The influence of micro-crystalline wax addition upon the rheological properties of model wax-oil gels is investigated. Addition of less than 1 wt% micro-crystalline wax to a model oil consisting of 5 wt% macro-crystalline wax in dodecane shows no significant impact on the WAT and gelation temperature. Beyond 1 wt% added micro-crystalline wax, increases in WAT and gelation temperature are observed, and are attributable to the higher crystallization temperature of the micro-crystalline wax. The effect of micro-crystalline wax addition upon the WAT and gelation temperature are shown to be attributed to merely overlapping compositions of macro-and microcrystalline wax. However, a substantive effect of micro-crystalline wax addition is observed on the yield stress. Addition of 0.13 wt% micro-crystalline wax reduces the yield stress of waxy oil model from 238.0 to 22.5 Pa. Addition of 0.5 wt% micro-crystalline wax decreases the yield stress to 5.4 Pa, which is close in value to the yield stress of neat 5 wt% micro-crystalline wax gel.2 Microscopic images reveal two mechanisms leading to formation of a weak mixed wax gels. At low to medium addition of micro-crystalline wax, micro-crystalline crystallites formed during cooling provide nucleation sites for subsequent precipitation of macro-crystalline wax. Macrocrystalline wax crystals formed in contact with micro-crystalline crystallites are smaller in size and the growth is localized, in comparison to neat macro-crystalline wax. Modified macro-crystalline wax precipitation leads to uneven dispersion of the macro-crystalline crystals in the liquid phase.At high concentration, micro-crystals form throughout the sample prior to precipitation of macrocrystalline wax. Hence, only small and discrete space remains for macro-crystalline crystals to grow, forming small crystals. Interlocking among macro-crystals is spatially hindered by the presence of micro-crystalline crystallites. In this condition, the system completely behaves as a micro-crystalline gel. This investigation provides a plausible mechanistic account for the known gel weakening activity of micro-crystalline wax.
The molecular weight distribution of four wax inhibitors was modified by either stepwise precipitation or ultrasonic disintegration, and the effect of the obtained inhibitor fractions on wax crystallization was studied. Stepwise precipitation yielded narrower molecular weight distributions as measured by size exclusion chromatography (SEC), whereas ultrasonic disintegration reduced the average molecular weight and increase the polydispersity index. The polymer hydrodynamic radius was mapped using nuclear magnetic resonance (NMR), and showed similar trends as SEC measurements. Wax appearance temperature (WAT) and gelation temperature of three model oils and one crude oil were tested using differential scanning calorimetry (DSC) and rheometry. Changes in molecular weight could improve as well as diminish WAT depression. Waxy gelation temperature showed similar trends as WAT measurements, but the influence of inhibitor molecular weight was more pronounced. The largest change in gelation temperature was measured for the lowest molecular weight fractions
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