CSTR - PFR - PBR

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1 1. Mole Balances o The Rate of Reaction, - o The Geneal Mole Balance Equation o Continuous low Reactos - CSTR (Continuous-Stied Tank Reacto) - PR (Tubula Reacto) - PBR (Packed-Bed Reacto) o Industial Reactos

2 0. Chemical Identity o Reaction - When a chemical species has lost its chemical identity o Identity of a chemical species - The kind, numbe, and configuation of that species atoms decomposition CH 3 CH 3 H 2 + CH 2 =CH 2 combination N 2 + O 2 2NO isomeization C 2 H 5 CH=CH 2 CH 2 =C(CH 3 ) 2 2/21/ Sping 2

3 1. Reaction Rate I (p.2) o Reaction Rate - The ate at which a species looses its chemical identity pe unit volume B = the ate of fomation of species pe unit volume - = the ate of a disappeaance of species pe unit volume B = the ate of fomation of species B pe unit volume o a catalytic eaction, we efe to - ', which is the ate of disappeaance of species on a pe mass of catalyst basis 2/21/ Sping 3

4 1. Reaction Rate II o Reaction Rate [Example] B - If B is being ceated at a ate of 0.2 moles pe lite pe second, ie, the ate of fomation of B is, B = 0.2 mole/l/s then is disappeaing at the same ate: - = 0.2 mole/l/s the ate of fomation of is = -0.2 mole/l/s 2/21/ Sping 4

5 1. Reaction Rate III o Is sodium hydoxide eacting? - Reaction ate definition, = dc /dt only holds fo constant volume batch system caied out to obtain chemical eaction ate data - Sodium hydoxide and ethyl acetate ae continuously fed to a apidly stied tank in which they eact to fom sodium acetate and ethanol: NaOH + CH 3 COOC 2 H 5 CH 3 COONa + C 2 H 5 OH 2/21/ Sping 5

6 1. Reaction Rate IV o Conside species j - j is the ate of fomation of species j pe unit volume [e.g. mol/dm 3 *s] - j is a function of concentation, tempeatue, pessue, and the type of catalyst (if any) - j is independent of the type of eaction system (batch, plug flow, etc.) - j is an algebaic equation, not a diffeential equation o Examples of othe ate laws k1c 1 k C 2 k k1 C 2/21/ Sping 6

7 1. Reaction Rate V o Self test - The convention fo ates of eaction + 2B 3C in which the ate of disappeaance of is 5 moles of pe dm 3 pe second at the stat of the eaction. - t the stat of the eaction (a) What is -? (b) What is the ate of fomation of B? (c) What is the ate of fomation of C? (d) What is the ate of disappeaance of C? (e) What is the ate of fomation of,? (f) What is - B? 2/21/ Sping 7

8 2. Geneal Mole Balance Equation (p.8) I o In a given bounday system - 0 = Enteing mola flow ate of (mol/time) = Exiting mola flow ate of (mol/time) G = Rate of geneation(fomation) of (mol/time) V = Volume (vol e.g. m 3 ) = ate of geneation(fomation) of (mole/time vol) N = numbe of moles of inside the system Volume V (mols) 2/21/ Sping 8

9 2. Geneal Mole Balance Equation II o Self Test 1. The ate law (a) is a diffeential equation T (b) elates eaction ate and concentation of eacting species T (c) is a function of tempeatue; T 2. The ate of fomation of species is pe unit volume (a) T (b) - T (c) the ate of geneation of species pe unit volume T (d) ' T (e) none of the above T 2/21/ Sping 9

10 2. Geneal Mole Balance Equation III 3. t a paticula time t, the ate of fomation of B in the eaction, B, is 10 mole/dm 3 *min. Which of the following ae tue? B a. The ate of disappeaance of B is -10 moles/dm 3 *min. b. The ate of fomation of is -10 mole/dm 3 *min. c. The ate of disappeaance of is 10 moles/dm 3 *min. d. = -10 moles/dm 3 *min e. - = 10 moles/dm 3 *min f. - B = -10 moles/dm 3 *min g. Some of the above h. ll of the above i. None of the above j. will disappea faste if a magician is pesent 2/21/ Sping 10

3. Batch Reactos I o Batch Reactos - Used fo a small-scale opeation, testing a new pocess not fully developed manufactuing expensive poducts pocesses difficult to convet to

