- Nitric acid properties
- Azeotropic acid
Nitric acid properties
Nitric acid (HNO3) is a strong acid and a powerful oxidizing agent. The concentration of commercial nitric acid destined for fertilizer production depends on the method of production and is usually in the range of 42% to 65%. Such acid is known as weak acid, unlike concentrated acid (96.0%-98.5%) that is used for other industrial purposes. Weak nitric acid is usually directed for captive use. Further properties of nitric acid are shown in Table 1.
Anhydrous HNO3 does not normally exist in liquid form. When strong solutions are distilled under special conditions, one obtains almost pure nitric acid having a concentration of 99.7%. When concentrated nitric acid is heated at atmospheric pressure, it boils at 78.2°C but begins to decompose and eventually yields a 68% HNO3 solution with a maximum boiling point of 120.5°C. When dilute solutions of nitric acid are concentrated under atmospheric pressure, a maximum boiling-point solution again corresponding to 68% HNO3 results (azeotropic concentration).
Further properties of nitric acid can be found in the literature. Typical impurities in HNO3 originate from ammonia or the process. The standard limits are the content of Cl2 – less than 5 ppmw, and HNO2 – less than 5 ppmw in most cases.
For the effect of other contaminants, including the recommended thresholds, the reader is referred to the Kirk-Othmer Encyclopedia and related references.
Azeotropic nitric acid
Nitric acid forms an azeotrope with water at about 68 wt% of nitric acid and a boiling point at atmospheric pressure of 122°C. There are various implications from the occurrence of such an azeotropic mixture and the reader is referred to the dedicated literature. Most industrial nitric acid plants produce a weak acid with a concentration below 68%, usually 55-65%. Few plants are designed to produce a 68% nitric acid concentration.
Nitric acid, Kirk-Othmer Encyclopedia of Chemical Technology, M. C. E. Groves, John Wiley and Sons, June 2020. https://doi.org/10.1002/0471238961.1409201803120118.a01.pub3.
Links to related IFS Proceedings and recordings
540, (2004), Nitric Acid Production and Abatement Technology Including Azeotropic Acid, L M Marzo
Links to External Resources
Fertilizer Manual, edited by the United Nations Industrial Development Organization (UNIDO) and the International Fertilizer Development Center (IFDC), Kluwer Academic Publishers, 1998, pages 209-220.
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The nitrogen industry – properties, G. D. Honti, Akademia Kiado, Budapest, Hungary, 1976, pages 409-413.
Various processes for the production of commercial-grade nitric acid, G. D. Honti, 1985, Fertilizer science and technology series, USA, pages 61-98.
Various processes for the production of concentrated nitric acid, G. D. Honti, Nitric acid and fertilizer nitrates, Marcel Dekker, New York – Basel, 1985, pages 99-130.
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