Abstract:
A catalyst composition for use in a polycondensation reaction for making poly(ethylene terephthalate) from terephthalic acid comprising: (a) an antimony salt catalyst present in a range from about 10 to about 1,000 ppm; (b) a metal salt catalyst of at least one of cobalt, magnesium, zinc, manganese, calcium, and lead, present in a range from about 10 to about 500 ppm; and (c) an alkali metal acetate, present in a range from about 10 to about 500 ppm; all amounts are based on the metallic elements relative to the theoretical yield of the poly(ethylene terephthalate), by weight, to be made from the terephthalic acid. The catalyst composition was found to have increased the reaction rate in the production of poly(ethylene terephthalate), as well as improved the color of the produced product, by reducing the degree of yellowness in the final poly(ethylene terephthalate) product. Attenuation of the yellowish color indicates a reduction in the amount of undesired side reaction product.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a novel catalytic composition for the preparation of poly(ethylene terephthalate). More specifically, the present invention relates to a novel catalyst composition for accelerating the esterification and condensation polymerization rates during the preparation of poly(ethylene terephthalate) from terephthalic acid, while minimizing the production of side reaction products, such that the produced products exhibit attenuated yellowness. 
     BACKGROUND OF THE INVENTION 
     Poly(ethylene terephthalate), or PET, is one of the most important synthetic fibers as well as is one of the most important engineering plastics. As a synthetic fiber, it can be used separately as long and short fibers or as various types of industrial fibers; it can also be used jointly with cotton or silk fibers in making consumer clothing. As an engineering plastics, poly(ethylene terephthalate) has a wide variety of industrial applications, and can be used in making bottles as well as microwavable kitchen wares. Poly(ethylene terephthalate) also finds many important applications in the food and electronic packing industries. 
     Poly(ethylene terephthalate) is manufactured commercially by the so-called DMT (dimethyl terephthalate) or TPA (terephthalic acid) process. In the early stages of the development of poly(ethylene terephthalate), because of the inadequate purity of the terephthalic acid raw material, poly(ethylene terephthalate) was manufactured primarily from the DMT process. In the past decades, however, as the purity of terephthalic acid has substantially improved, the TPA process becomes the predominate process for the commercial production of poly(ethylene terephthalate). 
     In the conventional DMT process for making poly(ethylene terephthalate), dimethyl terephthalate (DMT) and ethylene glycol (EG) are used as the raw materials which are reacted at 220°˜260° C., using at least an acetate of manganese, calcium, or zinc as the catalyst to promote the esterification reaction, which forms an intermediate product bis(2-hydroxyethyl terephthalate) (BHET). The intermediate product, bis(2-hydroxybutyl terephthalate), is then subject to a high temperature (250°˜290° C.) and high vacuum (less than 1 torr) polymerization environment, in the presence of a diantimony trioxide (Sb 2  O 3 ) or antimony acetate (Sb(OAc 3 )) catalyst. After the completion of the reaction, the unreacted ethylene glycol is removed from the reaction product to obtain the poly(ethylene terephthalate) final product. 
     The TPA process has become the predominate process for the commercial production of poly(ethylene terephthalate). In the conventional TPA process, terephthalic acid (TPA) and ethylene glycol are used as the raw material which are reacted at 220°˜265° C. to effectuate an esterification reaction. The acidic terephthalic itself serves as the catalyst. After condensation (dehydroxylation) as a result of the esterification reaction, an intermediate product of bis(2-hydroxyethyl terephthalate) is formed. The intermediate product of bis(2-hydroxyethyl terephthalate) is similarly subject to a high temperature (250°˜290° C.) and high vacuum (less than 1 torr) polymerization, using diantimony trioxide or antimony acetate as the catalyst. After the reaction, the unreacted butylene glycol is removed from the reaction mixture to obtain the poly(butylene terephthalate) final product. 
     Currently, the commercial processes in making poly(ethylene terephthalate) also can be classified into two types: batch process and continuous process. In the batch process, the esterification and polymerization reactions are conducted in separate steps--the esterification is proceeded in an esterification vessel, and the intermediate reaction products from the esterification reaction are moved to a polymerization vessel, where the polymerization reaction is carried out. In the continuous process, typically five reaction vessels are used. This compares to the two reaction vessels used in the batch process. In the five reaction vessels used in the continuous process, esterification reaction is carried out in the first two reaction vessels, the third reaction vessel is used for pre-polymerization, and the polymerization reaction is conducted in the last two reaction vessels. 
