KR20000006106A - process for producing aromatic carboxylic acid - Google Patents

Abstract

PURPOSE: A manufacturing method of the aromatic carboxylic acid is provided to start the oxide reaction by using little power and to efficiently react by collecting the energy after the reaction. CONSTITUTION: The manufacturing method of the aromatic carboxyl is formed by the steps of: driving a compressor(6) by feeding the power source with a power device(5); heating the molecular oxygen including gas, pressurized in the compressor(6); obtaining the rotating force by introducing the heated and pressurized gas to an expander(7); and starting the oxide reaction by feeding a certain quantity of the pressurized molecular oxygen including gas to a reactor.

Description

Process for producing aromatic carboxylic acid

The present invention relates to a method for producing an aromatic carboxylic acid by liquid phase oxidation of an alkyl aromatic compound having an alkyl substituent or partially oxidized alkyl substituent with a molecular oxygen-containing gas.

Aromatic carboxylic acids are important as basic chemicals, and in particular, aromatic dicarboxylic acids are preferably used as starting materials for fibers, resins and the like. For example, terephthalic acid is a starting material for producing polyester, and the demand is increasing recently.

Conventional methods for producing aromatic carboxylic acids generally dissolve an aromatic compound having a methyl substituent in a reaction solvent containing a lower aliphatic carboxylic acid such as acetic acid in an oxidation reactor, and in the presence of an oxidation catalyst composed of a heavy metal compound and a bromine compound A method of liquid phase oxidation by contact with a phase oxygen-containing gas is employed. In the above production method, an aromatic compound having an alkyl substituent, such as p-xylene, as a starting material in the oxidation reactor, a mixture of acetic acid and an oxidation catalyst as a reaction solvent, as well as a molecular oxygen-containing gas such as air is introduced to carry out an oxidation reaction to carry out an oxidation reaction. Aromatic carboxylic acid may be produced.

Since the oxidation reaction is an exothermic reaction, a method of recovering energy by supplying an expander (turbine) after heating or burning the exhaust gas of the oxidation reactor has been proposed (Japanese Patent Application Laid-Open No. 8-155226, WO96 / 11899). By connecting the axis of rotation of the expander to the shaft of the power device and air compressor serving as generator and motor, and expanding the oxidizing exhaust gas to operate the power device and the extruder, the power device recovers energy as power and the air compressor oxidizes The molecular oxygen-containing gas is fed to the reactor.

In this method, since the electric power device is used as an electric motor at the start of operation, the electric power is supplied to the electric power device to operate the air compressor to supply compressed air as an oxygen-containing gas to the oxidation reactor for oxidation reaction. When the reaction proceeds and the oxidizing exhaust gas is discharged, energy is recovered by the rotational force of the expander, and the air compressor and the power unit are operated by the rotational force, and as a result, the supply of power from the outside is not necessary.

The reaction according to the conventional method can be performed at low energy and low cost by recovering energy by using an expander and operating an air compressor and a generator, but it is necessary to supply power at the start of operation. In addition, a large amount of power is required when operating the air compressor directly connected to the expander and the power unit, so a large power supply is required. The large power supply is used only for starting the operation and is not used during normal operation, causing a problem of investment efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an aromatic carboxylic acid which can start an oxidation reaction using a small amount of power provided by a small-capacity electric supply device, and which can recover the energy efficiently after the start-up. will be.

1 is a flowchart showing a method for producing terephthalic acid, which is an embodiment of the present invention.

2 is a flowchart showing a method for producing terephthalic acid, which is another embodiment of the present invention.

The present invention is a process for preparing the following aromatic carboxylic acids:

(1) A method for producing an aromatic carboxylic acid by liquid phase oxidation of an alkyl aromatic compound with a molecular oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in a reactor, in the presence of an oxidation catalyst.

