Chemical oxygen carrier

Fig. 10. Chemical structures of some oxygen carriers (A) five-coordinate cobalt Schiff-base Co(salPr), (B) four-coordinate cobalt Schiff-base Co(3-MeOsaltmen), (C) cobalt dry-cave.

Conditions during start-up can have a dramatic impact on time required to reach reasonable performance levels and on the ultimate reactor performance. Dilution rate, loading rate as measured by chemical oxygen demand (COD), carrier choice, inoculum amount, inoculum strategy, and inoculum species distribution are critical parameters (Sreekrishnan et al., 1991 Araki and Harada, 1994 Austermann-Haun et al., 1994 Yongming et al., 1993). Pore characteristics have a strong influence on time required for start-up and on the ultimate biomass density in the... 

Cho, P., Mattisson, T., and Lyngfelt, A., Comparison of iron-, nickel-, copper- and manganese-based oxygen carriers for chemical-looping combustion, Fuel, 83(9), 1215,2004. 

Corbella, B.M. et al., Performance in a fixed-bed reactor of titania-supported nickel oxide as oxygen carriers for the chemical-looping combustion of methane in multicycle tests, I EC Res., 45(1), 157, 2006. 

This background in combination with their chemical stability makes these liquids promising candidates as oxygen carriers for artifical blood substitution.14... 

Ammonium nitrate is the most readily available and cheapest salt of nitric acid, now manufactured wholly from synthetic ammonia and from nitric acid obtained by oxidation of ammonia. Ammonium nitrate was prepared for the first time as early as in 1659 by Glauber. The original experiments with it as a component of explosive mixtures began in the second half of the nineteenth century. Ammonium nitrate is the most widely used oxygen carrier, since it is an ingredient of the commonest group of high explosives. The reasons for this are to be seen in its properties and those of its explosive mixtures appreciable chemical stability, and low sensitiveness to friction and to shock. 

One promising approach to facilitated transport pioneered by Nishide and coworkers at Wasada University is to chemically bind the oxygen carrier to the polymer backbone, which is then used to form a dense polymer film containing no solvent [28], In some examples, the carrier species is covalently bonded to the polymer matrix as shown in Figure 11.29(a). In other cases, the polymer matrix contains base liquids which complex with the carrier molecule through the base group as shown in Figure 11.29(b). Because these films contain no liquid solvent, they are inherently more stable than liquid membranes and also could be formed into thin films of the selective material in composite membrane form. So far the selectivities and fluxes of these membranes have been moderate. 

Only the ideal cases of an isothermal-isobaric combustion process will be assumed. This combustion is superior to the usual isobaric-adiabatic process. Such an assumption can be verified more easily than in a normal combustion process, since in the cases studied here the chemical reactions take place at the surface of the oxygen carriers. 

If, for the methane combustion, copper oxide is used as an oxygen carrier, the chemical reaction in the "reactor" A (see Figure 5) is ... 

Another possible oxygen carrier is nickel oxide,the chemical reaction in reactor A in Figure 6 would be ... 

These basic thermodynamic considerations show that intermediate reactions in combustion processes can be very advantageous and that in some cases most or all of the chemical energy could be harnessed as mechanical energy at least theoretically. Important questions of reaction kinetics, actual design and applicability of such a device of the selected oxygen carriers have not been included in these fundamental thermodynamic equilibrium studies. 

Flammable by spontaneous chemical reaction practically all nitrates are powerful oxidizing agents. Some nitrates may explode when shocked, exposed to heat or flame, or by spontaneous chemical reacdon (see also EXPLOSIVES, HIGH). AU the inorganic nitrates act as oxygen carriers under proper condidons, these can give up their oxygen to other materials which may in turn detonate. Ammonium nitrate has all the properdes of the other nitrates, but it is also able to detonate by itself under certain condidons. 

In spite of the many modern techniques available to the chemist, the known chemistry of polynuclear cobalt (III) complexes is essentially that deduced by Werner 60 years ago. Since his work, no new polynuclear cobalt complexes have been prepared and characterized and no new reactions uncovered. Modem work in this area is being aimed at attaining a better understanding of the electronic structures inherent in polynuclear ions, which would be of value in a variety of active fields. The chemistry of polynuclear complexes is important in such new areas as synthetic oxygen carriers, electron transfer reactions, and transition metal catalysis. The fact that these new investigations are solidly based on Werner s pioneer investigations testifies to the genius with which he opened up a new area of coordination chemistry, with only the simple chemical techniques available to him. His work in the area of polynuclear cobalt(III) ammine complexes should continue to serve as a model of solid research for some time to come. 

Among the several types of homogeneously catalyzed reactions, oxidation is perhaps the most relevant and applicable to chemical industry. The well-known Wacker oxidation of ethylene to ethylene oxide is the classic example, although this is not a true catalytic process since the palladium (II) ion becomes reduced to metallic palladium unless an oxygen carrier is present. Related to this is the commercial reaction of ethylene and acetic acid to form vinyl acetate, although the mechanism of this reaction does not seem to have yet been discussed publicly. Attempts to achieve selective oxidation of olefins or hydrocarbons heterogeneously do not seem very successful. 

Chemical Looping Combustion (CLC). CLC is an oxyfuel concept where combustion is achieved using a metal oxide as the oxygen carrier without mixing fuel and air. A schematic of CLC concept is shown in Figure 11.14. 

Aubry J M. Chemical sources of singlet oxygen. 3. Peroxidation of water soluble singlet oxygen carriers with the hydrogen peroxide-molybdate system. J Org Chem 1989 54 726-8... 

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