Tadeusz Dabros

Micropipette: a new technique in emulsion research

Abstract Micron-scale studies on emulsions have, to date, been largely limited to the imaging of colloidal structures. In this communication, micropipette techniques are introduced as a progression beyond mere visualization: using small suction pipettes, mechanical experiments are performed on individual emulsion drops, from which interfacial properties can be deduced. To demonstrate this technique, the interfacial tension, emulsion stability and adsorption characteristics are directly assessed at the surfaces of micron-sized water droplets that are dispersed in crude oil.

Stability and settling characteristics of solvent-diluted bitumen emulsions☆

When bitumen emulsions are diluted with aliphatic solvents at solvent-to-bitumen ratios above a certain value, water droplets, solids, and precipitated asphaltenes tend to form clusters that are much larger than the individual components. This work demonstrates that bitumen emulsions diluted with aliphatic solvent exhibit settling behavior distinctly different from that of bitumen emulsions diluted with aromatic solvent. The aliphatic system exhibits a zone settling mode with sharp interfaces. A characteristic interface appears as a discontinuity between the clean oil phase and the hindered settling zone. Laboratory techniques have been developed for measuring settling rates by tracking the interface positions with time. As an example, an experimentally observed settling curve was modeled by solving the conservation law hyperbolic equations.

Role of Asphaltenes in Stabilizing Thin Liquid Emulsion Films

Drainage kinetics, thickness, and stability of water-in-oil thin liquid emulsion films obtained from asphaltenes, heavy oil (bitumen), and deasphalted heavy oil (maltenes) diluted in toluene are studied. The results show that asphaltenes stabilize thin organic liquid films at much lower concentrations than maltenes and bitumen. The drainage of thin organic liquid films containing asphaltenes is significantly slower than the drainage of the films containing maltenes and bitumen. The films stabilized by asphaltenes are much thicker (40-90 nm) than those stabilized by maltenes (∼10 nm). Such significant variation in the film properties points to different stabilization mechanisms of thin organic liquid films. Apparent aging effects, including gradual increase of film thickness, rigidity of oil/water interface, and formation of submicrometer size aggregates, were observed for thin organic liquid films containing asphaltenes. No aging effects were observed for films containing maltenes and bitumen in toluene. The increasing stability and lower drainage dynamics of asphaltene-containing thin liquid films are attributed to specific ability of asphaltenes to self-assemble and form 3D network in the film. The characteristic length of stable films is well beyond the size of single asphaltene molecules, nanoaggregates, or even clusters of nanoaggregates reported in the literature. Buildup of such 3D structure modifies the rheological properties of the liquid film to be non-Newtonian with yield stress (gel like). Formation of such network structure appears to be responsible for the slower drainage of thin asphaltenes in toluene liquid films. The yield stress of liquid film as small as ∼10(-2) Pa is sufficient to stop the drainage before the film reaches the critical thickness at which film rupture occurs.

DESTABILIZATION OF WATER IN BITUMEN EMULSION BY WASHING WITH WATER

ABSTRACT In order to get more information about the mechanism of stabilization of water-in-diluted-bitumen emulsion, bitumen diluted with toluene (10%, 25%, and 50% in volume) was “washed” using different amounts of water (0.20% in volume). The washing water was emulsified and then separated by high-speed ultra-centrifugation. The supernatant was then used to create a second w/o emulsion with the addition of new water. Stability of the new emulsion was measured in terms of the water separation rate under a low centrifugal force It has been found that a very stable w/o emulsion was obtained in original diluted bitumen. However, after the diluted bitumen was pre-washed with a few per cent of water, the second emulsion became unstable. This indicates a significant effect of pre-washing with water on emulsion stability, possibly through the removal of emulsion stabilizing agents. Based on analytical results such as surface tension, and FTIR spectra, it appears that a small fraction of bitumen, mostly polar co...

