Contamination of oxygenates

Schematic diagrams of the apparatus, designed in our lab at< y, are shown in Fig. 1. Polymer flakes are placed, with a balls of about 5 mm dieter, in a glass an oule A about 4 cm in diameter and 7 cm in length. To the other end of the ampoule an ESR sample tube B is attached. Through connector C, the ampoule can be connected to a vacuum system and then evacuated to 10 mm Hg. After evacuation the connector is sealed off and the ampoule is removed from the vacuum system. The evacuated ampoule is now placed on a vibrator, wWch moves vertically at about 4 cycle per second. The procedure can be carried out in a Dewar flask containing coolant, such as liquid nitrogen, to fix the temperature. After some hours of this vibration, the crushed flakes are transferred to the ESR sample tube without raising the temperature of the sample. Ihen, sample tube containing the fractured flakes is placed in an ESR cavity at controlled temperature. The ball-mill apparatus permitted polymeric materials to be crushed in vacuum at low temperature and the ESR spectrum to be observed without contamination of oxygen.

Additionally the contamination of oxygen supplies (cylinder, valve, regulator, hoses, etc.) by oil or grease also has the capability of causing an explosion. 

As shown in a literature survey and critical evaluation of surface analysis methods by Quaglia and Weber (7), the most appropriate method to evaluate residual contamination of oxygen, nitrogen and carbon (for boron and phosphorus significant surface contaminations were never observed) on the surface of metallic samples is microanalysis by nuclear reactions (8-11). 

It should be further emphasized that the results are based on the assumption that oxygen was believed to be distributed relatively uniformly throughout the cross section in all parts of the weldment. A locally high concentration, such as a high surface contamination of oxygen or nitrogen, could result in a severe loss in ductility and could possibly even produce embrittlement... 

Atmospheric corrosion results from a metal s ambient-temperature reaction, with the earth s atmosphere as the corrosive environment. Atmospheric corrosion is electrochemical in nature, but differs from corrosion in aqueous solutions in that the electrochemical reactions occur under very thin layers of electrolyte on the metal surface. This influences the amount of oxygen present on the metal surface, since diffusion of oxygen from the atmosphere/electrolyte solution interface to the solution/metal interface is rapid. Atmospheric corrosion rates of metals are strongly influenced by moisture, temperature and presence of contaminants (e.g., NaCl, SO2,. ..). Hence, significantly different resistances to atmospheric corrosion are observed depending on the geographical location, whether mral, urban or marine. 

Environmental Aspects. Airborne particulate matter (187) and aerosol (188) samples from around the world have been found to contain a variety of organic monocarboxyhc and dicarboxyhc acids, including adipic acid. Traces of the acid found ia southern California air were related both to automobile exhaust emission (189) and, iadirecfly, to cyclohexene as a secondary aerosol precursor (via ozonolysis) (190). Dibasic acids (eg, succinic acid) have been found even ia such unlikely sources as the Murchison meteorite (191). PubHc health standards for adipic acid contamination of reservoir waters were evaluated with respect to toxicity, odor, taste, transparency, foam, and other criteria (192). BiodegradabiUty of adipic acid solutions was also evaluated with respect to BOD/theoretical oxygen demand ratio, rate, lag time, and other factors (193). 

The typical fluorination apparatus used in the LaMar process for these reactions is simple in design (Fig. 4) (33). It is essential that the materials of constmction are resistant to fluorine (34). The presence of even traces of oxygen or moisture can have a deleterious effect and, therefore, extreme precautions must be taken to eliminate these contaminants. 

Reduction. Hafnium oxide can be reduced using calcium metal to yield a fine, pyrophoric metal powder (see Calciumand calciumalloys). This powder contains considerable oxygen contamination because of oxygen s high solubility in hot hafnium, and caimot be consoHdated into ductile metal. To obtain low oxygen ductile hafnium, the feed must be an oxygen-free halide compound such as hafnium tetrachloride or potassium hexafluorohafnate [16871-86-6]. 

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

Minimum contained oxygen and maximum contaminant levels where specified for the several grades of oxygen. Contaminants given in volumes per million (vpm). Low purity oxygen (93%) has not been included. 

Steelmaking. Large amounts of oxygen are used in almost aU aspects of the steelmaking process, largely to oxidi2e the principal contaminants, eg, carbon, phosphoms, and sUicon. 

Wastes contaminated with aniline may be Hsted as RCRA Hazardous Waste, and if disposal is necessary, the waste disposal methods used must comply with U.S. federal, state, and local water poUution regulations. The aniline content of wastes containing high concentrations of aniline can be recovered by conventional distillation. Biological disposal of dilute aqueous aniline waste streams is feasible if the bacteria are acclimated to aniline. Aniline has a 5-day BOD of 1.89 g of oxygen per gram of aniline. 

Temperature. The temperature for combustion processes must be balanced between the minimum temperature required to combust the original contaminants and any intermediate by-products completely and the maximum temperature at which the ash becomes molten. Typical operating temperatures for thermal processes are incineration (750—1650°C), catalytic incineration (315—550°C), pyrolysis (475—815°C), and wet air oxidation (150—260°C at 10,350 kPa) (15). Pyrolysis is thermal decomposition in the absence of oxygen or with less than the stoichiometric amount of oxygen required. Because exhaust gases from pyrolytic operations are somewhat "dirty" with particulate matter and organics, pyrolysis is not often used for hazardous wastes. 

The use of neutralising amines in conjunction with an oxygen scavenger—metal passivator improves corrosion control in two ways. First, because any acidic species present is neutralized and pH is increased, the condensate becomes less corrosive. Second, most oxygen scavenger—passivators react more rapidly at the mildly alkaline conditions maintained by the amine than at lower pH levels. For these reasons, this combination treatment is gaining wide acceptance, particularly for the treatment of condensate systems that are contaminated by oxygen. 

Oxygen evolved from the anodes as well as some hydrogen from the cathodes produces a mist which is trapped by a froth maintained by adding cresyhc acid, sodium siUcate, and gum arabic, or glue plus cresol. Alkaline-earth carbonates prevent lead contamination of the cathode ziac. Most of the lead is deposited ia the cell sludge as iasoluble carbonate—sulfate. 

Bismuth Trioxide. Bismuth(Ill) oxide [1304-76-3] has a compHcated polymorphism. At times some of the reported phases deviate from Bi202 by baying too Htfle or too much oxygen at least in one instance, because of the ready contamination of Bi202 melts with siHcon, the reported phase... 

CO oxidation catalysis is understood in depth because potential surface contaminants such as carbon or sulfur are burned off under reaction conditions and because the rate of CO oxidation is almost independent of pressure over a wide range. Thus ultrahigh vacuum surface science experiments could be done in conjunction with measurements of reaction kinetics (71). The results show that at very low surface coverages, both reactants are adsorbed randomly on the surface CO is adsorbed intact and O2 is dissociated and adsorbed atomically. When the coverage by CO is more than 1/3 of a monolayer, chemisorption of oxygen is blocked. When CO is adsorbed at somewhat less than a monolayer, oxygen is adsorbed, and the two are present in separate domains. The reaction that forms CO2 on the surface then takes place at the domain boundaries. 

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