For a two-component homogeneous mixture, the saturated vapor pressure at a given temperature is determined when the saturated vapor pressures of the components are known

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This post was last edited by Wang Zongliang on 2012-2-23 at 11:35. Source of the question: Edited by Xia Qing and Chen Changgui, reviewed by Yao Yuying; Chapter 1 Distillation from \"Principles of Chemical Engineering\", Volume 2. *Question 2: The saturated vapor pressures of n-pentane (C5H12) and n-hexane (C6H14) are given in the appendix. Determine the equilibrium values for this solution at P = 13.3 Kpa. Assume that the solution is an ideal solution. Appendix: Temperature/°C
C5H12: 223.1, 233.0, 244.0, 251.0, 260.6, 275.1, 291.7, 309.3
C6H14: 248.2, 259.1, 276.9, 279.0, 289.0, 304.8, 322.8, 341.9

Saturated vapor pressure/kPa: 1.3, 2.6, 5.3, 8.0, 13.3, 26.0, 53.2, 101.3

Approach to solving the problem: (1) Based on the data in the appendix, the temperatures at which the saturated vapor pressures of these two-component ideal solutions are equal are known; thus, it is possible to calculate the saturated vapor pressures of these two components at the same temperature (the Antoine equation will be used for this purpose) ； (2) Using the saturated vapor pressures of the two components at the same temperature obtained, the vapor-liquid equilibrium data are calculated via Raoult’s law. Steps: (1) Determine the constants A, B, and C of the Antoine equation (P = A + B/(t+C)). These values can be found in reference manuals, or they can be calculated using the data provided in the problem (an Excel file is attached showing the calculation of the Antoine equation constants using the data from the accompanying table). By consulting relevant manuals, it can be found that A = B = C = (these constants are calculated using pressure in mmHg and temperature in K; therefore, unit conversion is necessary). (2) Using the Antoine equation, the saturated vapor pressures of the two substances at the same temperature can be determined. (3) Use Raoult’s law to determine the vapor-liquid phase compositions at various temperatures under a total pressure of 13.3 Kpa. This problem has a solution. Problems and discussions: (1) The antoin constant obtained is not consistent with the antoin constant calculated using the data given in the problem. (2) Comparison of vapor-liquid equilibrium data calculated using relative volatility with those calculated using Raoult’s law.