Mixing Rule to get critical properties of hydrocarbon mixture

[pyMorty]

Hi,

I'm trying to calculate decent approaches to saturation pressure of hydrocarbon mixtures (methane to hexane). In an attempt to avoid going through EOS I came across with Antoine equation, which seems to deliver pretty accurate results with pure gases. I wanted to give it a try using pseudocritical properties obtained by Kay's rule with a mixture of 0.8 methane and 0.2 ethane, but the results are anything close to a saturation curve calculated with EOS' software.

Is there any other mixing rule I can use to get decent pseudo properties to plug in into the Antoine equation? Would any kind of mixing rule also apply to Antoine parameters ( A, B and C)?

As I mentioned I can solve this by using a phase envelope software, but I'd like to do it in a spreadsheet for the mere pleasure of getting decent results on my own. Don´t need to be the most accurate, as long as it is close it will be great.

Thanks in advance.

 

[rotw]

I think there are few options of variants for mixing rules ; it would provide incremental improvement but as you get in the vicinity of the critical point, it is not going to be accurate and probably it will be subject significant error.

If you plan an escape, you must succeed as if you fail, you will be punished for trying. Never say or write down your plan. Heart is the only place where secrecy is granted.

 

[PaoloPemi]

pyMorty,
Antoine equation can be accurate for pure fluids but for mixtures phase equilibria you need a procedure to estimate fugacities for both vapor and liquid phases, as you noticed the errors introduced by assuming ideal behaviour are high,
the normal practice is to adopt some cubic EOS or multi-parameter Helmholtz-energy-explicit (see GERG etc.),
or, if you wish to estimate critical properties, see the formulations provided in books as The Properties of Gases and Liquids etc.

 

[pyMorty]

Thank you rotw and PaoloPemi. I'll keep looking up then.