Permeability tubular membranes

Extrusion can be defined as paste flow and extrudate formation from ceramic paste [1]. A membrane support must provide a high mechanical resistance and permeability. Tubular configurations correspond to this criterion and are adapted to the tangential filtration. 

Example 30.4. A tubular membrane with a diameter of 2 cm and a water permeability of 250 L/m -h-atm is being used for UF of cheese whey. The whey proteins have an average diffusivity of 4 x 10 cm /s, and the osmotic pressure in atmospheres is given by Jonsson s equation ... 

This reasoning leading to the best option being tubular membranes in a module does not necessarily apply for membrane reactors in which (partial) combustion takes place. The necessity of catalysts also sets extreme demands as to bed permeability. 

Yin, X., Hong, L. and Liu, Z. (2007). Asymmetric Tubular Oxygen-Permeable Ceramic Membrane Reactor for Partial Oxidation of Methane, J. Phys. Chem. C, 111, pp. 9194-9202. 

Fuertes and Menendez (2002) and Centeno and Fuertes (1999, 2001) have published a series of studies using this precursor. Centeno and Fuertes (1999) have spin coated a small amount of a novolak-type phenolic resin on the surface of carbon supports. The membranes were then carbonized in a tubular furnace from 500 to 1000°C in vacuum. The resulting membranes had O2/N2 selectivity of around 10 and CO2/CH4 selectivity of 160. This work was later extended and in that case (Centeno and Fuertes, 2001 Fuertes and Menendez, 2002) a novalak-type phenolic resin was deposited on the inner face of a ceramic tubular membrane used for ultrafiltration. The membrane was subsequently pyro-lyzed to 700°C. In some cases an oxidative pretreatment was used before pyrolysis or an oxidative posttreatment after pyrolysis. The resulting membranes had O2 permeabilities around 100 Barrers and O2/N2 selectivities around 12 at 25°C. Films dip coated with resin three times had lower permeability and only slightly higher selectivities than those dipped only once. For hydrocarbon mixtures, the separation performance was increased by several treatments air oxidation of the resin, air oxidation of the carbon, or chemical vapor deposition (CVD) posttreatment of the carbon. 

TFF module types include plate-and-frame (or cassettes), hollow fibers, tubes, monoliths, spirals, and vortex flow. Figures 20-52 and 20-53 show several common module types and the flow paths within each. Hollow fiber or tubular modules are made by potting the cast membrane fibers or tubes into end caps and enclosing the assembly in a shell. Similar to fibers or tubes, monoliths have their retentive layer coated on the inside of tubular flow channels or lumens with a high-permeability porous structure on the shell side. 

In some human studies where clinical chemistry measurements but no renal biopsies were performed, the only parameter of renal function shown to be affected was an increase in the levels of NAG in the urine. NAG is a lysosomal enzyme present in renal tubular cells that has been shown to be a sensitive indicator of early subclinical renal tubular disease. The mechanism by which lead affects the release of NAG from renal tubular cells is not known, but it is suggested that lead could attach to kidney cell membranes and alter membrane permeability (Chia et al. 1994). 

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