2,950 research outputs found

    Single and multicomponent sorption of CO2, CH4 and N-2 in a microporous metal-organic framework

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    Single and multicomponent fixed-bed adsorption of CO2, N-2, and CH4 on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO2 and the loadings of CH4 and N-2 are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO2 is one order of magnitude faster than for CH4 and N-2.This work was supported by an Award CHE 0718281 from the National Science Foundation (B.C.), the University of Texas-Pan American (UTPA) through a Faculty Research Council Award (B.C), in part by the Welch Foundation (Grant BG-0017) to the Department of Chemistry at UTPA. J.A.C.S. acknowledges financial support provided by national research grant FCT=POCTI=EQU=60828=2004 and by LSRE financing by FEDER=POCI=2010. P.S.B. acknowledges his Ph.D. scholarship by FCT (SFRH=BD=30994=2006), and L.B. acknowledges Henri Pieper Grant (Institute HEMES Gramme, Belgium) for the financial support

    Molecular Simulation of Transport and Storage in Shale

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    Over the past few years, the production of shale hydrocarbons has seen a renewed interest both in science and industry. Indeed, these fluids today constitute a significant energy and economic stake to compensate for the scarcity of so-called conventional resources. This is due to the fact that shale gases and oils represent enormous potential resources and are present all over the world. In shales, hydrocarbons are generally contained in microporous organic nanopores: kerogen. The kerogen is both the source rock of hydrocarbons and their reservoir. In shales, the extreme confinement of fluids in organic matter, high pressure-high temperature thermodynamic condition as well as very low permeabilities, imply a significant change in the state of the fluids (present in adsorbed form) and its transport mechanisms (diffusive). In this dissertation, we studied the physical properties (adsorption, transport) of kerogen as well as its carbon dioxide sequestration potential. The characteristic scales in the shales are of the order of a nanometer, which is accessible today by molecular simulations on supercomputers or even personal computers. Therefore, we have chosen to study kerogens by molecular simulation. The objective of this work is to stimulate a fundamental research on this subject in order to understand and model the mechanisms encountered in the shales and thus to respond responsibly and sustainably to the energy challenges of the years to come. Initially, the simplified kerogen models (carbon nanochannels and nanocapillaries) are developed and transport and storage of different gases are studied. This part of research is beneficial for developing analytical models of gas transport in organic nanopores. Furthermore, kerogens with different maturities were generated by molecular dynamics simulations under thermodynamic conditions typical of this type of reservoir (338 K, 20 MPa). In our simulations, the microporous network of kerogen is created by the inclusion of dummy particles, which were deleted after kerogen structure is created. The average density of the structures of organic matter created is in agreement with the experimental results obtained on such kerogens. The density is very strongly correlated with the stacking of the kerogenic polyaromatic clusters which is a strong indicator of the coherence of the simulated structures with respect to the experiments. We were interested in the transport of hydrocarbons in the kerogen and have identified the mechanisms of mass transfer through kerogens and we have been able to predict their evolution as a function of thermodynamic conditions (composition and pressure). Based on the results, it is demonstrated that the higher the maturity of kerogen, the higher is its adsorption capability. This is in agreement with experimental results of adsorption on kerogen. Furthermore, it is shown that the permeation of fluid through the kerogen membrane can be described by a diffusive formalism. The heavier alkanes have smaller diffusion coefficients and as a result, they may trap inside organic nanopores. Multicomponent diffusion of mixtures containing water and carbon dioxide is investigated and it is shown that water and carbon dioxide have lowest diffusion coefficients compared with hydrocarbons. The diffusion coefficients of hydrocarbons increases in presence of water due to higher adsorption capability of water and filling the adsorption sites. Adsorption molecular simulations of binary mixture of methane and carbon dioxide demonstrate that carbon dioxide have higher adsorption capabilities than methane. Binary mixture diffusion simulation of these two components also shows that carbon dioxide molecules have lower diffusion coefficients compared with methane. Therefore, injection of carbon dioxide into organic matter causes the methane molecules desorb and produce.;In conclusion, this dissertation work consisted of developing models, algorithms, and methodologies to predict the properties and mechanisms governing the behavior of the organic matter contained in the shales by employing molecular simulations . This work aims to improve our understanding of this type of resources

    Combination of Adsorption-Diffusion Model with Computational Fluid Dynamics for Simulation of a Tubular Membrane Made from SAPO-34 Thin Layer Supported by Stainless Steel for Separation of CO2 from CH4

