JP2015189714A - Method of producing aromatic dicarboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an aromatic dicarboxylic acid stably and continuously by discharging wet cake of an aromatic dicarboxylic acid stably out of a container and transferring.SOLUTION: A method of producing an aromatic dicarboxylic acid is based on liquid phase oxidation of a dialkyl aromatic hydrocarbon with molecular oxygen in a reaction medium and includes a transfer step of receiving, in a container, wet cake containing the aromatic dicarboxylic acid and liquid substances produced by the liquid phase oxidation and transferring the wet cake out of the container. The fluctuation range of the pressure difference between the pressure of the inside of the container and the pressure of the outside of the container, or the destination of the transfer step, is kept within the ±0.2 MPa range.

Description

  The present invention relates to a method for producing an aromatic dicarboxylic acid by liquid phase oxidation of a dialkyl aromatic hydrocarbon. Specifically, an aromatic dicarboxylic acid mixture obtained by liquid phase oxidation, which is solid at room temperature and containing a liquid substance, is stored in a container under a predetermined pressure, and the aromatic dicarboxylic acid is stably contained outside the container. It is a manufacturing method including the process made to transfer to. More specifically, the step of storing aromatic dicarboxylic acid containing a liquid substance composed of water or a mixture containing water and acetic acid, obtained by liquid phase oxidation, in a container and further stably transferring it to the outside of the container. It is related with the manufacturing method containing.

  Aromatic dicarboxylic acids generally use a heavy metal catalyst or the like to convert dialkyl aromatic hydrocarbons into a liquid phase with molecular oxygen at a pressure higher than atmospheric pressure or higher than the boiling point at atmospheric pressure of the reaction medium. Obtained by oxidation. The aromatic dicarboxylic acid product thus obtained is in the form of a slurry. As an example, when the aromatic dicarboxylic acid is high-purity terephthalic acid, crystallization and solid-liquid separation are performed from the slurry. , Washing and drying (hereinafter may be referred to as “CTA process”), followed by re-dissolution with water, hydrogenation, solid-liquid separation, washing and drying (hereinafter referred to as “PTA process”). A solid particulate product of terephthalic acid can be obtained through unit operations such as In both the CTA step and the PTA step, the aromatic dicarboxylic acid obtained by solid-liquid separation, a step of performing solid-liquid separation and washing at the same time, a drying step, etc. contains a liquid substance such as a slight reaction medium (hereinafter referred to as “reaction medium”). A mixture containing an aromatic dicarboxylic acid and a liquid substance may be referred to as a “wet cake”). However, when these wet cakes are transferred to and stored in vessels such as tanks, towers, and solid-liquid separators, and subsequently discharged to other containers, the moisture on internal structures such as the inner wall surface of the vessel and powder level gauges can be reduced. Stable transfer is extremely difficult due to the adhesion of cake or malfunction of the wet cake discharge mechanism and unstable discharge speed due to fluctuations in pressure balance inside and outside the container. There are still problems to be solved in terms of continued operation.

  As a method for solving these problems, for example, Patent Document 1 discloses that one or more electrode sensors are arranged to avoid pressure leakage when discharging a wet cake from a pressure filter. A method is described in which a liquid sealer such as viscous oil is introduced into the top of the wet cake and pushed out.

  In addition, Patent Document 2 describes that a rotary valve is used to take out a wet cake that has been solid-liquid separated and washed with a pressure rotary filter without blocking it in a state where the pressure is cut off.

  However, as reported in Patent Document 3, when the size of the rotary valve is increased as the size of the facility is increased, the space blocking function of the valve is lowered, and the leakage gas may adversely affect the dryer on the downstream side. There is. Therefore, Patent Document 3 proposes a solid content recovery system that prevents gas leakage from the pressure filter to the low pressure side.

  Patent Document 4 reports a method in which a part of an aromatic dicarboxylic acid product obtained from the drying step in the PTA step is mixed with a wet cake to obtain a synthetic cake.

  Furthermore, Patent Document 5 reports a method of extracting a wet cake retained in a chamber intermittently or continuously into a powder tank.

WO91 / 09661 Publication Japanese Patent Laid-Open No. 11-179115 JP 2005-118754 A JP 2004-217595 A JP 2002-336687 A

  However, in the method described in Patent Document 1, there are cost increase factors such as mixing into a product by using a sealer and using a screw conveyor.

  In addition, the invention described in Patent Document 3 has a screw conveyor installed downstream of the pressure filter, transported to the first rotary valve, transferred to a downstream buffer tank (atmospheric pressure), and further installed with a screw conveyor. A method of taking out using the second rotary valve is proposed, and the apparatus is extremely complicated. Even if it is limited only to the method of taking out the wet cake at the time of solid-liquid separation in the pressurized state, as described above, there is a lot of room for improvement, and the technology that can integrally process from wet cake to dry powder is still completed. Not.

  Furthermore, in the method described in Patent Document 4, adhesion of the wet cake in the tank is somewhat improved, but a drastic effect is not obtained.

  Furthermore, Patent Document 5 has no description that suppresses communication between the gas phases of the chamber and the powder tank, and there is a high possibility that pressure fluctuations in the chamber will occur. For this reason, the localization of the wet cake or the like is likely to occur, and there is a risk that stable transfer becomes difficult.

Therefore, the present invention provides a method for stably discharging and transferring the aromatic dicarboxylic acid wet cake to the outside of the container. More specifically, the wet cake stored in the container is free from fluctuations in pressure inside and outside of the container due to pressure leaks and fluctuations in the discharge speed, and the liquid substance contained in the wet cake is gasified and does not blow out of the container. Thus, it is an object to stably and continuously produce an aromatic dicarboxylic acid by discharging and transferring it out of the container.
Further, when the container is a wet cake hopper, the transfer of the wet cake is stabilized by suppressing the communication between the gas phases, and the pressure in the container is maintained by suppressing the communication between the gas phases. An object of the present invention is to stabilize the operation of the solid-liquid separation step and / or the washing step and to efficiently perform the drying operation in the subsequent step.

  The inventors of the present invention have made extensive studies in view of the above problems, and by setting the fluctuation range of the pressure difference between the pressure inside the container and the pressure outside the container, which is the transfer destination of the transfer process, within a certain range. The inventors have found that stable transfer of the wet cake to the outside of the container is possible, and that the aromatic dicarboxylic acid can be produced stably and continuously, and the present invention has been completed. That is, the gist of the present invention resides in the following [1] to [12].

[1] In a method for producing an aromatic dicarboxylic acid by liquid phase oxidation of a dialkyl aromatic hydrocarbon with molecular oxygen in a reaction medium, the aromatic dicarboxylic acid and a liquid substance obtained by the liquid phase oxidation are obtained. Storing the wet cake contained in a container, and then transferring the wet cake to the outside of the container, and the pressure difference between the pressure inside the container and the pressure outside the container, which is the transfer destination of the transfer process A method for producing an aromatic dicarboxylic acid, characterized in that the fluctuation range of is maintained within a range of ± 0.2 MPa.

[2] A wet cake is retained in the container substantially always at a predetermined amount or more, and the container outlet is applied in a state of being always sealed by the wet cake. The method for producing an aromatic dicarboxylic acid according to [1], wherein the amount per hour transferred of the wet cake is 0.001 or more and 0.5 or less.
[3] The position of the upper surface of the wet cake in the container is detected by a powder level meter, and the wet cake retention amount below the detected powder surface height is defined as 1 for the transfer amount of the wet cake per hour. The method for producing an aromatic dicarboxylic acid according to [1] or [2], wherein the method is 0.001 or more and 0.5 or less.
[4] At least a part of the liquid substance contained in the wet cake is evaporated together with the transfer of the wet cake to the outside of the container, [1] to [3] A method for producing an aromatic dicarboxylic acid.
[5] The aromatic according to any one of [1] to [4], wherein a pressure difference between the pressure inside the container and the pressure outside the container is 0.001 MPa or more and 5 MPa or less. A method for producing dicarboxylic acid.
[6] The method for producing an aromatic dicarboxylic acid according to any one of [1] to [5], wherein the pressure inside the container is 0.001 MPaG or more and 5 MPaG or less.
[7] The method for producing an aromatic dicarboxylic acid according to any one of [1] to [6], wherein the liquid substance contains water or a mixture of water and acetic acid.
[8] The content of the liquid substance in the wet cake is 0.01% by weight or more and 25% by weight or less with respect to the content of the aromatic dicarboxylic acid. The manufacturing method of aromatic dicarboxylic acid of any one.
[9] The amount of the wet cake in the container is detected by a powder meter, and the wet cake is transferred from the container outlet in conjunction with a mechanism having a transfer function connected to the container. The method for producing an aromatic dicarboxylic acid according to any one of [1] to [8].
[10] The method for producing an aromatic dicarboxylic acid according to [9], wherein the powder level meter is a contact type powder level meter.
[11] The method for producing an aromatic dicarboxylic acid according to any one of [1] to [10], wherein the aromatic dicarboxylic acid is terephthalic acid.

The mixture containing the aromatic dicarboxylic acid and the liquid substance is separated from the container by setting the fluctuation range of the pressure difference between the pressure inside the container and the pressure outside the container, which is the transfer destination of the transfer process, within a certain range. The present inventors have found that stable transfer is possible and completed the present invention. According to the present invention, in a situation where there is little blockage or accumulation in the container / pipe, and there is no drop in the container pressure due to pressure leakage, or there is no gas blow-through inside the container containing liquid substance vapor, it is stable outside the container. Thus, it has become possible to provide a method relating to the production of aromatic dicarboxylic acid to be discharged.
Furthermore, when the container is a wet cake hopper, the pressure difference between the pressure inside the container and the pressure outside the container is suppressed and held. The difference can be used effectively and useful drying can be performed.

Flow diagram showing an example of an aromatic dicarboxylic acid production process Schematic diagram showing an example of the wet cake transfer process Schematic diagram showing an example of powder level meter Sectional view showing an example of a cable used in powder level meter

  The present invention relates to a method for producing an aromatic dicarboxylic acid by liquid phase oxidation of a dialkyl aromatic hydrocarbon with molecular oxygen in a reaction medium, specifically, obtained by liquid phase oxidation. A mixture containing an aromatic dicarboxylic acid and a liquid substance (hereinafter sometimes simply referred to as “wet cake”) is placed in a container, and then the aromatic dicarboxylic acid having a transfer step of transferring the wet cake to the outside of the container. It is invention about the manufacturing method of an acid.

