WO2012114434A1

WO2012114434A1 - Method for treating purified terephthalic acid mother liquor

Info

Publication number: WO2012114434A1
Application number: PCT/JP2011/053701
Authority: WO
Inventors: 徳明原; 弘幸豊嶋; 初太郎山▲崎▼
Original assignee: 株式会社日立プラントテクノロジー
Priority date: 2011-02-21
Filing date: 2011-02-21
Publication date: 2012-08-30
Also published as: CN103443064B; CN103443064A; BR112013020492A2

Abstract

In the present invention, a purified terephthalic slurry generated in the process of producing high-purity terephthalic acid by liquid-phase oxidation and hydrogenation purification using p-xylene as a starting material is separated into a primary mother liquor and primary crystals of the purified terephthalic acid. Terephthalic acid as well as p-toluic acid and other dissolved matter are cooled and precipitated in the separated primary mother liquor, and separated by filtration to separate out and recover low-purity terephthalic acid crystals, as a part of a raw material for the liquid-phase oxidation reaction of p-xylene. Terephthalic acid crystals are newly added to and mixed in the separated primary mother liquor, and thereafter the mixture is fed to a cooling tank adjusted to have a reduced pressure less than atmospheric pressure, and cooled by pressure relief, thereby improving the filterability of the precipitated matter. The amount of residual dissolved matter in a secondary mother liquor also separated by filtration is reduced.

Description

Treatment of purified terephthalic acid mother liquor

In the present invention, a crude terephthalic acid crystal produced by liquid phase oxidation of para-xylene is dissolved in high-temperature, high-pressure water, hydrorefined, and then cooled to produce a purified terephthalic acid crystal slurry. In the process of producing high-purity purified terephthalic acid (PTA) by drying through solid-liquid separation and washing steps, the mother liquor (primary mother liquor) obtained from solid-liquid separation of the purified terephthalic acid crystal slurry is efficiently treated It relates to the processing method.

Para-xylene is used as a raw material to produce crude terephthalic acid (CTA) by liquid phase oxidation with an oxygen-containing gas in an acetic acid solvent in the presence of an oxidation catalyst, and then the crude terephthalic acid is dissolved in a high-temperature, high-pressure aqueous solvent. In the presence of a reduction catalyst, hydrorefining is performed with a hydrogen-containing gas to obtain a purified aqueous solution, and further through a crystallization step in which pressure-reducing cooling is performed to gradually reduce the pressure, a purified terephthalic acid crystal slurry is generated. The purified terephthalic acid crystal slurry is subjected to solid-liquid separation to recover crystals, and the purified terephthalic acid (PTA) crystal powder that has undergone the drying process is used to produce polyester for fibers, films, and bottles. Manufactured as an acid.

In such a production method, high-purity terephthalic acid crystals (primary crystals) are produced, and impurities such as 4-carboxybenzaldehyde (4-CBA) contained in crude terephthalic acid are converted to paratoluic acid by hydrogenation. After being reduced and cooled under pressure, a separated mother liquor (primary mother liquor) in which most of the p-toluic acid is dissolved is produced. At the same time, terephthalic acid that becomes saturated at the separation temperature is also dissolved in the primary mother liquor.

Therefore, the primary mother liquor is further cooled to precipitate dissolved terephthalic acid and dissolved impurities, recovering low-purity terephthalic acid crystals (secondary crystals) and coexisting in the oxidation reaction of para-xylene. Have been proposed (Japanese Patent Publication No. 56-35175, Japanese Patent Laid-Open No. 5-58948).

On the other hand, the mother liquor (secondary mother liquor) from which the low-purity terephthalic acid crystal (secondary crystal) has been separated is directly used as it is or as a water solvent for dissolving the crude terephthalic acid crystal by subjecting it to fractional distillation. A method of effectively using the secondary mother liquor such as using it has also been proposed.

