Investigation of hydrocarbons in the naphthenic and paraffinic froth treatment tailings

The oil sands reserves in Northern Alberta is the primary energy source for many consumers. The production of saleable oil sands generates large amounts of tailings waters, which are stored in dykes or ponds due to the zero-discharge policy. As global demand increases, oil production increases, leading to the storage of large volumes of tailings. This results in an increase in the overall emissions and impacting a facility's environmental footprint. The surface mining production process relies on the froth treatment process, which is responsible for producing two main streams: diluted bitumen froth and the waste tailings stream, known as froth treatment tailings (FTT). The addition of a paraffinic diluent or naphthenic diluent reduces the viscosity of the crude oil, the tailings streams from these processes are known as the paraffinic froth treatment tailings (PFT) and naphthenic froth treatment tailings (NFT). Paraffinic froth treatment process uses a mixture of alkanes while naphthenic forth treatment use a mixture of aliphatic, aromatic and naphthenic compounds. The focus of this thesis was on the froth treatment tailings (FTT) as this stream is known to have higher concentrations of hydrocarbons with trace amounts of solvents, despite the froth treatment tailings comprising 2% - 4% of the total tailings discharged by volume of the overall tailings. As well, this diluent is often found in the tailings stream. While current industrial practices rely on naphthenic froth treatment tailings, individual operators are choosing to rely on the alternative, which utilizes paraffinic diluents to reduce the viscosity. Based on the previous studies performed, there was a need for characterization studies of the hydrocarbons within this stream. Specifically, an understanding that the hydrocarbons exist in both the aqueous phase and the solids phases. Both tailings samples were centrifuged for separation into the aqueous and organic phases. Therefore, the separate studies on the filtered aqueous phase and the centrifuged solids were conducted. Chloroform was used to extract the hydrocarbons from the aqueous phase. The pH (3.0, 2.0, 1.0) and temperature (20 °C, 40 °C and 60 °C) was varied for the liquid-liquid extractions. Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR) was used to identify the functional groups of the hydrocarbons extracted. An increase in temperature led to slight increases in the O—H peaks for NFT and the PFT between 20 °C to 40 °C however, at 60 °C, the increase in temperature drove evaporation rather than the transfer of the acids from one phase to another. Toluene and heptane extracted the hydrocarbons for the solids phase of the tailings. The extractions were performed at 20°C, 40°C and 60°C and for 0.5 hours, 1 hour, 2 hours, 4 hours and 6 hours. Ultraviolet-Visible Spectroscopy confirmed presence of metal porphyrins as all samples corresponding to the Soret bands and certain extraction conditions showed indications of the etioporphyrin or the octethylprophyrin groups. NMR studies showed the presence of aromatic and aliphatic groups in the extracts, as well as clusters of peaks in the aliphatic and the aromatic regimes. This analysis is better understood by obtaining NMR spectra using a high-resolution NMR. Overall, the estimates of the hydrocarbons from the centrifugation and the TGA studies for the NFT and PFT are 83.3% and 73.1%.

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