PCS-724
Distribution of Pendant Alkyl Groups in the Argonne Premium Coals
Obeng, Marcus; Stock, Leon M.
Energy & Fuels
1996
10(4)
988-995
The ruthenium(VIII) oxidation reaction has been employed to determine the distribution of alkyl
groups that are bonded to aromatic structural elements in lignin and the Argonne Premium Coals.
The lignin, as expected, has few aromatic methyl groups, 0.02 per 100 carbon atoms. The results
for the coals, Beulah-Zap 0.86, Wyodak 1.16, Illinois No. 6 1.76, Blind Canyon 2.45, Pittsburgh
No. 8 2.05, Lewiston-Stockton 2.39, Upper Freeport 2.09, and Pocahontas No. 3 7.28 methyl
groups per 100 carbon atoms, exhibit a steeply stepped discontinuous rank dependence. The
abundances of the other small alkyl groups, which are least prevalent in the lignin and the
low-rank coals, range from about 0.2 ethyl and 0.05 propyl groups to about 0.01 butyl groups per
100 carbon atoms in the bituminous coals. The curious rank dependence for the methyl group
abundances may be the consequence of major structural changes that accompany the
transformation of a medium-volatile bituminous coal into a low-volatile bituminous coal. The
chemical origins of the methane that is formed during the pyrolytic decomposition of these fossil
materials are discussed. The analysis suggests that methane, the major portion of which is
obtained at high temperature after ethane and the other simple hydrocarbons have formed and the
paraffinic and hydroaromatic fragments have decomposed, is not produced predominantly from
the structural elements that exist in the unreacted coal through conventional processes such as
scission and ipso substitution. The methane that is formed at higher temperatures is accompanied
by even greater molecular quantities of dihydrogen. The observations suggest that methane is
produced by three reaction sequences involving oxidative condensation, hydrogen atom addition
reactions that produce reactive hydroaromatic compounds, and carbene chemistry that provides a
pathway to convert simple aromatic structures into methylated cyclopentane derivatives.
1. Upper Freeport,PA (UF)
2. Wyodak-Anderson, WY (WY)
3. Illinois #6 (IL)
4. Pittsburgh #8 (PIT)
5. Pocahontas #3 (POC)
6. Blind Canyon,UT (UT)
7. Lewiston-Stockton, WV (WV)
8. Beulah-Zap, ND (ND)