Investigation of the characteristics of microwave-assisted co-pyrolysis of biomass and waste plastics based on orthogonal experimental methods: Thermal degradation, kinetics and product distribution

Abstract

This research explores the synergistic effects and distribution of liquid products during microwave-assisted co-pyrolysis (MACP) of eucalyptus wood (EW) and polypropylene (PP). Firstly, thermal degradation and kinetics, of co-pyrolysis of EW and PP were investigated. The minimum average activation energy was observed at a mixing ratio of 50 % EW to 50 % PP, measuring 187.98 kJ/mol (KAS) and 189.82 kJ/mol (OFW), respectively. The effects of pyrolysis temperature, material ratio and microwave absorbent amount on the MACP of EW and PP were investigated based on the Orthogonal Design of Experiments (OED) method. The yield of three-phase product and chemical composition of liquid product were analyzed. The results indicated that the MACP of EW and PP significantly enhanced both the yield and quality of bio-oil. Optimal oil yield was achieved through MACP of EW and PP at 550℃ with a ratio of 30 % EW, 70 % PP, and 120 wt% microwave absorbent (SiC). The content of aromatic hydrocarbons peaked at the material ratio of 50 % EW and 50 % PP (E5P5) (42.53 %), while the content of monocyclic aromatic hydrocarbons (MAHs) was 3.59 %. The peak content of MAHs occurred at 550 ℃, but further temperature increase resulted in the transformation of MAHs into polycyclic aromatic hydrocarbons (PAHs). To optimize the content of MAHs in pyrolysis oil, the optimal MACP conditions are 550 ℃, E5P5 and 120 wt%SiC. The results of this research can act as a significant reference and offer practical insights for the effective generation of hydrocarbon-rich bio-oil via the MACP process involving biomass and waste plastics.