Marie-Hélène Simonot-Grange

Adsorption of chlorinated volatile organic compounds on hydrophobic faujasite: correlation between the thermodynamic and kinetic properties and the prediction of air cleaning

This work deals with a thermodynamic and kinetic study of the adsorption of single volatile organic compounds (VOCs) (dichloromethane (DCM), 1,2-dichloroethane (DCA), trichloroethene (TCE) and tetrachloroethene (PCE)) on a dealuminated faujasite Y by simultaneous measurements of the adsorbed amounts, adsorption heats and diffusivities. The type V isotherms and the weak values of derivative enthalpies allowed us to predict that the competitive adsorption of their mixture would be similar to a distillation. This prediction was verified experimentally: the breakthrough curves of VOC mixtures showed that the adsorbate with the higher boiling point displaced the adsorbate with the lower boiling point from the zeolite. The selectivity of the dealuminated faujasite thus decreased as PCE>TCE>DCA>DCM. The regeneration of this zeolite was total at 80°C.

Adsorption of gaseous p-xylene and m-xylene on NaY, KY, and BaY zeolites: Part 1. Adsorption equilibria of pure xylenes

Abstract Isothermal and isobaric adsorptions of p -xylene and m -xylene on NaY, KY, and BaY are studied by thermogravimetry between 25°C and 400°C, and 10 Pa and 1014 Pa. At low filling BaY shows a stronger affinity for xylenes than the other zeolites. At high temperature and low pressure its adsorption capacity is greater than those of NaY and KY. These two zeolites have a similar behavior and adsorb more m -xylene than p -xylene. At low temperature and high pressure KY adsorbs p -xylene like NaY and m -xylene like BaY, and, unlike NaY, the adsorption capacities of KY and BaY are higher for p -xylene than for m -xylene. The substitution of K + or Ba 2+ for Na + decreases the adsorption capacity of α-cages.

Characterization of the dealumination effect into H faujasites by adsorption: Part 1. The water molecule as a structural aluminum ion selective probe

The adsorption and desorption isotherms of water vapor are drawn at 25°C for dealuminated HY zeolites upon framework Si/Al ratio. The isotherms are compared to that of the parent NaY zeolite studied in a wide range of temperatures and filling coefficients (0.03 < θ < 1). The isotherm changes in shape from type I to type IV with an hysteresis loop changing from type H4 to type H2, as the Si/Al ratio increases. The Polanyi—Dubinin theory is used to determine the volume accessible to water. It decreases with increasing Si/Al ratios, down to zero at a Si/Al ratio of 35. Such a result is accounted for by the adsorption on the hydrophillic centers, which are the cations (H+) associated with the structural aluminum ions, each cation being coordinated on average by 9 H2O.

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

Abstract The adsorption isotherms of xylenes are described by Henrys law and Langmuirs 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 ability to adsorb xylenes than NaY and KY.

Differential calorimetric enthalpies of adsorption ofp-xylene andm-xylene on y faujasites at 25°C

AbstractThe differential enthalpies of adsorption ofp-xylene andm-xylene on NaY, KY and BaY zeolites were measured by isothermal calorimetry coupled with isothermal volumetry at 25‡C. Whatever the zeolite, the enthalpies of adsorption ofp-xylene andm-xylene at low filling were of the same order of magnitude. They did not show significantly the effect of the dipolar moment ofm-xylene. Their absolute values varied in the sequence Q0(pX/NaY)<Q0(pX/KY) =Q0(mX/KY)<Q0(pX/BaY)<Q0(mX/NaY) =Q0(mX/BaY)During the adsorption of the third molecule of xylene per α-cage, BaY zeolite exhibited specific behaviour: the differential enthalpies of adsorption decreased with the filling of the α-cages in such a way that they became lower than those of the other two zeolites. Some arguments concerning the structures of the zeolite and xylene molecules can explain such behaviour. Whatever the zeolite, the adsorption capacity of the α-cages was 3.5 molec.α−1. For relative pressures ranging from 0.2 to 0.5, an additional adsorption of about 0.1 molec.α−1 occurred on the external surface.

