A structured catalyst of ZSM-5/SiC foam for chemical recycling of waste plastics via catalytic pyrolysis

Catalytic pyrolysis is an attractive approach to chemical recycling of waste plastics, but the feasibility of this technology is challenged by a lack of viable technical catalysts that could perform properly in a large-scale operation. This calls for the scaling up of the catalyst from powders into shaped catalyst bodies with both the necessary physical properties and minimal mass transport limitations. A structured catalyst of ZSM-5/SiC foam was developed in this study to address this issue. The activity and stability of 4 differently shaped ZSM-5 catalysts were evaluated in a continuous process of the catalytic pyrolysis of polyethylene. The structured catalyst exhibited a stable selectivity to gasoline-range aromatic hydrocarbons of above 22% for 6 h under catalysis temperature of 450 °C and WHSV of 40 h−1, outperforming conventionally shaped ZSM-5 catalysts by up to 37 times. The superior stability was attributed to the enhanced mass transport associated with (1) the short diffusion path of the zeolite coating and (2) the tortuous channel geometry of the foam structure. The influence of important factors on the catalytic performance was also investigated, including coating layer thickness, ZSM-5 silica-to-alumina ratio, catalysis temperature, space velocity, and catalyst regeneration. The structured catalyst demonstrated excellent stability in all conditions and great potential to adjust product yield and composition by manipulating these factors, making it a promising catalyst for large scale operation of catalytic pyrolysis of waste plastics.