WO2004063139A1 - Method of centrifugal separation of slurry containing aromatic carboxylic acid - Google Patents

Abstract

A method for conducting a solid-liquid separation of a slurry using a centrifuge in an aromatic carboxylic acid production process, which comprises feeding a slurry containing terephthalic acid and acetic acid as a solvent to a final crystallizing vessel (1) through a flash valve (2) and carrying out crystallization in a state of boiling under reduced pressure to thereby flash-vaporize the solvent and precipitate crystals of terephthalic acid, and operating a centrifuge (4) under atmospheric pressure in the subsequent solid-liquid separation to recover the crystals of terephthalic acid. The method employs an operating pressure for the centrifugal separation step higher than that for the final crystallizing vessel (1), which results in the less susceptibility of the separation section to deposition of crystals, leading to the operation of the centrifuge with good stability and to the production of high purity aromatic carboxylic acid with good efficiency.

Description

 Technical field Centrifugal separation method of aromatic carboxylic acid-containing slurry

 The present invention relates to a method for centrifuging a slurry containing crystals in a process for producing an aromatic carboxylic acid and a method for producing high-purity terephthalic acid.

<Background technology>

 In general, as an industrial method for producing aromatic carboxylic acids such as terephthalic acid, an alkyl aromatic hydrocarbon such as para-xylene is used as a raw material in an acetic acid solvent in the presence of a catalyst containing cobalt, manganese, and bromine. There is known a method of producing terephthalic acid by subjecting a slurry containing crystals of terephthalic acid or other aromatic carboxylic acid produced by an oxidation reaction in a liquid phase with oxygen to a solid-liquid separation device. Solid-liquid separators include rotary vacuum filters, belt filters, and centrifugal separators.The centrifugal separator consists of a rotating powl cylinder and a screw conveyor installed in a vertical or horizontal drum. The supplied slurry is dispersed inside the rotating bowl cylinder, and has a mechanism in which the solids settled on the wall of the bowl due to centrifugal force are moved and discharged by a screw conveyor (Patent) Reference 1).

 [Patent Document 1] Japanese Patent Application Laid-Open No. 7-507291 (Page 10, lower left column and page 10, lower right column, Figures 3 and 4)

<Disclosure of Invention>

However, when the solid-liquid separation of the slurry is performed using the above-described centrifugal separator, the slurry is cooled by the reduced pressure in the centrifuge, and crystallization may occur locally, and the generated crystals rotate. The weight in the bowl will not be evenly distributed, and the stability (balance) of the bowl's rotating shaft will be degraded, causing vibration or even rotation. There is a problem that the efficiency of the solid-liquid separation treatment is deteriorated, for example, the speed is reduced. Similarly, when the mother liquor is cooled in a mother liquor overflow storage chamber or the like in which the separated mother liquor is temporarily stored, crystallization occurs, and crystals adhere and grow on the inner surface of the separation device, that is, There is a problem that scaling occurs and hinders the separation operation.

 Such a problem is a common problem in the production of terephthalic acid when a slurry is subjected to solid-liquid separation using a centrifuge.

 In view of the above, an object of the present invention is to solve the above-mentioned problems and to smoothly carry out solid-liquid separation by a centrifugal separator in a process for producing an aromatic carboxylic acid, particularly in a solid-liquid separation process of a slurry using a centrifugal separator. In other words, it is intended to efficiently produce high-purity terephthalic acid using such a method.

 In order to solve the above-mentioned problems, the present invention provides a method for performing solid-liquid separation of a water-based or acetic acid-based slurry containing an aromatic carboxylic acid in a saturated state by a centrifugal separator. The centrifugal separation method for aromatic carboxylic acid-containing slurry is characterized in that the pressure is higher than the saturated vapor pressure of the mother liquor of the aromatic carboxylic acid-containing slurry to be separated.

 The centrifugal separation method of the aromatic carboxylic acid-containing slurry of the present invention configured as described above is characterized in that the operating pressure at the time of centrifugation is higher than the saturation vapor pressure of the mother liquor of the slurry in the step before introducing the centrifuge. Because of the high setting, the slurry before centrifugation contains aromatic carboxylic acid in a saturated state, but the aromatic carboxylic acid saturation concentration rises during centrifugation, even though it contains a large amount of aromatic carboxylic acid. As a result, the crystals of the aromatic carboxylic acid hardly precipitate.

