Production of Polyethylene Terephthalate using a Nonmetallic Catalyst
Dr. Marsha Winston1, Jared Langson2, Angus Ferguson2, Dr. Robert Posey2
1Christ
Church Episcopal School , 2Furman University Department of Chemistry
Introduction
Results and Discussion
Polyethylene terephthalate (PET) is a condensation polymer of terephthalic acid (HOOC-C6H4-COOH) and
ethylene glycol (CH2OHCH2OH) that is used for fibers and films and has been made for decades using a
variety of metallic catalysts based on antimony, titanium, germanium, or tin (Figure 1). The catalyst most
commonly used is Sb2O3 because of performance and cost.
Run1 OrgCat, TMAH, TA, PC,
Slope2
*
ppm
ppm
g
g (Reaction
Rate)
Six PET syntheses were performed. A photograph of the product from Run 1 is shown in Figure 4.
2
1
1.5
O
1000
0
0
11
0.027
 Amps
of
Stirrer 1
O
TA
Table: Reactant concentrations of PET syntheses and properties of PET produced
EG
2
PET
750
20
0
11
The purpose of this study is to investigate the viability of producing PET using a novel organic catalyst and
to develop a working formulation to run a larger trial at a U.S. film manufacturer. The identity of the
catalyst is proprietary and is called ‘OrgCat’ herein. The PET must have properties that allow it to be
processed into stable film. In this study, PET produced from experimental trials has been evaluated for
appearance, elasticity, and presence of low molecular weight impurities such as PET oligomers and related
terephthalate esters.
Methods
100
Figure 4: PET strands and
pellets obtained from Run 1
150
200
 Time, minutes
An example of data used to monitor a PET synthesis reaction is shown in Figure 5. The amperage needed to
maintain the stirrer rate initially decreases slightly as the temperature increases but then increases significantly
as the polymerization progresses and PET molecular weight increases. The slope of the latter part of this curve
is proportional to the reaction rate.
A comparison of data from the latter part of the OrgCat catalyzed polymerization above to a similar Sb2O3
catalyzed polymerization from several months ago is shown in Figure 6 below. The graphs illustrate what is
seen in multiple PET syntheses - that OrgCat performs as a polymerization catalyst as Sb2O3 does.
Chemicals used in the experiments were BHET (bis-(hydroxyethyl) terephthalate), shown in Figure 2,
TA (terephthalic acid), OrgCat, a second proprietary chemical which is called PC herein, and buffer TMAH
(tetramethylammonium hydroxide). BHET as a starting material mimics latter stages of the terephthalic
acid and ethylene glycol reaction used in industrial operations.
Reaction time, reactor wall
and interior temperatures,
amps needed to maintain
the stirring rate, and
pressure are recorded. The
OrgCat and TMAH are
added early in the process.
PC is usually added at 11.5 amps more than the
lowest amps to increase
polymerization by reaction
with carboxylic acid end
groups
generated
by
polymerization of BHET.
The reaction is stopped
when the amps equal 2-2.5
more than the lowest amps
read during the reaction as
this
point
indicates
sufficiently high molecular
weight.
Figure 3: Small batch lab apparatus used for PET syntheses
At the end of the reaction, molten polymer is drawn in a cord shape from the bottom of the reactor and
immediately quenched in an ice bath.
Physical characteristics and elasticity of the PET are evaluated qualitatively. The percentage of oligomers
and low molecular weight substances in PET is measured by 24 hour xylene extraction. The xylene extract
is evaporated to dryness and the residue weighed.
(b) Sb Catalyst
 Amps of Stirrer
Slope: 0.027
1.5
1
0.014
2.0%
0.020
medium gold (2)
translucent (3)
dull (3)
Inelastic at 200
Elastic at 300
220
240
260
280
Time, minutes
300
5
6
900
1200
1000
10
10
20
5
104
52
0
0
11
2.2%
0.017
pale gold (1)
almost clear (1)
glossy (1)
Inelastic at 200
Elastic at 300
33
2.0%
medium gold (3) Inelastic at 200
somewhat clear (2) Elastic at 300
glossy (1)
33
2.1%
1763
0.025
0.029
pale gold (1)
almost clear (1)
glossy (1)
Inelastic at 500
Elastic at 600
---
1-3 stopped at Amps of stirrer at 2, Runs 4-6 stopped at Amps of stirrer at 2.5,
3Added in portions during reaction
data in polymerization with amps >0.5
 Runs 4 and 6 produce PET with an excellent appearance. The factors that produce acceptable appearance –
very low color, high clarity, and high glossiness – are not obvious, however.
 Elasticity of PET from all runs is too high. Based on simple manual examination, Run 1 is elastic at room
temperature and Runs 2-5 produce PET that becomes elastic just above room temperature. Run 6 becomes
elastic at 50-600C. High elasticity is attributed to the incorporation of diethylene glycol (DEG) in the polymer
chain. This occurs when EG reacts with available hydroxyl end groups during the polymerization or when
DEG formed by the dehydration of ethylene glycol reacts with carboxylic acid end groups. Run 6 PET
apparently has a lower DEG concentration. This linkage also disrupts the ability of the PET polymer chains to
crystallize. Crystallization is necessary in the film making process when PET is heated and drawn.
