KR20190033020A - Method of Producing Benzoic Acid by Reaction and Distillation of Acetophenone - Google Patents

Abstract

The present invention relates to a method for manufacturing a benzoic acid through a reactive distillation process of acetophenone. If the benzoic acid is manufactured by obtaining the benzoic acid by oxidizing acetophenone in the presence of an acetic acid solvent and a manganese salt catalyst, and then distilling a solvent and a mixture of unreacted acetophenone and the benzoic acid, it is possible to manufacture the benzoic acid in a high yield by maximizing the conversion ratio of acetophenone.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing benzoic acid by reactive distillation of acetophenone,

The present invention relates to a process for producing benzoic acid through a reactive distillation process of acetophenone, and more particularly, to a process for producing benzoic acid by oxidizing acetophenone in the presence of an acetic acid solvent and a manganese salt catalyst, Benzoic acid is distilled to produce benzoic acid in high yield and high purity.

Benzoic acid is a substance that can act as a mediator to produce various substances. Benzoic acid, which can be used in various industrial fields such as chromosomes, perfumes, preservatives, and fiber preparation, including phenol produced through the Snia Viscosa route, is one of the materials expected to increase steadily in the future.

Benzoic acid has been produced mainly by the selective oxidation of toluene. This oxidation reaction using manganese or cobalt salt as a catalyst proceeds by injecting air of about 10 atm with an oxidizing agent at a temperature of about 200 ° C. However, this process, in which the exothermic reaction occurs mainly at a relatively high temperature, incurs an additional cost for maintaining the temperature, and the risk that the reactor may rapidly rise to a high temperature if the temperature is not properly maintained. In addition, since the amount of benzoic acid produced per unit time is low even though high pressure air is used at high temperature, the yield of benzoic acid should be increased by recycling unreacted toluene. However, since toluene forms an azeotropic mixture with water, which is a byproduct which can easily be produced by a common organic reaction, there is also a disadvantage in that additional processing is required to separate the toluene from the product.

This problem is easily solved by replacing the toluene used as the reactant with acetophenone. This oxidation reaction, in which acetic acid is used as a solvent in the same manner as a manganese salt catalyst, can obtain a higher yield of benzoic acid than toluene even at a lower air pressure at a temperature of 100 ° C or lower . When the same reaction time and reactor size are used, not only the amount of unreacted acetophenone is small but also it is not difficult to separate it from the product because it does not form an azeotropic mixture with various byproducts that may be generated including water It also has an advantage. However, this process has the disadvantage that the reactant acetophenone is more expensive than toluene. Even if benzoic acid can be produced in a relatively smooth reaction condition, if the price of acetophenone itself is included, the price of benzoic acid becomes more expensive than when it is produced by toluene. Therefore, acetophenone is used in the production process of benzoic acid .

The inventors of the present invention have found that benzoic acid can be obtained by oxidizing acetophenone in the presence of an acetic acid solvent and a manganese salt catalyst to obtain a benzoic acid efficiently, It has been confirmed that when benzoic acid is produced by distillation of a mixture of phenon and benzoic acid, the efficiency of the oxidation reaction of acetophenone is maximized and high-purity benzoic acid can be produced at a high yield.

It is an object of the present invention to provide a process for producing high purity benzoic acid in high yield through an oxidation reaction for maximizing the acetophenone conversion rate and a distillation process for selectively distilling the oxidation product.

In order to achieve the above object, the present invention is characterized in that benzoic acid is obtained by oxidizing acetophenone in the presence of an acetic acid solvent and a manganese salt catalyst, and then the mixture of the solvent and unreacted acetophenone and benzoic acid is distilled to recover benzoic acid And a method for producing the benzoic acid.

According to the production method of the present invention, it is possible to produce benzoic acid at a high yield with high efficiency through an oxidation reaction for maximizing the conversion of acetophenone and a distillation process for selectively distilling the oxidation product or the solvent. Benzoic acid can be produced at a relatively low cost by using acetophenone in the form of a mixture which is generated as a byproduct of the basic process. In addition, the present invention can increase the yield of benzoic acid by minimizing the adverse reaction which can maximize the oxidation of acetophenone and inhibit the main reaction, by regulating the reaction environment and controlling the amount of additives and the like.

