Chapter 1. Lecture 1

Transcription

1 Chapter 1 Lecture 1 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 1 Introduction Definitions General Mole Balance Equation Batch (BR) Continuously Stirred Tank Reactor (CSTR) Plug Flow Reactor (PFR) Packed Bed Reactor (PBR) 2

3 Chemical Reaction Engineering Chemical reaction engineering is at the heart of virtually every chemical process. It separates the chemical engineer from other engineers. Industries that Draw Heavily on Chemical Reaction Engineering (CRE) are: CPI (Chemical Process Industries) Examples like Dow, DuPont, moco, Chevron Chapter 1 3

4 4 Chapter 1

5 Chapter 1 Smog (Ch. 1) Wetlands (Ch. 7 DVD-ROM) Hippo Digestion (Ch. 2) Oil Recovery (Ch. 7) Cobra Bites (Ch. 8 DVD-ROM) 5 Chemical Plant for Ethylene Glycol (Ch. 5) Lubricant Design (Ch. 9) Plant Safety (Ch. 11,12,13)

6 Materials on the Web 6

7 Let s Begin CRE Chapter 1 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. 7

8 Chapter 1 Chemical Identity chemical species is said to have reacted when it has lost its chemical identity. The identity of a chemical species is determined by the kind, number, and configuration of that species atoms. 8

9 Chapter 1 Chemical Identity chemical species is said to have reacted when it has lost its chemical identity. There are three ways for a species to loose its identity: 1. Decomposition CH 3 CH 3 H 2 + H 2 C=CH 2 2. Combination N 2 + O 2 2 NO 3. Isomerization C 2 H 5 CH=CH 2 CH 2 =C(CH 3 ) 2 9

10 Chapter 1 Reaction Rate The reaction rate is the rate at which a species looses its chemical identity per unit volume. The rate of a reaction (mol/dm 3 /s) can be expressed as either: The rate of Disappearance of reactant: -r or as The rate of Formation (Generation) of product: r P 10

11 Reaction Rate Consider the isomerization r B = the rate of formation of species per unit volume -r = the rate of a disappearance of species per unit volume r B = the rate of formation of species B per unit volume 11

12 Chapter 1 Reaction Rate EXMPLE: B If Species B is being formed at a rate of 0.2 moles per decimeter cubed per second, i.e., r B = 0.2 mole/dm 3 /s Then is disappearing at the same rate: -r = 0.2 mole/dm 3 /s The rate of formation (generation of ) is: r = -0.2 mole/dm 3 /s 12

13 Reaction Rate For a catalytic reaction we refer to r, which is the rate of disappearance of species on a per mass of catalyst basis. (mol/gcat/s) Chapter 1 NOTE: dc /dt is not the rate of reaction 13

14 Chapter 1 Reaction Rate Consider species j: 1. r j is the rate of formation of species j per unit volume [e.g. mol/dm 3 s] 2. r j is a function of concentration, temperature, pressure, and the type of catalyst (if any) 3. r j is independent of the type of reaction system (batch, plug flow, etc.) 4. r j is an algebraic equation, not a differential equation (e.g. -r = kc or -r = kc 2 ) 14

15 General Mole Balances 15 Building Block 1: F j0 F j G j System Volume, V time mole time mole time mole time mole dt dn G F F j Species of ccumulation Rate Molar j Species of Generation Rate Molar out j Species Rate of Flow Molar in j Species Rate of Flow Molar j j j j 0 Chapter 1

16 Building Block 1: General Mole Balances Chapter 1 If spatially uniform: G j r j V If NOT spatially uniform: V 1 16 G r j1 j1 rj1v1 G V 2 r j 2 j 2 rj 2V2

17 Building Block 1: General Mole Balances Chapter 1 G j n i1 r ji V i Take limit G j n r ji V i r j dv i1 lim V 0 n 17

18 Building Block 1: General Mole Balances System Volume, V Chapter 1 F 0 G F General Mole Balance on System Volume V In Out Generation ccumulation 18 F 0 F r dv dn dt

19 Chapter 1 Batch Reactor - Mole Balances Batch F 0 F r dv dn dt F 0 F 0 Well-Mixed r dv r V 19 dn dt r V

20 Chapter 1 Batch Reactor - Mole Balances Integrating dt dn r V when t t 0 N N 0 t N N t N N dn r V 0 20 Time necessary to reduce the number of moles of from N 0 to N.

21 Chapter 1 Batch Reactor - Mole Balances t N N dn r V 0 N 21 t

22 Chapter 1 CSTR - Mole Balances CSTR F 0 F r dv dn dt Steady State dn dt 0 22

23 Chapter 1 CSTR - Mole Balances Well Mixed r dv r V F 0 F r V 0 V F 0 F r 23 CSTR volume necessary to reduce the molar flow rate from F 0 to F.

