CN1284940A - Method and apparatus for recovering terephthalic acid - Google Patents

Abstract

The invention provides a method for recovering terephthalic acid, which can continuously produce terephthalic acid with higher purity. The process comprises dissolving crude terephthalic acid obtained by liquid-phase oxidation of paraxylene in water at a temperature at which the crude terephthalic acid is completely dissolved, purifying the aqueous solution by contacting the solution with a group VIII metal catalyst, dissolving the aqueous solution in the aqueous solution by rapid evaporation to recover terephthalic acid, and obtaining terephthalic acid crystals having a small impurity content, wherein the operating temperature range of each crystallization vessel is determined by the approximate formula y =266exP (-0.61 x), the value obtained by multiplying the value obtained by dividing the total number of stages by 1 by x … by the number of stages in each stage, and the temperature (DEG C) of y …. Thus, the temperature of each crystallization vessel can be set so that the balance between the amount of p-toluic acid and the amount of terephthalic acid crystals to be precipitated becomes appropriate, and as a result, a desired amount of high-purity terephthalic acid having a desired purity can be obtained.

Description

Recovery method and device for terephthalic acid

technical field

The present invention relates to a method and device for producing terephthalic acid, in particular to an aqueous solution of crude terephthalic acid obtained by refining p-xylene by using hydrogen in the presence of a Group VIII metal catalyst to obtain High-purity terephthalic acid A method and device for recovering terephthalic acid.

Background technique

Crude terephthalic acid obtained from the oxidation reaction of p-xylene contains a large amount of impurities such as 4-CBA and p-toluic acid, and has been used as a raw material for polyester after purification of these impurities.

The purification method of terephthalic acid is as follows, that is, the aqueous solution of crude terephthalic acid is treated with hydrogen reduction under high temperature and high pressure in the presence of a Group VIII metal catalyst such as Pd, Pt, and the treated aqueous solution is A method for recovering crystals of terephthalic acid (JP-A-41-16860).

As methods for recovering crystals of terephthalic acid, there are batch and continuous methods (British Patent No. 1152575).

The batch method is effective for producing high-purity terephthalic acid, but it is very disadvantageous operationally and economically when producing terephthalic acid in large quantities. For this reason, during the industrial production of terephthalic acid, a continuous method is generally adopted, and the method of using crystallization tanks is well known. Two or more of the crystallization tanks are connected in series, and the continuous rapid crystallization method is used to pass through the crystallization tanks separately. Lower the temperature and operate until the recovery temperature of terephthalic acid crystals reaches the same temperature as the treatment temperature of the next step, that is, the solid-liquid separation step (JP-A-50-49248).

The method of solid-liquid separation is well known. There is a method of centrifugally separating or filtering the raw material of terephthalic acid produced in the crystallization tank under the final temperature and pressure of the crystallization tank, and then undergoing solid-liquid separation in the first stage and reslurrying , The process of solid-liquid separation in the second stage is sent to the drying process to obtain terephthalic acid (JP-A-47-49049).

In addition, the method of solid-liquid separation is well known and also has several following methods, under pressurized state, utilizes the filtering device of band washing device, obtains the terephthalic acid of high purity (Japanese patent application publication No. 1-299618, Japanese publication No. 5- Publication No. 65246, Special Publication No. 6-506461).

In the hydrofinishing reaction, 4-CBA in crude terephthalic acid is mostly reduced to p-toluic acid by hydrogen in the presence of a Group VIII metal catalyst. For this reason, in the crystallization system, it is necessary to use a rapid cooling method to lower the temperature step by step to obtain terephthalic acid crystals with less impurities such as p-toluic acid. The problem at this time is that p-toluic acid, which forms a co-crystal in terephthalic acid, is contained in the terephthalic acid crystals although it retains sufficient water not yet saturated.

In order to prevent the eutectic of p-toluic acid contained in the crystallization of terephthalic acid, etc., and to more efficiently produce high-purity terephthalic acid with the required quality, it is preferable to update the operating conditions of each crystallization tank to achieve equilibrium. .

disclosure of invention

An object of the present invention is to provide a method for recovering terephthalic acid capable of continuously producing high-purity terephthalic acid.

Another object of the present invention is to provide a method for recovering terephthalic acid capable of producing higher-purity terephthalic acid.

