METHOD AND PLANT FOR THE RECOVERY OF TEREPHTHALIC ACID AND ETHYLENE GLYCOL FROM POLYETHYLENE TEREPHTHALATE WASTES

摘要

The subject of this invention is a method for utilisation of scrap polyethylene terephthalate (PET) packages as well as a plant to practise said method. The waste material is subjected to the disintegration and cleaning processes, and then its digestion follows which involves the use of urea or ammonia water at the volume which is in excess to the stoichiometric one, the process temperature of at least 200°C, and time of 30-120 minutes. The resulting purified solution of diammonium terephthalate is further processed by means of reduced-pressure distillation. The bottoms make the feed for the production of ethylene glycol (as the liquid product) and crystals of diammonium terephthalate which are further reacted with 50-96 % sulphuric acid; the volume of acid is selected to adjust pH of the reaction mixture at about 5. The reaction yields a suspension of crystalline terephthalic acid in the solution of ammonium sulphate. The crystals - after washing with demineralised water, filtration and drying operations - make the desired solid product. Crystallisation of the residual solution supplies solid ammonium sulphate. The plant to practise the method according to that invention comprises the following process units: scrap preparation unit, PET digestion unit, ethylene glycol distillation unit, terephthalic acid precipitation unit, and ammonium sulphate crystallisation unit.