5 replies to this topic

[trungphu]

Hi everyone,

 

I'm doing an academic project regarding to membrane transport. In my work, I have to calculate activity coefficient of water in water-ethanol mixture. It leads to determine the limiting activity coefficient of water in ethanol. Could someone here help me find out this coefficient or show me where I can find it?

 

Thanks in advance

[katmar]

You speak of the activity coefficient as though it were one number, but of course it is a function of temperature and composition.  There are prediction methods, but they are complicated and if you do not have access to a simulator to do it for you it is not really practical to do by hand.  The methods are discussed in the more advanced books like The Properties of Gases and Liquids by Poling et al.  Perry probably mentions it, but I have not checked.

 

You can also back-calculate the activity coefficient from actual VLE data if you know the vapor pressure curves for the components.  There is a lot of ethanol water VLE data freely available - several sources were mentioned in a thread on this forum  http://www.cheresour...12268-vle-help/

[Steve Hall]

In my book, I discuss activity coefficients in the chapter on fractionation, with an illustration of how to construct a vapor-liquid equilibrium curve using them. It so happens that the example is ethanol-water, so maybe the spreadsheet that accompanies the chapter will answer your questions. You can download it at: http://www.pipesizin..._templates.html (Chapter 3). Navigate to the "VLE Example 2" worksheet.

[trungphu]

Thanks for all your help, Mr Katmar and Mr. Hall

 

Unfortunately, I have encounter another problem with my academic project. I'm trying to calculate the viscosity of water-ethanol mixture with 80%.wt ethanol at 60oC. There are some equations to determine this value but those equations have some parameter I can not find. Could someone here help me out this problem or suggest me a table of viscosity of water-ethanol ? 

 

With gratitude

[katmar]

The ITEC Refining and Marketing Company publishes a very useful ebook on ethanol.  See page 62 of

http://www.itecref.c...ok_Equistar.pdf

 

It is sometimes not worth spending too much time hunting down accurate physical property data. Simply plug into your equation or spreadsheet the maximum and minimum values that the property could be and see if it does make any real difference.  Doing this before you spend any time searching will give you a good indication of how much effort you should put into finding accurate data. 

 

In this particular instance the behavior is strange because the viscosity of the mixture can be significantly higher than the viscosity of each component and looking at the graph mentioned above, the viscosity will be somewhere between 0.8 and 0.9 centipoise.  The ethanol-water system is non-ideal in many ways and the density is also difficult to predict from pure component data.

[trungphu]

Mr katmar,

Your advances is very helpful to me.

In my case, I'm doing a simulation, so I need a specific equation to programing.

Thank you so much for your data.