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CONTINOUS STIRRED TANK REACTOR (CSTR)
Based on the title, this experiment had done in order to fulfil the syllabus of Chemical Engineering Laboratory subject. Thus, the members of the group should to know more detail about the Continuous Stirrer Tank Reactor (CSTR) and to carry out the operation for the saponificaton of Sodium Hydroxide, NaOH and ethyl acetate, Et(Ac). The objectives of the experiment were to determine the reaction constant, k and to study the saponification reaction between NaOH and ethyl acetate. The reaction rate, rA was measured throughout 5 minutes interval for 25 minutes. Then the samples that added with hydrochloric acid, HCL and two drops of phenolpthalein indicator were titrated until the solution become light pink .. The reaction constant, k was obtained from slope of graph of 1/Ca vs. time The results obtained were according to the theory All the objectives were achieved. The values of the reaction constant were obtained. The experiments were supposed to be conducted carefully so that the results obtained for calculation are correct.
2.1 What Is The Continous Stirred Tank Reactor (CSTR) And How Does Its Function?
The continuous stirred tank reactor (CSTR) is also known as vat- or backmix reactor, is a common ideal reactor type in chemical engineering. CSTR are open systems, operate at steady state basis, where the conditions in the reactor do not change with time. Reactants are continuously fed into the reactor and the products are continously removed. A CSTR often refer to a model to estimate the key unit operation variable when using a continuous agitated tank reactor to reach a specified output. 
All calculation performed in CSTR are assume perfect mixing. In a perfect mixed reactor, the output composition is identical to composition of the material inside the reactor, which is a fuction of residence time and rate of reaction.
2.2 Application Of Continous Stirred Tank Reactor (CSTR) In Industries And Various Field.
Continous Stirred Tank Reactor are commonly used in industrial processing, primarily homogenous liquid-phase flow reactions, where constant agitation is required. They may be used by themselves, in series, or in battery. CSTR are also used in the pharmaceutical industy as a loop reactor when heated, pressurized fluid enter it and etc. A dimple jacketed pressure vessel is shown in the diagram 2.2.1 and half jacket reactor in the diagram 2.2.2.
Diagram 2.2.1 : Dimple Jacketed Pressure Vessel Diagram 2.2.2 : Half Jacket Reactor
CSTR like the diagram 2.2.3 below are always used in biological processes, such as cell cultures. The CSTR shown below can be used for high density animal cell culture in research or production. The vessels use are for single use.
Diagram 2.2.3 : CSTR use in biological processes
Fermentors are CSTRs used in biological processes in many industries, such as brewing, antibiotics, and waste treatment. In fermenters, large molecules are broken down into smaller molecules, with alcohol produced as by- product. The industrial fermentor on the figure 2.2.4 has a capacity 500 L and diagram 2.2.5 holds on 3.0 L.
Diagram 2.2.4 : 500 L capacity fermentor Diagram 2.2.5 : 3.0 L capacity fermentor
2.3 Advantages and Disadvantages of Continous Stirred Tank Reactor (CSTR)
CSTR is easiy maintained because its works as good temperature controller. Furthermore, CSTR is cheap to construct as well as has large heat capacity. In addition, the interior reactor is easily accessed.
The disadvantage of CSTR is the conversion of reactant to product per volume of the reactor is small compared to the other flow reactors.
Firstly, th objective of this experiment are to determine the reaction rate constant, k for batch reaction. Furthermore, to study saponification of ethyl acetate and sodium hydroxide.
4.1 IDEAL STIRRED-TANK REACTOR
A stirred-tank reactor (STR) may be operated either as a batch reactor or as a steady-state flow reactor (better known as Continuous Stirred-Tank Reactor (CSTR)). The key or main feature of this reactor is that mixing is complete so that properties such as temperature and concentration of the reaction mixture are uniform in all parts of the vessel. Material balance of a general chemical reaction is described below.
The conservation principle required that the mass of species A in an element of reactor volume V obeys the following statement:
Rate of A
Rate of A
Rate of A
Rate of A
4.2 BATCH STIRRED-TANK REACTOR (BSTR)
In batch reactions, there are no feed or exit streams and therefore equation (1) can be simplified into:
Rate of A
Rate of A
The rate of reaction of component A is defined as:
-rA = 1/V (dNA/dt) by reaction = [moles of A which appear by reaction]
[unit volume] [unit time]
By this definition, if A is a reaction product, the rate is positive; whereas if it is a reactant which is consumed, the rate is negative.