1 is a diagrammatic view of a reactor for reactive distillation according to an embodiment of the present invention.
2 is a schematic diagram of a continuous process of a reactor-distillation column according to an embodiment of the present invention.
3 is a schematic diagram of a reactive distillation process according to another embodiment of the present invention.
4 is a schematic diagram of a reactive distillation process according to another embodiment of the present invention.
5 is a graph showing the results of thermal safety tests of acetophenone and benzoic acid in Example 1 of the present invention.
6 is a graph comparing the results of temperature measurement experiments for selective distillation of acetophenone in Example 2 of the present invention.
7 is a graph comparing the results of the reaction distillation experiment with the results of the general reaction experiment in Example 3 of the present invention.
FIG. 8 is a graph comparing the influence of temperature on the conversion of acetophenone in the initial and late stages of the reaction in Example 4 of the present invention. FIG.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

The present invention relates to a process for producing acetophenone by oxidizing acetophenone in a Continuous Stirred Tank Reactor (CSTR) in which acetophenone conversion is maximized and separating the oxidation product from the distillation tower to produce benzoic acid. It was confirmed that the conversion of acetophenone was maximized and that high purity benzoic acid could be produced at a high yield.

Accordingly, the present invention relates in one aspect to a process for the production of benzoic acid by oxidation of acetophenone in the presence of an acetic acid solvent and a manganese salt catalyst, followed by distillation of the mixture of the solvent and unreacted acetophenone and benzoic acid to recover the benzoic acid And a method for producing the same.

Hereinafter, the present invention will be described in detail.

The present invention relates to a process for oxidizing acetophenone and producing benzoic acid using acetic acid as a solvent in the presence of a manganese salt catalyst, comprising the steps of producing a benzoic acid in a series of reaction-distillation stages through a continuous stirred tank reactor and a distillation column, A process for producing benzoic acid in one step through reactive distillation, and a process for producing benzoic acid through reactive distillation and a filter.

As a mechanism for producing high purity benzoic acid by one step by selective distillation of acetophenone in a reactive distillation process, acetophenone is oxidized in a high pressure continuous stirring tank reactor, and benzoic acid Thereby providing a series of processes for separating. The present invention proceeds with a high temperature distillation experiment of a mixture of acetophenone and benzoic acid and analyzes the result by gas chromatography to provide an optimum temperature for selectively distilling acetophenone.

The oxidation reaction of the acetophenone of the present invention includes a step of oxidizing a mixture containing acetophenone under air or oxygen by using acetic acid as a solvent and a manganese salt as a catalyst described below (oxidation reaction).

The distillation and separation of acetophenone of the present invention comprises heating a liquid mixture of acetophenone and benzoic acid to a high temperature to selectively vaporize acetophenone and recover benzoic acid (hereinafter referred to as distillation step).

The reactive distillation process according to the present invention can be carried out using a reactor as shown in FIG. The solvent still head (FIG. 1 (b)) at the top of FIG. 1 has a lower end (FIG. 1 (a), for example, a 250 ml flask ), And the substance can be delivered through the process of liquefaction at the upper end of the vapor phase which is boiled at a certain temperature or more at the lower end.

According to an embodiment of the present invention, the oxidation process and the distillation process may be sequentially performed in a reactive distillation apparatus in which a continuous stirred tank reactor (CSTR) and a distillation column are connected. The reactor-distillation tower sequential process is illustrated in FIG.

After the acetophenone is oxidized in the reactor, benzoic acid can be produced through separation in a separate distillation column. The solvent, the acetophenone mixed with the catalyst, is oxidized after entering the high-pressure continuous stirred tower reactor. The product of the reaction then enters the distillation column as the unreacted reactant. Benzoic acid, which is a relatively high boiling point material in the distillation column, is obtained at the bottom, and acetic acid, which is a solvent, and acetophenone, which is a reactant, are obtained at the top and then recycled to the reactor. Trace amounts of benzoic acid can also be injected into the reactants to facilitate the oxidation reaction through the autocatalytic reaction.

According to another embodiment of the present invention, acetophenone can be oxidized to benzoic acid through a one-step reactive distillation process. The reactive distillation process is shown in FIG.

The acetophenone mixed with the solvent and the catalyst is injected into a Reaction-Distillation Tower (RD tower). At the relatively low temperature, the acetophenone is oxidized to the reaction temperature and the acetophenone is distilled at the lower temperature to reduce the loss to the bottom. The liquid from the lower part enters the separation column to separate acetophenone and benzoic acid, and then acetophenone and acetic acid are injected again into the distillation column.

