Supercritical Fluid Extraction: a Technique for Recovering the Unrecoverable

Heidi Cossey, University of Alberta cossey@ualberta.ca

H. Cossey was also a 3MT participant. Watch the presentation here.

Keywords: oil sands, waste, oil recovery, carbon dioxide, residual oil

Alberta has the third largest oil reserve in the world [1]. Most of this oil is trapped within a mixture of sand and water – these mixtures are known as oil sands [2]. Oil sands deposits that are within 75 metres of the ground surface can be extracted through surface mining [1]. Surface mineable oil is an important source of energy in Alberta, however extracting it results in process waste streams. For every volume of surface mineable oil that is produced, twelve volumes of process waste are generated [3]. These process waste streams consist of water, sand, fines and residual oil. Residual oil is oil that has been left behind in these waste streams. This oil is a valuable resource, however there are currently no effective methods of recovering it. But what if we could recover the unrecoverable? What if we could find benefit in a waste stream?

 Figure 1. Sample of residual oil recovered using supercritical fluid extraction.

Figure 1. Sample of residual oil recovered using supercritical fluid extraction.

My research project involves utilizing an environmentally friendly technology to recover the oil that has been left behind in these waste streams. This technology is known as Supercritical Fluid Extraction. A supercritical fluid is a fluid that has been pressurized so that it acts like both a liquid and a gas. Like liquids, supercritical fluids are excellent at dissolving compounds and like gases, they can squeeze and spread into tight spaces. These properties are advantageous because it means that we can use a supercritical fluid to extract specific compounds from a mixture. For example, supercritical fluid extraction is commonly used to extract the caffeine out of coffee and tea [4]. The focus of my research is developing the use of supercritical fluid extraction for residual oil recovery from oil sands waste streams.

My research uses carbon dioxide (CO2) as the supercritical fluid. To begin the extraction process, the CO2 is pressurized to about 200 times normal air pressure, and is mixed with the oil sands waste stream. As they are mixed together, the residual oil dissolves into the supercritical CO2, successfully separating it from the rest of the waste stream. This new mixture of CO2 and residual oil is then depressurized causing the CO2 to return to a gaseous state. Because the CO2 is no longer supercritical, it can no longer dissolve the residual oil, and so the oil breaks away from CO2. The CO2 can then be recycled and reused in the process, preventing its contribution to the greenhouse gas effect, and the residual oil is a valuable resource that can now be utilized. Using this technology, I am able to recover a high percentage of the residual oil that is trapped within these waste streams. Figure 1 displays a vial containing a sample of the oil that I have recovered.

Residual oil is a potentially significant source of energy that currently remains unrecovered in oil sands waste streams. Supercritical fluid extraction is an innovative approach to recovering this residual oil. Using this technology, we can benefit from a waste stream by recovering a valuable resource that would have otherwise been lost.

References

[1] Oil sands: facts and stats [Internet]. Government of Alberta; c2017 [cited 2018 Mar 30]. Available from Open Alberta

 

[2] Oil production [Internet]. Government of Alberta; c2018 [cited 2018 Mar 30]. Available from Economic Dashboard Alberta

 

[3] Kasperski KL, Mikula RJ. Waste streams of mined oil sands: characteristics and remediation. Elements. 2011;7(6):387-92. DOI: 10.2113/gselements.7.6.387

 

[4] Knox, DE. Solubilities in supercritical fluids. Pure Appl Chem. 2005;77(3):513-30. DOI: 10.1351/pac200577030513