JP2009227623A - Method for producing aromatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for transporting a mother liquor obtained in a solid-liquid separation process in a pressurized state to an oxidation process without closing a transport piping in a method for producing an aromatic carboxylic acid. <P>SOLUTION: The method for producing an aromatic carboxylic acid at least comprises an oxidation process for oxidizing an alkyl aromatic compound in a solvent in a reactor in a pressurized state to form an aromatic carboxylic acid, a solid-liquid separation process for extracting the slurry containing the aromatic carboxylic acid and the solvent from the reactor, carrying out solid-liquid separation by a solid-liquid separation apparatus in a pressurized state and obtaining an aromatic carboxylic acid cake and a mother liquor, and a liquid transport process for transporting the mother liquor-containing liquid (I) to the reactor while maintaining the liquid in the pressurized state. The liquid (I) is heated in the liquid transport process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  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, p-xylene is pressurized with a gas containing molecular oxygen in the presence of a heavy metal catalyst mainly composed of cobalt and manganese and a bromine compound in an acetic acid solvent. A method for producing terephthalic acid by liquid phase oxidation is industrially carried out.

In recent years, proposals for reducing the amount of energy used have been made in consideration of the environmental aspect and cost. For example, Patent Documents 1 and 2 propose that a slurry containing terephthalic acid is subjected to solid-liquid separation under pressure to obtain terephthalic acid, and the mother liquor is returned to the oxidation step and reused.
International Publication No. 2004-043893 (US2006-014799) International Publication No. 2000-058257

As proposed in Patent Document 2, it is considered that the amount of energy used can be reduced by returning to the oxidation step while maintaining the temperature and pressure of the mother liquor separated into solid and liquid under pressure. However, industrially, an unintentional release pressure gradually occurs during the transfer from the solid-liquid separation process to the oxidation process, and there is a possibility that a dissolved material such as terephthalic acid is deposited in the pipe and clogs the pipe.
Since the mother liquor that has been subjected to solid-liquid separation is usually in a saturated solution state such as terephthalic acid, when the temperature drops due to the pressure release, crystals easily precipitate and accumulate, which closes the piping. In that case, it is necessary to stop the operation and remove the contents, and the stable operation is hindered. Therefore, in order to use the above technique practically, it is a problem to prevent the occurrence of such blockage.

  An object of the present invention is to provide a technique for transferring a mother liquor obtained in a pressurized solid-liquid separation step to an oxidation step without clogging a transfer pipe in a method for producing an aromatic carboxylic acid.

  The gist of the present invention is that an oxidation step in which an alkyl aromatic compound is oxidized in a solvent to produce an aromatic carboxylic acid in a pressurized reactor, and a slurry containing the aromatic carboxylic acid and the solvent is added to the reactor. The solid-liquid separation process for obtaining an aromatic carboxylic acid cake and a mother liquor by performing solid-liquid separation in a pressurized state with a solid-liquid separator and maintaining the pressurized state of the liquid (I) containing the mother liquor A process for producing an aromatic carboxylic acid comprising at least a liquid transfer step for transferring to the reaction apparatus as it is, wherein the liquid (I) is heated in the liquid transfer step. Lies in the way.

It is preferable that the liquid heating means is provided in at least a part of the pipe in the liquid transfer step, and it is more preferable that the liquid heating means is provided in 70% or more of the surface area of the pipe. Moreover, it is preferable that a liquid heating means heats piping with a heat medium 5-250 degreeC higher than the temperature of liquid (I).
In the liquid transfer step, it is preferable to transfer 50 to 100% by weight of the mother liquor obtained in the solid-liquid separation step to the reaction apparatus.

Preferably, the method further includes a washing step of washing the aromatic carboxylic acid cake in a pressurized state, and in the liquid transfer step, the liquid (I) contains at least a part of the washing waste liquid obtained in the washing step.
Alternatively, it further includes a washing step for washing the aromatic carboxylic acid cake in a pressurized state, and in the liquid transfer step, the liquid (II) containing the washing drainage liquid obtained in the washing step is supplied to the reactor while maintaining the pressurized state. In transferring, it is preferable to heat the liquid (II).

  In the liquid transfer step, it is preferable to transfer 60 to 100% by weight of the cleaning waste liquid obtained in the cleaning step to the reactor. Moreover, it is preferable that the temperature of the washing | cleaning liquid used for washing | cleaning in a washing | cleaning process is the range of -100- + 100 degreeC with respect to slurry temperature.

According to the present invention, in the aromatic carboxylic acid production method, the mother liquor obtained in the pressurized solid-liquid separation step can be transferred to the oxidation step without blocking the transfer pipe. For this reason, there is no need to frequently stop the operation and remove the contents, and a stable operation can be performed for a long time.
According to the present invention, the technology for returning the mother liquor separated into solid and liquid under pressure to the oxidation step while maintaining the pressurized state can be industrially applied. As a result, the amount of heat required for reheating the mother liquor can be reduced, and the decrease in catalyst activity can be suppressed, so that the amount of energy used in the aromatic carboxylic acid production plant can be reduced.