11 3. Batch Reactos I o Batch Reactos - Used fo a small-scale opeation, testing a new pocess not fully developed manufactuing expensive poducts pocesses difficult to convet to continuous opeation - dvantages high convesion - Disadvantages high labo cost pe batch vaiability of poduct quality difficulty of lage-scale poduction 2/21/ Sping 11

12 3. Batch Reactos II o Reaction ate - Neithe inflow not outflow V - Rxn ate is unifom thoughout the eacto volume dn dt - o isomeization of species B dv dn dt V j0 j V j dv dn dt j 2/21/ Sping 12

13 3. Batch Reactos III o Reaction time - Time t 1 to change N 0 N 1, (Geneally N 0 > N 1 ) dn dt - Reaanging - Integating V dt dn V t 1 N 0 dn N 1 V 2/21/ Sping 13

14 4. Continuous low Reactos I o Continuous-Stied tank Reacto 1 - CSTR, vat, o Backmix eacto - Pimaily fo liquid phase eactions - Opeated at steady state (pefectly mixed) T, C j, j inside CSTR is unifom esidence-time distibution study fo highly non-ideal mixing system 2/21/ Sping 14

15 4. Continuous low Reactos II o Continuous-Stied tank Reacto 2 - Geneal mole balance - Opeated at st-st - Design equation fo CSTR 0 V dv dn dt dn dt j0 0 o V j V V 0 j dv dv V dn dt j - With volumetic flow ate v, = C v 2/21/ Sping 15

16 4. Continuous low Reactos III o Tubula Reacto 1 - cylindical pipe nomally opeated at st-st - Used most often fo gas-phase xn - Reactants ae continually consumed as they flow down the length of the eacto - Plug flow along pipe 2/21/ Sping 16

17 4. Continuous low Reactos IV o Tubula Reacto 2 - Geneal mole balance - Opeated at st-st - Design equation fo PR - Diffeential w..t V - O d dv dn dt j0 0 d 0 dv j V j dv dn dt 0 V dv 0 j 2/21/ Sping 17

18 4. Continuous low Reactos V o Tubula Reacto 3 - Reaanging and integating between V = 0, = 0 V = V 1, = 1 V d 0 1 d 2/21/ Sping 18

19 4. Continuous low Reactos VI o Pack-Bed Reacto 1 - Involving fluid-solid heteogeneous xns the xn takes place on the suface of the catalysts xn at is based on mass of solid catalyst W (athe than on volume V - = mol eacted/s g cat. 2/21/ Sping 19

20 4. Continuous low Reactos VII o Pack-Bed Reacto 2 - Geneal mole balance - Opeated at st-st dn dt j0 0 j V j dv dn dt j - Design equation fo PBR - Diffeential w..t W - O d dw ' ' 0 V dw d dw ' 0 0 2/21/ Sping 20

21 4. Continuous low Reactos VIII o Pack-Bed Reacto 3 - Reaanging and integating between W = 0, = 0 W = W 1, = 1 W d ' 0 1 d ' 2/21/ Sping 21

22 5. Industial Reactos I o Liquid-Phase Reactions 1 - Semibatch eactos T contol by egulation of feed ate minimizing side xns to maintain conc of one of the eactants 2-phase xns whee gas bubbled out 2/21/ Sping 22

23 5. Industial Reactos II o Liquid-Phase Reactions 2 - CSTRs intense agitation equied stand alone o in seies elatively good T contol the smallest convesion lage size necessay 2/21/ Sping 23

24 5. Industial Reactos III o Gas-Phase Reactions 1 - PRs easy to maintain (no moving pats) the highest convesion difficult T contol hot spot if exothemic xn 2/21/ Sping 24

25 5. Industial Reactos IV o Gas-Phase Reactions 2 - PBRs basically the same to PRs with solid catalyst paticles the catalyst is toublesome to eplace channeling of the gas flow dead zone 2/21/ Sping 25

26 5. Industial Reactos V o Gas-Phase Reactions 3 - luidized-bed Reactos analogous to CSTR well mixed, even T distibution appoximately modeled as a CSTR [fo exact design, it need customizing] often high cost of eacto and catalyst egeneation 2/21/ Sping 26

Chapter 1: Mole Balances

Chapter 1: Mole Balances CHEMICL RECTION ENGINEERING (SK3223) Chapte : Mole Balances WN NORHRYTI WN SLLEH hayati@petoleum.utm.my RIZIN MD. KSMNI afiziana@petoleum.utm.my Rate of Reaction The eaction ate is the ate at which a species