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Reaction Engineering
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11/10/15
1
REACTION ENGINEERINGCKB 20104
Chapter 6 Non-isothermal Reactor
DesignDr. Kelly Yong Tau Len
Section of Chemical Engineering Technology UniKL MICETTel: 06-5512051
Email: [email protected], E-learning: CKB20104 – Kelly Yong
2
E-Learning Online Laboratory Quiz
Attempts allowed: 1The quiz will be available from
Sunday, 8 November 2015, 12:00 AMThis quiz will close at
Sunday, 15 November 2015, 11:59 PMTime limit: 15 minutes
Note: Please submit the attempt before the time expired or they are not counted
11/10/15
2
Chapter 66.1 The energy balance6.2 Algorithms for non-isothermal reaction design6.3 Equilibrium conversion6.4 Multiple steady-state
ObjectivesUpon the completion of this chapter, students are able to:o Describe the algorithm for CSTRs that are notoperated isothermally.
o Size adiabatic andnon adiabaticCSTRs.o Analyze NON-ISOTHERMALREVERSIBLE reactionso Carry out an analysis to determine the Multiple SteadyStates (MSS) in a CSTR
3
6.1 The Energy BalanceWHY WE NEED TO LEARN ENERGY BALANCE IN REACTION
ENGINEERING?
1.At times we need to calculate the volume necessary to achieve a conversion, X in a reactor.
2. For an exothermic reaction, the temperature profile vs. volume is given below
4
Reaction Temperature influenced
the Reactor Volume
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3
Lets say we have a CSTR and given a first order, exothermic liquid reaction carried out adiabatically (no heat loss or gained in the system).
5
1.Design equation for CSTR
VCSTR =FA0X−rA
2. Rate Law (First Order Reaction)−rA = kCA3.Because there is change of temperature during reaction therefore
k = k1 exp EaR
1T1
−1T
"
#$$
%
&''
(
)**
+
,--
4.Stochiometry for liquid phase givesCA =CA0 (1− X )
6.1 The Energy Balance
4. We combine equation 1, 2,3 and 4 to obtain
• In this equation, we have 3 unknowns (Volume, Temperature and Conversion) which need to be solved.
• Therefore we need another relationship relating X and T or T and V.
• This additional relationship can be found through energy balance equation
6
VCSTR =FA0X
k1expEaR
1T1−1T
"
#$$
%
&''
(
)**
+
,--CA0(1−X)
1stUnknown
2ndUnknown
3rdUnknown
6.1 The Energy Balance
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4
6.1 The Energy BalanceFirst Law Of Thermodynamics
7
Work done by system
Heat to the system
Inlet Molar Flow Rate
Inlet Enthalpy
Outlet Molar Flow Rate
Outlet Enthalpy
6.1 The Energy BalanceFirst Law Of Thermodynamics
8
General Energy Balance of An Open System
Q•
−W•
+ Eioi=1
n
∑ Fio − EiFii=1
n
∑ =d Esysdt
Heat to the system
Work done by the system Total sum or
energy in
Total sum or energy out
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5
6.1 The Energy Balance9
1. In terms of enthalpy (for open system), the energy balance becomes
1. And for steady state operation (accumulation = 0), the energy balance now becomes
Q•
−W•
+ Hioi=1
n
∑ Fio − HiFii=1
n
∑ =d Esysdt
Q•
−W•
+ Hioi=1
n
∑ Fio − HiFii=1
n
∑ = 0
We derive further this part
6.1 The Energy Balance 10
In : Hi0Fi0 = HA0FA0 +∑ HB0FB0 +HC0FC0 +HD0FD0 +HI 0FI 0Out : HiFi = HAFA +∑ HBFB +HCFC +HDFD +HIFI