However, this proposal suggests that the secondary mother liquor contains a lot of p-toluic acid, which is an impurity of purified terephthalic acid (PTA) crystals, so that it can be used directly as an aqueous solvent for dissolving crude terephthalic acid (CTA) crystals. After a fractional distillation process with a reflux ratio of 2 to 10 and a theoretical plate number of 25 to 125, the recovered water is washed with dissolved terephthalic acid dissolved water or purified terephthalic acid (PTA) crystals (primary crystals). It is used as water (Japanese Patent Laid-Open No. 5-58948).

These proposals are being put into practical use in commercial equipment for the production of high-purity terephthalic acid, with an increasing demand for polyester, recent resource saving, and a reduction in environmental impact. Therefore, due to the growing need for the use of a large amount of primary mother liquor, issues for practical use are becoming apparent.

As one of them, when the primary mother liquor is cooled, it is cooled to the final separation temperature all at once, but at this time, the secondary crystal particle size becomes fine, the secondary crystal recovery device becomes high load, and the cooling device It is said that there is a problem in practical use due to adhesion and blockage of fine crystals to the surface. Therefore, an improvement method has been proposed in which secondary crystals are precipitated using a plurality of cooling tanks that gradually reduce the pressure when the primary mother liquor is cooled by pressure relief (Japanese Patent Laid-Open No. 2006-8671).

In order to increase the amount of secondary mother liquor used, a method for removing paratoluic acid by bringing the secondary mother liquor into contact with a synthetic adsorbent such as SEPABEADS (Mitsubishi Chemical) has been proposed. (Japanese Patent Laid-Open No. 2006-8671)
In the above situation, the present inventors perform flash (release pressure) evaporation and / or heat evaporation of the primary mother liquor in the presence of terephthalic acid crystals, condensing and recovering the evaporated solvent vapor, A primary mother liquor treatment method has been proposed that increases the amount of reuse by obtaining reduced recovered water. It is possible to recover an aqueous medium in which p-toluic acid is further reduced by obtaining a condensate by evaporation without fractional distillation using a distillation column having a reflux ratio of 2 to 10 and a theoretical plate number of 25 to 125. It is a method (WO2009 / 141968).

Japanese Patent Publication No.56-35175 Japanese Patent Laid-Open No. 05-58948 JP 2006-8671 A International Publication No. 2009/141968

As described above, when the purified terephthalic acid separation mother liquor (primary mother liquor) is separated into the secondary crystals and the secondary mother liquor and applied to a practical apparatus, the suspension produced by the cooling method of the primary mother liquor is applied. Suspensions are difficult to handle because the suspended particles (secondary crystals) are fine and sticky, and separation of the suspended particles (secondary crystals) causes clogging of the filter and a decrease in the recovery rate. It is said.
On the other hand, since the secondary mother liquor remains in the dissolved impurities, in order to circulate and use it as dissolved water for hydrorefining, treatment by evaporation or distillation is required, but it is circulated and used without any treatment. However, there is a problem that it is limited by its use and its usage.

When producing purified terephthalic acid, the present invention separates and recovers low-purity terephthalic acid crystals (secondary crystals) from the mother liquor separated with the primary crystals (primary mother liquor) with simple processing steps and good filtration performance. For the purpose.

In addition, the present invention improves the yield of terephthalic acid by recycling and using low-purity terephthalic acid crystals (secondary crystals) separated and recovered with good filtration performance as part of the raw material for producing terephthalic acid. Furthermore, it aims at reducing the amount of dissolved impurities in the primary mother liquor to reduce the generation of water to be reused and the wastewater treatment load.

Generally, purified terephthalic acid crystal slurry is solid-liquid separated under pressure (0.2 to 0.9 MPa), and the separated mother liquor (primary mother liquor) is obtained at a temperature of about 120 to 170 ° C. under pressure. Therefore, the present inventors added terephthalic acid crystals to the primary mother liquor, mixed, then supplied to the cooling tank adjusted to a pressure lower than atmospheric pressure, cooled by pressure reduction, and precipitated the crystals Thus, a processing method capable of obtaining a cooled suspension with improved filtration characteristics was achieved.

