JP2009203163A - Drying method of terephthalic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simpler drying method of crude terephthalic acid and high-purity terephthalic acid. <P>SOLUTION: The drying method of terephthalic acid comprises using a fluidized bed dryer, where the drying method comprises a step of reducing the liquid content of terephthalic acid down to 14 wt.% or lower before a drying step by the fluidized bed dryer. Preferably, the liquid content of terephthalic acid is reduced down to 14 wt.% or lower by subjecting terephthalic acid to flash drying. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for drying terephthalic acid.

  In general, in the production process of terephthalic acid, which is a kind of aromatic carboxylic acid, in producing crude terephthalic acid, the method shown in FIG. 1 is performed. First, p-xylene B as a raw material is oxidized in the oxidation reactor 1 in a solvent composed of acetic acid A to produce terephthalic acid. Terephthalic acid is crystallized in the crystallization tank 2 to obtain a primary slurry C. The primary slurry C is introduced into the solid-liquid separator 3 and separated into the separated mother liquor D and the dehydrated cake E. The dehydrated cake E is fluidized by the drying gas in the drying device 4, thereby producing crude terephthalic acid crystals F Get. A primary solid-liquid separation step for separating the separated mother liquor D is performed.

Conventionally, a steam tube dryer has been used in the drying apparatus 4, but with an increase in production capacity in one plant in a recent terephthalic acid production plant, the steam tube dryer has become larger and expensive. Therefore, a simpler method for drying crude terephthalic acid has been demanded.
Next, in producing high-purity terephthalic acid from crude terephthalic acid, the method shown in FIG. 2 is performed. First, the crude terephthalic acid a obtained by using the above-described method for producing crude terephthalic acid in the mixing tank 21 is mixed with water b to form an initial slurry c. The initial slurry c is pressurized by the pump 22 and then the preheater 23. Heat to complete dissolution. By reducing the solution d with hydrogen in the hydrogenation reactor 24, 4-carboxylbenzaldehyde, which is a typical impurity in the crude terephthalic acid, is reduced to highly soluble p-toluic acid. The reducing treatment liquid e is cooled by releasing pressure in the crystallization tank 25 to crystallize terephthalic acid to obtain a slurry f. The slurry f is separated into a separation mother liquor j and a dehydrated cake g using a solid-liquid separation device 26, and the dehydrated cake g is fluidized with a drying gas in a drying device 27, whereby a high-temperature high-purity terephthalic acid crystal h is obtained. obtain.

Conventionally, a steam tube dryer has been used in the drying device 27. However, with an increase in production capacity in one plant in a recent high-purity terephthalic acid production plant, the steam tube dryer has become larger and expensive. . Therefore, a simpler method for drying high-purity terephthalic acid has been demanded.
JP 2004-315431 A

  It is to provide a simpler method for drying crude terephthalic acid and high-purity terephthalic acid.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors use a fluidized bed dryer as an alternative to the steam tube dryer in the drying devices 4 and 27, thereby reducing the equipment size and reducing the investment amount. I found it possible. However, when the steam tube dryer is replaced with a fluidized bed dryer, it has been found that there is a risk that the terephthalic acid crystals may be clogged and fixed in the fluidized bed dryer, resulting in a decrease in drying efficiency and further equipment shutdown.

Therefore, as a result of further intensive studies, the present inventors have found that the clogging and fixing of the terephthalic acid crystal in the fluidized bed dryer is caused by the liquid contained in the terephthalic acid crystal, and inserted into the fluidized bed dryer. The present invention was completed by controlling the liquid content of the terephthalic acid crystals. That is, the gist of the present invention resides in the following (1) to (6).
(1) A method of drying terephthalic acid using a fluidized bed dryer, comprising a step of reducing the liquid content of terephthalic acid to 14% by weight or less before the drying step by the fluidized bed dryer. A characteristic method for drying terephthalic acid.
(2) The drying method as described in (1) above, wherein the terephthalic acid is crude terephthalic acid containing 4-carboxybenzaldehyde obtained by oxidizing paraxylene.
(3) Terephthalic acid oxidizes para-xylene to produce crude terephthalic acid containing 4-carboxybenzaldehyde, and the resulting crude terephthalic acid is dissolved in an aqueous solvent to obtain a crude terephthalic acid aqueous solution. The 4-carboxybenzaldehyde in the acid aqueous solution is reduced with hydrogen in the presence of a catalyst to obtain a reduction reaction liquid obtained as p-toluic acid, and the reduction reaction liquid is cooled to crystallize the terephthalic acid crystals. The terephthalic acid obtained by solid-liquid separation of the terephthalic acid cake containing the terephthalic acid crystal as a main component and the reduction reaction mother liquor from the slurry, as described in (1) above Drying method.

