MX2010012094A

MX2010012094A - Method for treating separated mother liquor from terephthalic acid refinement.

Info

Publication number: MX2010012094A
Application number: MX2010012094A
Authority: MX
Inventors: Noriaki Hara; Hiroyuki Toyoshima; Hatsutaro Yamazaki
Original assignee: Hitachi Plant Technologies Ltd
Priority date: 2008-05-20
Filing date: 2009-05-11
Publication date: 2010-12-07
Also published as: CN102026952A; CN102026952B; WO2009141968A1

Abstract

Provided is a method for treating the separated mother liquor from terephthalic acid refinement whereby recovered water with little impurity is obtained cheaply and in large quantity from the primary mother liquor separated at the time of primary crystallization. The method of treating the mother liquor (primary mother liquor) wherein the refined terephthalic acid crystals (primary crystals) and mother liquor (primary mother liquor) are separated from the crystal slurry involves an evaporation process wherein the aforementioned mother liquor is evaporated in the presence of terephthalic acid crystals by heating and flash evaporation at a pressure below atmospheric pressure and separated into vapor and a mother liquor suspension of terephthalic acid crystals; a process whereby terephthalic-acid-containing crystals are separated from the aforementioned mother liquor suspension; and a process whereby the aforementioned vapor is condensed and condensed water is produced.

Description

METHOD FOR TREATING LIQUOR SEPARATE MOTHER OF REFINEMENT THEREFTAL ACID TECHNICAL FIELD The present invention relates to a method for treating a primary mother liquor separated from a crystalline slurry of a terephthalic acid purified in crystals and a mother liquor by producing a highly pure terephthalic acid. It is a technique to save resources that gives less environmental load by effectively treating a mother liquor separated from crystals of a purified terephthalic acid (primary mother liquor) discharged in a large quantity to be reused in the production of a highly pure terephthalic acid, which includes producing a crude terephthalic acid carrying out the phase oxidation reaction for paraxylene in an acetic solvent under the presence of an oxidation catalyst, then dissolving the crude terephthalic acid in water at a high temperature and a high pressure, crystallizing the aqueous solution which is purifies by purification of hydrogenation under the presence of a noble metal catalyst by evaporation by multiple step expansion and cooling thereby forming a slurry and recovering crystals of a purified terephthalic acid.

Particularly, it relates to a method for treating solvent water used for purification which includes Condensing the separated mother liquor (primary mother liquor) by rinsing and evaporation by heating under atmospheric pressure or lower, crystallizing and recovering an effective ingredient of aromatic carboxylic acids dissolved in the separated mother liquid (primary mother liquor) being able to supply and use the same as a production material for the crude terephthalic acid and, simultaneously, condensing and recovering an evaporated vapor, being able thus to recycle and use it as water necessary for the purification of the crude terephthalic acid.

PREVIOUS TECHNIQUE In the existing production of a highly pure terephthalic acid to prepare a crude terephthalic acid using paraxylene as a starting material in an acetic solvent by liquid phase oxidation reaction, dissolving crude terephthalic acid in water at a high temperature and high pressure Y . then obtaining a purified terephthalic acid by reduction of hydrogenation 4-carboxybenzaldehyde (4-CBA) contained as a normal impurity in crude terephthalic acid was converted to paratoluic acid (p-tA) which can be relatively easily separated from terephthalic acid by reduction by hydrogenation and then a slurry of terephthalic acid crystals was formed by a method, for example, pressure release cooling (cooling by expansion or expansion cooling) of the solution of dissolved aqueous terephthalic acid and crystals of a highly pure terephthalic acid at a lower paratoluic acid content (p-tA: 150 ppm or less) was recovered and produced by solid-liquid separation.

This is a method to take advantage of the separation and purification of terephthalic acid crystals that can be facilitated by reducing 4-carboxybenzaldehyde (4-CBA) that has high chemical affinity in terms of eutectic binding or adsorption with crystals of terephthalic acid to para-toluic acid (p-1). tA) that has relatively less affinity compared to it.

As a result, in the separated mother liquid (primary mother liquor) separated from crystals of purified terephthalic acid, the paratoluic acid formed by reduction was dissolved in an amount approximately to the amount of 4-carboxybenzaldehyde together with terephthalic acid dissolved in a saturated amount and, furthermore, a trace amount of metallic impurities contained in crude terephthalic acid (cobalt derived from oxidation catalyst, iron derived from corrosion of apparatus), etc.

In the production process for highly pure terephthalic acid, given that the water to a purity superior (pure water) obtained by ion exchange treatment, etc. it is used in a large quantity (from 2 to 10 times per volume of crude terephthalic acid) as solvent water to dissolve the crude terephthalic acid, the primary mother liquor gives a great environmental load both in view of quantity and quality and Results with environmental problems in the mother liquor are discarded as such. In addition, it is also an object to obtain a large quantity of solvent water (pure water) necessary for the purification of crude terephthalic acid and several proposals have been made for the solution of the objective.

The Patent Document (JP-B No. 56-35174) proposes a method to improve the performance of the entire process for the production of terephthalic acid by further cooling the separated mother liquor (primary mother liquor) to decrease the solubility of organic ingredients of the dissolved aromatic carboxylic acids, crystallizing terephthalic acid crystals to a reduced purity by crystallization of dissolved paratoluic acid and recovering them by recycling and incorporating them together in the paraxylene oxidation reaction. While the method suggests that the mother liquor separated from the secondary crystals (secondary mother liquor) mitigates the treatment load for waste water in view of the quality, it does not mention anything about the treatment of water waste.

