Method for producing formaldehyde and polyacetal

Abstract

To provide a method for producing formaldehyde capable of reducing negative influence on catalysts and the like during a process for producing formaldehyde by using methanol.SOLUTION: A method for producing formaldehyde using methanol as a raw material, the methanol containing nitrogen oxides, wherein the concentration of NO2 in the methanol, as detected by ion chromatographic analysis, is 0.002 mass ppm or more and 100 mass ppm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing formaldehyde and polyacetal. [Background technology]

[0002] Polyoxymethylene is used in a wide range of fields, including the automotive industry, the electrical industry, the home appliance industry, the medical industry, etc. Polyoxymethylene is produced from formaldehyde. Conventionally, a method of oxidizing methanol in the presence of a catalyst such as silver has been known as an industrial method for producing formaldehyde (Patent Document 1). Also, a method for producing formaldehyde by oxidizing methylal with a methanol oxidation catalyst has been proposed (Patent Document 2). Furthermore, a method has been disclosed in which formaldehyde is obtained by reacting methanol with formaldehyde to obtain methylal, and then oxidizing the methylal in the presence of an oxidation catalyst (Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 58-85834 [Patent Document 2] U.S. Patent No. 2,467,223 [Patent Document 3] Japanese Patent Application Publication No. 1-287051 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as described above, many catalysts for producing formaldehyde from methanol contain metals or metal components, and their activity can be reduced by the influence of compounds present in the reaction system, particularly compounds (impurities) contained in the raw material methanol. If the activity of the catalyst is reduced, the purity, selectivity, conversion rate, etc. of the formaldehyde obtained may decrease.

[0005] Therefore, the present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for producing formaldehyde that does not adversely affect catalysts and the like in the production process when producing formaldehyde using methanol, and to provide a method for producing polyacetal using the formaldehyde. [Means for solving the problem]

[0006] The present inventors have conducted extensive research into methods for producing formaldehyde using methanol as a raw material in order to solve the above-mentioned problems. As a result, they have focused on nitrogen oxides in the raw material methanol and found that the above-mentioned problems can be solved by setting the NO2 concentration (impurity concentration) in methanol within a specific range, thereby completing the present invention.

[0007] That is, the present invention is as follows. [1] A method for producing formaldehyde using methanol as a raw material, the methanol contains nitrogen oxides; A method for producing formaldehyde, characterized in that the concentration of NO2 in the methanol detected by ion chromatography is 0.002 mass ppm or more and 100 mass ppm or less. [2] The method for producing formaldehyde according to [1], wherein the formaldehyde is produced by oxidizing the methanol in the presence of a catalyst. [3] Step (1): obtaining methylal from the methanol; Step (2): producing formaldehyde from the methylal obtained in Step (1); The method for producing formaldehyde according to [1] or [2], comprising: [4] A method for producing polyacetal, characterized in that formaldehyde obtained by the production method according to any one of [1] to [3] is used as a raw material. [Effects of the Invention]

[0008] According to the present invention, when producing formaldehyde using methanol, adverse effects on catalysts and the like in the production process can be suppressed, and formaldehyde can be produced in a suitable manner. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram schematically illustrating an apparatus used in the production of formaldehyde by oxidation of methylal according to the present embodiment. [Figure 2] FIG. 1 is a diagram schematically illustrating an apparatus used in the production of formaldehyde by methanol oxidation in the presence of a catalyst according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail.

[0011] <Formaldehyde manufacturing method> The method for producing formaldehyde according to the present embodiment (hereinafter sometimes referred to as the "production method according to the present embodiment") includes the steps of: A method for producing formaldehyde using methanol as a raw material, comprising: the methanol contains nitrogen oxides; The concentration of NO2 in the methanol detected by ion chromatography is 0.002 mass ppm or more and 100 mass ppm or less.

[0012] In the production method of this embodiment, the methanol contains nitrogen oxides. The methanol may be produced by any known method, such as a method of producing methanol by reacting hydrogen with carbon monoxide produced by partial oxidation of coal or natural gas, or a method of producing methanol by fermentation using methane or the like with methanol-producing bacteria.

[0013] Examples of the nitrogen oxides include so-called NO, such as nitric oxide, nitrogen dioxide, nitrogen trioxide, nitrous oxide, dinitrogen trioxide, dinitrogen tetroxide, and dinitrogen pentoxide. x and compounds produced by reaction of these with water or metals, such as nitric acid, nitrous acid, potassium nitrate, potassium nitrite, sodium nitrate, and sodium nitrite.

[0014] The methanol of this embodiment has an NO concentration of 0.002 mass ppm or more and 100 mass ppm or less as detected by ion chromatography. This NO concentration range depends on the effect on the catalyst used in producing formaldehyde from methanol. The reason for this will be explained later when describing the method for producing formaldehyde from methanol.

[0015] Since the impurities contained in the methanol vary depending on the production method, NO2 may not be detected in the analysis by ion chromatography. In such cases, in order to favorably affect the catalyst, an appropriate amount of, for example, nitric oxide, nitrogen dioxide, nitrous acid, potassium nitrite, sodium nitrite, etc. may be added to the methanol to adjust the NO2 concentration to the above range.

[0016] Furthermore, for example, when methanol is produced by fermentation using a methanol-producing bacterium, the NO concentration detected by ion chromatography may be higher than the above-mentioned preferred range. In such cases, the amount of nitrogen oxides contained in the methanol may be adjusted to fall within the above-mentioned range by heating under reduced pressure, degassing, or other procedures.