A power device serving as a generator and a motor, a compressor for supplying molecular oxygen-containing gas to the reactor, and an expander for obtaining rotational force by gas expansion, is connected to a rotating shaft,

Supplying power to the power unit to run the compressor,

Heating the pressurized molecular oxygen-containing gas in a compressor,

The hot pressurized gas is introduced into the expander to expand and obtain rotational force,

A part of the molecular oxygen-containing gas pressurized in the compressor is supplied to the reactor to start the oxidation reaction,

After the start of the reaction, the oxidative exhaust gas is introduced into the expander to recover energy, thereby stopping the power supply to the power device and simultaneously generating power to the generator, and

A method for producing an aromatic carboxylic acid, which is characterized by sequentially increasing the supply of pressurized molecular oxygen-containing gas to the reactor and simultaneously reducing the supply to the expander.

(2) The method according to the above (1), wherein the oxidizing exhaust gas is introduced into the distillation column from the reactor to distillation to reflux the oil containing the reaction solvent into the reactor, and the exhaust gas from the distillation column is introduced into the expander to recover energy.

(3) The exhaust gas from the distillation column is cooled by the condenser and condensed, the condensate is refluxed to the distillation column, the exhaust gas from the condenser is introduced into the expander, and the newly generated steam is introduced into the steam turbine to recover energy. The method as described in (1) or (2).

(4) The method according to any one of (1) to (3) above, wherein the molecular oxygen-containing gas pressurized by the compressor is introduced into the combustor to combust the fuel, and then heated to introduce it into the expander.

(5) The method according to any one of (1) to (3), wherein the molecular oxygen-containing gas pressurized by the compressor is heated by a heat exchanger, introduced into an expander, and the exhaust gas from the expander is combusted by a combustor.

In the method for producing an aromatic carboxylic acid according to the present invention, as the starting raw material to be oxidized, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent (hereinafter, simply referred to as starting raw material) may be used. Such an aromatic compound may be a monocyclic or polycyclic compound. Examples of the alkyl substituent include alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group, n-propyl group and isopropyl group. Examples of some oxidized alkyl substituents include aldehyde groups, acyl, carboxyl groups, and hydroxyalkyl groups.

Specific examples of the aromatic compound having an alkyl substituent, that is, an aromatic hydrocarbon having an alkyl substituent include m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, p-xylene and trimethylbenzene Di or polyalkyl benzenes having 2 to 4 alkyl groups having 1 to 4 carbon atoms such as tetramethylbenzenes; Di or polyalkyl naphthalenes having 2 to 4 alkyl groups having 1 to 4 carbon atoms such as dimethylnaphthalene, diethylnaphthalene and diisopropylnaphthalene; Polyalkyl biphenyls which have 2-4 alkyl groups of 1 to 4 carbon atoms, such as dimethyl biphenyl, etc. are mentioned.

In addition, an aromatic compound having some oxidized alkyl substituents is a compound in which at least one alkyl group is partially oxidized to an oxidizing group such as an aldehyde group, an acyl group, a carboxyl group or a hydroxyalkyl group. Specific examples include 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-toluic acid, p-toluic acid, 3-formyl benzoic acid, 4-formyl benzoic acid, 2-methyl-6-formyl naphthalene, and the like. These are used alone or as a mixture of two or more kinds.

In the process according to the invention, catalysts of heavy metal compounds and bromine compounds are used. Examples of the heavy metal element in the heavy metal compound include cobalt, manganese, nickel, chromium, zirconium, copper, lead, hafnium, cerium, and the like, and these may be used alone or in combination of two or more thereof. In particular, cobalt and manganese may be used. It is preferable to use in combination.

Examples of such compounds of heavy metal elements include acetates, nitrates, acetylacetonates, naphthenates, stearates and bromide and the like, with acetate being particularly preferred.

Examples of the bromine compound include inorganic bromine compounds such as molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide; And organic bromine compounds such as methyl bromide, methylene bromide, bromoform, benzyl bromide, bromomethyltoluene, dibromoethane, tribromoethane and tetrabromoethane. These bromine compounds can also be used individually or as a mixture of 2 or more types.

In the present invention, the catalyst formed by combining the heavy metal compound and the bromine compound preferably contains 0.05 to 10 moles, preferably 0.1 to 2 moles of bromine atoms per mole of heavy metal atoms. The concentration of the catalyst is usually 10 to 10,000 ppm, preferably 100 to 5000 ppm, as a heavy metal element in the reaction solvent.

