Materials

Brine containing sodium chloride (NaCl, Fisher Scientific) in deionized water (pH = 6.8 ± 0.1) was used to prepare the surfactant solution. The alkaline solutions were a mixture of sodium carbonate (Na₂CO₃) and sodium chloride that were obtained from Fisher Scientific Company with ACS purity. Nitrogen gas with purity of 99.98% was used to generate foam. Normal hexadecane (n-C16, Sigma-Aldrich) as the model oil was used to represent the oleic phase. Hexadecane as the model oil was used with and without a naphthenic acid, which was decanoic acid (99% pure, Sigma) in this study. Decanoic acid (0.25 wt%) dissolved in n-hexadecane was used, which gives a total acid number (TAN) of 2.2 mg KOH/g oil determined by ASTM method D664. A commercial IOS with a high number of carbon chains prepared by the Shell Chemical Company was selected. The co-solvent was a sec-butyl alcohol (SBA, Merck, 99% pure), and a concentration of 0.5 wt% was used. In this study, IOS surfactant was used for all the experimental investigations, as this type of surfactant has been shown to have a low IFT and to be a relatively stable foam [7, 10, 11]. The synthesis steps and the chemical structures of IOS surfactant were reported by Barnes et al. [1, 2]. The surfactant solution was prepared using brine containing NaCl or a blend of NaCl and Na₂CO₃.