Multi-channel membrane

A recent development of a ceramic membrane appears to be promising for selectively removing oxygen from air. Multi-channel membrane elements have been fabricated for that purpose [Anonymous, 1995]. The membrane has the potential for reducing the cost of converting natural gas to synthesis gas. 

Product yield as a function of residence time for a fixed-bed reactor (triangles), a multi-channel microreactor (circles) and a multi-channel membrane microreactor (squares) (Lai etal., 2003) (Copyright permission 2006 Royal Society of Chemistry). 

Many commercial ceramic membranes nowadays come in the form of a monolith consisting of multiple, straight channels parallel to the axis of the cylindrical structure (Figure 3.6). The surfaces of the open channels are deposited with permselective membranes and possibly one or more intermediate support layers. The porous suppon of these multi-channel structures are produced by extrusion of ceramic pastes described above with a channel diameter of a few millimeters. Their lengths are somewhat limited by the size of the furnaces used to dry, calcine and sinter them and also by such practical considerations as the total compact weights to be supported during heat ueatment and the risk of distortion in the middle section. It should be noted that this type of honeycomb... 

The overall membrane element shape comes in different types sheet, single tube, hollow fiber, and multi-channel monolith. Photographs of some commercial membrane elements are shown in Figure 5.1. The use of disks (or sheets) has been confined to medical, pharmaceutical and laboratory applications, while tubes and monoliths are employed in larger-scale applications ranging from removal of bacteria from wine and beer fermentation to oil-water separation to waste water ueatmenL... 

A generalization of this concept of a monolithic multi-channel honeycomb structure is described in a patent by Hoover and Roberts [1978]. An integral support of porous ceramic material has a multiplicity of parallel passageways (or open channels). These passageways are substantially uniformly spaced. On the surface of these channels are coated with a permselective membrane layer. The feed stream flows inside the channels. The membrane, being the first layer in direct contact with the process stream, is selective to one or more species in the stream. In the normal cases of properly weued membrane pores, the permeate under a driving force will uansport through the membrane, any... 

Only a limited number of studies has begun to emerge in this area. The available studies encompass various levels of details. Some use CFD to focus the simulation on the How of liquid and particles through membrane pores while others model fluid flow through a single membrane tube. CFD simulation of fluid flow through a multi-channel monolithic membrane element has also been done. 

The cost of the support element and the lengthy steps involved in zeolite film synthesis makes zeolite membranes very expensive compared to the well established polymeric membranes. MFI membranes are relatively expensive and their price (about 5.000 /m2) is typically due by 50% to the support and by 50 % to chemicals. Consequently the development of template-free synthesis on cheaper supports (multi-channels, ceramic foils/plates, capillaries, hollow fibers) is seriously considered, in parallel with the development of continuous, automatic, reliable, and reproducible production methods. 

For reaching the same oxygen production, single-hole tubes of 10 mm diameter would increase the amount of units to 41, comparable to multi-channel monoliths (39 units). The extreme restriction in membrane length of hollow fiber systems would result in 1,800 modules. The difference in expansion behavior of vessel wall and membrane tubes can be compensated by mounting the tubes in a... 

We also developed a novel synthesis method ( in situ aging - microwave synthesis method) for microwave synthesis of zeolite membranes without seeding, which was adapted to the scale-up of the membrane synthesis to integrated supports (e.g. multi-channel tube modules and hollow fibers) [14],... 

Figure 3. Oat / iV/ge National Laboratory unsaturatedflow facility. The intact cores are contained in large polyvinyl chloride pipes, and a filter membrane was c ed to the sediments within a fabricated acrylic endcap at the lower boundary. Tension was maintained through the large white vacuum chambers, which also housed a fraction collector for samples of column effluent. Influent was delivered by a multi-channel pump at the upper boundary. Tensiometers, visible in the side of...

Some types of membrane and catalytic membranes for three-phase reactions prepared in the Genoa membrane research group. Porous flat sheet catalytic membrane (a) unsupported (b) supported on a polymeric non-woven substrate, (c) Hollow fibres (d) single-channel Pd membrane supported on alumina porous substrate (e) three-channel catalytic zeolite membrane (f) multi-channel porous alumina substrate. 

Partial oxidation of organic compounds (formic acid) Asymmetric porous ceramic membranes F t dispersed in the top layer Tubular single channel and multi-channel Liquid phase on the catalytic side, gas phase on the support side lojoiu et al. (2006, 2007)... 

In addition to the planar geometry, inorganic membranes can also be produced in flat disk, tubular (dead-end or not), monolithic multi-channel, or hollow fiber configurations as shown in Figure 1.6. Disk membranes are often used in the laboratory because they can easily be fabricated by the conventional pressing method. In the case of tubes, they can be assembled in a module containing a number of tubes connected to a single manifold system. 

The multi-channel monolithic form is developed to increase the mechanical robustness and the surface area-to-volume ratio, which gives more separation area per unit volume of membrane element. In the monolithic membranes, the monolith bulk is a porous support and the separation layer is produced on the inner surface of the channels. Therefore, feed is introduced in the channels and the permeate is obtained from the membrane wall, as shown in Figure 1.7. The surface area-to-volume ratio of the multi-channel monolithic membrane ranges from 130-400m m- compared with 30-250m m" for tubes. Honeycomb multichannel monolithic membranes can even reach up to 800 m m" of surface area-to-volume ratio. 

Figure 1.7 Schematic picture of a multi-channel monolithic membrane. Reproduced from [8], With permission from Elsevier.

Wan et al. [39] investigated the selective oxidation of aniline by hydrogen peroxide to azoxybenzene in a multi-channel MMR, with or without water removal, employing TS-1 nanozeolite as catalyst. The reaction was conducted at different residence times and temperatures. A hydrophilic ZSM-5 membrane was used to remove water selectively from the reaction mixture by membrane pervaporation. The results indicate that catalyst deactivation was reduced during the reaction. An improvement in the product yield and selectivity toward azoxybenzene was also observed. Increasing temperature was beneficial for both yield and selectivity, but beyond 340 K, microreactor operation was ineffective due to bubble formation and hydrogen peroxide decomposition. 

Extmsion to make tubular membranes (with a mono- or multi-channel geometry). 

Figure 17. Multi-channel activity in a patched membrane clamped at...

Y. Zhang, C. Qin, and J. Binner. (2006). Processing multi-channel alumina membranes by tape casting latex-based suspensions, Ceram. Int. 32 811-818. 

Voltage-dependent Ca2+ channels are a family of multi-subunit complexes of five proteins responding to membrane depolarisation with channel opening allowing the influx of calcium into a cell. Voltage-dependent calcium channels are subdivided into three subfamilies the HVA DHP-sensitive L-type calcium channels, the HVA DHP-insensitive calcium channels and the LVA T-type calcium channels [2]. 

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