Effect of the Asphaltene Oxidation Process on the Formation of Emulsions of Water in Oil (W/O) Model Solutions

In this paper, the formation of water in oil (W/O) model solution emulsions using untreated and oxidized asphaltenes as emulsifiers was evaluated. Emulsions were formed with deionized water and toluene at different water/toluene ratios (1:4, 1:1, and 4:1) and concentrations of asphaltenes of 100, 500, and 1000 mg/L. Asphaltenes were oxidized at two different temperatures of 373 and 473 K for various exposure times. Untreated and oxidized asphaltenes were characterized by thermogravimetric analyses, C, H, N, S and O elemental analyses, solvency tests in toluene, and qualitative structural indexes from Fourier-transform infrared spectroscopy. The emulsions were evaluated for stability, the percentage of oil in water (O/W) and W/O phases, interfacial tension (IFT), and mean droplet diameter. The asphaltenes solubility decreased up to 93% as the temperature of oxidation and the exposure time increased. The amount of W/O emulsion increases when asphaltene concentration, exposure time, and oxidation temperature increase. With oxidized asphaltenes at 373 and 473 K, the formation of W/O emulsions increased by approximately 30% and 70% for a fixed asphaltene concentration, respectively. IFT revealed that after oxidation, no carboxylic acids were formed. A hypothetical oxidation reaction of asphaltenes to ketones and sulphoxide, and nitrogen and alkyl chain removal is proposed.