In addition, Patent Document 2 (JP-A No. 5-58948) proposes an improvement for the terephthalic acid yield by mixing the secondary crystals as a low purity with the oxidation reaction medium and the use of at least a portion of the secondary mother liquor directly as such or after treatment as water to dissolve the crude terephthalic acid. In addition, it has a treatment method of carrying out the fractional distillation and using a distilled water as a cleaning water when separating and recovering the purified crystals of terephthalic acid (primary crystals).

As described above, since paratoluic acid is contained in a large amount (p-tA content: 300 to 1500 ppm) and impurities of metals, etc., are contained in the secondary mother liquor, when the secondary mother liquor is It reuses as it is untreated as water to dissolve the crude terephthalic acid, it can not be used for a large amount but it is used only for a small restricted amount.

In addition, evaporation can be considered as the method of treating the secondary mother liquor and, to reduce the entry of pollutants (p-tA, etc.) with distilled water, a fractional distillation treatment method at a sufficient reflux ratio has been indicted. However, since water that has a great heat is distilled latent evaporation (latent heat of evaporation: 539 kcal / kg, 100 ° C) at a sufficient reflux ratio in the fractional distillation treatment (reflux ratio: from 2 to 10, theoretical plate numbers: 25 to 125), this gives a great distillation load.

In addition, Patent Document 3 (JP-A No. 2006-8671) proposes a method for cooling the expanding primary mother liquor of multiple stages as a method for improving the crystallization property and the filtering capacity of secondary and secondary crystals. , for the treatment of the separated secondary mother liquor, the amount of impurities contained (p-tA, etc.) is decreased by contact with a synthetic adsorbent, for example, a type of styrene-divinylbenzene and can be reused, for example, in a solvent step for a crude terephthalic acid.

PREVIOUS TECHNIQUE Patent Document Patent Document 1. JP-B No. 56-35174 Patent Document 2. JP-A No. 5-58948 Patent Document 3. JP-A No. 2006-8671 DESCRIPTION OF THE INVENTION Problem to be Resolved by the Invention However, in the technique shown in the patent documents, contained impurity, particularly, paratoluic acid is removed from the secondary mother liquor after the separation and recovery of the secondary crystals and the mother liquor is recovered as treatment water and is reused for the production of purified terephthalic acid. Since the secondary mother liquor is treated for regeneration of the treatment water after the crystallization of the secondary crystals, it needs a number of steps and increases the cost of treatment. Consequently, it is difficult to reuse the recovered water obtained by the treatment in abundance.

Also, as a method to treat the mother liquid (primary mother liquor) after the separation and recovery of pure crystals of terephthalic acid in the production process of highly pure terephthalic acid starting from paraxylene, is a preferred method for improving the yield of terephthalic acid to crystallize crystals of the primary mother liquor by evaporation by expansion and cooling and by supplying the separated and recovered secondary crystals as a portion of the starting material supplied to the xylene oxidation reaction. However, it is an objective in this case crystallize the secondary crystals more efficiently and improve the filtering capacity when separating the crystals.

Furthermore, in the production of the purified terephthalic acid from the recovery of water in a lower content of impurities, particularly, the paratoluic acid of the mother liquor comprising solvent water for the dissolution of a crude terephthalic acid, it is an objective to provide a method of treatment not expensive and convenient able to reuse the water recovered in abundance, for example, as water re-dissolving water to clean the terephthalic acid.

It is an object of the present invention to provide a method for treating a mother liquor separated from a purified terephthalic acid to obtain water recovered with less impurities of a large quantity and inexpensively in the step of crystallizing secondary crystals of a primary mother liquor at crystallize primary crystals in the production of purified terephthalic acid.

Means to Solve the Problem As a result of previous studies on the problems described above, the present inventors have succeeded in recovering the secondary crystals while increasing the amount of crystallization by concentrating the primary mother liquor in which the acid crystals Terephthalic are previously incorporated by evaporation by expansion and evaporation by heating, separating and recovering the liquid as condensed water from the steam generated from the primary mother liquor and decreasing the absolute quantity of the mother liquor to form the secondary mother liquor, crystallizing the crystals of terephthalic acid as the secondary crystals and having success in the formation of the condensed guide to a lower content of impurities, particularly, paratoluic acid of the generated steam. Consequently, a treatment method capable of lowering the preload in large quantity in view of the quality and reduction of the treatment load has been obtained in view of the amount for the secondary mother liquor separated from the secondary crystals.

To solve the problems described above, the present invention includes, a primary separation step of dissolving a crude terephthalic acid formed by liquid phase oxidation reaction of paraxylene in an aqueous solvent at a high temperature and a high pressure, subjecting the same to reduction by hydrogenation under the presence of a noble metal catalyst, then forming a slurry of terephthalic acid crystals by cooling and crystallization and separating and recovering crystals of purified terephthalic acid (primary crystals) and a mother liquor (primary mother liquor) from the slurry of crystals); an evaporation step separating the separated mother liquid (primary mother liquor) in a solvent vapor and a suspension of mother liquor containing terephthalic acid crystals for at least one expansion and heating step under the presence of terephthalic acid crystals and at a pressure atmospheric or lower; a secondary separation step of separating and recovering contained terephthalic acid crystals (secondary crystals) from the mother liquor suspension; and a condensate passage to condense a vapor of generated solvents to form condensed water.

In addition, the incorporated terephthalic acid crystals are the evaporation step in an amount corresponding at least to the terephthalic acid dissolved in the primary mother liquor. In addition, the crystals of terephthalic acids are incorporated in the evaporation step by the addition of terephthalic acid crystals. In addition, a solvent vapor is generated in the evaporation pass under the pressure of at least one atmospheric pressure or at least one expansion and heating step without reflux or with a slight reflux, reflux ratio < 1).

