Browsing by Author "Economou, Ioannis G"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item CO2 Selective Metal Organic Framework ZIF-8 Modified Through IL Encapsulation: A Computational Study(2018-04-27) Mohamed, Amro Mamoon Osman; Economou, Ioannis G; Castier, Marcelo; Bouhali, OthomaneNano-scale porous solids are alternate candidates for COv2 handling towards the development of materials for post-combustion COv2 capture with low energy demands and milder operating conditions. Zeolitic imidazolate framework-8 (ZIF-8) is one of the most investigated Metal Organic Frameworks (MOFs) for separation of gas mixtures. In this work, we investigate a new approach of tailoring MOF separation efficiency, by confining pairs of three different ionic liquids (ILs) in the cages of ZIF-8 (IL@ZIF-8). ILs comprising 1-butyl-3-methylimidazolium cation [bmim+] and three distinct anions, bis(trifluoromethylsulfonyl)imide [Tfv2N-], tricyanomethanide [TCM-], and tertracyanoborate [B(CN)v4-], were used in this study. Molecular force fields, previously developed by Economou and co-workers for both the ZIF-8 framework and the ILs, are used in the molecular simulations of these systems. Monte Carlo simulations, employing an appropriate set of constraints, are utilized for the calculation of sorption of COv2/CHv4 and COv2/Nv2 mixtures. The results show an increase of the COv2 sorption compared to pristine ZIF-8 due to the presence of the IL, which increases the COv2 selectivity and capacity dramatically. Recently reported experiments agree with our findings. Moreover, we explore how COv2 selectivity and capacity vary with IL composition in the IL@ZIF-8 complex, as a mean to define an optimum IL composition in terms of the separation efficiency. As a result of the pore volume reduction in the structure, a tradeoff between capacity and selectivity is present. Therefore, a sorbent selection parameter that combines working capacity and equilibrium selectivity proposed by Range and Yang, alongside a regenerability factor, are used to further determine the best sorbent among other known materials. The regenerability factor is adopted to reflect the fractional percentage of adsorption sites that are available for regenerationItem Faculty Gathering & Lunch(2020-04-02) Economou, Ioannis GItem Microstructure and Performance Analysis of Polyethylene-Modified Asphalt(2020-07-22) Rehman, Amara; Abdala, Ahmed; Masad, Eyad A; Economou, Ioannis GAsphalt is one of the most commonly used materials in the road construction industry. Asphalt binder is used to bind aggregate particles to form the asphalt mixture, which is the material used for the construction of pavement layers. The properties of asphalt binder influence the durability and strength of the mixture. Virgin asphalt does not have the properties to withstand the severe service conditions as it is prone to resistance distresses such as rutting and cracking. Rutting is a result of plastic deformation due to application of heavy loads at elevated temperatures. Low temperatures cause thermal cracking while repetitive loading causes fatigue cracking. All these factors contribute to adverse effects on pavement performance and road safety leading to premature failures and extensive maintenance. The addition of modifiers to asphalt is a common technique to enhance the mechanical properties of virgin asphalt and reduce maintenance cost. These modifiers aim to increase asphalt resistance to permanent deformation at high temperatures and/or increase its resistance to cracking at low and intermediate temperatures. This study analyzed the effect of adding two different grades of low-density polyethylene (LDPE) (LDPE4 and LDEP70) and polyethylene wax to asphalt binder as modifiers to enhance performance. LDPE 70 had a much higher melt flow index and lower molecular weight than LDPE4. The analysis focused on the microstructure and rheological properties. Various tests including optical imaging, dynamic and steady shear rheological measurements, thermogravimetric analysis, and differential scanning calorimetry were conducted. The results indicate that LDPE 70 showed lower crystallinity than LDPE4 and performed better in terms of dispersion and uniform particle size distribution along with better performance grade of the binders. On the other hand, although, PE wax reduced the phase separation in LDPE4 blends, it caused agglomeration in LDPE70 blends. It is suggested that further research be done going forth with LDPE70 and other compatibilizers such as to reduce phase separation as PE wax is not a suitable one.Item Modeling Confined Fluids with the Multicomponent Potential Theory of Adsorption and the SAFT-VR Mie Equation of State(2020-07-07) Al Yazidi, Ahmed; Economou, Ioannis G; Castier, Marcelo; Seers, ThomasIn this work, the SAFT-VR Mie equation of state is combined with the Multicomponent Potential Theory of Adsorption (MPTA) in order to describe the phase equilibrium behavior of confined fluids due to their presence in an external field, namely a solid-fluid potential field. This is important for the