JP2000189753A - Treatment of waste gas from oxidation reaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method in which the bromine compd. such as methyl bromide and the combustible material incorporated in waste gas are efficiently burned and removed and pressure and heat energy are economically and sufficiently recovered from the high temp. combustion waste gas obtained by that process in a waste gas treating stage in which the waste gas generated from an oxidation reaction vessel is detoxified at the time of producing an arom. carboxylic acid by subjecting an alkyl arom. compd. to liquid phase oxidation with oxygen-containing gas in the presence of an oxidizing catalyst by using an aliphat. carboxylic acid solvent under pressure in the oxidation reaction vessel. SOLUTION: In the treating method of the waste gas from oxidation reaction, the treating method of the waste gas is subjected to combustion treatment, then the pressure and the heat energy are recovered at the first energy recovering system till the temp. in which the waste gas temp. does not become lower than it dew point, moreover, the energy is recovered at the second energy recovering system till the temp. in which the waste gas temp. becomes lower than its dew point, then a harmful material is removed by absorption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating an oxidation reaction exhaust gas. More specifically, when an aromatic carboxylic acid is produced by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in the presence of an oxidation catalyst in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor, The present invention relates to an exhaust gas treatment method for combusting exhaust gas from wastewater and economically recovering more energy from the treated exhaust gas.

[0002]

2. Description of the Related Art In an oxidation reactor, a methyl-substituted aromatic compound is subjected to oxygen-containing reaction using a reaction solvent containing a lower aliphatic carboxylic acid such as acetic acid under pressure in the presence of a catalyst containing a heavy metal compound and a bromine compound. A method of producing an aromatic carboxylic acid by contacting with a gas to perform liquid phase oxidation has already been industrially performed. For example, in the production of terephthalic acid, an oxidation reaction is performed by introducing paraxylene, a solvent mixture of acetic acid and a catalyst, and air as raw materials into an oxidation reactor. In such a production method, the oxidation reaction exhaust gas generated from the oxidation reactor contains, in addition to bromine compounds such as methyl bromide which are environmental pollutants, alkyl aromatic compounds such as para-xylene which are unreacted raw materials, and benzene. And flammable substances such as aliphatic carboxylic acids such as acetic acid and carbon monoxide as solvents. In particular, it is difficult to remove methyl bromide present in a trace amount in exhaust gas as it is.

[0003] Therefore, it is common practice to burn off the exhaust gas to convert flammable substances and the like into inorganic substances, and to absorb harmful components in the inorganic substances into liquid to render them harmless. At this time, energy is recovered from the exhaust gas at the same time. For example, JP-A-60-219421 discloses that
The pressurized off-gas from the pressurized liquid-phase oxidation process of aromatic compounds is burned in a contact combustor, the corrosive components are absorbed in an absorption tower, and then introduced into the pressurized working medium gas of the gas turbine cycle to power Is shown. According to this method, clean high-pressure exhaust gas can be used, but since the exhaust gas is absorbed and washed in a high-pressure state, the absorption tower must be a high-pressure facility, resulting in an excessive equipment cost.

[0004] International Publication No. WO 96/39595
According to the terephthalic acid production process, the exhaust gas containing a bromine compound is supplied to the catalytic combustion in a high pressure state,
Next, the exhaust gas is passed through a gas turbine to recover energy to a temperature at which the reaction products of bromine compounds (bromine gas and hydrogen bromide) generated by catalytic combustion do not condense, and then the reaction products of bromine compounds are removed by a scrubber. An exhaust gas treatment method is described. in this way,
Energy recovery is limited by temperature and energy recovery is inadequate.

[0005] Further, Japanese Patent Application Laid-Open No.
In Japanese Patent No. 5265, after an oxidation reaction exhaust gas during the production of terephthalic acid is subjected to a combustion treatment in the presence or absence of a catalyst, the exhaust gas is guided to a gas turbine to recover energy, and subsequently bromine gas and bromide in the exhaust gas are absorbed by an absorbent. A method for removing hydrogen has been presented. However, this publication does not describe more methods of energy recovery.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems in the treatment of an oxidation reaction exhaust gas from a conventional production process of an aromatic carboxylic acid. Under pressure, using an aliphatic carboxylic acid solvent, the alkyl aromatic compound in the presence of an oxidation catalyst,
When producing an aromatic carboxylic acid by performing liquid phase oxidation with an oxygen-containing gas, in an exhaust gas treatment step of detoxifying an oxidation reaction exhaust gas generated from an oxidation reactor, bromide, which is an environmental pollutant contained in the exhaust gas, is used. An object of the present invention is to provide a method for efficiently burning and removing a bromine compound such as methyl and a combustible substance, and economically and sufficiently recovering pressure and heat energy from a high-temperature flue gas obtained thereby.

