A home-made magnetic device was built with permanent magnets for treating scaling waters. Its efficiency was evaluated by measuring the remaining ionic calcium at the output of the device by means of ...an ion selective electrode. The scaling power of the treated water was estimated through an electrochemical scaling test. Chroamperometric curves and chronoelectrogravimetric curves were plotted to obtain the scaling time and the nucleation time of the scale deposition. The variation of the efficiency of the magnetic treatment was studied when the length of treatment, the flow velocity of the scaling water in the device, the material of the pipe where the scaling water flowed were changed. An empirical relationship, which gives the value of the efficiency in function of the length of treatment and the flow velocity, was proposed. Possible mechanisms of action of the magnetic treatment were discussed.
Isotherms and differential enthalpies of adsorption are obtained for nitrogen at ambient temperature on monovalent (Li+, Na+, K+) and divalent (Ca2+, Ba2+, Sr2+, Mn2+) substituted X-faujasite systems ...by microcalorimetry measurements. These experimental data are compared with those obtained by combining grand canonical Monte Carlo simulations and newly derived force fields for describing the interactions between the extra-framework cations and the adsorbates obtained from a simple model based only on the intrinsic properties of the cations. It is the first time that such good qualitative agreement is reported between experiment and simulation for a series of both monovalent and divalent cations.
Molecular simulations have been employed to explore at the microscopic scale the adsorption of CO in two families of sodium exchanged faujasite, NaX and NaY. As a preliminary step, density functional ...theory calculations have been conducted to derive new sets of potential parameters for accurately describing the interactions between CO and the extra-framework cations present within the supercage that act as preferential adsorption sites for the guest molecules. Two different parametrizations have been considered to discriminate the Na+ sites, Na+ SII and Na+ SIII′, involved in the interactions with CO. On the basis of these forcefields, Grand Canonical Monte Carlo simulations were further realized to first predict the adsorption properties (isotherms and enthalpies) of these two types of faujasites up to high pressure. This was followed by a careful analysis of the microscopic mechanism in play along the whole adsorption process with a special emphasis on understanding the arrangements of CO in the vicinity of the Na+ whether they occupy SII or SIII′ sites. These findings were discussed in light of the enthalpy profile obtained as a function of the loading and a few experimental data available in the literature. Finally, complementary simulations were realized with mobile extra-framework cations upon CO adsorption. It was evidenced that Na+ SII can migrate toward SIII′ sites in NaY, while in NaX, there is no cation redistribution within the supercage due to a steric hindrance. Such cation dynamics were shown to not drastically affect the adsorption properties of both Faujasites; however, this is a critical prerequisite to allow CO to form a double type interaction with both Na+ SIII′ and Na+ SII via its C- and O-ends respectively, as predicted in cation-exchanged zeolites using quantum chemical calculations.
The adsorption of small molecules (CO2, CO, H2, CH4, and N2) in a small pore zirconium terephthalate MOF was explored by combining quantum and force-field-based molecular simulations and experiments. ...The Density Functional Theory strategy was first validated by a very good agreement between the predicted and the experimental spectroscopic (infrared, NMR) and structural features of the selected MOF. These quantum calculations further predicted the preferential adsorption sites and the strength of the host/guest interactions for all confined molecules. These conclusions were favorably compared to force-field-based Monte Carlo simulations and microcalorimetry measurements. The water stability of this hybrid porous solid was equally explored as well as the interaction between the MOF and a well-known gas pollutant, that is, H2S.
The self-diffusion properties of pure CH4 and its binary mixture with CO2 within NaY zeolite have been investigated by combining an experimental quasi-elastic neutron scattering (QENS) technique and ...classical molecular dynamics simulations. The QENS measurements carried out at 200 K led to an unexpected self-diffusivity profile for pure CH4 with the presence of a maximum for a loading of 32 CH4/unit cell, which was never observed before for the diffusion of apolar species in a zeolite system with large windows. Molecular dynamics simulations were performed using two distinct microscopic models for representing the CH4/NaY interactions. Depending on the model, we are able to fairly reproduce either the magnitude or the profile of the self-diffusivity. Further analysis allowed us to provide some molecular insight into the diffusion mechanism in play. The QENS measurements report only a slight decrease of the self-diffusivity of CH4 in the presence of CO2 when the CO2 loading increases. Molecular dynamics simulations successfully capture this experimental trend and suggest a plausible microscopic diffusion mechanism in the case of this binary mixture.
Molecular Dynamics simulations have been carried out in NaX and NaY Faujasite systems to deepen understanding of the cation rearrangement during the CO2 adsorption process suggested by our recent ...diffusivity measurements. This study is a major contribution since the rearangement of the cations in Faujasite, the most promising adsorbent for CO2 storage, can represent a significant breakthrough in understanding the adsorption and diffusion processes at the mircroscopic scale. For NaY, it has been shown that at low and intermediate loadings, SII cations can migrate toward the center of the supercage due to strong interactions with the adsorbates, followed by a hopping of SI‘cation from the sodalite cage into the supercage to fill the vacant SII site. The SI cations are only displaced at a higher loading, leading to cation de-trapping out of the double six rings into the vacant SI‘ sites. For NaX, the SIII‘ cations which occupy the most accessible adsorption sites move significantly upon coordination to the carbon dioxide molecules. The SI‘ and SII cations remain consistently located in their initial sites whatever the loading. Indeed, the most probable migration mechanism involves SIII‘ cation displacements into nearby vacant SIII‘ sites.
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