JP4002083B2 - Dimethyl terephthalate composition and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to dimethyl terephthalate as a starting material for producing polyester, and more particularly to a dimethyl terephthalate composition having improved properties as a polyester material and a method for producing the same.
[0002]
[Prior art]
Dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) is a polyethylene terephthalate (hereinafter abbreviated as PET) which is a polycondensate with ethylene glycol (hereinafter sometimes abbreviated as EG). )), A representative method for producing the DMT is the Bitten-Hercules method (Witten-Hercules method).
[0003]
In this method, para-xylene (hereinafter sometimes abbreviated as PX) and methyl p-toluate are oxidized in air, and the resulting oxidation reaction mixture is esterified with methanol under high-temperature and high-pressure conditions to produce an esterification reaction mixture. This is a method for separating and purifying DMT from slag.
[0004]
However, DMT produced from PX by the above-described method (hereinafter sometimes abbreviated as PX-DMT) causes a hydrolysis reaction when contacted with water vapor and the like, resulting in a problem that an acid component is by-produced. In addition, since it contains a large amount of dimethyl hydroxyterephthalate (hereinafter sometimes abbreviated as HDT) by-produced by the oxidation reaction, there is a problem that the fluorescence intensity derived from the HDT is strong and the hue is poor.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to provide a DMT composition that solves the above-mentioned problems of the prior art, has a good hue, and suppresses an increase in acid value.
[0006]
[Means for Solving the Problems]
In view of the above-mentioned prior art, the inventors are not particularly present in PX-DMT, and can be easily mixed with DMT to prevent an increase in the acid value of DMT. We conducted intensive research on substances that have no effect.
[0007]
As a result, it is possible to prevent an increase in the acid value of DMT by containing a small amount of a compound having a specific structure, and to investigate a causative substance of DMT hue deterioration and to reduce the content thereof, a DMT having a good hue The present inventors have found that a composition can be produced and have completed the present invention.
[0008]
That is, the object of the present invention is to
A main component is dimethyl terephthalate, which contains 0.001 to 200 ppm of methyl 4- (1,3-dioxolan-2-yl) benzoate and 0 to 1 ppm of dimethyl hydroxyterephthalate. Can be achieved.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, first, it is necessary to obtain methyl 4- (1,3-dioxolan-2-yl) benzoate (hereinafter sometimes abbreviated as 4-DOMB). Examples include (1) a method obtained by synthesis, and (2) a method utilizing a by-product of a process of recovering DMT from polyalkylene terephthalate using EG and MeOH. 4-DOMB derived from either method Even so, the object of the present invention can be achieved by containing a small amount in DMT.
[0010]
In addition, as a synthesis method of the above (1), 4-carbomethoxybenzaldehyde and EG can be easily converted to 4-DOMB by heating at normal pressure at 80 to 150 ° C. in an equimolar amount under a known general-purpose acidic catalyst. Obtainable. Here, it is important to remove water by-produced by the dehydration reaction, and it is effective to use distillation or molecular sieve to remove the by-product water.
[0011]
On the other hand, the method of utilizing the by-product of the DMT recovery process of (2) above can utilize the by-product as it is, and the obtained 4-DOMB does not require a purification operation thereafter, and is therefore a very preferable method from an industrial viewpoint. It is.
[0012]
In this method, first, polyalkylene terephthalate is depolymerized in EG in the presence of a known depolymerization catalyst. Here, the polyalkylene terephthalate is polyethylene terephthalate, polytrimethylene terephthalate, or polybutylene terephthalate. If necessary, the mixture obtained by the depolymerization reaction is used to extract excess EG used in the depolymerization reaction, and then introduce it into the reactor together with MeOH and a substituted esterification reaction catalyst. DMT and alkylene glycol are formed, the reaction mixture is cooled, and then separated into a crude dimethyl terephthalate cake and mixed solution by a centrifuge.
[0013]
Next, (A) 1 to 5 times by weight of methanol was added to the obtained cake at 30 to 60 ° C., and then separated into a crude dimethyl terephthalate cake and mixed solution by a centrifuge again. (B) In purifying the obtained cake by distillation, for example, the top temperature of the distillation column is 160 to 210 ° C., the pressure is 2.7 to 13.3 kPa, and the reflux ratio is 0.1. It is possible to obtain a DMT composition containing 4-DOMB in a range of 0.001 to 200 ppm by controlling to be in a range of ˜2. Note that there is no problem even if the method (A) and the method (B) are used in combination.
