ABSTRACT From this experiment, our objectives are to carry out the saponification reaction between NaOH and Et(Ac) in plug flow reactor, to determined the reaction rate constant and the rate of reaction of the saponification process. First of all, the equipment is set up before started the experiment. After collecting the data, the value of reaction rate constant and rate of reaction is calculated. The reaction rate constant we get for 600ml/min flowrate is 17.25L/mol.min, for the 500mL/min reaction rate constant is 17.44L/mol.min, for the 400mL/min reaction rate constant is 15.93L/mol.min, for the 300mL/min reaction rate constant is 18.32L/mol.min, for the 200mL/min reaction rate constant is 25.58L/mol.min and for the 100mL/min reaction rate constant is 34.10L/mol.min. Besides that, we are also able to determine the rate of reaction for this process. The rate of reaction we get for flowrate of 600ml/min is 0.0373mol/L.min, for the 500mL/min the rate of reaction is 0.0304mol/L.min, for the 400mL/min the rate of reaction is 0.0237mol/L.min, for the 300mL/min the rate of reaction is 0.0155mol/L.min, for the 200mL/min the rate of reaction is 0.0068mol/L.min and for the 100mL/min the rate of reaction is 0.0016mol/L.min. Then, a graph of conversion factor against residence time is plotted. From the graph we can see that the conversion factor is directly proportional to the residence time. As the residence time increases, the conversion factor also increases. 1
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ABSTRACT
From this experiment, our objectives are to carry out the saponification reaction
between NaOH and Et(Ac) in plug flow reactor, to determined the reaction rate constant and
the rate of reaction of the saponification process. First of all, the equipment is set up before
started the experiment. After collecting the data, the value of reaction rate constant and rate
of reaction is calculated. The reaction rate constant we get for 600ml/min flowrate is
17.25L/mol.min, for the 500mL/min reaction rate constant is 17.44L/mol.min, for the
400mL/min reaction rate constant is 15.93L/mol.min, for the 300mL/min reaction rate
constant is 18.32L/mol.min, for the 200mL/min reaction rate constant is 25.58L/mol.min and
for the 100mL/min reaction rate constant is 34.10L/mol.min. Besides that, we are also able to
determine the rate of reaction for this process. The rate of reaction we get for flowrate of
600ml/min is 0.0373mol/L.min, for the 500mL/min the rate of reaction is 0.0304mol/L.min,
for the 400mL/min the rate of reaction is 0.0237mol/L.min, for the 300mL/min the rate of
reaction is 0.0155mol/L.min, for the 200mL/min the rate of reaction is 0.0068mol/L.min and
for the 100mL/min the rate of reaction is 0.0016mol/L.min. Then, a graph of conversion
factor against residence time is plotted. From the graph we can see that the conversion factor
is directly proportional to the residence time. As the residence time increases, the conversion
factor also increases.
1
INTRODUCTION
In addition to the Continue Stir Tank Reactor (CSTR) and batch reactors, another type of
reactor commonly used in industry is the tubular flow reactor. It consists of a cylindrical pipe
and is normally operated at steady state, as is the CSTR [1]. Tubular flow reactors are usually
used for gas phase-reactions. A schematic of industrial tubular reactors are shown in figure
below:
Figure 1: Tubular reactor schematic. Longitudal flow reactor.Excerpeted by special permission from Chem. Eng., 63(10),
211(Oct.1956). Copyright 1956 by McGraw-Hill, Inc., New York
In the tubular reactor, the reactants are continually consumed as they flow down the length of
the reactor. In the ideal tubular reactor, which is called the “plug flow” reactor, specific
assumptions are made about the extent of mixing:
1. no mixing in the axial direction, i.e., the direction of flow
2. complete mixing in the radial direction
3. a uniform velocity profile across the radius.
Plug flow reactor is an ideal tubular reactor with laminar flow behaviour. The reactants pass
through the tube; the reactants are converted progressively along the length of reactor. The
reactants are continuously consumed and the product is formed as the flow preceded the
length of the reactor. There is no radial variation in concentration. Consequently, the reaction
rate, which is function of concentration for all but zero-order reactions, will also vary axially.
Plug flow-no radial variations in velocity,concentrations, temperature, or reaction rate
2
Figure 2: Plug flow reactor
The validity of the assumptions will depend on the geometry of the reactor and the flow
conditions. Deviations, which are frequent but not always important, are of two kinds:
1. mixing in longitudinal direction due to vortices and turbulence
2. incomplete mixing in radial direction in laminar flow conditions
Flow in tubular reactor can be laminar, as with viscous fluids in small-diameter tubes, and
greatly deviate from ideal plug-flow behaviour, or turbulent, as with gases. 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 conveniently long reactors or may require unacceptable high feed
rates.
For most chemical reactions, it is impossible for the reaction to proceed to 100% completion.
The rate of reaction decreases as the percent completion increases until the point where the
system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs).
The equilibrium point for most systems is less than 100% complete. For this reason a
separation process, such as distillation, often follows a chemical reactor in order to separate
any remaining reagents or by products from the desired product. These reagents may
sometimes be reused at the beginning of the process, such as in the Haber process.
Tubular flow reactors are usually used for this application which are:
1. Large scale reactions
2. Fast reactions
3. Homogeneous or heterogeneous reactions
4. Continuous production
5. High temperature reactions
3
OBJECTIVES
The objectives of this experiment are:
1. To carry out the saponification reaction between NaOH and Et(Ac) in tubular flow
reactor.
