Ammonia is used for far more than cleaning your oven, making your crystal sparkle or repelling moths. Ammonia is the compound formed by the chemical combination of the two gaseous elements nitrogen and hydrogen in the molar proportion of 1 part nitrogen to 3 parts hydrogen. This relationship is shown in the chemical symbol for ammonia, NH3. On a weight basis, the ratio is 14 parts nitrogen to 3 parts hydrogen or approximately 82 percent nitrogen to 18 percent hydrogen.
At room temperature and atmospheric pressure, ammonia is a pungent, colorless gas. It may be compressed and cooled to a colorless liquid. Between melting and critical points, liquid ammonia exerts a vapor pressure that increases with rising temperature. When anhydrous ammonia in a closed container is in equilibrium with anhydrous ammonia vapor, the pressure within the container bears a definite relationship to the temperature. Anhydrous means “without water” and when used with ammonia indicates that the water content is less than 0.2 percent. This differentiates it from the various widely used aqueous solutions of ammonia.
Liquid ammonia is lighter than water, having a density of 45.57 lb/ft3 (681.9 kg/m3) at -28o (-33.3oC); as a gas, ammonia is lighter than air, its relative density is 0.597 compared to air at a pressure of 1 atm and a temperature of 32oF (0.0oC). Under the latter conditions, 1 lb (0.454 kg) of ammonia vapor occupies a volume of 20.78 ft3 (0.5884 m3).
|As a chemical compound, ammonia is highly associated and stable. Dissociation begins to occur at 840oF to 930oF (449oC to 499oC) and atmospheric pressure, with the products being nitrogen and hydrogen. Experiments conducted by the Underwriters’ Laboratories indicate that an ammonia-air mixture in a standard quartz bomb will not ignite at temperatures below 1560oF (849oC). When an iron bomb was used, the ignition temperature was 1200oF (6493C) due to a catalytic effect.|
Ammonia gas burns at atmospheric pressure, but only within the limited range of 16 percent to 25 percent by volume of ammonia in air. Ammonia is a highly reactive chemical, forming ammonium salts in reactions with inorganic and organic acids; amides in reactions with esters, acid anhydrides, acyl halides, carbon dioxide, or sulfonyl chlorides; and amines in reactions with halogen compounds or oxygen-containing compounds such as polyhydric phenols, alcohols, aldehydes, and aliphatic ring oxides.
Safety, Storage & Handling:
Personnel working with anhydrous ammonia should be thoroughly familiar with safety precautions for handling a gas corrosive to human tissue, as well as measures for handling emergencies. Use of welding or flame cutting equipment on or in an ammonia container is not recommended unless all ammonia has been purged and all of the residue has been removed.
Persons having chronic respiratory disease or persons who have shown evidence of undue sensitivity to ammonia should not be employed where they will be exposed to ammonia.
Ammonia is not a cumulative metabolic poison; ammonium ions are actually important constituents of living systems. However, ammonia in the ambient atmosphere has an intense irritating effect on the mucous membranes of the eyes, nose, throat, and lungs. High levels of ammonia can produce corrosive effects on tissues and cause laryngeal and bronchial spasm and edema so as to obstruct breathing. The pungent odor of ammonia affords a protective warning, and as long as people are conscious they can avoid breathing significantly contaminated air.
ACGIH recommends a Threshold Limit Value-Time-Weighted Average (TLV-TWA) of 25 ppm (17 mg/m3) for ammonia. The TLV-TWA is the time-weighted average concentration for a normal 8-hour workday and a 40-hr workweek, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect.
Also, ACGIH recommends a Threshold Limit Value-Short Term Exposure Limit (TLV-STEL) of 35 ppm (24 mg/m3) for ammonia. The TLV-STEL is the 15-minute TWA exposure that should not be exceeded at any time during a workday even if the 8-hour TWA is within the TLV-TWA. Exposures above the TLV-TWA up to the STEL should not be longer than 15 minutes and should not occur more than 4 times per day. There should be at least 60 minutes between successive exposures in this range. OSHA lists and 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 50 ppm (35mg/m3) for ammonia. TWA-PEL is the exposure limit that shall not be exceeded by the 8-hour TWA in any 8-hour work shift of a 40-hour workweek.
Since liquid ammonia vaporizes readily and has a great affinity for water, it may cause severe injury to the skin by freezing the tissue and subjecting it to caustic action and dehydration. A chemical burn, which may be severe, will result.
