WO2009081458A1

WO2009081458A1 - Method of filtering crystallization slurry

Info

Publication number: WO2009081458A1
Application number: PCT/JP2007/074518
Authority: WO
Inventors: Tokuaki Hara; Hiroyuki Toyoshima; Hatsutaro Yamazaki
Original assignee: Hitachi Plant Technologies, Ltd.
Priority date: 2007-12-20
Filing date: 2007-12-20
Publication date: 2009-07-02
Also published as: CN101903072B; CN101903072A

Abstract

In the prior art, crystals are separated and recovered from a crystallization slurry through, using a vacuum rotary filtering machine, suction filtering, crystal washing and liquid removing steps. In the washing step, portion of the solvent of a filtrate or washing liquid is evaporated and cooled by the suction of the washing liquid to thereby cause solute crystallization on the mesh of applied filter cloth. Consequently, the mesh of the filter cloth is clogged by crystal micrograins, so that formation of a filtration (crystal grain) layer by the suction filtration would become difficult. Further, passage of the washing liquid would become unsatisfactory to thereby cause continuation of continuous filtering/washing to be infeasible. Accordingly, it is intended to, in the rotary filtering method, inhibit clogging of filter cloth and attain prolonged continuation of filtering/washing. Microcrystal clogging on the mesh of the filter cloth has been inhibited by heating the washing liquid with the use of a heater so as to effect overheating until at least the temperature (pressure) for vapor generation and by feeding the washing liquid as a mixed phase flow entrained by generated vapor to a washing region within the filtering machine in the washing step. As a washing solvent, use is made of acetic acid overheated to 120°C or higher, preferably 130°C or higher, still preferably 140°C or higher. The washing solvent is overheated to preferably the temperature for about 7% or more vapor generation, still preferably the temperature for about 14% or more vapor generation.

Description

Filtration method of crystallization slurry

The present invention relates to a filtration method for efficiently performing continuous reduced pressure rotary filtration in which crystallization slurry is repeatedly subjected to steps of suction filtration, crystal washing, suction devolatilization, and crystal peeling in order, and particularly for recovering crystals by continuous reduced pressure rotary filtration. Further, the present invention relates to a filtration method capable of suppressing clogging of a filter medium (filter cloth) and allowing continuous filtration and washing treatment of crystals for a long time.

In a process for producing aromatic dicarboxylic acids by liquid phase oxidation of dialkyl aromatic hydrocarbons such as para-xylene and meta-xylene, the oxidation reaction product is reduced in pressure and reduced in temperature by releasing (flashing) the solvent from the pressure and temperature of the solvent. Then, after obtaining a product slurry in which crystals are precipitated, the crystallized slurry is filtered and washed by a continuous vacuum rotary filtration method to recover aromatic dicarboxylic acid crystals.

In addition, the above-mentioned crude aromatic dicarboxylic acid crystal obtained as another method is dissolved in water, and through a hydrorefining process, the product is similarly reduced in pressure and cooled to obtain a product slurry in which crystals are precipitated. After that, the crystallization slurry is filtered and washed by a continuous reduced pressure rotary filtration method to recover crystals.

As described above, the product obtained by the reaction is reduced in pressure and cooled to obtain a slurry of the product from various solvents in which crystals are precipitated, and then the crystallization slurry is filtered and washed by a continuous reduced pressure rotary filtration method. A method for recovering the crystal product produced by the reaction is often carried out in the production of organic chemical industrial products. For filtration, the filter cloth (filter material) is laid in a cylindrical shape or a belt shape, and the steps of suction filtration, crystal washing, suction drainage, and crystal peeling are repeated in order while rotating or moving the crystallization slurry. It is performed by a continuous vacuum rotary filtration / cleaning method.

In such a continuous filtration method, at the time of suction of the filtrate and washing liquid (washing solvent) in the suction filtration, crystal washing, and liquid removal processes, a part of the filtrate or the solvent of the washing liquid evaporates and cools down, and the mesh of the filter cloth. A solute is deposited on top. Therefore, if continuous filtration and washing are repeated, the fine particles of crystals are clogged in the mesh of the filter cloth, making it difficult to form a filtration (crystal particle) layer by suction filtration, and the washing liquid also passes through. Insufficient continuous filtration and cleaning cannot be performed.

