Kinetic Monte Carlo Modelling to Study Diffusion in Zeolite. Understanding the Impact of Dual Site Isotherm on the Loading Dependence of n-Hexane and n-Heptane Diffusivities in MFI Zeolite, as Revealed by QENS Experiments

ENERGIE:MATERIAUX+HJO:NLAInternational audienceThis study concerns the diffusion of single-component molecules in zeolites, characterised by an isotherm represented by a dual-site Langmuir model with a point of inflection. The systems investigated are n-hexane and n-heptane in MFI zeolite at 300 K. Experiments conducted using the Quasi-Elastic Neutron Scattering (QENS) technique have demonstrated that this inflection has an impact on the loading dependence of the transport Dt and corrected DC diffusion coefficients of these systems. The results of these experiments are described here. A Kinetic Monte Carlo study is then conducted, showing how the energy levels of the molecule adsorption sites in a zeolite affect the loading dependence of the diffusion coefficients of these molecules

Rigorous Multicomponent Reactive Separations Modelling : Complete Consideration of Reaction-Diffusion Phenomena

This paper gives the first step of the development of a rigorous multicomponent reactive separation model. Such a model is highly essential to further the optimization of acid gases removal plants (CO2 capture, gas treating, etc.) in terms of size and energy consumption, since chemical solvents are conventionally used.Firstly, two main modelling approaches are presented: the equilibrium-based and the rate-based approaches. Secondly, an extended rate-based model with rigorous modelling methodology for diffusion-reaction phenomena is proposed. The film theory and the generalized Maxwell-Stefan equations are used in order to characterize multicomponent interactions. The complete chain of chemical reactions is taken into account. The reactions can be kinetically controlled or at chemical equilibrium, and they are considered for both liquid film and liquid bulk. Thirdly, the method of numerical resolution is described. Coupling the generalized Maxwell-Stefan equations with chemical equilibrium equations leads to a highly non-linear Differential-Algebraic Equations system known as DAE index 3. The set of equations is discretized with finite-differences as its integration by Gear method is complex. The resulting algebraic system is resolved by the Newton- Raphson method. Finally, the present model and the associated methods of numerical resolution are validated for the example of esterification of methanol. This archetype non-electrolytic system permits an interesting analysis of reaction impact on mass transfer, especially near the phase interface. The numerical resolution of the model by Newton-Raphson method gives good results in terms of calculation time and convergence. The simulations show that the impact of reactions at chemical equilibrium and that of kinetically controlled reactions with high kinetics on mass transfer is relatively similar. Moreover, the Fick’s law is less adapted for multicomponent mixtures where some abnormalities such as counter-diffusion take place

Kinetic Monte Carlo study of binary diffusion in silicalite

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Kinetic Monte Carlo study of binary diffusion in silicalite

International audienceWe report a Kinetic Monte Carlo (KMC) study of the diffusion of linear n-hexane (nC6) and 2,2-dimethylbutane (22DMB) mixture in zeolite silicalite. We first investigated the loading dependences of single component self- and corrected diffusivities of nC6 at 300 K. Anisotropic transition rates are implemented to account for the distribution of the molecules within the zeolite framework. Repulsive guest-guest interactions are modeled using the parameter introduced by Reed and Ehrlich (Surf. Sci. 102:588–601, 1981). The results are in good agreement with recent experimental Quasi Elastic Neutron Scattering data of Jobic et al. (J. Phys. Chem. B 110:2195–2201, 2006), although the influence of the adsorption isotherm inflection is not reproduced. The binary diffusion study of nC6/22DMB mixtures was performed by implementing the nC6 transition rates used for the single component study while 22DMB molecules propagate via intersection-intersection hops. This KMC model allows for different saturation capacities and accounts for interactions between molecules by introducing f ij parameters. Results show the large impact of guest-guest interactions between nC6 and 22DMB on both self- and corrected diffusivities of the two components. Molecule-size effects are found to be predominant near 22DMB saturation capacity. Acceleration/deceleration effects already described in the literature are confirmed

Influence of Isotherm Inflection on the Loading Dependence of the Diffusivities of n-Hexane and n-Heptane in MFI Zeolite. Quasi-Elastic Neutron Scattering Experiments Supplemented by Molecular Simulations

Quasi-Elastic Neutron Scattering (QENS) experiments were carried out to determine (a) Fick diffusivity, D (b) self-diffusivity, D<SUB>self</SUB>, and (c) 1/Γ, the inverse of the thermodynamic correction factor, for n-hexane (nC6) and n-heptane (nC7) in MFI zeolite (all silica silicalite-1) at 300 κ for a variety of loadings. These experimental results are compared with configurational-bias Monte Carlo (CBMC) and molecular dynamics (MD) simulations of, respectively, the adsorption isotherms and diffusivities. For n-hexane, the CBMC simulated isotherm shows a slight inflection at a loading ϑ = 4 molecules per unit cell; this inflection manifests, also, in the loading dependence of 1/Γ, obtained from QENS. The trend in the loading dependence of the Fick D and D<SUB>self</SUB> of nC6 obtained from QENS matches the MD simulation results. For nC7 the CBMC simulated isotherm shows a strong inflection at a loading ϑ = 4 molecules per unit cell. At this loading ϑ = 4, 1/Γ tends to zero and there is a very good match between QENS and molecular simulations for the loading dependence of 1/Γ. Both MD simulations and QENS data on the Fick diffusivity shows a sharp maximum at a loading in the region of ϑ = 4. For both nC6 and nC7 the simulated values of diffusivity are about an order of magnitude higher than those determined from QENS

