Carbon nanotubes (CNTs) production from catalytic pyrolysis of waste plastics: The influence of catalyst and reaction pressure

The production of carbon nanotubes (CNTs) by catalytic pyrolysis of plastics is an environmentally friendly and promising method of waste treatment and energy/materials production. Three types of metal catalysts (Fe/cordierite, Ni/cordierite and Ni-Mg/cordierite) were utilized during the catalytic pyrolysis process of polypropylene in this work. Meanwhile, the influence of reaction pressure (0.5–1.25 MPa) on the synthesis of CNTs was investigated. Carbon formation, especially CNTs, through catalytic pyrolysis of plastics has been tested in a fixed bed reactor, and the materials have been analyzed by temperature program oxidation (TPO), scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM) and Raman spectroscopy. The highest yield around 93 wt.% filamentous carbon was obtained using the Ni-based catalyst. The strong metal-support interaction within the Ni-Mg-based catalyst suppressed CNTs growth and resulted in shorter and irregular cylindrical carbon tubes. The yield of more uniform and thick CNTs increased with the additional of appropriate reaction pressure, especially at 1.0 MPa (198 mg/g_PP). However, an excessive reaction pressure weakened CNTs growth and produced shorter length and larger diameters (around 30–50 nm) CNTs. The fraction of CNTs decreased when the reaction pressure was higher than 0.5 MPa.