Thermal Chemical Conversion of High-Density Polyethylene for the Production of Valuable Carbon Nanotubes Using Ni/AAO Membrane Catalyst

Thermal chemical conversion of waste plastics for syngas production is a promising alternative method for the management of waste plastics. However, one of the challenges of facilitating the deployment of this technology is the low economic benefit of waste-plastic recycling. By producing a high-value carbon nanotubes (CNTs) byproduct, an interesting alternative solution is provided. To further enhance the quality of CNTs produced from catalytic thermal chemical conversion of waste plastics, a template-based catalyst (Ni/anodic aluminum oxide, AAO) is proposed in this work. In addition, reaction temperature, Ni content and water injection were studied for their influences on the formation of CNTs on Ni/AAO using a two-stage fixed bed reactor. Various analytical methods, e.g., scanning electronic microscopy (SEM) and X-ray diffraction (XRD), were used to evaluate the performance of catalyst in relation to the production of CNTs. The results show that a higher loading of Ni on AAO resulted in the formation of metal particles with various sizes, thus leading to the production of nonuniform CNTs. In addition, an optimal catalytic temperature of 700 °C is suggested for the production of CNTs. Because the catalyst might not be activated at 600 °C, which produced a low yield of CNTs. However, a reaction temperature of 800 °C resulted in a low yield of CNTs. Carbon deposition decreased with an increase of steam injection, but the quality of CNTs formation in relation to the uniform of CNTs seemed to be improved in the presence of steam.