Thermodynamic study of ethane thin films adsorbed on MgO(100) powder

Trabelsi, Mohsen; Coulomb, J.P.

doi:10.1016/0039-6028(92)91462-k

Cited by 19 publications

(7 citation statements)

References 21 publications

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“…The remainder of the butane sorption is assumed to be multilayer surface condensation. Alkane sorption on graphite surfaces has been previously investigated, and it is known that multilayer sorption occurs. − Butane is not likely to be adsorbing between the MWNT carbon layers. Butane's radius of gyration is 2.89 Å, while the distance between the carbon layers is 3.35 Å.…”

Section: Resultsmentioning

confidence: 99%

Sorption of Butane on Carbon Multiwall Nanotubes at Room Temperature

et al. 2001

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Carbon multiwall nanotubes (MWNTs) can be used for separation processes if the mechanisms for sorption and desorption are known. This study describes the sorption mechanism for butane on MWNTs at room temperature and relative pressures ranging from 0 to 0.9. Previous workers have studied the sorption of hydrogen, − neon, − helium, nitrogen, and methane8-10 on nanotubes for storage purposes. Molecular dynamic simulations have been done to show that carbon nanotubes can be used as a separation tool to selectively separate isomers of monomethylnaphthalenes. Experiments have established that refrigerant mixtures, such as CHF2CF3 and CClF2CF3, can be successfully separated by using carbon nanotubes. Previous work in this lab has shown that carbon MWNTs can separate butane from methane when both are at low levels in a gas flow. This experimental result is in agreement with recent molecular dynamic simulations made for sorption of alkane mixtures on different types of single-walled carbon nanotubes (SWNTs). Morphology characterization of the MWNTs has been used to interpret the sorption data. Most of the butane was sorbed to the external surface of the MWNTs and only a small fraction of the butane condensed in the pores. No hysteresis was observed between sorption and desorption experiments. The weight fraction of butane sorbed depended inversely on the diameter of the MWNTs and was 5.3 wt % for one of the samples studied. Adsorption isotherms were modeled using a modified BET equation with coefficients consistent with the known morphology. Fixed bed adsorption systems that could use the exterior surface of MWNTs might be attractive for separations, particularly if electrical heating could be used for rapid desorption of sorbed molecules.

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Section: Resultsmentioning

confidence: 99%

Sorption of Butane on Carbon Multiwall Nanotubes at Room Temperature

et al. 2001

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“…There are seven or eight discernible diffraction peaks (Table ) that are not observable in Figure b, the most prominent of which are located at 1.48 ± 0.04 Å -1 and 1.67 ± 0.01 Å -1 . While some evidence of these two prominent features can be found in earlier data reported by Coulomb and Suzanne and their co-workers, − the statistical quality of this earlier data makes it difficult to identify any other features with certainty. The lower intensity peaks observed in the current study were not resolvable previously.…”

Section: Resultsmentioning

confidence: 76%

“…Each of these fits has an R -value >0.99. The dotted line shows the corresponding fit derived from the coefficients given by TC . The error in the measured pressure is negligible, although there is an uncertainty in determination of the SVP (and hence the temperature) of about 1% due to the asymptotic nature of the approach to SVP in an isotherm. …”

Section: Resultsmentioning

confidence: 99%

“…While the complex phase behavior in the ethane-on-graphite system has been thoroughly examined by Taub − and others, information concerning the ethane on MgO system is more limited. Several years ago, Trabelsi and Coulomb (hereafter known as TC) published a thermodynamic study of ethane adsorbed on MgO that included a set of isotherm measurements and a comparison of thermodynamic quantities that they derived with ethane adsorption data on other surfaces (graphite and sodium chloride) . Suzanne et al have performed an ultra high vacuum (UHV)-based structural study of monolayer, solid ethane films on MgO using low-energy electron diffraction (LEED). , In agreement with neutron diffraction data, they suggested that two, coverage-dependent solid phases, S1 and S2, form.…”

Section: Introductionmentioning

confidence: 96%

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Thermodynamic Investigation of Thin Films of Ethane Adsorbed on Magnesium Oxide

2005

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The layering properties of ethane on MgO(100) were measured between 91 and 144 K using high-resolution adsorption isotherms. In contrast to previous studies, the results demonstrate that only three layers are formed. The thermodynamic functions derived from the data (isosteric heat, differential enthalpy, and entropy of adsorption) compare well with literature values and show a steady trend toward the bulk properties as the number of layers increased. Phase transitions for two of the layers were identified by monitoring the changes in the two-dimensional isothermal compressibility as a function of chemical potential. Both of these phase transitions occur at approximately 127 K and within 1 K of each other. Through the use of neutron diffraction, it is possible to identify at least one solid surface phase that melts at approximately 75 K. The transition at 127 K is therefore a transition between a liquidlike phase and a hyper-critical fluid. A comparison is made between the present data and our recent study of methane on MgO.

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“…At present, larger polyatomic molecules are studied. A wide range of techniques [6][7][8][9] are used to improve the knowledge of the adsorption process by giving information on the isosteric heat of adsorption and to assess phase diagrams. In parallel way, calculations based either on ab initio methods [10] or on semi-empirical interaction potentials [11] have been performed to interpret the experimental findings on the statics and dynamics of these molecular monolayers.…”

Section: Introductionmentioning

confidence: 99%