(4) The drying method according to any one of (1) to (3) above, wherein the liquid content of terephthalic acid is reduced to 14% by weight or less by subjecting terephthalic acid to flash drying.
(5) Any of the above (1) to (4), wherein the step of reducing the liquid content of terephthalic acid to 14% by weight or less reduces the liquid content of terephthalic acid to 10% by weight or less. The drying method described in 1.
(6) The drying method according to any one of (1) to (5) above, wherein the temperature of terephthalic acid coming out of the fluidized bed dryer is 100 ° C. or lower.

  According to the present invention, a simple method for drying terephthalic acid can be provided.

Hereinafter, the present invention will be described in detail.
The terephthalic acid drying method of the present invention is a method of drying terephthalic acid using a fluidized bed dryer, and the liquid content of terephthalic acid is set to 13% by weight or less before the drying step using the fluidized bed dryer. It has the process to reduce, It is characterized by the above-mentioned.
The origin of the terephthalic acid to be dried in the present invention is not particularly limited. Even if it is crude terephthalic acid obtained by oxidizing paraxylene, the crude terephthalic acid aqueous solution is dissolved in water. In the presence of a platinum group metal catalyst, reduction treatment is performed by contacting with hydrogen, and the treatment liquid is crystallized to form a slurry, and the crystals in the slurry are separated with a terephthalic acid obtained by a solid-liquid separator. There may be. The water content of the terephthalic acid after solid-liquid separation is usually 15 to 20% by weight with respect to the terephthalic acid of the dehydrated cake G.

  The terephthalic acid as a product is required to have a moisture concentration of 0.12% by weight or less. Therefore, the terephthalic acid thus obtained needs to be sent to a drying process and dried. In the present invention, a fluidized bed dryer is used in the drying step, and the liquid content of terephthalic acid is set to 14% before the drying step in order to prevent clogging and fixing of the high purity terephthalic acid crystals in the fluidized bed dryer. It is essential to provide a process for reducing the percentage to less than or equal to%. The reduction of the liquid content is preferably less than 13% by weight, more preferably 10% by weight or less, and particularly preferably 8% by weight or less. In addition, since it becomes unnecessary to use a fluidized-bed dryer if there is too much drying in this step and the meaning of applying the present invention is lost, the reduction of the liquid content is usually up to 3% by weight, preferably up to 5% by weight. .

  The “liquid content” in the present invention is the weight ratio (W1 / W2) of the weight (W1) of the liquid adhering to the terephthalic acid cake to the weight (W2) of the solid content. In the present invention, when the liquid is water, the water content may be obtained by the Karl Fischer method. When the liquid adhering to the terephthalic acid cake is other than water, the weight (W1 + W2) of the mixed state of the liquid and the solid content is measured, and then removed by evaporating the liquid content using an oven. It can be determined by measuring the weight (W2) of the minute. In the present invention, the liquid is considered to have evaporated if there is no change in weight for 3 minutes or more in the state of heating at a normal pressure or above the boiling point and below the sublimation temperature of terephthalic acid (for example, 150 ° C.).

  As a method for reducing the liquid content of terephthalic acid to 14% by weight or less, (i) a method of flash-drying terephthalic acid, (ii) a method of pre-drying terephthalic acid with a heater, (iii) dried terephthalic acid crystals And the like. From the viewpoint of simplicity of the apparatus and compactness, a method of flash drying terephthalic acid is preferable.

