DD144258A5 - PROCESS FOR THE PRODUCTION OF DRIED TEREPHTHALIC ACID - Google Patents

Description

-1-21350

Field of application of the invention:

The invention relates to a process for the preparation of dried terephthalic acid by removing acetic acid and / or water from a slurry containing terephthalic acid and acetic acid and / or water.

Characteristic of the known solutions:

In the industrial production of terephthalic acid, a general method is used in which p-xylene is oxidized, the raw material in the presence of a salt or salts of one or more heavy metals such as Co or Co + Mn as a catalyst, with molecular oxygen, in a liquid medium of a lower aliphatic acid, usually E; acetic acid, is oxidized.

There are several types of this process that use different reaction conditions. In some, after the oxidation step, a purification step is carried out by hydrogenation in water to produce terephthalic acid of the desired purity. In others, when high purity is not desired, the terephthalic acid is obtained without a purification step.

In the industrial production of terephthalic acid, it is essential that a step is carried out in which terephthalic acid is obtained as a dry, powdery material and wherein it is separated from the solvent acetic acid and / or water.

In the past, a process has been used in which the terephthalic acid, after draining in a centrifuge, is

separator was dried. The heating and drying were carried out with steam in a rotary drying apparatus in a stream of non-condensing gas, such as nitrogen, In this way it is possible to reduce the residual liquid in the terephthalic acid after drying to about 0.1% by weight. -

However, the rate of drying is low in this method because the rate depends on the vapor pressure of the acetic acid and / or the water at the heating temperature. Therefore, many difficulties arise in drying: a long residence time in the drying apparatus, which requires a large apparatus, a reduced heat transfer efficiency due to the adhesion of terephthalic acid to the walls of the pipe in which the heating medium (steam) circulates and the associated laborious maintenance. The drying system further requires that the gas be recycled for drying, such as nitrogen, thereby requiring a recycle blower and related equipment such as a terephthalic acid recovery vessel and a heat exchanger for heating the gas for the dryer are. Furthermore, in order to operate the drying system, it is necessary to maintain a constant rate of run in the centrifuge separator in order to allow smooth introduction of the slurry into the rotary dryer with a screw conveyor. As the residual liquid content varies, the terephthalic acid introduced into the screw feeder becomes a solid mass, preventing its transfer and disrupting operation in the dryer system. Furthermore, complete gas sealing in the rotary dryer is difficult to achieve, and leaks inevitably occur in the dryer. which gas flows out.

Object of the invention:.

The present invention has for its object to avoid the above-mentioned difficulties in drying terephthalic acid. · -

According to the invention, a new process for the drying of terephthalic acid is to be made available in which the

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Operating difficulties are avoided and in which a rotary dryer can be used.

Explanation of the essence of the invention:

The invention thus relates to a process for the preparation of dried terephthalic acid.

In the accompanying figures, the invention will be explained in more detail. Show it: . ·

Fig. 1 is a flow diagram of an apparatus for carrying out the process according to the invention for the preparation of dried terephthalic acid.

Fig. 2 shows the relationship between the temperatures and the critical slurry concentrations defined in the present invention.

Fig. 3 shows the gas-liquid equilibrium curves of an acetic acid water system showing the relationship between the pressures in the separation chamber and the temperatures of the heating tube which are selected when the process is carried out under high pressure.

The invention thus relates to a process for the preparation of dried terephthalic acid by removing the acetic acid and / or the water from a slurry containing terephthalic acid and acetic acid and / or water, characterized in that the slurry is fed into a tubular heater. tubular heating device containing at least one heating tube which opens at one end in the separation chamber, and wherein the slurry is converted in the heating tube into a mixture of solid and gas, the mixture passed into the separation chamber for separating the solid components of the gas components to obtain the terephthalic acid in the form of a dried powder, and wherein the terephthalic acid content in the slurry is less than the value "C" represented by the formula

- 4 - £. C = (2.5 θ ° ' ⁴ + 66) oC +. (3.2 θ ^0/35 + 74) (1 - «)

is defined, wherein C is expressed in wt.%, the temperature θ ⁰ C of the heater tube, <Xdas molar ratio of water in the slurry medium and {1 -oi) indicate the molar ratio of acetic acid in the Aufschlänunungsmedium.

It was surprising that the above method can be carried out because it was considered that clogging necessarily takes place when a slurry of high concentration is introduced into a heating tube to vaporize the medium. ,

Reference to the accompanying drawings, the invention is explained in detail.

