JP2010248079A - Method of producing aromatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the efficiency of utilizing energy needed in the process of producing an aromatic carboxylic acid to reduce the energy consumption therein. <P>SOLUTION: There is provided a method of producing an aromatic carboxylic acid, including: a step of oxidizing an alkyl aromatic compound to produce an aromatic carboxylic acid; a step of separating and recovering the resulting aromatic carboxylic acid from the alkyl aromatic compound; and/or a step of reducing the resulting aromatic carboxylic acid obtained thereby, wherein the method is characterized in that at least a part of the energy used in one or more steps in the group of steps is supplied from a cogeneration system where thermal energy and electric energy are generated by burning fuel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing an aromatic carboxylic acid by oxidizing an alkyl aromatic compound.

  Aromatic carboxylic acids are useful as raw materials for polyester synthesis, and are usually produced by oxidizing an aromatic compound having an alkyl group (hereinafter referred to as an alkyl aromatic compound). Taking terephthalic acid as a typical aromatic carboxylic acid as an example, molecular oxygen is obtained using acetic acid as a solvent, p-xylene as a raw material in the presence of a heavy metal catalyst mainly composed of cobalt and manganese, and a bromine compound. A method of producing by liquid phase oxidation under pressure with a gas containing benzene has been industrially performed. On the other hand, aromatic carboxylic acids such as terephthalic acid are produced commercially on a large scale all over the world, so the energy consumption during production is large. From the viewpoint of reducing the burden on the global environment these days, energy conservation is achieved. Is expected.

  In recent years, proposals for reducing the amount of energy used have been made in consideration of the environmental aspect and cost. For example, regarding thermal energy, steam is generated from water by the thermal energy of exhaust gas generated in the process of producing aromatic carboxylic acid, and solid-liquid separation is performed without lowering the temperature of the terephthalic acid slurry obtained in the oxidation reaction process. Examples of suppressing thermal energy for heating the solvent recycled to the oxidation reaction step by performing, flash drying using its own latent heat and pressure when drying the terephthalic acid cake after solid-liquid separation, etc. .

  Patent Document 1 discloses a method for producing an aromatic carboxylic acid that includes a steam turbine, a generator that also serves as an electric motor, a compressor that supplies air to a reactor, and a rotating shaft of an expander that obtains rotational force by exhaust gas. An example of linking is described. According to Patent Document 1, after starting with a small amount of electric power, energy is efficiently recovered and used by obtaining a rotational force with exhaust gas and water vapor derived from a reactor and gradually moving to steady operation while generating power. It has been proposed that the amount can be reduced. However, according to this method, it is necessary to supply a large amount of electric power from the outside when starting up the compressor, which requires a large-scale power supply facility.

JP 2000-007608 A

As described above, various proposals have been made for recovery and reuse of by-product energy, but sufficient energy utilization efficiency has not yet been achieved in the production of aromatic carboxylic acids.
Aromatic carboxylic acids such as terephthalic acid are energy consuming processes including reaction, purification and separation processes at high temperature and pressure, and are generally produced in large-scale plants. For this reason, there are many examples in which necessary electric power, steam, etc. are produced and procured in the plant, respectively, but there is a demand for reducing energy consumption and the environmental and cost aspects. Although it is possible to transmit electric power generated by an electric power company, there is a problem in that energy transmission efficiency is reduced due to transmission loss when transmitting power from a remote location.

In view of the above problems, an object of the present invention is to improve the energy utilization efficiency required in the production process and reduce the energy consumption when producing an aromatic carboxylic acid. More specifically, the present invention generates heat energy and electric energy necessary for the production of aromatic carboxylic acid with high efficiency, and again generates substances and energy generated during the production of aromatic carboxylic acid to generate energy again. It aims at improving energy utilization efficiency by using as a source. Further, in the present invention, by improving the energy utilization efficiency required in the aromatic carboxylic acid production process, it is possible to suppress substantial carbon dioxide emissions from the production process and contribute to global environmental conservation. With the goal.

As a result of intensive studies, the present inventors have found that the above problem can be solved by using a cogeneration system that simultaneously generates thermal energy and electric energy by combustion of fuel as an energy supply method of an aromatic carboxylic acid production process. The present invention has been reached.
That is, the gist of the present invention is to oxidize an alkyl aromatic compound to produce an aromatic carboxylic acid, to separate and recover the produced aromatic carboxylic acid from the alkyl aromatic compound and / or to oxidize the alkyl aromatic compound. A process for reducing the aromatic carboxylic acid obtained as described above, wherein at least a part of the energy used in one or more steps of the process group is generated by combustion of fuel. The present invention resides in a method for producing an aromatic carboxylic acid, which is supplied by a cogeneration system that generates thermal energy and electric energy.

Moreover, in the manufacturing method of the said invention, it is preferable that the ratio (in kilowatt hour conversion) of the thermal energy with respect to the total amount of the thermal energy supplied by the said cogeneration system and an electrical energy is the range of 30%-90%.
In the production method of the present invention, it is preferable that the thermal energy is used for temperature increase and / or steam generation of a heat transfer oil used in one or more steps of the process group. It is also preferred that at least a portion of the steam generated by energy is introduced into a steam turbine and used to generate electrical energy.

  In the manufacturing method of the present invention, the cogeneration system includes a gas turbine engine and a generator, and the gas turbine engine combusts fuel to generate combustion gas, and oxygen-containing gas from outside the system. A compressor that sucks, compresses and supplies the compressed gas to the combustor, and an expander that is on the same axis as the compressor and the generator and expands the combustion gas to rotate the shaft. However, it is preferable that electric energy is generated by rotation of the shaft, and thermal energy is obtained from the exhaust gas of the expander.

Further, the production method of the present invention preferably includes at least one of the following methods.
(1) At least a part of the exhaust gas generated in the oxidation step is supplied to the expander.
(2) Steam is generated by heat exchange from the exhaust gas generated in the oxidation step, and at least a part of the generated steam is supplied to the steam turbine.
(3) The oxygen-containing gas compressed by the compressor is supplied to the oxidation process.
(4) The exhaust heat generated from the generator is used as thermal energy used in one or more processes of the process group.

  According to the present invention, in the aromatic carboxylic acid production process, the amount of fuel used can be significantly reduced by improving the energy utilization efficiency. Along with this, there is an advantage that various facilities can be made compact and the number of devices can be reduced. Furthermore, by suppressing the generation amount of heat and carbon dioxide from the manufacturing process, it is possible to suppress a substantial amount of carbon dioxide emission and the like and to make the process less affected by the global environment.

It is explanatory drawing for demonstrating an example of the cogeneration system used for the aromatic carboxylic acid manufacturing method of this invention. It is explanatory drawing for demonstrating another example of the cogeneration system used for the aromatic carboxylic acid manufacturing method of this invention. It is explanatory drawing for demonstrating an example of the manufacturing method of aromatic carboxylic acid of this invention. It is explanatory drawing for demonstrating an example of the hydrorefining process in the manufacturing method of aromatic carboxylic acid of this invention. It is explanatory drawing for demonstrating an example of the waste gas treatment process in the manufacturing method of aromatic carboxylic acid of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these contents without departing from the gist of the present invention, and can be implemented with various modifications.
[1] Cogeneration system The cogeneration system used in the method for producing an aromatic carboxylic acid of the present invention generates two or more kinds of energy, that is, thermal energy and electrical energy from primary energy (fuel). In particular, according to the cogeneration system, at least thermal energy and electrical energy can be generated simultaneously and continuously from primary energy.
The fuel used for the cogeneration system may be exhaust gas from the aromatic carboxylic acid production process or the fuel supplied from outside the system (outside the aromatic carboxylic acid production process). It is preferable to use as a component. In particular, it is preferable that fuel corresponding to 50% or more of the total energy (kilowatt hour conversion) generated from the cogeneration system is supplied from outside the system, and more preferably 70% or more.

  The cogeneration system according to the present invention is more energy efficient than generating only electric energy, and thus is advantageous in terms of equipment and cost, and has the advantage of being able to suppress the amount of carbon dioxide generated that is proportional to the amount of fuel consumed. Moreover, generation | occurrence | production of a power transmission loss can also be prevented by generating heat and electricity as needed in the place which requires electricity and heat. In addition, since the equipment can be made compact, waste of space can be eliminated and the energy supply reliability is high. If necessary, the energy generated by the cogeneration system in the present invention may be supplied outside the aromatic carboxylic acid production process. Moreover, in this invention, it can also use together with other energy generation sources other than a cogeneration system in manufacture of aromatic carboxylic acid.

  According to the present invention, since the generated thermal energy and electrical energy can be used effectively, the energy use efficiency (converted into kilowatt hours) can be 50% or more. According to a preferable example, it can be 60% or more, according to a more preferable example, 80% or more, and further preferably 90% or more. In addition, in this specification, energy use efficiency shows the sum total of the utilization energy amount with respect to the energy amount generated with the cogeneration system.

  The ratio of thermal energy to the total energy supplied by the cogeneration system (total amount of thermal energy and electrical energy) (kilowatt hour conversion) is preferably 30% or more, more preferably 40% or more, and still more preferably 50%. That's it. Further, the ratio of thermal energy is preferably 90% or less, more preferably 80% or less. By setting the heat / electric energy ratio within this range, the heat / electric energy consumption ratio in the aromatic carboxylic acid production process can be matched, and the energy utilization efficiency is maximized. Therefore, it is preferable in terms of cost and environment.

  As the cogeneration system, known systems using various prime movers can be used, and prime movers such as a gas turbine engine, a diesel engine, and a gas engine are used. Gas turbine engines generally have a thermal energy: electric energy production ratio of about 2: 1, and diesel and gas engines are about 1: 1. For this reason, especially when a gas turbine engine is used, it is easy to make the ratio of the thermal energy in the aromatic carboxylic acid production process within the above-mentioned preferable range. On the other hand, if it is out of the range, the energy utilization efficiency tends to decrease. As described above, the cogeneration system cannot be easily applied to all kinds of chemical manufacturing processes, and cannot easily enjoy the advantage of improving the energy utilization efficiency. Significant energy efficiency can be improved in the manufacturing process.