In this case, the filtration / washing process is stopped, the filter cloth is washed / dissolved with an alkaline solution such as an aqueous solution of caustic soda to eliminate clogging of the filter cloth, and the filtration / washing operation is restarted. Therefore, when recovering crystals from the crystallization slurry by a continuous reduced pressure rotary filtration method, an inefficient treatment operation for stopping the filtration / washing treatment as described above has been forced.

Therefore, as a conventional countermeasure, in Patent Document 1 (Japanese Patent Laid-Open No. 1-299618), suction filtration is performed by applying pressure to the crystallization slurry to be filtered or separated, or Patent Document 2 (Japanese Patent Laid-Open No. 2004-231636). In Patent Document 3 (Japanese Patent Application Laid-Open No. 2006-265124), the crystallization slurry is cooled to a temperature (about 90 ° C.) below the boiling point (under atmospheric pressure) of the solvent by boiling under reduced pressure or a heat exchanger, and then suction filtration is performed. A method has been proposed in which the evaporation of the solvent on the filter cloth is suppressed and the clogging of the mesh is suppressed. Patent Document 4 (Japanese Patent Application Laid-Open No. 2002-20324) discloses a method for completely removing crystal particles from a filter cloth and eliminating clogging by supplying a vapor of a solvent component to a blowing gas for crystal peeling. Has been proposed, and methods for efficient treatment with a long continuous filtration and washing time have been devised and proposed.

JP-A-1-299618 JP 2004-231636 A JP 2006-265124 A JP 2002-020324 A

However, in the method of Patent Document 1, it is necessary to pressurize the inside of the outer casing (casing) of the rotary filter, and not only the filter body but also incidental facilities such as a supply pump and a filtrate tank become heavy pressure-resistant facilities and reduce the equipment cost. Invite rise. Further, it is necessary to improve the equipment for smoothly transferring the collected wet crystals from under pressure to a dryer at normal pressure (atmospheric pressure) (Japanese Patent Application Laid-Open No. 11-179115, Special Table 2003-519205). Increases equipment costs.

In addition, when the crystallization slurry is filtered and separated by a conventional continuous reduced pressure rotation method under normal pressure, in

Patent Documents

2 and 3 by a method of reducing the solvent vapor pressure by cooling by boiling under reduced pressure or the like, the evaporation amount of the solvent is reduced. The improvement of clogging time (time until clogging occurs) is not sufficient. Incidentally, in Example 1 of Patent Document 2, the clogging time of the terephthalic acid production slurry at 90 ° C. is 55 hours, and in Example 1 of Patent Document 3, the clogging time of the terephthalic acid production slurry at 90 ° C. is 120 hours. .

Further, in Patent Document 4, in order to supply the vapor of the solvent component to the blowing gas for performing crystal peeling, moisture is given to the crystal dried in the previous step, and the wetness of the recovered crystal increases, and the subsequent drying step The load of increases.

The present invention provides a filtration method capable of suppressing clogging of a filter medium (filter cloth) and recovering continuous crystal filtration and washing for a long time when recovering crystals by continuous reduced pressure rotary filtration. is there. Further, even in a vacuum rotary filter performed under normal pressure (atmospheric pressure), the filter cloth is prevented from being clogged with crystallized particles, and can be continuously operated for a long time.

The present invention relates to a method for recovering crystals by continuous reduced pressure rotary filtration in which a slurry comprising crystals and a solvent is repeatedly filtered, washed, and peeled in order, and in the washing step, at least a temperature accompanied by vapor generation is overheated. The crystal is washed using the washed solvent.

In the process of producing aromatic carboxylic acid by air oxidation using aromatic hydrocarbon as a raw material in an acetic acid solution containing a catalyst, after the oxidation reaction, the continuous type is obtained from the crystallization slurry obtained by reducing the pressure and lowering the temperature. In recovering the aromatic carboxylic acid by rotary filtration under reduced pressure, the crystal is washed using a washing solvent heated to at least a temperature accompanied with vapor generation in the washing step.

