ASPEN Tutorial #3
ChE 473K Spring 2016
Hydrodealkylation of Toluene: A Look at Reactor Models
Problem Statement
Evaluate the various reactor models in AspenPlus for the hydrodealkylation of toluene.
Main Rxn: H2 + Toluene = methane + benzene
Side Rxn: 2C6H6 = C12 H10 + H2
Flowrate = 5475.9 lbmol/hr
Reactor pressure = 489 psia
Component Formula lbmol / hr
Hydrogen H2 2045.9
Methane CH4 3020.8
Benzene C6H6 46.2
Toluene C7H8 362.0
Biphenyl C12H10 1.0
Pressure = 494 psia
Temperature = 1200 F.
.
Use the Peng-Robinson equation of state model for the VLE.
A) Run an adiabatic (Q = 0) stoichiometric reactor module (RSTOIC) with a toluene conversion of 0.75 and a benzene conversion to biphenyl of 0.02. Determine the outlet stream composition and temperature.
B) Run an adiabatic equilibrium reactor (REQUIL)
C) Run an adiabatic Gibbs free energy minimization reactor (RGIBBS).
D) Run an adiabatic kinetic reactor (RPLUG) - determine the reactor dimensions that will yield 90.5 lbmol/hr of toluene in the reactor effluent. This will require using the Design-Spec feature.
Kinetics:
· concentrations in mol/L
· time in seconds
· activation energy in cal/mol
1. Specify components listed above by choosing Components>Specifications under the Properties environment.
2. While under the Properties environment, also specify the Method as PENG-ROB for Peng-Robinson equation of state model.
Part A- RStoic
3. Switch the Simulation environment, and draw your first reactor. This should be a stoichiometric reactor model (RSTOIC). This reactor is used when reaction kinetics are unknown or unimportant, the reaction stoichiometry is known, or you want to specify the extent of reaction or conversion. Connect a feed and product stream to the reactor. Streams and blocks may be renamed as desired.
4. Switch your global unit set to ENG. This can be done two ways. Either change the global unit set on the specification form under the Setup folder in the Properties environment or change the unit sets using the dropdown menu on the ribbon a the top of the screen. Changing the global unit set with make entering feed information easier.
5. Enter the desired feed information that is listed above.
6. Under the Reactor block Specifications tab, specify the pressure as 489 psia and the duty as 0.
7. Under the reactions tab, click “New” to create a new reaction. Enter the reactants, products, and respective coefficients as shown below. This is also the window where you specify the extent of reaction for Toluene as shown below.
8. Close the Reaction 1 screen and create a new reaction for the side reaction. Enter the reactants, products, and respective coefficients just as you did for the first reaction. Specify the extent of reaction for Benzene (specified in problem statement) just as you did for Toluene in the previous reaction
9. Once all inputs are complete, run the simulation and record the following information:
Outlet Stream Flow / HYDROGEN 1774.862 lbmol/hrMETHANE 3292.3 lbmol/hr
BENZENE 316.776 lbmol/hr
TOLUENE 90.5 lbmol/hr
BIPHENYL 1.462 lbmol/hr
Outlet Stream Temperature / 1265.043°F
Part B - REquil
1. Delete the previous material streams and block on the Main Flowsheet. Draw a new reactor using the REquil model. This model is used when some or all reactions reach equilibrium. REquil calculates chemical and phase equilibrium up to two phases solving stoichiometric chemical and phase equilibrium equations. All reactions are assumed to take place in the vapor phase unless the block is specified as “liquid-only.”
2. Connect material streams to the reactor. You will notice that there are now 3 red arrows or required streams for the reactor vs. the two for the RSTOIC reactor. The REQUIL reactor has a feed stream (but can be any number) and two product streams (a vapor phase and a liquid phase).
3. Enter the feed information under the Streams folder just as you did for the RSTOIC reactor.
4. Select the reactor form under the Blocks folder. Under Specifications, specify the pressure and duty just as with the RSTOIC reactor model.
