Abstract: High quality linear polyester resin is prepared by reacting in a first step or zone 2,6-naphthalene dicarboxylic acid with a molten prepolymer derived from a glycol and 2,6-naphthalene dicarboxylic acid to form a low molecular weight product of the first step or zone; reacting this resultant product with a glycol in at least two successive steps or zones of glycol addition to form prepolymer; and polymerizing at least a portion of the resulting prepolymer to form polyester resin which exhibits midpoint glass transition temperatures above about 123.degree. C. The resulting prepolymer is particularly suitable for reaction with the 2,6-naphthalene dicarboxylic acid in the first step or zone. Advantageously, at least a portion of the prepolymer is, therefore, returned to the first step or zone.

Abstract: A process is disclosed for preparing polyethylene terephthalate having a predetermined intrinsic viscosity which involves the direct esterification of terephthalic acid with ethylene glycol followed by the polycondensation of the esterification product using a polycondensation catalyst system containing cobalt, manganese-, and antimony-containing components.

Abstract: An improved method for producing purified terephthalic acid by catalytic hydrogenation is disclosed. Control of the reduction of colored compounds during the production of purified terephthalic acid is effected by modulating solution hydrogen concentration during hydrogenation.

Abstract: Fiber-grade quality terephthalic acid can be obtained by dissolving partially purified terephthalic acid: the product separated from catalyst components and impurities in acetic acid solvent portion of oxidation effluent, acetic acid washed and dried: either in deionized water or acetic acid at temperatures from 250.degree. C. and upward, contacting the solution and hydrogen gas with a hydrogenation catalyst preferably a platinum family metal disposed on an insoluble support followed by separation of the solution from catalyst, cooling the separated solution to precipitate terephthalic acid, recovering, washing and drying the precipitate. The use of deionized water in the purification route, with respect to the oxidative preparation of terephthalic acid, has the drawback of maintaining two distinctly different solvent systems and tolerating the rather limited water solubility of the p-toluic acid.