Extrusion International 6-2023

44 Extrusion International 6/2023 RECYCLING Dechlorination of PVC in Mixed Plastics on the Planetary Roller Extruder (PRE) prior to the Pyrolysis Recycling Process In recent years, ENTEX has developed various recycling processes in cooperation with partner companies, institutes and universities, e.g. for waste tyre rubber devulcanisation, film edge trim recycling, as well as numerous depolymerisation and other plastics recycling processes. Based on the diverse possibilities of the individually configurable, modular design of the ENTEX extruder construction kit, complex recycling processes for plastics have recently been developed and are becoming increasingly important. M ore and more sustainable plastic processes are required to recycle and deal with the enormous amount of plastic waste. ENTEX has developed a de- chlorination process to remove the chlorine from mixed polymer plastics of PP, PE and PVC for example, and al- low those mixed plastics to be recycled by pyrolysis. Pre-Screening/Straining of the Plastic Mix Before the dechlorination process, all foreign sub- stances must first be separated from the plastic mixture so that only the polymers remain. For this purpose, the mixture is heated to a temperature of over 200 °C, melt- ed and filtered to remove impurities. The purified plas - tic melt is then injected into the PRE. Dechlorination Process - Temperature and Residence Time Control The design of the PRE allows for effective heat trans- fer and temperature control. In addition, the PRE offers the volume and residence time required to raise the temperature of the mixed plastic melt to >300 °C and break down the PVC. The volume, process surface area and residence time in combi- nation with a highly efficient vacuum degassing system remove any volatiles, includ- ing chlorine gas, down to the lowest ppm level. Required Process Volume / Residence Time The PRE is unique in its rotating planetary roller sys- tem, which ensures constant material mixing and move- ment and provides a very large surface area for the mix- ing and heat exchange process, which is up to ten times larger than, for example, conventional mixing units such as twin screw extruders. This makes the PRE ideally suited for reactive process conditions where residence time, mechanical energy input and temperatures need to be controlled within very tight tolerances. Degassing at the Highest Vacuum Level and Extraction of Gasses to the Lowest PPM Any released volatile substances can be efficiently evacuated from the process at different points in the extruder process section. In the PRE, process zones with a vacuum of less than 1 mbar can be generated to ef- ficiently degas the extrudate. In addition, odours and possible toxic gases are removed, thus making a valu- Plant scheme of a dechlorination process with the planetary roller extruder Mass Temperature Process Steps PRE-M3 Post consumer plastic mixture melt Vacuum Pump Dechlorination Heating Holding Temperature Die Head Reactor 350°C 210°C Dechlorination Process