In order to solve the above-mentioned problems, the present invention is to dissolve crude terephthalic acid produced by liquid-phase oxidation of para-xylene in water under high temperature and high pressure, hydrotreat it, cool it, and purify terephthalic acid. When producing an acid crystal slurry and producing high-purity purified terephthalic acid from the crystal slurry,
A primary separation step of separating the purified terephthalic acid crystal slurry into purified terephthalic acid crystals (primary crystals) and a mother liquor (primary mother liquor);
A cooling suspension that generates a cooling suspension by adding terephthalic acid crystals to the separated mother liquor (primary mother liquor) and then supplying the terephthalic acid crystal to a cooling tank adjusted to a pressure lower than atmospheric pressure to perform pressure relief cooling. Generation process;
The cooling suspension is characterized by comprising a secondary separation step of separating and recovering low-purity terephthalic acid crystals (secondary crystals) by filtration and separation under a pressure of atmospheric pressure or higher.

In the primary separation step, the purified terephthalic acid crystal slurry is separated from a mother liquor (primary mother liquor) at a temperature of about 120 to 170 ° C. and a pressure higher than the vapor pressure of the slurry (about 0.2 to 0.9 MPa), In the cooling suspension generation process, terephthalic acid crystals are added to the separated mother liquor (primary mother liquor) and then supplied to a cooling tank adjusted to a reduced pressure of about 1.3 to 53 kPa (about 10 to 400 mmHg) to release the pressure. A cooling suspension is produced by cooling.

In the cooling suspension generation step, terephthalic acid crystals are prepared in a slurry with water and added to the separated mother liquor (primary mother liquor) in a proportion of 0.05 to 1% by weight. And

In the cooling suspension generation step, the terephthalic acid crystal added to the separated mother liquor (primary mother liquor) is a crystal powder obtained by drying purified terephthalic acid crystals.

In the secondary separation step, low-purity terephthalic acid crystals (secondary crystals) separated and recovered from the cooling suspension are used as part of the raw material for the liquid phase oxidation reaction of para-xylene. It is characterized by.

In the secondary separation step, the mother liquor (secondary mother liquor) separated from the cooling suspension is used as a part of water for dissolving crude terephthalic acid.

In the present invention, the suspended primary mother liquor to which terephthalic acid crystals have been added in advance and mixed is subjected to pressure cooling, so that precipitates dissolved in the primary mother liquor, particularly crystalline impurities such as terephthalic acid and p-toluic acid are added. The terephthalic acid crystal particles formed are deposited or adsorbed on the surface of the crystal as a nucleus, and the added terephthalic acid crystal particles are produced as grown. It is done.

The cooled suspension is recovered as low-purity terephthalic acid crystals (secondary crystals) to which impurities are more adhered by filtration separation. The filterability is improved and the adhesion of the secondary crystals is also improved, so that a practical suspension is obtained.

The recovered secondary crystals are supplied as a part of the raw material for producing terephthalic acid by liquid phase oxidation of para-xylene, and the crystallized terephthalic acid as well as reaction intermediates such as p-toluic acid, which is an impurity, are oxidized to terephthalic acid. The terephthalic acid crystals that contribute to the improvement of the yield and are added and mixed are also circulated and recovered, and there is no production loss.

On the other hand, the separated secondary mother liquor has a significantly reduced content of p-toluic acid as dissolved impurities and a small amount of dissolved metal compared to the secondary mother liquor separated by the conventional method without the addition of terephthalic acid crystals. It is also possible to increase the amount of reuse that is recycled in the aqueous solvent for chemical purification. In addition, the reduction of dissolved impurities in the secondary mother liquor reduces environmental burdens such as chemical oxygen demand (COD) when treating wastewater as industrial wastewater.

Although any terephthalic acid can be added to and mixed with terephthalic acid crystals, dried terephthalic acid is preferred, and the use of purified terephthalic acid (PTA) crystals, that is, high-purity terephthalic acid products contain p-toluic acid. Effective in reducing the amount. This is thought to be due to the fact that the terephthalic acid crystals are dried, which enlarges the crystal surface (increases pores and surface roughness) or activates it, increasing the adsorption power and the amount of terephthalic acid crystals. More dissolved impurities with good affinity are adsorbed on the surface of the added terephthalic acid crystal, and the residual impurities in the secondary mother liquor are reduced.

