Continuous Stirred Tank Reactor (Cstr) in Series

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UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMA CHEMICAL ENGINEERING LABORATORY III

(CHE575)

NAME : RM SYIBLI MILASI B R MUHAMAD FAKIH

STUDENT NO. : 2004624828

EXPERIMENT : CONTINUOUS STIRRED TANK REACTOR (CSTR) IN SERIES

DATE PERFORMED : 7TH _{FEBUARY 2006}

SEMESTER :

DISEMBER 2005 – APRIL 2006 PROGRAMME / CODE :

Bachelor of Engineering (Hons.) in Chemical Engineering / EH220

Remarks:

Checked by: Rechecked by: DR.RUZITAH

No. Title Allocated marks % Marks %

1 Abstract/Summary 5 2 Introduction 5 3 Aims/Objectives 5 4 Theory 5 5 Procedures 3 6 Apparatus 5 7 Results 20 8 Calculations 10 9 Discussions 20 10 Conclusions 10 11 Recommendations 5 12 References 5 13 Appendices 2 TOTAL 100

PK.FKK.PPM.MANUAL MAKMAL CHE565 (0)

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of the conductivity are stable enough where the readings of the conductivity are quit similar from one to another. After that, readings are continuously taken every 3 minutes until to the point that the conductivity values for the three reactors are closed to each other. Then the graph of the conductivity versus time was plotted

The graph that has been plotted is accordingly to the theory. From the graph we can determine the effect of the step change and pulse input to the concentration.

INTRODUCTION

In the majority of industrial chemical process, a reactor is the key item of equipment in which raw materials undergo a chemical change to form desired product. The design and operation of chemical reactors is thus crucial to the whole success of the industrial operation.

Reactors can widely form, depending on the nature of the feed materials and the products. Understanding non-steady behavior of process equipment is necessary for design and operation of automatic control systems. One particular type of process

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equipment is the continuous stirred tank reactor. In this reactor, it is important to determine the system response to a change in concentration. This response of concentration versus time is an indication of the ideality of the system.

OBJECTIVES

1. To determine the effect of step changes and pulse input to the concentration. 2. To determine the effect residence time on the response curve.

THEORY

General Mole Balance Equation

Assumptions

1) Steady state therefore

2) Well mixed therefore rA is the same throughout the reactor

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In terms of conversion

Reactors in Series

Given -rA as a function of conversion, , -rA = f(X), one can also design any

sequence of reactors in series provided there are no side streams by defining the overall conversion at any point.

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Mole Balance on Reactor 2

Given -rA = f(X) the Levenspiel Plot can be used to find the reactor volume

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Effect of Step Change in Input Concentration to the Concentration of Solute in Stirred Tank Reactors in Series.

When a step change of solute concentration is introduced at the feed of tank 1, the tank in series will experience a transient behavior as a Figure 7 below. The response will be dependent on the residence time of each reactor in series.

Concentration Concentration

Time Time Figure 8a. Step change input Figure 8b . Transient response of tank in series to the step input.

Effect of Pulse in Input Concentration to the Concentration of Solute in Stirred Tank in Series.

Reactor 1

Reactor 2

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Reactor 2 Reactor 1

Reactor 3

When a pulse input of solute concentration is introduced at the feed of tank 1, the transient behavior will be different than the step change input due to the

diminishing concentration from the input after pulsing as described in Figure 8.

Time Time Figure 8a: Pulse input Figure 8b: Transient response of tank in series to the pulse input.

PROCEDURES

Experiment 1: The Effect of Step Change Input

In this experiment a step-change input would be introduced and the progression of the tracer will be monitored via the conductivity measurements in all the three reactors.

• Tank 1 and tank 2 was filled up with 20L feeds deionised water.

• 300g of Sodium Chloride was dissolved in tank 1until the salts dissolve entirely and the solution is homogenous.

• Three way valve (V3) was set to position 2 so that deionised water from tank 2 will flow into reactor 1.

• Pump 2 was switched on to fill up all three reactors with deionised water.

• The flow rate (Fl1) was set to 150 ml/min by adjusting the needles valve (V4). Do

C o n ce n tr a ti o n C o n ce n tr a ti o n

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not use too high flow rate to avoid the over flow and make sure no air bubbles trapped in the piping. The stirrers 1, 2 and 3 were switched on.