In addition, the secondary crystals recovered in the secondary separation step are supplied at least as a portion of the starting material supplied to the liquid phase oxidation reaction. In addition, water The condensate formed in the condensation step is reused as a portion of an aqueous solvent to dissolve the crude terephthalic acid or as a portion of cleaning water to clean the purified crystals of terephthalic acid (primary crystals) (primary separation step). In addition, the solvent vapor is generated in the evaporation step at a reduced pressure by a temperature of 40 ° C to 80 ° C, an expansion and heating step. Furthermore, in the evaporation step, the solvent vapor is generated at an atmospheric pressure by expansion and then the solvent vapor is generated at a reduced pressure at a temperature of 40 to 80 ° C by expansion and heating. In addition, the solvent vapor is generated in an evaporation step using a heating medium at approximately 110 ° C or lower.

Effect of the Invention According to the invention, in the crystallization step of the secondary crystals of the first parent liquid separated by crystallization of the primary crystals, the vapor evaporated by the expansion and heating treatment of the primary mother liquor is condensed simultaneously and condensed water with less impurities It can be recovered in a large amount in a non-expensive way. The condensed liquid can be reused for purification of crude terephthalic acid and the amount of pure water supply can be greatly diminished.

In addition, by recovering the condensed water evaporated from the primary mother liquor, since the amount of secondary mother liquor remaining after separation and recovery decreases, the secondary mother liquor separated and discharged remaining decreases in view of the amount reduced by the solute (impurities) , noticeable mitigation of the environmental burden can be obtained.

In addition, since the amount of remaining mother liquor suspension is greatly reduced by the recovery of the evaporated condensed water, the separation time can be shortened together with the improvement for the filtering capacity of the suspended crystals to improve efficiency by separation of solid-liquid. Then, the amount of separated and recovered secondary crystals is increased (approximately 5% by weight being converted as the amount of terephthalic acid solution) and the yield and production cost for the production of the highly pure terephthalic acid can also be improved .

In the treatment for the primary mother liquor according to the method of the invention, since the mother liquor is condensed by evaporation with waste heat energy and a relatively low temperature (approximately 110 ° C or lower), instead of distillation load (reflux) of the fractional distillation of a large amount of mother liquor that was required as the existing after-treatment of the secondary mother liquor, the pure water for the purification of the crude terephthalic acid it can be recovered to greatly reduce the cost of treatment.

Brief Description of the Drawings Figure 1 shows a treatment flow as an example of practicing the process of the invention.

Figure 2 is a schematic view of an experimental apparatus used for the simulation of the example of the invention.

Figure 3 is a graph showing the relationship between paratoluic acid in condensed water and the amount of condensed water recovery obtained in the simulation test.

A Way to Carry Out the Invention Since the primary mother liquor as a treatment object in the example of the invention is separated and formed from 130 to 160 ° C (from about 2 to 5.5 kg / cm 2G), from about 0.1 to 0.3% by weight of terephthalic acid is usually It dissolves as a saturated solution of terephthalic acid at said temperature and the paratoluic acid is converted from 4-carboxybenzaldehyde content in a crude terephthalic acid is dissolved at a ratio of about 0.03 to 0.15% by weight in the primary mother liquor. In addition, solid particles of terephthalic acid crystals that escape by the recovery of the primary mother liquor from a solid-liquid separator are usually present in an amount of about 0.02% by weight or less.

For the amount of terephthalic acid crystals needed to practice the invention, the present inventors have found that it is sufficient to incorporate them by an amount corresponding at least to the amount of terephthalic acid dissolved in the primary mother liquor (from about 0.1 to 0.3%. in weigh).

Accordingly, it is a practically preferred method of incorporating the terephthalic acid crystals in a range of an amount corresponding to the amount dissolved in the primary mother liquor to an amount several times as large as the corresponding amount, or in an amount up to about 1% by weight based on the primary mother liquor. While incorporating. the crystals of terephthalic acid by about 1% by weight or more is effective in decreasing the content of paratoluic acid in the condensed water of formed vapors, it is not an amount necessary in order to recover and reuse the condensed water of the vapor formed. A method for controlling the amount incorporated by additionally supplying the terephthalic acid crystals before the expansion or heating treatment of the primary mother liquor is reliable, but the amount can also be controlled, for example, by using a separate one to increase the amount of crystals that cause the leaks to the primary mother liquid by solid-liquid separation of crystals of purified terephthalic acid.

The crystals additionally provided with terephthalic acid are preferably purified terephthalic acid (PTA) crystals produced as a highly pure terephthalic acid which does not increase the amount of impurities (p-tA, etc.).

Consequently, while fractional distillation was required for the recovery of the condensate at a lower content of impurities, particularly, paratoluic acid evaporating solvent water by expansion and heating while previously incorporating terephthalic acid crystals in the primary mother liquor, without heating to reflux (returning to an evaporation vessel) or with slight reflux (reflux ratio: 1 or less) as in the example of the invention.

It has also been found that water condensed to a lower paratoluic acid content is obtained by condensation through expansion by pressure having at least one step at atmospheric or lower temperature and evaporation by heating to a final temperature of 40 to 80 ° C. Consequently, in this example, since the amount of the secondary mother liquor separated from the remaining concentrated mother liquor suspension largely decreases by condensation through heating evaporation, the amount of crystallized terephthalic acid and para-toluic acid crystals is increased and the recovered amount of crystals (secondary crystals) is increased more than the existing method.