A+ baB→ c
aC + d
aD
SPECIES INITIAL (MOL) REMAINING (MOL)
A
B
C
D
FA0FB0 = FA0ΘB
FC0 = FA0ΘC
FD0 = FA0ΘD
FA = FA0 (1− X)
FB = FA0 (ΘB −baX)
FC = FA0 (ΘC +caX)
FD = FA0 (ΘD +daX)
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6
6.1 The Energy Balance11
Hi0Fi0 −i=1
n
∑ HiFii=1
n
∑ = HA0FA0 +HB0FB0 +HC0FC0 +HD0FD0 − (HAFA +HBFB +HCFC +HDFD )
= HA0FA0 −HAFA +HB0FB0 −HBFB +HC0FC0 −HCFC +HD0FD0 −HDFD
= HA0FA0 −HAFA0 (1− X)+HB0ΘBFA0 −HBFA0 ΘB −baX
$
%&
'
()
+HC0ΘCFA0 −HCFA0 ΘC +caX
$
%&
'
()+HD0ΘDFA0 −HDFA0 ΘD +
daX
$
%&
'
()
= HA0FA0 −HAFA0 +HAFA0X +HB0ΘBFA0 −HBΘBFA0+HBFA0baX
+HC0ΘCFA0 −HCΘCFA0 −HCFA0caX +HD0ΘDFA0 −HDΘDFA0 −HDFA0
daX
= FA0 HA0 −HA( )+ΘBFA0 HB0 −HB( )+ΘCFA0 HC0 −HC( )+ΘDFA0 HD0 −HD( )
+HAFA0X +HBFA0baX −HCFA0
caX −HDFA0
daX
= FA0[ HA0 −HA( )+ΘB HB0 −HB( )+ΘC HC0 −HC( )+ΘD HD0 −HD( )]
−daHD +
caHC −
baHB −HA
$
%&
'
()FA0X
6.1 The Energy Balance12
Hi0Fi0 −i=1
n
∑ HiFii=1
n
∑ =
= FA0[ HA0 −HA( )+ΘB HB0 −HB( )+ΘC HC0 −HC( )+ΘD HD0 −HD( )]
−daHD +
caHC −
baHB −HA
$
%&
'
()FA0X
FAO Θi (Hio −H i )i=1
n
∑
ΔHRx(T )FAOX
1. From the original energy balance equation
1. With manipulation of the molar flow rates, we obtain the energy balance
Q•
−W•
+ Hioi=1
n
∑ Fio − HiFii=1
n
∑ = 0
Q•
−W•
+ FAO Θi (H io−H i )i=1
n
∑ −ΔHRx(T )FAOX = 0
Heat of Reaction
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7
6.1 The Energy Balance13
4. From equation 3 previously
5. We know the enthalpy term is defined as following
6. Therefore the energy balance now becomes
Q•
−W•
+ FAO Θi (Hio −Hi )i=1
n
∑ −ΔHRx(T )FAOX = 0
Hio −Hi = ΔHi (T ) = Hf,ioo + CP dT
TR
To
∫$
%&&
'
())− Hf,i
o + CP dTTR
T
∫$
%&&
'
())
Hio −Hi = − CPi dTTo
T
∫ = −CPi (T −To )
Q•
−W•
−FAO ΘiCPi (T −To )i=1
n
∑ −ΔHRx(T )FAOX = 0
Reference T
Entrance T Reaction T
6.1 The Energy Balance14
7. From equation 5 previously
7. We know the heat of reaction, HRx term is defined as following
9. Therefore the energy balance now becomes
Q•
−W•
− FAO ΘiCPi (T −To )i=1
n
∑ −ΔHRx(T )FAOX = 0
ΔHRx(T ) = ΔHRx(TR )+ΔCP (T −TR )
Q•
−W•
− FAO ΘiCPi (T −To )i=1
n
∑ − FAOX ΔHRx(TR )+ΔCP (T −TR )%
&'(= 0
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8
7. From equation 5 previously
8. Work, W can be separated into flow work and other work, Ws. The term Ws(shaft work) could be produced from STIRRER in CSTR or turbine in PFR. Flow work are usually negligible compared to other terms therefore it is omitted.
9. Therefore the FINAL energy balance is
Q•
−W•
−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx(TR )+ΔCP (T −TR )%& '(= 0
6.1 The Energy Balance15
Q•
−Ws −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
Equation are given in Exam!
Now we learn to apply the Energy
Balance equation
16
11/10/15
9
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy Balance(Heat Capacity, Cpi)
17
1. Typical unit for heat capacity, Cpi of a reactant is represented as J/mol.K
2. The terms could be calculated for ALL REACTANT
ONLY. 3. Recall that Θi for product is zero.
ΘiCPii=1
n
∑
18
For example given a reaction of A + B à C + D with A as the basis of calculations, therefore:
withPIIPBPPi CCCCBAiΘ+Θ+=Θ∑
~~~
0
0
A
BB FF
=Θ
POSITIVE SIGN
REMEMBER:Only take the REACTANT
into consideration including INERT if its in the
reaction.
