Oil leakage and the discharge of oil/water mixtures by domestic and industrial consumers have caused not only severe environmental pollution and a threat to all species in the ecosystem but also a huge waste of precious resources. Therefore, the separation of oil/water mixtures, especially stable emulsion, has become an urgent global issue. Recently, materials containing a special wettability feature for oil and water have drawn immense attention because of their potential applications for oil/water separation application. In this paper, we systematically summarize the fundamental theories, separation mechanism, design strategies, and recent developments in materials with special wettability for separating stratified and emulsified oil/water mixtures. The related wetting theories that unveil the physical underlying mechanism of the oil/water separation mechanism are proposed, and the practical design criteria for oil/water separation materials are provided. Guided by the fundamental design criteria, various porous materials with special wettability characteristics, including those which are superhydrophilic/underwater superoleophobic, superhydrophobic/superoleophilic, and superhydrophilic/in-air superoleophobic, are systemically analyzed. These superwetting materials are widely employed to separate oil/water mixtures: from stratified oil/water to emulsified ones. In addition, the materials that implement the demulsification of emulsified oil/water mixtures via the ingenious design of the multiscale surface morphology and construction of special wettability are also discussed. In each section, we introduce the design ideas, base materials, preparation methods, and representative works in detail. Finally, the conclusions and challenges for the oil/water separation research field are discussed in depth.

Separation Mechanism and Construction of Surfaces with Special Wettability for Oil/Water Separation.

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

The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.

Control of zeolite framework flexibility and pore topology for separation of ethane and ethylene.

Interfacial behavior of asphaltenes.

Absolute ethylene/ethane separation is achieved by ethane exclusion on silver-exchanged zeolite A adsorbent. This molecular sieving type separation is attributed to the pore size of the adsorbent, which falls between ethylene and ethane kinetic diameters.

Absolute molecular sieve separation of ethylene/ethane mixtures with silver zeolite A.

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

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. ...

Role of asphaltenes in stabilizing thin liquid emulsion films.

The asphaltene fraction of crude oil is commonly considered to be responsible for the formation of highly undesirable, stable water-in-crude oil emulsions and rag layers. We developed a new procedure for subfractionation of asphaltenes based on their interfacial activity. The most interfacially active asphaltene (IAA) subfraction was extracted as an interfacial material from emulsified water droplets in asphaltene solution. The IAA subfraction represents less than 2 wt % of whole asphaltenes (WA), but its removal had a profound effect on interfacial and thin emulsion film properties. It was found that the IAA subfraction is a main contributor to emulsion stabilization and formation of rigid oil−water interfaces. IAA adsorbed irreversibly at the oil−water interface and formed interfacial layers of low compressibility. Thin emulsion films of toluene stabilized by IAA were thicker and exhibited severe aging effects in contrast to the films stabilized with remaining asphaltene fractions, which were thin and l...

Asphaltene Subfractions Responsible for Stabilizing Water-in-Crude Oil Emulsions. Part 1: Interfacial Behaviors

After successful isolation of the most interfacially active subfraction of asphaltenes (IAAs) reported in the first part of this series of publications, comprehensive chemical analyses including ES-MS, elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectrometry were used to determine how the molecular fingerprint features of IAAs are different from those of the remaining asphaltenes (RAs). Compared with the RAs, the IAA molecules were shown to have higher molecular weight and higher contents of heteroatoms (e.g., three times higher oxygen content). The analysis on the elemental content and FTIR spectroscopy suggested that IAAs contained higher contents of high-polarity sulfoxide groups than the RAs. The results of ES-MS, NMR, FTIR, and elemental analyses were used to construct average molecular representations of IAA and RA molecules. These structures were used in molecular dynamics (MD) simulation to study interfacial and aggregation behaviors of ...

Fan Yang

Papers

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

Role of asphaltenes in stabilizing thin liquid emulsion films.

Asphaltene Subfractions Responsible for Stabilizing Water-in-Crude Oil Emulsions. Part 1: Interfacial Behaviors

Asphaltene Subfractions Responsible for Stabilizing Water-in-Crude Oil Emulsions. Part 2: Molecular Representations and Molecular Dynamics Simulations

High pressure adsorptive separation of ethylene and ethane on Na-ETS-10