Effect of carbon dioxide on paraffinic bitumen froth treatment: Asphaltene precipitation from a commercial bitumen froth sample

Abstract

In this study, the effect of carbon dioxide in assisting paraffinic bitumen froth treatment was investigated. The work was divided into two parts, the effect of water addition on CO2-assisted asphaltene precipitation from a dry and clean bitumen sample by n-heptane and the effect of CO2 injection to a mixture of n-heptane and a commercial bitumen froth sample. It was found that water addition to the dry and clean bitumen improved the beneficial effect of CO2 on promoting asphaltene precipitation by nheptane, where asphaltene precipitation increased by 2.5 percentage points (or 19%) with the presence of water and CO2. The asphaltene precipitation enhancement may be due to chemical reactions between injected CO2 and water in the formation of carbonic acid in the aqueous phase, which destabilized asphaltene. On the other hand, no improvement was detected under the control tests (N2). Similar results were observed in the case of CO2 injection to paraffinic solvent (n-heptane) treatment of the commercial bitumen froth sample. The results indicated that when the commercial bitumen froth sample was mixed with n-heptane at a solvent/bitumen ratio of 1.08, the injection of 1.7 MPa CO2 increased the amount of precipitated asphaltene from 10.0 ± 0.1% (without CO2) to 15.2 ± 0.2% (with 1.7 MPa CO2) at 90 °C, indicating a potential reduction of solvent usage by about 66%.