Proprietes physico-chimiques de l'eau adsorbee dans les zeolithes 13X et 4A. I. Capacite d'adsorption de la vapeur d'eau en fonction de la pression et de la temperature

Abstract Over the range of filling degrees from 0.06 to 1 for the 13X zeolite, and from 0.16 to 1 for the 4A zeolite, two equations are necessary to calculate the sorption capacity as a function of the pressure and the temperature. One is available on the range of low filling degrees and expresses the predominance of adsorbed water-located charge attraction forces on the surface of zeolitic cavities, the other is available on the range of high filling degrees and expresses the predominance of adsorbed water-zeolitic framework and adsorbed water-adsorbed water dispersion forces.

Microporous volume and external surface of Y zeolites accessible to p-xylene and m-xylene

Abstract Isothermal adsorption of p-xylene and m-xylene on NaY, KY and BaY zeolites was studied by thermogravimetry at 25°C. Adsorption isotherms showed type H4 hysteresis associated with a xylenes adsorption process activated by the pressure. Experimental data were analysed with the t-method to distinguish the amounts of xylene adsorbed in the α-cages and on the external surface of crystallites. Results were compared with those previously achieved by calorimetry. Whatever may be the isomer and the Y zeolite, the adsorption capacity of α-cages at 25 °C is equal to 3.5 molecule α−1. At saturation, the amount of xylenes adsorbed on the external surface represents 13% of the total amount adsorbed on the zeolites and is twice as great for m-xylene than for p-xylene. The adsorption process on the external surface differs from that in α-cages by a low adsorption energy and a high adsorption rate.

Characterization of the dealumination effect into H faujasites by adsorption: Part 2. The hexane molecule as a pore volume probe

Abstract Thermogravimetric studies under controlled vapor pressure are made at 25°C to measure adsorption and desorption isotherms of n -hexane on a series of dealuminated HY zeolites. These had been characterized by water vapor adsorption in Part 1 of this paper. Contrary to what was observed for water adsorption, isotherms always show a very high adsorption capacity in the very low pressures and a H4 hysteresis loop. The micropore maximal volume accessible to the adsorbate, the mesopore volume, and the adsorption energy are discussed with regard to the dealumination degree of the HY zeolites.

Proprietes physico-chimiques de l'eau adsorbee dans les zeolithes 13X et 4A. II. Capacites thermiques de l'eau adsorbee, du systeme zeolithe—eau et de la zeolithe anhydre

Abstract The original determination of thermal capacities of adsorbed water in the 13X and 4A zeolites confirms the existence of two types of the adsorbate—adsorbent interactions characterized by the study of sorption capacity of water vapor as a function of the pressure and the temperature and shows up typical adsorbate—adsorbate restructurations of the 4A zeolite. In the range of high filling degrees, the water—zeolite system mixes perfectly, whereas in the range of low filling degrees, the zeolite has a strong influence on the adsorbate properties.

Co-adsorption of 1,2-dichloroethane and 1-bromo,2-chloroethane on zeolite ZSM-5 from the liquid and vapour phases, using the Myers-Prausnitz-Dubinin model

Abstract The adsorption/co-adsorption of 1,2-dichloroethane (DCA) and 1-bromo,2-chloroethane (BCA) from the vapour and the liquid phases by zeolite ZSM-5 at ambient temperature is reported, using Dubinins theory and the recent Myers-Prausnitz-Dubinin (MPD) theory. For adsorption from the liquid phase, the activity coefficients in the adsorbed and the liquid states are the same and no selectivity is observed. This is confirmed by the absence of an excess enthalpy of immersion of ZSM-5 into the mixtures. Adsorption from the vapour phase proceeds in two stages, as indicated by double Dubinin-Astakhov (DA) plots. If one considers only the domain of high relative pressure, co-adsorption is described by the MPD theory. The agreement between calculated and experimental compositions of adsorbate can be improved by using, as a first and good approximation, the activity coefficients of the liquid–solid equilibrium at the same composition. A good agreement is also observed between the enthalpies of immersion calculated from the DA equation and the experimental integral heats of adsorption. However, for vapour mixtures ZSM-5 shows selectivity in favour of the more volatile compound, 1-bromo,2-chloroethane. This probably results from adsorption at low pressures and could be due to differences in kinetics.