E251 Preservative

E251 can be combined with sulfuric acid to produce nitric acid, which is distilled off. At lower pressure the lower temperature needed results in less decomposition. The theoretical 2 moles of nitric acid per 1 mole of sulfuric acid results in a very high-end temperature, much decomposition and a solid neutral sulfate that is difficult to remove. When this reaction was important industrially, it was common practice to operate with sulfuric acid in excess to end on a mostly bisulfate product poured molten out of the retort.

Hobbyist gold refiners use E251 to make a hybrid aqua regia that dissolves gold and other metals.

Less common applications include as an oxidizer in fireworks, replacing potassium nitrate commonly found in black powder, and as a component in instant cold packs.

E251 is used together with potassium nitrate and calcium nitrate for heat storage and, more recently, for heat transfer in solar power plants. A mixture of E251, calcium nitrate and potassium nitrate is used as energy-storage material in prototype plants, such as Andasol Solar Power Station and the Archimedes project.

It is also used in the wastewater industry for facultative microorganism respiration. Nitrosomonas, a genus of microorganisms, consumes nitrate in preference to oxygen, enabling it to grow more rapidly in the wastewater to be treated.

E251 is also sometimes used by marine aquarists who utilize carbon-dosing techniques. It is used to increase nitrate levels in the water and promote bacterial growth.

Food

E251 Is also a food additive used as a preservative and color fixative in cured meats and poultry; it is listed under its INS number 251 or E number E251. It is approved for use in the EU, US, and Australia, and New Zealand. E251 should not be confused with E251, which is also a common food additive and preservative used, for example, in deli meats.