ABSTRACT This experiment has been conducted on 5th April 2013 at Pilot Plant Laboratory, UiTM Shah Alam. The experiment is conducted to achieve the objective that has been considered which is to examine the effect of pulse input and step change input in tubular flow reactor and to construct the residence time distribution function by using tubular machine. Based on the experiment, two experiment were conducted which is pulse input experiment and step change input experiment. In the pulse input experiment, the flow rate was set up at 700 m3 s-1 and let it for one minute before reading taken every 30 seconds until the conductivity reading is 0.0. in the other hand, the step change input experiment, the conductivity were observe every 30 seconds until the reading at Q2 is constant for 3 times.
INTRODUCTION A tubular reactor is a vessel through which flow is continuous, usually at steady state, and configured so that conversion of the chemicals and other dependent variables are functions of position within the reactor rather than of time. Flow in tubular reactors can be laminar , as with viscous fluids in small-diameter tubes, and greatly deviate from ideal plugflow behavior, or turbulent, as with gases. There are tubular flow reactors applications which arer:
Large-scale reactions
Fast reactions
Homogeneous or heterogeneous reactions
Continuous production
High-temperature reactions
In an ideal plug flow reactor, a pulse of tracer injected at the inlet would not undergo any dispersion as it passed through the reactor and would appear as a pulse at the outlet. The degree of dispersion that occurs in a real reactor can be assessed by following the concentration of tracer versus time at the exit. This procedure is called the stimulusresponse technique.
High temperature reactions Residence Time Distribution (RTD) analysis is a very efficient diagnosis tool that can beused to inspect the malfunction of chemical reactors. Residence time distributions are measured by introducing a non-reactive tracer into the system at the inlet. The concentration of the tracer is changed according to a known function and the response is found by measuring the concentration of the tracer at the outlet. The selected tracer should not modify the physical characteristics of the fluid (equal density, equal viscosity) and the introduction of the tracer should not modify the hydrodynamic conditions. In general, the change in tracer concentration will either be a pulse or a step. The residence time distribution of a real reactor deviated from that of an ideal reactor, depending on the hydrodynamics within the vessel. A non-zero variance indicates that there is some dispersion along the path of the fluid, which may be attributed to turbulence, a nonuniform velocity profile, or diffusion. If the mean of the expected time
curve arrives earlier than the
it indicates that there is stagnant fluid within the vessel. If the residence
time distribution curve shows more than one main peak it may indicate channeling, parallel paths to the exit, or strong internal circulation.
OBJECTIVES
To examine the effect of a pulse input and step change input in a tubular flow reactor.
To construct a residence time distribution (RTD) function for the tubular flow reactor.
THEORY A tubular reactor is a vessel through which flow is continuous, usually at steady state, and configured so that conversion of the chemicals and other dependent variables are functions of position within the reactor rather than of time. In the ideal tubular reactor, the fluids flow as if they were solid plugs or pistons, and reaction time is the same for all flowing material at any given tube cross section. Tubular reactors resemble batch reactors in providing initially high driving forces, which diminish as the reactions progress down the tubes. Tubular reactor are often used when continuous operation is required but without back-mixing of products and reactants. Flow in tubular reactors can be laminar, as with viscous fluids in small-diameter tubes, and greatly deviate from ideal plug-flow behavior, 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 inconveniently long reactors or may require unacceptably high feed rates. Tubular reactor is specially designed to allow detailed study of important process. The tubular reactor is one of three reactor types which are interchangeable on the reactor service unit. the reactions are monitored by conductivity probe as the conductivity of the solution changes with conversion of the reactant to product. This means that the inaccurate and inconvenient process of titration, which was formally used to monitor the reaction progress, is no longer necessary. The residence-time of an element of fluid leaving a reactor is the length of time spent by that element within the reactor. For a tubular reactor, under plug-flow conditions, the residence-time is the same for all elements of the effluent fluid. (K. G. Denbigh) The procedure would be to carried out experiments with tubular reactor at varying feed rates, measuring the extent of reaction of the stream leaving the reactor. One possible method might to add ‘inert’ gas to the acetaldehyde vapour in such quantity that the change in density between entry and exit of the reactor could be neglected. In that case, the batch reactor time and the residence-time would both be equal to the space-time.
Using the result of experiment, apply equation below to determine n and k (ε wil bw known from the stoichiometry).
