ABSTRACTThe experiment involves a continuous stirred tank reactor (cstr). This experiment is to determine the effect of temperature onto the reaction extent of conversion and to determine the reactions activation energy. Firstly the reactor is filled with sodium hydroxide, NaOH and Ethyl acetate, Et(Ac) until achieved 10 L. The flow rate of both solutions must same at 0.20 L/min. The solution is stirred and speed of 200 rpm. The water temperature is set at 50 C. The steady state conductivity and temperature values is recorded and then find the concentration of NaOH in reactor and the extent of conversion from calibration curve. The 50ml sample is collected then carried out the back titration procedure immediately. The experiment is repeated with different temperature; 55 C, 60 C and 75 C.

OBJECTIVES -To carry out a saponification reaction between NaOH and Et(Ac) in CSTR 40 litre. -To determine the effect of residence time onto the reaction extent of conversion. -To determine the rate constant. -To determine the reaction rate.

INTRODUCTIONReactor is one of equipment used mostly in the industrials sector. It changes the raw material into the desired product. A good reactor will give a high production and economical. One of criteria to choose or to design a good reactor is to know the effectiveness of the reactor itself. There a many types of reactor depending on the nature of the feed materials and products. One of the most important we need to know in the various chemical reaction was the rate of the reaction. The continuous stirred-tank reactor (CSTR) which is also known as vat- or back-mix reactor usually is a common ideal reactor type in chemical engineering. A CSTR often refers to a model used to estimate the key unit operation variables when using a continuous agitated-tank reactor to reach a specified output. This reactor works for all fluids, liquids, gases, and slurries. The behaviour of a CSTR is always modelled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR). All calculations performed with CISTRs assume perfect mixing. In a perfectly mixed reactor, the output composition is identical to composition of the material inside the reactor, which is a function of residence time and rate of reaction. CSTR used in this experiment, (model: BP 143) is designed for students experiments on chemical reaction in liquid phase under adiabatic and isothermal conditions. CSTR consists of two tanks of solutions and one reactor. The reactor is modelled in order to perform the saponification reaction between the sodium hydroxide and ethyl acetate. Saponification reaction of ethyl acetate and sodium hydroxide produced sodium acetate in a batch and the continuous stirred tank reactor evaluate the rate data needed to design a production scale reactor.

THEORYReaction Kinetics Reaction kinetics is the branch of chemistry that quantifies rates of reaction. An elementary chemical reaction is a chemical reaction whose rate corresponds to a stoichiometric equation. In symbols: A+BC+D and the reaction rate will be defined as: -r = k (cA) (cB) where k is referred as the specific reaction rate (constant). The overall order of reaction is defined as: n = + The Mass Balance Mass is a conservative entity, hence given a control volume V the sum of mass flows entering the system will equal the sum exiting minus (plus) the consumed (generated) or accumulated fractions:Rate of mass in- rate of mass out+ rate of mass generated- rate of mass consumed = rate of mass accumulation shortly: IN OUT + PROD CONS = ACC

Residence Time The reactors residence time is defined as the reactor volume divided by the total feed flow rates. Residence time, = Conversion The conversion (or fractional conversion), denoted X, is a frequently used measure of the degree of reaction. It i s defined as X=

EXPERIMENTAL PROCEDURES General Start-Up Procedures1) The following solution is prepared:

a) 40 L of sodium hydroxide, NaOH (0.1 M) b) 40 L of ethyl acetate, Et(Ac) (0.1M) c) 1 L of hydrochloric acid, HCl (0.25M), for quenching 2) Ensure that all valves are initially closed 3) The feed vessels are charged as follow. a) The charge port caps for vessels B1 and B2 is opened. b) The NaOH is carefully poured into vessel B1 and Et(Ac) into B2. c) The charge port for both vessels is closed. 4) The power for the control panel is turned on. 5) Check that there is sufficient water in thermostat T1 tank. Refilled is necessary. 6) Cooling water valves, V13 is opened and let the cooling water flow through the condenser W1. 7) Adjust the overflow tube to give a working volume of 10 L in reactor. 8) Valves V2, V3, V7, V8 and V11 were opened. 9) The unit was ready to run the experiment.

General Shut-Down Procedures 1) Keep the cooling water valve V13 open to allow the cooling water to continue flowing 2) Pumps P1 and P2 is switched off. Stirrer M1 is switch off. 3) The thermostat T1is switched off. Let the liquid in the reaction vessel R1 cool down to room temperature. 4) Cooling water valve V13 is closed. 5) Valves V2, V3, V7, and V8 were closed. Valves V4, V9 and V12 to drain the liquid from unit. 6) The power for the control panel is turned off.

Preparation of calibration curve for conversion versus conductivity 1) The following solutions is prepared a) 1L of sodium hydroxide, NaOH (0.1 M) b) 1L of sodium acetate, Et(Ac) (0.1M)c) 1L of deionised water, H2O

2) Determine the conductivity and NaOH concentration for each conversion values by mixing the following solutions into 100 mL of deionised water. a) 0% conversion : 100 mL NaOH

b) 25% conversion : 75 mL NaOH + 25 mL Et(Ac) c) 50% conversion : 50 mL NaOH + 50 mL Et(Ac) d) 75% conversion : 25 mL NaOH + 75 mL Et(Ac) e) 100% conversion : 100 mL Et(Ac)

Back Titration Procedures for manual Conversion Determination 1) A burette is filled up with 0.1 M NaOH solution. 2) 10 mL of 0.25 M HCl is measured in a flask 3) 50 mL sample is obtained from the experiment and immediately add the sample to the HCl in the flask to quench the saponification reaction. 4) 3 drops of phenolphthalein is added into the mixture. 5) The mixture is titrated with NaOH solution from the burette until the mixture is neutralized. The amount of NaOH is recorded.

