Method for producing formaldehyde

Abstract

To provide a method for producing formaldehyde that can reduce energy consumption in producing formaldehyde from an aqueous formaldehyde solution.SOLUTION: To solve the problem, the present invention includes the following steps (1) to (3). Step (1): reacting an aqueous formaldehyde solution with an alcohol; Step (2): separating a reaction solution prepared in Step (1) into an organic phase and an aqueous phase; and Step (3): thermally decomposing hemiformal present in the organic phase to yield formaldehyde and alcohol.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing formaldehyde.

Background Art

[0002] As a method for producing formaldehyde from an aqueous formaldehyde solution, the hemi-formalization method is known. For example, Patent Document 1 discloses a method in which formalin and polyethylene glycol are brought into contact to generate hemi-formal, and the hemi-formal obtained by evaporating and removing the water in the hemi-formal is thermally decomposed using a gas-liquid contact tower to obtain formaldehyde gas.

[0003] Also, Patent Document 2 discloses a method of reducing the amount of water contained in hemi-formal after evaporation and removal of water by using an alcohol that is contacted with an aqueous formaldehyde solution and has a solubility of 3.0 g or less in 100 g of water in the alcohol and a boiling point of 190°C or higher.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in all of the conventional methods for producing formaldehyde, in the production of the precursor hemiacetal formal, hemiacetal formal and water are dissolved in the hemiacetal formal mixture, and in order to produce formaldehyde by thermal decomposition, it is necessary to evaporate and remove water from the mixture. In such a method, in order to obtain hemiacetal formal from which water has been removed, almost all of the water contained in the aqueous formaldehyde solution is removed by evaporation, which requires a large amount of energy for evaporation and removal.

[0006] Furthermore, when the concentration of formaldehyde in the aqueous formaldehyde solution used is low, the amount of water evaporated and removed relative to the produced formaldehyde becomes relatively large, which is more disadvantageous from the perspective of the energy consumption per produced formaldehyde.

[0007] Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a method capable of reducing the energy consumption in the evaporation and removal of water in the production of formaldehyde by relatively reducing the amount of water evaporated and removed with respect to the hemiacetal formal of the produced formaldehyde precursor.

Means for Solving the Problems

[0008] As a result of repeated studies to solve the above problems, the present inventors have found that when an aqueous formaldehyde solution and an alcohol are reacted, an organic phase containing hemiacetal formal and an aqueous phase containing unreacted formaldehyde and water are generated, and by performing the step of separating the organic phase and the aqueous phase, and using an alcohol suitable for the method, the above problems can be solved, and the present invention has been completed.

[0009] That is, the present invention is as follows. [1] A method for producing formaldehyde including the following steps (1) to (3). Step (1): A step of reacting an aqueous formaldehyde solution and an alcohol. Step (2): A step of separating into an organic phase and an aqueous phase. Step (3): A step of thermally decomposing hemi - formaldehyde contained in the organic phase to obtain formaldehyde and alcohol. [2] The method for producing formaldehyde according to [1], wherein the solubility of water in 100 g of the alcohol is 4.0 g or less at 90 °C and 760 mmHg. [3] The alcohol has carbon atoms (C), hydrogen atoms (H) and oxygen atoms (O), and the ratio of the number of C to O (C / O) constituting the alcohol is C / O = 10 / 1 to 20 / 1 The method for producing formaldehyde according to [1], characterized in that. [4] The method according to [2], wherein the standard boiling point of the alcohol is 190 °C or higher. [5] The method for producing formaldehyde according to any one of [1] to [4], wherein the specific gravity of the alcohol at 100 °C is less than 1.00. [6] The method for producing formaldehyde according to any one of [1] to [5], characterized in that the alcohol obtained in the step (3) is reused as the alcohol in the step (1). [7] The method for producing formaldehyde according to any one of [1] to [6], wherein the aqueous phase separated in the step (2) is reused for the production of the aqueous formaldehyde solution.

Advantages of the Invention

[0010] According to the present invention, it is possible to reduce the energy consumption when producing formaldehyde from an aqueous formaldehyde solution.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail.

