Solution via phase equilibrium data fitting
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Recently, I needed to fit the phase equilibrium data for the absorption of CO2 by an MDEA-PZ solution. Data has been obtained from the literature; however, what is provided there is only the relationship between the equilibrium partial pressure of CO2 and its concentration in the liquid phase, and the total pressure is not given, which prevents me from calculating the equilibrium concentration of CO2 in the gas phase. (It is essentially solubility data rather than phase equilibrium data expressed in terms of concentrations.) I would like to ask: if I use the PXY regression system, does the pressure refer to the total pressure? The literature only provides data on the CO2 partial pressure at different temperatures and the corresponding CO2 liquid phase concentration; what should be done in such a case?
When fitting the phase equilibrium data for the absorption of CO2 by MDEA-PZ solution, if you obtain the relationship between the equilibrium partial pressure of CO2 and its concentration in the liquid phase, but have no information regarding the total pressure, this means that you cannot directly calculate the concentration of CO2 in the gas phase. When you refer to the PXY model for regression systems, P generally denotes the total pressure of the system, while X and Y represent the molar fractions of a certain component in the liquid phase and gas phase, respectively. However, since the data you have does not include the total pressure, you will not be able to use the PXY model for fitting directly. In this case, several strategies you can adopt include: 1. Assume total pressure: If it is reasonable to assume that the experiment was conducted at atmospheric pressure or under some constant total pressure, you can use this total pressure as an approximation to calculate the molar fraction of CO2 in the gas phase (Y). This will obviously introduce some errors, but it may be the only way in the absence of other information. 2. Search for additional data: Try to find more literature or materials to see if anyone has conducted similar experiments and reported the total pressure data, or locate online databases on the MDEA-PZ/CO2 system under similar conditions. 3. Contact the original author: If possible, try to contact the author of the original data and ask them whether they have any unreleased information regarding the total pressure. 4. Use non-traditional models: You may need to consider using other types of models, such as those based solely on the liquid phase, or adsorption isotherms, etc. For example, the relationship between partial pressure and solubility can be utilized via Henry’s law to predict the behavior under different conditions; this is generally valid for dilute solutions. 5. Experimental verification: If conditions permit, you can consider conducting experiments on your own to obtain complete phase equilibrium data, including the total pressure. Regardless of the method used, ensure that the approach you adopt is scientifically sound and be vigilant about potential errors. When reporting your fitting results, make sure to transparently describe the assumptions and limitations you’ve used. .
You may consider using Aspen’s analysis functions; apply Henry’s law to simulate and obtain the data you need