INTRODUCTIONBased on all industrial sector, mostly reactor is the main equipment that are used where it changes from the raw materials into the desire product that are needed. The criteria for the good reactor is it produced a high production and also economical. There are many types of reactor depending on the nature of the feed materials and products. The rate of reaction is the most important thing that we are considered in the reactor because it showed the effectiveness of the processing of the reactor. A most common ideal reactor type in chemical engineering is the continuous stirred tank reactor or known as CSTR. In a continuous stirred tank reactor (CSTR), reactants and products are continuously added and withdrawn from the reactor. The CSTR is the idealized opposite of the weel-stirred batch and tubular plug flow reactors. Analysis of selected combination of these reactors types can be useful in quantitatively evaluating more complex gas-, liquid-, and solid-flow behaviours.need to know in the various chemical reaction was the rate of the reaction.By studying the saponification reaction of ethyl acetate and sodium hydroxide to form sodium acetate in a batch and in a continuous stirred tank reactor, we can evaluate the rate data needed to design a production scale reactor.A stirred tank reactor (STR) may be operated either as a batch reactor or as a steady state flow 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 described below.The conservation principle requires that the mass of species A in an element of reactor volume dV obeys the following statement:(Rate of A into volume element) - (rate of A out of volume element) + (rate of A produced within volume element) = (rate of A accumulated within vol. element)

Objectives :1. To carry out saponification reaction between NaOH and Et(Ac) in CSTR.2. To determine the effect of residence time onto the reaction extent of conversion.3. To determine the reaction rate constant.

THEORY

IDEAL STIRRED-TANK REACTORA 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 ARate of A Rate of A Rate of A

into-out of+produced =Accumulated

volumevolumewithin volumewithin volume

elementelementelementElement

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

produced =accumulated

within volumewithin volume

elementelement

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.Rearranging equation (3),(-rA) V = NAO dXA dtIntegrating equation (4) gives,t = NAO dXA__ (-rA)V where t is the time required to achieve a conversion XA for either isothermal or non-isothermal operation.

1/-rAArea = t

CA

EFFECT OF TEMPERATURE ON RATE OF REACTIONAs 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 below:

T

C r3 r2 r1

Continuous Stirred Tank Reactors (CSTR) CSTR runs 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.

General Mole Balance Equation

AssumptionsSteady state, therefore dNA/dt = 0Well-mixed therefore is the same throughout the reactor. Rearranging the generation, V = (FAo FA)/ -rA In terms of conversion, X = (FAo FA) / FAo V = (FAoX) / -rAA calibration curve is a method used in analytical chemistry to determine theconcentrationof an unknown sample solution. It is a graph generated by experimental means, with the concentration of solution plotted on the x-axis and the observable variable for example, the solutions absorbance plotted on the y-axis. The curve is constructed by measuring the concentration and absorbance of several prepared solutions, called calibration standards. Once the curve has been plotted, the concentration of the unknown solution can be determined by placing it on the curve based on its absorbance or other observable variable.

PROCEDURES

General start-up Procedures:1. The following solution were prepared:i- 40L of sodium hydroxide, NaOH (0.1 M)ii- 40 L of ethyl acetate, Et (Ac) (0.1M)iii- 1 L of hydrochloric acid, HCl (0.25M) , for quenching.2. All valves were initially closed.3. The feed vessels were charged as follows:i- The charge port caps for vessels B1 and B2 were opened.ii- The NaOH solution was carefully poured into vessel B1 and Et (Ac) solution was poured into vessel B2.iii- The charge port caps for both vessels were closed.4. The power for control panel was turned on.5. Sufficient water in thermostat T1 was checked. Refill as necessary.6. The overflow tube was adjusted to give a working volume of 10L in the reactor R1.7. Valves V2, V3, V3, V7, V8 and V11 were opened.8. The unit was ready for experiment.General shut-down Procedures:1. The cooling water valve V13 was kept open to allow the cooling water to continue flowing.2. Pumps P1 and pumps P2 were switched off. Stirrer M1 was switched off.3. The thermostat T1 was switched off. The liquid in the reaction vessel R1 was let to cool down to room temperature.4. Cooling water V13 was closed.5. Valves V2, V3, V7, and V8 were closed. Valves V4, V9 and V12 were opened to drain any liquid from the unit.6. The power for control panel was turned off.

Preparation of Calibration Curve for Conversion vs Conductivity:1. The following solution were prepared:i- 1 L of sodium hydroxide, NaOH (0.1M)ii- 1 L of sodium acetate , Et (Ac) (0.1M)iii- 1 L of deionised water, H2O.2. The conductivity and NaoH concentration for each valu were determined by mixing the following solution into 100 mL of deionised water.i- 0% conversion : 100 mL NaOHii- 25% cinversion : 75 mL NaOH + 25 mL Et (Ac)iii- 50% conversion : 50 mL NaOH + 50 mL Et (Ac)iv- 75% conversion : 23 mL NaOH + 75 mL Et (Ac)v- 100% conversion : 100 mL Et (Ac)Back Titration Procedures for Manual Conversion Determination:1. A burette was filled up with 0.1 M NaOH solution.2. 10 mL of 0.25 M HCl was measured in a flask.3. A 50 mL sample was obtained from the experiment and immediate the sample was added to the HCl in the flask to quench the saponification reaction.4. A few drops of pH indicator were added into the mixture.5. The mixture was titrated with NaOH solution from the burette until the mixture was neutralized. The amount of NaOH titrated was recorded.Effect of Residence Time of The Reaction in a CSTR:1. The general start-up procedures was performed.2. Pump 1 and pump 2 were switched on and valves V5 and V10 were opened to obtain the highest possible flow rate into the reactor.3. The reactor was filled up with both of the solution until it is njust bout to overflow.4. Valves V5 and V10 were readjusted to give a flow rate of about 0.1 L/min. the flow rate for both valves must be same. The flow rate were recorded into a data.5. The stirrer M1 was switched on and the speed was set about 200 rpm.6. The conductivity value at Q1 was started monitoring until id does not change over time. This is to ensure that the reactor has reached steady state.7. The steady state conductivity value was recorded and the concentration of NaOH and extent of conversion in the reactor was found out from the calibration curve.8. Sampling valve V12 was opened and 100mL of sample was collected. It directly proceed with the back titration procedures to manually determine the concentration of NaOH in the reactor and extent of conversion.9. The experiments was repeated (steps 5-9) for different residence times by adjusting the feed flow rate of NaOH and Et(Ac) to about 0.15, 0.20, 0.25, and 0.30 L/min. the flow rate for both must be same.

