Unit 11. Laboratory Reactors

This website provides learning and teaching tools for a first course on kinetics and reaction engineering. The course is divided into four parts (I through IV). Here, in Part II of the course, the focus is on chemical reaction kinetics, and more specifically, on rate expressions, which are mathematical models of reaction rates. As you progress through Part II, you will learn how rate expressions are generated from experimental kinetics data.

The second section of Part II of the course focuses on gathering experimental data that can be used to test a rate expression. Obtaining those data requires the use of a reactor, and the subsequent analysis of the resulting data will require an accurate mathematical model for the reactor. Consequently Section B examines common types of laboratory reactors and models for them. The commonly used reactor models make assumptions about flow and other aspects of reactor operation, so methods for testing the conformity of experimental reactors to their models are discussed here. Section B also provides some guidelines for the generation of experimental kinetics data.

Unit 11 introduces models for three different types of reactors that are commonly used to generate kinetics data in the laboratory, namely batch reactors, continuously stirred tank reactors and plug flow reactors. The critical assumptions in each model are identified, preferred operational methods are discussed and examples are presented. It is critical to test a laboratory reactor to ensure it meets the assumptions being used to model it before using it to generate kinetics data. For a flow reactor, one way of doing this is to measure the age function or residence time distribution and compare it to that predicted by the reactor model. This process is described and illustrated in Unit 11, as well.

Learning Resources

• Archive (.zip) - Contains all learning resources listed below for this unit, except for the simulators
• Documents to Read:
  • Unit 11 Informational Reading (.pdf)
  • Example 11.1 (.pdf)
  • Example 11.2 (.pdf)
  • Example 11.3 (.pdf)
  • Example 11.4 (.pdf)
  • Example 11.5 (.pdf)
• Videos to Watch (please right-click and save, then play back locally on your computer):
  • Unit 11 Informational Video (.mov)
  • Example 11.1 Video (.mov)
  • Example 11.2 Video (.mov)
  • Example 11.3 Video (.mov)
  • Example 11.4 Video (.mov)
  • Example 11.5 Video (.mov)
• Reference Files:
  • Unit 11 Definitions, Nomenclature and Equations (.pdf)
• Other Files:
  • Example_11_4.m - MATLAB file used in the solution of Example 11.4
  • A video illustrating the response of a CSTR to step change and impulse stimuli. (.mov)
  • Stimulus-Response Simulators
    • CSTR Impulse Response Simulator (zipped .jar file)
    • CSTR Step Change Response Simulator (zipped .jar file)
    • PFR Step Change Response Simulator (zipped .jar file)
     
    Please note that these simulators are intended for educational purposes only. They should not be used for any other purpose, and if they are, the author does not bear any responsibility or liability for the consequences.
     
    The “zipped .jar file,” when unzipped, will produce a folder that contains a .jar file and a folder named "lib". Not surprisingly the latter folder contains additional libraries and files that the simulator uses. To run the simulator, launch the .jar file either from the command line using java -jar [name of .jar file], or by double clicking it if your operating system supports it. The simulators require JAVA 1.6 or later in order to run. There is a User's Guide under the Help menu that describes how to use the simulators.
     
    

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
  • Class Lesson Plan (.pdf)
  • Complete slides to make available to students after class
    • Keynote 09
    • PowerPoint
  • Solutions to the in-class activities to make available to students after class
    • Activity 11.2a Solution (.pdf)
    • Activity 11.2b Solution (.pdf)
    • Activity 11.2c Solution (.pdf)
  • MATLAB files used in the solutions to the in-class activities to make available to the students after class
    • Activity_11_2a.m
    • Activity_11_2b.m
• Alternative Questions (.pdf) that could be used in a pre-class quiz
• Alternative In-Class Learning Activities
  • Alternative Activity 11.1 (.zip) - an activity where students propose a method to measure the residence time distribution of the patrons of a popular night club.
  • Alternative Activity 11.2 (.pdf) - an activity where students examine real laboratory reactors.
  • Alternative Activity 11.3 (.zip) - an activity where students perform a web search to find examples of laboratory reactors.
  • Alternative Activity 11.4 (.zip) - an activity where students use a qualitative analysis to predict the shape of the response curves for the application of step and impulse stimuli to CSTRs and PFRs.
  • Alternative Activity 11.5 (.zip) - an activity where students act as fluid elements in a PFR and examine the response to step change and impulse stimuli.
  • Alternative Activity 11.6 (.zip) - an activity where students analyze data for the response of a reactor to a step change decrease in tracer concentration.
• Simulator Source files
  • CSTR Impulse Response Simulator (zipped .jar file)
  • CSTR Step Change Response Simulator (zipped .jar file)
  • PFR Step Change Response Simulator (zipped .jar file)
   
  Please note that these simulators are intended for educational purposes only. They should not be used for any other purpose, and if they are, the author does not bear any responsibility or liability for the consequences.
   
  The “Netbeans Project folders” contain the Netbeans java project used to create them. Providing them in this way will allow instructors or students familiar with java and the Netbeans development environment to modify them. They were developed using version 6.7 of Netbeans. They use the Swing Application Framework, which is not supported in version 7.1 or higher of the Netbeans IDE. They are no longer in development, and I am not available to consult on any issues encountered when using them.

Practice Problems

1. A reactor with a fluid volume of 10 L needs to be tested to determine whether it can be modeled accurately as an ideal CSTR. A steady flow of solvent at 25 L/min is established; there is no tracer in the solvent. Suddenly a valve is opened so that the flow into the reactor contains a tracer at a 3 M concentration. The data below (and in this Excel® workbook) were measured following the opening of the valve. Use these data to calculate the value of the age function for each measurement and plot the age function as a function of the fluid “age.”

(Problem Statement as .pdf file)

2. Derive an expression for the response of a reactor system that consists of two ideal CSTRs connected in series when an impulse stimulus is applied. Then use that expression to generate an expression for the age function for this reactor system. You may assume that the effluent from the first reactor immediately enters the second reactor without any time lag. You may further assume that the fluid volume in the reactors is constant, the volumetric flow rate is constant and the density of the fluid is constant. The reactor operates at steady state with no tracer in the feed prior to the stimulus which is applied to the inlet of the first reactor at time t = 0.

(Problem Statement as .pdf file)

3. The data given in problem 11.1 were actually the response of two CSTRs connected in series. The first reactor's fluid volume was 1 L and the second reactor's fluid volume was 9 L. Plot the age function from the experimental reactor and the age function for the two ideal reactors connected in series, and based upon the plot, decide whether the experimental reactors can be modeled as two ideal CSTRs connected in series.

(Problem Statement as .pdf file)

4. Suppose you have an 18 gal stirred tank in your lab that you want to use to perform kinetics experiments. You establish a steady flow of water through the reactor at a rate of 5 gal min^-1. You then start a timer, at just the same time that you start continuously adding dye to the inlet at a concentration of 2 oz gal^-1. You then proceed to measure the concentration of tracer in the outlet as a function of time. The resulting data are given in the table below. On the basis of the age function of the stirred tank, do you believe it can be modeled as an ideal CSTR?

(Problem Statement as .pdf file)

5. In order to test the ideality of a 0.65 gal stirred tank reactor, a steady 1 gal min^-1 flow of water was established in it. 25 g of a tracer were then dumped into the tank, and the mass concentration of tracer in the reactor effluent was measured as a function of time. The resulting data are listed in the table below and in the Excel file prob_11_5_data.xlsx. Based on the age function of the stirred tank reactor, can it be modeled as a perfectly mixed CSTR?

(Problem Statement as .pdf file)