  In the case of a cogeneration system using a gas turbine engine, usually, electric energy is generated by power generation by the engine, and thermal energy is obtained from the exhaust gas of the gas turbine engine. Since the exhaust gas of the gas turbine engine is extremely high in temperature, it has high quality as heat energy, and energy utilization efficiency is also increased. In particular, when heat energy is used for raising the temperature of the heat transfer oil or generating steam, high-temperature heat transfer oil or high-pressure steam is preferably obtained.

When fuel supplied from outside the system is used as the fuel used in the cogeneration system, the fuel is not limited as long as it is a combustible substance, but it is preferable to use fuel oil and / or fuel gas. As the fuel supplied from the outside, for example, kerosene, light oil, and A heavy oil can be used as the fuel oil, and natural gas, LNG, LPG, methane, ethane, propane, by-product gas outside the process, and the like can be used as the fuel gas. It is preferable to select a fuel that emits less carbon dioxide, such as natural gas, as the fuel because the carbon dioxide emissions can be further reduced by 20 to 30% based on the same calorific value as compared with the case where coal or heavy oil is used.
Furthermore, in the present invention, as described above, energy efficiency can be increased by partially using a gas containing a combustible substance such as exhaust gas discharged from the aromatic carboxylic acid production process as a fuel.

  In the present invention, combustible solid substances such as various kinds of wood, corn, rice, wheat, sugar cane, weeds, waste materials, and other various plants can be used as fuel. Furthermore, a substantial carbon dioxide emission can be further reduced by using a fuel using biomass. As the biomass fuel, bioethanol, biodiesel, methyl tertiary butyl ether, ethyl tertiary butyl ether and the like produced from these can be used. In addition, combustion aids can be used in combination, and examples thereof include, but are not limited to, methanol, methyl acetate, and hydrogen.

An example of a cogeneration system used in the method for producing an aromatic carboxylic acid of the present invention is shown in FIG. 1 (Example 1).
The gas turbine engine 4 includes a compressor 1, an electric motor 1a for starting the compressor, a combustor 2, and an expander (turbine) 3, and these are preferably integrated. The expander 3 is usually on the same axis as the compressor 1. The generator 5 is also on the same axis. The compressor starting motor 1a may be installed separately.

First, the compressor 1 is started by the compressor starting electric motor 1a. Air sucked from the air line 11 and cooled by the absorption chiller 6 is supplied to the compressor (axial flow compressor) 1 by a constant amount at a constant temperature, compressed, and sent to the combustor 2. In the compressor 1, it is desirable to compress air by an adiabatic compression method.

Furthermore, in this invention, a part of air compressed with the compressor 1 is supplied to the oxidation process of the aromatic carboxylic acid manufacturing process mentioned later, and is used as an oxygen source (molecular oxygen-containing gas B or B ′). Also good. By supplying the air compressed by the compressor 1 to the oxidation process, it is not necessary to provide a separate device for supplying the oxygen source, and the oxygen source is immediately supplied by starting the compressor 1. Is possible.

In the combustor 2, the fuel supplied from the fuel line 12 and the air compressed by the compressor 1 are mixed and burned to generate high-temperature and high-pressure combustion gas. The combustion gas is sent to the expander 3 and expanded. At this time, the expander 3 is rotated, and the compressor 1 and the generator 5 on the same axis are rotated. That is, high-temperature and high-pressure combustion gas is blown onto the turbine of the expander 3, and electric energy is taken out through the generator 5 by the rotational energy. The electrical energy generated by the generator 5 is supplied to the aromatic carboxylic acid production process through the power line 13. Since the compressor 1 is rotated once by the expander 3 after being started, the compressor starting motor 1a may be stopped.
The stationary blade provided in the compressor 1 preferably has a variable angle structure. By controlling the angle of the stationary blade according to the load fluctuation, the compression efficiency and the starting characteristic can be improved, and the system can be resistant to the load fluctuation.

  From the expander 3, electric energy is taken out as described above, and at the same time, high-temperature exhaust gas is supplied to the boiler 7 through the exhaust gas line 14. The water supplied to the boiler 7 through the water line 15 is heated by high-temperature exhaust gas to become high-pressure steam, and is supplied to the aromatic carboxylic acid production process through the steam line 16. The exhaust gas at the outlet of the boiler 7 is discharged through the exhaust gas line 17, but since it is still sufficiently hot, it can be used for generating steam by sending it to a heat exchanger or the like.

  As a preferred example, high-pressure steam obtained by the boiler 7 is introduced into a steam turbine (not shown) and used to generate electric energy. As described above, when the steam turbine is additionally provided in addition to the cogeneration system according to the present invention, the supply amount of the thermal energy and the electric energy can be further easily adjusted, and the total energy consumption can be suppressed. In addition, you may supply the vapor | steam after use to an aromatic carboxylic acid manufacturing process, and may use it as a heat source.

Since the combustion temperature in the combustor 2 of the gas turbine engine is usually as high as 500 ° C. or higher, it is very good as a heat energy source. The combustion temperature is preferably 800 ° C. or higher, more preferably 1200 ° C. or higher. In general, the combustion temperature is 1500 ° C. or lower, preferably 1300 ° C. or lower.
The temperature of the exhaust gas discharged from the expander 3 is usually 400 ° C. or higher, preferably 500 ° C. or higher. The higher the temperature of the exhaust gas is, the better the heat energy. The temperature of the exhaust gas is usually 800 ° C. or lower, preferably 600 ° C. or lower. By setting the temperature of the exhaust gas to be equal to or lower than the above upper limit value, it is possible to use a facility with low heat resistance, so that the cost can be reduced.

Since the combustor 2 and the expander 3 are exposed to a very high temperature, it is desirable that some or all of the materials are made of ceramics or a ceramic coating is applied.
Since the exhaust gas discharged from the outlet of the expander 3 has a high temperature and usually oxygen sufficient for combustion remains, a reheating system that injects fuel into the exhaust gas before the boiler 7 and burns it is provided. May be added. By performing additional cooking, the exhaust gas becomes higher in temperature and the amount of heat energy can be increased, more water and heat transfer oil can be heated, or more steam can be generated. Moreover, it is not necessary to increase the fuel supply amount significantly. The oxygen concentration in the exhaust gas at the outlet of the expander 3 is desirably in the range of 2 to 20% by volume.

The gas used for the combustion of fuel in the combustor 2 is not particularly limited as long as it is an oxygen-containing gas. For example, air, oxygen-enriched air, oxygen diluted with an inert gas, or the like can be used. Is preferably used industrially. Usually, most of the oxygen-containing gas is supplied from the compressor 1.
It is desirable to keep the air supply amount to the compressor 1 constant for stable operation and efficient operation of the system. For this reason, it is preferable to install a temperature control device at the air inlet of the compressor 1 to control the temperature of the air to keep it constant and to keep the air weight per unit volume constant. In controlling the temperature of the air, it may be heated or cooled. However, if it is cooled, the weight of air per unit volume can be increased. As a result, the amount of air that can be taken in increases and the compression efficiency can be increased.

  More preferably, an absorption refrigerator 6 is used to cool the air supplied to the compressor 1. The use of the absorption chiller 6 is particularly effective when a gas turbine engine is installed in a tropical or subtropical region or a temperate region where the temperature in summer is high. The absorption refrigerator is a refrigerator that obtains a low temperature by vaporizing at a low pressure by absorbing a refrigerant in a liquid having a high absorption capacity. A combination of water-lithium bromide and ammonia-water is widely used as the refrigerant-absorbing liquid in the absorption refrigerator, but is not limited thereto. By installing an absorption refrigerator, the temperature of the intake air to the compressor 1 of the gas turbine engine is preferably 25 ° C. or less, more preferably 20 ° C. or less, and even more preferably 10 ° C. or less. Usually, the intake air temperature to the compressor 1 is 0 ° C. or higher, preferably 5 ° C. or higher.

Another example of the cogeneration system used in the aromatic carboxylic acid production method of the present invention is shown in FIG. 2 (Example 2). 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.
The gas turbine engine 4 includes a compressor 1, an electric motor 1a for starting the compressor, a combustor 2, and an expander (turbine) 3, and these are preferably integrated. The expander 3 is usually on the same axis as the compressor 1. The generator 5 is also on the same axis.

  Hot exhaust gas is supplied from the expander 3 through the exhaust gas line 14 to the boiler 7. On the other hand, after the heat medium oil supplied from the heat medium oil line 18 is temporarily stored by providing an oil supply tank 8 as needed, it is supplied to the boiler 7 and heated to become a high-temperature heat medium oil. , And supplied to the aromatic carboxylic acid production process through the heat transfer oil line 19. The heating medium oil temperature after heating is usually 300 to 320 ° C. Usually, the heat transfer oil can be used for heating in a high-temperature additional oxidation step, heating in a reduction step, and the like in an aromatic carboxylic acid production process described later.

Further, the exhaust gas at the outlet of the boiler 7 is still at a high temperature and high pressure, and is supplied to the heat exchanger 9 through the exhaust gas line 17, and the water supplied through the water line 15 'is heated to become steam. The resulting steam is typically in the range of 0.1-6 MPa and is fed to the aromatic carboxylic acid production process through the steam line 16 '.
Examples of the heat transfer oil include organic, inorganic, silicone, fluorine, and mineral oils, and an organic heat transfer oil is preferable. Organic heat transfer oil has high thermal stability, can be used in a high temperature range, and is economical. Examples of the organic heat transfer oil include alkylbenzene, dibenzyl, and alkylnaphthalene, and examples of commercially available products include SK-OIL (trade name) and NeoSK-OIL (trade name) manufactured by Soken Technics Co., Ltd. is there.

Comparing Example 1 and Example 2, Example 1 is advantageous in that a higher pressure steam can be obtained and more electric energy can be obtained by using a steam turbine in combination. On the other hand, Example 2 has an advantage that heat energy can be more effectively used and energy utilization efficiency is higher than Example 1.
The gas turbine engine that can be used in the present invention is configured such that the compressor 1, the motor 1a for starting the compressor, the combustor 2, and the expander 3 are integrated so that the equipment is compact and the installation area is reduced. I can do it. In addition, as described above, the heat / electric energy generation ratio is close to the heat / electric energy consumption ratio in the aromatic carboxylic acid production process, and the heat / electric energy generation ratio is made closer by controlling the configuration and operating conditions of the apparatus. Energy efficiency can be maximized. Furthermore, since the combustion temperature of the gas turbine engine is extremely high, it is very good as a heat energy source, and there is an advantage that high-temperature heat transfer oil or high-pressure steam can be obtained.

