Separation of Acetone-Water with Aspen HYSYS V8.0 Liquid-Liquid Extraction with 3-Methylhexane as the Solvent 1. Lesson Objectives Learn how to build an extraction and solvent recovery flowsheet. Learn how to configure a liquid-liquid extractor and a distillation column. 2. Prerequisites Aspen HYSYS V8.0 3. Background Water has a high latent heat (heat of vaporization) compared to many other components. For the separation of a water-acetone mixture (50 wt-% each), it may be more energy efficient to use extraction instead of direct distillation. In this example, we utilize 3-methylhexane as a solvent to remove water via liquid-liquid extraction, followed by distillation to remove the solvent from acetone. The examples presented are solely intended to illustrate specific concepts and principles. They may not reflect an industrial application or real situation. 4. Problem Statement and Aspen HYSYS Solution Problem Statement Determine how much energy is required to separate a 50 wt-% acetone 50 wt-% water stream using 3- methylhexane as a solvent. Aspen HYSYS Solution 4.01. Start a new simulation in Aspen HYSYS V8.0. 4.02. Create a component list. In the Component Lists folder select Add. Add Acetone, Water, and 3- methylhexane to the component list. 1
4.03. Select property package. In the Fluid Packages folder select Add. Select PRSV as the property package. For information about the PRSV property package see Aspen HYSYS help. 4.04. Move to the simulation environment by clicking the Simulation button in the bottom left of the screen. 4.05. First we will add a Mixer to the flowsheet from the Model Palette. This mixer will serve to mix together the recycled solvent stream and the solvent make up stream. 2
4.06. Double click the mixer (MIX-100). Create two Inlet streams called Make Up and Solvent-Recycle. Create an Outlet stream called Solvent. 3
4.07. Double click on the Make Up stream. Specify a Temperature of 25 C, a Pressure of 1 bar, and a Molar Flow of 0. We will later assign this stream a flowrate, but for now it will have zero flow. In the Composition form enter a Mole Fraction of 1 for 3-methylhexane. 4.08. Double click on the Solvent-Recycle stream. Enter a Temperature of 30 C, a Pressure of 1 bar, and a Mass Flow of 150 kg/h. In the Composition form enter a Mole Fraction of 1 for 3-methylhexane. These specifications will serve as an initial guess as to what the actual recycle stream will be. 4
4.09. Add a Liquid-Liquid Extractor to the flowsheet from the Model Palette. 4.10. Double click on the extractor (T-100) to open the Liquid-Liquid Extractor Input Expert window. On the first page enter a Top Stage Inlet called Feed and select Solvent for the Bottom Stage Inlet. Change the number of stages to 8. Enter an Ovhd Light Liquid stream called Rich-Sol and a Bottoms Heavy Liquid stream called Water. Click Next when complete. 5
4.11. On Page 2 of the Input Expert enter Top and Bottom Stage Pressures of 1 bar. Click Next when complete. 4.12. On the final page of the Input Expert enter a Top Stage Temperature Estimate of 25 C. Click Done when complete to configure the column. 6
4.13. We must now define the feed stream. Go to the Worksheet tab in the Column: T-100 window. For the Feed stream enter a Temperature of 25 C, a Pressure of 1 bar, and a Mass Flow of 100 kg/h. 4.14. In the Compositions form under the Worksheet tab enter Mass Fractions of 0.5 for acetone and water in the Feed stream. 7
4.15. Click the Run button at the bottom of the Column: T-100 window to begin column calculations. The column should converge. 4.16. Check the composition of the Water stream exiting the bottom of the column. You will see that the mole fraction for water is 1. 8
4.17. We will now insert a Distillation Column Sub-Flowsheet from the Model Palette. 4.18. Double click the column (T-101) to open the Distillation Column Input Expert. On Page 1 enter the following information and click Next when complete. 9
4.19. On Page 2 of the Input Expert leave the default selections for a Once-through, Regular Hysys Reboiler. Click Next. 4.20. On Page 3 of the Input Expert enter Condenser and Reboiler Pressures of 1 bar. Click Next when complete. 10