  An example of the aromatic dicarboxylic acid is terephthalic acid. Terephthalic acid generally uses a heavy metal catalyst, uses para-xylene as a dialkyl aromatic hydrocarbon in the reaction medium, and is formed by molecular oxygen at a pressure higher than atmospheric pressure, at a temperature equal to or higher than the boiling point at atmospheric pressure of the reaction medium. Obtained by liquid phase oxidation. The terephthalic acid product thus obtained is in the form of a slurry, and the slurry further comprises a crude terephthalate comprising a crystallization step, a solid-liquid separation step and / or a solid-liquid separation / washing step, and an evaporation / drying step. After passing through the acid production process (CTA process), a purified terephthalic acid production process (PTA) further comprising water dissolution, hydrogenation reaction, crystallization process, solid-liquid separation process and / or solid-liquid separation / washing process, and evaporation / drying process The product terephthalic acid is obtained through the process.

  In both the CTA step and the PTA step, the aromatic dicarboxylic acid after the solid-liquid separation operation, the washing operation, and the drying operation in each step becomes a wet cake containing a liquid substance such as a slight reaction medium. When these wet cakes are transferred to and stored in a container such as a tank or tower and then discharged to another container, the wet cake adheres to internal structures such as the inner wall surface of the container or powder level gauge, or the wet cake. Stable transfer is extremely difficult due to the malfunction of the linkage with the discharge mechanism and the instability of the discharge speed due to fluctuations in the pressure balance inside and outside the container. Furthermore, when solid-liquid separation is performed at a high pressure, if a large pressure fluctuation occurs when the wet cake after solid-liquid separation is discharged from the container, the solid-liquid separation operation becomes unstable. Thus, there remains a problem to be solved in terms of continued stable operation.

  In the following, specific processes and examples of containers relating to the transfer of a wet cake that is the subject of the present invention will be described in detail with reference to FIG.

  Although various apparatuses can be considered as the container, the container in the case of the transfer of the wet cake containing the attached liquid substance that is the object of the present invention in relation to the production of the terephthalic acid is a wet cake hopper or a dry cake. Examples include a hopper such as a hopper.

[CTA process]
In the first half of FIG. 1, an example of one aspect of handling of the wet cake used in the present invention in the CTA process is shown. As the aromatic dicarboxylic acid, terephthalic acid is representatively shown.
The terephthalic acid is present in the presence of hydrogen bromide or the like under a heavy metal catalyst such as cobalt or manganese, and in a reaction medium such as an aliphatic carboxylic acid and / or water as a reaction medium, the raw material 100 such as paraxylene is subjected to high temperature and high pressure. Liquid phase oxidation is performed in the oxidation reaction apparatus 1 using molecular oxygen. After the oxidation reaction slurry 101 after the reaction is crystallized in the crystallization tank 2, the obtained crystallization slurry 102 is supplied to the separation washing and drying apparatus 14. The separation washing / drying device 14 is composed of a group of devices including a solid-liquid separation / washing device 3, a wet cake hopper 4, an evaporation / drying device 5, and a dry cake hopper 6. These devices may be independent individual devices, and one device may combine the functions of one or more devices.

  In this separation washing and drying apparatus 14, first, solid-liquid separation operation and cake washing operation are performed under pressure using a separation / washing facility 3 having a function capable of performing both solid-liquid separation and washing, under pressure, A separated and washed wet cake 103 having a liquid substance content of 5 to 25% by weight is obtained. Next, it is once stored in the wet cake hopper 4 and then transferred to the evaporation / drying device 5 where the concentration of liquid substance in the wet cake 103 separated and washed by the evaporation / drying device 5 is 0.01 to 1% by weight. After removing the liquid substance so as to become, it is stored in the dry cake hopper 6 and used for the next transfer. The wet cake hopper 4 may be provided in a part of the apparatus of the separation / cleaning facility 3.

  The dried wet cake 104 transferred to the dry cake hopper 6 is transferred to another process (for example, the PTA process using a bucket conveyor) by an arbitrary means. As another embodiment, after a wet cake having a liquid substance content concentration of 5 to 25% by weight is stored in the wet cake hopper 4, the dry cake hopper 6 having a pressure lower than the pressure of the wet cake hopper 4 is used. By directly discharging without passing through the dryer and evaporating (flashing) at least part of the liquid substance contained in the wet cake, at least part of solid-liquid separation, washing and drying is integrated in the separation washing and drying apparatus 14. The method to be performed is given. The dried wet cake 104 stored in the dry cake hopper 6 is transferred to another process (for example, the PTA process using a bucket conveyor or the like) by any means. In any embodiment, the dried wet cake 104 may be directly transferred to another process by any means without being stored in the hopper.

[PTA process]
In the latter half of FIG. 1, an example of another aspect of handling the wet cake used in the present invention in the PTA process is shown. That is, the handling of the wet cake shown in this example is a case where the high purity terephthalic acid 111 is produced by purifying the dry cake 105 discharged from the dry cake hopper 6 shown in the first half of FIG. That is, the dry cake 105 is dissolved in water, and impurities in the dry cake are reduced with a hydrogenation raw material 110 in the presence of a noble metal catalyst such as palladium in a reduction reactor 7 at high temperature and high pressure. The reduction reaction slurry 106 thus obtained is crystallized in the crystallization tank 8, and the obtained crystallization slurry 107 is supplied to the separation washing and drying apparatus 15. The separation washing / drying device 15 is composed of a group of solid-liquid separation / washing device 9, wet cake hopper 10, evaporation / drying device 11, and dry cake hopper 12. These devices may be independent individual devices, and one device may combine the functions of one or more devices.

  In this separation washing and drying apparatus 15, the separated and washed wet cake 108 having a concentration of 5 to 25% by weight of the liquid substance that has undergone solid-liquid separation and washing is once stored in the wet cake hopper 10, and then transferred. Further, the wet cake 109, which has been subjected to a drying treatment so that the concentration of the liquid substance is 0.01 to 1% by weight by applying the separated and washed wet cake 108 to the evaporation / drying device 11, is stored in the dry cake hopper 12. To be used for the next transfer. The wet cake hopper 10 may be provided in a part of the apparatus of the separation / cleaning facility 9. As another embodiment, after the separated and washed wet cake 108 having a liquid substance content concentration of 5 to 25% by weight is stored in the wet cake hopper 10, the dry cake having a pressure lower than the pressure of the wet cake hopper 10 is used. Evaporating (flashing) at least a part of the liquid substance in the wet cake directly to the hopper 12 without passing through the dryer, the evaporation / drying device 11 performs at least one of solid-liquid separation, washing and drying. One method is to integrate the parts. The wet cake stored in the dry cake hopper 12 is optionally transferred to another process, but is usually supplied to an additional drying device 13 to become high-purity terephthalic acid 111 as a product. In any embodiment, the dried wet cake 109 may be directly transferred to any other process without being stored in the hopper.

  As described above, wet cakes (separated and washed wet cakes 103 and 108, dried wet cakes 104 and 105, and dried wet cakes 104 and 105, which are accommodated in the wet cake hoppers 4 and 10 and the dry cake hoppers 6 and 12 in the CTA process and the PTA process shown in FIG. 109), in the past, although there is a difference in the concentration of the contained liquid material and a difference in properties, there is a pressure drop due to blow-off of gas in the container containing the vapor of the liquid substance, pressure leakage, or fluctuation in the container internal pressure. If it occurred, there was a problem with stable transport. In order to stably transfer the wet cake accommodated in the container as described above, the fluctuation range of the pressure difference between the pressure inside the container and the pressure outside the container, which is the transfer destination of the transfer process, is constant. It was found that by making it within the range, stable transfer between equipment containers becomes possible, and the present invention was completed.

[Details of CTA process]
In the following, the embodiment of the present invention used in the CTA process will be described in more detail in order according to the process with reference to FIG.

[Oxidation process]
In the oxidation reaction apparatus 1, the dialkyl aromatic hydrocarbon is subjected to liquid phase oxidation in a reaction medium to obtain an aromatic dicarboxylic acid slurry 101. When the aromatic dicarboxylic acid to be produced is terephthalic acid, the dialkyl aromatic hydrocarbon is paraxylene. At this time, it is desirable to oxidize 90% by weight or more, preferably 95% by weight or more of paraxylene to terephthalic acid.

  In addition, acetic acid is used as the reaction medium. The amount of acetic acid used is usually 2 to 6 times the weight of the alkyl aromatic compound. The acetic acid solvent may contain other components such as water of not more than 15% by weight, which does not affect the reaction. As the acetic acid solvent, recycle liquid obtained in the solid-liquid separation / washing process described later, recovered acetic acid obtained from dehydration operation for removing water by-produced by the oxidation reaction, and the like can be reused.

  As the dialkyl aromatic hydrocarbon, an alkyl group or an aromatic hydrocarbon having two partially oxidized alkyl groups can be used. The alkyl group may be monocyclic or polycyclic, and examples of the alkyl group include alkyl groups having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. Examples thereof include an aldehyde group, an acyl group, a carboxyl group, and a hydroxyalkyl group. Specific examples thereof include 2 alkyl groups having 1 to 4 carbon atoms such as m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, p-xylene, and trimethylbenzenes. Dialkylpolyphenyls such as dialkylnaphthalenes having 2 to 1 carbon atoms such as di- or polyalkylbenzenes having 4 to 4 carbon atoms, dimethylnaphthalenes, diethylnaphthalenes and diisopropylnaphthalenes, and dimethylbiphenyls, etc. Can be mentioned. An aromatic compound having a partially oxidized alkyl substituent is one in which one or two alkyl groups of the aromatic hydrocarbon having two alkyl groups are partially oxidized alkyl groups. Specific examples include 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-toluic acid, p-toluic acid, 3-formylbenzoic acid, 4-formylbenzoic acid, and 2-methyl6-formylnaphthalene. Etc. These may be used alone or as a mixture of two or more.

  In the oxidation step, the dialkyl aromatic hydrocarbon is usually oxidized with a molecular oxygen-containing gas. As the molecular oxygen-containing gas, for example, a gas containing molecular oxygen such as air, oxygen diluted with an inert gas, or oxygen-enriched air is used. In practice, air is used.

  Examples of the aromatic dicarboxylic acid of the present invention include terephthalic acid, isophthalic acid, 2.6-naphthalenedicarboxylic acid, 4.4'-biphenyldicarboxylic acid and the like. Among these, terephthalic acid is particularly preferable.