[0012] The method for producing formaldehyde of the present embodiment (hereinafter sometimes also referred to as "the production method of the present embodiment") is as follows. It includes the following steps (1) to (3). Step (1): A step of reacting an aqueous formaldehyde solution with an alcohol Step (2): A step of separating the reaction solution obtained in Step (1) into an organic phase and an aqueous phase Step (3): A step of thermally decomposing the hemi - formaldehyde contained in the organic phase to obtain formaldehyde and an alcohol

[0013] Hereinafter, the compounds used in this embodiment will be described. The aqueous formaldehyde solution is not particularly limited as long as it contains formaldehyde and water, and aqueous solutions of various concentrations can be used. When the formaldehyde concentration is too low, the efficiency in the production of hemi - formaldehyde decreases. Therefore, the formaldehyde concentration is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. On the other hand, when the formaldehyde concentration is too high, the aqueous formaldehyde solution tends to solidify, making handling complicated. Therefore, the formaldehyde concentration is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0014] The aqueous formaldehyde solution may contain methanol to avoid the polymerization of formaldehyde or to enhance the solubility of formaldehyde, and such an aqueous formaldehyde solution may be used.

[0015] The aqueous formaldehyde solution can be produced using known methods. For example, the methanol - excess method, air - excess method, etc. described on page 626 of the book "2020 Edition 17120 Chemical Commodities" (Chemical Industry Daily) can be used. It may also be an aqueous formaldehyde solution obtained by blowing a gas obtained by thermally decomposing polyacetal into a liquid containing water. Further, for example, an aqueous formaldehyde solution with a formaldehyde concentration of around 37% by mass, called formalin, can also be used.

[0016] In addition, the alcohol used in the production method of the present embodiment is preferably hydrophobic in order to separate the organic phase and the aqueous phase in step (2) described later. Here, "the alcohol is hydrophobic" means that the solubility of water in 100 g of the alcohol is 4.0 g or less at 90 °C and 720 mmHg.

[0017] For such a hydrophobic alcohol, when hemi - formal is produced, it can be separated into an organic phase containing hemi - formal and unreacted alcohol and an aqueous phase containing unreacted formaldehyde and water, and the water content of the organic phase can be reduced.

[0018] In addition, the alcohol used in the production method of the present embodiment has carbon atoms (C), hydrogen atoms (H), and oxygen atoms (O), and the ratio (C / O) of the number of carbon atoms (C) to the number of oxygen atoms (O) constituting the alcohol is C / O = 10 / 1 to 20 / 1 and preferably, the standard boiling point of the alcohol is 190 °C or higher.

[0019] Examples of the above - mentioned alcohol include, for example, the alcohol represented by the following formula (1). R-OH ···(1) (In the formula, R represents an aliphatic hydrocarbon group or an aromatic group having 10 or more carbon atoms, and the oxygen atom constituting the OH group is not bonded to the carbon atom constituting the aromatic ring.)

[0020] In the above formula (1), since the standard boiling point of the alcohol used in the present embodiment is 190 °C, the R group has 10 or more carbon atoms, more preferably 12 or more carbon atoms. On the other hand, when the number of carbon atoms is too large, the amount of alcohol that needs to be handled with respect to the amount of hemi - formal produced becomes too large and the production efficiency decreases. Therefore, the number of carbon atoms is 20 or less, more preferably 18 or less.

[0021] In the above formula (1), when the R group is an aliphatic hydrocarbon group, the aliphatic hydrocarbon group may be linear or branched. For example, a decyl group, a dodecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an octadecyl group, a nonadecyl group, etc. can be mentioned. In addition, any of the groups mentioned here may be a structural isomer thereof.

[0022] When the R group in the above formula (1) is an aromatic group, for example, a group in which a hydrocarbon group is bonded to an aromatic ring such as a phenylbutyl group, a phenylhexyl group, a phenyloctyl group, a diphenylmethyl group, a diphenylmethyl group, a diphenylethyl group, a diphenylpropyl group, a diphenylbutyl group, a diphenylpentyl group, etc., a group in which a plurality of aromatic rings are bonded to a hydrocarbon group, etc. can be mentioned. In addition, any of the groups mentioned here may be a structural isomer thereof.