In the method of the present invention, an aromatic carboxylic acid as a product is obtained by liquid phase oxidation of an alkyl aromatic compound as a starting material with a molecular oxygen-containing gas in a reaction solvent containing a lower aliphatic carboxylic acid in the presence of the catalyst in an oxidation reactor. .

Examples of the molecular oxygen-containing gas include oxygen, air, and the like, but practically, air is preferably used. The molecular oxygen-containing gas is supplied in excess of the amount necessary to oxidize the alkyl aromatic compound as a starting material to produce an aromatic carboxylic acid. When using air as a molecular oxygen containing gas, it is good to supply to a reaction system in the ratio of 2-20 Nm <3>, Preferably it is 5-15Nm <3> with respect to 1 kg of aromatic compounds which are starting materials. The molecular oxygen-containing gas is pressurized by a compressor and supplied to a reactor to perform an oxidation reaction.

Specific examples of the lower aliphatic carboxylic acid used as the reaction solvent include acetic acid, propionic acid and butyric acid. These lower aliphatic carboxylic acids may be used alone or as a mixture with water as the reaction solvent. Specific examples of the reaction solvent include acetic acid, propionic acid, butyric acid and mixtures thereof, or mixtures of these lower aliphatic carboxylic acids and water. Of these, a mixture of acetic acid and water is preferable, and in particular, a mixture of 1 to 20 parts by weight of water and preferably 5 to 15 parts by weight of water is preferably used with respect to 100 parts by weight of acetic acid.

The temperature of an oxidation reaction is 100-250 degreeC normally, Preferably the range of 150-220 degreeC is good. Moreover, reaction pressure should just be a pressure more than the pressure which can maintain a reaction system in a liquid phase.

By reacting in this way, the specific aromatic carboxylic acid corresponding to the aromatic compound used as a starting raw material can be obtained. Examples of the specific aromatic carboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4'-biphenyldicarboxylic acid; Aromatic tricarboxylic acids such as trimellitic acid and trimesic acid; Aromatic polycarboxylic acids, such as a pyromellitic acid, etc. are mentioned.

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

Since aromatic carboxylic acid, such as terephthalic acid produced in the oxidation reactor, precipitates as crystals to form a slurry, a crude product of the aromatic carboxylic acid can be obtained by taking out the slurry from the oxidation reactor, solid-liquid separation thereof, and recovering the crystals in the slurry.

The crude product crystal thus obtained contains an oxidation reaction intermediate or an impurity, so that the crude crystal is dissolved, subjected to a purification step of oxidizing and / or reducing, followed by a crystallization step to obtain a slurry containing crystals of aromatic carboxylic acid. By recovering crystals from this slurry, purified products of aromatic carboxylic acid can be obtained.

When performing the above-mentioned oxidation reaction, it is preferable to introduce an oxidizing exhaust gas into a distillation column (high pressure distillation column) connected to the upper portion of the oxidation reactor, and to distill using heat of the oxidation reactor. It is refluxed from the column bottom to the oxidation reactor, and the exhaust gas containing water vapor and a non-condensable gas is discharged from the tower top. The distillation column may be installed independently of the oxidation reactor as disclosed in Japanese Patent Application Publication No. 54-14098, or may be installed at the top of the oxidation reactor as disclosed in Japanese Patent Laid-Open No. Hei 6-279353. The distillation column may be a plate tower type, but a packed tower type is preferable, and at this time, a tray for collecting fine solids, such as crystals of aromatic carboxylic acids or oxidation catalysts, may be provided below the packed bed. desirable.

By distillation in such a distillation column, the oil containing the reaction solvent discharged accompanying the oxidation exhaust gas can be refluxed to the oxidation reactor. This fraction is refluxed to the oxidation reactor as a bottom liquid containing, in addition to the reaction solvent, an unreacted alkyl aromatic compound, a produced aromatic carboxylic acid, an oxidation catalyst, and the like in a concentrated state. Solids such as aromatic carboxylic acid crystals and oxidation catalysts are trapped at the bottom of the distillation column, and components having high boiling point flow out from the bottom of the distillation column, while reaction solvents containing lower aliphatic carboxylic acids and the like having low boiling point flow out at the relatively upper part of the distillation column.

