Composition and method for producing trioxane using the same

Abstract

Provided is a means with which trioxane can be continuously produced at a high yield.　Provided is a composition that contains (A) 58.5-65.5 mass% of formaldehyde, (B) 0.7-4.5 mass% of methanesulfonic acid, and (C) less than 0.007 mass% of a metal salt. The total content of the formaldehyde (A) and the methanesulfonic acid (B) is less than 68 mass%. The metal salt (C) includes at least one type selected from the group consisting of a nitrate, a nitrite and a persulfate.

Description

[Technical field]

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

[0002] Polyoxymethylene (POM) has excellent strength, elasticity, impact resistance, sliding properties, etc., and is therefore widely used in electronic devices, vehicles, etc. as fibers, films, gears, bearings, etc. Demand for polyoxymethylene (POM) is expanding due to its low cost and versatility.

[0003] Demand for trioxane (1,3,5-trioxane, TOX), which is used as a raw material for polyoxymethylene (POM), is also increasing, and a method for producing trioxane (TOX) in high yields is therefore required.

[0004] For example, Patent Document 1 describes an invention relating to a method for producing trioxane, which includes the steps of: 1) contacting formaldehyde with a catalyst containing at least methanesulfonic acid; 2) carrying out a reaction for trimerizing the formaldehyde to trioxane; and 3) separating the trioxane from the reaction medium.

[0005] Patent Document 1 describes that the method for producing trioxane makes it possible to improve the trioxane yield and trioxane selectivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-523998 A Summary of the Invention [Problem to be solved by the invention]

[0007] According to the method described in Patent Document 1, trioxane can be produced in high yield. However, it has been found that continuous production may be difficult because methanesulfonic acid is used.

[0008] Under these circumstances, there is a demand for a means for continuously producing trioxane in high yield. [Means for solving the problem]

[0009] The present invention includes, for example, the following aspects.

[0010] [1] (A) 58.5 to 65.5 mass% formaldehyde; (B) 0.7 to 4.5% by mass of methanesulfonic acid; (C) less than 0.007% by weight of a metal salt; A composition comprising: The total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68% by mass, (C) The composition, wherein the metal salt comprises at least one selected from the group consisting of nitrates, nitrites, and persulfates. [2] The composition according to the above [1], wherein the content of the (A) formaldehyde is 60 to 65.5 mass %. [3] The composition according to the above [1] or [2], wherein the content of the (B) methanesulfonic acid is 0.7 to 3.5 mass %. [4] The composition according to any one of the above [1] to [3], wherein the content of the (C) metal salt is 0.002 to 0.004 mass %. [5] A method for producing trioxane comprising the steps of: (A) reacting a solution containing formaldehyde, (B) methanesulfonic acid, and (C) a metal salt; A method for producing trioxane, wherein a reaction solution at equilibrium in the step of obtaining trioxane is the composition according to any one of [1] to [4]. Effect of the Invention

[0011] According to the present invention, a means for continuously producing trioxane in high yield is provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail.

[0013] <Composition> The composition according to the present invention contains (A) 58.5 to 65.5 mass% formaldehyde, (B) 0.7 to 4.5 mass% methanesulfonic acid, and (C) less than 0.007 mass% metal salt. In this case, the total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68 mass%. In addition, (C) metal salt contains at least one selected from the group consisting of nitrates, nitrites, and persulfates.

[0014] The above composition enables continuous production of trioxane in high yield.

[0015] Specifically, by using (B) methanesulfonic acid as the acid catalyst, trioxane can be produced in high yield.

[0016] On the other hand, the use of (B) methanesulfonic acid may make continuous production difficult. Specifically, (B) methanesulfonic acid is corrosive to metals, and may corrode metal (e.g., stainless steel (SUS)) equipment (e.g., piping) used in continuous production (especially industrial production, large-scale production). As a result, continuous production may be hindered. In addition, since methanesulfonic acid is a strong acid, (A) formaldehyde may polymerize in the presence of (B) methanesulfonic acid and be converted to paraformaldehyde, etc. Paraformaldehyde, etc. may adhere to and deposit in piping, etc., causing blockage, which may hinder continuous production.