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy Balance(Heat Capacity, Cpi)
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10
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy Balance(Temperature Definition & Difference)
19
1. T = Reaction temperature in which the reaction is conducted2. T0 = Entrance/Inlet Temperature of the reactant
3. TR = Reference Temperature in which the heat capacity at constant pressure, Cp or the heat of reaction, ΔHoRxwere obtained (usually 25oC) unless stated other value.
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy Balance(Heat of Reaction at reference temperature ΔHoRx (TR))
20
1. Heat of reaction at reference temperature (usually 25oC (unless stated other value) are specific depending on the reaction.
2. It is either given directly or can be tabulated based on the enthalpies of formation, Hof(TR) for all reactants and products involved in the reaction.
3. The enthalpies of formation of many compounds, Hof(TR) are usually tabulated at 25oC and can readily be found in any handbook.
4. ΔHo Rx (TR) is to indicate that in the formula, the heat of reaction ΔHo Rx is calculated at the reference temperature.
11/10/15
11
For example given a reaction of A + bBà cC + dDand enthalpies of formation, Hof(TR) of reactants (A and B), and products (C and D) are given, therefore:
ΔHRx (TR )
o =daHO
D(TR )+caHO
C(TR )−baHO
B(TR )−HO
A(TR )#
$%
&
'(
21
Positive for product Negative for reactantREMEMBER: REACTANT AND PRODUCT SHOULD BE TAKEN INTO
CONSIDERATION
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy Balance(Heat of Reaction at reference temperature ΔHoRx (TR))
22
EXAMPLECalculate ΔHo Rx (TR) when given the reaction as following:
SOLUTION: For the above reaction, the ΔHo Rx (TR) is as following:
From reference, it is found that the heat of formation of hydrogen, (Ho H2,(TR)) and nitrogen (Ho N2,(TR)) are zero at 25oC, and Ho NH3 (TR) = –11,020 cal/mol therefore
ΔHRx (TR )o = 2HO
NH 3(TR )−3HO
H 2(TR )−HO
N 2(TR )( )
ΔHRx (TR )o = 2(−11,020)−3(0)− 0 = −22,040cal /mol
6.1 The Energy Balance(Heat of Reaction at reference temperature ΔHoRx (TR))
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12
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy BalanceOverall Change In The Heat Capacity, ΔCp
23
1. The overall change in the heat capacity, ΔCp is based on per mole of A reacted during the reaction.
2. It can be obtained based on the heat capacities for all reactant and product, Cpi
3. These values can be found from any handbook.
1. It can be calculated based on the following method2. For example given a reaction of A + bBà cC + dDwith heat capacities, Cpi of reactants (A and B), and products (C and D) are given, therefore:
ΔCP =daCPD
+caCPC
−baCPB
−CPA
24
REMEMBER: REACTANT AND PRODUCT SHOULD BE TAKEN INTO CONSIDERATION
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
Positive for product Negative for reactant
6.1 The Energy BalanceOverall Change In The Heat Capacity, ΔCp
11/10/15
13
25
Calculate ΔCpwhen given the reaction as following:
SOLUTION:
6.1 The Energy BalanceOverall Change In The Heat Capacity, ΔCp
Q•
−WS−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.1 The Energy BalanceHeat Added to the Reactor
26
1. Q is HEAT added to the reactor when heating up a reaction is required.
2. For CSTR, the Q value can be calculated from a specified equation.
11/10/15
14
6.1 The Energy BalanceHeat added to CSTR with heat exchanger, Q
27
TO, FAO T, FA
Ta1, mc Ta2CSTR reactor
Heat exchanger
Heat transfer fluid enters the exchanger at a mass flow rate mc (kg/s) at a temperature Ta1 and
leaves at a temperature Ta2.
For exothermic reactions (T>Ta2>Ta1)
For endothermic reactions (Ta1>Ta2>T)
28
3. For moderate to low coolant rates:
4. For large coolant rates, Ta1 (Heat transfer fluid inlet temperature) = Ta2 (Heat transfer fluid outlet temperature)
U = Overall heat transfer coefficient of jacketA = Heat exchange area (steam jacket area)Cp,c = Heat capacity of the heat transfer fluidTa1 = Heat transfer fluid inlet temperature (jacket steam saturation temperature)T = Reaction temperature
⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎥⎥⎦
⎤
⎢⎢⎣
⎡
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ −−−=
c
cpc
apc CmUATTCmQ exp1)( 1
..
