No abstract

No abstract

No abstract

The buoyant drop method is a ubiquitous tool for addressing phenomena at the liquid−liquid interface via the determination of the interfacial tension (IFT) between two immiscible phases. Here, the focus is on how electrolytes (in an aqueous phase) and carboxylic acids (in a decane phase) impact the interfacial layer between the two phases. The IFT measurement provides a single number, which is not fulfilling when it comes to deducing information about a complex multiparameter system. Furthermore, the temporal evolution of IFT does not always reach a steady-state value on a time scale, which is realistic to use for comparative studies. We have investigated the temporal evolution of IFT in a series of experiments with varying compositions of the decane−carboxylic acid phase and the brine phase. The results show that there are at least two opposing effects in play. For water-soluble acids, the IFT initially increases with time until a turnover point is reached from where there is a gradual decay. The IFT at the turnover point is close to that of the pure water−decane system. For a poorly water-soluble acid, the IFT shows a much smaller increase and the turnover happens much faster. For a water-soluble acid, there is a high degree of sensitivity toward the electrolyte; it determines the position (in time) of the IFT peak and the steepness of the subsequent decay. Now, if the phases are reversed, that is, by placing a drop of brine in the decane− surfactant phase, the IFT decreases with time regardless of the acid and with little impact of the electrolyte and its concentration in the brine. We propose an explanation for the observed behavior (supported by COSMO-RS calculations), which is based on diffusion in and out of the two phases, solubility, and interfacial reactivity (i.e., aggregation between electrolytes and carboxylic acids).

Surface-active components in the form of intrinsic emulsifiers have been studied, and their possible role as demulsifiers has been assessed. Polar components were extracted from crude oil via three isolation methods involving liquid/liquid extraction at pH 14, liquid/liquid extraction at pH 1, and column chromatography. All three isolates were found to improve separation within hours independent of their concentration. The material isolated from acidic extraction was found to be the most efficient. An expanded chemical analysis of the isolates involving Fourier transform infrared spectroscopy, UV−vis spectroscopy, liquid chromatography–mass spectrometry, and liquid chromatography–tandem mass spectrometry analysis was employed to identify the polar compounds in the three isolates. The most polar components were found to be naphthenic acids and saturated and nonsaturated noncyclic carboxylic acids. The least polar compounds were found to be nitrogen-containing aromatic bases such as pyridines, quinolines, pyrroles, indoles, indolines, and carbazoles. A mixture of compounds with polarities between the acids and bases were identified as phenols, pyrans, benzopyrans, naphthopyrans, benzonaphtholpyrans, dibenzopyrans, dinaphthopyrans, and compounds containing both nitrogen and oxygen atoms. The fact that so many compounds are found in each extract makes it difficult to speculate on exactly what types of molecules are significantly contributing positively to the emulsion breaking and separation process. The suggested polar molecules from this work have been sufficiently precise for a follow-up study to be realistic and promising, where the dominating polar molecules in each category are synthesized and subjected to separation experiments. Finally, interesting observations were made that relate to oil maturity and origin.