These effects indicate that the content of impurities in the secondary crystal is increased, but intermediates such as p-toluic acid have a favorable result in increasing the yield of terephthalic acid as the recovery rate increases. Bring.

According to the present invention, by adding a crystal of terephthalic acid to the primary mother liquor, cooling under reduced pressure to less than atmospheric pressure, and then filtering and improving, the filterability of the product crystal separation is improved. In addition, the practical effect on the primary treatment method such as improvement of the recovery rate of secondary crystals and reduction of the impurity content in the secondary mother liquor is great. That is, the improvement in filterability improves the filtration rate and the stability of filtration, makes the filter smaller, and enables stable continuous or semi-continuous operation. In addition, the recovery rate of the secondary crystals is improved by stable operation, and the cost and labor of the equipment and maintenance of the filter are reduced.

Also, the improvement in the recovery rate of the secondary crystals greatly contributes to the improvement in the yield of crude terephthalic acid and purified terephthalic acid because the recovered secondary crystals are reused as part of the oxidation reaction raw material.

Furthermore, the reduction of dissolved impurities (paratoluic acid) in the secondary mother liquor leads to an improvement in the recovery rate of the secondary crystals, and the secondary mother liquor can be recycled in the water that dissolves crude terephthalic acid. Reduction. As a result, the amount of wastewater treated is reduced and the environmental load is reduced.

In addition, the reduction in the amount of secondary mother liquor that was not used in circulation not only reduces the amount of wastewater treated, but also reduces the load such as COD (chemical oxygen demand) of wastewater, leading to a reduction in the total wastewater treatment load, Great practical effect.

In addition, in order to reduce dissolved impurities (paratoluic acid) in the secondary mother liquor, no further treatment (Japanese Patent Laid-Open No. 2006-8671) for contacting with the synthetic adsorbent is required, and the effect of the present invention is achieved simultaneously with the treatment of the primary mother liquor. Is a simple processing method.

It is explanatory drawing which shows the whole process of high-purity terephthalic acid manufacture of this invention embodiment. It is explanatory drawing which shows the manufacturing process of a high purity terephthalic acid from the refinement | purification terephthalic acid crystal slurry of this invention embodiment, and the process of a separation primary mother liquor. It is explanatory drawing which performs the process test of the isolate | separated primary mother liquor of this invention embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows all steps of a high-purity terephthalic acid production method using para-xylene as a raw material, positioning of a primary mother liquor during separation of purified terephthalic acid crystals, secondary crystals after the treatment of the primary mother liquor according to the present invention, and The positioning of the next mother liquor and the flow of processing outline are shown. In the production process of crude terephthalic acid (CTA), crystallization is performed by oxidation reaction using paraxylene as a raw material, and then crude terephthalic acid (CTA) crystals are produced by a solid-liquid separator. In the production process of purified terephthalic acid (PTA), CTA crystals are prepared in a CTA slurry adjustment tank, dissolved, hydrorefined and cooled to obtain purified terephthalic acid crystal slurry, and then solid-liquid separator 1 Separated into PTA crystals and primary mother liquor.

After the terephthalic acid crystals are added to the primary mother liquor separated as described above, the primary mother liquor is produced as a cooled suspension in the pressure-reducing cooling tank 13 and separated into secondary crystals and secondary mother liquor by the filter 15.

The separated secondary crystals are reused as part of the crude terephthalic acid production raw material para-xylene, and the separated secondary mother liquor is a part of the aqueous solvent that dissolves the crude terephthalic acid crystals in the purified terephthalic acid production process. Will be reused. Secondary mother liquor that has not been reused is treated in a wastewater treatment process. In addition, the flow which uses a refined terephthalic acid (PTA) crystal as a terephthalic acid (TA) crystal added to a primary mother liquor is shown with the dotted line.