  The catalyst used when oxidizing the dialkyl aromatic hydrocarbon is not particularly limited as long as it has the ability to oxidize the dialkyl aromatic hydrocarbon and convert it to an aromatic dicarboxylic acid. Usually, a heavy metal compound is used, and a bromine compound may be used as a catalyst auxiliary as necessary. Examples of the heavy metal 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 combine cobalt and manganese. Examples of such heavy metal compounds include acetate, nitrate, acetylacetate, naphthenate, stearate and bromide, with acetate and bromide being particularly preferred.

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

  Specific examples of the catalyst for oxidizing a dialkyl aromatic hydrocarbon include a combination of cobalt, manganese, and bromine. In particular, a combination of cobalt acetate, manganese acetate, and hydrogen bromide, or cobalt bromide and manganese bromide is used. Preferred combinations. In the present invention, the catalyst composed of a combination of the heavy metal compound and the bromine compound is usually 0.05 mol or more, preferably 0.1 mol or more, per 1 mol of the heavy metal atom. On the other hand, it is usually 10 mol or less of bromine atom, preferably 5 mol or less. Moreover, such a catalyst is 10 ppm or more normally as a heavy metal density | concentration in a reaction solvent, Preferably it is 100 ppm or more. On the other hand, it is usually 10,000 ppm or less, and preferably 3,000 ppm or less.

  The reaction temperature of the oxidation reaction apparatus 1 is usually 140 ° C. or higher, preferably 150 ° C. or higher, more preferably 170 ° C. or higher. On the other hand, it is usually 230 ° C. or lower, preferably 210 ° C. or lower, and more preferably 200 ° C. or lower. If the reaction temperature exceeds 230 ° C., the amount of acetic acid solvent lost by combustion increases, which is not preferable.

  The reaction pressure of the oxidation reaction apparatus 1 needs to be equal to or higher than the pressure at which the reaction mixture can maintain a liquid phase at least at the above reaction temperature, and needs to exceed the normal pressure. Specifically, it is preferably 0.2 MPaG or more, and more preferably 1 MPaG or more. On the other hand, it is preferably 5 MPaG or less, and more preferably 2 MPaG or less. Specifically, the pressure is a pressure at which the composition of the reaction mixture and the boiling state at the set reaction temperature are maintained.

  The oxidation reaction is usually carried out continuously, and the reaction time (average residence time) is preferably 30 minutes or more, particularly preferably 40 minutes or more. If it is less than 30 minutes, the reaction becomes insufficient and the desired quality may not be obtained. On the other hand, it is preferably 300 minutes or less, and more preferably 150 minutes or less. If it exceeds 300 minutes, the combustion of acetic acid increases and the capacity of the oxidation reactor also increases, which is not economical.

  In order to adjust the water concentration of the acetic acid solvent as the reaction solvent, for example, a part of the condensate obtained by condensing the reaction gas generated in the oxidation reaction apparatus 1 is purged out of the system.

  The oxidation reaction apparatus 1 is preferably a tank equipped with a stirrer, but does not necessarily need to be equipped with a stirrer and may be of a bubble column type. The reactor 1 has a supply port for a molecular oxygen-containing gas, and a condenser (not shown) may be provided above the reactor as necessary. After the molecular oxygen-containing gas is used for the oxidation reaction of the alkyl aromatic compound, it is withdrawn from the reactor as a reaction gas accompanied by a large amount of acetic acid vapor, and mainly contains acetic acid in a condenser (not shown). After separating the condensate to be discharged, it is discharged as exhaust gas. Usually, the condensate contains water, and a part of the condensate is purged outside the system to adjust the water in the system, and the rest is refluxed to the oxidation reaction apparatus 1.

  Further, a further oxidation reaction may be performed after the oxidation reaction. In this additional oxidation reaction, the reaction mixture obtained in the oxidation reaction apparatus 1 is subjected to additional oxidation at a lower temperature than the first-stage reaction. If the dialkyl aromatic hydrocarbon is para-xylene, the molecule is usually added to the additional oxidation reactor (not shown) maintained at a low temperature of 5 ° C. to 20 ° C. from the reaction temperature without additional supply of the dialkyl aromatic hydrocarbon. Process by supplying gaseous oxygen-containing gas. The pressure at the time of the additional oxidation treatment needs to be at least the pressure at which the internal reaction mixture can maintain the liquid phase at least at the reaction temperature, and specifically 0.2 MPaG or more. On the other hand, it is desirable that it is 5 MPaG or less. The reaction time is 5 minutes or more. Moreover, it is good for it to be 120 minutes or less. The additional oxidation reaction may be performed twice or more. If necessary, additional oxidation treatment may be continued at a temperature higher than the reaction temperature described above.

[Crystallization]
Regardless of whether or not the additional oxidation reaction is applied, the obtained oxidation reaction slurry 101 may be subjected to crystallization treatment in the crystallization tank 2 as necessary. In this case, the pressure is reduced by evaporation under reduced pressure below the pressure in the oxidation step, and the aromatic dicarboxylic acid dissolved in the solvent is further precipitated to increase the recovery amount. However, when cooled by crystallization, the operation temperature of the subsequent solid-liquid separation step is lowered, and the internal energy retained in the system is reduced. Therefore, the crystallization operation is preferably omitted.

[Solid-liquid separation and washing]
Conventionally, the solid-liquid separation process and the washing process have been carried out in separate facilities, but recent advances in technology have made it possible to carry out the process in a single apparatus, thereby simplifying the process. Examples of the solid-liquid separation / washing apparatus 3 that can perform the solid-liquid separation process and the washing process in this way include, for example, a screen bowl type centrifuge, a rotary vacuum filter, a horizontal belt filter, and a rotary pressure filter. Is done. Among these, in the present invention, a screen bowl type centrifugal separator and a rotary pressure filter excellent in heat resistance in a high temperature / high pressure region are preferable. In the screen bowl type centrifuge, solid and liquid are separated by centrifugal force.

  There are no restrictions on the material and shape of the filter medium, and ceramic filters, wire meshes, metal bar screens, etc. are used, and are selected in consideration of corrosion resistance and clogging. The pressure when the oxidation reaction slurry 101 or the crystallization slurry 102 is processed by the solid-liquid separation / washing apparatus 3 is higher than the normal pressure and needs to be higher than the vapor pressure of the separation mother liquor at the separation operation temperature. By maintaining such a pressure, it is possible to substantially maintain the temperature level of the slurry 101, 102 and retain internal energy. Specifically, it is preferably 0.2 MPaG or more, and more preferably 0.3 MPaG or more. On the other hand, the upper limit is usually 22 MPaG or less, preferably 12 MPaG or less, more preferably 7 MPaG or less, and particularly preferably 1.5 MPaG or less. The solid-liquid separation / washing device 3 continues to wash the separated cake separated into solid and liquid to remove impurities and by-products attached to the separated cake.

  Acetic acid, water, or a mixture thereof is used for the cleaning liquid. The pressure at the time of washing is the same as in the case of the solid-liquid separation described above. The cleaning liquid is preferably at the same temperature as or higher than the separation cake so as not to reduce internal energy. Since the separated mother liquor and the washed liquor contain valuable components such as acetic acid solvent and aromatic carboxylic acid, the recycle mother liquor and purge mother liquor are branched and recycled while maintaining the pressure above the normal pressure. It is desirable to recycle the mother liquor to the oxidation process while maintaining the pressure without being cooled by releasing pressure. From the purge mother liquor, valuable components are recovered and reused, and the remainder is discarded.

[Storage of dry and wet cake]
The separated and cleaned wet cake 103 is stored in the wet cake hopper 4. The wet cake hopper 4 may be an individual container independent of the solid-liquid separation / washing device 3 or may be a wet cake retaining part forming a part of the solid-liquid separation / washing device 3. The separated and washed wet cake 103 contains 0.01 to 25% by weight of a liquid substance composed of acetic acid, water, or a mixture of acetic acid and water with respect to the aromatic dicarboxylic acid. It is desirable that the temperature of the wet cake hopper 4 is not lowered as much as possible from the temperature of the solid-liquid separation / washing device 3 so as to maintain the internal energy of the wet cake.

  Further, the pressure of the wet cake hopper 4 is preferably 0.001 MPaG or more, and more preferably 0.3 MPaG or more in order to prevent a temperature drop due to evaporation of the liquid substance. Further, the upper limit is preferably 5 MPaG or less, and more preferably 1.5 MPaG or less.

  Next, the wet cake is sent to the evaporation / drying device 5 where the liquid substance-containing concentration is 0.01 to 1% by weight and the liquid substance-containing concentration is further reduced. The dryer used is not particularly limited in the present invention, but a rotary kiln dryer, a fluidized bed dryer, and the like are exemplified as suitable ones. The pressure of the evaporation / drying device 5 is lower than the pressure of the wet cake hopper 4. When the internal energy of the wet cake introduced into the evaporation / drying device 5 is effectively maintained in the previous step and the temperature of the wet cake is close to or higher than the boiling point at normal pressure of the contained liquid substance, the evaporation / drying device 5 The evaporation of the liquid substance due to the internal energy of the wet cake occurs at the stage of being introduced into the cake, and at least a part of the role of the evaporation / drying process is achieved. Therefore, the energy consumption of the evaporation / drying apparatus 5 can be reduced. Is possible. The dry cake 104 is stored in the dry cake hopper 6 but may be directly transferred to the reduction reaction step 7 without being stored in the dry cake hopper 6.

  As another aspect, when the separated and washed wet cake 103 maintains a temperature sufficient to evaporate the liquid substance by its internal energy and reduce the content due to a decrease in pressure, the evaporation / drying device 5 is used. Without using it, it is also possible to store directly in a dry cake hopper with a pressure lower than that of the wet cake hopper 4 with evaporation of the liquid substance.

  Under such conditions, the wet cake is substantially always retained in the vicinity of the discharge mechanism in the container, so that a pressure seal layer made of the wet cake is formed and held in the container. The state which does not communicate can be maintained and this container exit can be applied in the state always sealed with the said wet cake. This prevents the gas phase gas in the container containing the vapor of the attached liquid substance from passing through the discharge mechanism, that is, the occurrence of blow-through. As a result, the pressure of the wet cake is suppressed and the wet cake can be stably discharged out of the container, and this pressure difference is effectively utilized in the drying process in the subsequent process of the wet cake hopper. In addition, useful drying can be performed. In order to always maintain the pressure seal layer in the container by the wet cake, the powder level detection mechanism for detecting the amount of the wet cake in the container, and the transfer speed and / or the discharge frequency controlled by this detection mechanism are By providing a wet cake discharging mechanism that is variable and appropriately adjusting the transfer capability, the wet cake retention amount in the container is always kept appropriately.

