Study of Phase Equilibria for the n-Butane

This study is concerned with comparing the closeness of calculated binary VLE data from the UNIFAC and Wilson models with the experimental data reported elsewhere [Courtial et al., Fluid Phase Equilibria., 2009, 277, 152-161]. This work also reports the existence of an azeotrope in the range of temperatures, pressures, and components for the n-butane + methanol system. The Wilson model was found to be sufficient in the investigation of excess Gibbs energy for the n-butane + methanol system for temperatures ranging from 323.22 K to 423.09 K. The relative deviations (RD) and absolute average deviations (AAD) for vapor-pressures and vapor compositions have been calculated by the UNIFAC and Wilson models for the binary system of n-butane + methanol for the considered temperature and pressure ranges. The AADs estimated by the UNIFAC model for the vapour compositions (y(AAD)) and vapour pressures (P-AAD) of the mixture of n-butane + methanol at T = 323.22 K are 0.00837 and 0.01026, respectively at T = 373.19 K are 0.00876 and 0.02552, respectively at T = 403.13 K are 0.015 and 0.855, respectively, and at T = 423.09 K are 0.026 and 3.869, respectively. Similarly, The AADs estimated by the Wilson model for the vapour compositions (y(AAD)) and vapour pressures (P-AAD) of the mixture of n-butane + methanol at T = 323.22 K are 0.002 and 0.006, respectively at T = 373.19 K are 0.029 and 0.052, respectively at T = 403.13 K are 0.065 and 0.905, respectively, and at T = 423.09 K are 0.081 and 0.482, respectively. The relative volatility of the experimental data has also been analysed.