Further, the aromatic hydrocarbon is a dialkyl aromatic hydrocarbon composed of para-xylene or meta-xylene, and the produced aromatic carboxylic acid is composed of terephthalic acid or isophthalic acid.

In the washing step, the crystal is washed with acetic acid heated to 120 ° C. or higher, preferably 130 ° C. or higher, more preferably 140 ° C. or higher as the cleaning solvent.

In the washing step, the crystal is washed using a washing solvent heated to a temperature at which the rate of vapor generation is preferably about 7% or more, more preferably about 14% or more. .

As described above, according to the present invention, at the time of separating and recovering crystals from the crystallization slurry, the clogging of the filter cloth is suppressed by washing the filtered crystals with at least a superheated washing solvent accompanied by vapor generation. The filtration and washing operation can be performed continuously for a long time, and the crystal recovery operation can be performed under normal pressure.

Furthermore, in a general-purpose continuous reduced-pressure rotary filter, it is only an improvement in heating control equipment that can supply the cleaning solvent by heating it to at least the temperature accompanied by vapor generation. It is not necessary to improve the equipment of the filter body such as, and the cost burden is small. And, as seen in the examples, there is a tendency that the cleaning effect of the crystal particle layer also increases, and the wetness (wetness) of the recovered crystals tends to decrease, which is also effective for the separation cleaning effect. It became.

As an embodiment of the present invention, an example in which crystals are recovered from a crystal-forming slurry in the production of terephthalic acid using a continuous vacuum rotary filter (generally a rotary vacuum filter: RVF) will be described.

FIG. 1 is a flow chart, and FIG. 2 schematically shows a filtration section of the continuous vacuum rotary filter 2 therein. First, the process of filtration / washing, draining, and peeling in the filter will be described.

In FIG. 2, the filter 2 is installed such that a cylindrical rotating body 11 having a filter surface with a filter medium (filter cloth) on the outer surface is rotated in the filter 2 so as to rotate in the clockwise direction. The partition wall is fixed so as not to rotate. While the rotating body 11 rotates in the clockwise direction, first, the crystallization slurry retained in the bottom 12 of the filter 2 in the filtration step is sucked from the filtration region 13 inside the rotating body 11 by the suction of the rotating body 11. A crystal grain layer is formed on the outer surface of the substrate. This is done by sucking the mother liquor of the crystallization slurry that has entered the filtration zone 13 into the filtrate tank 3 of FIG.

In the next cleaning step, the rotating surface 11 rotates while the filtration surface on which the crystal particle layer is formed is separated from the immersion of the crystal slurry, and rises up the cleaning / drainage zone 14 to reach the upper part. The cleaning liquid is supplied from the outside of the rotating body 11 to the upper surface of the crystal particle layer by a method such as spraying and spraying, and the cleaning liquid that has passed through the rotating body 11 passes through the cleaning / drainage area 14 in the cleaning drainage tank of FIG. 4 sucked. When the cleaning liquid passes through the rotating body 11, the cleaning liquid pushes out the residual mother liquor (slurry mother liquid) adhering to the surface of the crystal particle layer and the mesh of the filter medium, and is removed to the cleaning / drainage zone 14 inside the rotating body 11. To do.

Extrusion of residual mother liquor adhering to the filter media will contribute to suppression of mesh clogging. Here, the cleaning liquid (acetic acid) supplied by a method such as spraying and spraying is heated and controlled by the heater E-1 so that it is heated to at least a temperature exceeding the boiling point (118 ° C.) and accompanied by steam generation. The superheated cleaning liquid is sprayed on the surface of the filtration (crystal particle) layer with steam. The superheating temperature in the heater E-1 is preferably overheated to a temperature exceeding the boiling point (118 ° C.) with acetic acid, but by overheating to 120 ° C. or more, an improvement effect in suppressing clogging appears. Further, it is more preferable to overheat to about 130 ° C. or higher to increase the ratio of the steam generated during the introduction and spraying. However, heating of the cleaning liquid is considered to require at least the presence of the cleaning liquid at the time of introduction and spraying (the liquid disappears if it is overheated). I think it's not good.

