JPH11179115A - Method and apparatus for recovering crystal from slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent clogging and prevent a bad effect on other appliances by efficiently taking out wet cakes in the state that pressure is shut. SOLUTION: This method is for recovering a crystal from a crystal-containing slurry by a rotary filter 4 comprising a rotary filter medium 9. A crystal- containing slurry is supplied to a filtration region of the rotary filter medium 9, filtered in the pressurized state, and wet cakes formed on the filter medium 9 are washed in washing regions 9b, 9c, 9d. The washed wet cakes are peeled in a peeling process 9e and the peeled wet cakes are taken out by a rotary valve 20, so that a crystal can be recovered from the slurry.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for recovering crystals from a slurry containing crystals such as terephthalic acid.

[0002]

2. Description of the Related Art When terephthalic acid is produced by liquid-phase oxidation of paradialkylbenzene, the terephthalic acid formed is precipitated as crystals in a mother liquor, and a slurry containing terephthalic acid crystals is formed. When crystals are recovered from such a slurry, crude terephthalic acid is obtained. Also, by dissolving the crude terephthalic acid thus obtained, oxidizing treatment, and precipitating terephthalic acid through a purification process such as reduction treatment,
A slurry containing the crystals is obtained. When crystals are recovered from such a slurry, purified terephthalic acid is obtained.

[0003] Aromatic dicarboxylic acid slurries are also produced when other aromatic dicarboxylic acids are produced, such as when liquid-phase oxidation of dialkylnaphthalene to produce naphthalenedicarboxylic acid.

[0004] When recovering crystals from such a slurry, instead of filtering by a conventional filter or centrifugal separator, recrystallizing the crystals into a washing liquid and washing, and further repeating filtration by a centrifugal separator, a drum is used instead. There has been proposed a method of performing pressure suction filtration or pressure filtration under pressure using a rotary filter of a shape (for example, JP-A-1-2996).
18, JP-A-6-327915).

In this method, a horizontal cylindrical filter medium is rotated,
In this method, the slurry is supplied from the outside of the filter medium to perform filtration, and the wet cake captured on the outside of the filter medium is washed in a washing zone to remove impurities, and the crystals are collected as a wet cake. The washed wet cake is peeled off from the filter medium and then dried by a drier to produce a product, or sent to a purification step as it is.

In this method, in the case of suction filtration in which the filtrate is sucked, in order to prevent crystals from being precipitated due to a decrease in the temperature of the filtrate and clogging of the filter medium, filtration is performed by pressing the slurry side. Therefore, the outside of the filter medium is maintained in a pressurized state through the filtration zone, the washing zone, and the cake stripping zone of the filter media.

[0007] The crystals discharged from the rotary filter are usually extracted to a drier, but since the drier is generally operated at atmospheric pressure, the pressure between the rotary filter and the drier must be cut off. is necessary. Conventionally, a two-stage shutter was used to discharge the wet cake due to the pressure difference and gravity. However, when taking out a wet cake having adhesiveness such as terephthalic acid, it may adhere to the pipe or shutter and cause blockage. In addition, there is a problem that a large amount of gas is discharged together with the discharge of the cake, which adversely affects the dryer.

[0008] When the wet cake is transferred not to the dryer but to the refining process, it may affect other equipment.
It has almost the same problems. There is also a similar problem when other general pressure shut-off means such as a ball valve is used in place of the shutter.

[0009]

An object of the present invention is to efficiently take out a wet cake while shutting off the pressure,
An object of the present invention is to propose a method and an apparatus for recovering crystals from a slurry, which can prevent clogging and prevent adverse effects on other equipment.

[0010]

