Modification of ceramic membranes

Lin, Y. S., K. J. dc Vries and A. J. Burggraaf. 1989. CVD modification of ceramic membranes simulation and preliminary results. J. de Phys. Coll, dc Phys., Proc. 7th Europ. Corf, on Chemical Vapor Deposition vol. C5, p, 861. 

With ceramic membranes (showing Knudsen diffusion) acting on e g. hydrogen in the presence of a hydrocarbon or of carbon dioxide, the theoretical separation ctor amounts to 4-6. For industrial processes, these values are too low [4]. Modification of ceramic membranes and supports by deposition of new materials improves the separation markedly. Wrth controlled modification of thin amorphous silica-layers on ceramics, membranes can be obtained showing sqraration values upto 150 for... 

J. Randon, H. de Lucena Lira and R. Paterson, Improved separations using surface modification of ceramic membranes, in Yi Hua Ma (Ed.), Proceedings of the Third International Conference on Inorganic Membranes, 10-14 July 1994, Worcester, USA. Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA, pp. 429-435. 

Dafinov, A., Garcia-Vails, R. and Font, J. 2002. Modification of ceramic membranes by aleohol adsorption. 196 69—77. 

Randon J., Julbe A., David P., Jaafari K., Elmaleh S. Computer simulation ofinorganic membrane morphology. J. Colloid Interface Sci. 1993 161 377-388 Randon J., Blanc P., Paterson R. Modification of ceramic membrane surfaces using phosphoric add and alkyl phosphonic acids and its effects on ultrafiltration of BSA protein. J. Membr. Sci. 1995 98 119-129... 

The smallest poie diameters of ceramic membranes that can be obtained consistently by the straight sol-gel process without any modification has been in the range of 2.5 to 3.0 nm. This minimum pore size obtainable is determined by the smallest size of the primary sol particles that can be crystallized and the consideration of the effect of subsequent calcination on the pore size. Stable, non-aggregated nuclei finer than S nm are very difficult to generate. To produce membranes via the sol-gel route that are smaller than 2.5-3.0 nm requires further modifications by such techniques as adsorption or precipitation in the pores as will be discussed in tk>n 3.4.1. 

R.S.A. de Lange, J.H.A. Hekkink, K. Keizer and A.J. Burggraff, Microporous sol-gel modified membranes for hydrogen separation. Key Engirt. Mater., 61 62 (1991) 77. R.J.R. Ulhorn, K. Keizer and A.J. Burggraff, Synthesis of ceramic membranes. Part II. Modification of thin alumina films reservoir method. J. Mater. Sci., 17 (1992). 

The advantages of ceramic UF and MF membranes discussed earher in the chapter are often offset by their low selectivity, which makes their use economically unfeasible for many applications. These membranes separate solutes from solvents primarily by site exclusion, and to a lesser extent, by interactions with the membrane surface. The selectivity of ceramic membranes can be improved by modification of the membrane surface either by polymer grafting or graft polymerisation. The latter has the advantage of providing a covalently bonded brush layer of high surface coverage with minimal difiusional limitations and steric hindrance effects. 

Chu, L.Y., Wang, S. and Chen, W.M. 2005. Surface modification of ceramic-supported poly-ethersulfone membranes hy interfacial polymerization for reduced membrane fouling. 

Chu et al. [70] demonstrated a simple and effective route for the hydrophilic surface modification of ceramic-supported PES membranes by synthesizing a polyfvinyl alcohol) (PVA)/polyamide (PA) composite thin sinface layer with an interfacial polymerization method (IP) method. The reaction of the interfadal polymerization is schematically shown in Figure 2.7. A prepared tubular ceramic-supported PES membrane (both ends sealed) was immersed in a terephthaloyl chloride solution in benzene and... 

Sol-gel techniques have been widely used to prepare ceramic or glass materials with controlled microstructures. Applications of the sol-gel method in fabrication of high-temperature fuel cells are steadily reported. Modification of electrodes, electrolytes or electrolyte/electrode interface of the fuel cell has been also performed to produce components with improved microstructures. Recently, the sol-gel method has expanded into inorganic-organic hybrid membranes for low-temperature fuel cells. This paper presents an overview concerning current applications of sol-gel techniques in fabrication of fuel cell components. 

Metal oxides, used for manufacturing of ceramic nanofiltration membranes, are intrinsically hydrophilic. This limits the use of these membranes to polar solvents filtration of nonpolar solvents (n-hexane, toluene, cyclohexane) usually yields zero fluxes. Attempts have been made to modify the pore structure by adding hydrophobic groups, for example, in a silane coupling reaction [38, 43]. This approach is similar to modifications of ultrafiltration and microfiltration membranes... 

In this work for the first time magnetron sputtering (technologically effective method) was used for the modification of the tubular a-alumina ceramic support of the composite Pd - membrane. This modification could be realized due to the choice of Ni as hydrogen permeable metal instead of y-Al203 layers. It allows to use total effective cross section of the surface porous structure of the support in high temperature process of hydrogen purification by Pd membrane. 

Tubular composite (X-AI2O3 -based supports for Pd-containing metal membrane have been developed. Their distinction consists in using metal nickel for the modification of the porous structure of ceramic supports. Nickel is analog of palladium in many respects it is also effective catalyst for molecular hydrogen... 

Van Praag, W., V. Zaspalis, K. Keizer, J.G. van Ommen, J.R. Ross and AJ. Burggraaf, 1989, Preparation, modification and micropoious stnicture of alumina and titania ceramic membrane systems, in Pioc. 1st Int Conf. Inorg. Membr., Montpellier, France, p.397. 

Recent research efforts brought about new and exciting developments in membrane technology, some with direct implications for the membrane filtration of beer. For example, Stopka et al. [21] reported flux enhancement in the microfiltration of a beer yeast suspension when using a ceramic membrane with a helically stamped surface. A relatively simple modification of the ceramic membrane surface resulted in modified hydrodynamic conditions and disturbance of the fouling layer. As compared with a regular, smooth ceramic membrane of the same nominal pore size, the stamped membrane leads to higher flux and lower power consumption per unit volume of permeate at the same velocity of the feed. 

---