Measurement and Prediction of the Phase Behavior of Wax−Solvent Mixtures:  Significance of the Wax <i>Dis</i>appearance Temperature

Abstract

This study investigates the phase behavior of wax−solvent mixtures below their liquidus temperature, particularly between the wax disappearance temperature (WDT, recorded while heating the mixture) and the wax appearance temperature (WAT, recorded while cooling the mixture). The prepared wax−solvent mixtures comprised 6−22 mass % of a paraffinic wax (C 20 −C 40, with the mean carbon number of 28) dissolved in n -hexadecane (C 16 ) and Norpar13 (a paraffinic solvent, C 11 −C 15 ). For these mixtures, the WAT values were lower than the WDT values by 3.2 ± 0.6 °C. Gas chromatograph analyses of the liquid phase, at temperatures between the WDT and the pour-point temperature, were used to calculate the wax solubility and the composition of the dissolved wax. At temperatures below the WDT, the wax solubility decreased with decreasing temperature, and the liquid-phase concentrations of C 20 −C 27 were higher than those in the whole wax and those of C 29 + were lower. The experimental data compared satisfactorily with predictions from an available UNIQUAC-based model for the liquidus temperature as well as for the composition of C 20 + constituents in the liquid phase. This study establishes that the WDT rather than the WAT is closer to the liquidus or saturation temperature of “waxy” mixtures.