Removal of volatile components from plastic waste in liquid media : effect of temperature and particle size

Plastic recycling faces a range of challenges, including the removal of VOCs and odorous compounds. Despite the industrial relevance, understanding and optimizing washing procedures for plastics is often based on trial and error. To gain more understanding of the removal kinetics of VOCs, which contribute to the odor profile, the influence of temperature and particle size on their removal from plastic films and bottles were investigated at lab scale. For this purpose, the VOC removal from plastic films and bottles in water, caustic soda and a caustic soda + detergent solution was monitored at different temperatures and particle sizes by means of GC-MS analysis. It was found that an increase in temperature from 28.C to 85 degrees C results in an improved removal for all washing media (from 69 to 79% in water, 43 to 65% in caustic soda, and 65 to 72% using a caustic soda + detergent solution). Reducing particle size of plastic films from 1.1 cm to 0.045 cm increases the VOC removal from approximately 35% to 70%. For PE bottles, the effect of particle size was more pronounced than for films, due to the bigger change in specific surface area. The desorption-adsorption kinetics were most accurately described by a reversible first order kinetic model by implementing the Arrhenius equation for modelling the temperature dependence and a Power Law to account for the particle size. Thermodynamics indicate that adsorption of VOCs is favored over desorption, explaining why washing medium management is crucial for efficient removal of VOCs from plastic waste.