chapter
Terephthalic Acid (TPA) & Dimethyl Terephthalate (DMT)
WithG Margaret Wells
Pages 7

Most fibre-grade dimethyl terephthalate (DMT) is manufactured by the Dynamit Nobel technology based on p-xylene using oxidation and esterification steps. Considerable effort has been made by numerous producers to upgrade the purity of the Terephthalic Acid (TPA) made by these routes to reach the standard demanded by fibre manufactures. Because of difficulties with the purification of TPA, esteri-fication procedures have been developed in an attempt to obtain fibre-grade DMT. In the presence of carbon dioxide and a catalyst, consisting of cadmium oxide or zinc oxide, the potassium salt of phthalic anhydride is disproportionated to DMT. In spite of the use of specialized techniques, most TPA is used as polymer-grade TPA or converted to DMT. The bottoms are redistilled and crude DMT is obtained overhead. Both TPA and DMT are low-risk toxic hazards to health. Dust is an irritant to eyes, skin and lungs and prolonged exposure should be avoided.