the composition according to any one of claims 1 to 4.

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