12 replies to this topic

[asparagus]

Hello everyone, I am a final year student completing my degree in chemical engineering. I know it would seem terribly basic to many of you, but I do need a bit of help and guidance. I am asked to design a Distillation Column for Ethylbenzene recovery, so the main components in the feed process stream is Ethylbenzene, Styrene and minute amounts of Tar. I have chosen to do a Binary distillation, so I went on with finding out more about it, being told by my university colleagues that it's too easy. after much research I have found out that it's meant to be done under vacuum conditions, I have looked at Perrys, Coulson and Richardson, then this other separation principle book, I can see the formulae but I am terribly confused about the Operation conditions. Do I look for them? Should I have had them to begin with? Do I take up standard values from the handbook? I haven't the slightest idea on how to BEGIN, please feel free to ask questions cause I know I haven't provided enough info on my process section itself, but then again don't want to cram here too. Please do ask, I shall search and provide. I do not need someone to do it for me but merely a guidance. Thank you so much in Advance.

[thorium90]

These websites could prove enlightening

 

http://www.freepaten...om/3904484.html

 

http://www.cbi.com/i...-Styrene-12.pdf

 

http://klmtechgroup....r rev intro.pdf

 

It would appear the tar sort of assists in the distillation due to the close boiling points of EB and STY. This complicates things a little. But those links provide suitable insights into the operating conditions of current plants using the technology

Edited by thorium90, 21 February 2013 - 02:38 AM.

[asparagus]

Hi Thorium

Thank you very much for the links, the patents were an eye opener, when you said it complicated a bit(inclusion of tar) how much does it complicate things? because with in reason I can balance out the mass balance and not really count tar as a separate component. My tutor said it's fine I do that.

Now the patents have provided really useful data, but are not referred, do I just use the operating conditions from there and just provide reference that I have taken it from there, I have been recommended to look at Engineering Handbooks for certain values. But I get lost in that book.

 

From what I gathered, it certainly is a binary distillation method, and a vacuum one at that(because of the really close boiling point differences of 10^oC, And what is more accurate the Fenske Underwood? or McCabe.

Again thanks a million for the guidance.

[thorium90]

 when you said it complicated a bit(inclusion of tar) how much does it complicate things? because with in reason I can balance out the mass balance and not really count tar as a separate component.

 

From this line in the first link:

"The added styrene tar residue increases the relative volatility between ethylbenzene and styrene monomer"

Well, but if your tutor thinks its possible to ignore this effect, then it will be the standard kind of calculations then.

 

Some useful equations

Underwood: Minimum reflux ratio

Fenske: Minimum number of ideal trays

Gilliland: Tray efficiency

Murphree efficiency: Used with McCabe Thiele

Edited by thorium90, 21 February 2013 - 01:16 PM.

[tatenda]

thank you for that post it so clear.

I am doing the distillation of dimethly ether and carbon dioxide if you can find me some links so i can read around. I have been looking for some guidance but can not find any. thank you in advance

[thorium90]

Wow, how many projects must one do just to graduate?!!

Nevertheless, searching google is an easy task for many students nowadays. Rmb, GIYF...

 

http://www.ijest-ng....no1-pp10-21.pdf

 

http://www.google.co...s/US20110040129

[asparagus]

Not too many projects I assure you, but most of us are given different equipment to work on. I have been working on mine, and it's looking rocky, even different patent say different things, one say there's azetropes happening, others say we work with x amount of pressure, which is actually above atmospheric, then there is this whole issue of pressure drop, but I have already selected vacuum, anyway, since you have mentioned that there's an increase in the relative volatility(inclusion of tar), I believe that's a good thing cause it makes separation easier.

 

Oh Lord. It's worse cause I'm such a goldfiish at times, I select one path and then try another one, I need to learn to make up my mind.

 

My VLE diagram looks way too sketchy. I shall update after making progress(very slow at the moment) .

 

Thank you thorium, good luck tatenda with your design, are you designing a vacuum distillation column too? we could brain storm!

Edited by choudha4, 22 February 2013 - 10:14 PM.

[asparagus]

Hi Thorium,

 

How do you calculate the molar flow rate from mass flow-rate in a ''mixture'' cause I just divided it with the average molar mass of all my components Mr( I am guessing it's wrong because there the composition to consider?)

 

Hence asking. Thanks

[thorium90]

You need to brush up on your chemical engineering basics. Dig out all your textbooks, lecture notes and read them again.

Anyhow, this might refresh your memory.

http://en.wikipedia....ass_of_mixtures

[tatenda]

hi Thorium

thank you.. i actually shelved the design of the slurry bed reactor because of lack of information,i.e. in my country we do not have free access to recent journals and this technology is quite recent  thus now designing the distillation column

 

hi choudha4

i am not doing vacuum distillation but i did my internship where vacuum distillation was done what is that you want exactly? we can communicate via email if thats fine with you, good luck with yours too

[thorium90]

Distillation is not a very recent technology... Access to journals is never free. You always pay for them. When you are in a university, they deduct it from your school fees... Anyway, you have internet, so you still can theoretically access journals...

 

Attached Files

•  Technology vs usage.jpg   65.04KB   9 downloads

[asparagus]

Okay, I know I have come back to this much later that I ought to, but here's what happened, I believe if I have mentioned the value of the fraction of the more volatile component at the top product is low then someone could have informed that one can't even construct a McCabe theil diagram, and here I was thinking I am doing something wrong cause it looks odd, thinking that my basics needs brushing up and I was after all asking silly questions cause my doubts were in the wrong area.

 

To support what I have just said, I have come across a text book that says that

 

 

When concentrations of the more volatile component of either product is very low the steps on the McCabe-Thiele diagram become very small and difficult to plot. This problem can be overcome by re-plotting the top or bottom sections to a larger scale, or on log-log paper.

 

If the operating and equilibrium lines are straight, and they usually can be taken as such when the concentrations are small, the number of stages required can be calculated using the equations given by Robinson and Gilliland

 

 

After that I have made this interesting finding about Smoker's equation, where I can determine the number of stages for the separation of close boiling Isomers and if the relative volatility is constant and if they are low, which fits my process quite well, your thoughts thorium? Since I do get a very large number of stages according to reference books. Hence  McCabe diagram here is also impractical. 

 

 

 

[thorium90]

Hi,

 

I know this thread may be quite dead, but I think I just forgot about this thread. Lots of work now and following many threads so I forget which ones I havent replied!

 

Anyway, what I wanted to say was, although McCabe-Thiele is a graphical method, we have computers now. We don't need graph paper to draw curves now...

 

One can use excel to do the job. The attached spreadsheet is from Samir Khan's website.

 

http://excelcalculat...tion-excel.html

 

If you have Matlab, you can also use the following code.

 

http://www.mathworks...-binary-mixture

Attached Files

•  Binary Distillation McCabe Thiele.xlsx   39.44KB   31 downloads

Edited by thorium90, 20 May 2013 - 06:35 AM.