 Therefore, crystals do not locally precipitate in the centrifugal separator 、, and the balance of the rotating mechanism does not collapse, so that solid-liquid separation by the centrifugal separator can be performed smoothly. High-purity terephthalic acid can be produced efficiently.

The step before the introduction of the centrifugal separator having the above action may be a step of generating an aromatic carboxylic acid by an oxidation reaction in an acetic acid solvent, or a step of crystallizing the aromatic carboxylic acid by flash cooling of the slurry. It may be a step of analyzing. Similarly, a method for producing crude terephthalic acid using the above-described method for solid-liquid separation of a slurry can be employed, and further purification can be performed to produce high-purity terephthalic acid.

 That is, as a method for producing crude terephthalic acid that solves the above-mentioned problems, (i) liquid phase oxidation of para-xylene at a pressure of 1 to 2 MPa in the presence of a catalyst containing cobalt, manganese and bromine using acetic acid as a solvent. (Ii) solid-liquid separation of the obtained terephthalic acid-containing slurry by a centrifugal separator, and (iii) centrifugation of the terephthalic acid-containing solid into acetic acid and acetic acid. And / or washing with water.

 In the method for producing terephthalic acid in which the above steps (i) to (iii) are performed in order, the operating pressure at the time of centrifugation in the step (ii) is set to the saturated vapor pressure of the mother liquor of the terephthalic acid-containing slurry supplied as a separation target. The method for producing terephthalic acid, which is higher than the above, can be adopted.

 In the above method, the step (ii) and the step (iii) are performed in the same apparatus, and the supply temperature of acetic acid and / or water used for washing is adjusted to the temperature (T) ° of the slurry generated in the step (ii). It is preferable to set the temperature to (T-1 20) ° C or higher with respect to C.

 In the above method, it is preferable that the operation pressure at the time of centrifugation is 0.01 to 0.2 MPa higher than the saturated vapor pressure of the mother liquor of the terephthalic acid-containing slurry to be separated.

 Further, a method for producing high-purity terephthalic acid which solves the above-mentioned problems includes: (i) a step of producing crude terephthalic acid by subjecting paraxylene to liquid phase oxidation in the presence of a catalyst using acetic acid as a solvent.

 (ii) a step of dissolving the crude terephthalic acid in water, and reducing the concentration of 4-hydroxybenzaldehyde in this solution at 230 to 350 ° C in the presence of a catalyst;

(iii) A step of crystallization by flash cooling the reduced slurry stepwise in several crystallization tanks to 120 to 180 ° C. (iv) a step of subjecting the obtained terephthalic acid-containing slurry to solid-liquid separation by a centrifuge

 (V) washing the centrifuged terephthalic acid-containing solid with water

 In the method for producing high-purity terephthalic acid, which comprises performing the above steps (i) to (V) in order,

 A method for producing high-purity terephthalic acid can be adopted, wherein the operating pressure during centrifugation in the step (i V) is higher than the final crystallization pressure in the step of crystallization by flash cooling. .

 In the above-described manufacturing method, the process (i V) and the process (V) are performed in the same apparatus, and the supply temperature of the water used for cleaning is adjusted to the temperature (T) of the slurry generated in the process (iii). It is preferable that the temperature be (T−20) ° C. or higher with respect to ° C. Further, in the above-mentioned production method, a method for producing high-purity terephthalic acid, in which the operating pressure at the time of centrifugation is 0.01 to 0.2 MPa higher than the final crystallization pressure in the step of crystallization by flash cooling. It is preferable to employ it.

<Brief description of drawings>

 FIG. 1 is a system diagram of an apparatus showing a slurry-solid separation method of a first embodiment, and FIG. 2 is a system diagram of an apparatus showing a slurry-solid separation method of a slurry according to a second embodiment. In the figures, 1 is a crystallization tank, 2 is a flash valve, 4 is a centrifuge, 5 is an ejector, 6 is a condenser, 7 is a pump, 8 is a flash valve, and 9 is a crystallization tank.