Further, when starting the gas turbine engine, an electric motor for starting the compressor is used, but the power consumption is usually only 1/10 or less of that in the steady operation, and according to a more preferable example, it is 1/30 or less. is there. That is, unlike the prior art, large power is not required when starting up the aromatic carboxylic acid production apparatus.
Conventionally known gas turbine engines can be used and are not particularly limited. For example, M series, MF series manufactured by Mitsubishi Heavy Industries, LM series manufactured by Ishikawajima Harima Heavy Industries, M series, L series manufactured by Kawasaki Heavy Industries, Other examples include products manufactured by GE and SIEMENS. It is also possible to employ a steam injection type gas turbine. The output of the gas turbine engine may be determined according to the scale of the aromatic carboxylic acid production process to be applied, and is not particularly limited. However, the cogeneration system preferably has a power generation end output of 3 to 50 MW / group.
Further, the boiler using the exhaust gas preferably has a heating capacity (exchange heat amount) of 4 to 75 MMkcal / h / group (million kcal / h / group). Although the structure of a boiler is not limited, A round boiler, a water pipe boiler, a cast iron boiler, a special boiler, etc. are mentioned.

[2] Method for Producing Aromatic Carboxylic Acid Next, a method for producing an aromatic carboxylic acid to which the cogeneration system of the present invention is applied will be described.
The method for producing an aromatic carboxylic acid according to the present invention includes a step of oxidizing an alkyl aromatic compound to produce an aromatic carboxylic acid, and separating and recovering the produced aromatic carboxylic acid from the alkyl aromatic compound and / or an alkyl. And a step of reducing an aromatic carboxylic acid obtained by oxidizing an aromatic compound. The thermal energy and electrical energy supplied by the cogeneration system are used in one or more steps of the step group in the aromatic carboxylic acid production process.

  Electrical energy can be used for pressurization, stirring, separation, etc. in these process groups, and thermal energy can be used for heating, dissolution, etc., respectively. In particular, the heat energy is preferably used for raising the temperature of the heat transfer oil or generating steam, and these heat transfer oil and steam are preferably used for raising the temperature in each step. The process in which heat and / or electric energy is used is not limited as long as it is an aromatic carboxylic acid production process. The oxidation process, solid-liquid separation process, cake washing process, drying process, reduction process (hydrogenation process) described later, Any of a crystallization process, a waste treatment process, a catalyst recovery process, a catalyst regeneration process, a solvent recovery / distillation process, a wastewater treatment process, an exhaust gas treatment process, and the like may be used. Especially, it is preferable to make a cogeneration system into a supply source as a heat energy and an electrical energy which are used for an oxidation process, a solid-liquid separation process, and a reduction process.

Hereinafter, 1st embodiment of the manufacturing method of aromatic carboxylic acid is described in detail using FIG. In addition, this invention is not limited to what concerns on embodiment described below, In the range which does not deviate from the summary of this invention, it can change arbitrarily and can implement.
[Oxidation process]
In the oxidation step, the alkyl aromatic compound A as a raw material is introduced into the oxidation reactor 111, and the alkyl aromatic compound A is oxidized with the molecular oxygen-containing gas B in the solvent C to generate an aromatic carboxylic acid. A slurry D is obtained. In the present invention, the alkyl aromatic compound A is a concept including not only an aromatic compound having an alkyl group but also an aromatic compound having a partially oxidized alkyl group. In the present invention, the mixture of the raw material and the solvent includes various cases of a liquid phase, a gas-liquid two phase, and a gas-liquid-solid three phase, and is not limited.

As an operation for starting the aromatic carboxylic acid production apparatus using the gas turbine engine 4 in the present invention, first, the compressor 1 is started by supplying power to the motor 1a for starting the compressor. The compressed air and the fuel supplied from the fuel line 12 are combusted in the combustor 2, and the obtained high-temperature and high-pressure gas is blown to the expander 3 to obtain a rotational force. On the other hand, the oxidation reaction is started by supplying a part of the air compressed by the compressor to the oxidation reactor 111.
After starting the oxidation reaction, as described later, by supplying exhaust gas generated by the oxidation reaction to the combustor 2, part or all of air or fuel can be replaced. Thereafter, the compressor starting motor 1a stops and enters a steady operation.
By starting the aromatic carboxylic acid production apparatus using the gas turbine engine 4 as described above, the starting power can be reduced to about one-tenth, and preferably about one-third compared to the conventional method.

  The type of aromatic carboxylic acid targeted by the present invention is not limited. For example, orthophthalic acid, isophthalic acid, terephthalic acid, trimellitic acid (benzenetricarboxylic acid), 2,6- or 2,7-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid and the like. In particular, the present invention is preferably applied to the production of phthalic acids (orthophthalic acid, isophthalic acid, terephthalic acid), and particularly preferably applied to the production of terephthalic acid.

  Examples of the alkyl aromatic compound A that is a raw material for the aromatic carboxylic acid include di- and tri-alkylbenzenes, di- and tri-alkylnaphthalenes, and di- and tri-alkylbiphenyls. Preferably, o-xylene, m-xylene, p-xylene, o-, m-, or p-diisopropylbenzene, trimethylbenzenes, 2,6- or 2,7-dimethylnaphthalene, 2,6-diisopropylnaphthalene, Examples include 4,4′-dimethylbiphenyl. Among them, monocyclic or polycyclic aromatic compounds having 2 or more and 4 or less alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, n-propyl and isopropyl groups are reactive. Is preferable. The raw material alkyl aromatic compound may include a partially oxidized alkyl aromatic compound (partially oxidized alkyl aromatic compound), or all may be a partially oxidized alkyl aromatic compound.

  A partially oxidized alkyl aromatic compound is a compound in which the alkyl group in the above alkyl aromatic compound is oxidized to an aldehyde group, acyl group, carboxyl group, hydroxyalkyl group or the like, but the target aromatic carboxylic acid It is a compound that is not oxidized to the extent that Specifically, for example, 3-methylbenzaldehyde, 4-methylbenzaldehyde, 4-carboxybenzaldehyde (hereinafter referred to as “4CBA” as appropriate), p-tolualdehyde, m-toluic acid, p-toluic acid, 3-formyl. Examples thereof include benzoic acid, 4-formylbenzoic acid, and 2-methyl-6-formylnaphthalene.

As the raw material, these compounds may be used alone or as a mixture of two or more.
In summary, as the alkyl aromatic compound A, xylenes (o-xylene, m-xylene, p-xylene) are preferable, and p-xylene is particularly preferable. When p-xylene is used as the alkyl aromatic compound A, examples of the partially oxidized alkyl aromatic compound include 4CBA, p-tolualdehyde, p-toluic acid, and the like, and terephthalic acid is obtained as the aromatic carboxylic acid. .

The molecular oxygen-containing gas B may be any gas containing molecular oxygen. For example, air, oxygen-enriched air, oxygen diluted with an inert gas, or the like is used. Low cost air is industrially preferred. The supply amount of the molecular oxygen-containing gas B is usually 3 to 100 times mol as molecular oxygen with respect to p-xylene. The oxygen content of air is usually 21% by volume at the inlet.
As described above, the air compressed by the compressor 1 of the cogeneration system can be used as the supply source of the molecular oxygen-containing gas B. As a result, it is not necessary to separately provide a device for supplying the oxygen source, and the oxygen source can be immediately supplied by starting the compressor 1.

  When the alkyl aromatic compound A is oxidized, a catalyst is usually used. The type of the catalyst is not particularly limited as long as it has an ability to promote a reaction for oxidizing an alkyl aromatic compound to produce an aromatic carboxylic acid. A catalyst made of a heavy metal compound is preferred. Examples of the heavy metal contained in the heavy metal compound 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 cobalt and manganese in combination. Examples of such heavy metal compounds include acetate, nitrate, acetylacetonate, naphthenate, stearate and bromide. Of these, acetate and bromide are preferred.

  The catalyst may contain a catalyst auxiliary such as a bromine compound as necessary. Examples of the bromine compound include inorganic bromine compounds such as molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide, methyl bromide, methylene bromide, bromoform, benzyl bromide, Examples include bromomethyltoluene, dibromoethane, tribromoethane, and tetrabromoethane.

These catalysts and catalyst auxiliaries can be used alone or as a mixture of two or more. As a preferred embodiment, a cobalt and / or manganese compound is used, and a bromine compound is used as a catalyst auxiliary. Particularly preferred is a combination of cobalt acetate, manganese acetate and hydrogen bromide.
In the case of a catalyst comprising a combination of a heavy metal compound and a bromine compound, it is preferably 0.05 mol or more of bromine atom per mol of heavy metal atom, and preferably 10 mol or less of bromine atom. By setting this range, the catalytic activity is increased.

  The concentration of the catalyst is not particularly limited as long as the oxidation reaction of the alkyl aromatic compound can be promoted, but the concentration of heavy metal in the solvent is usually 10 ppm or more, preferably 100 ppm or more. On the other hand, the heavy metal concentration is usually 10,000 ppm or less, preferably 5000 ppm or less. The reaction rate is increased by setting the heavy metal concentration to the lower limit value or more, and the cost can be suppressed by setting the heavy metal concentration to the upper limit value or less, and the heavy metal concentration and bromine concentration in the effluent and exhaust gas can be reduced. preferable.

  As the solvent C, a solvent that can dissolve at least a part of the produced aromatic carboxylic acid is usually used. Note that, under normal pressure (hereinafter referred to as normal pressure in the present invention, “0.101 MPa” unless otherwise specified), even if the aromatic carboxylic acid is insoluble or hardly soluble, the oxidation reaction conditions It is sufficient if it can dissolve at least a part. The boiling point of the solvent C at normal pressure is preferably 40 ° C. or higher, more preferably 60 ° C. or higher, and preferably 200 ° C. or lower, more preferably 150 ° C. or lower. By setting it to the lower limit value or more, handling and recovery become easy, and by setting the upper limit value or less, solid-liquid separation and drying in the subsequent process become easy.

