Membranes material selection

Application Typical membrane material Selectivity (a) Average pressure-normalized flux [10-6 cm3(STP)/ cm2 s cmHg] Module design commonly used... 

Koros WJ and Heliums MW. Gas separation membrane material selection criteria Differences for weakly and strongly interacting feed components. Fluid Phase Equilibria 1989 53 339-354. 

Pereira CC, Rufino JRM, Habert AC, Noberga R, Cabral LMC, and Borges CP. Aroma compounds recovery of tropical fruit juice by pervaporation Membrane material selection and process evaluation. J. Food Eng. 2005 66(l) 77-87. 

A simple yet valuable criterion for candidate membrane material selection is the characteristic membrane thickness [41 ]. In the theory, the transport equations for diffusion in the solid, and for the surface exchange are linearized. It should therefore strictly be used when small Po -gradients are imposed across the membrane. In the next section, methods for measuring are briefly discussed. 

In the past, membrane material selection for gas separations (2 ) and liquid separations has often followed either an Edlsonlan or a common sense approach. For example, almost every polymer that can be formed Into a film has been characterized In terms of gas permeability (at least for a few common gases). In this volume, Chern et al. ( ) and Lloyd and Meluch W discuss membrane material selection In terms of physicochemical Interactions for gas mixture separations and liquid mixture separations, respectively. Hoehn (5 ) presents similar arguments for membrane material selection In general. In comparison to the wide variety of polymers investigated... 

Material Characterization and Evaluation. PhysIcochemlcal considerations can be useful in membrane material selection. However, it would be beneficial if one could experimentally verify that the proper choice has been made prior to undertaking the often difficult tasks of membrane preparation and characterization. In addition, it is frequently beneficial to have fully characterized the polymer prior to forming the membrane. 

Physicochemical Interactions between permeating molecules and the macromolecules which comprise the membrane structure are considered. Dispersive, polar and hydrogen-bonding Interactions are used to establish an Index which can be useful In membrane material selection. A number of material characterization and evaluation procedures are outlined. 

In this section, the physicochemical effects mentioned above are discussed In terms of how they Influence permeation, how the permeant and membrane material could be characterized in terms of these effects and how these Ideas can be used to assist In membrane material selection. 

Summary of Physicochemical Parameters. In the previous section steric parameters 4 . and were introduced to describe the effective size of solution components and the average size of the transport corridor, respectively. A variety of quantities that could be used to represent

dense membranes and the skin layer of reverse osmosis membranes in which the transport corridors are beyond the resolution capabilities of modern instruments and may be dynamic in nature. Therefore, any discussion of membrane material selection based on steric considerations must be qualitative. 

In pervaporatlon, reverse osmosis, ultrafiltration and to a lesser extent microfiltration, both steric and chemical factors Influence permeation and separation. Thus, proper membrane material selection la Important. While the physical structure of the membrane is in large part a function of membrane preparation procedures, the chemical nature and, to some degree, the physical properties of the membrane are dependent upon the chemical nature of the membrane material. Thus, membrane material selection based on the chemical nature of the polymer and the solution components to be separated is feasible. 

The solubility parameter has found previous use in membrane science. Casting solution components and composition have been selected using the Hansen solubility parameters (68-71). The total Hansen solubility parameter, which is equivalent to the Hildebrand parameter (.72), has been used to explain permeation and separation in reverse osmosis (23). Hansen s partial parameters have also been used to explain permeation and separation in pervaporatlon (61). The findings of these studies (61,73) plus those reported elsewhere in this volume (74) do lend credence to the use of 6, 6, and 6, for membrane material selection. 

Equation I provides a basis for membrane material selection. More precisely, the ratio can be used as a measure of... 

It must be re-emphaslzed at this point that the solubility parameter and Its use for quantifying physicochemical Interactions Is based on enthalplc considerations only entropic considerations are neglected. Consequently, while the Ideas outlined In this section provide a basis for membrane material selection (or at least for narrowing the number of possible choices), prediction of permeation and rejection remains elusive until the ability to predict effective transport corridor size 4 Is more firmly established. At that time the differences - 4, and ik, - i > can be used In conjunction with A and A for meiftrane Mterral... 

In actual fact, the membrane material selection process Is often not sophisticated. Merely the availability of a material capable of being formed into a dense or porous film or hollow fiber has stimulated membrane research efforts. 

Membrane material selection - Does a material exist with suitable permeabihty and selectivity to separate the components involved ... 

Membrane form - Can the membrane material selected be formed or appHed into a fihn or hollow-fiber form suited to the application ... 

Membrane material selection is dependent upon the mode of therapy employed. Convective therapies such as hemofiltration require a high hydraulic permeability and a large pore size, which might permit large molecules such as cytokines to pass through the fiber wall. Synthetic membranes are well suited for this role and are desired for most continuous, convective techniques (Jones, 1998). 

System Membrane Material Selectivity Flux (Irit/m hr) Ref... 

Elimelech 2004 Religa et al. 2013 Simon et al. 2013). However, the deterioration of membrane structures due to the acidic or alkaline solution can greatly shorten the membrane lifespan. The ability of the polymeric membrane to withstand an extreme pH condition will definitely determine the life expectancy of the membrane in certain applications. In addition, fouling control of polymeric membranes, through either operating condition adjustment or membrane material selection, is important in order for the wider employment of NF processes to become feasible. 

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