Department of Chemical Engineering, The University of Michigan, Ann Arbor, Ann Arbor, Michigan 48109, United States.
Langmuir. 2013 Jul 16;29(28):8799-808. doi: 10.1021/la401406k. Epub 2013 Jun 28.
This paper discusses time-resolved small-angle neutron scattering results that were used to investigate asphaltene structure and stability with and without a precipitant added in both crude oil and model oil. A novel approach was used to isolate the scattering from asphaltenes that are insoluble and in the process of aggregating from those that are soluble. It was found that both soluble and insoluble asphaltenes form fractal clusters in crude oil and the fractal dimension of the insoluble asphaltene clusters is higher than that of the soluble clusters. Adding heptane also increases the size of soluble asphaltene clusters without modifying the fractal dimension. Understanding the process of insoluble asphaltenes forming fractals with higher fractal dimensions will potentially reveal the microscopic asphaltene destabilization mechanism (i.e., how a precipitant modifies asphaltene-asphaltene interactions). It was concluded that because of the polydisperse nature of asphaltenes, no well-defined asphaltene phase stability envelope exists and small amounts of asphaltenes precipitated even at dilute precipitant concentrations. Asphaltenes that are stable in a crude oil-precipitant mixture are dispersed on the nanometer length scale. An asphaltene precipitation mechanism is proposed that is consistent with the experimental findings. Additionally, it was found that the heptane-insoluble asphaltene fraction is the dominant source of small-angle scattering in crude oil and the previously unobtainable asphaltene solubility at low heptane concentrations was measured.
本文讨论了时间分辨小角中子散射结果，这些结果用于研究在添加和不添加沉淀剂的情况下，原油和模型油中沥青质的结构和稳定性。本文采用了一种新方法来分离不溶性和正在聚集的沥青质的散射，以研究可溶性沥青质。结果发现，可溶性和不溶性沥青质在原油中都形成分形团簇，不溶性沥青质团簇的分形维数高于可溶性团簇。添加庚烷也会增加可溶性沥青质团簇的尺寸，而不会改变分形维数。了解不溶性沥青质形成分形维数更高的分形团簇的过程，可能会揭示微观沥青质失稳机制（即沉淀剂如何改变沥青质-沥青质相互作用）。结论是，由于沥青质的多分散性，不存在明确的沥青质相稳定性包络线，即使在沉淀剂浓度较低的情况下，也会有少量的沥青质沉淀。在原油-沉淀剂混合物中稳定的沥青质在纳米尺度上分散。提出了一种与实验结果一致的沥青质沉淀机制。此外，还发现庚烷不溶沥青质馏分是原油中小角散射的主要来源，并测量了以前无法获得的低庚烷浓度下的沥青质溶解度。
