Nitrous oxide removal

As discussed above the preferred technology for NOx removal in nitric add plants is selective catalytic reduction (SCR) using ammonia as a reductant and in many cases vanadium-pentoxide-type catalysts. Unfortunately, this process does not remove of N2O (nitrous oxide)221. 

Cobalt oxide (C03O4) catalysts are being used in some nitric acid plants as an alternative to platinum-rhodium (Pt-Rh). They generate less N2O, cost less and have a longer campaign life than Pt-Rh gauzes. (A paper in 2000 reported a conversion rate of ammonia to nitrous oxide as low as 0.5% over cobalt oxide catalyst)222. 

Absorption Column Turtbie L r Heat Exchanger H rJ. f Stack 

However cobalt oxide does have some drawbacks. Lower ammonia conversion efficiencies have been reported - as low as 88% to 92% in a high pressure plant compared with a typical value between 94% and 95% for Pt-Rh gauzes. The optimum operating temperature is 70 to 80°C lower than for Pt-Rh gauzes, and this could result in difficulties with the steam balance in a revamped plant. Cobalt oxide catalysts also suffer from reversible deactivation due to the reduction ofCo304 to CoO in the upper parts of the catalyst bed222. 

Nitrous Oxide Removal Between the Reactor and the Absorption Column Inlet 

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Figure 9.11. Nitrous oxide removal facility downstream of expander. (Reproduced by permission of Energy Research Centre of the Netherlands)...

Amino groups are acetylated normally and are converted to hydroxy compounds with nitrous acid. Tlie 2,3-diamino [2,3-f>] derivative gives an imidazolo fused pyridopyrazine with acetic anhydride (75USP3898216). The oxidative removal of hydrazino groups has been used to give ring-unsubstituted derivatives (79JHC305). 

Nitrous oxide [10024-97-2] M 44.0, h -88.5°. Washed with cone alkaline pyrogallol solution, to remove O2, CO2, and NO2, then dried by passage through columns of P2O5 or Drierite, and collected in a dry trap cooled in liquid N2. Further purified by ffeeze-pump-thaw and distn cycles under vacuum [Ryan and Freeman J Phys Chem 81 1455 1977],... 

Since nitrous oxide, NjO, is a designated "greenhouse" gas, and may contribute to depletion of the ozone layer, its removal from emissions to atmosphere is desirable [1]. However, there are several reports that NjO can be formed at low selectivity as an undesirable by-product of NO+CO conversions during the initial warm-up-from-cold periods in three-way-catalytic (TWC) converters or components thereof [1-3]. TWC s commonly contain Rhodium and Ceria and although N,0 dissociation over RhjO, has been extensively studied [4], the following are among mechanistic possibilities as yet... 

Van Deyck, F., Weiss, F.J., Verbeck, R. el al. (1985) Removal of nitrous oxide from gases containing hydrogen, nitric oxide and nitrous oxide, US Patent 4507271. 

Organic solvents inhaled by abusers include gasoline, glue, aerosols, amyl nitrite, butyl nitrite, typewriter correction fluid, lighter fluid, cleaning fluids, paint products, nail polish remover, waxes, and varnishes. Chemicals in these products include nitrous oxide, toluene, benzene, methanol, methylene chloride, acetone, methyl ethyl ketone, methyl butyl ketone, trichloroethylene, and trichloroethane. 

Nitrous oxide (N2O 99.0 %) and helium (He 99.999 %) from commerical cylinders were purified through a dry ice-methanol trap to remove water vapor. 

The reactor used consists of a Pyrex glass tube containing 260.6 g catalyst and was immersed in an oil bath. The temperature of the catalyst bed remained constant within + 0.1°C of the desired temperature. Oxygen (0 99.9%), nitrogen (N 99.9%), nitrous oxide (N ,0 99.99%), carbon dioxide (99.9%) and helium (He 99.999%) from commercial cylinders were purified through a dry ice-methanol trap to remove water vapor. 

N, O-Diacylated or O-alkylated N-hydroxysulfonamides release nitroxyl (HNO) upon hydrolysis or metabolic dealkylation, as determined by gas chromatographic identification of nitrous oxide in the reaction headspace [27-29, 38]. Scheme 7.5 depicts the decomposition of a representative compound (7) to a C-acyl nitroso species that hydrolyzes to yield HNO. Either hydrolysis or metabolism removes the O-acyl or O-alkyl group to give an N-hydroxy species that rapidly decomposes to give a sulfinic acid and an acyl nitroso species. This C-acyl nitroso species (8) hydrolyzes to the carboxylic acid and HNO (Scheme 7.5). These compounds demonstrate the ability to relax smooth muscle preparations in vitro and also inhibit aldehyde dehydrogenase, similar to other HNO donors [27, 29]. 

Oxidation of iodoalkanes involves removal of an electron from the halogen nonbonding orbital. The radical-cations of primary and secondary alkyl iodides can be identified in aqueous solution by their absorption spectra and have half-lives of microseconds [1]. They are formed during pulse radiolysis of the iodoalkane in aqueous solution in the presence of nitrous oxide. This system generates hydroxyl radicals, which remove an electron from the iodine atom lone pair. Iodoalkane radical-anions complex with the lone-pair on other heteroatoms to form a lollo three-electron bond. In aqueous solution, the radical-cation of iodomethane is involved in an equlibrium indicated by Equation 2.1. 

Until recent times, the only toxicological hazards attributable to nitrous oxide were those common to asphyxiants, with death or permanent brain injury occurring only under conditions of hypoxia. A number of untoward and toxic effects have now been associated with exposure. One of the earliest findings was that patients given 50% nitrous oxide and 50% oxygen for prolonged periods, to induce continuous sedation, developed bone marrow depression and granuloqn openia. The bone marrow usually returned to normal within a matter of days once the nitrous oxide was removed, but several deaths from aplastic anemia have been recorded. ... 

A reactive intermediate may be responsible for the copper catalysis of the hydroxylamine reaction. The intermediate formed in the silver-catalyzed reaction, if it has any real existence, is not further oxidized but breaks down into nitrogen and water. Oxidation of hydroxylamine by cupric ion, on the other hand, yields predominately nitrous oxide. The intermediate formed by the removal of a single electron from the hydroxylamine in this reaction must be further oxidized to yield the final product. Such an intermediate may react readily with silver ions in solution. 

According to the vendor, this project could provide a compact, low-cost reactor to treat aqueous mixed waste streams containing nitrates or nitrites, eliminate the need for chemical reagents, and minimize or eliminate secondary wastes such as nitrous oxide and secondary products such as ammonia, H2, and O2 that are prevalent with other nitrate destruction processes. By removing nitrates and nitrites from waste streams before they are sent to high-temperature thermal destruction and vitrification, production of NO can be decreased with the attendant decrease in off-gas system requirements. Biocatalytic nitrate destruction is applicable to a wide range of aqueous wastes with a highly variable composition. All information is from the vendor and has not been independently verified. 

Fig. 24. Adsorption of nitrous oxide on a platinum surface. Ordinate photoelectric yield I in electrons per light quantum. = 265.5 mg T = 83°K. (a) smashing of the N2O capsule (6) complete removal of the liquid air from N2O [according to (58)].

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