1. “Chemical Engineering Equilibrium Separations” Lectures 14 1 17 Oct 2012

2. Overview 2 AspenPlus: o Shortcut methods: DSTWU o Rigorous method: RADFRAC Efficiencies Introduction to multicomponent distillation (Chapter 9)

3. Multicomponent Distillation (Introduction) 3 In binary distillation we could specify x D and x B …. Now: define “Key Components” Decreasing Relative Volatility Keys 1 2Light 3Heavy 4 Most of LK obtained in distillate product Most of HK obtained in bottoms product Today, most multicomponent systems are solved rigorous simulation. But need to do shortcut methods to get good starting point (FUG-Kirkbride).

4. Multicomponent Shortcut Methods 4 Minimum number of stages: Fenske Equation

5. Multicomponent Shortcut Methods 5 Minimum reflux ratio: Underwood Equation Case A: NKs don’t distribute Case B & C: NKs distribute, or there is a “sandwich” NK: see Wankat; numerical iterative procedures can be involved. R = factor * R min Approximate number of equilibrium stages (N): Gilliland correlation

6. Gilliland Correlation 6 61 Data points over ranges: 1. No. components: 2 to 11 2. q : 0.28 to 1.42 3. P : vacuum to 42.4 bar 4.  : 1.11 to 4.05 5. R min : 0.53 to 9.09 6. N min : 3.4 to 60.3 Molokanov Eqn: Seader & Henley, 2006

7. Multicomponent Shortcut Methods 7 Optimum feed stage location (N F ): Kirkbride Equation DSTWU (AspenPlus) Uses Winn, Underwood, and Gilliland methods to find N min, R min, & N. Specify LK and HK recoveries in the distillate product stream If input -1.2 for reflux ratio; it finds N at R = 1.2 * R min. N given by DSTWU is number of equilibrium stages (includes partial condensers and/or partial reboilers)

8. In-Class Problem 8 benzene (17 mol%) toluene (66 mol%) m-xylene (17 mol%) F = 100 kmol/s sat’d liquid 1 atm DSTWU 1.0135 barPi star [bar] ComponentTbp oC80.1 oC123 oC Benzene80.11.01353.217 Toluene110.70.3871.42 m-Xylene139.10.1510.645

9. In-Class Problem 9

10. 10

11. In-Class Problem 11

12. In-Class Problem 12 By hand calculations first. Then use to verify AspenPlus results…

13. In-Class Problem 13

14. In-Class Problem 14

15. Homework Problem 15 benzene (17 mol%) toluene (66 mol%) m-xylene (17 mol%) F = 100 kmol/s sat’d liquid 1 atm X bz = 99 mol% X bz = 0.1 mol% DSTWU 1.0135 barPi star [bar] ComponentTbp oC80.1 oC123 oC Benzene80.11.01353.217 Toluene110.70.3871.42 m-Xylene139.10.1510.645

16. Overview 16 AspenPlus: o Shortcut methods: DSTWU o Rigorous method: RADFRAC Efficiencies Introduction to multicomponent distillation (Chapter 9)