JP2004231642A - Method for centrifugally separating slurry containing aromatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for performing a solid liquid separation by a centrifugal separator smoothly in the solid and liquid separation process especially using the centrifugal separator in the production process of the aromatic carboxylic acid to produce a high purity aromatic carboxylic acid in a good efficiency. <P>SOLUTION: This method for separating slurry containing the aromatic carboxylic acid is provided by supplying the slurry containing terephthalic acid by using acetic acid as a solvent into a crystallization vessel 1 from a flush valve 2, flash evaporating the solvent by performing the process in a boiling state under a reduced pressure to precipitate the crystal of terephthalic acid, and in the next solid liquid separating process, recovering the crystals of terephthalic acid by operating the centrifugal separator 4 under an atmospheric pressure. Since the operating pressure in the centrifugal separation is set at a higher pressure than that of the operating pressure in the final crystallization vessel 1, the crystals of terephthalic acid are hardly precipitated and the centrifugal separator can be operated in a good stability. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  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.

  In general, as an industrial production method of an aromatic carboxylic acid 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 for producing terephthalic acid by subjecting a slurry containing crystals of terephthalic acid or another aromatic carboxylic acid produced by an oxidation reaction in a liquid phase with oxygen to a treatment with a solid-liquid separator.

  Examples of the solid-liquid separator include a rotary vacuum filter, a belt filter, and a centrifugal separator.A centrifugal separator includes a rotating bowl cylinder and a screw conveyor installed in a vertical or horizontal drum. The supplied slurry is dispersed inside the rotating bowl cylindrical portion, and has a mechanism in which solids settled on the bowl wall by centrifugal force are moved and discharged by a screw conveyor (see Patent Document 1).

Japanese Unexamined Patent Publication No. Hei 7-507291 (lower left column on page 10, lower right column on page 10, FIGS. 3 and 4)

  However, when the solid-liquid separation of the slurry is performed using the above-described centrifugal separator, the slurry is cooled by decompression in the centrifuge, and crystallization may occur locally, and the bowl that rotates with the generated crystal may be used. The efficiency of the solid-liquid separation process deteriorates, for example, because the weight inside the container is not evenly distributed, and the stability (balance) of the rotating shaft of the bowl is deteriorated, causing vibration, and furthermore, the rotation speed is reduced. There is a problem. 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, scaling occurs. However, there is a problem that hinders the separation operation.

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

  Therefore, an object of the present invention is to solve the above-mentioned problems, and to smoothly perform solid-liquid separation by a centrifuge in a solid-liquid separation step of a slurry using a centrifuge, particularly in a process of producing an aromatic carboxylic acid. It is an object of the present invention to produce a high-purity aromatic carboxylic acid efficiently by using a method which can be used, and furthermore, by utilizing such a method.

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

  In the method for centrifuging an aromatic carboxylic acid-containing slurry of the present invention configured as described above, the operating pressure at the time of centrifuging is set higher than the saturated vapor pressure of the mother liquor of the slurry in the step before the introduction of the centrifuge. Therefore, even though the slurry before centrifugation contains a large amount of aromatic carboxylic acid in a saturated state, the saturation concentration of aromatic carboxylic acid increases during centrifugation, and the aromatic carboxylic acid becomes saturated. Acid crystals are less likely to precipitate.

  Therefore, local precipitation of crystals does not occur in the centrifugal separator, and the balance of the rotating mechanism does not break down, so that solid-liquid separation by the centrifugal separator can be performed smoothly. High purity terephthalic acid can be produced.

  The step before the introduction of the centrifugal separator in which the above action is exerted may be a step of generating an aromatic carboxylic acid by an oxidation reaction in an acetic acid solvent, or the step of crystallizing the aromatic carboxylic acid by flash cooling of the slurry. May be performed.

  Similarly, a method of producing crude terephthalic acid using the above-described solid-liquid separation method of the slurry can be adopted, and further purified to produce high-purity terephthalic acid.

That is, as a method for producing crude terephthalic acid which 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, Producing an acid-containing slurry, (ii) solid-liquid separating the obtained terephthalic acid-containing slurry by a centrifuge, and (iii) centrifuging the terephthalic acid-containing solid with acetic acid and / or water. The step of washing.
In the method for producing terephthalic acid in which the above steps (i) to (iii) are sequentially performed,
A method for producing terephthalic acid, wherein the operating pressure at the time of centrifugation in the step (ii) is made higher than the saturated vapor pressure of the mother liquor of the terephthalic acid-containing slurry to be separated, 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) ° C. of the slurry produced in the step (ii). On the other hand, the temperature is preferably (T-20) ° C. or higher.

  Further, it is preferable that the operation pressure at the time of centrifugation is higher by 0.01 to 0.2 MPa than the saturated vapor pressure of the mother liquor of the terephthalic acid-containing slurry supplied as a separation target.