[0017] Furthermore, the methanol may contain impurities within a conventionally known range. For example, when the methanol is analyzed by ion chromatography, chlorine (Cl), bromine (Br), sulfuric acid (SO), formic acid, acetic acid, etc. may be detected, and when inductively coupled plasma atomic emission spectroscopy (ICP-AES) is used, calcium (Ca), sodium (Na), zinc (Zn), etc. may be detected. The methanol may also contain water.

[0018] (Production of formaldehyde by oxidation of methanol in the presence of a catalyst) A first aspect of the method for producing formaldehyde according to the present embodiment is a method for producing formaldehyde by oxidizing the methanol in the presence of a catalyst.

[0019] When the methanol is oxidized in the presence of the catalyst, the methanol is supplied to the reactor as a gas, preferably mixed with steam and / or an inert gas such as nitrogen.

[0020] Pure oxygen or air can be used as an oxidizing agent for oxidizing the methanol. When air is used as the oxidizing agent, the ratio of oxygen to methanol is preferably 0.2 to 0.6 moles per mole of methanol. When methanol is supplied together with water vapor, the amount of water vapor is preferably 3.0 moles or less per mole of methanol.

[0021] The catalyst may be, for example, silver, iron oxide, molybdenum oxide, or the like. The shape of the catalyst is not particularly limited, and fine particles, powder, or granules may be used. The catalyst is preferably arranged so as to form a catalyst layer in the reactor, and the particle size distribution of the catalyst within the catalyst layer can be determined as desired.

[0022] The reaction temperature of the methanol is not particularly limited, but is preferably 400° C. or higher and 800° C. or lower, and the pressure at that time is preferably 0.5 atmospheres or higher and 2.0 atmospheres or lower. Furthermore, it is preferable that methanol is continuously supplied to the reactor and the reaction gas extracted from the reactor is appropriately cooled. The cooled reaction gas is preferably supplied to an absorption tower and absorbed in water or an aqueous formaldehyde solution.

[0023] The formaldehyde absorption tower may be a packed tower, a plate tower, a wetted-wall tower, or the like. Preferably, the absorption tower is operated in a manner such that a formaldehyde-containing gas is introduced into the bottom or lower part of the tower, an absorbing medium is supplied to the top of the tower, and countercurrent contact is carried out within the absorption tower. As the absorption medium, water or an aqueous formaldehyde solution is preferably used.

[0024] In the first embodiment, nitrogen oxides contained in the methanol also affect the catalytic activity as described above. The mechanism is not clear, but the present inventors speculate as follows. Here, the case where silver is used as the catalyst will be described.

[0025] For example, a silver catalyst may have a silver oxide coating formed by the air (oxygen) supplied together with methanol, resulting in a decrease in activity over time. If the methanol contains nitrogen oxides, the nitrogen oxides, such as nitrogen dioxide, react with water in the system to produce nitric acid, which then reacts with silver oxide to produce soluble silver nitrate, thereby suppressing the formation of a coating on the catalyst surface. On the other hand, if methanol contains too much nitrogen oxide, the nitric acid produced by the reaction of nitrogen dioxide with water in the system reacts directly with the catalytic silver and flows out of the system as silver nitrate, reducing the catalytic activity.

[0026] (Oxidation of methylal to produce formaldehyde) A second aspect of the production method of this embodiment is a method for producing formaldehyde including steps (1) and (2). Step (1): A step of producing methylal from methanol Step (2): A step of producing formaldehyde from the methylal obtained in step (1).

[0027] The catalyst used in step (1) may be a solid acid catalyst such as an ion exchange resin, a fluorinated alkylene resin sulfonic acid group derivative, a crystalline aluminosilicate, or a heteropolyacid, and an ion exchange resin, particularly a strongly acidic cation exchange resin, is preferably used. For example, when a solid acid catalyst is used, a solution containing methanol, formaldehyde and water is brought into solid-liquid contact with the solid acid catalyst, and a component containing methylal is obtained as a distillate by distillation.

[0028] The amount of methanol used is usually 1.0 to 1.5 times, preferably 1.0 to 1.2 times, relative to the stoichiometric reaction ratio of 2 with formaldehyde. The reaction temperature is not particularly limited, but is preferably 40°C or higher and lower than 90°C.

[0029] The step (2) is a step of producing formaldehyde from the methylal produced in the step (1).

[0030] The catalyst used in the step (2) may be silver, copper oxide, molybdenum, vanadium, iron molybdate, molybdenum activated with iron, manganese, magnesium, cadmium, calcium, or the like; phosphorus oxide or molybdenum oxide activated with manganese, magnesium, cadmium, calcium, or the like; or the like.

[0031] A catalyst containing iron and molybdenum, plus one or more metal elements selected from alkali metals, bismuth, chromium, tungsten, nickel, and cobalt as active ingredients, can also be used. The content ratio of these metal elements is preferably such that, in terms of atomic ratio, iron:molybdenum is 1.5 to 3.0, and the total of alkali metals, bismuth, chromium, tungsten, cobalt, and nickel is 0.001 to 0.1. For example, a catalyst in which the atomic ratio of molybdenum to iron, Mo / Fe, is 1.6 to 4.5, is preferred.

