Porous ceramic membranes preparation

III. BASIC PRINCIPLES IN POROUS CERAMIC MEMBRANE PREPARATION... 

Vercauteren S, Keizer K, Vansant EF, Luyten J, Leysen R. Porous ceramic membranes preparation, transport properties and applications. J Porous Mater. 1998 5 241-58. 

The thickness of porous ceramic membranes prepared in this manner is typically in the range of a few millimetres (Larbot, 1996), although thinner membranes have been realised (Sahibzada e/a/., 2000).Tape casting is a high volume production technique for fiat sheet membranes and is employed on both a research and commercial scale. 

In this case study, a zirconia-alumina membrane has been developed using the sol-gel technique with and without support.6-7 The porous ceramic was prepared to fabricate the membrane support. A thin film of aluminum and zirconium were formed on the porous ceramic support. Unsupported membrane was also prepared. The unsupported membrane was not strong enough to hold a high-pressure gradient it was very fragile and not useful... 

Hollow glass microbeads Porous ceramic membranes Microbeads coated by Ti02 particles Porous ceramic Ti02 and ZnO membranes prepared by sol-gel technique... 

The in situ membrane growth technique cannot be applied using the zeolite-based ceramic porous membrane as support, under hydrothermal conditions in a solution containing sodium hydroxide. The high pH conditions will cause membrane amorphization and lead to final dissolution. Therefore, we tried to synthesize an aluminophosphate zeolite such as AlP04-5 [105] over a zeolite porous ceramic membrane. For the synthesis of the AlP04-5-zeolite-based porous membrane composite, the in situ membrane growth technique [7,13,22] was chosen. Then, the support, that is, the zeolite-based porous ceramic membrane, was placed in contact with the synthesis mixture and, subsequently, subjected to a hydrothermal synthesis process [18]. The batch preparation was as follows [106] ... 

Different ways of preparing high performance porous ceramic membranes have been developed [13, 14], but most of the membranes used in CMRs are obtained via sol-gel processes [13-15, 23—25]. 

Xomeritakis G. and Lin Y.S., Chemical vapor deposition of solid oxides in porous media for ceramic membrane preparation. Comparison of experimental results with semianalytical solutions, Ind. Eng. Chem. Res, 55 2607 (1994). 

Organic or inorganic entities as well as polymer particles can also be used as template agents in the preparation of porous ceramic membranes following either the polymeric or the colloidal sol-gel route. The strategy to control microstructure in porous material is illustrated in Fig. 7.13. The template agents are trapped during matrix formation and eliminated in a second step with the aim to define the pore size in the final material. 

The porous ceramic membrane can be used to either separate biologically reacting material in reactors, or carry catalysts, microbes or enzymes to influence the desired reactions. An overview of the Japanese efforts for the establishment of membrane reactors in the "Aqua Renaissance 90 Project" are summarised by Kimura [95] a very recent review was written by Zaman and Chakma [96]. The preparation of microporous membranes (pore diameters smaller than 2 nm) for the application in membrane reactors is described by Keizer et al. [97] and Julbe et al. [98], however without detailing the membrane reactor itself. 

Porous metal membranes are commercially available in stainless steel and some other alloys (e.g.. Inconel, Hastelloy) and they are characterized by a macroporous structure. On the other hand, porous ceramic membranes can be found commercially in various oxides and combination of oxides (e.g., Al203,li02,Zr02, Si02) and pore size families in the mesopore and macropore ranges (e.g., from 1 nm to several microns). Most of the literature studies on three-phase catalytic membrane reactors have been carried out by developing catalytic ceramic membranes. The deposition techniques for the preparation of catalytic ceramic membranes involve methods widely used for the preparation of traditional supported catalysts (Pinna, 1998), and methods specifically developed for the preparation of structured catalysts (Cybulski and Moulijn, 2006). Other methods to introduce a catalytic species on a porous support include the chemical vapour deposition and physical vapour deposition (Daub et al, 2001). The catalyst deposition method has a strong influence on the catalytic membrane reactor performance. 

Porous ceramic membranes have been reviewed from the viewpoint of membrane preparation methods and applications for separation. These new classes of porous ceramic membranes hold considerable promise in applications such as separation at high temperatures. A membrane reaction where separation and reaction is combined in one system, will be realized using porous ceramic membranes, since most chemical reactions occur at high temperature where polymeric membranes cannot be applied. The preparation of porous ceramic membranes, which need to have uniform pore sizes, to be as thin as possible without defects, seems to represent a different strategy from conventional preparation of ceramic bulk bodies. This new research field of ceramic processing will contribute much to the development of membrane science and technology. 

Mosleh M. Preparation of micro porous ceramic membranes by flame generated aerosol nano-particles [dissertation]. Lyngby Technical University of Denmark, 2004. 

The dip-coating technique is widely used for the preparation of porous ceramic membranes [1]. Figure 2.7 illustrates the flow sheet of a dip-coating process. The prepared coatings may be adjustable between lOOnm and 100pm in thickness and the pore size covers from micropore to mesopore and part of the macropore range. 

Figure 2.7 Flow sheet of the preparation of porous ceramic membranes.

Abstract This chapter discusses the research and development of porous ceramic membranes and their application as membrane reactors (MRs) for both gas and liquid phase reaction and separation. The most commonly used preparation techniques for the synthesis of porous ceramic membranes are introduced first followed by a discussion of the various techniques used to characterise the membrane microstructure, pore network, permeation and separation behaviour. To further understand the structure-property relationships involved, an overview of the relevant gas transport mechanisms is presented here. Studies involving porous ceramic MRs are then reviewed. Of importance here is that while the general mesoporous natnre of these membranes does not allow excellent separation, they are still more than capable of enhancing reaction conversion and selectivity by acting as either a product separator or reactant distributor. The chapter closes by presenting the future research directions and considerations of porous ceramic MRs. 

There are a wide variety of techniques used for the preparation of porous ceramic membranes however, they all share the following common steps ... 

Preparation scheme of a porous ceramic membrane using conventional techniques. CVD, chemical vapour deposition EVD, electrochemical vapour deposition. 

The sol—gel technique has been used mosdy to prepare alumina membranes. Figure 18 shows a cross section of a composite alumina membrane made by sHp coating successive sols with different particle sizes onto a porous ceramic support. SiUca or titanium membranes could also be made by the same principles. Unsupported titanium dioxide membranes with pore sizes of 5 nm or less have been made by the sol—gel process (57). 

In this chapter membrane preparation techniques are organized by membrane structure isotropic membranes, anisotropic membranes, ceramic and metal membranes, and liquid membranes. Isotropic membranes have a uniform composition and structure throughout such membranes can be porous or dense. Anisotropic (or asymmetric) membranes, on the other hand, consist of a number of layers each with different structures and permeabilities. A typical anisotropic membrane has a relatively dense, thin surface layer supported on an open, much thicker micro-porous substrate. The surface layer performs the separation and is the principal barrier to flow through the membrane. The open support layer provides mechanical strength. Ceramic and metal membranes can be either isotropic or anisotropic. 

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