JP4262995B2 - Method for producing terephthalic acid cake suitable for polyester raw material - Google Patents

Description

【００５０】
【発明の効果】
本発明によれば、簡便な設備及び方法で、ポリエステルの直接重合法の原料として好適なテレフタル酸を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing terephthalic acid, which is a main raw material of a polyester resin widely used for fibers, films, industrial members, general molded articles and the like.
[0002]
[Prior art]
Various methods for industrially producing terephthalic acid (hereinafter sometimes abbreviated as TA) are known, one of which is dimethyl terephthalate (hereinafter sometimes abbreviated as DMT). A method of hydrolysis as a raw material is known (see, for example, Patent Documents 1 and 2).
[0003]
By the way, in the production of polyesters, particularly polyethylene terephthalate (hereinafter sometimes abbreviated as PET) by so-called direct polymerization method in which TA is esterified and then polycondensed, TA is ethylene glycol (hereinafter abbreviated as PET). Hereinafter, it may be abbreviated as EG.) Etc.) and is sent to the reaction system in a slurry state, but at this time, the power required for stirring during mixing is small, the viscosity of the slurry during transfer is low, and TA having excellent fluidity and high uniformity of reaction is desired. Furthermore, good fluidity is also required in powder handling such as TA transportation and storage.
[0004]
In order to obtain such a good slurry property and uniform reaction of TA, a large amount of alkylene glycol may be used with respect to TA, but an excessive amount of alkylene glycol is a side reaction product during polycondensation reaction. Occurrence increases, causing a melting point of the polymer, a decrease in the degree of polymerization, and further coloring.
[0005]
In order to avoid these drawbacks, it is sufficient to make the alkylene glycol as close to stoichiometric as possible. However, if the amount of alkylene glycol used is reduced, the power required for stirring in the slurry adjustment tank and the reactor increases, and the fluidity There is a problem that the required reaction time becomes longer due to poor reactivity. Therefore, TA which forms a slurry having good fluidity and reactivity with the minimum amount of alkylene glycol is suitable as a raw material for the direct polymerization method. Such properties largely depend on the particle size distribution of TA particles, and it is an important factor to optimize them.
[0006]
Various methods for controlling the particle size distribution of TA have been proposed. Typically, para-xylene is used as a starting material, and after liquid phase oxidation in a lower fatty acid solvent under a catalyst containing a transition metal compound and bromine, A method of controlling the particle size of TA produced by cooling in stages in a multistage recrystallization tank connected in series and controlling the conditions for precipitating TA dissolved in the solvent is known ( For example, see Patent Document 3).
[0007]
However, in this method, the conditions at the time of precipitation of the TA crystal are set mainly for the purpose of controlling the impurity concentration in the TA crystal. In order to lower the temperature step by step, a multi-stage recrystallization tank is required, and in order to dissolve all or part of the TA with low solubility in various solvents for recrystallization, recrystallization that can handle high temperatures and high pressures. Since there is a problem that a crystal tank is required and the capital investment amount is significantly increased, it is considerably difficult to control the particle size distribution by adjusting the conditions at the time of TA precipitation.
[0008]
On the other hand, instead of controlling the TA crystal precipitation conditions, the produced TA crystals are crushed in a slurry state and the particle size distribution is changed (for example, see Patent Document 4). A method of controlling the particle size distribution and changing the slurry characteristics by re-mixing after pulverizing with a crusher (for example, see Patent Document 5) has been proposed.
[0009]
However, these methods also promote the generation of a large amount of TA fine powder, and when an alkylene glycol slurry is used, the apparent viscosity of the slurry is significantly increased and the stirring power may be increased. Furthermore, since a pulverizer having a complicated structure is necessary, there is a problem that the amount of capital investment increases and maintenance and management for maintenance of the equipment require a great deal of labor.
[0010]
[Patent Document 1]
Japanese Patent Publication No.57-53332 [0011]
[Patent Document 2]
JP-A-8-231464
[Patent Document 3]
Japanese Patent Laid-Open No. 8-225489
[Patent Document 4]
JP-A-9-255619 [0014]
[Patent Document 5]
Japanese Patent Laid-Open No. 11-100350
[Problems to be solved by the invention]
An object of the present invention is to provide a terephthalic acid suitable as a raw material for a polyester direct polymerization method by solving the problems of the prior art and by simple equipment and method.