[0032] The form of the reactor used in the step (2) is not particularly limited. For example, a preferred example is a tubular reactor packed with an oxidation catalyst, in which a gas containing methylal and oxygen flows through the catalyst layer to produce formaldehyde. The catalyst packed in the tube may have a shape such as granules, cylinders, Raschig rings, or spokes rings.

[0033] In the step (2), the methylal used may be mixed with methanol. The reaction temperature is not particularly limited, but is preferably 250°C or higher and 400°C or lower.

[0034] In the second embodiment, nitrogen oxides contained in the methanol also affect the catalytic activity. Although the mechanism by which this occurs is not clear, the present inventors speculate that this is due to the following reasons.

[0035] The following describes the case where a strongly acidic cation exchange resin is used in step (1). Strongly acidic cation exchange resins have a structure in which sulfonic acid groups are attached to a cross-linked styrene skeleton. Continued use can result in the elimination of the sulfonic acid groups, reducing the activity of the strongly acidic cation exchange resin. Therefore, if the methanol contains nitrogen oxides, the nitrogen oxides react with water in the system to produce nitric acid, which then attaches to the benzene ring of the styrene skeleton of the cation exchange resin to form a nitro group. As a result, the nitro group attached to the benzene ring is an electron-withdrawing group, preventing the elimination of the sulfonic acid group and reducing the activity of the cation exchange resin.

[0036] If the methanol does not contain nitrogen oxides, the above-mentioned effects cannot be obtained, and the activity of the ion exchange resin may decrease as operation continues. On the other hand, if methanol contains too much nitrogen oxides, nitric acid derived from the nitrogen oxides reacts with the metal components contained in the catalyst used in step (2) to form metal nitrates, which causes the metal components to be desorbed from the catalyst layer and results in catalyst consumption. In this way, by setting the content of nitrogen oxides contained in the methanol to a specific range, a preferable effect can be exhibited in any method for producing formaldehyde from methanol.

[0037] The formaldehyde is preferably supplied to an absorption tower and absorbed in water or an aqueous formaldehyde solution. The absorption tower may be a packed tower, a plate tower, a wetted-wall tower, or the like. Preferably, the absorption tower is operated in a manner such that a formaldehyde-containing gas is introduced into the bottom or lower part of the tower, an absorbing medium is supplied to the top of the tower, and countercurrent contact is effected within the absorption tower. As the absorption medium, water or an aqueous formaldehyde solution is preferably used.

[0038] (Production of formaldehyde with low moisture content) The aqueous formaldehyde solution obtained in the absorption tower can be separated into formaldehyde having a higher water content than the aqueous solution and formaldehyde having a lower water content than the aqueous solution.

[0039] The formaldehyde can be separated by any known method, for example, by reacting an aqueous formaldehyde solution with an alcohol such as polyethylene glycol, cyclohexanol, or trimethylolpropane to produce hemiformal, separating formaldehyde with a high water content from hemiformal by distillation or the like, and then thermally decomposing the hemiformal to obtain formaldehyde with a low water content.

[0040] Formaldehyde with a low water content can be used, for example, in the production of polyacetal by polymerization of formaldehyde, while formaldehyde with a high water content can be used in processes such as the production of methylal.

[0041] <Production of trioxane> The formaldehyde obtained by the above method can be used to produce trioxane. For example, an aqueous solution containing trioxane is produced by heating an aqueous formaldehyde solution in the presence of a catalyst, which may be an inorganic acid such as sulfuric acid or nitric acid, an ion exchange resin, a fluorinated alkylene resin derivative with a sulfonic acid group, a crystalline aluminosilicate, a solid acid catalyst such as a heteropolyacid, or the like, and an ion exchange resin, particularly a strongly acidic cation exchange resin, is preferably used.

[0042] As a method for recovering trioxane from an aqueous solution containing trioxane, a known method can be used, for example, a method based on distillation separation, a method based on extraction separation, or a combination of these methods.

[0043] For example, an aqueous solution containing trioxane is distilled to recover an aqueous solution containing trioxane, water, and formaldehyde as a distillate. The distillate containing trioxane is then contacted with an organic solvent to extract trioxane into the organic solvent phase, and the extract is further purified to obtain high-purity trioxane. High purity trioxane can be used to produce polyacetals by polymerization of trioxane.

[0044] <Production of polyacetal> The method for producing polyacetal according to this embodiment uses formaldehyde obtained by the above-described production method according to this embodiment as a raw material. More specifically, the polymer can be produced by feeding formaldehyde gas, a chain transfer agent (molecular weight modifier), and a polymerization catalyst into a polymerization reactor containing a hydrocarbon polymerization solvent and polymerizing them by a slurry polymerization method. However, the polymerization method is not limited to the above, and polymerization can also be carried out by a known method.

[0045] The molecular weight of the polyoxymethylene homopolymer can be adjusted by chain transfer using a molecular weight regulator such as a carboxylic acid anhydride or a carboxylic acid, etc. As the molecular weight regulator, propionic anhydride and acetic anhydride are particularly preferred, and acetic anhydride is more preferred.

[0046] The amount of the molecular weight regulator to be incorporated may be adjusted and determined depending on the desired properties (particularly the melt flow rate) of the polyoxymethylene homopolymer.

