Oxide, nitrogen

Most nitrogen products have been based on nitrogen oxides and ammonia so the history of fixation of nitrogen as nitrogen oxides and ammonia is of interest. 

Nitrogen trioxide and nitrogen pentoxide are the anhydrides of nitrous acid and of nitric acid. They are difficult to prepare and are unstable. 

Nitrous oxide (laughing gas) is a colorless gas. It has a slightly sweet odor and taste and is somewhat soluble in water. It supports combustion of most substances almost as well as oxygen. Since the 1840 s the major use of nitrous oxide has been as an anesthetic - especially by dentists. It is also used as a propellant in some aerosol cans, in atomic absorption spectrophotometry, in cryosurgery and in racecar engines to provide extra power and acceleration. 

Nitric oxide is a colorless gas that is insoluble in water. It does not support the combustion of most substances. The most noticeable chemical characteristic of nitric oxide is the ease with which it combines with oxygen to form nitrogen dioxide. Nitric oxide is produced in considerable quantities in the industrial preparation of nitric acid. In these reactions the gas is not isolated. It is immediately oxidized to nitrogen dioxide. 

Nitrogen dioxide is a red-brown gas that is very soluble in water. It has an unpleasant odor and is quite poisonous. When nitrogen dioxide is cooled, its brown color fades to a pale yellow. Molecular weight determinations show that this yellow substance has a formula of N2O4 (nitrogen tetroxide)  

Canfield and Rohrback ° reported on the reaction of some electron-deficient difluo-roaminoalkenes with dinitrogen pentoxide in chloroform at subambient temperatures. Contrary to previous work that the /3-nitro-nitrate ester should be the main product, the corresponding vtc-dinitrate esters were isolated from these reactions l,4-bis(iV,iV-difiuoroamino)-2,3-butanediol dinitrate (55), 3,4-bis(iV,iV-difluoroamino)-l,2-butanediol dinitrate (56) and 3-(iV,iV-difluoroamino)-1,2-propanediol dinitrate (57) were isolated in 30 %, 27 %, and 55 % yields respectively, from the parent alkenes. 

There are two sources of nitrogen in the combustion process. Some fuels, notably coal and heavier oil, contain nitrogen compounds. When these fuels are burned they release oxides of nitrogen. The other source of nitrogen is the high temperature reaction of atmospheric oxygen and nitrogen. 

More properties of the oxides of nitrogen are given in the appendix. 

On the right-hand side of Fig. IS the atmospheric pathways of NH3 are plotted. Values of different terms are based on the references mentioned. In the figure, NH3 and NH4 burdens are also given. All numbers are expressed in nitrogen equivalents. In the total deposition value, a dry deposition of 10 x 10b t yr-1 is postulated. It should be noted that the accuracy of the values is not better than a factor of 2 or 3. It follows from these data that the residence time of NH3 in the atmosphere is around 5 days. 

During denitrification processes in acidic soil NO is produced by chemical destruction of nitrite. Under aerobic conditions or in the air, NO is oxidized to form N0220  

On the basis of the results of different authors Robinson and Robbins (1970) estimated concentrations of 2 ppb (NO) and 4 ppb (N02) for continental areas between 65° N and 65° S, while for other territories they proposed 0.2 ppb and 0.5 ppb, respectively. On the other hand, Soderlund and Svensson (1976) speculate that the sum of NO and N02 concentrations in clean tropospheric air, except temperate regions, is less than 1 ppb. Over temperate regions the NOx level is about 4 ppb. The above NOx levels for remote areas were confirmed recently by Cox (1977), who measured mean concentration of 0.12 ppb NO and 0.34 ppb N02 mean concentrations on the Irish West Coast. 

Soderlund and Swensson (1976) calculate for the global NOx—N burden values between 1 x 106 and 4 x 106 t by using the above tropospheric concentrations. 

As mentioned earlier, a large portion of NOx is of biological origin. The global strength of this source was calculated to be (21-89) x 1061 yr 1 by balancing source and sink terms (Soderlund and Svensson, 1976). Another NOx source at the Earth s surface is provided by man s activities. This source mainly arises from coal, gasoline 

Atomic oxygen can also react with hydrocarbons to form other chemicals that are toxic and also impart an odor to the air. On a sunny day only about 0.2 ppm of nitrogen oxides and 1 ppm of reactive hydrocarbons are sufficient to initiate these photochemical smog reactions. The hydrocarbons involved in these reactions come mostly from unburned petroleum products such as gasoline, and the nitrogen oxides come from the exhausts of internal combustion engines. 

In the following sections we shall look at the major ingredients of photochemical smog—the oxides of nitrogen and hydrocarbons, and the secondary pollutant ozone. 

