Energy Balances in Stirred Tank Reactors: Example Problems

Try to solve these problems before watching the solutions in the screencasts.

Example Problem 1

The liquid-phase reaction A → B takes place in an adiabatic batch reactor. The initial temperature is 100°C. Initially, the reactor (100 L volume) contains only A (CA0 = 5 mol/L). The heat of reaction is -14.6 kJ/mol and is independent of temperature. 
Heat capacity CPA = 83.6 J/(mol K) 
Reaction rate rA = -kCA2.5       k = 2.5 x 10-3e(-1760/T) (L/mol)1.5 s-1  
What is the reactor temperature when 60% of A has reacted?  How long does it take to reach 60% conversion of A?

Some additional example problems

Unsteady-State Adiabatic CSTR

Using information about an adiabatic CSTR, determine whether the reactant concentration is increasing or decreasing at short times.

Heat Transfer Rate for a Semibatch Reactor

An example of a semibatch reactor that necessitates heat transfer to maintain reaction temperature. Determine the rate of heat transfer as a function of time.

Example Problem 2

The liquid-phase reaction A + B → C takes place in an adiabatic semibatch reactor. The reaction is first order in A and first order in B. Initially, 500. mol of A are in the reactor at 25°C, and the initial volume is 50. L. Reactant B at 50°C is fed to the reactor at a molar flow rate at 10. mol/min and a volumetric flow rate of 1.0 L/min. The feed of B is stopped after 500. mol have been added. Plot temperature and number of moles of A, B, and C as a function of time up to 120 minutes. 
CPA = CPB = 15 cal/(mol K)        CPC = 30. cal/(mol K)
ΔH = -6,000 cal/(mol K)       k = 1.7 x 104e(-10,000/RT)


Adiabatic Semibatch Reactor Part 2 – Presents the POLYMATH program used to solve the differential equations generated in the screencast ‘Adiabatic Semibatch Reactor Part 1.