Dynamic modeling of a batch crystallization process: A stochastic approach for agglomeration and attrition process

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Transport and metabolism of xylem cytokinins during lateral bud release in decapitated chickpea (Cicer arietinum) seedlings

Although cytokinins (CKs) are widely thought to have a role in promoting shoot branching, there is little data supporting a causative or even a correlative relationship between endogenous CKs and timing of bud outgrowth. We previously showed that lateral bud CK content increased rapidly following shoot decapitation. However, it is not known whether roots are the source of this CK. Here, we have used shoot decapitation to instantaneously induce lateral bud release in chickpea seedlings. This treatment rapidly alters rate and direction of solvent and solute (including CK) trafficking, which may be a passive signalling mechanism central to initiation of lateral bud release. To evaluate changes in xylem transport, intact and decapitated plants were infiltrated with [H-3]zeatin riboside ([H-3]ZR), a water-soluble blue dye or [H-3]H2O by injection into the hypocotyl. All three tracers were recovered in virtually all parts of the shoot within I h of injection. In intact plants, solute accumulation in the lateral bud at node 1 was significantly less than in the adjacent stipule and nodal tissue. In decapitated plants, accumulation of [H-3]ZR and of blue dye in the same bud position was increased 3- to 10-fold relative to intact plants, whereas content of [H-3]H2O was greatly reduced indicating an increased solvent throughput. The stipule and cut stem, predicted to have high evapotranspiration rates, also showed increased solute content accompanied by enhanced depletion of [H-3]H2O. To assess whether metabolism modifies quantities of active CK reaching the buds, we followed the metabolic fate of [H-3]ZR injected at physiological concentrations. Within 1 h, 80-95% of [H-3]ZR was converted to other active CKs (mainly zeatin riboside-5'phosphate (ZRMP) and zeatin (Z)), other significant, but unconfirmed metabolites some of which may be active (O-acetylZR, O-acetylZRMP and a compound correlated with sites of high CK-concentrations) and inactive catabolites (adenosine, adenine, 5'AMP and water). Despite rapid metabolic degradation, the total active label, which was indicative of CK concentration in buds, increased rapidly following decapitation. It can be inferred that xylem sap CKs represent one source of active CKs appearing in lateral buds after shoot decapitation

Dating of modern music instrument combining the sharpest 14 C technology and independent expertise

International audienceFor dating modern music instruments dated between the 16 th and 19 th century, dendrochronology might not be carried out due to a too short tree-rings record and 14 C dating might a priori be ignored for historical periods as a 14 C physical measurement might result into several equiprobable age ranges. Several samplings and independent expertise are then required to make a well-considered choice between these intervals. Owing to the new generation of 14 C dating instruments, sampling without affecting the instrument integrity is now possible. The interdisciplinary framework allows combining any ante quem or post quem information on the age of music instruments. To illustrate this approach, we will draw on an ongoing project of modern music instruments gathering radiocarbon dating specialists and the museum curators. Our goal is to deepen the scientific knowledge about the origin and the long history of use and restoration of instruments kept at the Musée de la Musique. As an example, an Indian rudra-vina (E.997.24.1) was dated from the end of the 17 th century. Transcription of 14 C activity measured on two sub-samples yields four equiprobable calibrated date ranges. The comparison with a Govardhan's picturial representation of a similar rudra-vina allows to determine the most likely date range: [AD 1650-1683]. Likewise, a second example comes from a stringed Hindustani instrument named kinnari-vina (E.1444). It was supposedly dated from the 18 th century according to Musée's curators because of its organological features. The dating, based on 7 sub-samples, has brought to light a very likely restoration of the upper-nut whereas all other components are contemporaneous of the instrument manufacturing. The results obtained allow to reveal additions or changes (successive layers of history) since they emerged from the instrument factories. The multidisciplinary approach applied here is a benefit for establishing a "history" of use and restoration of music instruments with composite constitutions

Radiocarbon dating application to modern musical instruments: an interdisciplinary study

International audienceRelics dating: why not follow the example of dating of modern music instrument, combining the sharpest 14C technology and independent expertise?Dating historical relics partly meets the same issue than dating modern music instruments dated between the 16th and 19th century. For both woody relics and music instrument, dendrochronology might not be carried out due to a too short tree-rings record and 14C dating might a priori be ignored for historical periods as a 14C physical measurement might result into several equiprobable age ranges. Several samplings and independent expertise are then required to make a well-considered choice between these intervals. Owing to the new generation of 14C dating instruments, sampling without affecting the instrument or relics integrity is now possible. The interdisciplinary framework allows combining any ante quem or post quem information on the age of relics or music instruments. To illustrate this approach, we will draw on an on-going project of modern music instruments gathering radiocarbon dating specialists and the museum curators. Our goal is to deepen the scientific knowledge about the origin and the long history of use and restoration of instruments kept at the Musée de la musique. As an example, an Indian rudra-vina (E.997.24.1) was dated from the end of the 17th century. Transcription of 14C activity measured on two sub-samples yields four equiprobable calibrated date ranges. The comparison with a Govardhan’s picturial representation of a similar rudra-vina allows to determine the most likely date range: [AD 1650-1683]. Likewise, a second example comes from a stringed Hindustani instrument named kinnari-veena. It was supposedly dated from the 18th century according to Musée's curators because of its organological features. The dating, based on 7 sub-samples, has brought to light a very likely restoration of the upper-nut whereas all other components are contemporaneous of the instrument manufacturing. The results obtained allow to reveal additions or changes (successive layers of history) since they emerged from the instrument factories. The relics made of wood, bones or textile can also take benefit of such a multidisciplinary approach already applied on music instruments with composite constitutions