Effect of simulated flue gas on pentane-induced asphaltene precipitation in bitumen froth

In paraffinic bitumen froth treatment, a paraffinic solvent such as n-pentane is mixed with bitumen froth at a high solvent/bitumen ratio of 1.5 to 2.0. The purpose of the high solvent/bitumen ratio is to induce asphaltene precipitation which helps clean the bitumen so that it can be processed directly by a high-conversion refinery without the need of an upgrader. However, the high solvent/bitumen ratio inevitably increases the complexity and costs of the paraffinic froth treatment process. In this study, we have attempted to reduce the solvent/ bitumen ratio without affecting asphaltene precipitation by replacing part of the solvent with simulated flue gas (CO2/N2 mixture at 200 degrees C). The n-pentane/bitumen ratio was varied from 0.8 to 2.2, CO2 concentration in the gas mixtures from 0 to 100 vol%, gas pressure from 0.1 to 1.7 MPa, and temperature at 21 degrees C and 90celcius. Asphaltene contents in the bitumen products were measured following ASTM D4055, and the contents of water, solids, C, H, N, S in the products were measured by Karl Fischer titration, ashing and hot filtration, and CHNS elemental analysis. It was found that at the asphaltene precipitation onset n-pentane/bitumen ratio of 1.4 at 90 degrees C, the amount of precipitated asphaltenes was linearly correlated to the partial pressure of CO2; at the CO2 pressure of 1.7 MPa, about 50 % of the asphaltenes were precipitated, corresponding to an n-pentane/bitumen ratio of 2.2 when no CO2 was used. A solvent saving of about 36 % could therefore be achieved under these conditions without changing the quantity of asphaltene precipitation. The bitumen product quality was not affected when CO2 was used. This work provided useful information on the function of CO2 gas in assisting asphaltene precipitation, so that a lower n-pentane/bitumen ratio could be used, reducing process complexity and cost without affecting performance.