Abid Farooq, Latif Ullah
The catalytic pyrolysis of low-density polyethylene (LDPE) waste into high value hydrocarbons offers a sustainable route for circular polymer economy implementation. This study applies multivariate statistical analysis and mechanistic evaluation to compare the selectivity of H3PO4, steam, and ZnCl2 treated oat husk biochar catalysts in steering LDPE pyrolysis towards olefin rich or paraffin rich products. Gas chromatograph equipped mass spectrometer (GC-MS) data was analyzed using principal component analysis (PCA) to identify compositional clustering and catalyst specific signatures. PCA revealed that PC1 accounts for 69.0% of variance and PC1+PC2 for 93.7%, confirming distinct treatment separation in reduced chemical space. Olefinic compounds cluster toward positive PC1 (steam region: 56.3% olefins, 67% enhancement), while saturated alkanes dominate negative PC1 (H3PO4 region: 26.0% olefins, 23% suppression), with ZnCl2 positioned intermediately (50.7% olefins, 50% enhancement). Olefin/paraffin ratios highlighted steam as most selective (O/P = 1.29), ZnCl2 as balanced (1.03), and H3PO4 as paraffin promoting (0.35). ZnCl2 treated biochar combined moderate selectivity and diversity (21 compounds), whereas steam maximized olefin formation and H3PO4 increased compositional complexity. Mechanistically, steam catalysis proceeded via surface mediated dehydrogenation, ZnCl2 promoted Lewis acid driven C-C bond rearrangement and H3PO4 facilitated Brønsted acid catalyzed condensation. These findings established quantitative design criteria for catalyst selection and demonstrated viable pathways for LDPE valorization through selective pyrolysis.