Thermal-Chemical Recycling of Waste Plastics for Valuable Products

Plastic is rich in hydrogen and carbon resource. In year 2018, nearly 908,600 tons of waste plastics are disposed in Singapore according to a NEA report. However, the low recycling rate of plastic waste, which was only 4% that ranked the least among all kinds of waste and represented a huge waste of hydrogen and carbon resources, has been a great challenge for the sustainable development of whole society. The CO₂ emission from the current incineration process of waste plastics contributes large part in the greenhouse gas (GHG) emissions. Thermal-chemical recycling of waste plastics is a promising way to reduce waste with simultaneously conserving natural resources. In this work, waste plastic waste will be thermally vaporized (pyrolysis) firstly followed by a catalytic reforming/upgrading process, where hydrocarbon-containing compounds being converted to desired valuable products. As catalyst was very important for this process, experiments were performed into the influence of the catalyst where a series of different Ni or Fe modified catalysts were compared in relation to hydrogen yield and carbon nanomaterials production. Results found the catalyst synthesis method and the type of metal loading significantly influenced the products yields. Thick layers of carbon nanotubes, with diameters in the range of 20-40 nm and length up to tens of microns were obtained. A deep investigation on microstructure and crystalline phase of spent catalyst and products was also conducted for better understanding of the growth of carbon nanomaterials from pyrolysis-catalysis of plastic.