Catalytic pyrolysis of high-density polyethylene for the production of carbon nanomaterials: effect of pyrolysis temperature

A two-stage reaction process is followed to convert high-density polyethylene (HDPE) into carbon nanofilaments (CNFs) and hydrogen-rich gas. The experiments are performed in a continuous mode in a two-stage quartz reactor: thermal pyrolysis of HDPE followed by the catalytic decomposition of the pyrolysis gases over a nickel catalyst prepared from mining residues. To examine the effect of the pyrolysis temperature on the yield and quality of the final products, two steps were followed. First, non-catalytic pyrolysis experiments were run at different temperatures (600, 650, and 700 °C), and the products were examined. Second, pyrolysis–catalysis experiments were performed at the same pyrolysis temperatures and a fixed catalytic temperature (600 °C) to examine the CNF and hydrogen yields. The results showed that the production of carbon nanomaterials (CNMs) and H2 is optimal at 650 °C, with yields of 70.8 and 38.0 wt%, respectively. Scanning electron microscopy (SEM) revealed the presence of carbon filaments with different diameters and lengths at the three different temperatures. Moreover, thermogravimetric analysis (TGA) confirmed that the produced carbon is filamentous, with the presence of amorphous carbon at 700 °C.