High temperature tolerance tests

This cost differential can be tolerated only in applications in which polymeric membranes completely fail in the separation [78]. Demanding separation applications, where zeolite membranes could be justified, due to the high temperatures involved or the added value of the components, and have been tested at laboratory scale, are the following separation of isomers (i.e., butane isomers, xylene isomers), organic vapor separations, carbon dioxide from methane, LNG (liquefied natural gas) removal, olefines/paraffins and H2 from mixtures. In most cases, the separation is based on selective diffusion, selective adsorption, pore-blocking effects, molecular sieving, or combinations thereof. The performance or efficiency of a membrane in a mixture is determined by two parameters the separation selectivity and the permeation flux through the membrane. 

K (440 °C), which is the upper temperature tolerated by commercial Fe304/ Cr203 high-temperature water-gas shift catalysts employed in the study [87]. Research goals were to test membranes under simulated high-temperature water-gas shift reactor conditions, 613-713 K (340-440 °C), and to resist differential pressures over 30 bar [81]. Palladium-based catalyst layers were approximately 400 nm on each side. 

The KVK is provided with a redundant helium purification system. In additon to its classical layout, it is additionally equipped with an injection/doping system for injecting such substances as CO, CH4 and H2O into the helium circuit in order to adjust a detined helium atmosphere. This is very important for helium systems operating above 850 °C because the metallic materials applied in high temperature helium systems are very sensitive to the chemical attack by helium impurities (i.e., inner oxidation or carburization, decarburization or formation of stable oxide layers on the surfaces). The material tests have indicated that only a very deHned narrow band of a permissible helium atmosphere composition can be tolerated and the permissible narrow band becomes smaller with increasing temperatures. In order to test the helium components in the KVK under realistic conditions, it was necessary to operate with a controlled helium atmosphere, i.e., with controlled impurities in the helium. 

Inasmuch as the use of epichlorohydrin concept, Agel et al. [13] developed a new and cheap type of anion exchange membranes (AEM) by preparing the polyepichlorohydrin (PECH) graft quaternary amines (DABCO, TEA) for use in alkaline cells. It s a quasi-gas impervious polymer membrane. The ionic conductivity was much improved to 10 S cm due to the low crystallinity and the anion exchange between Cf and OH ions on the polymer side chains. For the first time, the alkaline SPE employed in alkaline fuel cell, the test results exhibited good performance and could tolerate at high temperature up to 120°C. 

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