The kind of the solvent C is not limited, Water etc. can also be used. In view of solubility and the like, it is preferable to contain an aliphatic carboxylic acid, and it is more preferable to use these as a main component. A solvent containing acetic acid, propionic acid, formic acid and butyric acid as main components is more preferable, and a solvent containing acetic acid as a main component is particularly preferable because of its solubility and ease of handling. The main component means that it accounts for 60% by weight or more of the total weight of the solvent. Particularly preferred is a mixture of acetic acid and water. The ratio of acetic acid to water is usually 1 part by weight or more, preferably 5 parts by weight or more with respect to 100 parts by weight of acetic acid. Moreover, it is 40 weight part or less normally, Preferably it is 25 weight part or less. The reaction efficiency can be improved by setting the ratio of water to 100 parts by weight of acetic acid to be not more than the above upper limit value, and combustion decomposition of acetic acid can be further reduced by setting the ratio to be not less than the lower limit value. Each source is preferred.
The amount of the solvent C can be appropriately changed depending on the solubility of the raw materials and the target reactant, but is preferably 1 or more times by weight and preferably 5 or less by weight with respect to the alkyl aromatic compound A.

  The oxidation reaction of the alkyl aromatic compound A is carried out in a pressurized reactor, that is, under a pressure exceeding the normal pressure. The pressure in the oxidation reactor 111 is preferably 0.2 MPa or more (absolute pressure; the same shall apply hereinafter), more preferably 0.5 MPa or more, and even more preferably 1 MPa or more. In order to increase the reaction efficiency of the liquid phase oxidation, it is more preferable to set the pressure at which the mixture of the solvent C and the alkyl aromatic compound A can maintain the liquid phase at the reaction temperature. Also, the pressure in the oxidation reactor 111 is preferably high so that the slurry after the reaction can be easily transferred to the solid-liquid separator. On the other hand, the pressure in the oxidation reactor 111 is usually 50 MPa or less. The pressure is preferably 10 MPa or less, more preferably 7 MPa or less, still more preferably 5 MPa or less, and particularly preferably 2 MPa or less. Side reactions and decomposition of compounds can be suppressed, and there is an advantage of suppressing a decrease in yield. Further, by keeping the pressure as low as possible, a reactor having a low pressure strength can be used, and costs can be reduced.

  The temperature of the oxidation reactor 111 is usually 100 ° C. or higher, preferably 140 ° C. or higher, more preferably 150 ° C. or higher. As the temperature is higher than the lower limit, there is an advantage that the reaction rate can be increased and the yield can be increased. The temperature is usually 600 ° C. or lower, preferably 300 ° C. or lower, more preferably 250 ° C. or lower, and further preferably 230 ° C. or lower. The lower the temperature is, the lower the amount of loss due to solvent combustion. Further, there is an advantage that the decomposition of the compound in the side reaction or oxidation reaction system can be suppressed and the decrease in yield can be suppressed.

The oxidation reaction is preferably performed continuously because production efficiency is increased.
The type of the oxidation reactor 111 is not limited, and any of, for example, a reactor with a stirrer, a bubble column reactor, a plug flow type (pipe flow type) reactor, or the like may be used. In order to increase the reaction efficiency, it is preferable to use a complete mixing tank reactor with a stirrer.

The reaction gas M is discharged as the condenser exhaust gas O after the condensate N mainly composed of the solvent C is condensed and separated in the condenser 112 as necessary. One condenser 112 may consist of a plurality of condensers.
The lower part of the oxidation reactor 111 is usually provided with a supply port for the molecular oxygen-containing gas B. After the supplied molecular oxygen-containing gas B is used for the oxidation reaction of the alkyl aromatic compound A, a large amount Is extracted from the top of the oxidation reactor 111 as a reaction gas M containing the vapor of the solvent C.

  The supply amount and the oxygen concentration of the molecular oxygen-containing gas B are preferably controlled so that the oxygen concentration in the condenser exhaust gas O falls within a specific range. The oxygen concentration in the condenser exhaust gas O is preferably 0.5% by volume or more, more preferably 2% by volume or more. There is an advantage that the reaction efficiency increases as the oxygen concentration is higher than the lower limit. The oxygen concentration is preferably controlled to 10% by volume or less, more preferably 7% by volume or less. Safety is enhanced by making the oxygen concentration lower than the upper limit. In addition, when the condenser 112 consists of two or more, let the exhaust gas of a final condenser be the condenser exhaust gas O. FIG.

Usually, the condensate N contains water, and a part thereof is purged outside the system to adjust the amount of water in the system, and the rest is refluxed to the oxidation reactor 111. Further, the condenser exhaust gas O may be branched into two flows, one being discharged out of the system, and the other being continuously circulated and supplied to the oxidation reactor 111. The exhaust gas discharged can be treated in an exhaust gas treatment process described later.
When an aliphatic carboxylic acid such as acetic acid is used as the solvent C, the water concentration of the solvent C in the oxidation reactor 111 can be adjusted within a preferable range as follows. That is, an aliphatic carboxylic acid such as pure acetic acid is supplied as the solvent C, and a part of the mother liquor F and the washing drainage J, which will be described later, is reused, and a part of the condensate N containing water is purged outside the system. The amount to be adjusted is adjusted. In this way, the water concentration of the solvent C can be suppressed to such an extent that the influence on the reaction can be ignored.

  Alternatively, a distillation column may be used in place of the condenser 112. A distillation column capable of separating an aliphatic carboxylic acid and water is connected to the oxidation reactor 111, and the reaction gas M generated in the oxidation reactor 111 is distilled in the distillation column. The amount of water in the system is recovered by recovering the aliphatic carboxylic acid having a reduced water concentration obtained from the bottom of the column in the oxidation reactor 111 and purging a component containing water obtained from the top of the column, for example, out of the system. Can be adjusted.

  In recent years, a method has also been proposed in which supercritical or subcritical water is used as the solvent C and an aromatic aromatic carboxylic acid is obtained by oxidizing an alkylaromatic compound under high temperature and pressure. This method is preferable in terms of environment and safety because an organic solvent such as acetic acid is not used. The temperature at the critical point of water is 374.3 ° C. and the pressure is 22.1 MPa, and the water in the supercritical state is water at a temperature and pressure above the critical point. The subcritical water refers to a state that is below the critical point and is supercritical, and generally has a temperature of 200 ° C. or higher, preferably 250 ° C. or higher, more preferably 280 ° C. or higher. Further, the temperature is usually 600 ° C. or lower, preferably 500 ° C. or lower, more preferably 400 ° C. or lower, from the viewpoints of suppression of decomposition of the alkyl aromatic compound, heat resistance of the process equipment, energy cost, and the like. The pressure is usually 6 MPa or more, preferably 10 MPa or more, and usually 50 MPa or less, preferably 40 MPa or less. In addition, as long as there is no remarkable bad influence on reaction, you may contain other arbitrary solvents.

  When supercritical or subcritical water is used as the solvent C, a catalyst is not essential in the reaction, but it is desirable to use a catalyst in order to increase the yield of aromatic carboxylic acid. For example, the oxidation catalyst described above Etc. can be used. The oxidation reactor 111 is not particularly limited as long as it can maintain a supercritical or subcritical state, but a continuous flow reactor capable of continuously performing the reaction is preferable because of its high productivity. When water in a supercritical or subcritical state is used as the solvent C, high temperature and high pressure conditions are necessary, and the required energy is larger than that of the conventional method. Therefore, the present invention is more effective.

  As a part of the oxidation step, after the oxidation reaction in the oxidation reactor 111, additional oxidation treatment may be performed as necessary. In the additional oxidation treatment, the reaction mixture obtained by the oxidation reaction in the oxidation reactor 111 is supplied with the molecular oxygen-containing gas B ′ without supplying the alkyl aromatic compound A in the additional oxidation reactor 111 ′. It is an oxidation treatment. The conditions for the additional oxidation treatment are the same as in the oxidation reaction in the oxidation reactor 111 except for the matters described below.

  As a preferred example of the additional oxidation treatment, the additional oxidation treatment is performed on the reaction mixture obtained in the oxidation reactor 111 in the additional oxidation reactor 111 ′ held at a lower temperature (hereinafter referred to as “low temperature additional oxidation”). When the alkyl aromatic compound A is p-xylene, the temperature of the additional oxidation reactor 111 ′ is preferably 1 ° C. or more lower than the oxidation reactor 111, more preferably 5 ° C. or more. Moreover, it is preferable to set it as 20 degrees C or less low temperature, More preferably, it is set as 15 degrees C or less low temperature. The specific temperature is usually 140 ° C. or higher, preferably 160 ° C. or higher. Moreover, it is 220 degrees C or less normally, More preferably, it is 200 degrees C or less. By setting the temperature of the low temperature additional oxidation reaction to the lower limit value or more, the aromatic carboxylic acid particles tend to dissolve and the purity tends to increase. Moreover, there exists a tendency for the production | generation of a coloring impurity to be suppressed by making temperature into the said upper limit or less.

  As another preferred example of the additional oxidation treatment, the additional reaction is performed on the reaction mixture obtained in the oxidation reactor 111 in the additional oxidation reactor 111 ′ held at a higher temperature (hereinafter referred to as “high temperature additional oxidation”). . If the alkyl aromatic compound A is p-xylene, the temperature of the additional oxidation reactor 111 ′ is preferably higher than the oxidation reactor 111 by 1 ° C. or higher, more preferably 30 ° C. or higher. Moreover, it is preferable to set it as 150 degreeC or less high temperature, More preferably, it is set as 100 degreeC or less high temperature. The specific temperature is usually 235 ° C. or higher, preferably 240 ° C. or higher. Moreover, it is 290 degrees C or less normally, More preferably, it is 280 degrees C or less. By setting the temperature of the high temperature post-oxidation reaction to the above lower limit or more, the aromatic carboxylic acid particles tend to dissolve and the purity tends to increase. Moreover, there exists a tendency for the production | generation of a coloring impurity to be suppressed by making temperature into the said upper limit or less.