 Adding TMAH may slightly reduce the elasticity. TMAH buffers the system and is used in current PET
industrial processes to reduce DEG.
Slope:
0.023
Slope:
0.023
2
1
0
0.5
4
1000
2.0%
2Latter
3
2
3
1Runs
4
2.5
 Amps of Stirrer
Figure 2: BHET
300
Figure 5: Change in stirrer amps of PET synthesis (Run 1)
using BHET, OrgCat, and PC
(a) OrgCat Catalyst
About 1250 g of PET are made in each synthesis using the
established lab-scale batch apparatus shown in Figure 3. BHET
and/or TA are added to a sealed, insulated reactor vessel with a
stirrer. The temperature of the vessel is gradually raised to 2903000C using a mantle and the stirrer is set at 20 rpm. Pressure is
reduced to low pressures (0.03-0.3 mmHg) as the reaction proceeds.
250
pale gold (1)
Elastic at 200
somewhat clear (2)
somewhat glossy (2)
Xylene
Extractibles
Inelastic at 200
Elastic at 300
Figure 1: The PET polymerization reaction of terephthalic acid (TA) and ethylene glycol (EG)
0
Elasticity
at 0C
medium gold (2)
translucent (3)
dull (3)
0.5
Metal catalysis is a growing concern because of the possibility of negative environmental and health effects
from use during processing and from trace amounts remaining in polyester end products. Use of antimony
is banned in Europe in food packaging and regulatory issues will likely occur in the future in the rest of the
world. Consequently, it would be advantageous if toxic metal catalysts could be replaced with nontoxic
organic catalysts without the potential for negative effects.
Appearance
(Rank: 1-Best to
3-Poorest)
100
150
200
250
 Time, minutes
300
Figure 6: A comparison of PET syntheses using (a) OrgCat (Run 1) and (b) Sb2O3
Additional syntheses were performed in this study in order to select a formula to recommend as a reasonable
trial in a 30 kg reactor at an industrial film manufacturer. The Table summarizes reactant concentrations of each
run and properties of the PET produced. Appearance is evaluated for color, clarity, and glossiness using a
subjective 1-3 scale.
For proper processing and end use properties, PET should 1) be inelastic at room temperature and above so it
can be heated and drawn into films that are stable after cooling, 2) be as clear, colorless, and bright as possible
for end use appearance, and 3) contain a small percent of polyester oligomers and low molecular weight
impurities which impact both processing and end use.
It is unrealistic to draw definite conclusions from these six runs because of multiple variations in reactant and
catalyst concentrations and in reaction conditions. Differences occurred in the process including rate of heating
and timing of addition of some reactants and the catalyst. There are several observations, however, that can be
reported.
 In the range of catalyst concentration studied, as OrgCat concentration increases, the rate of polymerization
generally tends to increase.
 Increasing concentration of TMAH may slightly decrease the rate of polymerization.
 The addition of TA was not observed to perform as a catalyst early in the polymerization of BHET although the
polymerization is acid catalyzed.
 Oligomers and low molecular weight impurities (Xylene Extactibles) uniformly comprise a low percentage of
the lab synthesized PET. A sample of commercially produced PET was measured as 1.1 % Extractibles.
To further evaluate the samples, polymers from each run were drawn, that is they were warmed and stretched to
maximum length and allowed to cool. All can be drawn extensively but return to an unstretched state when
reheated. Interestingly, Runs 4, 5, and 6 are observed to crystallize when drawn as shown by the formation of a
white, opaque area and evolution of heat. This observation suggests these runs produced PET with lower DEG
and is a promising indication of the potential for process improvement.
The observed variations in properties show the potential of alterations in the process to affect PET properties.
These alterations include reactant, catalyst, and buffer concentrations and timing of addition, heating rate,
stopping point, and length of reaction.
Conclusions
The most important conclusion of this study is that OrgCat performs as a catalyst for PET polymerization.
The PET syntheses performed indicate it is possible to modify reactant and catalyst concentrations and reaction
conditions to improve polymer properties.
Exact conclusions from this study on optimum reaction parameters are not possible because of the multiple
variations in trial runs. More trials using the small batch process and varying conditions would provide more
information to assist in reaction optimization. More detailed characterization of the PET produced, especially
measurement of incorporated DEG, would be beneficial in this regard.
It is possible however to use this information to select formulas for larger trials in an industrial setting. The
industrial process which uses TA and EG as the reactants and has sophisticated process controls are the next
level of development.
With the demonstration of the ability of OrgCat to catalyze PET polymerization, future work includes detailed
analysis of the formulation variables to optimize PET quality and production and investigation of the catalysis
mechanism.