JP3684348B2 - Method for producing polyethylene terephthalate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing polyethylene terephthalate using a bis (2-hydroxyethyl) terephthalate monomer as a starting material.
[0002]
[Prior art]
As a method for producing polyethylene terephthalate, a method of reacting dimethyl terephthalate or terephthalic acid with ethylene glycol is widely known. In the method using dimethyl terephthalate as a raw material (transesterification method), a catalyst is added to dimethyl terephthalate and ethylene glycol to conduct a transesterification reaction, and then the obtained bis (2-hydroxyethyl) terephthalate and the degree of polymerization are about 4 or less. Polyethylene terephthalate is produced by polycondensing a reaction product comprising an oligomer. On the other hand, the method using terephthalic acid as a raw material (direct polymerization method) is an esterification reaction of terephthalic acid and ethylene glycol, and then the average degree of polymerization including bis (2-hydroxyethyl) terephthalate obtained is 9-10. Polyethylene terephthalate is produced by polycondensation of oligomers.
[0003]
In these reactions, a side reaction in which diethylene glycol is produced from ethylene glycol also occurs simultaneously. This side reaction is promoted by the carboxyl group of terephthalic acid. If a large amount of diethylene glycol is contained in polyethylene terephthalate, the properties of polyethylene terephthalate, such as hydrolysis resistance, heat resistance, and light resistance, will deteriorate, causing problems such as coloration. It is necessary to do.
[0004]
For example, in the method using terephthalic acid, the formation of bis (2-hydroxyethyl) terephthalate theoretically requires 2 moles of ethylene glycol per mole of terephthalic acid, but this bis (2-hydroxyethyl) terephthalate is condensed. By using ethylene glycol generated in the esterification reaction with terephthalic acid, the ratio is made as small as possible, for example, about 1.02 to 1.1 mol, and a method of suppressing the production of diethylene glycol is taken. Yes.
[0005]
On the other hand, as described in JP-A No. 2000-169623, high-purity bis (2-hydroxyethyl) is obtained by using crude polyethylene terephthalate (chips or flakes) obtained by a used polyethylene terephthalate recovery process as a raw material. A method for producing polyethylene terephthalate by obtaining terephthalate and polycondensing it in the presence of a polymerization catalyst is also known. According to this method, spent polyethylene terephthalate is depolymerized with ethylene glycol, purified to high purity bis (2-hydroxyethyl) terephthalate, and this is polycondensed again into polyethylene terephthalate and ethylene glycol. By-products are not generated, and there is an advantage that ethylene glycol supplementation is unnecessary in principle. In addition, it is possible to recycle used polyethylene terephthalate products in a closed recycling system. However, since the content of diethylene glycol in the obtained polyethylene terephthalate is higher than that in the case of polyethylene terephthalate obtained by the direct polymerization method, there is a problem that the physical properties are deteriorated or colored (particularly, the color b value is increased). there were.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing polyethylene terephthalate having excellent physical properties using bis (2-hydroxyethyl) terephthalate.
[0007]
Another object of the present invention is that the content of bis (2-hydroxyethyl) terephthalate obtained by chemical recycling of used polyethylene terephthalate (that is, depolymerizing and purifying polyethylene terephthalate) is 97% by weight or more. And (1) a cation composed of Na, Mg, Ca, Fe, Co, Zn, Ti, Sn, Sb, Ge and P, and (2) composed of halogen, NO ₂ , NO ₃ , PO ₄ and SO _4. By using bis (2-hydroxyethyl) terephthalate having a total anion content of 15 ppm or less, it is an object of the present invention to provide a method for producing polyethylene terephthalate taking into account the recycling of used polyethylene terephthalate.
[0008]
Still other objects and advantages of the present invention will become apparent from the following description.
[0009]
[Means for Solving the Problems]
According to the present invention, the above objects and advantages of the present invention are that the oligomer produced by the oligomerization reaction of bis (2-hydroxyethyl) terephthalate, the transesterification product of dimethyl terephthalate and ethylene glycol, or terephthalic acid and ethylene glycol It is achieved by a method for producing polyethylene terephthalate, characterized in that a mixture containing the esterification reaction product is subjected to a prepolymerization reaction and further subjected to a polycondensation reaction to produce polyethylene terephthalate.
