Department of Technical Physics II/Polymer Physics, Institute of Physics, Faculty of Mathematics and Natural Science, Ilmenau University of Technology, P.O. Box 100565, D-98684 Ilmenau, Germany.
Molecules. 2021 Aug 28;26(17):5218. doi: 10.3390/molecules26175218.
The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions-either through steric hindrances or promoted by aromatic-aromatic interactions-are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes' NMR relaxation (T1 and T2) and translational diffusion () properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes' dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes' aromaticity on the maltene-asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity.
NMR 弛豫时间和扩散系数在原油中的分布源于大量不同的化学物质。此外，沥青质的存在为油质提供了不同的弛豫环境，这是由沥青质聚集体中的空间位阻和自由基的空间分布产生的。由于油质的动力学进一步受到油质和沥青质之间相互作用的影响，这些相互作用——无论是通过空间位阻还是芳香族相互作用来促进——都特别有趣。在这里，我们旨在通过比较模型溶液中沥青质存在与否时质子化和氘代油质不同分子大小和芳香度的 NMR 弛豫（T1 和 T2）和扩散（）性质，来研究它们之间的相互作用。描述油质在沥青质存在下的非指数弛豫的平均横向和纵向弛豫率之比及其相对于无沥青质溶液的变化情况进行了讨论。弛豫实验表明，在沥青质存在下，油质的动力学明显减慢，不同油质之间存在差异。虽然对于单链烷基苯，长脂肪链存在弛豫率比的平台，但并未明确发现油质的芳香度对油质-沥青质相互作用有影响。相比之下，沥青质存在时油质的扩散系数降低幅度很小，这归因于整体粘度的增加。