As shown in Fig. 1, a slurry of the AuE slurry tank 1 is introduced with a slurry pump 2 into a heating tube 3 of a tubular heater or a Rohrheizvorrbhtung. The introduced slurry is heated in an oven with a heating means such as steam (when heated above 100 ^° C.) or with hot water (when heated below 100 ^° C.), or with another heating medium or with an electric heater. As the slurry advances in the heating tube, the acetic acid and / or water evaporates to form a highly fluidizing mixture consisting of the two phases solid and gas. The outlet end 6 of the heating tube 3 opens into the separation chamber 7, from which the mixture is removed and where the solid and the gas separate.

The gas phase enters the cooler 8 and is condensed by cooling water 9 «. The condensate is passed into the receiving tank 10. , ..

Alternatively, the gas phase may be introduced as it is into an acetic acid recovery means for separating the acid from the water. When the obtained in the separation chamber gas component of acetic acid, the water with a certain

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Concentration contains, and when the recovered acetic acid is to be recycled to the reactor of p-xylene oxidation, the gas component, since the water content in the Essigsäui to be reduced, is passed into the acetic acid recovery column Ds for recovery of acetic acid therein. In this case, the gas component is introduced into the column with an acetic acid evaporator, which is present in the terephthalic acid manufacturing plant, to remove the impurity in the reaction mother liquor.

Even if the gas component is acetic acid containing water to some extent, the gas can be cooled to condense for recycling and reuse, other than the oxidation reaction as in the washing of the precipitated terephthalic acid. When the obtained gas component is acetic acid of high purity, it is preferable to condense and reuse the acid. On the other hand, if the gas mainly contains water, it should be condensed and sent to a water treatment stage.

The solid phase, namely terephthalic acid, accumulates in the separation chamber 7 in the form of a dry powder or an easily comminuted mass, which is taken continuously or discontinuously via a valve 11 at the bottom of the chamber 7. The separation chamber 7 is heated by means of a jacket 12, so that the gas phase does not condense in the chamber.

The system of terephthalic acid, acetic acid and / or water may, as long as it contains up to 70% by weight of solid component, be treated as sludge in the usual manner during transport, as with a slurry pump. About 75% is the limit that allows the treatment as a slurry, and a system of 80? Solid loses its mobility and must therefore be termed a wet solid rather than a slurry. However, in accordance with the present invention, systems having a high content, such as 80 to 90% solids or even more, can be treated. In the present application, the system, as long as it can be dried by this method, is called a "slurry".

Transport of a high concentration slurry, which may be heavily pumped by a slurry pump, is accomplished by collision with pressurized gas, such as nitrogen or steam, in the heating tube.

In the vaporization using a combination heating tube and separation chamber, when the slurry to be treated contains a small content of terephthalic acid, the amount of slurry medium and, accordingly, the amount of gas formed by evaporation of the medium is relatively large, compared to the amount of solid terephthalic acid, and thus the effect is enough '.': disturbing .. .. any powdery terephthalic acid and carry away. It can easily be seen that in this way a stable operation without clogging of the heating tube can be performed.

However, evaporation of a larger amount of medium requires that a larger amount of heat be transported through the heating tube. It is thus apparent that the working capacity of the device remains small. This is disadvantageous because of the procedural economy. For this reason, the slurry treated by the method of the invention should contain 50% or more by weight of terephthalic acid.

When the slurry contains a higher percentage of terephthalic acid, in contrast to the above case, the impact force of the medium and the gas is small and therefore clogging may occur. Therefore, it is preferable for industrial practice to treat a slurry of the highest concentration because the risk of clogging is lowest and the device is best utilized and the energy consumption is most favorable.

In the following, the above-mentioned formula will be explained in more detail. The composition of the sedimentation medium (OC and 1 ~ £ <) is a given condition and depends on the objective of the treatment. When the temperature of the heating tube is set to a certain value, the slurry to be introduced should have a concentration lower than the above

^z ~ Γ- 2 1 35C

critical concentration, calculated on the basis of temperature. Alternatively, when it is necessary to treat a slurry having a certain medium composition and a certain slurry concentration, the temperature of the heating tube should be higher than the value that satisfies the above-mentioned equation.

In Fig. 2, the above relationship is shown. The three curves show the critical slurry concentrations at different system temperatures of Λ = 0. (the medium consists only of acetic acid), Λ = 0.767 (acetic acid / water = 1 / 3.3) and (X = 1.0 (water only).) When the treatment of the slurry occurs under the conditions in the areas below these curves the treatment can be continued without a clogging] of the heating tube takes place.

