http://www.google.com/search?ei=lPLNWsjSOaacvQSIppzYDA&q=uses+of+Can+Peng+Robinson+equation&oq=uses+of+Can+Peng+Robinson+equation&gs_l=psy-ab.3..33i22i29i30k1.2280.12519.0.14027.87.20.0.0.0.0.392.1345.0j6j0j1.7.0....0...1c.1.64.psy-ab..86.1.195....0.tyhLcdcWP_w

If you are just interested in calculating vapour pressure of single compounds and if you have a good temperature dependency of your attractive parameter, then it should be fine. If you are looking for densities and other derivative properties, it depends on what level of accuracy you want to accept as deviations will be quite high.

For mixtures, it is far more complex, it will depend on many factors, the type of mixing rules that you are using....

Since cubic equations of state (CEOS) such as Peng-Robinson (PR) do not consider polar-polar interactions and hydrogen bonding, they cannot accurately model phase equilibria of polar compounds. These equations only consider the Van der Waals interactions and originally are developed for non-polar compounds. However, over the past years, many modified CEOS (e.g. PRSV) were introduced to make CEOS applicable for polar compounds by modifying the temperature and acentric factor dependence of the attractive term. Unfortunately, most of these models can only provide good results for vapor pressure and are not accurate for modeling densities and other thermodynamic properties.

To accurately describe phase equilibria of polar compounds, I recommend you to use advanced equations of state such as cubic plus association equation of state (CPA-EOS) or statistical association fluid theory (SAFT) EOS, which are suitable for describing phase equilibria of highly polar and strong association compounds. These equations of state can accurately model all thermodynamic properties. For example, the CPA-EOS can predict the saturated liquid density of water (over the reduced temperature range of 0.5 – 0.9) with average absolute error of about 0.5%, while the PR-EOS (with volume correction) gives average absolute error of about 6%.

Dear Amir,

It is surprising to me that I am getting very close values for vapour liquid equilibrium temperature for highly polar compounds with hydrogen bonding like water and ammonia using Peng Robinson equation with most simple van der waals mixing rule.

I am able to find accurate values of VLE properties for mixtures containing polar compounds using temperature dependent binary interaction parameters in van der waals mixing rule in Peng Robinson equation.

Dear Amit,

I guess you are working in low temperature, where the effect of hydrogen bonding is not significant in phase equilibria calculations. In low temperature, CEOS can provide acceptable results for VLE calculations, while as temperature increases they show high deviation. For example, Soave-Redlich-Kwong (SRK) equation of state gives average absolute error of about 1% in predicting saturated liquid density of water for 0.5 < Tr < 0.6, while for 0.8 < Tr < 0.9 the average absolute error is about 17%. Please make sure that you can get acceptable results for all temperature ranges.

I am just talking about VLE temperature and not of density or other properties. VLE temperature matches very closely at all pressures up to critical point. There is no effect of hydrogen bonding on VLE temperature prediction using Peng Robinson equation with most simple van der waals mixing rule.

If you mix it hydrocarbons the fugacities do very strange things when water content is above a few percent.