5. Under the Reactions tab, enter the reactants, products, and coefficients for the main reaction and the side reaction. You do not have to specify anything for the products generation area. REquil only needs the stoichiometry of the reaction. With no extent or temperature specified, REquil will assume the reaction reaches equilibrium.
6. Once all inputs are complete, run the simulation and record the following information:
Outlet Stream Flow / H2 1700.27 lbmol/hrMETHANE 3376.939 lbmol/hr
BENZENE 381.3214 lbmol/hr
TOLUENE 5.861385 lbmol/hr
DIPHE-01 11.50863 lbmol/hr
Outlet Stream Temperature / 1283.957°F
Part C - RGIBBS
1. Delete the previous material streams and block on the Main Flowsheet. Draw a new reactor using the RGibbs model. Similar to REquil, RGibbs also models chemical and phase equilibrium. RGibbs does not require reaction stoichiometry. RGibbs minimizes Gibbs free energy subject to atom balance constraints.
2. Connect material streams to the reactor. You will notice that there are now 2 red arrows or required streams for the reactor.
3. Enter the feed information under the Streams folder just as you did for the RSTOIC reactor.
4. Select the reactor form under the Blocks folder. Under Specifications, specify the pressure and duty. Leave the “Calculation option” as “calculate phase equilibrium and chemical equilibrium.” Notice that you have the option to use RGibbs to find phase equilibrium without reaction or to specify equilibrium conditions.
5. Click on the “Products” tab and select “Identify possible products”. Under products, select methane, benzene, biphenyl, and hydrogen.
6. Once all inputs are complete, run the simulation and record the following information:
Outlet Stream Flow / H2 580.9572 lbmol/hrMETHANE 4132.948 lbmol/hr
BENZENE 238.6162 lbmol/hr
TOLUENE 0 lbmol/hr
DIPHE-01 23.27955 lbmol/hr
Outlet Stream Temperature / 1627.512°F
Part D - RPLUG
1. Delete the previous material streams and block on the Main Flowsheet. Draw a new reactor using the RPlug model. RPlug models plug flow reactors with rate-based kinetic reactions only therefore you must know the kinetics of your reaction.
2. Connect material streams to the reactor. You will notice that there are now 2 red arrows or required streams for the reactor.
3. Enter the feed information under the Streams folder just as you did for the RSTOIC reactor.
4. Select the reactor form under the Blocks folder. Under Specifications, choose “adiabatic reactor” for your reactor type.
5. Under the Configuration tab, write 50 ft for the reactor length and 10 ft for the reactor diameter. These will serve as initial guesses for our design specs.
6. In the Reactions folder, Select “New”. Name the reaction R-1 and choose “Powerlaw” as type.
7. The Stoichiometry tab of R-1 should look like the following. The coefficients are from the reaction equation, and the exponents are from the rate equation.
8. The Kinetics tab should look like the following:
9. We can now go back to our reactor block and select R-1 under our “Reactions” tab
10. We are tasked with determining the reactor dimensions that will yield 90.5 lbmol/hr of toluene in the reactor effluent. To do this, we must use Design Specs. This can be found under the “Flowsheeting Options” folder under “Design Specs”. Select “New” and name it DS-1.
11. On the “Define” tab, you need to define the variable that you are specifying. Name a new variable “Tol2” as the mole flow of toluene in your product stream.
12. On the “Spec” tab, specify the target and tolerance level for your specified variable, TOL2. Our target is 90.5 lbmol/hr and an acceptable tolerance is 0.01.
13. The “Vary” tab is where we state our manipulated variable. This is the variable that Aspen will change to reach our target for the specified variable. We will vary the Block Length from 20 to 80 feet.
14. Once all inputs are complete, run the simulation and record the following information:
Outlet Stream Flow / HYDROGEN 1777.601 lbmol/hrMETHANE 3292.299 lbmol/hr
BENZENE 311.299 lbmol/hr
TOLUENE 90.50101 lbmol/hr
BIPHENYL 4.2 lbmol/hr
Outlet Stream Temperature / 1265.092°F
Reactor Length / 47.620847 feet