[0017] However, the composition of the present invention allows for continuous production of trioxane. Specifically, by using a specific (C) metal salt, a protective film is formed on the surface of metal equipment, preventing the corrosion of the metal equipment. In addition, by controlling the contents of (A) formaldehyde, (B) methanesulfonic acid, and (C) metal salt in the composition within a specific range, the production of paraformaldehyde and the like can be suppressed. As a result, corrosion of metal equipment and clogging of piping and the like can be prevented during continuous production, allowing for suitable continuous production.

[0018] Trioxane is produced by a trimerization reaction of formaldehyde, which is an equilibrium reaction. The composition according to the present invention means a reaction solution at equilibrium of the reaction. When the reaction solution at equilibrium has the composition of the composition according to the present invention, trioxane can be continuously produced in high yield, and corrosion of metal equipment and clogging of piping, etc. can be prevented during continuous production.

[0019] In this specification, "at equilibrium" means a time point at which no change is observed in the composition of the reaction solution after the conditions are fixed. For example, in the continuous production of trioxane, when formaldehyde (A) is added in one lump, the content of formaldehyde (A) in the reaction solution increases at the time of addition. In this case, the formaldehyde content gradually decreases as the formaldehyde is converted to trioxane, and the content of formaldehyde becomes a constant value at a certain point. The time point at which such equilibrium is reached is the time of equilibrium, and the reaction solution at the time of equilibrium is the composition of the present invention. In addition, for example, when a constant amount of trioxane is continuously distilled off, the trioxane produced is successively distilled off, so that the content of trioxane in the reaction solution gradually decreases, and a transition is made to new equilibrium conditions that assume the continuous distillation of trioxane. In this case, the content of formaldehyde becomes a constant value at a certain point. The time point at which equilibrium is reached under such new equilibrium conditions is the time of equilibrium, and the reaction solution at the time of equilibrium is the composition of the present invention. The composition of the composition (reaction solution) can be measured by the following method. That is, the (A) formaldehyde content can be measured by neutralizing titration with an acid of the sodium hydroxide produced by reacting with sodium sulfite, while the (B) methanesulfonic acid content and the (C) metal salt content can be measured by ion chromatography.

[0020] The composition of the composition according to the present invention (the composition of the reaction solution at equilibrium) can be adjusted, for example, by changing the reaction conditions, adding (A) formaldehyde, adding (B) methanesulfonic acid, adding (C) a metal salt, or distilling off the trioxane that is produced.

[0021] [(A) Formaldehyde] Formaldehyde is trimerized by the action of an acid to form trioxane.

[0022] The content of formaldehyde is 58.5 to 65.5 mass% based on the total mass of the composition, preferably 60 to 65.5 mass%, and from the viewpoint of a higher yield of trioxane, more preferably 62 to 65.5 mass%, and even more preferably 62 to 65 mass%. When the content of formaldehyde is 58.5 mass% or more, it is preferable because trioxane can be produced in a high yield. On the other hand, when the content of formaldehyde is 65.5 mass% or less, it is preferable because clogging of piping, etc. due to the generation of paraformaldehyde, etc. can be prevented.

[0023] Since formaldehyde is a gas, the raw materials used in the production of the composition include an aqueous formaldehyde solution (formalin), paraformaldehyde (formaldehyde oligomer), polyoxymethylene (formaldehyde polymer), etc. As described later, the composition is preferably a solution containing water and / or an organic solvent, and therefore, in the composition, formaldehyde is present in the form of a solution dissolved in water and / or an organic solvent.

[0024] [(B) Methanesulfonic acid] Methanesulfonic acid promotes the conversion of formaldehyde to trioxane.

[0025] The content of methanesulfonic acid is 0.7 to 4.5% by mass, preferably 0.7 to 3.5% by mass, from the viewpoint of obtaining a higher yield of trioxane, and more preferably 0.7 to 2.5% by mass, from the viewpoint of preventing clogging of piping, etc. due to the generation of paraformaldehyde, etc. When the content of methanesulfonic acid is 0.7% by mass or more, it is preferable because trioxane can be produced in high yield. On the other hand, when the content of methanesulfonic acid is 4.5% by mass or less, it is preferable because clogging of piping, etc. due to the generation of paraformaldehyde, etc. can be prevented.

[0026] 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, based on the total mass of the composition. If the total content is less than 68% by mass, clogging of pipes, etc. due to generation of paraformaldehyde, etc. can be prevented, which is preferable.

