Ceramic membranes alumina

Ceramic Membranes Alumina-based microfiltration membranes and porous carbon substrates are tightened for use as UF membranes usually by depositing a layer of zirconium oxide on the surface. 

Supported, multilayered (as5onmetric) - dense oxide or metal - porous ceramic membranes alumina, zirconia, titania, carbon - composite ceramic-metal, ceramic-ceramic layers on porous support tube, disk multilayers on porous support plate, disk, tube, monolith... 

Ceramic Membranes. Alumina membranes for UF have been introduced by Ceraver (Tarbes, France) (membrane division recently purchased by Alcoa). The Norton Co. (Worcester, MA) is reportedly about to introduce an alumina UF membrane in addition to its current MF membrane. 

Examples of commercial porous inorganic membranes are ceramic membranes (alumina, silica), glass and porous metals (stainless steel and silver). 

Key words mesoporous ceramic membranes, alumina, titania, zirconia, membrane reactors for dehydrogenation reactions. 

Fig. 16.25. Mixture of zirconia and alumina coated on the ceramic membrane.

The vast increase in the application of membranes has expanded our knowledge of fabrication of various types of membrane, such as organic and inorganic membranes. The inorganic membrane is frequently called a ceramic membrane. To fulfil the need of the market, ceramic membranes represent a distinct class of inorganic membrane. There are a few important parameters involved in ceramic membrane materials, in terms of porous structure, chemical composition and shape of the filter in use. In this research, zirconia-coated y-alumina membranes have been developed using the sol-gel technique. 

Figure 16.23 presents the alumina-coated ceramic membrane. There were opportunities to fabricate a crack-free ceramic membrane coated with y-alumina. The supported zirconia-alumina membrane on the ceramic support shows an irregular surface. The non-uniform surface of ceramic support causes the irregular surface on the top layer of the membrane. Some of the membrane sol was trapped in the porous ceramic support during coating, and caused the irregularity of the membrane surface. 

The zirconia membrane was obtained in a unique manner. Figure 16.24 shows light micrographs of the zirconia-alumina membrane coated on the ceramic support. The non-unifomity and crater-filled surface of the ceramic support was covered by the zirconia-alumina membrane layer. Zirconia was mounted by very thin or nano-layers on the ceramic membrane. 

A combination of alumina and zirconia was used as a strong nano-film on the ceramic membrane. SEM micrographs are shown in Figure 16.25. Observation by SEM shows that the zirconia-alumina membrane layer was properly adhered and could stand on the top of the porous ceramic support. 

We have successfully developed a new inorganic ceramic membrane coated with zirconium and alumina. A thin film of alumina and zirconia unsupported membrane was also fabricated. The successful method developed was the sol-gel technique. 

The only ceramic membranes of which results are published, are tubular microporous silica membranes provided by ECN (Petten, The Netherlands).[10] The membrane consists of several support layers of a- and y-alumina, and the selective top layer at the outer wall of the tube is made of amorphous silica (Figure 4.10).[24] The pore size lies between 0.5 and 0.8 nm. The membranes were used in homogeneous catalysis in supercritical carbon dioxide (see paragraph 4.6.1). No details about solvent and temperature influences are given but it is expected that these are less important than in the case of polymeric membranes. 

Terpstra, R. A., B. C. Bonekamp and H. J. Veringa. 1988. Preparation, characterization and some properties of tubular alpha alumina ceramic membranes for microfiltration and as a support for ultrafiltration and gas separation membranes. Desalination 70 395-404. 

For efficient separation, porous inorganic membranes need to be crack-free and uniform in pore size. An important reason for the increasing acceptance of ceramic membranes introduced in recent years is the consistent quality as exemplified in a scanning electron micrograph of the surface of a 0.2 micron pore diameter alumina membrane (Figure 3.3). 

The use of ceramic membranes in gas separations is not new. Since 1950, alumina membranes were used in the separation of UF isotopes. However, the separation factor is very low in this case (theoretically 1.004 ). 

Armor, J. N. 1989. Catalysis with fiermselective inorganic membranes. Appl. Catai 49 1-25. Anderson, M. A., M. J. Giesclmann and Q. Xu. 1988. Titania and alumina ceramic membranes. J. Membrane Science 39 243-258. 

Less information is available about the stability of ceramic membranes. It is generally thought that ceramic membranes have excellent solvent stability. Acid conditions may be more problematic it was shown [57] that an alumina nanofiltra-tion membrane was very sensitive to corrosion effects in dynamic experiments, whereas the performance of a similar titania membrane was stable in the pH range from 1.5 to 13. 

Finally, in chapter 9, conclusions are drawn and suggestions made for further research on (steam-stable) molecular sieving silica membranes or mesoporous y-alumina membranes. Though not all of the project objectives were obtained, progress was made in the synthesis of micro- and mesoporous membranes. Especially the development of steam stable membranes may be a large step forward in the development of ceramic membranes. 

R.J.R. Uhlhom, M.H.B.J. Huis in t Veld, K. Keizer and A.J. Burggraaf, Synthesis of Ceramic Membranes. Part 1. Synthesis of Non-Supported and Supported Gamma-Alumina Membranes without Defects , J. Mater. Sci., 27, 527-37 (1992). 

Ceramic membranes were first developed in the 1940s for uranium isotope enrichment processes. Important progress has been made since that time, mainly due to the improved knowledge of the physicochemical properties of the membrane precursors. Most CMR studies concern alumina membranes other oxides such as silica, titania, or zirconia are much less frequently mentioned. 

Normally when one of the two performance indicators of a porous ceramic membrane for gas separation (i.e., separation factor and permeability) is high, the other is low. It is, therefore, necessary to m e a compromise that offers the most economic benefit Often it is desirable to slightly sacrifice the separation factor for a substantial increase in the permeation flux. This has been found to be feasible with a 5% doping of silica in an alumina membrane [GaBui et al., 1992]. 

---