Thermo-catalytic co-pyrolysis of biomass and high-density polyethylene for improving the yield and quality of pyrolysis liquid

The overall goal of this research was to study the effects of temperature and pine-to-HDPE ratios on the pyrolysis products. Catalytic co-pyrolysis of pine and HDPE was carried out in a double-column staged reactor, wherein the temperature was varied as 450 °C, 500 °C, and 550 °C for each pine/HDPE ratio of 0/100, 25/75, 50/50, 75/25, and 100/0. Thermal cracking of the feedstock is initiated at the first column, and the zeolitic-based ZSM-5 catalyst offered secondary cracking at a catalyst-to-feedstock ratio of 1:1 in the second column of the reactor. Catalytic pyrolysis of HDPE produced 31 wt% pyrolysis oil (40 MJ/kg calorific value) with a selectivity of above 90% toward gasoline-range hydrocarbons at 500 °C. Comparatively, pine offered 26.3% wt.% pyrolysis liquid yield with 7.9% dark pyrolysis oil (30 MJ/kg calorific value) that has a gasoline selectivity of 69.3%. Thus, the addition of HDPE increased the gasoline selectivity by increasing the hydrogen/carbon effective (H/C_eff) ratio. At pine/HDPE ratio of 25/75, the pyrolysis oil content was 22.5% at 500 °C, which is 3 times more than that of pine pyrolysis. The optimum yield and higher gasoline selectivity were observed at 500 °C for 0/100 and 25/75 pine to HDPE ratios.