  Further, in order to appropriately manage the pressure in the container, the gas phase gas in the container is discharged by a vent pipe installed in the container as necessary. Moreover, high pressure gas is replenished in the container as needed.

As a result, in the transfer step of storing the wet cake obtained in the solid-liquid separation / washing process in the container (wet cake hopper 4 or the like) and then transferring it to the evaporation / drying device 5 or the dry cake hopper 6, And the pressure difference between the pressure outside the container. The pressure difference is preferably 0.001 MPa or more, more preferably 0.2 MPa or more, and further preferably 0.3 MPa or more. When the pressure difference is lower than the above range, when a discharge mechanism that discharges the wet cake using the pressure difference is employed, problems such as adhesion of the wet cake near the discharge mechanism and defective discharge may occur. On the other hand, the upper limit of the pressure difference is preferably 5 MPa or less, more preferably 2 MPa or less, and still more preferably 1.5 MPa or less. When the pressure difference is higher than the above range, there may be a problem that the discharge mechanism cannot appropriately suppress the discharge speed or exceeds the pressure resistance of the discharge mechanism. At this time, the pressure in the post-process is lower than the pressure in the container.
By the way, the “outside of the container” means the outside of the container. Specifically, in this transfer process, the process after the container (hereinafter referred to as “post-process”), that is, the next. Refers to the destination.

  By the way, in the present invention, it is preferable to adjust the interlocking of the powder level detection mechanism and the discharge mechanism so that the fluctuation range of the pressure difference (ΔP) is suppressed within a predetermined range. This is achieved by adjusting the wet cake transfer amount by controlling the transfer time of the wet cake, controlling the extraction valve opening, etc., and adjusting the position of the upper surface of the wet cake in the container and the set value of the retention amount of the wet cake. Is done. Thereby, even if there is an uneven state on the upper surface of the wet cake in the container, a through-hole is formed in the wet cake, and the pressure may fluctuate, it is possible to prevent the gas from being blown through.

  This fluctuation range ΔP is within a range of ± 0.2 MPa, preferably within a range of ± 0.15 MPa, and more preferably within a range of ± 0.1 MPa. Outside this range, an unexpected through-hole is formed in the seal layer of the wet cake, causing gas to blow through, destabilizing the discharge speed of the wet cake, and causing mechanical fatigue due to pressure fluctuations in the discharge mechanism. Sometimes. Further, when the solid-liquid separation / washing process is operated in substantially the same pressure section as the vessel, the solid-liquid separation / washing operation may become unstable.

  By satisfying each condition for forming a seal with a wet cake as described above, the seal layer is appropriately held, the pressure difference between the container and the post-process is stably maintained, and stable transfer between the equipment containers is possible. It becomes possible. And this allows the wet cake to be stably discharged out of the container in a state where there is no blockage or accumulation in the container or each pipe, and where there is no blowout due to pressure drop or fluctuation due to pressure leakage. Can do.

  The dry cake hopper 6 can be used in the same manner as when the wet cake hopper 4 is used as a container. When the dry cake hopper 6 is used as a container, the only difference from the case where the wet cake hopper 4 is used as a container is that the pressure difference ΔP inside and outside the container is 0.001 to 0.2 MPa.

  By the way, when the pressure sealing effect is impaired and the gas phase in the container communicates with the subsequent process through the discharge mechanism, the inside of the container and the subsequent process are directly connected, that is, there is a hole penetrating both in the wet cake. It will be possible. In this case, this hole reduces the pressure difference between the inlet side and the outlet side of the container, which may make it difficult to move the entire wet cake, and a gas phase containing a large amount of liquid substance vapor in the next step. Gas moves. As a result, there is a risk that a wet cake may remain in the container, and the pressure in the next process is increased, causing damage to the container and the device, and drying such as flash drying may be hindered. In some cases, re-adhesion of a liquid substance to a dry cake or the like may occur.

  The transfer to the outside of the container is preferably accompanied by evaporation of at least a part of the liquid substance contained in the wet cake. That is, when removing the liquid substance from the wet cake hopper 4 in which the separated wet cake 103 that has been separated and washed is stored, the liquid substance is shifted to a lower pressure state, and the liquid substance is released with internal energy for retaining the liquid substance. It is desirable to evaporate. Evaporation under pressure refers to a phenomenon in which a liquid substance evaporates due to the heat of a wet cake when a liquid whose pressure is higher than the boiling point at the low pressure after the transition is rapidly transferred to the low pressure state. . As a discharge mechanism for discharging the wet cake 103 from the pressure side to the low pressure side, a discharge valve is exemplified. Specifically, valves disclosed in WO91 / 09661 and US-55889079 can be used. Further, for example, a rotary valve other than the discharge valve may be used, or a plurality of valves may be used. The pressure in the wet cake hopper 4 is the same as or slightly lower than that in the solid-liquid separation / washing device 3. The evaporated liquid substance becomes evaporative gas and is sent to the processing facility through the vent line, and the accompanying aromatic dicarboxylic acid solid is recovered and reused together with acetic acid used as the cleaning liquid. It is desirable that the internal energy is sufficient to supply all the heat of evaporation of the liquid material, but if it is insufficient, it is further dried by heating if necessary.

  The pressure inside the container and the pressure outside the container are pressure gauges 36a and 41 that measure the pressure inside the pressure container, and the pressure gauge 36b that measures the pressure outside the pressure container (wet cake hopper 31) (FIG. 2). Can be detected using a dry cake hopper 37), and the pressure difference between them can be calculated and managed based on the detected data. Note that the pressure outside the pressure vessel (dry cake hopper 37) is a normal pressure.

  In the present invention, stabilization of the wet cake transfer in the wet cake hopper and the dry cake hopper between the apparatuses and the containers 3, 4, 5, and 6 in the CTA process is the aim of the present invention, which will be described in more detail below.

[Integration of solid-liquid separation, washing, drying and wet cake storage]
In the present invention, it is preferable to use a simple process in which the above-mentioned [solid-liquid separation / washing] and [drying / wet cake storage] are integrated, that is, the operation can be performed with the equipment integrated with the transfer step. It aims at stable operation by establishing a stable transfer method of wet cake in the process. Further, a process of omitting the crystallization step and processing the oxidation reaction slurry 101 by directly feeding it into the integrated equipment is more desirable. Figure 2 shows the image.

  While maintaining the high temperature and high pressure state of the reaction slurry liquid substance a, it is put into the solid-liquid separation and washing apparatus 30 to perform solid-liquid separation and washing, and the separated mother liquor and washing liquid c are discharged out of the system, and the wet cake b is stored in the wet cake hopper 31 and is intermittently withdrawn to the dry cake hopper 37 via the extraction valve 34, and the pressure difference between the wet cake hopper 31 and the dry cake hopper 37 and the internal energy held by the wet cake b The liquid material is evaporated to dryness to obtain a wet cake having a reduced content of the liquid material. The liquid substance e removed by evaporation is discharged out of the system as vapor. Subsequently, it is transferred to the next process via the extraction valve 40. Solid-liquid separation / washing apparatus 30 performs solid-liquid separation / washing while substantially maintaining the high-temperature / high-pressure conditions of the oxidation reaction or crystallization process, followed by pressure-release evaporation drying. However, in this process, there are the following problems in the wet cake hopper 31 for storing the wet cake b and the next dry cake hopper 37.

A. Since the difference between the pressure in the wet cake hopper 31 for distillation and the pressure in the downstream dry cake hopper 37 is large, the high-pressure gas in the wet cake hopper tends to be ejected downstream, and the pressure of the wet cake hopper 31 is maintained. For this reason, it is difficult to maintain conditions for proper solid-liquid separation and washing operations, such as requiring a large amount of supplementary gas. Further, the pressure becomes unstable, the pressure difference with the dry cake hopper 37 becomes unstable, and the stable transfer of the wet cake to the dry cake hopper 37 is hindered.
B. Since a large amount of gas moves from the wet cake hopper 31 to the dry cake hopper 37, the pressure of the dry cake hopper 37 is rapidly increased, and the hopper body or the valve 40 as an accompanying discharge mechanism may be damaged.
Various phenomena such as the above occur, and these cause the stable transfer of the wet cake in the hopper.

C. Wet cake by causing vapor of liquid material to blow down to downstream equipment, condensing and reattaching liquid material to wet cake transferred after drying, causing fluidity of wet cake to deteriorate and causing sticking in downstream equipment Transfer becomes impossible.
D. The discharge mechanism such as the discharge valve shaft is damaged by the pressure difference, and the wet cake cannot be transferred.
E. If the vapor of the liquid material is corrosive, the downstream equipment will be corroded by the ejected steam and shut down for repair.

  In the dry cake hopper 37 having the extraction valve 34 at the upper part and the extraction valve 40 at the lower part, the pressure is lower than that of the upstream wet cake hopper 31 and is atmospheric pressure or slightly higher than atmospheric pressure. Since the valve opens and closes intermittently and the fluctuation of internal pressure is large, the above problems c. ~ Ho. Various phenomena such as the above occur, and these cause the stable transfer of the wet cake in the hopper.

  As described above, the solid-liquid separation / washing device 30 → the wet cake hopper 31 → the dry cake hopper 37 → the device for the next process (not shown), and many problems are still unsolved to stably transfer the wet cake between the containers. The problem remains in the stable operation.

  Therefore, as a result of intensive studies, as described above, for example, the wet cake is retained in a certain range in a container such as a wet cake hopper, the container outlet is applied in a state that is always sealed by the wet cake, or By providing a powder level detection mechanism at a place where a through-hole is likely to occur in the container and constantly monitoring it, the fluctuation range of the pressure difference between the pressure inside the container and the pressure outside the container can be suppressed within a certain range. It is possible to suppress pressure drop due to gas blow-through in containers containing liquid substance vapor, pressure leakage and fluctuations in internal pressure of the container, and stable transfer between equipment containers and easy drying in the subsequent drying process I found out.

  Furthermore, since the pressure difference exists, the wet cake hopper 31 and the dry cake hopper 37 are simply connected without providing a special evaporation / drying device between the wet cake hopper 31 and the dry cake hopper 37. Evaporation / drying can be performed by flash drying with a sudden decrease in pressure when the container exits from the outlet.