Then, also in the separation, the amount of separated crystals (secondary crystals) is increased by the crystals of terephthalic acid previously incorporated in the primary mother liquor and it has also been found that the filtration rate for the suspension of formed mother liquor is improved . That is, while the separation of the mother liquor suspension is intended to clarify the filtration, it is considered that the presence of terephthalic acid crystals provides a body feed of a previous coating material (filtering aid to promote filtration) to Improve the filtration speed. Consequently, the time required for separation of secondary crystals is notoriously stored in association with the decrease in the amount of the secondary mother liquor.

In addition, also for the recovery of condensed water in the evaporation treatment existing in the secondary mother liquor in which the evaporation of the solvent vapor entered through paratoluic acid vapor and purification was required through distillation (reflux), it is considered that the paratoluic acid is furthermore supported and the generation of the paratoluic acid vapor is suppressed by adsorbing impurities to the terephthalic crystal particles which are added and incorporated into the primary mother liquor in the example of the invention wherein the terephthalic acid crystals are they previously incorporate into the primary mother liquor. Consequently, in this example, water condensed to a lower content of paratoluic acid is recovered without reflux or with slight reflux of condensed water evaporated (evaporation) by concentrating the primary mother liquor by evaporation by heating.

Consequently, the content of paratoluic acid in the recovered condensed water decreases to a large extent (to about 1/5 to 1/10) by evaporation by expansion and evaporation by heating the primary mother liquor without refluxing the condensed water (by evaporation) due to the incorporation of terephthalic acid crystals. While the content is different depending on the evaporation ratio of the solvent water, the primary mother liquor can be recovered in a large amount up to about 90% by weight thereof as the condemned water and can be used completely substantially.

Further, by slightly refluxing the condensed water (in an amount at a reflux ratio of 1 or less), the content of para-toluic acid further decreases markedly and most of the solvent water can be recovered and reused. Then, along with the decrease in the amount of the secondary mother liquor, the amount of precipitation of the secondary crystals is increased and the environmental load caused due to the treatment for the separated secondary mother liquor is also largely moderate.

Further, to evaporate the mother liquor to a suspension of 40 to 80 ° C by evaporation by heating at atmospheric pressure or below, particularly at reduced pressure, it has been found that a waste heat energy such as from vapor waste (steam at approximately 0.05 kg / cm2G and at approximately 110 ° C) discharged by a large amount of a production process for highly pure terephthalic acid, as well as other petrochemical processes, can be used as a heating medium for evaporation by expansion and heating. Consequently, the preparation of an additional heating means is not necessarily the heating means for evaporation and energy savings can be obtained.

As described above, by the method of incorporating the crystals of terephthalic acid into the primary mother liquor, the contained organic crystals (terephthalic acid, p-tA, etc.) improved for separation performance can be separated and recovered more quickly and used effectively and condensed water decreased in content of impurities, particularly, the content of paratoluic acid can be recovered by concentration by evaporation, or expanded with slight reflux (reflux ratio 0 to 1), or evaporation by heating. This then provides a method capable of greatly decreasing the additional amount of use of pure water necessary for the purification of a crude terephthalic acid. Consequently, a closed system capable of reducing the burden of environmental treatment is obtained by noticeably decreasing the amount of secondary mother liquor.

To practice the example, a crude terephthalic acid obtained from a production process of a crude terephthalic acid that starts from a step or submits the paraxylene to a liquid phase oxidation under the presence of an oxidation catalyst in an acetic acid solvent is dissolved in water at a high temperature and a high pressure and subjected to a hydrogenation reduction treatment under the presence of a noble metal catalyst. Then, it is passed through a step of forming a slurry of crystals of a purified terephthalic acid by cooling the slurry to a temperature of 130 to 160 ° C through evaporation by multi-stage expansion (not illustrated) and the slurry is supplied to a solid-liquid separator (separation of solid-liquid 1 in Figure 1).

The process flow for practicing the process of the invention shown in Figure 1 shows a flow starting from a separation step of a glass slurry of a purified terephthalic acid by the solid-liquid separator 1 and produces purified acid crystals. purified terephthalic obtained on one side by separation and simultaneously, a flow for the method of this example treating the separated mother liquor (primary mother liquor) on the other side.

At the beginning, the glass slurry at 130 to 160 ° C passes through an unillustrated step is subjected to solid-liquid separation by the solid-liquid separator 1 at a pressure of about 2 to 5.5 kg / cm2G and the separated crystals on one side are re-milled by a hot cleaning water heated to the same temperature (by heater El), cleaned for crystals in a slurry preparation tank 2 and then transferred to a slurry supply tank 3. Then, a highly pure terephthalic acid (terephthalic acid purified PTA) is produced by a method for separating the slurry in a solid-liquid separator 4 to obtain wet crystals of purified terephthalic acid (primary crystals) and then drying them in a dryer 5.

On the other hand, the separated mother liquor (primary mother liquid) is discharged from the solid-liquid separator 1, and is stored once substantially at a separation temperature (130 to 160 ° C) in a tank of primary mother liquor 6 for forming a starting mother liquor for the treatment method of this example. As described above, from about 0.1 to 0.3% by weight of terephthalic acid and from about 0.03 to 0.15% by weight of paratoluic acid usually dissolve in the primary mother liquor and the precipitates are usually present in an amount of about 0.02% by weight. weight or less as a solid ingredient (terephthalic acid ingredient) that leaks from the solid-liquid separation step.

By treatment of the mother liquor, an aqueous slurry of terephthalic acid is previously prepared in a slurry preparation tank 8. The terephthalic acid prepares at a concentration ratio of 10 to 30% by weight so that the slurry can be transferred uniformly. While appropriate, preferably the particle diameter, etc. is used. of the prepared terephthalic acid are not restricted, preferably a highly purified terephthalic acid (PTA) is used.

