Infrared Spectroscopic Analysis of the Composition of an Oil/Water Interfacial Film

Abstract

Interfacial tension plays an important role in reservoir mechanisms and in the production and processing of crude oil with coproduced water. Natural surfactants adhere to the oil/water (O/W) interface, which reduces the interfacial tension and in some cases leads to a solidified interfacial film with a significant impact on emulsion stability. These technical challenges are a result of the chemistry of the petroleum system, and hence optimization of production depends on a better understanding of this. The properties and composition of the interfacial film have been the subject of many studies. In this study, films of oil-related components were generated at the interface between oil and water. The interfacial material was recovered by skimming the interface remaining after repeated solvent washings. The recovered material was analyzed using Fourier transform infrared spectroscopy by attenuated total reflectance (FTIR ATR) to obtain both quantitative and qualitative information about the composition of the film. When compared to the spectrum of the total precipitated n-heptane asphaltenes, which show many aromatic features, the interfacial film shows surprisingly few of these. There is a substantial difference between the interfacial film material and the asphaltenes, especially in the aromatic C−H vibration range between 700 and 900 cm −1 . It is observed that oxygenated compounds, sulfoxides and carbonyls, and one specific type of aromatics are concentrated in the film. The latter also shows up in the oil and in the maltenes but less prominently. In a recent communication [Andersen et al. Energy Fuels 2016, 30 (6), 4475−4485], we showed that homologous series of fatty acids can be found in the interfacial film, and the current detailed examination of the FTIR spectra also indicates that the water interface serves as a "substrate" for specific adsorption of aromatic molecules that are not representative of the bulk asphaltenes.

Interfacial Viscoelasticity in Crude Oil-Water Systems to Understand Incremental Oil Recovery

“…This region indicates the absence of amine (-NH 2 ) groups in the interfacial films and the presence of a broad peak at 3200 cm −1 , representing the O-H group in carboxylic acids. This observation is consistent with similar observations in the literature Andersen et al (2017).…”

“…In addition, the peak at 1027 cm −1 indicates the accumulation of sulfoxide groups at the interface. All these demonstrate that the key contributor to the formation of the interfacial films are Polar aromatic groups with long chains and not the highly condensed aromatic groups (Andersen et al, 2017). The effect of sodium chloride.…”

Dynamic Asphaltene-Stearic Acid Competition at the Oil–Water Interface

“…Intuitively, one may also assume that the activity of the asphaltene constituents may vary broadly. Recently, Andersen et al 33 have confirmed that only specific types of asphaltenes are found at the interfaces, which means some types of asphaltenes are less surface-active and therefore also easily excluded.…”

Model Asphaltenes Adsorbed onto Methyl- and COOH-Terminated SAMs on Gold

“…The adsorption and positioning of natural asphaltene molecules at interfaces have been debated from having large aromatic cores parallel to interfaces to molecules positioned perpendicular to the interface. , Some of this apparent discrepancy is mainly due to the large geochemical variability in composition, molecular structure, and the observation that the molecular nature of adsorbed asphaltenes is different from the asphaltenes in bulk . Much interpretation has been based on interfacial tension analysis using the Gibbs–Langmuir approach estimating an average occupied area/molecule and the analogy with simple molecules .…”

“…6,40 Some of this apparent discrepancy is mainly due to the large geochemical variability in composition, molecular structure, and the observation that the molecular nature of adsorbed asphaltenes is different from the asphaltenes in bulk. 41 Much interpretation has been based on interfacial tension analysis using the Gibbs−Langmuir approach estimating an average occupied area/molecule and the analogy with simple molecules. 42 The latter may, even for simple molecules, show that simple polyaromatics are not adsorbed with the aromatic sheet parallel to the water−oil interface but is positioned in some angular ordered fashion.…”