(-rA) V = NAO dXA
Integrating equation gives,
t = NAO dXA__
where t is the time required to achieve a conversion XA for either isothermal or non-isothermal operation.
1/-rAArea = t1/-rAArea = t
Area = t
Area = t
4.3 EFFECT OF TEMPERATURE ON RATE OF REACTION
As we increase the temperature the rate of reaction increases. This is because, if we heat a substance, the particles move faster and so collide more frequently. That will speed up the rate of reaction. Collisions between molecules will be more violent at higher temperatures. The higher temperatures mean higher velocities. This means there will be less time between collisions. The frequency of collisions will increase. The increased number of collisions and the greater violence of collisions result in more effective collisions. The rate for the reaction increases. Reaction rates are roughly doubled when the temperature increases by 10 degrees Kelvin.
In any single homogenous reaction, temperature, composition and reaction rate are uniquely related. They can be represented graphically in one of three ways as shown in figure 4.3 below:
Figure 4.3 : the graphically related between homogenous reaction, temperature and reaction rate
Tube in taking the sampleTube in taking the samplereactorreactorController such as switch of pumpController such as switch of pump1) Continuous Stirred Tank Reactor (MODEL BP 100)
Tube in taking the sample
Tube in taking the sample
Controller such as switch of pump
Controller such as switch of pump
2) 0.1 M ethyl acetate – for reaction
3) 0.1 M and 0.25 M NaOH. – for reactor and titration respectively
4) 0.25 M HCL – for titration
5) Conical flask – used in titration
6) Burette – put of NaOH during titration and being put on the retort stand
7) Phenolphthalein – as the indicator in titration( the solution will turn light pink)
8) measuring cylinder – to measure the sample or used of solution to get correct calibration.
In the reactor
Firstly, before starting the experiment, the tank that contains of ethyl acetate and NaOH must be checked. Then, the experiment is started to fill the reactor with NaOH and ethyl acetate. The pump 1 is switched on to pump the ethyl acetate until reaches 1.25 liters or reaches the line that being marked on the reactor. Finished to fill with ethyl acetate then fill the reactor with NaOH by switch on the pump 2. This pump 2 is being switched on for the NaOH solution being pump until the solution reaches mark of 2.5 liters. The stirrer will be switched on and the speed be set at 180 rpm. The timing will be immediately started. At time t=1 minutes, the samples being taken about 50 mL by opened the valve 7 and the titration will be done. Then, the timing is reset for 5, 10, 15, 20 and 25 minutes. An example will be taken for the time taken. All of the sample will be titrated.
Firstly, 10 mL of HCL is put inside the conical flask and added 3 drops of phenolphthalein. After that, the sample that being taken will be mixed with this solution. Then, it is being titrated with NaOH until reaches light pink. The data for used of NaOH during titration was recorded.
7.1 The feed concentration, standard solution concentration with volume and volume of sample used.
Conc. of NaOH = 0.05 moles/liter
Conc. of Ethyl Acetate = 0.1 moles/liter
Conc. of HCl = 0.25 moles/liter
Volume of HCl = 10 moles/liter
Conc. of NaOH = 0.1 moles/liter
Volume of sample = 50 ml
Table 7.1 : The feed concentration, standard solution concentration with volume and volume of sample used.