Then, the primary mother liquor at a pressure (of about 2 to 5.5 kg / crr G) in the primary mother liquor tank 6 is supplied to an expansion evaporation tank 7 at an atmospheric pressure (ATM) in which the liquid Primary mother expands and the solvent water evaporates and cools to approximately 100 ° C. At the same time, a prepared glass slurry is supplied from the slurry preparation tank 8 and the terephthalic acid crystals are incorporated together during evaporation by expansion of the primary mother liquor. In this case, the amount of terephthalic acid is supplied in said amount ranging from an amount corresponding at least to that of terephthalic acid in the primary mother liquor (from 0.1 to 0.3% by weight) to a quantity several times as large. as the corresponding amount, so that the crystals of terephthalic acid are supplied to approximately 1% by weight roasted in the primary mother liquor.

However, in a case where the terephthalic acid as the solid ingredient that leaks through Solid-liquid separation is present by the quantity corresponding to the dissolved quantity or more, evaporation by expansion can be carried out without supplying the prepared terephthalic acid slurry. In addition, when the terephthalic acid crystals can be uniformly supplied as it is in powder form to the evaporation tank by expansion 7, it is no longer necessary to be supplied, particularly, in the state of the slurry.

The solvent vapor evaporated in the expansion evaporation tank 7 is condensed in an E-3 condenser and stored as a condensed water recovered in a condensed water storage tank 10. The recovered condensed water is used as an aqueous solvent for a crude terephthalic acid, as a portion of cleaning water by the solid-liquid separation of the purified terephthalic acid and as water for the purification of the crude terephthalic acid.

Then, the suspension of the mother liquor in the expansion evaporation tank 7 (at atmospheric pressure, 100 ° C) is supplied by an acid pump to the evaporator tank by expansion 9 under a controlled reduced pressure (-700 to -400 mmHg ) and is subjected to evaporation by expansion and cooling (from about 40 to 80 ° C). Simultaneously, the suspension of mother liquor at a reduced pressure is heated by an E-5 heater and the solvent water is evaporates and concentrates. The mother liquor suspension can also be heated by a heater disposed in the transfer line of the expansion evaporation tank 7. It is preferred to use a medium at a temperature of about 110 ° C or less as the heating medium and heat the medium using an E-5 heater that increases the temperature difference with respect to the suspension of the mother liquor (from 40 to 80 ° C) in the expansion evaporation tank 7.

The vapor evaporated in the expansion evaporation tank 9 is condensed by an E-4 condenser and trapped in a condensed water tank 11. In this case, a portion of the evaporated steam can be heated to reflux to the evaporation tank 9 by operating a partial condenser E-6 (by passing the cooling water), which is preferred to decrease the content of impurity (p-toluic acid) in the condensed water formed. For this purpose, it is preferably concentrated by adopting a multiple effect type evaporation method.

The condensed water trapped in the condensed water tank 11 is transferred to a condensed water storage tank 10 and used in a recycled manner as a recovered water bound with the condensed water from the expansion evaporation tank 7 for the purification of the crude terephthalic acid. . In the recycled water for purification, the content of paratoluic acid preferably it is about 10 ppm or less and more preferably about 5 ppm or less that will be used as the cleaning water for solid-liquid separation of the purified crystals of terephthalic acid. In addition, for the dissolution water to the crude terephthalic acid, the content of paratoluic acid is preferably about 20 ppm or less and more preferably, about 10 ppm or less.

In the recovery of the condensed water, that is, concentration of the primary mother liquor, the condensate of paratoluic acid in the recovered water tends to increase as the degree of concentration increases. In this example, while the content of paratoluic acid in the condensed water does not increase much even when the mother liquor is concentrated by about 10% and concentration is possible. Consequently, about 90% by weight of the solvent water in the primary mother liquor can be recovered. The paratoluic acid content decreases by refluxing the condensed water by partial condensation to provide reliable recovery of the condensed water by approximately 90% by weight.

The expansion evaporation tank 7 can be stored (bypassed), and the expansion can be carried out under reduced pressure (-700 to -400 mmHg) only in one passing through the evaporation tank by expansion 9 and, at the same time, the evaporation by heating can be carried out at a temperature of 40 to 80 ° C. In fact, the glass slurry of the terephthalic acid is supplied from the slurry preparation tank 8. Furthermore, in this example, the vapor evaporated by expansion and heating evaporation is preferably introduced such that it is introduced below the liquid surface in the Evaporation tanks for expansion 7 and 9.

Then, the mother liquor suspension decreased largely by concentration in the expansion evaporator tank 9, subjected to solid-liquid separation in a filter 12 and separated into secondary crystals and a secondary mother liquor. Since the crystallized suspensions (crystals) in the expansion evaporation tanks 7 and 9 respectively have a high paratoluic acid content and are formed as fine particles, the separated secondary crystals form less filterable sticky cakes. Accordingly, a clarification filter of the pressurization type is preferably used for filtration and filters such as a pressure filter, a FUNDABAC filter (manufactured by IHI Corporation) and a CRICKET filter (manufactured by Tsukishima Kikai Co., Ltd.) are used. preferably use.

The separated secondary mother liquor is discharged to a secondary mother liquor tank 13 and subjected to a waste water treatment and the amount thereof is largely reduced by evaporation and concentration and the dissolved impurity also decreases by cooling (40% by weight). at 80 ° C) at a reduced pressure. The amount of environmental loading is greatly decreased, for example, so that the amount of terephthalic acid solution is about 0.03% by weight or less and the amount of paratoluic acid solution is about 0.04% by weight or less and the load due to the treatment is mitigated largely in view of the quantity and quality when the treatment is discharged.

