Novel Caffeine-Assisted Aqueous Extraction Strategy for Enhanced Solubilization of Polycyclic Aromatic Hydrocarbons from Creosote-Treated Waste Wood

This study evaluates caffeine-assisted aqueous extraction systems for the enhanced extraction of Σ16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) from waste creosote-infused wood. Aqueous solutions of eight water-soluble organic acids were investigated with and without caffeine to assess its effect on PAH extraction. Caffeine improved extraction across all systems, but the extent of this improvement varied depending on the initial performance of each extraction agent without caffeine. Deionized water exhibited a negligible extraction yield (0.0027%), whereas caffeine addition increased the yield to 1.6886%, corresponding to a 625-fold improvement. Despite substantial differences among agents without caffeine, most caffeine-containing systems achieved similar extraction yields (4.2–5.3%), indicating that caffeine-induced hydrotropic solubilization became the dominant factor governing PAH extraction. Based on the maximum extraction performance achieved in the presence of caffeine, the investigated systems can be ranked as follows: acetic acid-caffeine > citric acid-caffeine > p-TsOH-caffeine ≈ tartaric acid-caffeine ≈ lactic acid-caffeine ≈ formic acid-caffeine > ascorbic acid-caffeine. These findings identify caffeine-assisted aqueous extraction as a promising approach for enhancing PAH extraction from creosote-treated waste wood while reducing reliance on conventional organic solvents in the primary extraction step.