Role of catalyst type in the selective production of naphtha and diesel hydrocarbons via cross-linked polyethylene (PEX) pyrolysis

This research investigated the role of catalyst nature in selective pyrolysis of cross-linked polyethylene (PEX) into highly valuable hydrocarbons (HCs) of naphtha and diesel to address circular economy targets. Catalytic pyrolysis process can be practically engineered for direct conversion of PEX into naphtha and diesel HCs by selecting upgrading catalysts with suitable properties. Selection of suitable catalyst types is critical as it significantly affects the distribution and quality of pyrolysis products and can help to reduce the environmental impact of the process on an industrial scale. Physical and chemical structures of catalysts, determined by catalyst features such as pore size, acidity, and chemical composition, control the shape of chemical reactions and consequently the selectivity towards products. Hence, activated carbon (AC), activated biochar (ABC), Bentonite (BENT), and zeolites were employed in catalytic pyrolysis of PEX using a micro-pyrolyzer coupled with online detectors of MS and FID. Experimental results indicated that AC and BENT were more selective towards both naphtha and diesel HCs while ABC proceeded mainly towards diesel formation. AC and ABC have a large surface area allowing them to capture a larger quantity of molecules. Alternatively, BENT, consisting of different metal oxides, also facilitated the selective formation of naphtha and diesel although it had very low surface area. While comparing the results obtained using AC, ABC, and BENT (low-acidic catalysts) with those achieved using high-acidic zeolites with considerably high specific surface area, the role of moderate acidity in selective conversion of PEX into naphtha and diesel HCs was evident.