Then, the crystal particle layer further rotates together with the rotator 11, and the internal suction is continued while moving from the upper part of the cleaning / dehydrating zone 14 to the right side, and the residual cleaning liquid in the crystal particle layer is the atmospheric vapor on the surface of the crystal particle layer. Then, the liquid is sucked together with the gas, and the liquid removal is performed while suppressing the evaporation of the residual cleaning liquid. By suppressing the evaporation, it is possible to suppress the precipitation of the solute of the residual cleaning liquid on the mesh of the filter cloth.

The crystal particle layer drained as described above is further rotated and moved to the crystal exfoliation region 15, and in the exfoliation region 15, an inert gas is sprayed from the inside of the rotating body 11 by the supply pulser M-2. Is removed from the rotating body 11, falls down the crystal discharge pipe 16, and is collected as wet terephthalic acid crystals in the screw discharge machine M- 1. Since the exfoliated crystals are heated to near the boiling point of the cleaning solvent, gas blowing in the exfoliation zone 15 causes evaporation of the residual cleaning liquid in the crystal particle layer, resulting in a decrease in wetness. The crystals from the screw discharger M-1 are supplied to the dryer 8 and become terephthalic acid crystals that are sufficiently dried.

The rotating body 11 from which the crystal has been peeled enters the slurry retaining portion of the bottom 12 while further rotating, starts suction filtration again, and is repeatedly filtered, washed and drained.
By the above method, the filtrate (mother liquid) sucked into the rotary body 11 by suction filtration in the process of filtering and washing on the rotary body filtration surface is almost recovered in the filtrate tank 3, and the solvent recovery process and oxidation are performed. It is recycled for reuse in the reaction. The vapor components not collected in the filtrate tank 3 are condensed in the upper cooler E-2, and the condensed liquid is collected and refluxed in the gas-liquid separation tank 5. The non-condensable gas component that has not been condensed is sucked into the vacuum pump M-3 and circulated, but excess gas is discharged out of the system.

Further, the cleaning waste liquid sucked into the rotating body 11 by the cleaning is recovered in the cleaning drain tank 4 like the slurry filtrate, and then the cooler E-3 → the gas-liquid separator 6 → the vacuum pump The condensate is collected and the non-condensable gas is circulated through the path M-3. Since the vacuum pump M-3 is expected to contain condensable vapor, it is preferable to use a liquid ring pump for suction and exhaust.

For filtration separation in which dangerous gas (vapor) such as acetic acid is used as a solvent for the production of terephthalic acid, the outer cover of the filter 2 is usually sealed and sealed with an inert gas or the like. is there. Therefore, it is sealed with a non-condensable gas that is sucked together with the filtration / cleaning liquid and circulated through the vacuum pump M-3, and the supply / replenishment of the gas is mainly performed with a blowing gas for crystal peeling.

When continuously collecting terephthalic acid crystals from the terephthalic acid crystallization slurry using the crystallization slurry filtration / separation system as described above, first, the high-temperature, high-pressure reaction product is released (flash) or the like. The terephthalic acid crystallization slurry whose pressure has been lowered and lowered is transferred to the slurry supply tank 1. In the slurry supply tank 1, the crystallization slurry is supplied to the bottom of the filter 2 while being circulated by an external pump. The crystallization slurry at the bottom of the filter 2 is suction filtered at the bottom of the cylindrical rotating body 11 by suction from the inside of the cylindrical rotating body 11, and the excess slurry overflows (overflows) and is returned to the slurry supply tank 1. The retained liquid level (filtrate level) of the slurry is maintained.

Next, the cleaning process will be described in detail. As described above, in the cleaning step, the supplied cleaning liquid (acetic acid) is heated and controlled so as to be heated to at least a temperature exceeding the boiling point (118 ° C.) and generating steam in the heater E-1.

