Prop-001 Revised: August 29, 2012 Generate Ethylene Vapor Pressure Curves with Aspen Plus® 1. Lesson Objectives Learn how to use the Methods Assistant to select physical property methods Generate vapor pressure curves for Ethylene 2. Prerequisites Aspen Plus V7.3.2 Introduction to vapor-liquid equilibrium 3. Background Separation processes involving vapor-liquid equilibrium exploit volatility differences which are indicated by the components’ vapor pressure. Higher vapor pressure means a component is more volatile. Ethylene is an important monomer for polymers and there are many ethylene plants around the world. A vital step in ethylene production is separating it from other compounds and as a result the vapor pressure of ethylene is an important physical property for ethylene production. 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 Plus Solution Problem Statement Determine the vapor pressure of ethylene at room temperature (25 °C), and its normal boiling point. Aspen Plus Solution If you are unfamiliar with how to start Aspen Plus, select components, or define methods, consult Get Started Guide for New Users of Aspen Plus.pdf for instructions. 1 Prop-001 Revised: August 29, 2012 4.01. Create a new simulation in Aspen Plus using the Blank Simulation template. 4.02. The Components | Specifications | Selection sheet is displayed. 4.03. We must first specify which components will be used in the simulation. Enter ETHYLENE into the first row under the Component ID column and hit enter. The Component ID is a user defined parameter that Aspen Plus will use to report and identify components in a given simulation. Aspen Plus will also guess as to which specie the user has entered based on the given Component ID and retrieve physical properties from its databases. The other fields can be entered manually if the information is incorrect or was not found. In our case, Aspen Plus successfully retrieved accurate information for ETHYLENE from the Component ID alone. 2 Prop-001 Revised: August 29, 2012 4.04. Next, we will specify the method that Aspen Plus will use to calculate physical properties in this simulation. We will be using the Methods assistant to help us select an appropriate Base method. Go to the Methods | Specifications | Global sheet by pressing the F4 key or using the tree view in the navigation pane. Click the Methods assistant… button. 4.05. The methods assistant window should appear. Click the Next button. 3 Prop-001 Revised: August 29, 2012 4.06. Click the Specify component type link. 4.07. Since we know ethylene is a small hydrocarbon, we will select Hydrocarbon system. 4 Prop-001 4.08. Revised: August 29, 2012 We are not using pseudocomponents or petroleum assays, so we will select the corresponding option. 5 Prop-001 4.09. Revised: August 29, 2012 The methods assistant is now displaying several methods that are well suited to our components. We will use the Peng Robinson equation of state. 6 Prop-001 4.10. Revised: August 29, 2012 Close the Assistant – Property method selection window. On the Methods | Specifications | Global sheet, set the Base Method field to Peng-Robinson which is listed as PENG-ROB. 7 Prop-001 4.11. Revised: August 29, 2012 Upon selecting this option, your window should now appear as follows. You are now ready to begin generating vapor curves for ethylene using the Peng-Robinson equation of state. 8 Prop-001 Revised: August 29, 2012 4.12. We will now generate a new analysis object. From the Home tab of the ribbon, click the Analysis | Pure button. 4.13. A pure component analysis, PURE-1, is created and the Analysis | PURE-1 | Input | Pure Component sheet is displayed. Note that the Run analysis button at the bottom of the sheet is not enabled because the necessary inputs for the analysis have not been entered yet. 9 Prop-001 4.14. Revised: August 29, 2012 Next, select the physical property you would like to analyze. In this case, select PL from the Property drop-down list. Physical properties are given unique identifiers in Aspen Plus. PL signifies vapor pressure of a liquid. Some commonly used ones are DHVL (enthalpy of vaporization), and PHI (fugacity). 10 Prop-001 4.15. Revised: August 29, 2012 Next, we will tell Aspen Plus what to plot. In the Temperature frame, set the Lower Limit to –110 and the Upper Limit to 25. In the Components frame, select ETHYLENE from the list of Available components and click the single right arrow. This will move only the selected items from the list on the left to the list on the right. Clicking the double arrow will move all of the items, which is useful for moving a large number of items. Note that the Run analysis button is now enabled. 11 Prop-001 4.16. Revised: August 29, 2012 Press the Run analysis button. This will generate a plot of the vapor pressure in a new tab. Note that at 25 °C, ethylene’s vapor pressure is about 70 bar. 12 Prop-001 4.17. Revised: August 29, 2012 Repeat actions from step 4.12 to step 4.16 except that we use -100 °C as the Upper limit instead of 25 °C. The generated plot is shown below. Note that the normal boiling point is about –104 °C. 13 Prop-001 Revised: August 29, 2012 5. Conclusions As we can see from the generated plots, ethylene is a very volatile component. At room temperature (25 °C), its vapor pressure is about 70 bar. From this analysis, we also see that ethylene’s normal boiling point temperature is about –104 °C. 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. 14
