Stabilization of Water-in-Oil Emulsions by Naphthenic Acids and Their Salts: Model Compounds, Role of pH, and Soap :Acid Ratio

Increasingly, crudes of high acidity are observed in production of petroleum reserves. Naphthenic acids, which are generally cyclic and branched aliphatic carboxylic acids, are interfacially active and adsorb at water–oil interfaces to form monolayers, liquid crystalline films, and other colloidal structures. A serious challenge in petroleum production is the resulting stabilization of water-in-oil emulsions, which can cause problems in topside and subside separators, and in refining processes. A variety of acids and their corresponding soaps have been thoroughly studied in order to investigate how these compounds interact in aqueous solutions at different pH, and how these association structures relate to emulsion formation and stability. The formation of aggregates and hence, the stabilizing properties of this class of material are strongly sensitive to the relative proportion of uncharged acid and charged soap anion. In this paper, we review our experimental results on naphthenic acid/ naphthenate stabilized emulsions utilizing several model compounds, including heptylbenzoic acid (HB), trans-4-pentylcyclohexane-carboxylic acid (PCA), and 5-b-cholanic acid (CA).