Supported carbon membranes

As an alternative to unsupported carbon membranes, the carbon separation layer can be supported on flat or tubular substrates to fabricate supported carbon membranes. In the case of supported membrane configuration, we have to consider the influence of the same experimental variables reported in symmetric unsupported flat carbon membranes (pyrolysis temperature. 

4 Schematic concept of a bimodal catalytic membrane (microporous 

The most commonly used polymer precursors for carbon membranes have been reported to be polyimides, polyfurfuryl alcohol, phenol formaldehyde resins and cellulose. Their common characteristic is that they do not melt during pyrolysis at high temperature, which keeps their original shape and structure during the thermal heating and decomposition process. In this sense, the commercially available Matrimid and Kapton are the fully imidized polyimides with high values. They do not abruptly change their 

As is the case with unsupported carbon membranes, pyrolysis temperature also influences the carbon structure of supported carbon membranes. Centeno et al. studied the effect of pyrolysis temperature on the permeance of phenolic resins supported on a ceramic tube. They showed how permeance decreases with an increase of pyrolysis temperature after 

Between 973°K and 1023°K, the membranes were highly effective in the separation of absorbable and non-absorbable spedes which were considered as ASCM instead of carbon molecular-sieving membranes. Over 1073 K the carbon structure becomes more ordered, which implies decrease of pore size causing molecular-sieving behavior. 

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Rao and Sircar [5-7] introduced nanoporous supported carbon membranes which were prepared by pyrolysis of PVDC layer coated on a macroporous graphite disk support. The diameter of the macropores of the dried polymer film was reduced to the order of nanometer as a result of a heat treatment at 1,000°C for 3 h. These membranes with mesopores could be used to separate hydrogen-hydrocarbon mixtures by the surface diffusion mechanism, in which gas molecules were selectively adsorbed on the pore wall. This transport mechanism is different from the molecular sieving mechanism. Therefore, these membranes were named as selective sitrface flow (SSF ) membranes. It consists of a thin (2-5 pm) layer of nanoporous carbon (effective pore diameter in the range of 5-6 A) supported on a mesoporous inert support such as graphite or alumina (effective pore diameter in the range of 0.3-1.0 pm). The procedures for making the selective surface flow membranes were described in [5, 7]. In particular, the requirements to produce a surface diffusion membrane were shown clearly in [7]. 

Wang H, Zhang L, Gavalas GR (2000) Preparation of supported carbon membranes from furfuryl alcohol by vapor deposition polymerization. J Membr Sci 177 (1-2) 25-31... 

For making the supported carbon membranes, various options are available for coating the supports with thin polymeric films, such as ultrasonic deposition [52, 53], dip coating [68], vapour deposition [60], spin coating [43], and spray coating [54], Ultrasonic deposition (UD) provides nearly zero spray velocity, droplet sizes that are often narrowly distributed in sizes from 10 to 10 pm, accurate compared to spray and misting [52]. 

Instead of the PA precursors, Hayashi et al. deposited a polyimide film on the outer surface of a porous alumina tube by dip-coating three times. After imidization and pyrolyzation at 973-1073 K, the carbon membranes were fabricated on porous alumina tube. The enhancement of the volume of micropores accessible to smaller molecules has been observed. Hayashi et al. obtained an optimal pyrolysis temperature of 973 K and maximum permeance was achieved. In order to improve selectivity, a carbon layer was further deposited on the resultant supported carbon membrane by chemical vapor deposition (CVD) of propylene at 923 K.The CVD process favors the deposition of carbon in micropores, which explains the increase of the selectivity of CO2/N2 from 47 to 73. 

A common problem in the fabrication of supported carbon membranes is related to cracks formation and the minimization of defects arising from pyrolysis. Figure 10.6 shows a supported carbon membrane obtained from a commercial polyimide Matrimid coated on a porous substrate after pyrolyz-ing at 973 K with a ramp rate of 2.5 K/min in Nj atmosphere. The differences of thermal expansion coefficients between substrate and coated polymer film during pyrolysis created a lot of cracks in the resultant carbon membrane. Therefore, the selection of polymer precursor, the optimization of pyrolysis temperature and the deposition parameters of the polymer layer are believed to be very important for avoiding such cracks. 

Fig. 9 Surface modification of cells with ssDNA-PEG-lipid. (a) Real-time monitoring of PEG-lipid incorporation into a supported lipid membrane by SPR. (r) A suspension of small unilamellar vesicles (SUV) of egg yolk lecithin (70 pg/mL) was applied to a CH3-SAM surface. A PEG-lipid solution (100 pg/mL) was then applied, (ii) Three types of PEG-lipids were compared PEG-DMPE (C14), PEG-DPPE (C16), and PEG-DSPE (C18) with acyl chains of 14, 16, and 18 carbons, respectively, (b) Confocal laser scanning microscopic image of an CCRF-CEM cell displays immobilized FITC-oligo(dA)2o hybridized to membrane-incorporated oligo(dT)20-PEG-lipid. (c) SPR sensorigrams of interaction between oligo(dA)2o-urokinase and the oligo (dT)2o-PEG-lipid incorporated into the cell surface, (i) BSA solution was applied to block nonspecific sites on the oligo(dT)20-incorporated substrate, (ii) Oligo(dA)20-urokinase (solid line) or oligo(dT)20-urokinase (dotted line) was applied...

Catalyst, Catalyst-Support, and Membrane Material Impact on Maximum Catalyst-Support Corrosion Rate Under Fully Developed H2 Starvation Conditions. Here, Advanced-Support is a Hypothetical Support with a 30-Fold Lower Corrosion Rate than Graphitized Vulcan Carbon and Membrane-X Refers to a Hypothetical Membrane with a 10-Fold Lower 02 Permeability. 

Conventional polymeric hydrogen separation membranes yield hydrogen at low pressure. Air Products and Chemicals has demonstrated a carbon membrane on an alumina support that removes hydrocarbons from hydrogen/hydrocarbon mixtures and leaves the hydrogen at high pressure40. 

With respect to carbon membranes, the molecular sieving carbon membranes, produced as unsupported flat, capillary tubes, or hollow fibers membranes, and supported membranes on a macropo-rous material are good in terms of separation properties as well as reasonable flux and stabilities, but are not yet commercially available at a sufficiently large scale, because of brittleness and cost among other drawbacks [3,6],... 

Centeno, T.A., Fuertes, A.B. (1999) Supported carbon molecular sieve membranes based on phenolic resin. J. Membr. Sci. 160(2), 201-211. 

Figure 2. Scanning electron micrograph of a cross section of the porous stainless steel supported Re-containing carbon membrane. Magnification is x3000. 1 - the stainless support 2 - the Re-carbon layer 3- Re-particles on the membrane surface.

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