Elements of
Chemical Reaction Engineering
6th Edition



Home

Essentials of
Chemical Reaction Engineering
Second Edition

  Select  Chapter  >>     TOC     Preface     1     2     3     4     5     6     7     8     9     10     11     12     13     14     15     16     17     18     Appendices  
›

By Chapter Hide

  • Objectives
  • Living Example Problems
  • Extra Help
  • - Summary Notes
  • - LearnChemE Screencasts
  • - FAQs
  • - Interactive Computer Modules
  • Additional Material
  • Self Test
  • i>Clicker Questions
  • Professional Reference Shelf

By Concept Hide

  • Interactive Modules
  • -Web Modules
  • -Interactive Computer Games
  • Living Example Problems

U of M Hide

  • Asynchronous Learning
  • ChE 344
  • ChE 528

Chapter 5: Isothermal Reactor Design: Conversion

Additional Homework Problems

CDP5-BC

(Ecological engineering) Several researchers have examined the feasibility of using wetlands to clean up high volumes of polluted water. Experimental wetland three (EW3) at the Des Moines Experimental Wetlands site in Illinois has a volume of 15,000,000 dm3 and an inflow of 70,000 dm3 of water per house from the Des Plaines River. The outflow eventually returns to the river. During late spring, the river water typically contains IMAGE 04eq04.gif of the herbicide atrazine. However, the maximum contaminant level (MCL) under the federal Drinking Water Act is As a first approximation treat EW3 as a perfectly mixed CSTR and assume that atrazine decomposition is first order with k= 0.0025 h -1.

(a) First consider that EW3 contains water but no atrazine at the time the flow from the river is diverted. Plot C A as a function of t for the case where the outflow is kept equal to inflow. After what time does C A reach 99% of its steady-state value? Is it below the MCL?
(b) Next consider the case where EW3 initially contains neither atrazine nor water. Outflow is kept at 50,000 dm 3 /h for 750 h. after which it becomes 70,000 dm 3 /h. Plot the concentration as a function of time and explain how it differs from the plot in part (a). Plot the number of moles of atrazine in EW3 versus time. Why is N A increasing while C Aversus time is decreasing?
(c) EW3 is operating initially at the steady-state conditions found in part (a). Suppose that weekly thunderstorms periodically increase the amount of atrazine leached into the Des Plaines River, thereby increasing the concentration in the inflow to EW3. Concentration as a function of time is given by

IMAGE 04eq5(a).gif

where the trigonometric argument is in radians. Plot C A0 and C A versus t on the same graph. Does the outflow exceed the MCL at any time? Do C A0 and C A reach their maximums and minimums at the same times? Does C Aever exceed C A0? How can this be?

(d) EW3 is operating initially at the steady-state conditions found in part (a). Suppose that there is a drought lasting 1000 h during which the evaporative flux of water from EW3 is 10,000 dm 3 /h. The overall water balance is such that the wetland volume remains constant, however. No atrazine leaves via evaporation. What does the concentration profile look like? How can this be explained?