[Meruyert]

Hi!

I have problems with ..problems   from "Chemical Reaction Engineering" 3rd Edition, Levenspiel.
My test is coming this Monday...  

If you have any idea, please let me know!
I would really appreciate any help.



Problems are:   15.3, 18.2, 18.22, 25.4 and 26.6  (Sorry for being selfish  )
If you need full text, I'll print it here, just let me know.

Thanks in advance

[Meruyert]

Here is the text  :

15.3
Assuming plug flow we calculate that a tubular reactor 12 m long would give 96% conversion of A for the second-order reaction A-->R. However, the fluid is very viscous, and the flow will be strongly laminar, thus we expect the convetion model, not the plug flow model, to closely represent the flow. How long should we make the reactor to insure 96% conversion of A?


18.2
A solid catalyzed first order reaction, e(epsilon) =0, takes place with 50% conversion in a basket type mixed reactor. What will be the conversion if the reactor size is trebled and all else - temperature, amount of catalyst, feed composition, and flow rate - remains unchanged?


18.22
In the absence of pore diffusion resistance a particular first-order gas reaction proceeds as reported below:
-r'''(A) = 10^(-6) mol/cubic cm cat*s
at given C(A) at 1 atm and 400C
What size of spherical catalyst pellets (effecive diffusion coefficient is given) would ensure that pore resistance effects do not intrude to slow the rate of reaction?

 
25.4
Spherical particles of zinc blende of size R=1 mm are roasted in an 8% oxygen stream at 900 C and 1 atm. The stoichiometry of the reaction is:
2ZnS + 3O2 -> 2ZnO + 2SO2
Assuming that reaction proceeds by the shrinking-core model calculate the time needed for complete conversion of a particle and the relative ressitance of ash layer diffusion during the operation.

Given data:
density of a solid
Reaction rate constant
De for gases in the ZnO layer

Note that film resistance can be safely neglected as long as a growing ash layer is present.



26.6
Solids of unchanged size, R=0.3 mm, are reacted with gas in a steady flow bench scale fluidized reactor with the following result.

F(0) = 10 gm/sec
W = 1000 gm
X(B) = 0.75
Also, the conversion is strongly temperature-sensitive suggesting that the reaction step is rate-controlling. Design a commercial sized fluidized bed reactor (find W) to treat 4 metric tons/hr of solid feed of size R=0.3 mm to 98% conversion.