24 Chapter 1 Plug Flow Reactor - Mole Balances 24

25 Plug Flow Reactor - Mole Balances V Chapter 1 F F V V V 25 In atv F V Out atv F V V V Generation in V r V 0 0

26 Plug Flow Reactor - Mole Balances Rearrange and take limit as ΔV0 Chapter 1 lim V 0 F V V V F V r df dv r 26 This is the volume necessary to reduce the entering molar flow rate (mol/s) from F 0 to the exit molar flow rate of F.

27 Plug Flow Reactor - Mole Balances PFR Chapter 1 F 0 F rdv dn dt Steady State dn dt 0 F F r dv

28 lternative Derivation Plug Flow Reactor - Mole Balances Differientiate with respect to V Chapter 1 0 df dv r df dv r The integral form is: V F F 0 df r 28 This is the volume necessary to reduce the entering molar flow rate (mol/s) from F 0 to the exit molar flow rate of F.

29 Packed Bed Reactor - Mole Balances PBR W Chapter 1 F F 29 F Steady State W F W W lim W 0 F W dn dt W W 0 W W rw F W W r dn dt

30 Chapter 1 Packed Bed Reactor - Mole Balances Rearrange: df dw r The integral form to find the catalyst weight is: W F F 0 df r PBR catalyst weight necessary to reduce the entering molar flow rate F 0 to molar flow rate F. 30

31 Chapter 1 31 Reactor Mole Balances Summary The GMBE applied to the four major reactor types (and the general reaction B) Reactor Differential lgebraic Integral Batch CSTR PFR PBR dn dt r df dv r V V F 0 F r t V N N 0 F F 0 dn r V df dr df dw df r W r F F 0 N F F t V W

32 Fast Forward to the 10 th Week of the Course Chapter 11 Reactors with Heat Effects EXMPLE: Production of Propylene Glycol in an diabatic CSTR Propylene glycol is produced by the hydrolysis of propylene oxide: CH 2 CH CH 3 H 2 O H 2 SO 4 CH 2 CH CH 3 O OH OH 32

33 Fast Forward to the 10 th Week of the Course Chapter 11 v 0 Propylene Glycol What are the exit conversion X and exit temperature T? Solution Let the reaction be represented by 33 +BC

34 34 Chapter 11

35 35 Chapter 11

36 36 Chapter 11

37 37 Chapter 11

38 38 Chapter 11

39 Chapter 11 Evaluate energy balance terms 39

40 40 Chapter 11

41 41 Chapter 11

42 nalysis We have applied our CRE algorithm to calculate the Conversion (X=0.84) and Temperature (T=614 R) in a 300 gallon CSTR operated adiabatically. T=535 R Chapter 11 +BC X=0.84 T=614 R 42

43 lgorithm Keeping Up 43

44 lgorithm Separations Filtration Distillation dsorption These topics do not build upon one another. 44

45 lgorithm Reaction Engineering Mole Balance Rate Laws Stoichiometry These topics build upon one another. 45

46 lgorithm Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance CRE lgorithm 46

47 lgorithm Mole Balance Rate Laws Be careful not to cut corners on any of the CRE building blocks while learning this material! 47

48 lgorithm Heat Effects Isothermal Design Stoichiometry Rate Laws Mole Balance 48 Otherwise, your lgorithm becomes unstable.

49 49 End of Lecture 1

50 Supplemental Slides dditional pplications of CRE 50

51 Supplemental Slides dditional pplications of CRE 51

52 Supplemental Slides dditional pplications of CRE 52

53 Supplemental Slides dditional pplications of CRE Hippo Digestion (Ch. 2) 53

54 Supplemental Slides dditional pplications of CRE 54

55 Supplemental Slides dditional pplications of CRE 55

56 Supplemental Slides dditional pplications of CRE Smog (Ch. 1) 56

57 Supplemental Slides dditional pplications of CRE 57 Chemical Plant for Ethylene Glycol (Ch. 5)

58 Supplemental Slides dditional pplications of CRE Wetlands (Ch. 7 DVD-ROM) Oil Recovery (Ch. 7) 58

59 Supplemental Slides dditional pplications of CRE Cobra Bites (Ch. 8 DVD-ROM) 59

60 Supplemental Slides dditional pplications of CRE Lubricant Design (Ch. 9) 60

61 Supplemental Slides dditional pplications of CRE Plant Safety (Ch. 11,12,13) 61