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

2. Outline Outline 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

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

4. Favorable Applications Westerterp (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. Subawalla Approach (Dissertation)
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 times non-rxtive column
- Diameter
• Through-put
• Catalyst density

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

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

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

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

10. 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)

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

12. TAME Reaction Rates
TAME Reaction Rates

13. TAME Concentration Profile

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

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

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

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

18. Novel System Data
Novel System Data

19. Novel System Data
Novel System Data

20. Simulation Validation - 50 psig

21. Simulation Validation – 35 psi

22. Effect of Pressure

23. Effect of Varying Feed Rate

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

25. Equations vs. Variables
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

27. Feed Disturbance With Manual Control

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

29. Control of Reactive Distillation
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

30. Dependency of Conversion on Reboiler Duty and Reflux Ratio

31. Conversion vs Reboiler Duty

32. Single Tray Conversion Estimation

33. Single Tray Purity Estimation

34. Feed Disturbance With Manual Control

35. Feed Disturbance with Simple PID Control

36. Conclusion and Future Work
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