An embodiment is shown and demonstrated about the manufacturing method of aromatic carboxylic acid of this invention.
As a method for producing aromatic carboxylic acid, there are an oxidation step in which an alkyl aromatic compound is oxidized in a solvent in a pressurized reactor to produce an aromatic carboxylic acid, and a slurry containing the aromatic carboxylic acid and the solvent. After extracting from the reactor, solid-liquid separation is performed in a solid-liquid separation device in a pressurized state to obtain an aromatic carboxylic acid cake and a mother liquor, and the liquid (I) containing the mother liquor is in a pressurized state. It can be set as the process at least including the liquid transfer process which transfers to a reaction apparatus, maintaining.

Hereinafter, the first embodiment of the method for producing an aromatic carboxylic acid will be described in detail with reference to 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.
First, the oxidation process will be described. The raw material alkyl aromatic compound A is introduced into the reactor 11, and the alkyl aromatic compound A is oxidized with the molecular oxygen-containing gas B in the solvent C to produce an aromatic carboxylic acid, which is a mixture with the solvent. 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 particularly limited.

  The type of the aromatic carboxylic acid to be produced is not particularly 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. It is done.

The alkyl aromatic compound A is oxidized by the molecular oxygen-containing gas B. 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.
When oxidizing alkyl aromatic compound A, a catalyst is preferably 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 can be promoted, but is usually 10 ppm or more, preferably 100 ppm or more as the heavy metal concentration in the solvent. On the other hand, the heavy metal concentration is usually 10,000 ppm or less, preferably 5000 ppm or less. By setting it to the lower limit or higher, the reaction rate increases, and by setting it to the upper limit or lower, the cost can be suppressed and the heavy metal concentration and bromine concentration in the effluent and exhaust gas can be reduced, which is preferable in terms of environment and safety.

  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 specifically 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 it to the upper limit or less, and the combustion decomposition of acetic acid can be further reduced by setting it to the lower limit or more.

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 of the reactor 11 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. Moreover, it is preferable that the pressure of the reactor 11 is high also in order to make it easy to transfer the slurry after the reaction to the solid-liquid separator. On the other hand, the pressure is usually 20 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 reactor 11 is usually 100 ° C. or higher. Preferably it is 140 degreeC or more, More preferably, it is 150 degreeC or more. The higher the lower limit, the higher the reaction rate and the higher the yield. The temperature is usually 400 ° C. or lower. Preferably it is 250 degrees C or less, More preferably, it is 230 degrees C or less. The lower the upper limit value, the smaller the amount of loss due to solvent combustion. Further, there is an advantage that side reaction and decomposition of the compound can be suppressed, and a decrease in yield can be suppressed.

The oxidation reaction is preferably performed continuously because production efficiency is increased.
The kind of the reactor 11 is not specifically limited, For example, any may be sufficient, such as a reactor with a stirrer, a bubble column reactor, a plug flow type (pipe flow type) reactor. In order to increase the reaction efficiency, it is preferable to use a complete mixing tank reactor with a stirrer.
The lower part of the reactor 11 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 of the oxygen-containing gas B is used. The reaction gas M containing the solvent C vapor is withdrawn from the top of the reactor 11.

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 12 as necessary. The condenser 12 may be a single stage or a plurality of stages.
The supply amount and oxygen concentration of the molecular oxygen-containing gas B are such that the oxygen concentration in the condenser exhaust gas O (when the condenser 12 is composed of a plurality of stages, the exhaust gas of the final stage condenser is the condenser exhaust gas O). It is preferable to control to be 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. The higher the lower limit value, the higher the reaction efficiency. Moreover, it controls so that it may become 10 volume% or less preferably, more preferably 7 volume% or less. Safety is improved by making it lower than the upper limit value.

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 reactor 11. 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 reactor 11.
When an aliphatic carboxylic acid such as acetic acid is used as the solvent C, the water concentration of the solvent C in the reactor 11 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 12. A distillation column capable of separating an aliphatic carboxylic acid and water is connected to the reactor 11, and the reaction gas M generated in the reactor 11 is distilled in the distillation column. The aliphatic carboxylic acid having a reduced water concentration obtained from the bottom of the tower is recovered in the reactor 11 and the water-containing component obtained from the top of the tower is purged out of the system, for example. Can be adjusted.

After the oxidation reaction in the reactor 11, additional oxidation treatment may be performed as necessary. In the additional oxidation treatment, the reaction mixture obtained by the oxidation reaction in the reactor 11 is oxidized by supplying the molecular oxygen-containing gas B ′ without supplying the alkyl aromatic compound A in the additional oxidation reactor 11 ′. Is to process.
As a preferred example of the additional oxidation treatment, the additional oxidation treatment is performed on the reaction mixture obtained in the reactor 11 in the additional oxidation reactor 11 ′ held at a lower temperature (hereinafter referred to as “low temperature additional oxidation”). If the alkyl aromatic compound A is p-xylene, the temperature of the additional oxidation reactor 11 ′ is preferably 1 ° C. or more lower than the reactor 11 and 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 it as 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 setting it as below an upper limit.

  As another preferred example of the additional oxidation treatment, the reaction mixture obtained in the reactor 11 is subjected to additional oxidation treatment in the additional oxidation reactor 11 ′ 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 11 ′ is preferably higher than the reactor 11 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 it as 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 setting it as below an upper limit.

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 11 ′ 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. 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 saved. The pressure is preferably 10 MPa or less, more preferably 5 MPa or less, and still more preferably 2 MPa or less. In order to efficiently introduce the slurry D from the reactor 11 into the additional oxidation reactor 11 ′, it is desirable that the pressure be lower than that in the reactor 11.

