JP2003146939A - Method for producing aromatic dicarboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved method for producing an aromatic dicarboxylic acid by solid/liquid separation of a slurry containing crystal of the aromatic dicarboxylic acid obtained by the reaction using a screen-type centrifugal separator with a screw conveyor installed inside while preventing the centrifugal separator from cloggings so as to efficiently carry out the solid/ liquid separation. SOLUTION: This method comprises making a liquid phase oxidation of the corresponding aromatic compound having (partially oxidized) alkyl substituents in a reaction medium in the presence of a catalyst with a molecular oxygen-containing gas and then making a solid/liquid separation of the slurry containing the crystal of the obtained aromatic dicarboxylic acid to collect the crystal; wherein for making the solid/liquid separation by continuously feeding the slurry into the screen-type centrifugal separator with the screw conveyor installed inside, a meshed screen through which 1-10 wt.% equivalent of the crystal in the slurry fed is passable is used as a screen for the centrifugal separator.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an aromatic dicarboxylic acid, and more specifically, for solid-liquid separation of a slurry containing crystals of an aromatic dicarboxylic acid obtained by a reaction, a screw conveyor is disposed inside. And a method for producing an aromatic dicarboxylic acid using a screen type centrifuge.

[0002]

Aromatic dicarboxylic acids are obtained by liquid-phase oxidation of an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent with a molecular oxygen-containing gas in a reaction solvent in the presence of a catalyst. It is produced by a method of solid-liquid separating the obtained slurry containing crystals of aromatic dicarboxylic acid to recover the crystals.

As the above solid-liquid separation method, a method of using a screen type centrifugal separator having a screw conveyor arranged therein has been proposed (for example, WO98 /
No. 18750).

By the way, when solid-liquid separation is performed through a screen, it is important to prevent clogging and efficiently perform solid-liquid separation. In particular, in the case of a screen type centrifugal separator in which a screw conveyor is arranged, clogging is promoted by a solidified layer (cake layer) formed inside the screen in a compacted state by the screw.

Japanese Unexamined Patent Publication (Kokai) No. 8-294643 proposes a scraper for scraping off the solidified layer in the screen in order to maintain the function of the screen, but the installation of the scraper complicates the apparatus. There's a problem. Regarding the screen opening of the screen, for example, "F
illumination & Separation (Se
p. 2000, p. 245) ”, there is a description that the opening of the screen should be set to 2 to 3 times the particle size of the solid matter to be separated in order to prevent particles from being caught on the screen and causing clogging. However, there is a problem that the amount of leakage is too large with such a screen with a large opening.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to obtain an aroma obtained by a reaction using a screen type centrifuge in which a screw conveyor is arranged. To provide a method for producing an aromatic dicarboxylic acid improved so as to prevent clogging of a centrifuge during solid-liquid separation of a slurry containing crystals of an aromatic dicarboxylic acid and to perform solid-liquid separation efficiently. It is in. Another object of the present invention is to provide a method for producing an aromatic dicarboxylic acid improved so that the purity of crystals recovered by the above solid-liquid separation can be increased.

[0007]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have conducted extensive studies on a solidified layer (cake layer) formed in a compacted state inside a screen by a screw, and as a result, The following findings were obtained. That is,
The solidified layer (cake layer) formed in a compacted state inside the screen by the relatively large-sized amorphous particles by leaking the relatively small-sized amorphous particles in the slurry from the screen, Does not cause large clogging. In addition, when the above-mentioned irregular-shaped particles are crystals, impurities are concentrated in crystals having a relatively small particle size, and therefore, due to the above-mentioned leakage,
The purity of the recovered crystals is increased.

