Ultrafiltration membranes pore volume distribution

Broens, Bargeman and Smolders( ) reported on the use of nitrogen sorption/desorption method for studying pore volume distributions in ultrafiltration membranes. The pore volume distributions were calculated for a cylindrical capillary model. More recent results from the same laboratory are published in this volume ( ). In our view, applicability of cylindrical pore models for asymmetric membranes should be verified, rather than assumed. This can be done, for example, by analysis of both branches of the sorption isotherm. For a reasonable model choice, the two pore volume distributions should be in substantial agreement. 

Zeman L, Tkacik G (1985) Pore volume distribution in ultrafiltration membranes. In Lloyd DR (ed) Materials science of synthetic membranes. ACS Symposium Series 269. American Chemical... 

In the presence of solutes with small molecular weights, concentration polarization is likely to occur but with much less effect than in the case of ultrafiltration as explained in Section 12.2.1. A theoretical model concerning separation of sucrose and raffinose by ultrafiltration membranes has been proposed by Baker et al. [53] which assumes transport of solvent and solute exclusively through pores. This model can apply to ceramic nanofilters as they exhibit a porous structure with a pore size distribution. The retention characteristics of a given membrane for a given solute is basically determined by its pore-size distribution. The partial volume flux jy through the pores which show no rejection to the solute can be expressed as a fraction of the total volume flux fy. 

Figure I - 20 gives the cumulative pore volume and the pore size distribution for a PPO poly(phenylene oxide) ultrafiltration membrane determined by thermoporometry [12]. Figure I - 21 gives the pore size distribution of a ceramic membrane determined by two methods gas adsorption-desorption and thermoporometry [13]. Both curves (and hence both methods) are in good agreement with each other. Similar results were found by Cuperus for Y-aJumina membranes [14].

Fig. 25. Reverse osmosis, ultrafiltration, microfiltration, and conventional filtration are related processes differing principally in the average pore diameter of the membrane filter. Reverse osmosis membranes are so dense that discrete pores do not exist transport occurs via statistically distributed free volume areas. The relative size of different solutes removed by each class of membrane is illustrated in this schematic.

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