[0010]
As described above, in the method for producing polyethylene terephthalate, both the method of producing from terephthalic acid and the method of producing from dimethyl terephthalate produce bis (2-hydroxyethyl) terephthalate as an intermediate product and polycondense it. Is. Accordingly, the present inventor can mix polyethylene with this bis (2-hydroxyethyl) terephthalate, for example, by mixing high-purity purified bis (2-hydroxyethyl) terephthalate obtained by depolymerization and purification of used polyethylene terephthalate. The present invention was completed as a result of intensive researches on the belief that terephthalate can be produced.
[0011]
In the use of the purified bis (2-hydroxyethyl) terephthalate, dimethyl terephthalate or terephthalic acid is added with ethylene glycol and purified bis (2-hydroxyethyl) terephthalate and reacted to obtain polyethylene terephthalate, and dimethyl terephthalate or terephthalic acid. There is a method of obtaining polyethylene terephthalate by adding an oligomerized product of purified bis (2-hydroxyethyl) terephthalate to an oligomer containing bis (2-hydroxyethyl) terephthalate produced by reacting styrene with ethylene glycol. In the former method, if purified bis (2-hydroxyethyl) terephthalate is added into a conventional transesterification reactor supplied with dimethyl terephthalate and ethylene glycol, or an esterification reactor supplied with terephthalic acid and ethylene glycol. At first glance, it seems to be a reasonable method. However, it is difficult to stabilize the quality of polyethylene terephthalate by strictly controlling the amount of ethylene glycol in the reactor and keeping the content of diethylene glycol constant, because the reaction becomes complicated by the former method. It is. In addition, when terephthalic acid is used, it is necessary to control the ratio of the hydroxyl group of bis (2-hydroxyethyl) terephthalate or oligomer to the carboxyl group of terephthalic acid, so that it goes through a commercial production scale and a continuous process. Considering stabilization of the quality of the obtained polyethylene terephthalate and control of the ratios of terephthalic acid, ethylene glycol and bis (2-hydroxyethyl) terephthalate as raw materials, it is more difficult to adopt this method.
[0012]
From the above, the present inventors include bis (2-hydroxyethyl) terephthalate produced by reacting dimethylterephthalate or terephthalic acid with ethylene glycol separately and separately oligomerizing purified bis (2-hydroxyethyl) terephthalate. The method of polymerizing by mixing with an oligomer is considered useful, and the present invention has been completed. According to the present invention, bis (2-hydroxyethyl) produced under conventional conditions if there is a sufficient margin in the capacity of the polycondensation step after the transesterification reactor or the esterification reactor in the existing equipment. The oligomerized reaction product of purified bis (2-hydroxyethyl) terephthalate can be mixed with the oligomer containing terephthalate to increase the production of polyethylene terephthalate. On the other hand, when the processing capacity is not sufficient, for example, the amount of the product by the transesterification reaction or the esterification reaction and the amount of the product by the oligomerization reaction so that the amount of the mixture corresponds to the processing capacity. You should balance with.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with specific examples. The bis (2-hydroxyethyl) terephthalate used in the present invention may be produced by any method. For example, according to the method disclosed in JP-A-2001-48835, used polyethylene terephthalate is converted into a known catalyst. By reacting with an excess of ethylene glycol in the presence of water and depolymerizing, a mixed solution of crude bis (2-hydroxyethyl) terephthalate and crude ethylene glycol is prepared, and this is adsorbed and ion-exchanged to obtain a colored product. After removing dissolved ions, cooling to crystallize bis (2-hydroxyethyl) terephthalate, solid-liquid separation from ethylene glycol, and molecular distillation of the resulting concentrated bis (2-hydroxyethyl) terephthalate Can be prepared. Moreover, it can prepare by the method described in international publication WO01 / 10812, Unexamined-Japanese-Patent No. 2000-53802, Unexamined-Japanese-Patent No. 2000-169623, etc. The purified bis (2-hydroxyethyl) terephthalate thus prepared has a bis (2-hydroxyethyl) terephthalate content of 97% by weight or more, and (i) Na, Mg, Ca, Fe, Co, The total content of cations composed of Zn, Ti, Sn, Sb, Ge and P and (ii) anions composed of halogen, NO ₂ , NO ₃ , PO ₄ and SO ₄ can be made 15 ppm or less. These cations and anions are mainly caused by compounds contained in used polyethylene terephthalate and compounds mixed with the polyethylene terephthalate in the depolymerization process, the purification process, and the like.
