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Tutorial 1. Reaction rate for the conversion of the ethylbenzene to styrene is
given in the below form:
πΆ8π»10 β πΆ8π»8 + π»2
βπ1(ππππ/ππ πππ‘. π ) = (πΎπ Γ ππΆ8π»10
β
πΎπ Γ ππΆ8π»8
Γ ππ»2
(1 + πΎπΆ8π»8
ππΆ8π»8
)
1)
βπ1(ππππ/ππ πππ‘. π )
= (2.3496 Γ e
(β(
158600
π π
))
Γ ππΆ8π»10
β 3.7594 Γ 10β12
Γ π
β(
34339
π π
)
Γ ππΆ8π»8
Γ
ππ»2
(1 + 1.13 Γ 10β4ππΆ8π»8
)
1)
Ethylbenzene also forms two more side reactions in the reactor which their reaction
rates are as below:
πΆ8π»10 β πΆ6π»6 + πΆπ»2πΆπ»2
βπ2(ππππ/ππ πππ‘. π ) = 1.37606 Γ 10β6
Γ π
β(
114200
π π
)
Γ ππΆ8π»10
πΆ8π»10 + π»2 β πΆ7π»8 + πΆπ»4
βπ3(ππππ/ππ πππ‘. π ) = 47.4107 Γ π
β(
208000
π π
)
Γ ππΆ8π»10
Show the effect of the reactorβs temperature and pressure on conversion and reaction
yield in a plug reactor. Feedβs properties: 60kmole ethylbenzene, 600kmole
Hydrogen @ 600β - Pressure of 1.5 atm. Catalytic reactor with 28000kg catalysts
and bed porosity of 0.455.
Source: Exercise 7.2 of Kamal I.M. al-Malah, ASPEN PLUS chemical
engineering application, Wiley (Page 222)
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Solution
Choose PENG-ROB as the appropriate thermodynamic package and obtain the pair
coefficients for the materials. In the flowsheet, define the Feed stream that enters the
RPlug reactor.
In the specifications tab of the reactor, choose reactor with specified temperature for
the reactor type and set it as 600β. In the configuration tab of the reactor, choose
the single pipe with diameter and length of 5m.
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In the tree menu of the case, open the reaction tab and enter the main reaction of the
ethylbenzene to styrene. At the stoichiometry, define the reaction. Considering the
reaction rate, the type of the reaction is non-ideal and LHHW.
πΆ8π»10 β πΆ8π»8 + π»2
In the kinetic tab, define the reaction rate equation in the appropriate form of the
Aspen Plus.
Appropriate form of the Aspen Plus.
Converting the given reaction rate to Aspen Plus form:
βπ1(ππππ/ππ πππ‘. π ) = (πΎπ Γ ππΆ8π»10
β πΎπ Γ ππΆ8π»8
Γ
ππ»2
(1 + πΎπΆ8π»8
ππΆ8π»8
)
1)
βπ1(ππππ/ππ πππ‘. π ) = πΎπ(ππΆ8π»10
β
πΎπ
πΎπ
Γ
ππΆ8π»8
Γ ππ»2
(1 + πΎπΆ8π»8
ππΆ8π»8
)
1)
For given reaction, in the kinetic factor we define the reaction constant Kf:
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In the Driving Force and adsorption, transform each expression in the below form
and define them in the proper fields. In the basis, choose Partial pressure for the basis
of the reaction rates.
ln π = π΄ +
π΅
π
+ πΆπ + ln(π)
For the coefficients of the Term 2, use the bellowβs expression and gain the
coefficients.
ln
πΎπ
πΎπ
= π΄ +
π΅
π
+ πΆπ + ln(π)
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In the Reaction section, define a new reaction as R-2 typed POWERLAW to enter
the side reactions. In the stoichiometry section, define the stoichiometry of the side
reactions.
In the kinetic, define the reaction rate suitable to Powerlaw reaction type.
Considering the catalytic reaction, in the Rate basis choose the βCat (wt)β and
reacting phase as βVaporβ.
