Título del libro: Transport Properties Of Polymeric Membranes
Título del capítulo: Activation Entropy for Diffusion of Gases Through Mixed Matrix Membranes
LUIS FELIPE DEL CASTILLO DAVILA;
Autores externos:
Idioma:
Inglés
Año de publicación:
2017
Palabras clave:
Crystallinity; Gas diffusion; Gas sorption; MMMs; MOFs; Permeability; Solubility
Resumen:
Diffusion in a polymeric membrane, according to the transition activated complex of Eyring, is described within the thermodynamic frame by two terms; one is the activation energy and the other the activation entropy. Both contributions describe to the membrane as barriers in series. Particularly, the activation energy is the high of such barriers, and is related to the enthalpic selectivity. It depends on the cohesive energy of the polymer and the kinetic radius of the particles. Whereas, the entropic selectivity is related to the necessary change of entropy to surmount the barrier, implying a change in the disorder at both side of the barrier or a change in the internal degree of freedom of the diffusive molecules, as in the example of the dioxide of carbon to go through the barriers of the membrane. The inclusion of organic and inorganic particles (fillers) with micro porosity, permeability resulting expresses the overlap of the two properties, the polymer and the filler (Maxwell model). Then the combined effect of the two phases as independents shows enthalpic and entropic selectivity. This case is recognized as the ideal one, since the real case the interaction filler-polymer creates different kind of trajectories around of dispersed phase, which presents new conditions of utility for the entropic selectivity. Now, we see several defined cases. 1.According to several previous works on the activation entropy in matrix mixed membranes and carbon molecular sieve membranes has been related to geometry of the trajectory and the increase of the energy of cohesion, specifically related to parameters of tortuosity and immovilization chain (matrix rigidization at the interfacial regions between the glass and the polymer).2.There is an additional effect on the diffusion selectivity produced by the activation entropy when gaseous particles found in his trajectory an abrupt change in their cross section. This happens when the particles pass through the windows of the dispersed phase to enter into their porous volume.3.Increases the amount of free volume (and the permeability), both in the interface around the dispersed phase and in the spaces available in inter crystalline meso porous of the dispersed phase. The Knudsen diffusion coefficient is modified by the tortuosity parameter and the final selectivity could be critical.4.The free volume could be reduced (and so permeability) around the dispersed phase by cause of clogged of the access channels into the dispersed phase by the polymeric chains. In this article we will discuss some cases of MMMs in recent publications to highlight the properties of the entropic selectivity. © 2018 Elsevier Inc. All rights reserved.
Entidades citadas de la UNAM:
ISBN:
9780128098851
Editorial:
Elsevier Nombre de la publicación:
Activation Entropy for Diffusion of Gases Through Mixed Matrix Membranes
Página inicial:
547
Página final:
572