[0014]
Next, the purified bis (2-hydroxyethyl) terephthalate thus obtained is put into an oligomerization reactor, and an oligomerization reaction is performed at 260 ° C. for 60 minutes in the presence of a polymerization catalyst. In this case, for example, when the oligomerization reaction is carried out at normal pressure, the composition of the reaction product is, in one example, 19.9% by weight of monomer, 22.5% by weight of dimer, 18.4% of trimer. Wt%, tetramer 12.8 wt%, pentamer 8.2 wt%, hexamer 5.3 wt%, heptamer 7.9 wt%, octamer 2.0 wt%, 9 amount It was 1.1% by weight of the product, 0.5% by weight of the 10-mer or more, and 5.9% by weight of ethylene-diethylene glycol terephthalate. On the other hand, when carried out under a reduced pressure of 13.3 kPa, in the corresponding example, the composition of the reaction product was 6.8 wt% monomer, 9.9 wt% dimer, 11.8 wt% trimer. , Tetramer 12.1 wt%, pentamer 10.7 wt%, hexamer 9.3 wt%, heptamer 7.9 wt%, octamer 6.5 wt%, 9mer 6 The content was 3% by weight, 2.1% by weight of 10-mer, 15.1% by weight of 11-mer or more, and 1.5% by weight of ethylene-diethylene glycol terephthalate. In each case, Sb ₂ O ₃ was used as the polymerization catalyst, and 0.0345 mol was added to 1 mol of bis (2-hydroxyethyl) terephthalate.
[0015]
As described above, when a large amount of ethylene glycol is present in the reaction system, diethylene glycol is produced, which adversely affects the physical properties of polyethylene terephthalate. Therefore, it is necessary to remove ethylene glycol from the reaction system. Here, since the boiling point of ethylene glycol is as high as about 198 ° C. under normal pressure, heating under reduced pressure is more effective than removing under normal pressure to remove it from the reaction system. In fact, when the above two experimental results are compared, 5.9% by weight of ethylene-diethylene glycol terephthalate is contained when polymerized at normal pressure, whereas 1.5% by weight under reduced pressure, and the reaction under reduced pressure. Is effective in suppressing the production of diethylene glycol. Moreover, it can be seen that oligomerization is promoted by removing ethylene glycol from the result that the polymerized under reduced pressure has relatively low molecular weight components.
[0016]
As a result of further studies by the inventor, it is advantageous that the oligomerization reaction is carried out at a temperature of 220 to 270 ° C. and a pressure of 7 to 70 kPa, more preferably 9 to 50 kPa, for 30 to 90 minutes. I found out. When the pressure is less than 7 kPa, the contents in the reactor are bumped, and when the pressure is more than 70 kPa, oligomerization takes a long time and increases diethylene glycol. In order to carry out the reaction in a stable state and reduce the low molecular weight components after the reaction, it is preferably carried out at 9 to 50 kPa. By performing the oligomerization reaction of polycondensation under a pressure of 10 to 30 kPa, an oligomer having a polymerization degree of 6 to 10 is generated.
