11 replies to this topic

[xerxes]

I need help...

Given a mixture containg 20% methane, 35% ethane, 20% propane and 25% heptane at 95oC and 30 bar...

(a) how wil i know the state of the system at the given condition?
( how will i determine the fugacity, fugacity coefficient of each species and the value of Z for the mixture?

please outline the steps or give me tips as to how the problem can be solved

thanks

[Art Montemayor]

xerxes:

There is nothing quite as lazy as a lazy student.

If you want us to do your homework, you are taking the wrong avenue. If you want "help" to find the solution and work out the problem, then show us how much time and effort you have put into this task yourself. Also tell us your level of study and what course you are taking that is related to this assignment.

If you don't know what fugacity is as well as not knowing what analytical methods and generalized charts are available, then yours is a lost cause as far as this Forum is concerned.

But if you are struggling with the subject and having a hard time, then tell us where you have hit a bump in the road and what is it that you don't comprehend. But also tell us what you have studied and how far into it you have gotten. That way, we can help you get back on your feet with understanding what you are up against.

Students on this Forum should fill in all the details on the personal background portion of the Forum registry. That way, we can all know who we are helping and how best to go about it.

Await your response.

[gvdlans]

Following site may be useful: http://www.questcons...rm/thermot.html


In addition to Art Montemayor's comments, when communicating please indicate whether you are using mole% or weight% and whether you are using bar(a) or bar(g).

[JEBradley]

Grrrr - no such unit as bar (a). - gauge pressure = pressure (not pressure absolute) + atmospheric pressure.

[NB humour me - long day at work and feeling grumpy].

[JEBradley]

Please ignore previous post!!!

Id like to jump to the defence of Xerxes - he isn't all that lazy (is he definately a student anyway??)

When I was at university Id have just copied the answers off someone else and have done with it. This got me a 1st class honours degree w. Distinction and a PhD. But I really regret not trying to understand the subject matter now.

Truth is, I haven't a clue how you work out the state of the specified system.

Just search on the internet though, or library, or ask your tutor because he'd be more than happy to help. And let me know the answer when you find out.

[gvdlans]

JEBradley,

For your information, you can simply delete a post in this forum... There is a delete button below each post that you are the author of.

[harsh]

To Xerxes,
To know in which state the mixture is in, calculate the dew point and bubble point of the mixture. To calculate these values refer the book Mass Transfer Operation by Robert Treybal. To be more precise refer the solved problem 9.3, for this you will require one chart called De Priester which is given in Perry's Chemical Engineer's Handbook section 13.

[xerxes]

i just asked for help, i believe i need not be attacked personally in a degrading manner,

sorry if i have to make this comment, but i thought i was dealing with professionals here

what i wanted is a direction as to how i could arrive with the answer, just wanted to validate whether what i am doing is correct

anyhow, you have a point of telling me to post where i hit the bump on my quest for answer, but since i have limited time online, i never managed to do just that
anyhow, i assumed a basis of 1 mole of the mixture...

i assumed that with that 1 mole of starting mixture, vapors will be formed so that V represents the number mo of moles of vapor and L represents the remaining liquid

i used the relation for ideal gas yi=pi/pt to determine the amount of vapor (V), summing yi and knowing it is <1, it means that the mixture is present as a VLE mixture

[xerxes]

Following site may be useful: http://www.questcons...rm/thermot.html


In addition to Art Montemayor's comments, when communicating please indicate whether you are using mole% or weight% and whether you are using bar(a) or bar(g).

the problem given to us never stated whether it is mass or mole %

i just assumed it was given in mole percent

[xerxes]

To Xerxes,
To know in which state the mixture is in, calculate the dew point and bubble point of the mixture. To calculate these values refer the book Mass Transfer Operation by Robert Treybal. To be more precise refer the solved problem 9.3, for this you will require one chart called De Priester which is given in Perry's Chemical Engineer's Handbook section 13.

thank you, i know how to compute for it, though it would require me to use softwarer to determine the bubble point and dew point of a multi component system, tis just we normally dont have access to this math softwares, so i decided to make use of a crude method

bad me, my prof said determine the state, so i did not went to dew point and bubble point calculations, hehehehe

[xerxes]

for the fugacity and fugacity coefficients, i made used of equations from thermo by smith, et.al

tis just that i have difficult calculating it using mathcad

anyways, this is the mathcad solution i did *sorry, the mathcad file is not permitted for upload


Problem 1

Given
T=95oC P=30 bar
(1) methane = 0.20
(2) ethane = 0.35
(3) propane = 0.20
(4) heptane = 0.25

Required:
(a) state of the system; justify
( estimate, fugacity, fugacity coefficient, Zmixture

Solution:

Assuming Ideal Gas behavior, the Psat ( in bar) for each component is evaluated using Antoine equation





If the mixture is saturated, Pi=Psati
On the basis of one mole of the mixture, the amount of the vapor would be:

Note that for ideal gas, mole fraction equals pressure fraction=volume fraction
Let V = the amount of the vapor and L=the amount of the liquid and that V + L=nt




The values of L and V shows that the mixture is in VLE state
















by Equation (11.67) though (11.71) of smith, van ness an abbot






by Equation (3.61) and (3.62) by smith van ness and abbot



by Equation (11.61) by smith van ness and abbot


*sorry but the equations cannot be pasted

[xerxes]

what i was never ble to do is to determine Zmixture, due to lack of time