  The additional oxidation treatment may be performed only once or may be performed continuously twice or more. For example, the low temperature additional oxidation may be performed twice or more, the low temperature additional oxidation and the high temperature additional oxidation may be performed once or more each time, or the high temperature additional oxidation may be performed twice or more. Preferably, the additional oxidation treatment is performed once or more, more preferably at least the low temperature additional oxidation is performed once.

The post-oxidation treatment is also preferably performed under a pressurized condition, that is, under a pressure exceeding the normal pressure, and more preferably at a pressure higher than the pressure at which the internal mixture can maintain the liquid phase at the reaction temperature. In order to facilitate the transfer of the slurry after the reaction to the solid-liquid separator, the pressure in the additional oxidation reactor 111 ′ is preferably high. Preferably it is 0.2 MPa or more, more preferably 0.5 MPa or more. On the other hand, the pressure is usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, and further preferably 2 MPa or less. By setting the pressure of the additional oxidation reaction within the above range, there is an advantage that side reaction and decomposition of the compound can be suppressed, and a decrease in yield is suppressed. Further, by keeping the pressure as low as possible, a reactor having a low pressure strength can be used, and costs can be saved. In order to efficiently introduce the slurry D from the oxidation reactor 111 into the additional oxidation reactor 111 ′, it is desirable that the pressure be lower than that in the oxidation reactor 111.
The supply amount of the molecular oxygen-containing gas B ′ is preferably 1 / 10,000 or more and preferably 1/5 or less of the supply amount of the molecular oxygen-containing gas B by volume.

  The oxidation reaction is performed as described above, and the slurry D or D ′ containing the aromatic carboxylic acid and the solvent C is extracted from the oxidation reactor 111 or the additional oxidation reactor 111 ′. The aromatic carboxylic acid is usually obtained as a solid, preferably as a crystal, and a slurry containing at least a solid compound and a solvent is obtained. A part of the aromatic carboxylic acid may be dissolved in the solvent C. The slurry D or D ′ may contain a catalyst, a raw material alkyl aromatic compound, a by-product (for example, a partially oxidized alkyl aromatic compound) and the like in addition to the solvent C and the aromatic carboxylic acid. Examples of by-products include 4CBA, p-tolualdehyde, p-toluic acid, and methyl acetate when terephthalic acid is produced from p-xylene.

  In the following, for the sake of convenience, a case will be described in which the reaction apparatus includes only the oxidation reactor 111 and the slurry D extracted from the oxidation reactor 111 is a slurry extracted from the reaction apparatus. This explanation is similarly applied to the case where the slurry D 'extracted from the additional oxidation reactor 111' is a slurry extracted from the reactor.

[Separation / recovery process]
In the present invention, the separation / recovery step refers to a step of separating and recovering the product aromatic carboxylic acid from the alkyl aromatic compound. This process includes a solid-liquid separation process, a cake washing process, a drying process, and the like.

[Solid-liquid separation process]
In the solid-liquid separation step, the slurry D is transferred to the solid-liquid separation device 113 for solid-liquid separation into a solvent and an aromatic carboxylic acid. If necessary, a crystallization step may be added before the solid-liquid separation step. A pump or a pressure valve may be provided between the oxidation reactor 111 and the solid-liquid separation device 113 to adjust the pressure of the slurry D as appropriate, but the pressure from the oxidation reactor 111 to the solid-liquid separation device 113 is increased. It is preferable to transport while maintaining the state.

  The solid-liquid separator 113 separates the slurry D into an aromatic carboxylic acid cake E and a mother liquor F in a pressurized state. When solid-liquid separation is performed in a pressurized state, a cake having a large internal energy is obtained, and there is an advantage that the cake adhering liquid can be efficiently evaporated in the subsequent cake drying step. Further, since the mother liquor F in a pressurized state is obtained, there is an advantage that energy for repressurization can be reduced if it is transferred to the reaction apparatus while being kept in the pressurized state and recycled as a solvent.

  The pressure in the solid-liquid separation step is usually 0.2 MPa or more, preferably 0.3 MPa or more, more preferably 0.5 MPa or more. In order to suppress evaporation of the mother liquor, it is desirable that the pressure be higher than the vapor pressure of the solvent C at that temperature. On the other hand, the pressure is usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, still more preferably 3 MPa or less, and particularly preferably 2 MPa or less. By using a lower pressure, a device with a slightly lower pressure resistance can be used, and costs can be reduced.

Further, the pressure of the solid-liquid separator is preferably higher than the vapor pressure of the slurry D by 0.01 MPa or more, more preferably 0.02 MPa or more. This is for suppressing evaporation of the mother liquor. On the other hand, the pressure of the solid-liquid separator is preferably 2.0 MPa or less higher than the vapor pressure of the slurry D, more preferably 1.0 MPa or less, and even more preferably 0.5 MPa or less.
A known device can be used as the solid-liquid separation device 113 without limitation. For example, a centrifugal separator such as a screen bowl decanter or a solid bowl decanter, a horizontal belt filter, a rotary pressure filter, a rotary vacuum filter, or the like is used. be able to.

[Mother liquor recycling process]
The mother liquor F separated by the solid-liquid separation device 113 is usually once accumulated in the mother liquor tank in the solid-liquid separation device 113 and then collected in the mother liquor tank 120, but the solvent used for the reaction is the main component, It contains dissolved aromatic carboxylic acid, unreacted alkyl aromatic compound, catalyst, by-product, water and the like. Therefore, the mother liquor F can be transferred to the oxidation reactor 111 to reuse the solvent, unreacted raw materials and catalyst, and return the aromatic carboxylic acid contained therein to the reaction system, thereby increasing the overall yield of the process. preferable. When solid-liquid separation is performed under pressure, it is preferable that the mother liquor F is transferred to the oxidation reactor 111 while maintaining the pressurized state because energy for repressurization can be saved. The temperature of the mother liquor tank 120 is usually 50 ° C. or higher, preferably 70 ° C. or higher, and is usually 190 ° C. or lower, preferably 180 ° C. or lower.

  In order to avoid accumulation of impurities such as by-products and catalysts in the process, a part of the mother liquor F is sent as a purge mother liquor to the disposal process 119 and discarded after treatment, and the remainder is recycled to the oxidation reactor 111 as a recycled mother liquor. Can send. The disposal process 119 includes, for example, a solvent evaporation process and a catalyst recovery process.

[Cake washing process]
The aromatic carboxylic acid cake E obtained by the solid-liquid separation device 113 may be dried as it is, but if it is washed by the washing device 114, impurities, by-products, catalysts, etc. can be removed, and the resulting aromatic Since the purity of carboxylic acid increases, it is preferable.
In the cleaning device 114, the aromatic carboxylic acid cake E is cleaned with the cleaning liquid H, and the mother liquid adhering to the cake is removed to obtain the cleaning cake G in which the impurity concentration is reduced. The cleaning liquid H used for the cleaning may be water or an organic solvent, and is not particularly limited, but is preferably compatible with the solvent C used in the oxidation reactor 111. For example, when the solvent C is a solvent containing acetic acid or water as a main component, the cleaning liquid H is acetic acid, water, or an acetic acid ester having a relatively low latent heat of evaporation such as methyl acetate, ethyl acetate, propyl acetate, or butyl acetate, or It is preferable to use a solvent mainly composed of these mixtures. It is more preferable that the main component is the same as that of the solvent C because the cleaning waste liquid J can be easily reused. When the solvent C is a solvent containing acetic acid as a main component, the cleaning liquid H is also preferably a solvent containing acetic acid as a main component, preferably a solvent containing 60 wt% or more of acetic acid, and a solvent containing 70 wt% or more. Particularly preferred.

The amount of the cleaning liquid H used for the cleaning is preferably 0.03 or more, more preferably 0.05 or more, and still more preferably 0.1 or more, by weight ratio to the solid content in the cake E. Moreover, Preferably it is 5.0 or less, More preferably, it is 4.0 or less, More preferably, it is 3.0 or less.
It is desirable that the pressure of the cleaning device 114 is in a pressurized state similar to the pressure of the solid-liquid separation device 113. When washing is performed in a pressurized state, a cake having a large internal energy is obtained, and there is an advantage that the cake adhering liquid can be efficiently evaporated in the subsequent cake drying step. Moreover, since the washing waste liquid J in a pressurized state is obtained, there is an advantage that energy for repressurization can be reduced if it is transferred to the reactor while being kept in the pressurized state and recycled as a solvent. The temperature of the washing drain tank 121 is usually 50 ° C. or higher, preferably 70 ° C. or higher. Moreover, it is 190 degrees C or less normally, Preferably it is 180 degrees C or less. Further, in order to suppress evaporation of the cleaning waste liquid J, it is desirable that the pressure is higher than the vapor pressure of the cleaning liquid at that temperature.

[Wash drainage recycling process]
In order to avoid the accumulation of impurities such as by-products and catalysts in the process, a part of the cleaning waste liquid J is sent to the disposal process 119 and discarded, and the remainder is sent to the oxidation reactor 111 for reuse. Is preferred. Thereby, accumulation of impurities in the process can be suppressed. The disposal process 119 includes, for example, a solvent evaporation process and a catalyst recovery process. When cleaning is performed under pressure, it is preferable to transfer the cleaning waste liquid J to the oxidation reactor 111 while maintaining the pressurized state, because energy for repressurization and reheating can be saved.
The recycling rate of the cleaning effluent J is not limited. However, the higher the value, the higher the reuse rate of valuable components in the cleaning effluent, and the load on the disposal process is reduced, so that the amount of waste can be reduced.

The mother liquid tank 120 and the cleaning drain tank 121 may be combined into one mother liquid / cleaning drain tank. In that case, the transfer to the oxidation reactor 111, the reuse of the solvent, the unreacted raw material and the catalyst, and the transfer to the disposal process and the disposal can be performed together. Hereinafter, the description regarding the mother liquor tank 120 and the cleaning drainage tank 121 includes such a mother liquor / cleaning drainage tank.
When the mother liquor F or the washing waste liquid J is transferred to the reactor, it may be transferred to any reactor in the reactor, but is preferably transferred to the oxidation reactor 111 in order to increase the reaction efficiency.

