Tandem catalytic pyrolysis of mixed plastic packaging wastes to produce BTEX over dual catalysts

Abstract

The ubiquitous challenges caused by the accumulation of mismanaged plastic solid wastes have seriously endangered ecological health. For enhancing the sustainable and environment-friendly conversion of mixed plastic packaging wastes into high-value benzene, toluene, ethylbenzene, and xylene (BTEX) while effectively reducing the coke deposition on catalysts, tandem catalytic pyrolysis of mixed packaging plastics over dual catalysts (MCM-41 and HZSM-5) was explored via a combination of in-situ catalysis and ex-situ catalysis in a two-stage fixed bed reactor. The selectivity of total and monocyclic aromatic hydrocarbons was nearly 100% and 85% with MCM-41 (500 °C) followed by HZSM-5 (550 °C), respectively. The BTEX production (245.33 mg/g) was considerably improved as compared to ex-situ catalysis of HZSM-5 (185.30 mg/g) and MCM-41/HZSM-5 (209.14 mg/g). Moreover, the total coke amount of tandem catalysis decreased to 14.25 mg/g than that of ex-situ catalysis of HZSM-5 (30.72 mg/g). The mechanisms analysis revealed that the pre-reforming effect of MCM-41 suppressed polycyclic aromatic hydrocarbons (PAHs) formation and coke deposition on the following HZSM-5 and meanwhile improved the utilization of internal acid sites for obtaining high-yield BTEX.