Exercise 9 Text

Page 1

1 Department of Energy Politecnico di Milano Via Lambruschini 4 - 20156 MILANO Exercises of “Fundamentals of Chemical Processes” Prof. Gianpiero Groppi Exercise 9 Estimation of the bubble temperature and of the dew temperature of a n-butane/n-hexane mixture A mixture, composed of 50% v/v n-butane and 50% v/v n-hexane, is maintained at 4.85 bar. Estimate its bubble temperature and dew temperature in the following cases:  Ideal gas and ideal mixture  Real gas and ideal mixture  Real gas and real mixture Assume the RKS equation of state. Data: AANTOINE BANTOINE CANTOINE TC [K] PC [bar] ω n‐C4H10 13.6608 2154.700 238.789 425.10 37.96 0.200 n‐C6H14 13.8193 2696.040 224.317 507.60 30.25 0.301 Antoine’s equation: P is kPa, T is °C i i i sat i CT BAP ln The Antoine’s Equation for Psat i is taken from J.M. Smith, H.C. Van Ness, M. M. Abbott, Introduction to Chemical Engineering Thermodynamics, 7th edition, McGraw Hill (2005). 2 RKS parameters    2 2 2 2 0.42748 0.08664 11 0.48 1.574 0.176 gas C C gas C C R gas gas RT a P RTb P ST S aPA RT bPB RT                    Fugacity Coefficient (Z root of the cubic equation)  ln , 1 ln ln AZ BTP Z Z B BZ      RKS parameters for mixtures and mixing rules   2 2 2 i i gas i i gas NC mix i i i NC mix i i i mix mix gas mix mix gas aPA RT bPB RT ax a bx b aPA RT bPB RT             Fugacity coefficient for the i-th specie in the  phase with x composition    mix mix mix i mix i mix mix mix i i BZZ BZ A A B B B AZB BxPT             lnln21,,ˆln   3 Solving procedure for the cubic equation 32 2 0 1 ZZZ ABB AB            2 3 23 3 2 27 3 42 7 p q qpD         If D>0, only 1 real solution is found.…