(416d) Density and Viscosity Data and Modeling for Liquid Bis(2-hydroxyethyl) Terephthalate (BHET) and Mixtures with Ethylene Glycol (EG)

Chemical recycling is an attractive alternative to address the global plastics accumulation problem. Glycolysis is a well-studied chemical recycling approach for polyethylene terephthalate (PET). It consists in reacting PET with ethylene glycol, typically at elevated temperatures, producing the monomer bis(2-hydroxyethyl) terephthalate (BHET). BHET can then be purified and used as feedstock in the production of fresh PET. BHET is a solid at ambient conditions with a melting temperature around 110 ^oC.

At reaction conditions, in depolymerization and in polymerization reactions, this substance is at temperatures above its melting point, in liquid state. However, there is very little information about the thermophysical properties of BHET in liquid state. Particularly, to our knowledge, densities and viscosities for liquid BHET were never reported in open literature. Knowledge about such properties is important for effective process design of either reaction. To fill in this gap, we have measured density and viscosity data for liquid BHET from 120 ^oC to 170 ^oC and 1 bar to 400 bar. A vibrating tube densimeter (Anton Paar DMA HPM) and an oscillating piston viscometer (Cambridge ViscoPro 2000) were used in the density and viscosity measurements, respectively.

PC-SAFT pure component parameters for BHET are identified correlating the experimental density data collected in this work along with literature vapor pressure data. Experimental mixture density data for BHET + EG is compared to PC-SAFT predictions. At last, the experimental viscosity data for pure BHET is correlated using entropy scaling and the model performance in the prediction and correlation of mixture viscosity data for BHET + EG is discussed.