Microwave pyrolysis of polymeric materials: Waste tires treatment and characterization of the value-added products

Waste tires are well known to have relevant disposal or reprocessing problems under environmental and economic sustainable conditions. These processes may be a challenge for industrial and academic research. In this contest pyrolysis represent a modern valid alternative to undergo treatment of waste tires as long as it will be possible to generate value-added products. Anyway improvements in the heat transfer technology are crucial to optimize the efficiency of the process itself. Here we describe the use of microwave (MW) irradiation as one of the most promising heating technologies for pyrolysis, due to its ability to heat quickly and directly any MW absorbing material. Experiments were run in a batch laboratory scale with an oven operating at a frequency of 2.45 GHz with a variable energy output up to 6 kW. A special attention was dedicated to the influence of operating variables on liquid product properties. The reaction was performed in a short time comparing with traditional heating techniques and the most performing conditions were achieved using a MW power of 3 kW per 0.2 kg of tires. Typical products were a solid residue (char) containing up to 92.03% of carbon and appreciable quantities of mineral matter, a low viscosity oil (<2.9 cP, with a large amount of single ring aromatic hydrocarbons) and a gas containing light hydrocarbons, hydrogen and only traces of N2. The three products collected had a high calorific value, respectively 34 MJ/kg for solid, 45 MJ/kg for liquid, and 46 MJ/kg for the gas fraction.

► Short pyrolysis time and manageable products properties were achieved.
► The microwave power and tire mass affect the yield and composition of products.
► The liquid is a low viscosity and density oil with high higher heating value.
► The gas contains low molecular weight aliphatic hydrocarbons and hydrogen.
► An evaluation of tire temperature during pyrolysis was realized.