To illustrate the method of this example specifically, the result of a simulation test is shown below. The method in this example is not restricted to the following simulated method. An experimental apparatus used to simulate the method for treating the mother liquor after the purification of terephthalic acid is shown in the schematic view of Figure 2.

As an expansion cooling tank, a 20 L autoclave having an agitator A (expansion and concentration tank) is set in a thermostatic water tank (approximately 100 ° C) 31 and an upper pipe 24 is connected through of refrigerants condensation Cl, C2, a valve V3, a condensate receiving tank D and a water drop trap E to a vacuum pump F by means of pipes 25, 26 28. The internal pressure of autoclave A (pressure gauge Pl in condensed receiving tank D) is controlled by pressure control of a control valve V4 connected to trap E (atmospheric pressure and reduced pressure).

A primary mother liquor is supplied from a primary mother liquor tank of a highly pure terephthalic acid production apparatus (not illustrated) through a flow meter M and a pipe 21 under the control of a flow rate through a valve I saw the autoclave A and expanded in it. Then, an aqueous slurry of about 20% by weight of terephthalic acid crystals prepared in a slurry preparation tank G having a stirrer is injected intermittently by a predetermined amount through a pipe 29 by a measuring injector H. The injector of measurement h has an intermittent injection system, under pressure, a predetermined volume of slurry (approximately 6 ml) by means of a pressurized gas by the operation of a valve connected to a measuring cylinder.

A cooled liquid suspension that remains in the autoclave A cooled by expansion evaporation is passed through a valve V2 (fully open) and extracted through a pipe 22 to a liquid suspension storage tank B having an agitator controlling the surface diluted in the autoclave A by the level of the pipe 22. The suspension of mother liquids is optionally extracted by a pipe 23 and a V6 valve connected to the bottom of it. When the expansion is carried out at an expansion pressure of an atmospheric pressure (ATM), a ventilation in the storage tank B and a pipe 22 at least is at an atmospheric pressure. When the expansion pressure is at least at a reduced pressure, the ventilation thereof is connected via a pipe 30 (dotted line) to the trap E so that the pressure in the suspended liquid storage tank B and the pipe 22 is at an identical pressure with the. expansion pressure.

On the other hand, in a case where the condensed water of the evaporated steam is not heated to reflux for concentration through evaporation by expansion and heating, the vapor evaporated is passed through the pipe 24, the condensation cooling C2 (water passage). ) and pipe 25 (valve V3 fully open) and received and measured in condensed receiving tank D as the condensed water evaporates. In addition, in a case of reflow heating of the dammed water, the amount of water passing in the condensing refrigerant Cl is It controls and is used as a partial condenser and the condensed water is received and measured in the condensate receiving tank D. To this end, a time of reception of condensed water to the condensed receiving tank D under constant heating is measured and the ratio at reflux is calculated by conversion.

A sample tube S is connected to the pipe 25, the condensed water (approximately 100 ml) during evaporation by expansion or concentration was sampled by a valve operation for supply to the sample tube S closing the valve V3 and served for the Paratoluic acid content analysis. The concentrated mother liquor suspension in the autoclave A was filtered under suction at a reduced pressure of 390 mmHg using a Buchner HOf funnel kit having a tank to hold moisture (not shown) and the filtration rate was measured and the filter cake composition and served for comparison.

Example 1 A primary mother liquor at a high temperature, high pressure (approximately 145 ° C, approximately 3 kg / cm2G) of a primary mother liquor tank of a highly pure terephthalic acid production apparatus was controlled at a rate of approximately 500 ml / min (by flow meter M9 by a valve VI, introduced directly in the liquid in autoclave A and expanded to an atmospheric pressure (ATM). Simultaneously, about 6 ml of a 20 wt% slurry of terephthalic acid was injected by the measuring injector H at 1 minute intervals through a pipe 29 into the supply pipe 21 of the primary mother liquor.

As a result of the evaporation by expansion for about one hour (without heating to reflux), condensed water was obtained at a ratio of about 41 ml / min (8.2% by weight based on the primary mother liquor) of tank D receiving the condensate . The content of p-toluic acid (para-toluic acid) in the evaporated condensed water was 2.1 ppm. With respect to the dissolution of 0.17% by weight of terephthalic acid in the primary mother liquor at 145 ° C (terephthalic acid solution: 0.17 g / 100 g of water), the supply of an aqueous slurry of 20% by weight of acid terephthalic (6 ml / min) incorporates the crystals of terephthalic acid by 0.26% by weight. Therefore, the terephthalic acid crystals are present in an amount of about 1.5 times as large as the corresponding amount of terephthalic acid solution.

Comparative Example 1 The method of Example 1 was carried out while the injection of the aqueous terephthalic acid slurry from the measuring injector H (V7 closed) was stopped to obtain condensed water evaporated in the same manner as in Example 1. The content of acid p -toluic in the condensed water was 9.5 ppm.

EXAMPLE 2 The primary mother liquor was introduced and the terephthalic acid slurry was injected in the same manner as in Example 1 and the expansion and cooling evaporation was carried out in the same manner as in Example 1 at a reduced pressure of 150 mmHg. inside the autoclave While maintaining the temperature at approximately 60 ° C. In this case, condensed water evaporated at a rate of 102 ml / min was obtained from the condensate receiving tank D (20.4% by weight based on the primary mother liquor) and the content of p-toluic acid was 2.7 ppm.

COMPARATIVE EXAMPLE 2 The method of example 2 was carried out when the injection of an aqueous slurry of terephthalic acid (closed V7) was stopped. The content of p-toluic acid in the condensed water in this case was 19 ppm.