[Details of apparatus according to FIG. 2]
A more detailed embodiment will be described below.
In general, the wet cake is transferred from the wet cake hopper by installing a powder level meter in or around the wet cake hopper 31 as described above, and using the extraction valve 34 installed at the boundary with the dry cake hopper 37. The wet cake b is opened intermittently or while adjusting the opening, and the wet cake b is transferred to the lower device (dry cake hopper). However, unlike the liquid surface, the wet cake surface has irregularities and is not horizontal, so the powder level meter has a problem in that an opening instruction is given to the mechanism for extracting the contents (for example, an extraction valve) at an inappropriate time. In the present invention, cake surface upper powder level meter (hereinafter may be simply referred to as “upper sensor”) 32, 38 and cake surface lower powder level meter (hereinafter may be simply referred to as “lower sensor”). As a specific example of the powder level meter used for 33, 39, the following powder level meter with improved powder level meter detection device and improved operation method based on the detection result is used, and the following pressure gauge is used for the sealing state: What added the structure confirmed by using is used suitably. Thereby, the retention amount of the wet cake b in the container is detected by the following powder level meter, and the wet cake b is transferred from the container outlet in conjunction with a mechanism having a transfer function connected to the container. Is possible.

  The upper sensors 32 and 38 are installed so as to protrude from the inner walls of containers such as the wet cake hopper 31 and the dry cake hopper 37 toward the central axis, and are arranged near the upper limit of the wet cake management range. And the distance from an exit is set according to the upper limit of the setting value of the said residence amount of a wet cake. As a result, if the wet cake accumulates too much in the container, the upper sensors 32 and 38 remain buried in the wet cake, so that the amount of wet cake introduced into the container is suppressed or the wet cake discharged from the container. It is possible to determine that the wet cake needs to be discharged by increasing the amount of water or by intermittently operating the discharge mechanism. On the other hand, if the wet cake stays below the stay, the upper sensors 32 and 38 are not in contact with the wet cake, so that the amount of wet cake introduced into the container is increased, It can be determined that it is necessary to reduce the amount of the wet cake discharged from the water or to intermittently stop the discharge mechanism.

  The lower sensors 33 and 39 are arranged in the vicinity of outlets in containers such as the wet cake hopper 31 and the dry cake hopper 37, and the distance from the outlet is set in accordance with the lower limit of the set value of the retention amount of the wet cake. Is set. For this reason, the lower sensors 33 and 39 are buried in the wet cake when normal operation is achieved. As a result, when a cavity is formed in the wet cake or the retention amount of the wet cake is abnormally reduced, the lower sensors 33 and 39 are not in contact with the wet cake, so that an appropriate retention amount of the wet cake is ensured. It can be recognized that it has not been made, and it is possible to take a coping action to eliminate this state.

The powder level gauge and pressure gauge used in the present invention will be described below.
(Powder level meter)
A representative example of the powder level meter used in the present invention is shown in FIG. A typical powder level meter shown in FIG. 3 is a contact-type powder level meter, and includes a sensor AA, a cable BB, and a current amplifier CC. The sensor AA is installed on the side or upper part of the DD such as a hopper in which the detection target substance is stored, and the electrical characteristic detected by the sensor AA is sent as a signal to the current amplifier CC via the cable BB to control the manufacturing process. And is used for operation control.

  The sensor AA includes a housing 61, a flange 62, a ground electrode part 63, an insulating part 64, and a detection electrode part 65. It is inserted and installed inside the hopper (wet popper 31, dry cake hopper 37) by the flange 62 or the like. When the wet cake inside the hopper is empty or at a low level, there is only air around the detection electrode unit 65, but when the wet cake accumulates and contacts the detection electrode unit 65 and the installation electrode unit 63, When the surrounding environment changes from air to a wet cake, the electrical characteristics change, and the signal is transmitted to the current amplifier CC installed outside the hopper via the cable BB, and the change in the electrical characteristics is recognized. The change in electrical characteristics is when measuring the amount of change that occurs between the two electrodes of the ground electrode portion 63 and the detection electrode portion 65, or when measuring the amount of change that occurs between the hopper and the detection electrode 65. In this case, the hopper and the ground electrode 63 are in close contact with the metal hopper wall surface by the flange 62 and are in electrical conduction. When measuring the amount of change occurring between the two electrodes of the ground electrode portion 63 and the detection electrode portion 65, it is assumed that both electrode portions are in the same environment, so the sensor AA is not inserted from the top of the hopper. It is preferable to insert horizontally or obliquely from the side.

  The current amplifier CC is preferably composed of an oscillation circuit, an amplifier circuit, a switching circuit, and a power supply unit, as well as a circuit necessary for detecting a change in electrical characteristics. In the oscillation circuit, a capacitor, a resistor, a coil, and the like are connected in series or in parallel, and are connected to a high-frequency oscillator to detect a change in electrical characteristics. It is preferable to include an amplifier circuit that amplifies a change in electrical characteristics, a switching circuit that performs current / voltage switching, sensitivity adjustment, and the like.

  The number of electrodes includes a two-pole type constituted by two electrodes and a three-pole type constituted by three electrodes, but is not particularly limited and any of them can be used.

  The material of the flange 62, the electrode part 63, and the detection electrode part 65 is selected from austenitic stainless steel, titanium, nickel alloy, etc. in consideration of corrosion resistance according to use conditions. The insulating part 64 is made of an insulating resin such as a fluorine-based resin or a polyacetal resin, and the power source housing 61 is made of a light metal such as aluminum.

(cable)
Further, the following improvements have been added to the cable BB. In the conventional method, the change in electrical characteristics when the sensor touches the cake is smaller than the change in electrical characteristics between the cable connecting the sensor and the current amplifier and in the cable body, and is detected by the sensor. As a result, it was found that the accuracy and reliability of the measured value of the electrical characteristic change was significantly reduced, and the cable internal structure was uniquely improved. That is, the change in electrical characteristics generated between the cables and in the cable body is minimized, and the change in electrical characteristics generated between the cables and in the cable body is detected by the sensor when the sensor contacts the cake. Improved to reduce the change in electrical properties. Specifically, a conductive shielding layer is disposed in the cable and the structure is protected by two or more insulators.

  In FIG. 4, the typical example which shows the cross section of this cable used by this invention was shown as a conceptual diagram. The cross-sectional view of the cable structure shown here is an example showing the concept, and is not limited to these.

  The shape of the cable which has been improved as described above is such that the coaxial cable connected to the detection electrode 65 and the coaxial cable connected to the ground electrode 63 or the hopper DD such as the hopper are independently current amplifiers as in the case 1. The two cables may be connected together to the current amplifier CC in the form of one cable as in the case 2. It is preferable that at least one of the two coaxial cables has a conductive shielding layer disposed coaxially with the conductor and is protected by two or more insulators. When using one cable that is a group of two cables, a conductive shielding layer is arranged coaxially with the conductor for at least one of the two conductors in the cable. The state of protection with an insulating layer is preferred.

  For the shielding layer, a metal net-like wire having high conductivity such as copper is used. An insulating resin such as polyethylene, polyvinyl chloride, or fluororesin is used for the insulating layer.

Below, the cross section of the cable that can be used in the present invention will be described in more detail.
Case 1 is a case where detection is performed using two coaxial cables, and Case 2 is a case where detection is performed using a single cable in which the cables are combined. Reference numeral 71 denotes a conductive wire from the detection electrode 65, and 72 denotes a conductive wire from the ground electrode 63 or a hopper.

  In case 1, both of the two coaxial cables are provided with a shielding layer 73 and two or more insulating layers 74 (1a), one example (1b) provided with a shielding layer on one side, and an insulating layer only on one side. One example (1c) is shown respectively.

  In case 2, one example (2a) in which a shielding layer 73 and two or more insulating layers 74 are individually provided around two conductors 71 and 72, and two examples (2b) provided only around one conductor. , 2c).

  The detection apparatus shown in FIG. 3 shows an example, and the present invention is not limited to this. As a specific example of another detection device used in addition to FIG. 3, a current amplifier built-in detection device (not shown) having no external cable connecting the sensor and the current amplifier is exemplified.

  The detection device includes a sensor and a current amplifier in order to minimize changes in electrical characteristics between the cables connecting the current amplifiers installed outside the hopper or the like where the sensors are installed and in the cable body. The cable which connects is eliminated, and the electric amplifier is built in the power supply unit. The detection device has a short internal cable length connecting the electric amplifier and the sensor tube, and therefore the influence of the change in the electrical characteristics caused by this cable can be made as small as possible compared to the external cable system connecting the sensor and the current amplifier. However, in the present invention, it is the best mode to have a structure in which the above-described conductive shielding layer is disposed on the internal cable of the detection device and is protected by two or more insulators.

  As the electrical characteristics, capacitance, resistance, impedance, admittance and the like are preferably used.

These contents are defined and explained below.
<Capacitance>
Capacitance refers to capacitance, which is the amount of charge stored between two conductors that are isolated or spaced apart. For example, when two flat metal plates are placed in parallel, the value of the capacitance C depends on the area S of the metal plates, the distance L between the metal plates, and the dielectric constant εs of the insulator between the metal plates. It is determined and expressed by the following formula.
C = εo · εs · S / L
[epsilon] o: dielectric constant under vacuum, unit is Farad (F) or picofarad (PF).

In the present invention, when capacitance is referred to as a change in electrical characteristics, it means that a substance is detected / measured by capturing a change in C represented by the above equation. Here, the dielectric constant is a basic electrical constant of a substance, and each substance has a specific dielectric constant. For example, when C in an empty state has a relative permittivity of air (ratio with permittivity under vacuum = ε / ε ₀ ) of 1 and C is 2PF, a relative permittivity of 3 in the space Is accumulated, C is 6 PF, and the difference of C is 4 PF. Therefore, the change is detected.

<Resistance>
Resistance is an electrical resistance that suppresses the flow of electricity, and the voltage decreases as the resistance increases. As a symbol, R is usually used, and the unit is ohm (Ω). In the case of an insulating material, the electric resistance becomes infinite, and electricity does not flow. In the case of a conductive substance, electricity flows according to the degree of conductivity, so that the change can be detected.

<Impedance>
Impedance is the ratio of voltage to current in an AC circuit and represents the difficulty of electricity flow. The concept of electrical resistance in DC is expanded and applied to AC. The symbol is usually Z, and the unit is ohm (Ω).

