Brine ions impacts on water-oil dynamic interfacial properties considering asphaltene and maltene constituents

Exploring the Effect of Relaxation Time, Natural Surfactant, and Potential Determining Ions (Ca2+, Mg2+, and SO42-) on the Dynamic Interfacial Tension Behavior of Model Oil-Brine Systems

This study examined how the concentration of asphaltene and divalent ions in various salinities affects the interfacial tension (IFT) between a model oil/brine using the pendant drop method. The oleic phase consisted of a mixture of toluene and n-heptane (heptol), to which asphaltene was added to investigate how asphaltene molecules affect the surface properties. The base fluid was prepared with a salinity of 40,000 ppm, and two additional solutions with concentrations of 4000 ppm (low salinity) and 80,000 ppm (high salinity) were created. The results revealed that increasing the concentration of asphaltene within certain salinity ranges led to a decrease in IFT. The lowest IFT was observed at the 40,000 ppm salinity level, indicating that at this optimal salinity, the maximum asphaltene concentration migrated to the heptol/brine interface, reducing the IFT from 23 mN/m to 16 mN/m. Additionally, a 0.5 % wt of asphaltene demonstrated a significant concentration of micellization of natural surfactants, suggesting that the interface was nearly saturated with asphaltene. Consequently, concentrations higher than this value did not significantly alter the IFT. In the final part of the study, the impact of divalent ions was investigated, revealing that as the concentration of Ca2+ ions increased up to fourfold, the IFT decreased to 15 mN/m, about 10 % less than the base case. This value represented the lowest IFT compared to Mg2+ and SO42-. Moreover, modeling the results indicated that the relaxation time decreased with increasing salinity, suggesting that higher salinity accelerated the process of asphaltene absorption at the interface.

Membrane Distillation of Saline Water Contaminated with Oil and Surfactants

Application of the membrane distillation (MD) process for the treatment of high-salinity solutions contaminated with oil and surfactants represents an interesting area of research. Therefore, the aim of this study is to investigate the effect of low-concentration surfactants in oil-contaminated high-salinity solutions on the MD process efficiency. For this purpose, hydrophobic capillary polypropylene (PP) membranes were tested during the long-term MD studies. Baltic Sea water and concentrated NaCl solutions were used as a feed. The feed water was contaminated with oil collected from bilge water and sodium dodecyl sulphate (SDS). It has been demonstrated that PP membranes were non-wetted during the separation of pure NaCl solutions over 960 h of the module exploitation. The presence of oil (100–150 mg/L) in concentrated NaCl solutions caused the adsorption of oil on the membranes surface and a decrease in the permeate flux of 30%. In turn, the presence of SDS (1.5–2.5 mg/L) in the oil-contaminated high-salinity solutions slightly accelerated the phenomenon of membrane wetting. The partial pores’ wetting accelerated the internal scaling and affected degradation of the membrane’s structure. Undoubtedly, the results obtained in the present study may have important implications for understanding the effect of low-concentration SDS on MD process efficiency.

Bacteria Cell Hydrophobicity and Interfacial Properties Relationships: A New MEOR Approach

For microbial enhanced oil recovery (MEOR), different mechanisms have been introduced. In some of these papers, the phenomena and mechanisms related to biosurfactants produced by certain microorganisms were discussed, while others studied the direct impacts of the properties of microorganisms on the related mechanisms. However, there are only very few papers dealing with the direct impacts of microorganisms on interfacial properties. In the present work, the interfacial properties of three bacteria MJ02 (Bacillus Subtilis type), MJ03 (Pseudomonas Aeruginosa type), and RAG1 (Acinetobacter Calcoaceticus type) with the hydrophobicity factors 2, 34, and 79% were studied, along with their direct impact on the water/heptane interfacial tension (IFT), dilational interfacial visco-elasticity, and emulsion stability. A relationship between the adsorption dynamics and IFT reduction with the hydrophobicity of the bacteria cells is found. The cells with highest hydrophobicity (79%) exhibit a very fast dynamic of adsorption and lead to relatively large interfacial elasticity values at short adsorption time. The maximum elasticity values (at the studied frequencies) are observed for bacteria cells with the intermediate hydrophobicity factor (34%); however, at longer adsorption times. The emulsification studies show that among the three bacteria, just RAG1 provides a good capability to stabilize crude oil in brine emulsions, which correlates with the observed fast dynamics of adsorption and high elasticity values at short times. The salinity of the aqueous phase is also discussed as an important factor for the emulsion formation and stabilization.

Evolution of adsorbed layers of asphaltenes at oil-water interfaces: A novel experimental protocol

HYPOTHESIS

Asphaltenes can form rigid interfacial films surrounding water droplets rendering water separation from crude oil sluggish. Therefore, the quantitative characterization of such complex film formation is of great importance. As the adsorbed layers of asphaltene illustrate crumpling under compression at certain conditions, the evolution process from soft to rigid states of the film can be evaluated considering standard deviations from Young-Laplace shape fitting.

EXPERIMENTAL

In this study, novel experimental protocols are introduced to investigate the evolution of adsorbed asphaltene layer to a film of aggregates at model oil/water interface by means of dynamic interfacial tension (IFT) and dilational surface rheology measurements. In particular, the surface elasticity and standard deviation from the Young-Laplace shape fitting (YL-SD) are introduced as important indicators for the transformation of a regular asphaltene adsorbed layer to a film of aggregates. Different parameters affecting the film formation and stability, such as aging time, asphaltene concentration, and history of interfacial dynamics, are discussed and linked to emulsion stability.

FINDINGS

It is shown for the first time that the standard deviation of drop profile fitting from the Young-Laplace equation can be used as a rigorous parameter to reveal the properties of the interfacial asphaltene film, which cannot be recognized by regular IFT measurements. Via this novel technique, it is revealed that the transformation of an asphaltene adsorbed layer to a rigid film depends not only on the asphaltene concentration but also on the aging time and the interfacial area perturbations. The results of this new method are supported by measurements of the dilational surface elasticity, which is known as an important parameter for the characterization of complex adsorbed layers, and further verified by an emulsion stability analysis.