Unit 38. Heterogeneous Catalytic Reactions

This website provides learning and teaching tools for a first course on kinetics and reaction engineering. In the preceding parts of the course, the reacting fluid was always treated as if it was homogeneous, and only ideal reactor types were considered. The knowledge gained to this point is sufficient for reaction engineering for many commercial processes. Nonetheless, there are situations where the reactor does not conform to one of the ideal types and/or the rates are affected by the kinetics of physical processes in addition to the chemical reaction rate. Part IV of the course surveys a few such situations. It does not provide an in-depth analysis of any of them, but the information provided should serve as a good foundation for further study.

This, final section of the course, considers situations where the kinetics are affected by factors other than the rate of the chemical reaction. This topic was introduced as part of the discussion on performing kinetics experiments in Part II of the course, specifically in Unit 12. The perspective and objective there was to ensure that these other factors were sufficiently small in magnitude so that they could be ignored. In Section A of this part of the course, specifically in Unit 37, it was noted that when two phases are present in a reactor, concentration and temperature gradients may exist near the interface between phases, and the design equations must properly account for those gradients. Section B of Part IV introduces a few ways that this can be accomplished. Once again, a limited, introductory presentation is offered with comprehensive treatment left for a second, more advanced course on kinetics and reaction engineering.

Unit 38 presents an abbreviated and simplified discussion of the modeling of packed bed reactors where significant concentration and/or temperature gradients exist. Such gradients may be present in the boundary layer between the bulk fluid and the external surface of the catalyst particles, or they may exist within the porous catalyst particles themselves. Unit 38 defines the Thiele modulus for first order reactions in spherical catalyst particles and demonstrates its relationship to the catalyst effectiveness factor, which is also defined in the unit. The unit shows how the ideal PFR model can be modified to account for such gradients by incorporation of an effectiveness factor. It also illustrates how an independent set of design equations for the catalyst phase can be formulated and used in conjunction with a set of design equations for the fluid phase in situations where the effectiveness factor changes along the length of the reactor.

Learning Resources

• Archive (.zip) - Contains all learning resources listed below for this unit
• Documents to Read:
  • Unit 38 Informational Reading (.pdf)
  • Example 38.1 (.pdf)
  • Example 38.2 (.pdf)
• Videos to Watch (please right-click and save, then play back locally on your computer):
  • Unit 38 Informational Video (.mov)
  • Example 38.1 Video (.mov)
  • Example 38.2 Video (.mov)
• Reference Files:
  • Unit 38 Definitions, Nomenclature and Equations (.pdf)
• Other Files:
  • Example_38_1.m - MATLAB file used to perform the calculations for Example 38.1
  • Example_38_2.m, Example_38_2a.m, Example_38_2b.m and Example_38_2_cat_bal.m - MATLAB files used to perform the calculations for Example 38.2

Teaching Resources

• Archive (.zip) - Contains all teaching resources listed below for this unit
• Sample Class
  • Online Pre-class Quiz (.pdf file)
  • Redacted slides to make available to students before class
    • Keynote 09
    • PowerPoint
  • Other files to make available to students before class
    • Worksheet for Activity 38.1
  • Class Lesson Plan (.pdf)
  • Complete slides to make available to students after class
    • Keynote 09
    • PowerPoint
  • Other files to make available to students after class
    • Activity_38_1.m - MATLAB files used in the solution of Activity 38
• Alternative Questions (.pdf) that could be used in a pre-class quiz

Practice Problems