Cre Handouts

1

CHP 303 – PROCESS CONTROL AND REACTION ENGINEERING LABORATORY

CRE1: Kinetics of saponification reaction from a batch reactor

AIM: To determine the kinetics of saponification reaction between ethyl acetate and

sodium hydroxide in a batch reactor.

APPARATUS: Reaction Flask/Reactor, Stirrer, Beakers, Burettes, Pipettes, Indicator

and ice bath

CHEMICALS: Ethyl acetate, Sodium hydroxide, Oxalic acid (or other standard acid for

making stock solution), Indicator.

PREPARATION:

(i) Prepare standard acid stock solution of 0.1N (contact lab. technician)

(ii) Prepare 1000 ml of sodium hydroxide solution of 0. 1N and determine its exact

normality with standard acid solution

(iii) Calculate volume of ethy1 acetate required per 100 ml of sodium hydroxide 0.1N

so that the normalities are 1:1 and 1:2.

EXPERIMENTAL PROCEDURE:

(i) Add 400 ml of sodium hydroxide solution into the reaction vessel and stir its

contents slowly with the stirrer

(ii) Add the calculated amount of ethyl acetate for concentration ratio of 1:1 or 1:2

into the reactor vessel and note the time as starting time for reaction. Immediately

take a simple of 2 ml from the reactor and quench it.

(iii) At specified time intervals, i.e. 1, 2, 3, 4, 5, 7, 10, 12, 15, 20, 25 min take samples

of 5 ml from the reactor and quench them in ice bath.

(iv) Titrate the samples with standard oxalic acid solution for determining the

concentration of the sodium hydroxide as a function of time.

2

THEORY:

Reaction :

NaOH + CH3 COOC2 H5 → CH3 COONa + C2 H5 OH

(A) + (B) → (C) + (D)

It is reported that the reaction is irreversible and the reaction orders with respect

to the reactant is unity. The rate expression is given by (elementary reaction):

BOAOAA

BOAOAAOBOABAA

CCforCKdtCd

CCforCCCCKCCkdt

dC

==−

≠+−==−

2

])([ (1)

(2)

DATA AND CALCULATIONS:

From the titration results, calculate the concentrations of the reactant A (sodium

hydroxide) in the reaction mixture at zero time and at other times.

Differential Method:

(i) Plot CA vs. t data.

(ii) Draw tangents at different values of CA.

(iii) Calculate slopes (dCA /dt) at each value of CA.

(iv) Plot (dCA/dt) vs. f (CA ) = CA {(CBO - CAO ) + CA )

(v) Calculate the rate constant, if the data gives a straight line passing

through the origin, from the slope of the line.

(vi) When the reactants are present in equimolal concentrations, plot ln(-dCA

/dt) vs. ln CA and determine the rate constant from the slope and the

overall order from the intercept.

Integral Method:

Integration of the equations (1) and (2) gives the following equations.

3

ln )3()(}){(

tkCCCC

CCCCAOBO

ABO

AAOBOAO −=+−

(i) Plot

ABO

AAOBOAO

AOBO CCCCCC

LnCC

])({{

)(1 +−

− vs. t

(ii) Calculate the rate constant from the slope of the line.

(iii) When the reactants are present in equimolal concentrations,

Plot 1/CA vs. t and calculate the rate constant from the slope of the line.

FURTHER WORK :

(a) Repeat the experiment with different initial concentrations of the reactant .

(b) Determine the order of reaction by half life method. Check the value of the rate

constant with that obtained above in your procedure.

(c) Repeat the experiment at different temperatures to completely determine the rate

equation, i.e. frequency factor and activation energy, and order of reaction.

RELEVANT BACKGROUND READING:

Fogler, H. Scott, Elements of Chemical Reaction Engineering, 3rd Ed., PHI India Pvt. Ltd.

(1999).

(Chapters 3, 5)

Levenspiel, O., Chemical Reaction Engineering, 3rd Ed., John Wiley and Sons (1999).

(Chapter 3)

1 1 (4)A AO

K tC C

− =


CRE2: Kinetics of hydrogen peroxide decomposition in a batch reactor

AIM: To determine the kinetics of hydrogen peroxide decomposition in a batch reactor.

