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Fundamental knowledge on the evolution of low temperature oxidized coke was a prerequisite towards a deep understanding of coke deposition and subsequent combustion of ultra-heavy oils during in-situ combustion (ISC) process. This study investigated the structural characterization (oxidation behavior, elemental composition, functional groups, and morphology) and elucidated evolution mechanism of cokes generated from the low temperature oxidation/pyrolysis of the ultra-heavy oil during ISC process. The results shown that, compared with pyrolytic coke, the intermediate groups of C-O/C-OH (1260–1060 cm−1) were further oxidized into C = O (1850–1650 cm−1) groups and finally converted into C = C groups (“coke peak”, 1590 cm−1) in highly conjugated aromatic structures for oxidized cokes. Besides, the oxidized coking condition would result in a higher degree of substitution (γCHAr1, γCHAr4) of aromatic rings (900–700 cm−1) and promote the evolution of N- and S- functional groups. Although >78 % of C 1 s belonged to the graphitic carbon for four cokes, morphologies of oxidized cokes were relatively coarse with much looser distribution. In addition, the corresponding enthalpies were in the order cokeLTO3 (25.51 kJ·g−1) > cokeLTP (24.22 kJ·g−1) > cokeLTO2 (23.23 kJ·g−1) > cokeLTO1 (17.45 kJ·g−1), indicating a considerable contribution of low temperature oxidation reactions on derived coke morphology, oxidizability and exothermicity, which contained complicated and crucial dehydrogenation, crosslinking and polymerization reactions to accelerate coke evolution.

Ionic liquids have been considered for application in petroleum separation (especially in unconventional oil production) as interfacial functional materials at pure state or aqueous solution state. Herein, the interactions between bitumen and silica in ionic liquids (i.e., [Emim][BF4]) aqueous solution and pure ionic liquids have been investigated by dynamic contact angle, atomic force microscopy (AFM) and sum-frequency generation spectroscopy (SFG). Results show that the addition of ionic liquids in water enhances the equilibrium degree of bitumen recession from silica surface, while negligible change has been observed when the bitumen coated plate was put into the pure ionic liquids. The force measurements by AFM demonstrate that the bitumen-silica adhesion force in different systems are in the order of: DI water >1 mM [Emim][BF4] > pure [Emim][BF4]. Results of SFG detection show that the addition of [Emim][BF4] in the aqueous solution strengthens the orientation of water molecules on the silica surface, while making the water molecules more disordered on the bitumen surface. Consequently, a positively charged Helmholtz-like layer is formed by the [Emim]+ cations on negatively charged silica and bitumen surfaces.

Separation of heavy hydrocarbons from mineral surfaces is highly dependent on the oil composition and their host rock surface properties. Herein, the petroleum is divided into SARA fractions (saturates, aromatics, resins, asphaltenes) to investigate their desorption behaviors on different types of mineral surfaces (silica (SiO2), kaolinite (Al2Si2O5(OH)4) and calcium carbonate (CaCO3)). The Quartz Crystal Microbalance with Dissipation (QCM-D) tests show that the saturates and aromatics could desorb from the mineral surfaces spontaneously even in water, while no desorption was observed for the asphaltenes and resins. Although the above desorption could be enhanced by alkaline or surfactant solutions, great difference still appears to different oil fractions. Oil characterization shows that the heavy fractions (i.e., asphaltenes, resins) possess richer acid groups than those of light fractions, allowing the stronger affinity of heavy fractions to the mineral surfaces through polar and chemical interactions. Additionally, the heavy fractions dominate in determining the desorption properties of bitumen (the mixed fractions), and lead to more significant wettability alteration to the mineral surfaces. Furthermore, the oil fractions desorption is also found to be highly influenced by the mineral types. Compared with silica, kaolinite has stronger affinity to the heavy oil fractions, leading to smaller amount of desorption. While on the calcium carbonate surface, less than 11% of the coated oil fractions are observed to be desorbed. Surface characterizations summarize that, due to the difference in mineral composition, the affinity of minerals to oil components in aqueous solutions is given as: calcium carbonate (positively charged calcium ions) > kaolinite (containing –AlOH, –SiOH groups and heavy metal elements) > silica (–SiOH group). The above results reveal the differences among bitumen subfractions and mineral types, allowing potential insights to the development of enhanced oil recovery, such as aqueous-nonaqueous hybrid extraction process, solvent extraction, CO2-enhanced oil recovery, etc.

A switchable solvent with a diamine structure called N, N, N′, N′-tetraethyl-1, 3-propanediamine (TEPDA) has been synthesized through an alkylation reaction. This solvent can switch between its hydrophilic and hydrophobic states with the addition or removal of CO2, respectively. It is found that TEPDA can be applied as an organic solvent and can be ionized in water to form cations. With these properties, TEPDA was proven to perform well with water in separating heavy oil from a carbonate solid surface, resulting in over 10% additional oil recovery. A mechanistic study shows that in this aqueous/non-aqueous hybrid process, TEPDA acts mainly as a solvent in softening and dissolving heavy hydrocarbons (dissolution effect). Meanwhile, a small amount of ionized TEPDA in the aqueous phase acts as a surface-active material accumulating at the oil–water and water–solid interfaces (interfacial modification). Both of these effects work to enhance the detachment of oil from solid surfaces. Additionally, the quality of the recovered heavy oil and the cleanliness of the residual solids are both improved. After extraction, TEPDA can be efficiently recycled by CO2 and N2 bubbling without huge energy consumption compared to distillation. Further tests show that this water-assisted TEPDA process also performs well in detaching oil from other solid surfaces, such as metal and silica.

Chemical demulsification is the most commonly used demulsification method for the separation of oil–water emulsions (W/O) in petroleum industry. Previous experiments demonstrate that the interfacially active asphaltenes (IAA) play the key role in stabilizing the heavy oil–water emulsions. Herein, the molecular dynamic simulation has been applied to reveal the molecular mechanisms on the stability and instability of the IAA-stabilized oil–water emulsions. It is found that IAA could accumulate at the oil–water interface and self-aggregate to form viscoelastic interfacial film through π-π stacking, hydrogen bonds (intermolecular and intramolecular) and other non-covalent bonds. Different types of hydrogen bonds (i.e., S = O…H-O, R-OH…H-O, N-H…N-R, S-H…S = O, S-H…S-R) are found between the IAA molecules due to the presence of heteroatoms (e.g., N, O, S) in IAA. Increasing the IAA concentration would increase the thickness of the IAA film which plays the key roles in stabilizing the emulsions. When the newly synthesized demulsifier (i.e., MJTJU-2) was added into the oil–water emulsion system, the oxygen groups (i.e., hydroxyl, ester groups, carboxyl groups, ether group) in demulsifier could weaken (at least 50%) or even break the hydrogen bonds and π-π stacking between IAAs and form new stronger hydrogen bonds with water molecules. This hydrogen bond reconstruction facilitates the breaking of the IAA film at the oil–water interface, allowing the coalescence of the water droplets in oil phase. This work would provide fundamental understanding for developing new way to efficiently demulsify the petroleum or similar oil–water emulsions.