, 10 is a pump, 11 is a centrifuge, 12 is a washing tank, 13 is a decompression tank, 14 is a centrifuge, and 15 is a dryer.

<Best mode for carrying out the invention>

 Hereinafter, the present invention will be described in detail.

 As a representative example, a method for producing terephthalic acid using para-xylene has been described.

The alkyl aromatic compound used as a raw material in the present invention is an aromatic compound obtained by liquid phase oxidation. Mono-, di-, and trialkylbenzenes and other alkylbenzenes that are converted to aromatic carboxylic acids such as monocarboxylic acids, aromatic dicarboxylic acids, and aromatic tricarboxylic acids, including those in which some of the alkyl groups have been oxidized. In particular, the present invention is preferably applied to the production of terephthalic acid. In this case, as the alkylaromatic compound used as a raw material, paraxylene can be mentioned.

 As the solvent used in the present invention, acetic acid which is a lower aliphatic carboxylic acid is preferable.

The amount of the solvent used is usually 2 to 6 times the weight of paraxylene as a raw material. As the acetic acid solvent, a solvent containing a small amount of water, specifically, 10% by weight or less of water can be used.

 In order to oxidize alkyl aromatic compounds such as para-xylene, molecular oxygen-containing gas is used. However, since simple equipment and low cost are used, air is usually used. In addition, dilution air and oxygen enrichment are used. Air can also be used.

 In order to oxidize the alkyl aromatic compound, a catalyst containing cobalt (Co), manganese (Mn) and bromine (Br) as constituent elements is usually used as a catalyst. Examples of the cobalt compound as a specific compound of such a catalyst component include cobalt acetate, cobalt naphthenate, and cobalt bromide. Examples of the manganese compound include manganese acetate, manganese naphthenate, and manganese bromide. Examples of the bromine compound include hydrogen bromide, sodium bromide, cobalt bromide, manganese bromide, and promethane.

 The reaction of oxidizing the alkyl aromatic compound in the liquid phase is carried out in the presence of a catalyst in an acetic acid solvent at a temperature of 140 to 230 ° C, preferably 150 to 210 ° C, and molecular oxygen at a temperature of 150 to 210 ° C. This is performed by oxidizing an alkyl aromatic compound such as para-xylene while continuously supplying the contained gas. The reaction pressure is a pressure at which the mixture can maintain a liquid phase at least at the reaction temperature or higher, and is usually 0.2 to 5 MPa, preferably 1 to 2 MPa.

Then, in the crystallization step, the reaction slurry is lowered to an appropriate temperature and pressure to obtain an aromatic sulfuric acid slurry. The number of crystallization stages is preferably 1 to 6 stages, more preferably 2 to 3 stages. The final step in the series of crystallization steps is performed under reduced pressure boiling. As a specific operation in the reduced-pressure boiling state, flash cooling is preferable. Note that flash cooling refers to cooling by releasing pressure.

 In the method for producing terephthalic acid in the method for producing terephthalic acid according to the embodiment shown in the apparatus system diagram in FIG. 1, the slurry containing terephthalic acid using acetic acid as a solvent is supplied from a flash valve 2 to a final crystallization tank 1, By performing this process in a boiling state under reduced pressure, the solvent is flash-evaporated to precipitate terephthalic acid crystals. Then, in the solid-liquid separation step, the terephthalic acid crystals are operated by operating the centrifugal separator 4 at atmospheric pressure. I am trying to collect it. Reference numeral 5 in the figure is an ejector, 6 is a condenser (condenser) for recovering the evaporated solvent component, and 7 is a pump.

 When the slurry is centrifuged as described above, the operating pressure, that is, the pressure received by the slurry due to the atmosphere in the centrifuge drum is higher than the saturated vapor pressure of the slurry mother liquor. For example, the operating pressure, that is, the pressure received by the slurry due to the atmosphere in the centrifuge drum may be normal pressure. This pressure is higher than the pressure that the slurry receives from the atmosphere just before the centrifuge is introduced (decompression by flash = less than atmospheric pressure), so the aromatic carboxylic acid is saturated in the slurry before centrifugation. Nevertheless, aromatic carboxylic acid crystals are less likely to precipitate during centrifugation.

