Traps condensing oxygen

When first starting up a vacuum system, let the pumps evacuate the system (if starting up the system for the first time) or the traps (if they have been vented to the atmosphere) for a few minutes before setting the traps into liquid nitrogen. Otherwise you are likely to condense oxygen in the traps and create a potentially dangerous situation when the pumps are turned off (see Sec. 7.4.3). 

Leave a stopcock open (to the atmosphere) at the end of an experiment to vent the system after the work is done. However, if you do this, be sure to remove the liquid nitrogen from the trap before opening the vent. Otherwise you will be condensing oxygen that is drawn in by the open vent. 

Separated Analytes. Cold trapping is used to separate volatile analytes from the main components of air in the field. Air is drawn by a pump through an inert, often nickel, metal tube immersed in a fluid at a very low temperature, for example, -150° C. The tube may be packed with some inert material such as Pyrex glass beads and the temperature is sufficient to condense most analytes but insufficient to condense oxygen or nitrogen. 

In fact, 17 is so stable that it can be trapped by oxygen to yield the dioxirane 19 in 55 % yield, the first derivative of this three-membe-red heterocycle which is stable in condensed phase. The 17->19 oxidation process proceeds... 

Carbon dioxide is often ignored in steam systems. However, when absorbed in water, it forms carbonic acid, which can be corrosive to all parts of the steam and condensate system. Its potential presence is frequently overlooked in the design of heat exchangers, steam traps, condensate systems, deaerators, and water-treating systems. Most steam systems require continual addition of makeup water to replace losses. Makeup water must be adequately treated, by demineralization or distillation, to remove carbonates and bicarbonates. If these are not removed, they can be thermally decomposed to carbon dioxide gas and carbonate and hydroxide ions. The ions will normally remain in the boiler water, but the caron dioxide will pass off with the steam as a gas. When the steam is condensed, the carbon dioxide will accumulate since is is noncondensable) be passed as a gas by the steam trap or if the condensate and carbon dioxide are not freely passed by the steam trap, become dissolved in the condensate and form carbonic acid. If carbonic acid is formed it can have a pH approaching 4 and be very corrosive to copper and steel. Even if both the gas and condensate are passed freely by the steam trap, the gas will become soluble in the condensate when subcooling occurs. If oxygen is present, the corrosion rate Is accelerated. 

TPO analyses were performed in a TPD/TPR 2900 (Micromeritics) equipment with a thermal conductivity detector a trap for sulfur compounds and a Pt/Silica bed for oxidation of CO and hydrocarbons to CO2. Eurthermore, it has a cold trap (isopropyl alcohol/liquid nitrogen) to condense CO2 and residual moisture. The combustion products are passed through the previous traps connected in series in order to remove other compounds different from O2 in the carrier gas. This ensures that the conductivity changes observed in the detector are attributed exclusively to changes in oxygen concentration in the carrier gas. 

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