Ammonia

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Ammonia
Chemical formula NH3
OTP appearance colorless, noxious gas 
Molar Mass(g/mol) 17 
Melting Point(°C) -77.7 
Boiling Point(°C) -33.3 
Density(g/cc) 0.00073 
Solubility in water(g/L) 310 (18.25M)
NFPA 704
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1
3
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Ammonia is a key industrial chemical. It is energetically expensive to synthesize chemically, but some biological processes produce it in small amounts.

Uses

Primary

Secondary

  • Antimicrobial: With a pH much higher than a neutral water solution, it denatures proteins and some other organics, leading to cell damage and eventually death of the organism.
  • Cleanser: Ammonia brings fats and oils into aqueous solution, making it an efficient cleanser for many types of dirt. The remaining water, containing ammonia, will evaporate leaving no wetness behind.
  • Fertilizer/Soil treatment: raises the nitrogen value and the pH of soil when used as a fertilizer
  • feedstock for nitrates via ammonia biofiltration

Natural occurrence

  • Ammonia is produced by fish, who excrete it in lieu of urine
  • Ammonia is produced by environmental bacteria acting on urine

Hazards

Ammonia is toxic. Annhydrous ammonia can kill you with a single lungfull. Treat both with care.

Production

Synthesis

Decomposition of urea

See Ammonia production from urine

Haber process

Main article Haber process

The haber process is a direct (catalyzed) synthesis of ammonia from hydrogen and nitrogen gasses.

Cyanamide process

Massively inefficient and only available after electrolysis, this process is unlikely to be used.[1]

  1. Produce calcium carbide with an arc furnace
    Ca + 2 C
    {
    2000°C}
    CaC2
  2. Flow nitrogen gas over the -carbide at 1000°C producing calcium cyanamide.
    CaC2 + N2
    {
    1000°C, 1 atm}
    CaCN2 + C
  3. Combine -cyanamide with water producing ammonia.
    CaCN2 + 3 H2O
    {
    OTP}
    CaCO3 + 2 NH3

Serpek process

  1. Expose magnesium to nitrogen in a hot environment, producing magnesium nitride.
    3 Mg + N2
    {
    800°C}
    Mg3N2
  2. Immerse magnesium nitride in water, producing ammonia.
    Mg3N2 + 6 H2O 3 Mg(OH)2 + 2 NH3

Purification

Concentration

The core of concentrating ammonia is to force ammonia out of a dilute solution and into a smaller volume of water, concentrating it in the second solution. The simplest way to do this is with heat. Heating a dilute solution of ammonia to 80-85°C will drive out much (two thirds or more) of the ammonia (as an ammonia-water vapor), leaving most of the water behind. This ammonia-water vapor is then absorbed into a smaller volume of cool water, effecting a concentration of the ammonia. Several factors can be applied to make this process more efficient:

  1. Adding a strong alkali (calcium oxide, potassium hydroxide, etc) to the original (heated) solution can help drive off the ammonia
  2. Passing the ammonia-water vapor through a dessicant (calcium oxide) will absorb the water, leaving dry ammonia to be absorbed, reducing the dilution of the second solution
  3. Providing a firmer "sink" for the ammonia

Heat stripping of dilute ammonia

Heat the ammonia solution and absorb the ammonia into a separate

  1. Place two volumes of dilute ammonia in a retort
  2. Place one volume cold distilled water in the receiver
  3. Direct the gas from the retort to bubble through the water in the receiver
  4. Heat the retort to 80-85°C
  5. Keep the receiver as cold as possible
  6. Apply heat until no further gas is evolved
  7. Remove the retort from the receiver before allowing it to cool (suckback)

Concentration by conversion

Many ammonium salts can be thermally decomposed. Convert dilute ammonia to something else such as ammonium chloride or ammonium (bi)carbonate, then decompose that, diferentially absorbing the ammonia and the other material.

  1. Add equimolar amounts of hydrochloric acid and ammonia in solution, producing ammonium chloride.
  2. Boil dilute ammonium chloride to concentrate
  3. Add sodium hydroxide to solution producing ammonia and salt (and more water)

Testing

Storage

Disposal

References

  1. US patent 1149653
    Link courtesy Google

See Also