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Effect of Aromatic Pendants in a Maleic Anhydride-co-Octadecene Polymer on the Precipitation of Asphaltenes Extracted from Heavy Crude Oil

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posted on 11.06.2021, 08:43 authored by Ruzhen Cheng, Run Zou, Long He, Lei Liu, Chang Cao, Xinyuan Li, Xuhong Guo, Jun Xu
The precipitation and deposition of asphaltenes often cause great troubles to the recovery and transportation of crude oil. Adding polymer inhibitors is an effective approach to prevent asphaltenes from clogging. In this study, maleic anhydride-co-octadecene copolymers with imidazolyl, phenyl, and pyridyl pendants were synthesized. The inhibition behaviors of two extracted asphaltenes in the presence of these copolymers were investigated, which were also identified by the rheological tests of the heavy crude oil sample. The chemical structure of both asphaltenes was analyzed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), elemental analysis, and time-of-flight (TOF) spectrometry. Both asphaltenes A and B have a high aromaticity and low H/C. However, asphaltene B has a much higher aromaticity and polarity than that of asphaltene A. Ultraviolet–visible spectroscopy, turbidity meter, and dynamic light scattering (DLS) were employed to determine the precipitation behaviors of asphaltenes in the absence and presence of copolymers. The influence of intrinsic properties of asphaltenes, polymer concentration, and aromatic group grafting ratio on asphaltene precipitation were also compared. It is found that the initial precipitation point (IPP) of both asphaltenes is increased most by the copolymer containing 2-aminopyridine (PMO-2-P), while the copolymer containing N-(3-aminopropyl)­imidazole (PMO-I) shows the worst inhibition performance. It is because that pyridine group has a stronger adsorption capacity with asphaltene than the imidazole group. The effect of various functional groups in copolymers on inhibiting asphaltene precipitation conforms to the following sequence: 2-aminopyridine > aniline > 4-aminopyridine > N-(3-aminopropyl)­imidazole. It is also found that high polymer concentration and grafting ratio are beneficial to inhibit the asphaltene precipitation. As a result of the π–π conjugation and hydrogen-bonding attractions between the aromatic groups in the copolymers and the asphaltenes, the polymers can be stably adsorbed onto the surface of the asphaltenes and prevent their aggregation.