The present invention has been completed on the basis of the above findings, and the gist of the invention is to provide a reaction solvent in the presence of a catalyst.
Liquid phase oxidation of an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent with a molecular oxygen-containing gas, and then solid-liquid separation of the resulting slurry containing crystals of an aromatic dicarboxylic acid to form crystals. In the method for producing an aromatic dicarboxylic acid to be recovered, in the screen-type centrifuge in which the screw conveyor is disposed, the slurry is continuously supplied to perform solid-liquid separation, and as a screen of the screen-type centrifuge, A method for producing an aromatic dicarboxylic acid is characterized by using a screen having an opening in which 1 to 10% by weight of the crystals in the supplied slurry leaks.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

First, the liquid phase oxidation reaction will be described. In the present invention, in a reaction solvent, in the presence of a catalyst, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent is liquid-phase oxidized with a molecular oxygen-containing gas to form a slurry containing an aromatic dicarboxylic acid. obtain.

As the reaction raw material, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent is used. The aromatic compound may be monocyclic or polycyclic. Further, as the above alkyl substituent,
For example, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and the like,
Examples of the partially oxidized alkyl group include a aldehyde group, an acyl group, a carboxyl group, and a hydroxyalkyl group.

Specific examples of the aromatic compound having an alkyl substituent (alkyl-substituted aromatic hydrocarbon) include m-diisopropylbenzene, p-diisopropylbenzene,
Dialkylbenzenes such as m-cymene, p-cymene, m-xylene and p-xylene; dialkylnaphthalenes such as dimethylnaphthalene, diethylnaphthalene and diisopropylnaphthalene; and dialkylbiphenyls such as dimethylbiphenyl. .

Specific examples of the aromatic compound having a partially oxidized alkyl substituent include 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-toluic acid, p.
-Toluic acid, 3-formylbenzoic acid, 4-formylbenzoic acid, formylnaphthalenecarboxylic acid, etc. are mentioned.

As the catalyst, a combination of a heavy metal compound and a bromine compound is used. Examples of the heavy metal in the heavy metal compound include cobalt, manganese, nickel, chromium, zirconium, copper, lead, hafnium and cerium. Examples of heavy metal compounds include:
Examples thereof include acetate, nitrate, acetylacetonate salt, naphthenate, stearate and bromide. Examples of the bromine compound include inorganic bromine compounds such as molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide; methyl bromide, methylene bromide, bromoform, benzyl bromide, bromo. Examples thereof include organic bromine compounds such as methyltoluene, dibromoethane, tribromoethane, and tetrabromoethane.

The proportions of heavy metal compound and bromine compound used are:
The ratio of bromine atom to 1 mol of heavy metal atom is usually selected from the range of 0.05 to 10 mol, preferably 0.1 to 2 mol. The amount of the catalyst used is selected from the range of usually 10 to 10000 ppm, preferably 100 to 5000 ppm, as the heavy metal concentration in the reaction solvent.

As the reaction solvent, a lower aliphatic carboxylic acid is preferably used. Specific examples of the lower aliphatic carboxylic acid include acetic acid, propionic acid, butyric acid and the like.
The lower aliphatic carboxylic acid can be used alone or in the form of a mixture by mixing with water. The amount of the reaction solvent used is selected from the range of usually 0.5 to 70 parts by weight, preferably 2 to 50 parts by weight, as a ratio to 1 part by weight of the raw material in the liquid phase part.

Examples of the molecular oxygen-containing gas include oxygen and air. The molecular oxygen-containing gas is supplied in excess of the amount required to oxidize the aromatic compound with the raw material into the aromatic carboxylic acid. When air is used, the amount used is usually 2 to 20 Nm3, preferably 2.5 to, as a ratio to 1 kg of the aromatic compound serving as an oxidizing raw material.
It is selected from the range of 15 Nm3.

Usually, the reaction is carried out at room temperature, and the reaction time is
It is usually selected from the range of 4 to 180 minutes, preferably 6 to 120 minutes. Here, when the oxidation reaction is carried out continuously, the above reaction time is a residence time. Part of the aromatic dicarboxylic acid produced by the reaction is precipitated as crystals, and a part of the aromatic dicarboxylic acid is dissolved in a solvent to form a slurry. For example, in the case of producing terephthalic acid by liquid phase oxidation of para-silene, it is usually composed of acetic acid as a reaction solvent, terephthalic acid crystals, a catalyst dissolved in the reaction solvent, unreacted raw materials, by-products and unprecipitated terephthalic acid. It The average particle size of terephthalic acid crystals is usually 120 μm ± 40 μm.

