continuous stirred tank reactor (cstr)

Module 4 : BKF2741 Chemical Reaction Engineering Laboratory I

1.0 Title Of Experiment

Effect Of Flowrate On Continous Stirred Reaction Process

2.0 Objective

To study the effect of flowrate on saponification of ethyl acetate and sodium hydroxide in CSTR.

3.0 Introduction

In chemical engineering, chemical reactors are vessels designed to contain chemical reactions.

The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers

design reactors to maximize net present value for the given reaction. Designers ensure that the reaction

proceeds with the highest efficiency towards the desired output product, producing the highest yield of

product while requiring the least amount of money to purchase and operate. Normal operating expenses

include energy input, energy removal, raw material costs, labor, etc. Energy changes can come in the

form of heating or cooling, pumping to increase pressure, frictional pressure loss (such as pressure drop

across a 90o elbow or an orifice plate), agitation, etc.

There are three main basic models used to estimate the most important process variables of

different chemical reactors:

batch reactor model (batch),

continuous stirred-tank reactor model (CSTR), and

plug flow reactor model (PFR).

In a CSTR, one or more fluid reagents are introduced into a tank reactor equipped with an

impeller while the reactor effluent is removed. The impeller stirs the reagents to ensure proper mixing.

Simply dividing the volume of the tank by the average volumetric flow rate through the tank gives the

residence time, or the average amount of time a discrete quantity of reagent spends inside the tank. Using

chemical kinetics, the reaction's expected percent completion can be calculated. Some important aspects

of the CSTR:

__________________________________________________________________________________FKKSA/BKF2741/Module/Rev01/2/08/10

http://en.wikipedia.org/wiki/Chemical_engineering

http://en.wikipedia.org/wiki/Chemical_reaction

http://en.wikipedia.org/wiki/Chemical_engineering


At steady-state, the flow rate in must equal the mass flow rate out, otherwise the tank will

overflow or go empty (transient state). While the reactor is in a transient state the model

equation must be derived from the differential mass and energy balances.

All calculations performed with CSTRs assume perfect mixing.

The reaction proceeds at the reaction rate associated with the final (output) concentration.

Often, it is economically beneficial to operate several CSTRs in series or in parallel. This

allows, for example, the first CSTR to operate at a higher reagent concentration and there-

fore a higher reaction rate. In these cases, the sizes of the reactors may be varied in order

to minimize the total capital investment required to implement the process.

In this experiment, the reaction need to be studied is

NaOH+CH 3COOC 2 H5→CH 3COONa+C2 H5 OH

Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt

of a carboxylic acid. The process is commonly used to refer to the reaction of a metallic alkali (base) with

a fat or oil to form soap. Here, sodium hydroxide is a caustic base. The alkali breaks the ester bond and

releases the fatty acid salt and glycerol. Soaps maybe precipated by salting it out with saturated sodium

chloride. The saponifacation value is the amount of base required to saponify a fat sample. The extent of

the reaction is determined by monitoring sodium hydroxide and sodium acetate concentrations using

conductivity measurements.



4.0 Experimental Procedure

1. CSTR 2. Beakers 3. Measuring Cylinders 4. Stop Watch

5. Sodium Hydroxide 6. Sodium Acetate 7. Ethyl Acetate

4.1 Preparation of calibration curve for Conversion vs. Conductivity

1. Prepare 1-L of 0.1 M sodium hydroxide (NaOH) solution and 1-L of 0.1 M sodium acetate

(Na(Ac)) solution.

2. Determine the conductivity for each conversion values by mixing the following solutions into

100 mL of deionised water.

i. 100 mL NaOH for 0% conversion

ii. 75 mL NaOH + 25 mL Na(Ac) for 25% conversion

iii. 50 mL NaOH + 50 mL Na(Ac) for 50% conversion

iv. 25 mL NaOH + 75 mL Na(Ac) for 75 % conversion

v. 100 mL Na(Ac) for 100% conversion

3. Plot the calibration curve of conversion vs. conductivity. Determine the slope and y-axis

intersept.

4.2. Experimental Procedure

1. Charge 10-L of 0.1 M Et(Ac) solution into feed tank T1.

2. Charge 10-L of 0.1 M NaOH solution into feed tank T2.

3. Set the 3-way valve V1 position towards pump P1 and 3-way valve V2 position towards pump

P2.

4. Open valves V3, V4 and V5.

5. Switch on pumps P1 and P2.

6. Adjust the needle valves V3 and V4 to obtain flowrates of approximately 100 mL/min on both

flowmeters FT1 and FT2. Make sure the flowrates are always maintained the same and check

that no air bubbles are trapped in the piping.__________________________________________________________________________________FKKSA/BKF2741/Module/Rev01/2/08/10


7. Allow both liquids to fill up all three reactors. Switch on stirrers 1, 2 and 3. Set the stirrer speeds

to approximately 200 rpm.

8. Start the stop watch.

9. Start monitoring the conductivity values (CT1, CT2 and CT3) and temperature values (TT1,

TT2 and TT3) every two minutes until they do not change over time (steady state). Stop the stop

watch and record the time and conductivity values. Determine the conversion in each reactors

from the calibration curve.

10. Repeat the experiment (steps 6 to 9) by changing the flowrate to 150mL/min.

4.3. Shutdown

1. After complete the experiment, drain off any liquids from the reactor and make sure that the

reactor and tubing are cleaned properly. Flush the system with de-ionized water until no traces

of salt are detected.

2. Dispose all liquids immediately after each experiment. Do not leave any solution or waste in the

tanks over a long period of time.

3. Wipe off any spillage from the unit immediately.

5.0 Additional Information

Molar mass of ethyl-acetate = 88.11g/mol

Molar mass of sodium hydroxide = 40 g/mol

Density of ethyl-acetate =0.895 g/ml



6.0 Discussion

1. Plot the calibration curve of conversion vs. conductivity and discuss relationship between these

parameters.

2. Plot a graph of conductivity / conversion vs. time for each flowrate. Discuss a plotted graph and

make a comparison in term of conversion for each flowrate.

3. Give the advantages of CSTR and compare with other types of reactors.

4. Give several applications of CSTR in chemical process or industries (at least 3 applications).

Process Diagram for Stirred Tank Reactors in Series


continuous stirred tank reactor (cstr)

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