Ammonium sulfate

Ammonium sulfate ((NH4)2SO4) is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer since the chemical contains 21% (w/w) nitrogen and 24% (w/w) sulfur. The chemical has also been used in flame retardant chemicals because, as a flame retardant, it increases the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char. Ammonium sulfate has been used as a wood preservative, but due to its hygroscopic nature, this use has been largely discontinued because of associated problems with metal fastener corrosion, dimensional instability, and finish failures.

Ammonium sulfate is produced by three different processes: (1) synthetic manufacture from pure ammonia and concentrated sulfuric acid, (2) as a coke oven by-product, (3) from ammonia scrubbing of tail gas at sulfuric acid (H2SO4) plants, and (4) as a by-product of caprolactam ((CH2)5COHN) production,

Typically, ammonium sulfate is produced by combining anhydrous ammonia and sulfuric acid:
In the process, a mixture of ammonia gas and water vapor is introduced into a reactor that contains a saturated solution of ammonium sulfate and about 2%–4% (v/v) of free sulfuric acid at 60°C (140°F); the heat of the reaction maintains the desired temperature. Concentrated sulfuric acid is added to keep the solution acidic and to retain its level of free acid. Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all of the water present in the system with the resulting formation of as dry powdery salt.