Mf=various values of feed rate τ= space-time from experiment, it should be able to draw a curve of τ against xout, the slope of which according to the first equation, should be
Taking the logarithm of both sides of equation, we can obtain
So, n and k can be obtain from the intercept and slope of the appropriate log-log plot. This approach that the experiments be isothermal (k and T outside the integral in the first equation). If the reactor is not isothermal, then the first equation must be written as
Where Tin is the temperature of the feed into the reactor Therefore, when the effect of wall heat transfer and of velocity gradient operate simultaneously they might, under rather special circumstance, give rise to a more complex kind of temperature profile. However, the most commonly observed profiles obtained with exothermic reactions in externally cooled reactors. The reason why the elementary design
method is erroneous when the transverse gradients are appreciable arises from the extreme sensitivity of reaction rate to changes of temperature. PROCEDURE Experiment 1: Pulse Input in a Tubular Flow Reactor 1. The general start-up procedures as in Section 4.1 is performed. 2. Valve V9 is opened and pump P1 is switch on. 3. Pump P1 flow controller is adjusted to give a constant flow rate of de-ionized water into the reactor R1 at approximately 700 ml/min at Fl-01. 4. Let the de-ionized water to continue flowing through the reactor until the inlet (Ql01) and outlet (Ql-02) conductivity values are stable at low levels. Both conductivities values are recorded. 5. Valve V9 is closed and pump P1 is switch off. 6. Valve V11 is opened and Pump P2 is switch on. The timer is started simultaneously. 7. Pump P2 flow controller is adjusted to give a constant flow rate of salt solution into the reactor R1 at 700 ml/min at Fl-02. 8. Let the salt solution to flow for 1 minute, then reset and restart the timer. This will start the time at the average pulse input. 9. Valve V11 is closed and pump P2 is switch off. Then, open valve V9 quickly and pump P1 is switch on. 10. Make sure that the de-ionized water flow rate is always maintained at 700 ml/min by adjusting P1 flow controller. 11. Both the inlet (Ql-01) and outlet (Ql-02) conductivity a value at regular intervals of 30 seconds is start recorded. 12. The conductivity values is continue recording until all readings are almost constant and approach the stable low level values.
Experiment 2: Step Change Input in a Tubular Flow Reactor 1. The general start-up procedures as in Section 4.1 is performed. 2. Valve V9 is opened and pump P1 is switch on. 3. Pump P1 flow controller is adjusted to give a constant flow rate of de-ionized water into the reactor R1 at approximately 700 ml/min at Fl-01. 4. Let the de-ionized water to continue flowing through the reactor until the inlet (Ql01) and outlet (Ql-02) conductivity values are stable at low levels. Both conductivities values are recorded. 5. Valve V9 is closed and pump P1 is switch off. 6. Valve V11 is opened and Pump P2 is switch on. The timer is started simultaneously. 7. Both the inlet (Ql-01) and outlet (Ql-02) conductivity a value at regular intervals of 30 seconds is start recorded. 8. The conductivity values is continue recording until all readings are almost constant.
APPARATUS AND MATERIALS
Tubular flow reactor
Deionized water
Sodium hydroxide
Ethyl acetate
RESULTS AND CALCULATIONS
Experiment 1: Pulse input in Tubular Flow Reactor Flow rate : 700mL/min Input type : Pulse input Time (min)
Conductivity (mS/cm) Inlet 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Outlet 0.0 0.0 0.2 1.8 2.1 1.1 0.1 0.0 0.0
Outlet conductivity vs Time Outlet COnductivity (mS/cm)
2.5 2 1.5 1
Conductivity (mS/cm) Outlet
0.5 0 0
1
-0.5
∫
( )
2
Time(min)
= Area under the graph
Area = ( - ) [
( )
3
( )
]
For time (1.0-1.5) minutes
4
5
Area = (
)[
(
)
]= 0.5 g .min
)
]= 0.975 g .min
] = (1.5– 1.0)[
For time (1.5 – 2.0) minutes
Area = (
)[
(
] = (2.0– 1.5)[
For time (2.0 – 2.5) minutes
Area = (
)[
(
)
] = (2.5– 2.0)[
]= 0.8 g .min
)
] = (3.0– 2.5)[
]= 0.3 g .min
For time (2.5 – 3.0) minutes
Area = (
So the total area or ∫
)[
(
( )
= ( 0.5+ 0.975 + 0.8 + 0.3) = 2.575 g.min/m3 ( )
For t = 0, C(t) = 0.0 ( ) For t = 0.5, C(t) = 0.0 ( ) For t = 1.0, C(t) = 0.2 ( ) For t = 1.5, C(t) = 1.8 ( ) For t = 2.0, C(t) = 2.1 ( )
