Liquid-liquid equilibrium of CO2/bitumen and CO2/bitumen/ethyl acetate systems with application to diluted bitumen transportation

Abstract

Bitumen transportation by pipelines requires dilution with solvents. These diluents are often expensive. Therefore, the utilization of liquid CO2 as a diluent to reduce or eliminate diluent consumption is of interest. However, there is limited data in the literature on the liquid-liquid equilibrium (LLE) of CO2 and bitumen. In this work, we report a new set of LLE data for MacKay River bitumen and liquid CO2 at ambient temperature. First, the LLE of bitumen/CO2 at various CO2 feed concentrations was studied. The density of light and heavy liquid phases, the viscosity of the heavy phase, and the heavy phase volume fraction were measured. It was shown that a CO2 feed concentration of 30 wt% is optimum for achieving maximum dissolution of CO2 in bitumen. Then, the effect of pressure on the LLE of bitumen/CO2 at a 30 wt% CO2 concentration was studied. The results revealed a significant reduction in bitumen viscosity from 300,000–1250 cP could be achieved at 21 °C. The results suggest that liquid CO2 can be utilized to reduce diluent consumption in pipeline transportation. The role of ethyl acetate (EA) as a co-solvent with CO2 was also examined. It was shown that the addition of EA to a mixture of bitumen/CO2 could further reduce the bitumen viscosity to satisfy the pipeline transportation criterion. The results reveal that CO2-assisted bitumen transportation in Canada can lead to the utilization of 0.16 Mt of CO2 daily, which is equivalent to a utilization potential of about 80 kg CO2/bbl of raw bitumen. The results also suggest a 73% reduction in fossil-based diluent usage, equivalent to ∼0.5 million barrels of crude oil.