In the case of emergency stop of the reaction, the condensed water at the top of the distillation column is refluxed to the oxidation reactor to rapidly dilute the reaction liquid in the oxidation reactor, but this can be prevented by installing a liquid discharge part in the distillation column. The liquid discharge part may discharge the condensate during normal operation and use the liquid discharge part for cleaning the crystal obtained by solid-liquid separation.

When the distillation column is provided in this way, the exhaust gas from the distillation column is cooled with cooling water in the condenser to condense the water vapor in the exhaust gas, and the condensate can be refluxed to the distillation column. In this case, it is preferable to recover the energy by evaporating the cooling water to generate steam and supplying the steam to the steam turbine. By using a plurality of condensers, the exhaust gas is sequentially passed through to condense in steps to obtain low energy steam from high energy steam.

If a kettle type is used as the condenser, steam can be generated without installing a vessel for generating steam. By controlling the temperature of the condenser and maintaining the temperature of the exhaust gas from the distillation process at 80 ° C or higher, most of the methyl acetate and other impurities can be preserved in the exhaust gas, and thus the effluent is effectively used for cleaning the crystals. It can be used and can be discharged out of the system without complicated wastewater treatment.

According to the present invention, the exhaust gas is immediately introduced from the oxidation reactor, or it is introduced into the distillation column for distillation, or after it is introduced into the condenser to condensate and heated by combustion, and then introduced into the expander to rotate the turbine to rotate the energy as rotational force. In this way, the compressor can be operated to supply molecular oxygen-containing gas to the oxidation reactor, and the power device can be operated to generate electric power. To this end, the rotary shafts of the power unit, the compressor and the expander are connected to each other and the rotary shafts of the steam turbine can also be connected when energy is recovered by introducing water vapor generated in the condenser into the steam turbine. This power device acts as a generator and, when powered, as a motor.

When starting the operation of the aromatic carboxylic acid production apparatus configured as described above, conventionally, the power supply was supplied to the power device to operate the compressor to supply the molecular oxygen-containing gas to the oxidation reactor to initiate the oxidation reaction. Power supply equipment is needed. To avoid this, the method of the present invention provides power to a power device to operate a compressor; Heating the molecular oxygen-containing gas pressurized by the compressor; Introducing the warm pressurized gas into the expander to expand the gas to obtain rotational force; Supplying a part of the molecular oxygen-containing gas pressurized in the compressor to the reactor to start the oxidation reaction; After the start of the reaction, oxidative exhaust gas is introduced into the expander to obtain rotational force; Generate power while stopping power supply to the power device; The supply of pressurized molecular oxygen-containing gas to the reactor is sequentially increased while the supply to the expander is reduced.

The molecular oxygen-containing gas pressurized by the compressor may be heated by fuel in the combustor prior to introduction into the expander, and the molecular oxygen-containing gas pressurized by the compressor may be heated in the heat exchanger before being introduced into the expander and the gas exiting the expander May be combusted in a combustor. In the latter case, the combustion exhaust gas can be introduced into a heat exchanger to heat the molecular oxygen-containing gas. The combustor is configured to combust fuel supplied from the outside at the start of operation, and gradually combust the oxidizing exhaust gas as the reaction proceeds.

The power supplied to the power device at the start of the operation can be 1/2 or less, preferably 1/4 to 1/2, of the drive power at the time of normal operation of the device. At this time, the pressure of the molecular oxygen-containing gas on the outlet side of the compressor can be 0.7 to 3 MPa, preferably 1 to 1.5 MPa (gauge pressure). Moreover, the heating temperature of molecular oxygen containing gas can be 300-1300 degreeC, Preferably it is 400-600 degreeC. The pressure before heating the molecular oxygen-containing gas and introducing it into the expander can be 0.6 to 2.9 MPa, preferably 0.9 to 1.4 MPa.

Although it is preferable to heat the entire amount of the molecular oxygen-containing gas pressurized by the compressor at the start of operation and supply it to the expander, a part of the gas may be supplied to the oxidation reactor from the beginning. In either case, as the rotational force is obtained by the expander, the supply of pressurized molecular oxygen-containing gas to the oxidation reactor in the compressor is sequentially increased, and the supply to the expander is reduced. At this time, the supply amount to the expander may be reduced to zero, but a small amount may be supplied as an oxygen source for combustion of the exhaust gas of the expander.