     One of the problems that have been encountered in the production of poly(ethylene terephthalate) is the undesired production of side reaction products, which typically appear as having a yellowish color. This problem is more profound with the TPA process. It has been observed that the faster the reaction rate, the greater the amount of the side reaction products that are produced. The presence of the side reaction products also causes the poly(ethylene terephthalate) to be tainted with an undesired and unpleasant yellow color. 
     Great Britain Pat. No. 1,135,233 teaches a process for the production of fiber-forming polyesters, i.e., poly(ethylene terephthalate), from terephthalic acid in which acetates of manganese or cobalt, or diantimony trioxide is used as a catalyst, and triphenyl phosphate is added as a stabilizer. Japan Laid-Open Pat. App. JP 79-146,893 teaches a catalyst composition containing tetramethyl titanate, cobalt acetate and calcium acetate which improves the yellow color problem observed during the production of poly(ethylene terephthalate) from terephthalic acid. Japan Laid-Open Pat. App. JP 79-163,996 teaches a catalyst composition containing diantimony trioxide, dibutyl tin diacetate, magnesium acetate and calcium acetate which also improves the yellow color problem observed during the production of poly(ethylene terephthalate) from terephthalic acid. Japan Laid-Open Pat. App. JP 80-116,722 teaches a catalyst composition containing tetramethyl titanate, cobalt acetate and calcium acetate which reduces the yellow color problem observed during the production of poly(ethylene terephthalate) from terephthalic acid. Japan Laid-Open Pat. App. JP 80-120,623 teaches the use of a phosphate as stabilizer when a catalyst composition containing diantimony trioxide, cobalt acetate and calcium acetate during the production from terephthalic acid of poly(ethylene terephthalate), which exhibits improved wovability. 
     Eur. Pat. App. EP 399,742 discloses a catalyst system including, for the first stage, zinc and/or cobalt, and for the second stage, zinc, magnesium, manganese, and/or cobalt, and antimony. Eur. Pat. App. EP 399,799 discloses a direct esterification of terephthalic acid with ethylene glycol followed by the polycondensation of the ester product using a catalyst system containing cobalt, manganese, and antimony components; the prepared poly(ethylene terephthalate) having a predetermined intrinsic viscosity. 
     U.S. Pat. Nos. 5,008,230, 5,077,259, 5166,311, 5,153,164, and 5,162,488 teach a catalyst system for the production of poly(ethylene terephthalate) from terephthalic acid and ethylene glycol, wherein the catalyst containing antimony, cobalt, and/or zinc, and at least one of zinc, magnesium, manganese or calcium. In these patents, it is taught that, by using the disclosed catalyst system, the reaction rate from terephthalic acid to poly(ethylene terephthalate) can be increased relative to the conventional catalyst, which contains only antimony component (i.e., diantimony trioxide). None of these patents, however, discusses the yellowing problems and the production of side reaction products that are associated with the use of catalyst to accelerate the esterification/polymerization reaction. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to develop an improved catalyst composition for the preparation of poly(ethylene terephthalate). More specifically, the primary object of the present invention is to develop an improved catalyst composition, which satisfactorily accelerates the esterification and the condensation polymerization rates during the preparation of poly(ethylene terephthalate), while minimizing or eliminating the yellowish color as well as minimizing or eliminating the production of the side reaction products. Alternatively, the primary object of the present invention is to develop an improved process, which utilizes an improved catalyst composition, for accelerating the production rate of poly(ethylene terephthalate) from terephthalic acid, while minimizing or eliminating the yellowish color as well as minimizing or eliminating the production of the undesired side reaction products. 