[0007]

According to the present invention, there is provided a method for treating an oxidation reaction exhaust gas, comprising the steps of converting an alkyl aromatic compound with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. In a method for producing an aromatic carboxylic acid under high temperature and high pressure by liquid phase oxidation, a step of detoxifying an oxidation reaction exhaust gas containing methyl bromide and a combustible substance generated in an oxidation reactor includes a step of burning the exhaust gas. Then, in the first energy recovery system, the pressure and heat energy are recovered to a temperature at which the exhaust gas temperature does not fall below the dew point, and further, the energy is recovered in the second energy recovery system until the exhaust gas temperature falls below the dew point. It is characterized by absorbing and removing harmful substances.

[0008] In the method of the present invention, it is preferable that the combustion treatment of the oxidation reaction exhaust gas is performed in the presence or absence of a catalyst after the exhaust gas is heated to a predetermined temperature in advance.

Further, in the method of the present invention, the first
Preferably, the energy recovery device used in the energy recovery system is a gas turbine and / or a heat exchanger, and the energy recovery device used in the second energy recovery system is a heat exchanger. preferable,

[0010] In a preferred embodiment of the method of the present invention, a corrosion-resistant material selected from plastic, carbon, Teflon, titanium and tantalum is used in a portion of the second energy recovery system which comes into contact with the exhaust gas of the energy recovery device. In another preferred aspect of the method of the present invention, a replaceable device is used in a portion of the second energy recovery system that comes into contact with the exhaust gas of the energy recovery device.

In the method of the present invention, it is preferable that the absorption and removal of the harmful substance is performed by bringing the exhaust gas into contact with an absorbing liquid by an absorption tower.

[0012] In a preferred embodiment of the method of the present invention,
The oxidation catalyst comprises a heavy metal compound and a bromine compound, and the aromatic carboxylic acid is terephthalic acid. In a preferred embodiment of the method of the present invention, a component of the bromine compound generated in the oxidation reactor is methyl bromide.

[0013]

DETAILED DESCRIPTION OF THE INVENTION As an oxidizing raw material for producing an aromatic carboxylic acid in the method of the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent can be used. Such an aromatic compound may be monocyclic or polycyclic. Examples of the alkyl substituent include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. Examples of the partially oxidized alkyl group include an aldehyde group, an acyl group, a carboxyl group, and a hydroxyalkyl group.

Specific examples of the aromatic compound having an alkyl substituent, that is, the alkyl-substituted aromatic hydrocarbon include, for example, m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, An alkyl group having 1 to 4 carbon atoms such as p-xylene, trimethylbenzenes and tetramethylbenzenes is
Di- or polyalkylbenzenes having four; two or more alkyl groups having 1 to 4 carbon atoms such as dimethylnaphthalenes, diethylnaphthalenes and diisopropylnaphthalenes;
Di- or polyalkylnaphthalenes having up to 4 alkyl groups having 1 to 4 carbon atoms such as dimethylbiphenyls;
And polyalkylbiphenyls having from 4 to 4.

In the aromatic compound having a partially oxidized alkyl substituent, the alkyl group in the upper compound is partially oxidized and oxidized to the aldehyde group, acyl group, carboxyl group or hydroxyalkyl group. Compound. Specific examples include, for example, 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-toluic acid, p-toluic acid, 3-formylbenzoic acid, 4-
Examples include formylbenzoic acid and 2-methyl-6-formylnaphthalenes. These are used alone or as a mixture of two or more.

