Nanofiltration ceramic membranes

Tsuru, T., Hironaka, D., Yoshioka, T., and Asaeda, M. (2003). Titania membranes for liquid phase separation effect of surface charge on flux. Sep. Purif. Technol. 25(2001) 307-314. Soria R., and Cominottim, S. (1996). Nanofiltration ceramic membranes, Proceedings of Fourth International Conference on Inorganic Membranes, pp. 194-197. 

Similar trends are developing for ceramic membranes applied in pervaporation and nanofiltration, although much slower because ceramic pervaporation and nanofiltration membranes are still sparsely available more experimental observations and experience with applications are needed in this field. Promising results were obtained by Sekulic et al. [61] for titania membranes that can be used in pervaporation as well as nanofiltration. 

We reported our recent developed membranes called carbon whisker membrane (CWM) and c on-coated coamic membrane. The CWM performed a better permeant flux in the filtration process in comparison with the membrane without whiskers. Also, CWMs have a self-cleaning function which can increase the separation efficiency during die filtration and increase die lift-time of the membrane. The carbon-coated ceramic membranes with various pore sizes can be made for the puipose of nanofiltration. 

Retention of ionic species modifies ionic concentrations in the feed and permeate liquids in such a way that osmotic pressure or electroosmotic phenomena cannot be neglected in mass transfer mechanisms. The reflexion coefficient, tr, in Equations 6.4 and 6.5 represents, respectively, the part of osmotic pressure force in the solvent flux and the diffusive part in solute transport through the membrane. One can see that when a is close or equal to zero the convective flux in the pores is dominant and mostly participates to solute transport in the membrane. On the contrary when diffusion phenomena are involved in species transport through the membrane, which means that the transmembrane pressure is exerted across an almost dense stmcture. Low UF and NF ceramic membranes stand in the former case due to their relatively high porous volume and pore sizes in the nanometer range. Recendy, relevant results have been published concerning the use of a computer simulation program able to predict solute retention and flux for ceramic and polymer nanofiltration membranes [21]. 

Lefebvre X, Palmeri J, Sandeaux J, Sandeaux R, David P, Maleyre B, Guizard C, Amblard P, Diaz J-F, and Lamaze B. Nanofiltration modelling A comparative study of the salt filtration performance of a charged ceramic membrane and an organic nanofilter using the computer simulation program NANOFLUX. Sep. Purif. Technol. 2003 32(1-3) 117-126. 

The formation of ceramic membranes for microfiltration, ultrafiltration or nanofiltration by association of various granular layers is now a common procedure [10]. Each layer is characterized by its thickness, h, its porosity, 8, and its mean pore diameter, dp. These parameters are controlled by the particle size, d, and the synthesis method. Each layer induces a resistance which may be predicted through the classical Carman-Kozeny model ... 

Fig. 12.12. Influence of zeta-potential (Stem-layer thickness 1) and Streaming-potential (electrokinematic flow) on ion rejection and volume flux for porous ceramic membranes exhibiting negatively charged pore walls. Cases of micropores (nanofiltration), mesopores (ultrafiltration) and macropores...

As a general conclusion to this part dedicated to nanofiltration with ceramic membranes one can assume that the general behaviour of these membranes can be assimilated to the behaviour of electrically charged organic nanofiltration membranes. However some specificities exist with ceramic nanofilters due to a sintered metal oxide grains derived porous structure and an amphoteric character... 

This chapter focuses on the chemical processing of ceramic membranes, which has to date constituted the major part of inorganic membrane development. Before going further into the ceramic aspect, it is important to understand the requirements for ceramic membrane materials in terms of porous structure, chemical composition, and shape. In separation technologies based on permselective membranes, the difference in filtered species ranges from micrometer-sized particles to nanometer-sized species, such as molecular solutes or gas molecules. One can see that the connected porosity of the membrane must be adapted to the class of products to be separated. For this reason, ceramic membrane manufacture is concerned with macropores above 0.1 pm in diameter for microfiltration, mesopores ranging from 0.1 pm to 2 nm for ultrafiltration, and nanopores less than 2 nm in diameter for nanofiltration, per-vaporation, or gas separation. Dense membranes are also of interest for gas... 

Recently much attention has been paid to ceramic membranes exhibiting a nanoporous structure with the aim of new membrane processes for the nanofiltration of liquids [26], pervaporation [27], gas separation [27,28], or catalysis... 

---