APPARATUS: Three- necked round bottom flask, condenser, gas volume measuring unit at

atmospheric pressure, constant temperature bath, thermometer, stopwatch.

CHEMICALS: Hydrogen peroxide, Potassium iodide.

PREPARATION:

The gas volume measuring unit consists of a 1 liter capacity measuring cylinder and a open

mouth glass bottle both connected at the bottom by a rubber tube. The top of the measuring

cylinder is covered with a lid with a 3- way stop valve.

Fill the measuring jar and the bottle with water such that the levels in the jar and the bottle

correspond to 1000 ml mark in the measuring cylinder when the 3- way stop cock is open to

atmosphere. Then keep aside the glass bottle without pouring out the water.

PROCEDURE:

(i) Connect the reaction flask and the gas measuring cylinder with rubber tubing with the

condenser in between.

(ii) Add 100/150 ml of distilled water in the flask and heat it up to the desired temperature

(i.e., 35° – 40° - 45° – 50° C) and add 5 to 10 ml of the given H2 O2 solution and a pinch

of KI salt.

(iii) Immediately turn the 3-way stop cock to connect the reactor with the gas measuring

cylinder and note the time as zero time.

(iv) Keep the overflow glass bottle next to the measuring cylinder and note the times for

change in volume of gas in the measuring cylinder by maintaining equal levels of water

in the cylinder and bottle.

(v) Note the time and volume of the gas collected at regular volume change in the cylinder

also.

THEORY

Reaction :

2H2 O2 2H2 O + O2

(A) (B) + (O)

It is reported that the reaction is irreversible and first order. The rate equation is:

- AA Ck

dtdC

=

DATA AND CALCULATIONS

Calculate the initial concentration of the hydrogen peroxide solution from the total volume Of

oxygen (VO2) obtained from known volume of H2O2 (5 ml). Gram-moles of Hydrogen peroxide

in 1 ml of the sample is given by

)/(5400,22

2222 mlmolegm

VC O

OH ××

=

Concentration of H2 O2 in the initial reaction mixture:

( )

2 2 2 2

2 2 2

0H O H O

AH O H O

C VC

V V

×=

+

The concentration of hydrogen peroxide in the reaction mixture at any time is given by:

AOt

A CV

VVC

∞

∞ −=

where Vt = volume of O2 liberated at time t.

Show the derivation of the above relationships and establish their correctness.

Differential Method:

(1) Plot Vt vs. t

(2) Plot CA vs. t

(3) Draw tangents at different values of CA and calculate (-d CA /dt) values.

(4) Plot ln(-dcA /dt) vs. ln CA

(5) Calculate the order and the rate constant from the intercept and the slope of the data line.

Integral Method:

Plot ln(CAO /CA ) vs. t.

The line should pass through origin and the rate constant is given by the slope of the line.

Compare the rate constants obtained in the differential and integral cases and commet.

FURTHER WORK

(a) Repeat the experiment at a fixed temperature and at 2-3 different initial concentration of H2

O2 and determine order by half life method.

(b) Repeat the experiment at different temperatures and determine the activation energy and

frequency factors from Arrhenius plot.


Fogler, H. Scott, Elements of Chemical Reaction Engineering, 3rd Ed., PHI India Pvt. Ltd. (1999).

(Chapters 3, 5)


(Chapter 3)

1


CRE3: Kinetics of saponification reaction from a semi‐batch stirred reactor

AIM: To determine the reaction rate/rate constant for saponification reaction between

ethyl acetate and sodium hydroxide in semi-batch mode of contacting.

APPARATUS: Storage tanks for the reactants, Reactor, Stirrer, Rotameters, Burettes,

Pipettes, Conical flasks, Ice bath.

CHEMICALS: Ethy1 acetate, sodium hydroxide, oxalic acid (or other standard acid for

making stock solution), indicator.

PREPARATION:

(i) Prepare approximately 0.1N solution of sodium hydroxide and fill the storage tank

with it.

(ii) Prepare ethy1 acetate solution of about 0.1N concentration and fill the storage tank

with it.

