Enhancing Hydrocarbon Production through Synergistic Effect Between Biomass and Plastics during Catalytic Co-Pyrolysis

Enhancing Hydrocarbon Production through Synergistic Effect between Biomass and Plastics during Catalytic Co-pyrolysis

Yuan Xue^a, Xianglan Bai^a

                                                  ^a Department of Mechanical Engineering, Iowa State University

Producing hydrocarbon fuels from biomass could help to relieve energy crisis and global warming caused by burning fossil fuels. While catalytic pyrolysis is a cost effective conversion technology, the yields of hydrocarbons obtained from biomass are usually low due to high oxygen content and hydrogen deficient nature of biomass. Waste plastics, on the other hand, represent abandoned energy source and are often rich in hydrogen and low in oxygen content. Thus co-processing biomass and waste plastics is not only good for sustainable energy and environmental protection, but also improves feedstock quality. In this study, catalytic co-pyrolysis of biomass and plastics was conducted using a tandem micropyrolyzer equipped with an ex-situ catalytic bed. Catalysts include HZSM-5, MoO₃ and the mixture of HZSM-5 and MoO₃, respectively. Mass balance was reported and pyrolysis vapors, light gases, catalytic coke and pyrolysis char were analyzed in detail to determine synergistic effects between biomass and plastics. It was found that co-converting biomass and plastics significantly improves both aromatic and aliphatic hydrocarbon yields by synergistic effects. Combination of MoO₃ and HZSM-5 resulted in the strongest synergistic effect during ex-situ catalytic pyrolysis. The synergistic effect was contributed by multiple factors, such as Diels-Alder reaction among biomass and plastic derivatives, contribution of plastic-derivatives to hydrocarbon pool, enhanced free radical depolymerization, as well as hydrogen transfer from plastics to biomass during thermal depolymerization.