Gases evolved during decoating of aluminium scrap in inert and oxidizing atmospheres.

Thermal removal of coatings on aluminium scrap in a delacquering unit prior to melting makes it possible to utilize the energy released by the combustion process in a closed and controlled manner, lower emissions, improve control of the remelting process, reduce dross generation and improve melt cleanliness. Polyester coated on aluminium was studied using both inert and oxidizing atmospheres. The coating was decomposed in a thermogravimetric/differential thermal analysis (TG/DTA) furnace, and the evolved gases were measured using a quadrupole mass spectroscopy (MS) Analysis of the evolved gases for the main weight losses are presented, together with the enthalpy changes. The mass losses, enthalpy produced and degradation products depend upon both the gas atmosphere and the heating rate. The data has been employed to develop a phenomenological model of pyrolysis and combustion of this coating. Such models can be used to choose suitable atmosphere and temperature profiles in industrial decoating units in order to improve efficiency, minimize energy consumption and to reduce and control emissions.