(I) Method of flash-drying terephthalic acid Flash drying is a method described in Japanese Patent Application Laid-Open No. 2002-336687, in which the pressure of terephthalic acid cake is lower than the pressure in the separator and the temperature in the separator It is a drying method in which the liquid attached to the cake is evaporated by the internal energy released by the movement to the lower temperature compound recovery zone. The difference between the pressure in the separation device and the pressure in the compound recovery zone is preferably 0.01 MPa to 22 MPa, more preferably 0.11 MPa to 12 MPa, and particularly preferably 0.21 MPa to 7 MPa. The temperature difference between the cake temperature in the separator and the cake discharged to the compound recovery zone is preferably 5 ° C to 250 ° C, more preferably 10 ° C to 200 ° C, and particularly preferably 20 to 170 ° C. By this method, the liquid content of the terephthalic acid cake is preferably 3% by weight or more, more preferably 6% by weight or more, and particularly preferably 9% by weight or more. Here, that the liquid content of the terephthalic acid cake is reduced by 3% by weight means that the liquid content of the cake is reduced from 15% to 12%, for example.

(Ii) Method of pre-drying terephthalic acid with a heater This method is a method in which a heater is provided in front of a drying apparatus to remove the liquid contained in the terephthalic acid cake by evaporation, thereby reducing the liquid content. The heating temperature is equal to or higher than the boiling point of the liquid, and the heating time may be selected by checking the liquid content. As a heat source for the heater, it is economically desirable to use steam produced as a by-product of the terephthalic acid production process. The liquid content of the terephthalic acid cake obtained by this method is preferably 10% by weight or less, more preferably 8% by weight or less. If the liquid content is too high, a large load is applied to the downstream drying apparatus, and there is a possibility that the cake adheres to the contact portion between the device and the cake, and causes problems due to sticking and accumulation.

(Iii) Method of mixing dried terephthalic acid crystals This method is specifically described in JP-A No. 2004-217595. This is a method of mixing a terephthalic acid cake having a high liquid content before entering the dryer with a product terephthalic acid having a liquid content of 0.12% by weight or less, preferably 0.10% by weight or less after drying. The liquid content after mixing the product terephthalic acid is preferably 10% by weight or less, more preferably 8% by weight or less. If the liquid content is too high, a large load is applied to the downstream drying apparatus, and there is a possibility that the cake adheres to the contact portion between the device and the cake, and causes problems due to sticking and accumulation.

Examples of the fluidized bed dryer in the present invention include a dryer described in JP-A No. 2004-315431.
Examples of the process for producing crude terephthalic acid include a procedure as shown in FIG.
First, p-xylene B ′ as a raw material is oxidized in an oxidation reactor 11 in a solvent composed of acetic acid A ′ to generate terephthalic acid. There is no need for only one oxidation reactor 11, and it is preferable that there are a plurality of oxidation reactors in series and the oxidation reaction is performed in multiple stages. The terephthalic acid produced in the oxidation reactor is cooled by reducing the pressure in the crystallization tank 12 to crystallize crystals mainly composed of the terephthalic acid, thereby obtaining a primary slurry C ′. In addition, it is preferable that there are a plurality of crystallization tanks 12 in series and crystallization is performed in multiple stages, rather than only one crystallization tank 12.

This primary slurry C ′ is introduced into the solid-liquid separator 13 to obtain separated mother liquor D ′ and dehydrated cake E ′.
In the present invention, the dehydrated cake E ′ is sent to the liquid content reduction step 14 to reduce the liquid content of terephthalic acid to 13% by weight or less. The terephthalic acid cake F ′ whose liquid content is reduced to 13% by weight or less is dried by the fluidized bed dryer 15 to obtain a crude terephthalic acid crystal G ′.

  Next, a solid-liquid separation method of the slurry C ′ in the solid-liquid separation device 13 will be described. The solid-liquid separation step is composed of two steps, a solid-liquid separation step and a washing step, and is generally carried out by separate devices, but a solid-liquid separation / washing device that can be carried out simultaneously may be used. Also in the present invention, an apparatus that simultaneously performs such solid-liquid separation and washing may be used. Examples of such an apparatus include (i) a screen bowl type centrifuge, (ii) a rotary vacuum filter, and (iii) a horizontal belt filter, and preferably a screen bowl type centrifuge.

