Chemical reaction engineering involves designing chemical reactors to optimize reaction rates and yields. There are several factors that influence reaction rates, including concentration, temperature, and catalysts. Common reactor types include batch, continuous stirred-tank (CSTR), and plug flow reactors. Reactors can be run in series or parallel to improve conversion levels. Residence time distribution is important for understanding flow patterns within real reactors.

1. Malik Ahmad Rid

3. 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.

4. Chemical Reactors
• An industrial chemical reactor is complex device in
which heat transfer, mass transfer, diffusion and
friction may occur along with chemical reaction with
provisions of safety and controls.
• Are vessels designed to contain chemical reactions

5. Basic Principles:
 All chemical processes are centered in a
chemical reactor. The design of a chemical
reactor Is the most important factor in
determining the overall process economics.

6. In addition to the basic data,
include
 A heat and mass transfer characteristics
 Physical, chemical and thermodynamic
properties of components taking part in the
reaction.
 CORROSION- erosion characteristics of any
potential hazard associated with reaction
system.
 Reaction Rate

7. Basic data:
 1. endothermic reactions(within- heating”
describes a process or reaction that absorbs energy
in the form of heat.)
2.exothermic reactions (Release energy in
the form of heat, light, or sound.)
Reaction rate (Speed at which a chemical
reaction proceeds, in terms of amount of product
formed or amount of reactant consumed per unit
time)

8. Factors Influencing Reaction
Rate
 Concentration
 The nature of reaction
 Temperature
 Pressure
 Catalyst
 Modeling Principle:
 Inputs + Sources = Output + Sink +
Accumulations

9. Basic Reactor Element
 1.Material Balances
 2.Heat Transfer and Mass Transfer
 Material Balances(Also called mass balance.
 Is an application of conservation of mass to the
analysis of physical systems.
 The mass that enters a system must, by conservation
of mass, either leave the system or accumulate within
the system.

10. Mathematically the mass balance for a
system without a chemical reaction is as
follows:
 Input = Output + Accumulation

11. Mass Transfer
 Is the phrase commonly used in engineering for physical
processes that involve molecular and convective transport
of atoms and molecules within physical system.
 Transfer of mass from high concentration to low
concentration
Heat Transfer
 Is the transition of thermal energy from a heated item
to a cooler item.
 Transfer of Thermal Energy

12. Modes Of Heat Transfer
 jacket,
• internal coils,
• external heat exchanger,
• cooling by vapor phase condensation
• fired heater.

15. Reactor types
 They can be classified according to the;
1. Modes of operation
 2. End use applications
 3. No. of phases
 4. A catalyst is use

16. Chemical Reactor on the
basis of operation:
1. Batch Modes
2. Semi Continuous Modes
3. Continuous Modes

34. CSTR IN
SERIES:
Lets have an simple
derivation and
example solved to
illustrate you .

35. Example :
For two CSTRS in series 40% conversion is
achieved in the first reactor . What is the
volume of each two reactor necessary to
achieve the 80% over all conversion of
entering specie first ?
Table processed data:
X 0.0 0.1 0.2 0.4 0.6 0.8
faO/-ra 0.89 1.09 1.33 2.05 3.54 8

38. Advantages in series/parallel
 These are commonly used In industrial
processing primarily in homogenous liquid
phase flow reactions where constant
agitation is required they may be used in
series and parallel.
 When agitation and good mixing is
required.

39. Disadvantages :
 It is not recommended for high pressure reactions
because of cost consideration. For high pressure
reactions it requires complex sealing arrangements for
the agitator which increase the initial as well as
maintenance cost.
 Conversion of these reactors is low due to this they are
not preferred.
 These reactors are not suited for high heat effect since
availability of both heat transfer coefficient and heat
transfer per unit area is low.

41. Multiple reactor system PFR (in
series) :
 Number of plug flow reactor in series are
theoretically same as equivalent volume of a single
plug flow reactor.
 Number of mixed flow reactor of equal size in
series may be used when we need high conversion
and can’t perform in a single reactor.

