Characterization of Inorganic Solids Present in Brazilian Crude Oil Emulsions Using Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectrometry (EDS): Evaluation of the Effect of Solvents

The characterization and identification of inorganic solids present in Brazilian crude oil emulsions were performed after the application of the ASTM D4807 procedure by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS). Three modified methods were evaluated to verify the solvent influence on the sediment content of crude oil emulsions with different saline and water amounts: (i) use of a toluene and isopropanol mixture (50% + 50%); (ii) use of a toluene + isopropanol + water mixture (50% + 49.5% + 0.5%); and (iii) use of an additional washing step with hot water of the inorganic solids retained on the nylon membrane filter (0.45 μm). Using the unmodified ASTM D4807 and SEM, different types of solid structures, such as “cubic”, “spherical”, and “star” type, “salt spheres”, and divided solids on the membrane surface, were identified. The main elements identified in the solid structures retained on the nylon membranes were Na, Cl, Ca, Ba, Fe, K, Mg, S, Si, and Sr using the EDS detector. For all proposed modifications of ASTM D4807, a significant reduction in sediment content was observed, probably due to the increase in solubility of the inorganic salts in the solvent mixtures used in these modifications. In modification “i”, a reduction higher than 50% was observed in sediment content for all crude oil emulsions analyzed by this alternative method. For modification “ii”, a reduction higher than 74% in sediment content was observed for the majority of crude oil samples. The results obtained for modification “iii” showed a reduction higher than 82% in sediment content when compared to the unmodified ASTM D4807. After the washing of the membranes with hot water (modification iii), only insoluble salts, such as sulfates of alkaline-earth elements, silica, and iron compounds, were identified on the nylon membrane surface. Modification “iii” can be considered as an alternative method for ASTM D4807, minimizing the crystallization of soluble salts on the nylon membrane surface. Finally, the solvent mixture used in the ASTM D4807 procedure seemed to play a significant role in sediment content determination, due to the crystallization of inorganic salts during the crude oil emulsion analysis.