 Preferably, the pressure of the slurry or the atmosphere in contact with the slurry is set at 0.01 to 0.2 MPa higher than the pressure of the atmosphere in contact with the slurry or the atmosphere before the introduction of the centrifuge. It is preferable that the pressure be as high as 0.3 to 0.0IMPa.

 The supply temperature of the slurry is at least 50 ° C, preferably 60 to 100 ° C, particularly preferably 70 to 90 ° C. If the final crystallization temperature is low, the amount of the aromatic carboxylic acid to be recovered is increased, which is advantageous. However, if the temperature is too low, a decompression device with a large degree of pressure reduction is required, which is disadvantageous.

Here, the separated solid may be washed with acetic acid and / or water. This fixed It is desirable to carry out the liquid separation and the washing in the same apparatus. As the solid-liquid separator, a solid bowl type centrifuge / a screen bowl type centrifuge is preferable. The supply temperature of acetic acid and / or water used for washing is preferably (T-20) ° C or more with respect to the temperature (T) ° C of the slurry to be supplied. The upper limit of the temperature of the cleaning solution is lower than the boiling point at the operating pressure in order to maintain the liquid state after being supplied, but the temperature of the slurry to be supplied increases because the amount of terephthalic acid dissolved in the cleaning solution increases at a high temperature. The temperature is preferably (T + 30) ° C or lower with respect to (T) ° C. By doing so, the temperature of the slurry or the separated cake is prevented from lowering, and operational problems due to crystallization of the mother liquor are prevented.

 As shown in the system diagram of FIG. 2, in the slurry centrifugation step of the embodiment, the water-soluble lipoxybenzaldehyde (4CBA) contained in the crude terephthalic acid was converted into water using an unshown reactor. A crystallization step of performing a hydrogenation (reduction) reaction in a solvent at 230 to 350 ° C in the presence of a catalyst and then vaporizing water by flash cooling through a flash valve 8 is performed in a 3 to 6 crystallization tank. The slurry in which terephthalic acid is saturated is supplied to the centrifuge 11 from the final crystallization tank 9 via the pump 10. After that, the separated cake is washed with water in the washing tank 12, flash-cooled to near atmospheric pressure in the decompression tank 13, and then introduced into the centrifuge 14 by the pump 10 to perform the second solid-liquid separation. After that, it is supplied to the dryer 15 to produce high-purity terephthalic acid crystals.

 Even in such a process, by setting the operating pressure of the centrifuges 11 and 14 higher than the saturated vapor pressure of the mother liquor of the supply slurry, the slurry before centrifugation is saturated with aromatic carboxylic acid. Nevertheless, during centrifugation, it is difficult for crystals of aromatic rubonic acid to precipitate due to the increased pressure difference.

The pressure of the slurry or the atmosphere in contact with the slurry is preferably set to 0.01 to 0.2 MPa higher than the pressure of the slurry or the atmosphere in contact with the slurry before the introduction of the centrifuge, and more preferably. 0.03 ~ 0. Only high pressure is good. The temperature of the slurry supplied to the centrifuge 11 is 120 to 180 ° C, preferably 130 to 180 ° C, and particularly preferably 140 to 170 ° C. Low final crystallization temperature However, if the temperature is too low, the eutectic of paratolylic acid generated by the reduction of 4CBA is promoted, and the resulting high-purity terephthalic acid This leads to poor quality. Similarly, the temperature of the slurry supplied to the centrifugal separator 14 is at least 50 ° C, preferably 60 to 120 ° C, and particularly preferably 90 to 11 ° C.

