Spiecker P Matthew, Gawrys Keith L, Kilpatrick Peter K
Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695, USA.
J Colloid Interface Sci. 2003 Nov 1;267(1):178-93. doi: 10.1016/s0021-9797(03)00641-6.
Asphaltenes from four different crude oils (Arab Heavy, B6, Canadon Seco, and Hondo) were fractionated in mixtures of heptane and toluene and analyzed chemically, by vapor pressure osmometry (VPO), and by small angle neutron scattering (SANS). Solubility profiles of the asphaltenes and their subfractions indicated strong cooperative asphaltene interactions of a particular subfraction that is polar and hydrogen bonding. This subfraction had lower H/C ratios and modestly higher N, V, Ni, and Fe contents than the less polar and more soluble subfraction of asphaltenes. VPO and SANS studies indicated that the less soluble subfractions formed aggregates that were considerably larger than the more soluble subfractions. In general, asphaltene aggregate size increased with decreasing solvent aromaticity up to the solubility limit, beyond which the aggregate size decreased with heptane addition. The presence of a low wavevector Q feature in the scattering curves at 25 degrees C indicated that the individual aggregates were flocculating; however, the intensity of the feature was diminished upon heating of the samples to 80 degrees C. The solubility mechanism for Canadon Seco asphaltenes, the largest aggregate formers, appears to be dominated by aromatic pi-bonding interactions due to their low H/C ratio and low nitrogen content. B6 and Hondo asphaltenes formed similar-sized aggregates in heptol and the solubility mechanism is most likely driven by polar interactions due to their relatively high H/C ratios and high nitrogen contents. Arab Heavy, the least polar asphaltene, had a H/C ratio similar to Canadon Seco but formed the smallest aggregates in heptol. The enhancement in polar and pi-bonding interactions for the less soluble subfraction indicated by elemental analysis is reflected by the aggregate size from SANS. The less soluble asphaltenes contribute the majority of species responsible for aggregation and likely cause many petroleum production problems such as pipeline deposition and water-in-oil emulsion stabilization.
对来自四种不同原油（阿拉伯重质原油、B6、加拿大塞科原油和洪多原油）的沥青质在庚烷和甲苯的混合物中进行分馏，并通过化学分析、蒸气压渗透法（VPO）和小角中子散射（SANS）进行分析。沥青质及其亚组分的溶解度曲线表明，一种极性且具有氢键作用的特定亚组分存在强烈的协同沥青质相互作用。与极性较小且更易溶解的沥青质亚组分相比，该亚组分具有较低的H/C比以及适度较高的N、V、Ni和Fe含量。VPO和SANS研究表明，较难溶解的亚组分形成的聚集体比更易溶解的亚组分大得多。一般来说，在达到溶解度极限之前，随着溶剂芳烃含量的降低，沥青质聚集体尺寸增大，超过该极限后，随着庚烷的加入聚集体尺寸减小。25℃时散射曲线中低波矢Q特征的存在表明单个聚集体正在絮凝；然而，将样品加热到80℃后，该特征的强度减弱。作为最大聚集体形成者的加拿大塞科原油沥青质的溶解机制，由于其低H/C比和低氮含量，似乎主要由芳香π键相互作用主导。B6和洪多原油沥青质在庚醇中形成类似尺寸的聚集体，其溶解机制很可能是由极性相互作用驱动的，因为它们具有相对较高的H/C比和高氮含量。阿拉伯重质原油是极性最小的沥青质，其H/C比与加拿大塞科原油相似，但在庚醇中形成的聚集体最小。元素分析表明，较难溶解的亚组分中极性和π键相互作用增强，这在SANS得到的聚集体尺寸中得到体现。较难溶解的沥青质是造成聚集的主要物质，可能会引发许多石油生产问题，如管道沉积和油包水乳液稳定化。
