How Fluorenone is Made

Abstract

A method for producing fluorenone which comprises, in the following order, a pretreatment step in which fluorene is heated in the presence of a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst and an oxidation step in which the fluorene and oxygen are continuously fed to conduct an oxidation reaction.

Description

[Technical Field]

[0001] The present invention relates to a method for producing fluorenone. [Background technology]

[0002] Fluorenone is used as a raw material or intermediate for chemicals, resins, etc. Specifically, it is a very useful compound as a raw material for electrophotographic photoreceptors, dyes, and optical resins.

[0003] As a method for producing fluorenone, a method of oxidizing fluorene has been used, and among them, a production method by liquid phase oxidation using an oxygen-containing gas such as air has been developed. For example, Patent Document 1 discloses a method for producing fluorenones in high yield, characterized in that fluorenes are oxidized with molecular oxygen in an organic solvent in the presence of a phase transfer catalyst and a solid alkali metal hydroxide. Furthermore, Patent Document 2 discloses a method for producing fluorenone in high yield by reacting a dimethyl sulfoxide solution of fluorene with oxygen molecules in the presence of a small amount of alkali metal hydroxide. Patent Document 3 discloses a method for obtaining diallyl ketone simply, economically, and in high yield, in which an aromatic compound is reacted with molecular oxygen using a lower saturated aliphatic monocarboxylic acid as a solvent and a heavy metal as an oxidation catalyst, and discloses a method for obtaining fluorenone as an example of this method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-182399 [Patent Document 2] U.S. Patent No. 3,875,237 [Patent Document 3] U.S. Patent No. 3,038,940 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 3 discloses an example of synthesizing fluorenone by the so-called Amoco process. In particular, the target product was obtained in a 76% yield by using ammonium bromide as a part of the cocatalyst. However, this reaction requires supplying oxygen in the presence of acetic acid as a solvent and heating to 205°C, which poses a risk of fire and explosion. In particular, an increase in the oxygen concentration in the off-gas (exhaust gas) poses a safety problem during industrial production. On the other hand, if the conditions of the oxidation reaction are changed to avoid such a risk, such as by reducing the amount of oxygen supplied, lowering the reaction temperature, or changing the catalyst, the conversion rate and selectivity will decrease accordingly, and the yield of the target product, fluorenone, will decrease. Therefore, there has been a need for a method for obtaining fluorenone safely and in high yields industrially. Therefore, an object of the present invention is to provide a method for producing fluorenone, which can produce fluorenone in high yield, has excellent conversion and selectivity, and is industrially safe. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by heating the raw material fluorene under specific conditions and then continuously supplying fluorene and oxygen to carry out an oxidation reaction. That is, the present invention relates to the following [1] to [9]. [1] A method for producing fluorenone, comprising, in this order, a pretreatment step of heating fluorene in the presence of a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst, and an oxidation step of continuously supplying fluorene and oxygen to carry out an oxidation reaction. [2] The method for producing fluorenone according to the above [1], wherein in the oxidation reaction, the molar ratio of continuously supplied oxygen to fluorene [oxygen / fluorene] is 0.5 to 4.0. [3] The method for producing fluorenone according to the above [1] or [2], wherein the heating temperature in the pretreatment step is 160 to 250°C. [4] The method for producing fluorenone according to any one of the above [1] to [3], wherein the heating time in the pretreatment step is 3 to 30 minutes. [5] The method for producing fluorenone according to any one of the above [1] to [4], wherein the reaction temperature of the oxidation reaction is 120 to 250°C. [6] The method for producing fluorenone according to any one of the above [1] to [5], wherein the reaction pressure of the oxidation reaction is 0.1 to 3.0 MPa. [7] The method for producing fluorenone according to any one of the above [1] to [6], wherein the metal catalyst is at least one selected from the group consisting of a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a nickel catalyst, and a cerium catalyst. [8] The method for producing fluorenone according to any one of the above [1] to [7], wherein the lower aliphatic carboxylic acid is acetic acid. [9] The method for producing fluorenone according to any one of the above [1] to [8], wherein oxygen is supplied by introducing air in the oxidation step. [Effects of the Invention]