[0027] The mass ratio (A / (A+B)) of the content of formaldehyde (A) to the total content of formaldehyde (A) and methanesulfonic acid (B) is preferably 0.900 to 0.995, more preferably 0.930 to 0.995, even more preferably 0.950 to 0.990, even more preferably 0.955 to 0.990, and even more preferably 0.970 to 0.985. When the mass ratio is in the above range, trioxane can be produced in high yield and clogging of piping, etc. due to the generation of paraformaldehyde, etc. can be prevented, which is preferable.

[0028] [Other acids] The composition according to the present invention may contain another acid. Here, "another acid" means an acid other than (B) methanesulfonic acid.

[0029] The other acid is not particularly limited, but examples thereof include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, perchloric acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, 1,5-naphthalenedisulfonic acid, etc. These other acids may be used alone or in combination of two or more kinds.

[0030] The content of the other acid is preferably 0.1 to 10 mass %, more preferably 0.1 to 3 mass %, and even more preferably 0.3 to 1 mass %, based on the total mass of the composition. When two or more kinds of other acids are contained, the total content thereof is preferably within the above range.

[0031] [(C) Metal salt] The metal salt forms a protective film on the metal surface of the pipe etc., and prevents the metal from being corroded by methanesulfonic acid. In this specification, the term "metal" means iron, steel and non-ferrous metals, preferably stainless steel (SUS) and carbon steel, and more preferably stainless steel (SUS).

[0032] The metal salt includes at least one selected from the group consisting of nitrates, nitrites, and persulfates.

[0033] The nitrate is not particularly limited, but examples thereof include sodium nitrate, potassium nitrate, magnesium nitrate, cerium nitrate, ammonium cerium nitrate, iron nitrate, molybdenum nitrate, and vanadium nitrate.

[0034] The nitrite is not particularly limited, but examples thereof include sodium nitrite, potassium nitrite, magnesium nitrite, cerium nitrite, ammonium cerium nitrite, iron nitrite, molybdenum nitrite, and vanadium nitrite.

[0035] The persulfate is not particularly limited, but examples thereof include sodium persulfate, potassium persulfate, magnesium persulfate, cerium persulfate, ammonium cerium persulfate, iron persulfate, molybdenum persulfate, and vanadium persulfate.

[0036] Among these, the metal salt preferably contains at least one selected from the group consisting of nitrates and nitrites, more preferably contains a nitrate, further preferably contains at least one selected from the group consisting of sodium nitrate, potassium nitrate, magnesium nitrate, cerium nitrate, and ammonium cerium nitrate, and particularly preferably contains sodium nitrate and / or potassium nitrate. The above-mentioned metal salts may be used alone or in combination of two or more.

[0037] 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, and even more preferably 0.002 to 0.004% by mass, relative to the total mass of the composition, from the viewpoint of preventing clogging of pipes, etc. due to the generation of paraformaldehyde, etc. When the content of the metal salt is less than 0.007% by mass, clogging of pipes, etc. due to the generation of paraformaldehyde, etc. can be prevented, which is preferable.

[0038] [water] The composition according to the present invention preferably contains water. When the composition contains water, it is possible to dissolve (A) formaldehyde. This makes it possible to prevent blockage of piping and the like due to the production of paraformaldehyde and the like. Furthermore, 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. This makes it possible to shift the equilibrium reaction of converting formaldehyde to trioxane toward the production of trioxane.

[0039] The water content is preferably 20 to 40% by mass, more preferably 30 to 40% by mass, and even more preferably 35 to 40% by mass, based on the total mass of the composition. When the water content is 20% by mass or more, formaldehyde can be suitably dissolved, and clogging of pipes, etc. due to the generation of paraformaldehyde, etc. can be prevented, which is preferable. On the other hand, when the water content is 40% by mass or less, trioxane can be produced in high yield, which is preferable.

[0040] [Organic solvents] The composition according to the present invention may contain an organic solvent. The organic solvent can suitably dissolve formaldehyde, thereby preventing the production of paraformaldehyde and the like.

[0041] [Trioxane] The composition according to the present invention is an equilibrium reaction liquid and therefore usually contains trioxane.

[0042] 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.

[0043] [Additives] The composition according to the present invention may contain an additive. The additive is not particularly limited, but may include an antifoaming agent, a surfactant, a stabilizer, etc. These additives may be used alone or in combination of two or more kinds.

