JPH11100350A - Production of terephthalic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce terephthalic acid that has slurry properties suitable for direct polymerization of polyethylene terephthalate by extracting a part of terephthalic acid slurry, pulverizing the extracted slurry with a wet-type grinder, combining them again and separating the recombined slurry into the solid phase and the liquid phase to collect the crystals of terephthalic acid and drying the crystals. SOLUTION: A part of the slurry of terephthalic acid, preferably less than 50 wt.% of the whole slurry is extracted, pulverized with a wet type grinder as high-speed rotary grinder (the pulverizing energy per 1 m<3> of the slurry is preferably (3-30 kWh) and then, they are combined again. Then, the slurry is separated into the solid phase and the liquid phase to collect the terephthalic acid crystals and the collected crystals are dried. The particle size distribution and the particle shape becomes freely controllable whereby a mixture of terephthalic acid glycol having excellent slurry properties and reactivity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing terephthalic acid. More specifically, the present invention relates to a method for producing terephthalic acid which is suitable as a raw material for producing polyester such as polyethylene terephthalate in terms of powder characteristics and slurry characteristics.
That is, the gist of the present invention is that terephthalic acid slurry obtained by liquid-phase oxidation of para-xylene with molecular oxygen, or crude terephthalic acid obtained by liquid-phase oxidation of para-xylene, under reducing conditions using an aqueous solvent as a medium. Slurry characteristics suitable for the so-called direct polymerization method, in which terephthalic acid is directly reacted with glycols in the production of polyethylene terephthalate by treating a part of the slurry crystallized after purification treatment with a wet mill and remixing, The present invention also relates to a method for producing terephthalic acid having excellent fluidity of powder, which is a problem in transporting and storing terephthalic acid.

[0002]

BACKGROUND OF THE INVENTION The production of terephthalic acid, which is the subject of the present invention, is usually carried out by converting para-xylene in a lower aliphatic carboxylic acid, for example, an acetic acid solvent, in the presence of a catalyst containing a transition metal compound such as cobalt and manganese and a bromine compound. , 170-230 ° C
This is carried out by liquid-phase oxidation with molecular oxygen under the following temperature conditions. The produced crude terephthalic acid is 10% by weight.
Since various impurities are contained in a relatively large amount including 4-carboxybenzaldehyde of about 00 to 10000 ppm, purification treatment is performed after paraxylene is oxidized.

The first method for purification is a method in which para-xylene is oxidized and then subjected to additional oxidation at a temperature higher than the reaction temperature. As a second purification method, the crude terephthalic acid obtained by the liquid phase oxidation of para-xylene is separated from the acetic acid solvent to form a slurry in an aqueous medium, which is then heated and dissolved, at a high temperature and pressure, in the presence of a platinum group catalyst. Method for reducing and refining by adding hydrogen at (JP-B-41-16860)
It has been known.

[0004] A slurry or aqueous solution of terephthalic acid purified by such a method is cooled stepwise in a plurality of crystallization tanks connected in series to precipitate terephthalic acid dissolved in a solvent, and then centrifuged. Separated by separation or the like, optionally washed, dried and used as a raw material for polyester (hereinafter, terephthalic acid obtained by such a purification method is used in a slurry in a lower aliphatic carboxylic acid solvent). Is referred to as “Q-TPA slurry”, and the slurry in the aqueous solvent is referred to as “P-TPA slurry”.)

[0005]

In the production of polyesters, particularly polyethylene terephthalate, by a direct polymerization method in which terephthalic acid and glycols are directly reacted, terephthalic acid is mixed with ethylene glycol or the like to form a slurry into the reaction system. At that time, it is desired that terephthalic acid be low in power required for stirring during mixing, low in viscosity of the slurry during transfer, excellent in fluidity, and highly uniform in reaction. Further, good fluidity is also required in handling powder such as transport and storage of terephthalic acid.

