High value olefins from polypropylene by in situ catalytic pyrolysis

The development of low-cost, renewable catalysts for catalyzing the pyrolysis of waste plastics to enable selective upgrading and recycling remains a major challenge. This study reports a novel biochar-loaded calcium-based catalyst that demonstrates excellent olefin selectivity and catalytic efficiency in situ pyrolysis of polypropylene, outperforming traditional catalysts in catalytic performance. The reaction was performed using an in-house developed carbon-based calcium catalyst, which was characterized and examined using a variety of analytical test methods. The effects of catalyst calcium metal loading, feedstock/catalyst ratio and reaction temperature on pyrolysis oil yield and olefin content were investigated. The results showed that olefins and cycloalkanes were the main components of pyrolysis oil in the catalytic pyrolysis experiments, with carbon number distribution between C₁₃ and C₂₅. Under optimal conditions (480 °C, 25 % Ca loading, feedstock/catalyst ratio of 1:0.2), a maximum pyrolysis oil yield of 93.75 % (0.91 g/g_pp) was achieved, with an olefin content of 58.87 % (0.55 g/g_pp). The high dispersion of Ca²⁺ species on the porous biochar support was found to synergistically promote C–C bond cleavage while suppressing coke formation via pore confinement and radical stabilization mechanisms. This work offers a promising strategy for the sustainable production of high-quality oils from plastic waste.