Q.=UA(Ta1 −T )
Usually we use this unless indicated otherwise
6.1 The Energy BalanceHeat added to CSTR with heat exchanger, Q
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15
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
29
X is given, calculate V and T T is given, calculate X and V
1.Design equation for CSTR: VCSTR =FA0X−rA
2. Rate Law (Elementary): − rA = kCA3. Stochiometry for liquid phase: CA =CA0 (1− X )
4. Change of temperare, k = k1 exp EaR
1T1
−1T
"
#$$
%
&''
(
)**
+
,--
4. Combine all to give: VCSTR =FA0X
k1 exp EaR
1T1
−1T
"
#$$
%
&''
(
)**
+
,--CA0 (1− X )1st Unknown
2ndUnknown
3rdUnknown
Q•
−Ws −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
30
X is given, calculate T first using energy balance equation
Calculate new k value
k = k1 exp ER
1T1
−1T
"
#$$
%
&''
(
)**
+
,--
Calculate VCSTR
VCSTR =FA0X
kCAO (1− X )
Using the T above to calculate the k
Scheme 1: X is given, calculate V and T
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
11/10/15
16
31
T is given, Calculate X and V
Calculate X from Energy Balance Equation
Q•
−WS −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
Calculate VCSTR
VCSTR =FA0X
kCAO (1− X )
Using the X above to calculate the V
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
32
Given the following reaction in a non adiabatic CSTR.
(V)(A)
(Ta)
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
11/10/15
17
33
(CPA)
(FA0)(T0)
(CPB) (CPC)
Given the following reaction in a non adiabatic CSTR.
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
34
1. Reaction is non-adiabatic, CSTR reactor, irreversible liquid phase, elementary reaction.
2. CSTR volume, V = 125 gal and conversion, X = 1.0 (proceeds to completion) so find the reaction temperature, T.
3. From question,
U
Ta
FAO
ΔHRx(TR )o
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
11/10/15
18
35
4. From the energy balance equation,
ΔCP =caCPC −
baCPB −CPA = 2(47.5)− 44.0−51.0 = 0
PCΔ
Q•
−WS −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
(CPA) (CPB) (CPC)
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
36
5. From the energy balance equation
Θi CPi =∑ CPA +ΘBCPB ,ΘB =10lbmol / hr10lbmol / hr
=1
Therefore Θi CPi =∑ CPA +CPB = 51.0+ 44.0 = 95.0 Btu / lb mol.oF
PiC
Q•
−W.s−FAO ΘiCPi (T −To )
i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
(CPA) (CPB) (CPC)
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
11/10/15
19
6. From the energy balance equation
Calculate the heat added into the reactor by the heat exchanger
Q•
−W.s−FAO ΘiCPi (T −To )
i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
37
Q.
=UA.
(Ta −T )
= (150 Btu / hr. ft 2.oF )(10 ft 2 )(365.9−T ) oF=1500(365.9−T )Btu / hr
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
38
7. From the energy balance equation
[ ] 0)()()(1
.=−Δ+Δ−−Θ−− ∑
=
•
RPRo
AO
n
iioPiiAOs TTCTHXFTTCFWQ
Rx
W.
s = 25hp× 9.486×10−4Btu / s
1.341×10−3hp×3600s1hr
= 63664Btu / hr
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
11/10/15
20
39
8. From the energy balance equation, substitute in all the values into the equation to obtain T as
Q•
−W.
s− FAO ΘiCPi (T −To )i=1
n
∑ − FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&'
()*= 0
where Q.
=1500(365.9−T ) Btuhr
, Ws = 63664 Btuhr
where Θi CPi =∑ 95.0 Btulb mol.oF
,ΔHRx(TR )
o =20,000 Btulb mol
,ΔCP = 0
where FA0 =10 lbmolhr
,T0 = 80 oF ,TR = 365.9 oF ,X =1(into completion)
Substitute all into equation1500(365.9−T )−63664− (10 )(95.0 )(T −80)− (10)(1)[20,000+0]= 0
T =147.4 oF
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for non-adiabatic System)
40
FOR ADIABATIC SYSTEM;; Q = 0,
The energy balance for CSTR with no heat exchange Q= 0
−Ws − FAO ΘiCPi (T −To )i=1
n
∑ − FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&'
()*= 0
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
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21
41
Given the following reaction in an adiabatic CSTR.
