well-founded theory. While Pitzer equations and others of similar
higher complexity have a better theoretical foundation and are
certainly a requirement for many situations involving highly concentrated
solutions, for the purpose of PCC modelling they are not
superior as too many parameters are simply not determinable. The
number of parameters means that a good agreement between the
model and the data will result, however the usefulness of these
parameters for prediction or extrapolation is limited by this overfitting.
To reliably determine the parameters of these complex
activity models requires substantial experimental effort and analysis.
In particular a careful sensitivity analysis of the model system
is essential.
The main advantages of a simpler activity model that adequately
represents the non-idealities in a physically meaningful are
twofold: the model parameters will be well defined by the data;
and once determined should be reusable across a range of conditions
and compositions. This has been demonstrated to be the case
for the SIT based approach in this work. This then provides a far
simpler model framework for inclusion in process modelling and
performance prediction tasks.
A remaining question is if the same type of simple SIT based
activity model can also be used to describe non-ideal kinetic
behaviour in CO2–amine–H2O systems. Non-idealities influence
the effective concentration of species in solution and thus impact on
reaction kinetics as well as the thermodynamics. Correct account of
this non-ideal behaviour should allow the determination of reaction
rate constants independent of composition in analogy to the
determination of equilibrium constants at zero ionic strength. The
suitability of a SIT based activity model for this is currently being
investigated.
References