In view of the above problems, the present invention has the following method, that is, the water raw material with a concentration of 22-30wt% crude terephthalic acid is heated up to 270-300 ° C, completely dissolved, and then hydrogenated, and the reacted terephthalic acid The diformic acid aqueous solution is supplied to the crystallization tanks of the 3rd to 5th sections sequentially, and the operating temperature of the crystallization tanks of each section is selected by the value represented by the following approximate formula, y=266exp(-0.61x)±5; [x: The value obtained by multiplying the value obtained by dividing the total number of stages by the number of stages of each stage, y: temperature (° C.)], setting the first crystallization tank to a temperature less than 240° C., setting the average residence time of each crystallization tank to Set at 10-60 minutes, supply the terephthalic acid aqueous solution or raw material to the stagnant liquid phase part to each tank, and separate the raw material obtained from the final crystallization tank into solid and liquid to obtain high-purity terephthalic acid .

Crude terephthalic acid obtained by liquid-phase oxidation of p-xylene is completely dissolved in an aqueous solution, and purified by a hydrogenation reaction in which the aqueous solution is contacted with hydrogen in the presence of a Group VIII metal catalyst. Impurities such as 4-CBA in crude terephthalic acid are responsible for the coloring of polyester products. In addition, these impurities are easily eutectic and contained in the crystals of terephthalic acid. Therefore, using the above reaction, 4- CBA is converted into p-toluic acid, and other impurities are purified by hydrocracking. And, the aqueous solution after the hydrogenation reaction is sent to the crystallization system. The crystallization system is composed of multi-stage crystallization tanks connected in series, and high-purity terephthalic acid crystals are obtained by rapid evaporation. In order to meet the quality requirements, the present invention provides the optimum operating conditions of each crystallization tank for the crystallization system.

In such a refining method, 22-30wt% of crude terephthalic acid water raw materials are completely dissolved to form an aqueous solution, and the temperature needs to be set at around 270-300°C, and in order to make the aqueous solution exist in a liquid state, keep the The vapor pressure of the aqueous solution is kept substantially higher than the vapor pressure of water, and hydrorefining is performed.

Thereafter, terephthalic acid is crystallized from the terephthalic acid aqueous solution in a state of high temperature and high pressure. At this time, impurities such as eutectic crystals represented by p-toluic acid reduced by hydrogenation are contained in the crystal particles of terephthalic acid. In this case, the purity is lowered, which is known from the above-mentioned patent publications and the like.

Here, using the water raw material with a concentration of 22-30 wt% used in hydrofinishing, various studies were carried out on the crystallization conditions in the crystallization operation, and the results also showed that Impurities such as p-toluic acid will be affected by the concentration of impurities in the liquid phase. As an operation, the temperature is the operating temperature of each crystallization tank that most affects the proportion of terephthalic acid crystallization. The higher the temperature of crystallization, the higher the temperature of p-toluic acid The less the inclusion, the greater the inclusion of p-toluic acid as the temperature decreased. Especially when it drops to 140-150°C, the amount of p-toluic acid increases significantly.

On the other hand, in terms of the crystallization recovery amount of terephthalic acid, the final crystallization tank, that is, the tank introduced into the process of solid-liquid separation and crystallization of terephthalic acid raw material is preferably at a low temperature.

Considering the antinomial operation at these temperatures, in order to obtain terephthalic acid with high purity and high recovery rate using the crystallization tank of 3-5 stages, it was found that temperature control according to the above approximate formula may obtain better results. And it found out that it is preferable to set the crystallization tank of the 1st stage to less than 240 degreeC in order to control temperature by the crystallization tank of 3-5 stages.

Moreover, as other operation conditions, it is affected by the residence time of each crystallization tank, and it is necessary to keep it for at least 10 minutes. It was found that when the residence time is lower than 10 minutes, crystals do not grow and the amount of impurities contained in the crystals tends to increase. And even if the residence time is prolonged too much, there is no great effect, and about 60 minutes or less is most suitable in view of the balance of the device.

Next, it is important to supply the aqueous solution and the raw meal to each crystallization tank by feeding it into the liquid phase part of the retentate in each tank, and rapidly cooling it. That is, the impurities are not contained in the terephthalic acid crystal particles due to the rapid cooling, and the crystals are dispersed and grown. In this case, terephthalic acid crystal particles need to be present as crystal nuclei in advance.

The preferred method is to set the operating temperature of the crystallization tank in the final stage to 140-150°C, carry out the solid-liquid separation in the first stage at this temperature and pressure, and then add water for re-slurrying to make the operating pressure Lower to normal temperature, carry out solid-liquid separation in the second stage, and recover terephthalic acid.