[0047] The polymerization catalyst is preferably an anionic polymerization catalyst, and more preferably an onium salt polymerization catalyst represented by the following general formula (1). [R 1 R 2 R 3 R 4 M] + X - ···(1) (In formula (1), R 1 , R 2 , R 3 and R 4 each independently represents an alkyl group, M represents an element having a lone electron pair, and X represents a nucleophilic group. The polymerization catalyst may be used alone or in combination of two or more.

[0048] Among onium salt-based polymerization catalysts, quaternary ammonium salt-based compounds such as tetramethylammonium bromide and dimethyldistearylammonium acetate are more preferred.

[0049] The hydrocarbon polymerization solvent is not particularly limited as long as it does not react with formaldehyde, but examples thereof include pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, benzene, etc., with hexane being particularly preferred. These hydrocarbon solvents may be used alone or in combination of two or more.

[0050] The crude polyoxymethylene homopolymer obtained by polymerization has thermally unstable terminal groups, and therefore, after catalyst deactivation, it is preferable to cap and stabilize the unstable terminal groups by reacting them with an esterifying agent, etherifying agent, or the like in the liquid or gas phase, in order to prevent decomposition of the polyoxymethylene during melt processing.

[0051] The terminal stabilization treatment of the crude polyoxymethylene homopolymer by esterification can be carried out, for example, by charging the crude polyoxymethylene homopolymer, an esterifying agent, and an esterification catalyst into an end-stabilization reactor optionally containing a hydrocarbon solvent, and allowing them to react. The reaction temperature and reaction time are preferably 130 to 165°C and 1 to 100 minutes, respectively.

[0052] As an esterifying agent for blocking and stabilizing the terminal groups of the crude polyoxymethylene homopolymer, an acid anhydride represented by the following general formula (2) can be used. R 5 COOCOR 6 ···(2) (In formula (2), R 5 and R 6 R each independently represents an alkyl group. 5 and R 6 may be the same or different. 5 and R 6 may be linked to each other to form a cyclic structure.

[0053] The esterifying agent is not limited to, but includes, for example, benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, and is preferably acetic anhydride. These esterifying agents may be used alone or in combination of two or more.

[0054] The esterification catalyst can be exemplified by an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms. An alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferred, and the amount added can be appropriately selected within the range of 1 to 1000 ppm by mass relative to the mass of the polyoxymethylene homopolymer. The alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is not limited to the following, but alkali metal salts of a carboxylic acid, among which lithium acetate, sodium acetate and potassium acetate are preferred.

[0055] The etherifying agent used to cap and stabilize the end groups of the crude polyoxymethylene homopolymer may be selected from orthoesters of aliphatic or aromatic acids and aliphatic, alicyclic, or aromatic alcohols, such as methyl orthoformate or ethyl orthoformate, methyl orthoacetate or ethyl orthoacetate, methyl orthobenzoate or ethyl orthobenzoate, and orthocarbonates, specifically ethyl orthocarbonate, and may be stabilized using a medium-strength organic acid such as p-toluenesulfonic acid, or a Lewis acid catalyst such as dimethyl sulfate and diethyl sulfate.

[0056] The solvent used in the etherification reaction when the terminal groups of the crude polyoxymethylene homopolymer are blocked and stabilized by etherification includes, but is not limited to, low-boiling aliphatic organic solvents such as pentane, hexane, cyclohexane, and benzene; alicyclic and aromatic hydrocarbon organic solvents; and halogenated lower aliphatic hydrocarbon organic solvents such as methylene chloride, chloroform, and carbon tetrachloride.

[0057] The polyoxymethylene homopolymer whose end groups have been stabilized by the above-mentioned method is adjusted to 100 to 150°C using a dryer such as a hot air dryer or a vacuum dryer to remove moisture and dry, thereby obtaining the desired polyoxymethylene homopolymer. <Production of polyacetal by polymerization of trioxane>

[0058] In the production of polyacetal by polymerization of trioxane, trioxane may contain one or more comonomers. The comonomers are components copolymerizable with trioxane, such as ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatane, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, and 1,6-hexanediol formal, and other cyclic ethers and / or cyclic formals. 1,3-dioxolane and 1,4-butanediol formal are particularly preferred.

[0059] The amount of the cyclic ether and / or cyclic formal added is preferably in the range of 1 to 20 mol % relative to 1 mol of the trioxane.

[0060] The trioxane may contain a low molecular weight acetal compound as a chain transfer agent for adjusting the molecular weight, and examples of the chain transfer agent include methylal, methoxymethylal, dimethoxymethylal, and trimethoxymethylal.

[0061] The amount of the low molecular weight acetal compound added is 0.1 × 10 per 1 mol of trioxane. -4 ~0.6×10 -2 It is preferably in the mol range.

[0062] Examples of the polymerization catalyst include Lewis acids, protonic acids, and their esters or anhydrides. Examples of Lewis acids include boric acid, tin, titanium, phosphorus, arsenic, and antimonides. Particularly preferred are boron trifluoride, boron trifluoride hydrates, and coordination complex compounds of boron trifluoride with an organic compound containing an oxygen atom or a sulfur atom. The amount of the polymerization catalyst added was 1×10 -9 ~1×10 -2The molar range is preferred.

