ASPHALTENE REJECTION VIA SUPERCRITICAL-FLUID EXTRACTION

Supercritical fluid extraction (SFE) of bitumen was carried out in a c ontinuous extractor using propane as the solvent at several temperatur es and pressures. The asphaltene contents of the residual fractions in the extractor were compared to the asphaltene content of the original bitumen. Asphaltenes were defined as pentane insolubles in this study . It was found that the absolute asphaltene content of the residual fr actions exceeded the asphaltene content of the original bitumen. Even when the asphaltene content was prorated by the weight per cent of the residual material, it was found to be higher than the bitumen asphalt ene content. The data established that the types of compounds separati ng as asphaltenes changed as the nature of the mixture was altered by SFE. The data also indicated that it may be inappropriate to perform a sphaltene material balances to assess the amount of precipitate. The a sphaltene content of the residual material varied depending on the ext raction conditions, and was as much as three to five times the bitumen asphaltene content. The asphaltene content of the residual material w as the maximum at the most efficient extraction condition, which was i n the vicinity of the critical temperature of propane. The H/C atomic ratio of the residual fractions was lower compared to the original bit umen, indicating that the ratio of polar to non-polar compounds may al so be important from precipitation considerations. Saturate and aromat ic compounds were preferentially extracted and the ratio of asphaltene s to resins increased in the residual fractions relative to the origin al bitumen.