Assessing the Technical Routes for Chemical Cycling of Waste Plastics to Light Olefins

Waste plastics have become the second biggest environmental concern following climate change. The method for chemical cycling of waste plastics into light olefins is proposed. Four potential technical routes, that is, plastics to light olefins via syngas through the Fischer–Tropsch process (PFTO), plastics to light olefins via syngas through the recently developed OX-ZEO process (PZTO), plastics to light olefins via methanol through the methanol-to-olefins process (PMTO), and plastics to light olefins via pyrolysis oil and gas through hydrocracking and steam cracking process (PPTO), were studied. The carbon footprint, energy efficiency, and economic performance were analyzed based on techno-economic evaluation and life cycle assessment. The results demonstrated that the overall carbon efficiency of the PFTO, PZTO, PMTO, and PPTO routes was about 26.61, 67.59, 95.49, and 47.81%, respectively. The PMTO route had the highest carbon efficiency of the four routes. The energy efficiency and CO2 emissions of PMTO were 55.60% and 0.55 t CO2/t olefin, respectively, better than the rest three routes with PFTO of 29.35% and 3.48 t CO2/t olefin, PZTO of 47.55% and 1.21 t CO2/t olefin, and PPTO of 47.21% and 0.69 t CO2/t olefin. Production costs decreased as the carbon efficiency increased. The product costs of the PFTO, PZTO, PMTO, and PPTO routes were about 6003.36, 5400.23, 4918.59, and 6763.13 Chinese Yuan (CNY)/t olefin, respectively, which were calculated according to the price system of raw materials and products. In summary, PMTO is the most promising route with superior performance in CO2 emissions, energy efficiency, and economics. As methanol-to-olefins (MTO) have already been commercialized, PMTO might provide a potential approach for large-scale cycling of waste plastics in the near future.