Clay-based catalyst for pyrolysis of polypropylene waste into fuels

Abstract

This study utilized montmorillonite clay as an eco-friendly, natural, widely accessible, and cost-effective catalyst in the pyrolysis of polypropylene (PP) waste. XRF analysis revealed the presence of different oxides such as SiO₂, Al₂O₃, CaO, K₂O, and Fe₂O₃. FTIR analysis further confirmed the presence of the oxides. XRD analysis revealed an increase in crystallinity of montmorillonite after calcination, while TGA analysis of calcined montmorillonite revealed lower weight loss compared to the raw sample. The non-catalytic pyrolysis yielded 31.25 % oil, whereas the catalytic process produced 34.45 % oil. Fractionation of the pyrolysis oil yielded different quantities; at 40–100 °C, the non-catalytic process produces 117 mL (23.4 %) of distillate, while the catalysis yields 61 mL (12.2 %), at 140–200 °C, the catalytic process produced 239 mL (47.8 %) and 126 mL (25.2 %) for the non-catalytic process, at 240–280 °C, catalytic process yields 91 mL (18.2 %), nearly double the 62 mL (12.4 %) obtained from the non-catalytic process. The specific gravity was found to range from 0.7922 to 0.8772 and 0.8202 to 0.8722, for non-catalytic and catalytic processes, while API of 47.11 (${\text{PP}}_{100}$), 39.16(${\text{PP}}_{200}$), $29.79\left({\text{PP}}_{280}\right)$ were recorded for non-catalytic fractionated oil, against 40.55 (${\text{PPM}}_{100}$), 41.01(${\text{PPM}}_{200}$), and 30.73 (${\text{PPM}}_{280}$) for catalyzed enhance oil, and the kinematic viscosity of fractionated oil derived from WPPs falls within the range of 0.57–1.71 cSt and 0.61 to 1.83 cSt for non-catalytic and catalytic processes. As revealed by gas chromatography-mass spectrometry results, hydrocarbons with number of carbons within the range of C₅–C₁₂, are the most abundant gasoline fraction, followed by diesel (C₁₃–C₂₄), with fuel oil (>C₂₄). The study has demonstrated the potential of the eco-friendly montmorillonite clay catalyst to enhance the production of valuable fuel products from waste polypropylene. This approach not only addresses critical environmental challenges but also aligns with global efforts to transition towards more sustainable and circular economy.