Ammonia

                                          

Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the formula NH3. A stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pungent smell. It is widely used in fertilizers, refrigerants, explosives, cleaning agents, and is a precursor for numerous chemicals. Biologically, it is a common nitrogenous waste, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to fertilisers. Around 70% of ammonia produced industrially is used to make fertilisers in various forms and composition, such as urea and diammonium phosphate. Ammonia in pure form is also applied directly into the soil.

Ammonia, either directly or indirectly, is also a building block for the synthesis of many chemicals. In many countries, it is classified as an extremely hazardous substance. Ammonia is toxic, causing damage to cells and tissues. For this reason it is excreted by most animals in the urine, in the form of dissolved urea.

Ammonia is produced biologically in a process called nitrogen fixation, but even more is generated industrially by the Haber process. The process helped revolutionize agriculture by providing cheap fertilizers. The global industrial production of ammonia in 2021 was 235 million tonnes. Industrial ammonia is transported by road in tankers, by rail in tank wagons, by sea in gas carriers, or in cylinders. Ammonia occurs in nature and has been detected in the interstellar medium.

Ammonia boils at −33.34 °C (−28.012 °F) at a pressure of one atmosphere, but the liquid can often be handled in the laboratory without external cooling. Household ammonia or ammonium hydroxide is a solution of ammonia in water.

Etymology-                                                                                                                                                    The name ammonia is derived from the name of the Egyptian deity Amun (Ammon in Greek) since priests and travelers of those temples would burn soils rich in ammonium chloride, which came from animal dung and urine. Pliny, in Book XXXI of his Natural History, refers to a salt named hammoniacum, so called because of the proximity of its source to the Temple of Jupiter Amun (Greek Ἄμμων Ammon) in the Roman province of Cyrenaica. However, the description Pliny gives of the salt does not conform to the properties of ammonium chloride. According to Herbert Hoover's commentary in his English translation of Georgius Agricola's De re metallica, it is likely to have been common sea salt. In any case, that salt ultimately gave ammonia and ammonium compounds their name.

Natural occurrence (abiological)-                                                                                                                  Traces of ammonia/ammonium are found in rainwater. Ammonium chloride (sal ammoniac), and ammonium sulfate are found in volcanic districts. Crystals of ammonium  bicarbonate have been found in Patagonia guano.

Ammonia is found throughout the Solar System on Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto, among other places: on smaller, icy bodies such as Pluto, ammonia can act as a geologically important antifreeze, as a mixture of water and ammonia can have a melting point as low as −100 °C (−148 °F; 173 K) if the ammonia concentration is high enough and thus allow such bodies to retain internal oceans and active geology at a far lower temperature than would be possible with water alone. Substances containing ammonia, or those that are similar to it, are called ammoniacal.

Properties-                                                                                                                                                    Liquid ammonia, Liquid NH3, Solid ammonia, Solid NH3, Two visible states of NH3.Ammonia is a colourless gas with a characteristically pungent smell. It is lighter than air, its density being 0.589 times that of air. It is easily liquefied due to the strong hydrogen bonding between molecules. Gaseous ammonia turns to a colourless liquid, which boils at −33.1 °C (−27.58 °F), and freezes to colourless crystals at −77.7 °C (−107.86 °F). Little data is available at very high temperatures and pressures, but the liquid-vapor critical point occurs at 405 K and 11.35 MPa.

Solid-                                                                                                                                                              The crystal symmetry is cubic, Pearson symbol cP16, space group P213 No.198, lattice constant 0.5125 nm.

Liquid-                                                                                                                                                            Liquid ammonia possesses strong ionising powers reflecting its high ε of 22 at −35 °C (−31 °F).[28] Liquid ammonia has a very high standard enthalpy change of vapourization (23.5 kJ/mol; for comparison, water's is 40.65 kJ/mol, methane 8.19 kJ/mol and phosphine 14.6 kJ/mol) and can be transported in pressurized or refrigerated vessels; however, at standard temperature and pressure liquid anhydrous ammonia will vaporize.

Solvent properties-                                                                                                                                  Ammonia readily dissolves in water. In an aqueous solution, it can be expelled by boiling. The aqueous solution of ammonia is basic, and may be described as aqueous ammonia or ammonium hydroxide. The maximum concentration of ammonia in water (a saturated solution) has a specific gravity of 0.880 and is often known as '.880 ammonia'.

Anhydrous ammonia, as we have seen, is a starting material for the production of ammonium nitrate; it can also be used as a fertilizer by injecting it directly into the ground, a practice common in North America. Another application is as the recirculating fluid in refrigeration systems, about which many spill incidents are reported despite guidelines for proper use. Its hazard characteristics differ markedly from those of ammonium nitrate, and it is therefore worth considering here as another example. As mentioned before, apart from being moderately explosive when mixed with air, ammonia is toxic. At normal ambient conditions, it is a gas. To store it in large quantities, it is either liquefied under pressure (about 10 bar at 25 °C) or is refrigerated (boiling point –33 °C). It can be contained in tanks of carbon steel or CrNi(Mo) steel. Stress corrosion can be avoided by a small addition of water (0.1–0.2%). Ammonia spill hazards are often underestimated, but they have resulted in a considerable number of casualties.

Despite all safety measures, loss of containment can occur as happened in the incident in Potchefstroom, South Africa, in 1973 where a horizontal cylindrical tank released 38 metric tons of anhydrous ammonia.14 Upon catastrophic rupture of a tank and release, the ammonia will be spilled partly as vapor and partly as a boiling liquid, which will spread over the ground whilst evaporating. The vapor is visible as a white cloud by absorption of, and reaction with, the moisture in the air. Initially the cloud is cold and heavy, but gradually, while dispersing and drifting with the wind, it heats up and becomes buoyant. For the dispersion of gas clouds, computational models have been developed about which some brief observations will be made in Chapter 3. In the case of Potchefstroom, the tank cracked and a hole was formed from which mainly vapor escaped. Because of the release, 18 people died, of whom four resided in a nearby area at a distance of 150–200 m, and 65 workers needed medical treatment. The toxic properties of ammonia are expressed as a probability distribution of lethality versus concentration inhaled over time or dose. This takes the form of a probit function, which is a transformed cumulative normal distribution presented as a straight line running from 1 to 99% lethality, depending on the vulnerability condition of the exposed people.

 The official Dutch ammonia probit figures predicted originally in 1992 (Green Book15) a 50% probability of lethality at 30 min exposure (LC50) of roughly 5.4 g/m3 air volume. In 2012, it was proposed16 to modify these figures to reduce the analogous dose to about 1.8 g/m3. Probit relations are also used to express extent of harm to people by heat and blast, as we shall see in Chapter 3. The evidence that can be extracted from an actual incident is very uncertain because there are source uncertainties, which have to be modeled for the dispersion, and there are strong cloud concentration fluctuations, which are not modeled. Furthermore, people will try to flee from the cloud, so the exposure times are very different and may tend to be short. In addition, there are local obstacles or partly sealed enclosures, which may provide some protection. Hence, even when the initial population density at various distances from the source can be estimated, counting victims does not provide data that can be used for accurate probit validation. We shall come back to this type of uncertainty when discussing the reliability of risk analysis figures in Chapter 3.

The release in Potchefstroom involved hot work on the tank but with the omission of any stress relief thereafter. Good maintenance on ammonia tanks remains a matter of continuous attention. Accidents keep on occurring. At the time of writing this text,17 a leak at a chemical plant in eastern Ukraine released ammonia causing the deaths of at least five people and injuring 20.

Ammonia (CASRN 7664-41-7) is another harmful chemical released by the paper industry. Ammonia, a.k.a. anhydrous ammonia, has a pungent odor and is usually found in gas form due to its boiling point of −33°C. The most common use of ammonia is the production of fertilizer: 83% of all ammonia is used in fertilizers. Ammonia is also commonly seen in household cleaning products in the form of ammonium hydroxide, which is simply ammonia dissolved in water. Producing the necessary amount of ammonia for the modern world is not an easy task, and it represents 1% of the world energy budget.

Ammonia can be released into the environment into air, water, soil, and groundwater. The most common releases of ammonia are effluent discharges from industrial processes and run-off from fertilized fields. Humans can be exposed to the hazards of ammonia through ingestion of contaminated food or water, inhalation or skin contact.

The EPA has classified anhydrous ammonia as an extremely hazardous substance. Ammonia is very corrosive, a property that causes most of the negative human health effects. Much like most toxic volatile liquids, ammonia vapor can cause chemical burns of the respiratory tract, skin, and eyes upon inhalation. Upon contact with the water present in skin, mucous membranes, and eyes, it forms ammonium hydroxide, which is a highly ionized weak base that causes tissue necrosis. Specifically, ammonium hydroxide causes saponification of cell membrane lipids resulting in cell disruption and death. Additionally, it dehydrates cells, which initiates an inflammatory response, and further damages the surrounding tissues. Direct contact with liquid ammonia results in cryogenic injury in addition to the alkali burns. Airway blockage and respiratory insufficiency may be lethal outcomes of exposure to anhydrous ammonia vapors or concentrated aerosols. Ingestion of concentrated ammonium solutions may produce severe burns and hemorrhage of the upper gastrointestinal (GI) tract. Hemorrhaging and open wounds of the GI tract can lead to infection and necrosis. The negative effects that have been observed in humans exposed to ammonia gas and ammonium salt aerosols have also been observed in animals. Hepatic and renal effects have been reported in animals and humans (US EPA, 1991c). The US EPA (1991c) has released the toxicological properties for ammonia given in Table 6.6.