Selective Solvent Deasphalting for Heavy Oil Emulsion Treatment

Solvents are often used to treat heavy oil emulsions such as bitumen froth produced in the recovery of bitumen from oil sands. It has been found that the aromaticity of the solvent and the solvent-to-bitumen dilution ratio (S/B, by wt) have profound effects on the stability of water-in-bitumen emulsions. An aliphatic solvent at a certain S/B not only partially precipitates asphaltenes from the solvent-diluted bitumen solution, but also, at the same time, promotes aggregation of the emulsified water droplets (WD), dispersed solids (DS), and precipitated asphaltenes (PA). The WD/DS/PA aggregates exhibit zone settling in solvent-diluted bitumen, and various distinct zones and corresponding interfaces develop during settling. Typically, the top zone is a clean oil phase containing less than 0.1 wt% water– plus–solids, the middle is an emulsion zone containing the WD/DS/PA aggregates, and the bottom is a compaction zone of the settled WD/DS/PA aggregates. The position of the sharp interface that develops between the oil phase and the emulsion zone can be tracked by visual observation with the help of proper illumination. An in-line transflectance probe coupled with a spectrophotometer via a fiber-optic cable is also developed for monitoring the settling of the WD/DS/PA aggregates. The settling rate depends on many factors and conditions including solvent type, S/B, temperature, and mixing conditions. Treatment of bitumen emulsions with aliphatic solvents not only produces clean bitumen but also leads to significant reductions in asphaltene content, coking propensity, and the concentrations of metals, sulfur, and nitrogen. The viscosity of the bitumen is also reduced, which, in turn, significantly reduces the amount of light diluent that must be blended with the bitumen in order to meet the pipelining specification for viscosity. Therefore, proper selection of solvent, S/B, and other process conditions make it possible to produce bitumen products to satisfy a variety of specifications. The term heavy oils usually refers to crudes with API gravity of less than 20◦. Heavy oils with API gravity less than 10◦ are also called extra heavy oils

Applications of colloidal force measurements using a microcollider apparatus to oil sand studies

Abstract Two colloidal force measurement techniques have been applied to oil sand studies both using the same apparatus called the microcollider. The techniques are colloidal particle scattering method for repulsion-dominant systems and hydrodynamic force balance method for attraction-dominant systems. The former is based on calculating the colloidal forces from the magnitude of particle–particle collision trajectory deflections. The latter is based on separating a colloidal doublet with increasing shear and calculating the maximum attractive force at the onset of the doublet breakup. Both methods involve the microscopic observation on two individual particles. The methods are also well suited to emulsion systems where the interaction forces as small as 10 −13 N between two droplets can be detected. In oil sand research, two stable emulsions: water-in-diluted bitumen and bitumen-in-water have been receiving considerable attention because of their detrimental effects on the industrial process. The droplet–droplet forces and the emulsion stability mechanism were determined for both emulsions using either one of the techniques. For the w/o emulsion, steric repulsion is the main contributor to the emulsion stability. For the o/w emulsion, all interactions are exclusively DLVO-type forces and the electrostatic force plays a major role in stabilizing the emulsion. Isolated protrusions of tens of nanometers in thickness have also been detected on bitumen surfaces. The protrusions enhance the repulsive force at a long distance but reduce it near the energy barrier, a useful feature that might help in destabilizing the system.

Analysis of energy balance during collision of an air bubble with a solid wall

The dynamics of bubble-wall collision is studied by means of numerical simulations to elucidate the mechanism of bubble rebound at a solid, no-slip wall in viscous liquid. Results obtained are compared with experimental data as well as data reported in the literature. Similarities and differences are discussed. Bubble trajectory, shape deformation, added mass variation as a function of distance from the wall, and relations between various forms of energy in the system during bubble impact, liquid film formation, and rebound are presented and analyzed. On the basis of this, collision time is quantitatively defined as a time interval during which pronounced changes of kinetic energy are observed. For a rising bubble colliding with a horizontal wall, series of collisions are observed, each associated with dissipation of kinetic energy, mainly in the thin film formed between the bubble and the wall.

Study on the Mechanism of Foaming from Bitumen Froth Treatment Tailings

In the processing of Alberta oil sands, stable foams sometimes form during recovery of solvent from bitumen froth treatment tailings. This may interrupt the normal operation of the solvent recovery unit. A laboratory study was conducted to identify the cause of foam formation. Foaming behavior was observed using a glass column in which light hydrocarbon vapor was bubbled into model clay suspensions as well as samples of the actual tailings. Experimental results indicate that the stable foams occur due to presence of fine solids contaminated by bitumen fractions and are not caused by the surfactants present in the tailings water.

EMULSIFICATION OF OIL SAND BITUMEN IN CAUSTIC SOLUTION

Bitumen in the form of concentrated bitumen-in-water emulsion can be transported using a pipeline. Froth, which is a product of water based extraction of bitumen from oil sands, can be emulsified using NaOH. The emulsion can then be inverted by lowering pH to recover the bitumen. NaOH concentration, salt concentration, temperature, and mechanical energy input affect the formation of the emulsion and its viscosity. Optimum conditions for emulsion formation and inversion were specified.