University of Nizwa

College of Engineering

Department of Chemical and Petrochemical Engineering

Unit Operations Laboratory
Batch Reactor

Objectives

  • To observe and control the operation of a batch reactor
  • To determine the maximum conversion and to verify the linearity of the % conversion with the temperature of reaction.
  • To determine the specific reaction rate (k) and the order of reaction
  • Determine the activation energy of the reaction

Theory

Researchers typically use a batch reactor to study reaction kinetics under ideal conditions. A batch reactor can be used to find the reaction rate constant, activation energy and order of the reaction. The use of a batch reactor for the most part eliminates the effects due to fluid flow on the resulting reaction rates. Consequently, the data reflect the intrinsic kinetics for the reaction being investigated.

Your goal for this experiment is to find the kinetics for a liquid-phase (mildly exothermic) irreversible reaction. The reaction chosen for the experiment is given below

This reaction is first order with respect to NaOH and ethyl acetate. You will determine if your experimental data confirms the order of the reaction and the activation energy. You will use two probes to measure the extent of reaction.

Data Analysis for Batch Reactor

For batch systems, the usual procedure is to collect concentration time data, which we then use to determine the rate law.

Data for homogenous reactions is most often obtained in a batch reactor. After postulating a rate law and combining it with a mole balance, we next use any or all of the methods in the steps 5 to process the data and arrive at the reaction orders and specific reaction rate constant.

Steps in Analyzing Rate Data for Batch Reactor

  1. Power law models for homogeneous reaction
  1. Mole balance for batch reactor
  1. Calculate as a function of concentration to determine reaction order
  1. Combine the mole balance and power law model and then take the natural log
  1. Find from versus t data by
  2. Graphical method
  3. Finite differential method
  4. Polynomial
  1. Plot versus and find reaction order , which is the slope of the line fit to the data
  1. Find k.

The Reaction Rate Constant

The reaction rate constant is not truly constant; it is merely independent of the concentrations of the species involved in the reaction. The quantity k is referred to as either the specific reaction rate or the rate constant. It is almost always strongly dependent on temperature.

The temperature dependence of the specific reaction rate k, could be correlated by the Arrhenius equation

Where A = preexponential fact or frequency factor

E = activation energy, J/mol or cal/mol

R = gas constant = 8.314 J/molK

T = absolute temperature K

The activation energy can be thought of as barrier to energy transfer between reaction molecules that must be overcome.

Set-up

Equipment and Accessories

  • LS-32001-6 Batch Reactor Unit w/ Data Acquisition System
  • 1 L of 2.3% Sodium hydroxide solution per each run
  • 1 L of 5% Ethyl acetate solution per each run

Chemical Preparation

2.3% Sodium hydroxide solution

  1. Weigh 23g/L of caustic soda (sodium hydroxide pellets) using a beaker and measuring scale.
  1. Add distilled water to the beaker and gently stir using a glass rod.
  1. Transfer the concentrated solution to a 1L measuring cylinder, and add distilled water until the volume reaches 1L.
  1. The solution is now 2.3% sodium hydroxide. Prepare additional batches as necessary.

5% Ethyl acetate solution

  1. Using a measuring cylinder, measure 50ml of ethyl acetate.
  1. Add distilled water until the volume reaches 1L and stir gently using a glass rod.
  1. The solution is now 5% ethyl acetate. Prepare additional batches as necessary.

NOTE

Dispose of all unused chemicals in an appropriate manner after the experiment. Under no circumstances should the chemicals be allowed to flow into the main drains.

Setup

Benchtop Chemical Reactors

LEGEND

A - Dosing Pump 2

B - Dosing Pump 1

C - Feed Tank 2 (Sodium Hydroxide)

D - Feed Tank 1 (Ethyl Acetate)