However, in any method, it is difficult to reduce the liquid content of the separated cake, that is, the liquid adhesion rate with respect to the solid content, to 10% by weight or less. If the liquid content is reduced by changing the design of the solid-liquid separator 13, excessive equipment is required. It becomes enhancement.
Next, the drying method of the terephthalic acid cake F ′ (the terephthalic acid cake whose liquid content is reduced to 14% by weight or less) in the fluidized bed dryer 15 will be described. The fluidized bed dryer 15 feeds the drying gas H ′, evaporates the liquid accompanying the terephthalic acid cake F ′, and dries it. Here, the liquid component contained in the terephthalic acid cake F ′ is mainly composed of acetic acid, and additionally contains by-product water in the oxidation reactor 11. Further, the dry gas is a gas having a humidity that does not cause condensation at the operating temperature of the drying apparatus when the liquid component contained in the terephthalic acid cake F ′ is accompanied and removed. It is necessary to consider the supply amount. In particular, on the upstream side of the drying gas H ′ in the fluidized bed dryer 15, since the amount of moisture accompanying it is larger than that on the downstream side, care must be taken to prevent condensation. When a gas having a dew point of −40 ° C. is used as the drying gas H ′, the supply amount of the drying gas H ′ is desirably 100 to 1000 m ³ in a standard state per ton of terephthalic acid in the terephthalic acid cake F ′. More desirably, the thickness is 300 to 800 m ³ . The standard state means a state where the temperature is 0 ° C. and the atmospheric pressure is 1 atm. Further, by fluidizing the terephthalic acid cake with the drying gas H ′, the effective drying area is increased, and the water in the terephthalic acid cake is almost vaporized in the form of surface evaporation. The temperature of the treated cake can be kept below 100 ° C.

  Further, the temperature of the drying gas H ′ can be arbitrarily determined within a range in which the processing temperature of the processing cake can be maintained, and may be 100 ° C. or higher at the initial time point. Furthermore, it is desirable to indirectly use a heat source such as water vapor for drying the terephthalic acid cake. As a result of this drying operation, the temperature of the crude terephthalic acid crystal G ′ obtained from the fluidized bed dryer 15 is preferably 70 to 100 ° C., more preferably 90 to 100 ° C. On the other hand, if the temperature is less than 70 ° C., it is advantageous for cooling, but since the temperature is low, the evaporation rate and the evaporation amount of the liquid component are reduced, and the originally required drying effect cannot be sufficiently obtained. Fear comes out.

  The dry gas H ′ is preferably a process gas, an inert gas, or a mixed gas thereof. The process gas refers to a gas generated in the step of producing the crude terephthalic acid from the paraxylene, the step of producing high-purity terephthalic acid from the crude terephthalic acid, and the steps associated therewith. As a specific example, a gas obtained by treating exhaust gas generated when the para-xylene is oxidized with air may be used. When the process gas is used, a large amount of gas can be obtained at low cost without preparing a separate gas. Moreover, the said inert gas means the gas which does not raise | generate reaction with the said terephthalic acid, for example, nitrogen, air, a noble gas, etc. are mentioned.

  The drying gas H ′ obtained by drying the terephthalic acid cake with the fluidized bed dryer 15 is discharged as the drying device exhaust gas I ′ outside the fluidized bed dryer 15 together with the evaporated liquid. However, depending on the supply amount of the drying gas H ′ of the fluidized bed dryer 15, the gas flow rate in the apparatus, the flow state, etc., not only the evaporated liquid but also the terephthalic acid solid content in the fluidized bed dryer exhaust gas I ′. In some cases, a crystalline product is also included. If these are discarded, the yield in the whole process is lowered.

  Accordingly, it is desirable that the cyclone 16 separates the terephthalic acid crystal contained in the fluidized bed dryer exhaust gas I ′ from the gas and collects it in the fluidized bed dryer 15. In the cyclone 16, the crystalline substance of the terephthalic acid contained in the fluidized bed dryer exhaust gas I ′ is collected by centrifugal force, and subjected to sedimentation separation treatment, from the cyclone exhaust gas K ′ that is a gas component. Separated solid J ′ is obtained.

  As another method, the scrubber 17 is used to scrub the fluidized bed dryer exhaust gas I ′ using acetic acid, and the above-mentioned crystals contained in the fluidized bed dryer exhaust gas I are converted into scrubber exhaust gas M ′. It is desirable to separate and recover as a recovered slurry. Further, the scrubber 17 scrubs the cyclone exhaust gas K ′ using acetic acid, and separates the above-mentioned crystals that cannot be recovered by the cyclone 16 but remain in the cyclone exhaust gas K ′ from the scrubber exhaust gas M ′. If the recovered slurry L ′ is recovered, it is desirable that the recovery process is more thorough.

