This investigation is focused on the behavior of nanofluid single drops in the liquid–liquid extraction process. The chemical system of toluene–acetic acid–water was used, and the drops were organic nanofluids containing magnetite or alumina nanoparticles. Synthesized nanoparticles were modified with fatty acids for hydrophobicity and ease of dispersion in the organic phase and were then characterized using different methods. Maximum enhancements in the rate of mass transfer of 157% and 121% were achieved using about 0.002 wt % magnetite and alumina nanoparticles, respectively; however, a decreasing variation was observed at higher concentrations. The microconvection and particle aggregation due to the interpenetration layers can provide this kind of variation. For the aim of modeling, the determined enhancement factors were correlated with an empirical expression that can be used, together with the Newman equation, for the prediction of the overall mass-transfer coefficient.

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The effect of almost low concentrations of alumina hydrophilic (bare surface) and hydrophobic (modified surface with hexadecanoic acid) nanoparticles on interfacial tension of methylbenzene (toluene)−water was investigated based on experimental results from drop weight tensiometry. Nanoparticles were suspended in either aqueous or organic phases to provide a stable nanofluid and then were contacted with another phase to measure the interfacial tension. A nanoparticle mass fraction range of 1•10 −5 to 5•10 −4 (± 5•10 −6 ) and a temperature range of [293.2 to 323.2 (± 0.1)] K were used. Interesting trends of interfacial tension variation were revealed with nanoparticles concentration, showing a sharp increase up to 55.7 mN•m −1 (± 0.1 mN•m −1 ) at 293.2 K, and a decrease to about 14.0 mN•m −1 at 323.2 K with hydrophilic and hydrophobic forms, respectively. The effect of increasing temperature was found to reduce interfacial tension within the used ranges and significantly higher with hydrophilic nanoparticles.

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