In order to obtain such a good slurry property and uniformity of the reaction of terephthalic acid, it is sufficient to use a large amount of glycols with respect to terephthalic acid. The generation of substances increases, which causes a decrease in the melting point and the degree of polymerization of the polymer, and further causes a coloring. In order to avoid these drawbacks, the glycols should be as close as possible to the stoichiometric amount, but if the amount of glycols used is reduced, the power required for stirring in the slurry preparation tank and in the reactor increases, and the fluidity, There are problems such as poor reactivity and a long reaction time. Further, when the number of large terephthalic acid particles increases, the amount of unreacted terephthalic acid increases in the polycondensation reaction. Therefore, it is desirable that the number of particles exceeding 200 microns is small.

Accordingly, terephthalic acid, which forms a slurry having good fluidity and reactivity with a necessary minimum amount of glycols, is suitable as a raw material for direct polymerization. Such properties largely depend on the particle size distribution of the terephthalic acid particles, and it is an important factor to optimize them. However, in the above-mentioned method for producing terephthalic acid, it is considerably difficult to control the particle size distribution by adjusting the crystallization conditions during the precipitation of terephthalic acid. One of the reasons is that the conditions at the time of the precipitation of terephthalic acid crystals are set mainly for the purpose of controlling the impurity concentration in the terephthalic acid crystals, so that the allowable operation range for controlling the particle size distribution is narrow. It is mentioned.

As a method conventionally proposed for controlling the particle size distribution of terephthalic acid, Japanese Patent Application Laid-Open No. 48-297 discloses a method.
In No. 35, terephthalic acid particles having an average particle diameter of 100 μm or more and terephthalic acid particles having an average particle diameter of 50 μm or more are 70 to 8.
A method of mixing 5% to 30-15% is described.
Japanese Patent Publication No. 49-20303 discloses that a slurry in a solvent having low solubility is circulated and agitated by a pump to gradually increase the apparent density while reducing the particle size and improve the slurry property. Methods for obtaining terephthalic acid having the same are described.

The above-mentioned method disclosed in JP-A-48-29735 requires equipment for separately storing and mixing terephthalic acids produced under different conditions, or two or more crystallization steps. It is not an economically advantageous method. Further, according to the method described in JP-B-49-20303, since the entire amount of the slurry is treated, the particle size becomes smaller as a whole, and the fluidity of the powder deteriorates. There is a problem that it is relatively small and it takes a long time to obtain a desired apparent density.

Furthermore, Japanese Patent Application Laid-Open No. 56-95921 describes a method of subjecting terephthalic acid crystals to a grinding treatment in a vessel at an elevated temperature in the absence of a solvent. There are problems such as complicated equipment and large power for grinding required for handling, and severe wear of the container. Accordingly, an object of the present invention is to directly react terephthalic acid with glycols, having slurry properties and reactivity suitable for a so-called direct polymerization method,
Another object of the present invention is to provide a production method capable of easily controlling the particle size distribution of terephthalic acid that simultaneously satisfies the powder fluidity.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above situation, and as a result, the powder fluidity, slurry characteristics, and reactivity of terephthalic acid particles are determined by the particle size distribution of terephthalic acid and the particle size. This is achieved by designing the shape in an optimal state, and as a means therefor, the terephthalic acid (Q-
In the production method of TPA or P-TPA), it has been found that it is possible by extracting a part of each slurry, treating it with a wet pulverizer and then remixing.
The present invention has been completed.

The target of the particle size distribution for simultaneously satisfying the above-mentioned desired properties of terephthalic acid is the relationship between the method of handling terephthalic acid in slurry or powder mixed with glycols, the capacity of equipment, and the like. Although not uniformly discussed, conceptually, from the viewpoint of reactivity with glycols, the amount of coarse particles, for example, 210 μm or less by a sieving method is 10% by weight or less, preferably 5% by weight.
It is as follows. The amount of the fine particles is preferably large in terms of slurry characteristics, but is preferably small in terms of powder fluidity. In order to satisfy both characteristics, for example, a sieving method of 44 μm or less is preferably 5 to 35% by weight, preferably 5 to 35% by weight. Is 10-2
5% by weight.

