Unit 32. Ideal Semi-Batch Reactors

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.

The preceding sections of Part III examined reaction engineering using one of the three ideal reactor types in isolation. Section E considers the important topic of matching the reactions being run to the reactor that is best-suited to those reactions. It examines ways in which the ideal reactors can be modified or augmented so that their performance is further improved. In all cases considered in this section, each reactor is still one of the three ideal types, and it is still modeled as described in the preceding sections. The things that differ from prior analyses are the external connections to the reactor or reactors. These changes lead to improved performance for a selected class of reaction, but they can also affect the mathematical approach used to solve the reactor model equations.

Unit 32 examines a way of augmenting the operating procedure for a batch reactor in order to enhance its performance characteristics under selected conditions. Specifically, this unit examines semi-batch reactors. In semi-batch processing, most of the reagents are treated as they would be under batch processing: they are put into the reactor prior to starting the reaction, and they are removed from the reactor after the reaction is terminated. In contrast to batch processing, during semi-batch processing, at least one reagent is added or removed while the reaction is taking place. This unit describes the modeling of reactors that are operated as semi-batch reactors.

Learning Resources

• Archive (.zip) - Contains all learning resources listed below for this unit
• Documents to Read:
  • Unit 32 Informational Reading (.pdf)
  • Example 32.1 (.pdf)
  • Example 32.2 (.pdf)
• Videos to Watch (please right-click and save, then play back locally on your computer):
  • Unit 32 Informational Video (.mov)
  • Example 32.1 Video (.mov)
  • Example 32.2 Video (.mov)
• Reference Files:
  • Unit 32 Definitions, Nomenclature and Equations (.pdf)
• Other Files:
  • Example_32_1.m - MATLAB file used to model the semi-batch reactor in Example 32.1
  • Example_32_2.m - MATLAB file used to analyze the semi-batch reactor in Example 32.2
  • Example_32_2_equil.m - MATLAB file used to model the equilibrated reactor in Example 32.2
  • Example_32_2_semi_a.m - MATLAB file used to model the semi-batch reactor in Example 32.2 during the time when the pressure valve is closed
  • Example_32_2_semi_b.m - MATLAB file used to model the semi-batch reactor in Example 32.2 during the time when the pressure valve is open

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 32.1
  • 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_32_1_batch.m - MATLAB file used to model the batch reactor in Activity 32.1
    • Activity_32_1_semi.m - MATLAB file used to model the semi-batch reactor in Activity 32.1

Practice Problems

1. Acid A is to be neutralized using base B by slowly adding a 2 M solution of the base to a 10 M solution of the acid. The neutralization reaction is irreversible with a heat of reaction equal to -44 kcal mol^-1. The reaction is first order in both acid and base with a pre-exponential factor of 8.11 x 10¹² L mol^-1 s^-1 and an activation energy of 17.7 kcal mol^-1. A jacketed, perfectly mixed, 25 L batch reactor will be charged with 4 L of the 10 M solution of A at 20 °C, while cooling water at 20 °C flows at 0.1 kg min^-1 to the perfectly mixed, 0.5 L jacket. The heat transfer area is 0.6 ft² and the heat transfer coefficient is 1.13 x 10⁴ cal ft^-2 h^-1 K^-1. The cooling water and the solutions of A and B may be taken to have a constant density of 1 g cm^-3 and a constant heat capacity of 1 cal g^-1 K^-1. The pressure in the reactor will be constant and equal to 1 atm. Plot the acid concentration and the reactor temperature as a function of time during which the base solution at 20 °C is being added at a rate of 1.0 L min^-1.

(Problem Statement as .pdf file)