Abstract: The invention concerns a method for producing terephthalate of alkaline metal and alkylene glycol from recuperated alkylene polyterephthalate. It comprises saponification of said alkylene terephthalates with an aqueous sodium solution, adding a sufficient volume of water to ensure solubilization of the entire alkaline metal terephthalate produced in the reaction medium liquid phase and crystallisation of the sodium terephthalate by concentration of said liquid phase. The resulting sodium terephthalate can be directly used for producing pure terephthalic acid usable for the renewed production of alkylene polyterephthalates to be used in the food industry.

Abstract: A method for recuperating from saponification products of alkaline polyterephthalate with soda where both terephthalate ions are in acid form and the sodium ions are in the form of soda is disclosed. In this method the sodium terephthalate solution resulting from dissolving the saponification products are subjected to a step of electrochemical pre-acidification to bring the pH to 4 to 7. Thereafter an electrochemical acidification step by electrolysis is undertaken to precipitate the terephthalic acid in the anode section and recuperate the soda in the cathode section which can be recycled.