FIG. 2 shows an overall process for producing high-purity terephthalic acid according to an embodiment of the present invention. In the production of high-purity terephthalic acid by performing liquid phase oxidation and hydrorefining using para-xylene as a starting material, the purified terephthalic acid crystal slurry is subjected to solid-liquid separation with a solid-liquid separator 1 under pressure, and purified terephthalic acid crystals ( Primary crystals) are collected and supplied to a schematic flow for producing high-purity terephthalic acid via the crystal washing tank 2.

The outline flow of the processing method of the embodiment of the present invention using the mother liquor (primary mother liquor) from which purified terephthalic acid crystals (primary crystals) are separated is as follows: primary mother liquor tank 10 → slurry preparation tank 12 → pressure-reduction cooling tank 13 → filter 15. → The secondary mother liquor tank 16 flows. Note that the description of the stirring blade of the container (tank) is provided with a stirrer because the content is slurry or suspension.

FIG. 3 is an explanatory diagram for performing a treatment test of the separated primary mother liquor according to the embodiment of the present invention. The purified terephthalic acid slurry produced in the purified terephthalic acid production process is solid-liquid separated to obtain purified terephthalic acid crystals and a separated mother liquor (primary mother liquor), and then the flow of processing of the primary mother liquor in the production process (purified terephthalic acid A flow (primary mother liquor treatment test area) in which the primary mother liquor is collected from the high temperature / high pressure primary mother liquor tank and the method of the present invention is carried out is shown separately from the production area). The filtration test was conducted by sampling a steady flow from the pressure-reducing cooling tank to the waste liquid treatment process.

An example of the embodiment of the present invention will be described with reference to FIG. A solid-liquid separation system for purified terephthalic acid crystal slurry performed under pressure (about 0.2 to 0.9 MPa) is further used for primary crystals obtained by centrifugation or filtration separation as described in JP-B-47-49049. A system for performing high-purity purified terephthalic acid crystals after washing by re-slurrying with water is as follows: solid-liquid separator 1 → crystal washing tank 2 → flash cooling tank 3 → slurry supply tank 4 → The flow of the solid-liquid separator 5 → the dryer 6, and the method according to the embodiment of the present invention is performed using the primary mother liquor obtained from the system as a starting material.

Starting from the primary mother liquor obtained by a system that collects purified terephthalic acid crystals (primary crystals) by carefully washing the terephthalic acid crystals after filtration separation described in JP-T 6-506461 in the same filter. It can also be used as a raw material.

In any of the above filtration separation methods, the primary mother liquor obtained by filtration separation through a filter medium contains a trace amount of suspended suspended solids (terephthalic acid crystal particles) in the mother liquor that is leaked (about 0.01% by weight or less). Therefore, when the primary mother liquor by filtration separation is selected as a starting material, the effect of the method of the embodiment of the present invention in which terephthalic acid crystals are added and mixed is expected more.

That is, in the production of purified terephthalic acid, the filterability of the secondary crystals and the remaining amount of dissolved impurities in the secondary mother liquor, which is the subject of the present invention, with respect to the primary mother liquor from the filtration separation of the purified terephthalic acid crystal slurry are improved. Needs for practical use were higher. In the primary mother liquor (primary mother liquor tank 10) obtained at about 120 to 170 ° C. under pressure (about 0.2 to 0.9 MPa), about 0.1 to 0.5% by weight of terephthalic acid is dissolved and paratoluic acid is about 0.03 as an impurity. It is dissolved at a rate of ~ 0.15% by weight.

In the embodiment of the present invention, terephthalic acid crystals are added to and mixed with the primary mother liquor. However, the terephthalic acid crystals to be added may be added directly and mixed as they are. It is preferable that the slurry is made into a slurry (40% by weight) (slurry preparation tank 12) and then fed and mixed in a primary mother liquor under pressure (about 0.2 to 0.9 MPa). The amount is supplied to be about 0.05 to 1% by weight with respect to the primary mother liquor, but it is preferable to add about 0.1 to 0.5% by weight to improve the filterability relative to the amount of terephthalic acid crystals added.

However, it should be recognized that increasing the amount added reduces the amount of dissolved paratoluic acid in the secondary mother liquor, but increases the process load of filtration separation and circulation of the added terephthalic acid crystals.