In the method of the present invention, heavy metal compounds and bromine compounds are preferably used as oxidation catalysts. Examples of such compounds are as follows. That is, as the heavy metal in the heavy metal compound,
Examples include cobalt, manganese, nickel, chromium, zirconium, copper, lead, hafnium and cerium. These can be used alone or in combination, but it is particularly preferable to use a combination of cobalt and manganese. Such heavy metal compounds include, for example, acetate, nitrate, acetylacetonate,
Naphthenate, stearate, bromide and the like can be mentioned, and acetate is particularly preferable.

Examples of the bromine compound catalyst include inorganic bromine compounds such as molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide; methyl bromide, methylene bromide, bromoform, And organic bromine compounds such as benzyl bromide, bromomethyltoluene, dibromoethane, tribromoethane, and tetrabromoethane. These bromine compounds are also used alone or as a mixture of two or more.

In the present invention, the catalyst comprising the combination of the heavy metal compound and the bromine compound is used in an amount of 0.05 to 10 mol, preferably 0.1 mol, of bromine atom per 1 mol of heavy metal atom.
Those having a range of 2 to 2 mol are desirable. Such a catalyst is usually used as a heavy metal concentration in a reaction solvent of 10 to 100.
It is used in the range of 00 ppm, preferably 100 to 5000 ppm. In the method of the present invention, in an oxidation reactor as an oxidation step, an aromatic compound serving as an oxidation raw material is converted into an oxygen-containing gas (in the present invention, oxygen) in a reaction solvent containing a lower aliphatic carboxylic acid in the presence of the catalyst. The liquid-phase oxidation is carried out by means of molecular oxygen.) To obtain an aromatic carboxylic acid as a product.

The oxygen-containing gas includes, for example, oxygen and air, but practically, air is preferably used. The oxygen-containing gas is supplied in excess of the amount required to oxidize the aromatic compound serving as the oxidation raw material to the aromatic carboxylic acid. When air is used as the oxygen-containing gas, 2 to 2 kg of an aromatic compound serving as an oxidation raw material is used.
It is desirably supplied to the reaction system at a rate of 0 Nm ³ , preferably 2.5 to 15 Nm ³ .

Specific examples of the lower aliphatic carboxylic acid used as the reaction solvent include acetic acid, propionic acid and butyric acid. The lower aliphatic carboxylic acid can be used alone as a reaction solvent, or can be mixed with water and used as a reaction solvent in the form of a mixture. Specific examples of the reaction solvent include, for example, acetic acid, propionic acid, butyric acid and mixtures thereof,
Alternatively, a mixture of these lower aliphatic carboxylic acids and water can be used. Among these, a mixture of acetic acid and water is preferable, and a mixture of 1 to 20 parts by weight of water, preferably 5 to 15 parts by weight of water is particularly desirable with respect to 100 parts by weight of acetic acid.

The temperature of the oxidation reaction is usually 100 to 250 ° C.,
Preferably, the range of 150 to 220 ° C is desirable. Also,
The reaction pressure may be any pressure as long as the reaction system can be maintained in a liquid phase.

By reacting in this manner, an aromatic carboxylic acid corresponding to the aromatic compound to be used as an oxidation raw material is obtained. Specific examples of the aromatic carboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-biphenyldicarboxylic acid; and aromatic acids such as trimellitic acid and trimesic acid. Aromatic tricarboxylic acids such as pyromellitic acid; and the like.

The method of the present invention is preferably applied to the production of an aromatic dicarboxylic acid or an aromatic carboxylic acid insoluble or soluble in a reaction solvent, particularly preferably to the production of terephthalic acid.

The oxidation reaction exhaust gas according to the present invention is obtained by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst, under high temperature and high pressure. Is generated from the oxidation reactor in the step of producing the aromatic carboxylic acid. The oxidation reaction exhaust gas is
Usually, it has a pressure of 5 kg / cm ² G or more, and originates in the catalyst to be used. In addition to bromine compounds such as methyl bromide which are environmental pollutants, alkyl aromatic compounds which are unreacted raw materials,
It contains flammable substances such as aliphatic carboxylic acids, benzene and carbon monoxide as solvents.