The type and concentration of the molecular oxygen-containing gas B ′ supplied for performing the additional oxidation treatment are the same as those in the description of the molecular oxygen-containing gas B, and will be omitted. The reaction gas M ′ discharged from the additional oxidation reactor 11 ′ contains oxygen and solvent C vapor, and is usually sent to a condenser or a distillation column.
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.

Although the kind of reactor which performs an additional oxidation process is not specifically limited, For example, the reactor of the same type as the reactor 11 etc. can be used. Other conditions for the additional oxidation treatment are the same as in the oxidation in the reactor 11.
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 reactor 11 or the additional oxidation reactor 11 ′. 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.

  Hereinafter, for the sake of convenience, a case will be described in which the reaction apparatus includes only the reactor 11, and the slurry D extracted from the reactor 11 is the slurry extracted from the reaction apparatus. However, this explanation is similarly applied to the case where the reaction apparatus includes the reactor 11 and the additional oxidation reactor 11 ′, and the slurry D ′ extracted from the additional oxidation reactor 11 ′ is a slurry extracted from the reaction apparatus. Is done.

  Next, the solid-liquid separation process will be described. The slurry D is transferred to the solid-liquid separator 13 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 reactor 11 and the solid-liquid separation device 13 to adjust the pressure of the slurry D as appropriate, but the pressurized state from the reactor 11 to the solid-liquid separation device 13 is maintained. It is preferable to transport while maintaining.

  The solid-liquid separator 13 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. Moreover, 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 a pressurized state and recycled as a solvent in a liquid transfer step described later. The handling of the mother liquor F will be described in detail later.

  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. By using a lower pressure, a device with a slightly lower pressure resistance can be used, and costs can be reduced. The pressure is 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.

  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 separator 13 without limitation. For example, a centrifuge 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.
The aromatic carboxylic acid cake E obtained by the solid-liquid separator 13 may be dried as it is, but if it is washed by the washing device 14, 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 14, the aromatic carboxylic acid cake E is washed with the washing liquid H, and the mother liquor adhering to the cake is removed to obtain a washing cake G in which the impurity concentration is reduced. The washing liquid H used for washing may be water or an organic solvent, and is not particularly limited, but is preferably compatible with the solvent C used in the reactor 11. 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 14 is a pressurized state similar to the pressure of the solid-liquid separation device 13. 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. In addition, since the pressurized washing waste liquid J 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 a pressurized state and recycled as a solvent in the liquid transfer step described later. is there. The handling of the cleaning effluent J will be described in detail later. 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.

When solid-liquid separation and washing are performed under pressure, the washing cake G is preferably dried by the drying device 16 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 16 or a plurality of the same or different devices.
The type of the drying device 16 is not particularly limited, but preferably a device that releases the attached liquid adhering to the cleaning cake G by releasing the pressure by moving the cleaning cake G from the high pressure state to the low pressure state, a so-called flash drying device. It is preferable to include. Relief pressure evaporation means that a liquid in a high pressure state is suddenly moved to a low pressure state where the temperature before the transition is equal to or higher than the boiling point of the pressure after the transition, and a part of the liquid is evaporated using its internal energy as the heat of vaporization. Say to do. According to this, since the washing cake G can be dried without adding further energy, it is preferable to evaporate as much of the adhering liquid as possible by releasing pressure evaporation in terms of energy cost saving.

  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. 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 15 (corresponding to 15 surrounded by a broken line 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 17 (corresponding to a broken line 17 in the figure) which can perform 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 has excellent heat resistance and can be used in a high temperature range close to the temperature of the reactor 11.

When the aromatic carboxylic acid crystals K thus obtained are insufficiently dried, it is preferable to provide a heating and drying device after the drying device 16 and further perform drying. The type of the heat drying apparatus is not particularly limited, but from the viewpoint of drying efficiency and cost, a fluidized bed drying apparatus (Fluidized Bed Dryer), a rotary drying apparatus (such as a steam tube dryer) is preferably used.
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 aromatic carboxylic acid crystal K obtained by the above-described steps is dissolved in a solvent such as water, and at least a part of impurities contained in the aromatic carboxylic acid crystal is reduced with a reducing agent such as hydrogen. For example, when producing terephthalic acid as an aromatic carboxylic acid, 4CBA contained in the terephthalic acid crystal is reduced and converted to p-toluic acid. Preferably, a hydrogenation catalyst containing a group 8-10 metal such as ruthenium, rhodium, palladium, platinum, osmium, or the like is used.

Thereafter, the obtained reaction product is crystallized mainly from an aromatic carboxylic acid in a crystallization tank, if necessary, and then separated into solid and liquid, and washed and dried as necessary to obtain a purity. A highly aromatic carboxylic acid crystal is obtained.
The method for producing an aromatic carboxylic acid according to the present invention does not require all the steps described above. The aromatic carboxylic acid is generated in the reactor 11 and transferred to the solid-liquid separation device 13, and the aromatic carboxylic acid is removed from the solvent. And the mother liquor may be transferred to the oxidation step. Moreover, you may provide apparatus and piping other than the above as needed.

