Petros Englezos

The hydrophilic property of cellulose substrates and their sensitivity to moisture limits their use in certain applications. The aim of this study is to enhance the barrier properties of cellulosic and lignocellulosic paper by utilizing environmentaly benign techniques. Chemical Vapor Deposition (CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), and Atomic Layer Deposition (ALD) techniques were employed to deposit Dichlorodimethylsilane (DCDMS), tetrafluoromethane (CF₄), and aluminum oxide (Al₂O₃) on cellulosic and lignocellulosic papers, respectively. A wide range of fiber sizes from unrefined, 927 µm, to highly refined, 177 µm, were employed to make handsheets and the effect of the chemicals and the deposition techniques, mentioned above, on wettability and gas permeability of the handsheets was investigated. In this regard, the contact angles on handsheets prepared with unrefined fibers are significantly higher (140°-153°) than those of the refined ones (95°-120°) due to their higher surface roughness. However, on handsheets formed with refined fibers, although the treatments resulted in a hydrophobic surface, the water droplets absorb to the handsheets over time. It is also shown that at certain fiber size (561 µm) the water vapor transmission rate (WVTR) reaches its minimum value and further decrease of the fiber size does not significantly affect the WVTR. In terms of wettability, the cellulosic and lignocellulosic substrates coated by deposition of CF₄ resulted in the highest contact angles (120°-153°). However, regarding moisture barrier properties, the Al₂O₃ deposited substrates resulted in the lowest WVTRs (2.1 g·m-²·day-¹). Moreover, the impact of fabrication method was studied and the fiber drying mechanism during sheet formation was also elucidated. It was found that casting of a Micro Fiber (MF) suspension on hydrophobic substrates results in formation of optically translucent films with mechanical and barrier properties similar to micro and nano fibrillated cellulose films. The manufacturing of the latter is energy intensive and hence the new method has potential advantage. Finally, Janus (hydrophilic-hydrophobic) fillers were fabricated and the effect of filler’s dual functionality on barrier properties of handsheets loaded with Janus fillers was investigated. Silanization of handsheets substrates in conjunction with dual functionality of fillers results in formation of a superhydrophobic handsheet.

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More than 120 depleted natural gas reservoirs in Alberta, Canada have been identified as potential sites for CO₂ storage at temperature and pressure conditions at which CO₂ may form gas hydrate. Reservoir simulations presented in the literature have demonstrated the feasibility of storing CO₂ in such reservoirs. In this thesis, the injection of CO₂ in a laboratory size reservoir (packed bed of silica particles) serving as a physical model for a depleted reservoir was studied. The hypothesis was that injecting CO₂ into the reservoir at gas hydrate formation conditions will be beneficial in terms of increased CO₂ storage density. It is noted that CO₂ is stored not only as hydrate but also some is dissolved in the residual pore water (not converted to hydrate) and some as a gas in the remaining pore space. The results indicate that hydrate formation enhances the CO₂ storage density. The work also demonstrated that substances like tapioca starch added to the water in small quantities (1 wt %) delayed the onset of hydrate nucleation in the earlier stage but subsequently more CO₂ was stored as hydrate compared to the tapioca starch-free systems. The delay in nucleation decreases the risk to form a hydrate plug in the injection system. The injection of the CO₂-rich mixture (90 mol % CO₂/10 mol % N₂), which is a typical composition of a flue gas after CO₂ capture process, into a reservoir with CH4 (simulating residual natural gas) was also studied in the laboratory reservoir. It was found that the total CO₂ storage density (in hydrate, gaseous and dissolved state) decreased from 143 kg/m³ (the CO₂ injection into a CH₄ free reservoir) to 119 kg/m³. Finally, relevant phase equilibrium data were obtained in a constant volume high pressure vessel and by calorimetry. The results were found to be in good agreement with thermodynamic model calculated values within ± 40 kPa and ± 0.2 K, respectively.

