Molecular Cage Nestling in the Liquid-Phase Adsorption of <i>n</i>-Alkanes in 5A Zeolite

Daems, Inge; Baron, Gino V.; Punnathanam, Sudeep N.; Snurr, Randall Q.; Denayer, Joeri

doi:10.1021/jp0668145

Cited by 36 publications

(51 citation statements)

References 37 publications

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“…However, the calculated values are lower by about 6 % than the ones obtained for the TMMSsilica system, despite taking into account the loss of conformational entropy well above that of the real molecular chain (i.e., not freely rotating chain and with excluded volume). All this shows that on adsorption the n-alkanes lose one degree of freedom and a number of conformations depending on the chain length of the hydrocarbon molecule with respect to the pore configuration of silica (Eder and Lercher 1997;Daems et al 2007). In the crystalline zeolites the straight and sinusoidal pore segments are narrow and impose stretching of the alkylchains along the pore axis, and then significant loss of entropy (Denayer et al 2003).…”

Section: Adsorption Thermodynamicsmentioning

confidence: 98%

Dependence of surface properties of silylated silica on the length of silane arms

et al. 2012

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Amorphous precipitated Zeosil 1165 MP silica was silylated with low grafting degrees of organosilicons bearing different alkoxy and hydrocarbon tails, like monomethoxy(dimethyl)octadecylsilane (DMODMS), monomethoxytrimethylsilane (TMMS), trimethoxymercaptopropylsilane (MPTS), and 3-octanoylthio-1-propyltriethoxysilane (NXT ® ). Thermogravimetry and Elemental Analysis were used to determine the degree of silane grafting and the final number of free silanol OH groups/nm 2 on the modified Zeosil surface. Free energy, enthalpy and entropy of adsorption of hydrocarbon probes were determined by Inverse Gas Chromatography at infinite dilution and dispersive component, γ d s , and specific interaction parameter, I sp , of the surface tension of the silica surface were calculated. Silylation changes the hydrophilic character of Zeosil silica to the hydrophobic one, on increasing the grafting degree and, mainly, the length of hydrocarbon tail of the silane

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Section: Adsorption Thermodynamicsmentioning

confidence: 98%

Dependence of surface properties of silylated silica on the length of silane arms

et al. 2012

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“…Many industrial separation processes based on adsorption work close to saturation conditions to operate cost efficiently. 10 − 13 Because separations are driven by entropic forces in this regime, 14 − 17 it is important to understand and study how entropy behaves in these systems to design a new generation of nanoporous materials for separations. 18 , 19 Separations based on adsorption rely on the equilibrium loading differences of the mixture components.…”

Section: Introductionmentioning

confidence: 99%

Behavior of the Enthalpy of Adsorption in Nanoporous Materials Close to Saturation Conditions

Torres‐Knoop

Poursaeidesfahani

Vlugt

et al. 2017

J. Chem. Theory Comput.

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Many important industrial separation processes based on adsorption operate close to saturation. In this regime, the underlying adsorption processes are mostly driven by entropic forces. At equilibrium, the entropy of adsorption is closely related to the enthalpy of adsorption. Thus, studying the behavior of the enthalpy of adsorption as a function of loading is fundamental to understanding separation processes. Unfortunately, close to saturation, the enthalpy of adsorption is hard to measure experimentally and hard to compute in simulations. In simulations, the enthalpy of adsorption is usually obtained from energy/particle fluctuations in the grand-canonical ensemble, but this methodology is hampered by vanishing insertions/deletions at high loading. To investigate the fundamental behavior of the enthalpy and entropy of adsorption at high loading, we develop a simplistic model of adsorption in a channel and show that at saturation the enthalpy of adsorption diverges to large positive values due to repulsive intermolecular interactions. However, there are many systems that can avoid repulsive intermolecular interactions and hence do not show this drastic increase in enthalpy of adsorption close to saturation. We find that the conventional grand-canonical Monte Carlo method is incapable of determining the enthalpy of adsorption from energy/particle fluctuations at high loading. Here, we show that by using the continuous fractional component Monte Carlo, the enthalpy of adsorption close to saturation conditions can be reliably obtained from the energy/particle fluctuations in the grand-canonical ensemble. The best method to study properties at saturation is the NVT energy (local-) slope methodology.

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“…For the thus developed models different terms came into common use, including “resonant diffusion” [ 12 , 13 ], “levitation effect” [ 14 , 15 ], “commensurate adsorption” [ 16 , 17 , 18 , 19 ] and “incommensurate diffusion” [ 19 , 20 , 21 ]. The scenario of the commensurate/incommensurate adsorption and diffusion was, in particular, evidenced by configurational-bias Monte Carlo (CBMC) and grand canonical Monte Carlo (GCMC) simulations revealing the configurations of guest molecules under confinement by the host material [ 16 , 22 , 23 , 24 ].…”

Section: Introductionmentioning

confidence: 99%

Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks

et al. 2018

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Molecular diffusion is commonly found to slow down with increasing molecular size. Deviations from this pattern occur in some host materials with pore sizes approaching the diameters of the guest molecules. A variety of theoretical models have been suggested to explain deviations from this pattern, but robust experimental data are scarcely available. Here, we present such data, obtained by monitoring the chain length dependence of the uptake of n-alkanes in the zeolitic imidazolate framework ZIF-4. A monotonic decrease in diffusivity from ethane to n-butane was observed, followed by an increase for n-pentane, and another decrease for n-hexane. This observation was confirmed by uptake measurements with n-butane/n-pentane mixtures, which yield faster uptake of n-pentane. Further evidence is provided by the observation of overshooting effects, i.e., by transient n-pentane concentrations exceeding the (eventually attained) equilibrium value. Accompanying grand canonical Monte Carlo simulations reveal, for the larger n-alkanes, significant differences between the adsorbed and gas phase molecular configurations, indicating strong confinement effects within ZIF-4, which, with increasing chain length, may be expected to give rise to configurational shifts facilitating molecular propagation at particular chain lengths.

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Molecular Cage Nestling in the Liquid-Phase Adsorption of n-Alkanes in 5A Zeolite

Cited by 36 publications

References 37 publications

Dependence of surface properties of silylated silica on the length of silane arms

Dependence of surface properties of silylated silica on the length of silane arms

Behavior of the Enthalpy of Adsorption in Nanoporous Materials Close to Saturation Conditions

Anomaly in the Chain Length Dependence of n-Alkane Diffusion in ZIF-4 Metal-Organic Frameworks

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