Search results for "Mass Transfer"
showing 10 items of 171 documents
Transport coefficients of n-butane into and through the surface of silicalite-1 from non-equilibrium molecular dynamics study
2009
We have studied coupled heat and mass transfer of n-butane through a membrane of silicalite-1. A description of the surface was given using non-equilibrium thermodynamics, and transport coefficients were determined. Three independent coefficients were found for the whole surface: the resistance to heat transfer, the coupling coefficient and the resistance to mass transfer. These coefficients were defined in stationary state. All resistances are significant, and show that the surface acts as a barrier to transport. A new scheme was devised to find the enthalpy of adsorption, from two particular coupling coefficients, namely the measurable heats of transfer. The method yields the enthalpy of …
Transfer coefficients for the liquid–vapor interface of a two-component mixture
2011
Abstract We present the excess entropy production for heat and mass transport across an interface of a non-ideal two-component mixture, using as interface variables the excess densities proposed by Gibbs. With the help of these variables we define the interface as an autonomous system in local equilibrium and study its transport properties. The entropy production determines the conjugate fluxes and forces, and equivalent forms are given. The forms contain finite differences of intensive variables into and across the surface as driving forces. These expressions for the fluxes serve as boundary conditions for integration across heterogeneous systems that are far from global equilibrium. The r…
Transfer of Water and Active Molecules at the Interfaces in Complex Food Systems: Theoretical and Practical Aspects
2011
Abstract During processing, storage and consumption, mass transfer of various molecules (water, gases, flavour compounds or other solutes) occur between the different phases in complex food products, and/or also between the complex food and its surroundings. These mass transfers can lead to physical and/or chemical changes and thus induce food quality modifications. The objective of this presentation is to better understand the behaviour of small molecules at the interfaces, especially in model heterogeneous food systems. Different techniques have been developed to characterize their properties and their impact on the mass transfers. Particularly, techniques such as rotative diffusion cell …
Convective mass transfer to partially recessed and porous electrodes
2003
Abstract The diffusional problem of a rotating porous electrode has been analysed based on the mass transfer equations for a partially blocked electrode. It is shown that the porous geometry leads to a dependence of the current on rotation rate identical to that corresponding to a coupled diffusion-activated electron transfer mechanism. The apparent rate constant, however, is related only to the geometry of the porous surface. It is shown that the characteristic diffusional length corresponds to the pore dimension modified by a term including the transition from linear to spherical diffusional geometry at the pore entrance. The theory is compared with experimental results for the reduction …
Abatement of Acid Orange 7 in macro and micro reactors. Effect of the electrocatalytic route
2014
Abstract The electrochemical treatment of aqueous solutions contaminated by Acid Orange 7 (AO7) was widely studied with the main objective to evaluate as the electrocatalytic route affects the performances of the degradation process in macro and microfluidic cells. Direct anodic oxidation (EO), electro-Fenton (EF), electro-generation of active chlorine (IOAC) and coupled processes were investigated in macro and microfluidic reactors in order to select more effective conditions for the treatment of such compound. The effect of numerous operative parameters (such as nature of the electrode materials, coupling of processes, flow rate, current density and inter-electrode distance) on the perfor…
Supported liquid membrane extraction of glyphosate metabolites
2001
Use of the supported liquid membrane (SLM) technique for (aminomethyl)phosphonic acid (AMPA) extraction is presented. For the extraction of this analyte a suitable SLM system involves a liquid membrane containing Aliquat 336 – a cationic carrier that facilitates AMPA transport. The extraction of this compound, as in the case of glyphosate, is dependent on the donor phase pH and the concentration and type of counter-ion in the acceptor phase, although some differences are also observed. In both cases the transport mechanism is counter-coupled transport in which the driving force of mass transport over the membrane is created by the gradient of chloride anions from the acceptor to donor phase.
Chromatographic Efficiency in Micellar Liquid Chromatography: Should it Be Still a Topic of Concern?
2013
Micellar liquid chromatography (MLC) was first proposed as an attractive alternative to avoid the use of organic solvents. It was soon apparent that pure micellar solutions yield poor efficiencies. This problem was remediated by the addition of a small amount of an organic solvent. However, the general opinion of the poor peak shape has prevailed as a handicap for MLC, in spite of the fact that the hybrid mode often offers similar or even improved efficiencies (for basic compounds) relative to that attained in the hydro-organic mode. Only the efficiencies for apolar non-ionizable compounds are still clearly inferior. This work describes the type of interactions and polarity changes with org…
Novel general expressions that describe the behavior of the height equivalent of a theoretical plate in chromatographic systems involving electricall…
2002
Novel general expressions are constructed and presented that describe the behavior of the height equivalent of a theoretical plate (plate height), H, as a function of the linear velocity, Vx, along the axis, x, of the column and the kinetic parameters that characterize the mass transfer and adsorption mechanisms in chromatographic columns. Open tube capillaries as well as columns packed with either non-porous or porous particles are studied. The porous particles could have unimodal or bimodal pore-size distributions and intraparticle convective fluid flow and pore diffusion are considered. The expressions for the plate height, H, presented in this work could be applicable to high-performanc…
A theoretical plate model accounting for slow kinetics in chromatographic elution.
2011
The chromatographic elution has been studied from different perspectives. However, in spite of the simplicity and evident deficiencies of the plate model proposed by Martin and Synge, it has served as a basis for the characterization of columns up-to-date. This approach envisions the chromatographic column as an arbitrary number of theoretical plates, each of them consisting of identical repeating portions of mobile phase and stationary phase. Solutes partition between both phases, reaching the equilibrium. Mobile phase transference between the theoretical plates is assumed to be infinitesimally stepwise (or continuous), giving rise to the mixing of the solutions in adjacent plates. This yi…
Comparative study of degassing membrane modules for the removal of methane from Expanded Granular Sludge Bed anaerobic reactor effluent
2016
Abstract The feasibility of an emergent technology for in situ removal/recovery of methane from the effluent of an Expanded Granular Sludge Bed (EGSB) anaerobic reactor has been studied. For this purpose, the performances of two commercial hollow fibre degassing contactors with different membrane materials – microporous (polypropylene, PP) and non-porous (polydimethylsiloxane, PDMS) – were compared. The influence of water fluxes (Q L /A membrane ranging from 22.6 to 377.4 L h −1 m −2 ), vacuum pressure (140–800 mbar), sweep gas fluxes (Q N2 /A membrane ranging from 0.14 × 10 3 to 4.44 × 10 3 L h −1 m −2 ), and mode of operation (liquid flowing in the lumen side or the shell side) was stu…