Next, solid-liquid separation will be described. In the present invention, the slurry containing the crystals of the aromatic dicarboxylic acid obtained in the above reaction is subjected to solid-liquid separation to recover the crystals.
The crude crystal thus recovered from the reaction step is generally processed in the purification step. Then, high-purity aromatic dicarboxylic acid is recovered by solid-liquid separation of the slurry generated in the refining step. Also, the crystals can be washed during the solid-liquid separation. A lower fatty acid such as acetic acid is preferably used as the washing liquid.

The above solid-liquid separation is carried out by using a screen type centrifuge in which a screw conveyor is arranged. In the present invention, as long as it is a separator capable of solid-liquid separation by the action of centrifugal force while transferring the object to be treated by a screw conveyor on the screen, screen-type centrifuges of various structures regardless of designation Can be used. For example, the so-called "decanter type centrifuge" (Japanese Patent Laid-Open No. Hei 7 (1999) -107242)
-155643), "Screen ball type de-counter centrifuge" (Japanese Patent Laid-Open No. 2000-350946).
WO98 / 18750, etc.) is known.

FIG. 1 is a sectional explanatory view of a suitable screen type centrifuge which can be used in the present invention. The screen-type centrifuge shown in this figure is a screw conveyor including an outer rotary cylinder (1) and a cylindrical rotary shaft (21) and a screw (22) provided in the outer rotary cylinder so as to be rotatable relative to each other. (2) and a slurry supply pipe (3) arranged inside the rotary shaft of the screw conveyor and supplying slurry into the rotary shaft. The rotating cylinder (1) is provided with a slurry supply port (23) for supplying a slurry, and the outer rotating cylinder (1) has a large diameter portion (11) on the base end side and an inclined portion (12) with a gradually reduced diameter. And a small diameter portion (13) provided with a screen (13a) are sequentially arranged, and a large diameter portion (1
An overflow port (4) is provided at the base end of (1), and a small diameter part (1
The tip of 3) has a structure in which a solid matter discharge port (5) is provided.

Further, as a preferred embodiment, the inside of the rotary shaft (21) of the screw conveyor is partitioned into a slurry supply section (21a) on the base end side and a cleaning liquid supply section (21b) on the tip end side, and the slurry supply section. (21a) is configured so that slurry can be supplied by the slurry supply pipe (3), and the cleaning liquid supply unit (21b) is formed by the slurry supply pipe (3).
A cleaning liquid is configured to be able to be supplied by a cleaning liquid supply pipe (6) inserted into the inside of the screw conveyor, and the cleaning liquid is supplied to the small diameter portion (13) of the outer rotary cylinder (1) at the tip side of the screw conveyor (2). A supply port (24) is provided.

The flange (7) of the drive shaft (7) for the outer rotary cylinder
A plurality of openings (71c) are provided in the outer peripheral portion of 1), and thereby a solid matter discharge port (5) is formed. In addition, the flange (8) of the drive shaft (8) for the screw conveyor
A plurality of openings (81c) are provided in the outer peripheral part of 1), and the overflow port (4) is constituted by this.

Each of the above elements is housed in a casing (9). The interior of the casing (9) is divided by the partition wall into the overflow liquid storage chamber (91) and the filtrate storage chamber (9).
2), it is divided into a solid material storage chamber (93), and the filtrate storage chamber (92) is further divided into three chambers (92) along the longitudinal direction of the small diameter portion (13) for convenience of sampling the filtrate.
It is divided by a partition wall into a), (92b), and (92c). Then, the overflow liquid storage chamber (91) and the filtrate storage chamber (92) in the respective chambers (92a), (92b),
(92c) and the solid matter storage chamber (93) are respectively provided with extraction pipes.

A feature of the present invention is that, as a screen of a screen type centrifuge, one of the crystals in the slurry supplied is used.
The point is to use a screen with an opening that leaks 10 to 10% by weight.

