DEMETO's depolymerisation concept and modelling approach

The DEMETO project aims to boost circular economy in polyethylene terephthalate (PET) and polyester production. The project was launched to develop an innovative, sustainable chemical recycling process for PET and polyester, based on microwave assisted hydrolysis for the recovery of virgin-grade monomers, namely Ethylene Glycol (MEG) and Terephthalic Acid (TA). Towards this goal, effluents from a pilot scale microwave reactor, where PET waste was hydrolysed, were treated through a series of purification steps to produce purified MEG and TA. The purification efficiency of the different steps was determined experimentally and, where was necessary, alternative purification methods were tested. Emphasis was also given on the elimination of chemical wastes.

Moreover and in order to have the possibility to scale-up the process (currently tested at pilot scale) in an optimum way, simulation tools (that will allow the examination of alternative process configurations and the overall process optimisation) needed to be developed. These simulation tools require a minimum set of data concerning the thermodynamic properties of the materials examined, which did not exist and had to be produced within this project.

Thermodynamic properties of the different purification streams as well as thermodynamic data describing the Solid-Liquid Equilibrium and the Vapor-Liquid Equilibrium of mixtures of the pure compounds of terephthalic acid, ethylene glycol, H2O, NaOH were also determined through time consuming and tedious experimental and theoretical work. Then the E-UNIQUAC model was updated with the above determined properties and thermodynamic data and was adapted for the simulation of the examined PET recycling process in ASPEN Plus environment.

See the figures below:

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