  Next, the liquid transfer process will be described. The mother liquor F obtained by the solid-liquid separator 13 is usually once accumulated in the mother liquor tank in the solid-liquid separator 13 and then recovered in the mother liquor tank 20, but the main component of the mother liquor F was used for the reaction. The solvent further includes dissolved aromatic carboxylic acid, unreacted alkyl aromatic compound, catalyst, by-product, water and the like. For this reason, when at least a part of the mother liquor F is transferred to the reactor 11 as the liquid (I), the solvent, unreacted raw materials, and catalyst can be reused, and the cost can be reduced. Moreover, the yield of the whole process can be raised by returning the aromatic carboxylic acid contained in a reaction system. In the present invention, solid-liquid separation is performed under pressure, and the liquid (I) containing the mother liquor F is transferred to the reactor 11 while maintaining the pressurized state. it can. The pressure in the liquid transfer process is desirably substantially the same as the pressure in the solid-liquid separation process.

  In addition, the cleaning drainage liquid J obtained by the cleaning device 14 can be once accumulated in the cleaning drainage tank in the cleaning device 14 and then collected in the cleaning drainage tank 21. The cleaning waste liquid J contains dissolved aromatic carboxylic acid, unreacted alkyl aromatic compound, catalyst, by-product, water, and the like at a lower concentration than the mother liquor F. For this reason, it is preferable that at least a part of the washing waste liquid J is transferred to the reactor 11 as the liquid (I) because the solvent, unreacted raw materials and catalyst can be reused. Moreover, the yield can be increased by returning the aromatic carboxylic acid contained in the reaction system, which is preferable. When washing is performed under pressure, it is preferable that the washing waste liquid J is transferred to the reactor 11 while maintaining the pressurized state because energy for repressurization and reheating can be saved.

The mother liquid tank 20 and the cleaning drain tank 21 may be combined into one mother liquid / cleaning drain tank. In that case, the transfer to the reactor 11, the reuse of the solvent, the unreacted raw material and the catalyst, and the transfer to the disposal process step 23 and the disposal can be performed together.
When liquid (I) is transferred to the reactor, it may be transferred to any reactor in the reactor. However, in order to increase the reaction efficiency, it is preferably transferred to the most upstream reactor.

  In the present invention, the liquid transfer step refers to the period from the point at which the mother liquor F is discharged from the solid-liquid separation step 13 to the reactor 11. The liquid transfer step is mainly composed of the pipe 22, and when the mother liquid tank 20 or the like is included in the middle, this is also regarded as a broad pipe. In the present invention, the liquid (I) is heated in the liquid transfer step. As a result, even when an unintentional release pressure or the like occurs in the transferred liquid (I), the liquid temperature can be prevented from lowering, and the piping is blocked due to the precipitation of dissolved aromatic carboxylic acids and by-products. Can be prevented. Accordingly, the process can be operated continuously and stably. Moreover, the fall of the liquid temperature introduce | transduced into a reaction apparatus is suppressed, the amount of energy for repressurization or reheating can be reduced, without giving a bad influence on reaction.

In heating the liquid (I), it is preferable to provide a liquid heating means at least in a part of the pipe for the liquid transfer process.
The material of the pipe 22 in the liquid transfer process is not particularly limited, and titanium, nickel, aluminum, alloy steel pipe, carbon steel, stainless steel, and the like are used, but titanium is most preferable from the corrosion resistance.

  The outer diameter of the pipe 22 is not particularly limited, but it is preferably 1 inch or more because blockage hardly occurs. Further, it is preferably 20 inches or less, more preferably 15 inches or less, and further preferably 10 inches or less. The temperature difference between the center of the liquid flowing in the pipe and the periphery of the pipe wall can be kept small, and the heating of the pipe is easily transmitted. The length of the pipe 22 is also not particularly limited, but is preferably 0.5 m or more, more preferably 5 m or more, and even more preferably 10 m or more. The degree of freedom of equipment layout increases. Moreover, Preferably it is 100 m or less, More preferably, it is 80 m or less, More preferably, it is 70 m or less. There are advantages such that the heating line is short, unnecessary heating is unnecessary, and the temperature of the liquid flowing in the piping is less likely to decrease.

Hereinafter, the heating method will be described in detail. The heating means is not simply a means for covering with a heat insulating material, a heat insulating material or the like, and heat having a temperature substantially higher than the liquid temperature in the pipe 22 during the liquid transfer process is applied from the outside. However, you may use together a heat insulating material, a heat insulating material, etc.
The heating means is not particularly limited. For example, as a method of heating using a heat medium, a method in which a heat pipe is installed inside the pipe 22 and heated from the inside through the heat medium (inner trace method), the outside of the pipe 22 is used. Heat pipe installed on the outside and heated from the outside through a heat medium (outer trace method), heat pipe having the same circle center is installed outside the pipe 22 to form a double pipe and the outside through the heat medium from the outside And heating method (double piping method). As a method of heating by electricity, a method of directly supplying current to the pipe 22 itself and heating the entire pipe as a heating element (direct method), energizing along the insulated wire to the pipe 22 and heating with Joule heat of the lead wire Examples thereof include a method (indirect method), a method in which an insulated conductor is wound around the pipe 22 and energized and heated by an induced current (intermediate method). Examples of other methods include a method of heating by heat exchange with a high-temperature slurry discharged from the reaction apparatus (slurry heat exchange method).