This heating is based on the knowledge obtained by the present inventors, that is, the crystal cleaning solvent (cleaning liquid) is heated to a temperature at which vapor generation occurs at least above the boiling point of the cleaning liquid, and the cleaning liquid is released. Based on the knowledge that clogging due to crystals in the filter cloth can be suppressed by supplying (flush) and washing the filtration (crystal particle) layer as a mixed phase flow of high-temperature (liquid boiling point) vapor and liquid vapor. ing.

The crystallization slurry is supplied to the filter 2 and suction filtered in the filter zone 13, and then the cleaning solution heated in the cleaning step in the cleaning zone 14 is supplied in a flash form. In the washing zone 14, the filtration (crystal particle) layer is washed at a high speed as a mixed-phase flow of vapor and liquid having an increased capacity accompanied by high-temperature (liquid boiling point) vapor. At the same time, by evaporating vapor (and a small amount of gas) present in the atmosphere on the surface of the filtration (crystal particle) layer, the generation of solvent vapor in the filtrate and washing waste liquid is suppressed, and the solute in the network is Clogging due to precipitation is suppressed. And in the decontamination zone that is continuous with the washing zone, the vapor (and small amount of gas) in the high-temperature wet atmosphere existing on the surface of the crystal particle layer is sucked and drained. Thus, precipitation of solute is suppressed.

That is, the introduction of the cleaning liquid in the pressure release (flush) state by overheating supply causes the casing of the filter 2 to be filled with high-temperature (liquid boiling point) vapor (wet gas), and the filter cloth sucks the slurry. After filtration, between the washing zone and the crystal peeling zone, high-temperature atmospheric vapor (wet gas) is sucked together with the filtrate and high-temperature washing solution and passed through the filter cloth, so clogging due to solute precipitation can be suppressed. It will be.

Therefore, in this embodiment, the temperature at which the cleaning liquid is heated is heated to a pressure exceeding the boiling point, and the pressure is released (flushed) and sprayed to the cleaning area in the atmospheric pressure state. The high-temperature (boiling point) vapor generated at the time can exist in the atmosphere (in the filter casing) on the surface of the crystal particle layer, so that the period until clogging (clogging time) is improved. become.

According to the examples described later, the clogging time is improved if several percent of the supplied cleaning liquid generates steam, and long-term continuous operation (the clogging time of the terephthalic acid-producing slurry at about 90 ° C. is about 10 days or more) is achieved. Therefore, it has been found that the cleaning solution to be supplied is heated to a temperature at which about 7% (calculated) or more of steam is generated. And it is suggested that it is sufficient to overheat to a temperature at which steam with a temperature of overheating of about 13% (calculated) or more is generated.

As described above, according to the present embodiment, the continuous vacuum rotary filter 2 under normal pressure that has been used in the past is implemented by the fact that a heater and a flash valve are installed in the supply line of the cleaning solvent. It is possible to operate the filter continuously for a long time with an easy improvement in terms of equipment. In addition, it is not limited to application to crystallization slurry from the production of aromatic dicarboxylic acid by oxidation reaction in acetic acid solvent, and there are many such as crystallization slurry of aromatic dicarboxylic acid crystal from water solvent The same method can be applied to crystallization slurries of organic industrial chemicals.

Next, the crystal particle layer on the filter cloth that has been washed and sucked and drained is peeled off by blowing (blowing) gas from the inside of the filter cloth. However, a peeling method such as gas blowing using a shock wave (pulsar) can be used. It is done. In that case, since the solvent vapor | steam is not mixed compared with the method of supplying the solvent vapor | steam of patent document 4 to blow gas, there exists a tendency for the wetness of the collect | recovered recovery | peeling peeling to become small, and it is preferable. In addition, since the crystal particle layer is maintained at a high temperature (solvent boiling point) during the cleaning / dehydrating process, there is also a decrease in wetness due to evaporation of the wet cleaning liquid remaining in the process of crystal peeling and crystal discharging. .

