Thermal recycling of polymers

Abstract

As most plastics are produced from oil, the recycling of plastic and rubber wastes is of increasing importance. Systems for the pyrolysis of plastic wastes with complete exclusion of oxygen use melting vessels, rotary kilns or fluidized bed processes. The pyrolysis of plastic wastes, scrap tyres and other polymeric materials in a fluidized bed has been carried out at the University of Hamburg, based on a three-step scale-up programme (laboratory plant 100 g/h, pilot plant 30 kg/h and prototype plant 150 kg/h). Up to 50% of the input plastic material is converted into liquid hydrocarbons. The product spectrum is comparable to that of a mixture of light benzene and bituminous coal tar, consisting of about 95% aromatics. By addition of lime it became possible to absorb completely the hydrogen chloride evolved from poly(vinyl chloride). The technology in a fluidized bed allows the pyrolysis of whole tyres to include aromatic compounds, gas, carbon black and steel wire. A first commercial demonstration plant using the fluidized bed process with an annual plant capacity of 5000–10,000 t has been erected.