Decomposition ammonia-sulfur dioxide

Ammonium sulfate [7783-20-2], (NH 2 U4, is a white, soluble, crystalline salt having a formula wt of 132.14. The crystals have a rhombic stmcture d is 1.769. An important factor in the crystallization of ammonium sulfate is the sensitivity of its crystal habit and size to the presence of other components in the crystallizing solution. If heated in a closed system ammonium sulfate melts at 513 2° C (14) if heated in an open system, the salt begins to decompose at 100°C, giving ammonia and ammonium bisulfate [7803-63-6], NH HSO, which melts at 146.9°C. Above 300°C, decomposition becomes more extensive giving sulfur dioxide, sulfur trioxide, water, and nitrogen, in addition to ammonia. 

Ammonium bisulfite can be used in place of the sulfur dioxide. The solution is treated with activated carbon and filtered to remove traces of sulfur. Excess ammonia is added and the solution evaporated if the anhydrous crystalline form is desired. The crystals ate dried at low temperature in the presence of ammonia to prevent decomposition (61—63). 

Ammonia, hydrogen sulfide, and sulfur dioxide may result from the decomposition of chemical treatments (although in large boiler plants, ammonia is often deliberately added to raise the boiler, steam, or condensate system pH). 

OSHA PEL TW A 0.01 mg(A /m3 ACGIH TLV WA 0.01 mg(Ag)/m3 DOT CLASSIFICATION Forbidden SAFETY PROFILE Explodes when heated above 270°C or on impact. Pure silver azide explodes at 340°. An electric field or irradiation by electron pulses can explode the crystals. Shock-sensitive when dry and has detonated 250°C. Solutions in aqueous ammonia explode above 100°C. Reacts to form more explosive products with iodine (forms iodine azide) bromine and other halogens. The presence of metal oxides or metal sulfides increases the azide s sensitivity to explosion. Mixtures with sulfur dioxide are explosive. When heated to decomposition it emits toxic fumes of NO,. See also AZIDES and SILVER COMPOUNDS. 

The Influence of Catalysts. The effect of ammonia has already been described above. At low pH the catalytic effect of ammonia is clearly due to chemical interactions between ammonia and sulfur dioxide, because in very concentrated solution, and in non-aqueous systems, N-S bonded compounds can be found and identified (10). At high pH, ammonia clearly catalyzes the decomposition of oxyacids, and, in liquid ammonia, even elemental sulfur is activated, even though N-S bonded products have not yet been clearly identified (11). 

When sulfuryl amide or imidodisulfamide is heated with strong sodium hydroxide solution, the sodium salt of amidosulfonic acid results. The free acid itself may be prepared in various ways for example, from urea and sulfuric acid, from many adducts of sulfur trioxide and ammonia, from hydroxylammonium salts and sulfur dioxide, or from SO and acetoxime. Amidosulfonic acid, which is colorless and melts at 205° with decomposition, has, as Baumgarten supposed (13), the structure (LXXXVII). 

Sulfur dioxide has a lifetime in the atmosphere of 0.5-2 days. This limits the distance that the SO2 may be transported to a few hundred kilometers. During this period the sulfuric acid may be partly neutralized, particularly with ammonia that results from the biological decomposition of organic matter. When this occurs, particles containing ammonium sulfate (NH4).S04 and different forms of acid ammonium sulfate such as NH4HSO4 and (NH4),H(S04)2 are formed. 

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