Nanoparticles for Waxy Crudes: Effect of Polymer Coverage and the Effect on Wax Crystallization

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• 作者：Jens Norrman ; Amalie Solberg ; Johan Sjöblom ; Kristofer Paso
• 刊名：Energy & Fuels
• 出版年：2016
• 出版时间：June 16, 2016
• 年：2016
• 卷：30
• 期：6
• 页码：5108-5114
• 全文大小：397K
• 年卷期：0
• ISSN：1520-5029

文摘

Nanoparticles coated with poly(octadecyl acrylate) (POA) pour-point depressants are investigated, and the effect of the amount of coating material is investigated and compared with the effect of the coating material without nanomaterial. Pour point depressing performance is demonstrated using a model waxy oil system in order to isolate material performance. The present study focus on the effect of how the amount of coverage of the nanoparticles affects the performance of the nanoparticles. In order to access this information, the adsorption of the poly(octadecyl acrylate) (POA) on silica (the material of the nanoparticles) was determined using a quartz crystal microbalance with dissipation monitoring (QCM-D). Adsorption was performed from two different solvents, toluene and dodecane, because the nanoparticles were been prepared from toluene while the model system used is dodecane-based. Using the QCM-D data, it was possible to prepare nanoparticles with different amounts of poly(octadecyl acrylate), as defined by amount of the silica covered, and investigate the effect of the coating material coverage on the performance of the nanoparticles in the model waxy oil system. The nanoparticle performance was estimated with rheology to determine differences in the strength of the wax gel formed, with differential scanning calorimetry (DSC) to assess the wax appearance temperature and any differences in crystallization, and visual observation of the formed wax with polarized microscopy. Rheological measurements showed that nanoparticles with low POA coverage had almost no effect on the strength of the formed wax gel, while nanoparticles with full coverage of POA significantly lowered the wax gel strength. Nanoparticles with more than full coverage of POA further lowered the strength of the formed wax gel. DSC showed that the wax appearance temperature is lowered by the nanoparticles, and that there is little or no effect when using nanoparticles with more POA than 100% coverage. DSC also showed that the presence of the nanoparticles changes the nature of the wax crystallization, most likely by introducing multiple nucleation centers, causing a sharp peak in crystallization (in contrast to the more broad crystallization of neat wax). Polarized microscopy showed that, in the presence of the nanoparticles, large particles were formed, compared to the added silica. There was also a reduced amount of birefringence, indicating a possible change in wax morphology. This change in wax morphology may hinder efficient formation of a volume spanning gel network, explaining the efficiency of the nanoparticles. By flushing water over a silica surface with adsorbed POA in a QCM-D, it was shown that the POA does not detach from the silica, even when exposed to large amounts of water. This opens up the possibility to recover the nanoparticles with the covering POA after usage, providing possible ecological benefits. The research conducted here shows that it is possible to further optimize the effect of coated nanoparticles on wax gels, such that already low dosages provided by such particles may be further reduced, affording viability from economic and environmental perspectives.