understanding, modeling and design of fluids confined in micro- and meso-pores pertinent to applications in hydrocarbon reservoirs, membrane-based separations and heterogeneous catalytic systems, to name but a few. The problem specifications are the temperature of the system, volume of the pores, and the number of moles of each component in the system. The formulation results in the minimization of the Helmholtz energy of the system subject to mass and pore-volume conservation constraints. This formulation, in addition to treating supercritical fluids, tackles the problem of pore-condensation of subcritical systems by employing a Helmholtz-based global phase stability analysis which allows us to detect the presence of phase instability inside the pores as well as locate the spatial location at which it takes place.Item Modeling of Thermodynamic Properties and Phase Equilibria of Multicomponent Systems Related to the Oil and Gas Industry using the PC-SAFT Equation of State(2015-06-22) El Meragawi, Sally; Economou, Ioannis G; Hall, Kenneth; Kelessidis, VassiliosEquations of state (EoS) have proved to be a reliable tool in chemical engineering thermodynamics for modeling the physical properties of complex systems. Various types of EoS have been developed based on different theories. For various reasons, some have become more popular for use in industry and academia. Of the popular EoS, two were chosen for investigation in this thesis. The first one was the Perturbed Chain- Statistical Associating Fluid Theory (PC-SAFT), an equation derived based on statistical mechanics and the second was the Peng-Robinson (PR) EoS, a cubic EoS commonly used in industry. In this work, the prediction capabilities of these two EoS were compared for several properties. The analysis began with an evaluation of their use in the prediction of the saturation properties of pure components and derivative properties from ambient conditions to the supercritical range. The particular derivative properties studied include the isochoric and isobaric heat capacities, the speed of sound, and the isothermal compressibility. In general, it was concluded that PC-SAFT outperforms PR in all cases. Next, the same primary and derivative properties of several binary and a select ternary mixture were studied. To improve agreement with experimental data, a binary interaction parameter was introduced and fitted to binary mixture vapor – liquid equilibria (VLE) data. This procedure drastically improved the accuracy of the models compared to the case where no binary interaction parameter used for the case of VLE predictions. However, for the case of the derivative properties, the use of the binary interaction parameter to ensure a more accurate representation of the interactions between molecules had only a marginal effect on the prediction of these properties. Finally, phase equilibria of hydrates were studied. As EoS for fluids are not designed to predict the properties of solid phases, the van der Waals-Platteeuw model was incorporated to allow for the prediction of three-phase equilibrium conditions of various hydrate formers. Specifically, this work focused on the equilibrium of a water-rich liquid phase, a hydrate phase and a vapor phase rich in a hydrate former. In all cases, calculations of the solid hydrate phase properties are based on the Kihara potential. This potential requires three parameters to be defined; initial values for which were found through a review of the literature. The accuracy of the predictions of the three-phase equilibrium is highly dependent on the reliability of these parameters. Thus, one of the parameters, the so-called ε parameter, was fitted to hydrate equilibrium data and resulted in a significant improvement in the accuracy of predictions of both PC-SAFT and PR EoS. The new set of parameters was then used to predict the three-phase equilibrium of several binary, ternary and quaternary mixtures of hydrate forming agents. Several conclusions are drawn from this work, including the observation that the accuracy of the models is reduced when the number of components increases.Item Prediction of the Three-Phase Coexistence Conditions of Pure Methane and Carbon Dioxide Hydrates Using Molecular Dynamics Simulations(2015-06-12) Costandy, Joseph GN; Economou, Ioannis G; Castier, Marcelo; Masad, EyadClathrate hydrates are solid crystals that consist of three-dimensional networks of hydrogen-bonded water molecules forming well-defined cages within which small “guest“ molecules are needed in order to stabilize the structures. More than 130 different molecules can form hydrates when mixed with water at relatively low temperatures and high pressures, including methane, ethane, propane, iso-butane, carbon dioxide, nitrogen and hydrogen. The accurate prediction of thermodynamic properties of clathrate hydrates has gained much attention due to the relevance of clathrate hydrates to many industrial applications. For example, hydrates play a major role in the problem of flow assurance in the oil and gas industry. They are also being considered for