 The solid separated by the centrifuge may be washed with water. It is desirable to carry out the solid-liquid separation and washing by this centrifuge in the same apparatus. As this solid-liquid separator, a solid bowl centrifuge / screen bowl centrifuge is preferable. The supply temperature of the water used for washing is preferably (T−20) ° C. or more with respect to the temperature (T) ° C. of the slurry to be supplied. The upper limit of the temperature of the cleaning liquid is equal to or lower than the boiling point at the operating pressure in order to maintain the liquid state after being supplied. However, when the temperature becomes high, the amount of terephthalic acid dissolved in the cleaning liquid increases. It is preferable that the temperature be (T + 30) ° C or lower with respect to T) ° C. By doing so, the temperature of the slurry or the separated cake is prevented from lowering, and operational problems due to crystallization of the mother liquor are prevented. Examples>

 [Example 1]

 Using acetic acid as a solvent, paraxylene is oxidized in the liquid phase at a pressure of 1.5 MPa in the presence of a catalyst containing Co / MnZBr to produce a terephthalic acid-containing slurry. The pressure was reduced to below (0.05MPa) and the mixture was flash-cooled to 90 ° C. When the obtained terephthalic acid slurry was subjected to solid-liquid separation with a centrifuge, the inside of the drum was set to atmospheric pressure to separate crude terephthalic acid. did.

Further, the crude terephthalic acid obtained in the next step is dissolved in water, and the 4-carboxybenzaldehyde in the dissolved product is reduced in the presence of a Group 8 metal catalyst, and the reduced product is flash-evaporated to 5-stage crystals. Was analyzed. The final crystallization conditions were 160 ° C. and 0.62 MPa. The resulting slurry containing terephthalic acid crystals was subjected to solid-liquid separation using a centrifuge at an operating pressure of 0.69 MPa in the process shown in FIG. After the release cake has been washed in the washing tank, the slurry that has been flash-cooled to atmospheric pressure is further supplied to a second centrifuge, where it is subjected to solid-liquid separation at an operating pressure of 0.12 MPa, and the separation cake is removed. Drying produced high-purity terephthalic acid.

 The solid-liquid separation by the centrifugal separator was performed continuously for 200 hours, but the balance was good at the time of rotation, no vibration was generated, and the solid-liquid separation was performed smoothly. From this, it is estimated that local precipitation of terephthalic acid did not occur in the centrifuge.

[Example 2]

 Using acetic acid as a solvent, paraxylene is oxidized in the liquid phase at a pressure of 1.5 MPa in the presence of a catalyst containing Co / MnZBr to produce a terephthalic acid-containing slurry. The pressure in the drum was reduced to atmospheric pressure or less (0.05 MPa), and the mixture was flash-cooled to 90 ° C. When the obtained terephthalic acid slurry was subjected to solid-liquid separation by a centrifugal separator, the pressure inside the drum was set to atmospheric pressure. The crude terephthalic acid was separated.

 At this time, a screen powl type centrifugal separator was used as a centrifugal separator, and the solid content was washed in the screen part using acetic acid at 95 ° C as a washing liquid. Solid-liquid separation and washing were performed continuously for 150 hours using a screen bowl type centrifugal separator. However, vibration was not generated during rotation, and solid-liquid separation was performed smoothly. From this, it is presumed that local precipitation of terephthalic acid in the centrifuge did not occur.

[Example 3]

Example 2 was carried out in the same manner as in Example 2 except that the temperature of acetic acid used as the cleaning solution was changed to 85 ° C. Solid-liquid separation and washing with a screen bowl centrifuge were performed continuously for 110 hours, but the balance was good and no vibration occurred during rotation, and solid-liquid separation could be performed smoothly. This suggests that no local deposition of terephthalic acid occurred in the centrifuge. Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

 This application is based on Japanese Patent Application (No. 2003-004846) filed on Jan. 10, 2003, the contents of which are incorporated herein by reference.

<Industrial applicability>

 The present invention relates to a method of centrifuging aromatic carboxylic acid crystals formed in a slurry, wherein the pressure of the slurry at the time of centrifugation is reduced by the pressure of the slurry at the time of bringing the aromatic carboxylic acid into a saturated state in the previous step. Higher, so that no local precipitation of crystals occurs in the centrifuge, the balance of the rotating mechanism is not lost, and solid-liquid separation by the centrifuge can be performed smoothly. Then, there is an advantage that high-purity terephthalic acid can be efficiently produced.

Claims

^ Range of request

1. In a method of solid-liquid separation of an aqueous or acetic acid slurry containing an aromatic carboxylic acid in a saturated state by a centrifuge,

 A method for centrifuging an aromatic sulfonic acid-containing slurry, wherein the operating pressure at the time of the centrifugation is higher than the saturated vapor pressure of the mother liquor of the aromatic carboxylic acid-containing slurry to be separated. .

