Imagine I would perform adsorption studies of ethyl acetate in water using a given resin. I wanted to use 5 mL flasks, closed with a rigid lid.
Now I would prepare a 1 g ethyl acetate/L solution at 20 C and put it in the flask and close the lid. If the experiment is performed at 70 C, after some point I guess the pressure in the flask will keep increasing until VLE is reached right? This is because ethyl acetate (preferentially) will tend to evaporate, if I am correct.
Would the increased pressure have an effect on adsorption? How could we keep the pressure constant at Patm? By taking out vapor phase with a syringe?
Thanks!
Adjust the volume of the mixture to the volume of the flask and there will be no second phase. Mixing or shaking can also help. Otherwise, the ethyl acetate transfer from the vapor phase to the liquid might be included in modelling.
Regards
So, considering the vapor system ideal, presuming the headspace to be filled with dry air and ethyl acetate in equilibrium at 20 Celsius and the vessel air-tight (which are pretty big assumptions).
Using antoine equation we get that for the ethyl acetate the Pvap(20)=0.138 bar and Pvap(70)=0.768bar. Using PV=nRT we can translate that Pvap to M(mol/L) and get 0.0056 M and 0.0273 M.
Using the same trick we can calculate the molarity of air 0.0422 M. For 1L, there will be 0.0422+0.0273-0.0056 moles present in the headspace which can be translated back to 1.8 bars.
The liquid shouldn't notice such a small change in dP.
Ps. for a more correct calculation of the headspace pressure, there's always Peng-Robingson and Aspen to solve the equations but I doubt the number will be much different.
The Antoine equation allows you to determine the saturated vapor pressure at a given temperature over a pure chemical compound. Having a saturated vapor pressure of ethyl acetate (EA) at 70oC (as above) and a saturated vapor pressure of water at the same temperature (0.312 bar) the relative volatility, a can be calculated. Then, using the equation y=ax/(1+(a-1)x), you can estimate the concentration of EA in vapor phase. ....... You could do so, if there was no air above the liquid in the tightly closed flask ?.
Of course, the presence of EA in the gas phase should not be overestimated. Its evaporation, despite the boiling point lower than the boiling point of water (77.1oC), will be impeded by the presence of air and its increasing pressure (thightly closed flask ?). The increase in partial air pressure should be approximately 18% (Charles's law). Considering the EA solubility (at 25oC 80 g / l), the EA concentration in water presumably does not exceed 5%. It follows that the pressure increase in the gas phase will mainly depend on the presence of air and steam in it. In this situation, the concentration of EA in the gas phase will be small and should not affect the adsorption process, such as the sum of partial air and steam pressures.
Because it's just guessing, it is better to prevent the presence of ethyl acetate in gaseous phase over the mixture I wrote in the first answer.
Regards.
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