What question did this study set out to answer?

This study aims to explore how the molecular structure of solvents impacts crude oil desorption from oily sludge.

April 6, 2026Open Access

Insight into the Desorption Behavior of Crude Oil from Oily Sludge using Solvent Extraction: Impact of Solvent Types with Typical Molecular Structures

XZXianwu ZhangZhongyuan University of Technology MZMenglong ZhangZhongyuan University of Technology YLYafei LiuZhongyuan University of Technology

Key Points

This study aims to explore how the molecular structure of solvents impacts crude oil desorption from oily sludge.
Analyzed four solvents: ethyl acetate, n-dodecane, petroleum ether, and toluene.
Used desorption isotherms, kinetics, and thermodynamics parameters to assess solvent efficiency.
Applied Freundlich isotherm and pseudo-first-order kinetic models.
Desorption processes followed the Freundlich model with endothermic extraction.
Toluene exhibited the highest oil removal efficiency compared to other solvents.
Solvent type affected the composition of recovered hydrocarbons, influencing proportions of heavy components.

Abstract

• Investigated the impact of solvent molecular structure on oil desorption behavior. • Oil desorption follows Freundlich model, mainly driven by hydrophobic interactions. • SARA analyses proved toluene removed most of the heavy components from oily sludge. • GC-MS revealed toluene extracted a broader range of crude oil components. • Dissolution and dispersion together govern the oil extraction from oily sludges. Organic solvent extraction is a key technique for recovering crude oil from oily sludge, yet the impact of solvent molecular structure on crude oil desorption behavior remains poorly understood. This study addresses this gap by systematically exploring the desorption performance of four representative solvents—ethyl acetate, n -dodecane, petroleum ether and toluene—in recovering crude oil from oily sludge particles. Desorption isotherms, kinetics, and apparent thermodynamics parameters (Δ G , Δ S and Δ H ) were analyzed to assess solvent efficacy. The results demonstrate that the desorption processes align with the Freundlich isotherm model and the pseudo-first-order kinetic model, with all extractions being endothermic, driven by hydrophobic interactions. Toluene exhibited the highest oil removal efficiency, followed by petroleum ether, n -dodecane, and ethyl acetate. This ranking underscores the significant role of the benzene ring structure in enhancing desorption, as compared to alkyl chains or polarity. Additionally, solvent type influenced the composition of recovered petroleum hydrocarbons, particularly the proportion of heavy components. Changes in particle morphology and dispersion further indicated the solvent-dependent nature of oil desorption. Based on these findings, we propose a two-stage extraction mechanism involving dissolution of crude oil and dispersion of oil-bound solid particles. This study improves understanding of solvent structure in oil-sludge separation and provides valuable insights for selecting effective solvents in treating oily sludge, with important implications for environmental and industrial applications.

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