Nanofiltration with ceramic membranes

12 — TRANSPORT AND FOULING PHENOMENA DM LIQUID PHASE SEPARATION 

The main characteristics of nanofiltration membranes made of oxide ceramics is that they exhibit a microporous structure with charged pore walls depending on pH and ionic strength of feed solutions. Three main cases are distinguished in the discussion of mechanisms involved in permeation and separation processes using microporous ceramic nanofilters  

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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... 

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. 

Salt rejection of a single electrolyte by a nanofiltration membrane in the absence of Donnan contribution can be described by Eqs. (12.9) and (12.10) according to the work of Spiegler and Kedem [57]. With ceramic nanofilters the Donnan contribution has to be taken into account due to the amphoteric... 

Both calculations by Perry and Schirg have been performed to describe and to predict the rejection characteristics of organic nanofiltration membranes when ionic and charged molecular solute mixtures are used in the feed solution. Recently experiments were carried out with ceramic nanofilters [67] which showed that similar properties can be obtained. As an example, results concerning the rejection of a dye/electrolyte mixture at pH = 9 through a zirconia nanofilter are reported in Table 12.5. 

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... 

As the newest development of the liquid filtration family, nanofiltration (NF) is capable of retaining small molecules from 200 to 1000 Da, and multivalent ions. The main current applications of NF polymeric membranes are dealing with the production of drinking and process water, the sulphate removal of seawater or the desalination of cheese whey. Ceramic nanofilters were... 

An inorganic membrane can be described as an asymmetric porous ceramic formed by a macroporous support with successive thin layers deposited on it. The support provides mechanical resistance to the medium. The successive layers are active in microfiltration (MF), ultrafiltration (UF) or nanofiltration (NF), depending on their pore diameters. 

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