Kinetic Studies in Batch Reactor Non Equimolar Feed


The design of a chemical reactor depend on the reaction rate equation and value of the reaction rate constant.This information is to be obtained invariably through laboratory-scale experiments conducted at constant temperature.The equipment used is generally of batch type in case of homogenous reactions and of flow type in case of heterogeneous / catalytic reactions. For simple explanation of kinetic method simple homogenous reactions normally used.

Example reaction : The aim of the experiment is to verify that the saponification of Ethyl acetate in dilute aqueous solution which is a second order reaction used to report the value of the reaction rate constant.

Apparatus required: Reactor vessel with stirrer, conical flasks, Burette, Pipette.

Chemicals required: NaOH solution, Ethyl Acetate, Hydrochloric acid, Oxalic acid, Phenolphthalein indicator.

Theory: The experimental batch reactor is usually operated isothermally at constant volume, because it is easy to interpret the results of such runs. This reactor relatively simple device adaptable to small-scale laboratory set-ups, and it needs but little auxiliary equipment or instrumentation. Thus, it is used whenever possible for obtaining homogeneous data.The starting point for all design is the material balance expressed for any reactant or product over a small element of volume. Reactants enters and leaves while accumulates and disappears by reaction within the element.

If the composition within the reactor is uniform (independent of position), the accounting may be made over the whole reactor. If the composition is not uniform (dependent on position), it must be made over a differential element of volume and then integrated across the whole reactor for the appropriate flow and concentration conditions.

A model reactor specification:
Reactor material : Stainless Steel
Diameter : 98 mm
Length : 200 mm
Capacity : 1.5 lts

In the batch reactor the reactants are initially charged into a container, are well mixed, and are left to react for a certain period. The resultant mixture is then discharged. This is unsteady state operation where the concentration changes with time. The concentration is independent of position, so we can make material balance over the entire reactor. Make a material balance for any component A. For such an accounting we usually select the limiting reactant.
Input flow rate  = 0 and Output flow rate = 0
Disappearance by reaction (moles / time) = (-rA) V
Accumulation of A (moles / time) = 
By replacing these terms in balance equation (1)
                         0 = 0 + ( -rA ) V - Accumulation of A
                         ( -rA ) V = Accumulation of A                                            -----------(2)
Rearranging and integrating equation (2) gives

For constant volume reactions (4)
The performance equation for Constant volume batch reactor is


Consider a second order irreversible bi-molecular elementary reaction given below
A + B k Products

The rate equation for above reaction is -rA = k CA CB -----------------------(5)
Let XA and XB are conversions of A and B at any time, the concentrations of A and B at any time in the reactor are
CA = CAO ( 1 - XA ) CB = CBO ( 1 – XB )
Substitute above expressions in equation (5)
-rA = k CAO ( 1 - XA ) CBO ( 1 – XB )
Rearrange Above Equation
-rA = k CAO ( 1 - XA ) (CBO – CBO XB ) --------------------------------------------(6)
at any time moles of B reacted is equal to moles of B reacted
moles of B reacted = CBO XB
moles of A reacted = CAO XA
CBO XB = CAO XA ----------------------------------------------------(7)
Substitute (7) in (6)
-rA = k CAO ( 1 - XA ) (CBO – CAO XA )
the above equation can be rearranged as
-rA = k CAO2 ( 1 - XA ) (M – XA ) ---------------------------------------(8)
where M = , the initial molar ratio of reactants.
Substitute equation (8) in equation (4)

Integration of above equation leads to (9) equation a performance equation of a batch reactor for second order reaction.

Let  =
Plot a graph of  Vs t, the slope of the graph is Rate constant K

 Prepare 1-liter NaOH solution.
 Estimate the strength of NaOH solution by using standard Oxalic acid.
 Estimate the strength of HCl solution by using standardized NaOH solution.
 Transfer given amount of NaOH solution into batch reactor.
 Take nearly 15 test tubes and transfer 10 ml of HCl solution into each conical flask.
 Switch on the stirrer
 Add some amount of ethyl acetate to the reactor such that Ethyl acetate is maintained as excess reactant.
 Transfer the reaction mixture into conical flask, which contains 10 ml of known HCl solution for every one minute time interval.
 Take the samples up to 20 minutes.
 Note down the room temperature.
 Titrate the contents of conical flask with NaOH solution to estimate the concentrations of Ethyl Acetate and NaOH concentrations.

Standardization of NaOH
Volume of Oxalic acid taken = Voxalic = ml.
Normality of Oxalic acid taken = Noxalic = N
Volume of NaOH rundown for neutralization of Oxalic acid =V1= ml.
Standardization of HCl
Volume of HCl taken = V2 = ml
Volume of NaOH rundown for neutralization of HCl = V3 = ml.
Volume of reaction mixture taken into a conical flask = Vsample = ml.
Volume of Hcl taken in conical flask. = VHCl = ml.
Volume of Ehtyl Acetate added to the reactor = VEthyl = ml.
Volume of NaOH taken in to the reactor = QNaoH = 2000 ml
gm moles of NaOH = gm moles of Ethyl acetate.

For equimolar feed

gm moles of NaOH = gm moles of Ethyl acetate.


Vethyl acetate = X Molecular weight of ethyl acetate

=------------- ml

For non-equimolar feed the volume of ethyl acetate is greater than the calculated volume.

S.No Time ( min ) Volume of NaOH rundown
VNaOH ( ml )

Normality of NaOH solution = NNaOH = = N
Normality of HCl solution = NHCl = = N
Estimation of initial concentrations:
Initial concentration of Ethyl Acetate = CB0¬ = =
Initial concentration of NaOH = CA0¬ =

Where  is the density of Ethyl Acetate
M.w is the molecular weight of Ethyl Acetate.
V is the volume of reaction mixture = VNaOH + VEthyl
Initial molar ratio of reactants M =

Analysis of reaction mixture:
Gram moles of HCl remaining = VNaOH NNaOH
Gram moles of NaOH present in reaction mixture
GMNaOH = Gram moles of HCl used for neutralization of NaOH remaining in reaction mixture
= Gram moles of HCl added – gram moles of HCl remaining.
Concentration of NaOH in reaction mixture, CA =

Conversion of NaOH
XA = 1 – ( CA / CA0)
 =
S. No time VNAOH CA A 

Plot a graph  vs time

 slope = k


The rate constant for the reaction of Ethyl Acetate with NaOH is ____________.


 In the manufacture of pharmaceutical products, dyes and dye intermediates and for testing new processes.

Need to know:

1. What is meant by Batch Reactor?
2. What are the industrial applications of Batch Reactor?
3. What is meant by Saponification?
4. Explain simple rate equation for Batch Reactor?
5. Describe the parameter studied in Batch Reactor experiment?
6. Write the simple chemical reaction equation for Saponification Reaction?
7. What do you learn from the given experiment?