Primary pollutants Pollutants emitted directly into the atmosphere 

Photodissociation Decomposition of a reactant, caused by the energy of light 

Free radical A species that has one or more unpaired electrons 

Since it is chemically inert no special materials of construction are required. Selected physical properties are listed in Table 9.20. 

Nitrous oxide is a colourless, non-flammable, non-corrosive gas with a sweetish odour and taste. It is prepared both in the laboratory and on a commercial scale by heating ammonium nitrate  

Heating must be terminated when two-thirds of the nitrate has decomposed since explosive nitrogen trichloride may be formed from traces of ammonium chloride impurity. 

Nitrous oxide may also be obtained by the controlled reduction of nitrates or nitrites, decomposition of hyponitrites, or thermal decomposition of hydroxylamine. 

It is transported in high pressure steel cylinders equipped with brass valves. 

Alkali-metal thionylimides are prepared by the reaction of McsSiNSO with the appropriate alkali-metal tert-butoxide in THF (Eq. 9.1). The more soluble [(MeaNlsS] salt has also been reported (Eq. 9.2).  

The tetramethylammonium salt [Me4N][NSO] is obtained by cation exchange between M[NSO] (M = Rb, Cs) and tetramethylammonium chloride in liquid ammonia. An X-ray structural determination reveals approximately equal bond lengths of 1.43 and 1.44 A for the S-N and S-O bonds, respectively, and a bond angle NSO of ca. 127°. The [NSO] anion (9.1) exhibits three characteristic bands in the IR spectrum at ca. 1270-1280, 985-1000 and 505-530 cm , corresponding to o(S-N), o(S-O) and (5(NSO), respectively. Ab initio molecular orbital calculations, including a correlation energy correction, indicate that the [NSO] anion is more stable than the isomer [SNO] by at least 9.1 kcal mol .  

It is transported in high pressure steel cylinders equipped with brass valves. Physical properties are summarized in Table 9.21 and the vapour pressure/temperature relationship  

Experimental data widi hydrogen powered ICE cars have shown that if optimized to low NOX levels by using ultra-lean mixtures, the former US standard of 0.6 g/km could be met without catalyst [69]. 

The present concentration of hydrogen in the atmosphere is 510 ppb which translates into a total mass of approx. 200 million tons, and the annual increase rate is 3 ppb. The average lifetime is two years before chemically bound or lost into space. The H2 emissions from the industrial use are with 1 million t/yr small compared with other natural and anthropogenic sources. In case of the hydrogen economy based on a 80 % CO2 reduction scenario, H2 emissions are predicted to be 1.1 - 1,4 million t/yr [108]. 

Hydrogen, and to a much higher extent, methane take part in a whole variety of chemical reactions in the atmosphere responsible for ozone depletion [108]. 

The ecological consequences of an accidental (liquid) hydrogen release are harmless due to its untoxic character compared with an uncontroled spill of fossil fuels [108]. 

Emissions of other pollutants, hydrocarbons or CO, from hydrogen combustion in ICE become significant, if the engine bums excess lubricating oil. These emissions can be minimized by regular inspection and maintenance [69]. 

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The sample is burned in oxygen at 1000°C. Nitrogen oxide, NO, is formed and transformed into NO2 by ozone, the NO2 thus formed being in an excited state NO. The return to the normal state of the molecule is accompanied by the emission of photons which are detected by photometry. This type of apparatus is very common today and is capable of reaching detectable limits of about 0.5 ppm. 

Lamp Method the sample is burned in a closed system in an atmosphere of 70% CO2 and 30% oxygen in order to avoid formation of nitrogen oxides. This method was to have been abandoned as it takes three hours to carry out, but remains officially required for jet fuel sulfur analysis. 

The density of heavy fuels is greater than 0.920 kg/1 at 15°C. The marine diesel consumers focus close attention on the fuel density because of having to centrifuge water out of the fuel. Beyond 0.991 kg/1, the density difference between the two phases —aqueous and hydrocarbon— becomes too small for correct operation of conventional centrifuges technical improvements are possible but costly. In extreme cases of fuels being too heavy, it is possible to rely on water-fuel emulsions, which can have some advantages of better atomization in the injection nozzle and a reduction of pollutant emissions such as smoke and nitrogen oxides. 

However, such a level can still be considered too high for vehicles having 3-way catalytic converters. In fact, results observed in the United States (Benson et al., 1991) and given in Figure 5.20 show that exhaust pollutant emissions, carbon monoxide, hydrocarbons and nitrogen oxides, increase from 10 to 15% when the sulfur level passes from 50 ppm to about 450 ppm. This is explained by an inhibiting action of sulfur on the catalyst though... 

