In the batch process, a mixture of dimethyl terephthalate and the glycol (slightly over 2 molar proportions) is heated to 150-210°C in the presence of a catalyst, usually acetates of lithium, manganese, and zinc. The product of the ester exchange, the bis(2-hydroxyethyl terephthalate), is melt polycondensed at 270-280°C at pressures of 66-133 psi in the presence of a catalyst. In the
14 In the early 1970s nitrile resins were considered good candidates for packaging carbonated beverages. However, safety issues related to trace amounts of toxic acrylonitrile in the plastic bottles precluded their use in this application.
continuous esterification process a mixture (paste) of terephthalic acid and the glycol (1:1.6 molar ratio) is esterified, usually in two stages at a temperature of 245-250oC. Water is removed as formed and the reaction is carried to 98% completion. The product, mixed with an antimony oxide catalyst, is polymerized, again in a two-stage process at a temperature of 255-298°C.
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