The project began with a comprehensive study of plastic waste in Denmark, using local and foreign resources to prepare a report. The report is believed to be important for those interested in continuing similar work, especially in Denmark. The document was prepared as an ongoing project, with information being collected and compiled alongside experimental work.
From the experimental perspective, the project focused on performing a feasibility study on polyolefins' hydrothermal processing (HTP). Experimental campaigns were conducted to screen the behavior of Polyethylene (PE), Polypropylene (PP), and Polystyrene (PS) under hot-compressed water conditions. The results showed that the strong C-C bonds with SP3 configuration in the polymer backbone of PE and PP made their hydrothermal decomposition almost invisible below 400 °C. At the same time, even at higher temperatures, the pyrolytic condition would outweigh the outcome significantly. However, PS showed promising results due to the existence of the tertiary bonds that made the structure prone to fracture under HTP conditions. While the decomposition of PS was recorded at a lower temperature than its thermal degradation temperature, the composition of the final product was far from an efficient conversion, especially from a circularity viewpoint. Application of pyrolysis condition at around thermal degradation temperature of PS in the presence of appropriate catalyst resulted in promising reproduction of Styrene.
The second half of the project focused on the treatment of PVC under HTP conditions. Due to Chlorine's inclusion in its chemical structure, PVC caused serious problems upon decomposition by producing highly corrosive HCl and forming a considerable amount of char under pyrolytic conditions. In this phase, a developed catalytic HTP of PVC was successfully implemented to remove around 98% of the Cl from PVC plastic waste, a great step toward the production of Refuse Derived Fuels (RDFs) with maximum of 1% chlorine contamination. The study was expected to be continued by working on different techniques of purification and separation, especially those licensed as PureStep technology. The project's main results were supposed to be disseminated in a summer school on plastic recycling, which AAU ENERGY will run.
