U.S. patent application number 09/793832 was filed with the patent office on 2001-08-23 for esterification process.
Invention is credited to Kurian, Joseph V., Liang, Yuanfeng, Putzig, Donald E..
Application Number | 20010016642 09/793832 |
Document ID | / |
Family ID | 23988979 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010016642 |
Kind Code |
A1 |
Kurian, Joseph V. ; et
al. |
August 23, 2001 |
Esterification process
Abstract
A process that can be used in an esterification and
polycondensation processes to produce a polyester such as, for
example, poly(trimethylene terephthalate) is disclosed. The process
comprises contacting an acid with 1,3-propanediol in the presence
of a catalyst comprising tin and titanium. A copolymer that
contains up to 20 mole percent of another acid and/or a second
alcohol is also disclosed. Further disclosed are a composition of,
or comprising, a bis(3-hydroxypropyl) terephthalate prepolymer or a
composition of, or comprising, a poly(trimethylene terephthalate)
polymer. The bis(3-hydroxypropyl) terephthalate prepolymer and
poly(trimethylene terephthalate) can each contain 10 to 100 ppm tin
and 10 to 200 ppm titanium relative to the terephthalic acid
content.
Inventors: |
Kurian, Joseph V.; (Newark,
DE) ; Liang, Yuanfeng; (Chadds Ford, PA) ;
Putzig, Donald E.; (Newark, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL DEPARTMENT - PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
23988979 |
Appl. No.: |
09/793832 |
Filed: |
February 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09793832 |
Feb 27, 2001 |
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09500340 |
Feb 8, 2000 |
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6255442 |
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Current U.S.
Class: |
528/308.6 ;
528/279; 528/283; 528/308 |
Current CPC
Class: |
C08G 63/16 20130101;
C08G 63/181 20130101; C08G 63/85 20130101 |
Class at
Publication: |
528/308.6 ;
528/279; 528/283; 528/308 |
International
Class: |
C08G 063/183 |
Claims
That which is claimed is:
1. A poly(trimethylene terephthalate) polymer composition (a)
comprising repeat units derived from terephthalic acid and
1,3-propanediol, (b) having a b value of less than about 10, and
(c) having an intrinsic viscosity (IV) in the range from about 0.74
to about 2.0, which poly(trimethylene terephthalate) polymer
composition does not contain a blue masking pigment.
2. The composition of claim 1 which composition does not contain
any masking pigment.
3. The composition of claim 1 wherein said b value is less than
about 8.
4. The composition of claim 1 wherein said b value is less than
about 6.
5. The composition of claim 1 wherein said b value is less than
about 5.
6. The composition of 1 further comprising repeat units derived
from a second acid, a second glycol, or both.
7. The composition of claim 1 wherein said b value is 4.06 or
less.
8. The composition of claim 1 wherein the L value is 75 or
higher.
9. The composition of claim 1 wherein said b value is
2.77-4.06.
10. The composition of claim 1 wherein the L value is 75-76.1.
11. The composition of claim 2 wherein said b value is less than
about 8.
12. The composition of claim 2 wherein said b value is less than
about 6 .
13. The composition of claim 2 wherein said b value is less than
about 5.
14. The composition of claim 2 wherein said b value is 4.06 or
less.
15. The composition of claim 2 wherein the L value is 75 or
higher.
16. The composition of claim 2 wherein said b value is
2.77-4.06.
17. The composition of claim 2 wherein the L value is 75-76.1.
18. The composition of claim 1 prepared by a process comprising
contactin, in the presence of a catalyst, an acid with
1,3-propanediol wherein said catalyst comprises tin and
titanium.
19. The composition of claim 2 prepared by a process comprising
contacting, in the presence of a catalyst, an acid with
1,3-propanediol wherein said catalyst comprises tin and
titanium.
20. The composition of claim 18 wherein the process is carried out
with a mole ratio of 1,3-propanediol to said acid is in the range
of from about 1.1:1 to about 2.2:1 and at a temperature in the
range of from about 155.degree. C. to about 250.degree. C., wherein
the tin is present in the amount between about 10 to 100 ppm based
on the weight of said acid and wherein the titanium is present in
the amount of 10 to 200 ppm based on the weight of said acid.