It is difficult and difficult to make such properties of terephthalic acid which are totally suitable appear in the above-mentioned crystallization process. As a result of various studies on the means, the present inventors have extracted a part of the slurry from terephthalic acid in a slurry state in the terephthalic acid production process and the purification process as described above. After wet pulverization (this pulverization is called “fine pulverization”),
It has been found that terephthalic acid having a desired property can be easily obtained by remixing.

That is, the re-mixing of a part of the slurry after the wet pulverization, which is the gist of the present invention, is conceptually pulverization of a part of the terephthalic acid particles, pulverization and re-mixing. This means, for example, that particles having a size of 44 μm or less in a sieving method are increased to a desired amount to improve the slurry properties when mixed with glycols.

When the entire amount of the slurry is subjected to a pulverizing treatment as a means for securing a desired amount of fine powder in the particle size distribution,
This is not preferable because not only a pulverizer having a large processing flow rate and a large power is required, but also a large decrease in the amount of coarse powder directly causes deterioration of powder flowability. The fine powder generated by the pulverization treatment is typically one in which coarse terephthalic acid particles have been crushed or cracked or one obtained by grinding, and the object of the present invention is achieved by any of these.

The place where a part of the slurry is extracted and pulverized and the place where the slurry is remixed may be in any slurry zone such as the above-mentioned crystallization tank and washing tank. Tanks may also be used, or may be separately installed. In some cases, a wet pulverizer may be directly connected in the middle of a line branched from the slurry line without necessarily providing a tank, and the pulverization may be performed after the pulverization process.

When a dedicated tank is provided for crushing a part of the slurry, it is preferable to carry out the treatment by a continuous flow method. However, one or two or more tanks are provided and a batch method is used. It is also possible to pulverize the mixture, check the particle size distribution if necessary, and then join and mix the remaining slurry withdrawn. The amount of slurry withdrawn for pulverization is usually 50% by weight or less, preferably 5 to 45% by weight, based on the total amount of slurry. Is determined in consideration of the particle size distribution of terephthalic acid in the slurry before the pulverization treatment, the slurry distribution capacity of the pulverizer, the pulverizing power, and the like.

The wet mill used is generally called a volume mill, and examples of usable types include a high-speed rotary mill, a stirring mill, a colloid mill, and a ball mill. Although the selection is made in consideration of the properties and the like, the purpose of the present invention can be achieved in any form since a relatively small flow rate obtained by extracting a part of the slurry, which is the gist of the present invention, is strongly pulverized.

However, agitating mills using a bead, a pin, or the like as a medium, millstone type colloid mills, ball mills, and the like may cause abrasion of the medium during the pulverization process, which may contaminate terephthalic acid in products. When adopting, it is necessary to pay close attention to quality control. Normally, a high-speed rotary pulverizer is preferable in terms of product contamination, controllability of pulverizing power and flow rate, maintenance, management, and the like.

On the other hand, when the terephthalic acid obtained as a product has a coarse powder that affects the reactivity with glycols, for example, a particle size of 210 μm or more, which is larger than the target and needs to be reduced, a fine powder is required. Therefore, it is necessary to use another wet mill for the entire amount of the slurry before extracting a part and / or the entire amount of the slurry after extracting, or to treat the entire amount of the slurry after remixing with a relatively weak force. It is effective.

Such a pulverizing operation using a relatively weak force (hereinafter referred to as “coarse pulverization”, and the pulverization essential in the present invention as “fine pulverization”) may be performed by combining a plurality of operations. Although this coarse pulverization is not always an essential requirement in the present invention, it is effective as a means for promoting the effects of the present invention. Observation of the process of crushing particles when relatively weak crushing treatment is performed, almost no crushing phenomena such as breaking of particles are observed, and processing in which the surface of particles is slightly ground, so-called `` grinding '' class This is a grinding process which is completely different from the case where a part of the above-mentioned slurry is subjected to the strong grinding process, since all the particles which have been processed at the same time are removed and the shape is rounded. As a result, the amount of coarse particles is reduced, and at the same time, the shape of the particles that have been treated is rounded due to the removal of the quadrangle, which is also related to the improvement of slurry characteristics and powder fluidity. .

