Spiecker P Matthew, Kilpatrick Peter K
Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.
Langmuir. 2004 May 11;20(10):4022-32. doi: 10.1021/la0356351.
A biconical bob interfacial shear rheometer was used to study the mechanical properties of asphaltenic films adsorbed at the oil-water interface. Solutions of asphaltenes isolated from four crude oils were dissolved in a model oil of heptane and toluene and allowed to adsorb and age in contact with water. Film elasticity (G') values were measured over a period of several days, and yield stresses and film masses were determined at the end of testing. The degree of film consolidation was determined from ratios of G'/film mass and yield stress/G'. Asphaltenes with higher concentrations of heavy metals (Ni, 330-360 ppm; V, 950-1000 ppm), lower aromaticity (H/C, 1.24-1.29), and higher polarity (N, 1.87-1.99) formed films of high elasticity, yield stress, and consolidation. Rapid adsorption kinetics and G' increases were seen when asphaltenes were near their solubility limit in heptane-toluene mixtures (approximately 50% (v/v) toluene). In solvents of greater aromaticity, adsorption kinetics and film masses were reduced at comparable aging times. Poor film forming asphaltenes had yield stress/G' values ((1.01-1.21) x 10(-2)) more than 4-fold lower than those of good film forming asphaltenes. n-heptane asphaltenes fractionated by filtering solutions prepared at low aromaticity (approximately 40% toluene in mixtures of heptane and toluene) possessed higher concentrations of heavy metals and nitrogen and higher aromaticity. The less soluble fractions of good film forming asphaltenes exhibited enhanced adsorption kinetics and higher G' and yield stress values in pure toluene. Replacing the asphaltene solutions with neat heptane-toluene highlighted the ability of films to consolidate and become more elastic over several hours. Adding resins in solution to a partially consolidated film caused a rapid reduction in elasticity followed by gradual but modest consolidation. This study is among the first to directly relate asphaltene chemistry to adsorption kinetics, adsorbed film mechanical properties, and consolidation kinetics.
使用双锥摆式界面剪切流变仪研究吸附在油水界面的沥青质薄膜的力学性能。将从四种原油中分离出的沥青质溶液溶解在庚烷和甲苯的模型油中，并使其与水接触吸附和老化。在几天的时间内测量薄膜弹性（G'）值，并在测试结束时测定屈服应力和薄膜质量。通过G'/薄膜质量和屈服应力/G'的比值确定薄膜固结程度。重金属（Ni，330 - 360 ppm；V，950 - 1000 ppm）浓度较高、芳香度较低（H/C，1.24 - 1.29）且极性较高（N，1.87 - 1.99）的沥青质形成具有高弹性、屈服应力和固结性的薄膜。当沥青质在庚烷 - 甲苯混合物中的溶解度接近其极限（约50%（v/v）甲苯）时，观察到快速吸附动力学和G'增加。在可比的老化时间下，在芳香度更高的溶剂中，吸附动力学和薄膜质量降低。成膜性差的沥青质的屈服应力/G'值（(1.01 - 1.21)×10(-2)）比成膜性好的沥青质低4倍以上。通过过滤在低芳香度（庚烷和甲苯混合物中约40%甲苯）下制备的溶液分离得到的正庚烷沥青质含有较高浓度的重金属和氮以及较高的芳香度。成膜性好的沥青质中较难溶解的部分在纯甲苯中表现出增强的吸附动力学以及更高的G'和屈服应力值。用纯庚烷 - 甲苯代替沥青质溶液突出了薄膜在数小时内固结并变得更具弹性的能力。向部分固结的薄膜溶液中添加树脂会导致弹性迅速降低，随后逐渐但适度地固结。这项研究首次直接将沥青质化学与吸附动力学、吸附薄膜力学性能和固结动力学联系起来。
