Improvement of Aromatics Selectivity from Catalytic Pyrolysis of Low-Density Polyethylene with Metal-Modified HZSM-5 in a CO₂ Atmosphere

Abstract

Catalytic pyrolysis has been emerging as a promising strategy to tackle solid pollution induced by waste plastics, whereas achieving high selectivity of targeted products like valuable light aromatics remains a huge challenge. In this work, a novel protocol that combing waste plastic conversion and greenhouse gas CO 2 utilization was proposed for the first time. Different metal (Fe, Ni, Co, Mn, Ag, and Cu)-modified HZSM-5 zeolites were fabricated and then used as catalysts for the catalytic pyrolysis of low-density polyethylene (LDPE) with CO 2 as the reaction atmosphere. The introduction of CO 2 enhanced the selectivity of aromatic hydrocarbons from LDPE catalytic pyrolysis in comparison with a N 2 atmosphere, and a high liquid yield of more than 70% containing aromatic hydrocarbons, alkanes, and olefins was obtained with CO 2 catalytic conversion to CO over a nickel-modified HZSM-5 catalyst. In addition, the total selectivity of aromatics was 56.82% with that of benzene, toluene, ethylbenzene, and xylene (BTEX) being 43.63% at 550 °C. Compared with untreated HZSM-5, the metal-modified HZSM-5 catalyst also enhanced anticoking performance during catalytic reactions with the assistance of active CO 2 molecules. Besides, the involved catalytic reaction mechanism was also interpreted. The current work may offer a fresh route to the chemical recycling of waste plastics with simultaneous green CO 2 reutilization, advancing the development of catalytic conversion of hydrogen-rich solid waste into value-added products.

Critical issues for the deployment of plastic waste pyrolysis

“…[55][56][57][58][59] Additionally, the introduction of a CO 2 atmosphere instead of N 2 in the LDPE catalytic pyrolysis over metal (Fe, Ni, Co, Mn, Ag, Cu)-modified mesoporous HZSM-5 increased meaningfully the selectivity towards aromatics. 60 In addition to zeolites, other materials showing weaker acidities have been also tested in plastic catalytic pyrolysis to increase the share of liquids. Thus, a number of clays have been explored.…”

“…Additionally, the introduction of a CO 2 atmosphere instead of N 2 in the LDPE catalytic pyrolysis over metal (Fe, Ni, Co, Mn, Ag, Cu)-modified mesoporous HZSM-5 increased meaningfully the selectivity towards aromatics. 60…”