Controlling the asphaltene precipitation behaviors by changing the position and number of nitrogen in the aromatic heterocyclic pendant of polymers with the assistance of DFT calculations

Abstract

As the largest component in crude oil, asphaltenes are apt to settle out and result in the blockage of pipeline during production and transportation, which largely reduces the safety and economic benefits. In this study, a series of poly(maleic anhydride‐octadecene)s (PMO) amidated by pyrimidine (MD), pyrazine (BQ), pyrazole (BZ), triazole (3DZ), triazine (6J3Q), phenyl triazine (6B3Q) and pyrazolo pyridine (ZBD) were synthesized. The interaction energies between the different polymers and asphaltene were calculated by using density functional theory (DFT). It shows that the greater the number of nitrogen‐containing groups and rings, the higher the interaction energy. Moreover, the position of the nitrogen on the aromatic ring also impacts the interaction energy. The interaction energy between asphaltene and polymer with adjacent N (PMO‐BZ) is larger than that with para‐N (PMO‐BQ) and interstitial N (PMO‐MD). In addition, the performance of polymers on asphaltene precipitation from model oil and crude oil is explored by UV–Vis spectroscopy, turbidity, dynamic light scattering (DLS) and rheological methods. The performance of polymers follows the sequence of PMO‐BZ > PMO‐6J3Q > PMO‐BQ > PMO‐MD > PMO‐6B3Q > PMO‐ZBD, which is not consistent with the change of interaction energy. Apparently, the efficiency of the polymer increases and then declines with the increase of interaction energy. Notably, the polymer (PMO‐BZ) containing monocyclic ring with adjacent N increased the IPP of asphaltenes from 0.363 to 0.800 and reduced the particle size from 1527.2 to 99.7 nm. The interaction energies of PMO‐BZ and PMO‐6J3Q with asphaltene are in the range of 15.87–17.04 KJ/mol, and the polymers with interaction energies in this range are more effective on asphaltene inhibition than the others. Consequently, the interaction energies obtained from DFT calculations can be used to guide the design and synthesis of polymers with nitrogen‐containing heterocyclic pendant for asphaltene inhibition.