In order to start the operation by introducing a large amount of molecular oxygen-containing gas into the oxidation reactor to start the reaction, the driving force of the compressor needs to be increased, so that a large amount of power must be supplied to the power device. However, a small driving force is sufficient if the molecular oxygen-containing gas is supplied to the expander. At this time, the energy recovered by the expander is obtained by heating the oxygen-containing gas, so the power supply amount to the power device is at least good. When energy recovery by the expander is started, the output of the compressor can be increased to supply molecular oxygen-containing gas to the oxidation reactor and at the same time reduce the power supply to the power device.

When the reaction is carried out by introducing a molecular oxygen-containing gas in the oxidation reactor, heat is generated by the exothermic reaction, while the heat is discharged in the oxidizing exhaust gas together with steam. The steam in the oxidizing exhaust gas is sent to a condenser via a distillation tower and condensed there, and at the same time, new steam generated is introduced into the steam turbine to recover energy. The exhaust gas of the distillation column is heated and then introduced into an expander to recover energy. In this way, when the normal operation is performed, the rotational force is obtained by the expander and the steam turbine in the above-described manner, so that the power supply to the power device is stopped, and conversely, electric power is generated by power generation.

In the above method, a reaction solvent such as acetic acid can be recovered by distilling the oxidizing exhaust gas in a distillation column connected to the oxidation reactor. Steam in the exhaust gas condenses in a condenser, most of the condensate is refluxed to the distillation column, and a portion of the condensate is discharged to the effluent.

Since the oxidized exhaust gas contains combustibles such as methyl acetate and carbon monoxide, the exhaust gas can be heated by burning these substances, and the heated gas can be introduced into the expander to recover energy, but useful substances such as methyl acetate You may collect. The combustion may be carried out before introducing the exhaust gas into the expander or afterwards. If combustion is performed before introduction into the expander, a heat exchanger for indirectly warming the exhaust gas introduced into the expander is eliminated, resulting in high energy efficiency. When the combustion is performed after the expander, a heat exchanger for indirectly heating the exhaust gas introduced into the expander is required. However, since the combustion can be performed by using a lower raw material at ordinary pressure, the scope of application of the present technology can be expanded. In this case, it is preferable to heat the exhaust gas indirectly by heat exchange with the combustion gas before introducing the exhaust gas into the expander.

Best mode for carrying out the invention

Hereinafter, the Example of this invention is described below, taking the manufacturing method of terephthalic acid as an example.

1 is a flowchart showing a method for producing terephthalic acid, which is an embodiment of the present invention. In Fig. 1, 1 is an oxidation reactor, and a packed bed distillation column 2 is directly connected to the upper portion thereof, and a condenser 3 is connected to the outlet side of the distillation column. The steam turbine 4, the power device 5 serving as a generator and a motor, the compressor 6 and the expander 7 are connected by a common rotary shaft 8. 9 is a combustor, 10 is a reaction chamber, and 11 is a gas scrubber.

The method for producing terephthalic acid in the steady state operation by the above apparatus comprises p-xylene as alkyl aromatic compound of starting material, acetic acid as reaction solvent, heavy metal compound and bromine compound as oxidation solvent from line (L1) to oxidation reactor (1). By supplying and supplying air as a molecular oxygen-containing gas from the line L2, liquid phase oxidation is performed under high temperature and high pressure to generate terephthalic acid. The terephthalic acid precipitates as a crystal of crude terephthalic acid (CTA) to form a slurry, which is taken out from the line (L3) and purified by a purification apparatus to produce high purity terephthalic acid (PTA) as a product.

The exhaust gas of the oxidation reactor 1 is introduced into the distillation column 2 in a state of high temperature and high pressure, and is distilled while passing through the packed bed 2a. The solids contained in the oxidizing exhaust gas are removed from the solids trap tray 2b under the packed bed 2a and then returned to the oxidation reactor 1. In the distillation column 2, high boiling by-products and components flow out to the bottom, and low boiling point acetic acid and components flow out from the upper portion. The fraction containing these components is collected together with the solids at the bottom of the column and refluxed to the oxidation reactor 1.