∫
( ) ( )
For t = 2.5, C(t) = 1.1 ( ) For t = 3.0, C(t) = 0.1 ( ) For t = 3.5, C(t) = 0.0 ( ) For t = 4.0, C(t) = 0.0 ( )
Time (min) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Conductivity Outlet 0.0 0.0 0.2 1.8 2.1 1.1 0.1 0.0 0.0
E(t) 0.0 0.0 0.07767 0.69903 0.81553 0.42718 0.038833 0.0 0.0
Residence time distribution (RTD) function for plug flow reactor
E(t)
E(t) vs Time 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -0.1 0
E(t)
1
2 3 Time(minutes)
4
5
For time (0 – 0.5)minutes = 0 For time (0.5 -1.0)minutes Area = (
)[
(
)
(
)
] = (1.5– 1)[
] = 0.19418
)
] = (2 – 1.5)[
] = 0.37864
(
)
] = (2.5 – 2)[
]= 0.310678
(
)
]
(
)
] = (1– 0.5)[
]= 0.019418
For time (1 – 1.5) minutes Area = (
)[
For time (1.5 – 2.0 )minutes Area = (
)[
(
For time (2.0 – 2.5) minutes Area = (
)[
For time (2.5 -3.0) minutes Area = (
)[
] = (3– 2.5)[
For time (3 -3.5) minutes Area = (
)[
] = (3.5- 3)[
]= 0.0097083
∫
( )
= Total area under the graph = (0.019418 + 0.37864 +0.310678 +
+
0.0097083 =0.834947 ( )
∫ time
Outlet
(min)
conductivity
E(t)
= 4(0.834947)= 3.339788
tE(t) (t-tm)2E(t)dt
(t-tm)3E(t)dt
(mS/cm) 0
0
0
0
0
0
0.5
0.0
0.0
0.0
0
0
1
0.2
0.077670
0.077670
0.425213
-0.994908
1.5
1.8
0.699903
1.049855
2.369046
-4.358542
2
2.1
0.815530
1.631060
1.463902
-1.961319
2.5
1.1
0.427180
1.067950
0.301266
-0.252999
3
0.1
0.038833
0.116499
0.004483
-0.001523
3.5
0.0
0.0
0.0
0
0
4
0.0
0.0
0.0
0
0
∑ =2.05912
∑=3.943034
∑=4.604257
∑=-7.56929
Mean residence time,
( )
∫
3.943034
=∫ (
Second moment, variance ,
) E(t) dt
= 4.604257 ∫ (
Third moment, skewness,
=
(
)
) E(t) dt (-7.56929) = -2.40816
Experiment 2: Step Change Input in a Turbular Flow Reactor Flow rate
= 700 mL/min
Input type : Step change Time (min)
Conductivity (mS/cm) Inlet 0.0 2.7 2.8 2.8 2.8 2.7 2.7 2.6 2.6
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
outlet 0.0 0.0 0.0 0.0 0.0 1.3 1.6 1.6 1.6
Outlet Conductivity vs Time 1.8 Outlet conductivity (mS/cm)
1.6 1.4 1.2 1 0.8
Conductivity (mS/cm) outlet
0.6 0.4 0.2 0 -0.2 0
1
2 3 Time(min)
4
5
σ2
s3
(t - tm) 2 * E(t)/
(t - tm) 3 * E(t)/
0.00000
0.00000
0.00000
0.00000
0.00000
0.00000
0.00000
0.0000
0.00000
0.00000
0.00000
0.00000
0.0
0.0000
0.00000
0.00000
0.00000
0.00000
2.8
0.0
0.0000
0.0000
0.0000
0.0000
0.0000
2.50
2.7
1.3
3.25
0.16209
0.02021
0.049713
0.12328
3.00
2.7
1.6
4.80
0.23940
0.03582
0.104910
0.31097
3.50
2.6
1.6
5.6
0.27930
0.04876
0.165923
0.57264
4.00
2.6
1.6
6.4
0.31920
0.06368
0.246677
0.84963
∑=20.05
∑=1.0008
∑=0.16847
∑= 0.567223
Time (min)
Conductivity (mS/cm)
C(t)
E(t)
tm
Inlet
Outlet
Ci∆t
0.00
0.0
0.0
0.0000
0.00000
0.50
2.7
0.0
0.0000
1.00
2.8
0.0
1.50
2.8
2.00
Ci(∆t)/∑Ci(∆t) t*E(t)/
Residence time distribution (RTD) function for plug flow reactor
E(t) vs Time 0.35 0.3 0.25
E(t)
0.2 0.15
E(t)
0.1 0.05 0 -0.05
0
1
2 Time(min)
3
4
5
∑=1.85652
SAMPLE OF CALCULATION ∫
()
So based on the table, Area is 20.05m2 Example of calculation at t=0.00min ()
(
)
( )
(
(
(
)
)
( )
)
DISCUSSION Firstly, the objective that need to be achieve for this tubular reactor experiment is to examine the effect of a pulse input and step change in a tubular reactor and also to construct the residence time distribution (RTD) function for the tubular flow reactor at the end of the experiment. The experiment was run at the 700 mL/min of flowrate. While the experiment is running, the conductivity for the inlet and outlet of the solution had been recorded at the period of time where until the conductivity of the solution is constant. For a tubular reactor, the flow that throught the vessel is continuous, usually at the steady state and also configured thus the conversion of the chemicals and other dependent variables are functions of position within the reactor rather than of time. For this experiment, we are examined the effects of flow for two types of reaction which are in pulse input and step change. The flowrate of solution is kept constant at 700 ml/min. For this types of experiments, the graph of outlet conductivity versus times had been plotted. Based on graph of pulse input, the outlet conductivity that had been plotted is 2.1 mS/cm at time of 2 minutes which are the highest value. After that, the conductivity is decrease within the time and comes to be constant at the time of 3.5 