The recovered slurry L ′ thus obtained may be sent to the mixing tank 11 and dissolved again in acetic acid A ′ together with p-xylene B ′, or sent to the solid-liquid separator 13 for washing the dehydrated cake C ′ with water. It is more desirable to use for the cleaning liquid. In either case, the recovered terephthalic acid or the like returns to the step of producing crude terephthalic acid.
Further, the scrubber exhaust gas M ′ contains liquid components in the fluidized bed dryer 15 and the scrubber 17. A liquid component is removed from the scrubber exhaust gas M ′ by using the gas processing device 18, and a part or all of the circulating gas N ′ having a humidity and a temperature satisfying the same conditions as the dry gas H ′ is partially or entirely. When used in the fluidized bed dryer 15 together with the drying gas H ′, the amount of exhaust gas discarded outside the system can be reduced.

Next, the process for producing high-purity terephthalic acid from crude terephthalic acid includes, for example, a procedure as shown in FIG.
First, crude terephthalic acid A is mixed with water B in a mixing tank 31 to form an initial slurry C. The initial slurry C is pressurized by a pump 32 and then heated by a preheater 33 to be completely dissolved. The obtained solution D is brought into contact with hydrogen in the hydrogenation reactor 34 to reduce the oxidation intermediate contained in the crude terephthalic acid, thereby purifying the crude terephthalic acid. This oxidized intermediate is an intermediate substance for purifying terephthalic acid by oxidizing para-xylene, mainly 4-carboxylbenzaldehyde, and the reducing substance is paratoluic acid with high water solubility.

  The refining treatment liquid E thus purified is cooled in the crystallization tank 35 while reducing the pressure, whereby crystals mainly composed of the terephthalic acid are crystallized to obtain a slurry F. In addition, it is preferable to have a plurality of crystallization tanks 35 in series and perform crystallization in a multistage manner, rather than only one crystallization tank 35. Since the oxidation intermediate is reduced to a highly water-soluble component in the hydrogenation reactor, most of the crystals crystallized here become the terephthalic acid. In order to crystallize, the final crystallization temperature is usually preferably 120 to 180 ° C. The slurry F is separated into a dehydrated cake G and a separated mother liquor J using a solid-liquid separator 36. Here, the dehydrated cake G is washed with water and the pressure is reduced to normal pressure. Generally, a centrifuge or a filter is used for the solid-liquid separator 36, and the water content of the dehydrated cake G with respect to the terephthalic acid is 15 to 20% by weight.

In the present invention, the dehydrated cake G is sent to the liquid content reduction step 37 to reduce the liquid content of terephthalic acid to 14% by weight or less. The terephthalic acid cake H whose liquid content is reduced to 14% by weight or less is dried by a fluidized bed dryer 38 to obtain high-purity terephthalic acid crystals I.
Next, a solid-liquid separation method of the slurry F in the solid-liquid separation device 36 will be described. The solid-liquid separation step includes two steps, a solid-liquid separation step and a washing step, and is generally performed by separate apparatuses, but a solid-liquid separation / cleaning apparatus that can be performed simultaneously may be used. Also in the present invention, an apparatus that simultaneously performs such solid-liquid separation and washing may be used. Examples of such an apparatus include a screen bowl type centrifuge, a rotary vacuum filter, a horizontal belt filter, and the like, and a screen bowl type centrifuge is preferable.

However, in any method, it is difficult to reduce the liquid content of the separated cake, that is, the liquid adhesion rate with respect to the solid content to 14% by weight or less. If the liquid content is reduced by changing the design of the solid-liquid separator 36, excessive equipment is required. It becomes enhancement.
Next, a method for drying the terephthalic acid cake H (the terephthalic acid cake whose liquid content is reduced to 14% by weight or less) in the fluidized bed dryer 38 will be described. The fluidized bed dryer 38 feeds the drying gas K and dries the terephthalic acid cake H. Here, the dry gas is a gas having a humidity that does not condense at the operating temperature of the drying apparatus when the moisture contained in the terephthalic acid cake H is accompanied and removed. It is necessary to consider the supply amount. In particular, on the upstream side of the drying gas K in the fluidized bed dryer 38, the amount of moisture accompanying the water is larger than that on the downstream side, so care must be taken to prevent condensation. When a gas having a dew point of −40 ° C. is used as the drying gas K, the supply amount of the drying gas K is desirably 100 to 1000 m ³ in a standard state per ton of terephthalic acid in the terephthalic acid cake H, and more desirably. Is 300-800 m ³ . The standard state means a state where the temperature is 0 ° C. and the atmospheric pressure is 1 atm.

