Microchanneled membranes

Fig. 7.22 Schematic of a microchannel membrane oxygenator form vitro testing [2811.

Figure 8.4 A membrane module consisting of a stack of planar microchanneled membranes (left) and the air flow path In each membrane (right).

Mejdell, A.L., Jpndahl, M., Peters, T.A. et al. (2009a) Experimental investigation of a microchannel membrane configuration with a 1.4 pm Pd/Ag23wt.% membrane-Effects of flow and pressure. Journal of Membrane Science, 327 (1-2), 6-10. 

With a similar approach to decrease the distance between the wall or catalyst layer and the membrane surface drastically, all-metallic membrane modules with micromachined plates directly attached to the membrane have been fabricated by KIT [129]. Pd-alloy foils with different thicknesses ranging from 61 pm to 3 pm have been leak-tight integrated in the modules by laser welding (see Figure 7.11). This is considered a very practical approach and represents the first step towards the anticipated compact multi-layered microchannel membrane reformer system. 

Figure 7.13 (a) compact reactor design based on stacked microchannel membrane modules... 

Figure 4.17 Sketch of the microchannel membrane reactor. Reproduced from [26], With permission from Elsevier.

Stretched Polymers MF membranes may be made by stretching (Fig. 20-68). Semicrystalline polymers, if stretched perpendicular to the axis of crystallite orientation, may fracture in such a way as to make reproducible microchannels. Best known are Goretex produced from Teflon , and Celgard produced from polyolefin. Stretched polymers have unusually large fractions of open space, giving them very high fluxes in the microfiltration of gases, for example. Most such materials are very hydrophobic. 

Another way to use silicon wafers as DLs was presented by Meyers and Maynard [77]. They developed a micro-PEMFC based on a bilayer design in which both the anode and the cathode current collectors were made out of conductive silicon wafers. Each of fhese componenfs had a series of microchannels formed on one of their surfaces, allowing fhe hydrogen and oxygen to flow through them. Before the charmels were machined, a layer of porous silicon was formed on top of the Si wafers and fhen fhe silicon material beneath the porous layer was electropolished away to form fhe channels. After the wafers were machined, the CEs were added to the surfaces. In this cell, the actual diffusion layers were the porous silicon layers located on top of the channels because they let the gases diffuse fhrough fhem toward the active sites near the membrane. 

Membrane emulsification allows a precise control of the droplet size and monodispersity but the scale up of this process is difficult. MicroChannel emulsification is a promising technique but the low production rates restrict its use to highly monodisperse systems intended for high-technology applications. 

Micropumps based on piezoelectrics are made of pumping chambers that are actuated by three piezoelectric lead zirconate titanate disks (PZT). The pump consists of an inlet, pump chambers, three silicon membranes, three normally closed active valves, three bulk PZT actuators, three actuation reservoirs, flow microchannels, and outlet. The actuator is controlled by the peristaltic motion that drives the liquid in the pump. The inlet and outlet of the micropump are made of a Pyrex glass, which makes it biocompatible. Gold is deposited between the actuators and the silicon membrane to act as an upper electrode. Silver functions as a lower electrode and is deposited on the sidewalls of the actuation reservoirs. In this design, three different pump chambers can be actuated separately by each bulk PZT actuator in a peristaltic motion. 

Fig. 14 Standard configuration of hollow-based sensors. Flow is injected from a reservoir to the microchannel that also forms the hollow waveguide. Light interacts with the flow after crossing the input membrane and the signal is read after the output membrane...

The membrane technology has been tested in microfluidic devices. Normally a membrane is mounted between two chips, which make a microchannel, and fluid is allowed to pass through the membrane channel. Some papers are available on this method, which are discussed here. Hisamoto et al. [61] reviewed the application of capillary assembled microchips on PDMS as an online... 

Figure 5.7 Layout and dimensions of a membrane-based preconcentration device, (a) Filter-CE unit, (b) concentrator-CE device, (c) dimension of microchannel, and (d) out look of concentrator-CE device [83].

In the ESy, a miniature FS membrane is supported by two small, identical pieces of PP plastic, constituting a miniaturized membrane unit called an ESy extraction card (see the inset in Figure 4.7), which is housed under mechanical pressure in a card holder. The two PP pieces have dimensions of 2 mm x 20 mm x 40 mm. The inner surface of each piece contains a machined groove defining a microchannel of 1.65 pL volume (0.125 mm depth x 0.6 mm width x 22 mm length). The very small piece of FS membrane (2 mm width x 22 mm length x 25 pm thickness) is fastened in... 

The distinguishing feature of membrane emulsification technique is that droplet size is controlled primarily by the choice of the membrane, its microchannel structure and few process parameters, which can be used to tune droplets and emulsion properties. Comparing to the conventional emulsification processes, the membrane emulsification permits a better control of droplet-size distribution to be obtained, low energy, and materials consumption, modular and easy scale-up. Nevertheless, productivity (m3/day) is much lower, and therefore the challenge in the future is the development of new membranes and modules to keep the known advantages and maximize productivity. 

FIGURE 3.22 General idea of polymer membrane formation at the interface of a two-phase organic/aqueous flow in an X-shaped microchannel layout [435]. Reprinted with permission from the American Chemical Society. 

In addition, a pulled capillary tip was inserted and glued to the end of a microchannel to be used as a disposable nanoelectrospray emitter. Membrane... 

Serial dilution was achieved in a PDMS microchannel network for immunoassay, as shown in Figure 10.10. Immunoassay of IgG antibodies present in HIV+ human serum was conducted. Using 1 1 dilution ratio and 10 sequential dilutions (only three are shown in Figure 10.10), a dynamic range of 210 or 1000 of the serum concentration was obtained. The HIV antigens (gp41, gpl20) were first adsorbed on a PC membrane, which was then sealed by the PDMS... 

Wang,Y.X., Cooper, J.W., Lee, C.S., DeVoe, D.L., Efficient electrospray ionization from polymer microchannels using integrated hydrophobic membranes. Labchip 2004, 4, 363-367. 

In addition to packed and wall-coated systems, numerous researchers have investigated the fabrication of membranes, within microchannels, in which catalytic material can be incorporated. Employing a protocol developed by Kenis et al. (1999), Uozumi et al. (2006) deposited a poly(acryla-mide)-triarylphosphane palladium membrane (PA-TAP-Pd) (1.3 pm (wide), 0.37 mmol g-1 Pd) within a glass microchannel [100 pm (wide) x40pm (deep) x 1.4 cm (long)]. Once formed, the membrane was used to catalyze a series of Suzuki-Miyaura C-C bond-forming reactions, the results of which are summarized in Table 21. 

Another immobilization method was described by Maeda and coworkers [344], They developed a facile and inexpensive preparation method for the formation of an enzyme-polymeric membrane on the inner wall of the microchannel (PTFE) through cross-linking polymerization in a laminar flow. With this approach, a-chymotrypsin was immobilized successfully. The activity of the immobilized enzyme was tested using N-glutaryl-L-phenylalanine p-nitroanilide as substrate, and the reaction products were analyzed offline by HPLC. There was no significant difference in the hydrolysis efficiency compared to solution-phase batchwise reactions using the same enzyme/substrate molar ratio (Scheme 4.87). 

---