The present invention is based upon the discovery that nontitanyl oxalates can enhance the catalytic functionality of titanyl
oxalate catalysts. This invention provides a novel catalytic composition containing a titanyl
oxalate catalyst and a metallic
oxalate catalyst
enhancer and optionally containing a metallic cocatalyst such as an
antimony based catalyst. A synergistic relationship has been discovered between titanyl oxalate catalyst and the catalyst
enhancer. A synergistic relationship has also been discovered between the titanyl oxalate catalyst, catalyst
enhancer and a metallic cocatalyst such as
antimony oxide or
antimony triacetate. Also provided is an improved process of producing
polyester by the polycondensation of
polyester forming reactants in the presence of a catalytically effective amount of a polycondensation catalyst, wherein the improvement comprises utilizing, as the polycondensation catalyst, the novel catalyst composition containing a titanyl oxalate such as
lithium titanyl oxalate and a catalyst enhancer such as a nontitanyl metallic oxalate like
lithium oxalate and optionally containing a
metallic catalyst such as
antimony oxide or antimony triacetate. The improved process produces an improved
polyester having lower
acetaldehyde numbers and good color. The titanyl oxalate / catalyst enhancer composition can be used as a polycondensation catalyst in combination with other catalysts to achieve synergistic catalytic activity. Preferred is a combination of
lithium or
potassium titanyl oxalate, Li2 or K2TiO(C2O4)2, lithium or
potassium oxalate, Li2 or K2(C2O4)2 with
antimony oxide or antimony triacetate or antimony trisglycoxide.