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首页> 外文期刊>Langmuir: The ACS Journal of Surfaces and Colloids >Interfacial Properties of Asphaltenes at Toluene-Water Interfaces
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Interfacial Properties of Asphaltenes at Toluene-Water Interfaces

机译：沥青-甲苯-水界面的界面性质

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摘要

Asphaltenes are "n-alkane insoluble" species in crude oil that stabilize water-in-oil emulsions. To understand asphaltene adsorption mechanisms at oil water interfaces and coalescence blockage, we first studied the behavior in aliphatic oil water systems in which asphaltenes are almost insoluble. They adsorbed as monomers, giving a unique master curve relating interfacial tension (IFT) to interfacial coverage through a Langmuir equation of state (EoS). The long-time surface coverage was independent of asphaltene bulk concentration and asymptotically approached the 2-D packing limit for polydisperse disks. On coalescence, the surface coverage exceeded the 2-D limit and the asphaltene film appeared to become, solidlike, apparently undergoing a transition to a soft glassy material and blocking further coalescence. However, real systems consist of mixtures of aliphatic and aromatic components in which asphaltenes may be quite soluble. To understand solubility effects, we focus here on how the increased bulk solubility of asphaltenes affects their interfacial properties in comparison to aliphatic oil water systems. Unlike the "almost irreversible" adsorption of asphaltenes where the asymptotic interfacial coverage was independent of the bulk concentration, an equilibrium surface pressure, dependent on bulk concentration, was obtained for toluene water systems because of adsorption being balanced by desorption. The equilibrium surface coverage could be obtained from the short- and long-term Ward-Tordai approximations. The behavior of the equilibrium surface pressure with the equilibrium surface coverage was then derived. These data for various asphaltene concentrations were used to determine the EoS, which for toluene water could also be fitted by the Langmuir EoS with Gamma(infinity) = 3.3 moleculem(2), the same value as that found for these asphaltenes in aliphatic media. Asphaltene solubility in the bulk phase only appears to affect the adsorption isotherm but not the EoS. Further support for these observations is provided by dilatational rheology experiments for the EoS and contraction experiments in which desorption to the equilibrium surface pressure was observed.
机译：沥青质是原油中的“正构烷烃不溶性”物质，可稳定油包水型乳液。为了了解沥青质在油水界面的吸附机理和聚结堵塞，我们首先研究了在沥青质几乎不溶的脂肪族油水系统中的行为。它们以单体形式吸附，通过Langmuir状态方程（EoS）给出了界面张力（IFT）与界面覆盖率相关的独特主曲线。长时间的表面覆盖率与沥青质的体积浓度无关，并且渐近地接近多分散盘的二维堆积极限。聚结时，表面覆盖率超过2-D极限，并且沥青质膜似乎变为固体，显然经历了向软玻璃状材料的转变并阻止了进一步的聚结。但是，实际的系统由脂族和芳族组分的混合物组成，其中沥青质可能非常易溶。为了理解溶解度的影响，我们将重点放在与脂肪油水系统相比，增加的沥青质的整体溶解度如何影响其界面性能。与沥青质的“几乎不可逆”吸附不同，沥青质的渐近界面覆盖率与体积浓度无关，而甲苯水系统则获得了取决于体积浓度的平衡表面压力，这是因为吸附通过解吸来平衡。可以从短期和长期Ward-Tordai近似获得平衡表面覆盖率。然后得出平衡表面压力与平衡表面覆盖率之间的关系。这些关于各种沥青质浓度的数据用于确定EoS，对于甲苯水，Langmuir EoS也可以用Gamma（无穷大）= 3.3分子/ nm（2）来拟合，与在脂肪族中这些沥青质所发现的值相同媒体。沥青质在本体相中的溶解度似乎仅影响吸附等温线，而不影响EoS。对于EoS的膨胀流变实验和收缩实验（其中观察到解吸到平衡表面压力）为这些观察提供了进一步的支持。

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