Exercises for Lecture 1

Dr Colin HareChemical Engineering

School of Process, Environmental and Materials EngineeringUniversity of Leeds

Tel. 32407e-mail c.l.hare@leeds.ac.uk

Example 1 Phase Diagram & Equilibrium Curve

Use Raoult's Law to calculate the vapour and liquid compositions in equilibrium (in mole fractions, y and x) for the benzene-toluene system using vapour pressure data measure at a pressure of 101.32 kPa as shown in the table below :

Solution to Example 1 Write Raoult's Law for a binary mixture of A and B

pA = Pvp,A xA ; pB = Pvp,B xB = Pvp,B (1 - xA) The total pressure, PT = pA + pB Replacing for the partial pressures and re-arrange, we have:

As Pvp,A xA = yA PT, then

The Vapour-Liquid Equilibrium data can be calculated at each temperature by substituting for total pressure (101.32 kPa) and the appropriate vapour pressures. For example, at 85.0 oC,

Solution to Example 1

One has the following Table:

Solution to Example 1

One has the following Table:

T (oC) xB yB xT yT KB KT αBT

80.1 1 1 0 0 1 - -

85.0 0.78 0.9 0.22 0.1 1.154 0.454 2.542

90.0 0.581 0.777 0.419 0.223 1.337 0.532 2.513

95.0 0.411 0.632 0.589 0.368 1.538 0.625 2.461

100.0 0.258 0.456 0.742 0.544 1.767 0.733 2.411

105.0 0.130 0.261 0.870 0.739 2.008 0.849 2.365

110.6 0 0 1 1 - 1 -

Solution to Example 1 (C) One can also plot the T-X-Y and X-Y diagrams