[0007] According to the production method of the present invention, it is possible to provide a method for producing fluorenone in high yield, with excellent conversion and selectivity, and with high industrial safety. DETAILED DESCRIPTION OF THE INVENTION

[0008] The method for producing fluorenone of the present invention includes, in this order, a pretreatment step of heating fluorene in the presence of a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst, and an oxidation step of continuously supplying fluorene and oxygen to carry out an oxidation reaction. The production method of the present invention will be described in detail below.

[0009] [Pretreatment process] In the method for producing fluorenone of the present invention, first, a pretreatment step is carried out in which fluorene is heated in the presence of a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst.

[0010] <Lower aliphatic carboxylic acids> The lower aliphatic carboxylic acid used in this step is preferably an aliphatic carboxylic acid having 1 to 4 carbon atoms, more preferably an aliphatic carboxylic acid having 2 to 3 carbon atoms, and even more preferably an aliphatic carboxylic acid having 2 carbon atoms. Specific examples of lower aliphatic carboxylic acids include at least one selected from the group consisting of formic acid, acetic acid, propionic acid, and butyric acid, more preferably at least one selected from the group consisting of acetic acid and propionic acid, and even more preferably acetic acid. When using acetic acid, a mixed solution may be prepared in advance by mixing water and acetic acid as described below, or acetic acid alone may be used. From the viewpoint of facilitating the dissolution of the bromine compound and the metal catalyst, it is preferable to use aqueous acetic acid, which is a mixed solution of water and acetic acid. The use of the above lower aliphatic carboxylic acids is preferred because it can increase the activity of the catalyst.

[0011] The amount of lower aliphatic carboxylic acid used in the pretreatment step is preferably 10 to 1000 parts by mass, more preferably 50 to 400 parts by mass, even more preferably 70 to 200 parts by mass, and even more preferably 80 to 100 parts by mass, relative to 100 parts by mass of the total fluorene. By adjusting the amount of the lower aliphatic carboxylic acid to the above range, it is possible to adjust the viscosity to an appropriate level in the pretreatment step and the subsequent oxidation step, which makes the mixture easier to handle and also makes it possible to control the reaction heat. The term "total fluorene" refers to "all fluorene introduced into the reaction vessel from the pretreatment step to the end of the oxidation step and used in the oxidation reaction." The same applies hereinafter. The lower aliphatic carboxylic acids may be used alone or in combination of two or more.

[0012] <Bromine compounds> The bromine compound used in this step is preferably hydrogen bromide, a bromide salt, or an organic bromine compound, more preferably at least one selected from the group consisting of hydrogen bromide and a bromide salt, and even more preferably hydrogen bromide. Hydrogen bromide is preferably used as an aqueous solution. Specific bromide salts include sodium bromide, potassium bromide, ammonium bromide, and the like.

[0013] The amount of the bromine compound used in the pretreatment step is, in bromine equivalent, preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, even more preferably 0.05 to 1 part by mass, and still more preferably 0.05 to 0.5 parts by mass, relative to 100 parts by mass of total fluorene. By setting the amount of the bromine compound within the above range, corrosion of the reaction vessel and the like is suppressed, while the reaction rate in the pretreatment step and the subsequent oxidation step is improved, and the yield is thereby improved, which is preferable. The bromine compound may be used alone or in combination of two or more.