[Drying process]
When the solid-liquid separation and washing are performed under pressure, the washing cake G is preferably dried by the drying device 116 to remove the adhering liquid remaining on the cake to obtain an aromatic carboxylic acid. Usually, it is obtained as an aromatic carboxylic acid crystal K. There may be only one drying device 116 or a plurality of the same or different devices.

The type of the drying device 116 is not limited, but preferably includes a device for allowing the attached cake adhering to the cleaning cake G to be released under pressure by shifting the cleaning cake G from the high pressure state to the low pressure state, so-called flash drying device. It is preferable. According to this, since the washing cake G can be dried without adding further energy, it is preferable for saving energy consumption.

  Examples of the drying apparatus capable of releasing pressure evaporation include a pressure drying apparatus provided with a discharge valve capable of extracting from a high pressure state to a low pressure state. From the cake holding tank in which the washing cake G is stored while maintaining the high pressure state, the discharge valve is opened to draw the washing cake G into a lower pressure powder retention tank, and the cake adhering liquid is removed by evaporation. The discharge valve may be a continuous or intermittent discharge system, and the drying apparatus may include one discharge valve or a plurality of discharge valves. The type of the valve is not particularly limited, but a valve having a high gas sealing property is preferable, and a ball valve, a butterfly valve, a rotary valve, a flap damper, a slide damper, a spindle valve, or the like can be used. In addition, it is preferable to adjust the timing and the number of times so that the amount of washing cake G retained in the powder retaining tank becomes constant during extraction by the discharge valve.

  Both steps may be performed by a solid-liquid separation and washing apparatus 115 (corresponding to a dashed box 115 in the figure) that can perform the solid-liquid separation process and the washing process with one apparatus. Further, these three steps may be performed by a solid / liquid separation washing / drying device 117 (corresponding to a broken line 117 in the figure) capable of performing the solid / liquid separation step, the washing step and the drying step with one apparatus. There is an advantage that the process can be simplified. Examples of such an apparatus include a centrifugal separator such as a screen bowl decanter and a solid bowl decanter, a horizontal belt filter, a rotary pressure filter, and a rotary vacuum filter. Among these, the screen bowl decanter is particularly preferable because it is excellent in heat resistance and can be used in a high temperature range close to the temperature of the oxidation reactor 111.

  When the aromatic carboxylic acid crystal K thus obtained is insufficiently dried, it is preferable to further dry by providing a heat drying device 118 after the drying device 116. An aromatic carboxylic acid crystal K ′ having a further reduced liquid content is obtained. The type of the heating and drying device 118 is not particularly limited, but a fluidized bed drying device, a rotary drying device (such as a steam tube dryer) is preferably used from the viewpoint of drying efficiency and cost.

[Reduction process]
An aromatic carboxylic acid is obtained from the alkyl aromatic compound by the above-described steps. The obtained aromatic carboxylic acid may be used as it is, or may be subjected to a reduction step in order to increase the purity.
Examples of the reduction step include a hydrorefining process (consisting of a dissolution step, a hydrogenation step, a crystallization step, a solid-liquid separation step, a washing step, a drying step, etc.). The hydrorefining process will be described with reference to FIG. As the dissolution step, the aromatic carboxylic acid crystal K or K ′ obtained by the above-described step is dissolved in the solvent P in the reactor 125. Hereinafter, the aromatic carboxylic acid crystal K will be described as a representative, but the same applies to the aromatic carboxylic acid crystal K ′.

  Or after making it melt | dissolve in another melt | dissolution tank beforehand, you may supply to the reactor 125. FIG. The aromatic carboxylic acid crystal K is usually dissolved in an amount of 1 to 80 parts by weight per 100 parts by weight of the solvent P. The solvent P to be used is not particularly limited as long as the aromatic carboxylic acid crystal K can be dissolved, and a solvent that does not chemically change the aromatic carboxylic acid crystal is used. The boiling point of the solvent P at normal pressure is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, still more preferably 60 ° C. or higher, preferably 200 ° C. or lower, more preferably 180 ° C. or lower, still more preferably 150 ° C. It is as follows. Handling and recovery are facilitated by setting the boiling point of the solvent P at normal pressure to the lower limit value or more, and solid-liquid separation and drying in subsequent steps are facilitated by setting the boiling point to the upper limit value or less.

Although the kind of solvent P is not limited, it is preferable that water is included from solubility, boiling point, and ease of handling, for example, when manufacturing a terephthalic acid, it is preferable to have water as a main component, More preferably, 90 A solvent in which% by weight is water, more preferably 100% by weight is preferred.
This process preferably uses a hydrogenation catalyst. For example, a group 8-10 metal catalyst such as ruthenium, rhodium, palladium, platinum, osmium is used. Of these, palladium is preferable. Usually, these are supported on activated carbon or the like and used as a fixed bed.

  Subsequently, a hydrogenation step is performed in which hydrogen W is introduced into the reactor 125 to reduce at least part of impurities contained in the aromatic carboxylic acid crystal. In performing the hydrogenation step, if the solubility of the aromatic carboxylic acid crystal K at room temperature is small, the temperature is preferably increased in order to increase the solubility in the solvent P. The temperature of the reduction reaction is usually 230 ° C. or higher, preferably 250 ° C. or higher. Moreover, it is 330 degrees C or less normally, Preferably it is 310 degrees C or less. Moreover, about a pressure, in order to maintain a solvent as a liquid, a pressure higher than vapor pressure is required, and it is 3 MPa or more normally, Preferably it is 5 MPa or more. Moreover, it is 20 MPa or less normally, Preferably it is 15 MPa or less, More preferably, it is 12 MPa or less. For example, when terephthalic acid is produced as an aromatic carboxylic acid by such a hydrogenation step, 4CBA contained in the terephthalic acid crystal can be reduced and converted to p-toluic acid.

[Crystalling process]
Thereafter, in order to crystallize the aromatic carboxylic acid again as necessary, the liquid composition X in which the aromatic carboxylic acid crystal K is dissolved in the solvent P is transferred to the crystallization tank 126. Crystals mainly composed of the aromatic carboxylic acid are crystallized by lowering the pressure in the crystallization tank 126 and cooling. Rather than having only one crystallization tank 126, it is preferable to have a plurality of crystallization tanks in series and perform crystallization in multiple stages. Crystallization may be either batch or continuous, but usually the pressure is lowered stepwise in two or more units, preferably three or more. Moreover, it is 6 or less normally, Preferably it is 5 or less. As a result, the solvent P flashes and the temperature in the system decreases.

  For example, when terephthalic acid is produced as an aromatic carboxylic acid, p-toluic acid with reduced 4CBA has higher solubility in water than terephthalic acid, and therefore terephthalic acid is preferentially precipitated in crystallization. However, when the pressure falls to atmospheric pressure, the temperature becomes about 100 ° C. and p-toluic acid is co-crystallized, so the final crystallization pressure is usually 0.1 MPa or more, preferably 0.2 MPa or more, more preferably 0.3 MPa or more, Particularly preferably, it is 0.5 MPa or more. The upper limit of the pressure range is preferably 3 MPa or less, more preferably 1 MPa or less, and particularly preferably 0.7 Pa or less. In addition, you may collect | recover the vapor | steam generate | occur | produced in the case of crystallization, and may reuse it in the manufacturing process of aromatic carboxylic acid.

When crystallization is performed in a plurality of crystallization tanks, the temperature of the first crystallization tank is preferably about 230 to 260 ° C. By setting the temperature to the same level as or slightly lower than the temperature of the hydrogenation reaction step, crystals having a high purity, a large particle size, and a uniform shape without distortion are obtained. The temperature of the second crystallization tank is preferably 20 ° C. or more lower than the temperature of the first crystallization tank, and more preferably 25 ° C. or less. Further, it is preferably 60 ° C. or lower, and preferably 55 ° C. or lower. By setting the temperature slightly lower than the temperature of the first crystallization tank, a crystal having a large particle size and a uniform shape without distortion is obtained. If necessary, a third and subsequent crystallization tanks may be provided, and the crystallization tanks are usually crystallized at substantially equal intervals up to 170 ° C. or less. As a result, crystals with high purity, large particle size, and uniform shape with no distortion are precipitated, so powder flowability and slurry properties (easy to make a good quality slurry when manufacturing polyester) An aromatic carboxylic acid crystal excellent in the above can be obtained.
In addition, when providing a crystallization process between the oxidation process and solid-liquid separation process mentioned above, it can also carry out as operation similar to the above.

Subsequently, the liquid composition X ′ that has undergone the crystallization step is subjected to solid-liquid separation using, for example, a solid-liquid separation device 113, washed with a washing device 114, and dried to obtain a high purity aromatic carboxylic acid crystal Y. can get. In addition, the method and apparatus in a solid-liquid separation process, a washing | cleaning process, and a drying process can be the same as that of the method and apparatus mentioned above. In FIG. 4, the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted here. The mother liquor R and the washing effluent U separated by the solid-liquid separator 113 are usually sent to a solvent recycling step, a discharging step, and the like after recovering valuable materials such as aromatic carboxylic acids, intermediates, and catalysts. Further, the mother liquor R may be recycled to the top of a distillation column directly connected to the oxidation reactor 111 of FIG. In FIG. 4, Q represents an aromatic carboxylic acid cake, and S represents a washed cake with a reduced impurity concentration.
Further, as a solid-liquid separation method of the liquid composition X ′, there is a method in which a mother liquor replacement tower is provided to replace the mother liquor in which the impurities are dissolved with the solvent L to facilitate the separation operation and then perform solid-liquid separation.

  In the method for producing an aromatic carboxylic acid according to the present invention, not all the steps described above are essential, but the aromatic carboxylic acid is generated in the oxidation reactor 111, transferred to the solid-liquid separation device 113, and the aromatic carboxylic acid is produced. What is necessary is just to isolate | separate carboxylic acid from a solvent. Moreover, you may provide apparatus and piping other than the above as needed.

[Exhaust gas treatment process]
The method for producing an aromatic carboxylic acid as described above preferably includes a treatment step for exhaust gas discharged in an oxidation step (including a supplemental oxidation reaction), a crystallization step, or the like. The exhaust gas treatment process will be described with reference to FIGS. 3 and 5 by taking the treatment process of the reaction gas M in the oxidation reactor 111 as an example.