Description
PRIORITY
[0001] This application is a Divisional of application Ser. No.
09/500,340 filed on Feb. 8, 2000, which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to a process for producing a
prepolymer and polyester from 1,3-propanediol by direct
esterification in the presence of a catalyst comprising tin and
titanium.
BACKGROUND OF THE INVENTION
[0003] Polyethylene terephthalate (PET) and polybutylene
terephthalate (PBT), generally referred to as "polyalkylene
terephthalates", are common commercial polyesters. Recently,
poly(trimethylene terephthalate), (PTT), also called polypropylene
terephthalate, has achieved commercial importance because of its
elasticity, as measured by its elastic recovery and resilience.
Based on the numbers of carbon atoms in the glycol used, the above
PET, PBT and PTT are also referred to as 2GT, 4GT and 3GT,
respectively.
[0004] Polyalkylene terephthalates commonly are produced by one of
two routes: (1) by transesterification of a dialkyl terephthalate
diester, typically dimethyl terephthalate, with a glycol to form an
intermediate bis-glycolate terephthalate, followed by
polycondensation to form the polyalkylene terephthalate; or (2) by
direct esterification of terephthalic acid (TPA) with a glycol to
form a bis-glycolate terephthalate, followed by polycondensation to
form the polyalkylene terephthalate.
[0005] In producing polyalkylene terephthalates by direct
esterification, terephthalic acid and an alkylene glycol are
reacted in the presence of a catalyst to form a monomer and water.
The water is removed as formed during the reaction. Oligomers
having a degree of polymerization of about 4 or less can also be
formed. Generally, during an esterification a mixture of monomer
and oligomer is produced. This mixture, also referred to as a
prepolymer, can then be polycondensed or polymerized at higher
temperatures under reduced pressure in the presence of a
polycondensation catalyst to form a desired polyester resin that is
suitable for carpets, textiles, films and many other end-uses.
[0006] These reactions can be carried out in a batch or continuous
process. The same or different catalysts can be used for the
esterification and polycondensation steps.
[0007] Esterification catalysts known in the art include titanium,
tin and zirconium compounds. Organo titanium and organo zirconium
compounds are disclosed in U.S. Pat. No. 3,056,818 for use as
esterification catalysts. The combination of organo tin and organo
titanium compounds for the esterification of terephthalic acid and
1,4-butanediol is disclosed in U.S. Pat. No. 3,936,421. The use of
tin-titanium complexes as esterification catalysts for 2GT and 4GT
is disclosed in U.S. Pat. No. 4,018,708 and U.S. Pat. No.
4,020,010. U.S. Pat. No. 5,015,759 (DuPont) discloses a process for
faster direct esterification of a diacid to make 2GT or 4GT using
relatively high amounts of an organo titanium, organo tin or organo
zirconium catalyst. None of these references discloses or suggest
that any of these catalysts can be used to produce 3GT.
[0008] The use of 3GT is handicapped by various difficulties in its
preparation. Surprisingly, using direct analogs of the processes
developed for preparation of 2GT and 4GT do not necessarily give
3GT with satisfactory properties.
[0009] For example, relatively high temperature (about 290.degree.
C.) esterification is considered commercially acceptable for 2GT
made from TPA. However, esterification to produce 3GT under similar
process conditions appeared to result in the significant liberation
of undesirable by-products, including acrolein and allyl alcohol.
In addition, the intermediate 3GT prepolymer was found to be highly
discolored under these conditions, an indication of poor 3GT
polymer quality. Similar esterification difficulties in processes
for the production of 4GT prepolymer by direct esterification have
led to a preference for the transesterification route using
dimethylterephthalate instead of terephthalic acid. For 3GT,
because of the greater availability of terephthalic acid in many
countries, it is important to develop a low temperature
esterification process for the commercial production of good
quality 3GT prepolymer.
[0010] U.S. Pat. No. 4,611,049 discloses a process for producing
3GT or 4GT using a sulfonic acid promoter to increase the rate of
polymerization when using an organo titanium or organo tin
catalyst.
