Preparation of aromatic hydrocarbons from fast pyrolysis of waste medical mask catalyzed by modified HZSM-5

Abstract

The safe and efficient utilization of waste medical masks has attracted worldwide attention. Fast pyrolysis with the catalysis of zeolites can provide a promising route for the production of value-added aromatic hydrocarbons from waste medical masks. Herein, HZSM-5 was employed and modified by metal loading (Ga, Mo) and alkali treatment for the ex-situ catalytic pyrolysis of mask filters. The non-catalytic pyrolysis of mask filters only led to a low yield of aromatics. When HZSM-5 catalysts were employed, the liquid long-chain olefins, cycloalkanes, and alcohols, as well as gaseous light hydrocarbons were mainly converted into aromatics. According to the micro-scale pyrolysis experiments, the alkali treatment as well as Ga and Mo loading further promoted the generation of aromatics, with aromatic yields of 52.8 wt%, 54.1 wt%, and 46.3 wt%, respectively. For alkali treatment, the NaOH concentration of 0.3 mol/L was most effective for aromatic production, due to the moderate change in the pore size. For metal loading, Ga loading had better performance than Mo loading because the former resulted in a higher specific surface area while the two modified catalysts possessed similar acid activity. When the two modification methods were combined, the yields of aromatics increased to 56.7 wt% and 60.3 wt% under the catalysis of Mo/Na-HZSM-5 and Ga/Na-HZSM-5. Based on the lab-scale experiments, the aromatic yield could reach 63.0 wt% with the catalysis of Ga/Na-HZSM-5, accompanied by a high selectivity of 87.6% for monocyclic aromatic hydrocarbons (MAHs). In summary, both MAHs and polycyclic aromatic hydrocarbons (PAHs) were promoted with these catalyst modification methods by expanding the mesopore size and adjusting acid site distribution, with greater promotion on the formation of MAHs.