UNIVERSITY OF PRETORIA

DEPARTEMENT OF CHEMICAL ENGINEERING

KINETICS (CKN 320)

August 2010 SEMESTER TEST 1 TIME : 1.75 HOURs

TOTAL 25

Read this before you start:

·  All Octave graphs should be redrawn on your script. No printouts allowed

·  Any form of communication on your computer will result in serious consequences. There are more ways to monitor this than you are aware of.

·  Take care in presenting your scripts. Remember that only the scripts will be marked and not the m files!

·  Remember that Octave is only a tool to help you with calculations. This is not an exam to test you computer/programming skills, it is an exam to test your insight in the subject. Remember to illustrate your insight neatly on the script!

·  Remember to give intermediate calculated values on the script, the m-file will not be marked.


Question 1 [17]

The following reversible and catalysed liquid phase reaction occurs in a constant volume batch reactor. The reaction is known to obey elementary kinetics.

A run was performed using the starting concentrations given in the Table below. The aim was to control the temperature at 50°C, but decent control was only achieved after 20 minutes (after 20 minutes the temperature remained at 50°C). Given the info in the table answer the following questions.

a)  Was the temperature in the first 20 minutes too hot or too cold? Give a reason. [2]

b)  What would the equilibrium conversion of A be if the run was performed at 100°C? You can use the same initial concentrations (@ t=0) as the run in the table. Clearly show your equations in terms of conversion (x) and initial concentrations. Bonus marks will be awarded for the correct numerical answer, but don’t spend too much time on the numerical solution. [5]

c)  Will the answer in (b) be higher or lower if the catalyst concentration was 10 g/l? [2]

d)  If only A and B are fed (@ 2mol/l A, 3 mol/l B and 10 g/l of catalyst) and the temperature is steady at 50°C right from the start, what will the rate of formation of C (with a mass basis) be at time zero. Give a numerical value. [8]

Question 2 [10]

a)  The following irreversible and catalysed liquid phase reaction is studied in a batch reactor:

The rate constant at 70°C is known to be 0.01 liter.g-1.s-1.Given initial concentrations as follow:

CAo=0.5 mol/l, CCo=0.7 mol/l , CDo=0.4 mol/l, Ccat=40 mg/l

What will the conversion be after 20 minutes of operation [3]

b)  The following gas phase reaction is studied in a constant volume batch reactor operating at 300K:

Equimolar amounts of A and B is charged at t=0 at a pressure of 2 bar. Given an isothermal run, what will the concentration of B be if the total pressure is 3.2 bar. [4]

c)  The following irreversible and catalysed liquid phase reaction is studied in a batch reactor:

The reaction rate constant at 20°C (defined with respect to A) is known to be 0.002

mol.g-1.s-1. How long will it take to convert 50% of a mixture containing 0.1 mol/l of A and 0.3 mol/l of B using 0.3 g/l of catalyst. [3]