Also, by fluidizing the terephthalic acid cake with the drying gas K, the effective drying area is increased, and the water in the terephthalic acid cake is almost vaporized in the form of surface evaporation. The temperature of the treated cake can be maintained below 100 ° C.
Further, the temperature of the drying gas K can be arbitrarily determined within a range in which the processing temperature of the processing cake can be maintained, and may be 100 ° C. or higher at the initial time point. Furthermore, it is desirable to indirectly use a heat source such as water vapor for drying the terephthalic acid cake. As a result of this drying operation, the temperature of the crystal I of high-purity terephthalic acid obtained from the fluidized bed dryer 38 is desirably 70 to 100 ° C, and more desirably 90 to 100 ° C. On the other hand, when the temperature is less than 70 ° C., it is advantageous for cooling, but since the temperature is low, the evaporation rate and the evaporation amount of water decrease, and the drying effect that is originally required may not be sufficiently obtained. Comes out.

  The dry gas K is desirably a process gas, an inert gas, or a mixed gas thereof. The process gas refers to a gas generated in the step of producing the crude terephthalic acid from the para-xylene, the step of producing the high-purity terephthalic acid from the crude terephthalic acid, and the steps associated therewith. As a specific example, a gas obtained by treating exhaust gas generated when the para-xylene is oxidized with air may be used. When the process gas is used, a large amount of gas can be obtained at low cost without preparing a separate gas. Moreover, the said inert gas means the gas which does not raise | generate reaction with the said terephthalic acid, for example, nitrogen, air, a noble gas, etc. are mentioned.

  The drying gas K obtained by drying the terephthalic acid cake with the fluidized bed dryer 38 is discharged as a drying device exhaust gas L outside the fluidized bed dryer 38 along with the evaporated water. However, depending on the supply amount of the drying gas K, the gas flow rate in the apparatus, the flow state, etc. of the fluidized bed dryer 38, not only the evaporated water but also the crystal that is the solid content of terephthalic acid in the fluidized bed dryer exhaust gas L. Things may also be included. If these are discarded, the yield in the whole process is lowered.

  Therefore, it is desirable that the cyclone 39 separates the crystalline substance, which is the terephthalic acid, contained in the fluidized bed dryer exhaust gas L from the gas component and collects it in the fluidized bed dryer 38. In the cyclone 39, the crystalline substance of the terephthalic acid contained in the fluidized bed dryer exhaust gas L is collected by centrifugal force, and is separated from the cyclone exhaust gas N, which is a gas component, by performing sedimentation treatment. Solid M is obtained.

  As another method, the scrubber 40 is used to scrub the fluidized bed dryer exhaust gas L using water to separate the crystals contained in the fluidized bed dryer exhaust gas L from the scrubber exhaust gas P. It is desirable to recover as a recovered slurry. Further, the scrubber 40 is used to scrub the cyclone exhaust gas N using water, and the crystallized matter that cannot be recovered by the cyclone 39 but remains in the cyclone exhaust gas N is separated from the scrubber exhaust gas P and recovered. When recovered as slurry Q, it is desirable that the recovery process be more thorough.

The recovered slurry Q thus obtained may be sent to the mixing tank 31 and dissolved again in the water B together with the crude terephthalic acid A. Alternatively, the recovered slurry Q may be sent to the solid-liquid separator 36 and used as washing water for washing the dehydrated cake G. It is more desirable to use it. In either case, the recovered terephthalic acid or the like returns to the step of producing high-purity terephthalic acid.
The scrubber exhaust gas P contains water in the fluidized bed dryer 38 and the scrubber 40. Moisture is removed from the scrubber exhaust gas P using the gas processing device 41, and a part or all of the circulating gas R having a humidity and temperature satisfying the same conditions as the dry gas K is fluidized bed dried. When used with the dry gas K in the machine 38, it is desirable because the amount of exhaust gas discarded outside the system can be reduced.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to a following example at all.
Synthesis Example 1: Production of high-purity terephthalic acid cake Paraxylene and acetic acid are continuously supplied to a liquid phase oxidation reactor in a facility where the production amount of terephthalic acid is 36 Ton / hr, and at the same time, cobalt acetate, manganese acetate, and odor are used as catalysts. Hydrogen fluoride was also continuously supplied, and an oxidation reaction was performed at a temperature of 197 ° C. and a pressure of 1.45 MPa. Air was used as a gas for performing the oxidation reaction. Subsequently, the oxidation slurry was continuously transferred to a low temperature additional oxidation reactor, and an oxidation reaction was performed at a temperature of 190 ° C. and a pressure of 1.3 MPa. Air was used as a gas for performing the oxidation reaction.