Handling Leaks and Emergencies:
A leak in an ammonia system can be detected by odor. The location of the leak may be determined with moist red litmus paper, moist filter paper impregnated with phenolphthalein, or by detection instruments. These chemical test papers change color in ammonia vapor. Other means of detection involve the use of sulfur dioxide, which forms a white fog in contact with ammonia paper.
Only personnel trained for and designated to handle emergencies should attempt to stop a leak. Respiratory equipment of a type suitable for ammonia must be worn. All persons not so equipped must leave the affected area until the leak has been stopped.
If ammonia vapor is released, the irritating effect of the vapor typically will force personnel to leave the area before they have been exposed to dangerous concentrations. To facilitate their rapid evacuation there should be sufficient well marked and easily accessible exits. If, despite all precautions, a person should become trapped in an ammonia atmosphere, he or she should breathe as little as possible and open his or her eyes only when necessary. Depending upon the concentration of ammonia, partial protection may be gained by holding a wet cloth over the nose and mouth. Since ammonia vapor in air will rise, a trapped person should remain close to the floor to take advantage of the lower vapor concentrations at that level.
With good ventilation or rapidly moving air currents, ammonia vapor, being lighter than air, can be expected to dissipate readily to the upper atmosphere without further action being necessary. Lacking these conditions, the concentration of ammonia vapor in air can be reduced effectively by the use of adequate volumes of water applied through spray or fog nozzles. Do not put water on a liquid ammonia spill since a violent production of vapor can result. Instead, use spray or fog nozzles on the vapor downward spill.
Under some circumstances, ammonia in a container is colder than the available water supply. At such times, water must not be sprayed on the container walls since it would heat the ammonia and aggravate any gas leak. If it is found necessary to dispose of ammonia, as from a leaking container, liquid ammonia may be discharged into a receptacle containing water sufficient to absorb it. Sufficient water may be considered as 10 parts of water to 1 part of ammonia. The ammonia must be injected into the water as near the bottom of the receptacle as practice.
First Aid – Call a physician immediately for any person who has been burned or overcome by ammonia. The patient should be removed to an area free from fumes, preferably a warm room. The patient should be placed in a reclining position with head and shoulders elevated and kept warm by the use of blankets or other cover.
Prior to medical aid by the physician, first aid measures should be taken. Their adoption in any specific case should, of course, be subject to prior endorsement by a competent medical advisor.
Inhalation – Any conscious person who has inhaled ammonia causing irritation should be assisted to an uncontaminated area to inhale fresh air. A person overcome by ammonia should immediately be carried to an uncontaminated area. If breathing has ceased, artificial respiration must be started immediately, preferably by trained personnel. If breathing is weak or has been restored by artificial respiration, oxygen may be administered.
Skin contact – The area affected should be immediately flooded with water if no safety shower is available, immerse in any available water of acceptable temperature. Water will have the effect of thawing out clothing, which may be frozen to the skin. Such clothing should be removed and flooding with water continued for at least 15 minutes. Do not apply safety salves or ointments or cover burns with dressing; however, protect the injured are with a clean cloth prior to medical care. Do not attempt to neutralize the ammonia. If ammonia has entered the nose or throat and the patient can swallow, have the patient drink large quantities of water. Never give anything by mouth to an unconscious person.
Eye contact – The eyes must be flooded immediately with copious quantities of clean water. Speed is essential. In isolated areas, water in a squeeze bottle, which can be carried in the pocket, is helpful for emergency irrigation purposes. Eye fountains should be used, but if they are not available, water may be poured over the eyes. In any case, the eyelids must be held open and the irrigation must continue for at least 30 minutes. The patient must receive prompt attention from a physician, preferably an ophthalmologist. Persons subject to ammonia exposure should not wear contact lenses.
About 80 percent of all ammonia produced in the United States is used in agriculture as a source of nitrogen, which is essential for plant growth. Nitrogen makes up about 16 percent of plant protein. When a fruit, vegetable, or grain crop is grown and harvested, nitrogen is removed from the soil. If the fertility of the land is to be maintained, nitrogen and other elements essential to plant growth such as potassium and phosphorus must be restored to the soil by fertilization. Depending upon the particular crop, up to 200 lb (90.7 kg) of nitrogen may be economically applied per acre.
