Characterization of the Moroccan Timahdit (X-layer) oil shale kerogen using pyrolysis and thermally assisted hydrolysis and methylation

The organic matter of the Moroccan Timahdit (X-layer) oil shale (Upper Cretaceous), mainly present as kerogen (or insoluble organic matter), was investigated using spectroscopic and pyrolytic methods. FT-IR and NMR indicate a dominant aliphatic nature for the studied material with a significant abundance of O-containing chemical groups. GC analysis of classical flash pyrolysate afforded only linear hydrocarbons as alkene/alkane doublets giving confirmation that decarboxylation of carboxylic acid groups can be a dominant process under these conditions. Flash and preparative thermally assisted hydrolysis and methylation (THM as defined by Challinor) techniques indicated that ester groups are significantly involved in the fixation or cross-linking of aliphatic chains in the kerogen. The identified tetra- and pentacyclic triterpenoids gave evidence that the studied sediment is immature, the evolution stage corresponding to diagenesis with a limited isomerization of triterpanes. The mechanisms of bond cleavage appear to differ when using flash or preparative THM techniques, probably as a consequence of experimental (temperature) conditions. Flash and preparative THM should be considered as complementary techniques which can be very useful for the structural investigation of complex forms of organic matter. (C) 2001 Elsevier Science B.V. All rights reserved.