[0014] <Metal catalyst> The metal catalyst used in this step is preferably at least one selected from the group consisting of transition metal catalysts and rare earth metal catalysts, and more preferably a transition metal catalyst. A specific transition metal catalyst is preferably at least one selected from the group consisting of a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a nickel catalyst, and a cerium catalyst, more preferably at least one selected from the group consisting of a cobalt catalyst and a manganese catalyst, and it is even more preferable to use both a cobalt catalyst and a manganese catalyst. As described above, the metal catalyst used in this step is preferably at least one selected from the group consisting of cobalt catalysts, manganese catalysts, zirconium catalysts, nickel catalysts, and cerium catalysts, more preferably at least one selected from the group consisting of cobalt catalysts and manganese catalysts. It is even more preferable to use both a cobalt catalyst and a manganese catalyst. The metal catalyst can be used in the form of a salt, a metal element, an oxide, a hydroxide, or the like, but the metal catalyst used in this step is preferably a salt, more preferably an aliphatic carboxylate, even more preferably a lower aliphatic carboxylate, and even more preferably an acetate. Among these, at least one selected from the group consisting of cobalt acetate and manganese acetate is even more preferred. The use of the above metal catalyst is preferred because fluorenone can be obtained in high yield.

[0015] The amount of metal catalyst used in the pretreatment step is, in terms of metal element, preferably 0.02 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, even more preferably 0.1 to 3 parts by mass, and even more preferably 0.1 to 1 part by mass, relative to 100 parts by mass of all fluorenes used as raw materials in the oxidation reaction. By setting the amount of the metal catalyst within the above range, the reaction rate in the pretreatment step and the subsequent oxidation step is improved while side reactions are suppressed, and the yield is improved, which is preferable. When the catalyst concentration is equal to or higher than the lower limit, the reaction rate and yield are improved, whereas when the catalyst concentration is equal to or lower than the upper limit, the catalyst cost is reduced and no adverse effects on the reaction occur. The metal catalyst may be used alone or in combination of two or more. The reason why the production method including this pretreatment step enables fluorenone to be obtained in high yield with excellent conversion and selectivity using fluorene as a raw material and also enables industrially safe production is not clear, but is thought to be as follows. In the pretreatment process, by heating fluorene in the presence of the catalyst, it is thought that a part of fluorene becomes active species, and the oxidation reaction can proceed smoothly from the initial stage of oxygen introduction.Therefore, it is thought that oxygen does not remain, and it is possible to produce with high safety.Furthermore, since raw materials are consumed evenly during the reaction, it is thought that side reactions are also suppressed, and the conversion rate and selectivity are excellent, and the yield is also increased.

[0016] <Water> In this step, water may be used, but it is preferable to use water because it makes the bromine compound more soluble. The amount of water used in the pretreatment step is preferably 1 to 200 parts by mass, more preferably 1 to 100 parts by mass, even more preferably 2 to 50 parts by mass, and even more preferably 3 to 10 parts by mass, relative to 100 parts by mass of all fluorenes used as raw materials in the oxidation reaction. When the water concentration is within the above range, the bromine compound can be dissolved while preventing a decrease in catalytic activity, and therefore the yield in the subsequent oxidation step can be improved.

[0017] <Conditions for pretreatment process> The amount of fluorene used in this step is preferably 1 to 50 mass%, more preferably 2 to 40 mass%, even more preferably 3 to 30 mass%, and still more preferably 5 to 20 mass%, based on the total amount of fluorene used as a raw material in the oxidation reaction. By setting the amount of fluorene used in this step within the above range, it is possible to suppress the increase in molecular weight of fluorene due to side reactions and the accompanying decrease in yield, which is preferable. The fluorene used in this step may be introduced all at once and heated, or may be introduced gradually and continuously. From the viewpoint of suppressing side reactions, it is preferable to introduce it continuously. When the fluorene is continuously introduced, the supply rate is preferably 0.1 to 10 parts by mass / min, more preferably 0.2 to 5 parts by mass / min, and even more preferably 0.3 to 3 parts by mass / min, where the total amount of fluorene is 100 parts by mass. Furthermore, the supply rate of fluorene in the pretreatment step is preferably 4 to 1700 parts by mass / min, more preferably 8 to 850 parts by mass / min, even more preferably 13 to 400 parts by mass / min, and even more preferably 130 to 300 parts by mass / min, based on 100 parts by mass of the metal catalyst.

