Phase Transitions in Petroleum Waxes Determined by Infrared Spectroscopy

Abstract

Inthe present paper attempts have been made to study the phase transition temperatures in petroleum waxes by infrared spectroscopy and the resulting data were correlated with phase transition temperatures obtained by differential scanning calorimetry (DSC).

Crystal Structure of Wax Lamellar InterfacesA Residual Petroleum Fraction Characterized by Electron Crystallography

“…The original residual wax comprised a distribution of chains from n-C 21 H 44 to n-C 39 H 80 , with the assayed concentrations of individual species tabulated by these authors. 8 For this study, a closely similar chain distribution (Figure 1) was obtained by weighing pure n-paraffins into a vial. This mixture was then co-melted on a hot plate, cooled, broken up and stirred, and remelted several times to obtain a uniform solid solution.…”

“…A DSC measurement of the reconstructed wax (Figure 2) yields results typical of narrow distillate cuts 8 where one can discern a premelt transition of an orthorhombic solid to a rotator phase before the true melt. The appearance of the premelt transition indicates the presence of a stable paraffin solid solution, as is also supported by diffraction measurements.…”

“…The premelt temperature of 55.6°and the melt temperature of 65.7 °C in the artificial chain assembly can be compared to the respective values 53.4 and 64.7 °C for the actual residual wax sample. 8 The model residual wax was crystallized for electron diffraction study using an epitaxial orientation method originally designed by Wittmann, Hodge, and Lotz. 10 First a dilute solution of the material was prepared in light petroleum, and a drop of this soution was evaporated onto the surface of a freshly cleaved mica sheet to leave a thin film of the paraffinic mass.…”

“…The model paraffin wax used in this study was based on a residual petroleum wax, termed “Wax J” when originally characterized by Gupta and Severin using high-temperature gas chromatography and supercritical fluid chromatography to determine the carbon chain distribution. The original residual wax comprised a distribution of chains from n -C 21 H 44 to n -C 39 H 80 , with the assayed concentrations of individual species tabulated by these authors . For this study, a closely similar chain distribution (Figure ) was obtained by weighing pure n -paraffins into a vial.…”

“…The appearance of the premelt transition indicates the presence of a stable paraffin solid solution, as is also supported by diffraction measurements. The premelt temperature of 55.6° and the melt temperature of 65.7 °C in the artificial chain assembly can be compared to the respective values 53.4 and 64.7 °C for the actual residual wax sample 2 DSC of the model paraffin wax with an endotherm due to a premelt rotator phase followed by one due to the true melt. …”