About 4.8 million tons of ammonia containing 82 percent nitrogen are applied directly to the soil each year in the united States. It can be injected at a depth of several inches below the surface of the soil by specially designed equipment, or it can be dissolved in irrigation water.
Ammonia is used extensively in the fertilizer industry to produce solid material such as ammonium salts, nitrate salts, and urea. Ammonium sulfate, ammonium nitrate, and ammonium phosphate are made directly by neutralizing the corresponding acids-sulfuric acid, nitric acid, and phosphoric acid-with ammonia. Urea is an organic compound formed by combining ammonia and carbon dioxide. Ammonium sulfate, ammonium nitrate, ammonium phosphate, and urea are used for direct application to the soil in dry form and in combination with other phosphate and potassium salts.
Ammonia is also used in the production of nitrogen fertilizer solutions that consist of ammonia, ammonium nitrate, urea, and water in various combinations. Some are pressure solutions and others are not. Non-pressure and low-pressure solutions are widely used for direct application to the soil. Pressure solutions containing free ammonia are used in the manufacture of high-analysis mixed fertilizers.
In addition to their use as fertilizers, ammonia and urea are used as a source of protein in ruminant livestock feeds. Urea is used in the mixed feed supplements to supply the nitrogen needed for the biosynthesis of proteins by the microorganisms in ruminating animals such as cattle, sheep, and goats.
Ammonia is oxidized in the production of nitric acid, the principal ammonia derivative used in making explosives. Both industrial and military explosives are divided into two main types: high explosives such as dynamite, nitroglycerine and TNT, which detonate rapidly to give a shattering blast for demolition purposes; and low explosives such as nitrocellulose, which detonate slowly to give a heaving/pushing effect for propellant or blasting applications. Dynamite, a general term for high explosives used in mining and construction, contains nitroglycerine or other organic nitrogen compounds absorbed in a combustible material. In ammonia dynamite, ammonium nitrate, made by reacting ammonia, and nitric acid, replaces all of the nitroglycerine. Blasting-gelatin dynamites consist of a colloidal mixture of nitroglycerine and nitrocellulose. The latter is made by treating cellulose with a mixture of nitric and sulfuric acids.
Ammonium nitrate is the principal base material in slurry explosives and lower-cost blasting agents. It can be converted to an effective blasting agent by proper mixing with carboniferous material such as fuel oil. Ammonium Nitrate/Fuel Oil (ANFO) mixtures are used extensively in open-pit mining and outdoor construction work because of ease of handling, availability, low cost, and safety.
Ammonia is required for the synthesis of ammonium salts and certain alkalies, dyes, pharmaceuticals, synthetic textile fibers, and plastics. Used both in self absorption- and compression- type systems, ammonia is the oldest, most efficient and economical mechanical refrigerant known.
Ammonia or dissociated ammonia is used in such metal-treating operations as nitriding, carbo-nitriding, bright annealing, furnace brazing, sintering, and other applications where protective atmospheres are required. Ammonia is used in pH control, in mineral beneficiation, in the neutralization of acidic components during petroleum refining, and in the treatment of acidic wastes. Dissociated ammonia provides a convenient source of hydrogen for hydrogenation and other applications.
Ammonia is used in extracting certain metals such as copper, nickel, and molybdenum from their ores.
Ammonia vapor is utilized as the developing agent for diazonium salts (white printing) and is also employed in the production of diazotype microfilm duplicates.
Ammonia is used in the scrubbers to neutralize sulfur oxides in their removal from stack gases in electric power generation and other furnace operations such as melting. It is also used to improve the efficiency of electrostatic precipitators in the removal of particulate matter.
Ammonia is highly soluble in water, forming aqueous ammonia (ammonium hydroxide or aqua ammonia, which has many applications. In a very dilute solution (2 percent to 5 percent ammonia) it is available as “household ammonia.”
Ammonia is used in water treatment in conjunction with chlorine. Ammonia is used to remove trihalomethanes from water. Water solutions of ammonia are used to regenerate weak anion exchange resins.
|Click on one of the examples below for corresponding case study|
|Chemical & Metal Treatment||Copper reclamation process|
|Refrigerantion||Large plant and low pressure systems|
|Metal Treating Operations||Nitriding, carbo-nitriding, bright annealing, furnace brazing, sintering, and other applications where protective atmospheres are required|
|And other applications where elevated ammonia pressures are needed.|
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