REACTORS - A. James Clark School of Engineering
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Transcript REACTORS - A. James Clark School of Engineering
REACTORS
By: Shaimaa Soarkati,
CHBE446
Section: 0301
A. James Clark School of Engineering
Constant Stirred Tank Reactor (CSTR)
Steady-state continuous flow of reactants (A) and Products (B). Wellmixed reactor, so exit stream has the same composition as reactants
in the tank
Phases present:
Liquid, Gas-liquid, Solid-liquid
Advantages:
Continuous process
Maintainable temperature
Simple design
Easy to clean
Low operating cost
Disadvantages:
Low conversion per unit volume
CSTR Equations
Mole Balance:
𝐹𝐴0 -𝐹𝐴 +
𝑉
𝑟 𝑑𝑉
0 𝐴
=
At steady state,
𝑑𝑁𝐴
𝑑𝑡
𝑑𝑁𝐴
𝑑𝑡
=0
Rate Law:
−𝑟𝐴 =
𝑘𝐶𝐴
1+𝐾𝐴 𝐶𝐴
Conversion:
𝑋=
𝐹𝐴0− 𝐹𝐴
𝐹𝐴0
𝑉=
𝐹𝐴0 𝑋
−𝑟𝐴
;
Note: The volume is also calculated by measuring the
area under the CSTR curve
Plug Flow Reactor (PFR)
A long reactor tube with consisting of many “plugs”
Concentration changes down the reactor (length-wise)
No radial variation in reaction rate/ concentration
For large scale
Heterogeneous and homogeneous reactions (fast)
Advantages:
High conversion per unit volume
Efficient heat transfer
Continuous process
Easy maintenance
Typically contain catalyst
Disadvantages:
Poor temperature control
Undesired thermal gradients possible
Poor mixing (static mixers)
PFR Equations
Mole Balance:
𝐹𝐴0 -𝐹𝐴 +
𝑉
𝑟 𝑑𝑉
0 𝐴
=
At steady state,
V=𝐹𝐴0
𝑋 𝑑𝑋
0 −𝑟𝐴
Rate law:
−𝑟𝐴 = 𝑘𝐶𝐴𝑛
Conversion:
𝑋=
𝐹𝐴0 −𝐹𝐴
𝐹𝐴0
Stoichiometry:
𝐶𝐴 =
𝐹𝐴
𝑣
𝑑𝑁𝐴
𝑑𝑡
𝑑𝑁𝐴
𝑑𝑡
=0
BATCH REACTOR
Reactants are supplied via the top two holes on the
reactor and nothing can be added or extracted while
the reaction process occurs.
Can be heated or cooled via jacket
Small scale
Used mostly for pharmaceutical or fermentation
processes
Advantages:
High conversion per unit volume
Can be used for multiple operations
Easy to clean
Disadvantages:
Varied product quality
High operation cost
Batch Reactor Equations
Mole Balance:
𝐹𝐴0 -𝐹𝐴 +
𝑉
𝑟 𝑑𝑉
0 𝐴
=
𝑑𝑁𝐴
𝑑𝑡
No inflow or outflow, 𝐹𝐴0 = 𝐹𝐴 = 0
𝑑𝑥
𝑑𝑡
=
−𝑟𝐴 𝑉
𝑁𝐴0
Rate Law:
−𝑟𝐴 = 𝑘[𝐶𝐴 −
𝐶𝐵 𝐶𝐶
]
𝐾𝐵
Conversion:
𝑡=
𝑋 𝑑𝑋
0 −𝑟𝐴 𝑉
Stoichiometry:
𝐶𝐴 =
𝑁𝐴
𝑣
= 𝐶𝐴0 (1 − 𝑋)
Heterogeneous Catalysis
Form of catalysis where the catalyst phase is
different from the reactants
Adsorption is an essential first step in
heterogeneous catalysis
Molecule in gas phase binds to a liquid or solid
surface
www.techrem.ruhr-uni-Bochum.de
Surface Reactions
Langmuir-Hinshelwood mechanism
Rideal-Eley mechanism
Precursor mechanism
http://cdn.comsol.com/wordpress/2015/02/Eley-Rideal-mechanism.png