     The improved catalyst composition disclosed in the present invention contains (1) about 10 to 1,000 ppm, by weight, of the theoretical value of poly(ethylene terephthalate) to be produced, of an antimony component; (2) about 10 to 500 ppm, by weight, of the theoretical value of poly(ethylene terephthalate) to be produced, of at least one of manganese, magnesium, zinc, cobalt, zinc, or lead component; and (3) about 10 to 500 ppm, by weight, of the theoretical value of poly(ethylene terephthalate) to be produced, of an alkali metal acetate. The improved catalyst composition disclosed in the present invention not only increases the reaction rate in the production of poly(ethylene terephthalate), it also improves the color of the produced product. The poly(ethylene terephthalate) produced using the catalyst composition disclosed in the present invention shows a slightly bluish color (low b-value or negative b-value); this is considered an improvement over the yellowish color when the conventional catalysts are used. Attenuation of the yellowish color indicates a reduction in the amount of undesired side reaction product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be described in detail with reference to the drawing showing the preferred embodiment of the present invention, wherein: 
     FIG. 1 is schematic diagram showing a preferred embodiment of the process disclosed in the present invention in making poly(ethylene terephthalate) from terephthalic acid and ethylene glycol. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention discloses an improved catalyst composition for accelerating the condensation polymerization rates during the preparation of poly(ethylene terephthalate), while minimizing or eliminating the yellowish color as well as minimizing or eliminating the production of the side reaction products. The improved catalyst composition disclosed in the present invention contains: (1) about 10 to 1,000 ppm of an antimony component; (2) about 10 to 500 ppm of at least one of manganese, magnesium, zinc, cobalt, zinc, or lead component; and (3) about 10 to 500 ppm of an alkali metal acetate. The amounts of the catalytic components are based on parts of the active element per one million parts, by weight, of the theoretical value of poly(ethylene terephthalate) to be produced. The improved catalyst composition disclosed in the present invention not only increases the reaction rate in the production of poly(ethylene terephthalate), it also improves the color of the produced product. The poly(ethylene terephthalate) produced using the catalyst composition disclosed in the present invention shows a reduction in the yellowness and a slightly bluish color (low b-value or negative b-value). Attenuation of the yellowish color indicates a reduction in the amount of undesired side reaction product. 
     The present invention will now be described more specifically with reference to the following examples. It is to be noted that the following descriptions of example including preferred embodiment of this invention are presented herein for purpose of illustration and description; it is not intended to be exhaustive or to limit the invention to the precise form disclosed. 
     Comparative Example 1 
     Terephthalic acid and ethylene glycol, in a molar ratio of 1:1.2, and a catalyst composition as shown in Table 1, were added to a reaction vessel. The catalyst composition (described as Sb/Co/Mn=300/30/88 in Table 1) contained 300 ppm diantimony trioxide, 30 ppm cobalt acetate, and 88 ppm manganese acetate. The content of each component in the catalyst composition was based on the metal element relative to the theoretical value of poly(ethylene terephthalate) to be produced. The reaction vessel was repeatedly (at least three times) pressurized by nitrogen to 3˜5 kg/cm 2 , then released to 0 kg/cm 2 , to purge air and oxygen. The thermal bath containing the reaction vessel was set at 290° C. It was considered the beginning time reaction when a stirrer inside the reaction vessel was set at 60 RPM to begin the esterification reaction, wherein the temperature of the fractional distillation column was set at 150° C. The reaction vessel was maintained at a nitrogen pressure of 3 kg/cm 2 . Reaction samples were repeatedly collected and analyzed. After the esterification reaction reached 80% completion, the nitrogen pressure in the reaction vessel was gradually released (in about three minutes). 
     Thereafter, the temperature of the thermal bath was raised to 330° C. A regular vacuum pump was used to pull vacuum from the reaction vessel so as to begin a pre-polymerization reaction. The vacuuming procedure was conducted in eight stages of 10, 20, 30, 40, 50, 60, 70, and 74 of the vacuum gauge readings, each stage took about five minutes, and the total vacuuming took about 40 minutes. Alter the completion of the pre-polymerization stage, a high-vacuum pump was connected to the reaction vessel to pull a high vacuum in the reaction vessel. The reaction vessel was then maintained at a high vacuum of 0.4˜0.5 torr to begin the polymerization reaction. After the voltage connected to the stirrer raised to a certain value, the polymerization reaction was stopped, and the content in the reaction vessel was removed. 
     The poly(ethylene terephthalate) prepared from the above procedure was analyzed for their color, and the results are summarized in Table 1. In Table 1, the L-value indicates the degree of whiteness, a plus 100 L-value indicates pure white and a negative 100 L-value indicates complete black. The b-value indicates the degree of yellowness, a small or negative b-value indicates less yellowness, or a bluish color. The measured L and b values from Comparative Example 1 are 78.4 and 3.3, respectively. 