minutes. From the result, it showed that it result was not differ from the theory that recorded that the conductivity is reaching zero at time of 4 minutes. Thus, the experiment 1 is succeed. In addition, for the graph of step change the outlet conductivity is increase within the time by started at time of 2.0 minutes which it inlet conductivity is 2.8 mS/min and then undergoes some increament until at minutes 4.0 which the outlet conductivity is 1.6 mS/min. There are differences between both of the graph where the outlet conductivity for step change is increase smoothly compare to pulse input where the outlet conductivity is increase at the some period of times and then it become decrease into the constant value. Next experiment, to construct the residence time distribution (RTD) function for the tubular flow reactor for pulse input and also step change. The residence time distribution is plotted based on exit time (E(t)) versus time from the data that had been recorded in the table. From the graph plotted, it almost same with the graph that are stated at the theory.
From the graph, it can be concluded tha the residence time distribution is depends on the outlet conductivity. For the pulse input graph, the residence time distribution calculated is 3.339788 minutes. besides, there are 3 data that had been obtained and calculated which are mean residence time,
tm
variance (second moment),σ2 and skewness (third moment),s3 that
recorded 3.943034, 4.604257 and -2.40816 respectively. The skewness for the pulse input give a negative value and it called negative skew. Compare ot the step change, the graph almost same to the outlet conductivity versus time which the residence time distribution (RTD) is increase within the time. For the step change, the mean residence time distribution that calculated is 0.02021 minutes. The other 2 data are also need to be calculate which are variance (second moment), σ2 and skewness (third moment), s3 are 0.049713 and 0.12328 respectively. The skewness give a positive value and it called positive skew compare to pulse input.
CONCLUSION From the experiment, we able to examine the effect of the pulse input and step change in a tubular flow reactor and we also can differentiate both of the effect. Besides, we also able to construct the residence time distribution (RTD) function for the tubular flow reactor. The conductivity for inlet and outlet after 3 minutes for pulse input are 0.00 mS/min and 0.1 mS/min while for the step change is 2.7 mS/min and 1.6 mS/min respectively. The outlet conductivity, C(t) that had been calculated for pulse input is 2.575 and for step change is 20.05. The distribution of exit time, E(t) is calculated for each 30 second until 4 minutes interval. The sum of E (t) for pulse input and step change are 2.05912 and 1.0008 respectively. The mean residence time, tm for pulse input is 3.943034 minutes and step change is 0.16847 minutes. The variance, σ2 and skewness, s3 are also calculated. For pulse input are 4.604257 and -2.4081 while for step change are 0.567223 and 1.85652. graph for outlet conductivity, C (t) against time and distribution of exit time, E (t) against time are plotted. The graph plotted almost the same as the theory which stated that exit time, E (t) is depends on the value of C (t).
RECOMMENDATION I.
Each experiment we must do the start-up and shut-down experiment first in order to make sure there are no left over in the chamber.
II.
Open and close the valve carefully according to the procedure given.
III.
The experiment should be conducted at the stable and unshaken place.
IV.
Make sure there are no leakages at the equipment.
REFERENCES:
(K. G. Denbigh, Chemical Reactor Theory: An Introduction, 41-45)
(Artin
hatzikioseyian,
Emmanouela
Remoundaki,http://www.metal.ntua.gr/~pkousi/e-learning/bioreactors/page_07.htm
http://www.neduet.edu.pk/Chemical/PDF/CHEMICAL%20REACTION%20ENGINEE RING%20LAB.pdf
Turbular
Reactor.
(n.d.).
Retrieved
April
2013,
from
Scrib:
http://www.scribd.com/doc/95675475/Turbular-Reactor
Wikipedia. (n.d.). Retrieved April 2013, from Plug Flow Reactor Model: http://en.wikipedia.org/wiki/Plug_flow_reactor_model
http://www.metal.ntua.gr/~pkousi/e-learning/bioreactors/page_07.htm
http://en.wikipedia.org/wiki/Residence_time_distribution
APPENDICES:
