Visual Measurements of Solid–Liquid Equilibria and Induction Times for Cyclohexane + Octadecane Mixtures at Pressures to 5 MPa

Abstract

A specialized apparatus designed for visual measurements of solid–liquid equilibrium (SLE) and solid–liquid–vapor equilibrium (SLVE) was constructed and used to measure liquidus (melting) temperatures in binary mixtures of cyclohexane (C6H12) and octadecane (C18H38) across the entire range of composition and at pressures from about (0.004 to 5.3) MPa. A Peltier-cooled copper tip immersed in the liquid mixture was used to determine both freezing and melting temperatures by varying the temperature of the copper tip relative to the stirred, bulk liquid. With the bulk liquid held at the mixture’s SLVE temperature, the induction time required to nucleate solid octadecane decreased exponentially as the subcooling of the copper tip increased, halving approximately every 0.25 K. At higher pressures, while the melting temperature of pure cyclohexane (cyC6) increased by about 0.55 K·MPa–1, at xcyC6 = 0.5675 it increased by only 0.15 K·MPa–1. The new data were compared with measurements reported in the literature, e...