Modeling of Reactive Distillation

1. Modeling of Reactive Distillation Modeling of Reactive Distillation John Schell Dr. R. Bruce Eldridge Dr. Thomas F. Edgar

2. Overview of Reactive Distillation Project Overview Tower Design Steady-State Models Dynamic Models and Control Individual Work Column Design and Operation Validation of Models Preliminary Dynamics and Control Studies Future Work Outline Outline

3. Homogeneous or Heterogeneous/ Catalytic Distillation First Patents in 1920s Applied in 1980s to Methyl Acetate Common applications: Ethylene Glycol MTBE, TAME, TAA Reactive Distillation Reactive Distillation

4. Favorable ApplicationsWesterterp (1992) • Match between reaction and distillation temperatures • Difference in relative volatility between product and one reactant • Fast reaction not requiring a large amount of catalyst • Others: liquid phase reaction, azeotrope considerations,exothermic reactions

5. 1. Decide on a Pre-reactor - Rate of reaction - >1/2 of initial reaction rate at 80% of equilibrium conversion 2. Pressure 3. Location of Zone 4. Estimate Catalyst - Isothermal Plug-flow reactor with ideal separators 5. Design Tower - Size reaction zone • Catalyst requirements • Column diameter - Determine reactant feed ratio - Feed location - Reflux ratio • High reflux rate - 2-3 times non-rxtive column - Diameter • Through-put • Catalyst density Subawalla Approach (Dissertation)

6. Project Overview • Design and Construct TAME Column • Validate Steady State Models • Develop Dynamic Models • Test Control Algorithms

7. Exothermic Equilibrium Limited 45-62% at 50-80 C Azeotropes Catalyst: Amberlyst-15 Methanol can inhibit rates. Rihko and Krause (1995) TAME Chemistry TAME Chemistry

8. 0.152-meter diameter column Finite reflux 7 meters of packing in 3 sections Fisher DeltaV Control Koch’s Katamaxpacking Unreacted C5, MeOH Reactive Distillation Column Recycle Back - Cracking Reactor 3.7 atm C5 from Cat Cracker Mixing Tank Pre-Reactor Makeup MeOH TAME Pilot Plant (SRP) Pilot Plant (SRP)

9. SRP Pilot Plant SRP Pilot Plant • Koch – Spool section, Katamax, Catalyst • SRP - $145K

10. Steady-State Multiplicity Steady-State Multiplicity • Bravo et al. (1993) • Observed multiple steady-states in TAME CD • Hauan et al. (1997) • dynamic simulation provided evidence in MTBE system • Nijuis et al. (1993) • found multiplicity in MTBE system • Jacobs and Krishna (1993) • found multiplicity in MTBE system

11. Steady-State Distillation Models Steady-State Distillation Models Packed Tower: Continuous Model Trayed Tower: Equilibrium Model Rate Model

12. TAME Reaction Rates TAME Reaction Rates

13. TAME Concentration Profile TAME Concentration Profile

14. Traditionally simulations use intrinsic reaction rate. Effective rate is a function of intrinsic rate and diffusion limitations. Effective Rate Molefraction Effective Reaction Rate Effective Reaction Rate

15. Fisher DeltaV Visual Basic Matlab, Visual Studio State Estimation Temperature Profiles Online Analyzers Control Algorithms PID Linear MPC Non-Linear MPC Control for TAME Tower Control for TAME Tower

16. Individual Work • Design and Construct RD Column for Novel System • Steady State Model Validation • Dynamic Models and Control Study

17. Kinetic Reaction Not Equilibrium limited Equilibrium Isomers Exothermic Kinetics from CSTR Experiments Feed is dominated by inerts Replace hazardous heterogeneous catalyst A + B C1 C1 C2 C3 Novel System

18. Novel System Data Novel System Data

19. Novel System Data Novel System Data

20. Simulation Validation - 50 psig Simulation Validation - 50 psig

21. Simulation Validation – 35 psi

22. Effect of Pressure

23. Effect of Varying Feed Rate

24. Aspen Custom Modeler/ Aspen Dynamics Validate Steady State Solution Validate Dynamic Studies Develop Control Algorithms PID Linear MPC NLMPC Dynamic Modeling and Control Study

25. Aspen Custom Modeler Aspen Custom Modeler • Formerly Speed-Up and DynaPlus • Equation Solver • Aspen Properties Plus • Tear Variables automatically selected • Solves Steady-State and Dynamic • Dynamic Events and Task Automation Equations vs. Variables

26. Validation of Dynamic Simulator Validation of Dynamic Simulator

27. Feed Disturbance With Manual Control Feed Disturbance With Manual Control

28. Configurations DB LV BV, LB… Goals Conversion Product Purity D R F L V Duty B Control of Reactive Distillation Control of Reactive Distillation

29. Bartlett and Wahnschafft (1997) Simple Feed-Forward/ Feed-Back PI Scheme Sneesby et al. (1999) Two point control with linear conversion estimator Kumar and Daoutidis (1999) Showed linear controllers unstable for ethylene glycol systems Demonstrated possible Nonlinear MPC scheme Control of Reactive Distillation Control of Reactive Distillation

30. Dependency of Conversion on Reboiler Duty and Reflux Ratio Dependency of Conversion on Reboiler Duty and Reflux Ratio

31. Conversion vs Reboiler Duty Conversion vs Reboiler Duty

32. Single Tray Conversion Estimation Single Tray Conversion Estimation

33. Single Tray Purity Estimation Single Tray Purity Estimation

34. Feed Disturbance With Manual Control Feed Disturbance With Manual Control

35. Feed Disturbance with Simple PID Control Feed Disturbance with Simple PID Control

36. TAME Tower Collect Data Validate Models Developing Advanced Models Improvements New chemical system Adjust for better dynamic studies Novel System Validate Dynamic Models Develop Control Algorithms Conclusion and Future Work Conclusion and Future Work