[0016]
[Means for Solving the Problems]
As a result of intensive studies in view of the above-described conventional techniques, the present inventors can obtain terephthalic acid suitable as a raw material for a direct polymerization method of polyester when the reaction liquid temperature is controlled immediately after the hydrolysis reaction and immediately before flash cooling. As a result, the present invention has been completed.
[0017]
That is, the object of the present invention is to
From water in which terephthalic acid is dissolved and precipitated terephthalic acid particles obtained by hydrolyzing dimethyl terephthalate using at least one reactor having a stirrer at a temperature of 230 to 350 ° C. and a conversion rate of 99% or more The high-temperature and high-pressure reaction liquid composed of the resulting slurry is cooled by flashing, and the resulting aqueous slurry of terephthalic acid particles is solid-liquid separated to obtain a wet terephthalic acid cake. A polyester raw material characterized in that when the conversion rate of decomposition becomes 97% or more, the reaction solution temperature is lowered from 230 to 350 ° C to 190 to 240 ° C , and then the conversion rate is set to 99% or more. It can be achieved by a method for producing a terephthalic acid cake suitable for the above.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
For the hydrolysis reaction step of DMT to TA under the high temperature and high pressure conditions performed by the method of the present invention, a known technique can be adopted, and DMT is 99% using at least one reactor having a stirrer. What is necessary is just to hydrolyze with a higher conversion.
[0019]
Here, a batch reactor or a continuous reactor can be used as the reactor, but it is particularly preferable to use two or more reactors, and it is particularly preferable to connect the reactors in series.
[0020]
In the production method of the present invention, it is preferable to control the weight ratio of water and DMT during the hydrolysis reaction to a range of 3: 1 to 1: 2. Here, when there is too much water in the system, a large amount of TA is dissolved in water, and the obtained TA contains a large amount of fine particles having a particle size of 45 μm or less, and TA having a good particle size distribution is obtained. On the other hand, if there is too much DMT, the apparent viscosity of the reaction solution becomes too high and the hydrolysis reaction does not proceed easily, and the resulting TA contains a large amount of coarse particles having a particle diameter of 250 μm or more. Similarly, TA having a good particle size distribution cannot be obtained. The weight ratio of water to DMT is preferably controlled in the range of 2: 1 to 1: 2, and particularly preferably the weight ratio of water to DMT is controlled in the range of 4: 5 to 3: 2.
[0021]
Here, as a method of controlling the weight ratio of water and DMT at the time of hydrolysis, the temperature of the hydrolysis reaction, the weight ratio of water to DMT at the start of the hydrolysis reaction, methanol generated by the hydrolysis reaction (hereinafter, (This may be abbreviated as MeOH.) The amount of water vapor that is entrained when the product is taken out of the system can be controlled by operating the operating conditions in the hydrolysis reaction. For example, the MeOH generated during the hydrolysis is stripped. Or when controlling the weight ratio of the water which is entrained and distilled when removed by distillation and the DMT supplied to the reactor, the weight ratio may be 1: 1 to 1: 8.
[0022]
Moreover, it is preferable that the reaction temperature at the time of hydrolysis exists in the range of 180-350 degreeC. When it is within this range, the hydrolysis reaction proceeds rapidly and there is little energy loss. The reaction temperature for the hydrolysis reaction is more preferably in the range of 180 to 300 ° C, and particularly preferably in the range of 230 to 260 ° C. The reaction pressure at this time is preferably 2.8 to 4.6 MPa (gauge pressure).
