High temperature pyrolysis of plastics in contact with liquid steel

Abstract

The possibility of high temperature pyrolysis for gasification of plastics as a thermal recycling method has been investigated. Special attention was given to plastics mixed with steel. Such samples could be expected as waste material from end of life vehicles. These materials were brought in contact with a liquid steel bath. A laboratory apparatus for high temperature pyrolysis was built up which consists of an inductively heated steel bath with an equipment to collect the products of pyrolysis. Pyrolysis was performed in various gas atmospheres, e.g. argon and oxygen and mixtures of nitrogen and oxygen. The plastic material could be dipped below the surface of the metal bath, being placed in a wire basket and by continuous feeding through a steel tube. The products of pyrolysis were analyzed and classified into dissolved carbon in steel, soot, liquid fraction and gaseous fraction. The liquid fraction was analyzed by means of gaschromatography coupled with mass spectrometry and the exhaust gas was analyzed by means of mass spectrometry. The experiments revealed that comparatively large amounts of soot were formed and also liquid fractions were formed. This should not occur, if the thermal equilibrium during pyrolysis is established. The composition of the gaseous fraction indicated that according to the ratio of hydrogen to methane a thermodynamic equilibrium temperature of ≈650°C was reached. Experiments in which the temperature of the degrading surface of the plastic material was measured directly confirmed these findings.