Reaction Rate • The reaction rate is the rate at which a species looses its chemical identity per unit volume.... Reaction Rate • The reaction rate is the rate at which a species looses [r]
Trang 1Chemical Reaction Engineering (CRE) is the
field that studies the rates and mechanisms ofchemical reactions and the design of the reactors in
which they take place
Lecture 1
1
Trang 2 Continuously Stirred Tank Reactor (CSTR)
Packed Bed Reactor (PBR)
Trang 3Chemical Reaction Engineering
3
Chemical reaction engineering is at the heart of
virtually every chemical process It separates thechemical engineer from other engineers
Industries that Draw Heavily on Chemical
Reaction Engineering (CRE) are:
CPI (Chemical Process Industries)
Examples like Dow, Amoco, Chevron, BSR, SK
Energy, etc
Trang 44
Trang 5Chemical Plant for Ethylene Glycol (Ch 5)
Smog (Ch 1)
Plant Safety (Ch 11,12,13)
Lubricant Design (Ch 9)
Cobra Bites (Ch 8 DVD-ROM)
Oil Recovery (Ch 7)
Wetlands (Ch 7 DVD-ROM)
Hippo Digestion (Ch 2)
5
Trang 6Let’s Begin CRE
Chemical Reaction Engineering (CRE) is
the field that studies the rates and
mechanisms of chemical reactions and the design of the reactors in which they take place.
Trang 7• A chemical species is said to have reacted
when it has lost its chemical identity.
Chemical Identity
Trang 8• A chemical species is said to have reacted
when it has lost its chemical identity.
• The identity of a chemical species is
determined by the kind, number, and
configuration of that species’ atoms.
Chemical Identity
Trang 9• A chemical species is said to have reacted
when it has lost its chemical identity.
1 Decomposition
Chemical Identity
Trang 10• A chemical species is said to have reacted
when it has lost its chemical identity.
1 Decomposition
2. Combination
Chemical Identity
Trang 11• A chemical species is said to have reacted
when it has lost its chemical identity.
1 Decomposition
2 Combination
3. Isomerization
Chemical Identity
Trang 12Chemical Identity
12
A chemical species is said to have reacted when
it has lost its chemical identity
There are three ways for a species to loose its
identity:
1 Decomposition CH 3 CH 3 H 2 + H 2 C=CH 2
2 Combination N 2 + O 2 2 NO
3 Isomerization C 2 H 5 CH=CH 2 CH 2 =C(CH 3 ) 2
Trang 13• The reaction rate is the rate at which a
species looses its chemical identity per unit volume.
Reaction Rate
Trang 14• The reaction rate is the rate at which a
species looses its chemical identity per unit volume.
• The rate of a reaction (mol/dm3/s) can be expressed as either
the rate of Disappearance: -rA
or as
the rate of Formation (Generation): rA
Reaction Rate
Trang 15Reaction Rate
Consider the isomerization AB
r A = the rate of formation of species A per unit volume
-r A = the rate of a disappearance of species A per unit volume
r B = the rate of formation of species B per unit volume
Trang 16Reaction Rate
• EXAMPLE: AB
If Species B is being formed at a rate of
0.2 moles per decimeter cubed per second, ie,
rB = 0.2 mole/dm3/s
Trang 20Reaction Rate
Consider species j:
• rj is the rate of formation of species j per unit volume [e.g mol/dm3/s]
Trang 22Reaction Rate
• rj is the rate of formation of species j per unit
volume [e.g mol/dm3/s]
• rj is a function of concentration, temperature,
pressure, and the type of catalyst (if any)
• rj is independent of the type of reaction system (batch reactor, plug flow reactor, etc.)
Trang 23Reaction Rate
• rj is the rate of formation of species j per unit volume [e.g mol/dm3/s]
• rj is a function of concentration,
temperature, pressure, and the type of
catalyst (if any)
• rj is independent of the type of reaction system (batch, plug flow, etc.)
• rj is an algebraic equation, not a
differential equation
Trang 24General Mole Balances
24
Building Block 1:
System Volume, V
mole time
mole time
mole
dt
dN G
F F
j Species of
on Accumulati
Rate Molar
j Species of
Generation
Rate Molar
out j
Species
of Rate
Flow Molar
in j Species
of Rate
Flow Molar
j j
j j0
Trang 25General Mole Balances
G j = j ∆
2 2
Trang 26General Mole Balances
Trang 27General Mole Balances
27
Building Block 1:
General Mole Balance on System Volume V
In − Out + Generation = Accumulation
FA 0 − FA + ∫ rAdV = dNA
dt
System Volume, V
Trang 28Batch Reactor Mole Balance
Trang 29Batch Reactor - Mole Balances
A A
A A
A A
F F
dt
dN dV
r F
rA = A
∫
Well-Mixed
Trang 30Batch Reactor - Mole Balances
dN t
0
30
A A
A A
N N
t t
N N
Trang 31Batch Reactor - Mole Balances
dN t
0
N A
t
31
Trang 32Continuously Stirred Tank Reactor
Mole Balance
Trang 33CSTR (Cont.)
Trang 34CSTR (Cont.)
Trang 38Plug Flow Reactor
Trang 39PFR Mole Balances
PFR:
Trang 40PFR Mole Balances (Cont.)
Trang 45Plug Flow Reactor - Mole Balances
r F
PFR
Trang 46Plug Flow Reactor - Mole Balances
0
The integral form is:
This is the volume necessary to reduce the
entering molar flow rate (mol/s) from FA0 to the
exit molar flow rate of FA
Alternative Derivation
Trang 47PFR Mole Balances (Cont.)
Trang 48Packed Bed Reactor Mole
Balance
PBR
Trang 49Packed Bed Reactor - Mole Balances
49
dt
dN W
r W
W F
W
F A − A + ∆ + A′∆ = A
A W
A W
W A
W
F F
Trang 50Packed Bed Reactor - Mole Balances
50
dFA
dW = ′ rA
Rearrange:
PBR catalyst weight necessary to reduce the
entering molar flow rate FA0 to molar flow rate FA
0
The integral form to find the catalyst weight is:
Trang 51Reactor Differential Algebraic Integral
The GMBE applied to the four major reactor types(and the general reaction AB)
dN t
Trang 52Homework 1: A 200-dm3 constant-volume batch reactor is
pressurized to 20 atm with a mixture of 75% A and 25% inert The gas-phase reaction is carried out isothermally at 227 C.
P = 20 atm
T = 227 C
a Assuming that the ideal gas law is valid, how many moles of A are
in the reactor initially? What is the initial concentration of A?
b If the reaction is first order:
Calculate the time necessary to consume 99% of A.
c If the reaction is second order:
Calculate the time to consume 80% of A Also calculate the pressure
in the reactor at this time if the temperature is 127 C.
Trang 53Homework 2: