Recycling waste plastics packaging to value-added products by two-step microwave cracking with different heating strategies

Waste plastics packaging (WPP) was converted into valuable products by two-step microwave cracking. The wax (38.47–72.53 wt%), gas (20.18–43.85 wt%) and solid (2.00–24.18 wt%) were produced in the first step, and the liquid (60.55–79.94 wt%), gas (18.44–38.45 wt%) and solid (1.00–5.56 wt%) were produced in the second step. Different heating strategies including the selection of absorbers and catalyst, the adjustment of heating power, the mass ratio of absorber to feedstock have been proposed to optimize the products in each step. Commercial spherical activated carbon, columnar activated carbon and molecular sieves type 4A have been used as absorbers and catalysts. The gas products (mainly H2, CH4, C2H4 and C3H6) can be used as combustion gas. The solid products (mainly CaO, TiO2 and SiO2) in the first step are suitable for absorbers because of their fast temperature rise (30–115 °C/min) in microwave field. The liquid products are distributed between C7 and C26, which are suitable for gasoline and diesel fractions. Absorbers have been used many times to reduce costs. Two-step method can effectively remove plastic additives, and other attachments in the first step, and the separation of ‘dirty’ process and ‘clean’ process can reduce the possibility of catalyst deactivation due to impurity coverage.