[0018] The heating temperature in the pretreatment step is preferably 160 to 250°C, more preferably 180 to 250°C, even more preferably 200 to 250°C, still more preferably 220 to 250°C, and even more preferably 220 to 240°C. The heating temperature is preferably set within the above range, since it is easy to control the reaction rate. The heating time in the pretreatment step may be changed as appropriate depending on the heating temperature, the amount of catalyst and raw materials, the size of the reaction vessel, the method of introducing the raw materials, etc., but is preferably 3 to 30 minutes, more preferably 3 to 20 minutes, even more preferably 3 to 15 minutes, and even more preferably 5 to 15 minutes. By setting the heating time within the above range, it is possible to suppress the increase in the molecular weight of fluorene due to side reactions and the accompanying decrease in yield, which is preferable. In this step, from the viewpoint of safety, it is preferable to introduce an inert gas such as nitrogen into the reaction vessel containing the raw materials before introducing oxygen. The inert gas may contain a trace amount of oxygen, which exists as an impurity and does not substantially contribute to the oxidation reaction. This pretreatment step is performed before oxygen is introduced. The starting point of this pretreatment step is the point at which the heating temperature in the presence of fluorene, a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst first exceeds the minimum set heating temperature (160°C when heating at 160 to 250°C). Note that, when any of fluorene, a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst is added after heating, the starting point of this pretreatment step is the point at which the heating temperature reaches the set heating temperature and all of fluorene, a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst are present in the reaction vessel. For example, when the heating temperature is set to the set heating temperature in the presence of a lower aliphatic carboxylic acid, a bromine compound, and a metal catalyst, and then fluorene is added to the reaction vessel, the starting point of the pretreatment step is the point at which fluorene is first added to the reaction vessel. The end point of this pretreatment step is the point at which the heating temperature finally falls below the minimum set heating temperature or the point at which oxygen supply is started. Note that if the heating temperature falls below the minimum set heating temperature during this pretreatment step, the time during which the heating temperature is below the minimum set heating temperature is not included in the heating time.

[0019] [Oxidation process] The method for producing fluorenone of the present invention includes, following the pretreatment step, an oxidation step in which fluorene and oxygen are continuously supplied to carry out an oxidation reaction. In this oxidation step, the remaining fluorene other than the fluorene added in the pretreatment step and oxygen are continuously supplied in the presence of a lower aliphatic carboxylic acid, a metal catalyst, and a bromine compound to oxidize the fluorene to obtain fluorenone.

[0020] Here, "continuously supplying fluorene and oxygen" means that the oxidation reaction of fluorene in the reaction vessel and the supply of fluorene and oxygen are carried out in parallel, and that fluorene and oxygen are supplied for more than 50% of the reaction time from the start of the oxidation reaction to the end of the oxidation reaction. In the method for producing fluorenone of the present invention, after the pretreatment process, by continuously supplying the raw material fluorene, it is possible to obtain fluorenone with high conversion rate and high selectivity under industrially safe conditions.The reason is not clear, but it is considered as follows. By pretreatment process, fluorene radical is generated, and then, when fluorene and oxygen as raw materials are continuously supplied, the supplied oxygen is used for oxidation reaction and consumed immediately after being introduced, so that the oxygen concentration in the off-gas (exhaust gas) during reaction can be reduced, and the reaction can be safely completed industrially without reaching the explosion limit for the vapor of lower aliphatic carboxylic acid.Furthermore, by using the oxygen and raw materials supplied as above in oxidation reaction successively, the oxidation reaction can proceed without the raw materials remaining in the reaction system and causing side reactions, so that it is thought that fluorenone can be obtained with high conversion rate and high selectivity.

