Phase membrane-sandwich type

The association constant for ion binding of Cyclo-(Pro-Gly)3 b nearly the same as that of antamanide, but the selectivity for Ca of Cydo-(Pro-Gly)3 is inferior to that for Na" " of antamanide (144). Cyclo-(Pro-Gly)3 resembles the K -specific cyclic hexadepdpeptide aiitibiotic enniatin (145), in the aspect that both cycUc compounds form sandwich-type comjdexes with ions. It is very likely that Cyclo-(Pro y)3 transports ions across a membrane vb the formation of a club sandwich-type complex. The metal-ion complex of Cyclo-(Pro<]tly)3 is extractable with water from organic phase. A specific behavior of clo-(Pro-Gly)3 in the ion tran rt throu a membrane b expected from fhb property. 

The first sandwich-type membrane separator used in FI liquid-liquid extraction was described by Kawase et al.[9] in 1979. Owing to its better performance compared to gravitational separators, it soon became the most frequently used type of phase separators. 

Factors which are reponed to influence the phase separation efficiency of sandwich-type membrane separators include ... 

The main drawback of the sandwich-type membrane separator is associated with the limited lifetime of the membrane. Operations are interrupted periodically due to breakdown of the membrane, which is particularly objectionable for applications in process control or continuous monitoring. In such cases, it is advisable to use a supporting grid for the membrane to prolong its lifetime, possibly with some sacrifice in the phase separation efficiency. 

Barnes and Wang [48,49] studied the performance of both sandwich and tubular-type dual-phase membrane gas-di sion separators in the determination of As(V) by hydride generation ICP-OES, and obtained better detection limits with a sandwich design, while both were found to be superior to using a gas-expansion separator. Their results seem to suggest that dual-phase membrane separators are better suited at least for combination to ICP-OES systems in comparison to gas expansion separators, but further research efforts may be necessary to reach decisive conclusions. 

T-tube phase segmentor and sandwich-type membrane phase separator. 300 cm long, 0.5 mm i.d. PTFE tubing extraction coil. 

PTFE sandwich-type membrane phase separator with PTFE microporous membrane. 

Electrochemical reactions take place at the catalyst layers of the fuel cell. At the anode and cathode, hydrogen is oxidized (eq 1) and oxygen is reduced (eq 2), respectively. These layers are often the thinnest in the fuel-cell sandwich but are perhaps the most complex because this is where electrochemical reactions take place and where all of the different types of phases exist. Thus, the membrane and diffusion media models must be used in the catalyst layer along with additional expressions related to the electrochemical kinetics on the supported electrocatalyst particles. 

A different type of a multiple membrane reactor system was proposed and modeled by Kim and Datta [5.68]. Their membrane reactor consists of liquid-phase catalytic layer supported on a porous matrix, which is sandwiched in between two different membranes. They considered a simple irreversible A- B reaction. The membrane, which is in contact... 

Generally, cell warming occurs due to heat generated in the electrochemical reactions and due to Joule electric power dissipated by the currents. The fuel cell sandwich supports two types of currents (i) electron current in the carbon threads of the GDL and CLs, and (ii) proton (ionic) current in the bulk membrane (electrolyte) and in the electroljde phase dispersed in the CL. For the sake of brevity, we will consider the proton current however, the discussion below is applicable to the ionic current in SOFCs as well. 

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