[0011] U.S. Pat. No. 5,340,909 discloses the use of an effective
catalytic amount of tin for the polycondensation step to make 3GT,
wherein about 100 to 650 ppm of tin based on the terephthalic acid
is given as the permissible range. To mask the resulting polymer
yellowness, a blue pigment may be added prior to the
polycondensation step. When the prepolymer is made by direct
esterification, a titanium catalyst (0-125 ppm) or a portion of the
above tin catalyst (0-650 ppm) may be used during this step. No
examples show the use or benefit of either titanium or tin
catalysts or both for direct esterification.
[0012] In the above processes for 3GT, too high an amount of
catalyst results in a color problem, while too low an amount
results in an unacceptably slow reaction. In particular, using a
high concentration of tin catalyst is inadvisable since it causes
discoloration and degradation of polymer as well as the formation
of large amounts of undesirable by-products. In addition, a high
amount of tin compounds remaining in the final polymer may be
undesirable in certain end-use applications. None of the above
references specifically disclose a combination of tin and titanium
catalysts for the direct esterification of terephthalic acid with
1,3-propylene glycol, nor is there any information to suggest that
there would be any advantage in using a combination of these two
catalysts for this process.
[0013] There is a need for an improved process for the direct
esterification of an acid such as, for example, terephthalic acid
with 1,3-propylene glycol. There is also a need to reduce the
reaction time for esterification, carry out the esterification at
relatively lower temperatures, reduce the concentration of tin in
the resulting polymer, and produce a product with improved color
without the need of a masking pigment.
SUMMARY OF THE INVENTION
[0014] In a first embodiment, the invention is directed to a
process comprising contacting an acid with 1,3-propanediol in the
presence of a catalyst comprising tin and titanium.
[0015] In a second embodiment, the invention is directed to a
composition of, or comprising, a bis(3-hydroxypropyl) terephthalate
prepolymer that can contain 10 to 100 ppm tin and 10 to 200 ppm
titanium relative to the terephthalic acid content.
[0016] In a third embodiment, the invention is directed to a
composition of, or comprising, a poly(trimethylene terephthalate)
polymer that can contain 10 to 100 ppm tin and 10 to 200 ppm
titanium relative to the terephthalic acid content.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The term "tin" and "titanium" used herein, unless otherwise
indicated, are interchangeable with "tin compound" or "titanium
compound".
[0018] A prepolymer such as, for example, 3GT prepolymer is
prepared by the catalytic esterification of terephthalic acid with
1,3-propanediol. The prepolymer can be then polymerized at a higher
temperature, using the same or additional catalysts, to make the
3GT polymer.
[0019] The process of the invention comprises contacting an acid,
preferably an organic diacid, with 1,3-propanediol in the presence
of a catalyst comprising tin and titanium. Any acids that can
produce an ester or polyester, when contacted with a glycol, can be
used.
[0020] The presently preferred organic diacid is an organic acid
having the formula of HO.sub.2CACO.sub.2H in which A is an alkylene
group, an arylene group, alkenylene group, or combinations of two
or more thereof. Each A has about 2 to about 30, preferably about 3
to about 25, more preferably about 4 to about 20, and most
preferably 4 to 15 carbon atoms per group. Examples of suitable
organic acids include, but are not limited to, terephthalic acid,
isophthalic acid, naphthalenedicarboxylic acid, succinic acid,
adipic acid, phthalic acid, glutaric acid, and combinations of two
or more thereof. The presently preferred organic diacid is
terephthalic acid or naphthalenedicarboxylic acid because the
polyesters such as, for example, 3GT, produced therefrom have a
wide range of industrial applications.
[0021] Any tin-containing compounds that can be used as an
esterificatin catalyst can be used. Generally, it can be an
inorganic tin compound or an organic tin compound. Examples of
suitable tin compounds include, but are not limited to,
n-butylstannoic acid, octylstannoic acid, dimethyltin oxide,
dibutyltin oxide, dioctyltin oxide, diphenyltin oxide,
tri-n-butyltin acetate, tri-n-butyltin chloride, tri-n-butyltin
fluoride, triethyltin chloride, triethyltin bromide, triethyltin
acetate, trimethyltin hydroxide, triphenyltin chloride,
triphenyltin bromide, triphenyltin acetate, or combinations of two
or more thereof. These tin compounds are believed commercially
available. For example, n-butylstannoic acid can be obtained from
the Witco Chemical Company.