Suspended primary mother liquor mixed with terephthalic acid crystals is directly supplied to the depressurization cooling tank 13 that is decompressed to about 1.3 to 53 kPa (about 10 to 400 mmHg) below atmospheric pressure using a vacuum pump or an ejector. A suspension is formed which is decompressed and evaporated to about 10-80 ° C. In addition, the cooling suspension may be generated by reducing the pressure of the plurality of cooling tanks to about 1.3 to 53 kPa (about 10 to 400 mmHg) below atmospheric pressure by stepwise releasing the pressure.

The effect of this embodiment can be obtained if the final cooling tank can be cooled by releasing pressure under a reduced pressure of about 1.3 to 53 kPa (about 10 to 400 mmHg) below atmospheric pressure to produce a cooled suspension.

The final temperature in the pressure-reduction cooling bath 13 is preferably a lower cooling temperature under a reduced pressure of less than atmospheric pressure from the viewpoint of crystallization and recovery of dissolved substances and reduction of dissolved impurities in the secondary mother liquor after separation. However, it is practically preferable to obtain a cooled suspension at about 30 to 65 ° C. under a reduced pressure of about 4 to 26 kPa (about 30 to 200 mmHg).

In addition, the evaporated vapor is condensed and recirculated to the pressure-reducing cooling tank 13, but is reconstituted as treated water having a reduced paratoluic acid content as evaporative condensed water proposed by the present inventors in WO2009 / 141968. It can also be used.

Next, the suspension in the pressure-relief cooling tank 13 is separated into secondary crystals and secondary mother liquor by a filter. In order to filter and separate a suspension containing fine particles that remain sticky, It is preferable to carry out clarification filtration under atmospheric pressure or pressure exceeding the pressure of the final cooling tank (below atmospheric pressure), press filter, hundback filter (manufactured by IHI), cricket filter (manufactured by Tsukishima Kikai Co., Ltd.) A pressure filter such as is used.

The separated secondary crystal is prepared as a raw material for the oxidation reaction of para-xylene, slurried with solvent acetic acid, and then used as a part of the raw material for producing terephthalic acid (secondary crystal flow in FIG. 1).

The secondary mother liquor will be reused as part of the dissolved water for dissolving and hydrotreating crude terephthalic acid, but the amount reused is dissolved impurities (paratriylic acid) remaining in the secondary mother liquor. It will be adjusted according to the amount. Although the secondary mother liquor that has not been used is directly treated as wastewater by a method such as activated sludge that has been carried out conventionally, the amount and load of wastewater treatment to be treated can be further reduced (secondary mother liquor flow in FIG. 1). .

Further, an aqueous solvent with a further reduced amount of impurities (a content of p-toluic acid) can be recovered by a treatment such as fractional distillation proposed in JP-A-5-58948.

Next, the embodiment of the present invention will be described more specifically using the following examples. However, the method of the present invention is not limited to the following examples.
(Example 1)
After producing crude terephthalic acid (CTA) by liquid-phase air oxidation of p-xylene, the obtained crude terephthalic acid is dissolved in water and hydrorefined at high temperature and pressure to produce high-purity terephthalic acid (PTA) During production, the purified terephthalic acid (PTA) crystal slurry at high temperature and high pressure (about 145 ° C, about 0.4 MPa) obtained from the crystallization process is solid-liquid separated to obtain purified terephthalic acid (PTA) crystals, washed and dried The process produces purified terephthalic acid (PTA).

