Abstract
It is still unclear how the presence of certain ions influences nonionic surfactant-stabilized emulsions. Hence, the purpose of this work is to investigate the effect of monovalent (NaCl) and divalent (CaCl2) ions on an oil-water emulsion stabilized by two different nonionic surfactants, Tergitol 15-S-7 (T15S7) and Span® 80 (SP80). Emulsions were formed in a 60 mm gravity-based separator of a nominal volume of 200 ml. In addition to a wide range of ion concentration, the study looked at the effect of low (800 RPM) and high (2500 RPM) mixing speeds at water-to-oil ratios (WORs) of 1:3 and 3:1. At low mixing speeds and WORs, experimental results showed that the presence of ion (regardless of its concentration or type) does not affect emulsions stabilized by SP80. However, when mixed at higher speeds, ions were shown to increase the volume of the same system. Data of SP80-stabilized emulsions also showed that the increase of WOR from 1:3 to 3:1 causes a significant drop in the volume of the emulsion regardless of ion type and/or concentration. On the contrary, at a WOR of 1:3, the presence of ions was shown to reduce the volume of T1S57-stabilized emulsions. However, although mixed at two different speeds, the separation kinetics of T15S7-stabilized emulsions became salt-independent after a few hours of formation.
