Chemical Reaction Engineering

Transcription

1 Lectue 3 hemical Reaction Engineeing (RE) is the field that studies the ates and mechanisms of chemical eactions and the design of the eactos in which they take place.

2 Web Lectue 3 lass Lectue 9-Thusday 3//03 Multiple Reactions with Heat Effects

3 Multiple Reactions with Heat Effects PFR/PBR: STR: U T dt dv Ua ( T ) + ( )( Δ ) a T ij H Rxij m j n i F j m q a 0 Pi i 0 ij Rxij j i ( T) F θ ( T T ) ( ) H ( T) 0 Pj 3 These equations ae coupled with the mole balances and ate law equations.

4 Multiple Reactions with Heat Effects Multiple Reactions Make sue each ate of eaction and ate law ae in espect to the same species (example, ); Subscipts must agee dt dv g g Fi Pi ij ΔH Rxij ΔH Rx + ΔH Rx 4

5 Multiple Reactions with Heat Effects Multiple Reactions ) Mole Balances: evey species (no convesion!) ) Rate Laws: elative ates net ates 5 3) Stoichiomety: F T 0 p T 0 F T T dp dw α p F T F T 0 T T 0

6 Multiple Reactions with Heat Effects Multiple Reactions 4) Heat Effects: dt dv g g g heat poduced heat emoved F ij i Pi ΔH Ua(T - T Rxij a ) (must have matching i, j) 6

7 7 Multiple Reactions with Heat Effects 4) Heat Effects: dt dv g Ua g ΔH F i R Pi ( T T ) a + ΔH R Fi P F P + FB PB + F P + F i dt Ua( T T ) a dv m! Pcool 5) Paametes i E, E, F 0 a, Ua,...etc D PD

8 Multiple Reactions with Heat Effects 4) Heat Effects: dt dv g F i Pi ( 3) ΔH Rx kj / (mole of eacted in eaction ) ΔH RxB +8kJ / (mole of B eacted in eaction ) g ΔH Rx + B ΔH RxB Use elative ates of eaction to get B in tems of the ate law that is given fo eaction, e.g., () 3 + B-- > D 8 - k 3 then B B 3

9 The complex gas phase eactions () + B k B ΔH RxB 5,000 cal mol B () + D k ΔH Rx 0,000 cal mol take place in a 0 dm 3 PFR with a heat exchange. Plot the tempeatue, concentations, mola flow ates down the length of the eacto fo the following opeations. E.g., Note any maximums o minimums on you plot along with how they change fo the diffeent types of opeations. (a) diabatic opeation (b) Heat exchange with constant T a (c) o cuent heat exchange (d) ounte cuent heat exchange (e) Fo pats (c) and (d), plot and g down the length of the eacto. What do you obseve? dditional Infomation P 0 cal mol K PB 0 cal mol K P 30 cal mol K PD 0 cal mol K k 40 ( dm 3 mol) s K at 300K and E 8,000 cal mol k ( dm 3 mol) s K at 300K and E,000 cal mol T0 0. mol dm 3, Pool cal g K, Ð m ool 0g s 9 Ua 80 cal dm 3 s K, T ao 35K, T 0 300K F 0 5 mol s, F B0 0 mol s, F 0 0, F D0 0

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14 Multiple Reactions with Heat Effects Multiple Reactions dt dv 4) Heat Effects: ( )( ΔH ) dt dv g g ij F i Pi ΔH Rij Rx Ua g ( T T ) F i a Pi heat poduced heat emoved (must have matching i, j) 4

15 Multiple Reactions with Heat Effects in a PFR and STR Examples: () + B k B and ΔH R 0,000cal mol () + 3 D k 3 and 5 ΔH R 0,000cal mol

16 Example : Liquid Phase STR ( ) B + k B NOTE: The specific eaction ate k is defined with espect to species. ( ) 3 + D k 3 NOTE: The specific eaction ate k is defined with espect to species. 6

17 Example : Liquid Phase STR The complex liquid phase eactions take place in a,500 dm 3 STR. The feed is equal mola in and B with F 0 00 mol/min, the volumetic flow ate is 00 dm 3 /min and the eation volume is 50 dm 3. Find the concentations of, B, and D existing in the eacto along with the existing selectivity. Plot F, F B, F, F D and S /D as a function of V 7

18 Example : Liquid Phase STR 8 Solution Liquid Phase STR ) Mole Balances: () () (3) (4) ) Net Rates: (5) f ( ) υ 0 0 υ 0 + V f ( B ) υ 0 B 0 υ 0 B + B V f ( ) υ 0 + V f ( D ) υ 0 D + D V +

19 Example : Liquid Phase STR 9 3) Stoichiomety: (6) (7) (8) (9) F B F B F D F D 4) Paametes: υ υ 0 0 υ 0 υ (0) υ 00 dm 3 0 min 3 () k 0 ( dm mol) min () k 5 0 ( 3 dm mol) 4 min

20 Example B: Liquid Phase PFR Takes place in a PFR. The feed is equal mola in and B and F 0 00 mol/min and the volumetic flow ate is 00 dm 3 /min. The eaction volume is 50 dm 3 and the ate constants ae: k 0( dm 3 mol) min k 5( dm 3 mol) 4 min Rate laws ae the same as Example. Plot F, F B, F, F D and S /D as a function of V. 0

21 Example B: Liquid Phase PFR ) Mole Balances:

22 Example B: Liquid Phase PFR ) Net Rates: (5) + (6) (7) B B + (8) ) Rate Laws: (9) D D k B (0) k 3

23 Example B: Liquid Phase PFR ) Relative Rates: B Reaction () B () Reaction (3) 3 D 3 3 (4) D 3

24 ( ) ( )( ) [ ]( ) ( ) ( )( ) [ ]( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 6 3 / 5 3 / exp 7 6 exp 5 3 D B D D B B B B T T R E k k k T T R E k k k Example B: Liquid Phase PFR ) Rate Laws:

25 Example B: Liquid Phase PFR 3) Stoichiomety: F T 0 p T 0 F T T F T 0 p T 0 F T T F T F + F B + F + F D ( ) F ( 7) B B T 0 p T 0 F T T F ( 9) D D T 0 p T 0 F T T dp dv αρ p F T F T 0 ( 8) ( 0) T T 0 ( ) 5

26 Multiple Reactions with Heat Effects 6 4) Heat Effects: dt dv dt dv g a g F i Ua m! Ua ( 3) ( T Ta ) ( 6) i Pi Pcool ΔH R + ΔH R ( 4) ( T T ) ( 5) a P FP + FB PB + F P + F Paametes: E, E, F 0,... o-uent D PD ( 7)

27 Selectivity If one wee to wite S /D F /F D in the Polymath pogam, Polymath would not execute because at V0, F 0 esulting in an undefined volume (infinity) at V0. To get aound this poblem we stat the calculation 0-4 dm 3 fom the eacto entance whee F D will not be zeo and use the following IF statement. (5) S ı D if ( V > 0.00) then F F D else 0 ( ) 7

28 Selectivity 8 3) Stoichiomety: (6) (7) (8) (9) F B F B F Paametes: D F D υ υ 0 0 υ 0 υ (0) υ 00 dm 3 0 min 3 () k 0 ( dm mol) min () k 5 0 ( 3 dm mol) 4 min

29 End of Web Lectue 3 lass Lectue 8 9