Enhancing hydrocarbon production via ex-situ catalytic co-pyrolysis of biomass and high-density polyethylene: Study of synergistic effect and aromatics selectivity.

We conducted ex-situ catalytic fast co-pyrolysis (co-CFP) of corn stalk (CS) and high-density polyethylene (HDPE) over HZSM-5 catalyst to enhance the production of hydrocarbons. The effect of pyrolysis temperature and CS-to-HDPE mass ratio (CS/HDPE) on the yield of condensable volatile organic products (CVOPs) and the relative content of hydrocarbons were studied. The synergisms between CS and HDPE were determined based on the difference between the experimental and theoretical CVOP and hydrocarbons content. The results showed that the addition of HDPE significantly promotes the production of CVOPs, reaching the maximum value at 750 °C. In the presence of HZSM-5, the CVOP and hydrocarbons production, especially aromatics, were enhanced further, and 650 °C and 700 °C were the preferable pyrolysis temperature for desired products. Benzene, toluene, and xylenes were the predominant aromatics during the CFP process due to the good shape-selectivity of HZSM-5, contributing to the highest selectivity of C5-C11 compounds in C5+ hydrocarbons. CS/HDPE mass ratio of 1:1 was a critical point for enhancing aromatics yield. CS/HDPE < 1 was the recommended mass ratio for increasing the relative aromatic hydrocarbons content, which increases as the CS/HDPE mass ratio decreases. Meanwhile, we presented the potential reaction pathways between CS and HDPE to explain the synergistic effects during the co-CFP process.