E - CSTR

F - Hot Water Tank

G - Batch Reactor

H - Delay Section

Ph and Conductivity Meters

LEGEND

A - PH Meter

B - Conductivity Meter

C - Main Switch

D - Stirrer Speed Regulator

E - Control Panel

Batch Reactor

LEGEND

A - Hot WaterInletPort

B - ChemicalFeedPort

C - DrainPort

D - PH Probe

E - Thermocouple

F - Agitator / Stirrer

G - VacuumPort

H - Pressure Gauge

I - Vacuum Gauge

J - Vacuum Valve

K - Heater

L - Conductivity Probe

Procedure

  1. SwitchON the main power on the unit.
  1. Set the temperature of the hot water tank to 300C and turn ON the heater
  1. Start pre heating the ethyl acetate and the sodium hydroxide at the same temperature as the heater (in this case , 300C) using the hot plates.
  1. When the heater has reached 300C, turn ON the Pump for hot water to circulate within the coils of the reactor tank, also turn ON the Batch Reactor heater.
  1. Fill the reactor with the pre-heated 700ml of 5% ethyl acetate solution then followed by the pre-heated 700ml of 2.3% sodium hydroxide solutionthrough the feed port of the batch reactor.
  1. Immediately screw the cap for the feed port back and ensure that it is screwed tightly to prevent air leakage.
  1. Switch on the agitator/stirrer and set the minimum speed of 200 rpm
  1. Record the pH and conductivity value at every 2 minutes interval at Table 1 . Notice that the conductivity should now begin to drop. Record until the readings reach a stable value (i.e. last least three consecutive readings are the same )
  1. Initial (t = 0) conductivity readings is difficult to determine using the reactor vessel as the reaction occurs very fast. Initial reading can be obtained by mixing the 300 ml pre heated ethyl acetate solution and the 300 ml pre-heated sodium hydroxide in a standard beaker. Immediately, take note of the initial conductivity, usually the highest conductivity reading is considered the initial readings. .
  1. Turn OFF the Pump and the batch reactor heater.
  1. Drain the product out from the drain port.
  1. Clean the reactor tank using distilled water before proceeding at the next temperature run. (note : reading of the conductivity should go back to almost zero)
  1. Repeat steps 2 to 11 but set the temperature of the hot water tanks to 45 and 550C . Record in Tables 2 and 3 respectively.
  1. Switch OFF the main power and power supply after conducting the experiment..

Data and Results

Table 1 :

Volume of tank / 2L
Temperature / 25°C
Stirrer speed / 200 rpm
Time (min) / Conductivity (ms/cm) / pH / Conversion %
0
2
4
6
8
10
12
14
16
18
20
22
24

Table 2 :

Volume of tank / 2L
Temperature / 50°C
Stirrer speed / 200 rpm
Time (min) / Conductivity (ms/cm) / pH / Conversion %
0
2
4
6
8
10
12
14
16
18
20
22
24

Table 3 :

Volume of tank / 2L
Temperature / 75°C
Stirrer speed / 200 rpm
Time (min) / Conductivity (ms/cm) / pH / Conversion %
0
2
4
6
8
10
12
14
16
18
20
22
24

Calculations

  1. %Conversion (X)

Where C(t) = conductivity at any time t

C(t=0) = initial conductivity

  1. Determine the order of reaction and reaction rate constant k by the following
  2. Show the complete derivation of the working formula
  3. Substitute the necessary data and show tabulated the result
  4. Use Graphical method to evaluate vs and show the graph (see p262 Fogler, 4th ed )
  5. Determine the order of reaction from the slope of the graph
  6. Determine the rate constant k using the graph
  1. From the above, give the specific rate of reaction
  1. Calculate the specific reaction rate for the other two temperatures in the same manner
  1. Calculate the activation energy E based from the k computed (see p. 95, Fogler )
  1. Tabulate k and Temperature T(K) in Excell
  2. Plot ln(k) in y axis vs 1/T
  3. Get the equation that best fit for the data. ( y = mx + b)

Slope m =

  1. Solve for E
  1. Show all the steps of the calculations, graphs and tabulated results on the report

Figures to be Prepared

  • Plot in one graph %Conversion (in y-axis) vs time (x-axis) the data in three tables at different temperature
  • vs
  • ln(k) in y axis vs 1/T

Discussions

  1. Give the analysis of the graphs %Conversion vs time. Comment on the effect of temperature on the %conversion of the reactant .
  1. Compare the order of reactionn, reaction rate constant k and activation energy E of the reaction with the literature value. Is there a reasonable agreement ?

References

Fogler H.S., Elements of Chemical Reaction Engineering , 4th Ed, Pearson International

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