Nitric acid

Nitric acid is a mineral oxygenated nitrogen compound with the formula HNO₃, ranked among the ten most widely produced industrial chemicals by volume. It forms a critical intermediate in the nitrogen value chain, positioned downstream of ammonia and upstream of nitrate fertilisers, urea, and numerous industrial derivatives. The bulk of nitric acid produced goes into inorganic fertilisers; it is chiefly neutralised with ammonia to produce ammonium nitrate^[1]. Other industrial applications include explosives, synthetic fibres (caprolactam, nylon), engineering plastics, and NOx reducers for flue-gas denitrification^[2][3].

Manufacture

The industrial process relies on catalytic oxidation of ammonia over a platinum-rhodium gauze, followed by absorption of nitrogen oxides in water. This synthesis route, known as the Ostwald process, proceeds in two main stages. In a first reactor, the ammonia-air mixture reacts at high temperature to yield nitrogen monoxide (NO). This gas is subsequently oxidised to nitrogen dioxide (NO₂), which is absorbed in a counter-current column of demineralised water, steam condensate, or process condensate, according to the reaction: 3 NO₂ + H₂O ↔ 2 HNO₃ + NO^[4].

The concentration of the acid obtained generally ranges between 50 and 65% by mass, depending on pressure, temperature, and the number of absorption stages^[4]. To produce concentrated acid, additional direct processes are required: liquid N₂O₄ reacts under pressure of approximately 50 bar with oxygen and dilute acid to form concentrated HNO₃^[5]. European units have capacities of 150 to 2,500 t/d, with roughly one hundred sites in operation in the EU-25, Switzerland, and Norway in 2006^[1].

Agronomic and industrial uses

In the fertiliser sector, nitric acid holds a central position in the production chain for nitrates. It serves as a second intermediate for manufacturing nitrates, notably ammonium nitrate and calcium ammonium nitrate (CAN), as well as nitrogen solutions (UAN)^[6][7]. Finished fertilisers also include NPK fertilisers^[6].

Non-agronomic outlets represent a significant share of demand. Nitric acid is used in the production of industrial explosives (ANFO, emulsions), caprolactam for polyamides, adipic acid, dinitrotoluene, nitrobenzene, as well as reagents for water treatment and catalytic reduction of nitrogen oxides in stationary installations and maritime transport^[2][3].

Market and trade

The nitric acid market is structurally tied to that of ammonia, whose production cost is dominated by the natural gas price. This fuel accounts for roughly 90% of ammonia's cash manufacturing costs when gas stands at 7 USD/MMBtu^[6]. This dependency explains why new nitrogen capacities (excluding China) concentrate in regions with low energy costs: the Middle East, North Africa, and North America^[6].

Unlike phosphate and potash markets, which are heavily geographically concentrated, the nitrogen sector shows greater fragmentation owing to the wide availability of feedstocks (natural gas and air)^[8]. Leading players in global nitrogen manufacturing include CF Industries, Yara International, Nutrien, Ostchem Group, OCI Global, TogliattiAzot, Koch Fertilizer, and EuroChem Group^[8].

Regulation and environment

Nitric acid production constitutes one of the major industrial sources of nitrous oxide (N₂O) emissions. The bibliographic references in the BREF LVIC-AAF document cite work on direct catalytic decomposition of N₂O, hydrocarbon-assisted reduction, as well as secondary and tertiary abatement processes tested at industrial scale^[9].

Installations fall under the EU Emissions Trading System (EU ETS) and, in due course, the Carbon Border Adjustment Mechanism (CBAM) for imports of nitrogen products. The Nitrates Directive also governs agricultural use of nitrate fertilisers, with indirect effects on nitric acid demand through regulations on spreading and vulnerable zones.