SUMMARY OF THE INVENTION The present invention is a method and an apparatus for recovering crystals from a slurry as described below. (1) A method for recovering crystals from a slurry containing crystals by a rotary filter having a rotary filter medium, comprising: supplying a slurry containing crystals to a filtration zone of the rotary filter medium and filtering the slurry under pressure; A method for recovering crystals from a slurry, comprising: a washing step of washing a wet cake formed in a washing zone, a peeling step of peeling the washed wet cake, and a cake removing step of removing the peeled wet cake by a rotary valve. . (2) The method according to the above (1), wherein the filtration and the washing are performed while the outside of the rotary filter medium is pressurized. (3) The washing step (1) or (2), wherein the washing is performed by supplying a washing liquid in a countercurrent manner from a plurality of nozzles.
The described method. (4) The above-mentioned (1) wherein the cake is taken out while the pressure is shut off by a rotary valve in the cake taking-out step.
Or the method according to any one of (3) to (3). (5) a rotary filter medium having a filtration zone, a washing zone and a stripping zone; a slurry supply means for supplying a slurry containing crystals to the filtration zone of the filter medium; a pressurizing means for pressing the slurry side of the filter medium; A rotary filter having a cleaning liquid supply means for supplying a cleaning liquid to the filter medium and a cake peeling means for peeling a wet cake in a peeling zone of the filter medium;
And a crystal recovery device for slurry from a slurry including a rotary valve for removing the peeled cake. (6) The apparatus according to the above (5), wherein the pressurizing means is a pressurizing means for pressurizing the entire outside of the filter medium. (7) The apparatus according to the above (5) or (6), wherein the cleaning liquid supply means has a plurality of nozzles for sequentially supplying the cleaning waste liquid in a countercurrent manner. (8) The rotary valve is provided with a rotary valve body having a seal portion that maintains a sealed state during rotation, and a cake housing portion formed between the seal portions (5) to (7).
An apparatus according to any one of the above.

The present invention is suitable for recovering crystals of terephthalic acid, but is also applicable to recovering crystals of hydroquinone, resorcin, naphthalenedicarboxylic acid and other crystals from slurry.

The rotary filter used in the present invention is provided with a rotatable filter medium having a filtration zone, a washing zone and a stripping zone rotatable along the direction of rotation, and a slurry containing crystals from a slurry supply means is supplied to the filtration zone of the filter medium. Supply,
The filtration is performed while the slurry side of the filter medium is pressurized by the pressurizing means, the cleaning liquid is supplied from the cleaning liquid supply means to the cleaning zone of the filter medium to perform cleaning, and the wet cake is peeled by the cake peeling means in the filter medium peeling zone. It is configured as follows.

Such a rotary filter may be a rotary pressure filter which pressurizes the slurry side of the rotary filter medium to perform filtration, or a rotary pressure / sucking filter which pressurizes the slurry side and suctions the filtrate side. The pressurizing means for the filter medium may be a means for pressurizing only the filtration zone, but generally a means for pressurizing the entire outside of the filter medium is used. As such a pressurizing means, it is preferable that the casing has an airtight structure and pressurizes by introducing a pressurized gas.

The cleaning liquid supply means is provided with a plurality of nozzles along the cleaning zone. A cleaning drainage receiver is provided at a position opposed to these nozzles, and the cleaning drainage received by the cleaning drainage receiver is provided. Is preferably supplied to the next nozzle to sequentially perform cleaning in a countercurrent manner, whereby the cleaning liquid can be effectively used to recover and use the crystal adhering component.

The rotary valve is capable of removing a peeled cake in a state where the pressure is shut off by rotating a rotary valve body having a seal portion that maintains a sealed state during rotation and a cake housing portion formed between the seal portions. Is preferred.

The recovery of crystals by the above-mentioned apparatus is performed as follows. That is, the slurry containing crystals is supplied to the filtration zone of the rotary filter medium, and the slurry is filtered under pressure, the wet cake formed on the filter medium is washed in the washing zone, and the washed wet cake is peeled in the stripping zone and peeled. The crystals are recovered from the slurry by removing the wet cake obtained by a rotary valve.

In the rotary vacuum filter in which the inside of the filter medium is decompressed, a part of the filtrate evaporates due to the decompression, and the temperature of the filtrate is lowered. As a result, dissolved impurities are precipitated and fine powder is easily generated. While the filter is likely to be clogged, pressurizing the outside of the filter medium can prevent a decrease in the temperature of the filtrate due to reduced pressure, so that the frequency of clogging is reduced.

By performing filtration and washing in a state in which the entire outside of the rotary filter medium is pressurized, the pressurized state can be easily maintained by a simple pressurizing means.
Even in this case, by taking out the peeling cake with the rotary valve, the peeling cake can be taken out stably without disturbing the pressurized state in a state where the pressure is shut off. This can eliminate adverse effects on devices.

By providing a plurality of nozzles as the cleaning liquid supply means and sequentially supplying the cleaning waste liquid in a countercurrent manner to perform cleaning, it is possible to recover a crystal-attached component at a high concentration with a small amount of the cleaning liquid and reuse it. In this case, a new washing liquid is supplied to the foremost washing zone in the rotating direction of the plurality of washing zones formed on the rotary filter to perform cake washing and solid-liquid separation, and the separated washing waste liquid is sequentially washed in the backward rotating direction. The cleaning liquid is supplied as a cleaning liquid for the zone, and the cleaning is repeated.The cleaning wastewater obtained from the cleaning zone at the end of the rotation direction of the filter medium is returned to the slurry generation step, whereby the components adhering to the crystals are recovered and used effectively. can do.

