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Unformatted text preview: Homework 1 Problem 2 Aspen™ Acrylonitrile 20 points possible due Friday September 2, 2011 Grader: Israel Problem Statement: Acrylonitrile is produced by the reaction of propylene, ammonia, and oxygen. C3H6 + NH3 + 3/2 O2 → C3H3N + 3 H2O The feed contains 10% propylene, 12% ammonia, and 78% air. A fractional conversion of 30% of the limiting reactant is achieved. Determine which reactant is limiting, the percentages by which each of the other reactants is in excess, and the molar flow rates of all product gas constituents for a 30% conversion of the limiting reactant, taking 100 moles of feed at a flowrate of 100 mol/s as a basis. This reaction occurs at 25°C and 1 bar. Method of Solution: Use the stoichiometric reactor in Aspen Plus™ to solve for the rate of acrylonitrile production. Solution: 1) Calculate the rate limiting reactant and the excess amounts of all other reactants. 2) Start the Aspen Plus™ program: All Programs → AspenTech → Process Modeling V7.2 → Aspen Plus → Aspen Plus User Interface 3) Select the Blank Simulation radio button and click OK. Page 1 of 8 4) If necessary, be sure that the program has a connection to an appropriate server and can access the software license (Local PC). 5) Eventually the Process Flowsheet Window will open, add a stoichiometric reactor to the flowsheet by clicking on the Reactors tab, then the RStoic button, and finally click once in the PFD work area to add the reactor. 6) The Select Mode Button is an arrow located above the Stream Library. When inserting an item into the flowsheet, that item will continue to be added with every mouse click until the Select Mode Button is selected. Click the Select Mode Button (arrow) or click the right mouse button to exit insert mode. Also, use the Select Mode Button to resize, move, delete, or select an icon. 7) To remove any unwanted objects, right‐click on the object and select Delete Block or click the <Delete> button and click OK. Page 2 of 8 8) Connect material streams to the feed and product streams of the stiochiometric reactor. Select the desired stream (material, heat, or work) from the Stream Library. Notice that when the mouse is pointing at a piece of equipment, arrows appear. Red arrows indicate streams that are required for the unit, and blue arrows indicate optional stream positions. 9) Open the Data Browser by clicking on the icon on the toolbar. First, add the system components. Click on the Components section of the Data Browser. 10) On the Selection tab click Find. The Find window will appear. Type “propylene” and click Find now. Select PROPYLENE and click Add. Page 3 of 8 11) Add the remaining process components and close the window. Note: If you add a component by mistake, close the Find window, right‐click on the row to delete and select delete row from the drop down menu. 12) Next, specify the property package that Aspen PlusTM will use to define the system. Open the Properties section by clicking on the folder. Click on Specifications. Page 4 of 8 13) On the Global tab, under Base method, select Peng Robinson. 14) Expand the Parameters and Binary Interactions sections and click the Next button,
, on the toolbar which will automatically change the radio box to a blue check mark signaling that the input is complete for this section. 15) To define the batch charge, click on Streams, then 1. The data browser should open. Set the temperature to 25°C, the pressure 1 bar, and a total flow of 100 mol/s. Change the flow units by using the drop‐down menu in the box above the units. Change the Composition units to Mole‐Frac and enter the feed composition 10% propylene, 12% ammonia, and 78% air (16.38% oxygen and 61.62% nitrogen). Page 5 of 8 16) To define the reactor, click on Blocks, B1, and Setup. Enter a pressure of 1 bar and a temperature of 25oC. Change the valid reaction phases to Vapor‐
Liquid‐FreeWater. 17) Open the Reactions tab and click the button at the bottom. The Stiochiometry window will open, select the appropriate reactants and products and enter the corresponding stiochiometric coefficients. Recall that reactants have negative coefficients and products have positive coefficients. Enter a 30% fractional conversion of the key component propylene. Click the button to close this window. Page 6 of 8 18) The system has been fully defined. Press F5 or the run button, , from the toolbar to run the simulation. Results/Considerations: The simulation results can be viewed in several ways, click on the Results Summary Custom Stream Summary to view all streams results or click on Blocks Stream Results to view the block results or open an individual stream and view the Results or Custom Stream Results. Before running this simulation, the limiting reactant was determined to be propylene. Using AspenTM the predicted flowrates of the water and Acrylonitrile are 9 and 3 mol/s, respectively. Check the results by opening the Stream 2 Custom Stream Results. If the results are not given in the correct units, click the unit and a dropdown arrow will appear, select the correct units from the dropdown menu. Page 7 of 8 Page 8 of 8 ...
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- Fall '11