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| Titel |
Water activity in polyol/water systems: new UNIFAC parameterization |
| VerfasserIn |
C. Marcolli, Th. Peter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 5, no. 6 ; Nr. 5, no. 6 (2005-06-17), S.1545-1555 |
| Datensatznummer |
250002904
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| Publikation (Nr.) |
 copernicus.org/acp-5-1545-2005.pdf |
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| Zusammenfassung |
| Water activities of a series of polyol/water systems were measured with an
AquaLab dew point water activity meter at 298K. The investigated polyols
with carbon numbers from n=2-7 are all in liquid state at room
temperature and miscible at any molar ratio with water. In aqueous solutions
with the same molar concentration, the diols with lower molecular weight
lead to lower water activities than those with higher molecular weights. For
diols with four or more carbon atoms, the hydrophilicity shows considerable
differences between isomers: The 1,2-isomers - consisting of a hydrophilic
and a hydrophobic part - bind less strongly to water than isomers with a
more balanced distribution of the hydroxyl groups. The experimental water
activities were compared with the predictions of the group contribution
method UNIFAC: the model predictions overestimate the water activity of
water/polyol systems of substances with two or more hydroxyl groups and
can not describe the decreased binding to water of isomers with hydrophobic
tails. To account for the differences between isomers, a modified UNIFAC
parameterization was developed, that allows to discriminate between three
types of alkyl groups depending on their position in the molecule. These new
group interaction parameters were calculated using water activities of
alcohol/water mixtures. This leads to a distinctly improved agreement of
model predictions with experimental results while largely keeping the
simplicity of the functional group approach. |
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