Toluene-Water system in Aspen

[sottocutaneo]

Hi all, I am Eng.Antonio Aulicino (University Federico II of Naples, Italy). I am using Aspen Properties to understand what is the suitable property method for a system with toluene and water. I do the Txy diagram and xy diagram, but i didn't found a property method that gives results in agreement with literature.

-What is the property method correct for toluene-water?

In the manual there is:
"For water-hydrocarbon applications, two liquid phases often coexist with a vapor phase. Aspen Properties has two approaches for modeling these types of vapor-liquid-liquid equilibrium calculations:
·Rigorous three-phase calculations
·Calculations with a free water approximation. When you use free water approximation, Aspen Properties assumes the water phase is pure liquid water (free water)."
What i have to do

-How i can do the rigorous three-phase calculations?

My first target is to design an absorber column for toluene with pure water. The second, and most important target, is to design an absorber column not with pure water, but with a solution of water and copolymer that enhanced the solubility of toluene in water.

-Is it possibile to change in Aspen, only some properies of water (such as the viscosity and the solubility of toluene)?

Thanks all

 

[MikeClay]

Most binary mixtures use parameters that give a reasonable fit over the entire range, but do not fit any one range well, this is especially true with water and hydrocarbons. If the tolune phase is vapor, the problem becomes a little easier. Aspen should have routines to estimate binary interaction parameters from data. Create a hypothetical tolune and change the binary interaction based on the data from the region of interest. This should give you a better fit with just about any activity model based thermo package.

Depending on the nature of the water/copolymer mixture data, it may be possible to create a hypothetical water also.

Good Luck. It's not an easy problem.

--Mike--

 

[sottocutaneo]

Mike thanks a lot for your answer.
There are news. With Aspen Properties I found a property method that appears to be suitable for water-toluene: UNIFAC (or UNIQUAC) + free water calculations. But it is clear that I can not use the free water calculation if I want to do an absorber column, so I thought, as you said Mike, to change the Henry's constant for the toluene in water (from the literature), and then, when I will use the solution water/copolymer, i will change another time the Henry's constant...i will try to do this tomorrow because I have just returned from the university and I am tired.
In Aspen I have never changed properties in a property method, so If you have any advice I would be very happy; however, tomorrow I will try reading the manual.
Thanks all

 

[MikeClay]

Depending on the tolune concentations, I'm not sure that henry's law will apply. In the past I've taken select binary data and used the simulator tools to regress new BIP's. I'm assuming ASPEN has similar utilities.

Sorry I can't be of more help.

--Mike--

 

[sottocutaneo]

Forum I have a problem. I created a pseudo-toluene. For the pseudo-Toluene I inserted the true data except the data of water solubility because I inserted the solubility of Toluene in the solution water-copolymer. The problem is that Aspen seems not to use the data I inserted, in fact the ammount of toluene dissolved in water is not the value that I inserted. To check the ammount of toluene dissolved in water i used a FLASH that can achieve the thermodynamic equilibrium, but, as I said, the final value of the amount of toluene dissolved in the water isn't the value that I have setted. I have the impression that Aspen doesn't use my data, why? I would like to insert the Henry's constant (but I don't know how), so I can give the Henry's constant corresponding to the solubility of toluene in the solution of water and copolymer. Thanks all

 

[siretb]

First have a look ar thread 798-63275 (this site)

In the past, I used UNIQUAC with ASPEN, on this system, with success.
could you attach you input file and the data you want to fit? We could have a look.

 

[sottocutaneo]

i want to insert the solubility data of toluene in the solution of water and copolymer, so, because the copolymer is about 2 % (w/w), I can approssimate the solution to pure water but I must change the water solubility of toluene and set the solubility of toluene in water+copolymer; so I created a pseudocomponent (toluene). One of the requested data for the pseudocomponent is the water solubility (in molar fraction) and I set it to the value of the solubility of toluene in the solution water-copolymer. Then, with a FLASH, i can see the equilibrium concentration, and I see that is not the value that I inserted. With my data I have an Henry's constant that is 10 - 30 atm,instead he seems to use an Henry's constant of 10000.
Thanks all