About Sulfuric Acid. Sulfuric Acid (a.k.a. H2SO4) is an inorganic compound, in the acid class. It is a colorless to slightly yellow, odorless, and viscous liquid, soluble in water and alcohol, used in many applications. Approximately 50% of the produced sulfuric acid is used in the fertilizer industry. Sulfuric Acid figures among the most important chemicals globally, in 2012 about 230 million tonnes of the commodity produced, with continuing growth in worldwide production been expected.

On commercial scale, this chemical commodity is manufactured essentially by the Contact Process, which involves the catalytic oxidation of sulfur dioxide (SO2), the absorption of the resulting sulfur trioxide (SO3) in Sulfuric Acid and dilution with water. This process has been greatly improved over the past century, mainly to increase sulfur dioxide conversion efficiency (lowering emissions). Nowadays, modern sulfuric acid plants are primarily based on the so-called Double Absorption, an evolution of the Contact Process that incorporates a preliminary SO3 absorption step ahead of the final catalytic oxidation.

Sulfuric acid can be manufactured from several sulfur-bearing raw materials, being elemental sulfur, spent sulfuric acid, and hydrogen sulfide the main ones. It is also widely produced as a by-product of nonferrous metal smelting (e.g. sulfide ores of copper, lead, molybdenum, zinc, or others). It is worth mentioning that, when manufactured from elemental sulfur or pyrite, Sulfuric Acid is a primary product and, consequently, its level of production is naturally sensitive to market conditions. On the other hand, the Sulfuric Acid manufactured from other sulfur-containing raw materials is a secondary product, in such a way that its production is dictated by the primary product market conditions. In fact, such secondary Sulfuric Acid - so-called fatal acid – is mainly produced as a means of disposing of waste from another processes, typically nonferrous metal smelters processing sulfide ores.

Sulfuric Acid should be kept away from water and moisture, as a highly exothermic reaction would occur, particularly at high acid concentrations. It is, at lower concentrations (30-70%), non-oxidizing and attacks the steel rapidly, particularly at elevated temperatures. High temperatures will cause an expansion of the volume, presenting a leakage risk. Temperature, concentration, and volumes must be carefully chosen to ensure a secure storage or transportation. Steel tank cars, 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.

Raw materials and the respective production processes employed in the manufacturing of Sulfuric Acid are listed below.

The uses and applications of Sulfuric Acid may vary according to its specification. The main forms of Sulfuric Acid are 33.5% aqueous solution (battery acid); 62.18% aqueous solution (fertilizer acid); 77.67% aqueous solution (tower acid); 98 to 99% aqueous solution (1.84 g/cm³); oleum/fuming ; 60 ºBé (1.71 g/cm³, 77.7% acid); technical grade (66 ºBé, 1.84 g/cm³, 93.2% acid); Food Chemical Codex grade (FCC, 49 to 51% purity); American Chemical Society grade (ACS, 95 to 98% purity); and chemically pure grade (CP, 98% purity).