As a vacuum rotary filter to which this embodiment can be applied, in addition to the vacuum rotary cylindrical filter 2 shown in FIGS. 1 and 2 called a rotary vacuum filter (RVF), a vacuum horizontal filter called a belt filter is used. A filter such as a band type filter may be used in which the filter cloth moves and suction filtration, crystal washing, suction liquid removal, and crystal peeling are repeated in this order for continuous filtration and washing.
Next, this embodiment will be specifically described by way of examples. In the process of producing crude terephthalic acid by air oxidation of para-xylene in the presence of cobalt, manganese and bromine catalysts in an acetic acid solvent, the slurry containing the crude terephthalic acid crystals flash-crystallized from the crystallization tank to the slurry supply tank 1 (FIG. 1), and filtered and washed with RVF2 according to the filtration and washing process described in the above embodiment and the flow of FIG. 1 to collect wet crystals. And after drying with dryer 8, it implemented by the method of collect | recovering crude terephthalic acid crystal powder.

The terephthalic acid-containing slurry in the slurry supply tank 1 supplied to the RVF 2 contains about 33 wt% terephthalic acid crystals in the reaction solvent (acetic acid) and has a temperature of about 90 ° C. RVF2 for crystal recovery uses a Young-type reduced-pressure rotating cylindrical filter (manufactured by Bird Co., USA), and rotates the cylindrical rotating body 11 under normal pressure (gas seal 100 mmAq or less) at a speed of 4.5 RPM. The vacuum pump E-3 (vacuum degree: about 400 mmHg) is suctioned through the filtrate tank 3 and the washing drainage tank 4, and suction filtration, crystal washing and suction drainage are performed. And a shock wave (maximum of about 0.2 Kg / cm 2 G). The recovered wet crystals dropped on the crystal discharge pipe 16 and dropped onto the receiving port of the screw discharge machine M-1 and transferred to the dryer 8.

The acetic acid cleaning liquid is heated (superheated) to a predetermined temperature by the heater E-1, and is introduced into the upper part of the cleaning zone 14 as a liquid (comparative example) or a flash vapor mixed phase (Examples 1 to 4). Washing was performed. The acetic acid for washing was heated through a heater E-1 using a pressurized metering pump (discharge pressure of about 5 Kg / cm 2 G), and adjusted and supplied at a ratio of about 0.6 weight to the supplied terephthalic acid crystals. Therefore, the supply of the cleaning liquid to the RVF 2 is a pressure release supply through the flash valve 17 from under pressure.

As described above, continuous suction filtration and washing treatment of the crude terephthalic acid crystallization slurry is continued, and the time until the filtration speed is greatly reduced due to clogging of the filter cloth is set as the clogging time, and the washing acetic acid is supplied. The continuous filtration / washing process was repeated while changing the temperature of the liquid. A table showing the relationship between the supply temperature of the cleaning acetic acid at that time and the time until clogging (clogging time) is shown in FIG.

From these results, the temperature of the supplied acetic acid was overheated (120 ° C.) exceeding the boiling point on the basis of a comparative example (temperature conventionally practiced) conducted at the same temperature as the supplied slurry (temperature without steam generation). In Example 1, it was found that the clogging time was improved. The clogging time was greatly improved at 130 ° C. (Example 2 / generated steam: about 7% in calculation), which is considered to have significant steam generation, but 140 ° C. or higher (Examples 3 and 4 / generation) Vapor: 14% or more calculated) was almost unchanged.

In addition, the terephthalic acid wet crystals obtained from RVF2 were collected at the receiving port of the crystal screw discharger M-1, and the wet rate (weight loss on drying wt%) of the recovered crystals and the ash content (ppm) as the contained inorganic substance were measured. 3 shows the relationship with the washing acetic acid temperature as a table. As a result, both tended to improve as the temperature of the washing acetic acid increased.

FIG. 4 is a graph showing the characteristics of Examples 1 to 4 shown in FIG. 3. The horizontal axis represents acetic acid temperature as a cleaning solution, and the vertical axis represents clogging time. Judging from this graph and FIG. 3, in the cleaning step, it is clogged that the crystal is cleaned using acetic acid heated to 120 ° C. or higher, preferably 130 ° C. or higher, more preferably 140 ° C. or higher as the cleaning solvent. The time can be lengthened. It can also be seen that the longest clogging time and a low wetting rate are obtained at 140 ° C. or higher, but are efficiently obtained at around 140 ° C. from the viewpoint of energy saving.

