Starch-based Polymers as Flocculants of Oil Sands Mature Fine Tailings and for Extraction of Bitumen from Oil Sands
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Date
2020-09-25
Authors
Zheng, Bowei
Journal Title
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Publisher
University of Waterloo
Abstract
Mature fine tailings (MFT) generated by oil sands extraction operations in Alberta pose significant environmental challenges. Polymeric flocculants are often needed to accelerate the consolidation and dewatering of MFT. A number of starch-based flocculants were synthesized and examined as flocculants for MFT. Thermoresponsive hydroxybutyl (HB) corn starch (HB-CS) and potato starch (HB-PS) were shown to flocculate 2 and 10 wt % MFT and their thermoresponsive behavior was absolutely required for optimal performance in that they were considerably more effective, in terms of initial settling rates (ISR) and supernatant turbidity (ST), for settling tests conducted at temperatures above their lower critical solution temperatures (LCSTs) than below. Cationic corn starch (Cat-CS) and potato starch (Cat-PS) were prepared by incorporating cationic moieties, N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC), on CS or PS in basic conditions. It was shown that both Cat-CS and Cat-PS exhibited excellent performance, in terms of ISR and ST, for flocculating 2 wt % MFT. A novel starch-based dual polymer flocculation process was proposed in that the dual polymer flocculants consisting of HB-CS and Cat-CS or HB-PS and Cat-PS were used to flocculate 2 and 10 wt % MFT. The dual polymer flocculants were in all aspects superior to the single polymer flocculant. An ISR as high as 52 m/h and a ST as low as 16 nephelometric turbidity units (NTU) can be achieved with the use of a dual polymer flocculant for the settling of 10 wt % MFT.
Processing aids are generally required to improve the recovery of bitumen from poor processing oil sands ores that contain a relatively high amount of divalent cations and fine and clay solids. In this thesis, starch-based polymers were examined as processing aids in an aqueous-solvent hybrid bitumen extraction process, in which toluene was added to oil sands slurry to facilitate bitumen liberation. The highest bitumen recovery, at 86 %, was achieved using thermoresponsive starch nanoparticles (TRSNPs) with an LCST of 32 oC at 1 gram per liter of the oil sands slurry and 50 mg of toluene when the extractions were conducted at 45 oC. When the extraction was conducted under the same conditions without the TRSNP, bitumen recovery from the poor processing ores was only 31 %. Moreover, cationic hydrophobically modified SNPs were shown to be a good demulsifier, which significantly enhanced bitumen recovery during the extraction process. The use of the cationic hydrophobically modified SNPs at 1 g/L along with 50 mg of toluene also improved bitumen recovery from aged oil sands ores and a bitumen recovery as high as 81 % was obtained. Without the starch-based polymers, a poor bitumen recovery of 28 % was achieved with 50 mg of toluene for the aged ores.
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Keywords
starch, cationic starch, thermoresponsive starch, biopolymers, flocculation, oil sands tailings, oil extraction, mature fine tailings, consolidation, dewatering