The low temperature additional oxidation slurry was continuously crystallized in a three-stage intermediate treatment tank, and solid-liquid separation was performed at atmospheric pressure. At this time, the liquid content of the cake separated into solid and liquid was 15.0% by weight.
Next, this cake was dried at atmospheric pressure with a steam tube dryer type dryer using a steam heating source. Steam having a pressure of 0.6 MPa is circulated around the dryer to heat the dryer. The cake adhering liquid evaporated by heating is taken out of the system by an inert gas circulating in the dryer. Here, the outlet temperature of the dryer is 140 ° C. The liquid content of the obtained crude terephthalic acid was 0.10% by weight.

Next, the crude terephthalic acid obtained in the above step and water were continuously supplied to a hydrogenation reactor, and a reduction reaction was performed at 290 ° C. and 8.6 MPa. Hydrogen was used as a gas for performing the reduction reaction.
The reducing slurry was continuously crystallized in a 5-stage intermediate treatment tank, and solid-liquid separation was performed at atmospheric pressure. At this time, the liquid content of the cake separated into solid and liquid was 15.0% by weight.
Next, this cake was dried at atmospheric pressure with a steam tube dryer type dryer using a steam heating source. Steam having a pressure of 0.6 MPa is circulated around the dryer to heat the dryer. The cake adhering liquid evaporated by heating is taken out of the system by an inert gas circulating in the dryer. Here, the outlet temperature of the dryer is 140 ° C. The liquid content of the obtained high purity terephthalic acid was 0.10% by weight.

  In order to carry out the experiments shown in the Examples to the high-purity terephthalic acid obtained by the above method, water was added to obtain terephthalic acid cakes having a moisture content of 14% by weight, 15% by weight and 20% by weight, respectively.

<Drying test using fluidized bed dryer>
The following fluidized drying tests were performed using a fluidized bed dryer 51 (inner diameter 300 mm, fluidized bed area 0.24 m ² ) shown in FIG.
To the fluidized bed dryer 51 is added terephthalic acid (a) added with water so as to have a moisture content of a specified weight%, and a dried gas (c) heated by a heater 52 is added to the fluidized bed dryer. In 51, the cake was dried by flowing. Nitrogen gas was used as the drying gas (c). The terephthalic acid crystals that passed through the fluidized bed dryer 51 were discharged from (b), and the water content of the discharged terephthalic acid crystals was analyzed using a Karl Fischer analyzer.

  The fluidized bed dryer exhaust gas (d) that has passed through the fluidized bed dryer 51 may contain not only the water evaporated from the terephthalic acid cake but also crystals of terephthalic acid. The terephthalic acid crystals were separated from the gas component from the exhaust gas (d) and recovered to the fluidized bed dryer 51. The fluidized bed dryer exhaust gas (e) after recovering the terephthalic acid crystals was discharged out of the system by the blower 54. Further, (g) is a steam pipe for indirect heating, and (b) is an outlet for condensed water of the steam. The temperature of the steam for heating is 151 ° C.

<Measurement of moisture content>
The water content in the examples was determined using the Karl Fischer method.
Example 1
The high-purity terephthalic acid cake having a water content (= liquid content) of 14% by weight obtained in Synthesis Example 1 is supplied to the fluidized bed dryer 51 at 200 kg / h, and dry nitrogen gas at 100 ° C. is fluidized bed dried. It adjusted so that it might become the superficial velocity 0.3m / s in a plane.