According to another embodiment of the present invention, the oxidation reaction may be performed at the upper end of the distillation column, and the lower portion may be distilled to selectively distill only the acetic acid solvent. This minimizes the bottom product and reduces the volume of subsequent steps. The reactive distillation process is illustrated in FIG.

After the product at the bottom of the distillation column is subjected to an additional separation process, the upper product of the distillation column can be recycled to the reactor for recycling. The distillation is preferably carried out at a temperature of 100 to 140 ° C. and a pressure of 0.1 to 50 atm.

After the product at the bottom of the distillation column is subjected to a solid-liquid separation process, the benzoic acid in a solid state can be obtained and the liquid state material can be recycled to the reactor for recycling.

The acetophenone according to the present invention may be pure acetophenone or a mixture, i.e., a crude acetophenone, in which acetophenone is produced as a main by-product in a factory.

In the present invention the catalyst used in acetophenone oxidation reaction may be a manganese anhydride or magnesium hydrate, the preferred example of a manganese anhydride is manganese nitrate _{(Mn (NO 3) 2)} , acetamide manganese (Mn (CH ₃ COO ) _2), manganese chloride (MnCl _2), manganese sulfate (MnSO ₄₎ and may be selected from the group consisting of a mixture thereof, manganese hydrate of manganese nitrate hydrate _{(Mn (NO 3) 2 ·} xH 2 O, x is 1 to 4) or acetal manganese hydrate (Mn (CH ₃ COO) ₂ .xH ₂ O, x is an integer of 1 to 4). Manganese nitrate and acetal manganese can be in the form of a hexahydrate (Mn (NO ₃ ) ₂ .4H ₂ O, Mn (CH ₃ COO) ₂ .4H ₂ O).

The oxidation reaction may be performed at an absolute pressure of 0.1 to 50 atm, preferably 1 to 10 atm, using air or oxygen as an oxidizing agent. If the pressure is less than 0.1 atm, the amount of the oxidizing agent is insufficient to activate the catalyst. If the pressure exceeds 50 atm, the reactor must withstand the high pressure.

In the oxidation reaction, the temperature of the reactant may be 50-150 ° C, preferably 90-110 ° C, and most preferably 95-105 ° C. The dehydration condensation and reduction degree of the reactants are minimized at 100 ° C., which maximizes the conversion of acetophenone, and the selectivity of benzoic acid is maximized. The oxidation power of manganese ions is high at the above-mentioned temperature range, thereby inhibiting the recycle of benzoic acid, and the reaction proceeds predominantly in the forward direction in the reaction formula 1, and dehydration condensation of the reaction is inhibited.

The distillation step may be carried out at a pressure of 0.01 to 10 atm under absolute pressure and at a temperature of 50 to 300 ° C. At distillation temperatures above 300 < 0 > C, the yield of benzoic acid may drop sharply due to side reactions of the reaction and product, and maintaining pressures below 0.01 atmospheres may be inefficient. The range of the desired distillation temperature may vary depending on the pressure. For example, in the case of normal pressure, a preferable distillation temperature may be a temperature of 190 占 폚 or more and less than 195 占 폚.

The amount of acetophenone in the oxidation reaction may be 1 to 30% by volume relative to the volume of the solvent acetic acid. When acetophenone of less than 1% by volume is added, excessive acetic acid is required to oxidize the same volume of acetophenone, which may be problematic in terms of cost. If the volume ratio exceeds 30% There is a problem that a part of benzoic acid as a product in acetic acid is not dissolved.

The amount of the catalyst in the oxidation reaction may be a molar ratio of 0.1-10% to the molar amount of the acetophenone as the reactant. When the catalyst is added at a volume ratio of less than 0.1%, there is a problem that the acetophenone can not be sufficiently oxidized by reducing the amount of the catalyst, which is relatively insufficient. When the volume ratio exceeds 10% There is a problem in that it is economically inefficient because the conversation rate does not increase.

As the amount of the catalyst increases, the conversion of acetophenone and the selectivity of benzoic acid become maximum, and the reduction and dehydration condensation of the reactant are minimized. As the amount of manganese ions acting as an oxidizing agent for acetophenone increases, the degree of oxidation of the reactant increases, conversely, the degree of reduction decreases, and more forward reaction occurs in the reaction formula 1 to inhibit dehydration condensation.

