Unit 22. Analysis of Steady State CSTRs

This website provides learning and teaching tools for a first course on kinetics and reaction engineering. Here, in Part III of the course, the focus is on the modeling of chemical reactors. In particular, it describes reaction engineering using the three ideal reactor types: perfectly mixed batch reactors, continuous flow stirred tank reactors and plug flow reactors. After considering each of the ideal reactor types in isolation, the focus shifts to ideal reactors that are combined with other reactors or equipment to better match the characteristics of the reactor to the reactions running within it.

Section C of Part III examines reaction engineering for continuous flow stirred tank reactors (CSTRs). As was done for batch reactors in the previous section of the course, common reaction engineering tasks are identified and the qualitative performance of CSTRs is examined. CSTRs are typically designed to operate at steady state, but getting them started and shutting them down involves transient operation. The mathematical analysis of transient reactors differs from that for steady state reactors, so these two situations are presented separately. In addition, CSTRs can display a phenomenon known as multiplicity of steady states which is discussed in this section.

CSTRs are typically designed to optimize their steady state operation. Accurate mathematical models are needed to perform such optimization or to perform other engineering tasks associated with the steady state operation of CSTRs. Unit 22 describes and illustrates how to quantitatively analyze a steady state CSTR using the design equations that were derived in Unit 17. In a manner similar to Unit 19 for batch reactors, it describes how to identify zero-valued and insignificant terms that can be dropped from the design equations. Heat transfer in a CSTR is essentially the same as heat transfer in a batch reactor, so the same energy balances on the heat transfer fluid that were used for batch reactors can be used to model CSTRs.

Learning Resources

• Archive (.zip) - Contains all learning resources listed below for this unit
• Documents to Read:
  • Unit 22 Informational Reading (.pdf)
  • Example 22.1 (.pdf)
  • Example 22.2 (.pdf)
  • Example 22.3 (.pdf)
• Videos to Watch (please right-click and save, then play back locally on your computer):
  • Unit 22 Informational Video (.mov)
  • Example 22.1 Video (.mov)
  • Example 22.2 Video (.mov)
  • Example 22.3 Video (.mov)
• Reference Files:
  • Unit 22 Definitions, Nomenclature and Equations (.pdf)
• Other Files:
  • Example_22_1.m - MATLAB file used in the solution of Example 22.1
  • Example_22_2.m - MATLAB file used in the solution of Example 22.2
  • Example_22_3.m - MATLAB file used in the solution of Example 22.3

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
  • Learning Activity Files to make available to students before class
    • Activity 1 Handout (.pdf)
    • Activity 2 Handout (.pdf)
  • 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_22_1.m - MATLAB file used in the solution of Activity 22.1
    • Activity_22_2.m and Activity_22_2a.m - MATLAB files used in the solution of Activity 22.2

Practice Problems

1. Find the feed temperature that maximizes the conversion in Example 22.1.

2. A 150 °C solution containing 2 mol L^-1 of A is fed to a 500 L CSTR at a rate of 250 L h^-1. A jacket surrounding the CSTR contains a fluid at a constant temperature of 180 °C. The contact area between the CSTR contents and the jacket is 2 m² and the overall heat transfer coefficient is equal to 500 kcal m^-2 h^-1 K^-1. Within the reactor reaction (2a) occurs at a rate given by equation (2b). The pre-exponential factor for the rate coefficient in equation (2) is 1.14 x 10⁹ L mol^-1 h^-1 and the activation energy is 16.2 kcal mol^-1. The reacting solution has a constant density and a constant heat capacity of 1.17 cal mL^-1 K^-1. The heat of reaction is 18.2 kcal mol^-1 and is independent of temperature. At steady state, what are the outlet temperature and the conversion of A?

(Problem Statement as .pdf file)