Bitumen may be separated from oil sand in surface mining operations by using an anhydrous process in which oil sand is mixed with a low boiling solvent such as naphtha. While the majority of bitumen is removed from the sand there is a residual amount of bitumen that remains on the sand and this residue also contains some of the solvent used in the process. It is important to effectively recover as much of the solvent trapped in the spent solids as possible. After most of the bitumen-solvent mixture has been removed from the sand, pressurized CO2 can be used as an anti-solvent to displace residual solvent in the spent sand bed.
In this study, an experimental investigation is made of the effect of capillary force to enhance solvent recovery by mechanical separation, before proceeding to CO2 extraction. Using a thin, semi-permeable layer can facilitate drainage of the solvent from coated sand by capillary force. The results indicate that by using a micro filter the solvent saturation in the sand can be decreased to about half of solvent saturation achievable without using a membrane. It is also possible to further decrease the solvent saturation in sand by pressurizing the air above the sand bed, but it is a slow process.
This experimental study suggests that higher efficiency can be obtained by this simple method and that it has potential to reduce the amount of CO2 required for the next step of solvent recovery by gas extraction.