Characterisation of the non-asphaltene products of mild chemical degradation of asphaltenes

The major steranes of the non-asphaltene fraction of Nigerian tar sand bitumen (maltene) are the c₂₇-c₂₉ diasteranes 13β(H),17α(H); 20R + S] and C₂₈-C₂₉ regular steranes 14β (H),17β (H); 20S]. The reducing metal reaction products of the corresponding asphaltenes (maltene-I) contain mainly C₂₇-C₂₉ regular steranes with the 14β(H),17β(H); 20R + S and 14α(H),17α(H); 20R + S configurations as well as the corresponding diasteranes having the 13β(H),17α(H); 20R + S configuration. These sterane distributions suggest that maltene-I corresponds to an unaltered oil whilst the maltene is equivalent to the product of severe biodegradation of maltene-I. This is consistent with maltene-I being the remnant of “original oil” trapped within the asphaltene matrix and protected from the effect of in-reservior biodégradation.Degradation of Nigerian asphaltenes by refluxing with ferric chloride-acetic anhydride or methanolic potassium hydroxide also releases soluble reaction products having the characteristics of unaltered oil such as the presence of n-alkanes having an unbiased distribution. These methods appear to be milder and more suitable than reducing metal reactions for releasing hydrocarbons occluded by asphaltenes.