Oxygen, removal

The electrochemical reduction of oxygen usually proceeds via two well-separated two-electron steps. The first step corresponds to the formation of hydrogen peroxide  

The half-wave potentials of these steps are approximately — 0.1 and — 0.9 V (versus the saturated calomel electrode). Hie exact stoichiometry of these steps is dependent on the medium. Hie large background current accruing from this stepwise oxygen reduction interferes with the measurement of many reducible analytes. In addition, the products of the oxygen reduction may affect the electrochemical process under investigation. 

Other methods have been developed for the removal of oxygen (particularly from flowing streams). These include the use of electrochemical or chemical (zinc) scrubbers, nitrogen-activated nebulizers, and chemical reduction (by addition of sodium sulfite or ascorbic acid). Alternately, it may be useful to employ voltam- 

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Chemical conversion processes can also be used for moisture and oxygen removal. These tend to be the same ones developed for the smaller point-of-use purifiers. Consequently there is Httle economy of scale and they are seldom able to be regenerated. 

A. Benchikha and D. R. Gaig, "The C4 Raffinate Tieatment Piocess Methanol Recoveiy/Oxygenate Removal," Piesentation at HUELS MTBE Symposium in Mad, West Geimany, Sept. 6, 1988. 

Extreme caution must be taken to prevent the possibility of fire when using flammable removers. Extra care must be taken when stripping on location to secure the area of ignition sources. When used on lacquer finishes, the dissolved finish and remover combined are extremely flammable. Natural mbber, neoprene, or other gloves suitable for use with the remover formula must be worn. The effect of skin contact with the remover is limited because there is immediate irritation and discomfort. Canister respirators are available for most petroleum and oxygenate remover solvents. Symptoms of long-term overexposure should be compared to symptoms of the major ingredients in the formula. 

Environmental Impact. The volume of waste remover from these products is remarkably increased when compared to methylene chloride, petroleum, and oxygenate removers, since both /V-methy1pyrro1idinone and dibasic esters have low vapor pressures. Recovery of the remover after use is difficult because the finish is tesolubili2ed by the remover. A representative dibasic ester formula appears below for a thickened water rinse finish remover. 

Oxygen Control. To meet industrial standards for both oxygen content and the allowable metal oxide levels in feed water, nearly complete oxygen removal is required. This can be accompHshed only by efficient mechanical deaeration supplemented by an effective and properly controlled chemical oxygen scavenger. 

A special case of C-20 oxygen removal is the treatment of the 17,20-aceto-nide of a 21-brorao-17a,20(o or )-dihydroxy steroid with sodium in aqueous dioxane to produce a 17a-hydroxy-17jS-vinyl compound in 60% yield... 

The mechanical deaeration oxygen removal process is not 100% efficient, however, and all boiler FW must be further deoxygenated by some form of chemical oxygen scavenger. 

In almost all industrial circumstances, a deaerator is a cost-effective oxygen-removing proposition that complements primary pretreatment equipment such as water softeners. 

NOTE The injection point of chelant should be into the boiler FW as far downsteam as possible from the deaerator and chemical oxygen scavenging point to permit sufficient time for effective oxygen removal to take place. 

Oxygen Removal Using Catalyzed Carbon Bed Technology... 

The oxygen removal reaction using a carbon bed catalyst is as shown below ... 

Oxygen Removal Using Gas Transfer Membrane (GTM)Technology... 

Where continuous demineralization of reactor coolant is provided, premature degradation of the strong base anion (SBA) resins may occur. To avoid this, oxygen removal by use of anion resin in the sulfite form is employed. 

Where oxygen removal is required, this includes the eradication of 02 from ... 

Conversely, larger and higher pressure boilers tend to employ mechanical deaeration systems and supplement this by using a smaller quantity of oxygen-removing chemical as a true scavenger. This is added to the base of the deaerator (the deaerator storage section). 

Similarly, when hydrazine feed is discontinued, it continues to appear in the BW because the fully reduced iron oxides provide an alternate oxygen removal reaction. 

Addition of oxygen, removal of hydrogen or loss of electrons. Oxygenation Treatment ... 

Miller, William S. (Ecolochem, Inc.). Oxygen Removal By Catalyzed Carbon Beds. EPRI Condensate Polishing Workshop, Electric Power Research Institute, USA, October 1985. 

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