7.2 The volume of Sodium Hydroxide needed to neutralize the sample solution
Volume of titrating NaOH (ml)
Volume of Quenching HCl Unreacted with NaOH in Sample (ml)
Volume of HCl Reacted with NaOH in Sample (ml)
Mole of HCl Reacted with NaOH in Sample
Mole of NaOH Unreacted in Sample
Table 7.2: The volume of Sodium Hydroxide needed to neutralize the sample solution
7.3 The concentration and mole fraction af reacted and unreacted sodium hydroxide,NaoH with Ethyl Acetate
Concentration of NaOH Unreacted with Ethyl Acetate (moles/litre),CA
Steady state Fraction Conversion of NaOH, XA
Concentration of NaOH Reacted with Ethyl Acetate (moles/litre)
Mole of NaOH Reacted with Ethyl Acetate in Sample
Concentration of Ethyl Acetate Reacted with NaOH (moles/litre)
Concentration of Ethyl Acetate unreacted (moles/litre)
Table 7.3: The concentration and mole fraction af reacted and unreacted sodium hydroxide,NaoH with Ethyl Acetate
Figure 7.3.1: Graph of 1/CA vs time (min)
Rate constant, k (Lmol-1min-1) = 25.304
8.0 SAMPLE CALCULATION
Volume of Quenching HCl Unreacted with NaOH in Sample (ml) :
= CNaOH,stdCHCl,std× Volume of titrating NaOH (ml)
Volume of HCl Reacted with NaOH in Sample (ml) :
=VHCl- Volume of Quenching HCl Unreacted with NaOH in Sample (ml)
Mole of HCl Reacted with NaOH in Sample :
= CHCl,std × Volume of HCl Reacted with NaOH in Sample (ml)
Mole of NaOH Unreacted in Sample = Mole of HCl Reacted with NaOH in Sample
Concentration of NaOH Unreacted with Ethyl Acetate (moles/litre) :
= Mole of HCl Reacted with NaOH in Sample Vs ×1000
Steady state Fraction Conversion of NaOH, XA :
=1 - Concentration of NaOH Unreacted with Ethyl Acetate (moles/litre)CAO
=1 - 0.01860.05
Concentration of NaOH Reacted with Ethyl Acetate (moles/litre) :
= CNaOH,o- Concentration of NaOH Unreacted with Ethyl Acetate moleslitre
Mole of NaOH Reacted with Ethyl Acetate in Sample :
= Concentration of NaOH Reacted with Ethyl Acetate moleslitre× Vs
Concentration of Ethyl Acetate Reacted with NaOH (moles/litre) :
=Mole of NaOH Reacted with Ethyl Acetate in Sample Vs
Concentration of Ethyl Acetate unreacted (moles/litre) :
= CEA,o- Concentration of Ethyl Acetate Reacted with NaOH moleslitre
NaOH + Et(Ac) Na(Ac) + EtOH
The experiment was carried out by using special hydroxide and ethyl acetate. Inside the reactor, the saponification of sodium hydroxide and ethyl acetate producing sodium acetate and ethanol. Order of the reaction is based on the powers of the concentration which are raised in the kinetic law. Based on result and the sample of calculation, the value of data was fitted to second order reaction.
From Arrhenius's equation, k = Ae-E/RT it show that the temperature has an effect to the reaction rate constant. It states that when the rate constant doubles, so wills the rate of reaction. The higher the temperature the faster the molecules move producing much more kinetic energy than normal. More collision is happen in order for a reaction to occur and thus larger fraction of molecules to provide the activation energy needed for the reaction. Activation energy, Ea is the minimum energy needed for the reaction to occur.
Therefore, the rate law for this experiment is:
-dCa/dt = kCa2
The time taken for each sample taken is from the first minute the time started and followed by the next 5th minute, 10th minute, 15th minute, 20th minute, and 25th minute. The volume of titrating sodium hydroxide to calculate the amount of quenching hydrochloric acid, phenolphthalein is used to be indicator of the mixture to be in neutral condition. Volume of quenching hydrochloric acid unreacted with sodium hydroxide in sample is calculated using the amount of sodium hydroxide titrated with the mixture.
The slopes of the graph are representing the specific reaction rate constant, K. K constant can be obtained by considering all the data obtained throughout the experiment. Based on the calculation, K can be calculated.
Since the reaction is second order, the reaction rate by the rate law is in the form of -ra =kCACB. Then for this experiment, the volume of quenching HCL unreacted with NaOH ins sample (ml) is 6.28 ml, 8.48 ml, 9.20 ml, 9.48 ml, 9.60 ml and 10.00 ml. Next, the volume of HCL reacted with NaOH in sample (ml) is 3.72 ml, 1.52 ml, 0.80 ml, 0.52 ml, 0.40 ml and 0.00 ml respectively.
