Patent GB-805855-A (GB)
Title: The preparation of polyethylene terephthalate
Inventor: GASSON EDWARD JAMES
IPC: C08L67/00
Filed: 1955-09-27
Abstract: Polyethylene terephthalate is produced from terephthalonitrile which has been prepared by contacting in the vapour phase a mixture of p-xylene, ammonia and molecular oxygen with a vanadium or molybdenum oxide containing catalyst at an elevated temperature.  The terephthalonitrile may be converted into polyethylene terephthalate in four different ways: (1) the terephthalonitrile is hydrolysed in the presence of acid or alkali and water, and the resulting terephthalic acid esterified with excess ethylene glycol to form a primary condensate which is then heated to form the polymer; (2) on hydrolysis of terephthalonitrile with water at an elevated temperature preferably in the presence of an alkaline catalyst diammonium terephthalate is formed (with or without terephthalamide and/or ammonium terephthalamate) which may then be esterified with excess ethylene glycol and the product further heated to form the polymer; (3) terephthalonitrile is treated with sulphuric or phosphoric acid at low temperatures and the complex so formed is mixed with water to produce terephthalamide which is then reacted with excess of ethylene glycol to form polyethylene terephthalate; (4) the sulphuric acid complex of terephthalonitrile may be heated with an aliphatic alcohol and the diester so formed converted by an ester interchange reaction, with ethylene glycol, to polyethylene terephthalate.  Alternatively a diester may be formed directly by heating the terephthalonitrile with an aliphatic alcohol and sulphuric acid.  Examples are given illustrating the various conditions of temperature and pressure, and the use of various catalysts, e.g. magnesium, sodium terephthalate, zinc borate and litharge.  Specifications 590,541, [Group XIII], 796,765, 796,766 and 803,172, [all in Group IV (b)], are referred to.ALSO:Terephthalonitrile is prepared by reacting p-xylene, ammonia and molecular oxygen in the vapour phase, in the presence of a catalyst of vanadium or molybdenum oxide, at elevated temperature. The catalyst may be supported on heat-treated activated alumina, which has been preferably heated to 1000 DEG  to 1500 DEG  C. for more than 3 hours, preferably 20 to 24 hours.  The vanadium oxide is preferably between 0.1 and 10 per cent by weight of the total catalyst and may be mixed with an inert diluting material such as brick, pumice, or carborundum.  The reaction is preferably carried out at a temperature of between 300 DEG  C. and 450 DEG  C. with a contact time of between 0.25 and 6 seconds, there being at least 5 per cent of oxygen in the mixture of reactants and at least 3 mols. of oxygen per mol. of hydrocarbon.  The ratio of ammonia to p-xylene is preferably between 1 1/2 and 2 times the theoretical ratio for the stoichiometric reaction and the concentration of p-xylene in the mixture of reactants about 1 1/2 per cent by volume. The hot gases formed during the reaction are cooled and the resulting solid terephthalonitrile may be purified by removing traces of p-tolunitrile by steam distillation.  The terephthalonitrile so formed may be converted into polyethylene terephthalate in several ways via intermediates, viz. (1) terephthalic acid, prepared by hydrolysing terephthalonitrile in the presence of an acid or alkali and water, or a mixture of water and an organic solvent; (2) terephthalamide prepared by treating the nitrile with sulphuric or phosphoric acid at low temperatures to form a complex and mixing the complex with water; (3) a diester of terephthalic acid prepared either by heating the terephthalonitrile sulphuric acid complex with the corresponding alcohol, or by direct esterification with an aliphatic alcohol having up to 6 carbon atoms, preferably ethanol or methanol; (4) diammonium terephthalate prepared by hydrolysis of the nitrile with water, preferably in the presence of an alkaline catalyst; (5) the glycol ester by heating any one of the aforementioned intermediates with ethylene glycol.  A catalyst, e.g. magnesium, sodium glycoxide, zinc borate or litharge, and an inert gas, e.g. nitrogen, may be present in reactions 3 and 5. Specifications 590,541, [Group XIII], 796,765, 796,766 and 803,172 are referred to.