[0023]
In the production method of the present invention, when the conversion rate of hydrolysis reaches 97% or more, it is necessary to set the reaction liquid to 190 to 240 ° C, preferably 190 to 230 ° C, and to convert the conversion rate to 99% or more. is there. When the reaction liquid in which the temperature difference before and after the flash operation in the flash operation described later becomes large is less than 190, the precipitated TA is excessively pulverized and a large amount of fine particles are generated. On the other hand, the reaction liquid temperature before the flash operation Is too high, and when it exceeds 240 ° C., a large amount of fine particles are generated after flushing because of the large amount of dissolved TA. In addition, in the state where the conversion rate is 97% or more, even if the reaction liquid temperature is within the above range, the conversion reaction proceeds by continuing to remove the generated MeOH. appear.
[0024]
In the production method of the present invention, the high-temperature / high-pressure reaction liquid after completion of the reaction, which is composed of a slurry composed of water in which TA is dissolved and precipitated TA particles, obtained by the above operation, is cooled by flashing. Here, it is preferable that the weight ratio of water and TA in the reaction solution immediately before the flash is in the range of 2: 1 to 1: 2. By setting it within such a range, it is possible to further reduce fine particles having a particle size of 45 μm or less and coarse particles having a particle size of 250 μm or more contained in TA particles generated by a flash operation described later.
[0025]
In addition, in the manufacturing method of this invention, DMT collect | recovered from the polyester waste can be used for a hydrolysis. Here, the polyester waste is a product mainly composed of polyester and / or waste mainly composed of polyester generated in the process of producing the product, and contains polyalkylene glycol. Specifically, recovered polyester fiber products, films, PET bottles and other recovered products, fiber waste at the time of production, film waste, resin waste and the like can be mentioned.
[0026]
In particular, when the DMT to be subjected to hydrolysis is recovered from a polyalkylene terephthalate contained in high-purity DMT or polyester waste by a depolymerization reaction with an alkylene glycol and a subsequent transesterification reaction with MeOH, Impurities such as 4-carboxybenzaldehyde (hereinafter sometimes abbreviated as 4-CBA) which is a typical impurity contained in TA obtained by para-xylene oxidation, which is a typical TA production method, This is preferable because a multistage recrystallization tank for removal is unnecessary.
[0027]
Next, the high-temperature and high-pressure reaction liquid after completion of the reaction composed of a slurry composed of water in which TA is dissolved and precipitated TA particles is cooled by flash. The reaction liquid in a pressurized state by this flush operation is depressurized to atmospheric pressure at a stretch, and the reaction liquid temperature rapidly decreases to about 100 to 105 ° C.
[0028]
By performing this flash operation, TA particles that had precipitated before the flash were somewhat destroyed by the impact due to the pressure difference during the flash, and the terephthalic acid dissolved before the flash was drastically reduced in solubility due to the flash. As a result, most of the particles are deposited as fine particles.
[0029]
The particle size after the TA particles deposited here are destroyed depends greatly on the particle size before flashing, but there is no problem as long as it is within the range of the hydrolysis reaction conditions of the present invention.
[0030]
The water / TA slurry cooled by the flash can be easily obtained as a wet TA cake by solid-liquid separation using a centrifuge or the like.
[0031]
In the TA cake thus obtained, TA particles having a particle size of 250 μm or more are 20% by weight or less, preferably 10% by weight or less, and TA particles having a particle size of 45 μm or less are 20% by weight or less of the whole. It is preferable that
[0032]
When the number of coarse particles having a particle diameter of 250 μm or more increases, when TA is used as a raw material for producing polyester, the reactivity thereof is low, so that there is a concern that unreacted terephthalic acid increases. On the other hand, if there are too many fine particles with a particle size of 45 μm or less, the apparent viscosity when TA cake is made into a slurry will increase, leading to a decrease in fluidity, which may cause problems such as blockage in the piping. Occurs.
[0033]
The total content of DMT and monomethyl terephthalate (hereinafter sometimes abbreviated as MMT) in the obtained TA cake is 1000 ppm or less.
[0034]
Moreover, it is preferable that the water | moisture content in TA cake accounts for 0.1 to 20 weight% on the basis of the cake total weight. It is difficult to operate at a water content of 0.1% by weight or less. On the other hand, if it exceeds 20% by weight, a large amount of energy is required when the drying process is performed later, and the drying process is performed. Even if it is supplied as a polyester raw material without much, a great amount of energy is required to remove moisture in the esterification step, which is not economical.
