[Altered State]

Hi,

I'm studying chemistry, but this year I had a Chemical Engineering subject, and today was the final exam, and in it, there was an mass balance exercise which I believe it's imposible to solve without more data.

This is the diagram:


1 initial flowing, and just 2 distillators...

The data they gave is the following:


Compsition of F (100kg/h):
20% of A
30% of B
50% of C

About P1:
It has the 75% of F's A total mass (i.e. 0.75*20= 15 kg)
B concentration in P1: 5%

About P2:
It has the 80% of F's B total mass (i.e. 0.8*30= 24 kg)
C concentration in P1: 4%

About P1:
It has the 80% of F's C total mass (i.e. 0.8*50= 40 kg)
A concentration in P1: 1%




And thats it.
Not even the total mass of P1, P2 or P3 or in the intermediate flowing.



The exam had 3 exercises, I solved correctly 2 of them in 30 minutes, and I spent 2:30h trying to figure how this one was, but I can't see a way.
I got a bunch of balance equations, but none of them gave me results, I think you need more data to solve this.

I'll talk to the professor tomorrow morning, but I'd really hope you could help me out with this.

Regards

[Borek]

And what is the question? Find everything?

Not that I see how to solve it, doesn't look like there are enough equations. Unless they meant P1 doesn't contain C or something like that. But don't take me too seriously, I am just trying to apply common logic to the problem.

[Altered State]

And what is the question? Find everything?

Not that I see how to solve it, doesn't look like there are enough equations. Unless they meant P1 doesn't contain C or something like that. But don't take me too seriously, I am just trying to apply common logic to the problem.

Of course that is not the question. The question is if it is solvable or not with the data given.
Is not in my opinion, and it aparently is not for every classmate I asked. I'm asking the professor tomorrow, but I wanted to be sure.

[mkurek]

Not sure if I'm reading your question correctly because you're rather unclear, but here's my go:

15 kg of A in stream P1 is correct. And are you told that P1 is made up of 5% B as well? Then the amount of B in P1 is solved for by:

.95*P1=15 kg, use this to solve for the total size of P1. Then P1*.05=B
(Now this is assuming that P1 is made up only of A and B, you don't really specify)

Remember to set up an individual mass balance for each component. Your input stream will equal the sums of the 3 output streams, this is true for not only the entire streams themselves, but each component of the streams as well.

EDIT: To make this more clear then, the amount of B in P3 can solved for by

(B in stream F) = (B in P1) + (B in P2) + (B in P3)

You already know how much B is in F and P2 from your calculations, I showed how to get the amount of B in P1 above, so now use this to solve for B in P3. The same process can be repeated for the other components.

[Borek]

(Now this is assuming that P1 is made up only of A and B, you don't really specify)

Have you bothered with reading earlier posts? Apparently not.

Unless they meant P1 doesn't contain C

[Borek]

And what is the question? Find everything?

Of course that is not the question.

You have lost me. You listed some description of the problem, but this description doesn't tell what you were asked to find. No matter how convoluted the problem statement is, it typically ends with "Find x" - and you have not told us what you were expected to find.

The question is if it is solvable or not with the data given.

If that were the question the answer would be "no" and the question would be perfectly valid. But somehow I think you misunderstood what I was asking about.

[Altered State]

And what is the question? Find everything?

Of course that is not the question.

You have lost me. You listed some description of the problem, but this description doesn't tell what you were asked to find. No matter how convoluted the problem statement is, it typically ends with "Find x" - and you have not told us what you were expected to find.

The question is if it is solvable or not with the data given.

If that were the question the answer would be "no" and the question would be perfectly valid. But somehow I think you misunderstood what I was asking about.

Oh, yes I definetly missunderstood you.

The question of the problem is to figure out what is the mass/hour of each product stream and what is it's composition. Basically, yes, to find everything.

[mkurek]

If you would just like to know if it is solvable you can perform a degrees of freedom analysis. Actually, whenever you are solving a mass transfer problem the first thing you should always do is set up your mass balance equations, and then perform a degrees of freedom analysis to determine if it is solvable before spending too much time on the problem. Did I not show that it was solvable though in my previous post? I believe it is.

And Borek, of course I saw your post but there wasn't exactly a clear response from the OP to clarify the question. All I was doing was stating that I was making an assumption in order to solve the problem. That's a very common thing to do.