Ceramic membranes fabrication

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. 

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. 

In the fabrication of ceramic membrane modules, several processing steps must be acconplished sol preparation, gelation, coating of supports, and firing at elevated tenperatures. Within each step, several independent variables can be used to tailor the properties of the ultimate product for the specific application of interest. Although discussion of the influence of these variables is beyond the scope of the present paper, a cursory treatment of each step and the most important variables will be given here. 

Li, Y.Y., Nomura, T., Sakoda, A., Suzuki, M. (2002b), Fabrication of carbon coated ceramic membranes by pyrolysis of methane using a modified chemical vapor deposition apparatus Journal of Membrane Science, 197,23-35. 

Until recently, air filtration for clean rooms uses dead-end fabric filters. They are not efficient in the particle diameter range of 0.1 to 0.5 pm and also suffer in many cases from two of the most important problems in clean room gases applications particle shedding and gas reactivity (or called hydrocarbon outgassing). Some ceramic membranes such as alumina membranes have made a visible entry into the clean room market as in-line gas filters. 

A recent development of a ceramic membrane appears to be promising for selectively removing oxygen from air. Multi-channel membrane elements have been fabricated for that purpose [Anonymous, 1995]. The membrane has the potential for reducing the cost of converting natural gas to synthesis gas. 

Miller BG, Wincek RT, Glick DC, Scaroni AW, Makris P, Krecker J, Jung G, and Stubblefield J. Ceramic membrane filters and conventional fabric filters for fine particulate removal from a coal-fired industrial boiler. Proceedings of the 23rd International Conference on Coal Utilization and Fuel Systems, Clearwater, FL, March 9-13, 1998 807-818. 

The MF membranes are usually made from natural or synthetic polymers such as cellulose acetate (CA), polyvinylidene difiuoride, polyamides, polysulfone, polycarbonate, polypropylene, and polytetrafiuoroethylene (FIFE) (13). Some of the newer MF membranes are ceramic membranes based on alumina, membranes formed during the anodizing of aluminium, and carbon membrane. Glass is being used as a membrane material. Zirconium oxide can also be deposited onto a porous carbon tube. Sintered metal membranes are fabricated from stainless steel, silver, gold, platinum, and nickel, in disks and tubes. The properties of membrane materials are directly reflected in their end applications. Some criteria for their selection are mechanical strength, temperature resistance, chemical compatibility, hydrophobility, hydrophilicity, permeability, permselectivity and the cost of membrane material as well as manufacturing process. 

An intriguing recent development has been the discovery that porous ceramic monoliths (fabricated for use as catalyst supports) can be lamination-coated with microporous or ultramicroporous barrier layers to yield high-area membrane modules [58]. It is reducing fabrication costs of ceramic membrane devices to levels comparable to (or less than) those of polymeric membrane devices, and it opens the door to development of large-area laminate devices with utility for particulate, macromolecular, or smaU-molecule separations. 

Because of the low cost and easy processing (manufacturing) polymers are the preferred material for the production of membranes. However, the field of inorganic membranes derived from ceramics is growing very fast. Common polymers used for membrane fabrication and the membrane types derived therefrom are summarized in Table 1. 

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