That is, the opening of the screen used in the present invention is, for example, 0.01 A to when the speed of crystals in the slurry continuously supplied is A (Kg / hr).
It must be of a size that can continuously leak 0.1 A (Kg / hr) equivalent amount. Since it is considered that the leakage of leakage occurs preferentially from crystals with a small grain size,
In the present invention, crystals having a relatively small particle size in the slurry will be leaked from the screen.

The specific openings are as follows.
That is, when the average particle size of the crystals in the slurry is B (μm), the screen opening is usually (B-10).
It is above (micrometer) and below (B + 80) micrometer, preferably (B-
5) It is not less than μm and not more than (B + 60) μm. Therefore, for example, when the average grain size of the crystals is 100 μm, the opening of the screen is usually 90 to 150 μm, preferably 95 to 130 μm.

The size of the aperture generally means the minimum width of the hole, and is determined as follows depending on the shape of the hole of the screen. That is, the size of the opening is the width of the hole in the case of a slit type, the diameter in the case of a circle, the minor axis of the hole in the case of an ellipse, the short side length of the hole in the case of a rectangle, and the square side in the case of a square. The length of one side of a hole, the shortest distance between two parallel sides of a hole in the case of a diamond, and the shortest distance between long sides of a hole in the case of a parallelogram other than the above.

The particle size of crystals in the slurry can be measured by various known methods for measuring the particle size of powder, but in the present invention, a laser scattering type particle size distribution measuring device is used. The measured value is used.

As a result of the above, in the case of the present invention, the inner side of the screen, specifically, the outer rotary cylinder (1) and the screw (2)
The solidified layer (cake layer) of crystals formed in a compacted state in the interval between 2) is composed of crystals having a relatively large grain size. The reason why large clogging is not caused in the case of such a solidified layer (cake layer) is not necessarily clear, but is presumed as follows.

That is, generally, a solidified layer (cake layer)
In the case of containing irregularly-shaped particles having a relatively small particle diameter, the element becomes strong due to the strong bridging action. On the other hand, the solidified layer (cake layer) composed of irregularly-shaped particles having a relatively large particle size is likely to collapse because there is no strong bridging action. Therefore, it is presumed that the above-mentioned solidified layer (cake layer) in the case of the present invention is constantly disintegrated and renewed, and it is therefore considered that it does not cause a large clogging.

When the above-mentioned screen screed having a ratio of the leakage amount of less than 1% by weight is used, the effect of preventing clogging is not achieved, and the screed of the screen exceeding 10% by weight is used. When it is used, the clogging prevention effect is saturated, but the amount of leakage is too large and it is not efficient.

Further, since the impurities are concentrated in the crystals having a relatively small particle size, the purity of the recovered crystals is increased due to the leakage. That is, in the case of producing terephthalic acid by liquid-phase oxidation of para-silene, crystals having a reduced concentration of para-toluic acid, which is a typical impurity, are recovered.

In the present invention, solid-liquid separation is performed as follows. The slurry is supplied from the slurry supply pipe (3) via the slurry supply section (21a) to the large diameter section (1) of the outer rotary cylinder (1).
1). Then, here, solid-liquid separation is performed by the centrifugal separation action of the outer rotating cylinder (1) rotating at high speed.

The separated liquid is taken out from the overflow port (4) through the overflow liquid storage chamber (91). On the other hand, the crystals are transferred from the inclined portion (12) to the small diameter portion (13) by the screw (22). At this time, the mother liquor in the crystals was removed from the screen (13
In a) they are separated by centrifugal force. At the same time, the cleaning liquid is supplied from the cleaning liquid supply pipe (6). The cleaning liquid is sprayed from the cleaning liquid supply (24) through the cleaning liquid supply unit (21b) onto the crystal being transferred. The washed and dehydrated crystals are taken out from the solid matter discharge port (5) through the solid matter storage chamber (93).

