Pyrolysis of Real-world Waste Plastics in a Thermo-catalytic Two-stages Fixed-bed Reactor

Abstract

Real-world waste plastics obtained from its final disposal on the municipal landfill of San Diego de la Unión (Guanajuato, México) were processed in a thermo-catalytic two-stage fixed-bed reactor using a commercial zeolite H-ZSM-5 catalyst. Single plastic low-density polyethylene (LDPE) was also processed and used as a reference. The physic composition of the real-SDU sample was PETE: HDPE: PVC: LDPE: PP: PS: OTHER= 14: 6: 2: 38: 24: 4:12. For non-catalytic pyrolysis, a liquid yield product was 85 and 65 wt.-% for single LDPE and the real-SDU sample, respectively. Real-SDU sample produced 3-fold more solid than LDPE (16 vs. 5 wt.-%). The proximate and ultimate analyses showed that solid residues would be composed mainly of ashes due to source contamination. The thermo-catalytic pyrolysis, using H-ZSM-5 as the catalyst, significantly increased the fraction of the light-gas products at the liquid fraction cost, compared to thermal pyrolysis. The solid yield was independent of the non-catalytic or thermo-catalytic reactions, so changes in yield distribution were related to the hydrocarbon's catalytic reformation during the thermal-pyrolysis first-stage reactor. In both LDPE and the real-SDU cases, the liquid yield decreased around 34 wt.-% concerning the non-catalytic reaction. Still, it improved the oil fraction's quality. The H-ZSM-5 catalyst promotes the cracking of heavier hydrocarbons produced in the thermal-pyrolysis stage reactor into lighter hydrocarbons, influencing the liquid products' chemical composition by 2-fold increasing the fuel range fraction (C₇-C₁₆). This process could be considered a technological option for the remediation of urban plastic wastes by producing hydrocarbons in the fuel range such as gasoline, jet, and diesel fuels.