Further, a method for producing high-purity terephthalic acid which solves the above-mentioned problems includes: (i) a step of liquid-phase oxidation of para-xylene in the presence of a catalyst using acetic acid to produce crude terephthalic acid; A step of dissolving the acid in water and reducing 4-carboxybenzaldehyde in the dissolved substance at 230 to 350 ° C. in the presence of a catalyst (iii) Stepwise reducing the reduced slurry in a plurality of crystallization tanks. Flash cooling to 120-180 ° C. for crystallization (iv) Solid-liquid separation of 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 sequentially performing the above steps (i) to (v),
A method for producing high-purity terephthalic acid, wherein the operation pressure at the time of centrifugal separation in the step (iv) is set higher than the final crystallization pressure in the step of crystallization by flash cooling.

  In the above-mentioned production method, the step (iv) and the step (v) are performed in the same apparatus, and the supply temperature of the water used for washing is set to the temperature (T) ° C. of the slurry generated in the step (iii). , (T-20) ° C. or higher.

  Further, in the above-described production method, a method for producing high-purity terephthalic acid is employed in which the operating pressure during centrifugation is higher by 0.01 to 0.2 MPa than the final crystallization pressure in the step of crystallization by flash cooling. Is preferred.

  The present invention provides a method for centrifuging the crystals of aromatic carboxylic acid generated in a slurry, wherein the pressure of the slurry at the time of centrifuging is higher than the pressure of the slurry at the time when the aromatic carboxylic acid is saturated in the previous step. As a result, the precipitation of crystals locally does not occur in the centrifuge, the balance of the rotating mechanism is not lost, and solid-liquid separation by the centrifuge can be performed smoothly. There is an advantage that high-purity terephthalic acid can be produced efficiently.

  Hereinafter, the present invention will be described in detail. As a representative example, the 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 alkyl benzene such as a mono-, di-, or trialkyl benzene that is converted into an aromatic carboxylic acid such as an aromatic monocarboxylic acid, an aromatic dicarboxylic acid, or an aromatic tricarboxylic acid by liquid phase oxidation. And also includes those in which a part of the alkyl group is oxidized. In particular, the present invention is preferably applied to the production of terephthalic acid. In this case, para-xylene is mentioned as the alkyl aromatic compound used as a raw material.

  As the solvent used in the present invention, acetic acid, which is a lower aliphatic carboxylic acid, is preferable, and the amount of the solvent is usually 2 to 6 times by weight based on paraxylene as a raw material. The acetic acid solvent may contain a small amount of water, specifically, 10% by weight or less of water.

  To oxidize alkyl aromatic compounds such as para-xylene, molecular oxygen-containing gas is used, but air is usually used because of simple equipment and low cost, and dilution air and oxygen enrichment are also 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 bromoethane.

  The reaction for 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., while continuously supplying a molecular oxygen-containing gas at a temperature of 150 to 210 ° C. This is performed by oxidizing an alkyl aromatic compound such as xylene. 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 carboxylic acid slurry. The number of crystallization stages is preferably 1 to 6 stages, more preferably 2 to 3 stages.

  The final step of the series of crystallization steps is performed under reduced pressure boiling. As a specific operation in the boiling state under reduced pressure, flash cooling is preferable. Note that flash cooling refers to cooling by releasing pressure.

  In the method for producing terephthalic acid according to the embodiment shown in the apparatus system diagram of FIG. 1, the step of performing solid-liquid separation by centrifugation of the slurry is performed by flushing the slurry containing terephthalic acid with acetic acid as a solvent to the final crystallization tank 1. 2, the solvent is flash-evaporated to precipitate terephthalic acid crystals by performing this process under reduced pressure boiling. Then, in the solid-liquid separation process, the centrifuge 4 is operated at atmospheric pressure. The terephthalic acid crystals are collected. Reference numeral 5 in the drawing denotes an ejector, 6 denotes a condenser (condenser) for recovering the evaporated solvent component, and 7 denotes a pump.

  When the slurry is centrifuged as described above, the operating pressure, ie, 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 immediately before introduction into the centrifuge (reduced pressure by flash = less than atmospheric pressure), so that in the step before centrifugation, the slurry is saturated with aromatic carboxylic acids. Nevertheless, during the centrifugation, the crystals of the aromatic carboxylic acid hardly precipitate.

  Preferably, the pressure of the slurry or the atmosphere in contact with the slurry is 0.01 to 0.2 MPa higher than the pressure of the atmosphere in contact with the slurry or the slurry in the step before introducing the centrifuge, and more preferably 0.03 MPa. It is preferable that the pressure be as high as 0.1 MPa.

