沥青质在高定向热解石墨表面络合机制的分子动力学模拟

Molecular dynamics simulation of complexation of asphaltenes on the surface of highly oriented pyrolytic graphite

沥青质在固体表面的络合机制是解决剩余油开采难题的重要理论基础。为了给聚集抑制剂和表面活性剂的开发提供理论依据,采用分子动力学模拟,系统研究了沥青质在高定向热解石墨表面附着、聚集的特征。通过计算表面吸附过程中沥青质的自由能变化,基于Yen-Mullins模型的定量判据,结合沥青质平均相互作用分子数和分子密度分布,定量分析了沥青质在固-液界面体系与溶液体系中聚集作用的差异。分子动力学模拟分析表明,固体表面会降低沥青质的聚集程度,加快聚集过程中的阶段分化,具体包括4个阶段的界面过程:①沥青质覆盖固体表面并逐渐铺满一层;②固体表面上形成纳米聚集体;③固体表面上纳米聚集体与溶液中的纳米聚集体通过边缘堆叠、T形堆叠形成簇状物;④固体表面的聚集体与溶液中的聚集体通过脂肪侧链接触形成絮凝物。

The complexation mechanism of asphaltenes on the solid surface provides an important theoretical basis for solving the difficulties in exploiting residual oil. To provide a theoretical basis for the development of aggregation inhibitors and surfactants, the attachment and aggregation characteristics of asphaltenes on the surface of highly oriented pyrolytic graphite were systematically studied using molecular dynamics simulations, and the free energy changes of asphaltenes during adsorption were calculated. Based on the quantitative criterion of Yen-Mullins model, in combination with the average interaction molecule numbers and density profiles of asphaltenes, this paper quantitatively analyzes the differences in asphaltene aggregation in the solid-liquid interface system and the solvent system. The analysis of molecular dynamics simulation shows that the solid surface will reduce the degree of asphaltene aggregation and accelerate the staged differentiation during aggregation. Four stages of interface process are involved.(1) Asphaltenes gradually cover the solid surface as a layer.(2) Nano-aggregates are formed on the solid surface.(3) Cluster compounds are formed by nano-aggregates on the solid surface and those in solvent through edge stacking and T-shaped stacking.(4) Flocculent polymers are formed by the aggregates on the solid surface contacted with those in solvent by aliphatic side chains.