Inspection for desorption behavior and desorption mechanism of oily sludge by thermodynamics and kinetics analysis

In this study, the solvent extraction experiment was investigated to probe the desorption behaviors and desorption mechanism of oily sludge with n-heptane as solvent. Desorption isotherms were analyzed and fitted by Langmuir, Freundlich and Redlich-Peterson equations at different temperatures. Then, the thermodynamics parameters such as standard free energy (Delta G degrees), standard enthalpy (Delta H degrees) and standard entropy (Delta S degrees) were calculated. Based on thermodynamics analysis and calculation, oil was proved to exist in the form of the colloidal dispersion system. In addition, the kinetics was fitted by the pseudo-first-order kinetic model and the pseudo-second-order kinetic model. Kinetic studies showed that desorption process of asphaltenes was restrained severely due to strong interactions between sludge and asphaltenes, and resins played a crucial role in asphaltenes desorption. The desorption mechanism was discussed based on experimental results and further analysis. The solvent effect and carry-over effect were deemed to be crucial to oil desorption. The carry-over effect is generated from electrostatic interactions, hydrogen bonds, electron donor-acceptor and pi-pi interactions, which was also the essence of asphaltenes desorption. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.