     The poly(ethylene terephthalate) prepared from Comparative Example 1 was also measured for its intrinsic viscosity (I.V.) using a Cannon No. 150 viscometer at a temperature of 30°±0.1° C. In making the intrinsic viscosity measurement, the poly(ethylene terephthalate) was dissolved in a solvent containing phenol/tetrachloroethane in a ratio of 6/4 by weight. The measured intrinsic viscosity, which is summarized in Table 1, was 0.65 dl/g. 
     Example 1 
     The procedure in making poly(ethylene terephthalate) in Example 1 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Mn/Li =300/30/88/36 in Table 1) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), 88 ppm manganese (in manganese acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 1 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 1. The measured L and b values and the measured intrinsic viscosity from Example 1 are 75.0, -1.2, and 0.64 dl/g, respectively. 
     Example 2 
     The procedure in making poly(ethylene terephthalate) in Example 2 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Mn/Na=300/30/88/36 in Table 1) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), 88 ppm manganese (in manganese acetate), and 36 ppm sodium (in sodium acetate). 
     The poly(ethylene terephthalate) prepared from Example 2 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 1. The measured L and b values and the measured intrinsic viscosity from Example 2 are 83.9, 2.5, and 0.64 dl/g, respectively. 
     Example 3 
     The procedure in making poly(ethylene terephthalate) in Example 3 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Mn/K =300/30/88/36 in Table 1) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), 88 ppm manganese (in manganese acetate), and 36 ppm potassium (in potassium acetate). 
     The poly(ethylene terephthalate) prepared from Example 3 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 1. The measured L and b values and the measured intrinsic viscosity from Example 3 are 77.5, 1.9, and 0.64 dl/g, respectively. 
     The b-values in Table 1 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 1__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 1  Sb/Co/Mn =           43      0.65    78.4                               3.3  300/30/88Example 1  Sb/Co/Mn/Li =           48      0.64    75.0                               -1.2  300/30/88/36Example 2  Sb/Co/Mn/Na =           52      0.64    83.9                               2.5  300/30/88/36Example 3  Sb/Co/Mn/K =           43      0.64    77.5                               1.9  300/30/88/36__________________________________________________________________________ 
    
     Comparative Example 2 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 2 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Mn/Zn=300/88/43 in Table 2) contained 300 ppm antimony (in diantimony trioxide), 88 ppm manganese (in manganese acetate), and 43 ppm zinc (in zinc acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 2 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 2. The measured L and b values and the measured intrinsic viscosity from Comparative Example 2 are 86.5, 4.6, and 0.63 dl/g, respectively. 
     Example 4 
     The procedure in making poly(ethylene terephthalate) in Example 4 was identical to that described in Comparative Example 2, except that the catalyst composition (described as Sb/Mn/Zn/Li =300/88/43/36 in Table 2) contained 300 ppm antimony (in diantimony trioxide), 88 ppm manganese (in manganese acetate), 43 ppm zinc (in zinc acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 4 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 2. The measured L and b values and the measured intrinsic viscosity from Example 4 are 84.5, 3.0, and 0.61 dl/g, respectively. 
     The b-values in Table 2 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 2__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 2  Sb/Mn/Zn =           28      0.63    86.5                               4.6  300/88/43Example 4  Sb/Mn/Zn/Li =           33      0.61    84.5                               3.0  300/88/43/36__________________________________________________________________________ 
    
     Comparative Example 3 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 3 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Ca=300/30/36 in Table 3) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), and 36 ppm calcium (in calcium acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 3 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 3. The measured L and b values and the measured intrinsic viscosity from Comparative Example 3 are 80.5, 3.8, and 0.65 dl/g, respectively. 
     Example 5 
     The procedure in making poly(ethylene terephthalate) in Example 5 was identical to that described in Comparative Example 3, except that the catalyst composition (described as Sb/Co/Ca/Li =300/30/36/36 in Table 3) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), 36 ppm calcium (in calcium acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 5 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 3. The measured L and b values and the measured intrinsic viscosity from Example 5 are 75.0, -1.1, and 0.65 dl/g, respectively. 
