PCS-726
Surface Thermodynamics for Hydrocarbons on Wyodak Coals
Glass, Amy S.; Stevenson, Damon S.
Energy & Fuels
1996
10(3)
797-805
Isosteric adsorption enthalpies and dispersive surface tensions have been measured for
hydrocarbons interacting with Wyodak coal surfaces. The results show that this coal's
intermolecular forces are complex. Saturated (n-alkane) adsorbates experience a low-energy
Wyodak coal surface with a dispersive surface tension of ~25 mJ/m2. Unsaturated (alkene and
aromatic) adsorbates have more exothermic interactions with the coal. The interactions of all
1-alkenes studied decrease in exothermicity by ~1.2 kcal/mol after heating the coal to 200 C.
Citric acid washing or HF-HCl demineralization causes the same increase (~1.2 kcal/mol) in the
1-alkenes' adsorption heats. These results demonstrate that unsaturated hydrocarbons interact
specifically with the Wyodak coal surface. This specific interaction most likely involves the
unsaturated portion of the hydrocarbon adsorbate and polar or ionic groups on the coal. Plots of
adsorption heat vs polarizability have different slopes for alkenes and alkanes, demonstrating that
the two types of adsorbates experience different nonspecific interactions with the coal as well.
Demineralizing the coal has no effect on the plots, but heating to 250 C, extracting in
tetrahydrofuran, or alkylating the coal gives the same plot of adsorption heat vs polarizability for
both types of adsorbates, demonstrating that these treatments result in a coal surface that has
similar nonspecific interactions with saturated and unsaturated hydrocarbons. These treatments
cause the coal's dispersive surface tension to increase to ~50 mJ/m2.
2. Wyodak-Anderson, WY (WY)