42. PFR Design Equation
• Similarly, the design equation for a PFR is
 FA0 dX/ dV = −rA
 • Therefore, V = FA0 X/-ra
Parallel Reactions in parallel reactors :
• When a reactant gives two product (desired, and
undesired)simultaneously with different rate constant then this is called a
parallel reaction.
• To keep maximum amount of desired product we can take following steps.
• Ifa1>a2 or the desired reaction is of higher order then keep reactant
concentration high for high product concentration.
• If a1<a2 than for desired reaction keep reactant concentration low.
• For a1=a2 change in reactant concentration will not affect the product then,
because rate constant k1 and k2 are different at different temperature so, we
can keep our temperature such that desired product will be high or use of
catalyst would be a option which are selective in nature.

43. Residence Time Distribution
• RTD is important factor from the point of view of real
equipment .
• Element of fluid will take different route through the
reactor and may take different length of time to pass
through the reactor.
• Ideal reactor design are made by considering volume
of reactor or time spend by all the reactant will be
same inside reactor.
• Completion of reaction will depend on time of
exposure inside the reactor.
• The distribution of time inside the reactor is called exit
age distribution E, have unite time-1

44. Residence time distribution
determination
 RTD can be determined by two experimental method.(Pulse input
experiment, and step input experiment )
 In pulse experimental method in a steady state system we will put a
pulse input of tracer and will plot the graph of this tracer
concentration with time at output.
 This graph will show time variation or age distribution of tracer
concentration with time.
 Another method of determination of RTD is by putting a step input
(Preferably unite step input) of tracer.
 Then we can plot the graph between the concentration versus time
graph of tracer.
 The slope versus time graph of this system will give us residence time
distribution .
 Step input method is more accurate than pulse input method although
impulse input would give the perfect distribution

45. Sizing CSTRs and PFRs :
 the CSTR volume will typically be greater than the PFR
volume for the same conditions (except when zero
order) – This is because the CSTR operates at the
lowest reaction rate while the PFR starts at a high rate
and decreases to the exit rate (which requires less
volume since it is inversely proportional to the rate) •
From a FA0 −rA vs. X plot, the reactor volumes can be
found from areas as shown in the sample Levenspiel

46. Batch Reactor :
Advantages : Limitations
 Suitable for small scale
production
 Suitable for proceeses where
different ranges of product
are to be obtained in the
same equipment
 Suitable for long taking
reactions
 Suitable for reaction with
superior selectivity
 Not suitable for long batch
sizes
 Closed system in which once
the product is entered only
comes out as a product after
the completion of reaction

47. CSTR:
Advantages: Limitations
 Highly flexible device
 Reactants can be removed during the
reaction
 It is economy beneficial to operate in
series and parallel
 Reaction can be carried out in
horizontal as well as vertical reactor.
 Continuous operation
 Good temperature control
 Easily adapts to two phase runs
 Good control
 Simplicity of construction
 Low operating (labor) cost
 Easy to clean
 More expensive and complex
than tubular units
 All calculations required for
CSTRS is perfected mixing
 At steady state flow rate must be
equal to the flow rate out other
wise tank will go empty r
overflow
 Lowest conversion per unit
volume
 By-passing and channeling
possible with poor agitation

48. Plug flow reactor:
Advantages : Limitations:
 Highly efficient than both at
the same volume.
 PFR’s have several pipes r
tubes in parallel
 Both the operations for
vertical and parallel are same
 They can be jacketed
 Regents can be introduced
other than the fixed inlet.
 Not economical for small
batches

49. CSTR in series/parallel advantages :
 When high conversions of reactants are needed,
several CSTRs in series/parallel can be used. Equally
good results can be obtained by dividing a single vessel
into compartments while minimizing back-mixing
and short-circuiting.
 The larger the number of CSTR stages, the closer the
performance approaches that of a tubular plug-flow
reactor.

50. PFR advantages in series/parallel
 Turbulent flow generally is preferred to laminar flow,
because mixing and heat transfer are improved.
 For slow reactions and especially in small laboratory
and pilot-plant reactors, establishing turbulent flow
can result in inconveniently long reactors or may
require unacceptably high feed rates.