Computer Simulation of Sorption and Transport in Zeolites

Papadopoulos, George K.; Theodorou, Doros N.

doi:10.1002/9783527610044.hetcat0090

Cited by 6 publications

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“…A treatment of mass transport phenomena via atomistic simulation presents the advantage, in comparison with macroscopic phenomenology, of predicting the magnitudes of diffusivities as well as their temperature, loading and composition dependencies. A literature survey on this subject can be found in refs − and in the rich amount of references therein.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics of Carbon Dioxide, Methane and Their Mixtures in a Zeolite Possessing Two Independent Pore Networks as Revealed by Computer Simulations

et al. 2009

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The molecular motion of methane (CH(4)) and carbon dioxide (CO(2)) sorbed in the two independent pore networks, being termed hereafter as large cavity (LC) and sinusoidal channel (SC) regions of the siliceous MWW-framework-type zeolite ITQ-1, is studied by means of atomistic computer simulation. Equilibrium molecular dynamics predicts different loading dependences for the two gases, for both the self and the collective (Maxwell-Stefan) diffusion coefficients; in particular, the transport coefficients of CH(4) go through a maximum as its loading in the zeolite increases, whereas CO(2) dynamics exhibits the decreasing trend with loading usually observed in nanoporous materials. The different loading dependence of the self-diffusivity for the two sorbates is attributed to their different probability density distribution within the supercages in the LC system of the ITQ-1 unit cell. The composition and occupancy dependence of the self-diffusivity of each component in their binary mixtures can be explained in terms of the selectivity for CO(2) sorption thermodynamics in the zeolite. The collective diffusivity loading dependence of the single and binary sorbate system is explainable on the basis of the strength of intermolecular interactions along the diffusion direction connecting the supercages by invoking the quasichemical mean field theory.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics of Carbon Dioxide, Methane and Their Mixtures in a Zeolite Possessing Two Independent Pore Networks as Revealed by Computer Simulations

et al. 2009

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“…We study the dynamics of molecules sorbed in ITQ-1 by means of equilibrium molecular dynamics (MD) simulations in the canonical (NVT) ensemble [74].…”

Section: Computation Detailsmentioning

confidence: 99%

Computational study of mass transport phenomena in zeolites

Sant¹

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The single and mixed sorbed phase dynamics of methane (CH 4 ) and carbon dioxide (CO 2 ) in the two independent pore networks, the large cavity (LC) and sinusoidal channel (SC), of the ITQ-1 zeolite (MWW framework type) are studied by means of atomistic computer simulations. Equilibrium molecular dynamics predicts different loading dependences for the two gases, for both the self-and the collective diffusion coefficients. In particular, the self-diffusivity of pure CO 2 exhibits the decreasing trend with loading which is usually observed in nanoporous materials, whereas the self-diffusivity of pure CH 4 displays a peculiar loading dependence which goes through a maximum if we consider only the CH 4 sorbed within the LC pore network of the ITQ-1 unit cell. From a qualitative perspective, the different loading dependence of the self-diffusivity for the two pure sorbates is attributed to their different probability density distribution inside the supercages of the LC pore network. Besides, the composition dependence of the self-diffusivity for each sorbate of the binary mixture can be explained in terms of the sorption thermodynamic selectivity for CO 2 in the zeolite.The loading dependence of the collective diffusivity comes from the evolution with loading of the self-diffusivity of the individual sorbed molecules and the many-body nature of the center of mass dynamics.To gain insight in the phenomena leading to the maximum in selfdiffusivity for pure CH 4 inside the LC of ITQ-1, we develop a new "mesoscopic" stochastic model which can describe the diffusive behavior of a system of particles at equilibrium. The model is based on discretizing space into slabs by drawing equispaced parallel planes along a coordinate direc- VII VIIIABSTRACT tion. A central role is played by the probability that a particle exits a slab via the face opposite to the one through which it entered (transmission probability), as opposed to exiting via the same face through which it entered (reflection probability). A simple second-order Markov process model invoking this probability is presented, leading to an expression for the selfdiffusivity, applicable for large slab widths, consistent with a continuous formulation of diffusional motion. The model is validated via molecular dynamics simulations in a bulk system of soft spheres across a wide range of densities.At this point, the concentration dependence of self-diffusivity within periodic media can be investigated by implementing the second-order Markov process model into a method, called diffusion through space discretization (DSD). Introducing the concept of minimum crossing surface, we obtain a unique decomposition of the self diffusion coefficient into two parameters with specific physical meanings. Two case studies showing a maximum in self-diffusivity as a function of concentration are investigated, along with two cases where such a maximum cannot be present.Finally, the DSD method is applied to the LC pore network of the ITQ-1 zeolite, for CH 4 and CO 2 , explaining the diffusivity...

