Fatty acid lithotype

Victorian brown coal occurs in five major lithotypes distinguishable by color index and petrography. Advantage has been taken of a rare 100 m continuous core to compare and contrast chemical variations occurring as a function of lithotype classification. For many parameters there is a much greater contrast between the different lithotypes than there is across the depth profile of (nearly) identical lithotypes. Molecular parameters, such as the distributions of hydrocarbons, fatty acids, triterpenoids and pertrifluoroacetic acid oxidation products, together with gross structural parameters derived from IR and C-NMR spectroscopic data, Rock-Eval and elemental analyses and the yields of specific extractable fractions are compared. 

This study reports the monocarboxylic fatty acid content of a series of brown coal lithotypes from the Latrobe Valley, Victoria, Australia. We have looked both at the solvent-extractable, or free, fatty acids (which include those extractable as esters or intact lipids) and at those that are released upon hydrolysis (saponification) of the residue after solvent extraction. The latter are presumably bound chemically to the coal matrix (kerogen) and are therefore designated as bound acids. The total acids are taken as the sum of the free and bound acids. 

The changes in fatty acid distributions and levels with lithotype might well be different from the changes observed with varying coal rank. In order to compare coals of significantly different rank, we also examined the monocarboxylic acids from a highly volatile bituminous coal. 

In the bound fractions the levels of high-molecular-weight fatty acids are still generally greater than those of the low-molecular-weight acids. The exception to this generalization is the medium dark lithotype, which shows almost equal levels of Cjg, C28 and C3Q n-fatty acids. 

The differences in fatty acid distributions brought about by varying lithotype are rather more subtle than the differences brought about by varying the rank, since variation of rank brings about a change in the position of the maximum of the distribution. 

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