[0021] <Oxidation reaction conditions, etc.> In this step, fluorene and oxygen are continuously supplied. The supply rate of fluorene may be constant or may be changed as appropriate during supply, but in consideration of ease of supply, it is preferable that the supply rate is substantially constant. The supply rate of fluorene in this oxidation step may be changed as appropriate depending on the size of the reaction vessel, but is preferably 0.1 to 10 parts by mass / min, more preferably 0.2 to 5 parts by mass / min, and even more preferably 0.3 to 3 parts by mass / min, when the total amount of fluorene is 100 parts by mass. From the viewpoint of appropriately controlling the reaction and enhancing safety, the supply rate of fluorene is preferably 4 to 1700 parts by mass / min, more preferably 8 to 850 parts by mass / min, even more preferably 13 to 400 parts by mass / min, and still more preferably 130 to 300 parts by mass / min, relative to 100 parts by mass of the metal catalyst.

[0022] The oxygen used in this step may be oxygen gas or a mixed gas with an inert gas, etc. Among these, in this step, it is preferable to supply oxygen by introducing air from the viewpoints of safety and economy. The oxygen supply rate may be constant or may be changed as appropriate during supply, but it is preferable that the supply rate be constant in consideration of ease of supply. The oxygen supply rate may be appropriately changed depending on the size of the reaction vessel and the supply rate of fluorene. In this step, the molar ratio of oxygen to fluorene continuously supplied [oxygen / fluorene] is preferably 0.5 to 4.0, more preferably 0.6 to 3.0, even more preferably 0.7 to 2.5, still more preferably 0.8 to 2.0, and even more preferably 0.9 to 1.5. By setting the feed ratio within the above range, the selectivity and yield of fluorenone are improved, which is preferable. As mentioned above, the supply rate of fluorene and oxygen and the molar ratio of these that are supplied are preferably substantially constant, from the viewpoint of the safety and yield improvement as the effect of the present invention, and also from the viewpoint of simplicity.However, with the progress of oxidation reaction, the ratio of raw material fluorene and oxygen that remain in reaction system and the amount of fluorene radical change, so the oxygen concentration in off-gas may change.In particular, when the oxygen concentration in off-gas increases, it is preferable to reduce the oxygen supply amount and the molar ratio of oxygen that is supplied and fluorene.

[0023] In order to complete the oxidation reaction even after the end of the fluorene supply, it is preferable to continuously supply oxygen. When the oxidation reaction is completed, oxygen is no longer absorbed, and the oxygen concentration in the off-gas increases, so the oxygen supply is terminated. From the viewpoint of safety, it is preferable to terminate the oxygen supply when the oxygen concentration in the off-gas is below the explosion limit of the lower aliphatic carboxylic acid.

[0024] The reaction temperature for the oxidation reaction is preferably 120 to 250°C, more preferably 140 to 250°C, even more preferably 200 to 250°C, still more preferably 220 to 250°C, and even more preferably 220 to 240°C. The reaction temperature is preferably set within the above range, since the conversion rate is improved. The reaction pressure of the oxidation reaction is preferably 0.1 to 3.0 MPa, more preferably 0.3 to 3.0 MPa, even more preferably 0.5 to 3.0 MPa, still more preferably 1.0 to 3.0 MPa, even more preferably 1.5 to 3.0 MPa, and still more preferably 1.5 to 2.5 MPa. The reaction time for the oxidation reaction may be appropriately changed depending on the reaction temperature, the amount of catalyst and raw materials, the size of the reaction vessel, the supply rate of raw materials, etc., but is preferably 30 to 300 minutes, more preferably 60 to 200 minutes, and even more preferably 80 to 120 minutes.

[0025] In this step, fluorene and oxygen are continuously supplied to the reaction mixture that has undergone the pretreatment step, which contains the lower aliphatic carboxylic acid, metal catalyst, and bromine compound used in the pretreatment step, and a portion of the fluorene added in the pretreatment step, as described above. It is simple and preferable to use the components used in the pretreatment step as they are in this step. In addition, a lower aliphatic carboxylic acid, a metal catalyst, and a bromine compound may be further added in this step. By adding the metal catalyst and the bromine compound, it becomes possible to continue the continuous reaction for a long time. When these are added in this step, it is preferable to supply them continuously as in the case of fluorene, and it is more preferable to supply them so that the supply amounts of the metal catalyst and fluorene are within the above-mentioned ranges.

