Adsorption modeling for contaminant removal in plastic dissolution recycling: Investigating an amino ketone-based red dye

Abstract

The widespread inclusion of additives in plastics has posed a significant challenge to increasing global plastic recycling rates. This study explores the potential of adsorption in non-aqueous environment as a novel approach for plastic waste dissolution recycling. Activated charcoal was selected as the adsorbent for the removal of Solvent Red 135, a commonly used amino ketone-based dye, from polystyrene (PS) solutions. Three solvents, namely o-xylene, limonene, and butyl acetate, were investigated. Adsorption experiments were conducted at 293 K, and the results were analyzed using both classical and statistical physics models. The activated charcoal exhibited the highest single component adsorption capacity for the dye when butyl acetate was used as the solvent, while it showed negligible adsorption for PS in all three solvents. When dealing with mixtures of the dye and 1.0 wt% PS in butyl acetate, a removal efficiency of 99% was achieved at an adsorbent dose of 2.0 g L-1. However, when the PS concentration in the solvent increased to 10 wt%, the required adsorbent dose rose to 3.3 g L-1. Modeling results indicated that monolayer adsorption occurred via a multi-molecular adsorption mechanism, with an approximate adsorbed dye molecule count of 1.5 per adsorption site. The adsorption energy for all three solvents ranged between 0 and 40 kJ mol-1, indicating that the adsorption process is predominantly driven by physical forces and is an endothermic process. This study presents a foundational assessment of adsorption as an effective solvent-based technique for the removal of additives in plastic recycling.