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For practical purposes, kinetic hydrate inhibitors must perform in a predictable manner in the field. However, the complexity of the petroleum fluid composition, the presence of dissolved electrolytes, and high driving force (overpressure or sub-cooling), make it difficult to impossible task to achieve. In this thesis, the performance of two chemical kinetic inhibitors, polyvinylcaprolactam (PVCap) and polyvinylpyrrolidone (PVP), and two biological ones, type I and III antifreeze proteins (AFP I and III) were evaluated under conditions mimicking oil and gas filed ones. The evaluation was done by using a double high pressure stirred vessel (crystallizer), a high-pressure cell in conjunction with a rotational rheometer and a high pressure micro differential scanning calorimeter. Although the above noted inhibitors were found to prolong the hydrate induction time and reduce the initial hydrate growth in saline solutions, the rate was found to increase when hydrate crystals started to form in the gas phase of the crystallizer. Circular dichroism experiments suggested that the saline solution does not perturb the structure of AFP I and III. However, in the presence of NaCl, the inhibitory activity of AFP I to prolong induction time decreased while AFP III was more active. Here, increase in induction time was ordered: no inhibitor
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Gas hydrates are crystalline compounds with cage-like structures formed by hydrogen-bonded water molecules hosting guest molecules such as light hydrocarbons and CO₂. They are known to:• represent a potential reserve of natural gas embedded in seabed and permafrost sediments• pose a flow assurance challenge to the oil and gas industryMolecular dynamics simulations are employed to study the processes of gas hydrate decomposition and inhibition.To mimic the porous environment of the real gas hydrate reservoirs, hydroxylated silica surfaces are included in the simulations and placed in contact with hydrate and water. Water molecules wet the silica surfaces and form a meniscus, confirming the hydrophilic properties of the hydroxylated silica surface. It is found that the silica surface alters the characteristics of the confined water up to ~6 Å away from the surface.The decomposition of methane hydrate in the presence of silica surfaces, 34 to 40 Å apart, follows a concerted behavior where layers of hydrate cages at the curved dissociation front collapse almost simultaneously. The rate of hydrate dissociation in contact with a silica surface is faster compared to that of a hydrate phase just in contact with bulk water. Additionally, the decomposition leads to the formation of methane-rich regions (nano-bubbles) in the liquid water phase.In more realistic simulations, gas reservoirs are added to the simulations to determine whether the formation of nano-bubbles is a general feature of the hydrate decomposition process. It is found that the nano-bubbles can form under simulation conditions where the dissociation rate is faster than the diffusion rate, thus generating dissolved methane mole fractions of greater than 0.044 that would lead to bubble nucleation.Finally, the binding mechanism of the alpha-helical 37 amino acid residue winter flounder antifreeze protein, which is a candidate as a kinetic hydrate inhibitor to methane hydrate, is determined to be the result of cooperative anchoring of the pendant methyl groups of the threonine and two alanine residues, four and seven places further down in the protein sequence, to the empty half cages at the hydrate surface.

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This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence, scanning speed and scanning overlap) on the wettability of the resulted micro/nano-patterned morphologies on stainless steel. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nanostructures. All of the produced structures were classified according to a newly defined parameter, the Laser Intensity Factor (LIF) that is a function of scanning speed and fluence of laser. By increasing LIF, the ablation rate and the periodicity of the asperities increase. In order to decrease the surface energy, all of the surfaces were coated with a fluorinated alkylsilane agent. Analysis of the wettability in terms of contact angle (CA) and contact angle hysteresis (CAH) revealed enhanced superhydrophobicity for most of these structures, particularly that possessing triple roughness pattern. This also exhibited a low CAH. The high permanent superhydrophobicity of this pattern is due to the special micro-nano structure of the surface that facilitates the Cassie-Baxter state. A new two-dimensional (2D) thermodynamic model is developed to predict the contact angle (CA) and contact angle hysteresis (CAH) of all types of surface geometries, particularly those with asperities having non-flattened tops. The model is evaluated by micro/nano sinusoidal and parabolic patterns fabricated by laser ablation. These microstructures are analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium CA and CAH. The effects of the geometrical details on maximizing the superhydrophobicity of the nano-patterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters, which may lead to lotus effect (high CA>150° and low CAH150° and high CAH>>10°).