[0023] As described above, the alcohol used in the production method of the present embodiment has a ratio of the number of carbon atoms (C) to oxygen atoms (O) constituting the alcohol of 10 / 1 to 20 / 1 = 10 / 1 to 20 / 1. Generally, in an organic compound composed of carbon atoms (C), hydrogen atoms (H), and oxygen atoms (O), when the ratio (C / O) of carbon atoms (C) to oxygen atoms (O) becomes smaller, the solubility in water increases. In the production method of the present embodiment, it is necessary that the alcohol, the hemiacetal formed by the reaction of the alcohol and formaldehyde, and the aqueous formaldehyde solution after the reaction with the alcohol are phase-separated. In addition, unreacted formaldehyde is often dissolved in the aqueous formaldehyde solution after the reaction with the alcohol. Although it is a preferable mode to reuse the aqueous formaldehyde solution after the reaction for another use, in such a case, it is preferable that the amount of alcohol dissolved in the aqueous formaldehyde solution after the reaction is small. For the above reasons, the ratio of carbon atoms (C) to oxygen atoms (O) (C / O) is preferably greater than 10 / 1, and more preferably greater than 12 / 1. On the other hand, if the ratio of carbon atoms (C) to oxygen atoms (O) (C / O) is too large, the amount of alcohol relative to the hydroxy group that reacts with formaldehyde increases. When producing formaldehyde using the hemiacetal produced in this embodiment, the reactor and the like become larger, and the energy required for heating and cooling of alcohol and the like may increase. From such a perspective, it is preferable that the ratio of carbon atoms (C) to oxygen atoms (O) (C / O) is smaller. Specifically, it is preferably 20 / 1 or less, and more preferably 18 / 1 or less.

[0024] Moreover, the alcohol used in the production method of this embodiment preferably has a standard boiling point of 190 °C or higher. This is because when producing gaseous formaldehyde by thermally decomposing the produced hemiacetal, the hemiacetal is heated, for example, preferably to 130 °C to 180 °C, more preferably to 140 °C to 170 °C, and the hemiacetal is often thermally decomposed. This is to reduce the amount of alcohol generated by the thermal decomposition of the hemiacetal mixed into the formaldehyde gas generated at such a temperature and to facilitate the purification of the formaldehyde gas.

[0025] The alcohol used in the production method of this embodiment preferably has a specific gravity of less than 1.00 at 100 °C. In this embodiment, in step (2) described later, an organic layer containing the hemiacetal produced by the reaction of formaldehyde and alcohol and unreacted alcohol and an aqueous layer containing unreacted formaldehyde are separated. If the specific gravity difference between the organic layer and the aqueous layer is small, it may be necessary to perform operations such as centrifugation because the organic layer and the aqueous layer are difficult to separate. Therefore, it is preferable that the specific gravity difference between the organic layer and the aqueous layer is large.

[0026] Generally, the aqueous solution containing the formaldehyde has a specific gravity greater than 1. For example, it is described on page 626 of the book "Chemical Products in the 2020 Edition 17120" (Chemical Industry Daily) that the specific gravity of a 37% aqueous solution (meta content 8%) is 1.0956.

[0027] In the production method of this embodiment, the separation in step (2) described later is preferably carried out in a temperature range of 70°C to 110°C, and it is preferable that the specific gravity difference between the organic layer and the aqueous layer is large in such a temperature range. As a result of the inventors' intensive studies, it was found that if the specific gravity of alcohol at 100°C is less than 1.00, the organic layer and the aqueous layer can be separated without performing any special operations. As described above, the larger the specific gravity difference between the organic layer and the aqueous layer, the better. Since the specific gravity of the organic layer is smaller than that of the aqueous layer, the specific gravity of alcohol at 100°C is more preferably less than 0.90, and even more preferably less than 0.85.

[0028] The specific gravity of alcohol at 100°C can be measured by a known method. However, as described in the examples below, alcohol can be put into a container of appropriate size immersed in an oil bath at 100°C, and its weight and volume can be measured to easily estimate the specific gravity.

