A major operational issue in the crude oil industry is the formation of intermediate rag layers, (primarily water-in-oil emulsions) in oil−water separation processes that limit the amount and quality of recoverable oil. In this study, the formation of rag layers is evaluated as a function of solvent−bitumen−water ratios, solvent aromaticity, and temperature, with various imaging techniques. Using these techniques, it is possible to obtain an estimate of the amount of oil, water, and asphalthenes in the rag layer and excess phases. On the basis of these material balances, it was observed that when bitumen is diluted with a more paraffinic (poor) solvent, such as Heptol 80/20 (80% heptane and 20% toluene), the asphaltenes in solution tend to adsorb/segregate at exposed oil−water interfaces, impacting the extent of rag layer formation. Diluting similar systems with a more aromatic solvent (Heptol 50/50) reduces the surface activity of the asphaltenes, and the stability of rag layers, as evidenced by lower asphaltene and oil losses to the rag layer. Furthermore, it was observed that increasing the temperature of the system minimizes rag layer formation and the fraction of oil lost to the rag layer. The better separation at high temperature could be explained by the lower viscosity of the oil, which results in improved oil drainage from the rag layer.
This work focuses on extending the HLD-NAC model to help predict the shape and viscosity of SDHS-toluene-water microemulsions from readily available formulation parameters. To do so, a new shapebased NAC model was introduced which relates the net and average curvatures to the length and radius of microemulsion droplets possessing a hypothesized cylindrical core with hemispherical end caps. Knowing the shape of these droplets, theoretical scattering profiles and maximum hydrodynamic radii were predicted. Furthermore, considering the predicted volume fraction of the dispersed droplets alongside the shape allows for the accurate prediction of the microemulsion viscosity. It was found that treating the microemulsion phase as a dilute suspension of rigid rods yielded predicted viscosities close to the experimental values near the bicontinuous phase transition limits. These correlations were further extended to published experimental data with regard to the viscosities of nonionic surfactant systems. The predicted microemulsion morphology and viscosity may be useful in the design of formulations for nanoparticle synthesis, enhanced oil recovery, and various environmental remediation technologies.
It has been confirmed that the structure of the alkyl group of an extended surfactant plays an important role in defining its interfacial properties. Alkyl groups containing a higher degree of b-branching (C2-branching) produce microemulsions with a larger characteristic length (n, the extent of solubilization in middle phases). This effect is explained on the basis that b-branching increases the hydrophobicity of the surfactant and decreases the optimal salinity of the microemulsion. Higher salinities produce a dehydration of the surfactant groups that lead to shorter extent of the interactions with the oil and the water. Larger characteristic lengths are desirable if the objective of the formulation is obtaining greater solubilization of oil and water, and lower interfacial tensions. Large characteristic lengths are, in most cases, associated with high interfacial rigidities, which are undesirable if rapid coalescence is required. However, mixtures of branched and linear extended surfactants produce large characteristic lengths and lower interfacial rigidities. The HLD-NAC model is able to reflect the experimental trends in solubilization of oil and water. The differences between the predictions of the model for the solubilization of oil and water in Type I and II formulations, respectively, highlight the complexities in the conformation of extended surfactants, particularly their PO groups, at oil-water interfaces and the need for advanced scattering techniques to evaluate these conformations.
It is well-known that surfactant−oil−water (SOW) emulsions undergo substantial changes in drop size (10-fold or more) and stability (up to 4 orders of magnitude) near the phase inversion point. Predicting these changes is important in numerous applications. However, the complex connection between composition, formulation properties, and hydrodynamic conditions limits the ability to predict the outcome of emulsification and demulsification processes. To address this gap, the hydrophilic−lipophilic deviation (HLD) was used to quantify the proximity to the inversion point, considering the composition of the formulation, temperature, and electrolyte concentration. The net-average-curvature (NAC) equations combined with the HLD predicted the density, interfacial tension, interfacial rigidity, and viscosity for the sodium dihexyl sulfosuccinate (SDHS)− toluene−water system. The predicted properties were incorporated in hydrodynamic models to predict the initial emulsion drop size. The calculated properties and initial drop size were then used in a modified version of the Davies and Rideal coalescence model that incorporates hole nucleation theory to predict emulsion stability. The predictions were consistent with the changes in emulsion drop size and stability around the phase inversion obtained for the SDHS−toluene−water system, and with stability values reported in the literature for ionic and nonionic SOW systems.
