1. Write description about how the PET is synthesized in industry and what’s the side
reactions, how to avoid these reactions and get the desired PET?
Solution:
Polyethylene terephthalate (PET) can be synthesized in two ways. The first method is a
direct reaction of diacid with diol. To produce PET, pure terephthalate acid (PTA) is
reacted with ethylene glycol (EG) as shown below;
This reaction is a typical Fisher type of esterification in which an acid is reacted with an
alcohol and follow the usual mechanism for that reaction. The fact that each molecule is
difunction produces a polymer by the reaction.
This is the polycondensation process of PTA and EG to form PEG
Fig. 1: Process flow for the direct esterification reaction in industry.
, The other synthesis of PET is an ester interchange of a diester and a diol. This is
transesterification reaction in which one ester is transformed into another.
The synthesis of PET by this method involves reaction of dimethylterephthalate (DMT)
with ethylene glycol (EG) as shown below;
150-200°C
Catalyst
150-200°C
270-280°C
Catalyst
The first industrial production for this type of synthesis was performed by Whinfield and
Dixon. As seen from Fig. 2, they used a transesterification of dimethylterephthalate
(DMT) and ethylene glycol (EG) in 1 : 2.4 ratio, distilling methanol out of the reaction
mixture as the synthesis progressed. Their polymerization was conducted at 270 – 280°C
in the presence of SbO3 catalyst. Later techniques employed in polymer industry use a
step growth polymerization of pure terephthalate acid (PTA) with excess of ethylene
glycol at 250°C and reaction pressure at 60psi. This formed a polymer of 1 to 6 repeating
units.
reactions, how to avoid these reactions and get the desired PET?
Solution:
Polyethylene terephthalate (PET) can be synthesized in two ways. The first method is a
direct reaction of diacid with diol. To produce PET, pure terephthalate acid (PTA) is
reacted with ethylene glycol (EG) as shown below;
This reaction is a typical Fisher type of esterification in which an acid is reacted with an
alcohol and follow the usual mechanism for that reaction. The fact that each molecule is
difunction produces a polymer by the reaction.
This is the polycondensation process of PTA and EG to form PEG
Fig. 1: Process flow for the direct esterification reaction in industry.
, The other synthesis of PET is an ester interchange of a diester and a diol. This is
transesterification reaction in which one ester is transformed into another.
The synthesis of PET by this method involves reaction of dimethylterephthalate (DMT)
with ethylene glycol (EG) as shown below;
150-200°C
Catalyst
150-200°C
270-280°C
Catalyst
The first industrial production for this type of synthesis was performed by Whinfield and
Dixon. As seen from Fig. 2, they used a transesterification of dimethylterephthalate
(DMT) and ethylene glycol (EG) in 1 : 2.4 ratio, distilling methanol out of the reaction
mixture as the synthesis progressed. Their polymerization was conducted at 270 – 280°C
in the presence of SbO3 catalyst. Later techniques employed in polymer industry use a
step growth polymerization of pure terephthalate acid (PTA) with excess of ethylene
glycol at 250°C and reaction pressure at 60psi. This formed a polymer of 1 to 6 repeating
units.
