Catalytic cracking of polystyrene pyrolysis oil: Effect of Nb₂O₅ and NiO/Nb₂O₅ catalyst on the liquid product composition

The catalytic cracking of polystyrene pyrolysis oil was investigated over a Nb₂O₅ and a NiO/Nb₂O₅ catalyst in a fixed bed reactor. First, the pyrolysis of two different polystyrene feedstock (polystyrene foam and polystyrene pellet) was carried out in a semi-batch reactor, and the resulting polystyrene pellets pyrolysis oil was selected for catalytic cracking reaction because of its high liquid yield (85%). Catalytic cracking experiments were then performed at different temperatures (350-500 °C) using Nb₂O₅ or NiO/Nb₂O₅ catalyst. Gas chromatography-mass spectrometry analysis of liquid product obtained from the catalytic cracking process showed that the dimers in the pyrolysis oil were converted to monomers during the catalytic cracking process. The catalytic cracking results also showed that the NiO/Nb₂O₅ catalyst (having slightly higher acidic sites) had slightly higher activity for monomer conversion than the Nb₂O₅ catalyst (having less acidic sites). X-ray diffraction, transmission electron microscopy, pyridine Fourier transform infrared spectroscopy, NH₃ Temperature Programmed Desorption and X-ray photoelectron spectroscopy were used to characterize the catalyst. The highest catalytic cracking activity was observed at 400 °C with the Nb₂O₅ catalyst with 4% toluene, 6% ethylbenzene, approximately 50% styrene, 13% α-methyl styrene, and only 6% of dimers in the liquid oil. The increase in temperature positively affected the yield of gases during catalytic cracking process.