[0063] The polymerization catalyst can also be used as a mixture with an organic solvent. The organic solvent used in this embodiment is preferably an aliphatic hydrocarbon compound or an ether compound without a hydroxyl group, which does not participate in or adversely affect the polymerization reaction. Specific examples include linear or cyclic aliphatic hydrocarbon compounds such as pentane, hexane, heptane, octane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane, and linear or cyclic ether compounds such as diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, dimethoxyethane, and tetrahydrofuran. The ratio of the polymerization catalyst to the organic solvent can be determined as desired.

[0064] In the production of polyacetal by the polymerization of trioxane, either a bulk method or a melt method can be employed as the polymerization method. The shape (structure) of the polymerization reactor used is not particularly limited, and either a two-screw paddle-type or screw-type stirring and mixing polymerization apparatus capable of passing a heat medium through a jacket is suitably used.

[0065] The temperature of the polymerization reactor is preferably 63 to 155° C. The residence (reaction) time in the polymerization reactor is preferably 0.1 to 30 minutes.

[0066] The polyacetal obtained by polymerization is introduced into an aqueous or organic solution containing at least one neutralizing deactivator, such as ammonia, amines such as triethylamine or tri-n-butylamine, hydroxides of alkali metals or alkaline earth metals, inorganic salts, or organic acid salts, and the polymerization catalyst is deactivated by continuously stirring the slurry at room temperature to 100°C for several minutes to several hours. The polyacetal that has undergone the deactivation treatment is filtered using a centrifuge and dried under nitrogen to obtain the desired polyacetal.

[0067] In the production of polyacetal, it is of course possible to use, in addition to the above components, other copolymer components capable of forming a block, branched or crosslinked structure.

[0068] The polyacetal produced by the above-described method can be blended with commonly used known additives, such as antioxidants, formic acid scavengers, weather (light) stabilizers, release (lubricants), reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposers, basic aids, antistatic agents, flame retardants, dyes, and fillers, as desired. Furthermore, the polyoxymethylene of this embodiment can be blended with other polymers to the extent that its physical properties are not impaired. The blending ratios of these additives are within appropriate ranges.

[0069] The polyacetal produced by the method of this embodiment and the polyacetal composition containing optional compounding agents can be subjected to various molding processes to produce molded articles and parts, which can be used for various applications. Its uses are not particularly limited, and it can be used for known uses of polyoxymethylene, such as electric and electronic components and industrial parts, including gears, cams, sliders, levers, arms, clutches, pulleys, rollers, key stems, key tops, shafts, bearings, guides, etc. It can also be used as automobile parts, such as fuel-related parts typified by gasoline tanks, fuel pump modules, valves, and gasoline tank flanges, door-related parts typified by door locks, door handles, window regulators, and speaker grills, seatbelt-related parts typified by seatbelt slip rings and press buttons, combination switch parts, and switches. [Example]

[0070] The following examples illustrate the present embodiments without limiting them.

[0071] <Ion chromatographic analysis> Methanol was diluted two-fold with ultrapure water (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare a measurement sample. The measurement conditions for ion chromatography were as follows: The analyzed elements were Cl, Br, NO2, NO3, SO4, formic acid, and acetic acid. Device: Tosoh IC 2010 (manufactured by Tosoh Corporation) Analysis mode: Suppressed-anion Detector: Electrical conductivity detector Column: Tosoh TSKgel guard column Super IC-AZ, inner diameter 4.6 mm, length 150 mm (manufactured by Tosoh Corporation) Column temperature: 40℃ Eluent composition: Mixture of sodium bicarbonate and sodium carbonate, sodium bicarbonate concentration 7.5 mM, sodium carbonate concentration 1.1 mM Eluent flow rate: 0.8mL / min Measurement sample injection volume: 30 μL Collection time: 30 min

[0072] <Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)> 10 g of methanol was placed in a Teflon (registered trademark) decomposition vessel and evaporated to dryness using a carbon block heater at 95° C. 0.5 mL of 30% hydrochloric acid and 7.5 mL of 68% nitric acid were added, followed by microwave thermal decomposition, and then ultrapure water (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to bring the total volume to 100 g. Both the 30% hydrochloric acid and 68% nitric acid used were ultra-high purity products (TAMAPURE-AA-100, manufactured by Tama Chemical Co., Ltd.). The conditions for carrying out the microwave thermal decomposition are as follows: Equipment: ETHOS one (Milestone General) Microwave power: 1000W Decomposition conditions: Heat at 200°C for 45 minutes, then hold for 20 minutes The measurement conditions for ICP-AES are as follows: Equipment: SPS3530UV-DD (Hitachi High-Tech Science) High frequency output: 1.2kW Plasma gas (Ar) flow rate: 16 L / min Auxiliary gas (Ar) flow rate: 0.5 L / min Carrier gas (Ar) pressure: 0.24MPa Carrier gas (Ar) flow rate: 0.3 L / min Chamber gas (Ar) flow rate: 0.6 L / min Purge gas (N2) flow rate: 5L / min Photometric height: 12mm The calibration curve was prepared as follows. A standard solution was prepared by diluting 1000 mg / L of ICP mixed standard solution with an aqueous acid solution. The standard solution concentration was 0.1 mg / L. The aqueous acid solution was prepared by adding 30% hydrochloric acid and 68% nitric acid to ultrapure water to achieve the same acid concentration as the digestion solution. A calibration curve was created with one calibration point using the ICP-AES measurement results of the standard solution.