[0026] [Other processes] The method for producing fluorenone of the present invention may include any steps other than the pretreatment step and the oxidation step. Optional steps included in the method for producing fluorenone of the present invention include a solvent removal step and a distillation step.

[0027] The solvent removal step is a step of removing lower aliphatic carboxylic acids and water, which are solvents with boiling points lower than that of fluorenone, the target product of this production method. By removing these solvents before removing by-products generated in the oxidation reaction and fluorene, the raw material, by distillation, the subsequent distillation step can be carried out efficiently. In the solvent removal step, in order to efficiently remove the solvent, the solvent may be removed by heating and distillation under reduced pressure, or the solvent may be removed by heating and distillation under normal pressure.

[0028] The distillation step may be carried out by any method as long as it can separate and recover the target fluorenone with high purity. The distillation temperature may be appropriately adjusted to about the boiling point of fluorenone under the pressure during distillation (the boiling point at 1 atmosphere is 342°C). For example, when the distillation pressure is adjusted to 3 kPa, the distillation temperature is preferably 150 to 300°C, more preferably 160 to 250°C, even more preferably 180 to 240°C, and still more preferably 180 to 220°C. When a distillation column is used in the distillation step, low boiling point components are suitably removed from the top of the column and high boiling point components are suitably removed from the bottom of the column to recover high purity fluorenone. [Example]

[0029] The present invention will be specifically described based on the following examples, but the present invention is not limited to these examples.

[0030] [evaluation] <Oxygen concentration in off-gas> The oxygen concentration in the off-gas was determined as follows. Equipment: Shimadzu Corporation Portable Oxygen Meter: POT-101 Measurement method: The gas exhaust pipe of the autoclave was connected to the oxygen meter, and the oxygen concentration in the off-gas was measured in real time and evaluated according to the following criteria. From the viewpoint of safety during industrial production, it is preferable that the oxygen concentration in the off-gas be 8% by volume or less, which is the explosion limit of acetic acid as the solvent. A lower oxygen concentration in the off-gas is preferable because it increases the degree of freedom in the reaction conditions from the viewpoint of safety. (Evaluation criteria) ○: The oxygen concentration in the off-gas was always 8% by volume or less during the oxidation reaction. △: The time during which the oxygen concentration in the off-gas exceeded 8% by volume was less than 10% of the oxidation reaction time. ×: The time during which the oxygen concentration in the off-gas exceeded 8% by volume was 10% or more of the oxidation reaction time.

[0031] <Conversion rate> The amount (mol) of fluorene contained in the oxidation reaction product after the oxidation step was calculated by the internal standard method using gas chromatography (internal standard: triphenylmethane), and the amount (mol) of fluorene consumed was determined by subtracting it from the amount (mol) of fluorene in the raw material. The conversion rate was calculated from the amount of fluorene consumed and the amount of fluorene in the raw material by the following formula: The conversion rate is the raw material conversion rate. Conversion rate (%) = (amount of fluorene consumed (moles)) / (amount of fluorene in the raw material (moles)) × 100 A higher conversion rate is preferable because it allows the raw material to be converted more efficiently into the product fluorenone.

[0032] <Fluorenone selectivity / fluorenone yield> The amount of fluorenone contained in the oxidation reaction product after the oxidation step (amount of fluorenone produced) (mol) was calculated by the internal standard method using gas chromatography (internal standard: triphenylmethane). The fluorenone selectivity was calculated from the amount of fluorenone produced and the amount of fluorene in the raw material (amount of fluorene consumed) according to the following formula. Selectivity (%) = (amount of fluorenone produced (mol)) / (amount of fluorene consumed (mol)) × 100 The fluorenone yield is a value calculated by multiplying the conversion rate by the fluorenone selectivity. Higher fluorenone selectivity and fluorenone yield are preferable because they enable more efficient production of high-purity fluorenone.

