the model calculated values using the regressed parameters, and
as can be seen the agreement across the full dataset is excellent.
Carbamate protonation is often not included in the chemistry
of CO2 and MEA. However, if it is removed from the model the
AARD% worsens to 21.6%. When included it improves the fit for
data points at high CO2 partial pressure. This is logical as based on
the determined pKa, and that found in previous work (Fernandes
et al., 2012a), it is only at low pH (pH < 8) that the concentration of
this species is significant.
The complexity of the activity model was increased to include
interaction parameters between the ions present at highest concentration.
These are the species MEAH+, MEACOO− and HCO3
−.
As these interaction parameters represent short range forces, only
ion pairs of opposite charge are considered. This added an additional
two parameters to the regression resulting in a significant
increase in the degree of freedom. The improvement in AARD% was
negligible such that their inclusion could not be justified.