AbstractThe conduction of this experiment is based on a few targets, namely to carry out saponification reaction between Sodium Hydroxide, NaOH and Ethyl Acetate, Et(AC), to determine the effect of residence time to the reaction's extent of conversion and lastly to evaluate the reaction rate constant of this particular saponification reaction. To achieve these targets, an experiment is finely designed so much so that these targets can be finely met. Such experiment involves using a unit called SOLTEQ Plug Flow Reactor (Model: BP 101), commonly known as PFR, as well as some common laboratory apparatus for titration process. To put it simply, the two solutions Sodium Hydroxide, NaOH and Ethyl Acetate, Et(Ac) were reacted in the PFR and the product is then analysed by the method of titration to determine how well did the reaction go. Hence, the experiment was conducted and the results shows that the amount of conversion of Sodium Hydroxide, NaOH is almost unchanged as residence time increases. Further details can be obtained in the results and discussion sections.

2.0 INTRODUCTION

Reactors are used in the chemical industry for millions of processes. There are many different types of reactors due to the numerous different factors that can control the formation of product during the reaction. Plug flow reactors are an idealized scenario where there is no mixing involved in the reactor. It is the opposite of the continuous-stirred tank reactor (CSTR), where the reaction mixture is perfectly mixed. The plug flow reactor has an inlet flow composed of the reactants. The reactant flows into the reactor and is then converted into the product by a certain chemical reaction. The product flows out of the reactor through the outlet flow. In many scenarios, a catalyst is involved in the reaction. A catalyst is a substance that is not involved in the chemical reaction but helps the reaction proceed at a faster rate. In biological reactions, an enzyme, which is a biological catalyst, coats the wall, and substrate is imported through the inlet flow.The Plug Flow Reactor (PFR) is an ideal flow reactor model in which plugs of fluid are assumed to move from the inlet to the outlet with no mixing or diffusion along the flow path. In an ideal PFR, 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 stimulus-response technique. The nature of the tracer peak gives an indication of the non-ideality that would be characteristic of the reactor under study. This equipment is designed to allow the study of the study of reaction rate constant and the effect of residence time on the conversion in a PFR. Residence time distributions are measured by introducing a non-reactive tracer into the system at the inlet. The concentration of the solution is changed according to a known function and the response is found by measuring the concentration of the solution at the outlet. The residence time distribution(RTD) of a chemical reactor is a probability distribution function that describes the amount of time a fluid element could spend inside the reactor.

3.0 OBJECTIVES

3.1 To carry out a saponification reaction between NaOH and Et(Ac) in a plug flow reactor.3.2 To determine the reaction rate constant.3.3 To determine the effect of residence time on the conversion in a plug flow reactor.

4.0 THEORY

4.1 Rate of Reaction and Rate Law

Simply put, rate of reaction can be roughly defined as the rate of disappearance of reactants or the rate of formation of products. When a chemical reaction is said to occur, a reactant(or several) diminishes and a product(or several) produced. This is what constitutes a chemical reaction. For example :

where A and B represent reactants while C and D represent products. In this reaction, A and B is being diminished and C and D is being produced. Rate of reaction, concerns itself with how fast the reactants diminish or how fast the product is formed. Rate of reaction of each species corresponds respectively to their stoichiometric coefficient. As such :

The negative sign indicates reactants. A usual equation for rA is :

wherek - rate constantCA - concentration of A speciesCB - concentration of B species - stoichiometric coefficient of A - stoichiometric coefficient of B

4.2 ConversionTaking species A as the basis, the reaction expression can be divided through the stoichiometric coefficient of species A, hence the reaction expression can be arranged as follows;

Conversion is an improved way of quantifying exactly how far has the reaction moved, or how many moles of products are formed for every mole of A has consumed. Conversion XA is the number of moles of A that have reacted per mole of A fed to the system. As seen below;

4.3 Plug Flow ReactorThis reactor is also known as tubular flow reactor which is usually used in industry complementary to CSTR. It consists of a cylindrical pipe and is usually operated at steady state. For analytical purposes, the flow in the system is considered to be highly turbulent and may be modeled by that of a plug flow. Therefore, there is no radial variation in concentration along the pipe.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.In an ideal tubular flow reactor, which is called plug flow reactor, specific assumptions are made regarding the extent of mixing;4.3.1 No mixing in the axial direction 4.3.2 Complete mixing in the radial direction 4.3.3 Uniform velocity profile across the radius.Tubular reactors are one type of flow reactors. It has continuous inflow and outflow of materials. In the tubular 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 stirring prevent complete mixing of the fluid in the tube.

