Documentation:CHBE Exam Wiki/Module 2 - Reactors

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CHBE 241
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Chemical and Biological Engineering
Welcome to the CHBE Exam Resources Wiki!

This wiki is intended to host past exams

with fully worked-out hints and solutions
Past Exams
Final Exam 2016W
Midterm Exam 1 2016W
Midterm Exam 2 2016W
Problem Sets
Module 1 - Process Basics
Module 2 - Reactors
Module 3 - Separations 1
Module 4 - Separations 2
Module 5 - Non-reactive Energy Balances
Module 6 - Reactive Energy Balances


Question 1

A stack gas contains mol percentages of 60% N2, 20% CO2, 10% O2 and the rest is water. What is the composition of CO2 on a dry basis?

Solution

Using a basis of 100 moles, the total number of moles of all the species present excluding water is
Hence, the total composition of CO2 on a dry basis is,



Question 2

Reindeers are a source of great contention in Jasper. Therefore it has been decided that their population should decrease by 100 reindeers/yr. If 500 reindeers are born each year, and wolves/bears eat 300 reindeers/yr, how many reindeers have to be relocated from Jasper to meet the goal?

Solution

Mass balance:



Question 3

The waste stream for a natural gas processing facility is treated to remove the sulfur dioxide where the initial concentration of SO2 is 5 mol% and the remainder is air. In a scrubber, the waste gas is mixed with pure water flowing at 100 L/min. The only mass transfer that occurs in this process is the transfer of some SO2 into the water. It was found that the concentration of SO2 in the waste gas vented and exiting water stream are 0.5 wt% and 40 wt% respectively.

Question 3a

Draw a block flow diagram for the described process.

Solution

Diagram for MOD 2 Q4 a CHBE 241


Question 3b

Calculate the molar flow rates of all the streams

Solution

Step 1 - Determine the molar flow rate for Stream 3


Step 2 - Determine the average molecular weight for Stream 4


Step 3 - Determine the molar flow rate for Stream 4

Using the water balance,


Step 4 - Determine the flow rates of Stream 1 and Stream 2

Overall balance,

Air balance,



The flow rate of the streams are,


Question 4

The following equation shows the combustion process of ammonia to produce nitric oxide:
4NH3 + 5O2 → 4NO + 6H2O

Question 4a

Calculate the ratio of O2 reacted to NO formed on a lb-mol basis

Solution



Question 4b

If ammonia is fed to a continuous reactor at a rate of 100.0 kmol/h, what oxygen feed rate would correspond to 50.0% excess O2 ?

Solution

The theoretical amount of O2 reacted is

The amount of O2 fed is


Question 4c

If 120 kg of oxygen and 60 kg of ammonia are fed into a batch reactor, determine

  • the limiting reactant
  • the percentage at which the other reactant is in excess
  • extent of reaction
  • mass of NO produced

Solution

Limiting reactant:

Hence, oxygen is the limiting reactant

Required NH3

Excess NH3


Extent of reaction:


Mass of NO:



Question 5

The production of monochloroethane (C2H5Cl) follows the following process in a reactor.


where dichloroethane (C2H4Cl2) is the undesired product. The selectivity of the desired to the undesired product is 3:1.

In the feed, chlorine (Cl2) and ethane (C2H6) are fed at 200 mol/hr and 100 mol/hr respectively. The outlet of the reactor is then fed into a separator where the desired product, C2H5Cl is separated in the bottoms while the top fraction contains only HCl, Cl2 and C2H4Cl2 which is removed from the system. Also, a recycle stream containing Cl2, C2H5Cl and C2H6 from the top stream feeds back to the initial feed stream where the 2 streams are mixed before being fed back into the reactor.

Question 5a

Draw a block flow diagram showing the important unit operations and streams in the process described above.

Solution

Solution for CHBE 241 MOD1Q5



Question 5b

Perform a degree of freedom analysis for the overall process and show whether the system is fully specified.

Solution
Parameter Values
Unknowns 6 (n4, n6,HCl, n6,Cl2, n6,C2H4Cl2,S1, S2 )
Species balances 5
Other relationships 1 (Selectivity)
DOF 0