Acid soluble biopolymeric substances (SBP) were isolated from different urban biowastes comprised of a range of materials available from metropolitan areas. These biowastes provided products with a chemical nature and solubility properties changing over a wide range and, thus, allowed to assess the effect of the variability of the chemical nature on molecular conformation and surface activity in water solution. For this scope, the SBP were characterized for chemical composition and molecular weight (MW) by microanalysis, potentiometric titration, (13)C NMR spectroscopy, and size exclusion chromatography (SEC) coupled with an online multiangle light scattering (MALS) detector. These materials were found to have 67-463 kg mol(-1) MW and 6-53 polydispersity index and to contain carboxylic acid and phenol groups bonded to aromatic and aliphatic C chains. An empirical parameter (LH) was calculated for use as an index of the lipophilic/hydrophilic C atoms ratio. The products solubility properties in solvents of different polarity, surface activity, power to enhance the water solubility of hydrophobic compounds, and particle size in water solution were also investigated by measurements of the products partition coefficient between polyethylene glycol and water (KPEGW) and of air-water surface tension (γ), water-hexane interfacial tension (IFT), disperse red orange dye solubility (DS), and dynamic light scattering (DLS) versus added SBP concentration (Cs). The results indicate that LH correlates well with KPEGW and with the products surface activity properties. Both γ and DS are shown to depend on Cs, although in opposite ways, that is, higher Cs values yield lower γ and higher DS values. Both DS-Cs and γ-Cs plots showed a significant slope change at approximately the same 1.8-2.5 g L(-1) Cs value. This suggested a change of molecular conformation taking place at the above Cs values. Hydrodynamic diameter values for SBP in solution at Cs ≤ 10 g L(-1) were found to range from 130 to 300 nm, consistent with their macromolecular nature. The DLS coupled to the γ data were consistent with molecules at the water-air interphase and in the bulk water phase having different conformations, but not significantly different molecular sizes. Molecular aggregates more likely form at 50-100 g L(-1) Cs. The results confirm that urban biowastes are a sustainable source of biobased products that may have real commercial perspectives.
A limiting factor impacting the quality and recovery of bitumen from oil sand operations is the formation of stable water-in-oil (w/o) and/or oil-in-water (o/w) emulsions during froth treatment. In a previous study, the impact of asphaltene partitioning on oilÀwater phase separation from the resulting emulsified phases (rag layers) was evaluated as a function of the solventÀbitumenÀwater ratio, temperature, and solvent aromaticity. In this work, the added effect of naphthenic amphiphiles at concentrations of 3 and 10 wt % on oilÀwater phase separation from similarly formulated rag layers is assessed. The observed phase behavior of these rag layers is discussed in view of interfacial coadsorption mechanisms proposed in the literature. A major finding is that, under alkaline process conditions, an increase in the concentration of sodium naphthenates (NaNs), produced as a result of naphthenic amphiphile dissociation, promotes a shift in emulsion morphology from w/o to o/w. The resulting transition from asphaltene-to NaN-controlled properties significantly limits oilÀwater phase separation as a result of an increase in the surface area to volume ratio of dispersed droplets and an enhancement of interfacial asphaltene partitioning. Contrary to NaN-free systems, it was also observed that both the temperature and solvent aromaticity have a minimal effect on the phase behavior of NaN formulations. Furthermore, undissociated naphthenic amphiphiles, referred to as naphthenic acids, are capable of promoting oilÀwater phase separation under acidic formulation conditions.
The partitioning of corrosion inhibitor (CI) products is a measure of their potential to protect oilfield pipelines. In this paper the hydrophilic-lipophilic deviation (HLD) model is first used to quantify their partitioning in terms of the characteristic curvature (C c,act ) of a series of anionic (alkoxylated phosphate esters) and cationic (alkoxylated amines, aromatic amines, imidazoline acetates and quaternary amines) actives. This parameter is expressed over a range of pHs within which pipeline corrosion occurs. The HLD model is next used to predict the partitioning of each active from water into toluene at increased salinities. Linear mixing rules are lastly used to predict the characteristic curvature of Product A (C c,mix ) as a function of the C c,act of a subset of actives.
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