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Increasing loading level of precipitated calcium carbonate (PCC) in high value added communication-grade papers from bleached thermo-mechanical pulp (TMP) beyond the current level not only further reduces the production cost but also mitigates the shortage of good quality wood fibres. This thesis explores the possibility to retain increased amounts of PCC by taking advantage of the most recent developments in starch and nanoparticle technologies. Response surface methodology was used to optimize the addition strategy of chemicals and evaluate their effects in laboratory trials using mill samples. Empirical process models were also constructed to predict the retention and drainage results. It was found that linear high charge cationic starch S880 always resulted in highest retention for PCC preflocculation strategy and best drainage performance regardless of conventional chemical addition sequence or PCC preflocculation strategy. PCC preflocculation by starch resulted in higher breaking length and burst indices compared to the conventional chemical addition sequence.The relationship among starch properties, process conditions, and floc properties was established through the investigation of PCC aggregation kinetic and floc structure evolution to allow the judicious selection of starch for PCC preflocculation. The population balance modelling approach was adopted to describe PCC flocculation. It was found that the linear high charge cationic starch S880 is associated with lower collision efficiency; lower restructure rate and higher energy dissipation rate to break up the flocs compared to the low charge cationic starch S858. The presence of NaCl was found to affect the high charge cationic starch S880 but had no influence on the low charge cationic starch S858. The collision efficiency decreases with the increase of the shear rate for both starches. The knowledge of the floc aggregation, breakage and restructure under various process conditions is expected to enable the manipulation of the floc with specified size, strength, and structure for better retention and drainage.

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The purpose of this dissertation is to contribute to the development of the predictive theory-based equation of state. The specific objectives are threefold: first, to improve the predictive capability of theory-based EOS in studying multiphase equilibrium in water-alcohol-hydrocarbon mixtures by taking into account long-ranged electrostatic interactions. The second objective is to develop a general treatment of polar-polarizable mixtures for any theory-based equation of state; and the third is to develop robust and reliable computational methods that conduct and simplify multiphase and stability calculations for theory-based equations of state. The long-ranged electrostatic interactions considered in this thesis are dipole-dipole, quadrupole-quadrupole and polarization. The electrostatic interactions are incorporated into the statistical association fluid theory (SAFT) using different polar approaches. The polar SAFT is utilized to predict multiphase equilibrium of water-alcohol-hydrocarbon mixtures. The results are compared to experimental data. Excellent prediction of multiphase equilibrium is obtained without adjusting experimental data including difficult mixtures such as water-hydrocarbons. This dissertation also presents a general treatment of polar-polarizable systems for theory-based equation of state for non-spherical molecules by the use of the self-consistent mean field theory proposed originally by Carnie and Patey (1982). The treatment is applicable for any kind of polarization arising from polar molecules including ions induced interactions. The theory is tested against simulation data and is applied to the statistical association fluid theory. The general theory is compared to simulation data and is shown to give excellent agreement. The developments in this dissertation also contribute to the subject of theory-based equations of state by developing a reliable and robust multiphase and stability testing method. The developed algorithm computes multiphase and stability simultaneously. The new algorithm is tested extensively on complex mixtures including water-hydrocarbon mixtures. Furthermore, the calculations of phase equilibrium from theory-based equations of state are significantly simplified by the use of the complex-step derivative approximation which computes derivatives numerically.

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The presence of inhibitors delayed hydrate nucleation and decreased the overall formation of methane/ethane/propane hydrate compared to pure water system. However, the two classes of inhibitors: chemical (Polyvinylpyrrolidone (PVP) and industrial inhibitor: H1W85281) and a biological (Type I and III antifreeze protein (AFP)) were distinguished by the formation of hydrates with different stabilities. A single hydrate-melting peak was seen with the AFP-III and this was consistent after re-crystallization. In contrast, multiple hydrate melting events were observed in the presence of the chemical inhibitors. In stirred reactor, onset of hydrate decomposition occurred earlier in the presence of the inhibitors compared to water controls. However, depending on the type of inhibitor present during crystallization, hydrate decomposition profiles were distinct, with a longer, two-stage decomposition profile in the presence of the chemical inhibitors. The fastest, single-stage decompositions were characteristic of hydrates in experiments with either of the AFPs. Powder X-ray diffraction and nuclear magnetic resonance spectroscopy showed that structure II hydrates dominated, as expected, but in the presence of the chemical inhibitors structure I was also present. Raman spectroscopy confirmed the complexity and the heterogeneity of the guest composition within these hydrates. However, in the presence of AFP-III, hydrates appeared to be relatively homogeneous structure II hydrates, with weaker evidence of structure I. When individual gas cage occupancies were calculated, in contrast to the near full occupancy of large cages with these inhibitors, almost 10% of the large cages were not filled when hydrates were formed in the presence of AFP-III, likely contributing to the easy decomposition of such hydrates seen in DSC and stirred reactor experiments.These results argue that thought must be given to inhibitor-mediated decomposition kinetics when designing and screening of new kinetic inhibitors. This is a necessary practical consideration for industry in cases when due to long shut in periods; hydrate formation may be unavoidable even when inhibitors are utilized. This heterogeneity suggests that using these chemical inhibitors (PVP and H1W85281) may present a special challenge to operators depending upon the gas mixture and environmental conditions, and that AFPs may offer a more predictable, efficacious solution in these cases.

