Marit-Helen Ese

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

Abstract 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‐β‐cholanic acid (CA). #A special tribute to Dr. Jan Czarnecki on the occasion of his 65th birthday.

Same system-different results: the importance of protein-introduction protocols in Langmuir-monolayer studies of lipid-protein interactions.

For studies of protein-lipid interactions, thin films at the air-water surface are often employed as model systems for cell membranes. A convenient manner in which to study these interactions is the Langmuir technique, which allows for formation of monolayer phospholipid films together with a choice of where and how to introduce proteins, according to the desired response variable. Here, a distinction has been made between different interaction protocols and it is also commented upon to what extent introduction of protein to a solution prior to spreading of a lipid film affects the results. This paper describes commonly used methods when working with Langmuir monolayers as membrane mimics and compares the results of four different experimental protocols: formation of a lipid film on top of a protein-containing subphase, injection of protein under an existing, semicompressed phospholipid film (surface pressure 5 mN/m), and deposition of a protein solution on top of a lipid film contained at either surface pressure 0 mN/m or at surface pressure 5 mN/m. Results obtained from Langmuir isotherms and Brewster angle microscope clearly differentiate between these methods and give insight into under which conditions and at which interfaces the protein interactions are predominant (protein-air or protein-lipid).

Emulsions Stabilized by Indigenous Reservoir Particles: Influence of Chemical Additive

Interfacially active inorganic particles from the reservoir are often produced together with crude oil. These fines can have a tendency to accumulate at the water/oil interface and eventually stabilize w/o and o/w emulsions. The properties of the particles will change through interactions with indigenous crude oil components and also with added production chemicals. In this work focus has been towards a real system with particles sampled from the separator located on an installation on the Norwegian continental shelf. Stabilizing properties of different particle fraction has been studied (for both oil and water continuous emulsions). It is reported that the solids interact strongly with chemical additives. Silicon oil, used as foam inhibitor during production, adsorbs to the limestone particles and alters the properties of the fines dramatically.

Emulsion Inversion in an Oil‐Surfactant‐Water System Based on Model Naphthenic Acids under Alkaline Conditions

Emulsion inversion has been studied in a system based on oil (toluene/heptane), 5β‐cholanic acid, and an alkaline brine solution by varying the concentration of sodium hydroxide. At an intermediate pH w/o emulsions were formed, and in the high pH region o/w emulsions were formed. Emulsion inversion occurred in the pH range 8.5–10. The w/o emulsions were consistently more stable compared to the o/w emulsions. Increasing the amount of acid enhanced the stability of the emulsions. Maximum stability was observed close to pH 8, where the ratio between the undissociated and dissociated acid was approximately 1.5. From light microscopy, it can be seen that the emulsions are stabilized by a liquid gel phase. At equilibrium the system consists of an oil phase, a liquid gel phase, and an aqueous phase. Increasing the oil fraction eventually gave only w/o emulsions in the pH range between 7 and 14. For these emulsions, no obvious difference in stability was observed at pH 8, while the stability of the emulsions in the high pH region was significantly enhanced. An increase of the ratio between toluene and heptane gave no obvious difference in either stability or type of emulsion while varying the pH. Use of a less lipophilic acid, such as 4‐octylbenzoic acid, gave very unstable w/o emulsions in the intermediate pH region, while stable o/w emulsions were found in the high pH region.