[0014]
As for HDT, since the HDT concentration in DMT directly leads to an increase in the fluorescence intensity of DMT, it is necessary to reduce the HDT concentration as much as possible. However, the HDT concentration in general PX-DMT is PX Since it is first formed by an oxidation reaction, HDT is produced as a by-product, and the final product DMT has a problem of containing 1 ppm or more of HDT. However, if the method of utilizing the by-product of the DMT recovery process (2) is adopted, a DMT composition having an HDT in the range of 0 to 1 ppm can be obtained.
[0015]
From the above, by obtaining a DMT composition containing 0.001 to 200 ppm of 4-DOMB and 0 to 1 ppm of HDT in DMT, an increase in acid value can be prevented, and the fluorescence intensity is low and the hue is low. It becomes possible to obtain a dimethyl terephthalate composition having improved properties as a good polyester raw material.
[0016]
In the present invention, in the case of the above method (A) and / or (B) using a polyester recovery process, the addition of 4-DOMB can be adopted without any problem, whether batch or continuous. In addition, when the method utilizing the by-product of the DMT recovery process described in (2) above is adopted and the following conditions are used, a DMT composition having a content of 4-DOMB and HDT within the scope of the present invention is obtained. It can be obtained relatively easily.
[0017]
That is, the depolymerization reaction of polyester by EG may be performed at a temperature of about 110 to 230 ° C. and a pressure of about 0.0 to 0.2 MPa (gauge pressure). When the temperature is within this range, the EG depolymerization reaction is sufficiently performed. . Here, when the depolymerization reaction temperature is less than 110 ° C., the depolymerization time becomes very long and the efficiency becomes inefficient. On the other hand, if the temperature exceeds 230 ° C., a high-pressure reactor is required, which is not preferable from the viewpoint of operation and safety.
[0018]
Further, the reaction temperature at the time of performing the substituted esterification reaction with MeOH is preferably in the range of 50 to 150 ° C., and the reaction pressure is preferably in the range of 0.0 to 0.59 MPa (gauge pressure). In this case, the substituted esterification reaction is sufficiently performed. The substituted esterification reaction time is preferably 30 minutes to 4 hours.
[0019]
Here, any known catalyst can be used as the depolymerization reaction catalyst and the substituted esterification reaction catalyst, but from the group consisting of carbonates, bicarbonates, and carboxylates of alkali metals and alkaline earth metals. It is preferable to use at least one selected metal salt compound from the viewpoint of high catalytic ability. Furthermore, it is particularly preferable to use sodium carbonate as any reaction catalyst.
[0020]
In the mixture obtained by this substituted esterification reaction, there are crude DMT, MeOH, EG, and by-products in the EG depolymerization reaction and substituted esterification reaction, and 4-DOMB, HDT, other dioxane, dimethyl ether. , Including water.
[0021]
When this mixture is used as it is, recrystallization operation, or when the DMT crystals are not completely dissolved, the mixture is heated and dissolved with a mixed solution. At this time, the substituted esterification reaction temperature is left as it is or after heating once in the range of 60 to 150 ° C. depending on the composition of the mixture, it is then cooled to the range of 10 to 50 ° C. If necessary, it is preferable to cool the mixture using the latent heat of the solvent.
[0022]
The DMT concentration in the mixed solution is preferably in the range of 10 to 40 wt%. If the concentration of DMT is less than 10 wt%, the amount of solvent used increases, which is not economically preferable.
[0023]
The recrystallized mixture is subjected to solid-liquid separation by centrifugation or the like, and then MeOH is added to the obtained cake for washing.
[0024]
The amount of MeOH to be added and the temperature at the time of washing are 1 to 5 times the amount of 30 to 60 ° C. based on the crude DMT cake, the washing effect, the solid-liquid slurry handling property, and economically preferable. In the washing step, 4-DOMB contained in the crude DMT cake is not completely removed. The number of cleanings may be about 1 to 3, but there is no problem even if the number of cleanings is further added.
