Ultrafiltration membranes properties

Traditionally, ultrafilters have been manufactured from cellulose acetate or cellulose nitrate. Several other materials, such as polyvinyl chloride and polycarbonate, are now also used in membrane manufacture. Such plastic-type membranes exhibit enhanced chemical and physical stability when compared with cellulose-based ultrafiltration membranes. An important prerequisite in manufacturing ultrafilters is that the material utilized exhibits low protein adsorptive properties. 

The retention properties of ultrafiltration membranes are expressed as Molecular Weight Cutoff (MWCO). This value refers to the approximate molecular weight (MW) of a dilute globular solute (i.e., a typical protein) which is 90% retained by the membrane. However, a molecule s shape can have a direct effect on its retention by a membrane. For example, linear molecules like DNA may find their way through pores that will retain a globular species of the same molecular weight. 

Membrane Properties. The performance range of ammonia-modified membranes in low pressure operation is indicated in Figure 6 along with the performance of the reference membrane (I, reference membrane IV, ammonia-modified membrane). The lower boundary of the performance range refers to a solvent-to-polymer ratio of 3, the upper boundary to a ratio of 4. While the salt rejection towards univalent ions of the ammonia-modified membrane is limited to below 80 %, the maximum low pressure flux is over 15 m /m d (approaching 400 gfd) at a sodium chloride rejection of the order of 10 %. This membrane thus exhibits the flux capability of an ultrafiltration membrane while retaining the features of reverse osmosis membranes, viz. asymmetry and pressure resistance. 

Jeon, Y. J., Byun, H. G., and Kim, S. K. (1999). Improvement of functional properties of cod frame protein hydrolysates using ultrafiltration membranes. Process Biochem. 35,471-478. 

Among the numerous approaches studied so far to minimize such phenomena in ED, it is worth citing pretreatment of the feed solution by coagulation (De Korosy et al., 1970) or microfiltration (MF) or ultrafiltration membrane processing (Ferrarini, 2001 Lewandowski et al., 1999 Pinacci et al., 2004), turbulence in the compartments, optimization of the process conditions, as well as modification of the membrane properties (Grebenyuk et al., 1998). However, all these methods are partially effective and hydraulic or chemical cleaning-in-place (CIP) is still needed today, thus... 

The goal of most of the early work on reverse osmosis was to produce desalination membranes with sodium chloride rejections greater than 98 %. More recently membranes with lower sodium chloride rejections but much higher water permeabilities have been produced. These membranes, which fall into a transition region between pure reverse osmosis membranes and pure ultrafiltration membranes, are called loose reverse osmosis, low-pressure reverse osmosis, or more commonly, nanofiltration membranes. Typically, nanofiltration membranes have sodium chloride rejections between 20 and 80 % and molecular weight cutoffs for dissolved organic solutes of 200-1000 dalton. These properties are intermediate between reverse osmosis membranes with a salt rejection of more than 90 % and molecular weight cut-off of less than 50 and ultrafiltration membranes with a salt rejection of less than 5 %. 

Wang, Y.Q. et al. (2005) Remarkable reduction of irreversible fouling and improvement of the permeation properties of poly(ether sulfone) ultrafiltration membranes by blending with pluronic F127. Langmuir, 21, 11856-11862. 

In this review dealing with recent advances in membrane science, the term membrane" will be used to indicate any medium which acts as a barrier to transport into or out of a region, provides selective transfer of one species over another or regelates the transport of a material to its environment at a controlled rate. In addition to the common usage of the word membrane" to indicate a dense polymer film, the above definition includes a variety of interesting cases such as highly porous ultrafiltration membranes and hydrophobic liquid membranes with selectivity properties which can be tailored by incorporation of materials which selectively complex with one of the species to be processed. The important topics of controlled release of chemicals from polymeric devices and removal of volatile monomers from addition polymers such as poly (vinyl chloride and poly (acrylonitrile are also treated here. 

Cherkasov A.N., Tsareva S.V., and Polotsky A.E., Selective properties of ultrafiltration membranes from the standpoint of concentration polarization and adsorption phenomena. Journal Membrane Science 104 1995 157-165. 

Ultrafiltration relies on the ability of a membrane to act as a selective barrier. One of the major properties of an ultrafiltration membrane is its ability to act as a sieve for macromolecular substances. The transmission of a particular solute through an ultrafiltration membrane can be expressed in several ways, a commonly used way being in terms of sieving coefficients. The intrinsic or real sieving coefficient (5j) is defined as... 

Chmielewski, A.G. and Harasimowicz, M., Influence of gamma and electron irradiation on transport properties of ultrafiltration membranes, Nukleonika, 37, 4, 61, 1992. 

D. B. Mosqueda-Jimenez, R. M. Narbaitz, T. Matsuura, G. Chowdhury, G. Pleizier, and J. P. Santerre, Influence of processing conditions on the properties of ultrafiltration membranes. Journal of Membrane Science (in press) (2004). 

Cheryan, M. Membrane properties. In Ultrafiltration and Microfiltration Handbook Technomic Publishing Company Lancaster, Pennsylvania, 1998 89-110. 

Following a brief review of the development of dynamic membranes and an overview of the current state of the art, Spencer (10) discusses dynamic polyblend membranes. In particular, he looks at the Influence that polymer selection and membrane preparation procedures have on membrane performance. Dynamic membranes composed of a poly(acrylic acid)/basic polyamine blend deposited on a ZOSS (hydrous zirconium oxide on stainless steel) ultrafiltration membrane are discussed. Their hyperfiltration or reverse osmosis properties are compared to the more traditional ZOPA (zirconium oxide plus poly(acrylic acid)) membrane. 

Commercial dynamic ultrafiltration membranes are produced by the Gaston County Dyeing Machine Co. and by CARRE, Inc. The former uses porous carbon tubes and the latter porous metal tubes as the membrane substrate and containment material. The ultrafiltration properties of the CARRE, Inc, ZOSS ultrafilter, hydrous zirconium oxide on porous stainless steel tubes, are provided in Table I as an example of a dynamic ultrafiltration membrane. 

Szymezyk, A. et al.. Characterisation of surface properties of ceramic ultrafiltration membranes by studying diffusion-driven transport and streaming potential. Desalination, 119, 303, 1998. 

---