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“…παράδειγμα, ένα τρισδιάστατο κυβικό ερμιτιανό πολυώνυμο (three-dimensional cubic Hermite polynomial)[99,103,104]. Αυτή η τακτική ελαττώνει σημαντικά τον υπολογιστικό χρόνο και επιτρέπει καλύτερη δειγματοληψία στο χώρο των φάσεων του συστήματος, αφού περιλαμβάνει μεγαλύτερο αριθμό μοναδιαίων κυψελίδων στο κουτί της προσομοίωσης[105].Το πλέγμα του ζεόλιθου χρειάζεται να είναι εύκαμπτο κυρίως στην περίπτωση που τα ροφημένα μόρια έχουν σχεδόν το ίδιο μέγεθος με τους πόρους του κρυστάλλου[105].Για παράδειγμα, οι Vlugt et al[106] βασιζόμενοι στη δουλειά των Demontis et al[107] πειραματικές, ιδιαίτερα όσο αυξανόταν το μήκος του αλκανίου (από βουτάνιο σε δεκάνιο). Η κίνηση ή όχι των κατιόντων επηρεάζει τη ρόφηση ρευστών στους κρυστάλλους αναλογικά με το μέγεθος των ροφημένων μορίων του ρευστού: όσο μεγαλύτερο είναι το μόριο, τόσο περισσότερο επηρεάζει η κίνησή τους τη ρόφηση.Αντίθετα, στην περίπτωση μικρών σε μέγεθος μορίων (π.χ.…”

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Προσομοίωση Διεργασιών Ρόφησης Αερίων Σε Νανοπορώδη Υλικά

Pantatosaki¹,

Παντατοσάκη²

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Ευχαριστώ τον καθηγητή μου κ. Α. Παπαϊωάννου για τη συνολική εποπτεία της διατριβής, τις συμβουλές του, καθώς και για την εμπιστοσύνη που μου έδειξε με την ανάθεση του θέματος. Ευχαριστώ εκ βαθέων τον Δρα. Γ. Κ. Παπαδόπουλο, ο οποίος, με τις πολύτιμες γνώσεις του, την εμπειρία του και την καθοδήγησή του, στάθηκε πραγματικός δάσκαλος για μένα σε όλη τη διάρκεια της διδακτορικής διατριβής. Ευχαριστώ, ακόμη, τον Δρα. Α. Στούμπο από το Ινστιτούτο Πυρηνικής Τεχνολογίας και Ακτινοπροστασίας του Ε.Κ.Ε.Φ.Ε. Δημόκριτος για την υποστήριξή του. Η διατριβή έγινε υπό την υποτροφία του Ινστιτούτου, διάρκειας 4 ½ χρόνων. Ευχαριστώ, επίσης, τον καθηγητή κ. Δ. Ν. Θεοδώρου για τη διάθεση του υπολογιστικού εξοπλισμού της Ομάδας Υπολογιστικής Επιστήμης και Τεχνικής των Υλικών. Ευχαριστίες προς τους καθηγητές κ. Μπουντουβή, κ. Παλυβό, και τις καθηγήτριες κ. Μανδαράκα, κ. Διακουλάκη για την εξασφάλιση χώρου εργασίας κατά τη διάρκεια της διατριβής. Ευχαριστώ τους γονείς μου, οι οποίοι κάνουν ο,τιδήποτε δυνατό για να φροντίζουν τα παιδιά τους. Και ευχαριστώ τη Σύλια, δε χρειάζεται να το εκφράσω με λόγια, γνωρίζει γιατί. Αθήνα, Απρίλιος 2007.

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Computer Simulation of Sorption and Transport in Zeolites

Abstract: The sections in this article are Introduction Reconstruction of Zeolitic Media Atomistic Reconstruction Mesoscopic Reconstruction A Stochastic B Particle‐Based … Show more

Cited by 6 publications

References 89 publications

Molecular Dynamics of Carbon Dioxide, Methane and Their Mixtures in a Zeolite Possessing Two Independent Pore Networks as Revealed by Computer Simulations

Molecular Dynamics of Carbon Dioxide, Methane and Their Mixtures in a Zeolite Possessing Two Independent Pore Networks as Revealed by Computer Simulations

Computational study of mass transport phenomena in zeolites

Προσομοίωση Διεργασιών Ρόφησης Αερίων Σε Νανοπορώδη Υλικά

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