Iron contaminants

Mild steel is a suitable material of constmction for storage and handling of DMAC at ambient temperatures. Aluminum or stainless steel is recommended for cases involving very stringent color or iron contamination requirements. Mild steel is not recommended for high temperature service or handling aqueous solutions of less than 50 mol % (82.86 wt %) DMAC. 

Use of excess sodium drives the reaction, usually done under an argon or helium blanket, to completion. After cooling, the excess sodium is leached with alcohol and the sodium and potassium fluorides are extracted with water, leaving a mass of metal powder. The metal powder is leached with hydrochloric acid to remove iron contamination from the cmcible. 

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. 

Shipping, analysis, and safety factors are similar to those of ammonium thiocyanate, except that the alkaU thiocyanates are more thermally stable. Sodium thiocyanate is best handled in 316 stainless steel. At room temperature where some iron contamination can be tolerated, type 304 can be used. Aluminum corrodes more rapidly than stainless steel, but some alloys can be used below 60°C. Some but not all mbber equipment is satisfactory. 

Steel tank cats, often lined to minimize iron contamination, are usually employed for high concentrations of sulfuric acid. Bottom outlets or valves are not allowed, nor are internal steam coils. Tank contents must be unloaded via standpipe. Using air pressure to unload is not recommended for safety reasons, but if air pressure is used, gauge pressures should be held at <0.21 MPa (30 psi). 

A chelant—polymer combination is an effective approach to controlling iron oxide. Adequate chelant is fed to complex hardness and soluble iron, with a slight excess to solubilize iron contamination. Polymers are then added to condition and disperse any remaining iron oxide contamination. 

Pebble mills are frequently Uned with nonmetalUc materials when iron contamination would harm a product such as a white pigment or cement. Belgian silex (silica) or porcelain block are popular Unings. Sihea linings and baU media have proved to wear better than other nonmetalUc materials. The higher density of siUca media increases the produclion capacity and power draft of a given mill. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Another variation is to use a pyramid-shaped tank at grade level with an inclined dewatering screw feeder. Refer to Figure 38 for an example. Tank materials are usually constructed from carbons steel, stainless steel, stainless clad, resin or epoxy-lined for those situations where iron contamination in the product is a concern, or if corrosion by the adsorbate in the carbon is possible. 

Occasionally we have found iron contaminants in aromatic steroids that have not been adequately purified. The methylation of a phenolic steroid with methyl sulfate and alkali is often carried out just prior to a Birch reduction and iron in the tap water precipitates with the steroid during the... 

In critical applications, if stainless steel is to be used near its limit (in terms of corrosion), and for cases such as welds, where a good finish cannot be otherwise achieved, additional passivation is required. Nitric acid (10-15 per cent by volume) is the best passivator. It also dissolves iron contamination. In circumstances where the use of nitric acid is not possible for safety or physical reasons (such as the underside of vessel roofs) passivation paste is appropriate. Both materials are used at ambient temperature and require a contact time of approximately 30 minutes. They must be removed by thorough rinsing with low chloride-content water. 

Stainless steels are used in a wide variety of applications and are most often selected because steel or cast iron would corrode at an unacceptably high rate or produce high levels of iron contamination in the proposed service environment. The main limitations on their uses are ... 

Of more serious practical significance is iron contamination of nickel-clad steel welds. Tables 3.39 and 3.40 show the increase in corrosion of various nickel-iron alloys which may occur when coupled to nickel in... 

With the added benefit of increased product purity (reduced iron contamination), near-zero operational costs speak to AP as the most underapplied corrosion control systems of the ages. 

FIGURE 11.5 Half-held spectrum of two interacting cubanes. The signal from dihydropyrimidine dehydrogenase is of low intensity due to the relative weakness of the dipolar interaction. The g = 4.3 signal is a dirty iron contamination. 

FERROSEP A magnetic process for removing iron contaminants from petroleum residues before desulfurization. Developed by Nippon Oil Company and Nippon Petroleum Refining... 

Mordant dyes are notoriously troublesome from the viewpoint of colour matching because the hue of the chromium complex usually differs greatly from that of the unmetallised parent dye (section 5.4.1). If other metal ions are present in the treatment bath or on the fibre during chroming, the colour obtained is likely to differ from that of the pure chromium complex. Certain important chrome dyes, including Cl Mordant Black 11 (3.29) and Black 17 (3.30), are particularly sensitive to traces of iron or copper. The hue of the black dyeings obtained is redder in the presence of copper and browner with iron contamination. The fastness to light and wet treatments may also prove inferior under these conditions. Even certain 1 2 metal-complex acid dyes show similar effects in the presence of these impurities,... 

Pozio, A., Silva, R. R, De Francesco, M. and Giorgi, L. 2003. Nafion degradation in PEFCs from end plate iron contamination. Electrochimica Acta 48 1543-1549. 

Cementation is the process of recovery of metals from dilute aqueous solution by reductive precipitation using another metal with a more negative electrode potential, e.g., Cu + Fe° Cu° + Fe. The product, in this case cement copper, is relatively impure because of iron contamination. However, cementation can be used in conjunction with a solvent extraction flow sheet to remove small amounts of a metallic impurity, for example, removal of copper from a nickel solution by cementation with nickel powder. Here the dissolved nickel conveniently augments the nickel already in solution. 

The polymer showed evidence of iron contamination at levels high enough to promote polymerization. (Iron is a known promoter of polymerization.)... 

KKjLiRK 4. Branch 3 of event tree (iron contamination branch). 

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