At that time, the separation mother liquor (primary mother liquor) obtained from the solid-liquid separation step is transferred to a waste liquid treatment step under atmospheric pressure through a high temperature / high pressure storage tank (high temperature / high pressure primary mother liquor) and processed. ing.
In carrying out the method of the present invention, a portion of the primary mother liquor in the high-temperature / high-pressure primary mother liquor tank of the purified terephthalic acid production area (FIG. 3) is separated by piping branching under high-temperature / high pressure (about 145 ° C, about 0.4 MPa). Taken (primary mother liquor treatment test area in Fig. 3), 100 parts by weight per unit time in a pressure-reducing cooling tank with a stirrer (equipped with a reflux condenser) adjusted to less than atmospheric pressure about 20kPa (about 150mmHg) by a vacuum pump The primary mother liquor is cooled under reduced pressure (temperature is about 60 ° C.). The terephthalic acid and paratoluic acid dissolved in the primary mother liquor were precipitated by the pressure relief cooling to form a cooled suspension, and then the mother liquor (primary mother liquor) of the purified terephthalic acid (PTA) production. It returned to the waste liquid treatment process (refined terephthalic acid production area of FIG. 3) and continuously discharged.

At that time, 20 wt% terephthalic acid crystals (dried purified terephthalic acid crystals (PTA powder)) water slurry was prepared in the slurry supply tank with a stirrer in the branch supply pipe of primary mother liquor under high temperature and high pressure. The terephthalic acid slurry is continuously supplied at a ratio of 0.75 wt% (PTA crystal addition rate 0.15%) with respect to the primary mother liquor, mixed with the primary mother liquor, and then supplied to the cooling tank to cool by pressure reduction. The cooling suspension at about 60 ° C. generated in the cooling tank is discharged back to the waste water treatment step for the primary mother liquor.

At that time, 100 parts of the continuously discharged cooling suspension is collected and subjected to a filtration test using a Buchner funnel equipped with an incubator to measure the filtration time and the content of paratoluic acid in the filtrate (secondary mother liquor). went. As a result, the filtration time was 42 sec, and the content of p-toluic acid in the secondary mother liquor was 0,025 wt%. (Table 1)
(Comparative Example 1)
In the method of Example 1, the addition of terephthalic acid crystals (supply of 20 wt% terephthalic acid crystal water slurry) was stopped, and the pressure-release cooling was performed to produce a cooled suspension.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, the filtration time was 620 sec and the content of p-toluic acid was 0.048 wt%. (Table 1)
(Example 2)
In the method of Example 1, 20 wt% terephthalic acid crystal water slurry is supplied at a ratio of 0.35 wt% (PTA crystal addition rate 0.07%) to the primary mother liquor, and is cooled by releasing pressure to produce a cooled suspension. did.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, each filtration time was 113 sec and the content of p-toluic acid was 0.033 wt%. (Table 1)
(Example 3)
In the method of Example 1, a 20 wt% terephthalic acid crystal water slurry was supplied at a ratio of 1.5 wt% (PTA crystal addition rate: 0.3%) to the primary mother liquor, and cooled under pressure to produce a cooled suspension. .
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, each filtration time was 38 sec, and the content of p-toluic acid was 0.017 wt%. (Table 1)
(Example 4)
In the method of Example 1, a 20 wt% terephthalic acid crystal water slurry was supplied at a rate of 2.25 wt% (PTA crystal addition rate 0.45%) to the primary mother liquor, cooled under pressure, and cooled and suspended. A liquid was produced.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, each filtration time was 41 sec, and the content of p-toluic acid was 0.011 wt%. (Table 1)
(Example 5)
In the method of Example 1, a 20 wt% terephthalic acid crystal water slurry was prepared using a wet cake (PTA crystals before drying) separated from the purified terephthalic acid crystal slurry, and 0.75 wt% (PTA) relative to the primary mother liquor. The crystal was added at a rate of 0.15%) and cooled under pressure to produce a cooled suspension.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, each filtration time was 40 sec and the content of p-toluic acid was 0.032 wt%. (Table 1)
(Example 6)
In the method of Example 1, the pressure-release cooling tank pressure was adjusted to about 7.3 kPa (about 55 mmHg temperature about 40 ° C.), and the pressure-release cooling was performed to produce a cooled suspension.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, the filtration time was 59 sec and the paratoluic acid content was 0.008 wt%. (Table 1)
(Example 7)
In the method of Example 1, the pressure-release cooling tank pressure was adjusted to about 47 kPa (about 355 mmHg temperature about 80 ° C.), and 20 wt% terephthalic acid crystal water slurry was added to 1.5 wt% (PTA crystal addition rate 0.3%) with respect to the primary mother liquor. %) Was applied to perform pressure relief cooling to produce a cooled suspension.
As in Example 1, the cooled suspension drainage was collected and subjected to a filtration test. As a result, the filtration time was 28 sec and the paratoluic acid content was 0.031 wt%. (Table 1)
(Comparative Example 2)
In the method of Example 7, the addition of terephthalic acid crystals (supply of 20 wt% terephthalic acid crystal water slurry) was stopped, and the pressure relief cooling was performed to produce a cooled suspension.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, the filtration time was 540 sec and the content of p-toluic acid was 0.092 wt%. (Table 1)
(Example 8)
In the method of Example 1, the pressure-reducing cooling tank pressure was adjusted to about 2.4 kPa (about 18 mmHg temperature: about 20 ° C.), and pressure-relief cooling was performed to produce a cooled suspension.
As in Example 1, the cooled suspension was collected and subjected to a filtration test. As a result, the filtration time was 94 sec and the paratoluic acid content was 0.003 wt%. (Table 1)
Table 1

