Process for producing polyesters using titanium-containing catal

Details Process for producing polyesters using titanium-containing catal Process for producing polyesters using titanium-containing catal

1998-02-12

2000-01-11

Mosley-Boykin, Terressa

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

528271, 528272, 528280, C08G 6300

Patent

active

060137568

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a method of manufacturing polyethylene terephthalate and mixed polyesters from terephthalic acid and ethylene glycol and other multi-functional alcohols and multi-basic carboxylic acids, using titanium catalysts, cobalt compounds and phosphorus-containing compounds as inhibitors.
The industrial production of polyethylene terephthalate and its mixed polyesters is normally carried out in two stages. In the first stage the multi-basic carboxylic acids, e.g. terephthalic acid or their alkyl esters are converted with ethylene glycol or a mixture of various multi-functional alcohols to form a low-molecular precondensate which in a second stage is polycondensed to form high-molecular polyethylene terephthalate or a corresponding copolyester. In order to achieve industrially practical conversion times and polyesters with a high molecular weight and a good product quality, both stages of the polyester manufacture require catalytic acceleration. Esterification of the terephthalic acids with ethylene glycol is already catalysed by the protons released from the tertephthalic acid and can be accelerated by specific compounds or can be influenced in its progress, e.g. with regard to the formation of by-products such as diethylene glycol. In order to accelerate the re-esterification and polycondensation, special catalysts must be used. Numerous compounds have been proposed as re-esterification and polycondensation catalysts. Preferably used are metal compounds which are described for example in H. Ludewig "Polyesterfasern" (Akademie-Verlag Berlin 1975).
Catalysts for polyester manufacture however not only catalyse the build-up reaction but to a differing degree accelerate breakdown reactions, heat resistance, the formation of by-products, the colour and the processing behaviour of the end product. In order to improve the production procedure and the product qualities, therefore, catalysts and catalyst combinations co-ordinated with the respective purpose, and catalyst inhibitors and stabilisers are used. Salts of organic acids with bivalent metals (e.g. manganese, zinc, cobalt or calcium acetate) are preferably used as re-esterification catalysts, which in themselves also catalyse the polycondensation reaction. Due to their catalytic action on breakdown reactions of the PET, the metal catalysts must be rendered inactive before the start of polycondensation by conversion with specific catalysts inhibitors. Phosphorus-containing compounds, such as phosphorous acids or phosphoric acids and their esters, are mainly used as inhibitors. Antimony, germanium and titanium compounds are preferably used as polycondensate catalysts. Antimony compounds have become widely used in the manufacture of PET for various fields of application, as they catalyse the polycondensation reaction relatively well and provide little stimulus for breakdown reactions and the formation of by-products. Disadvantages in the use of antimony compounds reside in their toxicity and a grey coloration of the polycondensate which is always observed, due to elementary antimony. The toxicity of the antimony compounds, especially of the antimony trioxide, which is preferably used as a polycondensation catalyst, has a disadvantageous effect on the one hand in the manufacturing process when starting and handling the catalyst solutions, and on the other hand in processing, use and disposal of the end products, leading to environmental pollution, as the antimony is partly washed out by water and passes into the waste water, or pollutes the air when the polyesters are burned.
In electrical and electronic components of PET, which remain at high temperatures for long periods, antimony tends to migrate and form coatings on the surface, which can lead to contact problems.
The colour tone of germanium-containing polyesters is indeed brighter than that of products containing antimony, yet germanium favours the formation of by-products, particularly diethylene glycol, and the thermal oxidative breakdown is catalysed.
In the first stage of polyester man

REFERENCES:
patent: 5744571 (1998-04-01), Hilbert et al.
H. Ludewig--Polyesterfasern; Akademie-Verlag Berlin 1997; pp. 113-121.

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