The pH of the oxidation reaction may be 0.01 to 5, preferably 0.01 to 2. When the pH is less than 0.01, there is a problem that the reactor or the like may be corroded due to the high acidity of the water, and when the pH is more than 5, the reaction activity of the catalyst is lost.

In the oxidation reaction, the reaction time may be 1 to 24 hours after the temperature rises.

When acetophenone is converted into benzoic acid by the oxidation reaction, formic acid (CH ₂ O ₂ ), benzaldehyde (C ₇ H ₆ O, benzaldehyde (BZ)), diphenylethanedione (C ₁₄ H ₁₀ O _{2 ,} diphenyethanedione (DE)), phenyl acetate _{(C 10 H 10 O 3,} phenyl acetate (PA)), 2- benzoyl-oxy-1-phenyl-ethanone _{(C 14 H 10 O 3,} 2- (benzoyloxy) -1-phenyl ethanone , 2B1P) can be mainly generated.

Formic acid in the by-product is formed by oxidation of formaldehyde formed in the course of the oxidation of acetophenone to benzoic acid, and PA is formed by dehydration condensation with benzoic acid, which is a solvent, as a solvent. Among the byproducts, BZ is produced by reduction of benzoic acid produced by oxidation, and DE is produced by dehydration condensation of the reduced BZ with benzoic acid. And 2B1P is produced by dehydration condensation of benzoic acid. The total reduction degree of the reactant can be calculated by the sum of the selectivities of BZ and DE formed by reduction of benzoic acid in the byproduct. The total dehydration condensation of the reactants can be calculated from the sum of the selectivities of DE, PA and 2B1P produced by dehydration condensation of benzoic acid.

In the oxidation reaction, the conversion of acetophenone or the yield of benzoic acid may vary with changes in temperature, pressure, amount of catalyst, and initial pH, and the yield of byproducts may vary.

In the oxidation reaction, the higher the conversion of acetophenone or the higher yield of benzoic acid, the lower the degree of reduction and dehydration condensation of the reaction product.

When the catalyst is used in the form of a hydrate in the oxidation reaction, the degree of dehydration condensation of the reactant is suppressed and the selectivity of benzoic acid is further increased, so that the reaction proceeds in an efficient direction to increase the yield of benzoic acid. And the increased pH of the reactants due to the increased production of benzoic acid leads to a more smooth reaction in the positive direction, leading to an increase in the conversion of acetophenone and a reduction in the degree of reduction of the reactants. When the hydrate is used as a catalyst in the oxidation reaction, the amount of the catalyst may be 0.8-1.2 mol% based on acetophenone.

When the acetophenone contained in the mixture is used in the oxidation reaction, the byproducts contained in addition to acetophenone may include dipropylene glycol or tripropylene glycol which may be generated during the production of propylene oxide.

In this mixture, the crude acetophenone may be used in an amount of 1 to 100 parts by weight, based on 100 parts by weight of acetophenone, of propylene glycol, dipropylene glycol, tripropylene glycol, cumene, ethylbenzene, methanol, acetone, 1-propanol and formaldehyde . Preferably, dipropylene glycol and tripropylene glycol may be contained in a mass ratio of 1 to 100% relative to acetophenone, respectively.

When the oxidation reaction is carried out with the above mixture, dipropylene glycol and tripropylene glycol are mostly hydrolyzed with propylene glycol and 1,3-propanediol and can be formed into other forms by dehydration condensation between them.

[Reaction Scheme 1]

2 Mn ^{2 +} + 2 H ⁺ + (1/2) O ₂ ? 2 Mn ^{3 +} + H ₂ O

Before the acetophenone is oxidized to benzoic acid, the manganese divalent ions added in the form of salts in the reaction through the reaction as shown in the reaction scheme 1 are oxidized to manganese trivalent ions. Oxidized manganese ions are oxidized to acetophenone and then reduced to manganese divalent ions and reoxidized by oxygen on the gas phase.

The present invention can also recycle 0.01 to 10% by weight of benzoic acid relative to acetophenone in the resulting benzoic acid.

In the present invention, it may include a step of oxidizing the manganese salt catalyst under air or oxygen Activated reaction).