FAO FBO
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
42
Given the following reaction in an adiabatic CSTR.
You are feeding 2500 lb mol/h of A and equal molar flowrate of B to the reactor. The feed stream consist of 46.62 ft3/hr of A and 233.1 ft3/hr of B. The temperature of both feed stream is 58oF prior to mixing but there is an immediate 17oF temperature rise upon mixing of the 2 feed streams caused by the heat of mixing. The entering temperature of all feed streams is thus taken to be 75oF.For the conditions similar to those, it is found that that the reaction is first order with respect to A and zero order with respect to B with the specific reaction rate given as
k = Ae-Ea/RT = 16.96x1012(e–32,400Btu/lb mol/RT)/hrCalculate the exit temperature at which the reaction is conducted and subsequently the CSTR volume when given the conversion as 10%. Assume the work done by stirrer is negligible.
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
11/10/15
22
43
Following data are given as following:
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
44
1. In this question, the exit conversion is given, X therefore we need to find the temperature, T at which the reaction is conducted and subsequently the volume of the CSTR, V
2. Based on the algorithm for adiabatic system,
X is given, calculate T first using energy balance equation
Calculate T from Energy Balance
Q−Ws −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
Because adiabatic, Q = 0 and stirring work negligible, Ws = 0Therefore equation becomes
−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
11/10/15
23
45
5. From the energy balance equationCalculate T
−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
We know ΔHRxo (TR ) = c
aHC(TR )
o −baHB(TR )
o −HA(TR )o
Therefore ΔHRx(TR)
0 = HC (TR )o −HB(TR )
o −HA(TR )o
= −226,000− (−123,000)− (−66,600) = −36,400 Btu / lb mol
Reference Temperature, TR
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
46
3. From the energy balance equation
4. Given FAO = 2500 lb mol/hr of A to the reactor and equal molar flowrate of B
Calculate T
−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
Θi CPi =∑ CPA +ΘBCPB ,ΘB =25002500
=1
Therefore Θi CPi =∑ CPA +CPB = 35.0+18.0 = 53.0 Btu / lb mol.oF
To = 75oFTR = 68oF
From Question:You are feeding 2500 lb mol/h of A and equal molar flowrate
of B
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
11/10/15
24
6. From the energy balance equation
Calculate T
−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
47
pAppp CCabC
acC know We
BC−−=Δ
Therefore ΔCp =CpC −CpB −CpA = 46−18−35 = −7 Btu / lb mol. oF
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
7. From the energy balance equation
8. Substitute in all the values we calculate previously to determine the reaction temperature, T when given the conversion, X = 0.1
Calculate T
−FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
48
−FAO ΘiCPi (T −To )i=1
n
∑ − FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&'
()*= 0
where ΔHRx(TR)0 = −36,400 Btu
lbmol, Θi CPi =∑ 53.0 Btu
lbmol.oF,ΔCp = −7 Btu
lbmol.oF
where FAO = 2500 lbmolhr
,T0 = 75oF ,TR = 68oF ,X = 0.1
Substitute in the equation,− 2500(53.0)(T −75)− (2500)(0.10)[−36,400+ (−7)(T −68)]= 0T = 144.9 oF
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
11/10/15
25
49
9. From the logarithm, we have solved T value. 10. Therefore next is to find the new k value when
reaction temperature, T is 144.9 oF. Given from the question that
k = Ae-Ea/RT = 16.96x1012(e-32,400Btu/lb mol/RT)/hr
k =16.96×1012e−32,400 Btu/lb mol
RT
=16.96×1012e−32,400 Btu/lb mol
(1.987Btu/lb mol. oR)(144.9+459.69 oR) / hr = 32.84 / hr
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
50
SOLUTION11.Next we obtain the volume of the CSTR, V.12.To find the initial concentration of A, we know FA0 = 2500 lb
mol/hr and the initial volumetric flowrate, as given in question as 46.62 ft3/hr of A and 233.1 ft3/hr of B. Therefore υ0,TOTAL = 46.62 + 233.1 ft3/hr = 279.72 ft3/hr
VCSTR =FA0X
kCAO (1− X )=
υ0Xk(1− X )
=279.72 ft
3
hr(0.1)
32.84hr
(1−0.1)"
#$
%
&'
= 0.95 ft3
6.2 Algorithms for non-isothermal reaction design (CSTR Algorithm for Adiabatic System)
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6.3 Equilibrium ConversionQUESTION: What Happen if its NON-ISOTHERMAL REVERSIBLE reactions? 1. The highest conversion can be achieved in reversible reactions is
the equilibrium conversion.2. For endothermic (need heat) reactions, the equilibrium conversion
increases with increasing temperature up to a maximum of 1.0.3. For exothermic (release heat) reactions, the equilibrium
conversion decreases with increasing temperature.