2. The aromatic carboxylic acid according to claim 1, wherein the slurry containing the aromatic carboxylic acid in a saturated state is a slurry in which an aromatic carboxylic acid is generated by an oxidation reaction in an acetic acid solvent. A centrifugal separation method for the contained slurry.

3. The slurry containing an aromatic carboxylic acid according to claim 1, wherein the slurry containing the aromatic carboxylic acid in a saturated state is a slurry in which the aromatic carboxylic acid is crystallized by flash cooling. Centrifugation method.

4. The operation pressure at the time of centrifugation is set to be higher than the saturation vapor pressure of the mother liquor of the aromatic carboxylic acid-containing slurry to be separated by 0.01 to 0.2 MPa. 4. The method for centrifuging an aromatic carboxylic acid-containing slurry according to any one of items 1 to 3.

5. The aromatic carboxylic acid-containing slurry according to any one of claims 1 to 4, wherein the centrifugal separator is a solid bowl type centrifuge or a screen poll type centrifuge. One centrifugation method.

6. (i) A process for producing a slurry containing terephthalic acid by subjecting paraxylene to liquid phase oxidation at a pressure of 1 to 2 MPa in the presence of a catalyst containing cobalt, manganese and bromine using acetic acid as a solvent (ii) a step of subjecting the obtained terephthalic acid-containing slurry to solid-liquid separation by a centrifuge

 (iiii) washing the centrifuged terephthalic acid-containing solid with acetic acid and / or water

 In the method for producing terephthalic acid in which the above steps (i) to (iii) are performed in order, the operating pressure at the time of centrifugation in the step (ii) is set to the saturated vapor pressure of the mother liquor of the terephthalic acid-containing slurry supplied as a separation target. Higher than

 'Method of producing acid.

7. Perform step (ii) and step (iii) in the same apparatus, and adjust the supply temperature of acetic acid and Z or water used for washing to the temperature (T) ° C of the slurry generated in step (ii). 7. The method for producing terephthalic acid according to claim 6, wherein the temperature is not less than (T-20) ° C.

8. The method according to claim 6, wherein the operating pressure at the time of centrifugation is 0.01 to 0.2 MPa higher than the saturated vapor pressure of the mother liquor of the supply-containing slurry to be separated. The method for producing terephthalic acid according to the above item.

9. The method for producing terephthalic acid according to claim 6, wherein the centrifuge is a solid bowl type centrifuge or a screen bowl type centrifuge.

10. (i) Step of liquid-phase oxidation of para-xylene using acetic acid as a solvent in the presence of a catalyst to produce crude terephthalic acid

 (ii) a step of dissolving the crude terephthalic acid in water, and subjecting the lyxate to a reduction treatment at a temperature of 230 to 350 ° C in the presence of a catalyst;

(iii) Stepwise reducing the slurry subjected to the reduction treatment in a plurality of crystallization tanks to 120-180 Crystallization process by flash cooling to ° c

 (i V) a step of solid-liquid separating the obtained terephthalic acid-containing slurry by a centrifuge

 (V) washing the centrifuged terephthalic acid-containing solid with water

 In the method for producing high-purity terephthalic acid, which comprises performing the above steps (i) to (V) in order,

 A method for producing high-purity terephthalic acid, characterized in that the operating pressure during centrifugation in the step (iV) is higher than the final crystallization pressure in the step of crystallization by flash cooling.

1 1. Perform the process (i V) and the process (V) in the same apparatus, and the supply temperature of the water used for washing is (T) with respect to the temperature (T) of the slurry generated in the process (iii). (11) The method for producing high-purity terephthalic acid according to claim 10, wherein the temperature is not lower than 20 ° C.

12. The claim 10 or claim 10, wherein the operating pressure at the time of centrifugation is 0.01 to 0.2 MPa higher than the final crystallization pressure in the step of crystallization by flash cooling. 11. The method for producing high-purity terephthalic acid according to item 1.

13. The method for producing high-purity terephthalic acid according to any one of claims 10 to 12, wherein the centrifuge is a solid bowl centrifuge or a screen bowl centrifuge. .