[0022] According to the invention, the preferred titanium compounds
are organic titanium compounds. Titanium tetrahydrocarbyloxides,
also referred to as tetraalkyl titanates herein, are presently most
preferred organic titanium compounds because they are readily
available and effective. Examples of suitable titanium
tetrahydrocarbyloxide compounds include those expressed by the
general formula Ti(OR).sub.4 where each R is individually selected
from an alkyl or aryl radical containing from 1 to about 30,
preferably 2 to about 18, and most preferably 2 to 12 carbon atoms
per radical and each R can be the same or different. Titanium
tetrahydrocarbyloxides in which the hydrocarboxyl group contains
from 2 to about 12 carbon atoms per radical which is a linear or
branched alkyl radical are most preferred because they are
relatively inexpensive, more readily available, and effective in
forming the solution. Suitable titanium tetrahydrocarbyloxides
include, but are not limited to, titanium tetraethoxide, titanium
tetrapropoxide, titanium tetraisopropoxide, titanium
tetra-n-butoxide, titanium tetrahexoxide, titanium tetra
2-ethylhexoxide, titanium tetraoctoxide, and combinations of two or
more thereof.
[0023] The titanium tetrahydrocarbyloxides suitable for use in the
present invention can be produced by, for example, mixing titanium
tetrachloride and an alcohol in the presence of a base, such as
ammonia, to form the titanium tetracarbyloxide or tetraalkyl
titanate. The alcohol can be ethanol, n-propanol, isopropanol,
n-butanol, or isobutanol. Titanium tetrahydrocarbyloxides thus
produced can be recovered by first removing by-product ammonium
chloride by any means known to one skilled in the art such as
filtration followed by distilling the titanium
tetrahydrocarbyloxides from the reaction mixture. This process can
be carried out at a temperature in the range of from about 0 to
about 150.degree. C. Titanates having longer alkyl groups can also
be produced by transesterification of those having R groups up to
C.sub.4 with alcohols having more than 4 carbon atoms per
molecule.
[0024] Examples of commercially available organic titanium
compounds include, but are not limited to, TYZOR.RTM. TPT and
TYZOR.RTM. TBT (tetra isopropyl titanate and tetra n-butyl
titanate, respectively) available from E. I. du Pont de Nemours and
Company, Wilmington, Del., U.S.A.
[0025] The weight ratio of the tin compound to the titanium
compound can be any ratio so long as the ratio can catalyze the
esterification of an acid and 1,3-propanediol. Generally, the ratio
can be about 0.01:1 to about 100:1 and preferably about 0.1:1 to
about 10:1.
[0026] According to the invention, the invention process can also
comprise contacting an acid with 1,3 propanediol in the presence of
a second glycol. The amount of the second glycol incorporated into
the final polyester can be up to about 20 mole percent of the
polyester. The present invention process can also produce a
copolymer in which the majority of repeat units are derived from
terephthalic acid and 1,3-propanediol and up to 20 mole percent of
the repeat units are derived from another acid or the second glycol
or both.
[0027] The presently preferred second glycol has the formula of
R(OH).sub.n, an alkylene glycol of the formula
(HO).sub.nA(OH).sub.n, or combinations thereof in which R and A are
the same as those disclosed above and n is 1 to about 10,
preferably 1 to about 7, and most preferably 1 to 5. Examples of
suitable second glycols include, but are not limited to, ethylene
glycol, propylene glycol, isopropylene glycol, butylene glycol,
1-methyl propylene glycol, pentylene glycol, diethylene glycol,
triethylene glycol, and combinations of two or more thereof. The
presently most preferred second glycol is an alkylene glycol such
as ethylene glycol.
[0028] According to the invention, the esterification catalyst can
be present in any concentration in the esterification medium so
long as the amount can catalyze the esterification of an acid.
Generally, the weight of the catalyst can be in the range of about
1 to about 1,000 and preferably about 5 to about 500 mg of the
catalyst per kg of the acid.