4.4 Residence Time Distribution FunctionResidence Time Distribution is a characteristic of the mixing that occurs in the chemical reactor. There is no axial mixing in a plug flow reactor, PFR and this omission can be seen in the Residence Time Distribution, RTD which is exhibited by this class of reactors. The continuous stirred tank reactor CSTR is thoroughly mixed and its RTD is hugely different as compared to the RTD of PFR.

5.0 APPARATUS

The unit used in this experiment is SOLTEQ Plug Flow Reactor (Model: BP101)

Fig. 5.1 : SOLTEQ Plug Flow Reactor (Model: BP101)

Plug Flow Reactor (Model: BP101) is used as it has been properly designed for students' experiment on chemical reactions in liquid phase under isothermal and adiabatic conditions. Included in the unit is a jacketed plug flow reactor; individual reactant feed tanks and pumps, temperature sensors and conductivity measuring sensor.Apart from that, there were also some laboratory apparatus involved such as :5.1 Burette5.2 Conical flask5.3 Measuring cylinder5.4 ph indicator5.5 BeakersAmong the chemicals used are :5.6 0.1 M Sodium Hydroxide, NaOH5.7 0.1 M Ethyl Acetate, Et(Ac)5.8 0.1 M Hydrochloric Acid, HCl5.9 De-ionised water

6.0 PROCEDURES

6.1 General Startup Procedures

6.1.1 All the valves are ensured closed except V4, V8 and V17. 6.1.2 The following solutions are prepared: i. 20 liter of NaOH (0.1M) ii. 20 liter of Et(Ac) (0.1M) iii. 1 liter of HCL (0.25M) for quenching 6.1.3 Feed tank B1 was filled with NaOH while feed tank B2 was filled with the Et(Ac). 6.1.4 The water jacket B4 was filled with water and pre-heater B5 was filled with clean water. 6.1.5 The power for the control panel was turned on. 6.1.6 Valves V2, V4, V6, V8, V9 and V11 were opened. 6.1.7 Both pumps P1 and P2 were switched on. P1 and P2 were adjusted to obtained flow rate approximately 300mL/min at both flow meters Fl-01 and Fl-02. Both flow rates were made sure to be equal.6.1.8 Both solutions then were allowed to flow through the reactor R1 and overflow into waste tank B3. 6.1.9 Valves V13 and V18 was opened. Pump P3 then was switched on in order to circulate the water through pre-heater B5. The stirrer motor M1 was switched on and set up to speed about 200 rpm to ensure homogeneous water jacket temperature. 6.2 Experiment Procedures6.2.1 The general starts up procedures were performed. 6.2.2 Valves V9 and V11 were opened. 6.2.3 Both the NaOH and Et(Ac) solutions were allowed to enter the plug reactor R1 and empty into the waste tank B3. 6.2.4 P1 and P2 were adjusted to give a constant flow rate of about 300 ml/min at flow meters FI-01 and FI-02. Both flow rates were ensured same. The flow rates were recorded. 6.2.5 The inlet (QI-01) and outlet (QI-02) were started to monitor the conductivity values until they do not change over time. This is to ensure that the reactor has reached steady state. 6.2.6 Both inlet and outlet steady state conductivity values were recorded. The concentration of NaOH exiting the reactor and extent of conversion from the calibration curve. 6.2.7 Optional. Sampling was opened from valve V15 and 50ml of sample was collected. A back titration procedure was carried out manually to determine the concentration of NaOH in the reactor and extent of conversion. 6.2.8 The experiment was repeated from step 4 to 7 for different residence times by reducing the feed flow rates of NaOH and Et(Ac) to about 250,200,150,100 and 50 ml/min. Both flow rates were made sure to be equal. 6.3 Back Titration Procedures6.3.1 The burette was filled up with 0.1 M NaOH solution. 6.3.2 10 mL of 0.25 M HCl was poured in a flask. 6.3.3 50 mL samples that were collected from the experiment at every controlled flow rate (300, 250, 200, 150, 100 and 50 mL/min) were added into the 10mL HCl to quench the saponification reaction. 6.3.4 3 drops of phenolphthalein were dropped into the mixture of sample and HCl. 6.3.5 The mixture then was titrated with NaOH until it turns light pink. 6.3.6 The amount of NaOH titrated was recorded.

7.0 RESULTS

Conversion Solution mixturesConcentration of NaOH (M)Conductivity (mS/cm)

0.1 m NaOH0.1 m Na(Ac)H2O

0 %100 mL-100 mL0.050010.7

25 %75 mL25 mL100 mL0.03759.7

50 %50 mL50 mL100 mL0.02507.5

75 %25 mL75 mL100 mL0.01255.6

100 %-100 mL100 mL0.00004.0

Table 7.1: Table for Preparation of Calibration CurveVolume of reactor = 4 LConcentration of NaOH in feed tank = 0.1 MConcentration of ethyl acetate, Et(Ac) in feed tank = 0.1 MVolume of 0.25 M HCL = 10 mL

No.Flow Rate of NaOH (ml/min)Flow Rate of Et(Ac) (ml/min)Total flow rate of solutions, Vo(nL/min)Outlet ConductivityQ2Volume of NaOH titrated(mL)Residence time, t(min)Conversion, X(%)Reaction rate constant, K(L/mol.min)Rate of reaction, -rA(mol/L.min)

13063046109.70.36.557450.61.53653.7496 X 10-3

22542595138.40.27.797350.41.30323.2061 X 10-3

32022054077.40.19.828050.21.02572.5438 X 10-3

41521543066.40.113.071950.20.77111.9124 X 10-3

51011042055.50.219.512250.40.52081.2813 X 10-3

651531044.70.238.461550.40.26426.4997 X 10-4

Table 7.2 : Data and Calculation from the Experiment

8.0 SAMPLE CALCULATIONS8.1 Residence Time For the data no. 1 in the Table 7.2Residence Time, Total flow rate, Vo = Flow rate of NaOH + Flow rate of Et(Ac)= 306 mL/min NaOH + 304 mL/min Et(Ac)= 610 mL/min= 0.61 L/minHence,Residence Time, = 6.5574 min8.2 ConversionFor the data no.1 in the Table 7.2:i. Moles of reacted NaOH, n1n1 = Concentration NaOH x Volume of NaOH titrated= 0.1 M x 0.0003 L = 0.00003 molii. Moles of unreacted HCl, n2Moles of unreacted HCl = Moles of reacted NaOHn2 = n1n2 = 0.00003 moliii. Volume of unreacted HCl, V1V1 = V1 = = 0.00012 Liv. Volume of HCl reacted, V2V2 = Total volume HCl V1V2 = 0.01 0.00012V2 = 0.00988 Lv. Moles of reacted HCl, n3n3= Concentration HCl X V2n3= 0.25 X 0.00988n3= 0.00247 molvi. Moles of unreacted NaOH, n4Moles of unreacted NaOH = Moles of unreacted HCln4 = n3n4 = 0.00247 molvii. Concentration of unreacted NaOHCNaOH unreacted = = = 0.0494 Mviii. XunreactedXunreacted = Xunreacted = Xunreacted = 0.494ix. Xreacted Xreacted = 1- Xunreacted = 1 - 0.494 = 0.506x. Conversion for data No. 1 in Table 7.20.506 x 100% = 50.6 %8.3 Reaction Rate Constant,k

For data no. 1 in Table 7.2;V0 = Total inlet flow rate V0 = 0.61 L/minVTFR = Volume for reactor = 4 LCAO = inlet concentration of NaOH = 0.1 MX = 0.506 = 1.5365 L.mol/min

