Alumina porous support tubes

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... 

The silicalite-alumina membrane was prepared after adding a solution containing the silicalite precursor (i e silica + template) to the above-mentioned porous tube (hereafter called support) and a specific hydrothermal treatment performed [8], under the chosen conditions no material is formed in the absence of the porous support. The tube is then calcined at 673 K for removing the template. 

Porous supported alumina membrane tube (in double pipe configuration), mean pore diameter 40 A. Feed enters the reactor at tube side, permeate at shell side. 

For the preparation of tubular silica membranes, commercially available mesoporous membranes [17] are used. These tubular supports have a total length of 25 cm and are enamelled at both ends, required for a gas-tight sealing with carbon seals to the reactor, so that an effective porous length of 20 cm remains. The tube consists of 4 layers. Layer 1, 2 and 3 consist of a-alumina with a thickness of 1.5 mm, 40 and 20 im and a pore diameter of 12, 0.9 and 0.2 im respectively. Layer 4 consists of y-alumina with a thickness of 3-4 im a Kelvin radius of 4 nm. A schematic drawing of the cross-section of a mesoporous support tube is provided in Figure 4. 

Guan G, Kusakabe K, and Morooka S. Separation of nitrogen from oxygen using a titanosilicate membrane prepared on a porous alpha-alumina support tube. Sep Sci Technol 2002 37(5) 1031-1039. 

The porous supports, in disc or tubular shaped form, were produced commercially (Velterop Company, Netherlands). The discs (25 mm in diameter and 2 mm in thickness) were available with different macropore sizes (0.08, 0.15, 2 and 9 pm). These macropores, which were formed between the sintered alumina grains are shown typically for a disc in Figure 1. The tubes with an outer diameter of 14 mm and a wall thickness of 3 mm were manufactured with pores of 2.5 pm and 9 pm. The macropore structure of these different types of supports was analysed by mercury porosimetry. Changes in the porosity which occurred after the hydrothermal treatment were also monitored. Figure 2 shows the highly uniform pore structure of a series of supports with different nominal pore sizes. 

A polycrystalline Y-type zeolite membrane was formed by hydrothermal synthesis on the outer surface of a porous a-alumina support tube, which was polished with a finely powdered X-type zeolite for use as seeds. When an equimolar mixture of CO2 and N2 was fed into the feed side, the CO2 permeance was nearly equal to that for the singlecomponent system, and the N2 permeance for the mixture was greatly decreased, especially at lower permeation temperatures. At 30"C, the permeance of CO2 was higher than 10- mol m-2 s- Pa-, and the permselectivity of CO2 to N2 was 20-100. 

A Y-type zeolite membrane was formed on a porous a-alumina support tube. The membranes produced separated CO2 from N2 at a permeance of the order of 10- mol m-2 s-i Pa-i and a selectivity of 20-100 at 30°C. This rapid and selective permeation was due to the pore-size controlled adsorption. 

Kusakabe et al.83 proposed selective CO oxidation membrane concept to facilitate SMR reaction. Yttria-stabilized zirconia (YSZ) membrane was deposited on the surface of a porous alumina support tube by sol-gel procedure. This again was impregnated with Pt and Rh aqueous solution to produce a Pt- or Rh-loaded YSZ membrane. With addition of 02 in the feed, oxidation of CO can bring CO concentration to the level appropriate for PEMFC (<30ppm). 

Support - porous alumina - porous carbon - porous metal plate, disc, tube, monolith plate, tube, hollow fibre woven structures, disc, tube... 

Carbosep membranes (Tech-Sep, France) are made of a zirconia layer attached to a porous carbon supporting tube assembled into modules containing up to 252 tubes. The same company produces Kerasep membranes of alumina or titania on a monolithic alumina-titania support containing 7-19 channels. 

The silica membrane was prepared through sol-gel deposition and chemical vapor deposition methods. The porous a-alumina tube (O.D., 5.0 mm I.D., 3.5 mm length, 300 mm), supplied by Nano Pore Materials Co. Ltd., Korea, was used as a support. The mean pore size and porosity of the support tube were 0.1 pm and 35%, respectively. Tlie effective length of membrane was 100-150 mm at the middle of the tube, and both edges were glazed with a SiO2-BaO-CaO sealant (Nippon Electric Glass, GA-13), and then calcined at 1200°C. 

The membrane reactor described by Champagnie, Tsotsis, and Minet (1990) consists of a porous membrane tube covered with Pt (Figure 4.10.73). The tube consists of a multilayered porous composite based on alumina. The first layer is only 5 p,m thick and has a unimodal pore structure (4nm). Successive layers are thicker with progressively larger pores and are supported on a layer (1.5 mm) with large pores of about 10 p.m. 