From the viewpoint of safety and cost, a heating method using a heating medium is preferable, and an outer trace method is most preferable. The amount of heat medium required is small, and if a heat insulating material is used in combination, the heating efficiency can be further increased.
As the heat medium, for example, heat medium oil, solvent, hot water, steam, air, and the like can be used, but heat medium oil is preferable. Examples of the heat transfer oil include organic, inorganic, silicone, fluorine, and mineral oils, and an organic heat transfer oil is preferable. It has high thermal stability, can be used in 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 and NeoSK-OIL (both manufactured by Soken Techniques Co., Ltd.).

  A heating medium having a temperature substantially higher than the temperature of the liquid (I) in the pipe 22 is used. The temperature of the heating medium is preferably 5 ° C. or higher, more preferably 20 ° C. or higher, and even more preferably 25 ° C. or higher than the temperature of the liquid (I). There is an advantage that solid content is difficult to be precipitated in the pipe 22. Moreover, it is preferable that the temperature of the heat medium usually does not exceed 250 ° C. higher than the temperature of the liquid (I). More preferably, it does not exceed 220 ° C. above the temperature of the liquid (I), and more preferably does not exceed 200 ° C. There is an advantage that the temperature of the liquid (I) is not increased unnecessarily and inactivation due to solvent burning or catalyst oxidation hardly occurs.

The material of the pipe through which the heat medium passes (heat medium pipe) is not particularly limited, and titanium, nickel, aluminum, alloy steel pipe, carbon steel, stainless steel, etc. are used, but stainless steel is most preferable from the viewpoint of corrosion resistance and thermal conductivity. .
When the outer trace method is used, one or more such heat medium pipes are provided around the pipe 22. Preferably two or more are provided. This is for heating the liquid (I) more evenly. However, it is usually 6 or less, and 4 or less are preferable. The outer diameter of the heat medium pipe is preferably 0.5 inches or more because heating efficiency is high and clogging is unlikely to occur. Further, it is preferably 10 inches or less, more preferably 8 inches or less, and further preferably 5 inches or less. The temperature difference between the central portion of the liquid flowing in the heat medium pipe and the pipe wall periphery can be kept small.

  In the outer trace method and the double piping method, it is preferable to cover the periphery of the heat medium piping with a heat insulating material. As the heat insulating material, for example, known materials such as glass wool, rock wool, calcium silicate, lightweight calcium silicate, extruded polystyrene foam, and rigid urethane foam can be used. Preferably, rock wool or calcium silicate is used. The thickness of the heat insulating material is preferably 10 mm or more, more preferably 20 mm or more. However, it is preferably 100 mm or less, more preferably 90 mm or less, and still more preferably 80 mm or less. The heat medium is not easily allowed to cool, the liquid (I) pipe is easily heated sufficiently, and is in an economically appropriate range.

  The liquid heating means may be provided so that at least a part of the pipe in the liquid transfer step is heated, but it is preferable to provide the liquid heating means on 70% or more of the surface area of the pipe. More preferably, it is 80% or more, more preferably 90% or more, and most preferably 100%. The whole can be heated uniformly, and the temperature distribution of the liquid (I) can be suppressed. If there are tanks etc. in the middle of the liquid transfer process, they are also included in the piping.

Since the temperature tends to decrease as the transfer distance of the liquid (I) increases, it is preferable to provide the liquid heating means so that the portion close to the reaction apparatus is particularly heated.
It is preferable that at least 1% or more of the surface area of the pipe 22 is heated by the liquid heating means as described above, more preferably 5% or more, and even more preferably 10% or more. Most preferably, it is 100%. The whole can be heated uniformly and the temperature distribution of the liquid (I) can be suppressed.

  In general, the skin temperature of the pipe (outer surface temperature of the pipe) in the liquid transfer step is preferably substantially higher than the temperature of the liquid (I). More preferably, it is higher than the temperature of the liquid (I) by 0.01 ° C. or higher, more preferably higher than the temperature of the liquid (I) by 0.1 ° C. or higher, particularly preferably higher than 1 ° C. There is an advantage that solid content is difficult to be precipitated in the pipe 22. Moreover, it is preferable that piping skin temperature does not become high temperature normally exceeding 100 degreeC rather than the temperature of liquid (I). More preferably, it does not exceed 50 ° C. above the temperature of the liquid (I), and more preferably does not exceed 30 ° C. There is an advantage that the temperature of the liquid (I) is not increased unnecessarily and inactivation due to solvent burning or catalyst oxidation hardly occurs.

  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 step 23 and discarded after treatment, and the remainder is sent as a recycled mother liquor to the reactor 11. be able to. The disposal process 23 includes, for example, a solvent evaporation process and a catalyst recovery process. The ratio (recycle rate) of the mother liquor transferred to the reactor is represented by {recycle mother liquor weight × 100 / (recycle mother liquor weight + purge mother liquor weight)}. The recycle rate is preferably 50% by weight or more, more preferably 60% by weight or more, and still more preferably 70% by weight or more. The reuse rate of valuable components in the mother liquor is increased, the load of the disposal process is reduced, and the amount of waste can be reduced. The recycling rate may be 100% by weight, preferably 90% by weight, and more preferably 80% by weight. Accumulation of impurities in the process can be suppressed, and the quality of the product aromatic carboxylic acid can be improved.