  The reaction gas M extracted from the oxidation reactor 111 of FIG. 3 is discharged as the condenser exhaust gas O after the condensate N mainly composed of the solvent C is condensed and separated in the condenser 112 as described above. At this time, steam is generated in the condenser 112 by heat exchange. This steam can be applied to the cogeneration system in the present invention. That is, the generated steam is heated through a preheater (not shown) as necessary, and then introduced into the steam turbine 221 from the steam line 251 in FIG. As a result, the compressor 220 connected on the same shaft rotates, the air introduced from the air line 250 is compressed, and electric energy is generated by the generator 222 also connected on the same shaft. The compressed air is utilized as the molecular oxygen-containing gas B or B ′ in the oxidation step, and the electric energy is supplied to the aromatic carboxylic acid production process through the power line 253. Reference numeral 252 denotes a condensate line.

  On the other hand, the condenser exhaust gas O generally contains useful components such as aliphatic carboxylic acid used as a solvent for oxidation reaction, unreacted raw materials and oxygen, by-products, carbon monoxide and carbon dioxide. The exhaust gas O is usually at a high pressure, and usually after separation and recovery of these useful components contained, energy recovery such as pressure and heat, etc. are performed, it is burned in a combustion device and rendered harmless and released to the outside.

  First, the condenser exhaust gas O is introduced from the exhaust gas line 201 to the lower part of the absorption tower 211, and the solvent is supplied from the upper solvent line 202 to dissolve and absorb the aliphatic carboxylic acid and its esters in this solvent. Remove from. In addition, the solvent here does not mean the solvent C (solvent for oxidation reaction). The structure of the absorption tower 211 is not limited, and various types such as a packed tower, a spray tower, and a wet wall tower are used, and a packed tower is preferable. In addition, scrubbers can be used. Usually, water is used as a solvent for dissolution and absorption.

At the top of the column, the aliphatic carboxylic acid is first absorbed, and at the bottom of the column, the esters are dissolved and absorbed by the absorbed aliphatic carboxylic acid. As a result, the recovered aliphatic carboxylic acid ester-containing liquid is discharged through the tower bottom line 205, the recovered aliphatic carboxylic acid-containing liquid is discharged through the tower middle line 204, and the absorption tower outlet gas is discharged through the tower top line 203. The recovered aliphatic carboxylic acid ester-containing liquid is preferable when it is returned to the oxidation reaction step and reused, since further ester by-products can be suppressed.

When the solvent is water, the recovered aliphatic carboxylic acid-containing liquid is preferably reused by returning the aliphatic carboxylic acid to the oxidation reaction step after dehydration in a dehydration tower. The loss of the solvent in the oxidation process can be suppressed. An azeotropic distillation column may be used for dehydration or the like.
The absorption tower outlet gas still maintains a high pressure state, and it is preferable to recover and reuse the pressure energy. Examples of the recovery method include a method of recovering energy with various turbines after exhaust gas is combusted, and a method of combusting after recovering energy with a gas expander or the like. The latter is desirable in view of energy loss in the combustion treatment process, but the former is preferable from the viewpoint of improving energy efficiency by the cogeneration system.

That is, energy can be recovered from the high-pressure absorption tower outlet gas by the expander in the cogeneration system. Preferably, after heating to about 150 to 160 ° C. with the heat exchanger 212, the heat exchanger 212 introduces it into the expander (gas expander) 213 and rotates it. Thereby, it can apply to the cogeneration system in this invention. That is, the compressor 220 connected on the same shaft rotates and the air introduced from the air line 250 is compressed, and electric energy is generated by the generator 222 also connected on the same shaft. To the aromatic carboxylic acid production process.
As described above, the condenser exhaust gas O is separated and recovered from useful components, then burned by the combustion device, detoxified, and discharged to the outside. The combustor 2 in the cogeneration system also serves as the position of this combustion device. That is, since the combustion temperature in the combustor 2 of the gas turbine engine is very high as described above, harmful components such as methyl bromide contained in the condenser exhaust gas O can be rendered harmless.

  Since the outlet gas discharged from the expander 213 contains carbon monoxide, methyl bromide, and the like, it is discharged into the atmosphere after being processed by the combustion device 214 and the absorption device 215. As a combustion method in the combustion device 214, known methods such as a direct combustion method using no catalyst, a catalytic combustion method using a catalyst, and a heat storage combustion method using a heat storage body can be used, and among them, a heat storage combustion method is preferable. Combustion treatment can be performed on the low-concentration methyl bromide-containing exhaust gas while suppressing the generation of bromine-based dioxins, which has the advantage of reducing the environmental burden. In addition, the heat recovery rate is high, and it is not necessary to always use a combustion burner and there is no need to separately supply an oxygen-containing gas such as air. Therefore, there is an advantage that the operating cost, equipment cost, and energy used can be reduced.

  Since components such as bromine and hydrogen bromide usually remain in the outlet gas of the incinerator 214, it is desirable that the absorber 215 absorbs it in gas-liquid contact with an alkali and a reducing agent. Caustic soda, caustic potash and the like are preferably used as the alkali, and sodium sulfite, urea and the like are preferably used as the reducing agent, but it is not necessary to be limited thereto. The absorption tower can be a packed tower, a spray tower, a wet wall tower, or a scrubber. The outlet gas of the absorber 215 is discharged from the exhaust gas line 216 after confirming that it is in a state where it can be released into the atmosphere.

  As another exhaust gas treatment method, a distillation tower may be provided between the oxidation reactor 111 and the condenser 112 instead of providing the absorption tower 211. The solvent C-containing fraction obtained in the distillation tower is refluxed to the reactor 111, the tower top fraction mainly composed of water is cooled by the condenser and the condensed water is refluxed to the distillation tower, and the exhaust gas from the condenser is It can be used in the same manner as the condenser exhaust gas O. Also, steam generated by heat exchange in the condenser can be used in the same manner as described above.

The process in which the thermal energy and electrical energy supplied by the cogeneration system of the present invention are used is not limited to the process described above, and may be an aromatic carboxylic acid production process. For example, oxidation process, solid-liquid separation process, mother liquor recycling process, cake washing process, washing drainage recycling process, drying process, reduction process, crystallization process, waste treatment process, catalyst recovery process, catalyst regeneration process, wastewater treatment process Any of the exhaust gas treatment process and the like may be used, and it may be used in a plurality of processes.
Further, when combined with recovering and utilizing the heat and pressure energy used in these steps, the energy can be further effectively utilized and the energy utilization efficiency can be further enhanced.

  In summary, an example of an optimal method for producing an aromatic carboxylic acid according to the present invention is as follows. In other words, reaction heat is generated in the oxidation process, and the reaction heat becomes thermal energy and pressure energy of the slurry obtained in the oxidation process, and these energies are solid-liquid separation process, mother liquor recycling process, cake washing process, washing waste. It can be used for a liquid recycling process, a drying process, and the like. In addition, the small amount of heat energy that is deficient in each of these processes is compensated by a cogeneration system. Similarly, the heat energy and pressure energy of the liquid composition obtained in the reduction process should be used for the crystallization process, solid-liquid separation process, mother liquor recycling process, cake washing process, washing drainage recycling process, drying process, etc. The small amount of heat energy that is lacking in each of these processes can be compensated with a cogeneration system. Furthermore, thermal energy and / or pressure energy generated by heat recovery from exhaust gas generated in the oxidation process, crystallization process, and the like is recovered as electric energy by being reduced to a cogeneration system or a steam turbine. As a result, it is possible to minimize the energy required not only at the time of starting the equipment but also at the time of steady handling.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to a following example at all.
[Comparative Example 1]
Terephthalic acid was produced from p-xylene using a process having a production process shown in FIGS. 3 to 5 and a production amount of terephthalic acid of 75 tons / hour.

  In the reactor of FIG. 3, 1 part by weight of p-xylene, 2.5 parts by weight of a solution (solvent: acetic acid containing 14% by weight of water) containing catalyst (cobalt acetate, manganese acetate in acetic acid and hydrogen bromide), 6.3 parts by weight of the mother liquor that is recycled while substantially maintaining the pressure and temperature at the time of separation is supplied from the solid-liquid separator, and compressed air is used so that the molecular oxygen is 20-fold mol with respect to p-xylene. Then, an oxidation reaction was continuously performed while adjusting the liquid level so that the reaction time (average residence time) was 90 minutes at a temperature of 197 ° C. and a pressure of 1.45 MPa (absolute pressure). The concentration of cobalt / manganese / bromine in the reaction solution was 280/280/700 ppm by weight, respectively. The oxygen concentration in the reaction gas discharged from the reactor was adjusted to 1.5 to 3% by volume.

Next, the slurry extracted from the reactor was continuously transferred to the additional oxidation reactor, supplied with compressed air, and subjected to low temperature additional oxidation at a temperature of 185 ° C., a pressure of 1.25 MPa, and a reaction time of 35 minutes. The oxygen concentration in the reaction gas discharged from the additional oxidation reactor was adjusted to 1.5 to 3% by volume.
The slurry extracted from the additional oxidation reactor was transferred to a screen bowl decanter, which was a pressurized solid / liquid separation washing / drying apparatus, while maintaining the temperature and pressure, and solid-liquid separated into a terephthalic acid cake and a mother liquor. The solid-liquid separation pressure was 0.9 to 1.0 MPa, the temperature was 180 to 190 ° C., and the rotation speed was about 2050 rpm.

80% by weight of the mother liquor thus obtained was returned to the reactor 11, and the remaining 20% by weight was sent to the waste treatment step to recover valuable components and then discharged through the waste water treatment step.
On the other hand, the obtained terephthalic acid cake was washed with a washing liquid at 190 to 195 ° C. containing about 10% by weight of water with respect to acetic acid to obtain a washing cake and a washing waste liquid. A metal bar screen was used as the filter medium, the pressure was 0.9 to 1.0 MPa, and the temperature was 190 to 195 ° C. The obtained washing cake is held in a cake holding tank while maintaining a pressure of 0.9 to 1.0 MPa and about 180 to 190 ° C., and then the discharge valve is opened to be extracted into a normal-pressure powder residence tank, and the attached liquid The solution was evaporated under reduced pressure and dried to obtain a dewatered cake.