[0017]
When producing copolymer polyethylene terephthalate, for example, a copolymer component is added to an oligomerization reactor of bis (2-hydroxyethyl) terephthalate to produce a copolymer oligomer with bis (2-hydroxyethyl) terephthalate. This may be mixed with dimethyl terephthalate or a reaction product of terephthalic acid and ethylene glycol and polycondensed. As the copolymer component, for example, a dicarboxylic acid such as isophthalic acid, naphthalenedicarboxylic acid or adipic acid, or a diol such as cyclohexanedimethanol can be used. The copolymerization ratio of the copolymer component is preferably 10 mol% or less with respect to the total acid component. The oligomerization reactor is supplied by mixing, for example, bis (2-hydroxyethyl) terephthalate and a copolymer component at a temperature equal to or higher than the melting point of bis (2-hydroxyethyl) terephthalate, and adding an appropriate solvent or dispersion medium. It can be performed in a state of using a solution or dispersion. Molten bis (2-hydroxyethyl) terephthalate has a low viscosity and is easy to handle. For example, when isophthalic acid is used as a copolymerization component, the viscosity of a 1: 1 weight ratio mixture with bis (2-hydroxyethyl) terephthalate is about 0.03 Pa · s at 120 ° C. Bis (2-hydroxyethyl) terephthalate is compatible with other diol components because both ends are hydroxyl groups. Therefore, when an appropriate diol is mixed as a copolymerization component, the melting point of the mixed solution is lowered, and the handleability is further improved.
[0018]
The transesterification reaction between dimethyl terephthalate and ethylene glycol or the esterification reaction between terephthalic acid and ethylene glycol can be performed by a known method. For example, the transesterification reaction can be carried out at a final temperature of 190 to 250 ° C. and normal pressure, with the amount of ethylene glycol based on dimethyl terephthalate being 2.01 to 3.0 mole times. Further, the esterification reaction can be carried out at a final temperature of 260 to 265 ° C. and a pressure of 100 to 150 kPa, with the amount of ethylene glycol with respect to terephthalic acid being 1.02 to 1.1 mol times. At this time, ethylene glycol distilled from the bis (2-hydroxyethyl) terephthalate oligomerization reactor may be condensed and used as a part of the raw material for the transesterification or esterification reaction.
[0019]
The product of the transesterification reaction or esterification reaction is mixed with the oligomerization reaction product, and the mixture is supplied to a prepolymerization reactor to produce a prepolymer having a polymerization degree of 25-30. Next, the polycondensation reaction is performed by supplying the final polymerizer to obtain the target product, polyethylene terephthalate. The mixing ratio of the product of the transesterification reaction or esterification reaction and the oligomerization reaction product is arbitrary, but is 1: 9 to 9: 1 by weight, or 2: 8 to 8: 2. It is preferable. The prepolymerization reaction is preferably performed at a temperature of 270 to 290 ° C. and a pressure of 0.5 to 30 kPa. The polycondensation reaction is preferably performed at a final temperature of 280 to 300 ° C. (preferably 280 to 290 ° C.) and a final pressure of 5 to 100 Pa.
[0020]
In addition, a polymerization catalyst, a stabilizer or other additives can be added to the oligomerization reactor of bis (2-hydroxyethyl) terephthalate. Examples of the polymerization catalyst include antimony compounds such as antimony trioxide and antimony acetate, and germanium compounds such as germanium dioxide. Examples of the stabilizer include phosphorous compounds such as phosphoric acid, phosphorous acid, di (or tri) methyl esters, and di (or tri) phenyl esters thereof. For example, these may be dissolved in ethylene glycol and added in the form of a solution, or dispersed in ethylene glycol and added in the form of a dispersion. Moreover, you may use the raw material bis (2-hydroxyethyl) terephthalate as a dispersion medium. The amount of the polymerization catalyst used is, for example, preferably 80 to 200 ppm as a germanium element, more preferably 100 to 150 ppm, and 150 to 300 ppm as an antimony element, and more preferably 170 to 250 ppm. Moreover, it is preferable that the usage-amount of a phosphorus compound is 20-50 ppm as a phosphorus element, and also 25-40 ppm.