EXAMPLE 3 After finishing the evaporation by expansion in Example 2, VI and V2- were closed (injection of primary mother liquor was stopped and extracted from the mother liquor suspension) and evaporation and concentration were carried out while maintaining the pressure at 150 mmHg and the temperature at approximately 60 ° C in the autoclave A without refluxing the vapor evaporated from the suspension of the mother liquid in the autoclave (cooling water that does not pass to the condensing cooler Cl).

The condensed water evaporated in the condensate receiving tank D was received and was measured at approximately 100 ml of the condensed water was sampled in the sample tube S after the condensed water was distilled in an amount of 5.6 L after starting the concentration. The content of p-toluic acid in the condensed water sampled was 4.3 ppm. Since the volume of the mother liquor suspension remaining in the autoclave A after finishing the evaporation by expansion of Example 2 was approximately 15 1 in view of the level of liquids, this corresponds to the concentration approximately 63% by weight after finish the evaporation by expansion (about 37% by weight of condensed water was obtained).

EXAMPLE 4 After Example 3, the suspension of the mother liquor in the autoclave A was further concentrated through evaporation without heating to reflux and the condensed water was sampled (approximately 100 ml) to the sample tube S after distilling the condensed water evaporated by 11.2. 1 (distilled by 5.6 1 in Example 3) after starting the concentration (after finishing the evaporation by expansion in Example 2). The content of p-toluic acid in the condensed water sampled was 9.7 ppm. This corresponds to the concentration at approximately 25% by weight after finishing the evaporation by expansion (approximately 75% by weight of condensed water was obtained).

EXAMPLE 5 After Example 4, the suspension of the mother liquor in the autoclave A was further evaporated and concentrated without heating under reflux and the condensed water (about 100 ml) was sampled in the sample tube S after the condensed water was distilled evaporated by 13 ml (distilled by 1.8 1 in Example 4) after starting the concentration (after finishing the evaporation by expansion in Example 2). The content of the p-toluic acid in the condensed water sampled was 16 ppm. This corresponds to the concentration at approximately 13% by weight after finishing the expansion (about 87% by weight of condensed water was obtained). This corresponds to the concentration of approximately 11% by weight when converted based on the amount of introduction of the primary mother liquor.

On the other hand, 200 ml of the mother liquor (liquid suspension) remaining in the autoclave A was sampled and a filtration test was carried out by a filtration equipment using the filter paper (5C). The time required for filtering in this case was 46 sec. In addition, the amount of terephthalic acid and the amount of p-toluic acid contained in the cake in the filter paper was 9.1% by weight and 2.4% by weight, respectively.

COMPARATIVE EXAMPLE 3 After finishing the expansion evaporation in Comparative Example 2, the suspension of the mother liquor in the autoclave A was filtered in the same manner as in Example 3 and the condensed water was sampled in the same manner as in Example 3, after of 5.6 1 of condensed water was distilled to the tank receiving the condensate D. The content of the p-toluic acid in the condensed water sampled was 31 ppm.

COMPARATIVE EXAMPLE 4 After Comparative Example 3, the suspension of the mother liquor in the autoclave A was further evaporated and concentrated without heating to reflux and the evaporated condensed water was sampled in the same manner as in Example 3 (approximately 100 ml) after distilling the condensed water evaporated by 11.2 1 (after finishing expansion evaporation in Comparative Example 2). The content of p-toluic acid in the condensed water sampled was 69 ppm.

COMPARATIVE EXAMPLE 5 After Comparative Example 34, the suspension of the mother liquor in the autoclave A was further evaporated and concentrated without heating to reflux and the evaporated condensed water was sampled in the same manner as in Example 3 (approximately 100 ml) after distilling the condensed water evaporated by 13 1 (after finishing evaporation by expansion in Comparative Example 2). The content of p-toluic acid in the condensed water sampled was 146 ppm. 200 ml of the mother liquor (suspension of liquids) remaining in the autoclave A were sampled and filtered in the same manner as in Example 5. The time required for filtration in this case was 432 sec. In addition, the content of terephthalic acid and the content of p-toluic acid contained in the cake on the filter paper was 5.5% by weight and 3.2% by weight, respectively.

EXAMPLE 6 The primary mother liquor was introduced and the terephthalic acid slurry was injected in the same manner as in Example 1 and evaporation was carried out by expansion and cooling in the same manner as in Example 1 while maintaining the pressure at 150 mmHg and the temperature at about 60 ° C inside the autoclave A (reproduction of Example 2). Condensed water evaporated at a rate of 101 ml / min (20.2% by weight based on the primary mother liquor) was obtained in the condensate receiving tank D and the content of p-toluic acid was 2.5 ppm in this case.

Then, VI and V2 were closed (introduction of primary mother liquor and extraction of mother liquor suspension stopped) and cooling water was passed to condensing cooler Cl at the reflux temperature of condensed water formed by partial condensation. and the mother liquor suspension was concentrated in the autoclave while maintaining the pressure at 150 mmHg and the temperature at about 60 ° C in the autoclave A. After receiving 5.6 1 of the condensed water in the tank receiving the condensate D, it was sampled in the same way as in the Example 3 and the content of p-toluic acid in the condensed water sampled was 2.6 ppm. In this case, the time required to receive 5.6 L of the condensed water at the time of receiving condensate D was 1.46 times as long as that of Example 3. Consequently, this means that the partial condensation corresponding to the reflux ratio of 0.46 was carried out in the condensing refrigerant Cl.

