If Europe is to achieve its plastics recycling targets, chemical recycling and mechanical recycling must complement each other, researchers from the Joint Research Centre (JRC) of the European Commission and the University of Gent and Maastricht concluded in a new study.
The study uses a material flow analysis (MFA) at a European level to provide quantitative estimates of the contribution of chemical recycling technologies to plastic recycling. The chemical recycling technologies considered are pyrolysis coupled with distillation, and hydrotreatment; gasification, coupled with Fischer-Tropsch Synthesis; and depolymerization.
The 10 polymers considered in the study are linear low density polyethylene, high density PE, polypropylene, PET, polystyrene, expanded PS, PVC, ABS, polyurethane and nylon. These polymers are applied in different sectors with their specific use and end-of-life fate. The five sectors included are packaging, building and construction, automotive, electronic, and agriculture.
The scientists modeled a 2018 status quo scenario and compared it with five potential scenarios in 2030, one that only looks at improved waste collection, sorting, and mechanical recycling technologies, and four exploring developments of chemical recycling options. The MFA results are compared by calculating four circularity indicators namely end-of-life recycling rate, plastic-to-plastic rate, plastic- to-chemicals rate, and plastic-to-fuels rate.
Results show that the best scenario is one where mechanical recycling is improved and chemical recycling is developed as a complementary technology. In that optimal scenario, it is possible to achieve 80 percent plastic recycling rate by 2030, with mechanical recycling contributing 46 percent and chemical recycling 34 percent, 15 percent from plastic-to-plastic recycling and 19 percent from plastic-to-chemicals.
“These findings illustrate the importance of balancing the plastic waste streams into [mechanical recycling] and [chemical recycling] options to reach the highest circularity potential possible, i.e. the two technologies need to be complementary and not competitive,” the scientists said.
The study also shows that chemical recycling will be critical to meeting European recycling targets. In the packaging sector, the 55 percent recycling targets by 2030 stated by the Plastic Packaging Waste Directive (PPWD) cannot be achieved only by improving the current waste management treatments (i.e., collection, sorting, and mechanical recycling) as the estimated end-of-life recycling rate would only be 49 percent, according to the study. Chemical recycling and solvent-based recycling options can contribute to reach the recycling targets set by PPWD, as the end-of-life recycling rate is then expected to increase to 73 percent to 81 percent.
The academics also noted that the plastic-to-plastic rate of chemical recycling can be improved, at the cost of plastic-to-chemical and plastic-to-fuel rates, by applying other pyrolysis conditions such as adding catalysts, hydrocracking, among others. One study suggests that the yield of olefins from a mixed polyolefin waste can increase up to around 75 percent by introducing catalysts. The limited plastic-to-plastic yield of current, unrefined, pyrolysis processes is often the target of chemical recycling critics.
The scientists shared their findings in “How much can chemical recycling contribute to plastic waste recycling in Europe? An assessment using material flow analysis modeling,” recently published in Resources, Conservation & Recycling.