Comparative Study on Pyrolysis Features of Woody Biomass and Waste Plastics by mean of Various Pyrolytic Systems

Abstract

In this study, in Part I, fast pyrolysis of pine wood sawdust was performed using 'screw type' and 'fluidized bed' pyrolyzer to investigate the effects of particle sizes on the mass balance and physicochemical properties of bio-oil. The particle size of pine wood sawdust was ranged from 1mm to 14mm, and the pyrolysis temperature was fixed at 500℃, the optimum temperature for bio-oil production. The results revealed that the type of pyrolyzer influenced the distribution of thermal degradation products (bio-oil, bio-char, and gas) from the woody biomass. The 'screw type' pyrolyzer was able to accept the feedstock of particle size ranged from 1mm to 14mm, while the 'fluidized bed' pyrolyzer could only accept the feedstock of particle size of 1mm and 2mm, but not 6mm and 14mm. The influence of feedstock particle size on the distribution of pyrolysis products in the 'screw type' pyrolyzer was not significant (bio-oil: 43.2% ~ 46.3%; biochar: 20.3% ~ 22.3%). However, the difference of pyrolysis product yields between two pyrolysis systems was significant. Within the same particle size, 'screw type' pyrolyzer produced less bio-oil and more gas compared with 'fluidized bed' pyrolyzer. Using GC/MS analysis, 25 chemical compounds were identified from the bio-oil. Part II, pine wood sawdust were catalytically pyrolyzed with polyethylene (PE) using analytical pyrolysis-GC/MS system to investigate the effect of plastic on improving the quality of pyrolysis products. The analytical pyrolysis was performed at 600℃, loading 3.0 mg of samples, and the pyrolytic vapor was directly injected into GC/MS to determine the chemical compounds of pyrolytic products. 35~50 chemical compounds were identified and classified into six groups: Monomeric Aromatic Hydrocarbon (MAH), Polycyclic Aromatic Hydrocarbon (PAH), Phenols, Furfurals, Alkenes, and Alkanes. The results showed that the co-pyrolysis of pine with PE significantly decreased the oxygen content in the pyrolytic products from 23.4% (pine only) to 0.3% (pine+PE/ZSM-5), which increased the HHV of pyrolytic products from 25.9 MJ/kg to 34.4 MJ/kg. It also revealed that the ratio of pine and PE did not heavily influence the concentration of petrochemicals (aromatic hydrocarbons + alkenes (C≤15) + alkanes (C≤13)). However, a higher plastic ratio led to a higher wax production, which would be a critical reason for poor condensation performance of bio-oil capture in condenser. Pine wood sawdust to PE ratio of 3:1 showed the best result of higher petrochemicals, and low wax formation.