LAUSR

Abstract The disposal of spent bleaching earth (SBE), an industrial refining waste from the bleaching process, is a crucial environmental issue. The objective of this work was thus to formulate a microemulsion-based washing agent for the removal of residual rice bran oil from SBE using the hydrophilic–lipophilic deviation (HLD) concept. The HLD equation was used to calculate the optimum salinity at various temperatures in the washing agent solution based on the alkane carbon number (ACN) of the rice bran oil. Three fatty alcohol ethoxylate surfactants (Dehydol LS series) were selected for use as nonionic surfactants. From the HLD equation and phase experiments, Dehydol LS3TH was selected to formulate the microemulsion-based washing agent for oil recovery from the SBE. The HLD equation predicted a Winsor Type III microemulsion to occur at 8.5 wt.% of NaCl at 25 °C. Phase behavior studies demonstrated that a Type III microemulsion occurred over a NaCl concentration range of 10–20 wt.%. From these results, a correlation was confirmed between the theoretical HLD prediction and the experimental phase behavior. In the oil recovery study, the microemulsion-based washing agent provided the highest total oil extraction efficiency: up to 71.38 ± 1.75% at the optimum salinity of 15 wt.% NaCl, and a contact time of 30 min at 25 °C. Thus, the HLD concept for predicting microemulsion formulation was found to be an effective way to formulate a microemulsion-based washing agent for vegetable oil removal from SBE.