MATERIALS AND APPARATUS

1. Continuous stirred tank reactor. Model: BP 1432. 50 mL burette3. 200 mL beaker4. Conical flask5. Solution :I- Sodium hydroxide, NaOH (0.1M)II- Ethyl acetate, Et (Ac) (0.1M)III- Deionised waterIV- Phenolphthalein 6. Conductivity probe7. 100 mL measuring cylinder.

RESULTS

Reactor volume : 40 LConcentration of NaOH in feed tank : 0.1 MConcentration of Et(Ac) in fee tank : 0.1 M

NoFlowrate of NaOH (mL/min)Flowrate of of Et(Ac) (mL/min)Total Flowrate of Solutions (mL/min)Outlet Conductivity(m/S/cm)Amount of NaOH (mL)

10.110.100.212.1426.37

20.140.150.291.9526.23

30.200.210.411.8625.90

40.240.250.491.8025.87

50.290.300.591.7725.80

*amount of NaOH (average)Flowrate (L/min)Volume of NaOH (mL)

1 2 3Average amount of NaOH (mL)

0.1026.0 26.6 26.526.37

0.1525.9 26.5 26.326.23

0.2025.8 25.9 26.025.90

0.2525.9 25.8 25.925.87

0.3025.6 25.9 25.925.80

SAMPLE CALCULATIONS

F0 = 0.21 ml/mini- Concentration of NaOH that entering the reactor, CNaOH0.

CNaOHo = CNaOHf = (0.1) = 0.05 mol/L

ii- Volume of unreacted quenching HCl,V2

V2 = (CNaOHs / CHCls) x V1 = (0.1/0.25) x 26.37 = 10.548 mL

iii- Volume of HCl reacted with NaOHin sample, V3

V3 = VHCls V2 = 10 10.548 = 0.548 ml

iv- Moles of HCl reacted with NaOH in sample, n1

n1 = (CHCls x V3) / 1000 = 0.25 x 0.548 /1000 = 0.000137 mol

v- Moles of unreacted NaOH in sample, n2

n2 = n1 = 0.000137 mol

vi- Concentration of unreacted NaOH in the reactor, CNaOH

CNaOH = n2/Vs x 1000= 0.000137/50 x 1000= 0.00274 mol/L

vii- Conversion of NaOH in the reactor, X

X = (1- CNaOH / CNaOHo) x 100% = (1 0.00274/0.05) x 100% = 94.52 %

Flowrate of NaOH (mL/min)Conversion,X (%)Residence time (min)

26.3794.5247.00

26.2395.0834.48

25.996.4024.39

25.8796.5220.41

25.896.8016.95

Graph of conversion against Residence timeDISCUSSION

To achieve three objectives which are to carry out the saponification process between NaOH and Et (Ac) in a CSTR reactor, to determine the effect of the residence time onto the reaction extent of conversion and lastly to determine the constant rate of reaction. From the data collected, graph had been plotted is residence time versus conversion.From the graph, the conversion of NaOH is seen to be increasing as the time increase, this is true from the theoretical analysis of the CSTR reactor. For the saponification process, it is one kind of process to make a soap. Saponification process is a continuous reaction. In this experiment, the reaction of saponification is quenching with hydrochloric acid to stop the reaction. The reaction rapidly reacts in increasing of experiment. Back titration is done to investigate if the reaction is stop.

CONCLUSION

Based on the objectives of this experiment, which is to determine the residence time onto the reaction extent of conversion, the relationship conversion and residence time was directly proportional. But the reaction rates constant were determined for all varies flow rate. From the calculated data, the rate constant of reaction is increasing when the conversion is higher. The experiment that was conducted can be described as successful as it obey the theoretical analysis with little errors.

RECOMMENDATIONS

1. Make sure reactor does not have any leaks and valve closed and opened as needed, controlled the valve carefully and slowly when adjusting the flow rate to obtain 0.10 L/min. It is to make sure flow rate will stabilize and the experiment will run smoothly.2. Repeat titrations two or three times because a lot of error comes from titration or use another method other than titration.3. Divide into two teams which is the first team in charge of the CSTR 40 liters machine while the second team would carry out the back titration procedures.4. Take conductivity reading when the conductivity not changes in time because it can change rapidly in short of time.

REFERENCES

1. Levenspiel, O, Chemical Reaction Engineering, John Wiley, 19722. Robert H.Perry, Don W.Green, Perrys Chemical Engineers Handbook, McGraw Hill,1998.3. Smith,J.M, Chemical Engineering Kinetics, McGraw Hill, 1981.

APPENDICES1