When the operating temperature of the crystallization tank in the final stage needs to be lowered for any reason, the amount of impurities such as p-toluic acid contained in the terephthalic acid crystals can be reduced by diluting with water. Especially when the temperature needs to be lowered under normal pressure, terephthalic acid of satisfactory quality can be recovered by feeding the same amount or more of water as the terephthalic acid raw meal in the crystallization tank of the final stage.

Moreover, under normal pressure, the solid-liquid separation device is set to one stage by cooperating with a solid-liquid separation device with a washing device. Since re-slurrying and the solid-liquid separation process in the second stage are not required, an atmospheric pressure device can be used in the solid-liquid separation process in the first stage, so the economical effect is good.

As long as these operating conditions are controlled, high-purity terephthalic acid can be recovered from the aqueous solution of terephthalic acid obtained by hydrofining.

A brief description of the drawings

Fig. 1 is a system flow diagram showing the first embodiment of the method for recovering terephthalic acid of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1

Using the apparatus shown in Fig. 1, high-purity terephthalic acid is produced. The amount of impurities (4-CBA, p-toluic acid, etc.) in the raw material crude terephthalic acid (CTA) used was about 3000 ppm-wt with respect to terephthalic acid. The CTA is mixed with ion-exchanged water in the CTA mixing tank 1 to obtain a terephthalic acid water raw meal with a concentration of 25 wt%. The mixed terephthalic acid water raw material was pressurized (about 90Kg/cm ² G) so as not to evaporate the water solvent, and heated to about 285°C. Make sure that the heated CTA raw meal stays temporarily in the CTA dissolving tank 3 and dissolves completely. Then, the dissolved CTA aqueous solution is passed into a hydrogenation reaction tank 4 filled with a commercially available Pd/C catalyst, and almost all of the CTA aqueous solution is reduced to p-toluic acid.

The terephthalic acid solution after the hydrogenation reaction is supplied to the crystallization tank 5 of the first section, the crystallization tank 6 of the second section, the crystallization tank 7 of the third section, the crystallization tank 8 of the fourth section, and the crystallization tank 9 of the fifth section In the liquid phase part of the crystallization system, the temperature is lowered by gradually reducing the pressure by pressure control. And the residence time of each crystallization tank is 20-40 minutes.

The terephthalic acid solution containing a large amount of terephthalic acid obtained in the crystallization tank 9 of the fifth stage is subjected to solid-liquid separation and drying in the module 10, and the final product of high-purity terephthalic acid is recovered.

The number of crystallization tanks was five, and the p-toluic acid content in high-purity terephthalic acid at the operating temperature of each crystallization tank was shown in Table 1.

Example 2 and 3

In the method of embodiment 1, embodiment 2 omits the crystallization tank 8 of the fourth section; embodiment 3 omits the crystallization tank 7 of the third section, and carries out the crystallization tank 8 of the fourth section. Table 1 shows the operating temperature of each crystallization tank and the p-toluic acid content in recovered terephthalic acid.

Table 1 Operating temperature of the first crystallization tank Operating temperature of the second crystallization tank The third crystallization tank operating temperature Operating temperature of the fourth crystallization tank Operating temperature of the 5th crystallization tank PT content in PTA crystals exam preparation Example 1 237°C 207°C 182°C 162°C 145°C 62ppm Example 2 230°C 195°C 167°C - 145°C 76ppm 4 stage crystallization Comparative example 1 205°C 190°C 175°C 160°C 145°C 104ppm Comparative example 2 250°C 220°C 187°C 160°C 145°C 96ppm Comparative example 3 235°C 205°C 183°C 162°C 145°C 129ppm Dwell time 5 minutes Comparative example 4 235°C 205°C 182°C 163°C 145°C 205ppm supplied to gas phase Example 3 220°C 167°C - - 145°C 87ppm 3 stage crystallization Comparative Example 5 229°C 195°C 165°C 145°C 99°C 330ppm Example 4 230°C 194°C 166°C 145°C 100°C 84ppm supply dilution water Comparative example 6 235°C 208°C 185°C 165°C 99°C 102ppm Example 5 238°C 207°C 184°C 163°C 146°C 65ppm

Comparative Examples 1, 2 and 5:

In the method of Example 1, as shown in Table 1, the operating temperature of each crystallization tank was changed. The p-toluic acid content in the obtained recovered terephthalic acid is shown in Table 1.

