1 / 27

Lecture 13

Lecture 13. 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. Today’s lecture. Complex Reactions A +2B  C A + 3C  D Liquid Phase PFR Liquid Phase CSTR Gas Phase PFR

idania
Download Presentation

Lecture 13

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 13 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.

  2. Today’slecture Complex Reactions A +2B  C A + 3C  D • Liquid Phase PFR • Liquid Phase CSTR • Gas Phase PFR • Gas Phase Membrane Reactor Sweep Gas Concentration Essentially Zero Sweep Gas Concentration Increases with Distance • Semi Batch Reactor

  3. Reactor Mole Balance Summary Batch Semibatch

  4. Reactor Mole Balance Summary CSTR PFR PBR Note: The reaction rates in the abovemolebalances are net rates.

  5. Reactor Mole Balance Summary The new things for multiple reactions are: Rates: Rate Law for everyreaction Relative Rates for everyreaction Net Rates of Reaction

  6. Gas Phase Multiple Reactions

  7. Note: Wecoulduse the gas phasemolebalance for liquids and then just express the concentration as: Flow: CA=FA/v0 Batch: CA=NA/V0 Note: The reaction rates in the above mole balances are net rates. The new things for multiple reactions are: Rate Law for everyreaction Relative Rates for everyreaction Net Rates of Reaction

  8. Net Rate of Reaction for species A For N reactions, the net rate of formation of species A is: For a given reaction i: (i) aiA+biB ciC+diD:

  9. Batch Flow

  10. Last Lecture Example A: LiquidPhase PFR The complexliquidphasereactionsfollowelementary rate laws NOTE: The specificreaction rate k1A is defined with respect to species A. NOTE: The specificreaction rate k2C is defined with respect to species C.

  11. ComplexReactions Example B: LiquidPhase CSTR Same reactions, rate laws, and rate constants as example A NOTE: The specificreaction rate k1A is defined with respect to species A. NOTE: The specificreaction rate k2C is defined with respect to species C.

  12. Example B: LiquidPhase CSTR The complexliquidphasereactionstakeplace in a 2,500 dm3 CSTR. The feed is equal molar in A and B with FA0=200 mol/min, the volumetric flow rate is 100 dm3/min and the reationvolume is 50 dm3. Find the concentrations of A, B, C and D existing in the reactoralong with the existingselectivity. Plot FA, FB, FC, FD and SC/D as a function of V

  13. Example B: LiquidPhase CSTR CSTR (1) A + 2B →C (2) 2A + 3C → D 1) Mole balance:

  14. 2) Rates: 3) Parameters:

  15. ComplexReactions Example C: Gas Phase PFR, No ΔP Same reactions, rate laws, and rate constants as example A NOTE: The specificreaction rate k1A is defined with respect to species A. NOTE: The specificreaction rate k2C is defined with respect to species C.

  16. Example C: Gas Phase PFR, No ΔP 1) Mole balance: 2) Rates:Same as CSTR (5)-(14)

  17. Example C: Gas Phase PFR, No ΔP 3) Stoich: 4) Selectivity:

  18. ComplexReactions Example D: MembraneReactor with ΔP Same reactions, rate laws, and rate constants as example A NOTE: The specificreaction rate k1A is defined with respect to species A. NOTE: The specificreaction rate k2C is defined with respect to species C.

  19. Example D: MembraneReactor with ΔP Weneed to reconsiderour pressure dropequation. When mass diffuses out of a membrane reactor there will be a decrease in the superficial mass flow rate, G. To account for this decrease in calculatingour pressure drop parameter, wewilltake the ratio of the superficialmassvelocity at anypoint in the reactor to the superficialmassvelocity at the entrance to the reactor. The superficialmass flow rates can be obtained by multiplying the species molar flow rates, Fi, by theirrespectivemolecularweights, Mwi, and thensumming over all species:

  20. Example D: MembraneReactor with ΔP Because the smallest molecule is the one diffusing out and has the lowest molecular weight, we will neglect the changes in the mass flow rate down the reactor and will take as first approximation. 1) Mole Balance: We also need to account for the molar rate of desired product C leaving in the sweep gas FCsg

  21. Example D: MembraneReactor with ΔP 2) Rates:Same (5)-(14) 3) Stoich:Same (15)-(20) 4) Sweep Gas Balance:

  22. Example D: MembraneReactor with ΔP Case 1Large sweep gas velocity Case 2Moderate to small sweep gas velocity Varyυsg to seechanges in profiles

  23. ComplexReactions Example E: LiquidSemibatch Same reactions, rate laws, and rate constants as example A NOTE: The specificreaction rate k1A is defined with respect to species A. NOTE: The specificreaction rate k2C is defined with respect to species C.

  24. Example E: Liquid Semibatch The complexliquidphasereactionstakeplace in a semibatchreactorwhere A is fed to B with FA0=3 mol/min. The volumetric flow rate is 10 dm3/min and the initial reactor volume is 1,000 dm3. The maximum volume is 2,000 dm3 and CA0=0.3 mol/dm3 and CB0=0.2 mol/dm3. Plot CA, CB, CC, CD and SS/D as a function of time.

  25. FA0 Example E: Liquid Semibatch B (1) A + 2B →C (2) 2A + 3C → D 1) Mole balance:

  26. Example E: Liquid Semibatch 2) Rates:Same (5)-(14) Net Rates, Rate Laws and relative rates – are the same as Liquid and Gas Phase PFR and LiquidPhase CSTR 3) Selectivity: 4) Parameters:

  27. End of Lecture 13

More Related