8.4 Rate of Reaction, -rA-rA = k (CA0)2 (1-X)2For data no. 1 in Table 7.2 :-rA = 1.5365 (0.1)2 (1 - 0.506)2 = 3.7496 x 10-3 mol.L/min

9.0 DISCUSSIONS

This experiment was conducted to determine the reaction rate constant and the effect of residence time on the conversion in a plug flow reactor. The solutions used are NaOH and Et(Ac). These two solutions react together in the PFR to complete saponification reaction. In this experiment, residence times have to be manipulated throughout the experiment and the effects of each one is studied. Residence time is varied by the means of changing the flow rates of the feed solutions. This is shown by the formula;Residence Time, From the equation above, it can be seen that residence time is a function of total flow rates of the feed. Hence, by varying the flow rate of the feed solutions, several residence times can be obtained and the effects of each one, studied.After the experiment is conducted, raw data consisting inlet flow rates, conductivity value and volume of NaOH used in the titration process are tabulated in Table 7.1 of the Result Section. From the raw data obtained, a series of calculations were made, as seen in the Sample of Calculation section, and the values of residence times, conversion of the reactions, reaction rate constants and rate of reactions were determined. These values are tabulated in Table 7.2 of the Result section.As the data of residence time and conversion from Table 7.2 is plotted into a graph, the graph is shown in Graph 7.1. The reason for plotting a graph with these two parameters is so that the effects of residence time can be studied. Conversion is a property that shows how much of the reaction has taken place. Hence, by comparing this property with the residence time parameter, one can analyze the effects of increasing residence time to the reaction itself.By analyzing Graph 7.1, it can be clearly seen that the conversion of the reaction remains fairly constant with the increasing residence time. Therefore, one can postulate that residence time is not a factor for reaction conversion, as far as plug flow reactors are concerned. One can also postulate that the reason for this phenomenon is that the PFR lacks a good mixing process. Since the PFR is designed not to stir the solution vigorously to maximize mixing process, the conversion of the reaction by using PFR is fairly low.However, since the experiment experienced some major errors in the back titration procedure, the output of the experiment was affected, and was not acceptable. According to the laboratory technician, the error was mainly come from instrumental errors. There might be contaminant in the equipments used and this may be caused by improper handling of the glassware. They might not be cleaned properly after used previously, and hence affect the outcomes of the experiments that come afterwards.Therefore, for the sake of learning and understanding, the data used in this report was based on the data given by the laboratory technician and from the previous successful experiment.

10.0 CONCLUSION

Saponification process was completed. However, the outcomes of the experiment were not accurate and discarded. Then, in order to determine the rate constant and the reaction rate, the previous data of a successful experiment was used. This was for the sake of learning and understanding.

11.0 RECOMMENDATIONS

11.1 Wash the glassware properly after used for convenience of the next users.11.2 Time the sample well. This is to reduce, or if possible, to avoid time-wasting in taking samples. 11.3 Monitor the flow rates constantly in order to make it remains constant throughout the reaction, as required.11.4 Before conducting the experiment, locate all valves properly and familiarize with their locations.11.5 Stop the titration immediately as soon as the indicator turned pink.

REFERENCES

Fogler, H.S (2006). Elements of Chemical Reaction Engineering (3rd Edition). Prentice Hall.

Levenspiel, O. (1999). Chemical Reaction Engineering (3rd Edition). John Wiley.

Kinetic Studies of the Saponification of Ethyl Acetate, Retrieved from http://www.researchgate.net/publication/229360677_Kinetic_Studies_on_Saponification_of_Ethyl_Acetate_Using_an_Innovative_Conductivity-Monitoring_Instrument_with_a_Pulsating_Sensor at 10th OCT 2015Tracer Studies in a Plug Flow reactor, Retrieved from http://www.egr.msu.edu/~hashsham/courses/ene806/docs/Plug%20Flow%20Reactor.pdf at 10th OCT 2015

APPENDICES

Graph 7.1 : Graph of Conversion VS Residence Time