Energy & Fuels, Vol.31, No.7, 6862-6875, 2017
Wax Precipitation Temperature Measurements Revisited: The Role of the Degree of Sample Confinement
In this work, the wax precipitation temperature (WPT) measurements of crude oils are revisited. The conventional methods used to assess the WPT of crude oils are analyzed and the results available are discussed in detail. In addition, three methods, namely polarized light microscopy, microdifferential scanning calorimetry (mu tDSC), and rheometry, are employed to evaluate the WPT of two Brazilian waxy crude oils. It is shown that polarized light microscopy and mu DSC are the most suitable methods to assess the WPT of crude oils and that rheometry can only be used for that purpose under very specific circumstances. In particular, the results indicate that rheometry is able to detect the WPT of crude oils only by decreasing the geometry gap to a small enough value. Moreover, it is shown that the degree of sample confinement has a key role on the accuracy of WPT measurements, so that care must be taken when using laboratory data to design field operations. Discussions on the origin of the effects of confinement and on how wax crystal dimensions vary with the initial cooling temperature are also provided.