The temperature zone for performing the coarse pulverization is not particularly limited. However, in a high temperature area where the solubility of terephthalic acid in the solvent exceeds 1%, the rearrangement of the crystals and the crushing of the particles by the pulverizer are performed in parallel. Is further improved, and the surface also exhibits a dense appearance, and the treatment effect is further increased, which is preferable. However, in an excessively high temperature range, the withstand pressure of the pulverizer and the corrosion resistance may become a problem depending on the type of the solvent. Therefore, the limit temperature band is determined in relation to these. Usually, each of the Q-TPA slurry and the P-TPA slurry is 75 ° C to 200 ° C, preferably 70 ° C to 200 ° C.
The temperature range is 60 ° C.

The crusher used for the coarse crushing process is generally called a “surface crusher”. Among them, a relatively large flow rate is used. In view of this, a high-speed rotary pulverizer is preferred. In addition, ordinary liquid feed pumps have a large processing capacity but a small crushing power, so that the processing conditions meet the requirements for achieving the object of the present invention, but the crushing power is too small to produce an effect. It is not practical because it takes a long time for the processing.

It should be noted that other combinations of the pulverizer and the rotating body than those described above can be applied without any limitation as long as the desired effects can be obtained in the present invention. When a high-speed rotary pulverizer is used for the wet pulverization process as described above, its rotating body (or rotating tooth) is commonly known as a hammer, a cage, a pin, a disintegrator, a blade, or the like. This can be achieved, but the blade type is particularly preferred. Normally, blades are provided with blades and grooves for the treatment liquid to flow, but by changing the size and depth, it is possible to bring out performance suitable for the purpose of grinding such as surface grinding or volume grinding. it can.

The gap between the fixed teeth and the rotating teeth of the high-speed rotary wet pulverizer is usually 5 mm or less, but the gap is relatively small in the fine pulverization processing and large in the coarse pulverization processing. The number of rotations of the rotating tooth or the peripheral speed of the tip is
The terephthalic acid particles to be treated are selected depending on the pulverizing strength of the terephthalic acid particles to be treated, the desired particle size distribution after treatment, and the like.
It is set as appropriate from the range of up to 60 meters.

The treatment by the wet crusher can achieve the purpose in one stage, but a plurality of crushers may be installed in series. This is appropriately determined according to the space of the installation place, the processing capacity of the crusher, the throughput of the slurry, and the like. In the present invention, the slurry of terephthalic acid and the water solvent usually contains terephthalic acid in an amount of 10 to 60% by weight, preferably 20 to 20% by weight.
It is treated as a slurry containing 〜50% by weight. The pulverization energy (pulverization power) per 1 m ³ of the processing slurry in the case of performing the pulverization processing to exhibit the effect of the present invention is 3 to 30 in the case of the strong pulverization processing for the purpose of pulverization.
kwh, preferably 8-22 kwh. 0.2 to 8 kwh, preferably 0.5 to 5 k, for coarse grinding
wh.

The grinding energy can be changed by changing any one or two or more of the types and gaps of the fixed teeth and the rotating teeth, the supply flow rate to the grinding machine, the number of rotations of the rotating teeth, and the like. It is convenient to change the number of rotations. The crushed slurry is separated into terephthalic acid by a centrifuge or a vacuum filter, washed with a fresh solvent if necessary, and then dried to obtain a product. By monitoring the particle size distribution with a particle size distribution meter in the slurry zone and controlling the conditions of the pulverizer, a product having a constant property can be stably obtained. In the case of coarse pulverization, it is preferable to monitor the particle size distribution after the treatment.

Further, the particle size distribution may be measured in an arbitrary slurry zone after each of the fine pulverization and the coarse pulverization, and the conditions of each pulverizer may be individually controlled. As the particle size distribution meter, indirect methods such as a laser diffraction scattering method, a sedimentation light transmission method, an electric resistance method, a microscopic method, a sieving method, and a viscometer can be used. It is suitable. The condition of the mill to be controlled is generally achieved by changing the flow rate and the number of revolutions of the slurry. However, depending on the state of the particle crushing, the type of the rotating teeth and the gap (clearance) with the fixed teeth are changed. It is also possible.