Next, the dewatered cake was subjected to the reduction step (hydrorefining process) shown in FIG. 4 for purification.
The dewatered cake was mixed with water to adjust the slurry concentration to 30% by weight, and then heated and pressurized to a temperature of 290 ° C. and a pressure of 8.5 MPa with steam and heat transfer oil, and then palladium was supported on activated carbon to The hydrogenation reaction column was introduced together with hydrogen to perform a hydrorefining reaction. After the reaction, the aqueous terephthalic acid solution was continuously transferred to a crystallization tank, and was sequentially cooled by releasing pressure in a four-stage crystallization step to cause crystallization. The slurry after crystallization was separated into a purified terephthalic acid cake and a mother liquor at 100 ° C. The mother liquor was discharged through the wastewater treatment process after recovering valuable components such as terephthalic acid and intermediates. The purified terephthalic acid cake was washed with water, dried by releasing pressure evaporation, and further dried by a fluidized bed dryer to obtain terephthalic acid crystals.

Further, the exhaust gases from the oxidation reactor and the additional oxidation reactor were integrated through a condenser, and processed as exhaust gas having a temperature of 45 ° C. and a pressure of 1.16 MPa in the exhaust gas treatment process shown in FIG.
That is, while supplying exhaust gas to the pressure absorption tower from the bottom of the tower, water was sprayed from the top of the tower to absorb acetic acid and the like in the exhaust gas, and further, methyl acetate and the like in the exhaust gas were dissolved and absorbed in the acetic acid and the like at the bottom of the tower. The absorbed methyl acetate was extracted from the bottom of the column as a recovered aliphatic carboxylic acid ester-containing liquid and returned to the reactor for reuse. Acetic acid and the like were extracted from the middle stage of the column as a recovered aliphatic carboxylic acid-containing liquid, dehydrated in a dehydration tower, and then returned to the reactor for reuse.

On the other hand, the gas that is the remainder of the exhaust gas exits from the top of the tower, is heated to 155 ° C. by a heat exchanger, is sent to an expander, is used as part of the driving power of the air compressor, and then is a gas having a pressure of 0.1 MPa. It became. This gas was introduced into a combustion device and an absorption device, confirmed to be harmless, and released to the atmosphere.
The above describes the main steps in the production of terephthalic acid, but includes other steps such as a vent gas treatment step, a catalyst recovery / regeneration step, and a solvent recovery step.

  As an energy supply system for these processes, electric energy is generated by in-house power generation using a diesel engine. Regarding thermal energy, process steam was generated by a heavy oil-fired steam boiler, and hot oil heated by a heavy oil-fired boiler was used as the heat transfer oil.

[Example 1]
As an energy supply system, terephthalic acid is produced in the same manner as in Comparative Example 1 except that the following operation is performed using the cogeneration system shown in FIG.
A cogeneration system using a gas turbine engine with a power generation end output of 17 MW is used, and heavy oil is used as fuel. A cogeneration system is started and electric energy is generated by a generator in the system. At the same time, a duct burner is installed in the exhaust gas duct discharged from the expander, and the hot exhaust gas obtained is introduced into the boiler to produce hot oil with an outlet temperature of 320 ° C., and the exhaust gas at the boiler outlet is heated. It introduce | transduces into an exchanger and obtains 0.15MPa vapor | steam and 0.7MPa vapor | steam.

By supplying the thermal energy and electric energy thus obtained to the terephthalic acid production process, terephthalic acid can be produced on the same scale as Comparative Example 1. The ratio of heat energy: electric energy supplied in this example is about 75:25 (converted to kilowatt hours).
Assuming that the total amount of energy supply during steady operation of Comparative Example 1 is 100, the total amount of energy supply during steady operation of Example 1 is about 80. That is, the amount of heat used can be reduced by the amount of heat compared to Comparative Example 1, and the amount of fuel consumption and the amount of carbon dioxide generated can be reduced by 20%. Furthermore, by switching the fuel from heavy oil to natural gas, the amount of carbon dioxide generated can be reduced by 30% or more compared to Comparative Example 1.

[Example 2]
As the energy supply system, terephthalic acid is produced in the same manner as in Comparative Example 1 except that the following operation is performed using the cogeneration system shown in FIG. 2 and the exhaust gas treatment system and the steam turbine shown in FIG.
A cogeneration system using a gas turbine engine with a power generation end output of 17 MW is used, and methane is used as fuel. Rotational energy and heat energy are generated from an expander of a gas turbine engine. The rotational energy rotates the compressor, introduces compressed air into the oxidation reactor, and introduces it into a generator installed on the same axis. Power is generated and power is supplied to the entire manufacturing process. On the other hand, heat energy is exhausted by installing a duct burner in the duct of the exhaust gas discharged from the expander, and the resulting high-temperature exhaust gas is introduced into the boiler to generate hot oil with an outlet temperature of 320 ° C. In the exhaust gas, residual energy is used for preheating compressed air and exhaust gas in a heat exchanger.
Reaction heat generated in the oxidation reaction caused by the compressed air introduced into the oxidation reactor is absorbed by a solvent such as acetic acid that evaporates, and high-pressure steam is generated by heat exchange in the condenser directly connected to the reactor. The generated high-pressure steam rotates the steam turbine and compresses air or the like used for the oxidation reaction in the compressor. At the same time, a generator connected on the same axis is rotated to recover electrical energy and reuse it in the manufacturing process.

By supplying the thermal energy and electric energy thus obtained to the terephthalic acid production process, terephthalic acid can be produced on the same scale as Comparative Example 1. In addition, the energy balance in a present Example is 57:43 in the ratio of the supplied thermal energy and electrical energy.
Assuming that the total energy supply amount in the steady operation of Comparative Example 1 is 100, the total energy supply amount in the steady operation of Example 2 is about 95. This is a fuel consumption of 5% and carbon dioxide emission. The amount can be reduced by 5%. As a result, about 10,000 tons of carbon dioxide can be reduced annually. In addition to reducing the amount of energy supplied, the replacement of heavy oil with methane is also added, resulting in significant carbon dioxide suppression. Moreover, it can be set as the process which does not perform the electric power supply from the outside except having supplied the electric power to the electric motor for starting a compressor. The total energy supply amount is higher than that in the first embodiment because the electric energy ratio is higher than that in the first embodiment.

DESCRIPTION OF SYMBOLS 1 Compressor 1a Compressor starting motor 2 Combustor 3 Expander (turbine)
4 Gas Turbine Engine 5 Generator 6 Absorption Refrigerator 7 Boiler 8 Oil Supply Tank 9 Heat Exchanger 11 Air Line 12 Fuel Line 13 Power Lines 14, 17, 20 Exhaust Line 15, 15 ′ Water Line 16, 16 ′ Steam Line 18, 19 Heat transfer oil line 111 Oxidation reactor 111 ′ Additional oxidation reactor 112 Condenser 113 Solid-liquid separation device 114 Cleaning device 115 Solid-liquid separation and cleaning device 116 Drying device 117 Solid-liquid separation cleaning and drying device 118 Heating and drying device 119 Disposal Process 120 Mother liquor tank 121 Cleaning drainage tank 125 Hydrogenation reactor 126 Crystallization tank 201 Exhaust gas line 202 Solvent line 203 Tower top line 204 Tower middle line 205 Tower bottom line 211 Absorption tower 212 Heat exchanger 213 Expander (gas expander) )
214 Combustion device 215 Absorption device 216 Exhaust gas line 220 Compressor 221 Steam turbine 222 Generator 250 Air line 251 Steam line 252 Condensation line 253 Power line A Alkyl aromatic compound B, B ′ Molecular oxygen-containing gas C Solvents D, D 'Slurry E Aromatic carboxylic acid cake F Mother liquor G Cleaning cake H Cleaning liquid J Cleaning drainage K, K' Aromatic carboxylic acid crystals M, M 'Reactive gas N Condensate O Condenser exhaust gas P Solvent Q Aromatic carboxylic acid cake R Mother liquor S Wash cake T Wash liquid U Wash drain W Hydrogen X, X 'Liquid composition Y, Y' Aromatic carboxylic acid crystals

Claims (6)

A process of oxidizing an alkyl aromatic compound to produce an aromatic carboxylic acid, and separating and recovering the generated aromatic carboxylic acid from the alkyl aromatic compound and / or an aromatic obtained by oxidizing the alkyl aromatic compound A method for producing an aromatic carboxylic acid comprising a step of reducing a carboxylic acid,
An aromatic carboxylic acid characterized in that at least part of the energy used in one or more steps of the group of steps is supplied by a cogeneration system that generates thermal and electrical energy by combustion of fuel. Production method.   The method for producing an aromatic carboxylic acid according to claim 1, wherein the ratio of thermal energy to the total amount of thermal energy and electrical energy supplied by the cogeneration system (kilowatt hour conversion) is in the range of 30% to 90%. .   The method for producing an aromatic carboxylic acid according to claim 1 or 2, wherein the thermal energy is used for raising a temperature of a heat transfer oil used in one or more steps of the step group and / or generating steam.   The method for producing an aromatic carboxylic acid according to claim 3, wherein at least a part of the steam generated by the thermal energy is introduced into a steam turbine and used for generating electric energy. The cogeneration system comprises a gas turbine engine and a generator;
The gas turbine engine is the same as the combustor that burns fuel to generate combustion gas, the compressor that sucks and compresses oxygen-containing gas from outside the system, and the compressor and the generator An expander that is on an axis and expands the combustion gas to rotate the shaft;
The manufacturing method of aromatic carboxylic acid of any one of Claims 1-4 in which the said generator produces | generates an electrical energy by rotation of the said axis | shaft, and obtains a thermal energy from the waste gas of the said expander. The method for producing an aromatic carboxylic acid according to claim 5, comprising at least one of the following methods.
(1) At least a part of the exhaust gas generated in the oxidation step is supplied to the expander.
(2) Steam is generated by heat exchange from the exhaust gas generated in the oxidation step, and at least a part of the generated steam is supplied to the steam turbine.
(3) The oxygen-containing gas compressed by the compressor is supplied to the oxidation process.
(4) The exhaust heat generated from the generator is used as thermal energy used in one or more processes of the process group.

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