The activation reaction of the catalyst can be carried out at a temperature lower than the oxidation reaction temperature, preferably at a low temperature of from 0 ° C to 10 ° C and at a pressure of from 0.1 to 50 atm.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

[Example]

Example  One: Side reaction  Experiment

A method for measuring the thermal stability of acetophenone and benzoic acid will be specifically described as follows.

The flask was mixed with only acetophenone and benzoic acid, heated to a specific temperature in the mantle, and reacted with the liquid for 3 hours. After the reaction, the liquid phase was subjected to qualitative analysis through On-line GC (Agilent 7890A) and Gas chromatography-Mass Spectrometer (Clarus 600 series + TurboMatrix HSS Trap). The results of the GC analysis of the reactants at 195 ° C and 220 ° C are shown on the left side of FIG. 5, and the products measured through the mass spectrometer are shown on the right side of FIG.

It can be seen from FIG. 5 that a molecule having a carbon number of 16 was generated at 220 ° C due to the dehydration condensation reaction and the like. Acetophenone as a reactant has a carbon number of 8 and a benzoic acid of 7, and it is presumed that acetophenone, which is not benzoic acid, is condensed at this temperature. The dehydration condensation reaction does not occur at a temperature lower than 195 DEG C and the temperature for selective distillation of acetophenone should also be lower than 195 DEG C. [

Example  2: Selective distillation experiment of acetophenone

A method for setting an optimum temperature for selectively distilling acetophenone in a mixture with benzoic acid will be specifically described as follows.

Acetophenone and benzoic acid were mixed at the lower end of the glass reactor for distillation installed as shown in FIG. 1, and 30 mL of ethanol was injected into the upper portion. The temperature at the upper end was maintained at room temperature while the lower end was heated to a specific temperature with the mantle, and the liquid phase at the lower end was distilled to the upper part while being maintained for 3 hours.

The liquid phase at the top of the reaction was subjected to quantitative and qualitative analysis via on-line GC. The liquid phase composition at the top according to temperature is shown in FIG.

From the results of FIG. 6, it can be seen that a significant amount of acetophenone, which has not been distilled at the uppermost stage at 180 ° C at normal pressure, is distilled at 190 ° C. Benzoic acid was not detected at the top even at 190 占 폚.

Example  3

A method for oxidizing acetophenone to benzoic acid through reactive distillation will be specifically described below.

3.15 mL of acetophenone, 27 mL of acetic acid, and 0.1104 g of acetic acid manganese tetrahydrate were injected into the upper portion of the installed glass reactor for distillation, and the temperature was elevated to 95 DEG C under oxygen injection at 50 mL / min. In the lower part, 6.3 mL of acetophenone and 8 mL of acetic acid were injected, and the temperature was raised to 190 ° C. After 1 hour and 30 minutes after reaching the upper temperature, additional 3 mL of acetic acid was added to facilitate the upper and lower distillation, and the reaction was further conducted for 1 hour and 30 minutes.

The liquid phase at the top of the reaction was subjected to quantitative and qualitative analysis via on-line GC. FIG. 7 shows the results of the experimental group subjected to the distillation at the bottom and the experimental results of the control group in which the reaction was carried out under the same conditions as above without the distillation.

As shown in Fig. 7, 1.98 mL of 3.15 mL of acetophenone was converted in the control group, and the selectivity to benzoic acid was measured to be 93.13%. On the other hand, in the reactive distillation experiment group, the addition amount of acetophenone resulted in the conversion of 2.23 mL, which was 8% more than that of the conventional acetophenone, and the selectivity to benzoic acid was constant at 93.09%.

Example  4: Catalytic Activation Experiment

A method of rapidly activating manganese chloride, which is a catalyst, will be described in detail as follows.

27 ml of acetic acid and 0.1104 g of acetic acid manganese tetrahydrate were charged into the flask, and the temperature was raised under oxygen injection of 50 mL / min. When the set temperature was reached, 3.15 mL of acetophenone was injected and sampling was performed 10 minutes and 7 hours after the reaction was started.

After the reaction, the liquid phase was subjected to quantitative and qualitative analysis through on-line GC. Experimental results on acetophenone conversion by temperature are shown in FIG.