  Even when the cleaning effluent J is transferred to the reactor, in order to avoid accumulation of impurities such as by-products and catalysts in the process, a part of the cleaning effluent J is used as the purge cleaning effluent to the disposal process step 23. It can be sent and discarded after processing, and the remainder can be sent to the reactor 11 as recycled cleaning waste liquid. The recycling rate of the cleaning waste liquid J is represented by {recycle cleaning waste liquid weight × 100 / (recycle cleaning waste liquid weight + purge cleaning drain weight)}, preferably 60% by weight or more, and more preferably 75% by weight or more. The reuse rate of valuable components in the washing effluent is increased, the load of the disposal process is reduced, and the amount of waste can be reduced. The recycling rate may be 100% by weight.

  The liquid (I) may contain at least a part of the washing drainage J in addition to the mother liquor F. Both can be mixed and transferred to simplify piping. Mixing may be performed in a pipe, or an intermediate tank may be provided for mixing. The mixing ratio is preferably 40 parts by weight or more, more preferably 60 parts by weight or more, and still more preferably 75 parts by weight or more with respect to 100 parts by weight of the mother liquor. Since the washing effluent usually has a low concentration of aromatic carboxylic acid or the like, mixing this has the advantage that solid analysis does not easily occur due to the temperature drop of the liquid (I). Further, the washing drainage is usually 150 parts by weight or less, preferably 130 parts by weight or less, and more preferably 110 parts by weight or less with respect to 100 parts by weight of the mother liquor. When the temperature of the cleaning waste liquid J is low, the temperature drop of the liquid (I) can be suppressed. Further, since the concentration of unreacted raw materials, intermediates, and catalyst components in the liquid (I) is high, it can be reused efficiently by transferring a small amount of liquid.

  When the cleaning waste liquid J is transferred to the reactor, the temperature of the cleaning liquid H used for cleaning in the cleaning step is within a range of −100 to + 100 ° C. with respect to the temperature of the slurry D in order to keep the temperature within a certain preferable range. Preferably there is. That is, it is preferable that the temperature of the cleaning liquid H is not higher than 100 ° C. with respect to the temperature of the slurry D. This is for reducing the energy of pressurization and heating in the reactor. In addition, when the liquid (I) is mixed with the mother liquor F, the liquid temperature is hardly lowered even if the amount of the cleaning waste liquid J is increased. More preferably, it is not a low temperature exceeding 70 ° C. with respect to the temperature of the slurry D, more preferably a low temperature exceeding 30 ° C., particularly preferably a low temperature exceeding 10 ° C. Moreover, it is preferable that the temperature of the washing | cleaning liquid H exceeds 100 degreeC with respect to the temperature of the slurry D, and is not high temperature. There is an advantage that inactivation due to solvent burning or catalyst oxidation hardly occurs. More preferably, it is not high temperature exceeding 80 ° C. with respect to the temperature of the slurry D, and more preferably not high temperature exceeding 50 ° C.

  The liquid (I) to be transferred includes a reaction solvent, an aromatic carboxylic acid, an unreacted raw material, an intermediate, and the like. For example, in the case of a terephthalic acid production process, aromatic components such as benzoic acid, p-toluic acid, 4CBA, isophthalic acid, orthophthalic acid, and trimethylbenzoic acid are included in addition to terephthalic acid and p-xylene. The concentration of the aromatic component (including the desired terephthalic acid) in the liquid (I) is preferably 30% by weight or less, more preferably 20% by weight or less, and still more preferably 10% by weight or less. The target concentration of aromatic components other than terephthalic acid is preferably 10% by weight or less, more preferably 8% by weight or less, and still more preferably 5% by weight or less. In any case, there is an advantage that the solid content is hardly precipitated in the pipe 22 and the pipe is not easily blocked. The concentration of aromatic components other than aromatic carboxylic acids is usually 50 ppm or more, preferably 100 ppm or more, more preferably 500 ppm or more.

  Further, the catalyst concentration in the liquid (I) is not particularly limited as long as it can promote the oxidation reaction, but the heavy metal concentration is usually 10 ppm or more, preferably 100 ppm or more, more preferably 200 ppm or more. The oxidation reaction in the reactor can be further promoted. On the other hand, the heavy metal concentration is usually 10,000 ppm or less, preferably 5000 ppm or less, more preferably 3000 ppm or less. Cost is reduced.

  As described above, the temperature of the liquid (I) heated in the liquid transfer step is preferably 90 ° C. or higher, more preferably 130 ° C. or higher, and further preferably 150 ° C. or higher as the temperature when introduced into the reaction apparatus. There is an advantage that solid content is difficult to be precipitated in the pipe 22. Moreover, 250 degrees C or less is preferable, 230 degrees C or less is more preferable, and 200 degrees C or less is still more preferable. There is an advantage that inactivation due to solvent burning or catalyst oxidation hardly occurs.

  Moreover, it is preferable that the pressure of the liquid (I) in that case does not exceed 0.3 MPa with respect to the pressure of the introduced reactor. More preferably, it is not lower than 0.25 MPa with respect to the pressure of the reactor, and more preferably substantially the same as the pressure of the reactor. This is to prevent backflow from the reaction apparatus. Moreover, it is preferable that it does not exceed 2 MPa with respect to the pressure of the introduced reactor. More preferably, it is not higher than 1 MPa, more preferably not higher than 0.5 MPa, with respect to the pressure of the reactor. This is to suppress energy costs and make it difficult to release pressure due to a pressure difference when introduced into the reactor.

