Alkali metal sulfates, sulfur dioxide

Alkali metal sulfates, sulfur dioxide detection, 121... 

Potassium permanganate Potassium sodium alloy 2-Propyn-l-ol Organic or readily oxidizable materials Air, carbon dioxide, carbon disulfide, halocarbons, metal oxides Alkali metals, mercury(II) sulfate, oxidizing materials, phosphorus pentoxide, sulfuric acid... 

NaHS04 - Na2S207 + H20 The normal salts of the alkali and alkaline earth metals and Pb do not readily decomp upon heating, but the sulfates of the nobler metals evolve sulfur trioxide or sulfur dioxide and 02 if the decompn temp is high (Ref 1)... 

Sulfates are widely known in the environment and a few such as those of calcium, strontium, barium, and lead are insoluble. The sulfates of magnesium and the alkali metals are soluble and so are typically found in brines and salt deposits. Sulfites are rarer because of the ease of oxidation, but calcium sulfite, perhaps as the hemihydrate, can be detected on the surface of building stone in urban atmospheres containing traces of sulfur dioxide (Gobbi et al, 1998). 

For this reaction the comparison of activity of various oxides cannot be carried out because most of them transform in reaction conditions into nonactive sulfates. The exception is vanadium pentoxide whose activity strongly increases when promoted by sulfates of alkali metals. As is clear from Fig. 15, the catalytic activity of vanadium catalysts, with the addition of different sulfates of alkali metals, changes identically in reactions of isotopic exchange in molecular oxygen and in the oxidation of sulfur dioxide. 

Fig. 15. Catalytic activity of vanadium pentoxide promoted with sulfates of various alkali metals. Curve 1— reaction of exchange of molecular oxygen curve 2—reaction of oxidation of sulfur dioxide.

Nickel is determined by the gravimetric dimethyl-glyoxime procedure after reduction of the compound with sulfur dioxide and hydrochloric acid. Iodine is determined as silver iodide after reduction with sulfur dioxide in sulfuric acid medium. Total active oxygen is calculated by measuring the quantity of iodine liberated from potassium iodide in acidic solution. Alkali metals are determined as sulfates in the filtrates from the nickel determinations. 

Sulfites,—The sulfites are decomposed by the stronger acids, with evolution of sulfur dioxid. Nitric acid oxidizes them to sulfates. The sulfites of the alkali metals are soluble, and are active reducing agents. 

Coal ash corrosion is a widespread problem for superheater and reheater tubes in coal fired power plants that bum high-sulfur coals. The accelerated corrosion is caused by liquid sulfates on the surface of the metal beneath an over-lying ash deposit. Coal ash corrosion is very severe between 540 and 740°C (1000°F and 1364°F) because of the formation of molten alkali iron-trisulfate. Considerable work has been done to predict corrosion rates based on the nature of the coal (its sulfur and ash content). This was accomplished by the exposure of various alloys to synthetic ash mixtures and synthetic flue gases. The corrosion rates of various alloys were repotted in the form of iso-corrosion curves for various sulfur dioxide, alkali sulfiite, and temperature combinations. An equation was developed to predict corrosion rates for selected alloys from details of the nature of ash by analyzing deposits removed from steam generator tubes and from test probes installed in a boiler [33]. Then laboratory tests were conducted using coupons of various tdloys coated with synthetic coal ash that was exposed to simulated combustion gas atmospheres. 

Suitable reducing agents, which act as activators, were combined with the water-soluble initiators to increase their activities. Some specific activators included were alkali metal bisulfites, alkali metal formaldehyde sulfoxylates or sulfur dioxide. Accelerators such as ferrous sulfate, silver nitrate, ferrous nitrate and silver nitrate may also be combined with the initiator. The amount of the initiator was varied from 0.02% to 1 % of the total weight of the monomer. It was important to control the pH of the polymerization medium between 5 and 8 adjustments were made by adding buffers such as carbonates, bicarbonates, phosphates. 

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