When the exhaust gas of the distillation column 2 passes through the condenser 3, water vapor contained in the exhaust gas is condensed by the cooling water on the condenser shell side. Most of the condensed water is refluxed to the distillation column (2), and part of the condensed water is taken out from the line (L4) as reaction generated water and used as reslurry water or washing water in the purification process. In the condenser 3, the cooling water on the shell side is evaporated by heat exchange to generate new water vapor. This water vapor is introduced into the steam turbine 4 from the line L5 to recover energy by the rotational force of the turbine, and then cooled and condensed by the cooling water 12a in the condenser 12, and as cooling water from the line L6. Circulation to the condenser (3).

The exhaust gas from which steam is separated from the condenser 3 maintains impurities such as methyl acetate in a gas state when the temperature at the outlet side of the condenser 3 is controlled to 30 to 150 ° C, preferably 80 to 120 ° C. . This exhaust gas is introduced into the combustor 9 from the line L7, and burned with the fuel supplied from the line L8 to heat it. Thereafter, the heated exhaust gas is introduced into the reaction chamber 10 to pass the catalyst layer to oxidize the flame retardant to purify the exhaust gas. The combustion gas of the combustor is introduced into the expander 7 from the line L9 and expanded to recover energy as the rotational force of the expander turbine.

The steam turbine 4 and the expander 7 are connected to a common rotating shaft 8 to form an energy recovery device, and the power device 5 and the compressor 6 are connected to the rotating shaft 8 as a load. It is. Accordingly, the compressor 6 is driven by the rotational force recovered by the steam turbine 4 and the expander 7 to compress the air supplied from the line L10, which is oxidized from the line L2 as molecular oxygen-containing gas. While supplying to the reactor 1 to perform an oxidation reaction, energy can be recovered as electric power by the power device 5.

The exhaust gas exiting the expander 7 is introduced into the gas scrubber 11 from the line L11 to be cleaned, and discharged out of the system from the line L12. In the gas scrubber 11, water is cooled by injecting water from the line L13 to the bottom packed bed 13a, and a reducing agent such as sodium formate and sodium hydroxide is added from the line L14 to the top packed bed 13b. By spraying an absorbing liquid containing an alkali such as the above, impurities such as hydrogen bromide and bromine formed by burning the organic bromine compound in the exhaust gas are absorbed and removed. The bottom water is discharged from the line L15 by the pump 14 and cooled by the coolant 15a in the heat exchanger 15 and circulated to the line L13, and part of it is discharged from the line L16. The absorbent liquid at the top is circulated from the line L17 to the line L14 by the pump 16.

At the start of the device, power is supplied to the power device 5 serving as an electric motor to close the valve 21 installed in the line L2 while driving the power device, and close the valve 22 installed in the line L20. Open. In this way, the compressor 6 is rotated to pressurize the air supplied from the line L10 to be supplied from the line L20 to the combustor 9. Here, the fuel supplied from the line L8 is burned to heat the gas, and then the heated gas is introduced from the line L9 into the expander 7 to drive the turbine to obtain rotational force.

The power supplied to the power device 5 at the start-up of the device is good enough to operate at a capacity of 25 to 50% when the compressor is in normal operation, and the pressure at the compressor outlet at this time can be 1 to 1.5 MPa. have. After that, the temperature of the air introduced by the combustion and introduced into the expander is 400-600 ° C., and the pressure is 0.9-1.4 MPa, thereby obtaining a rotational force from the expander 7 and driving the compressor 6 to sequentially operate during normal operation. Get close to the output.

In the meantime, the valve 21 is opened at any time, and pressurized air is introduced into the oxidation reactor 1 to start the reaction. As the reaction proceeds, high temperature exhaust gas containing a large amount of water vapor is emitted by the exotherm. The water vapor generated at the same time as the water condenses in the condenser 3 can be used to rotate the turbine. The exhaust gas is heated in the combustor 9 and then introduced into the reaction chamber 10 to oxidize the flame retardant contained in the gas, followed by introduction into the expander 7 to rotate the turbine, thereby sequentially proceeding to normal operation.