[0035]
The TA cake in the wet state obtained in the present invention may be dried or used as a raw material for obtaining a polyester by a direct polymerization method in a wet state without being dried. In particular, when the wet terephthalic acid cake is not subjected to a drying step, it is continuously made into a slurry with alkylene glycol in a wet state, and subsequently subjected to esterification reaction and polycondensation reaction, while maintaining the particle size distribution of the obtained TA cake. This is preferable because a slurry with alkylene glycol can be prepared. Here, the water accompanying the TA can be removed by evaporation in the esterification step, which is preferable because there is no problem and the drying step can be omitted.
[0036]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, each value in an Example was calculated | required with the following method.
[0037]
(1) Particle size distribution:
The measurement was performed according to “Method for screening chemical products” described in JIS K 0069. The openings of the sieves were 45, 75, 106, 150, 180, 212, 250 μm. The wet TA cake was slurried with water, and the frequency for each particle size measured by the wet sieving method was expressed in wt%.
[0038]
(2) Average particle size:
The wet TA cake is made into a slurry with water, and an appropriate amount is screened by a wet method using a JET SIEVE apparatus using 42, 60, 80, 120, 200, 250, 300, and 400 mesh. The unpassed portion of each sieve is dried together with the sieve, the weight of each is measured, plotted on a normal probability paper, and the particle size of 50% of the unpassed portion is taken as the average particle size.
[0039]
(3) Weight concentration (ppm) of DMT and MMT:
The TA cake is dried and dehydrated, and then analyzed by high performance liquid chromatography (equipment: HPLC D-7000, Hitachi, Ltd., packed column: RP-18; 2), and the concentrations of DMT and MMT are determined. Asked.
[0040]
(4) Slurry viscosity:
It mixed by the ratio of 1.6 mol of ethylene glycol with respect to 1 mol of TA cake samples with a moisture content of 13%, and the viscosity (Pa * s) under the temperature of 50 degreeC was measured and calculated | required with the B-type viscometer.
[0041]
(5) Slurry stability:
The viscosity is measured by the same method as the slurry viscosity (A). Further, the viscosity of the slurry after standing for 5 minutes was measured (B) and the value obtained by the following formula was used as an index of slurry stability.
[0042]
[Expression 1]
Slurry stability = B / A x 100 (%)
[0043]
(6) Evaluation:
The obtained TA cake was evaluated according to the following criteria.
A: Coarse particles of 10% by weight or less, slurry viscosity of 5 Pa · s or more, and slurry stability of 50% or more.
○: Coarse particles of 20% by weight or less, slurry viscosity of less than 5 Pa · s, and slurry stability of 50% or more.
X: The coarse particle exceeds 20% by weight, the slurry viscosity is less than 5 Pa · s, and the slurry stability is less than 50%.
[0044]
[Example 1]
A batch reactor (autoclave) having a 3 liter titanium stirrer was charged with DMT and pure water at a weight ratio of 1: 1, sealed, and heated to a liquid temperature of 180 ° C. Agitation was started. Thereafter, the temperature was further raised, and after the liquid temperature reached 250 ° C., the distillation pipe valve provided on the upper lid of the reactor was slightly opened, and while maintaining the liquid temperature at 250 ° C., methanol by-produced by the reaction was distilled off together with water vapor. At the same time, about 4 kg of water, the same amount as the distilled water, was continuously fed into the reactor.
[0045]
After 1 hour has passed, the reactor liquid temperature is lowered to 230 ° C. and maintained for 30 minutes while continuing the methanol distillation operation, and then the reaction liquid is transferred from the internal liquid take-out pipe to the atmospheric pressure tank and flushed. It was cooled with. Note that, by controlling the operating conditions during the hydrolysis reaction, the weight ratio of water and TA in the state of the reaction solution immediately before the flash was 4: 5.
[0046]
The terephthalic acid slurry obtained by flash was subjected to solid-liquid separation to obtain a terephthalic acid cake. In the TA cake thus obtained, as shown in Table 1, coarse particles of 250 μm or more accounted for 9.8% by weight, and fine particles of 45 μm or less accounted for 17.0% by weight, and the slurry viscosity was 3 0.7 Pa · s.