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    Modeling of CO2/CH4 separation using SAPO-34 tubular membrane was performed by computational fluid dynamics. The Maxwell-Stefan equations and Langmuir isotherms were used to describe the permeate flux through the membrane and the adsorption-diffusion, respectively. Three-dimensional Navier-Stokes momentum balances in feed and permeate side coupled with adsorption-diffusion equations from the membrane were simultaneously solved by ANSYS FLUENT software. The velocity and concentration profiles were determined in both feed and permeate sides. There was a good agreement between simulation and experimental results and root mean square deviation for CH4 and CO2 are 0.13 and 0.1 (mmol m-2 s-1), respectively. The concentration polarization effect was observed in the results. The effect of the process variables were investigated to find out the most influential parameters in permeation and purity. The impact of operating conditions on separation were studied and showed that for enhancement of separation efficiency of CO2 from CH4, feed pressure, feed flow rate and tube radius and number of membrane modules in series should be increased, whereas flow configuration has less significant effect

    Survey on Adsorption of Low Molecular Weight Compounds in Cu-BTC Metal–Organic Framework: Experimental Results and Thermodynamic Modeling

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    This contribution aims at providing a critical overview of experimental results for the sorption of low molecular weight compounds in the Cu-BTC Metal–Organic Framework (MOF) and of their interpretation using available and new, specifically developed, theoretical approaches. First, a literature review of experimental results for the sorption of gases and vapors is presented, with particular focus on the results obtained from vibrational spectroscopy techniques. Then, an overview of theoretical models available in the literature is presented starting from semiempirical theoretical approaches suitable to interpret the adsorption thermodynamics of gases and vapors in Cu-BTC. A more detailed description is provided of a recently proposed Lattice Fluid approach, the Rigid Adsorbent Lattice Fluid (RALF) model. In addition, to deal with the cases where specific self- and cross-interactions (e.g., H-bonding, Lewis acid/Lewis base interactions) play a role, a modification of the RALF model, i.e., the RALFHB model, is introduced here for the first time. An extension of both RALF and RALFHB is also presented to cope with the cases in which the heterogeneity of the rigid adsorbent displaying a different kind of adsorbent cages is of relevance, as it occurs for the adsorption of some low molecular weight substances in Cu-BTC MOF

    3D model of a Monolithic Honeycomb Adsorber for Electric Swing Adsorption for Carbon Dioxide Capture

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    The goal of this work was to develop a 3D model of Electric Swing Adsorption process for carbon dioxide capture from effluent gasses from power plants. Detailed 3D model of the composite honeycomb monolithic adsorber was developed for a single monolith channel and can be used to simulate and represent different physical properties: velocity, concentration and temperature. The advantage of this model is the fact that all physical properties and results can be presented visually in the 3D domain. COMSOL Multiphysics software was used for solving partial differential equations and simulations of adsorption and electrothermal desorption processes. Some simulation results are presented in this work. The results obtained from 3D simulations will be used for the adsorber model reduction to the 1D model which will be used for modeling and optimization of the whole ESA cycle due to its simplicity and computational demands. Simulation and optimization runs based on the 1D model will be performed in g-Proms software

    New pressure swing adsorption cycles for hydrogen purification from steam reforming off-gases

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    Tese de doutoramento. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto. 201

    Density functional theory-based adsorption isotherms for pure and flue gas mixtures on Mg-MOF-74. Application in CO2 capture swing adsorption processes

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    A simplified model is applied for the prediction of gas/solid adsorption isotherms of pure gases (i.e., CO2, N2, SO2) on the metal-organic framework Mg-MOF-74, based on periodic Density Functional Theory (DFT) calculations and a dual-site Langmuir approach (DFT/DSL), using a mean-field approximation for the inclusion of the lateral interactions. This model not only provides reliable adsorption isotherms (P ≤ 1 atm, 293 ≤ T ≤ 373 K) but also isosteric heats of adsorption in good agreement with both available experimental data and previous more refined models. Moreover, an extension of this model is used to study the effect of SO2 as an impurity in the efficiency of adsorption and desorption processes of some post-combustion gas mixtures. It is shown that a very low concentration of SO2 is enough to poison Mg-MOF-74 structure. Moreover, different swing adsorption techniques at different working conditions are analysed to reduce the impact of SO2 poisoning in CO2 separation
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