The pressure in the separation chamber can vary within a wide range. Operation at a pressure below atmospheric pressure or in a vacuum state is suitable if the volatile component is to be cooled and condensed.

The acetic acid separated from the terephthalic acid is recovered in many cases for reuse as a medium for the p-xylene oxidation state. When the operation is performed under reduced pressure in the separation chamber, the separated acetic acid or the acetic acid-containing water becomes an acetic acid evaporation device or in an acetic acid distillation column in the liquid state after cooling and condensing and heated again until it is in gaseous form. This cooling and reheating is disadvantageous because of the energy consumption, and it is therefore preferable to introduce the acetic acid into the gaseous state recovery plant. When the pressure in the separation chamber is lower than that in the acetic acid recovery column, it is preferable to introduce the gas component containing acetic acid by using an ejector. As the driving force for the ejector, acetic acid can be used entirely from the reboiler of the acetic acid recovery column.

In order to introduce the acetic acid in the vapor state, it is preferable to operate the separation chamber with a higher pressure, for example with normal pressure to zn a few kg / cm ² . As long as the gas component does not liquefy, there is no upper limit to the pressure. For practical reasons, however, it is preferable to use normal pressure of up to 6 kg / cm ² .absolutely or the like, because then the device is simple in construction and operation is easy. Too much pressure gives no particular advantage. The acetic acid sequestration unit into which the gas component is introduced is normally operated at normal pressure.

  When the pressure in the separation chamber is high, the temperature in the heating tube must be correspondingly high. The appropriate temperature for the heating tube also depends on the system of the slurry medium. «

Figure 3 'shows gas-liquid equilibrium curves of the systems in which acetic acid: water is expressed as 0: 100, 50:50 and 90:10 by weight, or δ = 1.000, c ≤ 0.767 and (x = 0.270) The areas under these curves are condensation areas in which the slurry medium is in liquid phase It is necessary to use the conditions in the areas above these curves A complete separation is done at a temperature of 20 ^{° C} C or higher than the equilibrium temperature is reached.

At too high a Tempäfafcor often deteriorates the quality of the product of terephthalic acid, for example, by Earbänderungen.Zur avoid a possible deterioration in quality, the maximum temperature of the fuel oil should not be above 240 ⁰ C.

If the residual liquid in the terephthalic acid product is to be extremely reduced, it is advisable to prepare the terephthalic acid in PuV or as an easily comminuted mass and, as shown in FIG. 1, to pass the valve 11 into the receiving vessel 13. The receptacle should be kept at a reduced pressure, which is lower than the pressure in the separation chamber, or it should be under vacuum, by connecting it to a Vac vacuum device. It is preferable that

It is further preferred to agitate a stream of dry inert gas, such as nitrogen, after it has been heated to some extent to pass through the receptacle. The Gasbeströmung is preferably carried out when it is working at reduced pressure. ·

According to the invention, the terephthalic acid thus dried can be obtained using a rotary dryer without d; Difficulties that occur in known methods can be observed. In the drying process of the present invention, a high-concentration slurry can be treated to obtain a high yield and low power consumption. In the method, when the conditions defined by the above equation are satisfied, clogging of the heating pipe does not occur, and stable operation is obtained.

The following embodiments illustrate the invention.

Embodiment 1

Using the apparatus shown in Fig. 1, the terephthalic acid slurry was dried. The separation chamber has a glass window through which the ejection of the terephthalic acid powder from the open end of the heating tube can be observed. Should a clogging occur, then you can see this immediately, because the ejection of the powder stops.

A slurry containing 80 wt.% Solids and its; Medium only consists of acetic acid, is in the heating tube eingelei tet. The loading of the slurry is smooth by suction from the separation chamber, which is maintained at 120 mm Hg. The Teir temperature of the heating tube is maintained at 80 ⁰ C with hot water.

The process is continued without clogging of the pipe. After 30 minutes of trial time, the terephthalic acid that has accumulated at the bottom of the separation chamber is taken out. In the product, the residual liquid content is reduced by

heat in an electric oven under nitrogen atmosphere for 2 hrs. This gives a value of 650 ppm.

Comparative Example 1

The same procedure is repeated as described in Example 1 with a higher terephthalic acid slurry content of 90%.

About 2 minutes after the start of the experiment, clogging occurs. The slurry is then pushed with compressed gas of 5 kg / cm ² , but the clogging is not eliminated.

If the slurry tank is placed under a pressure of 5 kg / cm ² absolutely from the beginning, clogging is also observed in a few minutes.

