Oxygen scavengers testing

Concern for personnel exposure to hydrazine has led to several innovations in packaging to minimize direct contact with hydrazine, eg, Olin s E-Z dmm systems. Carbohydrazide was introduced into this market for the same reason it is a soHd derivative of hydrazine, considered safer to handle because of its low vapor pressure. It hydrolyzes to release free hydrazine at elevated temperatures in the boiler. It is, however, fairly expensive and contributes to dissolved soHds (carbonates) in the water (193). In field tests, catalyzed hydrazine outperformed both hydrazine and carbohydrazide when the feedwater oxygen and iron levels were critical (194). A pubUshed comparison is available (195) of these and other proposed oxygen scavengers, eg, diethyUiydroxylarnine, ydroquinone, methyethylketoxime, and isoascorbic acid. 

The dibydrochloride salt is used as a photographic developer. It also is employed as an intermediate in the manufacture of fur dyes, in hair dyeing, as a reagent in testing for ammonia and formaldehyde, and as an oxygen scavenger in water to prevent boiler corrosion (173). 

The synergistic effect of a hydroperoxide decomposer, eg, dilauryl thiodipropionate [123-28-4] (34), and a radical scavenger, eg, tetrakis[methylene(3,5-di-/ f2 butyl-4-hydroxyhydrocinnamate)]methane (9), ia protecting polypropylene duting an oxygen-uptake test at 140°C is shown ia Table 3. 

Testing should be provided each week for pH, OH alkalinity, and oxygen scavenger to ensure that the proper levels are maintained. 

Recommended limits should be low because all solids in the feedwater will either deposit in the boiler or be earned over with the steam to the turbine. Consequently, water-treatment chemicals must be volatile. All cycles should have condensate-polishing systems to meet the limits show ll in Table 3. A schematic diagram is shown in Fig. 11. Laboratory tests as well as field studies show that high-flow-rate condensate-polishing systems 25 to 50 gal per min per sq ft (1015-2030 liters/minute/square meter) of cross-sectional bed area] perform as filters of suspended material and ionized particles. Ammonia is added to control the pH in die system. Fig. 12 indicates the amount of ammonia required, in terms of ppm or solution conductivity, to give a certain pH in the system. Hydrazine is added to the cycle for oxygen scavenging. 

Ascorbyl palmitate, laurate, and stearate were tested in this system. However, their water solubilities were so low that they did not function as oxygen scavengers until the pH was adjusted to 9 to solubilize all three esters. Subsequently they removed all of the oxygen from solution at 20 mg/bottle with 2 cm of headspace air. 

M.D. Baker, V.M. Marcy, Hydrazine as an oxygen scavenger—a progress report on tests at Springdale Station, Trans. ASME 78 (1956) 299-304. 

Suppliers usually provide the laboratory evaluation (using conventional test methods) of corrosion inhibitors, scale inhibitors, bactericides, and oxygen scavengers. User companies generally provide evaluation by field monitoring with corrosion specimens. Crevices may be incorporated in specimens to evaluate the possibility of localized corrosion, such as that related to oxygen contamination. 

Hydrazine (NH2NH2) also was evaluated as an oxygen scavenger. Under all conditions tested, hydrazine caused a rapid degradation of P-5(X) PAA. Hydrazine reacts with oxygen by means of a free radical mechanism, which is believed to be the cause of the rapid degradation. 

Only small decreases in the zirconium and magnesium concentrations ha e been observed, and in tests where titanium was used as an oxygen scavenger, no loss of U was observed. 

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