Depolymerization of HDPE to wax in the presence of a catalyst formed by homonuclear macrocyclic zirconium complex chemically bonded to alumina support

A homonuclear macrocyclic Zr–Zr complex was prepared starting with 2,6-diformyl-phenol and 1,2-phenylene diamine and is chemically bonded with carbamate-modified alumina. The TPD of the catalyst having adsorbed NH3 shows the presence of acid sites on the surface of the catalyst and the catalyst is stable under the reaction temperature studied. The catalytic depolymerization of commercially available high-density polyethylene (molecular weight 4.79 × 105) was carried out in the presence of nitrogen as well as oxygen at about pressure of 300 of kg/cm2 and temperature of 370 °C. Catalytic depolymerization in the presence N2 occurs with the time delay of 2 h (as opposed to 4 h for thermal depolymerization occurring above 400 °C) and stops with the formation of wax (as opposed to C5–C16 liquidous alkanes in thermal depolymerization). The wax thus formed was characterized and shown to be the Arge wax (available commercially) having a melting point of 80 °C and molecular weight of 392. We have proposed a kinetic model in which the catalyst forms a complex with polyethylene radical formed at high temperature, which gives depolymerization to form wax molecules.