In the present invention, the oxidation reaction exhaust gas containing these bromine compounds and flammable substances is first subjected to a combustion treatment, and then the high-temperature and high-pressure exhaust gas subjected to the combustion treatment is introduced into a first energy recovery system. The pressure and heat energy are recovered to a temperature at which the temperature of the exhaust gas after passing through the energy recovery system does not fall below the dew point of the exhaust gas, and further, the exhaust gas is guided to the second energy recovery system and passed through the second energy recovery system After recovering energy until the temperature of the subsequent exhaust gas becomes equal to or lower than the dew point of the exhaust gas, absorption of harmful substances remaining in the exhaust gas is removed. Hereinafter, each step of the oxidation reaction exhaust gas treatment method will be described.

The combustion treatment performed at the beginning of the exhaust gas treatment is as follows:
In the presence or absence of a catalyst, an exhaust gas combustion treatment method with or without the addition of fuel can be used.However, in order to surely combust bromine compounds such as methyl bromide that are difficult to combust, It is preferable that the exhaust gas is heated to a predetermined temperature in advance and then subjected to a combustion treatment in the presence or absence of a catalyst. The preheating temperature of the exhaust gas is preferably 300 ° C. or higher when performed in the presence of a catalyst, and is preferably 800 ° C. or higher when performed in the absence of a catalyst.

The following method is preferably performed as a specific combustion treatment method. (1) After adding an oxygen-containing gas to the exhaust gas together with the fuel as a fuel, the temperature is raised to 800 ° C. or more, and the combustion treatment is performed in the absence of a catalyst. (2) After adding an oxygen-containing gas together with fuel to the exhaust gas as a fuel, a part of the combustible substances in the exhaust gas is subjected to combustion treatment in the absence of a catalyst to raise the temperature to 300 ° C. or higher, and then the presence of the catalyst The remaining combustible substances and methyl bromide are burned down. (3) The exhaust gas is heated to a temperature of 300 ° C. or higher and is subjected to a combustion treatment in the presence of a catalyst. (4) The exhaust gas is heated to a temperature of 800 ° C. or more and burned in the absence of a catalyst.

The fuel added to the exhaust gas by these methods includes hydrogen, propane, butane, LPG, other organic substances, carbon monoxide and the like. The amount of addition is appropriately determined depending on the properties of the exhaust gas, the set temperature of the exhaust gas after the combustion treatment, and the like. The catalyst for oxidation used in the combustion treatment is not particularly limited, but any catalyst such as a well-known noble metal catalyst such as platinum or palladium, or an oxide base metal catalyst can be used.

By the combustion treatment, bromine compounds such as methyl bromide and combustible substances in the exhaust gas are completely oxidized. The composition of the exhaust gas after the combustion treatment is usually 20.0 to 9% for nitrogen.
5.0 mol%, oxygen 0.5 to 5.0 mol%, carbon dioxide gas 0.3 to 10.0 mol%, water 0.5 to 75.0 mol%. Bromine (Br ₂ )
And a small amount of hydrogen bromide. The bromine and hydrogen bromide are highly corrosive and may corrode devices such as gas turbines and heat exchangers used in energy recovery systems.

The inventors of the present invention have conducted intensive studies to solve this problem. As a result, if the temperature does not fall below the dew point of the exhaust gas (the temperature at which the saturated steam pressure at that temperature becomes equal to the steam partial pressure of the atmosphere), It was found that equipment using general-purpose stainless steel corrosion-resistant material had sufficient corrosion resistance. In other words, even under conditions where bromine and hydrogen bromide do not condense and exist in a gaseous state, if coexisting water vapor condenses, liquid water absorbs those corrosive gases and exhibits a strong corrosive effect, It has been found that corrosion is hardly caused by a general-purpose stainless steel corrosion-resistant material even if bromine or hydrogen bromide is present, if the temperature is maintained at a condition where water vapor does not condense, that is, at a temperature exceeding the dew point. Therefore, the first energy recovery system is provided with a gas turbine and / or a heat exchanger made of a general-purpose stainless steel corrosion-resistant material.

An example of the first energy recovery system is shown below. The high-temperature and high-pressure exhaust gas subjected to the combustion treatment is first introduced into a gas turbine, and pressure and thermal energy are recovered. The thermal energy is then recovered by passing through a heat exchanger. This heat exchanger may be used for heating the exhaust gas before the combustion treatment. The energy recovered by the gas turbine can be used as electric power by a generator directly connected to the gas turbine. In the present invention, the temperature of the exhaust gas discharged from the first energy recovery system is controlled so as not to be lower than the dew point. Thus, in the above example, the temperature of the exhaust gas leaving the heat exchanger is above the dew point in the atmosphere.