[0021]
In addition, matting agents such as titanium oxide, colorants such as dyes and pigments or other functionalizing agents such as silica, alumina, barium sulfate and ceramics may be added to the oligomerization reactor. For example, silica, alumina, barium sulfate or ceramic is kneaded at a temperature equal to or higher than the melting point of bis (2-hydroxyethyl) terephthalate and the bis (2-hydroxyethyl) terephthalate to obtain a kneaded product from which coarse particles are removed. Can be done in the state. In addition to the above-mentioned oligomerization reactor, these additives may be used in a dimethyl terephthalate transesterification reactor, a terephthalic acid esterification reactor, a pipe for transferring to a prepolymerization reactor, and a prepolymerization reactor. Any of them can be added. What is necessary is just to select an appropriate addition place according to the property of an additive. The amount of the additive is a conventionally known amount. For example, titanium oxide is in the range of 0.05 to 5.0% by weight, and silica, alumina, barium sulfate, and ceramic are each in the range of 0.1 to 5. It may be selected according to the purpose from the range of 0% by weight.
[0022]
【Example】
In order to describe the present invention more specifically, specific examples are given below. Needless to say, the present invention is not limited to this. The characteristics in the examples were measured by the following methods.
(1) degree of polymerization of the oligomer and amount 1) separation of the oligomer component
2) Identification by LC / MS LC / MS measurement was performed to identify the HPLC peak.
Measurement and identification were performed under the same conditions as described above using JEOL SX-102A type.
(2) Intrinsic viscosity of polymer 250 mg of a sample was dissolved in 25 ml of a mixed solution of phenol / tetrachloroethane (1/1) and measured at 30 ° C.
(3) Concentration of carboxyl group 0.3 g of a sample was dissolved in 30 ml of benzyl alcohol by heating and then cooled, 20 ml of chloroform was added, and titration with 0.01N-KOH was performed.
(4) Amount of diethylene glycol The amount of diethylene glycol was measured chromatographically using a solution obtained by methanolysis of 1 g of a sample, 30 ml of methanol and 2 mg of zinc acetate in a 100 ml Carius tube at 200 ° C.
(5) Esterification rate The acid value of the sample was measured, the residual amount of carboxyl groups was determined, and the esterification rate was calculated.
(6) Color of polymer (color)
After the sample polymer was dried and crystallized at 135 ° C. for 1 hour, Hunter values L, a, and b were measured with a color difference meter ZE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.
[0023]
Example 1
A slurry of ethylene glycol and terephthalic acid in a molar ratio of 1.06 is continuously charged into an esterification reactor at a flow rate of 300 kg / hour, and an esterification reaction is performed at a pressure of 150 kPa, a temperature of 262 ° C., and a residence time of 3.6 hours. It was. Next, in order to supply the product to the prepolymerization reactor, it was continuously extracted at a flow rate of 258 kg / hour through a pipe. At this time, when the extracted liquid was analyzed, the carboxyl group was 872.3 μeq / g, ethylene glycol was 0.16 wt%, diethylene glycol was 0.67 wt%, and the esterification rate was 91.3%.
[0024]
On the other hand, 165 kg of bis (2-hydroxyethyl) terephthalate and 5 kg of ethylene glycol solution of 2% by weight of antimony trioxide were charged into a 250 liter oligomerization reactor provided separately from the esterification reactor, pressure 13 kPa, temperature While ethylene glycol was distilled off at 265 ° C., oligomerization was carried out in a batch mode for 60 minutes. After introducing nitrogen and returning the pressure in the reactor to normal pressure, the ester is taken over 1 hour to mix the product with the esterification reaction product before being fed to the prepolymerization reactor. It supplied in the extraction piping of the chemical reactor. At this time, when the oligomerization product was analyzed, it was found that the carboxyl group was 82.8 μeq / g, ethylene glycol was 0.16 wt%, and diethylene glycol was 0.79 wt%.
[0025]
The esterification reaction product and the oligomerization reaction product were mixed with a 10-element static mixer provided in a pipe, and then supplied to the first prepolymerization reactor. Subsequently, it was supplied to the final polymerization vessel via the second prepolymerization reactor, and the produced polyethylene terephthalate was pelletized.
