Petros Englezos


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Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Surface engineering of wood fiber/filler networks (2019)

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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Storage of carbon dioxide in depleted natural gas reservoirs as gas hydrate (2016)

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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Laboratory evaluation of chemical and biological kinetic gas hydrate inhibitors (2015)

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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Molecular Mechanisms of Methane Hydrate Dissociation and Inhibition (2015)

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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Superhydrophobic Nanopatterned Interfaces: Optimization and Manufacturing (2014)

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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Application of nano-structured silica technology and modified starch biopolymers into highly precipitated calcium carbonate filled mechanical grade paper (2012)

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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Prediction and computation of phase equilibria in polar and polarizable mixtures using theory-based equation of state (2012)

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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Understanding the action of gas hydrate kinetic inhibitors (2012)

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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Separation of carbon dioxide from flue gas (post-combustion capture) via gas hydrate crystallization (2009)

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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Separation of carbon dioxide from fuel gas ("pre-combustion capture") via hydrate crystallization (2009)

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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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Thermodynamics and kinetics of CO2 hydrate formation in the presence of cellulose nanocrystals (2021)

The kinetics of gas hydrate formation are of interest in various energy and environmental applications of gas hydrates. One such example is the hydrate based gas separation (HBGS) as a possible method to capture CO₂ from either pre-combustion or post-combustion gas mixtures present in integrated gasification combined cycle (IGCC) and conventional power plants respectively. In such applications additives are included to improve the kinetics of gas hydrates. In this work, carbon dioxide hydrate was formed in aqueous suspensions of cellulose nanocrystals (CNC) and the induction time and rate of hydrate crystal growth was compared to data obtained with hydrates formed in pure water (blank). 24 runs were made for each group (blanks and CNCs). A suspension with a CNC concentration 0.75 wt% was employed to determine whether CNC could reduce the induction time and enhance hydrate growth rate as it has been reported for carbon nanotubes and other nanoparticle suspensions. Hydrate formation experiments were carried out in semi-batch mode setup in a high pressure crystallizer with overhead stirring. The temperature and the pressure were 274.15K and 2370 kPa respectively, this pressure is 1000 kPa above the equilibrium pressure of CO₂ hydrates at the mentioned temperature. Statistical analysis was performed with the data gathered to establish whether there is an effect of CNC nanoparticles in hydrate kinetics. The results show that the CNC did not have a statistically significant impact on CO₂ hydrate formation. This study also compared the results with data from the literature about the effect of other nanoparticles on gas hydrate formation.

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Enhanced Barrier Performance of Cellulosic Wood Fiber/Filler Network (2016)

Cellulose is an abundant material, which is widely used in papermaking. It is both a biodegradable and sustainable material. However, its hydrophilic nature may limit its applications in specific and novel areas such as waterproof packaging and paper based microfluidics. In this thesis, three different routes are followed to render the surface of the paper superhydrophobic. First, chemical vapor-phase silanization is done on handsheets made from wood pulp with untreated kaolin clay and precipitated calcium carbonate (PCC) as fillers. The effect of fiber length, filler’s type, size, and concentration on the barrier performance of handsheets is shown. Secondly, mircofibrillated cellulose (MFC), which serves as reinforcement agent in paper, is employed as an additive to change the hydrophilic property of paper. MFC is silanized to obtain hydrophobicity before being dispersed into the pulp suspension. Then the resulting paper undergoes an additional silanization (post-treatment). The third approach involves depositing Janus clay particles on untreated paper. A Janus particle has a hydrophobic and a hydrophilic surface. Because clay particles are hydrophilic, they are treated to obtain hydrophobicity on one side, while the other side remains hydrophilic. An efficient method to obtain these types of particles is the formation of a Pickering emulsion. The study here, focuses on the determining the barrier properties of the prepared superhydrophobic or hydrophobic papers: wettability, water vapor transmission rate (WVTR), and air permeability. The handsheets with shorter fiber length, precipitated calcium carbonate, smaller filler size and lower filler content, were found to exhibit lower WVTR values. The water contact angle of handsheets loaded with fillers, Janus clay particles and hydrophobic MFC, was found to be 120~130°, 141° and 134~144° respectively.

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Effect of chemical additives on z-direction filler distribution in paper (2013)

It is well known that paper properties such as opacity, printing quality, brightness, and roughness are affected by the z-direction mineral filler distribution. In this study, the effect of four different parameters (filler, starch, chemical retention aids and the machine parameter (vacuum)), on the z-direction filler distribution in paper samples was investigated.Paper samples were made using an apparatus that simulates a suction box. Different levels of filler (PCC), chemical additives and vacuum were chosen based on a central composite design. The effect of these parameters on filler distribution in cross-section of paper samples was investigated by using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX) which is a non-destructive technique. The area covering the thickness of the paper was divided into five layers and each layer was subjected to EDX analysis to obtain the calcium content through the paper thickness.The results indicated that the filler distribution in the z-direction of paper samples increased from the top side to the wire side. The calcium content in the layer near the wire side was significantly higher than in the other layers. The other layers had similar calcium content. The chemical additives as well as vacuum in suction box had a significant effect on the filler distribution. Increasing the filler and starch led to higher level of filler content in all layers through the sheet thickness. Increasing the vacuum and retention aids led to higher level of filler content in layers near the wire side. The effect of high charge density starch used in our study was significantly higher than the effect of retention aids in retaining the filler through the thickness of the paper. Based on the obtained data, a set of empirical models were constructed that can predict the filler distribution through the thickness of the paper.We validated our results by measuring the calcium content through applying image processing technique on the SEM cross-section images and measuring the ash content of paper samples. The results of both of these approaches confirmed the EDX measurements.

