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SCI colloid and surface chemistry group meeting: Transport of permanent and condensable gases in zeolite membranes
Author(s) -
Keiser Klaas,
Vroon Zerger A. E. P.,
Verweij Henk,
Burggraaf Anthonie J.
Publication year - 1996
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/(sici)1097-4660(199604)65:4<389::aid-jctb424>3.0.co;2-w
Subject(s) - chemical technology , chemical laboratory , chemistry , engineering , polymer science , biochemical engineering , chemical safety
389 methods like permeability or liquid displacement can be successfully applied to both inorganic and polymeric membranes. The main difference with static methods is that only active pores are described with these two last methods. Once the porous structure of the membrane has been properly characterised, appropriate phenomenological equations can be applied to describe transport phenomena. Generally the driving force used for liquid filtration is obtained by a pressure gradient A p applied between feed and permeate faces of the membrane. According to linear non-equilibrium thermodynamics, it has been traditional to characterise the permeability of a porous membrane with respect to transmembrane convective and diffusive transport of a neutral solute solution in terms of four parameters: hydraulic per-meability L , , diffusive permeability w and two reflective coefficients od and of respectively for solvent and solute. The hydraulic permeability is a measure of the ability to transport a volume of liquid under the action of the pressure difference across the membrane. This property is expressed as the proportionality coefficient between the volume flux J , and the transmembrane pressure Ap, when the solute is absent: L, = J,/Ap for pure solvent This definition also applies in the presence of a solute when the membrane is freely permeable to the solute or when the rejected entities in the feeding solution do not induce an osmotic phenomenon (micro-and ultrafiltration). In other cases, in particular for micro-porous membranes (nanofiltration), the flux is affected by osmotic pressure differences across the membrane. The volumetric flux expression for a solution generalises from the previous equation: J , = L,(Ap-od A n) in which A l l is the osmotic pressure difference at the membrane/solution interface due to the solute and bd is the Staverman osmotic reflexion coefficient. The diffusive permeability w characterises the trans-missibility of the membrane for the solute when the volumetric flux is constrained to be zero: w = J J A n for J , = 0 in which J , is the transmembrane molar flux for the solute. In general, solute transport by both convection and diffusion occurs and the two contributions are assumed to be additive, giving the general equation for transmembrane solute flux: J, = (1-a,)J, C + CDRT dc/dx in which R T dcldx = A l l (van't Hoff law), C is the average solute concentration on both sides of the membrane and of is the Staverman filtration …