51
Equilibrium Conversion
Reaction Temperature
Example for Exothermic reaction
6.3 Equilibrium Conversions (Reversible, Exothermic and Adiabatic Reactions)
52
1. To determine the maximum conversion, X that can be achieved in an EXOTHERMIC reaction carried out ADIABATICALLY (Q=0) in a REVERSIBLE REACTION, we find the intersection of the equilibrium-temperature plot with temperature-conversion relationships from the energy balance equation.
Equilibrium Conversion, Xe
Reaction Temperature, T
Equilibrium PlotPlot obtained from Energy balance equation
ToAdiabatic temperature
Inlet Temperature
T
XMaximum Conversion
Q•
−WS −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
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6.3 Equilibrium Conversions (Reversible, Exothermic and Adiabatic Reactions)
53
1. If inlet temperature is increased from T0 to T01, the energy balance line will be shifted to the right and parallel to the original line, as shown by the dashed line.
Equilibrium Conversion, Xe
Reaction Temperature, T
Equilibrium PlotPlot obtained from Energy balance
equation
ToNew Inlet Temperature
Inlet Temperature
T01
Q•
−WS −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )o +ΔCP (T −TR )%& '(= 0
6.3 Equilibrium Conversions (Reversible, Exothermic and Adiabatic Reactions)How to improve conversion for exothermic reaction?1. By connecting reactors in series with interstage cooling
54
Equilibrium Conversion, Xe
Reaction Temperature, T
Equilibrium PlotPlot obtained from Energy balance
equation
ToInlet Temperature
X1X2
Cooling down
Cooling down
X3Conversion
increases with interstage
cooling to Inlet Temperature
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6.3 Equilibrium Conversions (Reversible, Endothermic and Adiabatic Reactions)
How to improve conversion for ENDOTHERMIC reaction?1. By connecting reactors in series with interstage heating
55
Equilibrium Conversion, Xe
Reaction Temperature, T
Inlet TemperatureTo
Plot obtained from Energy
balance equation
Equilibrium Plot
X1 Heating up
Heating upX2X3Conversion
increases with interstage
heating to Inlet Temperature
6.4 Multiple Steady-state56
1. Lets say in our reaction, we don’t have both data of Conversion (X) and Reaction Temperature (T) but we know the Volume of Reactor (V)
2. If we consider a first order irreversible liquid phase reaction with single steady state in a CSTR we can obtain 2 separate plots of Conversion, X vs. Reaction Temperature
3. First plot is obtain when we calculate Conversion, XMBvs. Temperature based on Mass Balance Equation.
VCSTR =FA0XMB
kCA0 (1− XMB )=
v0XMB
k(1− XMB )
Rearrange we get XMB =VCSTRk
v0 +VCSTRk
When T changes, k = Ae−EaRT also changes
When k changes, XMB also changes
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6.4 Multiple Steady-state57
1. Second plot is obtain when we calculate Conversion, XEB vs. Temperature based on Energy Balance Equation.
Q•
−Ws −FAO ΘiCPi (T −To )i=1
n
∑ −FAOX ΔHRx (TR )
o +ΔCP (T −TR )%&
'(= 0
6.4 Multiple Steady-state58
1. By combining this 2 plot we can find the Reaction Conversion, X by determining its intersection.
Conversion, X
Reaction Temperature, T
Conversion plot from Mass Balance Equation, XMB
Conversion plot from Energy Balance Equation, XEB
X
To
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6.4 Multiple Steady-state59
1. If a reaction parameter were changed slightly, the XEB line could move slightly to the left and there might be more than one intersection between both plots.
2. When more than one intersection occurs, there is more than one set of conditions that satisfy both the energy balance and mole balance
3. This is called as multiple steady states at which the reaction may operate
Conversion, X
Reaction Temperature, T
Conversion plot from Mass Balance Equation, XMB
Conversion plot from Energy Balance Equation, XEB
X1
ToTo1
X2a
X2b