[0029] As described above, the method for producing formaldehyde of this embodiment includes the following steps (1) to (3). Step (1): A step of reacting an aqueous formaldehyde solution with alcohol Step (2): A step of separating the reaction solution obtained in step (1) into an organic phase and an aqueous phase Step (3): A step of thermally decomposing hemiacetal formaldehyde contained in the organic phase to obtain formaldehyde and alcohol

[0030] Hereinafter, each step will be described. The step (1) is a step of reacting an aqueous formaldehyde solution with alcohol to obtain a reaction solution containing hemiacetal formaldehyde. The temperature for reacting the aqueous formaldehyde solution with the alcohol is not particularly limited and can be set as appropriate. From the viewpoint of reactivity, it is preferably room temperature (about 20°C) or higher, more preferably 50°C or higher, and even more preferably 70°C or higher. On the other hand, when the reaction temperature is high, it may be difficult to control the temperature rise due to the heat of reaction. Therefore, it is preferably in the range of 110 °C or lower, more preferably 105 °C or lower. It is preferable to mix the aqueous formaldehyde solution and alcohol in a pre-heated state respectively.

[0031] In order to efficiently react formaldehyde with alcohol, the mixing ratio of the aqueous formaldehyde solution and the alcohol is preferably 0.3 or more, more preferably 0.5 or more, and even more preferably 1.0 or more in terms of the molar ratio of the hydroxyl group in the alcohol to formaldehyde. On the other hand, when the ratio increases, the amount of formaldehyde reacting per unit weight of alcohol decreases. Therefore, it is preferably 5.0 or less, more preferably 2.0 or less, and even more preferably 1.5 or less.

[0032] The reaction pressure in the step (1) varies depending on the composition of the reaction system, reaction temperature, reaction apparatus, etc., and can be carried out under reduced pressure, normal pressure, or increased pressure. Usually, it is preferably carried out in the range of 0.01 kPa to 10 MPa (absolute pressure). Considering the ease of industrial implementation, reduced pressure and normal pressure are preferred, and it is preferably in the range of 0.1 kPa to 0.1 MPa (absolute pressure).

[0033] The reaction time (residence time in the case of continuous reaction) varies depending on the composition of the reaction system, reaction temperature, reaction apparatus, reaction pressure, etc., but is usually 0.01 to 100 hours. The reaction time can also be determined by the production amount of the target compound. For example, the reaction can be terminated by sampling the reaction solution and confirming that the desired yield has been reached.

[0034] In the step (1), an aqueous formaldehyde solution and alcohol are supplied to a reactor, and formaldehyde and alcohol are reacted to produce hemiacetal. The reaction can be either batch or continuous. There are no particular restrictions on the reactor, and known reactors can be used, for example, a stirred tank, a tubular reactor, etc. These reactors may be equipped with devices such as a heat exchanger for heating and cooling as necessary, and a condenser for recovering the gasified components.

[0035] The reaction solution obtained by the above step (1) is separated into an organic phase containing hemi-formal and unreacted alcohol, and an aqueous phase containing unreacted formaldehyde and water. The state in which the organic phase and the aqueous phase are separated may be achieved under the conditions (temperature, pressure, etc.) for carrying out the subsequent step (2).

[0036] Step (2) is a step of separating the reaction solution obtained in step (1) into an organic phase and an aqueous phase. The method for carrying out step (2) is not particularly limited. When simple liquid-liquid separation can be carried out, such a method can be used. It is also possible to change the solubility by heating or cooling the liquid and then perform liquid-liquid separation. Further, when simple liquid-liquid separation is difficult due to the mixing of the aqueous phase in the organic phase or the mixing of the organic phase in the aqueous phase, the organic phase and the aqueous phase can be separated easily by centrifugation or the like and then liquid-liquid separation can be carried out. Furthermore, the solution can be cooled to solidify one of the organic phase or the aqueous phase and then solid-liquid separation can be carried out.

[0037] In step (2), the temperature for separating the aqueous phase and the organic phase can be set as appropriate. However, when heating or cooling, energy is required for heating or cooling, so it is preferably set to about the same level as the temperature at which step (1) is carried out, in the range of normal temperature (about 20°C) or higher, more preferably 50°C or higher, still more preferably 70°C or higher, and preferably 110°C or lower, more preferably 105°C or lower.