<Admittance>
Admittance is the ease of electricity flow in an AC circuit and is the reciprocal of impedance. The symbol is Y and the unit is Siemens (S). As a specific example of the detection device that recognizes the change in the electrical characteristics and grasps the upper surface of the wet cake to be measured according to the present invention, it can detect a change in electrical characteristics selected from capacitance, resistance, or a combination of the two. Capacitance type detection device, admittance type detection device for detecting admittance, impedance type detection device for detecting impedance, and further, an admittance type detection device for detecting admittance and an impedance type detection device for detecting impedance. Examples include a detection device.

  Under such circumstances, the capacitance detection device is preferably used in the present invention, more preferably an impedance detection device, and most preferably an admittance detection device.

  In addition, if there are no working parts in the container, and conditions suitable for continuously measuring the weight of the container, such as being able to effectively cut off vibrations from accompanying moving equipment, other than the powder level meter, By using a powder level meter such as a load cell, it is possible to measure the amount of residence of the internal wet cake without installing a contact-type powder level meter that causes adhesion of the wet cake inside the container.

(Pressure gauge)
The pressure gauge can be arbitrarily selected from commercially available instruments, but when the usage conditions are high temperature and high pressure and a corrosive substance such as acetic acid is contained, the material of the wetted part is preferably made of titanium.

Based on FIG. 2, the measurement method and operation method of the amount of powder in the wet cake hopper 31 will be described.
In the wet cake hopper 31, a powder level meter is installed to detect the state of the upper surface of the wet cake, and the extraction valve 34 installed at the boundary with the dry cake hopper 37 is opened and closed intermittently to open the wet cake b into the dry cake. Transfer to hopper 37. The problem at this time is
(1) When the wet cake is transferred and the wet cake surface is lowered, if the wet cake remains on the surface of the powder level meter, the measurement accuracy of the next measurement is lowered.
(2) If the sensor is located close to the outer wall surface, the measurement accuracy will drop, and the method of installing only in two places, upper and lower, will not detect the wet cake surface variation specific to the wet cake, and the wet cake surface will be locally Without recognizing the low situation, an instruction to open the extraction valve 34 is issued, and the wet cake blows off locally, destabilizing the transfer speed due to fluctuations in internal pressure, and inflow of high-pressure gas to the next process Cause damage to equipment.
(3) The wet cake handled by the present invention has high adhesiveness, and it adheres not only to the sensor surface but also to the tank wall surface, the extraction valve, etc., and accumulates in the wet cake hopper 31 and the dry cake hopper 37, leading to clogging. Occur.

The solution to the above problem was intensively studied and the following contents were improved.
(1) Measures to reduce measurement accuracy due to wet cake remaining on the sensor surface
1) The sensor metal surface is smoothed to make it easier for the solid to slide off.
2) Consider the sensor insertion angle.
3) After the wet cake to be deposited is deposited to a height at which the entire upper sensors 32 and 38 (H level) are buried, the condition is set so that an extraction instruction is issued.
4) A mechanism for ejecting gas for removing deposits is provided at the base or tip of the sensor.
Things are preferable.

Regarding the sensor insertion angle of 2), the preferred insertion angle of the sensor into the wet cake hopper and the dry cake hopper is 15 to 60 degrees below horizontal, particularly preferably 20 to 40 degrees.
3) As setting conditions, when the wet cake deposited at a position higher than the upper sensors 32 and 38 (H level) falls in the hopper, the wet cake attached to the sensor surface by the frictional resistance is dropped. If the speed (or time) is sufficient, the sensor surface does not substantially remain.

Regarding the sensor installation position in (2),
1) If the sensor is too close to the outer wall surface, the measurement accuracy is lowered. Therefore, the tip of the sensor is separated from the wall surface by at least 100 mm, preferably 150 mm or more.
2) It is preferable that at least one powder level sensor of the powder level meter is installed at the top and bottom, and at least two at the same height are installed at a total of three or more.
The installation position of the hopper inner lower part (L level) sensor is preferably installed at a height of at least 100 mm, preferably 150 mm or more from the hopper bottom so that a wet cake always stays in the hopper to form a seal. . The upper (H level) sensor can be installed in any number of positions higher than the L level sensor, but the hopper is fully filled with wet cake to receive wet cake from the previous process. It is preferable to install the wet cake surface at a position where it can be managed so as not to hinder.

Regarding the problem of (3) accumulation in the wet cake hopper 31 and dry cake hopper 37 leading to blockage, a hammering device, a vibration device, etc. by pneumatic drive or magnetic drive are installed outside the wall surface, and the wet cake hopper A preventive measure such as keeping the inner wall surface temperature of 31 at a temperature of 5 ° C. to 100 ° C., preferably 10 ° C. to 50 ° C. or higher from the internal temperature is preferable. As a heat retaining method, a coil (not shown) is wound around the wet cake hopper 31 and steam or hot oil is passed through. It is also effective to prevent clogging by disposing a material having excellent anti-adhesion properties such as Teflon at the wet cake contact portion on the inner surface of the hopper. In order to prevent adhesion, it is effective to suppress the liquid content of the wet cake to 25% by weight or less, preferably 20% by weight or less, and more preferably 15% by weight or less.

  Furthermore, strict pressure control that suppresses pressure loss as much as possible is necessary, and control of the valve opening time is also important. When the H level is reached, the extraction valve 34 is intermittently opened and discharged, but the condition for issuing the opening instruction is that both at least one pair of sensors at the H level are detected simultaneously, or only one of the powders is 20 seconds or longer. This is a case where the surface is detected, and the lower sensor 33 (L level) continuously detects the wet cake surface, and at least 8 to 10 seconds have elapsed after the end of the previous opening operation.

  What is important in the present invention is that the fluctuation range of the pressure difference between the inside and outside of the container is kept within a range of ± 0.2 MPa, and further, the retention amount of the wet cake in the container is per hour of the wet cake. When the transfer amount is set to 1, 0.001 to 0.5, the communication between the gas phase inside and outside the container is always prevented.

  Further, the position of the upper surface of the wet cake in the container is detected by a powder level meter, and the wet cake retention amount below the detected powder surface height is set to 1 for the transfer amount of the wet cake per hour. When it is set to 0.001 or more and 0.5 or less, it becomes easy to manage the fluctuation range of the pressure difference between the inside and outside of the container within the range, and the communication of the gas phase part can be more reliably prevented.

  The opening time is preferably 2 to 8 seconds, more preferably 3 to 7 seconds, and most preferably 4 to 6 seconds. If the opening time is long, a certain amount of residual amount cannot be secured and pressure leaks. The amount of decrease in the internal pressure of the wet cake hopper 31 is less than a maximum of 0.5 MPa, preferably less than 0.2 MPa, and more preferably less than 0.1 MPa. Specifically, using the lower sensor 33 (L level), the opening / closing time of the discharge valve 33 is set to an optimum value so that the height of the powder surface that has decreased as a result of a series of opening operations can still ensure sealing performance. This is achieved by doing so. A series of operations is preferably performed through a DCS (Distributed Control System) 35.

[Removal of wet cake from container]
In the present invention, in the vicinity of the surface of the wet cake, the powder level meter that detects the residence amount of the wet cake is arranged, and in conjunction with a mechanism (valve or the like) having a discharge function connected to the container, The wet cake is transferred from the outlet. Examples of the transfer function include the extraction valves 34 and 40.

  The extraction valve 34 is preferably one that can suppress pressure leakage of the wet cake hopper 31 as much as possible. Examples of the valve include a ball valve, a butterfly valve, a rotary valve, a flap damper, a slide damper, a spindle type valve, etc., but the seal part is in line contact, and a circular one is preferably used, specifically a spindle type A valve with a substantially conical valve body is desirable. In the method of installing multiple valves and adding a hopper, restrictions on pressure leakage are slightly relaxed, so other valves such as a surface contact type can also be used.

Next, based on FIG. 2, the measurement method and operation method of the powder amount in the dry cake hopper 37 are demonstrated below.
The dry cake hopper 37 is a pressure-resistant container having an extraction valve 34 at the top of the container and a wet cake discharge valve 40 having a reduced liquid deposit concentration at the bottom, and is discharged from the wet cake hopper 31. A transfer line for evaporative gas e, which is generated by evaporating the wet cake adhering liquid material due to pressure drop, is provided, and the evaporative gas is recovered and recycled through a recovery device such as a scrubber, and the rest is discharged. Is done. The wet cake b is discharged from the extraction valve 34 to the dry cake hopper 37, and the cake adhering liquid is evaporated and dried by the pressure difference between the hopper 31 and the hopper 37 and the release of internal energy held by the wet cake b. The concentration of the liquid deposit in the wet cake having a reduced concentration of the evaporated deposit is 0.01 to 1% by weight. The wet cake having a reduced liquid deposit concentration is transferred to the next process through the extraction valve 40.

  The extraction valve 40 is usually a rotary valve. A rotary valve rotates a rotor with several blades attached radially in a horizontal cylinder to discharge or supply powder. In the present invention, it is used to extract cake from a dry cake hopper. The amount of extraction is affected by fluctuations, and jetting and blow-through occur, so that problems such as deterioration of fluidity due to evaporation gas recondensing and adhering to the wet cake with reduced liquid deposit concentration downstream will not occur. In addition, it is necessary to always hold the wet cake surface so as not to cause the problem of damage to the rotary valve rotating shaft due to pressure fluctuation.

  In the present invention, the rotational speed of the rotary valve is controlled by the wet cake surface sensed by the powder level meter, and the state where the container is always sealed is maintained so that the wet cake surface is always secured. And The powder level gauge and pressure gauge 41 used for the dry cake hopper 37 can be the same as the powder level gauge and pressure gauges 36a and 36b used for the wet cake hopper 31. The same applies to the sensor installation position and the number of sensor bases. As another aspect, by using a powder level meter such as a load cell, it is possible to measure the amount of dwell of the internal wet cake without installing a powder level meter that causes adhesion of the wet cake inside the container. In this case as well, the concept of maintaining the normal state where the container is always sealed by controlling the wet cake surface by the number of rotations of a mechanism (such as a rotary valve) for extracting is the same. As a result, the pressure difference inside and outside the container, which is the point of the present invention, is stably maintained at 0.2 to 1.5 MPa around the wet cake hopper and ΔP around 0.001 to 0.2 MPa around the dry cake hopper. The

  When the contact-type powder level meter is used, the dwell amount of the wet cake in the container is lower than the detection unit of the contact-type powder level meter in the container. When the amount is 1, it is preferably 0.001 or more and 0.5 or less. Below this lower limit, it will be difficult to control the fluctuation range of the pressure difference to keep it within the range, local communication in the gas phase will occur, the appropriate pressure sealing effect will be lost, and the pressure difference will be kept constant. It can be difficult to keep. If this upper limit is exceeded, the required capacity of the container increases and the economy is impaired.