In the case of recovering terephthalic acid crystals, the concentration of acetic acid recovered in the washing effluent gradually increases by repeatedly using the washing effluent as the washing solution, and the acetic acid concentration in the final separation liquid is increased. Will be the largest. This separated liquid can be returned to the oxidation reactor and reused as a solvent for the oxidation reaction of para-xylene.

[0021]

As described above, according to the present invention, in a method and an apparatus for recovering crystals by applying pressure to the slurry side of a rotary filter and filtering to recover and wash and peel a wet cake, the peel cake is removed by a rotary valve. Since the wet cake is taken out, the wet cake is efficiently taken out in a state where the pressure is cut off, and the wet cake is prevented from being clogged and other devices are prevented from being adversely affected.

[0022]

Embodiments of the present invention will be described below. FIG. 1 is a system diagram showing an apparatus for recovering crystals from a slurry according to an embodiment of the present invention, and FIG. 2 is a sectional view of a rotary valve.

In FIG. 1, reference numeral 1 denotes an oxidation reactor, which is configured to introduce a raw material mixture from a line L1 and introduce a molecular oxygen-containing gas from a line L2 to perform an oxidation reaction. A line L3 for removing the slurry is connected to the flash drum 2 from the bottom of the oxidation reactor 1.
A line L <b> 4 having the pump 3 from the bottom of the flash drum 2 communicates with the slurry introduction path 5 of the rotary filter 4.

The rotary filter 4 is a rotary filter type filter that performs filtration by pressurizing the slurry side, and may be a rotary pressure filter that performs filtration only by pressurizing the slurry side. The filter may be a rotary pressure / sucking filter that performs filtration by suction.

The rotary filter 4 has a slurry introduction path 5 as a slurry supply means at the lower end, a housing 7 as a pressurizing means having a downward cake discharge path 6, and a housing 7 arranged in the housing 7 and not shown. 1 is rotated by a motor through a decompressor at a constant speed in the clockwise direction in FIG. 1, and a cylindrical rotary filter medium 9 serving as a filtration zone 9 a whose lower part is immersed in a slurry 8 collected at the bottom of the housing; A plurality of cleaning zones 9 formed on the liquid surface
A pair of spray nozzles 11a, 11b, 11c as cleaning liquid supply means arranged side by side in the direction opposite to the rotation direction of the rotary filter medium 9 on the outer side of b, 9c, 9d, and spray nozzles 11a, 11b excluding the spray nozzle 11c. The filter medium 9 is disposed inside the filter medium and is sprayed from the spray nozzles 11a and 11b.
Washing drainage receiving 12a for receiving the washing drainage is filtrate of the washing liquid which is sprayed on the cake above, 12b and are arranged to rotate the filter medium 9 inside the peeling zone 9e cake discharge port 6 side, the rotating filter medium 9 N ₂ An injection nozzle 13 is provided as a cake peeling means for peeling a cake adhered to the surface of the filter medium by blowing gas from the inside.

From the inside of the rotary filter medium 9 of the rotary filter 4, a line L5 for taking out filtrate and washing waste liquid communicates with the filtrate storage tank 14, and a line L6 having a pump 15 communicates with the oxidation reactor 1 from the bottom thereof. ing. A line L7 for supplying pure water as a new cleaning liquid is connected to the spray nozzle 11a. A line L8 is connected to the first cleaning drainage storage tank 16 from the cleaning drainage receiver 12a, and a line L9 having a pump 17 is connected to the spray nozzle 1 from the bottom thereof.
1b has been contacted. Line L1 from the washing drain receiver 12b
0 communicates with the second washing drainage storage tank 18, and a line L11 having a pump 19 from the bottom thereof communicates with the spray nozzle 11c. A pressure line L12 communicates with the upper part of the housing 7.

The cake discharge path 6 is connected to a dryer 22 via a cake discharge path 21 having a rotary valve 20. The dryer 22 dries the removed wet cake,
The dried crystal is taken out from the line L13 as a product. Reference numeral 23 denotes a condenser, which is connected by lines L16 and L17 so as to cool the vapor of the flash drum 2 and return the acetic acid condensed thereby to the flash drum 2. The condenser 23 is connected to a line L18 for introducing cooling water, a line L19 for discharging cooling water, and a line L20 for discharging non-condensable gas.