A test of the heating tube shows that the inside of the tube is completely packed with terephthalic acid in a wet state and in a powdered state.

Embodiments 2 to 10

The drying process of the terephthalic acid is repeated with various slurry contents, media compositions and temperatures of the heating tube that satisfy the conditions defined by the above-mentioned formula. The degree of vacuum in the separation chamber is also varied.

In all experiments, the operation could continue for a long time. Strongly dried terephthalic acid powder was obtained.

Vergleichbei games 2 to 7

The drying process was repeated with different slurry contents, media compositions and temperatures of the heating tube, which do not meet the conditions inherent in the process of the present invention.

21 3500 Results the above example of examples and Pressure i. d. Separating chamber (mmHg) Contin- uous, continuous liquid operation (ppm) - 11 a clogging of the heating tube the following Tables I and II using appropriate 120 3a 650 After a short operating time finds and you could not win a product. 300 7X0 instead of ι Operating conditions and the Temperatures and slurry contents Table I Examples 300 750 The Comparative examples are in Comparative examples are in FIG. 2 Up- temp. Sludge- dammingconcentration. Heizr. medium (wt%) ( ⁰ C) 300 350 Ie and listed. the reference number shown. ot = 0 80 80 300 420 The 92 200 300 ". 480 Verse. 95 250 300 470 1 Oi ^ = 1.0 75 120 300 460 y 2 85 200 600   ... 720! 3 "88 280 600 650 4 d = 0.767 85 120 300 560 5 88 200 6 Ot = 0 90 200 7 α = 1.0 85 200 8th (X "= 0 33 158 9 10 11

Table II Comparison Example

On- On Temp.d. Pressure i. Kontinuier No No sludges sludges heating d. separating Licher No No FFM mung sk onz , tube kaminer Business . no (constipation Verse. raedium / ft _Λ _ - ft / \ V vjT €. WHERE / ( ⁰ C) (MmHg) n. 5-6 min ») 1 C * = O 90 80 120 no (constipation after 2 minutes) 2 95 200 300 · no (constipation after 3 minutes) 3 di = 1.0 85 120 300 • 4 Il 88 200 300 5 95 280 300 6 O (= 0.767 90 120 300 7 94 200 300!

Embodiment 12

In the same apparatus used in Embodiment 1 to which a solid product receptacle is connected, a slurry containing 60% by weight of solid and a medium containing 90% by weight is introduced into the heater Acetic acid and 10 wt.% Of water is (c <= 0.27 0). The heating tube is heated with steam to 130 ⁰ C. The pressure in the separation chamber is 1 kg / cm ² or normal pressure.

The above conditions allow the process to be carried out without clogging the heating tube for a long time. After 10 minutes of experiment time, the valve is closed at the bottom of the Trermkammer and terephthalic acid removed from the receptacle.

The residual liquid is determined by the above method. It is 740 ppm.

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Exemplary embodiments 13 to 29 and comparative examples 8 to 13

The procedure of Example 12 is repeated using various slurry media, slurry concentrations, temperatures in the heating tube and pressures in the separation chamber.

The results of Examples 13 to 29 are shown in Table III and the results of Comparative Examples 8 to 13 in Table IV.

Table III Examples

verse

Auf Aufschläm-

Temp.d. Pressure i. Contoured acid product Heating d. Separating residueTI

concentration agreement. pipe chamber _p Licher river. Out- . medium (wt%) (° C) (kg / cnfabs) Re. see (ppm)

12 d = 0.270 60 130 1 13 Il 60 240 i. 34 Il 60 245 1 15 Il 60 185 5 16 Il 60 205 7.5 17 Il 60 215 10 18  I 60 245 12 19 Il 90 150 1 20 oj = 0.767 60 122 1.5 21 Il 60 • 245 1.5 22 Il ' 60 175 7 23 , Il 60 190 10th 24 Il   85 130 1 25 d = 1,000 ! 60 : 130 1.5- 26 Il 60 245 1.5 27 I! 60 185 7 28 It 60 200 10 29 Il 85 170 2

Well 740 η 510 gelbl. 510 Well 930 It 960 • n 1230 gelbl. 1250 Well 710 Well 710 gelbl. 480 Well 860 Il 1100 H 770 H 620 gelbl. 450 Well 810 It 780 η 580

Table IV. Comparative Examples

Aufschläinmungs verse. medium

Up temp.d. Pressure sludge heating d. separating

mungskonz. Ear chamber.-, (wt .-) O'C) (kg / CEh

Conti-acid product

 Licher Flues. Out-

Licher Flues. Off .abs) see operation (ppm)

= 0270

= 0767

= 1000

60. 60 60 60 60 60

120

195 115 185 125 195

7.5 1.5

10.5 1.5

10

not η

loading

Right

(large quantity)

contained moist masses

Äusführungsbeispiel

A ribbon blender is used as a receptacle for the terephthalic acid and the solid gas separation is carried out under the same conditions as in Example 12.

