Chemical Evaluation of Interfacial Materials in Petroleum: Comparison between Extraction Methods
Name: THAYNARA REGINA DE SOUZA COSTA
Publication date: 05/03/2026
Examining board:
Name |
Role |
|---|---|
| ELIANE VALÉRIA DE BARROS | Examinador Externo |
| EMANUELE CATARINA DA SILVA OLIVEIRA | Examinador Interno |
| LINDAMARA MARIA DE SOUZA | Coorientador |
| ROGERIO MESQUITA DE CARVALHO | Examinador Externo |
| WANDERSON ROMÃO | Presidente |
Summary: The formation and stability of water-in-oil (W/0) emulsions in petroleum are influenced by the presence of species that accumulate at the interface, collectively referred to as interfacial material (IM). Understanding their composition is essential to elucidating the mechanisms governing emulsion stability and interfacial rigidity. However, the chemical complexity of IM hinders the identification of its major constituents. In this study, IM fractions from four Brazilian crude oils were isolated using two methods-centrifugation followed by Dean-Stark distillation, and adsorption on wet silica-and characterised by negative-ion electrospray Fourier-transform ion cyclotron resonance mass spectrometry (ESI(-) FT-ICR MS), gas chromatography with flame ionisation detection (GC-FID), elemental analysis (CHNS-0), and mid-Fourier transform infrared spectroscopy (mid-FTIR). The ability of the IM fractions to stabilise emulsions was also evaluated. The results showed that IM fractions are more selective for highly polar oxygenated compounds (N2[H], NO[H], N02[H], N03[H], N04[H], O[H], 02[H], 02S[H], Q3[H], Q3S[H], Q4[H], NOS[H],
and Q4S[H]) and significantly suppress the ionization of carbazole-type species
(N[H]), along with higher carbon numbers and double bond equivalents (DBE). On one hand, the wet silica method proved selective for more polar species, enriching the IM in the 02[H] class, commonly related to the presence of Napththenic Acids (ANs), traditionally associated with the formation of rigid interfacial films. Centrifugation/Dean-Stark, on the other hand, preserved a more representative fraction of the interfacial material, allowing the detection of classes such as N02[H] and N03[H], whose lower polarity may explain their absence in some samples obtained by silica. GC-FID analysis confirmed a more aliphatic character in the IM fractions obtained by centrifugation, with a greater presence of hydrocarbons (HC). Elemental analysis and mid-FTIR spectrometry indicated that both extraction methods enrich the IM in polar and heteroatom-containing species relative to the crude oils, although with distinct selectivity. The IMW fraction (wet-silica interfacial material) concentrates more oxygenated, sulfur-containing, and unsaturated compounds, whereas IMR preserves relatively more saturated constituents, yielding a more chemically balanced fraction overall. Model emulsion tests further showed that IM fractions obtained by centrifugation/Dean-Stark impart greater stability to the W/0 system than those isolated using wet silica, reinforcing that W/0 emulsion stabilisation must consider both polar and nonpolar species simultaneously.
