At Fraunhofer ICT in Pfinztal, Germany, a continuous extraction process using a co-rotating twin-screw extruder has been developed. This continuous lab-scale process (~ 3-7 kg/h) for the removal of phthalate-based plasticizers (DEHP) from soft PVC was installed successfully. For optimized extraction conditions as main solvent supercritical carbon dioxide (scCO2) and an organic co-solvent were used.
Continuous extraction process for removing plasticizers from PVC with scCO2 and co-solvent
The key technical challenge to realize a high-pressure extraction zone in continuous extrusion is to adjust the screw design, so that there are the two “melt-sealings” that can seal the high-pressure extraction zone from the melting zone upstream and the degassing zone downstream. The screw design for the continuous extraction process has been developed and successfully tested in a twin-screw extruder. With this setup, extraction conditions could be improved to reach temperatures as low as 100°C and a pressure of up to 150 bar in the extraction zone. To capture the plasticizer a phase separator was used to separate the scCO2 from the dissolved plasticizer. First extrusion trials show low extraction efficiency due to low extraction time in the extruder, which is focus of further optimization.