2. To determine the reaction rate constant.
3. To determine the effect of residence time on the conversion in the tubular flow
reactor.
THEORY
In a plug flow reactor, the feed enters at one end of a cylindrical tube and the product stream
leaves at the other end. The long tube and the lack of provision for stirring prevent complete
mixing of the fluid in the tube. Hence the properties of the flowing stream will vary from one
point to another, namely in both radial and axial directions.
The rate expression can be shown to be
-rA = k [A] [B]
Where if [A] is equal to [B], this simplify to
-rA = k [A]2
In the general case the order of the reaction η is not known and is shown by
-rA = k [A]η
If the inlet concentration, [A] is known, k can be determined. The reaction:
f(x) = NaN x + NaNR² = 0 Graph X/(1-X) against residence time
Graph X/(1-X) against residence timeLinear (Graph X/(1-X) against residence time)
residence time
X/(1
-X)
Graph 1: Graph X/(1-X) against residence time
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SAMPLE CALCULATION Experiment 1: Slope = -0.043x Y-intercept = 6.892 Y = -0.043x + 6.892 Experiment 2: To find conversion of NaOH in the reactor
For volume of titrated NaOH, V1 = 0.0185L 1. Conc. Of NaOH entering the reactor, CNaOH,0,
Where concentration of NaOH in the feed vessel, CNaOH, f = 0.1 M CNaOH,0 = (CNaOH,f) / 2 = 0.1 M / 2 = 0.05 M 2. Volume of unreacted quenching HCl, V2,
Where concentration of NaOH used for titration, CNaOH,s = 0.1 M; Concentration of HCl in standars solution, CHCl,s = 0.25 M; Volume of titrated NaOH, V1 = 0.0185L.
V2 = (CNaOH,s / CHCl,s ) x V1
= (0.1M / 0.25 M) x 0.0185 L = 7.40 x 10-3 L
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3. Volume of HCl reacted with NaOH in sample, V3 Where volume of HCl for quenching, VHCl,s = 0.01 L
V3 = VHCl,s – V2 = 0.01 L – 7.40 x 10-3 L = 2.6 x 10-3 4. Moles of HCl reacted with NaOH in sample, n1
n1 = CHCl,s x V3 = 0.25 M x (2.6 x 10-3 L) = 6.5 x 10-4 mol 5. Moles of unreacted NaOH in sample n2 = n1 = 6.5 x 10-4 mol
6. Conc. Of unreacted NaOH in the reactor, CNaOH Where: volume of sample, Vs = 0.05 L
CNaOH = n2 / Vs = (6.5 x 10-4 mol) / 0.05 L = 3.25 x 10-5M 7. Conversion of NaOH in the reactor, X
X = (1 – (CNaOH / CNaOH,0 )) x 100% = (1– (3.25 x 10-5M / 0.05 M)) x 100% = 99.9 %
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To find residence time Where reactor volume, VTFR = 0.4 L and total feed flowrates, V0 = 0.593 L/min Residence time, = VTFR / V0 = 0.4 / 0.6 = 0.667 min To find reaction rate constant K = V0 (X) VPTRC (1-X) = 0.6 . 0.99 0.4 x 0.1 1- 0.99 = 1485 L/mol.min To find rate of reaction -rA = kCA02 ( 1 – X )2
= 1485 ( 0.1 ) 2 x ( 1 – 0.99 )2 = 1.485 x 10-3 mol / L.min
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SAMPLE OF CALCULATION
Reactor volume, υo = 0.4L Conversion, X = 53.49%
Flowrate of NaOH = 300mL/min Inlet conductivity = 9.3mS/cm
Flowrate of Et(Ac) = 300mL/min Outlet conductivity = 7.5mS/cm
Concentration of NaOH in feed tank = 0.1M
Concentration of Et(Ac) in feed tank = 0.1M
Residence time,
= V 0
= (0.4)/(0.6)
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= 0.67min
Reaction rate constant
k=v0
V TFRCAO ( X1−X )
k = 0.6/ (0.4 x 0.1) [0.5349/(1 – 0.5349)]
= 17.25 L/mol.min
Rate of reaction
-rA = kC2AO(1-X)2
= (17.25) (0.1)2(1 – 0.5349)
= 0.0373 mol/L.min
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DISCUSSIONS
By doing this experiment, we are able to carry out the saponification reaction between NaOH
and Et(Ac) in tubular flow reactor. At the end of the experiment, we are also able to
determine the reaction rate constant by using the formula and to determine the effect of
residence time on the conversion in the tubular flow reactor.
The experiment is started by running up the equipment in order to start the saponification
process. From Figure 3, the coiled reaction tube is where the saponification process to occur.
The saponification process can be done in two ways whether variation in temperature or
variation in contact time. In this experiment, we will let the flowrate of both solutions as the
varying components because the flowrate of both solutions is controlled by the temperature
of the reactor. At the end of the experiment, the saponification process is successfully done.
After that, we are needed to determine the reaction rate constant and the rate of the reaction
for the saponification process depends on the vary flowrate of both solution sodium
http://eleceng.dit.ie/gavin/DT275/CET%20MKII%20manual%20issue%2016.pdf at
8.00pm at 14 Feb 2011
4. http://en.wikipedia.org/wiki/Plug_flow_reactor_model at 8.30pm on 14 Feb 20115. http://www.che.boun.edu.tr/courses/che302/Chapter%2010.pdf at 9.45pm on 14 Feb