4.21. On Page 4 and 5 leave all fields blank. Click Done on the final page to configure the column. 4.22. We must define the design specifications for this column. Go to the Specs Summary form under the Design tab. Enter 1.2 for Reflux Ratio and make sure that the reflux ratio specification is the only active design specification. 4.23. We will now add a specification for the mole fraction of acetone in the distillate stream. Go to the Specs form under the Design tab. Click Add and select Column Component Fraction. Select Stream for Target Type, Acetone for Draw, enter 0.99 for Spec Value, and select Acetone for Component. 4.24. The Degrees of Freedom for the column should now be 0. Click the Run button to begin column calculations. The column should solve. 11
4.25. We now need to add a cooler to cool the bottoms stream in order to recycle it back to the mixer. Add a Cooler to the flowsheet from the Model Palette. 12
4.26. Double click on the cooler (E-100). Select stream Sol-Rec as the Inlet, and create an Outlet called Lean- Sol and an Energy stream called Q-Cool. 4.27. In the Worksheet tab enter an outlet Temperature of 30 C and a Pressure of 1 bar. The block should solve. 13
4.28. Now we will add a Spreadsheet to control to flowrate of solvent in the Make Up stream. 4.29. Double click on the spreadsheet (SPRDSHT-1). Go to the Spreadsheet tab and enter the following text in cells A1 and A2. 14
4.30. Right click on cell B1 and select Import Variable. Select Master Comp Molar Flow of 3-methylhexane in the acetone product stream. 4.31. Click on cell B2 and enter =B1. Right click on cell B2 and select Export Formula Result. Select the Molar Flow of stream Make Up. This will set the Make Up stream flowrate equal to the flowrate of solvent being lost in the product stream. 15
4.32. We will now recycle the bottoms streams from the second column in order to prevent throwing away acetone product. Add a Recycle block to the flowsheet from the Model Palette. 16
4.33. Double click on the recycle block (RCY-1). Select stream Sol-Rec as the Inlet and stream Solvent-Recycle as the Outlet. The flowsheet should solve. 4.34. We can now try to minimize the amount of solvent that we are recycling. It is possible that there are many solutions for the amount of solvent recycle, and we wish to find the optimum solution. We can vary the mass flow of the recycle stream and find where the reboiler duty is at the lowest. 4.35. Go to Case Studies in the navigation pane and click Add. In Case Study 1 click Add and select the Mass Flow of stream Solvent-Recycle and the Reboiler Duty of column T-101. Enter a Low Bound of 75 kg/h, a High Bound of 200 kg/h, and a Step Size of 5 kg/h. Click Run. 17
4.36. Check results. Go to the Plots tab and you will see that the reboiler duty is the lowest when the solvent recycle flow is around 75 kg/h. You may try setting the flowrate of Solvent-Recycle even lower, but you will find that the flowsheet will not converge. 18
4.37. Double click on stream Solvent-Recycle and enter a Mass Flow of 75 kg/h. The flowsheet should converge after a few moments. 4.38. Check results. Double click on column T-101 and go to the Cond./Reboiler form under the Performance tab. Make note of the Condenser and Reboiler Duty. 4.39. Double click on energy stream Q-Cool and make note of the cooling duty. 19
4.40. The total heating duty for this design is 16,270 kcal/h and the total cooling duty is 9,218 kcal/h. 4.41. Save this the HYSYS file as Dist-009H_Extraction.hsc. 5. Conclusions Based on the simulation results, it would require 16,270 kcal/h of heating and 9,218 kcal/h of cooling to separate the water acetone mixture via liquid-liquid extraction. This design is proven to be feasible, however it may or may not be the optimal design. Another option would be direct distillation of water and acetone. Direct distillation of water and acetone would require less equipment, but it may require more energy. 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 AspenTech. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS WORK and assumes no liability for any errors or omissions. In no event will AspenTech be liable to you for damages, including any loss of profits, lost savings, or other incidental or consequential damages arising out of the use of the information contained in, or the digital files supplied with or for use with, this work. This work and its contents are provided for educational purposes only. AspenTech, aspenone, and the Aspen leaf logo, are trademarks of Aspen Technology, Inc.. Brands and product names mentioned in this documentation are trademarks or service marks of their respective companies. 20