[0044] [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.

[0045] In one embodiment, from the viewpoint of suitably obtaining the effects of high-yield trioxane production, prevention of blockage of piping and the like due to generation of paraformaldehyde and the like, and prevention of metal corrosion, a preferred combination of the contents of (A) to (C) in the composition is preferably 59 to 65 mass% of (A), 0.5 to 2.5 mass% of (B), and 0.002 to 0.004 mass% of (C), with the total content of (A) formaldehyde and (B) methanesulfonic acid being 60 to 66 mass%, and more preferably 60 to 64 mass% of (A), 1 to 2 mass% of (B), and 0.002 to 0.004 mass% of (C), with the total content of (A) formaldehyde and (B) methanesulfonic acid being 61 to 66 mass%. In another embodiment, from the viewpoint of suitably obtaining a high yield of trioxane, a preferred combination of the contents of (A) to (C) in the composition is preferably 62 to 65 mass% of (A), 0.5 to 3.5 mass% of (B), and 0.002 to 0.004 mass% of (C), with the total content of (A) formaldehyde and (B) methanesulfonic acid being 64 to 67 mass%, and more preferably 63.5 to 65 mass% of (A), 1 to 3 mass% of (B), and 0.002 to 0.004 mass% of (C), with the total content of (A) formaldehyde and (B) methanesulfonic acid being 65 to 67 mass%.

[0046] <Method of producing trioxane> According to one embodiment of the present invention, there is provided a method for producing trioxane. 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. The method for producing trioxane may further include a trioxane purification step.

[0047] [Trioxane manufacturing process] The trioxane production process is a process in which a solution containing (A) formaldehyde, (B) methanesulfonic acid, and (C) a metal salt is reacted to obtain trioxane.

[0048] (solution) The solution contains (A) formaldehyde, (B) methanesulfonic acid, and (C) a metal salt, and may further contain other acids, water, organic solvents, additives, and the like.

[0049] The (A) formaldehyde, (B) methanesulfonic acid, (C) metal salt, other acid, water, organic solvent, additives, etc., are those described above.

[0050] The contents of (A) formaldehyde, (B) methanesulfonic acid, and (C) metal salt in the solution are preferably amounts such that the reaction solution at equilibrium has the above-mentioned composition, taking into consideration the production conditions set in the trioxane production process. The amounts of other acids, water, organic solvents, additives, etc. added can be appropriately set.

[0051] (reaction) (B) In the presence of methanesulfonic acid, (A) formaldehyde is trimerized to produce trioxane, where the trimerization is an equilibrium reaction.

[0052] In addition, by side reactions, formic acid, glycolic acid (CH2OHCOOH), methanol, and carbon dioxide may be produced. Furthermore, these by-products may react to form further by-products. However, when the reaction solution at equilibrium is adjusted to be the composition according to the present invention, the trimerization of formaldehyde can occur more selectively, and trioxane can be produced in high yield.

[0053] The reaction method is not particularly limited, and a known method can be applied. For example, the reaction method includes a method of heating the solution.

[0054] 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, the produced trioxane can be distilled out of the reaction system, and trioxane can be obtained in a higher yield.

[0055] The reaction pressure is not particularly limited, but is preferably 0.1×10 5 ~10×10 5 Pa is preferred, and 1×10 5 ~5×10 5 Pa is more preferable, and 1×10 5 ~2×10 5 It is more preferable that the reaction pressure is 10 Pa. By adjusting the reaction pressure, the produced trioxane can be distilled out of the reaction system, and trioxane can be obtained in a higher yield.

[0056] The reaction time is not particularly limited, but is preferably 0.1 to 10 hours, more preferably 0.3 to 5 hours, and further preferably 0.5 to 4 hours. By adjusting the reaction time, trioxane can be produced efficiently.

[0057] Since the trimerization of formaldehyde is an equilibrium reaction, it is preferable to distill off the product trioxane from the reaction system during the reaction. For example, when the composition contains water, trioxane forms an azeotropic mixture with water and is distilled off from the reaction system under the specified reaction conditions.

[0058] The trioxane distilled off (for example, an azeotropic mixture of trioxane and water) is preferably purified as it is in the trioxane purification step described below.