• The deionised water was continued pumped for about 10 minute until the conductivity readings for all three reactors were stable at low values.

• The values of conductivity were recorded at t0.

• The pump 2 was switched off after 5 minutes. The valve (V3) was switched to position 1 and the pump 1 was switched on. The timer was started.

• The conductivity values for each reactor were recorded every three minutes.

• Record the conductivity values were continued until reading for reactor 3 closed to reactor 1.

• Pump 2 was switched off and the valve (V4) was closed.

• All liquids in reactors were drained by opening valves V5 and V6.

Experiment 2: The Effect of Pulse Input

In this experiment a pulse input would be introduced and the progression of the tracer will be monitored via the conductivity measurements in all the three reactors.

• Tank 1 and tank 2 was filled up with 20L feeds deionised water.

• 300g of Sodium Chloride was dissolved in tank 1until the salts dissolve entirely and the solution is homogenous.

• Three way valve (V3) was set to position 2 so that deionised water from tank 2 will flow into reactor 1.

• Pump 2 was switched on to fill up all three reactors with deionised water.

• The flow rate (Fl1) was set to 150 ml/min by adjusting the needles valve (V4). Do not use too high flow rate to avoid the over flow and make sure no air bubbles trapped in the piping. The stirrers 1, 2 and 3 were switched on.

• The deionised water was continued pumped for about 10 minute until the conductivity readings for all three reactors were stable at low values.

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• The pump 2 was switched off after 5 minutes. The valve (V3) was switched to position 1 and the pump 1 was switched on. The timer was started.

• Let the pump 1 to operate for 5 minute, and then switched off pump 1. Switched the three ways valve (V3) back to position 2. The pump 2 was switched on.

• The conductivity values for each reactor were recorded every three minutes.

• Record the conductivity values were continued until reading for reactor 3 closed to reactor 1.

• Pump 2 was switched off and the valve (V4) was closed.

• All liquids in reactors were drained by opening valves V5 and V6.

APPARATUS

1. Distillation water 2. Sodium Chloride

3. Continuous reactor in series 4. Stirrer system

5. Feed tanks 6. Waste tank 7. Dead time coil 8. Computerize system 9. Stop watch

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SAMPLE OF CALCULATION

Vi = FA0 (XA,i - X A,i-1) / (-rA)i

Where Vi = volume of reactor i

F A,i = molal flow rate of A into the first reactor

XA,i = fractional conversion of A in the reactor i

XA,i-1 = fractional conversion of A in the reactor i-1

For first order reaction, -rA = k CA,I = kCA0 (1 – XA,i)

v = volumetric flow rate of A = 150mil/min = 0.15 liter/min For the first reactor: (V = 20 lit)

(-rA)1 = (kCA)1 = kCA,1 = k CA0 (1 – XA,1) CA0 = FA0 / v i.e., FA0 = vCA0 XA,i-1 = XA,0 = 0 Therefore, Tank 1 Vi = FA0 (XA,i – XA,i-1) / (-rA)i 20 = 0.15 (XA,1 – 0) / (0.158 x (1 – XA,1)) XA,1 = 0.95 Tank 2 Vi = FA0 (XA,i – XA,i-1) / (-rA)i 20 = 0.15 (XA,1 – 0.95) / (0.158 x (1 – XA,1)) XA,1 = 0.997 Tank 3 Vi = FA0 (XA,i – XA,i-1) / (-rA)i 20 = 0.15 (XA,1 – 0.997) / (0.158 x (1 – XA,1))

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XA,1 = 0.998

Discussion

In this experiment our objective is to determine the effect of step change and pulse input to the concentration in a continues stirred tank reactor in series. For that we have 2 experiment 1st_{the step change and 2}nd_{is the pulse input.}

We take the reading of the conductivity for the 3 different tanks for every 3 minutes and plotted graph conductivity versus time. For the 1st_{experiment the flow rate}

was 150 ml/min and we take 28 readings. We can see the effect of the step change to the concentration from the graph. Step change is a sudden change in a process variable. For this experiment our variable that been change is the input. Reactor feedstock is suddenly switched from one supply to another, causing sudden changes in feed concentration, flow, etc.