     The b-values in Table 3 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 3__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 3  Sb/Co/Ca =           43      0.65    80.5                               3.8  300/25/36Example 5  Sb/Co/Ca/Li =           46      0.65    75.0                               -1.1  300/25/36/36__________________________________________________________________________ 
    
     Comparative Example 4 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 4 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Mg=300/25/36 in Table 4) contained 300 ppm antimony (in diantimony trioxide), 25 ppm cobalt (in cobalt acetate), and 36 ppm magnesium (in magnesium acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 4 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 4. The measured L and b values and the measured intrinsic viscosity from Comparative Example 4 are 84.9, 4.5, and 0.64 dl/g, respectively. 
     Example 6 
     The procedure in making poly(ethylene terephthalate) in Example 6 was identical to that described in Comparative Example 4, except that the catalyst composition (described as Sb/Co/Mg/Li =300/25/36/36 in Table 4) contained 300 ppm antimony (in diantimony trioxide), 25 ppm cobalt (in cobalt acetate), 36 ppm magnesium (in magnesium acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 6 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 4. The measured L and b values and the measured intrinsic viscosity from Example 6 are 79.6, 3.8, and 0.64 dl/g, respectively. 
     Example 7 
     The procedure in making poly(ethylene terephthalate) in Example 7 was identical to that described in Comparative Example 4, except that the catalyst composition (described as Sb/Co/Mg/K =300/25/36/36 in Table 4) contained 300 ppm antimony (in diantimony trioxide), 25 ppm cobalt (in cobalt acetate), 36 ppm magnesium (in magnesium acetate), and 36 ppm potassium (in potassium acetate). 
     The poly(ethylene terephthalate) prepared from Example 7 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 4. The measured L and b values and the measured intrinsic viscosity from Example 7 are 81.6, 1.4, and 0.65 dl/g, respectively. 
     The b-values in Table 4 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 4__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 4  Sb/Co/Mg =           35      0.65    84.9                               4.5  300/25/36Example 6  Sb/Co/Mg/Li =           46      0.64    79.6                               3.8  300/25/36/36Example 7  Sb/Co/Mg/K =           33      0.65    81.6                               1.4  300/25/36/36__________________________________________________________________________ 
    
     Comparative Example 5 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 5 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Mg/Mn=300/36/88 in Table 5) contained 300 ppm antimony (in diantimony trioxide), 36 ppm magnesium (in magnesium acetate), and 88 ppm manganese (in manganese acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 5 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 5. The measured L and b values and the measured intrinsic viscosity from Comparative Example 5 are 78.7, 4.4, and 0.63 dl/g, respectively. 
     Example 8 
     The procedure in making poly(ethylene terephthalate) in Example 8 was identical to that described in Comparative Example 5, except that the catalyst composition (described as Sb/Mg/Mn/Li =300/36/88/36 in Table 5) contained 300 ppm antimony (in diantimony trioxide), 36 ppm magnesium (in magnesium acetate), 88 ppm manganese (in manganese acetate), and 36 ppm potassium (in potassium acetate). 
     The poly(ethylene terephthalate) prepared from Example 8 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 5. The measured L and b values and the measured intrinsic viscosity from Example 8 are 81.4, 4.0, and 0.624 dl/g, respectively. 
     The b-values in Table 5 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 5__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 5  Sb/Mg/Mn =           32      0.63    78.7                               4.6  300/36/88Example 8  Sb/Mg/Mn/Li =           33      0.624   81.4                               4.0  300/36/88/36__________________________________________________________________________ 
    
     Comparative Example 6 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 6 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Mn/Ca=300/88/36 in Table 6) contained 300 ppm antimony (in diantimony trioxide), 89 ppm manganese (in manganese acetate), and 36 ppm calcium (in calcium acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 6 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 6. The measured L and b values and the measured intrinsic viscosity from Comparative Example 6 are 75.6, 4.9, and 0.62 dl/g, respectively. 
     Example 9 
     The procedure in making poly(ethylene terephthalate) in Example 9 was identical to that described in Comparative Example 6, except that the catalyst composition (described as Sb/Mn/Ca/Li =300/88/36/36 in Table 6) contained 300 ppm antimony (in diantimony trioxide), 89 ppm manganese (in manganese acetate), 36 ppm calcium (in calcium acetate) and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 9 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 6. The measured L and b values and the measured intrinsic viscosity from Example 9 are 83.6, 2.9, and 0.62 dl/g, respectively. 
