STRUCTURAL-ANALYSIS BY NMR AND FIMS OF THE TAR-SAND BITUMEN OF BEMOLANGA (MALAGASY)

The detailed characterization of the tar-sand bitumen of Bemolanga (Ma lagasy) was performed with the aid of NMR and FIMS techniques. After p recipitation of the asphaltenes an elaborate separation of maltenes wa s carried out by HPLC. The number average molecular weight measurement s indicate that this bitumen is much heavier than American bitumens (M WBAR = 900 against 534 for the Athabasca bitumen for example). The mod eling shows that the average length of the alkyl chains and the ratio of the number of naphthenic rings to that of aromatic rings increase f rom the aromatic fractions to the resin fraction and then decrease for the asphaltenes. Moreover, the average length of the alkyl chains is always larger than that in the corresponding fraction of American bitu mens. All the results indicate that the saturated fraction does not co ntain many linear paraffins and is constituted of naphthenic rings on which alkyl chains are branched. The change from the saturated fractio n to the aromatic fraction with the same molecular weight is made by s ubstituting the naphthenic rings by aromatic rings. The more saturated character of the Malagasy bitumen with respect to other bitumens is e xplained by the difference in their geological origin; the Bemolanga b itumen, coming from a Rift basin, is relatively protected and, consequ ently, less subjected to degradation by microorganisms.