Recovery of green solvent contaminated with petroleum hydrocarbons by selective adsorption onto granular activated carbon

Abstract

Ethyl lactate (EL) has served as a promising green solvent for oil extraction from drill cuttings wastes. Its high commercial price and huge volume consumption currently pose a constraint regarding operational costs and environmental burdens. Therefore, this work aims to propose the adsorption by granular activated carbon (GAC) as a facile method for recycling the spent EL contaminated with oil. The results from batch experiments revealed that the adsorption of oil in EL was favorable and endothermic, reaching the maximum oil adsorptive capacity of 1053 mg g−1 at 35 °C. The adsorption process was best described by the Freundlich isotherm and pseudo-first order kinetic models. Oil adsorption mechanisms were mainly controlled by film diffusion, hydrophobic interaction, and coalescence. The competitive adsorption of EL onto GAC through hydrogen bonding and covalent bonding was also observed. For column adsorption, all breakthrough curves were well explained by Clark and bed depth service time models. The maximum breakthrough removal efficiency of 99.3% was achieved from the flow rate of 1 mL min−1, initial oil of 500 mg L−1 and bed height of 12 cm. The spent GAC was regenerated by heating at 350 °C, provided with a regeneration efficiency of 95% after five adsorption-desorption cycles. The payback period of using EL extraction and recovery was estimated at 1.8 years, considering secure landfill as a baseline. These findings prove the industrial applicability of GAC adsorption for solvent recovery and promote EL as a more economically feasible solvent for greener management of oil-contaminated drill cuttings.