[0073] <Method for measuring water content in methanol> Quantitative determination was carried out by the Karl Fischer method. Apparatus: CA-200 (Mitsubishi Chemical Analytical Co., Ltd.) Anolyte: Aquamicron® AKX Catholyte: Aquamicron (registered trademark) CXU Measurement method: Approximately 1 g of sample was weighed into a syringe and injected into the device. After the sample was injected, the total amount of water detected until the detection speed reached 0.02 μg / sec was divided by the amount of sample injected to calculate the water content (ppm).

[0074] [Example 1] Production of formaldehyde by oxidation of methylal Formaldehyde was produced using the apparatus shown in Figure 1. As a result of ion chromatographic analysis of the methanol used in Example 1, 0.01 mass ppm of Cl, 0.01 mass ppm of Br, 0.02 mass ppm of NO, 0.06 mass ppm of SO, and 0.05 mass ppm of formic acid were detected. However, NO and acetic acid were not detected. Furthermore, ICP-AES analysis of the methanol detected 0.2 ppm by mass of Ca and 0.2 ppm by mass of Na, but no Zn. Furthermore, the methanol contained 173 ppm by mass of water. A strongly acidic cation exchange resin (trade name: Amberlyst 35wet) was packed into reactors 9, 10, and 11. A 40 wt % aqueous formaldehyde solution was supplied from feed line 5 at a rate of 200 g / Hr, and methanol was supplied from feed line 2 at a rate of 170 g / Hr. Distillation column 1 was a packed column with a height of 2.5 m, with intermediate stages for extracting each liquid component. The extracted liquid was circulated to reactors 9, 10, and 11 by pumps and brought into solid-liquid contact with the oxygen absorber packed in the reactors. The reaction liquid containing methylal that left reactors 9, 10, and 11 was returned to distillation column 1 and brought into vapor-liquid contact with vapor rising from the bottom to the top of distillation column 1, so that the methylal concentration increased toward the top. The reflux liquid was returned to distillation column 1 to maintain the top temperature at 42°C. 200 g / hr of distillate was extracted from the top of distillation column 1 through distillation line 3. The methylal purity in the distillate was 99%. A tubular reactor 6 with an inner diameter of 21 mm and a length of 100 cm was packed with spoke rinse rings of iron molybdate-molybdenum trioxide (molybdenum / iron atomic ratio = 2.3). The upper 50 cm of the catalyst layer was packed with 75 vol% catalyst and 25 vol% ceramic Raschig rings, and the lower 50 cm was packed with catalyst alone. A heat medium heated to 260°C was circulated through the jacket 7 via the heat medium circulation line 15. A gas having a composition of 4 vol % of methylal from the distillate, 8.3 vol % of oxygen, 2 vol % of water, and the remainder nitrogen was supplied to the tube reactor 6 through a feed line 8. The internal temperature of the catalyst layer in the tube reactor 6 was 330°C. The gas produced by the reaction was recovered through a withdrawal line 16. The selectivity of the reaction of methylal to formaldehyde was 94%, and the conversion to formaldehyde was 93%. The amount of carbon monoxide produced as a by-product was 3% of the total formaldehyde produced. The gas recovered through the withdrawal line 16 was introduced into an absorption tower packed with Dixon packing. The gas was bubbled into the aqueous formaldehyde solution at the bottom of the absorption tower. Water was supplied from the top of the absorption tower, and the bubbling gas was brought into gas-liquid contact in the packed section. The amount of water supplied was adjusted so that the formaldehyde concentration at the bottom of the absorption tower was 65% by weight, and the aqueous formaldehyde solution was recovered. The above operation was continued, and after one month, 200 g / Hr of distillate was extracted from the top of distillation column 1 through distillation line 3, and the purity of methylal in the distillate was 99%. In addition, the selectivity of the reaction to formaldehyde and the conversion rate to formaldehyde remained unchanged.

[0075] [Comparative Example 1] Production of formaldehyde by oxidation of methylal As a result of ion chromatographic analysis of the methanol used in Comparative Example 1, 0.02 mass ppm of Cl, 0.02 mass ppm of Br, 120 mass ppm of NO, 0.05 mass ppm of SO, and 0.05 mass ppm of formic acid were detected. However, NO and acetic acid were not detected. Furthermore, ICP-AES analysis of the methanol detected 0.2 ppm by mass of Ca and 0.2 ppm by mass of Na, but no Zn. The methanol contained 160 ppm by mass of water. The same procedure as in Example 1 was carried out using the above methanol, and operation was continued for one month. After one month, 200 g / Hr of distillate was still extracted from the top of distillation column 1 through distillation line 3, and the purity of methylal in the distillate was 99%. However, the selectivity of the reaction to formaldehyde was 92%, and the conversion to formaldehyde was 92%, both of which had decreased.

[0076] [Comparative Example 2] Production of formaldehyde by oxidation of methylal As a result of ion chromatographic analysis of the methanol used in Comparative Example 2, the Cl content was 0.04 ppm by mass, and Br, NO2, NO3, SO4, formic acid, and acetic acid were not detected. Furthermore, ICP-AES analysis of the methanol detected 0.9 ppm by mass of Na, but no Ca or Zn. The methanol contained 155 ppm by mass of water. The same procedure as in Example 1 was carried out using the above methanol, and operation was continued for one month. After one month, a distillate was withdrawn from the top of distillation column 1 through distillation line 3 at a rate of 200 g / Hr. The purity of methylal in the distillate was 97%. The selectivity of the reaction to formaldehyde was 94%, and the conversion to formaldehyde was 93%.