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Superhydrophobic fibre networks loaded with functionalized fillers (2013)

In this thesis a series of fluorocarbon plasma treatment experiments (Plasma enhanced chemical deposition (PECVD)) were performed to study the effect of filler type and concentration on the wetting behavior of handsheets which are made from pulp using precipitated calcium carbonate (PCC), kaolin clay, and talc as a filler. The plasma treatment was performed in two steps; first using oxygen plasma in order to create nanoscale roughness on the surface of the handsheet; and second fluorocarbon deposition plasma in order to add a layer of low surface energy material. The contact angle of droplets of deionized water on all of the handsheets increased after plasma treatment. However, although some of the handsheets have low concentrations of filler, and therefore the fibre effect should be dominant after the treatment, it was found that the type of filler has a significant effect. It was also observed that roughness of the surface plays a key role in the wettability of handsheets and increased the hydrophobicity. The water vapor transmission rate values show that plasma hydrophobization does not prevent vapor uptake into the paper, although it is good barrier to water. The same plasma treatment was performed on the surface of PCC and kaolin clay fillers in order to fabricate partial hydrophobic fillers. The goal was to use these treated fillers in handsheets and study their wetting behavior. The plasma treatment on the surface of kaolin clay increased its contact angle, however no effect on PCC fillers was observed immediately after the treatment.

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Microbial Inhibition of Methane Clathrate Hydrates (2012)

Two microbial species were tested for inhibition of methane hydrates in a stirred crystallizer (subcooling of 2.34 K). The ice associating Chryseobacterium sp. Strain C14, grown in 0.5 wt% Tryptic Soy Broth (TSB) delayed hydrate nucleation, on average, by 30.3 hours compared to 37.9 hours for the PVP solutions. Escherichia coli TG2 in 0.5 wt% TSB was used as a non ice associating bacteria control and surprisingly had the longest induction period of 118.1 hours, suggesting that it was 3 times more effective as a hydrate inhibitor than PVP. The 0.5 wt% aq. TSB solution without bacteria delayed hydrate nucleation an average of 6.7 hours, whilst bacteria without TSB also showed significant inhibition. However, for the bacteria and bacteria + TSB systems, nucleation times were far more sporadic and time dependant than the simple systems of pure water and PVP. PVP decreased hydrate growth rate but increased gas consumption by nearly 4 fold. TSB without bacteria promoted gas consumption by over 2 fold but exhibited a slightly higher growth rate than the pure water solution. Reasons for the differences in growth profiles may be a result of the observed morphological differences in the hydrate phase. Chryseobacterium in 0.5 wt% aq. TSB had a distinct time dependency in growth characteristics and promoted growth rate almost 3 fold. E. coli in 0.5 wt% TSB showed a unique S-curve growth profile where the initial growth rate was very low. The differences in growth profiles of the two bacteria suggest different inhibition mechanisms. Ice-associating proteins likely play a significant role in hydrate formation, especially for Chryseobacterium which has shown inhibition of ice recrystallization. However, the interaction of other non-ice associating macromolecules may play a primary role in the observed inhibition and that biofilm formation may act as a barrier between the gas-liquid and/or heterogeneous nucleating solid-liquid interfaces which may help explain the significant inhibition observed by E. coli. Considering that both species of bacteria yielded significant hydrate inhibition, albeit somewhat unpredictable, but since the procedure is simple, the potential of employing bacteria as ‘Microbial Hydrate Inhibitors’ looks promising. However, consistent inhibitionwill be a challenge to overcome so that these organisms could be used as other KHI solutions.

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Prediction of Gas Hydrate Equilibrium (2012)

This thesis studies the application of Statistical Association Fluid Theory (SAFT) in the prediction of hydrate formation conditions. The main objective is to develop a robust, reliable and purely predictive model for calculating the formation of single hydrates former gases. The current study is based on the use of the algorithm proposed by Englezos et al. (1991). Simplified SAFT (Fu & Sandler 1995) was employed to model the vapor and liquid phases as well as the van der Waals-Platteew model to represent the hydrate phase.The predictive ability of the model was investigated on single hydrate formers in the presence of inhibitors. With this end in mind, the inhibiting effects of methanol and ethylene glycol on methane, ethane, propane and carbon dioxide incipient hydrate forming were studied. The calculated results were compared to the experimental data obtained from the literature. A deviation of less than 10% in pressure or 1℃ in temperature was desired. Additionally, the phase equilibria of water-methanol, methanol-methaen, methanol-ethane and methanol-propane were also studied.Excellent results were obtained from incipient hydrate calculations and the SAFT equation of state was found to be highly capable of tackling non-ideal mixtures such as water-alcohol and water-alcohol-hydrocarbon systems. Estimation of the SAFT pure component parameters and the temperature range over which the SAFT parameters are estimated was found to be crucial. To overcome this issue, several parameters were estimated over various different temperature ranges, and the one which provided the smallest average absolute deviation was selected.

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Kinetic study of methane hydrate formation in a bed of silica sand particles using magnetic resonance imaging (2010)

This thesis studies the formation and decomposition of methane hydrate crystal in an unconsolidated bed of silica sand particles. Hydrate processes were visualized by taking advantage of the ¹H magnetic resonance imaging technique, and the integrated intensity of magnetic resonance images was used to quantify the rate and kinetics.For all of the experiments, the initial pressure was 8 MPa and the temperature was kept constant at 1℃. Beds composed of 2 grams of sand were saturated with different amounts of water (0.44, 0.33, 0.22 and 0.11 mL) in order to examine the effect of water content of the bed on the kinetics of hydrate formation in porous media. Also, the effect of particle size was investigated by forming hydrate in beds with different particle size ranges (210-297, 125-210, 88-177 and
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