Chemistry of inorganic compounds – Oxygen or compound thereof
Patent
1980-07-15
1982-07-20
Meros, Edward J.
Chemistry of inorganic compounds
Oxygen or compound thereof
4232105, 423219, C01B 1302
Patent
active
043405789
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Technical Field
This invention relates to processes wherein oxygen is produced by a decomposition type chemical reaction, and then the oxygen deficient composition, termed an "oxygen acceptor", is regenerated for recycle by reaction with air or other oxygen containing gas mixture.
Background Art
The prior art of this field of invention includes U.S. Pat. Nos. 3,856,928, 3,579,292, 2,418,402, and 3,121,611. Numerous oxygen acceptors have been identified, including BaO, Na.sub.2 MnO.sub.3, CuCl.sub.2, SrO, and Hg. The attribute of chemical air separation processes as a class is that the high pressure air which undergoes reaction and thereby loses part of its oxygen is still at high pressure after the reaction. Therefore it can be expanded through a turboexpander, recovering most or all of its compression energy. In contrast, in cyrogenic processes the air must be cooled and then depressurized to develop the desired cooling effect, thereby expending the compression energy. The most efficient liquefaction processes consume electrical energy at the relatively high rate of 0.29 kwhr (1 MJ) per kg O.sub.2 produced, which is equivalent to a thermal input of 22.8 kcal/mole O.sub.2 or 1300 BTU/lb O.sub.2, given 33% conversion efficiency. Nevertheless, the liquefaction process has been superior to prior art chemical separation processes for various reasons. Most prior art processes have involved either an acceptor or an oxidized acceptor or both which are present in the solid state. This has made circulation of the acceptor composition difficult, and therefore most processes have been batch mode. Most batch mode processes have involved large pressure differences between the oxidation and decomposition parts of the cycle, and therefore have suffered from excessive vent and purge losses. Some processes have attempted to minimize this pressure difference by conducting the decomposition reaction at a higher temperature than the oxidation reaction. This imposes a large heat requirement: not only does the sensible heat of the acceptor have to be furnished, but the full endothermic heat requirement of the decomposition reaction must also be supplied. Those two heat requirements substantially exceed the 22.8 kcal/ mole needed for liquefaction. Another problem encountered in prior art processes is that the equilibrium pO.sub.2 of the acceptor composition withdrawn from the absorber has always necessarily been less than or equal to the pO.sub.2 of the exhaust gas withdrawn from the absorber. This is because oxygen can only be transferred from a gas to an acceptor if the pO.sub.2 of the gas is higher than that of the acceptor. Therefore the larger the fraction of oxygen extracted from the supply air, the lower the exhaust pO.sub.2 becomes, and hence the lower the equilibrium pO.sub.2 of the oxidized acceptor, making decomposition more difficult and inefficient. Other problems with the prior art processes are that some of them produce unacceptable amounts of impurities in the product gas, e.g. chlorine or mercury, and some experience an unacceptable loss rate of the acceptor, due to chemical breakdown, chemical inactivation, or other possible causes.
The background art which describes the chemical behavior of molten alkali metal nitrate and nitrite salts consists of numerous articles from technical journals, including the following: Bartholomew, R. F., The Journal of Physical Chemistry, 70, 1966, pages 3442-3446; and Freeman, E. S., The Journal of Physical Chemistry, 60, 1956, pages 1487-1493, published in Easton, Pennsylvania by the Mack Printing Co. Several characteristics of the reaction between those salts and oxygen have been noted. High levels of nitrogen oxides have been invariably noted, as high as several percent, which is several orders of magnitude above environmental limits. The reaction kinetics have been quantified, showing a relatively high activation energy. At higher temperatures the salt decomposes to the solid oxide.
DISCLOSURE OF INVENTION
The invention claimed is an oxygen acceptor comp
REFERENCES:
patent: 588615 (1897-08-01), Stuart
patent: 2418402 (1947-04-01), Gorin
patent: 3310381 (1967-03-01), Guerrieri
patent: 3766718 (1973-10-01), Campbell
patent: 3856928 (1974-12-01), Tarman et al.
Freeman, "J. Physical Chemistry", vol. 60, 156, pp. 1487-1493.
Bartholomew, "J. Physical Chemistry", vol. 70, 1966, pp. 3442-3446.
Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 10, 1966, pp. 854-855.
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