[0059] In the case of continuous production of trioxane, the method can be carried out by successively adding an aqueous formaldehyde solution to a reaction system in which methanesulfonic acid and a metal salt are present, and successively distilling off the resulting trioxane from the reaction system. In this case, the aqueous formaldehyde solution is preferably added in an amount such that the reaction solution at equilibrium has the composition of the composition according to the present invention, taking into consideration the reaction conditions, the amount of trioxane distilled off from the reaction system, and the like.

[0060] [Trioxane refining process] The trioxane purification step is a step of purifying the trioxane obtained in the trioxane production step. In this case, the "obtained trioxane" includes trioxane distilled out of the reaction system during the reaction (preferably an azeotropic mixture of trioxane and water) and the reaction solution after the reaction. In this case, the "obtained trioxane" may include, in addition to trioxane, formaldehyde, water, organic solvents, additives, by-products (formic acid, glycolic acid (CH2OHCOOH), methanol, carbon dioxide), droplet-derived components generated in the reaction system, piping-derived components, and the like.

[0061] The purification method is not particularly limited, but includes distillation, crystallization, filtration, extraction, etc. Among these, the purification method preferably includes distillation and / or extraction, and more preferably includes distillation. In addition, the purification method may be any known method.

[0062] At least one of the impurities other than trioxane separated in the purification step, such as formaldehyde, water, an organic solvent, etc., is preferably reused in the trioxane production step. EXAMPLES

[0063] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0064] [Example 1] (Production of trioxane) A solution containing (A) formaldehyde, (B) methanesulfonic acid, (C) sodium nitrate, and water was introduced into a reactor (reactor-piping (distillation line)-Allen condenser-distillate storage flask-piping (return line)-reactor) in which a distillate storage flask and an Allen condenser were connected by two pipes (distillation line and return line), and trioxane was produced by heating for 3 hours at a heat medium temperature of 130°C. The content of (A) formaldehyde in the reaction liquid (composition) at equilibrium after 3 hours was measured by neutralizing the methanesulfonic acid and by-product acid components (formic acid, etc.) in the composition with dilute hydrochloric acid in advance, and then reacting with sodium sulfite to produce sodium hydroxide, which was then subjected to neutralization titration with acid. 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 (instrument name: Dionex ICS-2100, 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, based on the total mass of the composition.

[0065] During this reaction, the trioxane produced in the reaction formed an azeotropic mixture with water and was distilled off from the reaction system. This shifted the equilibrium reaction of producing trioxane from formaldehyde toward the trioxane production side. The azeotropic mixture of trioxane and water was liquefied by being cooled in an Allen cooler through a pipe (distillation line) connected to the reactor, and was stored as a trioxane distillate in a distillate storage flask connected to the Allen cooler. When the amount of trioxane distillate in the distillate storage flask exceeded the storage capacity, the trioxane distillate in the distillate storage flask was returned to the reactor through a pipe (return line).

[0066] [Example 2] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 64 mass %.

[0067] [Example 3] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 64 mass%, and the content of (B) was adjusted to 2 mass%.

[0068] [Example 4] A composition was produced in the same manner as in Example 1, except that the content of (B) in the reaction liquid (composition) at equilibrium was adjusted to 3 mass %.

[0069] [Example 5] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 64 mass%, and the content of (B) was adjusted to 3 mass%.

[0070] [Example 6] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 63 mass%, and the content of (B) was adjusted to 4 mass%.

[0071] [Example 7] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (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%.

[0072] [Example 8] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (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%.

[0073] [Example 9] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (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%.

[0074] [Comparative Example 1] A composition was produced in the same manner as in Example 1, except that the content of (B) in the reaction liquid (composition) at equilibrium was adjusted to 0.5 mass %.

[0075] [Comparative Example 2] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 64 mass%, and the content of (B) was adjusted to 0.5 mass%.

[0076] [Comparative Example 3] A composition was produced in the same manner as in Example 1, except that the content of (B) in the reaction liquid (composition) at equilibrium was adjusted to 5 mass %.

[0077] [Comparative Example 4] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 66 mass %.

[0078] [Comparative Example 5] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 64 mass%, and the content of (B) was adjusted to 4 mass%.

[0079] [Comparative Example 6] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 58 mass%, and the content of (B) was adjusted to 2 mass%.

[0080] [Comparative Example 7] A composition was produced in the same manner as in Example 1, except that the content of (B) in the reaction liquid (composition) at equilibrium was adjusted to 2 mass %, and the content of (C) was adjusted to 0.01 mass %.