After 10 min. Experimental time, the valve 11 is closed and the pressure in the receptacle to 0.1 kg / cm ² abs. decreased. Then, nitrogen gas is introduced into the receptacle while stirring. The terephthalic acid is withdrawn after the pressure in the receptacle has been increased to atmospheric pressure. The residual liquid is determined. It is 350 ppm.

Embodiments 31 and

Embodiment 30 is repeated with different temperatures of the heating tube and different pressures in the separation chamber.

Ausf EADERSHIP example

Terephthalic acid is separated from the volatile materials under the same conditions as described in Example 12.

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After 10 minutes of trial, the valve at the bottom of the separation chamber is closed and nitrogen gas which has been slightly heated becomes: the receptacle at a rate of. 100 l / h for 5 minutes.

Embodiment 34

Example 31 is repeated except that the pressure i. the ribbon mixer 1.5 kg / cm ² abs. is. These conditions correspond to the modification of Example 4 in which a receptacle, but not in vacuum, is used under a pressure lower than that of the separation chamber.

The results of Examples 30 to 34 above are given in Table V.

The temperature-pressure conditions of Examples 13 to 34 and Comparative Examples 8 to 13 are graphically shown in FIG.

Table V Examples

Auf Aufpeakip. Pressure i. Pressure i. Saureproduk -: BchlMm- schlm- Heiz- d. Separating recording rest.

concentration agreement. tube chamber tube ₂ flow. Off-verse, medium (wt%) (C) (kg / cnTabs) (kg / cniabs) (ppm) see:

= 0270

60 130 1 0.1 350 Well 60 185 5 0.1 '320 ' tr 60 215 10 0.1 370 π 60 130 1 o.i 380 years η 60 185 5 1.5 780 years η

Claims (8)

Invention claims: A process for producing dried terephthalic acid by removing acetic acid and / or water from a slurry containing terephthalic acid and acetic acid and / or water, characterized by passing the slurry into a tube-type heater comprising at least one heating tube opening into a separation chamber at one end, the slurry in the heating tube being converted into a solid-gas mixture, passing the mixture into the separation chamber to separate the solid component and the gaseous component, and forming terephthalic acid in the form of a dried powder wherein the terephthalic acid content in the slurry is less than the value "C" represented by the equation: • C = (2.5 Θ ⁰ '' ⁴ + 66) ςλ + (3.2 θ ^{0 '35} + 74) (1- (X) is defined, wherein C is expressed as percent by weight, the temperature θ ⁰ C of the heater tube means "the molar ratio of water ^ _n is 3 _em In schlämmungsmedium and (1-tx) represents the molar ratio of the acetic acid in the slurry medium. 2. The method according to item 1, characterized in that the method is carried out with a pressure in the separation chamber, which is lower than atmospheric pressure. 3. The method according to item 2, characterized by passing the gas component separated in the separation chamber into an acetic acid recovery column, optionally using an acetic acid evaporation device, and using an ejector to recover the acetic acid. 4. The method according to item 1, characterized in that the method is carried out under such conditions that the pressure in the separation chamber is at or above atmospheric pressure, and that the temperature around the open end of the heating tube is at least 20 ° higher than the dew point of Slurry medium under pressure in the separation chamber. 5. The method according to item 4, characterized in that the pressure in the separation chamber in the range of atmospheric pressure to 6 kg / cm ² abs. lies. 6. The method according to any one of items 4 or 5, characterized by passing the gas component separated in the separation chamber in an acetic acid recovery column, optionally with the use of an acetic acid evaporation apparatus, for recovering the acetic acid. , 7. The method according to item 4, characterized in that the temperature in the heating tube 240 does not exceed ⁰ C. 8. The method according to any one of items 4 to 7, characterized in that the terephthalic acid powder is passed in a receptacle through a valve at the bottom of the separation chamber, and that the receptacle is operated at a reduced pressure which is lower than the pressure in the separation chamber , and / or that an inert gas is passed through the receptacle to further dry the terephthalic acid. Dazu_3_Seiten drawings