Multichannel supports

Ceraver s entry into the microfiltration and ultrafiltration field followed a completely different approach. In 1980, it became apparent that the type of product made by Ceraver for uranium enrichment, which was a tubular support and an intermediate layer with a pore diameter in the microfiltration range, might be declassified. Ceraver therefore developed a range of a-AljOj microfiltration membranes on an a-AljOs support with two key features first, the multichannel support and second, the possibility to backflush the filtrate in order to slow down fouling. 

The use of a multichannel support made of a sintered oxide carrying a separation layer deposited on the surface of the channels was not a new concept. This was described in the patent literature as far back as the 1960s (Manjikian 1966). The multichannel geometry is particularly attractive in terms of its sturdiness, lower production cost compared to the single tube or tube-bundle geometry and lower energy requirement in the cross-flow recirculation loop. However, Ceraver was the first company to industrially produce multichannel membranes. Since 1984 these membranes, which have 19 channels per element with a 4 mm channel diameter are sold under the trademark Membralox. ... 

In the early 1980s, former employees of Euroceral founded a small company located near Montpellier in France known as Ceram-Filtre. The rather less well-known Ceram-Filtre membranes comprise a multichannel support with 19 channels of 4 mm diameter and a microfiltration membrane made of an oxide. 

Trade-offs in performance advantages between the honeycomb multichannel supports and others that offer variable flow patterns are necessary for each application. More compact and efficient reactors will provide many novel opportunities not only to improve chemical processes in wide industrial practice, but to develop novel processes for more efficient operation in the near future. 

Some catalyst supports rely on a relatively low surface area stmctural member coated with a layer of a higher surface area support material. The automotive catalytic converter monolith support is an example of this technology. In this appHcation, a central core of multichanneled, low surface area, extmded ceramic about 10 cm in diameter is coated with high surface area partially hydrated alumina onto which are deposited small amounts of precious metals as the active catalytic species. 

Pellets or tablets (1.5-10 mm in diameter), rings (6-20 mm) and multichanneled pellets (20-40 mm in diameter and 10-20 mm high) are used when a high mechanical strength is required. They are produced by compressing a mixture of the support powder and several binders (kaolin day, stearic acid) and lubricants (graphite) in a press. 

A few other players in the nuclear membranes activity also developed inorganic membranes for the filtration of liquids. This was the case with Norton-USA who with the know-how of Euroceral developed MF membranes made of an 0-AI2O3 tubular support with an a-Al203 layer. The inner tube diameter was 3 mm and the outer diameter 5 mm. In 1988-1989, Norton also produced the multichannel membrane elements. These membranes produced by Norton are now sold by Millipore under the trademark Ceraflo . 

Inorganic membranes employed in reaction/transport studies were either in tubular form (a single membrane tube incorporating an inner tube side and an outer shell side in double pipe configuration or as multichannel monolith) or plate-shaped disks as shown in Figure 7.1 (Shinji et al. 1982, Zaspalis et al. 1990, Cussler 1988). For increased mechanical resistance the thin porous (usually mesoporous) membrane layers are usually supported on top of macroporous supports (pores 1-lS /im), very often via an intermediate porous layer, with pore size 100-1500 nm, (Keizer and Burggraaf 1988). 

To illustrate the functionality of the system a validation library was prepared and introduced into the reactor system. With the goal of achieving an optimal fluid distribution with a minimal pressure drop over the 96 reactor channels we used multichannel ceramic bodies ( miniliths ) as supports, which are impregnated with the corresponding catalyst precursor solutions in an automatic manner (for suitable technical solutions see Section 2). At each of the 96 reactor positions, a candidate material modified by impregnation is available for testing. The shadowed scheme... 

A great deal of evidence now exists to support the notion that the SIT detector approaches the characteristics of an ideal multichannel detector (20). Sensitivity on a per/channel basis is comparable to that of the the photomultipliers, so that almost... 

For membrane testing under process-conditions, select a commercially available macro-porous support that meets permeance and stability requirements. Make a well-considered choice between the different geometries available (flat, tubular, multichannel or hollow fibre) and test the support system under process-conditions. 

The microtiter plate array format involves immobilizing carbohydrates in wells of 96-, 384-, or 1536-well microtiter plates (see Fig. la). Each carbohydrate component is spatially separated from other components within the plate. Two of the primary advantages of a microtiter plate format are cost and simplicity. Carbohydrates can be distributed into wells using multichannel pipettors, and assay results can be measured using standard plate readers. Thus, the equipment and supplies needed for the array are relatively inexpensive and common. However, microtiter plates generally require larger amounts of each carbohydrate and can accommodate a smaller total number of components per support unit. 

Honeycomb multichannel ceramic membranes on micro-porous cordierite support... 

Different supports are used, (see Section 10.6.4) with different geometry (discs or tubes), thickness, porosity, tortuosity, composition (alumina, stainless steel, silicon carbide, mullite, zirconia, titania, etc.), and symmetry or asymmetry in its stmcture. Tubular supports are preferable compared to flat supports because they are easier to scale-up (implemented as multichannel modules). However, in laboratory-scale synthesis, it is usually found that making good quality zeolite membranes on a tubular support is more difficult than on a porous plate. One obvious reason is the fact that the area is usually smaller in flat supports, which decreases the likelihood of defects. In Figure 10.1, two commercial tubular supports, one made of a-alumina (left side) and the other of stainless steel (right side) used in zeolite membrane synthesis, are shown. Both ends of the a-alumina support are glazed and both ends of the stainless steel support are welded with nonporous stainless steel to assure a correct sealing in the membrane module and prevent gas bypass. 

Membralox membranes produced by US FUter/SCT (USA) is the name of a group of tubular and monolithic (multichannel) alumina membranes. The supporting system is formed by high-purity a-alumina multilayers with a final coating of alumina or zirconia. This system has now been developed further to obtain smaller pore diameters for nanofiltration and gas separation. 

To avoid high-pressure drop and clogging problems in randomly packed micro-structured reactors, multichannel reactors with catalytically active walls were proposed. The main problem is how to deposit a uniform catalyst layer in the microchannels. The thickness and porosity of the catalyst layer should also be enough to guarantee an adequate surface area. It is also possible to use methods of in situ growth of an oxide layer (e.g., by anodic oxidation of a metal substrate [169]) to form a washcoat of sufficient thickness to deposit an active component (metal particles). Suzuki et al. [170] have used this method to prepare Pt supported on nanoporous alumina obtained by anodic oxidation and integrate it into a microcatalytic combustor. Zeolite-coated microchannel reactors could be also prepared and they demonstrate higher productivity per mass of catalyst than conventional packed beds [171]. Also, a MSR where the microchannels are coated by a carbon layer, could be prepared [172]. 

The molecular structures of the surface vanadium oxide species on the different supports were examined with Raman spectroscopy. The Raman spectrometer system possessed a Spectra-Physics Ar+ laser (model 2020-05) tuned to the exciting line at 514.5 nm. The radiation intensity at the samples was varied from 10 to 70 mW. The scattered radiation was passed through a Spex Triplemate spectrometer (Model 1877) coupled to a Princeton Applied Research OMA III optical multichannel analyzer (Model 1463) with an intensified photo diode array cooled to 233 K. Slit widths ranged from 60 to 550 m. The overall resolution was better than 2 cm l. For the in situ Raman spectra of dehydrated samples, a pressed wafer was placed into a stationary sample holder that was installed in an in situ cell. Spectra were recorded in flowing oxygen at room temperature after the samples were dehydrated in flowing oxygen at 573 K. 

---