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This thesis examines the prospect of employing hydrate crystallization in a gas/liquid stirred vessel for separation of carbon dioxide (CO₂) from a flue gas mixture. A treated flue gas mixture contains CO₂, O₂ and N₂. Because O₂ and N₂ form hydrate at approximately same pressure-temperature conditions a model gas mixture to work with consists of 17 mol % CO₂ and 83 mol % N₂. Gas hydrates were formed in a 323 cm³ vessel at 273.7 K and constant pressures. The data enabled us to propose a process based on three hydrate stages coupled with a membrane separation stage. Two metrics, CO₂ recovery and separation factor were introduced to evaluate the efficiency of the process. The operating pressures were found to be 10, 5 and 2.5 MPa for the three stages. The high operating pressure required for the first stage necessitated the use of an additive to lower the pressure. Tetrahydrofuran (THF) was chosen and relevant thermodynamic and kinetic data were obtained and reported. The efficiency of the separation was also determined. It was concluded that a stream containing 96% CO₂ can be obtained from of a medium-pressure process consisting of three hydrate stages. The three stages operate at 2.5 MPa and 273.75 K without compromising the separation efficiency obtained without the addition of THF.A new apparatus was designed and built to demonstrate the hydrate process at a larger scale. The results showed an improvement in the kinetics and the separation efficiency. Finally, the kinetics of the hydrate crystallization were also studied using a fixed bed of silica sand particles and the results were compared with those obtained in the gas/liquid systems. The gas uptake was found to be significantly higher for the systems involving water dispersed in silica sand.

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Conventional coal-fired power plants that rely on the combustion of the coal are the largest anthropogenic point sources of atmospheric carbon dioxide (CO₂). An alternative approach of producing electricity with CO₂ capture is pre-combustion decarbonisation whereby the coal is used to produce an intermediate hydrogen-rich gas (CO₂/H₂ mixture). This route is known as integrated gasification combined cycle (IGCC). The CO₂/H₂ mixture is called fuel gas and is separated into a CO₂-rich and a H₂-rich stream. The H₂ may be burnt to produce electricity or used in fuel cells. The assumption is that the CO₂ can possibly be stored safely in a suitable geological formation. It is noted that other fossil fuels may be used in a similar manner as coal. This thesis examines the prospect of employing a novel method for the separation of carbon dioxide (CO₂) from CO₂/H₂ mixture (fuel gas mixture) via clathrate hydrate crystal formation. Experiments and theory are employed at the engineering (macroscopic) and molecular level to achieve the objectives. The focus is on the study of the thermodynamic and kinetic properties of CO₂/H₂ and CO₂/H₂/C₃H₈ hydrates. The basis for separation of the CO₂ is the fact that when a CO₂/H₂ or CO₂/H₂/C₃H₈ mixture is allowed to form hydrate, CO₂ preferentially gets incorporated into the hydrate phase. The addition of 2.5 mol % C₃H₈ in the fuel gas mixture was found to reduce the hydrate formation pressure and thus improve the process economics. Based on the data obtained a conceptual separation process was developed. It involves two hydrate stages coupled with a membrane-based gas separation stage. The two hydrate stages operate at ~3.5 MPa and 273.7 K. The power penalty for a 500 MW power plant is estimated to be about 2.5% of the power output. Crystal structures and cage occupancies for the CO₂/H₂ and the CO₂/H₂/C₃H₈ hydrate were determined using several spectroscopic techniques. This enabled an understanding of the separation efficiency values obtained for the process.

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