In Thailand, spent bleaching earth (SBE) (20–40 wt.% remaining oil), an industrial waste from edible oil refineries, has usually been disposed of by improper landfilling at industrial sites. This study aims to formulate microemulsion‐based washing solutions from mixed surfactants for cleaning SBE contaminated with crude rice bran oil using the hydrophilic–lipophilic deviation (HLD) concept. Binary nonionic‐anionic surfactant mixtures consisting of System A (Dehydol LS3TH‐Levenol WX), System B (Dehydol LS5TH‐Levenol WX), and System C (Dehydol LS7TH‐Levenol WX) were formulated for use as microemulsion‐based washing formulations. A HLDmixed equation extended with the excess free energy term (GEX/RT) was developed and proposed for predicting the optimum salinity. The optimum salinities obtained from the HLDmixed equation were close to those obtained from the phase behavior. In the SBE washing study, the mixed‐surfactant systems showed a washing efficiency of 90% with low surfactant adsorption capacity on bleaching earth (qmax = 0.01–0.03 mol g−1). The mixed surfactants showed improved washing performance compared to that of the single‐surfactant system. This work highlights the utility of using the HLD concept in designing microemulsion‐based washing formulations from surfactants for the removal of vegetable oil from SBE.
Abstract. An accurate determination of the hydrophilic-lipophilic nature of surfactants plays an important role in guiding microemulsion formation. The objective of this study is to determine the effect of ethoxylate numbers (EONs) (3, 5, and 7 moles) of nonionic surfactants on a phase inversion temperature (PIT) and optimum salinity based on the equivalent alkane carbon numbers (ACNs) of vegetable oils. Three vegetable oils, soybean oil, crude rice bran oil and crude palm oil, were selected for use as a surrogate oil to represent the residual oils found in spent bleaching earth. In this study, the hydrophilic-lipophilic deviation (HLD) was used to predict the optimum salinity (0-20 %wt.) at various temperatures (25-55°C). The results showed that the ACNs of crude rice bran oil, crude palm oil, and soybean oil were 15.41±0.35, 13.71±0.41, and 17.60±0.28, respectively. In comparison, these predictions with the experimental results, the data showed slight deviations in the optimum salinity with the specific temperature. Finally, the ACN and the surfactant characteristics obtained in this study were combined with the HLD equation and used to validate its practically and utility for guiding the optimum microemulsion formulation.
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