HW 7 - p 8.11 - LLE of Acetone from Water Using TCE - 9 pts
Please post all of your questions about this problem as comments on this post. I will respond with my own comments.
posted by Dr. B at 5:51 PM
Wednesday, November 15, 2006
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8 Comments:
do we need to construct extra tie lines to find Pmin? When I attempted this I got a funny looking curve and an implausible answer.
cowboy:
Yes, you need to construct a conjugate curve, as described on page 312. You could say the curve is funny looking, but the answer is ok. From what you have told me, I don't think I can help any more. If you are still stuck, tell me more or scan in your curve and email it to me.
For the mass balances, should we do an overall mass balance first, ie F+S=R3+E1 to get those values, and then do the individual stages after that? Trying to start with just a MB around stage 1 gives me 3 unknowns - E1, E2, and R1.
when i do MBs with water, i get rafinate flowrates that are twice the size of what i got using MIK. i'm following your method and have checked my work. is this normal?
karen
stripes:
Yes, start with a mass balances on the entire system.
anon:
The mass balance does turn out slightly differently depending on which species material balance you use with the total mass balance. The differences are caused by minor errors reading the mass fractions for M on the diagram. If your answer changes a lot when you use a different species material balance, then I suspect you did not read the mass fraction for M correctly.
An alternative approach is not to use M. Instead, simultaneously solve all 3 material balances for E1, RN and Smin. This will give you the correct result because you analytically determine M instead of plotting lines on the diagram.
Do we need to solve for the mass balance using the fractional stage as well or just the 3 stages that were found because the answer has four raffinate solutions of which I only have three of the answers
anon:
I got very nearly 4 stages, so I used 4 stages for my material balances. You don't need to try to do a fractional stage. If you use 3 stages instead of 4, please explain this to the grader on your paper.
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