Chemistry Reference
In-Depth Information
XYLENE DERIVATIVES
T
EREPHTHALIC
A
CID
AND
D
IMETHYL
T
EREPHTHALATE
Uses
Both terephthalic acid (TPA) and dimethyl terephthalate
(DMT) are used exclusively for the manufacture of
polyesters for textile fibers (e.g,. “Dacron”), films, soft-
drink bottles, and engineering resins for automotive
applications. The glycol used for most TPA-based
polyesters is ethylene glycol. The polyester is then known
as polyethylene terephthalate, or PET.
Manufacture
COOH
CH
3
COOCH
3
catalyst
CH
3
OH
+
O
2
(from air)
COOH
CH
3
COOCH
3
p
-xylene
terephthalate acid
dimethyl terephthalate
Suppliers
BP Amoco, DuPont, Eastman Chemical, KoSa.
The manufacture of
polyester
fibers and films requires high-purity starting
materials. Terephthalic acid is very difficult to purify because it cannot be
distilled and it is not soluble enough in any solvent for other types of
purification. The dimethyl ester of terephthalic acid (DMT) can be distilled
(although it is a high-melting solid) and so for many years the starting
material of choice to make polyester fibers was DMT. However, processes
were eventually developed that made very pure terephthalic acid directly so
that no purification was needed. Now, either starting material can be, and is,
used for making polyesters.
