Vapor-Liquid Equilibrium Modeling (NH3-CO2-H2O) with Pitzer Data

[mfernandez]

Hi,

 

I am interested in using GWB to model CO2-NH3-H2O vapor-liquid equilibria using Pitzer coefficients. Using thermo_phrqpitz.dat, this doesn't seem to be possible. Is their another data set that would allow me to do this? If not, would it be possible to edit one of the data sets in such a way to make this possible. It's worth noting that I'd like to include the carbamate ion species (e.g. H2NCOO-). There was a recent publication in the International Journal of Greenhouse Gas Control published recently (Author: Yin Xu, Title: Modeling of the NH3-CO2-H2O vapor-liquid equilibria behavior with species-group Pitzer activity coefficient model), that I though might be useful in this task. If the vapor-side modeling is not feasible, there would still be value in just modeling the closed aqueous system. If anyone has any suggestions, please let me know. Thanks!

[Brian Farrell]

Hi,

I would advise against simply adding new components to an existing Pitzer database. Pitzer datasets are not meant to be extensible like a thermo dataset which uses Debye-Huckel-based methods. You can, however, create your own dataset in GWB format if the data is available. Does your reference contain a list of equilibrium constants for reactions in the CO2-NH3-H2O system, as well as virial coefficients describing the interaction between pairs or triplets of species?

Currently, the GWB handles datasets using an early, simple implementation of the "Pitzer equations", as well as the more recent and commonly used Harvie-Moller-Weare formalism. For the latter, you can use the TEdit thermo data editor in GWB10 to define your chemical species, reactions and log Ks, and virial coefficients.

Perhaps other users have already compiled the necessary data or can offer some additional insight.

Hope this helps,

Brian Farrell

Aqueous Solutions

[mfernandez]

Thank you for your reply Brian. The paper that I'm referencing contains correlation parameters for the chemical equilibrium constants of several equations (Ai). Some of them are already in thermo_phrqpitz.dat, but a couple of them are not (deprotonation of water by ammonia, and formation of carbamate ion from ammonia and bicarbonate, both from Edwards 1978). It also includes Henry's constant parameters (Bi) and standard enthalpies of formation for NH3 and CO2 (from Rumpf 1998). The values unique to this paper are some parameters for Pitzer activity coefficients (eight binary and four ternary parameters). However I am not too familiar with the form of the equations or the data file structure, so I have no idea if this information can be integrated.

 

Please let me know if there is anything else I can provide to offer a better description. Thanks again for your help.

[Brian Farrell]

Hi,

 

I took a quick look at the reference you mentioned. I'm not positive, but this looks to be a non-standard, simplified implementation of the Pitzer equations. Specifically, the "species-group" aspect appears different from the Harvie-Moller-Weare formalism, which the GWB and most other modeling programs use.

 

Regards,

Brian