The conditions for solid-liquid separation are not particularly limited, but it is preferable to apply a centrifugal force of 300 to 5000 G on the screen and set the residence time for solid-liquid separation on the screen to 2 to 20 seconds. When the cleaning liquid supply port is provided, the above residence time is conditioned on the residence time after passing through the cleaning liquid supply area.

If the centrifugal force is less than 300 G, the residence time of the solid-liquid separation on the screen becomes too long, and
If it exceeds 0 G, stable operation of the centrifuge becomes difficult. A preferable centrifugal force is 500 to 3000G. Such adjustment of the centrifugal force is performed by controlling the rotation speed of the drive motor of the outer rotary cylinder (1).

When the residence time is less than 2 seconds, sufficient solid-liquid separation is not performed, and when it exceeds 20 seconds, the solid-liquid separation effect is saturated and the operation efficiency of the centrifuge is reduced. The preferred residence time is 3 to 5 seconds. The residence time can be adjusted by a design method such as the size (length) of the screen, as well as the difference in rotation speed between the outer rotary cylinder (1) and the screw conveyor (2) (that is, the transfer speed of the object to be processed on the screen). )
Can be performed by controlling the operating conditions.

[0039]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Examples 1 and 2 and Comparative Example 1 The screen-type centrifuge shown in FIG. 1 equipped with the screens (slit type) having the openings shown in Table 1 below was added to the terephthalic acid obtained in the process for producing terephthalic acid. Acid crystal-containing slurry (solid content concentration: 30 WT%, average particle size: 100 μm,
Paratoluic acid (P-TA) concentration in solid matter: 180 p
pm) was continuously supplied at 40 ° C. under normal pressure, and solid-liquid separation was performed under the conditions shown in Table 1. The centrifugal force in Table 1 shows the value on the screen. The results are shown in Table 1.

The average particle size of the terephthalic acid crystal is measured by a particle size distribution measuring device (“LASER” manufactured by Seishin Enterprise Co., Ltd.).
MICRON SIZER LMS-24 ") was used as the reading value of the particle size at which the integrated value was 50%. Further, the opening of the screen was obtained as an average value by enlarging the slit portion with a microscope and measuring the widths of holes at 360 points.

Example 3 In Example 1, the average particle size of the terephthalic acid crystals was 11
Example 1 except that a terephthalic acid crystal-containing slurry having a solid content of 0% and a solid content concentration of 30% by weight was used, a screen (slit type) having an opening of 150 μm was used, and a condition of 160 ° C. and 0.65 MPa was adopted. Similarly, solid-liquid separation was performed. The results are shown in Table 1.

[0043]

[Table 1]

As is clear from the results shown in Table 1, in the case of Examples 1 to 3, the liquid content of the recovered solid is lower than that in Comparative Example 1. This is because clogging was prevented and liquid was satisfactorily drained.

Reference Examples 1 to 6 In order to confirm the effect of the residence time, the conditions shown in Table 2 (however, the centrifugal force on the screen was 750 G) were used in Example 1
Solid-liquid separation was performed in the same manner as in. The liquid content of the recovered cake is shown in Table 2.

[0046]

[Table 2]

The residence time in Table 2 is the cleaning liquid supply port (2
4) The time after passing through the supply area of the cleaning liquid injected from 4) (specifically, the time after 2 seconds has passed from immediately below the cleaning liquid supply port (24)), including each residence time and the collected cake. The liquid ratio was determined as follows for convenience. That is, the filtrate sample was collected from the position corresponding to each of the above retention times, the solid concentration in the filtrate sample at each retention time was measured, and the liquid content of the recovered cake was calculated by mass balance calculation.

As is clear from the results shown in Table 2, in the case of Reference Examples 1 to 4, since the residence time was appropriate, the centrifuge was operated efficiently and the cakes that were sufficiently deliquored Is recovered. On the other hand, in Reference Examples 5 and 6, the liquid content of the recovered cake is high because the residence time is short.

[0049]

According to the present invention described above, the clogging of the centrifuge is prevented during the solid-liquid separation of the slurry containing the crystals of the aromatic dicarboxylic acid obtained by the reaction. Further, according to the present invention, the purity of crystals can be increased.
Therefore, the industrial value of the present invention is great.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view of a suitable screen type centrifuge that can be used in the present invention.