[0029] The catalyst can be produced by any method known to one
skilled in the art. For example, it can be produced by separately
combining the tin compound or titanium compound with the acid or
1,3-propanediol in an esterification medium. It can also be
produced in situ in an esterification medium by combining the tin
compound or titanium compound with the acid, 1,3-propanediol, or
both. Preferably, it is produced by combining the tin compound or
titanium compound before the contacting with the acid or
1,3-propanediol in an esterification medium. In other words, it is
preferred that a premixed catalyst comprising, consisting
essentially of, or consisting of the tin compound and the titanium
compound be produced before being contacted with the acid or
1,3-propanediol.
[0030] More preferably, the tin and titanium catalysts are mixed in
an organic solvent before adding to the reaction mass. Any solvent
that can substantially dissolve or disperse the catalyst and does
not interfere with polymerization can be used. For convenience, the
organic solvent can be 1,3-propanediol.
[0031] Preferably, the amount of tin used as catalyst is between
about 10 and 100 ppm and the amount of titanium used as catalyst is
between about 10 and 200 ppm, each elemental amount based on the
weight of acid present in the esterification medium.
[0032] The molar ratio of 1,3-propanediol to the acid can be any
ratio so long as the esterification can take place. Presently it is
preferred that the ratio be in the range of about 0.1:1 to about
10:1, preferably about 0.5:1 to about 5:1, and most preferably
1.1:1 to about 2.2:1. The esterification can be carried out under
any condition known to one skilled in the art. The condition can
include a temperature from about 100.degree. C. to about
300.degree. C., preferably about 155.degree. C. to about
250.degree. C. The esterification can be carried out under any
pressure that can accommodate the temperature.
[0033] In the second embodiment, a composition of, or comprising, a
bis(3-hydroxypropyl) terephthalate prepolymer is provided. The
prepolymer can be produced by the process or other processes. The
composition can contain about 10 to 100 ppm tin and 0 to 200 ppm
titanium relative to the terephthalic acid content. The term "ppm"
used herein refers to mg of elemental tin or titanium per kg
terephthalic acid.
[0034] The prepolymer can be produced by either batch or continuous
processes. In a batch process, the terephthalic acid is contacted
with 1,3-propanediol in the presence of a catalyst. In a continuous
process, the terephthalic acid and 1,3-propanediol are combined
with a recirculating stream of prepolymer in the presence of a
catalyst. Variations of these processes can also be used, as will
be apparent to one skilled in the art. The reaction temperature can
range from about 100 to about 300.degree. C., and at a pressure
that can accommodate the temperature range. The preferred
temperature ranges from about 155 to 250.degree. C. It is also
preferred that 1,3-propanediol be present in a slight molar excess
compared to the terephthalic acid as disclosed above. Terephthalic
acid is commercially available from E. I. duPont de Nemours and
Company and 1,3-propanediol is commercially available from the
Degussa Corporation.
[0035] In the third embodiment, a composition of, or comprising, a
poly(trimethylene terephthalate) polymer is provided. The
poly(trimethylene terephthalate) polymer can have an intrinsic
viscosity (IV) in the range from about 0.3 to about 2.0 and a b
value in the range of from less than about 10, preferably less than
8, more preferably less than about 6, and most preferably less than
about 5.
[0036] The composition can be produced from the prepolymer
disclosed above and can contain 10 to 100 ppm tin and 10 to 200 ppm
titanium relative to the terephthalic acid content. The term "ppm"
used herein refers to mg of elemental tin or titanium per kg
terephthalic acid.
[0037] The composition can be produced by a polymerization process,
which is also known as polycondensation in which a prepolymer is
polycondensed to form a polyester such as, for example,
poly(trimethylene terephthalate) or 3GT, with the elimination of
alcohol, as is known in the art. Typically, the alcohol can be
removed by distillation under reduced pressure. The catalyst
disclosed above can be used in the polycondensation step alone or
with an additional catalyst. Polymerization can be continued until
the resulting polymer has the desired degree of polycondensation,
as measured by its IV. Intrinsic viscosity is determined by
measuring the flow time of a solution of known polymer
concentration and the flow time of the polymer solvent in a
capillary viscometer, as set forth in ASTM D2857.95
[0038] The color of the resulting polymer is measured in terms of
the L-value and b-value, using an instrument such as the SP-78
Spectrophotometer. The L-value shows brightness, with the greater
the numerical value showing higher (desirable) brightness and the
b-value shows the degree of yellowness, with a higher numerical
value showing a higher (undesirable) degree of yellowness.