(iii) Prepare standard oxalic acid (or any other standard acid stock solution as directed

by the lab. technician) of about 0.1N.

(iv) Determine the normality of the sodium hydroxide solution prepared.

PROCEDURE:

(i) Take NaOH in the reactor to fill it to an appreciable level (seek guidance from the

lab. technician or instructor).

(ii) Start the stirrer slowly and maintain a suitable speed so as not to spill the liquid in

the reactor.

(iii) Adjust the flow rate of the ethyl acetate solution from the storage tank to about

30-50 ml/min.

2

(iv) Allow the ethyl acetate flow to the reactor at the prefixed flow rate.

(v) When the reaction mixture starts overflowing, start collecting samples of 2 ml and

quench in ice bath (note that the reactor is operating in semi-batch mode).

(vi) Start collecting the samples from the exit overflow until steady state is attained,

i.e. the composition of the last two samples has the same value (and essentially

the NaOH, which was in batch, has been flushed out of the system by the flowing

ethyl acetate solution).

(vii) Titrate the samples obtained with standard acid for determining the concentration

of the sodium hydroxide.

THEORY:

Reaction:

NaOH + CH3COOC2H5 → CH3COONa + C2H5OH

(A) + (B) → (C) + (D)

Rate equation = (-rA) = k CA CB (1)

Design equations for semi-batch reactor need to be derived from first principles, with

help from books by Fogler and Levenspiel. The derivation should be shown in the report.


Calculate the steady state exit concentration/conversion of the reactant (A) ie. Sodium

hydroxide. Measure the volume of the reactor and volumetric flow rate of the reactants.

Calculate the rate constant from the equations derived above.

FURTHER WORK:

Repeat the experiment with different flow rates/concentrations of the reactants and verify

the rate constant.


3


(1999).

(Chapter 4)


CRE4: Flow analogy for series and parallel reactions

AIM: To study series and parallel reactions using fluid flow analogy and determine the rate

constants.

APPARATUS: Burettes, Capillary tubes and stop watch.

CHEMICALS: Water.

PREPARATION:

Connect the burettes with the capillary tubes, measure the I.D. and lengths of the capillary tubes.

Setup is already prepared in the laboratory.

PROCEDURE:

(i) Empty all the three burettes.

(ii) Adjust the capillary tubes such that they are in zero/50 ml mark level in the burettes and the

liquid flows through them into the subsequent burettes (burettes kept downstream), smoothly.

(iii) Close the stop-cocks of the burettes and fill the top most burette to the zero level mark.

(iv) Open the stop cocks of the burettes except the lower-most burette and note down times for

changes in water levels of known values in each of the burettes.

Note: To avoid the difficulty of noting level vs. time data in the three burettes simultaneously, first

note time vs. level in the top most burette only. Repeat the experiment noting down level vs. time in

the middle burette. The level vs. time data in the lower most burette can be determined from material

balance for the three burettes. The level vs. time data in the first burette is independent of the flows

into the second and third burettes.

(v) Repeat the same procedure for parallel reaction arrangement of burettes/capillary tubes also,

designed to mimic a parallel reaction scheme.

THEORY:

Series Reaction:

Assuming first order reactions, the rate equations are:

(1)

(2)

(3)

At t = 0, CA = CA0 and CB = CC = 0. Using these initial conditions, the solution to equations (1)-(3)

can be found by integration over time:

exp (4)

exp exp (5)

(6)

The maximum concentration of the intermediate and the time at which the maximum occurs are,

respectively, given by:

/

(7)

(8) ‘

Please derive these relationships in your report.

We draw an analogy of the above reaction scheme with the burette-capillary arrangement. The first

burette empties into the second via flow through the capillary. Resistance to flow in the capillary

determines the speed of the emptying of the first burette. Thus, the first burette may be taken to the

first reactant A, and the rate constant of flow through the first capillary may be taken to be the first

rate constant k1. Similarly, for the second and third burettes and capillaries. Thus, the envisioned

fluid mechanical apparatus provides an analogy to the series reaction network.