In FIG. 2, the rotary valve 20 has a rotor 27 rotatably provided in a cylindrical casing 26 having a cake inlet 24 and a cake outlet 25. The rotor 27 has a plurality of convex seal portions 28 that maintain a sealed state during rotation, and a cake housing portion 29 formed in a concave shape between the seal portions 28. The seal portion 28 rotates in close contact with the inner wall of the casing 26 to shut off the pressure between the cake inlet 24 and the cake outlet 25, and the cake storage portion 29 stores and rotates the release cake 30 to remove the release cake. The cake is taken out from the cake inlet 24 side to the cake outlet 25 side.

The recovery of crystals from the slurry in the above apparatus is performed as follows. In the oxidation reactor 1, a raw material mixture containing para-xylene as a raw material, acetic acid as a solvent, and a catalyst is introduced from a line L1, and a molecular oxygen-containing gas such as air is introduced from a line L2. Is oxidized to terephthalic acid.

A slurry containing terephthalic acid crystals formed in the oxidation reactor 1 is supplied from a line L3 to a flash drum 2
Where it is depressurized, flushed and cooled.
The steam generated here is cooled and condensed in the condenser 23, the condensed liquid returns to the flash drum 2 from the line L17, and the non-condensed gas is discharged from the line L20. The slurry in the flash drum 2 is supplied to the line L4 by the pump 3.
To the slurry inlet 5 of the rotary filter 4.

In the rotary filter 4, when the rotary filter medium 9 is rotated clockwise in a state where an inert gas such as N ₂ gas is introduced from the line L12 and the inside of the casing is pressurized, the lower part of the filter medium is immersed. The slurry 8 at the bottom of the housing 7 is filtered in the filtration zone 9a where
And rises together with the rotating filter medium 9. Rotating filter media 9
Is washed while passing through the washing zones 9b, 9c, 9d to remove impurities adhering to the cake.

At this time, pure water is supplied as a new washing liquid from the line L7 and sprayed from the spray nozzle 11a at the forefront in the rotation direction of the filter medium 9, and the cake in the washing zone 9d is washed and solid-liquid separated. The cleaning waste liquid separated in the cleaning zone 9d enters the first cleaning waste liquid storage tank 16 from the cleaning waste liquid receiver 12a through the line L8, is sent from the line L9 to the spray nozzle 11b by the pump 17, and is sprayed as the cleaning liquid.
Washing and solid-liquid separation of the cake in the washing zone 9c behind the rotating direction are performed. The washing waste liquid received by the washing waste liquid receiver 12b enters the second washing waste liquid storage tank 18 from the line L10, and is sprayed from the spray nozzle 11c by the pump 19 from the line L11.
To be sprayed as a washing liquid, and the cake in the washing zone 9b at the rear end in the rotation direction is washed.

By sequentially supplying the washing liquid in the direction opposite to the rotating direction of the rotary filter medium 9, acetic acid and other components adhering to the crystals are recovered, and the concentration thereof is gradually increased. The washing effluent in the washing zone 9b at the rear end in the rotation direction has the highest concentration and flows down to the inside of the filter medium 9, enters the filtrate storage tank 14 from the line L5 together with the filtrate in the filtration zone 9a, and is pumped from the line L6 by the pump 15 to the oxidation reactor Sent back to 1
Used for reactions.

As described above, the cake adhering to the filter medium is repeatedly washed three times in the washing zones 9b to 9d to perform solid-liquid separation, and finally washed with pure water. Is efficiently removed. The cake adhering in a layer on the surface of the rotating filter medium 9 of the washing liquid is
N injected from the injection nozzle 13 in the separation zone 9e
It is separated from the rotary filter medium 9 by an inert gas such as _two gases and discharged from the cake discharge path 6.

The peeled cake discharged from the cake discharge passage 6 is taken out by a rotary valve 20 into a cake take-out passage 21 and sent to a dryer 22. Rotary valve is rotor 2
When the 7 rotates clockwise, the seal portion 28 rotates in close contact with the inner wall of the casing 26, whereby the pressure on the cake inlet 24 side and the cake outlet 25 side is shut off.
Then, the peeled cake 30 entered from the cake inlet 24 rotates while being housed in the cake housing part 29 and rotates in the cake outlet 2.
It is released to the 5 side.

As described above, since the release cake 30 is taken out from the rotary valve 20 while the pressure is shut off, the release cake 30 can be taken out stably while the slurry side of the rotary filter medium 9 of the rotary filter 4 is pressed. In addition, since the pressurized gas does not leak, the dryer 22 is not adversely affected.

The release cake 30 in the dryer 22 is dried to obtain powdery terephthalic acid crystals, which are taken out of the line L13 as a product.

