Visual Measurements Of Solid-Liquid Equilibria And Induction Times For Cyclohexane Plus Octadecane Mixtures At Pressures To 5 Mpa

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 (cyC(6)) increased by about 0.55 K.MPa-1, at X-cyC6 = 0.5675 it increased by only 0.15 K.MPa-1. The new data were compared with measurements reported in the literature, empirical correlations describing those literature data, and the predictions of models based on cubic equations of state (EOS), including the Peng-Robinson Advanced (PRA) EOS implemented in the software Multiflash. The best description of the data was achieved by adjusting the binary interaction parameter in the PRA model from 0 to -0.0324, which reduced the deviation of the SLVE data at the eutectic point (x(cyC6) approximate to 0.95) from (12.8 to -0.2) K. Although the accuracy of predictions made with the SLVE-tuned PRA EOS deteriorated slightly at pressures around 5 MPa, they were still as good as, or better, than the empirical correlations available for this system. Furthermore, the SLVE-tuned PRA EOS was more accurate at describing literature VLE data for this binary than the default PRA EOS, reducing the root mean square deviation in bubble temperature predictions from (6.7 to 0.67) K.