Partial molar and microstructural properties of binary propane + o-toluidine system near the critical point of pure solvent based on the VLE measurements and modeling with CP-PC-SAFT and mg-SAFT equation of states

Abstract

The isothermal VLE properties (PTxy relationship) of a binary supercritical (SC) C₃H₈ + o-toluidine mixture was measured by means of static-analytic method with fluid phase sampling at equilibrium conditions. The measurements were made at three temperatures of (393.15, 433.15, and 473.15) K and pressures up to 10.41 MPa. An experimental VLE apparatus, a high-temperature and high-pressure optical cell, has been used to measure the phase equilibrium properties (PTxy) of the binary SC C₃H₈ + o-toluidine mixture. The combined expanded absolute and relative uncertainties of the temperature, pressure, and the phase concentration measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated at 0.15 K, 0.5 %, 4.2 % (for x) and 4.8 % (for y), respectively. The critical curve data, $T_{\text{C}}$−$x$,$P_{\text{C}}$-$x$, and $P_{\text{C}}$− $T_{\text{C}}$ projections, have been derived based on the measured VLE data. The measured VLE and the derived critical curve data were used to estimate the theoretically important and physical meaning of Krichevskii parameter, ${\left(\frac{\partial P}{\partial x}\right)}_{T_C{V}_C}^{\infty }$. Thermodynamic (partial molar properties, ${\overline{V}}_2^{\infty },{\overline{H}}_2^{\infty },{\overline{C}}_{P2}^{\infty }$, and distribution equilibrium constant $K_D$), and microstructural (cluster’s size, $N_{\mathrm{exc}}^{\infty }$) properties of infinite-dilute C₃H₈ + o-toluidine mixture near the critical point of pure solvent (C₃H₈) were calculated based on the derived Krichevskii parameter and pure solvent (SC C₃H₈) properties. CP-PC-SAFT and mg-SAFT equation of state (EoS), with zero interaction parameter, $k_{12}$ = 0, for both models (pure prediction models, no adjustable parameters) were successfully applied to the present PTxy phase equilibria for the SC C₃H₈ + o-toluidine mixture. The present measured VLE data for C₃H₈ + o-toluidine system along with the reported pure compound properties of pure propane and o-toluidine have been used to examine the predictive capabilities of the theoretically based CP-PC-SAFT and mg-SAFT models of EoS. It was demonstrated that mg-SAFT is superior in predicting VLE of the C₃H₈ + o-toluidine system with $k_{12}$ = 0.