2 replies to this topic

[swift_eklipz]

I am asked to calculate and draw the vapor-liquid equilibrium (VLE) diagram of a binary mixture of acetone and glycerol,
given only the total pressure, P = 1 atm (760 mmHg). It says for me to explicitly plot the mole fraction of acetone
versus the mole fraction of glycerol.

I have no idea where to start. I was thinking of using Antoine's equation but this question doesn't relate to a temperature.
I have Googled endlessly for a step-by-step process but found nothing. I'd appreciate if someone could throw me a bone on how I start this off.

[gayathri]

I am asked to calculate and draw the vapor-liquid equilibrium (VLE) diagram of a binary mixture of acetone and glycerol,
given only the total pressure, P = 1 atm (760 mmHg). It says for me to explicitly plot the mole fraction of acetone
versus the mole fraction of glycerol.

I have no idea where to start. I was thinking of using Antoine's equation but this question doesn't relate to a temperature.
I have Googled endlessly for a step-by-step process but found nothing. I'd appreciate if someone could throw me a bone on how I start this off.

Hi....Let me share in the facts which i knew of VLE..Since u ve nt furnished all the data clearly let me assume certain conditions
1)If they were to form ideal solutions,the procedure is as follows
The boiling pt at 1 atm of the substances would be known.So u ve to arbitarily consider some values in between the boiling points for making your plot.(say a is bp of acetone and f bp of glycerol,then take values a,b,c,d,e,f)Then partial pressure values at particular temp can be got from perry for both constituents.Tptal pressure is known.

Using the formula,x=(Pt-Pa)/(Pa-Pb) mf of acetone is got.

y=(Pa*x)/Pt mf of glycerol is got

Pa,Pb are pp of acetone and glycerol.The boiling point determines the state of the two(vapour or liquid).Try out using relative volatility(to know the extent of separation)(Pa/Pb) equation also...

Hope this helps...

Gayathri

[sheiko]

I am asked to calculate and draw the vapor-liquid equilibrium (VLE) diagram of a binary mixture of acetone and glycerol,
given only the total pressure, P = 1 atm (760 mmHg). It says for me to explicitly plot the mole fraction of acetone
versus the mole fraction of glycerol.

I have no idea where to start. I was thinking of using Antoine's equation but this question doesn't relate to a temperature.
I have Googled endlessly for a step-by-step process but found nothing. I'd appreciate if someone could throw me a bone on how I start this off.

You can plot this two ways: (P vs T) @ a given composition OR (T vs mole composition) @ a given pressure. So ask your teacher wich representation he prefers and at wich composition (case P vs T) or pressure (case T vs x).

Assume the mixture is ideal i.e. the vapor phase behaves like an ideal gas (PV = nRT and Pi = yi*P) and the liquid phase behaves like an ideal liquid (Pi = xi*Psati) and perform flashes at different conditions in order to plot the bubble point curve and the dew point curve (which form the phase envelope).

Attached is a spreadsheet to perform the flash calculations. It has been done and checked by an active member of this forum. The ki values in the spreadsheet can be assumed equal to Psati/P for each component of an ideal mixture (indeed, Pi = yi*P = xi*Psati => yi = ki*xi with ki = Psati/P).

Above all, take your time to fully understand the proposed method before using it.

Attached Files

•  Flash_composition.xls   212KB   204 downloads

Edited by sheiko, 15 February 2010 - 02:40 PM.