Emulsion Polymerization of Poly-(Methyl Acrylate) for Flocculation and Dewatering of Oil Sands Tailings.

• Author / Creator

  Oscar Njiru

• This work adds to the continuing research efforts in Alberta to manage the accumulation of oil sands tailings and reduce the environmental footprint of oil sands’ operations. Oil sands tailings are unwanted by-products of surface-mining bitumen extraction processes. They are usually held in engineered artificial basins called tailing ponds. Mature fine tailings (MFT) are formed after a considerable period of gravity consolidation and are constituted of solids (~30-40 wt. %), traces of residual bitumen (~1-3 wt. %), and water (~60-70 wt. %). MFT predominantly contain negatively-charged fine solids (smaller than 44 μm) that form electrostatically stable suspensions. These stable MFT suspensions are the main concern in tailings treatment: if unattended, they can remain stable for decades. Recent estimates show that more than 1.2 trillion litres of tailings cover over 220 km2 of land in Alberta. To put this into perspective the volume of oil sands tailings would be enough to fill 480,000 Olympic-sized swimming pools or, to use a Canadian perspective, fill 3 million NFL hockey rinks to 1-inch thickness. Also, remember that a significant portion of these tailings are essentially contaminated water. The main goals in oil sands tailings remediation are to recover and recycle the high amount of water trapped therein and to ultimately reclaim the land they currently occupy.
  Industrial dewatering technologies mostly use polyacrylamide (PAM) flocculants. These flocculants hold water in their flocs via hydrogen bonding, making it hard to recover the water. In my thesis, I propose the use of acrylate-based polymers to tackle the aforementioned dewatering challenges posed by PAM flocculants. The main motivation to using these alternative flocculants is their hydrophobic backbones - a property I hope to harness to expel water more effectively from the sediment flocs.
   
  In my thesis, I specifically used poly (methyl acrylate) (PMA). PMA is naturally hydrophobic. Therefore, to achieve the water-solubility required of polymeric flocculants, I hydrolyzed PMA to water-soluble HPMA (hydrolyzed-PMA) and tuned the degree of water solubility of PMA by varying the extent of hydrolysis. Also, being a homopolymer, PMA is comparatively easier and inexpensive to synthesize, especially on an industrial scale. Consequently, it is easy to scale up its production to meet the demands of the oil sands industry.
  An integral part of this work was the use of emulsion polymerization to make PMA. This is a technique that is usually preferred for its ability to combine high polymerization rates (short batch cycle time) and high average molecular weight (MW). Emulsion polymerization of methyl acrylate allowed me to obtain a stable reaction mixture, high polymer weight fractions per batch, high polymer yields, and polymers with high MW that were comparable to a reference industrial PAM flocculant.
  The experimental work was guided by a design of experiment (central composite design) and the responses were modeled using a multiple linear regression model. I used PMA properties (degree of hydrolysis (DOH) and MW) as input/predictor variables and key flocculation parameters as output/response variables. The DOH was the sole significant predictor variable for the capillary suction time (CST) model. Supernatant turbidity and the initial settling rate (ISR) models had both the DOH and MW as significant predictor variables, but the DOH still had the dominant effect. This overriding significance of the DOH is, I propose, due to its crucial role in PMA water-solubility, chain extension, and generation of flocculation binding-sites. Generally, supernatant turbidity increased with polymer dosage, which I attributed to the dispersive sodium ions from the caustic solution used for hydrolysis. Flocculation tests on undiluted MFT using a water-soluble high-MW HPMA showed very promising results that exceeded the industrial dewatering requirements for high density tailings flocculation.
  In sum, the results presented in this thesis show that the success of HPMA as a tailings flocculant was mainly dictated by its DOH. And higher MW water-soluble HPMA grades were generally better flocculants, especially when used to treat MFT samples with high solids contents.

• Subjects / Keywords

  • Emulsion Polymerization
  • Oil Sands Tailings
  • Flocculation
  • Acrylates

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-1chs-6z64

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.