Ultrafiltration zirconia membranes

Direct deasphalting of petroleum residues. Ultrafiltration zirconia membranes with a pore diameter of 6.3 nm on carbon support have been used to remove asphaltenes from a long residue at a temperature of 150X [Guizard et al., 1994]. With a higher than normal... 

The ultrafiltration zirconia membrane system described above removes about 92% of the total suspended solids (TSS), 47% of the total dissolved solids (TDS), 12% of chromium and 13% of copper. However, the membrane also rejects some alkaline salts (about 9%) and consequently make-up with fresh cleaner is required. 

Wu, J. C., and Cheng, L. (2000). An improved synthesis of ultrafiltration zirconia membranes via the sol-gel route using alkoxide precursor./. Membr. Sci. 167 253-261. 

Zirconia membranes on carbon supports were originally developed by Union Carbide. Ultrafiltration membranes are commercially available now under trade names like Ucarsep and Carbosep. Their outstanding quality is their high chemical resistance which allows steam sterilization and cleaning procedures in the pH range 0-14 at temperatures up to 80°C. These systems consist of a sintered carbon tube with an ultrafiltration layer of a metallic oxide, usually zirconia. Typical tube dimensions are 10 mm (outer diameter) with a wall thickness of 2 mm (Gerster and Veyre 1985). 

Milk protein standardization for continuous cheese making can also be done by ultrafiltration using ceramic membranes. Zirconia membranes with an average molecular weight cut-off (MWCO) of 70,000 daltons on carbon supports have been used for this purpose. The objective for this application is to concentrate either the whole volume of the milk to a volume concentration factor of 1.3 to 1.6 or just a fraction of the feed volume to a volume concentration factor of 3 to 4 followed by mixing the concentrate with raw milk to reduce the requirement of milk storage space [Merin and Daufin, 1989]. 

Separation of lactic and propionic acids. The lactose fraction in the sweet whey permeate from cheese whey ultrafiltration can be fermented to produce lactic acid. In conjunction with the fermentation step, inorganic membranes have been tested in a continuous process to separate the lactic acid. This approach improves the productivity and reduces energy consumption compared to a conventional fermentation process. In addition, it produces a cell-free product. In a conventional process, some cells, although immobilized, are often detached and released to the product Zirconia membranes with a MWCX) of 20,000 daltons were operated at 42 C and a crossflow velocity of 2-5 m/s for this purpose [Boyaval et al., 1987]. The resulting permeate flux is 12-16 L/hr-m. To... 

The above process for recycling spent aqueous alkaline cleaners for metal manufacturing plants can utilize other ultrafiltration ceramic membranes with a mean pore diameter of 5 to 100 nm, although zirconia membranes are preferred [Bhave et al., 1993]. A crossflow velocity of 3 m/s and a TMP of less than 5 bars are recommended. 

Larbot A., Fabre J.-P, Guizard C., Cot L., Gillot J. New inorganic ultrafiltration membranes titania and zirconia membranes. J. Am. Ceram. Soc. 1989 72 257-261 Lee B., Zhang J. Preparation, structure evolution and dielectric properties ofBaTiOs thin films and powders by an aqueous sol-gel process. Thin Solid Films 2001 388 107-113 Lee D.-S., Liu T.-K. Preparation ofTi02 sol using TiC as a precursor. J. Sol-Gel Sci. Technol. 2002 25 121-136... 

Dynamic membranes are concentration—polarization layers formed in situ from the ultrafiltration of coUoidal material analogous to a precoat in conventional filter operations. Hydrous zirconia has been thoroughly investigated other materials include bentonite, poly(acryhc acid), and films deposited from the materials to be separated (18). 

Doyen, W., Andriansens, W., Molenberghs, B., and Leysen, R., A comparison between polysulfone, zirconia and organo-mineral membranes for use in ultrafiltration, J. Membr. Sci., 113, 1996. 

Since then, other colloidal oxide systems have been investigated in order to prepare ceramic mesoporous membranes designed for ultrafiltration. The preparation of an electronically conductive membrane from a Ru02 Ti02 mixed oxides sol and the application to an electro-ultrafiltration process [25,26], as well as the preparation of titania and zirconia ultrafiltration membranes [27], have been described following a colloidal process in which a partial destabilization of a metal oxide colloidal suspension is used to produce top layers with different pore size and pore volume in the mesoporous range. In agreement... 

This ligand then acts as a functionality locker when substoichiometric hydrolysis ratios are used. A ratio acacH/M greater than 1 prevents precipitation and leads to stable colloids or gels. Consequently, with a good formulation choice, sols can be prepared in air without precipitation. Either titania or zirconia ultrafiltration layers have been used as supports for these membranes. Figure 17 is a cross-sectional image of a zirconia microporous membrane that is 0.2 jum thick. 

Figure 17 Cross-sectional image of a zirconia microporous membrane obtained from a modified alkoxide precursor and deposited on a zirconia ultrafiltration layer.

Porous membranes can be made of polymers (polysulfones, polyacrylonitrile, polypropylene, silicones, perfluoropolymers, polyimides, polyamides, etc.), ceramics (alumina, silica, titania, zirconia, zeolites, etc.) or microporous carbons. Dense organic membranes are commonly used for molecular-scale separations involving gas and vapor mixtures, whereas the mean pore sizes of porous membranes is chosen considering the size of the species to be separated. Current membrane processes include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), gas and vapor separation (GS), and pervaporation (PV). Figure 1 indicates the types and sizes of species typically separated by these different separation processes. 

Arthanareeswaran, G. and Thanikaivelan, P. 2010. Fabrication of cellulose acetate-zirconia hybrid membranes for ultrafiltration applications Performance, structure and fouling analysis. Separation and Purification Technology lA 230-235. 

Nanohybrid materials have been furthermore used for ultra-/nanofiltration applications. Nanofiltration is a pressure-driven membrane separation process and can be used for the production of drinking water as well as for the treatment of process and waste waters. Some apphcations are desalination of brackish water, water softening, removal of micropollutants, and retention of dyes. Ultrafiltration membranes based on polysulfones filled with zirconia nanoparticles are usually prepared via a phase-inversion technique and have been used since 1990 [328]. Various studies were done in order to assess the effect of the addition of Zr02 to polysulfone-based ultrafiltration membranes [329] and the influence of filler loading on the compaction and filtration properties of membranes. The results indicate that the elastic strain of the nanohybrid membranes decreases and the time-dependent strain... 

In addition to such polymeric materials, inorganic (ceramic) materials have also been used for ultrafiltration membranes, especially alumina (AljC ) and zirconia (ZiOo), Figure VI -8 shows a multi-layer AI2O3 membrane in which the tOplayer is prepared via a sol-gel technique [6). 

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