[Details of PTA process (purification process)]
In the method for producing an aromatic dicarboxylic acid, in addition to the CTA step shown in the first half of FIG. 1, a production method is known in which a purification operation is added to obtain a higher purity product. Since the present invention can be applied to the purification process to simplify and integrate the process, high purity terephthalic acid will be described as an example based on the latter half of FIG.
Based on the first half of FIG. 1, after the CTA step of obtaining crude terephthalic acid by oxidation with molecular oxygen in the presence of a catalyst in a solvent mainly composed of acetic acid based on para-xylene, based on the latter half of FIG. High purity terephthalic acid is produced (PTA process). At this time, steps such as a crystallization step, a solid-liquid separation / washing step, and a drying step are the same steps as the CTA step, and conditions and methods similar to those of the CTA step can be adopted except as described below. .

  In FIG. 1, the wet cake 105 having a reduced liquid deposit concentration stored in the dry cake hopper 6 in the CTA process typically has 4-carboxybenzaldehyde (hereinafter referred to as “4-CBA”) as an impurity. Is usually present in an amount of about 500 to 5000 ppm, and a purification operation (PTA process) is required when higher purity is required. In the purification operation, 4-CBA, a main impurity, is converted to p-toluic acid by a reduction reaction with hydrogen, and p-toluic acid is selectively distributed to an aqueous phase using a difference in water solubility with terephthalic acid. Separate and remove the high purity terephthalic acid on the solid side and dry, while recycling the paratoluic acid in the aqueous solution.

Since it is necessary to dissolve terephthalic acid in a solvent mainly composed of water in order to carry out the reduction reaction, the temperature is usually raised to 230 to 330 ° C., preferably 250 to 310 ° C. The reaction pressure requires a pressure higher than the vapor pressure of water at the reaction temperature in order to maintain the solvent as a liquid, and is usually 3 to 12 MPaG, preferably 5 to 10 MPaG. The dissolved terephthalic acid aqueous solution is reacted in the reduction reactor 7. As a catalyst, a metal such as ruthenium, rhodium, palladium, platinum or osmium is usually supported on a carrier such as activated carbon and used as a fixed bed. Among these, palladium supported on activated carbon is preferable. The temperature is usually 260 to 320 ° C., preferably 270 to 300 ° C., and the hydrogen partial pressure is usually 0.5 to 20 kg / cm ² G.

[Crystallization]
The temperature and pressure of the reaction solution obtained by the reduction reaction are lowered, and terephthalic acid is crystallized in the crystallization tank 8. Usually, when the pressure is reduced stepwise in a continuous manner from 2 to 6 stages, preferably from 3 to 5 stages, the solvent flashes and the temperature in the system decreases. Since p-toluic acid obtained by reducing 4-CBA has higher water solubility than terephthalic acid, terephthalic acid is preferentially precipitated during crystallization. However, when the pressure falls to atmospheric pressure, p-toluic acid is eutectic, which is undesirable. The final pressure is 0.2 MPaG or more, preferably 0.3 MPaG or more, more preferably 0.5 MPaG or more. The upper limit of the pressure range is 3 MPaG or less, preferably 1 MPaG or less, and more preferably 0.7 MPaG or less.

[Solid-liquid separation and washing]
The crystallization slurry 107 is transferred to the solid-liquid separation / washing device 9, and the purified high-purity terephthalic acid and the aqueous solution containing by-products such as p-toluic acid are separated at a pressure higher than atmospheric pressure, and then washed with water. The 4-CBA concentration in high-purity terephthalic acid is reduced to 30 ppm or less. The lower limit of the solid-liquid separation pressure range is 0.2 MPaG or more, preferably 0.3 MPaG or more. The upper limit of the pressure range is 3 MPaG or less, preferably 1 MPaG or less, and more preferably 0.7 MPaG or less. The apparatus is preferably the screen bowl decanter or the pressure rotary filter shown in the CTA process.

[Storage of dry and wet cake]
The separated and washed wet cake 108 is sent to the wet cake hopper 10, and after storing the wet cake, it is transferred to the drying device 11 and heated, or the pressure is reduced to atmospheric pressure, and at least a part of the adhering liquid is flushed. Remove by evaporation.

[Integration of solid-liquid separation, washing, drying and wet cake storage]
The process 15 can be simplified by adopting the equipment 15 in which the above-mentioned [solid-liquid separation / washing] and [dry / wet cake storage] devices are integrated in the same manner as in the image diagram of FIG. In the CTA process of FIG. 1, the solid-liquid separation / washing apparatus is used without passing through the crystallization process, but in the case of a purification operation, it is desirable to pass through the crystallization process. The slurry 107 after crystallization is put into the integrated equipment 15 to perform solid-liquid separation, washing, drying, and storage of the wet cake. In the crystallization operation, some of the internal energy is consumed, the residual energy is reduced, and the liquid adhering liquid component of the purified terephthalic acid cake is mainly composed of water and has a larger latent heat of vaporization than acetic acid. Rather than allowing the liquid to evaporate and dry, the moisture content is 5-25% by weight in the wet cake hopper 10. It is possible to complete a mechanism for crystallization and evaporating and drying without wasting internal energy held by the reaction solution reduced at high temperature and pressure. The wet cake in which the liquid adhering substance is reduced by flushing using the internal energy difference in the evaporating and drying apparatus 11 is stored in the dry cake hopper 12 and finally transferred to the dryer for commercialization. . Since the concentration of the liquid deposit contained in the dry cake hopper is 1 to 15% by weight, it is dried by the additional drying device 13.

  The transfer of the wet cake stored in the wet cake hopper and the dry cake hopper in the PTA step is the same conditions and operations as the wet cake hopper and the dry cake hopper described in the CTA step, except that the liquid adhesion substance is water. And can be stably transferred by the apparatus.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention more concretely, this invention is not limited to a following example at all.

(Example 1)
In an equipment with high-purity terephthalic acid production of 100 Ton / hr, acetic acid approximately 5 times by weight of paraxylene, water approximately 0.4 times by weight of paraxylene, cobalt acetate, manganese acetate as catalyst, Hydrogen bromide was supplied, and the oxidation reaction was performed at a temperature of 197 ° C., a pressure of 1.45 MPaG, and a reaction time (average residence time) of 60 minutes. The amount of catalyst used is 300 ppm by weight in terms of metal for the cobalt component and the manganese component with respect to the solvent, and 700 ppm for the bromine component. Air was used as a gas for performing an oxidation reaction with molecular oxygen. At this time, the oxygen content of the air is 21%. Then, compressed air was supplied into the reactor so that the oxygen concentration in the gas discharged from the reactor was 6% by volume.

  Next, the oxidation slurry is continuously transferred to the additional oxidation reaction apparatus, and the temperature is 190 ° C., the pressure is 1.3 MPaG, and the reaction time is 40 minutes. It supplied so that the oxygen concentration in it might be 6 volume%, and the additional oxidation reaction was performed.

  The crude terephthalic acid cake slurry after the reaction was put into the apparatus shown in the image diagram of FIG. 2 where solid-liquid separation / washing and evaporation / drying could be integrally processed while maintaining the temperature and pressure. Solid-liquid separation / washing was performed by solid-liquid separation using a screen bowl decanter in the apparatus and washing with an aqueous acetic acid solution. The wet cake thus separated and washed was a mixture of acetic acid and water as a liquid adhering substance and was 10% by weight with respect to terephthalic acid, and was stored in a wet cake hopper in the apparatus. The temperature of the hopper was 200 ° C., and the pressure was almost maintained at 1.2 MPaG.

The amount of the wet cake retained in the apparatus was about 0.01 when the amount of the wet cake processed in one hour in the general apparatus was 1.
In order to maintain the pressure, a gas supply line having a source pressure higher than the internal pressure of the apparatus and a gas discharge line for releasing to the atmosphere are connected to the apparatus, and the opening degree of the automatic control valve installed in these lines Was automatically controlled according to changes in the internal pressure of the apparatus.

  Next, the wet cake is intermittently extracted through the discharge valve to the dry cake hopper in the apparatus having the discharge valve at the top and the rotary valve at the bottom. At the same time, the adhering liquid is flashed and evaporated, and the dried wet cake is the rotary valve. Is further extracted downstream. At this time, the pressure difference ΔP inside and outside the wet cake hopper was about 1.2 MPa.

  Inside the wet cake hopper, a powder level detection and measurement device equipped with a contact-type admittance sensor that measures changes in electrical characteristics is installed, and the powder level gauge and the mechanism for discharging (such as a discharge valve) are linked. In this way, the system opens intermittently when a certain condition is reached. As the discharge valve, a hydraulic cylinder type valve having a substantially conical valve body shape was used. A pair of upper sensors (H level) are arranged in the wet cake hopper near the upper surface of the wet cake (H1 & H2), and one lower sensor (L level) is installed in the lower cake of the hopper. As a cable connecting the sensor and the current amplifier, a cable that detects with two coaxial cables composed of a conductor portion, a shielding layer, and an insulating layer shown in 1a of case 1 shown in FIG. 7 was used.

  The material used for the sensor was Ti, and the material for the inner wall of the wet cake hopper was Ti. H1 and H2 sensors detect the presence of the powder surface at the same time, or one of the H1 or H2 sensors detects the presence of the powder surface for 20 seconds, and then confirm that the L sensor detects the presence of the powder surface Then, at least 10 seconds after the end of the last valve opening operation, an instruction to open the discharge valve for 4 seconds was transmitted through DCS (Distributed Control System) and extracted intermittently. These conditions were determined so that the fluctuation range of the internal pressure averaged to be ± 0.1 MPa or less.

