Ch E 441 - Chemical Kinetics and Reaction Engineering

1. Ch E 441 - Chemical Kinetics and Reaction Engineering Isothermal Reactor Design

2. Design Procedure Apply Mole Balance and Design Equation Find Rate Law Use stoichiometry to express as function of X Combine & evaluate to find VPFR,VCSTR or tbatch

3. A Simple Example 2nd order reaction A?B Batch; Liquid Phase Reaction

4. Another Simple Example elementary reaction A?B CSTR; Liquid Phase Reaction

5. And another simple example 2nd order reaction A?B CSTR; Liquid Phase Reaction

6. And another simple example 2nd order reaction A?B CSTR; Liquid Phase Reaction

7. One last simple example elementary reaction A?B PFR; Liquid Phase Reaction

8. A bit more complex example 2nd order in A, gas phase, ?mole, PFR

9. A bit more complex example 2nd order in A, gas phase reaction, PFR

10. An example with numbers An elementary gas phase reaction takes place in a CSTR at constant temperature (500 K) and constant pressure (16.4 atm). The feed is equal molar in A and B. 2A + B ? C

11. An example with numbers

12. A shady proposition A rather sinister-looking gentleman sidles up to you one night and in a sibilant whisper asks you to make him some methyl perchlorate. You question his motives because the product of the reaction between solid silver perchlorate and methyl iodide "explodes violently when struck" [M. F. Radies and T. Iredale, J. Phys. Chem., 48, 224 (1944)].

13. A shade tree detonation? He responds by telling you the truth: he owns a tree stump removal business, and he needs cheap explosives. The legal route has occurred to him, but his funds are quickly depleting.

14. A fiscal obligation You're not too comfortable with this situation, but you need the money. Yet, what you don't need is to destroy the lab. You decide to make the material in batch in a benzene solution, give the sinister stranger the product still in the benzene, and let him figure out how to get the methyl perchlorate out.

15. A question of duration! You use a vessel containing 30 dm3 of solution, starting with 0.7 M CH3I and 0.5 M AgClO4 concentrations. How long will it take you to convert 98% of the silver perchlorate? (You handle the silver perchlorate very carefully, since it, too, detonates with disturbing frequency when struck, jarred, or annoyed.)

16. Need more information The reaction stoichiometry is as: While the rate equation takes the form: at 298 K in benzene, k = 0.00042 (dm3/mol)3/2/s

17. Summarize the situation Batch Process V = 30 dm3 CBo = 0.5 mol/dm3 CAo = 0.7 mol/dm3 rB = -kCACB3/2 at T = 298 K k = 0.00042 (dm3/mol)3/2/s Final X = 0.98

18. No improvisation

19. No Improvisation

20. Mathcad exploitation

21. CD P4-BB The Des Plaines River Wetlands were constructed as illustrated in the aerial photograph. Water is pumped from the river to the left side of EW3 and the top of EW4, EW5, and EW6. The discharge of the wetlands is controlled by flow weirs. EW3, EW4, and EW5 all discharge to a common outlet before reentering the river whereas EW6 discharges into a lake before reentering the river. The lake was left out of the photo, but it is located on the left of EW6.

22. CD P4-BB Several researchers have examined the feasibility of using wetlands to clean up high volumes of polluted water. Experimental wetland three (EW3) at the Des Moines EW site in Illinois has a volume of 1.5x107 dm3 and an inflow of 70,000 dm3 of water per hour from the Des Plaines River. The outflow eventually returns to the river. During late spring, the river water typically contains 4.5 ?g/dm3 of the herbicide atrazine. However, the maximum contaminant level (MCL) under the federal Drinking Water Act is 3.0 ?g/dm3. As a first approximation, treat EW3 as a perfectly mixed CSTR and assume atrazine decomposition is first order with k= 0.0025 h-1.

23. Example CD P4-BB Assume EW3 contains no atrazine at the time the flow from the river is diverted. Plot CA as a function of time for the case where the outflow is kept equal to inflow. After what time does CA reach steady-state (99%)? Is it below the MCL?

24. Example CD P4-BB Consider the case where EW3 initially contains neither atrazine nor water. Outflow is maintained at 50,000 dm3/hr for 750 hr, inflow is 70,000 dm3/hr. Plot the concentration as a function of time and explain how it differs from the plot in the previous part. Plot the number of moles of atrazine in EW3 versus time. Why is NA(t) increasing while CA(t) is decreasing?

25. Example CD P4-BB EW3 is operating initially at the steady-state conditions simulated in the first question. Suppose weekly rain periodically increases the amount of atrazine leached into the Des Plaines River, thereby increasing the concentration in the inflow to EW3. Concentration as a function of time is given by where the trigonometric argument is in radians. Plot CA0(t) and CA(t) on the same graph. Does the outflow exceed the MCL at any time? Do CA0 and CA reach their maximums and minimums at the same times? Does CA ever exceed CA0? How can this be?

26. Example CD P4-BB EW3 operates at the steady-state as simulated in the first problem until a 1000 hr drought. During the drought, the evaporative flux of water from EW3 is 10,000 dm3/hr. The overall water balance is such that the wetland volume stays constant. No atrazine evaporates. What does the concentration profile look like? How can this be explained?

27. Simple example made harder 1st order catalytic reaction A?B PBR; Gas Phase Reaction, ?P in pipe

28. Simple example made not simple

29. Case 1 – Average Density

30. Case 1 – Average Density

31. Case 1 – Average Density

32. Case 2 – Variable Density

33. Case 2 – Variable Density

34. Case 2 – Variable Density

35. Other Entertaining Twists Spherical Packed-Bed Reactors Cross-sectional area no longer constant Ac = f(z), where z represents distance thru bed W = ?c(1-?)V(z) PFR Pressure Drop Similar to analysis just performed Includes the Fanning Friction Factor Membrane Reactors