Porous ceramic membranes process

Furneaux, R. C. and M. C. Thornton. 1988. Porous "ceramic membranes produced from anodizing aluminium. Brit. Cer. Proc., Advanced Ceramics in Chemical Process Engineering Eds. B. C. H. Steele and D. P. Thompson, vol. 43, pp. 93-101. 

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]. 

Membrane separation, which is a relatively new separation process, has been commercialized in the last two decades. The majority of membrane materials which have been commercialized thus far are polymeric. Porous ceramic membranes have great potential for opening up new types of applications to which polymeric membranes cannot be applied. This review will summarize the present status and a potential application of porous ceramics as materials for membrane separation. 

In the sol-gel process, porous ceramic membranes are manufactured by solcoating on porous substrates, and drying for gelling, followed by firing process. 

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. 

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. 

Gas separation membranes can be divided into two groups porous and non-porous (dense) membranes. TTie majority of porous membranes are made up of metal oxides these porous ceramic membranes were among the first to be appUed to separation processes when the pure isotope 235 of uranium was first separated from natural uranium in the mid-1940s. ... 

By contrast porous ceramic membranes had found application since the 1960s in the field of large-scale gas diffusion processes for uranium isotope separation. It was only in the 1980s that porous ceramic membranes found other non-nuclear industrial applications, mainly oriented towards microfiltration and ultrafiltration water treatment processes. 

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). 

A common method to slip-cast ceramic membranes is to start with a colloidal suspension or polymeric solution as described in the previous section. This is called a slip . The porous support system is dipped in the slip and the dispersion medium (in most cases water or alcohol-water mixtures) is forced into the pores of the support by a pressure drop (APJ created by capillary action of the microporous support. At the interface the solid particles are retained and concentrated at the entrance of pores to form a gel layer as in the case of sol-gel processes. It is important that formation of the gel layer starts... 

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