Info

where A is a measure of a molecule's polarizability, r represents its polarity, a and p are respectively acidity and basicity parameters, ^ is a measure of the dipole-induced dipole energy, y and £ interpret the asymmetry effect, v is molar volume, and dn is a

Flory-Huggins term which is usually minor anyway. The outstanding characteristic of this model is that it can predict activity coefficients at infinite dilution using only pure component parameters which are available in the parameter table.

The SPACE (solvatochromic parameters for activity coefficients estimation) method, developed by Hait et al. [48, 49], uses a much larger database and recently established scales of solvent and solute dipolarity and hydrogen bonding. The SPACE equation assumes additivity and independence of the various contributions to the cohesive energy density: (1) dispersion, (2) dipolar interactions, (3) hydrogen-bonding interactions, and (4) size differences:

The meanings of physical quantities in the above equation refer to Eq. (100). But the SPACE model uses effective values for solute parameters (r2r//, a2e(f, /?2 #), which are calculated by a linear interpolation of the SPACE solvent (1) and solute (2) parameters. Unfortunately, the complete SPACE parameters for all compounds studied are only provided in the supplementary material that must be ordered from the specified institution.

Table 10 gives the comparison of models 1,2, 3, as well as other liquid-phase activity coefficient models such as MOSCED and SPACE, in predicting the activity coefficient at infinite dilution from 11 alkanes in 67 solvents at 25 °C.

It is shown that MOSCED and SPACE models with small average relative deviations (ARD) are more attractive among these five models. In the UNIFAC models (models 1, 2 and 3), the modified UNIFAC (model 2) shows substantial improvement, like the example given above with the most accuracy. Although the y" -based UNIFAC (model 3) is undesirable with the greatest average relative deviation of up to 20.7%, the maximum error (170.5%) may counteract the accuracy.

Table 10

Comparison of activity coefficient at infinite dilution for different models

Table 10

Comparison of activity coefficient at infinite dilution for different models

Parameters

Model 1

Model 2

Model 3

Was this article helpful?

0 0

Post a comment