[0039] The following examples further illustrate the invention and
are not to be construed to unduly limit the scope of the invention.
The comparative examples show the use of tin or titanium catalysts
without the other being present. These results are summarized and
compared with the examples using the inventive combinations of tin
and titanium catalysts in subsequent Table 1.
COMPARATIVE EXAMPLE 1
[0040] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using only n-butylstannoic
acid as the esterification catalyst to form bis(3-hydroxypropyl)
terephthalate.
[0041] A 250 ml flask equipped with a stirrer was charged with 66.5
g of terephthalic acid (TPA), 48.7 g of 1,3-propanediol and 35 mg
of n-butylstannoic acid (298 ppm tin based on TPA) for a molar
ratio of 1,3-propanediol:TPA of 1.6:1. The flask was then purged
with nitrogen and the contents of the flask were heated with
stirring. When the temperature reached about 210.degree. C., water
started to evolve. The temperature was held at 210.degree. C., and
it took 3 hours to reach a clear solution indicating the end of
esterification reaction.
COMPARATIVE EXAMPLE 2
[0042] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using n-butylstannoic acid
(149 ppm tin based on TPA) as the esterification catalyst. The
procedure of Comparative Example 1 was followed except that 17.4 mg
of n-butylstannoic acid was used as the esterification catalyst. It
took 4.5 hours to reach a clear solution.
[0043] Upon the completion of esterification, the resulting monomer
was polymerized in the same reaction vessel at a temperature of
250.degree. C. and a pressure of 0.2 mm Hg in presence of an
additional 62 ppm titanium based on TPA. The poly(trimethylene
terephthalate) resin color and intrinsic viscosity (IV) are given
in Table 1.
COMPARATIVE EXAMPLE 3
[0044] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using n-butylstannoic acid
(99 ppm of tin based on TPA) as the esterification catalyst. The
procedure of Comparative Example 1 was followed except that 11.6 mg
of n-butylstannoic acid was used as the esterification catalyst. It
took 5.5 hours at 210.degree. C. to reach a clear solution.
COMPARATIVE EXAMPLE 4
[0045] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using n-butylstannoic acid
(62 ppm of tin based on TPA) as the esterification catalyst. The
procedure of Comparative Example 1 was followed except that 7.2 mg
of n-butylstannoic acid was used as the esterification catalyst. It
took 9 hours at 210.degree. C. to reach a clear solution.
COMPARATIVE EXAMPLE 5
[0046] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol in the absence of a
catalyst. The procedure of Comparative Example 1 was followed
except that no catalyst was used. It took more than 16 hours at
210.degree. C. to reach a clear solution.
COMPARATIVE EXAMPLE 6
[0047] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using tetraisopropyl
titanate (62 ppm of Ti based on TPA) as the esterification
catalyst. The procedure of Comparative Example 1 was followed
except that 24.4 mg of tetraisopropyl titanate was used as the
esterification catalyst. It took 7.5 hours at 210.degree. C. to
reach a clear solution.
EXAMPLE 1
[0048] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using a combination of
n-butylstannoic acid (31 ppm of tin based on TPA) and
tetraisopropyl titanate (62 ppm of Ti based on TPA) as the
esterification catalyst. The procedure of Comparative Example 1 was
followed except that 3.6 mg of n-butylstannoic acid and 24.4 mg of
tetraisopropyl titanate were used as the esterification catalyst.
It took 6 hours 45 minutes at 210.degree. C. to reach a clear
solution indicating the end of the esterification reaction.