EXAMPLE 7 After Example 6, the cooling water was passed through the condensing refrigerant Cl to reflux condensed water formed by partial condensation, the suspension of the mother liquor in the autoclave A was further concentrated and after receiving additionally 5.6 liters of condensed water in the condensate receiving tank D, it was sampled in the same manner as in Example 4 and the content of p-toluic acid in the condensed water sampled was 13.9 ppm. In this case, the time required to receive 5.6 1 of condensed water to the condensed receiving tank D was 1.58 times while in Example 4. Consequently, this means that the partial condensation corresponding to the reflux ratio of 0.58 was carried out in the condensing refrigerant Cl.

EXAMPLE 8 After Example 7, the cooling water was passed through the condensation condenser Cl to reflux the condensed water formed by partial condensation, the suspension of the mother liquor in the water formed by partial condensation, the suspension of the mother liquor in the autoclave A it was further concentrated and, after further receiving 1.8 1 of the condensed water in the condensate receiving tank D, was sampled in the same manner as in Example 5, and the content of p-toluic acid in the condensed water sampled was of 4.5 ppm. In this case, the time required to receive 1.8 1 of the condensed water to the condensate receiving tank was 1.68 times more than in Example 5. Consequently, this means that the partial condensation corresponding to the reflux ratio of 0.68 was carried out in the condensing refrigerant Cl. A filtration test for 200, mi of the residual mother liquor (suspension of mother liquor) in the autoclave A was carried out in the same manner as. in Example 5 in which the time required for the filtration was 52 sec. In addition, the terephthalic acid content and the acid content. p-toluic in the filter cake was .9.0% by weight, and 2.5% by weight.

Figure .3 shows a relationship between the content (ppm) of p-toluic acid in a condensed water and the amount of recovery (% by weight) of the condensed water obtained in the simulation test. A comparison is made for a case where terephthalic acid (PTA) crystals (?: Solid line) are present and a case where they are not present (A: dotted line) by expansion evaporation without heating to reflux and evaporation by heating, a case where the crystals of terephthalic acid are present (*: dotted chain) where the crystals of terephthalic acid are present in one case to carry out heating under reflux (reflux ratio: 1 or less) by partial condensation of vapors generated. The content of paratoluic acid in the water condensed in respective cases by evaporation by expansion and evaporation by heating are shown by the amount of recovery of the condensed water.

Explanation of letters and numbers: 1,4 solid-liquid separator 2.8 slurry control tank 3 grout supply tank 5 dryer 6 primary mother liquids tank 7.9 expansion evaporation tank 10 condensed water storage tank 11 condensed water tank 12 filter 13 secondary mother liquor tank E-l, E-5 heater E-3, E-4 condenser E-6 partial capacitor To autoclave (expansion tank and evaporation) B Liquid suspension storage tank C refrigerant (condenser) D condensate receiving tank E trap F vacuum pump G grout control tank h measuring injector M flow meter S sample tube V valve Pl pressure gauge TI thermometer

Claims

1. - A method to treat a separate mother liquor of purified terephthalic acid including: a primary separation step for dissolving a crude terephthalic acid formed by liquid phase oxidation reaction of paraxylene in an aqueous solvent at high temperature and high pressure, subjecting it to reduction by hydrogenation under the presence of a noble metal catalyst, then forming a slurry of terephthalic acid crystals by cooling and crystallization and separating and recovering crystals of purified terephthalic acid (primary crystals) a mother liquor (primary mother liquor) from the crystal slurry; an evaporation step of separating the separated mother liquor (primary mother liquor) in a solvent vapor and a mother liquor suspension containing terephthalic acid crystals for at least one expansion step under the presence of terephthalic acid crystals at a pressure atmospheric or lower; a secondary separation step for separating and recovering crystals containing terephthalic acid (secondary crystals) from the mother liquor suspension; and a condensation step to condense the solvent vapor generated to form a condensed water.

2. The method for treating a mother liquor separated from the purified terephthalic acid of claim 1, wherein the crystals of terephthalic acid are incorporated in the evaporation step by an amount corresponding at least to terephthalic acid dissolved in the mother liquor.

3. The method for treating a separate mother liquor of purified terephthalic acid according to claim 1 or 2, wherein the crystals of terephthalic acid are incorporated in the evaporation step by the addition of terephthalic acid crystals.

4. - The method for treating a separate mother liquor of purified terephthalic acid according to one of claims 1 to 3, wherein the evaporated vapor is generated in the evaporation step under atmospheric pressure or lower by expansion and heating including at least one step without heating to reflux, or with slight reflux (reflux ratio <1).

5. - The method for treating a separate mother liquor of purified terephthalic acid according to any of claims 1 to 4, wherein the secondary crystals recovered in the secondary separation step were supplied to at least a portion of a supplied starting material for the liquid phase oxidation reaction.

6. - The method for treating a separate mother liquor of purified terephthalic acid according to any of claims 1 to 5, wherein the condensed water formed in the condensation step is reused as a portion of an aqueous solvent to dissolve the crude terephthalic acid or as a portion of cleaning water to clean the crystals of purified terephthalic acid (primary crystals) (primary separation step).

7. - The method for treating a separate mother liquor of purified terephthalic acid according to any of claims 1 to 6, wherein the solvent vapor is generated in the evaporation step at a temperature of 40 to 80 ° C at a reduced pressure by one step of expansion and heating.

8. - The method for treating a separate mother liquor of purified terephthalic acid according to any of claims 1 to 6, wherein the solvent vapor is generated by expansion at an atmospheric pressure and then the solvent vapor is generated at a reduced pressure at a temperature of 40 to 80 ° C by expansion and heating. '

9. - The method for treating a separate mother liquor of purified terephthalic acid according to any of claims 1 to 8, wherein the solvent vapor is generated in the evaporation step using a heating medium at about 110 ° C or lower.