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Simulate a Reactive Distillation Column with Aspen Plus® V8.0

1. Lesson Objectives Learn how to specify reactions in Aspen Plus

Learn how to configure a reactive distillation column in Aspen Plus

2. Prerequisites Aspen Plus V8.0

3. Background Global warming and greenhouse gas emissions have been gaining more and more attention in the world. As a

result, CO2 capture has been a hot topic in both the academic world and in industry. This example shows how to

use Aspen Plus to simulate the process of CO2 capture using MDEA.

The examples presented are solely intended to illustrate specific concepts and principles. They may not

reflect an industrial application or real situation.

4. Aspen Plus Solution If you are unfamiliar with how to start Aspen Plus, select components, define methods, or construct a flowsheet,

consult Get Started Guide for New Users of Aspen Plus.pdf for instructions.

4.01. Start a new simulation using the Blank Simulation template in Aspen Plus.

4.02. The Components | Specification | Selection sheet is displayed. Enter WATER, CO2, N2, and MDEA for

Component ID. Enter C5H13NO2 in the Alias column for MDEA.

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4.03. Use the Elec Wizard to define the electrolytes in the system. Click the Elec Wizard button found on the

Components | Specifications | Selection sheet. On the window that pops up, select unsymmetric for

reference state for ionic components. Click the Next button.

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4.04. On the following window, select all available components, and check the box to include water

dissociation reaction. Click the Next button.

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4.05. The next window will allow you to remove any undesired reactions or species, and to choose the

property method. In this case we will not make any changes, click the Next button.

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4.06. Another window will appear asking to select the electrolyte simulation approach. True component

approach is the default option. Confirm that this option is selected and click the Next button.

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4.07. Finally, a summary window will appear. Click the Finish button on the Electrolyte Wizard window.

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4.08. You will notice that all components are defined now.

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4.09. Confirm Henry components. Go to the Components | Henry Comps | Global | Selection sheet, or press

the Next button (the F4 key) to get there.

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4.10. Confirm methods and parameters. Use the Next button (the F4 key) to confirm Base method on the

Methods | Specifications | Global sheet.

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4.11. Press the F4 key three times (one at a time) to confirm Binary Interaction parameters.

4.12. Press the F4 key twice (one at a time) to view Electrolyte Pairs.

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4.13. Create flowsheet. Go to the simulation environment by clicking the Simulation bar at the bottom left

corner of the screen.

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4.14. Place a RadFrac block onto the Main flowsheet and connect two feed streams, a vapor distillate stream,

and a liquid bottoms stream to the column inlet and outlet ports. Name the streams MDEA, FEED,

CLEANGAS, and RICH-SOL as shown below. Also, rename the RadFrac block ‘COL-MAIN’.

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4.15. Specify feed streams. Double click on the FEED stream or use the navigation pane to go to the Streams

| FEED | Input | Mixed sheet. Specify the Temperature, Pressure, Total flow rate, and Composition of

the FEED stream as shown below.

4.16. Define MDEA stream. Navigate to the Streams | MDEA | Input | Mixed sheet. Specify Temperature,

Pressure, Total flow rate, Composition, and Solvent, as shown below.

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4.17. Go to the Flash Options sheet. Specify the Valid phases as Liquid-Only. This option means that, when

specifying the temperature, pressure, and concentration of a stream, the stream will be only liquid.

4.18. Define reactions. Go to the Reactions folder in the simulation navigation pane. Click the New button

and select REAC-DIST as the type.

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4.19. For this process we have 5 individual reactions to input into the R-1 reaction group. Under the newly

created reaction group (R-1) click the New button to enter a new reaction. Select

Kinetic/Equilibrium/Conversion as the reaction type.

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4.20. For the first reaction, select MDEA+ and WATER in the Reactants frame and MDEA and H3O+ in the

Products frame. Enter a stoichiometric Coefficient of 1 for each component and select Equilibrium as

the Reaction type. Note that a minus sign is automatically added for numbers in the Coefficient column

in the Reactants frame.