According to the method of the present invention as described above,
The particle size distribution and particle shape of terephthalic acid can be freely controlled, and a mixture of terephthalic acid and glycols having properties excellent in slurry characteristics and reactivity can be obtained. It has been confirmed that this makes it possible to reduce the stirring power in the slurry preparation tank and the reactor, improve the transportability of the slurry to the piping, and have a favorable effect on the improvement of the reactivity due to the reduction of coarse particles.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the table of results, "slurry torque" refers to a stirring torque (gcm) when stirring at a ratio of 1.1 moles of ethylene glycol to 1 mole of terephthalic acid and stirring with a two-blade paddle type blade. "Body drainage" means 64mm
^The time (seconds) during which 300 grams of terephthalic acid was discharged from the cylindrical hopper having the opening ² is an index of powder fluidity.

The "particle size distribution" represents the frequency of each particle size measured by a wet classification method using 150 g of a dried terephthalic acid sample using a JIS standard sieve and expressed in terms of% by weight. The slurry torque is desirably as low as possible, and the powder dischargeability is desirably 150 seconds or less, preferably 120 seconds or less. Regarding the particle size distribution, for example, when the number of particles having a large particle size exceeding 200 microns increases, the reactivity deteriorates.

Example 1 A 40% by weight crude terephthalic acid acetic acid slurry obtained by subjecting para-xylene to liquid phase oxidation with molecular oxygen in the presence of a catalyst containing cobalt, manganese and a bromine compound in an acetic acid solvent was used. After the additional oxidation purification treatment at a higher temperature than the reaction temperature, the mixture was cooled stepwise to 120 ° C. in a crystallization tank provided with a three-stage stirrer in series. 1.0 part by volume of the slurry obtained in this manner was dispensed into a stirring tank, and a blade high-speed rotating wet pulverizer (rotating tooth diameter: 18) was used.
cm) using a batch method. Gap fixed teeth and rotary teeth of wet pulverizer is adjusted to 0.2 mm, 4470Rpm the rotational speed, and the circulation flow rate as 14 parts by volume / h, the slurry 1 m ³ per 14k in the process of 40 minutes
wh grinding energy was supplied.

The slurry before the fractionation is 20
The mixture was remixed so as to be equivalent to% by weight. After separating terephthalic acid from the mixed slurry with a vacuum filter, it was dried at 105 ° C. The properties of the terephthalic acid product thus obtained are shown in Table 1. Terephthalic acid having low slurry torque, excellent powder fluidity, and good properties with few coarse particles was obtained.

Example 2 Para-xylene was subjected to liquid phase oxidation and additional oxidation purification treatment and cooled to 102 ° C. in a crystallization tank.
1.0 part by volume of a slurry containing 0% by weight of terephthalic acid was filtered under reduced pressure, and the obtained wet cake of terephthalic acid was supplied to a stirring tank together with fresh acetic acid at 95 ° C. to reduce the terephthalic acid concentration to 40% by weight. The slurry was obtained. This was subjected to a circulation pulverization treatment for 6 minutes by a wet pulverizer, and pulverization energy of 2.1 kwh was supplied per 1 m ^{3 of} the slurry.

About 0.23 parts by volume of 23% by weight of the treated slurry was taken out to another pulverizing tank, and 9% by volume was further removed.
Min, i.e. milling energy per slurry 1 m ³ of about 1
The pulverization treatment was performed until it reached 4 kwh, and the mixture was mixed with the slurry before being extracted. The type of the crusher, the gap between the fixed teeth and the rotating teeth, the number of rotations of the crushing teeth, and the circulation flow rate were the same as in Example 1. After separating terephthalic acid from the mixed slurry with a vacuum filter, it was dried at 105 ° C. Table 2 shows the properties of the product terephthalic acid.

Example 3 A terephthalic acid crystal was separated from a crude terephthalic acid acetic acid slurry obtained by oxidizing para-xylene by a centrifugal separator, and then dried to prepare a 30% by weight water slurry. The slurry was heated to dissolve terephthalic acid, introduced into a column reactor filled with 0.5% by weight of palladium catalyst supported on activated carbon, and subjected to a reaction pressure of 9MP.
A hydrogen reduction purification treatment was performed at a reaction temperature of 290 ° C. This terephthalic acid aqueous solution was cooled stepwise to 152 ° C. in a series of five crystallization tanks having the same capacity to precipitate terephthalic acid crystals, and then centrifuged. .

