Isothermal Vapor–Liquid Equilibrium Measurements for Alcohol + Water/n-Hexane Azeotropic Systems Using Both Dynamic and Automated Static-Synthetic Methods

Isothermal vapor–liquid equilibrium measurements (pressure– temperature–liquid and vapor composition) were conducted for water (1) + propan-1-ol (2), n-hexane (1) + butan-2-ol (2), and n-hexane (1) + 2-methyl-propan-1-ol (2) at three temperatures, each using a dynamic moderate pressure equilibrium still. Additionally, pressure–temperature-overall composition measurements for the first two systems were conducted for the intermediate temperatures using a newly automated static-synthetic apparatus to confirm the operability of the automation scheme and to compare the model predictions of the vapor-phase compositions from the processed pressure–temperature–liquid composition data by the static-synthetic method with the experimental vapor compositions measured by the dynamic method. The automation scheme was developed and implemented on the original static total pressure vapor–liquid equilibrium apparatus of Raal et al. (Fluid Phase Equilib.2011, 310, 156–165) using the LabVIEW graphical programming language. In comparison to the manual operating mode, this scheme improved the efficiency of operation by reducing the man-hours involved and minimized the associated uncertainty with the measurement procedure with respect to liquid composition. Once executed, the control scheme requires approximately 2 days to produce a single 40-data point (pressure–temperature–liquid composition) isotherm and minimizes human intervention to 2–3 h in comparison to a 2-week long measurement procedure in the nonautomated operating mode and in excess of 3 weeks using the dynamic method with analysis by gas chromatography. All experimental data were modeled using the γ–Φ approach with the NRTL and UNIQUAC activity coefficient models and the virial equation of state with the Hayden and O’Connell correlation. For the pressure–temperature–liquid and vapor composition data measured, thermodynamic consistency testing was performed. The data sets passed the point test with 0.01 tolerance and the area test with 10% tolerance. Experimental vapor-phase compositions obtained by phase sampling in the dynamic method compared reasonably well with the predictions from the pressure–temperature–liquid composition data measured by the automated static-synthetic method.