Probing the interactions between asphaltenes and a PEO-PPO demulsifier at oil-water interface: Effect of temperature

HYPOTHESIS

Asphaltenes are primary stabilizers in water-in-oil (W/O) emulsions that cause corrosion and fouling issues. In oil sands industry, oil/water separation processes are generally conducted at high temperatures. A high temperature is expected to impact the interactions between asphaltenes and emulsion breakers (EBs), consequently influencing demulsification performance.

EXPERIMENTS

The adsorption and interactions of asphaltenes and a PEO-PPO type EB (Pluronic F68) at the oil-water interface were investigated at various temperatures, using tensiometer, quartz crystal microbalance with energy dissipation (QCM-D), and atomic force microscopy (AFM). The effect of temperature on EB's demulsification performance was explored through bottle tests. Additionally, demulsification mechanisms were studied using direct force measurements with the droplet probe AFM technique.

FINDINGS

Dynamic interfacial tension and QCM-D results demonstrate that the PEO-PPO type EB exhibits higher interfacial activity than asphaltenes and can disrupt rigid asphaltene films at the oil-water interfaces. Elevated temperatures accelerate the displacement of adsorbed asphaltenes by EB molecules, leading to sparse interfacial films, rapid droplet coalescence, and improved demulsification efficiency (supported by AFM and bottle test results). This work provides valuable insights into interfacial interactions between asphaltenes and EB at different temperatures, enhancing the understanding of demulsification mechanisms and offering useful implications for the development of efficient EBs to enhance oil/water separation performance.

Barrier kinetics of adsorption-desorption of alcohol monolayers on water under constant surface tension

The desorption of spread decanol and dodecanol monolayers at controlled constant surface tension is shown to proceed under mixed barrier-diffusion control; the role of the convective diffusion is also discussed. The desorption rate is measured as a function of the density of the monolayer and the temperature. The rate of barrier desorption increases as the monolayer approaches the collapse point, reaching an infinite value. The average desorption time of an adsorbed dodecanol molecule increases linearly with the area per molecule, and is phase-specific - it is higher for the liquid condensed state of the monolayer than for the liquid expanded. The desorption rate increases with temperature; the activation energy for desorption is independent of the compression and the surface phase. The increase of the intensity of convection is shown to produce a vanishingly thin diffusion layer and causes the desorption to proceed under pure barrier control. A schematic map of the adsorption-desorption regimes acting as a function of time and intensity of the convection is constructed. General expressions for the rate of adsorption and desorption of alcohols are formulated.

Dynamic Surface Tension: Industrial Applications and Characterisation of Commercial Surfactants*

In recent years dynamic surface tension has become increasingly used in industrial laboratories. For a wide range of applications it can be used to improve surfactant selection.

Dynamic surface tension is a non-linear function of surface age and concentration. This must be taken into account when comparing surfactants. The concepts of effectiveness (magnitude of effect) and efficiency (concentration required for desired effect) are discussed. Efficiency parameters are more time-consuming to measure, but may give more relevant and reliable information.

A ring test with an anionic surfactant using the maximum bubble pressure method showed good agreement between six laboratories. The results indicated that c20 (concentration for reducing surface tension by 20 mN m−1) at 0.1 s lifetime is a robust parameter for surfactant characterisation.

Surface properties of mixed monolayers of sulfobetaines and ionic surfactants

To study the influence of the head group in the properties of the mixed monolayers adsorbed at the air-water interface, the surface tension and surface potential of binary mixtures of surfactant have been determined as a function of the surfactant composition. Experiments were carried out with anionic-zwitterionic sodium dodecyl sulfate and dodecyl dimethyl ammoniopropane sulfonate (SDS/DDPS), and cationic-zwitterionic dodecyl trimethylammonium bromide and dodecyl dimethyl ammoniopropane sulfonate (DTAB/DDPS), and dodecyl trimethylammonium bromide and tetradecyl dimethyl ammoniopropane sulfonate (DTAB/TDPS). It was shown that mixed monolayers of cationic-zwitterionic surfactant exhibit small negative deviations of ideal behavior, whereas for SDS/DDPS monolayers show strong negative deviation from the ideality. Deviations of ideal behavior are interpreted by regular solution theory. The surface potential values agree very well with the concentration of the ionic component at the interface. The dynamic surface tension values show that the adsorption kinetics on the interface is a diffusion-controlled process. In monolayers with significant deviation of the ideal behavior, anionic-zwitterionic, there is some evidence of intermolecular attractions after diffusion of both surfactants at the interface.

A simplified method for predicting the dynamic surface tension of concentrated surfactant solutions

A simplified method for predicting the dynamic surface tension of concentrated surfactant solutions is proposed. It is implemented using the framework of the Henry's Law analytical solution to the Ward and Tordai equation for diffusion-controlled adsorption, with the necessary parameters being deduced from the measured equilibrium surface tension equation and a value for the surfactant monomer diffusivity. The method is tested by calculating the dynamic surface tension relaxations of aqueous C10E6 and C10E8 solutions over concentration ranges from well below to well above their critical micelle concentrations (cmc). Results are compared with measured relaxations over 0.001-50 s, and semiquantitative agreement is found, with the best results obtained for concentrations near the cmc. The predictive method may prove useful in such applications as the screening of candidate surfactants for inks used in inkjet printing.