[0038] In the above step (2), the pressure for separating the aqueous phase and the organic phase varies depending on the composition of the mixed solution, temperature, the apparatus used, etc., and can be carried out under reduced pressure, normal pressure, or increased pressure. Usually, however, it is preferably carried out in the range of 0.01 kPa to 10 MPa (absolute pressure). Considering the ease of industrial implementation, reduced pressure and normal pressure are preferred, and the range of 0.1 kPa to 0.1 MPa (absolute pressure) is more preferred.

[0039] The apparatus for carrying out the above step (2) is not particularly limited, and known apparatuses can be used. For example, non-powered extraction apparatuses such as packed towers, baffle towers, and perforated plate extraction towers, stirred extraction apparatuses such as mixer-settler extraction apparatuses, centrifugal extraction apparatuses, etc. may be used, or the mixed solution in the storage tank may be phase-separated, and the aqueous phase and the organic phase may be recovered respectively. These apparatuses may be equipped with apparatuses such as heat exchangers for heating and cooling, condensers for recovering gasified components, etc. as necessary.

[0040] The above step (2) may be carried out using the reactor in which the above step (1) was carried out, or a separate apparatus from step (1) may be prepared to transfer the mixed solution of step (1) for implementation.

[0041] Also, the organic phase recovered in the above step (2) is subjected to a thermal decomposition reaction in the subsequent step (3), and formaldehyde is produced by thermally decomposing the hemi-formal contained in the organic phase.

[0042] Furthermore, the organic phase recovered in the above step (2) may be directly used in step (3), or may be used in step (3) via a step of removing the water contained in the organic phase (referred to as "step (A)").

[0043] The above step (A) is a step of removing the water dissolved in the organic phase. The method of removing water is not particularly limited, and known methods such as evaporation and distillation of water, membrane separation, addition of dehydrating agents, etc. can be used.

[0044] When performing evaporation and distillation of water, the temperature of the organic layer liquid can be set as appropriate. However, when heating or cooling, since energy is required for heating or cooling, it is preferably set to approximately the same temperature as that at which step (2) was carried out, in the range of normal temperature (about 20°C) or higher, more preferably 50°C or higher, even more preferably 70°C or higher, and preferably 110°C or lower, more preferably 105°C or lower.

[0045] The pressure when performing evaporation and distillation of water varies depending on the composition of the mixed solution, temperature, apparatus used, etc., and can be carried out under reduced pressure, normal pressure, or increased pressure. Usually, it is preferably carried out in the range of 0.01 kPa to 10 MPa (absolute pressure). Considering the ease of industrial implementation, reduced pressure and normal pressure are preferred, and the range of 0.1 kPa to 0.1 MPa (absolute pressure) is preferred.

[0046] The apparatus for performing evaporation and distillation of water is not particularly limited, and known apparatuses can be used. A stirring tank, packed tower, tray tower, falling film type apparatus, etc. can be used. These apparatuses may be equipped with apparatuses such as heat exchangers for heating and cooling and condensers for recovering gasified components as necessary. Also, apparatuses necessary for performing evaporation and distillation of water can be added to the apparatus for performing step (2), and steps (2) and (3) can be carried out continuously.

[0047] When removing water in the organic layer by membrane separation, the temperature of the organic layer liquid can be set as appropriate. However, when heating or cooling, since energy is required for heating or cooling, it is preferably set to approximately the same temperature as that at which step (2) was carried out, in the range of normal temperature (about 20°C) or higher, more preferably 50°C or higher, even more preferably 70°C or higher, and preferably 110°C or lower, more preferably 105°C or lower.

[0048] The pressure during membrane separation varies depending on the composition of the mixed solution, temperature, the apparatus used, etc., and can be carried out under reduced pressure, normal pressure, or increased pressure. Usually, however, it is preferably carried out in the range of 0.01 kPa to 10 MPa (absolute pressure). Considering the ease of industrial implementation, reduced pressure and normal pressure are preferred, and the range of 0.1 kPa to 0.1 MPa (absolute pressure) is preferred.

[0049] The apparatus for membrane separation is not particularly limited, and known apparatuses can be used. Known membranes can also be used. For example, organic membranes made of cellulose acetate, polyimide, polysulfone, Teflon (registered trademark), etc., and inorganic membranes made of ceramics such as alumina and titania can be used, and a membrane of a suitable material is selected according to the organic layer.