[0033] Example 1 (Preparation of Fluorenone) (1. Pretreatment process) A catalyst solution was obtained by mixing cobalt acetate tetrahydrate, manganese acetate tetrahydrate, a 48 mass% aqueous hydrogen bromide solution, glacial acetic acid, and water so as to have a cobalt metal atomic concentration of 0.75 mass%, a manganese metal atomic concentration of 0.75 mass%, a bromide ion concentration of 0.075 mass%, an acetic acid concentration of 88.425 mass%, and a water concentration of 10 mass%. 150 g of the catalyst solution was charged into a 500 mL titanium autoclave equipped with a gas outlet pipe with a reflux condenser, a gas inlet pipe, a continuous raw material feed pump, and a stirrer, and the temperature and pressure were increased to 200°C (set temperature: 190-210°C) and 1.0 MPa under a nitrogen atmosphere. 14 g of fluorene was fed in 10 minutes. The throughput was 1.4 g / min.

[0034] (2. Oxidation process) After the pretreatment step was completed, the introduction of air was started simultaneously with the start of the additional feedstock, and the feedstock and air were continuously supplied. 136 g of the feedstock, fluorene, was supplied in 97.1 minutes. The throughput was 1.4 g / min. Air was supplied at 1.90 L / min (0.40 L / min in oxygen equivalent). 1.8 hours after the start of air supply, the oxygen concentration in the off-gas reached 8% by volume, and the supply was terminated. In this manner, an oxidation reaction product was obtained. The obtained oxidation reaction product was extracted and analyzed. The conversion was 100%, the fluorenone selectivity was 84.1 mol%, and the fluorenone yield was 84.1 mol%. The results are shown in Table 1.

[0035] Example 2 (Preparation of Fluorenone) 2. In the oxidation step, an oxidation reaction product was obtained in the same manner as in Example 1, except that the air supply rate and supply time were changed as shown in Table 1. The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0036] Example 3 (Preparation of Fluorenone) 1. In the pretreatment step, instead of the catalyst solution of Example 1, a catalyst solution obtained by mixing cobalt acetate tetrahydrate, manganese acetate tetrahydrate, a 48 mass% aqueous hydrogen bromide solution, glacial acetic acid, and water was used so as to have a cobalt metal atom concentration of 0.24 mass%, a manganese metal atom concentration of 0.15 mass%, a bromide ion concentration of 0.18 mass%, an acetic acid concentration of 89.61 mass%, and a water concentration of 10 mass%, and the supply amount, supply rate, supply time, and temperature of fluorene were changed as shown in Table 1. The set temperature was 220 to 240°C. Furthermore, in 2. oxidation step, an oxidation reaction product was obtained in the same manner as in Example 1, except that the supply amount, supply rate, supply time of fluorene, and supply rate, supply time of air, and conditions (temperature, pressure) were changed as shown in Table 1. The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0037] Example 4 (Preparation of Fluorenone) 2. In the oxidation step, an oxidation reaction product was obtained in the same manner as in Example 3, except that the supply time, supply rate, and air supply rate of fluorene were changed as shown in Table 1. The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0038] Example 5 (Preparation of Fluorenone) An oxidation reaction product was obtained in the same manner as in Example 3, except that 1. in the pretreatment step, the temperature was changed as shown in Table 1 (set temperature: 160 to 180°C), and 2. in the oxidation step, the temperature was changed as shown in Table 1 (set temperature: 160 to 180°C). The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0039] Example 6 (Preparation of Fluorenone) 1. In the pretreatment step, an oxidation reaction product was obtained in the same manner as in Example 3, except that the temperature was changed as shown in Table 1 (the set temperature was 160 to 180°C). The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0040] Comparative Example 1 (Production of Fluorenone) A catalyst solution was prepared as described in 1. Pretreatment step of Example 1, and 150 g of the catalyst solution was charged into a titanium autoclave having an internal volume of 500 mL and equipped with a gas outlet pipe with a reflux condenser, a gas inlet pipe, a raw material continuous liquid feed pump, and a stirrer. 1. Pretreatment step was not performed.