Yamamoto et al. [27,28] revealed the advantages of applying a microreactor for the dehydrogenation of cyclohexane by using a Pd membrane as a heterogeneous catalyst These authors demonstrated that the yield of this reaction can be doubled by inserting a stainless steel rod with a proper size into a tubular Pd membrane reactor supported by an a-alumina porous tube to form microchannels. 

They also formed the condensed polynuclear aromatic (COPNA) resin film on a porous a-alumina support tube. Next, a pinhole-free CMSM was produced by carbonization at 400-1,000°C [29], The mesopores of the COPNA-based caibon membranes did not penetrate through the total thickness of each membrane and served as channels which increased permeances by linking the micropores. CMSMs produced using COPNA and BPDA-pp ODA polyimdes showed similar permeation properties even though they had different pore stractures. This suggests that the micropores are responsible for the permselectivities of the carbonized membrane. Besides that, Fuertes [30] used phenohc resin in conjunction with the dip coating technique to prepare adsorption-selective carbon membrane supported on ceramic tubular membranes. 

When a gel is used as a membrane, the most difficult problem is how to prepare a thin membrane film due to the fact that it has low mechanical strength [13]. The use of a substrate can be a natural solution. If a gel is supported in the small pores of a porous polymeric membrane or an inorganic membrane, a mechanically stable thin gel membrane can be prepared. The authors used a thin silica-alumina porous membrane as shown in Fig. 12 in order to avoid the swelling of the substrate itself. This substrate was prepared by silica treatment on the surface of the thin alumina membrane, which was prepared by the sol-gel technique on the outer surface of a porous a-alumina tube. The thickness of the membrane was approximately several pm. The pore size can be somewhat controlled by the particle size of the alumina sol and its number of coating operations. The control of the pore size of the thin membrane is extremely important for proper use of the gel characteristics. There seems to be an optimum micropore size [14]. The majority of pore size used in this experiment was approximately several tens of nm. As pore size was large, there was no selective absorption of solvent by the substrate itself... 

The segmented cell in series design is being investigated by Mitsubishi Heavy Industries (Japan), ABB, and Rolls Royce. This cell contains segmented cells arranged in a thin, banded structure on a porous support alumina tube. The sealing is provided by the interconnect, which also serves as an electrical contact between the cathode of one cell and anode of the next cell (Fig. 4.18). The oxidant flows outside and the fuel flows from one cell to the next inside the tubular cell stack. 

Kusakabe, K., Yoneshige, S., Murata, A., and Morooka, S. (1996). Morphology and gas permeance of ZSM-5-type zeolite membrane formed on a porous a-alumina support tube. J. Membr. ScL 116, 39. 

Itoh et al. (2005) prepared a thin and firmly deposited Pd membrane applicable to surface catalysis. The technique and equipment developed in this study is based on CVD under a forced flow, where due to a pressure difference applied between the outside and the inside of the support tube the chemical vapours enter the porous layer of the support where they decompose. (CH3COO)2Pd was used as a Pd source. The tubular support made from a-alumina powder was porous and have an average pore diameter of 0.15 mm. The forced flow CVD was carried out by heating according to a temperature program under regulated vacuum pressure. The palladium membrane thus obtained was as thin as 2-4 pm and had a Hj/Nj selectivity >5000. 

These have now been superseded by capillary columns, which offer greatly improved separation efficiency. Fused silica capillary tubes are used which have internal diameters ranging from 0.1 mm (small bore) to 0.53 mm (large bore) with typical lengths in excess of 20 m. The wall-coated open tubular (WCOT) columns have the internal surface of the tube coated with the liquid (stationary) phase and no particulate supporting medium is required. An alternative form of column is the porous-layer open tubular (PLOT) column, which has an internal coating of an adsorbent such as alumina (aluminium oxide) and various coatings. Microlitre sample volumes are used with these capillary columns and the injection port usually incorporates a stream splitter. 

There are a number of examples of tube waU reactors, the most important being the automotive catalytic converter (ACC), which was described in the previous section. These reactors are made by coating an extruded ceramic monolith with noble metals supported on a thin wash coat of y-alumina. This reactor is used to oxidize hydrocarbons and CO to CO2 and H2O and also reduce NO to N2. The rates of these reactions are very fast after warmup, and the effectiveness factor within the porous wash coat is therefore very smaU. The reactions are also eternal mass transfer limited within the monohth after warmup. We wUl consider three limiting cases of this reactor, surface reaction limiting, external mass transfer limiting, and wash coat diffusion limiting. In each case we wiU assume a first-order irreversible reaction. 

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