4.21. Enter each reaction using this same procedure. The reactions are listed below.

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4.22. Make sure to input the correct stoichiometric coefficients and to select the correct reaction type for

each reaction. Also note that for kinetic reactions, an exponent must be defined for the reactants. In

reactions 4 and 5 the Exponent is 1 for all reactants. Leave the products exponent blank. Once the

stoichiometry is defined for each reaction, the kinetic and equilibrium parameters must be specified. Go

to the Reactions | R-1 | Kinetic sheet.

4.23. For reaction 4, enter a value of 4.3e+13 for k and a value of 13300 cal/mol for E.

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4.24. For reaction 5, enter a value of 3.75e+14 for k and a value of 25300 cal/mol for E. Note that you can

change reactions by using the pull down menu highlighted below.

4.25. For reactions 1, 2, and 3 we must enter equilibrium parameters. Go to the Reactions | R-1 |

Equilibrium sheet. For each reaction select Compute Keq from built-in expression and then enter the

values for A, B, C, and D. This is shown below.

Reaction #1

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Reaction #2

Reaction #3

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4.26. Specify column operating conditions. Navigate to the Blocks | COL-MAIN | Specifications | Setup |

Configuration sheet. Enter 30 for Number of stages, None for Condenser and None for Reboiler.

4.27. Go to the Streams sheet. For stream MDEA, enter On-Stage for Convention and 1 for Stage. For

stream FEED, enter On-Stage for Convention and 30 for Stage.

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4.28. Go to the Pressure sheet and specify 10 bar in the Top stage/Condenser pressure frame.

4.29. Specify reactions. Go to the Blocks | COL-MAIN | Specifications | Reactions | Specifications sheet.

Select R-1 as the Reaction ID, enter stage 1 for Starting stage and 30 for Ending stage.

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4.30. Go to the Blocks | COL-MAIN | Specifications | Reactions | Holdups sheet. Enter 1 for Starting stage,

30 for Ending stage, and 160 L for Liquid holdup.

4.31. Go to the Setup | Calculation Options | Reactions sheet. In Activity coefficient basis for Henry

components frame, select Aqueous as shown below

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4.32. Go to the Blocks | COL-MAIN | Specifications | Convergence | Convergence | Basic sheet. Change

Maximum iterations to 100.

4.33. Now, we need to get the flowsheet to converge. Go back to the Blocks | COL-MAIN | Specifications |

Reactions | Holdups sheet. Note that Liquid holdup should eventually be 160. Change it to 16. Then,

press the F5 key to run the simulation. The simulation should complete without any error or warning.

4.34. Go to the Blocks | COL-MAIN | Reactions | Holdups sheet. Change Liquid holdup to 50. Then, press

the F5 key to run the simulation. The simulation should complete without any error or warning.

4.35. Change Liquid holdup to 100. Then, press the F5 key to run the simulation. The simulation should

complete without any error or warning.

4.36. Change Liquid holdup to 160. Then, press the F5 key to run the simulation. The simulation should

complete without any error or warning.

4.37. Go to the Blocks | COL-MAIN | Specifications | Setup | Configuration sheet. Select Custom for

Convergence.

4.38. Go to the Blocks | COL-MAIN | Convergence | Estimates | Temperature sheet. Click the Generate

Estimates… button. In the popup dialog box, select options to generate the most estimates as shown

below. Then click Generate button and wait for estimate generation to complete.

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4.39. Go to the Blocks | COL-MAIN | Convergence | Convergence | Basic sheet. Change Algorithm to

Newton.

4.40. In the Advanced sheet, select Dogleg strategy for Stable-Meth.

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4.41. Click the button in the Home | Run group of the ribbon to reinitialize simulation. Run the

simulation again to ensure it still converges.

4.42. Check results. Go to the Results Summary | Streams | Material sheet. You can see that the stream

CLEANGAS contains significantly less CO2 than stream FEED.

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5. Conclusions This example shows that MDEA can be used to capture CO2. After completing this exercise you should be

familiar with how to specify reactions and configure RadFrac to simulate distillation columns involving reactions.

You should also learn how to modify some convergence options in RadFrac.

6. Copyright Copyright © 2012 by Aspen Technology, Inc. (“AspenTech”). All rights reserved. This work may not be

reproduced or distributed in any form or by any means without the prior written consent of

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