[0050] The step (3) is a step of thermally decomposing the hemi - formaldehyde contained in the organic phase separated in the step (2) to obtain formaldehyde and alcohol.

[0051] The temperature for carrying out the thermal decomposition of the hemi - formaldehyde can be set as appropriate. Preferably, it is 120 °C or higher, more preferably 130 °C or higher, and even more preferably 140 °C or higher. On the other hand, when the temperature of the thermal decomposition is too high, the yield may decrease due to side reactions, etc. Therefore, it is preferably 270 °C or lower, more preferably 250 °C or lower, and even more preferably 240 °C or lower.

[0052] The pressure during the thermal decomposition varies depending on the composition of the mixed solution, temperature, the apparatus used, etc., and can be carried out under reduced pressure, normal pressure, or increased pressure. Usually, however, it is preferably carried out in the range of 0.01 kPa to 10 MPa (absolute pressure). In order to suppress the amount of alcohol generated by thermal decomposition from mixing into the formaldehyde gas, a normal pressure or increased pressure system is preferred, and the range of 0.1 MPa to 1 MPa (absolute pressure) is preferred.

[0053] The liquid component recovered from the lower part of the falling-film type device can be reused as the alcohol in the process of producing hemi-formal, for example, in the process (1). Further, when the liquid component contains a large amount of unreacted hemi-formal, it can be supplied again to the falling-film type device and thermally decomposed.

[0054] The method for thermally decomposing the hemi-formal is not particularly limited, and either a batch type or a continuous type can be implemented. The device for performing the thermal decomposition is not particularly limited, and a known device can be used, and a stirring tank, a packed tower, a tray tower, a falling-film type device, etc. can be used. These devices may be equipped with devices such as a heat exchanger for heating and cooling as necessary, and a condenser for recovering part or all of the gasified components.

[0055] For example, when continuously performing the thermal decomposition of hemi-formal using a falling-film type device, the organic layer obtained in the process (3) is continuously supplied to the upper part of the falling-film type device, and a part of the formaldehyde and alcohol generated by the thermal decomposition of hemi-formal is taken out as a gas component from the upper part of the falling-film type device, and alcohol and unreacted hemi-formal can be recovered as a liquid component from the lower part of the falling-film type device.

[0056] The gas component taken out from the falling-film type device can be used as formaldehyde gas as it is, or the alcohol contained in the gas component can be partially condensed through a condenser and used as a gas with increased purity of formaldehyde. Further, the gas component can also be used after increasing the purity of formaldehyde by generating it using a polyalkylene glycol as disclosed in, for example, Japanese Patent No. 610587.

Example

[0057] Hereinafter, the present invention will be described in detail with specific examples and comparative examples, but the present invention is not limited to the following examples.

[0058] <Preparation of aqueous formaldehyde solution> Approximately 100 g of paraformaldehyde (manufactured by Fujifilm Wako Pure Chemical Corporation) was placed into a 300 mL flask connected with a glass tube for extracting formaldehyde gas and a line for introducing nitrogen. Nitrogen was circulated at 100 mL / min, and the flask was immersed in an oil bath adjusted to 150 °C. The tip of the glass tube was immersed in a formaldehyde solution (manufactured by Fujifilm Wako Pure Chemical Corporation), and the formaldehyde gas generated by the decomposition of paraformaldehyde was bubbled to prepare an aqueous formaldehyde solution.

[0059] <Method for Measuring the Amount of Formaldehyde, Water, and Methanol in the Liquid> The amounts of formaldehyde, water, and methanol in the liquid (either the organic layer or the aqueous layer) were measured under the following conditions using gas chromatography and calculated using a calibration curve prepared in advance. · Gas chromatography: GC-2014 (manufactured by Shimadzu Corporation) · Column: Porapak T (manufactured by GL Sciences Inc.) · Injection port temperature: 180 °C · Detector temperature: 180 °C · Detector: Thermal conductivity detector · Carrier gas: Helium · Column temperature: Held at 125 °C for 8 minutes, then heated at a rate of 20 °C / min to 180 °C and held for 22 minutes · Injection volume of the measurement sample: 5 μL · Method for preparing the measurement sample: Approximately 0.1 g of the sample was dissolved in approximately 1 g of acetone (manufactured by Fujifilm Wako Pure Chemical Corporation, ultra-dehydrated grade).

