A mixture of gases 11% CO2 - 89 % N2 (molar) at a temperature of 300 °C and total pressure of 1400 psi. ¿CO2 and N2 at these conditions are in the gas phase or in supercritical state? I mean, ¿what is the pressure to determine the behavior of each component (CO2, N2)?
The subject of fluid behavior is broad and diverse. I cover this at some length in my book, Thermodynamic and Transport Properties of Fluids, which will be free on 3/24/2020. https://www.amazon.com/dp/B07Q5L1CHT The software is always free at http://dudleybenton.altervista.org/software/FluidProperties.zip The fact that these gases are supercritical actually makes your work in this case easier.
The subject of fluid behavior is broad and diverse. I cover this at some length in my book, Thermodynamic and Transport Properties of Fluids, which will be free on 3/24/2020. https://www.amazon.com/dp/B07Q5L1CHT The software is always free at http://dudleybenton.altervista.org/software/FluidProperties.zip The fact that these gases are supercritical actually makes your work in this case easier.
Please, correct me if I wrong.
I think we must calculate partial pressure of each component of the mixture and then check if the parameters of selected gas are in supercritical stage???
Dear Juan,
In the present case one is interested in a temperature (300 oC) higher than the critical temperature of each component in the mixture. For N2 Tc=-147 oC and for C02 Tc=31oC. Therefore the mixture is certainly supercritical.
Following Reid, Prausnitz and Poling "The properties of gases and liquids" (McGraw-Hill 1988, pages 128-131), one can estimate the mixture critical temperature with a weighted average of the individual critical temperature Tc,i of component i. The contribution of of each gas being proportional to the molar fraction yi multiplied by a power of the critical volume Vc,i or the critical surface (Vc,i)^(2/3).
The phase behaviour of mixtures such as N2 mixed with CO2 is more generally described by using a "flash" algorithm based on an equation of state. The cubic equations of state such as the Redlich-Kwon-Soave or the Peng-Robinson equations of state allow very efficient calculation of the gas-liquid phase enveloppe of the (given) mixture in a pressure-temperature diagram. Typically these calculations have been calculated using the van der Waals equation of state by P.H. Konynenburg and R.L. Scott (Philosophical Trans. Roy. Soc. London. Series A, Vol. 298 , No 1442 (1980) pp 495-540). You will see that in the (P,T) diagram where you see a boiling line for a pure component (roughly exponential dependency of boiling pressure as a function of temperature) ending at the critical point, you see for a mixture a two-phase region where Liquid and Gas coexist for a given total composition (of the mixture). Each phase has in general a different composition depending on the position in the (P,T) diagram.
Note that the critical point is defined for multiple component mixtures as the point on the envelope of the two phase region where dew-point line and boiling point line meet. At this point the molar composition of the liquid and gas phases will be identical. You can see that the critical point of the mixture correspond often to a temperature intermediate between the critical temperature of the two components. The critical pressure is often higher than both individual critical pressures.
I guess that this is not your question. You probably are asking: Above which temperature will I never observe liquid in the mixture?
The highest temperature at which 2 phases (liquid-gas) can coexist is higher than the individual critical temperatures. There is in general a range of temperature for which liquid is formed by decreasing the pressure at fixed temperature. This is the so called retrograde condensation (does not exist in a single component).The highest pressure at which two phases (Liquid-gas coexistence) can be observed is higher than the individual critical pressures.
Regards
Mico
Dear Juan,
Your case: "A mixture of gases 11% CO2 - 89 % N2 (molar) at a temperature of 300 °C and total pressure of 1400 psi" is fairly simple. The mixture will almost certainly be a gas. 1400 psi is a rather low pressure and the temperature is MUCH higher than the critical temperatures of both components. Also the component with a relatively high critical temperature is only 11% of the mixture. The ideal gas low, will be an excellent approximation for this mixture. In the above quoted book of Reid et al. you will find methods to estimate the departure from ideal gas behaviour (pages 79-84).
Regards
Mico
Hello Andrey, yes you are wrong. You should not calculate only the partial pressure of each component, because at these conditions gases not are ideal ( Observe the critical conditions of the study gases) . This is a common mistake in many papers.
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