Nitrogen blanketing

The rate of hydrolysis of DMAC is very low, but increases somewhat in the presence of acids or bases. DMAC is a stable compound, but is mildly hygroscopic and desiccation and/or dry nitrogen blanketing of storage vessels are sometimes used to reduce water pick-up. In the absence of water, acids, or bases, DMAC is stable at temperatures up to its hoiling point at atmospheric pressure. Its greater stability enables more economical recovery by distillation relative to that of other similar solvents. 

Phenol. This is the monomer or raw material used in the largest quantity to make phenoHc resins (Table 1). As a soHd having a low melting point, phenol, C H OH, is usually stored, handled in Hquid form at 50—60°C, and stored under nitrogen blanket to prevent the formation of pink quinones. Iron contamination results in a black color. 

Larger volume cycloaUphatic amines and diamines, their worldwide major manufacturers and approximate January 1990 prices are shown in Table 4. Shipment of these Hquid products is by nitrogen-blanketed tank tmck or tank car. Dmm shipments are usually in carbon steel, DOT-17E. 

Liquid cycloahphatic amines and diamines have exacting purity and color standards. Almost all are sold to specification, not performance standards. Use as isocyanate precursors requites low water content criteria for these hygroscopic fluids, hence nitrogen blanketing is often specified for product sampling as well as storage and transport. 

Ah these polymerizations proceed only in the absence of oxygen or water, which react with the highly reactive propagating species. Polymerization is usuahy carried out in an inert, hydrocarbon solvent and under a nitrogen blanket. Under these conditions, polymers with narrow molecular-weight distributions and precise molecular weights can be produced in stoichiometric amounts. 

The use of nitrogen blanketing where appropriate on pumps, storage tanks, and other equipment to minimize the release of toxic organics. 

Reduce dust emissions at furnaces by covering iron runners when tapping the blast furnace and by using nitrogen blankets during tapping. 

Section 5.4.1 discussed the need for nitrogen blanketing. However, if it is to be effective, it must be designed and operated correctly. 

On one group of tanks the reducing valve on the nitrogen supply was installed at ground level (Figure 5-17). Hydrocarbon vapor condensed in the vertical section of the line and effectively isolated the tank from the nitrogen blanketing. 

An explosion and fire occurred on a fixed-roof tank that was supposed to be blanketed with nitrogen. After the explosion, it was found that the nitrogen supply had been isolated. Six months before the explosion the manager had personally checked that the nitrogen blanketing was in operation. But no later check had been carried out [8]. 

All safety equipment and systems should be scheduled for regular inspection and test. Nitrogen blanketing systems should be inspected at least weekly. It is not sufficient to check that the nitrogen is open to the tank. The atmosphere in the tank should be tested with a portable oxygen analyzer to make sure that the oxygen concentration is below 5%. 

Lai ge tanks (say. over 1,000 m ) blanketed with nitrogen should be fitted with low-pressure alarms to give immediate warning of the loss of nitrogen blanketing. 

Many explosions, some serious, have occurred in centrifuges handling flammable solvents because the nitrogen blanketing was not effective. 

If the inhibitor is not removed, dissolved oxygen reacting with the inhibitor TCB will prevent polymerization. In the absence of dissolved oxygen, polymerization will proceed at essentially the same rate as that of the uninhibited monomer. A nitrogen blanket can be used to remove the oxygen from the mixture prior to polymerization. 

The preparation of the organic phase is done in a second flask by mixing the toluene, nonsolvent (dodecane, etc.), DVB, styrene or any other monomer, surfactant, and azobis. Mix at 120 rpm under a nitrogen blanket and bring the solution to 40°C. 

Dimethyl sulfonium-2-pyridyl carbonyl methylide (Ypy-5) [65] initiated radical polymerization of styrene in dimethyl sulfoxide at 85 0.1°C for 6 h under a nitrogen blanket. (See Table 4.)... 

If dry lay-up procedures are not carried out entirely satisfactorily (e.g., if a nitrogen blanket is not permanently provided to the superheaters during the lay-up period), atmospheric moisture may condense and oxygen corrosion will ultimately occur. 

Deaerators taken out of service should be completely drained, dried, and provided with a nitrogen blanket during the lay-up period. When placed back on line, the DA should be on manual steam control. Heating should be gradual, and care is needed at the point of initial atmospheric boiling because steam flashing may occur in the FW discharge line. 

NOTE This book is not primarily intended for nuclear or utility power plant facilities, which often require ultrapure water of even higher specifications than those discussed in this chapter. Reaching the highest possible levels of purity requires additional controls, use of nitrogen blankets, submicron filters, and point-of-use polishers. 

Boilers should be effectively sealed and all connections blanked off to prevent air in-leakage. A nitrogen blanket is then provided to cap the system and its auxiliaries. 

Idle deaerators or FW heaters usually are isolated from the boiler section and subjected to steam or nitrogen blanketing. 

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