Separation Process Principles- 2n - Seader & Henley - Solutions Manual

11 continued xa xb hl kjkmol ya yb hv kjkmol t oc 567

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Unformatted text preview: t 25oC. This is a different datum than that used to get the given enthalpy of the hot feed. Pure A: boils at 56.7oC. Since CP of liquid =134 kJ/kmol-K, hL at 56.7oC = 134(56.7-25)=4248 kJ/kmol-K hV at 56.7oC =4248 + latent heat = 4248 + 29750 = 33998 kJ/kmol-K Pure B: boils at 100oC. Since CP of liquid =75.3 kJ/kmol-K, hL at 100oC = 75.3(100-25)=5648 kJ/kmol-K hV at 100oC =5648 + latent heat = 5648 + 42430 = 48078 kJ/kmol-K Equilibrium liquid mixture of 50 mol% A and 50 mol% B has a bubble point at 60oC. Therefore, hL = 0.5(134)(60-25) + 0.5(75.3)(60-25) = 3663 kJ/kmol-K Equilibrium vapor mixture of 85 mol% A and 15 mol% B has dew point of 60oC. Therefore, hV = 0.85[(134)(60-25) + 29750] + 0.15[(75.3)(60-25) + 42430] = 36034 kJ/kmol-K Calculations for other equilibrium mixtures are done in a similar manner and are summarized in the following table: Analysis: (continued) Exercise 4.11 (continued) xA xB hL, kJ/kmol yA yB hV, kJ/kmol T, oC 56.7 1.000 0.000 4248 1.000 0.000 33998 57.1 0.920 0.080 4151 0.944 0.056 34656 60.0 0.500 0.500 3663 0.850 0.150 36034 61.0 0.330 0.670 3408 0.837 0.163 36296 63.0 0.176 0.824 3254 0.805 0.195 36880 71.7 0.068 0.932 3703 0.692 0.308 39069 100.0 0.000 1.000 5648 0.000 1.000 48078 From this table, the h-x-y plot follows, with tie lines to connect the vapor-liquid equilibrium along the dew-point and bubble-point lines. Enthalpy-Composition Plot Exercise 4.12 Subject: Vaporizer and condenser heat duties for benzene (A) -toluene (B) mixtures, using an enthalpy-concentration diagram. Given: P = 1 atm. Vapor pressure data. Saturated liquid and vapor enthalpy data. Assumptions: Raoult's law. Find: (a) Construct an h-x-y plot. (b) Heat duty for 50 mol% vaporization of a 30 mol% A mixture, starting from liquid saturation temperature. Heat duty to condense the vapor and subcool it 10oC. Analysis: (a) First, compute the vapor and liquid equilibrium compositions at 1 atm and temperatures from 60 to 100oC using Raoult's law with the vapor pressure data. Eq. (2-44 ) applies, as well as the sum of the mole fractions in the phases in equilibrium. Thus, KA = s yA PA T = xA P s yB PB T = xB P , , yA + y B = 1 KB = xA + x B = 1 (1, 2) (3, 4) Equations (1) to (4) can be reduced to the following equations, xA = 1 − KB KA − KB , y A = KA x A (5, 6) Vapor pressure data in Exercises 4.6 for benzene, and 4.8 for toluene give Antoine equations, PAs = exp 15.5645 − 2602.34 , T + 211.271 PBs = exp 17.2741 − 3896.3 T + 255.67 (7, 8) Where vapor pressure is in torr and temperature is in oC. Solving, Eqs. (1) to (8), T, oC Ps of A, torr Ps of B, torr KA KB xA yA 80.1 759.9 290.0 0.9998 0.3816 1.000 85.0 880.8 342.7 1.1590 0.4510 0.775 90.0 1019.1 404.4 1.3409 0.5321 0.579 95.0 1173.4 474.9 1.5439 0.6249 0.408 100.0 1345.0 555.2 1.7697 0.7305 0.259 105.0 1535.0 646.2 2.0198 0.8503 0.128 110.5 1766.8 760.1 2.3248 1.0001 0.000 This covers the temperature range of co-existence of vapor and liquid. 1.000 0.899 0.776 0.630 0.459 0.259 0.000 E...
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.

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