Chemical Reaction Engineering Laboratory Saponification in a Tubular Flow Reactor

Introduction: The tubular flow reactor is one of the most common types of reactors used in the Chemical industry. It is an ideal reactor where all the fluid particles have same velocity and frictionless flow. The present experiment envisages illustrating the manner of measurement of reaction rates in a tubular flow setup, and the analysis of the data by the integral method for evaluation of the reaction rate constant.

Aim of the Experiment: The aim of the experiment is to carry out saponification of ethyl acetate in the given tubular flow assembly at constant temperature (Isothermal) and to determine the value of the rate constant on the basis of plug flow model :

CH3 COOC2 H5 + Na0H ------------ CH3 COONa + C2 H5OH

Materials required:
Ethyl acetate (aqueous, 0.1 M) : 10 liters,
Na0H (aqueous, 0.1 M) : 10 liters
HCl (aqueous, 0.05 M) : 500 ml,
Oxalic acid (standard, 0.1 M) : 100 ml
Measuring jars (100 ml) : 2 No.
Titration setup
1. With the help of standard oxalic acid, determine the normality of the NaOH solution taken in the tank ( ).
2. Prepare about 200 ml of 0.05M NaOH for purpose of backtitrations (N3).
3. Using the 0.05M Na0H, determine the normality of HCl solution (N1).
4. Start the pump-1 and feed Na0H to the reactor. Adjust the flowrate to a convenient reading RA of the rotameter.
5. Similarly start the pump-2 and feed EtAc to the reactor. Adjust the flow rate to another convenient reading, RB of the rotameter, so that the total flow of both the reactants together is about 75 cc to 100 cc per minute.
6. Check both Rotameter readings for constancy. Adjust suitably, if required.
7. Allow 30 minutes for steady state conditions to attain, keeping the flow rates constant.
8. Take 40ml of 0.05N HCl in a measuring jar. Collect about 25ml of the reactor effluent (sampling point-7) directly into this jar. Note the exact volume of the sample thus collected (V2).
9. Transfer the contents of the measuring jar into a labeled conical flask.,
10. Repeat steps 8 & 9 for all sampling points 6 to 1.
11. Backtitrate the contents of conical flasks with 0.05M NaOH and record the volume of
Na0H run down (V3).
12. Measure the total flow rate and the flow rate of Na0H by using measuring jar keeping RA & RB at the same levels.
13. Stop the pumps and close the valves
14. Note the room temperature.
- - - - - - - -

Note: When you collect samples start from sampling point-6 and go down so as not to disturb
the steady state operation.,


Preliminary titrations:
(i) Determination of Na0H concentration ( )
Volume of oxalic acid taken = 10 ml
Normality of oxalic acid = -------------- (given)
Volume of Na0H rundown = -------------- ml
Normality of NaOH ( ) =
(ii) Normality of Na0H used for back titration (N3):
(same as above )
(iii) Standardization of HCl
Volume of HCl taken = 25 ml
Volume of Na0H rundown = ------- ml,
Normality of Na0H (N3) =
Normality of HCl (N1) =

Sampling points
_____________________________________1 2 3 4 5 6 7
Outlet concentration of Na0H (CA) :

Flowrate, FA (lit/min)
Flowrate, FB (lit/min)
Vol. of HCl taken (V1) ml
Vol. of sample (V2) ml
Vol. of Na0H rundown in
back titration (V3 ) ml
CA =(V1 N1 –V3 N3)/V2 (mol/lit)
Outlet conc. of EtAc (CB):
Na0H conc. in feed
CAo = FA /(FA +FB) (mol/lit)
EtAc conc. in feed
CB0 = FB (0.1)/(FA + FB)(mol/lit)
CB = (CB0 – CA0) + CA

Evaluation of k by integral method:
Total flowrate F = FA +FB (lit/min)
Hold up volume (Vr) lit
Residence time = Vr /F (min)
{log (CB/ CA)}/(CB0 – CA0)

Plot {log (CB/ CA)}/(CB0 – CA0) versus and report the value of the reaction rate constant
k = ------------------------------------- lit/(g.mole)(min) at---------------o C
Selected questions:
1. What is the velocity of flow through the reactor ? Calculate the Reynolds number. How do these values compare with the usual values employed for pipe flow?
2. Plot CA versus t and determine the rates of reaction by measuring the slopes. Plot rA versus CA CB and check for straight line fit.
3. Comment on the validity of the plug flow model for the equipment used
4. Deduce the integral relation between CA and t for the reaction studied.
1. Ethyl acetate is a volatile substance (b.p.770C). Hence the tank must be
covered if the room temperature is high - say above 32oC
2. The Reynolds number should preferably be in the range of 1500 to 1800.
3. The reaction rate constant is about lit/(g.mole)(min) at ambient temperature; but the experimental value is likely to be different due to deviation from plug flow.

Sampling points
1 2 3 4 5 6 7
Holdup volume Vr (cc) 45 130 215 300 390 475 525