Asphaltenes (Asps) are operationally defined as the toluene-soluble but n-pentane- or n-heptane-insoluble fractions, e.g., of crude oils. Therefore, there is intense interest in determining the concentration of n-heptane required to precipitate Asps from their solutions in particular media (solvents, solvent mixtures, and maltenes). Here, we report on the dependence of Asp dissolution in binary mixtures of n-heptane (solvent 1, S1)/organic solvent (solvent 2, S2) over the entire mole fraction range of S2, χ_S2, and in few selected maltene models (n-heptane + S2 + benzothiazole + n-octyl-1-napthoate). The S2 employed were benzonitrile, cyclohexanone, ethyl benzoate, 1-methylnaphthalene, tetrahydropyran, and toluene. For all S2 and model maltenes, the dependence of wt % dissolved Asp (determined by mass and UV/vis absorbance) on χ_S2 was nonlinear. We attribute this nonlinear, i.e., nonideal dissolution behavior to “preferential solvation” of the Asp by a component(s) of the medium (binary solvent mixtures and maltenes). Although the occurrence of “solvent sorting” during Asp dissolution was alluded to, this is the first direct and unambiguous evidence for its occurrence. We used solvatochromism to corroborate our rationale about the origin of the Asp nonideal dissolution behavior. The term solvatochromism refers to the effect of the solvent on the color of solvatochromic probes, substances whose spectra are sensitive to the properties of the liquid medium, e.g., its empirical polarity, E_T(probe). Recently, we used (E)-2,6-di-tert-butyl-4-[2-(1-hexylquinolin-1-ium-4-yl)vinyl]phenolate, HxQMBu₂) to study Asp dissolution in pure solvents and model maltenes. We showed that E_T(HxQMBu₂) correlates linearly with Hildebrand solubility parameters of pure solvents as well as with lg (wt % dissolved Asps). In the present work, we studied the solvatochromic response of HxQMBu₂ in the above-mentioned n-heptane/S2 binary mixtures. Except for toluene/n-heptane mixtures, plots of E_T(HxQMBu₂) versus χ_S2 were nonlinear due to probe preferential solvation. We successfully fitted a solvation model to the solvatochromic and Asp dissolution data and extracted the enrichment of the solvation layers in the more polar component(s) of the binary mixture and model maltenes. Our results bear on the assessment of additives employed to stabilize Asps: in the absence of adverse effects of the additive on other properties (e.g., viscosity and water/oil emulsion stability), efficient additives should accumulate in the solvation layer of Asp particles where they displace the nonsolvents, e.g., the saturates.

中文翻译：

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沥青质在有机溶剂和马尔滕模型的二元混合物中的溶解：沥青质优先溶剂化的明确证据以及与评估沥青稳定剂的效率有关的证据

沥青质（Asps）在操作上定义为甲苯可溶但正戊烷或正庚烷不溶的馏分，例如原油。因此，对于确定在特定介质（溶剂，溶剂混合物和麦芽糖）中从其溶液中沉淀Asps所需的正庚烷浓度引起了极大的兴趣。在这里，我们的Asp溶解在的二元混合物的依赖性报告Ñ庚烷（溶剂1，S1）有机溶剂/过S2的整个摩尔分数范围（溶剂2，S2），χ _S2，并且在几个选定的马青烯模型（正庚烷+ S2 +苯并噻唑+ n-辛基-1-萘甲酸酯）。所使用的S 2为苯甲腈，环己酮，苯甲酸乙酯，1-甲基萘，四氢吡喃和甲苯。对于所有的S2和模型马青烯，溶解天冬氨酸重量％的依赖于χ（质量和UV / VIS吸光度测定）_S2是非线性的。我们将这种非线性（即非理想的溶解行为）归因于Asp通过介质（二元溶剂混合物和麦芽糖）的一种组分的“优先溶剂化”。尽管提到了在Asp溶解过程中“溶剂分选”的发生，但这是其发生的第一个直接且明确的证据。我们使用溶剂变色法来证实我们关于Asp非理想溶解行为起源的理论依据。术语溶剂变色是指溶剂对溶剂变色探针的颜色的影响，溶剂变色探针的光谱对液体介质的性质（例如，其经验极性E _T（探针））敏感。最近，我们使用（ē）-2,6-二叔丁基-4- [2-（1-（1-己基喹啉-1-基-4-基）乙烯基]酚]盐HxQMBu ₂），以研究Asp在纯溶剂和麦芽汁中的溶解。我们表明，E _T（HxQMBu ₂）与纯溶剂的Hildebrand溶解度参数以及lg（wt％溶解的Asps）线性相关。在本工作中，我们研究了在上述正庚烷/ S2二元混合物中HxQMBu ₂的溶剂化变色反应。除了甲苯/ Ñ庚烷的混合物，的曲线ë _Ť（HxQMBu ₂）与χ _S2由于探针优先溶剂化而呈非线性。我们成功地将溶剂化模型拟合到了溶剂化变色和Asp溶解数据，并提取了二元混合物和模型麦芽糖中极性更大的组分中的溶剂化层。我们的结果取决于对用于稳定Asps的添加剂的评估：在没有添加剂对其他性能（例如粘度和水/油乳液稳定性）的不利影响的情况下，有效的添加剂应在Asp颗粒的溶剂化层中积累取代非溶剂，例如饱和溶剂。