-Conditions for the first prepolymerization reaction: pressure 6.6 kPa, temperature 273 ° C, residence time 0.5 hours.
-Conditions for the second prepolymerization reaction: pressure 1.5 kPa, temperature 278 ° C., residence time 0.7 hours.
-Reaction conditions for final polymerization: pressure 53 Pa, temperature 285 ° C.
When the extracted liquid of the second prepolymerization reactor was analyzed, the intrinsic viscosity was 0.239 dl / g, the carboxyl group was 82.8 μeq / g, diethylene glycol was 0.811% by weight, and the esterification reaction rate was 99.20%. . The obtained polyethylene terephthalate has an intrinsic viscosity of 0.642 dl / g, a carboxyl group of 22.6 μeq / g, diethylene glycol of 0.865% by weight, a melting point of 260.9 ° C., and a chromaticity of L (brightness) = 90.2, a (redness) = − 2.1, b (yellowness) = − 4.7.
[0026]
Analysis of polyethylene terephthalate produced without adding the bis (2-hydroxyethyl) terephthalate oligomerization product revealed an intrinsic viscosity of 0.644 dl / g, carboxyl group of 21.8 μeq / g, diethylene glycol of 0.858% by weight, melting point. 260.8 ° C., chromaticity is L (brightness) = 90.2, a (redness) = − 2.2, b (yellowness) = − 4.7 by the Hunter method. There was no difference.
[0027]
The ethylene glycol distilled by oligomerization of bis (2-hydroxyethyl) terephthalate was analyzed to find water 0.49% by weight, diethylene glycol 0.23% by weight, oligomer 0.17% by weight, and the terephthalic acid A sufficiently usable value for the slurry was shown.
[0029]
【The invention's effect】
As described above, according to the method for producing polyethylene terephthalate of the present invention, the conventional transesterification product of dimethyl terephthalate and ethylene glycol or the esterification reaction product of terephthalic acid and ethylene glycol is converted into bis (2-hydroxy). By mixing and condensing an ethyl) terephthalate oligomer, polyethylene terephthalate having excellent physical properties can be produced. For example, by using bis (2-hydroxyethyl) terephthalate obtained by chemical recycling of used polyethylene terephthalate, recycling of used polyethylene terephthalate can be promoted.

Claims (5)

A mixture containing an oligomer produced by an oligomerization reaction of bis (2-hydroxyethyl) terephthalate and a transesterification product of dimethyl terephthalate and ethylene glycol or an esterification reaction product of terephthalic acid and ethylene glycol is used for a prepolymerization reaction. And a method for producing polyethylene terephthalate, which is further subjected to a polycondensation reaction to produce polyethylene terephthalate. The bis (2-hydroxyethyl) terephthalate contains 97% by weight or more of bis (2-hydroxyethyl) terephthalate, and (1) Na, Mg, Ca, Fe, Co, Zn, Ti, Sn, Sb, Ge _2. The method according to claim 1, wherein the total content of cations consisting of and P and (2) anions consisting of halogen, NO ₂ , NO ₃ , PO ₄ and SO ₄ is 15 ppm or less. At least one additive selected from the group consisting of a polymerization catalyst, a stabilizer and a copolymerization component together with bis (2-hydroxyethyl) terephthalate in a reactor for oligomerization of bis (2-hydroxyethyl) terephthalate Is mixed with bis (2-hydroxyethyl) terephthalate or ethylene glycol and added. The reactor for oligomerization of bis (2-hydroxyethyl) terephthalate is selected from the group consisting of titanium oxide, dyes, pigments, silica, alumina, barium sulfate and ceramics along with bis (2-hydroxyethyl) terephthalate The method according to claim 1, wherein at least one additive is mixed with bis (2-hydroxyethyl) terephthalate and added. The ethylene glycol distilled by the oligomerization reaction of bis (2-hydroxyethyl) terephthalate is used for the production of a transesterification product or an esterification reaction product used in the prepolymerization reaction. The method in any one of -4.