Comparative example 3

In the method of Example 1, the liquid level of each crystallization tank was lowered to adjust the residence time to about 5 minutes. The results are shown in Table 1.

Comparative example 4

In the method of Example 1, sending of the supply liquid to each crystallization tank was performed in the gas phase part. The results are shown in Table 1.

Example 4

In the method of Proportional Example 5, the same amount of ion-exchanged water as the terephthalic acid raw material kept in the crystallization tank of the fourth stage was supplied to the crystallization tank of the fifth stage, and the results are shown in Table 1.

Comparative example 6

In the method of Example 1, the CTA raw meal in the CTA mixing tank was mixed and formulated to be 28wt%. Table 1 shows the operating temperature of each crystallization tank and the p-toluic acid content in terephthalic acid.

Example 5

In the method of Example 1, the CTA raw meal in the CTA mixing tank was mixed and formulated to be 28wt%. Table 1 shows the operating temperature of each crystallization tank and the p-toluic acid content in terephthalic acid.

As mentioned above, according to the present invention, the temperature of each crystallization tank can be set so that the balance between the amount of p-toluic acid and the amount of precipitated terephthalic acid crystals is suitable, and as a result, a desired amount of p-toluic acid with a desired purity can be obtained. High purity terephthalic acid.

Claims (6)

1, a kind of recovery method of terephthalic acid, it is characterized in that, the raw material of crude terephthalic acid that with concentration are 22-30wt% are 270-300 ℃ scope, in the presence of the group VIII metal catalyzer after the hydrofinishing, the partial crystallization groove of the 3-5 section that use is connected in series is by the rapid evaporation method of cooling, this aqueous terephthalic acid solution is cooled off and partial crystallization recovery terephthalic acid interimly, in the method the 1st partial crystallization groove is set at and is lower than 240 ℃ temperature, the temperature that the service temperature of each partial crystallization groove is represented by following approximate expression afterwards, be cooled to 140-150 ℃ interimly, the average retention time of each partial crystallization groove is set at the 10-60 branch, in this delay liquid phase portion, carries out to the supply of each partial crystallization groove.

y=266exp(-0.61x)±5

X: remove 1 the value that obtains with the hop count of each section on duty with total hop count

Y: partial crystallization groove service temperature (℃) (140≤y＜240).

2, the recovery method of terephthalic acid as claimed in claim 1, it is characterized in that, in this recovery method, send into terminal section before the above dilution water of terephthalic acid raw material same amount that keeps in 1 section the partial crystallization groove, the working pressure of terminal section partial crystallization groove is set at below the normal pressure.

3, the recovery method of terephthalic acid as claimed in claim 2 is characterized in that, in this recovery method, the equipment for separating liquid from solid that has washing device that will operate below normal pressure in the subsequent handling of partial crystallization operation only is provided with 1 section.

4, a kind of retrieving arrangement of terephthalic acid, it is characterized in that, this retrieving arrangement is made of purification step, partial crystallization recycling step, the 1st temperature setting step, the 2nd temperature setting step, delay controlled step, wherein, purification step is the raw material of the crude terephthalic acid of 22-30wt% for hydrofinishing concentration in the presence of the group VIII metal catalyzer, in the temperature range of 270-300 ℃; The partial crystallization recycling step reclaims terephthalic acid for thereby the partial crystallization groove that utilizes the 3-5 section that is connected in series cools off this aqueous terephthalic acid solution partial crystallization by the rapid evaporation method of cooling interimly; The 1st temperature is set step and is lower than 240 ℃, the 2nd temperature for the temperature with the 1st partial crystallization groove is set at and sets step is set other each partial crystallization groove for the temperature of representing according to following approximate expression service temperature interimly; Be detained controlled step and be set at 10-60 minute for average retention time with each partial crystallization groove,

y=266exp(-0.61x)±5

X: remove 1 the value that obtains with the hop count of each section on duty with total hop count

Y: partial crystallization groove service temperature (℃) (140≤y＜240).

5, the retrieving arrangement of terephthalic acid as claimed in claim 4, it is characterized in that, in this retrieving arrangement, send into terminal section before the above dilution water of terephthalic acid raw material same amount that keeps in 1 section the partial crystallization groove, the working pressure of terminal section partial crystallization groove is set at below the normal pressure.

6, the recovery method of terephthalic acid is characterized in that, in this retrieving arrangement as claimed in claim 2, the equipment for separating liquid from solid of operating below the normal pressure in the subsequent step with final partial crystallization groove that has washing device only is provided with 1 section.