From fluid mechanics principles, a first order irreversible reaction can be represented by emptying of

a tank with a pipe line having laminar flow conditions (through Hagen-Poiseulle’s equation). The

equation relating level fall with time is given by (please derive this relationship in your report):

)10(32/'

)9('

241

1

DLdgk

hkdtdh

μρ=

=−

D = tank (burette) diameter

d = pipe (capillary tube) diameter

L = length of the pipe (capillary tube)

h = level in tank (burette) – function of time

µ = viscosity of liquid (water)

ρ = density of liquid (water)

Parallel Reaction Network:

A

Assuming first order the rate equations are given by:

B

C

k1

k2

)3(

)2(

)1()(

2

1

21

AC

AB

AA

Ckdt

dC

Ckdt

dC

CkkdtdC

=

=

+=−

At t = 0, CA = CA0 and CB = CC = 0. Using these initial conditions, the solution to equations (1)-(3)

can be found by integration over time:

exp (4)

1 exp (5)

1 exp (6)

Please derive these relationships in your report.


Series Reaction Network:

(i) Measure the height of the burettes w.r.t. the capillary tube level (centerline of horizontal

capillary). Measure the length and diameter of the capillary tube.

(ii) Plot h vs. t for three burettes on a single graph.

(iii) Plot - ln(h/h0) vs. t for the first burette data.

(iv) Note down the value of hmax for the second burette and the corresponding time.

(v) Determine the value of k1 from the slope of the second plot.

(vi) Calculate k1 /k2 ratio from equation (7) or (8) by trial and error.

(vii) Calculate the k2 from the above values.

(viii) Calculate the numerical values of k1’ and k2’ from equation (10) and verify with the above

values.

Parallel Reaction Network:

(i) Plot h vs. t for the three burettes on a single graph.

(ii) Plot - ln(h/h0) vs t data of the first burette

(iii) Calculate (k1 + k2) from the slope of the line of the above plot.

(iv) Calculate (k1/k2) ratio from the ratio of the maximum heights of the plot of the graphs of the

second and third burettes (CB and CC).

(v) Calculate individual values of k1 and k2.

FURTHER WORK

Repeat the experiment with some liquid initially present in the second and third burettes, i.e. CBO = 0

and CC0 = 0 at t = 0 and verify h vs. t data from the solutions of the equation (1), (2) and (3).


Fogler, H. Scott, Elements of Chemical Reaction Engineering, 3rd Ed., PHI India Pvt. Ltd. (1999).

(Chapter 6)


(Chapter 8)

1


CRE5: Reaction kinetics from an adiabatic batch reactor

AIM: To determine the kinetics of the reaction between hydrogen peroxide and

sodium thiosulphate in a batch reactor under adiabatic conditions.

APPARATUS: Reaction vessel (Thermos Flask), Thermocouple or thermometer.

CHEMICALS: Sodium thiosulphate solution and hydrogen peroxide solution.

PREPARATION: Take H2 O2 solution and 0.5m Na2 S2 O3 solutions (100 ml each).

PROCEDURE:

(i) Add the two reactants into the reaction flask and close the lid. Note the time as

the starting time for reaction.

(ii) Note the temperature vs. time date at regular intervals until there is no change

in the temperature of the reaction mixture.

THEORY:

A simple thermos flask acts as a very good adiabatic batch reactor, particularly is the

reaction is fast and the rate of heat transfer from the flask is slow in comparison.

Reaction:

2 Na2 S2 O3 + 4 H2 O2 → Na 2 S3 O6 + Na 2 SO4 + 4 H2 O

It is reported that the reaction is irreversible and first order w.r.to each reactant.

Rate equation is:

-rA = k CA CB (1)

Under adiabatic conditions, the heat balance gives:

dT/dt = ( )(/)() pTA CMrH −Δ− (2)

where, MT = total mass/moles of reaction mixture.

