Study on pyrolysis behavior of polymeric coated aluminium scrap using TGA and Py-GC/MS

Abstract

Polymeric-coated aluminium scrap obtained from a local recycling plant in Thailand was used as raw material. The thermal decomposition behavior and evolved gas from the pyrolysis of the polymeric fraction coated on the aluminium surface were investigated using thermogravimetric analysis (TGA) and pyrolysis-GC/MS (Py-GC/MS). Initially, thermogravimetric analysis (TGA) was used to study the thermal decomposition of all the coated aluminium scraps (white, black, and brown color). From the TGA results, a major thermal degradation at 300–480 °C associated with the decomposition of the polymeric fraction was found in all the powder-coated samples. The weight loss was 4.57 wt %, 3.56 wt %, and 1.64 wt % in the white-, black-, and brown-coated scraps, respectively. Then, the pyrolysis of the polymeric layer coated on the surface was investigated using a Py-GC/MS. The effect of pyrolysis temperature (400–600 °C) and the type of coated aluminium scrap on product selectivity was studied. In terms of pyrolysis, the polymeric materials used in the coating would decompose via scission reaction generating volatile compounds. At a temperature of 600 °C, the carboxylic end groups (40.46–45.62 %) and aliphatic HCs (19.69–25.34 %) were the major pyrolytic products with a small number of aromatic HCs (2.76–7.76 %). In addition, low fractions of N-containing compounds (3.05–8.08 %) produced from the decomposition of cross-link agents were found. The maximum temperature (600°C) promoted high selectivity of hydrocarbons (aromatic and aliphatic) from β-H scission, cracking, and deoxygenation reactions. Aliphatic hydrocarbons consisted of alkenes, alkynes, and cycloalkenes with carbon in the range of C5–C24, while aromatic hydrocarbons with carbon in the range of C6–C20 were composed of mainly toluene, biphenyl, styrene, etc. These organic products can be utilized as chemical raw materials as well as alternative fuel. Additionally, to identify the remaining components after heat treatment at 600 °C, the chemical analysis was performed using the EDX technique. The residue compositions after heat treatment at 600 °C were C, Ti, Ba, Pb, Si, Ca, Fe, and S, chiefly corresponding to TiO2, SiO2, CaO, Fe2O3 as pigments and BaSO4 as a filler. Thus, the removal of these inorganic components remaining after thermal de-coating process should be considered to maintain melting cleanliness.