[0025]
After the MeOH washing and solid-liquid separation, the crude DMT cake is heated and melted to further remove MeOH, and finally purified by distillation under reduced pressure, and the DMT composition is taken out as a fraction.
[0026]
The conditions for the distillation purification are carried out under a reduced pressure of 2.7 to 13.3 kPa, a tower top temperature of 160 to 210 ° C., and a reflux ratio of 0.1 to 2.0.
[0027]
4-DOMB has a slightly lower vapor pressure than DMT, and can be contained in a very small amount in the DMT composition obtained within this range. In distillation purification conditions, excessive strengthening is not preferable because it is difficult to detect 4-DOMB in the DMT composition, and excessive relaxation of the conditions is due to the acid value quality of the DMT composition being distilled out of the acid component. Should be avoided.
[0028]
Therefore, in order to contain 4-DOMB in an appropriate amount in the recovered DMT, a distillation column having 5 to 20 theoretical plates is used, and the top temperature is 5.3 to 9.3 kPa under reduced pressure. It is particularly preferable for quality control that the conditions are 180 to 195 ° C. and the reflux ratio is 0.3 to 1.0.
[0029]
On the other hand, since the amount of HDT produced as a by-product in the depolymerization reaction stage is very small, HDT can be adjusted to a desired HDT concentration by applying the above purification conditions.
[0030]
【Example】
The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.
[0031]
In addition, the qualitative analysis of 4-DOMB and HDT was performed by carrying out recrystallization extraction operation using an acetone solvent and MeOH solvent, and then concentrating and measuring in a special grade reagent acetone solvent. As the measuring apparatus, gas chromatography (apparatus: HP5890 manufactured by Hewlett-Packard Company, capillary column: DB-17 manufactured by J & W) was used.
[0032]
Further, quantitative analysis of 4-DOMB and HDT was performed using GC-MASS (apparatus: manufactured by Hewlett-Packard Company, GC / mass detector = HP6890 / HP5973, capillary column: DB-17 manufactured by J & W).
[0033]
The fluorescence intensity of DMT was measured using chloroform as a measurement solvent, excitation wavelength: 328 nm, and fluorescence wavelength: 454 nm. As the fluorometer, F-4500 manufactured by Hitachi, Ltd. was used.
[0034]
Bis-β-hydroxyethylene terephthalate (hereinafter sometimes abbreviated as BHET) and lower oligomer component are components using GPC (apparatus: L-4000 liquid chromatography, tetrahydrofuran solvent, manufactured by Hitachi, Ltd.). The composition ratio was determined.
[0035]
The alkali permeability of terephthalic acid is 50 g of 7.5 g of terephthalic acid described in “Chemical Engineering Vol. 58, No. 10, pp. 787-789 (1994, published by Chemical Industry Association)” (2 mol / L ) Was used as a solution using a potassium hydroxide aqueous solution, and the transmittance was determined from the transmittance at a wavelength of 340 nm with a path length of 1 cm.
[0036]
[Reference Example 1]
Trace component measurement was performed on white briquette-shaped DMT manufactured by Petrocell. The detected trace components include p-toluic acid, monomethyl terephthalate as the acid component, dimethyl isophthalate, dimethyl phthalate as the isomer, methyl p-toluate, 4-carbomethoxybenzaldehyde, o, m, p) A methyl mono-substituted dimethyl phthalate was detected, but 4-DOMB was not detected.
[0037]
Further, when 1.5 ppm of HDT was detected in the DMT and the fluorescence intensity was measured, the numerical value was 900.
[0038]
[Reference Example 2]
The alkali transmittance of high-purity terephthalic acid (hereinafter sometimes abbreviated as PTA) manufactured by Mitsui Chemicals, Inc. was measured and found to be 91%.
[0039]
[Example 1]
200 parts of EG were put into a 500 ml separable flask, 1.5 parts of sodium carbonate and 50 parts of polyethylene terephthalate were added, the temperature was raised while stirring at a stirring speed of 100 rpm, and the internal temperature was set to 185 ° C. When this state was maintained for 4 hours, the depolymerization reaction was completed. The resulting depolymerized product was concentrated by distillation under reduced pressure at 6.65 kPa, and the concentrated solution and 150 parts of EG as a fraction were recovered.
