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