Decomposition of polyethylene in radio-frequency nitrogen and water steam plasmas under reduced pressures

The possibility of radio-frequency (RF) nitrogen and water steam plasmas under reduced pressures for gasification of plastic waste as a thermal recycling method has been investigated in order to develop an innovative method for directly recycling plastic waste to hydrogen, synthesis gases or fuels. The products of pyrolysis were analyzed and classified into gaseous fraction and solid soot; and analytical interest was focused on the gaseous product composition. It was found that the electrode geometry, input power, reactor pressure and plasma working gas were the key parameters affecting the plasma characteristics and pyrolysis product. Experiments with different plasma media indicated that when polyethylene (PE) powder was injected into nitrogen plasma, the PE was decomposed and hydrogen formed as a main product by reaction with the plasma; when water steam plasma was used for conversion of PE, the carbon conversion to gas was dramatically enhanced in the presence of water steam, and the main gas products were carbon monoxide and hydrogen. Preliminary solid products analysis and pyrolysis mechanisms for the different plasmas processes were also discussed.