As we know the concentration can be calculated using electrical conductivity measurements and calibration supplied. The concentration is directly proportional to the conductivity.

The affect of the step change to the concentration for the 3 reactors are the same. When the step change of solute concentration was introduced at the feed of tank 1, the tank will experience a transient behavior as shown in the result. The concentration of in the reactor will increase in a period of time until it has reached a constant concentration. For every reactor it has its own concentration. Reactor 1 has the highest concentration following tank 2 and 3. The concentration if increasing because of the feed rate that been opened was the tank 1 that contain the dissolve chloride.

For the 2nd_{experiment the procedure is the same as experiment 1 except we}

change the pump from 1 to 2 and the flow rate was 200mil/min. For this experiment we want to see the effect of the pulse input. When we have plotted the graph we get a different result from the step change. The pulse input caused the concentration change drastically for every tank. For tank 1 the concentration decreased rapidly until it reaches a constant value. For tank 2 the concentrations 1st increase in a period of time then start decreasing until it reaches a constant value. For tank 3 the concentrations also increase and decrease but not rapidly. There are only a small different for every readings.

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The decreasing in the concentration happen because the feed was from tank 2 that contain only dissolve water without any sodium chloride.

Conclusions

From the experiment result it shows that a step change in input and a pulse in input have its own effect to the concentration. Each of this experiment has its own transient behavior. We compare the 1st_{graph and the 2}nd_graph.

For the 1st_{graph the change of the concentration for the 3 tank is almost the same.}

For the 2nd_{graph every tank has its own change of concentration. From both experiment}

we can conclude that change in input and pulse input has an effect to the concentration. For the step change it will increase the concentration until it reaches a constant value and for pulse input it will first increase then decrease until it reaches a constant value. The feed of the systems effect the concentration in the reactor, if the feed contain a

concentration then the concentration in the tank will increase and if the feed only contain deionised water then the concentration will decrease.

Every reactor has its own concentration, because of that we conclude that the residence time for each reactor is different. The value of the residence time depends on what happens in the reactor.

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Recommendations

After we have finished this experiment, we find that are several factors in this experiment that can be fixed to make sure that the experiment runs better. This is some of my recommendation for this experiment:

• When we are doing the experiment the program that used to record the data was not function. This cause us a high error in reading the data. My recommendation is to make sure better maintainers of the apparatus.

• The instruction in the lab manual for number 1,2 and 3 for both experiment is not clear and after we doing the experiment it seems that we did not follow the procedures 1,2 and 3. We just jump to step number 4, it cause us a waste of time and confusion. My recommendation is to make sure that the procedure is exactly the same as what we do in the experiment.

Reference

• Levenspiel, O, Chemical Reaction Engineering, John Wiley, 1972

• Robert H.Perry, Don W.Green, Perry’s Chemical Engineers’ Handbook, McGraw Hill,1998.

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Appendics

C1 C2

C3 Figure 5

Type of Reactor Characteristics

Continuously Stirred Tank Reactor (CSTR)

Run at steady state with continuous flow of reactants and products; the feed assumes a uniform composition throughout the reactor, exit stream has the same composition

as in the tank

Kinds of Phases Present

Usage Advantages Disadvantages

1. Liquid phase 2. Gas-liquid rxns 3. Solid-liquid rxns 1. When agitation is required 2. Series configurations for different concentration streams 1. Continuous operation 2. Good temperature control

3. Easily adapts to two phase runs

4. Good control 5. Simplicity of

construction

6 Low operating (labor) cost

1. Lowest conversion per unit volume 2. By-passing and channeling possible

Continuous Stirred Tank Reactor (Cstr) in Series

TABLE OF CONTENTS

ABSTRACT/SUMMARY……….….3

INTRODUCTION………...3-4

OBJECTIVES………4

THEORY………...4-8

PROCEDURES………..8-10

APPARATUS……….10

RESULTS………11-12

SAMPLE OF CALCULATIONS………13

DISCUSSION……….14-15

CONCLUSION……….15

RECOMMENDATION……….16

REFERENCES……….16

APPENDICES………...17

SUMMARY