[0077] [Example 2] Production of formaldehyde by methanol oxidation in the presence of a catalyst Formaldehyde was produced using the apparatus shown in Figure 2. The same methanol as that used in Example 1 was used. Silver was used as the catalyst, and a catalyst layer 63 was provided in a reactor 62. The catalyst layers were arranged vertically from top to bottom in the form of a first, second, and third layer, with the first layer containing silver particles with particle sizes of 0.2 mm to 0.75 mm, accounting for 15 wt % of the total catalyst weight, the second layer containing silver particles with particle sizes of 0.75 mm to 1.0 mm, accounting for 5.0 wt % of the total catalyst weight, and the third layer containing silver particles with particle sizes of 1.0 mm to 2.5 mm, accounting for 80 wt % of the total catalyst weight. Methanol was supplied to evaporator 1 through supply line 53. Methanol in evaporator 51 was extracted through circulation line 55, heated in heat exchanger 56, and then circulated to evaporator 51. Methanol vaporized in evaporator 51 was supplied to mixer 60 through methanol gas supply line 57. Air was supplied to mixer 60 through air supply line 58, and steam was supplied to mixer 60 through the steam supply line. A mixed gas adjusted in mixer 60 so that the molar ratio of methanol, water, and oxygen was 1:1.2:0.4 was supplied to reactor 62 through mixed gas line 61. The temperature of the reactor 62 was adjusted to be in the range of 550° C. to 600° C., and the reaction gas was extracted from the extraction line 64 . The reaction gas was then introduced into an absorption tower packed with Dixon packing. The reaction gas was bubbled into the aqueous formaldehyde solution at the bottom of the absorption tower. Water was supplied from the top of the absorption tower, and the bubbling gas was brought into gas-liquid contact in the packed section. The amount of water supplied was adjusted so that the formaldehyde concentration at the bottom of the absorption tower was 35 wt %, and the aqueous formaldehyde solution was recovered. The yield of formaldehyde relative to methanol was 88%. The above operation was continued for two months, but the formaldehyde yield remained unchanged.

[0078] [Comparative Example 3] Production of formaldehyde by methanol oxidation in the presence of a catalyst The same methanol as in Comparative Example 1 was used. Formaldehyde was produced in the same manner as in Example 2. Operation was continued under the same conditions, and after two months the formaldehyde yield reached 86%.

[0079] [Comparative Example 4] Production of formaldehyde by methanol oxidation in the presence of a catalyst The same methanol as in Comparative Example 2 was used. Operation was continued under the same conditions, and after two months the formaldehyde yield reached 86%.

[0080] [Example 3] Production of formaldehyde by oxidation of methanol in the presence of a catalyst Methanol produced by wood fermentation was analyzed by ion chromatography and found to contain 121 mass ppm of NO2. This methanol was heated to 50°C and bubbled with nitrogen, after which it was purified by distillation at atmospheric pressure. The resulting methanol was analyzed again by ion chromatography, and the following concentrations were detected: Cl 0.02 mass ppm, Br 0.01 mass ppm, NO 0.10 mass ppm, SO 0.03 mass ppm, and formic acid 0.01 mass ppm. However, NO and acetic acid were not detected. Furthermore, as a result of ICP-AES analysis of the methanol, 0.1 ppm by mass of Ca, 0.1 ppm by mass of Na, and 0.1 ppm by mass of Zn were detected. The methanol contained 120 ppm by mass of water. The operation was continued using this methanol under the same conditions as in Comparative Example 2, and after two months the yield of formaldehyde reached 88%.

[0081] [Example 4] Production of polyacetal (Production of trioxane) The aqueous formaldehyde solution produced in Example 1 was heated in the presence of sulfuric acid and Amberlyst (Organo Corporation), an ion exchange resin for strong acid catalysts, and supplied to a first distillation column. An aqueous solution distillate containing trioxane was obtained from the top of the distillation column. This aqueous solution distillate was mixed with benzene and separated into two layers to obtain a benzene solution containing trioxane. This benzene solution was supplied to the middle of a second distillation column and distilled. A solution containing benzene was withdrawn from the top of the column, and a solution containing trioxane, dioxymethylene dimethyl ether, trioxymethylene dimethyl ether, etc. was withdrawn from the bottom of the column. This solution containing trioxane and polyoxymethylene dimethyl ether was supplied to the middle stage of a third distillation column and distilled therein, and a distillate containing trioxane and dioxymethylene dimethyl ether was recovered from the top of the third distillation column, a distillate containing trioxane and trioxymethylene dimethyl ether was recovered from the bottom of the column, and a distillate containing trioxane was recovered from a side cut line provided at approximately 1 / 4 of the way from the top of the third distillation column. The distillate recovered from the side cut line had a trioxane content of 99% or more, and was then used to produce polyacetal. (Manufacturing of polyacetal) A catalyst solution was prepared by mixing boron trifluoride-dibutyl etherate (a complex compound of boron trifluoride) as a polymerization catalyst with cyclohexane as an organic solvent, with the concentration of the polymerization catalyst in the catalyst solution adjusted to 3.0% by mass. As a polymerization reactor, a jacketed two-screw paddle type continuous polymerization reactor (manufactured by Kurimoto, diameter 2B, L / D=14.8) through which a heat medium can be passed was adjusted to 80°C. A mixture of trioxane, 1,3-dioxolane (4.2 mol% relative to 1 mol of trioxane) as monomer components, and methylal as a low-molecular-weight acetal compound was continuously mixed in a pipe, and the catalyst solution was continuously supplied to a polymerization reactor through separate pipes to carry out a polymerization reaction, thereby obtaining crude polyacetal. At this time, the amount of polymerization catalyst relative to 1 mol of trioxane was 2.0 × 10 -5 The flow rate was adjusted appropriately so that the total amount of the solution was 100 mol. The crude polyacetal discharged from the polymerization reactor was sampled in an aqueous triethylamine solution (0.5% by mass), and then stirred at room temperature for 1 hour. Thereafter, the sample was filtered using a centrifuge and dried under nitrogen at 120°C for 3 hours. The mixture was then fed to a vented twin-screw extruder (L / D = 40) set at 200°C, and a 0.8% by mass aqueous solution of triethylamine was added to the terminal stabilization zone to a concentration of 20 ppm in terms of nitrogen. The mixture was stabilized by degassing under reduced pressure at 90 kPa and pelletized in a pelletizer. The mixture was then dried at 100°C for 2 hours to obtain polyacetal.