In this embodiment, the peeled cake 3 taken out
Although the example of drying 0 in the dryer 22 is shown, when the release cake 30 is sent to the purification step, it is sent to the purification step from the cake take-out path 21 and reslurried in a suspension device or the like for purification. Even in this case, the transfer can be performed without being affected by the pressurized gas.

In the above-mentioned method, washing and solid-liquid separation are repeated in a plurality of washing zones formed on the rotary filter medium 9, and the separated washing wastewater in each washing zone is supplied as a washing liquid in the washing zone behind the filter medium in the rotation direction. By doing so, crystals can be efficiently recovered from the slurry with a simple apparatus and operation, and acetic acid and other components attached to the crystals can be recovered at a high concentration and used effectively.

[0040]

Embodiments will be described below. Example 1 The rotary filter 4 was pressurized using the apparatus shown in FIGS.
1.5 kg / cm force ^TwoA, dryer 22 pressure is 1 kg /
cm^TwoRecover crystals from slurry as A
The release cake 30 was continuously extracted through the tube 20
The amount of gas discharged together with the release cake is about 30 Nm^Three
/ H. Also, clogging of the release cake extraction piping
Did not occur.

Comparative Example 1 Crystals were collected at the same pressure as in Example 1, and a ball valve was provided in two stages instead of a rotary valve. When the release cake was intermittently extracted, the amount of gas discharged together with the release cake Instantaneously became 1000 Nm ³ / H. For this reason, pressure was applied to the dryer 22, and crystal leakage occurred from the shaft sealing portion of the rotating part. Also, the clogging of the release cake extraction pipe occurred.

From the above results, it can be understood that by extracting the release cake with the rotary valve, the pressure is cut off, the release cake can be efficiently and stably taken out, and other adverse effects on the equipment can be eliminated.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an apparatus for recovering crystals from a slurry according to an embodiment.

FIG. 2 is a sectional view of a rotary valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxidation reactor 2 Flash drum 3,15,17,19 Pump 4 Rotary filter 5 Slurry introduction path 6 Cake discharge path 7 Housing 8 Slurry 9 Rotary filter medium 9a Filtration zone 9b, 9c, 9d Cleaning zone 9e Separation zone 11a, 11b, 11c Spray nozzles 12a, 12b Cleaning drainage receiving 13 Injection nozzle 14 Filtrate storage tank 16 First cleaning drainage storage tank 18 Second cleaning drainage storage tank 20 Rotary valve 21 Cake take-out path 22 Dryer 23 Condenser 24 Cake inlet 25 Cake outlet 26 Casing 27 Rotor 28 Seal part 29 Cake storage part 30 Peeling cake

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B01D 29/25 29/37 35/22

Claims (8)

[Claims] 1. A method for recovering crystals from a slurry containing crystals using a rotary filter having a rotary filter medium, comprising: supplying a slurry containing crystals to a filtration zone of the rotary filter medium and filtering the slurry under pressure; A crystal from a slurry including a washing step of washing a wet cake formed on a filter medium in a washing zone, a peeling step of peeling the washed wet cake, and a cake removing step of removing the peeled wet cake by a rotary valve. Collection method. 2. The method according to claim 1, wherein the filtration and the washing are performed while the outside of the rotary filter medium is pressurized. 3. The cleaning step wherein the cleaning step is performed by supplying a cleaning liquid from a plurality of nozzles in a countercurrent manner.
The described method. 4. The method according to claim 1, wherein in the cake removing step, the cake is taken out while the pressure is shut off by a rotary valve. 5. A rotary filter medium having a filtration zone, a washing zone and a stripping zone, a slurry supply means for supplying a slurry containing crystals to a filtration zone of the filter medium, a pressurizing means for pressurizing the slurry side of the filter medium, An apparatus for recovering crystals from a slurry, comprising: a rotary filter having a cleaning liquid supply means for supplying a cleaning liquid to a cleaning zone; and a cake peeling means for peeling a wet cake in a filter medium peeling zone; and a rotary valve for removing the peeled cake. 6. The apparatus according to claim 5, wherein the pressurizing means is a pressurizing means for pressurizing the entire outside of the filter medium. 7. The apparatus according to claim 5, wherein the cleaning liquid supply means has a plurality of nozzles for sequentially supplying the cleaning waste liquid in a countercurrent manner. 8. The rotary valve according to claim 5, wherein the rotary valve includes a rotary valve body having a seal portion for maintaining a sealed state during rotation, and a cake housing portion formed between the seal portions.
An apparatus according to any one of the above.