The flowchart of the embodiment which collect | recovers a crystal | crystallization using a filter from a crystal formation slurry. Schematic diagram of a continuous vacuum rotary filter (RVF). The table which shows the relationship between cleaning liquid temperature and clogging time. FIG. 5 is a characteristic diagram plotting Examples 1 to 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slurry supply tank 2 Continuous pressure reduction rotary filter 3 Filtrate tank 4

Cleaning drainage tank

5, 6 Gas-liquid separation tank 7 Seal liquid separation tank 8 Dryer 11 Rotating body 13 Filtration area 14 Washing / deliquidation area 15 Peeling area 17 Flush valve M-1 Screw discharger M-2 Inert gas supply pulser M-3 Vacuum pump E-1, E-5 Heater E-2, E-3, E-4 Cooler.

Claims

In the method of recovering crystals by continuous reduced pressure rotary filtration in which the slurry consisting of crystals and solvent is repeatedly filtered, washed, and peeled in order.
The method for filtering a crystallization slurry, wherein in the washing step, the crystal is washed using a washing solvent heated to at least a temperature accompanied with vapor generation.
In the process of producing aromatic carboxylic acid by air oxidation using aromatic hydrocarbon as a raw material in an acetic acid solution containing a catalyst, the continuous reduced-pressure rotation from the crystallization slurry obtained by the pressure reduction and temperature drop after oxidation reaction 2. The crystallization slurry according to claim 1, wherein, in recovering the aromatic carboxylic acid by filtration, the crystal is washed using a washing solvent heated to at least a temperature accompanied with vapor generation in the washing step. Filtration method.
The crystallization according to claim 2, wherein the aromatic hydrocarbon is a dialkyl aromatic hydrocarbon composed of para-xylene or meta-xylene, and the produced aromatic carboxylic acid is composed of terephthalic acid or isophthalic acid. Slurry filtration method.
3. The method for filtering a crystallization slurry according to claim 2, wherein in the washing step, crystals are washed using acetic acid heated to 120 ° C. or more as the washing solvent.
3. The method for filtering a crystallization slurry according to claim 2, wherein in the washing step, crystals are washed using acetic acid heated to 130 ° C. or more as the washing solvent.
The method for filtering a crystallization slurry according to claim 2, wherein in the washing step, crystals are washed using acetic acid heated to 140 ° C or higher as the washing solvent.
The method for filtering a crystallization slurry according to claim 3, wherein in the washing step, the crystals are washed using acetic acid heated to 120 ° C or higher as the washing solvent.
4. The method for filtering a crystallization slurry according to claim 3, wherein in the washing step, crystals are washed using acetic acid heated to 130 ° C. or more as the washing solvent.
4. The method for filtering a crystallization slurry according to claim 3, wherein in the washing step, crystals are washed using acetic acid heated to 140 ° C. or more as the washing solvent.
2. The method for filtering a crystallization slurry according to claim 1, wherein, in the washing step, the crystal is washed using a washing solvent heated to a temperature at which a rate of vapor generation is about 7% or more.
2. The method for filtering a crystallization slurry according to claim 1, wherein in the washing step, the crystals are washed using a washing solvent heated to a temperature at which the rate of vapor generation is about 14% or more.
3. The method for filtering a crystallization slurry according to claim 2, wherein in the washing step, the crystal is washed using a washing solvent heated to a temperature at which the rate of vapor generation is about 7% or more.
3. The method for filtering a crystallization slurry according to claim 2, wherein in the washing step, the crystals are washed using a washing solvent heated to a temperature at which a vapor generation rate is about 14% or more.
4. The method for filtering a crystallization slurry according to claim 3, wherein in the washing step, the crystal is washed using a washing solvent heated to a temperature at which the rate of vapor generation is about 7% or more.
4. The method for filtering a crystallization slurry according to claim 3, wherein in the washing step, the crystals are washed using a washing solvent heated to a temperature at which the rate of vapor generation is about 14% or more.