  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 aromatic carboxylic acid to be recovered increases, which is advantageous. However, if the temperature is too low, a pressure reducing device having a large degree of pressure reduction is required, which is disadvantageous.

  Here, the separated solid may be washed with acetic acid and / or water. The solid-liquid separation and the washing are desirably performed in the same apparatus, and the solid-liquid separator is preferably a solid bowl type centrifuge or a screen bowl type centrifuge. 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 supplied slurry. 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, if the temperature becomes high, the amount of terephthalic acid dissolved in the cleaning liquid increases. The temperature is preferably (T + 30) ° C. or lower with respect to (T) ° C. By doing so, the temperature of the slurry or the separation cake is prevented from lowering, and operational problems associated with crystallization of the mother liquor are prevented.

  As shown in the apparatus system diagram of FIG. 2, the centrifugation step of the slurry of the embodiment is performed by using 4-carboxybenzaldehyde (4CBA) contained in crude terephthalic acid in a water solvent using a reactor (not shown). A crystallization step of performing a hydrogenation (reduction) reaction at 350 ° C. in the presence of a catalyst, and then vaporizing water by flash cooling through a flash valve 8 is performed in a three- to six-stage crystallization tank. From 9, a slurry in which terephthalic acid is saturated is supplied to a centrifugal separator 11 via a pump 10. Thereafter, the separated cake is washed with water in the washing tank 12, further flash-cooled to about the atmospheric pressure in the reduced pressure tank 13, introduced into the centrifugal separator 14 by the pump 10, and solid-liquid separated, and then dried. The high-purity terephthalic acid crystals are supplied to the apparatus 15.

  Even in such a process, the operating pressure of the centrifuges 11 and 14 is set higher than the saturated vapor pressure of the mother liquor of the supply slurry, so that the slurry before centrifugal separation is saturated with aromatic carboxylic acid. At the time of centrifugation, crystals of the aromatic carboxylic acid hardly precipitate due to the increased pressure difference.

  Preferably, the pressure of the slurry or the atmosphere in contact with the slurry is 0.01 to 0.2 MPa higher than the pressure of the atmosphere in contact with the slurry or the slurry in the step before introducing the centrifuge, and more preferably 0.03 MPa. A high pressure of only about 0.1 MPa is preferable.

  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. If the final crystallization temperature is low, the amount of aromatic carboxylic acid recovered is advantageously increased, but if the temperature is too low, the eutectic of paratoluic acid generated by reduction of 4CBA is promoted, and The quality of the resulting high-purity terephthalic acid. Similarly, the temperature of the slurry supplied to the centrifuge 14 is at least 50 ° C, preferably 60 to 120 ° C, and particularly preferably 90 to 110 ° C.

  The solid separated by the centrifuge may be washed with water. It is desirable that the solid-liquid separation and washing by this centrifugal separator be performed in the same apparatus, and the solid-liquid separator is preferably a solid bowl type centrifuge or a screen bowl type centrifuge. 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 supplied slurry. 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, if the temperature becomes high, the amount of terephthalic acid dissolved in the cleaning liquid increases. The temperature is preferably (T + 30) ° C. or lower with respect to (T) ° C. By doing so, the temperature of the slurry or the separation cake is prevented from lowering, and operational problems associated with crystallization of the mother liquor are prevented.

[Example 1]
Using acetic acid as a solvent, para-xylene is oxidized in the liquid phase at a pressure of 1.5 MPa in the presence of a catalyst containing Co / Mn / Br to produce a terephthalic acid-containing slurry. The pressure was reduced to 0.05 MPa, and the mixture was flash-cooled to 90 ° C. When the obtained terephthalic acid slurry was subjected to solid-liquid separation with a centrifugal separator, the inside of the drum was set to atmospheric pressure to separate crude terephthalic acid.

  Further, the crude terephthalic acid obtained in the next step is dissolved in water, and 4-carboxybenzaldehyde in the dissolved substance is reduced in the presence of a Group VIII metal catalyst. Was analyzed. The final crystallization conditions were 160 ° C. and 0.62 MPa. The obtained slurry containing terephthalic acid crystals is subjected to solid-liquid separation using a centrifugal separator at an operating pressure of 0.69 MPa in the step shown in FIG. 2, and the obtained separation cake is washed in a suspension washing tank. The slurry flash-cooled to atmospheric pressure was further supplied to a second centrifugal separator, where it was subjected to solid-liquid separation at an operating pressure of 0.12 MPa, and the separation cake was dried to produce high-purity terephthalic acid.