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In the reactions of the RPlug reactor, add the two defined reaction set. In the Pressure
tab of the reactor, enter the inlet stream pressure as 1.5atm and pressure drop in the
reactor as 0.
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In the Catalysts of the reactor, activate βCatalyst present in reactorβ and enter the
specifications of the catalysts according to the given data.
After defining the catalyst in the reactor, run the simulation and observe the results.
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To study the effect of the reactorβs temperature and pressure on the reaction
conversion and yield, in the tree chart of the case βModel Analysis Tools/Sensivityβ,
define a new Sensivity case. In the Vary choose the reactorβs temperature between
500-700β and reactorβs pressure between 1-5 atm.
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To define the reation conversion and yield, molar flow of the ethylbenzene in the
feed stream is defined in the Sensivity/Define.
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In the Fortran section, write the below equation using Fortran programming
language.
πΆπππ£πππ πππ(%) =
πππππ ππππ€ πππ‘π ππ π ππ ππππ β πππππ ππππ€ πππ‘π ππ π ππ π‘βπ πππππ’ππ‘
πππππ ππππ€ πππ‘π ππ π ππ π‘βπ ππππ
Γ 100
πππππ(%) =
πππππ ππππ€ πππ‘π ππ π ππ π‘βπ πππππ’ππ‘
πππππ ππππ€ πππ‘π ππ π ππ π‘βπ ππππ
Γ 100
In the Tabulate, desired variables which is defined in the Fortran are entered.
In some cases to prevent a full circle between the first and end point, in the Options
tab activate the Do not execute base case and run the simulation. In the results, plot
the charts to see the effect of the temperature and pressure on the desired variables.
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Tutorial 2.
With considering the required modifications simulate the reverse propane cycle.
Propane cycle
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Solution
After defining propane in the Components section, choose Peng-Rob as the proper
thermodynamic package. In the simulation section, first define the βStream 3β
according to the given streamβs specs. Consider a thoeretical molar flow for the
stream to have the rest of the streams properties and afterward we determine the
proper value for the molar flow of this stream.
To restore the pressure drop in the chiller of the main propane cycle, a compressor
with 7kPa increasing pressure can be considered in the proceess path as the vapor
fraction of the stream equal to 1. Also to reverse the effec of the temperatureβs
change a cooler can be used.
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Cooler specs:
Coolerβs outlet is the βStream 2β and to reverse the pressure drop of the J-T valve, a
heater is used to have a vapor fraction of 1 for the stream. The outlet stream of the
heater is then entered into a compressor to increase the temperature.
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Specifications VF1:
So to increase the pressure a compressor is define and using another exchanger, set
the outlet streams vapor fraction as 0 and consider pressure drop as 0.
Simulation Hint:
To obtain the value for the pressure increase in compressor, you can gain the βStream
1β pressure using defining it and process it through a mixer to have the Aspen Plus
calculated the properties. Another approach is to calculate the pressure drop between
the βStream 1β and βS1β and enter its value as the increasing pressure value for the
compressor.
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Flowsheet:
Now to eliminate the two heat exchangers which there arenβt in the main flowsheet
originally (VF0 and VF1), a mixer to mix the energy streams of these two exchangers
is defined. With considering a βDesign Specβ the summation of these two energy
streams aims to be zero with changing the molar flow of the βStream 3β. In another
word, using this way these two equipmentβs effect neutralized in the process and the
reverse process achieves.
Flowsheet:
Parameters Design Spec:
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Design Spec results:
To gain the βStream 4β properties, first consider a pump (Cause the vapor fraction
of the βStream 1β equal 0) and then a heat exchanger (heater).
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Exchangerβs specifications:
To reverse a compressorβs effect, a valve can be installed in the process path and
with having the pressure of the βStream 3β you can enter the outlet pressure of the
valve.
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Valveβs Specification:
Then at the end to equalize the temperature of the outlet stream of the valve and
connect the cooling cycle of propane, a heat exchanger with pressure drop of 0 and
outlet temperature of -20β is applied. After that a mixer is used to connect the outlet
stream of the exchanger and the initial βStream 3β.