As shown in FIG. 8, the conversion rate of acetophenone tends to increase as the temperature approaches 100 ° C., but it can be seen that the conversion is higher at a temperature lower than 100 ° C. in the early stage of the reaction. The activity of the catalyst is highest at 100 ° C, but the activation time is the fastest at 92 ° C.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereto will be. Accordingly, the actual scope of the invention will be defined by the claims and their equivalents.

Claims (19)

Oxidizing acetophenone in the presence of an acetic acid solvent and a manganese salt catalyst to obtain a benzoic acid and then distilling a mixture of the solvent and unreacted acetophenone and benzoic acid to recover the benzoic acid.
The process for producing benzoic acid according to claim 1, wherein an oxidation process and a distillation process are sequentially performed in a reactive distillation apparatus in which a continuous stirred tank reactor (CSTR) and a distillation column are connected.
The reaction distillation apparatus according to claim 1, wherein the reactive distillation apparatus is a continuous reaction distillation apparatus in which a reactor is located at the top of a distillation column, acetophenone is fed to the top, and benzoic acid reacted to the distillation tower and benzoic acid is obtained at the bottom of the distillation tower. ≪ / RTI >
The process for producing benzoic acid according to claim 1, wherein the oxidation reaction is carried out at the upper end of the distillation column and the acetophenone is further distilled at the lower end to selectively distill only the acetic acid solvent.
5. The process for producing benzoic acid according to any one of claims 1 to 4, wherein the product at the bottom of the distillation column is subjected to an additional separation process, and the separated product at the upper end of the distillation column is recycled to the reactor.
The process for producing benzoic acid according to any one of claims 1 to 4, wherein the distillation is carried out at a temperature of 100 to 140 캜 and a pressure of 0.1 to 50 atm.
5. The process for producing benzoic acid according to claim 4, wherein the product at the bottom of the distillation column is subjected to a solid-liquid separation process to obtain a benzoic acid in a solid state, and a liquid substance is recycled to the reactor.
The process for producing benzoic acid according to claim 1, wherein the acetophenone is crude acetophenone.
The process for preparing benzoic acid according to claim 1, wherein the manganese salt catalyst is manganese anhydride or manganese hydrate.
10. The method of claim 9, wherein the manganese anhydride is manganese nitrate _{(Mn (NO 3) 2)} , acetamide manganese _{(Mn (CH 3 COO) 2} ), manganese chloride (MnCl _2), manganese sulfate (Mn (SO _{4) 2} (Mn (NO ₃ ) ₂ .xH ₂ O, x is an integer of 1 to 4) or acet manganese hydrate (Mn (CH ₃ COO)), and mixtures thereof. The manganese hydrate is selected from the group consisting of manganese nitrate hydrate ₂ xH ₂ O, and x is an integer of 1 to 4).
The process for producing benzoic acid according to claim 1, wherein acetophenone is added in an amount of 1 to 30% by volume relative to the acetic acid solvent.
The process for preparing benzoic acid according to claim 1, wherein the manganese salt catalyst is added in a molar ratio of 0.1 to 10% based on the acetophenone.
The method of claim 1, wherein the acetophenone is used in an amount of 1 to 100 parts by weight, based on 100 parts by weight of acetophenone, of propylene glycol, dipropylene glycol, tripropylene glycol, cumene, ethylbenzene, methanol, acetone, 1-propanol and formaldehyde Lt; RTI ID = 0.0 > 1, < / RTI >
9. The process according to claim 8, wherein the crude acetophenone comprises dipropylene glycol and tripropylene glycol.
2. The method of claim 1, wherein the oxidation is carried out at a temperature of from 50 to 150 DEG C and at a pressure of from 0.1 to 50 atm, and the distillation is carried out at a temperature of from 50 to 300 DEG C and at a pressure of from 0.01 to 10 atm.
The process for producing benzoic acid according to claim 1, wherein the pH of the oxidation reaction is 0.01-5.
The process for producing benzoic acid according to claim 1, wherein 0.01 to 10% by weight of benzoic acid is recycled to the acetophenone in the produced benzoic acid.
16. The process for producing benzoic acid according to claim 15, wherein the catalyst is activated at a temperature lower than the oxidation reaction temperature.
The process for producing benzoic acid according to claim 18, wherein the activation is carried out at a temperature of 0 to 10 ° C lower than the oxidation reaction temperature and at a pressure of 0.1 to 50 atm.

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