DESCRIPTION OF SYMBOLS 1, 5 ... Solid-liquid separator, 2 ... Crystal washing tank, 3 ... Flash cooling tank, 4 ... Slurry supply tank, 6 ... Dryer, 7 ... Cleaning drainage tank, 8, 9, 11, 14 ... Gas-liquid separation 10 ... primary mother liquor tank, 12 ... slurry adjusting tank, 13 ... pressure-release cooling tank, 15 ... filter, 16 ... secondary mother liquor tank.

Claims

Crude terephthalic acid produced by liquid-phase oxidation of para-xylene is dissolved in water at high temperature and high pressure, hydrorefined, and then cooled to produce a purified terephthalic acid crystal slurry. In producing high purity purified terephthalic acid,
A primary separation step of separating the purified terephthalic acid crystal slurry into purified terephthalic acid crystals (primary crystals) and a mother liquor (primary mother liquor);
A cooling suspension that generates a cooling suspension by adding terephthalic acid crystals to the separated mother liquor (primary mother liquor) and then supplying the terephthalic acid crystal to a cooling tank adjusted to a pressure lower than atmospheric pressure to perform pressure relief cooling. Generation process;
A purified terephthalic acid mother liquor comprising a secondary separation step of separating and recovering low purity terephthalic acid crystals (secondary crystals) by filtering and separating the cooled suspension at a pressure of atmospheric pressure or higher. Method.
In the primary separation step, the purified terephthalic acid crystal slurry is separated from the mother liquor (primary mother liquor) at a temperature of about 120 to 170 ° C. and a pressure higher than the vapor pressure of the slurry (about 0.2 to 0.9 MPa),
In the cooling suspension generation step, terephthalic acid crystals are added to the separated mother liquor (primary mother liquor), and then supplied to a cooling tank adjusted under a reduced pressure of about 1.3 to 53 kPa (about 10 to 400 mmHg) for release. The method for treating a purified terephthalic acid mother liquor according to claim 1, wherein a cooling suspension is produced by pressure cooling.
2. In the cooling suspension generation step, phthalic acid crystals are prepared in a slurry with water to the separated mother liquor (primary mother liquor) and added in a proportion of 0.05 to 1% by weight. Or a method for treating the purified terephthalic acid mother liquor according to 2.
The terephthalic acid crystal added to the separated mother liquor (primary mother liquor) in the cooling suspension generation step is a crystal powder obtained by drying purified terephthalic acid crystals. A method of treating the purified terephthalic acid mother liquor according to claim 1.
In the secondary separation step, low-purity terephthalic acid crystals (secondary crystals) separated and recovered from the cooling suspension are used as part of the raw material for the liquid phase oxidation reaction of para-xylene. The method for treating a purified terephthalic acid mother liquor according to any one of claims 1 to 4.
6. The secondary separation step, wherein the mother liquor separated from the cooling suspension (secondary mother liquor) is used as a part of water for dissolving crude terephthalic acid. A method of treating the purified terephthalic acid mother liquor according to claim 1.