The components of petroleum asphaltenes exhibit complex bridged structures comprising sulfur, nitrogen, aromatic, and naphthenic groups linked by alkyl chains. These components aggregate in crude o...

Supramolecular Assembly Model for Aggregation of Petroleum Asphaltenes

With the ever increasing demand for energy to meet the needs of growth in population and improvement in the living standards in particular in developing countries, the abundant unconventional oil reserves (about 70% of total world oil), such as heavy oil, oil/tar sands and shale oil, are playing an increasingly important role in securing global energy supply. Compared with the conventional reserves unconventional oil reserves are characterized by extremely high viscosity and density, combined with complex chemistry. As a result, petroleum production from unconventional oil reserves is much more difficult and costly with more serious environmental impacts. As a key underpinning science, understanding the interfacial phenomena involved in unconventional petroleum production, such as oil liberation from host rocks, oil–water emulsions and demulsification, is critical for developing novel processes to improve oil production while reducing GHG emission and other environmental impacts at a lower operating cost. In the past decade, significant efforts and advances have been made in applying the principles of interfacial sciences to better understand complex unconventional oil-systems, while many environmental and production challenges remain. In this critical review, the recent research findings and progress in the interfacial sciences related to unconventional petroleum production are critically reviewed. In particular, the chemistry of unconventional oils, liberation mechanisms of oil from host rocks and mechanisms of emulsion stability and destabilization in unconventional oil production systems are discussed in detail. This review also seeks to summarize the current state-of-the-art characterization techniques and brings forward the challenges and opportunities for future research in this important field of physical chemistry and petroleum.

Interfacial sciences in unconventional petroleum production: from fundamentals to applications

Most crude oils contain traces of vanadium, which cause significant detrimental impact during catalytic conversion and combustion. The concentrations in bitumen and vacuum residue are generally much higher, which poses a problem for the economical upgrading of these feedstocks. These problems are relevant since the world reserves of conventional light oils are dwindling and being replaced by an increasing amount of heavier feedstocks. In this article, the current understanding of the distribution and form of vanadium compounds within vacuum residue is critically discussed. The implications of this chemistry on prospects for new separation methods, other than deasphalting, are considered. Although only a small fraction of the vanadium is contained within the polar resin fraction (i.e., maltenes), this fraction has been most often characterized to determine the chemical form of the vanadium compounds. Various spectroscopic techniques have been used to determine that these resin soluble vanadium compounds ex...

Chemistry and Association of Vanadium Compounds in Heavy Oil and Bitumen, and Implications for Their Selective Removal

The demulsification mechanism of asphaltene-stabilized water-in-toluene emulsions by an ethylene-oxide–propylene oxide (EO–PO) based polymeric demulsifier was studied. Demulsification efficiency was determined by bottle tests and correlated to the physicochemical properties of asphaltene interfacial films after demulsifier addition. From bottle tests and droplet coalescence experiments, the demulsifier showed an optimal performance at 2.3 ppm (mass basis) in toluene. At high concentrations, the demulsification performance deteriorated due to the intrinsic stabilizing capacity of the demulsifier, which was attributed to steric repulsion between water droplets. Addition of demulsifier was shown to soften the asphaltene film (i.e., reduce the viscoelastic moduli of asphaltene films) under both shear and compressional interfacial deformations. Study of the macrostructures and the chemical composition of asphaltene film at the toluene–water interface after demulsifier addition demonstrated gradual penetration ...

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Demulsification Mechanism of Asphaltene-Stabilized Water-in-Oil Emulsions by a Polymeric Ethylene Oxide−Propylene Oxide Demulsifier

We present a model explaining the mechanism of water-in-oil (W/O) emulsion stabilization in petroleum systems. According to the model, W/O petroleum emulsions are stabilized by at least two types of chemicals:  one is a small subfraction of asphaltenes, and the other is a low-molecular-weight, surfactant-like material. Their competition for the oil/water interface is based on adsorption kinetics, rather than on differences in adsorption energies. The asphaltenic material adsorbs slowly and irreversibly and forms rigid skins. Surfactant-like species adsorb fast, reaching equilibrium. Both are effective emulsifiers; however, emulsion breaking requires different strategies, depending on the stabilizer.

On the Stabilization Mechanism of Water-in-Oil Emulsions in Petroleum Systems

A method includes diluting a bitumen source, such a bitumen froth from a hot water extraction process, with a hydrocarbon diluent such as naphtha, contacting the bitumen with a zone settling aid such as a polyoxyalkylate block polymer, flocculating water and fine solids in the diluted bitumen, separating the flocculated water and fine solids from the solvent-diluted bitumen, and producing dry, clean diluted bitumen. Preferably, the diluted bitumen will have less than 1.0 wt % water, but most preferably less than 0.7 wt % water. The method may further comprise maintaining the diluted bitumen under conditions that avoid the precipitation of asphaltenes from the bitumen, preferably such that the dry, clean diluted bitumen comprises essentially all, such as greater than 96%, of the asphaltene content from the bitumen source. Counter-current flow may be performed in a series of zone settling stages, such as with gravity settling.

Zone settling aid and method for producing dry diluted bitumen with reduced losses of asphaltenes

The ability to stabilize water-in-oil (W/O) emulsions for six studied asphaltene subfractions is dependent on their solubility rather than on their concentration, polarity, molecular weight, or other parameters. Paraffinic froth treatment technology recently introduced in the oil sand industry yields a clean bitumen product (<0.1 wt % water and <0.1 wt % solids) at a solvent-to-bitumen ratio above a critical value, which corresponds to the onset of asphaltene precipitation. Six subfractions of Athabasca bitumen asphaltenes were obtained by precipitation with a gradually increasing heptane-to-bitumen (H/B) ratio, from 1.25 to 40. The properties of the asphaltene subfractions obtained were investigated by elemental analysis, Fourier transform infrared (FTIR) and ultraviolet-visible (UV−vis) spectroscopy, and vapor pressure osmometry (VPO). There were no significant differences in the molecular masses of the six asphaltene subfractions. However, the aromaticity and the metalloporphyrin (vanadyl) content in t...

Investigation of Subfractions of Athabasca Asphaltenes and Their Role in Emulsion Stability

Samples of rag layer were collected using multiple bench-top, batch centrifugations with optical microslides inserted to a centrifuge cell in the last spinning. Image analysis of the samples provided data for approximate sedimentation rate analysis, based on fractal floc dimension and Smoluchowski coagulation kinetic equation. The analysis shows that, if a flocculating chemical is used as a demulsifier, overdosing will necessarily result in deterioration of the process performance. Optimization of the chemical dosage and accurate process control are thus necessary conditions to attain satisfactory dewatering process performance.

Xiaoli Yang

Papers

Zone settling aid and method for producing dry diluted bitumen with reduced losses of asphaltenes

Investigation of Subfractions of Athabasca Asphaltenes and Their Role in Emulsion Stability

On the “Rag Layer” and Diluted Bitumen Froth Dewatering

The effect of naphtha to bitumen ratio on properties of water in diluted bitumen emulsions

Nitrogen-functionalized bone chars with developed surface area for efficient adsorption of multiple aquatic pollutants