Search results for "ZEOLITE"

Adsorption of p-Xylene/m-Xylene Gas Mixtures on BaY and NaY Zeolites. Coadsorption Equilibria and Selectivities

1997

Coadsorption of the gases p-xylene and m-xylene on BaY and NaY was studied at 150 °C in the range of pressure 10-2-3 hPa. For BaY coadsorption isotherms and single-component adsorption isotherms are perfectly superimposed in the whole range of investigated pressure. The capacity of adsorption of BaY is 3 molecules α-1 for each single component as well as for each mixture under 3 hPa. For NaY coadsorption isotherms lie between those of single p-xylene and m-xylene. The capacity of adsorption of NaY for mixtures is in proportion to the composition of the initial adsorptive mixture and varies from the capacity of adsorption for single p-xylene (3.3 molecules α-1) to that for single m-xylene (3…

Selective adsorption of formaldehyde and water vapors in NaY and NaX zeolites

2019

International audience; Coadsorption of formaldehyde and water vapors on NaX and NaY zeolites is studied at 298 K in the pressure range 0-2 hPa by manometry coupled with gas phase chromatography and calorimetry. Coadsorption isotherms, adsorption selectivities and coadsorption heats are measured. Results show that the coadsorption process is selective for water at low filling and for formaldehyde at high filling. The adsorption selectivity for formaldehyde over water is however too low to consider the possibility of using such adsorbents for the development of air handling units. On the other hand, a preliminary study carried out on the adsorption of formaldehyde and water in pure gas phase…

Electrochemical characterization of iron sites in ex-framework FeZSM-5

2002

Abstract The electrochemical response of FeZSM-5 prepared by an ex-framework method has been studied using Paraloid B72 polymer film electrodes immersed in aqueous media using H2SO4, HCl, Na2EDTA and NaCl electrolytes. The ex-framework method comprises the hydrothermal synthesis of isomorphously substituted FeZSM-5, followed by calcination at 823 K and subsequent steam treatment (300 mbar H2O in N2) at 873 K. During this process iron is extracted to extra-framework positions. Also partial dealumination of the zeolite framework takes place. Characteristic voltammetric responses in the +1.0 to −0.6 V versus SCE potential range have been recorded and were used to characterize the iron species …

Adsorption of water vapor on X and Y zeolites exchanged with barium

2001

Abstract The adsorption of water vapor on BaY and BaX zeolites is studied by thermogravimetry and calorimetry under isothermal or isobaric conditions. The faujasite zeolite exhibits a stronger adsorption affinity for water molecules with barium than with sodium or potassium as exchangeable cations. The adsorption–desorption isotherm at 150°C shows a hysteresis loop attributed to the migration of compensating cations during their interaction with water molecules. Calorimetric measurements and the Dubinin–Radushkevich’s model both show that the adsorption of water occurs via a three-step mechanism: adsorption on compensating cations, formation of a monolayer on the walls and multilayer adsorp…

Ionic liquids binary mixtures and zeolites: a combination to promote carbohydrates conversion into 5-hydroxymethylfurfural

A microcalorimetric study of the different states of argon and nitrogen adsorbed AT 77 K on silicalite-I and ZSM-5

1992

The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16<Si/Al<120)) was studied by isothermal microcalorimetry, volumetry and neutron diffraction.

Confinement in micropores and enthalpies of physisorption

1994

Abstract The use of quasi-equilibrium volumetry associated with isothermal microcalorimetry at 77 K allows direct measurement of the interactions on adsorption of simple probe molecules within well crystallised aluminophosphate and zeolite molecular sieves. Four particular cases are presented which show: the effect of varying micropore diameter, the effect of adsorbing molecules with a favourable geometric compatibility with a given micropore system, the effect of varying the field potential within a given micropore system and finally, the effect of variable selective blocking of the micropore system.

A microcalorimetric comparison of the effect ofn-alkane preadsorption on the adsorption of argon and nitrogen on Silicalite-I

1994

Then-alkanes of different lengths were preadsorbed to selectively block part of the micropores of a MFI-type zeolite, Silicalite-I. The porosity available to argon and nitrogen was then studied by quasi-equilibrium adsorption microcalorimetry and volumetry at 77K and compared to what was found for the bare zeolite. Indeed, although partial adsorption ofn-alkanes does not alter the value of the differential enthalpies of adsorption for both argon and nitrogen, then-butane preadsorption diminishes the adsorption capacity by inducing inaccessible volumes in the micropore network. Moreover, the microcalorimetric experiments clearly show thatn-butane is not evenly distributed in the zeolite chan…

Coadsorption of hydrogen and deuterium on zeolites at cryogenic temperatures : influence of the sorbent’s properties on selectivity

2019

The adsorption of hydrogen and deuterium (single gases and mixtures) was studied on a series of zeolites with varied parameters (Si/Al ratio, nature of the charge-compensating cation, pore geometry and diameter of pore aperture). Thermodynamic adsorption selectivities towards deuterium with respect to hydrogen were measured in a large pressure range (0.1 – 1000 hPa) and for several temperatures (45 – 100 K). The adsorption selectivity was assessed using direct coadsorption measurements performed by manometry coupled with mass spectrometry. For all studied zeolites and experimental conditions, the coadsorption process is selective towards deuterium, in agreement with the literature. However,…

Adsorption of gaseous p-xylene and m-xylene on NaY, KY, and BaY zeolites. Part 2: Modeling. Enthalpies and entropies of adsorption

1995

Abstract The adsorption isotherms of xylenes are described by Henry's law and Langmuir's model on NaY and KY and the Dubinin-Radushkevich model on BaY. The isoteric enthalpies of adsorption show on each zeolite that the adsorbate-adsorbent interactions are nearly the same with both isomers. They are stronger on BaY than on NaY and KY. The adsorbate-adsorbate interactions are stronger with m-xylene than with p-xylene and especially outstanding on KY. The entropies of adsorption show that the mobility of the adsorbate is lower with m-xylene than with p-xylene. The isosteric free enthalpies of adsorption are related to the acidity of each zeolite. BaY has a stronger acidity and a greater abili…