Since the temperature of the exhaust gas discharged from the first energy recovery system is maintained at a temperature exceeding the dew point in the atmosphere, the temperature is sufficiently high. Therefore, the function of the second energy recovery system is to recover energy from the exhaust gas, and a heat exchanger is preferable as the energy recovery device used. Here, since the temperature of the exhaust gas after energy recovery is lower than the dew point, a highly corrosive gas such as bromine or hydrogen bromide is absorbed by condensed liquid water, and an energy recovery device that uses a more corrosion-resistant material Is required.
For example, an energy recovery device in which a corrosion-resistant material selected from plastic, carbon, Teflon, titanium and tantalum is used in a portion of the device that contacts exhaust gas is preferable.

According to another aspect of the present invention, it is preferable that a replaceable device is used in a portion of the second energy recovery system that comes into contact with the exhaust gas of the energy recovery device. In this case, the replaceable device serving as the exhaust gas path is periodically replaced according to the operation time, so that damage due to corrosion can be avoided. Thereby, the second
It is possible to use a general-purpose stainless steel corrosion-resistant material also in the energy recovery system in the energy recovery system. As for the replacement method, the entire apparatus may be replaced, or only a part of the piping or the like may be replaced.

Subsequently, the harmful substances remaining in the exhaust gas from the second energy recovery system are absorbed and removed. this is,
For example, it is performed by passing exhaust gas through an absorption tower (scrubber) and contacting with an absorbent of a harmful substance. An alkaline solution such as caustic soda and caustic potash, and a reducing agent such as sodium carbonate, sodium bicarbonate, sodium bromide, sodium sulfite, sodium formate, sodium sulfide, etc. are used as the absorbing solution in countercurrent contact with the exhaust gas in the absorption tower. Can be The exhaust gas from which the harmful substances are removed and which is discharged from the absorption tower can be used as a gas source for gaseous delivery of the product aromatic carboxylic acid by utilizing the remaining pressure, if necessary.

The method for treating an oxidation reaction exhaust gas of the present invention will be described below with reference to the drawings, in the case of producing terephthalic acid. FIG. 1 is an example of an apparatus configuration diagram when the method (1) is used for the combustion process. According to this method, a pressurized oxidation reaction exhaust gas generated in an oxidation reactor (not shown) is led from a line 8 to a combustion furnace 1a. , And the exhaust gas is burned by raising the temperature to 800 ° C. in the absence of a catalyst.

Next, the high-temperature and high-pressure exhaust gas obtained by the combustion treatment is first introduced into the gas turbine 3 to recover pressure and heat energy in the first energy recovery system, and then the exhaust gas from the gas turbine 3 is recovered. Heat exchanger 4
To exchange heat with the oxidation reaction exhaust gas led to the combustion furnace 1a to recover thermal energy. The exhaust gas temperature at the outlet of the heat exchanger 4 is controlled so as not to be lower than the dew point.

Subsequently, heat energy is further recovered in the heat exchanger 5 as a second energy recovery system.
At this time, the temperature of the exhaust gas is lower than the dew point. It is led to an absorption tower 6, where it is treated with an absorbing solution or a reducing agent from a line 9 to absorb and remove harmful substances such as bromine and hydrogen bromide, and discharged from a line 13 as a treated exhaust gas. The absorbent (line 14) after the treatment of the exhaust gas is recycled if necessary.

The gas turbine 3 can be used, for example, as a power source for an air compressor 7a for terephthalic acid production, which is directly connected to the gas turbine 3, and can be used to generate electricity in a generator 7b. The compressed air obtained by the air compressor 7a is used in the oxidation reaction of para-xylene.
It can be used as an oxygen-containing gas that is an oxidizing agent.
In addition, the exhaust gas (line 13) from the absorption tower 6 can be used as a gas source for gas pressure delivery of the product terephthalic acid, if necessary.