     The b-values in Table 6 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 6__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 6  Sb/Mn/Ca =           37      0.62    75.6                               4.9  300/88/36Example 9  Sb/Mn/Ca/Li =           28      0.62    83.6                               2.9  300/88/36/36__________________________________________________________________________ 
    
     Comparative Example 7 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 7 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Ca/Zn=300/36/43 in Table 7) contained 300 ppm antimony (in diantimony trioxide), 36 ppm calcium (in calcium acetate), and 43 ppm zinc (in zinc acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 7 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 7. The measured L and b values and the measured intrinsic viscosity from Comparative Example 7 are 86.5, 5.7, and 0.61 dl/g, respectively. 
     Example 10 
     The procedure in making poly(ethylene terephthalate) in Example 10 was identical to that described in Comparative Example 7, except that the catalyst composition (described as Sb/Ca/Zn/Li =300/36/43/36 in Table 7) contained 300 ppm antimony (in diantimony trioxide), 36 ppm calcium (in calcium acetate), 43 ppm zinc (in zinc acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 10 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 7. The measured L and b values and the measured intrinsic viscosity from Example 10 are 82.5, 4.7, and 0.65 dl/g, respectively. 
     The b-values in Table 7 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 7__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 7  Sb/Ca/Zn =           26      0.61    86.5                               5.7  300/36/43Example 10  Sb/Ca/Zn/Li =           36      0.65    82.5                               3.7  300/36/43/36__________________________________________________________________________ 
    
     Comparative Example 8 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 8 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Ca/Mg=300/36/36 in Table 8) contained 300 ppm antimony (in diantimony trioxide), 36 ppm calcium (in calcium acetate), and 36 ppm magnesium (in magnesium acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 8 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 8. The measured L and b values and the measured intrinsic viscosity from Comparative Example 8 are 82.8, 4.8, and 0.64 dl/g, respectively. 
     Example 11 
     The procedure in making poly(ethylene terephthalate) in Example 11 was identical to that described in Comparative Example 8, except that the catalyst composition (described as Sb/Ca/Mg/Li =300/36/36/36 in Table 8) contained 300 ppm antimony (in diantimony trioxide), 36 ppm calcium (in calcium acetate), 36 ppm magnesium (in magnesium acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 11 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 8. The measured L and b values and the measured intrinsic viscosity from Example 11 are 81.2, 2.8, and 0.66 dl/g, respectively. 
     The b-values in Table 8 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 8__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 8  Sb/Ca/Mg =           32      0.64    82.8                               4.8  300/36/36Example 11  Sb/Ca/Mg/Li =           30      0.66    81.2                               2.8  300/36/36/36__________________________________________________________________________ 
    
     Comparative Example 9 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 9 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Mn=300/32/89 in Table 9) contained 300 ppm antimony (in diantimony trioxide), 32 ppm cobalt (in cobalt acetate), and 89 ppm manganese (in manganese acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 9 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 9. The measured L and b values and the measured intrinsic viscosity from Comparative Example 9 are 79.8, 4.5, and 0.60 dl/g, respectively. 
     Example 12 
     The procedure in making poly(ethylene terephthalate) in Example 12 was identical to that described in Comparative Example 9, except that the catalyst composition (described as Sb/Co/Mn/Li =300/32/89/36 in Table 9) contained 300 ppm antimony (in diantimony trioxide), 32 ppm cobalt (in cobalt acetate), 89 ppm manganese (in manganese acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 12 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 9. The measured L and b values and the measured intrinsic viscosity from Example 12 are 73.9, 1.2, and 0.59 dl/g, respectively. 
     Example 13 
     The procedure in making poly(ethylene terephthalate) in Example 13 was identical to that described in Comparative Example 9, except that the catalyst composition (described as Sb/Co/Mn/Na=300/32/89/36 in Table 9) contained 300 ppm antimony (in diantimony trioxide), 32 ppm cobalt (in cobalt acetate), 89 ppm manganese (in manganese acetate), and 36 ppm sodium (in sodium acetate). 
     The poly(ethylene terephthalate) prepared from Example 13 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 9. The measured L and b values and the measured intrinsic viscosity from Example 13 are 79.9, 1.7, and 0.61 dl/g, respectively. 