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

[Example 2]
Using acetic acid as a solvent, para-xylene is oxidized in the liquid phase at a pressure of 1.5 MPa in the presence of a catalyst containing Co / Mn / Br to produce a terephthalic acid-containing slurry. The pressure was reduced to 0.05 MPa, and the mixture was flash-cooled to 90 ° C. When the obtained terephthalic acid slurry was subjected to solid-liquid separation with a centrifugal separator, the inside of the drum was set to atmospheric pressure to separate crude terephthalic acid.
At this time, a screen bowl type centrifugal separator was used as a centrifugal separator, and the screen was washed with acetic acid at 95 ° C. as a washing liquid.

  The solid-liquid separation and washing by the screen bowl type centrifugal separator were continuously performed for 150 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 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 a cleaning liquid was changed to 85 ° C. Solid-liquid separation and washing with the screen bowl type 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. From this, it is estimated that local precipitation of terephthalic acid in the centrifuge did not occur.

System diagram of the apparatus showing the slurry-solid separation method of the first embodiment System diagram of an apparatus showing the slurry-solid separation method of the second embodiment

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Crystallization tank 2 Flash valve 4 Centrifuge 5 Ejector 6 Condenser 7 Pump 8 Flash valve 9 Crystallization tank 10 Pump 11 Centrifuge 12 Suspension washing tank 13 Decompression tank 14 Centrifuge 15 Dryer

Claims (12)

In a method of solid-liquid separation of an aqueous or acetic acid-based slurry containing an aromatic carboxylic acid in a saturated state by a centrifuge,
A centrifugal separation method for an aromatic carboxylic acid-containing slurry, wherein an operation pressure at the time of the centrifugal separation is set higher than a saturated vapor pressure of a mother liquor of the aromatic carboxylic acid-containing slurry to be separated.   The method for centrifuging an aromatic carboxylic acid-containing slurry according to claim 1, wherein the slurry containing an 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.   The centrifugal separation method of an aromatic carboxylic acid-containing slurry 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.   4. The method according to claim 1, wherein the operation pressure at the time of centrifugation is higher than the saturated vapor pressure of the mother liquor of the aromatic carboxylic acid slurry to be supplied by 0.01 to 0.2 MPa. A method for centrifuging an aromatic carboxylic acid-containing slurry according to the above.   The method for centrifuging an aromatic carboxylic acid-containing slurry according to any one of claims 1 to 4, wherein the centrifuge is a solid bowl centrifuge or a screen bowl centrifuge. (I) a step of liquid phase oxidation of paraxylene 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 to produce a terephthalic acid-containing slurry (ii) a terephthalic acid-containing slurry obtained A step of solid-liquid separation of the slurry by a centrifuge (iii) a step of washing the centrifugally separated solid containing terephthalic acid with acetic acid and / or water; a step of performing the above steps (i) to (iii) in order In the manufacturing method,
A method for producing terephthalic acid, wherein an operation pressure at the time of centrifugation in the step (ii) is higher than a saturated vapor pressure of a mother liquor of a terephthalic acid-containing slurry to be supplied as a separation target.   Step (ii) and step (iii) are performed in the same apparatus, and the supply temperature of acetic acid and / or water used for washing is (T) ° C with respect to the temperature (T) ° C. of the slurry produced in step (ii). -20) The method for producing terephthalic acid according to claim 6, wherein the temperature is not lower than ℃.   The method for producing terephthalic acid according to claim 6 or 7, wherein the operation pressure at the time of centrifugation is set to be higher than the saturated vapor pressure of the mother liquor of the terephthalic acid-containing slurry to be separated by 0.01 to 0.2 MPa. (I) A step of liquid-phase oxidation of para-xylene in the presence of a catalyst using acetic acid as a solvent to produce crude terephthalic acid. (Ii) Dissolving crude terephthalic acid in water. Step (iv) of performing a reduction treatment in the presence of a catalyst at a temperature of up to 350 ° C. and flash-cooling the reduced slurry to 120 to 180 ° C. in a plurality of crystallization tanks to obtain a crystallization step (iv). (V) washing the centrifugally separated terephthalic acid-containing solid with water using a centrifugal separator The above steps (i) to (v) are performed in order. In the method for producing high-purity terephthalic acid,
A method for producing high-purity terephthalic acid, wherein the operating pressure at the time of centrifugation in the step (iv) is higher than the final crystallization pressure in the step of crystallization by flash cooling.   Steps (iv) and (v) are performed in the same apparatus, and the supply temperature of water used for washing is (T-20) ° C. with respect to the temperature (T) ° C. of the slurry generated in step (iii). The method for producing high-purity terephthalic acid according to claim 9, wherein the temperature is the above temperature.   The method for producing high-purity terephthalic acid according to claim 9 or 10, wherein the operating pressure at the time of centrifugation is higher than the final crystallization pressure in the step of crystallization by flash cooling.   The method for producing terephthalic acid according to any one of claims 6 to 11, wherein the centrifuge is a solid bowl centrifuge or a screen bowl centrifuge.

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