CONTENTS

Front Matter

Title Page, Preface and Acknowledgements
About the Author
Status, History, Issues and Updates
Complementary Textbooks
Teaching Notes and Resources
A Note about Numerical Solutions

Course Units

I. Chemical Reactions
1. Stoichiometry and Reaction Progress
2. Reaction Thermochemistry
3. Reaction Equilibrium
II. Chemical Reaction Kinetics
A. Rate Expressions
4. Reaction Rates and Temperature Effects
5. Empirical and Theoretical Rate Expressions
6. Reaction Mechanisms
7. The Steady State Approximation
8. Rate-Determining Step
9. Homogeneous and Enzymatic Catalysis
10. Heterogeneous Catalysis
B. Kinetics Experiments
11. Laboratory Reactors
12. Performing Kinetics Experiments
C. Analysis of Kinetics Data
13. CSTR Data Analysis
14. Differential Data Analysis
15. Integral Data Analysis
16. Numerical Data Analysis
III. Chemical Reaction Engineering
A. Ideal Reactors
17. Reactor Models and Reaction Types
B. Perfectly Mixed Batch Reactors
18. Reaction Engineering of Batch Reactors
19. Analysis of Batch Reactors
20. Optimization of Batch Reactor Processes
C. Continuous Flow Stirred Tank Reactors
21. Reaction Engineering of CSTRs
22. Analysis of Steady State CSTRs
23. Analysis of Transient CSTRs
24. Multiple Steady States in CSTRs
D. Plug Flow Reactors
25. Reaction Engineering of PFRs
26. Analysis of Steady State PFRs
27. Analysis of Transient PFRs
E. Matching Reactors to Reactions
28. Choosing a Reactor Type
29. Multiple Reactor Networks
30. Thermal Back-Mixing in a PFR
31. Back-Mixing in a PFR via Recycle
32. Ideal Semi-Batch Reactors
IV. Non-Ideal Reactions and Reactors
A. Alternatives to the Ideal Reactor Models
33. Axial Dispersion Model
34. 2-D and 3-D Tubular Reactor Models
35. Zoned Reactor Models
36. Segregated Flow Models
37. Overview of Multi-Phase Reactors
B. Coupled Chemical and Physical Kinetics
38. Heterogeneous Catalytic Reactions
39. Gas-Liquid Reactions
40. Gas-Solid Reactions

Supplemental Units

S1. Identifying Independent Reactions
S2. Solving Non-differential Equations
S3. Fitting Linear Models to Data
S4. Numerically Fitting Models to Data
S5. Solving Initial Value Differential Equations
S6. Solving Boundary Value Differential Equations

Unit 23. Analysis of Transient 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.

It was noted in Unit 22 that CSTRs are usually designed to operate at steady state for extended periods of time. Nonetheless, analysis of transient behavior is an essential and critical part of the overall design of a system. In the case of CSTRs, transient analysis is used to determine the best way to start up the reactor and to shut it down. It is used to understand how the reactor system will respond to changes in its operating parameters, be they intentional or unexpected. Another use of transient analysis is in the design of control systems for the reactor system. Unit 23 describes setting up the transient CSTR design equations for a system, common simplifications of those equations, and a general approach to solving them for the purpose of performing some reaction engineering or reactor design task.

Learning Resources

Teaching Resources

Practice Problems

1. 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 at these conditions, the outlet temperature is 167 °C and the conversion of A is 86%. Suppose that the temperature of the fluid in the jacket suddenly dropped to 160 °C. Calculate the temperature and conversion versus time until a new steady state is attained.

  A → B (2a)  
  r2a=k2aCA2 (2b)  

(Problem Statement as .pdf file)