Cp = avg. specific heat (mass/mole basis)

2

ΔH = heat of reaction

Note that the reaction rate constant k, itself is a function of temperature, and is

related via Arrhenius law:

/

Taking the reactants in stoichiometric proportions, the rate equation (1) can be

expressed as:

- rA = k 2AC (3)

Solving equations (2) and (3) together with the boundary condition:

At t = 0, T = T0 and CA = CA0

Gives:

RTE

O

AO eTT

CkdtdT

TT/0

2 .))(

1 −

∞∞ −=

− (4)

When reactants are not in stoichiometric proportions, i.e., when 2 , the

temperature variation is given by:

RTE

O

O

AO

BOAOO e

TTTT

CC

TTCkdtdT /]

)()(2

[)( −

∞∞ −

−−−= (5)


(i) Plot t vs. T data.

(ii) At different values of T calculate dT/dt by graphical method.

(iii) Plot ln[T

vsdtdT

TT1].

)1

2−∞

.

(iv) Calculate the activation energy from the slope of the line.

(v) Calculate the frequency factor from equation (4).

(vi) Repeat the similar procedure for the case of non-stoichiometric proportions,

in which case you have to get the parameters from equation (5).

3

FURTHER WORK:

Repeat the experiment with different initial concentrations of the reactants such that

2 and calculate the rate constant using equation (5).


Fogler, H. Scott, Elements of Chemical Reaction Engineering, 3rd Ed., PHI India Pvt.

Ltd. (1999).

(Chapter 8)


(Chapter 9)


CRE6: Kinetics of a gas‐solid non‐catalytic reaction

AIM: To determine the rate parameters, i.e. reaction rate constant and effective diffusion

coefficient for the reaction of calcium carbonate decomposition (gas-solid non-catalytic

reaction).

APPARATUS: Furnace, pelletizer, holders, microbalance, stop watch, thermocouple.

CHEMICALS: Calcium carbonate powder, or chalk.

PREPARATION: Prepare one dimensional pellets by compacting the reactant powder in

the pellet holder using the bench-vice under uniform pressure. The diameter, thickness

and weight of the pellets are then measured.

Alternatively, if plain chalk is supplied to you, then cut them into precise cylindrical

shapes and weigh them in the microbalance to ensure that you know the precise weight.

PROCEDURE:

Number the pellets (pellet holder) for identification. Raise the furnace

temperature to the desired reaction temperature. Keep all the pellets in the furnace at one

time (try to make sure that they all have similar dimensions and initial weights). Remove

each pellet after keeping them in the furnace for different reaction times and put them

immediately in a desiccator for cooling. Then, measure the weight loss of the pellets

corresponding to different reaction times.

THEORY:

Reaction: CaCO3 → CaO + CO2

B(S) → C(S) + A(g)

The reaction is assumed to proceed according to shrinking core model.

For chemical reaction rate controlling, the time of reaction for conversion X is given by:

t = )1(r

B

KXLρ

For mass transfer controlling, the time of reaction is:

)2(2

2

AEeff

B

AEg

B

CDXL

CKL

xt ρρ

+=

Where:

B = molar density of the solid

L = thickness of the pellet

X = conversion

Kg = mass transfer coefficient, m/sec

Kr = reaction rate constant, kg.mol/m2 sec

Deff = effective diffusion coefficient, m2/sec

CAE = equilibrium CO2 concentration at any given temperature.

The rate parameters are obtained by data according to equation (1) and (2). For

determining the chemical reaction rate constant, the experiments are conducted at lower

temperature 650-7500C and mass transfer coefficients the temperature are 750 to 9000C.


From the experiments with each pellet, the time versus weight loss is determined. Then

conversion is given by:

X = )3(∞−

−WWWW

O

tO

Where W0, Wt, W∞ are weight of the solid at zero time, any time and infinite time i.e.

completion of reaction. The time versus conversion for the different pellets is used to

calculate the rate parameters corresponding to one temperature.

For the calculations, the molecular diffusion coefficient DCO2-air can be calculated using

Chapman-Enskog equation and porosity can be calculated from true density and bulk

densities of the solid pellet and assuming tortuosity factor as 2.

τε /2 airCOeff DD −= (4)

The Deff values can be compared with the experimental value obtained according to

equation (2).

FURTHER WORK: Repeat the experiments at other temperatures for determining the

activation energies for reaction and diffusion constants.



(1999).

(Chapter 11)


(Chapter 25)

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