Department of Chemical Engineering Graduate Theses

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    Investigation of Mass Transfer Effects on Naphtha Surrogates Partitioning from Bitumen to Aqueous Phases in Athabascan Oil Sands Tailings Ponds
    Chemical Engineering; Ramsay, Juliana; Ramsay, Bruce; Mumford, Kevin
    The Athabascan oil sands deposits are one of the largest in the world. They have been the backbone of the Albertan economy and a major source of energy and petrochemical products in North America for several decades. Approximately half of the region’s bitumen production is generated from open-pit mining and is processed with the Clark’s hot water extraction process (CHWEP). The CHWEP produces and stores significant waste in oil sands tailings ponds (OSTPs). From these OSTPs, there are significant CH4 and CO2 emissions from biogenic activity, such as the biodegradation of diluent naphtha. These greenhouse gases (GHGs) are of substantial environmental concern. A better understanding of the mechanisms affecting their emission rates could be used to mitigate these GHG emissions while balancing other environmental concerns within the OSTPs. Compositional analysis of naphtha is complex, costly and time-consuming. The use of fluorescence spectroscopy with a single wavelength steady-state excitation over a broad emission spectrum range was found to reduce the cost, speed, and complexity of analysis for laboratory experiments to study aqueous soluble naphtha surrogates for bitumen-to-aqueous phase mass transfer experiments. The bio-accessibility of naphtha to microorganisms limits GHG emission rates. The mass transfer of naphtha surrogates from bituminous to aqueous phases was experimentally found to be severely impacted by the saline concentration of the aqueous phase. A combined theoretical and empirical model indicated that experiments with agitation achieved system equilibrium. The initial concentration of naphtha solubilized within bitumen droplets had minimal impact on mass transfer rates and equilibrium concentrations achieved over sessile 2D diffusional experiments. Sessile diffusional experiments achieved lower apparent equilibria than model predictions or results obtained in agitated (forced equilibria) experiments. Aqueous phase replacement experiments resulted in lower lumped mass transfer rate coefficients and apparent equilibria. These observations indicate that limitations of naphtha transfer to an aqueous phase exist due to low diffusivity rates within the bitumen droplets, developing concentration gradients over time, and/or the formation of an interfacial film between the bituminous and aqueous phases.
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    Amphiphilic Block-Random Copolymers as Stabilizers in Emulsion Polymerization
    Sanders, Connor; Chemical Engineering; Cunningham, Michael
    The objective of this thesis is to explore block-random copolymers of styrene and acrylic acid, PS-b-(PS-r-PAA), as stabilizers in emulsion polymerization. Small molecule surfactants are typically used to stabilize emulsion polymerizations, but they are detrimental to performance properties of the final products and can leach into the environment. Various replacements have been explored, and this thesis adds to that toolbox. First, a variety of PS-b-(PS-r-PAA) are synthesized and studied both in aqueous dispersion and as stabilizers in emulsion polymerizations of styrene. This study uncovered unique properties of the block-random copolymers in dispersion and as stabilizers and prompted further investigation to the mechanisms in emulsion polymerization. Second, the nucleation mechanism in emulsion polymerizations stabilized by block-random copolymers is investigated, resulting in the description of a seeded-coagulative nucleation mechanism and model. Both a mathematical and qualitative description of the process is presented. Next, PS-b-(PS-r-PAA) are studied in aqueous environments to elucidate the behaviour of block-random copolymers in the absence of emulsion polymerization. This study showed that self assembly and surface activity can be tuned with pH and ionic strength. The nature of the aggregates is discussed in the context of emulsion polymerization, showing that the seeded-coagulative nucleation mechanism is likely a result of the unique conformations of PS-b-(PS-r-PAA) aggregates. Finally, a zwitterionic surfactant bearing polymerizable functionality is explored in emulsion polymerization as another means to replacing typical small-molecule surfactants. The surfactant covalently binds to polymer particles because of its polymerizability and provides stability in both acidic and basic conditions owing to its zwitterionic nature. In this thesis, the overarching goal of replacing small molecule surfactants in emulsion polymerizations is explored using PS-b-(PS-r-PAA) and a reactive surfactant.
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    Applications of Protein-Constrained Genome-Scale Modelling for Strain Design and Context-Specific Metabolic Prototyping in Synthetic Biology
    Yao, Herbert; Chemical Engineering; Yang, Laurence
    Genome-scale modelling (GEM) has been a research interest and a potent tool in cell-level modelling for decades. Among all studies that uses GEM, the simplest genome-scale metabolic model (M-model) is used in the vast majority of cases due to its accessibility in published models and algorithms, despite having clear limitations. Incorporating protein constraints to M-model greatly mitigates some of its limitations, yet there is little consensus regarding the formulation and algorithms for the resulting metabolic model with protein constraints (PC-model). In this thesis, we are proposing a toolbox specifically for building PC-model and tailoring algorithms for it, with an ultimate goal of building a new PC-model community that can enhance the accuracy of in-silico experiment through GEM. In Chapter 2, we introduce a new method, OVERLAY, to decipher the metabolism of the cell for a given transcriptome measurement using PC-model. This is accomplished in three main phases: first, a computational pipeline is developed to incorporate the published M-model with the enzyme information of the cell to produce a PC-model; second, the protein level is constrained by the experimental gene expression data through solving a two-step quadratic optimization, resulting in a context-specific PC-model; last, the context-specific PC-model is explored using flux variability analysis. In a case study, OVERLAY is proven proficient in decoding cellular metabolism and suggesting metabolic reprogramming strategies. In Chapter 3, we adapted several algorithms (minimal cell, PC-OptKnock, MOPA, PC-dynamicFBA) that was designed for M-model into the appropriate form for PC-model, some with boosted utilities. These algorithms are all for strain design and metabolic engineering purposes, and we believe they would synergize well with OVERLAY to exploit the potential of PC-model as a tool for simulating biochemical productions and biotechnology.