FIG. 2 is an example of an apparatus configuration diagram when the method (2) is used for the combustion process. According to this method, the pressurized oxidation reaction exhaust gas generated in the oxidation reactor (not shown) is led to the combustion furnace 1a through the line 8, where the exhaust gas is supplied with the fuel from the line 11 and the line 12 as the fuel. After injecting air from the furnace and raising the temperature to 300 ° C. or higher in the absence of a catalyst, and burning a part of the combustible substances contained in the exhaust gas together with the above-mentioned fuel, the exhaust gas is converted into an exhaust gas filled with an oxidation catalyst. The mixture is led to the treatment reactor 2 to combust the methyl bromide together with the remaining combustible substances.

Next, in the first energy recovery system, pressure and heat energy are recovered from the obtained high-temperature and high-pressure combustion exhaust gas by the gas turbine 3 and the heat exchanger 4 as in the case of FIG. Subsequently, in the second energy recovery system, the heat energy is further recovered by the heat exchanger 5 in the same manner as described above, and then the harmful substances are absorbed and removed by the absorption tower 6 and discharged as a treated exhaust gas.

Here, the gas turbine 3 can be used, for example, to drive an air compressor 7a directly connected thereto. When the energy recovered by the gas turbine 3 is insufficient as a power source of the air compressor 7a for producing terephthalic acid, the electric motor 7c is connected to the air compressor 7a.
May be connected and supplemented. The exhaust gas (line 13) from the absorption tower 6 can be used as a gas source for pressure-feeding the product terephthalic acid, if necessary.

FIG. 3 is an example of an apparatus configuration diagram when the method (3) is used for the combustion processing. According to this method, the pressurized oxidation reaction exhaust gas generated in the oxidation reactor (not shown) is led from the line 8 to the heater 1b to raise the temperature to 300 ° C. or higher, and this is used for oxidation. It is led to an exhaust gas treatment reactor 2 filled with a catalyst, and simultaneously burns methyl bromide with combustible substances contained in the exhaust gas.

Next, in the first energy recovery system, pressure and heat energy are recovered from the obtained high-temperature and high-pressure combustion exhaust gas by the gas turbine 3 and the heat exchanger 4 as in the case of FIG. Subsequently, in the second energy recovery system, the energy is further recovered by the heat exchanger 5 in the same manner as described above, and then the harmful substances are absorbed and removed by the absorption tower 6 and discharged as treated exhaust gas.

Here, the gas turbine 3 can be used, for example, to generate electric power by a generator 7b directly connected to the gas turbine. Exhaust gas from the absorption tower 6 (line 1)
3) can be used as a gas source for gas pressure delivery of the product terephthalic acid, if necessary.

The exhaust gas treatment method of the present invention will be specifically described with reference to an embodiment of the method shown in FIG. The oxidation reaction exhaust gas (line 8) generated in the oxidation reactor (not shown) and having pressure and containing methyl bromide and flammable substances is supplied to the gas turbine 3
After exchanging heat with the exhaust gas from the heat exchanger 4, the heat is guided to another heater 1 b to raise the temperature to 450 ° C. This was led to an exhaust gas treatment reactor 2 filled with a platinum-based metal catalyst, and methyl bromide was simultaneously combusted with combustible substances contained in the exhaust gas. The composition of the exhaust gas after the treatment is approximately nitrogen 2
5.8 mol%, oxygen 0.9 mol%, carbon dioxide gas 0.6 mol%, water 72.7 mol%, and also contained trace amounts of bromine and hydrogen bromide. And the temperature and pressure at this time are 5
The temperature was 00 ° C and 11 atm.

This is introduced into the first energy recovery system,
First, pressure and heat energy were recovered by the gas turbine 3. As a result, the temperature and pressure of the exhaust gas are 320 ° C., 2
dropped to atm. This was further led to the heat exchanger 4 and used for preheating the oxidation reaction exhaust gas led to the exhaust gas treatment reactor 2, and as a result, the temperature was 200 ° C. and 2 atm. The dew point at this time was 110 ° C.

Thereafter, the exhaust gas was passed through a heat exchanger 5 having a tube made of titanium to recover energy up to 90 ° C.
It was introduced into the absorption tower 6 to remove harmful substances such as bromine and hydrogen bromide. Conventionally, only energy recovery up to the heat exchanger 4 could be performed due to the problem of corrosion. If the amount of energy recovery in that state was assumed to be 100%, 360% energy recovery could be performed in this embodiment.