[0047]
The TA cake had a DMT content of 25 ppm and an MMT content of 300 ppm. Other operating conditions were set as shown in Table 1.
[0048]
[Examples 2-6, Comparative Examples 1-4]
In Example 1, the same operation was performed except that the operating conditions were set as shown in Table 1. The results are shown in Table 1.
[0049]
[Table 1]

[0050]
【The invention's effect】
According to the present invention, terephthalic acid suitable as a raw material for a direct polymerization method of polyester can be provided with simple facilities and methods.

Claims (17)

From water in which terephthalic acid is dissolved and precipitated terephthalic acid particles obtained by hydrolyzing dimethyl terephthalate using at least one reactor having a stirrer at a temperature of 230 to 350 ° C. and a conversion rate of 99% or more When the high-temperature and high-pressure reaction liquid after the completion of the reaction composed of the slurry formed is cooled by flash, and the resulting water slurry of terephthalic acid particles is solid-liquid separated to obtain a wet terephthalic acid cake,
When the conversion rate of the hydrolysis is 97% or more, the reaction solution temperature is lowered from 230 to 350 ° C. to 190 to 240 ° C. , and then the conversion rate is set to 99% or more. A terephthalic acid cake manufacturing method suitable for polyester raw materials.   The production method according to claim 1, wherein the weight ratio of water and dimethyl terephthalate during the hydrolysis reaction is controlled in the range of 3: 1 to 1: 2.   Control of the weight ratio of water and dimethyl terephthalate during the hydrolysis reaction is such that the weight ratio of steam distilled from the reactor to dimethyl terephthalate supplied to the reactor is 1: 1 to 1: 8. The manufacturing method of Claim 2 performed by controlling to.   The production method according to claim 1, wherein the weight ratio of water in which terephthalic acid is dissolved in the reaction solution immediately before flashing to precipitated terephthalic acid is in the range of 2: 1 to 1: 2.   The method for producing terephthalic acid according to claim 1, wherein flash cooling of the reaction solution is performed in one stage.   The production method according to claim 1, wherein the reactor having a stirrer is a batch reactor or a continuous reactor.   The production method according to claim 1, wherein the hydrolysis is performed using two or more reactors having a stirrer. The manufacturing method of Claim 7 which connects the reactor which has a stirrer in series.   The production method according to claim 1, wherein the dimethyl terephthalate to be subjected to hydrolysis is dimethyl terephthalate recovered from polyester waste. Dimethyl terephthalate recovered from polyester waste, depolymerization reaction by alkylene glycol polyalkylene terephthalates contained in polyester waste, and subsequently were those recovered by transesterification with methanol, according to claim 9, wherein Production method. The production method according to claim 9 , wherein the polyester waste is a commercially available product mainly comprising polyester and / or waste mainly comprising polyester generated in the step of producing the product.   A terephthalic acid cake obtained by the method according to claim 1. The terephthalic acid cake according to claim 12 , wherein the terephthalic acid particles having a particle diameter of 250 µm or more are 20 wt% or less of the whole, and the terephthalic acid particles having a particle diameter of 45 µm or less are 20 wt% or less of the whole. The terephthalic acid cake according to claim 12 , wherein the total content of dimethyl terephthalate and monomethyl terephthalate is 1000 ppm or less. The terephthalic acid cake according to claim 12 , wherein the moisture in the cake accounts for 0.1 to 20% by weight, based on the total weight of the cake.   A method for producing a polyalkylene terephthalate, wherein the terephthalic acid cake obtained by the method according to claim 1 is continuously made into a slurry with alkylene glycol in a wet state without being subjected to a drying step, and subsequently subjected to esterification reaction and polycondensation reaction.   A method for producing a polyalkylene terephthalate, comprising subjecting the terephthalic acid cake obtained by the method according to claim 1 to a drying step, followed by slurrying with an alkylene glycol, followed by esterification reaction and polycondensation reaction.