[0060] <Method for Measuring the Specific Gravity of Alcohol at 100 °C> Approximately 50 g of alcohol was placed in an 110 mL screw neck vial (manufactured by AS ONE Corporation), and after measuring the weight (A) of the alcohol added, it was immersed in an oil bath to set the liquid temperature to 100°C. In this state, after marking the height of the alcohol liquid level in the screw neck vial, the alcohol was taken out. The screw neck vial was washed and dried, left standing overnight at 20°C, then filled with water at 20°C up to the marked height, the weight was measured, and assuming the specific gravity of water at 20°C was 0.998, the volume (B) of the water added was calculated. The value obtained by dividing A by B was taken as the specific gravity of alcohol at 100°C.

[0061] <Preparation of Formaldehyde Aqueous Solution> Approximately 100 g of paraformaldehyde (manufactured by FUJIFILM Wako Pure Chemical Corporation) was placed in a 300 mL flask connected with a glass tube for extracting formaldehyde gas and a line for introducing nitrogen. Nitrogen was circulated at 100 mL / min, and the flask was immersed in an oil bath adjusted to 150°C. The tip of the glass tube was immersed in a formaldehyde solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and formaldehyde gas generated by the decomposition of paraformaldehyde was bubbled to prepare a formaldehyde aqueous solution.

[0062] <Method for Measuring Water Solubility in Alcohol at 90°C> Approximately 50 g of alcohol and approximately 10 g of water were placed in an 110 mL screw neck vial (manufactured by AS ONE Corporation), and heated in an oil bath so that the temperature of the solution became 90°C. The organic phase was sampled with a syringe, the water content of the organic phase was measured with a Karl Fischer moisture meter, and the water solubility per 100 g of alcohol was determined. The measurement of the water content by the Karl Fischer moisture meter was carried out by the following method.

[0063] Apparatus: CA - 200 (manufactured by Mitsubishi Chemical Analytic Co., Ltd.) Anolyte: Aquamicron (registered trademark) AKX Catholyte: Aquamicron (registered trademark) CXU Measurement method: Approximately 1 g of the sample was weighed and placed in a syringe and injected into the apparatus. After the sample injection, the total amount of water detected until the detection rate reached 0.02 μg / sec was taken as the amount of water contained in the injected sample.

[0064] [Example 1] (1) 499.8 g of 1-decanol was placed in a 1 L separatory funnel and heated with a ribbon heater so that the liquid temperature reached 100°C. An aqueous formaldehyde solution was placed in a 500 mL separatory funnel and heated with a ribbon heater so that the liquid temperature reached 100°C. Here, the amounts of formaldehyde, water, and methanol contained in the aqueous formaldehyde solution used are shown in Table 1. After the liquid temperature reached 100°C, the aqueous formaldehyde solution was added to 1-decanol and stirred, and held at 100°C for 1 hour. The added aqueous formaldehyde solution was 20.35 g. (2) Then, after standing at 100°C for another 1 hour and confirming two-phase separation, the upper layer was recovered as the organic phase and the lower layer was recovered as the aqueous phase. The results of measuring the amounts of formaldehyde, water, and methanol contained in each of the organic phase and the aqueous phase by gas chromatography are shown in Table 1. Note that it is considered that the organic phase contains hemi-formal generated by the reaction. However, since it thermally decomposes at the injection port temperature when measured by gas chromatography, the formaldehyde detected by gas chromatography is derived from hemi-formal, and it can be considered that hemi-formal corresponding to the detected formaldehyde has been generated. Next, the organic phase was placed in a 1 L three-necked flask equipped with a distillation tube and a condenser, immersed in an oil bath at 100°C, and the water contained in the organic phase was distilled off by reducing the pressure to 50 kPa. The amount of the recovered water was about 28 g. (3) Subsequently, an organic phase was flowed at about 10 g / min on the wall surface of a glass tube (diameter 10 mm, length 300 mm) heated to 160 °C with a ribbon heater, and hemi formaldehyde contained in the organic phase was thermally decomposed to produce formaldehyde gas. The generated formaldehyde gas was bubbled through water through a tube and analyzed by gas chromatography to measure the amount of formaldehyde gas. As a result, the obtained formaldehyde gas was about 30 g.