[0041] (2. Oxidation process) The introduction of air began simultaneously with the start of the supply of the raw material fluorene, and the raw material and air were supplied continuously. 150 g of the raw material fluorene was supplied in 48.4 minutes. The throughput was 3.1 g / min. Air was supplied at 2.50 L / min (0.52 L / min in oxygen equivalent). The oxygen concentration in the off-gas exceeded 8% by volume immediately after the air supply began, and remained above 8% by volume until the air supply was completed (minimum concentration 11% by volume, maximum concentration 20% by volume). In this manner, the oxidation reaction product was obtained. The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0042] Comparative Example 2 (Production of Fluorenone) (1. Pretreatment process) A catalyst solution was prepared as described in 1. Pretreatment step of Example 1, and 150 g of the catalyst solution was placed in a 500 mL titanium autoclave equipped with a gas outlet pipe with a reflux condenser, a gas inlet pipe, a raw material continuous liquid feed pump, and a stirrer. The temperature and pressure were increased to 200°C (set temperature: 190 to 210°C) and 1.0 MPa under a nitrogen atmosphere. 150 g of fluorene was heated for 10 minutes.

[0043] (2. Oxidation process) After the pretreatment step was completed, air introduction was started and only air was supplied. Air was supplied at a rate of 1.90 L / min (0.40 L / min in oxygen equivalent). Air supply was stopped two hours after the start of air supply. In this way, an oxidation reaction product was obtained. The oxygen concentration in the off-gas and the evaluation results of the obtained product are shown in Table 1.

[0044] [Table 1]

[0045] From the results of the Examples shown in Table 1, it can be seen that the production method of the present invention can produce fluorenone in high yield, with excellent conversion and selectivity, and can produce high-purity fluorenone. Furthermore, it can be seen that the oxidation reaction can be carried out while suppressing the oxygen concentration in the off-gas, which means that the method is highly safe from an industrial standpoint.

Claims

1. A method for producing fluorenone, comprising a pretreatment step of heating fluorene in the presence of a lower aliphatic carboxylic acid, a bromine compound and a metal catalyst, and an oxidation step of continuously supplying fluorene and oxygen to carry out an oxidation reaction, in this order, wherein the lower aliphatic carboxylic acid is an aliphatic carboxylic acid having 1 to 4 carbon atoms.

2. 2. The method for producing fluorenone according to claim 1, wherein in the oxidation reaction, the molar ratio of continuously supplied oxygen to fluorene [oxygen / fluorene] is 0.5 to 4.

0.

3. The method for producing fluorenone according to claim 1 or 2, wherein the heating temperature in the pretreatment step is 160 to 250°C.

4. The method for producing fluorenone according to any one of claims 1 to 3, wherein the heating time in the pretreatment step is 3 to 30 minutes.

5. The method for producing fluorenone according to any one of claims 1 to 4, wherein the reaction temperature of the oxidation reaction is 120 to 250 ° C.

6. The method for producing fluorenone according to any one of claims 1 to 5, wherein the reaction pressure of the oxidation reaction is 0.1 to 3.0 MPa.

7. The method for producing fluorenone according to any one of claims 1 to 6, wherein the metal catalyst is at least one selected from the group consisting of a cobalt catalyst, a manganese catalyst, a zirconium catalyst, a nickel catalyst, and a cerium catalyst.

8. The method for producing fluorenone according to any one of claims 1 to 7, wherein the lower aliphatic carboxylic acid is acetic acid.

9. The method for producing fluorenone according to any one of claims 1 to 8, wherein oxygen is supplied by introducing air in the oxidation step.

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