use in gas transport and separation applications. In addition, the existence of methane hydrates in large quantities in nature makes them a potential energy source. In this work, Molecular Dynamics (MD) simulations have been used in order to determine the Hydrate – Liquid water – Guest coexistence line for methane and carbon dioxide hydrates. The direct phase coexistence method was used where slabs of the three constituent phases were separately equilibrated and then brought in contact at the conditions under investigation. In order to account for the stochastic nature of the hydrate growth and dissociation processes, many long, independent simulations at different conditions of temperature and pressure were conducted while avoiding bubble formation phenomena. This allowed for performing a statistical averaging of the results to identify the three-phase coexistence temperature at different pressures. Also, the erroneous use of dispersion tail corrections was investigated. For methane hydrates, where the Lorentz-Berthelot combining rules for the two force fields used gave accurate predictions for the solubility of methane in the aqueous phase, this approach yielded predictions that are in good agreement with experimental data. A correction to the Lorentz-Berthelot cross-interaction energy parameter was applied in the case of carbon dioxide hydrates to obtain accurate predictions of the solubility of carbon dioxide in the aqueous phase, which in turn resulted in equally accurate and consistent predictions of the three-phase coexistence temperature. Therefore, it was shown that both the water-water and water-guest interactions play an important role in the application of this methodology to the study of clathrate hydrate systems. For systems where the water-guest interactions can accurately predict guest solubility in water, the predictions of the three-phase coexistence are as accurate as the water force field used to predict the melting of ice. It was also shown that the methodology cannot be directly applied to low pressures for carbon dioxide hydrates, where a liquid-like layer of carbon dioxide is adsorbed at the water surface. Several possible causes for this deficiency are suggested, including the possible effect of box anisotropy and box size fluctuations at low pressures.Item Recent Advances in Renewable Energy Technologies(2020-04-08) Economou, Ioannis GItem Transport Properties of Shale Gas in Relation to Kerogen Porosity(2019-03-21) Vasileiadis, Manolis; Economou, Ioannis G; Peristeras, Loukas D.; Papavasileiou, Konstantinos DKerogen is a micro-porous amorphous solid, which consist the major component of the organic matter scattered in the potentially lucrative shale formations hosting shale gas. Deeper understanding of the way kerogen porosity characteristics affect the transport properties of hosted gas is important for the optimal design of the extraction process. In this work, we employ molecular simulation techniques in order to investigate the role of porosity on the adsorption and transport behavior of shale gas in overmature type II kerogen found at many currently productive shales. To account for the wide range of porosity characteristics present in the real system, a large set of 60 kerogen structures that exhibit a diverse set of void space attributes was used. Grand Canonical Monte Carlo (GCMC) simulations were performed for the study of the adsorption of CH4, C2H6, n-C4H10 and CO2 at 298.15 K and 398.15 K and a variety of 2 pressures. The amount adsorbed is found to correlate linearly with the porosity of the kerogen. Furthermore, the adsorption of a quaternary mixture of CH4, C2H6, CO2 and N2 was investigated in the same conditions, indicating that the composition resembling that of the shale gas is achieved under higher temperature and pressure values, i.e. conditions closer to these prevailing in the hosting shale field. The diffusion of CH4, C2H6 and CO2, both as pure components and as components of the quaternary mixture, was investigated using equilibrium Molecular Dynamics (MD) simulations at temperatures of 298.15 and 398.15 K and pressures of 1 and 250 atm. In addition to the effect of temperature and pressure, the importance of limiting pore diameter (LPD), maximum pore diameter (MPD), accessible volume (Vacc) and accessible surface (Sacc) on the observed adsorbed amount and diffusion coefficient was revealed by qualitative relationships. The diffusion across the models was found to be anisotropic and the maximum component of the diffusion coefficient to correlate linearly with LPD, indicating that the controlling step of the transport process is the crossing of the limiting pore region. Finally, the transport behavior of the pure compounds was compared with their transport properties when in mixture and it was found that the diffusion coefficient of each compound in the mixture is similar to the corresponding one in pure. This observation agrees with earlier studies in different kerogen models comprising wider pores that have revealed negligible cross-correlation Onsager coefficients.