Nitrogen cycle solutions

Devol, A. H. (2003). Nitrogen cycle—Solution to a marine mystery. Nature 422, 575—576. 

The Schlenk tube was filled with [Ru(allyl)2(COD)n] (6 mg), ((S j-BiNAP) (21 mg) and purged twice using vacuum/nitrogen cycles. Anhydrous acetone was added (2 mL) to give a white suspension. The solution was stirred for 30 minutes at room temperature. 

Figure 1. A simplified watershed nitrogen cycle, with major pathways (arrows) and their effects on the watershed hydrogen budget (numbers in circles) shown. Circled numbers represent the number of hydrogen ions transferred to the soil solution or surface water ( +1) or from the soil solution or surface water (-l)for every molecule of N03 or NH4 + that follows a given pathway. For example, nitrification follows the pathway for NH4 + assimilation into microbial biomass ( + l) and is leached out as N03 ( + 1), for a total hydrogen ion production of +2 for every molecule of N03 produced.

Ammonia is found in the environment as the result of natural and industrial processes. It is released into the environment by the breakdown of organic wastes, and it is a constituent of the soil, the atmosphere, and bodies of water. Ammonia is also a key intermediate in the nitrogen cycle and is a product of amino acid metabolism (WHO 1986). Anhydrous ammonia is used in the production of nitric acid, explosives, synthetic fibers, and fertilizers (Budavari 1989). It is used as a refrigerant as a corrosion inhibitor in the purification of water supplies in steel production as a catalyst for polymers as a preservative for latex and in the production of nitrocellulose, urea formaldehyde, sulfite cooking liquors, and nitroparaffins (ACGIH 1991 Lewis 1993). Ammonium hydroxide (10-35% ammonia) is a major constituent of many cleaning solutions. Ammonia... 

Table I. Equilibrium (a) and kinetic (b) isotopic fractionation factors (a) of importance to nitrogen cycling in lakes (Collister Hayes, 1991). As a first approximation, an a value of, for example, 1.020 implies a difference in of ca. 20%o between the reactant and product. In the case of N2 gas dis.solution, therefore, differs by less than l%o between the gaseous and aqueous phases, whereas gaseous ammonia liberated during ammonia volatilisation will be ca. i4%o lighter than the aqueous ammonia.

Polymer solutions (25 ml) were aged in pyrex ampules (50 ml) at 121 and 150 C to determine the extent of hydrolysis and cloud points. Oxygen was removed from the ampules by alternating vacuum and nitrogen cycles. Once deoxygenated, the ampules were torch sealed under a slight vacuum (-25Kpa). 

A flow diagram for the system is shown in Figure 5. Feed gas is dried, and ammonia and sulfur compounds are removed to prevent the irreversible buildup of insoluble salts in the system. Water and soHds formed by trace ammonia and sulfur compounds are removed in the solvent maintenance section (96). The pretreated carbon monoxide feed gas enters the absorber where it is selectively absorbed by a countercurrent flow of solvent to form a carbon monoxide complex with the active copper salt. The carbon monoxide-rich solution flows from the bottom of the absorber to a flash vessel where physically absorbed gas species such as hydrogen, nitrogen, and methane are removed. The solution is then sent to the stripper where the carbon monoxide is released from the complex by heating and pressure reduction to about 0.15 MPa (1.5 atm). The solvent is stripped of residual carbon monoxide, heat-exchanged with the stripper feed, and pumped to the top of the absorber to complete the cycle. 

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