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ENGR5003 / Week 6
ENGR263 2019 Q A1(a)Past paperOld spec ENGR263Third5 marks6 min

ENGR263 Process of Mass Transfer 2019 Q A1(a)[PARTIAL] Left out: Parts (b)-(d) (diffusion flux, mass transfer coefficient, stagnant-film flux) are ENGR5002 mass transfer and are in that bank as engr263-2019-a1; part (e) (azeotrope reading of the ethanol-water VLE diagram, alternative separation methods) is distillation and is off-syllabus.

A binary mixture of ethanol and water in the reboiler of a batch distillation column presents the following data:

  • Total pressure P=101 300 PaP = 101\,300\ \mathrm{Pa}
  • Temperature T=85∘CT = 85^\circ\mathrm{C}
  • Mole fraction of water in the liquid phase xw=0.6x_w = 0.6
  • Mole fraction of water in the vapour phase yw=0.70y_w = 0.70
  • Saturated vapour pressure of ethanol Pesat=135 087 PaP_e^{sat} = 135\,087\ \mathrm{Pa}
Formulas you may need
  • Raoult's law (ideal liquid and ideal vapour): yiP=xiPisaty_iP = x_iP_i^{sat} (learn this)
  1. (a)
    Calculate the composition of ethanol in the vapour phase in equilibrium with the liquid phase mixture, assuming both the vapour and liquid phases are ideal mixtures.
    [5]