Yan Peng,Xiangyu Zhang,Lihua Cheng,Hong Zhang,Jieyun Tang,Hong Chen,Qinzhen Fan,Xinping Ouyang
The presence of asphaltene, especially in heavy crude oil, causes difficulties in the de-watering/desalting process, which is the initial step of crude oil pretreatment. This study investigates the effect of asphaltenes on the stability of crude oil emulsions using a simulated oil system composed of toluene and n-heptane. It was found that asphaltenes behave like conventional surfactants, adsorbing at the oil–water interface and reducing interfacial tension. The critical aggregation concentration (CAC) of W/O emulsions formed from a toluene and n-heptane mixture (7:3 volume ratio) was found to be 0.05 g/L. When the asphaltene concentration was greater than CAC, the asphaltene aggregated into clusters, forming a viscoelastic interface film that enhanced the strength of the emulsion droplets. At an asphaltene concentration of 0.01 g/L, the storage modulus (G′) and loss modulus (G″) were 1.12 Pa·s and 8.94 Pa·s, respectively. The storage modulus G′ was less than the loss modulus G″, indicating that the viscoelastic nature of the emulsion, and both the G′ and G″ of the emulsions increased with the increasing asphaltene concentration. When the concentration reached 11 g/L, G′ and G″ were 1033 Pa·s and 416 Pa·s, respectively, with G′ exceeding G″, indicating that the emulsion became more stable. Moreover, increasing the solvent aromaticity led to a rise in the CAC of asphaltene, which was favorable for breaking emulsions. The findings imply that reducing the asphaltene content at the interfaces of oil–water by adding an aromatic solvent or blending with light crude oil is a feasible way to break the emulsion and further dewater and desalt.
The polymerization of three typical aromatic solvent-doped fullerene materials with similar hexagonal closest packed (hcp) structures (mesitylene/C60, m-dichlorobenzene/C60 and m-xylene/C60 solvates) is studied under high pressure and high temperature (HPHT, 1.5 GPa, 573 K and 2 GPa, 700 K, respectively). Raman and photoluminescence spectroscopies reveal that the intercalated aromatic solvents play a crucial role in tailoring the extent of polymerization of C60 molecules. In the solvates, the solvents confine formation of covalent bonds between C60 molecules to the 001 direction and the (001) plane of the hcp lattices, leading to the formation of mixed polymeric phases of monomers, dimers, one-dimensional (1D) chainlike oligomers, and two-dimensional (2D) tetragonal phase polymers under suitable HPHT conditions. The type and number of substituent groups of the aromatic solvents are found to have significant influence, determining the amounts and types of polymeric phases formed. Our studies enrich the understanding of the formation mechanisms for controllably fabricating polymeric fullerenes and facilitate targeted design and synthesis of unique fullerene-based carbon materials.
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