EXAMPLE 2
[0049] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using combination of
n-butylstannoic acid (99 ppm of tin based on TPA) and
tetraisopropyl titanate (62 ppm of Ti based on TPA) as the
esterification catalyst. The procedure of Comparative Example 1 was
followed except that 11.6 mg of n-butylstannoic acid and 24.4 mg of
tetraisopropyl titanate was added separately as the esterification
catalyst. It took 4 hours 15 minutes at 210.degree. C. to reach a
clear solution. Thereafter, the resulting monomer was polymerized
in the same reaction vessel at a temperature of 250.degree. C. and
a pressure of 0.2 mm Hg without any additional catalyst. The
poly(trimethylene terephthalate) resin color and IV are given in
Table 1.
EXAMPLE 3A
[0050] This example demonstrates the esterification reaction of
terephthalic acid with 1,3-propanediol using a pre-mixed solution
of n-butylstannoic acid (99 ppm of tin based on TPA) and
tetraisopropyl titanate (62 ppm of Ti based on TPA) as the
esterification catalyst. The procedure of Comparative Example 1 was
followed except that 11.6 mg of n-butylstannoic acid and 24.4 mg of
tetraisopropyl titanate were used as the esterification catalyst,
which were pre-mixed in 1,3-propanediol at room temperature. It
took 3 hours 10 minutes at 210.degree. C. to reach a clear
solution.
[0051] Upon the completion of esterification, the resulting
monomer, bis(3-hydroxypropyl)terephthalate, was polymerized in the
same vessel at a temperature of 250.degree. C. and a pressure of
0.2 mm Hg without additional catalyst. The poly(trimethylene
terephthalate) resin obtained had an IV of 0.78 dl/g and melting
point of 230.degree. C. (measured as the peak on the endotherm of
differential scanning calorimeter, DSC).
EXAMPLE 3B
[0052] The procedure of example 3A was repeated. It took 3 hours 15
minutes at 210.degree. C. to reach a clear solution. After
polymerization, the poly(trimethylene terephthalate) resin obtained
had an intrinsic viscosity of 0.89 dl/g.
[0053] Table 1 summarizes the results of the above examples. The
catalyst concentration used during the esterification reaction is
given in the table as the parts per million (ppm) relative to the
weight of TPA or as mg catalyst per kg TPA.
1TABLE 1 Direct Esterification Time and Polymer Ouality Ester-
Esterification ification Polymer Catalyst Time Viscosity Example
ppm (Sn/Ti) (hour) Polymer Color (IV) Comp. Ex. 1 298/0 3.0 Comp.
Ex. 2 149/0 4.5 L = 74.8; b = 4.2 0.74 Comp. Ex. 3 99/0 5.5 Comp.
Ex. 4 62/0 9 Comp. Ex. 5 0/0 16 Comp. Ex. 6 0/62 7.5 Example 1
31/62 6.75 Example 2 99/62 4.25 L = 75; b = 4.06 0.74 Ex. 3A 99/62
3.17 L = 76.1; b = 2.77 0.78 (premix) Ex. 3B 99/62 3.25 L = 76.1; b
= 2.98 0.89 (premix)
[0054] The results show that the tin content of the prepolymer of
the invention process (Example 1), in comparison to Comparative
Example 4, decreased by 50% while the reaction time is cut by 25%.
It demonstrated that the invention process increased the reaction
rate at lower tin content.
[0055] The results also show that the tin content of the prepolymer
(Example 2), in comparison to Comparative Example 2, decreased by a
third while the reaction rate and product color were also
improved.
[0056] The results further show that the invention process greatly
improved over the known process when the invention catalyst was
premixed. Example 3A and 3B, in comparison to Example 2, show that
premixing the tin and titanium catalysts had the shortest the
reaction time and produced a polymer having the highest L value,
lowest b value, and highest IV among those tested.
[0057] In summary, the invention catalyst, a combination of tin and
titanium catalysts, completes esterification faster than the
individual catalyst components thereby minimizing the time and
temperature required for esterification. The invention product is a
polyester such as 3GT of high quality having low tin concentration.
A high concentration of tin compounds causes discoloration and
degradation of polymer as well as the formation of large amounts of
by-products. Furthermore, the invention catalyst can be used for
both esterification and polycondensation thereby eliminating the
need for a separate catalyst during the polycondensation step.
* * * * *