It is preferable to increase the amount of air supplied to the oxidation reactor 1 sequentially by increasing the opening degree of the valve 21 and decreasing the opening degree of the valve 22, and you may change step by step. Supply of pressurized air to the oxidation reactor 1 may be performed at the same time as starting operation, or after increasing the rotational force of the expander 7. After the rotational force of the expander 7 is generated, the power supply to the power device 5 may be stopped at any point in time, but the power supply decreases as the output of the power device 5 driven by the rotational force of the expander 7 increases. It is good to configure as possible.

The supply of fuel and pressurized air to the combustor 9 is preferably limited to the amount necessary for combustion of the exhaust gas in the normal operation state. When the exhaust gas introduced into the combustor is hot and contains sufficient flammables and oxygen, the supply is stopped. Also good. As shown in FIG. 1, when the exhaust gas is combusted and immediately introduced into the expander 7 to recover energy, the heat exchanger for indirectly heating the exhaust gas introduced into the expander is not required, thereby increasing energy efficiency.

Fig. 2 is a flow chart showing another method for producing terephthalic acid of the present invention. In the present embodiment, the condenser 3 is composed of a plurality of stages of condensers 3a, 3b, and 3c, and the combustion furnace 18 is provided on the downstream side of the gas flow of the expander 7, and the exhaust gas of the condenser is After heating the combustion exhaust gas in the heat exchanger 19 and introducing the energy into the expander 7 to recover energy, the exhaust gas of the expander is purified at a temperature of 700 to 1300 ° C. without using a catalyst in the combustion furnace 18. Although the point which makes it burn in differs greatly, it is basically the same structure as FIG.

The production of terephthalic acid is basically carried out in the same manner as in the case of FIG. Water vapor generated in the condensers 3a, 3b, and 3c of the plurality of stages has different energies. The condenser 3a side is high energy of high temperature and high pressure, and the condenser 3c side is sequentially low energy. This water vapor is introduced into the steam turbine 4 from the lines L5a, L5b, and L5c, respectively, to recover energy as the rotational force of the turbine, and after being plural in the condenser 12, the lines L6a and L6b respectively from the line L6. And L6c) and circulated to the condensers 3a, 3b and 3c. This makes it possible to recover energy from the most efficient steam turbine depending on the energy level of the steam.

The exhaust gas from the condenser (3) (3c) is introduced into the heat exchanger (19) from the line (L7) and heated by the combustion gas, and then introduced into the expander (7) to expand the exhaust gas to recover energy. Then, it introduces into the combustion furnace 18 from the line L11. If necessary, air may be supplied from the line L18 to the heat exchanger 19 by the blower 17, and the air heated by the combustion gas may be burned together with the fuel from the line L8 as necessary. It supplies to 18 and burns the exhaust gas.

This combustion gas heats exhaust gas etc. by the heat exchanger 19, is processed by the gas scrubber 11, and is discharged | emitted from the line L12. The gas scrubber 11 is supplied with the absorbent liquid from the line L14 to the packed layer 13 to absorb impurities, and the absorbed liquid is discharged from the line L16. When the combustion is carried out at a high temperature, the bromine compound becomes hydrogen bromide and is absorbed by the water, so that the combustion gas can be treated using generated water or water discharged from the hydrogenation process.

In the heat exchanger 19, the plurality of water from the condenser 12 is introduced into the heat exchanger 19 via the line L21 and heated to be steam, and the steam is opened by opening the valve 23 from the line L22. Supply energy to (4) to recover energy. In the refining process, condensed water of steam used as a heat source for dissolving joterephthalic acid is supplied from line (L23) to line (L21) and heated to obtain steam. Re-use as a heat source for Distribution of these vapors is performed by the valves 22 and 24.