1.7 parts by volume of this slurry were collected in a stirring tank, and circulated for 65 minutes using a blade high-speed rotary wet pulverizer (rotary tooth diameter: 18 cm). The gap between the fixed teeth and the rotating teeth of the wet mill is 1.2 mm, the number of revolutions is 4860 rpm, and the circulation flow rate is 10 m ³ / h,
The supplied grinding energy is 13 kW per 1 m ³ of slurry
h. 20% of the slurry before fractionation
The mixture was remixed so as to be equivalent to% by weight. After separating terephthalic acid from the mixed slurry with a vacuum filter, it was dried at 105 ° C. The properties of the terephthalic acid product thus obtained are shown in Table-3.

Comparative Example 1 Table 1 shows the properties of terephthalic acid obtained in the same manner as in Example 1 except that the circulation treatment was not carried out by a wet mill. [Example 4] Terephthalic acid obtained in the same manner as in Example 1 except that the fractionated slurry was treated with a wet pulverizer and then remixed so as to be equivalent to 50% by weight with respect to the slurry before fractionation. Table 1 shows the properties.

Comparative Example 2 Table 2 shows the properties of terephthalic acid obtained in the same manner as in Example 2 except that the fractionated slurry was not subjected to the second circulation treatment by a wet grinder. [Comparative Example 3] Table 3 shows the properties of terephthalic acid obtained in the same manner as in Example 3 except that the circulating treatment was not performed by a wet mill.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

The terephthalic acid slurry is subjected to solid-liquid separation to obtain terephthalic acid crystals, which are dried to produce terephthalic acid as a product terephthalic acid. And then remixing, terephthalic acid having excellent slurry properties suitable for a so-called direct polymerization method in which terephthalic acid is directly reacted with glycols in the production of polyethylene terephthalate can be obtained. In addition, terephthalic acid having excellent fluidity of powder, which is a problem in transporting and storing terephthalic acid, can be produced.

Claims (10)

[Claims] 1. A method for producing terephthalic acid by solid-liquid separation of a terephthalic acid slurry to obtain terephthalic acid crystals and drying the terephthalic acid to obtain a product terephthalic acid. A method for producing terephthalic acid, comprising re-mixing after finely pulverizing the terephthalic acid. 2. The product terephthalic acid has a particle size of 210 μm.
The method according to claim 1, wherein the number of particles of m or more is 10% or less of the whole. 3. The method according to claim 1, wherein the amount of the slurry withdrawn for the pulverization treatment is 5 to 45% by weight based on the whole. 4. A pulverizing energy per 1 m ^{3 of} the slurry when the extracted slurry is finely pulverized is 3 to 3 μm.
The method according to claim 1, wherein the power is 30 kwh. 5. The method according to claim 1, wherein before the slurry is extracted for the fine pulverizing treatment, the whole amount is coarsely pulverized by a wet pulverizer different from that for the fine pulverizing processing. the method of. 6. The method according to claim 1, wherein the entire remaining amount after the slurry is extracted for the fine pulverizing treatment is coarsely pulverized by a wet pulverizer different from that for the fine pulverizing processing.
The method according to any of the above. 7. The method according to claim 1, wherein the whole amount of the slurry after re-mixing the slurry subjected to the fine pulverization treatment is subjected to a coarse pulverization treatment. 8. The method according to claim 5, wherein the coarse pulverization is performed with relatively smaller energy than the fine pulverization. 9. The method according to claim 5, wherein the crushing energy per 1 m ³ of the slurry in the coarse crushing is 0.2 to 8 kwh. 10. The wet pulverization process according to claim 1, wherein the particle size distribution of terephthalic acid particles in the slurry after the completion of the pulverization process is continuously monitored by a particle size distribution meter to control the conditions of the wet pulverization process. The method according to any of the above.