These are carbon monoxide, CO, unburned hydrocarbons (HC), and the nitrogen oxides, NO. In the U.S.A., a program called Auto/Oil (Burns et al., 1992), conducted by automotive manufacturers and petroleum companies, examined the effect of overall parameters of fuel composition on evaporative emissions and in the exhaust gases. The variables examined were the aromatics content between 20 and 45%, the olefins content between 5 and 20%, the MTBE content between 0 and 15% and finally the distillation end point between 138 and 182°C (more exactly, the 95% distilled point). 

Ozone, known for its beneficial role as a protective screen against ultraviolet radiation in the stratosphere, is a major pollutant at low altitudes (from 0 to 2000 m) affecting plants, animals and human beings. Ozone can be formed by a succession of photochemical reactions that preferentially involve hydrocarbons and nitrogen oxides emitted by the different combustion systems such as engines and furnaces. 

Influence of the Nitrogen Content of Heavy Fuels on Nitrogen Oxide Emissions... 

Agnew S F, Swanson B I, Jones L FI, Mills R L and Sohiferl D 1983 Chemistry of nitrogen oxide (N2O4) at high pressure observation of a reversible transformation between moleoular and ionio orystalline forms J. Phys. Chem. 

Pollution control such as the reduction of nitrogen oxides, halocarbons and hydrocarbons from flue gases [37] is another important field of plasma-assisted chemistry using non-thennal plasmas. The efficiency of plasma chemical reactions can be enhanced by introducing catalysts into the plasma [38, 39]. 

There are many compounds in existence which have a considerable positive enthalpy of formation. They are not made by direct union of the constituent elements in their standard states, but by some process in which the necessary energy is provided indirectly. Many known covalent hydrides (Chapter 5) are made by indirect methods (for example from other hydrides) or by supplying energy (in the form of heat or an electric discharge) to the direct reaction to dissociate the hydrogen molecules and also possibly vaporise the other element. Other known endothermic compounds include nitrogen oxide and ethyne (acetylene) all these compounds have considerable kinetic stability. 

Again, nitric acid readily dissolves lead but is unable to oxidise lead beyond the oxidation state -P 2. The reduction products of the nitric acid vary with the concentration of acid used, and a number of nitrogen oxides are usually obtained. Warm dilute nitric acid gives mainly nitrogen oxide, NO. 

In the presence of catalyst, usually platinum, ammonia is oxidised by oxygen (and air) to nitrogen oxide. NO. This reaction, used to obtain nitric acid from ammonia (p. 238), can be demonstrated in the laboratory using the apparatus shown in Figure 9.4 the oxygen rate should be slow. 

No reaction with nitrogen oxide Phosphorus burns leaving an equal volume of gas (nitrogen)... 

Paramagnetism implies the presence of single, unpaired, electrons. Hence nitrogen oxide is paramagnetic and so is any other molecule or ion containing unpaired electrons. If the total number of electrons in an ion or molecule is odd. then it must be paramagnetic but some molecules (e.g. Oj and ions have an even number of electrons and yet are paramagnetic because some of them are unpaired. 

Nitrogen oxide does show some ability to gain an electron and when passed into a solution of sodium in liquid ammonia, the... 

Non-metals — These are often oxidised to the corresponding oxoacid, and nitrogen oxide is formed. For example, sulphur gives sulphuric acid with cold concentrated nitric acid ... 

Nitrous acid is unstable, decomposing to give nitric acid and evolving nitrogen oxide ... 

Oxygen, like nitrogen oxide, NO, shows little tendency to dimerise although the presence of the unstable, weakly bonded species, tetratomic oxygen O4, has been reported as a constituent of liquid oxygen. 

At high temperatures oxygen reacts with the nitrogen in the air forming small amounts of nitrogen oxide (p. 210). Sulphur burns with a blue flame when heated in air to form sulphur dioxide SO2, and a little sulphur trioxide SO3. Selenium and tellurium also burn with a blue flame when heated in air, but form only their dioxides, Se02 and Te02. 

The final products are then sulphuric acid, nitrogen oxide and oxygen the two latter react and the cycle goes on. Theoretically therefore, the nitrous fumes are never used up. In practice, however, some slight replacement is needed and this is achieved by adding a little concentrated nitric acid to the mixture in the Glover tower ... 

When concentrated sulphuric acid is added to a nitrate in the presence of aqueous iron(II) sulphate, the nitrogen oxide liberated forms a brown complex [Fe(H20)5N0] which appears as a brown ring at the acid-aqueous interface (test for a nitrate, p 243). 

Ethylene Aluminum trichloride, carbon tetrachloride, chlorine, nitrogen oxides, tetrafluo-roethylene... 

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