The volume of titrating NaOH for experiment A was increased from 15.7 ml, 21.2 ml, 23.0 ml, 23.7 ml, 24.0 ml and 25.0 ml. That means the higher the concentration of HCL, the more volume of NaOH is needed to neutralize the mixture.
After calculating all the data obtained, values of constant k can be known. From the graph, the value k is 25.304 Lmol-1min-1.
After the experiment has been done and the parameters needed is found, a conclusion for this experiment had been made. The objective of this experiment obtained successfully. First and foremost, this reaction is a 2nd order. Therefore, the reaction rate by the rate law is in the form of -ra=kCACB. The second conclusion is that from the graph, the value k is 25.304 Lmol-1min-1.
In this experiment there have certain things that need to be considered on to get most accurate data and some suggestion to increase the accuracy. Firstly, the solution in reactor need to be sure completely mixed before the sample is taken. This is to prevent the error while doing the titration.
Secondly, while handling this chemical, student should use the gloves and googles if need. Then, when titration, make sure the 10 mL of HCL must be put into the conical flask and added with 3 drops of phenolphthalein then put the sample from the reactor. The titration need to be done carefully until it reaches the light pink.
Before taking the sample from the reactor, when opened the valve 7 the sample need to be throw a little bit then it can be taken for 50 mL. This is to prevent if the sample that contain in tube is not the best sample in the reactor.
Make sure all the flask, apparatus that involved in titration process is cleaned from chemicals because it will affect the titration results. Then, wait until the system stable before taking the reading, because sometimes, the system is not well reacted, but students already take the readings.
Furthermore, make sure all valves are in their right positions before starting the experiments to prevent any damages into the equipment. Before taking the sample, make sure flush the products a little bit, just to ensure there are no previous product in the outlet stream
Last but not least, do not let the temperature shoot higher or lower than the temperature needed. Make sure the temperatures are well controlled.
 Schmidt, Lanny D. (1998). The Engineering of Chemical Reactions. New York : Oxford University Press.
 Fogler, Scott H. Elements of Chemical Reaction Engineering, 3rd Edition, Englewood Cliffs,NJ : Prentice- Hall, 1998 , pp.180-191
 Wales, Stanley M. Chemical Process Equipment: Selection and Design. Boston : Butterworth- Heinemann, 1990, pp 578-595
 Perry, Robert H, and Don W. Green. Perry's Chemical Engineers' Handbook. 7th Edition, New York : McGraw- Hill Inc., 1997, pp 177-179
 Rate Constants and The Arrhenius Equation. Retrieved on APRIL 1, 2016 from http://www.chemguide.co.uk/physical/basicrates/arrhenius.html
(data refer to the last page)
Continous Stirred Tank Reactor (CSTR)
Titration Process of Sodium Hydroxide and Sample solution
The colour of the solution become light pink or pale pink
TABLE OF CONTENTS
1.0 ABSTRACT/SUMMARY 1
2.0 INTRODUCTION 2
2.1 What Is The Continous Stirred Tank Reactor (CSTR) And How Does Its Function? 2
2.2 Application Of Continous Stirred Tank Reactor (CSTR) In Industries And Various Field. 2
2.3 Advantages and Disadvantages of Continous Stirred Tank Reactor (CSTR) 4
3.0 OBJECTIVES 4
4.0 THEORY 5
4.1 IDEAL STIRRED-TANK REACTOR 5
4.2 BATCH STIRRED-TANK REACTOR (BSTR) 5
4.3 EFFECT OF TEMPERATURE ON RATE OF REACTION 7
5.0 APPARATUS 8
6.0 PROCEDURE 9
6.1 In the reactor 9
6.2 During titration 9
7.0 RESULT 10
7.1 The feed concentration, standard solution concentration with volume and volume of sample used. 10
7.2 The volume of Sodium Hydroxide needed to neutralize the sample solution 11
7.3 The concentration and mole fraction af reacted and unreacted sodium hydroxide,NaoH with Ethyl Acetate 11
8.0 SAMPLE CALCULATION 13
9.0 DISCUSSION 15
10.0 CONCLUSION 17
11.0 RECOMMENDATION 17
12.0 REFERENCES 18
13.0 APPENDICES 19
1/CA vs time (min)
y = 95.664x
R² = 0.9653