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    Physico-chemical Characteristics and Environmental Fate of a Hydrolytically Degradable Cationic Flocculant
    Russell, Derek; Chemical Engineering; Meunier, Louise; Hutchinson, Robin
    Polyacrylamide (PAM) flocculants are used frequently for wastewater treatment processes (WWTP). However, PAM is hydrophilic and generates loosely packed sediments, which makes further removal of water difficult. Therefore, a novel hydrolytically degradable flocculant, poly(lactic acid) choline iodide ester methacrylate [poly(PLA4ChMA)], was developed. This is a promising alternative because further dewatering occurs as this flocculant undergoes partial hydrolytic degradation. However, the characterization of poly(PLA4ChMA) and its environmental fate must be investigated. The objectives of this research were to characterize the degradation of poly(PLA4ChMA), and its interactions with mature fine tailings (MFT) and municipal wastewater, especially with respect to human exposure. In an initial study, the degradation products of poly(PLA4ChMA) were identified and quantified by proton nuclear magnetic resonance (1H-NMR) spectroscopy. Poly(PLA4ChMA) releases products with a molar ratio of lactyl lactate and lactic acid to choline iodide of ~2. The partially degraded water-insoluble flocculant contains on average two lactate units attached to each methacrylate unit of the backbone. Poly(PLA4ChMA) was then subjected to in-vitro gastrointestinal (GI) digestions with simulated MFT (kaolin), a model contaminant (naphthalene), and simulated municipal wastewater (SMW). Modified physiologically based extraction tests (PBETs) were developed to estimate the bioaccessibility of poly(PLA4ChMA) and naphthalene; i.e., the fraction of a contaminant solubilized in GI fluids and available for systemic absorption. Extracts were analyzed by 1H-NMR, gravimetry, and ultraviolet-visible spectrophotometry. Both poly(PLA4ChMA) and naphthalene have elevated bioaccessibility (85.8 100%) in gastric and intestinal PBET solutions in the absence of kaolin and SMW components. In the presence of kaolin, the bioaccessibility of poly(PLA4ChMA) is ~0%, which indicates that this flocculant sorbs onto kaolin throughout the PBET. Similarly, kaolin lowers the bioaccessibility of naphthalene in the gastric and intestinal phases to 78.4% and 32.7%, respectively. However, a negligible amount of poly(PLA4ChMA) sorbs onto SMW components during PBET. Thus, the poly(PLA4ChMA) exhibits nil bioaccessibility during PBET in the presence of SMW components. Conversely, the bioaccessibility of naphthalene dropped to 13.3% in the gastric solution but remained constant in the intestinal solution (~35%) after PBET. These results may be applied in appropriate wastewater treatments and to estimate potential risks associated with exposure to the flocculant.
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    Microplastics as Contaminant Vectors: Influencing the Bioaccessibility of Naphthalene from Freshwater
    Avazzadeh Samani, Farhad; Chemical Engineering; Meunier, Louise Jr
    Microplastics (MPs) are found throughout the environment and pose risks to human health as particulate pollutants. In addition, they have the potential to transfer environmental contaminants to humans and other sensitive receptors. However, there is a paucity of information on the vector effects of MPs for toxic persistent organic pollutants (POPs) in freshwater systems. The purpose of this research was to investigate the capacity of MPs to transfer naphthalene, a carcinogenic polycyclic aromatic hydrocarbon (PAHs), from freshwater systems to the human gastrointestinal tract (GIT). The focus was on characterizing the sorption mechanisms of naphthalene and its bioaccessibility (i.e., an estimate of the fraction of an ingested dose that becomes soluble in gastro-intestinal fluids). Three types of MPs, medium-density polyethylene (MDPE), polypropylene (PP), and polystyrene (PS), were selected as model compounds. The sorption behaviour of naphthalene onto these MPs was investigated through the kinetic and isotherm experiments in freshwater, and the bioaccessible fraction of naphthalene in the gastric and intestinal digestive phases was measured using a modified physiologically based extraction test (PBET). The effects of aging of MPs on the sorption of naphthalene was also investigated. The sorption kinetics of naphthalene onto MPs followed a pseudo second order model, with external mass transport as the rate-controlling step. Sorption was dominated by a hydrophobic interaction mechanism, as indicated by Langmuir and linear isotherm models. The sorption capacity of naphthalene followed the decreasing order of MDPE > PP > PS. The bioaccessibility of naphthalene was higher in the intestinal phase (28 to 60%) than in the gastric phase (24 to 40%). Artificial aging altered MP physico-chemical characteristics, with the sorption capacity of naphthalene decreasing by 25% for MDPE and increasing by 35% and 26% for PP and PS, respectively. These findings demonstrate that MPs can act as potential carriers for the transfer of POPs from freshwater environments to the human body. Consequently, MPs may provide a pathway (i.e., a vector effect) for human exposure to contaminants and pose a risk to human health. Further studies are necessary to assess the vector effect and risks of MPs for transferring other POPs in freshwater.