At the start of the device, power is first supplied to the power device 5 to rotate the compressor 6 to direct pressurized air from the line L20 via the valve 22 to the heat exchanger 19 where the air is heated. The heated pressurized air is then sent to the combustion furnace 18 via an expander 7, where the fuel supplied from line L8 is combusted. At the time of starting of such a device, the low pressure air from the line L19 may be supplied as needed. When this combustion gas is introduced into the heat exchanger 19, pressurized air supplied from the line L20 is heated to recover energy as a rotational force in the expander. In addition, in this system, even when electric power is not supplied to the electric power device, by supplying the fuel from the line L19 to the air and the line L8 by the blower 17 to raise the temperature of the combustion furnace 18, the condenser 12 is carried out. The same operation can be performed even if the condensed water returned from the evaporator is evaporated in the heat exchanger 19 to generate water vapor and introduced into the steam turbine 4 from the line L22 to generate a rotational force.

When rotational force is obtained by the expander 7, the opening degree of the said valve 21 is enlarged in order, and pressurized air is introduce | transduced into the oxidation reactor 1, and an oxidation reaction is started. Thereby, the opening degree of the said valve 22 is made small and it transfers to normal operation.

As shown in Fig. 2, when the exhaust gas is heated to pass through the expander 7, and then burned, a heat exchanger that indirectly warms the exhaust gas before introducing the exhaust gas into the expander is required, but combustion is of poor quality under normal pressure. It can also be used as a fuel, thereby broadening the scope of application of the present technology.

The excess steam, electric power, rotational force, etc. generated in the above process can be used not only in the manufacturing process but also in other fields. In addition, power devices acting as generators and motors can be replaced by emergency generators to secure emergency power for the plant.

1 and 2, the small capacity power supply equipment can start the oxidation reaction at a small power supply amount and proceed to the normal operation, so that energy can be recovered and manufactured efficiently after startup.

As described above, the aromatic carboxylic acid production method according to the present invention connects the rotating shafts of the power device, the compressor and the expander; Powering the power device to operate a compressor to pressurize the molecular oxygen-containing gas; Rotational force is obtained by heating and expanding this pressurized molecular oxygen-containing gas in an expander; It is a step of sequentially increasing the amount of molecular oxygen-containing gas introduced into the oxidation reactor and proceeding to the normal operation. Accordingly, the oxidation reaction can be started using a small amount of power from a small-capacity power plant. Can recover energy most efficiently.

Claims (5)

In a method for producing an aromatic carboxylic acid by liquid phase oxidation of an alkyl aromatic compound with a molecular oxygen-containing gas in the presence of an oxidation catalyst in a reaction solvent containing an aliphatic carboxylic acid in a reactor, Connecting a power unit acting as a generator and a motor, a compressor for supplying molecular oxygen-containing gas to the reactor, and a rotating shaft of the expander to obtain rotational force by gas expansion, Supplying power to the power unit to run the compressor, Heating the pressurized molecular oxygen-containing gas in a compressor, The hot pressurized gas is introduced into the expander to expand and obtain rotational force, A part of the molecular oxygen-containing gas pressurized in the compressor is supplied to the reactor to start the oxidation reaction, After the start of the reaction, the oxidative exhaust gas is introduced into the expander to recover energy, thereby stopping the power supply to the power device and simultaneously generating power to the generator, and A method for producing an aromatic carboxylic acid, which is characterized by sequentially increasing the supply of pressurized molecular oxygen-containing gas to the reactor and simultaneously reducing the supply to the expander. The method of claim 1, A method for producing an aromatic carboxylic acid in which an oxidizing exhaust gas is introduced into a distillation column from a reactor to perform distillation to reflux an oil containing a reaction solvent into the reactor, and at the same time, an exhaust gas from the distillation column is introduced into an expander to recover energy. The method according to claim 1 or 2, Production of an aromatic carboxylic acid which recovers energy by cooling exhaust gas from the distillation column in a condenser and condensing the reflux water into the distillation column, introducing the exhaust gas from the condenser into an expander, and introducing newly generated water vapor into a steam turbine. Way. The method according to any one of claims 1 to 3, A method for producing an aromatic carboxylic acid in which a molecular oxygen-containing gas pressurized by a compressor is introduced into a combustor to combust a fuel to be heated and then introduced into an expander. The method according to any one of claims 1 to 3, A method for producing an aromatic carboxylic acid in which a molecular oxygen-containing gas pressurized by a compressor is heated by a heat exchanger, introduced into an expander, and the exhaust gas from the expander is combusted in a combustor.