[0048]

According to the method for treating an oxidation reaction exhaust gas of the present invention, an alkyl aromatic compound is converted into an oxygen-containing gas at a high temperature and a high pressure in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. When producing an aromatic carboxylic acid by liquid phase oxidation, bromine compounds such as methyl bromide and flammable substances contained in exhaust gas generated from an oxidation reactor are efficiently burned and removed, and thereby obtained. Pressure and heat energy can be economically and sufficiently recovered from the generated high-temperature flue gas. Thereby, the production cost of the aromatic carboxylic acid can be reduced.

[Brief description of the drawings]

FIG. 1 is an example of an apparatus configuration diagram showing a method for treating an oxidation reaction exhaust gas from an aromatic carboxylic acid production step according to the present invention.

FIG. 2 is another example of an apparatus configuration diagram showing a method of treating an oxidation reaction exhaust gas from an aromatic carboxylic acid production step according to the present invention.

FIG. 3 is another example of an apparatus configuration diagram illustrating a method for treating an oxidation reaction exhaust gas from an aromatic carboxylic acid production step according to the present invention.

[Explanation of symbols]

 1a Combustion furnace 1b Heater 2 Exhaust gas treatment reactor 3 Gas turbine 4,5 Heat exchanger 6 Absorption tower (scrubber) 7a Air compressor 7b Generator 7c Electric motor 8 Oxidation reaction exhaust gas line 9,14 Absorbent liquid line 10 Air line 11 Fuel line 12 Compressed air line 13 Treated exhaust gas line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 19/00 C07C 63/26 F-term (Reference) 4D002 AA24 AC07 BA02 BA05 BA06 BA12 CA01 CA13 CA20 EA02 GA02 GA03 GB02 GB03 GB04 HA03 HA08 4G075 AA44 AA45 BD12 BD24 CA02 CA45 DA02 FB02 FB03 FB12 FC09 4H006 AA02 AC46 BA60 BA83 BB17 BC10 BC11 BC14 BE30 BJ50 BS30

Claims (9)

[Claims] 1. An aromatic carboxylic acid is produced at a high temperature and a high pressure by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in an oxidation reactor in the presence of an oxidation catalyst. In the method, the step of detoxifying an oxidation reaction exhaust gas containing a bromine compound and a combustible substance generated in the oxidation reactor is performed by burning the exhaust gas, and then the exhaust gas temperature is equal to or lower than its dew point in the first energy recovery system. A method for treating an oxidation reaction exhaust gas, comprising recovering pressure and thermal energy to a temperature at which no harmful substances are recovered, recovering energy until the exhaust gas temperature falls below the dew point in a second energy recovery system, and absorbing and removing harmful substances. 2. The method for treating an oxidation reaction exhaust gas according to claim 1, wherein the combustion treatment of the oxidation reaction exhaust gas is performed in the presence or absence of a catalyst after heating the exhaust gas to a predetermined temperature in advance. 3. An energy recovery device used in the first energy recovery system includes a gas turbine and / or a gas turbine.
The method for treating an oxidation reaction exhaust gas according to claim 1 or 2, which is a heat exchanger. 4. The method for treating an oxidation reaction exhaust gas according to claim 1, wherein the energy recovery device used in the second energy recovery system is a heat exchanger. 5. A corrosion-resistant material selected from plastic, carbon, Teflon, titanium and tantalum is used in a portion of the second energy recovery system in contact with exhaust gas of an energy recovery device. The method for treating the oxidation reaction exhaust gas according to the above. 6. The method for treating an oxidation reaction exhaust gas according to claim 1, wherein a replaceable device is used in a portion of the energy recovery device in the second energy recovery system that comes into contact with the exhaust gas. 7. The method for treating an oxidation reaction exhaust gas according to claim 1, wherein the absorption and removal of the harmful substance is performed by bringing the exhaust gas into contact with an absorbing liquid by an absorption tower. 8. The method according to claim 1, wherein the oxidation catalyst comprises a heavy metal compound and a bromine compound, and the aromatic carboxylic acid is terephthalic acid. 9. The method for treating an oxidation reaction exhaust gas according to claim 1, wherein a component of the bromine compound generated in the oxidation reactor is methyl bromide.