Modeling of Reactive Distillation

1
Modeling of Reactive Distillation
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
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 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
Subawalla Approach (Dissertation)

• 1. Decide on a Pre-reactor
• - Rate of reaction
• - gt1/2 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

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 50-80 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
• Kochs Katamax packing

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
Effective Reaction Rate
Effective Reaction Rate

• Traditionally simulations use intrinsic reaction
  rate.
• Effective rate is a function of intrinsic rate
  and diffusion limitations.

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

• Kinetic Reaction
• 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
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
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
Control of Reactive Distillation
Control of Reactive Distillation

• Configurations
• DB
• LV
• BV, LB
• Goals
• Conversion
• Product Purity

29
Control of Reactive Distillation
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
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
Conclusion and Future Work
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