Long-term chemical stability

More work is urgently needed if membranes are to be used in conditions of very large or very small pH values or in steam. This holds even more for the thermal stability for microporous membranes and for both chemical and thermal stability of membranes for nanofiltration. 

In catalytic membrane reactors the compatibility of catalysts and membrane material requires attention. 

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The long-term chemical stability of the electromembranes affects the economics of any ED application and is generally determined by assessing... 

Significant progress has been made in alleviating the first two physical causes of membrane instability. The magnitude of the long-term chemical stability problem depends on the process. It is a major issue for carriers used to transport oxygen and olefins, but for carriers used to transport carbon dioxide, chemical stability is a lesser problem. 

Cooley G E and Nix K J, 1998, Method for the Eabrication of an Electrochemical Cell, Having Long Term Chemical Stability. US Patent 5,785,912. 

Long-term chemical stability of the dried product. 

The lifetime of a stationary phase in small molecule purification strongly depends of course on the type of cmde material that has to be purified. In general, the current spherical phases on the market (bare silica, C8, C18, cyano, diol, amino. . . ) based on purified metal-free silica have a very good mechanical as well as a long-term chemical stability if they are used under the appropriate conditions. For example, on production scale, a cyano-modified silica stationary phase could be kept in the same column for about 4 years allowing to purify multiton quantities of product. 

Chemical properties Small volume pressure, low vapor pressure, compatibility with other materials, long-term chemical stability, nontoxic, no fire hazard Economical Low price, recyclable, abundant... 

Mineral fillers are compounded with polymers for several purposes which include for mechanical reinforcement, as pigments, for enhancement of electrical properties or for lowering the material costs and thermal behaviour. They have an important role in the polymer due to their ability to fulfill a variety of roles. The use of fillers in polymer compounds provides additional benefits, for instance, the dispersion of the filler during compounding onto a polymer surface prevents delamination. This assures the long-term chemical stability of introduced chains, in contrast to physically coated chains [51-53]. 

The phase behavior studies reported in Figure 4 were performed in a brine of similar salinity as in Figure 3, but containing additives to ensure long-term chemical stability of the polymer among these additives was 0.4% isopropanol. These additives have a marginal effect on phase behavior and the same increase in microemulsion/ aqueous phase interfacial tension has been observed. However, we did not find the drastic increases in viscosity reported in Figure 3. 

Four frequently used normal-phase (NP) solvents will be discussed in detail hexane, dichloromethane, isopropyl alcohol, and ethyl acetate. Hexane is one of the most frequently used NP solvents. As in the case of acetonitrile, the low UV cutoff wavelength of 195 nm and the low background absorbance at and above 210nm make hexane an excellent choice for the majority of compounds analyzed in the NP mode (see Fig. 1.2). (Note that cyclopentane, cyclohexane, and heptane have similar UV characteristics.) In addition, under normal circumstances hexane has excellent long-term chemical stability. Because of the limited solubility of hexane, and of related hydrocarbons, in water and acetonitrile, their use in reversed-phase separations is rare. 

Long-term chemical stability under simultaneous oxidizing/wet fuel environments at 650 900 °C... 

The quality of the final encapsulated lipid powder depends on a number of factors including, the amount of Hpid encapsulated, the fraction of lipid exposed to the environment, the long-term chemical stability of the lipid, the flowability of the powder, the dispersibility of the powder, etc. These parameters can be controlled by selecting appropriate concentrations and types of components to make up the initial emulsion, as well as appropriate operating parameters for the spray dryer (e.g. flow rates, inlet, and outlet temperatures). Water soluble polymers (such as proteins and polysaccharides) are often used as emulsifiers to stabilize oil-in-water emulsions prior to spray drying, and after re-dispersion of the dried powder into liquid. Alternatively, water soluble polymers may make up part of the wall material that helps encapsulate and protect the lipid in the powder during storage. 

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