The terephthalic acid crystals did not stick and the flow state was good. When the water content of the terephthalic acid crystal collected in (b) was measured, it was 0.11% by weight.
Comparative Example 1
As high-purity terephthalic acid supplied to the fluidized bed dryer 51, the high-purity terephthalic acid cake obtained in Synthesis Example 1 (liquid content = water content = 20% by weight) was used. I made it.

Immediately after the high-purity terephthalic acid cake was introduced, the high-purity terephthalic acid cake did not flow at all inside the fluidized bed dryer 31, and the experiment was stopped.
Comparative Example 2
The same procedure as in Example 1 was conducted except that high-purity terephthalic acid having a water content (= liquid content) of 15% by weight obtained in Synthesis Example 1 was supplied to the fluidized bed dryer 51 at 240 kg / h.

  The terephthalic acid crystals were fixed in the fluidized bed dryer 51. Therefore, the supply of the terephthalic acid cake was stopped every 15 minutes, and the fluidized bed dryer 51 was hit and fixed to the wall in the dryer by giving an impact. I had to drop terephthalic acid crystals. The water content of the terephthalic acid crystal sampled in (b) was 0.14% by weight.

Flow diagram showing an example of a method for producing crude terephthalic acid Flow diagram showing an example of a method for producing high-purity terephthalic acid Flow chart showing an example of a method for producing crude terephthalic acid Flow diagram showing an example of a method for producing high-purity terephthalic acid Diagram showing the fluid dryer used in the examples

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11: Oxidation reactor 2, 12: Crystallization tank 3, 13: Solid-liquid separator 4, 14: Drying device 15, 38, 54: Fluidized bed dryer 16, 39, 53: Cyclone 17, 40: Scrubber 18, 41: Gas treatment apparatus A, A ′: Acetic acid B, B ′: p-xylene C, C ′: Slurry D, D ′: Separation mother liquor E ′: Dehydrated cake F ′, H: Terephthalic acid cake G ′: Crude terephthalic acid crystals H ', K: Drying gas I', L: Fluidized dryer exhaust gas J ', M: Solid K', N: Cyclone exhaust gas L ', Q: Recovered slurry M', P: Scrubber Exhaust gas N ', R: Circulating gas 21, 31: Mixing tank 22, 32, 54: Pump 23, 33, 52: Preheater 24, 34: Hydrogenation reactor 25, 35: Crystallization tank 26, 36: Solid Liquid separation device 27: Drying device 37: Liquid content reduction step a, A: Crude terephthal Acid b, B: Water c, C: Initial slurry d, D: Solution e, E: Reduction treatment liquid f, F: Slurry g, G: Dehydrated cake h, I: High-purity terephthalic acid crystal j, J: Separation mother liquor A: Terephthalic acid B: Discharge port C: Drying gas D: Fluidized bed dryer exhaust gas E: Fluidized bed dryer exhaust gas

Claims (6)

  A method of drying terephthalic acid using a fluidized bed dryer, comprising a step of reducing the liquid content of terephthalic acid to 14% by weight or less before the drying step using the fluidized bed dryer. How to dry terephthalic acid.   The drying method according to claim 1, wherein the terephthalic acid is crude terephthalic acid containing 4-carboxybenzaldehyde obtained by oxidizing paraxylene.   Terephthalic acid oxidizes para-xylene to produce crude terephthalic acid containing 4-carboxybenzaldehyde, and the resulting crude terephthalic acid is dissolved in an aqueous solvent to obtain a crude terephthalic acid aqueous solution. The above 4-carboxybenzaldehyde was reduced with hydrogen in the presence of a catalyst to obtain a reduction reaction solution obtained as p-toluic acid, and the reduction reaction solution was cooled to crystallize the terephthalic acid crystals to form a slurry. 2. The drying method according to claim 1, wherein the terephthalic acid is obtained by solid-liquid separation of the terephthalic acid cake containing the terephthalic acid crystal as a main component and the reduction reaction mother liquor from the slurry.   4. The drying method according to claim 1, wherein the liquid content of terephthalic acid is reduced to 14% by weight or less by subjecting terephthalic acid to flash drying.   5. The drying method according to claim 1, wherein the step of reducing the liquid content of terephthalic acid to 14% by weight or less reduces the liquid content of terephthalic acid to 10% by weight or less.   The drying method according to any one of claims 1 to 5, wherein the temperature of terephthalic acid coming out of the fluidized bed dryer is 100 ° C or lower.

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