Elements of
Chemical Reaction Engineering
6th Edition



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Essentials of
Chemical Reaction Engineering
Second Edition

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Chapter 13: Unsteady State Nonisothermal Reactor Design

Example DVD13-2: Startup of a CSTR

 

Again we consider the production of propylene glycol (C) in a CSTR with a heat exchanger. Initially there is only water at 75°F and 0.1 wt % H2SO4 in the 1420-gallon reactor. The feed stream consists of 400 lb mol/h of propylene oxide (A), 5000 lb mol/h of water (B) containing 0.1 wt % H2SO4 ,and 20 lb mol /h of methanol (M). Plot the temperature and concentration of propylene oxide as a function of time, and a concentration vs. temperature graph for different entering temperatures.

  
     
 




Solution

  
     
 

image 09eq32.gif

  
     
  image 09eq33.gif




(CDE13-2.1)



(CDE13-2.2)



(CDE13-2.3)



(CDE13-2.4)
     
     
     
  image 09eq34.gif


(CDE13-2.5)


(CDE13-2.6)



(CDE13-2.7)




(CDE13-2.8)
  image 09eq35.gif

(CDE13-2.9)
       
   

 

  
       
  image 09eq36.gif

(CDE13-2.10)
     
 

Neglectingimage 09eq37.gifbecause it changes the heat of reaction insignificantly over the temperature range of the reaction, the heat of reaction is assumed constant at

  
     
  image 09eq39.gif  
     
 

The POLYMATH program is shown in Table CDE13-2.1. Figures CDE13-2.1 and CDE13-2.2 show the reactor temperature and concentration of propylene oxide as a function of time. One observes that both the concentration of A and the temperature oscillate around their steady-state values before coming to rest at these values. The corresponding phase-plane plot of concentration and temperature shows a spiral approach to the steady state (Figure CDE13-2.3).



Table CDE13-2.1



 


Figure CDE13-2.1
Temperature Time Trajectory


 


Figure CDE13-2.2
Concentration Time Trajectory


 


Figure CDE13-2.3
Concentration temperature phase plane Plot