  The wet cake in the dry cake hopper was pulled out to the cake collection device by controlling the number of rotations of the rotary valve so that the wet cake surface would not disappear while checking the position of the upper surface of the staying wet cake in the hopper. The amount of wet cake in the dry cake hopper is monitored by installing a load cell in the dry cake hopper, and it is confirmed that the gas phase in the dry cake hopper is sealed so that it does not communicate with the rotary valve. However, the extraction speed was adjusted by controlling a mechanism for extraction, for example, the valve rotation speed. Evaporated gas generated in the dry cake hopper was excluded in the exhaust gas treatment process through the vent line, and released into the atmosphere to maintain the pressure in the dry cake hopper at a pressure close to atmospheric pressure. The temperature of the outer wall surface of the wet cake hopper and the dry cake hopper was set to a temperature 30 ° C. higher than the internal temperature of each device by winding a coil around the outer surface of the hopper and heating it with hot oil. The liquid content in the collected wet cake was 0.05% by weight.

  By this method, no pressure leakage occurred, and the wet cake transfer was stably transferred, so that there was no situation where the operation was stopped for a long time to cope with the blockage, and continuous plant operation for 2 months or more could be realized.

(Example 2)
Since terephthalic acid obtained in the same manner as in Example 1 contains about 2000 ppm of impurities mainly composed of 4-CBA, it is further purified and provided as high-purity terephthalic acid.

The terephthalic acid cake containing 4-CBA or the like is mixed with water in a mixing tank, and then heated, pressurized and melted at 290 ° C. and 8.6 MPaG with steam and heat transfer oil, and then palladium-activated carbon is used as a fixed bed. A hydrogenation reaction is performed by introducing the hydrogenation reaction tower together with hydrogen. The aqueous solution of terephthalic acid after the reaction is continuously placed in a crystallization tank, and is successively subjected to pressure-release cooling and crystallization in a four-stage crystallization process to obtain a crystallization slurry. When the pressure is reduced to atmospheric pressure, the paratoluic acid produced by reduction of 4-CBA forms a eutectic with terephthalic acid and a purification effect cannot be obtained. Then, the pressurized and heated crystallization slurry is put into a solid-liquid separation / washing / drying apparatus. As the apparatus, the apparatus described in the image diagram of FIG. 3 capable of integrally processing solid-liquid separation / washing and drying / wet cake storage was used. For solid-liquid separation / washing, solid-liquid separation was performed with a screen bowl decanter in the apparatus, followed by washing with water. The wet cake separated and washed was water as a liquid adhering substance and was 10% by weight based on the solid terephthalic acid. It was stored in a wet cake hopper in the apparatus. The temperature of the hopper was 160 ° C., and the pressure was 0.7 MPaG.
Further, the accumulated amount of the wet cake retained in the apparatus was about 0.01 when the amount of the wet cake processed in one hour in the general apparatus was 1.

  Next, the discharge valve is intermittently withdrawn through the discharge valve into the dry cake hopper in the apparatus having the discharge valve at the upper part and the rotary valve at the lower part. It is extracted to the dry cake hopper through the valve. At this time, the pressure difference ΔP = 0.7 MPa between the inside and outside of the wet cake hopper. The powder level meter uses an admittance type sensor (same as CTA), and the powder level meter is linked with a mechanism for extraction (for example, a discharge valve) to open intermittently when a certain condition is reached. did. As the discharge valve, a spindle type valve (same as CTA) having a substantially conical valve body shape was used. A pair of upper sensors (H1 & H2) are placed in the wet cake hopper in the vicinity of the wet cake, and one lower sensor is installed in the wet cake at the lower part of the wet cake hopper. Discharge in the situation where the presence of the powder surface on the inlet side) or the presence of the wet cake is detected by the lower sensor after one of the H1 or H2 sensors detects the presence of the powder surface for 20 seconds. The instruction to open the valve for 4 seconds was controlled through DCS (Distributed Control System) and extracted intermittently. These conditions were determined so that the fluctuation range of the internal pressure averaged ± 0.1 MPa or less.

  The moisture content of the wet cake recovered in the dry cake hopper was 6%. Subsequently, the wet cake was dried with a steam tube dryer to obtain a high purity terephthalic acid cake having a water content of 0.1 wt% and a 4-CBA content of 10 ppm. By this method, since the wet cake transfer was stable, there was no situation where the operation was stopped for a long time to cope with the blockage, and continuous operation of the plant for 10 months or more could be realized.

(Comparative Example 1)
It is a comparative example with respect to Example 1. While maintaining the pressure and temperature of the slurry a obtained by performing the additional oxidation reaction in Example 1, the slurry a is put into the equipment manufactured for the purpose of integrating the solid-liquid separation cleaning and the evaporation drying process as shown in FIG. Solid-liquid separation, washing, drying, and storage of wet cake were performed. The equipment consists of a screen bowl decanter that performs solid-liquid separation and washing, a cake storage tank (wet cake hopper), and a cake collection tank (dry cake hopper). Valves are installed below the wet cake hopper and below the dry cake hopper. , Controls extraction from each hopper. The wet cake taken out from the screen bowl decanter is stored in the wet cake hopper, and when the wet cake surface reaches a certain height, it is extracted downstream by the extraction valve, and at the same time, the attached liquid is evaporated by flash evaporation. It is a structure to be dried. As a wet cake surface detection method, in the same manner as in Example 1, a pair of upper sensors (H1 and H2) are installed in the upper part of the wet cake hopper, and when the powder surface is detected at the same time, an extraction valve is used. Was controlled by DCS so as to be opened for a certain period of time. However, wet cake detection at the lower sensor position was not a necessary condition for opening the extraction valve.

  However, in this method, due to a temporary malfunction of the upper sensor, the extraction valve is frequently opened in a state where a sufficient amount of wet cake is not secured at the lower sensor position, and the wet cake is retained. It was not ensured that all the sealing layers were always secured. As a result, communication occurred between the gas phase portion in the wet cake hopper and the extraction valve, and a large amount of high-pressure gas in the hopper was blown through the dry cake hopper. At this time, the fluctuation range of the pressure difference between the inside and outside of the wet cake hopper cannot be kept within the control range, and greatly fluctuates to 0.2 MPa or more. As a result, the wet cake hopper partially drys in the wet cake hopper. Fluidity is reduced, causing localized wet cake blockage, contact with the upper screen bowl decanter equipment and damage, and large amounts of high pressure gas can cause large fluctuations in pressure in the dry cake hopper, causing the rotary valve to There was a situation such as damage that occurred, and there was a situation where it was unavoidable to stop the operation for a long time, and it was difficult to continue the continuous stable operation for a long time.

DESCRIPTION OF SYMBOLS 1 Oxidation reaction apparatus 2 Crystallization tank 3 Solid-liquid separation and washing apparatus 4 Wet cake hopper 5 Evaporation and drying apparatus 6 Dry cake hopper 7 Reduction reactor 8 Crystallization tank 9 Solid-liquid separation and washing apparatus 10 Wet cake hopper 11 Evaporation and drying Drying device 12 Dry cake hopper 13 Additional drying device 14 Separation washing drying device 15 Separation washing drying device

30 Solid-liquid separation / washing device 31 Wet cake hopper 32 Cake surface upper powder level meter 33 Cake surface lower powder level meter 34 Extraction valve 35 Dispersion control system 36a Pressure gauge 36b Pressure gauge 37 Dry cake hopper 38 Cake surface upper powder level meter 39 Lower cake surface powder level meter 40 Extraction valve 41 Pressure gauge 42 Distributed control system

61 Housing 62 Flange 63 Grounding electrode part 64 Insulating part 65 Detection electrode part

71 Lead wire from detection electrode 72 Lead wire from ground electrode or hopper 73 Shielding layer 74 Insulating layer

100 Raw materials, etc. (including recycling)
101 Oxidation reaction slurry 102 Crystallization slurry 103 Separated and washed wet cake 104 Dry wet cake 105 Dry cake 106 Reduction reaction slurry 107 Crystallization slurry 108 Separated and washed wet cake 109 Dry wet cake 110 Hydrogenated raw material 111 High purity terephthalate acid

a slurry liquid b wet cake c separation mother liquor / cleaning liquid d cake e cake adhering liquid AA sensor BB cable CC current amplifier

Claims (11)

In a method for producing an aromatic dicarboxylic acid by liquid phase oxidation of a dialkyl aromatic hydrocarbon with molecular oxygen in a reaction medium,
Storing the wet cake containing the aromatic dicarboxylic acid and the liquid substance obtained by the liquid phase oxidation in a container, and then transferring the wet cake to the outside of the container;
A method for producing an aromatic dicarboxylic acid, characterized in that a fluctuation range of a pressure difference between a pressure inside the container and a pressure outside the container, which is a transfer destination in a transfer step, is maintained within a range of ± 0.2 MPa. The wet cake is substantially always retained in a certain amount or more in the container, and the container outlet is applied in a state that is always sealed by the wet cake,
The fragrance according to claim 1, wherein the amount of the wet cake retained in the container is 0.001 or more and 0.5 or less when the transfer amount of the wet cake per hour is 1. For producing aromatic dicarboxylic acids.   When the position of the upper surface of the wet cake in the container is detected by a powder level meter, and the wet cake retention amount below the detected powder surface height is 1 when the transfer amount of the wet cake per hour is 1, It is 0.001 or more and 0.5 or less, The manufacturing method of aromatic dicarboxylic acid of Claim 1 or 2 characterized by the above-mentioned.   The aromatic dicarboxylic acid according to any one of claims 1 to 3, wherein at least a part of the liquid substance contained in the wet cake is evaporated together with the transfer of the wet cake to the outside of the container. Production method.   The method for producing an aromatic dicarboxylic acid according to any one of claims 1 to 4, wherein a pressure difference between the pressure inside the container and the pressure outside the container is 0.001 MPa or more and 5 MPa or less. .   The method for producing an aromatic dicarboxylic acid according to any one of claims 1 to 5, wherein the pressure inside the container is 0.001 MPaG or more and 5 MPaG or less.   The method for producing an aromatic dicarboxylic acid according to claim 1, wherein the liquid substance contains water or a mixture of water and acetic acid.   The content of the liquid substance in the wet cake is 0.01 wt% or more and 25 wt% or less with respect to the content of the aromatic dicarboxylic acid. The manufacturing method of aromatic dicarboxylic acid of description.   The amount of the wet cake in the container is detected by a powder level meter, and the wet cake is transferred from the container outlet in conjunction with a mechanism having a transfer function connected to the container. Item 9. A method for producing an aromatic dicarboxylic acid according to any one of Items 1 to 8.   The method for producing an aromatic dicarboxylic acid according to claim 9, wherein the powder level meter is a contact-type powder level meter.   The method for producing an aromatic dicarboxylic acid according to any one of claims 1 to 10, wherein the aromatic dicarboxylic acid is terephthalic acid.

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