Effect of Residence Time of The Reaction in a CSTR 1) Perform the general start-up procedures. 2) Switch on both pumps P1 and P2 simultaneously and open valves V5 and V10 to obtain the highest possible flow rate into the reactor. 3) Let the reactor fill up with both the solution until it is just about to overflow. 4) Readjust the valves V5 to V10 to give a flow rate of about 0.1 L/min. Make sure that both flow rates are the same. Record the flow rate. 5) Switch on the stirrer M1 and set the speed to about 200 rpm. 6) Start monitoring the conductivity value at Q1-401 until it does not change over time. This is to ensure that the reactor has reached steady state. 7) Record the steady state conductivity value and find the concentration of NaOH in the reactor and extent of conversion from the calibration curve. 8) Open sampling valve V12 and collect 50 mL sample. Carry out a back titration procedure to manually determine the concentration of NaOH in the reactor and extent of conversion.

APPARATUS

1) Continuous stirrer tank reactor Model: BP 143 2) 50 mL burette 3) 200 mL beaker 4) Conical flask 5) Conductivity probe 6) Solution : a) Sodium hydroxide (NaOH) 0.1M b) Ethyl Acetate (Et(Ac)) 0.1 M c) Deionised water d) Phenolphthalein 7) 100 mL Measuring cylinder

RESULTSReactor volume = 10 L

Concentration of NaOH in feed vessel = 0.1 M Concentration of Et(Ac) in feed vessel = 0.1 MTemp. ( C) Flow rate Of NaOH (ml/min) Flow rate Of Et(Ac) (ml/min) Vol. of NaOH Titrated (mL) 28.9 28.9 28.9 28.9 28.9 100 150 200 250 300 100 150 200 250 300 23.1 26.0 25.7 28.2 30.6 200 300 400 500 600 Total flow rate of sol. F0 (ml/min) Exit conc. NaOH, CNaOH, (M) Vol. of unreacted quenching HCl (mL)V2

Residence time, (min)

Conductivity (mS/cm) 5.50 5.09 5.05 5.03 4.92

Vol of H reacted with Na in samp (ml),V3

50 33 25 20 17

0.0038 -0.0020 -0.0014 -0.0064 -0.0112

9.24 10.40 10.28 9.28 12.24

0.76

-0.4

-0.2

-1.2

-2.2

Preparation of Calibration Curve Conversion Solution Mixture 0.1 M NaOH 0% 25% 50% 75% 100% 100 mL 75 mL 50 mL 25 mL 0.1 M Et(Ac) 25 mL 50 mL 75 mL 100 mL H2O 100 mL 100 mL 100 mL 100 mL 100 mL Concentration Of NaOH (M) 0.0500 0.0375 0.0250 0.0125 0.0000 Conductivity (mS/cm) 12.83 7.29 3.42 5.75 16.09

Rate Constant, k k (M-1s-1) 133.24 772.73 20.44x103 129.88 52.15 ln k 4.89 6.65 9.93 4.87 3.95 1/T (C-1) 0.035 0.035 0.035 0.035 0.035

No 1

Rate Constant, k (M-1s-1) 133.24

Reaction rate, -rA (M/s) 1.92 x 10-3

2 3 4 5

772.73 20.44x103 129.88 52.15

3.10 x 10-3 0.04 5.32 6.54 x 10-3

Graph of Calibration Curve

SAMPLE CALCULATIONS

NaOH + HCl NaCl + H2O

Unknown quantity: Concentration of NaOH in the reactor Known quantities: Volume of sample Concentration of NaOH in the feed vessel Volume of HCl for quenching Concentration of HCl in standard solution Volume of titrated NaOH Concentration of NaOH used for titration = = = VHCl,s = = = CHCl,s V1 CNaOH,s = Vs CNaOH,f = = = 10 mL = 0.25 mol/L mL 0.1 mol/L 50 mL 0.1 mol/L = CNaOH mol/L

Calculations: Conc. of NaOH entering the reactor, CNaOH,0 = Vol. of unreacted quenching HCl, V2 = = = = = = CNaOH,f x V1 VHCl,s - V2 (CHCl,s x V3)/1000 n1 n2/ Vs x 1000 (1) x 100% mol/L mL mL mol mol mol/L

Vol. of HCl reacted with NaOH in sample, V3 Moles of HCl reacted with NaOH in sample, n1 Moles of unreacted NaOH in sample, n2 Conc. of unreacted NaOH in the reactor, CNaOH Conversion of NaOH in the reactor, X

Residence time, =

= 10 L/(0.1+0.1) Lmin-1= 50 min Exit concentration of NaOH CNaOH,0 = V2 V3 n1 CNaOH,f = = = x V1 VHCl,s - V2 (CHCl,s x V3)/1000 = 0.05 mol/L = = = 0.1/0.25 x 23.1= 10 - 9.24 0.25 x 0.76/1000 9.24 mL = = 0.76 mL 1.9x10-4

n2 CNaOH X

= = =

n1 n2/ Vs x 1000 (1) x 100%

= = = =

1.9x10-4 mol 1.9x10-4/50x1000 = 0.0038 M

[1-(3.8x10-3/0.05)]x100% 92.4%

Rate constant k =

k1

= =

(0.1-0.0038)/50(0.0038)2 133.24 M-1s-1

Reaction rate -rA = kCA2

k= 133.24 -rA = = = kCA2 (133.24)(0.0038)2 1.92 x 10-3 M/s