[0081] [Comparative Example 8] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (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%.

[0082] [Comparative Example 9] A composition was produced in the same manner as in Example 1, except that the content of (B) in the reaction liquid (composition) at equilibrium was adjusted to 4 mass %, and the content of (C) was adjusted to 0.01 mass %.

[0083] [Comparative Example 10] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 64 mass%, the content of (B) was adjusted to 2 mass%, and (C) was not added.

[0084] [Comparative Example 11] A composition was produced in the same manner as in Example 1, except that the content of (A) in the reaction liquid (composition) at equilibrium was adjusted to 63 mass%, the content of (B) was adjusted to 4 mass%, and (C) was not added.

[0085] The compositions of the compositions in Examples 1 to 9 and Comparative Examples 1 to 11 are shown in Table 1 below.

[0086] [Table 1]

[0087] [evaluation] Various evaluations were carried out on the compositions of Examples 1 to 9 and Comparative Examples 1 to 11 or the trioxane distillate in the distillate storage flask.

[0088] (Trioxane content) After the reaction equilibrium was reached (3 hours later), the trioxane distillate was collected from the distillate storage flask, and the trioxane content in the trioxane distillate was measured by gas chromatography to calculate the trioxane content (TOX content) relative to the total mass of the trioxane distillate. In this case, the gas chromatography measurement was performed using a Nexis GC-2030 (Shimadzu Corporation) as the apparatus and a DB-WAX (Agilent Technology) as the column. A high TOX content indicates that trioxane was produced in high yield. The results are shown in Table 2 below.

[0089] (Appearance of reaction solution) After the reaction equilibrium was reached (3 hours later), the reaction liquid (composition) in the reactor was visually observed and the appearance of the reaction liquid was evaluated according to the following criteria. A high evaluation result for the appearance of the reaction liquid indicates that paraformaldehyde and the like were not produced from formaldehyde during the trioxane production process. For this reason, when trioxane is produced using the composition, clogging of piping and the like is unlikely to occur, making it suitable for continuous production. The results obtained are shown in Table 2 below.

[0090] ○: Colorless and transparent △: Slightly cloudy ×: Significantly cloudy

[0091] (Stainless Steel (SUS) Corrosive) After the reaction equilibrium was reached (3 hours later), a SUS316L test piece (length 60 mm, width 20 mm, thickness 2 mm, equipped with welded lines of the same material on both sides and a φ4 mm drilled through hole) was immersed in 100 g of the reaction liquid (composition) in the reactor and left to stand at 90° C. for 1 day. The mass loss rate (mass) of the test piece after immersion was calculated by the following formula.

[0092]

number

[0093] The SUS corrosiveness was evaluated according to the following criteria. A high evaluation result for SUS corrosiveness indicates that the composition is less likely to corrode SUS equipment. The results are shown in Table 2 below.

[0094] ○: Mass reduction rate less than 0.2 mass% ×: Mass reduction rate is 0.2 mass% or more

[0095] [Table 2]

[0096] From the results in Table 2, it is found that the compositions of Examples 1 to 9 can produce trioxane in high yield, prevent the by-production of paraformaldehyde and the like, and prevent corrosion of SUS. Therefore, it can be said that the compositions of Examples 1 to 9 can produce trioxane in high yield and are suitable for continuous production.

Claims

1. A method for producing trioxane, comprising the steps of reacting a solution containing (A) formaldehyde, (B) methanesulfonic acid, and (C) a metal salt, The reaction solution at equilibrium in the step of obtaining trioxane is (A) 58.5 to 65.5% by mass of formaldehyde; (B) 0.7 to 4.5% by mass of methanesulfonic acid; (C) less than 0.007% by mass of a metal salt; A composition comprising: The total content of (A) formaldehyde and (B) methanesulfonic acid is less than 68% by mass, (C) A method for producing trioxane, wherein the metal salt is a composition containing at least one selected from the group consisting of nitrates, nitrites, and persulfates.

2. The method according to claim 1, wherein the content of the formaldehyde (A) is 60 to 65.5 mass%.

3. The method according to claim 1, wherein the content of the methanesulfonic acid (B) is 0.7 to 3.5 mass%.

4. The method according to claim 1, wherein the content of the metal salt (C) is 0.002 to 0.004 mass %.

Images