[Explanation of symbols]

1: Outer rotary cylinder 11: Large diameter part 12: Inclined part 13: Small diameter part 13a: screen 2: Screw conveyor 21: rotating shaft 21a: Slurry supply unit 21b: Cleaning liquid supply unit 22: Screw 23: Slurry supply port 24: Cleaning liquid supply port 3: Slurry supply pipe 4: Overflow port 5: Solid matter discharge port 6: Cleaning liquid supply pipe 7: Drive shaft for outer rotary cylinder 71: Flange 71c: opening 8: Drive shaft for screw conveyor 81: Flange 81c: opening 9: Casing 91: Overflow liquid storage chamber 92: Filtrate storage room 93: Solid object storage chamber

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C07B 61/00 300 C07B 61/00 300 F term (reference) 4D057 AA07 AB01 AC02 AC06 AD01 AE03 AF05 BA18 BA36 BC06 BC16 CA01 CA02 CA07 CB02 4H006 AA02 AB46 AD17 BD82 4H039 CA65 CC30

Claims (6)

[Claims] 1. A liquid-phase oxidation of an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent with a molecular oxygen-containing gas in a reaction solvent in the presence of a catalyst, and then the obtained aromatic dicarboxylic acid. In a method for producing an aromatic dicarboxylic acid in which a slurry containing acid crystals is subjected to solid-liquid separation to recover crystals, the slurry is continuously supplied to a screen type centrifuge in which a screw conveyor is arranged to continuously solidify. In the liquid separation, as a screen of a screen type centrifuge, an opening screen in which 1 to 10% by weight of crystals in a slurry to be supplied leaks is used. Production method. 2. A screen type centrifuge, wherein an outer rotary cylinder (1), a cylindrical rotary shaft (21) and a screw (2) which are provided in the outer rotary cylinder so as to be rotatable relative to each other.
A screw conveyor (2) provided with 2) and a slurry supply pipe (3) arranged inside the rotary shaft of the screw conveyor and supplying slurry into the rotary shaft. A slurry supply port (23) for supplying slurry to the outer rotary cylinder (1) on the base end side of the
The outer rotary cylinder (1) is provided with a large diameter portion (1
1), a sloping portion (12) having a gradually reduced diameter, and a small diameter portion (13) provided with a screen (13a) are sequentially arranged, and the base end of the large diameter portion (11) overflows. An outlet (4) is provided, and a solid matter outlet (5) is provided at the tip of the small diameter portion (13).
The manufacturing method according to claim 1, wherein a screen-type centrifuge provided with is used. 3. The inside of the rotary shaft (21) of the screw conveyor is partitioned into a slurry supply part (21a) on the base end side and a cleaning liquid supply part (21b) on the tip end side, and the slurry supply part (21a) is The slurry supply pipe (3) is configured to be capable of supplying the slurry, and the cleaning liquid supply unit (21b).
Is configured such that the cleaning liquid can be supplied by the cleaning liquid supply pipe (6) inserted inside the slurry supply pipe (3), and the outer rotary cylinder (1) is provided at the tip side of the screw conveyor (2).
Cleaning liquid supply port (2) for supplying the cleaning liquid to the small diameter part (13) of
The manufacturing method according to claim 2, wherein 4) is provided. 4. The residence time of solid-liquid separation on the screen is 2
-20 seconds, provided that a cleaning liquid supply port is provided, the condition is that the residence time is after passing through the cleaning liquid supply area.
The manufacturing method according to claim 1, wherein a centrifugal force of 00 to 5000 G is applied. 5. The average particle size of crystals in the slurry is 80 to 1.
It is 40 micrometers, The manufacturing method in any one of Claims 1-4. 6. The average particle size of crystals in the slurry is B (μ
m), the screen opening is (B-10)
The manufacturing method according to claim 5, which is not less than μm and not more than (B + 80) μm.