     The b-values in Table 9 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 9__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 9  Sb/Co/Mn =           25      0.60    79.8                               4.5  300/32/89Example 12  Sb/Co/Mn/Li =           32      0.59    73.9                               1.2  300/32/89/36Example 13  Sb/Co/Mn/Na =           31      0.61    79.9                               1.7  300/32/89/36__________________________________________________________________________ 
    
     Comparative Example 10 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 10 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Ca=300/36 in Table 10) contained 300 ppm antimony (in diantimony trioxide) and 36 ppm calcium (in calcium acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 10 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 10. The measured L and b values and the measured intrinsic viscosity from Comparative Example 10 are 85.8, 6.7, and 0.66 dl/g, respectively. 
     Example 14 
     The procedure in making poly(ethylene terephthalate) in Example 14 was identical to that described in Comparative Example 10, except that the catalyst composition (described as Sb/Co/Li =300/36/36 in Table 10) contained 300 ppm antimony (in diantimony trioxide) 36 ppm calcium (in calcium acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 14 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 10. The measured L and b values and the measured intrinsic viscosity from Example 14 are 84.1, 4.8, and 0.65 dl/g, respectively. 
     The b-values in Table 10 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 10__________________________________________________________________________  Catalyst Polymerization                   Intrinsic                           L-  b-  Composition           Time (minutes)                   Viscosity (dl/g)                           value                               value__________________________________________________________________________Comp. Ex. 10  Sb/Ca = 300/36           48      0.66    85.8                               6.7Example 14  Sb/Ca/Li =           50      0.65    84.1                               4.8  300/36/36__________________________________________________________________________ 
    
     Comparative Example 11 
     The procedure in making poly(ethylene terephthalate) in Comparative Example 11 was identical to that described in Comparative Example 1, except that the catalyst composition (described as Sb/Co/Mn/Pb=300/30/88/20 in Table 11) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), 88 ppm manganese (in manganese acetate), and 20 ppm lead (in lead acetate). 
     The poly(ethylene terephthalate) prepared from Comparative Example 11 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 11. The measured L and b values and the measured intrinsic viscosity from Comparative Example 11 are 83.3, 1.3, and 0.65 dl/g, respectively. 
     Example 15 
     The procedure in making poly(ethylene terephthalate) in Example 15 was identical to that described in Comparative Example 11, except that the catalyst composition (described as Sb/Co/Mn/Pb/Li=300/30/88/20/36 in Table 11) contained 300 ppm antimony (in diantimony trioxide), 30 ppm cobalt (in cobalt acetate), 80 ppm manganese (in manganese acetate), 20 ppm lead (in lead acetate), and 36 ppm lithium (in lithium acetate). 
     The poly(ethylene terephthalate) prepared from Example 15 was analyzed for their color and intrinsic viscosity, and the results are summarized in Table 11. The measured L and b values and the measured intrinsic viscosity from Example 15 are 80.2, 0.9, and 0.64 dl/g, respectively. 
     The b-values in Table 11 show that the addition of the alkali metal acetate of the present invention to the catalyst composition improves the color of the poly(ethylene terephthalate) product. 
     
                                           TABLE 11__________________________________________________________________________  Catalyst   Polymerization                     Intrinsic                             L-  b-  Composition             Time (minutes)                     Viscosity (dl/g)                             value                                 value__________________________________________________________________________Comp. Ex. 11  Sb/Co/Mn/Pb =             40      0.65    83.3                                 1.3  300/30/88/20Example 15  Sb/Co/Mn/Pb/Li =             39      0.64    80.2                                 0.9  300/30/88/20/36__________________________________________________________________________ 
    
     In all the examples and comparative examples described above, the addition of the alkali metal acetate to a antimony based catalyst composition always resulted in the reduction of b-value, indicating a reduction of the yellowness of the poly(ethylene terephthalate) product and a reduction of undesired side reaction product. These comparisons clearly illustrate the advantageous properties of the catalyst composition of the present invention. 
     The foregoing description of the preferred embodiments of this invention has been presented for purposes of illustration and description. Obvious modifications or variations are possible in light of the above teaching. The embodiments were chosen and described to provide the best illustration of the principles of this invention and its practical application to thereby enable those skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.