[0065] [Examples 2 - 4] (1) was carried out under the same conditions as in Example 1, except that the alcohol shown in Table 1 was used instead of 1 - decanol. The results are shown in Table 1.

[0066] [Example 5] (1) was carried out under the same conditions as in Example 1, except that benzhydrol was used instead of 1 - decanol. When left standing at 100 °C for 1 hour, it was separated into an organic phase and an aqueous phase, but the two phases were not clearly separated (the boundary between the organic phase and the aqueous phase was not horizontal, and the aqueous phase was dispersed in the organic phase). Therefore, after separating into an upper layer and a lower layer using a centrifuge, the upper layer was recovered as the organic phase and the lower layer was recovered as the aqueous phase. The results are shown in Table 1.

[0067] [Comparative Example 1] When the same method as in Example 1 was carried out using 1 - octanol instead of 1 - decanol in (1), a uniform solution was formed when 1 - octanol and an aqueous formaldehyde solution were mixed, and no two - layer separation occurred. The results of sampling the solution and analyzing it by gas chromatography are shown in Table 2.

[0068] [Comparative Example 2] When the same method as in Example 1 was carried out using 2 - phenylethanol instead of 1 - decanol in (1), a uniform solution was formed when 1 - octanol and an aqueous formaldehyde solution were mixed, and no two - layer separation occurred. The results of sampling the solution and analyzing it by gas chromatography are shown in Table 2.

[0069]

Table 1

Table 2

[0070] From the results of Tables 1 and 2, in the alcohols of Examples 1 to 5 in the range of carbon atom / oxygen atom = 10 / 1 to 20 / 1, when manufacturing hemiformals, two layers were separated into an organic layer and an aqueous layer, and the water / formaldehyde concentration ratio in the organic layer became smaller compared to the water / formaldehyde concentration ratio in the aqueous formaldehyde solution used. On the other hand, in Comparative Examples 1 and 2 using alcohols outside the above range of carbon atom / oxygen atom, a uniform layer was formed without two-layer separation, and the water / formaldehyde concentration ratio was the same as that of the aqueous formaldehyde solution. Also, when comparing Comparative Example 1 and Example 3 using the same aqueous formaldehyde solution, the water / formaldehyde concentration ratio is smaller in Example 3. This is the same in the comparison between Comparative Example 2 and Examples 1, 2, 4, and 5. Thus, by specifying the alcohol when manufacturing hemiformals, the amount of water relative to hemiformals (which thermally decomposes into formaldehyde) can be reduced.

Industrial Applicability

[0071] According to the present invention, it becomes possible to reduce the energy consumption when manufacturing formaldehyde from an aqueous formaldehyde solution.

Claims

1. A method for producing formaldehyde, characterized by comprising the following steps (1) to (3). Step (1): A step of reacting an aqueous formaldehyde solution with an alcohol Step (2): A step of separating the reaction solution obtained in step (1) into an organic phase and an aqueous phase Step (3): A step of thermally decomposing the hemiacetal formal contained in the organic phase to obtain formaldehyde and an alcohol

2. The method for producing formaldehyde according to claim 1, characterized in that the solubility of water in 100 g of the alcohol is 4.0 g or less at 90 °C and 760 mmHg.

3. The alcohol has carbon atoms (C), hydrogen atoms (H) and oxygen atoms (O), and the ratio (C / O) of the number of C and O constituting the alcohol is C / O = 10 / 1 to 20 / 1 The method for producing formaldehyde according to claim 1 or 2, characterized in that it is as described above.

4. The method for producing formaldehyde according to claim 2, characterized in that the standard boiling point of the alcohol is 190 °C or higher.

5. The method for producing formaldehyde according to claim 1 or 2, characterized in that the specific gravity of the alcohol at 100 °C is less than 1.

00.

6. The method for producing formaldehyde according to claim 1 or 2, characterized in that the alcohol obtained in step (3) is reused as the alcohol in step (1).

7. The method for producing formaldehyde according to claim 1 or 2, characterized in that the aqueous phase separated in step (2) is reused for the production of the aqueous formaldehyde solution.

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