Chemical Reaction Engineering

Transcription

1 Lecture 2 Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of chemical reactions and the design of the reactors in which they take place. 1

2 Lecture 2 Review of Lecture 1 Definition of Conversion, Develop the Design Equations in terms of Size CSTRs and PRs given r = f() Conversion for Reactors in Series Review the all of the Tower of CRE 2

3 Review Lecture 1 3 Reactor Mole Balances Summary The GMBE applied to the four major reactor types (and the general reaction B) Reactor Differential lgebraic Integral Batch CSTR PR PBR dn dt r d dv r V V r t V N N dn r V d dr d dw d r W r N t V W

4 Review Lecture 1 CSTR Example Problem 3 dm 1 min C Given the following information, ind V C V? 1 C.1C C dm 3 min Liquid phase C 4

5 5 CSTR Example Problem (1) Mole Balance: r C C r C C r V kc r (2) Rate Law: (3) Stoichiometry: C Review Lecture 1

6 Review Lecture 1 CSTR Example Problem (4) Combine: V C C kc (5) Evaluate: C.1C V 1dm min 3 C.1C 1.23min.1 C dm 3 6 V dm 3

7 Define conversion, Consider the generic reaction: a b B c C d D Chose limiting reactant as basis of calculation: b c d B C D a a a Define conversion, moles reacted moles fed 7

8 Batch 8 V r dt d N dt dn d N dn N N N reacted Moles initially Moles remaining Moles Chapter 2

9 Batch dn dt r V N t t t Integrating, t N d r V The necessary t to achieve conversion. 9

10 CSTR Consider the generic reaction: a b B c C d D Chose limiting reactant as basis of calculation: b c d B C D a a a Define conversion, moles reacted moles fed 1

11 CSTR Steady State dn dt Well Mixed V r r dv r V 11

12 CSTR Moles leaving Moles entering V r V r Moles reacted r dv 12 CSTR volume necessary to achieve conversion.

13 PR d dv r Steady State d d dv r 13

14 PR V V V Integrating, V r d PR volume necessary to achieve conversion. 14

15 Reactor Mole Balances Summary in terms of conversion, Reactor Differential lgebraic Integral Batch CSTR N d dt r V V r t N d r V t 15 PR PBR d dv r V d r d dw d r W r W

16 Levenspiel Plots Reactor Sizing Given r as a function of conversion, -r = f(), one can size any type of reactor. We do this by constructing a Levenspiel plot. Here we plot either ( /-r ) or (1/-r ) as a function of. or ( /-r ) vs., the volume of a CSTR and the volume of a PR can be represented as the shaded areas in the Levenspiel Plots shown as: 16 g( r )

17 Levenspiel Plots r 17

18 CSTR r 1 rea = Volume of CSTR V r

19 PR 19

20 Levenspiel Plots 2

21 Numerical Evaluations of Integrals The integral to calculate the PR volume can be evaluated using method as Simpson s One-Third Rule: (See ppendix.4) Chapter 2 1 r ( 2 ) V x d r 3 r () r ( / 2) r ( ) 1 r 21 1 r ( 1 1 r () ) 1 2 Other numerical methods are: Trapezoidal Rule (uses two data points) Simpson s Three-Eight s Rule (uses four data points) ive-point Quadrature ormula

22 Reactors in Series Given: r as a function of conversion, one can also design any sequence of reactors in series by defining : total molesof reactedup to point i i molesof fed to first reactor Only valid if there are no side streams. Molar low rate of species at point i: 22 i i

23 Reactors in Series 23

24 Reactor 1: r r r V 24 V 1 r 1 Reactors in Series Chapter 2

25 Reactors in Series Reactor 2: V 2 2 r 1 d r V

26 V r V r V r 3 26 V 3 r Reactors in Series Reactor 3:

27 27 Reactors in Series

28 Reactors in Series Space time τ is the time necessary to process 1 reactor volume of fluid at entrance conditions. V 28

29 KEEPING UP The tower of CRE, is it stable? 29

30 lgorithm Reaction Engineering Mole Balance Rate Laws Stoichiometry These topics build upon one another. 3

31 lgorithm Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance CRE lgorithm 31

32 lgorithm Mole Balance Rate Laws Be careful not to cut corners on any of the CRE building blocks while learning this material! 32

33 lgorithm Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance 33 Otherwise, your lgorithm becomes unstable.

34 34 End of Lecture 2