Next, 2nd embodiment of the manufacturing method of aromatic carboxylic acid is described using FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.
In the method for producing aromatic carboxylic acid according to the present embodiment, in the liquid transfer step, separately from the liquid (I), the liquid (II) containing the washing waste liquid obtained in the washing step is maintained in a pressurized state while maintaining the pressurized state. It is comprised similarly to 1st embodiment except being comprised so that it may transfer to (2) and liquid (II) may be heated in that case, and the same control is performed. That is, the liquid (I) containing the mother liquor F is transferred to the reactor 11 through the pipe 22, and the liquid (II) containing the cleaning waste liquid J is transferred to the reactor 11 through the pipe 22 ′. In the present embodiment, the cleaning drainage J may be mixed with the liquid (I).

Since the description about the piping 22 and piping 22 'of this embodiment is the same as the description about the piping 22 in 1st embodiment, it abbreviate | omits. In addition, the description regarding the liquid (I) and the liquid (II) in the present embodiment is the same as the description of the liquid (I) in the first embodiment, and thus will be omitted.
Since the method for producing an aromatic carboxylic acid according to the present embodiment is configured as described above, there is an advantage that suitable heating conditions can be set for each of the liquid (I) and the liquid (II). For example, it is desirable to apply this embodiment when the temperatures of the mother liquor F and the cleaning waste liquid J are greatly different. Moreover, according to this embodiment, it is possible to obtain the same advantages as the first embodiment.

  Conversely, when the temperature difference between the mother liquor F and the cleaning waste liquid J is small, applying the first embodiment simplifies the piping, eliminates the need to install a plurality of liquid heating means, and reduces energy costs. There are advantages and desirable.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to a following example at all.
[Example 1]
An aromatic carboxylic acid was produced from an alkyl aromatic compound using the apparatus shown in FIG.
First, p-xylene is introduced into the reactor 11, and terephthalic acid is generated by oxidation with air in the presence of a catalyst in a solvent containing about 10% by weight of water with respect to acetic acid. Obtained. The amount (weight) of the solvent with respect to p-xylene is about 3 times. The supply amount of air was controlled such that the oxygen concentration in the condenser exhaust gas O was 3 to 7% by volume.

  A reactor equipped with a stirrer was used as the reactor 11, the temperature of the reactor was 185 to 195 ° C., the pressure was 1.0 to 1.7 MPa, and the reaction time (residence time) was about 1 hour. Cobalt acetate, manganese acetate and hydrogen bromide were used as the catalyst. Bromine atoms were 2.5 moles per mole of heavy metal atoms, and the heavy metal concentrations in the reaction solution were about 300 ppm for cobalt and about 300 ppm for manganese.

  The obtained slurry was extracted from the reactor 11 and transferred to the additional oxidation reactor 11 ′, and additional oxidation was performed once. As the additional oxidation reactor 11 ′, a reactor equipped with a stirrer was used, the reactor temperature was 180 to 194 ° C., the pressure was 0.9 to 1.7 MPa, and the reaction time was about 40 minutes to 60 minutes. The supply amount of air to the additional oxidation reactor 11 ′ is controlled so that the oxygen concentration in the condenser exhaust gas becomes 3 to 7% by volume, and 1/30 (volume ratio) of the supply amount of air to the reactor 11 ).

  The obtained slurry is extracted from the additional oxidation reactor 11 ′, pumped up by the pump 12, and transferred to a screen bowl decanter which is a pressurized solid / liquid separation washing / drying device 17 for solid / liquid separation. Separated into mother liquor. The slurry temperature was 180 to 194 ° C., 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.

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 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. The temperature of the dewatered cake was 110 to 120 ° C., and the liquid content was 0.1% by weight.

On the other hand, 80% by weight of the obtained mother liquor and 100% by weight of the washing waste liquid were mixed and returned to the reactor 11 through the pipe 22. The remaining 20% by weight of the mother liquor was sent to the disposal process. The pipe 22 (pipe diameter: 8 inches) was heated by the outer trace method using three heat medium pipes (pipe diameter: 1 inch) through which hot oil of 320 ° C. was passed. At this time, the temperature of the liquid in the pipe 22 was 180 to 190 ° C., and the pipe skin temperature was 180 to 195 ° C., which was 0.5 to 5 ° C. higher than the temperature of the liquid in the pipe 22.
As a result of the operation in this way, the operation did not stop even if it was operated continuously for 4 months.

[Example 2]
The operation was performed in the same manner as in Example 1 except that only one heat medium pipe was used. The temperature of the liquid in the pipe 22 was 180 to 190 ° C., and the pipe skin temperature was 180 to 190 ° C., which was the same as the temperature of the liquid in the pipe 22. As a result of performing the operation in this manner, liquid components were deposited at a plurality of locations in the pipe, but the operation was not stopped even if the operation was continued for 4 months.
In addition, the amount of heat required for heating in the reactor 11 was slightly larger than that in Example 1, and the heating cost was increased.

