11 replies to this topic

[Sau Jun]

Dear all,

I am working on one industrial distillation project. Regarding azeotropic distillation, may I know how benzene works as entrainer in Water/Isopropanol soolvent? Benzene and water will be coming out from the top of the distillation column first. May I know what is the reason and mechanism? How Benzene acts as entrainer in this azeotropic system?

[Ankur Shah]

hi!

you have asked a million dollar question. frankly, i am working with the same system ie of water and ipa, but mine is more of a college project, as i am still studying.

azeotropic distillation is an interesting problem to solve. we shall consider a binary system for this. (just like the one you have). we have all seen the y-x plots for different systems {starting from benzene-toluene {B-T} studied by most of us in class). now, for the ipa-water system, ipa is more volatile and hence its mole fractions (mfs) will be taken into consideration for this plot. the B-T system is highly simple.. but for the ipa-water system, the y-x curve crosses the y=x line. I am attaching a file which shows this for the ipa-water system at 1.25 bar. {this was made by hysys}.

now, since the equilibrium curve croses the y=x curve, we cannot obtain ipa as the top product, instead we will get the azeotropic composition at the top and water at the bottom. {please spend a fe minutes to understand this.}

Now, we need to BREAK the azeotrope. so, we add an entrianer {here u are using benzene ( B )}. B does not form an azeo with either ipa or water. once B is also in the system, we can no longer work with the y-x diagram, instead we need to generate a ternary plot or as it is better known a residue plot. a residue plot is a triangular diagram (either right traingle or equilateral).

These plots are not very simple to use. Your air is necessarily to cross the separtix which you shall obtain in this system.

frankly, it would be fairly complicated an issue to discuss over a network and hence, I highly recommend, you take a look at Douglas' plant design book {i doubt thats the correct name}. It has this system explained in great detail. Else, conceptual design of distillation systems by doherty and malone will also help.

Sorry for the limited help.

Regards,

Ankur Shah

Attached Files

•  ipa_water_125.JPG   41.51KB   317 downloads

[process equipment]

Off the top of my head...

Yes. When deciding between an entrainer and vacuum distillation, you need to first look at the VLE relationship between the components to be separated including the entrainer. If the boiling points of the components to be separated are very close and addition of a solvent can create a minimum boiling azeotrope, this may make it easier to separate. A solvent addition in distillation is also used when trying to break another azeotrope already in the system before the solvent.

Ex. If you want to separate toluene and methanol, a simple distillation will only bring up the tol-meoh azeotrope. But if a solvent, such as hexane, is added, it will azeotrope off with the meoh leaving the toluene behind. (for example purposes only)

On the other hand, if you are talking about an "entrainer" as in a liq-liq separation, you need to determine how soluble the entrainer is in each of the components and at what temperature would you see a liq-liq separation.

Dear all,

I was wondering if we could separate azeotropic binary components using membranes ?

Thanks,

PE

[Ankur Shah]

hey!

JD, you are using methanol for which system?

about finding out how much amount.. this is quite a sensitive calculation. firstly u need to know your feed flow rate. Then, you need to itterate to find out what NET composition you need as your feed. from here you should be able to find out the amount of entrainer.

although i have said so in 3 lines, i HIGHLY recommend reading Doherty, Malone's Conceptual design of distillation systems.

Ankur

[Sau Jun]

Hi just a quick question how do u decide how much of the entrainer to use. For my experiment im using Methanol as the entrainer.... Thx

JD, may i know which binary or ternary system does methanol be used as entrainer?

Hereby is my findings:

Ternary heterogeneous azeotropic temperature for
water-IPA-benzene : 65.74 C

Binary Azeotropes:
IPA-water : 80 C
IPA-benzene: 71.53 C
water-benzene: 69.31 C

Thus, benzene helps to remove water from IPA, and IPA will be product at the bottom of distillation column.

Does anybody know what is the composition of Ternary heterogeneous azeotropic water-IPA-benzene??

Thanks

[Allen_xin]

Hi all

As you mentioned water separation from IPA, I think pervaporation membrane is more suitable, specially for azeotropic mixture. if you are interested, please send me email, we can talk about this in detail.
allen_xin1982@hotmail.com

[pawan]

Sau Jun
Can u mention the composition of original IPA + water mix U r looking to separate.