[0040]
To this concentrated liquid, 0.5 parts of sodium carbonate and 100 parts of MeOH were added as a transesterification reaction catalyst, and the transesterification reaction was carried out at normal pressure while maintaining the liquid temperature at 75 ° C. and the stirring speed of 100 rpm.
[0041]
The resulting mixture was cooled to 40 ° C. and filtered through a glass 3G-4 filter. The crude DMT recovered on the filter was put into 100 parts of MeOH, heated to 40 ° C., washed with stirring, and filtered again with a glass filter. This washing was repeated twice.
[0042]
Crude DMT that could be captured on the filter was charged into a distillation apparatus, and vacuum distillation was performed under conditions of a pressure of 6.65 kPa at a reflux ratio of 0.5 to obtain a DMT composition as a fraction. Forty fractions were recovered. When the amount of DMT was measured by measuring the residue in the kettle, it was 2 parts. Based on the amount of polyethylene terephthalate added, the reaction rate of DMT was 93% by weight.
[0043]
In the DMT composition purified by distillation, 20 ppm of 4-DOMB and 0.5 ppm of HDT were detected. As a result of comparing the 4-DOMB and HDT in the DMT composition with 4-DOMB and HDT of the sample by GC-MASS analysis, it was confirmed that the detected fragment ions matched and had the same structure. It was.
[0044]
The quality of the purified DMT composition has a purity of 99.9% by weight or more, the acid value is 0.003 mg (KOH) / g (DMT), the fluorescence intensity is 330, and other quality characteristics are for reference. It was equivalent to the commercial product DMT used in the examples.
[0045]
[Example 2]
While maintaining 40 parts of the DMT composition obtained in Example 1 at 250 ° C. and a pressure of 3.92 MPa, water vapor was continuously blown, and excess water vapor and generated MeOH were continuously extracted to perform a hydrolysis reaction. . The reaction proceeded almost quantitatively and 33 parts by weight of terephthalic acid was produced.
[0046]
After adding 60 parts of MeOH to 30 parts of the obtained terephthalic acid and stirring and washing at 40 ° C., the terephthalic acid was filtered off and dried. When the alkali transmittance of the obtained terephthalic acid was measured, it was 90%, and no significant difference was observed with PTA manufactured by Mitsui Chemicals.
[0047]
[Example 3]
When 40 parts of the DMT composition obtained in Example 1 and 75 parts of EG were put into a separable flask and the temperature was raised with stirring at 100 rpm, MeOH was generated at around 200 ° C., and the start of the reaction was confirmed. . Distilled MeOH was distilled out of the system in two separation towers, and the entrained EG and DMT fractions were returned to the flask.
[0048]
As the reaction end point was reached when the flask internal temperature reached 220 to 250 ° C. while repeating the above operation, the required time was about 8 hours.
[0049]
When the composition of the obtained mixture was analyzed by gas chromatography, DMT was completely lost by the reaction. BHET was confirmed to be 45 wt% by the analysis and GPC analysis. Each of the other components showed a sharp molecular weight distribution, and was confirmed to be a dimer to pentamer lower oligomer.
[0050]
[Example 4]
Using the DMT composition obtained in Example 1 as a raw material, a PET production test was carried out according to a conventional method. Using manganese acetate catalyst, EI reaction was carried out under normal pressure up to 245 ° C. to obtain a lower oligomer mainly composed of BHET. Subsequently, antimony trioxide was added to the obtained lower oligomer mainly composed of BHET, and polymerization was carried out at 290 ° C. for 1.8 hours under a high vacuum of 0.1 kPa. The intrinsic viscosity of the obtained polymer was 0.70. Other polymer quality characteristics such as hue, thermal characteristics, and DEG content were almost the same analytical values as those of the polymer produced from the commercially available reagent DMT.
[0051]
About the obtained polymer, the volatile component was measured on the conditions of 200 degreeC x 60 minutes using the gas chromatography which attached the head space sampler apparatus (the Perkin-Elmer company make, HS40XL). As a result, 4-DOMB and HDT were not detected.
