Thermal decomposition behavior and characterization of automotive paint sludge

Abstract

Automotive paint sludge (APS) is a ubiquitous, recalcitrant waste product of the vehicle manufacturing process. The potential of APS for energy and chemical production via pyrolysis and gasification is undermined by the absence of methodologically consistent, cross-stream physicochemical characterization. This impedes process design for the valorization of APS. This work aims to rectify that by presenting a direct physicochemical characterization and thermogravimetric comparison of five APS types: electrocoat, phosphate coat, primer, base coat, and clear coat. Thermogravimetric (TGA/DTG) experiments were conducted at three heating rates, i.e., 5, 10, and 20°C/min, under both nitrogen and air atmospheres. The study revealed that the decomposition of APS occurs in three distinct stages. The first stage involves the removal of moisture and the release of volatile organic compounds (VOCs), occurring at temperatures ranging from 30°C to 220°C. The second stage, which occurs at approximately 220°C–550°C, exhibits a further subdivision profile comprising two subsections. This entails the devolatilization stage, which occurs between 200°C and 380°C. Subsequent to this, the cracking of resins, heavy hydrocarbons, and the formation of char occur at temperatures ranging from 380°C to 550°C. The third and final stage occurs at a range of 550°C–800°C, accounts for the least mass loss, and is characterized by the carbonization and decomposition of inorganic compounds. In this work, we have established temperature intervals for drying/VOC removal, VOC recovery, and secondary cracking/carbonization, providing comparative evidence to optimize APS-to-energy conversion.