In this study, we investigated the stability of asphaltene adsorption structures at the oil–water interface, focusing on the role of heteroatoms, by molecular dynamics simulations. We employed an oil (1:1 mixture of heptane and toluene, by volume)–water system and used 13 types of asphaltene molecules. Two sets of asphaltene models with the alkyl side chain at different locations were considered. For each set, six models were employed, which have essentially the same structures but with different heteroatoms (such as nitrogen, oxygen, and sulfur) on the aromatic ring (i.e., heteroaromatic ring). Besides 12 models, an additional asphaltene molecule with a carboxyl group at the end of the alkyl side chain was included. We evaluated the asphaltene adsorption Gibbs free energy at the oil–water interface using potential of mean force calculations. It is found that the basic pyridine-type nitrogen-containing asphaltene presents the highest adsorption Gibbs free energy among six asphaltene molecules for both sets. The heteroatom of the asphaltene molecule forms a hydrogen bond with the water molecules so that it can stabilize asphaltene adsorption at the oil–water interface. The strength of the hydrogen bond depends on the negative charge of the heteroatom, with the basic pyridine-type nitrogen being the highest, and the highest adsorption Gibbs free energy. Furthermore, it is found that the acidic pyrrole-type nitrogen-containing asphaltene has the most significant weak hydrogen bonding between the heteroaromatic ring and water molecules due to the charge of the carbon atom in that ring being higher than others. The thiophene-type sulfur-containing asphaltene has the most significant van der Waals interaction; the adsorption Gibbs free energy shows a significant value for both sets. The carboxyl asphaltene molecule has the highest affinity to the oil–water interface among 13 models because it has two heteroatoms. The detailed understanding of the asphaltene adsorption behavior presented in this study would be useful to solve the stability issue of oil–water emulsions in crude oil production.

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油水界面沥青质吸附自由能的评估：杂原子的作用

在这项研究中，我们通过分子动力学模拟研究了油水界面上沥青质吸附结构的稳定性，重点研究了杂原子的作用。我们使用了一种油（体积比为庚烷和甲苯的1：1混合物）-水系统，并使用了13种类型的沥青质分子。考虑了在不同位置具有烷基侧链的两组沥青质模型。对于每组，使用六个模型，它们具有基本相同的结构，但是在芳环（即杂芳环）上具有不同的杂原子（例如氮，氧和硫）。除12个模型外，还包括一个在烷基侧链末端带有羧基的沥青质分子。我们使用平均力计算的潜力评估了油水界面上沥青质吸附的吉布斯自由能。发现在这两个组的六个沥青质分子中，碱性吡啶型含氮沥青质均表现出最高的吸附吉布斯自由能。沥青质分子的杂原子与水分子形成氢键，因此可以稳定沥青质在油水界面的吸附。氢键的强度取决于杂原子的负电荷，碱性吡啶型氮最高，而吉布斯自由能最高。此外，发现由于在该芳香环中的碳原子的电荷比其他环更高，因此该酸性吡咯型含氮沥青质在杂芳族环与水分子之间具有最显着的弱氢键。噻吩型含硫沥青质具有最显着的范德华相互作用。两组的吸附吉布斯自由能均显示出显着价值。羧基沥青质分子对13个模型中的油水界面具有最高的亲和力，因为它具有两个杂原子。这项研究中对沥青质吸附行为的详细了解将有助于解决原油生产中油水乳液的稳定性问题。