[0052]
[Comparative Example 1]
In Example 1, distillation under reduced pressure was performed under the conditions of distillation of crude DMT at a pressure of 6.65 kPa and a reflux ratio of 0.05 to obtain a DMT composition as a fraction. Forty fractions were recovered. When the residue in the kettle was measured and the amount of DMT was measured, it was 2 parts, and the reaction rate of DMT was 93% by weight based on the added polyester.
[0053]
In the DMT composition purified by distillation, 4-DOMB was detected at 40 ppm and HDT was detected at 1.1 ppm.
[0054]
The quality of the purified DMT composition had a purity of 99.9% by weight or more, and the acid value was 0.003 mg (KOH) / g (DMT), but the fluorescence intensity showed a high value of 700. It was.
[0055]
[Comparative Example 2]
In Example 1, after the transesterification reaction, the obtained mixture was cooled to 40 ° C. and filtered through a glass 3G-4 filter. 45 parts of crude DMT recovered on the filter was put into 40 parts of MeOH, heated to 40 ° C. with stirring and washed, and filtered again with a glass filter. This washing was repeated twice.
[0056]
Crude DMT that could be captured on the filter was charged into a distillation apparatus, and distillation under reduced pressure was performed under conditions of a pressure of 6.65 kPa at a reflux ratio of 0.5, and DMT was obtained as a fraction. Forty fractions were recovered. When the residue in the kettle was measured and the amount of DMT was measured, it was 2 parts, and the reaction rate of DMT was 93% by weight based on the added polyester.
[0057]
In a DMT composition purified by distillation, 250 ppm of 4-DOMB and 0.5 ppm of HDT were detected.
[0058]
The quality of the purified DMT composition is 99.8% by weight, and the acid value is 0.01 mg (KOH) / g (DMT), which is the same quality as the commercial reagent DMT used in Reference Example 1. Those with a could not be obtained.
[0059]
【The invention's effect】
According to the present invention, a dimethyl terephthalate composition having improved properties as a polyester raw material can be provided.

Claims (5)

  A dimethyl terephthalate composition, wherein the main component is dimethyl terephthalate and contains 0.001-200 ppm of methyl 4- (1,3-dioxolan-2-yl) benzoate and 0-1 ppm of dimethyl hydroxyterephthalate.   The polyalkylene terephthalate is depolymerized with ethylene glycol, followed by substitution esterification with methanol to produce crude dimethyl terephthalate and alkylene glycol. The reaction mixture is cooled, and the crude terephthalate is centrifuged with a centrifuge. After carrying out the operation of separating into a dimethyl acid cake and a mixed solution, when the cake is distilled and purified to obtain a dimethyl terephthalate composition, the reflux ratio during the distillation and purification is controlled to 0.1-2. The main component is dimethyl terephthalate, characterized in that it contains 0.001 to 200 ppm of methyl 4- (1,3-dioxolan-2-yl) benzoate and 0 to 1 ppm of dimethyl hydroxyterephthalate. A method for producing a dimethyl acid composition.   The production method according to claim 2, wherein the polyalkylene terephthalate is at least one polyalkylene terephthalate selected from the group consisting of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.   The polyalkylene terephthalate is depolymerized with ethylene glycol, followed by substitution esterification with methanol to produce crude dimethyl terephthalate and alkylene glycol. The reaction mixture is cooled, and the crude terephthalate is centrifuged with a centrifuge. After separating into a dimethyl acid cake and a mixed solution, the cake is distilled and purified to obtain a dimethyl terephthalate composition. When the cake obtained by the centrifugation operation is subjected to a condition of 30 to 60 ° C. Then, after adding 1 to 5 times by weight methanol based on the cake, the operation of separating the dimethyl terephthalate cake and the mixed solution with a centrifuge again is performed, and then the obtained cake is purified by distillation. The main component is dimethyl terephthalate, characterized in that 4- (1,3-dioxolane- - yl) 0.001～200Ppm benzoate, containing 0~1ppm hydroxy dimethyl terephthalate, method of manufacturing dimethyl terephthalate composition.   The production method according to claim 4, wherein the polyalkylene terephthalate is at least one polyalkylene terephthalate selected from the group consisting of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.