[0082] [Example 5] Production of polyacetal (Production of formaldehyde gas) The aqueous formaldehyde solution prepared in Example 2 was used to produce formaldehyde gas. A hemiformal-containing solution was produced by contacting an aqueous formaldehyde solution with polyethylene glycol (molecular weight 300) heated to 105°C. The hemiformal-containing solution was fed into a Smith-type thin-film evaporator at 80°C and an internal pressure of 8 kPa, where water was evaporated and removed. The resulting solution was fed into a Smith-type thin-film evaporator at 100°C and an internal pressure of 3 kPa, where water was further evaporated and removed. The resulting solution was introduced into a Smith-type thin-film evaporator at 180°C and an internal nitrogen atmosphere at atmospheric pressure, where hemiformal was pyrolyzed. A portion of the gas component produced was absorbed in water and analyzed by gas chromatography. A peak was detected at the same retention time as the peak detected as formaldehyde when formalin (Fujifilm Wako Pure Chemical Industries, Ltd.) was analyzed; however, no peaks corresponding to polyethylene glycol or water were detected. The gas component produced was formaldehyde gas. The gas components were then absorbed in a 1 mol / L aqueous solution of sodium sulfite, and the sodium hydroxide produced was titrated with 1 / 10 N sulfuric acid to determine the amount of formaldehyde gas produced. (Manufacturing of polyacetal) The formaldehyde gas produced by the above method, dimethyl distearyl ammonium acetate as a polymerization catalyst, and acetic anhydride as a chain transfer agent were added to a normal hexane solution at 60°C, and polymerization was carried out. The amount of the polymerization catalyst added was 5.0 × 10 per 1 mol of formaldehyde. -5 The amount of acetic anhydride added was 0.5 × 10 mol per 1 mol of formaldehyde. -3 The granular polyacetal polymer was filtered using a centrifuge equipped with a filter cloth, and dried at 60°C for 10 hours in a nitrogen atmosphere to obtain crude polyacetal. Then, to the crude polyacetal, acetic anhydride in an amount equal to the weight of the crude polyacetal and normal hexane in an amount 1.5 times the weight of the crude polyacetal were added, and a 60% by mass aqueous solution of potassium acetate was added so that the potassium acetate concentration was 1 ppm by mass relative to the total amount of acetic anhydride and normal hexane. The mixture was stirred at 160°C for 1 hour under a nitrogen atmosphere to carry out esterification. The polyacetal after esterification was collected by filtration, washed three times with normal hexane, and then dried at 100°C for 2 hours under reduced pressure to obtain polyacetal. Industrial Applicability

[0083] According to the present invention, when producing formaldehyde using methanol, adverse effects on catalysts and the like in the production process can be suppressed, and formaldehyde can be produced in a suitable manner. [Explanation of symbols]

[0084] 1: Distillation tower 2, 5, 8: Feed lines 3: Distillation line 4, 16: Extraction line 6: Tube reactor 7: Heat medium jacket 9, 10, 11: Reactor 12: Condenser 13, 14: Buffer tank 15: Heat medium circulation line 17, 18, 19, 20, 21: Pump 51: Evaporator 52, 54: Pump 53: Feed Line 55:Circulation line 56: Heat exchanger 57: Methanol gas supply line 58: Air supply line 59: Steam supply line 60: Mixer 61: Mixed gas line 62: Reactor 63: Catalyst layer 64: Extraction line

Claims

1. A method for producing formaldehyde using methanol as a raw material, comprising: the methanol contains nitrogen oxides; NO in the methanol detected by ion chromatography analysis ２ The method for producing formaldehyde, wherein the concentration of the above is 0.002 ppm by mass or more and 100 ppm by mass or less.

2. 2. The method for producing formaldehyde according to claim 1, wherein the formaldehyde is produced by oxidizing the methanol in the presence of a catalyst.

3. Step (1): obtaining methylal from the methanol; Step (2): producing formaldehyde from the methylal obtained in step (1); The method for producing formaldehyde according to claim 1, comprising:

4. A method for producing polyacetal, characterized in that formaldehyde obtained by the production method according to any one of claims 1 to 3 is used as a raw material.

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