[Example 3]
The operation was performed in the same manner as in Example 1 except that the piping 22 was heated by the double piping method instead of the outer tracing method. The temperature of the liquid in the pipe 22 was 180 to 190 ° C., and the pipe skin temperature was 180 to 195 ° C., which was 0.5 to 5 ° C. higher than the temperature of the liquid in the pipe 22. As a result of the operation in this way, the operation did not stop even if it was operated continuously for 4 months. However, more hot oil was required than in Example 1, and the heating cost was slightly high.

[Example 4]
An aromatic carboxylic acid was produced under the same conditions as in Example 1 using the apparatus shown in FIG. 2, and the mother liquor and the washing waste liquid were returned separately to the reactor 11.
That is, the liquid consisting of the mother liquor was heated by three heat medium pipes (pipe diameter: 1 inch) through hot water of 320 ° C. through the pipe 22 (pipe diameter: 8 inches). The temperature of the liquid in the pipe 22 was 175 to 188 ° C., and the pipe skin temperature was 175 to 193 ° C., which was 0.5 to 5 ° C. higher than the temperature of the liquid in the pipe 22.

On the other hand, the liquid consisting of the washing waste liquid was heated by three heating medium pipes (pipe diameter 1 inch) through which hot oil of 320 ° C. was passed through the pipe 22 ′ (pipe diameter 8 inches). At this time, the temperature of the liquid in the pipe 22 ′ was 185 to 195 ° C., and the pipe skin temperature was 185 to 200 ° C., which was 0.5 to 5 ° C. higher than the temperature of the liquid in the pipe 22 ′.
As a result of the operation in this way, the operation did not stop even if it was operated continuously for 4 months. However, since the pipes 22 and 22 'were each heated by the heat medium pipe, more hot oil was required than in Example 1 and the heating cost was increased.

[Comparative Example 1]
The operation was performed in the same manner as in Example 1 except that the piping 22 was not heated by the heat medium piping. The temperature of the liquid in the pipe 22 was 170 to 180 ° C. As a result of the operation, the process was stopped after one month. As a result of investigating the cause of the process stop, terephthalic acid and intermediate crystals were precipitated in the pipe 22 and the pipe was blocked.

It is explanatory drawing for demonstrating 1st embodiment of this invention. It is explanatory drawing for demonstrating 2nd embodiment of this invention.

Explanation of symbols

11 Oxidation reactor 11 ′ Additional oxidation reactor 12 Condenser 13 Solid-liquid separation device 14 Cleaning device 15 Solid-liquid separation and cleaning device 16 Drying device 17 Solid-liquid separation and cleaning drying device 20 Mother liquid tank 21 Cleaning drainage tanks 22 and 22 ′ Liquid Transfer piping 23 Waste treatment process A Alkyl aromatic compound B, B 'Molecular oxygen-containing gas C Solvent D, D' Slurry E Aromatic carboxylic acid cake F Mother liquor G Cleaning cake H Cleaning liquid J Cleaning waste liquid K Aromatic carboxylic acid crystal M, M 'reaction gas N condensate O condenser exhaust gas

Claims (9)

An oxidation step of oxidizing an aromatic alkyl compound in a solvent to produce an aromatic carboxylic acid in a pressurized reactor;
After the slurry containing the aromatic carboxylic acid and the solvent is withdrawn from the reactor, a solid-liquid separation step for obtaining an aromatic carboxylic acid cake and a mother liquor by performing solid-liquid separation in a pressurized state with a solid-liquid separator, and A liquid transfer step of transferring the liquid (I) containing the mother liquor to the reaction apparatus while maintaining a pressurized state, and a method for producing an aromatic carboxylic acid, comprising:
A method for producing an aromatic carboxylic acid, wherein the liquid (I) is heated in the liquid transfer step.   The method for producing an aromatic carboxylic acid according to claim 1, wherein a liquid heating means is provided in at least a part of the pipe in the liquid transfer step.   The method for producing an aromatic carboxylic acid according to claim 2, wherein a liquid heating means is provided at 70% or more of the surface area of the pipe in the liquid transfer step.   The method for producing an aromatic carboxylic acid according to claim 2 or 3, wherein the liquid heating means heats the pipe with a heating medium higher by 5 to 250 ° C than the temperature of the liquid (I).   The method for producing an aromatic carboxylic acid according to any one of claims 1 to 4, wherein in the liquid transfer step, 50 to 100% by weight of the mother liquor obtained in the solid-liquid separation step is transferred to a reactor. And a washing step of washing the aromatic carboxylic acid cake under pressure.
The method for producing an aromatic carboxylic acid according to any one of claims 1 to 5, wherein, in the liquid transfer step, the liquid (I) includes at least a part of the cleaning waste liquid obtained in the cleaning step. And a washing step of washing the aromatic carboxylic acid cake under pressure.
In the liquid transfer step, the liquid (II) is heated when transferring the liquid (II) containing the cleaning waste liquid obtained in the cleaning step to the reactor while maintaining the pressurized state. The manufacturing method of aromatic carboxylic acid of any one of these.   The method for producing an aromatic carboxylic acid according to claim 6 or 7, wherein, in the liquid transfer step, 60 to 100% by weight of the cleaning effluent obtained in the cleaning step is transferred to a reactor.   The manufacturing method of aromatic carboxylic acid of any one of Claims 6-8 whose temperature of the washing | cleaning liquid used for washing | cleaning in this washing | cleaning process is the range of -100- + 100 degreeC with respect to this slurry temperature.

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