Christian Paulin

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.

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.

Diffusion of Oxygen in Cork

This work reports measurements of effective oxygen diffusion coefficient in raw cork. Kinetics of oxygen transfer through cork is studied at 298 K thanks to a homemade manometric device composed of two gas compartments separated by a cork wafer sample. The first compartment contains oxygen, whereas the second one is kept under dynamic vacuum. The pressure decrease in the first compartment is recorded as a function of time. The effective diffusion coefficient D(eff) is obtained by applying Ficks law to transient state using a numerical method based on finite differences. An analytical model derived from Ficks law applied to steady state is also proposed. Results given by these two methods are in close agreement with each other. The harmonic average of the effective diffusion coefficients obtained from the distribution of 15 cork wafers of 3 mm thickness is 1.1 × 10(-9) m(2) s(-1) with a large distribution over four decades. The statistical analysis of the Gaussian distribution obtained on a 3 mm cork wafer is extrapolated to a 48 mm cork wafer, which length corresponds to a full cork stopper. In this case, the probability density distribution gives a mean value of D(eff) equal to 1.6 × 10(-9) m(2) s(-1). This result shows that it is possible to obtain the effective diffusion coefficient of oxygen through cork from short time (few days) measurements performed on a thin cork wafer, whereas months are required to obtain the diffusion coefficient for a full cork stopper. Permeability and oxygen transfer rate are also calculated for comparison with data from other studies.

Thermal effects of water intrusion in hydrophobic nanoporous materials.

Liquid water intrusion in hydrophobic nanoporous silicalite-1, a pure siliceous zeolite, in isothermal conditions under high pressure produces an endothermic effect. After intrusion, confined water in zeolite pores is in a different state from that of the liquid bulk water. Such forced intrusion also chemically modifies the material and tends to render it slightly more hydrophilic.

EFFECT OF WATER CONTENT ON THE SELECTIVE COADSORPTION OF GASEOUS P-XYLENE AND M-XYLENE ON THE BAY ZEOLITE

The selective coadsorption of gaseous p-xylene and m-xylene is studied at 150°C on BaY with a water content which varies up to 3.5% in weight. The preadsorbed water seems to be located only in the plusmn;-cages, probably around the compensation cations in sites II. The water, which is the more strongly adsorbed component, is not replaced during the coadsorption of xylenes, and this leads to a weakening of the interactions between the aromatic ring and the compensation cation. As for the anhydrous zeolite, two selective adsorption processes are discerned according to the filling. At low filling, BaY adsorbs preferentially the more abundant isomer in the adsorpti ve mixture, and the presence of water has no significant effect on the selectiv- ity except for mixtures rich in p-xylene with which the selectivity is up to three time as great as that with the anhydrous zeolite. At high filling, BaY is selective for p-xylene whatever the composition of the adsorptive mixture, and the higher the water content, the...

Interaction Mechanisms between guaiacols and lignin: the conjugated double bond makes the difference.

Lignin is considered to be responsible for a selective sorption of phenolic compounds on wood. In order to investigate the mechanisms involved, two similar guaiacol compounds--only differing by the nature of the para side chain--were adsorbed on oak wood extracted lignin. Vapor sorption-desorption isotherms indicated that about 3.5 wt % of 4-vinylguaiacol is adsorbed near saturation whereas it is only 0.8% for 4-ethylguaiacol. For both compounds, the isotherms displayed a hysteresis though significantly greater for 4-vinylguaiacol. Analyses of the hydroxyl stretching region of FTIR spectra of the lignin/4-ethylguaiacol and lignin/4-vinylguaiacol complexes indicated that physisorption via hydrogen bonds occurs for both sorbates with lignin phenolic hydroxyl groups but which would be more condensed for the former than for the latter. According to NMR spectra, these phenolic hydroxyl groups correspond to non-etherified guaiacyl subunits. In contrast with other para substituents, the conjugated vinyl bond favors not only physisorption but also chemisorption as witnessed by the fact that upon desorption in the vapor phase, even after pumping under dynamic vacuum for several days, about 1 wt % of 4-vinylguaiacol remains adsorbed onto lignin.

Communication: Evidence of structural phase transitions in silicalite-1 by infrared spectroscopy.

The adsorption of trichloroethylene, perchloroethylene, and p-xylene on a MFI (Mobile-FIve) zeolite is studied using in situ FTIR spectroscopy at 298 K. Spectra of self-supported zeolites in contact with increasing pressures of pure gas were recorded at equilibrium in the mid-infrared domain. Analysis of the evolution of the shape and location of vibrational bands of the zeolite as a function of the amount adsorbed allowed the observation of structural modifications of the adsorbent for the first time by infrared spectroscopy.

About the Role of the Bottleneck/Cork Interface on Oxygen Transfer.

The transfer of oxygen through a corked bottleneck was investigated using a manometric technique. First, the effect of cork compression on oxygen transfer was evaluated without considering the glass/cork interface. No significant effect of cork compression (at 23% strain, corresponding to the compression level of cork in a bottleneck for still wines) was noticeable on the effective diffusion coefficient of oxygen. The mean value of the effective diffusion coefficient is equal to 10(-8) m(2) s(-1), with a statistical distribution ranging from 10(-10) to 10(-7) m(2) s(-1), which is of the same order of magnitude as for the non-compressed cork. Then, oxygen transfer through cork compressed in a glass bottleneck was determined to assess the effect of the glass/cork interface. In the particular case of a gradient-imposed diffusion of oxygen through our model corked bottleneck system (dry cork without surface treatment; 200 and ∼0 hPa of oxygen on both sides of the sample), the mean effective diffusion coefficient is of 5 × 10(-7) m(2) s(-1), thus revealing the possible importance of the role of the glass/stopper interface in the oxygen transfer.

17-P- 11- Macroscopic and microscopic investigations of the interaction of a chloroalkene on a MFI zeolite

Publisher Summary This chapter discusses gravimetric, microcalorimetric, in situ X-ray diffraction (XRD), and in situ Fourier Transform infrared spectroscopy (FTIR) spectroscopic studies of the interaction of trichloroethene and tetrachloroethene on high siliceous zeolites, which are carried out for the further knowledge of the adsorption processes of large admolecules in the microporous network of MFI adsorbents. Trichloroethene gives classic type I isotherms, whereas tetrachloroethene gives stepped isotherms at 298 K. Structural changes of the adsorbent are observed for the adsorption of either trichloroethene or tetrachloroethene. A comparative analysis of macroscopic and microscopic data is also proposed and correlations are established between thermodynamic and structural data.